Hydrogen peroxide-induced VCAM-1 expression in pancreatic islets and β-Cells through extracellular Ca2+ influx

BACKGROUND.: The use of porcine islets as alternatives to transplantable human islets is hampered by xenotransplant rejection. To identify molecular mechanisms that would allow subversion of xenoislet rejection, we investigated the role of H2O2 in vascular cell adhesion molecule-1 (VCAM-1) expression by porcine and mouse islets and β-cell lines. METHODS.: Porcine islets were treated with H2O2, tumor necrosis factor alpha, interferon-γ, interleukin-1β, and lipopolysaccharide, to assess the effects of inflammatory stimulators on VCAM-1 expression using flow cytometry. The role of Ca in H2O2-induced VCAM-1 expression was investigated in β-cell lines using an extracellular Ca chelator and Ca-depleted media. Furthermore, H2O2-induced VCAM-1 expression was measured in β-cells, pretreated with inhibitors of protein kinase C, phospholipase D, and phosphatidylinositol-3 kinase/Akt. Finally, H2O2-induced VCAM-1 expression was evaluated in porcine islets and rodent β-cell lines infected with an adenovirus encoding catalase, a H2O2-removing enzyme. RESULTS.: H2O2 was most potent inflammatory stimulator of VCAM-1 expression in porcine islets and had the greatest effect on VCAM-1 expression by β-cells. Signaling pathway analysis demonstrated that extracellular Ca influx was critical to H2O2-mediated VCAM-1 expression; however, protein kinase C, phospholipase D, and phosphatidylinositol-3 kinase/Akt activation were not required for VCAM-1 expression. Finally, catalase overexpression inhibited H2O2-induced VCAM-1 expression by islets and β-cell lines. CONCLUSION.: An extracellular calcium-dependent H2O2 pathway is the critical mediator of VCAM-1 expression by pancreatic islets and β-cells. Inhibition of this pathway by catalase overexpression in donor islets can be exploited to protect against xenoislet immune responses.