Evidence for effective structure-based neuromodulatory effects of new analogues of neurosteroid allopregnanolone

The neurosteroid allopregnanolone (AP) modulates neuroendocrine/neurobiological processes, including hypothalamic-pituitary-adrenocortical activities, pain, anxiety, neurogenesis and neuroprotection. These observations raised the hope of developing AP-based therapies against neuroendocrine and/or neurodegenerative disorders. However, the pleiotropic actions of AP, particularly its cell-proliferation-promoting effects, hamper the development of selective/targeted therapies. For example, although AP-induced neurogenesis may serve to compensate neuronal loss in degenerative brains, AP-evoked cell-proliferation is contraindicated for steroid-sensitive cancer patients. To foster progress, we synthesised 4 novel AP analogues of neurosteroids (ANS) designated BR053 (12-oxo-epi-AP), BR297 (O-allyl-epi-AP), BR351 (O-allyl-AP) and BR338 (12-oxo-AP). First, because AP is well-known as allosteric modulator of GABAA receptors (GABAA-R), we used the electrophysiological patch-clamp technique to determine the structure-activity relationship of our ANS on GABAA-activated current in NCB20 cells expressing functional GABAA-R. We found that the addition of 12-oxo-group did not significantly change the respective positive or negative allosteric effects of 3α-AP or 3β-(epi)-AP analogues. Importantly, substitution of the 3α-hydroxyl-group by 3α-O-allyl highly modified the ANS activities. Unlike AP, BR351 induced a long-lasting desensitisation/inhibition of GABAA-R. Interestingly, replacement of the 3β-hydroxyl by 3β-O-allyl (BR297) completely reversed the activity from negative to positive allosteric action. In a second step, we compared the actions of AP and ANS on SH-SY5Y neuronal cell viability/proliferation using MTT-reduction assays. Different dose-response curves were demonstrated for AP and the ANS. By contrast to AP, BR297 was totally devoid of cell-proliferative effect. Finally, we compared AP and ANS abilities to protect against oxidative stress-induced neuronal death pivotally involved in neurodegenerative diseases. Both BR351 and BR297 had notable advantages over AP in protecting SH-SY5Y cells against oxidative stress-induced death. Thus, BR297 appears to be a potent neuroprotective compound devoid of cell-proliferative activity. Altogether, our results suggest promising perspectives for the development of neurosteroid-based selective and effective strategies against neuroendocrine and/or neurodegenerative disorders.