Peritransplant treatment with cobalt protoporphyrin attenuates chronic renal allograft rejection

Summary Allogen‐independent injury contributes to chronic rejection in renal allografts and heme oxygenase‐1 (HO‐1) has been shown to be protective in a number of settings. This study evaluated the effect of renal allograft recipient HO‐1 up‐regulation on chronic rejection in a rat model. Rat (F344 to Lewis) renal transplantation recipients were grouped: (i) cyclosporine (CsA) alone (0.75 mg/kg s.c. × 10 day; n = 5); (ii) CsA + low dose cobalt protoporphyrin (CoPP) an HO‐1 inducer (0.5 mg/kg i.p. on days −5,0,5; n = 13) and (iii) CsA + high dose CoPP (5.0 mg/kg i.p. on days −5,0,5; n = 8). Renal function was assessed by serum creatinine levels on day 140. Histopathologic changes in allografts were graded. Morphometric analyses performed to objectively quantify the vascular changes and glomerulosclerosis. HO‐1 expression quantified by Western blot and both HO‐1 and endothelin (ET‐1) localized using immunohistochemistry. Recipients treated with CsA + high dose CoPP had significantly decreased cortical scarring, vascular hyalinization and intimal thickness. They also had a significant, dose dependant, reduction in luminal obliteration and glomerulosclerosis by morphometric analyses. This freedom from chronic rejection in recipients treated with CoPP translated into quiescent grafts at postoperative day 140 with immunostaining and Western blot demonstrating decreased level of HO‐1 versus controls (P = 0.012). In summary, the peritransplant up‐regulation of HO‐1 in renal allograft recipients significantly attenuates chronic rejection in rat renal allografts by inhibiting transplant vasculopathy.