Research projects

The purpose of the present study was to clarify the transporters mediating the fetal transfer of tryptophan and examine the importance of an adequate supply of tryptophan into the fetus. This study described the amount and localization of LAT1 protein, a transporter for large neutral amino acids including tryptophan, at the placental barrier. It is also observed that the tissue distribution of LAT1 substrate is suppressed by an increase of LAT1-substrate amino acids in the plasma. For serotonin, we have clarified OCTN1 protein accepts it as a substrate and is expressed at the placental barrier at term. However, the effect of tryptophan imbalance in the diet was negligible in the plasma concentration of amino acids.

Reported frequencies of oligohydramnios against 6 drugs of angiotensin II receptor antagonist (ARB) were investigated. The normalized frequency of irbesartan compared that of olmesartan was significantly low. We analyzed the pharmacological effect, placental transfer and fetal toxicity of irbesartan and olmesartan using the preeclampsia model rats. The irbesartan-administered group had the same fetal weight as the ARB-non-administered group and irbesartan had a lower fetal transfer than olmesartan. It was also shown that irbesartan was transported by OATP2B1 which is expressed in human placenta. The olmesartan-treated group had a reduced fetal weight compared to the ARB-non-treated group. In addition, no transport by OATP2B1 was observed. These findings suggest that irbesartan has a lower fetal transfer and less adverse fetal effect compared to olmesartan.

Syncytin-2, a molecule specifically expressed in the placenta, has membrane fusion capacities and contributes to the barrier formation through syncytialization. In this study, it is indicated that the uptake of JEG-3 cell-derived exosome to human hepatic HepG2 cells was significantly enhanced when the expression of syncytin-2 in JEG-3 cells was induced. The placenta-specific miRNA is detected from HepG2 cells exposed to JEG-3 cell-derived exosomes, implying that exosomal syncytin-2 is capable to mediate cell-to-cell communication through the exosome. However, the expression of MFSD2A, a receptor of syncytin-2, is found not to be constitutively expressed in the mouse liver. Therefore, it is necessary to further confirm whether syncytin-2-expressing exosome is preferably binds to hepatic cells. We also found that MFSD2A involves in the supply of docosahexaenoic acid to the fetus.

アンジオテンシンⅡ受容体拮抗薬(ARB) の胎児移行性にorganic anion transporter (OAT) 4が与える影響の評価とOAT4発現マーカーの探索を目的とし、OAT4を介した薬物輸送と胎盤特異的なOAT4の発現機構について検討した。ARBは、胎盤を透過して胎児腎に到達することでヒトに限定的な胎児毒性を示す。過去に、ARBであるolmesartanの胎盤関門胎児側基底細胞膜における輸送へのOAT4の関与について報告している。また、chlorideはOAT4を介した交換輸送の駆動力となることが提唱されることから、今回は、5種のARB (candesartan、irbesartan、losartan、telmisartan、valsartan)について、OAT4発現細胞による取り込みを、細胞外chloride非存在下で定量した。少なくともlosartan、candesartan、valsartanについては、OATを介した細胞内取り込みが示された。抗ヒスタミン薬cetirizineについてもOAT4を介した輸送方向性を解析し、OAT4がラセミ体のcetirizineのうち、levocetirizineのみを選択的に細胞内に取り込むことを示唆する結果を得た。OAT4の転写制御領域についての解析では、胎盤および腎臓由来OAT4 遺伝子の転写開始点が異なることを同定した。さらに、尿細管上皮および胎盤栄養膜モデル細胞における転写活性の比較から、胎盤におけるOAT4発現を司るプロモーター領域を明らにした。胎盤OAT4の5’隣接領域変異解析から、転写因子AP-2結合配列を含む領域が胎盤でのOAT4 基礎転写活性に必須の領域であることが示された。本研究より、ヒト胎児への薬物移行予測の発展に寄与する結果を得た。