BENZENE METABOLISM IN THE ISOLATED-PERFUSED MOUSE-LIVER

The hematotoxicity of benzene (BZ) requires its hepatic metabolism, th e release of metabolites into the circulation, and the access of metab olites to the bone marrow. Although a range of potentially toxic metab olites produced by the liver was identified using subcellular systems and isolated hepatocytes, these models do not allow identification of the metabolites released from the liver with respect to time and flow through the liver. We developed an isolated perfused mouse liver model to evaluate metabolites released following a single-pass of radiolabe led BZ and after recirculation of single-pass metabolites back through the liver. Reversing the path of flow through the liver changes the o rientation of hepatic oxidizing and conjugating enzymes with respect t o perfusate flow. Comparison of metabolite production following normal (orthograde, portal vein to hepatic vein) perfusion with reversed (re trograde) perfusion permitted an evaluation of the impact of zonal dis tributions of these enzymes on BZ metabolism. The major metabolites de tected by HPLC, irrespective of the direction of perfusion, were free phenol (P), phenylsulfate (PS), and phenylglucuronide (PG), plus lesse r amounts of hydroquinone (HQ) and hydroquinone glucuronide (HQG). Rec irculation of the products of single pass orthograde perfusion through the liver yielded P conjugates as well as low levels of free and conj ugated HQ. No free P was detected after recirculation. Although no qua litative differences between orthograde and retrograde perfusion were observed, the percentage of free P and P conjugates (PS + PG) found as free P was twice as great following orthograde perfusion as compared to retrograde perfusion. These results suggest that regional differenc es in the zonation of enzymes involved in oxidation and conjugation ma y play a critical role in hepatic BZ metabolism. (C) 1997 Academic Pre ss.