Patent Application
20240016894
The invention relates to methods and materials useful in treating creatine deficiency disorders.
Creatine has an essential role in energy homeostasis, being particularly important in muscle and the brain due to their fluctuating energy demands. Outside of the buffering and transport function of high-energy phosphates, creatine is important for neurite growth cone migration, dendritic and axonal elongation, co-transmission on GABA postsynaptic receptors in the central nervous system (CNS) (1-4) and neurotransmitter release (5). Most cells do not rely on ATP/ADP free diffusion; instead creatine kinase/phosphocreatine (CK/PCr) serve as energy storage for the immediate regeneration of ATP as a shuttle of high-energy phosphates between sites of ATP production and energy consumption (6).
Parallel to dietary consumption, creatine biosynthesis occurs in two enzymatic steps primarily in the liver, kidneys, and pancreas. In the first, L-arginine:glycine amidinotransferase (AGAT) catalyzes the formation of guanidinoacetate (GAA) from arginine and glycine; guanidinoacetate N-methyltransferase (GAMT; EC 2.1.1.2) subsequently catalyzes the formation of creatine by GAA methylation from S-adenosylmethionine (7). Once synthesized, creatine is distributed through the bloodstream and is taken up through the cellular creatine transporter solute carrier family 6 member 8 (SLC6A8), a sodium and chloride-dependent symporter, against a large concentration gradient (8). Phosphocreatine reversibly transfers its N-phosphoryl group to ADP to regenerate ATP to prevent tissues from running out of energy. As at least half of creatine is synthesized endogenously, deficits in synthesis or transport result in cerebral creatine deficiency syndromes.
The cerebral creatine deficiency syndromes include the two autosomal recessive creatine biosynthetic disorders GAMT deficiency (8, 9) (MIM 601240) and AGAT deficiency (8) (MIM 602360). Mutations of SLC6A8 (MIM 300352) affect creatine transport into cells. The hallmark of this family of disorders is the near-complete absence of creatine in the brain (10) and the associated, predominantly neurological, disease. While signs and symptoms can range from mild to severe, intellectual disability, global developmental delay, speech impairment, extrapyramidal movement disorders, autism spectrum disorder, and seizures are common in all three (8, 11, 12). Together, the creatine deficiency disorders may represent one of the most frequent metabolic disorders with a primarily neurological phenotype (7).
Of the creatine deficiency disorders, GAMT loss of function mutations tend to result in the most severe phenotype. While likely underdiagnosed (5), the prevalence is estimated to range from 1 in 114,072 (13) to 1 in 250,000 births (14) with a carrier frequency from 1 in 1475 (15) to 1 in 812 (16); numerous different mutations (missense being the most common) have been reported (15) scattered throughout the gene with no hotspot or predominant mutation. The alteration of the Cr/PCr/CK system appears to be of particular importance during early brain development (7). Developmental delay is typically detected at three to twelve months (8); muscular hypotonia, involuntary movements, ataxia and autistic or self-aggressive behavior are common (8, 17, 18). Severe expressive language delay is an almost constant feature (19); most patients have no speech or language and, if present, is extremely limited with marked intellectual disability. Extrapyramidal movements and seizures are characteristic and often refractory to antiepileptics. With deficiency of GAMT, creatine synthesis is markedly impaired while GAA, accumulating in the plasma, CSF, urine, brain and other tissues, is thought to be the cause of the severe phenotype (8, 17) with the associated neurocognitive dysfunction likely due to both the deficiency of creatine and the accumulation of guanidinoacetate (5).
In GAMT deficiency, treatment requires life-long high dose creatine due to the low blood brain barrier permeability (18, 20) as endogenous synthesis is not possible. Oral creatine has an unpleasant taste making it at times difficult to administer to children. In addition, high-dose creatine administration is not always benign, having resulted in nephrolithiasis in some creatine deficient patients (21). With creatine supplementation, however, GAA still accumulates from peripheral excess (5, 20) and while GAA-lowering strategies (e.g. ornithine supplementation, arginine restriction (17), which can be difficult to maintain (15)) can greatly decrease plasma and cerebrospinal fluid GAA, brain levels can remain 10 times above normal levels (18). This leaves children at risk for seizures and progressive CNS injury due to the neurotoxicity of GAA (22).
In view of the issues noted above, there is a need for new methods and materials useful to address creatine deficiency disorders.
Herein, we describe studies developing gene therapy approaches for GAMT as well as SLC6A8 genetic deficiencies in order to overcome the limitations of oral creatine therapy. As discussed below, illustrative working embodiments of the invention restored hepatic gene expression, led to weight gain, normalization of plasma and urine GAA levels, restoration of brain and plasma creatine, and resolution of behavioral abnormalities when administered to a murine model of the GAMT disorder. These findings have implications for development of new therapeutic approaches for GAMT and SLC6A8 creatine deficiencies.
The invention disclosed herein has a number of embodiments. Embodiments of the invention include methods of making a composition comprising combining together in an aqueous formulation a GAMT polynucleotide comprising SEQ ID NO: 1 or a SLC6A8 polynucleotide comprising SEQ ID NO: 2; and optionally a pharmaceutical excipient selected from the group consisting of: a preservative, a tonicity adjusting agent, a detergent, a viscosity adjusting agent, a sugar or a pH adjusting agent. In typical embodiments of the invention, the polynucleotide comprising SEQ ID NO: 1 or the polynucleotide comprising SEQ ID NO: 2 is disposed in an adeno-associated viral vector such that when the adeno-associated viral vector infects a human cell, a functional GAMT protein or a functional SLC6A8 protein is expressed. In illustrative embodiments of the invention, the adeno-associated viral vector construct also comprises: a polynucleotide comprising a terminal repeat sequence; a polynucleotide comprising a promoter sequence; and/or a polynucleotide comprising a polyA tail sequence.
Embodiments of the invention also include compositions of matter such as those comprising a polynucleotide comprising SEQ ID NO: 1; or a polynucleotide comprising SEQ ID NO: 2. In certain embodiments, the composition comprises: an adeno-associated viral vector comprising: a polynucleotide sequence comprising a terminal repeat sequence; a polynucleotide sequence comprising a tissue specific (e.g. liver specific, brain specific) or ubiquitous expressing promoter; the polynucleotide comprising SEQ ID NO: 1 or the polynucleotide comprising SEQ ID NO: 2 (as codon optimized and/or CpG-deleted); and a polynucleotide sequence comprising a polyA tail signal; and a pharmaceutical excipient. In some embodiments of the invention, the composition comprises an adeno-associated viral vector encoding the polynucleotide comprising SEQ ID NO: 1 which, when transduced into a human liver cell expresses functional GAMT protein. In other embodiments of the invention, the composition comprises an adeno-associated viral vector encoding the polynucleotide comprising SEQ ID NO: 2 which, which, when transduced into a human cell expresses SLC6A8 protein. Typically, the adeno-associated viral vector construct comprises: a polynucleotide comprising a terminal repeat sequence; a polynucleotide comprising a promoter sequence; or a polynucleotide comprising a polyA tail sequence.
Embodiments of the invention also include methods of delivering a polynucleotide encoding a GAMT protein polypeptide or a polynucleotide encoding a SLC6A8 protein polypeptide into human cells, the methods comprising: contacting a composition comprising SEQ ID NO: 1 or SEQ ID NO: 2 with the human cells so that adeno associated vector(s) infect the human cells, thereby delivering the polynucleotides into the human cells (e.g., in vivo liver cells). Typically in these methods, the cells are in vivo cells present in an individual diagnosed with a creatine deficiency. In typical embodiments of the invention, the adeno associated viral vector comprising these genes is delivered intravenously.
Embodiments of the invention also include kits comprising a polynucleotide comprising SEQ ID NO: 1 or a polynucleotide comprising SEQ ID NO: 2 disposed in one or more containers. Optionally, the kit comprises: an adeno-associated viral vector comprising: a polynucleotide sequence comprising a terminal repeat sequence; a polynucleotide sequence comprising a tissue specific promoter; the polynucleotide comprising SEQ ID NO: 1 or the polynucleotide comprising SEQ ID NO: 2; and a polynucleotide sequence comprising a polyA tail signal. In certain embodiments, the kit comprises an adeno-associated viral vector encoding the polynucleotide comprising SEQ ID NO: 1 which, when transduced into a human liver cell expresses functional GAMT protein. In certain embodiments, the kit comprises an adeno-associated viral vector encoding the polynucleotide comprising SEQ ID NO: 2 which, when transduced into a human cell expresses SLC6A8 protein.
Related embodiments of the invention include using the compositions disclosed herein in gene therapy methods to treat s creatine deficiency. Such methods include, for example methods of delivering codon optimized polynucleotides encoding a GAMT protein or a SLC6A8 protein into human cells comprising contacting a composition disclosed herein (e.g. a composition comprising a adeno-associated viral vector comprising a codon optimized GAMT or SLC6A8 polynucleotide sequence) with human cells so that adeno-associated vector(s) infect the cells, thereby delivering the polynucleotides into the cells. In certain embodiments of the invention, the cells are in vivo liver cells, for example in vivo liver cells present in an individual diagnosed with creatine deficiency disorders. Related embodiments of the invention include methods of treating a subject diagnosed with a creatine deficiency, comprising selecting a subject with a creatine deficiency and administering to the subject a therapeutically effective amount of a pharmaceutical composition disclosed herein.
Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating some embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.
In the description of embodiments, reference may be made to the accompanying figures which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized, and structural changes may be made without departing from the scope of the present invention. Many of the techniques and procedures described or referenced herein are well understood and commonly employed by those skilled in the art. Unless otherwise defined, all terms of art, notations and other scientific terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains. In some cases, terms with commonly understood meanings are defined herein for clarity and/or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over what is generally understood in the art.
All publications mentioned herein are incorporated herein by reference to disclose and describe aspects, methods and/or materials in connection with the cited publications (e.g. U.S. Patent Application Publication Numbers 20060115869, 20080176259, 20090311719, 20100183704 and 20190017069, and Diez-Fernandez C et al. Expert Opin Ther Targets, 2017 April; 21(4):391-399, doi: 10.1080/14728222.2017.1294685, Zhang G et al. J Clin Lab Anal. 2018 February; 32(2), doi: 10.1002/jcla.22241, Choi R et al. Ann Lab Med. 2017 January; 37(1):58-62, doi: 10.3343/alm.2017.37.1.58, Naso et al., BioDrugs (2017) 31:317-334, and Srinivasan et al., J Inherit Metab Dis. 2019 Mar. 6, doi: 10.1002/jimd.12067).
Creatine deficiency disorders are inborn errors of creatine metabolism, an energy homeostasis molecule. One of these, guanidinoacetate N-methyltransferase (GAMT) deficiency, has clinical characteristics that include features of autism, self-mutilation, intellectual disability and seizures with approximately 40% having a disorder of movement; failure to thrive can also be a component. Along with low creatine levels, guanidinoacetic acid (GAA) toxicity has been implicated in the pathophysiology of the disorder. Present-day therapy with oral creatine to control GAA lacks efficacy; seizures can persist. Dietary management and pharmacological ornithine treatment are challenging. Utilizing an AAV-based gene therapy approach to express human codon-optimized GAMT in hepatocytes, in situ hybridization and immunostaining demonstrated pan-hepatic GAMT expression. Serial collection of blood demonstrated a marked early and sustained reduction of GAA with normalization of plasma creatine; urinary GAA levels also markedly declined. The terminal time point demonstrated marked improvement in cerebral and myocardial creatine levels. In conjunction with the biochemical findings, treated mice gained weight to nearly match their wild type littermates, while behavioral studies demonstrated resolution of abnormalities; PET-CT imaging demonstrated improvement in brain metabolism. In conclusion, a gene therapy approach can result in long-term normalization of GAA with increased creatine in guanidinoacetate N-methyltransferase deficiency and at the same time resolves the behavioral phenotype in a murine model of the disorder. These findings have important implications for the development of a new therapy for this abnormality of creatine metabolism.
As noted above, embodiments of the invention include gene therapy methods that utilize adeno-associated virus (AAV). AAV is a non-enveloped virus that can be engineered to deliver DNA to target cells, which has attracted a significant amount of attention in the field, especially in clinical-stage experimental therapeutic strategies. The ability to generate recombinant AAV particles lacking any viral genes and containing DNA sequences of interest for various therapeutic applications has thus far proven to be one of the safest strategies for gene therapies. The review in Naso et al., BioDrugs (2017) 31:317-334 provides an overview of factors considered in the use of AAV as a vector for gene therapy. U.S. Patent Application Publication Numbers 20190017069 20180163227 20180104289 20170362670 20170348435 20170211095 20170304466 and 20170096682 disclose illustrative AAV methods and materials.
In certain embodiments, the composition comprises an adeno-associated viral vector that includes such a polynucleotide sequence operatively linked to a promoter. In this context, a wide variety of promoters can be used with embodiments of the invention including constitutive promoters that are expressed in a wide variety of cell types, as well as cell lineage specific promoters such as the thyroxine binding globulin (TBG promoter) which is liver-specific. Certain illustrative promoters are described, for example in Damdindorj, et al. (2014) A Comparative Analysis of Constitutive Promoters Located in Adeno-Associated Viral Vectors. PLoS ONE 9(8): e106472; as well as Pacak et al., (2008) Tissue specific promoters improve specificity of AAV9 mediated transgene expression following intra-vascular gene delivery in neonatal mice, Genet Vaccines Ther. 2008; 6: 13. Typically the compositions also includes a polynucleotide a polynucleotide sequence comprising a polyA tail signal; as well as a pharmaceutical excipient selected from the group consisting of a preservative, a tonicity adjusting agent, a detergent, a viscosity adjusting agent, a sugar or a pH adjusting agent.
Embodiments of the invention include compositions of matter such as those comprising a polynucleotide encoding a polypeptide that is encoded by SEQ ID NO: 1 (i.e., a GAMT protein); or a polynucleotide encoding a polypeptide that is encoded by SEQ ID NO: 2 (i.e., a SLC6A8 protein). In certain embodiments, the composition comprises: an adeno-associated viral vector comprising: a polynucleotide sequence comprising a terminal repeat sequence; a polynucleotide sequence comprising a tissue specific (e.g. liver specific) promoter; a polynucleotide encoding a polypeptide that is encoded by SEQ ID NO: 1; or a polynucleotide encoding a polypeptide that is encoded by SEQ ID NO: 2; and a polynucleotide sequence comprising a polyA tail signal; and a pharmaceutical excipient. In some embodiments of the invention, the composition comprises an adeno-associated viral vector including a polynucleotide encoding a GAMT polypeptide which, when transduced into a human liver cell expresses functional GAMT protein. In other embodiments of the invention, the composition comprises an adeno-associated viral vector including a polynucleotide encoding a SLC6A8 protein which, which, when transduced into a human cell expresses SLC6A8 protein. Typically, the adeno-associated viral vector construct comprises: a polynucleotide comprising a terminal repeat sequence; a polynucleotide comprising a promoter sequence; or a polynucleotide comprising a polyA tail sequence.
Other embodiments of the invention include kits such as a kit comprising a composition that includes a polynucleotide disclosed herein disposed in one or more containers. In certain embodiments of the invention, the kit comprises an adeno-associated viral vector comprising a polynucleotide sequence having a constellation of elements designed to facilitate GAMT or SLC6A8 protein expression in human cells, for example a sequence comprising a terminal repeat sequence, a polynucleotide sequence comprising a tissue (e.g., liver) specific promoter, a polynucleotide disclosed herein, a polynucleotide sequence comprising a polyA tail signal. The one or more containers can further comprise a pharmaceutical excipient selected from the group consisting of a preservative, a tonicity adjusting agent, a detergent, a viscosity adjusting agent, a sugar or a pH adjusting agent.
Compositions comprising AAV constructs (e.g. the AAV constructs disclosed herein) of the invention can be formulated as pharmaceutical compositions in a variety of forms adapted to the chosen route of administration. The compounds of the invention are typically administered in combination with a pharmaceutically acceptable vehicle such as an inert diluent. For compositions suitable for administration to humans, the term “excipient” is meant to include, but is not limited to, those ingredients described in Remington: The Science and Practice of Pharmacy, Lippincott Williams & Wilkins, 21st ed. (2006) the contents of which are incorporated by reference herein.
The compounds may also be administered in a variety of ways, for example intravenously. Solutions of the compounds can be prepared in water, optionally mixed with a nontoxic surfactant. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, triacetin, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations can contain a preservative to prevent the growth of microorganisms.
The pharmaceutical dosage forms suitable for injection or infusion can include sterile aqueous solutions or dispersions or sterile powders comprising the compounds which are adapted for the extemporaneous preparation of sterile injectable or infusible solutions or dispersions. In all cases, the ultimate dosage form should be sterile, fluid and stable under the conditions of manufacture and storage. The liquid carrier or vehicle can be a solvent or liquid dispersion medium comprising, for example, water, ethanol, a polyol (for example, glycerol, propylene glycol, liquid polyethylene glycols, and the like), vegetable oils, nontoxic glyceryl esters, and suitable mixtures thereof.
Useful liquid carriers include water, alcohols or glycols or water/alcohol/glycol blends, in which the compounds can be dissolved or dispersed at effective levels, optionally with the aid of non-toxic surfactants. Adjuvants such as additional antimicrobial agents can be added to optimize the properties for a given use.
Effective dosages and routes of administration of agents of the invention are conventional. The exact amount (effective dose) of the agent will vary from subject to subject, depending on, for example, the species, age, weight and general or clinical condition of the subject, the severity or mechanism of any disorder being treated, the particular agent or vehicle used, the method and scheduling of administration, and the like. A therapeutically effective dose can be determined empirically, by conventional procedures known to those of skill in the art. See e.g., The Pharmacological Basis of Therapeutics, Goodman and Gilman, eds., Macmillan Publishing Co., New York. For example, an effective dose can be estimated initially either in cell culture assays or in suitable animal models. The animal model may also be used to determine the appropriate concentration ranges and routes of administration. Such information can then be used to determine useful doses and routes for administration in humans. A therapeutic dose can also be selected by analogy to dosages for comparable therapeutic agents.
The particular mode of administration and the dosage regimen will be selected by the attending clinician, taking into account the particulars of the case (e.g., the subject, the disease, the disease state involved, and whether the treatment is prophylactic). Treatment may involve daily or multi-daily doses of compound(s) over a period of a few days to months.
In certain embodiments of the invention, AAV constructs disclosed herein may be used for the preparation of a pharmaceutical composition for the treatment of disease. Such disease may comprise a disease treatable by gene therapy, including creatine deficiency. The term “pharmaceutical composition”, as used herein, refers to a composition comprising a therapeutically effective amount of active agents of the present invention and at least one non-naturally occurring pharmaceutically acceptable excipient. Embodiments of the invention relate to pharmaceutical compositions comprising one or more AAV constructs disclosed herein in combination with a pharmaceutically acceptable excipient.
The terms “pharmaceutically acceptable excipient”, or “pharmaceutically acceptable carrier,” “pharmaceutically acceptable diluent,”, or “pharmaceutically acceptable vehicle,” used interchangeably herein, refer to a non-toxic solid, semisolid or liquid filler, diluent, encapsulating material or formulation auxiliary of any conventional type. A pharmaceutically acceptable carrier is essentially non-toxic to recipients at the dosages and concentrations employed and is compatible with other ingredients of the formulation. Suitable carriers include, but are not limited to water, dextrose, glycerol, saline, ethanol, and combinations thereof. The carrier can contain additional agents such as wetting or emulsifying agents, pH buffering agents, or adjuvants which enhance the effectiveness of the formulation.
The person skilled in the art will appreciate that the nature of the excipient in the pharmaceutical composition of the invention will depend to a great extent on the administration route. In the case of the pharmaceutical compositions formulated for use in gene therapy regimens, a pharmaceutical composition according to the invention normally contains the pharmaceutical composition of the invention mixed with one or more pharmaceutically acceptable excipients. These excipients can be, for example, inert fillers or diluents, such as sucrose, sorbitol, sugar, mannitol, microcrystalline cellulose, starches, including potato starch, calcium carbonate, sodium chloride, lactose, calcium phosphate, calcium sulfate or sodium phosphate; crumbling agents and disintegrants, for example cellulose derivatives, including microcrystalline cellulose, starches, including potato starch, sodium croscarmellose, alginates or alginic acid and chitosans; binding agents, for example sucrose, glucose, sorbitol, acacia, alginic acid, sodium alginate, gelatin, starch, pregelatinized starch, microcrystalline cellulose, aluminum magnesium silicate, sodium carboxymethylcellulose, methylcellulose, hydroxypropyl methylcellulose, ethylcellulose, polyvinylpyrrolidone, polyvinyl acetate or polyethylene glycol, and chitosans; lubricating agents, including glidants and antiadhesive agents, for example magnesium stearate, zinc stearate, stearic acid, silicas, hydrogenated vegetable oils or talc.
The present invention further provides methods associated with gene therapy regimens such as methods of delivering a nucleic acid encoding a codon optimized GAMT or SLC6A8 polynucleotide sequence into a cell so that the cell expresses GAMT or SLC6A8 protein. In such methods, the virus may be administered to the cell by standard viral transduction methods, as are known in the art. Preferably, the virus particles are added to the cells at the appropriate multiplicity of infection according to standard transduction methods appropriate for the particular target cells. Titers of virus to administer can vary, depending upon the target cell type and the particular virus vector, and may be determined by those of skill in the art without undue experimentation. Alternatively, administration of an AAV vector(s) of the present invention (e.g. the AAV constructs disclosed herein) can be accomplished by any other means known in the art.
Recombinant AAV virus vectors are preferably administered to the cell in a biologically-effective amount. A “biologically-effective” amount of the virus vector is an amount that is sufficient to result in infection (or transduction) and expression of the heterologous nucleic acid sequence in the cell. If the virus is administered to a cell in vivo (e.g., the virus is administered to a subject as described below), a “biologically-effective” amount of the virus vector is an amount that is sufficient to result in transduction and expression of the heterologous nucleic acid sequence in a target cell. The cell to be administered the inventive virus vector may be of any type, including but not limited to hepatic cells.
A “therapeutically-effective” amount as used herein is an amount that is sufficient to alleviate (e.g., mitigate, decrease, reduce) at least one of the symptoms associated with a disease state (e.g. one caused by GAMT or SLC6A8 deficiency). Alternatively stated, a “therapeutically-effective” amount is an amount that is sufficient to provide some improvement in the condition of the subject.
A further aspect of the invention is a method of treating subjects in vivo with the inventive viral constructs. Administration of the AAV constructs of the present invention to a human subject or an animal in need thereof can be by any means known in the art for administering virus vectors.
Exemplary modes of administration include oral, rectal, transmucosal, topical, transdermal, inhalation, parenteral (e.g., intravenous, subcutaneous, intradermal, intramuscular, and intraarticular) administration, and the like, as well as direct tissue or organ injection, alternatively, intrathecal, direct intramuscular, intraventricular, intravenous, intraperitoneal, intranasal, or intraocular injections. Injectables can be prepared in conventional forms, either as liquid solutions or suspensions, solid forms suitable for solution or suspensions in liquid prior to injection, or as emulsions. Alternatively, one may administer the virus in a local rather than systemic manner, for example in a depot or sustained-release formulation.
In particularly preformed embodiments of the invention, the nucleotide sequence(s) of interest is/are delivered to the liver of the subject. Administration to the liver may be achieved by any method known in art, including, but not limited to intravenous administration, intraportal administration, intrabilary administration, intra-arterial administration, and direct injection into the liver parenchyma.
Further aspects and embodiments of the invention are shown in the following examples.
Certain disclosure discussed in this Example is found in Khoja et al., Mol Ther Methods Clin Dev. 2022 Mar. 28; 25:278-296. doi: 10.1016/j.omtm.2022.03.015. eCollection 2022 Jun. 9 (hereinafter “Khoja et al.”).
As disclosed herein, we have developed a gene therapy approach for one of the creatine deficiency disorders called guanidonoacetate methyltransferase (GAMT) deficiency, an autosomal recessive disorder that causes of an array of symptoms or signs including hypotonia, involuntary extrapyramidal movements, seizures, slurred speech, and in some cases autism. Patients typically have elevated plasma guanidinoacetate (GAA) and reduced creatine, a high energy molecule needed for normal brain development and neuronal activity. We have taken two approaches and have tested these AAV vectors in a transgenic GAMT-deficient murine model. We have synthesized a codon-optimized cDNA of transcript variant 1 of GAMT for development of our viral vector approach. 1) We have developed an adeno-associated viral vector that expresses a codon-optimized human cDNA of GAMT under the control of a liver-specific promoter. When administered by intravenous route to GAMT deficient mice, plasma creatine increases and GAA declines, both to near normal values. Affected male and female mice, while reduced in size compared to littermates, after gene therapy increase in weight to match that of their GAMT wild type siblings. 2) We have developed an adeno-associated viral vector that expressed codon-optimized human cDNA of GAMT under a muscle-specific promoter. This has been administered intravenously and results in reduction of plasma GAA and a marked increase in creatine.
Aspects of these studies are discussed below.
AAV-GAMT is Useful to Control GAA and in the Restoration of Creatine with a Dose-Dependent Effect in a Transgenic Animal Model
Transgenic mice deficient in Gamt were developed as a knockout model and biochemically replicate GAMT deficiency in patients with markedly elevated guanidinoacetic acid and markedly reduced creatine in plasma and tissues (23). While they are biochemically similar to human patients, few behavioral deficits have been found (24). Gamt-deficient mice (8 weeks of age, C57Bl/6 background) were administered one of four escalating doses of AAV expressing human codon-optimized GAMT (hcoGAMT) under a liver-specific (thyroxine binding globulin (TBG)) promoter to determine the optimal dose for long-term testing (n=5 per group). Doses of 5×1012, 1×1013, 5×1013, and 1×1014 genome copies per kilogram (GC/kg) were intravenously administered after baseline blood sampling. Mice were euthanized 30 days after administration to assess dose and effect by multiple parameters.
AAV vector copy number per diploid hepatic genome in these Gamt−/− mice was determined at each dose (
AAV-mediated liver-specific GAMT expression was also evaluated by in situ hybridization with a codon-optimized human GAMT-specific probe in Gamt−/− mice. With increasing administered AAV dose, hepatic codon-optimized GAMT RNA expression increases as demonstrated by greater density of probe-specific chromogenic deposition (red; representative images in
With the marked increase in GAMT hepatic protein there is an improvement of the metabolic response. While plasma creatine (
Simultaneous with increases in creatine, plasma GAA levels declined. While markedly elevated pretreatment (red data points), a steady decline was detected with incremental dose increases (blue data points) (5×1012 GC/kg: 101.55±13.70 vs. 128.36±22.00 nmol/ml pretreatment, p<0.0001 vs. wild type; 1×1013 GC/kg: 82.83±29.00 vs. 128.69±30.10 nmol/ml pretreatment, p<0.0001 vs. wild type; 5×1013 GC/kg: 19.512±7.90 vs. 119.45±19.00 nmol/ml pretreatment, p=0.43 vs. wild type; 1×1014 GC/kg: 11.37±0.97 vs. 126.37±5.8 nmol/ml pretreatment, expressed as treated vs. untreated, n=5 per group) (
A single intravenous dose of AAV expressing human codon-optimized GAMT results in improved weight gain.
With the optimal intravenous dose now determined, equal numbers of genders and groups (Gamt+/+, Gamt−/−, treated Gamt−/−) of 2-month-old mice were analyzed (n=8 per genotype group with 4 males and 4 females included in each group) in a twelve-month study. Gamt+/+ and untreated Gamt−/− mice received vehicle alone while the experimental Gamt−/− group received 1×1014 GC/kg of AAV-TBG-hcoGAMT intravenously after baseline blood sampling. Mice were followed for 1 year with all groups having 100% survival (data not shown). While all male groups started with similar weights (Time 0: Gamt+/+26.18±1.10 g; Gamt−/− 24.85±1.03 g; treated Gamt−/− 24.53±0.75 g; WT vs. treated mutant p=0.091, WT vs. untreated mutant p=0.214) (
Female AAV-TBG-treated Gamt−/− mice fared even better. Female mice were of similar weight at the beginning of the study (WT vs treated mutant p=0.603; WT vs untreated mutant p=0.338). Similar to the male cohort, untreated Gamt−/− mice (red data points) had little weight gain after week 10 (weight at beginning of study: untreated Gamt−/− 19.08±1.25 grams vs. 20.23±1.24 grams at week 54). AAV-TBG-treated Gamt−/− mice (blue data points) were near equivalent in their course of weight gain and weights at 1 year as wild type controls (black data points) (at week 54, Gamt+/+25.70±1.45 vs. 24.95±0.58 gram in treated Gamt−/−) (
Untreated Gamt−/− mice of both genders were visibly thinner and, when handled, demonstrated less subcutaneous adipose tissue. To better understand the recovery in weight with gene therapy, mice were imaged with whole-body microCT at 8 months of age, and the adipose tissues were quantified by AMIDE software and visualized in the 3D mode by ORS Dragonfly software. With this imaging, the adipose tissue is easily identified as the visualization demonstrates. Comparing the three groups, there is a relative restoration of the adipose tissue in the treated Gamt−/− mice such that they resemble that of the Gamt wild type in both genders. microCT imaging of all groups (
Male mice demonstrate similar physical findings subjectively when handled, and microCT imaging also demonstrates reduced adipose tissue in untreated Gamt-deficient mice; similarly, some restoration of adipose tissue deposition was achieved with AAV-liver-specific-based gene therapy. Quantification of body weight (
AAV Administration Results in Long-Term Hepatic GAMT Expression with Control of GAA and Restoration of Creatine Levels in Plasma, Urine, and Tissues.
AAV viral genomes (
Pathognomonic to GAMT deficiency is markedly reduced plasma creatine with elevated GAA levels. GAA in Gamt−/− mice (
In GAMT deficiency, urinary GAA (
Tissue levels of GAA are markedly elevated in Gamt−/− mice; these declined substantially with AAV-mediated restoration of hepatic expression of enzyme (
Mice also demonstrated a marked improvement in creatine levels in tissues: Brain (F) 12.21 nmol/g in Gamt−/− to 7923.47±1601.89 nmol/g in treated Gamt−/− (8510.81±1373.37 in Gamt+/+), p=0.683 to Gamt+/+; Heart (G) 41.92±13.58 nmol/g in Gamt−/− to 8203.54±2356.80 nmol/g in treated Gamt−/− (8225.95±2160.20 in Gamt+/+), p>0.999 to Gamt+/+; Kidney (H) 0.00±0.00 nmol/g in Gamt−/− to 612.16±132.63 nmol/g in treated Gamt−/− (868.65±117.10 in Gamt+/+), p=0.003 to Gamt+/+; Liver (I) 0.00±0.00 nmol/g in Gamt−/− to 175.10±37.40 nmol/g in treated Gamt−/− (195.18±33.10 in Gamt+/+), p=0.485 to Gamt+/+; Muscle (J) 180.18±30.23 nmol/g in Gamt−/− to 17519.90±890.08 nmol/g in treated Gamt−/− (18681.10±2661.17 in Gamt+/+), p=0.442 to Gamt+/+.
CNS Metabolism and Behavioral Studies Show Resolution of Deficits with Gene Therapy.
Considering the importance of the creatine/phosphocreatine shuttle to cells with high-energy expenditures, we examined the uptake of glucose to the brain in Gamt-deficient mice. Fluorodeoxyglucose (18(F)-FDG)-positron-emission tomography (PET) is a well-established non-invasive imaging tool for monitoring changes in cerebral brain glucose metabolism in vivo. To examine restoration of hepatic Gamt and its effect as a treatment strategy in GAMT deficiency, we sought to examine the brain of this preclinical model. By measuring cerebral glucose metabolism with (18F)-FDG-PET we can detect neuronal dysfunction in vivo as brain glucose metabolism is determined by synaptic activity mainly in order to restore membrane potentials (26). To semi-quantitate tissue activity, we determined the activity divided by the decay-corrected activity injected into the mouse; this ratio is defined as the percent-injected dose per cubic centimeter in tissue (% ID/cc). Gamt-deficient mice showed decreased glucose uptake (
We similarly analyzed areas of the brain regarding the effect of GAMT deficiency and potential resolution with AAV-based hepatic gene therapy (
We evaluated if there was a substantial improvement in brain metabolism with restoration of GAMT activity in hepatocytes with a gene therapy approach and compared this to present day therapy with oral creatine supplementation. Regular chow was provided, followed by oral creatine supplementation, and later with AAV based hepatic gene therapy (regular chow only) where each mouse served as its own control (
Behavioral testing was performed at 8 months of age (
The Barnes maze is a hippocampus-dependent learning and memory task, similar to the Morris water maze, where mice learn the relationship between distal spatial cues and a fixed escape location (27). During the acquisition phase, mice undergo four daily training trials. After 4 days, the escape tunnel is removed, and a probe trial is conducted to assess reference memory 24 hours after the final training session (short-term memory), and 7 days after the final training session (long-term memory).
Untreated Gamt−/− mice showed deficits in learning, with an increase in primary latency to the escape hole, demonstrated by increased area under the curve (AUC) of the learning curve (see red data points in
Examination of short-term reference memory during the probe trial at 24 hours showed no statistically significant difference in latency or distance travelled between the groups (
Mice are known to utilize one of three search strategies when looking for the escape hole: a direct strategy using extra-maze spatial cues, a serial strategy around the perimeter of the maze, or a random strategy (Fig I). As learning progresses, Gamt+/+ and the treated Gamt−/− mice switch from using primarily non-hippocampal random (gray) and serial (orange) strategies, to a more hippocampal based direct strategy. (Note increase in size of blue proportion of activity from Day 1 to Day 4 in Gamt+/+ and treated Gamt−/− mice (from J to M).). In contrast, untreated GAMT−/− mice rely primarily on the serial search strategy, with reduced spatial pathway activity by day four compared to both the Gamt+/+ mice. In the probe trial at 24 hours (0), untreated Gamt-deficient mice (middle bar) have reduced direct pathway activity compared to the treated-Gamt−/− mice and Gamt wild types; by 1 week (P), a test of longer-term memory, the direct strategy is absent in untreated Gamt−/− mice (see middle bar), here mice rely primarily on the serial pathway and some random searching, the latter completely absent from wild type or treated Gamt−/− mice (see P, left and right bars).
Evaluation of muscle strength is an essential component of behavioral testing particularly with concern for a neuromuscular disorder or to evaluate treatments on motor performance. Grip strength was studied to measure the neuromuscular function as maximal muscle strength of forelimbs and hind limbs. The mice were assessed by gently grasping of the mouse on a grid connected to a sensor. All values obtained were normalized against mouse body weight (
GAMT deficiency (OMIM 601240) is one of the more common creatine deficiency disorders. Creatine has a critical role in energy metabolism of muscle and neurons, both tissues with high-energy demand, and serves as a phosphate energy buffer recycling ATP by the creatine-phosphocreatine system. Despite optimal present-day medical therapy including protein restriction and ornithine supplementation, chronically elevated GAA levels have plagued some children and are likely responsible for persistent seizures, autistic features, and other cognitive abnormalities (5, 18). While it has been hypothesized that GAA interacts with GABAA receptors (4, 28), the exact mechanism of brain injury has not been completely elucidated; both diminished creatine and elevated GAA likely contribute to the neurological phenotype (9, 29). Herein, we sought to explore, and have demonstrated, a gene therapy approach for GAMT deficiency allowing for normal and stable plasma creatine levels with control of plasma GAA.
The main findings of these studies demonstrate that expression of human codon-optimized guanidinoacetate N-methyltransferase in hepatocytes of affected mice results in sustained expression of hepatic GAMT with restoration of plasma creatine levels and resolution of hyperguanidinoacetic acidemia. Urinary GAA was normalized, and creatine levels were similar to wild type controls. While brain creatine levels were restored, cerebral GAA was not completely normalized; this is likely due to lack of restoration of brain GAMT expression as the AAV vector is tissue limited to hepatocytes by the TBG promoter. The dose of vector administered is substantial and while the TBG promoter has been associated with hepatocellular carcinoma at times when used in vectors administered to neonatal mice, we did not detect any tumors or other liver abnormalities in the mice of this study (when euthanized 12 months after vector administration at ˜14 months of age). While AAV8 may be the prototypical murine hepatotropic AAV, multiple other natural AAV serotypes are effective in transducing murine hepatocytes. These include AAV7, AAV9, and rh10, the latter being in the same Clade (Clade E) as serotype 8. We have successfully utilized serotype rh10 previously in murine hemophilia studies (30), murine arginase studies (31-33) and employed here for hepatocyte transduction in Gamt deficiency. Nevertheless, animals thrived with overall weight gain being similar to wild type littermate controls, including improvement in adipose deposition. Glucose consumption in the brain, while reduced in Gamt-deficient mice, was normalized with hepatic-based gene therapy. Motor and learning abnormalities present in mice with marked hyperguanidinoacetic acidemia and low creatine levels, as detected in behavioral testing, were largely resolved.
While GAMT in humans is expressed in high amounts in skeletal muscle, liver, heart and kidney, it is also expressed in the brain, albeit perhaps at lower levels (23); brain expression appears to be predominantly found in oligodendrocytes (34). The gene therapy approach employed in these studies utilized an adeno-associated viral vector expressing human GAMT under a liver-specific promoter, thus restricting expression to hepatocytes. It is evident from the data that this results in markedly improved and normalized creatine levels in the plasma, which is AAV dose-dependent. In addition, hepatocytes in male mice express GAMT from AAV at higher levels than from hepatocytes in female mice, consistent with the androgen-dependency of AAV transduction that has been previously demonstrated (25). There is some reduction in AAV genomes per hepatocyte from one month after administration to over 12 months at study completion. Hepatocyte turnover in the normal adult murine liver is slow overall as the life span of a hepatocyte is from 200 to 400 days; this may in part be the cause of this reduction (35). Levels of creatine are also normalized in the brain, heart, kidney, liver, and skeletal muscle. While GAA levels are simultaneously controlled in the plasma, heart, liver, and skeletal muscle, the brain and kidney, while markedly reduced, have persistent GAA levels. Unlike the heart and skeletal muscle where reduction in tissue GAA is likely from metabolic network flux through the plasma from reduction by the liver with restoration of GAMT enzymatic activity, this is less effective in the brain and kidney where endogenous enzymatic activity may be necessary for metabolic flux to be optimal. Both of these tissues normally possess endogenous Gamt expression, which is not restored with an AAV vector limited by a liver-specific promoter. Altering the vector to express in more tissues may address mildly persistent levels in these two organs.
While these studies demonstrate that despite the comparable mouse weights when these investigations began at 2 months of age, Gamt−/− mice gain less with time than Gamt+/+ controls and, as the PET-CT images demonstrate, do not appear to be due to mouse length or skeletal differences. While a marked reduction in adipose tissue mass has been previously described in murine Gamt deficiency (23), the studies conducted herein demonstrate that with restoration of GAMT expression there is improvement in the absolute fat mass as compared to both untreated Gamt−/− and Gamt+/+ controls. As has been previously demonstrated (23), the reduction in fat mass does not appear to be related to changes in levels of leptin, insulin, or adiponectin levels. It is not known if such reduced adiposity is present in GAMT-deficient patients.
Gamt-deficient mice in our studies demonstrated reduced brain glucose consumption; this was nearly resolved with hepatic-based GAMT gene therapy and was superior to mouse chow with creatine supplementation. In fact, the improvement in brain metabolism may be underestimated by the PET-CT studies. FDG uptake in the mouse brain decreases with age (36, 37) and this may have off-set the signal increase that creatine supplementation may have provided and reduced the signal intensity with the gene therapy approach.
In GAMT deficient patients, free ATP molecules and thus ATP levels in the brain are reported to be increased (38). High ATP levels inhibit glucose/fluorodeoxyglucose uptake and glycolysis through allosteric inhibition of phosphofructokinase (39, 40), consistent with the observation in our data. Thus, it is not unexpected that some behavioral findings would be present in affected mice. While the murine biochemical abnormalities of high plasma and urinary GAA along with low creatine are comparable to humans with the disorder (9), there is only one previous study reporting behavioral data in the murine Gamt-deficient model (24). In that report, Gamt−/− mice did not display severe neurological abnormalities: there was no gross ataxia or seizures (23). With more detailed investigation, the authors found that Gamt-deficient mice did show an inconspicuous finding of impaired retrieval of learned information (24); overall, this identified a subtle cognitive deficit. In the behavioral assays performed as part of this investigation, we found several previously undescribed abnormalities. Utilizing the Barnes maze, a hippocampal-dependent task similar to the Morris water maze, allowed for testing the ability of mice to learn the relationship between distal cues and a fixed escape location (27). In these studies, we detected evidence of a learning deficit during the acquisition phase. Compared to the Gamt+/+ mice, the untreated Gamt−/− mice acquire more slowly, having an abnormality in primary latency; untreated Gamt−/− mice also travel a longer distance to reach the escape location. These abnormalities in primary latency and distance traveled are resolved with AAV-based gene therapy. While examination of short-term memory lacked a statistically significant difference in latency, distance travelled or search strategy in Gamt-deficient mice, in tests of longer-term memory, the primary latency for the untreated Gamt−/− mice was prolonged approaching statistical significance. In addition, untreated Gamt−/− mice utilized a search strategy relying exclusively on serial and random methods while Gamt+/+ mice and treated Gamt−/− mice utilized a direct or spatial method as a much larger component of their search strategy. Together these findings suggest an abnormality in long-term memory that is largely resolved with AAV-based hepatic gene therapy even with incomplete resolution of brain GAA levels.
While gross ataxia was not detected in Gamt-deficient mice, motor abnormalities were present. While our studies were likely underpowered to detect statistically significant abnormalities in cerebellar function by rotarod testing (data not shown), Gamt-deficient mice did demonstrate a reduction in grip strength of the fore- and hind-paws; these motor performance issues were resolved with the gene therapy approach.
In conclusion, these studies developing a gene therapy method for GAMT deficiency led to the resolution of the majority of biochemical abnormalities in plasma, tissues and urine. Behavioral abnormalities in learning and motor activities, not previously reported in a murine model of the disorder, and abnormal brain metabolism were resolved with a gene therapy approach. GAA levels did not completely normalize in the brain; a more effective approach may include a ubiquitous promoter and a serotype that has increased ability cross the blood brain barrier. Additional alterations in the vector construct may also allow for decreased dose of administration. However, this first successful application of AAV-based gene therapy to GAMT deficiency suggests a path forward for clinical development of a gene therapy vector.
Materials and Methods
Molecular Cloning
Full length codon-optimized sequence of human GAMT (hcoGAMT) transcript variant 1 was synthesized and subcloned into pUC57-Simple vector by GenScript Biotech (Piscataway, NJ). The transgene containing 711 bp of hcoGAMT preceded by the Kozak sequence (GCCACC) was excised and subcloned into the pENN-AAV-TBG vector (provided by Julie Johnston PhD, University of Pennsylvania Vector Core) using MluI and KpnI restriction sites by standard molecular biology techniques. After confirmation of the transgene cloning using restriction digestion and Sanger sequencing, plasmid DNA (AAVrh10.TBG.PI.hGAMT-TV1co.rBG) was prepared using an EndoFree Plasmid Mega Kit (Qiagen, cat. 12381, Hilden, Germany).
The following is the complete hcoGAMT polynucleotide sequence:
The following is the complete hcoGAMT polypeptide sequence:
AAV Vector Development
Recombinant serotype rh10 adeno-associated viral vectors were produced at the University of Pennsylvania Vector Core (Philadelphia, PA) as previously described (41). In brief, polyethylenimine as a transfection agent was used to transfect AAV cis, AAV trans, and adenovirus helper plasmids into HEK 293 cells. Three days post-transfection, culture supernatants were collected and AAV particles were then purified by ultracentrifugation iodixanol step gradient. Viral titering by genome copy number was performed by digital droplet PCR using a sequence from the polyadenylation signal. In this context, a variety of AAV vector serotypes can be used (e.g., serotypes 8 and 9).
Mouse Procedures
The constitutive guanidinoacetate methyltransferase knockout mouse (Gamt−/−, B6.Cg-Gamttm1Isb) (23) was obtained as a kind gift from Jeff Huang PhD (Department of Biology, Georgetown University) (MTA obtained from Dr Dirk Isbrandt, University of Cologne) that had been maintained on the C57BL/6 background and was used for these studies. These mice were housed at UCLA under specific pathogen-free conditions; food and water were provided ad libitum and there were no periods of fasting. Mice were fed mouse chow free of animal fat or protein sources (Labdiet/PMI Nutrition International, St. Louis, MO, USA, (Picolab Selected Mouse 30 IF/9F, 5V5M)). Mice underwent genotyping by collecting a small ear clip and performing PCR. All attempts were made to include equal numbers of male and female mice with littermate controls. At 8-12 weeks of age, mice were administered 1×1014 genome copies (GC)/kg AAVrh10-TBG-hcoGAMT by intravenous injection; AAV was diluted in sterile pharmaceutical grade normal saline for injection. Mice were weighed weekly, blood was sampled by retroorbital collection under isoflurane anesthesia monthly, and urine was collected each 3 months. Mice were euthanized at 12 months by isoflurane overdose; tissues were collected and snap frozen with liquid nitrogen. Creatine (Sigma-Aldrich) was supplemented by oral gavage, dissolved in water
Ear tissue snip was obtained and genomic DNA isolated and purified (Extracta DNA Prep for PCR-Tissue, cat #95091, Quantabio, Beverly, MA). PCR was performed using AccuStart™ II GelTrack PCR SuperMix (QuantaBio #89235). PCR conditions were performed for 35 cycles: 94° C.×30 sec, 63° C.×30 sec, 72° C. for 30 sec. Wild type amplicon is 265 bp and mutant amplicon is 430 bp.
Anti-AAV ELISA
96 well plates were coated overnight at 4° C. with 1×109 gc of AAVrh10 vector preparations per well in PBS. Ultraviolet light was used for 30 minutes to inactivate the AAV. Plates were then washed with 1×PBS+5% Tween four times followed by the addition of 200 □l blocking buffer (1×PBS+5% FCS) per well and incubated at 37° C. for 2 h. Plates were then washed with 1×PBS+5% Tween four times followed by the addition of 100 ul diluted plasma sample per well with incubation at 37° C. for 2h. Plates were washed with 1×PBS+5% Tween four times followed by the addition of 50 μl 1:1000 diluted HRP-conjugated anti-mouse IgG (Thermo Fisher, Waltham, MA) to each well and were incubated at 37° C. for 1 h. Wells were washed with 1×PBS+5% Tween six times. Color development was then performed with the addition of 50 μl of OPD substrate followed by incubation at RT for 4 minutes. The reaction was then stopped by adding 50 μl of 2.5M H2SO4 and the plate was read at 492 nm wavelength. Positive control sera were obtained from serum samples of adult mice that had been injected with AAV and had previously anti-AAV antibody levels. AAV-treated animals (n=5) and uninjected controls (n=5) were tested four months after administration, four months after administration.
Analysis of Metabolic Profile from Urine and Plasma
The concentrations of guanidino compounds, including creatine, creatinine and guanidinoacetic acid, were determined in plasma or urine samples using Agilent 1260 Liquid Chromatography (LC) combined with triple-quad 6410B Mass Spectrometry (MS) (Santa Clara, CA). Briefly, 10 ul of 1 mM internal standard (IS) epsilon amino caproic acid (EACA) was added to 10 uL of plasma or urine sample. For measuring creatinine, samples were deproteinized, dried down and reconstituted in 0.1% formate in H2O (Solution A) and used for analysis by LC-MS. For measuring creatine and GAA, plasma or urine sample was derivatized with 3N HCL-Butanol, heated for 15 min. at 60° C., then dried and reconstituted with 100 ul of solution A for LC-MS analysis. Separation was performed with Agilent Poroshell 120 EC-C18 column with mobile phase consistent of solution A and solution B (0.1% formate in acetonitrile and 0.005% TFA). For underivatized samples, we used the MRM, 114-44 and 132-41 for creatinine and internal standard, respectively. For derivatized samples we used the MRM, 188-44, 188-69 and 174-101 for creatinine, GAA and internal standard, respectively.
ALT and AST were determined at CHOP Metabolomic Core using kits from BioVision (Milpitas, CA). (ALT Catalog #K752-100, AST kit Catalog #753-100). Analyses were performed per the manufacturer's instructions with the final measurement with a PerkinElmer spectrometer.
Analysis of Metabolic Profile from Tissues
1. Reagents
Formic acid LC/MS grade and Methanol HPLC grade were purchased from Fisher Scientific (Ottawa, ON). Trichloroacetic acid (TCA) was supplied by VWR International (Radnor, PA) and buthanol·HCL (3M) was from Regis (Morton Grove, IL). Chemicals for calibrators and internal standards, guanidinoacetic acid (GAA), L-arginine (Arg), creatine (CT), creatinine (CTN), ornithine-d6, arginine-d7, creatine-d3, and creatinine-d3 were purchased from Sigma-Aldrich Canada Co. (Oakville, ON). Tubes for tissue homogenisation, VWR 2 mL×2.8 mm Ceramic Hard tissue Homogenizing Mix and VWR 2 mL×1.4 mm Ceramic Soft Tissue Homogenizing Mix were purchased from VWR (VWR International, Radnor, PA).
2. Tissue Metabolites Preparation
30-60 mg of flash frozen kidney, heart or muscle were placed in a 2 mL tube containing 2.8 mm ceramic beads; liver or brain into a 2 mL tube containing 1.4 mm ceramic beads. Tubes were filled with 1 mL of cold water and processed on Omni Bead Raptor Elite at 5.65 m/s for 2 cycles of 1 min with a 10 second dwell time for kidney, heart and muscle and 4.85 m/s for 1 cycle of 20 seconds for liver and brain. Tissue homogenates, 300 μL were mixed with 75 30% TCA, vortexed and spun down at 13,000×rpm for 5 min to precipitate proteins. The cleared tissue homogenates were transferred into Eppendorf tubes and store at −80° C. or processed immediately for metabolites extraction. To extract metabolites for LC-MS/MS, 10 μL of the cleared tissue homogenate was mix with 10 μL of the internal standard and 500 μL methanol. All tubes were vortexed and spun down at 13,000×rpm for 5 min. The supernatant was transferred into a clean glass test tube and loaded onto the Microvap (Organomation, Berlin, MA) at 37° C. to evaporate the excess solvent. Dry residue was dissolved in 100 buthanol·HCL (3M) by vortexing and incubated at 60° C. for 30 min. After cooling to room temperature, derivatized samples were transferred onto the Microvap at 37° C. to evaporate the excess solvent. Dry residue was resuspended in 700 μL methanol and transferred into a 2 mL glass vial.
3. Liquid-Chromatography Tandem Mass Spectrometry (LC-MS/MS)
The method for CT metabolites analysis on LC-MS/MS was adapted with slight modifications from Tran at el. (42). The LC-MS/MS system consisted of an ExionLC AD UHPLC system coupled with QTRAP 6500plus (AB Sciex LLC, Framingham, MA). The metabolites separation was achieved using gradient binary elution at a flow rate of 0.7 mL/min and a temperature at 45° C. on a Kinetex C18 100 Å, 5 μm, 100×4.6 mm LC column (Phenomenex Inc., Torrance, CA). Solvent A consisted of 0.5 mmol/l ammonium formate, 0.1% (v/v) formic acid in water and solvent B consisted of 0.5 mmol/l ammonium formate, 0.1% (v/v) formic acid in methanol. The mobile phase was used at 100% A at 0 min; 100% B at 5.0 min; 100% B at 7.5 min; 100% A at 7.55 min; 100% A at 10 min. The injection volume was 1 μL. The mass spectrometry was performed at the positive ionization and multiple reaction monitoring (MRM) scan mode. The optimal ion transitions were as follows: CT—188.2→90.0, CTN—114.2→44.0, GAA—174.2→101.1, ARG—231.2→172.2, ORN—189.2→70.1, creatine-d3—191.2→93.0, creatinine-d3—117.2→47.0, guanidinoacetate-d2—176.2→103.1, arginine-d7—238.2→179.2, ornithine-d6—195.2→76.1. The ion source parameters were set at TEM—600° C., de-clustering potential—60.0, capillary voltage—5500 V, curtain gas—30, GS1—30, and GS2—20. Data processing and quantification was performed using Analyst 1.7.0 software (AB Sciex LLC, Framingham, MA).
4. Calibrators and Internal Standard (IS) for LC-MS/MS
Calibrators stock solutions were prepared by individually weighing compounds using an analytical balance and dissolving each in water at concentration of 5 mM for CT, ORN, ARG, CTN and 0.1 mM for GAA. Working solutions of calibrators were prepared from stocks by serial dilution to achieve final concentrations of 500, 250, 100, 50, 25, 10, 5, 2.5, 0 μM for CT, ORN, ARG, CTN and 10, 5, 2, 1, 0.5, 0.25, 0.1, 0.05, 0 μM for GAA. The IS was prepared as a mixture of ornithine-d6, arginine-d7, creatine-d3, and creatinine-d3 at concentration of 100 μM and guanidinoacetate-d2 at concentration of 10 μM in water. Calibrators and the IS were stored at −20° C. until use. Analytes were quantified using the signal intensity ratio of the compound to its IS and related to external calibration using the signal intensity ratio of the calibrator to its IS.
Western Blot
General preparation of the protein samples and Western blotting were carried out as described (43). Briefly, liver specimens were homogenized in RIPA buffer containing Halt™ Protease Inhibitor Cocktail (cat 78430, ThermoFisher, Waltham, MA) to isolate proteins. 50 μg of the total protein extract, quantified with Bio-Rad Protein Assay Dye (cat 5000006, BioRad, Hercules, CA), were separated by SDS-PAGE and probed with human GAMT antibody (Abcam, Catalog #ab126736; 1:1000 dilution). HRP-conjugated β-actin antibody (Santa Cruz Biotechnology, Dallas, TX, Catalog #sc-47778; 1:5000) was utilized as loading control. hGAMT was labeled by HRP-conjugated goat anti-rabbit IgG (Santa Cruz Biotechnology, Catalog #sc-2004; 1:5000), and targeted proteins were detected using SuperSignal™ West Pico PLUS Chemiluminescent Substrate (cat PI34579, ThermoFisher).
In Situ Hybridization
RNAscope in situ hybridization was performed using the Bond RX platform (Leica Biosystems) and the RNAscope 2.5 L reagent kit (Advanced Cell Diagnostics (ACD)) according to the manufacturer's protocol (Document Number: 322750-USM). Briefly, freshly cut 4 μm thick paraffin sections were stained. Following heat-induced epitope retrieval (HIER) (ACD HIER 15 min with ER2 at 95° C.) and proteinase digestion (ACD 15 min Protease), the slides were incubated for 2 hours at 40° C. with hGAMT-codon-No-XMm-C1 (ACD-ref 1003128-C1). Amplification steps were performed according to the ACD protocol. The chromogen was detected with the ACD RNAscope 2.5 LSx Reagent Kit-RED (Advanced Cell Diagnostics (ACD), Cat #: 322750). All stained slides were scanned at high magnification (×400) using a whole-slide scanning microscope (Aperio, Leica Biosystems).
GAMT qRT-PCR
Livers were removed from mice, and specimens were snap frozen in liquid nitrogen after being placed in Eppendorf tubes. RNA was extracted from livers with RNeasy Fibrous Tissue Mini Kit according to manufacturer's instructions (Qiagen, 74704). Briefly, tissue was homogenized in buffer then digested with proteinase K before extracting the supernatant containing unpurified RNA. RNA was then isolated by RNeasy column extraction and pure RNA was eluted with RNase-free water.
Once RNA was extracted, cDNA was synthesized with Applied Biosystems High-Capacity cDNA Reverse Transcription Kit with RNase Inhibitor kit (ThermoFisher, 43-749-66) following the manufacturer's instructions. qRT-PCR was performed using SYBR Green Supermix (BioRad, 17256274) and primers specific for the hcoGAMT, taking advantage of base pair differences in exon 1 between the human and mouse variants of GAMT (MluI 19 F (CACACCTTAGGATTCTGGGT (SEQ ID NO: 3)) and MluI R 3 (CCTCCTGAACCTTTGAAGC (SEQ ID NO: 4)) were synthesized. Primers for β-actin (mBeta-Actin F (CTAAGGCCAACCGTGAAAAG (SEQ ID NO: 5)) and mBeta-Actin R (ACCAGAGGCATACAGGGACA (SEQ ID NO: 6)) were used as a reference gene. qRT-PCR was performed for 40 cycles at a melting temperature of 56° C. Fold changes using the—ΔΔCt method were calculated. Animals as n=5 per group with males and females equally represented overall (20 mice).
AAV Copy Number Determination
Unfixed livers were homogenized, and DNA was extracted according to the manufacturer's instructions (Qiagen, 56605223). Standards were made using serial dilution of the parental viral plasmid. Both standards and extracted DNA were then loaded onto 96-well PCR plates (USA Scientific, 21034). qPCR was then performed according to protocol, detected by SYBR Green (Bio-Rad, 1725174). The vector copy number per diploid genome was calculated from equations obtained from the standards and their Ct values. The average of mice per group was used for comparisons.
Histology and Immunohistochemistry of Liver
Portions of explanted livers from euthanized animals were fixed in 10% neutral buffered formalin (v/v) for 48 hours and subsequently stored in 70% ethanol. Standard procedures were employed for processing and paraffin embedding of the tissues. Paraffin-embedded sections were cut at 4 μm thickness and paraffin removed with xylene and rehydrated through graded ethanol. Endogenous peroxidase activity was blocked with 3% hydrogen peroxide in methanol for 10 min. Heat-induced antigen retrieval (HIER) was carried out for all sections in 0.001 M EDTA buffer, pH=8.00 using a Biocare decloaker at 95° C. for 25 min. The slides were then stained with anti-GAMT antibody (ab 126736, 1-100, Abcam, Cambridge, UK); the signal was detected using the Dakocytomation Envision□ System Labelled Polymer HRP anti rabbit (Agilent K4003, ready to use). All sections were visualized with the diaminobenzidine reaction and counterstained with hematoxylin.
Micro-Positron Emission Tomography (PET)/Micro-Computed Tomography (CT) Imaging
Animals were anesthetized with 1.5% vaporized isoflurane, and injected with (18F)-FDG via tail vein. After 60 min (18F)-FDG uptake under a conscious condition, animals underwent micro-PET imaging (10 min static data acquisition) immediately followed by microCT imaging using the Genisys8 PET/CT scanner (Sofie Biosciences). PET data was decay corrected, and attenuation correction was performed using the CT images. Co-registered PET/CT data were analyzed and quantified using AMIDE software. Fat tissues in the CT scans were visualized in the 3D mode using the ORS Dragonfly software. Quantification of FDG uptake in individual areas of the brain was performed using mouse brain atlas previously developed (44).
Behavioral Testing
All behavioral testing included 8 mice per group (4 male and 4 female).
Grip Strength: Grip strength of the mice was assessed to examine muscle strength and stamina. Fore and hindlimb strength is measured using a customized grip strength meter (Chantillon apparatus, San Diego) mounted on a Plexiglas weighted base. Five trials were completed for the forelimbs and the hind limbs with at least one minute of rest between trials. Mice had at least 30 minutes of rest between the forelimb and hindlimb grip strength tests. For both tests, the maximum force was recorded in Newtons. For the forelimb test, the wire mesh grid grip was attached to the grip meter so that it would be parallel to the table surface. The mouse was lifted by the tail lowered so that the forelimbs were grasping the mesh grid and pulled away from the meter parallel to the table by the base of the tail in a quick manner. The results were then recorded and after one minute the test was repeated until 5 trials were achieved. For the hindlimb test, the mesh grid grip was adjusted to sit at a 45 degree angle from the line of the table. The mouse was again held by the base of the tail and allowed to grip the mesh grid with the hind limbs. The angle prevented it from gripping with the forepaws. The mouse was then pulled parallel to the table in a quick manner. After 1 minute, the test was repeated until five trials were achieved.
Barnes Maze: Mice were trained on the Barnes maze as described previously (45, 46). The maze consisted of a grey, non-reflective circular platform (91 cm diameter; Stoelting) with holes around the perimeter (5 cm diameter). Nineteen holes contained shallow, false-escape bottoms and one hole had the escape box. The arena was located in the center of the room with many extra-maze visual cues, including black and white geometric signs, two large lamps for bright light and a speaker for producing white noise.
Each day, the mice were tested in squads of 4. Mice were placed on the center of the table under a 2 L beaker for 30 s before the start of the trial. The first day consisted of one 5 min habituation trial under low light (<20 lux) with no escape and 2 trials under bright-light, where the mouse was guided to the escape box after 3 min of free exploration. Days 2-4 consisted of four 90 s trials with an inter-trial interval of ˜15 min, under bright lighting and white noise. The location of the escape box randomly varied by squad, but remained the same for each squad across training days. If mice did not enter the escape box by the end of the trial, they were guided to the escape box by the experimenter. Once the mouse entered the escape box, they were left for 30 s before being returned to their home cage. On days 6 and 13, mice were given a probe trial to assess short and long-term memory, respectively. For the probe trial, all holes contained the false-escape bottom, and mice were allowed to explore for 90 s.
All videos were recorded and analyzed using AnyMaze software (Stoelting). Because mice are more hesitant to enter the escape box, latency to first head entry (i.e., primary latency) into the escape box was used to assess learning (45). Additionally, each training trial was scored for the approach used to find the hole (e.g., direct, serial, or random). A direct approach was scored when the mouse moved towards the escape (within 2 holes of the escape box), and likely reflects the use of extra-maze cues and spatial memory to find the escape. A serial approach was scored when the mouse approached a hole more than 2 holes from the escape box and continued around the perimeter of the maze to find the escape. A random approach was scored when the mouse was more than 2 holes from the escape box and visited no more than 3 holes in a row to find the escape.
Statistical Evaluation
All collected data was analyzed with the GraphPad Prism v.9.0.1 (GraphPad Software, San Diego, CA) statistical package. All numerical data were expressed as mean±standard deviation (SD) except where noted otherwise, and p values, considered significant when <0.05, were determined using one-way ANOVA with Tukey's multiple comparison's test (i.e. for quantitative real-time PCR), or two-way ANOVA with Dunnett's multiple comparison's test. Error bars represent SD.
We have designed illustrative gene constructs with 1) a constitutive/ubiquitous promoter (chicken b-actin promoter) (named pAAV-CAG SLC6A8TV1 BH) and 2) a neuron-specific promoter (human synapsin) (named pAAV-hSyn SLC6A8TV1 BH).
GCTGCGCGCTCGCTCGCTCACTGAGGCCGCCCGGGCAAAGCCCGGGCGTCGGGCGACCTT
TGGTCGCCCGGCCTCAGTGAGCGAGCGAGCGCGCAGAGAGGGAGTGGCCAACTCCATCAC
TAGGGGTTCCTTGTAGTTAATGATTAACCCGCCATGCTACTTATCTACCAGGGTAATGGG
AGGAACCCCTAGTGATGGAGTTGGCCACTCCCTCTCTGCGCGCTCGCTCGCTCACTGAGG
CCGGGCGACCAAAGGTCGCCCGACGCCCGGGCTTTGCCCGGGCGGCCTCAGTGAGCGAGC
GAGCGCGCAGCCTTAATTAACCTAATTCACTGGCCGTCGTTTTACAACGTCGTGACTGGG
CTGCGCGCTCGCTCGCTCACTGAGGCCGCCCGGGCAAAGCCCGGGCGTCGGGCGACCTTT
GGTCGCCCGGCCTCAGTGAGCGAGCGAGCGCGCAGAGAGGGAGTGGCCAACTCCATCACT
AGGGGTTCCTTGTAGTTAATGATTAACCCGCCATGCTACTTATCTACGTAGCCATGCTCT
GAGTTGGCCACTCCCTCTCTGCGCGCTCGCTCGCTCACTGAGGCCGGGCGACCAAAGGTC
GCCCGACGCCCGGGCTTTGCCCGGGCGGCCTCAGTGAGCGAGCGAGCGCGCAGCCTTAAT
cccgggcgtcgggcgacctttggtcgcccggcctcagtga
gcgagcgagcgcgcagagagggagtggccaactccatcac
taggggttccttgtagttaatgattaacccgccatgctac
agttggccactccctctctgcgcgctcgctcgctcactga
ggccgggcgaccaaaggtcgcccgacgcccgggctttgcc
cgggcggcctcagtgagcgagcgagcgcgcagccttaatt
This concludes the description of embodiments of the present invention. The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching.
This application claims the benefit under 35 U.S.C. Section 119(e) of co-pending and U.S. Provisional Patent Application Ser. No. 63/337,786, filed on May 3, 2022 and entitled “METHODS AND MATERIALS FOR AMELIORATING CREATINE DEFICIENCY DISORDERS” which application is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 63337786 | May 2022 | US |
