Patent Application
20100120682
The present invention relates to compounds useful for increasing the body weight of a mammal. More specifically, the invention relates to compounds useful for increasing the body fat mass of a mammal.
In the industrialized world, the number of persons suffering from an excess of body weight is steadily increasing. However, there also exist individuals that for one or another reason suffer from the opposite condition, viz. underweight. Underweight may be due to a subnormal lean body mass or a subnormal body fat mass, or a combination of both.
In an individual, the total body fat, or body fat mass, consists of essential fat and storage fat. Essential fat is stored in the marrow of bones, heart, lungs, liver, spleen, kidneys, intestines, muscles and lipid rich tissues of the central nervous system, and is necessary for normal physiological functioning. In women, the essential fat also is necessary for the reproductive function, and women carry more than four times as much essential fat as men.
The other type of body fat, storage fat, is fat accumulated in adipose tissue. Besides functioning as energy reserves in times of need, it has a function of e.g. protecting organs and generating body heat.
Underweight may be due to several causes, such as rapid metabolism, poor/inadequate diet or starvation (malnutrition), malabsorption due to defective intestinal function, endocrine disturbances e.g. type I diabetes, psychological problems (such as anorexia nervosa, body dysmorphic disorder, stress and anxiety) and weight loss, due to chronic illnesses and ageing. While in general the underlying cause of the underweight will have to be treated per se, the underweight too may be a health hazard, and as such have to be treated in itself. Indeed, persons suffering from underweight generally have poor physical stamina, a weakened immune system, as well as being at higher risk of developing diseases such as osteoporosis, heart disease and vascular disease. Additionally, in the female sex, underweight can lead to delayed sexual development, retarded amenorrhoea or complications during pregnancy.
The term cachexia is used for a condition of physical wasting with loss of body fat and muscle mass. Generally, cachexia may be associated with and due to conditions such as cancer, required immunodeficiency syndrome (AIDS), cardiac diseases, infectious diseases, shock, burn, endotoxinemia, organ inflammation, surgery, diabetes, collagen diseases, radiotherapy, and chemotherapy. In many of these diseases, cachexia may significantly contribute to morbidity or mortality.
Another particular group of individuals that are susceptible to developing a cachectic state are those individuals that have undergone a gastrectomy, such as may be practiced on gastric cancer and ulcer patients. Liedman et al., 1997 reported a loss of body weight of about 10% within the first six months after gastrectomic surgery, mainly due to loss of body fat, in patients having undergone either subtotal or total gastrectomy.
An estimated 0.5 to 3.7 percent of females in the US suffer from anorexia nervosa in their lifetime (American Psychiatric Association Work Group on Eating Disorders, 2000). According to data from the National Association of Anorexia Nervosa and Associated Disorders (US), the mortality rate of individuals suffering from anorexia is about 5% for each decade and increases up to 20% for patients that have the illness for more than 20 years. In the UK, the Eating Disorders Association has estimated an 18% mortality rate for anorexia nervosa. Anorexia nervosa mainly afflicts young people. A person developing anorexia nervosa before adulthood may suffer stunted growth and subsequent low levels of essential hormones (including sex hormones) as well as chronically increased cortisol levels.
From the above, it appears that while anorexia nervosa admittedly may have psychological and socio-cultural causes, the condition, if permitted to develop too far, may need urgent clinical treatment including hospitalization and intravenous infusion or nasogastric tube-feeding of nutritients.
Attempts have been made to provide means of treating conditions of underweight or reduced body fat, such as cachexia and anorexia. Thus, U.S. Pat. No. 7,015,241 describes a method of treating anorexia by use of a sulfonamide derivative or sulfonic acid ester derivative that is said to stimulate the appetite. U.S. Pat. No. 6,387,883 describes methods of inhibiting metabolic and cytokine associated features of cachexia by use of a nutritional composition comprising an effective amount of various omega-3 fatty acids. U.S. Pat. No. 7,138,372 discloses an agent for preventing and/or treating cachexia comprising Tumour Cytotoxic Factor-II (TCF-II) or hepatocyte growth factor (HGF) as an effective ingredient.
WO04032952A1 describes the use of ghrelin or an analogue thereof for the preparation of a medicament for one or more of: treatment and/or prevention of loss of body weight and body fat, prophylaxis or treatment of cachexia, stimulation of appetite, stimulation of food intake, stimulation of weight gain, or increasing body fat mass, in a gastrectomized individual.
In cancer patients, in particular, various agents have been administered in attempts to retard or halt progressive cachexia. Thus, it has been suggested to use corticosteroids to alleviate symptoms such as anorexia, asthenia, and pain in patients with cancer. Significant improvements in appetite and a sense of well-being have been reported in randomized trials with prednisolone, methylprednisolone, or dexamethasone, though these improvements were not long-lasting and did not remain after completion of the studies (Willox et al., 1984; Bruera et al., 1985; Popiela et al., 1989; Della Cuna et al., 1989).
Megestrol acetate also has been observed to stimulate appetite and produce weight gain in a variety of cachectic cancer patients (Maltoni et al., 2001). In a study of the combination of appetite-stimulating properties of megestrol acetate and the antiinflammatory properties of ibuprofen it was suggested that this combination stabilized quality of life and produced weight gain in patients with advanced gastrointestinal cancer (McMillan et al., 1999).
Medroxyprogesterone acetate, a synthetic progestogen, also has been shown to increase appetite, however, without any weight gain being observed (Downer et al., 1993; Simons et al., 1996).
The cannabinoid dronabinol is another compound that has been found to stimulate appetite. In a study on cancer patients, higher doses of the compound, of 5.0 or 7.5 mg/d, were found to be more effective than the low dose of 2.5 mg/d, though, nonetheless, the patients continued to lose weight (Plasse et al., 1991; Nelson et al., 1994).
Another compound, the serotonin antagonist cyproheptadine, has been observed to produce weight gain in clinical situations. However, in patients with advanced malignant neoplasms, cyproheptadine treatment, while resulting in a decrease in nausea and mild enhancement in appetite, did not abate progressive weight loss (Kardinal et al., 1990).
The prokinetic agent Metoclopramide, at a dosage of 10 mg orally 4 times daily before meals and at bedtime, was shown to be effective in stimulating appetite and relieving other dyspeptic symptoms associated with anorexia in advanced cancer patients with delayed gastric emptying or gastroparesis (Nelson et al., 1993; Shivshanker et al., 1983).
Eicosapentaenoic acid (EPA), an ω-3 polyunsaturated fatty acid, has been shown to possess antitumor, as well as anticachexia, activities in animal cachexia models, inducing inhibition of weight loss accompanied by increases in total body fat and muscle mass (Dagnelie et al., 1994; Tisdale et al., 1990). In one study it was shown that while nutritional supplement alone did not attenuate the development of weight loss in cachectic cancer patients, nutritional supplement enriched with EPA resulted in significant weight gain (Barber et al., 1999).
The growth hormone secretagogue ghrelin has been shown to be capable of stimulating adiposity. Also, subcutaneous injections of a more stable synthetic ghrelin-receptor agonist GHRP-2 (growth hormone releasing peptide-2) were observed to produce dose-dependent increases in food intake and body weight (Tschop et al., 2002).
The inhibitor of prostaglandin synthesis ibuprofen has been reported to produce body weight gain, and to improve survival in cachectic cancer patients (Preston et al., 1995; Wigmore et al., 1995; Lundholm et al., 1994).
Finally, the antidiabetic drug glitazone (a thiazolidinedione) increases body weight considerably, which at least in part is due to increase in fat mass (Stumvoll & Haring, 2002; Fonesca, 2003). The effect is mediated by activation of the specific fat cell receptor PPAR-gamma, which, in turn, stimulates formation of new fat cells and also enhances lipid storage in adipocytes.
The metallo-enzyme tartrate resistant acid phosphatase (TRAP), also known as uteroferrin, purple acid phosphatase or type 5 acid phosphatase (Acp5), is a basic, iron-binding protein in mammals with high activity towards e.g. phosphoproteins and ATP. It exists either as a latent monomeric pro-enzyme of approximately 35 kDa or as a proteolytically processed two-subunit enzyme of approximately 22 and 16 kDa, respectively, linked by a disulphide bridge (Lang and Andersson, 2005; Ljusberg et al., 1999). The proteolytic processing (exerted by, for instance, cathepsin K) of the monomeric proenzyme excises part of an exposed loop region close to the active site and is permissive for the catalytic activation of TRAP (Ljusberg et al., 2005).
TRAP is found in a variety of organs, such as bone, spleen, lung and placenta and is found in various cell types. It is secreted in vivo by osteoclasts (Hollberg et al., 2005; Reinholt et al., 1990) and has been shown to be secreted in vitro by both macrophages and osteoclasts (Janckila et al., 2005). Intracellularly, TRAP is thought to participate in degradation of collagen fragments as well as of phagocytosed bacteria in osteoclasts (Halleen et al., 1999) and macrophages (Räisanen et al, 2005), respectively. Osteoclast secreted extracellular TRAP, on the other hand, has been proposed to participate in the regulation of osteoclast adhesion and migration (Andersson et al., 2003). However, the role of extracellular TRAP secreted from other cell types, including macrophages, is unknown.
The amino acid sequence of TRAP is represented by the sequence
In this amino acid sequence, the exposed loop region, the excision of which results in the catalytic activation of the enzyme, is represented by:
and corresponds to the sequence of the monomeric TRAP proenzyme located from amino acid no. 162 to amino acid no. 182.
The use of TRAP in diagnosis is disclosed in US patent application No. 20050074800, wherein methods of diagnosing joint disease are provided, comprising measuring concentration or activity of at least one joint disease-diagnostic enzyme, e.g. TRAP, in a tissue, cell, or fluid test sample taken from a joint of a test subject.
US patent application No. 20040228899, on the other hand, discloses devices suitable for orthopedic or dental implantation to bone, having TRAP adsorbed to a porous hydroxyapatite substratum.
In both cited US application, it is the involvement of TRAP in bone metabolism that is exploited.
PCT publication WO04041170 relates to relates to compositions containing proteins and methods of using those compositions for the diagnosis and treatment of immune related diseases. In the Sequence listing, containing more than 2500 sequences, the polypeptide sequence of TRAP is present. However, there is no example of use of this polypeptide in the description, which is largely speculative on the possible therapeutic utility of the polypeptides.
From the above description, it appears that there still exists a need for efficacious drugs for treating or preventing a condition of subnormal body fat mass, such as may be found in a cancer or heart failure patient, in an individual suffering from cachexia or in a person suffering from an eating disorder and in elderly patients who cannot achieve adequate nutrition. One object of the present invention is to provide such a drug.
This object is achieved, according to the present invention, on the basis of the surprising discovery, made by the present inventors, of a hitherto unknown and completely unexpected effect of the monomeric TRAP proenzyme on adipogenesis.
Thus, according to one aspect the present invention provides the use of an isolated polypeptide comprising an amino acid sequence having a sequence identity of at least 80%, preferably at least 85%, more preferably at least 90%, most preferably at least 95%, with the amino acid sequence represented by SEQ ID NO: 2, or a pharmaceutically acceptable salt thereof, for preparing a medicament for the treatment of a mammal to increase the body fat mass of said mammal, or to prevent or reduce loss of body fat mass of said mammal.
According to one aspect, the present invention provides an isolated polypeptide comprising an amino acid sequence having a sequence identity of at least 80%, preferably at least 85%, more preferably at least 90%, most preferably at least 95%, with the amino acid sequence represented by SEQ ID NO: 2, or a pharmaceutically acceptable salt thereof, for use as a medicament.
According to another aspect, the present invention provides a pharmaceutical composition comprising an isolated polypeptide comprising an amino acid sequence having a sequence identity of at least 80%, preferably at least 85%, more preferably at least 90%, most preferably at least 95%, with the amino acid sequence represented by SEQ ID NO: 2, or a pharmaceutically acceptable salt thereof, as well as a method of treatment of a mammal by administering the pharmaceutical composition to said mammal.
According to still another aspect, the present invention provides an isolated polypeptide comprising an amino acid sequence represented by SEQ ID NO: 2 or an amino acid sequence having a sequence identity with the amino acid sequence represented by SEQ ID NO: 2 of at least 80%, preferably at least 85%, more preferably at least 90%, most preferably at least 95%, for use as a medicament.
In one embodiment of the invention, the polypeptide comprises an amino acid sequence having a sequence identity of at least 80%, or at least 90%, preferably at least 95%, more preferably at least 98%, most preferably at least 99%, with the amino acid sequence represented by SEQ ID NO: 1.
In this embodiment, thus, the polypeptide comprises an amino acid sequence having a sequence identity of at least at least at least 80%, or at least 90%, preferably at least 95%, more preferably at least 98%, most preferably at least 99%, with the amino acid sequence represented by SEQ ID NO: 1, which amino acid sequence comprises an amino acid sequence having a sequence identity of at least 80%, preferably at least 85%, more preferably at least 90%, most preferably at least 95%, with the amino acid sequence represented by SEQ ID NO: 2.
In another embodiment of the invention, the polypeptide comprises monomeric proenzyme of TRAP.
According to another aspect, the invention provides the use of a compound capable of reducing the proteolytic processing of monomeric pro-enzyme of TRAP, for preparing a medicament for the treatment of a mammal to increase the body fat mass of said mammal, or to prevent or reduce the loss of body fat mass of said mammal.
Further aspects and embodiments of the invention are as defined in the claims.
p<0.05; **p<0.01; ***p<0.005
For the purpose of the present invention the term polypeptide is used analogously with oligopeptide, peptide and protein, if nothing else is indicated or apparent from the context.
The term “amino acid” should be construed as comprising both natural and non-natural amino acids. Any optically active amino acid may be in the “D” or “L” isomeric form.
For the purpose of the present invention, the term “identity” is used analogously with the term “homology”, referring to the percentage of amino acid residues in the a given amino acid sequence that are identical with the residue of the sequence to which it is compared. Thus, as an example, two polypeptides that are 90% homologous have a 90% sequence identity.
To assess identity between any two sequences, the sequences are aligned and, if necessary, gaps are introduced. The skilled person will be well aware of methods for performing such alignments, using any of the sequence analysis software packages that are commercially available.
Homologous polypeptides may comprise one or more, conservative or non-conservative, preferably conservative, amino acid substitutions. In a conservative amino acid substitution the substituting amino acid has similar size, hydrophobicity and hydrophilicity values, as well as similar electronic properties as the amino acid being substituted. As an example, substituting an alanine residue for a valine residue is considered a conservative substitution of one non-polar amino acid for another, while substituting a glutamic acid residue for an aspartic acid residue is considered a conservative substitution of one acidic amino acid for another, and so on. It is well within the knowledge of the skilled person to appreciate what amino acid may replace another one in order to obtain a conservative substitution.
A homologue of a polypeptide also may be one wherein at least one amino acid has been inserted or deleted, typically from 1 to 5 amino acids. To determine which amino acid residues can be substituted, inserted, or deleted while maintaining the enzymatic activity computer programs well known to the skilled person may be used, e.g. the DNAstar software (www.dnastar.com).
Any amino acid as well as the C-terminus and/or the N-terminus of the polypeptide may also be substituted by a moiety that may provide the polypeptide with some other beneficial feature, such as improved solubility, absorption and/or biological half life, which moiety may also be a protecting group of any functional group of the polypeptide. Suitable protecting groups are described in Greene's Protective Groups in Organic Synthesis, Peter G. M. Wuts, Theodora W. Greene, fourth ed., 2006, ISBN: 0471697540.
Examples of N-terminal protecting groups include acyl groups, while examples of C-terminal protecting groups include amine groups.
It will be well within the knowledge of the skilled person to identify suitable homologues and derivatives, e.g. having suitable N and/or C terminal protecting groups, of the inventive polypeptides, by preparing and assaying the homologue for adipogenetic effect, e.g. in an in vitro system, e.g. applying assay methods as described herein below.
The polypeptides of the present invention may be prepared by recombinant DNA techniques in cellular systems, e.g. microorganisms, such as bacteria and yeasts, or in insect or vertebrate cells. These techniques are well-known to the person skilled in the art, and suitable protocols are described e.g. in Sambrook, J.; Russell, D.; Molecular Cloning; A Laboratory Manual Cold Spring Habor, third edition, 2001.
In addition, the polypeptides of the invention can be chemically synthesized, cf. e.g., Creighton, T. E., Proteins: Structures and Molecular Principles, second edition, 1993, ISBN: 0716723174.
Non-classical amino acids or chemical amino acid analogs can be incorporated into the polypeptide by substitution or addition. Examples of non-classical amino acids are citrulline, homocitrulline, hydroxyproline, norleucine, norvaline, ornithine, sarcosine etc.
According to one aspect of the present invention, a pharmaceutical composition is provided, comprising an isolated polypeptide comprising an amino acid sequence having a sequence identity of at least 80%, preferably at least 85%, more preferably at least 90%, most preferably at least 95%, with the amino acid sequence represented by SEQ ID NO: 2, and/or an isolated polypeptide comprising an amino acid sequence having a sequence identity of at least 80%, or at least 90%, preferably at least 95%, more preferably at least 98%, most preferably at least 99%, with the amino acid sequence represented by SEQ ID NO: 1 and/or the monomeric pro-enzyme of tartrate-resistant acid phosphatase type 5 (TRAP).
The pharmaceutical composition of the invention preferably is in a form suitable for injection, e.g. subcutaneous injection, or in a form suitable for intravenous infusion. It may include a solution or dispersion of a polypeptide of the invention in a suitable, pharmaceutically acceptable carrier, for example, water, ethanol, polyol and suitable mixtures thereof, and vegetable oils.
The pharmaceutical composition also may be provided as a sterile powder for the extemporaneous preparation of a sterile solution or dispersion for injection.
The pharmaceutical composition of the invention should be stable under the conditions of manufacture and storage. Furthermore, it should be preserved against the contaminating action of microorganisms such as bacteria and fungi. To this end, an antibacterial agent and/or antifungal agent may be added, e.g. chlorobutanol, sorbic acid, thimerosal, and the like.
The pharmaceutical composition additionally may contain an isotonic agent, such as a sugar or sodium chloride. Also, a composition having a prolonged absorption can be prepared by the use of agents delaying absorption, for example, aluminum monostearate and gelatin.
As is well-known to the person skilled in the art, a sterile solution for injection may be prepared by admixing the active ingredient in a suitable solvent, optionally with any additive, e.g. such as mentioned herein above, and filtered sterilizing the solution thus obtained. A dispersion for injection may be prepared by admixing the active ingredient in a sterile carrier comprising the basic dispersion medium and optionally any additive, e.g. such as mentioned herein above.
The present invention also includes pharmaceutically acceptable salts of the polypeptides of the invention. Any such salt, of course, must have essentially the required biological activity according to the invention.
Examples of pharmaceutically acceptable salts are acid addition salts such as salts with hydrochloric, phosphoric, sulphuric acids, and organic acids, such as tartaric, acetic, citric, malic and lactic, fumaric acids; and pharmaceutically acceptable salts with alkali metals or alkaline earth metals or lower alkylammonium salts.
The medicament of the invention will comprise a therapeutically effective amount of the polypeptide of the invention, together with pharmaceutically acceptable carrier(s) and excipient(s), so as to provide a therapeutically effective dose for increasing the body fat mass of a mammal on administration thereof to the mammal, preventing a decrease of the body fat mass of the mammal, or arresting or reversing a decrease of the body fat mass of the mammal. The skilled person will be aware of methods for determining a therapeutically effective dose, by standard preclinical and clinical test procedures using cell cultures and/or experimental animals.
In any particular case, the administered dose may be determined by a physician, taking account of parameters such as the age, weight, condition and the type and severity of the disease of the patient to be treated. Typically, a therapeutically effective amount of the peptide or peptide derivative can range from about 0.1 mg per day to about 1000 mg per day for an adult. A typical daily dose is from about 0.1 to 50 mg per kg, preferably from about 1.0 mg per kg to 10 mg per kg of body weight, according to the activity of the specific therapeutic substance, the age, weight and condition of the subject to be treated, and the frequency and route of administration.
The polypeptide of the invention may be administered with at least one biologically active substance, either simultaneously or sequentially. If administered simultaneously, the polypeptide and the other biologically active substance(s) may be provided in separate compositions or combined within the same composition.
Examples of biologically active substances that may be used according to the present invention are compounds capable of increasing the general well-being and/or stimulating appetite and/or increasing the body weight; and compounds capable of reducing the proteolytic processing of monomeric pro-enzyme TRAP and/or compounds capable of reducing the proteolytic processing of the polypeptide of the invention.
Examples of compounds capable of increasing the general well-being and/or stimulating appetite and/or increasing the body weight are mentioned herein above in relation to the prior art, and are e.g. omega-3 fatty acids such as eicosapentaenoic acid; corticosteroids such as methylprednisolone, dexamethasone and prednisolone; megestrol acetate; medroxyprogesterone acetate; dronabinol; cyproheptadine; metoclopramide and ibuprofen, and it is contemplated that the biologically active agent may be selected from any of these, as well as from other compounds of similar effects as known to the skilled person, e.g. as mentioned in some of the patent documents referred to herein above.
Furthermore, it is contemplated that the polypeptide of the invention may be administered in combination with several of the above-mentioned other biologically active substances and/or in combination with one or several other biologically, optionally therapeutically, active substances as may be indicated in view of any particular condition associated with the subnormal body fat mass.
In one embodiment, it is contemplated that the polypeptide of the invention, optionally in combination with any of the above-mentioned other active substances, is administered in combination with a dosage of lipids or a diet enriched in nutritionally assimilable lipids.
Compounds capable of reducing the proteolytic processing of monomeric pro-enzyme TRAP are e.g. inhibitors of cathepsin K. Examples of such inhibitors are given e.g. in U.S. Pat. Nos. 6,274,336, 7,012,075, and in US patent application No. 20060122268.
As indicated herein above, the body fat mass can be measured by number of methods, and the term “body fat mass”, as used herein, should be construed as measured by any of these methods, known to the person skilled in the art.
The simplest way of determining a possible change of body fat mass, e.g. a loss of body fat mass, of an individual is by weighing the individual. Though of course this method does not take account of the possible change of body weight due to e.g. a change in muscle mass, it nonetheless may give a first indication of any change of the body fat mass. Also, such measurement may serve as a basis for determining the body mass index (BMI) of the individual. The BMI, defined as the body weight of an individual divided by the square of his or hers height, provides a simple means of assessing how much an individual's body weight departs from what is normal or desirable for a person of his or her height. Common definitions of BMI categories are as follows: starvation: BMI—less than 15 kg/m2; underweight—BMI less than 18.5 kg/m2; ideal—BMI from 18.5 to 25 kg/m2; overweight—BMI from 25 to 30 kg/m2; obese—BMI from 30 to 40 kg/m2; morbidly obese—BMI greater than 40 kg/m2. In general, people suffering from anorexia nervosa have a BMI of less than 17.5 kg/m2.
While simple, the BMI method of characterizing the body weight property of a person is not always correct. For example, the BMI does not take into account factors such as frame size, muscularity or varying proportions of e.g. bone, cartilage, and water weight among individuals. Thus, the accuracy of BMI in relation to actual levels of body fat mass may be distorted by such factors as fitness level, muscle mass, bone structure, gender, and ethnicity. Also, people with short stature and old people tend to have lower BMI values. It is considered, however, that the skilled person, e.g. a physician, will be able to take these factors into account when making the BMI assessment of any given individual.
Nevertheless, BMI categories are generally regarded as a satisfactory tool for measuring whether sedentary individuals are e.g. “underweight,” “overweight” or “obese”.
In one embodiment of the invention, the medicament is for treating a mammal suffering from a condition associated with a subnormal BMI or with a susceptibility of developing a subnormal BMI.
In one embodiment, a BMI lower than 18.5, e.g. lower than 18, lower than 17.5 or even lower than 17 is considered subnormal.
The body fat percentage provides another means of characterizing the body of an individual. The body fat percentage is the fraction of the total body mass that is adipose tissue, or body fat mass, the rest being the so-called lean body mass, e.g. bone, muscle, organ tissue, etc. In the US, the National Institute of Health has indicated that a recommended body fat percentage for women is 20-21%, and that for men it is 13-17%.
In one embodiment of the invention, the medicament is for the treatment of a mammal suffering from a condition associated with a subnormal body fat mass or body fat percentage or with a susceptibility of developing a subnormal body fat mass or body fat percentage.
In one embodiment, in a woman, a body fat percentage of lower than 20%, or a body fat percentage of lower than 19%, e.g. a body fat percentage of lower than 18% is considered as a subnormal value, whereas in a man, a body fat percentage of lower than 13%, or a body fat percentage of lower than 12%, e.g. a body fat percentage of lower than 11% is considered a subnormal value.
There exist several methods of determining the total body fat mass, well-known to the person skilled in the art, e.g. by Dual energy X-ray Absorptiometry (DXA); Average Density Measurement (Hydrostatic Weighing), or Bioelectrical Impedance Analysis (BIA); or by the simpler skinfold test (Durnin J. V. G. A. and M. M. Rahaman, 1967). In this latter test, the skinfold thickness is measured at various, representative sites on the body by use of calipers, and the measured data are used to calculate body fat by different calculation methods. As an example, Harpenden Skinfold Calipers are commercially available with detailed instructions manual, cf. www.fitnessassist.co.uk
For the purpose of the present invention, the terms “mammal” and “individual” are intended to refer to either an animal or human individual, if the contrary is not indicated or obvious from the context. The animal may be e.g. a farm animal, a domestic animal, a laboratory animal or a pet animal, e.g. a dog, a cat, a pig, a cow, a sheep, a rat, a rabbit, a mouse etc. Preferably, the mammal/individual is a human.
All of the above prior art documents referred to herein above are incorporated by reference.
Herein below, the invention will be illustrated by the following non-limiting examples.
Age-matched male and female mice from different litters (WT, TRAP+p and TRAP+) were kept under controlled light/dark conditions with food and water available ad libitum.
TRAP overexpressing transgenic FVB/N mice (FVB/N-trap+ or FVB/N-trap+p) were generated as previously described (Angel et al., 2000) and each litter was genotyped. Transgenic animals containing >30 copies of the TRAP gene were used.
Genomic DNA was purified using Puregene (Gentra, Minneapolis, Minn.) according to the manufacturer's protocol for DNA purification from mouse-tail. Primers (Invitrogen, Carlsbad, Calif.)/probes (Biosearch Technologies, Novato, Calif.) for SV40 and TRAP were used. The TRAP primers and probes were as follows: 5′ GCTACTTGCGGTTTCACTATGGA 3′ (SEQ ID NO: 3) and 5′ TGGTCATTTCTTTGGGGCTTATCT 3′ (SEQ ID NO: 4), and FAM labeled probe 5′TGTGAAGCCGCCCAGGGAGTCCTC 3′ (SEQ ID NO: 5), annealing temperature 62° C. qPCR was run as stated under “Total RNA purification and RT-qPCR” with the exception that iQ Supermix (Bio-Rad, Hercules, Calif.) was used.
Dual-energy X-ray absorptiometry (DXA) was performed as described [27]. Male (WT; n=24, TRAP+p; n=17, TRAP+; n=5) and female (WT; n=28, TRAP+p; n=14, TRAP+; n=9), 2-12 month mice were used (Supplementary Table IV). Statistical analysis was carried out using Kruskal Wallis test followed by Mann-Whitney U test.
Dual-energy X-ray absorptiometry was performed as described elsewhere (Nagy and Clair, 2000). Male (WT; n=24, TRAP+p; n=17, TRAP+; n=5) and female (WT; n=28, TRAP+p; n=14, TRAP+; n=9), 2-12 month mice were used. Statistical analysis was carried out using Kruskal Wallis test followed by Mann-Whitney U test.
Adipocyte size was determined as described (Reynisdottir et al., 1994). Adipose tissue was obtained from the animals (WT; n=8, TRAP+; n=8) and adipocytes were isolated by collagenase treatment. Using direct microscopy, the diameter of 100 cells was determined and the mean fat cell volume was calculated. Statistical analysis was carried out using ANOVA.
Animals were given a specific amount of food and the consumption was measured by weighing the remaining food every other day for two weeks. Food consumption was then calculated as intake of gram food/gram body weight over two weeks for male (WT; n=3, TRAP+; n=6) and female (WT; n=3, TRAP+; n=5) mice. Statistical analysis was carried out using Mann-Whitney U test.
Total RNA was extracted from gonadal or mesenteric adipose tissue of male and female mice (WT; n=11, TRAP+p; n=7, TRAP+; n=9) using RNeasy Lipid Tissue Mini Kit (QIAGEN, Hilden, Germany), treated with DNase (Invitrogen, Carlsbad, Calif.), quantified using Ribogreen (Invitrogen, Carlsbad, Calif.) and then transcribed using iScript cDNA Synthesis Kit (Bio-Rad, Hercules, Calif.). From human subjects, total RNA was extracted from 300 mg subcutaneous fat tissue (n=28) using RNeasy Mini Kit (QIAGEN, Hilden, Germany), determination of RNA purity and reverse transcription was performed as previously described (Hoffstedt et al., 2004). Real-Time PCR was carried out on an iCycler iQ Real Time PCR Detection System (Bio-Rad, Hercules, Calif.) in triplets using, for mouse cDNA, Platinum® SYBR® Green qPCR SuperMix UDG (Invitrogen, Carlsbad, Calif.) and, for human cDNA, iQ SYBR Green Supermix (Bio-Rad, Hercules, Calif.) both with the addition of 10 nM fluorescein (Bio-Rad, Hercules, Calif.) in a final volume of 25 μl. Program setting for mouse samples were as follows: 2 min at 50° C., 2 min at 95° C., 40 cycles of 15 sec at 95° C. and 30 sec at 62-64° C. (depending on primer pair). Program setting for human samples were as follows: 10 min at 95° C., 40 cycles of 15 sec at 95° C. 20 sec at 63° C. Primer pairs were optimized prior to use for primer concentration and annealing temperature to achieve PCR amplification efficiency between 95-105%. Mouse samples were normalized towards β-actin and human samples towards GAPDH. Relative quantification of mRNA was calculated using the “Comparative Ct method” as described in User Bulletin 2 from Applied Biosystems. For mice, statistical analysis was carried out using Mann-Whitney U test and for humans using ANOVA. Information in respect of the TRAP qPCR primers and conditions of use is given in Table 1, wherein Ann. temp. stands for the annealing temperature.
Measurement of TRAP Enzyme Activity Using pNPP as Substrate
TRAP enzyme activity was measured (Lang et al., 2001) in tissue homogenates prepared as follows. Adipose tissue from male and female mice (WT; n=11, TRAP+; n=10, TRAP+p; n=10) was homogenized in 0.15 M KCl+0.1% Triton X-100+Pefabloc (10 mg/ml)+Complete, Protease Inhibitor Cocktail Tablets (1 tablet/50 ml solution) (Boehringer Mannheim, Mannheim, Germany) and centrifuged at 3200×g for 30 minutes. The supernatant was then assayed for TRAP enzyme activity.
TRAP Protein is Effectively Taken Up by the Cells after In Vivo Administration to Rats
Recombinant monomeric TRAP (5 μg in 100 μl) was administered to 6 adult rats in vivo by local infusion into gonadal fat pads using osmotic pumps for 7 days. The contralateral fat pad in the same animal received the same treatment except that recombinant TRAP was omitted and instead only vehicle was infused for the same time period. The area of adipose tissue close to the site infused with the TRAP protein showed accumulation of TRAP in adipocytes, which show that the delivered TRAP protein is effectively taken up by the cells. This pattern was not observed in the adipocytes of the control fat pad. Measurement of adipocyte size showed a tendency to increased size distribution and infiltration of small adipocytes in treated compared to control regions, but this difference was not significant.
Human abdominal subcutaneous adipose tissue was obtained from different sources. For the isolation of pre-adipocytes and mesenchymal stem cells (MSC), tissue was obtained as the product of cosmetic liposuction on otherwise healthy non-obese women (body mass index (=BMI): 22-36 kg/m2; age 22-56 years; n=10). For immunohistochemistry, tissue was obtained during surgery from three obese subjects undergoing gastric banding. For the comparison of gene and protein expression in lean versus obese subjects a frozen (−70° C.) 300 mg tissue piece was used. It was obtained by needle biopsy from lean (BMI<25 kg/m2) or obese (BMI>30 kg/m2) but otherwise healthy women participating in ongoing studies of the genetic regulation of human fat cell function. For those in the gene expression study age (mean±SD) was 36±14 and 39±7 years in lean (n=14) and obese (n=14) subjects, respectively. BMI was 23±2 and 36±4 kg/m2 respectively. Fat cell volume was 450±140 and 822±240 pL in lean and obese, respectively. The obese group in the gene expression study was sub-divided in two groups according to fat cell size; hyperplasia (fat cell volume of 641±450 pL; n=7) and hypertrophia (cell volume of 1004±490 pL; n=7) with no between group difference in BMI. In the protein expression study age was 40±4 years (lean (n=7)) and 40±13 years (obese (n=12)), the BMI was 23±1 kg/m2 and 38±5 kg/m2, and fat cell volume was 490±190 pL and 868±223 pL, respectively. The obese group was sub-divided into a hyperplastic (fat cell volume 659±420 pL; n=6) and hypertrophic (fat cell volume 1077±570 pL; n=6) group) with no between group difference in BMI. Unpaired t-test was used to compare lean and obese subjects and adipose tissue versus adipocytes. ANOVA was used to compare lean subjects with the hypertrophic and hyperplastic groups. Degrees of freedom in these experiments were 1, 1 and 2, respectively.
Partially purified (for procedure see (Lang and Andersson, 2005)) culture media from 1×106 RAW 264.7 cells or 70 mU TRAP from WT/TRAP+p/TRAP+ adipose tissue were subjected to SDS-PAGE using 12% NuPage gels (Invitrogen, Carlsbad, Calif.) run with MOPS buffer and transferred to PVDF membranes (Bio-Rad, Hercules, Calif.).
Membranes were blocked using 1% TBST (100 mM Tris-HCl pH 7.6, 154 mM NaCl, 1% Tween-20) and stained with rabbit anti-mouse monomeric TRAP (Lang and Andersson, 2005) 1:1500 or rabbit anti rat total (Ek-Rylander et al., 1997) TRAP 1:1500 and goat anti rabbit HRP 1:10 000 (Calbiochem, La Jolla, Calif.) and developed using Renaissance (NEN Life Science, Boston, Mass.). Human samples; 100 μg of total protein total obtained from protein lysates was separated on 12% PAA-gels, transferred onto PVDF membranes and stained using rabbit anti-mouse monomeric TRAP or rabbit anti-rat total TRAP as described above. Bands were detected using Supersignal® (Pierce, Rockford, Ill.). Relative expression was determined using Chemidoc XRS System (Bio-Rad, Hercules, Calif.).
Immunohistochemistry was carried out mainly as previously described (Lang and Andersson, 2005). Mouse adipose tissue from male and female mice; paraffin sections (WT; n=3, TRAP+; n=3) were treated with 0.1% trypsin (Sigma-Aldrich, St. Louis, Mo.) at 37° C. for 30 minutes and stained for macrophages using F4/80 monoclonal antibody (1:50) (Serotec, Oxford, UK). ChemMate Detection Kit Peroxidase/DAB rabbit/mouse (Dako, Glostrup, Denmark) was used as secondary antibodies and developing solution. Human adipose tissues; microwave treated (1 mM EDTA pH 8 for 10 minutes at 900 W) paraffin sections were stained with rabbit anti-rat total TRAP 1:50 (Ek-Rylander et al., 1997) recognizing both monomeric and the two-subunit TRAP or rabbit anti-mouse monomeric TRAP antibody 1:50 (Lang and Andersson, 2005) and CD68 1:100 (Dako, Glostrup, Denmark). Secondary antibodies were ALEXA 568 goat anti-rabbit Fab2 1:250 and ALEXA 488 goat anti-mouse Fab2 fragments 1:100 (Invitrogen, Carlsbad, Calif.). Sections were then examined using a Leica TCS NT ArKr laser confocal microscope (Leica Microsystems AG, Wetzler, Germany).
Recombinant rat TRAP was expressed in Sf9 insect cells and purified as previously described (Wang et al., 2005). To generate the proteolytically processed form, recombinant rat TRAP was digested at 37° C. for 40 minutes with recombinant human cathepsin K in 5 mM NaOAc pH 5.5, 1 mM EDTA and 10 mM DTT using a 1:1 molar ratio.
For proliferation experiments (n=4, df=3); 3T3-L1 (ATCC (LGC Promochem, Borås, Sweden)) cells (2,000 cells/cm2) were cultured in DMEM/F12 Glutamax II, 4.5 g/L glucose, 1.5 g/L sodium bicarbonate, penicillin/streptomycin, 2.5% calf bovine serum+/−cleaved (600 U/mg) or monomeric (50 U/mg) TRAP (10−9 M-10−12 M). After 24, 48 and 72 h, cells were labeled for 2 h with BrdU, fixed and BrdU incorporation was measured using Cell Proliferation ELISA, BrdU kit (Roche, Mannheim, Germany).
For differentiation experiments (n=4, df=3); 3T3-L1 cells (6,000 cells/cm2) were grown into confluence in DMEM/F12 Glutamax II, 4.5 g/L glucose, 1.5 g/L sodium bicarbonate, penicillin/streptomycin, 10% calf bovine serum+/−cleaved or monomeric TRAP (10−9M-10−12M)). At 2-3 days after confluence, 0.5 mM isobutylmethylxanthine, 1 μM dexamethasone and 10 μg/ml bovine insulin was added to the media to start differentiation. Cells were then cultured+/−roziglitazone (1 μM), cleaved (600 U/mg) or monomeric (50 U/mg) TRAP (10−9M-10−12M). After 48 h, dexamethasone, isobutylmethylxanthine and roziglitazone were omitted. After an additional 48 h (i.e. 4 days after the start of differentiation), cells were lysed and GPDH activity was measured. Statistical analysis was performed using t-test.
Proliferation and Differentiation of Human Mesenchymal Stem Cells Derived from Adipose Tissue in Presence of TRAP
Human MSC were isolated from a subcutaneous lipoaspirate, grown to 60-70% confluence and passage for at least 20 passages, as described (Dicker et al., 2005). For proliferation experiments (n=3, df=2); hMSC (passage 9) (2,000 cells/cm2) were cultured in DMEM Glutamax I, 1 g/L glucose, penicillin/streptomycin, 2.5% fetal bovine serum in the presence or absence of cleaved (600 U/mg) or monomeric (50 U/mg) TRAP (10−9M-10−12M). After 48 h, cells were labeled for 2 h with BrdU, fixed and BrdU incorporation was measured as described above.
For differentiation experiments (n=3, df=2); hMSC (passage 18) were differentiated as described (Dicker et al., 2005). in the presence or absence of cleaved or monomeric TRAP (10−9 M). Twelve days after the start of differentiation cells were lysed and GPDH activity was measured. Statistical analysis was performed using t-test.
Differentiation and Proliferation of Preadipocytes Isolated from Human Adipose Tissue in Presence of TRAP.
Isolation of pre-adipocytes were performed. For proliferation experiments (n=3, df=2); cells (4000 cells/cm2) were cultured in growth medium containing 2.5% fetal bovine serum in the presence or absence of cleaved or monomeric TRAP (10−9M-10−12M). After 5 days, cells were labelled for 2 h with BrdU, fixed and BrdU incorporation was measured as described above. For differentiation experiments (n=3, df=2); cells were differentiated as described (Ryden et al., 2002). in the presence or absence of cleaved (600 U/mg) or monomeric (50 U/mg) TRAP (10−9M-10−12M). Twelve days after the start of differentiation, cells were lysed in GPDH buffer and GPDH activity was measured. Statistical analysis was performed using t-test.
Secretion of TRAP from Macrophages
RAW 264.7 cells were cultured in a 37° C. humidified 5% CO2 atmosphere in DMEM media (Gibco, St Louis, Mo.) supplemented with 10% FCS (Gibco, St Louis, Mo.) and 0.1 mg/ml gentamycin (Gibco, St Louis, Mo.). For stimulation, 0.25×106 RAW 264.7 cells/ml (passage 3) were treated with IFNγ (500 U/ml) (Invitrogen, Carlsbad, Calif.) for 16 h, and then with LPS (1 ng/μl) (Sigma-Aldrich, St. Louis, Mo.) for an additional 24 h.
Lipolysis and lipogenesis experiments were conducted on isolated adipocytes from fat (pooled fractions of gonadal, mesenteric and inguinal fat from the same animal) from male and female mice (WT; n=8 and TRAP+; n=8). After a 2 h incubation, the cell suspension was subjected to measurement of active uptake into total fat cell lipids (lipogenesis index). Statistical analysis was performed using ANOVA.
Glucose (WT; n=3 and TRAP+; n=3), HOMA index (WT; n=3 and TRAP+; n=3) and insulin (WT; n=8 and TRAP+; n=3) were determined individually on serum from male and female mice, using a Monarch automated analyzer (ILS Laboratories Scandinavia AB, Sollentuna, Sweden) or a RIA assay (Linco Research Inc., St. Charles, Mo.), respectively. Statistical analysis was performed using Mann-Whitney U test.
Serum levels of leptin in male and female mice >4 months of age (WT; n=26 and TRAP+; n=13) (Quantikine Mouse Leptin Immunoassay, R&D Systems, Inc., Minneapolis, Minn.), of adiponectin in male and female mice >4 months of age (WT; n=11 and TRAP+; n=7) (Adiponectin Mouse ELISA, BioVendor, Heidelberg, Germany) and of TNFα in male and female mice >4 months of age (WT; n=8 and TRAP+; n=5) (Ready-Set-Go! Mouse TNFα ELISA, ebioscience, San Diego, Calif.) was measured. Statistical analysis was carried out using Mann-Whitney U test.
For statistical analysis of mouse experiments with two independent group's t-test was performed. When more than two groups were present Kruskal-Wallis followed by Bonferronis correction were performed. Fat cell volume and HOMA index (log transformed to normalize values) were compared with waist using multiple regression analysis. Values are given as mean+SD. *p<0.05; **p<0.01; ***p<0.005
TRAP+ mice overexpressing both monomeric and proteolytically processed TRAP were found to weigh about 60% more than non-transgenic littermates (WT) already at 4 weeks of age (
Adipose tissue can expand due to hypertrophy and/or hyperplasia of adipocytes. Hypertrophy is present in most mouse models of obesity though at least two previous models have hyperplasia as the sole cause of obesity (Shepherd et al., 1993; Valet et al., 1993). Since no difference in adipocyte cell size was found between WT and TRAP+ mice (
Monomeric, but not Proteolytically Processed, TRAP is Increased Both at the mRNA and Protein Level in Adipose Tissue from Obese Human Subjects
The clinical significance of TRAP as a regulator of adipogenesis was investigated in adipose tissue of lean and obese humans. Both TRAP mRNA expression and monomeric TRAP protein expression were increased by 300% among the obese subjects compared to lean subjects (
To establish if the increased adipose tissue mass in TRAP+ mice and obese human subjects could be due to, at least partly, a direct effect of TRAP on adipocytes it was demonstrated, using a mouse pre-adipocyte cell line (3T3-L1), that monomeric TRAP, at 10-11-10-12 M, caused a 30% enhancement of cell proliferation (
Next, an effort was made to identify the cell type responsible for the production of monomeric TRAP in adipose tissue. In line with previous studies in animal models of obesity (Weisberg et al., 2003; Xu et al., 2003) mRNA for F4/80 and c-fms (
Since increased total body weight due to increased total body fat i.e. obesity, is known to be associated with a low-grade inflammation serum protein levels and/or mRNA levels for inflammatory markers known to be increased in obesity were measured in TRAP+ mice. The present inventors investigated three groups of factors, those mainly expressed by adipocytes (adiponectin, leptin, CCL2) (Bouloumie et al., 2005; Dahlman et al., 2005), those believed to be mainly expressed by cells from the stroma cell fraction i.e. likely macrophages (TNFα, IL1β, MMP9) (Bouloumie et al., 2005) and those believed to be expressed in both adipocytes and the stroma cell fraction (IL6) (Bouloumie et al., 2005). The mRNA levels of leptin and adiponectin was found to be unchanged between the TRAP+ and its WT littermates although the ratio between adiponectin and leptin is slightly shifted in favour of leptin. However, the serum leptin levels where increased in the TRAP+ mouse compared to WT mice leading to a non-significant shift in the ratio between adiponectin and leptin in favour of leptin. Also the mRNA levels of TNFα was increased in TRAP+ mice compared to WT littermates although serum TNFα only showed a non-significant increase (data not shown). On the other hand, neither CCL2, MMP9, IL1β nor IL6 was affected in the TRAP+ mice.
Adipocytes from Transgenic Mice Overexpressing TRAP are Metabolically Normal and the Animals has No Signs of Decreased Insulin Sensitivity
It is well known that insulin and catecholamine actions are altered in obesity which, at least in part, can be linked to the increased fat cell size seen in most models of obesity. However, adipocytes isolated from TRAP+ mice exhibited normal spontaneous basal lipolysis (
To explore the importance of fat cell size for in vivo insulin sensitivity the present inventors analysed the relationship between abdominal subcutaneous fat cell volume and HOMA-index, the latter a well established indirect measurement of insulin sensitivity in vivo. For this purpose, unpublished data were obtained from a previous study on 112 healthy women with a large interindividual variation in BMI (Wahrenberg et al., 2005). It had been previously demonstrated that waist is the strongest predictor for HOMA index (Wahrenberg et al., 2005). In the whole material and in the obese subgroup fat cell volume was an independent predictor for HOMA index, taking in account the influence of waist (cf. Table 2 herein below). In non obese only waist was a significant predictor. Thus, in obese subjects, the fat cell size is an independent determinator of insulin independent of the degree of fatness (measured as waist). Obese subjects with hyperplasia seem more insulin sensitive than obese subjects with adipocyte hypertrophy.
Mice engineered to overexpress TRAP presented an early onset of an obese phenotype with significantly increased body fat content that was not due to apparent over-eating, indicating that TRAP may have a direct effect on adipocytes. Adipose tissue can expand either by lipid filling of existing adipocytes resulting in large hypertrophic adipocytes or by increased differentiation of normally sized adipocytes resulting in hyperplastic obesity. In the TRAP overexpressing mouse adipocyte volume was normal and genes known to increase adipocyte differentiation (PPARγ, Gpd2) were either upregulated or showed such a tendency, whereas genes inhibiting adipocyte differentiation (pref-1) showed a tendency towards downregulation suggesting that the increased fat mass was largely due to enhanced differentiation and/or proliferation of adipocytes rather than lipid filling of pre-existing adipocytes, i.e. the TRAP+mouse develops hyperplastic obesity. This makes the model atypical since hyperthrophy is dominating in most mouse models of obesity though at least two previous models have hyperplasia as the major cause of obesity (Shepherd et al., 1993; Valet et al., 1993). The results from the TRAP overexpressing mouse also suggests that the monomeric form of TRAP is causing the effect of TRAP on adipogenesis, since a sub-strain of the mouse only expressing proteolytically processed TRAP in adipose tissue was lean. The mechanism underlying this difference between the sub-strains is unclear although it clearly illustrates the importance of the monomeric rather than the proteolytically processed form of TRAP for the development of the obese phenotype.
Monomeric TRAP is Increased in Patients Suffering from Obesity
The finding that TRAP overexpressing mice develops spontaneous hyperplastic obesity lead the present inventors to investigate if increase of TRAP is associated also with human obesity and, in fact, TRAP mRNA was increased in patients suffering from obesity. In consistence with the findings in the TRAP overexpressing mouse an increased expression of monomeric TRAP was found, but not proteolytically processed TRAP, in adipose tissue of obese subjects. Human obesity is usually characterized by a combination of hypertrophic adipocytes and an increased number of hyperplastic adipocytes, although hypertrophy usually dominates (Bonnet et al., 1979; Brook et al., 1972). However, some patients do present an obese phenotype with a higher percentage of hyperplastic (i.e. smaller than expected) adipocytes (Hirsch et al., 1989). When obese subjects were divided into a group with a shift towards hyperplastic obesity and one with a more pronounced hypertrophic obesity both TRAP mRNA and monomeric TRAP were increased in subjects with hypertrophic obesity compared to lean subjects but the expression was further increased in those with hyperplastic obesity. This indicates that monomeric TRAP is associated with enhanced formation of adipocytes, and thereby hyperplasia, also in human obesity.
The direct influence of TRAP on development of obesity in the TRAP overexpressing mice and in human obesity was subsequently addressed by experiments on mouse and human adipocyte progenitors where the potency of monomeric TRAP to enhance adipocyte proliferation as well as differentiation was assessed. In both hMSC and pre-adipocytes of mouse and human origin, monomeric TRAP stimulated proliferation weakly but exerted a stronger potentiation on differentiation. The effect on differentiation was indistinguishable in the presence or absence of the PPARy activator roziglitazone suggesting that the mechanisms for PPARy and monomeric TRAP signalling are not directly coupled. However, proteolytically processed TRAP had no effect on either proliferation or differentiation of adipocytes. This dual effect on both proliferation and differentiation increases the impact of monomeric TRAP although the effect at each stage may appear small, at least in respect to stimulation of proliferation. These combined results from the TRAP overexpressing mouse, obese human subjects and ex vivo proliferation and differentiation of pre-adipocytes suggest a potentially important functional action on adipogenesis of monomeric TRAP which hitherto has been recognized only as a latent pro-enzyme (Ljusberg et al., 1999).
Obesity has been found to be associated with a low-grade inflammation in adipose tissue (Fantuzzi, 2005; Wellen and Hotamisligil, 2003). This inflammation is characterized by an influx of macrophages into the adipose tissue (Weisberg et al., 2003; Xu et al., 2003). The increased influx of macrophages has been hypothesized to be a consequence of adipocyte necrosis because of adipocyte hypertrophy (Cinti et al., 2005) and/or increase of monocyte attractants such as MCP-1/CCL2 (Dahlman et al., 2005; Kamei et al., 2006; Kanda et al., 2006). When in the adipose tissue, these macrophages secrete different cytokines that affects the adipocytes for example TNFα (Uysal et al., 1997). Given that TRAP is normally expressed in cells from the myeloid linage (Hayman et al., 2000; Hayman et al., 2001; Lang and Andersson, 2005) the present inventors investigated if TRAP was expressed in this population also in adipose tissue of mouse and human origin, thus indicating a paracrine effect of monomeric TRAP on adipocytes. In mouse, almost 90% of the TRAP transcripts originate from the myeloid specific transcript 1C and in human tissue, TRAP was mainly expressed in CD68 positive macrophages. In vitro studies also confirmed previously published data (Janckila et al., 2005) that monomeric TRAP can be secreted from macrophage cell lines in vitro. In light of these data, a hypothesis is proposed in which macrophages controls the development of obesity by directly inducing adipogenesis. It is hypothesized that in a situation where there is an increased calorie intake resulting in increased adipose tissue mass and thereby macrophage influx, macrophages secreting monomeric TRAP induces adipogenesis by an, at least partly, PPARγ independent pathway, thus contributing to the increase of total adipose tissue mass.
Consequently, if this increase in secretion of monomeric TRAP is persistent, novel and small fat cells are formed contributing to the hyperplasia component of obese adipose tissue.
Consequences of Increased Expression and Secretion of TRAP from Macrophages in Adipose Tissue−Normal Adipocyte Size=Normal Metabolism, Gene Expression Profile and Insulin Sensitivity
Obesity is linked to insulin resistance (Hubert et al., 1983; Kissebah et al., 1982) and several studies have highlighted the correlation between adipocyte size rather than adipose tissue mass and insulin malfunction (Brook and Lloyd, 1973; Kissebah et al., 1982; Salans et al., 1973; Salans et al., 1968; Stern et al., 1972; Weyer et al., 2000). To explain this correlation at least two theories have been presented. One is that enlargement of adipocytes does not have pathophysiological significance by itself but is rather a manifestation of other pathogenic factors leading to insulin resistance (Jernas et al., 2006; Weyer et al., 2000; Winkler et al., 2003). One such factor is increased adipocyte lipolysin resulting in elevated fatty acids, which in turn cause insulin resistance (Amer, 2003). The second theory implies that enlarged adipocytes are themselves pathogenic for example by a change of gene expression profile involving, among others, altered expression of adipokines and cytokines (Weyer et al., 2000). Since the obese TRAP+ mice had normal fat cell size, their adipocyte metabolism, degree of insulin resistance and alteration in gene expression profile in adipose tissue were investigated. As judged by circulating insulin and glucose levels and by measurement of insulin action of lipolysis and lipogenesis, isolated fat cells from the obese TRAP+ mouse exhibited normal insulin sensitivity, although it can not be excluded that some alterations in insulin action in skeletal muscle or liver which were not directly examined. Furthermore, basal and catecholamine induced lipolysis were also normal in the obese mice. Thus, there was no evidence of enhanced expression of fatty acid mobilisation genes in adipose tissue in the TRAP+mouse. An increased amount of TNFα mRNA (though serum TNFα levels appeared normal) but no change in other cytokines such as IL1b and IL6 or the ratio between leptin and adiponectin were found. Thus, the absence of fat cell hypertrophy and the modest change in expression of cytokines associated with an innate immune response most likely explain why obese TRAP+mice had nor or little evidence of insulin resistance. The relation of fat cell size for in vivo insulin sensitivity in human also was investigated since previously published data suggests a relationship between these factors (Brook and Lloyd, 1973; Kissebah et al., 1982; Salans et al., 1973; Salans et al., 1968; Stern et al., 1972; Weyer et al., 2000). It was found that fat cell size is related to in vivo insulin sensitivity and this is independent of degree of adiposity only among the obese. Thus, it appears that in both man and mice the hyperplastic component of obesity is protective against insulin resistance. In summary, it appears that macrophage infiltration of adipose tissue is important for the formation of new and small fat cell during development of obesity. The mechanism by which macrophages increase proliferation and differentiation of adipocyte precursor cells is presumably by secretion of monomeric TRAP. These newly formed fat cells have normal lipid metabolism that makes the tissue prone to accumulate lipid.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0700363-5 | Feb 2007 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2008/050172 | 2/13/2008 | WO | 00 | 10/14/2009 |
| Number | Date | Country | |
|---|---|---|---|
| 60889820 | Feb 2007 | US |
