Eficencia fotodinamica das protoporfirinas IX de magnesio e zinco

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The photodynamic efficiency of protoporphyrin IX (PpIX) and its magnesium (MgPpIX) and zinc (ZnPpIX) derivatives were investigated by comparing the rate of tryptophan (Trp), bovine albumin (BSA) and erythrocytes photoxidation. The solutions of the biomolecules were irradiated with a mercury lamp, for a maximum period of 120 minutes and their photoxidations were monitored in measuring the fluorescence (Trp and BSA) or absorbance of oxyhemoglobin formation (erythrocytes). The photoxidation rate constant of PplX is found to be 0.9 times lower than ZnPplX and 3.4 times greater than MgPpIX. The BSA photoxidation rates of PplX were found to be 0.8 times lower or 1.05 times greater than ZnPplX and 1.7 times or 1.48 times greater than MgPplX after 6 or 48 minutes of irradiation, respectively. Solutions of 0.5% (v/v) erythrocytes were irradiated in the presence of 15 mmol. L photosensitizers. It was observed that the percentages of erythrocytes photo-oxidation, after 75 minutes of irradiation of the solution not submitted to a pre-incubation time with the sensitiser, were 68%.57% and 79% for PpIX, MgPplX and ZnPpIX, respectively. The percentages of red blood cell haemolysis, after 90 minutes of irradiation of the solution submitted to a pre-incubation time were 97%,84% and 100%. respectively. These results show that ZnPplX has similar efficiency as PplX for the photooxidation of simple molecules as Trp, as well as for complex structures of macromolecules (BSA) and cells (red blood cells). The efficiency of MgPplX when compared with PplX depends on the kind of substrate analyzed. The results show that the increasing of the structure complexity decreases the difference between the MgPplX and PplX photodynamic efficiency. In addition, it was verified that MgPplX is, among the three photosensitizers studied, the most susceptible compound for photobleaching under the conditions studied.velocity of sensitizer photobleaching and keep the photooxidation capacity of biomolecules when it is convenient, and then, to degrade totally the photosensitizer by just increasing the photobleaching rate. Despite the fact that the MgPplX is less efficient for aminoacids, it must be considered that in vivo application of photodynamic therapy involves complex structures. Thus, ZnPplX and MgPplX should be considered as potential agents for photodynamic therapy.

ASSUNTO(S)

fototerapia cancer fotoquimioterapia

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