title: Targeting lipoic acid to mitochondria: synthesis and characterization of a triphenylphosphonium-conjugated alpha-lipoyl derivative.
abstract: Lipoic acid (LA) is a widely used antioxidant that protects mitochondria from oxidative damage in vivo. Much of this protection is thought to be due to the reduction of LA to dihydrolipoic acid (LAH(2)). This reduction is catalyzed in vivo by thioredoxin, thioredoxin reductase (TrxR), and lipoamide dehydrogenase. We hypothesized that specifically targeting LA to mitochondria, the site of most cellular reactive oxygen species production, would make it a more effective antioxidant. To do this, we made a novel molecule, MitoLipoic acid, by attaching lipoic acid to the lipophilic triphenylphosphonium cation. MitoL was accumulated rapidly within mitochondria several-hundred fold driven by the membrane potential. MitoL was reduced to the active antioxidant dihydroMitoLipoic acid by thioredoxin and by lipoamide dehydrogenase but not by TrxR. In isolated mitochondria or cells MitoL was only slightly reduced (5-10%), while, in contrast, LA was extensively reduced. This difference was largely due to the reaction of LA with TrxR, which did not occur for MitoL. Furthermore, in cells MitoL was quantitatively converted to an S-methylated product. As a consequence of its lack of reduction, MitoL was not protective for mitochondria or cells against a range of oxidative stresses. These results suggest that the protective action of LA in vivo may require its reduction to LAH(2) and that this reduction is largely mediated by TrxR.
authors.affiliation: Medical Research Council Dunn Human Nutrition Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 2XY, UK.
authors.forename: Stephanie E
authors.initials: SE
authors.lastname: Brown
authors.forename: Meredith F
authors.initials: MF
authors.lastname: Ross
authors.forename: Alejandra
authors.initials: A
authors.lastname: Sanjuan-Pla
authors.forename: Abdul-Rahman B
authors.initials: AR
authors.lastname: Manas
authors.forename: Robin A J
authors.initials: RA
authors.lastname: Smith
authors.forename: Michael P
authors.initials: MP
authors.lastname: Murphy
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D008058:Dihydrolipoamide Dehydrogenase / Q000378:metabolism; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D051381:Rats; D017382:Reactive Oxygen Species; D008063:Thioctic Acid / Q000737:chemistry / Q000494:pharmacology*; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism
chemical_list: D000975:Antioxidants; D009943:Organophosphorus Compounds; D017382:Reactive Oxygen Species; D013879:Thioredoxins; D008063:Thioctic Acid; D008058:Dihydrolipoamide Dehydrogenase; D013880:Thioredoxin-Disulfide Reductase