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FacultyDepartment of Pharmacy
PositionAssistant Professor
Commentator Guide
Last Updated :2020/09/30

Research Activities

Research Areas

  • Life sciences, Clinical pharmacy

Published Papers

  • Inhibitory Effect of Ocimum gratissimum Leaf Extract on Postprandial Increase of Blood Glucose, Shimada, Hiroaki, Kuma, Chiaki, Iseri, Taichi, Matsumura, Shin-ichi, Kawase, Atsushi, Matsuura, Masayoshi, Iwaki, Masahiro, NATURAL PRODUCT COMMUNICATIONS, NATURAL PRODUCT COMMUNICATIONS, 14(10), Oct. 2019 , Refereed
    Summary:The tea of Ocimum gratissimum (OG) leaves has been commonly consumed by people living in Ishigaki Island, Okinawa prefecture, Japan, and is considered to be effective for improving diabetes mellitus. In this study, we aimed to clarify the inhibitory potential of OG leaves extract (OG-ext) on gastrointestinal glucose absorption and to provide theoretical evidence for the anti-hyperglycemic effect of OG-ext. The increase of blood glucose after oral administration of alpha-starch and glucose in mice was suppressed by co-administration of OG-ext. An in vitro enzymatic assay suggested that amylase and maltase were inhibited weakly by the addition of OG-ext. In Caco-2 cells, a human intestinal epithelial model, the sodium-dependent glucose transporter (SGLT) 1-mediated uptake of fluorescence glucose analog was inhibited significantly by the addition of OG-ext in a concentration-dependent manner. These results indicate that the inhibitory effect on SGLT1 is one of the mechanisms of the anti-hyperglycemic effect of the tea of OG leaves.
  • Involvement of diclofenac acyl-β-D-glucuronide in diclofenac-induced cytotoxicity in glutathione-depleted isolated murine hepatocytes co-cultured with peritoneal macrophages., Kawase A, Kaneto A, Ishibashi M, Kobayashi A, Shimada H, Iwaki M, Toxicology mechanisms and methods, Toxicology mechanisms and methods, 1 - 30, Nov. 2018 , Refereed
  • Major constituents of Cistanche tubulosa, echinacoside and acteoside, inhibit sodium-dependent glucose cotransporter 1-mediated glucose uptake by intestinal epithelial cells, Shimada, Hiroaki, Urabe, Yuichi, Okamoto, Yuhei, Li, Zheng, Kawase, Atsushi, Morikawa, Toshio, Tu, Pengfei, Muraoka, Osamu, Iwaki, Masahiro, JOURNAL OF FUNCTIONAL FOODS, JOURNAL OF FUNCTIONAL FOODS, 39, 91 - 95, Dec. 2017 , Refereed
    Summary:Echinacoside (ECH) and acteoside (ACT), the major constituents of Cistanche tubulosa, suppress the increase in postprandial blood glucose level. Although ECH and ACT have been reported to weakly inhibit alpha-glucosidases, the underlying mechanism remains unclear. Therefore, we focused on the regulatory mechanism of dietary glucose absorption: In this study, we aimed to clarify the inhibitory effects of ECH and ACT on sodium-dependent glucose cotransporter (SGLT) 1-mediated gastrointestinal glucose absorption. Uptake experiments were performed using human intestinal Caco-2 cells and the fluorescence glucose analogue, 2-deoxy-2-[(7-nitro-2,1,3benzoxadiazol-4-yDaminc]-n-glucose (2-NBDG). Sodium-dependent 2-NBDG uptake was successfully estimated and this uptake was completely inhibited by an SGLT inhibitor phlorizin. ECH and ACT inhibited sodium-dependent 2-NBDG uptake in a concentration-dependent manner. However, this inhibition was not observed under sodium-free condition. This study suggested that the inhibitory effects of ECH and ACT on SGLT1-mediated glucose uptake contribute to suppression of increased postprandial blood glucose level.
  • Contribution of Prostaglandin Transporter OATP2A1/SLCO2A1 to Placenta-to-Maternal Hormone Signaling and Labor Induction., Mai Inagaki, Tomohiro Nishimura, Takeo Nakanishi, Hiroaki Shimada, Saki Noguchi, Shin-Ichi Akanuma, Masanori Tachikawa, Ken-Ichi Hosoya, Ikumi Tamai, Emi Nakashima, Masatoshi Tomi, iScience, iScience, 23(5), 101098 - 101098, May 22 2020 , Refereed
    Summary:We evaluated the contribution of organic anion transporting polypeptide 2A1 (OATP2A1/SLCO2A1), a high-affinity carrier for prostaglandins (PGs), to the parturition process. At gestational day (GD) 15.5, OATP2A1 is co-localized with 15-hydroxy-PG dehydrogenase in the mouse placental junctional zone and facilitates PG degradation by delivering PGs to the cytoplasm. Slco2a1 (+/-) females mated with Slco2a1 (-/-) males frequently showed elevated circulating progesterone at GD18.5 and delayed parturition. Progesterone receptor inhibition by RU486 treatment at GD18.5 blocked the delay of parturition. In the junctional zone, PGE2 stimulated placental lactogen II (PL-II) production, resulting in higher expression of PL-II in Slco2a1 (-/-) placenta at GD18.5. Indomethacin treatment at GD15.5 suppressed the PL-II overproduction at GD18.5 in Slco2a1 (-/-) embryo-bearing dams, which promoted progesterone withdrawal and corrected the delayed parturition. These results suggest that extracellular PGE2 reduction by OATP2A1 at mid-pregnancy would be associated with progesterone withdrawal by suppressing PL-II production, triggering parturition onset.
  • The regulatory mechanism involved in the prostaglandin E2 disposition in carbon tetrachloride-induced liver injury., Hiroaki Shimada, Ryota Hashimoto, Aya Aoki, Saya Yamada, Ken-Ichi Oba, Atsushi Kawase, Takeo Nakanishi, Masahiro Iwaki, Prostaglandins, leukotrienes, and essential fatty acids, Prostaglandins, leukotrienes, and essential fatty acids, 155, 102081 - 102081, Apr. 2020 , Refereed
    Summary:Prostaglandin E2 (PGE2) exhibits hepatoprotective effects against various types of liver injury. However, there is little information on the disposition of endogenous PGE2 during liver injury. In the present study, we attempted to elucidate the mechanism involved in regulating PGE2 distribution during liver injury. Carbon tetrachloride (CCl4) was used to establish a liver injury mouse model. PGE2 was measured by LC-MS/MS. The plasma and hepatic PGE2 levels were significantly increased at 6 to 48 h after CCl4 treatment. The ratio of plasma levels of 13,14-dihydro-15-ketoPGE2 (PGEM), a major PGE2 metabolite, to PGE2 decreased significantly after CCl4 treatment. PGE2 synthesis and expression of enzymes related to PGE2 production were not induced, while the activity and mRNA expression of 15-prostaglandin dehydrogenase (15-PGDH/Hpgd), a major enzyme for PGE2 inactivation, decreased significantly in the liver of CCl4-treated mice compared to that of vehicle-treated control. The plasma and hepatic PGE2 levels were negatively correlated with the hepatic mRNA expression levels of Hpgd. Although the mRNA expression of organic anion transporting polypeptide 2A1 (OATP2A1/Slco2a1), a major PGE2 transporter, was upregulated, other hepatic OATPs decreased significantly at 24 h after CCl4 treatment. Immunohistochemical analysis indicated that 15-PGDH was mainly expressed in endothelial cells and that OATP2A1 was expressed at least in endothelial cells and Kupffer cells in the liver. These results suggest that the decreased 15-PGDH expression in hepatic endothelial cells is the principal mechanism for the increase in hepatic and plasma PGE2 levels due to the CCl4-induced liver injury.
  • Changes in Radixin Expression and Interaction with Efflux Transporters in the Liver of Adjuvant-Induced Arthritic Rats., Atsushi Kawase, Misaki Nakasaka, Hatsune Bando, Saori Yasuda, Hiroaki Shimada, Masahiro Iwaki, Inflammation, Inflammation, 43(1), 85 - 94, Feb. 2020 , Refereed
    Summary:Scaffold proteins such as radixin help to modulate the plasma membrane localization and transport activity of the multidrug resistance-associated protein 2 (MRP2/ABCC2) and P-glycoprotein (P-gp/ABCB1) efflux transporters in the liver. We examined changes in radixin expression and interaction with efflux transporters in adjuvant-induced arthritic (AA) rats, an animal model of rheumatoid arthritis, as well as in human liver cancer (HepG2) cells because inflammation affects drug pharmacokinetics via the efflux transporters. The expression levels of radixin and phosphorylated radixin (p-radixin) were measured 24 h after treatment with inflammatory cytokines comprising tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6 or sodium nitroprusside (SNP; a nitric oxide donor). The protein levels of radixin, MRP2, and P-gp in the rat liver were next examined. We also investigated whether inflammation affected the formation of complexes between radixin and MRP2 or P-gp. The mRNA and protein levels of radixin in HepG2 cells were significantly decreased by TNF-α treatment, while minimal changes were observed after treatment with IL-1β, IL-6 or SNP. TNF-α also significantly decreased the protein levels of p-radixin, suggesting that TNF-α inhibited the activation of radixin and thereby reduced the activity of the efflux transporters. Complex formation of radixin with MRP2 and P-gp was significantly decreased in AA rats but this was reversed by prednisolone and dexamethasone treatment, indicating that decreased interactions of radixin with MRP2 and P-gp likely occur during liver inflammation. These data suggest that liver inflammation reduces radixin function by decreasing its interactions with MRP2 and P-gp.
  • Decrease in Multidrug Resistance-associated Protein 2 Activities by Knockdown of Phosphatidylinositol 4-phosphate 5-kinase in Hepatocytes and Cancer Cells., Atsushi Kawase, Yuta Inoue, Miho Hirosoko, Yuka Sugihara, Hiroaki Shimada, Masahiro Iwaki, Journal of pharmacy & pharmaceutical sciences : a publication of the Canadian Society for Pharmaceutical Sciences, Societe canadienne des sciences pharmaceutiques, Journal of pharmacy & pharmaceutical sciences : a publication of the Canadian Society for Pharmaceutical Sciences, Societe canadienne des sciences pharmaceutiques, 22(1), 576 - 584, 2019 , Refereed
    Summary:PURPOSE: The plasma membrane localization and transport activity of multidrug resistance- associated protein 2 (MRP2/ABCC2) and P-glycoprotein (P-gp/ABCB1) efflux transporters are governed by transporter-associated proteins. Phosphatidylinositol 4,5-bisphosphate (PIP2) formed by phosphatidylinositol 4-phosphate 5-kinase type 1 (PIP5K1) activates the linker function of radixin for efflux transporters. Radixin is involved in the plasma membrane localization of efflux transporters. We examined whether PIP5K1 could be a target for the modulation of transporter activities in hepatocytes and cancer cells. METHODS: The effects of PIP5K1 depletion by siRNA in mouse primary hepatocytes, PANC1 human pancreatic carcinoma cells, and HepG2 human hepatocellular carcinoma cells on the intracellular accumulation of MRP2 and P-gp substrates were examined. RESULTS: PIP5K1A depletion resulted in increased intracellular accumulation of carboxydichlorofluorescein, a MRP2 fluorescent substrate, in mouse primary hepatocytes, PANC1 cells, and HepG2 cells. In PANC1 and HepG2 cells, the transport activities of MRP2 were significantly decreased by PIP5K1C depletion. However, the transport activities of P-gp were unchanged by PIP5K1 depletion. PIP2 levels were unchanged between control and PIP5K1A- or PIP5K1C-depleted HepG2 cells. MRP2 mRNA levels showed few changes in HepG2 cells following PIP5K1A or PIP5K1C depletion. The expression of phosphorylated radixin was decreased by PIP5K1A and PIP5K1C depletion, although total radixin levels were unchanged. CONCLUSIONS: These data suggest that PIP5K1A and PIP5K1C could be target proteins for modulating MRP2 function, partly because of the resulting changes of the linker function of radixin.
  • Changes in transporters and metabolizing enzymes in the livers of rats with bile duct ligation., Atsushi Kawase, Akira Kazaoka, Rei Yamamoto, Risa Minakata, Hiroaki Shimada, Masahiro Iwaki, Journal of pharmacy & pharmaceutical sciences : a publication of the Canadian Society for Pharmaceutical Sciences, Societe canadienne des sciences pharmaceutiques, Journal of pharmacy & pharmaceutical sciences : a publication of the Canadian Society for Pharmaceutical Sciences, Societe canadienne des sciences pharmaceutiques, 22(1), 457 - 465, 2019 , Refereed
    Summary:PURPOSE: Bile duct ligation (BDL) in experimental animals is widely used as an animal model of liver cholestasis and fibrosis. The transcriptional process and plasma membrane localization of transporters are regulated by nuclear receptors and scaffold proteins, respectively. However, the detailed changes of these factors in the livers of BDL rats remain unclear. To clarify the effects of BDL on the levels of transporters and metabolizing enzymes, nuclear receptors, and scaffold proteins, we investigated changes in mRNA and protein levels of livers from BDL rats. METHODS: Membrane proteins and microsomes were prepared from rats with BDL. The mRNA levels of transporters and nuclear receptors in livers of control and BDL rats were examined by real-time reverse transcription polymerase chain reaction. The protein levels of transporters, metabolizing enzymes and scaffold proteins in membrane proteins and microsomes were determined by liquid chromatography-tandem mass spectrometry-based targeted proteomics. RESULTS: Mdr1a mRNA was significantly decreased at 1 and 2 weeks of BDL. The mRNA levels of MRP2 were significantly decreased. The mRNA levels of nuclear receptors were significantly decreased in livers of 1-week BDL rats. The protein levels of P-gp were significantly increased by BDL. Regarding scaffold proteins, the protein levels of ezrin, moesin and EBP50 were significantly decreased at 2 weeks of BDL. The protein levels of radixin were significantly increased at 1 week of BDL. In 1-week BDL rats, the protein levels of metabolizing enzymes such as CYP and UGT were significantly decreased. CONCLUSIONS: This study reports the comprehensive changes of transporters, metabolizing enzymes, nuclear receptors, and ezrin/radixin/moesin proteins in the livers of BDL rats. The expression levels of nuclear receptors and radixin that regulate the transcription and localization of CYP and/or transporters were decreased by BDL.
  • Prostaglandin Transporter OATP2A1/SLCO2A1 Is Essential for Body Temperature Regulation during Fever., Yoshinobu Nakamura, Takeo Nakanishi, Hiroaki Shimada, Junya Shimizu, Rika Aotani, Shio Maruyama, Kei Higuchi, Takashi Okura, Yoshiharu Deguchi, Ikumi Tamai, The Journal of neuroscience : the official journal of the Society for Neuroscience, The Journal of neuroscience : the official journal of the Society for Neuroscience, 38(24), 5584 - 5595, Jun. 13 2018 , Refereed
    Summary:Prostaglandin E2 (PGE2) in the hypothalamus is a principal mediator of the febrile response. However, the role of organic anion transporting polypeptide 2A1 (OATP2A1/SLCO2A1), a prostaglandin transporter, in facilitating this response is unknown. Here, we investigated the effect of Slco2a1 deficiency on the body core temperature (Tc) and on the PGE2 concentration in hypothalamus interstitial fluid (Cisf) and CSF (Ccsf) of lipopolysaccharide (LPS; 100 μg/kg, i.p.)-treated mice of both sexes. Slco2a1-/- mice did not develop a febrile response. Ccsf was increased in Slco2a1+/+ and Slco2a1-/- mice, and Ccsf of Slco2a1-/- mice was well maintained at 5 h after LPS injection (1160 pg/ml) compared with Slco2a1+/+ mice (316 pg/ml). A microdialysis study revealed that Cisf peaked at 2 h after LPS injection in Slco2a1+/+ mice (841 pg/ml), whereas the increase in Cisf was negligible in Slco2a1-/- mice. The PGE2 plasma concentration in Slco2a1-/- mice (201 pg/ml) was significantly higher than that in Slco2a1+/+ mice (54 pg/ml) at 1 h after LPS injection, whereas the two groups showed similar PGE2 concentrations in the hypothalamus. Strong Oatp2a1 immunoreactivity was observed in F4/80-positive microglia and perivascular cells and in brain capillary endothelial cells. The changes in Tc and Cisf seen in LPS-injected Slco2a1+/+ mice were partially attenuated in monocyte-/macrophage-specific Slco2a1-/- (Slco2a1Fl/Fl/LysMCre/+) mice. Thus, OATP2A1 facilitates the LPS-induced febrile response by maintaining a high level of Cisf, possibly by regulating PGE2 secretion from F4/80-positive glial cells and/or facilitating PGE2 transport across the blood-brain barrier. These findings suggest that OATP2A1 is a useful therapeutic target for neuroinflammation.SIGNIFICANCE STATEMENT Fever is a physiological response caused by pyrogen-induced release of prostaglandin E2 (PGE2) in the hypothalamus, which plays a central role in regulating the set-point of body temperature. However, it is unclear whether the prostaglandin transporter OATP2A1/SLCO2A1 is involved in this response. We show here that LPS-induced fever is associated with increased PGE2 concentration in hypothalamus interstitial fluid (Cisf), but not in CSF (Ccsf), by means of a microdialysis study in global Slco2a1-knock-out mice and monocyte-/macrophage-specific Slco2a1-knock-out mice. The results suggest that OATP2A1 serves as a regulator of Cisf in F4/80-positive glial cells. OATP2A1 was detected immunohistochemically in brain capillary endothelial cells and, therefore, may also play a role in PGE2 transport across the blood-brain barrier.
  • Correlation between glucuronidation and covalent adducts formation with proteins of nonsteroidal anti-inflammatory drugs, Hiroaki Shimada, Yuri Kobayashi, Sakiko Tanahashi, Atsushi Kawase, Taro Ogiso, Masahiro Iwaki, European Journal of Pharmaceutical Sciences, European Journal of Pharmaceutical Sciences, 112, 132 - 138, Jan. 15 2018 , Refereed
    Summary:Nonsteroidal anti-inflammatory drugs (NSAIDs) can cause idiosyncratic liver injury. Mechanisms involved in NSAID-induced liver injury are complex. Previous studies have suggested that acyl glucuronide of NSAIDs (NSAIDs-Glu) plays an important role in the development of liver injury via covalently binds to proteins and the resultant adduct induces immunological toxicity. As only some NSAIDs-Glu are commercially available, the evaluation of covalent protein adduct formation using ready-made NSAIDs-Glu is difficult and inconvenient. Moreover, glucuronidation potency varies with the NSAID, including stereoisomers. Therefore, in this study, we simultaneously examined the glucuronidation and covalent adduct formation using enantiomers of parent NSAIDs (ibuprofen, naproxen, pranoprofen, ketoprofen, and flurbiprofen) in rat liver microsomes. Glucuronides and covalent adducts were quantified by HPLC. The amount of covalent adduct increased with NSAIDs-Glu formation in the rat liver microsomes in a time-dependent manner. A significant positive correlation was observed between the AUC of NSAIDs-Glu and that of covalent adduct, except ketoprofen. Although ketoprofen exhibited the highest glucuronidation rate among the NSAIDs investigated, the amount of covalent adduct was similar to that for pranoprofen, which had the lowest glucuronidation rate. Thus, it may be difficult for ketoprofen glucuronide to covalently bind with proteins in the rat liver microsomes. Our results suggested that the amount of glucuronide formed is a key factor in predicting covalent bond formation with protein in NSAIDs, in addition to degradability and bindability with proteins of NSAIDs-Glu. Further studies are required to confirm the relationship between the tendency of glucuronidation and the formation of covalent adducts of NSAIDs.
  • A novel role for OATP2A1/SLCO2A1 in a murine model of colon cancer, Takeo Nakanishi, Yasuhiro Ohno, Rika Aotani, Shio Maruyama, Hiroaki Shimada, Shunsuke Kamo, Hiroko Oshima, Masanobu Oshima, John D. Schuetz, Ikumi Tamai, SCIENTIFIC REPORTS, SCIENTIFIC REPORTS, 7(1), 16567, Nov. 2017 , Refereed
    Summary:Prostaglandin E-2 (PGE(2)) is associated with proliferation and angiogenesis in colorectal tumours. The role of prostaglandin transporter OATP2A1/SLCO2A1 in colon cancer tumorogenesis is unknown. We evaluated mice of various Slco2a1 genotypes in a murine model of colon cancer, the adenomatous polyposis (APC) mutant (Apc(Delta 716/+)) model. Median lifespan was significantly extended from 19 weeks in Slco2a1(+/+)/Apc(Delta 716/+) mice to 25 weeks in Slco2a1(-/-)/Apc(Delta 716/+) mice. Survival was directly related to a reduction in the number of large polyps in the Slco2a1(-/-)/Apc(Delta 716/+) compared to the Slco2a1(+/+)/Apc(Delta 716/+) or Slco2a1(+/-)/Apc(Delta 716/+) mice. The large polyps from the Slco2a1(-/-)/Apc(Delta 716/+) mice had significant reductions in microvascular density, consistent with the high expression of Slco2a1 in the tumour-associated vascular endothelial cells. Chemical suppression of OATP2A1 function significantly reduced tube formation and wound-healing activity of PGE2 in human vascular endothelial cells (HUVECs) although the amount of extracellular PGE2 was not affected by an OATP2A1 inhibitor. Further an in vivo model of angiogenesis, showed a significant reduction of haemoglobin content (54.2%) in sponges implanted into Slco2a1(-/-), compared to wildtype mice. These studies indicate that OATP2A1 is likely to promote tumorogenesis by PGE2 uptake into the endothelial cells, suggesting that blockade of OATP2A1 is an additional pharmacologic strategy to improve colon cancer outcomes.
  • Inhibition of Methotrexate Uptake via Organic Anion Transporters OAT1 and OAT3 by Glucuronides of Nonsteroidal Anti-inflammatory Drugs, Masahiro Iwaki, Hiroaki Shimada, Yuri Irino, Manami Take, Sachiko Egashira, BIOLOGICAL & PHARMACEUTICAL BULLETIN, BIOLOGICAL & PHARMACEUTICAL BULLETIN, 40(6), 926 - 931, Jun. 2017 , Refereed
    Summary:Combination therapy of non-steroidal anti-inflammatory drugs (NSAIDs) and methotrexate (MTX) sometimes triggers adverse effects, such as liver injury, renal failure, gastrointestinal disorders, and myelosuppression, owing to the reduction of MTX clearance. Previous reports have suggested that NSAIDs inhibit renal MTX uptake via organic anion transporters (OATs) and reduced folate transporter (RFC)-1 and efflux via multidrug resistance-associated proteins (MRPs). Recently, our laboratory found inhibitory effects of NSAIDs-glucuronide (NSAIDs-Glu), a major metabolite of NSAIDs, on MRP-mediated MTX transport as a new site of interaction between MTX and NSAIDs. However, it remains unclear that whether NSAIDs-Glu inhibit renal uptake of MTX. Therefore, the present study aimed to evaluate inhibitory effects of several NSAIDs-Glu (diclofenac, R- and S-ibuprofen, R- and S-flurbiprofen, and R- and S-naproxen) on human OAT1 and OAT3-mediated MTX transport. In this study, [H-3]MTX uptake was observed by using human OAT1 and OAT3-overexpressing HEK293 cells in the presence or absence of NSAIDs-Glu. All examined NSAIDs-Glu exhibited concentration-dependent inhibitory effects on MTX uptake via OAT1 and OAT3. Our results indicated that NSAIDs-Glu are more potent (5- to 15-fold) inhibitors of OAT3 than OAT1. Moreover, stereoselective inhibitory effects of NSAIDs-Glu on OATs-mediated MTX uptake were not observed, unlike on MRPs-mediated transport. These findings suggest that inhibition of OAT1 and OAT3-mediated renal uptake of MTX by plasma NSAIDs-Glu may be one of the competitive sites underlying complex drug interaction between MTX and NSAIDs.
  • Involvement of Reactive Metabolites of Diclofenac in Cytotoxicity in Sandwich-Cultured Rat Hepatocytes, Atsushi Kawase, Ryota Hashimoto, Mai Shibata, Hiroaki Shimada, Masahiro Iwaki, INTERNATIONAL JOURNAL OF TOXICOLOGY, INTERNATIONAL JOURNAL OF TOXICOLOGY, 36(3), 260 - 267, May 2017 , Refereed
    Summary:Background and Objectives: Diclofenac (DIC) is metabolized to reactive metabolites such as diclofenac acyl--d-glucuronide (DIC-AG). It is possible that such reactive metabolites could cause tissue damage by formation of covalent protein adducts and other modification of cellular proteins or by induction of immune responses against its covalent protein adducts. However, the detailed mechanisms of idiosyncratic drug-induced liver injury (DILI) have been unclear. The objective is to clarify the involvement of DIC-AG and 4hydroxydiclofenac (4OH-DIC) in acute DILI.Methods:We examined the effects of inhibiting DIC-AG and 4OH-DIC production on covalent protein adduct formation and lactate dehydrogenase leakage using sandwich-cultured rat hepatocytes (SCRHs).Results:After pretreatment of SCRH with (-)-borneol (BOR, a uridine diphosphate (UDP)-glucuronosyltransferase inhibitor) or sulfaphenazole (SUL, a cytochrome P450 2C9 inhibitor) for 30 minutes, intracellular concentrations of DIC, DIC-AG, and 4OH-DIC were determined after further treating cells with 300 M DIC for 3 hours. The decreased levels of reactive metabolites caused by BOR or SUL pretreatment resulted in decreased lactate dehydrogenase leakage from SCRH, although the formation of covalent protein adducts was not affected.Conclusion:These results suggested that both DIC-AG and 4OH-DIC may be involved in acute cytotoxicity by DIC.
  • Role of OATP2A1 in PGE(2) secretion from human colorectal cancer cells via exocytosis in response to oxidative stress, Taku Kasai, Takeo Nakanishi, Yasuhiro Ohno, Hiroaki Shimada, Yoshinobu Nakamura, Hiroshi Arakawa, Ikumi Tamai, EXPERIMENTAL CELL RESEARCH, EXPERIMENTAL CELL RESEARCH, 341(2), 123 - 131, Feb. 2016 , Refereed
    Summary:Chronic inflammation induced by reactive oxygen species is associated with increased risk of developing colorectal cancer (CRC), and prostaglandin E-2 (PGE(2)), which serves as a key mediator of inflammatory responses, plays an important role in CRC initiation and progression. Therefore, in the present study, we aimed to investigate the role of prostaglandin transporter OATP2A1/SLCO2A1 in the changes of PGE(2) disposition in CRC cells in response to oxidative stress. H2O2 induced translocation of cytoplasmic OATP2A1 to plasma membranes in LoVo and COLO 320DM cells, but not in Caco-2 cells. The shift of subcellular OATP2A1 was abolished in the presence of anti-oxidant N-acetyl-L-cysteine or an inhibitor of protein kinase C, which evokes exocytosis. Exposure of LoVo cells to H2O2 caused an increase in the amount of extracellular PGE(2) without changing the sum of intra- and extracellular PGE(2). OATP2A1 knockdown decreased extracellular PGE(2) in LoVo cells. In addition, extracellular PGE(2) was significantly reduced by exocytosis inhibitor cytochalasin D, suggesting that H2O2-induced PGE(2) release occurs in an exocytotic manner. Furthermore, mRNA expression of vascular endothelial growth factor (VEGF) was significantly reduced in LoVo cells by knockdown of OATP2A1. These results suggest that cytoplasmic OATP2A1 likely facilitates PGE(2) loading into suitable intracellular compartment(s) for efficient exocytotic PGE(2) release from CRC cells exposed to oxidative stress. (C) 2016 Elsevier Inc. All rights reserved.
  • Prostaglandin transporter (OATP2A1/SLCO2A1) contributes to local disposition of eicosapentaenoic acid-derived PGE(3), Tomoka Gose, Takeo Nakanishi, Shunsuke Kamo, Hiroaki Shimada, Katsumasa Otake, Ikumi Tamai, PROSTAGLANDINS & OTHER LIPID MEDIATORS, PROSTAGLANDINS & OTHER LIPID MEDIATORS, 122, 10 - 17, Jan. 2016 , Refereed
    Summary:Eicosapentaenoic acid (EPA)-derived prostaglandin E-3 (PGE(3)) possesses an anti-inflammatory effect; however, information for transporters that regulate its peri-cellular concentration is limited. The present study, therefore, aimed to clarify transporters involved in local disposition of PGE(3). PGE(3) uptake was assessed in HEK293 cells transfected with OATP2A1/SLCO2A1, OATP1B1/SLCO1B1, OATP2B1/SLCO2B1, OAT1/SLC22A6, OCT1/SLC22A1 or OCT2/SLC22A2 genes, compared with HEK293 cells transfected with plasmid vector alone (Mock). PGE(3) uptake by OATP2A1-expressing HEK293 cells (HEK/2A1) was the highest and followed by HEK/1B1, while no significantly higher uptake of PGE(3) than Mock cells was detected by other transporters. Saturation kinetics in PGE(3) uptake by HEK/2A1 estimated the K-m as 7.202 +/- 0.595 mu M, which was 22 times higher than that of PGE(2) (K-m = 0.331 +/- 0.131 mu M). Furthermore, tissue disposition of PGE(3) was examined in wild-type (WT) and Slco2a1-deficient (Slco2a1(-/-)) mice after oral administration of EPA ethyl ester (EPA-E) when they underwent intraperitoneal injection of endotoxin (e.g., lipopolysaccharide). PGE(3) concentration was significantly higher in the lung, and tended to increase in the colon, stomach, and kidney of Slco2a1(-/-), compared to WT mice. Ratio of PGE(2) metabolite 15-keto PGE(2) over PGE2 concentration was significantly lower in the lung and colon of Slco2a1(-/-) than that of WT mice, suggesting that PGE(3) metabolism is downregulated in Slco2a1(-/-) mice. In conclusion, PGE3 was found to be a substrate of OATP2A1, and local disposition of PGE(3) could be regulated by OATP2A1 at least in the lung. (C) 2015 Elsevier Inc. All rights reserved.
  • OATP2A1/SLCO2A1-mediated prostaglandin E-2 loading into intracellular acidic compartments of macrophages contributes to exocytotic secretion, Hiroaki Shimada, Yoshinobu Nakamura, Takeo Nakanishi, Ikumi Tamai, BIOCHEMICAL PHARMACOLOGY, BIOCHEMICAL PHARMACOLOGY, 98(4), 629 - 638, Dec. 2015 , Refereed
    Summary:There is significant evidence that the inducible cyclooxygenase isoform (COX-2) regulates the pericellular concentration of PGE(2); however, the mechanism of the secretory process remains unclear. The present study, therefore, aimed to evaluate the role of prostaglandin transporter (OATP2A1) in PGE(2) secretion from macrophages. lmmunofluorescence staining for Oatp2a1 (Slco2a1) was primarily detected in cytoplasmic domains, and was partially co-localized with anti-PGE(2) antibody, LysoTracker (R), and anti-lysosome-associated membrane protein (Lamp) I antibody in murine macrophage-derived RAW264 cells and peritoneal macrophages (PMs). PGE(2) uptake by subcellular fraction containing light lysosomes was reduced significantly in the presence of an OATP inhibitor and in Slco2a1(+/-) PMs. Secretion of PGE(2) and lysosome-specific N-acetyl-beta-D-glucosaminidase was enhanced in activated macrophagic cells, and diminished significantly under the Ca2+-depleted condition. The amount of PGE(2) secreted from lipopolysaccharide-activated Slco2a1(-/-) PMs was significantly lower than that from PMs from wild type (WT) mice. Expression of Cox-2 and 15-hydroxyprostaglandin dehydrogenase (15-Pgdh) was unchanged between PMs from Slco2a1(-/-) and WT mice. These results suggest that OATP2A1 is involved in PGE(2)-loading into intracellular acidic compartments, including light lysosomes. Thus, OATP2A1 contributes to PGE(2) secretion by macrophages via exocytosis induced by Ca2+ influx, independently of PGE(2) synthesis and metabolism. (C) 2015 Elsevier Inc. All rights reserved.

Conference Activities & Talks

  • The Role of OATP2A1/SLCO2A1 in PGE2 Secretion from Macrophages., Hiroaki Shimada, Takeo Nakanishi, Yoshinobu Nakamura, Shio Maruyama, Ikumi Tamai,   2015 11 13 , 招待有り


  • 砂漠人参カンカニクジュヨウの血糖上昇抑制作用メカニズムの解明, 島田紘明, 卜部裕一, 岡本雄平, 李征, 川瀬篤史, 森川敏生, 森川敏生, 村岡修, 村岡修, 村岡修, 岩城正宏, 岩城正宏, 岩城正宏, 生体膜と薬物の相互作用シンポジウム講演要旨集, 39th, 56‐57,   2017 10 26 ,
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