Unconjugated Bilirubin Inhibits VCAM-1-Mediated Transendothelial Leukocyte Migration

Abstract

During lymphocyte migration, engagement of VCAM-1 stimulates the generation of endothelial cell-derived reactive oxygen species (ROS) and activation of matrix metalloproteinases, facilitating endothelial retraction. Because bilirubin is a potent antioxidant, we examined the hypothesis that this bile pigment inhibits VCAM-1-dependent cellular events. The migration of isolated murine splenic lymphocytes across monolayers of murine endothelial cell lines (which constitutively express VCAM-1) is significantly inhibited by physiological concentrations of bilirubin, in the absence of an effect on lymphocyte adhesion. Bilirubin administration also suppresses VCAM-1-stimulated ROS generation and reduces endothelial cell matrix metalloproteinase activity. In a murine asthma model characterized by VCAM-1-dependent airway inflammation, treatment of C57BL6/J mice with i.p. bilirubin decreases the total leukocyte count in the lung parenchyma and lavage fluid, through specific inhibition of eosinophil and lymphocyte infiltration. Blood eosinophil counts were increased in bilirubin-treated animals, while VCAM-1 expression in the capillary endothelium and cytokine levels in both lung lavage and supernatants from cultured lymph node lymphocytes were unchanged, suggesting that bilirubin inhibits leukocyte migration. Conclusion: bilirubin blocks VCAM-1-dependent lymphocyte migration in vitro and ameliorates VCAM-1-mediated airway inflammation in vivo, apparently through the suppression of cellular ROS production. These findings support a potential role for bilirubin as an endogenous immunomodulatory agent.

VCAM-1 Activation of Endothelial Cell Protein Tyrosine Phosphatase 1B

“…Abs against the ligand for VCAM-1, ␣-4 integrin, have been administered as therapy for patients with multiple sclerosis or inflammatory bowel disease (47)(48)(49)(50). We have reported that in vivo treatment of mice with the ROS scavenger bilirubin blocks VCAM-1-dependent leukocyte migration but not the migration of leukocytes that use multiple endothelial cell adhesion molecules (46). These reports further emphasize that different adhesion molecules have different signaling pathways.…”

“…In vivo, in addition to VCAM-1, multiple endothelial cell adhesion molecules can mediate leukocyte infiltration into tissues, albeit through different signaling pathways (7,46). However, during VCAM-1-dependent inflammation, anti-VCAM-1 Abs block infiltration of eosinophils into the lung in experimental asthma and block T cell infiltration into the brain in experimental allergic encephalomyelitis (1,2).…”

Bilirubin protects grafts against nonspecific inflammation-induced injury in syngeneic intraportal islet transplantation

“…It displays anti-inflammatory activity in animal models of endotoxemia, septicemia and ischemia reperfusion injury (Fondevila et al, 2004;Wang et al, 2004;Keshavan et al, 2005;Lanone et al, 2005;Nakao et al, 2005;Overhaus et al, 2006;Kadl et al, 2007). Some of the proposed mechanisms of bilirubin including its ability to down-regulate expression of adhesion molecules, inhibit infiltration of inflammatory cells and production of nitric oxide (NO), and to reduce production of various inflammatory factors.…”

Signaling to heme oxygenase-1 and its anti-inflammatory therapeutic potential

“…Independently, beneficial effects of BR have directly been implicated in the protection against endothelial activation and dysfunction in human aortic endothelial cells [45]. Interestingly, BR has also been suggested to specifically reduce leukocyte transmigration to the site of an experimental inflammation via interaction with adhesion molecules [46].…”