兒茶素(-) epigallocatechin-3 gallate (EGCG) 的骨生成效果

Abstract

As life expectancies increase, osteoporosis remains the most common bone disease among humans, and it represents a major public health problem. Osteoporosis is defined as a skeletal disorder characterized by low bone mass and microarchitectural deterioration of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk. It is estimated to affect at least 25% of postmenopausal white women in the western world, or approximately 15 to 20 million American women. Nearly 1.3 million fractures in the United States are attributable to osteoporosis. Direct financial expenditures for treatment of these osteoporotic fractures are estimated at $10 billion to $15 billion annually. The 2005-2008 National Nutrition Survey in Taiwan also reported that for men and women over the age of 50, osteoporosis prevalence was 23.9% and 38.3%, respectively. The hip fracture rate (299/100,000 standardized for the world population in 2010) in Taiwan was among the highest worldwide reported by a recent systematic review. In Taiwan, the mortality rate of hip fractures in the elderly within the first year for women and men is about 15% and 22%, respectively, with the main cause of death being bedridden related infection. In addition the average medical costs of fracture per case are more than NT $100,000 (roughly US$ 3,300) for the acute care and may consume a significant amount of family and social resources. Accordingly, to search the ordinary foods that enhance osteogenesis is an important issue for the orthopedic investigators. Green tea is one of the most popular beverages in the world. The major catechins in green tea are (-)-epicatechin (EC), (-)-epicatechin gallate (EGC), (-)-epigallocatechin (EGC) and (-)-epigalloncatechin-3-gallate (EGCG). EGCG is the most widely-found catechin and has received by far the most attention. Recent studies have verified the beneficial effect of catechins in decreasing serum lipids, reducing blood pressure, and modulating immune responses and for use as antitumorigenic and antibacterial agents. Polyphenolic catechins, comprising an important extract of green tea, have been applied in the treatment of cancer, cardiovascular disease, dermatological problems, dental caries and even memory loss. Many of the benefits of green tea depend on its antioxidant and free radical scavenging activities. Previous epidemiological studies found that the bone mineral density (BMD) of post-menopausal women with tea drinking habit was higher than that without tea consumption. However, to the best of our knowledge, the effects of green tea catechins on osteogenic effects in pluripotent stem cells have rarely been investigated. There are many important osteogenic markers involving in the differentiation of osteoblastic linage, such as osteocalcin (OC), type I collagen (COL I), alkaline phosphatase (ALP). Osteocalcin is the only bone specific protein found. Type I collagen is the main structure protein of bone. Alkaline phosphatase is an ectoenzyme, which plays an important role in bone mineralization. All the above proteins are very relevant to osteogenesis. Additionally, growth factors such as bone morphogenetic protein 2 (BMP2) also modulate osteogenesis. The osteogenic markers were evaluated in the sturdies of this thesis Accordingly, we hypothesized that EGCG can enhance the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) and further improve BMD in osteoporosis and facture healing. In the study I of this thesis, we evaluated the effects of EGCG on murine and human BMSCs. We found EGCG increased the mRNA expression of osteogenic genes and protein expression of OC. Additionally, EGCG also increased ALP activities and eventually mineralization in BMSCs. Based on these findings, we further hypothesized that EGCG can increase BMD in vivo. In the study II of this thesis, we evaluate the in vivo effects of EGCG on ovariectomized (OVX) rats. We found EGCG increased BMD in the proximal tibia and improved micro-architecture in both lumbar spine and tibia. Besides, EGCG also increase bone volume in tibial cortex. The increase of bone volume may be related to BMP2 at least in part. In the study III of this thesis, we evaluated the effects of EGCG in fracture healing. We found EGCG can increase callus volume in fracture healing model. Moreover, EGCG also increases the mechanical strength of repaired bone in bending test. In conclusion, EGCG enhances the osteogenic differentiation of murine and human BMSCs. EGCG increases BMP2 expression and increase BMD in estrogen-deficient osteoporosis and, improve micro-architecture and fracture healing in rats. The dose of EGCG in this study is not toxic to rats. Previous study also showed the effective does in this study is also not toxic to humans. Our study will provide a basis for further human study of EGCG effect on osteoporosis and/or fracture healing.