摘要:砷 (arsenic)廣泛分佈於地球環境,是一種有毒類金屬元素。砷包括無機砷和有機砷,無機砷被認為較有機砷具有毒性,並且為人類的主要暴露來源。砷可分佈於生物體的毛髮,牙齒,內臟,指甲及骨骼等。許多流行病學研究證實,在美國和其他國家長期暴露於含砷之飲用水,會提高多種慢性疾病之發生率,例如癌症,周邊血管疾病,內分泌功能失調、糖尿病等。砷會累積在骨骼及骨髓中,骨組織被認為也是砷的目標器官之一。砷具有引起骨髓細胞毒性的能力;急性或慢性砷中毒已知會造成骨髓抑制,影響造血功能。有關砷對於骨骼系統的毒性及機制研究相對地少很多。負責骨生成的造骨細胞來自於骨髓中的間質幹細胞分化而成,而負責骨吸收的破骨細胞則來自造血幹細胞。當調控骨質之因子失調後會造成骨生成和骨吸收失去平衡進而產生骨質疏鬆症;但當間質幹細胞趨向於分化成脂肪細胞也會影響骨質疏鬆症發生。最近研究指出三價無機砷會引起骨髓間質幹細胞毒性;而三氧化二砷也會造成人類造骨細胞凋亡。但這些研究所使用的砷濃度屬於具細胞毒性之較高劑量範圍。目前尚無砷會影響正常骨髓幹細胞分化的有關報告,尤其是在不具細胞毒性之劑量範圍;而且也缺乏砷與骨質疏鬆症關係之文獻。近年來許多研究致力於骨質疏鬆症之病因及病理機制探討,其中包括糖尿病、內分泌系統及環境污染物等。故有關砷與骨質疏鬆症的關聯之研究有其重要性,值得深入探討。本計畫的目的在於利用細胞及實驗動物模式探討砷在不具細胞毒性之低劑量範圍內,對於骨髓幹細胞分化的影響及可能作用機制,以進一步對於砷在骨質疏鬆症上之可能角色的評估。計畫分三年進行由細胞模式到實驗動物模式的系列研究。第一年:細胞實驗模式:選擇不具細胞毒性的無機砷(0.05-1 μM;三價及五價砷)及其甲基代謝物,探討砷在短期和長期細胞培養下,對於骨髓幹細胞分化的影響及作用機制。第二年:實驗動物及合併一型糖尿病實驗動物模式:選擇低劑量範圍(0.01-2.5 ppm)的三價及五價無機砷及其甲基代謝物,探討實驗動物或合併骨質疏鬆症危險因子-一型糖尿病長期飲水砷暴露,是否會影響骨髓幹細胞分化,並誘導或加重骨質疏鬆症的發生,及其可能之細胞機制。第三年研究計畫:實驗動物及合併雌激素缺乏實驗動物模式:選擇低劑量範圍(0.01-2.5 ppm)的三價及五價無機砷及其甲基代謝物,探討實驗動物或合併骨質疏鬆症危險因子-雌激素缺乏狀態(切除卵巢)長期飲水砷暴露,是否會影響骨髓幹細胞分化,並誘導或加重骨質疏鬆症的發生,及其可能之細胞機制。本研究結果將可讓我們進一步了解低劑量範圍的砷化合物是否會影響骨髓幹細胞之生長/功能/分化和可能的分子機制,以及提供基礎醫學研究證據,來說明砷在骨質疏鬆症上之可能角色。
Abstract: Arsenic is widely distributed in the Earth's environment as a toxic metalloid element.Arsenic includes inorganic and organic forms. Inorganic arsenic is considered toxic thanorganic arsenic, and is the main human exposure source. Arsenic can be distributed inhair, teeth, organs, nails and bones of organisms. Many epidemiological studiesconfirmed that the long-term exposure to arsenic in drinking water will increase theincidence of several chronic diseases such as cancer, peripheral vascular disease,endocrine disorders, diabetes and so on in the United States and other countries. Bonetissue is considered one of the target organ of arsenic. Arsenic has the ability to causebone marrow toxicity; acute or chronic arsenic poisoning is known to cause bone marrowdepression, affecting hematopoiesis. Arsenic are known to accumulate in bone and bonemarrow; but in comparison to other systems, the researches for arsenic toxicity and itsrelated mechanisms in skeletal system are small lot. Bone formation is caused byosteoblasts derived from bone marrow mesenchymal stem cells, and osteoclasts derivedfrom hematopoietic stem cells lead to bone resorption. The dysfunction of regulatingfactors, which control the bone metabolism, will result in the loss of balance of boneformation and bone resorption, and thus cause osteoporosis. Recent studies have shownthat the trivalent inorganic arsenic can cause toxicity of bone marrow mesenchymal stemcells, and arsenic trioxide also causes apoptosis in human osteoblasts. However, theconcentrations of arsenic used in these studies are of high cytotoxic dose ranges. Thereare no scientific reports on the effects of arsenic on the differentiation in normal bonemarrow stem cells, especially in the non-cytotoxic dose ranges; the literatures for therelationship between arsenic and osteoporosis are also few. In recent years, many studiesdedicated to the causes of osteoporosis and its pathological mechanisms, includingdiabetes, endocrine system and environmental pollutants and other factors. Thus, thestudy of arsenic associated with osteoporosis is of importance, worthy of furtherexploration. The aims of this project are to use the cell and experimental animal modelsto explore the effects of non-cytotoxic low-dose arsenic on the differentiation of bonemarrow stem cells and its possible mechanisms, and to further evaluate the possible rolesof arsenic in osteoporosis. We plan a three-year project for a series of studies using cellmodels and experimental animal models.First year: cellular experimental study: choose non-cytotoxic inorganic arsenic doses(0.05-1 μM; trivalent and pentavalent arsenic) and its methylated metabolite toinvestigate their short-term and long-term ceffects and its possible mechanisms on the differentiation of bone marrow stem cells.Second year: experimental animal study or animal combined with type 1 diabetes:Choose low-dose range (0.01-2.5 ppm) of the trivalent and pentavalent inorganic arsenicand its methylated metabolite to investigate their long-term effects on bone marrow stemcell differentiation and the incidence of osteoporosis and the possible cellularmechanisms in experimental animals with or without type 1 diabetes exposed to arsenicin drinking water.Third year: experimental animal study or animal combined with estrogen deficiency:Choose low-dose range (0.01-2.5 ppm) of the trivalent and pentavalent inorganic arsenicand its methylated metabolite to investigate their long-term effects on bone marrow stemcell differentiation and the incidence of osteoporosis and the possible cellularmechanisms in experimental animals with or without estrogen deficiency (ovariectomy)exposed to arsenic in drinking water.The results of this study will help us understand low-dose arsenic compoundsaffecting bone marrow stem cell growth/function/differentiation and its possiblemolecular mechanisms, and provide the evidence of basic medical research on thepossible role of arsenic in osteoporosis.