Inhibitory effect of lead on tube formation by cultured human vascular endothelial cells

The effect of lead acetate (Pb) on the formation of capillary-like structures (tube formation) by cultured human umbilical vascular endothelial cells (HUVECs) was examined. HUVECs were seeded on a gelled basement membrane matrix (Matrigel). Treatment of HUVECs with 0.3-30.0 microM Pb for 24 hours inhibited the tube formation dose-dependently. The length of tube formation decreased time-dependently with 3.0-10.0 microM Pb. To elucidate the main target factor of Pb for this inhibition, the effects of Pb on the activity of protein kinase C (PKC) and Matrigel were examined. The addition of beta-phorbol 12-myristate 13-acetate (PMA, 50 nM), an activator of PKC, and isoquinolinesulfonamide derivative (H-7, 30 microM), an inhibitor of PKC, showed an increase and decrease in the tube formation, respectively. However, the results of simultaneous addition of Pb and either PMA or H-7 to HUVECs indicated that PMA and H-7 acted not synergistically but additively. When PKC activities in HUVECs were measured by a colorimetric assay after treatments with 3.0-10.0 microM Pb for 24 hours, there was no significant change in PKC activity in the cells. The Pb-inhibition of tube formation was suggested to be independent of PKC activity. Pretreatment of Matrigel with 3.0-10.0 microM Pb for different periods decreased the tube formation dose- and time-dependently. These findings suggest that Pb can inhibit the tube formation by HUVECs dose- and time-dependently and that the inhibitory effect of Pb could be dependent on the degeneration of Matrigel, not on PKC activity.