Evaluation of anti-inflammatory and immunomodulatory effects of Premna integrifolia extracts and assay-guided isolation of a COX-2/5-LOX dual inhibitor

Abstract

Premna integrifolia (Agnimantha brihat) is a traditional medicinal plant with a prominent place in Ayurveda, Siddha and Unani systems of medicine. In this study we have evaluated the anti-inflammatory and immunomodulatory properties of the Premna integrifolia root extracts employing cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), and 5-lipoxygenase (5-LOX) enzyme-based assays, lymphocyte proliferation assay, pro-and anti-inflammatory cytokines measurement. Petroleum ether extract (PEE) of Premna integrifolia showed potent inhibition of COX-2 and 5-LOX with IC₅₀ values of 6.15 μg/mL and 11.33 μg/mL respectively. In in vitro studies on RAW 264.7 cell line, PEE showed inhibition in the formation of nitric oxide (NO), pro-inflammatory cytokines (IL-1β, IL-6), prostaglandin E₂ (PGE₂) production, induction of anti-inflammatory cytokine (IL-2) and down-regulation of expression of COX-2, 5-LOX, TNF-α, IL-1β and iNOS. PEE also significantly reduced carrageenan-induced paw edema in mouse model of inflammation. Further, attempts in isolating the active principle(s) involved in these anti-inflammatory effects of PEE by separation on RP-HPLC resulted in the isolation of four active peaks, H1, H2, H3 and H5, inhibiting COX-1, COX-2 and 5-LOX, out of which H3 was identified as 6- hydroxy salvinolone (6-HS). Present findings reveal that PEE of roots of Premna integrifolia exhibits potent anti-inflammatory and immunomodulatory activities, which could form a potential source for development of anti-inflammatory drugs. 6-HS, a COX-2/5-LOX dual inhibitor along with other lead molecules isolated from PEE of Premna integrifolia may form lead molecules for the development of COX-LOX dual inhibitors.

Keywords: 5-Lipoxygenase; Ayurveda; Cyclooxygenase; Immunomodulation; Inflammation; Premna integrifolia.