Resumo

Increased levels of advanced glycation end products (AGEs) are found in Alzheimer´s and Parkinson´s diseases. Among the many reactive carbonyl compounds and AGE precursors, methylglyoxal is most likely to contribute to intracellular AGE formation, since it is extremely reactive and constantly produced in physiological conditions. Then, were evaluated the in vitro effects of methylglyoxal on the metabolism of glucose, glycine and lactate in C6 astroglial cells. For the measurement of lipid or protein synthesis and CO2 prodution, C6 glioma cell line were incubated in 1 mL DMEM (pH 7,4) without serum in the absence (control) or presence of methylglyoxal 400 µM, containing either (i) 5,5 mM D-glucose + 0,2 µCi D-[U-14C] glucose; (ii) 5,5 mM D-glucose + 0,4 mM glycine + 0,3 µCi [U-14C] glycine; (iii) 5,5 mM D-glucose + 5 mM or 10 mM L-lactate + 0,2 µCi L-[U-14C] lactate; (iiii) 10 mM D-glucose + 5 mM L-lactate + 0,2 µCi L-[U-14C] lactate. Before incubation, the reaction medium was gassed with a 95% O2:5% CO2 mixture for 30 s. Cells were incubated for 37°C for 1 h in a Dubnoff metabolic shaker (60 cycles/min). The contents of central well were transferred to vials and assayed to CO2 radioactivity in a liquid-scintillation counter. The flask contents were used to measure the radioactivity converted in lipids and incorporated in protein. Protein concentrations were determined using the Lowry´s method. Data are expressed as mean ± S.D. (pmol/mg protein/h). It was used n = 4, in quadruplicate, for each substrate studied. Statistical analysis of the results was carried out by Independent Student´s t-test and differences were considered significant when p<0.05. In C6 astroglial cells, the methylglyoxal at 400 µM increased the oxidation of glucose (106%) (1931 ± 150) and glycine (46%) (29 ± 5) to CO2 compared to control (glucose 936 ± 102; glycine 20 ± 1) and was not changed the oxidation of lactate to CO2 in all concentrations used: 5 mM lactate + 5,5 mM glucose (1181 ± 139; control 1263 ± 170), 5 mM lactate + 10 mM glucose (1349 ± 70; control 1590 ± 275) and 10 mM lactate + 5,5 mM glucose (956 ± 101; control 936 ± 227). Lipid synthesis from glucose (1638 ± 577) was not changed after the methylglyoxal exposure (1174 ± 358). Moreover, the lipid synthesis from glycine increased (45%) (220 ± 38; control 151 ± 24) and the protein synthesis decreased (68%) (38 ± 3; control 117 ± 21) in C6 cells treated with 400 µM methylglyoxal. Taken together, these results indicate that methylglyoxal impairs the energetic metabolism of glucose and glycine in C6 astroglial cells and this effect may lead to increased formation of AGEs and encourage the emergence or worsening of neurodegenerative diseases.