氯离子通道阻断剂对氧化剂诱导的肾小管上皮细胞损伤的保护 …

研究氯离子通道剂在氧化剂诱导的肾小管上皮细胞损伤中的作用。方法以Ｈ２Ｏ２诱导肾小管上皮细胞株损伤，观察Ｃｌ＾－通道阻断剂对受损细胞ＬＤＨ释放量、ＡＴＰ和ＤＮＡ降解程度的影响。结果Ｃｌ＾－通道阻断可使受损伤的ＬＤＨ释放量下降、ＡＴＰ含量回收升和ＤＮＡ降解程度减轻。     

高渗和低渗造影剂对人肾小管上皮细胞的毒性作用

目的 比较高渗造影剂（HOCM，泛影葡胺）和低渗造影剂（LOCM，欧乃派克）对人肾小管上皮细胞的毒性，探讨Bax／Bcl-2，半胱氨酸天冬氨酸蛋白酶（caspase）-3在造影剂诱导肾小管上皮细胞凋亡中的作用。方法 以HKC细胞株为研究对象，实验分为7组：HOCM1组（111mgI／ml），HOCM2组（74mgI／m1），LOCMl组（111mgI／m1），LOCM2组（74mgI／ml），甘露醇高渗对照组，甘露醇低渗对照组，培养基对照组。采用四甲基偶氮唑蓝（MTT）试验和乳酸脱氢酶（LDH）检测造影剂对体外培养HKC细胞的毒性作用。采用Hoechst染色、TUNEL染色、DNA琼脂糖凝胶电泳、电镜和流式细胞仪DNA分析方法观察造影剂对HKC细胞凋亡的作用。采用Westem印迹方法检测Bax和Bcl-2蛋白含量的变化。采用荧光比色法检测caspase-3活性。结果 HOCM和LOCM组培养液中LDH水平较对照组显著增高（P〈0．05），细胞活力较对照组显著降低（P〈0．05），且与渗透浓度，作用时间及碘离子浓度有关。HOCM可诱导肾小管上皮细胞凋亡，且明显高于甘露醇高渗对照（P〈0．05）。LOCM在本实验剂量不能诱导肾小管上皮细胞凋亡。HOCM在诱导HKC细胞凋亡时伴随有Bax、Bcl-2表达的上调，caspase-3活性升高。结论 HOCM和LOCM对肾小管上皮细胞均有毒性作用，LOCM的毒性作用明显小于HOCM。HOCM可诱导人肾小管上皮细胞凋亡且与高渗及碘离子浓度有关。Bax／Bcl-2、caspase-3可能参与了造影剂诱导人肾小管上皮细胞凋亡的调控。     

肾小管细胞氧化性损伤模型的建立

目的建立过氧化氢(H2O2)所致肾小管氧化性损伤模型。方法利用离体培养肾小管细胞建立氧化性损伤模型．观察肾小管细胞形态结构的改变及细胞存活率、乳酸脱氢酶(lactated dehydrogenase，LDH)释放率、脂质过氧化产物丙二醛(malondialdehyde．MDA)含量的变化，以及还原型谷胱甘肽的保护作用。结果H2O2所致肾小管细胞损伤．表现为细胞存活率降低，LDH释放增加和MDA含量增加。还原型谷胱甘肽能提高细胞存活率，降低LDH释放，减轻脂质过氧化反应。结论H2O2可复制离体肾小管氧化性损伤模型．还原型谷胱甘肽对损伤的肾小管上皮细胞有保护作用。     

细胞色素C在ATP耗竭诱导的肾小管上皮细胞凋亡中的作用

目的 研究线粒体细胞色素C的释放在ATP耗竭导致的肾小管上皮细胞凋亡中的作用和机制。方法 应用代谢抑制剂暂时性阻断细胞内ATP的生成，诱导细胞凋亡。利用JC-1测定线粒体膜电位的变化。以间接免疫荧光和western印迹检测细胞色素C在细胞内的分布。荧光肽法测定Caspase3的活性。琼脂糖凝胶电泳分析DNA碎解。结果 肾小管上皮细胞内ATP耗竭时，线粒体膜电位显著降低，细胞浆内细胞色素C的含量增多，Caspase3活性增强。细胞内ATP再恢复时，细胞色素C的释放和Caspase3活性继续增加，并出现DNA的碎解。结论 肾小管上皮细胞ATP耗竭时，线粒体细胞色素C的释放在介导Caspase依赖的细胞凋亡通路中发挥重要作用。     

半胱氨酸天冬氨酸3依赖的bcl-2的降解在ATP耗竭诱导肾小管上皮细胞凋亡中的作用

目的 研究ATP耗竭再恢复诱导的肾小管上皮细胞凋亡中,半胱氨酸天冬氨酸（caspase）3激活介导bcl-2降解的作用.方法 使用代谢抑制剂短暂阻断细胞内ATP的生成,诱导细胞凋亡.以Hoechst 33342染色观察凋亡细胞.应用编码人bcl-2 RNA的腺病毒感染细胞,使bcl-2在细胞内高表达.应用流式细胞仪,分析细胞凋亡和坏死的发生情况.以Western印迹检测caspase 3的活化以及bcl-2和bcl-2的降解产物.体外实验观察caspase 3和caspase 3特异性抑制剂DEVD对bcl-2降解产物的影响.结果 高表达bcl-2组与对照组比较,细胞ATP耗竭60min、90 min、120 min和再恢复60min后,可减少细胞凋亡50%,P＜0.05.肾小管上皮细胞ATP耗竭时,caspase 3被激活,bcl-2出现降解;细胞内ATP恢复时,bcl-2降解产物继续增多,并出现细胞凋亡.体外应用caspase 3可使bcl-2降解,而caspase3的特异性抑制剂DEVD能明显抑制caspase 3对bcl-2的降解.结论 肾小管上皮细胞ATP耗竭再恢复时,caspase 3激活及其介导的bcl-2降解在细胞凋亡中发挥重要作用.     

不同病理类型肾综患者尿蛋白对肾小管上皮细胞增殖和凋亡相关蛋白Fas表达的影响

目的：观察不同病理类型肾病综合征（NS）患者尿蛋白对肾小管上皮细胞（RTECs）增殖和凋亡的影响,以进一步明确尿蛋白所致肾小管-间质损害的机制.方法：（1）从局灶-节段性肾小球硬化症（FSGS）、膜性肾病（MN）、微小病变肾病（MCN）三种不同病理类型的NS患者尿液中提取尿蛋白,经成份分析、灭菌等处理后以0.5 mg/ml、1.0 mg/ml、2 mg/ml、4 mg/ml、8 mg/ml浓度分别刺激体外培养的HK-2细胞,另设空白对照组.（2）MTT法检测不同病理类型NS患者尿蛋白刺激后细胞的增殖情况.（3）乳酸脱氢酶（LDH）释放实验检测不同病理类型NS患者尿蛋白的细胞毒作用.（4）Western Blotting法检测Fas蛋白表达.结果：各病理类型所提取的尿蛋白成分相同,主要为白蛋白、转铁蛋白、IgG等,但各病理类型组成比例不同;肾小管上皮细胞MTT值低浓度有明显增殖作用,高浓度时细胞过度增殖则导致凋亡;肾小管上皮细胞LDH释放率和Fas蛋白的表达水平随尿蛋白浓度的升高而升高;以上各项检测指标中FSGS患者尿蛋白对HK-2细胞的作用最强,MN次之,MCD最弱.结论：在体外条件下,尿蛋白对RTECs呈剂量依赖性的细胞毒作用,低剂量尿蛋白诱导RTECs异常增殖,较高剂量尿蛋白可诱导RTECs凋亡;除尿蛋白的量决定了损伤严重程度外,尿蛋白的性质也决定了损伤的严重程度.     

丹参注射液对造影剂诱导的肾小管上皮细胞损伤的保护作用

目的：研究丹参注射液对造影剂碘海醇诱导的肾小管上皮细胞损伤的保护作用并对其作用机制进行探讨。方法：体外培养的人肾小管上皮细胞（HK-2细胞）,分为正常对照组、甘露醇对照组（与碘海醇渗透压相当）、造影剂对照组（碘海醇100mg/ml）、丹参防治组（碘海醇100mg/ml＋丹参注射液15mg/ml）。比色法测定细胞培养上清液LDH水平,MTT法测定细胞增殖活力,DCFH-DA荧光探针测定细胞内活性氧（ROS）,硫代巴比妥酸法测定细胞内MDA含量,黄嘌呤氧化酶法测定SOD活性,RT-PCR测定细胞内血红素加氧酶-1（HO-1）mRNA表达,Westernblot检测细胞内HO-1蛋白表达。结果：碘海醇100mg/ml可明显抑制HK-2细胞增殖、引起培养液中LDH水平上升、促使细胞内ROS和MDA含量增高而细胞内SOD活性下降,同时碘海醇可诱导HO-1mRNA和蛋白表达上调。加入丹参可明显降低培养液中LDH水平,促进细胞增殖,同时抑制细胞内ROS的产生,降低细胞内MDA含量,保护细胞内SOD活性,并使HO-1mRNA和蛋白表达进一步增强。结论：丹参对造影剂碘海醇所致肾小管上皮细胞具有明显的保护作用,其作用机制与其抗氧化能力及诱导HO-1表达有关。     

草酸钙晶体对大鼠肾小管上皮细胞损伤作用的实验研究

目的 通过研究一水草酸钙晶体粘附于体外培养的Wistar大鼠肾小管上皮细胞后引起的细胞功能变化，探讨尿路结石形成的机制。方法 分离、培养正常雄性Wistar大鼠的肾小管上皮细胞，在原代培养第5天时，将细胞分成3组（空白对照组，草酸组及一水草酸钙组），分别加入正常培养液，含有草酸钠（1、3、5mmol／L）的培养液及含有草酸钠（1、3、5mmol／L）和一水草酸钙晶体（5mmol／L）的培养液，实验8h后利用扫描电镜观察一水草酸钙晶体对肾小管上皮细胞的粘附情况，并分别用比色法测定细胞的钙镁ATP酶和钠钾ATP酶的活性，观察比较细胞功能的变化情况。结果 实验8h后，扫描电镜观察提示一水草酸钙组中有大量一水草酸钙晶体贴附于肾小管上皮细胞表面。①在三个草酸梯度浓度中，草酸组细胞钙镁ATP酶和钠钾ATP酶活性均未见明显下降，与对照组无显著性差异（P〉0．05）；②在三个草酸梯度浓度中，一水草酸钙组细胞钙镁ATP酶和钠钾ATP酶活性均明显下降。与对照组及草酸组有显著性差异（P〈0．05）；③在不同草酸浓度的一水草酸钙组间细胞钙镁ATP酶和钠钾ATP酶活性无显著性差异（P〉0．05）。结论 在高草酸环境下，对体外培养的Wistar大鼠的肾小管上皮细胞产生损伤作用的主要是一水草酸钙晶体而非游离草酸根离子。一水草酸钙晶体粘附于肾小管上皮细胞以后，可以造成细胞的损伤，这一机制可能有助于肾结石的发生。     

FSGS患者尿蛋白对肾小管上皮细胞活力及转分化的影响

目的：探讨局灶性-节段性肾小球硬化症（focal segmental glomerulosclerosis,FSGS）患者尿蛋白对肾小管上皮细胞（TECs）活力及转分化的影响。方法：用硫酸铵沉淀法提取FSGS患者尿液中的总蛋白成分,应用不同浓度尿蛋白处理体外培养人近端肾小管上皮细胞,然后应用全自动生化分析仪检测不同浓度尿蛋白刺激后HK-2细胞LDH值并计算其释放率、免疫细胞化学（ICC）法检测不同浓度尿蛋白刺激后HK-2细胞E-钙黏蛋白（e—cadherin）的表达水平和Western blotting法检测HK-2细胞α-平滑肌肌动蛋白（Q—SMA）蛋白表达水平。结果：所提取的尿蛋白主要成分为白蛋白、转铁蛋白和IgG等,分别占59．3％、15．3％和13．8％;肾小管上皮细胞LDH释放率和α—SMA蛋白的表达水平随尿蛋白浓度的升高而升高;E—cadherin的表达水平随着尿蛋白浓度的升高而下降。结论：FSGS尿蛋白可通过诱导肾小管上皮细胞损伤和转分化而促进肾小管-间质纤维化。     

枸橼酸减轻草酸钙晶体对大鼠肾小管上皮细胞损伤作用的实验研究

目的 通过研究枸橼酸能否减轻一水草酸钙（calcium oxalate monohydrate，COM）晶体对体外培养的Wistar大鼠肾小管上皮细胞造成的损伤，以探讨枸橼酸在尿路结石防治中的作用及其机制。方法分离、培养正常雄性Wistar大鼠的肾小管上皮细胞，在原代培养第5天时，将细胞分成3组（空白对照组、COM组及枸橼酸组），分别于各组培养液中培养2h后用比色法测定各组细胞培养基中丙二醛（malonaldehyde，MDA）的含量及细胞的钙镁ATP酶（Ca`2＋-Mg`2＋-ATPase）和钠钾ATP酶（Na`2＋K`＋-ATPase）的活性。结果①COM组和枸橼酸组细胞Ca2＋-Mg`2＋ATPase和Na`＋＋K`＋-ATPase活性均明显低于对照组（P〈0．05）；②与枸橼酸组相比，COM组细胞Ca`2＋-Mg`2＋-ATPase和a`＋＋K`＋-ATPase活性下降更加明显（P〈O．05）；③COM组和枸橼酸组细胞培养基中MDA的含量均明显高于对照组（P〈O．05）；④与枸橼酸组相比，COM组细胞培养基中MDA的含量更高（P〈O．05）。结论外源性枸橼酸能够减轻一水草酸钙晶体对体外培养的Wistar大鼠肾小管上皮细胞造成的脂质过氧化损伤。     

Inhibitors of poly (ADP-ribose) synthetase protect rat proximal tubular cells against oxidant stress.

BACKGROUND: The generation of reactive oxygen species (ROS) has been implicated in the pathogenesis of renal ischemia-reperfusion injury. ROS produce DNA strand breaks that lead to the activation of the DNA-repair enzyme poly (ADP-ribose) synthetase (PARS). Excessive PARS activation results in the depletion of its substrate, nicotinamide adenine dinucleotide (NAD) and subsequently of adenosine 5'-triphosphate (ATP), leading to cellular dysfunction and eventual cell death. The aim of this study was to investigate the effect of various PARS inhibitors on the cellular injury and death of rat renal proximal tubular (PT) cells exposed to hydrogen peroxide (H2O2). METHODS: Rat PT cell cultures were incubated with H2O2 (1 mM) either in the presence or absence of the PARS inhibitors 3-aminobenzamide (3-AB, 3 mM), 1,5-dihydroxyisoquinoline (0.3 mM) or nicotinamide (Nic, 3 mM), or increasing concentrations of desferrioxamine (0.03 to 3 mM) or catalase (0.03 to 3 U/ml). Cellular injury and death were determined using the MTT and lactate dehydrogenase (LDH) assays, respectively. H2O2-mediated PARS activation in rat PT cells and the effects of PARS inhibitors on PARS activity were determined by measurement of the incorporation of [3H]NAD into nuclear proteins. RESULTS: Incubation of rat PT cells with H2O2 significantly inhibited mitochondrial respiration and increased LDH release, respectively. Both desferrioxamine and catalase reduced H2O2-mediated cellular injury and death. All three PARS inhibitors significantly attenuated the H2O2-mediated decrease in mitochondrial respiration and the increase in LDH release. Incubation with H2O2 produced a significant increase in PARS activity that was significantly reduced by all PARS inhibitors. 3-Aminobenzoic acid (3 mM) and nicotinic acid (3 mM), structural analogs of 3-AB and Nic, respectively, which did not inhibit PARS activity, did not reduce the H2O2-mediated injury and necrosis in cultures of rat PT cells. CONCLUSION: We propose that PARS activation contributes to ROS-mediated injury of rat PT cells and, therefore, to the cellular injury and cell death associated with conditions of oxidant stress in the kidney.     

容量敏感外向整流性氯通道参与氧化应激介导的系膜细胞凋亡

目的 探讨容量敏感外向整流性(VSOR)氯通道在H2O2介导系膜细胞凋亡中的作用和可能的机制。 方法 全细胞膜片钳技术用于检测VSOR氯电流。细胞凋亡通过吖啶橙/溴化乙锭荧光染色、电子显微镜、TUNEL染色和半胱氨酸天冬氨酸蛋白酶(caspase)-3活性确定。 结果 150 μmol/L H2O2激活系膜细胞VSOR氯电流，H2O2激活的氯电流具有典型的VSOR氯电流电生理特性，包括：外向整流性、电压依赖性失活。对细胞外高渗透压敏感及被VSOR氯通道阻断剂抑制。VSOR氯通道阻断剂DIDS(100 μmol/L)，NPPB(10 μmol/L)和尼氟灭酸(10 μmol/L)明显抑制H2O2介导的系膜细胞凋亡。150 μmol/L H2O2处理2 h内，细胞容量明显下降，但这种细胞容量下降被100 μmol/L DIDS，10 μmol/L NPPB和10 μmol/L尼氟灭酸抑制。结论 VSOR氯通道参与H2O2介导的系膜细胞凋亡，其机制与介导凋亡性容量下降有关。     

Direct amphotericin B-mediated tubular toxicity: assessments of selected cytoprotective agents.

Amphotericin B (AB) may induce acute renal failure by vasoconstrictive and tubulo-toxic effects. Although mannitol, Ca2+ channel blockers, and lipid-based AB preparations have been suggested to mitigate in vivo AB nephrotoxicity, whether they confer direct tubular cytoprotection has not been defined. Therefore, this study assessed the impact of mannitol, verapamil/extracellular Ca2+, and cholesteryl sulfate (CS) AB binding on AB cytotoxicity, employing an isolated rat proximal tubular segment (PTS) preparation. After 30 to 60 minutes of incubation, 0.2 mg/ml of AB (Fungizone) caused marked toxicity, as assessed by LDH release (29 to 44%) and ATP depletion (greater than 90%). Approximately 40% of the LDH release could be attributed to deoxycholate, the standard AB (Fungizone) solubilizing agent. Both 100 mM mannitol and 100 mM glucose decreased AB-mediated LDH release, despite having a quantitatively trivial impact on ATP concentrations (increments of less than or equal to 1% at normal values). Dimethylthiourea (25 mM; equipotent to 100 mM mannitol/glucose as a hydroxyl radical scavenger) did not decrease LDH release. Neither verapamil addition (100 microM) nor Ca2+ removal from the PTS buffer had a protective effect. CS binding completely eliminated AB's toxicity (no LDH or ATP losses). The effect of AB and CS-AB on concomitant O2 deprivation/reoxygenation (30 min/15 min) PTS injury was also assessed. AB and hypoxia/reoxygenation caused additive, not synergistic, LDH release whereas CS-AB had no adverse effect.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of ceramide synthase in oxidant injury to renal tubular epithelial cells.

Ceramide has been implicated to play an important role in the cell signaling pathway involved in apoptosis. Most studies that have used the apoptotic model of cellular injury have suggested that enhanced ceramide generation is the result of the breakdown of sphingomyelin by sphingomyelinases. However, the role of ceramide synthase in enhanced ceramide generation in response to oxidant stress has not been previously examined in any tissue. Hydrogen peroxide (H(2)O(2)) (1 mM) resulted in a rapid increase in ceramide generation (as measured by in vitro diacylglycerol kinase assay) in LLC-PK1 cells. The intracellular ceramide level was significantly increased at 5 min after exposure of cells to H(2)O(2) and thereafter continuously increased up to 60 min. H(2)O(2) also resulted in a rapid increase (within 5 min) in ceramide synthase activity (as measured by incorporation of [(14)C] from the labeled palmytoyl-CoA into dihydroceramide) in microsomes. In contrast, the exposure of cells to H(2)O(2) did not result in any significant change in sphingomyelin content or acid or neutral sphingomyelinase activity. An increase in ceramide production induced by H(2)O(2) preceded any evidence of DNA damage and cell death. The specific inhibitor of ceramide synthase, fumonisin B1 (50 microM), was able to suppress H(2)O(2)-induced ceramide generation and provided a marked protection against H(2)O(2)-induced DNA strand breaks, DNA fragmentation, and cell death. Taken together, these data provide the first evidence that H(2)O(2) is a regulator of ceramide synthase rather than sphingomyelinases and that ceramide synthase-dependent ceramide generation plays a key role in DNA damage and cell death in oxidant stress to renal tubular epithelial cells.     

Sphingomyelinase and membrane sphingomyelin content: determinants ofProximal tubule cell susceptibility to injury

Ceramides acutely accumulate in proximal tubules during injury. Pathogenic relevance of this change is suggested by observations that adding ceramide to tubular cells alters superimposed hypoxic and toxic attack. Ceramide accumulation during cell injury is thought to arise from sphingomyelinase (SMase)-mediated sphingomyelin (SM) hydrolysis +/- decreased catabolism. Thus, ceramide addition to cells cannot precisely simulate pathophysiologic events. Therefore, this study assessed direct effects of SMase activity on tubular cell viability under basal conditions and during superimposed attack. Cultured human proximal tubule (HK-2) cells were exposed to differing SMase doses. Its effects on cell phospholipids, ceramides, proliferation rates, and susceptibility to injury (ATP depletion, Fe-mediated oxidant stress) were assessed. Because SMase reduces cell SM content, the effect of exogenous SM on membrane injury (intact cells, isolated vesicles) was also tested. Finally, because SM decreases membrane fluidity, the impact of a fluidizing agent (A(2)C) on membrane injury (phospholipase A(2), lipid peroxidation) was addressed. SMase reduced HK-2 SM content by approximately 33%, but only modest ceramide increments resulted (suggesting high endogenous ceramidase activity). SMase, by itself, caused no cell death (lactate dehydrogenase release). However, it was mildly antiproliferative, and it dramatically predisposed to both ATP depletion- and Fe-mediated attack. SMase also predisposed isolated vesicles to damage, suggesting that its impact on intact cells reflects a direct membrane effect. Adding SM to intact cells (or vesicles) mitigated ATP depletion and Fe- and phospholipase A(2)-induced damage. In contrast, A(2)C rendered membranes more vulnerable to attack. SMase predisposes tubular cells to superimposed ATP depletion and oxidant injury. This may be explained by SM losses, and not simply cytotoxic ceramide gains, given that SM can directly decrease cell/membrane damage. The ability of SM to decrease membrane fluidity may explain, at least in part, its cytoprotective effect.     

Reactive oxygen molecule-mediated injury in endothelial and renal tubular epithelial cells in vitro

To investigate renal tubular epithelial cell injury mediated by reactive oxygen molecules and to explore the relative susceptibility of epithelial cells and endothelial cells to oxidant injury, we determined cell injury in human umbilical vein endothelial cells and in four renal tubular epithelial cell lines including LLC-PK1, MDCK, OK and normal human kidney cortical epithelial cells (NHK-C). Cells were exposed to reactive oxygen molecules including superoxide anion, hydrogen peroxide and hydroxyl radical generated by xanthine oxidase and hypoxanthine. We determined early sublethal injury with efflux of 3H-adenine metabolites and a decline in ATP levels, while late lytic injury and cell detachment were determined by release of 51chromium. When the cells were exposed to 25, 50, and 100 mU/ml xanthine oxidase with 5.0 mM hypoxanthine, ATP levels were significantly lower (P less than 0.001) in LLC-PK1, NHK-C and OK cells compared to MDCK cells while ATP levels were significantly lower (P less than 0.01) in endothelial cells compared to all tubular cell lines. A similar pattern of injury was seen with efflux of 3H-adenine metabolites. When the cells were exposed to 50 mU/ml xanthine oxidase with 5.0 mM hypoxanthine for five hours, total 51chromium release was significantly (P less than 0.001) greater in LLC-PK1, NHK-C and OK cells compared to MDCK cells, while total 51chromium release was significantly (P less than 0.001) greater in endothelial cells compared to all tubular cells. However, lytic injury was the greatest in LLC-PK1 cells and NHK-C cells while cell detachment was the greatest in endothelial cells. MDCK cells were remarkably resistant to oxidant-mediated cell detachment and cell lysis. In addition, we determined ATP levels, 3H-adenine release and 51chromium release in LLC-PK1, NHK-C and endothelial cells in the presence of superoxide dismutase to dismute superoxide anion, catalase to metabolize hydrogen peroxide, DMPO to trap hydroxyl radical and DMTU to scavenge hydrogen peroxide and hydroxyl radical. We found that catalase and DMTU (scavengers of hydrogen peroxide) provided significant protection from ATP depletion, prevented efflux of 3H-adenine metabolites and cell detachment while DMPO (scavenger of hydroxyl radical) prevented lytic injury. In addition, we found that the membrane-permeable iron chelator, phenanthroline, and preincubation with deferoxamine prevented cell detachment and cell lysis, confirming the role of hydroxyl radical in cell injury.(ABSTRACT TRUNCATED AT 400 WORDS)     

Calcium phosphate-induced renal epithelial injury and stone formation: involvement of reactive oxygen species

BACKGROUND: Crystal formation and retention are critical events for the formation of kidney stones. Oxalate and calcium oxalate (CaOx) crystals are injurious to renal epithelium, and membranes of injured cells promote crystal adherence and retention. Calcium phosphate (CaP) is the most common crystal in both urine and stones, most likely to form in the early segments of the nephron and can nucleate CaOx in a metastable solution. We hypothesized that CaP can also injure the renal epithelial cells. METHODS: We exposed proximal tubular origin line derived from pig proximal tubules (LLC-PK1), and collecting duct origin Madin-Darby canine kidney (MDCK) cell lines to various concentrations of Brushite (Br) crystals and investigated staining with Trypan Blue and the release of lactate dehydrogenase (LDH) into the medium as an indicator of injury. In order to determine the involvement of reactive oxygen species, we also measured LDH release in the presence of superoxide dismutase (SOD) and production of hydrogen peroxide (H2O2) and 8-isoprostane (8-IP) in the presence of the catalase. RESULTS: Exposure to Br crystals was associated with LDH release by both cell types, induced the production of H2O2 and 8-IP. Presence of SOD and catalase reduced LDH release as well as staining with trypan blue. Catalase was also associated with reduced production of H2O2 and 8-IP. CONCLUSION: Brushite crystals are injurious to cells of both the proximal tubules as well as collecting ducts. Injury is mediated by reactive oxygen species. We propose that CaP crystals can independently interact with renal epithelium, promote sites for crystal attachment, and then either grow into mature CaP stones or create sites for CaOx crystal nucleation, retention, and stone development.     

Mechanism of protection of oxidant-injured endothelial cells by glutamine

Glutamine supplementation before oxidant exposure has recently been shown to significantly enhance adenosine triphosphate (ATP) levels and viability in endothelial cells. The aim of this study was to determine if glutamine can help cells after oxidant injury has been initiated and to demonstrate the mechanism of its action. The activity of glyceraldehyde 3-phosphate dehydrogenase was measured in bovine pulmonary artery endothelial cells exposed to H2O2 (0 to 10 mmol/L). Glyceraldehyde 3-phosphate dehydrogenase activity was completely inhibited by 10 mmol/L H2O2 after 1 minute, resulting in inhibition of glycolysis. The endothelial cells were then exposed to 10 mmol/L H2O2, with glutamine (2 mmol/L) being added at different times in relation to the injury. ATP levels were monitored during a 3-hour time course, and short-term viability was measured 6 hours after addition of the oxidant. Significant improvement of endothelial cell ATP levels and short-term viability was seen with addition of glutamine as late as 15 minutes after addition of H2O2. Mitochondrial inhibition with oligomycin (650 nmol/L) abolished the protective effect of glutamine on ATP levels and short-term viability. Cellular survival at 24 hours was not enhanced by glutamine, which suggests that ATP may not be the only factor determining long-term survival after oxidant injury.     

Plasma membrane cholesterol: a critical determinant of cellular energetics and tubular resistance to attack

BACKGROUND: Cholesterol is a major component of plasma membranes, forming membrane microdomains ("rafts" or "caveolae") via hydrophobic interactions with sphingolipids. We have recently demonstrated that tubule cholesterol levels rise by 18 hours following diverse forms of injury, and this change helps to protect kidneys from further damage (so-called acquired cytoresistance). The present study was undertaken to better define the effects of membrane cholesterol/microdomains on tubule homeostasis and cell susceptibility to superimposed attack. METHODS: Plasma membrane cholesterol was perturbed in normal mouse proximal tubular segments with either cholesterol esterase (CE) or cholesterol oxidase (CO). Alternatively, cholesterol-sphingomyelin complexes were altered by sphingomyelinase (SMase) treatment. Changes in cell energetics (ATP/ADP ratios + ouabain), viability [lactate dehydrogenase (LDH) release], phospholipid profiles, and susceptibility to injury (Fe-induced oxidant stress, PLA2, Ca2+ ionophore) were determined. The impacts of selected cytoprotectants were also assessed. RESULTS: Within 15 minutes, CE and CO each induced approximately 90% ATP/ADP ratio suppressions. These were seen prior to lethal cell injury (LDH release), and it was ouabain resistant (suggesting decreased ATP production, not increased consumption). SMase also depressed ATP without inducing cell death. After 45 minutes, CE and CO each caused marked cytotoxicity (up to 70% LDH release). However, different injury mechanisms were operative since (1) CE, but not CO, toxicity significantly altered cell phospholipid profiles, and (2) 2 mmol/L glycine completely blocked CE- but not CO-mediated cell death. Antioxidants also failed to attenuate CO cytotoxicity. Disturbing cholesterol/microdomains with a sublytic CE dose dramatically increased tubule susceptibility to Fe-mediated oxidative stress and Ca2+ overload, but not PLA2-mediated damage. CONCLUSION: Intact plasma membrane cholesterol/microdomains are critical for maintaining cell viability both under basal conditions and during superimposed attack. When perturbed, complex injury pathways can be impacted, with potential implications for both the induction of acute tubular damage and the emergence of the postinjury cytoresistance state.     

Angiotensin II receptor blocker inhibits tumour necrosis factor-alpha-induced cell damage in human renal proximal tubular epithelial cells

Aim: We investigated the effect of angiotensin II (AII) type 1 (AT1) and angiotensin II type 2 (AT2) receptor blockers on tumour necrosis factor alpha (TNF‐α)‐induced cell damage in human renal proximal tubular epithelial cells (RPTEC). Methods: The lactate dehydrogenase (LDH) and N‐acetyl‐beta‐glucosaminidase (NAG) release into the medium after TNF‐α treatment in RPTEC were determined using modified commercial procedures. In addition, the levels of caspase 3/7 activity in RPTEC were measured after TNF‐α treatment with ΑΤ1 or AT2 receptor blockers. Finally we investigated the change of p22phox protein levels after TNF‐α with ΑΤ1 or AT2 receptor blockers in RPTEC. Results: Tumour necrosis factor alpha (10^?8 mol/L) significantly increased LDH and NAG release into the medium from RPTEC. ΑΤ1 receptor blockers, olmesartan and valsartan (10^?9?10^?6 mol/L) showed a significant reduction on TNF‐α‐induced LDH and NAG release in RPTEC. AT2 receptor blocker, PD123319 (10^?7?10^?5 mol/L) also decreased TNF‐α‐induced LDH and NAG release in RPTEC. Blockade of both ΑΤ1 and AT2 receptor indicated additional reduction on TNF‐α‐induced LDH and NAG release. TNF‐α (10^?8 mol/L) treatment showed small but significant increases of caspase 3/7 activity in RPTEC, and AT1 and AT2 receptor blockers (10^?8 mol/L) comparably decreased TNF‐α‐induced caspase 3/7 activity. Significant increases of p22phox protein levels were observed in TNF‐α‐treated group in RPTEC. However, only ΑΤ1 (10^?8 mol/L) but not AT2 (10^?5 mol/L) receptor blocker significantly decreased TNF‐α‐induced p22phox protein levels. Conclusion: The present study demonstrates that TNF‐α induces renal tubular cell damage in RPTEC and AT1/AT2 receptor blockers showed cytoprotective effects probably via at least partly different mechanism.