消渴草粗萃物減緩高脂飲食及STZ誘發第二型糖尿病大鼠肝臟脂肪變性及發炎反應之探討

Abstract

第2型糖尿病（type 2 diabetes mellitus, T2DM）常合併有非酒精性脂肪肝病（Non-alcoholic fatty liver disease, NAFLD）發生。流行病學研究顯示，同時患有T2DM及NAFLD的病患併發糖尿病微血管病變風險高於僅患T2DM之病患。蘆莉草（Ruellia tuberosa L. , RTL）又稱消渴草，是一種廣泛分佈於東亞的多年生草本植物，坊間作為抗糖尿病和抗發炎之民俗草藥使用。本實驗室先前證實RTL具有緩解高血糖、胰島素阻抗及改善肝臟解毒之功能。本研究進一步以高脂飲食與STZ誘導T2DM合併NAFLD動物模式，探討消渴草水萃物及醇萃物對於肝臟胰島素阻抗及NAFLD病程機轉的影響。 西方墨點法結果顯示，消渴草水萃物及醇萃物顯著增加T2DM合併NAFLD大鼠之胰島素受體受質1（IRS-1）蛋白質之表現量（p< 0.05），其中消渴草水萃物亦顯著增加磷酸化蛋白激酶B (p-Akt)/ 蛋白激酶B (Akt)表現（p < 0.05）。肝臟脂肪代謝相關蛋白質分析結果發現，消渴草水萃物顯著減少T2DM合併NAFLD大鼠肝臟SREBP1和乙酰輔酶A羧化酶（ACC）蛋白質之表現量（p < 0.05）；而消渴草醇萃物則能顯著降低肝臟SREBP1和脂肪酸合成酶（FAS）蛋白質表現量（p < 0.05）。此外，發現消渴草水萃物及醇萃物可透過降低肝臟發炎路徑IKK而非JNK蛋白質表現來減少促發炎細胞激素如TNF-α，IL-6和IL-1β之含量。 綜合以上結果推測，消渴草可藉由提高肝臟胰島素敏感性減緩T2DM合併NAFLD大鼠胰島素抵抗。消渴草水萃物或醇萃物改善肝臟脂肪變性係透過降低肝臟內生性脂肪合成作用有關的蛋白質表現，而非增加肝臟脂肪β氧化作用。此外，消渴草亦可抑制肝臟發炎路徑蛋白IKK磷酸化及減少促發炎細胞激素分泌，以減輕T2DM合併NAFLD大鼠肝臟非酒精脂肪肝炎的進展。Non-alcoholic fatty liver disease (NAFLD) occurs commonly in type 2 diabetes mellitus (T2DM). Studies suggest that individuals with both T2DM and NAFLD may increase the risk of microvascular diabetic complica¬tions. Ruellia tuberosa L. (RTL) is a perennial herb widely distributed in Eastern Asia and has been used as anti-diabetes and anti-inflammation fork medicine. We previously reported RTL may alleviate hyperglycemia, insulin resistance and improve detoxification function in animal model. In this study, we investigated the effect of RTL on hepatic insulin signaling pathways, hepatic steatosis and anti-inflammation ability in multiple low-dose streptozotocin (STZ) plus high-fat diet-induced T2DM with NAFLD rats. The result from western blotting shows that the protein expressions of total insulin receptor substrate-1 (IRS-1) were significant increased by both water and ethanol extract from RTL in T2DM with NAFLD rats (p<0.05). Furthermore, Water extract from RTL were also significant increased protein expressions of phosphor-protein kinase B (p-Akt)/ protein kinase B (Akt) (p<0.05). According to the results of protein expressions related to hepatic fat metabolism. We found that water extract from RTL were significant reduced sterol regulatory element-binding protein 1 (SREBP1) and acetyl-CoA carboxylase (ACC) in T2DM with NAFLD rats (p<0.05). Water extract from RTL were significant reduced SREBP1 and fatty acid synthase (FAS) in T2DM with NAFLD rats (p<0.05). Moreover, pro-inflammatory cytokine such as TNF-α, IL-6 and IL-1β were reduced by both water and ethanol extract from RTL in T2DM with NAFLD rats. Western blot analysis revealed that both water and ethanol extract from RTL decreased the protein expressions of hepatic inflammation pathway IKK, but not JNK in T2DM with NAFLD rats. Above observation suggests that both water and ethanol RTL extracts significantly alleviate hepatic insulin resistance in T2DM with NAFLD rats via improving hepatic insulin sensitivity. Water or ethanol extract from RTL alleviate hepatic steatosis via down-regulated expression of hepatic de novo lipogenesis-related proteins, rather than increased hepatic lipid β-oxidantion. In addition, RTL may have protective potential on the progression of hepatic inflammation via reducing pro-inflammatory cytokines and alleviating hepatic inflammation signaling protein IKK, but not JNK in T2DM with NAFLD rats.