The mitochondrial permeability transition mediates both necrotic and apoptotic death of hepatocytes exposed to Br-A23187

Mitostasis, Calcium and Free Radicals in Health, Aging and Neurodegeneration

Mitochondria play key roles in ATP supply, calcium homeostasis, redox balance control and apoptosis, which in neurons are fundamental for neurotransmission and to allow synaptic plasticity. Their functional integrity is maintained by mitostasis, a process that involves mitochondrial transport, anchoring, fusion and fission processes regulated by different signaling pathways but mainly by the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). PGC-1α also favors Ca²⁺ homeostasis, reduces oxidative stress, modulates inflammatory processes and mobilizes mitochondria to where they are needed. To achieve their functions, mitochondria are tightly connected to the endoplasmic reticulum (ER) through specialized structures of the ER termed mitochondria-associated membranes (MAMs), which facilitate the communication between these two organelles mainly to aim Ca²⁺ buffering. Alterations in mitochondrial activity enhance reactive oxygen species (ROS) production, disturbing the physiological metabolism and causing cell damage. Furthermore, cytosolic Ca²⁺ overload results in an increase in mitochondrial Ca²⁺, resulting in mitochondrial dysfunction and the induction of mitochondrial permeability transition pore (mPTP) opening, leading to mitochondrial swelling and cell death through apoptosis as demonstrated in several neuropathologies. In summary, mitochondrial homeostasis is critical to maintain neuronal function; in fact, their regulation aims to improve neuronal viability and to protect against aging and neurodegenerative diseases.

Mitophagy in Cerebral Ischemia and Ischemia/Reperfusion Injury

Ischemic stroke is a severe cerebrovascular disease with high mortality and morbidity. In recent years, reperfusion treatments based on thrombolytic and thrombectomy are major managements for ischemic stroke patients, and the recanalization time window has been extended to over 24 h. However, with the extension of the time window, the risk of ischemia/reperfusion (I/R) injury following reperfusion therapy becomes a big challenge for patient outcomes. I/R injury leads to neuronal death due to the imbalance in metabolic supply and demand, which is usually related to mitochondrial dysfunction. Mitophagy is a type of selective autophagy referring to the process of specific autophagic elimination of damaged or dysfunctional mitochondria to prevent the generation of excessive reactive oxygen species (ROS) and the subsequent cell death. Recent advances have implicated the protective role of mitophagy in cerebral ischemia is mainly associated with its neuroprotective effects in I/R injury. This review discusses the involvement of mitochondria dynamics and mitophagy in the pathophysiology of ischemic stroke and I/R injury in particular, focusing on the therapeutic potential of mitophagy regulation and the possibility of using mitophagy-related interventions as an adjunctive approach for neuroprotective time window extension after ischemic stroke.

Cell death due to electroporation - A review

Exposure of cells to high voltage electric pulses increases transiently membrane permeability through membrane electroporation. Electroporation can be reversible and is used in gene transfer and enhanced drug delivery but can also lead to cell death. Electroporation resulting in cell death (termed as irreversible electroporation) has been successfully used as a new non-thermal ablation method of soft tissue such as tumours or arrhythmogenic heart tissue. Even though the mechanisms of cell death can influence the outcome of electroporation-based treatments due to use of different electric pulse parameters and conditions, these are not elucidated yet. We review the mechanisms of cell death after electroporation reported in literature, cell injuries that may lead to cell death after electroporation and membrane repair mechanisms involved. The knowledge of membrane repair and cell death mechanisms after cell exposure to electric pulses, targets of electric field in cells need to be identified to optimize existing and develop of new electroporation-based techniques used in medicine, biotechnology, and food technology.

SEC24A facilitates colocalization and Ca2 + flux between the endoplasmic reticulum and mitochondria

A genome-wide screen recently identified SEC24A as a novel mediator of thapsigargin-induced cell death in HAP1 cells. Here, we determined the cellular mechanism and specificity of SEC24A-mediated cytotoxicity. Measurement of Ca²⁺ levels using organelle-specific fluorescent indicator dyes showed that Ca²⁺ efflux from endoplasmic reticulum (ER) and influx into mitochondria were significantly impaired in SEC24A-knockout cells. Furthermore, SEC24A-knockout cells also showed ∼44% less colocalization of mitochondria and peripheral tubular ER. Knockout of SEC24A, but not its paralogs SEC24B, SEC24C or SEC24D, rescued HAP1 cells from cell death induced by three different inhibitors of sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPases (SERCA) but not from cell death induced by a topoisomerase inhibitor. Thapsigargin-treated SEC24A-knockout cells showed a ∼2.5-fold increase in autophagic flux and ∼10-fold reduction in apoptosis compared to wild-type cells. Taken together, our findings indicate that SEC24A plays a previously unrecognized role in regulating association and Ca²⁺ flux between the ER and mitochondria, thereby impacting processes dependent on mitochondrial Ca²⁺ levels, including autophagy and apoptosis.

Quercetin alleviates styrene oxide-induced cytotoxicity in cortical neurons in vitro via modulation of oxidative stress and apoptosis

Styrene 7,8-oxide (SO) is the principal metabolite of styrene, an industrial neurotoxic compound which causes various neurodegenerative disorders. The present study aimed to explore the mechanisms of SO cytotoxicity (0.5 - 4 mM) in primary cortical neurons and to evaluate the neuroprotective potential of quercetin (QUER). Our results showed that exposure to SO decreased viability of cortical neurons in a concentration-dependent manner. In the presence of QUER, cell viability was increased significantly. The neuroprotective effects of QUER were associated with the reduction of intracellular Reactive Oxygen Species (ROS), the decrease in calcium overload and the restoration of mitochondrial membrane depolarization caused by SO. Additionally, to evaluate neuronal death mechanisms triggered by SO, cells were incubated with Ac-DEVD-CHO, Calpeptin and Necrostatin-1, pharmacological inhibitors of caspase-3, calpains and necroptosis respectively. The data showed that the three inhibitors reduced cell death induced by SO and suggested the implication of apoptotic, necrotic and necroptotic pathways. However, western blot analysis showed that QUER attenuated the activation of caspase-3 but did not prevent calpain activity. Taken together, these data indicated that the cytotoxicity of SO was mediated by oxidative stress and apoptosis, necrosis and necroptosis mechanisms, while the neuroprotection provided by QUER against SO depended mainly on its anti-apoptotic activity.

Hepatoprotective Essential Oils: A Review

Objectives

Several toxins and molecules are able to damage the liver, causing the hepato-toxicity. This disorder can be protected naturally, by some essential oils obtained from different plants. In this review we are cited some of these compounds that have been tested by their hepatoprotective effect.

Methods

We reviewed 83 articles published between 1981 and 2018 in English via three databases Sciencedirect, Springer and PubMed. So, we have used the keywords Hepatoprotective effect, liver disease, plants and essential oils.

Results and conclusion

In this work, we classified the plants; contain the essential oils, in alphabetical order as a table containing the scientific, family names, information plants, the experimental assay and the results obtained from the hepatoprotective studies. We have described 27 species belonging to 12 families Lamiaceae (7 species), Asteraceae (6 species), Umbellifereae (3 species), Apiaceae (3 species) are the main families which enclose the species that was studied. The study also includes the major compounds isolated from some of these essential oils. The most of those compounds belong to terpene class essentially cineol, carvacrol and thymol. Thus, the different essential oils that have been cited in this review were shown that have an antioxidant activity.

Retinal Characterization of the Thy1-GCaMP3 Transgenic Mouse Line After Optic Nerve Transection

Purpose

GCaMP3 is a genetically encoded calcium indicator for monitoring intracellular calcium dynamics. We characterized the expression pattern and functional properties of GCaMP3 in the Thy1-GCaMP3 transgenic mouse retina.

Methods

To determine the specificity of GCaMP3 expression, Thy1-GCaMP3 (B6; CBA-Tg(Thy1-GCaMP3)6Gfng/J) retinas were processed for immunohistochemistry with anti-green fluorescent protein (anti-GFP, to enhance GCaMP3 fluorescence), anti-RBPMS (retinal ganglion cell [RGC]-specific marker), and antibodies against amacrine cell markers (ChAT, GABA, GAD67, syntaxin). Calcium imaging was used to characterize functional responses of GCaMP3-expressing (GCaMP+) cells by recording calcium transients evoked by superfusion of kainic acid (KA; 10, 50, or 100 μM). In a subset of animals, optic nerve transection (ONT) was performed 3, 5, or 7 days prior to calcium imaging.

Results

GFP immunoreactivity colocalized with RBPMS but not amacrine cell markers in both ONT and non-ONT (control) groups. Calcium transients evoked by KA were reduced after ONT (50 μM KA; ΔF/F0 [SD]; control: 1.00 [0.67], day 3: 0.50 [0.35], day 5: 0.31 [0.28], day 7: 0.35 [0.36]; P < 0.05 versus control). There was also a decrease in the number of GCaMP3+ cells after ONT (cells/mm2 [SD]; control: 2198 [453], day 3: 2224 [643], day 5: 1383 [375], day 7: 913 [178]; P < 0.05). Furthermore, the proportion of GCaMP3+ cells that responded to KA decreased after ONT (50 μM KA, 97%, 54%, 47%, and 58%; control, 3, 5, and 7 days, respectively).

Conclusions

Following ONT, functional RGC responses are lost prior to the loss of RGC somata, suggesting that anatomical markers of RGCs may underestimate the extent of RGC dysfunction.

Mitochondrial dysfunction as a mechanism of drug-induced hepatotoxicity: current understanding and future perspectives

Mitochondria are critical cellular organelles for energy generation and are now also recognized as playing important roles in cellular signaling. Their central role in energy metabolism, as well as their high abundance in hepatocytes, make them important targets for drug-induced hepatotoxicity. This review summarizes the current mechanistic understanding of the role of mitochondria in drug-induced hepatotoxicity caused by acetaminophen, diclofenac, anti-tuberculosis drugs such as rifampin and isoniazid, anti-epileptic drugs such as valproic acid and constituents of herbal supplements such as pyrrolizidine alkaloids. The utilization of circulating mitochondrial-specific biomarkers in understanding mechanisms of toxicity in humans will also be examined. In summary, it is well-established that mitochondria are central to acetaminophen-induced cell death. However, the most promising areas for clinically useful therapeutic interventions after acetaminophen toxicity may involve the promotion of adaptive responses and repair processes including mitophagy and mitochondrial biogenesis, In contrast, the limited understanding of the role of mitochondria in various aspects of hepatotoxicity by most other drugs and herbs requires more detailed mechanistic investigations in both animals and humans. Development of clinically relevant animal models and more translational studies using mechanistic biomarkers are critical for progress in this area.

Relevance for patients:This review focuses on the role of mitochondrial dysfunction in liver injury mechanisms of clinically important drugs like acetaminophen, diclofenac, rifampicin, isoniazid, amiodarone and others. A better understanding ofthe mechanisms in animal models and their translation to patients will be critical for the identification of new therapeutic targets.

The Role of BCL-2 Family Members in Acute Kidney Injury

B-cell lymphoma 2 (BCL-2) family proteins gather at the biologic cross-roads of renal cell survival: the outer mitochondrial membrane. Despite shared sequence and structural features, members of this conserved protein family constantly antagonize each other in a life-and-death battle. BCL-2 members innocently reside within renal cells until activated or de-activated by physiologic stresses caused by common nephrotoxins, transient ischemia, or acute glomerulonephritis. Recent experimental data not only illuminate the intricate mechanisms of apoptosis, the most familiar form of BCL-2-mediated cell death, but emphasizes their newfound roles in necrosis, necroptosis, membrane pore transition regulated necrosis, and other forms of acute cell demise. A major paradigm shift in non-cell death roles of the BCL-2 family has occurred. BCL-2 proteins also regulate critical daily renal cell housekeeping functions including cell metabolism, autophagy (an effective means for recycling cell components), mitochondrial morphology (organelle fission and fusion), as well as mitochondrial biogenesis. This article considers new concepts in the biochemical and structural regulation of BCL-2 proteins that contribute to membrane pore permeabilization, a universal feature of cell death. Despite these advances, persistent BCL-2 family mysteries continue to challenge cell biologists. Given their interface with many intracellular functions, it is likely that BCL-2 proteins determine cell viability under many pathologic circumstances relevant to the nephrologist and, as a consequence, represent an ideal therapeutic target.

MTI-101 treatment inducing activation of Stim1 and TRPC1 expression is a determinant of response in multiple myeloma

The emergence of drug resistance continues to be a major hurdle towards improving patient outcomes for the treatment of Multiple Myeloma. MTI-101 is a first-in-class peptidomimetic that binds a CD44/ITGA4 containing complex and triggers necrotic cell death in multiple myeloma cell lines. In this report, we show that acquisition of resistance to MTI-101 correlates with changes in expression of genes predicted to attenuate Ca²⁺ flux. Consistent with the acquired resistant genotype, MTI-101 treatment induces a rapid and robust increase in intracellular Ca²⁺ levels in the parental cells; a finding that was attenuated in the acquired drug resistant cell line. Mechanistically, we show that pharmacological inhibition of store operated channels or reduction in the expression of a component of the store operated Ca²⁺ channel, TRPC1 blocks MTI-101 induced cell death. Importantly, MTI-101 is more potent in specimens obtained from relapsed myeloma patients, suggesting that relapse may occur at a cost for increased sensitivity to Ca²⁺ overload mediated cell death. Finally, we demonstrate that MTI-101 is synergistic when combined with bortezomib, using both myeloma cell lines and primary myeloma patient specimens. Together, these data continue to support the development of this novel class of compounds for the treatment of relapsed myeloma.

Real-time analysis of the detailed sequence of cellular events in mAb-mediated complement-dependent cytotoxicity of B-cell lines and of chronic lymphocytic leukemia B-cells

Complement-dependent cytotoxicity is an important mechanism of action of certain mAbs used in cancer immunotherapy, including ofatumumab and rituximab. However, the detailed sequence of cellular changes that occur in nucleated cells attacked by mAb and complement has not been delineated. Recently developed CD20 mAbs, engineered to form hexamers on binding to cells, react with B-cells in serum, chelate C1q, and then activate complement and promote cell killing considerably more effectively than their wild-type precursors. We used these engineered mAbs as a model to investigate the sequence of events that occur when mAbs bind to B-cell lines and to primary cells from patients with chronic lymphocytic leukemia and then activate complement. Based on four-color confocal microscopy real-time movies and high resolution digital imaging, we find that after CD20 mAb binding and C1q uptake, C3b deposits on cells, followed by Ca(2+) influx, revealed by bright green signals generated on cells labeled with FLUO-4, a Ca(2+) indicator. The bright FLUO-4/Ca(2+) signal fades, replaced by punctate green signals in mitochondria, indicating Ca(2+) localization. This step leads to mitochondrial poisoning followed by cell death. The entire sequence is completed in <2 min for hexamerization-enhanced CD20 mAb-mediated killing. To our knowledge this is the first time the entire process has been characterized in detail in real time. By identifying multiple discrete steps in the cytotoxic pathway for nucleated cells our findings may inform future development and more effective application of complement-fixing mAbs to cancer treatment.

The Effect of Hypoxic Preconditioning on Induced Schwann Cells under Hypoxic Conditions

OBJECT

Our objective was to explore the protective effects of hypoxic preconditioning on induced Schwann cells exposed to an environment with low concentrations of oxygen. It has been observed that hypoxic preconditioning of induced Schwann cells can promote axonal regeneration under low oxygen conditions.

METHOD

Rat bone marrow mesenchymal stem cells (MSCs) were differentiated into Schwann cells and divided into a normal oxygen control group, a hypoxia-preconditioning group and a hypoxia group. The ultrastructure of each of these groups of cells was observed by electron microscopy. In addition, flow cytometry was used to measure changes in mitochondrial membrane potential. Annexin V-FITC/PI staining was used to detect apoptosis, and Western blots were used to detect the expression of Bcl-2/Bax. Fluorescence microscopic observations of axonal growth in NG-108 cells under hypoxic conditions were also performed.

RESULTS

The hypoxia-preconditioning group maintained mitochondrial cell membrane and crista integrity, and these cells exhibited less edema than the hypoxia group. In addition, the cells in the hypoxia-preconditioning group were found to be in early stages of apoptosis, whereas cells from the hypoxia group were in the later stages of apoptosis. The hypoxia-preconditioning group also had higher levels of Bcl-2/Bax expression and longer NG-108 cell axons than were observed in the hypoxia group.

CONCLUSION

Hypoxic preconditioning can improve the physiological state of Schwann cells in a severe hypoxia environment and improve the ability to promote neurite outgrowth.

Enhanced Production of Adenosine Triphosphate by Pharmacological Activation of Adenosine Monophosphate-Activated Protein Kinase Ameliorates Acetaminophen-Induced Liver Injury

The hepatic cell death induced by acetaminophen (APAP) is closely related to cellular adenosine triphosphate (ATP) depletion, which is mainly caused by mitochondrial dysfunction. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a key sensor of low energy status. AMPK regulates metabolic homeostasis by stimulating catabolic metabolism and suppressing anabolic pathways to increase cellular energy levels. We found that the decrease in active phosphorylation of AMPK in response to APAP correlates with decreased ATP levels, in vivo. Therefore, we hypothesized that the enhanced production of ATP via AMPK stimulation can lead to amelioration of APAP-induced liver failure. A769662, an allosteric activator of AMPK, produced a strong synergistic effect on AMPK Thr172 phosphorylation with APAP in primary hepatocytes and liver tissue. Interestingly, activation of AMPK by A769662 ameliorated the APAP-induced hepatotoxicity in C57BL/6N mice treated with APAP at a dose of 400 mg/kg intraperitoneally. However, mice treated with APAP alone developed massive centrilobular necrosis, and APAP increased their serum alanine aminotransferase and aspartate aminotransferase levels. Furthermore, A769662 administration prevented the loss of intracellular ATP without interfering with the APAP-mediated reduction of mitochondrial dysfunction. In contrast, inhibition of glycolysis by 2-deoxy-glucose eliminated the beneficial effects of A769662 on APAP-mediated liver injury. In conclusion, A769662 can effectively protect mice against APAP-induced liver injury through ATP synthesis by anaerobic glycolysis. Furthermore, stimulation of AMPK may have potential therapeutic application for APAP overdose.

Systems Biology Approach Reveals a Calcium-Dependent Mechanism for Basal Toxicity in Daphnia magna

The expanding diversity and ever increasing amounts of man-made chemicals discharged to the environment pose largely unknown hazards to ecosystem and human health. The concept of adverse outcome pathways (AOPs) emerged as a comprehensive framework for risk assessment. However, the limited mechanistic information available for most chemicals and a lack of biological pathway annotation in many species represent significant challenges to effective implementation of this approach. Here, a systems level, multistep modeling strategy demonstrates how to integrate information on chemical structure with mechanistic insight from genomic studies, and phenotypic effects to define a putative adverse outcome pathway. Results indicated that transcriptional changes indicative of intracellular calcium mobilization were significantly overrepresented in Daphnia magna (DM) exposed to sublethal doses of presumed narcotic chemicals with log Kow ≥ 1.8. Treatment of DM with a calcium ATPase pump inhibitor substantially recapitulated the common transcriptional changes. We hypothesize that calcium mobilization is a potential key molecular initiating event in DM basal (narcosis) toxicity. Heart beat rate analysis and metabolome analysis indicated sublethal effects consistent with perturbations of calcium preceding overt acute toxicity. Together, the results indicate that altered calcium homeostasis may be a key early event in basal toxicity or narcosis induced by lipophilic compounds.

Hepatoprotective Effect of Pretreatment with Thymus vulgaris Essential Oil in Experimental Model of Acetaminophen-Induced Injury

Acute liver damage caused by acetaminophen overdose is a significant clinical problem and could benefit from new therapeutic strategies. Objective. This study investigated the hepatoprotective effect of Thymus vulgaris essential oil (TEO), which is used popularly for various beneficial effects, such as its antiseptic, carminative, and antimicrobial effects. The hepatoprotective activity of TEO was determined by assessing serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) in mice. Their livers were then used to determine myeloperoxidase (MPO) enzyme activity and subjected to histological analysis. In vitro antioxidant activity was evaluated by assessing the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH•)-scavenging effects of TEO and TEO-induced lipid peroxidation. TEO reduced the levels of the serum marker enzymes AST, ALT, and ALP and MPO activity. The histopathological analysis indicated that TEO prevented acetaminophen-induced necrosis. The essential oil also exhibited antioxidant activity, reflected by its DPPH radical-scavenging effects and in the lipid peroxidation assay. These results suggest that TEO has hepatoprotective effects on acetaminophen-induced hepatic damage in mice.

Metabolomics evaluation of the effects of green tea extract on acetaminophen-induced hepatotoxicity in mice

Green tea has been purported to have beneficial health effects including protective effects against oxidative stress. Acetaminophen (APAP) is a widely used analgesic drug that can cause acute liver injury in overdose situations. These studies explored the effects of green tea extract (GTE) on APAP-induced hepatotoxicity in liver tissue extracts using ultra performance liquid chromatography/quadrupole time-of-flight mass spectrometry and nuclear magnetic resonance spectroscopy. Mice were orally administered GTE, APAP or GTE and APAP under three scenarios. APAP alone caused a high degree of hepatocyte necrosis associated with increases in serum transaminases and alterations in multiple metabolic pathways. The time of GTE oral administration relative to APAP either protected against or potentiated the APAP-induced hepatotoxicity. Dose dependent decreases in histopathology scores and serum transaminases were noted when GTE was administered prior to APAP; whereas, the opposite occurred when GTE was administered after APAP. Similarly, metabolites altered by APAP alone were less changed when GTE was given prior to APAP. Significantly altered pathways included fatty acid metabolism, glycerophospholipid metabolism, glutathione metabolism, and energy pathways. These studies demonstrate the complex interaction between GTE and APAP and the need to employ novel analytical strategies to understand the effects of dietary supplements on pharmaceutical compounds.

Modulation of intracellular calcium homeostasis blocks autophagosome formation

Cellular stress responses often involve elevation of cytosolic calcium levels, and this has been suggested to stimulate autophagy. Here, however, we demonstrated that agents that alter intracellular calcium ion homeostasis and induce ER stress-the calcium ionophore A23187 and the sarco/endoplasmic reticulum Ca (2+)-ATPase inhibitor thapsigargin (TG)-potently inhibit autophagy. This anti-autophagic effect occurred under both nutrient-rich and amino acid starvation conditions, and was reflected by a strong reduction in autophagic degradation of long-lived proteins. Furthermore, we found that the calcium-modulating agents inhibited autophagosome biogenesis at a step after the acquisition of WIPI1, but prior to the closure of the autophagosome. The latter was evident from the virtually complete inability of A23187- or TG-treated cells to sequester cytosolic lactate dehydrogenase. Moreover, we observed a decrease in both the number and size of starvation-induced EGFP-LC3 puncta as well as reduced numbers of mRFP-LC3 puncta in a tandem fluorescent mRFP-EGFP-LC3 cell line. The anti-autophagic effect of A23187 and TG was independent of ER stress, as chemical or siRNA-mediated inhibition of the unfolded protein response did not alter the ability of the calcium modulators to block autophagy. Finally, and remarkably, we found that the anti-autophagic activity of the calcium modulators did not require sustained or bulk changes in cytosolic calcium levels. In conclusion, we propose that local perturbations in intracellular calcium levels can exert inhibitory effects on autophagy at the stage of autophagosome expansion and closure.

High-throughput respirometric assay identifies predictive toxicophore of mitochondrial injury

Many environmental chemicals and drugs negatively affect human health through deleterious effects on mitochondrial function. Currently there is no chemical library of mitochondrial toxicants, and no reliable methods for predicting mitochondrial toxicity. We hypothesized that discrete toxicophores defined by distinct chemical entities can identify previously unidentified mitochondrial toxicants. We used a respirometric assay to screen 1760 compounds (5 μM) from the LOPAC and ChemBridge DIVERSet libraries. Thirty-one of the assayed compounds decreased uncoupled respiration, a stress test for mitochondrial dysfunction, prior to a decrease in cell viability and reduced the oxygen consumption rate in isolated mitochondria. The mitochondrial toxicants were grouped by chemical similarity and two clusters containing four compounds each were identified. Cheminformatic analysis of one of the clusters identified previously uncharacterized mitochondrial toxicants from the ChemBridge DIVERSet. This approach will enable the identification of mitochondrial toxicants and advance the prediction of mitochondrial toxicity for both drug discovery and risk assessment.

The role of calcium in VDAC1 oligomerization and mitochondria-mediated apoptosis

The voltage-dependent anion channel (VDAC), located at the outer mitochondria membrane (OMM), mediates interactions between mitochondria and other parts of the cell by transporting anions, cations, ATP, Ca(2+), and metabolites. Substantial evidence points to VDAC1 as being a key player in apoptosis, regulating the release of apoptogenic proteins from mitochondria, such as cytochrome c, and interacting with anti-apoptotic proteins. Recently, we demonstrated that VDAC1 oligomerization is a general mechanism common to numerous apoptogens acting via different initiating cascades and proposed that a protein-conducting channel formed within a VDAC1 homo/hetero oligomer mediates cytochrome c release. However, the molecular mechanism responsible for VDAC1 oligomerization remains unclear. Several studies have shown that mitochondrial Ca(2+) is involved in apoptosis induction and that VDAC1 possesses Ca(2+)-binding sites and mediates Ca(2+) transport across the OMM. Here, the relationship between the cellular Ca(2+) level, [Ca(2+)]i, VDAC1 oligomerization and apoptosis was studied. Decreasing [Ca(2+)]i using the cell-permeable Ca(2+) chelating reagent BAPTA-AM was found to inhibit VDAC1 oligomerization and apoptosis, while increasing [Ca(2+)]i using Ca(2+) ionophore resulted in VDAC1 oligomerization and apoptosis induction in the absence of apoptotic stimuli. Moreover, induction of apoptosis elevated [Ca(2+)]i, concomitantly with VDAC1 oligomerization. AzRu-mediated inhibition of mitochondrial Ca(2+) transport decreased VDAC1 oligomerization, suggesting that mitochondrial Ca(2+) is required for VDAC1 oligomerization. In addition, increased [Ca(2+)]i levels up-regulate VDAC1 expression. These results suggest that Ca(2+) promotes VDAC1 oligomerization via activation of a yet unknown signaling pathway or by increasing VDAC1 expression, leading to apoptosis. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

High cytosolic free calcium level signals apoptosis through mitochondria-caspase mediated pathway in rat eggs cultured in vitro

The present study was aimed to find out whether an increase of cytosolic free calcium level induces egg apoptosis through mitochondria-caspase mediated pathway. To increase cytosolic free calcium level and morphological apoptotic changes, ovulated eggs were cultured in Ca(2+)/Mg(2+) free media-199 with or without various concentrations of calcium ionophore (0.5, 1, 2, 3, 4 μM) for 3 h in vitro. The morphological apoptotic changes, cytosolic free calcium level, hydrogen peroxide (H(2)O(2)) concentration, catalase activity, cytochrome c concentration, caspase-9 and caspase-3 activities and DNA fragmentation were analyzed. Calcium ionophore induced morphological apoptotic features in a concentration-dependent manner followed by degeneration at higher concentrations (3 and 4 μM). Calcium ionophore increased cytosolic free calcium level, induced generation of hydrogen peroxide (H(2)O(2)) and inhibited catalase activity in treated eggs. The increased H(2)O(2) concentration was associated with increased cytochrome c concentration, caspase-9 and caspase-3 activities that resulted in the induction of morphological features characteristic of egg apoptosis. The increased caspase-3 activity finally induced DNA fragmentation as evidenced by TUNEL positive staining in calcium ionophore-treated eggs. These findings suggest that high cytosolic free calcium level induces generation of H(2)O(2) that leads to egg apoptosis through mitochondria-caspase mediated pathway.

Genetic ablation of calcium-independent phospholipase A(2)γ (iPLA(2)γ) attenuates calcium-induced opening of the mitochondrial permeability transition pore and resultant cytochrome c release

Herein, we demonstrate that calcium-independent phospholipase A(2)γ (iPLA(2)γ) is a critical mechanistic participant in the calcium-induced opening of the mitochondrial permeability transition pore (mPTP). Liver mitochondria from iPLA(2)γ(-/-) mice were markedly resistant to calcium-induced swelling in the presence or absence of phosphate in comparison with wild-type littermates. Furthermore, the iPLA(2)γ enantioselective inhibitor (R)-(E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one ((R)-BEL) was markedly more potent than (S)-BEL in inhibiting mPTP opening in mitochondria from wild-type liver in comparison with hepatic mitochondria from iPLA(2)γ(-/-) mice. Intriguingly, low micromolar concentrations of long chain fatty acyl-CoAs and the non-hydrolyzable thioether analog of palmitoyl-CoA markedly accelerated Ca(2+)-induced mPTP opening in liver mitochondria from wild-type mice. The addition of l-carnitine enabled the metabolic channeling of acyl-CoA through carnitine palmitoyltransferases (CPT-1/2) and attenuated the palmitoyl-CoA-mediated amplification of calcium-induced mPTP opening. In contrast, mitochondria from iPLA(2)γ(-/-) mice were insensitive to fatty acyl-CoA-mediated augmentation of calcium-induced mPTP opening. Moreover, mitochondria from iPLA(2)γ(-/-) mouse liver were resistant to Ca(2+)/t-butyl hydroperoxide-induced mPTP opening in comparison with wild-type littermates. In support of these findings, cytochrome c release from iPLA(2)γ(-/-) mitochondria was dramatically decreased in response to calcium in the presence or absence of either t-butyl hydroperoxide or phenylarsine oxide in comparison with wild-type littermates. Collectively, these results identify iPLA(2)γ as an important mechanistic component of the mPTP, define its downstream products as potent regulators of mPTP opening, and demonstrate the integrated roles of mitochondrial bioenergetics and lipidomic flux in modulating mPTP opening promoting the activation of necrotic and necroapoptotic pathways of cell death.

Mitochondrial permeability transition in rat hepatocytes after anoxia/reoxygenation: role of Ca2+-dependent mitochondrial formation of reactive oxygen species

Onset of the mitochondrial permeability transition (MPT) is the penultimate event leading to lethal cellular ischemia-reperfusion injury, but the mechanisms precipitating the MPT after reperfusion remain unclear. Here, we investigated the role of mitochondrial free Ca(2+) and reactive oxygen species (ROS) in pH- and MPT-dependent reperfusion injury to hepatocytes. Cultured rat hepatocytes were incubated in anoxic Krebs-Ringer-HEPES buffer at pH 6.2 for 4 h and then reoxygenated at pH 7.4 to simulate ischemia-reperfusion. Some cells were loaded with the Ca(2+) chelators, BAPTA/AM and 2-[(2-bis-[carboxymethyl]aono-5-methoxyphenyl)-methyl-6-methoxy-8-bis[carboxymethyl]aminoquinoline, either by a cold loading protocol for intramitochondrial loading or by warm incubation for cytosolic loading. Cell death was assessed by propidium iodide fluorometry and immunoblotting. Mitochondrial Ca(2+), inner membrane permeability, membrane potential, and ROS formation were monitored with Rhod-2, calcein, tetramethylrhodamine methylester, and dihydrodichlorofluorescein, respectively. Necrotic cell death increased after reoxygenation. Necrosis was blocked by 1 μM cyclosporin A, an MPT inhibitor, and by reoxygenation at pH 6.2. Confocal imaging of Rhod-2, calcein, and dichlorofluorescein revealed that an increase of mitochondrial Ca(2+) and ROS preceded onset of the MPT after reoxygenation. Intramitochondrial Ca(2+) chelation, but not cytosolic Ca(2+) chelation, prevented ROS formation and subsequent necrotic and apoptotic cell death. Reoxygenation with the antioxidants, desferal or diphenylphenylenediamine, also suppressed MPT-mediated cell death. However, inhibition of cytosolic ROS by apocynin or diphenyleneiodonium chloride failed to prevent reoxygenation-induced cell death. In conclusion, Ca(2+)-dependent mitochondrial ROS formation is the molecular signal culminating in onset of the MPT after reoxygenation of anoxic hepatocytes, leading to cell death.

The mitochondrial permeability transition pore and its role in anaesthesia-triggered cellular protection during ischaemia-reperfusion injury

This review summarises the most recent data in support of the role of the mitochondrial permeability transition pore (mPTP) in ischaemia-reperfusion injury, how anaesthetic agents interact with this molecular channel, and the relevance this holds for current anaesthetic practice. Ischaemia results in damage to the electron transport chain of enzymes and sets into play the assembly of a non-specific mega-channel (the mPTP) that transgresses the inner mitochondrial membrane. During reperfusion, uncontrolled opening of the mPTP causes widespread depolarisation of the inner mitochondrial membrane, hydrolysis of ATP, mitochondrial rupture and eventual necrotic cell death. Similarly, transient opening of the mPTP during less substantial ischaemia leads to differential swelling of the intermembrane space compared to the mitochondrial matrix, rupture of the outer mitochondrial membrane and release of pro-apoptotic factors into the cytosol. Recent data suggests that cellular protection from volatile anaesthetic agents follows specific downstream interactions with this molecular channel that are initiated early during anaesthesia. Intravenous anaesthetic agents also prevent the opening of the mPTP during reperfusion. Although by dissimilar mechanisms, both volatiles and propofol promote cell survival by preventing uncontrolled opening of the mPTP after ischaemia. It is now considered that anaesthetic-induced closure of the mPTP is the underlying effector mechanism that is responsible for the cytoprotection previously demonstrated in clinical studies investigating anaesthetic-mediated cardiac and neuroprotection. Manipulation of mPTP function offers a novel means of preventing ischaemic cell injury. Anaesthetic agents occupy a unique niche in the pharmacological armamentarium available for use in preventing cell death following ischaemia-reperfusion injury.

Direct therapeutic applications of calcium electroporation to effectively induce tumor necrosis

Electroporation of cells with short, high-voltage pulses causes a transient permeabilization of cell membranes that permits passage of otherwise nonpermeating ions and molecules. In this study, we illustrate how electroporation with isotonic calcium can achieve highly effective cancer cell kill in vivo. Calcium electroporation elicited dramatic antitumor responses in which 89% of treated tumors were eliminated. Histologic analyses indicated complete tumor necrosis. Mechanistically, calcium electroporation caused acute ATP depletion likely due to a combination of increased cellular use of ATP, decreased production of ATP due to effects on the mitochondria, as well as loss of ATP through the permeabilized cell membrane. Taken together, our findings offer a preclinical proof of concept for the use of electroporation to load cancer cells with calcium as an efficient anticancer treatment. Electroporation equipment is already used clinically to enhance the delivery of chemotherapy to superficial tumors, with trials on internal tumors in progress, enabling the introduction of calcium electroporation to clinical use. Moreover, the safety profile, availability, and low cost of calcium facilitate access to this technology for many cancer patients in developed and developing countries.

The hepatoprotective effects of adenine nucleotide translocator-2 against aging and oxidative stress

Mitochondrial adenine nucleotide translocator (ANT) plays important roles in the regulation of mitochondrial permeability transition and cell bioenergetics. The mouse has three ANT isoforms (1, 2 and 4) showing tissue-specific expression patterns. Although ANT1 is known to have a pro-apoptotic property, the specific functions of ANT2 have not been well determined. In the present study, ANT2 expression was significantly lower in the aged rat liver and in a liver fibrosis model. To explore the protective role of ANT2 in the liver, we established a hepa1c1c7 cell line overexpressing ANT2. Overexpression of ANT2 caused hepa1c1c7 cells to be more resistant to oxidative stress, and mitochondrial membrane potential (MMP, ∆Ψm) was relatively intact in ANT2-overexpressing cells under oxidative stress. In addition, ANT2 was found to increase ATP production by influencing mitochondrial bioenergetics. These results imply that the hepatoprotective effect of ANT2 is due to the stabilization of MMP and enhanced ATP production, and thus, maintaining ANT2 levels in the liver might be important to enhance resistance to aging and oxidative stress.

Benzo(a)pyrene-induced mitochondrial dysfunction and cell death in p53-null Hep3B cells

Benzo(a)pyrene (BaP) has been shown to induce apoptosis and necrosis in various cell types. However, the effect of BaP on mitochondria function and p73, and their possible roles in BaP-induced cell death have not been well studied. This study focused on mitochondria-mediated cell death and the occurrence of p73 protein accumulation in BaP-treated human hepatoma Hep3B (p53-null) cells. We found that BaP (8, 16, 32 and 64μM) induced early necrosis at 12h and delayed apoptosis at 24h. BaP dramatically induced ethoxyresorufin-O-deethylase activity and led to significant increase in oxidative stress at early time points (6 and 12h). Necrotic cell death was concurrent with loss of mitochondrial membrane potential, decrease in the ATP level and activities of Na(+)/K(+)-ATPase and Ca(2+)/Mg(2+)-ATPase. However, these changes were reversed in the process of apoptosis. In addition, after BaP treatment, c-Jun N-terminal kinase (JNK) and Bax were activated during apoptosis and no change in p73 protein level was observed. These results revealed that the cells with mitochondria dysfunction and ATP depletion underwent necrosis at early time point and apoptosis afterward when they recovered from mitochondrial dysfunction and ATP depletion. Activation of JNK and Bax possibly contributed to BaP-induced apoptosis.

Liver regeneration and the atrophy-hypertrophy complex

The atrophy-hypertrophy complex (AHC) refers to the controlled restoration of liver parenchyma following hepatocyte loss. Different types of injury (e.g., toxins, ischemia/reperfusion, biliary obstruction, and resection) elicit the same hypertrophic response in the remnant liver. The AHC involves complex anatomical, histological, cellular, and molecular processes. The signals responsible for these processes are both intrinsic and extrinsic to the liver and involve both physical and molecular events. In patients in whom resection of large liver malignancies would result in an inadequate functional liver remnant, preoperative portal vein embolization may increase the remnant liver sufficiently to permit aggressive resections. Through continued basic science research, the cellular mechanisms of the AHC may be maximized to permit curative resections in patients with potentially prohibitive liver function.

Multiscale modeling of tumorigenesis induced by mitochondrial incapacitation in cell death

There is a renewed interest in tumorigenesis provoked by glycolysis and prosurvival autophagy following the mitochondrial permeability transition during cell death. To investigate such mitochondrial dysfunction, we have developed a multiscale model by integrating the dynamic behaviors of essential oncogenic proteins, cells, and their microenvironment. We found that 1) the concentration of cellular ATP (adenosine triphosphate) available during the autophagy-related processes is a critical factor in determining tumorigenesis; 2) mitochondrial aging rate has a significant influence on this tumorigenic effect, 3) specific hypoxic and oxidative stresses work cooperatively for tumorigenesis during cell death. We conclude that the cellular mitochondrial status is critical in triggering tumorigenesis during the cell death process, particularly under harsh microenvironments.

Mitochondrial permeability transition in Ca(2+)-dependent apoptosis and necrosis

A variety of stimuli utilize an increase of cytosolic free Ca(2+) concentration as a second messenger to transmit signals, through Ca(2+) release from the endoplasmic reticulum or opening of plasma membrane Ca(2+) channels. Mitochondria contribute to the tight spatiotemporal control of this process by accumulating Ca(2+), thus shaping the return of cytosolic Ca(2+) to resting levels. The rise of mitochondrial matrix free Ca(2+) concentration stimulates oxidative metabolism; yet, in the presence of a variety of sensitizing factors of pathophysiological relevance, the matrix Ca(2+) increase can also lead to opening of the permeability transition pore (PTP), a high conductance inner membrane channel. While transient openings may serve the purpose of providing a fast Ca(2+) release mechanism, persistent PTP opening is followed by deregulated release of matrix Ca(2+), termination of oxidative phosphorylation, matrix swelling with inner membrane unfolding and eventually outer membrane rupture with release of apoptogenic proteins and cell death. Thus, a rise in mitochondrial Ca(2+) can convey both apoptotic and necrotic death signals by inducing opening of the PTP. Understanding the signalling networks that govern changes in mitochondrial free Ca(2+) concentration, their interplay with Ca(2+) signalling in other subcellular compartments, and regulation of PTP has important implications in the fine comprehension of the main biological routines of the cell and in disease pathogenesis.

Mitophagy selectively degrades individual damaged mitochondria after photoirradiation

Damaged and dysfunctional mitochondria are proposed to be removed by autophagy. However, selective degradation of damaged mitochondria by autophagy (mitophagy) has yet to be experimentally verified. In this study, we investigated the cellular fate of individual mitochondria damaged by photoirradiation in hepatocytes isolated from transgenic mice expressing green fluorescent protein fused to microtubule-associated protein 1 light chain 3, a marker of forming and newly formed autophagosomes. Photoirradiation with 488-nm light induced mitochondrial depolarization (release of tetramethylrhodamine methylester [TMRM]) in a dose-dependent fashion. At lower doses of light, mitochondria depolarized transiently with re-polarization within 3 min. With greater light, mitochondrial depolarization became irreversible. Irreversible, but not reversible, photodamage induced autophagosome formation after 32±5 min. Photodamage-induced mitophagy was independent of TMRM, as photodamage also induced mitophagy in the absence of TMRM. Photoirradiation with 543-nm light did not induce mitophagy. As revealed by uptake of LysoTracker Red, mitochondria weakly acidified after photodamage before a much stronger acidification after autophagosome formation. Photodamage-induced mitophagy was not blocked by phosphatidylinositol 3-kinase inhibition with 3-methyladenine (10 mM) or wortmannin (100 nM). In conclusion, individual damaged mitochondria become selectively degraded by mitophagy, but photodamage-induced mitophagic sequestration occurs independently of the phosphatidylinositol 3-kinase signaling pathway, the classical upstream signaling pathway of nutrient deprivation-induced autophagy.

Mitochondrial degradation by autophagy (mitophagy) in GFP-LC3 transgenic hepatocytes during nutrient deprivation

Fasting in vivo and nutrient deprivation in vitro enhance sequestration of mitochondria and other organelles by autophagy for recycling of essential nutrients. Here our goal was to use a transgenic mouse strain expressing green fluorescent protein (GFP) fused to rat microtubule-associated protein-1 light chain 3 (LC3), a marker protein for autophagy, to characterize the dynamics of mitochondrial turnover by autophagy (mitophagy) in hepatocytes during nutrient deprivation. In complete growth medium, GFP-LC3 fluorescence was distributed diffusely in the cytosol and incorporated in mostly small (0.2-0.3 μm) patches in proximity to mitochondria, which likely represent preautophagic structures (PAS). After nutrient deprivation plus 1 μM glucagon to simulate fasting, PAS grew into green cups (phagophores) and then rings (autophagosomes) that enveloped individual mitochondria, a process that was blocked by 3-methyladenine. Autophagic sequestration of mitochondria took place in 6.5 ± 0.4 min and often occurred coordinately with mitochondrial fission. After ring formation and apparent sequestration, mitochondria depolarized in 11.8 ± 1.4 min, as indicated by loss of tetramethylrhodamine methylester fluorescence. After ring formation, LysoTracker Red uptake, a marker of acidification, occurred gradually, becoming fully evident at 9.9 ± 1.9 min of ring formation. After acidification, GFP-LC3 fluorescence dispersed. PicoGreen labeling of mitochondrial DNA (mtDNA) showed that mtDNA was also sequestered and degraded in autophagosomes. Overall, the results indicate that PAS serve as nucleation sites for mitophagy in hepatocytes during nutrient deprivation. After autophagosome formation, mitochondrial depolarization and vesicular acidification occur, and mitochondrial contents, including mtDNA, are degraded.

Inhibition of the mitochondrial permeability transition by protein kinase A in rat liver mitochondria and hepatocytes

NO and cGMP administered at reperfusion after ischaemia prevent injury to hepatocytes mediated by the MPT (mitochondrial permeability transition). To characterize further the mechanism of protection, the ability of hepatic cytosol in combination with cyclic nucleotides to delay onset of the calcium-induced MPT was evaluated in isolated rat liver mitochondria. Liver cytosol plus cGMP or cAMP dose-dependently inhibited the MPT, required ATP hydrolysis for inhibition and did not inhibit mitochondrial calcium uptake. Specific peptide inhibitors for PKA (protein kinase A), but not PKG (protein kinase G), abolished cytosol-induced inhibition of MPT onset. Activity assays showed a cGMP- and cAMP-stimulated protein kinase activity in liver cytosol that was completely inhibited by PKI, a PKA peptide inhibitor. Size-exclusion chromatography of liver cytosol produced a single peak of cGMP/cAMP-stimulated kinase activity with an estimated protein size of 180-220 kDa. This fraction was PKI-sensitive and delayed onset of the MPT. Incubation of active catalytic PKA subunit directly with mitochondria in the absence of cytosol and cyclic nucleotide also delayed MPT onset, and incubation with purified outer membranes led to phosphorylation of a major 31 kDa band. After ischaemia, administration at reperfusion of membrane-permeant cAMPs and cAMP-mobilizing glucagon prevented reperfusion injury to hepatocytes. In conclusion, PKA in liver cytosol activated by cGMP or cAMP acts directly on mitochondria to delay onset of the MPT and protect hepatocytes from cell death after ischaemia/reperfusion.

The dual role of calcium as messenger and stressor in cell damage, death, and survival

Ca(2+) is an important second messenger participating in many cellular activities; when physicochemical insults deregulate its delicate homeostasis, it acts as an intrinsic stressor, producing/increasing cell damage. Damage elicits both repair and death responses; intriguingly, in those responses Ca(2+) also participates as second messenger. This delineates a dual role for Ca(2+) in cell stress, making difficult to separate the different and multiple mechanisms required for Ca(2+)-mediated control of cell survival and apoptosis. Here we attempt to disentangle the two scenarios, examining on the one side, the events implicated in deregulated Ca(2+) toxicity and the mechanisms through which this elicits reparative or death pathways; on the other, reviewing the role of Ca(2+) as a messenger in the transduction of these same signaling events.

Mitochondrial involvement in drug-induced liver injury

Mitochondrial dysfunction is a major mechanism of liver injury. A parent drug or its reactive metabolite can trigger outer mitochondrial membrane permeabilization or rupture due to mitochondrial permeability transition. The latter can severely deplete ATP and cause liver cell necrosis, or it can instead lead to apoptosis by releasing cytochrome c, which activates caspases in the cytosol. Necrosis and apoptosis can trigger cytolytic hepatitis resulting in lethal fulminant hepatitis in some patients. Other drugs severely inhibit mitochondrial function and trigger extensive microvesicular steatosis, hypoglycaemia, coma, and death. Milder and more prolonged forms of drug-induced mitochondrial dysfunction can also cause macrovacuolar steatosis. Although this is a benign liver lesion in the short-term, it can progress to steatohepatitis and then to cirrhosis. Patient susceptibility to drug-induced mitochondrial dysfunction and liver injury can sometimes be explained by genetic or acquired variations in drug metabolism and/or elimination that increase the concentration of the toxic species (parent drug or metabolite). Susceptibility may also be increased by the presence of another condition, which also impairs mitochondrial function, such as an inborn mitochondrial cytopathy, beta-oxidation defect, certain viral infections, pregnancy, or the obesity-associated metabolic syndrome. Liver injury due to mitochondrial dysfunction can have important consequences for pharmaceutical companies. It has led to the interruption of clinical trials, the recall of several drugs after marketing, or the introduction of severe black box warnings by drug agencies. Pharmaceutical companies should systematically investigate mitochondrial effects during lead selection or preclinical safety studies.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Mitochondrial calcium and the permeability transition in cell death

Dysregulation of Ca(2+) has long been implicated to be important in cell injury. A Ca(2+)-linked process important in necrosis and apoptosis (or necrapoptosis) is the mitochondrial permeability transition (MPT). In the MPT, large conductance permeability transition (PT) pores open that make the mitochondrial inner membrane abruptly permeable to solutes up to 1500 Da. The importance of Ca(2+) in MPT induction varies with circumstance. Ca(2+) overload is sufficient to induce the MPT. By contrast after ischemia-reperfusion to cardiac myocytes, Ca(2+) overload is the consequence of bioenergetic failure after the MPT rather than its cause. In other models, such as cytotoxicity from Reye-related agents and storage-reperfusion injury to liver grafts, Ca(2+) appears to be permissive to MPT onset. Lastly in oxidative stress, increased mitochondrial Ca(2+) and ROS generation act synergistically to produce the MPT and cell death. Thus, the exact role of Ca(2+) for inducing the MPT and cell death depends on the particular biologic setting.

20(S)-ginsenoside Rg3, a neuroprotective agent, inhibits mitochondrial permeability transition pores in rat brain

Ginseng, the root of Panax ginseng C.A. Meyer (Araliaceae), is a well-known traditional Chinese herbal medicine. Ginsenosides, which are triterpene derivatives that contain sugar moieties, are the main active ingredients of ginseng. 20(S)-Ginsenoside Rg3, a triterpene glycoside which chemically belongs to the protopanaxadiol ginsenoside group, is effective in attenuating brain infarction after cerebral ischemia, but the detailed mechanism is not known. This study examined the effect of 20(S)-ginsenoside Rg3 on mitochondrial permeability transition pore (MPTP) in the rat brain. 20(S)-Ginsenoside Rg3 at 2-16 microm inhibited Ca(2+)- and H(2)O(2)-induced swelling of mitochondria isolated from rat brains. The addition of Ca(2+) generated reactive oxygen species (ROS) in isolated mitochondria. 20(S)-Ginsenoside Rg3 (2-16 microm) inhibited Ca(2+) induced generation of ROS. At the same time, 20(S)-ginsenoside Rg3 significantly improved mitochondrial energy metabolism, enhanced ATP levels and the respiratory control ratio. These results suggest that 20(S)-ginsenoside Rg3 inhibits the opening of MPTP by free radical scavenging action in the brain, and this implies that inhibition of MPTP may contribute to the neuroprotective effect of 20(S)-ginsenoside Rg3.

Mitochondrial permeability transition in liver ischemia and reperfusion: role of c-Jun N-terminal kinase 2

The mitochondrial permeability transition (MPT) mediates hepatic necrosis after ischemia and reperfusion (I/R). Here, we studied the role of c-Jun N-terminal kinase 2 (JNK2) in MPT-induced liver injury. Wildtype (WT) and JNK2 knockout (KO) mice underwent 70% liver ischemia for 1 hr followed by reperfusion for 8 hr, after which hepatocyte injury and animal survival was assessed. Compared with WT, JNK2 KO mice had 38% less alanine transaminase release and 39% less necrosis by histology. Survival out to 14 days was also greater in JNK2 KO mice (57% vs. 11%), and overall Kaplan-Meier survival was improved. No difference in apoptosis was observed. Intravital multiphoton microscopy of potential-indicating rhodamine 123 after reperfusion revealed depolarized mitochondria in 82% of WT hepatocytes, which decreased to 43% in JNK2 KO hepatocytes. In conclusion, JNK2 contributes to hepatocellular injury and death after I/R in association with increased mitochondrial dysfunction via the MPT.

Hydroxysafflor yellow A inhibits rat brain mitochondrial permeability transition pores by a free radical scavenging action

Hydroxysafflor yellow A (HSYA), the major and most active antioxidant from Carthamus tinctorius L., has been clinically prescribed in China to treat patients with cerebral ischemia, but the detailed mechanism is not known. This study examines the effect of HSYA on mitochondrial permeability transition pores (mtPTP) in the rat brain. HSYA at 10-80 micromol.l(-1) inhibited Ca(2+)- and H(2)O(2)-induced swelling of mitochondria isolated from rat brains. The addition of Ca(2+) generated reactive oxygen species (ROS) in isolated mitochondria. HSYA (10-80 micromol.l(-1)) inhibited Ca(2+)-induced generation of ROS. At the same time, HSYA significantly improved mitochondrial energy metabolism, enhanced ATP levels and the respiratory control ratio. These results suggest that HSYA inhibits the opening of mtPTP by a free radical scavenging action in the brain, and this may contribute to the neuroprotective effect of HSYA.

Minocycline and N-methyl-4-isoleucine cyclosporin (NIM811) mitigate storage/reperfusion injury after rat liver transplantation through suppression of the mitochondrial permeability transition

Graft failure after liver transplantation may involve mitochondrial dysfunction. We examined whether prevention of mitochondrial injury would improve graft function. Orthotopic rat liver transplantation was performed after 18 hours' cold storage in University of Wisconsin solution and treatment with vehicle, minocycline, tetracycline, or N-methyl-4-isoleucine cyclosporin (NIM811) of explants and recipients. Serum alanine aminotransferase (ALT), necrosis, and apoptosis were assessed 6 hours after implantation. Mitochondrial polarization and cell viability were assessed by intravital microscopy. Respiration and the mitochondrial permeability transition (MPT) were assessed in isolated rat liver mitochondria. After transplantation with vehicle or tetracycline, ALT increased to 5242 U/L and 4373 U/L, respectively. Minocycline and NIM811 treatment decreased ALT to 2374 U/L and 2159 U/L, respectively (P < 0.01). Necrosis and terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) also decreased from 21.4% and 21 cells/field, respectively, after vehicle to 10.1% and 6 cells/field after minocycline and to 8.7% and 5.2 cells/field after NIM811 (P < 0.05). Additionally, minocycline decreased caspase-3 activity in graft homogenates (P < 0.05). Long-term graft survival was 27% and 33%, respectively, after vehicle and tetracycline treatment, which increased to 60% and 70% after minocycline and NIM811 (P < 0.05). In isolated mitochondria, minocycline and NIM811 but not tetracycline blocked the MPT. Minocycline blocked the MPT by decreasing mitochondrial Ca(2+) uptake, whereas NIM811 blocks by interaction with cyclophilin D. Intravital microscopy showed that minocycline and NIM811 preserved mitochondrial polarization and cell viability after transplantation (P < 0.05).

CONCLUSION

Minocycline and NIM811 attenuated graft injury after rat liver transplantation and improved graft survival. Minocycline and/or NIM811 might be useful clinically in hepatic surgery and transplantation.

Role of mitochondria in silica-induced apoptosis of alveolar macrophages: inhibition of apoptosis by rhodamine 6G and N-acetyl-L-cysteine

Induction of apoptosis by silica in alveolar macrophages (AM) may be a critical step in silica-induced lung injury and pulmonary fibrosis. This study investigated the mechanism(s) through which silica induces apoptosis in AM and their production of proinflammatory cytokines. Using N-acetyl-L-cysteine (NAC) for glutathione (GSH) synthesis and removal of reactive oxygen species (ROS), and rhodamine 6G (R6G) to inhibit the mitochondrial-dependent function, this study found that silica-induced apoptosis of rat AM in primary culture is mitochondria dependent and exhibits a mechanism involving ROS generation, increased mitochondrial release of cytochrome c, and the activation of caspase 9, but not caspase 8, activity. Silica-induced apoptosis was accompanied by a lowering of intracellular and mitochondrial GSH (mGSH) and was blocked by pretreatment of cells with NAC or R6G. When cells were exposed to silica and then treated with either NAC or R6G, silica-induced apoptosis was not affected by the blocking agent. In addition, R6G, which inhibited cellular ATP production and mitochondrial ROS generation, had no effect on apoptosis induced by exogenous hydrogen peroxide or superoxide. Pretreatment of cells with NAC or R6G also inhibited silica-induced production of interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha, but the inhibition of these cytokines with agents known to block their secretion did not protect cells from silica-induced apoptosis. Data indicate that silica-induced apoptosis is mediated through mitochondrial generation of ROS, which may be inhibited by pretreatment of cells with R6G that prevents ROS generation, or with NAC that maintains a high level of mGSH. The secretion of IL-1beta and TNF-alpha by silica-exposed AM was markedly inhibited by NAC and R6G, suggesting that the production of these cytokines is also ROS dependent.