Resumo

Objectives: It has been shown that elevation of plasma methionine (Met) may occur in several genetic abnormalities, such as methionine adenosyltransferase activity deficiency, homocystinuria and glycine N-methyltransferase. Hypermethioninemic patients can present cerebral alterations, whose underlying mechanisms are not completely established. Therefore, in the present we investigated the influence of antioxidants (vitamins E plus C) on the effect mediated by Met on Na+,K+-ATPase activity in rat hippocampus. Besides, we verified whether the alterations on the enzyme after chronic administration of Met and/or antioxidants were associated with changes in relative expression of Na+,K+-ATPase catalytic subunits. Methods and Results: Wistar rats were treated daily with twice subcutaneous injection of saline (control) or Met (1.34 – 2.68 umol/g of body weight) from the 6th to the 28th day of life and were sacrificed 12 h later. In another set of experiments, concomitantly to chronic Met-treatment, rats received a single daily intraperitoneal injection of vitamins E (40 mg/kg) plus C (100 mg/kg) or vehicle. Na+,K+-ATPase activity was determined in synaptic plasma membranes from hippocampus and the analysis of gene expression of enzyme was carried out by a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) assay. Our results showed that concomitant administration of antioxidants prevented significantly the inhibition of enzyme caused by Met (Control: 1184±55.80, VitE&C: 1227±92.29, Met: 741±10.92, Met+VitE&C: 922±49.89; n=5). Besides, we demonstrated that transcription of catalytic subunits of Na+,K+-ATPase was not altered by chronic exposure to Met and vitamins E plus C (alpha-1=Control: 1.00±0.058, VitE&C: 1.08±0.031, Met: 0.95±0.051, Met+VitE&C: 1.02±0.048; alpha-2=Control: 1.07±0.049, VitE&C: 1.22±0.057, Met: 1.1±0.06, Met+VitE&C: 1.15±0.03; alpha-3= Control: 1.21±0.046, VitE&C: 1.28±0.042, Met: 1.11±0.045, Met+VitE&C: 1.15±0.03; n=4-5). Data are expressed as mean ± SE. Conclusion: These data suggest that alteration of Na+,K+-ATPase activity caused by chronic hypermethioninemia is probably associated with oxidative damage and that this parameter may be involved in the neurological dysfunction observed in hypermethioninemic patients.