title: Imidazole-4-acetic acid, a new lead structure for interaction with the taurine transporter in outer blood-retinal barrier cells.
abstract: Retinal diseases leading to impaired vision and ultimately blindness are mainly characterized by ischemic and hypoxic stress. Targeting the retinal ρ-containing γ-aminobutyric acid type A receptors (ρ GABAARs) and thereby decreasing the retinal neuronal activity has been proposed as a novel therapeutic approach. The taurine transporter (TAUT) plays a key role in the retinal transport of GABA and has been previously suggested to display a higher functional activity in the retina compared to the brain. TAUT would therefore stand as a suitable target for the selective delivery of ρ GABAAR ligands into the retina. Consequently, an in vitro model of TAUT at the outer blood-retinal barrier (BRB) was developed and characterized using the ARPE-19 cell line. Furthermore, the structural requirements of GABAAR ligands for interacting with TAUT at the BRB were investigated for a series of standard GABAAR ligands by testing their ability to inhibit the TAUT-mediated influx of taurine in ARPE-19 cells. Results showed that taurine influx was seven-fold higher when the ARPE-19 cells were cultured under hyperosmotic conditions and was demonstrated to display saturable kinetics (Km=27.7±2.2μM and Jmax=24.2±0.6pmol/cm2·min). Furthermore, the taurine influx was significantly inhibited in a concentration-dependent manner by GABA and imidazole-4-acetic acid (IAA), which is a naturally occurring metabolite of histamine. These compounds display similar Kivalues of 644.2μM and 658.6μM, respectively. Moreover, IAA demonstrated higher inhibitory properties than the other tested GABA analogs: 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), 4,5,6,7-tetrahydropyrazolo[5,4-c]pyridin-3-ol (Aza-THIP), muscimol, and thiomuscimol. These studies demonstrated that IAA interacts with TAUT, which makes IAA a new lead structure in the development of new compounds, which are not only interacting with TAUT but also potent ρ GABAAR ligands.
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark; Department of Pharmacy, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Sophie
authors.initials: S
authors.lastname: Valembois
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Krall
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Bente
authors.initials: B
authors.lastname: Frølund
authors.affiliation: Department of Pharmacy, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark. Electronic address: steffansen@sdu.dk.
authors.forename: Bente
authors.initials: B
authors.lastname: Steffansen
mesh_terms: D001813:Blood-Retinal Barrier / Q000166:cytology / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D007093:Imidazoles / Q000737:chemistry / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009997:Osmotic Pressure; D018079:Receptors, GABA / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000378:metabolism*; D013654:Taurine / Q000378:metabolism; D000099247:Taurine Transporters
chemical_list: D007093:Imidazoles; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D018079:Receptors, GABA; D011963:Receptors, GABA-A; D013654:Taurine; D000099247:Taurine Transporters; C087200:GABA-C receptor; C005954:imidazoleacetic acid
keywords: ARPE-19 cells; Human taurine transporter; Imidazole-4-acetic acid; γ-Aminobutyric acid receptors