Comparison of Reactive Oxygen Species Production Activity and Binding Ability of Porphyrins in Cell Membrane Models

Abstract

Photo dynamic therapy (PDT) is a widespread medical treatment based on the light-triggered generation of reactive oxygen species (ROS) by porphyrin derivatives. ROS may cause oxidative damage to membranes as well as to DNA and, in consequence, ultimately kill cells. Hence, the binding ability, the location within liposomes as simple cellular membrane models, and the ROS production ability of porphyrins are of outstanding interest. Earlier we determined the location of mesoporphyrin IX dimethyl ester (MPE) and its non-esterified form, mesoporphyrin IX dihydrochloride (MPCl) in small unilamellar vesicles (SUV) with fluorescence line narrowing spectroscopy (FLN). Here we investigated the production of ROS by the photosensitizers in the aqueous medium of the vesicles and in the lipid bilayer environment. The monocomponent vesicles were formed of various saturated phosphatidylcholines. The amount of generated oxygen radicals in the aqueous media was measured on the basis of the produced tri-iodide (I3-) from potassium iodide (KI) in the presence of molybdenum (MoO4) catalyst, which was followed by absorption spectrophotometry. The ROS in the lipophilic membranes and in near-membrane regions was measured with a dihydrorhodamine derivative by fluorescence spectroscopy. We observed in general that the binding ability of MPE is considerably higher than that of MPCl. In aqueous media (without liposomes) MPCl was highly effective in ROS formation whereas in case of MPE no similar effect was observed. Liposome-incorporated MPCl produced ROS in much higher amounts than the MPE in the aqueous medium of the liposomes. In near-membrane regions MPE produced ROS in the same amount as MPCl.