Mesenchymal stem cells regulate activation of microglia cells to improve hippocampal injury of heat stroke rats.

Heat stroke is a severe systemic inflammatory response disease caused by high fever, mainly with nervous system damage. Mesenchymal stem cells (MSCs) are currently believed to have anti-inflammation and immunomodulatory effects. Therefore, we aimed to explore the protective effect and mechanism of MSCs on heat stroke-induced excessive inflammation and neurological dysfunction. We established a heat stroke model in rats under conditions of continuous high temperature and high humidity. After modeling, rats were randomly divided into heat stroke model group, MSCs treatment group and normal temperature control group without any treatment. We performed survival analysis, neurological deficit score, histological staining of hippocampus and cerebellum, immunofluorescence staining of microglia, detection of inflammatory and chemokine levels in the hippocampus and cerebellum in each group. We found that MSCs treatment not only significantly reduced early (day 3) and late (day 28) mortality, but also prominently reduced nerve injury in heat stroke rats, and improved pathology and neuronal cell damage in the hippocampus and cerebellum. In addition, MSCs treatment can significantly inhibit the over-activation of hippocampal microglia in heat stroke rats and the levels of pro-inflammatory factors and chemokines in the hippocampus. Early treatment of MSCs can greatly promote the activation of cerebellar microglia in heat stroke rats. Meanwhile, MSCs treatment has an inhibitory effect on the level of chemokine in the cerebellum of rats in the early stage of heat stroke. In conclusion, the application of MSCs in the treatment of heat stroke in rats can significantly reduce mortality and neurological deficits and improve hippocampal damage, possibly by inhibiting the excessive activation of hippocampal microglia in heat stroke rats.

Lack of lymphocytes exacerbate heat stroke severity in male mice through enhanced inflammatory response.

Though it has long been thought that the immune system is implicated in the pathophysiology of heat stroke, the underlying mechanisms are still poorly understood. As it has been reported in the literature that lymphocyte disturbance occurs in heat stroke patients or animals, we attempted to seek experimental evidence to define the role of lymphocytes in the pathophysiology of heat stroke. In our study, we used male Balb/c mice to establish a passive heat stroke model. We found that lymphocyte-deficient Severe combined immunodeficient (SCID) mice exposed to heat stress exhibited exacerbated heat stroke severity, which could be indicated by increased rates of mortality and serum levels of inflammatory cytokines compared to wildtype control mice. We further showed, through the depletion of T lymphocytes in wildtype mice and the transfer of wildtype lymphocytes into SCID mice, respectively, that T lymphocytes were both necessary and sufficient to alleviate the severity of heat stroke by inhibiting the early inflammatory response. Moreover, we found that the severity of heat injuries in heat-stressed wildtype mice showed great inter-individual variability, and the early number of T lymphocytes could be negatively associated with the severity of heat stroke. Our results suggest that lack of T lymphocytes could exacerbate the severity of heat stroke by augmenting inflammatory response, and the early circulating T lymphocytes may serve as a potential biomarker for the diagnosis of heat stroke.

Exosomes Derived From Heat Stroke Cases Carry miRNAs Associated With Inflammation and Coagulation Cascade.

The pathological mechanism underlying heat stroke (HS) is associated with the dysbalanced inflammation and coagulation cascade. Cell-derived circulating extracellular vesicles (EVs), as a novel pathway mediating intercellular communication, are associated with the immune response and inflammation in critical inflammatory syndromes, such as sepsis. Although these vesicles contain genetic material correlated with their biological function, their molecular cargo during HS remains unknown. In this study, we evaluate the presence of microRNAs (miRNAs) and messenger RNAs (mRNAs) associated with inflammatory responses and coagulation cascade in exosomes of patients with HS. Blood samples were collected from three patients with HS at the time of admission to the intensive care unit; three healthy volunteers were selected as control. Exosomes were isolated using ultracentrifugation, and their miRNA content was profiled using next-generation sequencing; mRNA content was evaluated using qPCR array. Compared with those from healthy volunteers, exosomes from patients with HS showed substantial changes in the expression of 202 exosomal miRNAs (154 upregulated and 48 downregulated miRNAs). The most upregulated miRNAs included miR-511-3p, miR-122-5p, miR-155-3p, miR-1290, and let7-5p, whereas the most downregulated ones included miR-150-3p, 146a-5p, and 151a-3p. Gene ontology enrichment of the miRNAs of patients with HS compared with control subjects were associated mostly with inflammatory response, including T cell activation, B cell receptor signaling, dendritic cell chemotaxis and leukocyte migration, and platelet activation and blood coagulation. The identified miRNAs were primarily enriched to the signal transduction pathways namely, T cell receptor signaling, Ras signaling, chemokine signaling, platelet activation, and leukocyte transendothelial migration, all of which are associated with inflammation and hemostasis. Multiple targeted mRNAs associated with the inflammatory response, blood coagulation, and platelet activation were further verified in serum exosomes. Exosomes from patients with HS convey miRNAs and mRNAs associated with pathogenic pathways, including inflammatory response and coagulation cascade. Exosomes may represent a novel mechanism for intercellular communication during HS.

The Role of Skeletal Muscles in Exertional Heat Stroke Pathophysiology.

The active participation of skeletal muscles is a unique characteristic of exertional heat stroke. Nevertheless, the only well-documented link between skeletal muscle activities and exertional heat stroke pathophysiology is the extensive muscle damage (e. g., rhabdomyolysis) and subsequent leakage of intramuscular content into the circulation of exertional heat stroke victims. Here, we will present and discuss rarely explored roles of skeletal muscles in the context of exertional heat stroke pathophysiology and recovery. This includes an overview of heat production that contributes to severe hyperthermia and the synthesis and secretion of bioactive molecules, such as cytokines, chemokines and acute phase proteins. These molecules can alter the overall inflammatory status from pro- to anti-inflammatory, affecting other organ systems and influencing recovery. The activation of innate immunity can determine whether a victim is ready to return to physical activity or experiences a prolonged convalescence. We also provide a brief discussion on whether heat acclimation can shift skeletal muscle secretory phenotype to prevent or aid recovery from exertional heat stroke. We conclude that skeletal muscles should be considered as a key organ system in exertional heat stroke pathophysiology.

Regulatory T Cells Could Improve Intestinal Barrier Dysfunction in Heatstroke.

Intestinal barrier dysfunction plays a pivotal role in multiorgan dysfunction during heatstroke (HS). Neutrophils are involved in intestinal inflammation and thus dampen the mucosal integrity. Regulatory T cells (Tregs) have been shown to orchestrate neutrophils and thus sustain mucosal integrity in miscellaneous inflammation-related diseases. However, whether Tregs are involved in HS-induced intestinal barrier dysfunction remains unknown. Thus, we investigated whether Tregs could alleviate intestinal barrier dysfunction in mice. We found that HS could induce intestinal injury and mucosal barrier dysfunction 0, 24, and 72 h after heat stress. Flow cytometry revealed an increase of neutrophil infiltration and a decrease of Treg frequencies in the small intestinal epithelium 72 h after heat stress. Treg depletion starting 2 days before HS exacerbated intestinal damage and mucosal barrier dysfunction. Adoptive transfer of Tregs at 0 h improved intestinal injury and mucosal barrier dysfunction at 72 h. The manipulation of Tregs affected the neutrophil frequencies in the small intestinal epithelium 72 h after heat stress. Our study demonstrated that Tregs could improve HS-induced intestinal barrier dysfunction, probably via modulation of neutrophils in the intestine of mice during HS.

JAK2/STAT3 pathway mediating inflammatory responses in heatstroke-induced rats.

Heatstroke not only directly induces cell injury, but also causes large amounts of inflammatory mediators release and cells with extensive biological activities to induce a systemic inflammatory response and immune dysfunction. This study aimed to observe the effects of JAK2 inhibitor AG490 on the brain injury and inflammatory responses of rats with systemic heatstroke. Under the light microscope, the hippocampus tissues of rat with heatstroke were edema and apoptotic rate was increased. Up-regulation of malondialdehyde (MDA), nitric oxide synthase (iNOS), reactive oxygen species (ROS) and down-regulation of superoxide dismutase (SOD) were also found after heatstroke in rats, which compared with that of the control group. Heatstroke induced inflammation factors secretions and up-regulated levels of matrix metallopeptidase 2 and 9 (MMP2 and MMP-9) and systemic inflammatory response molecules including intercellular adhesion molecule-1 (ICAM-1), tumor necrosis factor-beta 1 (TNF-ß1) and cyclooxygenase-2 (COX-2). However, the JAK2 inhibitor AG490 was significantly attenuated the brain injury and inflammatory responses induced by heatstroke in rats. The survival time of heatstroke rats showed that AG490 notably lived longer than heatstroke rats without AG490 treatment. These findings suggest that AG490 may prevent the occurrence of heatstroke via inhibiting the JAK2/STAT3 pathway and the systemic inflammatory responses.

Heat stroke.

Heat stroke is a life-threatening condition clinically diagnosed as a severe elevation in body temperature with central nervous system dysfunction that often includes combativeness, delirium, seizures, and coma. Classic heat stroke primarily occurs in immunocompromised individuals during annual heat waves. Exertional heat stroke is observed in young fit individuals performing strenuous physical activity in hot or temperature environments. Long-term consequences of heat stroke are thought to be due to a systemic inflammatory response syndrome. This article provides a comprehensive review of recent advances in the identification of risk factors that predispose to heat stroke, the role of endotoxin and cytokines in mediation of multi-organ damage, the incidence of hypothermia and fever during heat stroke recovery, clinical biomarkers of organ damage severity, and protective cooling strategies. Risk factors include environmental factors, medications, drug use, compromised health status, and genetic conditions. The role of endotoxin and cytokines is discussed in the framework of research conducted over 30 years ago that requires reassessment to more clearly identify the role of these factors in the systemic inflammatory response syndrome. We challenge the notion that hypothalamic damage is responsible for thermoregulatory disturbances during heat stroke recovery and highlight recent advances in our understanding of the regulated nature of these responses. The need for more sensitive clinical biomarkers of organ damage is examined. Conventional and emerging cooling methods are discussed with reference to protection against peripheral organ damage and selective brain cooling.

Modeling the inflammatory response in the hypothalamus ensuing heat stroke: iterative cycle of model calibration, identifiability analysis, experimental design and data collection.

Heat Stroke (HS) is a life-threatening illness caused by prolonged exposure to heat that causes severe hyperthermia and nervous system abnormalities. The long term consequences of HS are poorly understood and deeper insight is required to find possible treatment strategies. Elevated pro- and anti-inflammatory cytokines during HS recovery suggest to play a major role in the immune response. In this study, we developed a mathematical model to understand the interactions and dynamics of cytokines in the hypothalamus, the main thermoregulatory center in the brain. Uncertainty and identifiability analysis of the calibrated model parameters revealed non-identifiable parameters due to the limited amount of data. To overcome the lack of identifiability of the parameters, an iterative cycle of optimal experimental design, data collection, re-calibration and model reduction was applied and further informative experiments were suggested. Additionally, a new method of approximating the prior distribution of the parameters for Bayesian optimal experimental design based on the profile likelihood is presented.

Modeling the intra- and extracellular cytokine signaling pathway under heat stroke in the liver.

Heat stroke (HS) is a life-threatening illness induced by prolonged exposure to a hot environment that causes central nervous system abnormalities and severe hyperthermia. Current data suggest that the pathophysiological responses to heat stroke may not only be due to the immediate effects of heat exposure per se but also the result of a systemic inflammatory response syndrome (SIRS). The observation that pro- (e.g., IL-1) and anti-inflammatory (e.g., IL-10) cytokines are elevated concomitantly during recovery suggests a complex network of interactions involved in the manifestation of heat-induced SIRS. In this study, we measured a set of circulating cytokine/soluble cytokine receptor proteins and liver cytokine and receptor mRNA accumulation in wild-type and tumor necrosis factor (TNF) receptor knockout mice to assess the effect of neutralization of TNF signaling on the SIRS following HS. Using a systems approach, we developed a computational model describing dynamic changes (intra- and extracellular events) in the cytokine signaling pathways in response to HS that was fitted to novel genomic (liver mRNA accumulation) and proteomic (circulating cytokines and receptors) data using global optimization. The model allows integration of relevant biological knowledge and formulation of new hypotheses regarding the molecular mechanisms behind the complex etiology of HS that may serve as future therapeutic targets. Moreover, using our unique modeling framework, we explored cytokine signaling pathways with three in silico experiments (e.g. by simulating different heat insult scenarios and responses in cytokine knockout strains in silico).

Increased cytokine and chemokine gene expression in the CNS of mice during heat stroke recovery.

Heat stroke (HS) is characterized by a systemic inflammatory response syndrome (SIRS) consisting of profound core temperature (Tc) changes in mice. Encephalopathy is common at HS collapse, but inflammatory changes occurring in the brain during the SIRS remain unidentified. We determined the association between inflammatory gene expression changes in the brain with Tc disturbances during HS recovery in mice. Gene expression changes of heat shock protein (HSP)72, heme oxygenase (hmox1), cytokines (IL-1ß, IL-6, TNF-α), cyclooxygenase enzymes (COX-1, COX-2), chemokines (MCP-1, MIP-1α, MIP-1ß, CX3CR1), and glia activation markers (CD14, aif1, vimentin) were examined in the hypothalamus (HY) and hippocampus (HC) of control (Tc ∼ 36.0°C) and HS mice at Tc,Max (42.7°C), hypothermia depth (HD; 29.3 ± 0.4°C), and fever (37.8 ± 0.3°C). HSP72 (HY

Heat stroke activates a stress-induced cytokine response in skeletal muscle.

Heat stroke (HS) induces a rapid elevation in a number of circulating cytokines. This is often attributed to the stimulatory effects of endotoxin, released from damaged intestine, on immune cells. However, parenchymal cells also produce cytokines, and skeletal muscle, comprising a large proportion of body mass, is thought to participate. We tested the hypothesis that skeletal muscle exhibits a cytokine response to HS that parallels the systemic response in conscious mice heated to a core temperature of 42.4°C (TcMax). Diaphragm and hindlimb muscles showed a rapid rise in interleukin-6 (IL-6) and interleuin-10 (IL-10) mRNA and transient inhibition of tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß) throughout early recovery, a pattern that parallels changes in circulating cytokines. IL-6 protein was transiently elevated in both muscles at ∼32 min after reaching TcMax. Other responses observed included an upregulation of toll-like receptor-4 (TLR-4) and heat shock protein-72 (HSP-72) mRNA but no change in TLR-2 or HSP25 mRNA. Furthermore, c-jun and c-fos mRNA increased. Together, c-jun/c-fos form the activator protein-1 (AP-1) transcription factor, critical for stress-induced regulation of IL-6. Interestingly, a second "late-phase" (24 h) cytokine response, with increases in IL-6, IL-10, IL-1ß, and TNF-α protein, were observed in hindlimb but not diaphragm muscle. These results demonstrate that skeletal muscle responds to HS with a distinct "stress-induced immune response," characterized by an early upregulation of IL-6, IL-10, and TLR-4 and suppression of IL-1ß and TNF-α mRNA, a pattern discrete from classic innate immune cytokine responses.

Melatonin reduces acute lung inflammation, edema, and hemorrhage in heatstroke rats.

AIM: To assess the therapeutic effect of melatonin on heat-induced acute lung inflammation and injury in rats. METHODS: Heatstroke was induced by exposing anesthetized rats to heat stress (36 °C, 100 min). Rats were treated with vehicle or melatonin (0.2, 1, 5 mg/kg) by intravenous administration 100 min after the initiatioin of heatstroke and were allowed to recover at room temperature (26 °C). The acute lung injury was quantified by morphological examination and by determination of the volume of pleural exudates, the number of polymorphonuclear (PMN) cells, and the myeloperoxidase (MPO) activity. The concentrations of tumor necrosis factor, interleukin (IL)-1ß, IL-6, and IL-10 in bronchoalveolar fluid (BALF) were measured by ELISA. Nitric oxide (NO) level was determined by Griess method. The levels of glutamate and lactate-to-pyruvate ratio were analyzed by CMA600 microdialysis analyzer. The concentrations of hydroxyl radicals were measured by a procedure based on the hydroxylation of sodium salicylates leading to the production of 2,3-dihydroxybenzoic acid (DHBA). RESULTS: Melatonin (1 and 5 mg/kg) significantly (i) prolonged the survival time of heartstroke rats (117 and 186 min vs 59 min); (ii) attenuated heatstroke-induced hyperthermia and hypotension; (iii) attenuated acute lung injury, including edema, neutrophil infiltration, and hemorrhage scores; (iv) down-regulated exudate volume, BALF PMN cell number, and MPO activity; (v) decreased the BALF levels of lung inflammation response cytokines like TNF-alpha, interleukin (IL)-1ß, and IL-6 but further increased the level of an anti-inflammatory cytokine IL-10; (vi) reduced BALF levels of glutamate, lactate-to-pyruvate ratio, NO, 2,3-DHBA, and lactate dehydrogenase. CONCLUSION: Melatonin may improve the outcome of heatstroke in rats by attenuating acute lung inflammation and injury.

Attenuating heat-induced acute lung inflammation and injury by dextromethorphan in rats.

Dextromethorphan (DM) has been shown to protect against endotoxic shock in mice. Heatstroke resembles sepsis in many respects. The objective of this study was to examine the heat-induced acute lung inflammation and injury in rats with or without DM, and for comparison with those of the rats with MK-801 (an N-methyl-D-aspartate receptor antagonist), SA4503 (a sigma-1 receptor agonist), or fluoxetine (a serotonin reuptake inhibitor). Heatstroke was induced by exposing the anesthetized rats to heat stress (43°C for 68 min). At 68 minutes after start of heat stress, animals treated with vehicle medium, DM (10-30 mg/kg of body weight, intramuscular), MK-801 (1 mg/kg of body weight, intraperitoneal), SA4503 (1 mg/kg of body weight, intraperitoneal), or fluoxetine (5 mg/kg of body weight, intraperitoneal) were allowed to recover at room temperature (26°C). As compared with vehicle-treated heatstroke rats (25-31 min; n = 8), DM (30 mg/kg)-treated heatstroke rats and MK-801 (1 mg/kg)-treated heatstroke rats had significantly greater survival time (193-209 min [n = 7] and 121-133 min [n = 8], respectively). However, the survival times for the SA4503-treated heatstroke rats (28-34 min; n = 8) or the fluoxetine-treated heatstroke rats (20-26 min; n = 8) were not significantly different from the vehicle-treated heatstroke rats. DM treatment significantly: (1) reduced acute lung injury, including edema, neutrophils infiltration, and hemorrhage scores; (2) decreased acute pleurisy; and (3) decreased bronchoalveolar fluid levels of the proinflammatory cytokines, and ischemia and oxidative damage markers during heatstroke. Our results indicate that DM therapy may improve outcomes of heatstroke in rats by antagonizing the N-methyl-D-aspartate receptors.

Heat stroke: role of the systemic inflammatory response.

Heat stroke is a life-threatening illness that is characterized clinically by central nervous system dysfunction, including delirium, seizures, or coma and severe hyperthermia. Rapid cooling and support of multi-organ function are the most effective clinical treatments, but many patients experience permanent neurological impairments or death despite these efforts. The highest incidence of heat stroke deaths occurs in very young or elderly individuals during summer heat waves, with ∼ 200 deaths per year in the United States. Young, fit individuals may experience exertional heat stroke while performing strenuous physical activity in temperate or hot climates. Factors that predispose to heat stroke collapse include pre-existing illness, cardiovascular disease, drug use, and poor fitness level. For decades the magnitude of the hyperthermic response in heat stroke patients was considered the primary determinant of morbidity and mortality. However, recent clinical and experimental evidence suggests a complex interplay between heat cytotoxicity, coagulation, and the systemic inflammatory response syndrome (SIRS) that ensues following damage to the gut and other organs. Cytokines are immune modulators that have been implicated as adverse mediators of the SIRS, but recent data suggest a protective role for these proteins in the resolution of inflammation. Multi-organ system failure is the ultimate cause of mortality, and recent experimental data indicate that current clinical markers of heat stroke recovery may not adequately reflect heat stroke recovery in all cases. Currently heat stroke is a more preventable than treatable condition, and novel therapeutics are required to improve patient outcome.

Moderate hypothermia suppressed excessive generation of superoxide anion radical and inflammatory reactions in blood and liver in heatstroke: laboratory study in rats.

Abstract The study was performed to demonstrate superoxide radical (O(2).-) generation, systemic inflammation and liver injury caused by heatstroke and to reveal suppressive effects of moderate hypothermia. Heatstroke was defined as achieving pharyngeal temperature of 40 degrees C with arterial pressure reduction. Heatstroke rats were divided to four groups by the temperature after the onset; 40 degrees C, 37 degrees C, 32 degrees C and sham-treated with 37 degrees C. O(2).- current was measured continuously in the right atrium using an electrochemical O(2).- sensor. The O(2).- current increased in all groups except for the sham-treated group during the induction. After the onset of heatstroke, the O(2).- current was suppressed with temperature-dependency. Plasma and liver high-mobility group box 1, intercellular adhesion molecule-1, plasma aspartate aminotransferase and alanine aminotransferase were also suppressed with the suppression of O(2).- generation. Therefore, excessive O(2).- generation might be a key factor in heatstroke and the suppression with moderate hypothermia would be a therapeutic modality.

High-dose antithrombin III prevents heat stroke by attenuating systemic inflammation in rats.

OBJECTIVE: Systemic inflammatory mediators, including the high mobility group box 1 (HMGB1) protein, play important roles in the development of various inflammatory conditions. Although anticoagulants, such as antithrombin III (AT III), inhibit inflammation resulting from various causes, their anti-inflammatory mechanism of action is not well understood. Nevertheless, as heat stroke is a severe inflammatory response disease, we hypothesized that AT III would inhibit inflammation and prevent heat stress-induced acute heat stroke. METHODS: Male Wistar rats received a bolus injection of saline or 250 U of AT III per kg of body weight into the tail vein, followed by heat stress (exposure to 42 degrees C for 30 min). Levels of cytokines (interleukin-1 beta, interleukin-6, and TNF-alpha), NOx, and HMGB1 were measured in serum and tissue at regular intervals for 6 h after the heat stress induction. RESULTS: Levels of cytokines, NOx, and HMGB1 in serum decreased over time in AT III-treated rats. AT III pretreatment also reduced NOx levels during heat stress-induced inflammation. As a result, AT III pretreatment improved survival in a rat model of heat stress-induced acute inflammation. CONCLUSIONS: Our data suggest that AT III pretreatment inhibited the secretion of cytokines, NOx, and HMGB1, and prevented heat stress-induced acute inflammation.

Human umbilical cord blood cells protect against hypothalamic apoptosis and systemic inflammation response during heatstroke in rats.

BACKGROUND: Intravenous administration of human umbilical cord blood cells (HUCBC) has been shown to improve heatstroke by reducing arterial hypotension as well as cerebral ischemia and damage in a rat model. To extend these findings, we assessed both hypothalamic neuronal apoptosis and systemic inflammatory responses in the presence of HUCBCs or vehicle medium immediately after initiation of heatstroke. METHODS: Anesthetized rats, immediately after the initiation of heat stress, were divided into two groups and given either serum-free lymphocyte medium (0.3mL per rat, intravenously) or HUCBCs (5 x 10(6) in 0.3 mL serum-free lymphocyte medium, intravenously). Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. Heatstroke was induced by exposing the anesthetized rats to a high ambient temperature of 43 degrees C for 68 minutes. RESULTS: After the onset of heatstroke, animals treated with serum-free lymphocyte medium displayed hyperthermia, hypotension, bradycardia, hypothalamic neuronal apoptosis and degeneration, and up-regulation of systemic inflammatory response molecules including serum tumor necrosis factor-alpha, soluble intercellular adhesion molecule-1 and E-selectin. Heatstroke-induced hypotension, bradycardia, hypothalamic neuronal apoptosis and degeneration, and increased systemic inflammatory response molecules were significantly inhibited by HUCBC treatment. Although heatstroke-induced hyperthermia was not affected by HUCBC treatment, the serum levels of the anti-inflammatory cytokine interleukin-10 were significantly increased by HUCBC therapy during hyperthermia. CONCLUSIONS: These findings suggest that HUCBC transplantation may prevent the occurrence of heatstroke by reducing hypothalamic neuronal damage and the systemic inflammatory responses.

Pre-existing lipopolysaccharide may increase the risk of heatstroke in rats.

BACKGROUND: : We attempted to ascertain whether pre-existing inflammatory state [caused by exogenous administration of lipopolysaccharide (LPS)] exacerbated multiorgan dysfunction in experimental heatstroke. DESIGN: : Immediately after the start of heat stress (42 degrees C), anesthetized rats were divided into 2 major groups and given 0.9% NaCl solution (10 mL/kg of body weight, intravenously) or LPS (10 mg/kg of body weight, intravenously). On heat exposure, the occurrence of both hyperthermia (>42.0 degrees C) and hypotension (mean arterial pressure <50 mm Hg) was taken as the time point for heatstroke onset. RESULTS: : The LPS-treated, but not the saline-treated, animals underwent the heat stress for 52 minutes, displayed heatstroke syndromes. As compared with those of the saline controls, the LPS-treated rats had higher extent of activated inflammation (evidenced by increased plasma levels of interleukin-1beta, tumor necrosis factor-alpha, and interleukin-6), hypercoagulable state (evidenced by increased levels of prothrombin time, activated partial thromboplastin time, and D-dimer, but decreased levels of both protein C and platelet counts), and multiorgan apoptosis and dysfunction (evidenced by increased plasma levels of creatinine, blood urea nitrogen, alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase). CONCLUSION: : Our results suggest that pre-existing inflammatory state may exacerbate the multiorgan injury during heat exposure. This tends to promote that pre-existing infection or sepsis may increase the risk of heatstroke.

Activated protein C can be used as a prophylactic as well as a therapeutic agent for heat stroke in rodents.

The present study was attempted to assess the prophylactic and the therapeutic effect of human recombinant activated protein C (APC; drotrecogin-alpha, activated) in experimental heat stroke. Anesthetized rats were divided into two groups and given vehicle solution 1 h before the start or immediately after the termination of heat stress (isotonic sodium chloride solution, 2 mL kg(-1) of body weight, i.v.) or APC (1-10 mg in 2 mL of isotonic sodium chloride solution per kilogram of body weight, i.v.). They were exposed to ambient temperature of 40 degrees C for 100 min to induce heat stroke. When the vehicle-pretreated rats underwent heat stress, their survival time values were found to be 57 to 71 min. Pretreatment or treatment with APC significantly increased survival time (122-221 min). All vehicle-pretreated heat stroke animals displayed systemic inflammation (evidenced by increased TNF-alpha, IL-1alpha, and IL-6) and activated coagulation (evidenced by increased levels of activated partial thromboplastin time, prothrombin time, and D-dimer and decreased levels of both platelet count and protein C). Biochemical assay also revealed that both renal and hepatic dysfunction (e.g., increased plasma levels of blood urea nitrogen, creatinine, adenine aminotransferase, aspartate aminotransferase, and alkaline phosphatase) were noted during heat stroke. A significant decrease in both cerebral blood flow and partial pressure of oxygen in hypothalamus were also observed in vehicle-pretreated heat stroke animals. These heat stroke reactions were all significantly reduced by pretreatment or treatment with human recombinant APC. The results indicate that human recombinant APC can be used as a prophylactic and a therapeutic agent for experimental heat stroke by ameliorating systemic inflammation, hypercoagulable state, and multiple organ dysfunction.

Human umbilical cord blood cells or estrogen may be beneficial in treating heatstroke.

This current review summarized animal models of heatstroke experimentation that promote our current knowledge of therapeutic effects on cerebrovascular dysfunction, coagulopathy, and/or systemic inflammation with human umbilical cord blood cells (HUCBCs) or estrogen in the setting of heatstroke. Accumulating evidences have demonstrated that HUCBCs provide a promising new therapeutic method against neurodegenerative diseases, such as stroke, traumatic brain injury, and spinal cord injury as well as blood disease. More recently, we have also demonstrated that post- or pretreatment by HUCBCs may resuscitate heatstroke rats with by reducing circulatory shock, and cerebral nitric oxide overload and ischemic injury. Moreover, CD34+ cells sorted from HUCBCs may improve survival by attenuating inflammatory, coagulopathy, and multiorgan dysfunction during experimental heatstroke. Many researchers indicated pro- (e.g. tumor necrosis factor-alpha [TNF-alpha]) and anti-inflammatory (e.g. interleukin-10 [IL-10]) cytokines in the peripheral blood stream correlate with severity of circulatory shock, cerebral ischemia and hypoxia, and neuronal damage occurring in heatstroke. It has been shown that intravenous administration of CD34+ cells can secrete therapeutic molecules, such as neurotrophic factors, and attenuate systemic inflammatory reactions by decreasing serum TNF-alpha but increasing IL-10 during heatstroke. Another line of evidence has suggested that estrogen influences the severity of injury associated with cerebrovascular shock. Recently, we also successfully demonstrated estrogen resuscitated heatstroke rats by ameliorating systemic inflammation. Conclusively, HUCBCs or estrogen may be employed as a beneficial therapeutic strategy in prevention and repair of cerebrovascular dysfunction, coagulopathy, and/or systemic inflammation during heatstroke.