TITLE:
Kinetic Characterization of Na,K-ATPase Inhibition by the Acetaminophen Metabolite N-Acetylbenzoquinoneimine
AUTHORS:
Jeff B. Helms, Lauren P. Saunders, Jamie Meyer, Charles J. Costa, Eric Plowman, Nick Williford, Matthew Corbitt, Jeremy P. Holden, Craig Gatto
KEYWORDS:
Na, K-ATPase, Paracetamol, N-Acetylbenzoquinoneimine, Overdose, Renal, Electrophillic
JOURNAL NAME:
Open Journal of Molecular and Integrative Physiology,
Vol.5 No.1,
February
3,
2015
ABSTRACT: N-acetylbenzoquinoneimine (NABQI) is a toxic metabolite of the common analgesic acetaminophen (APAP). NABQI is an electrophilic intermediate formed via the oxidation of APAP within the cytochrome P450 system. Within the normally recommended low-dose use of APAP, NABQI is a minor metabolite which is either quickly reduced back to APAP or conjugated to Glutathione (GSH) producing an innocuous by-product. However, with overdose or prolonged high-dose usage of acetaminophen, GSH levels can become depleted and the bioactive NABQI is thought to form adducts with proteins and oxidize protein sulfhydryls producing intra- and intermolecular disulfide bridges in proteins. In this work we investigated the effect of NABQI on purified kidney Na,K-ATPase to see if the clinical renal insufficiencies seen in APAP overdose may be linked to inhibition of the Na,K-ATPase. Our work has shown that NABQI does indeed inhibit the Na,K-ATPase in a dose dependent (IC50 = 19.8 ± 2.9 μM) and irreversible manner. Interestingly, brief storage of NABQI at -20°C eliminates the irreversible effects of the compound, and leads to a product that remains a potent reversible inhibitor of the Na,K-ATPase (IC50 = 58.7 ± 19.5 μM). Further, the reversible inhibition produced by stored NABQI competes with para-nitrop.