Increase in gamma-glutamylcysteine synthetase activity as a mechanism for butylated hydroxyanisole-mediated elevation of hepatic glutathione.

Previous studies have demonstrated that dietary administration of butylated hydroxyanisole (BHA) and other phenolic antioxidants increases hepatic glutathione (GSH). The purpose of this study was to examine whether BHA increases GSH by increasing the activity of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in hepatic GSH biosynthesis. Male Swiss-Webster mice were fed BHA in the diet at various doses (0.05-0.75%, w/w, of diet) for 14 days. An additional study examined the effects of 0.75% BHA on hepatic GSH and GCS activity at 1, 4, 8, and 14 days, and at various times following cessation of the BHA diet. BHA increased both GSH and GCS activity in a dose- and time-dependent fashion. At the maximal dose of 0.75% BHA, hepatic GSH and GCS activity was increased by 1.5-fold and 2.1-fold, respectively, by Day 8, and remained at this level at Day 14. GSH was initially depleted at 1 day on the BHA diet, but had returned to control levels at Day 4. Upon removal of the BHA diet, both GCS and GSH returned to control values within 4 days. Hepatic cytosolic GCS activity from BHA-treated mice was inhibited by GSH in a manner similar to that of GCS from untreated mice. These data demonstrate that GCS activity is increased by BHA, and that this increase may be responsible for the elevation of hepatic GSH after BHA treatment observed previously. Whether the BHA-mediated increase in GCS activity is the result of enhanced transcriptional activation of the GCS gene, or results from stabilization of existing GCS enzyme activity, requires further investigation.