Nutrient deprivation is a stimulus for oxidative stress and is an established method for induction of cell autophagy and apoptosis. The aims of this study were to identify conditions that evoke superoxide production in cultured human umbilical vein endothelial cells (HUVECs), determine the mechanism of action for this response, and examine whether the stimulus might facilitate the adhesion of human isolated neutrophils to the HUVECs. HUVECs were incubated in M199 medium under conditions of serum starvation (serum-free M199 medium), low serum (medium containing 2% fetal calf serum), and high serum (medium containing 20% fetal calf serum). HUVECs were also incubated under proinflammatory conditions, in medium supplemented with 50ng/ml tumor necrosis factor-α (TNF-α) or neutrophils preactivated with 10nM phorbol 12-myristate 13-acetate (PMA). Superoxide production was increased fourfold in serum-starved HUVECs compared to cells incubated in 20% medium, and this was reduced by inhibitors of the mitochondrial electron transport chain and mitochondrial Ca(2+) uniporter. Superoxide production was 23.6% higher in HUVECs incubated with TNF-α in 2% medium compared to 2% medium alone, but unchanged with TNF-α in 20% medium. PMA-activated neutrophils adhered to morphologically aberrant HUVECs, which were mainly evident under the low-serum condition. The findings show a role of mitochondrial enzymes in superoxide production in response to nutrient deprivation and suggest that proinflammatory responses in HUVECs become manifest when HUVECs are in an already-compromised state.
Keywords: Free radicals; HUVECs; Reactive oxygen species; Serum deprivation; Superoxide; Tumor necrosis factor-α.
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