Effects of green tea catechins on membrane fluidity.

Catechins originating from green tea have been used in plaque inhibition for caries prevention and treatment for liver damage because of their antibacterial activity against cariogenic bacteria and protective activity on hepatic cells. The effects of catechins on membrane fluidity were studied by a fluorescence polarization method using liposomes prepared with dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine to assess their pharmacological mechanism at micromol/l levels found in human body fluids after clinical application. All eight catechins tested, ranging from 1 to 1,000 micromol/l, significantly reduced membrane fluidity in both hydrophilic and hydrophobic regions of lipid bilayers. Catechin gallate esters were superior in fluidity reduction to the corresponding nonesters. The fluidity-reducing degree was different between the cis and trans forms, suggesting the stereospecific activity of catechins. A reference antiplaque agent, chlorhexidine, similarly reduced membrane fluidity at the antibacterial concentration. (+)-Catechin (250 micromol/l) and (-)-epigallocatechin gallate (2.5 micromol/l) significantly prevented the membrane fluidization induced by hepatotoxic chloroform. These results indicate that the reduction in membrane fluidity is responsible for the antiplaque and hepatoprotective effects of green tea catechins.