Tokushima University / Educator and Researcher Directory --- Koga, Takeru

Personal Web Page

https://wwp.ait.tokushima-u.ac.jp/bb-b5lab/ait.Tokushima-u.ac.jp/bb-b5lab/

https://researchmap.jp/Takeru_Koga (researchmap)

https://orcid.org/0000-0003-0481-1532 (ORCID)

Field of Study

○	Bioorganic Chemistry, Food Organic Chemistry, Natural Products Chemistry

Subject of Study

○	食品に含まれる生物活性物質に関する研究

Book / Paper

(See https://researchmap.jp/Takeru_Koga (researchmap) for Published Book / Papers / Presentations.)

Academic Paper (Judged Full Paper):

1.	Saki Morimoto, Takeru Koga, Saho Miyazaki and Akihiro Tai : Neurite outgrowthpromoting furanocoumarins isolated from sudachi juice in PC12 cells, Bioscience, Biotechnology, and Biochemistry, 90, 9, 1147-1153, 2026. (Link to Publication Site) ● Publication site (DOI): 10.1093/bbb/zbag092 (Link to Search Site for Scientific Articles) ● Search Scopus @ Elsevier (DOI): 10.1093/bbb/zbag092 (DOI: 10.1093/bbb/zbag092)
2.	Takeru Koga, Aina Yoshida, Mayuko Tomisawa, Mitsuhiro Nakamura and Akihiro Tai : Development of a highly sensitive, highly selective and high-throughput method for determination of total ascorbic acid, Analyst, 150, 13, 2865-2871, 2025. (Summary) A highly sensitive, highly selective, and high-throughput method for determination of intracellular total ascorbic acid (AA) was developed by measuring the fluorescence intensity of 1,2-diamino-4,5-methylenedioxibenzene (MDB)-labeled AA. First, the reaction buffer, temperature, pH, and time were investigated to establish optimal reaction conditions, and it was found that AA was detected with high sensitivity by reacting oxidized AA and MDB in 100 mM citrate buffer (pH 5.0) for 10 min at room temperature. Next, a scale-up synthesis was performed to determine the chemical structure of the MDB-labeled AA, and its excitation and emission wavelengths were optimized to 375 and 450 nm, respectively. HPLC analysis revealed that MDB reacts with AA with high selectivity under the established conditions. It was also found that AA could be determined under optimal reaction conditions, regardless of the presence or absence of cellular components. In conclusion, the established method for determination of AA with MDB can quantify AA in the range of 25 nM to 20 μM in a microplate with a detection limit of 10 nM. Furthermore, the method was confirmed to be able to quantify intracellular AA in a cell line by comparison with a standard HPLC method. This method is applicable to highly sensitive, highly selective, and high-throughput analysis and could be applied to the determination of AA in various cells used in the evaluation of AA activity. (Keyword) Ascorbic Acid / Humans / Limit of Detection / Chromatography, High Pressure Liquid / High-Throughput Screening Assays / Spectrometry, Fluorescence / Hydrogen-Ion Concentration / Fluorescent Dyes / Temperature (Link to Publication Site) ● Publication site (DOI): 10.1039/d5an00319a (Link to Search Site for Scientific Articles) ● PubMed @ National Institutes of Health, US National Library of Medicine (PMID): 40444429 ● Summary page in Scopus @ Elsevier: 2-s2.0-105006926517 (DOI: 10.1039/d5an00319a, PubMed: 40444429, Elsevier: Scopus)
3.	Takeru Koga, Naoaki Kawahara, Mei Aburada, Asako Ono, Shiori Mae, Aina Yoshida, Yuji Iwaoka, Hideyuki Ito and Akihiro Tai : Antiallergic activity of 3-O-dodecyl-L-ascorbic acid, Molecules, 29, 1, 69, 2024. (Summary) 2--Alkyl-l-ascorbic acids and 3--alkyl-l-ascorbic acids were synthesized, and their degranulation inhibitory activities were evaluated. Among ascorbic acid derivatives with butyl, octyl, dodecyl, hexadecyl, and octadecyl groups introduced at the C-2 or C-3 positions, an AA derivative with a dodecyl group introduced at the C-3 position, 3--dodecyl-l-ascorbic acid (compound ), showed the strongest inhibitory activity against antigen-stimulated degranulation. Compound also inhibited calcium ionophore-stimulated degranulation. Compound , in which the hydroxyl group at the C-6 position of compound was substituted with an amino group, and compound , in which the dodecyloxy group at the C-3 position of compound was exchanged with a dodecylamino group, were synthesized, and these derivatives showed weaker inhibitory activity against antigen-stimulated degranulation than that of compound . In addition, orally administered compound inhibited passive cutaneous anaphylaxis reactions in mice with a potency equal to that of oxatomide, an antiallergic agent. These results suggest that compound may be a candidate for antiallergic treatment. (Keyword) Animals / Mice / Anti-Allergic Agents / Ascorbic Acid (Tokushima University Institutional Repository) ● Metadata: 2000201 (Link to Publication Site) ● Publication site (DOI): 10.3390/molecules29010069 (Link to Search Site for Scientific Articles) ● PubMed @ National Institutes of Health, US National Library of Medicine (PMID): 38202652 ● Search Scopus @ Elsevier (PMID): 38202652 ● Search Scopus @ Elsevier (DOI): 10.3390/molecules29010069 (Tokushima University Institutional Repository: 2000201, DOI: 10.3390/molecules29010069, PubMed: 38202652)
4.	Takeru Koga, Hideyuki Ito, Yuji Iwaoka, Toshiro Noshita and Akihiro Tai : Neurite outgrowth-promoting compounds from the petals of Paeonia lactiflora in PC12 cells, Molecules, 27, 22, 7670, 2022. (Tokushima University Institutional Repository) ● Metadata: 2010856 (Link to Publication Site) ● Publication site (DOI): 10.3390/molecules27227670 (Link to Search Site for Scientific Articles) ● Search Scopus @ Elsevier (DOI): 10.3390/molecules27227670 (Tokushima University Institutional Repository: 2010856, DOI: 10.3390/molecules27227670)
5.	Takeru Koga, Nanako Shiki, Hideyuki Ito, Yuji Iwaoka and Akihiro Tai : Degranulation inhibitors from petals of Coreopsis grandiflora, Records of Natural Products, 16, 6, 645-650, 2022. (Link to Publication Site) ● Publication site (DOI): 10.25135/rnp.319.2202.2351 (Link to Search Site for Scientific Articles) ● Summary page in Scopus @ Elsevier: 2-s2.0-85137021962 (DOI: 10.25135/rnp.319.2202.2351, Elsevier: Scopus)
6.	Yuji Iwaoka, Misaki Fukushima, Hideyuki Ito, Takeru Koga, Naoaki Kawahara and Akihiro Tai : Synthesis of ascorbic acid derivatives with different types of C8 straight acyl chain and their neurite outgrowth-enhancing activities, Journal of Nutritional Science and Vitaminology, 68, 3, 236-239, 2022. (Summary) We previously reported that 2-O-α-D-glucopyranosyl-6-O-octanoyl-L-ascorbic acid, having a C straight acyl chain, at a concentration of 100 μM remarkably enhanced nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells after being metabolized to L-ascorbic acid (AA) as an active form by esterase and α-glucosidase. In this study, to examine the structure-activity relationship of 6-O-substituted AA derivatives with a C straight acyl chain for neurite outgrowth-promoting activity, we synthesized AA derivatives 1-4 and compared their activities for promoting NGF-induced neurite outgrowth in PC12 cells. AA derivatives 1-4 showed neurite outgrowth-enhancing activity at 100 μM, while AA derivative 2 also showed the enhancing activity at 3 μM. Furthermore, AA derivative 2 as well as AA enhanced NGF-induced neurite outgrowth after being incorporated into PC12 cells via sodium-dependent vitamin C transporter as an anion transporter. The results suggested that AA derivative 2 has neurite outgrowth-enhancing activity in its intact form at a low concentration (3 μM) and that AA derivatives 1-4 showed their activities in the form of AA, a metabolite of these derivatives, at a higher concentration (100 μM). (Keyword) Animals / Ascorbic Acid / Esterases / Nerve Growth Factor / Neuronal Outgrowth / Rats / alpha-Glucosidases (Link to Publication Site) ● Publication site (DOI): 10.3177/jnsv.68.236 (Link to Search Site for Scientific Articles) ● PubMed @ National Institutes of Health, US National Library of Medicine (PMID): 35768255 ● Search Scopus @ Elsevier (PMID): 35768255 ● Search Scopus @ Elsevier (DOI): 10.3177/jnsv.68.236 (DOI: 10.3177/jnsv.68.236, PubMed: 35768255)
7.	Takeru Koga and Akihiro Tai : Neurite outgrowth-promoting compounds from cockscomb hydrolysate, Nutrients, 14, 7, 1422, 2022. (Summary) Cockscomb hydrolysate was found to have neurite outgrowth-promoting activity in PC12 cells. To investigate the neurite outgrowth-promoting compounds derived from cockscomb hydrolysate, bioassay-guided purification was carried out. Purified active fractions were obtained by liquid-liquid partition, followed by column chromatography. High-performance liquid chromatography and proton nuclear magnetic resonance analyses of the purified active fractions clarified that the main compounds are threonine, alanine, valine, and methionine. By screening for 20 kinds of amino acids, it was shown that valine and methionine, but not threonine and alanine, have neurite outgrowth-promoting activity. The results of activity evaluation of the mixture of amino acids indicated that alanine enhanced the activity of valine and that the mixture of valine and methionine showed a higher ratio of neurite formation than did each of them alone. On the other hand, dipeptides formed by valine and methionine showed weak neurite outgrowth-promoting activity. A mixture of threonine, alanine, valine, and methionine at the same concentrations as those in cockscomb hydrolysate showed neurite outgrowth-promoting activity comparable to that of cockscomb hydrolysate although threonine, alanine, valine, and methionine alone did not show activity at their concentrations in cockscomb hydrolysate. Therefore, the strong neurite outgrowth-promoting activity of cockscomb hydrolysate was considered to be due to the synergistic effect of threonine, alanine, valine, and methionine. (Keyword) Alanine / Amino Acids / Animals / Methionine / Neurites / Neuronal Outgrowth / PC12 Cells / Rats / Threonine / Valine (Tokushima University Institutional Repository) ● Metadata: 2010088 (Link to Publication Site) ● Publication site (DOI): 10.3390/nu14071422 (Link to Search Site for Scientific Articles) ● PubMed @ National Institutes of Health, US National Library of Medicine (PMID): 35406035 ● Search Scopus @ Elsevier (PMID): 35406035 ● Search Scopus @ Elsevier (DOI): 10.3390/nu14071422 (Tokushima University Institutional Repository: 2010088, DOI: 10.3390/nu14071422, PubMed: 35406035)
8.	Toshiro Noshita, Kentaro Fujita, Takeru Koga, Hidekazu Ouchi and Akihiro Tai : Synthesis and biological activity of (±)-7,3',4'-trihydroxyhomoisoflavan and its analogs, Bioorganic & Medicinal Chemistry Letters, 31, 127674, 2021. (Summary) Acetylcholinesterase (AChE) inhibitors and neurite outgrowth promoters are thought to alleviate the symptoms of degenerative brain disorders, such as Alzheimer's disease. We designed and synthesized a series of homoisoflavonoids based on the structure of natural homoisoflavan isolated from Dracaena cambodiana dragon's blood. The homoisoflavonoids were then evaluated as AChE inhibitors and neurite outgrowth promoters. The catechol structure of the homoisoflavan B rings was important for AChE inhibition, and some of the homoisoflavonoids significantly promoted neurite outgrowth induced by nerve growth factor (NGF). (Keyword) Acetylcholinesterase / Animals / Cholinesterase Inhibitors / Dose-Response Relationship, Drug / Dracaena / Humans / Molecular Docking Simulation / Molecular Structure / Nerve Growth Factors / Neurites / PC12 Cells / Rats / Structure-Activity Relationship (Link to Publication Site) ● Publication site (DOI): 10.1016/j.bmcl.2020.127674 (Link to Search Site for Scientific Articles) ● PubMed @ National Institutes of Health, US National Library of Medicine (PMID): 33161123 ● Search Scopus @ Elsevier (PMID): 33161123 ● Search Scopus @ Elsevier (DOI): 10.1016/j.bmcl.2020.127674 (DOI: 10.1016/j.bmcl.2020.127674, PubMed: 33161123)
9.	Takeru Koga, Takaiku Sakamoto, Eiji Sakuradani and Akihiro Tai : Neurite Outgrowth-Promoting Activity of Compounds in PC12 Cells from Sunflower Seeds, Molecules, 25, 20, 4748, 2020. (Summary) In the current super-aging society, the establishment of methods for prevention and treatment of Alzheimer's disease (AD) is an urgent task. One of the causes of AD is thought to be a decrease in the revel of nerve growth factor (NGF) in the brain. Compounds showing NGF-mimicking activity and NGF-enhancing activity have been examined as possible agents for improving symptoms. In the present study, sunflower seed extract was found to have neurite outgrowth-promoting activity, which is an NGF-enhancing activity, in PC12 cells. To investigate neurite outgrowth-promoting compounds from sunflower seed extract, bioassay-guided purification was carried out. The purified active fraction was obtained by liquid-liquid partition followed by some column chromatographies. Proton nuclear magnetic resonance and gas chromatography-mass spectrometry analyses of the purified active fraction indicated that the fraction was a mixture of β-sitosterol, stigmasterol and campesterol, with β-sitosterol being the main component. Neurite outgrowth-promoting activities of β-sitosterol, stigmasterol, campesterol and cholesterol were evaluated in PC12 cells. β-Sitosterol and stigmasterol showed the strongest activity of the four sterol compounds (β-sitosterol stigmasterol > campesterol > cholesterol), and cholesterol did not show any activity. The results indicated that β-sitosterol was the major component responsible for the neurite outgrowth-promoting activity of sunflower seeds. Results of immunostaining also showed that promotion by β-sitosterol of neurite formation induced by NGF was accompanied by neurofilament expression. β-Sitosterol, which showed NGF-enhancing activity, might be a candidate ingredient in food for prevention of AD. (Keyword) Alzheimer's disease / sunflower seed / NGF / β-sitosterol / neurite outgrowth-promoting activit (Tokushima University Institutional Repository) ● Metadata: 2009163 (Link to Publication Site) ● Publication site (DOI): 10.3390/molecules25204748 (Link to Search Site for Scientific Articles) ● Search Scopus @ Elsevier (DOI): 10.3390/molecules25204748 (Tokushima University Institutional Repository: 2009163, DOI: 10.3390/molecules25204748)

Review, Commentary:

1.	Takeru Koga and Akihiro Tai : クラブアップルの果実由来の2-O-β-D-グルコピラノシル-L-アスコルビン酸の発見, Vitamins, 100, 1, 63-65, Feb. 2026.
2.	Takeru Koga, YOSHIDA Aina, 富澤真由子, Mitsuhiro Nakamura and Akihiro Tai : 高感度，高選択性，ハイスループットな総アスコルビン酸定量法の開発, Vitamins, 100, 1, 47-49, Feb. 2026.
3.	Yugo Itoh, Takeru Koga and Akihiro Tai : アスコルビル化された天然物の新たな発見, Vitamins, 99, 4, 345-348, Jun. 2025.
4.	Yugo Itoh, Takeru Koga and Akihiro Tai : 還元型酸化グラフェンをセンサーとした新たなビタミンC定量法の開発, Vitamins, 99, 2, 106-108, Apr. 2025.
5.	Yugo Itoh, Takeru Koga and Akihiro Tai : ビタミンCを用いた抗菌繊維の開発, Vitamins, 98, 9, 427-429, Sep. 2024.
6.	Takeru Koga, Naoaki Kawahara, 油田芽衣, 大野朝子, Shiori Mae, Aina Yoshida, 岩岡裕二, 伊東秀之 and Akihiro Tai : 3-O-Dodecyl-L-ascorbic acidの抗アレルギー作用, Vitamins, 98, 5/6, 296-300, Jun. 2024.

Proceeding of Domestic Conference:

1.	KAMI Fukuya, KIKUCHI Moe, Takeru Koga and Akihiro Tai : α,β-不飽和アルデヒド–アスコルビン酸付加体の新機能の発見, 日本ビタミン学会第78回大会, Jun. 2026.
2.	KIKUCHI Moe, Takeru Koga and Akihiro Tai : モノアシル化アスコルビン酸誘導体の脱顆粒抑制作用, 日本ビタミン学会第78回大会, Jun. 2026.
3.	MORIMOTO Saki, MIYAZAKI Saho, Takeru Koga and Akihiro Tai : PC12細胞において神経突起形成促進作用を示すスダチ果汁由来化合物, 日本農芸化学会2026年度大会, Mar. 2026.
4.	小渕優, 野下俊朗, Takeru Koga and Akihiro Tai : ラン科植物から単離されたビベンジル類の全合成と生物活性に関する研究, 日本農芸化学会2026年度大会, Mar. 2026.
5.	Sena TATEISHI, 鵜飼夕菜, 三浦勇輝, 小倉由資, 滝川浩郷, Taiki Fushimi, Mitsugu Akagawa, 須貝智也, 棟方涼介, 矢崎一史, Takeru Koga, Akihiro Tai and Rie Mukai : プレニル化によるケンフェロールの抗酸化活性の変化, 日本農芸化学会中四国支部第73回講演会, Jan. 2026.
6.	Haru Niimi, Takeru Koga and Akihiro Tai : 2位アシル化アスコルビン酸誘導体の神経突起形成促進作用, 日本農芸化学会2025年度関西・中四国・西日本支部合同大会, Sep. 2025.
7.	Ryoma Takami, Takaiku Sakamoto, Eiji Sakuradani, Takeru Koga and Akihiro Tai : もちきび・もちあわ中の神経突起形成促進作用成分, 日本農芸化学会2025年度関西・中四国・西日本支部合同大会, Sep. 2025.
8.	Yugo Itoh, Takeru Koga and Akihiro Tai : ビタミンC類似体の抗酸化作用, 日本農芸化学会2025年度関西・中四国・西日本支部合同大会, Sep. 2025.
9.	斎木彩花, Takeru Koga, 小縣綾, Akihiro Tai and 野下俊朗 : 龍血由来のホモイソフラバンから設計された2-(3',4'-dihydroxybenzyl)-1,2,3,4-tetrahydronaphthaleneは，強力なアセチルコリンエステラーゼ阻害活性と，顕著な神経突起伸長促進作用を示す, 日本薬学会第145年会, Mar. 2025.
10.	Takeru Koga, 伊東秀之, 岩岡裕二, 野下俊朗 and Akihiro Tai : PC12細胞において神経突起伸長促進作用を示すシャクヤクの花弁由来物質, 日本農芸化学会2025年度大会, Mar. 2025.
11.	Onishi Hina, YAMADA Sara, Chizuru Sasaki, Takeru Koga and Akihiro Tai : ウルシ廃材の総合的有効利用法に関する研究, 日本生物工学会西日本支部大会2024, Nov. 2024.
12.	Sara Yamada, Takeru Koga and Akihiro Tai : トマト脇芽廃棄物由来の脱顆粒抑制物質, 日本農芸化学会2024年度中四国支部大会(第69回講演会), Sep. 2024.
13.	Saho Miyazaki, Takeru Koga and Akihiro Tai : スダチ果汁由来の神経突起形成促進物質, 日本農芸化学会2024年度中四国支部大会(第69回講演会), Sep. 2024.
14.	Shiori Nishioka, 青田湧介, 加来田博貴, Takeru Koga and Akihiro Tai : 蛍光ラベル化アスコルビン酸誘導体のライブセルイメージング, 日本ビタミン学会第76回大会, Jun. 2024.
15.	立石晟菜, 韓俊文, 棟方涼介, 矢埼一史, Takeru Koga, Akihiro Tai and Rie Mukai : プレニル化がケンフェロールの抗酸化性に及ぼす影響, 日本農芸化学会 2024年度東京大会, Mar. 2024.
16.	Naoaki Kawahara, 前史織, Takeru Koga, 伊東秀之, 岩岡裕二 and Akihiro Tai : 3-O-Dodecyl-L-ascorbic acidの抗アレルギー作用, 日本農芸化学会中四国支部第67回講演会(例会), Jan. 2024.
17.	立石晟菜, 韓俊文, 棟方涼介, 矢埼一史, Takeru Koga, Akihiro Tai and Rie Mukai : プレニルケンフェロールの抗酸化性の比較, 第28回日本フードファクター学会学術集会無礼講学会におけるブレイクスルー, Nov. 2023.
18.	Masamichi Kurokawa, Takeru Koga and Akihiro Tai : ヤローの花由来の脱顆粒抑制物質, 学会創立100周年記念日本農芸学会2023年度中四国・西日本支部合同大会, Sep. 2023.
19.	庄野陸, 韓俊文, 棟方涼介, Akihiro Tai, 矢﨑一史, Takeru Koga and Rie Mukai : プレニルフラボノイドの抗アレルギー作用, 学会創立100周年記念日本農芸学会2023年度中四国・西日本支部合同大会, Sep. 2023.
20.	Takeru Koga, Naoaki Kawahara, 油田芽衣, 清水菜々栄, 岩岡裕二, 伊東秀之 and Akihiro Tai : アルキルアスコルビン酸誘導体の神経突起形成促進作用, 日本ビタミン学会第75回大会, Jun. 2023.
21.	Hina Ohnishi, Takeru Koga and Akihiro Tai : 6-N-アシルアスコルビン酸誘導体の脱顆粒抑制作用, 日本ビタミン学会第75回大会, Jun. 2023.

Et cetera, Workshop:

1.	Akihiro Tai, KAWAHARA Naoaki, 油田芽衣, 清水菜々栄 and Takeru Koga : アルキルアスコルビン酸誘導体の神経突起形成促進作用と構造活性相関, 第177回ビタミンC研究委員会, Mar. 2026.
2.	Takeru Koga : 食品由来の神経突起形成促進物質に関する研究, 日本農芸化学会中四国支部支部創立25周年記念第41回若手研究者シンポジウム, Jun. 2025.
3.	Akihiro Tai, 大野朝子, Shiori Mae, 千振正登, Naoaki Kawahara, 伊東秀之 and Takeru Koga : アルキルアスコルビン酸誘導体の脱顆粒抑制作用と構造活性相関, 第174回ビタミンC研究委員会, Mar. 2025.
4.	Takeru Koga : シャクヤクの花由来の神経突起形成促進物質に関する研究, 第16回ホームカミングデイ, 徳島大学工業会, 研究紹介, May 2024.
5.	Takeru Koga : シャクヤクの花由来の神経突起形成促進物質に関する研究, 第21回徳島大学社会産業理工学研究交流会2023, 若手講演, Sep. 2023.
6.	Akihiro Tai, Aina Yoshida, Mitsuhiro Nakamura and Takeru Koga : アスコルビン酸の高感度ハイスループット定量法, 第169回ビタミンC研究委員会, Jun. 2023.

Patent:

1.	Akihiro Tai, Takeru Koga and 若山祥夫 : 神経分化促進剤, 2022-130428 (Aug. 2022), 2022-163215 (Oct. 2022), 7412713 (Jan. 2024).
2.	Akihiro Tai, Takeru Koga and 若山祥夫 : 神経伸長促進剤, 2018-102184 (May 2018), 2018-203722 (Dec. 2018), 7142284 (Sep. 2022).
3.	Akihiro Tai, Takeru Koga and 若山祥夫 : 神経形成促進剤，内服剤，培地用添加剤，細胞希釈液用添加剤，培地および細胞希釈液, 2018-098569 (May 2018), 2019-202954 (Nov. 2019), .

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Assistant Professor : Koga, Takeru

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