Neurosteroids as Selective Inhibitors of Glycine Receptor Activity: Structure-Activity Relationship Study on Endogenous Androstanes and Androstenes.

Julia V Bukanova,Elena I Solntseva,Eva Kudova

doi:10.3389/fnmol.2020.00044

Abstract

The ability of androstane and androstene neurosteroids with modifications at C-17, C-5, and C-3 (compounds 1-9) to influence the functional activity of inhibitory glycine and γ-aminobutyric acid (GABA) receptors was estimated. The glycine- and GABA-induced chloride current (IGly and IGABA) were measured in isolated pyramidal neurons of the rat hippocampus and isolated rat cerebellar Purkinje cells, correspondingly, using the patch-clamp technique. Our results demonstrate that all the nine neurosteroids display similar biological activity, namely, they strongly inhibited IGly and weakly inhibited IGABA. The threshold concentration of neurosteroids inducing effects on IGly was 0.1 μM, and for effects on IGABA was 10–50 μM. Moreover, our compounds accelerated desensitization of the IGly with the IC50 values varying from 0.12 to 0.49 μM and decreased the peak amplitude with IC50 values varying from 16 to 22 μM. Interestingly, our study revealed that only compounds 4 (epiandrosterone) and 8 (dehydroepiandrosterone) were able to cause a significant change in IGABA in 10 μM concentration. Moreover, compounds 3 (testosterone), 5 (epitestosterone), 6 (dihydroandrostenedione), and 9 (etiocholanedione) did not modulate IGABA up to the concentration of 50 μM. Thus, we conclude that compounds 3, 5, 6, and 9 may be identified as selective modulators of IGly. Our results offer new avenues of investigation in the field of drug-like selective modulators of IGly.

Highlights

Γ-Aminobutyric acid receptors type A and glycine receptor (GABAAR and GlyR) channels are the major inhibitory ligand-gated ion channels of the central nervous system which mediate both fast synaptic and tonic extrasynaptic inhibition (Lynch, 2009; Ziegler et al, 2009; Yevenes and Zeilhofer, 2011)
The IGly is larger in amplitude and more stable on hippocampal cells, and, the IGABA is more convenient to study on Purkinje cells, since glycine and γ-aminobutyric acid (GABA) receptors on Purkinje cells are more homogeneous (Kelley et al, 2013)
Our experiments demonstrate that neuronal GlyRs are highly sensitive, whilst neuronal GABAARs are weakly sensitive to tested compounds 1-9

Summary

Introduction

Γ-Aminobutyric acid receptors type A and glycine receptor (GABAAR and GlyR) channels are the major inhibitory ligand-gated ion channels of the central nervous system which mediate both fast synaptic and tonic extrasynaptic inhibition (Lynch, 2009; Ziegler et al, 2009; Yevenes and Zeilhofer, 2011). PROG is metabolized to 5α- or 5β-dihydroprogesterone, followed by their reduction to 3α-hydroxy-5α-pregnan-20-one (allopregnanolone) or 3α-hydroxy-5β-pregnan-20-one (pregnanolone) These compounds and their synthetic analogs are mainly known as potent modulators of GABAARs (Chen et al, 2019) and N-methyl-D-aspartate receptors (NMDARs) (Burnell et al, 2019), respectively. NS and NAS are effective modulators of GABAAR-induced chloride current (IGABA) and their modulatory action is dependent on their structure and subtype (for a review, see: Majewska et al, 1988; Wu et al, 1990; Belelli and Lambert, 2005; Korinek et al, 2011; King, 2013; Zorumski et al, 2013) Those that potentiate GABA activity are termed as “potentiating NS” and these include, e.g., allopregnanolone (3α-hydroxy-5α-pregnan-20-one) or pregnanolone (3α-hydroxy-5β-pregnan-20-one) (Park-Chung et al, 1999). The biological potential of androstane and androstene skeletons (Figure 1F) concerning their effect on GlyR remains unknown

Methods

Results

Conclusion