title: Inhibition of endothelial- and neuronal-type, but not inducible-type, nitric oxide synthase by the oxidized cholesterol metabolite secosterol aldehyde: Implications for vascular and neurodegenerative diseases.
abstract: The cholesterol ozonolysis products secosterol-A and its aldolization product secosterol-B were recently detected in human atherosclerotic tissues and brain specimens, and have been postulated to play pivotal roles in the pathogenesis of atherosclerosis and neurodegenerative diseases. We examined several oxidized cholesterol metabolites including secosterol-A, secosterol-B, 25-hydroxycholesterol, 5β,6β-epoxycholesterol and 7-ketocholesterol for their effects on the activities of three nitric oxide synthases. In contrast to other oxidized metabolites, secosterol-A was found to be a potent inhibitor against the neuronal- and endothelial-type, but not the inducible-type nitric oxide synthase, with IC(50) values of 22 ± 1 and 50 ± 5 µM, respectively. The calmodulin-binding regions of the neuronal- and endothelial-nitric oxide synthases contain lysine residues which are not present in the inducible-type nitric oxide synthase. Secosterol-A modifies proteins through the formation of a Schiff base with the lysine epsilon-amino group. It is possible that secosterol-A modifies lysine residues of constitutive nitric oxide synthases, leading to the inhibition of enzymatic activities. As nitric oxide is a critical signaling molecule in vascular function and in long-term potentiation, its reduced production through inhibition of constitutive nitric oxide synthases by secosterol-A may contribute to the development of atherosclerosis and memory impairment in particular neurodegenerative diseases.
authors.affiliation: Laboratory of Biochemistry and Global Center of Excellence Program, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka 422-8526, Japan.
authors.forename: Ying-Ling
authors.initials: YL
authors.lastname: Lai
authors.forename: Susumu
authors.initials: S
authors.lastname: Tomono
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Miyoshi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ohshima