9-Hydroxy-8-oxypalmatine, a novel liver-mediated oxymetabolite of palmatine, alleviates hyperuricemia and kidney inflammation in hyperuricemic mice.

Ethnopharmacological Relevance: Palmatine is a main bioactive alkaloid of Cortex Phellodendri, which has been commonly prescribed for the treatment of hyperuricemia (HUA) in China. The metabolites of palmatine were crucial to its prominent biological activity. 9-Hydroxy-8-oxypalmatine (9-OPAL) is a novel liver-mediated secondary oxymetabolite of palmatine.

Aim Of The Study: The current study was to assess the efficacy of 9-OPAL, a novel liver-mediated secondary oxymetabolite of palmatine derived from Cortex Phellodendri, in experimental HUA mouse model and further explore its underlying mechanism.

Materials And Methods: An in vitro metabolic experiment with oxypalmatine was carried out using liver samples. We separated and identified a novel liver metabolite, and investigated its anti-HUA effect in mice. HUA mice were induced by potassium oxonate and hypoxanthine daily for one week. After 1 h of modeling, mice were orally administered with different doses of 9-OPAL (5, 10 and 20 mg/kg). The pathological changes of the kidneys were evaluated using hematoxylin-eosin staining (H&E). The acute toxicity of 9-OPAL was assessed. The effects of 9-OPAL on serum levels of uric acid (UA), adenosine deaminase (ADA), xanthine oxidase (XOD), creatinine (CRE), blood urea nitrogen (BUN) and inflammatory cytokines were measured by enzyme-linked immunosorbent assay (ELISA) or biochemical method. Furthermore, Western blot, quantitative real-time PCR (qRT-PCR) and molecular docking were used to investigate the effect of 9-OPAL on the expression of renal urate transporters and NLRP3 signaling pathway in HUA mice.

Results: 9-OPAL had been discovered to be a novel liver-mediated oxymetabolite of palmatine for the first time. Treatment with 9-OPAL significantly reduced the UA, CRE as well as BUN levels, and also effectively attenuated abnormal renal histopathological deterioration with favorable safety profile. Besides, 9-OPAL significantly decreased the serum and hepatic activities of XOD and ADA, dramatically inhibited the up-regulation of UA transporter protein 1 (URAT1) and glucose transporter protein 9 (GLUT9), and reversed the down-regulation of organic anion transporter protein 1 (OAT1). Additionally, 9-OPAL effectively mitigated the renal inflammatory markers (TNF-α, IL-1β, IL-6 and IL-18), and downregulated the transcriptional and translational expressions of renal Nod-like receptor family pyrin domain containing 3 (NLRP3), caspase-1, apoptosis-associated speck-like (ASC) and IL-1β in HUA mice. Molecular docking results revealed 9-OPAL bound firmly with XOD, OAT1, GLUT9, URAT1, NLRP3, caspase-1, ASC and IL-1β.

Conclusions: 9-OPAL was found to be a novel liver-mediated secondary metabolite of palmatine with favorable safety profile. 9-OPAL had eminent anti-hyperuricemic and renal-protective effects, and the mechanisms might be intimately associated with repressing XOD activities, modulating renal urate transporter expression and suppressing the NLRP3 inflammasome activation. Our investigation might also provide further experimental evidence for the traditional application of Cortex Phellodendri in the treatment of HUA.