M.Sc. Defence: Tania Kjellerup Lind

Title: Unraveling mechanistic aspects for new nano-medicine uptake by cell membranes

Abstract:

Antibiotic multi-resistance amongst bacteria is an ever increasing problem which has to be addressed with novel approaches before long, if this already serious public health issue is to be contained. Natu-rally occurring antimicrobial peptides, which are part of the innate immune defense in many organ-isms, are likely to become one of the answers in this matter. Other promising candidates are the hy-perbranched polymeric nanoparticles called dendrimers, which are distinguished by their well-defined size and multivalent distribution of functional groups.

These two strong assets have been joined into novel antimicrobial peptide dendrimer drugs, with high activity towards various bacteria, synthesized by the group of Z. Urbanczyk-Lipkowska in Poland. The uptake mechanism of three of these dendrimers has been studied on model membranes of differing complexity. The interaction was observed to be highly dependent on the fluidity of the membranes. For ratios of POPC and DPPC allowing for the membrane to attain one single liquid phase, the interac-tion was dominated by mixed micelle formation with surface aggregation and partly removal of the membrane in a detergent-like manner. Dendrimers interacting with a membrane in the coexistence regime, containing solid domains rich in DPPC surrounded by fluid POPC, showed preferential interac-tion with the uid phase corroborating a requirement for fluidity. In contrast, a solid state membrane composed of pure DPPC showed excessive stacking of bilayer patches upon interaction.

A protocol for formation of supported lipid membranes composed of lipids extracted from Escherichia coli was successfully established, allowing for following the interaction with antimicrobial agents. Stacking of bilayer patches and translocation of dendrimers was observed for this bacterial mimetic system below the transition temperature. The body temperature might have profound impact on the uptake mechanism, perhaps allowing for integration of lipids into mixed aggregates, as seen for fluid model membranes.

The mechanism of action was investigated by a combination of surface sensitive techniques individual-ly contributing with complementary information on the interfacial interactions occurring upon den-drimer introduction.
 

Supervisor: assoc. prof. Marité Cárdenas Gómez