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 peroxidation. The purpose of this study was to determine whether gangliosides are affected by lactic acid-induced oxidation in rat brain tissues. Cortical brain slices were incubated at 37 degrees C for 5 or 17 h in Krebs-Ringer buffer containing 20 mM lactic acid (final pH 5.5) previously equilibrated with 100% O-2. Damage from lipid peroxidation was estimated by measurement of thiobarbituric acid-reactive substances (TEARS) and analysis of polyunsaturated fatty acids (PUFAs). Gangliosides were studied by high-performance thin-layer chromatography. Incubation with lactic acid induced overproduction of TEARS, whereas PUFAs were only slightly degraded, even after 17 h of incubation. However, the major modifications in the ganglioside profile occurred after 17 h of incubation. Gangliosides GD1a and GT1b decreased in conjunction with a substantial increase in the GM1 percentage. The addition of butylated-hydroxytoluene and desferrioxamine in the incubation medium, or incubation under 100% nitrogen, abolished TEARS production but not the ganglioside modifications, indicating that the change in ganglioside distribution was not related to oxidative stress induced by lactic acid. To investigate the possibility of an enzymatic process activated by the pH shift, slices were incubated with lactic acid in presence of 2,3-dehydro-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 lactic acidosis.