Bilirubin Oxidation Provoked by Nitric Oxide Radicals Predicts the Progression of Acute Cardiac Allograft Rejection

Abstract

Bilirubin, a strong intrinsic antioxidant, quenches free radicals produced under inflammatory conditions. The oxidized bilirubin metabolites, i.e. biopyrrins, are immediately excreted into urine and can indicate the intensity of oxidation in vivo. Our preliminary studies suggested the involvement of reactive nitrogen species (RNS) in generation of biopyrrins. However, little is known about biological significance of bilirubin oxidation by RNS. Here, we analyzed the correlation between bilirubin oxidation and nitric oxide (NO) radicals during rat acute cardiac allograft rejection. In allograft recipients, urinary biopyrrins steeply increased on day 3 prior to the increase in myocardial tissue damage marker, serum troponin-T. In contrast, no significant changes in urinary biopyrrins were evident in recipients of isografts or cyclosporine-A treated allografts. Urinary nitrotyrosine, a marker of oxidation by NO radicals also increased on day 3, while administration of a NO synthase inhibitor, N G -monomethyl-Larginine apparently diminished the elevation of urinary biopyrrins as well as nitrotyrosine. Immunohistochemistry revealed enhanced local expression of heme oxygenase-1, biopyrrins and nitrotyrosine in allografts in accordance with the cellular infiltrates, suggesting that changes in urinary biopyrrins reflect the bilirubin oxidation in grafts undergoing rejection. These results indicate that locally evoked bilirubin oxidation by NO radicals can predict the progression of rejection.

Biphasic Elevation of Bilirubin Oxidation During Myocardial Ischemia Reperfusion

“…30,31 Biopyrrins are immediately excreted in urine because of their hydrophilic properties and thus can reflect the severity of oxidative stress. 25,[32][33][34][35][36][37][38] Biopyrrin synthesis reflects NO radicals, 25 so urinary biopyrrin levels can indicate ongoing changes in oxidative stress in vivo and thus function as a marker of oxidative stress.The time course of urinary and tissue biopyrrin levels in rat models of cardiac transplantation and hepatic ischemia reperfusion has been investigated. 25,32 A cardiac transplantation study showed that levels of urinary biopyrrins become more rapidly and sensitively elevated than either urinary 8-hydroxy-2'-deoxyguanosine or serum troponin-T during …”

“…30,31 Biopyrrins are immediately excreted in urine because of their hydrophilic properties and thus can reflect the severity of oxidative stress. 25,[32][33][34][35][36][37][38] Biopyrrin synthesis reflects NO radicals, 25 so urinary biopyrrin levels can indicate ongoing changes in oxidative stress in vivo and thus function as a marker of oxidative stress.…”

“…25,32 A cardiac transplantation study showed that levels of urinary biopyrrins become more rapidly and sensitively elevated than either urinary 8-hydroxy-2'-deoxyguanosine or serum troponin-T during …”

“…[18][19][20][21] Its synthesis is regulated by the rate-limiting enzyme, heme oxygenase-1 (HO-1), which is rapidly induced by oxidative stress and inflammatory reactions caused by factors such as cytokines, ischemia and NO. [22][23][24][25][26][27][28][29] Bilirubin generates several hydrophilic metabolites called biopyrrins upon oxidation and these can be detected using the anti-bilirubin monoclonal antibody 24G7. 30,31 Biopyrrins are immediately excreted in urine because of their hydrophilic properties and thus can reflect the severity of oxidative stress.…”

The complex role of iNOS in acutely rejecting cardiac transplants

“…Treatment of recipients with these agents either prolonged graft survival [35,36], had no effect on graft survival [37,38] or decreased graft survival [39]. None of these studies provided information on either graft function prior to graft failure or independent evaluation of histological rejection scores.…”