PubMed · 10789383
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L E Rhodes. 2000. Photodynamic therapy.. https://doi.org/10.12968/hosp.2000.61.3.1292
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The spectral properties of photosensitizer HpD, human serum albumin (HSA) and their complex have been studied. The results show that HpD can form HpD-HSA complex with HSA in physiological condition. Compared with pure HpD, the maximum absorption and the fluorescence peaks for HpD-HSA complex had 8-10 nm red-shift. When HpD-HSA complex was excited by the light of corresponding to excitation peaks of HSA (228 and 279 nm) and HpD (394 nm), it was found that the absorption of HSA and HpD both contributed to the emission of HpD-HSA complex at 622 nm. The complex of HpD-HSA was individually excited by wavelengths corresponding to HpD absorption peaks of 402, 502, 537 and 570 nm, and the excitation efficiency of HpD-HSA at pumping wavelength of 537 and 570 nm was higher than that of HpD. The results demonstrate that the red-shift caused by the interaction of HpD and the special proteins in blood should be considered in selecting the excitation and emission wavelength in photodynamic diagnosis and therapy. The results also indicate that the excitation efficiency of porphyrin-protein complex in vivo is higher than that of HpD in vitro when a longer wavelength light corresponding to the week absorption peaks of porphyrin-protein complex is used in photodynamic therapy.
The spectral properties of new photosensitizer ZnPcS2P2, PsD-007 and HMME, as well as traditional photosensitizer HpD have been studied by comparing their spectra in physiological saline and in physiological saline with 10 percent serum. Experimental results show that the maximum absorption peaks for PsD-007, HMME and HpD in the physiological saline with 10 percent serum appear at 400 nm in the soret region, while at 670 nm for ZnPcS2P2. The fluorescence excitation spectra closely resemble the absorption spectra. When excited by the light at the wavelengths of 413 and 514.5 nm, the fluorescence emission peaks for PsD-007, HMME and HpD appear at 625 and 690 nm, respectively. The fluorescent excitation efficiency of the same photosensitizer with the same concentration excited by the light at the wavelength of 413 nm is about three fold higher than that at 514.5 nm. Furthermore, the fluorescent excitation efficiency is the highest for HMME, but is lower for HpD and lowest for PsD-007. These results are significant in the selection of photosensitizers for photodynamic diagnosis and therapy.
The illumination of haematoporphyrin, meso-tetraphenylporphyrin tetrasulphonate and haematoporphyrin derivative in aqueous solution causes two simultaneously occurring processes: photodegradation and the formation of stable photoproducts absorbing in the red spectral region. In the case of haematoporphyrin and its derivatives, these photoproducts have an absorption maximum around 640 nm (photoproduct 640). The former process, which is detected as the bleaching of the porphyrin absorption spectrum as well as a decrease in the fluorescence intensity, is slightly dependent on the solution pH and becomes dominant when the formation of the photoproduct reaches saturation. For the most part, the photodegradation can be explained as the opening of the porphyrin ring, leading to an increase in light absorbance in the UV region. The formation of photoproduct 640 is closely related to the aggregation state of the porphyrins, and shows a distinct dependence on the medium pH. The effectiveness of photoproduct 640 formation strongly increases in neutral and alkaline solutions, whereas the porphyrins are photostable below pH 5. The spectroscopic features of the photoproducts of haematoporphyrin and haematoporphyrin derivative, with absorption bands in the visible region, are similar to those of chlorin and/or porphyrin-chlorin linked systems. On the basis of these spectroscopic studies, it is suggested that photoproduct 640 is a chlorin-type molecule formed predominantly from the aggregates of porphyrins when photo-oxidation and photoreduction are in competition.