S -Nitrosoalbumin–Mediated Relaxation Is Enhanced by Ascorbate and Copper

Abstract

Abstract-S-nitrosoalbumin (SNO-Alb) is a major reservoir of releasable nitric oxide (NO) in plasma. In preeclampsia, a pregnancy-specific disorder associated with endothelial dysfunction, we previously found significant elevations in plasma SNO-Alb concentrations and decreased plasma ascorbate (Asc) levels. This increased SNO-Alb may result from low-plasma Asc if Asc, along with transition metals (eg, copper [Cu]) are necessary for release of NO from S-nitrosothiols. We propose that vasodilator effects of SNO-Alb, mediated by release of NO, are fully realized only when Asc/Cu availability is sufficient. Relaxation responses to SNO-Alb or the control reduced human serum albumin (SH-Alb), and responses to pooled plasma from normal or preeclamptic pregnancies were examined in isolated mouse arteries. Arteries preconstricted with phenylephrine were exposed to SNO-Alb or SH-Alb at physiologically relevant concentrations. When free Cu was added in excess (10 mol/L), NO release was not dependent on Asc. However, when Cu was added at lower (physiological) levels, NO release was dependent on Asc. The addition of Asc and Cu to SNO-Alb stimulated vasodilatory responses in isolated arteries Ͼ90%, whereas no change in the SH-Alb (5%) response was observed. Preeclampsia plasma with higher levels of SNO-Alb caused arteries to relax 44.1Ϯ4.7%, whereas normal pregnancy plasma caused 11.9Ϯ4.2% relaxation (Pϭ0.007). These data indicate that SNO-Alb alone or in plasma can act as a potent vasodilator, and that sufficient Asc/Cu promotes this action. We suggest that the higher circulating levels of SNO-Alb, in women with preeclampsia, reflect a deficiency in Asc/Cu-mediated release of NO from SNO-Alb. Key Words: preeclampsia Ⅲ pregnancy Ⅲ nitric oxide Ⅲ oxidative stress Ⅲ antioxidants P reeclampsia is a major cause of maternal and neonatal morbidity and mortality. The clinical manifestations of this pregnancy-specific disorder include hypertension and proteinuria developing after 20 weeks of gestation. Placental abnormalities and maternal endothelial dysfunction/activation are thought to contribute to vasospasm and the onset of the maternal syndrome. It has been hypothesized that oxidative stress plays a role in the pathophysiology of preeclampsia. Evidence of oxidative stress in combination with profound depletion of plasma ascorbate (Asc) has been reported in women with preeclampsia. [1][2][3][4] Asc concentrations in women with preeclampsia are nearly half those of matched normal pregnant controls (Ϸ40 versus 25 mol/L). 5 The implications of this reduction in plasma Asc are currently not clear. Plasma Asc levels are inversely related to blood pressures in men without a history of hypertension. 6,7 Asc and vitamin E supplementation in women at high risk for preeclampsia was associated with a reduction in markers of endothelial dysfunction and in the incidence of preeclampsia. 5,8 Although the decreased incidence of preeclampsia was associated with decreased biochemical indices of oxidative stress and poor placental function, the me...

Recent Progress Toward the Understanding of the Pathophysiology of Hypertension During Preeclampsia

“…38 Gandley et al recently suggested that the higher circulating levels of S-nitrosoalbumin in women with preeclampsia reflect a deficiency in ascorbate-mediated release of NO from S-nitrosoalbumin. 41 These deficiencies in antioxidants may have important vascular effects in preeclampsia. For example, Ramirez and colleagues recently reported that moderate ascorbate deprivation increases mesenteric artery myogenic responsiveness during pregnancy and that this increase may results from a decrease in NO-mediated modulation of the myogenic contractile response.…”

Assessment of nitric oxide signals by triiodide chemiluminescence

“…Additionally, NO can be transported in endocrine or paracrine fashion by reacting with heme iron and cysteine thiols in proteins [hemoglobin (Hb) and albumin] and peptides (glutathione and cysteinlyglycine) to form NO adducts with longer biological lifetimes (3)(4)(5); release of NO bioactivity from stable adducts is effected by allosteric and redox-based mechanisms that alter FeNO or S-nitrosothiol (SNO) reactivity (5,6). An updated discussion of the factors influencing reactivity of S-nitrosohemoglobin, S-nitrosoalbumin, and low-molecular-weight SNO in the context of vasoregulation (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) can be found in supporting information (SI) Text.…”

“…Accordingly, bond dissociation energies of RSNO are reported to vary from Ϸ22 to 32 kcal⅐mol Ϫ1 (6,26), and the dissociation constants of FeNO can vary by a factor of Ͼ10 6 (13,23,24), translating to intrinsic FeNO/SNO lifetimes ranging from seconds to years. Environmental factors that have been reported to influence SNO stability and reactivity, directly or through elicited conformational changes in proteins, include pH (low and high) (5,6,20,26), metal ions (Ca, Mg, Cu, and Fe) (6,14,20,27,28), nucleophiles (ascorbate, thiolate, and amine) (6,13), local hydrophobicity (denaturants) (29), oxidants and reductants (6,19), proteolytic enzymes (30), alkylators (31), O 2 tension (5,32), and various intramolecular interactions (H-bonding, S-, N-, O-coordination, and aromatic residue interactions) (6,16,20,22,(33)(34)(35)(36). Many of these factors also affect FeNO stability (17,23,24).…”

Functional characterization of two S-nitroso-l-cysteine transporters, which mediate movement of NO equivalents into vascular cells

“…The short half-life of NO can be prolonged by reaction with sulfhydryl groups of proteins or low molecular thiols to form more stable, biologically active S-nitrosothiols (23,32). Although the actual concentration in the circulation is debated, S-nitrosothiols are known to be formed in vivo (8,10,17,31,33,39) and are proposed to mediate diverse biological responses (7, 9). Among the circulating S-nitrosothiols, S-nitrosoalbumin is an important species and may act as reservoir of NO (8,31,34,35).…”