Medicinal values of fruit peels from Citrus sinensis, Punica granatum, and Musa paradisiaca with respect to alterations in tissue lipid peroxidation and serum concentration of glucose, insulin, and thyroid hormones

Peel extracts from Citrus sinensis, Punica granatum, and Musa paradisiaca were investigated for their effects on tissue lipid peroxidation (LPO) and on the concentration of thyroid hormones, insulin, and glucose in male rats. In vitro inhibition of H2O2-induced LPO in red blood cells of rats by 0.25, 0.50, 1.0, and 2.0 mu g/mL C. sinensis, P. granatum, and M. paradisiaca peel extracts was observed in a dose-specific manner. Maximum inhibition was observed at 0.50 mu g/mL C. sinensis, 2.0 mu g/mL P. granatum, and 1.0 mu g/mL M. paradisiaca. In the in vivo investigation, out of four different concentrations of each peel extract, 25, 200, and 100 mg/kg C. sinensis, P. granatum, and M. paradisiaca, respectively, were found to maximally inhibit hepatic LPO. The most effective doses were further evaluated for effects on serum triiodothyronine (T-3), thyroxine (T-4), insulin, and glucose concentrations. C. sinensis exhibited antithyroidal, hypoglycemic, and insulin stimulatory activities, in addition to inhibition of LPO, as it significantly decreased the serum T-4 (P < .05) and glucose (P < .001) concentrations with a concomitant increase in insulin levels (P < .05). P. granatum decreased LPO in hepatic, cardiac, and renal tissues (P < .01, P < .001, and P < .05, respectively) and serum glucose concentration (P < .01). M. paradisiaca strongly inhibited the serum level of thyroid hormones (P < .01 for both T-3 and T-4) but increased the level of glucose (P < .05). These findings reveal the hitherto unknown potential of the tested peel extracts in the regulation of thyroid function and glucose metabolism. Besides antiperoxidative activity, C. sinensis extract has antithyroidal, hypoglycemic, and insulin stimulatory properties, which suggest its potential to ameliorate both hyperthyroidism and diabetes mellitus.