title: Dihydrolipoic acid inhibits 15-lipoxygenase-dependent lipid peroxidation.
abstract: The potential antioxidant effects of the hydrophobic therapeutic agent lipoic acid (LA) and of its reduced form dihydrolipoic acid (DHLA) on the peroxidation of either linoleic acid or human non-HDL fraction catalyzed by soybean 15-lipoxygenase (SLO) and rabbit reticulocyte 15-lipoxygenase (RR15-LOX) were investigated. DHLA, but not LA, did inhibit SLO-dependent lipid peroxidation, showing an IC(50) of 15 microM with linoleic acid and 5 microM with the non-HDL fraction. In specific experiments performed with linoleic acid, inhibition of SLO activity by DHLA was irreversible and of a complete, noncompetitive type. In comparison with DHLA, the well-known lipoxygenase inhibitor nordihydroguaiaretic acid and the nonspecific iron reductant sodium dithionite inhibited SLO-dependent linoleic acid peroxidation with an IC(50) of 4 and 100 microM, respectively, while the hydrophilic thiol N-acetylcysteine, albeit possessing iron-reducing and radical-scavenging properties, was ineffective. Remarkably, DHLA, but not LA, was also able to inhibit the peroxidation of linoleic acid and of the non-HDL fraction catalyzed by RR15-LOX with an IC(50) of, respectively, 10 and 5 microM. Finally, DHLA, but once again not LA, could readily reduce simple ferric ions and scavenge efficiently the stable free radical 1,1-diphenyl-2-pycrylhydrazyl in ethanol; DHLA was considerably less effective against 2,2'-azobis(2-amidinopropane) dihydrochloride-mediated, peroxyl radical-induced non-HDL peroxidation, showing an IC(50) of 850 microM. Thus, DHLA, at therapeutically relevant concentrations, can counteract 15-lipoxygenase-dependent lipid peroxidation; this antioxidant effect may stem primarily from reduction of the active ferric 15-lipoxygenase form to the inactive ferrous state after DHLA-enzyme hydrophobic interaction and, possibly, from scavenging of fatty acid peroxyl radicals formed during lipoperoxidative processes. Inhibition of 15-lipoxygenase oxidative activity by DHLA could occur in the clinical setting, eventually resulting in specific antioxidant and antiatherogenic effects.
authors: Dipartimento di Medicina e Scienze dell'Invecchiamento and Centro di Scienze dell'Invecchiamento-Fondazione Universita' G. d'Annunzio, Chieti, Italy. piersd@tiscalinet.it
authors: Domenico
authors: D
authors: Lapenna
authors: Giuliano
authors: G
authors: Ciofani
authors: Sante Donato
authors: SD
authors: Pierdomenico
authors: Maria Adele
authors: MA
authors: Giamberardino
authors: Franco
authors: F
authors: Cuccurullo
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D001093:Arachidonate 15-Lipoxygenase / Q000378:metabolism*; D004227:Dithionite / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism; D006801:Humans; D019787:Linoleic Acid / Q000737:chemistry / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects*; D016859:Lipoxygenase Inhibitors; D009637:Masoprocol / Q000494:pharmacology; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology*; D013025:Glycine max / Q000201:enzymology*; D008063:Thioctic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D000975:Antioxidants; D016166:Free Radical Scavengers; D005609:Free Radicals; D016859:Lipoxygenase Inhibitors; D004227:Dithionite; D008063:Thioctic Acid; D009637:Masoprocol; C015144:dihydrolipoic acid; D019787:Linoleic Acid; D001093:Arachidonate 15-Lipoxygenase; D000111:Acetylcysteine