Drug-induced heat-shock preconditioning improves postischemic ventricular recovery after cardiopulmonary bypass

Heat shock protein 90 inhibition and multi-target approach to maximize cardioprotection in ischaemic injury

Despite several advances in medicine, ischaemic heart disease remains a major cause of morbidity and mortality. The unravelling of molecular mechanisms underlying disease pathophysiology has revealed targets for pharmacological interventions. However, transfer of these pharmcological possibilities to clinical use has been disappointing. Considering the complexity of ischaemic disease at the cellular and molecular levels, an equally multifaceted treatment approach may be envisioned. The pharmacological principle of 'one target, one key' may fall short in such contexts, and optimal treatment may involve one or many agents directed against complementary targets. Here, we introduce a 'multi-target approach to cardioprotection' and propose heat shock protein 90 (HSP90) as a target of interest. We report on a member of a distinct class of HSP90 inhibitor possessing pleiotropic activity, which we found to exhibit potent infarct-sparing effects.

The Possible Role of Nitric Oxide Pathway in Pentylenetetrazole Preconditioning Against Seizure in Mice

Preconditioning is defined as an induction of adaptive response in organs against lethal stimulation provoked by subsequent mild sublethal stress. Several chemical agents have been demonstrated to cause brain tolerance through preconditioning. The aim of the present study is to test the hypothesis that preconditioning with pentylenetetrazole (PTZ) may have protective effect against seizure induced by i.v. infusion of PTZ. Mice were preconditioned by low-dose administration of PTZ (25 mg/kg) for 5 consecutive days, and the threshold of seizure elicited by i.v. infusion of PTZ was measured. To investigate the possible role of nitric oxide, NOS inhibitor enzymes, including L-NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) (10 mg/kg), aminoguanidine (AG) (50 mg/kg), 7-nitroindazole (7-NI) (15 mg/kg), and L-arginine (L-arg) (60 mg/kg), were administered concomitantly with PTZ in both acute and chronic phases. Determination of seizure threshold revealed significant enhancement after preconditioning with low dose of PTZ. While the protective effect of PTZ preconditioning was enhanced after the administration of L-arg, it was reversed following administration of L-NAME and 7NI, suggesting the involvement of nitric oxide pathway as an underlying mechanism of PTZ-induced preconditioning. Preconditioning with PTZ led to brain tolerance and adaptive response in animal model of PTZ-induced seizure. This effect is in part due to the involvement of nitric oxide pathway.

Bridging translation for acute kidney injury with better preclinical modeling of human disease

The current lack of effective therapeutics for patients with acute kidney injury (AKI) represents an important and unmet medical need. Given the importance of the clinical problem, it is time for us to take a few steps back and reexamine current practices. The focus of this review is to explore the extent to which failure of therapeutic translation from animal studies to human studies stems from deficiencies in the preclinical models of AKI. We will evaluate whether the preclinical models of AKI that are commonly used recapitulate the known pathophysiologies of AKI that are being modeled in humans, focusing on four common scenarios that are studied in clinical therapeutic intervention trials: cardiac surgery-induced AKI; contrast-induced AKI; cisplatin-induced AKI; and sepsis associated AKI. Based on our observations, we have identified a number of common limitations in current preclinical modeling of AKI that could be addressed. In the long term, we suggest that progress in developing better preclinical models of AKI will depend on developing a better understanding of human AKI. To this this end, we suggest that there is a need to develop greater in-depth molecular analyses of kidney biopsy tissues coupled with improved clinical and molecular classification of patients with AKI.

Distal tubular epithelial cells of the kidney: Potential support for proximal tubular cell survival after renal injury

The tubular epithelium of the kidney is susceptible to injury from many causes, such as ischemia-reperfusion and the associated oxidative stress, nephrotoxins, inflammatory and immune disorders and many others. The outcome is often acute kidney injury, which may progress to chronic kidney disease and fibrosis. Acute kidney injury involves not only direct injury to the distal tubular (DT) and proximal tubular (PT) epithelium during and immediately following the injurious event, but the closely-associated and sometimes dysfunctional renal vascular endothelium also plays an important part in modulating the tubular epithelial injury. In comparison with the PT, the DT epithelium is less sensitive to cell death, especially after ischemic injury. It is more prone to apoptosis than necrosis when it dies, and has key paracrine and autocrine functions in secreting an array of inflammatory, reparative, and survival cytokines that include chemotactic cytokines, polypeptide growth factors, and vasoactive peptides. In a neighborly way, the cytokines and growth factors secreted by the DT epithelium may then act positively on the ischemia-sensitive PT that has receptors to many of these proteins, but may not be able to synthesize them. A more complete understanding of these cellular events will allow protection against nephron destruction, regeneration leading to re-epithelialization of the injured tubules, or prevention of progression to chronic kidney disease. This review looks at these functions in the DT epithelial cells, specifically the cells in the medullary thick ascending limb of the loop of Henle, in contrast with those of the straight segment of the PT.

Cardioprotective effect of the Hibiscus rosa sinensis flowers in an oxidative stress model of myocardial ischemic reperfusion injury in rat

BACKGROUND

The present study investigates the cardioprotective effects of Hibiscus rosa sinensis in myocardial ischemic reperfusion injury, particularly in terms of its antioxidant effects.

METHODS

The medicinal values of the flowers of Hibiscus rosa sinensis (Chinese rose) have been mentioned in ancient literature as useful in disorders of the heart. Dried pulverized flower of Hibiscus rosa sinensis was administered orally to Wistar albino rats (150-200 gms) in three different doses [125, 250 and 500 mg/kg in 2% carboxy methyl cellulose (CMC)], 6 days per week for 4 weeks. Thereafter, rats were sacrificed; either for the determination of baseline changes in cardiac endogenous antioxidants [superoxide dismutase, reduced glutathione and catalase] or the hearts were subjected to isoproterenol induced myocardial necrosis.

RESULTS

There was significant increase in the baseline contents of thiobarbituric acid reactive substances (TBARS) [a measure of lipid per oxidation] with both doses of Hibiscus Rosa sinensis. In the 250 mg/kg treated group, there was significant increase in superoxide dismutase, reduced glutathione, and catalase levels but not in the 125 and 500 mg/kg treated groups. Significant rise in myocardial thiobarbituric acid reactive substances and loss of superoxide dismutase, catalase and reduced glutathione (suggestive of increased oxidative stress) occurred in the vehicle treated hearts subjected to in vivo myocardial ischemic reperfusion injury.

CONCLUSION

It may be concluded that flower of Hibiscus rosa sinensis (250 mg/kg) augments endogenous antioxidant compounds of rat heart and also prevents the myocardium from isoproterenol induced myocardial injury.

Induction of Thioredoxin and Mitochondrial Survival Proteins Mediates Preconditioning-Induced Cardioprotection and Neuroprotection

Delayed cardio- and neuroprotection are observed following a preconditioning procedure evoked by a brief and nontoxic oxidative stress due to deprivation of oxygen, glucose, serum, trophic factors, and/or antioxidative enzymes. Preconditioning protection can be observed in vivo and is under clinical trials for preservation of cell viability following organ transplants of liver. Previous studies indicated that ischemic preconditioning increases the expression of heat-shock proteins (HSPs) and nitric oxide synthase (NOS). Our pilot studies indicate that the treatment of neuronal NOS inhibitor (7-nitroindazole) and 6Br-cGMP blocks and mimics, respectively, preconditioning protection in human neuroblastoma SH-SY5Y cells. This minireview focuses on nitric oxide-mediated cellular adaptation and the related cGMP/PKG signaling pathway in a compensatory mechanism underlying preconditioning-induced hormesis. Both preconditioning and 6Br-cGMP increase the induction of human thioredoxin (Trx) mRNA and protein for cytoprotection, which is largely prevented by transfection of cells with Trx antisense but not sense oligonucleotides. Cytosolic Trx1 and mitochondrial Trx2 suppress free radical formation, lipid peroxidation, oxidative stress, and mitochondria-dependent apoptosis; knock out/down of either Trx1 or Trx2 is detrimental to cell survival. Other recent findings indicate that a transgenic increase of Trx in mice increases tolerance against oxidative nigral injury caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Trx1 can be translocated into nucleus and phosphoactivated CREB for a delayed induction of mitochondrial anti-apoptotic Bcl-2 and antioxidative MnSOD that is known to increase vitality and survival of cells in the brain and the heart. In conclusion, preconditioning adaptation or a brief oxidative stress induces a delayed nitric oxide-mediated compensatory mechanism for cell survival and vitality in the central nervous system and the cardiovascular system. Preconditioning-induced adaptive tolerance may be signaling through a cGMP-dependent induction of cytosolic redox protein Trx1 and subsequently mitochondrial proteins such as Bcl-2, MnSOD, and perhaps Trx2 or HSP70.

ORAL ADMINISTRATION OF GERANYLGERANYLACETONE IMPROVES SURVIVAL RATE IN A RAT ENDOTOXIN SHOCK MODEL: ADMINISTRATION TIMING AND HEAT SHOCK PROTEIN 70 INDUCTION

The present study was performed to determine whether oral pretreatment with geranylgeranylacetone (GGA) inhibits proinflammatory cytokine liberation and nitric oxide (NO) production in lipopolysaccharide (LPS)-treated rats and protects rats against death from LPS-induced endotoxin shock, and whether such protection by GGA is related to heat shock protein (HSP) 70 induction in multiple organs of rats. GGA (200 mg/kg) was given orally to rats. LPS (20 mg/kg) was administered intraperitoneally 4, 8, 16, or 24 h after GGA administration. The survival of rats was monitored over 24 h after LPS administration. GGA treatment at 8 or 16 h before LPS dramatically improved the survival rate of LPS-treated rats. Plasma levels of proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-6) and NO 6 h after LPS administration in these GGA-pretreated rats were less than one-half of those in rats treated with LPS alone. A GGA challenge 8 or 16 h before LPS administration enhanced HSP70 expression in rat organs after LPS. Treatment with GGA 8 h before LPS minimized hepatic and renal damage. Furthermore, the protective effect of GGA on mortality in LPS-treated rats was inhibited with quercetin, known as an HSP70 inhibitor. These results suggest that oral administration of GGA at an optimal time before LPS injection induces and enhances HSP70 expression in several organs, inhibits proinflammatory cytokine and NO production, and prevents organ damage, resulting in an improved survival rate.

Modulating the Endoplasmic Reticulum Stress Response with trans-4,5-Dihydroxy-1,2-Dithiane Prevents Chemically Induced Renal Injury In Vivo

Agents that disrupt functions of the endoplasmic reticulum (ER) induce expression of ER stress-response genes including ER chaperones. Increased expression of the major ER chaperone, Grp78, protects cells, including renal epithelial cells, from chemically induced injury and death in vitro. In this study, we determined if pharmacological manipulation of the ER stress-response gene is an effective strategy to protect the kidney from chemical stress in vivo. Treatment with trans-4,5-dihydroxy-1,2-dithiane (DTTox), a novel inducer of ER stress proteins, stimulated a time-and dose-dependent increase in Grp78 expression in the kidney, but it did not cause detectable injury. Furthermore, prior treatment with DTTox protected the proximal tubular epithelium against a subsequent challenge with the nephrotoxicant S-(1,1,2,2,-tetrafluoroethyl)-L-cysteine (TFEC). In contrast, activating a heat shock response did not have a protective effect. Prior treatment with DTTox did not reduce covalent binding of radiolabeled reactive metabolites of (35)S-TFEC to renal proteins, indicating that protection was not due to an effect on the metabolic activation of TFEC to the reactive metabolite(s) responsible for renal injury. Antisense grp78 expression in the renal epithelial cell line LLC-PK1 blocked the DTTox-induced Grp78 increase and ablated the protective effect against TFEC damage, indicating that the induction of grp78 expression and the ER stress response were critical for the protective effect of DTTox. These findings suggest that increased expression of Grp78 plays a major role in the protection of renal epithelial cells from reactive intermediate-induced chemical injury in vivo and that pharmacological manipulation is an effective strategy to prevent damage by some classes of nephrotoxicants.

Protection "outside the box" (skeletal remote preconditioning) in rat model is triggered by free radical pathway

BACKGROUND

Remote preconditioning (RPC) for myocardial protection had been demonstrated in several organs, such as the kidney and mesentery artery. The aim of study was to investigate the effect of skeletal ischemia/reperfusion on coronary artery occlusion-induced myocardial infarction and to investigate the role of the free radicals.

MATERIAL AND METHODS

RPC was performed in rats by a repeated four-cycle 10-min ischemia-reperfusion of femoral artery. Four experimental groups were included: I, sham group; II, RPC only; III, infarction only; and IV, which incorporated both RPC and infarction. A chemiluminescence study showed significant elevation of free radicals in groups with RPC, and pretreated mercaptopropionyl-glycine (MPG), a free radical scavenger, abolished the production of free radicals.

RESULTS

The infarct size was significantly reduced for group IV (24.7 +/- 8.8%) compared with group III (51.4 +/- 9.1%; P < 0.001), and the effect was abolished by pretreatment with MPG (49.2 +/- 6.3% in MPG + III versus 50.1 +/- 8.2% in MPG + IV; P > 0.05). Cardiac enzymes also revealed significant decrease in the level for group IV compared with group III, and the protective effect could be abolished by MPG. Western blotting of heat shock protein (HSP) revealed that consistent elevation of HSP 25 and 70 in groups II, III, and IV, and the elevation can be abrogated by pretreatment with MPG. The expression of the antioxidant enzymes, Mn-superoxidase dismutase and glutathione peroxidase, in the area of risk were consistently elevated in groups II, III, and IV, similar to HSP.

CONCLUSIONS

The skeletal RPC in rats can produce a protective effect in an infarction model that may be triggered through free radical pathway, and the protective effect was associated with HSP and antioxidant enzymes.

Geranylgeranylacetone ameliorates ischemic acute renal failure via induction of Hsp70

BACKGROUND

Heat shock proteins (HSPs) are well known as cytoprotective proteins. Geranylgeranylacetone (GGA), an antiulcer agent, has recently been shown to induce Hsp70. This study was performed to investigate the renoprotective properties of GGA.

METHODS

The effect of GGA on the induction of the major HSPs (Hsp90, Hsp70, Hsc70, Hsp60, and Hsp32) was studied in the rat kidney or rat primary cultures of tubular epithelial cells (R-TECs) by Western blot. Localization of Hsp70 was determined by immunohistochemistry. The renoprotective effects of GGA were studied using a rat model of ischemia/reperfusion (I/R) injury. GGA (400 mg/kg), GGA with quercetin pretreatment (100 mg/kg), or a vehicle was given to rats 24 hours and again 1 hour prior to the induction of I/R injury. Rats were sacrificed at 24 hours after reperfusion. Histologic analyses and terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) assay were performed. Blood urea nitrogen (BUN) and serum creatinine was also measured. The cytoprotective properties of GGA were also studied in vitro by treating R-TECs with GGA (10 mumol/L) or a vehicle, followed by incubation in culture medium with oxidative stress condition (0.5 mmol/L hydrogen peroxide) or ischemic condition (2 nmol/L NaCN and 20 mmol/L 2-deoxyglucose in the absence of medium glucose).

RESULTS

Oral administration of GGA induced Hsp70 expression in the kidney (which peaked at 24 hours) but did not induce Hsp90, Hsc70, Hsp60, or Hsp32. The induction of Hsp70 was blocked by quercetin. Immunohistochemistry showed that Hsp70 was localized mainly in the tubular epithelial cells. Preconditioning rats with GGA significantly decreased BUN and serum creatinine levels after I/R injury. Histologic examination revealed that GGA significantly attenuated tubular damage and macrophage infiltration. The number of TUNEL-positive cells also decreased significantly in the GGA group. Quercetin, an inhibitor of Hsp70 induction, eliminated these renoprotective effects of GGA. In in vitro study, GGA-induced Hsp70 in R-TECs, which peaked at 2 to 4 hours. Both oxidative stress and ischemic stimuli induced apoptosis in R-TECs. GGA significantly suppressed the number of apoptotic cells in both conditions.

CONCLUSION

The results support the hypothesis that GGA induces Hsp70, protects tubular epithelial cells from apoptosis, and thus ameliorates tubular damage by I/R injury. The present study suggests that GGA would be a useful tool in treating acute renal failure or preventing transplanted kidney damage in the clinical setting.

Cyclosporine protects against ischemia/reperfusion injury in rat kidneys

Renal ischemia followed by reperfusion leads to acute renal failure in both native kidneys and renal allografts. Cyclosporine A (CsA) has been used as an immunosuppressive agent in organ transplantation. In the present study, the effect of CsA on ischemia/reperfusion (I/R)-induced injury in the kidney was investigated. Ischemia/reperfusion injury caused a significant deterioration in the renal function, morphology and gave rise to a severe oxidative stress in the kidney. At 3 mg/kg i.v., CsA significantly improved the functional and histological parameters and attenuated the oxidative stress induced by renal ischemia/reperfusion. From the results of our study, it can be concluded that low-dose CsA pretreatment preconditions the rat kidneys against subsequent ischemia/reperfusion injury.

Heat shock proteins in the regulation of apoptosis: new strategies in tumor therapy: a comprehensive review

Heat shock proteins (Hsp) form the most ancient defense system in all living organisms on earth. These proteins act as molecular chaperones by helping in the refolding of misfolded proteins and assisting in their elimination if they become irreversibly damaged. Hsp interact with a number of cellular systems and form efficient cytoprotective mechanisms. However, in some cases, wherein it is better if the cell dies, there is no reason for any further defense. Programmed cell death is a widely conserved general phenomenon helping in many processes involving the reconstruction of multicellular organisms, as well as in the elimination of old or damaged cells. Here, we review some novel elements of the apoptotic process, such as its interrelationship with cellular senescence and necrosis, as well as bacterial apoptosis. We also give a survey of the most important elements of the apoptotic machinery and show the various modes of how Hsp interact with the apoptotic events in detail. We review caspase-independent apoptotic pathways and anoikis as well. Finally, we show the emerging variety of pharmacological interventions inhibiting or, just conversely, inducing Hsp and review the emergence of Hsp as novel therapeutic targets in anticancer protocols.

Ventricular tachyarrhythmias in a canine model of LQT3: arrhythmogenic effects of sympathetic activity and therapeutic effects of mexiletine

The ventricular tachyarrhythmias associated with the LQT3 syndrome are typically bradycardia-dependent. However, some episodes can be associated with exercise or emotional stress, suggesting a different arrhythmogenic mechanism when sympathetic activity predominates. This study examined the potential arrhythmogenic mechanisms during periods of autonomically mediated transient heart rate acceleration in a canine anthopleurin-A model of LQT3 syndrome. Using plunge needle electrodes, transmural unipolar electrograms of the left ventricle were recorded from endocardial (Endo), mid-myocardial (Mid) and epicardial (Epi) sites. The activation-recovery interval (ARI) was measured to estimate local refractoriness. The cardiac cycle length was gradually shortened by cessation of vagal stimulation (vagal stimulation protocol (VSP)), and intramural electrograms and onset mode of ventricular tachyarrhythmias were analyzed in 7 experiments. The VSP was performed 8 times before and 5 times after administration of mexiletine in each experiment. Before mexiletine, vagal stimulation slowed the heart rate and created large transmural ARI dispersion because of a greater ARI prolongation at Mid rather than Epi/Endo sites. After cessation of vagal stimulation, unipolar electrograms started to show ARI alternans and ventricular premature beats developed sporadically. Sustained ventricular tachyarrhythmias were induced in 12 of the 56 trials of the VSP. Initiation of ventricular tachyarrhythmias was associated with delayed conduction at Mid/Endo sites. Mexiletine attenuated transmural ARI dispersion, and neither ARI alternans nor ventricular tachyarrhythmias was observed during all 35 trials of the VSP after mexiletine administration. Heart rate acceleration induced by an abrupt shift to a state of predominant sympathetic activity enhances arrhythmias in this LQT3 model. Mexiletine homogenizes ventricular repolarization, suppresses premature complexes and was antiarrhythmic during ventricular tachyarrhythmias induced by the VSP.

Ischemia-reperfusion-induced lung injury

Ischemia-reperfusion-induced lung injury is characterized by nonspecific alveolar damage, lung edema, and hypoxemia occurring within 72 hours after lung transplantation. The most severe form may lead to primary graft failure and remains a significant cause of morbidity and mortality after lung transplantation. Over the past decade, better understanding of the mechanisms of ischemia-reperfusion injury, improvements in the technique of lung preservation, and the development of a new preservation solution specifically for the lung have been associated with a reduction in the incidence of primary graft failure from approximately 30 to 15% or less. Several strategies have also been introduced into clinical practice for the prevention and treatment of ischemia-reperfusion-induced lung injury with various degrees of success. However, only three randomized, double-blinded, placebo-controlled trials on ischemia-reperfusion-induced lung injury have been reported in the literature. In the future, the development of new agents and their application in prospective clinical trials are to be expected to prevent the occurrence of this potentially devastating complication and to further improve the success of lung transplantation.

Preoperative glutamine administration induces heat-shock protein 70 expression and attenuates cardiopulmonary bypass-induced inflammatory response by regulating nitric oxide synthase activity

BACKGROUND

Heat-shock protein 70 (HSP70) plays a major role in the pathophysiology of inflammation, and the induction of HSP70 before the onset of inflammation can reduce organ damage through a self-protective system. Glutamine is known to be an inducer of HSP70, and its preoperative administration seems useful in attenuating cardiopulmonary bypass (CPB)-induced inflammatory response.

METHODS AND RESULTS

Adult male Sprague-Dawley rats (group G, received 100 mg/kg of glutamine via the right jugular vein 3 times per day for 1 week and just before the initiation of CPB; group C served as control) underwent CPB (60 minutes, 100 mL/kg per minute, 34 degrees C) and were killed 3 hours after the termination of CPB. Group G showed significantly lower plasma concentrations of interleukin-6 and interleukin-8 after CPB termination. Myocardial and respiratory damages were significantly attenuated in group G, as evidenced by Langendorff perfusion, respiratory index, and neutrophil adherence. HSP70 expressions in the heart, lung, and liver were detected only in group G before CPB and were markedly stronger in group G 3 hours after CPB termination. Although plasma nitrate+nitrite concentrations were not significantly different between the groups, endothelial-constitutive nitric oxide synthase (NOS) activity was markedly preserved and inducible NOS activity was markedly attenuated in the tissues of group G.

CONCLUSIONS

These results suggest that preoperative glutamine administration induces HSP70 expression before CPB and attenuates CPB-induced inflammation by regulating NOS activity, which may be a prospective management for conferring tolerance to CPB-induced inflammatory response through a self-protective mechanism.

Chronic garlic administration protects rat heart against oxidative stress induced by ischemic reperfusion injury

BACKGROUND

Oxidative stress plays a major role in the biochemical and pathological changes associated with myocardial ischemic-reperfusion injury (IRI). The need to identify agents with a potential for preventing such damage has assumed great importance. Chronic oral administration of raw garlic has been previously reported to augment myocardial endogenous antioxidants. In the present study, the effect of chronic oral administration of raw garlic homogenate on oxidative stress induced by ischemic-reperfusion injury in isolated rat heart was investigated.

RESULTS

Raw garlic homogenate (125, 250 and 500 mg/kg once daily for 30 days) was administered orally in Wistar albino rats. Thereafter, hearts were isolated and subjected to IRI (9 min. of global ischemia, followed by 12 min of reperfusion; perfusion with K-H buffer solution; 37 degrees C, 60 mm Hg.). Significant myocyte injury and rise in myocardial TBARS along with reduction in myocardial SOD, catalase, GSH and GPx were observed following IRI. Depletion of myocardial endogenous antioxidants and rise in TBARS were significantly less in the garlic-treated rat hearts. Oxidative stress induced cellular damage as indicated by ultrastructural changes, like disruption of myofilament, Z-band architecture along with mitochondrial changes were significantly less.

CONCLUSIONS

The study strongly suggests that chronic garlic administration prevents oxidative stress and associated ultrastructural changes, induced by myocardial ischemic-reperfusion injury.

Free-radical production triggered by hyperthermia contributes to heat stress-induced cardioprotection in isolated rat hearts

1. Heat stress (HS) is known to protect the myocardium against ischaemic damage. It has been reported that reactive oxygen species (ROS) are abundantly produced during this stress. Since mechanisms triggering the HS-induced cardioprotection remain unknown, we investigated the role of ROS in the genesis of this protective phenomenon. 2. Rats were divided into four groups (n=8 in each group), subjected to either hyperthermia (42 degrees C internal temperature for 15 min) or sham anaesthesia and treated or not with N-2-mercaptopropionyl glycine (MPG), a synthetic antioxidant, 10 min before HS. 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. Myocardial Hsp 27 and 70 expression was assessed by Western blot analysis (n=4). Cardiac activities of antioxidant enzymes (superoxide dismutase and glutathione peroxidase) were also examined (n=4). 3. Infarct-to-risk zone ratio was significantly reduced in HS (17+/-1.3%) compared to Sham (34.3+/-1.7%) hearts. This effect was abolished by MPG pretreatment (40.6+/-1.9% in HS+MPG vs. 39.8+/-2.5% in Sham+MPG hearts). This cardioprotection was associated with an enhanced Hsp 27 and 70 expression, which was not modified by MPG pretreatment. Antioxidant enzyme activities was not modified by heat stress or MPG pretreatment. 4. Free radical production following hyperthermia appears to play a role in the heat stress induced cardioprotection, independently of Hsp levels. Antioxidant enzyme activities do not seem to be implicated in this cardioprotective mechanism.

Inhibition of the ubiquitin-proteasome pathway induces differential heat-shock protein response in cardiomyocytes and renders early cardiac protection

The effects of proteasome inhibition (PI) on heat-shock protein (HSP) expression in cardiomyocytes were investigated. Neonatal rat cardiomyocytes were incubated with MG132 (0.1-10 microM) for 1 h. Induction of various HSPs was determined by real-time PCR and Western blotting. PI induced a 2- to 3-fold increase in HSP27, HSP60, and HSP90, and a 18-fold increase in HSP70 mRNA expression, whereas HSP40 levels were unaffected. Western blotting revealed increased protein expression for HSP70 after PI. Similar results were obtained with MG262. HSP induction correlated with enhanced survival of neonatal cardiomyocytes after sublethal heat stress in XTT testing. In papillary muscles, pretreatment with MG132 (10 microM, 90 min) was associated with enhanced recovery of the contractile parameters after a 40-min hypoxia. In these proof-of-principle experiments, we show that PI induces differential heat-shock response in cardiomyocytes, accompanied by enhanced cell survival and functional recovery after various forms of stress.

Pharmacological preconditioning with low-dose cyclosporine or FK506 reduces subsequent ischemia/reperfusion injury in rat kidney

BACKGROUND

Ischemia/reperfusion (I/R) injury in the early posttransplant period is closely associated with delayed recovery of graft function, increased acute rejection, and late allograft dysfunction. Pharmacological preconditioning with low-dose cyclosporine (CsA) or FK506 was performed to induce ischemic tolerance in rat kidney with I/R injury.

METHODS

Low-dose CsA (3 mg/kg, administered i.v.) or FK506 (0.3 mg/kg i.v.) were used to induce ischemic tolerance in Sprague-Dawley rats, and the induction of heat shock protein (hsp) 70 by CsA or FK506 was evaluated overtime. Rats were pretreated with CsA or FK506 6 hr before I/R injury when hsp70 was maximally expressed, and were killed 24 hr later. The effect of pharmacological preconditioning on subsequent I/R injury was evaluated in terms of renal function, histopathology score, assays for apoptosis (DNA fragmentation analysis, TUNEL staining, expressions of pro-apoptotic genes, and caspase activity), and the expression of inflammatory cytokine genes (interleukin-1 and tumor necrosis factor-alpha).

RESULTS

Preconditioning with low-dose CsA or FK506 significantly improved renal function and renal histology, compared to rats with I/R injury. Apoptotic cell death (typical DNA laddering and increased TUNEL-positive cells) in rat kidneys with I/R injury, was decreased by pretreatment with low-dose CsA or FK506. Increased expression of pro-apoptotic genes (Fas, Fas-ligand, caspase 1 and 3) and activated caspases in ischemic rat kidneys were decreased after CsA or FK506 pretreatment.

CONCLUSIONS

Pretreatment with low-dose CsA or FK506 prevents subsequent I/R injury, and this effect may be related to the induction of hsp70. Pretreatment of renal donors with low-dose CsA or FK506 may result in an improvement in immediate posttransplant function.

Single oral dose of geranylgeranylacetone induces heat-shock protein 72 and renders protection against ischemia/reperfusion injury in rat heart

BACKGROUND

Induction of heat-shock proteins (HSPs) results in cardioprotection against ischemic insult. Geranylgeranylacetone (GGA), known as an antiulcer agent, reportedly induces HSP72 in the gastric mucosa and small intestine of rats. The present study tested the hypothesis that oral GGA would induce HSP72 in the heart and thus render cardioprotection against ischemia/reperfusion injury in rats.

METHODS AND RESULTS

Cardiac expression of HSPs was quantitatively evaluated in rats by Western blot analysis. Ten minutes of whole-body hyperthermia induced HSP72 expression in the rat hearts. A single oral dose of GGA (200 mg/kg) also induced expression of HSP72, which peaked at 24 hours after administration. Therefore, isolated perfused heart experiments using a Langendorff apparatus were performed 24 hours after administration of 200 mg/kg GGA (GGA group) or vehicle (control group). After a 5-minute stabilization period, no-flow global ischemia was given for 20, 40, or 60 minutes, followed by 30 minutes of reperfusion. During reperfusion, the functional recovery was greater and the released creatine kinase was less in the GGA group than in the control group. Electron microscopy findings revealed that the ischemia/reperfusion-induced damage of myocardial cells was prevented in GGA-treated myocytes.

CONCLUSIONS

The results suggest that oral GGA is cardioprotective against ischemic insult through its induction of HSP72.

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.

Transgene overexpression of alphaB crystallin confers simultaneous protection against cardiomyocyte apoptosis and necrosis during myocardial ischemia and reperfusion

We investigated whether enhanced expression of alphaB crystallin, a stress-inducible molecular chaperone of the small heat shock family, can protect myocardial contractile apparatus against ischemia reperfusion (I/R) injury. Transgenic mice overexpressing alphaB crystallin were generated using the 0.76 kb rat alphaB crystallin cDNA cloned into a pCAGGS plasmid driven by a human cytomegalovirus expression system. Southern analysis confirmed transgene integration and Northern and Western blotting characterized expression (3.1-fold and 6.9-fold elevations in myocardial mRNA and protein levels, respectively). Extent of functional recovery over a 3 h reperfusion period following a 20 min ischemic period in transgenic and wild-type mouse hearts was assessed using an ex vivo work-performing heart preparation. The transgenic group displayed significantly higher values of DP at R45 min (29.14+/-1.9 mm Hg vs. 17.6+/-0.7 mm Hg), R60 min (31.56+/-1.7 mm Hg vs. 17.8+/-0.8 mm Hg), and R75 min (32.5+/-2.2 mm Hg vs. 16.9+/-0.9 mm Hg), and of dLVP/dt at R45 min (1740.2+/-111.5 mm Hg.s-1 vs. 548.7+/-82.2 mm Hg.s-1) and R60 min (1199.8+/-104.6 mm Hg.s-1 vs. 466.9+/-61.1 mm Hg.s-1). The transgenic group also displayed development of less oxidative stress, decreased extent of infarction, and attenuated cardiomyocyte apoptotic cell death. Transgene overexpression of alphaB crystallin was therefore successful in diminishing the independent contributory effects of both necrosis and apoptosis on I/R-induced cell death.

The role of opioid receptors in hypoxic preconditioning against seizures in brain

Preconditioning is defined as an adaptive mechanism produced by short periods of hypoxia/ischemia, resulting in protection against subsequent ischemic insult, and development of seizures. Results of the present study demonstrate that an episode of normobar hypoxia reduces the susceptibility to convulsions induced by pentylenetetrazol (PTZ) 30 min, 24 h, as well as 4 and 7 days later. Administration of morphine showed similar effects after 24 h. Naloxone, given before ischemic preconditioning, as well as morphine, blocked the development of the protection. Administration of D-Ala-Met-enkephalin-Gly-ol (DAMGO - a selective mu-opioid receptor agonist), as well as trans-3, 4-dichloro-N-methyl-N-[7-(1-pyrrolidinyl) cycloexilbenzeneacetamide ethane sulfonate] (U-69,593 - a selective kappa-opioid receptor agonist), mimicked the effects of hypoxic preconditioning (HPC). (-)-N-(Cyclopropylmethyl)-4,14-dimethoxymorphinan-6-one (cyprodime - a selective mu-opioid receptor antagonist, as well as nor-binaltorphimine dihydrochloride (nor-BNI - selective kappa-opioid receptors antagonist), given before HPC as well as before respective opioid receptor agonists, blocked the development of the protection. This study provides evidence that mu- and kappa-opioid receptors are involved in HPC against seizures in the brain.

Preconditioning the Brain and Heart: Implications for Cardiac Surgery

Despite many recent advances in emboli detection, aortic imaging, myocardial preservation, and perfusion equipment, ischemic injury to the heart and brain remains a serious complications after cardiac surgery. Hypoperfusion (particularly in the heart) and microem boli (particularly in the brain) during cardiopulmonary bypass constitute the etiology of ischemia. Although hypothermia has traditionally been the mainstay for systemic protection from transient ischemia, there has been a general trend to accept warmer heart and core temperatures during bypass, which increases the poten tial for ischemic injury to various organs. This article discusses recent advances in the understanding of myocardial and brain preconditioning and their poten tial role to provide additional protection during cardiac surgery.

Activation and regulation of Hsp32 and Hsp70

Endothelial cells (EC) play a key role in the propagation of inflammatory responses. Better understanding of inflammatory processes in EC might provide new ways of controlling inflammation. We report here that the known antioxidant pyrrolidinedithiocarbamate (PDTC) leads to time and dose dependent activation of heat-shock protein 70 (Hsp70) as well as Hsp32 in EC. We further demonstrate that PDTC activates heat-shock factor 1 (HSF1), one of several transcription factor involved in the upregulation of heat-shock proteins. And more importantly, we demonstrate that Hsp32 as well as Hsp70 can be upregulated independently of the transcription factor nuclear factor kappaB (NF-kappaB). The presented data provide further insight into the mechanism of Hsp32 and Hsp70 regulation, as well as further distinguishing these genes from other so called 'protective genes' whose upregulation depends on the activation of NF-kappaB. These findings indicate that Hsp32 and Hsp70 might be ideal candidates among protective genes. Hsp32 and Hsp70 provide many desirable protective effects but, being independent of NF-kappaB, would leave open the option to interfere with the upregulation of proinflammatory genes by modulating the activation of NF-kappaB.

Myocardial self-preservative effect of heat shock protein 70 on an immature lamb heart

BACKGROUND

Heat shock proteins have been shown to enhance myocardial tolerance of ischemia-reperfusion injury and are induced in the myocardium of many animals by various stressors.

METHODS

To assess the effects and time course of the inducible form of heat shock protein 70, we raised the rectal temperature of 15 neonatal lambs to 43 degrees C for 15 minutes. At 15, 30, 60, and 120 minutes and 24 hours after heat shock, hearts were subjected to immunoblot analysis for heat shock protein (hsp 72/73). Twenty-four hours after heat shock, neonatal lamb hearts (n = 8) were subjected to 2 hours of cold cardioplegic ischemia (HSP group). Eight neonatal lamb hearts without heat shock served as control. After 60 minutes of reperfusion, left ventricular systolic and diastolic function, coronary blood flow (CBF), myocardial oxygen consumption (MVO2), and lactate levels were measured. Endothelial function was assessed by measuring in situ coronary vascular resistance response to acetylcholine and trinitroglycerine.

RESULTS

The HSP group showed a significantly higher recovery of systolic function as well as MVO, and a lower lactate level compared to the control group at 60 minutes after reperfusion. Recovery of coronary endothelial function was also significantly better in the HSP group than in the control group. Inducible form of HSP 70 was expressed 15 minutes after heat shock and continued to be observed at 24 hours after the stress.

CONCLUSIONS

Heat shock stress associated with the production of inducible heat shock proteins improved the recovery of ventricular function as well as endothelial function and aerobic metabolism after hypothermic cardioplegic ischemia. Induction of heat shock proteins by any means prior to planned hypothermic ischemia may lead to a new approach for myocardial protection.

Oxygen free radical signaling in ischemic preconditioning

This review will focus on the free radical signaling mechanism of preconditioning. The results from our laboratory as well as studies from other laboratories suggest that reactive oxygen species function as second messenger during myocardial adaptation to ischemia. This review provides evidence for the first time that tyrosine kinase and MAP kinases are the targets for reactive oxygen species generated in the preconditioned myocardium. The finding that p38 MAP kinase might be upstream of NF kappa B further supports our previous reports that MAPKAP kinase 2 could be the most likely link between the preconditioning and adaptation mediated by gene expression. p38 activation appears to be an important step in the translocation and activation of the nuclear transcription factor NF kappa B, which in turn may be involved in the induction of the expression of a variety of stress-inducible genes.

Ischemic preconditioning triggers tyrosine kinase signaling: a potential role for MAPKAP kinase 2

Myocardial adaptation to ischemia has been shown to activate protein tyrosine kinase, potentiating activation of phospholipase D, which leads to the stimulation of mitogen-activated protein (MAP) kinases and MAP kinase-activated protein (MAPKAP) kinase 2. The present study sought to further examine the signal transduction pathway for the MAPKAP kinase 2 activation during ischemic adaptation. Isolated perfused rat hearts were adapted to ischemic stress by repeated ischemia and reperfusion. Hearts were pretreated with genistein to block tyrosine kinase, whereas SB-203580 was used to inhibit p38 MAP kinases. Western blot analysis demonstrated that p38 MAP kinase is phosphorylated during ischemic stress adaptation. Phosphorylation of p38 MAP kinase was blocked by genistein, suggesting that activation of p38 MAP kinase during ischemic adaptation is mediated by a tyrosine kinase signaling pathway. MAPKAP kinase 2 was estimated by following in vitro phosphorylation with recombinant human heat shock protein 27 as specific substrate for MAPKAP kinase 2. Again, both genistein and SB-203580 blocked the activation of MAPKAP kinase 2 during myocardial adaptation to ischemia. Immunofluorescence microscopy with anti-p38-antibody revealed that p38 MAP kinase is primarily localized in perinuclear regions. p38 MAP kinase moves to the nucleus after ischemic stress adaptation. After ischemia and reperfusion, cytoplasmic striations in the myocytes become obvious, indicating translocation of p38 MAP kinase from nucleus to cytoplasm. Corroborating these results, myocardial adaptation to ischemia improved the left ventricular functions and reduced myocardial infarction that were reversed by blocking either tyrosine kinase or p38 MAP kinase. These results demonstrate that myocardial adaptation to ischemia triggers a tyrosine kinase-regulated signaling pathway, leading to the translocation and activation of p38 MAP kinase and implicating a role for MAPKAP kinase 2.

Heat stress pretreatment mitigates postischemic arachidonic acid accumulation in rat heart

Heat stress pretreatment of the heart is known to protect this organ against an ischemic/reperfusion insult 24 h later. Degradation of membrane phospholipids resulting in tissue accumulation of polyunsaturated fatty acids, such as arachidonic acid, is thought to play an important role in the multifactorial process of ischemia/reperfusion-induced damage. The present study was conducted to test the hypothesis that heat stress mitigates the postischemic accumulation of arachidonic acid in myocardial tissue, as a sign of enhanced membrane phospholipid degradation. The experiments were performed on hearts isolated from rats either 24 h after total body heat treatment (42 degrees C for 15 min) or 24 h after sham treatment (control). Hearts were made ischemic for 45 min and reperfused for another 45 min. Heat pretreatment resulted in a significant improvement of postischemic hemodynamic performance of the isolated rat hearts. The release of creatine kinase was reduced from 30 +/- 14 (control group) to 17 +/- 5 units/g wet wt per 45 min (heat-pretreated group) (p < or = 0.05). Moreover, the tissue content of the inducible heat stress protein HSP70 was found to be increased 3-fold 24 h after heat treatment. Preischemic tissue levels of arachidonic acid did not differ between heat-pretreated and control hearts. The postischemic ventricular content of arachidonic acid was found to be significantly reduced in heat-pretreated hearts compared to sham-treated controls (6.6 +/- 3.3. vs. 17.8 +/- 12.0 nmol/g wet wt). The findings suggest that mitigation of membrane phospholipid degradation is a potential mechanism of heat stress-mediated protection against the deleterious effects of ischemia and reperfusion on cardiac cells.

Influence of heat stress on myocardial metabolism and functional recovery after cardioplegic arrest: a 31P N.M.R study

OBJECTIVE

Heat stress and induction of heat shock proteins confer protection against myocardial ischemia-reperfusion injury; however the precise mechanisms of this effect remain unknown. We investigated the influence of heat stress on metabolic and functional recovery after cardioplegic arrest, in a protocol mimicking clinical donor heart preservation.

METHODS

Langendorff perfused rat hearts in control group (C, n = 6) and heat stressed (24 h prior to experiment) group (HS, n = 6) were subjected to 4 h of ischemia at 4 degrees C following cardioplegic arrest (St. Thomas' No. 1). 31P nuclear magnetic resonance spectroscopy was used to follow changes in ATP, phosphocreatine and inorganic phosphate concentrations during the pre-ischemic, ischemic and reperfusion periods. Myocardial adenine nucleotide levels in hearts at the end of experiments and purine catabolite release in coronary effluent during reperfusion, were evaluated using high performance liquid chromatography. Mechanical function in the pre-ischemic and reperfusion periods was evaluated using an intraventricular balloon. Western immunoblotting was used to quantitate HSP70 expression.

RESULTS

Although baseline concentrations of ATP and phosphocreatine were similar in C and HS groups, the rate of high-energy phosphate depletion was attenuated during the early phase of ischemia in HS groups. On reperfusion, recovery of ATP was 10-20% greater in HS versus C groups; phosphocreatine levels also recovered better in the HS group, transiently reaching levels 40% higher in HS versus C groups. The concentrations of adenine nucleotides in hearts were significantly higher in the HS versus C groups. These changes were associated with an attenuation of total purine catabolite release in the coronary effluent in HS versus C groups. A significant improvement in relative recovery of developed pressure was shown in HS versus C groups in the post-ischemic periods.

CONCLUSIONS

Heat stress causes beneficial changes in high-energy phosphate metabolism in the rat heart subjected to cardioplegic arrest and ischemia. Improved mechanical recovery in HS versus C groups was associated with a decreased rate of high-energy phosphate depletion and increased recovery of ATP and phosphocreatine levels during reperfusion. Changes in energy metabolism may play a role in the mechanism of cardioprotection by heat stress during prolonged hypothermic cardiac arrest. rights reserved.

Ischemic preconditioning prior to myocardial protection with cold blood cardioplegia in coronary surgery

OBJECTIVE

Encouraging results on myocardial preconditioning in experimental models of infarction, stunning or prolonged ischemia raise the question whether preconditioning techniques may enhance conventional cardioplegic protection used for routine coronary surgery.

METHODS

A prospective clinical trial was conducted to investigate the effect of additional ischemic normothermic preconditioning prior to cardioplegic arrest applying cold blood cardioplegia in patients scheduled for routine coronary surgery (3 vessel disease, left ventricular ejection fraction > 50%). Two cross clamp periods of 5 min with the hearts beating in sinus rhythm were applied followed by 10 min of reperfusion, each (n = 7, group I). Inducing moderate hypothermia cold blood cardioplegia was delivered antegradely. In control groups, cold intermittent blood cardioplegia (n = 7, group II) was used alone. Coronary sinus effluents were analyzed for release of creatine kinase (CK), CK-MB, lactate, and troponin T at 1, 3, 6, 9, and 12 h. In addition, postoperative catecholamine requirements were monitored.

RESULTS

The procedure was tolerated well, and no perioperative myocardial infarction in any of the groups studied occurred. Concentrations of lactate tended to be higher in group I, but this difference was not significant. In addition, no significant differences for concentrations of CK, CK-MB, and troponin T were found. Following ischemic preconditioning an increased dosage of dopamine was required within the first 12 h postoperatively (group I: 2.63 +/- 1.44 microg/kg/min, group II: 0.89 +/- 1.06 microg/kg/min).

CONCLUSIONS

Combining ischemic preconditioning and cardioplegic protection with cold blood cardioplegia does not appear to ameliorate myocardial protection when compared to cardioplegic protection applying cold blood cardioplegia alone. Inversely, contractile function seemed to be impaired when applying this protocol of ischemic preconditioning.

Inflammatory response to cardiopulmonary bypass: mechanisms involved and possible therapeutic strategies

BACKGROUND

Recent study of the inflammatory reactions occurring during and after cardiopulmonary bypass (CPB) has improved our understanding of the involvement of the inflammatory cascade in perioperative injury. However, the exact mechanisms of this complex response remain to be fully determined.

METHODS

Literature on the inflammatory response to CPB was reviewed to define current knowledge on the possible pathways and mediators involved, and to discuss recent developments of therapeutic interventions aimed at attenuating the inflammatory response to CPB.

RESULTS

CPB has been shown to induce complement activation, endotoxin release, leukocyte activation, the expression of adhesion molecules, and the release of many inflammatory mediators including oxygen-free radicals, arachidonic acid metabolites, cytokines, platelet-activating factor, nitric oxide, and endothelins. Therapies aimed at interfering with the inflammatory response include the administration of pharmacologic agents such as corticosteroids, aprotinin, and antioxidants, as well as modification of techniques and equipment by the use of heparin-coated CPB circuits, intraoperative leukocyte depletion, and ultrafiltration.

CONCLUSIONS

Improved understanding of the inflammatory reactions to CPB can lead to improved patient outcome by enabling the development of novel therapies aimed at limiting this response.

Induction of early immediate genes and programmed cell death following cardioplegic arrest in human hearts

OBJECTIVE

Under experimental conditions cardiac stress may induce early immediate genes. Of these, heat shock proteins like hsp 70 have been linked to preconditioning and cellular salvage. Protooncogenes like c-fos and c-jun act as transcription factors for other genes and may be involved in the regulation of programmed cell death.

METHODS

Patients, 30, undergoing elective coronary artery bypass grafting, received either cold antegrade St. Thomas II or Bretschneider or Hamburg cardioplegic solutions with ten patients in each group. Tissue from right atria was removed before cardiopulmonary bypass and following cardioplegic arrest and reperfusion. Tissues were examined by Northern blots, immunohistochemistry, and in situ nick-end labeling of fragmented DNA as evidence for programmed cell death.

RESULTS

There were no significant preoperative or operative differences between groups. Following cardioplegia and reperfusion, a significant induction of both protooncogene and heat shock protein 70 mRNA was observed. Whereas levels of hsp 70 were increased about two-fold in all groups (P < 0.05), induction of c-fos and c-jun was most pronounced following the Hamburg cardioplegic solution (P < 0.05 versus baseline and for differences to other groups). Induction on the protein level was confirmed using immunohistochemistry that furthermore, identified cardiac myocytes and endothelial cells being the cell types that expressed these genes. In contrast to prebypass samples, in situ nick-end labeling of fragmented DNA following cardioplegic arrest and reperfusion was positive, preponderately in subendocardial myocytes and endothelial cells.

CONCLUSIONS

Cold cardioplegia is a potent stimulus for induction of the early immediate genes examined in human hearts. Increased expression of protooncogenes may be deleterious to cardiac myocytes as indicated by in situ nick-end labeling of DNA fragments. Differences in gene induction may add additional information for the evaluation of different cardioplegic strategies.

Induction of myocardial heat shock protein 70 during cardiac surgery

Animal experiments have shown that members of the heat shock protein (HSP) family have cytoprotective properties against ischaemia. In experimentally induced cardiac ischaemia, the induction of HSP70s correlates with reduced infarct size and enhanced myocardial function and endothelial recovery. Direct evidence that increased myocardial HSP70 expression result in cytoprotection during ischaemia has also been obtained using transgenic mice overexpressing either rat or human HSP72. This study examined the induction and expression of myocardial HSP70s after an obligatory period of ischaemia in patients during cardiac surgery. The level of HSP72/HSC73 protein in Tru-cut biopsies of the myocardium, taken before and after an acute ischaemic insult, was examined using a polyclonal antibody. The amount of HSP72 mRNA in the biopsies was also determined by reverse transcriptase polymerase chain reaction (RT-PCR) and correlated HSP72/HSC73 protein expression. In four patients subjected to brief alternating periods of normothermic ischaemia and reperfusion, the amount of myocardial HSP72/HSC73 protein was increased several fold after ischaemic insult. This was accompanied by increased expression of HSP72 mRNA. In contrast, the amounts of myocardial HSP72/HSC73 protein and HSP72 mRNA were unchanged in a patient subjected to a single prolonged period of hypothermic ischaemia. Given the proven myocardial protective properties of HSP72 in experimental models, it is postulated that the observed induction of HSP72 may have a similar function in man.

Expression of immediate early genes after cardioplegic arrest and reperfusion

BACKGROUND

Induction of protooncogenes such as c-fos, c-jun, and EGR-1 has been implicated in cellular growth and differentiation. Heat-shock proteins (HSPs) such as hsp 70 may mediate resistance to ischemia after heat shock and ischemic preconditioning. The effects of cardioplegia on the regulation of these immediate early genes are unclear.

METHODS

Isolated rat hearts were subjected to different cold (5 degrees C) or normothermic (35 degrees C) cardioplegic solutions and reperfused with normothermic Krebs-Henseleit buffer. Right atrial biopsy specimens from patients undergoing coronary artery bypass grafting with cold cardioplegic arrest were taken before and after cardiopulmonary bypass. Analysis of immediate early gene messenger RNAs was performed using Northern blots. Related proteins were localized by immunohistochemistry.

RESULTS

In rat hearts, cold cardioplegia for 40 minutes with Bretschneider or St. Thomas' II solution followed by 40 minutes' reperfusion resulted in a significant increase in left ventricular c-fos, EGR-1, and c-jun messenger RNA levels (4.0-, 3.1-, and 3.0-fold, respectively, with Bretschneider solution and 3.7-, 2.8-, and 2.1-fold, respectively, with St. Thomas' II solution) compared with control hearts perfused at 35 degrees C with Krebs-Henseleit buffer. Normothermic cardioplegia with St. Thomas' II solution was without effect, whereas sequential perfusion with Krebs-Henseleit buffer at 5 degrees C and 35 degrees C resulted in a similar increase in protooncogene messenger RNA levels. Only cold Bretschneider solution was related to a 5.2-fold induction of hsp 70 messenger RNA levels. Likewise, rat atrial tissues and samples from patients after cardiopulmonary bypass displayed a significant induction of these immediate early genes. Monoclonal antibodies against c-FOS and HSP 70 proteins stained nuclei and perinuclear spaces of endothelial cells and cardiac myocytes.

CONCLUSIONS

Cold cardioplegic arrest and normothermic reperfusion are potent triggers for immediate early gene induction. Hypothermia emerged as the prime stimulus for the examined protooncogenes. In contrast, hsp 70 induction was dependent on the cardioplegic solution.

Delayed protection of the ischemic heart--from pathophysiology to therapeutic applications

Preconditioning the heart with brief episodes of ischemia paradoxically increases its resistance to subsequent ischemic episodes, and markedly limits infarct size. Although preconditioning is now considered as the most powerful antiischemic intervention known, its beneficial effects are short-lived since they are lost if the reperfusion period after preconditioning is extended past 2-3 h. There is, however, some evidence of a delayed phase of protection, manifest 24 h after the initial preconditioning stimulus, associated with a decrease in infarct size, a prevention of postischemic contractile dysfunction (stunning) and a reduction in endothelial injury. The delayed beneficial effects of preconditioning resemble those induced by prior heat stress, and might be related to the expression of stress proteins (heat shock proteins or HSP). Evidence for a role of HSP derives from observations showing that brief ischemia is a potent stimulus for HSP expression. Moreover, transfection of isolated cells with HSP or overexpression of HSP in transgenic mice renders the myocytes more resistant to ischemia. Once produced, HSP are believed to facilitate protein synthesis, stabilize newly formed proteins and repair denatured ones. Alternatively, delayed preconditioning may be mediated by antioxidant enzymes such as superoxide dismutase or catalase, which are also upregulated by ischemia and this could lead to a lesser production of oxygen-derived free radicals during reperfusion. Indeed, in isolated myocytes, prevention of hypoxia-induced expression of superoxide dismutase (using an antisense oligonucleotide) abolished the delayed protective effect of preconditioning. Importantly, recent in vivo evidence suggests that the delayed protection may be mediated by adenosine, through activation of A1-receptors, and by stimulation of protein kinase C. Finally, although the exact mechanisms by which preconditioning induces delayed protection are still mostly unknown, the fact that the expression of protective proteins such as HSP can be induced by many other means than ischemia suggests that it is possible to pharmacologically stimulate this expression and thus possibly mimic the endogenous protective pathway. This could lead to the development of new pharmacological interventions which induce delayed myocardial protection in clinical situations such as angioplasty, coronary bypass surgery or even in patients at high risk of infarction.