Antioxidant properties of Gymnosporia buxifolia Szyszyl / Cecile Killian

• Main Author: Killian, Cecile
• Language: en
• Published: North-West University 2013
• Online Access: http://hdl.handle.net/10394/8783

Chemistry of natural products is a research field with endless potential and with the global increase in natural product research, many plants have shown immense potential in therapeutic uses. Questions about the long term safety of synthetic antioxidants have increased the demand for natural antioxidants. Natural antioxidants have better long-term safety and stability and have the capacity to improve food quality and can act as nutraceuticals to terminate free radical chain reactions in biological systems. The primary factor in various degenerative diseases, like Parkinson's disease and Alzheimer's disease, is oxidative stress induced by oxygen radicals. These reactive oxygen species are generated by normal metabolic processes and are capable of damaging a wide range of essential biomolecules. The oxidation of cellular oxidizable substrate can be prevented and delayed by antioxidants. Antioxidants scavenge reactive oxygen species by preventing the generation of reactive oxygen species by activating a battery of detoxifying proteins. A literature survey was done and 21 plants were selected for screening for antioxidant activity. These plants were selected based on previous studies done on plants in the same families. Plant leaves were collected and dried. The leaves were then extracted by soxhlet extraction using solvents in order of increased polarity (petroleum ether, dichloromethane, ethyl acetate and ethanol). The crude plant extracts were used for screening by assessing the total antioxidant capacity by measurement of the oxygen radical absorbance capacity (ORAC) and the ferric reducing antioxidant power (FRAP). The Frap results in terms of vitamin C equivalents ranged from as low as 0.000 ± 0.000 IJM for the Acacia karroo petroleum ether and dichloromethane phase to as high as 9009.32 ± 130.714 1-1M for the Lippia javanica ethanol phase. The ORAC results in terms of Trolox equivalent ranges from as low as -1491.8 ± 2271-JM for So/enostemon rotundifolius petroleum ether phase to as high as 75908.1 ± 1336 IJM for Lippia javanica ethyl acetate phase. The higher the results the better it is. Gymnosporia buxifolia was selected due to high ORAC and FRAP values and the availability of large quantities of plant material. The four crude extracts, from the soxhlet extraction of Gymnosporia buxifo/ia, were tested using the nitroblue tetrazolium assay and the thiobarbaturic assay (lipid peroxidation). Nitroblue tetrazolium (NBT} is reduced to nitroblue diformazan (NBD) in the presence of the superoxide anion radical. The capacity of the crude plant extract to scavenge the superoxide radical anion determines the antioxidant capacity of the extract. The thiobarbaturic assay is one of the most widely used methods for lipid peroxidation in biological samples. The principle of this assay is based on the reduction of malondialdehyde equivalents with tiobarbaturic acid to form a pink colour complex. The ethanol crude plant extract of Gymnosporia buxifolia showed the best transformation of nitroblue tetrazolium to nitroblue diformazan indicating a reduction in superoxide radical anions. It reduced the KCN from 88.791 ± 6.34 diformazan (IJM/mg protein) to 24.273 ± 5.29 diformazan (IJM/mg protein) which is very good. It also illustrated the best reduction in lipid peroxidation. It reduced the Toxin from 0.009931 ± 0.000999 malondialdehyde (nmol/mg tissue) to 0.000596 ± 0.000221 malondialdehyde (nmol/mg tissue) which is very good. The ethanol extract was chosen for isolation of active compound(s). Two compounds were isolated using column chromatography, thin layer chromatography, solid phase extraction and selective precipitation. D-mannitol or dulcitol (galactitol) or a combination of the two and a compound with a dihyro-~-agarofuran sesquiterpenoid core skeleton is proposed by comparing spectra generated with nuclear magnetic resonance, mass spectrometry and infrared spectrometry. The antioxidant activity of the two compounds was assessed using lipid peroxidation with both showing activity. === Thesis (M.Sc. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2009