Indomethacin/ibuprofen-like anti-inflammatory agents selectively potentiate the gamma-aminobutyric acid-antagonistic effects of several norfloxacin-like quinolone antibacterial agents on [35S]t-butylbicyclophosphorothionate binding.
Four piperazinoquinolone antibacterial drugs (norfloxacin, ciprofloxacin, enoxacin, and pipemidic acid), known to be gamma-aminobutyric acid (GABA) antagonists, fully reversed the inhibitory effect of GABA on [35S]t-butylbicyclophosphorothionate ([35S] TBPS) binding to rat brain membranes in vitro. Twelve indomethacin/ibuprofen-like arylalkanoic acid (AAA) anti-inflammatory drugs alone had no effect on [35S]TBPS binding, or on its inhibition by GABA, but potentiated the GABA-antagonistic effects of the four quinolones. Felbinac (4-biphenylacetic acid) was most potent in this respect (EC50 = 110 nM, together with 5 microM norfloxacin), followed by flurbiprofen > anirolac > metiazinic acid > tolmetin = ketoprofen = fenbufen = indomethacin > fenoprofen > ibuprofen = (+)-naproxen = sulindac. Other anti-inflammatory analgesic drugs, including aspirin, diclofenac, diflunisal, meclofenamic acid, mefenamic acid, nambumetone, phenacetin, piroxicam, and phenylbutazone, failed to potentiate the GABA-antagonistic effect of norfloxacin. Felbinac (1 microM) increased the GABA-antagonistic potencies of norfloxacin and enoxacin about 26-fold, while increasing those of ciprofloxacin and pipemidic acid 7-fold and 2.3-fold, respectively. Using subsaturating concentrations of the four quinolones, concentration-response curves for felbinac yielded EC50 values ranging from 110 nM with 5 microM norfloxacin to 1.3 microM with 100 microM pipemidic acid. Three other piperazinoquinolone antibacterial agents (amifloxacin, difloxacin, and fleroxacin) and four nonpiperazinoquinolone anti-bacterial agents (oxolinic acid, cinoxacin, nalidixic acid, and piromidic acid) were much weaker GABA antagonists and were not significantly potentiated by felbinac. All other known GABAA receptor blockers tested, including R 5135, pitrazepin, bicuculline, SR 95531, strychnine, D-tubocurarine, thebaine, securinine, theophylline, and caffeine, were not potentiated by felbinac. Our results suggest that norfloxacin and related piperazinoquinolones, acting at GABAA receptors, may induce a high affinity binding site for indomethacin/ibuprofen-like anti-inflammatory agents (the AAA site) that, when occupied, reciprocally increases the affinities of the quinolones for GABAA receptors. The AAA binding site may be a new site in the GABAA receptor complex.
Nathan Kline Institute, Orangeburg, New York 10962.
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D042462:4-Quinolones; D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D001643:Bridged Bicyclo Compounds / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic; D004357:Drug Synergism; D005260:Female; D018756:GABA Antagonists; D066298:In Vitro Techniques; D008297:Male; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects*
D042462:4-Quinolones; D000890:Anti-Infective Agents; D000894:Anti-Inflammatory Agents, Non-Steroidal; D001643:Bridged Bicyclo Compounds; D019086:Bridged Bicyclo Compounds, Heterocyclic; D018756:GABA Antagonists; D011963:Receptors, GABA-A; C037476:tert-butylbicyclophosphorothionate