Investigation into the usefulness of cynomolgus monkeys with spontaneously elevated intraocular pressure as a model for glaucoma treatment research.

Many glaucoma treatments focus on lowering intraocular pressure (IOP), with novel drugs continuing to be developed. One widely used model involves raising IOP by applying a laser to the trabecular iris angle (TIA) of cynomolgus monkeys to damage the trabecular meshwork. This model, however, presents challenges such as varying IOP values, potential trabecular meshwork damage, and risk of animal distress. This study investigated whether animals with naturally high IOP (>25 mmHg) could be used to effectively evaluate IOP-lowering drugs, thereby possibly replacing laser-induced models. Relationships between TIA size, IOP, and pupil diameter were also examined. Three representative IOP-lowering drugs (latanoprost, timolol, ripasudil) were administered, followed by multiple IOP measurements and assessment of corneal thickness, TIA, and pupil diameter via anterior segment optical coherence tomography (AS-OCT). There was a positive correlation was noted between IOP and corneal thickness before instillation, and a negative correlation between IOP and TIA before instillation. Our findings suggest animals with naturally high IOP could be beneficial for glaucoma research and development as a viable replacement for the laser-induced model and that measuring TIA using AS-OCT along with IOP yields a more detailed evaluation.

Creation of Retinal Vein Occlusion Model in Cynomolgus Monkeys and Determination of its Pathological Features.

OBJECTIVE: A retinal vein occlusion (RVO) is a relatively common retinal vascular disorder, especially in the elderly. Many experiments have been performed on patients with an RVO but performing any type of experiments and especially longitudinal experiments on humans is difficult, if not impossible, on ethical grounds. Therefore, we have created a retinal vein occlusion (RVO) model by laser irradiation of cynomolgus monkeys after intravenous injection of rose bengal. We evaluated the pathological changes of the retina, and the effects of ranibizumab, an anti-vascular endothelial growth factor (VEGF) antibody, on the characteristics of the RVO. METHODS: The integrity of the vascular system was evaluated by fluorescein angiography (FA), and the retinal thickness and volume were determined by optical coherence tomography (OCT). The cytokines and growth factors in the aqueous humour were identified by multiplex profiling. RESULTS: Our results showed that ranibizumab decreased the degree of vascular leakage and retinal edema at 1-3 days (acute phase) and 3-7 days (subacute phase), and suppressed foveal thinning at 28-42 days (chronic phase) after the laser irradiation. Ranibizumab also decreased the area of the foveal avascular zone, and the area was negatively and significantly correlated with the thickness of the ganglion cell layer (GCL) complex. Furthermore, ranibizumab reduced the increased expression of VEGF in the aqueous humor, but did not affect the expressions of interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP-1), angiopoietin-1 (ANG-1), or angiopoietin-2 (ANG-2). These findings suggest that ranibizumab attenuates the retinal edema and subsequent retinal atrophy in part by neutralizing VEGF. However, other cytokines and growth factors were also affected by the ranibizumab, which suggests that not only VEGF but also other unidentified agents might play a role in the pathogenesis of the RVO. CONCLUSION: We have created a non-human primate RVO model, which resembles the clinical RVO pathology. In this model, an injection of ranibizumab leads to a reduction in vascular leakage and the retinal thickness and volume by blocking the expression of VEGF. Our model might be useful for investigating the pathological mechanisms of RVOs and explore new therapeutic agents for RVO.

Anti-vascular Endothelial Growth Factor Antibody Limits the Vascular Leakage and Decreases Subretinal Fibrosis in a Cynomolgus Monkey Choroidal Neovascularization Model.

OBJECTIVE: This study was conducted to evaluate the effects of anti-vascular endothelial growth factor (VEGF) antibody (bevacizumab) on vascular leakage and fibrosis in a monkey choroidal neovascularization (CNV) model. The relationship between fibrotic tissue and subretinal hyper-reflective material (SHRM), in optical coherence tomography (OCT) images, was also investigated. METHODS: Experimental CNV was induced in male cynomolgus monkeys by laser photocoagulation. Intravitreal injection of bevacizumab at 0.5 mg/eye/dosing was initiated 2 weeks before or after laser irradiation and thereafter, conducted intermittently at 2- or 3-week intervals. Fluorescein fundus angiography (FA) and OCT imaging were conducted weekly from 2 to 7 weeks after laser irradiation. CNV leakage was evaluated by an established grading method using FA images. To assess the fibrosis and scarring, Masson's trichrome specimens of each CNV lesion were prepared, and morphometric analysis was conducted using an image analysis software. RESULTS: The effects of bevacizumab on vascular leakage were shown using an established evaluation method. Morphometric analysis of Masson's trichrome-stained (MT) specimens revealed that collagen fiber synthesis was suppressed by bevacizumab pre-treatment (-29.2%) or post-treatment (-19.2%). SHRM was detected in OCT images in a monkey CNV model, and a significant correlation between the SHRM area in the OCT images and the collagen fiber area in the MT specimens was noted. CONCLUSION: In the established cynomolgus monkey CNV model, bevacizumab prevented blood leakage but could not completely suppress fibrosis. SHRM in the OCT images reflected retinal fibrous tissue in a laser-induced CNV monkey model. This model might be useful for elucidating the pathology and development therapy for neovascularization or fibrosis.

Visual Evoked Potential Recovery by Subretinal Implantation of Photoelectric Dye-Coupled Thin Film Retinal Prosthesis in Monkey Eyes With Macular Degeneration.

Retinal prosthesis or artificial retina is a promising modality of treatment for outer retinal degeneration, caused by primary and secondary loss of photoreceptor cells, in hereditary retinal dystrophy and age-related macular degeneration, respectively. Okayama University-type retinal prosthesis (OUReP) is a photoelectric dye-coupled polyethylene film which generates electric potential in response to light and stimulates nearby neurons. The dye-coupled films were implanted by vitreous surgery in the subretinal space of monkey eyes with macular degeneration which had been induced by cobalt chloride injection from the scleral side. A pilot 1-month observation study involved 6 monkeys and a pivotal 6-month observation study involved 8 monkeys. Of 8 monkeys in 6-month group, 3 monkeys underwent dye-coupled film removal at 5 months and were observed further for 1 month. The amplitude of visual evoked potential which had been reduced by macular degeneration did recover at 1 month after film implantation and maintained the level at 6 months. Optical coherence tomography showed no retinal detachment, and full-field electroretinograms maintained a-wave and b-wave amplitudes, indicative of no retinal toxicity. Pathological examinations after 6-month implantation showed structural integrity of the inner retinal layer in close apposition to dye-coupled films. The implanted films which were removed by vitrectomy 5 months later showed light-evoked surface electric potentials by scanning Kelvin probe measurement. The photoelectric dye-coupled film (OUReP), which serves as a light-receiver and a displacement current generator in the subretinal space of the eye, has a potential for recovering vision in diseases with photoreceptor cell loss, such as retinitis pigmentosa and age-related macular degeneration.

Effects of Diets with Different Proportions of Protein/Carbohydrate on Retinal Manifestations in db Mice.

BACKGROUND/AIM: Diabetic nephropathy is aggravated by a higher intake of total protein. The effects of diets with different proportions of protein and carbohydrate on diabetic retinopathy in db mice, a type-2 diabetes animal model, were examined, as well as diabetic nephropathy. MATERIALS AND METHODS: Control and db mice at 5 weeks of age were fed the diets (% energy of protein/carbohydrate/fat; L-diet: 12/71/17; H-diet: 24/59/17) under ad libitum conditions and pair-feeding conditions for 6 weeks, respectively. RESULTS: Mice fed the H-diet showed significantly greater retinal thickness by optical coherence tomography, and lower mRNA levels of angiotensinogen. Comparing combinations of diets and genotypes, db-H mice showed significantly higher mRNA levels of angiotensin-converting enzyme, advanced glycosylation end product-specific receptor, and cluster of differentiation molecule 11b (a microglial marker) than db-L mice. CONCLUSION: Dietary protein and carbohydrate proportions influenced retinal manifestations, including retinal thickness and gene expression in control and diabetic mice.

Relationship between Elevated Intraocular Pressure and Divided Peripapillary Sector Retinal Nerve Fiber Layer Thickness in a Cynomolgus Monkey Laser-Induced Ocular Hypertension Model.

AIMS: We investigated the relationship between elevated intraocular pressure (IOP) and changes in global and peripapillary sector retinal nerve fiber layer (RNFL) thickness around the optic nerve head (ONH) in the laser-induced ocular hypertension monkey model. METHODS: To induce high IOP, green laser photocoagulation burns were applied around the trabecular meshwork of 1 eye from each of 12 cynomolgus monkeys. The animals had been acclimated to IOP measurement under conscious conditions for more than 2 months, and IOP was chronologically measured. RNFL thickness was measured for 6 peripapillary sectors and global area using spectral-domain optical coherence tomography. RESULTS: After model induction, marked IOP elevation and enlarged optic disk cupping were observed. Thinning of the RNFL associated with elevated IOP was observed around the ONH from 6 until 9 weeks after laser treatment, and the degree of reduction in RNFL thickness varied between the peripapillary sectors. Correlations between cumulative IOP elevation and RNFL thickness reduction were statistically significant for the temporal-superior (p = 0.024), nasal-inferior (p = 0.044), and temporal (p = 0.049) sectors, and global RNFL (p = 0.018). CONCLUSIONS: These results suggest that this model reflected the pathology of clinical glaucoma in terms of the specific pattern of RNFL thinning around the ONH.

Keratoconus in a cynomolgus monkey.

In a seven-year-old male cynomolgus monkey, erythema of the upper eyelid and forehead and corneal opacity, edema and conical protrusion in the eye were observed. At necropsy, ophthalmological and serological examinations revealed binocular corneal opacity and conical protrusion and a high IgE level, respectively. Thinning of the epithelium and stroma of the cornea were noted histopathologically. At the center of the corneal epithelium, the number of epithelial cells was reduced, their cytoplasm was poorer and the basal cells were flatter than at the periphery. Bowman's membrane was folded with partial loss or breakage. Collagen fibers were compacted or disarranged, and the keratocytes were increased in the stroma, with focal pyknosis or loss of the endothelium and folding of Descemet's membrane. Electron microscopical examination revealed atrophy of the corneal epithelial basal cells. This is the first report of a case of keratoconus in a cynomolgus monkey.