Treatment of animals or certain cells with carbon monoxide (CO), a product of heme degradation by heme oxygenase-1 (HO-1), has potent anti-inflammatory and antiapoptotic effects that contribute to the survival of transplanted organs. We report here that inducing HO-1 in, or administering CO to, only the donor can be used in a therapeutic manner to sustain the survival of transplanted allogeneic islets. Similar treatments of only the islets or only the recipient are also salutary. Administering CO only to the donor frequently leads to longterm survival of those islets in untreated allogeneic recipients, which are then antigen-specifically tolerant. Several proinflammatory and proapoptotic genes that are strongly induced in islets after transplantation in the untreated situation were significantly suppressed after administering CO to the donor without further treatment. These included tumor necrosis factor-␣, inducible nitric oxide synthase, monocyte chemoattractant protein-1, granzyme B, and Fas/Fas ligand, all of which contribute to the pathogenesis of the rejection of transplanted islets. This correlated with a lesser infiltration of recipient macrophages into the transplanted islets. Our present findings show that induction of HO-1 in, or administration of CO to, only the donor, islets, or the recipient or combinations of such treatments improve allogeneic islet survival. Diabetes 54:1400 -1406, 2005 T ransplantation of islets is an important approach to the treatment of diabetes. Although recent changes in immunosuppression and other facets of the transplant procedure have improved results (1,2), cells in the islets after transplantation frequently undergo apoptosis, and islet function is compromised. Thus, more islets are needed for each transplant, leading to a greater shortage of islets.Data from others and ourselves show that the induced expression of heme oxygenase-1 (HO-1) in recipients, which leads to the expression of HO-1 in islets as well as elsewhere, has salutary effects in terms of sustaining graft survival (3,4). These findings have been interpreted to suggest that the expression of HO-1 protects the islet cells from apoptosis as well as suppresses the proinflammatory response of the recipient (5,6).HO-1 degrades heme into three products: carbon monoxide (CO), biliverdin, and Fe ϩϩ . Biliverdin is converted to bilirubin by biliverdin reductase, and Fe ϩϩ stimulates an iron pump that removes free iron from the cells as well as leads to the upregulation of ferritin, an iron-binding protein. Each of these products has protective (antiapoptotic and/or anti-inflammatory) properties, and one or more of them likely accounts for the protection afforded by HO-1 in any given situation (7-9).There is accumulating evidence that in the majority of the disease models in which HO-1 is beneficial, administration of exogenous CO can substitute for HO-1 action (10 -13). That is, if HO-1 is absent or its action blocked, the administered CO will have the "same" effects as if HO-1 were expressed. Based on these find...

Induction of heme oxygenase-1 (HO-1) expression in recipients of allogeneic islets can lead to long-term survival (>100 d) of those islets. We tested whether administration of bilirubin would substitute for the beneficial effects of HO-1 expression in islet transplantation. Administering bilirubin to the recipient (B6AF1) or incubating islets in a bilirubin-containing solution ex vivo led to long-term survival of allogeneic islets in a significant percentage of cases. In addition, administering bilirubin to only the donor frequently led to long-term survival of DBA/2 islets in B6AF1 recipients and significantly prolonged graft survival of BALB/c islets in C57BL/6 recipients. Donor treatment with bilirubin up-regulated mRNA expression of protective genes such as HO-1 and bcl-2 and suppressed proinflammatory and proapoptotic genes including monocyte chemoattractant protein-1 and caspase-3 and -8 in the islet grafts before transplantation. Furthermore, treatment of only the donor suppressed the expression of proinflammatory cytokines including TNF-alpha, inducible nitric oxide synthase, monocyte chemoattractant protein-1, and other proapoptotic and proinflammatory genes normally seen in the islets after transplantation. Donor treatment also reduced the number of macrophages that infiltrated the islet grafts in the recipients. Preincubation of betaTC3 cells with bilirubin also protected the cells from lipid peroxidation. Our data suggests that the potent antioxidant and antiinflammatory actions of bilirubin may contribute to islet survival.