ALTERATIONS IN THE GANGLIOSIDE COMPOSITION OF RAT CORTICAL BRAIN-SLICES DURING EXPERIMENTAL LACTIC-ACIDOSIS - IMPLICATION OF AN ENZYMATIC PROCESS INDEPENDENT OF THE OXIDATIVE STRESS

Several in vitro studies have shown that lactic acidosis plays a role in brain damage by enhancing free radical formation and lipid peroxida tion. The purpose of this study was to determine whether gangliosides are affected by lactic acid-induced oxidation in rat brain tissues. Co rtical brain slices were incubated at 37 degrees C for 5 or 17 h in Kr ebs-Ringer buffer containing 20 mM lactic acid (final pH 5.5) previous ly equilibrated with 100% O-2. Damage from lipid peroxidation was esti mated by measurement of thiobarbituric acid-reactive substances (TEARS ) and analysis of polyunsaturated fatty acids (PUFAs). Gangliosides we re studied by high-performance thin-layer chromatography. Incubation w ith lactic acid induced overproduction of TEARS, whereas PUFAs were on ly slightly degraded, even after 17 h of incubation. However, the majo r modifications in the ganglioside profile occurred after 17 h of incu bation. Gangliosides GD1a and GT1b decreased in conjunction with a sub stantial increase in the GM1 percentage. The addition of butylated-hyd roxytoluene and desferrioxamine in the incubation medium, or incubatio n under 100% nitrogen, abolished TEARS production but not the ganglios ide modifications, indicating that the change in ganglioside distribut ion was not related to oxidative stress induced by lactic acid. To inv estigate the possibility of an enzymatic process activated by the pH s hift, slices were incubated with lactic acid in presence of 2,3-dehydr o-2-deoxy-N-acetylneuraminic acid, a specific inhibitor of sialidase. In these conditions, no change in gangliosides profile occurred. These results demonstrate that sialidase is responsible for the alterations in the gangliosides composition of rat cortical brain slices during l actic acidosis.