NITRIC OXIDE PRODUCTION IN RENAL TRANSPLANT RECIPIENTS AND iNOS EXPRESSION IN RENAL ALLOGRAFTS

Abstract

11 Purpose: Nitric oxide (NO) has been reported to be involved in acute allograft rejection process in animal models, and previously also in human. The present study is to investigate kinetics of NO metabolites, as an index of NO production, in recipients after renal transplantation. Furthermore, expression of inducible NO synthase (iNOS) in allografts was examined to investigate a site of NO production. Methods: Serum and urine samples at various points from 21 renal transplant recipients were retrospectively evaluated. The recipients were consisted with 3 groups as follows; Control group: recipients with uneventful clinical course (n=12), AR group: recipients with biopsyproven acute rejection episodes (Grade Ia∼IIa : n=6), ATN group: recipients with ATN episodes (n=3). All patients received cyclosporine or tacrolimus-based immunosuppression. Stable metabolites of NO (NO2− + NO3− = NOx) were measured by Griess method using HPLC. Furthermore, immunohistochemical staining was performed to evaluate expression of iNOS in allograft core-biopsy specimens. Results: In control group, serum levels of NOx significantly decreased after renal transplantation from 50.1±23.7 μmol/L at pre-transplantation to 9.0±4.6 μmol/L at 2 days after transplantation (p<0.05). Thereafter, serum levels of NOx was stabilized at baseline levels between 16 and 20 μmol/L. In AR group, serum levels of NOx significantly increased from 20.4±4.0 μmol/L to 52.8±31.7 μmol/L at 2.1±1.5 (0∼4 days, p<0.05) days prior to the increase of serum levels of creatinine (Cr), and increase up to 82.2±56.4 μmol/L, respectively. Successful anti-rejection therapy showed the significant decrease in serum levels of NOx at 3 to 5 days after anti-rejection therapy was started, while the significant decrease in serum levels of Cr was observed at 6 days or thereafter. Interestingly, in a case of steroid resistant rejection, serum NOx continued to increase until OKT-3 treatment diminished the acute rejection. Serum levels of NOx in ATN group and urinary NOx/Cr ratio in any groups did not reveal a significant change. Immunohistochemical staining of iNOS was observed in large graft-infiltrating cells during severe acute rejection (Grade IIa), which is morphologically consistent with macrophages. Conclusion: These results indicate serum levels of NOx may serve as a sensitive marker to diagnose acute rejection and to judge the response to anti-rejection therapy.