Lasers in Medical Science

, Volume 18, Issue 1, pp 56–62

A spectroscopic study of the photobleaching of protoporphyrin IX in solution

  • M. B. Ericson
  • S. Grapengiesser
  • F. Gudmundson
  • A-M. Wennberg
  • O. Larkö
  • J. Moan
  • A. Rosén
Original Article

DOI: 10.1007/s10103-002-0254-2

Cite this article as:
Ericson, M., Grapengiesser, S., Gudmundson, F. et al. Lasers Med Sci (2003) 18: 56. doi:10.1007/s10103-002-0254-2

Abstract

 Photodynamic therapy (PDT) has developed into an important new clinical treatment for cancer during the past 30 years. The method is non-invasive and based on the photochemical activity of a photosensitising agent present in cells and tissues. In so-called ALA-PDT, protoporphyrin IX (Pp IX) is induced from aminolaevulinic acid (ALA) applied topically or systemically. It has been shown that Pp IX is photodegraded by a photo-oxidation process and that its photoproducts have a characteristic absorption band around 670 nm, as observed both in solution and in cells incubated with ALA. In this study, the involvement of oxygen in the photobleaching process was verified by studying the effect of oxygen depletion using the freeze–pump–thaw (FPT) method. A solution of Pp IX in dimethylformamide (DMF) was exposed to light in the wavelength region 600–700 nm (peak centred at 620 (±25) nm) both in the presence and in the absence of oxygen. The bleaching process was observed by absorbance and fluorescence measurements. Photobleaching was observed in the presence of oxygen, as verified by the build-up of a photoproduct absorbing at 670 nm. When the sample was deoxygenated with the FPT method, the photoproduct absorption peak at 670 nm was missing. These results confirm that the formation of photoprotopor-phyrin is a photo-oxidation process and that no photobleaching takes place in the absence of oxygen. When comparing our results to the studies carried out by N2 bubbling, the N2 bubbling seems to be insufficient to remove the oxygen completely from the solution.

Keywords Absorbance Fluorescence Oxygen Photobleaching Photodynamic therapy Protoporphyrin IX 

Copyright information

© 2003 Springer-Verlag London Lim ited

Authors and Affiliations

  • M. B. Ericson
    • 1
  • S. Grapengiesser
    • 1
  • F. Gudmundson
    • 1
  • A-M. Wennberg
    • 2
  • O. Larkö
    • 2
  • J. Moan
    • 3
  • A. Rosén
    • 1
  1. 1.Department of Experimental Physics, School of Physics and Engineering Physics, Chalmers University of Technology, Göteborg University, SE – 412 96 Göteborg, Sweden Tel.: +46-31-7723296 Fax: +46-31-7723496 e-mail: mica@fy.chalmers.seSE
  2. 2.Department of Dermatology, Sahlgrenska University Hospital, Göteborg University, Göteborg, SwedenSE
  3. 3.Department of Biophysics, Institute of Cancer Research, Montebello, N-0310 Oslo, NorwayNO

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