7. Conclusions

Many pharmacokinetics studies of green tea catechins were conducted on rodents and less studies in rabbits, dogs, or human. Most of them are oral administration studies. Although the plasma levels of total catechins are at submicromolar level, which is below the effective dose in many in vitro studies, tissue dispositions could be much higher. Ungallated catechins are mainly metabolized by phase II process in the small intestine and liver to form glucuronide/ sulfate conjugates in the plasma and urine while gallated catechins mostly remain intact in the plasma and are excreted through bile and metabolized by microflora in the colon. High levels of small metabolized phenolic acids can be reabsorbed into blood stream that may contribute to the in vivo biological effects.

Catechins can be widely distributed into various tissues including lung, eye, brain, gastrointestinal tract, kidney, bladder, and even passing through the placenta to the fetal organs. The disposition can be stereo-specific, and affected by food, drug, and catechins themselves indicating the absorption and distribution may involve some sort of transporters mechanisms. Before applying green tea catechins for therapeutic purpose, it is essential to understand their pharmacokinetics behavior and metabolites profiles not only in the plasma but also in various tissues in animals and in humans.
