Evidence for endothelial cell activation/injury in heatstroke

"Unravelling the impacts of climatic heat events on cardiovascular health in animal models"

Climate change has led to an increase in high ambient temperatures, causing extreme heat events worldwide. According to the World Meteorological Organization (WMO), July 2023 marked a historic milestone as the Earth reached its hottest recorded temperature, precisely hitting the critical threshold of 1.5 °C set by the Paris Agreement. This distressing development led to a stark warning from the United Nations, signaling the dawn of what they call "an era of global boiling". The increasing global temperatures can result in high heat stress which leads to various physiological and biochemical alterations in the human body. Given that cardiovascular diseases (CVDs) are a leading cause of morbidity and mortality globally, heat events exacerbate this public health issue. While clinical and in-vitro studies have suggested a range of pathophysiological and biochemical mechanisms underlying the body's response to heat stress, the complex nature of organ-system level interactions makes precise investigation challenging. To address this knowledge gap effectively, the use of animal models exposed to acute or chronic heat stress can be invaluable. These models can closely replicate the multifaceted effects observed in humans during heat stress conditions. Despite extensive independent reviews, limited focus has been shed on the high heat-induced cardiovascular complications and their mechanisms, particularly utilizing animal models. Therefore, in this comprehensive review, we highlight the crucial biomarkers altered during heat stress, contributing significantly to various CVDs. We explore potential mechanisms underlying heat-induced cardiovascular dysfunction and damage, delving into various animal models. While traditional rodent models are commonly employed, we also examine less conventional models, including ruminants, broilers, canines, and primates. Furthermore, we delve into various potential therapeutic approaches and preventive measures. These insights hold significant promise for the development of more effective clinical interventions against the effects of heat stress on the human cardiovascular system.

Insights into pathophysiology and therapeutic strategies for heat stroke: Lessons from a baboon model

Heat stroke is a perilous condition marked by severe hyperthermia and extensive multiorgan dysfunction, posing a considerable risk of mortality if not promptly identified and treated. Furthermore, the complex biological mechanisms underlying heat stroke-induced tissue and cell damage across organ systems remain incompletely understood. This knowledge gap has hindered the advancement of effective preventive and therapeutic strategies against this condition. In this narrative review, we synthesize key insights gained over a decade using a translational baboon model of heat stroke. By replicating heat stroke pathology in a non-human primate species that closely resembles humans, we have unveiled novel insights into the pathways of organ injury and cell death elicited by this condition. Here, we contextualize and integrate the lessons learned concerning heat stroke pathophysiology and recovery, areas that are inherently challenging to investigate directly in human subjects. We suggest novel research directions to advance the understanding of the complex mechanisms underlying cell death and organ injury. This may lead to precise therapeutic strategies that benefit individuals suffering from this debilitating condition.

Construction and Validation of the Nomogram Based on von Willebrand Factor Predicting Mortality in Patients with Heatstroke

Heatstroke (HS), a severe condition, can develop multiple organ dysfunction syndrome and death. However, at present, no early reliable index exists for risk stratification and prognosis. von Willebrand factor (vWF), a marker of vascular endothelial injury, is a key regulatory target of inflammation and coagulation, which is closely associated with the pathogenesis of HS. vWF was reported as a prognostic marker in several infectious and noninfectious severe illness such as COVID-19, sepsis, and trauma. Although early increased level of vWF is seen in HS, the relationship between vWF and mortality is to be elucidated. Clinical data of patients with HS in a tertiary hospital were recorded and analyzed. It was shown that plasma vWF concentrations at admission were significantly increased in the nonsurvivors (351% ± 105%) compared with survivors (278% ± 104%, p = 0.021). After multivariate logistic regression analysis it was shown that vWF (odds ratio [OR] = 1.010; 95% confidence interval [CI], 1.002-1.18; p = 0.017), hemoglobin (Hb) (OR = 0.954; 95% CI, 0.931-0.979; p < 0.001), and hematocrit (HCT) in blood (OR = 0.859; 95% CI, 0.790-0.934; p < 0.001) were independent factors of in-hospital mortality in HS. The nomogram based on vWF and Hb was constructed in patients with HS. The area under curve under the receiver operating characteristic of this prediction model was 0.860 (95% CI, 0.773-0.923) and cutoff was 0.15, with Youden index 0.5840, which were not significantly different to sequential organ failure assessment (p = 0.0644), Acute Physiology and Chronic Health Evaluation II (APACHE II) (p = 0.7976), and systemic inflammatory response syndrome (SIRS) scores (p = 0.3274). The prediction model that integrated vWF and Hb showed a better predicting efficiency than single variable, and a higher specificity (81.48%) than APACHE II (72.84%) and SIRS (72.84%) scores. In summary, vWF, as an independent risk factor for in-hospital mortality, combined with Hb, could effectively prognosis the mortality in HS patients at early stage.

The role of platelets in heat-related illness and heat-induced coagulopathy

Heat-related illness is becoming more problematic due to ongoing global warming. Heat-related injury causes systemic inflammation and coagulopathy, due to leukocyte, platelet, and vascular endothelial cell activation and injury. Hyperthermia directly modulates platelet function and can induce cellular damage. Meanwhile, heat also affects platelet function via activated coagulation, excess inflammation, production of cytokines, and heat shock proteins. Aberrant hyperthermia-induced interactions between leukocytes and endothelial cells are also involved in platelet regulation. Heat-induced coagulopathy commonly progresses to disseminated intravascular coagulation (DIC), leading to multiple organ failure and in some cases enhanced bleeding. Consequently, platelet count, prothrombin time, and DIC score are useful for evaluating the severity of heat-related illness in addition to other organ damage markers such as Glasgow Coma Scale, creatinine, and bilirubin. Despite the increasing risk, therapeutic modalities targeting platelets are limited and no established therapy exists. In this review, we summarize the current knowledge about the role of platelets in the pathogenesis, diagnosis, and management of heat-related illness.

Inflammation, coagulation, and cellular injury in heat-induced shock

BACKGROUND

The number of heatstroke victims hit record numbers in 2022 as global warming continues. In heat-induced injuries, circulatory shock is the most severe and deadly complication. This review aims to examine the mechanisms and potential approaches to heat-induced shock and the life-threatening complications of heatstroke.

METHODS

A computer-based online search was performed using the PubMed database and Web of Science database for published articles concerning heatstroke, shock, inflammation, coagulopathy, endothelial cell, cell death, and heat shock proteins.

RESULTS

Dehydration and heat-induced cardiomyopathy were reported as the major causes of heat-induced shock, although other heat-induced injuries are also involved in the pathogenesis of circulatory shock. In addition to dehydration, the blood volume decreases considerably due to the increased vascular permeability as a consequence of endothelial damage. Systemic inflammation is induced by factors that include elevated cytokine and chemokine levels, dysregulated coagulation/fibrinolytic responses, and the release of damage-associated molecular patterns (DAMPs) from necrotic cell death that cause distributive shock. The cytoprotective heat shock proteins can also facilitate circulatory disturbance under excess heat stress.

CONCLUSIONS

Multiple mechanisms are involved in the pathogenesis of heat-induced shock. In addition to dehydration, heat stress-induced cardiomyopathy due to the thermal damage of mitochondria, upregulated inflammation via damage-associated molecular patterns released from oncotic cells, unbalanced coagulation/fibrinolysis, and endothelial damage are the major factors that are related to circulatory shock.

A comparative study of effects of curcumin and its nanoparticles on the growth, immunity and heat stress resistance of Nile tilapia (Oreochromis niloticus)

This study evaluated the effects of dietary supplementation with free- or nano-curcumin on the growth performance, immune status and heat stress resistance of Nile tilapia (Oreochromis niloticus). Seven isonitrogenous (28% protein) and isocaloric (445 kcal/100 g DM) diets were prepared. Six diets were supplemented with three levels of nano-curcumin (50 (CN50), 100 (CN100), 200 (CN200) mg kg^-1 diet) or free-curcumin (50 (C50), 100 (C100), 200 (C200) mg kg^-1 diet), and the control diet was left without an additive (CON). Fish (13.54 ± 0.32 g) (mean ± SD) fed the experimental diets for 65 days. Following the feeding trial, the fish were exposed to the acute heat stress by gradually raising the water temperature from 25 to 40 °C within 3 h. The fish were then exposed to 40 °C for 4 h. Results revealed the superiority of nano-curcumin over its free-form in enhancing the growth performance, with the highest results obtained at CN100, followed by CN200. Only heat stress, not the experimental diets, increased the platelets, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), leukocytes and neutrophils count, while lymphocytes decreased. The CN50 and CN100 groups showed lower activity of liver enzymes (alanine aminotransferase (ALT) and aspartate aminotransferase (AST)) than the other treatments, while C200 gave the highest activity of these enzymes. The highest immunoglobulin (IgM) levels were detected in CN100, CN200, C100 and C200, followed by CN50. The C200 group showed higher levels of complement 3 and complement 4 (C3 and C4, respectively) than the other treatments. The C50 and CON groups gave the lowest values of IgM, C3 and C4. Cortisol levels were significantly lower in the CN50 and CN100 groups compared to the other groups. After the heat stress, ALT, AST, IgM, C3, C4, cortisol and glucose increased. Thus, nano-curcumin is more effective than its free-form in enhancing the resistance to heat stress, inducing innate immunity, lowering the stress indicators and promoting growth performance of Nile tilapia with the best concentration at 100 mg kg^-1 diet.

Biomarkers of heatstroke-induced organ injury and repair

NEW FINDINGS

What is the topic of this review? The status and potential role of novel biological markers (biomarkers) that can help identify the patients at risk of organ injury or long-term complications following heatstroke. What advances does it highlight? Numerous biomarkers were identified related to many aspects of generalized heatstroke-induced cellular injury and tissue damage, and heatstroke-provoked cardiovascular, renal, cerebral, intestinal and skeletal muscle injury. No novel biomarkers were identified for liver or lung injury.

ABSTRACT

Classic and exertional heatstroke cause acute injury and damage across numerous organ systems. Moreover, heatstroke survivors may sustain long-term neurological, cardiovascular and renal complications with a persistent risk of death. In this context, biomarkers, defined as biological samples obtained from heatstroke patients, are needed to detect early organ injury, and predict outcomes to develop novel organ preservation therapeutic strategies. This narrative review provides preliminary insights that will guide the development and future utilization of these biomarkers. To this end, we have identified numerous biomarkers of widespread heatstroke-associated cellular injury, tissue damage and repair (extracellular heat shock proteins 72 and 60, high mobility group box protein 1, histone H3, and interleukin-1α), and other organ-specific biomarkers including those related to the cardiovascular system (cardiac troponin I, endothelium-derived factors, circulation endothelial cells, adhesion molecules, thrombomodulin and von Willebrand factor antigen), the kidneys (plasma and urinary neutrophil gelatinase-associated lipocalin), the intestines (intestinal fatty acid-binding protein 2), the brain (serum S100β and neuron-specific enolase) and skeletal muscle (creatine kinase, myoglobin). No specific biomarkers have been identified so far for liver or lung injury in heatstroke. Before translating the identified biomarkers into clinical practice, additional preclinical and clinical prospective studies are required to further understand their clinical utility, particularly for the biomarkers related to long-term post-heatstroke health outcomes.

Classic and exertional heatstroke

In the past two decades, record-breaking heatwaves have caused an increasing number of heat-related deaths, including heatstroke, globally. Heatstroke is a heat illness characterized by the rapid rise of core body temperature above 40 °C and central nervous system dysfunction. It is categorized as classic when it results from passive exposure to extreme environmental heat and as exertional when it develops during strenuous exercise. Classic heatstroke occurs in epidemic form and contributes to 9-37% of heat-related fatalities during heatwaves. Exertional heatstroke sporadically affects predominantly young and healthy individuals. Under intensive care, mortality reaches 26.5% and 63.2% in exertional and classic heatstroke, respectively. Pathological studies disclose endothelial cell injury, inflammation, widespread thrombosis and bleeding in most organs. Survivors of heatstroke may experience long-term neurological and cardiovascular complications with a persistent risk of death. No specific therapy other than rapid cooling is available. Physiological and morphological factors contribute to the susceptibility to heatstroke. Future research should identify genetic factors that further describe individual heat illness risk and form the basis of precision-based public health response. Prioritizing research towards fundamental mechanism and diagnostic biomarker discovery is crucial for the design of specific management approaches.

Heatstroke-induced coagulopathy: Biomarkers, mechanistic insights, and patient management

Heatstroke is increasingly becoming a significant concern due to global warming. Systemic inflammation and coagulopathy are the two major factors that provoke life-threatening organ dysfunction in heatstroke. Dysregulated thermo-control induces cellular injury, damage-associated molecular patterns release, hyperinflammation, and hypercoagulation with suppressed fibrinolysis to produce heatstroke-induced coagulopathy (HSIC). HSIC can progress to disseminated intravascular coagulation and multiorgan failure if severe enough. Platelet count, D-dimer, soluble thrombomodulin, and inflammation biomarkers such as interleukin-6 and histone H3 are promising markers for HSIC. In exertional heatstroke, the measurement of myoglobin is helpful to anticipate renal dysfunction. However, the optimal cutoff for each biomarker has not been determined. Except for initial cooling and hydration, effective therapy continues to be explored, and the use of antiinflammatory and anticoagulant therapies is under investigation. Despite the rapidly increasing risk, our knowledge is limited, and further study is warranted. In this review, we examine current information and what future efforts are needed to better understand and manage HSIC.

Climate change and nephrology

Climate change should be of special concern for the nephrologist, as the kidney has a critical role in protecting the host from dehydration, but it is also a favorite target of heat stress and dehydration. Here we discuss how rising temperatures and extreme heat events may affect the kidney. The most severe presentation of heat stress is heat stroke, which can result in severe electrolyte disturbance and both acute and chronic kidney disease (CKD). However, lesser levels of heat stress also have multiple effects, including exacerbating kidney disease and precipitating cardiovascular events in subjects with established kidney disease. Heat stress can also increase the risk for kidney stones, cause multiple electrolyte abnormalities and induce both acute and chronic kidney disease. Recently there have been multiple epidemics of CKD of uncertain etiology in various regions of the world, including Mesoamerica, Sri Lanka, India and Thailand. There is increasing evidence that climate change and heat stress may play a contributory role in these conditions, although other causes, including toxins, could also be involved. As climate change worsens, the nephrologist should prepare for an increase in diseases associated with heat stress and dehydration.

Nanodelivery of traditional Chinese Gingko Biloba extract EGb-761 and bilobalide BN-52021 induces superior neuroprotective effects on pathophysiology of heat stroke

Military personnel often exposed to high summer heat are vulnerable to heat stroke (HS) resulting in abnormal brain function and mental anomalies. There are reasons to believe that leakage of the blood-brain barrier (BBB) due to hyperthermia and development of brain edema could result in brain pathology. Thus, exploration of suitable therapeutic strategies is needed to induce neuroprotection in HS. Extracts of Gingko Biloba (EGb-761) is traditionally used in a variety of mental disorders in Chinese traditional medicine since ages. In this chapter, effects of TiO2 nanowired EGb-761 and BN-52021 delivery to treat brain pathologies in HS is discussed based on our own investigations. We observed that TiO2 nanowired delivery of EGb-761 or TiO2 BN-52021 is able to attenuate more that 80% reduction in the brain pathology in HS as compared to conventional drug delivery. The functional outcome after HS is also significantly improved by nanowired delivery of EGb-761 and BN-52021. These observations are the first to suggest that nanowired delivery of EGb-761 and BN-52021 has superior therapeutic effects in HS not reported earlier. The clinical significance in relation to the military medicine is discussed.

miR‑3613‑3p/MAP3K2/p38/caspase‑3 pathway regulates the heat‑stress‑induced apoptosis of endothelial cells

Previous studies have identified microRNA (miRNA/miR)-3613-3p as a heat stress (HS)-related miRNA in endothelial cells that can lead to apoptosis. However, the mechanism underlying the miR-3613-3p-mediated apoptosis of HS-exposed endothelial cells remains unclear. In the present study, western blot analysis and reverse transcription-quantitative PCR were used to determine protein and miRNA expression levels, respectively. Annexin V-fluorescein isothiocyanate/propidium iodide staining, caspase-3 activity measurements and DNA fragmentation assays were performed to detect apoptosis. To evaluate whether mitogen-activated protein kinase kinase kinase 2 (MAP3K2) was a direct target of miR-3613-3p, a luciferase reporter assay was performed. In addition, transient transfection was used to carry out loss- and gain-of-function experiments. The results revealed that miR-3613-3p expression was reduced in human umbilical vein endothelial cells (HUVECs) following HS, which led to apoptosis. Mechanistically, following HS, a decrease in miR-3613-3p binding to the 3′-untranslated region of MAP3K2 directly upregulated its expression, and the downstream p38 and caspase-3 pathways, thereby leading to apoptosis. Taken together, the results of the present study demonstrated that HS suppressed miR-3613-3p expression, which activated the MAP3K2/p38/caspase-3 pathway, leading to the apoptosis of HUVECs. In conclusion, the miR-3613-3p/MAP3K2/p38/caspase-3 pathway may serve an indispensable role in regulating the progression of apoptosis, indicating a regulatory role of miR-3613-3p in the pathophysiology of HS-exposed endothelial cells.

Physiological factors characterizing heat-vulnerable older adults: A narrative review

More frequent and intense periods of extreme heat (heatwaves) represent the most direct challenge to human health posed by climate change. Older adults are particularly vulnerable, especially those with common age-associated chronic health conditions (e.g., cardiovascular disease, hypertension, obesity, type 2 diabetes, chronic kidney disease). In parallel, the global population is aging and age-associated disease rates are on the rise. Impairments in the physiological responses tasked with maintaining homeostasis during heat exposure have long been thought to contribute to increased risk of health disorders in older adults during heatwaves. As such, a comprehensive overview of the provisional links between age-related physiological dysfunction and elevated risk of heat-related injury in older adults would be of great value to healthcare officials and policy makers concerned with protecting heat-vulnerable sectors of the population from the adverse health impacts of heatwaves. In this narrative review, we therefore summarize our current understanding of the physiological mechanisms by which aging impairs the regulation of body temperature, hemodynamic stability and hydration status. We then examine how these impairments may contribute to acute pathophysiological events common during heatwaves (e.g., heatstroke, major adverse cardiovascular events, acute kidney injury) and discuss how age-associated chronic health conditions may exacerbate those impairments. Finally, we briefly consider the importance of physiological research in the development of climate-health programs aimed at protecting heat-vulnerable individuals.

Establishment and effectiveness evaluation of a scoring system for exertional heat stroke by retrospective analysis

BACKGROUND

Heat stroke (HS) is a serious, life-threatening disease. However, there is no scoring system for HS so far. This research is to establish a scoring system that can quantitatively assess the severity of exertional heat stroke (EHS).

METHODS

Data were collected from a total of 170 exertional heat stroke (EHS) patients between 2005 and 2016 from 52 hospitals in China. Univariate statistical methods and comparison of the area under the receiver operating characteristic (ROC) curve (AUC) were used to screen exertional heat stroke score (EHSS) parameters, including but not limited body temperature (T), Glasgow Coma Scale (GCS) and others. By comparing the sizes of the AUCs of the APACHE II, SOFA and EHSS assessments, the effectiveness of EHSS in evaluating the prognosis of EHS patients was verified.

RESULTS

Through screening with a series of methods, as described above, the present study determined 12 parameters - body temperature (T), GCS, pH, lactate (Lac), platelet count (PLT), prothrombin time (PT), fibrinogen (Fib), troponin I (TnI), aspartate aminotransferase (AST), total bilirubin (TBIL), creatinine (Cr) and acute gastrointestinal injury (AGI) classification - as EHSS parameters. It is a 0-47 point system designed to reflect increasing severity of heat stroke. Low (EHSS< 20) and high scores (EHSS> 35) showed 100% survival and 100% mortality, respectively. We found that AUCEHSS > AUCSOFA > AUCAPACHE II.

CONCLUSION

A total of 12 parameters - T, GCS, pH, Lac, PLT, PT, Fib, TnI, AST, TBIL, Cr and gastrointestinal AGI classification - are the EHSS parameters with the best effectiveness in evaluating the prognosis of EHS patients. As EHSS score increases, the mortality rate of EHS patients gradually increases.

N-Methyl-3,4-methylendioxymethamphetamine (MDMA)-related coagulopathy and rhabdomyolysis: A case series and literature review

Coagulation changes, thrombosis, and hemorrhage have been described in patients following N-methyl-3,4-methylenedioxymethylamphetamine (MDMA) intoxication who subsequently developed serotonin syndrome and rhabdomyolysis. The clinical features and mechanism of this remain poorly described. We describe 5 sequential cases admitted to critical care due to severe recreational MDMA toxicity where coagulopathy occurred, and discuss key clinical issues. All patients presented with hyperpyrexia then developed subsequent rhabdomyolysis accompanied by a coagulopathy within 24 hours of presentation. This included a severe thrombocytopenia, prolonged coagulation times, grossly elevated D-dimer levels, and hypofibrogenemia. Multiorgan dysfunction was seen in all patients, including stroke in one patient and major hemorrhage in another. In 2 cases, low-dose low-molecular-weight heparin was used early after presentation, with no significant bleeding complications. Blood products usage was high but variable between the patients with lower use in those who received low-molecular-weight heparin early. Other treatments included intravascular therapeutic cooling, renal replacement therapy with large filter pores and cyprohepatidine. Current evidence suggests that in this group, rhabdomyolysis with subsequent myosin release may be a profound activator of coagulation leading to disseminated intravascular coagulation. Myosin-activated coagulation seems a potential cause of MDMA-related coagulopathy in the setting of rhabdomyolysis and serotonin syndrome. Further studies are needed to validate this and explore the use of low-molecular-weight heparin to reduce the clinical effects of this coagulopathy.

Analysis of potential functional significance of microRNA‑3613‑3p in human umbilical vein endothelial cells affected by heat stress

Dysregulation of microRNA‑3613‑3p (miR‑3613‑3p) was previously reported in endothelial cells (ECs) during heat stress. The aim of the present study was to investigate the precise role of miR‑3613‑3p in heat stress. In the present study, potential gene targets of miR‑3613‑3p in heat‑treated ECs were assessed, and the potential effects of miR‑3613‑3p were determined using Gene Ontology enrichment analysis. Kyoto Encyclopedia of Genes and Genomes pathway analysis was used to identify signaling pathways that may be affected by miR‑3613‑3p in heat‑treated cells. Reverse transcription‑quantitative PCR, western blotting and annexin V‑FITC/propidium iodide staining were performed to detect miRNA expression, protein expression and apoptosis, respectively. Luciferase gene reporter assay was performed to evaluate the association between miR‑3613‑3p and mitogen‑activated protein kinase kinase kinase 2 (MAP3K2). Bioinformatics analysis revealed 865 potential gene targets for miR‑3613‑3p and a series of functions and pathways in heat‑treated ECs. 'Negative regulation of apoptotic process' was identified as a potential function of miR‑3613‑3p. In addition, functional analysis confirmed the downregulated expression levels of miR‑3613‑3p in ECs during heat stress, which was accompanied by an increase in apoptosis; restoration of miR‑3613‑3p expression inhibited apoptosis. MAP3K2 protein was demonstrated to be upregulated in heat‑treated ECs, and overexpression of miR‑3613‑3p reduced MAP3K2 expression levels. Additionally, MAP3K2 was targeted by miR‑3613‑3p. These results indicated that miR‑3613‑3p may have complicated roles in ECs under heat stress. miR‑3613‑3p may serve an important role in the apoptosis of heat‑treated ECs, and this effect may be partly achieved by targeting MAP3K2.

Ser46 phosphorylation of p53 is an essential event in prolyl-isomerase Pin1-mediated p53-independent apoptosis in response to heat stress

Heat stroke has increased in frequency worldwide in recent years and continues to have a high morbidity and mortality. Identification of the mechanisms mediating heat stoke is important and necessary. Our preliminary study revealed heat stress (HS)-induced apoptosis of vascular endothelial cells was associated with reactive oxygen species (ROS)-induced p53 translocation into mitochondria. Previous studies have suggested the prolyl-isomerase Pin1 regulates p53 functioning through specific binding to p53 phosphorylation sites. Based on these studies, we presumed Pin1 is a key intermediate in regulation of mitochondrial p53 translocation through a HS-induced ROS-p53 transcription-independent apoptosis pathway. In this context, we revealed p53 had a crucial role in a HS-induced mitochondrial apoptotic pathway, where p53 protein rapidly translocated into mitochondria in endothelial cells both in vitro and in vivo. In particular, HS caused an increase in p53 phosphorylation at Ser46 that facilitated interactions with phosphorylation-dependent prolyl-isomerase Pin1, which has a key role in promoting HS-induced localization of p53 to mitochondria. Furthermore, we also found ROS production was a critical mediator in HS-induced Pin1/p53 signaling and was involved in regulating mitochondrial apoptosis pathway activation. Therefore, we have contributed to our profound understanding of the mechanism underlying HS-induced endothelial dysfunction in an effort to reduce the mortality and morbidity of heat stroke.

Heat Sepsis Precedes Heat Toxicity in the Pathophysiology of Heat Stroke-A New Paradigm on an Ancient Disease

Heat stroke (HS) is an ancient illness dating back more than 2000 years and continues to be a health threat and to cause fatality during physical exertion, especially in military personnel, fire-fighters, athletes, and outdoor laborers. The current paradigm in the pathophysiology and prevention of HS focuses predominantly on heat as the primary trigger and driver of HS, which has not changed significantly for centuries. However, pathological and clinical reports from HS victims and research evidence from animal and human studies support the notion that heat alone does not fully explain the pathophysiology of HS and that HS may also be triggered and driven by heat- and exercise-induced endotoxemia. Exposure to heat and exercise stresses independently promote the translocation of lipopolysaccharides (LPS) from gram-negative bacteria in the gut to blood in the circulatory system. Blood concentration of LPS can increase to a threshold that triggers the systemic inflammatory response, leading to the downstream ramifications of cellular and organ damage with sepsis as the end point i.e., heat sepsis. The dual pathway model (DPM) of HS proposed that HS is triggered by two independent pathways sequentially along the core temperature continuum of >40 °C. HS is triggered by heat sepsis at Tc < 42 °C and by the heat toxicity at Tc > 42 °C, where the direct effects of heat alone can cause cellular and organ damage. Therefore, heat sepsis precedes heat toxicity in the pathophysiology of HS.

Pyroptosis of HUVECs can be induced by heat stroke

Heat stroke is a serious pathological condition with high mortality. Vascular endothelial cell injury is a key feature in the pathogenesis of heat stroke, but the specific pathophysiological process whereby this occurs is still unclear. Currently, relevant studies are primarily based upon examination of apoptosis. Recently, pyroptosis, a new form of inflammation-related programmed cell death, was also demonstrated to be involved in heat stroke pathophysiology. Herein, we present evidence that vascular endothelial cell pyroptosis can be induced by heat stress in a time- and temperature-dependent manner. Furthermore, this process can be significantly inhibited by GSDMD siRNA. These findings suggest a new therapeutic target for heat stroke.

Endogenous genetic risk factor for serious heatstroke: the thermolabile phenotype of carnitine palmitoyltransferase II variant

Aim

In serious heatstroke, elevated body temperature (>40°C) is considered the main cause of illness. Mitochondrial carnitine palmitoyltransferase II (CPT II) plays an important role in adenosine triphosphate (ATP) generation from long‐chain fatty acids, and its thermolabile phenotype of CPT2 polymorphisms leads to ATP production loss under high fever. Whether by heatstroke or influenza, high fever suppresses mitochondrial ATP production in patients with the thermolabile phenotype of CPT2 polymorphisms. We investigated the relation between CPT2 polymorphism and severity of heatstroke with a body temperature of over 40°C.

Methods

We analyzed blood chemistry test results, Japanese Association for Acute Medicine Disseminated Intravascular Coagulation (JAAM DIC), Acute Physiologic and Chronic Health Evaluation II, and Sequential Organ Failure Assessment (SOFA) scores, and CPT2 polymorphisms in 24 consecutive patients with severe heatstroke at two university hospitals.

Results

Eleven patients carried thermolabile CPT II variants (rs2229291; c.1055T˃G [p.Phe352Cys]) (F352C), and the genotype frequency was greater in heatstroke patients than in healthy volunteers. There was no significant difference in body temperature or blood chemistry data at emergency room arrival between patients with and without the CPT II variants. However, hospital days were longer and initial antithrombin activity was significantly lower in the variant group, suggesting a possible link with early phase vascular endothelial cell dysfunction. The JAAM DIC diagnostic criteria and SOFA scores were also higher in the group. There were no differences in the serum albumin, serum creatine kinase, and fibrin degradation product levels, and platelet counts.

Conclusions

In addition to known risks (e.g., environmental temperature and old age), the CPT II polymorphism [F352C] can be a predisposing genetic risk factor for serious heatstroke with organ disfunction, and lower antithrombin activity.

Markers and Biomarkers of Endothelium: When Something Is Rotten in the State

Endothelium is a community of endothelial cells (ECs), which line the blood and lymphatic vessels, thus forming an interface between the tissues and the blood or lympha. This strategic position of endothelium infers its indispensable functional role in controlling vasoregulation, haemostasis, and inflammation. The state of endothelium is simultaneously the cause and effect of many diseases, and this is coupled with modifications of endothelial phenotype represented by markers and with biochemical profile of blood represented by biomarkers. In this paper, we briefly review data on the functional role of endothelium, give definitions of endothelial markers and biomarkers, touch on the methodological approaches for revealing biomarkers, present an implicit role of endothelium in some toxicological mechanistic studies, and survey the role of reactive oxygen species (ROS) in modulation of endothelial status.

Non-Exertional Heatstroke: A Case Report and Review of the Literature

BACKGROUND Heatstroke (HS) is a life-threatening condition characterized by an elevation of the core body temperature above 40°C, central nervous system dysfunction, and possible multi-organ failure. HS can trigger systemic inflammation, disseminated intravascular coagulation (DIC), rhabdomyolysis, cerebral edema and seizures, pulmonary edema, heart dysfunctions, and renal and hepatic failure. CASE REPORT We report the case of a 41-year-old Romanian woman with a history of alcoholism who developed HS after arriving by bus in Verona, Italy in June 2016. The patient developed consecutive multi-organ dysfunction, including liver and renal failure, rhabdomyolysis, DIC, and arrhythmia. The patient was successfully treated with conservative measures. After 17 days, she recovered completely. CONCLUSIONS The exact mechanism of HS-related multiple organ dysfunction is not completely understood and its pathogenesis is complex. It involves inflammation, oxidative stress, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction. Development of a model in which chronic alcohol abuse alters oxidative, inflammatory, and ER stress response could also be a conceivable solution to the positive prognosis of severe HS patients, in which liver failure has a prominent role.

Sodium tanshinone IIA sulfonate improves inflammation, aortic endothelial cell apoptosis, disseminated intravascular coagulation and multiple organ damage in a rat heat stroke model

The aim of the present study was to investigate the effects of sodium tanshinone IIA sulfonate (STS) on inflammatory responses, aortic endothelial cell apoptosis, disseminated intravascular coagulation (DIC) and multiple organ damage in an animal model of classic heat stroke (CHS). The rats in the heat stroke (HS) and STS-treated heat stroke (STS-HS) groups were placed into a pre-warmed animal temperature controller (ATC) at 35°C. The moment at which the rectal temperature reached 43.5°C was considered as the time of onset of HS. In the HS groups, the rats were removed from the ATC and allowed to recover at 26°C for 0, 2, 6 or 12 h. In the STS-HS groups, the rats received femoral vein injections of 5–40 mg/kg STS immediately following the onset of HS and were subsequently placed at a temperature of 26°C to recover for 6 h. In the present study, the serum levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 were assessed using ELISA, and the numbers of apoptotic aortic endothelial cells were investigated using terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling combined with immunofluorescence. In the HS groups, the serum levels of TNF-α, IL-1β and IL-6, as well as the numbers of apoptotic aortic endothelial cells were increased compared with the normothermic control group. Additionally, the plasma prothrombin time, activated partial thromboplastin time and D-dimer level were significantly increased in the HS group compared with the normothermic control group following recovery for 6 h. By contrast, the platelet count was decreased in the HS group compared with the normothermic control group. The serum levels of creatinine, blood urea nitrogen, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase and lactate dehydrogenase were increased and histopathological damage to multiple organs was observed in the HS group following recovery for 6 h. In the STS-HS groups, cytokine levels and apoptotic aortic endothelial cell numbers were reduced compared with the HS group after 6 h recovery. STS (40 mg/kg) treatment additionally improved the serum levels of organ injury indicators and plasma indicators of coagulopathy, and prevented histopathological damage to multiple organs. These findings demonstrated that STS treatment may ameliorate multiple organ damage by attenuating inflammatory responses, aortic endothelial cell apoptosis and DIC in CHS. These results suggested that STS may hold potential as an alternative therapeutic strategy for the treatment of patients with HS.

PAR1‑mediated c‑Jun activation promotes heat stress‑induced early stage apoptosis of human umbilical vein endothelial cells

Our previous study indicated that when human umbilical vein endothelial cells (HUVECs), which are involved in endothelial barrier function, are heat stressed, levels of protease-activated receptor 1 (PAR1) are increased significantly. In the present study, it was demonstrated that PAR1 serves a vital role in heat stress-induced HUVEC apoptosis. When the PAR1 inhibitor, SCH79797 (SCH), or a small interfering RNA (siRNA) targeting PAR1 were used to inhibit PAR1 signaling, a marked decrease in cell apoptosis, caspase-3 activity and the expression of the pro-apoptotic protein B-cell lymphoma 2 (Bcl-2) associated X (Bax), as well as increased expression of the anti-apoptotic Bcl-2 family member, myeloid cell leukemia 1 (Mcl-1), were observed. In addition, heat stress-induced apoptosis, caspase-3 activity and the expression of Bax were significantly increased following administration of the PAR1 agonist, TFLLR-NH2 or adenovirus overexpression of PAR1. This was accompanied by decreased protein expression levels of Mcl-1. Furthermore, it was identified that the DNA binding activity of the nuclear factor (NF)-κB p65 subunit increased and c-Jun activation was reduced as a result of inhibition of PAR1 signaling by SCH or siRNA-mediated PAR1 knockdown in heat stress-induced HUVECs. Additionally, our previous study reported that NF-κB p65 activation may have an anti-apoptosis effect on heat stressed HUVECs, whereas in the present study c-Jun activation had a pro-apoptosis effect on heat stressed HUVECs. Taken together, these results indicated that PAR1 signaling-mediated c-Jun activation promotes early apoptosis of HUVEC cells induced by heat stress.

Electrolyte disturbances and risk factors of acute kidney injury patients receiving dialysis in exertional heat stroke

Background

Exertional heat stroke (EHS) is a life-threatening illness and leads to multi-organ dysfunction including acute kidney injury (AKI). The clinical significance of abnormal electrolytes and renal outcomes in ESH patients has been poorly documented. We aim to exhibit the electrolyte abnormalities, renal outcomes and risk factors of patients with AKI receiving dialysis in EHS.

Methods

A retrospective cohort study in EHS patients between 2003 and 2014 were conducted. Clinical and laboratory outcomes including serum and urine electrolytes, AKI and dialysis were assessed on admission, during hospitalization and at the time of their discharge from the hospital. A logistic regression analysis was performed for risk factors of acute dialysis.

Results

All 66 subjects with mean age 22.1 ± 4.3 years were included. On admission, the common electrolyte disturbances were hypokalemia (71.2 %), hypophosphatemia (59.1 %), hyponatremia (53.0 %), hypocalcemia (51.5 %), and hypomagnesemia (34.9 %). Electrolytes depletion was confirmed as renal loss (potassium loss; 54.2 %, phosphate loss; 86.7 %, sodium loss; 64.7 % and magnesium loss; 83.3 %). During hospitalization ranging from 2 to 209 days, 90.9 % patients suffered from AKI with 16.7 % receiving acute dialysis, and 3 % patients died. At discharge, AKI and electrolyte abnormalities had dramatically improved. The prognosis factors for AKI receiving dialysis were identified as neurological status, renal function and serum muscle enzyme at time of admission.

Conclusion

The study suggests that hypoelectrolytemia and AKI are frequently observed in patients with EHS. Neurological impairment, impaired renal function, and increased serum muscle enzyme should be considered risk factors of acute dialysis.

Heat stress pretreatment decreases lipopolysaccharide-induced apoptosis via the p38 signaling pathway in human umbilical vein endothelial cells

The present study aimed to investigate vascular endothelial apoptosis, and the regulatory molecules involved in the condition of heatstroke caused by direct hyperthermia due to high core temperature and gut‑derived endotoxemia. Human umbilical vascular endothelial cells (HUVECs) were isolated and treated with heat stress (43˚C for 1 h), lipopolysaccharide (LPS; 1 µg/ml), or a combination of heat stress pretreatment followed by LPS. Caspase‑3 activity, DNA fragmentation, and cell viability, determined using a 3‑(4, 5‑dimethyl thiazol‑2‑yl)‑2,5‑diphenyl tetrazolium bromide assay, were measured to examine cellular apoptosis. Changes in the expression levels of heat shock protein (HSP) 27, HSP90 and B‑cell lymphoma 2 (Bcl‑2), and the phosphorylation of p38 were detected using Western blot assays. The specific inhibitor of p38, SB203580, was also used. LPS induced endothelial apoptosis, as indicated by increased caspase‑3 activity, a high level of DNA fragmentation and low cell viability. LPS also increased p38 phosphorylation and decreased the expression levels of HSP27, HSP90 and Bcl‑2. Heat stress pretreatment inhibited LPS‑induced cellular apoptosis, increased the phosphorylation of p38, and increased the expression levels of HSP27, HSP90 and Bcl‑2. Pretreatment with SB203580 had effects similar to those of heat stress in the amelioration of LPS‑induced effects. These findings demonstrated that heat stress pretreatment decreased LPS‑induced Bcl‑2‑associated apoptosis in HUVECs by attenuating p38 activation, thereby increasing the expression levels of HSP27 and HSP90.

A retrospective study of clinical profile and outcomes of critically ill patients with heat-related illness

Background and Aims:

Heat-related illness (HRI) due to high ambient temperatures is a common feature during the Indian summer. HRI often results in Intensive Care Unit (ICU) admissions and are associated with significant morbidity and mortality. However, published report on the effects of HRI among the Indian population is lacking. This study was undertaken to identify the profile of patients admitted to ICU with clinical features of HRI and study their clinical outcomes.

Methods:

This was a retrospective case series of patients admitted with features of HRI during the summer of 2012 in our multidisciplinary ICU. Data on demographics, co-morbid illness, admission severity of illness (Acute Physiology and Chronic Health Evaluation II [APACHE II]), organ failure scores (Sequential Organ Failure Assessment [SOFA]) and neuroimaging studies were collected. Outcome data studied included mortality, ICU length of stay (LOS), ventilator days and hospital LOS. Statistical analysis was performed using Student's t-test, Chi-square test and multivariate analysis.

Results:

Twenty-six patients met the diagnostic criteria for HRI. Fifteen were males. The mean age was 53.12 ± 18.6 years. Mean APACHE II score was 19.6 ± 7.7 and mean SOFA score was 7.5 ± 2.6. The common presenting symptoms were fever with neurological impairment (100%) and gastrointestinal symptoms (30%). Major organ systems involvement include neurological (100%), renal (57%), hepatic (34%) and coagulation abnormalities (26%). Most common metabolic abnormality noted was hyponatraemia (73%). Magnetic resonance imaging findings suggestive of heat stroke were seen in 5 of 26 patients. Mortality rate was 34%. 8 of 17 survivors had residual neurological impairment.

Conclusion:

HRI carries a high mortality and significant neurological morbidity.

Predictive Factors for Hospitalization of Patients with Heat Illness in Yamaguchi, Japan

The objective of the study was to investigate the predictive factors for the hospitalization of patients who presented with mild to moderate heat illness at an emergency department. We conducted a retrospective survey of hospitals with an emergency department in Yamaguchi Prefecture, Japan. The survey questionnaire entries included patient age, sex, use of an ambulance, vital signs, blood examination conducted at the emergency department, the length of hospitalization, and outcome. We analyzed the predictive factors for hospitalization in patients with heat illness. A total of 127 patients were analyzed. Of these, 49 (37%) were admitted, with 59% discharged on the day following admission. In univariate analysis, the following inpatient characteristics were predictive for hospitalization: old age, low Glasgow Coma Scale score, elevated body temperature, increased serum C-reactive protein, and increased blood urea nitrogen. In logistic regression multivariate analysis, the following were predictive factors for hospitalization: age of ≥ 65 years (odds ratio (OR) 4.91; 95% confidence interval (CI) 1.42–17.00), body temperature (OR 1.97; 95% CI 1.14–3.41), Glasgow Coma Scale (OR 0.40; 95% CI 0.16–0.98), and creatinine (OR 2.92; 95% CI 1.23–6.94). The results suggest that the elderly with hyperthermia, disturbance of consciousness, and elevated serum creatinine have an increased risk for hospitalization with heat illness.

NF-κB signaling is essential for resistance to heat stress-induced early stage apoptosis in human umbilical vein endothelial cells

Cell apoptosis induced by heat stress is regulated by a complex signaling network. We previously reported that a p53-dependent pathway is involved. Here, we present evidence that NF-κB signaling plays a crucial role in preventing heat stress-induced early apoptosis. Human umbilical vein endothelial cells (HUVECs) were examined and increased phosphorylation of p65 and IκBα were detected, without IκBα degradation. When NF-κB signaling was inhibited by BAY11-7082, or a small interference RNA (siRNA) targeting p65, a significant increase in cell apoptosis and caspase-3 activity was observed, as well as reduced expression and translocation of HSP27 into the nucleus, an accumulation of reactive oxygen species, and prolonged phosphorylation of mitogen-activated protein kinases (MAPKs). In addition, an association between HSP27 and p65 was identified which may enhance NF-κB activation. When HSP27 was overexpressed, pretreatment of HUVECs with the antioxidant, apocynin, or N-acetyl cysteine, suppressed apoptosis. Similarly, inhibition of JNK and p38 with SP600125 and SB203580, respectively, also suppressed apoptosis, whereas siRNA-mediated HSP27 knockdown and treatment with the ERK 1/2 inhibitor PD98059 did otherwise. In conclusion, these findings suggest a novel role for an NF-κB signaling pathway involving HSP27, ROS, and MAPKs that confers a protective effect against heat stress-induced cell apoptosis.

Heat stress induced apoptosis is triggered by transcription-independent p53, Ca(2+) dyshomeostasis and the subsequent Bax mitochondrial translocation

In this study, We demonstrated that Bax mitochondrial translocation plays a vital role in the initiation of the mitochondrial signaling pathway upon activation by heat stress. In addition, both p53 mitochondrial translocation and Ca²⁺ signal mediated MPTP opening activate Bax mitochondrial translocation. Employing pifithrin-α (a p53 mitochondrial translocation inhibitor) and CsA (a permeability transition pore (MPTP) inhibitor), we found that heat stress induced Bax mitochondrial translocation was significantly inhibited in cells pretreated with both PFT and CsA. Furthermore, we demonstrated that generation of reactive oxygen species (ROS) is a critical mediator in heat stress induced apoptosis and that the antioxidant MnTBAP significantly decreased heat stress induced p53 mitochondrial translocation and Ca²⁺ signal mediated MPTP opening, as well as the subsequent Bax mitochondrial translocation and activation of the caspase cascade. Taken together, our results indicate that heat stress induces apoptosis through the mitochondrial pathway with ROS dependent mitochondrial p53 translocation and Ca²⁺ dyshomeostasis, and the ensuing intro Bax mitochondrial translocation as the upstream events involved in triggering the apoptotic process observed upon cellular exposure to heat stress.

Heat stress induces apoptosis through transcription-independent p53-mediated mitochondrial pathways in human umbilical vein endothelial cell

Cells apoptosis induced by intense heat stress is the prominent feature of heat-related illness. However, little is known about the biological effects of heat stress on cells apoptosis. Herein, we presented evidence that intense heat stress could induce early apoptosis of HUVEC cells through activating mitochondrial pathway with changes in mitochondrial membrane potential(ΔΨm), release of cytochrome c, and activation of caspase-9 and -3. We further revealed that p53 played a crucial role in heat stress-induced early apoptosis, with p53 protein rapidly translocated into mitochondria. Using pifithrin-α(PFT), a p53's mitochondrial translocation inhibitor, we found that pretreated with PFT, heat stress induced mitochondrial p53 translocation was significantly suppressed, accompanied by a significant alleviation in the loss of ΔΨm, cytochrome c release and caspase-9 activation. Furthermore, we also found that generation of reactive oxygen species (ROS) was a critical mediator in heat stress-induced apoptosis. In addition, the antioxidant MnTMPyP significantly decreased the heat stress-induced p53's mitochondrial translocation, followed by the loss of ΔΨm, cytochrome c release, caspase-9 activation and heat stress-mediated apoptosis. Conclusively, these findings indicate the contribution of the transcription-independent mitochondrial p53 pathway to early apoptosis in HUVEC cells induced by oxidative stress in response to intense heat stress.

Comparative analysis of αB-crystallin expression in heat-stressed myocardial cells in vivo and in vitro

Relationships between αB-crystallin expression patterns and pathological changes of myocardial cells after heat stress were examined in vitro and in vivo in this study using the H₉C₂ cell line and Sprague-Dawley rats, respectively. Histopathological lesions, characterized by acute degeneration, karyopyknosis and loss of a defined nucleus, became more severe in rat hearts over the course of heat stress treatment from 20 min to 100 min. The expression of αB-crystallin in rat hearts showed a significant decrease (P<0.05) throughout the heat stress treatment period, except at the 40 min time point. Likewise, decreased αB-crystallin expression was also observed in the H₉C₂ cell line exposed to a high temperature in vitro, although its expression recovered to normal levels at later time points (80 and 100 min) and the cellular damage was less severe. The results suggest that αB-crystallin is mobilized early after exposure to a high temperature to interact with damaged proteins but that the myocardial cells cannot produce sufficient αB-crystallin for protection against heat stress. Lower αB-crystallin expression levels were accompanied by obvious cell/tissue damage, suggesting that the abundance of this protein is associated with protective effects in myocardial cells in vitro and in vivo. Thus, αB-crystallin is a potential biomarker of heat stress.

A case of severe heatstroke and review of pathophysiology, clinical presentation, and treatment

Heatstroke is life-threatening condition characterized by hyperthermia and central nervous system disturbances. It can also be classified as a form of systemic inflammatory response syndrome with multiple organ dysfunction and in many ways resembles sepsis. Like sepsis, most patients with heatstroke demonstrate a hyperdynamic hemodynamic response. In contrast to sepsis, rhabdomyolysis may complicate management and initial fluid resuscitation is not well defined. We present an illustrative case report and review of literature.

Ischemic electrocardiographic changes and elevated troponin from severe heatstroke in an adolescent

BACKGROUND

Heatstroke can result in significant diffuse tissue derangement, which can result in multiple organ system dysfunction. The heart can equally be affected and ischemia and infarction may occur.

OBJECTIVE

This study aimed to present the potential complications from heatstroke to the myocardium.

CASE

A case of a 15-year-old adolescent boy who collapsed after playing football in a hot summer day was found to be hyperthermic and poorly perfused. He had ischemic electrocardiographic changes and elevated cardiac enzymes but with normal coronary arteries.

CONCLUSIONS

Heatstroke can lead to morbidity and mortality. Tissue damage during heatstroke is believed to result from uncoupling during oxidative phosphorylation. It is important to realize that heart damage can occur from heatstroke and that appropriate diagnostic and therapeutic measures are required for a good outcome.

Successful treatment of severe heatstroke with therapeutic hypothermia by a noninvasive external cooling system

Heatstroke is a life-threatening disease; however, no pharmacologic treatment has proven to be effective. In severe cases with multiple organ dysfunction, the mortality remains high and many patients inevitably develop permanent neurologic damage. We report a near-fatal case of exertional heatstroke with multiple organ dysfunction, including generalized convulsions, acute lung injury, and disseminated intravascular coagulation, successfully treated with induced therapeutic hypothermia (33°C [91.4°F]) by a noninvasive external cooling system. After treatment, the patient completely recovered, without any neurologic sequelae during 1 year of follow-up. To our knowledge, this is the first reported case of using therapeutic hypothermia in heatstroke.

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.

Recombinant activated protein C attenuates endothelial injury and inhibits procoagulant microparticles release in baboon heatstroke

OBJECTIVE

We tested the hypothesis that the antithrombotic and cytoprotective effects of recombinant human activated protein C (rhAPC) protect baboons against the lethal effects of heatstroke.

METHODS AND RESULTS

Fourteen anesthetized baboons assigned randomly to rhAPC (n=7) or control group (n=7) were heat-stressed in a prewarmed incubator at 44 to 47 degrees C until systolic blood pressure fell below 90 mm Hg, which signaled severe heatstroke. rhAPC was administered intravenously (24 microg/kg/h) for 12 hours at onset of heatstroke. Heat stress induced coagulation and fibrinolysis activation as evidenced by a significant increase from baseline levels in plasma levels of thrombin-antithrombin (TAT) complexes, tissue plasminogen activator, and D-dimer. Heat stress elicited cell activation/injury as assessed by the release of interleukin (IL)-6, soluble thrombomodulin, and procoagulant microparticles (MPs). rhAPC did not significantly reduce heatstroke-induced thrombin generation, and D-dimer and had no effect on fibrinolytic activity. In contrast, rhAPC infusion attenuated significantly the plasma rise of IL-6 and inhibited the release of soluble thrombomodulin and MPs as compared with control group. No difference in survival was observed between rhAPC-treated and control group.

CONCLUSIONS

rhAPC given to heatstroke baboons provided cytoprotection, but had no effect on heatstroke-induced coagulation activation and fibrin formation. Inhibition of MPs by rhAPC suggested a novel mechanism of action for this protein.

Heat Stroke Deaths Caused by Electric Blankets

Heat stroke is the most serious and potentially life-threatening condition of the heat-related illnesses. Heat stroke deaths caused by electric blanket are rarely reported. In this paper, we report 2 cases of fatal heat stroke caused by overheating from electric blankets in winter. One was a 41-year-old man who was found unresponsive in bed on an electric blanket. His wife shared the same bed with him and was found unconscious. The wife's axillary temperature was 40 degrees C (104 degrees C) when she was admitted to the hospital. She fully recovered after medical treatment. The husband was pronounced dead at scene, with rectal temperature at 41.2 degrees C (106.2 degrees C). The other was a 13-year-old girl who was found dead in bed on an electric blanket, with rectal temperature at 41 degrees C (105.8 degrees F). The literature is reviewed, and the pertinent findings, including scene investigations, postmortem examination, the risk and mechanism of fatal heat stroke caused by using electric blanket, are discussed.

CEREBROVASCULAR DYSFUNCTION IS AN ATTRACTIVE TARGET FOR THERAPY IN HEAT STROKE¶

1. The aim of the present review is to summarize clinical observations and results of animal models that advance the knowledge of the attenuation of cerebrovascular dysfunction in the setting of heat stroke. It is a narrative review of selected published literature from Medline over the period 1959-2005. 2. All heat-stressed rodents, even under general anaesthesia, have hyperthermia, systemic inflammation, hypercoagulable state, arterial hypotension and tissue ischaemia and injury in multiple organs. These findings demonstrate that rodent heat stroke models can nearly mirror the full spectrum of human heat stroke. Experimental heat stroke fulfills the empirical triad used for the diagnosis of classical human heat stroke, namely hyperthermia, central nervous system alterations and a history of heat stress. 3. These physiological dysfunctions and survival during heat stroke can be improved by whole-body or brain cooling therapy adopted immediately after the onset of heat stroke. 4. However, in the absence of body or brain cooling, these heat stroke reactions can still be reduced by the following measures: (i) fluid replacement with 3% NaCl solution, 10% human albumin or hydroxyethyl starch; (ii) intravenous delivery of anti-inflammatory drugs, free radical scavengers or interleukin-1 receptor antagonists; (iii) hyperbaric oxygen therapy; or (iv) transplantation of human umbilical cord blood cells. 5. In addition, before initiation of heat stress, prior manipulations with one of the following measures was found to be able to protect against heat stroke reactions: (i) systemic delivery of alpha-tocopherol, mannitol, inducible nitric oxide synthase inhibitors, mu-opioid receptor antagonists, endothelin ETA receptor antagonists, serotoninergic nerve depletors or receptor antagonists, or glutamate receptor antagonists; or (ii) heat shock protein 72 preconditioning. 6. There is compelling evidence that cerebrovascular dysfunction is an attractive target for therapy in heat stroke.

The roles of exercise-induced immune system disturbances in the pathology of heat stroke : the dual pathway model of heat stroke

Heat stroke is a life-threatening condition that can be fatal if not appropriately managed. Although heat stroke has been recognised as a medical condition for centuries, a universally accepted definition of heat stroke is lacking and the pathology of heat stroke is not fully understood. Information derived from autopsy reports and the clinical presentation of patients with heat stroke indicates that hyperthermia, septicaemia, central nervous system impairment and cardiovascular failure play important roles in the pathology of heat stroke. The current models of heat stroke advocate that heat stroke is triggered by hyperthermia but is driven by endotoxaemia. Endotoxaemia triggers the systemic inflammatory response, which can lead to systemic coagulation and haemorrhage, necrosis, cell death and multi-organ failure. However, the current heat stroke models cannot fully explain the discrepancies in high core temperature (Tc) as a trigger of heat stroke within and between individuals. Research on the concept of critical Tc as a limitation to endurance exercise implies that a high Tc may function as a signal to trigger the protective mechanisms against heat stroke. Athletes undergoing a period of intense training are subjected to a variety of immune and gastrointestinal (GI) disturbances. The immune disturbances include the suppression of immune cells and their functions, suppression of cell-mediated immunity, translocation of lipopolysaccharide (LPS), suppression of anti-LPS antibodies, increased macrophage activity due to muscle tissue damage, and increased concentration of circulating inflammatory and pyrogenic cytokines. Common symptoms of exercise-induced GI disturbances include diarrhoea, vomiting, gastrointestinal bleeding, and cramps, which may increase gut-related LPS translocation. This article discusses the current evidence that supports the argument that these exercise-induced immune and GI disturbances may contribute to the development of endotoxaemia and heat stroke. When endotoxaemia can be tolerated or prevented, continuing exercise and heat exposure will elevate Tc to a higher level (>42 degrees C), where heat stroke may occur through the direct thermal effects of heat on organ tissues and cells. We also discuss the evidence suggesting that heat stroke may occur through endotoxaemia (heat sepsis), the primary pathway of heat stroke, or hyperthermia, the secondary pathway of heat stroke. The existence of these two pathways of heat stroke and the contribution of exercise-induced immune and GI disturbances in the primary pathway of heat stroke are illustrated in the dual pathway model of heat stroke. This model of heat stroke suggests that prolonged intense exercise suppresses anti-LPS mechanisms, and promotes inflammatory and pyrogenic activities in the pathway of heat stroke.