Nitric oxide in early ischaemia reperfusion injury during human orthotopic liver transplantation

Altered nitric oxide (NO) metabolism has been shown to contribute to ischemia-reperfusion (IR) injury in animal models. However, similar studies have not been performed in human liver transplantation (LT). In this study, we examined nitrate, nitrite, and nitrosothiols (NOx), NO synthases (endothelial [constitutive] nitric oxide synthase [eNOS] and inducible nitric oxide synthase [iNOS]), and nitrotyrosine in early IR injury after human LT.

Paired biopsies were obtained from nine donor livers before cold ischemia (retrieval biopsy) and after reimplantation (reperfusion biopsy). Sections were graded for reperfusion injury using the Suzuki score. NO was detected by chemiluminescence after reduction of NOx. Expression of eNOS and iNOS was by Western blot and reverse transcriptase polymerase chain reaction and peroxynitrite by immunodetection of 3-nitrotyrosine.

Reperfusion biopsies showed histologic evidence of injury (median Suzuki score: retrieval 2, reperfusion 6, P=0.008) and neutrophil infiltration. NOx was reduced after reperfusion from 5.41 microM/100 mg (median, range 2.17-13.39 microM) to 3.51 microM (1.45-5.66 microM, P=0.05). eNOS protein was reduced after reperfusion from 0.6 units (median, range 0.45-1 unit) in retrieval biopsies to 0.39 units in reperfusion biopsies (range 0.2-0.79 units, P=0.007). There was no change in eNOS or iNOS mRNA expression or iNOS protein. Western blotting showed increased nitrotyrosine formation after reperfusion, median 0.42 (range 0.16-0.87) units in retrieval biopsies and 0.68 (0.29-1.06) units in reperfusion samples (P=0.007) and localized to periportal regions.

iNOS protein may not contribute to early reperfusion injury during human LT. However, reduced NO bioavailability caused by reduced eNOS may contribute significantly to damage at this time point.