title: Characterization of the photoproducts of protoporphyrin IX bound to human serum albumin and immunoglobulin G.
abstract: Clinically useful photosensitisers (PSs) are likely bound to subcellular and molecular targets during phototherapy. Binding to a macromolecule has the potential to change the photophysical and photochemical characteristics of the PSs that are crucial for their phototoxicity and cell-killing activity. We investigated the effects of binding of a specific PS (protoporphyrin IX or PPIX) to two proteins, human serum albumin (HSA) and a commercially available immunoglobulin (IgG). These two proteins provide two different environments for PPIX. The albumin binds PPIX in hydrophobic binding sites located in subdomain IIA and IIIA, conversely IgG leaves PPIX exposed to the solvent. We show that photophysical parameters such as emission maxima and fluorescence lifetime depend on the binding site. Our results indicate that the different binding site yields very different rates of formation of photoproducts (more than three times higher for PPIX bound to HSA than to IgG) and that different mechanisms of formation may be occurring. Our characterization shows the relevance of protein binding for the photochemistry and ultimately the phototoxicity of PSs.
authors.affiliation: The Scottish PDT Centre, Department of Dermatology and Photobiology Unit, Ninewells Hospital and Medical School, Dundee, UK. lbrancaleon@utsa.edu
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Brancaleon
authors.forename: Steven W
authors.initials: SW
authors.lastname: Magennis
authors.forename: Ifor D W
authors.initials: ID
authors.lastname: Samuel
authors.forename: Ebinazar
authors.initials: E
authors.lastname: Namdas
authors.forename: Andrea
authors.initials: A
authors.lastname: Lesar
authors.forename: Harry
authors.initials: H
authors.lastname: Moseley
mesh_terms: D017484:Dermatitis, Phototoxic; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D007700:Kinetics; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000494:pharmacology; D011485:Protein Binding; D011524:Protoporphyrins / Q000378:metabolism*; D012709:Serum Albumin / Q000378:metabolism*; D012997:Solvents; D013050:Spectrometry, Fluorescence
chemical_list: D007074:Immunoglobulin G; D017319:Photosensitizing Agents; D011524:Protoporphyrins; D012709:Serum Albumin; D012997:Solvents; C028025:protoporphyrin IX