Selected Contribution: Hypothermic protection of the ischemic heart via alterations in apoptotic pathways as assessed by gene array analysis

Abstract

Hypothermia improves resistance to ischemia in the cardioplegia-arrested heart. This adaptive process produces changes in specific signaling pathways for mitochondrial proteins and heat-shock response. To further test for hypothermic modulation of other signaling pathways such as apoptosis, we used various molecular techniques, including cDNA arrays. Isolated rabbit hearts were perfused and exposed to ischemic cardioplegic arrest for 2 h at 34 degrees C [ischemic group (I); n = 13] or at 30 degrees C before and during ischemia [hypothermic group (H); n = 12]. Developed pressure, the maximum first derivative of left ventricular pressure, oxygen consumption, and pressure-rate product (P < 0.05) recovery were superior in H compared with in I during reperfusion. mRNA expression for the mitochondrial proteins, adenine translocase and the beta-subunit of F1-ATPase, was preserved by hypothermia. cDNA arrays revealed that ischemia altered expression of 13 genes. Hypothermia modified this response to ischemia for eight genes, six related to apoptosis. A marked, near fivefold increase in transformation-related protein 53 in I was virtually abrogated in H. Hypothermia also increased expression for the anti-apoptotic Bcl-2 homologue Bcl-x relative to I but decreased expression for the proapoptotic Bcl-2 homologue bak. These data imply that hypothermia modifies signaling pathways for apoptosis and suggest possible mechanisms for hypothermia-induced myocardial protection.

Hypothermia in cardiogenic shock reduces systemic t-PA release

“…It has been shown that mild hypothermia can prevent ischemic cells from entering apoptosis through prevention of mitochondrial dysfunction and inhibition of caspase release [25][26][27]. Moreover, hypothermia has been shown to improve ion homeostasis, decrease free radical formation, stabilize cellular membranes and prevent intracellular acidosis [21].…”

“…In an experimental setting, mild hypothermia has a positive effect on contractility, but deep hypothermia has been associated with deterioration in cardiac function [19,20]. The tissue-protective mechanism of action is multi-factorial and partly unknown [20][21][22][23][24][25][26][27]. We recently found that hypothermia reduces ischemia related coronary t-PA release, suggesting a possible role for t-PA as a mechanism for reperfusion injury that may be affected by hypothermia [28].…”

Mild hypothermia markedly reduces ischemia related coronary t-PA release

“…However, reduced oxygen demand does not fully explain the positive effects of hypothermia and several additive effects have been suggested [35]. It has been shown that mild hypothermia can prevent ischemic cells from entering apoptosis through prevention of mitochondrial dysfunction and inhibition of caspase release [36][37][38]. Moreover, therapeutic hypothermia has been shown to improve ion homeostasis, suppress ischemia induced inflammatory reactions, decrease free radical formation, stabilize cellular membranes and prevent intracellular acidosis [39].…”

Moderate hypothermia prevents neural cell apoptosis following spinal cord ischemia in rabbits

“…The first-strand cDNA was synthesized by SuperScript II reverse transcriptase (Invitrogen) at 42°C for 1 h. The reaction was terminated at 70°C for 15 min. 1 µL of the cDNA mixture was used for subsequent PCR (10 µL) with the following primer set: bcl-2 forward, 5'-GTGGCCTTCTTTGAGTTCG-3'; bcl-2 reverse, 5'-CTTCAGAGACAGCCAGGAG-3' (product size 212bp) [16] p53 forward, 5'-ACCTTCCGACACAGCGTGGT-3'; p53 reverse, 5'-CTCCATCCAGCGGCTTCTTC-3' (349bp) [17] glyceraldehyde-3-phosphate dehydrogenase (GAPDH) forward, 5'-ACCACGGTG CACGCCATCAC-3', GAPDH reverse, 5'-TCCACCACCCTGTT GCTGTA-3' (454bp). PCR were conducted with an initial denaturation at 94°C for 5 min followed by 35 cycles (bcl-2 and p53) and 25 cycles (GAPDH) of amplification.…”