Antioxidant, antidiabetic and cardioprotective activities of Dicoma anomala (sond.) used in the Basotho traditional medicine
Balogun, Fatai Oladunni
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Dicoma anomala (Sond.) belongs to the Asteraceae family and locally called Hloenya (South Sotho), fever or stomach bush (Afrikaans). The plant is used in the management of various diseases, particularly diabetes mellitus among the Basotho tribe of eastern Free State Province, South Africa. The study evaluates the antioxidant, antidiabetic and cardioprotective potentials of the plant as a way of validating the folkloric usage. The result of in vitro antioxidant assays [2, 2- azino-bis (3-ethylbenzothiazoline-6-) sulfonic acid (ABTS), reducing power, superoxide anion, hydroxyl radicals, 1,1-diphenyl-2-picryl hydrazyl (DPPH) radicals, etc.] as well as phytochemicals (such as total phenol, total flavonoids and total antioxidant capacity) in various concentrations (1.56-25 μg/ml) tested using water, ethanol, hydro-ethanol and methanol extracts of the plant’s root revealed that the water extract exhibited the best activity with half maximal inhibitory concentration (IC50: 15.20, 11.70, and 0.84 μg/mL) in DPPH, hydroxyl radical, and superoxide anion radicals respectively. The four extracts also possessed high phenolic contents, total antioxidant capacity with lower total flavonoids content. The effect of treatment with 125, 250 and 250 mg/kg body weight (b.w.) aqueous roots extract of Dicoma anomala (AQRED) was investigated in vivo in CCl4- induced hepatotoxic rats in a 15-day curative and prophylactic study. The result revealed that pre-treatment and treatment with AQRED lowers the elevated serum activities of aspartate transaminase (AST), alanine aminotransferase (ALT) and the level of thiobarbituric acid reactive species (TBARS) while restoring the activities of liver antioxidant enzymes such as catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD) towards normal control in a dose-dependent manner. This result proved the antioxidant and hepatoprotective activity of the plant. The in vitro antidiabetic potential of D. anomala was investigated via the inhibition of α-amylase and α-glucosidase using same extracts (as above) at the range of 1.56 - 25.00 μg/mL concentrations. All the tested extracts of the plant were active against both enzymes, although, the most potent against α-amylase and α -glucosidase was hydro-ethanol (IC50: 9.00 μg/mL) and water (IC50: 27.41 μg/mL) respectively. Similarly, aqueous extract of the D. anomala displayed competitive and non-competitive inhibition of α -amylase and α -glucosidase respectively using Lineweaver-Burk plot. Treatment with AQRED at concentration 125, 250 and 500 mg/kg b.w. in Wistar rats reversed towards control the elevated blood glucose levels, lipid peroxidation, lipid profile, glycosylated haemoglobin and activities of gluconeogenesis enzymes, with concomitant reduction in the activities of enzymatic antioxidants, glycolytic enzymes as well as the high-density lipoprotein –cholesterol (HDL-c) brought about by streptozotocin induction. Thus, the study proved the antihyperglycaemic activity of the plant. Additionally, AQRED at 125, 250 and 500 mg/kg b.w. was evaluated for its ameliorative activity against isoproterenol (ISP) –induced cardiotoxicity in an animal model. The results from the evaluated biochemical parameters revealed significant (p<0.05) elevation in the serum level of AST, ALT, creatine phosphokinase (CPK) and lipid peroxidation while significantly (p<0.05) reducing CAT and GPx levels. Treatment with different doses of AQRED significantly reversed towards normal the activities of these enzymes and cardiac lipid peroxidation towards control. The result obtained in the study is suggestive of cardioprotective efficacy of AQRED in ameliorating cardiovascular-related ailments. The toxicological implications of oral administration of the plant via acute (15 days) and subchronic (90 days) oral toxicity studies was evaluated in Wistar rats (both sexes) using the three concentrations (125, 250 and 500 mg/kg). The findings revealed no mortalities or observed clinical signs of toxicity in all the rats during both investigation periods. In subchronic toxicity testing similarly, administration of AQRED did not cause any significant (p ˃ 0.05) changes in the organ-body weight, haematological parameters and blood chemistry between the experimental animals and the control except in platelet count, alkaline phosphatase (ALP) and sodium levels where a significant increase (p < 0.05) in these parameters was observed. The data obtained indicate that the lethal dose (LD50) of AQRED is in excess of 2000 mg/kg and its oral administration for 90 days is unlikely to cause any toxic effects. In conclusion, the results from this study proved the antioxidant, antihyperglycaemic and cardioprotective potentials of AQRED. The results further validate the folkloric usage of the plant in the management of diabetes mellitus among the Basotho tribe of Eastern Free State Province, South Africa.