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

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 (I(Gly) and I(GABA)) 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 I(Gly) and weakly inhibited I(GABA). The threshold concentration of neurosteroids inducing effects on I(Gly) was 0.1 μM, and for effects on I(GABA) was 10–50 μM. Moreover, our compounds accelerated desensitization of the I(Gly) with the IC(50) values varying from 0.12 to 0.49 μM and decreased the peak amplitude with IC(50) 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 I(GABA) in 10 μM concentration. Moreover, compounds 3 (testosterone), 5 (epitestosterone), 6 (dihydroandrostenedione), and 9 (etiocholanedione) did not modulate I(GABA) up to the concentration of 50 μM. Thus, we conclude that compounds 3, 5, 6, and 9 may be identified as selective modulators of I(Gly). Our results offer new avenues of investigation in the field of drug-like selective modulators of I(Gly).