Abstract
The presence in orange juice of compounds that specifically inhibit the P-glycoprotein (P-gp) drug efflux transporter, but not the cytochrome P450 (CYP) isozyme CYP3A4, was investigated. The uptake of [3H]vinblastine, a substrate of P-gp, by Caco-2 cells was measured. An ethyl acetate extract of orange juice did not affect the initial uptake rate of [3H]vinblastine but significantly increased the steady-state uptake, as did cyclosporin A (20 μM), an inhibitor of P-gp. No significant effect on the uptake of 3-O-[3H]methylglucose or [14C]phenylalanine by Caco-2 cells was found, compared with the control. When the extract was separated on a Cosmosil column, the eluate with 70% methanol showed the most potent ability to increase [3H]vinblastine uptake. Additional separation of the 70% methanol eluate on a silica gel column with hexane-acetone (3:1) gave 3,3′,4′,5,6,7,8-heptamethoxyflavone (HMF) and 4′,5,6,7,8-pentamethoxyflavone (tangeretin). HMF, tangeretin, and 3′,4′,5,6,7,8-hexamethoxyflavone (nobiletin), another methoxyflavone contained in orange juice, all increased the steady-state uptake of [3H]vinblastine by Caco-2 cells in a concentration-dependent manner. The order of potency of these compounds at the concentration of 50 μM was tangeretin > HMF > nobiletin. None of these methoxyflavones inhibited 6β-hydroxylation of testosterone catalyzed by CYP3A4. The ethyl acetate extract of orange juice and these methoxyflavones also increased steady-state [3H]vinblastine uptake by LLC-GA5-COL300 cells (a cell line transfected with human MDR1 cDNA). We conclude that these methoxyflavones enhanced vinblastine uptake by specifically inhibiting drug efflux via P-gp. They may have potential as agents for reversing multidrug resistance or for recovering the bioavailability of certain drugs.
Footnotes
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Send reprint requests to: Yasufumi Sawada, Ph.D., Professor, Department of Pharmaceutics, Graduate School of Pharmaceutical Sciences, Kyushu University, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-8582, Japan. E-mail:yasufumi{at}yakuzai.phar.kyushu-u.ac.jp
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↵1 This work was supported in part by a grant from the Urakami Foundation, Asahi Breweries Foundation, the SKYLARK Food Science Institute, and grants-in-aid for scientific research from the Ministry of Education, Science, Sports, and Culture, Japan.
- Abbreviations:
- GFJ
- grapefruit juice
- CYP
- cytochrome P450
- DHBG
- 5-[(6,7-dihydroxy-6-keto-2-octenyl)oxy]psoralen
- HBBS
- Hanks' balanced salt solution
- HMF
- 3,3′,4′,5,6,7,8-heptamethoxyflavone
- LDH
- lactate dehydrogenase
- nobiletin
- 3′,4′,5,6,7,8-hexamethoxyflavone
- P-gp
- P-glycoprotein
- tangeretin
- 4′,5,6,7,8-pentamethoxyflavone
- MES
- 4-morpholineethanesulfonic acid
- Received April 20, 1999.
- Accepted December 3, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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