Background: Glycyrrhizic acid (GA) is a glycoside that has shown considerable promise as a
penetration enhancer and drug carrier to improve the absorption of poorly water-soluble drugs. The
aggregation behavior of GA and its ability to form large micelles at higher solution concentrations are
thought to contribute to these bioavailability enhancing properties. The oral absorption of Paclitaxel
(PTX) for example, an anti-cancer agent which exhibits poor oral bioavailability, has been found to
significantly increase in the presence of GA.
Methods: In an attempt to visualize the aggregation behavior of GA and its subsequent association with
PTX, 100 ns molecular dynamics simulation of a 5 mM aqueous solution of GA with 10 molecules of
PTX was conducted using GROMACS and an all-atom forcefield.
Results: Aggregation of GA molecules was found to occur quickly at this level of saturation leading to
two stable aggregates of 13 and 17 GA molecules with an effective radius of 10.17 nm to 10.92 nm.
These aggregates form not in isolation, but together with PTX molecule embedded within the structures,
which reduces the number of interactions and hydrogen-bonding with water.
Conclusion: GA aggregation occurs around PTX molecules in solution, forming co-joined GA-PTX
cluster units at a ratio of 3:1. These clusters remain stable for the remainder of the 100ns simulation and
serve to isolate and protect PTX from the aqueous environment.