Antimycobacterial, antioxidant activity and toxicity of extracts from the roots of Rauvolfia vomitoria and R. caffra

AIM: This study aimed to investigate the antimycobacterial activity of total alkaloid and ethanolic aqueous extracts of Rauvolfia vomitoria and R. caffra. It further aimed to evaluate antioxidant activity and cytotoxicity effect of the extracts which would have shown high antimycobacterial efficacy. METHODS: The alkaloids from the roots of two plant species were extracted according to standard procedures. Antimycobacterial activity of the extracts was evaluated using a two fold microdilution method. The antioxidant activity of the alkaloids and ethanolic extracts was determined using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and reducing capacity assays. The potential cytotoxicity of the extracts was evaluated using brine shrimp toxicity assay. Comparison of alkaloidal composition of the two alkaloidal extracts was done using HPLC analysis. RESULTS: The study revealed that, alkaloid extracts from the roots of Rauvolfia species had higher antimycobacterial activity against Mycobacterium madagascariense (MM) and M. indicus pranii (MIP). The minimum inhibition concentration (MIC) values of alkaloid extracts ranged between 0.078 to 1.25 mg/ml, while the ethanolic extracts were generally moderately active against test organism. The alkaloids and ethanolic aqueous extracts of R. vomitoria exhibited high antioxidant activity. In the cytotoxicity assay, extracts did not exhibit any toxicity against brine shrimps. CONCLUSION: The alkaloids from the roots of R. vomitoria have high antimycobacterial and antioxidant activity. The alkaloids ability to inhibit the growth of two Mycobacterium strains may be associated to its antioxidant activity. The cytotoxicity of the most active extract is negligible when compared to the standard anticancer drug, this may explain why R. vomitoria is highly used in the treatment of various infectious and physiological ailments