Epigallocatechin gallate preserves endothelial function by reducing the endogenous nitric oxide synthase inhibitor level

Abstract

Asymmetric dimethylarginine (ADMA), the endogenous nitric oxide synthase inhibitor, is thought to be a key factor contributing to endothelial dysfunction. Tea catechins can cause an endothelium-dependent vasorelaxation. The present study examined the effect of epigallocatechin gallate (EGCG), the major component of tea catechins, on endothelial dysfunction induced by native low density lipoprotein (LDL) in rats and oxidized LDL (ox-LDL) in cultured endothelial cells, and whether the protective effect of EGCG is related to reduction of ADMA level. A single injection of LDL (4 mg x kg(-1), i.v.) markedly reduced endothelium-dependent relaxation and the serum nitrite/nitrate (NO) level, and increased serum concentrations of ADMA, malondialdehyde (MDA), and tumor necrosis factor-alpha (TNF-alpha). EGCG (10 or 50 mg x kg(-1), i.p.) significantly attenuated the inhibition of vasodilator response to acetylcholine and the decreased serum nitrite/nitrate level, and reduced the elevated levels of ADMA, MDA, and TNF-alpha. Exposure of endothelial cells to ox-LDL (100 microg x mL(-1)) for 24 h markedly increased the medium levels of lactate dehydrogenase (LDH), ADMA, TNF-alpha, and MDA, and decreased the level of nitrite/nitrate in the medium and the activity of dimethylarginine dimethylaminohydrolase (DDAH) in the endothelial cells. EGCG (10 and 100 microg x mL(-1)) significantly decreased the levels of LDH, ADMA, TNF-alpha, and MDA, and increased the level of nitrite/nitrate and the activity of DDAH. These results suggest that EGCG protects endothelial dysfunction induced by native LDL in vivo or by ox-LDL in endothelial cells, and the protective effect of EGCG on the endothelium is related to decrease in ADMA level via increasing of DDAH activity.