Decrease in heart mitochondrial creatine kinase activity due to oxygen free radicals

Creatine and Resistance Training: A Combined Approach to Attenuate Doxorubicin-Induced Cardiotoxicity

Doxorubicin (DOX), a potent chemotherapy agent, useful in the treatment of solid tumors, lymphomas, and leukemias, is limited by its potentially lethal cardiotoxicity. However, exercise has been consistently shown to mitigate the side effects of DOX, including cardiotoxicity. To date, most studies examining the relationship between exercise and DOX-induced cardiotoxicity have focused on aerobic exercise, with very few examining the role of anerobic activity. Therefore, this investigation explored the potential of creatine (CR) and resistance training (RT) in preserving cardiac health during DOX therapy. Male Sprague-Dawley rats were grouped into RT, RT + CR, sedentary (SED), and SED + CR, with each division further branching into saline (SAL) or DOX-treated subsets post-10 weeks of RT or SED activity. RT comprised progressive training utilizing specialized cages for bipedal stance feeding. CR-treated groups ingested water mixed with 1% CR monohydrate and 5% dextrose, while control animals received 5% dextrose. At week 10, DOX was administered (2 mg/kg/week) over 4-weeks to an 8 mg/kg cumulative dose. Cardiac function post-DOX treatment was assessed via transthoracic echocardiography. Left ventricular diameter during diastole was lower in DOX + CR, RT + DOX, and RT + CR + DOX compared to SED + DOX (p < 0.05). Additionally, cardiac mass was significantly greater in RT + CR + DOX SED + DOX animals (p < 0.05). These results suggest RT and CR supplementation, separately and in combination, could attenuate some measures of DOX-induced cardiotoxicity and may offer a cost-effective way to complement cancer treatments and enhance patient outcomes. More investigations are essential to better understand CR's prolonged effects during DOX therapy and its clinical implications.

Chemoptogenetic ablation of neuronal mitochondria in vivo with spatiotemporal precision and controllable severity

Mitochondrial dysfunction is implicated in the pathogenesis of multiple neurological diseases, but elucidation of underlying mechanisms is limited experimentally by the inability to damage specific mitochondria in defined neuronal groups. We developed a precision chemoptogenetic approach to target neuronal mitochondria in the intact nervous system in vivo. MG2I, a chemical fluorogen, produces singlet oxygen when bound to the fluorogen-activating protein dL5** and exposed to far-red light. Transgenic zebrafish expressing dL5** within neuronal mitochondria showed dramatic MG2I- and light-dependent neurobehavioral deficits, caused by neuronal bioenergetic crisis and acute neuronal depolarization. These abnormalities resulted from loss of neuronal respiration, associated with mitochondrial fragmentation, swelling and elimination of cristae. Remaining cellular ultrastructure was preserved initially, but cellular pathology downstream of mitochondrial damage eventually culminated in neuronal death. Our work provides powerful new chemoptogenetic tools for investigating mitochondrial homeostasis and pathophysiology and shows a direct relationship between mitochondrial function, neuronal biogenetics and whole-animal behavior.

Tyrosine inhibits creatine kinase activity in cerebral cortex of young rats

Tyrosine accumulates in inborn errors of tyrosine catabolism, especially in tyrosinemia type II, where tyrosine levels are highly elevated in tissues and physiological fluids of affected patients. Tyrosinemia type II is a disorder of autosomal recessive inheritance characterized by neurological symptoms similar to those observed in patients with creatine deficiency syndromes. Considering that the mechanisms of brain damage in these disorders are poorly known, in the present study our main objective was to investigate the in vivo and in vitro effects of different concentrations and preincubation times of tyrosine on cytosolic and mitochondrial creatine kinase activities of the cerebral cortex from 14-day-old Wistar rats. The cytosolic CK was reduced by 15% at 1 mM and 32% at 2 mM tyrosine. Similarly, the mitochondrial CK was inhibited by 15% at 1 mM and 22% at 2 mM tyrosine. We observed that the inhibition caused by tyrosine was concentration-dependent and was prevented by reduced glutathione. Results also indicated that mitochondrial, but not cytosolic creatine kinase activity was inhibited by tyrosine in a time-dependent way. Finally, a single injection of L-Tyrosine methyl ester administered i.p. decreased cytosolic (31%) and mitochondrial (18%) creatine kinase activities of brain cortex from rats. Considering that creatine kinase is an enzyme dependent of thiol residues for its function and tyrosine induces oxidative stress, the results suggest that the inhibition caused by tyrosine might occur by oxidation of essential sulfhydryl groups of the enzyme. In case this also occurs in patients with tyrosinemia, it is possible that creatine kinase inhibition may contribute to the neurological dysfunction characteristic of tyrosinemia.

Regulation and pharmacology of the mitochondrial permeability transition pore

The 'mitochondrial permeability transition', characterized by a sudden induced change of the inner mitochondrial membrane permeability for water as well as for small substances ( Collapse

Key Words

• adenine nucleotide translocator
• cyclophilin d
• mitochondrial voltage-dependent anion channel
• hexokinase
• creatine kinase
• mitochondrial peripheral benzodiazepine receptor
• bcl-2
• glycogen synthase kinase-3β

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MESH Headings

• Adenine Nucleotide Translocator 1/metabolism
• Animals
• Cardiovascular Agents/pharmacology
• Creatine Kinase, Mitochondrial Form/metabolism
• Peptidyl-Prolyl Isomerase F
• Cyclophilins/metabolism
• Hexokinase/metabolism
• Humans
• Lipid Metabolism
• Membrane Potential, Mitochondrial
• Mitochondria, Heart/drug effects
• Mitochondria, Heart/metabolism
• Mitochondrial Membrane Transport Proteins/chemistry
• Mitochondrial Membrane Transport Proteins/drug effects
• Mitochondrial Membrane Transport Proteins/genetics
• Mitochondrial Membrane Transport Proteins/metabolism
• Mitochondrial Permeability Transition Pore
• Myocardium/metabolism
• Phosphates/metabolism
• Receptors, GABA-A/metabolism
• Voltage-Dependent Anion Channels/metabolism

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Grants

• Intramural NIH HHS

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Affiliation(s)

Dmitry B. Zorov
Magdalena Juhaszova
Yael Yaniv
H. Bradley Nuss
Su Wang
Steven J. Sollott Laboratory of Cardiovascular Science, Gerontology Research Center, Box 13, Intramural Research Program, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825, USA

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Arginine administration reduces creatine kinase activity in rat cerebellum

In the present study were evaluated the in vivo effects of arginine administration on creatine kinase (CK) activity in cerebellum of rats. We also tested the influence of antioxidants, namely alpha-tocopherol and ascorbic acid and the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), on the effects elicited by Arg in order to investigate the possible participation of nitric oxide (NO) and/or its derivatives peroxynitrite (ONOO(-)) and other/or free radicals on the effects of arginine on CK activity. Sixty-day-old rats were treated with a single i.p. injection of saline (control, group I), arginine (0.8 g/kg) (group II), L-NAME (2.0 mg/kg or 20.0 mg/kg) (group III) or Arg (0.8 g/kg) plus L-NAME (2.0 mg/kg or 20.0 mg/kg) (group IV) and were killed 1 h later. In another set of experiments, the animals were pretreated for 1 week with daily i.p. administration of saline (control) or alpha-tocopherol (40 mg/kg) and ascorbic acid (100 mg/kg). Twelve hours after the last injection of the antioxidants, the rats received one i.p. injection of arginine (0.8 g/kg) or saline and were killed 1 h later. Results showed that total and cytosolic CK activities were significantly inhibited by arginine administration in cerebellum of rats, in contrast to mitochondrial CK activity which was not affected by this amino acid. Furthermore, simultaneous injection of L-NAME (20.0 mg/kg) and treatment with alpha-tocopherol and ascorbic acid prevented these effects. The data indicate that the reduction of CK activity in cerebellum of rats caused by arginine was probably mediated by NO and/or its derivatives ONOO(-)and other free radicals. Considering the importance of CK for the maintenance of energy homeostasis in the brain, if this enzyme inhibition also occurs in hyperargininemic patients, it is possible that CK inhibition may be one of the mechanisms by which arginine is neurotoxic in hyperargininemia.

Magnesium deficiency augments myocardial response to reactive oxygen species

Magnesium (Mg) deficiency and oxidative stress are independently implicated in the etiopathogenesis of various cardiovascular disorders. This study was undertaken to examine the hypothesis that Mg deficiency augments the myocardial response to oxidative stress. Electrically stimulated rat papillary muscle was used for recording the contractile variation. Biochemical variables of energy metabolism (adenosine triphosphate (ATP) and creatine phosphate) and markers of tissue injury (lactate dehydrogenase (LDH) release and lipidperoxidation), which can affect myocardial contractility, were assayed in Langendorff-perfused rat hearts. Hydrogen peroxide (100 micromol/L) was used as the source of reactive oxygen species. The negative inotropic response to H2O2 was significantly higher in Mg deficiency (0.48 mmol Mg/L) than in Mg sufficiency (1.2 mmol Mg/L). Low Mg levels did not affect ATP levels or tissue lipid peroxidation. However, H2O2 induced a decrease in ATP; enhanced lipid peroxidation and the release of LDH were augmented by Mg deficiency. Increased lipid peroxidation associated with a decrease in available energy might be responsible for the augmentation of the negative inotropic response to H2O2 in Mg deficiency. The observations from this study validate the hypothesis that myocardial response to oxidative stress is augmented by Mg deficiency. This observation has significance in ischemia-reperfusion injury, where Mg deficiency can have an additive effect on the debilitating consequences.

Protein oxidation and cellular homeostasis: Emphasis on metabolism

Reactive oxygen species (ROS) are generated as the result of a number of physiological and pathological processes. Once formed ROS can promote multiple forms of oxidative damage, including protein oxidation, and thereby influence the function of a diverse array of cellular processes. This review summarizes the mechanisms by which ROS are generated in a variety of cell types, outlines the mechanisms which control the levels of ROS, and describes specific proteins which are common targets of ROS. Additionally, this review outlines cellular processes which can degrade or repair oxidized proteins, and ultimately describes the potential outcomes of protein oxidation on cellular homeostasis. In particular, this review focuses on the relationship between elevations in protein oxidation and multiple aspects of cellular metabolism. Together, this review describes a potential role for elevated levels of protein oxidation contributing to cellular dysfunction and oxidative stress via impacts on cellular metabolism.

Inhibition of the electron transport chain and creatine kinase activity by ethylmalonic acid in human skeletal muscle

Ethylmalonic aciduria is a common finding in patients affected by short-chain acyl-CoA dehydrogenase (SCAD) deficiency and other diseases characterized by encephalopathy, muscular symptomatology, and lactic acidemia. Considering that the pathophysiological mechanisms of these disorders are practically unknown and that lactic acidosis suggest an impairment of energy production, the objective of the present work was to investigate the in vitro effect of ethylmalonic acid (EMA), at concentrations varying from 0.25 to 5.0 mM, on important parameters of energy metabolism in human skeletal muscle, such as the activities of the respiratory chain complexes and of creatine kinase, which are responsible for most of the ATP produced and transferred inside the cell. We verified that EMA significantly inhibited the activity of complex I-III at concentrations as low as 0.25 mM, complex II-III at 1 mM and higher concentrations, and complex II at the concentration of 5 mM. In contrast, complex IV was not inhibited by the acid. Finally, we observed that the activity of creatine kinase was significantly inhibited by EMA at the concentrations of 1 and 5 mM. These results suggest that EMA compromises energy metabolism in human skeletal muscle. In case the in vitro effects detected in the present study also occur in vivo, it is tempting to speculate that they may contribute, at least in part, to explain the hypotonia/myopathy, as well as the increased concentrations of lactic acid present in the patients affected by illnesses in which EMA accumulates.

Mitochondrial creatine kinase in human health and disease

Mitochondrial creatine kinase (MtCK), together with cytosolic creatine kinase isoenzymes and the highly diffusible CK reaction product, phosphocreatine, provide a temporal and spatial energy buffer to maintain cellular energy homeostasis. Mitochondrial proteolipid complexes containing MtCK form microcompartments that are involved in channeling energy in form of phosphocreatine rather than ATP into the cytosol. Under situations of compromised cellular energy state, which are often linked to ischemia, oxidative stress and calcium overload, two characteristics of mitochondrial creatine kinase are particularly relevant: its exquisite susceptibility to oxidative modifications and the compensatory up-regulation of its gene expression, in some cases leading to accumulation of crystalline MtCK inclusion bodies in mitochondria that are the clinical hallmarks for mitochondrial cytopathies. Both of these events may either impair or reinforce, respectively, the functions of mitochondrial MtCK complexes in cellular energy supply and protection of mitochondria form the so-called permeability transition leading to apoptosis or necrosis.

Expression and carbonylation of creatine kinase in the quadriceps femoris muscles of patients with chronic obstructive pulmonary disease

Oxidative protein modification involving carbonylation has recently been identified as an important factor in skeletal muscle dysfunction in patients with chronic obstructive pulmonary disease (COPD). However, the exact identity of modified proteins inside limb muscles of patients with COPD remains unknown. We used 2D electrophoresis, immunoblotting, and mass spectrometry to identify carbonylated proteins in the vastus lateralis muscle of 12 patients with COPD and 6 control subjects. Both creatine kinase (CK) and carbonic anhydrase III (CAIII) were identified as being strongly carbonylated in this muscle in both groups of subjects. Total CK activity, CK protein expression, and the intensity of CK carbonylation were significantly greater in the muscles of patients with COPD as compared with control subjects, whereas CAIII protein expression and intensity of carbonylation were similar in the two groups. In patients with COPD, CK activity and protein expression correlated positively with FEV(1) and V O(2)max, whereas the intensity of CK carbonylation correlated negatively with the same parameters. These results indicate that oxygen radicals selectively target CK and CAIII inside limb muscles of humans. The observation that the intensity of CK carbonylation correlates negatively with CK activity in limb muscles of patients with COPD suggests that carbonylation may have a deleterious effect on CK activity, and may contribute to impaired CK function in the limb muscles of these patients.

D-2-hydroxyglutaric acid inhibits creatine kinase activity from cardiac and skeletal muscle of young rats

BACKGROUND

Tissue accumulation of high amounts of D-2-hydroxyglutaric acid (DGA) is the biochemical hallmark of the inherited neurometabolic disorder D-2-hydroxyglutaric aciduria (DHGA). Patients affected by this disease usually present hypotonia, muscular weakness, hypertrophy and cardiomyopathy, besides severe neurological findings. However, the underlying mechanisms of muscle injury in this disorder are virtually unknown.

MATERIALS AND METHODS

In the present study we have evaluated the in vitro role of DGA, at concentrations ranging from 0.25 to 5.0 mM, on total, cytosolic and mitochondrial creatine kinase activities from skeletal and cardiac muscle of 30-day-old Wistar rats. We also tested the effects of various antioxidants on the effects elicited by DGA.

RESULTS

We first verified that total creatine kinase (CK) activity from homogenates was significantly inhibited by DGA (22-24% inhibition) in skeletal and cardiac muscle, and that this activity was approximately threefold higher in skeletal muscle than in cardiac muscle. We also observed that CK activities from mitochondrial (Mi-CK) and cytosolic (Cy-CK) preparations from skeletal muscle and cardiac muscle were also inhibited (12-35% inhibition) by DGA at concentrations as low as 0.25 mm, with the effect being more pronounced in cardiac muscle preparations. Finally, we verified that the DGA-inhibitory effect was fully prevented by preincubation of the homogenates with reduced glutathione and cysteine, suggesting that this effect is possibly mediated by modification of essential thiol groups of the enzyme. Furthermore, alpha-tocopherol, melatonin and the inhibitor of nitric oxide synthase L-NAME were unable to prevent this effect, indicating that the most common reactive oxygen and nitrogen species were not involved in the inhibition of CK provoked by DGA.

CONCLUSION

Considering the importance of creatine kinase activity for cellular energy homeostasis, our results suggest that inhibition of this enzyme by increased levels of DGA might be an important mechanism involved in the myopathy and cardiomyopathy of patients affected by DHGA.

Inhibition of mitochondrial creatine kinase activity by D-2-hydroxyglutaric acid in cerebellum of young rats

D-2-Hydroxyglutaric aciduria (DHGA) is a neurometabolic disorder biochemically characterized by tissue accumulation and excretion of high amounts of D-2-hydroxyglutaric acid (DGA). Although the affected patients have predominantly severe neurological findings, the underlying mechanisms of brain injury are virtually unknown. In previous studies we have demonstrated that DGA, at concentrations as low as 0.25 mM, significantly decreased creatine kinase activity and other parameters of energy metabolism in cerebral cortex of young rats. In the present study, we investigated the effect of DGA (0.25-5 mM) on total creatine kinase (tCK) activity, as well as on CK activity in cytosolic (Cy-CK) and mitochondrial (Mi-CK) preparations from cerebellum of 30-day-old Wistar rats in order to test whether the inhibitory effect of DGA on CK was tissue specific. We verified that tCK (22% inhibition) and Mi-CK (40% inhibition) activities were moderately inhibited by DGA at concentrations of 2.5 mM and higher, in contrast to Cy-CK, which was not affected by the acid. Kinetic studies revealed that the inhibitory effect of DGA was noncompetitive in relation to phosphocreatine. We also observed that this inhibition was fully prevented by preincubation of the homogenates with reduced glutathione, suggesting that the inhibition of CK activity by DGA is possibly mediated by modification of essential thiol groups of the enzyme. Our present results therefore demonstrate a relatively weak inhibitory effect of DGA on cerebellum Mi-CK activity, as compared to that provoked in cerebral cortex, and may possibly be related to the neuropathology of DHGA, characterized by cerebral cortex abnormalities.

Ethylmalonic acid inhibits mitochondrial creatine kinase activity from cerebral cortex of young rats in vitro

Short-chain acyl-CoA dehydrogenase (SCAD) deficiency is an inherited metabolic disorder biochemically characterized by tissue accumulation of predominantly ethylmalonic acid (EMA) and clinically by neurological dysfunction. In the present study we investigated the in vitro effects of EMA on the activity of the mitochondrial (Mi-CK) and cytosolic (Cy-CK) creatine kinase isoforms from cerebral cortex, skeletal muscle, and cardiac muscle of young rats. CK activities were measured in the mitochondrial and cytosolic fractions prepared from whole-tissue homogenates of 30-day-old Wistar rats. The acid was added to the incubation medium at concentrations ranging from 0.5 to 2.5 mM. EMA had no effect on Cy-CK activity, but significantly inhibited the activity of Mi-CK at 1.0 mM and higher concentrations in the brain. In contrast, both Mi-CK and Cy-CK from skeletal muscle and cardiac muscle were not affected by the metabolite. We also evaluated the effect of the antioxidants glutathione (GSH), ascorbic acid, and alpha-tocopherol and the nitric oxide synthase inhibitor L-NAME on the inhibitory action of EMA on cerebral cortex Mi-CK activity. We observed that the drugs did not modify Mi-CK activity per se, but GSH and ascorbic acid prevented the inhibitory effect of EMA when co-incubated with the acid. In contrast, L-NAME and alpha-tocopherol could not revert the inhibition provoked by EMA on Mi-CK activity. Considering the importance of CK for brain energy homeostasis, it is proposed that the inhibition of Mi-CK activity may be associated to the neurological symptoms characteristic of SCAD deficiency.

Differential effects of peroxynitrite on human mitochondrial creatine kinase isoenzymes. Inactivation, octamer destabilization, and identification of involved residues

Creatine kinase isoenzymes are very susceptible to free radical damage and are inactivated by superoxide radicals and peroxynitrite. In this study, we have analyzed the effects of peroxynitrite on enzymatic activity and octamer stability of the two human mitochondrial isoenzymes (ubiquitous mitochondrial creatine kinase (uMtCK) and sarcomeric mitochondrial creatine kinase (sMtCK)), as well as of chicken sMtCK, and identified the involved residues. Inactivation by peroxynitrite was concentration-dependent and similar for both types of MtCK isoenzymes. Because peroxynitrite did not lower the residual activity of a sMtCK mutant missing the active site cysteine (C278G), oxidation of this residue is sufficient to explain MtCK inactivation. Mass spectrometric analysis confirmed oxidation of Cys-278 and further revealed oxidation of the C-terminal Cys-358, possibly involved in MtCK/membrane interaction. Peroxynitrite also led to concentration-dependent dissociation of MtCK octamers into dimers. In this study, ubiquitous uMtCK was much more stable than sarcomeric sMtCK. Mass spectrometric analysis revealed chemical modifications in peptide Gly-263-Arg-271 located at the dimer/dimer interface, including oxidation of Met-267 and nitration of Trp-268 and/or Trp-264, the latter being a very critical residue for octamer stability. These data demonstrate that peroxynitrite affects the octameric state of MtCK and confirms human sMtCK as the generally more susceptible isoenzyme. The results provide a molecular explanation of how oxidative damage can lead to inactivation and decreased octamer/dimer ratio of MtCK, as seen in neurodegenerative diseases and heart pathology, respectively.

Inhibition of creatine kinase activity in vitro by ethylmalonic acid in cerebral cortex of young rats

Short-chain acyl-CoA dehydrogenase deficiency is an inherited metabolic disorder biochemically characterized by tissue accumulation of ethylmalonic (EMA) and methylsuccinic (MSA) acids and clinically by severe neurological symptoms. In the present study we investigated the in vitro effects of EMA and MSA on the activity of creatine kinase (CK) in homogenates from cerebral cortex, skeletal and cardiac muscle of rats. EMA significantly inhibited CK activity from cerebral cortex, but did not affect this activity in skeletal and cardiac muscle. Furthermore, MSA had no effect on this enzyme in all tested tissues. Glutathione (GSH), ascorbic acid and alpha-tocopherol, and the nitric oxide synthase inhibitor L-NAME, did not affect the enzyme activity per se, but GSH fully prevented the inhibitory effect of EMA when co-incubated with EMA. In contrast, alpha-tocopherol, ascorbic acid and L-NAME did not influence the inhibitory effect of the acid. The data suggest that inhibition of brain CK activity by EMA is possibly mediated by oxidation of essential groups of the enzyme, which are protected by the potent intracellular, endogenous, naturally occurring antioxidant GSH.

Reduced creatine kinase activity in transgenic amyotrophic lateral sclerosis mice

Creatine (Cr), the substrate of the creatine kinase (CK) isoenzymes, was shown to be neuroprotective in several models of neurodegeneration, including amyotrophic lateral sclerosis (ALS). In order to investigate the mechanism of this beneficial effect, we determined CK activities and mitochondrial respiration rates in tissues from G93A transgenic mice, which overexpress a mutant form of human superoxide dismutase associated with familial ALS (FALS). While respiration rates of mitochondria from G93A transgenic or wild-type control mice isolated from spinal cord showed no difference, a significant and dramatic loss of CK activity could be detected in these tissues. In homogenates from spinal cord of G93A transgenic mice, CK activity decreased to 49% and in mitochondrial fractions to 67% compared to CK activities in wild-type control mice. Feeding the G93A transgenic mice with 2% Cr, the same tissues showed no statistically significant increase of CK activity compared to regular fed G93A transgenic mice. Experiments with isolated mitochondria, however, showed that Cr and adenosine triphosphate (ATP) protected mitochondrial CK activity against peroxynitrite-induced inactivation, which may play a role in tissue damage in neurodegeneration. Our data provide evidence for oxidative damage to the CK system in ALS, which may contribute to impaired energy metabolism and neurodegeneration.

Oxidation of proteinaceous cysteine residues by dopamine-derived H2O2 in PC12 cells

Cellular metabolism of dopamine (DA) generates H2O2, which is further reduced to hydroxyl radicals in the presence of iron. Cellular damage inflicted by DA-derived hydroxyl radicals is thought to contribute to Parkinson's disease. We have previously developed procedures for detecting proteins that contain H2O2-sensitive cysteine (or selenocysteine) residues. Using these procedures, we identified ERP72 and ERP60, two members of the protein disulfide isomerase family, creatine kinase, glyceraldehyde-3-phosphate dehydrogenase, phospholipase C-gamma1, and thioredoxin reductase as the targets of DA-derived H2O2. Experiments with purified enzymes identified the essential Cys residues of creatine kinase and glyceraldehyde-3-phosphate dehydrogenase, that are specifically oxidized by H2O2. Although the identified proteins represent only a fraction of the targets of DA-derived H2O2, functional impairment of these proteins has previously been associated with cell death. The oxidation of proteins that contain reactive Cys residues by DA-derived H2O2 is therefore proposed both to be largely responsible for DA-induced apoptosis in neuronal cells and to play an important role in the pathogenesis of Parkinson's disease.

Calcium activation of heart mitochondrial oxidative phosphorylation: rapid kinetics of mVO2, NADH, AND light scattering

Parallel activation of heart mitochondria NADH and ATP production by Ca(2+) has been shown to involve the Ca(2+)-sensitive dehydrogenases and the F(0)F(1)-ATPase. In the current study we hypothesize that the response time of Ca(2+)-activated ATP production is rapid enough to support step changes in myocardial workload ( approximately 100 ms). To test this hypothesis, the rapid kinetics of Ca(2+) activation of mV(O(2)), [NADH], and light scattering were evaluated in isolated porcine heart mitochondria at 37 degrees C using a variety of optical techniques. The addition of Ca(2+) was associated with an initial response time (IRT) of mV(O(2)) that was dose-dependent with a minimum IRT of 0.27 +/- 0.02 s (n = 41) at 535 nm Ca(2+). The IRTs for NADH fluorescence and light scattering in response to Ca(2+) additions were similar to mV(O(2)). The Ca(2+) IRT for mV(O(2)) was significantly shorter than 1.6 mm ADP (2.36 +/- 0.47 s; p < or = 0.001, n = 13), 2.2 mm P(i) (2.32 +/- 0.29, p < or = 0.001, n = 13), or 10 mm creatine (15.6.+/-1.18 s, p < or = 0.001, n = 18) under similar experimental conditions. Calcium effects were inhibited with 8 microm ruthenium red (2.4 +/- 0.31 s; p < or = 0.001, n = 16) and reversed with EGTA (1.6 +/- 0.44; p < or = 0.01, n = 6). Estimates of Ca(2+) uptake into mitochondria using optical Ca(2+) indicators trapped in the matrix revealed a sufficiently rapid uptake to cause the metabolic effects observed. These data are consistent with the notion that extramitochondrial Ca(2+) can modify ATP production, via an increase in matrix Ca(2+) content, rapidly enough to support cardiac work transitions in vivo.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

Role of oxidative stress in cardiovascular diseases

OBJECTIVES

In view of the critical role of intracellular Ca2 overload in the genesis of myocyte dysfunction and the ability of reactive oxygen species (ROS) to induce the intracellular Ca2+-overload, this article is concerned with analysis of the existing literature with respect to the role of oxidative stress in different types of cardiovascular diseases.

OBSERVATIONS

Oxidative stress in cardiac and vascular myocytes describes the injury caused to cells resulting from increased formation of ROS and/or decreased antioxidant reserve. The increase in the generation of ROS seems to be due to impaired mitochondrial reduction of molecular oxygen, secretion of ROS by white blood cells, endothelial dysfunction, auto-oxidation of catecholamines, as well as exposure to radiation or air pollution. On the other hand, depression in the antioxidant reserve, which serves as a defense mechanism in cardiac and vascular myocytes, appears to be due to the exhaustion and/or changes in gene expression. The deleterious effects of ROS are mainly due to abilities of ROS to produce changes in subcellular organelles, and induce intracellular Ca2+-overload. Although the cause-effect relationship of oxidative stress with any of the cardiovascular diseases still remains to be established, increased formation of ROS indicating the presence of oxidative stress has been observed in a wide variety of experimental and clinical conditions. Furthermore, antioxidant therapy has been shown to exert beneficial effects in hypertension, atherosclerosis, ischemic heart disease, cardiomyopathies and congestive heart failure.

CONCLUSIONS

The existing evidence support the view that oxidative stress may play a crucial role in cardiac and vascular abnormalities in different types of cardiovascular diseases and that the antioxidant therapy may prove beneficial in combating these problems.

Modification of creatine kinase by S-nitrosothiols: S-nitrosation vs. S-thiolation

Creatine kinase is reversibly inhibited by incubation with S-nitrosothiols. Loss of enzyme activity is associated with the depletion of 5,5'-dithiobis (2-nitrobenzoic acid)-accessible thiol groups, and is not due to nitric oxide release from RSNO. Full enzymatic activity and protein thiol content are restored by incubation of the S-nitrosothiol-modified protein with glutathione. S-nitroso-N-acetylpenicillamine, which contains a more sterically hindered S-nitroso group than S-nitrosoglutathione, predominantly modifies the protein thiol to an S-nitrosothiol via a transnitrosation reaction. In contrast, S-nitrosoglutathione modifies creatine kinase predominantly by S-thiolation. Both S-nitroso-N-acetylpenicillamine and S-nitrosoglutathione modify bovine serum albumin to an S-nitroso derivative. This indicates that S-thiolation and S-nitrosation are both relevant reactions for S-nitrosothiols, and the relative importance of these reactions in biological systems depends on both the environment of the protein thiol and on the chemical nature of the S-nitrosothiol.

Crystal structure of human ubiquitous mitochondrial creatine kinase

Creatine kinase (CK), catalyzing the reversible trans-phosphorylation between ATP and creatine, plays a key role in the energy metabolism of cells with high and fluctuating energy requirements. We have solved the X-ray structure of octameric human ubiquitous mitochondrial CK (uMtCK) at 2.7 A resolution, representing the first human CK structure. The structure is very similar to the previously determined structure of sarcomeric mitochondrial CK (sMtCK). The cuboidal octamer has 422 point group symmetry with four dimers arranged along the fourfold axis and a central channel of approximately 20 A diameter, which extends through the whole octamer. Structural differences with respect to sMtCK are found in isoform-specific regions important for octamer formation and membrane binding. Octameric uMtCK is stabilized by numerous additional polar interactions between the N-termini of neighboring dimers, which extend into the central channel and form clamp-like structures, and by a pair of salt bridges in the hydrophobic interaction patch. The five C-terminal residues of uMtCK, carrying positive charges likely to be involved in phospholipid-binding, are poorly defined by electron density, indicating a more flexible region than the corresponding one in sMtCK. The structural differences between uMtCK and sMtCK are consistent with biochemical studies on octamer stability and membrane binding of the two isoforms.

Free radical induced inactivation of creatine kinase: sites of interaction, protection, and recovery

The study aims at a clarification of the oxidative damage of creatine kinase isoenzymes by X-ray-induced water radiolysis. The radical species generated by this method (under appropriate conditions) are similar to those discussed in the context of mitochondrial energy metabolism. The decay of the enzyme activity is accompanied by a strong decrease of the number of accessible SH groups and by a reduction of the endogenous tryptophan fluorescence. Free radical effects are diminished if irradiation is carried out in the presence of 2-mercaptoethanol. Partial recovery of the activity (repair) is observed if 2-mercaptoethanol is added after irradiation. The experiments suggest a twofold importance of thiol reagents (RSH): to reduce the concentration of free radicals by scavenger reactions and to modify the inactivation mechanism in such a way that efficient repair of enzyme damage may be achieved. Cysteine 282 of MM-CK (Cys-278 in the case of Mi-CK) seems to play a crucial role in this respect. Blockage of the SH group of cysteine 282 by oxidized glutathione effectively protects the enzyme against inactivation by NO(*)(2) radicals. In the absence of nitrogen dioxide and of thiol reagents, however, inactivation seems to proceed via a less specific mechanism involving additional targets of the enzyme.

Role of high-energy phosphate metabolism in hydrogen peroxide-induced cardiac dysfunction

This study was undertaken to clarify the role of high-energy phosphate metabolism in hydrogen peroxide-induced cardiac dysfunction using phosphorus and fluorine nuclear magnetic resonance spectroscopy. The exposure of a Langendorff-perfused heart to hydrogen peroxide (200-400 micromol/L, 8 min) provoked biphasic contractile dysfunction characterized by a transient depression of left ventricular developed pressure during the administration of hydrogen peroxide and a delayed elevation of left ventricular end-diastolic pressure after the washout of hydrogen peroxide. The initial phase of cardiac dysfunction correlated well with the accumulation of sugar phosphates (r = 0.89, p < 0.01). Furthermore, we demonstrated that glibenclamide, a potent inhibitor of the ATP-sensitive K+ channel, attenuated the initial depression of developed pressure. On the other hand, the delayed elevation of end-diastolic pressure correlated well with the total ATP depletion (r = 0.96, p < 0.01). However, ATP loss was supposed to be a mere result from the increased ATP consumption corresponding to a rise in intracellular free Ca2+ (from the control value of 315+/-23 nmol/L to 708+/-104 after the administration of hydrogen peroxide, p < 0.01), which also paralleled the elevation of end-diastolic pressure. Thus glycolytic inhibition and intracellular Ca2+ overload are independently responsible for the biphasic contractile dysfunction induced by hydrogen peroxide.

Increased neuronal glucose-6-phosphate dehydrogenase and sulfhydryl levels indicate reductive compensation to oxidative stress in Alzheimer disease

We analyzed glucose-6-phosphate dehydrogenase, the rate-controlling enzyme of the pentose phosphate pathway and free sulfhydryls, to study redox balance in Alzheimer disease. Glucose-6-phosphate dehydrogenase plays a pivotal role in homeostatic redox control by providing reducing equivalents to glutathione, the major nonenzymatic cellular antioxidant. There is a multitude of evidence that marks oxidative stress proximally in the natural history of Alzheimer disease. Consistent with a role for glutathione in defense against increased reactive oxygen, we found an upregulation of glucose-6-phosphate dehydrogenase together with increased sulfhydryls in Alzheimer disease. These data indicate that reductive compensation may play an important role in combating oxidative stress in Alzheimer disease.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Roles of reactive oxygen species: signaling and regulation of cellular functions

Reactive oxygen species (ROS) are the side products (H2O2, O2.-, and OH.) of general metabolism and are also produced specifically by the NADPH oxidase system in most cell types. Cells have a very efficient antioxidant defense to counteract the toxic effect of ROS. The physiological significance of ROS is that ROS at low concentrations are able to mediate cellular functions through the same steps of intracellular signaling, which are activated by natural stimuli. Moreover, a variety of natural stimuli act through the intracellular formation of ROS that change the intracellular redox state (oxidation-reduction). Thus, the redox state is a part of intracellular signaling. As such, ROS are now considered signal molecules at nontoxic concentrations. Progress has been achieved in studying the oxidative activation of gene transcription in animal cells and bacteria. Changes in the redox state of intracellular thiols are considered to be an important mechanism that regulates cell functions.

Determination of mitochondrial creatine kinase fluxes in intact heart mitochondria using 31P-saturation transfer nuclear magnetic resonance spectroscopy

Forward (-->ATP) and reverse (-->CrP) fluxes through the creatine kinase reaction were determined in isolated rat and bovine heart mitochondria and with soluble MM-CK from rabbit skeletal muscle, using 31P-saturation transfer NMR. With soluble MM-CK forward and reverse fluxes were identical in the absence and presence of BSA or rat liver mitochondria. Addition of liver mitochondria decreased fluxes with increasing mitochondria concentration. The fluxf/Vmax(f) ratio was 0.006 with 10 mg BSA and 0.04 with 10 mg rat liver mitochondria, respectively. With heart mitochondria, fluxr was considerably higher than fluxf and the fluxf/Vmax(f) ratio was 1.7 for rat heart and 0.22 for bovine heart. It is concluded that in the presence of isolated mitochondria, the flux through the creatine kinase is driven by the mitochondrial ATP-ADP turnover. Therefore the fluxf/Vmax(f) ratio is highest for rat heart mitochondria with a high ATP-ADP turnover, intermediate for bovine heart mitochondria and low for MM-CK in the presence of liver mitochondria. It is lowest with MM-CK alone, where the creatine kinase reaction is at equilibrium and external ATP-ADP turnover is absent. The higher reverse than forward fluxes of mitochondrial creatine kinase determined at steady state by saturation transfer NMR, are caused mainly by a high ATP<-->Pi exchange in heart mitochondria preparations, having a high ATPase activity, compared to liver mitochondria.

Mitochondrial creatine kinase is a prime target of peroxynitrite-induced modification and inactivation

The reaction of peroxynitrite (PN) with sarcomeric mitochondrial creatine kinase (Mib-CK; EC 2.7.3.2) was observed at different stages of complexity (i) with purified Mi-CK, (ii) with enzyme bound on isolated mitoplasts, and (iii) within intact respiring mitochondria. Creatine-stimulated respiration was abolished by PN concentrations likely to be physiological and far before the respiratory chain itself was affected, thus demonstrating that Mi-CK is a prime target for inactivation by PN in intact mitochondria. The inactivation by PN of Mi-CK was reversed by 22% with 2-mercaptoethanol. More remarkable protective effects were noticed with the full set of CK substrates, e.g. 30 and 50% protection with MgATP plus creatine and MgADP plus phosphocreatine, respectively, but not with each substrate alone. These data indicate an involvement of the active-site Cys-278 residue of Mi-CK in this process. Furthermore, changes in endogenous tryptophan fluorescence intensity and spectral changes after reaction of Mi-CK with PN suggest additional modifications of Trp and Tyr residues. PN-inactivated Mi-CK can no longer be efficiently converted into dimers by incubation with reagents inducing a transition state analog complex at the active site. Thus, obviously, upon reaction of octameric Mi-CK with PN, the octamer-dimer equilibrium of Mi-CK is also affected. The consequences for cellular energy homeostasis and calcium handling are discussed.

Effects of gamma-glutamylcysteine ethyl ester on heart mitochondrial creatine kinase activity: involvement of sulfhydryl groups

To study the mechanism of the protective effect of gamma-glutamylcysteine ethyl ester, mitochondrial creatine kinase activity of rat heart was measured. Gamma-glutamylcysteine ethyl ester had a protective effect against the depression of creatine kinase activity induced by xanthine + xanthine oxidase or hydrogen peroxide. Gamma-glutamylcysteine ethyl ester also prevented the depression of creatine kinase activity induced by N-ethylmaleimide. It is suggested that the protective effect of gamma-glutamylcysteine ethyl ester is related to oxygen free radicals or to reduction of the sulfhydryl groups of the enzyme which were previously oxidized by oxygen free radicals.

Rapid and irreversible inhibition of creatine kinase by peroxynitrite

We examined the ability of peroxynitrite and other .NO-derived oxidants to inhibit creatine kinase (CK). Peroxynitrite potently inhibited CK activity and depleted protein thiols. The rate constant for this reaction was 8.85x10(5) M(-1) s(-1). Glutathione did not reactivate CK activity nor did it regenerate protein thiol content. In contrast, glutathione reactivated CK, and regenerated protein thiols, after inhibition by either .NO or oxidized glutathione (GSSG). Peroxynitrite did not irreversibly inhibit CK after it had been treated with GSSG to block protein thiols. We conclude that thiol oxidation is a critical event leading to inactivation of CK by peroxynitrite.

Preservation of phosphagen kinase function during transient hypoxia via enzyme abundance or resistance to oxidative inactivation

Mammalian lactate dehydrogenase and phosphofructokinase are more susceptible in vitro to superoxide (O2) and hydroxyl (.OH) radicals than pyruvate kinase and glucose-6-phosphate dehydrogenase, suggesting that differential inactivation of regulatory enzymes contributes to the metabolic disintegration in stenoxic tissues during transient hypoxia. Likewise, creatine kinase in smooth muscle from porcine ileum is significantly reduced by hypoxia-reoxygenation ex vivo from 300 (+/- 18.2 SE, n = 8) to 196 U.g wet wt-1 (+/- 16.7, P < 0.001, ANOVA). Conversely, arginine kinase, from the myocardium of Limulus polyphemus, a species that tolerates anoxia for days was 2.9-fold less susceptible to oxidative inactivation. To examine whether preservation of kinase function is related to euryoxic capacity, a combination of non-invasive 31P-NMR spectroscopy and enzyme-linked assays was used to follow ATP and phosphagen status during hypoxia-reoxygenation in porcine ileum smooth muscle, L. polyphemus myocardium, and the myocardium of Argopecten irradians, a scallop species tolerant of hypoxia for only 24 h. Despite wide differences in phylogeny, euryoxic capacity and oxidative vulnerability of the phosphagen kinases, in all three tissues, the phosphagen pool recovered concomitant with ATP during reoxygenation, thereby revealing competent kinase function. In the mammalian tissue, such preservation of kinase function is facilitated by a 2400-fold excess of enzyme activity.

Creatine kinase is the main target of reactive oxygen species in cardiac myofibrils

Reactive oxygen species (ROS) have been reported to alter cardiac myofibrillar function as well as myofibrillar enzymes such as myosin ATPase and creatine kinase (CK). To understand their precise mode and site of action in myofibrils, the effects of the xanthine/xanthine oxidase (X/XO) system or of hydrogen peroxide (H2O2) have been studied in the presence and in the absence of phosphocreatine (PCr) in Triton X-100-treated cardiac fibers. We found that xanthine oxidase (XO), with or without xanthine, induced a decrease in maximal Ca(2+)-activated tension. We attributed this effect to the high contaminating proteolytic activity in commercial XO preparations, since it could be prevented a protease inhibitor, phenylmethylsulfonyl fluoride (PMSF), and it could be mimicked by trypsin. In further experiments, XO was pre-treated with 1 mmo1/L PMSF. Superoxide anion production by the X/XO system, characterized by electron paramagnetic resonance spin-trapping technique, was not altered by PMSF. A slight increase in maximal force was then observed either with X/XO (100 mumol/L per 30 mIU/mL) or H2O2. pMgATP-rigor tension relationships have been established in the presence and in the absence of PCr to separate the effects of ROS on myosin ATPase and myofibrillar-bound CK. In the absence of PCr, pMgATP50, the pMgATP necessary to induce half-maximal rigor tension, was reduced from 5.03 +/- 0.17 (n = 21) to 4.22 +/- 0.22 (n = 4) after 25 minutes of incubation in the presence one of 30 mIU/mL. XO and 100 mumol/L xanthine or to 4.04 +/- 0.1 (n = 11) after incubation in the presence of 2.5 mmol/L H2O2. The ROS effects were partially prevented or antagonized by 1 mmol/L dithiothreitol. No effect was observed on pMgATP50 when PCr was absent. pCa-tension relationships have been evaluated to assess the effects of ROS on active tension development. Incubations with H2O2 induced on increase in Ca2+ sensitivity and resting tension when MgATP was provided through myofibrillar CK (PCr and MgADP as substrates) but not when MgATP was added directly. These results suggest that myofibrillar CK was inhibited by ROS. Active stiffness and the time constant of tension changes after quick stretches applied to the fibers were dose-dependently increased by H2O2 only in the presence of PCr. In addition, myofibrillar CK but not myosin ATPase enzymatic activity was depressed after incubation with either ROS. These results suggest that ROS mainly alters CK in myofibrils, probably by the oxidation of its essential sulfhydryl groups. Such CK inactivation results in a decrease in the intramyofibrillar ATP-to-ADP ratio. The effects of ROS on cytosolic and bound CKs may take part in the overall process of myocardial stunning after cardiac ischemia and reperfusion.

Monohydroperoxidized fatty acids but not 4-hydroxynonenal induced acute cardiac cell damage

Unsaturated fatty acids constitutive of cardiac membranal lipid matrix are one of the primary targets for reactive oxygen species generated during ischemia-reperfusion cycle. Lipid peroxidation is a cascade of intricate reactions involving the successive formations of fatty acids hydroperoxides and aldehydic compounds such as alkenals derived from the oxidative fragmentation of these hydroperoxides. The potential deleterious effects of different classes of lipid peroxidation products on cardiac cells were compared using three in vitro approaches: (i) cardiomyocyte integrity, (ii) electromechanical activity of papillary muscle, and (iii) atrial contractility. The following products of lipid peroxidation were tested: (i) photoperoxidized arachidonic acid pooling hydroperoxidized derivatives and aldehydic compounds, (ii) fatty acids hydroperoxides, and (iii) 4-hydroxynonenal, a characteristic alkenal derived from the oxidative fragmentation of hydroperoxidized n-6 fatty acids. Only fatty acids hydroperoxides induced drastic loss of cellular integrity and severe disturbances in electromechanical activity of cardiomyocytes. 4-hydroxynonenal induced only a slight leak of lactate dehydrogenase at high concentrations and did not modify the electromechanical behavior of cardiac preparations. Under our conditions, monohydroperoxidized fatty acids but not 4-hydroxynonenal induced acute cardiac cell damages. In conclusion, lipid hydroperoxides can be considered both as markers of oxidative injury and relay sources of oxidative stress.

Cardioprotective potency of the radical scavenger S-2-(3 aminopropylamino) ethylphosphorothioic acid in the post-ischaemic rat heart

S-2-(3 aminopropylamino) ethylphosphorothioic acid (WR-2721) shown to surpass radical scavenging thiols in their radioprotective efficacy in cancer-type diseases has been tested for its protective potential in the reperfused heart. We investigated the radical scavenger properties of the compound in a radical generating system in vitro as well as in isolated rat hearts subjected to 30 min ischaemia and 30 min reperfusion with the electron-paramagnetic resonance spin trap technique. The action on high-energy phosphates is observed by means of phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy while its influence on left ventricular systolic segmental length change (SSLC) during 60 min reperfusion following 60 min regional ischaemia was assessed with a fibreoptic system in anaesthetized open-chest rats. WR-2721 (0.1 mM) reduced the vascular concentration of radical adduct in isolated hearts by up to 78% (275 +/- 84% of pre-ischaemic baseline values vs 1260 +/- 413%, p < 0.05) between 5 and 12.5 min reperfusion. This was accompanied by a reduction of the left ventricular end diastolic pressure to pre-ischaemic values at 30 min of reperfusion (9 +/- 6 mmHg vs 42 +/- 8 mmHg in the absence of WR-2721, p < 0.02). An accelerated recovery of creatine phosphate levels (78 +/- 5% of pre-ischaemia values vs 41 +/- 5% within 60 min reperfusion: p < 0.05) was observed under similar conditions with NMR-spectroscopy, although the post-ischaemic tissue content of adenosine triphosphate was not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen free radicals and human disease

Oxygen free radicals are very reactive molecules which can react with every cellular component. They are normally produced in organisms being involved in various biologic reactions. However, too high levels of these partially-reduced O2 species can give rise to functional and morphologic disturbances in cells. There is evidence to implicate oxygen free radicals as important pathologic mediators in many human disease processes.

Decrease in yeast glucose-6-phosphate dehydrogenase activity due to oxygen free radicals

1. u.v. radiations and copper acetate, as free radical generating systems, determine a significant diminishing of glucose-6-phosphate dehydrogenase activity in the homogenates of Saccharomyces cerevisiae. 2. The inactivation is proportional to the concentration of the formed free radicals, existing a direct dependence on the action time of the free radicals generating systems and on the irradiation dose. The decrease of the enzyme catalytic activity is correlated with the increase of the malondialdehyde concentration. 3. The affinity for the substrate of the enzyme under the action of free radicals does not change significantly compared to the native enzyme: the Km value for NADP is halved, whilst that for glucose-6-phosphate remains unchanged. 4. The electrophoretic study shows evidence of five electrophoretic bands with enzymatic activity in the native extract and the disappearance of one molecular form under the free radical action.