Abstract
Fraxinus angustifolia leaves and bark are used in traditional medicine against various inflammatory-related pathologies incumbent to reactive oxygen species (ROS) generation by the NADH oxidase activity of enzymes such as xanthine oxidoreductase (XOR). This study was designed to investigate the in vitro and in vivo inhibitory activities of this enzyme by Fraxinus angustifolia extracts. The leaf organic phase of ethyl acetate (LFA) and its bark aqueous counterpart (BFA) showed the strongest anti-NADH oxidase activity in vitro (IC50 = 38.51 and 42.04 µg mL-1, respectively). They consequently suppressed superoxide generation both enzymatically (53% and 19%, respectively) and nonenzymatically (34% and 19%, respectively). These results were corroborated in vivo, with high antiNADH oxidase potential of the leaves and bark extracts (75.32% and 51.32%, respectively) concomitant with moderate hypouricemic activities (36.84% and 38.59%, respectively). Bio-guided fractionation led to the identification, by LC-DAD-MS/MS, of esculin and calcelarioside in bark and kaempferol glucoside in leaves as the main compounds responsible for the anti-NADH oxidase activity of XOR. These results plead in favor of the use of F. angustifolia as a source of potentially interesting therapeutic substances.
Highlights
Xanthine oxidase (XO) and xanthine dehydrogenase (XDH) are interconvertible forms of the same enzyme, known as xanthine oxidoreductase (XOR)
The amount of total phenols ranged from 326 to 1143 mg VAE g−1 extract for leaves, the highest being that of the aqueous chloroform extract phase (1144 mg VAE g−1 extract)
Lower ranges were noticed for bark extracts (25 to 189 mg VAE g−1), the most prominent being that of the organic ethyl acetate phase (189 mg VAE g−1 extract)
Summary
Xanthine oxidase (XO) and xanthine dehydrogenase (XDH) are interconvertible forms of the same enzyme, known as xanthine oxidoreductase (XOR). In a mammalian fresh tissue, XOR exists under the XDH form, which is NAD-dependent and produces primarily NADH at the FAD site (Waud and Rajagopalan, 1976; Hattori, 1989). This form is converted to an O2- dependent type (XO) during the procedures of extraction and purification. Both forms of the enzyme show NADH oxidase activity, with generation of ROS, but XDH is somewhat more effective in this respect (Atmani et al, 2005). ROS species are directly produced by XOR, with uric acid as its end product, whereas they are generated secondarily by XDH, as the enzyme produces primarily the reduced
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