ABSTRACT:Glutathione S-transferase Mu 1 (GSTM1) has been regarded as one of the key enzymes involved in phase II reactions in the liver, because of its high expression level. In this study, we generated mice with disrupted glutathione S-transferase Mu 1 gene (Gstm1-null mice) by gene targeting, and characterized the phenotypes by cytosolic and in vivo studies. The resulting Gstm1-null mice appeared to be normal and were fertile. Expression analyses for the Gstm1-null mice revealed a deletion of Gstm1 mRNA and a small decrease in glutathione S-transferase alpha 3 mRNA. In the enzymatic study, GST activities toward 1,2-dichloro-4-nitrobenzene (DCNB) and 1-chloro-2,4-dinitrobenzene (CDNB) in the liver and kidney cytosols were markedly lower in Gstm1-null mice than in the wild-type control. Gstm1-null mice had GST activities of only 6.1 to 21.0% of the wild-type control to DCNB and 26.0 to 78.6% of the wild-type control to CDNB. After a single oral administration of DCNB to Gstm1-null mice, the plasma concentration of DCNB showed larger AUC 0-24 (5.1-5.3 times, versus the wild-type control) and higher C max (2.1-2.2 times, versus the wild-type control), with a correspondingly lower level of glutathione-related metabolite (AUC 0-24 , 9.4-17.9%; and C max , 9.7-15.6% of the wild-type control). In conclusion, Gstm1-null mice showed markedly low ability for glutathione conjugation to DCNB in the cytosol and in vivo and would be useful as a deficient model of GSTM1 for absorption, distribution, metabolism, and excretion/toxicology studies.

To assess modification of thioacetamide-induced hepatotoxicity in mice fed a high-fat diet, male C57BL/6J mice were fed a normal rodent diet or a high-fat diet for 8 weeks and then treated once intraperitoneally with thioacetamide at 50 mg/kg body weight. At 24 and 48 hours after administration, massive centrilobular hepatocellular necrosis was observed in mice fed the normal rodent diet, while the necrosis was less severe in mice fed the high-fat diet. In contrast, severe swelling of hepatocytes was observed in mice fed the high-fat diet. In addition, mice fed the high-fat diet displayed more than a 4-fold higher number of BrdU-positive hepatocytes compared with mice fed the normal rodent diet at 48 hours after thioacetamide treatment. To clarify the mechanisms by which the hepatic necrosis was attenuated, we investigated exposure to thioacetamide and one of its metabolites, the expression of CYP2E1, which converts thioacetamide to reactive metabolites, and the content of glutathione S-transferases in the liver. However, the reduced hepatocellular necrosis noted in mice fed the high-fat diet could not be explained by the differences in exposure to thioacetamide or thioacetamide sulfoxide or by differences in the expression of drug-metabolizing enzymes. On the other hand, at 8 hours after thioacetamide administration, hepatic total glutathione in mice fed the high-fat diet was significantly lower than that in mice fed the normal diet. Hence, decreased hepatic glutathione amount is a candidate for the mechanism of the attenuated necrosis. In conclusion, this study revealed that thioacetamide-induced hepatic necrosis was attenuated in mice fed the high-fat diet.

-Plasma protein binding is an important factor for the kinetics of drugs and how they act composition, can affect drug binding and subsequent drug response. In the present study, we investigated the toxicokinetics (TK) and/or toxicodynamics (TD) of diclofenac and propranolol comparing pregnant Sparague-Dawley (SD) rats with non-pregnant SD rats in terms of protein binding and drug distribution.1 -acid glycoprotein (AGP), respectively. After a single administration of diclofenac, the area under plasma concentration-time curve (AUC) based on free diclofenac in pregnant rats was 3.9 times higher than that in non-pregnant rats. This difference is considered to be due to a lower concentration of serum albumin and a higher concentration of -ical examination, more severe gastrointestinal toxicity was observed in pregnant rats at 24 hr after dosing. This severe toxicity was likely to be correlated with the higher AUC. With respect to propranolol, the difference of the AUC based on free propranolol was not clear although the concentration of serum AGP was lower in pregnant rats. However, the binding analysis data suggested a difference of protein binding at a lower propranolol concentration range. Consequently, lowered serum proteins and increased NEFA in pregnant rats can lead to low protein binding, subsequent increase in free drug concentrations, and eventual increase in the TD of drugs.

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