Lipophilic antioxidant

Kaneko et al. (1993) have described a group of lipophilic ascorbic-acid analogues that have been studied in cultured human umbilical vein endothelial cells that were first incubated with test drug and then exposed to lipid hydroperoxides. Although ascorbate itself did not protect the endothelial cells, derivatives like CV3611 protected. Pretreatment was necessary. CV3611 was synergistic with vitamin E. The authors concluded that these lipophilic antioxidants incorporate into endothelial cell membranes where they are effective inhibitors of lipid peroxidation. In contrast, lipophobic antioxidants were not effective in their hands (Kaneko et al., 1993). 

Figure 32 Disappearance and appearance kinetics of transcellular flux of the lipophilic antioxidant PNU-78,517 (pKa 6.5) across MDCK cell monolayers in Transwell systems at 37°C. Donor solutions contained 3% bovine serum albumin (BSA), and receiver solutions contained 0.5-5% BSA at pH 7.4. [Redrawn from Raub et al. (1993) with permission from the publisher.]... 

T. J., Increased lipophilicity and subsequent cell partitioning decrease passive transcellular diffusion of novel, highly lipophilic antioxidants,... 

Sawada, G. A., Williams, L. R., Lutzke, B. S., Raub, T. J., Novel, highly lipophilic antioxidants readily diffuse across the blood-brain barrier and access intracellular sites,... 

The ORAC assay proposed by Ou and others (2001) is limited to hydrophilic antioxidants because of the aqueous environment of the assay. However, lipophilic antioxidants play a critical role in biological defense systems. Huang and others (2002) expanded the assay to the lipidic fraction by introducing a randomly methylated 13-cyclodextrin (RMCD) as a water-solubility enhancer for lipophilic antioxidants. Various kinds of foods, including fruit juices and drinks, fruits, vegetables, nuts, and dried fruits, have been evaluated with this method (Zhou and Yu 2006 Wu and others 2004 Kevers and others 2007 Wang and Ballington 2007 Almeida and others 2008 Mullen and others 2007). 

In 2003, Prior and others described methods for the extraction and analysis of hydrophilic and lipophilic antioxidants, using modifications of the ORAC procedure. These methods provide, for the first time, the ability to obtain a measure of total antioxidant capacity in the protein free plasma, using the same peroxyl radical generator for both lipophilic and hydrophilic antioxidants. This assay was also used to measure the total antioxidant capacity of guava fruit extracts (Thaipong and others 2006). 

Some years later, Miller and others (1996) described a modified TEAC assay that is able to determine the antioxidant activity of carotenoids. In the improved version, ABTS,+, the oxidant, is generated by oxidation of 2,2 -azinobis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS2 ) with manganese dioxide. A similar approach was described by Re and others (1999) in which ABTS was oxidized with potassium persulfate (Fig. 10.2), this version of the TEAC assay is applicable to both water soluble and lipophilic antioxidants (Re and others 1999 Pellegrini and others 1999). 

Alcolea JF, Cano A, Acosta M and Arnao MB. 2002. Hydrophilic and lipophilic antioxidant activities of grapes. Nahrung/Food 46(5) 353-356. 

Cano A and Arnao MB. 2005. Hydrophilic and lipophilic antioxidant activity in different leaves of three lettuce varieties. In J Food Prop 8(3) 521—528. 

Cho YS, Yeum KJ, Chen CY, Beretta G, Tang G, Krinsky NI, Yoon S, Lee-Kim YC, Blumberg JB and Russell RM. 2007. Phytonutrients affecting hydrophilic and lipophilic antioxidant activities in fruits, vegetables and legumes. J Sci Food Agric 87(6) 1096-1107. 

Huang D, Ou B, Hampsch-Woodill M, Flanagan JA and Deemer EK. 2002. Development and validation of oxygen radical absorbance capacity assay for lipophilic antioxidants using randomly methylated (3-cyclodextrin as the solubility enhancer. J Agric Food Chem 50(7) 1815-1821. 

Prior RL, Hoang H, Gu L, Wu X, Bacchiocca M, Howard L, Hampsch-Woodill M, Huang D, Ou B and Jacob R. 2003. Assays for hydrophilic and lipophilic antioxidant capacity (oxygen radical absorbance capacity (ORACfl)) of plasma and other biological and food samples. J Agric Food Chem 51(ll) 3273-3279. 

Silva BM, Andrade PB, Valentao P, Ferreres F, Seabra RM and Ferreira M A. 2004. Quince (Cydonia oblonga Miller) fruit (pulp, peel, and seed) and jam antioxidant activity. J Agric Food Chem 52(15) 4705-4712. Silva DHS, Pereira FC, Zanoni MVB and Yoshida M. 2001. Lipophilic antioxidants from Iryanthera juruensis fruits. Phytochemistry 57(3) 437 J42. 

The possible prooxidant effects of a major lipophilic antioxidant vitamin E (a-tocopherol) have already been discussed in Chapter 25. Yamashita et al. [82] showed that a-tocopherol induced extensive DNA damage including base modification and strand breakage in the... 

Sawada GA, Barsuhn CL, Lutzke BS, Houghton ME, Padbury GE, Ho NFH, Raub TJ (1999) Increased lipophilicity and subsequent cell partitioning decrease passive transcellular diffusion of novel, highly lipophilic antioxidants. J Pharmacol Exp Ther 288 1317-1326. 

Butylated hydroxytoluene (BHT) (33) is another widely used lipophilic antioxidant. Inhibition of 12-LO and 15-LO has been reported at millimolar concentrations, with somewhat more potent activity against CO [58,111,112]. More recently, BHT was found to inhibit 5-LO from potato [113] and RBL-1 cells [114] at concentrations near 1 / M. However, anti-inflammatory activity has not been reported. 

Vitamin E or a-tocopherol is a lipophilic antioxidant which animals cannot synthesize. However vi-... 

Engelmann B. (2004). Plasmalogens targets for oxidants and major lipophilic antioxidants. Biochem. Soc. Trans. 32 147-150. 

The contribution of lipophilic antioxidants is small. Escobar et al. (E5) found that the TAC of lipophilic antoxidants in blood plasma was 16.5 1.5 pM and corresponded almost exclusively to a-tocopherol the concentration of this compound in the blood plasma, analyzed independently, was 17.6 0.3 pM. Popov and Lewin (PI9) found TAC of lipid-soluble antioxidants in blood plasma to be 28.0 8.1 /u.M, a value comparable with the concentration of a-tocopherol (20.5 6.6 /U.M). These (and other) results confirm that a-tocopherol is the main lipid-soluble antioxidant of blood plasma (II) and indicates that the contribution of the lipid-soluble antioxidants to TAC of blood plasma is in fact negligible, taking into account that TAC of human blood plasma is of the order of 1 mM (see later). The contribution of ascorbic acid is also low. This situation may differ considerably in other biological fluids and tissue homogenates. In seminal plasma, the concentration ratio of ascorbate to urate is about 1 (G3). Ascorbate and urate contribute 29% of the fast TRAP of human seminal plasma the share of proteins and polyphenolic compounds is 57%, whereas tyrosine contributes 15% of the slow TRAP (R14) (Table 7). Ascorbate and uric acid account for about half of TAC of human tears (K3). TAC of urine is determined mainly by urate and proteins (K5). 

Passi, S. et al., The combined use of oral and topical lipophilic antioxidants increases their levels both in sebum and stratum corneum, Biofactors, 18, 289, 2003. 

Tijburg, L.B., Wiseman, S.A., Meijer, G.W., and Weststrate, J.A. 1997. Effects of green tea, black tea and dietary lipophilic antioxidants on LDL oxidizability and atherosclerosis in hypercholester-olaemic rabbits. Atherosclerosis 135, 37-47. 

In this chapter we summarize work from our laboratory in which we have tested these predictions. The hairless mouse is our model. Initial experiments utilized excised skin while later studies used an in vivo system. We irradiated these systems with either UVA (320 100 nm), UVB (290-320 nm), or simulated sunlight in a pattern of UVA and UVB which closely matched natural sunlight. We have measured UV-induced changes in antioxidants, lipid peroxidation, and the effects of dietary supplementation with the major chain-breaking lipophilic antioxidant, a-tocopherol, on UV-induced skin damage. 

In the second experiment, mice were irradiated with the highest dose from the dose-response experiment. Concentrations of lipid hydroperoxides and lipophilic antioxidants were measured simultaneously on single skin samples from irradiated and non-irradiated sides of each mouse. The lipid hydroperoxide assay directly measured lipid peroxidation and thus was superior to the TBARS assay, which is indirect. Lipid-peroxyl radicals have been linked to chemically induced cutaneous carcinogenesis [31] as well as to UV-light-induced cutaneous carcinogenesis [32],... 

Fig. 8. Response of cutaneous lipophilic antioxidants to increasing doses of simulated sunlight (combined UVA and UVB). The lowest dose (0.25 J/cm2) is the equivalent of about 0.1 MED the highest dose (25 J/cm2) is the equivalent of about 10MED.

Fig. 9. Concentrations of cutaneous lipophilic antioxidants after a single large dose (25J/cm2) of simulated sunlight. Total quinol/one = ubiquinol + ubiquinone, n = 6. Inset (A) concentration of lipid hydroperoxides in the same skin samples, irradiated and non-irradiated (none detectable in non-irradiated samples). Statistically different from unirradiated controls double asterisks, p < 0.01 ...

The cutaneous vitamin E concentrations of mice were augmented by feeding them diets containing either 30 IU/kg diet a-tocopherol (n = 8) or lOOOOIU/kg diet a-tocopherol (n = 12). At intervals in the feeding regimen, mice from each group were irradiated with UV light, skin was sampled, and its content of lipophilic antioxidants and lipid hydroperoxides was analyzed as described for Experiment 1. 

Fig. 13. Relationships between lipophilic antioxidants and lipid hydroperoxides in irradiated skin. (A) There was no relationship between decrease in a-tocopherol and appearance of lipid hydroperoxides. (B) There was a significant (p < 0.05) relationship between decrease in total Q (quinols + quinones) and appearance of lipid hydroperoxides.

Adorn, K.K. Liu, R.H. 2005. Rapid peroxyl radical scavenging capacity (PSC) assay for assessing both hydrophilic and lipophilic antioxidants. J. Agric. Food Chem. 53 6572-6580. 

---