Heat Preconditioning Research Articles

Carbohydrate Metabolism in Diabetic Rat’s Heart – The Effects of Acetylsalicylic Acid and Heat Preconditioning as HSP70 Inducers

Abstract The myocardium of diabetic subjects displays reduced HSP70 protein level and weak myocardial protection. However, the heart possesses an ability to produce heat shock proteins (HSPs) after exposure to sublethal heat stress. Acetylsalicylicacid (ASA) has the property of pharmacological induction of HSPs. We evaluated the common effects of single dose ASA-pretreatment, prior to heat preconditioning (HP), over carbohydrate metabolism-related enzymes and substrates in the heart of diabetic rats. Streptozotocin-diabetes caused significant decrease of HSP70 protein level, stimulation of the gluconeogenic processes and inhibition of glycolytic processes in the heart. HP-diabetic hearts have significantly higher HSP70 protein level, lower glycogen, glucose-6-phosphate content, glycogen phosphorylase and hexokinase activity, and higher glucose levels and PFK activity. ASA-pretreatment of HP-diabetic animals caused additional increase of HSP70, additional decrease of glycogen, glucose-6-phosphate, glycogen phosphorylase and hexokinase, and additional increase of glucose and PFK in the heart. In conclusion, HP is physiological inducer of HSP70 level in heart and tends to reverse carbohydrate - related disturbances in diabetic rats. ASA, given prior to HP, is a potent HSP70 co-inducer and causes additional increase of HSP70 protein level in heart. ASA, given in a combination to HP, have shown more evident protective effects against subsequent intense of stress.

Heat precondition is a potential strategy to combat hepatic injury triggered by severe heat stress

AimEnvironmental heat stress alters physiological and biochemical functions which leads to multiorgan dysfunction including severe hepatic injury in animals. We hypothesize that heat preconditioning can be potential intervention in combating heat illnesses. Main methodsSprague Dawley rats were exposed to moderate heat stress, severe heat stress and heat preconditioning in heat simulation chamber. Mean arterial pressure, heart rate, skin and core temperature were monitored in pre and post heat exposed animals. After stress exposure, blood for hemodynamic and liver tissue for liver function tests, oxidative stress, inflammatory variables and structural studies were collected from rats. Hepatic mitochondria were isolated to study the key structural alterations and functional changes by transmission electron microscopy. Key findingsThe effect of heat precondition shows improvement in time to attain the core temperature, weight loss, blood pressure and heart rate in rats. Results exhibited decreased levels of liver function tests, elevated levels of free radicals and inflammatory cytokines in heat exposed liver as compared with heat preconditioned animals. Expression levels of mitochondrial heat shock protein 60, superoxide dismutase 1 and uncoupling protein 1 along with activity of electron transport chain complexes I-V were examined and found to be increased in heat preconditioned as compared to heat stressed animals. Morphological studies of liver parenchyma demonstrated reduction in structural deterioration of hepatic lobules and restoration of mitochondrial structural integrity in heat preconditioned rats. SignificancePresent study suggests that heat preconditioning intervention plays a crucial role in protection against heat induced hepatic injury in animals.

Nicotinamide and heat preconditioning - Effects on hepatic HSP70, carbohydrate and oxidative disturbances in STZ-induced diabetic rats.

Nicotinamide (NA) is known to have antioxidant potential and partially to protect insulin-secreting cells against diabetogenic agent STZ (streptozotocin). In a combination to heat stress (HS), NA is also known to induce heat-shock proteins (HSPs) production. Heat preconditioning (HP) and HSPs have cytoprotective effects against development of cellular injury caused by application of subsequent stressor. We aimed to determine if pretreatment with NA and HP (as HSP70 -inducers) can affect STZ-induced diabetic disturbances in rats. NA-pretreatment (250mg/kg b.w., 7 days) and heat preconditioning (41±1°C, 45min) of diabetic rats was performed. The changes in hepatic carbohydrate- and antioxidative-related enzymes and substrates were investigated. NA-pretreatment, alone or in combination with HS, resulted in significant increase of HSP70 concentration in the liver of control and diabetic rats. Compared to diabetic controls, pretreatment with NA, in combination with HP, resulted in decrease of blood and liver glucose, increase of glycogen and glucose-6-phosphate level, increase of glycogenolytic/glycolytic enzymes, decrease of gluconeogenic enzymes, as well as an increase of glutathione content and glutathione peroxidase, decrease of glutathione reductase and catalase activities. NA is a potent HSP70 coinducer, alone or in a combination with HS in the liver of both control and diabetic rats. Pretreatment with NA, accompanied by HP, has a pronounced corrective effect on STZ-induced diabetes disturbances in the key hepatic carbohydrate- and antioxidative-related parameters. It seems that this corrective effect is based on the increased production of hepatic HSP70.

Preparation of a sugarcane bagasse-based substrate for second-generation ethanol: Effect of pasteurisation conditions on dephenolisation

Second-generation ethanol process uses lignocellulose, but a pre-treatment is required to degrade lignin before saccharification. Biological pre-treatment, using phenoloxidases, represents a cheap and eco-friendly option. Mould contamination can be overcome by heat pre-conditioning of substrates. Pasteurisation can be a mild and sustainable option. A 5-level response-surface experimental design was performed to test the effect of different time and temperatures on lignocellulolytic activities and substrate dephenolisation. Substrate microbial communities were characterised via catabolic profiles to determine functional diversity changes after pasteurisation. Temperatures ranging from 70 to 75 °C and time from 5 to 10 h led to the highest laccase activities and 30% of substrate dephenolisation was achieved while avoiding mould contamination. The per cent of O-Alkyl (polysaccharides) did not vary significantly, meaning that polysaccharides were not extensively consumed. Microbial communities were less catabolically diversified (H’ = 1.2) but more active (AWCD = 0.9) and could degrade polysaccharides.

Heat-Shock Protein 70-Mediated Heat Preconditioning Attenuates Hepatic Carbohydrate and Oxidative Disturbances in Rats With Type 1 Diabetes.

Heat preconditioning and heat-shock protein (HSP) synthesis have significant cytoprotective effects against the development of cellular injury caused by the application of a subsequent stressor, which were found to depend on the time period between the stressors. We aimed to determine the most efficient recovery time (6h or 24h) following heat-stress exposure and prior application of diabetic streptozotocin (STZ) on the moderation of carbohydrate and oxidative metabolic disturbances caused by diabetes. Experiment animals (Wistar rats) were exposed to acute heat stress at 41±1°C for 45min, followed by 6-h or 24-h recovery times at room temperature before sacrifice or STZ administration. Our findings indicate that acute heat stress with 6-h or 24-h recovery periods results in a significant rise in the hepatic heat-shock protein 70 (HSP70) levels (even more so after 24h), glycogen breakdown and stable glycemia, followed by reduced glycolytic and gluconeogenic activity (after 24h) (glucose-6-phosphatase, fructose-1,6-bisphosphatase); stimulates antioxidative activity (glutathione peroxidase, glutathione reductase) (after 6h); and decreases glutathione and catalase activity (after 24h). Heat preconditioning (with 6-h and 24-h recovery periods) prior to STZ-induced diabetes increases HSP70 levels and causes lower serum glucose levels, higher glycogen and glucose-6-phosphate levels, lower glucose-6-phosphatase levels and glycogen phosphorylase and hexokinase levels but also elevates glutathione reductase and glutathione peroxidase activity compared to untreated STZ animals. Based on our findings, heat preconditioning and HSP70 induction in rats with type 1 diabetes attenuates STZ-induced metabolic alterations in hepatic carbohydrate metabolism and oxidative states. These changes are more evident at 24h recovery post-acute heat stress, based on the most evident accumulation of HSP70 in this time frame.

A randomised controlled feasibility trial to evaluate local heat preconditioning on wound healing after reconstructive breast surgery: the preHEAT trial

ObjectivepreHEAT was a randomised controlled feasibility trial to determine how best to measure skin necrosis in breast reconstruction to inform the design of a larger multicentre trial.BackgroundMastectomy skin flap necrosis (MSFN) is a serious complication resulting in prolonged wound healing. Local heat preconditioning of the MSF before surgery has been shown to reduce skin necrosis in immediate breast reconstruction patients (IBR).MethodpreHEAT was a single-centre, randomised control two-arm single-blind parallel arm feasibility trial of local heat preconditioning in breast cancer patients undergoing SSM and NSM at Guy’s and St Thomas’ Hospital, London, UK. All patients undergoing IBR above the age of 18 were included. Intervention patients heated breast skin to 43 °C in three, 30-min cycles interrupted by spontaneous cooling using hot water bottles. The primary aim was to compare measurement of skin necrosis using binary ‘yes/no’ assessment, the SKIN score, and wound area.ResultsOne hundred forty-one patients were randomised over a 2-year period (71 heated group, 70 controls). There was near perfect agreement between assessors using the “yes/no” measurement of necrosis. The proportion of patients experiencing necrosis in controls was 35% (n = 23/66) in the heated 26% (n = 18/68]). In the control group, 17% (n = 4/23) patients experiencing necrosis required surgical intervention for necrosis compared to 11% (n = 2/18) in the heated group.ConclusionThe binary outcome of MSFN “yes/no” is a suitable and reliable primary outcome measure of necrosis and was superior to the SKIN Score or necrosis area. The trial study design is feasible for a larger definitive trial.Trial registrationISRCTN15744669. Date of registration: 25/02/2018

Heat preconditioning and aspirin treatment attenuate hepatic carbohydrate-related disturbances in diabetic rats

Heat preconditioning (HP) is a powerful adaptive and protective phenomenon and induces moderation of diabetic alterations in glycogen metabolism of rats. Aspirin (acetylsalicylic acid, ASA), as a multifunctional drug has also been reported to exert hypoglycemic effects in the treatment of diabetes. We estimated the effect of HP (45 min/41 ± 0.5 °C/24 h recovery) and single dose aspirin (100 mg/kg b.w./i.p) treatment over carbohydrate-related enzymes and substrates in a time-dependent (2, 7 and 14 days) manner of duration of diabetes in the liver of rats.Heat preconditioning resulted in lower liver glucose concentration, but higher HK activity and lower G6P-ase; very evident and significantly higher glycogen content and GPho-ase activity, as well as very evident and significantly lower F1,6BP-ase and higher PFK activity compared to control diabetic animals.Aspirin pretreatment of HP-diabetic animals is manifested with significantly lower blood and liver glucose, higher G6P concentration, lower G6P-ase and HK activity as well as higher Glk content and GPho-ase activity, compared both to diabetic and HP-diabetic animals.In conclusion, both HP and aspirin, as physiological and pharmacological inductors of HSP70, respectively, attenuate the carbohydrate-related disturbances in diabetic rats, with almost tendency to normalisation to the control values for most of the estimated parameters.

Measuring skin necrosis in a randomised controlled feasibility trial of heat preconditioning on wound healing after reconstructive breast surgery: study protocol and statistical analysis plan for the PREHEAT trial

BackgroundEssential strategies are needed to help reduce the number of post-operative complications and associated costs for breast cancer patients undergoing reconstructive breast surgery. Evidence suggests that local heat preconditioning could help improve the provision of this procedure by reducing skin necrosis. Before testing the effectiveness of heat preconditioning in a definitive randomised controlled trial (RCT), we must first establish the best way to measure skin necrosis and estimate the event rate using this definition.MethodsPREHEAT is a single-blind randomised controlled feasibility trial comparing local heat preconditioning, using a hot water bottle, against standard care on skin necrosis among breast cancer patients undergoing reconstructive breast surgery. The primary objective of this study is to determine the best way to measure skin necrosis and to estimate the event rate using this definition in each trial arm. Secondary feasibility objectives include estimating recruitment and 30 day follow-up retention rates, levels of compliance with the heating protocol, length of stay in hospital and the rates of surgical versus conservative management of skin necrosis. The information from these objectives will inform the design of a larger definitive effectiveness and cost-effectiveness RCT.DiscussionThis article describes the PREHEAT trial protocol and detailed statistical analysis plan, which includes the pre-specified criteria and process for establishing the best way to measure necrosis. This study will provide the evidence needed to establish the best way to measure skin necrosis, to use as the primary outcome in a future RCT to definitively test the effectiveness of local heat preconditioning. The pre-specified statistical analysis plan, developed prior to unblinded data extraction, sets out the analysis strategy and a comparative framework to support a committee evaluation of skin necrosis measurements. It will increase the transparency of the data analysis for the PREHEAT trial.Trial registrationISRCTN ISRCTN15744669. Registered 25 February 2015

Effect of single and repeated heat stress on chemical signals of heat shock response cascade in the rat's heart.

Exposure to sublethal heat stress activates a complex cascade of signaling events, such as activators (NO), signal molecules (PKCε), and mediators (HSP70 and COX-2), leading to implementation of heat preconditioning, an adaptive mechanism which makes the organism more tolerant to additional stress. We investigated the time frame in which these chemical signals are triggered after heat stress (41 ± 0.5°С/45min), single or repeated (24 or 72h after the first one) in heart tissue of male Wistar rats. The animals were allowed to recover 24, 48 or 72h at room temperature. Single heat stress caused a significant increase of the concentration of HSP70, NO, and PKC level and decrease of COX-2 level 24h after the heat stress, which in the next course of recovery gradually normalized. The second heat stress, 24h after the first one, caused a significant reduction of the HSP70 levels, concentration of NO and PKCɛ, and significant increase of COX-2 concentration. The second exposure, 72h after the first heat stress, caused more expressive changes of HSP70 and NO in the 24h-recovery groups. The level of PKCɛ was not significantly changed, but there was significantly increased COX-2 concentration during recovery. Serum activity of AST, ALT, and CK was reduced after single exposure and increased after repeated exposure to heat stress, in both time intervals. In conclusion, a longer period of recovery (72h) between two consecutive sessions of heat stress is necessary to achieve more expressive changes in mediators (HSP70) and triggers (NO) of heat preconditioning.

Physiological and pharmacological inductors of HSP70 enhance the antioxidative defense mechanisms of the liver and pancreas in diabetic rats.

Heat preconditioning (HP) is a powerful adaptive and protective phenomenon and the heat stress proteins (HSPs) it produces are an important determinant for the development of diabetic complications. Aspirin has been reported to modulate heat shock response in different organisms through increased induction of HSPs and is also known to exert antioxidative and radical scavenging effects in diabetes. We estimated the effect of physiological (heat stress: 45 min at 41 ± 0.5 °C) and pharmacological (aspirin treatment) induction of HSP70 on several parameters of oxidative state in the pancreas and liver of diabetic rats. Diabetes increased HSP70 level and decreased poly(ADP) ribose polymerase (PARP), glutathione (GSH), and glutathione peroxidase (GPx) activities in the pancreas. In the liver, there was reduction of HSP70 level, GSH concentration, and CAT activity, while GPx and GR activity were enhanced. HP of diabetic rats caused an additional increase of HSP70, GSH, and antioxidant enzymes in both organs. Pre-treatment of HP-diabetic animals with aspirin led to an additional increase of PARP and HSP70. Both HP and aspirin, as physiological and pharmacological inductors of HSP70, respectively, enhanced the antioxidative defense mechanisms of the liver and pancreas in diabetic rats.

Heat shock protein 72 may improve hypotension by increasing cardiac mechanical efficiency and arterial elastance in heatstroke rats

ObjectiveWe attempted to test the hypothesis that preinduction of heat shock protein (HSP) 72 in the heart would improve left ventricular performance in rat heatstroke. MethodsCardiac expression of HSP 72 was quantitatively evaluated by western blot analysis in rats 0h, 12h, or 72h after mild heat preconditioning (MHP; 43°C for 30min). They were subjected to severe heat stress (SHS; 43°C for 70min) to induce heatstroke. A 1.2F catheter-tip pressure transducer was inserted into the left ventricle of these group rats under general anesthesia to record hemodynamic in the closed chest with a pressure–volume loop module data recording and analysis system. ResultsAt the time point of heatstroke onset, compared with normothermic controls, group rats with 12h post-MHP had significantly increased cardiac HSP 72, decreased hyperthermia, decreased hypotension, decreased bradycardia, increased end-systolic pressure, increased end-diastolic pressure, increased stroke volume, decreased end-systolic volume, decreased end-diastolic pressure, increased cardiac output, increased ejection fraction, increased stroke work, increased arterial elastance, and decreased time constant of fall in ventricular pressure by Glantz-methods. With the loss of cardiac HSP 72 expression observed at 72h in post-MHP group rats, an insignificant protection against left ventricular performance was observed. ConclusionPreinduction of cardiac HSP 72 may improve hypotension in heatstroke rats by increasing both cardiac mechanical efficiency and arterial elastance.

Chronic Heat Preconditioning Enhances Skeletal Muscle Function during Hypoxia and Reoxygenation

Skeletal muscle that is exposed to hypoxia followed by reoxygenation (H/R) is susceptible to dysfunction and fatigue. However, the mechanisms that underlie skeletal muscle fatigue during H/R are not completely understood. The purpose of our study was to determine the role that chronic heat preconditioning (CHP) may play in protecting skeletal muscle against the deleterious effects of H/R. We hypothesized that CHP would mitigate skeletal muscle fatigue and attenuate ROS formation during H/R. During CHP treatment, C57BL/6 mice were housed in a heating chamber at 42°C for 30 minutes. Next, the mice were transferred to another chamber at room temperature for 30 minutes. This cycle was repeated 3 times per day, 5 days/week, for 2 weeks. Following CHP, mice were sacrificed and their diaphragms were removed for muscle function analysis. The muscle strips were electrically stimulated in a contraction chamber filled with Ringer's solution during H/R. Our data revealed that CHP significantly increased muscle function during hypoxia (31.5 ± 1.7% for treated vs. 13.1 ± 2.7% for control, p < 0.05; expressed as percent of the maximal force at the end of the contraction protocol) and also showed a trend to increase muscle fatigue resistance during reoxygenation. We monitored cellular levels of reactive oxygen species (ROS) via confocal microscopy by utilizing dihydrofluorescein diacetate (Hfluor‐DA), which is a fluorescent probe sensitive to intracellular ROS. Compared to the non‐treated group, CHP‐treated muscle strips demonstrated mitigated ROS fluorescence at the end of both hypoxia and reoxygenation periods, respectively (p < 0.05). Our results suggest that CHP may play a protective role against muscle fatigue and ROS formation during H/R in skeletal muscle.Support or Funding InformationSupported by OU General Fund G110

The extent of heat tolerance depends on the heat shock protein 72 levels in cultured primary hypothalamic neurons

We attempted to investigate whether severe heat‐induced hypothalamic cell injury and apoptosis can be affected by modulating heat shock protein (HSP) 72 levels. Cell viability was determined using 3‐(4,5‐dimethyl‐2‐thiazolyl)‐2,5‐diphenyl‐2‐ H‐ tetrazolium bromide staining, whereas apoptosis was evidenced using flow cytometry. The viability or the percentage of apoptotic cells in the cultured primary hypothalamic cells were significantly (p<0.01) reduced by severe heat shock (43oC for 120 min). Cell injury and apoptosis caused by severe heat could be significantly attenuated or exacerbated by increasing cellular levels of HSP72 with mild heat preconditioning (42oC for 30 min; 8 h before the onset of heat shock) or decreasing the cellular levels of HSP72 with pSUPER/siRNA hsp72 plasmid (8 h before onset of severe heat shock), respectively. In addition, the beneficial effects of mild heat preconditioning in reducing cell injury and apoptosis could be significantly (p<0.05) reversed by silencing of selected gene and knockdown of HSP72 with pSUPER/siRNA hsp72. Our data indicated that the extent of heat tolerance of cultured primary hypothalamic cells depends on the cellular levels of HSP72.

Cathepsin B is involved in the heat shock induced cardiomyocytes apoptosis as well as the anti-apoptosis effect of HSP-70.

Cathepsin B is one of the major lysosomal cysteine proteases that plays an important role in apoptosis. Herein, we investigated whether Cathepsin B is involved in cardiomyocyte apoptosis caused by hyperthermic injury (HI) and heat shock protein (HSP)-70 protects these cells from HI-induced apoptosis mediated by Cathepsin. HI was produced in H9C2 cells by putting them in a circulating 43 °C water bath for 120 min, whereas preinduction of HSP-70 was produced in H9C2 cells by mild heat preconditioning (or putting them in 42 °C water bath for 30 min) 8 h before the start of HI. It was found that HI caused both cardiomyocyte apoptosis and increased Cathepsin B activity in H9C2 cells. E-64-c, in addition to reducing Cathepsin B activity, significantly attenuated HI-induced cardiomyocyte apoptosis (evidenced by increased apoptotic cell numbers, increased tuncated Bid (t-Bid), increased cytochrome C, increased caspase-9/-3, and decreased Bcl-2/Bax) in H9C2 cells. In addition, preinduction of HSP-70 by mild heat preconditioning or inhibition of HSP-70 by Tripolide significantly attenuated or exacerbated respectively both the cardiomyocyte apoptosis and increased Cathepsin B activity in H9C2 cells. Furthermore, the beneficial effects of pre-induction of HSP-70 by mild heat production in reducing both cardiomyocyte apoptosis and increased Cathepsin B activity caused by HI can be significantly reduced by Triptolide preconditioning. These results indicate that Cathepsin B is involved in HI-induced cardiomyocyte apoptosis in H9C2 cells and HSP-70 protects these cells from HI-induced cardiomyocyte apoptosis through Cathepsin B pathways.

The heat-shock protein-70–induced renoprotective effect is partially mediated by CD4+CD25+Foxp3+ regulatory T cells in ischemia/reperfusion-induced acute kidney injury

Recent reports suggest the presence of heat-shock protein (HSP)-reactive T cells with a regulatory phenotype in various inflammatory diseases. To test whether HSP exerts renoprotective effects through regulatory T cells (Tregs), ischemia/reperfusion injury was done with or without heat preconditioning in mice. Splenocytes from heat-preconditioned mice had Treg expansion and a reduced proliferative response upon mitogenic stimulus. T cells from heat-preconditioned mice failed to reconstitute postischemic injury when adoptively transferred to T cell-deficient nu/nu mice in contrast to those from control mice. Tregs were also increased in heat-preconditioned ischemic kidneys. Depleting Tregs before heat preconditioning abolished the renoprotective effect, while adoptive transfer of these cells back into Treg-depleted mice partially restored the beneficial effect of heat preconditioning. Inhibition of HSP70 by quercetin suppressed Treg expansion, as well as renoprotective effects. Transferring Tregs in quercetin-treated heat-preconditioned mice partially restored the beneficial effect of heat preconditioning. The specificity of immune cell HSP70 in renoprotection was confirmed by partial restoration of kidney injury when T cells from HSP70-deficient heat preconditioned mice were adoptively transferred to nu/nu mice. Thus, the renoprotective effect of HSP70 may be partially mediated by a direct immunomodulatory effect through Tregs. Better understanding of immunomodulatory mechanisms of various stress proteins might facilitate discovery of new preventive strategies in acute kidney injury.

Heat-shock protein-70 and regulatory T cell–mediated protection from ischemic injury

Heat preconditioning induces heat-shock protein-70 upregulation and protects from renal ischemia/reperfusion injury. Kim et al. report that heat-shock protein-70 and regulatory T cells play a key role in protective heat preconditioning. This work reinforces the utility of inducing heat-shock protein-70 expression by pharmacological agents as a novel therapy for the prevention and treatment of ischemic kidney injury.

Attenuating heat-induced cellular autophagy, apoptosis and damage in H9c2 cardiomyocytes by pre-inducing HSP70 with heat shock preconditioning

Purpose: We sought to assess whether heat-induced autophagy, apoptosis and cell damage in H9c2 cells can be affected by pre-inducing HSP70 (heat shock protein 70).Materials and methods: Cell viability was determined using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl tetrazolium bromide staining and a lactate dehydrogenase assay. Apoptosis was evidenced using both flow cytometry and counting caspase-3 positive cells, whereas autophagy was evidenced by the increased LC3-II expression and lysosomal activity.Results: The viability of H9c2 cells was temperature-dependently (40–44 °C) and time-dependently (90–180 min) significantly (p < 0.05) reduced by severe heat, which caused cell damage, apoptosis and autophagy. Heat-induced cell injury could be attenuated by pretreatment with 3-methylademine (an autophagy inhibitor) or Z-DEVD-FMK (a caspase-3 inhibitor). Neither apoptosis nor autophagy over the levels found in normothermic controls was induced in heat-shock preconditioned controls (no subsequent heat injury). The beneficial effects of mild heat preconditioning (preventing heat-induced cell damage, apoptosis and autophagy) were significantly attenuated by inhibiting HSP70 overexpression with triptolide (Tripterygium wilfordii) pretreatment.Conclusion: We conclude that pre-inducing HSP70 attenuates heat-stimulated cell autophagy, apoptosis and damage in the heart. However, this requires in vivo confirmation.

Elimination of Eccentric Exercise-Induced Interleukin-6 Response by Heat Preconditioning

Exercise training lowers the mortality rate of animals under heat stress. It is currently unknown whether heat preconditioning can attenuate exercise-induced increases in circulating interleukin-6 (IL-6) for athletes. Sixteen male basketball players were randomly assigned to the control (n = 8) and heat preconditioning (n = 8) groups. The heat preconditioning program consisted of a 30-min hot water immersion at 41°C performed every 72 h up to 4 sessions, which slightly elevated circulating creatine kinase (CK) and thiobarbituric acid-reactive substances (TBARS) by 27% and 21%, respectively (P ＜ 0.05). Seventy two hours after the last hot water immersion, both groups were challenged with an acute bout of eccentric exercise (6 squats at 85% maximal voluntary effort for 6 sets), which elicited significant increases in IL-6 (+120%) and CK (+34%) above pre-exercise level of the control group (P ＜ 0.05). This increase was absent in the heat preconditioning group. Heart rate variability (HRV) and high frequency power (HF) were increased following heat preconditioning, and remained elevated after exercise challenge. Our study provides evidence that eccentric exercise-induced stress response can be attenuated by a heat preconditioning protocol at 41°C.

The in vitro preconditioning of myoblasts to enhance subsequent survival in an in vivo tissue engineering chamber model

The effects of in vitro preconditioning protocols on the ultimate survival of myoblasts implanted in an in vivo tissue engineering chamber were examined. In vitro testing: L6 myoblasts were preconditioned by heat (42 °C; 1.5 h); hypoxia (<8% O2; 1.5 h); or nitric oxide donors: S-nitroso-N-acetylpenicillamine (SNAP, 200 μM, 1.5 h) or 1-[N-(2-aminoethyl)-N-(2-aminoethyl)amino]-diazen-1-ium-1,2-diolate (DETA-NONOate, 500 μM, 7 h). Following a rest phase preconditioned cells were exposed to 24 h hypoxia, and demonstrated minimal overall cell loss, whilst controls (not preconditioned, but exposed to 24 h hypoxia) demonstrated a 44% cell loss. Phosphoimmunoblot analysis of pro-survival signaling pathways revealed significant activation of serine threonine kinase Akt with DETA-NONOate (p < 0.01) and heat preconditioning (p < 0.05). DETA-NONOate also activated ERK 1/2 signaling (p < 0.05). In vivo implantation: 100,000 preconditioned (heat, hypoxia, or DETA-NONOate) myoblasts were implanted in SCID mouse tissue engineering chambers. 100,000 (not preconditioned) myoblasts were implanted in control chambers. At 3 weeks, morphometric assessment of surviving myoblasts indicated myoblast percent volume (p = 0.012) and myoblasts/mm2 (p = 0.0005) overall significantly increased in preconditioned myoblast chambers compared to control, with DETA-NONOate-preconditioned myoblasts demonstrating the greatest increase in survival (p = 0.007 and p = 0.001 respectively). DETA-NONOate therefore has potential therapeutic benefits to significantly improve survival of transplanted cells.

Temperature dependent plasticity of habituation in the crayfish

To determine the effects of thermal preconditioning on a simple form of learning and memory, habituation, we preconditioned crayfish with extreme temperatures and subsequently analysed their effects on mechanosensory input that evokes a response in the lateral giant interneurons, within the normal temperature range of the animal. We found that repetitive stimulation with a 1 s interstimulus interval led to habituation of the response the lateral giant in control animals at 22°C. Neither heat nor cold preconditioning had any effect on the probability of evoking a response in the lateral giant nor on the rate at which habituation occurred. With a 1 min interstimulus interval, however, the rate of habituation of the lateral giant in the heat-preconditioned group was less than either the control or cold-preconditioned animals. The effect of heat or cold pre-exposure was specific to the input to the lateral giant at control temperatures. For example, at 22°C prior heat and cold preconditioning had no effect on spontaneous reductor motor neurone activity. They did, however, provide thermoprotection at extreme temperatures, with the probability of spontaneous activity higher in the cold-preconditioned group at low temperatures but higher in the heat-preconditioned group at higher temperatures.