On the mechanisms of phenothiazine-induced mitochondrial permeability transition: Thiol oxidation, strict Ca2+ dependence, and cyt c release

Targeting autophagy by antipsychotic phenothiazines: potential drug repurposing for cancer therapy

Cancer is recognized as the major cause of death worldwide and the most challenging public health issues. Tumor cells exhibit molecular adaptations and metabolic reprograming to sustain their high proliferative rate and autophagy plays a pivotal role to supply the high demand for metabolic substrates and for recycling cellular components, which has attracted the attention of the researchers. The modulation of the autophagic process sensitizes tumor cells to chemotherapy-induced cell death and reverts drug resistance. In this regard, many in vitro and in vivo studies having shown the anticancer activity of phenothiazine (PTZ) derivatives due to their potent cytotoxicity in tumor cells. Interestingly, PTZ have been used as antiemetics in antitumor chemotherapy-induced vomiting, maybe exerting a combined antitumor effect. Among the mechanisms of cytotoxicity, the modulation of autophagy by these drugs has been highlighted. Therefore, the use of PTZ derivatives can be considered as a repurposing strategy in antitumor chemotherapy. Here, we provided an overview of the effects of antipsychotic PTZ on autophagy in tumor cells, evidencing the molecular targets and discussing the underlying mechanisms. The modulation of autophagy by PTZ in tumor cells have been consistently related to their cytotoxic action. These effects depend on the derivative, their concentration, and also the type of cancer. Most data have shown the impairment of autophagic flux by PTZ, probably due to the blockade of lysosome-autophagosome fusion, but some studies have also suggested the induction of autophagy. These data highlight the therapeutic potential of targeting autophagy by PTZ in cancer chemotherapy.

Phenothiazine derivatives and their impact on the necroptosis and necrosis processes. A review

The current review focuses on the effect of phenothiazine derivatives, tested in vitro, on necrosis and necroptosis, the latter constitutes one of the kinds of programmed cell death. Necroptosis is a necrotic and inflammatory type of programmed cell death. Phenothiazines are D1 and D2-like family receptor antagonists, which are used in the treatment of schizophrenia. Necroptosis begins from TNF-α, whose synthesis is stimulated by dopamine receptors, thus it can be concluded that phenothiazine derivatives may modulate necroptosis. We identified 19 papers reporting in vitro assays of necroptosis and necrosis in which phenothiazine derivatives, and both normal and cancer cell lines were used. Chlorpromazine, fluphenazine, levomepromazine, perphenazine, promethazine, thioridazine, trifluoperazine, and novel derivatives can modulate necroptosis and necrosis. The type of a drug, concentration and a cell line have an impact on the ultimate effect. Unfortunately, the authors confirmed both processes on the basis of TNF-α and ATP levels as well as the final steps of necrosis/necroptosis related to membrane permeability (PI staining, LDH release, and HMGB1 amount), which makes it impossible to understand the complete mechanism of phenothiazines impact on necroptosis and necrosis. Studies analyzing the effect of phenothiazines on RIPK1, RIPK3, or MLKL has not been performed yet. Only the analysis of the expression of those proteins as well as necrosis and necroptosis inhibitors can help us to comprehend how phenothiazine derivatives act, and how to improve their therapeutic potential.

Rosemary (Rosmarinus officinalis L.) Glycolic Extract Protects Liver Mitochondria from Oxidative Damage and Prevents Acetaminophen-Induced Hepatotoxicity

Rosmarinus officinalis L. (rosemary) is an aromatic culinary herb. Native to the Mediterranean region, it is currently cultivated worldwide. In addition to its use as a condiment in food preparation and in teas, rosemary has been widely employed in folk medicine and cosmetics. Several beneficial effects have been described for rosemary, including antimicrobial and antioxidant activities. Here, we investigated the mechanisms accounting for the antioxidant activity of the glycolic extract of R. officinalis (Ro) in isolated rat liver mitochondria (RLM) under oxidative stress conditions. We also investigated its protective effect against acetaminophen-induced hepatotoxicity in vivo. A crude extract was obtained by fractionated percolation, using propylene glycol as a solvent due to its polarity and cosmeceutical compatibility. The quantification of substances with recognized antioxidant action revealed the presence of phenols and flavonoids. Dereplication studies carried out through LC-MS/MS and GC-MS, supported by The Global Natural Product Social Molecular Networking (GNPS) platform, annotated several phenolic compounds, confirming the previous observation. In accordance, Ro decreased the production of reactive oxygen species (ROS) elicited by Fe2+ or t-BOOH and inhibited the lipid peroxidation of mitochondrial membranes in a concentration-dependent manner in RLM. Such an effect was also observed in liposomes as membrane models. Ro also prevented the oxidation of mitochondrial protein thiol groups and reduced glutathione (GSH). In model systems, Ro exhibited a potent scavenger activity toward 2,2′-diphenyl-1-picrylhydrazyl (DPPH) radicals and superoxide anions. It also demonstrated an Fe2+ chelating activity. Moreover, Ro did not exhibit cytotoxicity or dissipate the mitochondrial membrane potential (∆Ψ) in rat liver fibroblasts (BRL3A cells). To evaluate whether such antioxidant protective activity observed in vitro could also be achieved in vivo, a well-established model of hepatotoxicity induced by acute exposure to acetaminophen (AAP) was used. This model depletes GSH and promotes oxidative-stress-mediated tissue damage. The treatment of rats with 0.05% Ro, administered intraperitoneally for four days, resulted in inhibition of AAP-induced lipid peroxidation of the liver and the prevention of hepatotoxicity, maintaining alanine and aspartate aminotransferase (ALT/AST) levels equal to those of the normal, non-treated rats. Together, these findings highlight the potent antioxidant activity of rosemary, which is able to protect mitochondria from oxidative damage in vitro, and effects such as the antioxidant and hepatoprotective effects observed in vivo.

Mahuang Xixin Fuzi decoction ameliorates apoptosis via the mitochondrial-mediated signaling pathway in MCM cells

ETHNOPHARMACOLOGICAL RELEVANCE

Mahuang Xixin Fuzi Decoction (MXF), as a classical prescription of traditional Chinese medicine (TCM), has been used to treat the symptoms of fever, nasal congestion and headache in elderly people for almost a thousand years.

AIM OF THE STUDY

The purpose of this study was to evaluate the effects and possible mechanisms of MXF on thermal stimulation-induced mouse cardiac myocytes (MCM) cell apoptosis.

MATERIALS AND METHODS

The apoptosis of the MCM cell model was induced by a PCR-calculated temperature control system with a gradual heating pattern at 43 °C for 1 h. The cytotoxic effects were determined using real-time cell analyzer (RTCA) technology. Annexin V-FITC/7-AAD staining, and JC-1 fluorescence were used to assess apoptosis. Specific substrates, enzyme-linked immunosorbent assays (ELISAs), and Western blotting were used to identify proteins in the mitochondrial-mediated pathway. The identification of chemical components in the mouse heart was performed by ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry analysis.

RESULTS

MXF inhibited apoptosis through the mitochondrial-mediated signaling pathway, including ameliorating ∆Ψm reduction, blocking mitochondrial Cyt C release, reducing Bax levels and increasing Bcl-2 levels, suppressing caspase-9 and caspase-3 activation in cytoplasmic fractions. Moreover, the components of MXF that act on the heart are mainly ephedra alkaloids and aconitine alkaloids.

CONCLUSIONS

The findings demonstrated that MXF treatment markedly reduced MCM cell apoptosis induced by thermal stimulation, which may be ascribed to the mitochondrial-mediated signaling pathway.

Targeting Ca2+ and Mitochondrial Homeostasis by Antipsychotic Thioridazine in Leukemia Cells

Mitochondria have pivotal roles in cellular physiology including energy metabolism, reactive oxygen species production, Ca2+ homeostasis, and apoptosis. Altered mitochondrial morphology and function is a common feature of cancer cells and the regulation of mitochondrial homeostasis has been identified as a key to the response to chemotherapeutic agents in human leukemias. Here, we explore the mechanistic aspects of cytotoxicity produced by thioridazine (TR), an antipsychotic drug that has been investigated for its anticancer potential in human leukemia cellular models. TR exerts selective cytotoxicity against human leukemia cells in vitro. A PCR array provided a general view of the expression of genes involved in cell death pathways. TR immediately produced a pulse of cytosolic Ca2+, followed by mitochondrial uptake, resulting in mitochondrial permeabilization, caspase 9/3 activation, endoplasmic reticulum stress, and apoptosis. Ca2+ chelators, thiol reducer dithiothreitol, or CHOP knockdown prevented TR-induced cell death. TR also exhibited potent cytotoxicity against BCL-2/BCL-xL-overexpressing leukemia cells. Additionally, previous studies have shown that TR exhibits potent antitumor activity in vivo in different solid tumor models. These findings show that TR induces a Ca2+-mediated apoptosis with involvement of mitochondrial permeabilization and ER stress in leukemia and it emphasizes the pharmacological potential of TR as an adjuvant in antitumor chemotherapy.

The Joint Influence of Tl+ and Thiol-Modifying Agents on Rat Liver Mitochondrial Parameters In Vitro

Recent data have shown that the mitochondrial permeability transition pore (MPTP) is the complex of the Ca²⁺-modified adenine nucleotide translocase (ANT) and the Ca²⁺-modified ATP synthase. We found in a previous study that ANT conformational changes may be involved in Tl⁺-induced MPTP opening in the inner membrane of Ca²⁺-loaded rat liver mitochondria. In this study, the effects of thiol-modifying agents (eosin-5-maleimide (EMA), fluorescein isothiocyanate (FITC), Cu(o-phenanthroline)₂ (Cu(OP)₂), and embelin (Emb)), and MPTP inhibitors (ADP, cyclosporine A (CsA), n-ethylmaleimide (NEM), and trifluoperazine (TFP)) on MPTP opening were tested simultaneously with increases in swelling, membrane potential (ΔΨ_mito) decline, decreases in state 3, 4, and 3U_DNP (2,4-dinitrophenol-uncoupled) respiration, and changes in the inner membrane free thiol group content. The effects of these thiol-modifying agents on the studied mitochondrial characteristics were multidirectional and showed a clear dependence on their concentration. This research suggests that Tl⁺-induced MPTP opening in the inner membrane of calcium-loaded mitochondria may be caused by the interaction of used reagents (EMA, FITC, Emb, Cu(OP)₂) with active groups of ANT, the mitochondrial phosphate carrier (PiC) and the mitochondrial respiratory chain complexes. This study provides further insight into the causes of thallium toxicity and may be useful in the development of new treatments for thallium poisoning.

Control of Ca2+ and metabolic homeostasis by the Na+/Ca2+ exchangers (NCXs) in health and disease

Spatial and temporal control of calcium (Ca²⁺) levels is essential for the background rhythms and responses of living cells to environmental stimuli. Whatever other regulators a given cellular activity may have, localized and wider scale Ca²⁺ events (sparks, transients, and waves) are hierarchical determinants of fundamental processes such as cell contraction, excitability, growth, metabolism and survival. Different cell types express specific channels, pumps and exchangers to efficiently generate and adapt Ca²⁺ patterns to cell requirements. The Na⁺/Ca²⁺ exchangers (NCXs) in particular contribute to Ca²⁺ homeostasis by buffering intracellular Ca²⁺ loads according to the electrochemical gradients of substrate ions - i.e., Ca²⁺ and sodium (Na⁺) - and under a dynamic control of redundant regulatory processes. An interesting feature of NCX emerges from the strict relationship that connects transporter activity with cell metabolism: on the one hand NCX operates under constant control of ATP-dependent regulatory processes, on the other hand the ion fluxes generated through NCX provide mechanistic support for the Na⁺-driven uptake of glutamate and Ca²⁺ influx to fuel mitochondrial respiration. Proof of concept evidence highlights therapeutic potential of preserving a timed and balanced NCX activity in a growing rate of diseases (including excitability, neurodegenerative, and proliferative disorders) because of an improved ability of stressed cells to safely maintain ion gradients and mitochondrial bioenergetics. Here, we will summarize and review recent works that have focused on the pathophysiological roles of NCXs in balancing the two-way relationship between Ca²⁺ signals and metabolism.

AMPK activation induced by promethazine increases NOXA expression and Beclin-1 phosphorylation and drives autophagy-associated apoptosis in chronic myeloid leukemia

Relapse and drug resistance is still major challenges in the treatment of leukemia. Promethazine, an antihistaminic phenothiazine derivative, has been used to prevent chemotherapy-induced emesis, although there is no report about its antitumor potential. Thus, we evaluated the promethazine cytotoxicity against several leukemia cells and the underlying mechanisms were investigated. Promethazine exhibited potent and selective cytotoxicity against all leukemia cell types in vitro at clinically relevant concentrations. Philadelphia positive chronic myeloid leukemia (CML) K562 cells were the most sensitive cell line. The cytotoxicity of promethazine in these cells was triggered by the activation of AMPK and inhibition of PI3K/AKT/mTOR pathway. The subsequent downstream effects were NOXA increase, MCL-1 decrease, and Beclin-1 activation, resulting in autophagy-associated apoptosis. These data highlight targeting autophagy may represent an interesting strategy in CML therapy, and also the antitumor potential of promethazine by acting in AMPK and PI3K/AKT/mTOR signaling pathways. Since this drug is currently used with relative low side effects, its repurposing may represent a new therapeutic opportunity for leukemia treatment.

Increased lipid peroxidation, apoptosis and selective cytotoxicity in colon cancer cell line LoVo and its doxorubicin-resistant subline LoVo/Dx in the presence of newly synthesized phenothiazine derivatives

Cancer cells often develop the resistance to pro-apoptotic signaling that makes them invulnerable to conventional treatment. Therapeutic strategies that make cancer cells enter the path of apoptosis are desirable due to the avoidance of inflammatory reaction that usually accompanies necrosis. In the present study phenothiazines (fluphenazine and four recently synthesized derivatives) were investigated in order to identify compounds with a potent anticancer activity. Since phenothiazines are known as multidrug resistance modulators the sensitive human colorectal adenocarcinoma cell line (LoVo) and its doxorubicin-resistant, ABCB1 overexpressing, subline (LoVo/Dx) have been employed as a model system. In studied cancer cells cytotoxic effect of the phenothiazine derivatives was accompanied by apoptosis and autophagy induction as well as by the increase of cellular lipid peroxidation and intracellular reactive oxygen species generation. Molecular modelling revealed that reactivity of phenothazines (manifested by their low energy gap) but not lipophilicity was positively correlated with their anticancer potency, pro-oxidant properties and apoptosis induction ability. Additionally, some of the studied compounds turned out to be more potent cytotoxic and pro-apoptotic agents in doxorubicin-resistant (LoVo/Dx) cells than in sensitive ones (LoVo). The hypothesis was assumed that studied phenothiazine derivatives induced apoptotic cell death by increasing the production of reactive oxygen species.

Magnesium in schizophrenia

Many psychopathological symptoms, including schizophrenia, can be associated with magnesium metabolism disturbances. In the literature, contradictory data exist regarding magnesium levels in patients with this disorder. However, this situation might be caused by determination of extracellular concentration of magnesium; although, this is mainly an intracellular ion. There are no data concerning determination of the ionized fraction of magnesium in patients with schizophrenia, while the ionized fraction represents 67% of the total pool of magnesium in healthy people. Also, the mechanism of magnesium action-the effect of magnesium ions on NMDA and GABA receptors-has not yet been fully investigated. There are preliminary studies aimed at increasing the effectiveness of schizophrenia pharmacotherapy via magnesium supplementation. Multidirectional activity of magnesium can significantly increase its therapeutic effect in psychiatry. This observation is confirmed by recent studies conducted by various research teams. However, further studies on the role of magnesium supplementation in patients with schizophrenia are needed.

Drug induced mitochondrial dysfunction: Mechanisms and adverse clinical consequences

Several commonly used medications impair mitochondrial function resulting in adverse effects or toxicities. Drug induced mitochondrial dysfunction may be a consequence of increased production of reactive oxygen species, altered mitochondrial permeability transition, impaired mitochondrial respiration, mitochondrial DNA damage or inhibition of beta-oxidation of fatty acids. The clinical manifestation depends on the specific drug and its effect on mitochondria. Given the ubiquitous presence of mitochondria and its central role in cellular metabolism, drug-mitochondrial interactions may manifest clinically as hepatotoxicity, enteropathy, myelosuppression, lipodystrophy syndrome or neuropsychiatric adverse effects, to name a few. The current review focuses on specific drug groups which adversely affect mitochondria, the mechanisms involved and the clinical consequences based on the data available from experimental and clinical studies. Knowledge of these adverse drug-mitochondrial interactions may help the clinicians foresee potential issues in individual patients, prevent adverse drug reactions or alter drug regimens to enhance patient safety.

Thioridazine Alters the Cell-Envelope Permeability of Mycobacterium tuberculosis

The increasing occurrence of multidrug resistant tuberculosis exerts a major burden on treatment of this infectious disease. Thioridazine, previously used as a neuroleptic, is active against extensively drug resistant tuberculosis when added to other second- and third-line antibiotics. By quantitatively studying the proteome of thioridazine-treated Mycobacterium tuberculosis, we discovered the differential abundance of several proteins that are involved in the maintenance of the cell-envelope permeability barrier. By assessing the accumulation of fluorescent dyes in mycobacterial cells over time, we demonstrate that long-term drug exposure of M. tuberculosis indeed increased the cell-envelope permeability. The results of the current study demonstrate that thioridazine induced an increase in cell-envelope permeability and thereby the enhanced uptake of compounds. These results serve as a novel explanation to the previously reported synergistic effects between thioridazine and other antituberculosis drugs. This new insight in the working mechanism of this antituberculosis compound could open novel perspectives of future drug-administration regimens in combinational therapy.

Binding of phenothiazines into allosteric hydrophobic pocket of human thioredoxin 1

Thioredoxins are multifunctional oxidoreductase proteins implicated in the antioxidant cellular apparatus and oxidative stress. They are involved in several pathologies and are promising anticancer targets. Identification of noncatalytic binding sites is of great interest for designing new allosteric inhibitors of thioredoxin. In a recent work, we predicted normal mode motions of human thioredoxin 1 and identified two major putative hydrophobic binding sites. In this work we investigated noncovalent interactions of human thioredoxin 1 with three phenotiazinic drugs acting as prooxidant compounds by using molecular docking and circular dichroism spectrometry to probe ligand binding into the previously predicted allosteric hydrophobic pockets. Our in silico and CD spectrometry experiments suggested one preferred allosteric binding site involving helix 3 and adopting the best druggable conformation identified by NMA. The CD spectra showed binding of thioridazine into thioredoxin 1 and suggested partial helix unfolding, which most probably concerns helix 3. Taken together, these data support the strategy to design thioredoxin inhibitors targeting a druggable allosteric binding site.

Data-driven identification of structural alerts for mitigating the risk of drug-induced human liver injuries

Background

The use of structural alerts to de-prioritize compounds with undesirable features as drug candidates has been gaining in popularity. Hundreds of molecular structural moieties have been proposed as structural alerts. An emerging issue is that strict application of these alerts will result in a significant reduction of the chemistry space for new drug discovery, as more than half of the oral drugs on the market match at least one of the alerts. To mitigate this issue, we propose to apply a rigorous statistical analysis to derive/validate structural alerts before use.

Method

To derive human liver toxicity structural alerts, we retrieved all small-molecule entries from LiverTox, a U.S. National Institutes of Health online resource for information on human liver injuries induced by prescription and over-the-counter drugs and dietary supplements. We classified the compounds into hepatotoxic, nonhepatotoxic, and possible hepatotoxic classes, and performed detailed statistical analyses to identify molecular structural fragments highly enriched in the hepatotoxic class beyond random distribution as structural alerts for human liver injuries.

Results

We identified 12 molecular fragments present in multiple marketed drugs that one can consider as common “drug-like” fragments, yet they are strongly associated with drug-induced human liver injuries. Thus, these fragments may be considered as robust hepatotoxicity structural alerts suitable for use in drug discovery screening programs.

Conclusions

The use of structural alerts has contributed to the identification of many compounds with potential toxicity issues in modern drug discovery. However, with a large number of structural alerts published to date without proper validation, application of these alerts may restrict the chemistry space and prevent discovery of valuable drugs. To mitigate this issue, we showed how to use statistical analyses to develop a small, robust, and broadly applicable set of structural alerts.

Graphical abstract

Toxic effects of xylazine on endothelial cells in combination with cocaine and 6-monoacetylmorphine

The use of xylazine as a drug of abuse has emerged worldwide in the last 7 years, including Puerto Rico. Clinical findings reported that xylazine users present greater physiological deterioration, than heroin users. The aim of this study was to assess the xylazine toxicity on endothelial cells, as this is one of the first tissues impact upon administration. Human umbilical vein endothelial cells in culture were treated with xylazine, cocaine, 6-monoacetylmorphine (heroin metabolite) and its combinations, at concentrations of 0.10-400 μM, for periods of 24, 48 and 72 h. IC50 were calculated and the Annexin V assay implemented to determine the cell death mechanism. Results indicated IC50 values at 24h as follow: xylazine 62 μM, cocaine 210 μM, 6-monoacetylmorphine 300 μM. When these drugs were combined the IC50 value was 57 μM. Annexin V results indicated cell death by an apoptosis mechanism in cells treated with xylazine or in combination. Results demonstrated that xylazine use inhibits the endothelial cell proliferation, at lower concentrations than cocaine and 6-monoacetylmorphine. These findings contribute to the understanding of the toxicity mechanisms induced by xylazine on endothelial cells.

UV-light effects on cytochrome c modulated by the aggregation state of phenothiazines

The present study shows the factors that modulate the photodamage promoted by phenothiazines. Cytochrome c was irradiated with UV light for 120 min, over a pH range from 4.0 to 8.0, in the absence and in the presence of different concentrations of thioridazine (TR) and fluphenazine (FP). In the absence of phenothiazines, the maximal rate of a Soret band blue shift (nm/min) from 409 to 406 nm was obtained at pH 4.0 (0.028 nm/min). The presence of phenothiazines at the concentration range 10-25 µmol/L amplified and accelerated a cytochrome c blue shift (409 to 405 nm, at a rate = 0.041 nm/min). Above 25 µmol/L, crescent concentrations of phenothiazines contributed to cytochrome c protection with (maximal at 2500 µmol/L). Scanning electronic microscopy revealed the formation of nanostructures. The pH also influenced the effect of low phenothiazine concentrations on cytochrome c. Thus, the predominance of phenothiazine-promoted cytochrome c damage or protection depends on a balance of the following factors: the yield of photo-generated drug cation radicals, which is favored by acidic pH; the stability of the cation radicals, which is favored by the drug aggregation; and the cytochrome c structure, modulated by the pH.

Effect of garlic-derived organosulfur compounds on mitochondrial function and integrity in isolated mouse liver mitochondria

The objectives of this work were to evaluate the direct effects of diallysulfide (DAS) and diallyldisulfide (DADS), two major organosulfur compounds of garlic oil, on mitochondrial function and integrity, by using isolated mouse liver mitochondria in a cell-free system. DADS produced concentration-dependent mitochondrial swelling over the range 125-1000μM, while DAS was ineffective. Swelling experiments performed with de-energized or energized mitochondria showed similar maximal swelling amplitudes. Cyclosporin A (1μM), or ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA, 1mM) were ineffective in inhibiting DADS-induced mitochondrial swelling. DADS produced a minor (12%) decrease in mitochondrial membrane protein thiols, but did not induce clustering of mitochondrial membrane proteins. Incubation of mitochondria with DADS (but not DAS) produced an increase in the oxidation rate of 2',7' dichlorofluorescein diacetate (DCFH-DA), together with depletion of reduced glutathione (GSH) and increased lipid peroxidation. DADS (but not DAS) produced a concentration-dependent dissipation of the mitochondrial membrane potential, but did not induce cytochrome c release. DADS-dependent effects, including mitochondrial swelling, DCFH-DA oxidation, lipid peroxidation and loss of mitochondrial membrane potential, were inhibited by antioxidants and iron chelators. These results suggest that DADS causes direct impairment of mitochondrial function as the result of oxidation of the membrane lipid phase initiated by the GSH- and iron-dependent generation of oxidants.

Release of NO from a nitrosyl ruthenium complex through oxidation of mitochondrial NADH and effects on mitochondria

Nitrosyl ruthenium complexes are promising NO donor agents with numerous advantages for the biologic applications of NO. We have characterized the NO release from the nitrosyl ruthenium complex [Ru(NO(2))(bpy)(2)(4-pic)](+) (I) and the reactive oxygen/nitrogen species (ROS/RNS)-mediated NO actions on isolated rat liver mitochondria. The results indicated that oxidation of mitochondrial NADH promotes NO release from (I) in a manner mediated by NO(2) formation (at neutral pH) as in mammalian cells, followed by an oxygen atom transfer mechanism (OAT). The NO released from (I) uncoupled mitochondria at low concentrations/incubation times and inhibited the respiratory chain at high concentrations/incubation times. In the presence of ROS generated by mitochondria NO gave rise to peroxynitrite, which, in turn, inhibited the respiratory chain and oxidized membrane protein-thiols to elicit a Ca(2+)-independent mitochondrial permeability transition; this process was only partially inhibited by cyclosporine-A, almost fully inhibited by the thiol reagent N-ethylmaleimide (NEM) and fully inhibited by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). These actions correlated with the release of cytochrome c from isolated mitochondria as detected by Western blotting analysis. These events, typically involved in cell necrosis and/or apoptosis denote a potential specific action of (I) and analogs against tumor cells via mitochondria-mediated processes.

Cysteine 203 of cyclophilin D is critical for cyclophilin D activation of the mitochondrial permeability transition pore

The mitochondrial permeability transition pore (mPTP) opening plays a critical role in mediating cell death during ischemia/reperfusion (I/R) injury. Our previous studies have shown that cysteine 203 of cyclophilin D (CypD), a critical mPTP mediator, undergoes protein S-nitrosylation (SNO). To investigate the role of cysteine 203 in mPTP activation, we mutated cysteine 203 of CypD to a serine residue (C203S) and determined its effect on mPTP opening. Treatment of WT mouse embryonic fibroblasts (MEFs) with H(2)O(2) resulted in an 50% loss of the mitochondrial calcein fluorescence, suggesting substantial activation of the mPTP. Consistent with the reported role of CypD in mPTP activation, CypD null (CypD(-/-)) MEFs exhibited significantly less mPTP opening. Addition of a nitric oxide donor, GSNO, to WT but not CypD(-/-) MEFs prior to H(2)O(2) attenuated mPTP opening. To test whether Cys-203 is required for this protection, we infected CypD(-/-) MEFs with a C203S-CypD vector. Surprisingly, C203S-CypD reconstituted MEFs were resistant to mPTP opening in the presence or absence of GSNO, suggesting a crucial role for Cys-203 in mPTP activation. To determine whether mutation of C203S-CypD would alter mPTP in vivo, we injected a recombinant adenovirus encoding C203S-CypD or WT CypD into CypD(-/-) mice via tail vein. Mitochondria isolated from livers of CypD(-/-) mice or mice expressing C203S-CypD were resistant to Ca(2+)-induced swelling as compared with WT CypD-reconstituted mice. Our results indicate that the Cys-203 residue of CypD is necessary for redox stress-induced activation of mPTP.

Mitochondrial glutathione transferases involving a new function for membrane permeability transition pore regulation

The mitochondria in mammalian cells are a predominant resource of reactive oxygen species (ROS), which are produced during respiration-coupled oxidative metabolism or various chemical stresses. End-products from membrane-lipid peroxidation caused by ROS are highly toxic, thereby their elimination/scavenging are protective of mitochondria and cells against oxidative damages. In mitochondria, soluble (kappa, alpha, mu, pi, zeta) and membrane-bound glutathione transferases (GSTs) (MGST1) are distributed. Mitochondrial GSTs display both glutathione transferase and peroxidase activities that detoxify such harmful products through glutathione (GSH) conjugation or GSH-mediated peroxide reduction. Some GST isoenzymes are induced by oxidative stress, an adaptation mechanism for the protection of cells from oxidative stress. Membrane-bound MGST1 is activated through the thiol modification in oxidative conditions. Protective action of MGST1 against oxidative stress has been confirmed using MCF7 cells highly expressed of MGST1. In recent years, mitochondria have been recognized as a regulator of cell death via both apoptosis and necrosis, where oxidative stress-induced alteration of the membrane permeability is an important step. Recent studies have shown that MGST1 in the inner mitochondrial membrane could interact with the mitochondrial permeability transition (MPT) regulator proteins, such as adenine nucleotide translocator (ANT) and/or cyclophilin D, and could contribute to oxidant-induced MPT pores. Interaction of GST alpha with ANT has also been shown. In this review, functions of the mitochondrial GSTs, including a new role for mitochondria-mediated cell death, are described.