The properties of polyunsaturated lecithins in monolayers and liposomes and the interactions of these lecithins with cholesterol

Abstract

1. 1. The force-area characteristics of monolayers of synthetic lecithins with one to six double bonds in one acyl chain have been studied.

2. 2. The area per molecule increases stepwise. The most significant increase is observed after the introduction of the first double bond. The subsequent introduction of two, three or four double bonds or polyunsaturated chains at both ester positions produces some further increase.

3. 3. The interaction with cholesterol depends on the unsaturation and the distribution of the double bonds between the acyl chains.

4. 4. A condensing effect with cholesterol was evident for (1-stearoyl-2-oleoyl)-3-lecithin, (1-palmitoyl-2-lineoyl)-3-lecithin, (1-palmitoyl-2-linolenoyl)-3-lecithin, (1-palmitoyl-2-arachidonoyl)-3-lecithin at 22°. No effect is observed for (1,2-dilinoleoyl)-3-lecithin and (1,2-dilinolenoyl)-3-lecithin. (1-palmitoyl-2-docosahexaenoyl)-3-lecithin shows a limited effect at 22°, but no effect at 37°.

5. 5. No significant differences in behavior are found for the two structural isomers with a mono- or disaturated chain at the 1- or 2-position.

6. 6. The permeability of liposomes, derived from the above mentioned lecithins, to glucose, erythritol and glycerol increases in the same order as the area per molecule at the air-water interface.

7. 7. The presence of cholesterol reduced the permeability to glucose, erythritol, glycerol only for the lecithins which showed a condensation effect.

8. 8. The unsaturation and the distribution of the double bonds appear to be of critical importance for the barrier properties of lecithins and for the interaction with cholesterol.