Prevention of Early Islet Graft Failure by Selective Inducible Nitric Oxide Synthase Inhibitors after Pig to Nude Rat Intraportal Islet Transplantation. Transplantation 2001; 71: 179???184.: Brandhorst D, Brandhorst H, Zwolinski A, Nahidi F, Bretzel RG

Until recently (1), the results of human islet transplantation have not been impressive with less than 10% of type 1 diabetic patients receiving an islet graft being insulin-independent at 1 year posttransplant (2). Of the 33 insulin-independent recipients reported, over half received islets from more than one pancreas. The outstanding success reported recently by Shapiro et al., where 7/7 type 1 diabetic patients all became insulin independent, has been partly ascribed to the use of multiple (sequential) grafts as well as the use of steroid-free immunosuppression. The article being commented on (Brandhorst et al.) may partially explain why this phenomenon is observed. The majority of the successful transplants (30/33 from the Islet Transplant Registry and 7/7 from the work by Shapiro et al.) were performed by intraportal infusion and this is generally seen as the optimal way of transplanting patients. However, it has been known for many years that in animal models other sites such as the kidney capsule or the spleen can be equally or even more successful than intraportal allogeneic islet grafts (2). In the report by Brandhorst et al. they first compared intraportal xenogeneic (porcine) with kidney subcapsular porcine islet transplantation into the nude rat. The streptozotocin-induced diabetic nude rat was used to avoid confounding factors that would be introduced if cell-mediated immune responses were involved such as in a fully immune competent animal. Thus they were studying only inflammatory reactions inevitably induced in the liver by the infusion of islets. Although kidney capsule transplants were 100% successful seven of eight of the intraportal grafts with the same number of islets (4000 IEQ) failed to bring about any form of glucose control. Circulating levels of nitrite and nitrate were significantly elevated in the intraportally grafted rats at days 1 and 2 posttransplant but were unaffected in the subcapsular grafts. Three of four inducible nitric oxide synthase (iNOS) inhibitors [S-methyl-isothiourea, S-(2-aminoethyl)-isothiourea (AE-ITU) and dexamethasone), when administered during the period of islet engraftment, all led to greatly improved graft survival at 21 days with AE-ITU-treated rats having 85% graft survival. Interestingly, L-N-monomethyl-arginine (LNMMA) which has previously been shown to block nitric oxide production in euthymic Lewis rats was ineffective. This may have been due to secondary metabolic effects induced by this drug. The impressive improvements in intraportal islet graft survival by the use of iNOS inhibitors can be predicted by the “injury response” concept proposed by Halloran (3). In this he links the nonspecific injury experienced by the liver, after the intraportal infusion of the islets, with the initiation of cytokine release. Such cytokines may have direct effects on islets, as with iNOS, because islets have been shown to constitutively express relatively low levels of antioxidants compared with other cells (4). In the situation where allogeneic islets are transplanted this nonspecific injury then goes on to intensify the specific immune response. What then are the implications of this study to the possibilities of improving clinical islet transplant success? Although, generally, vitamin A, B6, and E supplements are given as part of the procedure for islet transplantation these may not be as effective antioxidants as the drugs studied by Brandhorst et al. Before the publication of the results from Schapiro et al. (1) the previously best reported results (5) achieved 14.3% success in a series of patients receiving islets from only one donor and the mean time of insulin-independence in this study was 10.6 months. The greatly improved success of the Schapiro study has largely been put down to the use of a nonsteroidal immunosuppression protocol as it is well known that glucocorticoids are inherently diabetogenic (directly impair islet function). However, none of the Schapiro patients achieved insulin-independence after the first transplant (i.e., all required subsequent grafts) even though the mean number of islets infused into these seven patients was an impressive 389,016673,769 IEQ. There can be little doubt that the glucocorticoid-free immunosuppressive protocol used here has helped to achieve these impressive clinical results but the need to use multiple grafts is likely to hamper successful and efficient clinical islet transplant centers being established world-wide. Thus the combined use of more effective iNOS inhibitors (as described by Brandhorst et al.) at the time of intraportal islet transplant along with the new developments in steroid-free Address correspondence to: R.F. L. James, PhD, Department of Surgery, University of Leicester, Robert Kilpatrick Building, Royal Infirmary, Leicester LE2 7LX, UK.