Giant vesicles under oxidative stress induced by a membrane-anchored photosensitizer.
We have synthesized the amphiphile photosensitizer PE-porph consisting of a porphyrin bound to a lipid headgroup. We studied by optical microscopy the response to light irradiation of giant unilamellar vesicles of mixtures of unsaturated phosphatidylcholine lipids and PE-porph. In this configuration, singlet oxygen is produced at the bilayer surface by the anchored porphyrin. Under irradiation, the PE-porph decorated giant unilamellar vesicles exhibit a rapid increase in surface area with concomitant morphological changes. We quantify the surface area increase of the bilayers as a function of time and photosensitizer molar fraction. We attribute this expansion to hydroperoxide formation by the reaction of the singlet oxygen with the unsaturated bonds. Considering data from numeric simulations of relative area increase per phospholipid oxidized (15%), we measure the efficiency of the oxidative reactions. We conclude that for every 270 singlet oxygen molecules produced by the layer of anchored porphyrins, one eventually reacts to generate a hydroperoxide species. Remarkably, the integrity of the membrane is preserved in the full experimental range explored here, up to a hydroperoxide content of 60%, inducing an 8% relative area expansion.
Riske
Karin A
KA
Departamento de Biofísica, Universidade Federal de São Paulo, São Paulo, Brazil.
Sudbrack
Tatiane P
TP
Archilha
Nathaly L
NL
Uchoa
Adjaci F
AF
Schroder
André P
AP
Marques
Carlos M
CM
Baptista
Maurício S
MS
Itri
Rosangela
R
D003198:Computer Simulation; D005453:Fluorescence; D008027:Light; D008051:Lipid Bilayers / Q000737:chemistry* / Q000528:radiation effects; D008856:Microscopy, Fluorescence; D008956:Models, Chemical; D018384:Oxidative Stress; D010100:Oxygen / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry / Q000528:radiation effects; D010714:Phosphatidylethanolamines / Q000737:chemistry* / Q000528:radiation effects; D017319:Photosensitizing Agents / Q000737:chemistry* / Q000528:radiation effects; D011166:Porphyrins / Q000737:chemistry* / Q000528:radiation effects; D013997:Time Factors; D053835:Unilamellar Liposomes / Q000737:chemistry* / Q000528:radiation effects
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D017319:Photosensitizing Agents; D011166:Porphyrins; D053835:Unilamellar Liposomes; C545325:dimethyl 8,13-divinyl-3,7,12,17-tetramethyl-21H,23H-porphine-2,18-dipropyl-dimyristoylphosphatidylethanolamine; D010100:Oxygen; C028694:1-palmitoyl-2-oleoylphosphatidylcholine