Electrophoretic evidence for the impairment of complexes of the respiratory chain during iron/ascorbate induced peroxidation in isolated rat liver mitochondria

Galangin, a natural flavonoid reduces mitochondrial oxidative damage in streptozotocin-induced diabetic rats

Objective: We designed this study to observe the effect of galangin on damaged mitochondria in the liver of diabetic rats.

Methods: Male albino Wistar rats were made diabetic by injecting streptozotocin (STZ) intraperitoneally (40 mg kg⁻¹ body weight (BW)). Galangin (8 mg kg⁻¹ BW) or glibenclamide (600 µg kg⁻¹ BW) was given orally daily once for 45 days to both healthy and diabetic rats.

Results: Diabetic rats showed significant (P < 0.05) increase in liver mitochondrial oxidant [Thiobarbituric acid reactive substance (TBARS)] level and a significant decrease in enzymatic [superoxide dismutase (SOD), glutathione peroxidase (GPx)] and non-enzymatic (reduced glutathione (GSH)) antioxidant levels when compared with healthy rats. The mitochondrial enzymes isocitrate dehydrogenase (ICDH), alpha-ketoglutarate dehydrogenase (α-KGDH), succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) and mitochondrial respiratory chain enzymes NADH-dehydrogenase and Cytochrome c-oxidase were decreased significantly (P < 0.05) in diabetic rats when compared with healthy rats. A natural flavonoid galangin administered to hyperglycemia-induced rats resulted in the following findings as compared to hyperglycemia-induced control rats: the oxidant levels decreased significantly (P < 0.05); the enzymatic and non-enzymatic antioxidant levels increased significantly (P < 0.05) and the function of mitochondrial enzymes and the mitochondrial respiratory chain enzymes increased significantly (P < 0.05).

Conclusion: From the results, we conclude that galangin could maintain liver mitochondrial function in diabetic rats.

Xanthogranulomatous panniculitis of the head of an aquarium-maintained California moray

An aquarium-maintained male California moray Gymnothorax mordax had a symmetrical enlargement of the soft tissues of the head dorsal to the cranium for 2 years prior to its death. This individual was anesthetized for radiographic and ultrasonographic examination of the lesion, and blood was collected for plasma biochemical analytes and lipid profiles. Radiographs and ultrasound of the lesion demonstrated a symmetrical and homogeneous soft tissue density that was consistent with adipose tissue. Plasma cholesterol and triglyceride values appeared elevated; therefore, the animal's diet was amended to decrease fat consumption. Triglyceride values decreased after dietary changes were made; however, values for cholesterol, high-density lipoproteins, and low-density lipoproteins fluctuated but remained largely unchanged. Histopathological assessment of the lesion revealed localized xanthogranulomatous inflammation of hypodermal adipose tissue. The etiology of the lesion in this animal was never determined. This paper describes the first documented case of localized xanthogranulomatous panniculitis in a California moray and demonstrates the need for additional research on specific dietary requirements, species-specific physiological differences, and lesions involving the adipose tissue of morays in comparison with other teleost species.

Comparative study of the in vitro protective effects of several antioxidants on elongation factor 2 under oxidative stress conditions

One of the biochemical pathways affected by aging in all organisms is protein synthesis. Previous reports from our laboratory have indicated that the elongation step is specially affected by aging as a consequence of alterations in elongation factor-2 (eEF-2). In the present work, we studied in vitro the effectiveness of several individual nutritional antioxidants in protecting the levels of hepatic eEF-2 subjected to oxidative stress induced by cumene hydroperoxide. The in vitro system employed consisted of rat liver homogenates treated with cumene hydroperoxide. The antioxidants used in this study were lipoic acid, coenzyme Q10, tethrahydrofolic acid, and N-tert-butyl-alpha-phenylnitrone. The results indicate that the antioxidants have different capacities to prevent eEF-2 loss, folic acid being the most effective. A comparison between the antioxidants used and their potential pro-oxidant activity is also discussed, on the basis of the oxidative stress parameters measured.

Photo-induced toxicity of four polycyclic aromatic hydrocarbons, singly and in combination, to the marine diatom Phaeodactylum tricornutum

Polycyclic aromatic hydrocarbons (PAHs) enter the aquatic environment by various routes and are usually found as mixtures in the water. Many studies have shown that solar ultraviolet (UV) radiation can greatly enhance the toxicity of some PAHs to a variety of marine species. In the present study, we tested the phototoxicity of four PAHs with simple structures, both alone and in binary combinations, to a species of marine diatom, Phaeodactylum tricornutum, in the laboratory. The results indicated that simulated solar UV radiation not only enhanced the toxicity of the different PAHs to this alga, but also changed their relative toxic strengths. The photo-induced toxicity of PAHs to this alga might be a synergistic effect of photo-modification and photosensitization reactions, causing the microalgal cells to suffer oxidative stress. Four binary mixtures of these PAHs were found to have a synergistic joint action mode, while two binary mixtures displayed an antagonistic reaction, revealing a complex pattern of possible interactions of PAHs with marine diatoms.

Analysis of age-associated changes in mitochondrial free radical generation by rat testis

Throughout spermatogenesis, mitochondria undergo a morphological and functional differentiation. Mitochondria are involved in the production of reactive oxygen species (ROS), considered one of the mediators of ageing. Particularly, lipid peroxidation is regarded as a major phenomenon by which ROS can impair cellular function. In the present study, we examined the production of superoxide anion, superoxide dismutase activity and the effect of Fe(2+)/ascorbate induced-lipid peroxidation on the respiratory chain activities of testis mitochondria throughout the process of spermatogenesis and ageing. Mitochondria from rat testes generated superoxide anion, mainly using NADH as substrate, which increased according to age. The activity of SOD is age-dependent and greatly stimulated during the first wave of spermatogenesis, but decreases in adulthood and old age. TBARS concentration was also markedly increased by ageing. The activity of mitochondrial respiratory chain complexes is differentially affected by oxidative stress induced by iron/ascorbate, succinate-dehydrogenase activity being less vulnerable than that of NADH-dehydrogenase and cytochrome c oxidase. The data suggest that ageing is accompanied by reduced activity of SOD, leading to excessive oxidative stress and enhanced lipid peroxidation that compromises the functionality of the electron transport chain. The data support the concept that mitochondrial function is an important determinant in ageing.

Two-dimensional blue native/SDS gel electrophoresis of multiprotein complexes from Helicobacter pylori

The study of protein interactions constitutes an important domain to understand the physiology and pathogenesis of microorganisms. The two-dimensional blue native/SDS-PAGE was initially reported to analyze membrane protein complexes. In this study, both cytoplasmic and membrane complexes of a bacterium, the strain J99 of the gastric pathogen Helicobacter pylori, were analyzed by this method. It was possible to identify 34 different proteins grouped in 13 multiprotein complexes, 11 from the cytoplasm and two from the membrane, either previously reported partially or totally in the literature. Besides complexes involved in H. pylori physiology, this method allowed the description of interactions involving known pathogenic factors such as (i) urease with the heat shock protein GroEL or with the putative ketol-acid reductoisomerase IlvC and (ii) the cag pathogenicity island CagA protein with the DNA gyrase GyrA as well as insight on the partners of TsaA, a peroxide reductase/stress-dependent molecular chaperone. The two-dimensional blue native/SDS-PAGE combined with mass spectrometry is a potential tool to study the differences in complexes isolated in various situations and also to study the interactions between bacterial and eucaryotic cell proteins.

Molecular biomarkers of oxidative stress in aquatic organisms in relation to toxic environmental pollutants

The potential of oxygen free radicals and other reactive oxygen species (ROS) to damage tissues and cellular components, called oxidative stress, in biological systems has become a topic of significant interest for environmental toxicology studies. The balance between prooxidant endogenous and exogenous factors (i.e., environmental pollutants) and antioxidant defenses (enzymatic and nonenzymatic) in biological systems can be used to assess toxic effects under stressful environmental conditions, especially oxidative damage induced by different classes of chemical pollutants. The role of these antioxidant systems and their sensitivity can be of great importance in environmental toxicology studies. In the past decade, numerous studies on the effects of oxidative stress caused by some environmental pollutants in terrestrial and aquatic species were published. Increased numbers of agricultural and industrial chemicals are entering the aquatic environment and being taken up into tissues of aquatic organisms. Transition metals, polycyclic aromatic hydrocarbons, organochlorine and organophosphate pesticides, polychlorinated biphenyls, dioxins, and other xenobiotics play important roles in the mechanistic aspects of oxidative damage. Such a diverse array of pollutants stimulate a variety of toxicity mechanisms, such as oxidative damage to membrane lipids, DNA, and proteins and changes to antioxidant enzymes. Although there are considerable gaps in our knowledge of cellular damage, response mechanisms, repair processes, and disease etiology in biological systems, free radical reactions and the production of toxic ROS are known to be responsible for a variety of oxidative damages leading to adverse health effects and diseases. In the past decade, mammalian species were used as models for the study of molecular biomarkers of oxidative stress caused by environmental pollutants to elucidate the mechanisms underlying cellular oxidative damage and to study the adverse effects of some environmental pollutants with oxidative potential in chronic exposure and/or sublethal concentrations. This review summarizes current knowledge and advances in the understanding of such oxidative processes in biological systems. This knowledge is extended to specific applications in aquatic organisms because of their sensitivity to oxidative pollutants, their filtration capacity, and their potential for environmental toxicology studies.

Induction of Reactive Oxygen Species by Bisphenol A and Abrogation of Bisphenol A-Induced Cell Injury by DJ-1

DJ-1 was first identified as an activated ras-dependent oncogene. DJ-1 is related to male fertility, and its expression in sperm decreases in response to exposure to a number of reproductive toxicants. DJ-1 has been associated with the onset of familial Parkinson's disease (PD) in humans, and has been found to have activity against oxidative damage by eliminating reactive oxygen species (ROS). In this study, we investigated the role of DJ-1 in oxidative stresses by administration of bisphenol A (BPA), which has been reported to induce oxidative stress in rodents, to male mice and cultured cells. In male mice, we found that BPA significantly increased the expression level of DJ-1 in the sperm and brain. In cultured Neuro2a and GC1 cells, we found that BPA induced ROS production and significantly compromised mitochondrial function concomitant with elevated expression and oxidization of DJ-1. DJ-1 was found to maintain the complex I activity against BPA-induced oxidative stress after the localization in mitochondria. The results showed that DJ-1 plays a role in the prevention of mitochondrial injury-induced cell death.

Cytochrome c oxidase is decreased in Alzheimer's disease platelets

Cytochrome c oxidase (COX) activity reportedly is reduced in Alzheimer's disease (AD) brain and platelets. The reasons for the defect in either tissue are unknown, but its presence in a non-degenerating tissue suggests it is not simply a consequence of neurodegeneration. We now offer confirmation of the AD platelet COX defect. Compared to age-matched controls, in mitochondria isolated from AD platelets there was a 15% decrease in COX activity despite the fact that COX subunits were present at normal levels. Platelet ATP levels were diminished in AD (from 11.33 +/- 0.52 to 9.11 +/- 0.72 nmol/mg), while reactive oxygen species (ROS) were increased (from 97.03 +/- 25.9 to 338.3 +/- 100 K/mg). Platelet membrane fluidity, Vitamin E, and cholesterol content were similar between groups. We conclude that COX catalytic activity is indeed diminished in AD platelet mitochondria, does not result from altered membrane fluidity, and is associated with ROS overproduction and ATP under-production.

"In vitro" effect of cumene hydroperoxide on hepatic elongation factor-2 and its protection by melatonin

We have examined by immunoblotting the effect of three oxidant compounds on the level of hepatic elongation factor-2 (eEF-2). Rat liver homogenates were exposed to cumene hydroperoxide (CH), 2-2'-azobis (2-aminopropane) dihydrochloride (AAPH) and H(2)O(2). Only CH treatment produced the disappearance of eEF-2, probably due to a phenomena of peptide bond cleavage. The direct implication of free radical species in this process is evident because of the fact that the inclusion of a free radical scavenger such as melatonin prevented the eEF-2 depletion. The results also suggest that the disappearance of eEF-2 induced by CH can be linked to a lipid peroxidant process, which could account for the decline of protein synthesis in aging and other circumstances where lipid peroxidation is high.

Mechanism in the reaction of cytochrome c oxidase with organic hydroperoxides: an ESR spin-trapping investigation

Organic hydroperoxides are of great utility in probing the reaction mechanism and the toxicological consequences of lipid peroxidation. In the present study, ESR spin-trapping was employed to investigate the peroxidation of mitochondrial cytochrome c oxidase (CcO) with t-butyl hydroperoxide (t-BuOOH) and cumene hydroperoxide (CumOOH). The spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used to detect the radical species formed from the reaction of CcO with t-BuOOH. The presence of t-BuOOH-derived alkoxyl radical (t-BuO*) as the primary radical indicates reductive scission of the O-O bond by CcO. The ESR signal of DMPO/*Ot-Bu can be partially abolished by cyanide, implying that the reductive cleavage involved the haem a(3)Cu(B) binuclear site of CcO. A nitroso spin trap, 2-methyl-2-nitrosopropane (MNP), was used to detect and identify radical species from the reaction of CcO with CumOOH. In addition to the t-BuOOH-derived methyl, hydroxylmethyl and tertiary carbon-centred radicals, a protein-derived radical was detected. The intensity of the ESR signal from the protein radical increased with the CumOOH concentration at low CumOOH/CcO ratios, with maximal intensity at a ratio of 100 mol of CumOOH/mol of CcO. The immobilized protein radical adduct of MNP was stable and persistent after dialysis; it was also resistant to proteolytic digestion, suggesting that it was formed in the transmembrane region, a region that is not accessible to proteases. Its signal was greatly enhanced when CcO cysteine residues were chemically modified by N-ethylmaleimide, when the tryptophan residues in CcO were oxidized by N-bromosuccimide, and when tyrosine residues on the surface of CcO were iodinated, showing that a radical equilibrium was established among the cysteine, tryptophan and tyrosine residues of the protein-centred radical. Pre-treatment of CcO with cyanide prevented detectable MNP adduct formation, confirming that the haem a(3)-Cu(B) binuclear centre was the initial reaction site. When the CcO was pre-treated with 10 mM (100 equivalents) of CumOOH, the enzyme activity decreased by more than 20%. This inhibition was persistent after dialysis, suggesting that the detected protein-centred radical was, in part, involved in the irreversible inactivation by CumOOH. Visible spectroscopic analysis revealed that the haem a of CcO was not affected during the reaction. However, the addition of pyridine to the reaction mixture under alkaline conditions resulted in the destruction of the haem centre of CcO, suggesting that its protein matrix rather than its haem a is the target of oxidative damage by the organic hydroperoxide.

An electron spin resonance spin-trapping investigation of the free radicals formed by the reaction of mitochondrial cytochrome c oxidase with H2O2

The reaction of purified bovine mitochondrial cytochrome c oxidase (CcO) and hydrogen peroxide was studied using the ESR spin-trapping technique. A protein-centered radical adduct was trapped by 5, 5-dimethyl-1-pyrroline N-oxide and was assigned to a thiyl radical adduct based on its hyperfine coupling constants of aN = 14.7 G and abetaH = 15.7 G. The ESR spectra obtained using the nitroso spin traps 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS) and 2-methyl-2-nitrosopropane (MNP) indicated that both DBNBS/.CcO and MNP/.CcO radical adducts are immobilized nitroxides formed by the trapping of protein-derived radicals. Alkylation of the free thiols on the enzyme with N-ethylmaleimide (NEM) prevented 5, 5-dimethyl-1-pyrroline N-oxide adduct formation and changed the spectra of the MNP and DBNBS radical adducts. Nonspecific protease treatment of MNP-d9/.NEM-CcO converted its spectrum from that of an immobilized nitroxide to an isotropic three-line spectrum characteristic of rapid molecular motion. Super-hyperfine couplings were detected in this spectrum and assigned to the MNP/.tyrosyl adduct(s). The inhibition of either CcO or NEM-CcO with potassium cyanide prevented detectable MNP adduct formation, indicating heme involvement in the reaction. The results indicate that one or more cysteine residues are the preferred reductant of the presumed ferryl porphyrin cation radical residue intermediate. When the cysteine residues are blocked with NEM, one or more tyrosine residues become the preferred reductant, forming the tyrosyl radical.

Mitochondrial oxidative alterations following partial hepatectomy

Mitochondria, isolated from rat livers during the early phase of liver regeneration (7-24 h after partial hepatectomy), show: (i) decrease in the rate of ATP synthesis; (ii) increase of malondialdehyde and of oxidized protein production; (iii) decrease of the content of intramitochondrial glutathione and of protein thiols on mitochondrial proteins; (iv) increase of the glutathione bound to mitochondrial proteins by disulfide bonds. These observations suggest an increase of production of oxygen radicals in liver mitochondria, following partial hepatectomy, which can alter the function of the enzymes involved in the oxidative phosphorylation. Blue-native gel electrophoresis of rat liver mitochondria, isolated after partial hepatectomy, shows, during the early phase of liver regeneration (0-24 h after partial hepatectomy), a progressive decrease of the content of F0F1-ATP synthase complex. The amount of glutathione bound to the F0F1-ATP synthase, electroeluted from the blue-native gels, progressively increased during the early phase of liver regeneration. It is concluded that partial hepatectomy causes mitochondrial oxidative stress that, in turn, modifies proteins (such as F0F1-ATP synthase) involved in the mitochondrial oxidative phosphorylation.

Mitochondrial function is differentially affected upon oxidative stress

The mechanisms that lead to mitochondrial damage under oxidative stress conditions were examined in synaptosomes treated with ascorbate/iron. A loss of membrane integrity, evaluated by electron microscopy and by LDH leakage, was observed in peroxidized synaptosomes and it was prevented by pre-incubation with vitamin E (150 microM) and idebenone (50 microM). ATP levels decreased, in synaptosomes exposed to ascorbate/iron, as compared to controls. NADH-ubiquinone oxidoreductase (Cx I) and cytochrome c oxidase (Cx IV) activities were unchanged after ascorbate/iron treatment, whereas succinate-ubiquinone oxidoreductase (Cx II), ubiquinol cytochrome c reductase (Cx III) and ATP-synthase (Cx V) activities were reduced by 55%, 40%, and 55%, respectively. The decrease of complex II and ATP-synthase activities was prevented by reduced glutathione (GSH), whereas the other antioxidants tested (vitamin E and idebenone) were ineffective. However, vitamin E, idebenone and GSH prevented the reduction of complex III activity observed in synaptosomes treated with ascorbate/iron. GSH protective effect suggests that the oxidation of protein SH-groups is involved in the inhibition of complexes II, III and V activity, whereas vitamin E and idebenone protection suggests that membrane lipid peroxidation is also involved in the reduction of complex III activity. These results may indicate that the inhibition of the mitochondrial respiratory chain enzymatic complexes, that are differentially affected by oxidative stress, can be recovered by specific antioxidants.

Comparison of protein oxidation and aldehyde formation during oxidative stress in isolated mitochondria

Oxidative stress is known to cause oxidative protein modification and the generation of reactive aldehydes derived from lipid peroxidation. Extent and kinetics of both processes were investigated during oxidative damage of isolated rat liver mitochondria treated with iron/ascorbate. The monofunctional aldehydes 4-hydroxynonenal (4-HNE), n-hexanal, n-pentanal, n-nonanal, n-heptanal, 2-octenal, 4-hydroxydecenal as well as thiobarbituric acid reactive substances (TBARS) were detected. The kinetics of aldehyde generation showed a lag-phase preceding an exponential increase. In contrast, oxidative protein modification, assessed as 2,4-dinitrophenylhydrazine (DNPH) reactive protein-bound carbonyls, continuously increased without detectable lag-phase. Western blot analysis confirmed these findings but did not allow the identification of individual proteins preferentially oxidized. Protein modification by 4-HNE, determined by immunoblotting, was in parallel to the formation of this aldehyde determined by HPLC. These results suggest that protein oxidation occurs during the time of functional decline of mitochondria, i.e. in the lag-phase of lipid peroxidation. This protein modification seems not to be caused by 4-HNE.

The protective effect of vitamin E, idebenone and reduced glutathione on free radical mediated injury in rat brain synaptosomes

In the present study the effect of ascorbate (0.8 mM)/iron (2.5 microM) on lipid and protein oxidation, in Synaptosomes isolated from rat brain cortex, was evaluated. Vitamin E, idebenone and reduced glutathione were used as free radicals scavengers, in order to analyze the mechanism involved in ascorbate/iron-induced oxidative stress. An increased formation of reactive oxygen species (ROS) in the cytosol and in the mitochondria was observed, in ascorbate/iron treated synaptosomes. Idebenone (50 microM) prevented the increased formation of ROS in both synaptosomal compartments, vitamin E (150 microM) protected partially this formation in mitochondria, whereas reduced glutathione (250 microM) (GSH) was ineffective. After ascorbate/iron treatment an increase in lipid peroxidation occurred as compared to control, which was completely inhibited by idebenone. A decrease in protein-SH content was also observed, and it was prevented by Vitamin E, idebenone and GSH. When synaptosomes were treated with ascorbate/iron the levels of GSH decreased, and the levels of oxidized glutathione (GSSG) increased as compared to controls under these conditions. Glutathione peroxidase activity was unchanged, whereas an inhibition of glutathione reductase activity was observed. These data suggest that the increased formation of free radicals in synaptosomes leads to lipid and protein oxidation, the role of the endogenous GSH being essential to protect protein thiol-groups against oxidative damage in order to maintain enzyme activity.

Impairment of hepatic mitochondrial respiratory function following storage and orthotopic transplantation of rat livers

Prolonged storage of organs for transplant results in tissue damage which may be compounded on reperfusion of the graft tissue. The effect of storage times was examined on hepatic mitochondrial oxygen consumption and activities of complexes I, II-III, IV, and V in mitochondria isolated from rat liver isografts stored for 25 min and 24 h pre- and posttransplantation. While Complex I activity was significantly (P < 0.05) inhibited under all the conditions studied, Complex II-III activity was only significantly (P < 0.05) reduced following transplantation of 24-h stored tissue. Complex IV activity remained unchanged under all the conditions studied. Although Complex V activity was significantly damaged within the first 25 min of ischemia, activity values were partially recovered to control levels following 3 h of reperfusion after transplantation. Prolonged (24 h) storage induced decreases in Complex V activity which were irrecoverable. Mitochondria subjected to 25 min ischemia alone also showed a significant (P < 0.01) decrease in NAD(+)-linked respiratory control indices due to a stimulated state 4 rate. The 24-h storage and transplantation brought about a significantly (P < 0.001) greater inhibition of respiratory control and state 3 respiration. FAD-linked respiration parameters were significantly (P < 0.05) affected in livers subjected to prolonged (24 h) storage or transplantation. These data suggest that a loss of membrane integrity coupled with an inhibition of Complexes I and V and an involvement of Complex II-III in 24-h stored hepatic transplants accounts for mitochondrial respiratory dysfunction in hepatic transplantation injury. No indication of Complex IV damage was found in this study. This study shows that damage to specific mitochondrial complexes occurs as a consequence of hypothermic ischemic injury.

Short-term impairment of energy production in isolated rat liver mitochondria by hypoxia/reoxygenation: involvement of oxidative protein modification

The aim of the present study was to elucidate the role of mitochondria in liver impairment after ischaemia/reperfusion. It is commonly assumed that mitochondria are in part responsible for tissue damage by impaired oxidative phosphorylation as a consequence of the attack of radicals generated within the mitochondria. The principal support for this hypothesis was found by exposing isolated mitochondria to temporary hypoxia in combination with alterations of substrate supply. Rat liver mitochondria treated in this way responded with impaired ADP-stimulated respiration after reoxygenation, which decreased with time of hypoxia and reoxygenation. The decline of the activity of the NADH-cytochrome c-oxidoreductase complex found under these conditions is likely to cause the drop in active respiration. No changes in the content of respiratory chain complexes, determined by Blue Native PAGE, could be demonstrated. However, oxidative modifications of mitochondrial proteins, indicated by carbonyl formation, were found. Likewise, products of lipid peroxidation, such as lipid peroxides and malondialdehyde, were formed. Mitochondria were still able to build up a transmembrane potential and did not show drastic changes in membrane conductivity after hypoxia/reoxygenation stress. The presence of water-soluble antioxidants exhibited a beneficial effect, diminishing the decline of active respiration after 5 min of hypoxia and 10 min of reoxygenation. These observations strongly suggest that mitochondria play a pathogenic role in ischaemia/reperfusion injury, which is at least in part mediated by an oxygen-derived free-radical-linked mechanism.

Oxidative metabolism in rat hepatocytes and mitochondria during sepsis

We hypothesized that cellular oxygen consumption is abnormal during sepsis as a result of increased oxidative stress and selective mitochondrial damage. In a rat model of sepsis (cecal ligation and puncture), we studied the respiratory characteristics of isolated hepatocytes and liver mitochondria 16 h after onset of septic injury. Endogenous respiration by isolated cells was decreased during sepsis, while cyanide-resistant (nonmitochondrial) respiration was unaffected. Maximal oxygen consumption in ADP-supplemented, permeabilized hepatocytes was decreased with succinate as the substrate, but not with malate + glutamate or TMPD + ascorbate. In contrast, maximum oxygen consumption (State 3) by isolated liver mitochondria increased up to 35% during sepsis using either succinate or malate + glutamate as substrate. The electrophoretic features and mobility of nondenatured mitochondrial respiratory complexes were similar in control and septic hepatocytes, with the exception of decreased Complex V protein in sepsis. Structural evaluation of mitochondria in fixed liver slices by electron microscopy showed mitochondrial swelling in most of the septic animals. Measurements of oxidative stress during sepsis suggested an increase in hydroxylation of salicylate by isolated hepatocytes, and mitochondrial protein carbonyl content was increased significantly. Induction of iNOS in hepatocytes after 16 h of sepsis was variable, and little release of the oxidation products of NO. was detected. These findings are interpreted to mean that hepatocytes contain a mixed population of injured and hyperfunctional mitochondria during sepsis.

Biochemistry and pathology of radical-mediated protein oxidation

Radical-mediated damage to proteins may be initiated by electron leakage, metal-ion-dependent reactions and autoxidation of lipids and sugars. The consequent protein oxidation is O2-dependent, and involves several propagating radicals, notably alkoxyl radicals. Its products include several categories of reactive species, and a range of stable products whose chemistry is currently being elucidated. Among the reactive products, protein hydroperoxides can generate further radical fluxes on reaction with transition-metal ions; protein-bound reductants (notably dopa) can reduce transition-metal ions and thereby facilitate their reaction with hydroperoxides; and aldehydes may participate in Schiff-base formation and other reactions. Cells can detoxify some of the reactive species, e.g. by reducing protein hydroperoxides to unreactive hydroxides. Oxidized proteins are often functionally inactive and their unfolding is associated with enhanced susceptibility to proteinases. Thus cells can generally remove oxidized proteins by proteolysis. However, certain oxidized proteins are poorly handled by cells, and together with possible alterations in the rate of production of oxidized proteins, this may contribute to the observed accumulation and damaging actions of oxidized proteins during aging and in pathologies such as diabetes, atherosclerosis and neurodegenerative diseases. Protein oxidation may also sometimes play controlling roles in cellular remodelling and cell growth. Proteins are also key targets in defensive cytolysis and in inflammatory self-damage. The possibility of selective protection against protein oxidation (antioxidation) is raised.

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.