green tea polyphenols novel and potent inhibitors of squalene epoxidase the green tea gallocatechins epigallocatechin3ogallate egcg ic50 069 microm gallocatechin3ogallate gcg ic50 067 microm epicatechin3ogallate ecg ic50 13 microm and theasinensin a ic50 013 microm were found to be potent and selective inhibitors of rat squalene epoxidase se a ratelimiting enzyme of cholesterol biogenesis on the other hand flavan3ols without galloyl group at c3 did not show significant enzyme inhibition it was demonstrated for the first time that the cholesterol lowering effect of green tea may be attributed to their potent se inhibition activities inhibition kinetics revealed that egcg inhibited se in noncompetitive ki 074 microm and nontimedependent manner the potent enzyme inhibition would be caused by specific binding to the enzyme and by scavenging reactive oxygen species required for the monooxygenase reaction