title: Tocopheramine succinate and tocopheryl succinate: mechanism of mitochondrial inhibition and superoxide radical production.
abstract: Tocopherols (TOH) are lipophilic antioxidants which require the phenolic OH group for their redox activity. In contrast, non-redox active esters of α-TOH with succinate (α-TOS) were shown to possess proapoptotic activity in cancer cells. It was suggested that this activity is mediated via mitochondrial inhibition with subsequent O2(-) production triggering apoptosis and that the modification of the linker between the succinate and the lipophilic chroman may modulate this activity. However, the specific mechanism and the influence of the linker are not clear yet on the level of the mitochondrial respiratory chain. Therefore, this study systematically compared the effects of α-TOH acetate (α-TOA), α-TOS and α-tocopheramine succinate (α-TNS) in cells and submitochondrial particles (SMP). The results showed that not all cancer cell lines are highly sensitive to α-TOS and α-TNS. In HeLa cells α-TNS did more effectively reduce cell viability than α-TOS. The complex I activity of SMP was little affected by α-TNS and α-TOS while the complex II activity was much more inhibited (IC50=42±8μM α-TOS, 106±8μM α-TNS, respectively) than by α-TOA (IC50 >1000μM). Also the complex III activity was inhibited by α-TNS (IC50=137±6μM) and α-TOS (IC50=315±23μM). Oxygen consumption of NADH- or succinate-respiring SMP, involving the whole electron transfer machinery, was dose-dependently decreased by α-TOS and α-TNS, but only marginal effects were observed in the presence of α-TOA. In contrast to the similar inhibition pattern of α-TOS and α-TNS, only α-TOS triggered O2(-) formation in succinate- and NADH-respiring SMP. Inhibitor studies excluded complex I as O2(-) source and suggested an involvement of complex III in O2(-) production. In cancer cells only α-TOS was reproducibly able to increase O2(-) levels above the background level but neither α-TNS nor α-TOA. Furthermore, the stability of α-TNS in liver homogenates was significantly lower than that of α-TOS. In conclusion, this suggests that α-TNS although it has a structure similar to α-TOS is not acting via the same mechanism and that for α-TOS not only complex II but also complex III interactions are involved.
authors.affiliation: Institute of Pharmacology and Toxicology, Dept. of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria; University of Applied Sciences Wiener Neustadt (FHWN), Wiener Neustadt, Austria.
authors.forename: Julia
authors.initials: J
authors.lastname: Gruber
authors.affiliation: Institute of Pharmacology and Toxicology, Dept. of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Katrin
authors.initials: K
authors.lastname: Staniek
authors.affiliation: Institute of Medicinal Biochemistry, Dept. of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Christopher
authors.initials: C
authors.lastname: Krewenka
authors.affiliation: Institute of Medicinal Biochemistry, Dept. of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Moldzio
authors.affiliation: Dept. of Chemistry, University of Natural Resources and Life Sciences, Vienna, Austria.
authors.forename: Anjan
authors.initials: A
authors.lastname: Patel
authors.affiliation: Dept. of Chemistry, University of Natural Resources and Life Sciences, Vienna, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Böhmdorfer
authors.affiliation: Dept. of Chemistry, University of Natural Resources and Life Sciences, Vienna, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rosenau
authors.affiliation: Institute of Pharmacology and Toxicology, Dept. of Biomedical Sciences, University of Veterinary Medicine, Vienna, Austria. Electronic address: Lars.Gille@vetmeduni.ac.at.
authors.forename: Lars
authors.initials: L
authors.lastname: Gille
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D042967:Electron Transport Complex I / Q000037:antagonists & inhibitors / Q000378:metabolism; D042963:Electron Transport Complex II / Q000037:antagonists & inhibitors / Q000378:metabolism; D014450:Electron Transport Complex III / Q000037:antagonists & inhibitors / Q000378:metabolism; D005609:Free Radicals / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D015394:Molecular Structure; D013329:Structure-Activity Relationship; D013367:Submitochondrial Particles / Q000187:drug effects / Q000378:metabolism; D013386:Succinates / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D013481:Superoxides / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014810:Vitamin E / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D024502:alpha-Tocopherol / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D005609:Free Radicals; D013386:Succinates; D013481:Superoxides; D014810:Vitamin E; C092252:alpha-tocopheramine; D042963:Electron Transport Complex II; D042967:Electron Transport Complex I; D014450:Electron Transport Complex III; D024502:alpha-Tocopherol
keywords: Electron spin resonance spectroscopy; Mitochondria; Superoxide radicals; Tocopheramine succinate; Tocopheryl succinate