Detailed mechanistic investigation into the S-nitrosation of cysteamine

Abstract

The nitrosation of cysteamine (H2NCH2CH2SH) to produce cysteamine-S-nitrosothiol (CANO) was studied in slightly acidic medium by using nitrous acid prepared in situ. The stoichiometry of the reaction was H2NCH2CH2SH + HNO2 → H2NCH2CH2SNO + H2O. On prolonged standing, the nitrosothiol decomposed quantitatively to yield the disulfide, cystamine: 2H2NCH2CH2SNO → H2NCH2CH2S–SCH2CH2NH2 + 2NO. NO2 and N2O3 are not the primary nitrosating agents, since their precursor (NO) was not detected during the nitrosation process. The reaction is first order in nitrous acid, thus implicating it as the major nitrosating agent in mildly acidic pH conditions. Acid catalyzes nitrosation after nitrous acid has saturated, implicating the protonated nitrous acid species, the nitrosonium cation (NO+) as a contributing nitrosating species in highly acidic environments. The acid catalysis at constant nitrous acid concentrations suggests that the nitrosonium cation nitrosates at a much higher rate than nitrous acid. Bimolecular rate constants for the nitrosation of cysteamine by nitrous acid and by the nitrosonium cation were deduced to be 17.9 ± 1.5 (mol/L)−1 s−1 and 6.7 × 104 (mol/L)−1 s−1, respectively. Both Cu(I) and Cu(II) ions were effective catalysts for the formation and decomposition of the cysteamine nitrosothiol. Cu(II) ions could catalyze the nitrosation of cysteamine in neutral conditions, whereas Cu(I) could only catalyze in acidic conditions. Transnitrosation kinetics of CANO with glutathione showed the formation of cystamine and the mixed disulfide with no formation of oxidized glutathione (GSSG). The nitrosation reaction was satisfactorily simulated by a simple reaction scheme involving eight reactions.

Cysteamine, an Endogenous Aminothiol, and Cystamine, the Disulfide Product of Oxidation, Increase Pseudomonas aeruginosa Sensitivity to Reactive Oxygen and Nitrogen Species and Potentiate Therapeutic Antibiotics against Bacterial Infection

“…CTM had more pronounced potentiation of the MIC than CYS ( Table 1 ), but CYS formed an adduct species with SNAP and NaNO 2 that was bacteriostatic in nature. This was evident from a color change (to pink) in microtiter plates used in checkerboard experiments at high concentrations to determine the relative effects on the MIC, and peaks in UV spectroscopy at 333 nm and 545 nm, characteristic of the S-nitrosothiol compound S -nitrosocysteamine, although the identity was not confirmed ( 36 ). Like other biological S-nitrosothiol compounds, the reaction between the NO donor and thiol was optimal under slightly acidic pH conditions ( 36 ) but within physiological parameters ( 37 ) for inflamed tissues ( Fig.…”

“…The potential interplay of CYS and other innate immune effector molecules, such as NO, is fascinating. S -Nitrosocysteamine has been considered a potential NO carrier ( 36 ), but it was thought to be too short-lived a molecule for use therapeutically. The identity of this adduct needs to be confirmed with nuclear magnetic resonance (NMR) spectroscopy.…”

Natural Products Containing a Nitrogen–Sulfur Bond

“…Non-amino acid cellular thiols were also shown to be nitroslylated under physiological conditions, and their involvement in regulation of various physiological processes through controlled release of NO is currently under intensive investigation. S -Nitrosation of cysteamine to S -nitroso-cysteamine ( 111 ) was proposed to serve as an alternative nitric oxide carrier system, but it is yet to be proven to be relevant in vivo . − …”