Photodegradation of Protoporphyrin-dimethylester in Solution and in Organized Environments

Abstract

The degradation of sensitizers used in photodynamic therapy (PDT) involves photooxidation either by molecular oxygen or by oxygen intermediates which leads to hydroxyaldehyde and formyl products or to ring opening. Our investigations focused on the spectroscopic changes which protoporphyrin-dimethylester (PP) exhibits upon irradiation. As the microenvironment strongly influences the effects, we used an aprotic organic solvent, L-alpha-phosphatidylcholine dioleoyl (DOPC) liposomes and isogenic fibrosarcoma cells (SSKII) as carriers for PP. Hydroxyaldehyde product isomers develop a new absorption band centred around 670 nm and a new emission band at 676 nm. These characteristics can be used to discriminate them from formyl products and intact PP. In organic solvents, the formation of the hydroxyaldehyde products dominates. In DOPC liposomes and cells, the hydroxyaldehyde yield drops and photooxidation results in attack of the macrocycle. Time-resolved fluorescence spectroscopy of monomeric PP in an organic solvent gives a monoexponential decay time tau of 10.1 +/- 1.3 ns. Upon irradiation a second component with a decay time of 4.9 +/- 0.6 ns, resulting from the hydroxyaldehyde product, was detected. In liposomes and cells the monomeric decay time was significantly longer (15 ns) due to the altered microenvironment. Additionally, we observed in liposomes and in cells a small contribution of a short component (1 ns) which is attributed to an aggregated sensitizer species. In irradiated cells the aggregated fraction doubles, indicating a change in the microenvironment caused by the photodynamic action of the sensitizer.

Phototransformations of 5-Aminolevulinic Acid-induced Protoporphyrin IX in vitro: A Spectroscopic Study¶

“…Several porphyrin-type formyl derivatives are formed during phototransformation of PpIX (19,20). The photophysical properties of Ppp and its dimethyl ester in organic solutions and biological environments has been investigated by several groups (16,17,(21)(22)(23)(24).…”

“…PpIX is one of the most photolabile sensitizers (14). Several photoproducts with absorption in the red spectral region have been detected after light exposure of PpIX in organic solvents, in cell cultures and in tissues in vivo (15)(16)(17)(18). The processes leading to these products are dependent on various internal features of the surrounding microenvironment (e.g.…”

Matrix-assisted laser desorption/Ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry: a method to characterize temoporpfin photoproducts

“…This process, usually called 'photobleaching', involves a decrease in absorbance for certain spectral bands, variations of the fluorescence intensity or the formation of new absorption and emission bands. 7 The m-THPC photodegradation has been observed in aqueous 8 and organic solutions, 9 in vitro, 10 in vivo in tumor-bearing mice 11 and in clinical practice. 12 Studyies of the photobleaching reaction are particularly important for two reasons: (1) Identification of photobleaching products, which can be photodynamically active, thus opening the possibility for 'extended' photodynamic therapy; (2) Measurement of the photochemical reactions that reflect the potential therapeutic effect and thus help to match the light dose.…”

Comparison of the Photodynamic Effect of Exogenous Photoprotoporphyrin and Protoporphyrin IX on PAM 212 Murine Keratinocytes¶

“…PpIX is a highly photolabile porphyrin absorbing light throughout the visible spectral region and emitting characteristic red fluorescence over the 600-730 nm range. On irradiation, new fluorescence bands are observed corresponding to a range of ''photoproducts'' (11)(12)(13)(14)(15)(16)(17). The main component of these photoproducts produced in the presence of oxygen is a chlorin moiety, photoprotoporphyrin (Ppp), with peak absorption around 670 nm and peak fluorescence emission around 674 nm.…”

“…The photodegradation mechanisms have been presented and summarized in the literature (18)(19)(20)(21). Because some of the photoproducts can be effective photosensitizers and can be activated by red light, the extent of PpIX photobleaching, whether in cells or animal models (17)(18)(19)(20)(21), may not necessarily correlate with the overall reduction in the PDT effect. This has stimulated interest in the role of Ppp in the overall efficacy of ALA-PDT (as summarized in Refs.…”