Effect of vitamin B(12) supplementation on retinal lesions in diabetic rats

PURPOSE: Diabetic retinopathy (DR) is the most common complication of diabetes involving microvasculature and neuronal alterations in the retina. Previously, we reported that vitamin B(12) deficiency could be an independent risk factor for DR in humans. However, the effect of vitamin B(12) supplementation in experimental DR is unknown. Thus, in this study, we investigated the impact of dietary supplementation of vitamin B(12) on retinal changes in diabetic rats. METHODS: Diabetes was induced in 2-month-old Sprague-Dawley rats and maintained for 4 months. One group of diabetic rats were fed normal levels of vitamin B(12), and one group double the quantity of vitamin B(12) (50 µg/kg diet). Vitamin B(12) and homocysteine levels in the plasma were analyzed with radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC), respectively. At the end of 4 months of experimentation, the eyeballs were collected. Retinal changes were analyzed with hematoxylin and eosin (H&E) staining, immunoblotting, and immunofluorescence methods. RESULTS: Dietary supplementation of vitamin B(12) had no effect on food intake, bodyweight, fasting blood glucose, and plasma homocysteine levels in the diabetic rats. However, vitamin B(12) supplementation prevented loss of rhodopsin, and overexpression of VEGF, and completely prevented overexpression of HIF1α, GFAP, and endoplasmic reticulum (ER) stress markers (GRP78, ATF6α, XBP1, CHOP, and caspase 12) in the diabetic rat retina. Further, vitamin B(12) ameliorated apoptosis in the retina as shown with terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) and prevented retinal thinning. CONCLUSIONS: Vitamin B(12) supplementation of diabetic rats appeared to be beneficial by circumventing retinal hypoxia, VEGF overexpression, and ER stress-mediated cell death in the retina. The present study adds another potential therapeutic strategy of vitamin B(12) in diabetes.