Inhibition of N-nitrosobenzylmethylamine metabolism and DNAbinding in cultured rat esophagus by ellagic acid

Abstract

The effect of ellagic acid (EA), a naturally occurring plant phenol, on the metabolism, DNA binding and DNA adduct formation of N-nitrosobenzylmethylamine (NBMA) in cultured explants of rat esophagus was investigated. Explants were incubated in medium containing EA at non-toxic concentrations of 10, 50 and 100 μM for 16 h, followed by the addition of 1 μM [³H]NBMA and EA for 12 h. Explant DNA was isolated by phenol extraction and hydroxylapatite chromatography, and benzaldehyde formation was determined by HPLC analysis of the culture medium. EA produced a significant inhibition in the total covalent binding of NBMA metabolites to DNA and in the production of benzaldehyde in the medium. After acid hydrolysis of the isolated DNA, the NBMA-DNA adducts were separated by HPLC. EA caused a dose-dependent decrease in the formation of N⁷-methylguanine and O⁶-methylguanine adducts. These results suggest that EA inhibits both the metabolism of NBMA and the binding of NBMA metabolites to DNA in cultured rat esophagus.