Microcirculatory Disorders and Protective Role of Antioxidant in Severe Heat Stroke: A Rat Study

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.

Effects of norepinephrine on colonic tight junction protein expression during heat stress

Stress induced by changes in the internal or external environment in humans and animals leads to intestinal epithelial damage, in a manner that is associated with impaired intestinal barrier function. However, the role of the stress hormone norepinephrine (NE) in impairments in barrier function remains poorly understood. In the present study, a rat heat-exposed model was used to observe changes in the tight junction proteins Occludin and zonula occludens-1 (ZO-1), in addition to those in protease-activated receptor 2 (PAR-2) and transient receptor potential ankyrin 1 channel (TRPA1) in colon. The levels of plasma NE were detected using an ELISA kit. Different concentrations of NE were used to culture the human colon cell line Caco-2 for 6 and 24 h to investigate the cell viability using Cell Counting Kit-8 assay, whilst the expression levels of Occludin, ZO-1, PAR-2 and TRPA1 were examined using western blotting and immunofluorescence in Caco-2 cells and immunohistrochemistry in rat colon tissues. Although there was no clear histological damage to the rat colonic mucosa, there were decreased expression levels of tight junction proteins Occludin and ZO-1 after heat exposure. In addition, PAR-2 expression was increased by heat exposure. It was found that TRPA1 expression was concentrated to the luminal surface of the colon in the heat exposed group compared with that in the control group. After the administration of increasing concentrations of NE for 6 h, treatment did not affect cell viability. Furthermore, after application of NE for 24 h, cell viability gradually increased as the NE concentration was elevated from 10 to 100 µM. However, no significant increase in viability was observed when the cells were treated with 120 and 160 µM NE. Occludin expression was decreased when 10 µM NE was applied for 6 or 24 h. By contrast, 60 µM NE significantly downregulated Occludin expression in the 6 h group, but caused an insignificant decrease in the 24 h group. It was found that ZO-1 expression was upregulated after treatment with 10 µM NE for 6 h, whilst downregulation was observed after treatment with 10 µM NE for 24 h. PAR-2 protein expression was increased after application of NE for both 6 and 24 h, but not after treatment with 60 µM NE. In addition, TRPA1 expression was not affected by the treatment of NE, but increased positive staining was observed on the luminal side of the mucosa, which appeared to be concentrated in the cells of the luminal side in the rat colon after heat exposure. Collectively, the present results suggested that expression of tight junction proteins Occludin and ZO-1, in addition to that of PAR-2, can be regulated by NE, which may contribute to impairments in barrier function observed during heat stress.

Intestinal Injury in Heat Stroke

BACKGROUND

Heat stroke is a life-threatening syndrome that is characterized by its severe clinical symptoms, rapid progression, and high rate of mortality. Recently, research has indicated that a dysfunctional intestinal epithelia barrier plays an important role in the pathophysiology of heat stroke. Protecting the intestines from heat stress had been identified as a potentially effective treatment for patients with heat stroke and may reduce the innate immune response caused by endotoxins in circulation.

OBJECTIVES

The aim of this review is to discuss this key event in heat stroke and to describe the mechanism during progression.

DISCUSSION

Direct injuries and secondary impairments of the intestine induced by heat stress are discussed; recent studies that refer to intestine-specific prevention and treatment in heat stroke and heat stress-induced injuries are also summarized.

CONCLUSIONS

A more detailed pathogenesis of heat stroke needs to be elucidated so that potentially effective means of treatment and prevention of heat stroke can be developed and studied.

Large-depth-of-field full-field optical angiography

A large-depth-of-field full-field optical angiography (LD-FFOA) method is developed to expand the depth-of-field (DOF) using a contrast pyramid fusion algorithm (CPFA). The absorption intensity fluctuation modulation effect is utilized to obtain full-field optical angiography (FFOA) images at different focus positions. The CPFA is used to process these FFOA images with different focuses. By selecting high-contrast areas, the CPFA can highlight the characteristics and details of blood vessels to obtain LD-FFOA images. In the optimal case of the proposed method, the DOF for FFOA is more than tripled using 10 differently focused FFOA images. Both the phantom and animal experimental results show that the LD-FFOA resolves FFOA defocusing issues induced by surface and thickness inhomogeneities in biological samples. The proposed method can be potentially applied to practical biological experiments.

Microcirculatory Disorders and Protective Role of Xuebijing in Severe Heat Stroke

This study was conducted to explore underlying mechanism of microcirculation dysfunction and protectiverole of Xuebijing in heat stroke. Forty rats were divided into: control, vehicle + heat stress (HS), superoxide dismutase (SOD) + HS, and Xuebijing + HS groups. Rats in heat stress groups were subjected to continuous heat stress in infant incubator 1 h after tail vein injection of the tested compound and spinotrapezius preparation. Velocity of blood flow through micro-vessels and vascular diameter were detected in real time. Another 27 rats were divided into: vehicle, SOD, and Xuebijing groups, then further divided into three subgroups each: control, Tcore = 38 °C, Tcore = 41 °C. Rats were sacrificed, and spinotrapezius single-cell suspensions were prepared for detecting SOD and reactive oxygen species (ROS). The results showed that heat stress decreased SOD activity, increased ROS levels, and reduced the blood flow rate. Xuebijing increased SOD activity, decreased ROS levels and exhibited a protective effect in terms of blood flow rate but was less protective than SOD. The survival time in Xuebijing + HS group was longer than that in vehicle group but shorter than that in SOD + HS group. The results suggested Xuebijing could decrease ROS levels and have protective effects in severe heat stroke.