NAC (N-Acetyl Cysteine)vsPolygala Tenuifolia

NAC provides cysteine, the rate-limiting substrate for glutathione (GSH) synthesis via gamma-glutamylcysteine ligase (GCLC) and glutathione synthetase (GSS). GSH is the primary intracellular antioxidant, essential for GPx and GST-mediated detoxification of reactive oxygen species in neurons. NAC also modulates glutamate via the cystine-glutamate antiporter (System Xc-, composed of xCT and 4F2hc) — NAC is deacetylated to cysteine, which exchanges for glutamate; the increased extracellular cystine is reduced to cysteine intracellularly, while the exchange increases extrasynaptic glutamate, which activates inhibitory mGlu2/3 autoreceptors on presynaptic terminals, reducing excessive glutamatergic signaling and compulsive behaviors. This glutamate modulation is the basis for psychiatric applications (OCD, addiction). NAC may also directly modulate NMDA receptors via redox sites.

The saponins (tenuigenin, polygalasaponins, onjisaponins) and oligosaccharide esters (3,6'-disinapoyl sucrose, tenuifolisides) have multiple neurological actions. They inhibit acetylcholinesterase (AChE) at the catalytic site, increasing synaptic acetylcholine and enhancing muscarinic M1/M4 and nicotinic receptor signaling. They promote BDNF and NGF expression via CREB and ERK/MAPK pathways, supporting neuroplasticity and neurogenesis in the hippocampus and subventricular zone. They modulate NMDA receptor function (possibly as positive allosteric modulators at the glycine site) and enhance long-term potentiation (LTP) via CaMKII and PKC. The anti-depressant effects involve monoaminergic modulation — increasing dopamine and norepinephrine via MAO inhibition or reuptake modulation — and HPA axis regulation (reducing CRH and cortisol). Tenuigenin may also activate TrkB receptors directly.