Efeito da metformina em sistemas de reparo de DNA

• Autor(a) principal: Claudio, Izabel de Lorena Paula
• Data de Publicação: 2009
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/12575
• topic: Metformin; Hypoglicemic agents; DNA repair; Diabetes; Metformina; Agentes Hipoglicêmicos; Reparo de DNA; Diabetes; CNPQ::CIENCIAS BIOLOGICAS::FISIOLOGIA::FISIOLOGIA DE ORGAOS E SISTEMAS::FISIOLOGIA ENDOCRINA

Cells prevent the formation of injuries in DNA preserving integrity of the genetic information, through repair mechanisms. The accumulation of these injuries or the deficiency in one repair mechanism can produce mutations in cells, leading to neoplasic transformation. Injuries in the DNA can be associated with Diabetes Mellitus (DM) and little is known regarding possible disturbance in the repair system, associated with this syndrome. The use of metformin (MET), a insulin sensitizer, can be associated with reduced incidence and improvement in the prognostic of certain types of cancer in DM. In this study, we are suggesting in prokaryotes and eukaryotes deficient in repair enzymes that MET acts through these enzymes, to protect against the damages in DNA. Cells XPD, deficient in the enzyme of repair XPD, pre-treated with MET (1mM) and radiated with UVC, showed lower survival, evaluated through Trypan Blue test of cell viability in comparison with MRC5 control cells. The same occurring with bacterial strains AB1885, BH20 and AB2463 deficient in repair enzymes UvrB and Fpg and the SOS system, respectively, when pre-treated with MET (20mg/ml=168mM) and radiated with UVC compared with its survival without UVC. Strains AB1885 and BH20 transformed into proficient of all the repair systems through, and submitted to the same treatment with MET and equal dose of UVC the used in the wild strain (AB1157), we observed an increase of its survival. Studying the strains GY4765 (SOS+) proficient on the autocatalytic activity of the SOS system, using the same conditions of treatment, also had increase of its survival in relation to the control, being also this system tested through Chromotest SOS where the MET expressed the SOS genes. Through alkaline electroforese in agarose gel to evaluate the repair activity on the bacterial strain AB1157 (proficient of all repair systems) the pre-treatment with MET and irradiation with UVC, confirmed the action of MET in activating repair systems. It was demonstrated, also, the existence of a synergic action of MET and insulin, when cells from patients with of breast cancer of (MCF7), transfected with BRCA1 gene (HRR). The treatment with MET (20mg/ml) did not increase the expression of this gene, but when combined with insulin (10nM) we observed an increase in the expression of this gene, evaluated in the Luciferase assay. When MRC5cells has been submitted to the pre-treatment with MET and insulin and exposed with UVC, had its higher survival of those radiated without insulin. XPD cells, treated with MET and insulin, did not show any protection agains UVC exposure. In conclusion MET treatment in prokaryotes active DNA repair, but needs UvrB enzymes (NER), fpg (BER) and SOS system to protect the cell against the deleterious effect of the UVC. In eukaryotes, MET needs XPD repair enzyme, (NER) to promote the same protection against the action of the UVC that is bigger when associated with insulin. Possibly, MET also increases the expression of BRCA1gene (HRR) when associated with insulin.