A Role for CHAC1 in Acetaminophen Hepatotoxicity

Acetaminophen (APAP) is a commonly used pain reliever and a well‐established, dose‐related hepatotoxin. Hepatotoxicity occurs when metabolism of excessive APAP generates high concentrations of the reactive metabolite N‐acetyl‐p‐benzoquinone imine (NAPQI). NAPQI depletes cellular glutathione (GSH) and forms protein adducts leading to cellular stress, mitochondrial dysfunction, and, ultimately, oncotic necrosis of Zone 3 hepatocytes. The endoplasmic reticulum (ER) stress pathway is important to maintain cellular protein folding abilities in times of stress. However, extended or aberrant ER stress signaling can lead to apoptosis through the PERK‐ATF4‐CHOP pathway. Our research explores the regulation and contribution of CHAC1, an enzyme within this pathway, in response to APAP overdose. As purified mouse and yeast CHAC1 was shown to degrade GSH, the consequences of CHAC1 overexpression on GSH levels in human liver was explored in a human hepatoma cell line (HepG2). Overexpression of CHAC1 by transient transfection leads to a ~50% reduction in total GSH levels. As depletion of GSH is an important step in the pathology of APAP hepatotoxicity, the expression of CHAC1 mRNA in HepG2 cells was examined following 24‐hour treatment with 30mM APAP. CHAC1 mRNA was induced five‐fold by APAP, along with other components of the PERK‐ATF4‐CHOP pathway. Interestingly, overexpression of CHAC1 in HepG2 cells treated with APAP led to increased toxicity versus APAP alone, implicating a role for CHAC1 in response to APAP. Overall, these data implicate a new role for CHAC1 in the pathology of drug‐induced liver injury.