The acute respiratory exposure by intratracheal instillation of Sprague–Dawley rats with diesel particulate matter induces retinal thickening

Context: Adverse health effects of ambient particulate matter (PM) have been demonstrated in humans, mostly in terms of respiratory and cardiovascular events. However, whether ambient particle could affect the eyes had not been fully revealed. Objective: This study investigated the effect of acute respiratory exposure to PM on eyes. Methods: Diesel exhaust product (DEP) of 200 mg/l was given endotracheally in Sprague–Dawley rats for 1 h (n = 12) and compared to normal control (n = 4). We enucleated eyes and histologically evaluated. Immunohistochemical stains for CD34 (Dako, Glostrup, Denmark, 1:50) and Ki-67 (DakoCytomation, Glostrup, Denmark, 1:150) were performed to evaluate new vessel formation and proliferation activity. Results: After endotracheal DEP exposure, the thickness of retina was significantly increased to 258 ± 96 μm in DEP group, while that of control was 113 ± 9 μm (p = 0.025). Among the retinal structure, inner plexiform, inner and outer nuclear and rod/cone cell layers were significantly thickened (p = 0.00, 0.017, 0.004, 0.001, respectively). The outer plexiform layer of DEP group showed a tendency of thickening, but statistically insignificant. The afferent fiber and ganglion cell layer showed no thickness difference between two groups, but prominent capillaries with congestion were noted in DEP group. Neither neovascularization nor increased proliferation was demonstrated on CD34 and Ki-67 immunohistochemical staining in DEP group. Conclusion: This study shows that the acute respiratory exposure of ambient PM increased retinal thickness, especially inner plexiform, inner and outer nuclear and rod/cone cell layers. We thought that increase of retinal thickness in DEP group resulted in hypoxia-induced edema.