Published papers

The retinal capillary endothelial cells are connected to each other by tight junctions that play a key role in permeability as the inner blood-retinal barrier (inner BRB). Thus, understanding the inner BRB transport mechanism is an important step towards drug targeting of the retina. Nevertheless, inner BRB transport studies have been very limited in number since it is not easy to use the retinal capillaries, which are very small in size, for in vitro transport studies. Conditionally immortalized rat retinal capillary endothelial cells (TR-iBRB), pericytes (TR-rPCT) and Müller cell lines (TR-MUL) have been established from transgenic rats harboring the temperature-sensitive simian virus 40 large T-antigen gene. These cell lines posses respective cell type markers and maintain certain in vivo functions. Using a combination of newly developed cell lines and in vivo studies, we have elucidated the mechanism whereby vitamin C, L-cystine, and creatine are supplied to the retina. TR-iBRB cells are also able to identify transporters and apply to study regulation of transporters under pathophysiological conditions. Furthermore, these cell lines permit the investigation of cell-to-cell interactions and the expression of inner BRB-specific genes between TR-iBRB and other cell lines. © 2005 Pharmaceutical Society of Japan.

The purpose of this study was to quantify gene expression levels of the ATP-binding cassette (ABC) transporter A and C subfamilies ABCA1-A9, and ABCC1-6/Mrp1-6, C10/Mrp7 in mouse retinal vascular endothelial cells (RVEC) using a combination of a magnetic isolation method for mouse RVEC and real-time quantitative PCR analysis. The transcript level of endothelial cell markers, such as CD31, Tie-2, claudin-5, occludin, ABCB1a/mdr1a, and ABCG2, were more than 20-fold higher than those in the non-RVEC fraction, suggesting that RVEC in the RVEC fraction are concentrated at least 20-fold compared with those of the non-RVEC fraction. In the ABCA1 to A9 families, the transcript level of ABCA3 and A9 in the RVEC fraction was 1.2- and 32-fold higher than that in the non-RVEC fraction. Although ABCA3 was expressed in both the RVEC and non-RVEC fractions, A9 is predominantly expressed in the RVEC fraction. In the ABCC1 to C6 and C10 families, the transcript level of ABCC3, C4, and C6 in the RVEC fraction was 27-, 251-, and 242-fold higher, respectively, than that in the non-RVEC fraction, suggesting that ABCC3, C4, and C6 are predominantly expressed in the RVEC. In conclusion, ABCA3, ABCA9, ABCC3, ABCC4, and ABCC6 mRNAs are predominantly expressed at the inner blood-retina barrier (inner BRB) and appear to play a major role in the efflux transport of their substrates at the inner BRB. © 2007 Elsevier Inc. All rights reserved.

Administration of antiviral drugs to pregnant women with influenza, human immunodeficiency virus (HIV), and herpes simplex virus (HSV) infections is widely accepted as an effective treatment to safeguard the health of the mother and fetus. This review deals with the transfer of antiviral drugs to the fetus across the placental barrier, which is formed by an epithelial layer of syncytiotrophoblasts. First, the structure, function, and developmental change of the placenta and the placental barrier are briefly presented. We then review the transplacental permeability of antiviral drugs, such as oseltamivir for influenza, antiretrovirals (e.g., zidovudine, didanosine, and saquinavir) for HIV, and acyclovir for HSV, focusing on the involvement of ATP-binding cassette, organic anion/cation, and nucleoside transporters. The increasing evidence that is becoming available about transport mechanisms operating at the placental barrier is expected to be useful in the development of techniques to control fetal and placental transfer of antiviral drugs, and thereby to obtain maximum therapeutic benefit while minimizing potential fetal toxicity. © 2011 Wiley-Liss, Inc. and the American Pharmacists Association.

Introduction: There is an increasing need for managing rapidly progressing retinal diseases because of the potential loss of vision. Although systemic drug administration is one possible route for treating retinal diseases, retinal transfer of therapeutic drugs from the circulating blood is strictly regulated by the bloodretinal barrier (BRB). Areas covered: This review discusses the constraints and challenges of drug delivery to the retina. In addition, this article discusses the properties of drugs and the conditions of the BRB that affect drug permeability. The reader will gain insights into the strategies for developing therapeutic drugs that are able to cross the BRB for treating retinal diseases. Further, the reader will gain insights into the role of BRB physiology including barrier functions, and the effect of influx and efflux transporters on retinal drug delivery. Expert opinion: When designing and selecting optimal drug candidates, it's important to consider the fact that they should be recognized by influx transporters and that efflux transporters at the BRB should be avoided. Although lipophilic cationic drugs are known to be transported to the brain across the bloodbrain barrier, verapamil transport to the retina is substantially higher than to the brain. Therefore, lipophilic cationic drugs do have a great ability to increase influx transport across the BRB. © 2011 Informa UK, Ltd.

Substrate-induced upregulation of ATP-binding cassette subfamily G member 2 (ABCG2) has been well studied in cancer cells, but it is also important to understand whether ABCG2 is upregulated by its substrates in tissues in which it is constitutively expressed. In the present study, we aimed to clarify the regulatory mechanism of Abcg2 expression by its substrate, mitoxantrone, in placental cells. Abcg2 mRNA expression in rat placental TR-TBT 18d-1 cells treated with 10μM mitoxantrone for 24h was increased, compared with that in nontreated cells, whereas 10μM pheophorbide-a had no effect. Methylated CpG level in the promoter region of the Abcg2 gene was low and was not altered by mitoxantrone. On the contrary, mitoxantrone markedly increased the expression of estrogen receptor (ER) α and progesterone receptor (PR) B. Fulvestrant, an ER antagonist, attenuated the mitoxantrone-induced increase of Abcg2 mRNA expression, whereas mifepristone, a PR antagonist, had little effect. 17β-estradiol, an ER ligand, positively regulated the mitoxantrone-induced increase of Abcg2 expression. DNA demethylation by 5-aza-2-deoxycytidine treatment increased ERα expression, but mitoxantrone failed to facilitate the demethylation of ERα promoter in TR-TBT 18d-1 cells. In conclusion, Abcg2 expression is induced by mitoxantrone via the induction of ERα in TR-TBT 18d-1 cells. © 2013 Wiley Periodicals, Inc.

Patients benefit from drug therapy not only through pharmacological mechanisms, but also through non-pharmacological action (placebo effect), which may be mediated in part by the prefrontal area of the brain. We consider that the difference between responders and non-responders to placebo might be related to polymorphisms in the serotonin transporter-linked polymorphic region (5-HTTLPR). To study this idea, we performed a randomized double-blind clinical trial using caffeine and lactose (placebo). Activity in the prefrontal area of the brain was measured in terms of blood flow by means of near-infrared spectroscopy (NIRS) as an objective indicator. Self-reported feelings of drowsiness on established scales were used as subjective indicators. Twenty-one subjects in block A took caffeine on the first day and placebo on the third day, and 21 in block B took placebo on the first day and placebo on the third day. After placebo administration, improvement of sleepiness was significantly enhanced, a similar extent to that after caffeine medication. Among the 42 subjects, 22 showed S/S type polymorphism in the serotonin transporter (52.4 %), 17 showed S/L type (40.5 %) and 3 showed L/L type (7.10 %). Statistical analysis of the results indicate that subjects with L/L genotype showed a significantly greater placebo response in terms of both self-reported feeling of drowsiness and blood flow in the prefrontal area of the brain associated with working memory (46 area). Our results indicate that the L/L genotype of 5-HTTLPR, which is rare in Japanese (3.2 %) but common in Americans (32.2 %), may be associated with a greater placebo effect.