Liposomal membranes. XIX. Interaction between spermicidal agents and liposomes reconstituted with boar spermatozoal lipids.

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Abstract
To evaluate the spermicidal effect of several nonionic surfactants against human spermatozoa, the physicochemical lysis of liposomal membranes by the surfactants has been investigated. Surfactants employed in this work were menfegol (TS-88), nonoxynol-9 (INP-90), octoxynol-9 (NOP-90), hexadecyltrimethylammonium bromide (CTAB), and sodium dodecylsulfate (SDS). Lysis of liposomes by these spermicidal surfactants was quantitatively followed by monitoring the induced release of carboxyfluorescein (CF) encapsulated in the interior of liposomes. When the liposomes reconstituted with boar spermatozoal lipids and about 31% (by wt.) cholesterol were employed, the sequence in efficiency of the surfactant-induced CF release from the liposomes was significantly correlated with that of efficiency of the surfactants in immobilizing human sperm (p<0.05). On the other hand, when egg lecithin liposomes or the liposomes reconstituted with boar spermatozoal lipids and cholesterol less than 21% (by wt.) were utilized, the sequence in efficiency of CF release from these liposomes coincided with that in the inhibiting effect of the surfactants on the fertilizing ability of sea urchin sperm. These effects were closely correlated with the membrane fluidity as controlled by the cholesterol content or lipid composition. Among menfegol analogues from TS-40 through TS-200, the efficiency in induced CF release from the liposomes showed a maximum at around ten ethylene oxide units length of the hydrophilic moiety in the surfactant. This was also the case for spermicidal effect of the TS-series surfactants. The data obtained are discussed at the molecular level from the viewpoint of the structural characteristics of the surfactants.