Correlation between anticonvulsant activity and inhibitory action on glial gamma-aminobutyric acid uptake of the highly selective mouse gamma-aminobutyric acid transporter 1 inhibitor 3-hydroxy-4-amino-4,5,6,7-tetrahydro-1,2-benzisoxazole and its N-alkylated analogs.
The inhibitory effect of 3-hydroxy-4-amino-4,5,6,7-tetrahydro-1,2-benzisoxazole (exo-THPO) and its N-methylated (N-methyl-exo-THPO) and N-ethylated (N-ethyl-exo-THPO) analogs, derived from gamma-aminobutyric acid (GABA) and 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) on GABA transport was investigated using cultured neocortical neurons (GABA-ergic) and astrocytes and cloned mouse GABA transporters GAT1-4 expressed in human embryonic kidney (HEK) 293 cells. Anticonvulsant activity was assessed after i.c.v. administration to Frings audiogenic seizure-susceptible mice. Anticonvulsant activity of the O-pivaloyloxymethyl prodrug of N-methyl-exo-THPO was assessed after i.p. administration. Results from these studies were compared with those obtained from similar studies with the novel anticonvulsant drug tiagabine, which acts via inhibition of GABA transport. exo-THPO and its N-alkyl analogs inhibited neuronal, astrocytic, and GAT1-mediated GABA transport but not GABA uptake mediated by GAT2-4. N-Methyl-exo-THPO was 8-fold more potent as an inhibitor of astrocytic versus neuronal GABA uptake. The IC(50) value for inhibition of GABA uptake by GAT1 closely reflected its IC(50) value for inhibition of neuronal uptake. Tiagabine was approximately 1000-fold more potent than exo-THPO and its alkyl derivatives as an inhibitor of GABA uptake in cultured neural cells and GAT1-expressing HEK 293 cells. exo-THPO, its alkylated analogs, and tiagabine displayed a time- and dose-dependent inhibition of audiogenic seizures after i.c.v. administration. N-Methyl-exo-THPO was the most potent anticonvulsant among the exo-THPO compounds tested and only slightly less potent than tiagabine. The findings suggest a correlation between anticonvulsant efficacy and selective inhibition of astroglial GABA uptake. Furthermore, results obtained with the N-methyl-exo-THPO prodrug demonstrate the feasibility of developing a glial-selective GABA uptake inhibitor with systemic bioavailability.
Anticonvulsant Screening Project, Department of Pharmacology and Toxicology, University of Utah, 20 S. 2030 E, Room 408, Salt Lake City, UT 84112, USA. swhite@hsc.utah.edu
H Steve
HS
White
Alan
A
Sarup
Tina
T
Bolvig
Anders S
AS
Kristensen
Gitte
G
Petersen
Nathan
N
Nelson
Darryl S
DS
Pickering
Orla M
OM
Larsson
Bente
B
Frølund
Povl
P
Krogsgaard-Larsen
Arne
A
Schousboe
D000478:Alkylation; D000818:Animals; D000831:Animals, Newborn; D000927:Anticonvulsants / Q000494:pharmacology*; D001253:Astrocytes / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D050485:GABA Plasma Membrane Transport Proteins; D007555:Isoxazoles / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D026901:Membrane Transport Proteins; D051379:Mice; D008815:Mice, Inbred Strains; D009457:Neuroglia / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D027361:Organic Anion Transporters; D017397:Prefrontal Cortex / Q000166:cytology / Q000502:physiology; D013329:Structure-Activity Relationship; D005680:gamma-Aminobutyric Acid / Q000493:pharmacokinetics*
D000927:Anticonvulsants; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D007555:Isoxazoles; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; C493413:SLC6A1 protein, human; C493414:Slc6a1 protein, mouse; C490439:Slc6a12 protein, mouse; C026804:4,5,6,7-tetrahydroisoxazolo(4,5-c)pyridin-3-ol; D005680:gamma-Aminobutyric Acid