Theacrine and strictinin, two major ingredients for the anti-influenza activity of Yunnan Kucha tea

Ethnopharmacological relevance: Kucha tea plant (Camellia assamica var. kucha Chang et Wang) is regarded as a mutant variety of wild Pu'er tea plant found in few mountain areas of Yunnan, China. Its fresh young leaves and shoots are picked by the indigenous aborigines in these local areas to prepare an herbal tea for the treatment of common cold empirically. Materials and methods: Two extra compounds of relative abundance were detected in Kucha tea in comparison with Pu'er tea, and their chemical structures were identified as chlorogenic acid and theacrine. These two compounds as well as two major compounds, strictinin and caffeine, in Kucha tea were evaluated for their cytotoxicity and inhibitory effects on human influenza virus A/Puerto Rico/8/34 by analyzing viral protein expression and progeny production. Results: No or low cytotoxicity was detected for the four Kucha compounds when their concentrations were below 100 mu M. Expression of viral NS1 protein was significantly inhibited by chlorogenic acid, theacrine or strictinin, but not caffeine at a concentration of 100 mu M. The relative inhibitory potency was detected as chlorogenic acid < theacrine < strictinin, and both theacrine and strictinin displayed significant inhibition at a concentration of 50 mu M. According to a plaque assay, viral progeny production was significantly reduced by theacrine or strictinin, but not by chlorogenic acid or caffeine under the same concentration of 100 mu M. Conclusion: It is suggested that theacrine and strictinin are two major ingredients responsible for the anti influenza activity of Yunnan Kucha tea traditionally used for the treatment of common cold.