Objective. Mallotus oppositifolius (Geiseler) Müll. Arg. (Euphorbiaceae) is folklorically used to “treat” diabetic conditions in some parts of Nigeria therefore the study, to investigate the extract of the leaves for activities on hyperglycaemia, lipid peroxidation, and increased cholesterol levels in vivo in alloxan diabetic rats as well as its potential antioxidant activity in vitro. Methods. Albino rats (240–280？g) were given an injection of 120？mg/kg body weight, i.p. of alloxan monohydrate. After 8 days, diabetic animals with elevated fasting blood glucose levels (>9？mmol/L) were considered and selected for the study. Results. Oral treatment with the extract administered every 12？h by gavage at doses of 100, 200, and 400？mg/kg of the extract to the test rats, for 14 days, resulted in a significant dose-dependent decrease in blood glucose levels from 12.82 ± 1.02？mmol/dL to 4.92 ± 2.01？mmol/dL at the highest dose of 400？mg/kg compared to the control drug and glibenclamide as well as attendant significant decline in diabetic rats employed in the study. Conclusion. The extract also showed in vitro concentration-dependent antioxidant activity following the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and ferric reducing assays. Findings further suggest the presence of active antidiabetic and antioxidant principles in M. oppositifolius leaves. 1. Introduction Diabetes mellitus (DM) is a multifactorial syndrome resulting from a variable interaction of hereditary and environmental factors. It is characterized by inapt hyperglycaemia caused by damaged β-cells of the pancreas or resistance to the action of insulin at the cellular level, or possibly a combination of both factors [1, 2]. DM affects more than 200 million people worldwide and is projected to be one of the world’s major killers in the next 25 years , Nigeria with about 160 million people has the highest number of people with diabetes (approximately 1,338 × 103), thus, the highest diabetes prevalence in the African Region (19.1%), as well as the highest number of people with impaired glucose tolerance with an estimate of about 3.85 million people. With on-going researches in diabetes and oral hypoglycaemic agents (OHA), the management of DM is still a global problem. One important area in diabetes management receiving particular attention today is that of herbal hypoglycaemic agents. Several factors such as dyslipidemia or hyperlipidemia which are involved in the microvascular and macrovascular complications as well as hyperglycemia are associated with the diabetes disease which is the major cause of
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