The Effects of Nicotine in Choroidal Neovascularization: Characterization of Nicotinic Receptors in Choroid and Reduction of Choroidal Neovascularization Size and Severity via Receptor Blockade

Abstract

Abstract: : Purpose: Cigarette smoking has been associated with an increased risk of age-related macular degeneration (ARMD) and choroidal neovascularization (CNV). We have previously demonstrated the effects of nicotine, a major toxic component of cigarette smoke, in increasing CNV size and severity in a mouse model. We sought to characterize nicotinic receptor subtypes in the choroid and reverse the effects of nicotine on increasing CNV size and severity via receptor blockade. Methods: A laser model for CNV was used in C57BL/6 mice. Immunohistochemical characterization of nicotinic receptors was carried out in sections of choroid and CNV. Receptor subtypes analyzed included α–3, α–5, α–7, ß–2, ανδ ß–4. Nicotinic receptor blockade with hexamethonium was performed via subconjunctival delivery in mice concurrently receiving nicotine in drinking water. Two control groups were used: mice receiving nicotine and no hexamethonium, and mice receiving hexamethonium and no nicotine. Experimental and control animals were then injected with fluoresceinated dextran, then the right eyes were removed and prepared for flat-mount analysis of CNV surface area. The mice were then perfused and fixed with glutaraldehyde and formalin. The left eyes were removed for histopathologic analysis. Results: Receptor analysis demonstrated expression of subtypes associated with vascular endothelial cells and angiogenesis. Older mice exposed to only nicotine had larger CNV (2.2 ± 0.2 disc areas) as compared to mice receiving nicotine + hexamethonium (1.3 ± 0.3 DA) or mice receiving hexamethonium alone ( 1.2 ± 0.3 DA). Conclusions: Nicotinic receptors, specifically subtypes associated with vascular endothelial cells and angiogenesis, are presented in the choroid. Nicotine-induced increased size and severity of CNV may be blocked with concurrent administration of a nicotinic receptor blocker.

Keywords: age-related macular degeneration • choroid: neovascularization • animal model