Kinetics and Docking Studies of a COX-2 Inhibitor Isolated from Terminalia bellerica Fruits

Abstract

Triphala is an Ayurvedic herbal formulation consisting of equal parts of three myrobalans: Terminalia chebula, Terminalia bellerica and Emblica officinalis. We recently reported that chebulagic acid (CA) isolated from Terminalia chebula is a potent COX-2/5-LOX dual inhibitor. In this study, compounds isolated from Terminalia bellerica were tested for inhibition against COX and 5-LOX. One of the fractionated compounds showed potent inhibition against COX enzymes with no inhibition against 5-LOX. It was identified as gallic acid (GA) by LC-MS, NMR and IR analyses. We report here the inhibitory effects of GA, with an IC(50) value of 74 nM against COX-2 and 1500 nM for COX-1, showing ≈20 fold preference towards COX-2. Further docking studies revealed that GA binds in the active site of COX-2 at the non-steroidal anti-inflammatory drug (NSAID) binding site. The carboxylate moiety of GA interacts with Arg120 and Glu524. Based on substrate dependent kinetics, GA was found to be a competitive inhibitor of both COX-1 and COX-2, with more affinity towards COX-2. Taken together, our studies indicate that GA is a selective inhibitor of COX-2. Being a small natural product with selective and reversible inhibition of COX-2, GA would form a lead molecule for developing potent anti-inflammatory drug candidates.

Isolation and characterization of gallic acid and methyl gallate from the seed coats of Givotia rottleriformis Griff. and their anti-proliferative effect on human epidermoid carcinoma A431 cells

“…However, these fractions did not show any significant inhibition on 5-LOX enzyme activity. Earlier studies have demonstrated that COXs and LOXs are the key enzymes that play an important role in inflammation and carcinogenesis [10] , [11] , [52] . Only 5 and 6 chromatographed fractions that inhibited the A431 cell proliferation was further subjected to active compound isolation by RP-HPLC.…”

“…The cytotoxic effect of GA and MG was investigated in various cancer cells [11] , [26] , [53] , [54] , [55] . The GA isolated from Terminalia bellerica potentially inhibited COX-1 and COX-2 enzymes in a concentration dependent manner [10] . Similarly, MG also showed dual COX-2/5-LOX inhibitory activity; however, 5-LOX inhibition was based on the leukotriene C 4 [36] .…”

“…The gallic acid is isolated from plants [9] , [10] and the antioxidant and anticancer effect of GA were well reported in most of the cancer cells [9] , [11] , [12] , [13] , [14] , [15] , [16] , [17] . Many of GA derived chemical derivatives were also shown to have good anti-cancer properties [18] .…”

Exploration of binding site pattern in arachidonic acid metabolizing enzymes, Cyclooxygenases and Lipoxygenases

“…There are three COX isoforms, COX-1, COX-2, and COX-3 [ 1 - 3 ]. COX-1, constitutively expressed in most tissues synthesizes PGs at low levels, and is presumed to function primarily in the maintenance of physiological functions [ 4 - 7 ]. The inducible isoform of COX, COX-2 is induced by several and plays a direct role in inflammation, cancer and various other diseases [ 8 , 9 ].…”

COX-2 structural analysis and docking studies with gallic acid structural analogues

“…As part of the search for natural anti-inflammatory agents from medicinal plants, Emblica officinalis extracts showed good medicinal values towards inflammation. Gallic acid (GA) is a naturally occurring polyhydroxyphenolic compound and an excellent free radical scavenger to inhibit COX isoforms (Madlener et al [2007]; Pal et al [2010]; Reddy et al [2010]). Presence of high levels of gallic acid in Emblica officinalis gives a special status and medicinal value for treating inflammatory diseases (Ramakrishna et al [2011]).…”