title: Carnosic acid protects neuronal HT22 Cells through activation of the antioxidant-responsive element in free carboxylic acid- and catechol hydroxyl moieties-dependent manners.
abstract: In a previous study, we found that carnosic acid (CA) protected cortical neurons by activating the Keap1/Nrf2 pathway, which activation was initiated by S-alkylation of the critical cysteine thiol of the Keap1 protein by the "electrophilic"quinone-type of CA [T. Satoh, K. Kosaka, K. Itoh, A. Kobayashi, M. Yamamoto, Y. Shimojo, C. Kitajima, J. Cui, J. Kamins, S. Okamoto, T. Shirasawa, S.A. Lipton, Carnosic acid, a catechol-type electrophilic compound, protects neurons both in vitro and in vivo through activation of the Keap1/Nrf2 pathway via S-alkylation of targeted cysteines on Keap1. J Neurochem., in press]. In the present study, we used HT22 cells, a neuronal cell line, to test CA derivatives that might be more suitable for in vivo use, as an electrophile like CA might react with other molecules prior to reaching its intended target. CA and carnosol protected the HT22 cells against oxidative glutamate toxicity. CA activated the transcriptional antioxidant-responsive element of phase-2 genes including hemeoxygenase-1, NADPH-dependent quinone oxidoreductase, and gamma-glutamyl cysteine ligase, all of which provide neuroprotection by regulating cellular redox. This finding was confirmed by the result that CA significantly increased the level of glutathione. We synthesized a series of its analogues in which CA was esterified at its catechol hydroxyl moieties to prevent the oxidation from the catechol to quinone form or esterified at those moieties and its carbonic acid to stop the conversion from CA to carnosol. In both cases, the conversion and oxidation cannot occur until the alkyl groups are removed by an intracellular esterase. Thus, the most potent active form as the activator of the Keap1/Nrf2 pathway, the quinone-type CA, will be produced inside the cells. However, neither chemical modulation potentiated the neuroprotective effects, possibly because of increased lipophilicity. These results suggest that the neuroprotective effects of CA critically require both free carboxylic acid and catechol hydroxyl moieties. Thus, the hydrophilicity of CA might be a critical feature for its neuroprotective effects.
authors.affiliation: Department of Welfare Engineering, Faculty of Engineering, Iwate University, Ueda 4-3-5, Morioka, Iwate 020-8551, Japan. tsatoh@iwate-u.a.cjp
authors.forename: Takumi
authors.initials: T
authors.lastname: Satoh
authors.forename: Masanori
authors.initials: M
authors.lastname: Izumi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Inukai
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Tsutsumi
authors.forename: Naoto
authors.initials: N
authors.lastname: Nakayama
authors.forename: Kunio
authors.initials: K
authors.lastname: Kosaka
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Shimojo
authors.forename: Chieko
authors.initials: C
authors.lastname: Kitajima
authors.forename: Ken
authors.initials: K
authors.lastname: Itoh
authors.forename: Toshio
authors.initials: T
authors.lastname: Yokoi
authors.forename: Takuji
authors.initials: T
authors.lastname: Shirasawa
mesh_terms: D045784:Abietanes / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002264:Carboxylic Acids / Q000737:chemistry / Q000378:metabolism; D002396:Catechols / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D019610:Cytoprotection / Q000187:drug effects* / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D004353:Drug Evaluation, Preclinical / Q000379:methods; D004950:Esterases / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D017665:Hydroxyl Radical / Q000737:chemistry / Q000378:metabolism; D000072019:Kelch-Like ECH-Associated Protein 1; D008563:Membrane Lipids / Q000378:metabolism; D051379:Mice; D015394:Molecular Structure; D051267:NF-E2-Related Factor 2 / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology*; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects* / Q000502:physiology; D010616:Phenanthrenes / Q000737:chemistry / Q000378:metabolism; D010936:Plant Extracts / Q000494:pharmacology*; D020218:Response Elements / Q000187:drug effects* / Q000235:genetics; D013256:Steroids / Q000737:chemistry / Q000494:pharmacology
chemical_list: D045784:Abietanes; D048868:Adaptor Proteins, Signal Transducing; D000975:Antioxidants; D002264:Carboxylic Acids; D002396:Catechols; D003598:Cytoskeletal Proteins; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D008563:Membrane Lipids; D051267:NF-E2-Related Factor 2; D018696:Neuroprotective Agents; D010616:Phenanthrenes; D010936:Plant Extracts; D013256:Steroids; D017665:Hydroxyl Radical; C068623:carnosol; D004950:Esterases; D005978:Glutathione; C018381:salvin