Dopamine induces apoptosis through an oxidation-involved SAPK/JNK activation pathway

MPTP activates c-Jun NH(2)-terminal kinase (JNK) and its upstream regulatory kinase MKK4 in nigrostriatal neurons in vivo

The neuropathology of Parkinson's disease is reflected in experimental animals treated with the selective nigrostriatal dopaminergic neurotoxin MPTP. Neurons exposed to MPTP (MPP(+)) express morphological features of apoptosis, although the intracellular pathways that produce this morphology have not been established. The c-Jun NH(2)-terminal kinase (JNK) signaling cascade has been implicated as a mediator of MPTP-induced apoptotic neuronal death based on the ability of CEP-1347/KT-7515, an inhibitor of JNK activation, to attenuate MPTP-induced nigrostriatal dopaminergic degeneration. In these studies, MPTP-mediated activation of the JNK signaling pathway was assessed in the nigrostriatal system of MPTP-treated mice. MPTP elevated levels of phosphorylated JNK and JNK kinase (MKK4; also known as SEK1 or JNKK), by 2.5- and fivefold, respectively. Peak elevations occurred soon after administration of MPTP and coincided with peak CNS levels of MPP(+). Increased MKK4 phosphorylation, but not JNK phosphorylation, was found in the striatum, suggesting that activation of MKK4 occurs in injured dopaminergic terminals. Both JNK and MKK4 phosphorylations were attenuated by pretreatment with l-deprenyl, indicating that these phosphorylation events were mediated by MPP(+). Moreover, CEP-1347/KT-7515 inhibited MPTP-mediated MKK4 and JNK signaling at a dose that attenuates MPTP-induced dopaminergic loss. These data implicate this signaling pathway in MPTP-mediated nigrostriatal dopaminergic death and suggest that it may be activated in the degenerative process in Parkinson's disease.

The calcium-sensing receptor stimulates JNK in MDCK cells

The calcium-sensing receptor (CaR) stimulates ERK1 in rat fibroblasts, but its effect on other MAP kinases is not known. We used a model of renal distal tubule, the MDCK cell, to determine the effects of CaR stimulation on Jun kinase (JNK) activity. Stimulation of the CaR with 5 mM Ca(2+) resulted in a time-dependent increase in JNK activity. Activation of JNK occurred preferentially with stimulation on the basal surface relative to the apical surface. Basal administration of the CaR agonist gadolinium (30 microm) also stimulated JNK activity. Pertussis toxin blocked the ability of both CaR agonists to stimulate JNK, indicating that the effect was mediated through G(ialpha) class G proteins. Finally, we used confocal microscopy to determine that the CaR was located predominantly on the basal surface. These studies demonstrate for the first time that the CaR stimulates JNK activity.

17 beta-estradiol protects lymphocytes against dopamine and iron-induced apoptosis by a genomic-independent mechanism. Implication in Parkinson's disease

Dopamine (DA) in combination with iron (Fe(2+)) has been demonstrated to induce apoptosis in neuronal-like PC12 cells by an oxidative stress mechanism. To get a better insight of cell death and protective mechanisms in DA/Fe(2+)-induced toxicity, we investigated the effects of DA/Fe(2+) and the antioxidant action of 17 beta-estradiol (E2) in peripheral blood lymphocytes (PBL). We found that DA/Fe(2+)-induces apoptosis in PBL via a hydrogen peroxide (H(2)O(2))-mediated oxidative mechanism, which in turn triggers a cascade of molecular events requiring RNA and de novo protein synthesis. We have also demonstrated that E2 prevents significantly DA/Fe(2+)-induced apoptosis in PBL by directly inhibiting the intracellular accumulation of peroxides generated by DA/Fe(2+)-reaction. This protective activity is independent of the presence or activation of the estrogen receptors (ERs). These data further support and validate our previous hypothesis that DA/Fe(2+)/H(2)O(2) could be a general mediator of oxidative stress through a common cell death mechanism in both neuronal and nonneuronal cells. These findings may be particularly relevant to the potential approaches to rescue and prolong the survival of neurons by estrogens in patients with Parkinson's disease (PD).

Cellular glutathione status modulates polychlorinated biphenyl-induced stress response and apoptosis in vascular endothelial cells

Exposure to environmental contaminants, such as polychlorinated biphenyls (PCBs), may severely compromise normal function of vascular endothelial cells (EC). We have previously shown that PCB 77 (3,3',4,4'-tetrachlorobiphenyl), an arylhydrocarbon receptor (AhR) agonist, can induce oxidative stress in cultured EC. We now show that PCB 77 can activate EC and induce a cellular stress response that is reflected by the activation of c-Jun N-terminal/stress-activated protein kinases (JNK/SAPK). Our data also suggest that this PCB 77-mediated stress response can be modulated by the intracellular glutathione content. EC treated with buthionine-sulphoximine (BSO), an inhibitor of glutathione synthesis, further enhanced PCB-induced JNK/SAPK activity. This stress response was sustained only in the presence of BSO plus PCB 77. Media supplementation with the glutathione precursor N-acetyl-cysteine (NAC) reduced PCB 77-induced JNK/SAPK. Intracellular glutathione also may be implicated in PCB-induced EC apoptosis. Individual treatment with PCB, BSO, or linoleic acid induced activation of caspase 3. Compared to PCB 77 alone, annexin V activity was further amplified during combined treatment with BSO and PCB 77. DNA fragmentation was mostly observed when cells were treated with both BSO and PCB 77. The caspase 3-specific inhibitor DEVD-CHO protected cells against PCB 77/BSO-mediated apoptosis and inhibited the caspase activity without affecting JNK/SAPK activation or cellular glutathione levels. These results suggest that AhR ligands, such as PCB 77, cause vascular EC dysfunction by modulating intracellular glutathione, which subsequently leads to activation of stress-specific kinases. Furthermore, inhibition of glutathione synthesis by BSO can further potentiate the PCB 77-induced stress response and ultimately lead to apoptotic cell death.

Transforming growth factor-beta 1 suppresses serum deprivation-induced death of A549 cells through differential effects on c-Jun and JNK activities

Transforming growth factor (TGF)-beta1, a pleiotropic cytokine involved in regulating growth and differentiation, can exert both pro-apoptotic and anti-apoptotic effects depending on the cell type or circumstances. We observed that TGF-beta1 blocked apoptosis resulting from serum withdrawal in A549 human lung carcinoma cells. This was associated with suppression of JNK activation that occurs concomitant with the onset of apoptosis in the absence of TGF-beta1, suggesting that JNK plays an active role in the death process and that TGF-beta1 exerts its protective influence by altering JNK activity. Overexpression of a dominant negative mutant form of SEK1, an upstream activator of JNK, likewise suppressed JNK activation and inhibited apoptosis. Investigation of early events following TGF-beta1 treatment revealed an early induction and phosphorylation of c-Jun that was absent in cells subjected to serum withdrawal alone. That TGF-beta1-induced expression of c-Jun is important for survival was supported by the finding that overexpression of non-phosphosphorylatable dominant negative mutant c-Jun, c-Jun(S73A), attenuated the protective influence of TGF-beta1. Our findings suggest that JNK activation is a late but essential event in serum deprivation-induced apoptosis in A549 cells. TGF-beta1 prevents apoptosis, in part, through the early induction and phosphorylation of c-Jun, which in turn results in attenuated JNK activation.

Involvement of p38 mitogen-activated protein kinase activation in bromocriptine-induced apoptosis in rat pituitary GH3 cells

Bromocriptine, a dopamine D(2) receptor agonist, is a therapeutic agent for patients with prolactinoma and hyperprolactinemia. In this study we demonstrated that bromocriptine induced activation of p38 mitogen-activated protein (MAP) kinase, with concomitant induction of apoptosis in rat pituitary adenoma cell line GH3 cells. Treatment of GH3 cells for 48 h with bromocriptine increased the p38 MAP kinase activity up to 3- to 5-fold and simultaneously increased the number of apoptotic cells. Inclusion in the medium of SB212090 or SB203580, specific p38 MAP kinase inhibitors, completely abolished the bromocriptine-induced activation of p38 MAP kinase and significantly reduced the number of apoptotic cells. The bromocriptine-induced p38 MAP kinase activation was not prevented by S(-)-eticropride hydrochloride, a specific D(2) receptor antagonist. Treatment with either epidermal growth factor (EGF) or thyrotropin-releasing hormone (TRH), which stimulates p44/42 MAP kinase, rescued cells from the bromocriptine-induced apoptosis, with concomitant inhibition of the bromocriptine-induced p38 MAP kinase activation. These results suggest that bromocriptine induces apoptosis in association with p38 MAP kinase activation, and that the p44/42 MAP kinase signaling through EGF and TRH receptors has an opposing effect on p38 MAP kinase activation as well as on apoptosis induced with bromocriptine in GH3 cells.

The inhibition of ERK/MAPK not the activation of JNK/SAPK is primarily required to induce apoptosis in chronic myelogenous leukemic K562 cells

In this study, the downstream signaling of Bcr-Abl tyrosine kinase responsible for apoptosis resistance was investigated. DNA fragmentation, a hallmark of apoptosis, was observed after 2 days of herbimycin A treatment with a peak on 3 day. During the apoptosis induced by the treatment of herbimycin A, stress-activated protein kinase (SAPK) and p38 kinase were activated time- and dose-dependently, while extracellular signal-regulated kinase (ERK) was inhibited. However, apoptosis was induced by the treatment of PD98059, a specific inhibitor of MEK (MAPK or ERK kinase), not by the treatment of sorbitol, a strong activator of SAPK and p38 kinase. Although K562 cells were very resistant to sorbitol-induced apoptosis, DNA fragmentation was induced rapidly in Jurkat, HL-60 and U937 cells after exposure to sorbitol, despite that these apoptosis-sensitive cells have similar or lower activities of JNK/SAPK and p38 kinase compared with K562 cells after treatment of sorbitol. K562 cells had a much higher basal activity of ERK/MAPK than other apoptosis-sensitive cell lines, which were very susceptible to apoptosis induced by low dose of PD98059 compared with K562 cells. In HL-60 cells, sorbitol-induced apoptosis was prevented by the treatment of phorbol myristate 13-acetate (PMA), which activates the ERK/MAPK pathway, and this was blocked by PD98059. From these results, it could be suggested that the inhibition of ERK/MAPK not the activation of JNK/SAPK is primarily required to induce apoptosis in K562 cells.

Paclitaxel-induced cell death: where the cell cycle and apoptosis come together

BACKGROUND

Compelling evidence indicates that paclitaxel kills cancer cells through the induction of apoptosis. Paclitaxel binds microtubules and causes kinetic suppression (stabilization) of microtubule dynamics. The consequent arrest of the cell cycle at mitotic phase has been considered to be the cause of paclitaxel-induced cytotoxicity. However, the biochemical events, downstream from paclitaxel's binding to microtubules, that lead to apoptosis are not well understood.

METHODS

The authors examined recent scientific literature about the mechanisms by which paclitaxel exerts cytotoxicity.

RESULTS

In addition to an arrest of the cell cycle at the mitotic phase in paclitaxel-treated cells, recent discoveries of activation of signaling molecules by paclitaxel and paclitaxel-induced transcriptional activation of various genes indicate that paclitaxel initiates apoptosis through multiple mechanisms. The checkpoint of mitotic spindle assembly, aberrant activation of cyclin-dependent kinases, and the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) are shown to be involved in paclitaxel-induced apoptosis. Consistent with observations that microtubules of different status (e.g., cytoskeletal microtubules vs. mitotic spindles) have different sensitivity to paclitaxel, the concentration of paclitaxel appears to be the major determinant of its apoptogenic mechanisms.

CONCLUSIONS

Advances in research of the cell cycle and apoptosis have extended our understanding of the mechanisms of paclitaxel-induced cell death. Further elucidation of resistance and enhancement of paclitaxel-induced apoptosis should expedite the development of better paclitaxel-based regimens for cancer therapy.

Caspase-dependent and -independent events in apoptosis induced by hydrogen peroxide

To define the role of caspase-3 in H2O2-induced apoptosis, we introduced caspase-3 cDNA into MCF-7 breast carcinoma cells that otherwise lack caspase-3 expression. H2O2 treatment induced DNA fragmentation and nuclear condensation in the caspase-3-expressing cells, but not in the caspase-3-deficient cells. This indicated that caspase-3 is essential for nuclear events. However, H2O2 induced an externalization of membrane phosphatidylserine (PS) and cell death regardless of caspase-3 expression. These events were not suppressed by Ac-DEVD-CHO and Z-VAD-fmk, which inhibit DEVD-specific caspases and a broad spectrum of caspases, respectively. In Jurkat T cells, these inhibitors abolished H2O2-induced PS relocalization, but not cell death. Therefore, caspases appear to be dispensable for lethality by H2O2, but required for PS redistribution in a cell-type-specific manner.

JNK and p38 stresskinases--degenerative effectors of signal-transduction-cascades in the nervous system

The c-Jun N-terminal kinases (JNKs, also called stress activated protein kinases. SAPKs) and p38 kinases constitute together with extracellular signal-regulated kinases (ERKs) the family of MAP kinases. Whereas the functions of JNKs under physiological conditions are largely unknown, there is raising evidence that JNKs are potent effectors of apoptosis or degeneration of neurons in vitro and in the brain. The activation of the inducible transcription factor c-Jun by N-terminal phosphorylation is a central event in JNK-mediated degenerative processes that depend on de novo protein synthesis. At the post-translational level, cytoplasmic degenerative actions of JNKs might comprise inhibition of Bcl-2 and steroid hormone-receptor signaling or hyperphosphorylation of tau; and at transcriptional level, JNKs might trigger the induction of the apoptotic effectors p53 and Fas-Ligand by phosphorylation of c-Jun. The role of p38 is the nervous system is poorly understood, but its activation is also considered as part of the neuronal stress response. This review informs about the genetic processing, the regulation of activity and the biochemical actions of JNK and p38 isoforms in general. In the second part, we summarize the findings on expression and activation of JNKs and p38 under neurodegenerative condition. A particular focus is also put on the putative function of JNK under physiological conditions and for neuroprotection.

Inhibition of hypoxia/reoxygenation-induced apoptosis by an antisense oligonucleotide targeted to JNK1 in human kidney cells

17-fold) increase in DNA fragmentation. Fluorescence microscopy, using DNA binding dyes, demonstrated that cell death following hypoxia/reoxygenation was due predominantly to apoptosis and not necrosis. Furthermore, reoxygenation, but not hypoxia alone, caused a time-dependent increase in the activation of JNK as monitored by western blot analysis using a phospho-specific JNK antibody. In contrast, p38 mitogen-activated protein kinase was activated following hypoxia, but this activation was not augmented during reoxygenation. Exposure of human kidney cells to a 2'-methoxyethyl mixed backbone antisense oligonucleotide directed against human JNK1 (JNK1 AS) resulted in a potent suppression of JNK mRNA and protein expression, whereas a 6-base mismatch control oligonucleotide was without effect. Moreover, a significant diminution of reoxygenation-induced apoptosis was observed in cells exposed to JNK1 AS but not to the mismatch control oligonucleotide. Taken together, these results strongly indicate that activation of the JNK signaling cascade is a major mechanism whereby hypoxia/reoxygenation induces apoptosis.

Apoptosis of peripheral blood lymphocytes is induced by catecholamines

We explored the mechanism through which patients sometimes show immunosuppression after cardiac surgery. To test the hypothesis that commonly used drugs could cause apoptosis of immune cells, the proapoptotic effects of heparin and catecholamines (dopamine and dobutamine) on peripheral blood lymphocytes were evaluated. Peripheral blood lymphocytes were purified from blood samples of normal healthy volunteers. These cells were cultured in the presence of heparin, dobutamine or dopamine. The apoptosis was quantified by Annexin V fluorescent assay, by DNA content and by morphological assessment. Lymphocytes did not show significant levels of apoptosis induction after 24 hours of incubation with heparin. Both dopamine and dobutamine demonstrated a clear apoptosis inducing effect on lymphocytic population after 24 and 48 hours of culture, in concentrations comparable with the clinically used levels. Apoptosis was time and concentration dependent for both catecholamines. The dopamine and dobutamine effect on lymphocyte viability was due, at least partially, to lymphocyte beta receptor engagement, as proved by blocking the receptor with propranolol. These results suggest that catecholamines could induce apoptosis of lymphocytes. This finding may be associated with immunosuppression observed in patients undergoing cardiac surgery.

Persistent activation of ERK contributes to glutamate-induced oxidative toxicity in a neuronal cell line and primary cortical neuron cultures

Oxidative stress can trigger neuronal cell death and has been implicated in several chronic neurological diseases and in acute neurological injury. Oxidative toxicity can be induced by glutamate treatment in cells that lack ionotrophic glutamate receptors, such as the immortalized HT22 hippocampal cell line and immature primary cortical neurons. Previously, we found that neuroprotective effects of geldanamycin, a benzoquinone ansamycin, in HT22 cells were associated with a down-regulation of c-Raf-1, an upstream activator of the extracellular signal-regulated protein kinases (ERKs). ERK activation, although often attributed strictly to neuronal cell survival and proliferation, can also be associated with neuronal cell death that occurs in response to specific insults. In this report we show that delayed and persistent activation of ERKs is associated with glutamate-induced oxidative toxicity in HT22 cells and immature primary cortical neuron cultures. Furthermore, we find that U0126, a specific inhibitor of the ERK-activating kinase, MEK-1/2, protects both HT22 cells and immature primary cortical neuron cultures from glutamate toxicity. Glutamate-induced ERK activation requires the production of specific arachidonic acid metabolites and appears to be downstream of a burst of reactive oxygen species (ROS) accumulation characteristic of oxidative stress in HT22 cells. However, inhibition of ERK activation reduces glutamate-induced intracellular Ca(2+) accumulation. We hypothesize that the precise kinetics and duration of ERK activation may determine whether downstream targets are mobilized to enhance neuronal cell survival or ensure cellular demise.

Downregulation of JNK/SAPK activity is associated with the cross-resistance to P-glycoprotein-unrelated drugs in multidrug-resistant FM3A/M cells overexpressing P-glycoprotein

In the present study, cross-drug resistance in multidrug-resistant (MDR) cells, which overexpress P-glycoprotein (Pgp), a mdr1 gene product, against Pgp-unrelated drugs, and its relevance to c-Jun N-terminal kinase (JNK)/stress-activated protein kinase (SAPK) activity were examined. The multidrug-resistant FM3A/M cells overexpressing Pgp were resistant to apoptotic cell death induced either by Pgp-related drugs including vincristine and vinblastine, which are pumped out by Pgp, or by the Pgp-unrelated drugs including 5'-fluorouracil (5-FU) and bleomycin, which are not targets for Pgp, compared with the parental FM3A cells. Verapamil reversed the resistance of FM3A/M cells to apoptosis induced by the Pgp-related drugs but not that induced by the Pgp-unrelated drugs. Interestingly, FM3A/M cells have shown significantly lower basal and drug-stimulated JNK/SAPK activities than FM3A cells. After transfection with pEBG-SEK or pEBG-SAPK constructs, FM3A/M cells recovered the basal and Pgp-unrelated drug-stimulated activities of JNK/SAPK and the susceptibility to Pgp-unrelated drug-induced apoptotic cell death comparable to those of FM3A cells. Furthermore, FM3A cells became resistant to apoptotic cell death induced by vincristine and 5-FU after transfection with pEBG-SEK(K --> R), a dominant negative inhibitory mutant of SEK. These results suggest that downregulation of JNK/SAPK activity appears to confer on Pgp-associated FM3A/M cells a cross-resistance to Pgp-unrelated drugs.

JNK1 is inactivated during thiamine deficiency-induced apoptosis in human neuroblastoma cells

Thiamine deficiency results in selective neuronal damage. A number of mechanisms have been proposed to account for brain damage associated with thiamine deficiency and to account for the focal nature of the loss of neurons. One proposed mechanism is programmed cell death. We found efficient induction of apoptosis in human neuroblastoma cells when the cells were deprived of thiamine. Although extensive mitochondrial damage was seen, the release of cytochrome c was not the triggering mechanism for thiamine deficiency-induced apoptosis. Instead, the activity of the cJun amino terminal kinase Jnk1 was lost, and this loss correlated temporally with induction of apoptosis. The loss was specific for Jnk1; Jnk2/3 activity remained unchanged. Loss of Jnk1 activity was not found in lymphoblasts, a cell type that did not undergo apoptosis when deprived of thiamine. These findings suggest that thiamine deficiency results in a cellular stress that brings about the loss of Jnk1 activity and the loss of its function of protecting cells from programmed cell death. We postulate that focal sensitivity to thiamine deficiency results, in part, from specific neuronal cell types being susceptible to the inactivation of Jnk1 in response to depletion of cellular thiamine.

Molecular mechanism of monoamine toxicity in Parkinson's disease: hypothetical cell death model

Although there have been experimental approaches to understanding the etiology of Parkinson's disease, the cause of cell degeneration in this neurological disorder remains a mystery. Herein, a hypothetical model is proposed to explain the mechanism leading neurons to die. The model is based on recent experimental evidence and it attempts to dissect the actions of dopamine and metal ions as potential triggers for the activation of an ordered cascade of events of the cell death machinery.

Review of apoptosis vs. necrosis of substantia nigra pars compacta in Parkinson's disease

The discovery that melanized neurons of the pars compacta of substantia nigra (pcSN) degenerate in the midbrain of human Parkinsonians is nearly a century old, but only in this decade have we gained insights into mechanisms underlying this neuronal loss. Although it had long been assumed that pcSN neurons underwent necrosis, recent (1) in vitro studies on isolated neurons, (2) in vivo studies in animals treated with neurotoxins, and (3) postmortem study of human Parkinsonian brain provide strong evidence that pcSN cells may be lost more from apoptosis (i.e., cell suicide) than from necrosis. This paper gives some historical perspective, but focuses primarily on mechanisms involved in both necrosis and apoptosis of neurons, primarily dopaminergic, and reviews the recent literature relating to apoptosis and apoptotic factors now identified in neurons undergoing neurotoxin-induced death and in postmortem human Parkinsonian brain. The weight of evidence in favor of apoptosis and apoptotic factors in these neurons, provides us with tools needed to develop anti-apoptotic factors that can be targeted to proteins on genes, so that it may be possible to decelerate or prevent the progressive neuronal cell loss in human Parkinsonians or in humans with other neurodegenerative disorders.

The roles of dopamine oxidative stress and dopamine receptor signaling in aging and age-related neurodegeneration

Aging is accompanied by a decline of functions controlled by the central dopaminergic system, such as reduced locomotor activity, motivation, impairment of memory formation, and learning deficits. The molecular mechanisms underlying age-related impairment of dopaminergic functions are unknown. Current literature and our own recent work, which are reviewed and summarized in the present paper, suggest that dopamine oxidative stress and its subsequent signaling may contribute to the aging of dopaminergic system.

Dopamine stimulates redox-tyrosine kinase signaling and p38 MAPK in activation of astrocytic C6-D2L cells

An increase in dopamine (DA) availability in rat brain has been suggested to participate in certain neurodegenerative processes. However, the regulatory effects of DA on glial cells have not been extensively studied. Using a rat C6 glioma cell line stably expressing recombinant D2L receptors, we have found that micromolar levels of DA stimulate mitogenesis and glial fibrillary acidic protein (GFAP) expression, both serving as parameters of reactive gliosis. This mitogenesis occurs about 29 h after exposure to DA and requires D2-receptor-mediated intracellular redox-tyrosine kinase activation. Either DA or quinpirole, a D2 receptor agonist, stimulates protein tyrosine phosphorylation. Application of either DPI, a potent inhibitor of NADPH-dependent oxidase, or NAC, an anti-oxidant, effectively prevented DA-induced tyrosine phosphorylation and DNA synthesis. Preincubation of (+)-butaclamol, a D2 receptor antagonist, inhibits both DA-stimulated tyrosine phosphorylation and mitogenesis. DA at micromolar levels also stimulates GFAP expression. This DA-regulated GFAP expression can be completely inhibited by SB203580, a selective p38 MAPK inhibitor, but not influenced by (+)-butaclamol and genistein, a protein tyrosine kinase inhibitor. Thus, our data suggest that regulation of DNA synthesis and GFAP expression induced by DA is mediated by independent signaling pathways. The mitogenesis requires a D2-receptor-mediated protein tyrosine kinase cascade, while GFAP expression needs a D2-receptor-independent p38 MAPK activation. This observation may help to understand the processes of reactive gliosis in some dopaminergic-related neurodegenerative diseases.

Cocaine induces cell death within the primate fetal cerebral wall

Transferase dUTP nick-end labelling (TUNEL) analysis was used to compare the occurrence of cell death in the cerebral wall of cocaine-exposed and drug-naïve monkey fetuses. The rhesus monkeys providing the drug-exposed fetuses received 10 mg/kg of cocaine orally (in fruit treats) in the morning and in the evening between pregnancy days 50 and 65. The control pregnant animals received fruit treats only. The fetuses were removed for analysis by Caesarean section 10 h after the last cocaine treatment. The sections of the cerebral wall from the cocaine-exposed fetuses contained significantly higher numbers of TUNEL-positive nuclei (counted either per section area or per 1000 unlabeled nuclei) than the matching sections from the drug-naïve fetuses. This elevation in the number of TUNEL-positive cells was observed through the entire depth of the fetal cerebral wall including its proliferative and intermediate zones, cortical plate and the marginal zone. The present study demonstrates that consumption of cocaine during pregnancy can result in increased occurrence of cell death in the developing cerebrum.

Differential effect of dopamine catabolism and uptake inhibition on dopamine-induced calcium dysregulation and viability loss

The present study was aimed at evaluating of the effects of dopamine (DA) toxicity on PC12 cells' calcium homeostasis, cellular viability, and free radical levels. Moreover, the effect of receptor inhibition, and DA metabolism and reuptake antagonism on all parameters was also evaluated. Acute treatment with DA impaired the ability of PC12 cells to buffer excess calcium after K+-depolarization, decreased cellular viability by approximately 35%, and increased free radical levels by about 10% in a dose dependent manner. Pretreatment with both active and inactive pargyl monoamine oxidase inhibitors (MAOi) protected PC12 cells from DA toxicity on cellular viability and free radical levels, regardless of the presence or absence of their target enzymes in PC12 cells. These results suggest a lack of specific involvement of DA metabolism by MAO in dopamine's effects on cellular viability and production of free radicals. However, DA-induced dysregulation of calcium homeostasis seems to be more specifically mediated by DA metabolism by MAO. Results indicate that, in order for toxicity to occur the DA must be taken up into the cells. DA receptors do not mediate dopamine cytoxicity, and the D2 receptor plays a modest role in DA-induced calcium dysregulation and generation of free radicals. Moreover, DA-induced cell viability loss is not mediated by calcium, nor by caspase-3 enzyme, but is prevented by inhibition of mitochondrial permeability transition pores.

Role of redox potential and reactive oxygen species in stress signaling

Stress-activated signaling cascades are affected by altered redox potential. Key contributors to altered redox potential are reactive oxygen species (ROS) which are formed, in most cases, by exogenous genotoxic agents including irradiation, inflammatory cytokines and chemical carcinogens. ROS and altered redox potential can be considered as the primary intracellular changes which regulate protein kinases, thereby serving as an important cellular component linking external stimuli with signal transduction in stress response. The mechanisms, which underlie the ROS-mediated response, involve direct alteration of kinases and transcription factors, and indirect modulation of cysteine-rich redox-sensitive proteins exemplified by thioredoxin and glutathione S-transferase. This review summarizes the current understanding of the mechanisms contributing to ROS-related changes in key stress activated signaling cascades.

Modulation of brain mitochondrial membrane permeability and synaptosomal Ca2+ transport by dopamine oxidation

Effects of dopamine on the membrane permeability transition, thioredoxin reductase activity, production of free radicals and oxidation of sulfhydryl groups in brain mitochondria and the Ca2+ uptake by Na+-Ca2+ exchange and sulfhydryl oxidation in brain synaptosomes were examined. The brain mitochondrial swelling and the fall of transmembrane potential were altered by pretreatment of dopamine in a dose dependent manner. Depressive effect of dopamine on mitochondrial swelling was reversed by 10 microg/ml catalase, and 10 mM DMSO. The activities of thioredoxin reductase in intact or disrupted mitochondria were decreased by dopamine (1-100 microM), 25 microM Zn2+ and 50 microM Mn2+. Dopamine-inhibited enzyme activity was reversed by 10 microg/ml SOD and 10 microg/ml catalase. Pretreatment of dopamine decreased Ca2+ transport in synaptosomes, which was restored by 10 microg/ml SOD and 10 mM DMSO. Dopamine (1-100 microM) in the medium containing mitochondria produced superoxide anion and hydrogen peroxide, while its effect on nitrite production was very weak. The oxidation of sulfhydryl groups in mitochondria and synaptosomes were enhanced by dopamine with increasing incubation times. Results suggest that dopamine could modulate membrane permeability in mitochondria and calcium transport at nerve terminals, which may be ascribed to the action of free radicals and the loss of reduced sulfhydryl groups.

Semaphorins as mediators of neuronal apoptosis

Shrinkage and collapse of the neuritic network are often observed during the process of neuronal apoptosis. However, the molecular and biochemical basis for the axonal damage associated with neuronal cell death is still unclear. We present evidence for the involvement of axon guidance molecules with repulsive cues in neuronal cell death. Using the differential display approach, an up-regulation of collapsin response mediator protein was detected in sympathetic neurons undergoing dopamine-induced apoptosis. A synchronized induction of mRNA of the secreted collapsin-1 and the intracellular collapsin response mediator protein that preceded commitment of neurons to apoptosis was detected. Antibodies directed against a conserved collapsin-derived peptide provided marked and prolonged protection of several neuronal cell types from dopamine-induced apoptosis. Moreover, neuronal apoptosis was inhibited by antibodies against neuropilin-1, a putative component of the semaphorin III/collapsin-1 receptor. Induction of neuronal apoptosis was also caused by exposure of neurons to semaphorin III-alkaline phosphatase secreted from 293EBNA cells. Anti-collapsin-1 antibodies were effective in blocking the semaphorin III-induced death process. We therefore suggest that, before their death, apoptosis-destined neurons may produce and secrete destructive axon guidance molecules that can affect their neighboring cells and thus transfer a "death signal" across specific and susceptible neuronal populations.

Neurotoxic and neuroprotective actions of catecholamines in cortical neurons

We examined the possibility that catecholamines (CA) could act as endogenous modulators of neuronal death. Exposure to high doses (>100 microM) of dopamine (DA) caused widespread neuronal death within 24 h in mouse cortical cell cultures and was accompanied by cell body shrinkage, aggregation and condensation of nuclear chromatin, and prominent internucleosomal DNA fragmentation. Epinephrine, but not norepinephrine (NE), was slightly toxic to neurons at doses higher than 1 mM. DA-induced death was attenuated by the addition of three different anti-apoptosis agents, 1 microgram/ml cycloheximide, 25 mM K(+), or 100 ng/ml brain-derived neurotrophic factor (BDNF). While treatment with 100 microM N-acetyl-l-cysteine attenuated DA neurotoxicity, neither the glutamate antagonists (10 microM MK-801 plus 50 microM CNQX) nor several antioxidants [trolox, 100 microM; Mn (III) tetrakis (4-benzoic acid) porphyrin chloride, 100 microM; Mn (III) tetrakis (1-methyl-4-pyridyl) prophyrin pentachloride, 100 microM; N-tert-butyl-alpha-phenylnitrone, 3 mM] prevented the CA-induced apoptosis. Interestingly, all CA at 1-30 microM attenuated free radical-mediated neuronal necrosis following exposure to 30 microM Fe(2+) or 200 microM H(2)O(2), which was insensitive to DA or NE antagonists. Like trolox, CA reduced levels of the stable free radical 1,1-diphenyl-2-picrylhydrazyl under cell-free conditions, raising the possibility that CA as an antioxidant protects neurons. We also found that the neuroprotective effect of CA prolonged the protective effects of BDNF against serum deprivation. The present findings suggest that CA induces apoptosis at high doses but prevents free radical-mediated neurotoxicity as an anti-oxidant without being coupled to the receptors.

MAPK activation determines renal epithelial cell survival during oxidative injury

Ischemia/reperfusion (I/R) injury induces both functional and morphological changes in the kidney. Necrosis, predominantly of the proximal tubule (PT), is the hallmark of this model of renal injury, whereas cells of the distal nephron survive, apparently intact. We examined whether differences in cellular outcome of the various regions of the nephron may be due to segmental variation in the activation of the mitogen-activated protein kinases (MAPKs) in response to I/R injury. Whereas c-Jun N-terminal kinase (JNK) is activated in both the cortex and inner stripe of the outer medulla, the extracellular regulated kinase (ERK) pathway is activated only in the inner stripe in which thick ascending limb (TAL) cells predominate. These studies are consistent with the notion that ERK activation is essential for survival. To test this hypothesis directly, we studied an in vitro system in which manipulation of these pathways and their effects on cellular survival could be examined. Oxidant injury was induced in mouse PT and TAL cells in culture by the catabolism of hypoxanthine by xanthine oxidase. PT cells were found to be more sensitive than TAL cells to oxidative stress as assessed by cell counting, light microscopy, propidium iodide uptake, and fluorescence-activated cell sorting (FACS) analysis. Immunoprecipitation/kinase analysis revealed that JNK activation occurred in both cell types, whereas ERK activation occurred only in TAL cells. We then examined the effect of PD-098059, a MAP kinase kinase (MEK)-1 inhibitor of the ERK pathway, on PT and TAL survival. In TAL cells, ERK inhibition reduced cell survival nearly fourfold (P < 0.001) after oxidant exposure. In PT cells, activation of the ERK pathway by insulin-like growth factor I (IGF-I) increased survival by threefold (P < 0.001), and this IGF-I-enhanced cell survival was inhibited by PD-098059. These results indicate that cell survival in the kidney after ischemia may be dependent on ERK activation, suggesting that this pathway may be a target for therapeutic treatment in I/R injury.

Intrastriatal dopamine injection induces apoptosis through oxidation-involved activation of transcription factors AP-1 and NF-kappaB in rats

ABSTRACT More and more evidence suggests that increases in dopamine (DA) in striata may participate in neurodegenerative processes during acute ischemia, hypoxia, and excitotoxicity. With a rat model of intrastriatal DA injection, we studied the molecular events involved in DA toxicity. Intrastriatal injections of DA in amounts from 1 to 2 micromol result in apoptotic cell death, as indicated by terminal deoxynucleotidyl transferase labeling of DNA strand breaks and Klenow polymerase-catalyzed [(32)P]deoxycytidine triphosphate-labeled DNA laddering. Injections of DA produce a strong and prolonged activated protein 1 (AP-1) activity that contains c-fos, c-jun, and phosphorylated c-jun protein. DA injections also stimulate the activity of nuclear factor-kappaB (NF-kappaB), an oxidative stress-responsive transcription factor. Injection of curcumin at a dose that selectively inhibits AP-1 activation without affecting NF-kappaB activity attenuates DNA laddering induced by DA. Preinjection with SN50, a specific permeable recombinant NF-kappaB translocation inhibitor peptide, reduces DA-induced NF-kappaB activation and apoptosis. Moreover, preinjection of the antioxidant GSH significantly inhibits both DA-induced activation of transcription factors AP-1 and NF-kappaB and subsequent apoptosis. Thus, our data suggest that DA-oxidative stress-induced apoptosis in vivo is mediated by activation of transcription factors AP-1 and NF-kappaB.

Bcl-2 and Bcl-X(L) block thapsigargin-induced nitric oxide generation, c-Jun NH(2)-terminal kinase activity, and apoptosis

The proteins Bcl-2 and Bcl-X(L) prevent apoptosis, but their mechanism of action is unclear. We examined the role of Bcl-2 and Bcl-X(L) in the regulation of cytosolic Ca(2+), nitric oxide production (NO), c-Jun NH(2)-terminal kinase (JNK) activation, and apoptosis in Jurkat T cells. Thapsigargin (TG), an inhibitor of the endoplasmic reticulum-associated Ca(2+) ATPase, was used to disrupt Ca(2+) homeostasis. TG acutely elevated intracellular free Ca(2+) and mitochondrial Ca(2+) levels and induced NO production and apoptosis in Jurkat cells transfected with vector (JT/Neo). Buffering of this Ca(2+) response with 1, 2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester (BAPTA-AM) or inhibiting NO synthase activity with N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) blocked TG-induced NO production and apoptosis in JT/Neo cells. By contrast, while TG produced comparable early changes in the Ca(2+) level (i.e., within 3 h) in Jurkat cells overexpressing Bcl-2 and Bcl-X(L) (JT/Bcl-2 or JT/Bcl-X(L)), NO production, late (36-h) Ca(2+) accumulation, and apoptosis were dramatically reduced compared to those in JT/Neo cells. Exposure of JT/Bcl-2 and JT/Bcl-X(L) cells to the NO donor, S-nitroso-N-acetylpenacillamine (SNAP) resulted in apoptosis comparable to that seen in JT/Neo cells. TG also activated the JNK pathway, which was blocked by L-NAME. Transient expression of a dominant negative mutant SEK1 (Lys-->Arg), an upstream kinase of JNK, prevented both TG-induced JNK activation and apoptosis. A dominant negative c-Jun mutant also reduced TG-induced apoptosis. Overexpression of Bcl-2 or Bcl-X(L) inhibited TG-induced loss in mitochondrial membrane potential, release of cytochrome c, and activation of caspase-3 and JNK. Inhibition of caspase-3 activation blocked TG-induced JNK activation, suggesting that JNK activation occurred downstream of caspase-3. Thus, TG-induced Ca(2+) release leads to NO generation followed by mitochondrial changes including cytochrome c release and caspase-3 activation. Caspase-3 activation leads to activation of the JNK pathway and apoptosis. In summary, Ca(2+)-dependent activation of NO production mediates apoptosis after TG exposure in JT/Neo cells. JT/Bcl-2 and JT/Bcl-X(L) cells are susceptible to NO-mediated apoptosis, but Bcl-2 and Bcl-X(L) protect the cells against TG-induced apoptosis by negatively regulating Ca(2+)-sensitive NO synthase activity or expression.

Expression, purification, and biochemical characterization of SAG, a ring finger redox-sensitive protein

We recently reported the cloning and characterization of SAG (sensitive to apoptosis gene), a novel zinc RING finger protein, that is redox responsive and protects mammalian cells from apoptosis. Here we report the expression, purification, and biochemical characterization of SAG. Bacterially expressed SAG is brown in color and dithiothreitol (DTT)-sensitive. SAG forms large oligomers without DTT that can be reduced into a monomer in the presence of DTT. These features help us to purify SAG using the chromatography with or without DTT. Likewise, purified SAG is redox sensitive. Upon H2O2 exposure, SAG forms oligomers as well as monomer doublets due to the formation of the inter- or intramolecular disulfide bonds, respectively. This process can be reversed by DTT or prevented by pretreatment with the alkylating reagent, N-ethylmaleimide (NEM). Although SAG contains two putative heme-binding sites and a RING finger domain, the protein appears not to bind with heme and to lack transcription factor activity as determined in a Gal4-fusion/transactivation assay. Wildtype, but not RING finger domain-disrupted SAG mutants, prevents copper-induced lipid peroxidation. These results, along with our previous observations, suggest that SAG is an intracellular antioxidant molecule that may act as a redox sensor to buffer oxidative-stress induced damage.

Two distinct mechanisms are involved in 6-hydroxydopamine- and MPP+-induced dopaminergic neuronal cell death: role of caspases, ROS, and JNK

In this study, we examined the possibility that MPTP and 6-hydroxydopamine (6-OHDA) act on distinct cell death pathways in a murine dopaminergic neuronal cell line, MN9D. First, we found that cells treated with 6-OHDA accompanied ultrastructural changes typical of apoptosis, whereas MPP+ treatment induced necrotic manifestations. Proteolytic cleavage of poly-(ADP-ribose)polymerase by caspase was induced by 6-OHDA, whereas it remained uncleaved up to 32 h after MPP+ treatment and subsequently disappeared. Accordingly, 6-OHDA- but not MPP(+)-induced cell death was significantly attenuated in the presence of a broad-spectrum caspase inhibitor, N-benzyloxy-carbonyl-Val-Ala-Asp-fluomethylketone (Z-VAD-fmk). As measured by fluorometric probes, the level of reactive oxygen species (ROS) significantly increased after 6-OHDA treatment. In contrast, the level of dihydroethidium-sensitive ROS following MPP+ treatment remained unchanged while a slight increase in dichlorofluorescin-sentive ROS was temporarily observed. As demonstrated by immunoblot analysis, the level of superoxide dismutase was down-regulated following 6-OHDA treatment, whereas it remained unchanged after MPP+ treatment. Cotreatment of cells with antioxidants such as N-acetylcysteine or Mn(III)tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP, cell-permeable superoxide dismutase mimetic) rescued 6-OHDA- but not MPP(+)-induced cell death, whereas inclusion of catalase or N(G)-nitro-L-arginine had no effect in both cases. In addition, 6-OHDA induced ROS-mediated c-Jun N-terminal kinase (JNK) activation that was attenuated in the presence of N-acetylcysteine or MnTBAP but not catalase or Z-VAD-fmk. In contrast, MPP+ has little effect on JNK activity, indicating that ROS and/or ROS-induced cell death signaling pathway seems to play an essential role in 6-OHDA-mediated apoptosis but not in MPP(+)-induced necrosis in a mesencephalon-derived, dopaminergic neuronal cell line.

Glucose-induced oxidative stress and programmed cell death in diabetic neuropathy

The Diabetes Control and Complications Trial (DCCT) established the importance of hyperglyemia and other consequences of insulin deficiency in the pathogenesis of diabetic neuropathy, but the precise mechanisms by which metabolic alterations produce peripheral nerve fiber damage and loss remain unclear. Emerging data from human and animal studies suggest that glucose-derived oxidative stress may play a central role, linking together many of the other currently invoked pathogenetic mechanisms such as the aldose reductase and glycation pathways, vascular dysfunction, and impaired neurotrophic support. These relationships suggest combinations of pharmacological interventions that may synergistically protect the peripheral nervous system (PNS) against the metabolic derangements of diabetes mellitus.

The Jnk1 and Jnk2 protein kinases are required for regional specific apoptosis during early brain development

The c-Jun NH2-terminal kinase (Jnk) family is implicated in apoptosis, but its function in brain development is unclear. Here, we address this issue using mutant mice lacking different members of the family (Jnk1, Jnk2, and Jnk3). Mice deficient in Jnk1, Jnk2, Jnk3, and Jnk1/Jnk3 or Jnk2/Jnk3 double mutants all survived normally. Compound mutants lacking Jnk1 and Jnk2 genes were embryonic lethal and had severe dysregulation of apoptosis in brain. Specifically, there was a reduction of cell death in the lateral edges of hindbrain prior to neural tube closure. In contrast, increased apoptosis and caspase activation were found in the mutant forebrain, leading to precocious degeneration. These results suggest that Jnk1 and Jnk2 regulate region-specific apoptosis during early brain development.

Cytotoxic and genotoxic potential of dopamine

A variety of in vitro and in vivo studies demonstrate that dopamine is a toxic molecule that may contribute to neurodegenerative disorders such as Parkinson's disease and ischemia-induced striatal damage. While much attention has focused on the fact that the metabolism of dopamine produces reactive oxygen species (peroxide, superoxide, and hydroxyl radical), growing evidence suggests that the neurotransmitter itself may play a direct role in the neurodegenerative process. Oxidation of the dopamine molecule produces a reactive quinone moiety that is capable of covalently modifying and damaging cellular macromolecules. This quinone formation occurs spontaneously, can be accelerated by metal ions (manganese or iron), and also arises from selected enzyme-catalyzed reactions. Macromolecular damage, combined with increased oxidant stress, may trigger cellular responses that eventually lead to cell death. Reactive quinones have long been known to represent environmental toxicants and, within the context of dopamine metabolism, may also play a role in pathological processes associated with neurodegeneration. The present discussion will review the oxidative metabolism of dopamine and describe experimental evidence suggesting that dopamine quinone may contribute to the cytotoxic and genotoxic potential of this essential neurotransmitter.

Interaction between sodium ascorbate and dopamine

The interaction between sodium ascorbate and dopamine was investigated by three different parameters: radical intensity, prooxidant action, and cytotoxicity induction. Sodium ascorbate and dopamine produced the doublet and quartet ESR signals under alkaline conditions (pH 8.0-9.5), respectively. Addition of increasing concentrations of sodium ascorbate completely scavenged the dopamine radical and replaced the latter with its own radical. Similarly, dopamine slightly, but significantly reduced the radical intensity of sodium ascorbate. These two compounds stimulated the methionine oxidation and hydrogen peroxide generation in culture medium, but in combination, their stimulation activities were weakened. Both of these two compounds dose-dependently reduced the viable cell number of human oral squamous carcinoma HSC-4 cells, and their cytotoxic activity was significantly reduced by catalase. When these two compounds were mixed together before adding to HSC-4 cells, both of their cytotoxic activities were diminished. The present study demonstrates the interaction between sodium ascorbate and dopamine, which might modify their biological activities and generation of nerve disorders such as Parkinson's disease.

Biochemical determinants of apoptosis and necrosis

Although apoptosis and necrosis were originally thought to be entirely distinct mechanisms of cell death, recent work has shown that the processes are regulated by many of the same biochemical intermediates, most notably the levels of cellular ATP, Ca2+, reactive oxygen species, and thiol antioxidants. Beyond a certain threshold, it appears that stress-induced changes in these modulators 'switches' the cell death mechanism from apoptosis to necrosis. Importantly, even when this occurs, cell death can be attenuated by bcl-2 and caspase inhibitors, which are known for their abilities to block apoptosis. This review will summarize these observations within the context of what is currently known about the effector machinery for apoptotic cell death, and possible mechanistic explanations for the switch between apoptosis and necrosis will be provided.

Phosphatidylinositol 3-kinase gamma mediates shear stress-dependent activation of JNK in endothelial cells

Shear stress differentially activates extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) by mechanisms involving Galphai2 and Gbeta/gamma proteins, respectively, in bovine aortic endothelial cells (BAEC). The early events in this signaling mechanism by which G proteins regulate ERK and JNK in response to shear stress have not been defined. Here we show that BAEC endogenously express a G protein-dependent form of phosphatidylinositol 3-kinase, PI3Kgamma, and its activity is stimulated by shear stress. PI3Kgamma activity was measured in vitro using BAEC that were transiently transfected with an epitope-tagged PI3Kgamma (vsv-PI3Kgamma). Exposure of BAEC to shear stress rapidly and transiently stimulated the activity of vsv-PI3Kgamma (maximum by 15 s, with a return to basal after 1-min exposure to 5 dyn/cm2 shear stress). Activity of vsv-PI3Kgamma was stimulated by shear stress intensities as low as 0.5 dyn/cm2. Treatment of BAEC with an inhibitor of PI3K, wortmannin, inhibited shear-dependent activation of JNK but had no effect on that of ERK. Furthermore, expression of a kinase-inactive mutant (PI3KgammaK799R) in BAEC inhibited the shear-dependent activation of JNK but not ERK. Taken together, these results suggest that PI3Kgamma selectively regulates the shear-sensitive JNK pathway. This differential and novel signaling pathway may be responsible for coordinating various mechanosensitive events in endothelial cells.

Activation of c-jun N-terminal kinase/stress-activated protein kinase and the decreased ratio of Bcl-2 to Bax are associated with the auto-oxidized dopamine-induced apoptosis in PC12 cells

Current concepts of the pathogenesis of Parkinson's disease center on the formation of reactive oxygen species (ROS). Dopamine is one of the major sources of ROS. In this study, the molecular events during the dopamine-induced apoptosis in PC-12 cells were studied using auto-oxidized dopamine. Auto-oxidized-dopamine induced DNA fragmentation and activation of c-jun N-terminal kinase (JNK)/stress-activated protein kinase (SAPK) faster and stronger than dopamine. Furthermore, N-acetylcysteine, an antioxidant, prevented the auto-oxidized dopamine-induced JNK/SAPK activation and DNA fragmentation. Meanwhile, Bcl-2 started to decrease after onset of apoptosis, and Bax was increased up to beginning of apoptosis, and thereafter decreased. Therefore, these results suggested that activation of JNK/SAPK and the decreased ratio of antiapoptotic Bcl-2 to proapoptotic Bax appear to be associated with the dopamine-induced apoptosis.

Involvement of caspase-like proteinases in apoptosis of neuronal PC12 cells and primary cultured microglia induced by 6-hydroxydopamine

Activation of proteolytic enzymes, including the caspase family of proteinases, is a feature characteristic of the apoptotic program. In the present study, we examined a potential role of intracellular proteinases in the death of neuronal PC12 and primary cultured rat microglial cells induced by 6-hydroxydopamine (6-OHDA). In both neuronal PC12 and microglial cells, 6-OHDA (10-200 microM) induced apoptosis in a dose-dependent manner as judged by the DNA break. The 6-OHDA was ineffective in Bcl-2-overexpressing neuronal PC12 cells. Pretreatment of these cells with two caspase inhibitors, acetyl-Try-Val-Ala-Asp-aldehyde and acetyl-Asp-Glu-Val-Asp-aldehyde, prevented the 6-OHDA-induced apoptosis. Pepstatin A and leupeptin, potent inhibitors of aspartic and cysteine proteinases, respectively, partly inhibited the apoptosis of microglia but not neuronal PC12 cells. In contrast, GBR12935, a dopamine uptake inhibitor, significantly inhibited the apoptotic death of neuronal PC12 cells but not microglia. These results suggest that mechanisms by which 6-OHDA induces apoptosis in these two cell types are distinct; 6-OHDA incorporated into neuronal PC12 cells and its metabolites may activate the caspase-like enzymes, whereas oxidative metabolites of the agent produced extracellularly may activate the caspase and the endosomal/lysosomal proteolytic systems in microglia.