Aminoguanidine Protects Against Intracranial Hypertension and Cerebral Ischemic Injury in Experimental Heatstroke

Inhibition of nitric oxide synthase or cystathionine gamma-lyase abolishes leptin-induced fever in male rats

Leptin is an adipokine that regulates energy balance and immune function. Peripheral leptin administration elicits prostaglandin E₂-dependent fever in rats. The gasotransmitters nitric oxide (NO) and hydrogen sulfide (H₂S) are also involved in lipopolysaccharide (LPS)-induced fever response. However, there is no data in the literature indicating if these gasotransmitters have a role in leptin-induced fever response. Here, we investigate the inhibition of NO and H₂S enzymes neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS), and cystathionine γ-lyase (CSE) in leptin-induced fever response, respectively. Selective nNOS inhibitor 7-nitroindazole (7-NI), selective iNOS inhibitor aminoguanidine (AG), and CSE inhibitor dl-propargylglycine (PAG) were administered intraperitoneally (ip). Body temperature (Tb), food intake, and body mass were recorded in fasted male rats. Leptin (0.5 mg/kg ip) induced a significant increase in Tb, whereas AG (50 mg/kg ip), 7-NI (10 mg/kg ip), or PAG (50 mg/kg ip) caused no changes in Tb. AG, 7-NI, or PAG abolished leptin increase in Tb. Our results highlight the potential involvement of iNOS, nNOS, and CSE in leptin-induced febrile response without affecting anorexic response to leptin in fasted male rats 24 h after leptin injection. Interestingly, all the inhibitors alone had the same anorexic effect induced by leptin. These findings have implications for understanding the role of NO and H₂S in leptin-induced febrile response.

Co-administration of Nanowired Oxiracetam and Neprilysin with Monoclonal Antibodies to Amyloid Beta Peptide and p-Tau Thwarted Exacerbation of Brain Pathology in Concussive Head Injury at Hot Environment

Environmental temperature adversely affects the outcome of concussive head injury (CHI)-induced brain pathology. Studies from our laboratory showed that animals reared at either cold environment or at hot environment exacerbate brain pathology following CHI. Our previous experiments showed that nanowired delivery of oxiracetam significantly attenuated CHI-induced brain pathology and associated neurovascular changes. Military personnel are the most susceptible to CHI caused by explosion, blasts, missile or blunt head trauma leading to lifetime functional and cognitive impairments affecting the quality of life. Severe CHI leads to instant death and/or lifetime paralysis. Military personnel engaged in combat operations are often subjected to extreme high or low environmental temperature zones across the globe. Thus, further exploration of novel therapeutic agents at cold or hot ambient temperatures following CHI are the need of the hour. CHI is also a major risk factor for developing Alzheimer's disease by enhancing amyloid beta peptide deposits in the brain. In this review, effect of hot environment on CHI-induced brain pathology is discussed. In addition, whether nanodelivery of oxiracetam together with neprilysin and monoclonal antibodies (mAb) to amyloid beta peptide and p-tau could lead to superior neuroprotection in CHI is explored. Our results show that co-administration of oxiracetam with neprilysin and mAb to AβP and p-tau significantly induced superior neuroprotection following CHI in hot environment, not reported earlier.

Cerebral Vascular Control and Metabolism in Heat Stress

This review provides an in-depth update on the impact of heat stress on cerebrovascular functioning. The regulation of cerebral temperature, blood flow, and metabolism are discussed. We further provide an overview of vascular permeability, the neurocognitive changes, and the key clinical implications and pathologies known to confound cerebral functioning during hyperthermia. A reduction in cerebral blood flow (CBF), derived primarily from a respiratory-induced alkalosis, underscores the cerebrovascular changes to hyperthermia. Arterial pressures may also become compromised because of reduced peripheral resistance secondary to skin vasodilatation. Therefore, when hyperthermia is combined with conditions that increase cardiovascular strain, for example, orthostasis or dehydration, the inability to preserve cerebral perfusion pressure further reduces CBF. A reduced cerebral perfusion pressure is in turn the primary mechanism for impaired tolerance to orthostatic challenges. Any reduction in CBF attenuates the brain's convective heat loss, while the hyperthermic-induced increase in metabolic rate increases the cerebral heat gain. This paradoxical uncoupling of CBF to metabolism increases brain temperature, and potentiates a condition whereby cerebral oxygenation may be compromised. With levels of experimentally viable passive hyperthermia (up to 39.5-40.0 °C core temperature), the associated reduction in CBF (∼ 30%) and increase in cerebral metabolic demand (∼ 10%) is likely compensated by increases in cerebral oxygen extraction. However, severe increases in whole-body and brain temperature may increase blood-brain barrier permeability, potentially leading to cerebral vasogenic edema. The cerebrovascular challenges associated with hyperthermia are of paramount importance for populations with compromised thermoregulatory control--for example, spinal cord injury, elderly, and those with preexisting cardiovascular diseases.

Therapeutic treatment with ascorbate rescues mice from heat stroke-induced death by attenuating systemic inflammatory response and hypothalamic neuronal damage

The impact of ascorbate on oxidative stress-related diseases is moderate because of its limited oral bioavailability and rapid clearance. However, recent evidence of the clinical benefit of parenteral vitamin C administration has emerged, especially in critical care. Heatstroke is defined as a form of excessive hyperthermia associated with a systemic inflammatory response that results in multiple organ dysfunctions in which central nervous system disorders such as delirium, convulsions, and coma are predominant. The thermoregulatory, immune, coagulation and tissue injury responses of heatstroke closely resemble those observed during sepsis and are likely mediated by similar cellular mechanisms. This study was performed by using the characteristic high lethality rate and sepsis-mimic systemic inflammatory response of a murine model of heat stroke to test our hypothesis that supra-physiological doses of ascorbate may have therapeutic use in critical care. We demonstrated that parenteral administration of ascorbate abrogated the lethality and thermoregulatory dysfunction in murine model of heat stroke by attenuating heat stroke-induced accelerated systemic inflammatory, coagulation responses and the resultant multiple organ injury, especially in hypothalamus. Overall, our findings support the hypothesis and notion that supra-physiological doses of ascorbate may have therapeutic use in critical care.

Ischemic and oxidative damage to the hypothalamus may be responsible for heat stroke

The hypothalamus may be involved in regulating homeostasis, motivation, and emotional behavior by controlling autonomic and endocrine activity. The hypothalamus communicates input from the thalamus to the pituitary gland, reticular activating substance, limbic system, and neocortex. This allows the output of pituitary hormones to respond to changes in autonomic nervous system activity. Environmental heat stress increases cutaneous blood flow and metabolism, and progressively decreases splanchnic blood flow. Severe heat exposure also decreases mean arterial pressure (MAP), increases intracranial pressure (ICP), and decreases cerebral perfusion pressure (CPP = MAP - ICP), all of which lead to cerebral ischemia and hypoxia. Compared with normothermic controls, rodents with heatstroke have higher hypothalamic values of cellular ischemia (e.g., glutamate and lactate-to-pyruvate ratio) and damage (e.g., glycerol) markers, pro-oxidant enzymes (e.g., lipid peroxidation and glutathione oxidation), proinflammatory cytokines (e.g., interleukin-1β and tumor necrosis factor-α), inducible nitric oxide synthase-dependent nitric oxide, and an indicator for the accumulation of polymorphonuclear leukocytes (e.g., myeloperoxidase activity), as well as neuronal damage (e.g., apoptosis, necrosis, and autophagy) after heatstroke. Hypothalamic values of antioxidant defenses (e.g., glutathione peroxidase and glutathione reductase), however, are lower. The ischemic, hypoxic, and oxidative damage to the hypothalamus during heatstroke may cause multiple organ dysfunction or failure through hypothalamic-pituitary-adrenal axis mechanisms. Finding the link between the signaling and heatstroke-induced hypothalamic oxidative and ischemic damage might allow us to clinically attenuate heatstroke. In particular, free radical scavengers, heat shock protein-70 inducers, hypervolemic hemodilution, inducible nitric oxide synthase inhibitors, progenitor stem cells, flutamide, estrogen, interleukin-1 receptor antagonists, glucocorticoid, activated protein C, and baicalin mitigate preclinical heatstroke levels.

RNA interference-produced autoregulation of inducible nitric oxide synthase expression

Vector-mediated delivery of short-hairpin RNA (shRNA) to regulate gene expression holds a great therapeutic promise. We hypothesize that gene expression can be autoregulated with RNA interference. We used inducible nitric oxide synthase (iNOS) as a gene model to test this hypothesis. Lipopolysaccharide dose-dependently increased iNOS in rat aortic smooth muscle cells and the nitrite production from these cells. These increases were attenuated in cells transfected with plasmids containing code for iNOS shRNA whose expression was controlled by an iNOS promoter. The production of shRNA was lipopolysaccharide dose-dependent. The lipopolysaccharide-induced iNOS expression in rat C6 glioma cells also was attenuated by transfection with plasmids containing the iNOS shRNA code. These results provide proof-of-concept evidence for using RNA interference technique to achieve autoregulation of gene expression.

Reduction of ischemic and oxidative damage to the hypothalamus by hyperbaric oxygen in heatstroke mice

The aims of the present paper were to ascertain whether the heat-induced ischemia and oxidative damage to the hypothalamus and lethality in mice could be ameliorated by hyperbaric oxygen therapy. When normobaric air-treated mice underwent heat treatment, the fractional survival and core temperature at 4 hours after heat stress were found to be 0 of 12 and 34 degrees C +/- 0.3 degrees C, respectively. In hyperbaric oxygen-treated mice, when exposed to the same treatment, both fractional survival and core temperature values were significantly increased to new values of 12/12 and 37.3 degrees C +/- 0.3 degrees C, respectively. Compared to normobaric air-treated heatstroke mice, hyperbaric oxygen-treated mice displayed lower hypothalamic values of cellular ischemia and damage markers, prooxidant enzymes, proinflammatory cytokines, inducible nitric oxide synthase-dependent nitric oxide, and neuronal damage score. The data indicate that hyperbaric oxygen may improve outcomes of heatstroke by normalization of hypothalamic and thermoregulatory function in mice.

Attenuation of acute lung inflammation and injury by whole body cooling in a rat heatstroke model

Whole body cooling is the current therapy of choice for heatstroke because the therapeutic agents are not available. In this study, we assessed the effects of whole body cooling on several indices of acute lung inflammation and injury which might occur during heatstroke. Anesthetized rats were randomized into the following groups and given (a) no treatment or (b) whole body cooling immediately after onset of heatstroke. As compared with the normothermic controls, the untreated heatstroke rats had higher levels of pleural exudates volume and polymorphonuclear cell numbers, lung myloperoxidase activity and inducible nitric oxide synthase expression, histologic lung injury score, and bronchoalveolar proinflammatory cytokines and glutamate, and PaCO2. In contrast, the values of mean arterial pressure, heart rate, PaO2, pH, and blood HCO3(-) were all significantly lower during heatstroke. The acute lung inflammation and injury and electrolyte imbalance that occurred during heatstroke were significantly reduced by whole body cooling. In conclusion, we identified heat-induced acute lung inflammation and injury and electrolyte imbalance could be ameliorated by whole body cooling.

The novel nitric oxide synthase inhibitor 4-amino-tetrahydro-L-biopterine prevents brain edema formation and intracranial hypertension following traumatic brain injury in mice

Brain edema formation, resulting in increased intracranial pressure (ICP), is one of the most deleterious consequences of traumatic brain injury (TBI). Nitric oxide (NO) has previously been shown to be involved in the damage of the blood-brain barrier (BBB) and, thus, in the formation of post-traumatic brain edema; however, this knowledge never resulted in a clinically relevant therapeutic option because available NO synthase inhibitors have serious side effects in man. The aim of the current study was to investigate the therapeutic efficacy of VAS203, a novel tetrahydrobiopterine (BH3)-based NOS inhibitor, in experimental TBI. When added to isolated vessels rings obtained from rat basilar and middle cerebral arteries (n = 32-35) VAS203 showed the same vasoconstrictive effect as the classical NO synthase inhibitor L-(G)-nitro-arginine-methylester (L-NAME). VAS203 passed the BBB both in healthy and traumatized mouse brain (C57/BL6, n = 5 per group) and did not show any systemic side effects at therapeutic concentrations. When administered 30 min after experimental TBI (controlled cortical impact, 2.2 mg/kg/min i.v., n = 7 per group), VAS203 prevented any further increase in ICP or deterioration of cerebral blood flow. This effect was dose-dependent and long-lasting (i.e., 24 h after trauma, brain edema formation was still significantly reduced [-40%, p < 0.008; n = 7 per group] and functional improvements were present up to 7 days after TBI [p < 0.02 on post-trauma day 6; n = 8 per group]). Therefore, VAS203 may represent a promising candidate for the treatment of acute intracranial hypertension following TBI.

Protective effect of transgenic expression of porcine heat shock protein 70 on hypothalamic ischemic and oxidative damage in a mouse model of heatstroke

Background

Transgenic mice have been used to examine the role of heat shock protein (HSP)72 in experimental heatstroke. Transgenic mice that were heterozygous for a porcine HSP70β gene ([+] HSP72) and transgene-negative littermate controls ([-] HSP72), under pentobarbital sodium anesthesia, were subjected to heat stress to induce heatstroke. It was found that the overexpression of HSP72 in multiple organs improved survival during heatstroke by reducing hypotension and cerebral ischemia and damage in mice. Herein we attempted to further assess the effect of heat exposure on thermoregulatory function, hypothalamic integration, and survival in unrestrained, unanesthetized [+]HSP72 and compare with those of [-]HSP72. In this research with the transgenic mice, we first conducted several biochemical, physiologic and histological determinations and then investigated the beneficial effects of HSP72 overexpression on the identified hypothalamic deficits, thermoregulatory dysfunction, and mortality during heatstroke.

Results

We report here that when [-]HSP72 mice underwent heat stress (ambient temperature 42.4°C for 1 h), the fraction survival and core temperature at 4 h after heat stress were found to be 0 of 12 and 34.2°C ± 0.4°C, respectively. Mice that survived to day 4 after heat stress were considered as survivors. In [+]HSP72 mice, when exposed to the same heat treatment, both fraction survival and core temperature values were significantly increased to new values of 12/12 and 37.4°C ± 0.3°C, respectively. Compared to [-]HSP mice, [+]HSP72 mice displayed lower hypothalamic values of cellular ischemia (e.g., glutamate and lactate-to-pyruvate ratio) and damage (e.g., glycerol) markers, pro-oxidant enzymes (e.g., lipid peroxidation and glutathione oxidation), pro-inflammatory cytokines (e.g., interleukin-1beta and tumor necrosis factor-alpha), and neuronal damage score evaluated 4 h after heat stress. In contrast, [+]HSP72 mice had higher hypothalamic values of antioxidant defences (e.g., glutathione peroxidase and glutathione reductase), ATP, and HSP72 expression.

Conclusion

This study indicates that HSP72 overexpression appears to be critical to the development of thermotolerance and protection from heat-induced hypothalamic ischemic and oxidative damage.

Premarin can act via estrogen receptors to rescue mice from heatstroke-induced lethality

The present study was conducted to assess whether Premarin, a water-soluble estrogen sulfate, can act via estrogen receptors (ERs) to rescue mice from heat-induced lethality. Unanesthetized, unrestrained mice were exposed to ambient temperature of 42.4 degrees C to induce heatstroke (HS). Another group of mice was exposed to room temperature (24 degrees C) and used as normothermic controls. They were given isotonic sodium chloride solution, Premarin (0.1 - 1.0 mg/kg of body weight, i.p.), or Premarin (1 mg/kg of body weight, i.p.) plus the nonselective ER antagonist ICI 182, 780 (0.25 mg/kg of body weight, i.p.) 1 h after the termination of heat stress. Their physiologic and biochemical parameters were continuously monitored. Mice that survived on day 4 of heat treatment were considered survivors. When the vehicle-treated mice underwent heat, the fraction survival and core temperature at +4 h of body heating were found to be 0 of 12 and 34.4 degrees C +/- 3 degrees C, respectively. Administration of Premarin (1 mg/kg) 1 h after the cessation of heat stress rescued the mice from heat-induced death (fraction survival, 12/12) and reduced the hypothermia (core temperature, 37.3 degrees C). The beneficial effects of Premarin in ameliorating lethality and hypothermia can be abolished by simultaneous administration of ICI 182, 780. Both IL-10 (an anti-inflammatory cytokine) and estradiol in the serum were increased significantly in heat-stressed mice administered Premarin compared with vehicle-treated HS group. Heat-induced apoptosis, as indicated by terminal deoxynucleotidyl-transferase-mediated alpha UDP-biotin nick end-labeling staining, in the spleen, liver, and kidney were significantly reduced by Premarin. The increased levels of cellular ischemia (e.g., glutamate, lactate-to-pyruvate ratio, and nitrite) and damage (e.g., glycerol) markers and iNOS expression in the hypothalamus during HS were decreased significantly by Premarin therapy. The levels of proinflammatory cytokines (e.g., IL-1 beta and TNF-alpha) and renal and hepatic dysfunction markers in plasma that are up-regulated in heat stressed mice were significantly lower in Premarin-administered mice. The data indicate that Premarin may act via ERs to rescue mice form HS-induced lethality.

Cerebral blood flow regulation by nitric oxide: recent advances

Nitric oxide (NO) is undoubtedly quite an important intercellular messenger in cerebral and peripheral hemodynamics. This molecule, formed by constitutive isomers of NO synthase, endothelial nitric-oxide synthase, and neuronal nitric-oxide synthase, plays pivotal roles in the regulation of cerebral blood flow and cell viability and in the protection of nerve cells or fibers against pathogenic factors associated with cerebral ischemia, trauma, and hemorrhage. Cerebral blood flow is increased and cerebral vascular resistance is decreased by NO derived from endothelial cells, autonomic nitrergic nerves, or brain neurons under resting and stimulated conditions. Somatosensory stimulation also evokes cerebral vasodilatation mediated by neurogenic NO. Oxygen and carbon dioxide alter cerebral blood flow and vascular tone mainly via constitutively formed NO. Endothelial dysfunction impairs cerebral hemodynamics by reducing the bioavailability of NO and increasing the production of reactive oxygen species (ROS). The NO-ROS interaction is an important issue in discussing blood flow and cell viability in the brain. Recent studies on brain circulation provide quite useful information concerning the physiological roles of NO produced by constitutive isoforms of nitric-oxide synthase and how NO may promote cerebral pathogenesis under certain conditions, including cerebral ischemia/stroke, cerebral vasospasm after subarachnoid hemorrhage, and brain injury. This information would contribute to better understanding of cerebral hemodynamic regulation and its dysfunction and to development of novel therapeutic measures to treat diseases of the central nervous system.

l-ARGININE CAUSES AMELIORATION OF CEREBROVASCULAR DYSFUNCTION AND BRAIN INFLAMMATION DURING EXPERIMENTAL HEATSTROKE

Cerebrovascular dysfunction ensuing from severe heatstroke includes intracranial hypertension, cerebral hypoperfusion, and brain inflammation. We attempted to assess whether L-arginine improves survival during experimental heatstroke by attenuating these reactions. Anesthetized rats, 70 min after the start of heat stress (43 degrees C), were divided into two major groups and given the following: vehicle solution (1 mL/kg body weight) or L-arginine (50-250 mg/kg body weight) intravenously. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiological and biochemical parameters were continuously monitored. When the vehicle-treated rats underwent heat stress, their survival time values were found to be 20 to 26 min. Treatment with i.v. doses of L-arginine significantly improved the survival rate during heatstroke (54-245 min). As compared with those of normothermic controls, all vehicle-treated heatstroke animals displayed higher levels of core temperature, intracranial pressure, and NO metabolite, glutamate, glycerol, lactate-pyruvate ratio, and dihydroxybenzoic acid in hypothalamus. In addition, hypothalamic levels of IL-1beta and TNF-alpha were elevated after heatstroke onset. In contrast, all vehicle-treated heatstroke animals had lower levels of MAP, cerebral perfusion pressure, cerebral blood flow, and brain partial pressure of oxygen. Administration of L-arginine immediately after the onset of heatstroke significantly reduced the intracranial hypertension and the increased levels of NO metabolite, glutamate, glycerol, lactate-pyruvate ratio, and dihydroxybenzoic acid in the hypothalamus that occurred during heatstroke. The heatstroke-induced increased levels of IL-1beta and TNF-alpha in the hypothalamus were suppressed by L-arginine treatment. In contrast, the hypothalamic levels of IL-10 were significantly elevated by L-arginine during heatstroke. The results suggest that L-arginine may cause attenuation of heatstroke by reducing cerebrovascular dysfunction and brain inflammation.

Human umbilical cord blood-derived CD34+ cells can be used as a prophylactic agent for experimental heatstroke

We attempted to assess the prophylactic effect of human umbilical cord blood-derived CD34(+) cells in experimental heatstroke. Anesthetized rats, 1 day before heat stress, were divided into 2 major groups and given CD34(-) cells (defined by 1 x 10(6) human cord blood lymphocytes and monocytes that contained <0.2% CD34(+) cells) or CD34(+) cells (defined by 1 x 10(6) human cord blood lymphocytes and monocytes that contained >95% CD34(+) cells). They were exposed to ambient temperature of 43 degrees C for 70 min to induce heatstroke. When the CD34(-) cells-treated or untreated rats underwent heat stress, their survival time values were found to be 20-24 min. Pretreatment with CD34(+) cells significantly increased survival time (123-351 min). As compared with normothermic controls, all CD34(-) cells-treated heatstroke animals displayed hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. However, these heatstroke reactions all were significantly suppressed by CD34(+) cells pretreatment. In addition, the levels of interleukin-10 in plasma and glial cell line-derived neurotrophic factors in brain were all significantly increased after CD34(+) cell administration during heatstroke. Our data indicate that human umbilical cord-derived CD34(+) cells can be used as a prophylactic agent for experimental heatstroke.

Human umbilical cord blood-derived CD34+ cells cause attenuation of multiorgan dysfunction during experimental heatstroke

Multiorgan dysfunction ensuing from severe heatstroke includes hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. We attempted to assess whether human umbilical cord blood-derived CD34+ cell therapy improves survival during experimental heatstroke by attenuating multiorgan dysfunction. Anesthetized rats, immediately after the onset of heatstroke, were divided into 2 major groups and given CD34- or CD34+ cells (1 x 10(5)-5 x 10(5)/mL/kg body weight) i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. Hypotension, hepatic and renal failure (evidenced by increased serum urea nitrogen, creatinine, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels in plasma), hypercoagulable state (evidenced by increased prothrombin time, activated partial thromboplastin time, and D-dimer, and decreased platelet count and protein C in plasma), activated inflammation (evidence by increased TNF-alpha levels in serum), and cerebral dysfunction (evidenced by intracranial hypertension, cerebral hypoperfusion and hypoxia, and cerebral ischemia and injury) were monitored. When the CD34- cell-treated or untreated rats underwent heat stress, their survival time values were found to be 19 to 23 min. Resuscitation with CD34+ cells significantly improved survival time (duration, 63-291 min). As compared with normothermic controls, all CD34- cell-treated heatstroke animals displayed hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. However, CD34+ cell therapy significantly caused attenuation of all the above-mentioned heatstroke reactions. In addition, the levels of IL-10 in plasma and glial cell line-derived neurotrophic factors in brain were all significantly increased after CD34+ cell therapy during heatstroke. Our data indicate that CD34+ cell therapy may resuscitate persons who had a heatstroke by reducing multiorgan dysfunction or failure.

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.

Resuscitation from experimental heatstroke by brain cooling therapy

We have used hypothermic retrograde jugular venous flush to cool the brain previously and to provide better resuscitation than peripheral cold saline infusion during heatstroke in the rat. The current study was performed to assess the effects of brain cooling further on production of reactive nitrogen species, reactive oxygen species, tumor necrosis factor-alpha, and interleukin-10 in both serum and brain during heatstroke. Rats, under general anaesthesia, were randomized into the following groups and given: (a) 36 degrees C or (b) 4 degrees C saline infusion in the external jugular vein immediately after onset of heatstroke. They were exposed to an ambient temperature of 43 degrees C for exactly 70 min to induce heatstroke. When the 36 degrees C saline-treated rats underwent heat stress, their survival time values were found to be 21-25 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline greatly improved survival (226-268 min). Compared with the normothermic controls, the 36 degrees C saline-treated heatstroke rats displayed higher levels of brain temperature, intracranial pressure, serum and hypothalamic nitric oxide metabolite, tumor necrosis factor-alpha and dihydroxybenzoic acid as well as hypothalamic inducible nitric oxide synthase immunoreactivity. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and hypothalamic levels of local blood flow, and partial pressure of oxygen were all significantly lower during heatstroke. The cerebrovascular dysfunction, the increased levels of nitric oxide metabolites, tumor necrosis factor-alpha, and dihydroxybenzoic acid in both the serum and the hypothalamus, and the increased levels of hypothalamic inducible nitric oxide synthase immunoreactivity occurred during heatstroke were significantly suppressed by brain cooling. Although the serum and hypothalamic interleukin-10 maintained at a negligible level before stress, they were significantly elevated by brain cooling during heatstroke. These findings suggest that brain cooling may resuscitate persons who had heatstroke by decreasing overproduction of reactive nitrogen species, tumor necrosis factor-alpha, reactive oxygen species and cerebrovascular dysfunction, but increasing production of interleukin-10.

Exercise pretraining protects against cerebral ischaemia induced by heat stroke in rats

BACKGROUND

In the rat brain, heat-stroke-induced damage to cerebral neurons is attenuated through heat-shock-induced overexpression of heat-shock protein 72 (HSP72).

OBJECTIVE

To ascertain whether progressive exercise preconditioning induces HSP72 expression in the rat brain and prevents heat-stroke-induced cerebral ischaemia and injury.

METHODS

Male Wistar rats were randomly assigned to either a sedentary group or an exercise group. Those in the exercise group progressively ran on a treadmill 5 days/week, for 30-60 min/day at an intensity of 20-30 m/min for 3 weeks. The effects of heat stroke on mean arterial pressure, cerebral blood flow, brain ischaemia markers (glutamate, lactate/pyruvate ratio and nitric oxide), a cerebral injury marker (glycerol) and brain neuronal damage score in the preconditioned animals were compared with effects in unexercised controls. Heat stroke was induced by exposing urethane-anaesthetised animals to a temperature of 43 degrees C for 55 min, which caused the body temperature to reach 42 degrees C.

RESULTS

Three weeks of progressive exercise pretreatment induced HSP72 preconditioning in the brain and conferred significant protection against heat-stroke-induced hyperthermia, arterial hypotension, cerebral ischaemia and neuronal damage; it also prolonged survival.

CONCLUSIONS

Exercise for 3 weeks can improve heat tolerance as well as attenuate heat-stroke-induced cerebral ischaemia in rats. The maintenance of mean arterial pressure and cerebral blood flow at appropriate levels in the rat brain may be related to overexpression of HSP72.

Inhibition of neuronal nitric oxide synthase causes attenuation of cerebrovascular dysfunction in experimental heatstroke

The present study was performed to assess the prophylactic effect of 7-nitroindazole (7-NI), an inhibitor of neuronal nitric oxide synthase (nNOS), in an animal model of heatstroke. Anesthetized rats, immediately before the start of heat stress, were divided into two major groups and given the following: vehicle solution (1 mL per kg body weight) or 7-NI (5-20mg/mL per kg body weight) intraperitoneally. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiologic and biochemical parameters were continuously monitored. When the vehicle-pretreated rats underwent heat stress, their survival time values were found to be 21-25 min. Pretreatment with intraperitoneal doses of 7-NI significantly improved survival during heatstroke (55-164 min). As compared to those of normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of core temperature, intracranial pressure, nitric oxide metabolite (NO(2)(-)), glutamate, glycerol, lactate/pyruvate ratio, neuronal damage score and nNOS expression in the hypothalamus, and tumor necrosis factor-alpha (TNF-alpha) in the serum. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain PO(2). Administration of 7-NI before the start of heat exposure significantly reduced the hyperthermia, intracranial hypertension, nNOS-dependent NO(2)(-), glutamate, glycerol, lactate/pyruvate ratio, and neuronal damage score in the hypothalamus, as well as overproduction of TNF-alpha in the serum that occurred during heatstroke. The data show that reduction of nNOS-dependent NO(2)(-) with 7-NI causes attenuation of cerebrovascular dysfunction, hyperthermia, and TNF-alpha overproduction during heatstroke in the rat.

Platonin, a cyanine photosensitizing dye, is effective for attenuation of heatstroke in rats

The present study was performed to assess the prophylactic effect of platonin, a cyanine photosensitizing dye and an inhibitor of proinflammatory cytokines, in an animal model of heatstroke. Anesthetized rats were immediately divided into 2 major groups after the start of heat stress and administered either isotonic sodium chloride solution (dose, 1 mL/kg of body weight i.v.) or platonin (dose, 12.5-50 microg/mL per kilogram of body weight i.v.). They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. Their physiological and biochemical parameters were continuously monitored. When the isotonic sodium chloride solution-pretreated rats underwent heat stress, their survival time values were found to be from 20 to 24 min. Pretreatment with intravenous doses of platonin (12.5-50 microg/mL per kilogram of body weight) immediately after the start of heat exposure significantly improved survival time during heatstroke (duration, 63-185 min). As compared with normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of creatinine, serum urea nitrogen, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, tumor necrosis factor alpha, prothrombin time, activated partial thromboplastin time and D-dimer in the plasma, cellular ischemia and injury markers in striatum, and intracranial pressure. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, brain Po2, and platelet count and protein C in the plasma. Immediately after the start of heat exposure, the previous administration of platonin significantly improved survival time by reducing the systemic inflammation, hypercoagulable state, and tissue ischemia and damage during heatstroke. The results demonstrate that platonin is effective for attenuation of heatstroke reactions.

The flavonoid baicalin protects against cerebrovascular dysfunction and brain inflammation in experimental heatstroke

The present study was performed to assess the prophylactic effect of baicalin, a flavonoid compound, in an animal model of heatstroke. Anesthetized rats, immediately before the start of heat stress, were divided into two major groups and given the following: vehicle solution (1mL per kg body weight) or baicalin (10-40mg per kg body weight) intravenously. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. Their physiologic and biochemical parameters were continuously monitored. When the vehicle-pretreated rats underwent heat stress, their survival time values were found to be 20-28min. Pretreatment with intravenous doses of baicalin significantly improved survival during heatstroke (65-248min). As compared to those of normothermic controls, all vehicle-pretreated heatstroke animals displayed higher levels of core temperature, intracranial pressure, and nitric oxide metabolite (NO(2)(-)), glutamate, glycerol, lactate/pyruvate ratio, and dihydroxybenzoic acid (DHBA) in hypothalamus. In addition, both serum and hypothalamic levels of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) as well as plasma levels of creatinine, serum urea nitrogen, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase and alkaline phosphatase were elevated after heatstroke onset. In contrast, all vehicle-pretreated heatstroke animals had lower levels of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain PO(2). Administration of baicalin before the start of heat exposure significantly reduced the hyperthermia, intracranial hypertension, and the increased levels of NO(2)(-), glutamate, glycerol, lactate/pyruvate ratio, and DHBA in the hypothalamus that occurred during heatstroke. The heatstroke-induced increased levels of IL-1beta and TNF-alpha in both the serum and hypothalamus, and renal and hepatic dysfunction were suppressed by baicalin pretreatment. In contrast, both the serum and hypothalamic levels of IL-10 were significantly elevated by baicalin during heatstroke. We successfully demonstrated that baicalin can be used as a prophylactic agent for heatstroke. In particular, baicalin may protect against cerebrovascular dysfunction and brain inflammation in heatstroke.

Oxidative stress and ischemic injuries in heat stroke

When rats were exposed to high environmental temperature (e.g., 42 or 43 degrees C), hyperthermia, hypotension, and cerebral ischemia and damage occurred during heat stroke were associated with increased production of free radicals (specifically hydroxyl radicals and superoxide anions), higher lipid peroxidation, lower enzymatic antioxidant defenses, and higher enzymatic pro-oxidants in the brain of heat stroke-affected rats. Pretreatment with conventional hydroxyl radical scavengers (e.g., mannitol or alpha-tocopherol) prevented increased production of hydroxyl radicals, increased levels of lipid peroxidation, and ischemic neuronal damage in different brain structures attenuated with heat stroke and increased subsequent survival time. Heat shock preconditioning (a mild sublethal heat exposure for 15min) or regular, daily exercise for at least 3 weeks, in addition to inducing overproduction of heat shock protein 72 in multiple organs including brain, significantly attenuated the heat stroke-induced hyperthermia, hypotension, cerebral ischemia and damage, and overproduction of hydroxyl radicals and lipid peroxidation. The precise function of heat shock protein 72 are unknown, but there is considerable evidence that these proteins are essential for survival at both normal and elevated temperatures. They also play a critical role in the development of thermotolerance and protection from oxidative damage associated with cerebral ischemia and energy depletion during heat stroke. In addition, Shengmai San or magnolol (Chinese herbal medicines) or hypervolemic hemodilution (produced by intravenous infusion of 10% human albumin) is effective for prevention and repair of ischemic and oxidative damage in the brain during heat stroke. Thus, it appears that heat shock protein 72 preconditioning induced by prior heat shock or regular exercise training, as well as pretreatment with Shengmai San or magnolol is able to prevent the oxidative damage during heat stroke. On the other hand, hypervolemic hemodilution, Shengmai San, or magnolol is able to treat the oxidative damage after heat stroke onset.

Cellular mechanisms of neuronal damage from hyperthermia

Hyperthermia can cause brain damage and also exacerbate the brain damage produced by stroke and amphetamines. The developing brain is especially sensitive to hyperthermia. The severity of, and mechanisms underlying, hyperthermia-induced neuronal death depend on both temperature and duration of exposure. Severe hyperthermia can produce necrotic neuronal death. For a window of less severe heat stresses, cultured neurons exhibit a delayed death with apoptotic characteristics including cytochrome c release and caspase activation. Little is known about mechanisms of hyperthermia-induced damage upstream of these late apoptotic effects. This chapter considers several possible upstream mechanisms, drawing on both in vivo and in vitro studies of the nervous system and other tissues. Hyperthermia-induced damage in some non-neuronal cells includes endoplasmic reticular stress due to denaturing of nascent polypeptide chains, as well as nuclear and cytoskeletal damage. Evidence is presented that hyperthermia produces mitochondrial damage, including depolarization, in cultured mammalian neurons.

Hypothermic preconditioning reduces Purkinje cell death possibly by preventing the over-expression of inducible nitric oxide synthase in rat cerebellar slices after an in vitro simulated ischemia

We showed that hypothermic preconditioning (HPC) increased survival of Purkinje neurons in rat cerebellar slices after oxygen-glucose deprivation (OGD). HPC also reduced the OGD-increased expression of high mobility group I (Y) proteins, a transcription factor that can enhance inducible nitric oxide synthase (iNOS) expression. iNOS is a putatively damaging protein that contributes to ischemic brain injury. Heat shock proteins (HSPs) can be induced by various stimuli to protect cells. We hypothesize that HPC induces neuroprotection by reducing the expression of putatively damaging proteins such as iNOS and/or by increasing the expression of putatively protective proteins such as HSPs. Cerebellar slices were prepared from adult male Sprague-Dawley rats and incubated in circulating artificial cerebrospinal fluid. OGD was for 20 min at 37 degrees C and was followed by a 5-h recovery at 37 degrees C before slices were used for morphological, immunohistochemical and Western analyses. HPC was performed by incubating slices at 33 degrees C for 20 min at 1 h before the OGD. HPC and aminoguanidine, an iNOS inhibitor, prevented OGD-induced Purkinje cell death/injury. OGD increased the expression of iNOS and nitrosylated proteins. These increases were abolished by aminoguanidine and HPC. Interestingly, the expression of HSP70 was increased by OGD but not by HPC. Our results suggest that an increased iNOS expression contributes to the pathophysiology of OGD-induced Purkinje neuronal death in our model. Our results also suggest the involvement of inhibiting the expression of the putatively damaging iNOS proteins in the HPC-induced neuroprotection. HSP70 may not contribute to the HPC-induced neuroprotection.

BRAIN COOLING CAUSES ATTENUATION OF CEREBRAL OXIDATIVE STRESS, SYSTEMIC INFLAMMATION, ACTIVATED COAGULATION, AND TISSUE ISCHEMIA/INJURY DURING HEATSTROKE

The purpose of the present study was to assess the therapeutic effect of hypothermic retrograde jugular vein flush (HRJVF) on heatstroke. HRJVF was accomplished by infusion of 4 degrees C isotonic sodium chloride solution via the external jugular vein (1.7 mL/100 g of body weight over 5 min). Immediately after the onset of heatstroke, anesthetized rats were divided into 2 major groups and given the following: 36 degrees C or 4 degrees C isotonic sodium chloride solution, i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats was exposed to room temperature (24 degrees C) and used as normothermic controls. When the 36 degrees C saline-treated rats underwent heat exposure, their survival time values were found to be 23 to 28 min. Immediately after the onset of heatstroke, resuscitation with an i.v. dose of 4 degrees C saline significantly improved survival during heatstroke (208-252 min). All heat-stressed animals displayed systemic inflammation and activated coagulation, evidenced by increased tumor necrosis factor alpha, prothrombin time, activated partial thromboplastin time, and d-dimer, and decreased platelet count and protein C. Biochemical markers evidenced cellular ischemia and injury/dysfunction: plasma levels of blood urea nitrogen, creatinine, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and alkaline phosphatase; and striatal levels of glycerol, glutamate, and lactate/pyruvate; dihydroxy benzoic acid, lipid peroxidation, oxidized-form glutathione reduced-form glutathione, dopamine, and serotonin were all elevated during heatstroke. Core and brain temperatures and intracranial pressure were also increased during heatstroke. In contrast, the values of mean arterial pressure, cerebral perfusion pressure, and striatal levels of local blood flow, partial pressure of oxygen, superoxide dismutase, catalase, glutathione peroxidase, and glutathions reductase activities were all significantly lower during heatstroke. The circulatory dysfunction, systemic inflammation, hypercoagulable state, and cerebral oxidative stress, ischemia, and damage during heatstroke were all significantly suppressed by HRJVF. These findings demonstrate that brain cooling caused by HRJVF therapy may resuscitate persons who had a stroke by attenuating cerebral oxidative stress, systemic inflammation, activated coagulation, and tissue ischemia/injury during heatstroke.

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.

Cardiovascular responses and neurotransmitter changes during static muscle contraction following blockade of inducible nitric oxide synthase (iNOS) within the ventrolateral medulla

The enzyme nitric oxide synthase (NOS) which is necessary for the production of nitric oxide from L-arginine exists in three isoforms: neuronal NOS (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS). Our previous studies have demonstrated the roles of nNOS and eNOS within the rostral (RVLM) and caudal ventrolateral medulla (CVLM) in modulating cardiovascular responses during static skeletal muscle contraction via altering localized glutamate and GABA levels (Brain Res. 977 (2003) 80-89; Neuroscience Res. 52 (2005) 21-30). In this study, we investigated the role of iNOS within the RVLM and CVLM on cardiovascular responses and glutamatergic/GABAergic neurotransmission during the exercise pressor reflex. Bilateral microdialysis of a selective iNOS antagonist, aminoguanidine (AGN; 1.0 microM), for 60 min into the RVLM attenuated increases in mean arterial pressure (MAP), heart rate (HR), and extracellular glutamate levels during a static muscle contraction. Levels of GABA within the RVLM were increased. After 120 min of discontinuation of the drug, MAP and HR responses and glutamate/GABA concentrations recovered to baseline values during a subsequent muscle contraction. In contrast, bilateral application of AGN (1.0 microM) into CVLM potentiated cardiovascular responses and glutamate concentration while attenuating levels of GABA during a static muscle contraction. All values recovered after 120 min of discontinuation of the drug. These results demonstrate that iNOS within the ventrolateral medulla plays an important role in modulating cardiovascular responses and glutamatergic/GABAergic neurotransmission that regulates the exercise pressor reflex.

Infusion of human umbilical cord blood cells protect against cerebral ischemia and damage during heatstroke in the rat

Intravenously delivered human umbilical cord blood cells (HUCBC) have been previously shown to improve both morphologic and functional recovery of heat-stroked rats. To extend these findings, we examined both the morphologic and functional alterations in the presence of HUCBC or human peripheral mononuclear cells (PBMC) 24 h before initiation of heatstroke. Anesthetized rats, 1 day before the initiation of heatstroke, were divided into three major groups and given the following: (a) serum-free lymphocyte medium (0.3 ml) intravenously; (b) PBMC (5 x 10(6) in 0.3 ml serum-free lymphocyte medium); or (c) HUCBC (5 x 10(6) in 0.3 ml serum-free lymphocyte medium). Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. In vehicle-treated heatstroke rats, their mean arterial pressure, cerebral blood flow, and brain PO(2) were all lower than in normothermic controls after the onset of heatstroke. However, their body temperatures and striatal levels of inducible nitric oxide synthase (iNOS)-dependent NO, ischemia and damage markers (e.g., glycerol, glutamate, and lactate/pyruvate ratio), and neuronal damage in the striatum were all greater. The heatstroke-induced arterial hypotension, cerebral ischemia and hypoxia, and increased levels of iNOS-dependent NO in the striatum were all significantly reduced by pretreatment with HUCBC, but not with PBMC. Moreover, HUCBC were localized by immunohistochemistry and PCR analysis in the injured brain structures and spleen. These findings indicate that HUCBC transplantation, in addition to having therapeutic values, can be a good choice for preventing heatstroke occurrence.

Arginine metabolic pathways determine its therapeutic benefit in experimental heatstroke: role of Th1/Th2 cytokine balance

We have demonstrated that therapeutic administration of L-arginine (L-arg) (120 mg/kg) at +2 h of whole body hyperthermia (WBH) could rescue the mice from heatstroke-induced death. Studies were undertaken to elucidate the role of L-arg in the immunomodulation of the heat-stressed mice. Administration of L-arginine (L-arg), (120 mg/kg, i.p.), at +2 h of WBH, rescued the mice from heat-induced death and reduced the hypothermia. At +4 and +24 h of WBH, levels of IL-1beta, IFN-gamma, nitrite, TNF-alpha, IL-4, TGF-beta1, inducible form of nitric oxide synthase (iNOS), and corticosterone significantly increased compared to the sham group. The elevated levels of Th(1) cytokines, namely TNF-alpha, IL-1beta, IFN-gamma, nitrite, and iNOS, decreased significantly both at +4 and +24 h of WBH, following L-arg administration. However, L-arg administration did not reduce the increased levels of Th(2) cytokines, namely IL-4 and TGF-beta1, in WBH mice at +4 h of WBH. L-arg administration significantly increased the levels of Th(2) cytokines at +24 h of WBH, compared to the saline-treated WBH mice. L-arg administration significantly increased both the splenic and hepatic arginase activity at +4 and +24 h of WBH compared to the saline-treated WBH mice. L-NAME treatment at +2 h of WBH and anti-TGF-beta antibody treatment at 0 h of WBH significantly increased the mortality compared to the saline-treated WBH mice. Altered liver histopathology was attenuated following the administration of L-arg at +2 h of WBH. These results suggest that therapeutic administration of L-arg at appropriate concentration and time attenuates the acute inflammatory response, leading to the rescue of mice from heatstroke.

Pathophysiological factors underlying heatstroke

Heatstroke is a life-threatening illness characterized by an elevated core body temperature (>40 degrees C) and dysfunction of central nervous system, which results in delirium, convulsions, or coma. Despite adequate hypothermia or other care-therapy, heatstroke is often fatal. On the basis of our knowledge of the pathophysiology on heatstroke, we hypothesized that heatstroke is a form of hyperthermia associated with the acute physiological alterations, the cytotoxicity of heat, systemic inflammatory response, oxidative damage and attenuated heat-shock response leading to a syndrome of multi-organ dysfunction. In view of above-mentioned situation, the physiological factors underlying heatstroke and the corresponding possible therapeutic strategies to avert the complications of this disorder would be summarized in this review so as to provide some therapeutic guidelines for heatstroke. Heatstroke is a very complicated process. Acute physiological alterations, such as low arterial hypotension, intracranial hypertension, cerebral hypoperfusion, cerebral ischemia, and increased intracellular metabolism rate, occurred while exposed to a high ambient temperature. Hyperpyrexia caused cytotoxicity, resulting the degradation and aggregation of extensive intracellular proteins, influencing the change of membrane stability and fluidity, damaging the transmembrane transport of protein and the function of surface receptor, and inducing different cytoskeletal changes. Heatstroke resembles sepsis in many aspects, and endotoxemia and cytokines may be implicated in its pathogenesis. The concentration of interleukin-6 was positively correlated with the severity of heatstroke. The excessive accumulation of cytotoxic free radicals and oxidative damage may occur in the brain tissues during the genesis and development of heatstroke. The circulatory shock and cerebral ischemia resultant from heatstroke correlated closely with the free radicals (especially free radicals of peroxide and superoxide), the peroxidation of lipids, and low activity of antioxidase in the brain. Heat-shock proteins (Hsps) played a critical role during the process obtaining thermotolerance, therefore, protected from stress-induce cellular damage. Host factors or physiologically limiting factors, for instance, aging, existing illness, dehydration, deep insomnia, lack of acclimation to heat, inadequate physical fitness, and certain genetic polymorphisms were associated with a low level of Hsps expression and might favor the progression from heat stress to heatstroke. Some measures, such as molecular chaperonines, anti-inflammatory agents, antioxidant agents, and modulators of Hsps would be good for the patients with heatstroke.

Lentivirus infection causes neuroinflammation and neuronal injury in dorsal root ganglia: pathogenic effects of STAT-1 and inducible nitric oxide synthase

Distal sensory polyneuropathy (DSP) is currently the most common neurological complication of HIV infection in the developed world and is characterized by sensory neuronal injury accompanied by inflammation, which is clinically manifested as disabling pain and gait instability. We previously showed that feline immunodeficiency virus (FIV) infection of cats caused DSP together with immunosuppression in cats, similar to that observed in HIV-infected humans. In this study, we investigated the pathogenic mechanisms underlying the development of FIV-induced DSP using feline dorsal root ganglia (DRG) cultures, consisting of neurons, Schwann cells, and macrophages. FIV-infected cultures exhibited viral Ags (p24 and envelope) in macrophages accompanied by neuronal injury, indicated by neurite retraction, neuronal loss and decreased soma size, compared with mock-infected (control) cultures. FIV infection up-regulated inducible NO synthase (iNOS), STAT-1, and TNF-alpha mRNA levels in DRG cultures. Increased STAT-1 and iNOS mRNA levels were also observed in DRGs from FIV-infected animals relative to mock-infected controls. Similarly, immunolabeling studies of DRGs from FIV-infected animals showed that macrophages were the principal sources of STAT-1 and iNOS protein production. The iNOS inhibitor aminoguanidine reduced nitrotyrosine and protein carbonyl levels, together with preventing neuronal injury in FIV-infected DRG cultures. The present studies indicate that FIV infection of DRGs directly contributes to axonal and neuronal injury through a mechanism involving macrophage immune activation, which is mediated by STAT-1 and iNOS activation.

SHENG MAI SAN, A CHINESE HERBAL MEDICINE, PROTECTS AGAINST RENAL ISCHAEMIC INJURY DURING HEAT STROKE IN THE RAT

1. There is evidence that the induction of inducible nitric oxide synthase (iNOS) and peroxynitrite by ischaemia/reperfusion may lead to renal cell injury. Herein, we investigated whether Sheng mai san (SMS), a Chinese herbal medicine, protects against renal ischaemic injury during heat stroke by reducing iNOS-dependent nitric oxide (NO) and peroxynitrite formation. 2. Urethane-anaesthetized rats were exposed to heat stress (ambient temperature 43 degrees C) to induce heat stroke. Control rats were exposed to 24 degrees C. Mean arterial pressure and renal blood flow after the onset of heat stroke were significantly lower in heat stroke rats than in control rats. However, both colonic temperature and renal damage score were greater in heat stroke rats compared with control rats. Similarly, plasma NO, creatinine and blood urea nitrogen (BUN), as well as the renal immunoreactivity of iNOS and peroxynitrite, were significantly higher in heat stroke rats compared with their normothermic controls. 3. Pretreatment with SMS (1.2 g/day per rat for 7 consecutive days before the initiation of heat stress) significantly attenuated the heat stroke-induced arterial hypotension, hyperthermia, renal ischaemia and damage, the increased renal immunoreactivity of iNOS and peroxynitrite and the increased plasma levels of NO, creatinine and BUN. Pretreatment with SMS resulted in a prolongation of survival time in heat stroke. 4. The results of the present study suggest that SMS protects against renal ischaemic damage by reducing iNOS-dependent NO and peroxynitrite production during heat stroke.

Resuscitation from experimental heatstroke by transplantation of human umbilical cord blood cells

OBJECTIVE

Human umbilical cord blood cells (HUCBCs) are effective in the treatment of conventional stroke in experimental models. In the study described herein, we administered HUCBCs into the femoral vein or directly into the cerebral ventricular system and assessed their effects on circulatory shock, cerebral ischemia, and damage during heatstroke.

DESIGN

Controlled, prospective study.

SETTING

Hospital medical research laboratory.

SUBJECTS

Sprague-Dawley rats (287 +/- 16 g body weight, males).

INTERVENTIONS

Anesthetized rats, immediately after the onset of heatstroke, were divided into four major groups and given the following: a) normal saline or AIM-V medium intravenously (0.3 mL) or intracerebroventricularly (10 microL); b) peripheral blood mononuclear cells (5 x 10 in 0.3 mL AIM-V medium, intravenously, or 5 x 10 in 10 microL AIM-V medium, intracerebroventricularly); or c) HUCBCs (5 x 10 in 0.3 mL AIM-V medium, intravenously, or 5 x 10 in 10 microL AIM-V medium, intracerebroventricularly). Another group of rats, under urethane anesthesia, were exposed to room temperature (26 degrees C) and used as normothermic controls. Urethane-anesthetized animals were exposed to an ambient temperature of 43 degrees C to induce heatstroke. Their physiologic and biochemical parameters were continuously monitored.

MEASUREMENTS AND MAIN RESULTS

When the vehicle-treated rats underwent heat exposure, their survival time values were found to be 21-23 mins. Resuscitation with intravenous or intracerebroventricular doses of HUCBCs, but not peripheral blood mononuclear cells, immediately at the onset of heatstroke significantly improved survival during heatstroke (61-148 mins). As compared with values for normothermic controls, the vehicle-treated heatstroke rats had lower mean arterial pressure, cerebral blood flow, and brain PO2 values but higher intracranial pressure and cerebral ischemia values and more injury markers. The circulatory shock, intracranial hypertension, cerebral hypoperfusion and hypoxia, increment of cerebral ischemia, and damage markers during heatstroke were all significantly attenuated by intravenous or intracerebroventricular delivery of HUCBCs but not peripheral blood mononuclear cells.

CONCLUSIONS

We successfully demonstrate that HUCBC therapy may resuscitate heatstroke victims by reducing circulatory shock and cerebral ischemic injury; central delivery of HUCBCs seems superior to systemic delivery of HUCBCs in resuscitating patients with heatstroke.

Shengmai San, a Chinese Herbal Medicine Protects Against Rat Heat Stroke by Reducing Inflammatory Cytokines and Nitric Oxide Formation

The aim of the present study was to ascertain whether the possible occurrence of overproduction of inducible nitric oxide synthase (iNOS)-dependent nitric oxide (NO) in the brain and inflammatory cytokines in the peripheral blood exhibited during heat stroke can be reduced by prior administration of Shengmai San, a Chinese herbal medicine. Aminoguanidine, an iNOS inhibitor, was evaluated at the same time as a reference (positive control). Urethane-anesthetized rats were exposed to heat stress (ambient temperature of 43 degrees C) to induce heat stroke. Control rats were exposed to 24 degrees C. Mean arterial pressure and cerebral blood flow after the onset of heat stroke were all significantly lower than in control rats. However, cerebral iNOS immunoreactivity and NO levels were all greater after the onset of heat stroke. The serum levels of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha were all increased after the onset of heat stroke. Shengmai San (1.2 g/ml per rat) or aminoguanidine (30 micromol/ml per rat) was administered orally, daily, and consecutively for 7 days before the initiation of heat stress; and this significantly attenuated the heat stress-induced arterial hypotension, cerebral ischemia, and increased levels of brain iNOS-dependent NO production and serum cytokines formation. Shengmai San shared with the aminoguanidine almost the same efficacy in reducing iNOS-dependent NO and cytokines overproduction during heat stroke. These results suggest that Shengmai San or aminoguanidine protects against heat stroke-induced arterial hypotension and cerebral ischemia by inhibition of iNOS-dependent NO overproduction in the brain and excessive accumulation of several inflammatory cytokines in the peripheral blood stream.

Naltrexone Protects Against Hypotension, Hyperthermia, and β-Endorphin Overproduction During Heatstroke in the Rat

Heat stroke is characterized by hyperthermia, arterial hypotension, decreased baroreflex sensitivity, and increased serum levels of beta-endorphin. Whereas naltrexone may have therapeutic potential in heat stroke, the underlying mechanism remains unclear. We tested the hypothesis that naltrexone may attenuate heat stroke by reducing hyperthermia, hypotension, decreased baroreceptor sensitivity, and/or increased serum levels of beta-endorphin. Heat stroke was induced by exposing the anesthetized adult Sprague-Dawley rats in an incubator at 43 degrees C. The moment in which the mean arterial pressure dropped irreversibly from the peak level was taken as the onset of heat stroke. Control rats were exposed to 24 degrees C. Mean arterial pressure, baroreceptor sensitivity, and maximal reflex bradycardia, after the onset of heat stroke, were all significantly lower than in control rats. However, rectal temperature and serum levels of beta-endorphin were all greater after the onset of heat stroke. Intravenous delivery of naltrexone (10 mg/kg) 20 min before the initiation of heat stress, but not immediately at the onset of heat stroke, significantly attenuated the above-mentioned reactions. Accordingly, naltrexone improved survival during heat stroke. These results suggest that naltrexone protects against hypotension and decrement of both baroreceptor sensitivity and maximal reflex bradycardia during heat stroke by reducing both hyperthermia and increment of serum beta-endorphin and thus improves survival.

Chinese Herbal Medicine, Shengmai San, Is Effective for Improving Circulatory Shock and Oxidative Damage in the Brain During Heatstroke

The aim of this study was to investigate the effect of Shengmai San (SMS), a traditional Chinese herbal medicine, on heatstroke-induced circulatory shock and oxidative damage in the brain in rats. Anesthetized rats were exposed to a high ambient temperature (43 degrees C) to induce heatstroke. After the onset of heatstroke, the values of mean arterial pressure, cerebral perfusion pressure, cerebral blood flow, and brain partial pressure of O(2) were all significantly lower than those in normothermic controls. However, the values of intracranial pressure, brain and colonic temperatures, and brain levels of free radicals, lipid peroxidation, and cellular ischemia and damage markers were all greater in heatstroke rats compared with those of normothermic controls. Pretreatment or post-treatment with SMS significantly reduced the hypotension, intracranial hypertension, cerebral hypoperfusion and hypoxia and increased levels of ischemia and damage markers in the brain during heatstroke. The protective effects exerted by SMS pretreatment is superior to those of SMS post-treatment. The results demonstrate that SMS is effective for prevention and repair of circulatory shock and ischemic and oxidative damage in the brain during heatstroke.

Selective Inhibition of Inducible Nitric Oxide Synthase Attenuates Renal Ischemia and Damage in Experimental Heatstroke

The aim of the present study was to determine whether the possible occurrence of renal ischemia and damage during heatstroke can be suppressed by prior administration of L-N6-(1-iminoethyl) lysine (L-NIL), a selective inducible nitric oxide synthase (iNOS) inhibitor. Urethane-anesthetized rats were exposed to heat stress (43 degrees C) to induce heatstroke. Control rats were exposed to 24 degrees C. Mean arterial pressure and renal blood flow after the onset of heatstroke both were significantly lower in vehicle-treated heatstroke rats than in normothermic controls. However, both the body temperature and renal damage scores were greater in vehicle-treated heatstroke rats compared with normothermic controls. Plasma nitric oxide (NO), creatinine, and blood urea nitrogen (BUN), as well as the renal immunoreactivity of iNOS and peroxynitrite all were significantly higher in vehicle-treated heatstroke rats compared with their normothermic controls. Pretreatment with L-NIL (3 mg/kg, administered intravenously and immediately at the onset of heat stress) significantly attenuated heatstroke-induced hyperthermia, arterial hypotension, renal ischemia and damage, increased renal levels of immunoreactivity of iNOS and peroxynitrite, and increased plasma levels of NO, creatinine, and BUN. Accordingly, pretreatment with L-NIL significantly improved survival during heatstroke. The results suggest that selective inhibition of iNOS-dependent NO and peroxynitrite formation protects against renal ischemia and damage during heatstroke by reducing hyperthermia and arterial hypotension.