Davies Gerald F, Roesler William J, Ovsenek Nick, Bharadwaj Lalita A
Department of Biochemistry, University of Saskatchewan, 107 Wiggins Road, Sask, S7N 5E5, Saskatoon, Canada.
Pharmacol Res. 2003 Jul;48(1):119-26.
Troglitazone (TRG) is an antidiabetic agent that increases the insulin sensitivity of target tissues in non-insulin-dependent diabetes mellitus. Therapy with troglitazone has been associated with severe hepatic injury in a small percentage of patients and the mechanism of TRG-induced hepatotoxicity remains unclear. A family of highly conserved stress proteins identified as heat shock proteins (Hsps), are well-known to protect cells against a wide variety of toxic conditions such as extreme temperature changes, oxidative stress and toxic drugs. The stress-inducible Hsp 70 protein is one of the best-known endogenous factors protecting cells from injury under various stress conditions. Here we examined the effects of TRG on Hsp 70 mRNA and protein expression in primary cultures of rat hepatocytes. We also investigated the effects of TRG in an in vivo model by examining Hsp 70 protein levels in livers prepared from C57 mice fed a 0.2% dietary admixture of TRG. Levels of Hsp 70 mRNA increased in a concentration-dependent manner in rat hepatocytes treated for 8h with increasing concentrations of TRG. However, Hsp 70 protein levels decreased significantly in cells treated with increasing concentrations of TRG. C57 mice fed a 0.2% admixture of TRG for 10 days, also demonstrated decreased liver Hsp 70 protein levels. To investigate whether TRG decreased Hsp 70 protein levels by activating the ubiquitin-proteasome pathway, cells were pretreated with 10 microM lactacystin, a potent and specific inhibitor of this pathway. Lactacystin pretreatment failed to prevent TRG-induced decrease in Hsp 70 protein. The data suggests that TRG-induced effects may be mediated through another system of regulated proteolysis or may involve a post-transcriptional regulator mechanism. The mechanism of TRG-induced hepatotoxicity remains unclear, however, the effects induced by TRG on Hsp 70 may, in part, play a role.
曲格列酮（TRG）是一种抗糖尿病药物，可提高非胰岛素依赖型糖尿病患者靶组织的胰岛素敏感性。在一小部分患者中，曲格列酮治疗与严重肝损伤有关，而TRG诱导肝毒性的机制仍不清楚。一类被鉴定为热休克蛋白（Hsps）的高度保守应激蛋白，众所周知可保护细胞免受多种毒性条件的影响，如极端温度变化、氧化应激和有毒药物。应激诱导的Hsp 70蛋白是在各种应激条件下保护细胞免受损伤的最著名内源性因子之一。在此，我们研究了TRG对原代培养大鼠肝细胞中Hsp 70 mRNA和蛋白表达的影响。我们还通过检测喂食含0.2%TRG饮食混合物的C57小鼠肝脏中的Hsp 70蛋白水平，研究了TRG在体内模型中的作用。用浓度递增的TRG处理大鼠肝细胞8小时后，Hsp 70 mRNA水平呈浓度依赖性增加。然而，用浓度递增的TRG处理的细胞中，Hsp 70蛋白水平显著降低。喂食含0.2%TRG混合物10天的C57小鼠，肝脏Hsp 70蛋白水平也降低。为了研究TRG是否通过激活泛素-蛋白酶体途径降低Hsp 70蛋白水平，细胞先用10 microM乳胞素预处理，乳胞素是该途径的一种有效且特异性抑制剂。乳胞素预处理未能阻止TRG诱导的Hsp 70蛋白降低。数据表明，TRG诱导的效应可能通过另一种调节蛋白水解系统介导，或可能涉及转录后调节机制。TRG诱导肝毒性的机制仍不清楚，然而，TRG对Hsp 70的影响可能在一定程度上起作用。
