Volatile nitrosamine levels and genotoxicity of food samples from high‐risk areas for nasopharyngeal carcinoma before and after nitrosation

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Abstract
Traditional life‐style, especially food habits, infection by Ep‐stein‐Barr virus (EBV) and genetic factors, have been associated with an increased risk of nasopharyngeal carcinoma (NPC). N‐Nitroso compounds and other carcinogens either present in food or formed endogenously, as well as food constituents that activate EBV, have been suspected as etiological factors in NPC pathogenesis. For their characterization preserved food items, frequently consumed in NPC endemic areas in Tunisia, South China and Greenland, were sampled and screened for the presence of mutagens and volatile nitro‐samines before and after nitrosation. Aqueous extracts as well as 2 organic extracts of the samples were assayed for genotoxicity in 2 Salmonella typhimurium strains and the SOS chromotest. The same extracts had previously been analyzed for volatile nitrosamines and for EBV‐activating substances in Raji cells. In our study, 13 out of 16 food samples showed a weak, directly‐acting genotoxicity in the SOS chromotest in at least one of the extracts, but only one sample from Greenland was found to be weakly mutagenic in Salmonella TA 98. Chemical nitrosation for 9 out of 15 samples of aqueous food extracts increased the genotoxic effect in the SOS chromotest. Levels of volatile nitrosamines were also elevated for 12 out of 15 samples; highest levels of N‐nitroso‐dimethylamine were found in hard salted and dried fish from China (1,200 μg/kg) and highest N‐nitrosopyrrolidine levels in a Tunisian spice (3,840 μg/kg). In non‐nitrosated aqueous food extracts, the level of volatile nitrosamines and genotoxic activities were not correlated with the EBV‐inducing activity of the same samples. After chemical nitrosation, EBV‐inducing activity was decreased or showed no change and was not correlated with increases in either the genotoxicity or the nitro‐samine levels. Our results suggest that EBV‐activating compounds belong to a different class of substances. However, there was an association between the changes in genotoxicity and nitrosamine levels due to nitrosation.