Patent Application
20240023525
The present invention belongs to the field of research tools for glaucoma, more specifically it relates to a non-human animal model of chronic glaucoma. In addition, the invention refers to a method for the preparation of said animal model, as well as to the use of thereof.
Glaucoma is a degenerative optic neuropathy in which irreversible vision loss is produced by the gradual death of retinal ganglion cells (RGC), although affectation in other retinal layers has also been observed in recent studies (Vidal-Sanz et al., Prog. Brain. Res. 2015; 220:1-35). According to the World Health Organization (WHO), it is the second leading cause of irreversible blindness in the world and the first in developed countries, with over 61 million people affected, although it is estimated that this prevalence is actually 20-25% higher due to frequent undiagnosed cases, as this pathology is asymptomatic until its late stages. It is believed that 7 million glaucoma patients have already lost their vision. Over 2 million cases are registered in the world every year, and the pathology is expected to affect 80 million people (according to “World Glaucoma Association” data). In response to the growing disease burden derived from chronic ocular conditions, the WHO coordinates a worldwide research attempt focused on identifying services and policies to fight neurodegenerative pathologies, being glaucoma among them.
The main modifiable risk factor which is currently known is intraocular pressure (IOP) increase, which hinders blood supply to the retina, compromising it by the pressure excess. This damages neural structures with optic nerve atrophy. Furthermore, it is argued that the pressure increase in the optic nerve connective tissues interrupts the axo-plasmatic flow, blocking the arrival of endogenous neurotrophic factors to the neuronal body from the axons (Pease et al., Invest. Ophtalmol. Vis. Sci., 2000, 41(3):764-774). Although it is considered there is risk of suffering from glaucoma when IOP is high, not every patient with high IOP develops glaucoma, nor a decrease in IOP assures protection against the development of the disease (Ritch et al., Ophtalmol. Clin. North Am., 2005, 18(4):597-609). Therefore, in the last decade other important factors in the genesis and the development of neuronal degeneration in the retina have been studied, proving that the neurodegeneration process can be described, chronologically, in three steps:
There are different types of glaucoma, being primary open-angle glaucoma (OAG) the most frequent as well as one of the most usual causes of blindness in the world. It is characterized by slow and progressive clinical process due to the fact that gradual and chronic IOP increase does not produce pain or discomfort and, at the first stages, loss of visual field is not perceptible by patients, although as it develops it causes malfunctions in the visual field and progressive vision loss. Once these symptoms appear, they are irreversible and might imply the disease is in an advanced stage of its evolution. The main therapy is based on reducing IOP with hypotensive eyedrops, drainage implants or surgery, depending on stage and severity.
In addition, physiopathological studies of OAG showed that once neuronal death starts, even when patients present IOP between limits considered normal, a flood of damaging proinflammatory and proapoptotic substances of RGC is unleashed, which causes the death of the adjacent neurons, known, as mentioned before, as secondary degeneration (Ritch et al., Ophthalmol. Clin. North Am., 2005, 18(4):597-609). Therefore, the use of neuroprotective therapies in the treatment of glaucoma results in an alternative way to therapies based on IOP control, which are sometimes deficient in many glaucomatous pathologies and in patients with normal IOP values.
The main problem to evaluate the efficacy of hypotensive treatments or to develop new therapies resides in the absence of a chronic and slow glaucoma animal model that simulates a human one. Nowadays most animal models in retinal degeneration are acute models, either by genetic failure or induced damage, obtaining abrupt deterioration of the tissue in few weeks. On the one hand, these models do not reproduce the reality of retinal pathologies in human beings, whose nature is chronic and where retinal damage usually takes years to appear (Dey et al Cell Transplant. 2018 February; 27(2):213-229, Mukai et al PLoS ONE. 2019. 14(1): e02087132019). On the other hand, acute models of degeneration are not useful to assess modified release systems, which present as great potential their capacity to extend the release of active substances in small quantities for months (Nadal-Nicolas et al., Invest. Ophtalmol. Vis. Sci. 2016; 57(3):1183-92). Furthermore, these acute glaucoma animal models do not allow testing the efficacy of new therapies (hypotensive, neuronal protective, etc.) because in few days the optic nerve of the animal is completely and irreversibly atrophied and therefore no treatment has enough time to stop the disease progression.
In order to broaden and improve the knowledge of glaucomatous pathologies, several animal models have been developed in the last decades (Dey et al Cell Transplant. 2018 February; 27(2):213-229 in which it has been resorted to an increase in IOP secondary to a decrease in the flow of aqueous humor, either through cauterization, ligature and/or sclerosis of episcleral veins, either by mechanical blockage of the trabecular meshwork with non-biodegradable particles injected in the anterior chamber, or through the use of corticoids (which reduce aqueous humor outflow when inhibiting cellular phagocytosis in the trabecular meshwork, thus avoiding the cleaning of the waste channels (Zeng et al. Current Eye Research 2019). The model of episcleral sclerosis using a hypertonic saline solution has proved to increase IOP in a sustained manner with retinotopic death of RGC (Morrison et al., Exp. Eye Res. 1997, 64:84-96; Vecino et al., Glaucoma Basic and Clinical Concepts 2011, First edition, Croatia Intech:319-334; Chen et al., Invest. Ophtalmol. Vis. Sci. 2011, 52(1):5-16), albeit acute optic nerve atrophy appears in the animal in merely few weeks.
Further animal models of glaucoma have been reported in the prior art so far (Struebing el al Prog. Mol. Biol. Trans. Sci. 2015; Bouhenni et al. J. Biomed. Biotech., 2012; Agarwal et al Expert Opin Drug Discov. 2017; Biswas and Wan Acta Ophthalmol. 2019) but no research group has achieved the creation of an animal model which mimics OAG and allows assessing new reliable therapies.
The present invention represents a new model of chronic animal glaucoma based on the injection of biodegradable microspheres (Ms) of PLGA, PLA or PGA (poly-lactic-co-glycolic-acid, polylactic acid or polyglycolic acid) in the anterior chamber of the eye in a mammal, preferably a rat, which produces a progressive and chronic increase of IOP and consequently, a chronic neurodegenerative process which simulates the conditions which appear in chronic glaucoma patients. Until now, biodegradable microparticles had never been used for this purpose. Biodegradable microparticles produce mechanical blockage in the trabecular meshwork which can be accompanied by a pharmacological effect if the particles are loaded with pharmacological agents able to provide damage at this level. All these events cause a slow, persistent and progressive rise of IOP with slow retinal degeneration of the ganglion cell layer and the optic nerve, simulating OAG physiopathology.
This invention allows to use biodegradable microspheres not only as active substance administration systems (Garcia-Caballero et al. Eur J Pharm Sci. 2017a; 103:19-26) but also as a useful tool to create ocular hypertensive animal models which are able to reproduce chronic human pathologies.
The main object of the present invention is represented by a non-human animal mammalian model of chronic glaucoma wherein the animal has intraocular PLGA, PLA or PGA microparticles, optionally loaded, in order to induce progressive increase of intraocular pressure.
It is also an object of the invention a method for preparing the non-human animal mammalian model of chronic glaucoma according to the invention which comprises the intraocular injection in the animal's eye of an aqueous suspension of PLGA, PLA or PGA microparticles optionally loaded.
It is finally an object, the use of the non-human animal mammalian model of the invention for the study of physiopathology of glaucoma as well as a tool for pharmacological, biomaterial and/or surgical studies.
In a first aspect, the invention refers to a non-human animal mammalian model of chronic glaucoma wherein the animal has intraocular PLGA, PLA or PGA microparticles, optionally loaded, in order to induce increase of intraocular pressure.
The PLGA, PLA or PGA microparticles may be introduced in the eye in an unloaded form or loaded with any substance which may have an effect or an influence in the timing, intensity or any other parameter affecting the onset and development of the pathology. Although it is not primarily the aim in the present invention, the substance loaded in the microparticles can also be used for testing its therapeutic effect once the negative effects on retina and optic nerve degeneration of the animal model of the invention have started to become apparent.
In a particular embodiment of the invention the PLGA, PLA or PGA microparticles are loaded with dexamethasone or with a combination of dexamethasone and fibronectin. The use of PLGA, PLA or PGA microparticles loaded with dexamethasone or with a combination of dexamethasone and fibronectin have proven as effective in reducing the number of ocular injections needed in order to achieve the onset and development of the glaucomatous pathology.
The animal model of the invention is a chronic glaucoma model with ocular hypertension for at least 6 months' time (24 weeks). The model implies a gradual increase, without large fluctuations and with sustained IOP values, which produces a retinal, RGC and optic nerve neurodegeneration that mimics the one in chronic OAG.
The administration of biodegradable microparticles of PLGA, PLA or PGA, preferably in the anterior chamber of the eye has proven to cause a mechanical stop in the drainage of aqueous humor and a mild inflammatory reaction at a local level and, in the case of loaded microparticles, also the sustained release of substances such as dexamethasone (Dex) and fibronectin (Fibro) have proven to alter the trabecular meshwork.
The use of biodegradable microspheres or microparticles such as PLGA, PLA or PGA microparticles by means of corneal injections provide an animal model with a healthy ocular surface and anterior segment, no lens opacities, free visual axis, ocular biocompatibility, as well as, the need for less reinjections since microspheres' residues remain in the eye. Advantageously, the PLGA, PLA or PGA biomaterials used in the elaboration of microspheres are biocompatible, being CO2 and H2O the products of their degradation (Herrero-Vanrell et al., 2001). According to molecular weight and composition, these polymers can have different degradation rates, ranging from months to years. Furthermore, these polymers have been used to create controlled drug delivery systems and that is why they are useful in the context of the invention to induce increased IOP and, at the same time, to release substances in a sustained and controlled manner in the case of loaded microparticles that can exert additional effects to be studied or tested.
In a particular and preferred embodiment of the invention, the non-human animal mammalian model is a rodent, such as a rat, a mouse or a guinea pig. In the more preferred embodiment of the invention, the non-human animal mammalian model is a rat.
With regard to the size of the microparticles used in the context of the present invention, the microparticles of PLGA, PLA or PGA, optionally loaded, have a particle size between 5 μm and 40 μm, more preferably between 10 μm and 20 μm.
The microparticles may be injected in different part of the eye thereby causing a gradual increase of IOP, however in the preferred embodiment of the invention the intraocular microparticles optionally loaded are introduced and so present in the anterior chamber of the eye of the animal causing a gradual increase of IOP. The administration of the microparticles in the anterior chamber of the non-human mammal's eye produces a chronic intraocular pressure rise with ganglion cell death, which simulates the primary open-angle glaucoma of human physiopathology without negatively affecting other visual or motor functions in the eye. The process is not painful for the animal as it produces a gradual increase of IOP but not acute hypertension nor ischemia, nor retinal occlusions, nor corneal edema. Moreover, it is a simple surgical technique.
The resulting non-human mammal animal model thus mimics a chronic open-angle glaucoma of humans and has the following characteristics:
Since the non-human mammal animal model of the invention evolves in chronic gradual retinal, RGC and optic nerve degeneration, it has the advantage that it allows treating and/or preventing neuroretinal loss in a functional damage frame before cell death and the subsequent secondary degeneration occur, focusing on detection and early treatment of neurodegeneration. As such it represents an hypertensive and neurodegenerative ocular model which can be used as a potential effective tool for later pharmacological, biomaterial and/or surgical studies.
In addition, although primarily focused in the study of the physiopathology of glaucoma as well as in the development of innovative treatments of glaucoma, the animal model of the present invention can also be used as a research tool for the rest of the pathologies that cause optic nerve degeneration (ischemic optic neuropathology, hereditary optic neuropathology, tox-nutritional optic neuropathology, etc.)
The non-human mammal animal model of the present invention when compared with the well-established episcleral injection of hypertonic saline solution model, has the advantage of causing intraocular pressure in a slow, progressive and sustained manner over time, with an associated relevant ganglion cell and RNFL (Retinal Nerve Fiber layer) thickness loss, although in a slower and less aggressive manner, with fewer reinjections and also a better preserved ocular surface.
A further aspect of the present invention is a method for generating or preparing the non-human animal mammalian model of chronic glaucoma of the invention comprising the intraocular injection in the animal's eye of a suspension, preferably an aqueous suspension, of PLGA, PLA or PGA microparticles, optionally loaded.
In particular and preferred embodiment of the method, the microparticles are loaded with dexamethasone or with a combination of dexamethasone and fibronectin. As explained before, the use of these compounds or substances have proven to effectively reduce the number of ocular injections needed in order to achieve the onset and development of the physiological and anatomical symptoms of glaucoma. For example, when non-loaded PLGA microparticles are used in the development of the animal model, microparticles were injected 7 times in 24 weeks. However, when the same microparticles are loaded with dexamethasone the frequency of injection can be reduced to two injections in the 24 weeks study, namely at the start of the study an in week 4. In the case the same microparticles are loaded with dexamethasone and fibronectin a single injection at the start of the 24 week study is enough for achieving the desired effects.
The preferred embodiment of the method for generating a non-human mammalian model of chronic glaucoma comprises using a rodent such as a rat, a mouse or a guinea pig. In a particularly preferred embodiment, the animal used in the method is a rat.
As already mentioned, although the method for producing the animal model of glaucoma of the invention can comprise the injection of the microparticles of loaded PLGA, PLA or PGA in different parts or compartments of the animal's eye, the method of the invention preferably comprises that the intraocular injection is performed in the anterior chamber of the eye of the animal.
The optionally loaded microparticles injected must have a particle size between 5 and 40 μm, more preferably between 10 μm and 20 μm. They are preferably injected in aqueous suspension with a concentration of optionally loaded microparticles of preferably 0.005% to 20% by weight of the total suspension. A volume of 1 μl to 5 μl of the aqueous suspension of microparticles optionally loaded is generally and preferably-injected in the animal's eye.
Prior to injection, animals are preferably anesthetized by any usual mean. For the correct injection the use of atraumatic forceps is highly recommended. The forceps allow holding the eyeball by using the eyelid skin as girth thus avoiding sudden an intense eyeball prolapse. Injection can be then performed by usual means such as a needle or microneedle, preferably a glass microneedle.
The final aspect of the invention refers to the use of the non-human animal mammalian model of glaucoma of the present invention.
The more important application of the non-human animal mammalian model of the present invention is for its use in the study of physiopathology of glaucoma. More particularly, the present animal model is a research tool for the study of chronic OAG as the pathology evolves in the model with a progressive and chronic increase of IOP and consequently, a chronic neurodegenerative process which simulates the conditions which appear in chronic glaucoma patients. The mechanism works causing both a mechanical and pharmacological blockage in the trabecular meshwork and which can simulate OAG physiopathology and cause a slow, persistent and progressive rise of IOP with slow retinal degeneration, including among others: retinal ganglion cell layer, optic nerve, photoreceptors layer, activation and proliferation of glial cells, etc.
As a model of glaucoma, the non-human animal mammalian model of the present invention is useful as a tool for pharmacological, biomaterial and/or surgical studies.
The development and validation of the non-human animal mammalian model of glaucoma of the present invention was achieved on the basis of the results of a study which is the object of the next examples. The conditions and methods used in the study will become apparent in the next examples.
This invention involves animal experimentation for its development, therefore it adjusted to comply with the current legislation, both the European directive (2010/63/EU) and the Spanish Royal Decree (RD 53/2013), as well as the Animals Protection regulation (Ley11/2003) in Aragon, which establishes basic rules applicable to the protection of animals used for experimental purposes.
Conversely, the staff in charge of working with animals is qualified to do so and followed the Order ECC/566/2015 which establishes the requirements to be met by the researchers who operate with animals used, bred or provided for the purpose of experimentation and other scientific purposes.
Studies were carried out in the research support center of the Centre for Biomedical Research in Aragon (CIBA) and Aragon Institute of Health Research (IIS Aragon), accredited center who has an animal experimentation department, classified as breeding, suppliers and users' facility (in accordance with article 13 del R.D. 1201/2005 for the protection of animals used for experimentation).
On the one hand, this invention allows reducing the number of animals used, since it generates long periods of ocular hypertension with progressive and chronic rise in the IOP in the same animal, and structural and functional follow-up performed through non-invasive tests such as OCT (optical coherence tomography) and ERG (Electroretinography).
Besides, we created a refined model of glaucoma in which the intervention to generate it is minimally invasive by means of corneal injection. It does not produce the common sudden hypertension that occurs in the known prior art models and which could be the cause of the pain, but instead hypertension is progressive and asymptomatic, as it happens in the human pathology.
The model was achieved by injecting biocompatible and biodegradable material, and as an ‘add-on’ reducing the need for multiple reinjections to maintain ocular hypertension. For example, a total of 7 injections were needed in 6 months for the hypertensive curve achievement; 2 in the model using Ms loaded with dexamethasone and just 1 injection in the model by Ms co-loaded with dexamethasone and fibronectin.
In addition to reducing the number of interventions in the animal, surgical time oscillated between 6 and 7 minutes from the beginning of the anesthetic induction to ocular injection and introduction in an oxygen enrichment box for kind recovery. A model of chronic glaucoma has been achieved inflicting as little discomfort on the animal as possible, being minimally invasive, without the need of genetic modification that could alter its biology and/or tumorigenesis, easy to conduct and reproducible, approaching to the real human glaucomatous pathology.
Biodegradable microspheres (Ms) were elaborated using the solvent extraction-evaporation method from a previously formed emulsion composed by an inner oily phase and an external aqueous phase (O/W emulsion). The polymer used was PLGA 50:50 with a molecular weight of 16,000 g/mol GPC and an inherent viscosity of 0.24 dl/g [Resomer 502]. The method employed for microspheres preparation was the following: PLGA (400 mg) was dissolved in methylene chloride (2 mL). This organic phase was emulsified with 5 mL of PVA MiliQ water solution 1% (w/v) using a homogenizer (Polytron® RECO, Kinematica, GmbHT PT3000, Lucerna, Swithzerland) at 7,000 rpm for 1 minute. The formed emulsion was poured onto 100 mL of PVA MiliQ water solution 0.1% (w/v) and maintained under magnetic stirring for 3 hours to allow organic solvent extraction and evaporation, and subsequently Ms maturation. Afterwards, Ms were washed in MilliQ water in order to remove PVA and separated in two granulometric fractions (38-20 μm and 20-10 μm) employing three sieves (mesh size 38, 20 and 10 μm). Finally, Ms were freeze-dried (Freezing: −60° C./15 min, drying: −60° C./12 h/0.1 mBar) and storage at −30° C. in dry conditions
Two granulometric fractions were selected for in vivo study with non-loaded Ms (10-20 and 20-38 micrometers). Injections were performed at basal, 2, 4 and 8, 12, 16 and 20 weeks. Using Ms sized 10-20, as comparable results were obtained comparing to the hypersaline episcleral model.
PLGA microspheres are homogeneous degradable matrices in which active compounds can be included and subsequently released for several months, depending on the polymer and active characteristics. In this case, we have prepared dexamethasone loaded PLGA microspheres in the 10-20 micrometer range using the same polymer mentioned before.
Dex-loaded PLGA Ms were obtained following the already mentioned Oil-in-/Water (O/W) emulsion solvent extraction-evaporation technique. First, PLGA (400 mg) was dissolved in methylene chloride (2 mL). Micronized Dexamethasone (40 mg) was added to the polymeric solution and dispersed by ultrasonication (Ultrasons; J.P. Selecta, Barcelona, Spain) for 5 minutes and further sonicated (Sonicator XL; Heat Systems, Inc., Farmingdale, NY, USA) for 1 minute at 4° C. to obtain an homogenous dispersion. The so-formed O-phase was emulsified adding 5 mL of PVA MiliQ water solution 1% (w/v) through a homogenizer (Polytron® RECO, Kinematica, GmbHT PT3000, Lucerna, Swithzerland) at 7,000 rpm for 1 minute. The resulting O/W emulsion was incorporated to 100 mL of PVA MiliQ water solution 0.1% (w/v) and stirred for 3 hours leading to Ms maturation.
Once maturation step was completed, MiliQ water was employed to wash Ms, removing the remaining surfactant PVA. Subsequently, the 20-10 μm size fraction was selected, freeze-dried (Freezing: −60° C./15 min, drying: −60° C./12 h/0.1 mBar) and storage at −30° C. in dry conditions
In a third part of the study dexamethasone/fibronectine-loaded PLGA microspheres were prepared as follows: The water-in-oil-in-water (W/O/W) double emulsion solvent extraction-evaporation technique was employed for dexamethasone/fibronectine-loaded PLGA microspheres elaboration. Briefly, micronized Dex (40 mg) was added to a polymeric solution (400 mg of PLGA dissolved in 2 mL of methylene chloride). The suspension was homogenized by ultrasonication with ice-water bath (Ultrasons; J.P. Selecta, Barcelona, Spain) for 5 minutes and sonication (Sonicator XL; Heat Systems, Inc., Farmingdale, NY, USA) for 1 additional minute in ice-water bath. The inner aqueous phase composed by 20 μL of fibronectine water solution (containing 42.8 μg of fibronectin) was added to this organic phase and emulsified by sonication (Sonicator XL; Heat Systems, Inc., Farmingdale, NY, USA) for 30 seconds at 4° C. to create the initial W1/O emulsion. Afterwards, 5 mL of PVA MiliQ water solution 1% (w/v) were added to the mentioned W1/O emulsion and the mixture was emulsified (Polytron® RECO, Kinematica, GmbHT PT3000, Lucerna, Swithzerland) at 7,000 rpm for 1 minute to form the final W/O/W emulsion that was finally added to 100 mL of PVA MiliQ water solution 0.1% (w/v) to get hardening by organic solvent extraction and evaporation under magnetic stirring at room temperature for 3 hours. After that, MSs were washed with MiliQ water to remove surface PVA. The desired granulometric size fraction (20-10 μm) was collected by sieving, freeze-dried (Freezing: −60° C./15 min, drying: −60° C./12 h/0.1 mBar) and storage at −30° C. in dry conditions.
Loaded and non-loaded PLGA Ms characterization was performed in terms of morphological evaluation, mean particle size and particle size distribution, encapsulation efficiency and in vitro release studies (for loaded Ms). Production yield percentage of the selected granulometric fraction was also determined.
Production yield percentage was calculated according to the following equation (1).
Gold sputter-coated freeze-dried loaded and non-loaded PLGA Ms were observed by scanning electron microscopy (SEM, Jeol, JSM-6335F, Tokyo, Japan).
Particle size and particle size distribution were measured by dual light scattering (Microtrac® S3500 Series Particle Size Analyzer, Montgomeryville, PA, USA). Volume mean diameters (±standard deviation) obtained from 3 measurements were used to express the mean particle size.
The HPLC/MS system was composed by a liquid chromatography instrument (Waters 1525 binary HPLC pump and Waters 2707 autosampler) employing a Nova-Pak C18 column (4 μm, ID 2.1 mm×150 mm) coupled to a guard column (4 μm, 3.9 mm×20 mm), both maintained at 45° C. MS detector (Waters 3100 single quadrupole mass spectrometer) was connected to this system via Empower 2 (Waters, Milford, USA). The ESI source was adjusted in the positive ion mode (ESI(+)) for Dex detection. Selected ion recordings (SIR) DX mass (m/z) 147.10 was measured under mass spectrometer source conditions of 3.5 kV electrospray voltage, 130° C. heated capillary temperature. Nebulization (100 L/h flow rate, 130° C. source temperature, 5 V extractor voltage) and desolvation (400 L/h flow rate, 300° C. desolvation temperature) were performed employing nitrogen gas (>99.999%). An isocratic HPLC method was developed to quantify Dex encapsulation efficiency and release from Ms. This method was composed by 50% ammonium acetate 15 mM/1 mL formic acid in MiliQ water and 50% acetonitrile at a flow rate 0.3 mL/min.
A known amount of Dex-loaded PLGA Ms (1 mg) was dissolved in 2.5 mL of methylene chloride. Then, 6 mL of methanol were incorporated in order to precipitate the dissolved polymer. After vortex mixing and centrifugation (5,000 rpm for 5 minutes at 20° C.), the etanol:methanol supernatant was collected, filtered (0.22 μm) and analyzed using the previously described HPLC/MS method for dexamethasone quantification.
2.6 In Vitro Dexamethasone Release Studies from Dex-Loaded and Dex/Fibro-Loaded PLGA Ms
A Dex-loaded PLGA Ms suspensions (2.5 mg/mL) was prepared in quadruplicate using phosphate buffered saline (PBS, pH 7.4) with sodium azide (0.02% (w/v) as release media using 2 mL Eppendorf tubes. The so-prepared samples were located in a water shaker bath (100 rpm, 37° C., Memmert Shaking Bath, Memmert, Schwabach, Germany). Supernatants were periodically collected after gently centrifugation (5,000 rpm for 5 min, 20° C.), filtered (0.22 μm) for dexamethasone quantification by HPLC/MS employing the method previously mentioned). At each time point, the tubes containing the remaining Ms samples were refilled with fresh release media to continue with the release study. The same protocol was performed at each time-point.
In order to mimic the animal study, a second “dose” of 2.5 mg of Dex-loaded PLGA Ms were included at 28-days post-study to each sample, also increasing the amount of release media to maintain the initial suspension concentration. The release study was performed as explained before for 140 additional days (total time of in vitro release study: 168 days, that is 24 weeks).
2.7 In Vitro Fibronectin Release Studies from Dex/Fibro-Loaded PLGA Ms
2.5 mg of dexamethasone/fibronectin-loaded PLGA Ms were suspended in phosphate buffered saline (1 ml, PBS, pH 7.4) including sodium azide (0.02% (w/v) and bovine serum albumin (BSA) (1%) in a 2 mL low-binding Eppendorf tubes. The suspension was placed in a water shaker bath (100 rpm, 37° C., Memmert Shaking Bath, Memmert Schwabach, Germany) (n=2). At pre-set times, the so-prepared samples were centrifuged (5,000 rpm, 5 minutes, 20° C.), the supernatants were removed for Fibronectine quantification by Enzyme-Linked ImmunoSorbent Assay (ELISA). At each time point, the tubes containing the remaining microspheres were refilled with fresh PBS/azide/BSA media to continue with the release study.
Thus far, there are no studies which approach the development of a chronic glaucoma animal model using this methodology with PLGA biodegradable microspheres.
During the development of this invention, we have proved that the injection of 2 microliters of PLGA microsphere suspensions (10%) (w:y), when injected in the anterior chamber of the rats' eyes, is mainly stored in the trabecular meshwork provoking a stop at the transition of the aqueous humor, inducing a slow and progressive increase in the IOP. This IOP increase results in chronic glaucoma, slow degeneration of the ganglion cell layer and loss of progressive visual capacity in the animal.
In order to correctly develop the new animal model, a well stablished model (which is an episcleral veins sclerosis model by injecting a hypertonic solution —NaCl 1.8M-) was compared with the new proposed strategy. In a first step two particle size ranges were used: (38/20 μm) and (20/10 μm). The comparative study was performed for 8-week study. The three models were characterized through weekly clinical analysis and measurements of IOP; biweekly structural study with optical coherent tomography (OCT) (0, 2, 4, 6, 8 weeks), and baseline and final functional study with electroretinogram (ERG). In the group of microspheres, their position was visualized at a trabecular level through direct visualization proving the preferential localization of microspheres at the inferior iridiocorneal angle (due to higher density of Ms compared to aqueous humor).
The episcleral sclerosis model and the long-term 20/10 μm microspheres model were subsequently compared in a long-term study (24-week study). Both models were characterized through clinical analysis and weekly IOP measuring, structural study with in vivo OCT at baseline 8, 12, 18 and 24 weeks (because earlier times were deeply analysed in the preliminary) and functional study with ERG at 0, 12 and 24 weeks.
For both 24-weeks studies performed with loaded Ms (dexamethasone and co-loaded dexamethasone-fibronectin) clinical signs and IOP were recorded weekly, OCT at 0, 2, 4, 6, 8, 12, 18, 24 weeks and ERG at 0, 12, 24 weeks in order to compare with non-loaded Ms.
In all experiences the first injection of microspheres were performed in 4-week-old Long Evans rats weighed between 50 and 100 grams at the beginning of the study.
In the 8-week study 25 animals were used in the episcleral model, 16 animals in the 38/20 microspheres and 23 in the 20/10 microspheres. In the long-term (24-weeks) study 25 animals were employed in the episcleral model and 25 in the non-loaded microspheres. In the 24-week study performed with dexamethasone loaded microspheres 43 animals were used. Finally, in the 24-week study with dexamethasone-fibronectin loaded microspheres 45 animals were used. All cohorts were composed by 40% males and 60% females.
The experiment was approved by the Committee on Animal Research and Ethics (PI34/17) according to ARVO requests. Likewise, the premise of using the least number of rats was accomplished so as to obtain a reliable average value in each of the programmed post-injection times.
An hour before starting the surgical procedure the animal received a subcutaneous injection of buprenorphine (0.05 mg/kg) to avoid any intra- or postoperative discomfort, buprenorphine produced an intraoperative miosis, which opens the iridocorneal angle and protects the lens from a iatrogenic trauma with the glass micropipette.
The anesthetic induction was carried out in an induction box with a mixture of 3% sevoflurane and 1.5% oxygen. Once the animal was asleep, 1 drop of topical corneal anesthetic (doble anesthetic Colircusi®) and a povidone-iodine solution (10% Betadine®) was instilled for ocular cleaning. The same action was repeated in the surgical table. The animal remains under gas anesthesia with a nose-mouth mask and temperature control in the course of the surgical procedure.
Freeze-dried PLGA microspheres were reconstituted in a saline solution NaCl 0.9%, at a concentration of 10% (w:v), vortexed and pipetted until achieving a yellowish-white homogeneous suspension.
By means of atraumatic forceps the eyeball is held using the eyelid skin as girth, avoiding sudden and intense eyeball prolapse. 2 microlitres of particles suspension were injected with a glass microneedle by a 10 microlitres Hamilton® syringe. The injection was performed in the superotemporal quadrant in clear cornea, between the limbo-corneal and apex, eluding visual axis and valved to avoid reflux.
The animal was allowed to recovering in a box with temperature control and 2% oxygen enrichment. This leads to a progressive awakening without hyperpressure, vasalva or ocular discomfort. The complete surgical procedure was performed in 7 minutes from induction to complete recuperation.
The corneal surface appearance, the anterior chamber (to confirm the presence of microspheres inside as well as to discard any acute inflammatory reactions or bleeding), the iris and the crystalline were assessed, 24 hours post-injection and weekly until the end of the study.
3.3. IOP Measuring:
IOP measuring were carried out weekly with the rebound tonometer Tonolab® (Tonolab; Tiolat Oy Helsinki, Finland). The measurements were always performed in the morning under gas anesthesia (sevofluorane 3%) not exceeding 3 minutes to avoid changes in the IOP due to the anesthetic effect. The final measurement was the average of 3 consecutive measuring, being this the average of 6 consecutive rebounds, which makes a total of 18 measurements.
OCT is a technique of digital image analysis widely used in ophthalmology. It registers light from a source which rebounds in the retina and is able to take high resolution tomography slides, which allow identifying retinal layers similar to an in vivo histological analysis. The advantages of this powerful test are that it is not invasive, it is comfortable for the patient and examiner, fast, accurate, reliable and easy to carry out even in animals which do not focus sight. It allows visualization, analysis, and a quantitative follow-up of parameters such as thickness of the nerve fiber layers in the retina around the optic nerve, and the thickness of each layer of the retina (by segmentation) to the level of the posterior pole of the eye. This test was carried out in every eye using the latest technology of a fourier-domain device (high-resolution Spectralis, Heidelberg Engeneering, Germany). The version for rodents of this system acquires cross sectional images by means of 61 b-scans around of 3 mm of length centered in the optic nerve—and a contact lens adapted on rat's cornea to get higher quality images. In order to carry out this test, the animal received intraperitoneal mixture of ketamine (60 mg/kg)-dexmedetomidine (0.25 mg/kg) anaesthesia as well as a mixture of tetracaine (1 mg/ml)-oxibuprocaine (4 mg/ml) topical ocular anaesthesia and kept under thermal control during the procedure.
3.5. Functional Study with Electroretinogram (ERG):
ERG (Roland Consult® RETIanimal ERG, Germany) allows efficient characterization of animal models, since it assesses the functioning of the retina and the transmission of visual impulse to the brain. This test was performed in a dark room after darkness acclimation for at least 12 hours and pupillary dilation with tropicamide and phenylephrine eyedrops. It was carried out under intraperitoneal ketamine-dexmedetomidine anesthesia and thermal control.
Dark-adapted flash scotopic ERG (specific to assess middle and outer retina layers such as bipolar and photoreceptor) and light-adapted photopic negative response (PhNR) protocol (specific for RGC evaluation) were used.
With these two tests (OCT and ERG) structural and functional damage of retina and specifically the ganglion cell layer in alive animals were determined without causing harm nor sacrifice in the different established examination times. These techniques allow the monitorization of the illness using the less number of animals and trying to cause the less damage as possible (both tests are non-invasive and therefore do not cause damage to animals, only risks due to cumulative anesthesia).
4.1. Preliminary Study: Ms (20/10) and (38/20) for 8 Weeks of Follow-Up and Comparison with the Epiescleral Model.
PLGA Ms prepared showed a production yield (PY) between 43 and 46% for the 38-20 μm size range, while the 20-10 μm fraction resulted in a PY % between 37 and 40%. In both cases a monodisperse distribution of particle size was observed. The mean particle size for each size range is compiled in table 1.
According to SEM pictures, both size fractions showed spherical particles in the micro-range with non-porous smooth surfaces (
No infection, intraocular inflammation (synechae), cataract formation, neither retinal detachment was found in any ocular hypertensive (OHT) model but corneal surface was better preserved in the Ms20/10 and Ms38/20 models. Microparticles showed a tendency to localize at the inferior iridocorneal angle. In some cases they agglomerate forming a solid depot. This disposition allowed a clear visual axis and subsequently a correct OCT and ERG acquisition (
Injection of PLGA Ms in the anterior chamber was able to promote a continuous elevation of IOP. OHT was detected three weeks after first injection in both microspheres models, but since first week in EPIm. The Ms38/20 model showed more fluctuations in IOP values. High percentages of OHT (>20 mmHg) eyes were found over time in all the three models but EPI model showed the biggest percentages at nearly all times explored (
Both Ms models and epiescleral model experienced a progressive decrease in retina, Retinal Nerve Fiber Layer (RNFL) and Ganglion Cell Layer (GCL) and although fluctuations in thickness were observed in all the three models, the Ms38/20 model showed the biggest one (table 2). The percentual loss of OCT thickness (change of thickness respect to baseline measurement of each variable) was also analyzed and the Ms 38/20 model showed at the end of the study, the highest percentage thickness loss in all OCT parameters. The GCL parameter experienced the biggest loss in each Ms model (
EPI and Ms 38/20 models showed higher loss in the outer retinal sectors and all models showed higher percentage loss in the superior-inferior axis sectors in RNFL. Moreover all OHT models showed higher loss in the inner sectors of GCL and RE from both EPI and Ms 20/10 models experienced the same percentage loss trend by OCT sectors (S>I>N>T) (
The RE loss rate per day and mmHg that IOP had increased in each week was calculated and expressed in μm/mmHg/day from all OCT sectors average to standardized the neuroretinal loss. The Ms 38/20 model experienced the more important loss rate (in average) in the Retina, RNFL and GCL over the study and it occurred at most examinations. EPI and Ms 20/10 models experienced similarly loss rate in RNFL (0.0033 vs 0.0030 μm/mmHg/day) at the end of the study (week 8) (table 3).
As comparable results were found between EPI and Ms 20/10 models, deeper analysis was performed and statistical differences were only found in 12 from 135 OCT parameters (table 4), so models resulted highly comparable. The
Lower values according to the b-wave amplitude were recorded with scotopic flash ERG for both Ms 38/20 and Ms 20/10 models at week 8. Although slightly lower signals were found for Ms 38/20 model compared to the Ms 20/10 model (
According to the presented results, and due to the similarities found between the epiescleral model and the Ms20/10 model. A long-term study was planned comparing both methods.
4.2. Study of Reproducibility of Ms (20/10) for 24 Weeks of Follow-Up and Comparison with the Epiescleral Model.
The PLGA non-loaded Ms (size range 20-10 μm) used were the same used in the preliminary study (see Table 1 and
None case of infection, severe intraocular inflammation or retinal detachment or cataract formation and better preserved corneal surface was found in Ms20/10 model, compared with the EPI model. In the Ms20/10 model microspheres were seen in the anterior chamber of the eye during the 24 weeks (
Ms20/10 model showed statistical tendency to decrease in thickness of Retina, RNFL and GCL over time (table 5) as EPIm also did (
Both models were compared and no statistical differences were found in thickness in most parameters analyzed. In fact, only 6 from the 135 OCT parameters studied showed statistical differences between models. In general, EPIm showed a tendency to retinal thicker (in fair grey color) and GCL thinner (in dark grey color) over time (table 6).
The percentage loss in thickness was also quantified. In both models, the inner sectors of the superior-inferior axis in Retina and RNFL experienced the highest percentage thickness loss at every late time examined (
The
In this longer 24-week study the Ms20/10 at 6 week was not injected, as done in the preliminary and as consequence the retinal and GCL degeneration delayed obtaining similar values of percentage thickness loss found at week 8 (−14.14%) in the preliminary study until week 18-24 (−12.66% and −18.33% respectively) in this ulterior 24-week study. It suggests that we could modulate the timing of degeneration according to the number of injections performed.
The loss rate expressed in microns per mmHg and day extracted from all sectors average was also quantified in both eyes and models compared as standardization. The highest loss rate in the OHT inducted eye (RE) was found in RNFL followed by GCL and finally Retina; so based on IOP (mmHg) the RNFL was the structure earlier and more severe affected. In average of the follow-up the EPI and Ms20/10 models showed exactly the same rate loss in RNFL (−0.005 μm/mmHg/d) but at 24 w the loss rate in EPIm was in all the three OCT parameters higher than Ms20/10 (table 7).
Both OHT models showed progressive decrease in neuro-retinal functionality at week 12 and week 24 in dark and light adapted tests. In general, EPIm showed statistical slower (in latency) or lower (in amplitude) recordings than Ms20/10.
In dark adapted cells from both models, a-wave (from photoreceptors) showed smaller amplitude but faster response than b-wave (from intermediate cells), but both also experienced the lowest recordings within the first phases stimuli by the lightest flash intensities. EPIm showed statistical slower records in a-wave up to week 12 but also in b-wave over the study (
Light adapted test by PhNR protocol was performed to specifically study the RGC functionality. In this case the EPIm showed a statistical slower response at week 12 that inverted later (
4.3 Resembling OHT Curve and Neuroretinal Degeneration Using Fewer Ocular Injections with Loaded PLGA Microspheres. (DEXAMETHASONE).
Dexamethasone-loaded PLGA Ms showed a production yield of 77.34% for the 20-10 μm fraction. The particle size distribution resulted unimodal, with a mean particle size of 13.13±0.60 μm. The drug loading was 60.70±1.03 μg Dex/mg Ms, meaning 66.77±1.14% of encapsulation efficiency.
SEM images (
The in vitro release profile of dexamethasone from PLGA microspheres showed the typical multiphasic shape release form PLGA microspheres, combining rapid and slow release periods.
From day 0 to day 7 a rapid release occurred leading to a total release of 62 μg, followed by a slow release period to day 28 with an average release rate of 0.191 μg/day. After the inclusion of additional amount of microspheres in the release media a new rapid release happened, delivering 94.5 μg in the following 3 days. Subsequently a second slow release rate of 0.30 μg/day was observed from day 31 to day 91 of in vitro release study. No dexamethasone release was observed from day 91 to end of the study (day 168) (
4.3.2. Ophthalmological Clinical Signs and Intraocular Pressure
Ocular injections were generally well tolerated; the visual axis maintained clear allowing suitable tests. The iridocorneal angle was open, appearing normal by light microscopy. As cons, four animals developed peripheral mild corneal leucomas that did not preclude proper testing and follow-up. One rat developed cataract with pupillary seclusion and ocular hypotension, so this animal was discarded for results.
The IOP increased in both eyes over follow-up. The injected right eye (RE) experienced increase (4 mmHg) since the first week, reached ocular hypertension (OHT) (>20 mmHg) at week 5 and maintained significantly higher than the contralateral left eye (LE) up to week 9 (23.22±3.63 vs 19.68±4.03 mmHg, p=0.013). LE reached OHT at week 8 and even out number at later times (16.46±2.11 vs 21.88±4.21 mmHg, p=0.029) (
Both eyes experienced a progressive decreased thickness in retina, RNFL and GCL over 6 months follow-up. RE showed lower thickness in all sectors explored except nasal sectors, with statistical differences up to week 8 than LE. At week 24 RE showed smaller thickness in RNFL and GCL but higher values in retina (table 8).
Fluctuations were observed in both eyes and they were more evident in retina and at week 12. RE experienced the same fluctuation tendency in RNFL and GCL, and similarly occurred in LE but 2 weeks postponed (
The
The neuroretinal percentage loss by OCT sectors from retina, RFNL and GCL was quantified and loss tendency analyzed (see
Variability in retina alteration was observed in RE over time alternating from outer to inner sectors, however, in LE the outer sectors experienced tendency to bigger percentage loss in thickness. The superior-inferior sectors from vertical axis in RNFL were the most often altered. In GCL, the inner sectors showed bigger percentage loss at any time explored in both eyes; and the nasal-temporal sectors from the horizontal axis were the most affected and the inferior sector the least.
The loss rate expressed in microns per mmHg and day extracted from all sectors average was also quantified in both eyes and times. The highest levels of thickness loss were found in Retina at early times (up to 8 weeks) and in RNFL at intermediate and later times. In average, the highest loss rate was found in retina, followed by RNFL and then GCL. RE showed a higher loss rate in RNFL but lower in retina than its no-injected contralateral LE (
The RE showed longer latency and smaller amplitude in all the dark adapted (DA) phases explored over time and the biggest decrease in signal was found from baseline to week 12. The light adapted PhNR protocol also showed diminished signal over time and RE smaller compared to LE (see
4.4 Resembling OHT Curve and Neuroretinal Degeneration Using Single Ocular Injection with Loaded PLGA Microspheres. (DEXAMETHASONE-FIBRONECTINE).
Ms showed a production yield of 55.14% for the 20-10 μm fraction. The particle size distribution resulted unimodal with a mean particle size value of 14.81±0.30 μm.
The dexamethasone encapsulation efficiency measurements lead to a 79.13±2.64% of the initial drug included during the preparation procedure (71.94±2.40 μg Dex/mg Ms). Unfortunately, the fibronectine lability made impossible the real quantification of the protein loaded.
SEM images evidenced the presence of spherical and regular sized Ms with porous and slightly rough surface (
Both dexamethasone and fibronectin in vitro release profile showed a multiphasic shape combining rapid and slow release periods typically observed for PLGA microspheres.
Dexamethasone showed an initial release in the first 10 days of the in vitro study of 53 μg Dex/mg Ms, followed by a slow release step of 0.0125 μg Deximg Ms/day from day 10 to day 38 and another one of 0.0015 μg Dex/mg Ms/day from day 38 to day 77. After that, no Dex release was observed until the end of the study, although the drug remained in the microspheres resulted in almost 20% of the initial charge (
Animals did not show infection, intraocular inflammation, cataract formation or retinal detachment and the surface was well preserved which let correct OCT and ERG acquisitions. The MsDexaFibro floated on the aqueous humor, showing a tendency to localize at the superior iridocorneal angle. This disposition allowed a clear visual axis. One animal developed corneal leucoma and other an iridocorneal synechia that did not preclude proper testing and follow-up. Another third rat developed a focus of vitreoretinitis so this animal was discarded from the study.
It was found a mild and sustained IOP increase over the study. The injected right eye (RE) showed statistical significant higher measurements than the non-injected left eye (LE) up to 6 week but then this difference vanished though both eyes experienced a progressive lap increase up to 24 week. Both eyes reached ocular hypertension (OHT) (>20 mmHg) at week 11. IOP fluctuations were observed over the study (
All the three R, RNFL and GCL protocols showed a progressive decrease in neuroretinal thickness over the study. Although very few OCT sectors showed statistical significance (p<0.05) between RE and LE, a tendency to lower thickness measurements was detected in the injected eyes over the study except at week 12 (see table 9). The averaged thickness over the study was also calculated; R experienced the biggest decrease in thickness followed by RNFL and GCL and it occurred in both eyes. However, an increasing fluctuation was detected at week 12 especially in injected RE (
The RNFL parameter showed the highest percentage loss in thickness at every time explored, then GCL and finally R. The injected RE showed lower thickness percentual loss in RNFL and GCL than the non-injected LE (
The scotopic ERG did not show statistical differences in latency or amplitude but RE experienced a tendency to longer signals in b-wave as well as smaller a-wave and b-wave amplitude compared to LE and over the study. The RE showed maintained scotopic functionality comparing to an increasing functionality of LE at 12 w. However, the light adapted PhNR protocol detected smaller amplitudes statistically significant in the injected RE (
| Number | Date | Country | Kind |
|---|---|---|---|
| 19383213.6 | Dec 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/087153 | 12/18/2020 | WO |
