Role of the intestinal microflora in the formation of DNA and haemoglobin adducts in rats treated with 2-nitrofluorene and 2-aminofluorene by gavage

The role of the intestinal microflora in the metabolic activationof nitroarenes and arylamines was studied in female Wistar ratsthat received a dose of 1 mmol/kg 2-aminofluorene (2-AF) insunflower oil by gavage. Another group received the same doseof 2-nitrofluorene (2-NF). A third group of animals was usedas controls. Germfree (GF) rats, GF rats with a rat microflora(RM) and GF rats with a human microflora (HM) were treated.After treatment with 2-AF significant differences were observedin the formation of haemoglobin (Hb) adducts and DNA adducts.The 2-AF-Hb adduct level (mean ± SD) observed in GF rats(0.57 ± 0.13 µmol/g Hb) was considerably lowerthan that observed in RM rats (5.1 ± 0.6) and in HM rats(6.2 ± 13). DNA adduct levels showed the opposite pattern:levels of adducts co-migrating with deoxyguanosin-8-yl-aminofluorene(dG-C8-AF) in liver tissue were higher in GF rats (4.6 ±1.4 fmol/µg DNA) as compared to RM rats (2.6 ±0.04) or HM rats (2.0 ± 0.7). In lung tissue and whiteblood cells a similar influence of the intestinal microfloraon DNA adduct levels was observed. These results suggest thatthe intestinal microflora cleaves conjugates of 2-AF or N-hydroxy-2-AF,thus facilitating entero-hepatic recirculation of these compoundsand enhancing the formation of reactive intermediates bindingto Hb. The latter is not observed for DNA adduct formation,indicating that most of these adducts have been formed aftera single passage through the liver. After treatment with 2-NF,Hb and DNA adduct levels were much lower. An adduct spot wasobserved that was not presentin rats that received 2-AF. InGF animals only very low levels of DNA adducts co-migratingwith dG-C8-AF or deoxyguanosin-8-yl-acetyl-aminofluorene andno Hb adducts were observed, indicating that the metabolic activityof the microflora is an essential step in both Hb and DNA adductformation.