Pharmacokinetics of Acetaminophen-Protein Adducts in Adults with Acetaminophen Overdose and Acute Liver Failure

Abstract

ABSTRACT:Acetaminophen (APAP)-induced liver toxicity occurs with formation of APAP-protein adducts. These adducts are formed by hepatic metabolism of APAP to N-acetyl-p-benzoquinone imine, which covalently binds to hepatic proteins as 3-(cystein-S-yl)-APAP adducts. Adducts are released into blood during hepatocyte lysis. We previously showed that adducts could be quantified by high-performance liquid chromatography with electrochemical detection following proteolytic hydrolysis, and that the concentration of adducts in serum of overdose patients correlated with toxicity. The following study examined the pharmacokinetic profile and clinical associations of adducts in 53 adults with acute APAP overdose resulting in acute liver failure. A population pharmacokinetic analysis using nonlinear mixed effects (statistical regression type) models was conducted; individual empiric Bayesian estimates were determined for the elimination rate constant and elimination half-life. Correlations between clinical and laboratory data were examined relative to adduct concentrations using nonparametric statistical approaches. Peak concentrations of APAP-protein adducts correlated with peak aminotransferase concentrations (r ‫؍‬ 0.779) in adults with APAP-related acute liver failure. Adducts did not correlate with bilirubin, creatinine, and APAP concentration at admission, international normalized ratio for prothrombin time, or reported APAP dose. After N-acetylcysteine therapy, adducts exhibited first-order disappearance. The mean elimination rate constant and elimination half-life were 0.42 ؎ 0.09 days ؊1 and 1.72 ؎ 0.34 days, respectively, and estimates from the population model were in strong agreement with these data. Adducts were detected in some patient samples 12 days postingestion. The persistence and specificity of APAP-protein adducts as correlates of toxicity support their use as specific biomarkers of APAP toxicity in patients with acute liver injury. Acetaminophen [APAP;acetamide; C 8 H 9 NO 2 ] overdose has recently been identified as a major cause of acute liver failure (ALF) in the United States (Larson et al., 2005). Currently, the diagnosis of APAP overdose is dependent on the history of a large dose of APAP, defined as 7.5 g of APAP in adults (Rumack et al., 1981), supported by an elevated level of APAP in peripheral blood (Smilkstein et al., 1988;Rumack, 2002). Many patients develop ALF rapidly, characterized by encephalopathy and the presence of coagulopathy [international normalized ratio (INR) Ն 1.5]; in these patients, the history of ingestion and specific dosing information may be difficult to obtain. Furthermore, the interpretation of measured APAP concentrations in peripheral blood requires knowledge of the precise time of ingestion of a single large dose of APAP.Overdoses of APAP result in the generation of APAP-protein adducts, which are produced by the binding of the reactive metabolite, N-acetyl-p-benzoquinone imine (Dahlin et al., 1984), to cysteine groups on protein as 3-(cystein-S-yl)-APAP adducts (Ho...

Confirming the Causative Role of Acetaminophen in Indeterminate Acute Liver Failure Using Acetaminophen-Cysteine Adducts

“…Current acetaminophen treatment protocols require direct measurement of a patient's serum acetaminophen concentration, which is interpreted using the RumackMatthew nomogram. This nomogram, however, was only validated in acute, single ingestion, immediate release acetaminophen overdoses with known time of ingestion [7]. Most cases of ALF due to acetaminophen are not from single acute ingestions but rather from repeated supratherapeutic use of acetaminophen-containing products including OTC preparations and APAP/opioid combination products.…”

“…This delayed clearance is critical in considering the utility of APAP-CYS adducts as a diagnostic test. If a patient presents for care in later stages of hepatotoxicity, the prolonged presence of elevated adduct concentrations may be essential in helping clinicians to diagnose acetaminophen-associated ALF [7].…”

Prolonged Acetaminophen-Protein Adduct Elimination During Renal Failure, Lack of Adduct Removal by Hemodiafiltration, and Urinary Adduct Concentrations After Acetaminophen Overdose

“…Indeed, serum APAP-protein adducts can be detected in human beings following therapeutic doses of APAP, with serum APAP-CYS concentrations remaining at or below 1 μM [6]. In contrast, serum APAP-CYS concentrations have been reported to rise above about 1 μM in patients with known APAP-induced hepatotoxicity when serum alanine aminotransferase (ALT) activity exceeds 1,000 IU/L, with higher ALT activities associated with higher serum APAP-CYS concentrations [7].…”

Protein-Derived Acetaminophen-Cysteine Can Be Detected After Repeated Supratherapeutic Ingestion of Acetaminophen in the Absence of Hepatotoxicity

“…During overdose of APAP or when glutathione stores are reduced, NAPQI is released within the cell and forms covalent links with many macromolecules, particularly the sulfhydryl group on cysteine components of proteins (APAP-CYS protein adducts) [4,5]. There is data to indicate that APAP-CYS protein adducts form as a byproduct of simple hepatocellular exposure (not overdose) to APAP in the form of NAPQI [2,6].…”