![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
School of Pharmacy and Pharmaceutical Sciences, University of
Manchester
Microsomal protein recovery and hepatocellularity have been
determined and investigated as scaling factors for interrelating clearance by hepatic microsomes, freshly isolated hepatocytes and whole
liver from untreated (UT) rats and rats treated with either the
cytochrome P450 inducer phenobarbital (PB) or dexamethasone (DEX).
Hepatocellularity in UT rats (1.1 × 108 hepatocytes/g
liver) was not significantly different after either PB or DEX induction
(1.1 and 1.3 × 108 hepatocytes/g liver,
respectively). However the microsomal protein recovery index, which
provides a scaling factor that is inversely related to the efficiency
of the microsomal preparation procedure, was 47 mg/g liver in both PB
and DEX microsomes and differs from UT rats (60 mg/g liver). These
contrasting findings are consistent with the interlaboratory trends in
the literature, indicating that, although hepatocellularity estimates
are in good accord, microsomal recovery can vary 2-fold; this has
implications for scaling.
The oxidation of diazepam to its three primary metabolites was measured
in PB and DEX microsomes and hepatocytes and the scaling factors were
applied to these data and previously reported UT data. Marked changes
in kinetics occur on induction resulting in a shift in the major
pathway. In particular, 3-hydroxylation is induced over 20-fold by DEX.
Diazepam CLint was determined in
vivo after administration of a bolus dose into the hepatic portal
vein of UT, PB, and DEX rats; values of 127, 191, and 323 ml/min/SRW
(where SRW is a standard rat weight of 250 g), respectively, were
obtained. Using these scaling factors, the hepatocyte predictions of
CLint were excellent (99, 144, and 297 ml/min/SRW for UT, PB, and DEX, respectively), whereas only the DEX
prediction (248 ml/min/SRW) was accurate for the microsomal system,
with a substantial underprediction for UT and PB (46 and 68 ml/min/SRW,
respectively). Evidence is presented for product inhibition, resulting
from accumulation of primary metabolites within the microsomal
preparation, as the mechanism responsible for this underprediction.
These results illustrate that the scaling factor approach is applicable
to induced livers in which both cytochrome P450 complement and zonal
distribution are altered. These data, together with our previous
studies, demonstrate that CLint in cells
(2.4-297 ml/min/SRW), microsomes (2.7-248 ml/min/SRW), and in
vivo (1.5-323 ml/min/SRW) are related in a linear fashion and
hence inherently both in vitro systems are of equal value
in predicting in vivo CLint.
This article has been cited by other articles:
|
|
 |
|
  L. M. Sweeney, K. D. Thrall, T. S. Poet, R. A. Corley, T. J. Weber, B. J. Locey, J. Clarkson, S. Sager, and M. L. Gargas Physiologically Based Pharmacokinetic Modeling of 1,4-Dioxane in Rats, Mice, and Humans Toxicol. Sci., January 1, 2008; 101(1): 32 - 50. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Alcorn, F. A. Elbarbry, M. Z. Allouh, and P. J. McNamara Evaluation of the Assumptions of an Ontogeny Model of Rat Hepatic Cytochrome P450 Activity Drug Metab. Dispos., December 1, 2007; 35(12): 2225 - 2231. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. A. M. de Graaf, R. de Kanter, M. H. de Jager, R. Camacho, E. Langenkamp, E. G. van de Kerkhof, and G. M. M. Groothuis EMPIRICAL VALIDATION OF A RAT IN VITRO ORGAN SLICE MODEL AS A TOOL FOR IN VIVO CLEARANCE PREDICTION Drug Metab. Dispos., April 1, 2006; 34(4): 591 - 599. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. M. Jones and J. B. Houston SUBSTRATE DEPLETION APPROACH FOR DETERMINING IN VITRO METABOLIC CLEARANCE: TIME DEPENDENCIES IN HEPATOCYTE AND MICROSOMAL INCUBATIONS Drug Metab. Dispos., September 1, 2004; 32(9): 973 - 982. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. S. Salonen, L. Nyman, A. R. Boobis, R. J. Edwards, P. Watts, B. G. Lake, R. J. Price, A. B. Renwick, M.-J. Gomez-Lechon, J. V. Castell, et al. COMPARATIVE STUDIES ON THE CYTOCHROME P450-ASSOCIATED METABOLISM AND INTERACTION POTENTIAL OF SELEGILINE BETWEEN HUMAN LIVER-DERIVED IN VITRO SYSTEMS Drug Metab. Dispos., September 1, 2003; 31(9): 1093 - 1102. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Projean, B. Baune, R. Farinotti, J.-P. Flinois, P. Beaune, A.-M. Taburet, and J. Ducharme IN VITRO METABOLISM OF CHLOROQUINE: IDENTIFICATION OF CYP2C8, CYP3A4, AND CYP2D6 AS THE MAIN ISOFORMS CATALYZING N-DESETHYLCHLOROQUINE FORMATION Drug Metab. Dispos., June 1, 2003; 31(6): 748 - 754. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. S. Bogdanffy Vinyl Acetate-Induced Intracellular Acidification: Implications for Risk Assessment Toxicol. Sci., April 1, 2002; 66(2): 320 - 326. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Nestorov, I. Gueorguieva, H. M. Jones, B. Houston, and M. Rowland Incorporating Measures of Variability and Uncertainty into the Prediction of in Vivo Hepatic Clearance from in Vitro Data Drug Metab. Dispos., March 1, 2002; 30(3): 276 - 282. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. E. Witherow and J. B. Houston Sigmoidal Kinetics of CYP3A Substrates: An Approach for Scaling Dextromethorphan Metabolism in Hepatic Microsomes and Isolated Hepatocytes to Predict In Vivo Clearance in Rat J. Pharmacol. Exp. Ther., July 1, 1999; 290(1): 58 - 65. [Abstract] [Full Text]
|
|
|
|
|
|
D. J. Carlile, N. Hakooz, and J. B. Houston Kinetics of Drug Metabolism in Rat Liver Slices: IV. Comparison of Ethoxycoumarin Clearance by Liver Slices, Isolated Hepatocytes, and Hepatic Microsomes from Rats Pretreated with Known Modifiers of Cytochrome P-450 Activity Drug Metab. Dispos., April 1, 1999; 27(4): 526 - 532. [Abstract] [Full Text]
|
|
|
|
|
|
R. E. White Short- and Long-Term Projections About the Use of Drug Metabolism in Drug Discovery and Development Drug Metab. Dispos., December 1, 1998; 26(12): 1213 - 1216. [Abstract] [Full Text]
|
|
|
|
|
|
D. J. Carlile, A. J. Stevens, E. I. L. Ashforth, D. Waghela, and J. B. Houston In Vivo Clearance of Ethoxycoumarin and Its Prediction from In Vitro Systems. Use of Drug Depletion and Metabolite Formation Methods in Hepatic Microsomes and Isolated Hepatocytes Drug Metab. Dispos., March 1, 1998; 26(3): 216 - 221. [Abstract] [Full Text]
|
|
 |
 |
 |
|
 |
 |
 |
