The adverse and beneficial effects of polyphenols in green and black teas in vitro and in vivo

Abstract

Although numerous studies highlight the health benefits of tea, excessive consumption has been linked to toxic conditions. Thus, understanding the optimal consumption of tea is essential to minimize toxicity while maximizing its benefits. In this study, we investigated the effects of eight green tea samples (G1-G8) and eight black tea samples (R1-R8) from Camellia sinensis, the most popular teas in Asian culture, on RSC96 Schwann neural cells and embryonic cardiomyocyte H9c2 cells. The results showed that the IC₅₀ (mg/ml, weight/volume) of both tea types were inversely proportional to their polyphenol content, suggesting a relationship between toxicity and polyphenol levels in both green and black tea. Interestingly, green teas generally have higher polyphenol content than black teas. We also assessed the protective effects of tea in vitro by pretreating cells with the teas at indicated doses of polyphenol and subsequently exposing them to H₂O₂. Both tea types significantly reduced the decline in cell viability for both cell lines, and there was no significant difference in protective polyphenol concentrations for green (G3 & G7) and black (R3 & R8) teas at effective concentrations (EC20 and EC40). To evaluate the preventative effects of tea in vivo, we examined the impact of two green (G3 & G7) and two black (R3 & R8) teas with varying polyphenol content on dextran sulfate sodium (DSS)-induced inflammatory colitis in mice. Tea-treated groups exhibited significantly lower inflammatory scores (DAI) than the control group. DSS treatment in the control group led to shortened colorectal lengths in mice, while tea co-treatment partially prevented this loss. Histological analysis revealed that G7 and R3 (with a moderate polyphenol content) treatment improved colorectal crypt structure, decreased the severity of inflammatory ulcerative colitis, and significantly reduced histological scores compared to the control group. However, G3 and R8 (with high and low doses of polyphenol content, respectively) did not show these effects, suggesting that a moderate polyphenol level in both tea types is optimal for preventative benefits.

Keywords: H9c2 cells; RSC96 cells; black tea; colorectal colitis.; green tea; protective effects; toxicity.