Mitochondria as regulators of apoptosis: doubt no more

Activation of c-Jun N-terminal kinase mediates tanshinone IIA-induced apoptosis in KBM-5 chronic myeloid leukemia cells

Aim of this study was to identify the molecular mechanisms of tanshinone IIA-induced apoptosis in chronic myelogenous leukemia (CML) cells. Cytotoxicity of tanshinone IIA was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Our data demonstrate that tanshinone IIA induced apoptosis by increasing the sub-G1 DNA contents and DNA fragmentation in KBM-5 CML cell line. In addition, tanshinone IIA significantly reduced mitochondrial membrane potential (MMP), mediated cytochrome c release from mitochondria and activated caspase-3 and 9, indicating mitochondria-dependent apoptosis by tanshinone IIA. Tanshinone IIA attenuated expression of several apoptosis-related proteins such as c-inhibitor of apoptosis protein (IAP) 2, Mcl-1(L) and Bcl-2. Interestingly, although tanshinone IIA notably enhanced the phosphorylation of both c-Jun N-terminal protein kinase (JNK) and p38, JNK inhibitor, but not p38 inhibitor, reversed tanshinone IIA-induced apoptosis. Our findings suggest that tanshinone IIA induces mitochondria-dependent apoptosis via activation of JNK in KBM 5 cells as a potent anti-cancer agent for CML therapy.

Verrucarin A, a protein synthesis inhibitor, induces growth inhibition and apoptosis in breast cancer cell lines MDA-MB-231 and T47D

Verrucarin A (VA), a protein synthesis inhibitor, derived from the pathogen fungus Myrothecium verrucaria, inhibits growth of leukemia cell lines and activates caspases and apoptosis and inflammatory signaling in macrophages. We have investigated VA-induced growth inhibition in breast cancer cells MDA-MB-231 and T47D and, particularly, the mechanism of VA-induced apoptosis. VA treatment brought about apoptotic cell death in a dose- and time-dependent manner which was associated with chromatin condensation, cell shrinkage, nuclear fragmentation and intracellular ROS production. Mitochondrial membrane depolarization, activation of caspase-3, down-regulation of Bcl-2 expression and up-regulation of Bax and p53 expression were observed. VA thus affects the viability of both the breast cancer cells by triggering ROS-mediated intrinsic mechanism of apoptosis.

Streptococcus pneumoniae ClpP protease induces apoptosis via caspase-independent pathway in human neuroblastoma cells: cytoplasmic relocalization of p53

Streptococcus pneumoniae causes the most severe form of the bacterial meningitis which is the major cause of bacterial meningitis. Virulence factors produced by S. pneumoniae have been known to contribute significantly to the disease process. ClpP protease (ClpP) which is essential for virulence and survival under stress conditions in S. pneumoniae was examined for the ability to induce apoptosis and the mechanism of the induction of apoptosis in human neuron-like cells, SK-N-SH neuroblastoma cells. ClpP inhibited cell growth and induced apoptosis in SK-N-SH cells. Treatment with ClpP resulted in hypodiploid DNA contents, increased Bax/Bcl-2 ratio and induction of reactive oxygen species (ROS) production. The release of cytochrome c from mitochondria into the cytosol, which is an initiator of the activation of caspase cascades, was not observed in ClpP-treated cells. In addition, pretreatment with Z-Val-Ala-Asp-fluoromethylketone (Z-VAD-fmk), a broad spectrum caspase inhibitor, could not rescue apoptotic cells from ClpP toxicity. Coincidently, caspase-3 and -8 activation and cleavage of PARP were not detected. Moreover, caspase independent apoptosis-inducing factor (AIF) was released from mitochondria and translocated to the nucleus in response to ClpP. We also found that ClpP treatment resulted in the increase of p53 activity and cytoplasmic p53 levels were increased by ClpP, suggesting that functional activation of p53 is intact despite increased cytoplasmic accumulation. Taken together, these data suggest that ClpP contributes to neuronal damage in meningitis and provide further insight into the mechanisms underlying action of pneumococcal virulence factors during bacterial pathogenesis.

Bax induces cytochrome c release by multiple mechanisms in mitochondria from MCF7 cells

Bax, a pro-apoptotic member of the Bcl-2 family of proteins has the ability to form transmembrane pores large enough to allow cytochrome c (Cyt c) release, as well as to activate the mitochondrial permeability transition pore (mPTP); however, no differential study has been conducted to clarify which one of these mechanisms predominates over the other in the same system. In the present study, we treated isolated mitochondria from MCF7 cells with recombinant protein Bax and tested the efficacy of the mPTP inhibitor cyclosporin A (CsA) and of the Bax channel blocker (Bcb) to inhibit cytochrome c release. We also, induced apoptosis in MCF7 cell cultures with TNF-α plus cycloheximide to determine the effect of such compounds in apoptosis induction via mPTP or Bax oligomerization. Cytochrome c release was totally prevented by CsA and partially by Bcb when apoptosis was induced with recombinant Bax in isolated mitochondria from MCF7 cells. CsA increased the number of living cells in cell culture, as compared with the effect of Bax channel blocker. These results indicate that mPTP activation is the predominant pathway for Bax-induced cytochrome c release from MCF7 mitochondria and for apoptosis induction in the whole cell.

DC-81-enediyne induces apoptosis of human melanoma A375 cells: involvement of the ROS, p38 MAPK, and AP-1 signaling pathways

Melanoma is one of the most chemoresistant cancers in patient care. The remission rate of current therapy remains low. DC-81, an antitumor antibiotic produced by Streptomyces species, belongs to pyrrolo[2,1-c][1,4]benzodiazepine (PBD), which is a potent inhibitor of nucleic acid synthesis. An enediyne contains either DNA intercalating groups or DNA minor groove binding functions and these are potent DNA-damaging agents due to their ability to generate benzenoid diradicals. We have previously reported an efficient synthesis and antitumor activity of a series of novel PBD hybrids linked with enediyne. The purpose of this study was to examine the mechanism of the antiproliferative effect of DC-81-enediyne agent on human melanoma A375 cells. DC-81-enediyne induced an increase in Ca(2+) level and reactive oxygen species (ROS) generation as detected by flow cytometric assay. Western blot analysis showed that DC-81-enediyne induced the phosphorylation of p38 and activating transcription factor 2 (ATF-2). By using the luciferase reporter assay, activating protein-1 (AP-1) activity was further enhanced after A375 cells were treated with graded concentrations of DC-81-enediyne. DC-81-enediyne treatment-induced A375 cell apoptosis was significantly abrogated by the addition of Ca(2+), ROS, and p38 inhibitors. Collectively, our studies indicate that DC-81-enediyne induces A375 cell apoptosis through an increased Ca(2+) and ROS generation, which involves p38 phosphorylation and enhanced ATF-2/AP-1 expressions, leading to caspase-3 activity, poly(ADP-ribose)polymerase cleavage, M30 CytoDeath staining, and subsequent apoptotic cell death.

Respiratory complex III dysfunction in humans and the use of yeast as a model organism to study mitochondrial myopathy and associated diseases

The bc1 complex or complex III is a central component of the aerobic respiratory chain in prokaryotic and eukaryotic organisms. It catalyzes the oxidation of quinols and the reduction of cytochrome c, establishing a proton motive force used to synthesize adenosine triphosphate (ATP) by the F1Fo ATP synthase. In eukaryotes, the complex III is located in the inner mitochondrial membrane. The genes coding for the complex III have a dual origin. While cytochrome b is encoded by the mitochondrial genome, all the other subunits are encoded by the nuclear genome. In this review, we compile an exhaustive list of the known human mutations and associated pathologies found in the mitochondrially-encoded cytochrome b gene as well as the fewer mutations in the nuclear genes coding for the complex III structural subunits and accessory proteins such as BCS1L involved in the assembly of the complex III. Due to the inherent difficulties of studying human biopsy material associated with complex III dysfunction, we also review the work that has been conducted to study the pathologies with the easy to handle eukaryotic microorganism, the yeast Saccharomyces cerevisiae. Phenotypes, biochemical data and possible effects due to the mutations are also discussed in the context of the known three-dimensional structure of the eukaryotic complex III. This article is part of a Special Issue entitled: Respiratory complex III and related bc complexes.

Nigral neurons are likely to die of a mechanism other than classical apoptosis in Parkinson's disease

The finding of apoptosis in Parkinson's disease (PD) represents a contentious issue. In fact, there is increasing evidence that an alternative mechanism of cell death is at work in the parkinsonian substantia nigra, which we tentatively term aposklesis. Unlike apoptosis, aposklesis ("withering") lacks the morphological signs of apoptosis and takes a slow course which is in agreement with the predicted rate of dopaminergic cell death in PD. Cells undergoing aposklesis may stain positive in the TUNEL reaction and show a reticular nuclear labeling but lack any significant chromatin condensation and the formation of apoptotic bodies. Not only neurons but also glial cells appear to undergo this form of cell death, which represents a relatively common finding in degenerative diseases of the CNS.

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.

The obesity-related peptide leptin sensitizes cardiac mitochondria to calcium-induced permeability transition pore opening and apoptosis

The obesity-related 16 kDa peptide leptin is synthesized primarily in white adipocytes although its production has been reported in other tissues including the heart. There is emerging evidence that leptin may contribute to cardiac pathology especially that related to myocardial remodelling and heart failure. In view of the importance of mitochondria to these processes, the goal of the present study is to determine the effect of leptin on mitochondria permeability transition pore opening and the potential consequence in terms of development of apoptosis. Experiments were performed using neonatal rat ventricular myocytes exposed to 3.1 nM (50 ng/ml) leptin for 24 hours. Mitochondrial transition pore opening was analyzed as the capacity of mitochondria to retain the dye calcein-AM in presence of 200 µM CaCl2. Leptin significantly increased pore opening although the effect was markedly more pronounced in digitonin-permeabilized myocytes in the presence of calcium with both effects prevented by the transition pore inhibitor sanglifehrin A. These effects were associated with increased apoptosis as evidenced by increased TUNEL staining and caspase 3 activity, both of which were prevented by the transition pore inhibitor sanglifehrin A. Leptin enhanced Stat3 activation whereas a Stat 3 inhibitor peptide prevented leptin-induced mitochondrial transition pore opening as well as the hypertrophic and pro-apoptotic effects of the peptide. Inhibition of the RhoA/ROCK pathway prevented the hypertrophic response to leptin but had no effect on increased pore opening following leptin administration. We conclude that leptin can enhance calcium-mediated, Stat3-dependent pro-apoptotic effects as a result of increased mitochondrial transition pore opening and independently of its hypertrophic actions. Leptin may therefore contribute to mitochondrial dysfunction and the development of apoptosis in the diseased myocardium particularly under conditions of excessive intracellular calcium accumulation.

Effect of PACAP in central and peripheral nerve injuries

Pituitary adenylate cyclase activating polypeptide (PACAP) is a bioactive peptide with diverse effects in the nervous system. In addition to its more classic role as a neuromodulator, PACAP functions as a neurotrophic factor. Several neurotrophic factors have been shown to play an important role in the endogenous response following both cerebral ischemia and traumatic brain injury and to be effective when given exogenously. A number of studies have shown the neuroprotective effect of PACAP in different models of ischemia, neurodegenerative diseases and retinal degeneration. The aim of this review is to summarize the findings on the neuroprotective potential of PACAP in models of different traumatic nerve injuries. Expression of endogenous PACAP and its specific PAC1 receptor is elevated in different parts of the central and peripheral nervous system after traumatic injuries. Some experiments demonstrate the protective effect of exogenous PACAP treatment in different traumatic brain injury models, in facial nerve and optic nerve trauma. The upregulation of endogenous PACAP and its receptors and the protective effect of exogenous PACAP after different central and peripheral nerve injuries show the important function of PACAP in neuronal regeneration indicating that PACAP may also be a promising therapeutic agent in injuries of the nervous system.

Clavulanic acid inhibits MPP⁺-induced ROS generation and subsequent loss of dopaminergic cells

Clavulanic acid is a psychoactive compound that has been shown to modulate central nervous system activity. Importantly, in neurotoxin-induced animal models, clavulanic acid has been shown to improve motor function (Huh et al., 2010) suggesting that it can be neuroprotective; however, the mechanism as how clavulanic acid can induce neuroprotection is not known. We demonstrate here that clavulanic acid abrogates the effects of the neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) which mimics Parkinson's disease (PD) by inducing neurodegeneration. To further establish the mechanism we identified that clavulanic acid inhibits neurotoxin-induced loss of mitochondrial membrane potential and ROS production. Consistent with these results, neurotoxin-induced increase in Bax levels was also decreased in clavulanic acid treated cells. Importantly, neurotoxin-induced release of cytochrome c levels as well as caspase activation was also inhibited in clavulanic acid treated cells. In addition, Bcl-xl levels were also restored and the Bcl-xl/Bax ratio that is critical for inducing apoptosis was increased in clavulanic acid treated cells. Overall, these results suggest that clavulanic acid is intimately involved in inhibiting neurotoxin-induced loss of mitochondrial function and induction of apoptosis that contributes towards neuronal survival.

Rad knockdown induces mitochondrial apoptosis in bortezomib resistant leukemia and lymphoma cells

To understand the molecular mechanism(s) underlying bortezomib resistance, we sought to identify potential target genes that were differentially expressed in bortezomib-resistant leukemia cells versus parental controls. Microarray analysis revealed that the mRNA levels of Rad (Ras associated with diabetes) were higher in the bortezomib-resistant Jurkat (Jurkat-R) cells than in the parental control cells. The importance of Rad for bortezomib resistance was supported by three observations. First, Rad knockdown overcame bortezomib resistance and induced mitochondrial apoptosis via Noxa/Bcl-2 modulation. Second, Rad decreased cell death in response to bortezomib. Third, leukemia and lymphoma cell lines (K-562, Raji, IM-9 and Jurkat-R) with elevated Rad expression levels showed higher degrees of bortezomib resistance versus those (Sup-B15, JVM-2, U266 and Jurkat) with low Rad expression levels (r=0.48, P=0.0004). Thus, Rad over expression could be a molecular target to improve bortezomib sensitivity in human leukemia and lymphoma.

SIRT3 protects from hypoxia and staurosporine-mediated cell death by maintaining mitochondrial membrane potential and intracellular pH

Mitochondrial sirtuin 3 (SIRT3) mediates cellular resistance toward various forms of stress. Here, we show that in mammalian cells subjected to hypoxia and staurosporine treatment SIRT3 prevents loss of mitochondrial membrane potential (ΔΨ(mt)), intracellular acidification and reactive oxygen species accumulation. Our results indicate that: (i) SIRT3 inhibits mitochondrial permeability transition and loss of membrane potential by preventing HKII binding to the mitochondria, (ii) SIRT3 increases catalytic activity of the mitochondrial carbonic anhydrase VB, thereby preventing intracellular acidification, Bax activation and apoptotic cell death. In conclusion we propose that, in mammalian cells, SIRT3 has a central role in connecting changes in ΔΨ(mt), intracellular pH and mitochondrial-regulated apoptotic pathways.

Down-regulation of Notch receptor signaling pathway induces caspase-dependent and caspase-independent apoptosis in lung squamous cell carcinoma cells

Notch receptor signaling pathway (NRSP) is increasingly linked to carcinogenesis. Non-small cell lung cancer (NSCLC) appears to actively utilize this conserved developmental pathway. The aims of this study are to determine whether or not Notch 1-4 are overexpressed in NSCLC tissues compared with normal lung tissues and whether inhibiting NRSP could induce caspase-dependent or caspase-independent apoptosis. Immunohistochemistry was used to evaluate the expression of Notch 1-4 in 101 NSCLC tissue samples and 30 normal lung tissue samples. DAPT was used to repress NRSP in SK-MES-1 cells. Apoptosis was determined by Annexin V and PI staining. Cleaved poly ADP-ribose polymerase (PARP) was measured by Western blot; X-linked inhibitor of apoptosis protein (XIAP) and Survivin were assessed by qRT-PCR and Western blot; the release of second mitochondria-derived activator of caspase (Smac) from mitochondria to cytoplasm was evaluated by Western blot; the subcellular locations of endonuclease G (Endo G) and apoptosis inducing factor (AIF) were observed by Western blot and indirect immunofluorescence analysis. (Mech Dev, 98, 2000, 95) Notch 1-4 are up-regulated in NSCLC tissues and Notch 1, 2 are positively correlated with lymph node metastasis, (Proc Natl Acad Sci U S A, 106, 2009, 22293) DAPT treatment could inhibit NRSP and induce apoptosis, with a marked increase in cleaved PARP, decreases in XIAP and Survivin proteins and concomitant release of Smac, EndoG, and AIF from mitochondria, indicating that inhibiting NRSP by DAPT triggers caspase-dependent and caspase-independent apoptosis.

Reactive oxygen/nitrogen species and their functional correlations in neurodegenerative diseases

The continuous production and efflux of reactive oxygen/nitrogen species from endogenous and exogenous sources can damage biological molecules and initiate a cascade of events. Mitochondria are pivotal in controlling cell survival and death. Cumulative oxidative stress, disrupted mitochondrial respiration, and mitochondrial damage are related with various neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and others. Biochemical cascades of apoptosis are mediated in signaling molecules, including protein kinases and transcription factors. The expressions in the pro-apoptotic signal transduction networks may indeed promote cell death and degeneration in brain cells. The regulation of that protein phosphorylation by kinases and phosphatases is emerging as a prerequisite mechanism in the control of the apoptotic cell death program. In this review, we attempt to put forth the evidence for possible mechanistic explanations for involvement of free radicals in the pathogenesis of neurodegenerative diseases.

Thy28 partially prevents apoptosis induction following engagement of membrane immunoglobulin in WEHI-231 B lymphoma cells

Thy28 protein is conserved among plants, bacteria, and mammalian cells. Nuclear Thy28 protein is substantially expressed in testis, liver, and immune cells such as lymphocytes. Lymphocyte apoptosis plays a crucial role in homeostasis and formation of a diverse lymphocyte repertoire. In this study, we examined whether Thy28 affects induction of apoptosis in WEHI-231 B lymphoma cells following engagement of membrane immunoglobulin (mIg). Once they were established, the Thy28-overexpressing WEHI-231 cells showed similar expression levels of IgM and class I major histocompatibility complex (MHC) molecule compared with controls. The Thy28-overexpressing cells were considerably resistant to loss of mitochondrial membrane potential (ΔΨm), caspase-3 activation, and increase in annexin-positive cells upon mIg engagement. These changes were concomitant with an increase in G1 phase associated with upregulation of p27^Kip1. The anti-IgM-induced sustained activation of c-Jun N-terminal kinase (JNK), which was associated with late-phase hydrogen peroxide (H₂O₂) production, was partially reduced in the Thy28-expressing cells relative to controls. Taken together, the data suggest that in WEHI-231 B lymphoma cells, Thy28 regulates mIg-mediated apoptotic events through the JNK-H₂O₂ activation pathway, concomitant with an accumulation of cells in G1 phase associated with upregulation of p27^Kip1 in WEHI-231 B lymphoma cells.

Role of hesperetin (a natural flavonoid) and its analogue on apoptosis in HT-29 human colon adenocarcinoma cell line--a comparative study

Colon cancer is one of the serious health problems in most developed countries and its incidence rate is increasing in India. Hesperetin (HN) (3',5,7-trihydroxy-4'-methoxyflavonone) and hesperetin analogue (HA) were tested for their apoptosis inducing ability. Methyl thiazolyl tetrazolium assay revealed a dose as well as duration-dependent reduction of HT-29 (colon adenocarcinoma) cellular growth in response to HN and HA treatment. At 24 h 70 μM of HN and 32 μM of HA showed 50% reduction of HT-29 cellular growth. Acridine orange/ethidium bromide staining showed apoptotic features of cell death induced by HN and HA. Rhodamine 123 staining showed significant reduction in mitochondrial membrane potential induced by HN and HA. HN and HA induced DNA damage was confirmed by comet tail formation. Lipid peroxidation markers (TBARS) and protein oxidation marker (PCC) were significantly elevated in HN and HA treated groups. Enzymic antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) were slightly decreased in their activities compared to control (untreated HT-29 cells). Results of Western blot analysis of apoptosis associated genes revealed an increase in cytochrome C, Bax, cleaved caspase-3 expression and a decrease in Bcl-2 expression. These findings indicate that HN and HA induce apoptosis on HT-29 via Bax dependent mitochondrial pathway involving oxidant/antioxidant imbalance.

Targeting metabolism with arsenic trioxide and dichloroacetate in breast cancer cells

BACKGROUND

Cancer cells have a different metabolic profile compared to normal cells. The Warburg effect (increased aerobic glycolysis) and glutaminolysis (increased mitochondrial activity from glutamine catabolism) are well known hallmarks of cancer and are accompanied by increased lactate production, hyperpolarized mitochondrial membrane and increased production of reactive oxygen species.

METHODS

In this study we target the Warburg effect with dichloroacetate (DCA) and the increased mitochondrial activity of glutaminolysis with arsenic trioxide (ATO) in breast cancer cells, measuring cell proliferation, cell death and mitochondrial characteristics.

RESULTS

The combination of DCA and ATO was more effective at inhibiting cell proliferation and inducing cell death than either drug alone. We examined the effect of these treatments on mitochondrial membrane potential, reactive oxygen species production and ATP levels and have identified new molecular mechanisms within the mitochondria for both ATO and DCA: ATO reduces mitochondrial function through the inhibition of cytochrome C oxidase (complex IV of the electron transport chain) while DCA up-regulates ATP synthase β subunit expression. The potentiation of ATO cytotoxicity by DCA is correlated with strong suppression of the expression of c-Myc and HIF-1α, and decreased expression of the survival protein Bcl-2.

CONCLUSION

This study is the first to demonstrate that targeting two key metabolic hallmarks of cancer is an effective anti-cancer strategy with therapeutic potential.

Metabolic remodeling precedes mitochondrial outer membrane permeabilization in human glioma xenograft cells

Glioma cancer cells adapt to changing microenvironment and shift from mitochondrial oxidative phosphorylation to aerobic glycolysis for their metabolic needs irrespective of oxygen availability. In the present study, we show that silencing MMP-9 in combination with uPAR/cathepsin B switch the glycolytic metabolism of glioma cells to oxidative phosphorylation (OXPHOS) and generate reactive oxygen species (ROS) to predispose glioma cells to mitochondrial outer membrane permeabilization. shRNA for MMP-9 and uPAR (pMU) as well as shRNA for MMP-9 and cathepsin B (pMC) activated complexes of mitochondria involved in OXPHOS and inhibited glycolytic hexokinase expression. The decreased interaction of hexokinase 2 with mitochondria in the treated cells indicated the inhibition of glycolysis activation. Overexpression of Akt reversed the pMU- and pMC-mediated OXPHOS to glycolysis switch. The OXPHOS un-coupler oligomycin A altered the expression levels of the Bcl-2 family of proteins; treatment with pMU or pMC reversed this effect and induced mitochondrial outer membrane permeabilization. In addition, our results show changes in mitochondrial pore transition to release cytochrome c due to changes in the VDAC-Bcl-XL and BAX-BAK interaction with pMU and pMC treatments. Taken together, our results suggest that pMU and pMC treatments switch glioma cells from the glycolytic to the OXPHOS pathway through an inhibitory effect on Akt, ROS induction and an increase of cytosolic cytochrome c accumulation. These results demonstrate the potential of pMU and pMC as therapeutic candidates for the treatment of glioma.

l-Theanine prevents alcoholic liver injury through enhancing the antioxidant capability of hepatocytes

l-Theanine is a unique amino acid in green tea. We here evaluated the protective effects of l-theanine on ethanol-induced liver injury in vitro and in vivo. Our results revealed that l-theanine significantly protected hepatocytes against ethanol-induced cell cytotoxicity which displayed by decrease of viability and increase of LDH and AST. Furthermore, the experiments of DAPI staining, pro-caspase3 level and PARP cleavage determination indicated that l-theanine inhibited ethanol-induced L02 cell apoptosis. Mechanically, l-theanine inhibited loss of mitochondrial membrane potential and prevented cytochrome c release from mitochondria in ethanol-treated L02 cells. l-Theanine also prevented ethanol-triggered ROS and MDA generation in L02 cells. l-Theanine restored the antioxidant capability of hepatocytes including GSH content and SOD activity which were reduced by ethanol. In vivo experiments showed that l-theanine significantly inhibited ethanol-stimulated the increase of ALT, AST, TG and MDA in mice. Histopathological examination demonstrated that l-theanine pretreated to mice apparently diminished ethanol-induced fat droplets. In accordance with the in vitro study, l-theanine significantly inhibited ethanol-induced reduction of mouse antioxidant capability which included the activities of SOD, CAT and GR, and level of GSH. These results indicated that l-theanine prevented ethanol-induced liver injury through enhancing hepatocyte antioxidant abilities.

GL-V9, a newly synthetic flavonoid derivative, induces mitochondrial-mediated apoptosis and G2/M cell cycle arrest in human hepatocellular carcinoma HepG2 cells

We recently established that GL-V9, a newly synthetic flavonoid derivative, is an active cytotoxic component. In this study, we demonstrated that GL-V9 inhibited cells growth via inducing apoptosis and G2/M cell cycle arrest in human hepatocellular carcinoma HepG2 cells. Following the treatment of HepG2 cells with GL-V9, we observed poly (ADP-ribose) polymerase (PARP) cleavage and activation of caspase-3 and caspase-9, while caspase-8 remained unchanged. The expression ratio of Bcl-2/Bax was also decreased in GL-V9-treated cells. Meanwhile, the cell cycle-related proteins, such as cyclin B1, CDK1 and cdc25 were down-regulated in GL-V9-induced G2/M cell cycle arrest. Furthermore, we showed that GL-V9-induced apoptosis in HepG2 cells was achieved through mitochondrial pathway. It also regulated changes of mitochondrial membrane potential and increased the production of intracellular reactive oxygen species. Besides, the growth inhibitory effect of GL-V9 was examined in vivo using murine implanted tumor model. These studies indicate that GL-V9 shows promise as a therapeutic agent against human hepatoma.

Esculetin ameliorates carbon tetrachloride-mediated hepatic apoptosis in rats

Esculetin (ESC) is a coumarin that is present in several plants such as Fraxinus rhynchophylla and Artemisia capillaris. Our previous study found that FR ethanol extract (FR_EtOH) significantly ameliorated rats’ liver function. This study was intended to investigate the protective mechanism of ESC in hepatic apoptosis in rats induced by carbon tetrachloride. Rat hepatic apoptosis was induced by oral administration of CCl₄. All rats were administered orally with CCl₄ (20%, 0.5 mL/rat) twice a week for 8 weeks. Rats in the ESC groups were treated daily with ESC, and silymarin group were treated daily with silymarin. Serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) as well as the activities of the anti-oxidative enzymes glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase in the liver were measured. In addition, expression of liver apoptosis proteins and anti-apoptotic proteins were detected. ESC (100, 500 mg/kg) significantly reduced the elevated activities of serum ALT and AST caused by CCl₄ and significantly increased the activities of catalase, GPx and SOD. Furthermore, ESC (100, 500 mg/kg) significantly decreased the levels of the proapoptotic proteins (t-Bid, Bak and Bad) and significantly increased the levels of the anti-apoptotic proteins (Bcl-2 and Bcl-xL). ESC inhibited the release of cytochrome c from mitochondria. In addition, the levels of activated caspase-9 and activated caspase-3 were significantly decreased in rats treated with ESC than those in rats treated with CCl₄ alone. ESC significantly reduced CCl₄-induced hepatic apoptosis in rats.

Dexamethasone decreases cholestatic liver injury via inhibition of intrinsic pathway with simultaneous enhancement of mitochondrial biogenesis

BACKGROUND

Mitochondria are known to be involved in cholestatic liver injury. We tested the hypothesis that glucocorticoids can modulate mitochondrial function to alleviate cholestatic liver injury.

METHODS

A rat model of cholestasis was established by bile duct ligation (BDL), with a sham group receiving laparotomy without BDL, and a group receiving dexamethasone (DEX) treatment after BDL.

RESULTS

The liver function including total bilirubin levels, alanine transaminase and aspartate transaminase activities was significantly improved in the DEX treatment group in comparison to the BDL group. There was a significant upregulation of liver peroxisome proliferator-activated receptor γ coactivator-1α and mitochondrial transcriptional factor A protein between 6 and 72 h was found in the DEX group. DEX treatment significantly down-regulated Bax, caspase 9 and caspase 3 expression induced by BDL at 24-72 h, but had little effect on the expression of caspase 8, Bcl(2,) Fas and Fas-FasL complex. Consequently, the number of apoptotic liver cells in the DEX group was significantly less than in the BDL group at 72 h.

CONCLUSION

Our results indicate that glucocorticoids decreases cholestatic liver injury within hours after BDL. Early glucocorticoids treatment can enhance the mitochondrial biogenesis and modulate the intrinsic but not extrinsic pathway of apoptosis following BDL.

Rapid microfluidic perfusion enabling kinetic studies of lipid ion channels in a bilayer lipid membrane chip

There is growing recognition that lipids play key roles in ion channel physiology, both through the dynamic formation and dissolution of lipid ion channels and by indirect regulation of protein ion channels. Because existing technologies cannot rapidly modulate the local (bio)chemical conditions at artificial bilayer lipid membranes used in ion channel studies, the ability to elucidate the dynamics of these lipid-lipid and lipid-protein interactions has been limited. Here we demonstrate a microfluidic system supporting exceptionally rapid perfusion of reagents to an on-chip bilayer lipid membrane, enabling the responses of lipid ion channels to dynamic changes in membrane boundary conditions to be probed. The thermoplastic microfluidic system allows initial perfusion of reagents to the membrane in less than 1 s, and enables kinetic behaviors with time constants below 10 s to be directly measured. Application of the platform is demonstrated toward kinetic studies of ceramide, a biologically important lipid known to self-assemble into transmembrane ion channels, in response to dynamic treatments of small ions (La(3+)) and proteins (Bcl-x(L) mutant). The results reveal the broader potential of the technology for studies of membrane biophysics, including lipid ion channel dynamics, lipid-protein interactions, and the regulation of protein ion channels by lipid micro domains.

Mitochondrial dysfunction and transactivation of p53-dependent apoptotic genes in BaP-treated human fetal lung fibroblasts

Benzo(a)pyrene (BaP) has been shown to be an inducer of apoptosis. However, mechanisms involved in BaP-induced mitochondrial dysfunction are not well-known. In this study, human fetal lung fibroblasts cells were treated with BaP (8, 16, 32, 64 and 128 μM) for 4 and 12 h. Cell viability, intracellular level of reactive oxygen species (ROS), total antioxidant capacity (T-AOC), mitochondrial membrane potential (Δ Ψm) and cytochrome c release were determined. Changes in transcriptional levels of p53-dependent apoptotic genes ( p53, APAF1, CASPASE3, CASPASE9, NOXA and PUMA) were measured. At time point of 4 h, BaP induced the intracellular ROS generation in 64 ( p < .05) and 128 μM BaP groups ( p < .01) but decreased the T-AOC activities in 32, 64 ( p < .05 for both) and 128 μM BaP groups ( p < .01). At time point of 12 h, Δ Ψm significantly decreased in ≥32 μM BaP groups ( p < .05 for all). Amount of mitochondrial cytochrome c significantly increased in 128 μM BaP group ( p < .01). Transcriptional levels of CASPASE3, CASPASE9, APAF1 and PUMA were up-regulated in all BaP groups ( p < .05 for all) and in ≥32 μM groups for NOXA ( p < .05). But only in 16 μM BaP group a relatively little expression of p53 mRNA was observed ( p < .05). The results indicate that in the earlier period BaP promoted the generation of excessive ROS and subsequently the mitochondrial depolarization, whereas transactivations of the p53-dependent apoptotic genes were significantly induced at the later period.

Changes of mitochondrial ultrastructures and function in central nervous tissue of hens treated with tri-ortho-cresyl phosphate (TOCP)

Tri-ortho-cresyl phosphate (TOCP), an organophosphorus ester, is capable of producing organophosphorus ester-induced delayed neurotoxicity (OPIDN) in humans and sensitive animals. The mechanism of OPIDN has not been fully understood. The present study has been designed to evaluate the role of mitochondrial dysfunctions in the development of OPIDN. Adult hens were treated with 750 mg/kg·bw TOCP by gavage and control hens were given an equivalent volume of corn oil. On day 1, 5, 15, 21 post-dosing, respectively, hens were anesthetized by intraperitoneal injection of sodium pentobarbital and perfused with 4% paraformaldehyde. The cerebral cortex cinerea and the ventral horn of lumbar spinal cord were dissected for electron microscopy. Another batch of hens were randomly divided into three experimental groups and control group. Hens in experimental groups were, respectively, given 185, 375, 750 mg/kg·bw TOCP orally and control group received solvent. After 1, 5, 15, 21 days of administration, they were sacrificed and the cerebrum and spinal cord dissected for the determination of the mitochondrial permeability transition (MPT), membrane potential (Δψ(m)) and the activity of succinate dehydrogenase. Structural changes of mitochondria were observed in hens' nervous tissues, including vacuolation and fission, which increased with time post-dosing. MPT was increased in both the cerebrum and spinal cord, with the most noticeable increase in the spinal cord. Δψ(m) was decreased in both the cerebrum and spinal cord, although there was no significant difference in the three treated groups and control group. The activity of mitochondrial succinate dehydrogenase assayed by methyl thiazolyl tetrazolium (MTT) reduction also confirmed mitochondrial dysfunctions following development of OPIDN. The results suggested mitochondrial dysfunction might partly account for the development of OPIDN induced by TOCP.

Inhibition of cadmium-induced apoptosis by glutathione S-transferase P1 via mitogen-activated protein kinases and mitochondrial pathways

Cadmium is a well-known toxic metal for the kidney. Glutathione S-transferase P1 (GSTP1) plays an important role in the detoxification and xenobiotics metabolism. Here, we investigated whether GSTP1 affected Cd(2+)-induced apoptotic cell death in human embryonic kidney cell line (HEK) 293 cells. We showed that in HEK293 cells, silencing of GSTP1 expression through RNA interference reinforced the loss in cell viability induced by Cd(2+). Overexpression of GSTP1 inhibited loss of mitochondrial membrane potential, prevented cytochrome c release from mitochondria and caspase-3 activation, inhibited mitogen-activated protein kinases (MAPKs) including ERK, JNK and p38, and suppressed apoptosis induced by Cd(2+). The oligonucleosomal DNA fragmentation assay also demonstrated that overexpression of GSTP1 by adenovirus infection prevented Cd(2+)-induced apoptosis in primary renal tubule cells. Our data suggest that GSTP1 was an endogenous inhibitor of Cd(2+)-induced apoptosis.

[Pro-apoptotic function of hepatitis B virus X protein]

Infection of hepatitis B virus (HBV) is a main cause of liver diseases including hepatitis, cirrhosis and hepatocellular carcinoma (HCC). Among the HBV-encoded proteins, the HBV X protein (HBx) has been suspected to be strongly involved in HBV-associated liver pathogenesis. HBx, a virally encoded multifunctional regulator, has been shown to induce apoptosis, anti-apoptosis, proliferation, and transformation of cells depending on the cell lines, model systems used, assay protocols, and research groups. Among the several activities of HBx, the pro-apoptotic function of HBx will be discussed in this review. Given that the disruption of apoptosis pathway by HBx contributes to the liver pathogenesis, a better understanding of the molecular interference in the cellular pro-apoptotic networks by HBx will provide useful clues for the intervention in HBV-mediated liver diseases.

Efficient photodynamic therapy against gram-positive and gram-negative bacteria using THPTS, a cationic photosensitizer excited by infrared wavelength

The worldwide rise in the rates of antibiotic resistance of bacteria underlines the need for alternative antibacterial agents. A promising approach to kill antibiotic-resistant bacteria uses light in combination with a photosensitizer to induce a phototoxic reaction. Concentrations of 1, 10 and 100µM of tetrahydroporphyrin-tetratosylat (THPTS) and different incubation times (30, 90 and 180min) were used to measure photodynamic efficiency against two Gram-positive strains of S.aureus (MSSA and MRSA), and two Gram-negative strains of E.coli and P.aeruginosa. We found that phototoxicity of the drug is independent of the antibiotic resistance pattern when incubated in PBS for the investigated strains. Also, an incubation with 100µM THPTS followed by illumination, yielded a 6lg (≥99.999%) decrease in the viable numbers of all bacteria strains tested, indicating that the THPTS drug has a high degree of photodynamic inactivation. We then modulated incubation time, photosensitizer concentration and monitored the effect of serum on the THPTS activity. In doing so, we established the conditions to obtain the strongest bactericidal effect. Our results suggest that this new and highly pure synthetic compound should improve the efficiency of photodynamic therapy against multiresistant bacteria and has a significant potential for clinical applications in the treatment of nosocomial infections.

Role of metallothionein in cadmium traffic and toxicity in kidneys and other mammalian organs

Metallothioneins are cysteine-rich, small metal-binding proteins present in various mammalian tissues. Of the four common metallothioneins, MT-1 and MT-2 (MTs) are expressed in most tissues, MT-3 is predominantly present in brain, whereas MT-4 is restricted to the squamous epithelia. The expression of MT-1 and MT-2 in some organs exhibits sex, age, and strain differences, and inducibility with a variety of stimuli. In adult mammals, MTs have been localized largely in the cell cytoplasm, but also in lysosomes, mitochondria and nuclei. The major physiological functions of MTs include homeostasis of essential metals Zn and Cu, protection against cytotoxicity of Cd and other toxic metals, and scavenging free radicals generated in oxidative stress. The role of MTs in Cd-induced acute and chronic toxicity, particularly in liver and kidneys, is reviewed in more details. In acute toxicity, liver is the primary target, whereas in chronic toxicity, kidneys are major targets of Cd. The intracellular MTs bind Cd ions and form CdMT. In chronic intoxication, Cd stimulates de novo synthesis of MTs; it is assumed that toxicity in the cells starts when loading with Cd ions exceeds the buffering capacity of intracellular MTs. CdMT, released from the Cd-injured organs, or when applied parenterally for experimental purposes, reaches the kidneys via circulation, where it is filtered, endocytosed in the proximal tubule cells, and degraded in lysosomes. Liberated Cd can immediately affect the cell structures and functions. The resulting proteinuria and CdMT in the urine can be used as biomarkers of tubular injury.

Maternal diabetes increases apoptosis in mice oocytes, not 2-cell embryos

Apoptosis may be closely involved in diabetes-induced embryonic malformations. We aimed to investigate the occurrence of apoptosis at an early stage of development, in oocytes and 2-cell embryos of streptozotocin-induced diabetic mice and nondiabetic mice. Diabetic mouse ovarian sections stained with hematoxylin and eosin showed reduced number of growing follicles and delayed oocyte development. Annexin V-positive oocytes were higher in number in diabetic mice than in nondiabetic mice. Quantitative RT-PCR and immunofluorescence analysis revealed the expression of Bax and caspase-3 significantly higher in diabetic than nondiabetic oocytes. In contrast, 2-cell embryos of diabetic and nondiabetic mice showed no annexin V-positive staining. Bax expression was elevated in diabetic 2-cell embryos, but caspase-3 expression did not significantly differ between diabetic and nondiabetic 2-cell embryos. Electron microscopy revealed increased number of swollen mitochondria in diabetic 2-cell embryos. These results suggested that maternal diabetes might increase oocyte apoptosis by a Bax-caspase-3 pathway to play a role in embryonic malformations by delayed oocyte development. Development of 2-cell embryos might be adversely affected by maternal diabetes, but not through Bax-regulated caspase-3 apoptotic pathway.

A glycine site-specific NMDA receptor antagonist protects retina ganglion cells from ischemic injury by modulating apoptotic cascades

Glutamate neurotoxicity is one of the causative factors leading to neural degeneration including retina. Inhibition of NMDA receptors has been shown neuroprotective effects. However, specifically inhibition of glycine subunit in NMDA receptors and its effects on retina neural protection has not been tested. In this study, using a glycine site-specific NMDA receptor antagonist, we investigated its neuroprotective effects on rat retinal ganglion cells (RGCs) from a transient ischemic injury and its possible underlying mechanisms. Following an ischemia/reperfusion injury the structural damages of rat retinas were assessed by an immunofluorescence method and the apoptosis of retinal neural cells was evaluated by using a terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) method. The survived RGCs were labeled by retrograde manner and counted on whole-mounted retinas. In the presence of glycine site-specific NMDA receptor antagonist, the thickness of retina was sustained, especially in the inner nuclear layers compared with mock controls. While a significantly higher numbers of TUNEL-positive apoptotic cells and fewer of RGCs were observed in the retina without the glycine antagonist, indicating its strong protective roles. Some apoptotic factors such as Bax, Bcl-2, CAMK II, COX1, COX4, Caspase-3, and GRIN1 gene have been tested from retinal samples with or without the glycine antagonist. A significantly lower of expressions of Bax, CAMK II, COX1, COX4, Caspase-3, and GRIN1 have been shown in the retinas with the antagonist. Bcl-2/Bax ratio was significantly higher with the antagonist, suggested that the glycine site-specific NMDA receptor antagonist protecting RGC death might through inhibition of apoptotic signaling.

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.

Pathogenesis of increased sensitivity of hepatocytes to injury in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is closely associated with genetic, environmental, and metabolic stress. Elevated sensitivity of hepatocytes to injury is found in NAFLD in some circumstances, such as exposure to hepatotoxic substances (carbon tetrachloride, alcohol) and cholestasis. Mitochondrial dysfunction, free fatty acids, oxidative stress, inflammatory factor and calcium overload in hepatocytes play an important role in the pathogenesis of increased sensitivity of hepatocytes to injury in NAFLD. Further elucidation of the pathogenesis of hepatocyte sensitivity to injury may provide a new strategy for prevention and treatment of NAFLD.

CFTR mediates apoptotic volume decrease and cell death by controlling glutathione efflux and ROS production in cultured mice proximal tubules

We have previously shown that despite the presence of mRNA encoding CFTR, renal proximal cells do not exhibit cAMP-sensitive Cl−conductance (Rubera I, Tauc M, Bidet M, Poujeol C, Cuiller B, Watrin A, Touret N, Poujeol P. Am J Physiol Renal Physiol 275: F651–F663, 1998). Nevertheless, in these cells, CFTR plays a crucial role in the control of the volume-sensitive outwardly rectifying (VSOR) activated Cl−currents during hypotonic shock. The aim of this study was to determine the role of CFTR in the regulation of apoptosis volume decrease (AVD) and the apoptosis phenomenon. For this purpose, renal cells were immortalized from primary cultures of proximal convoluted tubules from cftr+/+and cftr−/−mice. Apoptosis was induced by staurosporine (STS; 1 μM). Cell volume, Cl−conductance, caspase-3 activity, intracellular level of reactive oxygen species (ROS), and glutathione content (GSH/GSSG) were monitored during AVD. In cftr+/+cells, AVD and caspase-3 activation were strongly impaired by conventional Cl−channel blockers and by a specific CFTR inhibitor (CFTRinh-172; 5 μM). STS induced activation of CFTR conductance within 15 min, which was progressively replaced by VSOR Cl−currents after 60 min of exposure. In parallel, STS induced an increase in ROS content in the time course of VSOR Cl−current activation. This increase was impaired by CFTRinh-172 and was not observed in cftr−/−cells. Furthermore, the intracellular GSH/GSSG content decreased during STS exposure in cftr+/+cells only. In conclusion, CFTR could play a key role in the cascade of events leading to apoptosis. This role probably involves control of the intracellular ROS balance by some CFTR-dependent modulation of GSH concentration.

Antiapoptotic effects of dietary antioxidants towards N-nitrosopiperidine and N-nitrosodibutylamine-induced apoptosis in HL-60 and HepG2 cells

The aim of this work was to determine the effect of vitamin C, diallyl disulfide (DADS) and dipropyl disulfide (DPDS) towards N-nitrosopiperidine (NPIP) and N-nitrosodibutylamine (NDBA)-induced apoptosis in human leukemia (HL-60) and hepatoma (HepG2) cell lines using the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. None of the vitamin C (5-50 microm), DADS and DPDS (1-5 microm) concentrations selected induced a significant percentage of apoptosis. In simultaneous treatments, vitamin C, DADS and DPDS reduced the apoptosis induced by NPIP and NDBA in HL-60 and HepG2 cells (around 70% of reduction). We also investigated its scavenging activities towards reactive oxygen species (ROS) produced by NPIP and NDBA using 2',7'-dichlorodihydrofluorescein diacetate in both cell lines. ROS production induced by both N-nitrosamine was reduced to control levels by vitamin C (5-50 microm) in a dose-dependent manner. However, DADS (5 microm) increased ROS levels induced by NPIP and NDBA in HL-60 (40 and 20% increase, respectively) and HepG2 cells (18% increase), whereas DPDS was more efficient scavenger of ROS at the lowest concentration (1 microm) in both HL-60 (52 and 25% reduction, respectively) and HepG2 cells (24% reduction). The data demonstrated that the scavenging ability of vitamin C and DPDS could contribute to inhibition of the NPIP- and NDBA-induced apoptosis. However, more than one mechanism, such as inhibition of phase I and/or induction of phase II enzymes, could be implicated in the protective effect of dietary antioxidants towards NPIP- and NDBA-induced apoptosis in HL-60 and HepG2 cells.

Biochemical mechanisms in drug-induced liver injury: Certainties and doubts

Drug-induced liver injury is a significant and still unresolved clinical problem. Limitations to knowledge about the mechanisms of toxicity render incomplete the detection of hepatotoxic potential during preclinical development. Several xenobiotics are lipophilic substances and their transformation into hydrophilic compounds by the cytochrome P-450 system results in production of toxic metabolites. Aging, preexisting liver disease, enzyme induction or inhibition, genetic variances, local O₂ supply and, above all, the intrinsic molecular properties of the drug may affect this process. Necrotic death follows antioxidant consumption and oxidation of intracellular proteins, which determine increased permeability of mitochondrial membranes, loss of potential, decreased ATP synthesis, inhibition of Ca²⁺-dependent ATPase, reduced capability to sequester Ca²⁺ within mitochondria, and membrane bleb formation. Conversely, activation of nucleases and energetic participation of mitochondria are the main intracellular mechanisms that lead to apoptosis. Non-parenchymal hepatic cells are inducers of hepatocellular injury and targets for damage. Activation of the immune system promotes idiosyncratic reactions that result in hepatic necrosis or cholestasis, in which different HLA genotypes might play a major role. This review focuses on current knowledge of the mechanisms of drug-induced liver injury and recent advances on newly discovered mechanisms of liver damage. Future perspectives including new frontiers for research are discussed.