Differential susceptibility of brain areas to cyanide involves different modes of cell death

Evaluation of the health risks related to the presence of cyanogenic glycosides in foods other than raw apricot kernels

In 2016, the EFSA Panel on Contaminants in the Food Chain (CONTAM) published a scientific opinion on the acute health risks related to the presence of cyanogenic glycosides (CNGs) in raw apricot kernels in which an acute reference dose (ARfD) of 20 μg/kg body weight (bw) was established for cyanide (CN). In the present opinion, the CONTAM Panel concluded that this ARfD is applicable for acute effects of CN regardless the dietary source. To account for differences in cyanide bioavailability after ingestion of certain food items, specific factors were used. Estimated mean acute dietary exposures to cyanide from foods containing CNGs did not exceed the ARfD in any age group. At the 95th percentile, the ARfD was exceeded up to about 2.5-fold in some surveys for children and adolescent age groups. The main contributors to exposures were biscuits, juice or nectar and pastries and cakes that could potentially contain CNGs. Taking into account the conservatism in the exposure assessment and in derivation of the ARfD, it is unlikely that this estimated exceedance would result in adverse effects. The limited data from animal and human studies do not allow the derivation of a chronic health-based guidance value (HBGV) for cyanide, and thus, chronic risks could not be assessed.

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.

Circulatory Failure During Noninhaled Forms of Cyanide Intoxication

Our objective was to determine how circulatory failure develops following systemic administration of potassium cyanide (KCN). We used a noninhaled modality of intoxication, wherein the change in breathing pattern would not influence the diffusion of CN into the blood, akin to the effects of ingesting toxic levels of CN. In a group of 300 to 400 g rats, CN-induced coma (CN i.p., 7 mg/kg) produced a central apnea within 2 to 3 min along with a potent and prolonged gasping pattern leading to autoresuscitation in 38% of the animals. Motor deficits and neuronal necrosis were nevertheless observed in the surviving animals. To clarify the mechanisms leading to potential autoresuscitation versus asystole, 12 urethane-anesthetized rats were then exposed to the lowest possible levels of CN exposure that would lead to breathing depression within 7 to 8 min; this dose averaged 0.375 mg/kg/min i.v. At this level of intoxication, a cardiac depression developed several minutes only after the onset of the apnea, leading to cardiac asystole as PaO2 reached value approximately 15 Torr, unless breathing was maintained by mechanical ventilation or through spontaneous gasping. Higher levels of KCN exposure in 10 animals provoked a primary cardiac depression, which led to a rapid cardiac arrest by pulseless electrical activity (PEA) despite the maintenance of PaO2 by mechanical ventilation. These effects were totally unrelated to the potassium contained in KCN. It is concluded that circulatory failure can develop as a direct consequence of CN-induced apnea but in a narrow range of exposure. In this "low" range, maintaining pulmonary gas exchange after exposure, through mechanical ventilation (or spontaneous gasping), can reverse cardiac depression and restore spontaneous breathing. At higher level of intoxication, cardiac depression is to be treated as a specific and spontaneously irreversible consequence of CN exposure, leading to a PEA.

Intoxication by Cyanide in Pregnant Sows: Prenatal and Postnatal Evaluation

Cyanide is a ubiquitous chemical in the environment and has been associated with many intoxication episodes; however, little is known about its potentially toxic effects on development. The aim of this study was to evaluate the effects of maternal exposure to potassium cyanide (KCN) during pregnancy on both sows and their offspring. Twenty-four pregnant sows were allocated into four groups that orally received different doses of KCN (0.0, 2.0, 4.0, and 6.0 mg/kg of body weight) from day 21 of pregnancy to term. The KCN-treated sows showed histological lesions in the CNS, thyroid follicle enlargement, thyroid epithelial thickening, colloid reabsorption changes, and vacuolar degeneration of the renal tubular epithelium. Sows treated with 4.0 mg/kg KCN showed an increase in the number of dead piglets at birth. Weaned piglets from all KCN-treated groups showed histological lesions in the thyroid glands with features similar to those found in their mothers. The exposure of pregnant sows to cyanide thus caused toxic effects in both mothers and piglets. We suggest that swine can serve as a useful animal model to assess the neurological, goitrogenic, and reproductive effects of cyanide toxicosis.

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).

Involvement of JNK and caspase activation in hoiamide A-induced neurotoxicity in neocortical neurons

The frequent occurrence of Moorea producens (formerly Lyngbya majuscula) blooms has been associated with adverse effects on human health. Hoiamide A is a structurally unique cyclic depsipeptide isolated from an assemblage of the marine cyanobacteria M. producens and Phormidiumgracile. We examined the influence of hoiamide A on neurite outgrowth in neocortical neurons and found that it suppressed neurite outgrowth with an IC₅₀ value of 4.89 nM. Further study demonstrated that hoiamide A stimulated lactic acid dehydrogenase (LDH) efflux, nuclear condensation and caspase-3 activity with EC₅₀ values of 3.66, 2.55 and 4.33 nM, respectively. These data indicated that hoiamide A triggered a unique neuronal death profile that involves both necrotic and apoptotic mechanisms. The similar potencies and similar time-response relationships between LDH efflux and caspase-3 activation/nuclear condensation suggested that both necrosis and apoptosis may derive from interaction with a common molecular target. The broad-spectrum caspase inhibitor, Z-VAD-FMK completely inhibited hoiamide A-induced neurotoxicity. Additionally, hoiamide A stimulated JNK phosphorylation, and a JNK inhibitor attenuated hoiamide A-induced neurotoxicity. Collectively, these data demonstrate that hoiamide A-induced neuronal death requires both JNK and caspase signaling pathways. The potent neurotoxicity and unique neuronal cell death profile of hoiamide A represents a novel neurotoxic chemotype from marine cyanobacteria.

Extrapyramidal system neurotoxicity: animal models

The central nervous system's extrapyramidal system provides involuntary motor control to the muscles of the head, neck, and limbs. Toxicants that affect the extrapyramidal system are generally clinically characterized by impaired motor control, which is usually the result of basal ganglionic dysfunction. A variety of extrapyramidal syndromes are recognized in humans and include Parkinson's disease, secondary parkinsonism, other degenerative diseases of the basal ganglia, and clinical syndromes that result in dystonia, dyskinesia, essential tremor, and other forms of tremor and chorea. This chapter briefly reviews the anatomy of the extrapyramidal system and discusses several naturally occurring and experimental models that target the mammalian (nonhuman) extrapyramidal system. Topics discussed include extrapyramidal syndromes associated with antipsychotic drugs, carbon monoxide, reserpine, cyanide, rotenone, paraquat, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and manganese. In most cases, animals are used as experimental models to improve our understanding of the toxicity and pathogenesis of these agents. Another agent discussed in this chapter, yellowstar thistle poisoning in horses, however, represents an important spontaneous cause of parkinsonism that naturally occurs in animals. The central focus of the chapter is on animal models, especially the concordance between clinical signs, neurochemical changes, and neuropathology between animals and people.

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.

Cerebrovascular changes in the rat brain in two models of ischemia

BACKGROUND

Vascular occlusion and cyanide neurotoxicity induces oxidative stress and degeneration in the brain. This oxidant induced stress changes the vascular dynamics of cerebral blood vessels, and participates in homeostatic response mechanisms which balance oxygen supply to hypoxic stress-sensitive neurons. The associated changes in vascular morphology include remodeling of the microvasculature and endothelial changes, alterations in regional circulation and variations in the blood brain barrier (BBB). This study compares alterations in physiology of the cerebral artery after a short-term oxidative stress induced by cyanide toxicity and vascular occlusion.

METHOD

Adult Wistar rats (N=30) were divided into three groups; vascular occlusion (VO) (n=12), potassium cyanide administration (CN) (n=12) and Control-CO (n=6). The CN rates were treated with 30mg/kg of orally administered KCN while the VO was subjected to global vascular occlusion, both for a duration of 10 days, described as the treatment phase. Control animals were fed on normal rat chow and water for 10 days. At the end of the treatment phase, n=6 animals in each of the VO, CN and VO groups were anesthetized with sodium pentobarbital (50IP) and the CCA exposed, after which pin electrodes were implanted to record the spikes form the tunica media of the CCA. After day 10, treatment was discontinued for these animals, each remaining in the VO and CN groups (VO-I and CN-I) until day 20 (withdrawal phase) following which the spikes were recorded using the procedure described above.

RESULTS/DISCUSSION

Vascular occlusion and cyanide toxicity increased vascular resistance in the MCA (reduced lumen thickness ratio) and increased the diameter of the CCA after the treatment phase of 10 days. After 10 days of withdrawal, the VO group showed a reduction in resistance and an increase in the lumen width/wall thickness ratio (LWR) while the CN group showed increased resistance and a reduction in LWR.

CONCLUSION

Cyanide toxicity increased vascular resistance by inducing degenerative changes in the wall of the artery while vascular occlusion increased resistance through mechanical stress and increased thickness of arterial wall. After the withdrawal phase, vascular resistance diminished in the VO to a significantly greater extent than the CN.

Cross-species and tissue variations in cyanide detoxification rates in rodents and non-human primates on protein-restricted diet

We sought to elucidate the impact of diet, cyanide or cyanate exposure on mammalian cyanide detoxification capabilities (CDC). Male rats (~8 weeks old) (N=52) on 75% sulfur amino acid (SAA)-deficient diet were treated with NaCN (2.5mg/kg bw) or NaOCN (50mg/kg bw) for 6 weeks. Macaca fascicularis monkeys (~12 years old) (N=12) were exclusively fed cassava for 5 weeks. CDC was assessed in plasma, or spinal cord, or brain. In rats, NaCN induced seizures under SAA-restricted diet whereas NaOCN induced motor deficits. No deficits were observed in non-human primates. Under normal diet, the CDC were up to ~80× faster in the nervous system (14 ms to produce one μmol of thiocyanate from the detoxification of cyanide) relative to plasma. Spinal cord CDC was impaired by NaCN, NaOCN, or SAA deficiency. In M. fascicularis, plasma CDC changed proportionally to total proteins (r=0.43; p<0.001). The plasma CDC was ~2× relative to that of rodents. The nervous system susceptibility to cyanide may result from a "multiple hit" by the toxicity of cyanide or its cyanate metabolite, the influences of dietary deficiencies, and the tissue variations in CDC. Chronic dietary reliance on cassava may cause metabolic derangement including poor CDC.

Severe nigrostriatal degeneration without clinical parkinsonism in patients with polymerase gamma mutations

The role of mitochondria in the pathogenesis of neurodegeneration is an area of intense study. It is known that defects in proteins involved in mitochondrial quality control can cause Parkinson's disease, and there is increasing evidence linking mitochondrial dysfunction, and particularly mitochondrial DNA abnormalities, to neuronal loss in the substantia nigra. Mutations in the catalytic subunit of polymerase gamma are among the most common causes of mitochondrial disease and owing to its role in mitochondrial DNA homeostasis, polymerase gamma defects are often considered a paradigm for mitochondrial diseases generally. Yet, despite this, parkinsonism is uncommon with polymerase gamma defects. In this study, we investigated structural and functional changes in the substantia nigra of 11 patients with polymerase gamma encephalopathy. We characterized the mitochondrial DNA abnormalities and examined the respiratory chain in neurons of the substantia nigra. We also investigated nigrostriatal integrity and function using a combination of post-mortem and in vivo functional studies with dopamine transporter imaging and positron emission tomography. At the cellular level, dopaminergic nigral neurons of patients with polymerase gamma encephalopathy contained a significantly lower copy number of mitochondrial DNA (depletion) and higher levels of deletions than normal control subjects. A selective and progressive complex I deficiency was seen and this was associated with a severe and progressive loss of the dopaminergic neurons of the pars compacta. Dopamine transporter imaging and positron emission tomography showed that the degree of nigral neuronal loss and nigrostriatal depletion were severe and appeared greater even than that seen in idiopathic Parkinson's disease. Despite this, however, none of our patients showed any signs of parkinsonism. The additional presence of both thalamic and cerebellar dysfunction in our patients suggested that these may play a role in counteracting the effects of basal ganglia dysfunction and prevent the development of clinical parkinsonism.

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.

Cyanide-induced apoptosis of dopaminergic cells is promoted by BNIP3 and Bax modulation of endoplasmic reticulum-mitochondrial Ca2+ levels

Cyanide is a potent neurotoxicant that can produce dopaminergic neuronal death in the substantia nigra and is associated with a Parkinson-like syndrome. In this study involvement of Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (BNIP3), a BH3-only Bcl-2 protein, in cyanide-induced death of dopaminergic cells was determined in mice and Mes 23.5 cells. Treatment of mice with cyanide up-regulated BNIP3 and Bax expression in tyrosine hydroxylase (TH)-positive cells of the substantia nigra, and progressive loss of TH-positive neurons was observed over a 9-day period. In Mes 23.5 dopaminergic cells, cyanide stimulated translocalization of BNIP3 to both endoplasmic reticulum (ER) and mitochondria. In ER, BNIP3 stimulated release of Ca(2+) into the cytosol, followed by accumulation of mitochondrial Ca(2+), resulting in reduction of mitochondrial membrane potential (Deltapsi(m)) and eventually cell death. Cyanide also activated Bax to colocalize with BNIP3 in ER and mitochondria. Forced overexpression of BNIP3 activated Bax, whereas gene silencing reduced Bax activity. Knockdown of Bax expression by small interfering RNA blocked the BNIP3-mediated changes in ER and mitochondrial Ca(2+) to block cyanide-induced mitochondrial dysfunction and cell death. These findings show that BNIP3-mediates cyanide-induced dopaminergic cell death through a Bax downstream signal that mobilizes ER Ca(2+) stores, followed by mitochondrial Ca(2+) overload.

Cyanide-induced death of dopaminergic cells is mediated by uncoupling protein-2 up-regulation and reduced Bcl-2 expression

Cyanide is a potent inhibitor of mitochondrial oxidative metabolism and produces mitochondria-mediated death of dopaminergic neurons and sublethal intoxications that are associated with a Parkinson-like syndrome. Cyanide toxicity is enhanced when mitochondrial uncoupling is stimulated following up-regulation of uncoupling protein-2 (UCP-2). In this study, the role of a pro-survival protein, Bcl-2, in cyanide-mediated cell death was determined in a rat dopaminergic immortalized mesencephalic cell line (N27 cells). Following pharmacological up-regulation of UCP-2 by treatment with Wy14,643, cyanide reduced cellular Bcl-2 expression by increasing proteasomal degradation of the protein. The increased turnover of Bcl-2 was mediated by an increase of oxidative stress following UCP-2 up-regulation. The oxidative stress involved depletion of mitochondrial glutathione (mtGSH) and increased H2O2 generation. Repletion of mtGSH by loading cells with glutathione ethyl ester reduced H2O2 generation and in turn blocked the cyanide-induced decrease of Bcl-2. To determine if UCP-2 mediated the response, RNAi knock down was conducted. The RNAi decreased cyanide-induced depletion of mtGSH, reduced H2O2 accumulation, and inhibited down-regulation of Bcl-2, thus blocking cell death. To confirm the role of Bcl-2 down-regulation in the cell death, it was shown that over-expression of Bcl-2 by cDNA transfection attenuated the enhancement of cyanide toxicity after UCP-2 up-regulation. It was concluded that UCP-2 up-regulation sensitizes cells to cyanide by increasing cellular oxidative stress, leading to an increase of Bcl-2 degradation. Then the reduced Bcl-2 levels sensitize the cells to cyanide-mediated cell death.

Effects of acrylonitrile on antioxidant status of different brain regions in rats

While the adverse effects of acrylonitrile (AN) on the central nervous system (CNS) are known to be mediated, at least in part, by the generation of free radicals and oxidative stress, there is a paucity of data on region-specific alterations in biomarkers of oxidative stress in the brain of AN-exposed animals. The present study was designed to examine the effects of AN on biomarkers of oxidative stress in several brain regions of adult Sprague-Dawley rats. Daily intraperitoneal (i.p.) treatment of animals to 0 (control, normal saline solution), 25, 50 or 75mgAN/kg body weight for 7 days resulted in statistically significant (p<0.05) increases in the levels of lipid peroxidation product, malondialdehyde (MDA), in the cortex and cerebellum; a statistically significant (p<0.05) decrease MDA levels were noted in the striatum. Contents of reduced glutathione (GSH) were significantly (p<0.05) decreased in cortex, cerebellum and hippocampus. The activities of the antioxidant enzymes, superoxide dismutase (SOD) and glutathione peroxidase (GPx) were differentially affected by AN and these effects were brain region-specific and AN dose-dependent. Taken together, these data suggest brain region-specific effects of AN on lipid peroxidation, activities of antioxidant enzymes and non-enzymatic antioxidant levels. These effects may provide biochemical evidence for AN-induced neurobehavioral damage and disturbance of monoamine neurotransmitters.

The cerebral effects of ascent to high altitudes

Cellular hypoxia is the common final pathway of brain injury that occurs not just after asphyxia, but also when cerebral perfusion is impaired directly (eg, embolic stroke) or indirectly (eg, raised intracranial pressure after head injury). We Review recent advances in the understanding of neurological clinical syndromes that occur on exposure to high altitudes, including high altitude headache (HAH), acute mountain sickness (AMS), and high altitude cerebral oedema (HACE), and the genetics, molecular mechanisms, and physiology that underpin them. We also present the vasogenic and cytotoxic bases for HACE and explore venous hypertension as a possible contributory factor. Although the factors that control susceptibility to HACE are poorly understood, the effects of exposure to altitude (and thus hypobaric hypoxia) might provide a reproducible model for the study of cerebral cellular hypoxia in healthy individuals. The effects of hypobaric hypoxia might also provide new insights into the understanding of hypoxia in the clinical setting.

Interaction of cyanide and nitric oxide with cytochrome c oxidase: implications for acute cyanide toxicity

Acute cyanide toxicity is attributed to inhibition of cytochrome c oxidase (CcOX), the oxygen-reducing component of mitochondrial electron transport; however, the mitochondrial action of cyanide is complex and not completely understood. State-3 oxygen consumption and CcOX activity were studied in rat N27 mesencephalic cells to examine the functional interaction of cyanide and nitric oxide (NO). KCN produced a concentration-dependent inhibition of cellular respiration. Cyanide's median inhibitory concentration (IC50) of oxygen consumption (13.2 +/- 1.8microM) was higher than the CcOX IC50 (7.2 +/- 0.1microM). Based on respiratory threshold analysis, 60% inhibition of CcOX was necessary before oxygen consumption was decreased. Addition of high levels of exogenous NO (100microM S-nitroso-N-acetyl-DL-penicillamine) attenuated cyanide inhibition of both respiration and CcOX. On the other hand, when endogenous NO generation was blocked by an NOS inhibitor (N(omega)-monomethyl-L-arginine ester), the cyanide IC50 for both respiration and CcOX increased to 59.6 +/- 0.9microM and 102 +/- 10microM, respectively, thus showing constitutive, low-level NO production enhanced cyanide inhibition. Laser scanning cytometry showed that cyanide elevated mitochondrial NO, which then was available to interact with CcOX to enhance the inhibition. It is concluded that the rapid, potent action of cyanide is due in part to mitochondrial generation of NO, which enhances inhibition of CcOX. At low mitochondrial oxygen tensions, the cyanide-NO interaction would be increased. Also, the antidotal action of sodium nitrite is partly explained by generation of high mitochondrial levels of NO, which antagonizes the CcOX inhibition.

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.

Uncoupling protein-2 up-regulation and enhanced cyanide toxicity are mediated by PPARalpha activation and oxidative stress

Uncoupling protein 2 (UCP-2) is an inner mitochondrial membrane proton carrier that modulates mitochondrial membrane potential (DeltaPsi(m)) and uncouples oxidative phosphorylation. We have shown that up-regulation of UCP-2 by Wy14,643, a selective peroxisome proliferator-activated receptor-alpha (PPARalpha) agonist, enhances cyanide cytotoxicity. The pathway by which Wy14,643 up-regulates UCP-2 was determined in a dopaminergic cell line (N27 cells). Since dopaminergic mesencephalic cells are a primary brain target of cyanide, the N27 immortalized mesencephalic cell was used in this study. Wy14,643 produced a concentration- and time-dependent up-regulation of UCP-2 that was linked to enhanced cyanide-induced cell death. MK886 (PPARalpha antagonist) or PPARalpha knock-down by RNA interference (RNAi) inhibited PPARalpha activity as shown by the peroxisome proliferator response element-luciferase reporter assay, but only partially decreased up-regulation of UCP-2. The role of oxidative stress as an alternative pathway to UCP-2 up-regulation was determined. Wy14,643 induced a rapid surge of ROS generation and loading cells with glutathione ethyl ester (GSH-EE) or pre-treatment with vitamin E attenuated up-regulation of UCP-2. On the other hand, RNAi knockdown of PPARalpha did not alter ROS generation, suggesting a PPARalpha-independent component to the response. Co-treatment with PPARalpha-RNAi and GSH-EE blocked both the up-regulation of UCP-2 by Wy14,643 and the cyanide-induced cell death. It was concluded that a PPARalpha-mediated pathway and an oxidative stress pathway independent of PPARalpha mediate the up-regulation of UCP-2 and subsequent increased vulnerability to cyanide-induced cytotoxicity.

Effects of Long-term Cyanide Ingestion by Pigs

Animal performance and health status are adversely affected by long-term cyanide ingestion; however, the effects of cyanide ingestion by pigs have not been fully determined. The aim of the present study was to determine the effects of prolonged exposure to different doses of potassium cyanide (KCN) in growing-finishing swine. Twenty-four pigs, 45 days of age, were divided into four equal groups and treated with different doses of KCN: 0, 2.0, 4.0 or 6.0 mg per kg body weight per day for 70 consecutive days. The results showed a significant alteration in thiocyanate, creatinine and urea levels and in alanine aminotransferase activity of swine dosed with 4.0 and 6.0 mg/kg/KCN. Thyroid weight was significantly increased in those pigs from 4.0 mg/kg KCN group, but no change in cholesterol, triiodothyronine or thyroline levels were observed. Body and carcase weights, body weight gain, and bacon thickness were not affected by KCN treatment. The histopathological study revealed increased numbers of vacuoles in the colloid of thyroid follicles, degeneration of cerebellar white matter and Purkinje cells, degeneration of renal tubular epithelial cells, caryolysis and pyknosis in hepatocytes, and disturbance of the normal lobular architecture of the liver in all treated pigs. Thus, long-term administration of KCN to swine affects several tissues and could adversely affect animal production.

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.

Regulation of human male germ cell death by modulators of ATP production

The understanding of testicular physiology, pathology, and male fertility issues requires knowledge of male germ cell death and energy production. Here, we induced human male germ cell apoptosis (detected by Southern blot analysis of DNA fragmentation, TUNEL, activation of caspases-3 and -9, and electron microscopy) by incubating seminiferous tubule segments under hormone- and serum-free conditions. Inhibitors of complexes I to IV of mitochondrial respiration, exposure to anoxia, and inhibition of F0F1-ATPase (with oligomycin) decreased the ATP levels (analyzed by HPLC) and suppressed apoptosis at 4 h. Uncoupler 2,4-dinitrophenol (DNP) and oligomycin combination also suppressed death at 4 h, as did the DNP alone. Inhibition of glycolysis by 2-deoxyglucose neither suppressed nor further induced apoptosis nor altered the antiapoptotic effects of the mitochondrial inhibitors. Furthermore, Fas system activation did not modify the effects of mitochondrial modulators. After 24 h, delayed male germ cell apoptosis was observed despite the presence of the mitochondrial inhibitors. We conclude that the mitochondrial ATP production machinery plays an important role in regulating in vitro-induced primary pathways of human male germ apoptosis. The ATP synthesized by the F0F1-ATPase seems to be the crucial death regulator, rather than any of the complexes (I-IV) alone, the functional electron transport chain, or the membrane potential. We also conclude that there seem to be secondary pathways of human testicular cell apoptosis that do not require mitochondrial ATP production. The present study emphasizes the role of the main catabolic pathways in the complex network of regulating events of male germ cell life and death.

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.

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.

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.

Receptor mechanisms mediating cyanide generation in PC12 cells and rat brain

Cyanide is generated in neurons and this report examines the two different receptors which mediate cyanide formation in neuronal tissue. An opiate receptor blocked by naloxone increases cyanide production both in rat brain and in rat pheochromocytoma (PC12) cells. A muscarinic receptor in PC12 cells releases cyanide and the effect is blocked by atropine. In rat brain, in vivo, a muscarinic agonist inhibits cyanide generation, possibly by acting on receptor subtypes different from those in PC12 cells. Cyanide generation by a muscarinic agonist in PC12 cells is blocked by pertussis toxin but that caused by an opiate is not. Thus, two different receptors and two different second messenger systems can mediate cyanide generation in PC12 cells. In parallel with the in vivo data, cultured primary rat cortical cells also show decreased cyanide release following muscarinic stimulation. Both blockade of cyanide generation by muscarinic receptor activation and cyanide release by opiate agonists from cortical cells are pertussis toxin insensitive. Similarly, little cyanide generation was seen following cholera toxin treatment. These data indicate that opiate receptors increase and muscarinic receptors decrease cyanide production in rat brain tissue by G-protein independent mechanisms. This work supports the suggestion that the powerful actions of cyanide may be important for neuromodulation in the CNS.

Chemical anoxia delays germ cell apoptosis in the human testis

An understanding of testicular physiology and pathology requires knowledge of the regulation of cell death. Previous observation of suppression of apoptosis by hypoxia suggested a role for ATP in germ cell death. However, the exact effects of ATP production on germ cell death and of apoptosis on the levels of ATP and other adenine nucleotides (ANs) have remained unclear. We investigated the levels of ANs during human testicular apoptosis (analyzed by HPLC) and the role of chemical anoxia in germ cell death (detected by Southern blot analysis of DNA fragmentation, in situ end labeling of DNA, and electron microscopy). Incubation of seminiferous tubule segments under serum-free conditions induced apoptosis and concomitantly decreased the levels of ANs. Chemical anoxia, induced with potassium cyanide (KCN), an inhibitor of mitochondrial respiration, dropped ATP levels further and suppressed apoptosis at 4 h. After 24 h, many of the testicular cells underwent delayed apoptosis despite ATP depletion. Some cells showed signs of necrosis or toxicity. The addition of 2-deoxyglucose, an antimetabolite of glycolysis, did not alter the results obtained with KCN alone, whereas a toxic concentration of hydrogen peroxide switched apoptosis to necrosis. In most of the testicular cells, mitochondrial respiration appears to play a crucial role in controlling primary cell death cascades. In the human testis, there seem to be secondary apoptotic pathways that do not require functional respiration (or ATP).

Dynamic recording of cell death in the in vitro dorsal vagal nucleus of rats in response to metabolic arrest

Anoxic/ischemic neuronal death is usually assessed in cell cultures or in vivo within a time window of 24 h to several days using the nucleic acid stain propidium iodide or histological techniques. Accordingly, there is limited information on the time course of such neuronal death. We loaded acute rat brain stem slices with propidium iodide for dynamic fluorometric recording of metabolic arrest-related cell death in the dorsal vagal nucleus. This model was chosen because dorsal vagal neurons show a graded response to metabolic inhibition: anoxia and aglycemia cause a sustained hyperpolarization, whereas ischemia induces a glutamate-mediated, irreversible depolarization. We found that the number of propidium iodide-labeled cells increased from 27% to 43% of total cell count within 1-7 h after preparation of slices. Compared with these untreated control slices, cyanide-induced anoxia (30 min) or aglycemia (1 h) did not cause further cell death, whereas 3-h aglycemia destroyed an additional 13% of cells. Ischemia (1 h) due to cyanide plus iodoacetate immediately labeled an additional 20% of cells, and an additional 48% of cells were destroyed within the following 3 h of postischemia. Continuous recording of propidium iodide fluorescence showed that loss of membrane integrity started within 25 min after onset of the ischemic depolarization and the concomitant intracellular Ca(2+) rise. The results show that propidium iodide can be used to monitor cell death in acute brain slices. Our findings suggest that pronounced cell death occurs within a period of 1-4 h after onset of metabolic arrest and is apparently due to necrotic/oncotic mechanisms.

Neuropathologic study of long term cyanide administration to goats

Cyanogenic glycosides, which release cyanide, are present in several plant species of high importance for animal production, such as cassava and sorghum. Several human neurological diseases have been associated with chronic cyanide exposure. On the other hand, these effects in ruminants are almost unknown. Thus, the objective of the present study was to determine the long-term lesions of the central nervous system (CNS) caused by daily administration of potassium cyanide (KCN) to goats. Thirty-four male goats were divided into five groups, respectively treated orally with 0 (control), 0.3, 0.6, 1.2 or 3.0 mg KCN/kg/day for 5 months. At the end of the experiment, the whole CNS of each animal was collected for histopathology and immunohistochemistry for apoptotic markers (BAX, BCl2 and CPP32) and for glial fibrillary acid protein (GFAP; vimentin). The results showed the presence of spheroids in the pons, medulla oblongata, and ventral horn of the spinal cord, gliosis and spongiosis in medulla oblongata, gliosis in the pons, and damaged Purkinje cells in the cerebellum from goats that received the higher cyanide dose. In goats from the 1.2 mg KCN/kg group we observed congestion and hemorrhage in the cerebellum, and spheroids in the spinal cord. Gliosis was confirmed by GFAP protein expression. Immunohistochemistry for apoptotic markers and typical apoptotic morphology suggested apoptosis did not participate in the pathogenesis of the observed lesions. Thus, chronic cyanide exposure can promote neuropathological lesions also in goats, and this species can be a useful ruminant model to study the neurotoxic effects of long-term cyanide exposure.

Cyanide induces different modes of death in cortical and mesencephalon cells

A comparative study was conducted in rat primary cortical (CX) and mesencephalic (MC) neurons to investigate intracellular cascades activated during cyanide-induced injury and to determine the point at which the cascades diverge to produce either apoptosis or necrosis. Cyanide treatment (400 microM) for 24 h produced primarily apoptosis in CX cells, whereas the same concentration of cyanide induced predominantly necrosis in MC cells as indicated by increased propidium iodide staining and cellular lactate dehydrogenase efflux. Cyanide increased generation of cellular reactive oxygen species (ROS) in both CX and MC cells, but the rate of formation and nature of the oxidative species varied with cell type. Catalase decreased cyanide-induced ROS generation in CX but not in MC cells. Nitric oxide generation was more prominent after cyanide treatment of MC compared with CX cells. N-Methyl-D-aspartate receptors were more involved in CX apoptosis than in MC necrosis. Mitochondrial membrane potential decreased moderately in CX cells on exposure to cyanide, whereas MC cells responded with a more pronounced reduction in potential. In CX cells cyanide produced a concentration-dependent release of cytochrome c from mitochondria and increased caspase activity, whereas little change was seen in MC neurons. Thus, cyanide-induced necrosis of MC cells involved generation of excessive amounts of nitric oxide and superoxide accompanied by mitochondrial depolarization. In contrast cyanide causes a lower level of oxidative stress in CX cells, involving mainly hydrogen peroxide and superoxide, and a moderate change in mitochondrial membrane potential that lead to cytochrome c release, caspase activation, and apoptosis.

Effects of long-term low-dose cyanide administration to rats

Chronic exposure to cyanide has been associated with development of pancreatic diabetes, hypothyroidism, and several neurological diseases in both humans and animals. However, there is a limited number of experimental models for these pathologies. Thus, in the present study 0, 0.15, 0.3, or 0.6 mg KCN/kg body weight/day was administered for 3 months to 26 rats. On the last day, plasma samples were obtained for glucose, cholesterol, and thyroidal hormone measurement, and the pancreas, thyroids, and whole central nervous system were collected for histopathologic study. There were no significant difference in plasma concentrations of the substances measured between groups, and no lesions were found in the pancrease or thyroid. The CNS of experimental animals revealed the presence of spheroids on the ventral horn of the spinal cord, neuron loss in the hippocampus, damaged Purkinje cells, and loss of cerebellar white matter. In conclusion, cyanide administration could promote neuropathological lesions in rats without affecting pancreas or thyroid gland metabolism.

NF-kappaB-mediated up-regulation of Bcl-X(S) and Bax contributes to cytochrome c release in cyanide-induced apoptosis

Cyanide induces apoptosis through cytochrome c activated caspase cascade in primary cultured cortical neurons. The underlying mechanism for cytochrome c release from mitochondria after cyanide treatment is still unclear. In this study, the roles of endogenous Bcl-2 proteins in cyanide-induced apoptosis were investigated. After cyanide (100-500 microm) treatment for 24 h, two pro-apoptotic Bcl-2 proteins, Bcl-X(S) and Bax were up-regulated as shown by western blot and RT-PCR analysis. The expression levels of two antiapoptotic Bcl-2 proteins, Bcl-2 and Bcl-X(L), remained unchanged after cyanide treatment, whereas the mRNA levels of Bcl-X(S) and Bax began to increase within 2 h and their protein levels increased 6 h after treatment. NF-kappaB, a redox-sensitive transcription factor activated after cyanide treatment, is responsible for the up-regulation of Bcl-X(S) and Bax. SN50, which is a synthetic peptide that blocks translocation of NF-kappaB from cytosol to nucleus, inhibited the up-regulation of Bcl-X(S) and Bax. Similar results were obtained using a specific kappaB decoy DNA. NMDA receptor activation and reactive oxygen species (ROS) generation are upstream events of NF-kappaB activation, as blockade of these two events by MK801, l-NAME or PBN inhibited cyanide-induced up-regulation of Bcl-X(S) and Bax. Up-regulation of pro-apoptotic Bcl-X(S) and Bax contributed to cyanide-induced cytochrome c release, because SN50 and a specific Bax antisense oligodeoxynucleotide significantly reduced release of cytochrome c from mitochondria as shown by western blot analysis. It was concluded that NF-kappaB-mediated up-regulation of Bcl-X(S) and Bax is involved in regulating cytochrome c release in cyanide-induced apoptosis.

Preconditioning-induced protection against cyanide-induced neurotoxicity is mediated by preserving mitochondrial function

The central nervous system is one of the main target organs in cyanide toxicity. In this study, primary cultures of chick embryonic neurons were used to characterize sodium cyanide (NaCN)-induced cell death and to investigate the mechanism of NaCN-mediated preconditioning. After treatment of the cells with 1mM NaCN for 1h followed by a NaCN-free incubation period of 23 h, we observed features of apoptosis such as a reduction in nuclear size, chromatin condensation and nuclear fragmentation as evaluated by nuclear staining with Hoechst 33258 and electron microscopy. In addition, NaCN-induced neurotoxicity was reduced by the protein synthesis inhibitor cycloheximide (CHX) suggesting an active type of cell death. Most of the neurons with condensed chromatin and a shrunken nuclei also showed membrane damage at a late stage. Mitochondrial membrane potential as well as the protein levels of Bcl-2 and Bcl-x(L) decreased 15-60 min and 1-3 h after the exposure to NaCN (1mM, 1h), respectively. Preconditioning caused by incubating chick neurons with 100 microM NaCN for 30 min followed by a NaCN-free interval of 24h significantly protected the neurons against subsequent NaCN (1mM, 1h)-induced damage. Preconditioning prevented NaCN-induced decrease in the mitochondrial membrane potential as well as in the protein levels of Bcl-2 and Bcl-x(L) suggesting that preconditioning-induced neuroprotection is mediated by preserving mitochondrial function.

Disruption of cochlear potentials by chemical asphyxiants. Cyanide and carbon monoxide

While ischemia, hypoxic hypoxia, and carbon monoxide (CO) have received extensive study designed to characterize mechanisms by which they disrupt cochlear function, little data are available concerning cyanide's potential to disrupt auditory function. In this study, disruption of the compound action potential (CAP) and endocochlear potential (EP) by cyanide and CO was compared in rats treated with potassium cyanide (KCN) (7 mg/kg ip), saline, CO (35 ml/kg ip), and air. Acute KCN administration significantly suppressed CAP and EP transiently. The effect was seen initially on EP with CAP impairment occurring a few minutes later. Acute CO injection also suppressed the CAP significantly, but the effect was far smaller, occurred later in time, and lasted longer than the effect of KCN. The effect of CO on EP was equivocal. There was a good correspondence between blood cyanide levels and impairment of cochlear function; carboxyhemoglobin (HbCO) levels were elevated during the period when cochlear function was impaired, but recovery of cochlear function preceded the return of normal oxyhemoglobin. Both KCN and CO had somewhat preferential effects on high-frequency tones. Repeated cyanide administration caused a persistent CAP threshold elevation despite the rapid recovery of EP and CAP observed following acute KCN administration. The data suggest that acute KCN administration has a prominent disruptive effect at the stria vascularis presumably by disrupting the electron transport chain in this metabolically active structure. The principal target for acute CO ototoxicity in the cochlea is probably not the stria vascularis.

Pharmacological interventions of cyanide-induced cytotoxicity and DNA damage in isolated rat thymocytes and their protective efficacy in vivo

Cyanide inhibits the mitochondrial respiratory chain enzyme cytochrome oxidase causing histotoxic hypoxia. It is primarily considered as a neurotoxin but its other toxic manifestations are also well documented. Cyanide-induced apoptosis in neuronal cells has also been demonstrated recently. At the same time we also reported that potassium cyanide (KCN) produces extensive cytotoxicity and DNA fragmentation in rat thymocytes. The DNA damage was sensitive to elevated levels of extracellular Ca2+ and was attenuated by Zn2+ (modulator of Ca2+ dependent endonuclease), N-acetylcysteine (free radical scavenger) and diltiazem (Ca2+ channel blocker). In a continuation of this work, in the present study we have shown that the cytotoxicity and DNA fragmentation induced by 5 mM KCN was preceded by loss of mitochondrial integrity (MTT assay and rhodamine-123 staining) and nuclear viability (propidium iodide uptake) which were mediated by generation of reactive oxygen species (DCHF-DA staining). The DNA damage was also accompanied by nuclear fragmentation (Hoechst 33342 staining), a phenomenon that characterises the 'apoptotic' type of cell death. The in vitro toxic insult of KCN was challenged by pre-treatment (0.5 h), simultaneous treatment or post-treatment (0.5-3 h) of various pharmacological agents viz., Trolox (antioxidant), EGTA (Ca2+ modulator) and aurintricarboxylic acid (ATA; Ca2+/Mg2+ dependent endonuclease inhibitor). In addition, Quercetin (antioxidant) was tested as simultaneous treatment alone and was found to be ineffective. On the basis of various biochemical indices and DNA fragmentation (quantitative and qualitative), simultaneous treatment of Trolox was found to be the most effective in attenuating cyanide toxicity in vitro. This protection can be attributed to interventions in oxidative stress-mediated cell injury which is an early event preceding DNA damage. Both EGTA and ATA could not prevent this damage. Trolox also increased the LD(50) of KCN in mice 2.5-fold as compared to 1.8- and 1.6-fold for EGTA and ATA, respectively.

Cyanide interaction with redox modulatory sites enhances NMDA receptor responses

Activation of NMDA receptors plays an important role in cyanide neurotoxicity. Cyanide indirectly activates the receptor by inducing neuronal release of glutamate and also enhances receptor-mediated responses by a direct interaction with the receptor complex. This study investigated the mechanism in cerebellar granule cells by which cyanide enhances NMDA-induced Ca2+ influx. Cyanide (50 microM) increased the influx of Ca2+ over the NMDA concentration range of 0.5-500 microM. Experiments showed that cyanide does not interact with the receptor's glycine or PKC mediated phosphorylation regulatory sites. N-ethylmaleimide, a thiol alkylating agent which inactivates the redox regulatory sites of the receptor, blocked the enhancing effect of cyanide. Pretreatment of cells with 5,5-dithio-bis-2-nitrobenzoic acid (DTNB), a compound that oxidizes the receptor redox sites, had no effect on the response to cyanide. On the other hand, the nonpermeant reducing agents, dithiothreitol or cysteine, further increased the cyanide effect. These observations can be explained by cyanide interacting with redox sensitive disulfide groups that are not accessible to the non-permeant reducing agents. It is proposed that cyanide interacts with a redox site(s) located either on the intracellular receptor domain or in the transmembrane hydrophobic domain. Furthermore the enhancement by cyanide of the excitotoxic actions of NMDA involves receptor sites that are sensitive to oxidation/reduction and this interaction contributes to the neurotoxic action of cyanide.

Cyanide-induced apoptosis involves oxidative-stress-activated NF-kappaB in cortical neurons

The central nervous system is one of the main target organs in cyanide toxicity. Primary cultured cortical neurons were used to study the cellular mechanisms underlying cyanide-induced cytotoxicity. After exposure to KCN (100-300 microM) for 24 h, cortical neurons underwent apoptosis as characterized by positive TUNEL staining. Reactive oxygen species (ROS) play an important role in cyanide-induced neuronal apoptosis; immediately after cyanide (100-300 microM) treatment, ROS generation was observed and continued to be elevated for up to 3 h. NMDA receptor activation and subsequent Ca(2+) influx contribute in part to cyanide-induced ROS formation, since the selective NMDA receptor antagonist MK801 and intracellular Ca(2+) chelator BAPTA blocked ROS generation. Interestingly, caspases, recently reported to be involved in neuronal apoptosis, play a role in the late phase of ROS production after cyanide stimulation. Z-VAD, a nonspecific caspase inhibitor, blocked ROS generated 1 h after cyanide treatment, but it had no effect on ROS generated immediately after cyanide treatment. Nuclear factor kappaB (NF-kappaB), a redox-sensitive transcription factor, was activated dose dependently after cyanide treatment. Blockade of ROS generation by MK801, Z-VAD, and various antioxidants also blocked the activation of NF-kappaB. SN50, a synthetic peptide which inhibits the nuclear translocation of NF-kappaB, blocked cyanide-induced apoptotic cell death. These results indicate that NF-kappaB plays an important role in cyanide-induced apoptosis in cortical neurons, and the caspases may contribute in part to the activation of NF-kappaB after cyanide treatment by inducing the late phase of ROS generation.

Pharmacologic properties of phenyl N-tert-butylnitrone

Phenyl N-tert-butylnitrone (PBN) is the parent of a family of nitrones used as spin-trapping agents to trap free radicals. PBN's pharmacological effects in animal models are extensive, ranging from protection against death after endotoxin shock, protection from ischemia-reperfusion injury, to increasing the life span of mice. Recent additions to the list include protection from bacterial meningitis, thalidomide-induced teratogenicity, drug-induced diabetogenesis, and choline-deficient hepatocarcinogenesis. Because PBN reacts with oxygen radicals to produce less reactive species, it has been suggested that this is the basis of its pharmacological effects. However, there has been no hard evidence for this notation. Nevertheless, many investigators have used the presence of PBN's pharmacologic effect as evidence for free radical involvement in their models. Mechanistic studies on the PBN's antisepsis action revealed that PBN inhibits expression of various pro-inflammatory genes, suggesting that the protective action involves more than a straightforward free radical-scavenging mechanism. Previous and recent developments in the investigations on the pharmacologic properties of PBN are described in this review.