Metabolism and Effects on Endogenous Metabolism of Paracetamol (Acetaminophen) in a Porcine Model of Liver Failure

Abstract

The metabolic fate, toxicity, and effects on endogenous metabolism of paracetamol (acetaminophen, APAP) in 22 female Landrace cross large white pigs were evaluated in a model of acute liver failure (ALF). Anesthetized pigs were initially dosed at 250 mg/kg via an oroduodenal tube with APAP serum concentrations maintained above 300 mg/l using maintenance doses of 0.5–4 g/h until ALF. Studies were undertaken to determine both the metabolic fate of APAP and its effects on the endogenous metabolic phenotype of ALF in using 1H NMR spectroscopy. Increased concentrations of citrate combined with pre-ALF increases in circulating lactate, pyruvate, and alanine in plasma suggest mitochondrial dysfunction and a switch in hepatic energy metabolism to glycolysis in response to APAP treatment. A specific liquid chromatography-tandem mass spectrometry assay was used to quantify APAP and metabolites. The major circulating and urinary metabolite of APAP was the phenolic glucuronide (APAP-G), followed by p-aminophenol glucuronide (PAP-G) formed from N-deacetylated APAP. The PAP produced by N-deacetylation was the likely cause of the methemoglobinemia and kidney toxicity observed in this, and previous, studies in the pig. The phenolic sulfate of APAP, and the glutathione-derived metabolites of the drug were only found as minor components (with the cysteinyl conjugate detected but not the mercapturate). Given its low sulfation, combined with significant capacity for N-deacetylation the pig may represent a poor translational model for toxicology studies for compounds undergoing significant metabolism by sulfation, or which contain amide bonds which when hydrolyzed to unmask an aniline lead to toxicity. However, the pig may provide a useful model where extensive amide hydrolysis is seen for drugs or environmental chemicals in humans, but not in, eg, the rat and dog which are the preclinical species normally employed for safety assessment.

The Potential Role of Metabolomics in Drug-Induced Liver Injury (DILI) Assessment

“…Among the papers reviewed, a subset of metabolites appeared consistently altered in different studies, reinforcing their potential as DILI biomarkers. That was the case of lactate, which appeared to increase in [47,55,79,84,95], in agreement with other studies in rat serum [97], mouse plasma [98], or pig plasma [99]. Lactate is metabolised mainly by the liver, so increased levels might reflect decreased clearance due to impaired hepatic function.…”

The Analysis of Acetaminophen (Paracetamol) and Seven Metabolites in Rat, Pig and Human Plasma by U(H)PLC–MS

“…The method was found to be linear over the concentration range measured (16-500 μg/ml) for PAP-G (see Supplementary Tables 20 & 21). A representative chromatogram for pig plasma following the administration of APAP is shown in Supplementary Figure 2 and the application of the method to a pig hepatotoxicity study has recently been described [19].…”

Normothermic Ex Vivo Liver Platform Using Porcine Slaughterhouse Livers for Disease Modeling

“…This is most likely due to the fact that only one bolus of APAP was given to show toxicity, whereas in most studied cases, plasma concentrations were kept at a constant level as opposed to the present study. Additionally, even higher concentrations of APAP could be needed to reach ALF in pigs [ 67 , 68 ]. Similar to other hepatoxicity studies using ex vivo perfused slaughterhouse pig livers [ 45 ], liver weight was increased in the current model over the time of perfusion, probably due to edema formation in livers.…”