The transfer of antioxidants between liposomes

Abstract

A quantitative study is reported on a comparison of antioxidant action of the a-tocopherol model 2,2,5,6,7-pentamethyl-6-hydroxychroman (PMHC), 2,6-di-tert-butyl-4-methoxvphenol (DBHA) and a-tocopherol when these antioxidants are delivered to peroxidizing dilinoleoylphosphatidylcholine (DLPC) bilayers by (a) intermembrane transfer between donor dimyristoylphosphatidylcholine (DMPC) liposomes and acceptor DLPC liposomes, versus (b) the conventional coevaporation methods. The profiles of inhibited oxidation using method (a) were comparable with those of method (b) during inhibited peroxidation of DLPC liposomes, initiated by lipid-soluble azo-bis-dimethylvaleronitrile (ADVN), and quantitative determinations of the rate of chain initiation, R_i, were the same for the two methods. Differences observed, between antioxidant action by methods (a) and (b), when using the water-soluble initiator azo-bis-amidinopropane hydrochloride (ABAP), are attributed to slow diffusion of ABAP through the multilamellar DLPC system and a resultant non-uniform initiation. PMHC underwent facile intermembrane transfer through a barrier of dialysis tubing, from donor DMPC liposomes to acceptor DLPC or DMPC liposomes, based on analytical and quantitative inhibition studies. α-Tocopherol was comparatively slow to undergo intermembrane transfer by direct contact between liposomes and transferred only slightly through a barrier. The slight but measurable solubility of PMHC and DBHA in the aqueous phase supports a pathway of intermembrane transfer involving a water-soluble intermediate.