Heat stress attenuates free radical release in the isolated perfused rat heart

Heat shock response during the resolution of inflammation and its progressive suppression in chronic-degenerative inflammatory diseases

The heat shock response (HSR) is a crucial biochemical pathway that orchestrates the resolution of inflammation, primarily under proteotoxic stress conditions. This process hinges on the upregulation of heat shock proteins (HSPs) and other chaperones, notably the 70 kDa family of heat shock proteins, under the command of the heat shock transcription factor-1. However, in the context of chronic degenerative disorders characterized by persistent low-grade inflammation (such as insulin resistance, obesity, type 2 diabetes, nonalcoholic fatty liver disease, and cardiovascular diseases) a gradual suppression of the HSR does occur. This work delves into the mechanisms behind this phenomenon. It explores how the Western diet and sedentary lifestyle, culminating in the endoplasmic reticulum stress within adipose tissue cells, trigger a cascade of events. This cascade includes the unfolded protein response and activation of the NOD-like receptor pyrin domain-containing protein-3 inflammasome, leading to the emergence of the senescence-associated secretory phenotype and the propagation of inflammation throughout the body. Notably, the activation of the NOD-like receptor pyrin domain-containing protein-3 inflammasome not only fuels inflammation but also sabotages the HSR by degrading human antigen R, a crucial mRNA-binding protein responsible for maintaining heat shock transcription factor-1 mRNA expression and stability on heat shock gene promoters. This paper underscores the imperative need to comprehend how chronic inflammation stifles the HSR and the clinical significance of evaluating the HSR using cost-effective and accessible tools. Such understanding is pivotal in the development of innovative strategies aimed at the prevention and treatment of these chronic inflammatory ailments, which continue to take a heavy toll on global health and well-being.

Endothelial extracellular vesicles contain protective proteins and rescue ischemia-reperfusion injury in a human heart-on-chip

Extracellular vesicles (EVs) derived from various stem cell sources induce cardioprotective effects during ischemia-reperfusion injury (IRI). These have been attributed mainly to the antiapoptotic, proangiogenic, microRNA (miRNA) cargo within the stem cell-derived EVs. However, the mechanisms of EV-mediated endothelial signaling to cardiomyocytes, as well as their therapeutic potential toward ischemic myocardial injury, are not clear. EV content beyond miRNA that may contribute to cardioprotection has not been fully illuminated. This study characterized the protein cargo of human vascular endothelial EVs (EEVs) to identify lead cardioactive proteins and assessed the effect of EEVs on human laminar cardiac tissues (hlCTs) exposed to IRI. We mapped the protein content of human vascular EEVs and identified proteins that were previously associated with cellular metabolism, redox state, and calcium handling, among other processes. Analysis of the protein landscape of human cardiomyocytes revealed corresponding modifications induced by EEV treatment. To assess their human-specific cardioprotection in vitro, we developed a human heart-on-a-chip IRI assay using human stem cell-derived, engineered cardiac tissues. We found that EEVs alleviated cardiac cell death as well as the loss in contractile capacity during and after simulated IRI in an uptake- and dose-dependent manner. Moreover, we found that EEVs increased the respiratory capacity of normoxic cardiomyocytes. These results suggest that vascular EEVs rescue hlCTs exposed to IRI possibly by supplementing injured myocytes with cargo that supports multiple metabolic and salvage pathways and therefore may serve as a multitargeted therapy for IRI.

Effects of aerial exposure on oxidative stress, antioxidant and non-specific immune responses of juvenile sea cucumber Apostichopus japonicus under low temperature

Desiccation is a commonly stressful situation experienced by sea cucumber during transportation without/less water. The present study was conducted to investigate the effects of aerial exposure on the survival, oxidative damage, antioxidant capacity, immune-related response and gene expression of Apostichopus japonicus at different low temperatures. After acclimation, sea cucumbers were randomly divided into 3 groups, which were exposed to 5 °C, 10 °C and 15 °C in the closed laboratory condition, respectively. Each group has three parallel replicates. During the experiment, coelomic fluid and respiratory tree of A. japonicus were sampled at the time points of 0, 3, 6, 12, 24 and 48 h post-desiccation for further analysis. The results showed that the survival rates of sea cucumber significantly decreased as time prolonged, and those of 5 °C at 6-48 h of desiccation were significantly higher than 15 °C. Most oxidative damage parameters (e.g., O₂^- production, MDA, LPO and PC contents) significant increased after 6-12 h of desiccation. Antioxidant enzyme activities and T-AOC in coelomic fluid firstly increased and then decreased during aerial exposure, indicating that sea cucumber could adjust antioxidant defense to reduce the concentrations of ROS and MDA as a strategy for protecting organisms from oxidative damage in the early stage (0-6 h) of desiccation. The relative expression levels of Hsp90 and Hsp70 mRNA in respiratory tree of sea cucumber exhibited similar rise-fall trends with antioxidant parameters, while immune enzyme activities of ACP, AKP, LSZ and T-NOS, and gene expression of TLR, Rel and p105 all significantly decreased as time prolonged. Overall, low temperature postponed the process of ROS formation and the depression of antioxidant and non-specific immune responses of sea cucumber within a certain extent, which implied that it might play a positive role in improvement of desiccation tolerance. This study not only contribute to better understand the adaption mechanisms of A. japonicus to desiccation stress, but also provide valuable information for sea cucumber culture and transportation.

Repetitively hypoxic preconditioning attenuates ischemia/reperfusion-induced liver dysfunction through upregulation of hypoxia-induced factor-1 alpha-dependent mitochondrial Bcl-xl in rat

Repetitive hypoxic preconditioning (HP) enforces protective effects to subsequently severe hypoxic/ischemic stress. We hypothesized that HP may provide protection against ischemia/reperfusion (I/R) injury in rat livers via hypoxia-induced factor-1 alpha (HIF-1α)/reactive oxygen species (ROS)-dependent defensive mechanisms. Female Wistar rats were exposed to hypoxia (15 h/day) in a hypobaric hypoxic chamber (5500 m) for HP induction, whereas the others were kept in sea level. These rats were subjected to 45 min of hepatic ischemia by portal vein occlusion followed by 6 h of reperfusion. We evaluated HIF-1α in nuclear extracts, MnSOD, CuZnSOD, catalase, Bad/Bcl-xL/caspase 3/poly-(ADP-ribose)-polymerase (PARP), mitochondrial Bcl-xL, and cytosolic cytochrome C expression with Western blot and nitroblue tetrazolium/3-nitrotyrosine stain. Kupffer cell infiltration and terminal deoxynucleotidyl transferase-mediated nick-end labeling method apoptosis were determined by immunocytochemistry. The ROS value from liver surface and bile was detected by an ultrasensitive chemiluminescence-amplification method. Hepatic function was assessed with plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. HP increased nuclear translocation of HIF-1α and enhanced Bcl-xL, MnSOD, CuZnSOD, and catalase protein expression in a time-dependent manner. The response of HP enhanced hepatic HIF-1α, and Bcl-xL expression was abrogated by a HIF-1α inhibitor YC-1. Hepatic I/R increased ROS levels, myeloperoxidase activity, Kupffer cell infiltration, ALT and AST levels associated with the enhancement of cytosolic Bad translocation to mitochondria, release of cytochrome C to cytosol, and activation of caspase 3/PARP-mediated apoptosis. HP significantly ameliorated hepatic I/R-enhanced oxidative stress, apoptosis, and mitochondrial and hepatic dysfunction. In summary, HP enhances HIF-1α/ROS-dependent cascades to upregulate mitochondrial Bcl-xL protein expression and to confer protection against I/R injury in the livers.

Effects of high temperature on biochemical parameters, oxidative stress, DNA damage and apoptosis of pufferfish (Takifugu obscurus)

Water temperature is an important environmental factor that affects physiology and biochemical activities of fish. In this study, we investigated of high temperature on biochemical parameters, oxidative stress, DNA damage and apoptosis of pufferfish. Thermal stress could significantly increase the levels of AST, ALT, LDH, GLU and TG, whereas the levels of ALP and TP decrease significantly. In addition, thermal stress also decreased total blood cell count, inhibited cell viability, and subsequently lead to DNA damage and apoptosis. The mRNA levels of p53, caspase-9 and caspase-3 were up-regulated under thermal stress. These results suggested that caspase-dependent and p53 signaling pathways could play important roles in thermal stress-induced apoptosis in fish. Furthermore, the gene expression of SOD, CAT, HSP90 and C3 were induced by thermal stress. This study provides new insights into the mechanism whereby thermal stress affects physiological responses and apoptosis in pufferfish.

Effects of age and exercise on inflammatory cytokines, HSP70 and HSP90 gene expression and protein content in Standardbred horses

We hypothesised that the cortisol response to acute exercise, markers of oxidative stress, expression of inflammatory cytokines, heat shock protein (HSP)70 and HSP90 expression in whole blood and skeletal muscle, and HSP70 and HSP90 protein concentrations in skeletal muscle are altered by age and in response to acute submaximal exercise in horses. Young (n=6; 5.5±2.8 year) and aged (n=6; 22.6±2.25 year) unconditioned Standardbred mares underwent an acute submaximal exercise test. Blood samples were collected and analysed for plasma cortisol and malondialdehyde (MDA) concentrations, and for cytokine and HSP gene expression pre- and post-exercise. Gluteus medius biopsies were obtained for analysis of cytokine and HSP gene expression pre- and at 0, 4, 24 and 48 h post-exercise. Data were analysed for main effects using a two-way ANOVA for repeated measures. Post-hoc comparisons of means were conducted using Student-Neuman-Keuls for pair-wise multiple comparisons where appropriate. Acute submaximal exercise increased plasma cortisol concentration in both young and aged mares, and the duration of the post-exercise rise in cortisol was altered in aged horses. Plasma MDA concentration and expression of tumour necrosis factor-α (TNF-α) and interleukin (IL)-6 were unchanged in blood and muscle. Exercise increased IL-1β expression in whole blood of young and aged mares, with young mares having greater exercise-induced expression at 2 (P<0.001) and 4 (P=0.019) h post-exercise. Both young and aged horses had increased HSP70 expression in whole blood following acute exercise, with young horses exhibiting 3-fold greater HSP70 expression than aged mares at 2 h post-exercise. HSP90 expression in whole blood following exercise was increased only in young horses. Both young and aged horses had increased HSP90 expression in skeletal muscle following exercise, but there was no difference due to age. However, the timing of HSP70 expression was different between young and aged horses. The age-related changes in cortisol and IL-1β expression following acute submaximal exercise can have implications for energy homeostasis and the adaption to such disturbances at a cellular and whole animal level. Quantification of HSP expression in whole blood may be a useful biomarker, with implications for cellular adaptation and survival in aged horses.

Influence of temperature in thermal and oxidative stress responses in estuarine fish

The influence of increasing temperatures in thermal and oxidative stress responses were studied in the muscle of several estuarine fish species (Diplodus vulgaris, Diplodus sargus, Dicentrarchus labrax, Gobius niger and Liza ramada). Selected fish were collected in July at the Tagus estuary (24±0.9°C; salinity of 30±4‰; pH=8). Fish were subjected to a temperature increase of 1°C.h(-1) until they reached their Critical Thermal Maximum (CTMax), starting at 24°C (control temperature). Muscle samples were collected during the trial and results showed that oxidative stress biomarkers are highly sensitive to temperature. Results from stress oxidative enzymes show alterations with increasing temperature in all tested species. Catalase (CAT; EC 1.11.1.6) activity significantly increased in L. ramada, D. labrax and decreased in D. vulgaris. Glutathione S-transferase (GST; EC 2.5.1.18) activity increased in L. ramada, D. sargus, D. vulgaris, and D. labrax. In G. niger it showed a cycle of increase-decrease. Lipid peroxidation (LPO) increased in L. ramada, D. sargus and D. labrax. With respect to correlation analysis (Pearson; Spearman r), the results showed that oxidation products and antioxidant defenses were correlated in L. ramada (LPO-CAT and LPO-GST, D. sargus (LPO-CAT), and D. labrax (LPO-CAT). Oxidative biomarkers were correlated with thermal stress biomarker (Hsp70) in L. ramada (CAT-Hsp70), D. vulgaris (LPO-Hsp70), D. labrax (GST-Hsp70) and G. niger (LPO-Hsp70). In conclusion, oxidative stress does occur with increasing temperatures and there seems to be a relation between thermal stress response and oxidative stress response. The results suggest that oxidative stress biomarkers should be applied with caution, particularly in field multi-species/multi-environment studies.

Increased inducible heat shock protein 72 expression associated with PBMC isolated from patients with haematological tumours

BACKGROUND

Heat shock protein 72 (Hsp72) is a highly inducible stress protein and molecular chaperone. Cancers have been shown to be associated with increased Hsp72 expression within the tumour itself and this may lead to resistance to apoptosis.

METHODS

Peripheral blood mononuclear cells (PBMC) were isolated from patients diagnosed with chronic lymphocytic leukaemia (CLL) (n = 27) and chronic myelomonocytic leukaemia (CMML) (n = 16) and Hsp72 expression was characterized on both the cell surface and intracellularly by flow cytometry. To allow for comparison PBMC from breast cancer patients (n = 25) and healthy volunteers (n = 19) were included.

RESULTS

Both lymphocytes and monocytes from CLL and CMML patients showed high levels of total Hsp72 expression (4-6 fold increase) in comparison to breast cancer and healthy subjects. The majority of Hsp72 in these tumours was determined to be cell-surface expressed (64-93% of cell total Hsp72).

CONCLUSIONS

A correlation was observed between lymphocyte and monocyte total Hsp72 expression (p < 0.001) suggesting a common stress response pathway may exist in these blood cells and there are stress conditions present within the circulation. Hsp72 expression was not found to be related to white blood cell count.

The effect of hyperbaric oxygen preconditioning on heat shock protein 72 expression following in vitro stress in human monocytes

Hyperbaric oxygen (HBO) is thought to confer protection to cells via a cellular response to free radicals. This process may involve increased expression of heat shock proteins, in particular the highly inducible heat shock protein 72 (Hsp72). Healthy male volunteers (n = 16) were subjected to HBO for 1 h at 2.8 ATA. Inducible Hsp72 expression was measured by flow cytometry pre-, post- and 4 h-post HBO. Peripheral blood mononuclear cells (PBMC) were isolated from whole blood via density centrifugation pre-, post- and 4 h post-HBO. PBMC were then subjected to an in vitro heat shock at 40°C or hypoxia at 37°C (5% O(2)) with a control at 37°C. Cells were then analysed for Hsp72 expression by flow cytometry. Monocytes showed no significant changes in Hsp72 expression following HBO. No detectable Hsp72 was seen in lymphocytes or neutrophils. Following in vitro hypoxic exposure, a significant increase in Hsp72 expression was observed in monocytes isolated immediately post- (p = 0.006) and 4 h post-HBO (p = 0.010) in comparison to control values. HBO does not induce Hsp72 expression in PBMC. The reported benefits of HBO in terms of pre-conditioning are not due to inducement of Hsp72 expression in circulating blood cells, but may involve an enhancement of the stress response.

Repetitive hypoxic preconditioning attenuates renal ischemia/reperfusion induced oxidative injury via upregulating HIF-1 alpha-dependent bcl-2 signaling

BACKGROUND

In response to ischemic/hypoxic preconditioning, tissues/organs exhibit protective responses to subsequent and severe ischemic stress. We hypothesized that repetitive hypoxic preconditioning (RHP) may provide long-lasting protection than single preconditioning against ischemia/reperfusion injury in rat kidneys through hypoxia-induced factor (HIF)-1-dependent pathway.

METHODS

For RHP induction, female Wistar rats were subjected to intermittent hypoxic exposure (380 Torr) 15 hr/day for 28 days.

RESULTS

RHP increased renal HIF-1 alpha mRNA and protein expression and triggered HIF-1 alpha-dependent renal Bcl-2 protein expression in a time-dependent manner. When returning to normoxia, increased RHP exposure prolonged renal Bcl-2 expression. Forty-five minutes of renal ischemia with 4 hr of reperfusion enhanced O2- levels and proapoptotic mechanisms, including enhanced cytosolic Bax translocation to mitochondria, release of cytochrome c to cytosol, activation of caspase 3, poly-(ADP-ribose)-polymerase fragments, tubular apoptosis, blood urea nitrogen, and creatinine level. RHP treatment depressed renal O2- production, mitochondrial Bax translocation and cytochrome c release, and tubular apoptosis. In the primary tubular cultures from RHP-treated kidneys, antisense oligodeoxyribonucleotides of bcl-2 abrogated this protection.

CONCLUSIONS

RHP activates an HIF-1 alpha-dependent signaling cascade leading to an increase in Bcl-2 protein expression, an inhibition in cytosolic Bax and mitochondrial cytochrome c translocation, and a hypoxic/ischemia tolerance against renal ischemia/reperfusion injury.

Hypoxic preconditioning reinforces HIF-alpha-dependent HSP70 signaling to reduce ischemic renal failure-induced renal tubular apoptosis and autophagy

AIMS

Repetitive hypoxic preconditioning (RHP) may provide more efficient protection than single hypoxic preconditioning against renal ischemia/reperfusion-induced injury via hypoxia-induced factor 1alpha (HIF-1alpha)-dependent heat shock protein 70 (HSP70) pathways.

MAIN METHODS

Wistar rats were subjected to intermittent hypoxic exposure (15h/day), whereas controls were kept at sea level. We evaluated renal expression of HIF-1alpha, HSP70, the endoplasmic reticulum stress protein GRP78, caspase 12, Beclin-1, and poly-(ADP-ribose)-polymerase (PARP) with western blotting. Renal apoptosis determined by terminal transferase dUTP nick end labeling (TUNEL), Beclin-1-dependent autophagy, and monocyte/macrophage (ED-1) infiltration were evaluated by immunocytochemistry. Renal function was determined with blood urea nitrogen (BUN) and plasma creatinine levels. HIF-1alpha inhibitors and Deoxyribonucleotide (DNA) or Ribonucleotide (RNA) interference of HSP70 were used to evaluate their possible roles in this process.

KEY FINDINGS

Renal HIF-1alpha and HSP70 expression were enhanced by hypoxic preconditioning and inhibited by the HIF-1alpha inhibitor, YC-1, as well as phosphatidylinositol 3-kinase (PI3K)/Akt inhibitors. After the return to normoxia, renal HSP70 protein levels were maintained for one week in the RHP group, but they decayed after one day in the single hypoxic preconditioning group. Ischemia/reperfusion significantly increased renal TUNEL-apoptosis, Beclin-1-dependent autophagy, ED-1 infiltration, expression of GRP78, caspase 12, Beclin-1, PARP, and BUN and plasma creatinine levels in control rats. RHP significantly decreased all ischemia/reperfusion-enhanced parameters. Intraperitoneal pretreatment with YC-1 and quercetin (an inhibitor of HSP70 induction) eliminated RHP-induced protection. Anti-sense oligodeoxyribonucleotides or interference RNA targeting HSP70 abrogated the protection against hypoxia/reoxygenation-induced oxidative injury in RHP-treated proximal tubules.

SIGNIFICANCE

We demonstrate that RHP promotes HIF-1alpha-dependent HSP70 signaling to reduce renal ischemia/reperfusion injury.

Ischemic conditioning by short periods of reperfusion attenuates renal ischemia/reperfusion induced apoptosis and autophagy in the rat

Prolonged ischemia amplified iscehemia/reperfusion (IR) induced renal apoptosis and autophagy. We hypothesize that ischemic conditioning (IC) by a briefly intermittent reperfusion during a prolonged ischemic phase may ameliorate IR induced renal dysfunction. We evaluated the antioxidant/oxidant mechanism, autophagy and apoptosis in the uninephrectomized Wistar rats subjected to sham control, 4 stages of 15-min IC (I15 x 4), 2 stages of 30-min IC (I30 x 2), and total 60-min ischema (I60) in the kidney followed by 4 or 24 hours of reperfusion. By use of ATP assay, monitoring O2-. amounts, autophagy and apoptosis analysis of rat kidneys, I60 followed by 4 hours of reperfusion decreased renal ATP and enhanced reactive oxygen species (ROS) level and proapoptotic and autophagic mechanisms, including enhanced Bax/Bcl-2 ratio, cytochrome C release, active caspase 3, poly-(ADP-ribose)-polymerase (PARP) degradation fragments, microtubule-associated protein light chain 3 (LC3) and Beclin-1 expression and subsequently tubular apoptosis and autophagy associated with elevated blood urea nitrogen and creatinine level. I30 x 2, not I15 x 4 decreased ROS production and cytochrome C release, increased Manganese superoxide dismutase (MnSOD), Copper-Zn superoxide dismutase (CuZnSOD) and catalase expression and provided a more efficient protection than I60 against IR induced tubular apoptosis and autophagy and blood urea nitrogen and creatinine level. We conclude that 60-min renal ischemia enhanced renal tubular oxidative stress, proapoptosis and autophagy in the rat kidneys. Two stages of 30-min ischemia with 3-min reperfusion significantly preserved renal ATP content, increased antioxidant defense mechanisms and decreased ischemia/reperfusion enhanced renal tubular oxidative stress, cytosolic cytochrome C release, proapoptosis and autophagy in rat kidneys.

Inducible heat shock protein 70 and its role in preconditioning and exercise

Heat shock proteins (Hsp) are well known to be expressed in response to a range of cellular stresses. They are known to convey protection against protein denaturation and a subsequent immediate stress. Inducible heat shock protein 70 (Hsp70) is among the most studied of these stress proteins and its role and function are discussed here in terms of thermal and in particular exercise preconditioning. Preconditioning has been shown to confer cellular protection via expression Hsp, which may be of benefit in preventing protein damage following subsequent periods of exercise. Many studies have used animal models to gather data on Hsp70 and these and the most recent human studies are discussed.

Can hyperbaric oxygen be used as adjunctive heart failure therapy through the induction of endogenous heat shock proteins?

Heart failure (HF) is a chronic condition that is expected to increase in incidence along with increased life expectancy and an aging population. As the incidence of HF increases, the cost to national healthcare budgets is expected to run into the billions. The costs of lost productivity and increased social reliance on state support must also be considered. Recently, acute myocardial infarction (AMI) has come to be seen as the major contributing factor to HF. Although thrombolysis may restore coronary perfusion after an AMI, it may also introduce ischemic reperfusion injury (IRI). In an attempt to ameliorate sustained protein damage caused by IRI, endogenous chaperone proteins known as heat shock proteins (HSPs) are induced as a consequence of the stress of IRI. Recently, hyperbaric oxygen has been shown to induce the production of HSPs in noncardiac tissue, with a resultant protective effect. This current opinion review article suggests a possible role for hyperbaric oxygen, as a technologically modern drug, in augmenting the induction of endogenous HSPs to repair and improve the function of failing hearts that have been damaged by AMI and IRI. In addition, this simple, safe, noninvasive drug may prove useful in easing the economic burden of HF on already overextended health resources.

A possible role of HSP70 in mediating cardioprotection in patients undergoing CABG

Heat shock protein 70 (HSP70) has been reported to be involved in myocardial self-preservation system. This study shows direct evidence of the effect of HSP70 on lymphocytes during ischemia and reperfusion in CABG (coronary artery bypass graft) surgery. Lymphocytes were separated from the blood obtained from 10 patients undergoing CABG at different time intervals. (i) Baseline samples (drawn before onset of bypass), (ii) ischemic samples (30 min after cross-clamp) and (iii) reperfusion samples (10 min after the cross clamp removal) were incubated with recombinant HSP70 and the cells were harvested after 36 h. The effect of HSP70 was monitored by measuring second messengers such as intracellular calcium, protein kinase C (PKC) and inositol triphosphate (IP3). In addition CD69 expression was also measured. The results showed a significant decrease in intracellular calcium and CD69 expression in ischemia and further in reperfusion samples as compared to their respective untriggered controls. PKC and IP3 levels however remained unaffected. The protective effect of HSP70 during ischemia and reperfusion could thus be attributed to decreasing intracellular calcium and CD69 expression. This study could therefore provide a mechanism of cardioprotection afforded by HSP70.

Heat stress increases endothelium-dependent relaxations and prevents reperfusion-induced endothelial dysfunction

1. Heat stress has been widely used to stimulate the expression of stress proteins and is associated with various cardiovascular changes, including anti-ischaemic effects. However, the effect of heat stress on endothelial function is less clear. 2. Heat stress was induced in anaesthetized rats by increasing body temperature to 42 degrees C for 15 min. Twenty-four hours later, segments of rat aorta and mesenteric and coronary arteries were mounted in organ chambers. 3. Heat stress markedly increased relaxation to acetylcholine (ACh) in all three blood vessels studied, without affecting the response to the nitric oxide (NO) donor sydnonimine-1. 4. Heat stress also increased aortic relaxation to histamine and the calcium ionophore A23187. 5. In the aorta, an inhibitor of NO synthesis abolished the response to ACh in both control and heat stressed-rings, whereas a cyclo-oxygenase inhibitor had no effect. 6. Heat stress also prevented completely the impaired response to ACh in coronary arteries isolated from rats subjected to myocardial ischaemia and reperfusion. 7. Thus, heat stress increases the stimulated release of NO the rat aorta and mesenteric and coronary arteries and prevents reperfusion-induced injury at the level of the coronary endothelium.

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.

Oral administration of Lactobacillus induces cardioprotection

OBJECTIVES

Our goal was to investigate the potential of oral administration of Lactobacillus to induce cardioprotection against ischemia-reperfusion injury in rat hearts, and to determine whether this protection is associated with myocardial catalase activation and heat shock protein 70 expression.

DESIGN

Lactobacillus was administered orally to rats on a daily basis, from 1 to 21 days before global ischemia. Global ischemia was produced by full-stop flow in isolated Langendorff-perfused rat hearts for 20 minutes and was followed by reperfusion. Similarly, saline was administered to control animals.

RESULTS

Lactobacillus significantly reduced reperfusion tachyarrhythmia and improved functional recovery of the ischemic rat hearts. These cardioprotective effects were associated with reduction of norepinephrine release at the first minute of reperfusion, activation of myocardial catalase, and overexpression of 70 kd heat stress protein at ischemia and reperfusion (p < 0.05).

CONCLUSIONS

Oral administration of Lactobacillus produces marked cardioprotection against ischemia-reperfusion injury. This effect is attributed to activation of the cellular defense system, manifested by activation of the antioxidant pathway, and by expression of protective proteins. Norepinephrine is involved in this process. The results of this study suggest that Lactobacillus, which is generally considered safe, could serve as a basis for the development of a new agent for preventive therapy of various ischemic heart syndromes.

Heat pretreatment differentially affects cardiac fatty acid accumulation during ischemia and postischemic reperfusion

We investigated whether the cardioprotection induced by heat stress (HS) pretreatment is associated with mitigation of phospholipid degradation during the ischemic and/or postischemic period. The hearts, isolated from control rats and from heat-pretreated rats (42 degrees C for 15 min) either 30 min (HS0.5-h) or 24 h (HS24-h) earlier, were subjected to 45 min of no-flow ischemia, followed by 45 min of reperfusion. Unesterified arachidonic acid (AA) accumulation was taken as a measure for phospholipid degradation. Significantly improved postischemic ventricular functional recovery was only found in the HS24-h group. During ischemia, AA accumulated comparably in control and both HS groups. During reperfusion in control and HS0.5-h hearts, AA further accumulated (control hearts from 82 +/- 33 to 109 +/- 51 nmol/g dry wt, not significant; HS-0.5h hearts from 52 +/- 22 to 120 +/- 53 nmol/g dry wt; P < 0.05). In contrast, AA was lower at the end of the reperfusion phase in HS24-h hearts than at the end of the preceding ischemic period (74 +/- 18 vs. 46 +/- 23 nmol/g dry wt; P < 0.05). Thus accelerated reperfusion-induced degradation of phospholipids in control hearts is completely absent in HS24-h hearts. Furthermore, the lack of functional improvement in HS0.5-h hearts is also associated with a lack of beneficial effect on lipid homeostasis. Therefore, it is proposed that enhanced membrane stability during reperfusion is a key mediator in the heat-induced cardioprotection.

Blocking free radical production via adenoviral gene transfer decreases cardiac ischemia-reperfusion injury

Periods of cardiac ischemia followed by reperfusion can lead to either transient loss of function (stunning) or permanent functional loss stemming from infarction, depending upon the length of the ischemic period. In either case the primary mediator of the injury may by oxygen-derived free radicals generated upon the reestablishment of blood flow. The heart's primary defense against peroxide, glutathione peroxidase, is depleted during ischemia. Thus, the ischemic myocardium might derive significant protection from increased levels of the enzyme, catalase, which can remove hydrogen peroxide in a redox-independent manner. To test these assertions, we studied the ability of adenoviral gene transfer to increase intracellular antioxidant activity via catalase expression. What we observed was that increasing catalase activity in the heart was sufficient to prevent the stunning associated with 15 min of ischemia followed by reperfusion.

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.

Stress (heat shock) proteins: molecular chaperones in cardiovascular biology and disease

How a cell responds to stress is a central problem in cardiovascular biology. Diverse physiological stresses (eg, heat, hemodynamics, mutant proteins, and oxidative injury) produce multiple changes in a cell that ultimately affect protein structures and function. Cells from different phyla initiate a cascade of events that engage essential proteins, the molecular chaperones, in decisions to repair or degrade damaged proteins as a defense strategy to ensure survival. Accumulative evidence indicates that molecular chaperones such as the heat shock family of stress proteins (HSPs) actively participate in an array of cellular processes, including cytoprotection. The versatility of the ubiquitous HSP family is further enhanced by stress-inducible regulatory networks, both at the transcriptional and posttranscriptional levels. In the present review, we discuss the regulation and function of HSP chaperones and their clinical significance in conditions such as cardiac hypertrophy, vascular wall injury, cardiac surgery, ischemic preconditioning, aging, and, conceivably, mutations in genes encoding contractile proteins and ion channels.

ATP-sensitive potassium channel mediates delayed ischemic protection by heat stress in rabbit heart

Heat shock protects against myocardial ischemia-reperfusion injury possibly via increased expression of heat shock proteins. The direct evidence of heat shock protein protection in vivo remains circumstantial, and no other new mechanism of protection has been proposed. Recent studies suggest that opening of ATP-sensitive K+ channels (KATP channels) plays an important role in ischemic preconditioning; however, it is not known whether this channel is also important in delayed protection conferred by heat shock. Anesthetized rabbits underwent heat shock treatment by raising core temperature to 42 degrees C for 15 min. Twenty-four hours later, the animals were reanesthetized and subjected to regional ischemia-reperfusion. The specific KATP channel blockers glibenclamide (0.3 mg/kg i.p.) and sodium 5-hydroxydecanoate (5HD; 5 mg/kg i.v.) were used to block the channel function. The drugs were administered at two different times, either pre-heat stress or preischemia. Infarct size was determined by triphenyltetrazolium chloride staining. The 72-kDa heat shock protein (HSP 72) was measured by Western blots. Our results show that heat shock produced a marked reduction in infarct size (39.4 +/- 8.1 to 14.3 +/- 2.5% of risk area, P < 0.05). Glibenclamide and 5HD completely abolished heat shock-induced reduction in infarct size (42.3 +/- 0.32 and 33.7 +/- 4.8%) when given before ischemia-reperfusion; however, these antagonists failed to block protection when administered before the onset of heat shock. Furthermore, the enhanced expression of HSP 72 in heat shock groups was not diminished by glibenclamide or 5HD, suggesting a lack of a direct role of this protein in conferring cardiac protection by heat shock. The complete blockade of cardiac protection by glibenclamide and 5HD strongly suggests that opening of this channel is a very important component of heat shock-induced ischemic protection in rabbit hearts.

Compensatory up-regulation of cardiac SR Ca2+-pump by heat-shock counteracts SR Ca2+-channel activation by ischemia/reperfusion

We tested the hypothesis that heat-shock protected myocardial Ca2+-cycling by sarcoplasmic reticulum from ischemia and reperfusion (I/R) injury. Twenty-four hours after increasing body temperature to 42 degrees C for 15 min, rat hearts were isolated, Langendorff-perfused, and subjected to 30 min ischemia then 30 min reperfusion. Left ventricles were homogenized and their ionized Ca2+ concentration monitored with indo- during Ca2+-uptake in the presence and absence of the Ca2+-release channel (CRC) modulator ryanodine. Tissue content of heat-shock protein 72 (HSP 72) was analyzed. Exposure to I/R resulted in a 37% enhancement of CRC activity but no effect on Ca2+-pumping activity, resulting in 25% decreased net Ca2+-uptake activity. Pre-exposure to heat-shock resulted in a 10-fold increase in HSP 72, and a 25% enhancement of maximal Ca2+-pumping activity which counteracted the effect of I/R on CRC and net Ca2+-uptake activities. This protection of SR Ca2+-cycling was associated with partial protection of myocardial physiological performance. Net Ca2+-uptake activity was correlated with the left ventricular developed pressure and its rate of change. We conclude that one of the mechanisms by which heat-shock protects myocardium from I/R injury is to upregulate SR Ca2+-pumping activity to counteract the enhanced SR Ca2+-release produced by I/R.

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.

Detection of hydroxyl and carbon-centred radicals by EPR spectroscopy after ischaemia and reperfusion of the rat kidney

Recent studies suggest that oxygen-derived free radicals are involved in mediating renal reperfusion injury. EPR spectroscopy and spin trapping with the spin traps DMPO and PBN, were used to detect and quantitate the formation of hydroxyl radicals in rat kidney after ischaemia-reperfusion in vivo and in vitro in the isolated rat kidney perfused in the absence of leucocytes. EPR analysis of homogenised kidneys and of venous samples did not detect radical adducts with either spin trap. With PBN, radical adducts were not detected in vitro. When DMPO was used as the spin trap in kidneys perfused without albumin in the perfusate, EPR signals characteristic of hydroxyl and carbon-centred radical adducts were detected during early reperfusion following ischaemia. These studies confirm the generation of hydroxyl radicals during ischaemia-reperfusion in kidney. During reperfusion the total DMPO adduct concentration reached 4.35 +/- 1.05 nmol/g kidney/3 min, p < 0.05. In control kidneys total adduct were present at lower concentration (2.55 +/- 1.1 nmol/g kidney/3 min). Addition of 15 mM dimethylthiourea abolished formation of these adducts following ischaemia-reperfusion but did not prevent a reduction in glomerular filtration rate. These results indicate that significant levels of hydroxyl and carbon-centred radicals are formed in the absence of circulating neutrophils during early renal reperfusion following ischaemia.

Catalase inhibition with 3-amino-1,2,4-triazole does not abolish infarct size reduction in heat-shocked rats

BACKGROUND

Recent studies have shown that improved myocardial salvage after heat-shock pretreatment correlates with the amount of induced cardiac heat-shock protein (HSP)72. However, heat shock also induces myocardial catalase activity, potentially reducing free radical-mediated ischemic injury. The aim of the present study was to determine whether catalase inhibition with 3-amino-1,2,4-triazole (3-AT) abolishes the reduction of infarct size conferred by heat-shock treatment in rats.

METHODS AND RESULTS

Myocardial catalase activity was measured in both heat-shocked and control rats 60 minutes after either 3-AT (1000 mg/kg IV) or saline infusion. In separate experiments, heat-shocked and control rats were treated with 3-AT or saline 60 minutes before being subjected to 35 minutes of left coronary artery occlusion and 120 minutes of reperfusion. Infarct size was determined by dual perfusion with triphenyltetrazolium chloride and phthalocyanine blue dye. Heat-shock treatment significantly increased myocardial catalase compared with control animals (180.5 +/- 4.8, n = 6, versus 86.2 +/- 14.7, n = 5, units/g wet wt; P < .05). Treatment with 3-AT significantly reduced myocardial catalase activity in both heat-shocked and control animals (29.6 +/- 5.7, n = 5, and 36.4 +/- 15.3, n = 6, respectively). Heat-shock treatment significantly reduced infarct size in rats that were both treated and untreated with 3-AT compared with respective control groups (22.5 +/- 3.7%, n = 26, 28.2 +/- 4.0%, n = 22, 52.0 +/- 3.0%, n = 23, and 48.6 +/- 3.2%, n = 26, respectively; P < .0001 for both heat-shocked groups versus both control groups; infarct mass/risk area mass x 100).

CONCLUSIONS

Catalase inhibition with 3-AT does not abolish the reduction of infarct size in heat-shocked rats.

Hsp70 in myocardial ischaemia

Numerous reports suggest that stress protein accumulation confers protection in various mammalian tissues against differing stresses. The purpose of this article is to review the evidence that stress proteins, in particular hsp70, are able to alter the resistance of the heart to subsequent ischaemic and non-ischaemic injury and to discuss the possible physiological basis for this apparent protection. The possible, though unlikely involvement of heat stress proteins in classical ischaemic preconditioning is addressed as is the possibility of their involvement in a delayed second window of protection.