動脈硬化（atherosclerosis）是導致心血管疾病的主因。在動脈硬化形成的過程中，已充分證實骨髓過氧化酶（Mycloperoxidase, MPO）扮演最為關鍵的角色。骨髓過氧化酶會使得脂質氧化並累積在血管內層，形成粥樣化脆弱型斑塊。此不穩定斑塊受到骨髓過氧化酶催化而形成的過氧化物質所破壞，會破裂而形成血栓，導致危及性命的中風和心肌梗塞。如能發展非侵入性體內造影以偵測MPO的活性，將為醫學上早期診斷動脈硬化一有利的方法。本研究擬以111In-bis-5HT-DTPA小分子試劑偵測apoE基因剔除小鼠體內MPO之活性。
方法： 111In-bis-5HT-DTPA小分子試劑中之5HT受MPO催化產生之過氧化物作用，會自行聚合或與蛋白質結合，增加小分子體積，減緩清除，延長累積在病灶部位。使用In-111放射核種標誌在bis-5HT-DTPA上，先在MPO酵素實驗中確認其聚合能力。動物模式選擇apoE基因剔除小鼠，進行粥狀動脈硬化之生成，並用血脂分析和組織病理學確認斑塊及MPO之產生。進一步利用nanoSPECT/CT 造影以及生物分佈試驗，評估111In-bis-5HT-DTPA為粥狀動脈硬化老鼠模式造影劑的可行性。
結果：本實驗經質譜及核磁共振譜確認bis-5HT-DTPA之合成。111In-bis-5HT-DTPA能於大鼠血清中達到90%以上之穩定度。MALDI-TOF確認此試劑能自體聚合。於nanoSPECT/CT 造影實驗，可發現在apoE基因剔除小鼠的心臟周圍累積明顯高於基因正常鼠。而在生物分佈實驗中，111In-bis-5HT-DTPA在apoE基因剔除小鼠的主動脈累積量是基因正常鼠的1.38±0.03倍(注射後一小時)。且在注射後半小時到一小時間，111In-bis-5HT-DTPA在apoE基因剔除小鼠的主動脈的清除速率在統計上顯現小於基因正常鼠，分別為0.14±0.09 % ID/g/h 和3.88±0.25 % ID/g/h。
結論：從造影及生物分佈結果發現111In-bis-5HT-DTPA在apoE基因剔除小鼠的主動脈累積明顯大於基因正常鼠，且在粥狀動脈硬化的主動脈血管壁中有較長時間的累積。本研究初步呈現111In-bis-5HT-DTPA小分子放射試劑在粥狀動脈硬化模式中，因MPO酵素作用，自體聚合或和蛋白質結合而影響藥物動力學、生物分佈、影像診斷的結果。

Myeloperoxidase(MPO) plays an important role in formation of atherosclerotic plaques. MPO can activate lipid oxidization and localization in the intima of blood vessel wall, resulting in lipid cores in atherosclerotic plaque. If the lipid core dominates the plaque, the latter would become unstable and easily ruptured, forming thrombi that circulate in the blood. It would be very dangerous to make thrombi obstruct the blood vessels, causing fatal disease such as stroke and myocardial infarction. Hence, early detection of MPO within the blood vessels may be of great importance for clinical management of related vascular diseases.
Method: In this study, a radioactive agent, 111In-bis-5HT-DTPA was synthesized to detect MPO for early diagnosis. The 5HT base agent could oligomerize by itself or with proteins through a specific mechanism mediated by myeloperoxidase. For in vitro study, the agent was incubated with myeloperoxidase and hydrogen peroxide to confirm the aggregation with the enzyme. For animal study, apoE knockout mice were used to generate plaque and atherosclerosis changes for investigation with blood analysis and histopathologic studies. NanoSPECT/CT imaging and biodistribution assay were carried out to ensure the binding (with MPO) of 111In-Bis-5HT-DTPA with MPO in a murine atherosclerotic model.
Results: Bis-5HT-DTPA was synthesized and its structure confirmed by1H-NMR and ESI-MASS. 111In-bis-5HT-DTPA synthesized in this study exhibited ≧ 95% radiochemical purity and high stability in rat plasma. MALDI-TOF spectrum demonstrated that the 5HT base agent could oligomerize by itself. The nanoSPECT/CT imaging study indicated that the accumulation of
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111In-Bis-5HT-DTPA around the heart in apo E knockout mice was apparently more significant than that of the wild type mice. In the biodistribution study, the artery wall uptake of 111In-bis-5HT-DTPA oligomer in the artery wall of apo E knockout mice was about 1.38±0.03-fold higher than that in the wild type mice at 1 hour. The elimination rate of 111In-bis-5HT-DTPA from the blood vessel in apoE KO mice was 0.14±0.09 % ID/g/h, whereas that in the wild type mice was 3.88±0.25 % ID/g/h (P = 0.010, P<0.05).
Conclusion: From the imaging and biodistribution study, the radioactivity signal around the heart in apo E knockout mice is significantly higher than that of the wild type mice. It revealed that 111In-Bis-5HT-DTPA can accumulate1.38±0.03-fold higher in the aorta of apo E knockout mice than in the wild type mice. In summary, this study has described a fundamental radionuclide pharmacokinetic and biodistribution results in apoE knockout mice and possible utilization of oligomerization in 111In-Bis-5HT-DTPA for early detection of myeloperoxidase within the blood vessel wall.

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