Bilirubin as an antioxidant in micelles and lipid bilayers: its contribution to the total antioxidant capacity of human blood plasma.
The antioxidant capacities, antioxidant activities, k(inh), and stoichiometric factors, n, of water-soluble derivatives of bilirubin (BR), BR-human serum albumin (BR-HSA), and BR-ditaurate disodium conjugate (BRC) were determined in aqueous/lipid dispersions of sodium dodecyl sulfate (SDS) micelles/methyl linoleate and in bilayers of dilinoleoylphosphatidylcholine (DLPC) during initiation by water-soluble azo-bis-amidinopropane dihydrochloride (ABAP). The inhibition rate constants for BRC and BR-HSA were similar in micelles (k(inh) approximately 1.3 x 10(4) M(-1) s(-1)), where n approximately 2, whereas the k(inh) for BR-HSA dropped by (1/2) in bilayers. The dimethyl ester of bilirubin (BRDE) gave a k(inh) only one-tenth that of the vitamin E analog, pentamethylhydroxychroman (PMHC) in SDS micelles/methyl linoleate when initiated by lipid-soluble azo-bis-2,4-dimethylvaleronitrile (DMVN). Biliverdin hydrochloride (BVHCl) was NOT an effective peroxyl radical-trapping agent in the micellar phase during initiation by ABAP or DMVN containing methyl linoleate but it inhibited oxygen uptake in the aqueous phase. Both BRC and BR-HSA extended the total radical antioxidant parameter (TRAP) of human blood plasma and their contribution to TRAP was in the range of 5-10% of the natural TRAP of blood plasma, depending on the BR content determined in the blood plasma.
MacLean
Patricia D
PD
Department of Chemistry, Mount Allison University, 63C York Street, Sackville, New Brunswick, Canada E4L 1G8.
Drake
Emily C
EC
Ross
L
L
Barclay
C
C
D000418:Albumins / Q000737:chemistry; D000975:Antioxidants / Q000737:chemistry*; D001663:Bilirubin / Q000031:analogs & derivatives / Q000737:chemistry*; D001664:Biliverdine / Q000737:chemistry; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry*; D008823:Micelles; D010084:Oxidation-Reduction; D010949:Plasma / Q000737:chemistry*; D013654:Taurine / Q000031:analogs & derivatives / Q000737:chemistry
D000418:Albumins; D000975:Antioxidants; D008051:Lipid Bilayers; D008823:Micelles; D013654:Taurine; C054146:bilirubin ditaurine; D001664:Biliverdine; D001663:Bilirubin