ROLE OF THE INTESTINAL MICROFLORA IN THE FORMATION OF DNA AND HEMOGLOBIN ADDUCTS IN RATS TREATED WITH 2-NITROFLUORENE AND 2-AMINOFLUORENE BY GAVAGE

The role of the intestinal microflora in the metabolic activation of n itroarenes and arylamines was studied in female Wister rats that recei ved a dose of 1 mmol/kg 2-aminofluorene (2-AF) in sunflower oil by gav age. Another group received the same dose of 2-nitrofluorene (2-NF). A third group of animals was used as controls. Germfree (GF) rats, GF r ats with a rat microflora (RM) and GF rats with a human microflora (HM ) were treated. After treatment with 2-AF significant differences were observed in the formation of haemoglobin (Db) adducts and DNA adducts . The 2-AF-Hb adduct level (mean +/- SD) observed in GF rats (0.57 +/- 0.13 mu mol/g Hb) was considerably lower than that observed in RM rat s (5.1 +/- 0.6) and in HM rats (6.2 +/- 1.3). DNA adduct levels showed the opposite pattern: levels of adducts co-migrating with deoxyguanos in-8-yl-aminofluorene (dG-C8-AF) in liver tissue were higher in GF rat s (4.6 +/- 1.4 fmol/mu g DNA) as compared to RM rats (2.6 +/- 0.04) or HM rats (2.0 +/- 0.7). In lung tissue and white blood cells a similar influence of the intestinal microflora on DNA adduct levels was obser ved. These results suggest that the intestinal microflora cleaves conj ugates of 2-AF or N-hydroxy-2-AF, thus facilitating enterohepatic reci rculation of these compounds and enhancing the formation of reactive i ntermediates binding to Hb. The latter is not observed for DNA adduct formation, indicating that most of these adducts have been formed afte r a single passage through the liver. After treatment with 2-NF, Hb an d DNA adduct levels were much lower. An adduct spot was observed that was not present in rats that received 2-AF. In GF animals only very lo w levels of DNA adducts co-migrating with dG-C8-AF or deoxyguanosin-8- yl-acetyl-aminofluorene and no Db adducts were observed, indicating th at the metabolic activity of the microflora is an essential step in bo th Db and DNA adduct formation.