Anethole dithiolethione, a putative neuroprotectant, increases intracellular and extracellular glutathione levels during starvation of cultured astroglial cells

Astroglial cells protect neurons against oxidative damage. The antioxidant glutathione plays a pivotal role in the neuroprotective action of astroglial cells which is impaired following loss of glutathione. Anethole dithiolethlone (ADT), a sulfur-containing compound which is used in humans as a secretagogue, increases glutathione levels in cultured astroglial cells under "physiological" conditions and is thought thereby to protect against oxidative damage. Presently we report the effect of ADT (3-100 mu M) on glutathione content of and efflux from rat primary astroglia-rich cultures under "pathological" conditions, i.e., extended deprivation of glucose and amino acids. Although cellular viability was not affected significantly, starvation of these cultures for 24 h in a bicarbonate buffer lacking glucose and amino acids led to a decrease in glutathione and protein content of approximately 43% and 40%, respectively. Although no effect on the protein loss occurred, the presence of ADT during starvation counteracted the starvation-induced loss of intracellular glutathione in a concentration-dependent way. At a concentration of 100 mu M ADT even a significant increase in astroglial glutathione content was noted after 24 h of starvation. Alike intracellular glutathione levels, the amount of glutathione found in the buffer was elevated substantially if ADT was present during starvation. This ADT-mediated, apparent increase in glutathione efflux was additive to the stimulatory effect on extracellular glutathione levels of acivicin (100 mu M), an inhibitor of extracellular enzymatic glutathione breakdown. However, the ADT-induced elevation of both intra- and extracellular glutathione content during starvation was prevented completely by coincubation with buthionine sulfoximine (10 mu M), an inhibitor of glutathione synthesis. These results demonstrate that, most likely through stimulation of glutathione synthesis, ADT enables astroglial cells to maintain higher intra- and extracellular levels of glutathione under adverse conditions. Considering the lowered glutathione levels in neurodegenerative syndromes, we conclude that further evaluation of the therapeutic potential of the compound is warranted.