Induction of endothelial iNOS by 4-hydroxyhexenal through NF-κB activation

Lipid peroxidation and its end-product, 4-hydroxyhexenal (HHE), are known to affect redox balance during aging, which causes various degenerative processes including vascular alterations from endothelial cell deterioration. To better understand the molecular action of HHE in the development of vascular abnormalities during the aging process, we investigated whether the upregulation of inducible endothelial nitric oxide synthase (iNOS) by HHE is mediated through nuclear factor κB (NF-κB) activation. Results indicate that HHE stimulates iNOS by the transcriptional regulation of NF-κB activation through cytosolic κB degradation inhibitors (IκB). Pretreatment with NF-κB inhibitors Bay 11-7082 and N-acetyl cysteine (NAC) suppressed the upregulation of iNOS by blunting IκB degradation and NF-κB binding activity. Because inflammatory stimuli induce iNOS to generate large amounts of nitric oxide (NO), intracellular NO levels in the presence of Bay 11-7082, NAC, and caffeic acid methyl ester were estimated. These inhibitors significantly suppressed the HHE-induced NO levels to a basal level. These findings strongly suggest that in endothelial cells, HHE induces iNOS gene expression through NF-κB activation, which can lead to vascular dysfunction by the activation of various proinflammatory genes.