Subcellular binding and effects on calcium homeostasis produced by acetaminophen and a nonhepatotoxic regioisomer, 3′-hydroxyacetanilide, in mouse liver

Acetaminophen (250 mg/kg) administered intraperitoneally to fasted, phenobarbital-induced mice produced hepatotoxicity. No hepatotoxicity was observed after the administration of the regioisomer 3′-hydroxyacetanilide (600 mg/kg). Similar levels of covalent binding to liver homogenates occurred in mice receiving either acetaminophen or 3′-hydroxyacetanilide at these doses. However, subcellular fractionation techniques revealed that the acetaminophen treatment produced greater levels of covalent binding to mitochondrial proteins than 3′-hydroxyacetanilide. In addition, acetaminophen depleted mitochondrial glutathione levels more extensively than 3′-hydroxyacetanilide. Plasma membrane calcium-ATPase activity was reduced to 79.8% and 55.7% of control values at 1 h and 6 h, respectively, following the administration of acetaminophen. No inhibition of this enzyme was detected in mice receiving 3′-hydroxyacetanilide. Acetaminophen also induced alterations in mitochondrial calcium levels and decreased the ability of isolated mitochondria to sequester calcium. These effects were not produced by 3′-hydroxyacetanilide. Our results indicate that acetaminophen induces alterations in calcium homeostasis while 3′-hydroxyacetanilide does not.