Investigation of chemical components and pharmaceutical potential of Carpobrotus species

Objectives: To investigate the chemistry and pharmaceutical potential of three Carpobrotus species found in Tasmania, C. edulis, C. rossii and C. aequilaterus. Methods: The plant juice and methanolic extracts of plants were analysed for chemical constituents by LC-MS, GC-MS, HPLC-DAD, HPLC-ELSD, flame photometry, elemental analysis, acid titration and gravimetric analysis. Based on folklore use, a gel formulation containing plant juice of C. rossii was used in both a placebo controlled double-blinded clinical trial to investigate its potential as a common hand wart treatment, and in a histamine skin prick model to investigate topical anti-inflammatory activity. The antioxidant activity of the plant juice of the three species was also measured by the DPPH, FRAP and β-carotene assays, and the contribution of ascorbic acid was investigated. The antioxidant activity was isolated in a single fraction using Sephadex LH-20 gel and the fraction was analysed by LC-MS. Results: Both plant juice and methanolic extract contained flavonoids, tannins and carbohydrates. The plant juice contained, in addition, inorganic salts, titratable acids and volatile constituents that were primarily grassy aldehydes. Novel flavonoids whose structures have yet to be elucidated were present in the C. rossii. The anti-wart trial was conducted over an 8 week period and recruited a total of 50 subjects of whom 41 subjects (19 cases, 22 controls) completed the study. The histamine skin prick model was used in 12 subjects. Both the anti-wart trial and the histamine skin prick model failed to show any significant effects of C. rossii extract. The plant juices from C. edulis, C. rossii and C. aequilaterus were all found to have very strong antioxidant activity with typical levels equivalent to around 13 mg/ml of rutin, 2.5 mg/ml of gallic acid or 9 mg/ml of ascorbic acid. Ascorbic acid levels could account for about 10% of antioxidant activity. Antioxidant activity guided fractionation by gel filtration column chromatography and analysis of this fraction by LC-MS showed the presence of condensed tannins as major chemical constituents, which appeared to account for the majority of the antioxidant activity. LC-MS analysis of C. rossii showed the presence of flavonoids that contained a substituent consistent with the rarely encountered 3-hydroxy-3-methylglutaric acid moiety. Conclusion: C. rossii extract gel is not effective in the treatment of common warts and does not possess topical anti-inflammatory action against histamine. There is significant antioxidant activity present in Carpobrotus species. Further investigation of the antioxidant compounds and their potential therapeutic applications are warranted. Further screening for other biological activities, particularly of the novel flavonoids, is also recommended