For many years, it has been recognized that some compounds in several foods have beneficial medicinal effects to health. Among these, flavonoids exhibit various physiological and pharmacological properties such as antioxidative, antibacterial, antimutagenic and anticancer activities. These polyphenolic compounds are found ubiquitously in foods of plant origins.
Green tea is one of the major sources of polyphenol compounds. Because of low toxicity, some of flavonoids are thought to have potential to be developed into a new class of prophylactic or therapeutic agents against various kinds of diseases. This study was performed to investigate the effects of green tea extract and polyphenols on the proliferation and activity of osteoblasts and generation of osteoclasts. Green tea extract increased the proliferation of osteoblasts at relatively low concentration (10-12 - 10-9 M). However, they inhibited the proliferation and viability of osteoblasts at higher concentrations (10-8 - 10-5 M). Green tea extract increased the alkaline phosphatase (ALP) activities of HOS cells. Green tea extract increased ALP activity of ROS17/2.8 cells at lower concentrations, and decreased it at higher concentrations. Green tea extract inhibited the generation of osteoclasts. Polyphenols, such as catechin, epicatechin and epigallocatechin gallate (EGCG), increased the proliferation of osteoblasts at lower concentrations. Epicatechin increased the ALP activities of osteoblasts at lower concentrations. Catechin inhibited the proliferation of HOS cells at higher concentration. However, it stimulated the proliferation of ROS17/2.8 cells. Higher concentrations of EGCG increased the ALP activities of HOS and ROS17 /2.8 cells. Polyphenols when treated with lower concentration, stimulated the generation of osteoclasts. However, catechin and EGCG inhibited the generation of osteoclasts at higher concentrations. Taken together, this result indicates that green tea extract and polyphenols, when used at appropriate concentrations, may stimulate the proliferation and activities of osteoblast, while inhibiting generation of osteoclasts. These compounds could be useful as prophylactic and therapeutic agents for many bone diseases which accompanies massive bone loss.
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