Manabu Tada

Effect of methylmercury (CH3HgCl) injury on nitric oxide synthase (NOS) activity in cultured human umbilical vascular endothelial cells

The effects of methylmercury (CH3HgCl; MeHg) on the production of nitric oxide (NO) and the activity of the enzyme, nitric oxide synthase (NOS), in cultured human umbilical vascular endothelial cells (HUVEC) were examined. To assess the production of NO by HUVEC, platelet aggregation experiments were performed using cuvettes lined with HUVEC. Thrombin (0.05 U/ml)-induced platelet aggregation was inhibited in HUVEC pretreated with indomethacin (1 microM), an inhibitor of the cyclo-oxygenase pathway. The anti-platelet aggregatory effect of HUVEC treated with indomethacin was decreased dose-dependently by 48-h pretreatment with MeHg (0.5-2 microM). The effect of MeHg on the NADPH diaphorase staining of NOS in HUVEC showed dose-dependent cytotoxicity in regard to NOS activity. These findings suggest that MeHg inhibits the production of NO by HUVEC, an action which may be dependent on the cytotoxic effect exerted by MeHg on NOS activity.

Inhibitory effect of methylmercury on migration and tube formation by cultured human vascular endothelial cells

The effect of methylmercury chloride (MeHg) on migration and tube formation by cultured human umbilical vein endothelial cells (HUVECs) was quantitatively analyzed. The distance of endothelial cell outgrowth from the scraped edge of a monolayer was measured. HUVEC outgrowth was inhibited by MeHg (1.0–5.0 μM) treatment in a dose-dependent manner. Tube formation was studied by culturing the cells on gelled basement membrane matrix (Matrigel). Treatment of HUVECs with 0.1–5.0 μM MeHg for 24 h inhibited tube formation dose-dependently. These results suggest that migration and tube formation by HUVECs are susceptible to MeHg cytotoxicity, and that MeHg could be injurious to endothelial cell function, which may be involved in the pathogenesis of arteriosclerosis.

Effect of cadmium (CdCl2) on cell proliferation and production of EDRF (endothelium-derived relaxing factor) by cultured human umbilical arterial endothelial cells

The effect of cadmium chloride (CdCl2) on cell proliferation and EDRF (endothelium-derived relaxing factor) production by cultured human umbilical arterial endothelial cells (HUAECs) was investigated. The viability of HUAECs decreased dose-dependently after the addition of Cd (cadmium chloride). Morphologic examination by phase contrast microscopy revealed severe damaging effects of Cd at higher concentrations. The cytotoxic effect of Cd on DNA synthesis was also concentration-dependent. The effect of Cd on EDRF production by indomethacin-treated HUAECs was assessed by its anti-platelet aggeragory effect. Platelet aggregation studies were carried out in cuvettes lined with HUAECs using an aggregometer. The anti-platelet aggregatory effect was decreased dose-dependently by pretreatment with Cd. These findings suggest that HUAECs are susceptible to concentration-dependent Cd cytotoxicity, and that Cd can inhibit the production of EDRF by HUAECs.

Effect of lead on tube formation by cultured human vascular endothelial cells

The effect of lead acetate (Pb) on the growth of and tube formation by cultured human umbilical vascular endothelial cells (HUVEC) was examined. HUVEC were collected by enzymatic digestion with collagenase. The number of viable cells of HUVEC was negligibly affected by cultivation with Pb at concentrations of 1–100 μM, but was slightly reduced by cultivation at 500 μM. Tube formation was studied by culturing the cells on a gelled basement membranen matrix (Matrigel). Treatment of HUVEC with 0.1–50.0 μM Pb for 24 h inhibited tube formation dose-dependently. The length of tube formation decreased time-dependently with 1.0 μM Pb. These findings suggest that Pb inhibits the formation of a capillary network by HUVEC, and that Pb could be injurious to endothelials cell function.

High temperature enhances cytotoxicity of mercury (HgCl2) on HeLa S3 cells.

The combined effect of mercury (HgCl2) and high temperature on the growth and synthesis of nucleic acid and protein, and on the cell cycle of HeLa S3 cells was investigated. The subsequent growth of the cells was dose-dependently inhibited by mercury at 37.2° and 41.2°C. The inhibitory effect of mercury on subsequent growth was enhanced at the higher temperature. IC50 values for DNA and RNA synthesis but not protein synthesis, at 41.2°C, were significantly lower than those at 37.2°C (P<0.05,P<0.01, respectively). Flow cytometric analysis using synchronous cells indicated the possibility of blocking of cell cycle progression in the early part of S phase by the combined treatment. These results suggest that the cytotoxicity of mercury to cell growth was enhanced at the higher temperature and that this enhancement is related to the increased inhibitory effect of mercury on DNA and RNA synthesis and on the cell cycle at high temperatures.