Cytochrome c oxidase and cardiolipin alterations in response to skeletal muscle ischaemia and reperfusion

Cardiac phospholipidome is altered during ischemia and reperfusion in an ex vivo rat model

Acute myocardial infarction (AMI) is the leading cause of death, morbidity, and health costs worldwide. In AMI, a sudden blockage of blood flow causes myocardial ischemia and cell death. Reperfusion after ischemia has paradoxical effects and may exacerbate the myocardial injury, a process known as ischemic reperfusion injury. In this work we evaluated the lipidome of isolated rat hearts, maintained in controlled perfusion (CT), undergoing global ischemia (ISC) or ischemia followed by reperfusion (IR). 153 polar lipid levels were significantly different between conditions. 48 features had q < 0.001 and included 8 phosphatidylcholines and 4 lysophospholipids, which were lower in ISC compared to CT, and even lower in the IR group, suggesting that IR induces more profound changes than ISC. We observed that the levels of 16 alkyl acyl phospholipids were significantly altered during ISC and IR. Overall, these data indicate that myocardial lipid remodelling and possibly damage occurs to a greater extent during reperfusion. The adaptation of cardiac lipidome during ISC and IR described is consistent with the presence of oxidative damage and may reflect the impact of AMI on the lipidome at the cellular level and provide new insights into the role of lipids in the pathophysiology of acute myocardial ischemia/reperfusion injury.

Succinate dehydrogenase: Prospect for neurodegenerative diseases

Onset of Alzheimer's, Parkinson's and Huntington's diseases as neurodegenerative disorders is increased by age. Alleviation of clinical symptoms and protection of neurons against degeneration are the main aspects of researches to establish new therapeutic strategies. Many studies have shown that mitochondria play crucial roles in high energy demand tissues like brain. Impairments in mitochondrial activity and physiology can makes neurons vulnerable to stress and degeneration. Succinate dehydrogenase (SDH) connects tricarboxylic cycle to the electron transport chain. Therefore, dysfunction of the SDH could impair mitochondrial activity, ATP generation and energy hemostasis in the cell. Exceed lipid synthesis, induction of the excitotoxicity in neurodegenerative disorders could be controlled by SDH through direct and indirect mechanism. In addition, mutation in SDH correlates with the onset of neurodegenerative disorders. Therefore, SDH could behave as a key regulator in neuroprotection. This review will present recent findings which are about SDH activity and related pathways which could play important roles in neuronal survival. Additionally, we will discuss about all possibilities which candidate SDH as a neuroprotective agent.

Chronology of mitochondrial and cellular events during skeletal muscle ischemia-reperfusion

Peripheral artery disease (PAD) is a common circulatory disorder of the lower limb arteries that reduces functional capacity and quality of life of patients. Despite relatively effective available treatments, PAD is a serious public health issue associated with significant morbidity and mortality. Ischemia-reperfusion (I/R) cycles during PAD are responsible for insufficient oxygen supply, mitochondriopathy, free radical production, and inflammation and lead to events that contribute to myocyte death and remote organ failure. However, the chronology of mitochondrial and cellular events during the ischemic period and at the moment of reperfusion in skeletal muscle fibers has been poorly reviewed. Thus, after a review of the basal myocyte state and normal mitochondrial biology, we discuss the physiopathology of ischemia and reperfusion at the mitochondrial and cellular levels. First we describe the chronology of the deleterious biochemical and mitochondrial mechanisms activated by I/R. Then we discuss skeletal muscle I/R injury in the muscle environment, mitochondrial dynamics, and inflammation. A better understanding of the chronology of the events underlying I/R will allow us to identify key factors in the development of this pathology and point to suitable new therapies. Emerging data on mitochondrial dynamics should help identify new molecular and therapeutic targets and develop protective strategies against PAD.

Human neuronal coenzyme Q10 deficiency results in global loss of mitochondrial respiratory chain activity, increased mitochondrial oxidative stress and reversal of ATP synthase activity: implications for pathogenesis and treatment

Disorders of coenzyme Q(10) (CoQ(10)) biosynthesis represent the most treatable subgroup of mitochondrial diseases. Neurological involvement is frequently observed in CoQ(10) deficiency, typically presenting as cerebellar ataxia and/or seizures. The aetiology of the neurological presentation of CoQ(10) deficiency has yet to be fully elucidated and therefore in order to investigate these phenomena we have established a neuronal cell model of CoQ(10) deficiency by treatment of neuronal SH-SY5Y cell line with para-aminobenzoic acid (PABA). PABA is a competitive inhibitor of the CoQ(10) biosynthetic pathway enzyme, COQ2. PABA treatment (1 mM) resulted in a 54 % decrease (46 % residual CoQ(10)) decrease in neuronal CoQ(10) status (p < 0.01). Reduction of neuronal CoQ(10) status was accompanied by a progressive decrease in mitochondrial respiratory chain enzyme activities, with a 67.5 % decrease in cellular ATP production at 46 % residual CoQ(10). Mitochondrial oxidative stress increased four-fold at 77 % and 46 % residual CoQ(10). A 40 % increase in mitochondrial membrane potential was detected at 46 % residual CoQ(10) with depolarisation following oligomycin treatment suggesting a reversal of complex V activity. This neuronal cell model provides insights into the effects of CoQ(10) deficiency on neuronal mitochondrial function and oxidative stress, and will be an important tool to evaluate candidate therapies for neurological conditions associated with CoQ(10) deficiency.

Toxic influence of organophosphate, carbamate, and organochlorine pesticides on cellular metabolism of lipids, proteins, and carbohydrates: a systematic review

Pesticides, including organophosphate (OP), organochlorine (OC), and carbamate (CB) compounds, are widely used in agricultural and indoor purposes. OP and CB act as acetyl cholinesterase (AChE) inhibitors that affect lots of organs such as peripheral and central nervous systems, muscles, liver, pancreas, and brain, whereas OC are neurotoxic involved in alteration of ion channels. There are several reports about metabolic disorders, hyperglycemia, and also oxidative stress in acute and chronic exposures to pesticides that are linked with diabetes and other metabolic disorders. In this respect, there are several in vitro and in vivo but few clinical studies about mechanism underlying these effects. Bibliographic databases were searched for the years 1963-2010 and resulted in 1652 articles. After elimination of duplicates or irrelevant papers, 204 papers were included and reviewed. Results indicated that OP and CB impair the enzymatic pathways involved in metabolism of carbohydrates, fats and protein within cytoplasm, mitochondria, and proxisomes. It is believed that OP and CB show this effect through inhibition of AChE or affecting target organs directly. OC mostly affect lipid metabolism in the adipose tissues and change glucose pathway in other cells. As a shared mechanism, all OP, CB and OC induce cellular oxidative stress via affecting mitochondrial function and therefore disrupt neuronal and hormonal status of the body. Establishing proper epidemiological studies to explore exact relationships between exposure levels to these pesticides and rate of resulted metabolic disorders in human will be helpful.

Impaired mitochondrial functions in organophosphate induced delayed neuropathy in rats

Acute exposure to organophosphates induces a delayed neurodegenerative condition known as organophosphate-induced delayed neuropathy (OPIDN). The mechanism of OPIDN has not been fully understood as it does not involve cholinergic crisis. The present study has been designed to evaluate the role of mitochondrial dysfunctions in the development of OPIDN. OPIDN was induced in rats by administering acute dose of monocrotophos (MCP, 20 mg/kg body weight, orally) or dichlorvos (DDVP, 200 mg/kg body weight, subcutaneously), 15-20 min after treatment with antidotes [atropine (20 mg/kg body weight) and 2-PAM (100 mg/kg body weight) intraperitoneally]. MDA levels were observed to be higher and thiol content was lower in mitochondria from brain regions of OP exposed animals. This was accompanied by decreased activities of the mitochondrial enzymes; NADH dehydrogenase, succinate dehydrogenase, and cytochrome oxidase. In addition, mitochondrial functions assessed by MTT reduction also confirmed mitochondrial dysfunctions following development of OPIDN. The spatial long-term memory evaluated using elevated plus-maze test was observed to be deficit in OPIDN. The results suggest impaired mitochondrial functions as a mechanism involved in the development of organophosphate induced delayed neuropathy.

Mismatch recovery of regional cerebral blood flow and brain temperature during reperfusion after prolonged brain ischemia in gerbils

BACKGROUND

Recovery of cerebral reperfusion after stroke or cardiac arrest can take a long time. We aimed to identify differences in the postischemic recovery of physiologic parameters between short and prolonged brain ischemia.

METHODS

Eighteen Mongolian gerbils were assigned to one of three groups: 5-minute (G5), 15-minute (G15), or 30-minute (G30) ischemia. With the use of our original microspectroscopy system, global ischemic reperfusion was performed. We measured changes in regional cerebral blood flow (r-CBF), microvessel diameter, and brain temperature (BrT) simultaneously. We also monitored somatosensory evoked potentials (SEPs) to evaluate electrophysiologic response.

RESULTS

Both G5 and G15 showed concurrent recovery of r-CBF and BrT with hyperemia and hyperthermia, respectively, 10 to 15 minutes after reperfusion. The increase in BrT was <1 degree C and recovered to baseline within 60 minutes after reperfusion. In G30, recovery of r-CBF was significantly delayed relative to that of BrT. The increase in BrT was >2 degrees C, peaking approximately 15 minutes after reperfusion, and then maintained increases of >1 degree C for 120 minutes. SEPs in G5 and G15 showed concomitant recovery with that of r-CBF, whereas SEP recovery in G30 was delayed relative to that of r-CBF, eventually disappearing. All except one of the G30 gerbils died within 24 hours, but all in G5 and G15 survived.

CONCLUSIONS

These results suggest that mismatch recovery of r-CBF and BrT after prolonged ischemia initiates metabolic derangement in brain tissue, leading to the electrochemical dysfunction and mortality.

Mitochondrial involvement in transhemispheric diaschisis following hypoxia-ischemia: Clomethiazole-mediated amelioration

Mitochondria play a central role in both the physiological and pathophysiological regulation of cell survival/death. Increasing evidence places mitochondrial dysfunction at the center of many neuropathological conditions. The present study investigates the extent of mitochondrial dysfunction in cortical, hippocampal and cerebellar tissues in a rat model of hypoxia-ischemia (HI). We hypothesized that; mitochondrial dysfunction in situ may be prevented by treatment with clomethiazole (CMZ), a GABA(A) receptor agonist. Assessment of mitochondrial FAD-linked respiration at both 1- and 3-day post-HI revealed a marked decrease in activity from ipsilateral cortical and hippocampal regions (P<0.001). In addition, small changes were seen in contralateral cortical and hippocampal tissues as well as in the cerebellum at 3-days (P<0.05). Assessment of the mitochondrial electron transport chain (complexes I-V), and mitochondrial markers of integrity (citrate synthase) and oxidative stress (aconitase) confirmed mitochondrial impairment in ipsilateral regions following HI. Complexes I, II-III, V and citrate synthase were also impaired in contralateral regions and cerebellum 3-days post-HI. Treatment with CMZ (414 mg/kg/day via minipumps) provided marked protection to all aspects of neuronal tissue assessed. Circulating cytokine (interleukin [IL]-1alpha, IL-1beta, tumor necrosis factor [TNF]-alpha, granulocyte macrophage colony-stimulating factor [GM-CSF], IL-4 and IL-10) levels were also assessed in these animals 3-days post-HI. Plasma IL-1alpha, IL-1beta, TNF-alpha and GM-CSF levels were significantly increased post-HI. Treatment with CMZ ameliorated the increases in IL-1alpha, IL-1beta, TNF-alpha and GM-CSF levels while increasing plasma IL-4 and IL-10 levels. This study provides evidence of the extent of mitochondrial damage following an HI-insult. In addition, we have shown that protection afforded by CMZ extends to preservation of mitochondrial function and integrity via anti-inflammatory mediated pathways.

Role of cardiolipin alterations in mitochondrial dysfunction and disease

Cardiolipin (CL) is a structurally unique dimeric phospholipid localized in the inner mitochondrial membrane where it is required for optimal mitochondrial function. In addition to its role in maintaining membrane potential and architecture, CL is known to provide essential structural and functional support to several proteins involved in mitochondrial bioenergetics. A loss of CL content, alterations in its acyl chain composition, and/or CL peroxidation have been associated with mitochondrial dysfunction in multiple tissues in a variety of pathological conditions, including ischemia, hypothyroidism, aging, and heart failure. Recently, aberrations in CL metabolism have been implicated as a primary causative factor in the cardioskeletal myopathy known as Barth syndrome, underscoring an important role of CL in human health and disease. The purpose of this review is to provide an overview of evidence that has linked changes in the CL profile to mitochondrial dysfunction in various pathological conditions. In addition, a brief overview of CL function and biosynthesis, and a discussion of methods used to examine CL in biological tissues are provided.

Contribution of peroxidized cardiolipin to inactivation of bovine heart cytochrome c oxidase

The lipid-soluble peroxides, tert-butyl hydroperoxide and peroxidized cardiolipin, each react with bovine cytochrome c oxidase and cause a loss of electron-transport activity. Coinciding with loss of activity is oxidation of Trp19 and Trp48 within subunits VIIc and IV, and partial dissociation of subunits VIa and VIIa. tert-Butyl hydroperoxide initiates these structural and functional changes of cytochrome c oxidase by three mechanisms: (1) radical generation at the binuclear center; (2) direct oxidation of Trp19 and Trp48; and (3) peroxidation of bound cardiolipin. All three mechanisms contribute to inactivation since blocking a single mechanism only partially prevents oxidative damage. The first mechanism is similar to that described for hydrogen peroxide [Biochemistry43:1003-1009; 2004], while the second and third mechanism are unique to organic hydroperoxides. Peroxidized cardiolipin inactivates cytochrome c oxidase in the absence of tert-butyl hydroperoxide and oxidizes the same tryptophans within the nuclear-encoded subunits. Peroxidized cardiolipin also inactivates cardiolipin-free cytochrome c oxidase rather than restoring full activity. Cardiolipin-free cytochrome c oxidase, although it does not contain cardiolipin, is still inactivated by tert-butyl hydroperoxide, indicating that the other oxidation products contribute to the inactivation of cytochrome c oxidase. We conclude that both peroxidized cardiolipin and tert-butyl hydroperoxide react with and triggers a cascade of structural alterations within cytochrome c oxidase. The summation of these events leads to cytochrome c oxidase inactivation.

Muscle tissue oxygen tension and oxidative metabolism during ischemia and reperfusion

BACKGROUND

Recent studies have shown a relationship between alterations in tissue oxygen metabolism and cellular changes following ischemia and reperfusion, such as energy store depletion and intracellular acidosis. The aim of this study was to evaluate the relationship between tissue energy metabolism and intramuscular tissue oxygen tension in the mobilized latissimus dorsi muscle.

MATERIAL AND METHODS

The latissimus dorsi muscle was raised in New Zealand white rabbits (n = 10, 2.5 +/- 0.5 kg). During 4 h of ischemia and 2 h of reperfusion, the intramuscular tissue oxygen tension (Licox PO2-microcatheter probe) and the status of phosphorylated muscle energy metabolites were measured using a high-field 31P-NMR spectrometer. Linear correlation was performed between 31P-NMR data and tissue oxygen tension readings.

RESULTS

The tissue oxygen tension (PO2) values correlated significantly with phosphocreatine (PCr) (r = 0.96, P < 0.001), beta-adenosin triphosphate (beta-ATP) (r = 0.64, P <0.01), and intracellular pH (r = 0.82, P <0.001).

CONCLUSIONS

On the basis of these findings, we conclude that the data provided by tissue oxygen tension measurement offer a real time minimally invasive estimate of muscle oxidative metabolism during ischemia and reperfusion.

Neuroprotective effects of (-)-epigallocatechin gallate following hypoxia-ischemia-induced brain damage: novel mechanisms of action

(-)-Epigallocatechin gallate (EGCG) is a potent antioxidant that is neuroprotective against ischemia-induced brain damage. However, the neuroprotective effects and possible mechanisms of action of EGCG after hypoxia-ischemia (HI) have not been investigated. Therefore, we used a modified "Levine" model of HI to determine the effects of EGCG. Wistar rats were treated with either 0.9% saline or 50 mg/kg EGCG daily for 1 day and 1 h before HI induction and for a further 2 days post-HI. At 26-days-old, both groups underwent permanent left common carotid artery occlusion and exposure to 8% oxygen/92% nitrogen atmosphere for 1 h. Histological assessment showed that EGCG significantly reduced infarct volume (38.0+/-16.4 mm(3)) in comparison to HI + saline (99.6+/-15.6 mm(3)). In addition, EGCG significantly reduced total (622.6+/-85.8 pmol L-[(3)H]citrulline/30 min/mg protein) and inducible nitric oxide synthase (iNOS) activity (143.2+/-77.3 pmol L-[(3)H]citrulline/30 min/mg protein) in comparison to HI+saline controls (996.6+/-113.6 and 329.7+/-59.6 pmol L-[(3)H]citrulline/30 min/mg protein for total NOS and iNOS activity, respectively). Western blot analysis demonstrated that iNOS protein expression was also reduced. In contrast, EGCG significantly increased endothelial and neuronal NOS protein expression compared with HI controls. EGCG also significantly preserved mitochondrial energetics (complex I-V) and citrate synthase activity. This study demonstrates that the neuroprotective effects of EGCG are, in part, due to modulation of NOS isoforms and preservation of mitochondrial complex activity and integrity. We therefore conclude that the in vivo neuroprotective effects of EGCG are not exclusively due to its antioxidant effects but involve more complex signal transduction mechanisms.

Neuroprotective effects of spermine following hypoxia‐ischemia‐induced brain damage: A mechanistic study

The polyamines (spermine, putrescine, and spermidine) can have neurotoxic or neuroprotective properties in models of neurodegeneration. However, assessment in a model of hypoxia-ischemia (HI) has not been defined. Furthermore, the putative mechanisms of neuroprotection have not been elucidated. Therefore, the present study examined the effects of the polyamines in a rat pup model of HI and determined effects on key enzymes involved in inflammation, namely, nitric oxide synthase (NOS) and arginase. In addition, effects on mitochondrial function were investigated. The polyamines or saline were administered i.p. at 10mg/kg/day for 6 days post-HI. Histological assessment 7 days post-HI revealed that only spermine significantly (P<0.01) reduced infarct size from 46.14 +/- 10.4 mm3 (HI + saline) to 4.9 +/- 2.7 mm3. NOS activity was significantly increased following spermine treatment in the left (ligated) hemisphere compared with nonintervention controls (P<0.01) and HI + saline (P<0.05). In contrast, spermine decreased arginase activity compared with HI + saline but was still significantly elevated in comparison to nonintervention controls (P<0.01). Assessment of mitochondrial function in the HI + saline group, revealed significant and extensive damage to complex-I (P<0.01) and IV (P<0.001) and loss of citrate synthase activity (P<0.05). No effect on complex II-III was observed. Spermine treatment significantly prevented all these effects. This study has therefore confirmed the neuroprotective effects of spermine in vivo. However, for the first time, we have shown that this effect may, in part, be due to increased NOS activity and preservation of mitochondrial function.

Preservation of rat skeletal muscle energy metabolism by illumination

Skeletal muscle viability is crucially dependent on the tissue levels of its high energy phosphates. In this study we investigated the effect of the preservation medium Perfadex and illumination with Singlet Oxygen Energy (SOE). Singlet oxygen can be produced photochemically by energy transfer from an excited photosensitizer. The energy emitted from singlet oxygen upon relaxation to its triplet state is captured as photons at 634 nm and is here referred to as SOE. Rat hind limb rectus femoris muscles were preserved for five hours at 22 degrees C in Perfadex, saline, SOE illuminated Perfadex or SOE illuminated saline. Extracts of the muscles were analysed by 31P NMR. Data were analysed using two-way analysis of variance and are given as mean values micromol/g dry weight) +/- SEM. The ATP concentration was higher (p = 0.006) in saline groups (4.52) compared with Perfadex groups (2.82). There was no statistically significant difference in PCr between the saline groups (1.25) and Perfadex groups (0.82). However, there were higher (p = 0.003) ATP in the SOE illuminated groups (4.61) compared with the non-illuminated groups (2.73). The PCr was also higher (p < 0.0001) in the SOE illuminated groups (1.89) compared with the non-illuminated groups (0.18). In conclusion, Perfadex in this experimental model was incapable of preserving the high energy phosphates in skeletal muscle during 5 hours of ischemia. Illumination with SOE at 634 nm improved the preservation potential, in terms of a positive effect on the energy status of the muscle cell.

Improved energetic recovery of skeletal muscle in response to ischemia and reperfusion injury followed by in vivo 31P-magnetic resonance spectroscopy

It is of great clinical interest to improve postischemic tissue recovery during microsurgical transfers. The effect of singlet oxygen energy (SOE) as photon illumination at 634 nm on rat skeletal muscle during ischemia and postischemic reperfusion was investigated noninvasively and continuously by in vivo (31)P-magnetic resonance spectroscopy ((31)P-MRS). A model of pedicled rat rectus femoris muscle was used, where phosphorous metabolites were followed before onset of ischemia (control), after 4 h of ischemia, and after 1 h of reperfusion. Two groups were studied: one control group (n = 10), and one SOE-treated group (n = 10). Blood perfusion was measured by laser Doppler flowmetry (LDF) during the study. After 4 h of ischemia, ATP levels were 72% and 51% of normal control values in the illuminated group and the control group, respectively (P < 0.05). After 1 h of postischemic reperfusion, phosphocreatine (PCr) recovered to 79% and adenosine triphosphate (ATP) to 71% in the illuminated group, whereas in the control group, the recovery was 57% and 51%, respectively (P < 0.05). It is concluded that singlet oxygen energy has a beneficial effect on the energy state of skeletal muscle during ischemia and postischemic reperfusion.

Alterations in cytochrome c oxidase activity and energy metabolites in response to kainic acid-induced status epilepticus

The effects of kainic acid (KA)-induced limbic seizures have been investigated on cytochrome c oxidase (COx) activity, COx subunit IV mRNA abundance, ATP and phosphocreatine (PCr) levels in amygdala, hippocampus and frontal cortex of rat brain. Rats were killed either 1 h, three days or seven days after the onset of status epilepticus (SE) by CO2 and decapitation for the assay of COx activity and by head-focused microwave for the determination of ATP and PCr. Within 1 h COx activity and COx subunit IV mRNA increased in all brain areas tested between 120% and 130% of control activity, followed by a significant reduction from control, in amygdala and hippocampus on day three and seven, respectively. In amygdala, ATP and PCr levels were reduced to 44% and 49% of control 1 h after seizures. No significant recovery was seen on day three or seven. Pretreatment of rats with the spin trapping agent N-tert-butyl-alpha-phenylnitrone (PBN, 200 mg kg(-1), i.p.) 30 min before KA administration had no effect on SE, but protected COx activity and attenuated changes in energy metabolites. Pretreatment for three days with the endogenous antioxidant vitamin E (Vit-E, 100 mg/kg, i.p.) had an even greater protective effect than PBN. Both pretreatment regimens attenuated KA-induced neurodegenerative changes, as assessed by histology and prevention of the decrease of COx subunit IV mRNA and COx activity in hippocampus and amygdala, otherwise seen following KA-treatment alone. These findings suggest a close relationship between SE-induced neuronal injury and deficits in energy metabolism due to mitochondrial dysfunction.

Loss of molecular interaction between cytochrome c and cardiolipin due to lipid peroxidation

To explore the molecular mechanism underlying the translocation of cytochrome c from the mitochondrial inner membrane to the cytosol during apoptosis, we analyzed the molecular interaction between cytochrome c and cardiolipin (CL) by (1)H NMR spectroscopy. Bovine heart CL induced a drastic broadening of the linewidth of the downfield signals at 31.4 and 34.2 ppm assigned to the heme methyl group-3 and -8, respectively, of horse heart cytochrome c. In contrast, CL mono- and dihydroperoxides were less active in broadening the signals than CL, and CL trihydroperoxides induced almost no broadening of their linewidth. This finding suggests that the peroxidation of CL induces a release of cytochrome c from mitochondria into the cytosol, which release induces apoptosis in the cells.

Protective effect of Phyllanthus fraternus against carbon tetrachloride-induced mitochondrial dysfunction

The effect of carbon tetrachloride administration on liver mitochondrial function and the protective effect of an aqueous extract of Phyllanthus fraternus were studied in rats. The following changes were observed in mitochondria due to the administration of carbon tetrachloride. 1) A decrease in the rate of respiration, respiratory control ratio and P/O ratio using glutamate and malate or succinate as substrates. 2) A decrease in the activities of NADH dehydrogenase (35%), succinate dehydrogenase (76%) and cytochrome c oxidase (51%). The rate of electron transfer through site I, site II and site III was studied independently and found to be significantly decreased. 3) A decrease in the content of cytochrome aa3 (34%). 4) A significant decrease in the levels of phospholipids particularly cardiolipin and a significant increase in the lipid peroxide level was observed. The carbon tetrachloride induced toxicity may be partly due to the lipid peroxidation and partly due to the effect on protein synthesis. Administration of rats with an aqueous extract of P. fraternus prior to carbon tetrachloride administration showed significant protection on the carbon tetrachloride induced mitochondrial dysfunction on all the parameters studied.

Potential roles of myoglobin autoxidation in myocardial ischemia-reperfusion injury

The source(s) of reactive partially reduced oxygen species associated with myocardial ischemia/reperfusion injury remain unclear and controversial. Myoglobin has not been viewed as a participant but is present in relatively high concentrations in heart muscle and, even under normal conditions, undergoes reactions that generate met (Fe3+) species and also superoxide, hydrogen peroxide, and other oxidants, albeit slowly. The degree to which the decrease in pH and the freeing of copper ions, as well as the variations in pO2 associated with ischemia and reperfusion increase the rates of such myoglobin reactions has been investigated. Solutions of extensively purified myoglobin from bovine heart in 50 mM sodium phosphate buffer were examined at 37 degrees C. Sufficiently marked rate increases were observed to indicate that reactions of myoglobin can indeed contribute substantially to the oxidant stress associated with ischemia/reperfusion injury in myocardial tissues. These findings provide additional targets for therapeutic interventions.

Heightened resistance of the neonatal brain to ischemia-reperfusion involves a lack of mitochondrial damage in the nerve terminal

Mitochondria are known targets of ischemia-reperfusion injury in adult brain. Although neonates are more resistant to ischemic episodes, the mechanisms accounting for this are not yet fully understood. The aim of this study therefore was to determine whether a difference in post-ischemic mitochondrial function may play a role in the heightened recovery of the neonatal brain following ischemia-reperfusion. We have therefore compared the effects of an in vitro model of ischemia on the enzymes of the mitochondrial respiratory chain in isolated nerve terminals (synaptosomes) from neonatal and adult rats. Ischemia caused a significant, reversible decrease in mitochondrial Complex I activity in both adult and neonatal preparations. In neonatal preparations alone, ischemia also led to a significant decrease in mitochondrial Complexes II-III activity. Following 30 min of reperfusion mitochondrial Complexes II-III and IV exhibited decreased activity in synaptosomes from adult, but not neonatal rats. These data suggest a difference in the susceptibility of adult as compared to neonatal nerve terminal mitochondria to ischemia-reperfusion. These data show for the first time that nerve terminal mitochondria from immature animals remain undamaged following a period of ischemia and reperfusion, in contrast to nerve terminal mitochondria from the adult brain. This adds to the growing body of evidence that mitochondrial function plays a key role in neuronal death following cerebral ischemia reperfusion.

Nitric oxide, mitochondria and neurological disease

Damage to the mitochondrial electron transport chain has been suggested to be an important factor in the pathogenesis of a range of neurological disorders, such as Parkinson's disease, Alzheimer's disease, multiple sclerosis, stroke and amyotrophic lateral sclerosis. There is also a growing body of evidence to implicate excessive or inappropriate generation of nitric oxide (NO) in these disorders. It is now well documented that NO and its toxic metabolite, peroxynitrite (ONOO-), can inhibit components of the mitochondrial respiratory chain leading, if damage is severe enough, to a cellular energy deficiency state. Within the brain, the susceptibility of different brain cell types to NO and ONOO- exposure may be dependent on factors such as the intracellular reduced glutathione (GSH) concentration and an ability to increase glycolytic flux in the face of mitochondrial damage. Thus neurones, in contrast to astrocytes, appear particularly vulnerable to the action of these molecules. Following cytokine exposure, astrocytes can increase NO generation, due to de novo synthesis of the inducible form of nitric oxide synthase (NOS). Whilst the NO/ONOO- so formed may not affect astrocyte survival, these molecules may diffuse out to cause mitochondrial damage, and possibly cell death, to other cells, such as neurones, in close proximity. Evidence is now available to support this scenario for neurological disorders, such as multiple sclerosis. In other conditions, such as ischaemia, increased availability of glutamate may lead to an activation of a calcium-dependent nitric oxide synthase associated with neurones. Such increased/inappropriate NO formation may contribute to energy depletion and neuronal cell death. The evidence available for NO/ONOO--mediated mitochondrial damage in various neurological disorders is considered and potential therapeutic strategies are proposed.

Lipid peroxidation and changes in cytochrome c oxidase and xanthine oxidase activity in organophosphorus anticholinesterase induced myopathy

A possible role of radical oxygen species (ROS) initiated lipid peroxidation in diisopropylphosphorofluoridate (DFP)-induced muscle necrosis was investigated by quantifying muscle changes in F2-isoprostanes, novel and extremely accurate markers of lipid peroxidation in vivo. A significant increase in F2-isoprostanes of 56% was found in the diaphragm of rats 60 min after DFP-induced fasciculations. As possible source of ROS initiating lipid peroxidation, the cytocrome-c oxidase (Cyt-ox) and xanthine dehydrogenase-xanthine oxidase (XD-XO) systems were investigated. Within 30 min of onset of fasciculations Cyt-ox activity was reduced by 50% from 0.526 to 0.263 mumol/mg prot/min and XO activity increased from 0.242 to 0.541 mumol/mg prot/min. Total XD-XO activity was unchanged, indicating a conversion from XD into XO. In rats pretreatment with the neuromuscular blocking agent d-tubocurarine, prevented DFP-induced fasciculations, increases in F2-isoprostanes and changes in Cyt-ox or XD-XO. The decrease in Cyt-ox and increase in XO suggest that ROS are produced during DFP induced muscle fasciculations initiating lipid peroxidation and subsequent myopathy.

Glutamate neurotoxicity is associated with nitric oxide-mediated mitochondrial dysfunction and glutathione depletion

The role of mitochondrial energy metabolism in glutamate mediated neurotoxicity was studied in rat neurones in primary culture. A brief (15 min) exposure of the neurones to glutamate caused a dose-dependent (0.01-1 mM) increase in cyclic GMP levels together with delayed (24 h) neurotoxicity and ATP depletion. These effects were prevented by either the nitric oxide (.NO) synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (NAME; 1 mM) or by the N-methyl-D-aspartate (NMDA) glutamate-subtype receptor antagonist D-(-)-2-amino-5-phosphonopentanoate (APV; 0.1 mM). Glutamate exposure (0.1 mM and 1 mM) followed by 24 h of incubation caused the inhibition of succinate-cytochrome c reductase (20-25%) and cytochrome c oxidase (31%) activities in the surviving neurones, without affecting NADH-coenzyme-Q1 reductase activity. The rate of oxygen consumption was impaired in neurones exposed to 1 mM glutamate, either with glucose (by 26%) or succinate (by 39%) as substrates. These effects on the mitochondrial respiratory chain and neuronal respiration, together with the observed glutathione depletion (20%) by glutamate exposure were completely prevented by NAME or APV. Our results suggest that mitochondrial dysfunction and impairment of antioxidant status may account for glutamate-mediated neurotoxicity via a mechanism involving .NO biosynthesis.

In vivo 31P NMR OSIRIS of bioenergetic changes in rabbit kidneys during and after ischaemia: effect of pretreatment with an indeno-indole compound

Changes in energy phosphates of rabbit kidneys subjected to ischaemia-reperfusion have been measured in vivo with volume selective 31P NMR spectroscopy. The effects of pretreatment with a new lipid peroxidation inhibitor (indeno-indol derivate--code name H290/51) on the bioenergetic changes were analysed. The left kidney was moved to a subcutaneous pocket to facilitate exact positioning over the surface coil. A 1H NMR image was acquired and a 3.5-mL cube selected for 31P NMR spectra. 31P NMR spectra were recorded before occlusion of the left renal artery, during 1 h of ischaemia and 2 hours of reperfusion. Ischaemia induced drastic changes in the levels of inorganic phosphates and ATP as well as intracellular acidosis. A normalization was observed during reperfusion. Two hours after reperfusion significantly higher values for beta-ATP/Pi and intracellular pH were recorded in the animals pretreated with H290/51. The present technique allows quantitative analyses of changes in kidney bioenergetics in vivo during different experimental conditions. The importance of ischaemia-reperfusion induced lipid peroxidation for mitochondrial function is emphasized.

Inflammatory responses to ischemia and reperfusion in skeletal muscle

Skeletal muscle ischemia and reperfusion is now recognized as one form of acute inflammation in which activated leukocytes play a key role. Although restoration of flow is essential in alleviating ischemic injury, reperfusion initiates a complex series of reactions which lead to neutrophil accumulation, microvascular barrier disruption, and edema formation. A large body of evidence exists which suggests that leukocyte adhesion to and emigration across postcapillary venules plays a crucial role in the genesis of reperfusion injury in skeletal muscle. Reactive oxygen species generated by xanthine oxidase and other enzymes promote the formation of proinflammatory stimuli, modify the expression of adhesion molecules on the surface of leukocytes and endothelial cells, and reduce the bioavailability of the potent antiadhesive agent nitric oxide. As a consequence of these events, leukocytes begin to form loose adhesive interactions with postcapillary venular endothelium (leukocyte rolling). If the proinflammatory stimulus is sufficient, leukocytes may become firmly adherent (stationary adhesion) to the venular endothelium. Those leukocytes which become firmly adherent may then diapedese into the perivascular space. The emigrated leukocytes induce parenchymal cell injury via a directed release of oxidants and hydrolytic enzymes. In addition, the emigrating leukocytes also exacerbate ischemic injury by disrupting the microvascular barrier during their egress across the vasculature. As a consequence of this increase in microvascular permeability, transcapillary fluid filtration is enhanced and edema results. The resultant increase in interstitial tissue pressure physically compresses the capillaries, thereby preventing microvascular perfusion and thus promoting the development of the no-reflow phenomenon. The purpose of this review is to summarize the available information regarding these mechanisms of skeletal muscle ischemia/reperfusion injury.

Interrelationships between astrocyte function, oxidative stress and antioxidant status within the central nervous system

Astrocytes have, until recently, been thought of as the passive supporting elements of the central nervous system. However, recent developments suggest that these cells actually play a crucial and vital role in the overall physiology of the brain. Astrocytes selectively express a host of cell membrane and nuclear receptors that are responsive to various neuroactive compounds. In addition, the cell membrane has a number of important transporters for these compounds. Direct evidence for the selective co-expression of neurotransmitters, transporters on both neurons and astrocytes, provides additional evidence for metabolic compartmentation within the central nervous system. Oxidative stress as defined by the excessive production of free radicals can alter dramatically the function of the cell. The free radical nitric oxide has attracted a considerable amount of attention recently, due to its role as a physiological second messenger but also because of its neurotoxic potential when produced in excess. We provide, therefore, an in-depth discussion on how this free radical and its metabolites affect the intra and intercellular physiology of the astrocyte(s) and surrounding neurons. Finally, we look at the ways in which astrocytes can counteract the production of free radicals in general by using their antioxidant pathways. The glutathione antioxidant system will be the focus of attention, since astrocytes have an enormous capacity for, and efficiency built into this particular system.

Lipid peroxidation and changes in the ubiquinone content and the respiratory chain enzymes of submitochondrial particles

The relationship between, lipid peroxidation induced by ascorbate and adenosine ADP/Fe3+, and its effect on the respiratory chain activities of beef heart submitochondrial particles has been investigated. Lipid peroxidation, measured as thiobarbituric acid reactive substance formation, resulted in an inhibition of the NADH and succinate oxidase activities. Examination of several partial reactions of the respiratory chain revealed inactivation primarily of those involving endogenous ubiquinone, i.e., NADH- and succinate-ubiquinone1 and cytochrome c reductases. Ubiquinol-cytochrome c reductase, measured with reduced ubiquinone2 as electron donor, was unaffected. The amount of NADH- or succinate-reducible cytochrome b in the presence of cyanide was strongly decreased, but could be recovered by the addition of antimycin. There occurred a substantial decrease of the ubiquinone content in the course of lipid peroxidation, with a linear relationship between this decrease and the NADH and succinate oxidase activities. The results are consistent with the conclusion that the ubiquinone pool undergoes an oxidative modification during lipid peroxidation, to a form that can no longer function as a component of the respiratory chain. Lipid peroxidation also led to a partial inhibition of the succinate dehydrogenase and cytochrome c oxidase activities and a minor decrease of the cytochrome c and cytochrome a contents. Reduction of endogenous ubiquinone prevented lipid peroxidation as well as the concomitant modification of ubiquinone and inactivation of the respiratory chain. These observations suggest that the destruction of ubiquinone through lipid peroxidation is the primary cause of inactivation of the respiratory chain, and emphasize the antioxidant role of ubiquinol in preventing these effects. The possible implications of these findings for regulation of the cellular turnover of ubiquinone by the prevailing oxidative stress are discussed.

Altered glutathione levels in ischemic and postischemic skeletal muscle: difference between severe and moderate ischemic insult

The purpose of the present study was to investigate how the duration of ischemia and reperfusion affect the glutathione (GSH) levels in skeletal muscle and to assess the presence of oxidative stress by quantitating oxidized glutathione (GSSG) and the ratio of GSSG/GSH. The amounts of GSH and GSSG were quantitated in the tibialis anterior muscle of the rat hind limb after 2 and 4 hours of tourniquet ischemia and after 1 and 5 hours of reperfusion, and the levels were compared to those in nonischemic control tibialis anterior muscles. In muscles subjected to 2 hours of ischemia, the levels of GSH, GSSG, and the ratio GSSG/GSH did not differ significantly from those of nonischemic controls. After 4 hours of ischemia without reperfusion, the GSH levels were slightly increased, compared to controls (p < 0.05). After 1 hour of reperfusion following 4 hours of ischemia, the levels of GSH decreased by 50% compared to control (p < 0.01), and still after 5 hours of reperfusion the levels of GSH were 50% lower than control levels. The GSSG/ GSH ratio did not change during 1 and 5 hours of reperfusion compared to control. A major finding in this study was that, during reperfusion after severe ischemia of 4 hours, there was a marked depletion of glutathione, which was not seen after a moderate ischemic insult of 2 hours.

Xanthine oxidase and superoxide radicals in portal triad crossclamping-induced microvascular reperfusion injury of the liver

Although reactive oxygen metabolites may play a pivotal role in mediating microvascular reperfusion injury, the source of these radicals is still a matter of controversy. With the use of spectrophotometry and intravital microscopy we studied the role of xanthine oxidase and superoxide radicals in portal triad crossclamping-induced microvascular injury in rats. After 20 min of global hepatic ischemia and splanchnic vascular congestion, followed by 40 min of reperfusion (n = 8), xanthine oxidase activities in hepatic venous (26.9 +/- 4.7 nmol/ml x min) and systemic arterial blood (16.3 +/- 2.5 nmol/ml x min) were found significantly (p < .01) increased when compared with sham-operated controls (6.8 +/- 0.9 and 6.0 +/- 0.8 nmol/ml x min, n = 8). The increase of xanthine oxidase activity was accompanied by oxygen radical-mediated intravascular hemolysis. Intravital microscopy (n = 6) revealed accumulation of leukocytes within the postischemic hepatic microvasculature with stasis in sinusoids (75.9 +/- 8.9 per liver lobule) and adherence to the endothelial lining of postsinusoidal venules (534.7 +/- 125.3 per mm2 endothelial surface). Concomitantly, compromised microvascular reperfusion was characterized by perfusion deficits of individual sinusoids (25.6 +/- 4.0% nonperfused sinusoids). The xanthine oxidase inhibitor allopurinol (50 mg/kg b.wt., orally, n = 6) and the radical scavenger superoxide dismutase (60000 IU/kg b.wt., IV, n = 6) effectively (p < .01) inhibited both sinusoidal leukostasis (16.1 +/- 2.6 and 32.1 +/- 3.1 cells/lobule) and venular leukocyte adherence (247.6 +/- 7.9 and 205.0 +/- 38.0 cells/mm2), and, hence, reduced microcirculatory deteriorations, indicated by the attenuation of sinusoidal perfusion failure (2.8 +/- 0.8 and 9.0 +/- 3.1%). Our results support the hypothesis that portal triad crossclamping-induced microvascular reperfusion injury is triggered by superoxide radicals derived from the xanthine oxidase system.

Endogenous ubiquinol prevents protein modification accompanying lipid peroxidation in beef heart submitochondrial particles

This article is a study of the relationship between lipid peroxidation and protein modification in beef heart submitochondrial particles, and the protective effect of endogenous ubiquinol (reduced coenzyme Q) against these effects. ADP-Fe3+ and ascorbate were used to initiate lipid peroxidation and protein modification, which were monitored by measuring TBARS and protein carbonylation, respectively. Endogenous ubiquinone was reduced by the addition of succinate and antimycin. The parameters investigated included extraction and reincorporation of ubiquinone, and comparison of the effect of ubiquinol with those of various antioxidant compounds and enzymes, as well as the iron chelator EDTA. Under all conditions employed there was a close correlation between lipid peroxidation and protein carbonylation, and the inhibition of these effects by endogenous ubiquinol. SDS-PAGE analysis revealed a differential effect on individual protein components and its prevention by ubiquinol. Conceivable mechanisms behind the observed oxidative modifications of membrane phospholipids and proteins and of the role of ubiquinol in preventing these effects are considered.

Role of mitochondria in the etiology and pathogenesis of Parkinson's disease

We discuss the etiology and pathogenesis of Parkinson's disease (PD). Our group and others have found a decrease in complex I of the mitochondrial electron transfer complex in the substantia nigra of patients with PD; in addition, we reported loss of the alpha-ketoglutarate dehydrogenase complex (KGDHC) in the substantia nigra. Dual loss of complex I and the KGDHC will deleteriously affect the electron transport and ATP synthesis; we believe that energy crisis is the most important mechanism of nigral cell death in PD. Oxidative stress has also been implicated as an important contributor to nigral cell death in PD, but we believe that oxidative stress is a secondary phenomenon to respiratory failure, because respiratory failure will increase oxygen free-radical formation and consume glutathione. The primary cause of mitochondrial respiratory failure has not been elucidated yet, but additive effect of environmental neurotoxins in genetically predisposed persons appears to be the most likely possibility.

Depletion of brain glutathione is accompanied by impaired mitochondrial function and decreased N-acetyl aspartate concentration

The effect of depletion of reduced glutathione (GSH) on brain mitochondrial function and N-acetyl aspartate concentration has been investigated. Using pre-weanling rats, GSH was depleted by L-buthionine sulfoximine administration for up to 10 days. In both whole brain homogenates and purified mitochondrial preparations complex IV (cytochrome c oxidase) activity was decreased, by up to 27%, as a result of this treatment. In addition, after 10 days of GSH depletion, citrate synthase activity was significantly reduced, by 18%, in the purified mitochondrial preparations, but not in whole brain homogenates, suggesting increased leakiness of the mitochondrial membrane. The whole brain N-acetyl aspartate concentration was also significantly depleted at this time point, by 11%. It is concluded that brain GSH is important for the maintenance of optimum mitochondrial function and that prolonged depletion leads also to loss of neuronal integrity. The relevance of these findings to Parkinson's disease and the inborn errors of glutathione metabolism are also discussed.

Coenzymes Q9 and Q10 in skeletal and cardiac muscle in tumour-bearing exercising rats

Physical exercise increases metabolic rate, and induces both adaptational biogenesis of mitochondria in skeletal muscle and an increase in antioxidant capacity. The onset of experimental anorexia and cachexia can be delayed by voluntary exercise. As skeletal muscle is the main target for cancer cachexia, we determined the levels of coenzymes Q9 and Q10 in skeletal muscle from tumour-bearing exercising rats, and compared them to those of sedentary tumour-bearers and controls. Both tumour-bearing groups had increased levels of coenzymes Q9 and Q10 in the anterior tibial muscle (P < 0.05 for exercised animals). In the soleus muscle, only the tumour-bearing exercising animals demonstrated an increase in the levels of both coenzymes (P < 0.05). In cardiac muscle, the presence of tumour and exercise reduced the levels of coenzymes below that of sedentary controls. Exercise counteracted the anaemia in the tumour-bearing host (P < 0.05). In conclusion, the increase in antioxidant capacity in skeletal muscle indicates a defence mechanism in the tumour-bearing hosts which is augmented by physical exercise.

Trolox protects mitochondrial complex IV from nitric oxide-mediated damage in astrocytes

The efficacy of cystine, ascorbate and trolox, a vitamin E analogue, at protecting against nitric oxide-mediated mitochondrial complex IV damage has been investigated in cultured astrocytes. Of these compounds, only trolox afforded protection. It is suggested that lipid peroxidation is responsible for nitric oxide-mediated mitochondrial damage and that inhibitors of this process may be of therapeutic benefit in conditions where excessive nitric oxide production is implicated.

Purine metabolism during microsurgical transfer of human skeletal muscle

The effect of ischaemia followed by reperfusion on energy metabolism was studied in human skeletal muscle after microsurgical free transfer. Muscle biopsy specimens from 11 patients treated by free muscle transfer for facial palsy, injury to an extremity, or scalp defect were studied. The biopsy specimens were taken during ischaemia and after one hour of reperfusion, respectively. They were analysed for ATP to uric acid and creatine phosphate by high pressure liquid chromatography. Ischaemia lasting one or two hours affected the energy metabolism of the muscle cell as evidenced by a 50% reduction in creatine phosphate; a 20% reduction in ATP and in the energy charge; a 100% increase in inosine monophosphate, and a 700% increase in hypoxanthine and xanthine. Reperfusion for one hour improved these figures somewhat, and induced the production of uric acid. Skeletal muscle can therefore tolerate ischaemia for up to two hours in the clinical situation without permanent damage to the tissues.

In vivo 31P nuclear magnetic resonance evidence of the salvage effect of ascorbate on the postischemic reperfused rat skeletal muscle

The effect of 32 mM ascorbate on the time courses of phosphocreatine (PCr), inorganic phosphate (Pi), adenosine triphosphate (ATP) and intracellular pH in rat skeletal muscle during ischemia and reperfusion was investigated in vivo using 31P nuclear magnetic resonance (NMR) spectroscopy. Ascorbate was administered intravenously prior to induction of ischemia and at the time of reperfusion. The changes in PCr/(PCr+Pi), ATP and pH were similar in the non-treated and in the treated groups during ischemia. PCr/(PCr+Pi) fell to < 10% and ATP to approximately 30% of the preischemic values after 4 hours of arrested circulation, and pH decreased considerably. Postischemic reperfusion was followed continuously for 150 minutes. At the time of reflow, treatment with ascorbate had an immediate, positive effect on the recovery of high energy phosphates and pH. The level of PCr/(PCr+Pi) was 86% higher (p < 0.001) and the ATP level was 40% higher (p < 0.001) in the treated group than in the control group by the end of the reperfusion period. The results provide in vivo evidence for a salvaging effect of ascorbate on ischemia-reperfusion injury in skeletal muscle, probably owing to its antioxidant function and other ancillary effects, mainly its provision of additional buffer capacity.

Role of neutrophil-endothelial cell adhesion in inflammatory disorders

Polymorphonuclear leukocytes are armed with an impressive arsenal of bactericidal agents that allow these cells to play a vital role in host defense against invading pathogens. However, these same agents can produce extensive cellular damage in host tissues when leukocytes are activated during inflammatory conditions. Recognition of this fact, when coupled with the observation that leukocyte adhesion to post-capillary venules is a critical first step in the inflammatory process, has led to the development of the concept that inhibition of neutrophil-endothelial cell adhesion (NECA) may represent a novel therapeutic strategy for the prevention of leukocyte-dependent injury in inflammatory conditions. Indeed, pharmacological or immunologic inhibition of NECA reduces cellular injury, dysfunction, and necrosis induced by ischemia/reperfusion, circulatory shock and resuscitation, organ transplantation, cardiopulmonary bypass, frostbite, and thermal trauma. NECA also appears to play an important role in the pathobiology of airway inflammation and asthma, pulmonary oxygen toxicity, arthritis, bacterial meningitis, and cerebral malaria. The aim of this review is to summarize the evidence implicating NECA in the pathogenesis of these inflammatory conditions.

Reactive oxygen metabolites, neutrophils, and the pathogenesis of ischemic-tissue/reperfusion

Considerable research effort has been directed at elucidating the mechanisms underlying the pathophysiologic alterations associated with reperfusion (reoxygenation) of ischemic (hypoxic) tissues. As a consequence of this intensive effort, a large body of evidence has accumulated, implicating a role for reactive oxygen metabolites and activated granulocytes in the genesis of postischemic cellular dysfunction. Figure 1 summarizes a hypothesis that has been proposed to explain the interaction of xanthine oxidase-derived oxidants, granulocyte infiltration, and the microvascular and parenchymal cell dysfunction that occurs in postischemic tissues. According to this scheme, xanthine oxidase-derived oxidants, produced at reperfusion, initiate the formation and release of proinflammatory agents, which subsequently attract and activate granulocytes. The activated neutrophils adhere to the microvascular endothelium, extravasate, and release cytotoxic oxidants and proteases, which contribute to tissue dysfunction. The aim of this review is to summarize the evidence that we and others have accumulated in support of this hypothesis.

Generation of free radicals in Langendorff and working hearts during normoxia, hypoxia, and reoxygenation

The release of .OH and alkyl free radicals into the coronary flow were compared in Langendorff perfused and working rat hearts during normoxia (30 min), hypoxia (30 min) and reoxygenation (60 min) by means of spin-trapping techniques using 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). In Langendorff hearts, there was a small but steady increase in the radical concentration during the course of hypoxia and reoxygenation. At the start of reoxygenation, only small initial peaks of hydroxyl and alkyl radicals occurred. After a general decrease of free radical production during hypoxia, working hearts produced nearly double the amount of free radicals during reoxygenation as Langendorff hearts. After an initial large increase during early reoxygenation, the amount of free radicals produced fluctuated on a high level during the remaining reoxygenation period. Heart work is thus correlated with an increased production of free radicals, possibly due to an increase in oxygen consumption by the heart.

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

This study was undertaken to examine the effects of oxygen free radicals on mitochondrial creatine kinase activity in rat heart. Xanthine plus xanthine oxidase (superoxide anion radical generating system) reduced mitochondrial creatine kinase activity both in a dose- and a time-dependent manner. Superoxide dismutase showed a protective effect on depression in creatine kinase activity due to xanthine plus xanthine oxidase. Hydrogen peroxide inhibited creatine kinase activity in a dose-dependent manner, this inhibition was protected by the addition of catalase. In order to understand the detailed mechanisms by which oxygen free radicals inhibit mitochondrial creatine kinase activity, the effects of oxygen free radicals on mitochondrial sulfhydryl groups were examined. Mitochondrial sulfhydryl groups contents were decreased by xanthine plus xanthine oxidase or hydrogen peroxide; this depression in sulfhydryl groups contents was prevented by the addition of superoxide dismutase or catalase. N-Ethylmaleimide (sulfhydryl group reagent) expressed inhibitory effects on the creatine kinase activity both in a dose- and a time-dependent manner; dithiothreitol or cysteine (sulfhydryl group reductant) showed protective effects on the creatine kinase activity depression induced by N-ethylmaleimide. Dithiothreitol or cysteine also blocked the depression of mitochondrial creatine kinase activity caused by xanthine plus xanthine oxidase or hydrogen peroxide. These results lead us to conclude that oxygen free radicals may inhibit mitochondrial creatine kinase activity by modifying sulfhydryl groups in the enzyme protein.

Cardiolipins and biomembrane function

Evidence is discussed for roles of cardiolipins in oxidative phosphorylation mechanisms that regulate State 4 respiration by returning ejected protons across and over bacterial and mitochondrial membrane phospholipids, and that regulate State 3 respiration through the relative contributions of proteins that transport protons, electrons and/or metabolites. The barrier properties of phospholipid bilayers support and regulate the slow proton leak that is the basis for State 4 respiration. Proton permeability is in the range 10(-3)-10(-4) cm s-1 in mitochondria and in protein-free membranes formed from extracted mitochondrial phospholipids or from stable synthetic phosphatidylcholines or phosphatidylethanolamines. The roles of cardiolipins in proton conductance in model phospholipid membrane systems need to be assessed in view of new findings by Hübner et al. [313]: saturated cardiolipins form bilayers whilst natural highly unsaturated cardiolipins form nonlamellar phases. Mitochondrial cardiolipins apparently participate in bilayers formed by phosphatidylcholines and phosphatidylethanolamines. It is not yet clear if cardiolipins themselves conduct protons back across the membrane according to their degree of fatty acyl saturation, and/or modulate proton conductance by phosphatidylcholines and phosphatidylethanolamines. Mitochondrial cardiolipins, especially those with high 18:2 acyl contents, strongly bind many carrier and enzyme proteins that are involved in oxidative phosphorylation, some of which contribute to regulation of State 3 respiration. The role of cardiolipins in biomembrane protein function has been examined by measuring retained phospholipids and phospholipid binding in purified proteins, and by reconstituting delipidated proteins. The reconstitution criterion for the significance of cardiolipin-protein interactions has been catalytical activity; proton-pumping and multiprotein interactions have yet to be correlated. Some proteins, e.g., cytochrome c oxidase are catalytically active when dimyristoylphosphatidylcholine replaces retained cardiolipins. Cardiolipin-protein interactions orient membrane proteins, matrix proteins, and on the outerface receptors, enzymes, and some leader peptides for import; activate enzymes or keep them inactive unless the inner membrane is disrupted; and modulate formation of nonbilayer HII-phases. The capacity of the proton-exchanging uncoupling protein to accelerate thermogenic respiration in brown adipose tissue mitochondria of cold-adapted animals is not apparently affected by the increased cardiolipin unsaturation; this protein seems to take over the protonophoric role of cardiolipins in other mitochondria. Many in vivo influences that affect proton leakage and carrier rates selectively alter cardiolipins in amount per mitochondrial phospholipids, in fatty acyl composition and perhaps in sidedness; other mitochondrial membrane phospholipids respond less or not at all.(ABSTRACT TRUNCATED AT 400 WORDS)