BIOLOGICAL-ACTIVITIES OF THE INTESTINAL MICROFLORA IN MICE TREATED WITH ANTIBIOTICS OR UNTREATED AND THE EFFECTS OF THE MICROFLORA ON ABSORPTION AND METABOLIC-ACTIVATION OF ORALLY-ADMINISTERED GLUTATHIONE CONJUGATES OF K-REGION EPOXIDES OF 1-NITROPYRENE

To elucidate the effects of the intestinal microflora on absorption an d activation of glutathione conjugates of 4,5-epoxy-4,5-dihydro-1-nitr opyrene (1-NP 4,5-oxide) and 9,10-epoxy-9,10-dihydro-1-nitropyrene (1- NP 9,10-oxide), we investigated the biological activities of the micro flora in specific-pathogen-free (SPF) mice and SPF mice treated with v arious antibiotics and established the methodology of antibiotic treat ment to eliminate the intestinal microflora. Mice were given various k inds of antibiotics by intragastric gavage twice a day for five days. A mixture of antibiotics bacitracin (BC), neomycin (NM) and streptomyc in (SM) was the most effective in reducing the various activities of t he intestinal microflora. The treatment decreased the bacterial counts and the activities of enzymes of the intestinal contents cysteine con jugate beta-lyase (beta-lyase), beta-glucuronidase and nitroreductase which were derived from the intestinal microflora, but did not affect the activities of gamma-glutamyltransferase and aminopeptidase which w ere derived from host tissue cells. Furthermore, the treatment did not affect absorption of glucose from the intestinal tract, body weight o r liver enzyme activities. The treatment with only an aminoglycoside a ntibiotic, kanamycin or NM, decreased neither the number of anaerobes in the intestine nor the beta-lyase or nitroreductase activities from the intestinal contents. Glutathione conjugates of [H-3]-1-NP oxides w ere administered to two groups of ICR mice that had been treated with antibiotics (BC, NM, SM) or saline (control group) orally. The radioac tivity in the blood increased and reached the maximum level 2 or 3 h a fter administration of the conjugates in the control group; however, t hat in the antibiotic-treated group was only slightly increased if at all. Excretion of [H-3]-labeled metabolites into the urine was approxi mately 20% of the total dose in the control group, but it was <2% in t he antibiotic-treated group during 48 h. After 48 h, DNA in the lower intestinal mucosa was extracted and the DNA adducts were analyzed by t he P-32-postlabeling method. Three new DNA adducts were detected in th e lower intestinal mucosa of the control group but not of the antibiot ic-treated group. These results suggest that the intestinal microflora plays an important role in absorption of the metabolites of glutathio ne conjugates of 1-NP oxides from the intestinal tract and activation of the metabolites in the intestine.