Cyanide interaction with redox modulatory sites enhances NMDA receptor responses

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.

Non-specificity of ethylene inhibitors: 'double-edged' tools to find out new targets involved in the root morphogenetic programme

In the last decade, genetic and pharmacological approaches have been used to explore ethylene biosynthesis and perception in order to study the role of ethylene and ethylene/auxin interaction in root architecture development. However, recent findings with pharmacological approaches highlight the non-specificity of commonly used inhibitors. This suggests that caution is required for interpreting these studies and that the use of pharmacological agents is a 'double-edged' tool. On one hand, non-specific effects make interpretation difficult unless other experiments, such as with different mutants or with multiple diversely acting chemicals, are conducted. On the other hand, the non-specificity of inhibitors opens up the possibility of uncovering some ligands or modulators of new receptors such as plant glutamate-like receptors and importance of some metabolic hubs in carbon and nitrogen metabolism such as the pyridoxal phosphate biosynthesis involved in the regulation of the root morphogenetic programme. Identification of such targets is a critical issue to improve the efficiency of absorption of macronutrients in relation to root the morphogenetic programme.

Novel relationships between B12, folate and markers of inflammation, oxidative stress and NAD(H) levels, systemically and in the CNS of a healthy human cohort

OBJECTIVE

To evaluate the relationship between folate, cobalamin (Cbl), and homocysteine (Hcy), and markers of inflammation and oxidative stress within the periphery and central nervous system (CNS) of a healthy human cohort.

METHODS

Thirty-five matched cerebrospinal fluid (CSF) and plasma samples were collected from consenting participants who required a spinal tap for the administration of anaesthetic. Plasma concentrations of Hcy and both plasma and CSF levels of folate, Cbl, nicotinamide adenine dinucleotide (NAD(H)) and markers of inflammation (interleukin-6, IL-6), and oxidative stress (F2-isoprostanes, 8-hydroxy-2'-deoxyguanosine (8-OHdG), and total antioxidant capacity (TAC)) were quantified.

RESULTS

In the peripheral circulation, positive associations were observed between plasma folate and Cbl, and plasma TAC (P ≤ 0.01; P ≤ 0.01) and plasma NAD(H) (P ≤ 0.05; P ≤ 0.05) levels, respectively. Plasma folate was inversely associated with plasma Hcy concentrations (P ≤ 0.05); however, no statistically significant relationships were observed between plasma Hcy and plasma markers of inflammation, oxidative stress, or [NAD(H)]. Within the CNS plasma Hcy correlated positively with CSF IL-6 (P ≤ 0.01) and negatively with CSF NAD(H) (P ≤ 0.05) concentrations. An inverse association was observed between CSF folate and CSF levels of IL-6 (P ≤ 0.05). Unexpectedly, a positive association between CSF Cbl and CSF 8-OHdG levels was also found (P ≤ 0.01).

DISCUSSION

These results indicate that folate and Cbl concentrations may influence the levels of oxidative damage, inflammation, and NAD(H), both systemically and within the CNS.

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.

Alpha-lipoic acid protects against potassium cyanide-induced seizures and mortality

This study was proposed to investigate the potential protective effect of alpha-lipoic acid (α-LA) against potassium cyanide (KCN)-induced seizures and lethality in mice. The intraperitoneal ED(50) value of KCN, as measured by induction of clonic and tonic seizures was increased by pretreatment of mice with α-LA (25, 50 and 100 mg/kg) intraperitoneally in a dose-dependent manner. Similarly, the intraperitoneal LD(50) value of KCN, based on 24h mortality, was increased by pretreatment with α-LA in a dose-dependent manner. Intraperitoneal injection of the estimated ED(50) of KCN (4.8 mg/kg) into mice increased, 1h later, nitric oxide (NO) production and brain glutamate and malondialdehyde (MDA) levels. The estimated ED(50) of KCN also decreased brain intracellular reduced glutathione (GSH) level and glutathione peroxidase (GSH-Px) activity in these animals. Administration of the estimated LD(50) of KCN (6 mg/kg) produced, 24h later, similar marked biochemical alterations in surviving animals. Pretreatment of mice with α-LA inhibited; dose-dependently KCN (ED(50) and LD(50))-induced an increase in NO production and brain MDA level as well as a decrease in brain intracellular GSH level and GSH-Px activity. The elevation induced by KCN in brain glutamate level was not inhibited by α-LA. It can be concluded that the protective effect of α-LA against KCN-induced seizures and lethality may be due to inhibition of NO overproduction and maintenance of intracellular antioxidant defense mechanisms.

Facilitation of spontaneous glycine release by anoxia potentiates NMDA receptor current in the hypoglossal motor neurons of the rat

Deficiency in energy supply, such as occurs during hypoxia, anoxia, metabolic stress and mitochondrial failure, strongly affects the excitability of central neurons. Such lowered energy supply evokes various changes in spontaneous synaptic input to the hippocampal and cortical neurons. However, how this energy deprivation affects synaptic input to motor neurons, which are also vulnerable to energy deprivation, has never been addressed. Here we report for the first time the effect of metabolic stress on synaptic input to motor neurons by recording postsynaptic currents in the hypoglossal nucleus. Chemical anoxia with NaCN (1 mm) and anoxia with 95% N(2) induced a persistent inward current and a marked and robust increase in action potential-independent synaptic input. This increase was abolished by strychnine, but not by picrotoxin, CNQX or MK-801, indicating glycine release facilitation. Blockade of voltage-dependent Ca(2+) channels and extracellular Ca(2+) deprivation strongly attenuated this facilitation. The amplitude of inward currents evoked by local application of NMDA to the motor neurons in the presence of strychnine was significantly increased during NaCN application. A saturating concentration of d-serine occluded this potentiation, suggesting that released glycine activated the glycine-binding sites of NMDA receptors. By contrast, neurons in the dorsal motor nucleus of the vagus showed no detectable change in synaptic input in response to NaCN. These data suggest that increase in synaptically released glycine in response to metabolic stress may play an exacerbating role in NMDA receptor-mediated excitotoxicity in motor neurons.

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.