ABSTRACT:This study investigated the role of a multispecific organic anion transporter, Oatp1a4/Slco1a4, in drug transport across the blood-brain barrier. In vitro transport studies using human embryonic kidney 293 cells expressing mouse Oatp1a4 identified the following compounds as ]-enkephalin was unchanged. The blood-to-brain transport of digoxin was significantly lower in Oatp1a4(؊/؊) mice than in wild-type mice only when P-gp was inhibited by N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918). Taken together, these results show that Oatp1a4 can mediate the brain-to-blood and blood-to-brain transport of its substrate drugs across the blood-brain barrier. The brain-to-plasma ratio of taurocholate, pitavastatin, and rosuvastatin was close to the capillary volume in wild-type mice, and it was not affected by Oatp1a4 dysfunction. Whether Oatp1a4 can deliver drugs from the blood to the brain remains controversial.

ABSTRACT:The role of breast cancer resistance protein (BCRP/ABCG2) in limiting the brain and testis penetration of xenobiotic compounds in the blood-brain and -testis barriers was investigated using Bcrp The brain and testis are highly protected from the invasion of xenobiotic compounds by the blood-brain barrier (BBB) and bloodtestis barrier (BTB). The BBB is formed by brain microvascular endothelial cells, whereas myoid and Sertoli cells are involved in the BTB in addition to the endothelial cells (Bart et al., 2002;Kusuhara and Sugiyama, 2005;Scherrmann, 2005). In addition to the highly developed tight junctions between adjacent cells, the BBB and BTB express multiple xenobiotic transporters characterized by broad substrate specificities. They actively extrude xenobiotic compounds into the circulating blood and, thereby, limit tissue penetration from the circulating blood. On the luminal side of the BBB, ABC transporters, such as P-glycoprotein (P-gp/MDR1/ABCB1), multidrug resistanceassociated protein 1 (MRP1/ABCC1) and -4 (MRP4/ABCC4), and breast cancer resistance protein (BCRP/ABCG2), are expressed (Schinkel, 1999;Leggas et al., 2004;Lee et al., 2005;Leslie et al., 2005;Scherrmann, 2005). Among them, P-gp is the best characterized transporter providing a barrier function for the BBB. Cumulative studies have shown that it plays a key role in limiting the penetration of a variety of drugs and toxins (Schinkel, 1999;Scherrmann, 2005). Immunohistochemical analysis has demonstrated the expression of P-gp, MRP1, and BCRP in the BTB (Bart et al., 2004;Augustine et al., 2005). In vivo studies using Mdr1a Ϫ/Ϫ or Mrp1 Ϫ/Ϫ mice have shown their roles in protecting the testis from invasion by their substrates (Wijnholds et al., 1998;Uhr et al., 2000).The present study is focused on BCRP in the BBB and BTB. BCRP is a member of the ABC G-transporter family . Cumulative in vivo studies, particularly using Bcrp Ϫ/Ϫ mice, have shown the importance of BCRP in limiting oral absorption and mediating the biliary and urinary excretion of xenobiotic compounds (Jonker et al., 2002;van Herwaarden et al., 2003;Mizuno et al., 2004;Adachi et al., 2005;Kondo et al., 2005;Ando et al., 2007). The functional role of BCRP in the BBB was first demonstrated by Breedveld et al. (2005), who showed that the brain distribution of imatinib was significantly increased in Bcrp Ϫ/Ϫ mice, although subsequent analysis showed that P-gp plays a significant role in limiting

ABSTRACT:Oseltamivir is an ethyl ester prodrug of [3R,4R,5S]-4-acetamido-5-amino-3-(1-ethylpropoxy)-1-cyclohexene-1-carboxylate phosphate (Ro 64-0802), the anti-influenza drug. Abnormal behavior has been suspected to be associated with oseltamivir medication in Japan. The purpose of the present study is to examine the involvement of transporters in the brain distribution of oseltamivir and its active form Ro 64-0802 across the blood-brain barrier (BBB). The brain-to-plasma concentration ratio (K p,brain ) of oseltamivir after i.v. infusion of oseltamivir in FVB mice was increased by pretreatment with N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918), a dual inhibitor for P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp), whereas that of Ro 64-0802 was only slightly increased. Furthermore, the distribution volume of Ro 64-0802 following i.v. administration of Ro 64-0802 in the brain was similar to the capillary volume, suggesting its minimal distribution. The K p,brain value of oseltamivir in multidrug-resistant (Mdr) 1a/1b P-gp knockout mice was 5.5-fold higher than that in wild-type mice and comparable with that obtained by pretreatment with GF120918, whereas it was unchanged in Bcrp knockout mice. The K p,brain value of oseltamivir was significantly higher in newborn rats, which is in good agreement with the ontogenetic expression profile of P-gp. Intracellular accumulation of oseltamivir was lower in human and mouse P-gp-expressing cells, which was reversed by P-gp inhibitor valspodar (PSC833). These results suggest that P-gp limits the brain uptake of oseltamivir at the BBB and that Ro 64-0802 itself barely crosses the BBB. However, it may be possible that Ro 64-0802 is formed in the brain from the oseltamivir, considering the presence of carboxylesterase in the brain endothelial cells.Oseltamivir (Fig. 1) is an ester prodrug of Ro 64-0802, a potent and selective inhibitor of neuraminidase, resulting in an inhibition of release of influenza virus from the host cells and growth of influenza virus. Oseltamivir is used in the treatment and prophylaxis of both Influenzavirus A and Influenzavirus B (Bardsley-Elliot and Noble, 1999). The number of prescribed oseltamivir has reached approximately 10 million in Japan, which accounted for 75% of the world total in 2006. Recently, abnormal behavior has been reported in influenza patients prescribed oseltamivir (http://www.fda.gov/cder/ drug/infopage/tamiflu/QA20051117.htm; Fuyuno, 2007). According to a report by the Ministry of Health, Labor, and Welfare, the number of people who behaved abnormally following oseltamivir treatment has increased to 211 (0.002% of all patients), approximately 80% of whom are teenagers or younger. The relationship between abnormal behavior and oseltamivir medication remains an open question and has not yet been elucidated. The Ministry of Health, Labor, and Welfare has published a caution for oseltamivir medication to teenagers or younger...

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ABSTRACT:Incubation of human liver microsomes with diclofenac in the presence of NADPH resulted in a decrease in testosterone 6␤-hydroxylation activity. The decrease in the activity followed time-and concentration-dependent kinetics, required oxidative metabolism, and was resistant to reduced glutathione, suggesting that diclofenac causes a mechanism-based inactivation of cytochrome P450 (P450) 3A4 (CYP3A4). The inactivation was reproduced by using microsomes from B-lymphoblastoid cell lines expressing CYP3A4 instead of human liver microsomes. No other monooxygenase activities measured as indexes of P450 enzymes; CYP2C8, CYP2C9, or CYP2C19 was inactivated by the same incubation procedure. Quinidine, a stimulant of CYP3A4-mediated diclofenac 5-hydroxylation, did not affect the inactivation of CYP3A4 assessed by testosterone 6␤-hydroxylation activity but accelerated the inactivation assessed by diazepam 3-hydroxylation activity. These results supported the idea that diclofenac 5-hydroxylation is involved in the inactivation of CYP3A4 and described for the first time a stimulation of mechanism-based inactivation attributable to CYP3A4 heterotropic cooperativity. Preincubation of human liver microsomes with 5-hydroxydiclofenac instead of diclofenac did not cause the inactivation of CYP3A4, suggesting that 5-hydroxydiclofenac is not a precursor of a postulated reactive metabolite that inactivates CYP3A4, and thus 5-hydroxylation step is critical to inactivation of CYP3A4.