Changes on POPC:DPPC:Cholesterol and hydroperoxized POPCOOH:DPPC:Cholesterol lipid bilayers promoted by photo-oxidation

We investigated how lipid photo-oxidation may affect plasma membrane models
represented by giant unilamellar vesicles (GUVs). Here, we compare the effect of
methylene blue (MB) photo-activation (concentration ranging from 10 to 20 microM)
upon lipid bilayers containing POPC:DPPC:Cholesterol (Chol) in comparison to
those containing a hydroperoxized lipid POPCOOH:DPPC:Cholesterol. Interestingly,
in the absence of MB, POPC:DPPC:Chol at molar ratio 1:1:1 does not present liquidordered (Lo) – liquid disordered (Ld) phase separation evidenced by fluorescence
optical microscopy. Under irradiation, the membranes initially fluctuate due to an
increase in surface area of 20%, followed by phase separation whereas the GUV
morphology remains spherical. On the other hand, membranes composed of
POPCOOH:DPPC:Chol already present Lo-Ld phase coexistence without MB photoirradiation. Upon MB photo-activation, two distinct scenarios are observed: i) GUVs
loose optical contrast (increase their permeability without increasing in area), but
phase separation is kept as pre-irradiated; 2) GUVs present an outward budding of
Lo phase that remains over time irradiation or is recovered to their initial spherical
shape followed by optical contrast fading. These results will be compared with the
action of another photosensitizer pheophorbide that is highly hydrophobic and
located at membrane in comparison to MB that partitions preferentially at aqueous
environment.
This work was supported by Conselho Nac. Des. Cient. Tecnologico (CNPq) PIBIC
fellowship to LC. RI is recipient from research CNPq fellowship