Novel approach for fast comparative evaluation of the potency of new photosensitizers using model lipid membranes

Abstract

The novel approach for fast comparative evaluation of the potency of new photosensitizers using model lipid membranes is described and substantiated. For this purpose, mixed Langmuir monolayers and Langmuir-Blodgett films containing one of the typical relatively easy photodegradable lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and one of the examined photosensitizers (PSs) are proposed as the models. The changes in the macroscopic properties of such model PS + POPC membranes upon irradiation with visible light (the photo-destruction processes) were recorded using two different methods: commonly used water contact angle measurements and new express method based on the estimation of the changes of the model mixed monolayer mechanical characteristics. The study have been carried out for two series of PSs, cationic and neutral ones. The results of water contact angel measurements have clearly demonstrated that this method can be used for studying the photodestruction of artificial lipid membranes on solid substrates and for comparison of the efficiency of new PSs. However, since model making and measurements are complex and time-consuming, it restricts the preliminary analysis of PSs efficiency. In this work, we suggest rather a simple method for the rapid comparative evaluation of new PSs based on easy and fast measurements, such as recording the surface pressure during irradiation of a PS-containing monolayer directly at an aqueous subphase and determining the mechanical properties of a model monolayer by the oscillating barrier method. The results have demonstrated that the proposed methods are quite valid for studying the photodegradation of artificial lipid membranes and comparing the efficiency of new PSs. In particular, we have shown that these methods can be used not only for multiparametric monitoring of the photodegradation kinetics but also for comparing the efficiency of PSs in lipid structures. The universality of the proposed methods for assessing the effectiveness of PDT at the use of PSs of various structures was demonstrated. The results of this study indicate that cationic PSs exhibit superior activity compared to neutral and anionic ones.