Cyanide poisoning: pathophysiology and treatment recommendations.
(1/2221)
This paper aims to assess and compare currently available antidotes for cyanide poisoning. Such evaluation, however, is difficult. Thus, extrapolation from the results of animal studies has potential pitfalls, as significant inter-species differences in response may exist, and these experiments often involve administration of toxin and antidote almost simultaneously, rather than incorporating a more realistic time delay before initiation of treatment. Direct inference from human case reports is also problematic; either because of uncertainties over the exposure levels involved (and hence the likely outcome without treatment), or because of difficulties in identifying the specific contribution of a particular antidote within the overall treatment regimen. Certainly an effort to compare the relative efficacy of cyanide antidotes produces equivocal findings, with no single regimen clearly standing out. Indeed, factors such as the risks of antidote toxicity to various individuals and other practical issues, may be more important considerations. There is therefore no single treatment regimen which is best for all situations. Besides individual risk factors for antidote toxicity, the nature of the exposure and hence its likely severity, the evolving clinical features and the number of persons involved and their proximity to hospital facilities, all need to be considered. Clinically mild poisoning may be treated by rest, oxygen and amyl nitrite. Intravenous antidotes are indicated for moderate poisoning. Where the diagnosis is uncertain, sodium thiosulphate may be the first choice. With severe poisoning, an additional agent is required. Given the various risks with methaemoglobin formers or with unselective use of kelocyanor, hydroxocobalamin may be preferred from a purely risk-benefit perspective. However the former alternatives will likely remain important. (+info)
Nitric oxide inhibits cardiac energy production via inhibition of mitochondrial creatine kinase.
(2/2221)
Nitric oxide biosynthesis in cardiac muscle leads to a decreased oxygen consumption and lower ATP synthesis. It is suggested that this effect of nitric oxide is mainly due to the inhibition of the mitochondrial respiratory chain enzyme, cytochrome c oxidase. However, this work demonstrates that nitric oxide is able to inhibit soluble mitochondrial creatine kinase (CK), mitochondrial CK bound in purified mitochondria, CK in situ in skinned fibres as well as the functional activity of mitochondrial CK in situ in skinned fibres. Since mitochondrial isoenzyme is functionally coupled to oxidative phosphorylation, its inhibition also leads to decreased sensitivity of mitochondrial respiration to ADP and thus decreases ATP synthesis and oxygen consumption under physiological ADP concentrations. (+info)
Bcl-xL prevents cell death following growth factor withdrawal by facilitating mitochondrial ATP/ADP exchange.
(3/2221)
Growth factor withdrawal is associated with a metabolic arrest that can result in apoptosis. Cell death is preceded by loss of outer mitochondrial membrane integrity and cytochrome c release. These mitochondrial events appear to follow a relative increase in mitochondrial membrane potential. This change in membrane potential results from the failure of the adenine nucleotide translocator (ANT)/voltage-dependent anion channel (VDAC) complex to maintain ATP/ADP exchange. Bcl-xL expression allows growth factor-deprived cells to maintain sufficient mitochondrial ATP/ADP exchange to sustain coupled respiration. These data demonstrate that mitochondrial adenylate transport is under active regulation. Efficient exchange of ADP for ATP is promoted by Bcl-xL expression permitting oxidative phosphorylation to be regulated by cellular ATP/ADP levels and allowing mitochondria to adapt to changes in metabolic demand. (+info)
Nitric-oxide-induced apoptosis in human leukemic lines requires mitochondrial lipid degradation and cytochrome C release.
(4/2221)
We have previously shown that nitric oxide (NO) stimulates apoptosis in different human neoplastic lymphoid cell lines through activation of caspases not only via CD95/CD95L interaction, but also independently of such death receptors. Here we investigated mitochondria-dependent mechanisms of NO-induced apoptosis in Jurkat leukemic cells. NO donor glycerol trinitrate (at the concentration, which induces apoptotic cell death) caused (1) a significant decrease in the concentration of cardiolipin, a major mitochondrial lipid; (2) a downregulation in respiratory chain complex activities; (3) a release of the mitochondrial protein cytochrome c into the cytosol; and (4) an activation of caspase-9 and caspase-3. These changes were accompanied by an increase in the number of cells with low mitochondrial transmembrane potential and with a high level of reactive oxygen species production. Higher resistance of the CD95-resistant Jurkat subclone (APO-R) cells to NO-mediated apoptosis correlated with the absence of cytochrome c release and with less alterations in other mitochondrial parameters. An inhibitor of lipid peroxidation, trolox, significantly suppressed NO-mediated apoptosis in APO-S Jurkat cells, whereas bongkrekic acid (BA), which blocks mitochondrial permeability transition, provided only a moderate antiapoptotic effect. Transfection of Jurkat cells with bcl-2 led to a complete block of apoptosis due to the prevention of changes in mitochondrial functions. We suggest that the mitochondrial damage (in particular, cardiolipin degradation and cytochrome c release) induced by NO in human leukemia cells plays a crucial role in the subsequent activation of caspase and apoptosis. (+info)
Changes in mitochondrial phosphorylative activity and adenylate energy charge of regenerating rabbit liver.
(5/2221)
The changes in the cellular concentrations of ATP, ADP, and AMP and in oxidative phosphorylation of mitochondria were investigated in the remaining liver of partially hepatectomized rabbits. The energy charge (defined as half of the average number of anhydride-bonded phosphate groups per adenosine moiety) of the liver remnant decreased from 0.866 to 0.767 (p less than 0.01) within 24 hr after hepatectomy, and then increased to a substantially higher level than normal within 7 days. On the other hand, the mitochondrial phosphyorylative activity increased rapidly to 170 per cent of the control within 12 hr and then retruned to normal within 7 days. The mitochondrial phosphorylative activity was inversely correlated with energy charge of the liver remnant (r = -0.75, p less less than 0.01). The maximal enhancement of mitochondrial phosphorylative activity was found in mitochondria obtained from the liver remnant with the lowest level of energy charge, suggesting a response of mitochondria in vivo involving enhanced biosynthetic ATP-utilizing reactions at an early stage of the regenerating process. The enhancement of phosphorylative activity was accompanied by a rise in the respiratory control ratio, P/O ratio and state 3 respiration. The adenylate kinase [EC 2.7.4.3] activity in the liver remnant increased to more than 160% of the control within 2 days after partial hepatectomy, while the pyruvate kinase [EC 2.7.1.40] activity decreased remarkably. However, the changes in the two enzyme activities did not correlate with those of mitochondrial phosphorylative activity or the energy charge of the liver remnant. (+info)
Efficiency of oxidative phosphorylation and energy dissipation by H+ ion recycling in rat-liver mitochondrial metabolizing pyruvate.
(6/2221)
A method was developed for the calculation of metabolic fluxes through individual enzymatic reactions of pyruvate metabolism including the citric acid cycle in rat liver mitochondrial incubated at metabolic states between state 4 and state 3. This method is based on the measurement of the specific radioactivities of the products formed from [2-14C]pyruvate. With this procedure the energy balance of mitochondria incubated in the presence of [2-14C]pyruvate, ATP, bicarbonate and phosphate at different ATP/ADP ratios in the medium was calculated. The ATP/ADP ratios were maintained at a steady state with creatine kinase plus creatine as a phosphoryl acceptor. The calculations revealed that by adding increasing concentrations of creatine up to 20 mM the energy dissipated by the mitochondria decreased but showed a local maximum at 13mM creatine. Omission of bicarbonate from the medium led to a shift of this maximum. When energy dissipation was minimal the overall P/O ratio was maximal. The amount of energy dissipated was paralleled by the magnitude of the pH gradient across the inner membrane. From these results it was concluded that the recycling of H+ ions which consists of a passive leakage of H+ ions into the matrix and an active extrusion of these ions out of this compartment, is an important energy dissipating process. The H+ ion recycling is thus one of the processes which give rise to the state 4 respiration in mitochondria. (+info)
Influence of bioenergetic stress on heat shock protein gene expression in nucleated red blood cells of fish.
(7/2221)
The physiological and biochemical signals that induce stress protein (HSP) synthesis remain conjectural. In this study, we used the nucleated red blood cells from rainbow trout, Oncorhynchus mykiss, to address the interaction between energy status and HSP gene expression. Heat shock (25 degrees C) did not significantly affect ATP levels but resulted in an increase in HSP70 mRNA. Hypoxia alone did not induce HSP transcription in these cells despite a significant depression in ATP. Inhibition of oxidative phosphorylation with azide, in the absence of thermal stress, decreased ATP by 56% and increased lactate production by 62% but did not induce HSP gene transcription. Inhibition of oxidative phosphorylation and glycolysis with azide and iodoacetic acid respectively, decreased ATP by 79% and prevented lactate production, but did not induce either HSP70 or HSP30 gene transcription in these cells. This study demonstrates that a reduction in the cellular energy status will not induce stress protein gene transcription in rainbow trout red blood cells and may, in fact, limit induction during extreme metabolic inhibition. (+info)
Uncouplers of oxidative phosphorylation can enhance a Fas death signal.
(8/2221)
Recent work suggests a participation of mitochondria in apoptotic cell death. This role includes the release of apoptogenic molecules into the cytosol preceding or after a loss of mitochondrial membrane potential DeltaPsim. The two uncouplers of oxidative phosphorylation carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2, 4-dinitrophenol (DNP) reduce DeltaPsim by direct attack of the proton gradient across the inner mitochondrial membrane. Here we show that both compounds enhance the apoptosis-inducing capacity of Fas/APO-1/CD95 signaling in Jurkat and CEM cells without causing apoptotic changes on their own account. This amplification occurred upstream or at the level of caspases and was not inhibited by Bcl-2. The effect could be blocked by the cowpox protein CrmA and is thus likely to require caspase 8 activity. Apoptosis induction by staurosporine in Jurkat cells as well as by Fas in SKW6 cells was unaffected by CCCP and DNP. The role of cytochrome c during Fas-DNP signaling was investigated. No early cytochrome c release from mitochondria was detected by Western blotting. Functional assays with cytoplasmic preparations from Fas-DNP-treated cells also indicated that there was no major contribution by cytochrome c or caspase 9 to the activation of effector caspases. Furthermore, an increase of rhodamine-123 uptake into intact cells, which has been explained by mitochondrial swelling, occurred considerably later than the caspase activation and was blocked by Z-VAD-fmk. These data show that uncouplers of oxidative phosphorylation can presensitize some but not all cells for a Fas death signal and provide information about the existence of separate pathways in the induction of apoptosis. (+info)