INTERACTION OF MANGANESE-MESOPORPHYRIN WITH OLEIC-ACID VESICLES

We investigated the interaction between manganese(III)mesoporphyrin (M nMeso), a metalloporphyrin, and liposome membranes containing oleic ac id (OA; cis-9-octadecenoic acid). MnMeso associates preferentially wit h OA but minimally with egg phosphatidylcholine (EPC). Using small uni lamellar vesicles, we characterized the MnMeso-OA binding at neutral p H. Our data suggest that MnMeso binds to the OA bilayer with K-d = 6.8 x 10(-4) M; the binding stoichiometry of MnMeso-OA was 1:3.4. This OA -MnMeso interaction was analyzed further for changes in the T1 relaxat ion property of MnMeso. OA increased the T1 of MnMeso significantly mo re than did EPC, suggesting that the OA-MnMeso interaction was stronge r than that of PC-MnMeso. The side-chain specificity of the OA interac tion with this porphyrin derivative was further supported in an experi ment with manganese meso-tetra(4-sulfonatophenyl)porphine, which lacks hydrophobic side chains for OA interaction. The association of MnMeso with the OA membrane was proposed according to the structure of MnMes o and OA and, further verified using electron microscopy. A strong ass ociation of MnMeso with OA, an absorption enhancer of the gastrointest inal tract, may be useful for delivery of MnMeso as an oral contrast a gent for magnetic resonance imaging.