Modulation of TNF-α, IL-1β and myeloperoxidase contributes to the anti-inflammatory and analgesic effects of Paullinia pinnata Linn (Sapindaceae) extracts in complete Freund's adjuvant-induced mono-arthritis in rats

Ethnopharmacological relevance: Paullinia pinnata Linn (Sapindaceae) is used in Cameroonian ethnomedicine for the treatment of arthritis. Its leafy aqueous (AEPP) and methanol (MEPP) extracts have shown potent preventive effects in mono-arthritis but their curative effects and their mechanism of action remain unknown. Aim: This work evaluates the effects of AEPP and MEPP on Complete Freund's Adjuvant (CFA)-induced septic mono-arthritis (SM-A) and their mechanism of action. Materials and methods: SM-A was induced by intra-ankle injection of CFA (50 μl) in both male and female rats. On day 8 after, rats were administered orally with AEPP and MEPP (100 and 200 mg/kg/day) for 14 days. Methotrexate (250 μg/kg/day) was used as reference drug. Hyperalgesia and inflammation were monitored after a single (acute) or during the 14 days repeated (chronic) treatment. Thereafter, plasma samples were collected for TNF-α and IL-1β assays, and the synovial liquid of the injected ankle for myeloperoxidase (MPO) quantification. The in vitro analgesic potential of MEPP was evaluated on human induced pluripotent stem cell (hiPSC)-derived sensory neurons using a MEA system or via calcium imaging in mouse dorsal root ganglion neurons (DRGs), while its cytotoxicity was assayed in HEK-293 cells. The phytochemical investigations of MEPP were performed using high resolution MS/MS molecular networking. Results: Both single and repeated administration of AEPP or MEPP significantly reduced hyperalgesia (p < 0.001) and oedema induced by CFA, with up to 97.8% inhibition of pain and complete resorption of inflammation. AEPP and MEPP at the dose of 100 mg/kg/day, significantly (p < 0.01) inhibited plasma TNF-α by 51.5% while all the doses significantly (p < 0.001) reduced IL-1β by up to 88% and MPO by 90%. MEPP did not induce any detectable cytotoxicity in HEK-293 cells, significantly reduced neuronal firing (p < 0.05 to p < 0.0001) in hiPSC neurons, but the intracellular calcium concentration in mouse DRGs actually increased with higher doses of MEPP extract application. LC-MS/MS analysis identified 8 known compounds from the MEPP. Conclusion: These results show that P. pinnata's leaves possess restorative effects against CFA-induced SM-A. The inhibition of TNF-α, IL-1β and the reduction of inflammatory cells infiltration may contribute to these activities, together with the inhibition of cell firing. It remains unclear why MEPP increases calcium influx in mouse DRGs while reducing firing in human cells and reducing indices of pain in rats.