chloride conductance: nootropics and compounds | sci-wiki

Hydroxydione

Hydroxydione is a synthetic pregnane neuroactive steroid that, introduced by Pfizer in 1955 under the trade name Viadril (also Presuren), became the first steroid used as an intravenous general anesthetic. The parent steroid, 21-hydroxy-5-beta-pregnane-3,20-dione, is almost insoluble in water; esterifying its 21-hydroxyl group with succinic acid and forming the sodium salt yields hydroxydione sodium succinate, a water-soluble prodrug that plasma esterases (enzymes that cleave ester bonds) hydrolyze in vivo to release the active steroid. Like later neurosteroid anesthetics such as alfaxalone, it produces hypnosis by acting as a positive allosteric modulator of the GABA-A receptor (the brain's principal inhibitory chloride ion channel), without meaningful analgesic or classical hormonal activity. Although valued for a wide margin of cardiovascular and respiratory safety, its very slow onset and a high incidence of injection-site thrombophlebitis (painful inflammation and clotting of the vein) led to its abandonment, yet it remains historically pivotal as the origin of the entire field of steroid anesthesia.

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Anesthetic

Minaxolone

Minaxolone is a synthetic water-soluble aminosteroid (a steroid carrying a basic amino group) developed by Glaxo in the late 1970s as an intravenous general anaesthetic and a successor to Althesin. Structurally it is a 2-beta-ethoxy, 11-alpha-(dimethylamino) derivative of the neuroactive pregnane skeleton, and it acts as a potent positive allosteric modulator at the neurosteroid recognition site of the GABA-A receptor (the brain's principal inhibitory chloride ion channel), enhancing inhibitory conductance to produce hypnosis and surgical anaesthesia. Its basic amino group conferred solubility in water, avoiding the Cremophor EL vehicle (a polyethoxylated castor oil solubiliser) that made earlier lipophilic steroid anaesthetics prone to anaphylactoid reactions. After clinical trials conducted between roughly 1979 and 1982, its development was halted over toxicity and genotoxicity concerns arising in long-term rodent studies, and it was never marketed.

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Neurosteroid

SAGE-324

SAGE-324 (also designated BIIB124) is an investigational, orally bioavailable synthetic neuroactive steroid that acts as a positive allosteric modulator (a compound that amplifies a receptor's response to its natural signal) of GABA-A receptors (the brain's principal inhibitory chloride ion channels). Developed on the Sage Therapeutics neuroactive-steroid platform and co-developed with Biogen, it is a next-generation analog engineered for a long duration of action suitable for once-daily oral dosing, distinguishing it from the intravenous and short-acting neurosteroids that preceded it. Its lead clinical indication is essential tremor (a common movement disorder marked by rhythmic shaking of the hands and arms), where the randomized Phase 2 KINETIC trial met its primary endpoint; it has also been explored in the context of epilepsy. As a synthetic congener within the same chemical lineage as brexanolone and zuranolone, SAGE-324 represents an effort to translate the potent inhibitory pharmacology of endogenous neurosteroids into a chronically dosable oral therapeutic.

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