Adsorption Induced Single Layer Area Increase and Collapse of Vesicles
May 24,2012 @ Kavli Institute
Dan HuDepartment of Mathematics &Institute of Natural SciencesShanghai Jiao Tong UniversityJoint work with Yukun Wang & Dongqing Wei
Background---Antimicrobials
1. Alarming increase in bacterial resistanceTraditional antibiotics --- drug resistanceSuper bacteria
2. Membrane - permeabilizing antimicrobial peptides (AMPs)Less induced resistance
3. Mimics of AMPsDiversityPossibly---Less metabolizablePossibly---Low immunogenicity
AMP mechanisms
William et al. 2011
Possible mechanism of membrane permeabilization induced by AMPs:
Mimics C8 (C6, C4)
Polyoctamethylene guanidine hydrochloride is mimics of AMPs
Amphiphilic & ChargedC8 (n=3): 8 CH2 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 mechanismRupture of membrane?
Instantaneous pores?
Vesicles (POPC:PSM:CHOL=1:1:1) before and after applying C8 (50 )mlg /
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)
0.685±0.008nm2
0.664±0.007nm2
0.638±0.009nm2
C8 C6 C4
Pure POPC 0.615nm2
Drug & POPC
C4 C6 C8
POPC 3.74±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 value With big PDI value
Experimental validation on POPC membrane
POPC vesicle fluorescent dye leakage experiment with different vesicle size
C4 C6 C8 0.5ug/ml no signal 0.5ug/ml no signal 0.5ug/ml 3.0%1ug/ml no signal 1ug/ml no signal 1ug/ml 6.0%3ug/ml no signal 3ug/ml no signal 3ug/ml 10%10ug/ml no signal 10ug/ml no signal 10ug/ml 33%100ug/mlno signal 100ug/mlno signal 100ug/ml 50%
C4 C6 C8 0.5ug/ml no signal 0.5ug/ml 11%0.5ug/ml 22%1ug/ml no signal 1ug/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/ml no signal 0.5ug/ml no signal1ug/ml no signal 1ug/ml no signal3ug/ml no signal 3ug/ml no signal10ug/ml no signal 10ug/ml no signal100ug/ml
no signal100ug/ml
no signal
C8 10ug/ml 33%100ug/ml 58%150ug/ml 58%250ug/ml 59%100ug/ml 57%
Filter size
400nm
100nm
50nm
PDI 0.8 0.105 0.08
average D
183nm
93nm 52nm
50nm
100nm
The size and PDI (PolydisDersity Index)
measured by dynamical light scatter
Leakage result
Modeling study
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Thickness; :
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Results: No rupture when is small. Small leakage whenMulti-rupture
or Rsmall. is or R
Modeling study
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Other possible effects:1. Partially filled Relaxation through deformation
2. Tolerance to stretch Energy barrier
Effectively reduce * to
Modeling study
.11 have we, and ofsolution a find To
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have we,2/ :Define
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ncrr
cnh
Rch
Ec
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.
PDIAverage
Diameter blank 1 >1umc4 1 >1um
c6 0.8800~600n
m
c8 0.105100~200n
m
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
Thank you!
