Mechanical Postconditioning Promotes Glucose Metabolism and AMPK Activity in Parallel with Improved Post-Ischemic Recovery in an Isolated Rat Heart Model of Donation after Circulatory Death

Abstract

Donation after circulatory death (DCD) could improve donor heart availability; however, warm ischemia-reperfusion injury raises concerns about graft quality. Mechanical postconditioning (MPC) may limit injury, but mechanisms remain incompletely characterized. Therefore, we investigated the roles of glucose metabolism and key signaling molecules in MPC using an isolated rat heart model of DCD. Hearts underwent 20 min perfusion, 30 min global ischemia, and 60 minu reperfusion with or without MPC (two cycles: 30 s reperfusion—30 s ischemia). Despite identical perfusion conditions, MPC either significantly decreased (low recovery = LoR; 32 ± 5%; p < 0.05), or increased (high recovery = HiR; 59 ± 7%; p < 0.05) the recovery of left ventricular work compared with no MPC (47 ± 9%). Glucose uptake and glycolysis were increased in HiR vs. LoR hearts (p < 0.05), but glucose oxidation was unchanged. Furthermore, in HiR vs. LoR hearts, phosphorylation of raptor, a downstream target of AMPK, increased (p < 0.05), cytochrome c release (p < 0.05) decreased, and TNFα content tended to decrease. Increased glucose uptake and glycolysis, lower mitochondrial damage, and a trend towards decreased pro-inflammatory cytokines occurred specifically in HiR vs. LoR MPC hearts, which may result from greater AMPK activation. Thus, we identify endogenous cellular mechanisms that occur specifically with cardioprotective MPC, which could be elicited in the development of effective reperfusion strategies for DCD cardiac grafts.

Comparison of Experimental Rat Models in Donation After Circulatory Death (DCD): in-situ vs. ex-situ Ischemia

“…As systemic changes during the withdrawal phase and ischemia in situ can influence post-ischemic cardiac recovery, it is essential that they are reflected in experimental models. Over the last years, we developed an ex-situ model that includes specific DCD-relevant conditions (3)(4)(5)(6)8) with, e.g., tight temperature control during warm ischemia and the use of supraphysiologic perfusate FFA concentrations (1.2 mM palmitate) prior to ischemia. Nonetheless, some differences in post-ischemic recovery between in-situ and ex-situ models persist and may be explained by systemic changes during withdrawal and ischemia in situ.…”

“…In order to evaluate strategies for improving current DCD protocols, the choice of the most appropriate and clinically relevant animal models is essential. The ex-situ working rat heart system is a well-established experimental model that has been used in several studies to investigate cardioprotective strategies and ischemic tolerance in the context of DCD (3)(4)(5)(6)(7)(8). With this model, the pre-ischemic and ischemic phases are carried out in the ex-situ heart preparation.…”

Pre-ischemic Lactate Levels Affect Post-ischemic Recovery in an Isolated Rat Heart Model of Donation After Circulatory Death (DCD)

“…Total tissue calcium content was determined with the Colorimetric Calcium Detection Assay kit (Abcam, Cambridge, UK) according to the manufacturer's instructions. As a control and for method validation, calcium tissue content was measured in a comparable series of non-ischemic control hearts that were previously perfused for another study ( 33 ).…”

Immune Modulation as a Key Mechanism for the Protective Effects of Remote Ischemic Conditioning After Stroke

“…There is also evidence that AMPK reduces the ischemic injury by triggering autophagy (catabolic) pathways in several organs, including heart ( 102 – 105 ) and kidney ( 106 ). However, the extent to which AMPK-induced autophagy plays a protective or destructive role in conditions of cerebral ischemia is unclear ( 107 , 108 ).…”