Metabolism of 1,8‐dinitropyrene by human, rhesus monkey, and rat intestinal microflora

Abstract

Dinitropyrenes (DNPs) are highly mutagenic in the Salmonella reversion assay and are tumorigenic in rodents. Bacterial nitroreductases have been implicated in the mutagenic activation of DNPs. In this study, we investigated the metabolism of 1,8‐dinitropyrene (1,8‐DNP) by anaerobic bacterial suspensions derived from human feces, and the intestinal contents of rhesus monkeys and rats. The 1,8‐DNP metabolites were isolated by reversed‐phase high performance liquid chromatography, and identified by comparison of their chromatographic and mass spectral properties with those of authentic compounds. All of the intestinal microflora metabolized 1,8‐DNP to 1‐amino‐8‐nitropyrene and 1,8‐diaminopyrene. The mutagenic activity of samples extracted from incubations of human or rat intestinal microflora cultured with 1,8‐DNP was measured by reversion of Salmonella typhimurium TA98. There was a decrease in the mutagenic activities of the extracts with time of incubation that correlated with increased 1‐amino‐8‐nitropyrene and 1,8‐diaminopyrene formation. The decreased mutagenicity of the 1,8‐DNP metabolites was confirmed by conducting assays with authentic 1‐amino‐8‐nitropyrene and 1,8‐diaminopyrene. Both compounds showed much lower mutagenic activity compared to 1,8‐DNP. The results indicate that intestinal microflora have the ability to metabolize 1,8‐DNP to amine derivatives that are less mutagenic than the parent compound.

Reduction of nitroaromatic compounds by anaerobic bacteria isolated from the human gastrointestinal tract

“…The abilities of pure cultures of bacteria and of intestinal microflora from humans and several animal species to reduce nitro-PAHs to amino-PAHs has been shown previously (4,5,14,17,23,24). However, the specific bacteria in the human gastrointestinal tract that reduce these environmental pollutants have not been previously identified.…”

“…Nitro-PAHs were also added to ethyl acetate extracts of bacterial cultures and used in the mutagenicity assay as controls. Ethyl acetate-extracted metabolites were dried, dissolved in dimethyl sulfoxide, and tested for mutagenicity by using S. typhimurium TA98 (5). Effect of pH on nitroreductase activity.…”

“…Nitro-PAHs are metabolized by both reductive and oxidative pathways (nitroreduction, ring oxidation, or a combination of the two) (8,9,18,29,32,33,37). The reduction of nitro groups is catalyzed by several mammalian enzymes and also by intestinal bacteria (4,5,14,15,17,23,24,32).…”

“…Intestinal microflora, which are dominated by obligate anaerobes, can modify a wide range of environmental chemicals either directly or through the enterohepatic circulation (17). Various anaerobic human, monkey, and rat intestinal microflora are capable of rapidly metabolizing 1-nitropyrene, dinitropyrenes, and 6-nitrochrysene to aromatic amines (4,5,14,17,23,24). In addition, anaerobic bacteria commonly associated with the gastrointestinal tract reduce nitro-PAHs to aromatic amines, indicating nitroreductase activity in these bacteria (4,15,17,18,24).…”

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

“…Because it is known that a wide range of intestinal bacterial species are able to reduce aromatic nitro compounds (16), it is possible that species other than the ones that were identified from the cecum contents are responsible for the observed difference in adduct formation. Qualitative differences in the nitroreducing potential between the microflora from humans, rhesus monkeys, and rats are reported (21). The difference between the Hb adduct levels formed by the control animals equipped with a human or rat microflora are not statistically significant.…”