Effects of dietary supplementation of N-acetylcysteine on cigarette smoke-related DNA adducts in rat tissues

Cigarette smoking plays a major role in the etiology of several human cancers. It is believed that formation of DNA adducts is an initial step in the carcinogenic process. In this study, we have examined the ability of dietary N-acetylcysteine (NAC) to inhibit the formation of cigarette smoke- related DNA adducts in various tissues of rats. Female Sprague-Dawley tats were exposed to cigarette smoke (10 mg TPM/m³) in a whole-body exposure chamber for 6 h per day, seven days a week for four weeks. The smoke-exposed groups were provided either an unrefined diet or diets supplemented with low (5,000 ppm) or high (20,000 ppm) dose of NAC. A sham group was given control diet and maintained on filtered ambient air. Tissue DNA analysis of smoke- exposed rats by nuclease P1-version of the ³²P-postlabeling assay showed up to 6 adducts in the following descending order expressed as total adducts/10¹⁰ nucleotides: 1 predominant (no. 5) and 4 (no. 1-no. 4) minor adducts in the lung (219±36), 6 minor adducts in the heart (93±11), 5 adducts in the trachea (50±16), and 4 adducts in the bladder (50±3.5); sham-treated animals showed 2 or 3 adducts in each tissue but at 4-20-fold lower levels. Dietary intervention with either high or low dose of NAC did not affect the levels of most adducts, except for the following: a 30-40% increase (P<0.05) for adducts 3 and 4 in the lung; a 40-50% decrease (P<0.05) for adduct 2 in the trachea; and a 30% increase (P<0.05) for adduct 2 in the bladder. In a second experiment conducted under identical conditions, most major and minor adducts remained unaffected with NAC intervention, except for adduct 2 in the trachea which was somewhat diminished. These results suggest that dietary NAC intervention does not significantly influence the levels of most major and minor adducts. However, some minor adducts in the lung, trachea and bladder were modulated differentially.