Carbon monoxide releasing molecules inhibit cell death resulting from renal transplantation related stress.

PURPOSE: Organ cold storage and subsequent transplantation are associated with significant ischemia-reperfusion injury, leading to cell death, graft inflammation and decreased graft function. MATERIALS AND METHODS: CORM-3s reduce oxidative stress and prevent inflammation in kidneys stored at 4C and subsequently transplanted. Graft survival and function are markedly improved compared to kidneys preserved and stored in University of Wisconsin solution alone. We determined whether CORM-3 has direct antiapoptotic effects on in vitro preparations of human HUVECs exposed to anoxic conditions. We also determined whether direct administration of CORM-3 to renal grafts before and/or after cold storage would prevent renal damage during the transplantation process. RESULTS: CORM-3 supplementation led to a significantly increased frequency of live cells (mean ± SD 72.3% ± 1.9%, p <0.01), reduced apoptosis (14.9% ± 6.1%, p <0.01) and decreased mitochondrial transmembrane potential (40.2% ± 7.2%, p <0.05) in HUVECs exposed to 20 hours of cold storage compared to controls (11.6% ± 3.5%, 82.2% ± 2.3% and 78.2% ± 3.2%, respectively). In keeping with this antiapoptotic effect CORM-3 supplementation led to a mean 7.4 ± 2.1-fold up-regulation in Bcl-2 gene expression. CORM-3 supplementation in standard preservation solution was most beneficial at initial ischemic injury and before cold storage exposure. However, additional reflushing before vascular reperfusion showed an additive benefit to graft survival and function after transplantation. This was confirmed by decreased glomerular and tubular necrosis, and apoptosis in double flushed grafts. CONCLUSIONS: CORM-3 supplementation in standard University of Wisconsin solution has a significant impact on decreasing cellular and graft injury, and improving survival through its antiapoptotic effects, which are likely mediated through mitochondrial membrane stabilization.

Carbon monoxide-releasing molecules protect against ischemia-reperfusion injury during kidney transplantation.

Carbon monoxide (CO) can provide beneficial antiapoptotic and anti-inflammatory effects in the context of ischemia-reperfusion injury (IRI). Here we tested the ability of pretreating the kidney donor with carbon monoxide-releasing molecules (CORM) to prevent IRI in a transplant model. Isogeneic Brown Norway donor rats were pretreated with CORM-2 18 h before kidney retrieval. The kidneys were then cold-preserved for 26 h and transplanted into Lewis rat recipients that had undergone bilateral nephrectomy. Allografts from Brown Norway to Lewis rats were also performed after 6 h of cold ischemic time with low-dose tacrolimus treatment. All recipients receiving CORM-2-treated isografts survived the transplant process and had near-normal serum creatinine levels, whereas all control animals died of uremia by the third post-operative day. This beneficial effect was also seen in isografted Lewis recipients receiving kidneys perfused with CORM-3, indicating that CORMs have direct effects on the kidney. Pretreatment of human umbilical vein endothelial cells in culture with CORM-2 for 1 h significantly reduced cytokine-induced nicotinamide adenine dinucleotide phosphate-dependent production of superoxide, activation of the inflammation-relevant transcription factor nuclear factor-κB, upregulated expression of E-selectin and intercellular adhesion molecule-1 adhesion proteins, and leukocyte adhesion to the endothelial cells. Thus, CORM-2-derived CO protects renal transplants from IRI by modulating inflammation.

Alteration in CD45RBhi/CD45RBlo T-cell ratio following CD45RB monoclonal-antibody therapy occurs by selective deletion of CD45RBhi effector cells.

Tolerance induction by CD45RB monoclonal antibody (mAb) in murine allograft models is associated with an alteration in the CD45RBlo/CD45RBhi T-cell ratio in favor of CD45RBlo T cells, which can function as regulatory cells and promote tolerance. It has been proposed that inversion of the CD45RBhi/CD45RBlo normal T-cell ratio by mAb can occur by down-regulation of CD45RB surface molecules expressed by T cells. Because CD45RB mAb infusion can lead to a reduction in peripheral T cells, we tested whether other mechanisms might participate in the inversion of the CD45RBhi/CD45RBlo ratio, including apoptosis of CD45RBhi cells. We report that CD45RB mAb led to rapid elimination of both CD4+ and CD8+ T cells in vitro. Importantly, CD45RB mAb selectively eliminated CD45RBhi T cells without affecting the viability of CD45RBlo T cells. Furthermore, the death of T cells occurred with a reduction in mitochondrial transmembrane potential and DNA fragmentation but with little evidence of nuclear condensation and cell shrinkage typically found with cells undergoing apoptosis. We propose that CD45RB mAb therapy may promote a dominant regulatory T-cell population that has the capacity to inhibit rejection by the selective elimination of CD45RBhi effector T cells. This occurs by a process that does not involve the classic morphologic features of apoptosis. Strategies that facilitate an inversion of the CD45RBhi/CD45RBlo T-cell subset ratio may improve the efficacy of CD45RB mAb, and therapeutic measures that prevent deletion of CD45RBhi T cells may need to be avoided to achieve tolerance clinically.