Abstract
This study aims to screen possible antioxidant potentials of methanol extract and polar fractions of Vernonia calvoana leaves and its phytochemical constituents since the leaves are used ethno medically in managing ailments like wounds, blood pressure, inflammation, arthritis, and bone diseases. Dried leaves (900 g) were ground and de-fatted with n-hexane. The dry marc was extracted using 80% methanol and water. Filtrate was concentrated using rotary evaporator at 40°C. Acute toxicity study and phytochemical analysis were performed with crude extract. Fractionation of crude extract using gradient concentrations of methanol and distilled water yielded 4 fractions - F1, F2, F3 and F4. Fractions with the crude were used for in vitro antioxidant studies. From the results, crude extract showed no signs of toxicity in mice at 2000 mg/kg orally. Phytochemical screening showed presence of alkaloids, flavonoids, tannins, phenols, steroids, saponins, terpenes, arthroquinones, carbohydrates and glycosides. The highest percentage antioxidant activity observed with crude extract was 72.37 at 500 µg/ml in DPPH spectrophotometric assay. DPPH results showed percentage antioxidant activity of 81.4% at 500 µg/ml of F1 and 67.73% at 500 µg/ml of F2. The FRAP values of the crude extract, F1, F2, F3 and F4 at 500 µg/ml were 1.957, 2.234, 1.731, 1.245 and 1.025 µM respectively. These results showed that the activities of methanol extract of leaves of V. calvoana may be dependent on the concentration of the extracting solvent. Vernonia species are known to contain abundant saponins and flavonoids which are polar compounds and readily soluble in methanol. This may explain the above observed antioxidant activities and thus, the use of the leaves in different traditional curative therapies in Southern Nigeria. Key words: Vernonia calvoana, leaves, antioxidants, crude extract, phytochemicals.
Highlights
Many physiological defects, imbalances and disease states have been attributed to oxidative stress in living systems (Braca et al, 2002)
Phytochemical analysis of the crude methanol extract showed the presence of alkaloids, flavonoids, tannins, phenols, steroids, saponins, terpenes, arthroquinones, carbohydrates++ and glycosides ++
The Ferric reducing/antioxidant power (FRAP) results were similar to the diphenyl-2picrylhydrazyl radical (DPPH) with F1 at 500 μg/mL giving a FRAP value of 2.211 ± 0.08 which is slightly higher than that of ascorbic acid even at 1000 μg/mL (FRAP value of ascorbic acid between 100 and 1000 μg/mL is 2) (Table 2 and Figure 1)
Summary
Imbalances and disease states have been attributed to oxidative stress in living systems (Braca et al, 2002). Oxidative stress have been shown to be caused by free radicals, including the superoxide radical, hydroxyl radical (OH), hydrogen peroxide (H2O2), lipid peroxide radicals and reactive. There is need for novel antioxidants with better pharmacological potencies and medicinal plants readily provide sources for such novel drugs discovery (Fabricant and Farnsworths, 2001). The searches for plant-derived medication have accelerated in recent years as ethnopharmacologists, botanists, microbiologists, and natural products chemists are greatly involved in exploring the universe for phytochemicals and „„leads‟‟ which could be developed for treatment of numerous diseases (Nwaehujor et al, 2013)
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