Adsorption Induced Single Layer Area Increase and Collapse of Vesicles May Kavli Institute Dan Hu Department of Mathematics &Institute of Natural Sciences Shanghai Jiao Tong University Joint work with Yukun Wang & Dongqing Wei

Background---Antimicrobials 1.Alarming increase in bacterial resistance Traditional antibiotics --- drug resistance Super bacteria 2. Membrane - permeabilizing antimicrobial peptides (AMPs) Less induced resistance 3. Mimics of AMPs Diversity Possibly---Less metabolizable Possibly---Low immunogenicity

AMP mechanisms William et al Possible mechanism of membrane permeabilization induced by AMPs:

Mimics C8 (C6, C4) Polyoctamethylene guanidine hydrochloride is mimics of AMPs Amphiphilic & Charged C8 (n=3): 8 CH 2 in each monomer.

Leakage of fluorescence dye (50nm POPC liposome induced by C8)

Leak mechanism of C8 1. Charges Hard to form trans-membrane structures through thermal fluctuation 2. Maximum Leakage < 100% No steady trans-membrane pores 3. Possible mechanism Rupture of membrane? Instantaneous pores?

Vesicles (POPC:PSM:CHOL=1:1:1) before and after applying C8 (50 ) Vesicle rupture

Effects of the drug Adsorption ---- out layer area increase ---- shape change & rupture

Is the area really increased? ---- MD simulation Effective area per lipid MD time (ns) ±0.008 nm ±0.007 nm ±0.009 nm 2 C8C6C4 Pure POPC 0.615nm 2 Drug & POPC

C4C6C8 POPC3.74±1.46%7.97 ±1.13%11.4±1.34% POPC:CHOL:PSM-0.732±1.21%3.66±0.49%5.61±0.24% Summary of area extension rate

The molecular origin of different extension rate mammalian membrane by C4 and C8

Experimental method vesicle fluorescent dye leakage experiment Dynamical light scatter experiment Used to measure the size distribution of the liposome in the solution The size and PDI (PolydisDersity Index) measured by dynamical light scatter With small PDI valueWith big PDI value

Experimental validation on POPC membrane POPC vesicle fluorescent dye leakage experiment with different vesicle size C4 C6 C8 0.5ug/mlno signal0.5ug/mlno signal0.5ug/ml 3.0% 1ug/mlno signal1ug/mlno signal1ug/ml 6.0% 3ug/mlno signal3ug/mlno signal3ug/ml 10% 10ug/mlno signal10ug/mlno signal10ug/ml 33% 100ug/mlno signal100ug/mlno signal100ug/ml 50% C4 C6 C8 0.5ug/mlno signal0.5ug/ml 11% 0.5ug/ml 22% 1ug/mlno signal1ug/ml 13% 1ug/ml 26% 3ug/ml 3.6% 3ug/ml 7.5% 3ug/ml 33% 10ug/ml 8.4% 10ug/ml 7.4% 10ug/ml 40% 100ug/ml 6.8% 100ug/ml 5.0% 100ug/ml 41% 400nm C4 C6 0.5ug/mlno signal0.5ug/mlno signal 1ug/mlno signal1ug/mlno signal 3ug/mlno signal3ug/mlno signal 10ug/mlno signal10ug/mlno signal 100ug/mlno signal100ug/mlno signal C8 10ug/ml 33% 100ug/ml 58% 150ug/ml 58% 250ug/ml 59% 100ug/ml 57% Filter size 400nm100nm50nm PDI average D 183nm93nm52nm 50nm 100nm The size and PDI (PolydisDersity Index) measured by dynamical light scatter

Leakage result

Modeling study Results: No rupture when is small. Small leakage when Multi-rupture

Modeling study Other possible effects: 1. Partially filled Relaxation through deformation 2. Tolerance to stretch Energy barrier Effectively reduce

Modeling study

C4 50ug/ml C8 50ug/ml C6 50ug/ml Add water Drug effect POPC:PSM:CHOL =1:1:1

C4 50ug/ml C8 50ug/ml C6 50ug/ml Add water The size and PDI of liposome can be measured by Dynamic Light Scattering technique. PDI Average Diameter blank1>1um c41>1um c ~600nm c ~200nm Experimental validation on mammalian membrane

1. Area extension can induce vesicle rupture. 2. Content releasing and rupture are size dependent. 3. Differences in membranes can be used in drug designing. conclusion

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