Impaired Corneal Sensation and Nerve Loss in a Type 2 Rat Model of Chronic Diabetes Is Reversible With Combination Therapy of Menhaden Oil, α-Lipoic Acid, and Enalapril

PURPOSE:This study investigated the efficacy of monotherapy versus combination of menhaden oil, α-lipoic acid, and enalapril on corneal sensation and morphometry and other neuropathy-related endpoints in a rat model of type 2 diabetes. METHODS:Male Sprague-Dawley rats (aged 12 weeks) were fed a high-fat diet for 8 weeks followed by 30 mg/kg streptozotocin. After 16 weeks of hyperglycemia, 12-week treatments consisting of menhaden oil, α-lipoic acid, enalapril, or their combination were initiated. Before and after treatments, we performed analyses of multiple neural and vascular endpoints including corneal sensitivity, corneal nerve density, vascular reactivity of epineurial arterioles, motor and sensory nerve conduction velocity, intraepidermal nerve fiber density, and thermal nociception. RESULTS:Before treatment, all the neural and vascular endpoints in diabetic rats were impaired. Treating diabetic rats with monotherapy was effective in improving neural and vascular deficits with menhaden oil being most efficacious. However, the combination therapy provided the greatest benefit and improved/reversed all nerve and vascular deficits. The effect of combination therapy on corneal relative sensitivity and structure (in mm/mm), primary endpoints for this study, for control, diabetic, and diabetic treated rats was 4.2 ± 1.4 and 7.5 ± 0.5, 12.1 ± 1.3* and 3.8 ± 0.2*, and 6.6 ± 2.3 and 7.3 ± 0.5, respectively (*P < 0.05 compared with control rats; P < 0.05 compared with diabetic rats). CONCLUSIONS:These studies suggest that a combination therapeutic approach may be most effective for treating vascular and neural complications of type 2 diabetes.