Giulivi C, Lavagno C C, Lucesoli F, Bermúdez M J, Boveris A
Department of Molecular Pharmacology and Toxicology, School of Pharmacy, University of Southern California, Los Angeles 90033, USA.
Free Radic Biol Med. 1995 Feb;18(2):203-13. doi: 10.1016/0891-5849(94)00111-v.
Paraquat poisoning and hyperbaric oxygen exposure are well established models of oxidative stress in lung. The aim of this study was focused on the contribution of oxygen free radicals and other cytotoxic species, such as lipid hydroperoxides, to the overall toxicity. Adult Wistar rats were injected with paraquat (30 or 60 mg/kg b.w.) or exposed to hyperbaric oxygen (0.2 MPa), and several parameters of lung damage were measured. Both treatments resulted in increased spontaneous lung chemiluminescence, number of lung PMN, malondialdehyde content, lung edema, and pleural liquid. Of note, spontaneous lung chemiluminescence, used to monitor the steady-state concentration of oxygen free radicals in vivo, did not increase significantly after either treatment. The increase in spontaneous lung chemiluminescence started after PMN migration, being both maxima separated by a delay time of 4-6 h. After PMN migrated and became activated in the lung, the survival of the animals started to decline. Thus, PMN can be considered as additional sources of oxygen free radicals supported by the subsequent increase in chemiluminescence. Their role in lung damage was evidenced by the increase in lung edema, augmented pleural liquid, and decreased survival after PMN migration. Lipid hydroperoxide concentration in lung membranes was also increased after either treatment. This increased concentration may be a consequence of an increased rate of lipid peroxidation, initiated by oxidative stress on lipid membranes, or by an inhibition of their catabolism. Ester lipid hydroperoxides normally produced in membranes cannot be catabolized directly by the glutathione peroxidase-reductase system unless phospholipase A2 catalyses the release of free lipid hydroperoxides. In both experimental models, phospholipase A2 activity was decreased to almost negligible values. Betamethasone (1 mg/ml; IV) administered to the rats 3 h before paraquat injection accelerated the decrease in survival and phospholipase A2 inactivation. Inactivation of phospholipase A2, detected in paraquat or oxygen exposed rats, could be attributed to a O2(.-)-driven Fenton reaction. However, phospholipase A2 inactivation by betamethasone pretreatment may be attributed to the presence of lipocortin, a corticosteroid-inducible factor and inhibitor of phospholipase A2. Besides the mechanism underlying the inactivation of phospholipase A2, the increase in lipid hydroperoxides may indicate their role as long-lived cytotoxic species that contribute to the damage already initiated by oxidative stress. Indeed, lipid hydroperoxides are very well known modifiers of membrane physical properties.
百草枯中毒和高压氧暴露是公认的肺氧化应激模型。本研究的目的聚焦于氧自由基和其他细胞毒性物质（如脂质氢过氧化物）对整体毒性的作用。给成年Wistar大鼠注射百草枯（30或60mg/kg体重）或使其暴露于高压氧（0.2MPa），并测量肺损伤的几个参数。两种处理均导致自发性肺化学发光增加、肺中性粒细胞数量增加、丙二醛含量增加、肺水肿和胸腔积液。值得注意的是，用于监测体内氧自由基稳态浓度的自发性肺化学发光在两种处理后均未显著增加。自发性肺化学发光的增加在中性粒细胞迁移后开始，两者的最大值相隔4 - 6小时的延迟时间。在中性粒细胞迁移并在肺中被激活后，动物的存活率开始下降。因此，中性粒细胞可被视为由随后化学发光增加所支持的氧自由基的额外来源。它们在肺损伤中的作用通过肺水肿增加、胸腔积液增多以及中性粒细胞迁移后存活率降低得以证明。两种处理后肺膜中脂质氢过氧化物浓度也增加。这种浓度增加可能是脂质膜氧化应激引发的脂质过氧化速率增加的结果，或者是其分解代谢受到抑制的结果。膜中正常产生的酯脂质氢过氧化物不能直接被谷胱甘肽过氧化物酶 - 还原酶系统分解代谢，除非磷脂酶A2催化释放游离脂质氢过氧化物。在两个实验模型中，磷脂酶A2活性均降至几乎可忽略不计的值。在注射百草枯前3小时给大鼠静脉注射倍他米松（1mg/ml）加速了存活率的下降和磷脂酶A2失活。在百草枯或氧暴露大鼠中检测到的磷脂酶A2失活可能归因于超氧阴离子驱动的芬顿反应。然而，倍他米松预处理导致的磷脂酶A2失活可能归因于脂皮质素的存在，脂皮质素是一种皮质类固醇诱导因子和磷脂酶A2的抑制剂。除了磷脂酶A失活的潜在机制外，脂质氢过氧化物的增加可能表明它们作为长寿细胞毒性物质的作用，这些物质促成了氧化应激已经引发的损伤。实际上，脂质氢过氧化物是非常著名的膜物理性质调节剂。
