Nicotinamide Prevents Retinal Vascular Dropout in a Rat Model of Ocular Hypertension and Supports Ocular Blood Supply in Glaucoma Patients

Abstract

Purpose: To investigate whether nicotinamide (NAM) modulates retinal vasculature in glaucoma.

Methods: This was a prospective controlled clinical trial investigating animal and human histopathology. Participants included normotensive and ocular hypertensive rats, postmortem human ocular tissue, glaucoma patients (n = 90), and healthy controls (n = 30). The study utilized histopathology, computer-assisted retinal vasculature analysis, optical coherence tomography angiography (OCTA), and NAM treatment. The main outcome measures included retinal vascular parameters in rats as assessed by AngioTool; retinal vasculature integrity in rats and humans as assessed by histopathology, antibody-staining, and ImageJ-based measurements; and retinal perfusion density (PD) and flux index in humans as assessed by OCTA.

Results: A number of vessel parameters were altered in ocular hypertension/glaucoma compared to healthy controls. NAM treatment improved the retinal vasculature in ocular hypertensive rats, with an increase in mean vessel area, percentage area covered by vessels, total vessel length, total junctions, and junction density as assessed by AngioTool (all P < 0.05); vessel wall integrity as assessed by VE-cadherin antibody staining was also improved (P < 0.01). In humans, as assessed by OCTA, increases in PD in the optic nerve head and macula complete image (0.7%, P = 0.04 and 1.0%, P = 0.002, respectively) in healthy controls, and an increase in the temporal quadrant of the macula (0.7%, P = 0.02) in glaucoma patients was seen after NAM treatment.

Conclusions: NAM can prevent retinal vascular damage in an animal model of glaucoma. After NAM treatment, glaucoma patients and healthy controls demonstrated a small increase in retinal vessel parameters as assessed by OCTA.

Figure 1.

Study schedule for the clinical trial. PEX, pseudoexfoliation.

Figure 2.

Example of OCTA scans of the ONH and macula. (A) OCTA scan of the superficial retinal vasculature of the ONH area, with the inner boundary being the inner limiting membrane and the outer boundary being the retinal nerve fiber layer. The perfusion density (P) and flux index (F) are shown for each quadrant. (B) OCTA scan of the macular superficial retinal vasculature, with the inner boundary being the inner limiting membrane and the outer boundary being the inner plexiform layer. The perfusion density is shown for each quadrant and the central region.

Figure 3.

Vascular remodeling following OHT and protection by NAM. (A) Retinal vasculature was labeled with isolectin B4 to explore vascular changes induced by OHT or NAM treatment. The superficial plexus was imaged to assess vascular morphology (top row) (n = 9 NT eyes, n = 6 OHT eyes, n = 7 OHT–NAM 200 mg/kg/d eyes, n = 7 OHT–NAM 400 mg/kg/d eyes, and n = 10 OHT–NAM 800 mg/kg/d eyes). AngioTool was used to reconstruct blood vessels (bottom row; red, vessels; blue, junctions). (B–J) OHT induced significant vascular remodeling as indicated in average vessel length and vessel area. In OHT eyes of NAM-treated rats, this remodeling was partially prevented in a dose-dependent manner, as indicated by several AngioTool-specific parameters (area covered by vessels, junction density, total number of junctions, mean lacunarity, total vessel length, and vessel area). Lacunarity is a measure of space filling within the image. High lacunarity indicates less space filling by blood vessels. Scale bar: 400 µm. *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 4.

Loss of vascular integrity following OHT and partial protection by NAM. (A, B) To assess blood vessel integrity in the central and peripheral retina, sections from paraffin-embedded rat eyes were stained with antibodies against CD31, CLDN-5, and VE-cadherin (n = 8 NT eyes, n = 12 OHT eyes, and n = 12 OHT–NAM 800 mg/kg/d eyes). (C–E) OHT induced loss of vascular integrity as assessed by percentage cover of CD31, CLDN-5, and VE-cadherin in central and peripheral vessel walls. NAM treatment partially prevented this remodeling in more peripheral retina. (F) To determine whether this loss is also detectable in human retina, formalin-fixed, paraffin-embedded enucleated eyes from human glaucoma patients (n = 6) and non-glaucomatous controls (n = 7) were stained with anti-CD31. The percentage cover of CD31 in central and peripheral vessels was significantly reduced in glaucoma (G).