Scavenging of Free Radicals by Tenoxicam: A Participating Mechanism in the Antirheumatic/Antiinflammatory Efficacy of the Drug
1996; Wiley; Volume: 329; Issue: 10 Linguagem: Inglês
10.1002/ardp.19963291007
ISSN1521-4184
AutoresRoberto Maffei Facino, M. Carini, Luisella Saibene,
Tópico(s)Antioxidant Activity and Oxidative Stress
ResumoAbstract The radical scavenging activity of tenoxicam against hydroxyl (HO⋅), superoxide (O 2 ⋅− ), and peroxyl (LOO⋅) radicals, all of them involved in the inflammatory reactions, has been tested in different cell‐free systems and by different techniques. Tenoxicam is a good scavenger of both HO⋅ radicals (IC 50 = 56.7 μM), as determined by Electron Spin Resonance (ESR) spectroscopy with the spin trapping (5,5‐dimethyl‐1‐pyrroline N ‐oxide, DMPO) technique, and O 2 ⋅− radicals generated by the phenazine methosulfate/reduced β‐nicotinamide adenine dinucleotide (PMS/NADH) system. The high reactivity of the drug towards HO⋅ was confirmed by the rate constant of reaction with HO⋅ ( k ⋍ 10 10 M −1 s −1 ), determined by competition kinetic studies with N,N ‐dimethyl‐4‐nitrosoaniline. In addition at a μM level (1–5 μM) it dose‐dependently prevents the phycoerythrin peroxidation induced by the water‐soluble azoinitiator 2,2‐azobis(2‐amidinopropane) dihydrochloride (ABAP), indicating a quenching effect on aqueous peroxyl radicals. The HO⋅‐entrapping capacity was confirmed in models more close to the in vivo situation: tenoxicam inhibits the HO⋅‐induced depolymerization of hyaluronic acid already at 15 μM and the HO⋅‐driven lipid peroxidation in phosphatidylcholine liposomes (PCL) with an IC 50 of 10 μM. In this membrane model it delays at 1–10 μM level the decomposition of phosphatidylcholine hydroperoxides to short‐chain alkenals (markers: total carbonyl functions as 2,4‐dinitrophenylhydrazones and conjugated dienes). The high susceptibility of the drug of HO⋅ attack is also demonstrated by its extensive degradation (HPLC studies) when irradiated with HO⋅ radicals. The antioxidant component of tenoxicam evidenced in this study sheds some light on the hitherto undefined mechanism of the antiinflammatory action of the drug.
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