Inhibition of paraquat-induced autophagy accelerates the apoptotic cell death in neuroblastoma SH-SY5Y cells.

Autophagy is a degradative mechanism involved in the recycling and turnover of cytoplasmic constituents from eukaryotic cells. This phenomenon of autophagy has been observed in neurons from patients with Parkinson's disease (PD), suggesting a functional role for autophagy in neuronal cell death. On the other hand, it has been demonstrated that exposure to pesticides can be a risk factor in the incidence of PD. In this sense, paraquat (PQ) (1,1'-dimethyl-4,4'-bipyridinium dichloride), a widely used herbicide that is structurally similar to the known dopaminergic neurotoxicant MPP(+) (1-methyl-4-phenyl-pyridine), has been suggested as a potential etiologic factor for the development of PD. The current study shows, for the first time, that low concentrations of PQ induce several characteristics of autophagy in human neuroblastoma SH-SY5Y cells. In this way, PQ induced the accumulation of autophagic vacuoles (AVs) in the cytoplasm and the recruitment of a LC3-GFP fusion protein to AVs. Furthermore, the cells treated with PQ showed an increase of the long-lived protein degradation which is blocked in the presence of the autophagy inhibitor 3-methyladenine and regulated by the mammalian target of rapamycin (mTOR) signaling. Finally, the cells succumbed to cell death with hallmarks of apoptosis such as phosphatidylserine exposure, caspase activation, and chromatin condensation. While caspase inhibition retarded cell death, autophagy inhibition accelerated the apoptotic cell death induced by PQ. Altogether, these findings show the relationship between autophagy and apoptotic cell death in human neuroblastoma cells treated with PQ.     

鱼藤素对SH-SY5Y神经母细胞瘤细胞凋亡的诱导作用

目的研究鱼藤素对SH-SY5Y细胞凋亡的诱导作用。方法鱼藤素(0、0.625、1.25、2.5、5、10、20μmol·L~(-1))处理SH-SY5Y细胞24、48、72 h后,CCK-8法测定细胞存活率。鱼藤素(0、8、20、50μmol·L~(-1))处理SH-SY5Y细胞24 h,光镜下及AO/EB双染分别观察细胞形态和凋亡形态,流式细胞术检测细胞凋亡率,DCFH-DA荧光探针法检测细胞活性氧水平,分光光度法检测caspase-3活化程度。结果鱼藤素对SH-SY5Y细胞存活率呈时间和浓度依赖性抑制作用,作用24、48、72 h的IC50值分别为(26.07±2.18)、(18.33±0.94)、(12.5±1.49)μmol·L~(-1)。鱼藤素处理24 h后,细胞凋亡率、细胞活性氧水平明显上升(P<0.05),caspase-3活化程度升高,且三者均有浓度-效应特征。结论鱼藤素可抑制SH-SY5Y细胞存活,诱导细胞凋亡,其机制可能与升高活性氧水平和活化caspase-3相关。     

Apoptosis induced by acrylamide in SH-SY5Y cells

Acrylamide (1–5 mM) dose-dependently decreased cell viability in human neuroblastoma cells (SH-SY5Y). The caspase-3 activity and cell population in sub-G₁ phase were elevated and peaked on exposure to 3 mM acrylamide, while both were less so at higher dose (4 and 5 mM). Z-VAD-fmk, a pan-caspase inhibitor, lowered the apparent cytotoxicity of acrylamide. U0126, a specific inhibitor of extracellular signal-regulated protein kinase (ERK) kinase, suppressed the elevation of caspase-3 activities as well as that of sub-G₁ population. Thus, although mechanisms other than caspase-dependent apoptosis may be involved, apoptotic process seems to take place in the genesis of toxicity of acrylamide in SH-SY5Y cells through ERK pathway and activation of caspase-3.     

中脑星形胶质细胞来源的神经营养因子对糖氧剥夺/再灌注诱导的SH-SY5Y细胞损伤的保护作用

目的研究中脑星形胶质细胞来源的神经营养因子(mesencephalic astrocyte-derived neurotrophic factor,MANF)对糖氧剥夺/再灌注(oxygen-glucose deprivation/reperfusion,OGD/R)诱导的人神经母细胞瘤细胞(SH-SY5Y)损伤的保护作用。方法体外培养SH-SY5Y细胞,对细胞进行糖氧剥夺(OGD)6 h,再灌注(R)12 h。在再灌注时期,根据是否给予重组人MANF蛋白处理(2μmol·L-1,12 h),将细胞分为正常对照组(NC)、NC+MANF组、OGD/R组和OGD/R+MANF组。随后光学显微镜下观察SH-SY5Y细胞形态的改变,MTT法检测细胞存活率,PI染色法检测细胞死亡率,免疫印迹法检测内源性MANF蛋白、内质网(ER)应激相关蛋白GRP78/Bi P、p-IRE1、p-e IF2α及促凋亡蛋白cleaved caspase-3和CHOP的表达。结果光学显微镜下可见OGD/R组SH-SY5Y细胞胞体变小、变圆,突起缩短或消失。进一步研究发现,MANF能明显改善OGD/R诱导的SHSY5Y细胞存活率下降和死亡率增加。免疫印迹法检测发现:OGD/R组细胞内源性MANF蛋白表达增高;ER应激相关蛋白GRP78/Bi P、p-IRE1、p-e IF2α表达增高;促凋亡蛋白CHOP及cleaved caspase-3的表达明显高于NC组。给予重组人MANF蛋白可降低OGD/R组GRP78/Bi P、CHOP及cleaved caspase-3的表达水平。结论 OGD/R可诱导凋亡性ER应激;MANF蛋白可通过抑制OGD/R诱导的凋亡性ER应激而对SH-SY5Y细胞具有保护作用。     

Time-dependent protective and harmful effects of quercetin on 6-OHDA-induced toxicity in neuronal SH-SY5Y cells

Numerous reports have described the effects of quercetin in models of neurodegenerative diseases, or cancer, resulting in a very complex and sometimes paradoxical picture. Understanding how quercetin causes either protection or cell death in the same model is both tempting and essential. We used the 6-OHDA-induced toxicity model in SH-SY5Y cells, applying graded concentrations of quercetin for a variable time period and following cell viability with MTT-assay and LDH-release as well as caspase-3-like activity. We detected a time-dependent action of quercetin and distinguished an early protective effect from a late toxic one. In addition, we revealed a narrower therapeutic dose-range of quercetin than previously reported in the literature, demonstrating that the toxic effects of quercetin occurred at a concentration only 2-fold higher than the one that produced the greatest protection. We also demonstrated, to our knowledge for the first time, that quercetin itself directly inhibits caspase-3-like activity in a dose-dependent manner. Finally, single doses of quercetin failed to protect against 6-OHDA toxicity in a unilateral rat model of Parkinson's disease. In conclusion, our data may offer an explanation for the dualistic effect of quercetin reported in the literature. In fact, in most studies suggesting quercetin protection against oxidative stressors, the experimental setting failed to include prolonged exposure, and therefore the toxic effects may have been missed. This study supports previous in vivo studies that cast doubt on the efficacy of quercetin against neurodegenerative diseases due to its delayed toxicity.     

Neuroprotection by Spirulina platensis protean extract and phycocyanin against iron-induced toxicity in SH-SY5Y neuroblastoma cells.

We investigated the effect of Spirulina platensis protean extract and the biliprotein phycocyanin isolated from this microalga, on the activities of the antioxidant enzymes SOD, CAT, GPx, and GR, lipid peroxidation inhibitory activity and glutathione levels after the iron induced oxidative stress in SH-SY5Y neuroblastoma cells. Iron is one of the most important agents that produce oxidative stress and decline of neuronal functions. S. platensis protean extract and phycocyanin exert the antioxidant activity by protecting the activity of the cellular antioxidant enzymes total GPx, GPx-Se and GR and by increasing reduced glutathione in cells against oxidative stress induced by iron. These results suggested that S. platensis protean extract is a powerful antioxidant through a mechanism related to antioxidant activity, capable of interfering with radical-mediated cell death. S. platensis may be useful in diseases known to be aggravated by reactive oxygen species and in the development of novel treatments for neurodegenerative disorders as long as iron has been implicated in the neuropathology of several neurodegenerative disorders such as Alzheimer's or Parkinson diseases.     

Neurofunctional endpoints assessed in human neuroblastoma SH-SY5Y cells for estimation of acute systemic toxicity

The objective of the EU-funded integrated project ACuteTox is to develop a strategy in which general cytotoxicity, together with organ-specific toxicity and biokinetic features, are used for the estimation of human acute systemic toxicity. Our role in the project is to characterise the effect of reference chemicals with regard to neurotoxicity. We studied cell membrane potential (CMP), noradrenalin (NA) uptake, acetylcholine esterase (AChE) activity, acetylcholine receptor (AChR) signalling and voltage-operated calcium channel (VOCC) function in human neuroblastoma SH-SY5Y cells after exposure to 23 pharmaceuticals, pesticides or industrial chemicals. Neurotoxic alert chemicals were identified by comparing the obtained data with cytotoxicity data from the neutral red uptake assay in 3T3 mouse fibroblasts. Furthermore, neurotoxic concentrations were correlated with estimated human lethal blood concentrations (LC50). The CMP assay was the most sensitive assay, identifying eight chemicals as neurotoxic alerts and improving the LC50 correlation for nicotine, lindane, atropine and methadone. The NA uptake assay identified five neurotoxic alert chemicals and improved the LC50 correlation for atropine, diazepam, verapamil and methadone. The AChE, AChR and VOCC assays showed limited potential for detection of acute toxicity. The CMP assay was further evaluated by testing 36 additional reference chemicals. Five neurotoxic alert chemicals were generated and orphendrine and amitriptyline showed improved LC50 correlation. Due to the high sensitivity and the simplicity of the test protocol, the CMP assay constitutes a good candidate assay to be included in an in vitro test strategy for prediction of acute systemic toxicity.     

Carbon monoxide derived from heme oxygenase-2 mediates reduction of methylmercury toxicity in SH-SY5Y cells

We examined the contribution of carbon monoxide (CO), an enzymatic product of heme oxygenase (HO), to methylmercury (MeHg) cytotoxicity in SH-SY5Y cells, because this gas molecule is reported to activate Nrf2, which plays a protective role against MeHg-mediated cell damage. Exposure of SH-SY5Y cells to CO gas resulted in protection against MeHg cytotoxicity, with activation of Nrf2. Interestingly, pretreatment with tin-protoporphyrin IX, a specific inhibitor of HO, caused a reduction in basal Nrf2 activity and thus enhanced sensitivity to MeHg. No induction of isoform 1 of HO (HO-1) was seen during MeHg exposure, but constitutive expression of isoform 2 (HO-2) occurred, suggesting that CO produced by HO-2 is the main participant in the protection against MeHg toxicity. Studies of small interfering RNA-mediated knockdown of HO-2 in the cells supported this possibility. Our results suggest that CO gas and its producing enzyme HO-2 are key molecules in cellular protection against MeHg, presumably through basal activation of Nrf2.     

"Ecstasy"-induced toxicity in SH-SY5Y differentiated cells: role of hyperthermia and metabolites

3,4-Methylenedioxymethamphetamine (MDMA; “ecstasy”) is a recreational hallucinogenic drug of abuse known to elicit neurotoxic properties. Hepatic formation of neurotoxic metabolites is thought to play a major role in MDMA-related neurotoxicity, though the mechanisms involved are still unclear. Here, we studied the neurotoxicity mechanisms and stability of MDMA and 6 of its major human metabolites, namely α-methyldopamine (α-MeDA) and N-methyl-α-methyldopamine (N-Me-α-MeDA) and their correspondent glutathione (GSH) and N-acetyl-cysteine (NAC) conjugates, under normothermic (37 °C) or hyperthermic conditions (40 °C), using cultured SH-SY5Y differentiated cells. We showed that MDMA metabolites exhibited toxicity to SH-SY5Y differentiated cells, being the GSH and NAC conjugates more toxic than their catecholic precursors and MDMA. Furthermore, whereas the toxicity of the catechol metabolites was potentiated by hyperthermia, NAC-conjugated metabolites revealed higher toxicity under normothermia and GSH-conjugated metabolites-induced toxicity was temperature-independent. Moreover, a time-dependent decrease in extracellular concentration of MDMA metabolites was observed, which was potentiated by hyperthermia. The antioxidant NAC significantly protected against the neurotoxic effects of MDMA metabolites. MDMA metabolites increased intracellular glutathione levels, though depletion in thiol content was observed in MDMA-exposed cells. Finally, the neurotoxic effects induced by the MDMA metabolite N-Me-α-MeDA involved caspase 3 activation. In conclusion, this study evaluated the stability of MDMA metabolites in vitro, and demonstrated that the catechol MDMA metabolites and their GSH and NAC conjugates, rather than MDMA itself, exhibited neurotoxic actions in SH-SY5Y differentiated cells, which were differently affected by hyperthermia, thus highlighting a major role for reactive metabolites and hyperthermia in MDMA’s neurotoxicity.     

CyclinB2 and BIRC5 genes as surrogate biomarkers for neurite outgrowth in SH-SY5Y subclonal cells

Neurite outgrowth plays a key role in neuronal development and regeneration, and is the hallmark assay for the effects of neurotrophic factors such as nerve growth factor (NGF). However, measuring neurite outgrowth is a slow and resource-intensive process. We therefore wanted to identify surrogate biomarkers for neurite outgrowth activity by gene expression analysis in SH-O10 cells, a subclone of the human SH-SY5Y neuroblastoma cell line but with much higher NGF-induced neurite outgrowth activity. Microarray analysis identified seven genes where mRNA levels were changed. NGF-induced decreases in levels of two genes, CyclinB2 and BIRC5, were confirmed by quantitative real-time RT–PCR. Levels of NGF-induced decreases in CyclinB2 and BIRC5 mRNA in several SH-SY5Y subclones with different neurite outgrowth responses correlated with their neurite outgrowth activities. Decreases in CyclinB2 and BIRC5 mRNA induced by FK506 or retinoic acid, both of which exert potentiation of NGF-induced neurite outgrowth effects but with different mechanisms, also correlated with their neurite outgrowth activities. In conclusion, decreasing levels of CyclinB2 and BIRC5 mRNA strongly correlate with neurite outgrowth activities in terms of NGF-related effect in SH-SY5Y subclonal cells, and have potential to become quantitative surrogate biomarkers for measuring NGF-related neurite outgrowth.     

类叶升麻苷对鱼藤酮致SH-SY5Y细胞凋亡的保护作用

目的探讨类叶升麻苷对鱼藤酮致多巴胺能神经元SH-SY5Y细胞凋亡的保护作用及其机制。方法采用MTT法检测细胞存活率,以荧光染料Hoechst33342染色分析细胞核的形态学变化,用流式细胞仪定量分析细胞凋亡峰,以2,′7′-二氢二氯荧光黄双乙酸钠(DCFH-DA)为标记探针检测细胞内活性氧的产生。结果①0.5μmol.L-1的鱼藤酮处理SH-SY5Y细胞48 h能引起细胞存活率的显著下降;诱导细胞发生凋亡,凋亡率达47.39%;大部分细胞胞体皱缩,突起缩短消失或断裂;染色质皱缩、浓缩、断裂及形成凋亡小体;细胞内活性氧水平上升。②预先用盐生肉苁蓉提取物类叶升麻苷(10,20或40 mg.L-1)处理细胞6 h,可提高细胞存活率;明显改善鱼藤酮引起的细胞形态学变化;流式细胞仪检测凋亡率分别降低到25.87%,23.97%,10.45%;以DCFH-DA为标记探针检测到20 mg.L-1类叶升麻苷可明显抑制鱼藤酮引起的细胞内活性氧产生。结论类叶升麻苷能抑制鱼藤酮诱导的多巴胺能神经元SH-SY5Y细胞凋亡,其神经细胞保护作用可能与降低细胞内活性氧水平有关。     

Possible involvement of both endoplasmic reticulum-and mitochondria-dependent pathways in thapsigargin-induced apoptosis in human neuroblastoma SH-SY5Y cells

Recently, it has been shown that endoplasmic reticulum (ER) stress causes apoptosis. However, the mechanism of the ER stress-dependent pathway is not fully understood. In human neuroblastoma SH-SY5Y cells, we detected a caspase-12-like protein that has a molecular mass (approximately 60 kDa) similar to that of mouse caspase-12. Thapsigargin, an inhibitor of ER-associated Ca(2+)-ATPase, induced the degradation of caspase-12-like protein. In addition, the degradation of caspases-9 and -3, cleavage of poly(ADP-ribose) polymerase, DNA fragmentation, and cell death were also observed. Pretreatment with phorbol-12-myristate-13-acetate, which induces the expression of antiapoptotic Bcl-2, inhibited thapsigargin-induced degradation of caspases-9 and -3, but not caspase-12-like protein degradation. A caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp(OCH(3))-CH(2)F, inhibited the degradation of caspase-12-like protein, but not that of caspases-9 and -3. These results suggest that thapsigargin may induce the activation of both ER- and mitochondria-dependent pathways in human SH-SY5Y cells.     

梓醇对乳胞素诱导SH-SY5Y细胞损伤的保护作用

目的探讨梓醇对蛋白酶体抑制剂乳胞素诱导的人神经母细胞瘤(SH-SY5Y)细胞损伤的保护作用及其可能机制。方法梓醇10μmol·L-1预处理SH-SY5Y细胞1 h后,加入乳胞素10μmol·L-1继续处理24 h。倒置显微镜下观察细胞形态的变化,MTT比色法检测细胞存活率,流式细胞仪检测细胞凋亡率,Hoechst33258染色观察细胞核形态的变化,酶联免疫吸附检测细胞内20S蛋白酶体含量。结果与正常对照组相比,梓醇10μmol·L-1对细胞存活率、形态和凋亡及20S蛋白酶体含量无显著差异;乳胞素10μmol·L-1组细胞存活率为(72.0±1.8)%,明显降低(P<0.05),细胞凋亡率为(64.7±2.6)%,明显增高(P<0.05)。Hoechst33258染色发现梓醇细胞核形态改变,出现凋亡小体;细胞内20S蛋白酶体含量降低60%,差异具有统计学意义(P<0.05)。与乳胞素10μmol·L-1组相比,梓醇10μmol·L-1预处理组细胞存活率(87.9±2.2)%明显增高(P<0.05),细胞凋亡率为(51.4±1.5)%,明显降低(P<0.05)。Hoechst33258染色发现,梓醇细胞核形态明显改善;细胞内20S蛋白酶体含量升高了1.9倍,差异具有统计学意义(P<0.05)。结论梓醇对乳胞素诱导的SH-SY5Y细胞损伤具有保护作用,其机制可能与梓醇提高SH-SY5Y细胞内20S蛋白酶体含量有关。     

五味子甲素对MPP~+诱导的SH-SY5Y细胞毒性作用的影响

目的初步探讨不同浓度的五味子甲素(SchA)对MPP+诱导的SH-SY5Y细胞毒性的影响。方法体外培养多巴胺能神经细胞SH-SY5Y,四唑盐比色法(MTT法)观察不同浓度的MPP+对SH-SY5Y细胞增殖的影响后,检测不同浓度的SchA对SH-SY5Y细胞的影响,筛选其无毒剂量后形态学及MTT法进一步观察一定浓度的SchA对MPP+引起的SH-SY5Y细胞毒性作用是否具有保护作用。结果与对照组相比,0.1～1.5 mmol/L MPP+染毒48 h均可引起SH-SY5Y细胞生长增殖抑制;0.5～5μmol/L SchA对SH-SY5Y细胞没有毒性作用,其中2～5μmol/L SchA均可明显抑制MPP+对SH-SY5Y细胞的毒性作用。结论 MPP+对SH-SY5Y细胞增殖有明显的抑制作用,而一定浓度的SchA能有效抑制MPP+的细胞毒性。     

丁氟螨酯对SH-SY5Y细胞的毒性作用及其机制

目的研究丁氟螨酯对人经神经母细胞瘤细胞SH-SY5Y细胞的毒性作用及其机制。方法加入丁氟螨酯0.03,0.06,0.125,0.25,0.5,1,2,2.6,4,6,8和16 mmol·L~(-1)处理SH-SY5Y细胞48 h,MTT法测定细胞存活;DCFH-DA荧光探针标记法检测细胞内活性氧(ROS)水平;JC-1标记法检测细胞线粒体膜电位;Hoechst 33258染色观察细胞核形态;碘化丙啶(PI)染色和流式细胞仪检测细胞周期和细胞凋亡;Western蛋白印迹法检测磷酸化P38蛋白(p-P38)和磷酸化Jun激酶(p-JNK)表达水平。结果与溶剂(DMSO)对照组相比,共孵育48 h后,丁氟螨酯≥0.06 mmol·L~(-1)时可降低细胞存活率(P<0.05),且随浓度增高细胞存活率有降低趋势,IC_(50)为2.6 mmol·L~(-1);丁氟螨酯1,2,4和6 mmol·L~(-1)组细胞ROS水平升高(P<0.01),线粒体膜电位下降(P<0.01)。Hoechst 33258染色结果显示,丁氟螨酯2,4和6 mmol·L~(-1)组SH-SY5Y细胞出现颗粒状荧光,细胞核固缩和崩解;流式细胞仪检测结果显示,丁氟螨酯2,4和6 mmol·L~(-1)组细胞凋亡率由DMSO对照组的(0.7±0.1)%分别上升至(6.7±0.1)%,(72.4±8.6)%和(90.7±3.2)%(P<0.01);丁氟螨酯4和6 mmol·L~(-1)组G_1期细胞较DMSO对照组明显增加(P<0.01);Western蛋白印迹结果表明,丁氟螨酯4和6 mmol·L~(-1)组p-JNK表达均升高(P<0.01),丁氟螨酯6 mmol·L~(-1)组p-P38表达水平增加(P<0.01)。结论丁氟螨酯可能通过氧化损伤、激活P38蛋白和JNK蛋白诱导SH-SY5Y细胞G_1期阻滞和凋亡。     

Paraquat induces cyclooxygenase-2 (COX-2) implicated toxicity in human neuroblastoma SH-SY5Y cells

Paraquat produces dopaminergic pathologies of Parkinson’s disease, in which cyclooxygenase-2 (COX-2) is implicated. However, it is unclear whether paraquat induces toxicity within dopaminergic neurons through COX-2. To address this, human neuroblastoma SH-SY5Y cells were treated with paraquat and then the involving mechanism of COX-2 was investigated. We initially examined the involvement of COX-2 in paraquat-induced toxicity. Data suggest that COX-2 is implicated in paraquat-induced reduction of viability in SY5Y cells. Then, to confirm the presence of COX-2 in SY5Y cells, we examined COX-2 mRNA and protein levels, which are regulated by NF-κB. Data indicate that paraquat activates NF-κB and up-regulates COX-2. We then checked quinone-bound proteins as quinones produced by COX-2 bind to intracellular proteins. Paraquat obviously forms quinone-bound proteins, in particular, quinone-bound DJ-1 and this formation is attenuated by meloxicam. Finally, we investigated antioxidant system including nuclear factor erythroid-related factor 2 (Nrf2), gamma glutamylcysteine synthetase (γGCS), and glutathione (GSH) as DJ-1 is linked to Nrf2 and Nrf2 regulates γGCS expression and γGCS is a GSH synthesis enzyme. Paraquat decreases protein levels of Nrf2 and γGCS and intracellular GSH level and these decreases are alleviated by meloxicam. Therefore, collectively, our data indicate that paraquat induces COX-2 implicated toxicity in SY5Y cells. In conclusion, current findings support the idea that paraquat might produce toxicity in dopaminergic neurons through COX-2.     

Mu-opioid receptor binding in intact SH-SY5Y neuroblastoma cells

In order to determine affinities at the mu opioid receptor binding was conducted to intact SH-SY5Y neuroblastoma cells using the mu-selective ligand [3H][H-D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2] [( 3H]CTOP). Binding appeared to be a single receptor site, and a single state of the mu receptor. Under intact cell conditions, some but not all mu agonists display low affinity binding, while antagonists maintain high affinity for the mu receptor. These studies indicate the usefulness of [3H]CTOP for the determination of affinities at the mu receptor under physiological conditions.     

Organophosphorus compound-induced apoptosis in SH-SY5Y human neuroblastoma cells

Organophosphorus (OP) compounds have been shown to be cytotoxic to SH-SY5Y human neuroblastoma cell cultures. The mechanisms involved in OP compound-induced cell death (apoptosis versus necrosis) were assessed morphologically by looking at nuclear fragmentation and budding using the fluorescent stain Hoechst 33342 (10 microgram/ml). Hoechst staining revealed significant paraoxon (1 mM), parathion (1 mM), phenyl saligenin phosphate (PSP, 10 and 100 microM), tri-ortho-tolyl phosphate (TOTP, 100 microM and 1 mM), and triphenyl phosphite (TPPi, 1 mM) induced time-dependent increases in traditional apoptosis (p < 0.05). In many cells, PSP and TOTP (1 mM) also induced nuclear condensation with little fragmentation or budding. Pretreatment with cyclosporin A (500 nM, 30 h) decreased apoptosis following 1 mM parathion and TOTP exposures. Apoptotic nuclear changes were verified by DNA gel electrophoresis. Activation of caspase-3, a cysteine aspartate protease, was also monitored. OP compounds induced significant time-dependent increases in caspase-3 activation following paraoxon (1 mM), parathion (100 microM, 1 mM), PSP (10 microM, 100 microM, 1 mM), TOTP (100 microM, 1 mM), and TPPi (1 mM) exposure (p < 0.05). Pretreatment with cyclosporin A (500 nM, 30 h) significantly decreased caspase-3 activation during extended incubations with paraoxon, parathion, and TPPi (p < 0.05). In addition, pretreatment with the caspase-3 inhibitor Ac-DEVD-CHO and the caspase-8 inhibitor Ac-IETD-CHO (25 microM, 8 h) significantly decreased caspase-3 activation following exposure to 1 mM PSP and parathion (p < 0.05). Pretreatment with the serine protease inhibitor phenylmethyl sulfonyl fluoride (PMSF; 1 mM, 8 h) also significantly decreased caspase activation following 1 mM PSP and TOTP exposures (p < 0.05). Alteration of OP compound-induced nuclear fragmentation or caspase-3 activation by pretreatment with cyclosporin A, Ac-IETD-CHO, or PMSF suggested that OP compound-induced cytotoxicity may be modulated through multiple sites, including mitochondrial permeability pores, receptor-mediated caspase pathways, or serine proteases.