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 gamma-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 mu M, and for effects on I-GABA was 10-50 mu M. Moreover, our compounds accelerated desensitization of the I-Gly with the IC50 values varying from 0.12 to 0.49 mu M and decreased the peak amplitude with IC50 values varying from 16 to 22 mu M. Interestingly, our study revealed that only compounds 4 (epiandrosterone) and 8 (dehydroepiandrosterone) were able to cause a significant change in I-GABA in 10 mu M concentration. Moreover, compounds 3 (testosterone), 5 (epitestosterone), 6 (dihydroandrostenedione), and 9 (etiocholanedione) did not modulate I-GABA up to the concentration of 50 mu M. 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.