Efficacy of mild hypothermia for the treatment of patients with cardiac arrest

Protective effects of mild hypothermia against hepatic injury in rats with acute liver failure

INTRODUCTION AND OBJECTIVES

Acute liver failure (ALF) is a severe disease which is associated with a high mortality rate. As mild hypothermia has been shown to have protective effects on the brain, this study aimed to determine whether it also provides protection to the liver in rats with ALF and to explore its underlying mechanism.

MATERIALS AND METHODS

In total, 72 rats were divided into 3 groups: control group (CG, treated with normal saline), normothermia group (NG, treated with d-galactosamine and lipopolysaccharide; d-GalN/LPS), and mild hypothermia group (MHG, treated with d-GalN/LPS and kept in a state of mild hypothermia, defined as an anal temperature of 32-35°C). The rats were examined at 4, 8, and 12h after treatment.

RESULTS

Mild hypothermia treatment significantly reduced serum alanine transaminase and aspartate transaminase levels and improved the liver condition of rats with d-GalN/LPS-induced ALF at 12h. Serum tumor necrosis factor-alpha levels were significantly lower in the MHG than in the NG at 4h, but no significant differences were observed in the interleukin-10 levels between the NG and MHG at any time. The serum and hepatic levels of high mobility group box 1 were significantly lower in the MHG than in the NG at 8 and 12h. The protein expression levels of cytochrome C and cleaved-caspase 3 in hepatic tissues were significantly lower in the MHG than in the NG at 8h.

CONCLUSION

Mild hypothermia improved the liver conditions of rats with ALF via its anti-inflammatory and anti-apoptotic effects.

Therapeutic hypothermia attenuates global cerebral reperfusion-induced mitochondrial damage by suppressing dynamin-related protein 1 activation and mitochondria-mediated apoptosis in a cardiac arrest rat model

Therapeutic hypothermia is effective to attenuate brain ischemia/reperfusion (I/R) injury after cardiac arrest, and multiple mechanisms have been proposed. Dynamin-related protein 1 (Drp1), a large GTPases of dynamin superfamily, predominantly controls mitochondrial fission and is related to IR-induced Cyt C release and apoptosis. However, the effect of therapeutic hypothermia on Drp1 and mitochondrial fission after cardiac arrest remains still unclear. In this study, non-cardiac arrest and post-cardiac arrest rats received 6-h normothermia (37-38°C) or therapeutic hypothermia (32-34°C), and the hippocampus was harvested at 6h and 72h after cardiac arrest. Results showed the expression of Drp1 and Cyt C increased after cardiac arrest, but therapeutic hypothermia partially reversed this increase at 6h after cardiac arrest. Transmission electron microscopy (TEM) also showed a change in morphology following therapeutic hypothermia after cardiac arrest. Moreover, therapeutic hypothermia could decrease the histopathological damage, inhibit the apoptosis of CA1 neurons and improve the survival and neurological outcomes at 72h after cardiac arrest. Taken together, our study demonstrates that therapeutic hypothermia is neuroprotective against global cerebral I/R injury, which is, at least partially, ascribed to the inhibition Drp1 and Cyt C expression and the protection of mitochondrial structure.

Therapeutic Hypothermia Enhances Cold-Inducible RNA-Binding Protein Expression and Inhibits Mitochondrial Apoptosis in a Rat Model of Cardiac Arrest

Therapeutic hypothermia is well known for its protective effect against brain injury after cardiac arrest, but the exact mechanism remains unclear. Cold-inducible RNA-binding protein (CIRP), a member of cold shock protein, enables mammalian cells to withstand decreased temperature by regulating gene translation. However, the role of CIRP in global cerebral ischemia after therapeutic hypothermia has not been clearly elucidated. In the present study, rats resuscitated from 4 min of cardiac arrest were separately treated with therapeutic hypothermia (immediately after return of spontaneous circulation (ROSC); targeted temperature at 33 °C) and therapeutic normothermia (targeted temperature at 36.8 °C) for 6 h. The hippocampus was harvested at 0 h (baseline), 6 h, 12 h, 1 day, 3 days, and 7 days after ROSC. The expression of CIRP messenger RNA (mRNA) was assessed by real-time PCR. CIRP and mitochondrial apoptosis-associated proteins were tested by Western blot. The histological changes and neurological function were respectively evaluated by hematoxylin-eosin staining and neurological deficit score (NDS). Compared with baseline, rats resuscitated from cardiac arrest showed increased expression of CIRP, Bax, Caspase 9, and Caspase 3 and decreased expression of Bcl-2 in hippocampus (P < 0.05). However, therapeutic hypothermia after ROSC alleviated the alterations of Bax, Caspase 9, Caspase 3, and Bcl-2, while further increased the hippocampal expression of CIRP mRNA and protein, when compared with the normothermia rats (P < 0.05). In addition, compared with the therapeutic normothermia rats, histopathological damage in CA1 zone and NDS were respectively decreased and increased in the hypothermia rats (P < 0.05). Our findings suggest that 32 °C therapeutic hypothermia exerts an important neuroprotective effects by up-regulating CIRP expression and inhibiting mitochondrial apoptosis factor production in the cardiac arrest rat model.