Cosupplementation With Coenzyme Q Prevents the Prooxidant Effect of α-Tocopherol and Increases the Resistance of LDL to Transition Metal–Dependent Oxidation Initiation by Shane R. Thomas, Jiří Neužil, and Roland Stocker Arterioscler Thromb Vasc Biol Volume 16(5):687-696 May 1, 1996 Copyright © American Heart Association, Inc. All rights reserved.

Oxidation of human LDL in Ham’s F-10 medium. Oxidation of human LDL in Ham’s F-10 medium. LDL (final concentration, 0.1 mg protein/mL) was incubated in Ham’s F-10 medium, and aliquots were extracted and analyzed for α-TOH (•), CE-OOH (□), and CEPUFAs (▪). CEPUFA data represent the amount of cholesteryl linoleate plus cholesteryl arachidonate consumed. The results shown represent mean±SEM of four separate experiments, each using LDL from a single donor. Shane R. Thomas et al. Arterioscler Thromb Vasc Biol. 1996;16:687-696 Copyright © American Heart Association, Inc. All rights reserved.

In vitro enrichment of LDL with α-TOH increases the susceptibility of LDL to oxidation initiation by human MDMs cultured in Ham’s F-10 medium. In vitro enrichment of LDL with α-TOH increases the susceptibility of LDL to oxidation initiation by human MDMs cultured in Ham’s F-10 medium. LDL (final concentration, 0.1 mg protein/mL), either α-TOH–enriched (squares) or native (circles), was incubated in Ham’s F-10 medium in the absence (open symbols) or presence (closed symbols) of human MDMs (1×106 cells/well). Aliquots were extracted and analyzed for CE-OOH (A) and α-TOH (B). Note that the α-TOH level is expressed as percent of the vitamin content present in each LDL sample at the beginning of the oxidation. The 100% values of α-TOH were 15.7±4.9 μmol/L and 2.3±0.3 μmol/L for enriched and native LDLs, respectively. The results shown represent mean±SEM of four separate experiments carried out in duplicate using LDL from a single donor. *Significant difference between lines of CE-OOH values of supplemented vs corresponding control LDL. Shane R. Thomas et al. Arterioscler Thromb Vasc Biol. 1996;16:687-696 Copyright © American Heart Association, Inc. All rights reserved.

Resistance of vitamin E–deficient LDL, isolated from a FIVE patient, to oxidation initiated by Ham’s F-10 medium. Resistance of vitamin E–deficient LDL, isolated from a FIVE patient, to oxidation initiated by Ham’s F-10 medium. Isolated LDL (final concentration, 0.1 mg/mL) prepared from the plasma of the FIVE patient either before (α-TOH–deficient LDL; open symbols) or after (α-TOH–supplemented LDL; closed symbols) dietary supplementation with α-TOH was incubated in Ham’s F-10 medium. At the time points indicated, aliquots were extracted and analyzed for α-TOH (circles) and CE-OOH (squares). Shane R. Thomas et al. Arterioscler Thromb Vasc Biol. 1996;16:687-696 Copyright © American Heart Association, Inc. All rights reserved.

Effect of dietary enrichment with either α-TOH or coenzyme Q on LDL oxidation initiated by Ham’s F-10 medium. Effect of dietary enrichment with either α-TOH or coenzyme Q on LDL oxidation initiated by Ham’s F-10 medium. LDL was incubated in Ham’s F-10 medium at a final concentration of 0.1 to 0.2 mg/mL. Enriched LDL samples were obtained from subjects supplemented with either α-TOH (A) (n=4) or coenzyme Q (B) for 6 hours (n=3) (•) or 5 days (n=8) (▪), and their oxidation was compared with the corresponding native LDL isolated from nonsupplemented plasma after 6 hours (○) or 5 days (□) of storage (see “Methods”). The results shown represent the mean±SEM of three to eight separate experiments, each carried out in duplicate. *Significant difference between lines of CE-OOH values of supplemented vs the corresponding control LDL. Shane R. Thomas et al. Arterioscler Thromb Vasc Biol. 1996;16:687-696 Copyright © American Heart Association, Inc. All rights reserved.

Cosupplementation with coenzyme Q efficiently protects LDL against the prooxidant effect of α-TOH supplementation alone. Cosupplementation with coenzyme Q efficiently protects LDL against the prooxidant effect of α-TOH supplementation alone. LDL was incubated in Ham’s F-10 medium at a final concentration of 0.1 to 0.2 mg protein/mL. The oxidation of enriched LDL samples from 8 subjects supplemented initially with α-TOH alone for 6 hours (•) and then cosupplemented with α-TOH and coenzyme Q for 5 days (▪) was compared with that of native LDL isolated from plasma taken before supplementation and stored for 6 hours (○) or 5 days (□). Note that the α-TOH level is expressed as percentage of the vitamin content present in each LDL sample at the beginning of the oxidation. The 100% values for α-TOH were 1.8±0.6 μmol/L for control LDL, 3.25±0.7 μmol/L for α-TOH–enriched LDL, and 4.7±0.8 μmol/L for coenriched LDL. The results shown represent mean±SEM of (A) (n=8) and (B) (n=4) separate experiments carried out in duplicate. *Significant difference between lines of CE-OOH values of supplemented vs the corresponding control LDL. Shane R. Thomas et al. Arterioscler Thromb Vasc Biol. 1996;16:687-696 Copyright © American Heart Association, Inc. All rights reserved.

Model of TMP for LDL lipid oxidation and antioxidation. Model of TMP for LDL lipid oxidation and antioxidation. As the most reactive component of LDL, α-TOH is oxidized first when LDL encounters an aqueous radical (eg, ROO• or Cu2+). On reaction with the aqueous radical, α-TOH is converted to α-TO• , which itself can undergo at least three different reactions resulting in regeneration of α-TOH. Reaction pathways 1 and 2 represent antioxidant activity of α-TOH (which requires coantioxidants), whereas pathway 3 represents prooxidant activity of α-TOH. In pathways 1 and 2, α-TO• reacts with either LDL-associated CoQ10H2 or the aqueous ascorbate (AH−) or albumin-bound bilirubin (HSA-BR). The resulting ubisemiquinone radical (CoQ10−•), formed due to the interaction of α-TO• with CoQ10H2, autooxidizes to CoQ10 inside LDL, and the resulting charged O2−• escapes to the aqueous phase, where it decays to nonradical products (NRP). In the case of the aqueous coantioxidants, the putative bilirubin (BR•) and ascorbyl (A−•) radicals decay to aqueous albumin-bound biliverdin (HSA-BV) and NRP, respectively. In the absence of coantioxidants (AH−, HSA-BR, and CoQ10H2) and under conditions of low radical flux, the prooxidant activity of α-TOH is apparent (pathway 3), where α-TO• is forced to react with a polyunsaturated lipid (LH), producing a carbon-centered lipid radical (L•), with the estimated rate constant for this TMP rate-limiting reaction being 0.1 mol·L−1·s−1.33 L• will add molecular oxygen (O2), forming a lipid peroxyl radical (LOO•) that propagates lipid peroxidation by reacting with another α-TOH, thereby regenerating α-TO•. Under conditions of high radical flux, pathway 4 becomes prevalent, which is characterized by increased levels of radical-radical termination reactions involving α-TO•. In pathway 4, α-TO• is eliminated by reaction with a second α-TO• (not shown) or oxidation-initiating aqueous radical, resulting in net α-TOH consumption and LDL lipid antioxidation. It is proposed that this pathway predominates in the action of vitamin E in the commonly used high radical flux Cu2+/LDL oxidation system. Shane R. Thomas et al. Arterioscler Thromb Vasc Biol. 1996;16:687-696 Copyright © American Heart Association, Inc. All rights reserved.