Investigation of the mechanism of enhanced effect of EGCG on huperzine A's inhibition of acetylcholinesterase activity in rats by a multispectroscopic method.

The mechanism of enhanced effect of (-)-epigallocatechin-3-gallate (EGCG) on huperzine A's (HUP) inhibition of acetylcholinesterase (AChE) activity in rats was investigated. The inhibitory effects of HUP at 10 and 5 microg/kg on AChE activity were quite weak in the whole phase. In contrast, upon addition of EGCG (100 mg/kg) to the HUP 10 and 5 microg/kg groups, remarkably enhanced inhibitory effects with maximum inhibitory percentages of 90.94 and 88.13% were observed under the same conditions. EGCG also can greatly prolong the inhibitory time. The mechanism of the enhanced effects of EGCG on HUP's inhibition of AChE activity was investigated by steady fluorescence spectroscopy, infrared spectroscopy, and ultraviolet spectroscopy. HUP hardly interacted with the main transport protein, whereas there was a very strong binding interaction between EGCG and bovine serum albumin. The enhanced transport of HUP is a possible cause of the enhanced effect of EGCG on HUP bioactivity.