In vitro keratinocyte antiproliferant effect of Centella asiatica extract and triterpenoid saponins

Psoriasis is a hyperproliferative skin disorder estimated to be present in 1-3 % of most populations. Conventional therapy using corticosteroids, Vitamin D analogs and cytotoxic agents eg psoralens is associated with low success rate and many side effects. Traditional plant remedies may provide leads for new treatments. A rapid-throughput, in vitro bioassay has been utilised to examine plants for inhibitory effects on the growth of SVK-14 keratinocytes. Centella asiatica, a reputed anti-psoriatic herb, has been compared against the psoralen-containing seeds of Psoralea corylifolia and the synthetic anti-psoriatic agent dithranol (anthralin). Aqueous extracts of Psoralea corylifolia and Centella asiatica inhibited keratinocyte replication with IC₅₀ values of 18.4 ± 0.6 μg/ml and 209.9 ± 9.8 mg/ml respectively prior to treatment with polyvinyipolypyrrolidone (PVPP) and 36.3 ± 3.3 mg/ml and 238.0 ± 2.5 mg/ml respectively after PVPP treatment of the extracts. The effect produced by C. asiatica is thus unlikely to be due to phenolic compounds. It may, however, be due to its two consitituent triterpenoid glycosides madecassoside and asiaticoside which had IC₅₀ values of 8.6 ± 0.1 μM and 8.4 ± 0.6 μM respectively. These values were comparable to their concentrations in the crude extract and to the IC₅₀ of dithranol (5.2 ± 0.4 μM). These results suggest that the potential use of C. asiatica extracts as a topical anti-psoriatic agent is worthy of further investigation.