Dhaunsi G S, Singh I, Orak J K, Singh A K
Department of Pediatrics, Medical University of South Carolina, Charleston 29425.
Carcinogenesis. 1994 Sep;15(9):1923-30. doi: 10.1093/carcin/15.9.1923.
To understand the mechanism of peroxisome proliferator-induced oxidative stress in non-mutagenic carcinogenesis, the effect of ciprofibrate, a peroxisome proliferator, on the activities and protein amounts of various antioxidant enzymes in different subcellular compartments was examined. Ciprofibrate treatment for short-term (3 weeks) as well as long-term (12 weeks) duration increased the total cellular catalase activity, whereas superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities were decreased significantly. Withdrawal of ciprofibrate from the diet did not normalize these activities. The observed decreases in total cellular SOD and GPX activities following ciprofibrate treatment were due to significant decreases in cytosolic CuZn SOD and GPX, whereas mitochondrial levels of Mn SOD and GPX were relatively unchanged. The peroxisomal CuZn SOD and GPX activities were increased significantly after both short- and long-term treatment, whereas catalase activity was reduced. Western blot analysis of cytoplasm for GPX and CuZn SOD showed a significant decrease in GPX and CuZn SOD proteins. Mitochondrial GPX protein was found to be slightly decreased, whereas Mn SOD protein levels did not show any significant change. The excessive production of H2O2 by oxidases and O2- by the cytochrome P450 enzyme system, along with the observed loss of antioxidant protection by loss of activities of catalase in peroxisomes and GPX and CuZn SOD in cytoplasm, may be the critical factors in peroxisomal proliferator-induced oxidative stress and initiation and promotion of carcinogenesis by this class of non-mutagenic agents. Both enzyme activities, as well as protein amounts of GPX and CuZn SOD, were higher in peroxisomes but lower in cytoplasm in ciprofibrate-treated liver as compared to control liver. The Mn SOD protein was decreased in peroxisomes, whereas mitochondrial Mn SOD was relatively unaffected in ciprofibrate-treated liver as compared to control. These observations suggest that the regulation of expression of peroxisomal CuZn SOD and Mn SOD is different from their counterparts in other cellular compartments.
为了解过氧化物酶体增殖物诱导的氧化应激在非致突变性致癌作用中的机制，研究了过氧化物酶体增殖物环丙贝特对不同亚细胞区室中各种抗氧化酶活性和蛋白量的影响。短期（3周）和长期（12周）的环丙贝特处理均增加了细胞总的过氧化氢酶活性，而超氧化物歧化酶（SOD）和谷胱甘肽过氧化物酶（GPX）活性则显著降低。从饮食中撤去环丙贝特后，这些活性并未恢复正常。环丙贝特处理后观察到的细胞总SOD和GPX活性降低是由于胞质铜锌SOD和GPX显著减少，而线粒体中的锰SOD和GPX水平相对未变。短期和长期处理后，过氧化物酶体铜锌SOD和GPX活性均显著增加，而过氧化氢酶活性降低。对细胞质中GPX和铜锌SOD进行蛋白质印迹分析显示，GPX和铜锌SOD蛋白显著减少。发现线粒体GPX蛋白略有减少，而锰SOD蛋白水平未显示任何显著变化。氧化酶过度产生H2O2以及细胞色素P450酶系统产生O2-，同时观察到过氧化物酶体中过氧化氢酶活性丧失以及细胞质中GPX和铜锌SOD活性丧失导致抗氧化保护作用缺失，可能是过氧化物酶体增殖物诱导氧化应激以及这类非致突变剂引发和促进致癌作用的关键因素。与对照肝脏相比，环丙贝特处理的肝脏中，过氧化物酶体中的两种酶活性以及GPX和铜锌SOD的蛋白量均较高，但细胞质中的较低。过氧化物酶体中的锰SOD蛋白减少，而与对照相比，环丙贝特处理的肝脏中线粒体锰SOD相对未受影响。这些观察结果表明，过氧化物酶体铜锌SOD和锰SOD表达的调节与其在其他细胞区室中的对应物不同。
