title: Membrane photosensitization by hematoporphyrin and hematoporphyrin derivative.
abstract: HPD-A, the putative active biologic component of HPD, photosensitized lysis of large phosphatidylcholine liposomes and lipid peroxidation in small liposomes with oxygen enhancement ratios from 4 to 5. Unambiguous proof was obtained that this damage was mediated by singlet oxygen. Spectral data indicates that HPD-A localizes in a heterogeneous environment in the large liposomes and within the membrane bilayer of the small liposomes. The latter was accompanied by a shift of the Soret band from 364 nm to 398 nm and a 2-3 fold increase of the fluorescence. The presence of human serum albumin protected the large liposomes from photosensitized damage by HPD-A and inhibited the diffusion of HPD-A into the small liposomes. In connection with photoradiation therapy, these findings suggest that aggregated HPD-A and the more fluorescent, disaggregated HPD-A may act as photodynamic sensitizers after localization, and that binding of HPD-A to serum protein protects the aggregated form and inhibits photodynamic damage to membranes. However, protein photooxidation is feasible in the protein-bound state.
mesh_terms: D002462:Cell Membrane / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D017324:Hematoporphyrin Derivative; D006415:Hematoporphyrins; D008054:Lipid Peroxides; D008081:Liposomes; D008563:Membrane Lipids; D008961:Models, Structural; D010084:Oxidation-Reduction; D010100:Oxygen / Q000633:toxicity; D010713:Phosphatidylcholines; D010777:Photochemistry; D012709:Serum Albumin; D013329:Structure-Activity Relationship
chemical_list: D006415:Hematoporphyrins; D008054:Lipid Peroxides; D008081:Liposomes; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D012709:Serum Albumin; D017324:Hematoporphyrin Derivative; D010100:Oxygen