Nitroreduction and formation of hemoglobin adducts in rats with a human intestinal microflora

In the covalent binding of nitroarenes to macromolecules, nitroreduction is an important step. The intestinal microflora represents an enormous potential of bacterial nitroreductase activity. As a consequence, the in vivo nitroreduction of orally administered nitroarenes is primarily located in the intestine. In this study, we have investigated the nitroreduction of 2-nitrofluorene (2-NF) by a human microflora in female Wistar rats. Germ-free (GF) rats were equipped with a bacterial flora derived from human feces. Nontreated GF rats and GF animals equipped with a conventional rat flora were used as controls. The composition of the human and the conventional microflora isolated from the rats were consistent with the microflora of the administered feces. In the rats receiving only sunflower seed oil, no adducts were detected. The animals equipped with a human or rat microflora that received 2-aminofluorene (2-AF) formed 2-AF hemoglobin (Hb)-adducts at average levels (mean +/- SEM) of 5.3 +/- 0.3 and 6.7 +/- 0.7 mumole/g Hb, respectively. After 2-NF administration, the adduct levels were 0.022 +/- 0.003 and 0.043 +/- 0.010 mumole/g Hb, respectively. In the GF rats, an adduct level of 0.57 +/- 0.09 was determined after 2-AF administration and no adducts were detected after 2-NF administration. The results show that nitroreduction by an acquired human intestinal microflora and subsequent adduct formation can be studied in the rat in vivo.