title: Supplementation with beta-carotene in vivo and in vitro does not inhibit low density lipoprotein oxidation.
abstract: The inhibition of low density lipoprotein (LDL) oxidation has been postulated as one mechanism by which antioxidants may prevent the development of atherosclerosis. Available data on the ability of beta-carotene to inhibit LDL oxidation are conflicting. We examined the role of in vivo and in vitro supplementation with beta-carotene on metal ion-dependent (cupric ions, Cu2+) and metal ion-independent (2,2'-azobis[2-amidinopropane]dihydrochloride, AAPH) oxidation of LDL as measured by the formation of conjugated dienes (absorbance at 234 nm). Sixteen subjects were supplemented with 50-100 mg of beta-carotene on alternate days for 3 weeks following a week-long loading dose of 100 mg/day. Plasma beta-carotene levels rose 5.5-fold, while LDL beta-carotene levels rose 8.5-fold. Oxidation of LDL by Cu2+ or AAPH was not significantly delayed after in vivo supplementation with beta-carotene compared with baseline. For AAPH, the lag phase (in minutes) was 75 +/- 8 at baseline and 83 +/- 14 after supplementation (P = 0.07). For Cu2+, the lag phase was 172 +/- 41 at baseline and decreased to 130 +/- 24 after supplementation (P < 0.01). Similarly, no protective effect against Cu(2+)-induced oxidation was observed when beta-carotene was added to LDL in vitro. Supplementation of plasma with beta-carotene in vitro prior to LDL isolation also did not enhance LDL's resistance to Cu(2+)- or AAPH-induced oxidation, despite a 5-fold increase in LDL beta-carotene levels over vehicle control.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Gaziano
authors.forename: A
authors.initials: A
authors.lastname: Hatta
authors.forename: M
authors.initials: M
authors.lastname: Flynn
authors.forename: E J
authors.initials: EJ
authors.lastname: Johnson
authors.forename: N I
authors.initials: NI
authors.lastname: Krinsky
authors.forename: P M
authors.initials: PM
authors.lastname: Ridker
authors.forename: C H
authors.initials: CH
authors.lastname: Hennekens
authors.forename: B
authors.initials: B
authors.lastname: Frei
mesh_terms: D000328:Adult; D002338:Carotenoids / Q000097:blood / Q000494:pharmacology*; D005260:Female; D006801:Humans; D015227:Lipid Peroxidation / Q000187:drug effects; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction / Q000187:drug effects; D019207:beta Carotene
chemical_list: D008077:Lipoproteins, LDL; D019207:beta Carotene; D002338:Carotenoids