Stigmasterol can be new steroidal drug for neurological disorders: Evidence of the GABAergic mechanism via receptor modulation

Background: Gamma-aminobutyric acid A (GABA(A)) receptors have been implicated in anxiety and epileptic disorders. Hypothesis/Purpose: This study aimed to investigate the effects of stigmasterol, a plant sterol (phytosterol) isolated from Artemisia indica Linn on neurological disorders. Methods: Stigmasterol was evaluated on various recombinant GABA(A) receptor subtypes expressed in Xenopus laevis oocytes and its anxiolytic and anticonvulsant potential was assessed using the elevated plus maze (EPM), light-dark box (LDB) test, and pentylenetetrazole- (PTZ-) induced seizure paradigms. Furthermore, computational modeling of alpha 2 beta 2 gamma 2L, alpha 4 beta 3 delta, and alpha 4 beta 3 subtypes was performed to gain insights into the GABAergic mechanism of stigmasterol. For the first time, a model of GABAd subtype was generated. Stigmasterol was targeted to all the binding sites (neurotransmitters, positive and negative modulator binding sites) of GABA(A) alpha 2 beta 2 gamma 2L, alpha 4 beta 3, and alpha 4 beta 3 delta complexes by in silico docking. Results: Stigmasterol enhanced GABA-induced currents at ternary alpha 2 beta 2 gamma 2L, alpha 4 beta 3 delta, and binary alpha 4 beta 3 GABAAR subtypes. The potentiation of GABA-induced currents at extrasynaptic alpha 4 beta 3 delta was significantly higher compared to the binary alpha 4 beta 3 subtype, indicating that the d subunit is important for efficacy. Stigmasterol was found to be a potent positive modulator of the extrasynaptic alpha 4 beta 3 delta subtype, which was also confirmed by computational analysis. The computational analysis reveals that stigmasterol preferentially binds at the transmembrane region shared by positive modulators or a binding site constituted by the M2-M3 region of alpha 4 and M1-M2 of beta 3 at alpha 4 beta 3 delta complex. In in vivo studies, Stigmasterol (0.5-3.0 mg/kg, i.p.) exerted significant anxiolytic and anticonvulsant effects in an identical manner of allopregnanolone, indicating the involvement of a GABAergic mechanism. Conclusion: To our knowledge, this is the first study reporting the positive modulation of GABA(A) receptors, anxiolytic and anticonvulsant potential of stigmasterol. Thus, stigmasterol is considered to be a candidate steroidal drug for the treatment of neurological disorders due to its positive modulation of GABA receptors.

Automated summary

The study showed that stigmasterol is a potential candidate for the treatment of neurological disorders by modulating GABA receptors, which can alleviate anxiety and seizure symptoms.