DL-TBOA is an inhibitor of excitatory amino acid transporters (EAATs), with IC50 values of 67 and 5.5 μM for glutamate uptake in COS-1 cells expressing human EAAT1 and EAAT2, respectively. It inhibits inward currents induced by L-aspartate in EAAT4-expressing Xenopus oocytes (Ki = 4.4 μM) and by L-glutamate in EAAT5-expressing oocytes (Ki = 3.2 μM) voltage-clamped at -60 mV. In vivo, DL-TBOA (500 μM, intrahippocampal perfusion) increases extracellular aspartate, glutamate, and alanine levels in rat hippocampus. Intrahippocampal injection of DL-TBOA increases lesion volume in the rat CA1 region in a dose-dependent manner and induces hyperexcitability, wet-dog shakes, salivation, forelimb myoclonus, limbic seizures, and epileptic EEG discharges at a dose of 25 nmol. DL-TBOA (5 and 10 μg, intrathecal) induces antinociception in the second phase of the formalin test in rats when administered 10 minutes prior to formalin.
DL-TBOA is a non-transportable excitatory amino acid transporter (EAAT) inhibitor (1). DL-TBOA is a glutamate uptake inhibitor.
dl-tboa inhibited the uptake of [14c]glutamate in cos-1 cells overexpressing the human excitatory amino acid transporter-1 (eaat1) (ki = 42 μm) with almost the same potency as dl-threo-b-hydroxyaspartate (ki = 58 μm). with regard to the human excitatory amino acid transporter-2 (eaat2), the inhibitory effect of dl-tboa (ki = 5.7 μm) was much more potent than that of dihydrokainate (ki = 79 μm), which is well known as a selective blocker of this subtype. [1].
microdialysis administration of 500 μm dl-tboa into the hippocampus increased 3.4- and nine-fold the extracellular levels of aspartate and glutamate, respectively. upon stereotaxic administration it induced neuronal damage dose-dependently in ca1 and dentate gyrus, and convulsive behavior. electroencephalographic recording showed limbic seizures appearance in the hippocampus after dl-tboa infusion. [2].
[1] shimamoto k, lebrun b, yasuda-kamatani y, sakaitani m, shigeri y, yumoto n, nakajima t. dl-threo-beta-benzyloxyaspartate, a potent blocker of excitatory amino acid transporters. mol pharmacol. 1998 feb;53(2):195-201.
[2] montiel t, camacho a, estrada-sánchez am, massieu l. differential effects of the substrate inhibitor l-trans-pyrrolidine-2,4-dicarboxylate (pdc) and the non-substrate inhibitor dl-threo-beta-benzyloxyaspartate (dl-tboa) of glutamate transporters on neuronal damage and extracellular amino acid levels in rat brain in vivo. neuroscience. 2005;133(3):667-78.
