Novel method for inducing rapid, controllable therapeutic hypothermia in rats using a perivascular implanted closed-loop cooling circuit

Water Rewarming After Seawater Hypothermia Mitigates IL-1β in Both Intestinal Tissue and Blood

In this study, the rat models of severe hypothermia induced by seawater immersion were established in artificial seawater immersion at 15°C for 5 hours. With the rewarming measurement of 37°C water bath, the rewarming effects were evaluated by monitoring basic vital signs and dynamically detecting intestinal inflammation cytokines. Fifty Sprague-Dawley rats were randomly divided into five groups including the control group (group C), hypothermia group (group H), 2-hour rewarming group (group R2), 6-hour rewarming group (group R6), and 12-hour rewarming group (group R12), with 10 in each group. The basic vital signs of rats (i.e., core temperature, respiration, heart rate, and muscle tremor) were constantly recorded. The inflammatory factors were detected in the intestinal tissue via a protein chip GSR-CAA-67 of Innopsys, and the verification by reverse transcription-quantitative polymerase chain reaction. The levels of cytokines (interleukin IL-1β, IL-6, and IL-10) were detected from blood samples collected at the end of the observation period via enzyme-linked immunosorbent assay. The expression landscape of IL-1β in the intestinal tissue was validated by immunohistochemistry. Five hours of immersion in artificial seawater at 15°C successfully induced severe hypothermia of rats. After 2 hours of constant water bath rewarming at 37°C, the basic vital signs recovered to the normal level and maintained stably as well as the acute inflammatory reaction alleviated effectively, which indicated that 37°C of water immersion rewarming had the potential to be a suitable method for early treatment of water immersion hypothermia. After the process of hypothermia, several inflammatory cytokines of rats in rewarming groups changed distinctly with IL-1β, showing the most significant variations compared with group C, which confirmed IL-1β as a potential monitoring biomarker referring to the therapeutic effect of rewarming for severe hypothermia caused by seawater immersion.

Differential effects of hypothermia on neurovascular unit determine protective or toxic results: Toward optimized therapeutic hypothermia

Therapeutic hypothermia (TH) benefits survivors of cardiac arrest and neonatal hypoxic-ischemic injury and may benefit stroke patients. Large TH clinical trials, however, have shown mixed results. Given the substantial pre-clinical literature supporting TH, we explored possible mechanisms for clinical trial variability. Using a standard rodent stroke model (n = 20 per group), we found smaller infarctions after 2 h pre- or post-reperfusion TH compared to 4 h. To explore the mechanism of this discrepancy, we used primary cell cultures of rodent neurons, astrocytes, or endothelial cells subjected to oxygen-glucose deprivation (OGD). Then, cells were randomly assigned to 33℃, 35℃ or 37℃ for varying durations after varying delay times. Both 33 and 35℃ TH effectively preserved all cell types, although 33℃ was superior. Longer cooling durations overcame moderate delays to cooling initiation. In contrast, TH interfered with astrocyte paracrine protection of neurons in a temperature-dependent manner. These findings suggest that longer TH is needed to overcome delays to TH onset, but shorter TH durations may be superior to longer, perhaps due to suppression of astrocytic paracrine support of neurons during injury. We propose a scheme for optimizing TH after cerebral injury to stimulate further studies of cardiac arrest and stroke.

Therapeutic hypothermia for ischemic stroke; pathophysiology and future promise

Therapeutic hypothermia, or cooling of the body or brain for the purposes of preserving organ viability, is one of the most robust neuroprotectants at both the preclinical and clinical levels. Although therapeutic hypothermia has been shown to improve outcome from related clinical conditions, the significance in ischemic stroke is still under investigation. Numerous pre-clinical studies of therapeutic hypothermia has suggested optimal cooling conditions, such as depth, duration, and temporal therapeutic window for effective neuroprotection. Several studies have also explored mechanisms underlying the mechanisms of neuroprotection by therapeutic hypothermia. As such, it appears that cooling affects multiple aspects of brain pathophysiology, and regulates almost every pathway involved in the evolution of ischemic stroke. This multifaceted mechanism is thought to contribute to its strong neuroprotective effect. In order to carry out this therapy in optimal clinical settings, methodological and pathophysiological understanding is crucial. However, more investigation is still needed to better understand the underlying mechanisms of this intervention, and to overcome clinical barriers which seem to preclude the routine use therapeutic hypothermia in stroke. This article is part of the Special Issue entitled 'Cerebral Ischemia'.