Peeter Tähepôld

Pretreating rats with hyperoxia attenuates ischemia-reperfusion injury of the heart.

Oxidative stress may precondition the heart. The present study investigated whether hyperoxia elicits a preconditioning-like response. Rats were kept in a hyperoxic (>95% O2) environment for 60 or 180 minutes. Hearts were Langendorff-perfused immediately or 24 hours after hyperoxia, and exposed to 25 minutes of global ischemia and 60 minutes of reperfusion. Whole blood was sampled after 60 and 180 minutes of hyperoxia for oxidative stress markers. Hearts were sampled immediately or 24 hours after hyperoxia for measurement of antioxidants, lipid peroxidation products, heat shock protein 72 and endothelial nitric oxide synthase. At the end of reperfusion after 1 h hyperoxia, infarct size was determined by tetrazolium staining. Hyperoxia increased serum levels of conjugated dienes, reduced serum antioxidative protection, reduced reperfusion arrhythmias in most groups, and improved myocardial function. Infarct size was reduced from 45% of myocardial tissue in controls to 22% in treated animals. The myocardial activity of antioxidant enzymes, content of heat shock protein 72, and endothelial nitric oxide synthase in myocardial tissue were not influenced. In conclusion, hyperoxia induces a low-graded systemic oxidative stress, improves postischemic cardiac function and reduces infarct size. The mediators of protection remain to be determined.

Cardioprotection by breathing hyperoxic gas—relation to oxygen concentration and exposure time in rats and mice

OBJECTIVES Breathing a hyperoxic gas (> or =95% O(2)) protects against ischaemia-reperfusion injury in rat and mouse hearts. The present study investigated how oxygen concentration and duration of hyperoxic exposure influenced cardioprotection, and whether hyperoxia might induce delayed cardioprotection (after 24 h). METHODS Animals were kept in normal air or in a hyperoxic environment, and their hearts were isolated and Langendorff-perfused immediately or 24 h thereafter. Global ischaemia was induced for 25 min in rats and 40 min in mice, followed by 60 min of reperfusion. Infarct size was determined by triphenyl tetrazolium chloride staining. RESULTS In rats exposure to > or =95, 80, and 60%, but not to 40% of oxygen immediately before heart isolation and perfusion improved postischaemic functional recovery. Eighty or more percent of oxygen also reduced infarct size. A preconditioning-like effect could be evoked by 60 or 180 min of hyperoxia, giving both immediate and delayed protection. In the mouse heart protection could be induced by pretreatment for 15 or 30, but not by 60 min with > or =95% oxygen. The protective effect of hyperoxia in mice could be evoked in the immediate model only. CONCLUSIONS Hyperoxia protects the isolated rat and mouse heart against ischaemia-reperfusion injury, but some species-different responses exist. The protection depends on both oxygen concentration in inspired air, and duration of hyperoxic exposure.

Preconditioning protects the severely atherosclerotic mouse heart

BACKGROUND Coronary atherosclerosis has profound effects on vascular and myocardial biology, and it has been speculated that the atherosclerotic heart does not benefit from ischemic preconditioning. METHODS To investigate if atherosclerosis would influence the preconditioning response, Apolipoprotein E/low density lipoprotein (LDL) receptor double knockout mice (ApoE/LDLr-/-) were fed an atherogenic diet (21% fat, 0.15% cholesterol) for 6 to 8 months. At that time, extensive atherosclerotic lesions throughout the coronary tree were seen in transverse sections stained with Oil Red-O. Hearts of ApoE/LDLr-/- mice were Langendorff-perfused with 40 minutes of global ischemia and 60 minutes reperfusion, and compared with C57BL/6 controls. Preconditioning with two episodes of 2 minutes of ischemia and 5 minutes reperfusion, or exposing the mice to a hyperoxic environment (O2 > 98%) for 60 minutes before heart perfusion, was performed. RESULTS Hearts of mice with coronary atherosclerosis had worse postischemic function, and increased infarct size and troponin T release compared to hearts of C57BL/6 mice. Ischemic preconditioning improved postischemic ventricular function, and reduced myocardial infarct size and troponin T release in both normal and ApoE/LDLr-/- mice. The effects were most pronounced in ApoE/LDLr-/- hearts. Exposure to hyperoxia exerted a similar protection of function and cell viability of ApoE/LDLr-/- mice hearts. CONCLUSIONS These findings suggest that the severely atherosclerotic heart may be protected by preconditioning induced by ischemia or hyperoxia.

Pretreatment with methylprednisolone protects the isolated rat heart against ischaemic and oxidative damage

Methylprednisolone (MP), a synthetic glucocorticoid, is widely used clinically and experimentally as acute antiinflammatory treatment. The molecular actions of MP indicate that pretreatment with this drug may be cardioprotective. We investigated if giving rats MP prior to excising their hearts for Langendorff-perfusion protected cardiac function against oxidative stress, and if this was mediated by increasing antioxidant defence or influencing myocardial nitric oxide synthase (NOS). Rats (n=6–11 in each group) were injected with MP (40 mg/kg i.m.) or vehicle 24 and 12 h before Langendorff-perfusion with 30 min global ischaemia and 60 min reperfusion, or 10 min perfusion with 180 μmol/L hydrogen peroxide. Other hearts were exposed to 30 min global ischaemia 5 days after MP-injection. Additional hearts were sampled before, during, and after ischaemia for analyzing tissue activity of antioxidant enzymes. Tissue endothelial and inducible NOS (eNOS and iNOS) were investigated by immunoblotting and semiquantitative RT-PCR in a time-course after MP injection. Pretreatment with MP improved left ventricular function and increased coronary flow during postischaemic reperfusion, and this effect was sustained 5 days afterwards. When exposing hearts to hydrogen peroxide, MP improved coronary flow. Catalase, glutathione peroxidase, and oxidized glutathione were increased during reperfusion of MP-treated hearts compared to vehicle only. MP did not influence eNOS at protein or mRNA level. iNOS could not be detected by immunoblotting, indicating low cardiac enzyme content. Its mRNA initially increased the first hour after injection, thereafter decreased. In conclusions, pretreating rats with MP protects the heart against ischaemia-reperfusion dysfunction. This effect could be due to increase of tissue antioxidant activity during reperfusion. MP did not influence cardiac eNOS. mRNA for iNOS was influenced by MP, but the corresponding protein could not be detected.

Off-Pump Coronary Surgery causes Immediate Release of Myocardial Damage Markers

Off-pump coronary surgery does not eliminate the risks of ischemia-reperfusion injury. The main objective of this study was to describe the extent and time course of changes in myocardial metabolism and development of myocardial injury associated with revascularization. Coronary sinus and arterial blood samples for measurement of troponin I, creatine kinase MB, lactate, glutathione, and interleukin-6 were taken from 23 patients prior to grafting, after completion of each anastomosis, and up to the 1st postoperative morning. The results were evaluated together with parameters of cardiac function. Release of lactate, creatinine kinase MB, and troponin I into the coronary sinus was evident after completion of the 1st graft, and increased over time. During the procedure, only trace amounts of oxidized and reduced glutathione were detected in coronary sinus and arterial blood. Significant increases in interleukin-6 were found in coronary sinus samples after 5 and 20 min of reperfusion. Surgical trauma during off-pump coronary surgery is sufficient to activate an inflammatory response in the myocardium, together with unfavorable metabolic conditions to cause myocardial necrosis.

Effects of 60 minutes of hyperoxia followed by normoxia before coronary artery bypass grafting on the inflammatory response profile and myocardial injury

BackgroundIschemic preconditioning induces tolerance against ischemia-reperfusion injury prior a sustained ischemic insult. In experimental studies, exposure to hyperoxia for a limited time before ischemia induces a low-grade systemic oxidative stress and evokes an (ischemic) preconditioning-like effect of the myocardium. We hypothesised that pre-treatment by hyperoxia favours enchanced myocardial protection described by decreased release of cTn T in the 1st postoperative morning and reduces the release of inflammatory cytokines.MethodsForty patients with stable coronary artery disease underwent coronary artery bypass grafting with cardiopulmonary bypass. They were ventilated with 40 or >96% oxygen for 60 minutes followed by by 33 (18–59) min normoxia before cardioplegia.ResultsIn the 1st postoperative morning concentrations of cTnT did not differ between groups ((0.44 (0.26-0.55) ng/mL in control and 0.45 (0.37-0.71) ng/mL in hyperoxia group). Sixty minutes after declamping the aorta, ratios of IL-10/IL-6 (0.73 in controls and 1.47 in hyperoxia, p = 0.03) and IL-10/TNF-α (2.91 and 8.81, resp., p = 0.015) were significantly drifted towards anti-inflammatory, whereas interleukins 6, 8and TNF-α and interferon-γ showed marked postoperative rise, but no intergroup differences were found.ConclusionsPre-treatment by 60 minutes of hyperoxia did not reduce postoperative leak of cTn T in patients undergoing coronary artery bypass surgery. In the hyperoxia group higher release of anti-inflammatory IL-10 caused drifting of IL-10/IL-6 and IL-10/TNF-α towards anti-inflammatory.

A comparison of differential oscillometric device with invasive mean arterial blood pressure monitoring in intensive care patients

Non‐invasive beat‐to‐beat mean arterial pressure (MAP) in finger arteries recorded by the differential oscillometric device was compared with MAP recorded invasively from A. radialis in 22 patients after cardiac surgery. Based on all 132 paired measurements, the MAP values measured at the radial artery were 2.7 ± 4.9 mmHg higher than those measured on fingers. Among 22 patients there were 8 patients receiving inotropic support, their difference being 2.1 ± 5.6 mmHg. The present study revealed that the mean discrepancy between the invasive radial pressure and finger pressure was small; however, patient data sets showed marked variability in average pressure differences when examined individually.

Pretreatment by Hyperoxia - A Tool to Reduce Ischaemia-Reperfusion Injury in the Myocardium

Atherosclerosis leads to narrowing and occlusion of coronary arteries, resulting in inadequate oxygen supply for maintenance of normal oxidative metabolism. To avoid profound ischaemia and subsequent necrosis of cardiomyocytes, blood flow has to be restored by means of thrombolysis, percutaneous coronary intervention, or surgical revascularisation. Besides restoring oxygen supply to the cells, introduction of molecular oxygen to the ischaemic tissue results in a spectrum of unfavourable events, termed altogether as reperfusion injury. Exposure to hyperoxia for a limited time before ischaemia induces a low-grade oxidative stress and evokes an (ischaemic) preconditioning-like effect in the myocardium, which protects the heart from subsequent injury. This review addresses the effects of pretreatment by hyperoxia both in experimental and clinical setting.

Adaptation to Ischemia by in vivo Exposure to Hyperoxia—Signalling through Mitogen Activated Protein Kinases and Nuclear Factor Kappa B

We have established a model of adaptation to ischemia by breathing a hyperoxic gas mixture, which may be directly employed in clinical practice. Hyperoxia improves postischemic function and reduces myocardial necrosis in globally and regionally ischemic rat and mouse hearts, protects hearts of animals with severe atherosclerosis, and modulates in vitro reactivity of isolated aortic rings. Hyperoxic preconditioning is most efficient when the inspired oxygen fraction is >80% oxygen, with different exposure times in rats and mice. In rats the protection is both immediate and delayed, while in mice only immediate protection can be evoked. Exposure to hyperoxia causes an oxidative stress evident as increased serum lipid peroxidation products and reduced antioxidant defence. When breathing hyperoxic gas a rapid nuclear translocation of nuclear factor kappa B (NFκB) in the lungs is followed by a cardiac NFκB activation. In conjunction with hyperoxia the mitogen activated protein kinases (MAPK) p38, ERK1/2, and JNK are phosphorylated in the heart. Pharmacological inhibition of NFκB activation abolished the beneficial effects of hyperoxia. During Langendorff-perfusion with induced global ischemia, phosphorylation of MAPK as well as translocation of NFκB is reduced in animals subjected to hyperoxia prior to the experiments, the latter perhaps due to increased formation of the NFκB inhibitor IkBα. A posssible role for the NFκB-regulated gene inducible nitric oxide synthase (iNOS) in the hyperoxia response was investigated in knock out mice, who had no functional or antiinfarct protection of preconditioning by either hyperoxia or classic ischemic preconditioning. However, neither cardiac iNOS nor contents of antioxidants, heat shock protein 70, or endothelial NOS in the heart increased after hyperoxia. Thus, the signal transduction pathways and organ effectors of hyperoxic protection are not fully determined, but appear to involve MAPK and NFκB. Hyperoxia may have a large potential in the pretreatment of patients undergoing not only open heart procedures, but also in front of any major surgery.

Hüperoksia – kas uus võimalus südamelihase kaitseks?

Aeroobsetele organismidele on hapnik elutahtis ja hapniku defitsiit viib organismi kahjustusele. Nii sudamelihase isheemia reperfusioonikahjustuse kui ka isheemilise eelkohastumuse patofusioloogias mangivad olulist osa hapniku reaktiivsed osakesed. Hapniku korge osarohk ja kestev ekspositsioon voivad pohjustada hapniku reaktiivsete osakeste kestva liigproduktsiooni, mis uletab organismi antioksudantse kaitsevoime ja kutsub esile kahjustava oksudatiivse stressi. Samas on hapniku reaktiivsetel osakestel oluline fusioloogiline roll rakkude signaalmolekulidena, mis osalevad rakusiseste adaptatsioonimehhanismide aktivatsioonil. Eesti Arst 2003; 82 (1): 22–28