Modulatory effects of Thai medicinal plant extract on proinflammatory cytokines-induced apoptosis in human keratinocyte HaCaT cells
It has been experimentally proven that proinflammatory cytokines, interferon (IFN)-y and tumor necrosis factor (TNF)-a are able to synergistically induce apoptosis in HaCaT keratinocyte cells. The present study aimed to elucidate modulatory effects of ethanolic extracts derived from Thai traditional medicinal plants on IFN-y/TNF-a-caused HaCaT apoptosis and correlate with their natural phenolic content. Using 3-(4-5 dimethylthiozol-2-yl) 2-5 diphenyl-tetrazolium bromide (MTT) assay, we found that herbal extracts derived from members of the Acanthaceae family, Rhinacanthus nasutus (L.) Kurz (0.1, 1 and 10 μg/ml) and Clinacanthus nutans (Burm.f.) Lindau (1 and 100 μg/ml), significantly inhibited the IFN-y/TNF-a- induced HaCaT apoptosis, while members of the Zingiberaceae family, Curcuma longa L. and Alpinia galanga (L.) Willd, significantly enhanced apoptosis when a concentration of 100 μg/ml was used. Furthermore, the ethanolic plant extracts were found to possess different amounts of total phenolics ranging from 1.64 to 10.04 mg GAE/g as determined using Folin-Ciocalteu assay. The richest phenolic sources were R. nasutus (10.04 ± 1.12 mg GAE/g) and C. longa (7.49 ± 0.50 mg GAE/g), whereas the least phenolic source was Centella asiatica (1.64 ± 0.84 mg GAE/g). Taken together, we found certain modulatory effects of Thai medicinal extracts on IFN-y/TNF-a-induced apoptosis in HaCaT cells, but these findings might not be directly correlated with their natural phenolic content. Therefore, further investigations on different types of natural phenolic contents in these Thai medicinal extracts and their relevant molecular mechanisms in keratinocytes, should be carried out in the near future.
Key words: Interferon, tumor necrosis factor, Thai medicinal herbs, apoptosis, phenolics, human keratinocytes.