Nitric oxide production and nitric oxide synthase expression in acute human renal allograft rejection

BACKGROUND: Nitric oxide (NO) is produced by nitric oxide synthases (NOS), which are either constitutively expressed in the kidney or inducible, in resident and infiltrating cells during inflammation and allograft rejection. NO is rapidly degraded to the stable end products nitrite and nitrate, which can be measured in serum and urine, and may serve as noninvasive markers of kidney allograft rejection. METHODS: Total nitrite and nitrate levels (NOx) were measured in serum and urine thrice weekly after an overnight fast in 18 consecutive patients following renal cadaveric transplantation. Inducible NOS (iNOS) and endothelial NOS (eNOS) expression was immunochemically determined in renal biopsy specimens with or without acute rejection (AR). RESULTS: Serum NOx levels increased days before AR and were significantly higher at the moment of AR (27+/-12.4 micromol/L) compared with recipients with an uncomplicated course (13+/-7.6 micromol/L), but not compared with recipients with cyclosporine (CsA) toxicity (20+/-13.0 micromol/L). Urinary NOx levels were significantly lower during AR (20+/-13.6 micromol/mmol creatinine) compared with an uncomplicated course (64+/-25.2 micromol/mmol creatinine) or CsA toxicity (53.8+/-28.3 micromol/mmol creatinine). Interstitial and glomerular iNOS expression was significantly increased in biopsy specimens showing AR. Unexpectedly, glomerular eNOS expression was significantly decreased in patients with AR. CONCLUSIONS: This study reports differences in NOx levels in serum and urine, which may help discriminate AR episodes from an uncomplicated course or CsA toxicity. As expected, renal iNOS expression is increased in acute allograft rejection. The decrease in glomerular eNOS expression suggests an intriguing link between acute and chronic rejection.