Parishin A reduces hepatic encephalopathy via gut microbiota increasing the activity of intestinal EAAT3 to reduce blood ammonia

Hepatic encephalopathy (HE) is a neuropsychiatric disorder associated with liver dysfunction. Increasing evidence suggests that the gut microbiota plays a critical role in its pathogenesis, yet effective treatment options remain limited. Parishin A (PA), a natural phenolic compound isolated from Gastrodia elata, exhibits promising neuroprotective effects and is currently in Phase II clinical trials. This study firstly reveals the therapeutic potential of PA in ameliorating HE via a gut microbiota-mediated mechanism. PA is specifically metabolized by gut microbiota into M1 (1,2-Di-O-[4-(β-D-glucopyranosyloxy) benzyl] citrate), M2 (1-O-[4-(β-D-glucopyranosyloxy) benzyl] citrate) and M3 (4-(β-D-glucopyranosyloxy) benzyl alcohol), of which M2 and M3 are active. PA enriches Clostridium butyricum and Bifidobacterium longum, stimulating gut-derived glutamate (Glu) production and accelerating its entry into the portal circulation through upregulation of Excitatory amino acid transporter 3 (EAAT3), thus facilitating hepatic uptake. Meanwhile, PA enhances hepatic glutamine synthetase (GS) activity, catalyzing free ammonia by converting Glu to Gln, thereby reducing serum ammonia. M2 and M3 similarly upregulate the expression of intestinal EAAT3 and hepatic GS. Additionally, PA and its metabolites improve intestinal barrier by promoting the production of beneficial short chain fatty acids (SCFAs), indirectly decreasing serum ammonia. Consequently, ammonia entry into the brain across the blood-brain barrier is limited, ameliorating HE. The efficacy and underlying mechanism of PA are further validated by oral administration of Clostridium butyricum, Bifidobacterium longum and their combination. This is the first study on pharmacological activity and complex mechanism of natural drugs mediated by multiple bacterial species, which provides insight to investigate analogous natural products.