Controlled Rewarming after Hypothermia: Adding a New Principle to Renal Preservation

Abstract

Early graft dysfunction due to preservation/reperfusion injury still represents a notable issue after kidney transplantation, affecting long term prognosis of graft viability. One trigger of postischemic cell dysfunction could be recognized in the abrupt temperature shift from hypo- to normothermia, leading to mitochondrial dysfunction and proapoptotic signal transduction. Here we propose a technique to cope with this "rewarming injury" by interposing a period of gentle warming up by hypo- to subnormothermic machine perfusion of the isolated graft prior to warm reperfusion. Porcine kidneys were subjected either to 18 hours of hypothermic machine preservation (HMP) or 18 hours static cold storage + 3 hours of gentle, machine controlled oxygenated rewarming (COR). Functional integrity was evaluated in both groups by subsequent normothermic reperfusion in vitro. The functional benefit of COR was documented by an approximately twofold increase in renal clearances of creatinine as well as urea upon warm reperfusion, compared to controls. This was accompanied with a notable mitigation of postischemic mitochondrial dys-homeostasis. COR significantly improved renal oxygen consumption and maintained total NAD tissue content upon reperfusion. Mitochondrial initiation of cellular apoptosis, as evidenced by activation of caspase 9 was also largely prevented after COR but not in controls. The concept of gentle regenerative graft rewarming could become a valuable adjunct in renal transplantation.

Keywords: kidney; machine perfusion; preservation; reperfusion injury; rewarming.

Figure 1

Controlled oxygenated rewarming: gentle elevation of graft temperature upon oxygenated extracorporeal machine perfusion prior to warm reperfusion.

Figure 2

Renal clearances of creatinine and urea upon reperfusion after 18 hours of HMP (HMP), 18 hours cold storage + 3 hours of HMP (CS + HMP) or 18 hours of cold storage + 3 hours of controlled oxygenated rewarming (COR). N = 7 per group (*p < 0.05 [area under the curve, AUC] vs. HMP). Model specific normal range, obtained from nonischemic organs, is represented by the gray area, for comparison.

Figure 3

Effect of controlled oxygenated rewarming after cold storage (COR) compared to hypothermic machine perfusion (HMP) or 18 hours cold storage + 3 hours of HMP (CS + HMP) on total NAD content and caspase 9 activity upon warm reperfusion of isolated porcine kidneys (*p < 0.05 vs. HMP).

Figure 4

Renal oxygen consumption during reperfusion after 18 hours of HMP (HMP), 18 hours cold storage + 3 hours of HMP (CS + HMP) or 18 hours of cold storage + 3 hours of controlled oxygenated rewarming (COR). N = 7 per group (*p < 0.05 [area under the curve, AUC] vs. HMP). Model specific normal range, obtained from nonischemic organs, is represented by the gray area, for comparison.