Green tea polyphenols have been shown to inhibit nitrosamine-mediated carcinogenesis in in vitro bladder models (Chung et al, 1993).
It has also been shown that aspirin inhibited nitrosamine induced lung carcinogenesis [ 27], and it reduced COX-2 enzyme levels in lung cancer cell lines [ 28].
In vivo, ZER inhibits diethyl nitrosamine (DEN) and dietary 2-acetylaminofluorene- (AAF-) induced Sprague Dawley rat hepatocarcinogenesis.
For total nitrite (dietary nitrite + 5% dietary nitrate) it is important to note that vegetables are the main contributor for dietary nitrate, many of which are also rich in vitamin C--a vitamin known to inhibit the formation of nitrosamines under normal gastric conditions.
In addition, it has been proposed that butyrate reduces the risk of colon cancer, due to its ability to inhibit the genotoxic capacity of nitrosamines and hydrogen peroxide, as well as to induce different levels of apoptosis, differentiation and cessation of the cellular cycle of colon cancer in animal models [ 46].
The majority of compounds that inhibit the formation of carcinogens prevent the formation of nitrosamines from secondary amines and nitrite in an acidic environment.
Polyphenols can inhibit hemeprotein-induced peroxidation in the stomach and decrease DNA base deamination or nitrosamine formation by HNO2-derived reactive nitrogen species [ 41].
Using NNK, a tobacco-specific nitrosamine carcinogen, as an example, it has been shown that isothiocyanates potently inhibit NNK-induced lung carcinogenesis in animal models, which is closely correlated with their ability to inhibit NNK-activating phase 1 enzymes [ 8, 9].
It was previously demonstrated that Bcl-2 could inhibit apoptosis and also inhibit multiple DNA-repair pathways; thus, tumour cells exposed to DNA-damaging substances, like nitrosamine, exhibited an accumulation of Bcl-2 in the nuclei [44].
