Ž . European Journal of Pharmacology 395 2000 193–201 www.elsevier.nlrlocaterejphar Effect of bioflavonoids on vincristine transport across blood–brain barrier 1 Yoshiharu Mitsunaga a , Hitomi Takanaga a , Hirotami Matsuo a , Mikihiko Naito b , Takashi Tsuruo b , Hisakazu Ohtani a , Yasufumi Sawada a, ) a Graduate School of Pharmaceutical Sciences, Kyushu UniÕersity, 3-1-1 Maidashi, Higashi, Fukuoka 812-8582, Japan b Institute of Molecular and Cellular Biosciences, UniÕersity of Tokyo, Bunkyo, Tokyo 113-0032, Japan Received 28 January 2000; received in revised form 23 February 2000; accepted 29 February 2000 Abstract Several grapefruit juice bioflavonoids, including quercetin, are reported to stimulate P-glycoprotein-mediated drug efflux from cultured tumor cells. To see whether these bioflavonoids alter the permeation of vincristine across the blood–brain barrier, we conducted Ž . experiments with cultured mouse brain capillary endothelial cells MBEC4 cells in vitro and ddY mice in vivo. The steady-state uptake w 3 x of H vincristine by MBEC4 cells was decreased by 10 mM quercetin, but increased by 50 mM quercetin. Similarly, the in vivo w 3 x brain-to-plasma concentration ratio of H vincristine in ddY mice was decreased by coadministration of 0.1 mgrkg quercetin, but w 3 x increased by 1.0 mgrkg quercetin. Kaempferol had a similar biphasic effect on the in vitro uptake of H vincristine. Other aglycones Ž . w 3 x Ž tested chrysin, flavon, hesperetin, naringenin increased H vincristine uptake in the 10–50 mM range, and glycosides hesperidin, . naringin, rutin were without effect. We then addressed the mechanism of the concentration-dependent biphasic action of quercetin. w 3 x Verapamil, a P-glycoprotein inhibitor, inhibited the efflux of H vincristine from MBEC4 cells, while 10 mM quercetin significantly w 3 x stimulated it. The uptake of H vincristine by MBEC4 cells was increased by inhibitors of protein kinase C, but decreased by phorbol Ž . 12-myristate-13-acetate PMA , as well as by 10 mM quercetin. The phosphorylation level of P-glycoprotein was increased in the Ž Ž . presence of 5 mM quercetin or 100 nM PMA, but decreased by the protein kinase C inhibitor H7 1- 5-isoquinolinesulfonyl -2-methyl- . w 3 x piperazine, 30 mM . We conclude that low concentrations of quercetin indirectly activate the transport of H vincristine by enhancing the Ž . phosphorylation and hence activity of P-glycoprotein, whereas high concentrations of quercetin inhibit P-glycoprotein. Our results indicate that patients taking drugs which are P-glycoprotein substrates may need to restrict their intake of bioflavonoid-containing foods and beverages, such as grapefruit juice. q 2000 Elsevier Science B.V. All rights reserved. Keywords: P-Glycoprotein; Bioflavonoid; Blood–brain barrier; Vincristine; Protein kinase C 1. Introduction Large amounts of bioflavonoids are ingested because of their abundance and wide distribution in foods and bever- ages. Recently, it has been reported that co-administration of grapefruit juice with various drugs led to an increase in the plasma concentration of the drugs, and these drug– grapefruit juice interactions may be caused by Ž bioflavonoids Bailey et al., 1991, 1993, 1995; Benton et ) Corresponding author. Tel.: q 81-92-642-6610; fax: q 81-92-642- 6614. Ž . E-mail address: yasufumi@yakuzai.phar.kyushu-u.ac.jp Y. Sawada . 1 This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan. al., 1994; Ducharme et al., 1995; Kupferschmidt et al., . 1995 . For example, the bioavailability of dihydropyridine 2q Ž Ca channel blockers felodipine, nifedipine, nicardipine . Ž and manidipine , an immunosuppressive agent cyclo- . Ž . sporine A , a benzodiazepine narcoleptic midazolam and Ž . an antiallergic agent terfenadine was significantly in- Ž creased by the co-administration of grapefruit juice Bailey et al., 1991, 1993, 1995; Benton et al., 1994; Ducharme et . al., 1995; Kupferschmidt et al., 1995 . Among several possible mechanisms for the above interactions such as enhanced absorption, altered plasma protein binding or impaired hepatic metabolism by grapefruit juice, impaired first-pass metabolism due to the inhibition of the intestinal Ž . enzyme CYP cytochrome P 450 -3A was considered the most plausible. 0014-2999r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0014-2999 00 00180-1