Green Tea’s Inhibitory Effects on Cigarette Smoke-Induced Carcinogenesis

Green tea has been long recognized as a healthy beverage due to its high content of polyphenols and antioxidants. In recent years, studies have found that green tea polyphenols have inhibitory effects on various cancers, including lung cancer. Lung cancer is the leading cause of cancer-related deaths worldwide, and cigarette smoking is responsible for 80-90% of all lung cancer deaths in the United States. Therefore, it is of great interest to explore the potential of green tea in preventing cigarette smoke-induced carcinogenesis.

Cigarette smoke contains numerous carcinogens, including polycyclic aromatic hydrocarbons (PAHs), nitrosamines, and reactive oxygen species (ROS). The carcinogenic effect of cigarette smoking is associated with both the carcinogens and radicals contained in the smoke and tar. Studies have found that green tea polyphenols have a stronger inhibitory effect on the mutagenicity of cigarette smoke condensate (CSC) than other antioxidants, including ellagic acid, butylated hydroxyanisol, ascorbic acid, ß-carotene, and tocopherol. In addition, green tea polyphenols have been shown to inhibit chromosomal aberrations induced by CSC in vitro.

Intercellular communication plays an important role in carcinogenesis, and gap-junction-mediated intercellular communication has been found to be inhibited by CSC. However, green tea polyphenols have been found to prevent CSC-induced inhibition of intercellular communication in vitro. In an in vivo study, topical application of CSC increased the epidermal thickness of mouse skin about twofold, while treatment with green tea polyphenols reduced the CSC-induced epidermal thickness to a normal level.

In an in vivo-in vitro transformation of rat tracheal epithelial cells, green tea polyphenols significantly inhibited the transformation induced by benzo[a]pyrene (Bap) in rat tracheal epithelial cells. Moreover, green tea and its major component, epigallocatechin-3-gallate (EGCG), have been found to show a protective effect against tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis in A/J mice. The study indicated that EGCG appeared to be a major active component for this inhibitory activity.

In a human epidemiological study, the frequency of micronuclei in peripheral-blood lymphocytes in 220 healthy cigarette smokers was detected by a micronucleous test. The results show that cigarette smoking significantly increases the frequency of micronuclei in lymphocytes as compared with healthy non-smokers, and green tea consumption decreases the frequency of micronuclei in smokers.

In conclusion, green tea polyphenols have been found to have inhibitory effects on cigarette smoke-induced carcinogenesis, including mutagenesis, chromosomal aberrations, intercellular communication inhibition, and transformation of rat tracheal epithelial cells. Moreover, green tea and its major component EGCG have been found to show a protective effect against NNK-induced lung tumorigenesis in A/J mice. These findings suggest that green tea consumption may be a promising strategy for preventing lung cancer, especially in smokers.