Multiple actions of fenamates and other nonsteroidal anti-inflammatory drugs on GABAA receptors

Abstract

The nonsteroidal anti-inflammatory drug (NSAID) niflumic acid, a fenamate in structure, has many molecular targets, one of them being specific subtypes of the main inhibitory ligand-gated anion channel, the GABA A receptor. Here, we report on the effects of other fenamates and other classes of NSAIDs on brain picrotoxinin-sensitive GABA A receptors, using an autoradiographic assay with [ 35 S]TBPS as a ligand on mouse brain sections. We found that the other fenamates studied (flufenamic acid, meclofenamic acid, mefenamic acid and tolfenamic acid) affected the autoradiographic signal at low micromolar concentrations in a facilitatory-like allosteric fashion, i.e., without having affinity to the [ 35 S]TBPS binding site. Unlike niflumic acid that shows clear preference for inhibiting cerebellar granule cell layer GABA A receptors, the other fenamates showed little brain regional selectivity, indicating that their actions are not receptor-subtype selective. Of the non-fenamate NSAIDs studied at 100 µM concentration, diclofenac induced the greatest inhibition of the binding, which is not surprising as it has close structural similarity with the potent fenamate meclofenamic acid. Using two-electrode voltage-clamp assays on Xenopus oocytes, the effect of niflumic acid was found to be dependent on the β subunit variant and the presence of γ2 subunit in rat recombinant α1β and α1βγ2 GABA A receptors, with the β1 allowing the niflumic acid inhibition and β3 the stimulation of the receptor-mediated currents. In summary, the fenamate NSAIDs constitute an interesting class of compounds that could be used for development of potent GABA A receptor allosteric agonists with other targets to moderate inflammation, pain and associated anxiety/depression.

Tiratricol, a thyroid hormone metabolite, has potent inhibitory activity against human dihydroorotate dehydrogenase

“…Atovaquone is a naphthoquinone‐bearing compound, and has been reported to have inhibitory activity against both human DHODH and rat DHODH, but the IC 50 value for rat DHODH inhibition is much lower than that for human DHODH inhibition (Knecht et al, 2000). Tolfenamic acid, niflumic acid, and mefenamic acid are all fenamate nonsteroidal anti‐inflammatory drugs (NSAIDs) (Mansikkamaki et al, 2019). A number of fenamic acid derivatives have been discovered to have potent hDHODH inhibitory activities through structure‐guided fragment selection and virtual screening (Fritzson et al, 2010; Walse et al, 2008).…”

Antiseizure properties of fenamate NSAIDs determined in mature human stem-cell derived neuroglial circuits

“…To our knowledge, fenamates are unique because they are both anti-inflammatory and highly subunit-selective modulators of GABA A receptors at low micromolar concentrations (Halliwell et al, 1999;Mansikkamäki et al, 2019;Rossokhin et al, 2019). These NSAIDs also cross the blood brain barrier indicating that they have central nervous system actions.…”

“…Work from this lab, for example, first reported that mefenamic acid potentiates GABA A -receptor mediated currents recorded from recombinant human α1β2γ2 receptors expressed in Xenopus oocytes and HEK-293 cells but inhibits GABA currents recorded from α1β1γ2 GABA A receptors in these expressions systems (Halliwell et al, 1999). Similarly, niflumic acid potentiates recombinant rat α1β3γ2 GABA currents recorded from Xenopus oocytes but inhibits α1β1γ2 GABA mediated responses (Mansikkamäki et al, 2019). Point mutation experiments and molecular modeling show that potentiation of GABA A receptors by fenamates occurs via an allosteric site in the transmembrane 2 domain of the β2 and β3 subunits shared with the general anaesthetic, etomidate and the antiseizure agent, loreclezole (Halliwell et al, 1999;Mansikkamäki et al, 2019).…”

“…Fenamate NSAIDs including mefenamic acid, flufenamic acid, tolfenamic acid and niflumic acid, are broad spectrum cyclooxygenase (I and II) inhibitors with antipyretic, antiinflammatory and analgesic properties (Hill and Zawia, 2021). This class of NSAID also uniquely modulates GABA A receptors in a highly subunit-dependent manner (Halliwell et al, 1999;Mansikkamäki et al, 2019). Work from this lab, for example, first reported that mefenamic acid potentiates GABA A -receptor mediated currents recorded from recombinant human α1β2γ2 receptors expressed in Xenopus oocytes and HEK-293 cells but inhibits GABA currents recorded from α1β1γ2 GABA A receptors in these expressions systems (Halliwell et al, 1999).…”

“…Similarly, niflumic acid potentiates recombinant rat α1β3γ2 GABA currents recorded from Xenopus oocytes but inhibits α1β1γ2 GABA mediated responses (Mansikkamäki et al, 2019). Point mutation experiments and molecular modeling show that potentiation of GABA A receptors by fenamates occurs via an allosteric site in the transmembrane 2 domain of the β2 and β3 subunits shared with the general anaesthetic, etomidate and the antiseizure agent, loreclezole (Halliwell et al, 1999;Mansikkamäki et al, 2019).…”