MODULATION OF ADHESION MOLECULE EXPRESSION ON ENDOTHELIAL-CELLS BY VERAPAMIL AND OTHER CA++ CHANNEL BLOCKERS

Cytokine-induced expression of adhesion molecules on leukocytes and en dothelial cells (EC) is a crucial point in the process of organ transp lant rejection. It has been shown that protein kinase C (PKC) is invol ved in this activation process. Verapamil and other calcium channel bl ockers seem to possess immunosuppressive qualities in vivo and in vitr o; some authors suggested that this is due to PKC- or calmodulin-antag onism. Thus our objectives were to further investigate the second-mess enger systems involved in the stimulation of EC and to analyze whether the beneficial influence of calcium channel blockers on the outcome o f transplantation is due to impaired expression of adhesion molecules on EC. Our results, obtained in an in vitro model using human umbilica l vein EC, show that IL-1-induced expression of intercellular adhesion molecule-1 (ICAM-1) is in part mediated by PKC and that parallel acti vation of calmodulin is required. Expression of ICAM-1 was reduced to 38.5 % by PKC-inhibitor H7 acid to 77.2 % by calmodulin-inhibitor W7. In addition, data on the intracellular events in TNF-alpha-induced exp ression of vascular cell adhesion molecule-1 (VCAM-1) is presented, sh owing that both PKC and, to a higher extent, calmodulin, are involved in this process. Expression of VCAM-1 was reduced to 63.7% by H7 and t o 27.7 % by W7. IL-1-induced expression of endothelial leukocyte adhes ion molecule-1 (ELAM-1) is PKC-dependent but insensitive to blocking o f calmodulin. Though activation of adhesion molecule expression utiliz es PKC and/or calmodulin as second-messenger pathways the investigated calcium channel blockers verapamil (R- and S-enantiomers), diltiazem and Ro 40-5967 failed to inhibit adhesion molecule expression. Surpris ingly, higher concentrations of verapamil (> 12.5 mu g/ml) or Ro 40-59 67 (5 mu g/ml) significantly enhanced IL-1-induced expression of ELAM- 1. ICAM-2-expression was also enhanced by verapamil, but nor by Ro 40- 5967 or diltiazem. This enhancement was only seen if verapamil was add ed maximally one hour after the cytokine stimulus indicating that tran scriptional modulation is responsible for the observed effects. Our fi ndings indicate that calcium channel blockers have an immunomodulating effect independent of adhesion molecule expression.