Superoxide anion, control

STUDY ON CHEMILUMINESCENT PROBES FOR SUPEROXIDE ANIONS CONTROL OF CHEMILUMINESCENCE RESONANCE ENERGY TRANSFER BY CYCLOMALTOOLIGOSACCHARIDE (CYCLODEXTRIN)... 

Many transition metal complexes have been considered as synzymes for superoxide anion dismutation and activity as SOD mimics. The stability and toxicity of any metal complex intended for pharmaceutical application is of paramount concern, and the complex must also be determined to be truly catalytic for superoxide ion dismutation. Because the catalytic activity of SOD1, for instance, is essentially diffusion-controlled with rates of 2 x 1 () M 1 s 1, fast analytic techniques must be used to directly measure the decay of superoxide anion in testing complexes as SOD mimics. One needs to distinguish between the uncatalyzed stoichiometric decay of the superoxide anion (second-order kinetic behavior) and true catalytic SOD dismutation (first-order behavior with [O ] [synzyme] and many turnovers of SOD mimic catalytic behavior). Indirect detection methods such as those in which a steady-state concentration of superoxide anion is generated from a xanthine/xanthine oxidase system will not measure catalytic synzyme behavior but instead will evaluate the potential SOD mimic as a stoichiometric superoxide scavenger. Two methodologies, stopped-flow kinetic analysis and pulse radiolysis, are fast methods that will measure SOD mimic catalytic behavior. These methods are briefly described in reference 11 and in Section 3.7.2 of Chapter 3. 

It has now been more than a decade since Beckman and his collaborators first disclosed their observations that the combination of two relatively unreactive, yet biologically relevant free radicals, superoxide anion and nitric oxide, would produce a new highly reactive physiologically important reagent. The interaction of these two presumably innocuous species appears to be diffusion controlled and produces a thermally stable peroxy anion, peroxynitrite (equation 1). ... 

In aprotic solvents the superoxide anion is a very weak oxidant the uptake of a proton from the substrate is followed by the dismutation of HOj Thus stable solutions of O/ can be prepared by controlled-potential coulometry... 

The selectivity of the trap towards hydroxyl radicals was demonstrated by several control experiments using different radicals, showing that the formation of the respective hydroxylation product, 5-hydroxy-6-0-zso-propyl-y-tocopherol (57), was caused exclusively by hydroxyl radicals, but not by hydroperoxyl, alkylperoxyl, alkoxyl, nitroxyl, or superoxide anion radicals. These radicals caused the formation of spin adducts from standard nitrone-and pyrroline-based spin traps, whereas a chemical change of spin trap 56 was only observed in the case of hydroxyl radicals. This result was independent of the use of monophasic, biphasic, or micellar reaction systems in all OH radical generating test systems, the trapping product 57 was found. For quantitation, compound 57 was extracted with petrol ether, separated by adsorption onto basic alumina and subsequently oxidized in a quantitative reaction to a-tocored, the deeply red-colored 5,6-tocopheryldione, which was subsequently determined by UV spectrophotometry (Scheme 23). 

Hyperglycemia-induced enhanced oxidative stress has also been reported in cultured VSMC and different tissues from STZ-diabetic rats (Baynes and Thorpe 1999 Baynes 1991 Cai and Harrison 2000). In addition, the contribution of enhanced production of superoxide anion (02 ) in the decreased expression of Gia proteins has recently been reported in aortic VSMC from STZ-diabetic rats and A10 cells exposed to high glucose (Li et al. 2008). Antioxidants such as a-tocopherol and NAC—scavengers of 02 —and DPI (an inhibitor of NADPH oxidase) that restored the enhanced levels of O2- induced by hyperglycemia also restored the hyperglycemia-induced decreased expression of Gia-2 and Gia-3 to control levels (Li et al. 2008). These studies implicate NADPH oxidase/C>2 in... 

SOD activity was assessed using a Ransod kit (Randox Laboratories Ltd.) that quenches the rate of inhibition of 2-(4-iodophenyl)-3-(4-nitrophenol)-5-phenyltetrazolium (INT) reduction by the superoxide anion released after xanthine oxidation with xanthine oxidase. One unit of SOD causes a 50% inhibition rate and the activity was expressed as U mL of whole blood and reported to the normal range. In each case, appropriate control serum for quality control had been used. 

A striking example is control of the steady state level of superoxide radical anion (Oj"). Although superoxide anions are not very reactive, they playa prominent role in oxidative stress by triggering formation of peroxy nitrite. The control of their steady state level is thus vital for cells. In most living organisms the well-known metalloenzyme superoxide dismutase (SOD), present in almost all aerobic cells catalyzes the disproportionation of into HjOj and Oj ... 

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