Stéphane Tanguy

Trace elements and cardioprotection: increasing endogenous glutathione peroxidase activity by oral selenium supplementation in rats limits reperfusion-induced arrhythmias.

Oxyradicals have been implicated as a possible cause of reperfusion-arrhythmias (RA). However, the use of diverse exogenous oxyradical scavengers designed to reduce RA has given contradictory results. The aim of the present study was to determine whether enhancing the activity of the main endogenous enzyme involved in peroxide elimination in cardiac cells, namely glutathione peroxidase, may limit RA in isolated heart preparations by increasing their antioxidant status. For this purpose, a group of 15 male Wistar rats received a selenium enriched diet for ten weeks (1.5 mg Se/kg diet). Control animals (n = 15) received a standard diet containing 0.05 mg Se/kg diet. The incidence of early ventricular arrhythmias was investigated during the reperfusion period following 10 min regional ischemia induced ex-vivo by left coronary artery ligation. Our results show that selenium-supplementation significantly increased the global selenium status of the animals. In the isolated heart preparations, the selenium supplementation induced a significant reduction of the severity of RA as assessed by the arrhythmia score and the limitation of the incidence of both ventricular tachycardia (control: 91% vs selenium: 36%, p < 0.05) and irreversible ventricular fibrillation (control: 45% vs selenium: 0%, p < 0.05). These effects were associated with a significant increase in cardiac mitochondrial and cytosolic glutathione peroxidase activities in both the left and the right ventricles. These results illustrate the potential protective effect of selenium against ischemia-reperfusion injury and suggest that peroxides might play a key role in the genesis of some aspects of the reperfusion syndrome.

Impact of dietary selenium intake on cardiac health: Experimental approaches and human studies

Selenium, a dietary trace mineral, essential for humans and animals, exerts its effects mainly through its incorporation into selenoproteins. Adequate selenium intake is needed to maximize the activity of selenoproteins, among which glutathione peroxidases have been shown to play a major role in cellular defense against oxidative stress initiated by excess reactive oxygen species. In humans, a low selenium status has been linked to increased risk of various diseases, including heart disease. The main objective of this review is to present current knowledge on the role of selenium in cardiac health. Experimental studies have shown that selenium may exert protective effects on cardiac tissue in animal models involving oxidative stress. Because of the narrow safety margin of this mineral, most interventional studies in humans have reported inconsistent findings. Major determinants of selenium status in humans are not well understood and several nondietary factors might be associated with reduced selenium status. In this review, we discuss recent studies regarding the role of selenoproteins in the cardiovascular system, the effect of dietary intake on selenium status, the impact of selenium status on cardiac health, and the cellular mechanisms that can be involved in the physiological and toxic effects of selenium.

Diet Modulates Endogenous Thrombin Generation, A Biological Estimate of Thrombosis Risk, Independently of the Metabolic Status

Objective—High endogenous thrombin potential (ETP) is associated with venous and arterial thrombosis. Better knowledge of environmental influences on ETP may help to prevent thrombosis. Methods and Results—Weaning rats exhibited high ETP values that decreased in low-fat diet and remained elevated on high-fat diet. In adult rats, high-fat diet–induced ETP increase was independent of coagulation factors, obesity, and insulin resistance and negatively associated with polyunsaturated fatty acid levels. Switching from high-fat diet to low-fat diet reversed the procoagulant phenotype with a slower kinetic than the normalization of hyperinsulinemia. In humans, ETP was independent of body weight whereas it was negatively associated with nutritional markers such as the percentage of energy provided by proteins, the protein:fat ratio, circulating phenolic compounds, and omega-3 polyunsaturated fatty acid. A recommended 3-month healthy diet with reduced energy density, including lipids, decreased ETP (−21%; P<0.0001). Changes in ETP were not associated with body weight, insulin sensitivity, or coagulation factor variations, but correlated negatively with plasma docosahexaenoic acid, a nutritional status sensitive fatty acid, and compounds reflecting vegetable intake. Conclusion—Diet plays a pivotal role in regulating ETP, independently of obesity and insulin resistance. Global nutritional recommendations could be useful in primary prevention of venous thrombosis.

Aortic vasoreactivity during prolonged hypoxia and hypoxia-reoxygenation in senescent rats

To determine the effects of prolonged hypoxia and hypoxia-reoxygenation in senescent blood vessels, isolated aortic rings from 4- and 24-month-old (mo) Wistar rats were submitted to prolonged hypoxia (50 min) or hypoxia/reoxygenation (20 min/30 min) and contractile function recorded. Phenylephrine-induced contraction and sodium nitroprusside- and acetylcholine-induced relaxations were measured after hypoxia or after hypoxia/reoxygenation. In 24 mo group, prolonged hypoxia increased (+83%, P<0.01) and prolonged initial hypoxic contraction, while hypoxic relaxation and delayed contraction were unchanged. Relaxation to acetylcholine was more reduced than in 4 mo group while contraction to phenylephrine and relaxation to sodium nitroprusside were similarly impaired. During reoxygenation, contraction was of same amplitude at both ages and the relaxation to acetylcholine was impaired but to a similar extent in both groups. In conclusion, hypoxic stress induces a greater endothelium-injury in senescent aorta, and increased transient hypoxic contraction, without aggravation of late hypoxic contraction. Aging does not exacerbate the impairment of aortic vasoreactivity after hypoxia-reoxygenation, especially endothelium-dependent relaxation, in sharp contrast to prolonged hypoxia. These age-related changes in vascular sensitivity to oxygen deprivation are different from those observed in coronary arteries, indicating that vasoreactivity during such pathological stress strongly depends on the type of vessel, especially during aging.

Deep Hypothermic Cardiac Arrest Treated by Extracorporeal Life Support in a Porcine Model: Does the Rewarming Method Matter?

OBJECTIVESnExtracorporeal life support (ECLS) is the reference rewarming technique of accidental deep hypothermic cardiac arrest (DHCA). This study was designed to examine the impact of different rewarming blood flow rates and temperature setting of ECLS on cardiopulmonary lesions after DHCA in a porcine model of accidental hypothermia.nnnMETHODSnTwenty-four pigs were cannulated for ECLS, cooled until DHCA occurred, and subjected to 30 minutes of cardiac arrest. During the rewarming phase, we compared a low blood flow rate of 1.5 L/min versus a high flow rate of 3.0 L/min as well as two-temperature-setting rewarming strategies: a temperature during ECLS adjusted to 5°C above the central core temperature versus 38°C maintained throughout the rewarming phase. Cardiac output, hemodynamics and pulmonary function parameters were evaluated. Biologic markers of ischemia-reperfusion injuries were analyzed at baseline and at the end of the experiment.nnnRESULTSnDHCA occurred at 21.2 ± 2°C. There was a trend for better cardiac output in groups with high blood flow (p = 0.053), with no interaction between ECLS flow and temperature (p = 0.63), a trend toward lower pulmonary vascular resistance (PVR; p = 0.075) and a significant decrease in arterial PVR in groups with high blood flow (p = 0.013) with no interaction (p = 0.47 and p = 0.60 for PVR and arterial PVR, respectively). Serum interleukin-6, tumor necrosis factor-α, receptor for advanced glycation end products (RAGE), and neuron-specific enolase were significantly increased between baseline and endpoint. The increase in the serum RAGE concentration was higher in the 38°C rewarming temperature groups compared to 5°C above adjusted temperature. There were no other significant differences in biomarkers.nnnCONCLUSIONSnWe developed a porcine model of DHCA treated by ECLS. Our data suggest that cardiac output tended to improve with a high-flow-rate rewarming strategy while a high-temperature delta between core temperature and ECLS increased the RAGE markers of lung injury.

The impact of cardiac ischemia/reperfusion on the mitochondria–cytoskeleton interactions

Cardiac ischemia-reperfusion (IR) injury compromises mitochondrial oxidative phosphorylation (OxPhos) and compartmentalized intracellular energy transfer via the phosphocreatine/creatine kinase (CK) network. The restriction of ATP/ADP diffusion at the level of the mitochondrial outer membrane (MOM) is an essential element of compartmentalized energy transfer. In adult cardiomyocytes, the MOM permeability to ADP is regulated by the interaction of voltage-dependent anion channel with cytoskeletal proteins, particularly with β tubulin II. The IR-injury alters the expression and the intracellular arrangement of cytoskeletal proteins. The objective of the present study was to investigate the impact of IR on the intracellular arrangement of β tubulin II and its effect on the regulation of mitochondrial respiration. Perfused rat hearts were subjected to total ischemia (for 20min (I20) and 45min (I45)) or to ischemia followed by 30min of reperfusion (I20R and I45R groups). High resolution respirometry and fluorescent confocal microscopy were used to study respiration, β tubulin II and mitochondrial arrangements in cardiac fibers. The results of these experiments evidence a heterogeneous response of mitochondria to IR-induced damage. Moreover, the intracellular rearrangement of β tubulin II, which in the control group colocalized with mitochondria, was associated with increased apparent affinity of OxPhos for ADP, decreased regulation of respiration by creatine without altering mitochondrial CK activity and the ratio between octameric to dimeric isoenzymes. The results of this study allow us to highlight changes of mitochondrial interactions with cytoskeleton as one of the possible mechanisms underlying cardiac IR injury.

Cardiopulmonary responses during the cooling and the extracorporeal life support rewarming phases in a porcine model of accidental deep hypothermic cardiac arrest.

BackgroundThis study aimed to assess cardiac and pulmonary pathophysiological responses during cooling and extracorporeal life support (ECLS) rewarming in a porcine model of deep hypothermic cardiac arrest (DHCA). In addition, we evaluated whether providing a lower flow rate of ECLS during the rewarming phase might attenuate cardiopulmonary injuries.MethodsTwenty pigs were cannulated for ECLS, cooled until DHCA occurred and subjected to 30xa0min of cardiac arrest. In order to assess the physiological impact of ECLS on cardiac output we measured flow in the pulmonary artery using Doppler echocardiography as well as a modified thermodilution technique using the Swan-Ganz catheter (injection site in the right ventricle). The animals were randomized into two groups during rewarming: a group with a low blood flow rate of 1.5xa0L/min (LF group) and a group with a normal flow rate of 3.0xa0L/min (NF group). The ECLS temperature was adjusted to 5xa0°C above the central core. Cardiac output, hemodynamics and pulmonary function parameters were evaluated.ResultsDuring the cooling phase, cardiac output, heart rhythm and blood pressure decreased continuously. Pulmonary artery pressure tended to increase at 32xa0°C compared to the initial value (20.2u2009±u20091.7xa0mmHg vs. 29.1u2009±u20095.6xa0mmHg, pu2009=u20090.09). During rewarming, arterial blood pressure was higher in the NF than in the LF group at 20° and 25xa0°C (pu2009=u20090.003 and 0.05, respectively). After rewarming to 35xa0°C, cardiac output was 3.9u2009±u20090.5xa0L/min in the NF group vs. 2.7u2009±u20090.5xa0L/min in LF group (pu2009=u20090.06). At the end of rewarming under ECLS cardiac output was inversely proportional to the ECLS flow rate. Moreover, the ECLS flow rate did not significantly change pulmonary vascular resistance.DiscussionUsing a newly developed experimental model of DHCA treated by ECLS, we assessed the cardiac and pulmonary pathophysiological response during the cooling phase and the ECLS rewarming phase. Despite lower metabolic need during hypothermia, a low ECLS blood flow rate during rewarming did not improved cardiopulmonary injuries after rewarming.ConclusionA low ECLS flow rate during the rewarming phase did not attenuate pulmonary lesions, increased blood lactate level and tended to decrease cardiac output after rewarming. A normal ECLS flow rate did not increase pulmonary vascular resistance compared to a low flow rate. This experimental model on pigs contributes a number of pathophysiological findings relevant to the rewarming strategy for patients who have undergone accidental DHCA.

PO5 L’alimentation, un moyen pour moduler la génération de thrombine, étape clé du phénomène de thrombose

Objectif Lassociation entre lobesite et la pathologie thrombotique est partiellement expliquee par un etat dhypercoagulabilite dont les determinants meritent detre mieux caracterises. Dans ce but nous avons mesure leffet de modifications de lalimentation sur la generation de thrombine (GT), enzyme cle de la thrombose, dune part chez le rat atteint ou non de syndrome metabolique (SM) et dautre part dans une population a risque cardiovasculaire modere. Patients et methodes Animaux : 170 rats±SM (Boullu-Ciocca S, et al. 2008), ont recu une alimentation standard (STD) ou riche en graisses (HFD, saindoux) ± agoniste du recepteur au GLP-1 : Byetta). Patients (cohorte Medi-RIVAGE) : 65 individus ont suivi pendant 3 mois un regime mediterraneen ou issu des recommandations de lAmerican Heart Association. Resultats Chez le rat, 4 semaines apres le sevrage, le STD diminue significativement la GT, contrairement au HFD qui la maintient elevee. A lâge adulte (16 semaines) lHFD augmente la GT, independamment du SM, du poids, de lintolerance au glucose et de linsulino-resistance. La GT est correlee au poids du foie, aux concentrations circulantes de triglycerides et de cholesterol et faiblement aux taux de facteur VII. Apres larret du HFD, 4 semaines suffisent pour normaliser la GT, independamment du poids et des parametres metaboliques. Le Byetta diminue le poids, ameliore letat metabolique sans modifier la GT. Chez lhomme, la GT est, comme attendu, associee aux taux de facteurs de lhemostase mais egalement, et de maniere independante, a des marqueurs nutritionnels. Le suivi des recommandations nutritionnelles diminue significativement la GT (21 %). Cette reduction nest associee ni a celles des facteurs hemostatiques ni au SM mais a celles de marqueurs nutritionnels. Conclusion Les recommandations alimentaires (diminutions de lapport en graisses saturees) diminuent significativement la GT independamment de lobesite et linsulino-resistance. Lintervention nutritionnelle est a considerer dans la prise en charge du risque thrombotique.

OP6: Endothelium-independent vascular reactivity in high-fat diet-fed rats: role of vascular wall and perivascular adipose tissue oxidative stress

Background and aims visceral obesity is a risk factor for cardiovascular diseases. Perivascular adipose tissue (PVAT) is a visceral fat depot close to the vessel wall which therefore could directly influence vascular reactivity. Diet-induced alterations in endothelium-dependent vascular reactivity have been well investigated. Diet-induced changes in endothelium-independent vascular reactivity have received less attention. Material and Methods we studied in 5-month-old rats fed low-fat (LFD) or high-fat diet (HFD) from weaning vascular reactivity using phenylephrine (PE)-stimulated isolated endothelium-removed aortic rings without or with their PVAT (PVAT - or PVAT +, respectively), Results HFD induced an increase in mesenteric and PVAT fat mass, and enhanced systemic and mesenteric AT Tbars while it decreased aortic and PVAT Tbars. When PVAT - rings were incubated with increasing doses of PE, maximal contraction and EC50 were not different between groups. The presence of PVAT decreased the maximal contraction to the same extent in rings obtained from LFD- or HFD-fed rats. Incubation with catalase suppressed the anticontractile properties of PVAT, indicating that this effect was mediated through H2O2. Transfer experiments of PVAT conditioned medium demonstrated that PVAT was the site of H2O2 synthesis. In LFD PVAT- rings, oxidative stress-associated procontractile activity was generated by xanthine oxidase and cytochrome c oxidase. In HFD PVAT- rings oxidative stress-associated procontractile activity increased and was generated, in addition to the above-mentioned enzymes, by NADPH oxidase. Catalase-induced H2O2 dismutation had prorelaxing properties, comparable in rings obtained from LFD or HFD fed rats. Superoxide dismutase (SOD) was devoid of effect in LFD rings, whereas it had a prorelaxing activity in HFD rings. These observations suggest that, in addition to H2O2, O2.- has a procontractile activity in the aortic wall of HFD rats. In aorta HFD increased the mRNAs coding for NADPH oxidase (p47 phox, p67phox, and NOX4), xanthine oxidase, SOD and catalase, suggesting an increased dismutation activity. PVAT modified the effect of the various drugs tested. The increased anticontractile activity of PVAT found after reactive oxygen species scavenging was reduced in HFD fed rats compared with LFD fed animals. Inhibition of O2.- dismutation resulting from DETC-induced SOD blocking led to a procontractile effect of PVAT in both groups, this effect being reduced in HFD compared to LFD rats. NADPH blockade did not affect the anticontractile properties of PVAT in both groups. Xanthine oxidase blockade amplified the anticontractile effect of PVAT in LFD animals while it reversed this effect in HFD rats. In rings obtained from LFD animals cytochrome c oxidase blockade reversed the anticontractile effect of PVAT in LFD animals whereas it was devoid of effect in HFD rats. In PVAT, HFD increased the mRNAs coding for cytochrome c oxidase, glutathione peroxidase and UCP-1 and -3. Conclusion our data show that HFD-induced obesity was associated with NADPH-dependent increased oxidative stress-associated procontractile activity in the aortic wall. Such phenomenon was counteracted by enhanced dismutation activity in the aortic wall and decreased procontractile activity provided by the PVAT. As a consequence, these observations predict that any defect in the above-mentioned counterregulatory mechanisms can have deleterious functional consequences.

OP9: Diet modulates endogenous thrombin generation, a biological estimate of thrombosis risk, independently of the metabolic status

Background and aims The association between obesity and thrombosis might be explained by a hypercoagulable state. In addition, it is still discussed controversially whether obesity, fat diet or metabolic disturbances are the main influence factors of the changes in the coagulation system. Methods and Results In this study, we investigated the effect of postnatal overfeeding and high fat diet (HFD) on thrombin generation. Endogenous Thrombin potential (ETP) was measured using the Calibrated Automated Thrombogram. Weaning rats exhibited high ETP values that decreased under low-fat diet (LFD) and remained elevated upon HFD. In adult rats, HFD-induced ETP increase was independent of coagulation factors, obesity and insulin resistance and negatively associated with polyunsaturated fatty acid (PUFA) levels. Switching from HFD to LFD reversed the procoagulant phenotype with a slower kinetic than the normalization of hyperinsulinemia. In humans, ETP was independent of body weight while it was negatively associated with nutritional markers such as the percentage of energy provided by proteins, the protein/fat ratio, and circulating phenolic compounds and omega-3 PUFA. A recommended 3-month healthy diet with reduced energy density, including lipids, decreased ETP (−21%; P Conclusion Diet plays a pivotal role in regulating ETP, independently of obesity and insulin resistance. Global nutritional recommendations could be useful in primary prevention of thrombosis.