NAC protects by replenishing glutathione with cysteine being critical for protection. (A) Time course of hepatic glutathione+glutathione disulfide (GSH+GSSG) levels after treatment with 300 mg/kg APAP in mice. Animals also received vehicle (saline), 0.65 mmol/kg GSH, or 0.65 mmol/kg NAC iv 1.5 h after APAP. (B) Plasma ALT indicative of liver injury after treatment of mice with 300 mg/kg APAP for 6 h. Animals also received saline as vehicle or 0.65 mmol/kg NAC (l-NAC), 1.95 mmol/kg NAC (h-NAC), a mixture of 3 amino acids (0.65 mmol/kg of glycine, glutamic acid, and NAC) (3AS) required for GSH synthesis or a mixture of 2 amino acids (0.98 mmol/kg glycine and glutamic acid) (2AS) iv 1.5 h after APAP. Data represent mean ± standard error of n = 4–5 animals per time point. *p < 0.05 (compared with APAP/saline). Data adapted from Ref. (112). ALT, alanine aminotransferase; NAC, N-acetylcysteine.