Nitric oxide (NO) production in human umbilical vein endothelial cells (HUVECs) exposed to three physicochemically different TiO
particles and compared to control cells. The NO production was measured in absence or presence of the NO synthase inhibitor diphenyleneiodonium chloride (DPI). Values are means ± SEM. * P < 0.05 control versus nTiO2. # P < 0.05 significant treatment effect within group.