Acetaminophen metabolism by the perfused rat liver twelve hours after acetaminophen overdose

A urinary metabonomics analysis of long-term effect of acetochlor exposure on rats by ultra-performance liquid chromatography/mass spectrometry

The study was to assess the long-term toxic effects of acetochlor on rats. Two different doses (42.96 and 107.4 mg/kg body weight/day) of acetochlor were administered to Wistar rats through their food for over 24 weeks. Rat urine samples were collected at two time-points for the measurements of the metabonomics profiles with ultra-performance liquid chromatography-mass spectrometry (UPLC-MSMS). The results of clinical chemistry and histopathology suggested that long-term use of acetochlor in rats caused liver and kidney damage, and dysfunction of antioxidant system. The urinary metabonomics analysis indicated that the high and low-dose exposure of acetochlor could cause alterations of these metabonomics in urine in the rat. Significant changes of the levels of hippuric acid (0.403-fold decrease), citric acid (0.430-fold decrease), pantothenic acid (0.486-fold decrease), uracil (0.419-fold decrease), β-Alanine (0.325-fold decrease), nonanedioic acid (0.445-fold decrease), L-tyrosine (0.410-fold decrease), D-glucuronic acid (8.389-fold increase) and 2-ethyl-6-methyl-N-methyl-2-chloro-acetanilide in urine were observed. In addition, it may interfere with the fatty acid synthesis, the pyrimidine degradation and pantothenate biosynthesis. The level of 2-ethyl-6-methyl-N-methyl-2-chloro-acetanilide is detected in all treated groups which is not found in the control groups, indicating which can be used as an early, sensitive marker of acetochlor exposure in rat. This study illustrates the important utility of metabonomics approaches to understand the toxicity of long-term exposure of acetochlor.

Hepatic kinetics of SCP-1 (N-[alpha-(1,2-benzisothiazol-3(2H)-ona-1, 1-dioxide-2-yl)-acetyl]-p-aminophenol) compared with acetaminophen in isolated rat liver

The hepatic disposition of a new analgesic, SCP-1, a derivative of acetaminophen, was studied in the isolated perfused rat liver using a recirculating system. The aim of this study was to compare the kinetic parameters of this molecule with those of acetaminophen. Sprague-Dawley rat (230-330 g) livers were perfused for 2 h with 250 ml Krebs-Henseleit bicarbonate buffer containing SCP-1 or acetaminophen, 0.07 mmol l(-1) (n=4), 0.28 mmol l(-1) (n=4), and 0.8 mmol l(-1) (n=4) (approximately one, four and ten times the therapeutic doses in man, respectively). Perfusate samples were collected from the efflux at various times. The SCP-1 and acetaminophen perfusate concentrations were assayed by a HPLC method. Pharmacokinetic analysis was carried out using a computer program. There were significant differences between the hepatic kinetics of SCP-1 and those of acetaminophen. Thus, SCP-1 elimination half-life (mean 14.8+/-10.0 min) was shorter than that of the acetaminophen (186.1+/-27.7 min) (t=11.6, P=0.0001). While the half-life of SCP-1 increases with concentration, the half-life of acetaminophen remains constant as the concentration increases. The hepatic clearance was higher for SCP-1 than acetaminophen (mean 19.01+/-14.5 ml min(-1) vs. 1.29+/-0.08 ml min(-1), respectively) (t=2.44, P<0.05), and it behaved according to dose-dependent kinetics. The SCP-1 extraction ratio was higher (mean 0.63+/-0.49) than for acetaminophen (0.04+/-0.01) (t=2.41, P<0.05) and this parameter tended to decrease as the perfusate concentrations of SCP-1 increased. It was concluded that the hepatic kinetics of SCP-1 behaved according to dose-dependent kinetics, and statistically significant differences were found between pharmacokinetics parameters of both drugs studied.

Factors and conditions affecting the glucuronidation of oxazepam

The aim of the present work was to investigate the impact of disease states and environmental and host factors on the glucuronidation of oxazepam. Glucuronidation represents quantitatively one of the most important metabolic conjugation pathways (phase II) in man for the inactivation and detoxication of xenobiotics and endogenous compounds and the liver is the major site for it to take place. Far less attention has been paid to the conjugation reactions in previous clinical research in this field compared to the immense interest in the oxidative biotransformation pathways (phase I). This fact is mainly due to the latter giving rise to active or reactive metabolites with a toxicological potential. The metabolism of oxazepam expresses exclusively the capacity for glucuronide formation. It was a prerequisite to establish the bioavailability of oxazepam prior to succeeding studies on the oral disposition of the drug. A preparation for intravenous administration was created. Clearance was chosen as measurement of the capacity to glucuronidate oxazepam. Severe decompensated liver disease was associated with a significant decrease in oxazepam clearance, that became even more obvious when corrected for by a diminished binding to plasma proteins. This increase in free fraction of oxazepam was substantial and could mainly be accounted for by low plasma albumin values. The results are in part a settlement with earlier studies on glucuronidation in liver disease and they may undoubtedly be ascribed to the severe degree of liver disease. For the first time it was shown that hypothyroidism led to a decline in the clearance and metabolism of oxazepam and paracetamol that is mainly biotransformed by glucuronidation. It was concluded that the enzymes responsible for glucuronidation in hypothyroidism are under the influence of thyroid hormones as is the case with oxidative enzymes. Further studies focused on the effect of host and environmental factors on glucuronidation. A commercially available very low calorie product for the treatment of obesity resulted in a decrease in oxazepam clearance and a lack of co-factors as a consequence of the low calorie intake was explanatorily proposed. Beta-adrenoceptor antagonists are often prescribed together with other drugs and close knowledge on interactions is mandatory but insufficient in regard of drugs being glucuronidated. Despite the mutual metabolic pathway labetalol exerted no dispositional alterations concerning oxazepam. It was moreover suggested that very elderly subjects between the age of 80 to 94 years had a reduced clearance of oxazepam.(ABSTRACT TRUNCATED AT 400 WORDS)

Simultaneous measurements of glutathione and activated sulphate (PAPS) synthesis rates and the effects of selective inhibition of glutathione conjugation or sulphation of acetaminophen

The aim of the present study was to examine the effects of the hepatotoxic drug acetaminophen (AA) on the synthesis rates of glutathione (GSH), activated sulphate (PAPS; adenosine 3'-phosphate 5'-phosphosulphate) and the AA metabolites AA-GSH and AA-sulphate after selective inhibition of GSH biosynthesis or sulphation in isolated rat hepatocytes. Selective inhibition of the two interdependent metabolic pathways was accomplished by buthionine sulphoximine (BSO) and 2,6-dichloro-4-nitrophenol (DCNP). The synthesis rates of GSH and PAPS were determined simultaneously by a previously described method based on trapping of radioactivity (35S) in the pre-labelled GSH and PAPS pools. Pre-incubation with 10 mM BSO for 30 min depleted GSH by 38% (P < 0.05) and PAPS by 27% (P < 0.05). The depletion resulted in increased PAPS synthesis at low, non-toxic [5-19 nmol/(10(6) cells.min)] (P < 0.05) and at high, toxic [7-30 nmol/10(6) cells.min)] (P < 0.05) AA concentrations. In both cases sulphur is diverted from GSH biosynthesis to sulphoxidation and PAPS synthesis, thereby maintaining the PAPS pool and preserving the sulphation capacity. This corresponds to the finding that AA sulphation was unaffected by BSO irrespective of AA concentration [6 vs 5 and 20 vs 17 nmol/(10(6) cells.hr), respectively]. Even though the GSH synthesis was halved after BSO pre-incubation, the GSH conjugating capacity of AA was well preserved. Incubation with 200 microM DCNP and 5 mM AA diminished PAPS synthesis from 24 to 10 nmol/(10(6) cells.min) (P < 0.02) and reduced AA-sulphate synthesis by 67% compared to experiments without DCNP incubation [4.8 vs 14.7 nmol/(10(6) cells.hr)] (P < 0.05). GSH and AA-GSH synthesis rates did not change compared to control experiments in which sulphation was not inhibited [1165 vs 1487 nmol/(10(6) cells.min), respectively] and [1.7 vs 1.7 nmol/(10(6) cells.hr), respectively]. This indicates that increased sulphur availability due to decreased PAPS synthesis is unable to raise the cysteine pool and stimulate the gamma-glutamyl cycle and GSH synthesis.