Green tea extract and its metabolites induce biochemical changes linked to hepatotoxicity in HepG2 cells

Green tea has been consumed for thousands of years and its concentrated extract is now a popular herbal supplement frequently consumed in isolation or as part of a multi-ingredient product. Green tea extract (GTE) is commonly used for its wide range of purported health benefits and, as with most herbal supplements, its sale on the Australian market is regulated by the Therapeutic Goods Administration without requiring pre-market safety or efficacy analysis. Unfortunately, GTE has been implicated in over 50 cases of liver damage in the last 20 years, a number of which resulted in transplantation as the only option for patient survival. Despite the clear link between this supplement and liver injury in these individuals, little is currently known in regards to which biochemical pathways are affected during GTE-induced hepatotoxicity and the extent to which this is mediated by metabolic products of GTE. In this study, GTE and individual catechins were metabolised with S9 human liver fraction and subsequently analysed using untargeted metabolomics. The results confirmed that some metabolism of the GTE had occurred, with the production of at least 17 GTE metabolites. Of these suspected metabolites, 10 were also found in the metabolised catechins, suggesting that more than half of these compounds were metabolites of the catechins in GTE. To assess hepatotoxicity, HepG2 cells were exposed to either unmetabolised or metabolised GTE at doses equivalent to 1 mg/mL. Additionally, to assess the impact of GTE on drug-induced liver injury, another group of cells were exposed to 15 mM paracetamol, 1 mg/mL GTE or a combination of both treatments. The exposure period for all treatments was 24 h, after which small molecule metabolites were extracted from harvested cells and analysed using untargeted metabolomics. Changes were observed in amino acids, carbohydrates and fatty acids in all treatment groups, and the same biochemical pathways appeared to be affected in all GTE treatment variations. Cell treatment with GTE metabolites appeared to yield less cytotoxicity than those treated with unmetabolised GTE. It was unable to be determined whether GTE exacerbated paracetamol-induced hepatotoxicity from the results obtained in this study. Overall, the findings from this study suggested that GTE causes disruption to cellular lipids, proteins, nucleic acids and the mitochondria, potentially as a result of oxidative stress. Given the popularity and ready availability of GTE, regulation of herbal supplements containing this product must be improved to ensure consumer safety and ultimately prevent further cases of liver damage