4-Hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) Inhibits Peroxynitrite-Mediated Phenol Nitration

Abstract

Peroxynitrite (PN), a very reactive oxidant formed by the combination of superoxide and nitric oxide, appears to play a role in producing tissue damage in a number of inflammatory conditions. Pharmacological scavenging and decomposition of PN within these areas has therapeutic value in several tissue injury models. Recently, we have been interested in nitroxide free radical-containing compounds as possible scavengers of PN decomposition products. Nitroxides can undergo redox reactions to the corresponding hydroxylamine anion or oxoammonium cation in biological systems as shown by its ability to react with superoxide, leading to the formation of hydrogen peroxide and molecular oxygen. We found that 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) inhibits PN-mediated nitration of phenolic compounds in the presence of a large molar excess of PN, suggesting a catalytic-like mechanism. In these experiments, Tempol inhibited PN-mediated nitration over the pH range of 6.5-8.5. This inhibition was specific for nitration and had no effect on hydroxylation. After the inhibition of PN-mediated nitration, Tempol was recovered from the reaction mixtures unmodified. In addition, Tempol was effective in protecting PC-12 cells from death induced by SIN-1, a PN-generating compound. The exact mechanism of Tempol's interaction with PN is not clear; however, we propose that an intermediate in this reaction may be a nitrogen dioxide radical-Tempol complex. This complex could react with water to form either nitrite or nitrate, or with a phenol radical to produce nitrophenol or nitrosophenol products and regenerate the nitroxide.

Temporal relationship of peroxynitrite-induced oxidative damage, calpain-mediated cytoskeletal degradation and neurodegeneration after traumatic brain injury

“…Furthermore, our in vitro studies with isolated brain mitochondria have demonstrated that application of compounds such as penicillamine, which scavenges PN anion (ONOO − ) and peroxynitrous acid (ONOOH) (Hall et al, 1999), or tempol, which catalytically scavenge PN-derived oxygen radicals (e.g. •NO 2 , •CO 3 ) (Carroll et al, 2000), can protect against PNmediated mitochondrial respiratory dysfunction and oxidative damage (Singh et al, 2006b). Both penicillamine (Hall et al, 1999) and tempol (Beit-Yannai et al, 1996) have been reported to improve neurological recovery in rodent TBI models.…”

Neuroprotective Effects of Tempol, a Catalytic Scavenger of Peroxynitrite-Derived Free Radicals, in a Mouse Traumatic Brain Injury Model

“…The mice were anesthetized with isoflurane (3.0%), shaved, and then placed in a stereotaxic frame (David Kopf Instruments, Tujunga, CA, USA). Throughout the surgery, the mice were provided with constant isoflurane (SurgiVet 100 Series) and oxygen (SurgiVet,O 2 Figure 1 Top: chemical structure of tempol and the chemistry of its catalytic scavenging of PN-derived nitrogen dioxide (KNO 2 ) and carbonate radicals ( K CO 3 ) (Carroll et al, 2000).…”

“…Nitroxides have been shown to catalytically convert superoxide radical (O 2 K À ) to hydrogen peroxide and oxygen just like superoxide dismutase. However, it has been shown more recently that tempol can also catalytically decompose the PN-derived free radicals nitrogen dioxide ( K NO 2 ) and carbonate ( K CO 3 ) with a very rapid rate constant (Carroll et al, 2000), as illustrated in Figure 1. Thus, because of its multiple antioxidant properties, and its membrane permeability, tempol or similar nitroxide compounds may have considerable therapeutic value in protection against PN-mediated oxidative damage.…”

Drug development in spinal cord injury: What is the FDA looking for?

“…Peroxynitrite is capable of causing widespread damage to lipids, proteins, and nucleic acids. Prototypical scavengers of peroxynitrite include penicillamine and Tempol, both of which are neuroprotective in cell culture and in vivo models of acute CNS injury [41,42].…”