Severity of lethal ischemia/reperfusion injury in rat hearts subjected to ischemic preconditioning is increased under conditions of simulated hyperglycemia.

The aim of our study was to characterize resistance to ischemia/reperfusion (I/R) injury in Langendorff-perfused rat hearts and effectivity of ischemic preconditioning (PC) under condition of simulated acute hyperglycemia (SAHG) by perfusion of the hearts with Krebs-Henseleit (KH) solution with elevated glucose concentration (22 mmol/l). I/R injury was induced by 30-min coronary occlusion followed by 120-min reperfusion and PC by two cycles of 5-min occlusion/5-min reperfusion, prior to I/R. The severity of I/R injury was characterized by determination of the size of infarction (IS, expressed in % of area at risk size) and the amount of heart-type fatty acid binding protein (h-FABP, a marker of cell injury) released from the hearts to the effluent. Significantly smaller IS (8.8+/-1 %) and lower total amount of released h-FABP (1808+/-660 pmol) in PC group compared with IS 17.1+/-1.2 % (p<0.01) and amount of h-FABP (8803+/-2415 pmol, p<0.05) in the non-PC control hearts perfused with standard KH solution (glucose 11 mmol/l) confirmed protective effects of PC. In contrast, in SAHG groups, PC enhanced IS (21.4+/-2.2 vs. 14.3+/-1.3 %, p<0.05) and increased total amount of h-FABP (5541+/-229 vs. 3458+/-283 pmol, p<0.05) compared with respective non-PC controls. Results suggest that PC has negative effect on resistance of the hearts to I/R injury under conditions of elevated glucose in vitro.

Upregulation of genes involved in cardiac metabolism enhances myocardial resistance to ischemia/reperfusion in the rat heart.

UNLABELLED: Genes encoding enzymes involved in fatty acids (FA) and glucose oxidation are transcriptionally regulated by peroxisome proliferator-activated receptors (PPAR), members of the nuclear receptor superfamily. Under conditions associated with O(2) deficiency, PPAR-alpha modulates substrate switch (between FA and glucose) aimed at the adequate energy production to maintain basic cardiac function. Both, positive and negative effects of PPAR-alpha activation on myocardial ischemia/reperfusion (I/R) injury have been reported. Moreover, the role of PPAR-mediated metabolic shifts in cardioprotective mechanisms of preconditioning (PC) is relatively less investigated. We explored the effects of PPAR-alpha upregulation mimicking a delayed "second window" of PC on I/R injury in the rat heart and potential downstream mechanisms involved. Pretreatment of rats with PPAR-alpha agonist WY-14643 (WY, 1 mg/kg, i.p.) 24 h prior to I/R reduced post-ischemic stunning, arrhythmias and the extent of lethal injury (infarct size) and apoptosis (caspase-3 expression) in isolated hearts exposed to 30-min global ischemia and 2-h reperfusion. Protection was associated with remarkably increased expression of PPAR-alpha target genes promoting FA utilization (medium-chain acyl-CoA dehydrogenase, pyruvate dehydrogenase kinase-4 and carnitine palmitoyltransferase I) and reduced expression of glucose transporter GLUT-4 responsible for glucose transport and metabolism. In addition, enhanced Akt phosphorylation and protein levels of eNOS, in conjunction with blunting of cardioprotection by NOS inhibitor L-NAME, were observed in the WY-treated hearts. CONCLUSIONS: upregulation of PPAR-alpha target metabolic genes involved in FA oxidation may underlie a delayed phase PC-like protection in the rat heart. Potential non-genomic effects of PPAR-alpha-mediated cardioprotection may involve activation of prosurvival PI3K/Akt pathway and its downstream targets such as eNOS and subsequently reduced apoptosis.

Treatment of rats with hypolipidemic compound pirinixic acid protects their hearts against ischemic injury: are mitochondrial K(ATP) channels and reactive oxygen species involved?

Hypolipidemic compound pirinixic acid (WY-14643, WY) is known to exert pleiotropic (other than primary) effects, such as activation of peroxisome proliferator-activated receptors (PPAR-alpha), transcription factors regulating different cardiac functions. Their role in ischemia-reperfusion (I/R) injury and cardioprotection is less clear, although protective effects of PPAR agonists have been documented. This study was designed to explore the effects of WY on the I/R injury in the rat heart and potential mechanisms involved, including mitochondrial K(ATP) channels (mitoK(ATP)) opening and production of reactive oxygen species (ROS). Langendorff-perfused hearts of rats intragastrally treated with WY (3 mg/kg/day) for 5 days and of control animals were subjected to 30-min global ischemia and 2-h reperfusion with or without 15-min perfusion with mitoK(ATP) blocker 5-hydroxydecanoate (5-HD) prior to I/R. Evaluation of the infarct size (IS, TTC staining) served as the main end-point of protection. Lipid peroxidation (a marker of ROS production) was determined by measurement of myocardial concentration of conjugated dienes (CD), whereas protein expression of endothelial NO synthase was analysed by Western blotting. A 2-fold increase in the cardiac protein levels of eNOS after treatment with WY was accompanied by lower post-I/R levels of CD compared with those in the hearts of untreated controls, although WY itself enhanced ROS generation prior to ischemia. IS was reduced by 47 % in the hearts of WY-treated rats (P<0.05), and this effect was reversed by 5-HD. Results suggest that PPAR-alpha activation may confer protection against lethal I/R injury in the rat heart that involves up-regulation of eNOS, mitoK(ATP) opening and reduced oxidative stress during I/R.

The impact of lifestyle-related risk factors on cardiac response to ischemia and possibilities to restore impaired ischemic tolerance.

Risk factors (RF) of cardiovascular diseases associated with modern lifestyle, such as stress, chronically increased blood pressure, hyperglycemia and dyslipidemia have a negative impact on the heart exposed to ischemia: they may facilitate its lethal injury (myocardial infarction) and occurrence of sudden death due to ventricular arrhythmias. On the other hand, some stressful stimuli related to RF including reactive oxygen species, transient episodes of ischemia (hypoxia), high glucose and other may play a dual role in the pathogenesis of ischemia/reperfusion (I/R) injury (IRI). Besides their deleterious effects, these factors may trigger adaptive processes in the heart resulting in greater resistance against IRI, which is also a characteristic feature of the female myocardium. However, sensitivity to ischemia is increasing with age in both genders. Current research indicates that comorbidity related to lifestyle may impair the cardiac response to acute ischemia not only by interference with pathophysiological mechanisms of IRI per se, but via suppression of intrinsic protective mechanisms in the heart and its ability to tolerate the ischemic challenges, although the role of RF has not been unequivocally proven. Moreover, even pathologically altered myocardium need not completely lose its adaptive potential. In addition, increased ischemic tolerance can be induced by the pleiotropic (independent of the primary) effects of some hypolipidemic and antidiabetic drugs, even in the diseased myocardium. This review addresses the issue of the impact of RF on cellular cardioprotective mechanisms and the possibilities to restore adaptive potential in subjects challenged with several RF. Reactivation of adaptive processes in the myocardium taking into consideration gender and age can contribute to optimalization of antiischemic therapy.

[Presence of cardiovascular risk factors in secondary school students in two Slovak regions]. / Pritomnost' rizikoých faktorov kardiovaskulárnych ochorení u stredoskolskej mládeze v dvoch rôznych regiónoch Slovenska.

The World Health Organization estimates that in 2020 will die of ischemic heart disease (CHD) 11.1 million people in the world, while in 2002 it was 7.22 million, of which in Europe nearly two million. High incidence particularly in developed countries emphasizes mainly on risk factors (RF) of lifestyle. Similar, not good, is the situation in Slovakia. Since the wrong habits, leading to the development of cardiovascular disease (CVD), are created in childhood and young age, we focused on the exploration of risk factors related to the lifestyle of young people in secondary schools in Slovakia (in capital city and regional city with a high proportion of students from rural areas). The survey results clearly confirm the high incidence of many RF in teenage age already, which in future may increase the risk of CVD and other civilization diseases.

Impaired cardiac ischemic tolerance in spontaneously hypertensive rats is attenuated by adaptation to chronic and acute stress.

Chronic hypertension may have a negative impact on the myocardial response to ischemia. On the other hand, intrinsic ischemic tolerance may persist even in the pathologically altered hearts of hypertensive animals, and may be modified by short- or long-term adaptation to different stressful conditions. The effects of long-term limitation of living space (ie, crowding stress [CS]) and brief ischemia-induced stress on cardiac response to ischemia/reperfusion (I/R) injury are not yet fully characterized in hypertensive subjects. The present study was designed to test the influence of chronic and acute stress on the myocardial response to I/R in spontaneously hypertensive rats (SHR) compared with their effects in normotensive counterparts. In both groups, chronic, eight-week CS was induced by caging five rats per cage in cages designed for two rats (200 cm(2)/rat), while controls (C) were housed four to a cage in cages designed for six animals (480 cm(2)/rat). Acute stress was evoked by one cycle of I/R (5 min each, ischemic preconditioning) before sustained I/R in isolated Langendorff-perfused hearts of normotensive and SHR rats. At baseline conditions, the effects of CS were manifested only as a further increase in blood pressure in SHR, and by marked limitation of coronary perfusion in normotensive animals, while no changes in heart mechanical function were observed in any of the groups. Postischemic recovery of contractile function, severity of ventricular arrhythmias and lethal injury (infarction size) were worsened in the hypertrophied hearts of C-SHR compared with normotensive C. However, myo-cardial stunning and reperfusion-induced ventricular arrhythmias were attenuated by CS in SHR, which was different from deterioration of I/R injury in the hearts of normotensive animals. In contrast, ischemic preconditioning conferred an effective protection against I/R in both groups, although the extent of anti-infarct and anti-arrhythmic effects was lower in SHR. Both forms of stress may improve the altered response to ischemia in hypertensive subjects. In contrast to short-term preconditioning stress, chronic psychosocial stress was associated with a higher risk of lethal arrhythmias and contractile failure in normotensive animals exposed to an acute ischemic challenge.

Distinct effects of acute pretreatment with lipophilic and hydrophilic statins on myocardial stunning, arrhythmias and lethal injury in the rat heart subjected to ischemia/reperfusion.

Although both lipophilic and more hydrophilic statins share the same pathway of the inhibition of HMG-CoA reductase, their pleiotropic cardioprotective effects associated with the ability to cross cellular membranes, including membranes of heart cells, may differ. To test this hypothesis, isolated rat hearts were Langendorff-perfused either with simvastatin (S, 10 micromol/l) or pravastatin (P, 30 micromol/l), 15 min prior to ischemia. Control untreated hearts (C) were perfused with perfusion medium only. Postischemic contractile dysfunction, reperfusion-induced ventricular arrhythmias and infarct size were investigated after exposure of the hearts to 30-min global ischemia and 2-h reperfusion. Both lipophilic S and hydrophilic P reduced the severity of ventricular arrhythmias (arrhythmia score) from 4.3 +/- 0.2 in C to 3.0 +/- 0 and 2.7 +/- 0.2 in S and P, respectively, (both P < 0.05), decreased the duration of ventricular tachycardia and suppressed ventricular fibrillation. Likewise, the extent of lethal injury (infarct size) determined by tetrazolium staining and expressed in percentage of risk area, was significantly lower in both treated groups, moreover, the effect of P was more pronounced (27 +/- 2 % and 10 +/- 2 % in S and P groups, respectively, vs. 42 +/- 1 % in C; P < 0.05). In contrast, only S, but not P, was able to improve postischemic recovery of left ventricular developed pressure (LVDP; 48 +/- 12 % of preischemic values vs. 25 +/- 4 % in C and 21 +/ -7 % in P groups; P < 0.05). Our results suggest that differences in water solubility of statins indicating a different ability to cross cardiac membranes may underlie their distinct cardioprotective effects on myocardial stunning and lethal injury induced by ischemia/reperfusion.

Subcellular mechanisms of adaptation in the diabetic myocardium: Relevance to ischemic preconditioning in the nondiseased heart.

Although hyperglycemia is one factor that determines the outcome of myocardial ischemic insult, it is still not clear whether it is causally related to decreased ischemic tolerance in diabetic patients. In contrast to clinical and epidemiological studies demonstrating a higher risk of cardiovascular disorders in diabetic patients, experimental data are not unequivocal and suggest that, aside from higher myocardial vulnerability, diabetes mellitus may be associated with the triggering of adaptive processes leading to paradoxically lower susceptibility to ischemia. It has been proposed that this phenomenon shares some molecular pathways with short-term preconditioning and other forms of endogenous protection against ischemia/reperfusion injury in the nondiseased heart. The present article reviews some controversial findings of enhanced resistance to ischemia in the diabetic heart that stem from experimental studies in different models of myocardial ischemia/reperfusion injury. Specifically, it addresses the issue of potential mechanisms of increased resistance to ischemia in an experimental model of streptozotocin-induced diabetes, particularly with respect to the role of reactive oxygen species, hyperglycemia as one of the stress factors, and cell-signalling mechanisms mediated by 'prosurvival' cascades of protein kinases in relation to the mechanisms of classical ischemic preconditioning. Finally, mechanisms involved in the suppression of protection in the diabetic myocardium including the effect of concomitant pathology, such as hypercholesterolemia, are discussed.