RESUMO
The effect of sodium diethyldithiocarbamate (DDC) and S-2-aminoethyl-isothiouronicadenosin-5-triphosphate (adeturon) in the induction of Escherichia coli SOS response promoted by gamma-irradiation was studied by measuring the induction of sulA gene and the induction of lambda prophage. Furthermore, as a way of measure the exonuclease activity in gamma-irradiated cells in the presence or absence of both compounds, the DNA degradation was determined. Adeturon did not affected DNA degradation, but inhibited the induction of the SOS functions studied. On the contrary, DDC inhibited DNA degradation as well as the induction of the sulA gene, but enhanced lambda induction in E. coli lysogenic strains. These results indicate that both compounds diminish the DNA damage produced by gamma-irradiation and also suggest that the mechanisms of radioprotection must be different. Thus, radioprotection mediated by DDC should involve free hydroxyl radical scavenging and a minor activity of exonuclease. The enhancement of phage induction in E. coli cells that DDC produces could be attributed to its quelant effect and this would not be not probably directly related to radioprotection. Adeturon, as thiols, may serve also as scavenging agent of free hydroxyl radicals, diminishing indirectly the DNA damage level. In addition, adeturon must interact with DNA in the same form that other aminothiol compounds do it. This interaction, mediated by amino groups of adeturon, may serve to concentrate these compounds near of the DNA damage site, increasing the potential for the thiol portion of the molecule to donate hydrogen, decreasing the damage level on DNA molecule. However, adeturon do not modify the exonuclease activity. Some topic about the possible clinical application of both compounds are discussed.
Assuntos
Trifosfato de Adenosina/análogos & derivados , Ditiocarb/farmacologia , Proteínas de Escherichia coli , Escherichia coli/efeitos da radiação , Raios gama/efeitos adversos , Protetores contra Radiação/farmacologia , beta-Aminoetil Isotioureia/análogos & derivados , Trifosfato de Adenosina/farmacologia , Proteínas de Bactérias/efeitos dos fármacos , Proteínas de Bactérias/genética , Proteínas de Bactérias/efeitos da radiação , Bacteriófago lambda/genética , Bacteriófago lambda/efeitos da radiação , Dano ao DNA/efeitos da radiação , DNA Bacteriano/efeitos dos fármacos , DNA Bacteriano/metabolismo , DNA Bacteriano/efeitos da radiação , Escherichia coli/efeitos dos fármacos , Escherichia coli/genética , Resposta SOS em Genética/efeitos dos fármacos , Resposta SOS em Genética/genética , Resposta SOS em Genética/efeitos da radiação , beta-Aminoetil Isotioureia/farmacologiaRESUMO
Nowadays, labelled polyclonal and monoclonal antibodies are widely used for immunoscintigraphic diagnosis of different diseases. Technetium-99m is often considered to be the label of choice for radioimmunodiagnosis for reasons of cost, availability and imaging properties, in spite of its relatively short physical half-life (6.01 h). The existing labelling methods may be classified into two types: direct approaches, in which disulphide bridges within are reduced to generate endogenous sulfhydryl groups able to efficiently bind technetium due to their strong chelating capacity and indirect methods, in which an exogenous chelator is covalently attached to the protein to serve as the binding site. All these procedures have their advantages and drawbacks. There is no consensus among the authors about which of the methods is the best. The employed approach depends on the particular situation. The aim of the present work is to show an update about the available procedures for 99mTc-labelling of antibodies and its fragments.