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.