We have since over 12 years studied the effect of lipolytic enzymes on lipid liquid crystalline nano-particle structure, including the relation between the lipolytic activity and substrate nano-structure.1-3 The aim is to provide relevant substrates to monitor and assay the effect of different lipolytic enzymes on these lipid assemblies. This will help to design new vehicles for more efficient and even targeting drug delivery. Well-ordered liquid crystalline nanoparticles (LCNPs) have been used as substrates for lipase to establish the relation between the catalytic activity and the change of structure determined by cryo-TEM and synchrotron SAXD.
We show that the sequence of phases formed are controlled by pH: At pH 8.0 and above bicontinuous Im3m cubic LCNPs, based on monoolein, transform into “sponge”-like assemblies and disordered multilamellar onion-like structures upon exposure to lipase. At pH 7.5 and below lipolysis induced phase transitions of the inner core of the particles, following the sequence Im3m cubic – reversed hexagonal – reversed micellar Fd3m cubic – reversed micelles.
Enzyme catalysed degradation of GDO in cubic micellar (Fd3m) nanoparticles of 50/50 (wt%/wt%) soy phosphatidyl choline (SPC)/glycerol dioleate (GDO), the particles retain their morphology. Here the I2 structure with negative membrane curvature tend to form LC structures of gradually less negative curvature (2D hexagonal, bicontinuous cubic and sponge) before the lamellar phase is formed.
We have also probed the lipase action at the lipid aqueous interface using neutron reflectometry and lipase active and inactive mutants.
1. Borné, J.; Nylander, T.; Khan, A. J. Phys. Chem. B, 2002, 106, 10492-10500.
2. J. Barauskas, T. Nylander, in Delivery and controlled release of bioactives in foods and neutraceuticals, N. Garti, Ed. (Woodhead Publishing Ltd, Cambridge, 2008), 107-131.
3. M. Wadsater, J. Barauskas, T. Nylander, F. Tiberg. ACS Appl. Mat. Interfaces 2014, in print.
Tommy.Nylander@fkem1.lu.se
