Abstract
Lipid peroxidation was photosensitized in egg phosphatidylcholine (EPC) liposomes by hematoporphyrin (HP), hematoporphyrin derivative (HpD) and urorporphyrin I (Uro-I). Photosensitization by HP was type II via singlet oxygen ( 1O 2) for the monomeric and dimeric states and type I for aggregated HP. Uro-I was an efficient type II 1O 2 photosensitizer. The HpD fraction enriched in the active biological component (HpD-A) was a type II 1O 2 photosensitizer at high and low concentrations. The spectral differences between HpD-A in buffer and solubilized in small EPC liposomes are attributed to a conformation change of a key dimer constituent from a folded to a planar geometry. The implications of the results for the action mechanism in photoradiation therapy of tumors with these porphyrins are discussed.
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