A 26-year-old woman with a 6-month history of depression accompanied by active suicidal ideation ingests 35 g of acetaminophen. She quickly experiences nausea and vomiting. Within 1 day, she becomes progressively obtunded. On physical examination, her temperature is 36.9deg C, pulse is 75/min, respirations are 15/min, and blood pressure is 100/65 mm Hg. She is treated with N-acetylcysteine. Depletion of which of the following is most likely to accentuate her organ damage?