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The Reduction of N-Hydroxy-4-acetylaminobiphenyl by the Intestinal Microflora of the Rat¹

Department of Pharmacology, Harvard Medical School, Beth Israel Hospital, Boston, Massachusetts 02215

The role of the intestinal flora in the conversion of N-hydroxy-4-acetyl-aminobiphenyl (N-OH-AABP) to 4-acetylaminobiphenyl has been examined. This reaction, which reverses the metabolic activation of the parent carcinogen, can be demonstrated in cultures of some bacteria indigenous to the intestinal microflora. These include cultures of Clostridium sp., Clostridium perfringens, Peptostreptococcus productus I, and Bacteroides fragilis ss. thetaiotaomicron and ss. vulgatus. In contrast, cultures of Lactobacillus plantarum and Escherichia coli show little or no capacity for this reaction. The reduction of N-OH-AABP is also carried out by homogenates of liver, kidney, and brain. On a weight basis, the cecal flora is considerably more active in reducing N-OH-AABP than are homogenates of tissues of the gastrointestinal tract. The cecal flora also has a greater activity for reducing N-OH-AABP than the stomach flora, an observation which may relate to the induction of tumors in the forestomach but not in the cecum of rats fed this compound.

The products of the metabolism of N-OH-AABP have been compared in germ-free and conventional animals. Glucuronide conjugates of N-OH-AABP are found in the cecal contents and feces only of the germ-free rats, while 4-acetylaminobiphenyl is found in the feces only of conventional rats. These results suggest that the flora, by hydrolyzing glucuronides and reducing N-OH-AABP, may influence the level of metabolites of 4-acetylaminobiphenyl which are critical for carcinogenesis.

¹ These studies were supported by Grant 15260-01 from the National Cancer Institute and a grant from the William F. Milton Fund of Harvard University.

Received 3/19/75. Accepted 7/23/75.