Abstract
The discovery of immunostimulating complex formation by the saponin Quil A from
the plant Quillaja saponaria with cholesterol and a phospholipid opened
up new avenues for the development of drug delivery systems for vaccine
application with additional adjuvant properties. In this study, β-escin,
a monodesmosidic triterpene saponin from horse chestnut, was investigated in
terms of its interaction with liposomal components (cholesterol,
dipalmitoylphosphatidylcholine) by Langmuir film balance studies and with regard
to particle formation visualized by transmission electron microscopy. A strong
interaction of β-escin with cholesterol was observed by Langmuir
isotherms due to the intercalation of the saponin into the monolayer, whereas no
interaction occurred with dipalmitoylphosphatidylcholine. Transmission electron
microscopy studies also confirmed the strong interaction of β-escin with
cholesterol. In aqueous pseudo-ternary systems (β-escin,
dipalmitoylphosphatidylcholine, cholesterol) and in pseudo-binary systems
(β-escin, cholesterol), new colloidal structures built up from
ring-like and worm-like subunits were observed with a size of about
100 – 200 nm. These colloidal structures are formed in pseudo-binary systems by
aggregation of the subunits, whereas in pseudo-ternary systems, they are formed
among others by attacking the liposomal membrane. The rehydration of the
liposomal dispersions in NANOpure water or Tris buffer pH 7.4 (140 mM) resulted
in the same particle formation. In contrast, the sequence of the dispersionsʼ
production process affected the particle formation. Unless adding the saponin to
the other components from the beginning, just a liposomal dispersion was formed
without any colloidal aggregates of the subunits mentioned above.
Key words
β-escin -
Aesculus hippocastanum
- Sapindaceae - horse chestnut - cholesterol - phospholipid - colloidal structure
- langmuir film balance - TEM
