Low activities of glutathione-related enzymes as factors in the genesis of urinary bladder cancer

A comparative study of reduced glutathione (GSH) concentrations and activities of GSH related-enzymes in urinary bladder transitional epithelium (UBTE), urinary bladder nontransitional tissue (UBNT), and liver of the rabbit, was carried out to investigate the reasons for the susceptibility of UBTE towards peroxidase-mediated chemical carcinogenesis. Cooxidative activation of chemical carcinogens by prostaglandin H synthase occurs at high levels in UBTE and minimally in UBNT. Other peroxidases are also likely to activate carcinogenic xenobiotics in the urinary bladder. GSH concentrations in UBTE and UBNT were low compared to that in the liver. gamma-Glutamyl transpeptidase activities were much lower in UBTE and in UBNT than those in the liver. Activities of selenium-dependent and selenium-independent glutathione peroxidases were very low in UBTE and UBNT. Cytosolic glutathione S-transferase activity towards 1,2-epoxy-(4-nitrophenoxy)propane was very low in UBTE. Microsomal glutathione S-transferase activity towards 1-chloro-2,4-dinitrobenzene was much lower in UBTE than in the liver. We propose that the low GSH concentration and diminished activities of glutathione peroxidases, gamma-glutamyl transpeptidase, and certain isozymes of glutathione S-transferase could be responsible for the vulnerability of UBTE towards chemical carcinogenesis.     

Metabolic oxidation of acetaminophen (Paracetamol) mediated by cytochrome P-450 mixed-function oxidase and prostaglandin endoperoxide synthetase in rabbit kidney

Long-term abuse of acetaminophen, in combination with other antipyretic analgesics, is thought to be responsible for papillary necrosis in analgesic nephropathy. Cytochrome P-450-mediated oxidative metabolism requiring NADPH and O₂ has been believed, to date, to be the sole pathway for the toxic metabolic activation of acetaminophen. Using microsomes from different regions of rabbit kidney, protein covalent binding of acetaminophen by NADPH-dependent metabolism was highest in cortex, less in outer medulla, and minimal in inner medulla. In vivo studies have shown that the highest binding of acetaminophen occurred in renal inner medulla compared to liver and renal cortex. However, cytochrome P-450 could not be detected in rabbit renal inner medulla. Hence, another metabolic pathway for the activation of acetaminophen was presumed to be operative in renal inner medulla. This alternate pathway was recognized as cooxidation of acetaminophen mediated by prostaglandin endoperoxide synthetase, requiring arachidonic acid as well as O₂, and was found to be active predominantly in renal inner medulla. Glutathione, ascorbic acid, and ethoxyquin inhibited protein covalent binding of acetaminophen arising from both pathways. Indomethacin and aspirin inhibited only the arachidonic acid-dependent cooxidation of acetaminophen. Butylated hydroxyanisole inhibited both NADPH- and arachidonic acid-dependent metabolism, the latter more effectively. Arachidonic acid-dependent metabolism of acetaminophen is probably mediated by the hydroperoxidase activity of prostaglandin endoperoxide synthetase. This alternate pathway could be a significant contributing factor for the genesis of papillary necrosis, as manifested in analgesic nephropathy.     

^1H磁共振波谱在大鼠C6脑胶质瘤致痫性评估中的应用

目的:1H磁共振波谱是研究活体脑组织及肿瘤组织代谢与生化指标测定的非侵袭技术,实验通过对种植C6脑胶质瘤大鼠的1H磁共振波谱在体观察,为非侵袭性评价肿瘤的致痫性提供帮助。方法:实验于2007-03/07在中国医科大学附属盛京医院中心实验室完成。①分组处理:选用雌性近交系Wistar大鼠共40只,随机分为实验组和对照组两组各20只。实验组制作C6脑胶质瘤移植动物模型,根据皮质脑电图记录结果确定癫痫发作,并将其分为致痫组与非致痫组;对照组在相同部位注射等量Ham'sF-12培养液。②观察指标:所有大鼠取出内置皮质电极后行1H磁共振波谱检查。分别选择肿瘤周围区及肿瘤实质区作为感兴趣区对每一体积元进行化学位移成像。所测定的主要代谢产物包括N-乙酰基天门冬氨酸、肌酸、胆碱、乳酸/脂质、谷氨酸及γ-氨基丁酸。以肌酸为参照波峰,分别计算各代谢产物与肌酸波的积分面积进行比较。结果:32只大鼠纳入结果分析。①实验组大鼠C6脑胶质瘤肿瘤实质区及肿瘤周围区胆碱及脂质波峰高于对照组(P<0.01,0.05);而肿瘤实质区N-乙酰基天门冬氨酸及谷氨酸波峰高于对照组(P<0.05)。②C6脑胶质瘤致痫组肿瘤周围区谷氨酸波峰高于非致痫组(P<0.01);而γ-氨基丁酸波峰低于非致痫组(P<0.01)。同时,肿瘤周围区乳酸/肌酸两组间比较差异也具有统计学意义(P<0.05)。结论:①1H磁共振波谱检查可为脑胶质瘤的恶性程度及其侵袭性的活体判定提供依据。②通过活体监测肿瘤周围皮质谷氨酸与γ-氨基丁酸二者含量的变化,也可为非侵袭性评价肿瘤的致痫性提供帮助。     

Covalent binding of metabolites of acetaminophen to kidney protein and depletion of renal glutathione

Experiments in CD-1 mice and Sprague-Dawley rats were carried out to determine the extent to which biochemical changes described previously for acute acetaminophen-induced hepatotoxicity might be applicable to the kidney. After intraperitoneal injection of acetaminophen, tissue glutathione and covalent binding of tritiated metabolites of acetaminophen to tissue protein were measured for liver, kidney cortex and kidney papilla. Glutathione was reduced more in mice than in rats, and more in liver than in kidney, without appearance of oxidized glutathione in either tissue. Covalent binding was likewise greater in mice than in rats and greater in liver than in kidney. The determination of covalent binding was extremely sensitive to the trace radiochemical impurities of the labeled drug. With prior administration of 3-methyl-cholanthrene, the induced changes were far greater in liver than in kidney, suggesting that the formation of a reactive metabolite from acetaminophen occurred in each organ by slightly different mechanisms. At doses less than those associated with demonstrable acute toxicity, the duration of covalent binding to protein was longer for renal papilla than for renal cortex or for liver. The results may be applicable to the pathogenesis of both acute and chronic nephrotoxicity.