Cyanide induces different modes of death in cortical and mesencephalon cells

The two faces of cyanide: an environmental toxin and a potential novel mammalian gasotransmitter

Cyanide is traditionally viewed as a cytotoxic agent, with its primary mode of action being the inhibition of mitochondrial Complex IV (cytochrome c oxidase). However, recent studies demonstrate that the effect of cyanide on Complex IV in various mammalian cells is biphasic: in lower concentrations (nanomolar to low micromolar) cyanide stimulates Complex IV activity, increases ATP production and accelerates cell proliferation, while at higher concentrations (high micromolar to low millimolar) it produces the previously known ('classic') toxic effects. The first part of the article describes the cytotoxic actions of cyanide in the context of environmental toxicology, and highlights pathophysiological conditions (e.g., cystic fibrosis with Pseudomonas colonization) where bacterially produced cyanide exerts deleterious effects to the host. The second part of the article summarizes the mammalian sources of cyanide production and overviews the emerging concept that mammalian cells may produce cyanide, in low concentrations, to serve biological regulatory roles. Cyanide fulfills many of the general criteria as a 'classical' mammalian gasotransmitter and shares some common features with the current members of this class: nitric oxide, carbon monoxide, and hydrogen sulfide.

Targeting Necrosis: Elastase-like Protease Inhibitors Curtail Necrotic Cell Death Both In Vitro and in Three In Vivo Disease Models

Necrosis is the main mode of cell death, which leads to multiple clinical conditions affecting hundreds of millions of people worldwide. Its molecular mechanisms are poorly understood, hampering therapeutics development. Here, we identify key proteolytic activities essential for necrosis using various biochemical approaches, enzymatic assays, medicinal chemistry, and siRNA library screening. These findings provide strategies to treat and prevent necrosis, including known medicines used for other indications, siRNAs, and establish a platform for the design of new inhibitory molecules. Indeed, inhibitors of these pathways demonstrated protective activity in vitro and in vivo in animal models of traumatic brain injury, acute myocardial infarction, and drug-induced liver toxicity. Consequently, this study may pave the way for the development of novel therapies for the treatment, inhibition, or prevention of a large number of hitherto untreatable diseases.

Hydroxyobtustyrene protects neuronal cells from chemical hypoxia-induced cell death

Hydroxyobtustyrene is a derivative of cinnamyl phenol isolated from Dalbergia odorifera T. Chen. The heartwood, known as 'JiangXiang', is a traditional Chinese medicine. Previous studies showed that hydroxyobtustyrene inhibited the biosynthesis of prostaglandins, which are mediators of neuronal cell death in ischemia. However, it currently remains unclear whether hydroxyobtustyrene protects neurons against ischemic stress. In the present study, we investigated the protective effects of hydroxyobtustyrene against sodium cyanide (NaCN)-induced chemical ischemia. Hippocampal neurons were cultured from the cerebral cortices of E18 Wistar rats. The effects of hydroxyobtustyrene on neuronal survival and trophic effects were estimated under lower and higher cell density conditions. After the treatment of 1 mM NaCN with or without hydroxyobtustyrene, an MTT assay, Hoechst staining, and immunocytochemistry for cyclooxygenase (COX)-2 were performed. Hydroxyobtustyrene increased cell viability under lower, but not normal density conditions. Neither the neurite number nor the length was influenced by hydroxyobtustyrene. NaCN significantly decreased viability and increased fragmentation in cell nuclei, and these changes were prevented by hydroxyobtustyrene. Moreover, NaCN increased the number of COX-2-positive neurons, and this was significantly prevented by the co-treatment with hydroxyobtustyrene. Therefore, hydroxyobtustyrene protected cultured hippocampal neurons against NaCN-induced chemical ischemia, which may be mediated by the inhibition of COX-2 production.

Oxidative damage mediated iNOS and UCP-2 upregulation in rat brain after sub-acute cyanide exposure: dose and time-dependent effects

Cyanide-induced chemical hypoxia is responsible for pronounced oxidative damage in the central nervous system. The disruption of mitochondrial oxidative metabolism has been associated with upregulation of uncoupling proteins (UCPs). The present study addresses the dose- and time-dependent effect of sub-acute cyanide exposure on various non-enzymatic and enzymatic oxidative stress markers and their correlation with inducible-nitric oxide synthase (iNOS) and uncoupling protein-2 (UCP-2) expression. Animals received (oral) triple distilled water (vehicle control), 0.25 LD50 potassium cyanide (KCN) or 0.50 LD50 KCN daily for 21 d. Animals were sacrificed on 7, 14 and 21 d post-exposure to measure serum cyanide and nitrite, and brain malondialdehyde (MDA), reduced glutathione (GSH), glutathione disulfide (GSSG), cytochrome c oxidase (CCO), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR) and catalase (CA) levels, together with iNOS and UCP-2 expression, and DNA damage. The study revealed that a dose- and time-dependent increase in cyanide concentration was accompanied by corresponding CCO inhibition and elevated MDA levels. Decrease in GSH levels was not followed by reciprocal change in GSSG levels. Diminution of SOD, GPx, GR and CA activity was congruent with elevated nitrite levels and upregulation of iNOS and UCP-2 expression, without any DNA damage. It was concluded that long-term cyanide exposure caused oxidative stress, accompanied by upregulation of iNOS. The upregulation of UCP-2 further sensitized the cells to cyanide and accentuated the oxidative stress, which was independent of DNA damage.

Humanin Derivatives Inhibit Necrotic Cell Death in Neurons

Humanin and its derivatives are peptides known for their protective antiapoptotic effects against Alzheimer's disease. Herein, we identify a novel function of the humanin-derivative AGA(C8R)-HNG17 (namely, protection against cellular necrosis). Necrosis is one of the main modes of cell death, which was until recently considered an unmoderated process. However, recent findings suggest the opposite. We have found that AGA(C8R)-HNG17 confers protection against necrosis in the neuronal cell lines PC-12 and NSC-34, where necrosis is induced in a glucose-free medium by either chemohypoxia or by a shift from apoptosis to necrosis. Our studies in traumatic brain injury models in mice, where necrosis is the main mode of neuronal cell death, have shown that AGA(C8R)-HNG17 has a protective effect. This result is demonstrated by a decrease in a neuronal severity score and by a reduction in brain edema, as measured by magnetic resonance imaging (MRI). An insight into the peptide's antinecrotic mechanism was attained through measurements of cellular ATP levels in PC-12 cells under necrotic conditions, showing that the peptide mitigates a necrosis-associated decrease in ATP levels. Further, we demonstrate the peptide's direct enhancement of the activity of ATP synthase activity, isolated from rat-liver mitochondria, suggesting that AGA(C8R)-HNG17 targets the mitochondria and regulates cellular ATP levels. Thus, AGA(C8R)-HNG17 has potential use for the development of drug therapies for necrosis-related diseases, for example, traumatic brain injury, stroke, myocardial infarction, and other conditions for which no efficient drug-based treatment is currently available. Finally, this study provides new insight into the mechanisms underlying the antinecrotic mode of action of AGA(C8R)-HNG17.

Protection from cyanide-induced brain injury by the Nrf2 transcriptional activator carnosic acid

Cyanide is a life-threatening, bioterrorist agent, preventing cellular respiration by inhibiting cytochrome c oxidase, resulting in cardiopulmonary failure, hypoxic brain injury, and death within minutes. However, even after treatment with various antidotes to protect cytochrome oxidase, cyanide intoxication in humans can induce a delayed-onset neurological syndrome that includes symptoms of Parkinsonism. Additional mechanisms are thought to underlie cyanide-induced neuronal damage, including generation of reactive oxygen species. This may account for the fact that antioxidants prevent some aspects of cyanide-induced neuronal damage. Here, as a potential preemptive countermeasure against a bioterrorist attack with cyanide, we tested the CNS protective effect of carnosic acid (CA), a pro-electrophilic compound found in the herb rosemary. CA crosses the blood-brain barrier to up-regulate endogenous antioxidant enzymes via activation of the Nrf2 transcriptional pathway. We demonstrate that CA exerts neuroprotective effects on cyanide-induced brain damage in cultured rodent and human-induced pluripotent stem cell-derived neurons in vitro, and in vivo in various brain areas of a non-Swiss albino mouse model of cyanide poisoning that simulates damage observed in the human brain. Cyanide, a potential bioterrorist agent, can produce a chronic delayed-onset neurological syndrome that includes symptoms of Parkinsonism. Here, cyanide poisoning treated with the proelectrophillic compound carnosic acid, results in reduced neuronal cell death in both in vitro and in vivo models through activation of the Nrf2/ARE transcriptional pathway. Carnosic acid is therefore a potential treatment for the toxic central nervous system (CNS) effects of cyanide poisoning. ARE, antioxidant responsive element; Nrf2 (NFE2L2, Nuclear factor (erythroid-derived 2)-like 2).

Pre-conditioning with low-level laser (light) therapy: light before the storm

Pre-conditioning by ischemia, hyperthermia, hypothermia, hyperbaric oxygen (and numerous other modalities) is a rapidly growing area of investigation that is used in pathological conditions where tissue damage may be expected. The damage caused by surgery, heart attack, or stroke can be mitigated by pre-treating the local or distant tissue with low levels of a stress-inducing stimulus, that can induce a protective response against subsequent major damage. Low-level laser (light) therapy (LLLT) has been used for nearly 50 years to enhance tissue healing and to relieve pain, inflammation and swelling. The photons are absorbed in cytochrome(c) oxidase (unit four in the mitochondrial respiratory chain), and this enzyme activation increases electron transport, respiration, oxygen consumption and ATP production. A complex signaling cascade is initiated leading to activation of transcription factors and up- and down-regulation of numerous genes. Recently it has become apparent that LLLT can also be effective if delivered to normal cells or tissue before the actual insult or trauma, in a pre-conditioning mode. Muscles are protected, nerves feel less pain, and LLLT can protect against a subsequent heart attack. These examples point the way to wider use of LLLT as a pre-conditioning modality to prevent pain and increase healing after surgical/medical procedures and possibly to increase athletic performance.

Comparative study of non-invasive methods for assessing Daphnia magna embryo toxicity

Embryos, unlike adults, are typically sessile, which allows for an increase in the available metrics that can be used to assess chemical toxicity. We investigate Daphnia magna development rate and oxygen consumption as toxicity metrics and compare them to arrested embryo development using four different techniques with potassium cyanide (KCN) as a common toxicant. The EC50 (95 % CI) for arrested development was 2,535 (1,747-3,677) μg/L KCN. Using pixel intensity changes, recorded with difference imaging, we semi-quantitatively assessed a decrease in development rate at 200 μg/L KCN, threefold lower than the arrested development lowest observed effect concentration (LOEC). Respirometry and self-referencing (SR) microsensors were two unique techniques used to assess oxygen consumption. Using respirometry, an increase in oxygen consumption was found in the 5 μg/L KCN treatment and a decrease for 148 μg/L, but no change was found for the 78 μg/L KCN treatment. Whereas, with SR microsensors, we were able to detect significant changes in oxygen consumption for all three treatments: 5, 78, and 148 μg/L KCN. While SR offered the highest sensitivity, the respirometry platform developed for this study was much easier to use to measure the same endpoint. Oxygen consumption may be subject to change during the development process, meaning consumption assessment techniques may only be useful only for short-term experiments. Development rate was a more sensitive endpoint though was only reliable four of the six embryonic developmental stages examined. Despite being the least sensitive endpoint, arrested embryo development was the only technique capable of assessing the embryos throughout all developmental stages. In conclusion, each metric has advantages and limitations, but because all are non-invasive, it is possible to use any combination of the three.

Cardiolipin plays a role in KCN-induced necrosis

Cardiolipin (CL) is a unique anionic, dimeric phospholipid found almost exclusively in the inner mitochondrial membrane and is essential for the function of numerous enzymes that are involved in mitochondrial energy metabolism. While the role of cardiolipin in apoptosis is well established, its involvement in necrosis is enigmatic. In the present study, KCN-induced necrosis in U937 cells was used as an experimental model to assess the role of CL in necrosis. KCN addition to U937 cells induced reactive oxygen species (ROS) formation, while the antioxidants inhibited necrosis, indicating that ROS play a role in KCN-induced cell death. Further, CL oxidation was confirmed by the monomer green fluorescence of 10-N-nonyl acridine orange (NAO) and by TLC. Utilizing the red fluorescence of the dimeric NAO, redistribution of CL in mitochondrial membrane during necrosis was revealed. We also showed that the catalytic activity of purified adenosine triphosphate (ATP) synthase complex, known to be modulated by cardiolipin, decreased following KCN treatment. All these events occurred at an early phase of the necrotic process prior to rupture of the cell membrane. Furthermore, CL-deficient HeLa cells were found to be resistant to KCN-induced necrosis as compared with the wild type cells. We suggest that KCN, an effective reversible inhibitor of cytochrome oxidase and thereby of the respiratory chain leads to ROS increase, which in turn oxidizes CL (amongst other membrane phospholipids) and leads to mitochondrial membrane lipid reorganization and loss of CL symmetry. Finally, the resistance of CL-deficient cells to necrosis further supports the notion that CL, which undergoes oxidation during necrotic cell death, is an integral part of the milieu of events taking place in mitochondria leading to membrane disorganization and mitochondrial dysfunction.

Surviving acute cyanide poisoning: a longitudinal neuropsychological investigation with interval MRI

We report the case of a 22-year-old woman who presented with self-poisoning by cyanide ingestion. We have elected to pay particular attention to describing the neuropsychological sequelae of cyanide poisoning, and the evolution of these deficits over a 6-month period. Prominent deficits in episodic memory were noted from an early stage, which were consistent with the findings noted on structural neuroimaging. These deficits remained persistent, although improving in severity over the follow-up period. No focal neurological deficits or abnormal involuntary movements emerged, and the patient's overall functional status remained satisfactory. The patient's psychiatric presentation and background history are briefly discussed.

A disposable blood cyanide sensor

Deaths due to smoke inhalation in fires are often due to poisoning by HCN. Rapid administration of antidotes can result in complete resuscitation of the patient but judicious dosing requires the knowledge of the level of cyanide exposure. Rapid sensitive means for blood cyanide quantitation are needed. Hydroxocyanocobinamide (OH(CN)Cbi) reacts with cyanide rapidly; this is accompanied by a large spectral change. The disposable device consists of a pair of nested petri dish bottoms and a single top that fits the outer bottom dish. The top cover has a diametrically strung porous polypropylene membrane tube filled with aqueous OH(CN)Cbi. One end of the tube terminates in an amber (583nm) light emitting diode; the other end in a photodiode via an acrylic optical fiber. An aliquot of the blood sample is put in the inner dish, the assembly covered and acid is added through a port in the cover. Evolved HCN diffuses into the OH(CN)Cbi solution and the absorbance in the long path porous membrane tube cell is measured within 160 s. The LOD was 0.047, 1.0, 0.15, 5.0 and 2.2 μM, respectively, for water (1 mL), bovine blood (100 μL, 1 mL), and rabbit blood (20 μL, 50 μL). RSDs were<10% in all cases and the linear range extended from 0.5 to 200 μM. The method was validated against a microdiffusion approach and applied to the measurement of cyanide in rabbit and human blood. The disposable device permits field measurement of blood cyanide in <4 min.

Decay accelerating factor (CD55) protects neuronal cells from chemical hypoxia-induced injury

Background

Activated complement system is known to mediate neuroinflammation and neurodegeneration following exposure to hypoxic-ischemic insults. Therefore, inhibition of the complement activation cascade may represent a potential therapeutic strategy for the management of ischemic brain injury. Decay-accelerating factor (DAF, also known as CD55) inhibits complement activation by suppressing the function of C3/C5 convertases, thereby limiting local generation or deposition of C3a/C5a and membrane attack complex (MAC or C5b-9) production. The present study investigates the ability of DAF to protect primary cultured neuronal cells subjected to sodium cyanide (NaCN)-induced hypoxia from degeneration and apoptosis.

Methods

Cultured primary cortical neurons from embryonic Sprague-Dawley rats were assigned one of four groups: control, DAF treatment alone, hypoxic, or hypoxic treated with DAF. Hypoxic cultures were exposed to NaCN for 1 hour, rinsed, followed by 24 hour exposure to 200 ng/ml of recombinant human DAF in normal medium. Human DAF was used in the present study and it has been shown to effectively regulate complement activation in rats. Neuronal cell function, morphology and viability were investigated by measuring plateau depolarization potential, counting the number dendritic spines, and observing TUNEL and MTT assays. Complement C3, C3a, C3a receptor (R) production, C3a-C3aR interaction and MAC formation were assessed along with the generation of activated caspase-9, activated caspase-3, and activated Src.

Results

When compared to controls, hypoxic cells had fewer dendritic spines, reduced plateau depolarization accompanied by increased apoptotic activity and accumulation of MAC, as well as up-regulation of C3, C3a and C3aR, enhancement of C3a-C3aR engagement, and elevated caspase and Src activity. Treatment of hypoxic cells with 200 ng/ml of recombinant human DAF resulted in attenuation of neuronal apoptosis and exerted significant protection against neuronal dendritic spine loss and plateau depolarization reduction. Furthermore, treatment with DAF resulted in decreased accumulation of C3a, MAC, C3a-C3aR interaction, caspase-9, activated caspase-3, and pTyr416-Src (activated Src) tyrosine kinase.

Conclusion

DAF was found to reduce neuronal cell death and apoptosis in NaCN induced hypoxia. This effect is attributed to the ability of DAF to limit complement activation and inhibit the activity of Src and caspases 9 and 3. This study supports the inhibiting of complement as a neuroprotective strategy against CNS ischemia/reperfusion injury.

Pseudomonas aeruginosa AlgR controls cyanide production in an AlgZ-dependent manner

Pseudomonas aeruginosa is an opportunistic pathogen that causes chronic infections in individuals suffering from the genetic disorder cystic fibrosis. In P. aeruginosa, the transcriptional regulator AlgR controls a variety of virulence factors, including alginate production, twitching motility, biofilm formation, quorum sensing, and hydrogen cyanide (HCN) production. In this study, the regulation of HCN production was examined. Strains lacking AlgR or the putative AlgR sensor AlgZ produced significantly less HCN than did a nonmucoid isogenic parent. In contrast, algR and algZ mutants showed increased HCN production in an alginate-producing (mucoid) background. HCN production was optimal in a 5% O2 environment. In addition, cyanide production was elevated in bacteria grown on an agar surface compared to bacteria grown in planktonic culture. A conserved AlgR phosphorylation site (aspartate at amino acid position 54), which is required for surface-dependent twitching motility but not alginate production, was found to be critical for cyanide production. Nuclease protection mapping of the hcnA promoter identified a new transcriptional start site required for HCN production. A subset of clinical isolates that lack this start site produced small amounts of cyanide. Taken together, these data show that the P. aeruginosa hcnA promoter contains three transcriptional start sites and that HCN production is regulated by AlgZ and AlgR and is maximal under microaerobic conditions when the organism is surface attached.

The mitochondrial impairment, oxidative stress and neurodegeneration connection: reality or just an attractive hypothesis?

Aging is the most important risk factor for common neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. Aging in the central nervous system has been associated with elevated mutation load in mitochondrial DNA, defects in mitochondrial respiration and increased oxidative damage. These observations support a 'vicious cycle' theory which states that there is a feedback mechanism connecting these events in aging and age-associated neurodegeneration. Despite being an extremely attractive hypothesis, the bulk of the evidence supporting the mitochondrial vicious cycle model comes from pharmacological experiments in which the modes of mitochondrial enzyme inhibition are far from those observed in real life. Furthermore, recent in vivo evidence does not support this model. In this review, we focus on the relationship among the components of the putative vicious cycle, with particular emphasis on the role of mitochondrial defects on oxidative stress.

Upregulation of BNIP3 and translocation to mitochondria mediates cyanide-induced apoptosis in cortical cells

Bcl-2/adenovirus E1B 19-kDa-interacting protein 3 (BNIP3), a Bcl-2 homology domain 3 (BH3) domain only protein, has been identified as a mitochondrial mediator of hypoxia-induced cell death. Since cyanide produces histotoxic anoxia (chemical hypoxia), the present study was undertaken in primary rat cortical cells to determine involvement of the BNIP3 signaling pathway in cyanide-induced death. Over a 20 h exposure KCN increased BNIP3 expression, followed by a concentration-related apoptotic death. To determine if BNIP3 plays a role in the cell death, expression was either increased with BNIP3 cDNA (BNIP3+) or knocked down with small interfering RNA (RNAi). In BNIP3+ cells, cyanide-induced apoptotic death was markedly enhanced and preceded by reduction of mitochondrial membrane potential (delta psim), release of cytochrome c from mitochondria and elevated caspase 3 and 7 activity. Pretreatment with the pan-caspase inhibitor N-benzyloxycarbonyl-Ala-Asp-fluoromethyl ketone (zVAD-fmk) suppressed BNIP3+-mediated cell death, thus confirming a caspase-dependent apoptosis. On the other hand, BNIP3 knockdown by RNAi or antagonism of BNIP3 by a transmembrane-deleted dominant-negative mutant (BNIP3 delta TM) markedly reduced cell death. Immunohistochemical imaging showed that cyanide stimulated translocation of BNIP3 from cytosol to mitochondria and displacement studies with BNIP3 delta TM showed that integration of BNIP3 into the mitochondrial outer membrane was necessary for the cell death. In BNIP3+ cells, cyclosporin-A, an inhibitor of mitochondrial pore transition, blocked the cyanide-induced reduction of delta psim and decreased the apoptotic death. These results demonstrate in cortical cells that cyanide induces a rapid upregulation of BNIP3 expression, followed by translocation to the mitochondrial outer membrane to reduce delta psim. This was followed by mitochondrial release of cytochrome c to execute a caspase-dependent cell death.

HIF-1alpha activation by a redox-sensitive pathway mediates cyanide-induced BNIP3 upregulation and mitochondrial-dependent cell death

Cyanide produces degeneration of the nervous system in which different modes of cell death are activated in the vulnerable brain areas. In brain, the mechanism underlying the cell death is not clear. In this study, an immortalized dopaminergic cell line was used to characterize the cell death signaling cascade activated by cyanide. Cyanide-treated cells exhibited a time- and concentration-dependent apoptosis that was caspase independent. Cyanide induced a rapid surge of intracellular reactive oxygen species (ROS) generation, followed by p38 mitogen-activated protein kinase (MAPK) activation and nuclear accumulation of hypoxia-inducible factor-1alpha (HIF-1alpha). Activation of p38 MAPK and HIF-1alpha accumulation were attenuated by N-acetyl-L-cysteine (antioxidant), catalase (hydrogen peroxide scavenger), or a selective p38 MAPK inhibitor (SB203580). Cyanide activated the hypoxia response element (HRE) promoter, which was also blocked by the antioxidants and SB203580. HRE activation was followed by increased BNIP3 gene transcription, as reflected by elevated BNIP3 mRNA and protein levels. BNIP3 upregulation was reduced by selective RNAi knockdown of HIF-1alpha. Overexpression of BNIP3 produced mitochondrial dysfunction (reduced membrane potential), caspase-independent apoptosis, and sensitization of the cells to cyanide-induced toxicity. Expression of a dominant-negative mutant or RNAi knockdown of BNIP3 protected the cells from cyanide. It was concluded that cyanide activated the HIF-1alpha-mediated pathway of BNIP3 induction through a redox-sensitive process. Increased BNIP3 expression then served as an initiator of mitochondrial-mediated death.

Omapatrilat enhances adrenomedullin's reduction of cardiomyocyte cell death

The objective of this study was to determine whether adrenomedullin, a vasodilator peptide, modulates the process of cell death in cardiomyocytes and whether its effect would be enhanced by the endopeptidase inhibitor omapatrilat, which reduces adrenomedullin degradation. Further, we sought to determine whether the effect of adrenomedullin involved an action to preserve mitochondrial transmembrane potential (DeltaPsi(m)). Cardiomyocytes in culture were treated with agents that interrupted the mitochondrial electron transport chain, inhibiting glycolysis and oxidative phosphorylation. Cell death was evaluated by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay and DeltaPsi(m) was assessed by fluorescent microscopy. Cytochrome c loss from mitochondria and appearance in cytosol was determined by Western blotting. Potassium cyanide (KCN) plus deoxyglucose or antimycin A, for 24 h, produced significant (p<0.01) concentration-dependent reductions in cell viability or increases in cell death. Adrenomedullin reduced cell death produced in this manner and the effect of adrenomedullin was enhanced by treatment with omapatrilat. In contrast, there was no additional reduction in cell death by lisinopril treatment. Omapatrilat plus adrenomedullin reduced the KCN plus deoxyglucose-induced increase in cytosolic cytochrome c. A likely mechanism centers on the ability of adrenomedullin plus omapatrilat to prevent the decline in mitochondrial DeltaPsi(m) produced by KCN plus deoxyglucose treatment. In summary, adrenomedullin plus omapatrilat limited the decline in mitochondrial DeltaPsi(m) that accompanies interruption of mitochondrial metabolism and limited the extent of cell death in cardiomyocytes treated with KCN plus deoxyglucose or antimycin. Adrenomedullin plus the endopeptidase inhibitor omapatrilat may be a useful strategy to protect cardiomyocytes from cell death, in conditions associated with impairment of mitochondrial function.

Optical and pharmacological tools to investigate the role of mitochondria during oxidative stress and neurodegeneration

Mitochondria are critical for cellular adenosine triphosphate (ATP) production; however, recent studies suggest that these organelles fulfill a much broader range of tasks. For example, they are involved in the regulation of cytosolic Ca(2+) levels, intracellular pH and apoptosis, and are the major source of reactive oxygen species (ROS). Various reactive molecules that originate from mitochondria, such as ROS, are critical in pathological events, such as ischemia, as well as in physiological events such as long-term potentiation, neuronal-vascular coupling and neuronal-glial interactions. Due to their key roles in the regulation of several cellular functions, the dysfunction of mitochondria may be critical in various brain disorders. There has been increasing interest in the development of tools that modulate mitochondrial function, and the refinement of techniques that allow for real time monitoring of mitochondria, particularly within their intact cellular environment. Innovative imaging techniques are especially powerful since they allow for mitochondrial visualization at high resolution, tracking of mitochondrial structures and optical real time monitoring of parameters of mitochondrial function. The techniques discussed include classic imaging techniques, such as rhodamine-123, the highly advanced semi-conductor nanoparticles (quantum dots), and wide field microscopy as well as high-resolution multiphoton imaging. We have highlighted the use of these techniques to study mitochondrial function in brain tissue and have included studies from our laboratories in which these techniques have been successfully applied.

PPARalpha-mediated upregulation of uncoupling protein-2 switches cyanide-induced apoptosis to necrosis in primary cortical cells

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a member of the nuclear factor PPAR family that regulates a variety of cellular functions, including lipid metabolism, cellular oxidative stress defense, and inflammatory responses. Based on the report that Wy14,643, a PPARalpha agonist, can upregulate uncoupling protein-2 (UCP-2), this study was conducted in primary cortical cells to determine if PPARalpha activation enhances cyanide-induced neurotoxicity through changes in the level of UCP-2. PCR and Western blot analysis showed that Wy14,643 upregulated UCP-2 transcriptionally over a 12-h period. This response was mediated by PPARalpha since it was blocked by MK886, a selective PPARalpha antagonist. The effect of UCP-2 upregulation on the cytotoxic response to cyanide was quantitated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (apoptosis) and propidium iodide staining (necrosis). Wy14,643 switched the mode of cyanide-induced cell death from apoptosis to necrosis. Cell death was preceded by marked mitochondrial dysfunction, as reflected by depletion of ATP and reduction of the mitochondrial membrane potential (DeltaPsim). Knock down of UCP-2 expression by RNA interference blocked the Wy14,643-mediated enhancement of cyanide-induced mitochondrial dysfunction and the switch of the cell death mode, thus confirming that the response was mediated by upregulation of UCP-2. This study shows that PPARalpha activation can upregulate UCP-2 expression, which in turn enhances cyanide-induced necrotic cell death through an increase of mitochondrial dysfunction.

Evidence for a functional genetic polymorphism of the human mercaptopyruvate sulfurtransferase (MPST), a cyanide detoxification enzyme

Mercaptopyruvate sulfurtransferase (MPST) plays a central role in both cysteine degradation and cyanide detoxification. Moreover, deficiency in MPST activity has been suggested to be responsible for a rare inheritable disorder known as mercaptolactate-cysteine disulfiduria (MCDU). To date, no mutation of the human MPST gene has been reported. We developed a screening strategy to search for mutations in the MPST gene of 50 unrelated French individuals. Two intronic polymorphisms (IVS1-110C>G and IVS2+39C>T) and a nonsense mutation (Tyr(85)Stop) were identified and their functional consequences were assessed in vivo by measurement of erythrocyte MPST activity and/or in vitro using heterologous expression or transient transfection assay. The nonsense mutation likely leads to the synthesis of a severely truncated protein without enzymatic activity, as supported by our in vitro data. This work constitutes the first report of the existence of a functional genetic polymorphism affecting MPST and should be of great help to investigate certain disorders such as MCDU.

Inducible nitric oxide synthase up-regulation and mitochondrial glutathione depletion mediate cyanide-induced necrosis in mesencephalic cells

We have previously shown in rat primary cultured mesencephalic cells that cyanide induces a high level of oxidative stress and necrotic death. To evaluate the mechanism of the cytotoxicity, the effects of cyanide on intracellular glutathione (GSH) pools and inducible nitric oxide synthase (iNOS)-mediated reactive nitrogen species (RNS) generation were studied. Cyanide rapidly depleted intracellular GSH. Restoration of GSH blocked cell death, whereas depletion of GSH by synthesis inhibition increased the necrosis. Selective depletion of mitochondrial GSH (mtGSH) increased oxidative stress and enhanced cell death, whereas the cytoplasmic pool was not critical to cell survival. These actions were accompanied by increased iNOS expression as determined by Western blot analysis, RT-PCR and immunohistochemistry. Up-regulation of iNOS led to increased generation of NO as reflected by elevated nitrite levels (an end product of NO metabolism). It was determined by use of a selective inhibitor that up-regulation of iNOS expression was transcriptionally regulated by activation of nuclear factor-kappaB, a redox-sensitive transcription factor. It was concluded that, in cyanide-mediated neurotoxicity, mtGSH is a vital component of the cellular antioxidant defense, and its depletion can lead to oxidative stress-mediated iNOS up-regulation, thus enhancing RNS generation and necrosis.

Photobiomodulation partially rescues visual cortical neurons from cyanide-induced apoptosis

Near-infrared light via light-emitting diode treatment has documented therapeutic effects on neurons functionally inactivated by tetrodotoxin or methanol intoxication. Light-emitting diode pretreatment also reduced potassium cyanide-induced cell death, but the mode of death via the apoptotic or necrotic pathway was unclear. The current study tested our hypothesis that light-emitting diode rescues neurons from apoptotic cell death. Primary neuronal cultures from postnatal rat visual cortex were pretreated with light-emitting diode for 10 min at a total energy density of 30 J/cm2 before exposing to potassium cyanide for 28 h. With 100 or 300 microM potassium cyanide, neurons died mainly via the apoptotic pathway, as confirmed by electron microscopy, Hoechst 33258, single-stranded DNA, Bax, and active caspase-3. In the presence of caspase inhibitor I, the percentage of apoptotic cells in 300microM potassium cyanide was significantly decreased. Light-emitting diode pretreatment reduced apoptosis from 36% to 17.9% (100 microM potassium cyanide) and from 58.9% to 39.6% (300 microM potassium cyanide), representing a 50.3% and 32.8% reduction, respectively. Light-emitting diode pretreatment significantly decreased the expression of caspase-3 elicited by potassium cyanide. It also reversed the potassium cyanide-induced increased expression of Bax and decreased expression of Bcl-2 to control levels. Moreover, light-emitting diode decreased the intensity of 5-(and -6) chloromethy-2', 7-dichlorodihydrofluorescein diacetate acetyl ester, a marker of reactive oxygen species, in neurons exposed to 300 microM potassium cyanide. These results indicate that light-emitting diode pretreatment partially protects neurons against cyanide-induced caspase-mediated apoptosis, most likely by decreasing reactive oxygen species production, down-regulating pro-apoptotic proteins and activating anti-apoptotic proteins, as well as increasing energy metabolism in neurons as reported previously.

Underlying mechanism of hypoxic preconditioning decreasing apoptosis induced by anoxia in cultured hippocampal neurons

It is known that hypoxic preconditioning (HP, a brief period of sublethal hypoxia) provides neuroprotection against subsequent severe anoxia, but the mechanisms of this increased tolerance have not been fully elucidated. A hypoxic preconditioning model was established by exposing a 4-day hippocampal culture to 1% O(2) for 20 min/day for 8 days. The preconditioning significantly decreased the number of apoptotic neurons at reoxygenation 24 h after 4 h of severe anoxia (0% O(2)). Further study demonstrated that the degradation of mitochondrial membrane potential (MMP) was greatly inhibited and the expression of B-cell lymphoma protein-2 (Bcl-2) was increased considerably after severe anoxia in the HP groups. These results indicate that the increased anoxic tolerance, which is induced by HP in cultured hippocampal cells, may be correlated with Bcl-2 overexpression and enhanced stability of MMP, which ultimately reduces apoptosis 24 h after reoxygenation.

Mitochondrial depolarization following hydrogen sulfide exposure in erythrocytes from a sulfide-tolerant marine invertebrate

Sulfide-tolerant marine invertebrates employ a variety of mechanisms to detoxify sulfide once it has entered their bodies, but their integumentary,respiratory epithelium and circulatory cells may still be exposed to toxic sulfide concentrations. To investigate whether sulfide exposure is toxic to mitochondria of a sulfide-tolerant invertebrate, we used the fluorescent dyes JC-1 and TMRM to determine the effect of sulfide exposure on mitochondrial depolarization in erythrocytes from the annelid Glycera dibranchiata. In erythrocytes exposed to 0.11-1.9 mmol l-1 sulfide for 1 h, the dyes showed fluorescence changes consistent with sulfide-induced mitochondrial depolarization. At the highest sulfide concentration, the extent of depolarization was equivalent to that caused by the mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). Even when induced by as little as 0.3 mmol l-1 sulfide, the depolarization was not reversible over a subsequent 5 h recovery period. The mechanism of toxicity was likely not via inhibition of cytochrome c oxidase (COX),since other COX inhibitors and other mitochondrial electron transport chain inhibitors did not produce similar effects. Furthermore, pharmacological inhibition of the mitochondrial permeability transition pore failed to prevent sulfide-induced depolarization. Finally, increased oxidation of the free radical indicators H2DCFDA and MitoSOX™ in erythrocytes exposed to sulfide suggests that sulfide oxidation increased oxidative stress and superoxide production, respectively. Together, these results indicate that sulfide exposure causes mitochondrial depolarization in cells of a sulfide-tolerant annelid, and that this effect, which differs from the actions of other COX inhibitors, may be via increased free radical damage.

Up-regulation of uncoupling protein 2 by cyanide is linked with cytotoxicity in mesencephalic cells

Uncoupling protein 2 (UCP-2) regulates mitochondrial function by increasing proton leak across the inner membrane to dissociate respiration from ATP synthesis and reduce reactive oxygen species generation. A number of studies have shown that UCP-2 expression protects cells from oxidative stress mediated injuries. In the current study, we show UCP-2-mediated reduction in mitochondrial function contributes to the mitochondrial dysfunction and the necrotic death of primary cultured mesencephalic cells (MCs) after exposure to cyanide, a complex IV inhibitor. The necrotic cell death was directly related to the level of mitochondrial dysfunction, as shown by reduction in ATP levels and decreased mitochondrial membrane potential. Treatment with cyanide for 6 h or longer upregulated UCP-2 expression. Blockade of up-regulation with a transcription or a translational inhibitor reduced the response to cyanide. Knockdown with RNAi or transfection with a UCP-2 dominant-negative interfering mutant reduced the cyanide-induced mitochondrial dysfunction and cell death, showing that constitutive expression of UCP-2 plays a role in the response to cyanide. Overexpression of UCP-2 by transfection with human full-length cDNA potentiated the cyanide toxicity. These findings indicate that UCP-2 can serve as a regulator of mitochondria-mediated necrotic cell death, in which enhanced expression can increase the vulnerability of primary MCs to injury due to complex IV-mediated inhibition by cyanide.

Hypoxia-induced apoptosis in adult rat dorsal root ganglion neurons in vitro

Following spinal root injury, dorsal root ganglia suffer mechanical trauma and compromised blood supply. Little is known about the consequences for neuronal survival. Here we used cyanide treatment in vitro to examine effects of moderate hypoxia on adult rat dorsal root ganglion cells identified by GAP-43 immunostaining. 400 microM-4 mM cyanide caused sustained increases in intracellular Ca2+. Cyanide at 2 mM led to a significant increase in apoptosis, detected using TUNEL labelling and confirmed by ultrastructural analysis, and a further increase when cultures were left overnight in fresh medium. Our study shows that dorsal root ganglion neurons die by apoptosis following hypoxia and that cell death increases over time. Cyanide response provides a simple assay for testing neuroprotective agents and examining underlying mechanisms.

Rapid sodium cyanide depletion in cell culture media: Outgassing of hydrogen cyanide at physiological pH

During the course of in vitro studies on cyanide exposure with SH-SY5Y human neuroblastoma cells, we found that sodium cyanide (NaCN) up to a concentration of 10 mM had no significant toxic effect under our culture conditions. Further investigation of this apparent cyanide resistance revealed that the sodium cyanide was being rapidly depleted from the cell culture medium. Cyanide was interacting with constituents of the cell culture medium and was somehow being detoxified or removed from solution. The reaction of cyanide with cell culture media in 96-well culture plates reduced cyanide concentrations rapidly (80-90% in 2 h at 37 degrees C). Running the same reaction in capped tubes significantly reduced cyanide loss from solution. Incubation of cyanide with individual constituents of the cell culture medium in solution showed that glucose, phenol red, and amino acids all acted to detoxify or remove cyanide from solution. When amino acids or buffers were incubated with sodium cyanide in aqueous solution at pH 7.4, hydrogen cyanide (HCN) was found to degas from the solutions. We compared HCN outgassing over a range of pH values. As expected, HCN remained very soluble at high pH, but as the pH was reduced to 7.0, the rate of HCN formation and outgassing increased dramatically. Acid-base reactions involving cyanide and proton donors, such as amino acids and other cell culture media constituents, at physiological pH result in rapid HCN outgassing from solution at 37 degrees C. These results indicate that previous in vitro cyanide toxicity studies done in standard culture media with prolonged incubation times using gas-exchanging culture containers might have to be reevaluated in light of the fact that the effective cyanide concentrations in the culture media were significantly lower than reported.

Enhancement of Cyanide-Induced Mitochondrial Dysfunction and Cortical Cell Necrosis by Uncoupling Protein-2

Uncoupling protein 2 (UCP-2) is expressed in the inner mitochondrial membrane and modulates mitochondrial function by partially uncoupling oxidative phosphorylation, and it has been reported to modulate cell death. Cyanide is a potent neurotoxin that inhibits complex IV to alter mitochondrial function to induce neuronal death. In primary rat cortical cells KCN produced an apoptotic death at 200-400 microM. Higher concentrations of potassium cyanide (KCN) (500-600 microM) switched the mode of death from apoptosis to necrosis. In necrotic cells, ATP levels were severely depleted as compared to cortical cells undergoing apoptosis. To determine if UCP-2 expression could alter KCN-induced cell death, cells were transiently transfected with full-length human UCP-2 cDNA (UCP-2+). Overexpression switched the mode of death produced by KCN (400 microM) from apoptosis to necrosis. The change in cell death was mediated by impaired mitochondrial function as reflected by a marked decrease of ATP levels and reduction in mitochondrial membrane potential. RNA interference or transfection with a dominant interfering mutant blocked the necrotic response observed in UCP-2+ cells. Additionally, treatment of UCP-2+ cells with cyclosporin A blocked necrosis, indicating the involvement of mitochondrial permeability pore transition in the necrotic death. These results show that increased expression of UCP-2 alters the response to a potent mitochondrial toxin by switching the mode of cell death from apoptosis to necrosis. It is concluded that UCP-2 levels influence cellular responses to cyanide-induced mitochondrial dysfunction.

Photobiomodulation directly benefits primary neurons functionally inactivated by toxins: role of cytochrome c oxidase

Far red and near infrared (NIR) light promotes wound healing, but the mechanism is poorly understood. Our previous studies using 670 nm light-emitting diode (LED) arrays suggest that cytochrome c oxidase, a photoacceptor in the NIR range, plays an important role in therapeutic photobiomodulation. If this is true, then an irreversible inhibitor of cytochrome c oxidase, potassium cyanide (KCN), should compete with LED and reduce its beneficial effects. This hypothesis was tested on primary cultured neurons. LED treatment partially restored enzyme activity blocked by 10-100 microm KCN. It significantly reduced neuronal cell death induced by 300 microm KCN from 83.6 to 43.5%. However, at 1-100 mm KCN, the protective effects of LED decreased, and neuronal deaths increased. LED significantly restored neuronal ATP content only at 10 microm KCN but not at higher concentrations of KCN tested. Pretreatment with LED enhanced efficacy of LED during exposure to 10 or 100 microm KCN but did not restore enzyme activity to control levels. In contrast, LED was able to completely reverse the detrimental effect of tetrodotoxin, which only indirectly down-regulated enzyme levels. Among the wavelengths tested (670, 728, 770, 830, and 880 nm), the most effective ones (830 nm, 670 nm) paralleled the NIR absorption spectrum of oxidized cytochrome c oxidase, whereas the least effective wavelength, 728 nm, did not. The results are consistent with our hypothesis that the mechanism of photobiomodulation involves the up-regulation of cytochrome c oxidase, leading to increased energy metabolism in neurons functionally inactivated by toxins.

Calcineurin-mediated Bad translocation regulates cyanide-induced neuronal apoptosis

In cyanide-induced apoptosis, an increase in cytosolic free Ca2+ and generation of reactive oxygen species are initiation stimuli for apoptotic cell death. Previous studies have shown that cyanide-stimulated translocation of Bax (Bcl-associated X protein) to mitochondria is linked with release of cytochrome c and subsequent activation of a caspase cascade [Shou, Li, Prabhakaran, Borowitz and Isom (2003) Toxicol. Sci. 75, 99-107]. In the present study, the relationship of the cyanide-induced increase in cytosolic free Ca2+ to activation of Bad ( Bcl-2/Bcl-X(L)- antagonist, causing cell death) was determined in cortical cells. Bad is a Ca2+-sensitive pro-apoptotic Bcl-2 protein, which on activation translocates from cytosol to mitochondria to initiate cytochrome c release. In cultured primary cortical cells, cyanide produced a concentration- and time-dependent translocation of Bad from cytosol to mitochondria. Translocation occurred early in the apoptotic response, since mitochondrial Bad was detected within 1 h of cyanide treatment. Mitochondrial levels of the protein continued to increase up to 12 h post-cyanide exposure. Concurrent with Bad translocation, a Ca2+-sensitive increase in cellular calcineurin activity was observed. Increased cytosolic Ca2+ and calcineurin activation stimulated Bad translocation since BAPTA [bis-(o-aminophenoxy)ethane-N, N, N', N'-tetra-acetic acid], an intracellular Ca2+ chelator, and cyclosporin A, a calcineurin inhibitor, significantly reduced translocation. BAPTA also blocked release of cytochrome c from mitochondria as well as apoptosis. Furthermore, treatment of cells with the calcineurin inhibitors cyclosporin A or FK506 blocked the apoptotic response, linking calcineurin activation and the subsequent translocation of Bad to cell death. These observations show that by inducing a rapid increase in cytosolic free Ca2+, cyanide can partially initiate the apoptotic cascade through a calcineurin-mediated translocation of Bad to mitochondria.

Caspase inhibition switches the mode of cell death induced by cyanide by enhancing reactive oxygen species generation and PARP-1 activation

Execution of apoptosis can involve activation of the caspase family of proteases. Recent studies show that caspase inhibition can switch the morphology of cell death from apoptotic to necrotic without altering the level of death among cell populations. In the present study, the effect of caspase inhibition on cortical (CX) cell death induced by cyanide was investigated. In primary cultured CX cells exposed to cyanide (400 microM), death was primarily apoptotic as indicated by positive TUNEL staining. Reactive oxygen species (ROS) generation and subsequent caspase activation mediated the apoptosis. Inhibition of the caspase cascade with zVAD-fmk switched the apoptotic response to necrotic cell death, as assessed by increased cellular efflux of LDH and propidium iodide uptake by the cells. The change in death mode was accompanied by a marked increase in poly (ADP-ribose) polymerase-1 (PARP-1) activity, reactive oxygen species (ROS) generation, a reduction in the mitochondrial membrane potential (Delta psi(m)), and reduced cellular ATP. Prior treatment of cells with 3-aminobenzamide (3-AB), a PARP-1 inhibitor, prevented the cells from undergoing necrosis and preserved intracellular ATP levels. These findings indicate that apoptosis and necrosis share common initiation pathways and caspase inhibition can switch the apoptotic response to necrosis. Inhibition of PARP-1 preserves cellular ATP levels and in turn blocks execution of the necrotic death pathway.

Cyanide enhancement of dopamine-induced apoptosis in mesencephalic cells involves mitochondrial dysfunction and oxidative stress

Dopamine (DA)-induced neurotoxicity is potentiated when cellular metabolism is compromised. Since cyanide is a neurotoxin that produces mitochondrial dysfunction and stimulates intracellular generation of reactive oxygen species (ROS), KCN was used to study DA-induced apoptosis in primary cultured mesencephalon cells. Treatment of neurons with DA (300 microM) for 24h produced apoptosis as determined by TUNEL staining, DNA fragmentation and increased caspase activity. Pretreatment with KCN (100 microM) 30min prior to DA increased the number of cells undergoing apoptosis. When added to the cells alone, this concentration of KCN did not induce apoptosis. DA stimulated intracellular generation of ROS, and treatment with KCN enhanced ROS generation. Treatment of cells with glutathione or uric acid (antioxidants/scavengers) attenuated both the increase in ROS generation and the apoptosis, demonstrating that ROS are initiators of the cytotoxicity. Studies on the sequence of events mediating the response showed that DA-induced depolarization of the mitochondrial membrane was dependent on ROS generation and KCN enhanced this action of DA. Following changes in mitochondrial membrane potential, cytochrome c was released from mitochondria, leading to caspase activation and eventually cell death. These results demonstrate that oxidative stress and mitochondrial dysfunction are initiators of DA-induced apoptosis. Subsequent cytochrome c release activates the caspase effector component of apoptosis. Cyanide potentiates the neurotoxicity of DA by enhancing the generation of ROS and impairing mitochondrial function.