*Purpose: The donation after circulatory death (DCD) donors has the potential to match the increasing need for transplantable organs, however, DCD kidneys have a higher risk of primary graft dysfunction or delayed graft function. Although static cold storage (SCS) has been the gold standard for organ preservation to reduce metabolism and oxygen demand, DCD kidneys are more susceptible to cold ischemic injury. Recent murine studies have shown the effect of simple static subnormothermic storage (SSS) on maintaining the physiologic and metabolic function of DCD organs without increasing the risk of oxygen demand. In this translational study, we evaluated the efficacy of SSS of extended warm ischemic porcine kidneys especially focused on 1) preoperative assessment by machine perfusion (MP), and 2) longitudinal assessment by kidney transplant (KTx) model using miniature swine.

*Methods: Kidneys of twelve MHC-inbred CLAWN miniature swine were subjected to 120 min of warm ischemia (WI) followed by either 60 min of SCS (4°C group) or SSS (22°C group) with extracellular-type solution. As experiment 1, the preserved 120-min WI kidneys were perfused with normothermic MHC-matched oxygenated red blood cells in Ringer’s solution for 120 min at mean arterial pressure (MAP) of 85 mmHg using cardiopulmonary bypass. As physiologic parameters, renal blood flow (RBF), MAP and urine output were monitored continuously and intrarenal resistance (IRR) was calculated. As a metabolic parameter, blood gas analysis was performed every 15 min to calculate oxygen consumption. As experiment 2, the preserved 120-min WI kidneys were transplanted into MHC-matched recipients with 12-days of continuous tacrolimus (blood level: 20-25 ng/ml). Renal function was monitored by serum creatinine (sCr) and renal biopsies.

*Results: Experiment 1: All of the 120-min WI kidneys preserved for 60 min at either 4 or 22°C were successfully perfused using our established method of normothemic MP for 120 minutes. Although all kidneys showed the same macroscopic appearance during MP in both groups, physiologic or metabolic parameters in 22°C group revealed better condition of the kidneys compared to 4°C group (22°C vs 4°C: mean RBF 26.7 ± 4.7 vs 10.0 ± 0.0 ml/min, mean IRR 3.5 ± 0.5 vs 8.7 ± 0.1 mmHg/ml/min, total urine output 14.3 ± 5.3 vs 5.4 ± 3.6 ml, oxygen consumption 223.5 ± 38.6 vs 92.5 ± 15.6 ml/min/g), suggesting that 22°C-preserved WI kidneys show better outcome following KTx.Experiment 2: In KTx model, peak sCr of the animals in 22°C Group was lower than that of 4°C Group (22°C vs 4°C: peak Cre 3.9 ± 0.6 vs 8.9 ± 0.3 mg/dl, p=0.0015). Kidney biopsies taken 4 days after transplantation revealed renal tubular necrosis over wide spread areas in 4°C group, while renal tubular necrosis was limited in 22°C group. Moreover, prompt regeneration of tubular epithelium was observed indicated by positive PCNA cells in 22°C group.

*Conclusions: We demonstrated that subnormothermic (22°C) organ preservation of kidney grafts exposed to 120-min warm ischemic time was more effective than hypothermic (4°C) preservation in miniature swine. To our knowledge, this is the first demonstration of the applicability of static subnormothermic storage in preclinical large animals.

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