Determination of withaferin a content of root, stem and leaf extracts of withania somnifera (l) dunal collected in Kenya
Withania somnifera (L.) Dunal know as Ashwagandha belong to Solanaceae family. It is an annual herb growing in dry and arid soil as a wild plant. It is extensively used in most of the Indian herbal pharmaceuticals and nutraceuticals. It is widely cultivated in India and throughout the Middle East and is also found in eastern Africa. In Kenya, it grows wildly and is widely spread especially in drier areas. The plant is well described in Ayurveda, the ancient Indian system of plant medicine for immunomodulation and anti-aging effect. The plant root is used as an anti-inflammatory, antitumor, anti-aging, anti-Alzheimer‟s disease, anti-stress, anti-oxidant, for mind or memory boosting, immunostimulant, as an aphrodisiac and for rejuvenation, as neuroleptic, for reducing blood sugar and cholesterol levels and as a diuretic. Most of the beneficial ph In this study, the plant was collected from different areas in Kenya where it is known to grow naturally. The powdered dry root, stem and leave materials of the plant were subjected to solvent extraction using composition of methanol-water (60:40). Quantitative determination of withaferin-A in the samples was carried out using RP-HPLC performed isocratically with acetonitrile/ water (75:25) as the mobile phase. The column temperature was kept at 27 oC, flow rate and sample volume were set to 1.0 ml/min and 20 µl, respectively. All separations were monitored at 225 nm. Stability studies and efficiency of extraction of withaferin-A were also carried out. Results and Discussion The analysis of Withania somnifera root, stem and leaf confirmed the presence of withaferin-A in all parts of the plant but with significant differences in content. Withaferin-A content was highest in the leaves, with an average of 0.95 %w/w; the highest percentage recorded in a single leaf sample being 1.69 % w/w. This compound was lowest in stems, with an average of 0.29 %w/w, the highest content recorded in a single stem sample being 0.49 % w/w. The average withaferin-A content in the roots was 0.51 %w/w, with the highest content recorded in a single root sample being 0.77 %w/w. Two imported market products RT8 and RTA9 formulated from Withania somnifera root were analyzed. The percentage contents of withaferin-A in RTA8 and RTA9 were 0.16 % w/w in each. The Kenyan Withania somnifera plant collected from Limuru in Kiambu county showed the highest percentage withaferin-A content in the roots and stems, contents being 0.77 %w/w and 0.49 %w/w respectively, while the withaferin-A content in the leaves of the same plant collected in Limuru was the second highest (1.64 %w/w). Leaf samples collected from Narok town and environs in Narok county contained the highest withaferin-A content (1.69 %w/w). Conclusion and Recommendation From the results of this research, the Kenyan Withania somnifera root appears had higher content of the pharmacologically active compound withaferin-A than the imported root formulations of the plant. The Kenyan plant also has more withaferin-A in the leaves than other parts. Kenyan Withania somnifera could be endangered due to over use of the roots, whilst herbal pharmaceutical products derived from Withania somnifera leaves and stems products could offer useful alternatives to the Withania somnifera root products. Thus, Withania somnifera leaves and stems products merit further investigation. Further studies should also be carried out to determine the effects of agro-ecological and pest infestation on the active compounds in Withania somnifera.