Investigation of Foscan interactions with plasma proteins

The present study investigates the interaction of the second generation photosensitizer Foscan with plasma albumin and lipoproteins. Spectroscopic studies indicated the presence of monomeric and aggregated Foscan species upon addition to plasma protein solutions. Kinetics of Foscan disaggregation in albumin-enriched solutions were very sensitive to the protein concentration and incubation temperature. Kinetic analysis demonstrated that two types of Foscan aggregated species could be involved in disaggregation: dimers with a rate constant of k1 = (2.30+/-0.15) x 10(-3) s(-1) and higher aggregates with rate constants varying from (0.55+/-0.04) x 10(-3) s(-1) for the lowest to the (0.17+/-0.02) x 10(-3) s(-1) for the highest albumin concentration. Disaggregation considerably increased with the temperature rise from 15 degrees C to 37 degrees C. Compared to albumin, Foscan disaggregation kinetics in the presence of lipoproteins displayed poorer dependency on lipoprotein concentrations and smaller variations in disaggregation rate constants. Gel-filtration chromatography analysis of Foscan in albumin solutions demonstrated the presence of aggregated fraction of free, non-bound to protein Foscan and monomeric Foscan, bound to protein.