Time course of tolerance to ischemia-reperfusion injury and induction of heat shock protein 72 by heat stress in the rat heart

Heat Shock Proteins: Protection and Potential Biomarkers for Ischemic Injury of Cardiomyocytes After Surgery

The heat shock proteins are endogenous proteins with the ability to act as molecular chaperones. Methods that provide cell protection by way of some damage can positively influence the results of surgery. The present review summarizes current knowledge concerning the cardioprotective role of the heat shock proteins as occurs in heart damage, including relevant information about the stresses that regulate the expression of these proteins and their potential role as biomarkers of heart disease.

Heat induces interleukin-6 in skeletal muscle cells via TRPV1/PKC/CREB pathways

Interleukin-6 (IL-6) is released from skeletal muscle cells and induced by exercise, heat, catecholamine, glucose, lipopolysaccharide, reactive oxygen species, and inflammation. However, the mechanism that induces release of IL-6 from skeletal muscle cells remains unknown. Thermosensitive transient receptor potential (TRP) proteins such as TRPV1-4 play vital roles in cellular functions. In this study we hypothesized that TRPV1 senses heat, transmits a signal into the nucleus, and produces IL-6. The purpose of the present study is to investigate the underlying mechanisms whereby skeletal muscle cells sense and respond to heat. When mouse myoblast cells were exposed to 37-42°C for 2 h, mRNA expression of IL-6 increased in a temperature-dependent manner. Heat also increased IL-6 secretion in myoblast cells. A fura 2 fluorescence dual-wavelength excitation method showed that heat increased intracellular calcium flux in a temperature-dependent manner. Intracellular calcium flux and IL-6 mRNA expression were increased by the TRPV1 agonists capsaicin and N-arachidonoyldopamine and decreased by the TRPV1 antagonists AMG9810 and SB366791 and siRNA-mediated knockdown of TRPV1. TRPV2, 3, and 4 agonists did not change intracellular calcium flux. Western blotting with inhibitors demonstrated that heat increased phosphorylation levels of TRPV1, followed by PKC and cAMP response element-binding protein (CREB). PKC inhibitors, Gö6983 and staurosporine, CREB inhibitors, curcumin and naphthol AS-E, and knockdown of CREB suppressed the heat-induced increases in IL-6. These results indicate that heat increases IL-6 in skeletal muscle cells through the TRPV1, PKC, and CREB signal transduction pathway.NEW & NOTEWORTHY Heat increases the release of interleukin-6 (IL-6) from skeletal muscle cells. IL-6 has been shown to serve immune responses and metabolic functions in muscle. It can be anti-inflammatory as well as proinflammatory. However, the mechanism that induces release of IL-6 from skeletal muscle cells remains unknown. Here we show that heat increases IL-6 in skeletal muscle cells through the transient receptor potential vannilloid 1, PKC, and cAMP response element-binding protein signal transduction pathway.

Cytoprotective regulation of the mitochondrial permeability transition pore is impaired in type 2 diabetic Goto-Kakizaki rat hearts

Our recent studies indicated that up-regulation of calcineurin activity and unfolded protein responses (UPRs) disrupt cytoprotective Akt- and ERK-signaling in OLETF, a model of obese type 2 diabetes (T2DM). To determine whether the mechanisms can be generalized, we used Goto-Kakizaki rats (GK), a model of non-obese T2DM, in this study. Infarct sizes after 20-min ischemia/2-h reperfusion were similar in GK and non-diabetic controls, Wistar rats (Wistar). However, erythropoietin (EPO) limited infarct size in Wistar (64.0±5.3% vs. 45.7±4.4%, p<0.05) but not in GK (56.2±2.2% vs. 52.6±2.3%). Levels of calcineurin activity and EPO-induced phosphorylation of Akt and ERK were similar in GK and Wistar, though cytosolic HSP70 level was 50% lower and mitochondrial HSP60 level was 60% higher in GK. EPO preserved mitochondrial calcium retention capacity (CRC), an index of the threshold for opening of the mitochondrial permeability transition pore (mPTP), after ischemia/reperfusion in Wistar but not in GK. Interaction of cyclophilin D (CypD) with mitochondrial inorganic phosphate carrier (PiC), which sensitizes the mPTP, was enhanced in GK. There was a negative exponential relationship between CypD-PiC interaction and CRC upon reperfusion, indicating that increase in CRC by reduction of CypD-PiC interaction is smaller when CypD-PiC interaction level is at a higher range. A chemical chaperone, 4-phenylbutyric acid, attenuated the changes in HSPs and CypD-PiC interaction and restored responses of CRC and infarct size to EPO in GK. These results suggest that cytoprotective regulation of the mPTP is impaired in GK by enhanced CypD-PiC interaction in which UPRs are involved.

Thermotolerance does not reduce the size or remodeling of radiofrequency lesions in the rat myocardium

PURPOSE

Late lesion extension may be involved in the genesis of delayed radiofrequency (RF) effects. Because RF lesion is thermally mediated, we hypothesized that induction of heat shock response (thermotolerance) would modulate lesion healing. We evaluated the effects of thermotolerance on the dimensions and remodeling of RF lesions in a rat model of heart failure.

METHODS

Wistar rats (weight 300 g) subjected to heat stress (n = 22, internal temperature of 42 °C for 10 min) were compared to controls (n = 22, internal temperature of 37 °C for 10 min). After 48 h (peak of HSP70 myocardial concentration), a modified unipolar RF lesion (customized catheter, tip 4.5 mm in diameter; 12 W; 10 s) was created on the left ventricular free wall. Animals were sacrificed 2 h (n = 10 per group) and 4 weeks (n = 12 per group) after ablation for lesion analysis. An echocardiogram was obtained at 4 weeks.

RESULTS

There was no difference between groups regarding the size of acute (controls 27 ± 2 vs. treated 27 ± 3 mm(2)) and chronic lesions (controls 17 ± 1 vs. treated 19 ± 1 mm(2)). Histology of lesions did not differ between groups. The echocardiogram revealed dilation of the cavities and moderate systolic dysfunction without difference between groups. Acute lesion dimensions were similar between control and treated animals over time (ablation undertaken 3, 12, 24, 48, and 72 h after hyperthermia) and also using a conventional ablation catheter (50 °C; 15 W; 10 s).

CONCLUSION

Thermotolerance does not reduce the size or remodeling of RF lesions in the rat myocardium.

Anti-heat shock protein 70 autoantibody epitope changes and BD091 promotes atherosclerosis in rats

It has been previously reported that the plasma levels of autoantibodies against heat shock protein 70 (HSP70) are elevated in atherosclerosis. The aim of the present study was to elucidate whether anti-HSP70 antibodies are involved in the pathogenesis of atherosclerosis. To determine this, we chose rats as an atherosclerosis model. Titers of plasma anti-HSP70 autoantibody were determined by ELISA. After the intravenous administration of antibody into the tail, the damaged areas of aorta were stained with Evans Blue, atheromatous plaque were stained by Oil Red O, and then they were measured and quantified with AxioVision computer software. The number of macrophages ([Formula: see text]), smooth muscle cells (SMCs), and T cells were determined by immunocytochemistry. The level of anti-HSP70 IgG1 antibody was apparently increased in the AS group at the tenth week, and one hybridoma of HSP70 antibody (BD091, IgG1, recognizing C-terminal) had the same binding epitope as plasma anti-HSP70 autoantibodies. After intravenous administration, the lesion area of aorta with BD091 was significantly larger than those of IgG(mouse) and SPA-810. Moreover, injection of BD091 resulted in significant endothelium damage, followed by a greater accumulation of [Formula: see text], T cells, and SMCs in lesions than in the control. In conclusion, BD091 reaction with HSP70 expressed on arterial endothelial cells inducing endothelium damage triggers the inflammatory response in the vessel wall that accelerates atherosclerosis in rats. BD091 shares the same binding epitope with HSP70 autoantibodies. These data indicated that a specific epitope of anti-HSP70 autoantibody participated in the pathogenesis of atherosclerosis.

Hsp70 and cardiac surgery: molecular chaperone and inflammatory regulator with compartmentalized effects

Open heart surgery is a unique model to study the interplay between cellular injury, regulation of inflammatory responses and tissue repair. Stress-inducible heat shock protein 70-kDa (Hsp70) provides a molecular link between these events. In addition to molecular chaperoning, Hsp70 exerts modulatory effects on endothelial cells and leukocytes involved in inflammatory networks. Hsp70 residing in the intracellular compartment is part of an inhibitory feedback loop that acts on nuclear factor kappaB (NF-kappaB). In contrast, extracellular Hsp70 is recognized by multiple germline-encoded immune receptors, e.g., Toll-like receptor (TLR) 2, TLR4, LOX-1, CD91, CD94, CCR5 and CD40. Hsp70 is thereby able to enhance chemotaxis, phagocytosis and cytolytic activity of innate immune cells and stimulate antigen-specific responses. These apparent contradictory pro- and anti-inflammatory effects of endogenous Hsp70 in the context of cardiac surgery are still not fully understood. An all-embracing model of the compartmentalized effects of endogenous Hsp70 in the orchestration of inflammatory responses in cardiac surgery is proposed.

Heat stress alters G-protein coupled receptor-mediated function and endothelium-dependent relaxation in rat mesenteric artery

Heat stress has been demonstrated to have strong cardiovascular effects. However, the underlying mechanism-mediated cardiovascular effects are still not fully understood. The present study was designed to examine if heat stress alters vascular G-protein coupled receptor-mediated vasomotion and endothelium function in rat mesenteric artery. Rats were divided into two groups, heat stress rats and control. The G-protein coupled receptors of endothelin type B (ETB) receptor-, endothelin type A (ETA) receptor-, 5-hydroxytryptamine (5-HT) receptor-, calcitonin gene-related peptide (CGRP) receptor-, alpha-adrenoceptor-mediated vosoactivity and endothelium-dependent relaxation on rat mesenteric artery ring segments were monitored by a myograph system. The plasma level of CGRP was determined by radioimmunological assay. Compared with control arterial segments, the contractile response curves of sarafotoxin 6c, a selective ETB receptor agonist and 5-HT in the arterial segments from heat stress rats were shifted towards left. An increased maximum contraction (Emax) induced by sarafotoxin 6c, but not 5-HT, was seen in the arterial segments from heat stress rats. CGRP-induced relaxation in endothelium-denuded arterial segments from heat stress rats was enhanced. The relaxation in endothelium-intact arterial segments induced by acetylcholine was significantly decreased in heat stress rats. In addition, the plasma concentration of CGRP was increased in heat stress rats. The endothelium-dependent relaxation was characterized and shown there was a decrease in nitric oxide and endothelium-derived hyperpolarizing factor-mediated relaxation in the arterial segments from heat stress rats. In conclusion, heat stress induces an enhanced vascular endothelin ETB-, 5-HT-receptors-mediated contraction, an enhanced CGRP-receptor-induced relaxation and damage to endothelium-dependent relaxation.

Hsp70 may protect cardiomyocytes from stress-induced injury by inhibiting Fas-mediated apoptosis

Expression of Hsp70 is an endogenous mechanism by which living cells adapt to stress and the protection of Hsp70 may interfere with the apoptotic machinery in a variety of ways. Here, we observed the change of Hsp70 expression in rat myocardium under stress and explored the protective effect of Hsp70 on the Fas-mediated pathway to cardiomyocyte apoptosis. The results showed that restraint stress led to cardiac dysfunction and structural damage of the myocardium, as well as activation of the Fas pathway. A similar increase in the Fas expression level, caspase-8/3 activity, and the apoptotic rate of the cardiomyocyte also were found, which indicated that Fas-mediated apoptosis of cardiomyocytes might be one of the mechanisms of cardiomyocyte injury induced by stress. Changes in Hsp70 levels and distribution occurred during the stress process, which correlated with the severity of myocardium injury. Heat preconditioning induced the upregulation of Hsp70 synthesis, which in turn may have mitigated subsequent restraint stress-induced damage, including electrocardiography (ECG) abnormality, myocardium damage, and cell death. Moreover, Hsp70 overexpression induced by heat preconditioning had no effect on Fas expression in the cardiomyocyte, but could inhibit activation of caspase-8/3 induced by the Fas signaling pathway and, as a result, prevent cell apoptosis. These results suggest that Hsp70 is capable of protecting the cardiomyocyte from stress-induced injury by inhibiting Fas-mediated apoptosis, and Hsp70 could be considered a target in future drugs to prevent cardiovascular injury caused by stress.

Immunohistochemical assesment of heat shock protein 70 in adenoid tissue

OBJECTIVES

To evaluate the expression of heat shock protein 70 (HSP70) and its relation to histopathologic parameters in adenoid hypertrophy and hyperplasia. In addition, HSP70 expression in adenoid tissue was compared with in adult and childhood.

METHODS

Paraffin-embedded adenoid tissue sections were obtained from 19 childhood and 15 adult patients. Expression of HSP70 was evaluated by immunohistochemical staining using anti-HSP70 monoclonal antibody and correlated with histopathologic parameters.

RESULTS

Positive HSP70 expression was observed mainly in the mucosal epithelium, lymphocytes in germinal centers, interfollicular lymphocytes, subepithelial plasma cells and vascular endothelium. HSP70 immunoreactivity in the mucosal epithelium with severe intraepithelial lymphocytic infiltration in childhood patients was higher than in adult patients. Although, the immunoreactivity of HSP70 was detected strongly in whole layer of metaplastic squamous epithelium, it was stained only in basal layers in respiratuary epithelium, Lymphocytes stained with HSP70 in germinal center and interfollicular areas of adenoid tissues was higher in childhood patients than in adults.

CONCLUSIONS

These data suggest that HSP70 expression may have an important role in pathogenesis of adenoid hyperplasia, especially, in childhood.

Organ preconditioning: the past, current status, and related lung studies

Preconditioning (PC) has emerged as a powerful method for experimentally and clinically attenuating various types of organ injuries. In this paper related clinical and basic research issues on organ preconditioning issues were systemically reviewed. Since lung injuries, including ischemia-reperfusion and others, play important roles in many clinical results, including thromboembolism, trauma, thermal injury, hypovolemic and endotoxin shock, reimplantation response after organ transplantation, and many respiratory diseases in critical care. It is of interest to uncover methods, including the PCs, to protect the lung from the above injuries. However, related studies on pulmonary PC are relatively rare and still being developed, so we will review previous literature on experimental and clinical studies on pulmonary PC in the following paragraphs.

Myocardial hypoperfusion/reperfusion tolerance with exercise training in hypertension

The purpose of this study was to examine whether exercise training, superimposed on compensated-concentric hypertrophy, could increase myocardial hypoperfusion-reperfusion (H/R) tolerance. Female Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) (age: 4 mo; N = 40) were placed into a sedentary (SED) or exercise training (TRD) group (treadmill running; 25 m/min, 1 h/day, 5 days/wk for 16 wk). Four groups were studied: WKY-SED ( n = 10), WKY-TRD ( n = 10), SHR-SED ( n = 10), and SHR-TRD ( n = 10). Blood pressure and heart rate were determined, and in vitro isolated heart performance was measured with a retrogradely perfused, Langendorff isovolumic preparation. The H/R protocol consisted of a 75% reduction in coronary flow for 17 min followed by 30 min of reperfusion. Although the rate-pressure product was significantly elevated in SHR relative to WKY, training-induced bradycardia reduced the rate-pressure product in SHR-TRD ( P < 0.05) without an attenuation in systolic blood pressure. Heart-to-body weight ratio was greater in both groups of SHR vs. WKY-SED ( P < 0.001). Absolute and relative myocardial tolerance to H/R was greater in WKY-TRD and both groups of SHR relative to WKY-SED ( P < 0.05). Endurance training superimposed on hypertension-induced compensated hypertrophy conferred no further cardioprotection to H/R. Postreperfusion 72-kDa heat shock protein abundance was enhanced in WKY-TRD and both groups of SHR relative to WKY-SED ( P < 0.05) and was highly correlated with absolute left ventricular functional recovery during reperfusion ( R2= 0.86, P < 0.0001). These data suggest that both compensated hypertrophy associated with short-term hypertension and endurance training individually improved H/R and that increased postreperfusion 72-kDa heat shock protein abundance was, in part, associated with the cardioprotective phenotype observed in this study.

Oral administration of geranylgeranylacetone blunts the endothelial dysfunction induced by ischemia and reperfusion in the rat heart

It has been shown that geranylgeranylacetone (GGA) protects heart against ischemia/reperfusion injury via enhanced heat shock protein 72 (HSP72) expression in rats. In the present study, we investigated the protective effect of GGA on ischemia/reperfusion-induced endothelial dysfunction. Rats were given oral GGA (GGA group) or vehicle (CON group), and 24 hours later their hearts were removed and placed in the Langendorff apparatus for 30-minute low-flow ischemia followed by 30-minute reperfusion. GGA improved the postischemic functional recovery (P < 0.01), which was abolished by N-nitro-L-arginine methyl ester (L-NAME, NO synthase inhibitor). NO production during both ischemia and reperfusion were increased in the GGA group, and the acetylcholine (ACh)-induced (endothelium-dependent) vasodilation, measured as the percentage decrease in coronary perfusion pressure after ischemia/reperfusion (14.9 +/- 1.3%), was preserved as compared with that in the CON group (7.9 +/- 1.4%). LY294002, a phosphatidylinositol 3 (PI3) kinase inhibitor, abolished the protective effects of GGA on endothelial-dependent coronary vasodilation and NO production, whereas Y27632 (Rho kinase inhibitor) increased endothelium-dependent coronary vasodilation and NO production in CON group toward the level seen in GGA group. The amount of adrenomedullin in the coronary effluent at basal condition was lower in the GGA group than in the CON group (P < 0.05), and during both ischemia and reperfusion there was no difference in the amount of adrenomedullin between the GGA and CON groups. In addition, no difference was observed in the amount of endothelin-1 between the GGA and CON groups. These results indicate that GGA attenuates the ischemia/reperfusion-induced coronary endothelial dysfunction, which may contribute to its cardioprotective effect. The PI3 kinase and/or Rho kinase pathways appear to be involved in this process, whereas adrenomedullin and endothelin-1 are not necessary for the GGA-induced cardioprotection.

Reduction of Skeletal Muscle Injury in Composite Tissue Allotransplantation by Heat Stress Preconditioning

Ischemia-reperfusion injury is a dominant factor limiting tissue survival in any microsurgical tissue transplantation, a fact that also applies to allogeneic hand transplantation. The clinical experience of the 12 human hand transplantations indicates that shorter ischemia times result in reduced tissue damage and, ultimately, in better hand function. Heat stress preconditioning and the accompanying up-regulation of the heat shock protein 72 have been shown to reduce the ischemia-reperfusion injury following ischemia of various organs, including organ transplantation. The aim of this study was to reduce the ischemia-reperfusion injury in a model of composite tissue allotransplantation. Allogeneic hind limb transplantations were performed from Lewis (donor) to Brown-Norway rats. Donor rats in group A (n = 10) received a prior heat shock whereas rats in group B (n = 10) did not receive any prior heat shock. Group C served as a control group without transplantation. The transplantations were performed 24 hours after the heat shock, at which time the heat shock protein 72 was shown to be up-regulated. The outcome was evaluated 24 hours after transplantation by nitroblue tetrazolium staining and wet-to-dry weight ratio of muscle slices (anterior tibial muscle). The nitroblue tetrazolium staining showed a significant reduction of necrotic muscle in group A (prior heat shock) (p = 0.005). The wet-to-dry ratio was significantly reduced in group A (prior heat shock), indicating less muscle edema and less tissue damage (p = 0.05). Heat shock preconditioning 24 hours before an ischemic event leads to an up-regulation of heat shock protein 72 in muscle and to a tissue protection reducing ischemia-reperfusion injury in composite tissue transplantation.

New insight into the signalling pathways of heat stress-induced myocardial preconditioning: protein kinase Cepsilon translocation and heat shock protein 27 phosphorylation

1. Heat stress (HS) is known to induce delayed preconditioning against myocardial infarction 24 h later, but the exact signalling pathway of this response remains to be elucidated. In previous studies, we have shown evidence for the implication of protein kinase C (PKC) and p38 mitogen-activated protein kinase (MAPK) in the HS-induced reduction in infarct size. Furthermore, in their phosphorylated state, small heat shock proteins (Hsp27) seem to confer cytoskeletal protection. In the present study, we sought to determine the effect of HS on the subcellular distribution of PKC isoforms and on Hsp27 phosphorylation. 2. Rats were subjected to either HS (42 degrees C for 15 min; HS group) or sham anaesthesia (sham group) before their hearts were excised. Myocardial tissue extracts obtained 20 min or 24 h after HS were processed for western blot analysis. 3. In the HS group, PKCepsilon translocated from the cytosolic to the particulate fraction (4426 +/- 128 vs 6258 +/- 316 arbitrary units; P = 0.002). Chelerythrine (5 mg/kg, i.p.), a PKC inhibitor, abolished this translocation. Western blot analysis of Hsp27 24 h after HS showed a marked increase in protein expression and phosphorylation in the particulate fraction. 4. In the present study, we have shown that HS induces the translocation of PKCepsilon from the cytosolic to the particulate fraction. Along with our previous observation that PKC is a trigger of HS-induced myocardial preconditioning, the results of the present study suggest an important role of the epsilon isoform of PKC in this cardioprotective mechanism. Furthermore, we have also demonstrated that the cytoprotective protein Hsp27 is phosphorylated following HS. Therefore, we can conclude that PKC and MAPK/Hsp27 are involved in the signalling pathway of HS-induced cardioprotection.

Protein kinase C-dependent activation of P44/42 mitogen-activated protein kinase and heat shock protein 70 in signal transduction during hepatocyte ischemic preconditioning

AIM: To investigate the significance of protein kinase C (PKC), P44/42 mitogen-activated protein kinase (MAPKs) and heat shock protein (HSP)70 signal transduction during hepatocyte ischemic preconditioning.

METHODS: In this study we used an in vitro ischemic preconditioning (IP) model for hepatocytes and an in vivo model for rat liver to investigate the significance of protein kinase C (PKC), P44/42 mitogen-activated protein kinase (P44/42 MAPKs) and heat shock protein 70 (HSP70) signal transduction in IP. Through a normal liver cell hypoxic preconditioning (HP) model in which cultured normal liver cells were subjected to 3 cycles of 5 min of incubation under hypoxic conditions followed by 5 min of reoxygenation and subsequently exposed to hypoxia and reoxygenation for 6 h and 9 h respectively. PKC inhibitor, activator and MEK inhibitor were utilized to analyze the phosphorylation of PKC, the expression of P44/42 MAPKs and HSP70. Viability and cellular ultrastructure were also observed. By using rat liver as an in vivo model of liver preconditioning (3 cycles of 10-min occlusion and 10-min reperfusion), in vivo phosphorylation of PKC and P44/42MAPKs, HSP70 expression were further analyzed. AST/ALT concentration, cellular structure and ultrastruture were also observed. All the data were statistically analyzed.

RESULTS: Similar results were obtained in both in vivo and in vitro IP models. Compared with the control without IP (or HP), the phosphorylation of PKC and P44/42 MAPKs and the expression of HSP70 were obviously increased in IP (or HP) treated model in which cytoprotection could be found. The effects of preconditioning were mimicked by stimulating PKC with 4β phorobol-12-myristate13-acetate (PMA). Conversely, inhibiting PKC with chelerythrine abolished the protection given by preconditioning. PD98059, inhibitor of MEK (the upstream kinase of P44/42MAPKs), also reverted the cytoprotection exerted by preconditioning.

CONCLUSION: The results demonstrate that preconditioning induces a rapid activation of P44/42MAPKs and PKC activation plays a pivotal role in the activation of P44/42 MAPKs pathway that participates in the preservation of liver cells. HSP expression is regulated by signals in PKC dependent P44/ 42 MAPKs pathway.

Effects of heat shock protein 70 activation by metabolic inhibition preconditioning or kappa-opioid receptor stimulation on Ca2+ homeostasis in rat ventricular myocytes subjected to ischemic insults

Heat shock protein 70 (HSP70) mediates delayed cardioprotection of preconditioning. Cytosolic calcium ([Ca(2+)])(i) overload precipitates injury, whereas attenuation of [Ca(2+)](i) overload is believed to be responsible for cardioprotection. There is evidence suggesting a link between HSP70 and [Ca(2+)](i) homeostasis. We hypothesize that activation of HSP70 by preconditioning may restore [Ca(2+)](i) homeostasis altered by ischemic insults. To test the hypothesis, we determined the effects of preconditioning with metabolic inhibition or pretreating with U50,488H [trans-(+)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide (a kappa-opioid receptor agonist)] on viability and injury, HSP70 expression, and [Ca(2+)](i) in ventricular myocytes subjected to metabolic inhibition and anoxia (MI/A), with blockade of HSP70 synthesis. In myocytes with vehicle pretreatment, the percentage of dead cells determined by trypan blue exclusion, the injury reflected by release of lactate dehydrogenase, and the resting [Ca(2+)](i) measured by spectrofluorometry significantly increased, whereas the amplitude of electrically induced [Ca(2+)](i) transient decreased, after 10 min with 10 mM 2-deoxy-d-glucose and 10 mM sodium dithionite, known to cause MI/A. However, when myocytes were subjected for 30 min to either 20 mM lactate and 10 mM 2-deoxy-d-glucose (MIP) or 30 microM U50,488H (UP) 20 h before MI/A, the changes in viability and injury, and [Ca(2+)](i) responses were significantly attenuated. These were accompanied by a significantly increased HSP70 expression. Furthermore, blockade of HSP70 synthesis with selective antisense oligonucleotides abolished the beneficial effects of MIP or UP. This study provides first evidence that activation of HSP70 induced by preconditioning, which conferred delayed cardioprotection, restored partially the [Ca(2+)](i) homeostasis altered by ischemic insults.

Effect of prenatal hypoxia on heat stress-mediated cardioprotection in adult rat heart

Fetal programming has profound effects on cardiovascular function in later adult life. We tested the hypothesis that chronic hypoxic exposure during fetal development downregulates endogenous cardioprotective mechanisms in adult rats. Time-dated pregnant rats were divided between normoxic and hypoxic (10.5% O2 from days 15 to 21 of gestation) groups. The male progeny were studied at 2 mo of age. Rats were subjected to heat stress (42 degrees C for 15 min). After 24 h, hearts were excised and subjected to 30 min of global ischemia and 1 h of reperfusion. Prenatal hypoxia did not change adult rat body weight and heart weight, but significantly increased the cross-sectional area of a left ventricular (LV) myocyte. Heat stress significantly improved postischemic recovery of LV function in normoxic control rats, but not in prenatally hypoxic rats. The infarct size in the LV resulting from ischemia-reperfusion was reduced by the heat stress pretreatment in control rats, but not in prenatally hypoxic rats. In accordance, heat stress significantly increased LV myocardial content of heat shock protein 70 only in normoxic control rats. In addition, there was a significant decrease in the LV myocardial content of the PKC-epsilon isoform in prenatally hypoxic rats compared with control rats. We conclude that prenatal hypoxia causes in utero programming of hsp70 gene in the LV, leading to an inhibition of its response to heat stress and a loss of cardioprotection in later adult life.

Effect of Hyperglycemia and Nitric Oxide Synthase Inhibition on Heat Tolerance and Induction of Heat Shock Protein 72 κDa in Vivo

Diabetes and nitric oxide synthase (NOS) inhibition both exacerbate mesenteric ischemia/reperfusion injury. Heat shock protein 72 (HSP-72) protects against κDa ischemia/reperfusion damage in vivo. The effect of diabetes on HSP-72 expression in vivo is unknown. The aim of this study was to determine the effects of diabetes and NOS inhibition on HSP-72 induction in vivo. Rats were assigned to four groups: control (C), streptozotocin-induced diabetic (D), acute hyperglycemia (A), and L- Nω-nitro-l-arginine treated (L). Rats were subjected to hyperthermia and allowed to recover for 4 hours. Intestine and liver samples from heated (H) and nonheated (NH) rats were analyzed for HSP-72 by Western blot. HSP-72 levels were increased significantly in CH compared to CNH rats. No deaths occurred in CH rats; however, death rates were significant in AH, DH, and LH rats. DH rats died earlier than LH and AH rats. HSP-72 in liver and intestine was reduced significantly in LH rats. When compared with CH rats the surviving AH and DH rats exhibited similar HSP-72 levels in the liver. Diabetes, acute hyperglycemia, and L- Nω-nitro-l-arginine treatment lower heat stress tolerance. NOS is required for HSP-72 expression, but not survival. Diabetics who survive heat stress moderately express HSP-72. Characterization of altered thermotolerance and HSP-72 may provide mechanisms for the deranged diabetic stress response.

Role of protein kinase C in geranylgeranylacetone-induced expression of heat-shock protein 72 and cardioprotection in the rat heart

We recently demonstrated that oral administration of geranylgeranylacetone (GGA), an antiulcer agent, induces heat-shock protein 72 (HSP72) in the rat heart and renders cardioprotection against ischemia/reperfusion injury. However, the signaling pathways remain to be elucidated. The present study tested the hypothesis that oral GGA would activate protein kinase C (PKC), leading to the phosphorylation and translocation of heat-shock factor 1 (HSF1), and thus, promote the expression of HSP72 protein. Rats were classified into four groups: a control (CNT) group (vehicle administration), a GGA group (GGA 200 mg/kg administration), a chelerythrine (CHE)-CNT group (pretreated with intravenous (i.v.) injection of 5 mg/kg CHE before vehicle administration), and a CHE-GGA group (pretreated with CHE before GGA administration). After 24 h administration, oral GGA-induced overexpression of HSP72, increased amount of the phosphorylated form of HSF1 in the nucleus, produced heat-shock element-specific DNA-HSF1 complex, and caused translocation of protein kinase C (PKC)delta, all of which were prevented by pretreatment with CHE. GGA also increased the PKC activity in a particulate fraction, which was prevented by pretreatment with rottlerin, a specific inhibitor of PKCdelta. Isolated-perfused heart experiments revealed that the better functional recovery observed in the GGA group during the reperfusion period following the 20 min of no-flow global ischemia, compared with the CNT group, was abolished by pretreatment with CHE. These results suggest that activation of PKC (translocation of PKCdelta), which primes the phosphorylation of HSF1, plays an essential role in the cardiac overexpression of HSP72 by GGA that leads to cardioprotection.

The induction of heat shock protein-72 attenuates cisplatin-induced acute renal failure in rats

Induction of heat shock proteins (HSPs) is thought to play a protective role in ischaemic acute renal failure (ARF). However the role of HSPs in nephrotoxic ARF is not well explored. The aim of this study was to clarify the effects of the induction of HSP70s on cisplatin (CDDP) (6 mg/kg i.v.)-induced ARF in rats. Uranyl acetate (UA) or sodium arsenite (SA) were administered i.v. 14 days or 1 day respectively before CDDP injection to induce HSPs. Serum creatinine (SCr), tubular damage score and the numbers of apoptotic (TUNEL-positive) cells were examined 5 days after CDDP injection. The expression of HSP72, B-cell lymphoma gene product-2 (Bcl-2) and Bax were evaluated by Western blot analysis. We also investigated the effect of co-administration of chelerythrine chloride (Chel), which inhibits the induction of HSPs, with SA on the expression of HSP72 and nephrotoxicity. Pretreatment with UA or SA significantly induced renal HSP72 expression. Both UA and SA attenuated the CDDP-induced increase in SCr and tubular damage scores. Co-administration of Chel with SA abolished the SA-induced increment of HSP72 and the beneficial effects of SA. The protective effects of the induction of HSP72 were associated with an increased renal Bcl-2/Bax ratio and the reduction of TUNEL-positive cells in the outer stripe of outer medulla. Our findings suggest that HSP72 attenuates CDDP-induced nephrotoxicity. The protective effects of HSP72 are associated with an increased Bcl-2/Bax ratio and less apoptosis.

Lipopolysaccharide pretreatment attenuates myocardial infarct size: A possible mechanism involving heat shock protein 70-inhibitory kappaBalpha complex and attenuation of nuclear factor kappaB

OBJECTIVE

Lipopolysaccharide pretreatment is known to reduce myocardial infarct size, but the mechanism has not been elucidated. We hypothesized that heat shock protein 70, induced by lipopolysaccharide pretreatment, formed complexes with inhibitory kappaBalpha, thereby inhibiting degradation and attenuating activation of nuclear factor kappaB and cellular injury in rat myocardium.

METHODS

Fifteen Sprague-Dawley rats were given saline solution (control group) or lipopolysaccharide. After 48 hours, 5 hearts in each group were excised without ischemia for examination of heat shock protein 70 and inhibitory kappaBalpha levels and detection of heat shock protein 70-inhibitory kappaBalpha complexes. Myocardium from the remaining 10 rats in each group was exposed to 30 minutes of ischemia and 30 minutes of reperfusion (n = 5) to evaluate nuclear factor kappaB activity or to 24 hours of reperfusion (n = 5) to evaluate infarct size.

RESULTS

Infarct size was reduced in the lipopolysaccharide group (P <.05). Nuclear factor kappaB was activated in the control ischemia group and attenuated in the lipopolysaccharide group (P <.05). Heat shock protein 70 levels were increased in the lipopolysaccharide group (P <.05), but inhibitory kappaBalpha levels were similar in both groups. Heat shock protein 70-inhibitory kappaBalpha complexes were detected only in the lipopolysaccharide group. Colocalization of the 2 proteins was observed in the lipopolysaccharide group.

CONCLUSIONS

Heat shock protein 70, induced by lipopolysaccharide pretreatment, forms complexes with inhibitory kappaBalpha and attenuates activation of nuclear factor kappaB and myocardial infarct size. Our results suggest that attenuation of nuclear factor kappaB through a mechanism forming heat shock protein 70-inhibitory kappaBalpha complexes might protect the myocardium from ischemia-reperfusion injury.

Elevated body temperature during myocardial ischemia/reperfusion exacerbates necrosis and worsens no-reflow

PURPOSE

The effects of an elevated body temperature on infarct size were tested in a rabbit model of ischemia/reperfusion.

METHODS

Before coronary artery occlusion, body temperature was raised from baseline at 38.6 +/- 0.1 degrees C to 40.3 +/- 0.2 degrees C in nine treated rabbits. Temperature in eight normothermic rabbits was 38.4 +/- 0.2 degrees C. Both groups received 30 min coronary occlusion and 3 h reperfusion.

RESULTS

In normothermic rabbits, 36 +/- 6% of the ischemic risk region became necrotic but in hyperthermic rabbits myocardial necrosis was significantly increased to 57 +/- 3% of the risk region (P < 0.005) despite similar risk regions and an equal degree of regional myocardial blood flow (RMBF) reduction during ischemia in both groups. Infarct size correlated positively with body temperature (r = 0.66, P < 0.004). RMBF was 43% lower during reperfusion in the previously ischemic areas of hyperthermic hearts compared with the control group (P < 0.04), suggesting worsened no-reflow.

CONCLUSION

Elevation in body temperature by even a few degrees can aggravate necrosis during acute myocardial infarction and worsens no-reflow.

Heme oxygenase-1 pathway is involved in delayed protection induced by heat stress against cardiac ischemia-reperfusion injury

Previous studies have shown that heme oxygenase-1 (HO-1), a heat stress protein (HSP32), has a beneficial effect on the ischemic myocardium. The purpose of the present study was to explore whether HO-1 is involved in delayed cardioprotection provided by heat stress in vivo. Sprague--Dawley rats were pretreated with whole body hyperthermia (rectal 42 degrees C) for 15 min followed by ischemia-reperfusion 24 h later. Ischemia-reperfusion injury was induced by 45 min of coronary artery occlusion followed by a 3-h reperfusion. Myocardial injury degree was evaluated by measurement of infarct size and serum creatine kinase (CK) activity. The expression of HO-1 mRNA and protein in myocardial tissues were measured. Pretreatment with hyperthemia significantly reduced infarct size and CK release during reperfusion, which was completely blocked by pretreatment with ZnPP-9, an inhibitor of HO and methylene blue, an inhibitor of soluble guanylate cyclase. Heat stress also significantly increased the expression of HO-1 mRNA and protein, and the effect was not affected by pretreatment with methylene blue. The present results suggest that the HO-1 pathway is involved in the mediation of delayed cardioprotection by heat stress in rats.

Heat shock proteins and cardiovascular pathophysiology

In the eukaryotic cell an intrinsic mechanism is present providing the ability to defend itself against external stressors from various sources. This defense mechanism probably evolved from the presence of a group of chaperones, playing a crucial role in governing proper protein assembly, folding, and transport. Upregulation of the synthesis of a number of these proteins upon environmental stress establishes a unique defense system to maintain cellular protein homeostasis and to ensure survival of the cell. In the cardiovascular system this enhanced protein synthesis leads to a transient but powerful increase in tolerance to such endangering situations as ischemia, hypoxia, oxidative injury, and endotoxemia. These so-called heat shock proteins interfere with several physiological processes within several cell organelles and, for proper functioning, are translocated to different compartments following stress-induced synthesis. In this review we describe the physiological role of heat shock proteins and discuss their protective potential against various stress agents in the cardiovascular system.

Neutrophil-endothelial cell interactions during the development of tolerance to ischaemia/reperfusion in isolated cells

Ischaemia/reperfusion (I/R) tolerance refers to the phenomenon by which the inflammation and associated sequelae induced by I/R is ameliorated by an I/R challenge imposed 24 h earlier. The development of I/R tolerance is dependent on the synthesis of new proteins. In vivo and in vitro studies provide support for nitric oxide synthase (NOS), antioxidant enzymes, and heat shock proteins (HSPs) as the effector proteins. Activation of the nuclear transcription factor, NFkappaB, appears to be a prerequisite for the development of I/R tolerance. In vitro approaches using anoxia/reoxygenation (A/R) to mimic I/R have provided insights into the complexity of the development of I/R tolerance, i.e. different cells may use different signalling pathways to develop A/R tolerance and influence the responses of adjacent cells during the process. The use of cells from genetically altered mice is expediting attempts to unravel specific mechanisms involved in the development of A/R tolerance.

Mitogen-activated protein kinases mediate heat shock-induced delayed protection in mouse heart

We determined the role of p38 mitogen-activated protein kinase (MAPK), 72-kDa heat shock protein (HSP72), and antioxidant enzymes in whole body heat stress (HS)-induced cardioprotection in mouse hearts. Adult male mice were treated with either HS or anesthesia only. At 0.5, 48, 72, or 120 h later, the hearts were subjected to 20 min of global ischemia and 30 min of reperfusion in Langendorff mode. A significant protection against ischemia-reperfusion injury was observed 48 h after HS as demonstrated by: 1) reduction in infarct size; 2) decrease in leakage of lactate dehydrogenase; and 3) enhanced postischemic ventricular contractile function. No such protection was observed at other post-HS time points. HS caused an ~25% increase in phosphorylated c-Jun NH2-terminal kinase (JNK) but not p38 MAPK in the heart during the first 2-h post-HS time period. Cardioprotection was abolished by the MAPK inhibitor SB-203580, which also partially suppressed the HS-induced JNK phosphorylation. The protective effect was associated with a two- to threefold increase in HSP72 protein accumulation, but not antioxidant enzyme activities (catalase and Cu/Zn and Mn SOD) in the myocardium. Although HSP72 levels remained high 72 h after HS, the cardioprotection had already disappeared. We conclude that HS induces a transient delayed cardioprotection at 48 h after thermal stress in mice which appears to be mediated via a MAPK-signaling pathway.

Geranylgeranylacetone, a heat shock protein inducer, prevents primary graft nonfunction in rat liver transplantation

BACKGROUND

Heat shock proteins (HSPs) are well known as cytoprotective proteins. Geranylgeranylacetone (GGA), a nontoxic anti-ulcer drug, was recently shown to have HSP-inducing capacity. In the present study, the activity of GGA was tested in a rat orthotopic liver transplantation (OLT) model to determine whether the compound has beneficial effects in warm ischemia-reperfusion injury.

METHODS

Either GGA or a control vehicle was orally administered to donor rats before graft harvest. Harvested livers were subjected to 45-min warm ischemia (37 degrees C) followed by OLT. HSP mRNA expressions and HSP syntheses in the graft livers were evaluated by reverse transcriptase polymerase chain reaction and Western blot analysis, respectively.

RESULTS

When the donors were treated with a vehicle, all recipients died of primary nonfunction within 2 days after OLT. In contrast, when the donors were treated with GGA (200 mg/kg per day) for 4 weeks, the 7-day survival rate of recipients was dramatically improved (90%). By giving a high dose of GGA (600 mg/kg per day) for 1 week, a similar improvement in recipient survival was seen (83.3%). GGA administration accumulated mRNA for both HSP72 and HSP90 in the livers even before warm ischemia and facilitated the syntheses of HSP72 and HSP90 after warm ischemia. In addition, GGA pretreatment also significantly reduced the serum levels of tumor necrosis factor-alpha (TNF-alpha) after reperfusion.

CONCLUSIONS

These findings indicate that both the enhanced induction of HSPs and the suppression of a cytotoxic mediator (TNF-alpha) might be involved in the beneficial effects of GGA on ischemia-reperfusion injury. Thus, oral administration of GGA would be a useful tool for preventing primary nonfunction in liver transplantation.

Heat shock prevents simulated ischemia-induced apoptosis in renal tubular cells via a PKC-dependent mechanism

Heat shock produces cellular tolerance to a variety of adverse conditions; however, the protective effect of heat shock on renal cell ischemic injury remains unclear. Protein kinase C (PKC) has been implicated in the signaling mechanisms of acute preconditioning, yet it remains unknown whether PKC mediates heat shock-induced delayed preconditioning in renal cells. To study this, renal tubular cells (LLC-PK1) were exposed to thermal stress (43 degrees C) for 1 h and heat shock protein (HSP) 72 induction was confirmed by Western blot analysis. Cells were subjected to simulated ischemia 24 h after thermal stress, and the effect of heat shock (delayed preconditioning) on ischemia-induced apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling) and B cell lymphoma 2 (Bcl(2)) expression (Western) was determined. Subsequently, the effect of PKC inhibition on HSP72 induction and heat stress-induced ischemic tolerance was evaluated. Thermal stress induced HSP72 production, increased Bcl(2) expression, and prevented simulated ischemia-induced renal tubular cell apoptosis. PKC inhibition abolished thermal induction of HSP72 and prevented heat stress-induced ischemic tolerance. These data demonstrate that thermal stress protects renal tubular cells from simulated ischemia-induced apoptosis through a PKC-dependent mechanism.

Inducible HSP70 mediates delayed cardioprotection via U-50488H pretreatment in rat ventricular myocytes

To test the hypothesis that heat-shock proteins (HSPs) mediate delayed cardioprotection of prior kappa-opioid receptor (kappa-OR) stimulation, we first correlated cellular injury and viability with the expression of HSP70s in isolated rat ventricular myocytes subjected to prior kappa-OR stimulation with the selective agonist trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]benzeneacetamide (U-50488H) and delayed lethal simulated ischemia (LSI). Cell injury and viability were indicated by lactate dehydrogenase release and trypan blue exclusion, respectively. The reduced injury and increased viability after pretreatment with U-50488H were concentration dependent and correlated directly with the expression of both stress-inducible (HSP70) and constitutive (HSC70) proteins. The effects mimic those with metabolic inhibition preconditioning (MIP). The cardioprotection against LSI by pretreatment with U-50488H and MIP was abolished and antagonized, respectively, via blockade of the kappa-OR by its selective antagonist, nor-binaltorphimine. We also found that blockade of the production of HSP70 but not HSC70 blocked the inhibitory effect of pretreatment with U-50488H on injury and viability. These observations provide evidence that stress-inducible HSP70 mediates delayed cardioprotection of prior kappa-OR stimulation.

The late phase of preconditioning

Unlike the early phase of preconditioning (PC), which lasts 2 to 3 hours and protects against infarction but not against stunning, the late phase of PC lasts 3 to 4 days and protects against both infarction and stunning, suggesting that it may have greater clinical relevance. It is now clear that late PC is a polygenic phenomenon that requires the simultaneous activation of multiple stress-responsive genes. Chemical signals released by a sublethal ischemic stress (such as NO, reactive oxygen species, and adenosine) trigger a complex cascade of signaling events that includes the activation of protein kinase C, Src protein tyrosine kinases, and nuclear factor kappaB and culminates in increased synthesis of inducible NO synthase, cyclooxygenase-2, aldose reductase, Mn superoxide dismutase, and probably other cardioprotective proteins. An analogous sequence of events can be triggered by a variety of stimuli, such as heat stress, exercise, and cytokines. Thus, late PC appears to be a universal response of the heart to stress in general. Importantly, the cardioprotective effects of late PC can be reproduced pharmacologically with clinically relevant agents (eg, NO donors, adenosine receptor agonists, endotoxin derivatives, or opioid receptor agonists), suggesting that this phenomenon might be exploited for therapeutic purposes. The purpose of this review is to summarize current information regarding the pathophysiology and mechanism of late PC.

The involvement of cytokines in the second window of ischaemic preconditioning

We utilized a rat model of myocardial infarction to investigate whether manganese superoxide dismutase (Mn-SOD), an intrinsic radical scavenger, and tumour necrosis factor- alpha (TNF-alpha) and/or interleukin-1beta (IL-1beta) are involved in the late phase of ischaemic preconditioning (IP). IP was induced in anaesthetized rats by four 3-min left coronary artery (LCA) occlusions, each separated by 10 min of reperfusion. Twenty-four hours after the repetitive brief ischaemia, the LCA was occluded for 20 min followed by reperfusion for 48 h. IP reduced the infarct size by approximately 46% as determined after 48 h of reperfusion. Antisense oligodeoxynucleotides to Mn-SOD inhibited the increases in Mn-SOD content and activity, and abolished the expected decrease in myocardial infarct size. Sense or scrambled oligodeoxynucleotides did not abolish either Mn-SOD induction or tolerance to ischaemia/reperfusion. The simultaneous administration of the antibodies to TNF-alpha (0.5 ml) and IL-1beta (0.5 mg) prior to IP abolished the cardioprotection and the increase in Mn-SOD activity induced by IP. We conclude that the induction and activation of Mn-SOD, mediated by TNF-alpha and IL-1beta after IP, plays an important role in the acquisition of late-phase cardioprotection against ischaemia/reperfusion injury in rats.

Involvement of cytokines in the mechanism of whole-body hyperthermia-induced cardioprotection

BACKGROUND

Hyperthermia increases cardiac tolerance to ischemia/reperfusion injury and activates manganese superoxide dismutase (Mn-SOD), an intrinsic radical scavenger, in myocardium in a biphasic manner. Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) induced a biphasic cardioprotection that corresponded to the activation of Mn-SOD. However, a direct association between Mn-SOD activation in myocardium and the acquisition of tolerance to ischemia/reperfusion injury induced by hyperthermia and the involvement of the cytokines in the signal transduction pathway for the hyperthermia-induced cardioprotection have not yet been elucidated.

METHODS AND RESULTS

Hyperthermia was induced in anesthetized rats by placement in a temperature-controlled water bath. At 0.5 and 72 hours after hyperthermia, ischemia was induced by occlusion of the left coronary artery for 20 minutes, followed by reperfusion for 48 hours. Inhibition of the increases in Mn-SOD content and activity 72 hours after hyperthermia by the administration of antisense oligodeoxynucleotides to Mn-SOD abolished the expected decrease in myocardial infarct size. The simultaneous administration of neutralizing antibodies to TNF-alpha and IL-1beta before hyperthermia abolished the biphasic cardioprotection and increase in Mn-SOD activity.

CONCLUSIONS

The increase in Mn-SOD activity mediated through the production of TNF-alpha and IL-1beta by whole-body hyperthermia is important in the acquisition of early- and late-phase cardioprotection against ischemia/reperfusion injury in rats.

Adenosine A(1) receptor activation induces delayed preconditioning in rats mediated by manganese superoxide dismutase

BACKGROUND

We have previously described a second window of protection against infarction in rabbits 24 to 72 hours after adenosine A(1) receptor (A(1)R) activation. In this study, we examined the potential role of the mitochondrial antioxidant manganese superoxide dismutase (Mn-SOD) as a potential end effector in mediating this protection.

METHODS AND RESULTS

Rats were treated with an intravenous bolus of the A(1)R agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA, 75 microg/kg) or saline vehicle. They were also given a 5 mg/kg IV infusion of a 22-mer phosphorothioate oligodeoxynucleotide (ODN) with sequence antisense to the initiation site of rat Mn-SOD mRNA. Sense ODN and scrambled ODN were used as controls. Twenty-four hours later, hearts were isolated and perfused with buffer at constant pressure and subjected to 35 minutes of regional ischemia and 2 hours of reperfusion. Treatment with CCPA compared with saline vehicle (control) significantly reduced infarct size, expressed as percentage of myocardium at risk (22.3+/-3.3% versus 42.1+/-3.8%, respectively; P=0.001). This protection was completely abolished by prior treatment with antisense ODN, which had no effect on its own. Neither sense ODN nor scrambled ODN had an effect on the CCPA-induced delayed cardioprotection. In separate animals, 24 hours after the same treatment, hearts were assayed for Mn-SOD content and activity. CCPA treatment induced a significant increase in myocardial Mn-SOD content and activity compared with the control condition; this increase was abolished by pretreatment with antisense ODN.

CONCLUSIONS

This is the first study to show that transient A(1)R activation induces delayed cardioprotection in the rat. These results strongly suggest an important role for mitochondrial Mn-SOD as a potential end effector of this protection.

Monophosphoryl lipid A provides biphasic cardioprotection against ischaemia-reperfusion injury in rat hearts

1 We utilized a rat model of myocardial infarction to investigate whether cardioprotection by monophosphoryl lipid A (MLA) is provided in the early and late phases, as well as to determine whether this cardioprotection may be related to the activation of manganese superoxide dismutase (Mn-SOD), an intrinsic radical scavenger. 2 Pretreatment with MLA (0.5 or 1.0 mg kg-1, i.v.) 24 h prior to 20-min left coronary artery (LCA) occlusion and 48-h reperfusion significantly decreased the incidence of ventricular fibrillation (VF) during ischaemia, as well as infarct size. Pretreatment with lower concentrations of MLA, however, was ineffective. 3 When we examined the time course of MLA (0.5 mg kg-1)-induced cardioprotection, both infarct size and the incidence of VF were significantly reduced in rats pretreated with MLA 0.5 h and 24 h before occlusion. We observed no differences, however, 2 and 72 h after MLA treatment. 4 The activity of Mn-SOD paralleled the cardioprotective effects of MLA. Mn-SOD activity in the myocardium was significantly enhanced in rats pretreated with MLA (0.5 mg kg-1) 0.5 and 24 h before. Mn-SOD activity was not altered, however, in rats pretreated 2 or 72 h before. Lower MLA concentrations were not effective even 24 h after the treatment. 5 We conclude that MLA treatment induced a biphasic pattern of cardioprotection. The pattern of Mn-SOD activity suggests that this enzyme may play a major role in the acquisition of cardioprotection against ischaemia-reperfusion injury.

Exercise provides direct biphasic cardioprotection via manganese superoxide dismutase activation

Epidemiologic investigations have shown that exercise reduces morbidity and mortality from coronary artery disease. In this study, using a rat model, we attempted to determine whether exercise can reduce ischemic injury to the heart and elucidate a mechanism for the cardioprotective effect of exercise. Results showed that exercise significantly reduced the magnitude of a myocardial infarction in biphasic manner. The time course for cardioprotection resembled that of the change in manganese superoxide dismutase (Mn-SOD) activity. The administration of the antisense oligodeoxyribonucleotide to Mn-SOD abolished the expected decrease in infarct size. We showed that the level of tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta) increased after exercise. The simultaneous administration of the neutralizing antibodies to the cytokines abolished the exercise-induced cardioprotection and the activation of Mn-SOD. Furthermore, TNF-alpha can mimic the biphasic pattern of cardioprotection and activation of Mn-SOD. An antioxidant completely abolished cardioprotection and the activation of Mn-SOD by exercise or the injection of TNF-alpha as well as exercise-induced increase in TNF-alpha and IL-1beta. The production of reactive oxygen species and endogenous TNF-alpha and IL-1beta induced by exercise leads to the activation of Mn-SOD, which plays major roles in the acquisition of biphasic cardioprotection against ischemia/reperfusion injury in rats.

Heat stress proteins and myocardial protection: experimental model or potential clinical tool?

Heat stress proteins (hsp) are induced by a variety of stimuli including elevated temperature, ischaemia, hypoxia, pressure overload and some chemicals. They help to maintain the metabolic and structural integrity of the cell, as a protective response to external stresses. They are known to protect the myocardium from the damaging effects of ischaemia and reperfusion. The heat stress response results in accumulation of heat stress proteins. The beneficial effects associated with their expression include improved endothelial and mechanical recovery of the ischaemic heart. In addition, preservation of high energy phosphates and reduction in infarct size. It has also been shown that critical amounts of hsp70 are necessary to ensure protection of the myocardium. However, questions remain regarding the biochemical mechanisms underlying this protective effect. Alterations in the cell metabolism and chaperone function of cells expressing heat shock proteins, are thought to be responsible. Despite the obvious clinical benefits related to the heat stress response in a clinical setting, the application of this phenomena remains limited. Heat, both quantitatively and qualitatively is one of the best inducers of heat stress proteins. However, the effects of heat stress are nonspecific and intracellular damage is a common occurrence. The search for alternative stimuli, particularly within the fields of pharmacotherapy or genetic manipulation may offer more viable options, if the heat stress response is take its place as an established strategy for myocardial protection.

Myocardial adaptation to ischaemia--the preconditioning phenomenon

The phenomenon of ischaemic preconditioning, highlights a new and endogenous route to myocardial protection, which we believe could be exploited in our search for new therapeutic ways to protect the infarcting myocardium. Ischaemic preconditioning has been shown to be associated with both an early, or acute phase of protection lasting approximately 1-2 hours, as well as a delayed phase or "second window of protection" seen at least 24 hours following the initial sublethal ischaemic insult, and lasting up to 72 hours. We believe that both responses are triggered by similar receptor mediated events in addition to using the similar signalling pathways involving kinase cascades. However it is thought that the ultimate target or end-effector through which the protection is manifest may be different for the early vs. late effects. Some evidence exists that the end-effector involved in early preconditioning may be via the ATP-sensitive potassium channel (K(ATP)). With respect to the second window of protection, the cellular mechanisms underlying this are not fully understood at present, however we believe that they may be dependent upon a similar signalling transduction pathway with upregulation of cytoprotective proteins such as the heat stress proteins, and/or anti-oxidant proteins. Evidence demonstrating that preconditioning can occur in the human myocardium is also accumulating. In this respect cultured human ventricular myocytes as well as human atrial muscle have been shown to be preconditioned with brief episodes of simulated ischemia. These human preparations also respond to the known triggers and possible end-effectors of preconditioning, (e.g. adenosine receptor stimulation and K(ATP) channel opening) as well as being able to elicit their responses through the PKC signalling pathway. Further support for this phenomenon, in man, comes from PTCA studies demonstrating that this invasive procedure can put patients into a "preconditioned state"; this effect being associated with reduced ischaemic symptoms as well as the involvement of the adenosine receptor and K(ATP) channel. Of further interest is the observation that patients with a previous history of angina, prior to a MI, sustain smaller infarcts and have an improved survival. However the most direct evidence that preconditioning occurs in man comes from studies in patients undergoing coronary artery bypass surgery. The above evidence that preconditioning can occur in man makes it now possible to begin to design clinical studies investigating cardioprotective properties of drugs that can specifically mimic this phenomenon.

Heat stress response and myocardial protection

Prior whole-body hyperthermia is able to protect the myocardium against ischaemia-reperfusion injury by reducing cellular necrosis, preserving the ventricular function and preventing the occurrence of arrhythmias. These cardioprotective effects are associated with reduction of oxidative stress, preservation of the high-energy phosphate levels and synthesis of heat stress proteins. A better understanding of this powerful protective adaptation of the myocytes would be of interest for potential clinical application, and rational design of specific agents that activate this mechanism will hopefully follow soon.

Heat shock improves recovery and provides protection against global ischemia after hypothermic storage

BACKGROUND

Improved methods of donor heart preparation before preservation could allow for prolonged storage and permit remote procurement of these organs. Previous studies have shown that overexpression of heat-shock protein 72 provides protection against ischemic cardiac damage. We sought to determine whether rats subjected to heat stress with only 6-hour recovery could acquire protection to a subsequent heart storage for 12 hours at 4 degrees C.

METHODS

Three groups of animals (n = 10 each) were studied: control, sham-treated, and heat-shocked rats (whole-body hyperthermia 42 degrees C for 15 minutes). After 12-hour cold ischemia hearts were reperfused on a Langendorff column. To confirm any differences in functional recovery, hearts were then subjected to an additional 15-minute period of warm global ischemia after which function and lactate dehydrogenase enzyme leakage were measured.

RESULTS

Heat-shocked animals showed marked improvements compared with controls in left ventricular developed pressure (63+/-4 mm Hg versus 44+/-4 mm Hg, p<0.05) heart rate x developed pressure (13,883+/-1,174 beats per minute x mm Hg versus 8,492+/-1,564 beats per minute x mm Hg, p<0.05), rate of ventricular pressure increase (1,912+/-112 mm Hg/second versus 1,215+/-162 mm Hg/second, p<0.005), rate of ventricular pressure decrease (1,258+/-89 mm Hg/second versus 774+/-106 mm Hg/second, p<0.005). Diastolic compliance and lactate dehydrogenase release were improved in heatshocked animals compared with controls and sham-treated animals. Differences between heat-shocked animals and control or sham-treated animals were further increased after the additional 15-minute period of warm ischemia. Western blot experiments confirmed increased heat-shock protein 72 levels in heat-shocked animals (>threefold) compared with sham-treated animals and controls.

CONCLUSIONS

Heat shock 6 hours before heart removal resulted in marked expression of heat-shock protein 72 and protected isolated rat hearts by increased functional recovery and decreased cellular necrosis after 12-hour cold ischemia in a protocol mimicking that of heart preservation for transplantation. Protection was further confirmed after an additional 15-minute period of warm ischemia.

Whole-body hyperthermia provides biphasic cardioprotection against ischemia/reperfusion injury in the rat

BACKGROUND

Hyperthermia increases cardiac tolerance to ischemia/reperfusion injury 24 hours after the heat stress. Free radicals and redox mechanisms have been implicated in such tolerance. However, the time course and its relation to the induction of antioxidative enzymes in the protection induced by whole-body hyperthermia against ischemia/reperfusion injury are unknown.

METHODS AND RESULTS

Hyperthermia was induced in anesthetized rats by placement in a temperature-controlled water bath. After the defined recovery interval(s) at room temperature, ischemia was induced by occlusion of the left coronary artery for 20 minutes, followed by reperfusion for 48 hours. The exposure to hyperthermia led to a recovery interval- dependent, biphasic reduction in the incidence of ventricular fibrillation during ischemia and in the size of the myocardial infarct as determined after 48 hours of reperfusion. The time course of the late-phase (24- to 96-hour recovery interval) but not the early-phase (0.5 hour) cardioprotection depended on the degree of hyperthermia. The time course of the increase in myocardial manganese superoxide dismutase (Mn-SOD) activity corresponded to that of the cardioprotective effects, although an increase in the content of Mn-SOD and of heat shock protein 72 corresponded only to the late-phase effects. Administration of an antioxidant before hyperthermia abolished the early- and late-phase cardioprotection and the increase in Mn-SOD activity.

CONCLUSIONS

THe activation of Mn-SOD mediated by free radical production during hyperthermia is important in the acquisition of early-phase and late-phase cardioprotection against ischemia/reperfusion injury in rats.

Infarct size-reducing effect of heat stress and alpha1 adrenoceptors in rats

1. Noradrenaline (NA), which is abundantly released during heat stress (HS), is known to induce both delayed cardioprotection and heat stress protein (HSP) 72 expression by the mediation of alpha, adrenoceptors. Therefore, we have investigated the implication of alpha1 adrenoceptors in HS-induced resistance to myocardial infarction, in the isolated rat heart model. 2. Rats were pretreated with prazosin (1 mg kg(-1), i.p., Praz) or 5-methylurapidil (3 mg kg(-1), i.v., 5MU) or chloroethylclonidine (3 mg kg(-1), i.v., CEC) or vehicle (V) in order to selectively antagonize alpha1, alpha1A and alpha1B adrenoceptors. They were then either heat stressed (42 degrees C for 15 min) or sham anaesthetized. Twenty-four hours later. their hearts were isolated, retrogradely perfused, and subjected to a 30 min occlusion of the left coronary artery followed by 120 min of reperfusion. 3. Infarct-to-risk ratio was significantly reduced in HS+V (15.4+/-1.8%) compared to Sham+V (35.7+/-1.3%) hearts. This effect was abolished in Praz-treated (29.1+/-1.6% in HS+Praz vs 34.1+/-4.0% in Sham+Praz), 5MU-treated (34.5+/-2.2% in HS+5MU vs 31.2+/-2.0% in Sham+5MU) and CEC-treated (33.4+/-3.0% in HS+CEC vs 32.4+/-1.3% in Sham+CEC) groups. Western blot analysis of myocardial HSP72 showed an HS-induced increase of this protein, which was not modified by Praz, 5MU and CEC pretreatments. 4. We conclude that both alpha1A and alpha1B adrenoceptor subtypes appear to play a role in the heat stress-induced cardioprotection, independently of the HSP72 level. Further investigations are required to elucidate the precise role of HSPs in this adaptative response.