Anti-inflammatory and antioxidant potential of Guaianolide isolated from Cyathocline purpurea: Role of COX-2 inhibition.

Background: Inflammation activated by oxidative stress can cause various diseases, such as asthma, rheumatoid arthritis, cancer, diabetes, etc. Plant constituents with sesquiterpene lactones possess antioxidant and anti-inflammatory properties.

Aim: To determine the antioxidant and anti-inflammatory potential of isolated phytoconstituent from Cyathocline purpurea Buch-Ham ex D (CP). Don in laboratory animals. Furthermore, to understand the interactions involved in the binding of this compound to cyclooxygenase-2 (COX-2) via computational docking.

Methods: Phytoconstituent was isolated, purified and well characterized (using IR, NMR, and MS) from ethyl acetate fraction of CP methanolic extract. It was then evaluated for its in-vitro antioxidant activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydrogen peroxide (HO) and hydroxyl (OH) radical assays as well as in-vivo anti-inflammatory potential against carrageenan-induced paw edema model in rats. The molecular docking study was performed against the crystal structure of COX-2 to evaluate the binding potential of phytoconstituent towards this enzyme.

Results: The isolated compound 6α-hydroxy-4 [14], 10 [15]-guainadien-8α, 12-olide (HGN) showed significant (p<0.001) antioxidant activity with IC values of 76μg/mL. Administration of HGN (10 and 20mg/kg) significantly (p<0.001) reduced the increased paw volume after subplantar administration of carrageenan. It also exhibits good binding affinity towards with COX-2 with a docking score of -8.98 and Glide binding energy of -36.488kcal/mol shedding light on the potential mechanism of anti-inflammatory action.

Conclusions: The presence of hydroxyl group in HGN provides a credential to its in-vivo anti-inflammatory and in-vitro antioxidant activities. Furthermore, the good binding affinity of HGN for the active site of COX-2 may open novel vistas in therapeutic option with natural antioxidants like Cyathocline purpurea to treat various inflammatory disorders.