目前已有超過百分之四的世界人口罹患糖尿病。糖尿病常伴隨高血糖、 高血脂、高血壓、肥胖及高血同半胱氨酸等現象，因此糖尿病患具有較高的心血 管疾病發生率及致死率。高血同半胱氨酸為一心血管疾病之獨立危險因子，罹患 心血管疾病之糖尿病患若同時有同半胱氨酸異常現象可能促使其心血管疾病惡 化。糖尿病中同半胱氨酸代謝異常由來已久，然而其中機制未明。臨床上腎病變 之糖尿病患有高血同半胱氨酸，而部份無腎病變之糖尿病患其同半胱氨酸卻偏 低，因此臨床上糖尿病狀態中的胰島素及血糖之失衡現象與同半胱氨酸代謝路徑 之間的交互影響仍未有定論。過去研究發現多種同半胱氨酸代謝的關鍵酶在糖尿 病狀態中表現異常，但其中多項機制亦尚未闡明。有別於他人過去之研究，本計 畫將以獨特創新的系統，對糖尿病過程當中同半胱氨酸代謝異常現象做一全面性 地探討。我們提出假說認為糖尿病狀態中之胰島素及血糖異常透過抑制同半胱氨 酸轉硫基反應促進其再甲基化並增進腺甘甲硫氨酸合成而直接影響甲基傳遞，進 而改變體內甲基平衡進而影響甲基化甚而進一步造成體內特定基因表觀遺傳上 之變化。另一方面近期研究中我們發現苷胺酸氮甲基轉移酶基因剔除鼠有低血糖 以及異常肝醣沉積，顯示體內甲基族失衡現象亦可能會同時回過來影響體內糖代 謝，因此兩者間可能有交互作用。本計畫包含了一系列完整的研究，首先將建立 細胞模型，接著以飲食誘發、藥物誘發及遺傳動物模式發展活體內追蹤系統，以 穩定同位素及氣相質譜儀之獨特技術，針對糖尿病狀態中之因胰島素分泌缺陷而 產生之高血糖、或胰島素抗性之高血糖等異常病理狀態對同半胱氨酸代謝中轉硫 基反應、甲基族傳遞及DNA甲基化等反應路徑之影響，以及各路徑之間的動態 平衡做全面性之探討。本研究期能透過獨特技術及創新系統解開許多糖尿病狀態 中同半胱氨酸代謝異常未知的之機制，透徹了解糖尿病狀態中的胰島素及血糖之 失衡現象與同半胱氨酸代謝及其間之交互作用對而對此領域有所貢獻。未來希望 透過深入了解其中機制進而能對同半胱氨酸代謝異常有較好的控制及改善，減少 糖尿病中與同半胱氨酸代謝異常相關之併發症。此項研究成果對於臨床上糖尿病 所引起之同半胱氨酸代謝異常之機制及其間交互作用有重要啟示，對糖尿病患心 血管疾病疾病的控制預防有重要參考價值，研究成果將同時提供生化營養代謝學 術上及臨床實用上多層面資訊。

根據102-103年「國民營養健康狀況變遷調查」結果，有89.9%的國中生、85.3%的高中學生每週至少喝1次含糖飲料；其中，國中生平均每週喝超過6次、高中生平均每週喝將近8次，19-64歲成人平均每週喝將近7次。喝甜飲料不但無法解渴，反而容易攝取過多熱量及游離糖（free sugar）（指製造商、食物製備者或消費者額外添加至食品中之單糖及雙糖，以及蜂蜜、糖漿及果汁中天然存在的糖分）。
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目前對於營養素與基因體交互作用的了解尚無法完全解釋飲食成分中的各種營養訊號 (如代謝產物、胜肽、脂質) 如何透過高度協調作用全面性地影響不同各生化生理代謝途徑中數以千計之基因表現及功能。常見的表觀遺傳修飾包括甲基化、乙醯基化、磷酸化、微小RNA等，其不改變核苷酸序列而改變基因或蛋白質之表現及功能。我們推測飲食因子若改變單碳代謝循環中的甲基供需平衡或流量分配，可能進一步透過甲基化或其他表觀遺傳修飾來調節基因表現及功能，進一步影響人類長期健康。本計劃將建立平台及模式系統並以所建立的系統謹慎篩選出具表觀遺傳調節潛力的特定飲食因子、探討其在體內與體外如何改變甲基供應和甲基動力平衡、並探討這些因子如何透過表觀遺傳調節作用調節基因功能。

根據102-103年「國民營養健康狀況變遷調查」結果，有89.9%的國中生、85.3%的高中學生每週至少喝1次含糖飲料；其中，國中生平均每週喝超過6次、高中生平均每週喝將近8次，19-64歲成人平均每週喝將近7次。
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目前對於營養素與基因體交互作用的了解尚無法完全解釋飲食成分中的各種營養訊號 (如代謝產物、胜肽、脂質) 如何透過高度協調作用全面性地影響不同各生化生理代謝途徑中數以千計之基因表現及功能。常見的表觀遺傳修飾包括甲基化、乙醯基化、磷酸化、微小RNA等，其不改變核苷酸序列而改變基因或蛋白質之表現及功能。我們推測飲食因子若改變單碳代謝循環中的甲基供需平衡或流量分配，可能進一步透過甲基化或其他表觀遺傳修飾來調節基因表現及功能，進一步影響人類長期健康。本計劃將建立平台及模式系統並以所建立的系統謹慎篩選出具表觀遺傳調節潛力的特定飲食因子、探討其在體內與體外如何改變甲基供應和甲基動力平衡、並探討這些因子如何透過表觀遺傳調節作用調節基因功能。

Our previous study demonstrated novel finding of a direct promoting effect of high cellular insulin or glucose exposure on homocysteine remethylation, adoMet synthase activity, and adoMet synthesis. We have also provided new evidence indicating that when hepatic tissue is exposed to elevated insulin or glucose, the cellular methylation balance is altered. Hyperleptinemia is commonly seen in humans suffering from metabolic syndrome or type II diabetes; and leptin concentration has been suggested as an independent predictor of type II diabetes in men. However, the impact of path physiological elevations in leptin on homocysteine metabolism is not fully illustrated. The objective of the study was to investigate the impact of elevated leptin on homocysteine metabolism and methyl group kinetics in vivo. Effects of long-term leptin administration on homocysteine transmethylation and transsulfuration metabolic fluxes were investigated in mouse models using stable isotopic tracers and gas chromatography/mass spectrometry. Homocysteine remethylation and transsulfuration metabolic fluxes were investigated using stable isotopic tracers and gas chromatography/mass spectrometry. The methylation status was determined. Our preliminary in vivo study indicated that long-term leptin administration altered homocysteine metabolism in a tissue specific manner.
本研究室近期在體外研究發現胰島素對於細胞內同半胱胺酸代謝影響顯著。另外也發現當細胞暴露在高糖情況時其同半胱氨酸轉硫反應會受到抑制而其再甲基化代謝路徑會促進而提腺甘甲硫氨酸合成。除血糖及胰島素異常，人類的第二型糖尿病常伴隨高瘦體素血症。瘦體素是一種脂肪細胞生成的細胞激素。有研究顯示瘦體素在代謝症候群的發展過程中可能扮演獨立的角色，然而瘦體素如何影響同半胱胺酸代謝以及甲基動態平衡目前尚未闡明。本研究以動物模式長期介入生理劑量的瘦體素探討其對於同半胱胺酸代謝影響，並以同位素及氣相層析質譜儀分析體內實驗中瘦體素如何影響同半胱胺酸轉硫及轉甲基代謝分流，並對於體內長期暴露在瘦體素狀況時甲基族動態平衡做全面性探討。同半胱胺酸代謝異常是心血管疾病獨立危險因子之一。細胞內的同半胱胺酸可透過再甲基化作用合成甲硫胺酸或是經轉硫作用降解。本研究對於釐清糖尿病或代謝症候群或其他高瘦體素血症狀況對於體內同半胱胺酸轉甲基與轉硫代謝機轉之影響有所貢獻。

Background. Defection in insulin secretion or insulin action divided diabetes into two group: Type I and Type II diabetes. Type I diabetes, accompanying hyperglycemia and hypoinsulinia. Type II diabetes was commonly associating with obesity, hyperglycemia and hyperinsulinia. The previous study has reported that diabetes might disrupt methyl group metabolism. The goal of this study was to determine the alterations in methyl group metabolism causing by the conditions of diabetes; and further, influence the status of genomic methylation.

Methods. We study two main types of diabetes separately, STZ-treated mice as Type I diabetic model and db/db transgenic mice as Type II diabetic model. We performed a methionine-load test to estimate the influence of diabetes on homocysteine metabolism. The metabolites involved in transsulfuration: homocysteine, cysteine, Cys-Gly and total GSH concentrations in plasma were analyzed. AdoMet, AdoHcy, enzyme activity of MAT and SAHH were determined. To investigate status of global DNA methylation, percentage of methylated cytidine, DNMT activity and abundance of protein associated with DNA methylation were determined. The impact of diabetes on pathway fluxes of one-carbon metabolism was illustrated by stable isopotic tracers.

Results. We examined the impact of Type I and Type II diabetes on homocysteine production and found that plasma homocysteine and cysteine concentrations were lower in the both diabetic groups at all time points. The transsulfuration fluxes were increased in both mice model. However, GSH and Cys-Gly concentrations were increased in Type I diabetes alone. In Type I diabetes, there was no significant change in hepatic concentration of adoMet and adoHcy, whereas adoMet was elevated and adoHcy was reduced in Type II diabetes at 42 wk. Hepatic MAT activity was lower but MAT abundance was elevated in Type I diabetes and Type II diabetes at 28 wk. Hepatic adoMet/adoHcy ratio did not differ in diabetic mice compared with the controls. However, the remethylation fluxes in both mice model were increased. In addition, hepatic DNMT activity, DNMT1 and DNMT3a abundance were lower in Type I diabetic mice than in control mice with the decreased content of 5MdC. Moreover, hepatic DNMT activity, DNMT1 and DNMT3a abundance were elevated in Type II diabetes at all time point, ultimately resulting in the rising content of 5MdC in DNA.

Conclusion. During the Type I diabetes status, methyl group metabolism was disturbed with genomic hypomethylation in the mice liver. Compare with Type I diabetes, Type II diabetes have the equivalent alterations in transmethylation and homocysteine production, whereas have distinct impact on DNA methylation that the 5MdC was increased. We suggest that must be different factors affect the DNA methylation status and related reactions within two models. The related further studies are underway.