BACKGROUND & AIMS:
Acetaminophen overdose is a major cause of acute liver failure (ALF). Mitochondrial SH3BP5 (also called SAB) and phosphorylation of JNK mediate the hepatotoxic effects of acetaminophen. We investigated the involvement of steroidogenic acute regulatory protein (STARD1), a mitochondrial cholesterol transporter, in this process and sensitization by valproic acid (VPA), which depletes glutathione and stimulates steroidogenesis.
Non-fasted C57BL/6J mice (control) and mice with liver-specific deletion of STARD1 (Stard1ΔHep), (SabΔHep), or JNK1 and JNK2 (Jnk1+2ΔHep) were given VPA with or without acetaminophen. Liver tissues were collected and analyzed by histology and immunohistochemistry and for SH3BP5 acetaminophen metabolism, endoplasmic reticulum (ER) stress, and mitochondrial function. Adult human hepatocytes were transplanted into FRGN mice to create mice with humanized livers.
Administration of VPA before administration of acetaminophen increased the severity of liver damage in control mice. The combination of VPA and acetaminophen increased expression of CYP2E1, formation of NAPQI protein adducts, and depletion of glutathione from liver tissues of control mice, resulting in ER stress and the upregulation of STARD1. Livers from control mice given VPA and acetaminophen accumulated cholesterol in the mitochondria and had sustained mitochondrial depletion of glutathione and mitochondrial dysfunction. Inhibition of ER stress, by administration of tauroursodeoxycholic acid to control mice, prevented upregulation of STARD1 in liver and protected the mice from hepatoxicity following administration of VPA and acetaminophen. Administration of N-acetylcysteine to control mice prevented VPA- and acetaminophen-induced ER stress and liver injury. Stard1ΔHep mice were resistant to induction of ALF by VPA and acetaminophen, despite increased mitochondrial levels of glutathione and phosphorylated JNK; we made similar observations in fasted Stard1ΔHep mice given acetaminophen alone. SabΔHep mice or Jnk1+2ΔHep mice did not develop ALF following administration of VPA and acetaminophen. The ability of VPA to increase the severity of acetaminophen-induced liver damage was observed in FRGN mice with humanized liver.
In studies of mice, we found that upregulation of STARD1 following ER stress mediates acetaminophen hepatoxicity via SH3BP5 and phosphorylation of JNK1 and JNK2.