Mechanisms of hypericin incorporation to explain the photooxidation outcomes in phospholipid biomembrane models.

Cell membranes are the first barriers for drug binding and key for the action of photosensitizers (PS). Herein, we report on the incorporation of the PS hypericin into Langmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) to represent eukaryotic cell membranes, and 1,2-dioleoyl-sn-glycero-3-phospho(1'-rac-glycerol) (DOPG) to mimic bacterial membranes. Surface pressure (π) vs mean molecular area (Å) isotherms showed a high degree of interaction (binding, penetration and relative solubilization) of hypericin into DPPC and DOPC monolayers. On the other hand, electrostatic repulsions govern the interactions with DOPG and DOPS, favoring hypericin self-aggregation, as visualized by Brewster angle microscopy (BAM). Indeed, the larger domains in BAM were consistent with the greater expansion of DOPG monolayers with incorporated hypericin, owing to stronger electrostatic repulsions. In contrast to DPPC, light-irradiation of DOPC monolayers containing hypericin induced loss of material due to hydrocarbon chain cleavage triggered by contact-dependent reactions between triplet excited state of hypericin and chain unsaturations. The mild effects noted for both irradiated DOPS and DOPG monolayers are attributed to hypericin self-aggregation, which may have decreased the singlet oxygen quantum yield (Φ1O2) via self-quenching, despite the increased instability induced in the monolayers.

Evidence of photoinduced lipid hydroperoxidation in Langmuir monolayers containing Eosin Y.

Photodynamic therapy (PDT) efficiency depends on many factors including the incorporation of the photosensitizer (PS) in cell membranes and possible lipid hydroperoxidation. In this study, we show that hydroperoxidation may be photoinduced when eosin Y is incorporated into Langmuir monolayers that serve as cell membrane models. This occurs for Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), which have unsaturation in their hydrophobic chains. In contrast, light irradiation had no effect on monolayers of saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Evidence of hydroperoxidation was obtained from the area increase in eosin-containing DOPC and POPC monolayers upon irradiation, which was accompanied by a decrease in monolayer thickness according to grazing incidence X-ray off-specular scattering (GIXOS) data. Furthermore, the changes in polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) induced by irradiation were consistent with hydroperoxide migration toward the lipid hydrophilic heads.. In summary, this combination of experimental methods allowed us to determine the effects of eosin Y interaction with cell membrane models under irradiation, which may be associated with the underlying mechanisms of eosin Y as photosensitizer in PDT.