Stimulation of the Production of Prostaglandin E₂ by Ethyl Gallate, a Natural Phenolic Compound Richly Contained in Longan.

Ethyl gallate is a phenolic compound richly contained in Longan. In traditional Chinese medicine, Longan is widely known as a fruit with "hot" properties, with a tendency to promote inflammatory and certain other responses. The mechanism for its proinflammatory as well as health beneficial effects is poorly understood. Based on our earlier observation that certain natural phenolic compounds can serve as reducing cosubstrates for cyclooxygenases (COXs), we sought to test a hypothesis that ethyl gallate may activate the catalytic activity of the COX enzymes. Results from studies using cultured cells and animals show that ethyl gallate can activate the production of prostaglandin E₂, a representative prostaglandin tested in this study. Computational analysis indicates that ethyl gallate can activate the peroxidase active sites of COX-1 and COX-2 by serving as a reducing cosubstrate. The effect of ethyl gallate is abrogated by galangin, which is known to bind to the same peroxidase active sites of COX-1 and COX-2 as a competitive inhibitor. The findings of this study offer support for a novel hypothesis that the proinflammatory as well as health beneficial effects of Longan may partly attributable to the activation of COX-1 and COX-2 by ethyl gallate.