Carbon monoxide inhalation protects rat kidney grafts from ischemia/reperfusion injury

Abstract

Introduction: Carbon monoxide (CO), a product of heme metabolism by heme oxygenases(HO), is known to provide protection against oxidative stress via anti-inflammatory and anti-apoptotic actions. We hypothesized in this study that a low concentration of inhaled CO would protect transplanted kidney grafts from cold ischemia-reperfusion (I/R) injury. Methods: Lewis rat kidney grafts, preserved in UW at 4°C for 24 hrs was orthotopicaly transplanted into binephrectomized syngeneic Lewis rats. Recipients were exposed to CO (250 ppm) in air for 1hr before and then continuously for 24 hrs post-transplantation. Animals were sacrificed 1, 3, 6, and 24 hrs after transplantation. The efficacy of CO was assessed by evaluating serum creatinine levels, graft cytokine mRNA levels (real time RT-PCR), HO-1 expression (mRNA levels and Western blot), measurement of graft microcirculation, serum IL-6 and NO2/NO3, immunopathology, vascular casting and transmission electron microscopy. Results: Rapid upregulation of mRNA for IL-6, IL-1β, TNF-α, ICAM-1, HO-1 and iNOS was observed in the grafts obtained from air-exposed control recipients within 3 hrs after transplantation, resulting in histopathological evidences of acute tubular necrosis, interstitial hemorrhage and edema, apoptotic debris and protein casts inside the tubular lumen. Serum creatinine levels were significantly elevated by 6 and 24 hrs. In contrast, the increase of these inflammatory mediators was markedly inhibited in CO-treated animals, which correlated with significantly lower serum creatinine levels and improved renal cortical blood flow. CO was able to preserve the glomerular vascular architecture and podocyte viability in the kidney graft. Transplant-induced HO-1 protein expression was downregulated in CO treated recipients at 6 and 24 hrs post-reperfusion. There was less tubular cell apoptosis as evidenced by caspase-3 immunostaining. In addition, markedly less ED-1 macrophage infiltration was observed in grafts treated with CO. Conclusions: This study demonstrates that exposure of kidney graft recipients to CO at a low non-toxic concentration can impart important protective effects in renal I/R injury and improve function of renal grafts following extended cold preservation and transplantation.