Role of blood–brain barrier organic anion transporter 3 (OAT3) in the efflux of indoxyl sulfate, a uremic toxin: its involvement in neurotransmitter metabolite clearance from the brain

• Published in: Journal of neurochemistry Vol. 83; no. 1; pp. 57 - 66
• Main Authors: Ohtsuki, Sumio, Asaba, Hiroshi, Takanaga, Hitomi, Deguchi, Tsuneo, Hosoya, Ken‐ichi, Otagiri, Masaki, Terasaki, Tetsuya
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-10-2002; Blackwell
• Subjects: Animals; Antimetabolites - pharmacology; Biological and medical sciences; Biological Transport - drug effects; Biological Transport - physiology; Blood-Brain Barrier - drug effects; Blood-Brain Barrier - physiology; blood–brain barrier; Brain - blood supply; Brain - metabolism; Capillaries - cytology; Capillaries - metabolism; Cells, Cultured; Cerebral circulation. Blood-brain barrier. Choroid plexus. Cerebrospinal fluid. Circumventricular organ. Meninges; Chromatography, High Pressure Liquid; Dose-Response Relationship, Drug; efflux transport; Endothelium, Vascular - cytology; Endothelium, Vascular - metabolism; Fundamental and applied biological sciences. Psychology; GABA Agonists - pharmacology; Homovanillic Acid - pharmacology; Indican - metabolism; Indican - pharmacokinetics; indoxyl sulfate; Male; Microinjections; Neurotransmitter Agents - metabolism; Oocytes - metabolism; organic anion transporter 3 (OAT3); Organic Anion Transporters, Sodium-Independent - genetics; Organic Anion Transporters, Sodium-Independent - metabolism; p-Aminohippuric Acid - pharmacology; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - biosynthesis; Uremia - metabolism; uremic toxin; Vertebrates: nervous system and sense organs; Xenopus laevis; Rat; Metabolite; Biological transport; Rodentia; Central nervous system; Organic anion transporter OAT3; Clearance; Blood brain barrier; Toxin; Vertebrata; Organic anion; Mammalia; Neurotransmitter; Brain (vertebrata)
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.2002.01108.x

Renal impairment is associated with CNS dysfunctions and the accumulation of uremic toxins, such as indoxyl sulfate, in blood. To evaluate the relevance of indoxyl sulfate to CNS dysfunctions, we investigated the brain‐to‐blood transport of indoxyl sulfate at the blood–brain barrier (BBB) using the Brain Efflux Index method. [3H]Indoxyl sulfate undergoes efflux transport with an efflux transport rate of 1.08 × 10−2/min, and the process is saturable with a Km of 298 µm. This process is inhibited by para‐aminohippuric acid, probenecid, benzylpenicillin, cimetidine and uremic toxinins, such as hippuric acidand 3‐carboxy‐4‐methyl‐5‐propyl‐2‐furanpropanoic acid. RT–PCR revealed that an OAT3 mRNA is expressed in conditionally immortalized rat brain capillary endothelial cell lines and rat brain capillary fraction. Xenopus oocytes expressing OAT3 were found to exhibit [3H]indoxyl sulfate uptake, which was significantly inhibited by neurotransmitter metabolites, such as homovanillic acid and 3‐methoxy‐4‐hydroxymandelic acid, and by acyclovir, cefazolin, baclofen, 6‐mercaptopurine, benzoic acid, and ketoprofen. These results suggest that OAT3 mediates the brain‐to‐blood transport of indoxyl sulfate, and is also involved in the efflux transport of neurotransmitter metabolites and drugs. Therefore, inhibition of the brain‐to‐blood transport involving OAT3 would occur in uremia and lead to the accumulation of neurotransmitter metabolites and drugs in the brain.