(±)-3-Hydroxy-4,5,6,6a-tetrahydro-3aH-pyrrolo [3,4 -d]-isoxazole-4-carboxylic acid (HIP-A) and (±)-3-hydroxy-4,5,6, 6a-tetrahydro-3aH-pyrrolo[3,4-d]isoxazole-6-carboxylic acid (HIP-B) are selective inhibitors of excitatory amino acid transporters (EAATs), as potent as dl-threo-β-benzyloxyaspartic acid (TBOA). We report here that the active isomers are (–)-HIP-A and (+)-HIP-B, being approximately 150- and 10-fold more potent than the corresponding enantiomers as inhibitors of [3H]aspartate uptake in rat brain synaptosomes and hEAAT1–3-expressing cells. Comparable IC50 values were found on the three hEAAT subtypes. (–)-HIP-A maintained the remarkable property, previously reported with the racemates, of inhibiting synaptosomal glutamate-induced [3H]d-aspartate release (reverse transport) at concentrations significantly lower than those inhibiting [3H]l-glutamate uptake. New data suggest that the noncompetitive-like interaction described previously is probably the consequence of an insurmountable, long-lasting impairment of EAAT's function. Some minutes of preincubation are required to induce this impairment, the duration of preincubation having more effect on inhibition of glutamate-induced release than of glutamate uptake. In organotypic rat hippocampal slices and mixed mouse brain cortical cultures, TBOA, but not (–)-HIP-A, had toxic effects. Under ischemic conditions, a neuroprotective effect was found with 10 to 30 μM (–)-HIP-A, but not with 10 to 30 μM TBOA or 100 μM (–)-HIP-A. The effect of (–)-HIP-A suggests that, under ischemia, EAATs mediate both release (reverse transport) and uptake of glutamate. The neuroprotection with the lower (–)-HIP-A concentrations may indicate a selective inhibition of the reverse transport confirming the data obtained in synaptosomes. The selective interference with glutamate-induced glutamate release might offer a new strategy for neuroprotective action.
Neuroprotective effects of the novel glutamate transporter inhibitor (-)-3-hydroxy-4,5,6,6a-tetrahydro-3aH-pyrrolo[3,4-d]isoxazole-4-carboxylic acid, which preferentially inhibits reverse transport (glutamate release) compared with glutamate reuptake / S. Colleoni, A.A. Jensen, E. Landucci, E. Fumagalli, P. Conti, A. Pinto, M. De Amici, D.E. Pellegrini Giampietro, C. De Micheli, T. Mennini, M. Gobbi. - In: THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS. - ISSN 0022-3565. - 326:2(2008 Aug), pp. 646-656. [10.1124/jpet.107.135251]
Neuroprotective effects of the novel glutamate transporter inhibitor (-)-3-hydroxy-4,5,6,6a-tetrahydro-3aH-pyrrolo[3,4-d]isoxazole-4-carboxylic acid, which preferentially inhibits reverse transport (glutamate release) compared with glutamate reuptake
S. ColleoniPrimo
;E. Fumagalli;P. Conti;A. Pinto;M. De Amici;C. De Micheli;
2008
Abstract
(±)-3-Hydroxy-4,5,6,6a-tetrahydro-3aH-pyrrolo [3,4 -d]-isoxazole-4-carboxylic acid (HIP-A) and (±)-3-hydroxy-4,5,6, 6a-tetrahydro-3aH-pyrrolo[3,4-d]isoxazole-6-carboxylic acid (HIP-B) are selective inhibitors of excitatory amino acid transporters (EAATs), as potent as dl-threo-β-benzyloxyaspartic acid (TBOA). We report here that the active isomers are (–)-HIP-A and (+)-HIP-B, being approximately 150- and 10-fold more potent than the corresponding enantiomers as inhibitors of [3H]aspartate uptake in rat brain synaptosomes and hEAAT1–3-expressing cells. Comparable IC50 values were found on the three hEAAT subtypes. (–)-HIP-A maintained the remarkable property, previously reported with the racemates, of inhibiting synaptosomal glutamate-induced [3H]d-aspartate release (reverse transport) at concentrations significantly lower than those inhibiting [3H]l-glutamate uptake. New data suggest that the noncompetitive-like interaction described previously is probably the consequence of an insurmountable, long-lasting impairment of EAAT's function. Some minutes of preincubation are required to induce this impairment, the duration of preincubation having more effect on inhibition of glutamate-induced release than of glutamate uptake. In organotypic rat hippocampal slices and mixed mouse brain cortical cultures, TBOA, but not (–)-HIP-A, had toxic effects. Under ischemic conditions, a neuroprotective effect was found with 10 to 30 μM (–)-HIP-A, but not with 10 to 30 μM TBOA or 100 μM (–)-HIP-A. The effect of (–)-HIP-A suggests that, under ischemia, EAATs mediate both release (reverse transport) and uptake of glutamate. The neuroprotection with the lower (–)-HIP-A concentrations may indicate a selective inhibition of the reverse transport confirming the data obtained in synaptosomes. The selective interference with glutamate-induced glutamate release might offer a new strategy for neuroprotective action.File | Dimensione | Formato | |
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