Expression of nitric oxide and inducible nitric oxide synthase in acute renal allograft rejection in the rat

Background: Recent studies have shown that nitric oxide (NO) synthases, particularly inducible nitric oxide synthase (i-NOS), are induced in acute rejection episodes following heart, liver, pancreas and kidney allotransplantation. Furthermore, tissue and cellular injury has been demonstrated to be mediated by peroxynitrite (ONOO-), a metabolite of NO as well as a potent oxidant. However, a detailed relationship between NO, i-NOS and graft injury in transplantation remains elusive. Methods: The present study used the following models of renal transplantation in rats: allografts (n = 5, Brown-Norway to Lewis [LEW] rats), isografts (n = 5, LEW to LEW) and allografts treated with aminoguanidine (AG), an i-NOS inhibitor (n = 5). Blood urea nitrogen (BUN), serum creatinine (SCr) and urinary and serum nitrosocompounds (NOx) were measured on days 2, 4 and 7 post-transplant. Western blot analysis of i-NOS protein expression and measurement of i-NOS activity were carried out in grafts harvested on Day 7, along with immunohistochemical and histopathological examinations. Results: In the allograft group, both BUN and SCr levels increased markedly on Day 7, in parallel with a sharp increase in NOx. A band stained by anti-i-NOS antibody was detected at approximately 130 kDa, along with high levels of i-NOS activity and diffusely distributed i-NOS-positive cells (macrophages). Histologically, an acute rejection episode was confirmed (Grade 3 according to Banff classifications). In the AG group, reduced renal function and graft injury were significantly less severe than in the allograft group. Conclusions: In rat renal allograft acute rejection, markedly increased levels of serum NOx were observed, along with enhanced tissue i-NOS activity, together resulting in graft injury. AG administration suppressed the increase of serum NOx levels, with concomitant mitigation of tissue injury and renal function impairment.