Fish oil, resolvins and diabetic neuropathic pain
Peripheral neuropathy affects approximately 50% of patients with diabetes. Experimental trials, performed by the author of this study, using a fish oil as treatment in animal models of type 1 and type 2 diabetes, have shown that it could delay progression of the disease. The authors have previously shown that daily treatment with resolvin D1 improves peripheral neuropathy. Resolvins and protectins are metabolites of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), respectively. E-series resolvins are derived from EPA while D-series resolvins come from DHA. The authors wondered whether the methyl esters of resolvins D1 and D2 (which have a longer biological half-life) were more effective than the resolvins in their effect on peripheral neuropathy. To check this, a murine model of type 2 diabetes was created (C57BL/6J mice, using a combination of a high-fat diet for eight weeks and treatment at high dose of streptozotocin). After leaving the hyperglycaemia untreated for eight weeks, the mice received fish oil daily in their diet or 1 ng/g of body weight of resolvin D1, E1 or resolvin D1 or D2 methyl ester. Various neurological variables were assessed. Neither the fish oil nor the resolvins improved the hyperglycaemia. The untreated mice developed thermal hypoalgesia, mechanical allodynia, lower motor and sensory conduction velocity and reduced cornea and skin innervation. However, these parameters improved significantly with the administration of fish oil and resolvins (the authors’ hypothesis was not proven, as the methyl esters of the resolvins were less effective than the resolvins). This trial shows that dietary supplementation with fish oil could represent a safe and effective treatment for diabetic peripheral neuropathy. The underlying mechanism associated with the production of E1 resolvins (derived from EPA) and D1 resolvins (derived from DHA).