The depth of porphyrin in a membrane and the membrane's physical properties affect the photosensitizing efficiency

Adina Lavi, Hana Weitman, Robert T. Holmes, Kevin M. Smith, Benjamin Ehrenberg

Research output: Contribution to journalArticlepeer-review

140 Scopus citations

Abstract

Photosensitized biological processes, as applied in photodynamic therapy, are based on light-triggered generation of molecular singlet oxygen by a membrane-residing sensitizer. Most of the sensitizers currently used are hydrophobic or amphiphilic porphyrins and their analogs. The possible activity of the short-lived singlet oxygen is limited to the time it is diffusing in the membrane, before it emerges into the aqueous environment. In this paper we demonstrate the enhancement of the photosensitization process that is obtained by newly synthesized protoporphyrin derivatives, which insert their tetrapyrrole chromophore deeper into the lipid bilayer of liposomes. The insertion was measured by fluorescence quenching by iodide and the photosensitization efficiency was measured with 9,10-dimethylanthracene, a fluorescent chemical target for singlet oxygen. We also show that when the bilayer undergoes a melting phase transition, or when it is fluidized by benzyl alcohol, the sensitization efficiency decreases because of the enhanced diffusion of singlet oxygen. The addition of cholesterol or of dimyristoyl phosphatydilcholine to the bilayer moves the porphyrin deeper into the bilayer; however, the ensuing effect on the sensitization efficiency is different in these two cases. These results could possibly define an additional criterion for the choice and design of hydrophobic, membrane-bound photosensitizers.

Original languageEnglish
Pages (from-to)2101-2110
Number of pages10
JournalBiophysical Journal
Volume82
Issue number4
DOIs
StatePublished - Apr 2002

Bibliographical note

Funding Information:
We acknowledge the support (grant No. 9800364) of the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel (to B.E.), and National Institutes of Health grant HL-22252 (to K.M.S.). B. Ehrenberg also acknowledges the support of the Michael David Falk Chair in Laser Phototherapy.

Funding

We acknowledge the support (grant No. 9800364) of the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel (to B.E.), and National Institutes of Health grant HL-22252 (to K.M.S.). B. Ehrenberg also acknowledges the support of the Michael David Falk Chair in Laser Phototherapy.

FundersFunder number
Michael David Falk Chair
National Institutes of Health
National Heart, Lung, and Blood InstituteR01HL022252
United States-Israel Binational Science Foundation

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