MECHANISMS OF CELL ACTIVATION BY HEAVY-METAL IONS

Heavy metal ions can be released by corroding metallic implants into t he surrounding tissue. When they enter blood vessels some of them are carried by proteins like albumin and can be taken up by endothelial ce lls lining the vessels. To study their involvement in the inflammatory response we investigated heavy metal ion induced effects in cultured human vascular endothelial cells (HUVECs). NiCl2 and CoCl2 upregulate, especially in concentrations of 1 mM, the expression of adhesion mole cules (e.g., E-selectin and intercellular adhesion molecule-1), as wel l as the cytokines IL-6 and IL-8, as shown by enzyme immunoassay and N orthern blot analysis. In addition, possible signal transduction mecha nisms were elucidated. The HUVECs were treated with various selective inhibitory drugs followed by the incubation of metal ions before measu ring the expression of the above-mentioned endothelial factors. Two pr otein kinase inhibitors (H-7 and H-8) strongly repressed Ni2+ and Co2 enhanced expression, as did the phospholipase A2 inhibitor quinacrine . Other selective inhibitors of protein kinases C or A, or cGMP-depend ent protein kinases, as well as calcium antagonists like 1,2-bis(2-ami nophenoxy)ethan-N,N,N',N'-tetraacetic acid and 3,4,5-trimethoxybenzosa ure 8-(diethylamino)-octylester and inhibitors of receptor mediated en docytosis (primary amines), had no influence. We showed that NiCl2 and CoCl2 activate the translocation of the transcription factor nuclear factor (NF)-kappa B into the cell nucleus and enhance its binding to a NF-kappa B consensus sequence as shown by mobility shift analysis. Fu rthermore, we demonstrated the activation of AP-1. Despite the repress ion of heavy metal induced adhesion molecule synthesis, we did not det ect any inhibition of NF-kappa B translocation by H-7 or H-8. Therefor e, it must be concluded that heavy metal ions like Ni2+ and Co2+ activ ate two or more signal transduction pathways in endothelial cells. We clearly showed that there is one pathway in which H-7 and H-8 sensitiv e protein kinases are involved and a second pathway leading to NF-kapp a B activation, which is insensitive to H-7 and H-8. Our results demon strate that heavy metal ions induce mechanisms of gene activation in e ndothelial cells as do proinflammatory mediators, indicating that corr oding metal ion containing biomaterials can provoke inflammatory react ions by known, as well as by yet unknown, intracellular signaling path ways. (C) 1998 John Wiley & Sons, Inc.