In this study, we
investigated the effects of drugs on membrane
function in which lipid peroxidation was inhibited by the antioxidant
Trolox (TRO) in liposomes containing egg yolk lecithin. Local anesthetics
(LAs), such as lidocaine (LID) and dibucaine (DIB), were used as model
drugs. The effect of LAs on the inhibitory activity of TRO was evaluated
by calculating the pI50from the inhibition
constantKcalculated by curve fitting. pI50TROindicates the strength of TRO
membrane protective function. pI50LAindicates the strength of LA activity. LAs inhibited lipid
peroxidation in a dose-dependent manner and decreased pI50TRO. The effect of DIB on pI50TROwas 1.9 times more than that of LID.
This result indicated that LA may improve the fluidity of the membrane,
which may facilitate the migration of TRO from the membrane to the
liquid phase. As a result, TRO is less likely to suppress lipid peroxidation
within the lipid membrane, possibly resulting in a decrease in pI50TRO. The effect of TRO on pI50LAwas found to be similar in both,
indicating that it did not depend on the type of the model drug. These
results suggest that our developed procedure successfully quantified
the effects of LAs on lipid membrane functions. We were able to obtain
the characteristics of model drugs independent of TRO by simultaneously
measuring and analyzing the lipid peroxidation inhibitory activities
of TRO and model drugs in liposomes.