Chronic administration of ethanol leaf extract of Moringa oleifera Lam. (Moringaceae) may compromise glycaemic efficacy of Sitagliptin with no significant effect in retinopathy in a diabetic rat model

Ethnopharmacological relevance: Moringa oleifera Lam. (Moringaceae) has gained awareness for its antidiabetic effect, and is used as alternative therapy or concurrently with orthodox medicines such as sitagliptin in diabetes mellitus. This is without ascertaining the possibility of drug-herb interactions, which could either lead to enhanced antidiabetic efficacy, increased toxicity, or compromised glycaemic control with negative consequence in diabetic retinopathy. Aim of the study: To investigate the effect, of sitagliptin (50 mg/kg), Moringa oleifera (300 mg/kg) leaf extract, and a combination of both on glycaemic control parameters, lenticular opacity and changes in retinal microvasculature in alloxan (150 mg/kg i.p) induced diabetic rat model. Materials and method: Seven groups of eight rats per group were used, with groups I, II and VII as normal (NC), diabetic (DC) and post-prandial controls (PPC). Groups III to VI were diabetic rats on sitagliptin (III), M. oleifera (IV), sitagliptin and M. oleifera (SM) (V), for 42 days with 2 weeks delayed treatment in a post-prandial hyperglycaemic group (PPSM) (VI). Glycaemic control parameters, insulin levels, body weights, and effects of retinal microvasculature on lenticular opacity/morphology were investigated. Results: A significant decrease in fasting blood glucose (FBG) levels was displayed in SM group from day 14(60%) (p < 0.01) to day 28 (38%) (p < 0.01) of treatment, compared to day 1. Thereafter, a steady increase of up to 57% on day 42 compared to day 28 was observed. A significant decrease in random blood glucose (RBG) levels, were demonstrated on day 42 (24%) (p < 0.001), compared to day 1. No significant difference was seen in mean serum levels of insulin across groups. No significant changes in body weights. Evidence of mild lenticular opacity was observed, with no significant effect in pathologic lesions in the retina. Conclusion: The chronic co-administration of sitagliptin and M. oleifera showed a progressive decrease in anti hyperglycaemic effect of sitagliptin, and although it delayed the onset of lenticular opacity (i.e. cataract-like changes) it did not prevent the progression nor ameliorated pathologic lesions in the retina.