| Summary: | Parkinson's disease, a disease first described by James Parkinson two centuries ago is one of the most common neurodegenerative diseases. The prominent feature of this disease is the selective degeneration of dopaminergic neurons in the substantia nigra of the midbrain resulting in a decrease in dopamine levels in the brain. The substantia nigra appears to be an area of the brain that is highly susceptible to oxidative stress. Supplementation with antioxidants may protect the neurons from the damaging effects of oxidation by reacting with oxygen radicals and other reactive oxygen species (ROS).
The aim of this study was to investigate the antioxidant properties of the leaves of the plant Plumbago auriculata and to evaluate its antioxidant activity on rats. Four solvents; petroleum ether, dichloromethane, ethyl acetate and ethanol were used successively to extract substances from the leaves of the plant using the soxhlet apparatus. The Thiobarbituric Acid-Reactive Substances (TBARS) and the Nitro-Blue Tetrazolium (NBT) assays were performed to evaluate antioxidant activity. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was done to determine the relative toxicity of each extract. The results showed that the ethyl acetate and the ethanol crude extracts had significantly higher antioxidant activity than the petroleum ether and the dichloromethane extracts.
In the TBARS assay the ethanol and ethyl acetate extracts each at 2.5 mg/ml reduced malondialdehyde (MDA) levels significantly (p < 0.001) compared to the toxin (H²O² + FeCl³ + Vit. C). Ethanol and ethyl acetate extracts each had values of 0.0058 nm MDA/mg tissue and 0.0067 nm MDA/mg tissue respectively in comparison to the toxin's 0.0257 nm MDA/mg tissue. Results of the NBT assay results showed that at concentration ranges of 0.625 -2.5 mg/ml, the ethyl acetate and ethanol extracts had the best (p < 0.001) superoxide scavenging activity compared to the toxin (KCN). The ethyl acetate and petroleum ether extracts significantly inhibited the proliferation of HeLa cells by 11.52 % (p < 0.05) and 27.3 % (p < 0.001) respectively at 10 mg/mL, compared to the control when evaluated with the MTT assay. Although the MTT assay results showed toxicity with the 10 mg/ml concentration of the ethyl acetate extract, this extract is one of the two extracts that had the most promising antioxidant activity. It is possible that different compounds in each extract contributed to the antioxidant activity and toxicity. Therefore, the ethyl acetate extract was put through bioassay-guided fractionation using column chromatography to isolate antioxidant compounds.
Two compounds, PS and OS were isolated. 13C NMR, DEPT 13C NMR, 1H NMR and FT-IR were used to characterize 'the structures of the isolated compounds. PS was found to be β-sitosterol, while OS was proposed to be β-carotene. OS reduced MDA levels significantly at all concentrations. At 2.5 mg/ml, the reduction in MDA was almost to the level of the control. The isolated compounds are common in most plants and are known to have antioxidant activity. Further fractionation needs to be done to isolate less common compounds. === Thesis (M.Sc. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2010.
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