GLUCURONIDATION OF DROXYMETHYL)NITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE,A METABOLICALLY ACTIVATED FORM OF 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE, BY PHENOBARBITAL-TREATED RATS

In the rat, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induc es lung tumors independent of the route of administration. To exert it s carcinogenic potential, NNK must be metabolically activated. Like mo st nitrosamines NNK is activated by alpha-hydroxylation. The striking tissue specificity of tumor induction by nitrosamines has been primari ly attributed to the efficient alpha-hydroxylation of a particular nit rosamine by its target tissue. Two other factors which may contribute to this are the following: the relative capacity of different tissues to detoxify the alpha-hydroxynitrosamine and the preferential uptake o f the active metabolite by the target tissue. In the present study we report the characterization of the O-glucuronide of ydroxymethyl)nitro samino)-1-(3-pyridyl)-1-butanone (alpha-hydroxymethylNNK-Gluc). The fo rmation of this glucuronide could either serve as a detoxification pat hway or provide a stable transport form of the alpha-hydroxylated meta bolite. In addition, the metabolism of NNK to a glucuronide of the alp ha-hydroxynitrosamine provides the first definitive evidence for the f ormation of alpha-hydroxymethylNNK. alpha-HydroxymethylNNK-Gluc was pr esent in the urine of rats treated with phenobarbital (PB) and NNK. It was also formed by hepatocytes from PB-treated rats, accounting for 4 % of the total metabolites in the media following incubation with 1 mu M NNK. The data that support the identity of this metabolite as alpha -hydroxymethylNNK-Gluc are as follows. (1) Incubation of this metaboli te with beta-glucuronidase resulted in the quantitative release of 4-h ydroxy-1-(3-pyridyl)-1-butanone (HPB), the decomposition product of al pha-hydroxymethylNNK. (2) This glucuronide was detected by radioflow H PLC analysis when NNK which was tritium labeled in either the pyridine ring or the methyl group was used. Therefore, it contains both these functional groups. (3) When hepatocyte media was analyzed for this glu curonide (molecular weight 399) using LC/MS with selected ion monitori ng in the positive ion mode, a peak that was sensitive to beta-glucuro nidase treatment, with m/z (M + H), was detected at the correct retent ion time. LC/MS/MS analysis of this peak with selection of m/z 400 gen erated daughter ions of m/z 206, 176, 148, and 106. This fragmentation is consistent with this metabolite being alpha-hydroxymethylNNK-Gluc.