應用活體成像技術觀測脂肪肝中細胞動態與微血管循環

Abstract

肝臟累積過多脂肪時稱之為脂肪肝 (fatty liver, steatosis)，為盛行於已開發國家的一種代謝疾病。脂肪肝會影響肝功能，嚴重時會發展成肝纖維化甚至肝硬化或肝癌。以往研究顯示脂肪肝之微血管循環出現異常，且白血球亦有活化現象，然而對於這些議題較少來自於活體研究的直接證據。在此，我們運用光學活體顯微成像技術以及拉曼光譜分析，搭配傳統檢測方法，研究不同肝臟疾病 (包含了輕微脂肪肝、脂肪肝炎和含高膽固醇之脂肪變性肝臟疾病) 肝小葉狀況及微血管循環以及細胞的動態過程。傳統肝臟檢測以及拉曼光譜分析的結果清楚顯示這些疾病模型有截然不同的肝小葉形貌及脂肪組成。在活體肝臟光學成像中，我們明確觀察到脂肪肝炎表現出發炎反應、嚴重肝小葉損傷以及微血管循環異常，而輕微脂肪肝模型下亦表現出發炎反應，其他疾病模型則只表現出輕微肝小葉損傷。利用活體光學成像，我們進一步發現血小板與白血球可能對微血管循環異常扮演著重要腳色。然而其活化途徑以及影響微血管循環的機轉則仍需進一步探討。

Nonalcoholic fatty liver disease (NAFLD) characterized with an excessive accumulation of fat in the liver tissue has become a prevalent metabolic disease in the developed world. NAFLD could disturb liver function and might progress to fibrosis, cirrhosis and even hepatocellular carcinoma. Past studies have shown that microcirculatory disorder in the sinusoids and activation of leukocytes are associated with NAFLD, our understanding to the role of these phenomena remains incomplete in part due to the lack of tools to decipher these dynamic processes at the microscopic scale in vivo. Herein we employed intravital optical imaging combined with Raman spectral analysis and traditional examinations to interrogate rat models of liver diseases developed to varied severities including mild and severe fatty liver (nonalcoholic steatohepatitis, NASH), and a liver disease characterized with high cholesterol accumulation. Our studies focus on the conditions of hepatic lobules and microcirculation as well as the cells dynamics. The histological and biochemical examination and Raman spectral analysis show that the morphologies of hepatic lobules and lipid profiles differed among these disease models. With intravital imaging, we show that the NASH model exhibits characteristics of inflammation, strong association between leukocytes and platelets, severe lobule injury and impaired microcirculation while other liver disease models present only mild lobule injury. Our preliminary result indicates that the activation of platelets might play an important role in the microcirculatory impairment in NASH. Further mechanistic study is required to elucidate the underlying pathogenesis.