Oxidative changes in hypoxic rat heart tissue

Unravelling protein aggregation as an ageing related process or a neuropathological response

Protein aggregation is normally associated with amyloidosis, namely motor neurone, Alzheimer's, Parkinson's or prion diseases. However, recent results have unveiled a concept of gradual increase of protein aggregation associated with the ageing process, apparently not necessarily associated with pathological conditions. Given that protein aggregation is sufficient to activate stress-response and inflammation, impairing protein synthesis and quality control mechanisms, the former is assumed to negatively affect cellular metabolism and behaviour. In this review the state of the art in protein aggregation research is discussed, namely the relationship between pathology and proteostasis. The role of pathology and ageing in overriding protein quality-control mechanisms, and consequently, the effect of these faulty cellular processes on pathological and healthy ageing, are also addressed.

Elevated Levels of Apelin-36 in Heart Failure Due to Chronic Systemic Hypoxia

Apelin is a novel adipokine identified as an endogenous ligand of the specific orphan receptor APJ. Among the various isoforms of apelin, an increase in the apelin-36 plasma level has been associated with oxidative stress, and this isoform has various biological effects, such as positive inotropic, vasodilatory, and antiatherosclerotic effects. Therefore, apelin-36 may be used as a biomarker of heart failure (HF). Advances in the understanding of the molecular mechanisms underlying HF cannot be achieved without the use of animal models. However, it is unclear whether chronic systemic hypoxia can cause HF in rats. The present study aimed to determine whether chronic systemic hypoxia can cause HF in rats and whether apelin-36 can be used as a biomarker of HF. The study included Sprague-Dawley rats. The rats were randomly divided into seven groups ( n  = 4). One of the groups was a control group, and the six other groups were exposed to hypoxia (8% O2) for different durations (6 hours, 1 day, 3 days, 5 days, 7 days, and 14 days). The exposure groups showed ventricular hypertrophy accompanied by myocardial structural damage, which indicated ventricular remodeling. In addition, the exposure groups showed elevated apelin-36 plasma levels and signs of oxidative stress. Moreover, gel electrophoresis of heart tissue showed five bands that corresponded to apelin isotypes, including apelin-36. In an experimental rat HF model with chronic systemic hypoxia, apelin-36 was elevated along with oxidative stress. Apelin-36 along with oxidative stress may serve as a biomarker of HF in this model.

Heat shock protein-27 delays acute rejection after cardiac transplantation: an experimental model

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Background

Rejection is the major obstacle to survival after cardiac transplantation. We investigated whether overexpression of heat shock protein (Hsp)-27 in mouse hearts protects against acute rejection and the mechanisms of such protection.

Methods

Hearts from B10.A mice overexpressing human Hsp-27 (Hsp-27tg), or Hsp-27–negative hearts from littermate controls (LCs) were transplanted into allogeneic C57BL/6 mice. The immune response to B10.A hearts was investigated using quantitative polymerase chain reaction for CD3+, CD4+, CD8+ T cells, and CD14+ monocytes and cytokines (interferon-γ, interleukin [IL]-2, tumor necrosis factor-α, IL-1β, IL-4, IL-5, IL-10, transforming growth factor-β) in allografts at days 2, 5, and 12 after transplantation. The effect of Hsp-27 on ischemia-induced caspase activation and immune activation was investigated.

Results

Survival of Hsp-27tg hearts (35±10.37 days, n=10) was significantly prolonged compared with LCs (13.6±3.06 days, n=10, P=0.0004). Hsp-27tg hearts expressed significantly more messenger RNA (mRNA) markers of CD14+ monocytes at day 2 and less mRNA markers of CD3+ and CD8+T cells at day 5 compared with LCs. There was more IL-4 mRNA in Hsp-27tg hearts at day 2 and less interferon-γ mRNA at day 5 compared with LCs. Heat shock protein-27tg hearts subjected to ischemia or to 24 hr ischemia-reperfusion injury demonstrated significantly less apoptosis and activation of caspases 3, 9, and 1 than LCs. T cells removed from C57BL/6 recipients of Hsp-27tg hearts produced a vigorous memory response to B10.A antigens, suggesting immune activation was not inhibited by Hsp-27.

Conclusion

Heat shock protein-27 delays allograft rejection, by inhibiting tissue damage, through probably an antiapoptotic pathway. It may also promote an anti-inflammatory subset of monocytes.

The ubiquitin proteasome system and myocardial ischemia

The ubiquitin proteasome system (UPS) has been the subject of intensive research over the past 20 years to define its role in normal physiology and in pathophysiology. Many of these studies have focused in on the cardiovascular system and have determined that the UPS becomes dysfunctional in several pathologies such as familial and idiopathic cardiomyopathies, atherosclerosis, and myocardial ischemia. This review presents a synopsis of the literature as it relates to the role of the UPS in myocardial ischemia. Studies have shown that the UPS is dysfunctional during myocardial ischemia, and recent studies have shed some light on possible mechanisms. Other studies have defined a role for the UPS in ischemic preconditioning which is best associated with myocardial ischemia and is thus presented here. Very recent studies have started to define roles for specific proteasome subunits and components of the ubiquitination machinery in various aspects of myocardial ischemia. Lastly, despite the evidence linking myocardial ischemia and proteasome dysfunction, there are continuing suggestions that proteasome inhibitors may be useful to mitigate ischemic injury. This review presents the rationale behind this and discusses both supportive and nonsupportive studies and presents possible future directions that may help in clarifying this controversy.

Resveratrol: French paradox revisited

Resveratrol is a polyphenol that plays a potentially important role in many disorders and has been studied in different diseases. The research on this chemical started through the “French paradox,” which describes improved cardiovascular outcomes despite a high-fat diet in French people. Since then, resveratrol has been broadly studied and shown to have antioxidant, anti-inflammatory, anti-proliferative, and anti-angiogenic effects, with those on oxidative stress possibly being most important and underlying some of the others, but many signaling pathways are among the molecular targets of resveratrol. In concert they may be beneficial in many disorders, particularly in diseases where oxidative stress plays an important role. The main focus of this review will be the pathways affected by resveratrol. Based on these mechanistic considerations, the involvement of resveratrol especially in cardiovascular diseases, cancer, neurodegenerative diseases, and possibly in longevity will be is addressed.

The ubiquitin-proteasome system and cardiovascular disease

Over the past decade, the role of the ubiquitin-proteasome system (UPS) has been the subject of numerous studies to elucidate its role in cardiovascular physiology and pathophysiology. There have been many advances in this field including the use of proteomics to achieve a better understanding of how the cardiac proteasome is regulated. Moreover, improved methods for the assessment of UPS function and the development of genetic models to study the role of the UPS have led to the realization that often the function of this system deviates from the norm in many cardiovascular pathologies. Hence, dysfunction has been described in atherosclerosis, familial cardiac proteinopathies, idiopathic dilated cardiomyopathies, and myocardial ischemia. This has led to numerous studies of the ubiquitin protein (E3) ligases and their roles in cardiac physiology and pathophysiology. This has also led to the controversial proposition of treating atherosclerosis, cardiac hypertrophy, and myocardial ischemia with proteasome inhibitors. Furthering our knowledge of this system may help in the development of new UPS-based therapeutic modalities for mitigation of cardiovascular disease.

Physiological roles of taurine in heart and muscle

Taurine (aminoethane sulfonic acid) is an ubiquitous compound, found in very high concentrations in heart and muscle. Although taurine is classified as an amino acid, it does not participate in peptide bond formation. Nonetheless, the amino group of taurine is involved in a number of important conjugation reactions as well as in the scavenging of hypochlorous acid. Because taurine is a fairly inert compound, it is an ideal modulator of basic processes, such as osmotic pressure, cation homeostasis, enzyme activity, receptor regulation, cell development and cell signalling. The present review discusses several physiological functions of taurine. First, the observation that taurine depletion leads to the development of a cardiomyopathy indicates a role for taurine in the maintenance of normal contractile function. Evidence is provided that this function of taurine is mediated by changes in the activity of key Ca²⁺ transporters and the modulation Ca²⁺ sensitivity of the myofibrils. Second, in some species, taurine is an established osmoregulator, however, in mammalian heart the osmoregulatory function of taurine has recently been questioned. Third, taurine functions as an indirect regulator of oxidative stress. Although this action of taurine has been widely discussed, its mechanism of action is unclear. A potential mechanism for the antioxidant activity of taurine is discussed. Fourth, taurine stabilizes membranes through direct interactions with phospholipids. However, its inhibition of the enzyme, phospholipid N-methyltransferase, alters the phosphatidylcholine and phosphatidylethanolamine content of membranes, which in turn affects the function of key proteins within the membrane. Finally, taurine serves as a modulator of protein kinases and phosphatases within the cardiomyocyte. The mechanism of this action has not been studied. Taurine is a chemically simple compound, but it has profound effects on cells. This has led to the suggestion that taurine is an essential or semi-essential nutrient for many mammals.

The ubiquitin-proteasome system in myocardial ischaemia and preconditioning

The ubiquitin-proteasome system (UPS) represents the major pathway for degradation of intracellular proteins. This article reviews the major components and configurations of the UPS including the 26S proteasome and 11S activated proteasome relevant to myocardial ischaemia. We then present the evidence that the UPS is dysfunctional during myocardial ischaemia as well as potential consequences of this, including dysregulation of target substrates, many of them active signalling proteins, and accumulation of oxidized proteins. As part of this discussion, potential mechanisms, including ATP depletion, inhibition by insoluble protein aggregates, and oxidation of proteasome and regulatory particle subunits, are discussed. Finally, the evidence suggesting a role for the UPS in ischaemic preconditioning is presented. Much of this is inferential but clearly indicates the need for additional research.

Mitochondria protection from hypoxia/reoxygenation injury with mitochondria heat shock protein 70 overexpression

The majority of mitochondrial proteins are encoded by nuclear genes and synthesized in the cytosol as preproteins containing a mitochondria import sequence. Preproteins traverse the outer mitochondrial membrane in an unfolded state and then translocate through the inner membrane into the matrix via import machinery that includes mitochondrial heat shock protein 70 (mtHSP70). Neonatal rat cardiac myocytes (NCM) infected with an adenoviral vector expressing mtHSP70 or an empty control (Adv(-)) for 48 h were submitted to 8 h of simulated ischemia (hypoxia) followed by 16 h of reperfusion (reoxygenation). Infection with mtHSP70 virus yielded an increase in mtHSP70 protein in NCM mitochondria compared with Adv(-) (P < 0.05). Cell viability after simulated ischemia/reperfusion (I/R) was decreased in both Adv(-) and mtHSP70 groups, relative to control (P < 0.05), but mtHSP70-infected NCM had enhanced viability after I/R relative to Adv-infected NCM (P < 0.05). Simulated I/R caused an increase in reactive oxygen species generation and lipid peroxidation in Adv-infected NCM (P < 0.05, for both) that was not observed in mtHSP70-infected NCM. Mitochondrial complex III and IV activities were greater in mtHSP70-infected NCM after simulated I/R compared with Adv(-) (P < 0.05 for both). After simulated I/R, ATP content increased in mtHSP70-infected NCM, compared with Adv(-) (P < 0.05). Apoptotic markers were decreased in mtHSP70-infected NCM compared with Adv(-) after simulated I/R (P < 0.05). These results indicate that overexpression of mtHSP70 protects the mitochondria against damage from simulated I/R that may be due to a decrease in reactive oxygen species leading to preservation of mitochondrial complex function activities and ATP formation.

Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease

Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.

Hypoxia-induced reactive oxygen species formation in skeletal muscle

The existence of hypoxia-induced reactive oxygen species (ROS) production remains controversial. However, numerous observations with a variety of methods and in many cells and tissue types are supportive of this idea. Skeletal muscle appears to behave much like heart in that in the early stages of hypoxia there is a transient elevation in ROS, whereas in chronic exposure to very severe hypoxia there is evidence of ongoing oxidative stress. Important remaining questions that are addressed in this review include the following. Are there levels of PO2 in skeletal muscle, typical of physiological or mildly pathophysiological conditions, that are low enough to induce significant ROS production? Does the ROS associated with muscle contractile activity reflect imbalances in oxygen uptake and demand that drive the cell to a more reduced state? What are the possible molecular mechanisms by which ROS may be elevated in hypoxic skeletal muscle? Is the production of ROS in hypoxia of physiological significance, both with respect to cell signaling pathways promoting cell function and with respect to damaging effects of long-term exposure? Discussion of these and other topics leads to general conclusions that hypoxia-induced ROS may be a normal physiological response to imbalance in oxygen supply and demand or environmental stress and may play a yet undefined role in normal response mechanisms to these stimuli. However, in chronic and extreme hypoxic exposure, muscles may fail to maintain a normal redox homeostasis, resulting in cell injury or dysfunction.

Ischemia-reperfusion leads to depletion of glutathione content and augmentation of malondialdehyde production in the rat heart from overproduction of oxidants: can caffeic acid phenethyl ester (CAPE) protect the heart?

During restoration of blood flow of the ischemic heart induced by coronary occlusion, free radicals cause lipid peroxidation with myocardial injury. Lipid peroxidation end-products, such as malondialdehyde (MDA), have been used to assess oxygen free radical-mediated injury of the ischemic-reperfused (I/R) myocardium in rats. This experimental study assessed the preventive effect of caffeic acid phenthyl ester (CAPE), antioxidant, on I/R-induced lipid peroxidation in the rat heart. We are also interested in the role of CAPE on glutathione (GSH) levels, an antioxidant whose levels are influenced by oxidative stress. I/R leads to the depletion of GSH which is the major intracellular nonprotein sulphydryl and plays an important role in the maintenance of cellular proteins and lipid in their functional state and acts primarily to protect these important structures against the threat of oxidation. In addition, we also examined morphologic changes in the heart by using light microscopy. The left coronary artery was occluded for 30 min and then reperfused for 120 min more before the experiment was terminated. CAPE (50 microM kg(-1)) was administered 10 min prior to ischemia and during occlusion by infusion. At the end of the reperfusion period, rats were sacrificed, and the heart was quickly removed for biochemical determination and histopathological analysis. I/R was accompanied by a significant increase in MDA production and decrease in GSH content in the rat heart. Administration of CAPE reduced MDA production and prevented depletion of GSH content. These beneficial changes in these biochemical parameters were also associated with parallel changes in histopathological appearance. These findings imply that I/R plays a causal role in heart injury due to overproduction of oxygen radicals or insufficient antioxidant and CAPE exert cardioprotective effects probably by the radical scavenging and antioxidant activities.

Reactive oxygen species formation in the transition to hypoxia in skeletal muscle

Many tissues produce reactive oxygen species (ROS) during reoxygenation after hypoxia or ischemia; however, whether ROS are formed during hypoxia is controversial. We tested the hypothesis that ROS are generated in skeletal muscle during exposure to acute hypoxia before reoxygenation. Isolated rat diaphragm strips were loaded with dihydrofluorescein-DA (Hfluor-DA), a probe that is oxidized to fluorescein (Fluor) by intracellular ROS. Changes in fluorescence due to Fluor, NADH, and FAD were measured using a tissue fluorometer. The system had a detection limit of 1 μM H2O2 applied to the muscle superfusate. When the superfusion buffer was changed rapidly from 95% O2 to 0%, 5%, 21%, or 40% O2, transient elevations in Fluor were observed that were proportional to the rise in NADH fluorescence and inversely proportional to the level of O2 exposure. This signal could be inhibited completely with 40 μM ebselen, a glutathione peroxidase mimic. After brief hypoxia exposure (10 min) or exposure to brief periods of H2O2, the fluorescence signal returned to baseline. Furthermore, tissues loaded with the oxidized form of the probe (Fluor-DA) showed a similar pattern of response that could be inhibited with ebselen. These results suggest that Fluor exists in a partially reversible redox state within the tissue. When Hfluor-loaded tissues were contracted with low-frequency twitches, Fluor emission and NADH emission were significantly elevated in a way that resembled the hypoxia-induced signal. We conclude that in the transition to low intracellular Po2, a burst of intracellular ROS is formed that may have functional implications regarding skeletal muscle O2-sensing systems and responses to acute metabolic stress.

Effects of modulation of nitric oxide on rat diaphragm isotonic contractility during hypoxia

Nitric oxide (NO) is essential for optimal myofilament function of the rat diaphragm in vitro during active shortening. Little is known about the role of NO in muscle contraction under hypoxic conditions. Hypoxia might increase the NO synthase (NOS) activity within the rat diaphragm. We hypothesized that NO plays a protective role in isotonic contractile and fatigue properties during hypoxia in vitro. The effects of the NOS inhibitor N(G)-monomethyl-l-arginine (l-NMMA), the NO scavenger hemoglobin, and the NO donor spermine NONOate on shortening velocity, power generation, and isotonic fatigability during hypoxia were evaluated (Po(2) approximately 7 kPa). l-NMMA and hemoglobin slowed the shortening velocity, depressed power generation, and increased isotonic fatigability during hypoxia. The effects of l-NMMA were prevented by coadministration with the NOS substrate l-arginine. Spermine NONOate did not alter isotonic contractile and fatigue properties during hypoxia. These results indicate that endogenous NO is needed for optimal muscle contraction of the rat diaphragm in vitro during hypoxia.

Lipid peroxidation-derived aldehydes and oxidative stress in the failing heart: role of aldose reductase

Lipid peroxidation-derived aldehydes (LP-DA) can propagate oxidative injury and are detoxified by the aldose reductase (AR) enzyme pathway in myocardium. Whether there are alterations in the AR axis in heart failure (HF) is unknown. Sixteen instrumented dogs were studied before and after either 24 h or 4 wk of rapid left ventricular (LV) pacing (early and late HF, respectively). Six unpaced dogs served as controls. In early HF, there was subtle depression of LV performance (maximum rate of LV pressure rise, P < 0.05 vs. baseline) but no chamber enlargement, whereas in late HF there was significant (P < 0.05) contractile depression and LV dilatation. Oxidative stress was increased at both time points, indexed by tissue malondialdehyde, total glutathione, and free C6-C9 LP-DA (P < 0.025 vs. control). AR protein levels and activity decreased progressively during HF (P < 0.025 early/late HF vs. control); however, AR mRNA expression decreased only in late HF (P < 0.005 vs. early HF and control). DNA binding of tonicity-responsive enhancer binding protein (TonEBP, a transcriptional regulator of AR) paralleled AR mRNA, declining >50% in late HF (P < 0.025 vs. control). We conclude that AR levels and attendant myocardial capacity to detoxify LP-DA decline during the development of HF. In early HF, decreased AR occurs due to a translational or posttranslational mechanism, whereas in late HF reduced TonEBP transcriptional activation and AR downregulation contribute significantly. Reduced AR-mediated LP-DA metabolism contributes importantly to LP-DA accumulation in the failing heart and thus may augment chronic oxidative injury.

Free radicals in hypoxic rat diaphragm contractility: no role for xanthine oxidase

Recent evidence indicates that hypoxia enhances the generation of oxidants. Little is known about the role of free radicals in contractility of the rat diaphragm during hypoxia. We hypothesized that antioxidants improve contractility of the hypoxic rat diaphragm and that xanthine oxidase (XO) is an important source of free radicals in the hypoxic diaphragm. The effects of N-acetylcysteine (NAC; 18 mM), Tiron (10 mM), and the XO inhibitor allopurinol (250 microM) were studied on isometric and isotonic force generation during hypoxia (PO(2) approximately 7 kPa). NAC and Tiron decreased maximal force generation, slowed the shortening velocity, and decreased the power output. Fatigue rate was decreased in the presence of either NAC or Tiron. Allopurinol did not alter the contractility or fatigability of the diaphragm. During hyperoxia (PO(2) approximately 85 kPa), neither NAC nor allopurinol affected the contractility or fatigability of the diaphragm. Thus free radicals play a significant role in diaphragm contractility during hypoxia. Whether antioxidants exert a beneficial or harmful effect on muscle performance depends on the contraction pattern of the muscle. Free radicals generated by XO do not play a role in diaphragm contractility during either hypoxia or hyperoxia.

Glutathione supplementation and training increases myocardial resistance to ischemia-reperfusion in vivo

The present study examined the effects of oral reduced glutathione (GSH) supplementation in conjunction with endurance training on contractile function, antioxidant defense, and oxidative damage in response to ischemia-reperfusion (I/R) in rat hearts. Female Sprague-Dawley rats (age 4 mo, n = 72) were randomly assigned to a treadmill-trained (T; 25 m/min, 15% grade, for 75 min/day, 5 days/wk, for 10 wk) or untrained (U) group. Each group was further divided into rats receiving 5 g GSH/kg diet during the final 17 days of training (GSH-S) and control (C) groups. One-half of each group of rats was subjected to I/R by surgical occlusion of the main coronary artery for 45 min, followed by 30-min reperfusion or sham operation. Left ventriclar (LV) peak systolic pressure (LVSP) and contractility (+dP/dt), measured with a catheter inserted into the LV via the carotid artery, decreased with I/R in all groups (P < 0.05). However, LVSP with I/R in the T/GSH-S group was 9.5%, 17%, and 18% higher (P < 0.05) than that in the U/GSH-S, T/C, and U/C groups, respectively. +dP/dt with I/R was 19%, 27%, and 29% (P < 0.05) greater in the T/GSH-S group versus the T/C, U/GSH-S, and U/C groups, respectively. I/R decreased heart GSH content by 12-17% (P < 0.05) and increased oxidized glutathione (GSSG) by 20-27% (P < 0.05). T/GSH-S hearts showed 15% higher GSH (P < 0.05) and a 32% higher GSH-to-GSSG ratio (P < 0.05) than the U/C group at the end of I/R. Myocardial superoxide dismutase, GSH peroxidase, glutathione reductase, and gamma-glutamyl transpeptidase activities were increased with treadmill training in both GSH-S and C rats. I/R induced myocardial lipid peroxidation and lactate dehydrogenase release were attenuated with T/GSH-S treatment. The present data indicate that training in conjunction with dietary GSH supplementation can increase myocardial GSH content and antioxidant defense capacity, thereby protecting the intact heart against oxidative damage and functional retardation caused by I/R.

Invited review: Adaptive responses of skeletal muscle to intermittent hypoxia: the known and the unknown

Intermittent hypoxia (IH) describes conditions of repeated, transient reductions in O2 that may trigger unique adaptations. Rest periods during IH may avoid potentially detrimental effects of long-term O2 deprivation. For skeletal muscle, IH can occur in conditions of obstructive sleep apnea, transient altitude exposures (with or without exercise), intermittent claudication, cardiopulmonary resuscitation, neonatal blood flow obstruction, and diving responses of marine animals. Although it is likely that adaptations in these conditions vary, some patterns emerge. Low levels of hypoxia shift metabolic enzyme activity toward greater aerobic poise; extreme hypoxia shifts metabolism toward greater anaerobic potential. Some conditions of IH may also inhibit lactate release during exercise. Many related cellular phenomena could be involved in the response, including activation of specific O2 sensors, reactive oxygen and nitrogen species, preconditioning, hypoxia-induced transcription factors, regulation of ion channels, and influences of paracrine/hormonal stimuli. The net effect of a variety of adaptive programs to IH may be to preserve contractile function and cell integrity in hypoxia or anoxia, a response that does not always translate into improvements in exercise performance.

Systemic hypoxia increases leukocyte emigration and vascular permeability in conscious rats

We recently observed that acute systemic hypoxia produces rapid increases in leukocyte adherence in the mesenteric microcirculation of the anesthetized rat Wood JG, Johnson JS, Mattioli LF, and Gonzalez NC. J Appl Physiol 87: 1734-1740, 1999; Wood JG, Mattioli LF, and Gonzalez NC. J Appl Physiol 87: 873-881, 1999. Hypoxia-induced leukocyte adherence is associated with an increase in reactive oxygen species (ROS) generation and is attenuated by antioxidants or interventions that increase tissue levels of nitric oxide (NO). These results suggest that the acute effects of hypoxia on leukocyte-endothelial interactions are caused by a change in the ROS-NO balance. The present experiments were designed to extend our observations of the initial microcirculatory response to hypoxia; specifically, we wanted to determine whether the response to systemic hypoxia involves increased microvascular permeability and leukocyte emigration and whether ROS generation and decreased NO levels contribute to these responses. At this time, there is conflicting evidence, from in vitro studies, regarding the effect of hypoxia on these indexes of vascular function. Our studies were carried out in the physiological setting of the conscious animal, in which a prolonged hypoxic exposure is possible without the adverse effects that may develop under anesthesia. The central observation of these studies is that conscious animals exposed for 4 h to environmental hypoxia show increased microvascular permeability and emigration of leukocytes into the extravascular space of the mesenteric circulation. Furthermore, these events are dependent on increased ROS generation and, possibly, a subsequent decrease in tissue NO levels during systemic hypoxia. Our results show that systemic hypoxia profoundly affects vascular endothelial function through changes in the ROS-NO balance in the conscious animal.

Acyloin production from aldehydes in the perfused rat heart: the potential role of pyruvate dehydrogenase

Aldehydes represent an important class of cytotoxic products derived from free radical-induced lipid peroxidation which may contribute to reperfusion injury following myocardial infarct. Metabolism of aldehydes in the heart has not been well characterized aside from conjugation of unsaturated aldehydes with glutathione. However, aliphatic aldehydes like hexanal do not form stable glutathione conjugates. We have recently demonstrated in vitro that pig heart pyruvate dehydrogenase catalyses a reaction between pyruvate and saturated aldehydes to produce acyloins (3-hydroxyalkan-2-ones). In the present study, rat hearts were perfused with various aldehydes and pyruvate. Acyloins were generated from saturated aldehydes (butanal, hexanal or nonanal), but not from 2-hexanal (an unsaturated aldehyde) or malondialdehyde. Hearts perfused with 2 mM pyruvate and 10-100 microM hexanal rapidly took up hexanal in a dose-related manner (140-850 nmol/min), and released 3-hydroxyoctan-2-one (0.7-30 nmol/min), 2,3-octanediol (0-12 nmol/min) and hexanol (10-200 nmol/min). Small quantities of hexanoic acid (about 10 nmol/min) were also released. The rate of release of acyloin metabolites rose with increased concentration of hexanal, whereas hexanol release attained a plateau when hexanal infusion concentrations rose above 50 microM. Up to 50% of hexanal uptake could be accounted for by metabolite release. Less than 0.5% of hexanal uptake was found to be bound to acid-precipitable macromolecules. When hearts perfused with 50 microM hexanal and 2 mM pyruvate were subjected to a 15 min ischaemic period, the rates of release of 2,3-octanediol, 3-hydroxyoctan-2-one, hexanol and hexanoate during the reperfusion period were not significantly different from those in the pre-ischaemic period. Our results indicate that saturated aldehydes can be metabolically converted by the heart into stable diffusible compounds.