Zager R A, Burkhart K
Department of Medicine, University of Washington, Seattle, USA.
Kidney Int. 1997 Oct;52(4):942-52. doi: 10.1038/ki.1997.416.
Increased production of reactive oxygen metabolites (ROM) can contribute to the initiation phase of nephrotoxic and ischemic acute renal failure (ARF). However, whether altered ROM expression also exists during the maintenance phase of ARF has not been adequately assessed. Since diverse forms of tubular injury can initiate a "cytoresistant state," this study tested whether a down-regulation of ROM expression might develop in the aftermath of acute tubular damage, potentially limiting renal susceptibility to further attack. To test this hypothesis, rats were subjected to either mild myohemoglobinuria (glycerol injection) or bilateral ureteral obstruction and 24 hours later, cytoresistant proximal tubular segments (PTS) were isolated to assess ROM expression. PTS from sham operated rats were used to establish normal values. Both sets of cytoresistant PTS manifested approximately 75% reductions in H2O2 levels, as assessed by the phenol red/horseradish peroxidase technique (P < 0.01 to 0.001). A 40% reduction in hydroxyl radical (.OH) levels was also observed (salicylate trap method), thereby substantiating decreased oxidant stress in cytoresistant PTS. Catalase, glutathione peroxidase, and free iron levels were comparable in control and cytoresistant PTS, suggesting that decreased H2O2 production (such as by mitochondria) was the cause of the decreased oxidant stress. To test this latter hypothesis, H2O2 expression by control and cytoresistant PTS was assessed in the presence of respiratory chain inhibitors. Although site 1 and site 3 inhibition markedly suppressed H2O2 production in control PTS, they had no impact on H2O2 production in cytoresistant PTS, implying that production at these sites was already maximally suppressed. Correlates of the decreased mitochondrial H2O2 production were improvements in cell energetics (increased ATP/ADP ratios with Na ionophore treatment) and approximately 40 to 90% increases in PTS/renal cortical glutathione content. We conclude that: (1) proximal tubule H2O2/.OH expression can be downregulated during the maintenance phase of ARF; (2) this seemingly reflects a decrease in mitochondrial ROM generation; and (3) the associated improvements in glutathione content and/or cellular energetics could conceivably contribute to a post-injury cytoresistant state.
活性氧代谢产物（ROM）生成增加可促使肾毒性和缺血性急性肾衰竭（ARF）的起始阶段发生。然而，ARF维持阶段是否也存在ROM表达改变尚未得到充分评估。由于多种形式的肾小管损伤可引发一种“细胞抵抗状态”，本研究检测了急性肾小管损伤后ROM表达是否会下调，这可能会限制肾脏对进一步攻击的易感性。为验证这一假设，对大鼠进行轻度肌红蛋白尿（甘油注射）或双侧输尿管梗阻处理，24小时后，分离出具有细胞抵抗能力的近端肾小管节段（PTS）以评估ROM表达。来自假手术大鼠的PTS用于确定正常值。通过酚红/辣根过氧化物酶技术评估，两组具有细胞抵抗能力的PTS的H2O2水平均降低了约75%（P<0.01至0.001）。还观察到羟自由基（·OH）水平降低了40%（水杨酸捕获法），从而证实具有细胞抵抗能力的PTS中氧化应激降低。对照组和具有细胞抵抗能力的PTS中的过氧化氢酶、谷胱甘肽过氧化物酶和游离铁水平相当，表明H2O2生成减少（如由线粒体减少）是氧化应激降低的原因。为验证后一假设，在存在呼吸链抑制剂的情况下评估对照组和具有细胞抵抗能力的PTS的H2O2表达。尽管位点1和位点3抑制显著抑制了对照组PTS中的H2O2生成，但它们对具有细胞抵抗能力的PTS中的H2O2生成没有影响，这意味着这些位点的生成已经被最大程度地抑制。线粒体H2O2生成减少的相关因素包括细胞能量学的改善（用钠离子载体处理后ATP/ADP比值增加）以及PTS/肾皮质谷胱甘肽含量增加约40%至90%。我们得出结论：（1）在ARF维持阶段近端肾小管H2O2/·OH表达可下调；（2）这似乎反映了线粒体ROM生成减少；（3）谷胱甘肽含量和/或细胞能量学的相关改善可能有助于损伤后的细胞抵抗状态。
