利用斑馬魚活體實驗來探討雙磷酸鹽造成顎骨壞死之可能機制

A new insight into the mechanism of bisphosphonate-related osteonecrosis of the jaw using zebrafish as a model

吳俊學(Chun-Hsieh Wu)

指導教授 ： 王若松

共同指導教授 ： 張百恩(Bei-En Chang)

國立臺灣大學/牙醫專業學院/臨床牙醫學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.02854

摘要

雙磷酸鹽(bisphosphonate)是骨骼中與羥基磷灰石相結合的焦磷酸鹽(pyrophosphate)之人工合成類似物。體內自然生成之焦磷酸鹽可在血清與尿液中被發現，但因其結構式不穩定，無法經由口服服用，因此開發出結構穩定的雙磷酸鹽。此類藥物主要被認為可抑制蝕骨細胞功能，因此具有抑制骨骼再吸收之作用。目前，此類藥物已相當廣泛地用於治療骨質疏鬆以及骨溶性骨轉移之癌症病人，由此突顯出其重要性。

然而，最近的臨床報告發現此類藥物對骨骼及傷口修復可能具有副作用。有關雙磷酸鹽可能造成顎骨壞死 (bisphosphonate-related osteonecrosis of the jaw, BRONJ)在2003年出現最早被發表的臨床病例。由於陸續有一些相關的發現報告，此臨床現象已開始引起注意並且令一些執行牙科手術之牙醫師以及治療癌症之醫師感到相當困惑。目前，造成BRONJ之詳細機制尚待釐清，由於其影響層面很廣，包含牙科拔牙、植牙、牙周手術，以及癌症病人骨轉移之治療皆與之相關，因此BRONJ之研究實為迫切而重要之議題。

至今並未有使用斑馬魚來研究BRONJ之相關文獻，本實驗選用斑馬魚，主要因為其為脊椎動物硬骨魚類 (Danio rerio, osteichthye 硬骨魚綱)，其尾鰭再生方式與人類膜內骨再生模式相似，而且其硬骨可以利用alizarin red染色或以calcein進行活體染色，故本實驗計劃以斑馬魚建立起一個全新有效的活體動物模式，來探討雙磷酸鹽對骨骼生成、恆定及代謝(turnover)作用之影響，以期獲得活體(in vivo)的研究證據來解析BRONJ發生之機制。

本實驗先從形態學著手，魚苗部分首先利用alcian blue軟骨染色來觀察alendronate是否對魚苗軟骨發育過程有影響。之後再利用calcein硬骨染色來觀察此藥物對魚苗早期顏面及脊椎骨骼礦化過程(day 5~day 14)是否有影響。成魚部分首先利用alizarin red染色和calcein活體染色來觀察此藥物對成魚尾鰭切除後再生之型態是否有影響。之後再以acridine orange染色來觀察此藥物在成魚尾鰭再生時是否會造成細胞死亡。最後以原位雜合反應(in situ hybridization)分析尾鰭再生時浸泡藥物是否會造成不同時期之骨母細胞(osteoblast)基因表現出現異常。

實驗結果顯示，alendronate對魚苗軟骨及硬骨早期發育再生無顯著影響。成魚尾鰭再生部分發現骨質生成具有劑量效應；低劑量具有促進骨質生成作用，反之，較高劑量反而抑制骨質生成。另外，我發現alendronate在尾鰭再生之骨質鰭條週圍具有一些細胞毒性，可造成細胞死亡(apoptosis)。原位雜合反應則發現低劑量藥物可促進骨母細胞早期基因Runx2表現，而高劑量藥物則抑制此基因表現。由以上結果我們可以獲得一個可能造成BRONJ之初步結論：因此藥物為bone hook，對硬骨有很高的親和力，故會隨著時間逐漸鍵結在硬骨上，當有傷口形成時(如尾鰭切除)，造成局部骨頭代謝速率(turnover rate)急遽上升，局部釋放出大量藥物，造成周圍細胞死亡並影響傷口癒合過程，推測此可能為造成BRONJ之主因。

關鍵詞：骨壞死、雙磷酸鹽、斑馬魚、骨生成

關鍵字

骨壞死 ； 雙磷酸鹽 ； 斑馬魚 ； 骨生成

並列摘要

Bisphosphonates, analogues of endogenous pyrophosphate which binds to hydroxyapatite in bone, are synthetic drugs for treating osteoporosis. Endogenous pyrophosphate found in serum and urine is unstable and easily metabolized. In contrast, bisphosphonates have been developed as drugs due to their stability and affinity to bone, conferring the inhibition of bone-resorption probably mediated by impeding osteoclast function. To date, they have been broadly employed in medication for the patients with osteoporosis and metastatic osteolytic cancers, which betrays their impact on clinical therapies.

However, recent clinical reports have implicated these drugs in adverse effects on bone and wound healing. The first report about “bisphosphonate-related osteonecrosis of the jaw”(BRONJ) was published in 2003. Consecutively, many correlated cases have been identified. These contentious clinical phenomena begin to overwhelm and baffle the dentists as well as other medical doctors who have encountered the patients using bisphosphonates. The underlying detailed mechanism of BRONJ still remains elusive. The prevalent application of these drugs and its implication in dental surgeries and cancer therapies suggest this is an important compelling issue for medical research.

To date, there is no related research of BRONJ using zebrafish as a model. The teleost zebrafish (Danio rerio, osteichthye), a vertebrate animal model, has been extensively applied in bio-medical research, including osteogenesis. The regeneration of zebrafish caudal fin is similar to the regeneration of human intramembranous bone. The bone and cartilage of the fish can be easily visualized by staining, facilitating the observation of their morphologies. In this study, I utilize zebrafish to analyze the effects of bisphosphonate on bone re-growth for quantitative and qualitative analyses, dissect the etiology of BRONJ and unravel the underlying molecular mechanism by in vivo evidences.

At first I analyzed the morphologies of zebrafish embryos after treatment with alendronate. I observed the development of larvae cartilage by alcian blue staining and early facial and spinal bone mineralization(day 5~day 14) by calcein staining. In adult zebrafish, I observed the morphology of fin regeneration after amputation by alizarin red and calcein (in vivo) staining. Analysis of cell apoptosis was done by acridine orange and I perform in situ hybridization to detect early and late gene markers of osteoblast and osteoclast to unveil the gene expression patterns.

My results show that alendronate has no effect on larva cartilage development and early bone mineralization. But it has a dose-dependent effect on bone mineralization of adult fin regeneration. Low dose augments this process, while higher dose impedes it. Futhermore, it seems that this drug exerts cytotoxicity on the cells encompassing bone matrix, resulting in cell apoptosis. I found by in situ hybridization that low dose of alendronate augments the expression of Runx2, an early gene marker of osteoblast and higher dose suppress its expression. In conclusion: The results suggest the main cause of BRONJ is that alendronate is a bone hook and cumulatively bound in bone. When wound formation, the local bone turnover rate increases rapidly and releases large quantity of alendronate, which causes the death of cells surrounding fin rays and impedes the wound healing.

Keywords: bisphosphonate, osteonecrosis, zebrafish, bone

並列關鍵字

bisphosphonate ； osteonecrosis ； zebrafish ； bone

參考文獻

AAOMS. (2007). American Association of Oral and Maxillofacial Surgeons position paper on bisphosphonate-related osteonecrosis of the jaws. J Oral Maxillofac Surg 65, 369-76.

Adami, S., Bhalla, A. K., Dorizzi, R., Montesanti, F., Rosini, S., Salvagno, G. and Lo Cascio, V. (1987). The acute-phase response after bisphosphonate administration. Calcif Tissue Int 41, 326-31.

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