癌細胞誘發骨疼痛模式小鼠腦中與鴉片類藥物止痛相關之影像定位研究

Abstract

癌細胞誘發骨疼痛（CIBP）是一種癌症晚期病患常見的慢性疼痛現象，當癌細胞轉移到骨骼後經常引起病患難以承受的疼痛。雖然癌症引發的疼痛是臨床上極大的問題之一，但目前對於CIBP的病理機制還尚未清楚。本研究的目的為結合小鼠正子暨電腦斷層掃描造影（PET/CT）與疼痛行為測試，藉由CIBP小鼠自發性疼痛情況下腦部葡萄糖代謝率變化結果，找出乳癌細胞誘發骨疼痛以及CIBP常用止痛藥，嗎啡止痛作用的相關腦區。我們首先將4T1小鼠乳癌细胞注入至BALB/c小鼠股骨之骨髓腔中，利用18F-NaF-PET掃描造影追蹤癌細胞在骨骼內的發展結果，建立乳癌細胞誘發骨疼痛的小鼠動物模式。之後利用此注射4T1乳癌細胞的 CIBP小鼠動物模式，並以注射磷酸鹽緩衝液（PBS）的小鼠作為sham控制組，於手術前、手術後第7天、第10天以及第14天進行自發性疼痛、機械性觸感痛及冷觸感痛的行為測試，確認動物的疼痛發展狀態，之後於手術第16天測試不同劑量的嗎啡止痛效果。另外，我們利用18F-FDG-PET掃描造影，在手術前、手術後第14天以及手術後第16天給予嗎啡後進行掃描，探討CIBP小鼠自發性疼痛時以及給予嗎啡止痛時的腦部葡萄糖代謝變化。實驗結果顯示，小鼠於注入4T1乳癌細胞14天後會產生顯著性的自發性疼痛、機械性觸感痛及冷觸感痛現象，在給予小鼠15 mg/kg的嗎啡後30至60分鐘，對於自發性疼痛、機械性觸感痛以及冷觸感痛都有顯著的止痛效果。比較小鼠腦部的葡萄糖代謝率變化後發現，動物的活動狀態會影響疼痛相關腦區結果的判讀，小鼠活動時感覺與運動皮質區活性上升，在睡覺時結果相反。將活動參數去除後CIBP的PET分析結果顯示，兩側島腦（insular cortex）與兩側次級體感覺皮質（secondary somatosensory cortex）腦區的葡萄糖代謝活性顯著上升，而嗎啡可能是藉由抑制異側島腦與次級體感覺皮質腦區，以及活化韁核（habenula）與中腦導水管周圍灰質（PAG）腦區產生止痛作用，顯示異側島腦與S2腦區很有可能是參與CIBP小鼠疼痛之重要角色。

Cancer-induced bone pain (CIBP) is a common pain in patients with advanced cancer. When cancer metastasizes to the bone, it can cause persistent and unbearable pain which often cause patient’s physical and mental suffering. Although CIBP is one of the most serious clinical problems, the pathophysiological mechanism of CIBP has not been elucidated. Opioid, such as morphine, is commonly used in cancer pain management. The aim of this study is to combine the positron emission tomography-computed tomography (PET/CT) imaging and pain behavior tests to investigate the pain- and morphine analgesia-related brain regions in the CIBP mice. We injected 4T1 mouse breast cancer cells into left femur bone marrow cavity of the BALB/c mice, using 18F-NaF as tracer to evaluate the development of cancer cells in the bone environment. Mice in sham control group were injected with phosphate buffered saline. Then, we measured pain related behaviors with limb use observation, von Frey filaments test and acetone stimulus on the day before surgery, Day 7, Day 10 and Day 14 after the surgery to confirm pain development. Morphine doses (10, 15, 30 mg/kg, i.p.) were administered on Day 16 after the surgery. In addition, we investigated spontaneous pain and morphine-analgesic effect on CIBP mice brain by 18F-fluorodeoxyglucose (FDG) PET/CT. In the PET imaging study, each mouse was scanned 3 times: before bone surgery, Day 14, after the surgery, and Day 16, 30 min after the 15 mg/kg morphine treatment. Our results showed that the CIBP mice showed significant spontaneous pain, mechanical allodynia and cold allodynia on 14 days after the 4T1 cancer cells injection. Morphine dose 15 mg/kg was sufficient to relieve spontaneous pain, mechanical and cold allodynia of the CIBP mice between 30 to 60 minutes post-treatment. In PET study, brain glucose metabolic activity of sensory and motor cortex in mice increased during movement, and the results were reversed during sleeping. In order to prevent these results interfering the analysis of CIBP-related brain regions, we removed the activity parameters, and the results showed that in the CIBP condition, glucose metabolic activity were significant increased in bilateral insular cortex and bilateral S2. Morphine analgesia effect may be produced by the observed suppressing contralateral insular cortex and contralateral S2 brain regions, as well as activation of the habenula and PAG. Our data suggest that contralateral insular cortex and contralateral S2 may play an important role in the CIBP.