Inter-individual differences in the activity of CYP3A4 in the small intestine contribute to the low and variable oral bioavailability observed for many drugs that are CYP3A substrates. This variability appears to be the result of large differences in the specific content of CYP3A4 in duodenal enterocytes. From a therapeutic perspective, large differences in first-pass intestinal extraction efficiency can lead to variable systemic drug exposure and variable pharmacological effects following oral administration of doses that are appropriate for the "average" patient, increasing the risk of therapeutic failure and adverse toxicity. The cause of variable intestinal CYP3A expression is largely unknown, but thought to involve both genetic and environmental factors. Importantly, we have shown previously that the most biologically active form of vitamin D, 1,25-dihydroxy vitamin D3 (1,25(OH)2D3), enhances transcription of the CYP3A4 gene in a VDR-dependent manner and that CYP3A4 in turn can catalyze the metabolic clearance of 1,25(OH)2D3. The overall objectives of this grant proposal are to determine whether or not intestinal CYP3A4 is regulated in vivo by the following sequential process: formation and biliary excretion of a 25(OH)D3-glucuronide conjugate, hydrolysis of the conjugate to 25(OH)D3 in the proximal intestinal lumen and its absorption into the primary enterocytes, where it is converted to 1,25(OH)2D3 by CYP27B1. Active hormone produced in the enterocyte in this manner can regulate the expression of CYP3A4 and other VDR target genes, including the calcium transport proteins TRPV6 and calbindin D9k. We will test this hypothesis by identifying and characterizing the hepatic transporters involved in the biliary excretion of vitamin D conjugates in humans and testing whether or not these conjugates can affect the expression and function of VDR target genes in cultured human enterocytes. Because CYP3A4 can catalyze the oxidative metabolism of 1,25(OH)2D3, we also propose that activation of hPXR in the small intestine by known receptor agonists enhances intestinal 1,25(OH)2D3 clearance, resulting in a decrease in the formation of calcium transporters, and a potential change in systemic indices of calcium homeostasis. We will test this hypothesis with the use of cultured human hepatocytes, enterocytes and primary tubular epithelial cells, a novel microfluidic, 3-dimensional model of the human intestinal mucosa and the conduct of an in vivo CYP3A4 interaction study in healthy volunteers. Elucidating the molecular basis of inter-individual differences in CYP3A-dependent drug metabolism could enhance the ability of the drug industry to develop safe and efficacious drugs through a clearer understanding of how other medications, the environment, and disease states might impinge on the disposition of new drug candidates that are intestinal CYP3A substrates. In addition, if our hypothesis about the participation of CYP3A4 in negative feedback control of 1,25(OH)2D3 genomic effects within the small intestine proves correct, it could point to relatively simple ways (e.g., grapefruit juice consumption) to prevent the adverse effects of potent hPXR agonists on bone health in "at-risk" patients.

Public Health Relevance

Completion of the specific aims proposed in this grant application should improve our understanding of the molecular basis for inter-individual differences in CYP3A4-dependent drug metabolism and potentially enhance the safety and efficacy of existing and new drugs used to treat disease. Moreover, it may provide a scientific basis for the effective prevention of some adverse drug effects that lead to osteoporosis.

Agency
National Institute of Health (NIH)
Type
Research Project (R01)
Project #
2R01GM063666-09
Application #
8757851
Study Section
Xenobiotic and Nutrient Disposition and Action Study Section (XNDA)
Program Officer
Okita, Richard T
Project Start
Project End
Budget Start
Budget End
Support Year
9
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Washington
Department
Pharmacology
Type
Schools of Pharmacy
DUNS #
City
Seattle
State
WA
Country
United States
Zip Code
98195
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Wang, Zhican; Schuetz, Erin G; Xu, Yang et al. (2013) Interplay between vitamin D and the drug metabolizing enzyme CYP3A4. J Steroid Biochem Mol Biol 136:54-8
Wang, Zhican; Lin, Yvonne S; Dickmann, Leslie J et al. (2013) Enhancement of hepatic 4-hydroxylation of 25-hydroxyvitamin D3 through CYP3A4 induction in vitro and in vivo: implications for drug-induced osteomalacia. J Bone Miner Res 28:1101-16
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Isoherranen, Nina; Ludington, Shana R; Givens, Raymond C et al. (2008) The influence of CYP3A5 expression on the extent of hepatic CYP3A inhibition is substrate-dependent: an in vitro-in vivo evaluation. Drug Metab Dispos 36:146-54
Hashizume, Takanori; Xu, Yang; Mohutsky, Michael A et al. (2008) Identification of human UDP-glucuronosyltransferases catalyzing hepatic 1alpha,25-dihydroxyvitamin D3 conjugation. Biochem Pharmacol 75:1240-50

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