The permeability transition pore. Control points of a cyclosporin A-sensitive mitochondrial channel involved in cell death

Ca(2+)-calmodulin antagonist chlorpromazine and poly(ADP-ribose) polymerase modulators 4-aminobenzamide and nicotinamide influence hepatic expression of BCL-XL and P53 and protect against acetaminophen-induced programmed and unprogrammed cell death in mice

Acetaminophen (AAP), the analgesic hepatotoxicant, is a powerful inducer of oxidative stress, DNA fragmentation, and apoptosis. The anti-apoptotic oncogene bcl-XL, and the pro-apoptotic oncogene p53 are two key regulators of cell cycle progression and/or apoptosis subsequent to DNA damage in vitro and in vivo. This study investigated the effect of AAP on the expression of these oncogenes and whether agents that modulate DNA fragmentation (chlorpromazine, CPZ) and DNA repair through poly(ADP-Ribose) polymerase (PARP) activity (4-AB: 4-aminobenzamide) can protect against AAP-induced hepatotoxicity by inhibiting oxidative stress, DNA fragmentation, and/or by altering the expression of bcl-XL and p53. In addition, the protective effect of supplemental nicotinamide (NICO), known to be depleted in cells with high PARP activity during DNA repair, is similarly evaluated. Male ICR mice (3 months old) were administered vehicle alone; nontoxic doses of 4-AB (400 mg/kg, ip), NICO (250 mg/kg, ip) or CPZ (25 mg/kg, ip), hepatotoxic dose of AAP alone (500 mg/kg, ip), or AAP plus one of the protective agents 1 h later. All animals were sacrificed 24 h following AAP administration. Serum alanine aminotransferase activity (ALT), hepatic histopathology and lipid peroxidation, DNA damage, and expression of bcl-XL and p53 (western blot analysis) were compared in various groups. All of the three agents significantly prevented AAP-induced liver injury, lipid peroxidation, DNA damage, and associated apoptotic and necrotic cell deaths, 4-AB being the most effective and NICO the least. Compared to control, there was a considerable decrease in bcl-XL expression, and an increase in p53 expression in AAP-exposed livers. The effect of AAP on bcl-XL was antagonized and that on p53 was synergized by the PARP-modulator 4-AB as well as NICO, whereas the endonuclease inhibitor CPZ was without effect on either bcl-XL or p53 expression. These results suggest that the hepatotoxic effect of AAP involves multiple mechanisms including oxidative stress, upregulation of endonuclease (or caspase-activated DNAse) and alteration of pro- and anti-apoptotic oncogenes. The observed antagonism of AAP-induced hepatocellular apoptosis and/or necrosis by modulators of multiple processes including DNA repair suggests the likelihood that a more effective therapy against AAP intoxication should involve a combination of antidotes.

Binding of human immunodeficiency virus type 1 gp120 to CXCR4 induces mitochondrial transmembrane depolarization and cytochrome c-mediated apoptosis independently of Fas signaling

Apoptosis of CD4(+) T lymphocytes, induced by contact between human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (gp120) and its receptors, could contribute to the cell depletion observed in HIV-infected individuals. CXCR4 appears to play an important role in gp120-induced cell death, but the mechanisms involved in this apoptotic process remain poorly understood. To get insight into the signal transduction pathways connecting CXCR4 to apoptosis following gp120 binding, we used different cell lines expressing wild-type CXCR4 and a truncated form of CD4 that binds gp120 but lacks the ability to transduce signals. The present study demonstrates that (i) the interaction of cell-associated gp120 with CXCR4-expressing target cells triggers a rapid dissipation of the mitochondrial transmembrane potential resulting in the cytosolic release of cytochrome c from the mitochondria to cytosol, concurrent with activation of caspase-9 and -3; (ii) this apoptotic process is independent of Fas signaling; and (iii) cooperation with a CD4 signal is not required. In addition, following coculture with cells expressing gp120, a Fas-independent apoptosis involving mitochondria and caspase activation is also observed in primary umbilical cord blood CD4(+) T lymphocytes expressing high levels of CXCR4. Thus, this gp120-mediated apoptotic pathway may contribute to CD4(+) T-cell depletion in AIDS.

Apoptosis and mitochondrial damage in INS-1 cells treated with alloxan

To evaluate the participation of mitochondrial damage, oxygen radicals and cell death in diabetes mellitus, we designed a way to investigate INS-1 cells, rat pancreatic beta-cell line, to die by treatment with alloxan which generate reactive oxygen species (ROS). Incubation of INS-1 cells with alloxan for 24 h resulted in a decrease in viability of cells as well as inhibition of glucose-stimulated insulin release; this could be prevented by antioxidants, vitamin E and butylated hydroxyanisol (BHA). The formation of a DNA ladder and the distribution of phosphatidylserine at the external surface of plasma membrane were observed as indicators of apoptosis in the cells treated with alloxan at concentrations below 0.5 mM. The formation of DNA ladder was prevented by vitamin E, BHA and catalase, suggesting that the ROS is involved in the process of apoptosis in INS-1 cells treated with alloxan. Lower levels of intracellular ATP, collapse of mitochondrial membrane potential and release of cytochrome c from mitochondria were also observed in INS-1 cells treated with alloxan, suggesting that alloxan caused the damage of mitochondria in cells and was related to the process of apoptosis. In contrast, rat liver RLC-18 cells treated with alloxan were not observed in the decrease of viability. It follows from the present study that mitochondrial damages by ROS generated from alloxan is linked to apoptosis in INS-1 cells.

The effect of aliphatic, naphthenic, and aromatic hydrocarbons on production of reactive oxygen species and reactive nitrogen species in rat brain synaptosome fraction: the involvement of calcium, nitric oxide synthase, mitochondria, and phospholipase A11Abbreviations: BIM, bisindolylmaleimide; [Ca2+]i, concentration of intracellular calcium; ChAT, cholin acetyltransferase; CSA, cyclosporin A; DCF, 2′,7′-dichlorofluorescein; H2DCF-DA, 2′,7′-dichlorodihydrofluorescin diacetate; DEDA, dimethyleicosadienoic acid; ERK, extracellular signal-regulated kinases; Fura-2 AM, 5-oxazolecarboxylic acid, 2-(6-(bis(2-((acetyloxy)methoxy)-2-oxoethyl)amino)-5-(2-(bis(2-((acetyloxy)methoxy)-2oxoethyl)amino)-5-methylphenoxy)ethoxy)-2-benzofuranyl)-, (acetyloxy) methyl ester; GABA-T, gamma-aminobutyric acid transaminase; HBSS, Hanks’ balanced salt solution; La3+, lanthanum; MAPK, mitogen-activated protein kinase; MeHg, methyl mercury; MEK, extracellular signal-regulated protein kinase; MeOH, methanol; MTP, mitochondrial permeability transition pore; L-NAME, Nω-nitro-l-arginine methyl ester; NO·, nitrogen oxide; NOS, NO· synthase; O2·−, superoxide; PLA2, phospholipase A2; PKC, protein kinase C; RNS, reactive nitrogen species; ROS, reactive oxygen species; SOD, superoxide dismutase; TMB, 1,2,4-trimethylbenzene; TMCH, 1,2,4-trimethylcyclohexane; and U73122, 1-(6-[17beta-3-methoxyestra- 1,3,5(10)-trien- 17-yl]-aminohexyl)- 1H-pyrrole-2,5-dione

This study investigated the effects of C7 and C9 aliphatic (n-heptane, n-nonane), naphthenic (methylcyclohexane, 1,2,4-trimethylcyclohexane (TMCH)) and aromatic (toluene, 1,2,4-trimethylbenzene (TMB)) hydrocarbons on the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in rat brain synaptosome fraction. Methyl mercury (MeHg) was included as a positive control. Exposure of the synaptosomes to the hydrocarbons produced a concentration-dependent linear increase in the formation of the fluorescence of 2',7'-dichlorofluorescein (DCF) as a measure of the production of ROS and RNS. Formation of RNS was demonstrated by preincubation of the synaptosome fraction with the neuronal nitric oxide synthase (nNOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME), which reduced the MeHg and TMCH-stimulated fluorescence by 51% and 65%, respectively. The naphthenic hydrocarbon TMCH showed the strongest potential for ROS and RNS formation in rat brain synaptosomes, followed by TMB, toluene, n-nonane, n-heptane, and methylcyclohexane, respectively. TMCH was selected for mechanistic studies of the formation of ROS. Both MeHg and TMCH induced an increase in intracellular calcium concentration [Ca(2+)]i as measured with Fura-2. Blockade of voltage-dependent Ca(2+) channels with lanthanum prior to stimulation with MeHg and TMCH led to a reduction in the ROS/RNS formation of 72% and 70%, respectively. Furthermore, addition of cyclosporin A (CSA), a blocker of the mitochondrial permeability transition pore (MTP), lowered both the MeHg and TMCH-elevated DCF fluorescence by 72% and 59%. Preincubation of the synaptosome fraction with the protein tyrosine kinase inhibitor genistein lowered the MeHg and TMCH-stimulated fluorescence by 85% and 91%, respectively. Addition of the extracellular signal-regulated protein kinase (MEK)-1 and -2 inhibitor U0126 reduced the fluorescence stimulated by MeHg and TMCH by 62% and 63%. Furthermore, the protein kinase C inhibitor bisindolylmaleimide reduced the fluorescence stimulated by MeHg and TMCH by 52% and 56%. The compound 1-(6-[17beta-3-methoxyestra- 1,3,5(10)-trien- 17-yl]-aminohexyl)-1H-pyrrole-2,5-dione (U73122), which inhibits phospholipase C, was shown to decrease the ROS and RNS formation induced by MeHg and TMCH by 49% and 64%, respectively. The phospholipase A2 (PLA2) inhibitor 7,7-dimethyl eicosadienoic acid (DEDA) reduced fluorescence in response to MeHg and TMCH by 49% and 54%. Simultaneous addition of L-NAME, CSA, and DEDA to the synaptosome fraction totally abolished the DCF fluorescence. In conclusion, C7 and C9 aliphatic, naphthenic, and aromatic hydrocarbons stimulated formation of ROS and RNS in rat brain synaptosomes. The naphthenic hydrocarbon TMCH stimulated formation of ROS and RNS in the synaptosomes through Ca(2+)-dependent activation of PLA2 and nNOS, and through increased transition permeability of the MTP. Exposure of humans to the naphthenic hydrocarbon TMCH may stimulate formation of free radicals in the brain, which may be a key factor leading to neurotoxicity.

Cerebral energy metabolism in hepatic encephalopathy and hyperammonemia

Hepatic encephalopathy (HE) is an important cause of morbidity and mortality in patients with severe liver disease. Although the molecular basis for the neurological disorder in HE remains elusive, elevated ammonia and its chief metabolite glutamine are believed to be important factors responsible for altered cerebral functions, including multiple neurotransmitter system(s) failure, altered bioenergetics, and more recently oxidative stress. Accumulated evidence suggests that direct interference of ammonia at several points in cerebral energy metabolism, including glycolysis, TCA cycle, and the electron transport chain, could lead to energy depletion. Additionally, recent studies from our laboratory have invoked the possibility that ammonia and glutamine may induce the mitochondrial permeability transition in astrocytes, a process capable of causing mitochondrial dysfunction. Altered mitochondrial metabolism appears to be an important mechanism responsible for the cerebral abnormalities associated with HE and other hyperammonemic states.

Proinflammatory cytokines promote glial heme oxygenase-1 expression and mitochondrial iron deposition: implications for multiple sclerosis

Proinflammatory cytokines, pathological iron deposition, and oxidative stress have been implicated in the pathogenesis of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). HO-1 mRNA levels and mitochondrial uptake of [(55)Fe]Cl(3)-derived iron were measured in rat astroglial cultures exposed to interleukin-1beta (IL-1beta) or tumor necrosis factor-alpha (TNF-alpha) alone or in combination with the heme oxygenase-1 (HO-1) inhibitors, tin mesoporphyrin (SnMP) or dexamthasone (DEX), or interferon beta1b (INF-beta). HO-1 expression in astrocytes was evaluated by immunohistochemical staining of spinal cord tissue derived from MS and control subjects. IL-1beta or TNF-alpha promoted sequestration of non-transferrin-derived (55)Fe by astroglial mitochondria. HO-1 inhibitors, mitochondrial permeability transition pore (MTP) blockers and antioxidants significantly attenuated cytokine-related mitochondrial iron sequestration in these cells. IFN-beta decreased HO-1 expression and mitochondrial iron sequestration in IL-1beta- and TNF-alpha-challenged astroglia. The percentage of astrocytes coexpressing HO-1 in affected spinal cord from MS patients (57.3% +/- 12.8%) was significantly greater (p < 0.05) than in normal spinal cord derived from controls subjects (15.4% +/- 8.4%). HO-1 is over-expressed in MS spinal cord astroglia and may promote mitochondrial iron deposition in MS plaques. In MS, IFN-beta may attenuate glial HO-1 gene induction and aberrant mitochondrial iron deposition accruing from exposure to proinflammatory cytokines.

Synthesis of ganglioside GD3 and its comparison with bovine GD3 with regard to oligodendrocyte apoptosis mitochondrial damage

2,3-Dehydroneuraminic acid derivative 5 was transformed in five efficient steps into sialyl donor 2, which has a phenylthio group on the beta-side of the 3-position for anchimeric assistance and a diethyl phosphite residue as leaving group at the anomeric carbon. The known GM3 intermediate 10 was transformed into the 4b,4c,8c-O-unprotected acceptor 3, which was then allowed to react with 2 by using TMSOTf as catalyst and acetonitrile as solvent to afford the desired tetrasaccharide 12, which has an alpha(2-8)-linkage between two neuraminic acid residues. Removal of the phenylthio group gave intermediate 13, which was transformed into O-tetraosyl trichloroacetimidate 16 as glycosyl donor. Application of the azidosphingosine glycosylation procedure furnished GD3 (1) in high overall yield. Comparison of synthetic GD3 with bovine-brain-derived GD3 showed that there were similar effects in GD3-triggered uncoupling of mitochondrial respiration and in induction of apoptosis in oligodendrocytes.

Apoptotic cell death of cultured salamander photoreceptors induced by cccp: CsA-insensitive mitochondrial permeability transition

Photoreceptor degeneration is mediated by apoptosis in several animal models, although the underlying mechanisms are yet to be elucidated. We present here an apoptotic model based on a primary cell culture of tiger salamander photoreceptors, in which treatment with carbonyl cyanide m-chlorophenylhydrazone (cccp), a protonophore, induced apoptosis. Cells exposed to cccp showed condensed nuclei and displayed positive TdT-dUTP terminal nick-end labeling (TUNEL). In addition, 10–100 microM cccp rapidly induced a reduction of Delta psi(m) and &gt; or = 30 microM cccp induced a significant leakage of calcein from mitochondria to cytosol and nucleus, indicating a change in mitochondrial inner membrane permeability. Cyclosporin A (CsA), a transition pore blocker, did not prevent the cccp-induced MPT or the cccp-evoked apoptotic cell death, suggesting that cccp-induced apoptotic process was mediated by a CsA-insensitive pathway. This cell model provides an in vitro tool for studying mechanisms of photoreceptor apoptosis in isolated photoreceptors and may provide clues to the etiology of retinal degeneration.

Protective effect of harmaline and harmalol against dopamine- and 6-hydroxydopamine-induced oxidative damage of brain mitochondria and synaptosomes, and viability loss of PC12 cells

The present study elucidated the protective effect of beta-carbolines (harmaline, harmalol and harmine) against oxidative damage of brain mitochondria, synaptosomes and PC12 cells induced by either dopamine or 6-hydroxydopamine. Harmaline, harmalol and antioxidant enzymes (superoxide dismutase/SOD and catalase) decreased the alteration of mitochondrial swelling and membrane potential induced by 200 microM dopamine or 100 microM 6-hydroxydopamine. Deprenyl attenuated the dopamine-induced mitochondrial dysfunction but did not reduce the effect of 6-hydroxydopamine. While beta-carbolines inhibited the electron flow in mitochondria, they did not enhance the depressant effect of catecholamines. beta-Carbolines and antioxidant enzymes reversed the depression of synaptosomal Ca2+ uptake induced by 10 microM catecholamines. The compounds inhibited the catecholamine-induced thioredoxin reductase inhibition, thiol oxidation and carbonyl formation in mitochondria and synaptosomes. beta-Carbolines decreased the reactive species-induced deoxyribose degradation. Harmaline and harmalol reduced the catecholamine-induced loss of the transmembrane potential and of cell viability in PC12 cells. beta-Carbolines alone did not show a significant cytotoxic effect on PC12 cells. The results suggest that beta-carbolines may attenuate the dopamine- or 6-hydroxydopamine-induced alteration of brain mitochondrial and synaptosomal functions, and viability loss in PC12 cells, by a scavenging action on reactive oxygen species and inhibition of thiol oxidation.

Role of astrocytes in pathogenesis of ischemic brain injury

Astrocytes play an important role in the homeostasis of the CNS both in normal conditions and after ischemic injury. The swelling of astrocytes is observed during and several seconds after brain ischemia. Then ischemia stimulates sequential morphological and biochemical changes in glia and induces its proliferation. Reactive astrocytes demonstrate stellate morphology, increased glial fibrillary acidic protein (GFAP) immunoreactivity, increased number of mitochondria as well as elevated enzymatic and non-enzymatic antioxidant activities. Astrocytes can re-uptake and metabolize glutamate and in this way they control its extracellular concentration. The ability of astrocytes to protect neurons against the toxic action of free radicals depends on their specific energy metabolism, high glutathione level, increased antioxidant enzyme activity (catalase, superoxide dismutase, glutathione peroxidase) and overexpression of antiapoptotic bcl-2 gene. Astrocytes produce cytokines (TNF-alpha, IL-1, IL-6) involved in the initiation and maintaining of immunological response in the CNS. In astrocytes, like in neurones, ischemia induces the expression of immediate early genes: c-fos, c-jun, fos B, jun B, jun D, Krox-24, NGFI-B and others. The protein products of these genes modulate the expression of different proteins, both destructive ones and those involved in the neuroprotective processes.

Early release of cytochrome C and activation of caspase-3 in hyperglycemic rats subjected to transient forebrain ischemia

The mechanisms underlying the aggravating effect of hyperglycemia on brain damage are still elusive. The present study was designed to test our hypothesis that hyperglycemia-mediated damage is caused by mitochondrial dysfunction with mitochondrial release of cytochrome c (cyt c) to the cytoplasm, which leads to activation of caspase-3, the executioner of cell death. We induced 15 min of forebrain ischemia, followed by 0.5, 1, and 3 h of recirculation in sham, normoglycemic and hyperglycemic rats. Release of cyt c was observed in the neocortex and CA3 in hyperglycemic rats after only 0.5 h of reperfusion, when no obvious neuronal damage was observed. The release of cyt c persisted after 1 and 3 h of reperfusion. Activation of caspase-3 was observed after 1 and 3 h of recovery in hyperglycemic animals. No cyt c release or caspase-3 activation was observed in sham-operated controls while a mild increase of cyt c was observed in normoglycemic ischemic animals after 1 and 3 h of reperfusion. The findings that there is caspase activation and cyt c relocation support a notion that the biochemical changes that constitute programmed cell death occur after ischemia and contribute, at least in part, to hyperglycemia-aggravated ischemic neuronal death.

Regulation of the mitochondrial permeability transition by matrix Ca(2+) and voltage during anoxia/reoxygenation

We studied the interplay between matrix Ca(2+) concentration ([Ca(2+)]) and mitochondrial membrane potential (Deltapsi) in regulation of the mitochondrial permeability transition (MPT) during anoxia and reoxygenation. Without Ca(2+) loading, anoxia caused near-synchronous Deltapsi dissipation, mitochondrial Ca(2+) efflux, and matrix volume shrinkage when a critically low PO(2) was reached, which was rapidly reversible upon reoxygenation. These changes were related to electron transport inhibition, not MPT. Cyclosporin A-sensitive MPT did occur when extramitochondrial [Ca(2+)] was increased to promote significant Ca(2+) uptake during anoxia, depending on the Ca(2+) load size and ability to maintain Deltapsi. However, when [Ca(2+)] was increased after complete Deltapsi dissipation, MPT did not occur until reoxygenation, at which time reactivation of electron transport led to partial Deltapsi regeneration. In the setting of elevated extramitochondrial Ca(2+), this enhanced matrix Ca(2+) uptake while promoting MPT because of less than full recovery of Deltapsi. The interplay between Deltapsi and matrix [Ca(2+)] in accelerating or inhibiting MPT during anoxia/reoxygenation has implications for preventing reoxygenation injury associated with MPT.

Apoptosis and liver diseases: recent concepts of mechanism and significance

Apoptosis, or programmed cell death, is a highly conserved mechanism that plays an essential role in numerous normal developmental and regulatory processes and disease states. It is mediated by a variable interaction among several components of the cell, including cell surface death receptors, the caspase cascade, mitochondrial metabolism and energetics, and the cytoskeleton. Even in those instances in which cell surface death receptors play a role, mitochondria are often central to the process, not only in mediating the death program, but in initiating it as well. In regard to mitochondrial involvement, a key role is hypothesized for an interaction among AMP-activated protein kinase, cytoskeletal intermediate filaments, and mitochondrial oxidation of fatty acids. This proposed interaction may be a critical element in the pathogenesis of intramitochondrial oxidative stress, diminished inner membrane potential (delta psi(m)), and other mitochondrial changes that contribute to cell death. Apoptosis may participate in a wide variety of disease processes, ranging from chemical and physical injury to viral infection and cancer, but its mechanistic and functional relationship to these conditions remains incompletely understood. Despite this, an understanding of the mechanisms involved and of the identity of potential pharmacologic targets is increasing, and warrants an optimistic view of their potential for clinical application.

The effects of singlet oxygen produced by photodynamic action on the mitochondrial permeability transition differ in accordance with the localization of the sensitizer

We have examined whether the effects of singlet oxygen (1O2) produced by photodynamic action on the mitochondrial permeability transition (PT) can be modulated by the localization of photosensitizers in irradiated mitochondria. We have previously shown that oxidation due to 1O2 photogenerated in hematoporphyrin (HP)-loaded mitochondria can prevent opening of the PT pores, likely after degradation of some critical histidines (Salet et al, 1997, J. Biol. Chem. 272, 21938-21943). Equally, in the present study we have irradiated mitochondria in the presence of a structurally different photosensitizer producing 1O2, namely 4,5',8-trimethylpsoralen (TMP). Fluorescence studies show that TMP binds to protein sites which differ from those of HP. In sharp contrast with HP, TMP-driven photodynamic action triggers per se pore opening. Interestingly, this inducing effect is inhibited when TMP-treated mitochondria are irradiated after addition of mersalyl, a specific reagent protecting thiol groups of the inner mitochondrial membrane that are oriented toward the external hydrophilic phase. This fact suggests that 1O2-mediated thiol oxidation is responsible for TMP-photoinduced pore opening. Taken together, these findings suggest that 1O2 can activate or inactivate a cellular function such as mitochondrial PT depending on the site where it is produced in the mitochondrial membrane.

Mitochondria in eosinophils: functional role in apoptosis but not respiration

In most eukaryotic cells, mitochondria use the respiratory chain to produce a proton gradient, which is then harnessed for the synthesis of ATP. Recently, mitochondrial roles in regulation of apoptosis have been discovered in many cell types. Eosinophils (Eos) die by apoptosis, but the presence and function of mitochondria in Eos are unknown. This study found that Eos contain mitochondria in small numbers, as shown by labeling with membrane potential-sensitive dyes and in situ PCR for a mitochondrial gene. Eos generate mitochondrial membrane potential from hydrolysis of ATP rather than from respiration, as shown by mitochondrial respiratory inhibitors and mitochondrial uncouplers. The mitochondria provide insignificant respiration but can induce apoptosis, as shown by using the mitochondrial F(1)F(0)-ATPase inhibitor oligomycin and translocation of cytochrome c. Thus during differentiation of Eos, although respiration is lost, the other central role of mitochondria, the induction of apoptosis, is retained.

Plasma membrane depolarization without repolarization is an early molecular event in anti-Fas-induced apoptosis

The movement of intracellular monovalent cations has previously been shown to play a critical role in events leading to the characteristics associated with apoptosis. A loss of intracellular potassium and sodium occurs during apoptotic cell shrinkage establishing an intracellular environment favorable for nuclease activity and caspase activation. We have now investigated the potential movement of monovalent ions in Jurkat cells that occur prior to cell shrinkage following the induction of apoptosis. A rapid increase in intracellular sodium occurs early after apoptotic stimuli suggesting that the normal negative plasma membrane potential may change during cell death. We report here that diverse apoptotic stimuli caused a rapid cellular depolarization of Jurkat T-cells that occurs prior to and after cell shrinkage. In addition to the early increase in intracellular Na(+), (86)Rb(+) studies reveal a rapid inhibition of K(+) uptake in response to anti-Fas. These effects on Na(+) and K(+) ions were accounted for by the inactivation of the Na(+)/K(+)-ATPase protein and its activity. Furthermore, ouabain, a cardiac glycoside inhibitor of the Na(+)/K(+)-ATPase, potentiated anti-Fas-induced apoptosis. Finally, activation of an anti-apoptotic signal, i.e. protein kinase C, prevented both cellular depolarization in response to anti-Fas and all downstream characteristics associated with apoptosis. Thus cellular depolarization is an important early event in anti-Fas-induced apoptosis, and the inability of cells to repolarize via inhibition of the Na(+)/K(+)-ATPase is a likely regulatory component of the death process.

Effects of intracarotid arterial injection of cyclosporin A and spontaneous hypothermia on brain damage incurred after a long period of global ischemia

A recent study showed that a single intracarotid arterial injection of cyclosporin A (CsA) can dramatically reduce infarct volume in rats subjected to transient focal ischemia. The present experiments were undertaken to investigate whether intracarotid arterial injection of CsA reduces brain damage after global ischemia. Since hypothermia is also an efficacious factor in preventing ischemic brain damage, in the second part of the experiments we tested whether a combination of hypothermia and CsA would provide additional brain protection. Global ischemia of a 30-min duration was induced in the rat. CsA (10 mg/kg) was injected into the carotid artery immediately after reperfusion. Hypothermia was instituted after ischemia by allowing spontaneous head temperature to fall to 30-32 degrees C, while body temperature was upheld at 37 degrees C. The results demonstrated that vehicle-treated animals could not survive beyond 1-2 days after reperfusion, and the histopathological outcome in a separate group of rats perfusion-fixed after 1 day reperfusion showed 80-100% brain damage in the caudoputamen, and in the hippocampal CA1, CA3, CA4 and dentate gyrus subregions. Microinfarction and grade 3 damage were frequently observed in the cingulate and parietal cortex and in the thalamus. CsA moderately prolonged animal survival to 3 days after reperfusion and reduced brain damage to grade 2 in the cortical areas and the thalamus. Hypothermia further increased animal survival to at least 6 days after reperfusion and reduced brain damage to 30% in the caudoputamen, to close to zero in the CA3, CA4, and dentate gyrus, and to grade 1-2 in the cortical areas and the thalamus. The combination of hypothermia and CsA did not give additional protection.

Fatty acid-induced apoptosis in neonatal cardiomyocytes: redox signaling

Exposure of neonatal rat cardiac myocytes to palmitate and glucose produces apoptosis as seen by cytochrome c release, caspase 3-like activation, DNA laddering, and poly(ADP-ribose) polymerase cleavage. The purpose of this study was to understand the role of reactive oxygen species in the initiation of programmed cell death by palmitate. We found that palmitate (but not oleate) produces inhibition of carnitine palmitoyltransferase I, accumulation of ceramide, and inhibition of electron transport complex III. These events are subsequent to cytochrome c release and loss of the mitochondrial membrane potential. No differences in H2O2 production or N-terminal c-Jun kinase phosphorylation were detected between myocytes incubated in palmitate and control myocytes (nonapoptotic) incubated in oleate. These results suggest that the palmitate-induced loss of the mitochondrial membrane potential is not associated with H2O2 synthesis and that a membrane potential is required to generate reactive oxygen species following ceramide inhibition of complex III.

The multidrug resistance protein MRP1 mediates the release of glutathione disulfide from rat astrocytes during oxidative stress

The release of glutathione disulfide has been considered an important process for the maintenance of a reduced thiol redox potential in cells during oxidative stress. In cultured rat astrocytes, permanent hydrogen peroxide-induced oxidative stress caused a rapid increase in intracellular glutathione disulfide, which was followed by the appearance of glutathione disulfide in the medium. Under these conditions, the viability of the cells was not compromised. In the presence of cyclosporin A and the quinoline-derivative MK571, inhibitors of multidrug resistance proteins (MRP1 and MRP2), glutathione disulfide accumulated in cells and the release of glutathione disulfide from astrocytes during H2O2 stress was potently inhibited, suggesting a contribution of MRP1 or MRP2 in the release of glutathione disulfide from astrocytes. Using RT-PCR we amplified a cDNA from astroglial RNA with a high degree of homology to MRP1 from humans and mouse. In contrast, no fragment was amplified by using primers specific for rat MRP2. In addition, the presence of MRP1 protein in astrocytes was demonstrated by its immunolocalization in cells expressing the astroglial marker protein glial fibrillary acidic protein. Our data identify rat astrocytes as a MRP1-expressin, brain cell type and demonstrate that this transporter participates in the release of glutathione disulfide from astrocytes during oxidative stress.

Cytochrome c release, mitochondrial membrane depolarization, caspase-3 activation, and Bax-alpha cleavage during IFN-alpha-induced apoptosis in Daudi B lymphoma cells

Interferon-alpha (IFN-alpha) displays antitumor action by inducing direct cytotoxicity against tumor cells in addition to generation of cytotoxic cells. The IFN-alpha-induced direct cytotoxicity is at least partly due to induction of apoptosis. In the present study, we examined signaling pathways implicated in IFN-alpha-induced apoptosis in Daudi cells. Release of cytochrome c from mitochondria to cytosol was found after 12 h incubation with IFN-alpha, followed by a decline in mitochondrial membrane potential (Delta psi(m)) and procaspase-3 activation at 24 and 36 h, respectively. Cleavage of endogenous Bax-alpha (21 kDa), generating an 18-kDa fragment (p18 Bax-alpha), was found at 36 h. Although the endogenous p21 Bax-alpha was located in both cytosol and mitochondrial membranes, the p18 Bax-alpha resided only on mitochondrial membranes. IFN-alpha-induced apoptosis occurred 48 h after stimulation, with a further increase in proportion up to 72 h. Pretreatment with pancaspase inhibitor Z-VAD-fmk substantially inhibited the IFN-alpha-mediated Bax-alpha cleavage and apoptosis, but not the decline in Delta psi(m), suggesting the possibility that caspase-3 activation is implicated in the Bax-alpha cleavage, probably leading to amplification of the apoptotic processes. Our results suggest that modulation of endogenous p21 Bax-alpha is implicated in IFN-alpha-induced apoptosis.

Anaerobic and aerobic pathways for salvage of proximal tubules from hypoxia-induced mitochondrial injury

We have further examined the mechanisms for a severe mitochondrial energetic deficit, deenergization, and impaired respiration in complex I that develop in kidney proximal tubules during hypoxia-reoxygenation, and their prevention and reversal by supplementation with alpha-ketoglutarate (alpha-KG) + aspartate. The abnormalities preceded the mitochondrial permeability transition and cytochrome c loss. Anaerobic metabolism of alpha-KG + aspartate generated ATP and maintained mitochondrial membrane potential. Other citric-acid cycle intermediates that can promote anaerobic metabolism (malate and fumarate) were also effective singly or in combination with alpha-KG. Succinate, the end product of these anaerobic pathways that can bypass complex I, was not protective when provided only during hypoxia. However, during reoxygenation, succinate also rescued the tubules, and its benefit, like that of alpha-KG + malate, persisted after the extra substrate was withdrawn. Thus proximal tubules can be salvaged from hypoxia-reoxygenation mitochondrial injury by both anaerobic metabolism of citric-acid cycle intermediates and aerobic metabolism of succinate. These results bear on the understanding of a fundamental mode of mitochondrial dysfunction during tubule injury and on strategies to prevent and reverse it.

A metabolic role for mitochondria in palmitate-induced cardiac myocyte apoptosis

After cardiac ischemia, long-chain fatty acids, such as palmitate, increase in plasma and heart. Palmitate has previously been shown to cause apoptosis in cardiac myocytes. Cultured neonatal rat cardiac myocytes were studied to assess mitochondrial alterations during apoptosis. Phosphatidylserine translocation and caspase 3-like activity confirmed the apoptotic action of palmitate. Cytosolic cytochrome c was detected at 8 h and plateaued at 12 h. The mitochondrial membrane potential (DeltaPsi) in tetramethylrhodamine ethyl ester-loaded cardiac myocytes decreased significantly in individual mitochondria by 8 h. This loss was heterogeneous, with a few energized mitochondria per myocyte remaining at 24 h. Total ATP levels remained high at 16 h. The DeltaPsi loss was delayed by cyclosporin A, a mitochondrial permeability transition inhibitor. Mitochondrial swelling accompanied changes in DeltaPsi. Carnitine palmitoyltransferase I activity fell at 16 h; this decline was accompanied by ceramide increases that paralleled decreased complex III activity. We conclude that carnitine palmitoyltransferase I inhibition, ceramide accumulation, and complex III inhibition are downstream events in cardiac apoptosis mediated by palmitate and occur independent of events leading to caspase 3-like activation.

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.

Bcl-2 prevents mitochondrial permeability transition and cytochrome c release via maintenance of reduced pyridine nucleotides

Digitonin-permeabilized PC12 and GT1-7 neural cells exhibited a cyclosporin A-sensitive decrease in mitochondrial membrane potential, increased volume, and release of the pro-apoptotic factor cytochrome c in the presence of Ca2+ and the mitochondrial permeability transition (MPT) inducers t-butyl hydroperoxide (t-bOOH) or phenylarsine oxide (PhAsO). Although the concentration of PhAsO required to induce the MPT was similar for Bcl-2 negative and Bcl-2 overexpressing transfected cells (Bcl-2(+)), the level of t-bOOH necessary for triggering the MPT was much higher for Bcl-2(+) cells. A higher concentration of t-bOOH was also necessary for promoting the oxidation of mitochondrial pyridine nucleotides in Bcl-2(+) cells. The sensitivity of Bcl-2(- ) cell mitochondria to t-bOOH but not PhAsO could be overcome by the use of conditions that protect the pyridine nucleotides against oxidation. We conclude that the increased ability of Bcl-2(+) cells to maintain mitochondrial pyridine nucleotides in a reduced redox state is a sufficient explanation for their resistance to MPT under conditions of oxidative stress induced by Ca2+ plus t-bOOH.

Cyclosporin A enhances survival, ameliorates brain damage, and prevents secondary mitochondrial dysfunction after a 30-minute period of transient cerebral ischemia

Cyclosporin A (CsA) has been shown to be efficacious in protecting against ischemic injury after short periods (5 to 10 min) of forebrain ischemia. The present experiments were undertaken to study if a long period of forebrain ischemia (30 min), induced at a brain temperature of 37 degrees C, is compatible with survival and if the brain damage incurred can be ameliorated by CsA. The results showed that animals subjected to 30 min of forebrain ischemia at a brain temperature of 37 degrees C failed to survive after the first 24 h of recovery and showed extensive neuronal necrosis in all selectively vulnerable regions after 1 day of survival. CsA, when injected in combination with an intracerebral lesion to open the blood-brain barrier, markedly prolonged the survival time. CsA-injected animals also showed amelioration of histological lesions, an effect that was sustained for at least 4 days. Experiments with mitochondria isolated from the neocortex and hippocampus showed that state 3 respiratory rates decreased during ischemia, recovered after 1 and 3 h of recirculation, and then showed a secondary decline at 6 h. Administration of CsA prevented this secondary decline. Measurements of neocortical cerebral blood flow showed that there was no secondary hypoperfusion prior to secondary mitochondrial dysfunction, implying that changes in blood flow may not be responsible for the rapidly developing, secondary brain damage. The results thus demonstrate that if brain temperature is upheld at 37 degrees C, a 30-min period of ischemia is not compatible with survival after the first day of recovery, and gross histopathological damage develops within that period. CsA was efficacious in prolonging animal survival, ameliorating brain damage, and preventing the secondary mitochondrial dysfunction. Since CsA blocks the mitochondrial permeability transition pore its action may, at least in part, be on mitochondrial integrity and function.

In vivo control of respiration by cytochrome c oxidase in human cells

The metabolic control of oxidative phosphorylation (OXPHOS) has attracted increasing attention in recent years, especially due to its importance for understanding the role of mitochondrial DNA mutations in human diseases and aging. Experiments on isolated mitochondria have indicated that a relatively small fraction of each of several components of the electron transport chain is sufficient to sustain a normal respiration rate. These experiments, however, may have not reflected the in vivo situation, due to the possible loss of essential metabolites during organelle isolation and the disruption of the normal interactions of mitochondria with the cytoskeleton, which may be important for the channeling of respiratory substrate to the organelles. To obtain direct evidence on this question, in particular, as concerns the in vivo control of respiration by cytochrome c oxidase (COX), we have developed an approach for measuring COX activity in intact cells, by means of cyanide titration, either as an isolated step or as a respiratory chain-integrated step. The method has been applied to a variety of human cell types, including wild-type and mtDNA mutation-carrying cells, several tumor-derived semidifferentiated cell lines, as well as specialized cells removed from the organism. The results obtained strongly support the following conclusions: (i) the in vivo control of respiration by COX is much tighter than has been generally assumed on the basis of experiments carried out on isolated mitochondria; (ii) COX thresholds depend on the respiratory fluxes under which they are measured; and (iii) measurements of relative enzyme capacities are needed for understanding the role of mitochondrial respiratory complexes in human physiopathology.

Aging enhances the activation of the permeability transition pore in mitochondria

Aging is associated with mitochondrial dysfunction in several tissues. However, it is not known how the observed mitochondrial dysfunction is related to aging-associated tissue degeneration. We have shown previously that the activation of the permeability transition pore (PTP), which is believed to play a critical role in cell necrosis and apoptosis, is enhanced in spleen lymphocytes from old mice. Here we show that the threshold for calcium-induced, cyclosporin-sensitive, calcium release was significantly lower in isolated brain and liver mitochondria from aging mice. Thus, aging mice exhibit enhanced PTP activation in lymphocytes, brain, and liver. These results suggest that aging increases the susceptibility to calcium-dependent cell death (e.g., excitotoxicity, ischemia-reperfusion damage) in the brain, liver, and possibly other tissues. In addition, other pathways to apoptosis or necrosis that depend on PTP activation are also likely to be enhanced by aging.

The internal structure of mitochondria

Electron microscopic (EM) tomography is providing important new insights into the internal organization of mitochondria. The standard baffle model for cristae structure, called into question years ago, has now clearly been shown to be inaccurate. Depending on source and conformational state, cristae can vary from simple tubular structures to more complex lamellar structures merging with the inner boundary membrane through tubular structures 28 nm in diameter. The structural information provided by EM tomography has important implications for mitochondrial bioenergetics, biogenesis and the role of mitochondria in apoptosis. The structural paradigm defined by EM tomography is helping in the design of new experimental approaches to mitochondrial function.

Flufenamic acid as an inducer of mitochondrial permeability transition

To assess the mechanism by which mitochondrial permeability transition (MPT) is induced by the nonpolar carboxylic acids, we investigated the effects of flufenamic acid (3'-trifluoromethyl diphenylamine-2-carboxylic acid, FA) on mitochondrial respiration, electrical transmembrane potential difference (delta psi), osmotic swelling, Ca2+ efflux, NAD(P)H oxidation and reactive oxygen species (ROS) generation. Succinate-energized isolated rat liver mitochondria incubated in the absence or presence of 10 microM Ca2+, 5 microM ruthenium red (RR) or 1 microM cyclosporin A (CsA) were used. The dose response-curves for both respiration release and delta psi dissipation were nearly linear, presenting an IC50 of approximately 10 microM and reaching saturation within 25-50 microM, indicating that FA causes mitochondrial uncoupling by a protonophoric mechanism. Within this same concentration range FA showed the ability to induce MPT in energized mitochondria incubated with 10 microM Ca2+, followed by delta psi dissipation and Ca2+ efflux, and even in deenergized mitochondria incubated with 0.5 mM Ca2+. ADP, Mg2+, trifluoperazine (TFP) and N-ethylmaleimide (NEM) reduced the extent of FA-promoted swelling in energized mitochondria by approximately one half, whereas dithiothreitol (DTT) slightly enhanced it. NAD(P)H oxidation and ROS generation (H2O2 production) by mitochondria were markedly stimulated by FA; these responses were partly prevented by CsA, suggesting that they may be implicated as both a cause and effect of FA-induced MPT. FA incubated with mitochondria under swelling assay conditions caused a decrease of approximately 40% in the content of protein thiol groups reacting with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). The present results are consistent with a ROS-intermediated sensitization of MPT by a direct or indirect FA interaction with inner mitochondrial membrane at a site which is in equilibrium with the NAD(P)H pool, namely thiol groups of integral membrane proteins.

[(3)H]-trimetazidine mitochondrial binding sites: regulation by cations, effect of trimetazidine derivatives and other agents and interaction with an endogenous substance

Trimetazidine, an antiischaemic drug, has been shown to restore impaired mitochondrial functions. Specific binding sites for [(3)H]-trimetazidine have been previously detected in liver mitochondria. In the present study we confirm this observation and provide additional evidence for the involvement of these sites in the pharmacological effects of the drug. Inhibition experiments using a series of trimetazidine derivatives revealed the presence of three classes of binding sites. An N-benzyl substituted analogue of trimetazidine exhibited a very high affinity (K(i)=7 nM) for one of these classes of sites. Compounds from different pharmacological classes were evaluated for their ability to inhibit [(3)H]-trimetazidine binding. Among the drugs tested pentazocine, ifenprodil, opipramol, perphenazine, haloperidol, and to a lower extent prenylamine, carbetapentane and dextromethorphan competed with high affinity, suggesting a similarity of high affinity [(3)H]-trimetazidine sites with sigma receptors. [(3)H]-Trimetazidine binding was modulated by pH. Neutral trimetazidine had about 10 fold higher affinity than protonated trimetazidine for its mitochondrial binding sites. Various cations also affected [(3)H]-trimetazidine binding. Ca(2+) was the most potent inhibitor and totally suppressed the binding of [(3)H]-trimetazidine to the sites of medium affinity. An endogenous cytosolic ligand was able to displace [(3)H]-trimetazidine from its binding sites. Its activity was not affected by boiling for 15 min, suggesting a non-protein compound. These data suggest that mitochondrial [(3)H]-trimetazidine binding sites could have a physiological relevance and be involved in the antiischaemic effects of the drug.

Cytokines induce both necrosis and apoptosis via a common Bcl-2-inhibitable pathway in rat insulin-producing cells

The presence of activated macrophages within pancreatic islets in insulin-dependent diabetes mellitus suggests an involvement of beta-cell death by necrosis. The aim of this study was to investigate the frequencies and mechanisms of cytokine-induced beta-cell apoptosis and necrosis and the possible protection mediated by the antiapoptotic gene bcl-2. A combination of interleukin-1beta, interferon-gamma, and tumor necrosis factor-alpha increased both necrosis (17% of cells) and apoptosis (5% of cells) in isolated whole rat islets, as determined by vital staining and fluorescence microscopy. Hyperexpression of Bcl-2, achieved by stable transfection using a multicopy viral vector containing a bcl-2 complementary DNA in rat insulin-producing RINm5F cells, counteracted both apoptosis and necrosis. Cytokine-induced cleavage of the caspase-3 substrate poly(ADP-ribose) polymerase (which, in other cell types, may occur downstream or independently of a Bcl-2-preventable mitochondrial permeability transition) was observed in control- but neither in bcl-2-transfected cells nor in the presence of the iNOS inhibitor N(G)-methyl-L-arginine. Tumor necrosis factor-alpha alone did not clearly induce cell death or poly(ADP-ribose) polymerase-cleavage. These findings suggest that cytokines induce both necrosis and apoptosis in insulin-producing cells via a common Bcl-2-preventable nitric oxide-dependent pathway, which may involve mitochondrial permeability transition. The necrosis:apoptosis ratio might be increased by a relative lack of caspase activity.

Ethanol potentiates tumor necrosis factor-alpha cytotoxicity in hepatoma cells and primary rat hepatocytes by promoting induction of the mitochondrial permeability transition

In the present study, tumor necrosis factor-alpha (TNF-alpha) cytotoxicity is shown to be potentiated by ethanol exposure in vitro in the human hepatoma cell line, HepG2, and in rat primary hepatocytes. Exposure of HepG2 cells and primary hepatocytes for 48 hours to concentrations of ethanol ranging between 50 and 100 mmol/L significantly increased TNF-alpha cytotoxicity compared with cells treated with TNF-alpha alone. The cell killing was associated with, and dependent on, the development of the mitochondrial permeability transition (MPT). Two inhibitors of MPT pore opening, cyclosporin A and bongkrekic acid, prevented TNF-alpha cytotoxicity in the presence of ethanol. In addition to inhibiting cell death caused by TNF-alpha, blockade of MPT pore opening prevented mitochondrial depolarization, cytochrome c redistribution from the mitochondria to the cytosol, caspase 3 activation, and oligonucleosomal DNA fragmentation. Unlike the potentiation of TNF-alpha cytotoxicity by the translational inhibitor cycloheximide, ethanol promoted TNF-alpha-induced cell killing by a mechanism that was independent of caspase-8 activity. HepG2 cells overexpressing cytochrome-P4502E1 were even more sensitized by ethanol to induction of the MPT by TNF-alpha and the resultant cytotoxicity than wild-type HepG2 cells. In addition, primary hepatocytes isolated from chronically ethanol-fed rats showed enhanced susceptibility to TNF-alpha cytotoxicity compared with their isocalorically matched controls. Again as with the HepG2 cells, inhibiting MPT pore opening prevented the cytotoxicity of TNF-alpha in the primary hepatocytes isolated from ethanol-fed animals.

Does the plant mitochondrion integrate cellular stress and regulate programmed cell death?

Research on programmed cell death in plants is providing insight into the primordial mechanism of programmed cell death in all eukaryotes. Much of the attention in studies on animal programmed cell death has focused on determining the importance of signal proteases termed caspases. However, it has recently been shown that cell death can still occur even when the caspase cascade is blocked, revealing that there is an underlying oncotic default pathway. Many programmed plant cell deaths also appear to be oncotic. Shared features of plant and animal programmed cell death can be used to deduce the primordial components of eukaryotic programmed cell death. From this perspective, we must ask whether the mitochondrion is a common factor that can serve in plant and animal cell death as a stress sensor and as a dispatcher of programmed cell death.

Hypothetical pathophysiology of acute encephalopathy and encephalitis related to influenza virus infection and hypothermia therapy

BACKGROUND

To establish a treatment strategy for acute encephalopathy and encephalitis associated with influenza virus infection, the pathophysiology of the disease was investigated through manifestations and laboratory findings of patients.

PATIENTS AND METHODS

A child with central nervous system (CNS) complications during the course of influenza virus infection was analyzed in view of immunologic abnormalities. In addition, four children with acute encephalopathy and encephalitis were enrolled in the hypothermia treatment for the purpose of stabilizing the cytokine storm in the CNS.

RESULTS

The CNS symptoms preceded the systemic progression to the failure of multiple organs (MOF) and disseminated intravascular coagulopathy (DIC). The mild hypothermia suppressed the brain edema on computed tomography (CT) scanning and protected the brain from the subsequent irreversible neural cell damage.

CONCLUSION

The replicated viruses at the nasopharyngeal epithelium may disrupt the olfactory mucosa and gain access to the brain via the olfactory nerve system. The direct virus-glial cell interaction or viral stimulation of the glial cells induces the production and accumulation of the pro-inflammatory cytokines, especially tumor necrosis factor (TNF)-alpha, in the CNS. The cytokine storm results in neural cell damage as well as the apoptosis of astrocytes, due to the TNF-alpha-induced mitochondrial respiratory failure. The disruption of the blood-brain barrier progresses to the systemic cytokine storm, resulting in DIC and MOF. Mild hypothermia appears promising in stabilizing the immune activation and the brain edema to protect the brain from ongoing functional, apoptotic neural and glial damage and the systemic expansion of the cytokine storm.

Interaction among mitochondria, mitogen-activated protein kinases, and nuclear factor-kappaB in cellular models of Parkinson's disease

Oxidative stress induced by acute complex I inhibition with 1-methyl-4-phenylpyridinium ion activated biphasically the stress-activated c-Jun N-terminal kinase (JNK) and the early transcription factor nuclear factor-kappaB (NF-kappaB) in SH-SY5Y neuroblastoma cells. Early JNK activation was dependent on mitochondrial adenine nucleotide translocator (ANT) activity, whereas late-phase JNK activation and the cleavage of signaling proteins Raf-1 and mitogen-activated protein kinase (MAPK) kinase (MEK) kinase (MEKK)-1 appeared to be ANT-independent. Early NF-kappaB activation depended on MEK, later activation required an intact electron transport chain (ETC), and Parkinson's disease (PD) cybrid (mitochondrial transgenic cytoplasmic hybrid) cells had increased basal NF-kappaB activation. Mitochondria appear capable of signaling ETC impairment through MAPK modules and inducing protective NF-kappaB responses, which are increased by PD mitochondrial genes amplified in cybrid cells. Irreversible commitment to apoptosis in this cell model may derive from loss of Raf-1 and cleavage/activation of MEKK-1, processes reported in other models to be caspase-mediated. Therapeutic strategies that reduce mitochondrial activation of proapoptotic MAPK modules, i.e., JNK, and enhance survival pathways, i.e., NF-kappaB, may offer neuroprotection in this debilitating disease.

Mitochondrial calcium signaling driven by the IP3 receptor

Many agonists bring about their effects on cellular functions through a rise in cytosolic [Ca2+] ([Ca2+]c) mediated by the second messenger inositol 1,4,5-trisphosphate (IP3). Imaging studies of single cells have demonstrated that [Ca2+]c signals display cell specific spatiotemporal organization that is established by coordinated activation of IP3 receptor Ca2+ channels. Evidence emerges that cytosolic calcium signals elicited by activation of the IP3 receptors are efficiently transmitted to the mitochondria. An important function of mitochondrial calcium signals is to activate the Ca2+-sensitive mitochondrial dehydrogenases, and thereby to meet demands for increased energy in stimulated cells. Activation of the permeability transition pore (PTP) by mitochondrial calcium signals may also be involved in the control of cell death. Furthermore, mitochondrial Ca2+ transport appears to modulate the spatiotemporal organization of [Ca2+]c responses evoked by IP3 and so mitochondria may be important in cytosolic calcium signaling as well. This paper summarizes recent research to elucidate the mechanisms and significance of IP3-dependent mitochondrial calcium signaling.

The local control of cytosolic Ca2+ as a propagator of CNS communication--integration of mitochondrial transport mechanisms and cellular responses

Ca2+ signals propagate in wave form along individual cells of the central nervous system (CNS) and through networks of connected cells of neuronal and multiple glial cell types. In order for wave fronts to convey information, signaling mechanisms are required that allow waves to propagate reproducibly and without decrement in signal strength over long distances. CNS Ca2+ waves are under specific integrated local control, made possible by interactions at local subcellular microdomains between endoplasmic reticulum and mitochondria. Active mitochondria located near the mouth of inositol trisphosphate receptor (InsP3R) channel clusters in glia take up Ca2+, which may prevent a buildup of Ca2+ around the InsP3R channel, thereby decreasing the rate of Ca2+-induced receptor inactivation, and prolonging channel open time. Mitochondria may amplify InsP3-dependent Ca2+ signals by a transient permeability transition in response to Ca2+ uptake into the mitochondrion. Other evidence suggests privileged access into mitochondria for Ca2+ entering neurons by glutamatergic receptor channels. This enables specific signal modulation as the Ca2+ wave is propagated into neurons, such that mitochondria located close to glutamate channels can prolong the neuronal cytosolic response time by successive uptake and release of Ca2+. Disruption of mitochondrial function deregulates the ability of CNS-derived cells to undergo normal Ca2+ signaling and wave propagation.

Programmed cell death in 2',3'-dideoxycytidine-resistant human monoblastoid U937 cells

2',3'-Dideoxycytidine is a powerful in vitro inhibitor of human immunodeficiency virus and is currently used in the treatment of acquired immunodeficiency syndrome. A long-term exposure of U937 monoblastoid cells to dideoxycytidine induces the selection of drug-resistant cells (U937-R). In previous studies, we investigated some important biochemical properties and functional activities, such as basal respiration, protein kinase C activity, superoxide anion release, and the level of reduced glutathione, which were found to be higher in the drug-resistant cell line, compared to the parental one. In the present study, we evaluated the response of the two cell lines to the induction of apoptosis by treatment with staurosporine and okadaic acid, which interfere with the protein kinase and phosphatase pathways, respectively. Moreover, knowing that GSH plays a crucial role in the regulation of nitric oxide-dependent apoptosis, U937-R and parental lines have been treated with SIN-1, which is known to generate significant amounts of O2 and nitric oxide. Resistant and parental cells have been analysed by light and electron microscopy and agarose gel electrophoresis of isolated DNA has been performed. The obtained results demonstrate a different susceptibility of U937-R cell line to apoptosis induced with the three triggers. U937-R cells show more advanced apoptotic features if compared with parental cells, after staurosporine treatment. Differently, the okadaic acid does not induce a different behaviour in the two models. On the contrary, the agent SIN-1 determines an increased number of apoptotic cells in the U937 line. The results suggest that a higher level of protein kinase C and glutathione could prevent programmed cell death in U937-R.

Alternative mitochondrial functions in cell physiopathology: beyond ATP production

It is well known that mitochondria are the main site for ATP generation within most tissues. However, mitochondria also participate in a surprising number of alternative activities, including intracellular Ca2+ regulation, thermogenesis and the control of apoptosis. In addition, mitochondria are the main cellular generators of reactive oxygen species, and may trigger necrotic cell death under conditions of oxidative stress. This review concentrates on these alternative mitochondrial functions, and their role in cell physiopathology.

Effect of the oxidative stress induced by adriamycin on rat hepatocyte bioenergetics during ageing

We have investigated the effect of ageing and of adriamycin treatment on the bioenergetics of isolated rat hepatocytes. Ageing per se, whilst being associated with a striking increase of hydrogen peroxide in the cells, induces only minor changes on mitochondrial functions. The adriamycin treatment induces a decrease of the mitochondrial membrane potential in situ and a consistent increase of the superoxide anion cellular content independently of the donor's age, whilst the hydrogen peroxide is significantly higher in aged than in adult rat hepatocytes. Kinetic studies in isolated mitochondria show that the mitochondrial respiratory chain activity (NADH --> O2) of 50 microM adriamycin-treated hepatocytes is lowered both in adult and aged rats. The same adriamycin concentration induces a slight decrease of the maximal rate of ATP hydrolysis in both young and aged rats, without affecting the Km for the substrate. However, at drug concentrations lower than 50 microM, both ATPase and NADH oxidation activities decrease significantly in aged rats only. The results suggest that free radicals increase during ageing in rat hepatocytes but are unable to induce major modifications of mitochondrial bioenergetics. This contrasts with the damaging effect of adriamycin, suggesting that some effects of the drug may be due to other reasons besides oxidative stress.

Isolation, purification, and characterization of a rat liver mitochondrial protein disulfide isomerase

The isolation and purification to electrophoretical homogeneity and characterization of a protein disulfide isomerase from rat liver mitochondria is reported. The purified enzyme exhibits a single band on sodium dodecylsulfatepolyacrylamide gel electrophoresis with an apparent molecular weight of approximately 54 kDa. Comparatively, the microsomal form shows an apparent molecular weight of 57 kDa indicating that the two forms are slightly different. The antibody raised against the microsomal isoform does not recognize the mitochondrial enzyme. To characterize the enzyme, different classical methodologies utilized for protein disulfide isomerase estimation have been adopted. The isolated enzyme is active with all of them, indicating that it comprises all the features of a typical protein disulfide isomerase. At the mitochondrial level the enzyme appears mostly localized at the membrane level. Its potential involvement in mitochondrial membrane permeability control is also discussed.

Oxidative stress and adenine nucleotide control of mitochondrial permeability transition

Mitochondria can initiate apoptosis by releasing cytochrome c after undergoing a calcium-dependent permeability transition (MPT). Although the MPT is enhanced by oxidative stress and prevented by adenine nucleotides such as adenosine 5'-diphosphate (ADP), the hypothesis has not been tested that oxidants regulate the effects of exogenous adenine nucleotides on the MPT and cytochrome c release. We found that cytochrome c release from intact rat liver mitochondria depended strictly on pore opening and not on membrane potential, and that MPT-enhancing oxidative stress also augmented cytochrome c release. At low oxidative stress, micromolar (ADP) and low adenosine 5'-triphosphate (ATP)/ADP ratio inhibited the MPT and cytochrome c release, whereas ATP or high ATP/ADP had only a slight effect. In freshly isolated mitochondria, the time to half-maximal MPT was related to the log of the ATP/ADP ratio. This function was shifted to shorter times by oxidative stress which decreased ADP protection and caused ATP to accelerate the calcium-dependent MPT. By comparison, mitochondria treated with reducing agents and those isolated from septic rats were protected from the MPT by both nucleotides. These results indicate that oxidation-sensitive site(s) in the membrane regulate the effects of adenine nucleotides on the MPT. The oxidant-based differences in the effects of ADP and ATP on the pore support the novel hypothesis that failure of the cell to consume ATP and provide adequate ADP at the adenine nucleotide transporter during oxidative stress predisposes to cytochrome c release and initiation of apoptosis.

The pro-apoptotic proteins, Bid and Bax, cause a limited permeabilization of the mitochondrial outer membrane that is enhanced by cytosol

During apoptosis, an important pathway leading to caspase activation involves the release of cytochrome c from the intermembrane space of mitochondria. Using a cell-free system based on Xenopus egg extracts, we examined changes in the outer mitochondrial membrane accompanying cytochrome c efflux. The pro-apoptotic proteins, Bid and Bax, as well as factors present in Xenopus egg cytosol, each induced cytochrome c release when incubated with isolated mitochondria. These factors caused a permeabilization of the outer membrane that allowed the corelease of multiple intermembrane space proteins: cytochrome c, adenylate kinase and sulfite oxidase. The efflux process is thus nonspecific. None of the cytochrome c-releasing factors caused detectable mitochondrial swelling, arguing that matrix swelling is not required for outer membrane permeability in this system. Bid and Bax caused complete release of cytochrome c but only a limited permeabilization of the outer membrane, as measured by the accessibility of inner membrane-associated respiratory complexes III and IV to exogenously added cytochrome c. However, outer membrane permeability was strikingly increased by a macromolecular cytosolic factor, termed PEF (permeability enhancing factor). We hypothesize that PEF activity could help determine whether cells can recover from mitochondrial cytochrome c release.

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.

Cyclosporin A attenuates acute mitochondrial dysfunction following traumatic brain injury

Experimental traumatic brain injury (TBI) results in a rapid and significant necrosis of cortical tissue at the site of injury. In the ensuring hours and days, secondary injury exacerbates the primary damage, resulting in significant neurological dysfunction. Recent reports from our lab and others have demonstrated that the immunosuppressant cyclosporin A (CsA) is neuroprotective following TBI. The opening of the mitochondrial permeability transition pore (MPTP) is inhibited by CsA, thereby maintaining the mitochondrial membrane potential and calcium homeostasis in isolated mitochondrial. In the present study we utilized a unilateral controlled cortical impact model of TBI to assess mitochondrial dysfunction in both isolated mitochondria and synaptosomes to elucidate the neuroprotective role of CsA. The results demonstrate that administration of CsA 15 min postinjury significantly attenuates mitochondrial dysfunction as measured using several biochemical assays of mitochondria integrity and energetics. Following TBI, mitochondria isolated from the injured cortex of animals treated with CsA demonstrate a significant increase in mitochondria membrane potential and are resistant to the induction of mitochondrial permeability transition compared to vehicle-treated animals. Similarly, synaptosomes isolated from CsA-treated animals demonstrate a significant increase in mitochondria membrane potential, accompanied by lower levels of intramitochondrial Ca2+ and reactive oxygen species production than seen in vehicle-treated animals. These results suggest that the neuroprotective properties of CsA are mediated through modulation of the MPTP and maintenance of mitochondria homeostasis. Amelioration of cortical damage with CsA indicates that pharmacological therapies can be devised which will significantly alter neurological outcome after injury.

Mitochondrial transport of cations: channels, exchangers, and permeability transition

This review provides a selective history of how studies of mitochondrial cation transport (K+, Na+, Ca2+) developed in relation to the major themes of research in bioenergetics. It then covers in some detail specific transport pathways for these cations, and it introduces and discusses open problems about their nature and physiological function, particularly in relation to volume regulation and Ca2+ homeostasis. The review should provide the basic elements needed to understand both earlier mitochondrial literature and current problems associated with mitochondrial transport of cations and hopefully will foster new interest in the molecular definition of mitochondrial cation channels and exchangers as well as their roles in cell physiology.