No abstract

S-Nitrosothiols (RSNOs) are considered to play important roles in storing, transporting, and releasing nitric oxide (nitrogen monoxide, NO) in vivo. Although tertiary RSNOs are known to be intrinsically more stable than primary RSNOs, the correlation between the structure of primary RSNOs and the kinetics of thermal NO release in solution has not been established yet. We have characterized the kinetics of thermal NO release from three primary RSNOs: S-nitrosocysteine (CySNO), S-nitroso-N-acetylcysteine (SNAC), and Snitrosoglutatione (GSNO) in aqueous solutions. It was found that the rates of NO release are strongly affected by the initial concentration of the solutions. Increasing the concentration of CySNO and SNAC from 1.0 × 10 -1 to 61.0 mmol L -1 led to 5.7-and 14.6-fold increases in their initial rates of decomposition, respectively, whereas GSNO was much less affected (a 2-fold increase). However, a smaller increase in concentration (0.1 to 1.0 mM) led to a 4.6-fold decrease, on average, in the rates of NO release in the three cases. This result was assigned to the combination of an autocatalytic effect promoted by the secondary reaction of thyil radicals with authentic RSNO molecules, which accelerates the decomposition reaction in concentrated solutions, and a nongeminate (diffusive, outside the cage) radical pair recombination effect that leads to a reduction in the rates of reaction in dilute solutions. In the low-concentration range, GSNO and SNAC were shown to be significantly more stable than CySNO. This result is in accordance with the conclusions derived from singlepoint energy calculations at the MP2/6-31G(2df,p)//MP2/6-31G(d) level of theory, which have shown that the acetamido group that is present in SNAC plays a key role in increasing the S-N bond strength. These results show that comparisons of stability among different S-nitrosothiols in solution must take the concentration effect carefully into account and indicate that the half-lives of primary RSNOs found in vivo can be partially determined by their intrinsic structural properties.

S-nitrosothiols have many biological activities and may act as nitric oxide (NO) carriers and donors, prolonging NO half-life in vivo. In spite of their great potential as therapeutic agents, most S-nitrosothiols are too unstable to isolate. We have shown that the S-nitroso adduct of N-acetylcysteine (SNAC) can be synthesized directly in aqueous and polyethylene glycol (PEG) 400 matrix by using a reactive gaseous (NO/O2) mixture. Spectral monitoring of the S-N bond cleavage showed that SNAC, synthesized by this method, is relatively stable in nonbuffered aqueous solution at 25 degrees C in the dark and that its stability is greatly increased in PEG matrix, resulting in a 28-fold decrease in its initial rate of thermal decomposition. Irradiation with UV light (lambda = 333 nm) accelerated the rate of decomposition of SNAC to NO in both matrices, indicating that SNAC may find use for the photogeneration of NO. The quantum yield for SNAC decomposition decreased from 0.65 +/- 0.15 in aqueous solution to 0.047 +/- 0.005 in PEG 400 matrix. This increased stability in PEG matrix was assigned to a cage effect promoted by the PEG microenvironment that increases the rate of geminated radical pair recombination in the homolytic S-N bond cleavage process. This effect allowed for the storage of SNAC in PEG at -20 degrees C in the dark for more than 10 weeks with negligible decomposition. Such stabilization may represent a viable option for the synthesis, storage and handling of S-nitrosothiol solutions for biomedical applications.

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We investigated the ability of S-nitroso-N-acetylcyseine (SNAC) to prevent structural and functional myocardial alterations in hypercholesterolemic mice. C57BL6 wild-type (WT) and LDL-R-/- male mice (S) were fed a standard diet for 15 days. LDL-R-/- mice (S) showed an 11% increase in blood pressure, 62% decrease in left atrial contractility, and lower CD40L and eNOS expression relative to WT. LDL-R-/- mice fed an atherogenic diet for 15 days (Chol) showed significant increased left ventricular mass compared to S, which was characterized by: (1) 1.25-fold increase in the LV weight/body weight ratio and cardiomyocyte diameter; (2) enhanced expression of the NOS isoforms, CD40L, and collagen amount; and (3) no alteration in the atrial contractile performance. Administration of SNAC to Chol mice (Chol + SNAC) (0.51 micromol/kg/day for 15 day, IP) prevented increased left ventricular mass, collagen deposit, NOS isoforms, and CD40L overexpression, but it had no effect on the increased blood pressure or atrial basal hypocontractility. Deletion of the LDL receptor gene in mice resulted in hypertension and a marked left atrial contractile deficit, which may be related to eNOS underexpression. Our data show that SNAC treatment has an antiinflammatory action that might contribute to prevention of structural and functional myocardial alterations in atherosclerotic mice independently of changes in blood pressure.