Green and Black Tea Polyphenols: Inhibition of Carcinogenesis in Experimental Studies

Carcinogenesis, the process of cancer development, is a complex and multifactorial process that involves genetic, environmental, and lifestyle factors. Experimental studies have shown that green tea or black tea extracts and their polyphenolic components may play a beneficial role in inhibiting the development of cancer in different organs.

One of the most significant findings in experimental studies is the inhibition of esophageal papillomas and carcinomas of the esophagus and forestomach in mice by the administration of water-soluble green tea extract. This inhibition was observed in mice that were induced with nitrososarcosine, a carcinogen formed in vivo from sarcosine and NaNO2. Similarly, oral feeding of Chinese tea infusions inhibited esophageal tumors induced by the in vivo formation of N-nitrosomethylbenzylamine from its precursors methylbenzylamine and NaNO2 in rats. These findings suggest that green tea and black tea polyphenols may have protective effects against esophageal cancer.

In addition to esophageal cancer, green tea polyphenols have also been found to inhibit glandular stomach carcinogenesis induced by MNNG in rats. EGCG, a type of polyphenol found in green tea, has been found to inhibit duodenal tumors in mice treated with N-ethyl-N-nitrosoguanidine. Furthermore, oral feeding of GTEC or EGCG has been shown to significantly inhibit the incidence of large intestinal tumors induced by subcutaneous injection of 1,2-dimethylhydrazine in mice. These findings suggest that green tea and its polyphenols may have protective effects against stomach, duodenal, and large intestinal cancers.

Tea polyphenols have also been found to have protective effects against liver cancer. In rat hepatocarcinogenesis, gamma-glutamyl transpeptidase (GGT)-positive foci were induced by diethylnitrosamine (DEN) and 2-acetylaminofluorene (2AAF) treatment or by DEN and phenobarbital (PB) treatment. Administration of GTEC significantly inhibited the development of GGT-positive foci in both experiments, indicating anti-initiation and anti-promotion effects on hepatocarcinogenesis. Additionally, green tea or black tea in the basal diet inhibited AFB1-induced GGT-positive hepatocyte foci in rats. These findings suggest that green tea and black tea polyphenols may have protective effects against liver cancer.

Tea and tea polyphenols have also been demonstrated to have inhibitory effects on carcinogenesis in other organs, such as pancreatic cancer in the golden hamster, small intestinal tumors in rats, and mammary tumors in rats. Moreover, green tea infusion has been found to inhibit in vitro invasion and in vivo metastasis of mouse lung carcinoma cells. These findings suggest that tea and its polyphenols may have beneficial effects on cancer prevention and treatment in various organs.

In conclusion, experimental studies have demonstrated that green tea and black tea polyphenols may have protective effects against the development of cancer in different organs. These findings suggest that tea and its polyphenols may have a potential role in cancer prevention and treatment. However, more studies are needed to elucidate the underlying mechanisms and to determine the appropriate dose and duration of tea consumption for optimal cancer prevention and treatment.