Abstract

This study evaluated the anti-diabetic and antioxidant potential of methanolic extract of Helianthus annuus L. leaves in alloxan-induced hyperglycemic rats. Fresh leaves of the plant were collected from their local habitat in the University of Nigeria, Nsukka environment. The extract was prepared by cold maceration using 80 % methanol at environmental temperature with intermittent sharing for 48 h to obtain a yield of 10.04 % w/w dry Helianthus annuus extract (HAE). The extract was tolerated by the rats, which showed no overt signs of toxicity at the dose range 300 – 3600 mg/kg) tested. Even the highest does of 3600 mg/kg did not cause mortality in the rats. The crude extract produced dose- and time-dependent reduction in fasting blood sugar (FBS) level. HAE (600 mg/kg) at 6 hour post treatment, significantly (p < 0.05) decreased FBS when compared with DW treated group. However this was not significant (p > 0.05) when compared with GLB- 15 treated group. The normoglycemic OGTT showed no significant (p > 0.05) difference in FBS level between all the treated groups. At 2 hour post glucose load, there was no significant (p > 0.05) difference compared with the 0 hour FBS level. In hyperglycaemic OGTT, HAE (600 mg/kg) at 2 hour was significantly (p < 0.05) lower when compared with the control. However, this was not significant (p > 0.05) when compared with GLB (2 mg/kg) treated group. The separation of the extract yielded thirteen (13) fractions. Bioactivity screening of the fractions at 60 mg/kg showed various degrees of reduction in FBS in time-dependent manner. The HAE, fractions 8-10 and 13 caused 66.74, 61.36, 70.63 and 78.03% reductions in FBS, respectively. Phytochemical spot tests of the HAE showed the presence of saponins, alkaloids, flavonoids, terpenes, glycosides, tannins and carbohydrates while fractions 8 and 10 contain mainly glycosides and sterols and fraction 13 contains mainly tannins. In vitro anti-oxidant tests at 400 µg/ml showed that HAE, fractions 8-10 and 13 gave 89.00, 30.42, 88.03 and 92.72 % anti-oxidant activity, respectively using DPPH model and 3.69, 0.95, 0.67 and 0.28 anti-oxidant potential, respectively in FRAP model. Ascorbic acid used as control has antioxidant potential of 2.00 using FRAP model. The study validates the use of the preparations from H. annuus leaves in folklore diabetic therapy