Determination of paracetamol and its four major metabolites in mouse plasma by reversed-phase ion-pair high-performance liquid chromatography

Period1 mediates rhythmic metabolism of toxins by interacting with CYP2E1

The biological clock is an endogenous biological timing system, which controls metabolic functions in almost all organs. Nutrient metabolism, substrate processing, and detoxification are circadian controlled in livers. However, how the clock genes respond to toxins and influence toxicity keeps unclear. We identified the clock gene Per1 was specifically elevated in mice exposed to toxins such as carbon tetrachloride (CCl₄). Mice lacking Per1 slowed down the metabolic rate of toxins including CCl₄, capsaicin, and acetaminophen, exhibiting relatively more residues in the plasma. Liver injury and fibrosis induced by acute and chronic CCl₄ exposure were markedly alleviated in Per1-deficient mice. These processes involved the binding of PER1 protein and hepatocyte nuclear factor-1alpha (HNF-1α), which enhances the recruitment of HNF-1α to cytochrome P450 2E1 (Cyp2e1) promoter and increases Cyp2e1 expression, thereby promoting metabolism for toxins in the livers. These results indicate that PER1 mediates the metabolism of toxins and appropriate suppression of Per1 response is a potential therapeutic target for toxin-induced hepatotoxicity.

Adenosine 5'-monophosphate blocks acetaminophen toxicity by increasing ubiquitination-mediated ASK1 degradation

Acetaminophen (APAP) overdose is the most frequent cause of drug-induced liver failure in the world. Hepatic c-jun NH2-terminal protein kinase (JNK) activation is thought to be a consequence of oxidative stress produced during APAP metabolism. Activation of JNK signals causes hepatocellular damage with necrotic and apoptotic cell death. Here we found that APAP caused a feedback increase in plasma adenosine 5′-monophsphate (5′-AMP). We demonstrated that co-administration of APAP and 5′-AMP significantly ameliorated APAP-induced hepatotoxicity in mice, without influences on APAP metabolism and its analgesic function. The mechanism of protection by 5′-AMP was through inhibiting APAP-induced activation of JNK, and attenuating downstream c-jun and c-fos gene expression. This was triggered by attenuating apoptosis signal-regulated kinase 1(ASK1) methylation and increasing ubiquitination-mediated ASK1 protein degradation. Our findings indicate that replacing the current APAP with a safe and functional APAP/5′-AMP formulation could prevent APAP-induced hepatotoxicity.

Validation thin layer chromatography for the determination of acetaminophen in tablets and comparison with a pharmacopeial method

Adsorption thin layer chromatography (NP-TLC) with densitometry has been established for the identification and the quantification of acetaminophen in three leading commercial products of pharmaceutical tablets coded as brand: P1 (Product no. 1), P2 (Product no. 2), and P3 (Product no. 3). Applied chromatographic conditions have separated acetaminophen from its related substances, namely, 4-aminophenol and and 4′-chloroacetanilide. UV densitometry was performed in absorbance mode at 248 nm. The presented method was validated by specificity, range, linearity, accuracy, precision, detection limit, quantitative limit, and robustness. The TLC-densitometric method was also compared with a pharmacopeial UV-spectrophotometric method for the assay of acetaminophen, and the results confirmed statistically that the NP-TLC-densitometric method can be used as a substitute method. It could be said that the validated NP-TLC-densitometric method is suitable for the routine analysis of acetaminophen in quantity control laboratories.

Synthesis and characterization of bromophenol glucuronide and sulfate conjugates for their direct LC-MS/MS quantification in human urine as potential exposure markers for polybrominated diphenyl ethers

Bromophenol glucuronide and sulfate conjugates have been reported to be products of mammalian metabolism of polybrominated diphenyl ethers (PBDEs), a group of additive flame-retardants found ubiquitously in the environment. In order to explore their occurrence in human urine, four water-soluble bromophenol conjugates, namely, 2,4-dibromophenyl glucuronide, 2,4,6-tribromophenyl glucuronide, 2,4-dibromophenyl sulfate, and 2,4,6-tribromophenyl sulfate, were synthesized, purified, and characterized. An analytical protocol using solid-phase extraction and ion-paired liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS/MS) quantification has been developed for the direct and simultaneous determination of these glucuronide and sulfate conjugates in human urine samples. The limit of detections for all analytes were below 13 pg mL(-1), with 73-101% analyte recovery and 7.2-8.6% repeatability. The method was applied to analyze 20 human urine samples collected randomly from voluntary donors in Hong Kong SAR, China. All the samples were found to contain one or more of the bromophenol conjugates, with concentration ranging from 0.13-2.45 μg g(-1) creatinine. To the best of our knowledge, this is the first analytical protocol for the direct and simultaneous monitoring of these potential phase II metabolites of PBDEs in human urine. Our results have also suggested the potential of these bromophenol conjugates in human urine to be convenient molecular markers for the quantification of population exposure to PBDEs.

Reversed phase ion-pair high performance liquid chromatographic gradient separation of related impurities in 2,4-disulfonic acid benzaldehyde di-sodium salt

A reversed phase ion-pair gradient liquid chromatographic method has been developed and validated for purity determination of the hydrophilic compound 2,4-disulfonic acid benzaldehyde di-sodium salt (2,4-DSAD) containing both hydrophilic and more lipophilic related impurities. Mixtures of acetonitrile-phosphate buffer containing tetrahexylammonium hydrogen sulfate as the ion-pairing reagent were used as the mobile phase. A linear gradient, which generated simultaneous change in the concentration of organic modifier, buffer concentration and the concentration of ion-pairing reagent, was applied. The method allows detection of impurities at low levels (0.01% w/w). Excellent repeatability for both retention time (RSD< or =0.3%, n = 6) and detector response (RSD = 0.03%, n = 6 for the main peak and RSD = 6%, n = 6, for an impurity at 0.01 area% level) was obtained. The method was shown to be robust for routine analysis and has been successfully transferred to the quality control laboratory.

Determination of paracetamol: historical evolution

Paracetamol is a common analgesic and antipyretic drug that is used for the relief of fever, headaches and other minor aches and pains. Their determination in pharmaceuticals is of paramount importance, since an overdose of paracetamol can cause fulminating hepatic necrosis and other toxic effects. Many analytical methodologies have been proposed for the determination of paracetamol. The aim of the present study is to evaluate the utility of different techniques for quantification of paracetamol content in pharmaceutical formulations and biological samples.

Pharmacokinetic variations of acetaminophen according to liver dysfunction and portal hypertension status

AIM

To study the pharmacokinetic and metabolism profiles of a single dose of acetaminophen in patients with cirrhosis.

METHODS

Oral acetaminophen (1000 mg) was administered to seven healthy subjects and 14 patients with cirrhosis (nine Child-Pugh A or B and five Child-Pugh C grade), being five without and nine with oesophageal varices. Plasma levels of acetaminophen and its metabolites were determined by HPLC.

RESULTS

Patients showed a higher mean area under the curve concentration-time (67.4 +/- 22.4 mg h/L vs. 38.8 +/- 4.3 mg h/L; P = 0.01), a lower clearance (166.7 +/- 85.0 mL/min vs. 367.8 +/- 62.5 mL/min; P = 0.01) and higher elimination half-life (3.8 +/- 1.1 h vs. 2.0 +/- 0.4 h; P = 0.01) of acetaminophen than healthy volunteers. The appearance in blood and the urinary excretion of metabolites in patients did not differ from healthy subjects. Absorption profile was faster in patients. Patients with lower mean and systolic arterial pressure had lower AUC of acetaminophen, independently of liver dysfunction stage.

CONCLUSIONS

Patients with cirrhosis had a higher AUC and lower clearance of acetaminophen. Acetaminophen attained earlier therapeutic concentrations in patients with oesophageal varices. Mean and systolic arterial pressures were significantly associated with AUC suggesting the importance of the haemodynamic function on the pharmacokinetics of acetaminophen in patients with cirrhosis.

Development and optimization of a reversed-phase high-performance liquid chromatographic method for the determination of acetaminophen and its major metabolites in rabbit plasma and urine after a toxic dose

A reversed-phase high-performance liquid chromatographic method with detection at 242 nm was developed, optimized and validated for the determination of acetaminophen (A) and its major metabolites glucuronide (AG) and sulfate (AS) conjugates in rabbit plasma and urine after a toxic dose. m-Aminophenol was used as internal standard (IS). A Hypersil BDS RP-C18 column (250 x 4.6 mm), 5 microm particle size, was equilibrated with a mobile phase composed of aqueous buffer solution of KH2PO4 0.05 M containing 1% CH3COOH (pH 6.5) and methanol (95:5, v/v). Its flow rate was 1.5 ml/min. Calibration curves of A, AG and AS were linear in the concentration ranges of 0.5-250, 1-200, 0.5-100 microg/ml in plasma and 1-200, 0.5-150, 0.5-100 microg/ml in urine matrix, respectively. Limits of detection and quantitation were calculated in all cases and extensive recovery studies were also performed. Intra-day relative standard deviation (R.S.D.) for A, AG and AS in plasma was less than 5, 4, 2% and in urine less than 4, 7, 4%, respectively, while the corresponding inter-day values were 7, 6, 4% and 5, 8, 6%, respectively.

Mangafodipir prevents liver injury induced by acetaminophen in the mouse

BACKGROUND/AIMS

Acute liver failure (ALF), characterized by massive hepatocyte necrosis, is often caused by drug poisoning, particularly with acetaminophen (APAP). Hepatocyte necrosis is consecutive to glutathione depletion by NAPQI, a metabolite of APAP, and to mitochondrial damages caused by reactive oxygen species (ROS) overproduction. Considering the structure of Mangafodipir, a contrast agent currently used in magnetic resonance imaging of the liver, we hypothesized that this molecule could exert an antioxidant activity and be possibly used as a treatment of APAP-induced ALF.

METHODS/RESULTS

Mangafodipir is endowed with superoxide dismutase, catalase, and glutathione reductase activities. It can inhibit ROS production by hepatocytes in culture, and protect those cells from oxidative stresses induced by exposure to xanthine oxidase, H(2)O(2), or UV light. Moreover, preventive or curative administration of Mangafodipir to mice with APAP-induced ALF significantly increases survival rates, and abrogates aspartate aminotransferase elevation and histological damage.

CONCLUSIONS

Those data point out the potential interest of Mangafodipir in the treatment of toxic ALF in humans.

Protective effect of stiripentol on acetaminophen-induced hepatotoxicity in rat

Acetaminophen (APAP) is mainly eliminated at a therapeutic dose through glucuronidation and sulfatation and a small fraction is oxidized by cytochromes P450 (CYP) 2E1, 3A4, and 1A2 to N-acetyl-p-benzoquinone-imine (NAPQI), a highly reactive metabolite further conjugated with glutathione into APAP-GSH, and then metabolized to APAP-cystein and APAP-mercapturate excreted in urine. After APAP overdose, the glucuronidation and sulfatation pathways are saturated and the production of NAPQI increases, causing hepatic injury. Stiripentol (STP); (200 mg/kg), an anticonvulsant drug inhibitor of CYP1A2 and CYP3A4 in vivo in humans was tested against APAP-induced toxicity in rat in comparison with N-acetylcysteine (NAC; 100 mg/kg). The mortality rates 24 h after APAP overdose (2 x 500 mg/kg) were 63% (control), 38% (NAC), 0% (STP), and 4% (STP + NAC). The mean plasma transaminase concentrations 5 and 24 h after overdose were significantly higher in control than in STP and NAC groups. The percentage of rats without microscopic liver necrosis 5 h after APAP overdose was significantly higher in rats receiving STP (100%), NAC (83%), or STP + NAC (83%) than controls (42%). In another experiment, four similar groups were administered 50 mg/kg APAP. Plasma AUC(0-5 h) for APAP-GSH, APAP-cystein, and APAP-mercapturate as well as urine APAP-mercapturate mean amounts were significantly lower in STP animals than in the other groups. STP (200 mg/kg) inhibited NAPQI synthesis through CYP inhibition, thus preventing both liver necrosis and mortality in rats.

Rapid liquid chromatographic assay for the determination of acetaminophen in plasma after propacetamol administration: application to pharmacokinetic studies

A simple method for the rapid estimation of acetaminophen in plasma is described here. p-Propionamidophenol was used as internal standard. The assay involved a single ethyl acetate extraction and liquid chromatographic analysis at a wavelength of 242 nm using a reversed-phase encapped column, with a mobile phase of acetonitrile and 0.005 M potassium dihydrogen phosphate adjusted at pH 3.00. The limit of quantitation of acetaminophen by this method was 0.05 microg ml(-1), only 0.1 ml of the plasma sample was required for the determination. The calibration graph was linear from 0.05 to 100 microg ml(-1). Intra and inter-day precision (CV) did not exceed 8.93%. Mean recoveries of 90.31% with a CV of 1.38% were obtained. Applicability of the method was demonstrated by a pharmacokinetic study in normal volunteers who received 2 mg propacetamol.

Heterogeneity of paracetamol metabolism in Gilbert's syndrome

Gilbert's syndrome (GS) is an inherited bilirubin UDP-glucuronosyl transferase deficiency. The object of this study was to investigate the possible effects of this disorder on the metabolism of a drug, such as paracetamol, which is basically eliminated by hepatic glucuronidation. We studied 32 healthy volunteers and 18 people with GS, all of whom were given 1.5 g of paracetamol orally. In the 24 h urine collected, we determined the elimination of free paracetamol, the conjugates (glucuronide, sulphate) and the oxidation products (cysteine, mercapturic acid) by high pressure liquid chromatography (HPLC). The results are given as a percentage of the total quantity of paracetamol eliminated. The patients with GS were divided into 2 subgroups (GS-I and GS-II) according to whether glucuronidation was more or less than 50%. The overall results of the GS group showed no significant difference in the urinary elimination of metabolites as compared to the control group. However, in subgroup GS-I, a reduction in glucuronidation (P = 0.0012) and an increase in oxidation (P = 0.0051) was seen, as compared with the other 2 groups. There was inverse correlation between the glucuronide produced by conjugation and the oxidation products (r = -0.8718; P<0.005). People with GS are a heterogeneous group with respect to the metabolism of paracetamol. In one subgroup this was normal. In the other subgroup there was a marked reduction in glucuronidation and an increase in oxidation. These changes could mean that people in this subgroup are more liable to liver damage after an overdose of paracetamol.

Paracetamol metabolism in two ethnically different Spanish populations

The 24 h urinary excretion of paracetamol and its metabolites following a single oral dose of 1.5 g was compared in two ethnically different Spanish populations: 39 volunteers from the Basque country and 32 from Alicante. The urinary concentrations of unchanged paracetamol and its glucuronide, sulphate, cysteine, and mercapturic acid conjugates were determined by high-performance liquid chromatography. Statistically significant differences in the urinary excretion of unchanged paracetamol and the fractional urinary recovery of each conjugate between subjects from Alicante and subjects from the Basque country were not found. In both populations, an inverse relationship between glucuronide and sulphate conjugation following a bimodal frequency distribution pattern was found. In contrast to paracetamol oxidation, intersubject variation in paracetamol conjugation was negligible. The urinary excretion of unchanged paracetamol was higher in smokers than in nonsmokers. As compared with other studies, the urinary excretion of oxidation-derived paracetamol metabolites in both Spanish populations was intermediate and significantly different than that found in Caucasians from Scotland and West Africans (Ghana). This may determine a susceptibility to paracetamol hepatotoxicity following overdosage in the Spanish population.

Protective effect of diltiazem against acetaminophen hepatotoxicity in mice

There is evidence that an increase in cytosolic Ca++ concentration is a terminal event in the progression to cell death in toxic liver injury. We have compared the hepatoprotective effects of N-acetylcysteine (1 g/kg) and the calcium channel blocking agent, diltiazem (24 mg/kg), when given at 30 min, 3 h and 6 h after single intraperitoneal overdoses of acetaminophen (500 mg/kg) in mice. Overall beneficial effects on mortality, liver necrosis score, and plasma alanine aminotransferase (ALT) activity were found in diltiazem-treated mice 24 h after acetaminophen overdose. However, the most marked effects were obtained when diltiazem was given 6 h after acetaminophen. N-acetylcysteine was more effective than diltiazem at 30 min and 3 h, although it was less effective at 6 h. Mean plasma concentrations of the mercapturate metabolite (hepatic oxidative metabolism) were not significantly different among animals receiving acetaminophen alone or in combination with diltiazem, which suggests that the hepatoprotective effects of diltiazem are not exerted by inhibition of drug metabolic enzymes.