HMGB1 released from pyroptotic vascular endothelial cells promotes immune disorders in exertional heatstroke.

BACKGROUND AND OBJECTIVE: Exertional heatstroke (EHS) mainly occurs in healthy young people with rapid onset and high mortality. EHS immune disorders can cause systemic inflammatory responses and multiple organ failure; however, the underlying mechanisms remain unclear. As high mobility group box 1 (HMGB1) is a prototypical alarmin that activates inflammatory and immune responses, this study aimed to investigate the effect and mechanism of HMGB1 in the pathogenesis of EHS. METHODS: Peripheral blood mononuclear cell (PBMC) transcriptome sequencing of healthy volunteers, classical heatstroke patients, and EHS patients was performed. A mouse model of EHS was established and murine tissue damage was evaluated by H&E staining. HMGB1 localization and release were visualized using immunofluorescence staining. Human umbilical vein endothelial cells (HUVECs) and THP-1 cells were co-cultured to study the effects of HMGB1 on macrophages. A neutralizing anti-HMGB1 antibody was used to evaluate the efficacy of EHS treatment in mice. RESULTS: Plasma and serum HMGB1 levels were significantly increased in EHS patients or mice. EHS-induced endothelial cell pyroptosis promoted HMGB1 release in mice. HMGB1 derived from endothelial cell pyroptosis enhanced macrophage pyroptosis, resulting in immune disorders under EHS conditions. Administration of anti-HMGB1 markedly alleviated tissue injury and systemic inflammatory responses after EHS. CONCLUSIONS: The release of HMGB1 from pyroptotic endothelial cells after EHS promotes pyroptosis of macrophages and systemic inflammatory response, and HMGB1-neutralizing antibody therapy has good application prospects for EHS.

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.

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.

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).

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.

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.

Concentrations of soluble tumor necrosis factor and interleukin-6 receptors in heatstroke and heatstress.

OBJECTIVE: Increased proinflammatory cytokine concentrations have been implicated in the pathogenesis of heatstroke. Soluble cytokine receptors can modulate circulating cytokine activities. We examined the possible role of soluble tumor necrosis factor receptors (sTNFR 60, sTNFR 80) and interleukin-6 receptor (sIL-6R) in heatstroke by determining their concentrations before and after cooling, as well as in heatstressed controls. DESIGN: Prospective controlled study. SETTING: Heatstroke Center, Makkah, Saudi Arabia (1993 pilgrimage). PATIENTS: Twenty-five consecutive heatstroke patients before and after cooling, 14 heatstressed controls (HSC), and 13 normal controls (NC). MEASUREMENTS AND MAIN RESULTS: Concentrations of sTNFR 60, sTNFR 80, and sIL-6R, as well as their ligands, were measured using commercially available enzyme-linked immunosorbent assay kits. Mean sTNFR 60 concentration was increased in heatstroke (p <.0001, vs. NC; p < .0001, vs. HSC) and in HSC (p = .004, vs. NC). Mean sTNFR 80 concentration was increased in heatstroke and decreased in HSC (p = .01, heatstroke vs. HSC). Mean sIL-6R concentration was decreased in heatstroke and increased in HSC (p = .04, heatstroke vs. NC; p = .001, heatstroke vs. HSC). IL-6 was undetectable in NC and mean IL-6 concentration was more increased in heatstroke than in HSC (p = .001). Rectal temperature and creatinine concentrations correlated significantly with sTNFR 60, sTNFR 80, sIL-6R, and IL-6 concentrations. After cooling, mean concentrations of sIL-6R and sTNFR 80 increased significantly, whereas the mean sTNFR 60 concentration did not change. Residual neurologic deficits were associated with higher precooling IL-6 (p = .002) and postcooling sTNFRs (p < .0001) concentrations. CONCLUSIONS: Significant changes in cytokine receptor concentrations are associated with heatstress. In heatstroke, the changes are more pronounced, and for some cytokine receptors, the changes are in the opposite direction (compared with changes in heatstress). Concentrations of IL-6 and sTNFRs correlate with hyperthermia and outcome. Cooling did not normalize sTNFR concentrations, suggesting failure to control the inflammatory response.