Prevention of tick-borne diseases: challenge to recent medicine.

Abstract: Ticks represent important vectors and reservoirs of pathogens, causing a number of diseases in humans and animals, and significant damage to livestock every year. Modern research into protection against ticks and tick-borne diseases focuses mainly on the feeding stage, i.e. the period when ticks take their blood meal from their hosts during which pathogens are transmitted. Physiological functions in ticks, such as food intake, saliva production, reproduction, development, and others are under control of neuropeptides and peptide hormones which may be involved in pathogen transmission that cause Lyme borreliosis or tick-borne encephalitis. According to current knowledge, ticks are not reservoirs or vectors for the spread of COVID-19 disease. The search for new vaccination methods to protect against ticks and their transmissible pathogens is a challenge for current science in view of global changes, including the increasing migration of the human population. Highlights: • Tick-borne diseases have an increasing incidence due to climate change and increased human migration• To date, there is no evidence of transmission of coronavirus COVID-19 by tick as a vector• To date, there are only a few modern, effective, and actively- used vaccines against ticks or tick-borne diseases• Neuropeptides and their receptors expressed in ticks may be potentially used for vaccine design.

Cardioprotective Effects of PPARß/δ Activation against Ischemia/Reperfusion Injury in Rat Heart Are Associated with ALDH2 Upregulation, Amelioration of Oxidative Stress and Preservation of Mitochondrial Energy Production.

Accumulating evidence support the cardioprotective properties of the nuclear receptor peroxisome proliferator activated receptor ß/δ (PPARß/δ); however, the underlying mechanisms are not yet fully elucidated. The aim of the study was to further investigate the mechanisms underlying PPARß/δ-mediated cardioprotection in the setting of myocardial ischemia/reperfusion (I/R). For this purpose, rats were treated with PPARß/δ agonist GW0742 and/or antagonist GSK0660 in vivo and hearts were subjected to ex vivo global ischemia followed by reperfusion. PPARß/δ activation improved left ventricular developed pressure recovery, reduced infarct size (IS) and incidence of reperfusion-induced ventricular arrhythmias while it also up-regulated superoxide dismutase 2, catalase and uncoupling protein 3 resulting in attenuation of oxidative stress as evidenced by the reduction in 4-hydroxy-2-nonenal protein adducts and protein carbonyl formation. PPARß/δ activation also increased both mRNA expression and enzymatic activity of aldehyde dehydrogenase 2 (ALDH2); inhibition of ALDH2 abrogated the IS limiting effect of PPARß/δ activation. Furthermore, upregulation of PGC-1α and isocitrate dehydrogenase 2 mRNA expression, increased citrate synthase activity as well as mitochondrial ATP content indicated improvement in mitochondrial content and energy production. These data provide new mechanistic insight into the cardioprotective properties of PPARß/δ in I/R pointing to ALDH2 as a direct downstream target and suggesting that PPARß/δ activation alleviates myocardial I/R injury through coordinated stimulation of the antioxidant defense of the heart and preservation of mitochondrial function.

Changes in mitochondrial properties may contribute to enhanced resistance to ischemia-reperfusion injury in the diabetic rat heart.

Diabetes mellitus, besides having deleterious effects, induces cardiac adaptation that may reduce the heart's susceptibility to ischemia-reperfusion (IR) injury. This study aimed to investigate whether changes in mitochondrial properties are involved in the mechanisms of increased resistance of the diabetic heart to IR. Adult male Wistar rats were made diabetic by a single dose of streptozotocin (65 mg·kg-1, i.p.), and on the day 8, Langendorff-perfused hearts were subjected to 30 min global ischemia and 40 min reperfusion. Baseline preischemic parameters in the diabetic hearts did not differ markedly from those in the nondiabetic controls, except for lower left ventricular developed pressure, higher mitochondrial membrane fluidity, and protein levels of manganese superoxide dismutase. On the other hand, diabetic hearts showed significantly better post-IR functional restoration and reduced arrhythmogenesis associated with lower reactive oxygen species production as compared with healthy controls. IR decreased membrane fluidity in both experimental groups; however, it led to a complete recovery of mitochondrial Mg2+-ATPase activity in diabetics in contrast to its reduction in nondiabetics. These findings indicate that the heart may become adapted to diabetes-induced alterations that might increase its tolerance to an ischemic insult. Preserved mitochondrial function might play a role in the mechanisms of the heart's resistance to IR injury in diabetics.

Noninvasive approach to mend the broken heart: Is "remote conditioning" a promising strategy for application in humans?

Currently, there are no satisfactory interventions to protect the heart against the detrimental effects of ischemia-reperfusion injury. Although ischemic preconditioning (PC) is the most powerful form of intrinsic cardioprotection, its application in humans is limited to planned interventions, due to its short duration and technical requirements. However, many organs/tissues are capable of producing "remote" PC (RPC) when subjected to brief bouts of ischemia-reperfusion. RPC was first described in the heart where brief ischemia in one territory led to protection in other area. Later on, RPC started to be used in patients with acute myocardial infarction, albeit with ambiguous results. It is hypothesized that the connection between the signal triggered in remote organ and protection induced in the heart can be mediated by humoral and neural pathways, as well as via systemic response to short sublethal ischemia. However, although RPC has a potentially important clinical role, our understanding of the mechanistic pathways linking the local stimulus to the remote organ remains incomplete. Nevertheless, RPC appears as a cost-effective and easily performed intervention. Elucidation of protective mechanisms activated in the remote organ may have therapeutic and diagnostic implications in the management of myocardial ischemia and lead to development of pharmacological RPC mimetics.

Naproxen and Diclofenac Attenuate Atorvastatin-induced Preconditioning of the Myocardium.

Statins reduce infarct size (IS) in ischemia-reperfusion injury of the myocardium. Inhibition of cyclooxygenase-2 (COX-2) attenuates this benefit. We investigated the effect of two widely used non-selective non-steroidal anti-inflammatory drugs (NSAIDs) with different degree of anti-COX-2 activity on atorvastatin-mediated preconditioning. Wistar rats received oral atorvastatin (10 mg∙kg-1∙day-1), naproxen (10 mg∙kg-1∙day-1), diclofenac (8 mg∙kg-1∙day-1), atorvastatin+naproxen, atorvastatin+diclofenac or water for three days. Hearts were then excised and perfused in the Langendorff system. Area at risk (AR) and IS were determined after 30 min of regional ischemia and 120 min of reperfusion. Atorvastatin reduced IS by 51.3% compared with controls (14.7 ± 3.9% vs. 30.2 ± 4.6% of the AR; P < 0.001). Naproxen and diclofenac alone did not alter IS compared to control. Diclofenac completely abrogated atorvastatin-mediated protection of the myocardium. Naproxen significantly attenuated but did not eliminate the IS reducing the effect of atorvastatin when compared with controls (P = 0.038). The difference in IS between the atorvastatin+naproxen group and the atorvastatin+diclofenac group showed a strong trend in reaching statistical significance (P = 0.058), but was not found to be significant. Our results suggest relatively small, but noticeable differences among non-selective NSAIDs in their potential to attenuate statin-mediated preconditioning.

Myocardial connexin-43 is upregulated in response to acute cardiac injury in rats.

We aimed to explore whether myocardial intercellular channel protein connexin-43 (Cx43) along with PKCε and MMP-2 might be implicated in responses to acute cardiac injury induced by 2 distinct sublethal interventions in Wistar rats. Animals underwent either single chest irradiation at dose of 25 Gy or subcutaneous injection of isoproterenol (ISO, 120 mg/kg) and were compared with untreated controls. Forty-two days post-interventions, the hearts were excised and left ventricles were used for analysis. The findings showed an increase of total as well as phosphorylated forms of myocardial Cx43 regardless of the type of interventions. Enhanced phosphorylation of Cx43 coincided with increased PKCε expression in both models. Elevation of Cx43 was associated with its enhanced distribution on lateral surfaces of the cardiomyocytes in response to both interventions, while focal areas of fibrosis without Cx43 were found in post-ISO but not post-irradiated rat hearts. In parallel, MMP-2 activity was decreased in the former while increased in the latter. Cardiac function was maintained and the susceptibility of the hearts to ischemia or malignant arrhythmias was not deteriorated 42 days after interventions when compared with controls. Altogether, the findings indicate that myocardial Cx43 is most likely implicated in potentially salutary responses to acute heart injury.

Effect of antihypertensive agents - captopril and nifedipine - on the functional properties of rat heart mitochondria.

OBJECTIVES: Investigation of acute effect on cellular bioenergetics provides the opportunity to characterize the possible adverse effects of drugs more comprehensively. This study aimed to investigate the changes in biochemical and biophysical properties of heart mitochondria induced by captopril and nifedipine antihypertensive treatment. MATERIALS AND METHODS: Male, 12-week-old Wistar rats in two experimental models (in vivo and in vitro) were used. In four groups, the effects of escalating doses of captopril, nifedipine and combination of captopril + nifedipine added to the incubation medium (in vitro) or administered per os to rat (in vivo) on mitochondrial ATP synthase activity and membrane fluidity were monitored. RESULTS: In the in vitro model we observed a significant inhibitory effect of treatment on the ATP synthase activity (P<0.05) with nonsignificant differences in membrane fluidity. Decrease in the value of maximum reaction rate Vmax (P<0.05) without any change in the value of Michaelis-Menten constant Km, indicative of a noncompetitive inhibition, was presented. At the in vivo level, we did not demonstrate any significant changes in the ATP synthase activity and the membrane fluidity in rats receiving captopril, nifedipine, and combined therapy. CONCLUSION: In vitro kinetics study revealed that antihypertensive drugs (captopril and nifedipine) directly interact with mitochondrial ATP synthase. In vivo experiment did not prove any acute effect on myocardial bioenergetics and suggest that drugs do not enter cardiomyocyte and have no direct effect on mitochondria.

Pleiotropic Effects of Simvastatin on Some Calcium Regulatory and Myofibrillar Proteins in Ischemic/Reperfused Heart: Causality of Statins Cardioprotection?

BACKGROUND: It is known that statins possess beneficial cardioprotective effects irrespective of lipidlowering action and that cardiac injury due ischemia/reperfusion is associated with Ca2+ dysregulation resulting in contractile dysfunction. OBJECTIVE: With this background, we tested a hypothesis that simvastatin influences signaling of Ca2+/calmodulindependent protein kinase IIδ (CaMKIIδ), a protein kinase regulating both Ca2+ homeostasis and thick filament function, and thereby might underlie the mitigation of ischemia/reperfusion (I/R)-induced cardiac dysfunction. METHOD: Isolated hearts of control and simvastatin-treated (p.o. 10 mg/kg, 5 days) rats were subjected to global I and R and Western blotting was used to study the expression/activation of certain signaling proteins. RESULTS: Simvastatin treatment did not modify the plasma lipid levels; however, it recovered depressed cardiac performance and reduced reperfusion arrhythmias without affecting the activation of CaMKIIδ through phosphorylation of Thr287. Activation of its downstreams, such as phospholamban (PLN) and cardiac myosin-binding protein C (cMyBP-C) at Thr17 and Ser282, respectively, was in accordance with the levels of pThr287-CaMKIIδ. Total expression of these proteins, however, did not follow the same pattern and was either unchanged (CaMKIIδ, cMYBP-C) or increased (PLN). Likewise, PLN/SERCA2a (sarco/endoplasmic reticulum Ca2+-ATPase 2a) ratio in I/R hearts was unaffected by the treatment. On the other hand, simvastatin reversed the increased protein expression of protein phosphatase 1ß (PP1ß), but not protein phosphatase 2A (PP2A), in I/R hearts. CONCLUSION: A lower rate of dephosphorylation and thereby a delay in inactivation of phosphorylated proteins due to a decrease in PP1ß, rather than effects on phosphorylation of CaMKIIδ and its downstreams, such as PLN and cMyBP-C, may underlie beneficial effects of simvastatin in I/R hearts.

Effect of crowding stress on tolerance to ischemia-reperfusion injury in young male and female hypertensive rats: molecular mechanisms.

Sex and social stress may represent risk factors in the etiology of hypertension and heart response to ischemia-reperfusion (I/R) injury. Phosphatidylinositol 3-kinase/protein kinase B (Akt) plays an important role in the processes associated with hypertension and myocardial tolerance to I/R, and may be involved in myocardial stress reaction. The impact of chronic stress on the response to I/R was investigated in the hearts of 7-week-old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats of both sexes. Stress was induced by reducing living space to 70 cm(2)/100 g body mass of rat for 2 weeks, while the controls were kept at 200 cm(2)/100 g. Langendorff-perfused hearts, subjected to I/R, exhibited higher vulnerability to ventricular tachycardia in crowd-stressed SHR vs. the control rats, and this was more pronounced in the males. Myocardial infarction was not affected by crowding stress in any of the groups. Male and female SHR showed increased activation of cardiac Akt, whereas nitric oxide synthase activity (NOS) with pro-apoptotic signaling decreased in the males but was not altered in the females (vs. WKY rats). NOS was enhanced in the female SHR and WKY groups by comparison with the respective males. Stress only reduced NOS activity in the SHR groups, and without changes in apoptotic markers. In conclusion, we showed that stress in young SHR mainly affects the nonlethal markers for I/R, and has no impact on myocardial infarction and apoptosis, despite reduced NOS activity.

Mechanisms of cardiac radiation injury and potential preventive approaches.

In addition to cytostatic treatment and surgery, the most common cancer treatment is gamma radiation. Despite sophisticated radiological techniques however, in addition to irradiation of the tumor, irradiation of the surrounding healthy tissue also takes place, which results in various side-effects, depending on the absorbed dose of radiation. Radiation either damages the cell DNA directly, or indirectly via the formation of oxygen radicals that in addition to the DNA damage, react with all cell organelles and interfere with their molecular mechanisms. The main features of radiation injury besides DNA damage is inflammation and increased expression of pro-inflammatory genes and cytokines. Endothelial damage and dysfunction of capillaries and small blood vessels plays a particularly important role in radiation injury. This review is focused on summarizing the currently available data concerning the mechanisms of radiation injury, as well as the effectiveness of various antioxidants, anti-inflammatory cytokines, and cytoprotective substances that may be utilized in preventing, mitigating, or treating the toxic effects of ionizing radiation on the heart.

Pleiotropic preconditioning-like cardioprotective effects of hypolipidemic drugs in acute ischemia-reperfusion in normal and hypertensive rats.

Although pleiotropy, which is defined as multiple effects derived from a single gene, was recognized many years ago, and considerable progress has since been achieved in this field, it is not very clear how much this feature of a drug is clinically relevant. During the last decade, beneficial pleiotropic effects from hypolipidemic drugs (as in, effects that are different from the primary ones) have been associated with reduction of cardiovascular risk. As with statins, the agonists of peroxisome proliferator-activated receptors (PPARs), niacin and fibrates, have been suggested to exhibit pleiotropic activity that could significantly modify the outcome of a cardiovascular ailment. This review examines findings demonstrating the impacts of treatment with hypolipidemic drugs on cardiac response to ischemia in a setting of acute ischemia-reperfusion, in relation to PPAR activation. Specifically, it addresses the issue of susceptibility to ischemia, with particular regard to the preconditioning-like cardioprotection conferred by hypolipidemic drugs, as well as the potential molecular mechanisms behind this cardioprotection. Finally, the involvement of PPAR activation in the mechanisms of non-metabolic cardioprotective effects from hypolipidemic drugs, and their effects on normal and pathologically altered myocardium (in the hearts of hypertensive rats) is also discussed.

Mitigation of postischemic cardiac contractile dysfunction by CaMKII inhibition: effects on programmed necrotic and apoptotic cell death.

While Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) has been suggested to be an important protein regulating heart function upon ischemia/reperfusion (I/R), the mechanisms responsible are not fully known. Furthermore, it is not known whether CaMKII activation can modulate necroptosis, a recently described form of programmed cell death. In order to investigate these issues, Langendroff-perfused rat hearts were subjected to global ischemia and reperfusion, and CaMKII inhibition was achieved by adding the CaMKII inhibitor KN-93 (0.5 µmol/dm(3)) to the perfusion solution before the induction of ischemia. Immunoblotting was used to detect changes in expression of proteins modulating both necroptotic and apoptotic cell death. CaMKII inhibition normalized I/R induced increases in expression of necroptotic RIP1 and caspase-8 along with proteins of the intrinsic apoptotic pathway, namely cytochrome c and caspase-9. In addition, it increased the Bcl-2/Bax ratio and reduced caspase-3 and cleaved PARP1 content suggesting reduction of cell death. These changes coexisted with improvement of postischemic contractile function. On the other hand, there was no correlation between levels of pT287-CaMKIIδ and LVDP recovery after I/R. These results demonstrate for the first time that CaMKII inhibition may mitigate cardiac contractile dysfunction, at least partially, by limiting the contents of not only apoptotic, but also necroptotic proteins. Phosphorylation of CaMKII seems unlikely to determine the degree of postischemic recovery of contractile function.

Delayed cardioprotective effects of WY-14643 are associated with inhibition of MMP-2 and modulation of Bcl-2 family proteins through PPAR-α activation in rat hearts subjected to global ischaemia-reperfusion.

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors regulating cardiac lipid metabolism and energy homeostasis. Although the activation of PPARs has been implicated in cardioprotection, the molecular mechanisms are largely unexplored. In this study, we aimed to investigate the effect of the PPAR-α agonist WY-14643 (WY), mimicking a delayed effect of preconditioning in rat hearts exposed to acute ischaemia-reperfusion (I/R) 24 h later, and to define whether antioxidative and antiapoptotic mechanisms are involved. Treatment with WY markedly attenuated post-ischaemic contractile dysfunction (as evidenced by the reduced infarct size), the higher left ventricular developed pressure (LVDP) recovery, and the decreased occurrence of arrhythmias. These effects were abolished in the presence of the PPAR-α antagonist MK886. Heme oxygenase-1, a key antioxidative enzyme implicated in cytoprotection, was upregulated in response to WY at baseline, but was markedly reduced after I/R, indicating reduced oxidative stress. WY treatment was also associated with decreased mRNA levels and enzymatic activity of matrix metalloproteinase-2, and increased ratios of Bcl-2:Bax proteins. These results indicate that PPAR-α activation by its selective ligand WY may confer delayed preconditioning-like protection in rat hearts subjected to I/R by modulating oxidative stress, activation of matrix metalloproteinase-2, and expression of Bcl-2 and Bax.

Prolonged oxytocin treatment in rats affects intracellular signaling and induces myocardial protection against infarction.

Oxytocin is a hormone, which is released into the circulation in response to acute or chronic stress stimuli. One of the important targets of oxytocin is cardiovascular system. Present studies were aimed at testing the hypothesis that prolonged treatment with oxytocin (simulation of stress-induced rise in circulating oxytocin) activates intracellular signaling pathways playing a role in ischemia/reperfusion injury. Furthermore, we tested protective effects of oxytocin treatment in vivo against cardiac injury induced by ischemia/reperfusion of isolated hearts. Male Wistar rats were treated with oxytocin or vehicle continuously via osmotic minipumps for 2 weeks. The hearts were used for biochemical measurements or isolated for Langendorff perfusion. Treatment with oxytocin resulted in a significant increase in specific phosphorylation (activation) of p38-MAPK and Akt kinase, an increase in phosphorylated Hsp27 and an elevation in atrial natriuretic peptide (ANP) levels in left ventricular heart tissue. There were no significant changes in the activation of MMP-2 and ERK in the left heart ventricle of oxytocin-treated rats. Postischemic recovery of functional parameters LVDP, RPP, +dP/dtmax and -dP/dtmax was better in the hearts of oxytocin-treated rats compared to that in the controls. Oxytocin treatment significantly reduced infarct size to 15.1 + 3.2% as compared to 32.4 + 3.5% in vehicle-treated rats (p < 0.01). This is the first evidence for cardioprotective effects of oxytocin administered in vivo simulating chronic stress-induced elevation in plasma oxytocin. The present results show that positive effects of oxytocin that may ameliorate negative consequences of stress on the heart are, at least in part, mediated through p38-MAPK and Akt kinase pathways.

PPAR-alpha activation as a preconditioning-like intervention in rats in vivo confers myocardial protection against acute ischaemia-reperfusion injury: involvement of PI3K-Akt.

Peroxisome proliferator-activated receptors (PPAR) regulate the expression of genes involved in lipid metabolism, energy production, and inflammation. Their role in ischaemia-reperfusion (I/R) is less clear, although research indicates involvement of PPARs in some forms of preconditioning. This study aimed to explore the effects of PPAR-α activation on the I/R injury and potential cardioprotective downstream mechanisms involved. Langendorff-perfused hearts of rats pretreated with the selective PPAR-α agonist WY-14643 (WY, pirinixic acid; 3 mg·(kg body mass)·day(-1); 5 days) were subjected to 30 min ischaemia - 2 h reperfusion with or without the phosphatidylinositol 3-kinase (PI3K)-Akt inhibitor wortmannin for the evaluation of functional (left ventricular developed pressure, LVDP) recovery, infarct size (IS), and reperfusion-induced arrhythmias. A 2-fold increase in baseline PPAR-α mRNA levels (qPCR) in the WY-treated group and higher post-I/R PPAR-α levels compared with those in untreated controls were accompanied by similar changes in the expression of PPAR-α target genes PDK4 and mCPT-1, regulating glucose and fatty acid metabolism, and by enhanced Akt phosphorylation. Post-ischaemic LVDP restoration in WY-treated hearts reached 60% ± 9% of the pre-ischaemic values compared with 24% ± 3% in the control hearts (P < 0.05), coupled with reduced IS and incidence of ventricular fibrillation that was blunted by wortmannin. Results indicate that PPAR-α up-regulation may confer preconditioning-like protection via metabolic effects. Downstream mechanisms of PPAR-α-mediated cardioprotection may involve PI3K-Akt activation.

Upregulation of CaMKIIδ during ischaemia-reperfusion is associated with reperfusion-induced arrhythmias and mechanical dysfunction of the rat heart: involvement of sarcolemmal Ca2+-cycling proteins.

Although Ca(2+)/calmodulin-dependent protein kinase II delta (CaMKIIδ) has been implicated in development of different phenotypes of myocardial ischaemia-reperfusion injury, its involvement in arrhythmogenesis and cardiac stunning is not sufficiently elucidated. Moreover, the mechanisms by which CaMKIIδ mediates disturbances in excitation-contraction coupling, are not exactly known. To investigate this, KN-93 (0.5 µmol/L), a CaMKII inhibitor, was administered before induction of global ischaemia and reperfusion in isolated Langendorff-perfused rat hearts. Expression of CaMKIIδ and the sarcollemal Ca(2+)-cycling proteins, known to be activated during reperfusion, was analyzed using immunoblotting. KN-93 reduced reperfusion-induced ectopic activity and the incidence of ventricular fibrillation. Likewise, the severity of arrhythmias was lower in KN-treated hearts. During the pre-ischaemia phase, neither inotropic nor chronotropic effects were elicited by KN-93, whereas post-ischaemic contractile recovery was significantly improved. Ischaemia-reperfusion increased the expression of CaMKIIδ and sodium-calcium exchanger (NCX1) proteins without any influence on the protein content of alpha 1c, a pore-forming subunit of L-type calcium channels (LTCCs). On the other hand, inhibition of CaMKII normalized changes in the expression of CaMKIIδ and NCX1. Taken together, CaMKIIδ seems to regulate its own turnover and to be an important component of cascade integrating NCX1, rather than LTCCs that promote ischaemia-reperfusion-induced contractile dysfunction and arrhythmias.

The role of PPAR in myocardial response to ischemia in normal and diseased heart.

Peroxisome proliferator-activated receptors (PPAR), ligand-activated transcription factors, belong to the nuclear hormone receptor superfamily regulating expression of genes involved in different aspects of lipid metabolism, inflammation and cardiac energy production. Activation of PPAR-α isoform by its natural ligands, fatty acids (FA) and eicosanoids, promotes mitochondrial FA oxidation as the primary ATP-generating pathway. On the other hand, PPAR-γ regulates lipid anabolism or storage, while, until recently, the function of PPAR-ß/δ has been less explored. Under conditions associated with acute or chronic oxygen deprivation, PPAR-α modulates expression of genes that determine substrate switch (FA vs. glucose) aimed at maintenance of basic cardiac function. Although PPAR-α and PPAR-γ synthetic agonists, hypolipidemic and antidiabetic drugs, have been reported to protect the heart against ischemia/reperfusion injury, it is still a matter of debate whether PPAR activation plays a beneficial or detrimental role in myocardial response to ischemia, in particular, in pathological conditions. This article reviews some findings demonstrating the impact of PPAR activation on cardiac resistance to ischemia in normal and pathologically altered heart. Specifically, it addresses the issue of susceptibility to ischemia in the diabetic myocardium, with particular regards to the role of PPAR. Finally, involvement of PPAR in the mechanisms of lipid-independent cardioprotective effects of some hypolipidemic drugs is also discussed.

Hemidesmus indicus and Hibiscus rosa-sinensis Affect Ischemia Reperfusion Injury in Isolated Rat Hearts.

Hemidesmus indicus (L.) R. Br. (HI) and Hibiscus rosa-sinensis L. (HRS) are widely used traditional medicine. We investigated cardioprotective effects of these plants applied for 15 min at concentrations of 90, 180, and 360 µg/mL in Langendorff-perfused rat hearts prior to 25-min global ischemia/120-min reperfusion (I/R). Functional recovery (left ventricular developed pressure-LVDP, and rate of development of pressure), reperfusion arrhythmias, and infarct size (TTC staining) served as the endpoints. A transient increase in LVDP (32%-75%) occurred at all concentrations of HI, while coronary flow (CF) was significantly increased after HI 180 and 360. Only a moderate increase in LVDP (21% and 55%) and a tendency to increase CF was observed at HRS 180 and 360. HI and HRS at 180 and 360 significantly improved postischemic recovery of LVDP. Both the drugs dose-dependently reduced the numbers of ectopic beats and duration of ventricular tachycardia. The size of infarction was significantly decreased by HI 360, while HRS significantly reduced the infarct size at all concentrations in a dose-dependent manner. Thus, it can be concluded that HI might cause vasodilation, positive inotropic effect, and cardioprotection, while HRS might cause these effects at higher concentrations. However, further study is needed to elucidate the exact mechanism of their actions.

Acute treatment with polyphenol quercetin improves postischemic recovery of isolated perfused rat hearts after global ischemia.

Quercetin is a plant-derived bioflavonoid with potentially beneficial effects on the cardiovascular system. Studies focused on the efficiency of flavonoids against ischemia-reperfusion (I/R) injury have demonstrated that quercetin exerts robust protective effects in renal, cerebral, and hepatic I/R models. However, there is only limited evidence about the effect of quercetin on myocardial I/R injury. Therefore, the aim of the current study was to examine the effect of quercetin on isolated rat heart during ischemia and reperfusion. Rat hearts perfused according to Langendorff at 37 degrees C were examined during 25 min global ischemia followed by 120 min reperfusion. Quercetin (15 micromol/L) was administered either 15 min before ischemia (group Q1), or during the entire reperfusion period (group Q2). Changes in functional parameters of the hearts were measured during the initial 40 min of reperfusion. At the end of the experiment, the hearts were stained with tetrazolium to estimate the size of infarction (IS). Our study showed that quercetin improved postischemic recovery of functional parameters of isolated hearts in both treated groups. This improvement was manifested by significantly higher values of left ventricular developed pressure (LVDP) and the maximal rates of pressure development and fall (+(dP/dt)max and -(dP/dt)max) and by significantly lower increase of end-diastolic pressure. Coronary flow was not significantly changed during reperfusion in the group treated before ischemia, but was significantly increased in the group treated during reperfusion. Quercetin also significantly reduced IS in both groups, more markedly in postischemically treated group. We conclude that acute quercetin treatment exerts significant positive effects on isolated hearts during I/R injury. These results are consistent with the beneficial effects of quercetin and other flavonoids on the cardiovascular system.

Influence of ischemia/reperfusion and modulation of PI3K/Akt kinase pathway on matrix metalloproteinase-2 in rat hearts.

Matrix metalloproteinases (MMPs) are enzymes that play an important role in degradation and remodeling of extracellular matrix and MMP-2 has been also shown as a primary mediator of the acute mechanical dysfunction of the heart immediately after ischemia/reperfusion (I/R). The aims of the study were to investigate the influence of I/R on MMP-2 and to study the effects of wortmannin on modulation of MMP-2 activities after cycle of short I/R procedures (ischemic preconditioning, IP). Wortmannin is a specific inhibitor of PI3K/Akt kinase pathway activation of which was found to play a role in infarct size limiting mechanisms in the rat heart. In the study isolated Langendorff-perfused rat hearts subjected to protocols of prolonged (test) I/R and/or IP were used. Wortmannin was infused before and during the reperfusion phase of IP. The levels and activation of proteins were determined by immunoblot assay. The MMP-2 activities were measured by zymography. We found that ischemia induced time-dependent activation of tissue pro-MMP-2. Strong activation occurred after 15 min ischemia, during prolonged ischemia and following reperfusion the activities of this form of MMP-2 declined. The specific activities of both 72 and 63 kDa forms of MMP-2 were increased in perfusates collected during reperfusion after 30 min ischemia and these activities peaked in the first minute of reperfusion. Cycle of short ischemia and reperfusion that led to increased cardiac tolerance against prolonged I/R reduced 72 kDa MMP-2 activities and induced also an activation of Akt kinase. The application of wortmannin was connected with inhibition of IP-mediated Akt kinase activation. Moreover, the actions of wortmannin were linked with modulation of MMP-2 activities. Our results suggest that MMP-2 may be involved in the responses of rat hearts to ischemia and point to possible relationship between Akt kinase and modulation of MMP-2 activities in rat hearts.