DANOS EM DNA PRODUZIDOS POR OXIGÊNCIO SINGLETE EM TERAPIA FOTODINÂMICA

Paolo Di Mascio (*)

 

 

O objetivo da nossa pesquisa é investigar os aspectos fundamentais da química e bioquímica de espécies reativas de oxigênio e de nitrogênio, particularmente, uma forma eletronicamente ativada do oxigênio molecular, o oxigênio singlete, implicado em vários processos fisiológicos e patológicos. Enfatizamos a identificação, os mecanismos de geração e lesões estruturais em biomoléculas e microestruturas celulares. Proteínas, lipídios insaturados e DNA são alvos biológicos preferenciais destas espécies, disparando respostas biológicas normais ou deletérias.

 

Our attention focused on the chemical sources and the noxious behaviour of molecular oxygen/nitrogen-derived free radicals in biological systems, a growing and fascinating research area of utmost chemical interest and medical relevance.

Since 1990, our studies have focused on identifying the mechanism by which singlet oxygen (¹O₂) and other reactive oxygen/nitrogen species play their physiological and pathological roles. We have devoted efforts to develop suitable ¹O₂ generators based on the thermolysis of endoperoxides. These compounds are chemically inert and have been employed as versatile sources of ¹O₂. We have used this approach in our studies to detect ¹O₂-induced damage in cells (DNA, lipids, proteins) and to screen biologically occurring compounds for the quenching of ¹O₂. Recently, we synthesized the first water-soluble naphthalene endoperoxide isotopically labeled as a source of singlet oxygen-18 (¹⁸[¹O₂]). This compound can be used in biological systems with a high ¹⁸[¹O₂] yield. The application of a sensitive and specific method, using mass spectrometry with electrospray ionization developed in our laboratory, allows for the study of ¹O₂ reaction in biological media, aiming to respond to the strong interest in the role of nutrition in the prevention and pathogenesis of cancer. It has also been suggested that carotenoids aid in cancer prevention. We have worked on lycopene and other oxycarotenoids as biomolecules capable of protection against DNA damage. In addition to being published in specialized journals, our work has been publicized by the media (TV, the press and in workshops). Another major contribution was to demonstrate that 5-aminolevulinic acid (ALA), a heme precursor accumulated in inborn (e.g., acute intermittent porphyria (AIP), tyrosinosis) and acquired (e.g., lead poisoning) porphyries, are probably implicated in hepatic disease, such as hepatocellular carcinoma (HCC). We demonstrated that ALA has a pro-oxidant potential and is able to promote the formation of DNA lesions such as strand-breaks and oxidized bases in vitro and in vivo. Further studies revealed adduct formation between 2'-deoxyguanosine and 4,5-dioxovaleric acids and 3,6-dihydropyrazine-2,5-dipropanoic acid-induced DNA damage. Considering all these types of DNA damage induced by ALA derivatives, we suggested a possible correlation between high ALA concentrations, transition metal ions, aldehydes, and the carcinogenic process. We think that chronically high levels of ALA in AIP patients may play an important role in the induction of DNA damage. The formation of alkylated and oxidized bases may trigger mutagenic processes, leading to an increased risk of HCC development in AIP patients.

 

 

(*) Departamento de Bioquímica

Instituto de Química

Universidade de São Paulo

pdmascio@iq.usp.br.