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Eler GJ, Santos IS, de Moraes AG, Mito MS, Comar JF, Peralta RM, Bracht A. Kinetics of the transformation of n-propyl gallate and structural analogs in the perfused rat liver. Toxicol Appl Pharmacol 2013; 273:35-46. [DOI: 10.1016/j.taap.2013.08.026] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Revised: 08/08/2013] [Accepted: 08/26/2013] [Indexed: 10/26/2022]
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2
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Lappin G, Shishikura Y, Jochemsen R, Weaver RJ, Gesson C, Brian Houston J, Oosterhuis B, Bjerrum OJ, Grynkiewicz G, Alder J, Rowland M, Garner C. Comparative pharmacokinetics between a microdose and therapeutic dose for clarithromycin, sumatriptan, propafenone, paracetamol (acetaminophen), and phenobarbital in human volunteers. Eur J Pharm Sci 2011; 43:141-50. [DOI: 10.1016/j.ejps.2011.04.009] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Revised: 02/24/2011] [Accepted: 04/12/2011] [Indexed: 11/17/2022]
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Pang KS, Morris ME, Sun H. Formed and preformed metabolites: facts and comparisons. J Pharm Pharmacol 2010; 60:1247-75. [DOI: 10.1211/jpp.60.10.0001] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Abstract
The administration of metabolites arising from new drug entities is often employed in drug discovery to investigate their associated toxicity. It is expected that administration of metabolites can predict the exposure of metabolites originating from the administration of precursor drug. Whether exact and meaningful information can be obtained from this has been a topic of debate. This communication summarizes observations and theoretical relationships based on physiological modelling for the liver, kidney and intestine, three major eliminating organs/tissues. Theoretical solutions based on physiological modelling of organs were solved, and the results suggest that deviations are expected. Here, examples of metabolite kinetics observed mostly in perfused organs that did not match predictions are provided. For the liver, discrepancies in fate between formed and preformed metabolites may be explained by the heterogeneity of enzymes, the presence of membrane barriers and whether transporters are involved. For the kidney, differences have been attributed to glomerular filtration of the preformed but not the formed metabolite. For the intestine, the complexity of segregated flows to the enterocyte and serosal layers and differences in metabolism due to the route of administration are addressed. Administration of the metabolite may or may not directly reflect the toxicity associated with drug use. However, kinetic data on the preformed metabolite will be extremely useful to develop a sound model for modelling and simulations; in-vitro evidence on metabolite handling at the target organ is also paramount. Subsequent modelling and simulation of metabolite data arising from a combined model based on both drug and preformed metabolite data are needed to improve predictions on the behaviours of formed metabolites.
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Affiliation(s)
- K Sandy Pang
- Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, Ontario, M5S 3M2, Canada
| | - Marilyn E Morris
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, State University of New York, Amherst, NY 14260, USA
| | - Huadong Sun
- Leslie Dan Faculty of Pharmacy, University of Toronto, 144 College Street, Toronto, Ontario, M5S 3M2, Canada
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Pang KS. Safety testing of metabolites: Expectations and outcomes. Chem Biol Interact 2008; 179:45-59. [PMID: 18926805 DOI: 10.1016/j.cbi.2008.09.013] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2008] [Revised: 09/12/2008] [Accepted: 09/15/2008] [Indexed: 12/18/2022]
Abstract
Metabolites arising from chemical entities, old or new, are often mediators of toxicity. Frequently, metabolites are investigated in test animals, with the expectation that the resultant toxicity or activity will mimic the exposure of their formed counterparts. This communication described observations that showed discrepant kinetics between formed and preformed metabolites in the liver, intestine, and kidney, major drug removal organs. Differences in the observed areas under the curve (AUCs) or the extraction ratios (Es) of formed and preformed metabolites in the liver had been attributed to zonal, enzyme heterogeneity, membrane barriers, or transporters. Preformed and formed metabolite also differed in their handling by the kidney; only the preformed and not the formed metabolite would be filtered. In the intestine, differences in the absorption of the precursor and the metabolite and the flow pattern in the intestine would bring about discrepancy in the time-courses of the formed vs. preformed metabolites. Analytical solutions of the AUCs of the metabolites and extraction ratios, based on physiological modeling of the liver, kidney, and intestine, showed that the AUC of the preformed, administered metabolite was dependent only on metabolite parameters, whereas the AUC of the formed metabolite was modulated additionally by the metabolic, secretory and intestinal absorptive intrinsic clearances of the precursor drug. Hence, administration of the synthetic metabolite would not reflect the toxicity associated with the metabolite formed via bioactivation. However, data on preformed metabolite may be used for simultaneous fitting by a combined model of drug and metabolite. Such a strategy is shown to be successful in risk assessment of environmental chemicals. Upon refinement of the resultant model with data on metabolite transport and handling by modeling and simulations, the resultant model would be more robust to provide improved predictions on metabolite toxicity pursuant to drug administration.
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Prueksaritanont T, Lin JH, Baillie TA. Complicating factors in safety testing of drug metabolites: Kinetic differences between generated and preformed metabolites. Toxicol Appl Pharmacol 2006; 217:143-52. [PMID: 17055014 DOI: 10.1016/j.taap.2006.08.009] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2006] [Revised: 08/25/2006] [Accepted: 08/29/2006] [Indexed: 12/15/2022]
Abstract
This paper aims to provide a scientifically based perspective on issues surrounding the proposed toxicology testing of synthetic drug metabolites as a means of ensuring adequate nonclinical safety evaluation of drug candidates that generate metabolites considered either to be unique to humans or are present at much higher levels in humans than in preclinical species. We put forward a number of theoretical considerations and present several specific examples where the kinetic behavior of a preformed metabolite given to animals or humans differs from that of the corresponding metabolite generated endogenously from its parent. The potential ramifications of this phenomenon are that the results of toxicity testing of the preformed metabolite may be misleading and fail to characterize the true toxicological contribution of the metabolite when formed from the parent. It is anticipated that such complications would be evident in situations where (a) differences exist in the accumulation of the preformed versus generated metabolites in specific tissues, and (b) the metabolite undergoes sequential metabolism to a downstream product that is toxic, leading to differences in tissue-specific toxicity. Owing to the complex nature of this subject, there is a need to treat drug metabolite issues in safety assessment on a case-by-case basis, in which a knowledge of metabolite kinetics is employed to validate experimental paradigms that entail administration of preformed metabolites to animal models.
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Stenken JA, Ståhle L, Lunte CE, Southard MZ. Monitoring in situ liver metabolism in rats using microdialysis. Comparison of microdialysis mass-transport model predictions to experimental metabolite generation data. J Pharm Sci 1998; 87:311-20. [PMID: 9523984 DOI: 10.1021/js970288z] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The generation of metabolites from two model compounds, phenacetin and acetaminophen, included in the perfusion fluid of a microdialysis probe implanted into rat liver was studied. When 60 microM phenacetin was included in the perfusion fluid using a flow rate of 1.0 microL/min, acetaminophen and acetaminophen sulfate were recovered at concentrations that ranged between 0.4 and 1.6 microM. Acetaminophen sulfate ([AS]gain) diffused back into the microdialysis probe on a micromolar percentage basis of 8.9+/-2.4% (n = 3) when acetaminophen was passed through the probe at a concentration between 11 and 12 microM. When 220-240 microM acetaminophen was passed through the probe, the percentage of acetaminophen sulfate recovered was 4.8+/-1.4% (n = 3) (P < 0.1 compared to the 11 microM group). No acetaminophen glucuronide was detected in the dialysate samples. A mathematical model that describes mass transport in microdialysis sampling was used to predict the concentration of metabolite that could be recovered into the dialysate after the loss of a substrate compound that undergoes metabolism. The model predicts a metabolite recovery of 23.6% using estimates for phenacetin metabolism and 21.5% using estimates for acetaminophen metabolism. The results presented here indicate that microdialysis has potential to be used to study local in situ metabolism and with further refinements of the microdialysis mass-transport model may be used to estimate in vivo metabolic formation rates.
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Affiliation(s)
- J A Stenken
- Department of Chemistry and Center for Bioanalytical Research, University of Kansas, Lawrence 66045-0046, USA.
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Ballinger LN, Cross SE, Roberts MS. Availability and mean transit times of phenol and its metabolites in the isolated perfused rat liver: normal and retrograde studies using tracer concentrations of phenol. J Pharm Pharmacol 1995; 47:949-56. [PMID: 8708991 DOI: 10.1111/j.2042-7158.1995.tb03276.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Phenolic compounds are frequently detoxified by the formation of sulphate and glucuronic acid conjugates in the liver. These conjugates are formed in the hepatocytes and then either transported into the bile or back into the blood. In this study, we examined the transport kinetics of phenol and its metabolites in the isolated perfused rat liver by monitoring the outflow profiles of these compounds after a bolus input in a single pass preparation. Phenol was almost exclusively metabolized to phenyl sulphate (97%) at the trace concentrations used, with the amount of phenol and metabolites excreted into the bile being minimal (3.5%). The metabolite formed was rapidly transported back into the perfusate, with mean transit times of 17.4 and 12.3 s anterograde and 24.9 and 24.2 s retrograde at flow rates of 15 and 30 mL min-1 respectively, which were intermediate between those of Evans blue and water. The outflow concentration-time profile for phenyl sulphate formation was unaffected by the addition of another organic anion (bromosulphophthalein). The effect of enzyme zonation on outflow concentration-time profiles was also investigated using retrograde perfusions. The transit time ratios for generated metabolite to water for anterograde perfusions (0.6) was found to be more than twice that for retrograde perfusions (0.23) at 15 mL min-1 and approximately 1.6 times greater at 30 mL min-1, being 0.58 and 0.37 respectively. The relative ratios obtained are consistent with previous findings that normalized variance of solutes in the retrograde perfusions is greater than that for anterograde perfusions.
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Affiliation(s)
- L N Ballinger
- Department of Medicine, University of Queensland, Brisbane, Australia
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Pang KS. Acinar factors in drug processing: protein binding, futile cycling, and cosubstrate. Drug Metab Rev 1995; 27:325-68. [PMID: 7641582 DOI: 10.3109/03602539509029829] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- K S Pang
- Faculty of Pharmacy, University of Toronto, Canada
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Pang KS, Schwab AJ, Goresky CA, Chiba M. Transport, binding, and metabolism of sulfate conjugates in the liver. Chem Biol Interact 1994; 92:179-207. [PMID: 8033253 DOI: 10.1016/0009-2797(94)90063-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Sulfate conjugates are a heterogeneous class of polar, anionic metabolites that result from the conjugation of endogenous and exogenous compounds. Sulfate conjugates exhibit a high degree of binding to albumin, the extent of which usually exceeds those of their parent compounds. Preponderant direct and indirect evidence suggests that sulfation activity is slightly higher in the periportal than in the perivenous (centrilobular) region of the liver, but recent immunohistochemical studies imply that specific isoforms of the sulfotransferases may also be preferentially localized in the perivenous region. Entry of sulfate conjugates into the liver cell is poor unless discrete carriers are present. Although known transport carriers exist for the sulfated bile acids, the specificity of the carriers for drug sulfate conjugates is presently unknown. The removal of sulfates is usually by way of biliary excretion while, on occasion, sulfates can be desulfated and participate in futile cycling with their parent compounds. The binding, transport, and hepatic elimination of various drug sulfate conjugates are examined. Non-recirculating studies carried out in the perfused rat liver with the multiple indicator dilution technique under varying input sulfate conjugate concentrations have provided essential information on the effects of vascular (red blood cells and plasma protein) binding on transport and removal of the conjugates. These studies clearly demonstrate the need to study protein binding, transmembrane transfer characteristics across the liver basolateral (sinusoidal) and canalicular membranes, and enzyme zonation in a distributed-in-space fashion in order to properly define the handling of sulfate conjugates in the liver.
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Affiliation(s)
- K S Pang
- Faculty of Pharmacy, University of Toronto, Ontario, Canada
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Goresky CA, Pang KS, Schwab AJ, Barker F, Cherry WF, Bach GG. Uptake of a protein-bound polar compound, acetaminophen sulfate, by perfused rat liver. Hepatology 1992; 16:173-90. [PMID: 1618470 DOI: 10.1002/hep.1840160129] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The hepatocytic entry of acetaminophen sulfate conjugate was examined in the rat liver, perfused with red cells with and without albumin, by use of the multiple-indicator dilution technique. [3H]acetaminophen sulfate was injected into the portal vein in a bolus of blood containing 51Cr-labeled red blood cells (a vascular reference), sucrose (a low-molecular-weight interstitial reference) or 125I-labeled albumin (a high-molecular-weight interstitial reference, included when albumin was present), and the time courses of their outflow into the hepatic venous blood were observed. The [3H]acetaminophen sulfate, which binds partially to albumin, emerged between albumin and sucrose in the presence of albumin, processed the upslope of the sucrose curve and showed a late low-in-magnitude tailing; the precession disappeared in the absence of albumin. Biliary excretion of [3H]acetaminophen sulfate was less than 1% of the dose. Quantitative evaluation with a barrier-limited, space-distributed variable transit time model (including rapidly equilibrating albumin binding) accounted for the albumin effect on [3H]acetaminophen sulfate behavior and demonstrated a low liver cell permeability for the acetaminophen sulfate and a small interstitial binding space for its nonalbumin-bound fraction in excess of that for sucrose, which in the absence of albumin was of similar dimensions.
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Affiliation(s)
- C A Goresky
- McGill University Medical Clinic, Montreal General Hospital, Quebec, Canada
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Itinose AM, Sakuno ML, Bracht A. Metabolic effects of acetaminophen. Studies in the isolated perfused rat liver. Cell Biochem Funct 1989; 7:263-73. [PMID: 2605769 DOI: 10.1002/cbf.290070405] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The effects of acetaminophen on the metabolism of the isolated perfused rat liver were investigated. The following results were obtained: (1) Acetaminophen increased glucose release and glycolysis from endogenous glycogen (glycogenolysis). (2) Oxygen uptake, gluconeogenesis from either pyruvate or fructose and glycogen synthesis were inhibited. (3) In isolated rat liver mitochondria acetaminophen decreased state III and state IV respiration; it also decreased the ADP/O ratio and the respiratory control ratio. (4) The action of acetaminophen on glycogenolysis was not affected by N-acetylcysteine; this compound, however, increased glycogen synthesis. (5) The effects of acetaminophen are reversible. It was concluded that glycogen depletion by acetaminophen can be produced by two mechanisms. The first, as previously demonstrated by several workers, depends on irreversible binding of a reactive metabolite. The second, however, is reversible and depends primarily on an inhibition of mitochondrial energy metabolism.
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Affiliation(s)
- A M Itinose
- Laboratory of Liver Metabolism, University of Maringá, Brazil
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12
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Pang KS, Lee WF, Cherry WF, Yuen V, Accaputo J, Fayz S, Schwab AJ, Goresky CA. Effects of perfusate flow rate on measured blood volume, disse space, intracellular water space, and drug extraction in the perfused rat liver preparation: characterization by the multiple indicator dilution technique. JOURNAL OF PHARMACOKINETICS AND BIOPHARMACEUTICS 1988; 16:595-632. [PMID: 3074996 DOI: 10.1007/bf01062014] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The effect of hepatic blood flow on the elimination of several highly cleared substrates was studied in the once-through perfused rat liver preparation. A constant and low input concentration of ethanol (2.0 mM), [14C]-phenacetin and [3H]-acetaminophen (0.36 and 0.14 microM, respectively), or meperidine (8.1 microM) was delivered once-through the rat liver preparation in five flow periods (greater than 35 min each); control flow periods at 12 ml/min were interrupted by flow changes to 8 or 16 ml/min. The steady-state hepatic availabilities (F or outflow survivals) at 12 ml/min were ethanol, 0.075 +/- 0.038; [14C]-phenacetin, 0.15 +/- 0.059; [3H]-acetaminophen, 0.34 +/- 0.051; meperidine, 0.047 +/- 0.017. Flow-induced changes were different among the compounds: with reduced flow (8 ml/min), F was decreased for ethanol (0.061 +/- 0.032) and [3H]-acetaminophen (0.28 +/- 0.051), as expected, but was increased for [14C]-phenacetin (0.20 +/- 0.068) and meperidine (0.05 +/- 0.03); with an elevation of flow (to 16 ml/min), F was increased for all compounds, as expected of shorter sojourn times: ethanol, 0.13 +/- 0.065; [14C]-phenacetin, 0.22 +/- 0.062; [3H]-acetaminophen, 0.43 +/- 0.063; meperidine, 0.055 +/- 0.022. A marked increase in F for ethanol had occurred when flow changed from 12 to 16 ml/min due to nonlinear metabolism; the latter was confirmed by a reduction in the extraction ratios at increasing concentrations (1.8 to 11.4 mM); this condition was not present for the other compounds. In order to explain the observations, we used the multiple indicator dilution technique to investigate the flow-induced behaviors of tissue distribution spaces of vascular and intracellular references in the perfused rat liver preparation.
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Affiliation(s)
- K S Pang
- Faculty of Pharmacy, University of Toronto, Ontario, Canada
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Cha YN, Dong MS, Hong SS. Functional relationship between initial oxidation of 7-ethoxycoumarin and subsequent conjugation of 7-hydroxycoumarin in isolated perfused rat livers. Chem Biol Interact 1987; 61:125-37. [PMID: 3829139 DOI: 10.1016/0009-2797(87)90034-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Functional relationship between the initial mixed function oxidation of 7-ethoxycoumarin (EC) to 7-hydroxycoumarin (HC) and the subsequent conjugation of this metabolite to sulfate ester and glucuronide has been studied using isolated perfused rat livers. When increasing concentrations of EC (from 25 to 200 microM) were infused, perfused liver can oxidize only up to about 60 nmol of the infused EC to HC per min/g liver tissue. Most of this HC metabolite was released as sulfate ester, but there was a dose dependent shift to a more significant glucuronidation at the expense of the sulfate form. The dose dependent shift observed upon infusions with increasing dose of EC was not extensive so that the major portion of metabolite released was always the sulfate ester. However, the shift observed with HC was extensive and the major portion released was the glucuronide conjugate. Upon infusions with increasing concentrations of HC, the maximal rates of sulfation and glucuronidation were found to be 60 nmol and 120 nmol of HC conjugated per min/g liver tissue, respectively. Furthermore, the ranges in the rates of conjugation for the infused HC were divided into a sulfate ester 'zone' (less than 20 nmol), a dose-dependent shift 'zone' (between 20 and 180 nmol) with the 'cross-over' occurring at 80 nmol/min/g liver, and reaching the maximal conjugation 'capacity' rate (180 nmol), above which the unconjugated free form of HC was released. Under conditions when EC was infused into normal rat livers, the calculated maximal oxidation rate was only 60 nmol of HC produced/min/g liver. Consequently, under such a condition, the oxidation rate may never reach the 'cross-over' rate and this explains the lack of extensive dose-dependent shift and further indicates that there remained a large reserve conjugation capacity (120 nmol/min/g).
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Poulsen HE, Lerche A, Skovgaard LT. Acetaminophen metabolism by the perfused rat liver twelve hours after acetaminophen overdose. Biochem Pharmacol 1985; 34:3729-33. [PMID: 4052111 DOI: 10.1016/0006-2952(85)90238-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The effect of a toxic dose of acetaminophen on the hepatic conjugations of acetaminophen was studied in single pass perfused livers from rats given acetaminophen overdose 12 hr prior to perfusion and from control rats. Four different acetaminophen concentrations (0.1-6 mmol/1) were used in each perfusion. Glucuronidation of acetaminophen was increased and sulfation of acetaminophen occurred at an unchanged rate in acetaminophen damaged livers as compared to control livers. Hepatic glutathione concentrations declined to about 0.4 mumol/g liver during perfusion, possibly due to excretion of glutathione to perfusion medium, but in spite of this the formation of glutathione conjugates was increased with acetaminophen concentrations increasing up to about 5 mmol. We conclude that decreased sulfation, glucuronidation and glutathione conjugation in the liver is not present in the early development of acetaminophen-induced hepatic damage.
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Conway JG, Kauffman FC, Thurman RG. Effect of glucose on 7-hydroxycoumarin glucuronide production in periportal and pericentral regions of the liver lobule. Biochem J 1985; 226:749-56. [PMID: 3985943 PMCID: PMC1144773 DOI: 10.1042/bj2260749] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The effect of starvation and glucose addition on glucuronidation was assessed in sublobular regions of the lobule in perfused livers from phenobarbital-treated rats. Fibre-optic micro-light guides were placed on periportal and pericentral areas on the surface of livers to monitor the fluorescence (excitation 366 nm, emission 450 nm) of free 7-hydroxycoumarin from the tissue surface. After infusion of 7-hydroxycoumarin (80 microM) under normoxic conditions, steady-state increases in fluorescence were reached in 6-8 min in both regions. Subsequently, the formation of non-fluorescent 7-hydroxycoumarin glucuronide was inhibited completely by perfusion with N2-saturated perfusate containing 20 mM-ethanol. The difference in fluorescence between anoxic and normoxic perfusions was due to glucuronidation under these conditions. In livers from fed rats, rates of glucuronidation in periportal and pericentral regions of the liver lobule were 8 and 19 mumol/h per g, respectively. In contrast, rates of glucuronidation were 3 and 9 mumol/h per g, respectively, in periportal and pericentral regions of livers from starved rats. Infusion of glucose (20 mM) had no effect on rates of glucuronidation in livers from fed rats; however, glucose increased rates of glucuronidation rapidly (half-time, t0.5 = 1.5 min) in periportal and pericentral regions to 7 and 17 mumol/h per g, respectively in livers from starved rats. These results indicate that the rapid synthesis of the cofactor UDP-glucuronic acid derived from glucose is an important rate-determinant for glucuronidation of 7-hydroxycoumarin in both periportal and pericentral regions of livers from starved rats.
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