Dipalmitoylphosphatidylcholine liposomes with soybean-derived sterols and cholesterol as a carrier for the oral administration of insulin in rats

Abstract

Dipalmitoylphosphatidylcholine (DPPC) liposomes with a soybean-derived sterol mixture (SS) or cholesterol (Ch) were examined as a carrier for the oral administration of insulin in rats. Four kinds of liposomes were prepared: liposomes containing SS or Ch (molar ratio of DPPC/X = 7:2 or 7:4, X = SS or Ch), respectively. The pharmacological availability was greater and the lag time for the glucose reduction was later in the order of DPPC/SS (7:4) > DPPC/SS (7:2) > DPPC/Ch (7:4) >> DPPC/Ch (7:2)-liposomes. This order appears to correspond well with that of the rigidity of the lipomosal membrane. In particular, DPPC/SS (7:4)-liposomes reduced blood glucose levels for up to 21 in rats oral administration. The highest absolute pharmacological availability was 31.6% at a dose of 20.0 IU/kg of DPPC/SS (7:4)-liposomes among the liposomes in comparison to intraveous administration.