Reactions of PTIO and Carboxy-PTIO with ·NO, ·NO2, andO2.¯

Abstract

Nitronyl nitroxides, such as derivatives of 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIOs), react with ⅐ NO to form the corresponding imino nitroxides (PTIs) and ⅐ NO 2 . PTIOs are considered as monitors of ⅐ NO, stoichiometric sources of ⅐ NO 2 , biochemical and physiological effectors, specific tools for the elimination of ⅐ NO, and potential therapeutic agents. However, a better understanding of the chemical properties of PTIOs, especially following their reaction with ⅐ NO, is necessary to resolve many of the reported discrepancies surrounding the effects of PTIOs and to better characterize their potential therapeutic activity. We have generated electrochemically the oxidized and reduced forms of PTIO and carboxy-PTIO (C-PTIO), characterized their absorption spectra, and determined the reduction potentials for the oxoammonium/nitroxide and nitroxide/hydroxylamine couples. The rate constants for the reaction of ⅐ NO 2 with PTIO and C-PTIO to form the corresponding oxoammonium cations (PTIO ؉ s) and nitrite were determined to be (1. Nitric oxide ( ⅐ NO) 1 is synthesized by ⅐ NO synthase from the substrate L-arginine in a wide variety of cell types and is a major participant in numerous beneficial physiological functions such as blood pressure regulation, inhibition of platelet aggregation, and neurotransmission (1). However, high steadystate levels of ⅐ NO function critically in modulating inflammatory, infectious, and degenerative diseases (2-6). The reaction of ⅐ NO with metalloproteins can abrogate the function of proteins (7, 8). Moreover, the reactions of ⅐ NO with oxygen and superoxide convert ⅐ NO into other reactive nitrogen species such as ONOO Ϫ , ⅐ NO 2 , or N 2 O 3 , which can react with virtually all of the classes of biomolecules including amino acids, lipids, DNA, thiols, and metals (5, 6, 9 -11). One therapeutic approach to ameliorate ⅐ NO-induced biological damage is to use ⅐ NO scavengers, preferably selective scavengers that distinguish between free ⅐ NO and species exhibiting ⅐ NO-like biological activity.The use of nitronyl nitroxides, such as 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), as selective traps for ⅐ NO is rapidly increasing as reflected by the numerous publications in the recent biomedical literature. PTIO and its derivatives were shown to react with ⅐ NO to form the corresponding imino nitroxides and ⅐ NO 2 (12-16), where k 1 ϭ (0.5 Ϫ 16) ϫ 10 4 M Ϫ1 s Ϫ1 (Reaction 1) (12, 14, 16).Both the nitronyl nitroxide and the imino nitroxide are detectable and distinguishable by EPR spectroscopy, and various PTIOs are used as spin traps for ⅐ NO (13, 14, 16 -18). In addition, Akaike et al. (12) demonstrated that excess of ⅐ NO 2 had no effect on the EPR spectrum of PTIOs and, subsequently, Reaction 1 has been adopted to generate ⅐ NO 2 (19,20). Likewise, direct scavenging of ⅐ NO by PTIOs has been shown to inhibit endothelium-derived relaxing factor (EDRF) in bioassay in vitro (12), to cause cell cycle alteration, to result in oxidative stress and a...

The reaction products of sulfide and S-nitrosoglutathione are potent vasorelaxants

“…To evaluate the importance of NO in the observed relaxation effects (Figs 3 and 4), the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) was applied [39]. cPTIO (100 μM) alone had no effect on basal vascular tone, but significantly increased contraction in the presence of phenylephrine ( Fig.…”

Pathways and key intermediates required for obligate aerobic ammonia-dependent chemolithotrophy in bacteria and Thaumarchaeota

“…N. multiformis was cultivated in 20 ml phosphate-buffered mineral medium (Skinner and Walker, 1961) amended with 1 mM NH 4 Cl and pH was adjusted regularly with 5% Na 2 CO 3 . In early to mid-exponential phase of growth, 150 μM of 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO; Sigma-Aldrich, Vienna, Austria), a chemical that scavenges NO (Goldstein et al, 2003) was injected into the cultures. Ammonium consumption and nitrite production were measured over a period of 6-8 days using standard colorimetric assays (Clesceri et al, 1998) and N 2 O was measured via GC (AGILENT 6890N, Vienna, Austria; injector: 120°C, detector: 350°C, oven: 35°C, carrier gas: N 2 ) in connection with an automatic sample-injection system (DANI HSS 86.50, Head-space-Sampler, Sprockhövel, Germany).…”

The Reaction between Nitrite and Oxyhemoglobin

“…To examine if NO 2 radical is an important intermediate in the reaction mechanism, we examined the effect of CPTIO. Goldstein and co-workers (21) have recently shown that the nitronyl nitroxide CPTIO reacts with NO 2 with a rate constant of 1.5 ϫ 10 7 M Ϫ1 s Ϫ1 yielding nitrite and CPTIO ϩ cation. The reaction is reversible with an equilibrium constant of 145.…”