Detection and follow-up, after partial liver resection, of the urinary paracetamol metabolites by proton NMR spectroscopy.

BACKGROUND: Combination drug therapy is often used to achieve optimal analgesia in surgery. Paracetamol can be used as one component of an analgesic regime following hepatic resection. OBJECTIVE: This study was designed to investigate paracetamol and its metabolites by proton NMR spectroscopy in patient urine and to assess whether N-acetyl-p-benzoquinone imine (NAPQI, a hepatotoxic metabolite) formation is increased after liver resection. METHOD: We studied the excretion of acetaminophen and its metabolites by 5 patients who were operated on for partial liver resection by proton NMR spectroscopy. As an intravenous infusion 1 g of paracetamol was given over 15 min every 6 h during 48 h. The first injection was given in the operating theatre after liver resection was completed. Urine samples were collected before injection (T1) and 24 and 48 h after the first injection (T2 and T3); the samples were frozen and kept at -20°C up to the analysis by NMR spectroscopy. RESULTS: Metabolites of the paracetamol were detected for all patients. Among the discerned metabolites, 4 were identified as metabolites of paracetamol: paracetamol glucuronide, paracetamol sulfate, N-acetyl-L-cysteinyl paracetamol (metabolite of NAPQI) and paracetamol. Their ratios, respectively, were: 46-82.9, 12.6-30.0, 0.5-5.5 and 1.43-3.54%. CONCLUSION: This study showed that there was no increase in the formation of toxic metabolite (NAPQI) after treatment with paracetamol in these few cases of liver resections. A larger study is necessary to confirm these results.

A 1H NMR-based metabolomics approach for mechanistic insight into acetaminophen-induced hepatotoxicity.

The widely used analgesic-antipyretic drug acetaminophen (APAP) is known to cause serious liver necrosis at high doses in man and experimental animals. For studies of toxic processes, 1H NMR spectroscopy of biofluids allows monitoring of endogenous metabolite profiles that alter characteristically in response to changes in physiological status. Herein, a 1H NMR metabolomics approach was applied to the investigation of APAP toxicity in rats and the effect of phenobarbital (PB) on APAP-induced hepatotoxicity. Metabolite differences due to hepatotoxicity were observed in 1H NMR spectra of serum and urine, and enhanced APAP hepatotoxicity by pretreatment with PB was clearly shown by a principal components analysis of the spectral data. NMR spectra of APAP-dosed rat urine provided profiles of APAP-related compounds together with endogenous metabolites. By comparison of endogenous and APAP-related metabolite spectra with those from rats pretreated with PB, it was possible to show the importance of oxidative metabolism of APAP to N-acetyl-p-benzoquinone, an essential step in APAP hepatotoxicity.

Ethanol and production of the hepatotoxic metabolite of acetaminophen in healthy adults.

BACKGROUND: Recent case reports suggest that consumption of ethanol may increase the risk of liver injury induced by acetaminophen (INN, paracetamol). However, this possibility is at odds with previous clinical studies that showed that acute ethanol ingestion could protect against hepatotoxicity by inhibiting CYP-mediated acetaminophen oxidation. We tested the hypothesis that ethanol ingestion can increase susceptibility to acetaminophen toxicity if acetaminophen ingestion occurs shortly after ethanol is cleared from the body. METHODS: Ten healthy volunteers each received a 6-hour intravenous infusion of ethanol (to achieve a blood concentration of 100 mg/dL ethanol) or 5% dextrose in water, administered in random order. Acetaminophen (500 mg) was ingested 8 hours after the end of the infusion. Blood and urine were collected for assessment of formation of N-acetyl-p-benzoquinone imine (NAPQI), the hepatotoxic metabolite of acetaminophen. RESULTS: Mean NAPQI formation was enhanced by 22% (range, 2% to 38%; P < .03) when the acetaminophen dose was given after an ethanol infusion, compared with after 5% dextrose in water infusion. This mean increase was similar in magnitude to that predicted by a mathematical model describing the induction of CYP2E1, the main enzyme catalyzing NAPQI formation, by a mechanism of enzyme stabilization. CONCLUSIONS: Consumption of up to one 750-mL bottle of wine, six 12-ounce cans of beer, or 9 ounces of 80-proof liquor over the course of a single evening modestly increases the fraction of an acetaminophen dose converted to its toxic metabolite, NAPQI, when acetaminophen is ingested soon after ethanol has been cleared from the body. This change in acetaminophen metabolism may present an incremental increase in the risk of acetaminophen hepatotoxicity.

An autopsy case of prolidase deficiency.

A 25-year-old female who suffered from longstanding incurable leg ulcers was found to have prolidase deficiency with iminodipeptiduria. On ultrastructural studies of autopsy specimens, the lamina densa of the epidermal basement membrane was found to show irregular splitting and the basement membranes of the dermal blood vessels were lamellated with interruptions. Lamellar changes and splitting of the basement membranes of the renal tubules, interstitial blood vessels and glomerular capillaries also occurred. These morphological abnormalities seem to be one of causes of the clinical symptomatology.

Human erythrocyte prolidase and prolidase deficiency.

Biochemical studies on human prolidase (EC 3.4.13.9) and prolidase deficiency are described. The urine sample from a 32-year-old female with prolidase deficiency was examined. Diagnosis was based on clinical features and defects of prolidase in her erythrocytes. She excreted massive amounts of iminopeptides, where three major peptides were identified; aspartyl-proline, glutamyl-proline and glycyl-proline. The prolidase was purified approximately 10,000-fold from the normal human erythrocytes through an eight step procedure. The purified enzyme consisted of two identical subunits of which the molecular weight was calculated to be 55,000. The relative cleavage rates of the enzyme for glycyl-L-proline, L-alanyl-L-proline, L-leucyl-L-proline, L-prolyl-L-proline, and glycyl-hydroxy-L-proline were 100%, 53%, 27%, 31% and 2%, respectively. The relative substrate specificity of the enzyme offers a reasonable explantation for the presence of a higher level of urinary imidodipeptides in a patient with prolidase deficiency. An attempt at erythrocyte transfusion was performed, aimed at enzyme replacement therapy. After the transfusion (erythrocytes from 800 ml of whole blood), the prolidase activity of the peripheral erythrocyte was elevated to approximately 35% of the normal values and gradually decreased (half-life, 41 days). During this period urinary peptide-bound proline was monitored, but no significant change was observed.

Studies on a patient with iminopeptiduria. I. Identification of urinary iminopeptides.

A patient suffering from recurrent ulcers on the legs was found to excrete large amounts of iminodipeptides in the urine. Among the iminodipeptides excreted, Glu-Hyp, Asp-Pro, Glu-Pro, Leu-Hyp, Gly-Pro, Thr-Pro, Ser-Pro, Ala-Pro, Val-Pro, Ile-Pro, Leu-Pro, and Phe-Pro were identified and their quantities estimated. Some of the iminopeptides had to be synthesized for purposes of identification.