Anti-inflammatory Effect of Picrorhiza kurroa in Experimental Models of Inflammation

Picrorhiza kurroa is an important medicinal plant in the Ayurvedic system of medicine. The root and rhizome of this plant are used for the treatment of various liver and inflammatory conditions. In the present study, we sought to investigate the anti-inflammatory activity of P. kurroa rhizome extract against carrageenan-induced paw edema and cotton pellet implantation-induced granuloma formation in rats. In addition, its immunomodulatory activity was evaluated in Complete Freund's Adjuvant-induced stimulation of a peritoneal macrophage model and lipopolysaccharide-stimulated RAW 264.7 murine macrophages. Pretreatment with P. kurroa rhizome extract inhibited carrageenan-induced paw edema and cotton pellet-induced granuloma formation in a dose-dependent manner. This was associated with reduced levels of inflammatory cytokines (TNF-α, IL-1β, IL-6) accompanied with increased anti-inflammatory cytokine (IL-10) in the serum and peritoneal macrophages. Additionally, P. kurroa rhizome extract inhibited inflammatory TNF-receptor 1 and cyclooxygenase-2 in Complete Freund's Adjuvant-induced activated peritoneal macrophages. Furthermore, P. kurroa rhizome extract treatment significantly inhibited iNOS and suppressed the activation of NF-κB through inhibition of its phosphorylation and by blocking the activation of IκB kinase alpha in lipopolysaccharide-stimulated RAW264.7 macrophages. Taken together, these results suggest that P. kurroa has anti-inflammatory activity that is mediated through the suppression of macrophage-derived cytokine and mediators via suppression of NF-κB signaling.