Photosensitization of liposomal membranes by hematoporphyrin derivative.

The putative tumor-localizing and -photosensitizing fraction of hematoporphyrin derivative, the fastest migrating fraction of hematoporphyrin derivative separated by polyacrylamide gel filtration (HPD-A), photosensitized lipid peroxidation and membrane lysis in egg phosphatidylcholine liposomes. The rate of membrane damage was approximately 4-fold faster in oxygen compared to anoxia, with evidence for the involvement of singlet oxygen. The diffusion of HPD-A into small liposomes led to a shift of the Soret band from 363 nm in buffer to 398 nm accompanied by 4-fold enhancement of the fluorescence. The presence of human serum albumin retarded the diffusion of HPD-A into small liposomes, which is attributed to partial complexing of the HPD-A. A different effect of serum albumin was the protection of large liposomes from photosensitized lysis by incorporated HPD-A. This protection is attributed to scavenging of singlet oxygen, as evidenced by oxidation of tryptophan in the protein.