在停經後與老化過程中,活性氧的累積以及抗氧化防禦系統能力的降低,導致氧化壓力的形成,並藉此促進蝕骨細胞的形成以及成骨細胞的凋亡,最終造成骨質的流失。NF-E2相關因子2 (nuclear factor E2-related factor 2, Nrf 2) 為調控體內抗氧化防禦系統之關鍵轉錄因子;已有研究證實Nrf 2基因剔除小鼠其骨髓細胞於RANKL (receptor activator of nuclear factor kappa-B ligand) 誘導下,所分化形成的蝕骨細胞數量以及骨吸收活性皆顯著高於野生型 (wild type)。因此本研究以實驗室前人所構築於人類舌頭上皮鱗狀細胞癌 (Ca9-22) 之抗氧化平台,篩選出具有最佳Nrf 2轉錄活性之化合物川陳皮素 (nobiletin)、中國橄欖乙酸乙酯萃取物 (COE-EA)、咖啡酸醯胺衍生物 (36-25B) 與金雀異黃酮 (genistein)。Genistein為一植物性雌激素,已有文獻證實其具有降低骨質疏鬆發生的潛能。本研究藉由Bacillus subtilis natto BCRC 80517將金雀異黃酮進行發酵,得生物轉換之產物金雀異黃酮磷酸酯 (Genistein 7-O-phosphate, G7P),以改善其水不溶之特性,經後續純化可得G7P純度為78.8 %。分別利用Balb/c小鼠與RAW 264.7巨噬細胞株建構蝕骨細胞模式中,藉由蝕骨細胞的標誌酵素-抗酒石酸酸性磷酸酶 (tartrate-resistant acid phosphatase, TRAP) 染色與活性確立模式的建立,於其分化過程中觀察到高量活性氧 (reactive oxygen species, ROS) 的產生,同時Nrf2下游基因HO-1的mRNA表現量大幅降低。反之,若介入Nrf2活化劑tert-butylhydroquinone (TBHQ) 則可抑制ROS的產生,顯示Nrf2活化劑具有抗骨質疏鬆的潛力。為確保蝕骨細胞與成骨細胞間的代謝平衡,以Balb/c小鼠建立初代成骨細胞模式,並藉alizarin red S染鈣試驗確認成骨細胞可執行礦化功能,確立模式的建立。未來可將蝕骨與成骨細胞模式應用於各式化合物的篩選,以得出具有抗骨質疏鬆潛力之化合物。
During menopause and aging, gradual accumulation of reactive oxygen species together with progressive decline of endogenous antioxidant defense system lead to increased oxidative stress, accelerate formation of osteoclast and promote apoptosis of osteoblast, resulting in loss of bone mass. Nuclear factor E2-related factor 2 (Nrf 2) is the key transcription factor of antioxidant defense system; studies have shown that under receptor activator of nuclear factor kappa-B ligand (RANKL) induction, the bone marrow cells isolated from Nrf 2 knockout mice exhibited higher differentiation capacity and bone resorption activity than those of wild type mice. Accordingly, we used an ARE-driven reporter stable cell line to screen Nrf2 activators, and results demonastrate that nobiletin, Chinese olive ethyl acetate extract (COE-EA), caffeamide derivative (36-25B) and genistein are our candidate compounds. Genistein is a phytoestrogen proven to reduce osteoporotic incidence. Fermentation of genistein by Bacillus subtilis natto BCRC 80517 improved water solubility and bioavailability. The bioconversion product, genistein 7-O-phosphate, following a series of purification steps was obtained with a purity of approximately 78.8%. Two in vitro osteoclast models were established from Balb/c mouse primary osteoclast culture and with the murine macrophage cell line RAW 264.7. Tartrate-resistant acid phosphatase (TRAP) is a marker enzyme of osteoclast. Investigation of the number of the TRAP-positive cells and TRAP activity was used to confirm the models. Increased ROS and decreased mRNA level of HO-1, a downstream target of Nrf 2, was observed during differentiation of the osteoclastic cells. On the other hand, such effect was abrogated by a classical Nrf 2 activator, tert-butylhydroquinone (TBHQ), suggesting that Nrf 2 activators may have anti-osteoporotic potential. In order to maintain the delicate balance between osteoclast and osteoblast in vivo, the effects of the compounds on osteoblast were observed. Primary osteoblast culture from Balb/c mouse was established andalizarin red S was used to stain calcium deposits to confirm osteoblastic mineralization. The in vitro osteoclast and osteoblast models will be useful to screen out new compounds with anti-osteoporotic potential.
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