KS370G對於小鼠代謝及心血管系統保護作用之研究

Abstract

咖啡酸苯乙酯(caffeic acid phenylethyl ester)是蜂膠的主要成分，廣泛存在於自然界中，並且具有抗糖尿病以及心血管保護的作用。然而，咖啡酸苯乙酯在生物體內容易被酯酶(esterase)代謝而失去效用，因此生體可用率不高。在本研究中，我們利用ICR小鼠模式，探討咖啡酸苯乙酯以及白藜蘆醇(resveratrol)結構類似物—咖啡酸苯乙醯胺(caffeic acid phenylethyl amide，KS370G)對於代謝以及心血管是否具有保護作用。 在KS370G降血糖作用的實驗中，我們使用正常的小鼠、streptozocin誘發的第一型糖尿病小鼠以及飲食誘發的第二型糖尿病小鼠進行研究。單劑量口服給予KS370G可有效降低正常以及糖尿病小鼠的血糖值，同時也可增加正常以及第二型糖尿病小鼠血中的胰島素含量，1mg/kg以上的KS370G也可改善腹腔注射的葡萄糖耐受性，增加肝臟以及骨骼肌的肝糖含量。因此，KS370G的降血糖作用可能與增加胰島素含量以及葡萄糖利用率有關。在長期實驗中，我們也發現除了改善血糖與血脂，在Langendorff缺氧-再灌流的心臟模式中，給予KS370G的糖尿病小鼠具有比較大的冠狀動脈血流量以及比較小的缺氧-再灌流的心臟梗塞部分。更進一步的研究中顯示，至少有兩條訊息傳遞途徑與KS370G的保護作用有關：抗氧化酵素MnSOD的增加，以及肝臟中發炎因子TNFα和NFkB的減少。然而，更詳細的機轉還需要其他更多的實驗釐清。 心血管疾病，包括心臟肥大、心肌缺氧以及心衰竭，是造成糖尿病人死亡的最主要原因。在面臨壓力過載的情況時，心肌肥大是一個重要的代償機制，但是持續的使心臟過度工作可能導致代償失敗而引起心臟不正常的肥大，增加心衰竭發生的機率。在本研究中，我們也評估KS370G對於左心室肥大以及左心室功能的影響，我們利用腹部動脈結紮手術使心臟面臨壓力過載，在手術後的隔天開始給予一天一次口服1mg/kg的KS370G，手術八週後對肥大的心臟進行研究。我們發現長期口服給予KS370G能壓力過載引起的抑制心肌肥大，並且改善心臟功能，同時可降低血中心房利鈉素(atrial natriuretic peptide)和乳酸去氫酶(lactate dehydrogenase)的含量。此外長期口服給予也能顯著降低壓力過載引起的α-SMA表現增加以及ERK, AKT和GSK3β磷酸化增加的現象，減少心肌中膠原蛋白的囤積。 總而言之，KS370G可以保護飲食或是streptozocin引起的代謝異常，透過減少ERK, AKT和GSK3β的磷酸化而改善左心室功能和抑制心肌肥大，本研究顯示長期給予KS370G具有對抗糖尿病以及其併發症的保護潛力。

Caffeic acid phenyl ester, a major component of propolis, is distributed wildly in nature and has anti-diabetic and cardiovascular protective effects. However, rapid decomposition by esterase leads to its low bioavailability in vivo. In this study, metabolic and cardiovascular effects of oral caffeic acid phenylethyl amide (KS370G), whose structure is similar to caffeic acid phenyl ester and resveratrol, were investigated in ICR mice. Normal ICR, streptozotocin-induced diabetic (T1DM) and diet-induced diabetic (T2DM) mice were used in the study of antihyperglycemic actions of KS370G. Single oral administration of KS370G decreased the plasma glucose levels in both normal and diabetic mice. It was found that KS370G could stimulate the release of insulin in both normal and T2DM mice, and a dose of 1 mg per kg KS370G could significantly attenuate the increase of plasma glucose induced by an intraperitoneal glucose challenge test in normal and diabetic mice. Similar treatment with KS370G significantly increased glycogen content in both liver and skeletal muscle. Hence, the hypoglycemic effect of KS370G in normal and diabetic mice could be attributed to the stimulation of insulin release and the increase of glucose utilization. In chronic study, we also found that KS370G increased coronary flow and decreased infarct size after global ischemia-reperfusion in Langendorff perfused heart. Further study indicated that at least two pathways might be involved in such beneficial effects: the induction of the antioxidant protein MnSOD and the decrease of the proinflammatory cytokine TNFα and NFkB in the liver. However, the detailed mechanisms of KS370G need further studies. Cardiovascular disease, including hypertrophy, ischemia and heart failure, is the major cause of mortality in diabetic patients. Cardiac hypertrophy is an important compensatory mechanism in response to a pressure overload, but a sustained excessive cardiac workload may deteriorate to maladaptive hypertrophy and to increased risk of heart failure. In this study, we also evaluated the effects of KS370G on left ventricular hypertrophy and function. Abdominal aortic banding was performed by constricting the abdominal aorta and hypertrophied heart was studied at 8 weeks after the operation. After the operation, KS370G 1mg/kg (K1 group) was administered by oral gavage once a day. We found that chronic oral treatment with 1mg/kg KS370G inhibited cardiac hypertrophy and improved cardiac function induced by pressure overload. KS370G also decreased the plasma levels of atrial natriuretic peptide and lactate dehydrogenase. Besides, pressure overload-induced increase of α-SMA, phosphorylation of ERK, AKT and GSK3β were significantly reduced by chronic oral treatment with KS370G. We also found that chronic oral treatment with KS370G reduced cardiac collagen accumulation. In conclusion KS370G protected against diet or streptozocin-induced metabolic changes, improved left ventricular function and inhibited cardiac hypertrophy through the decrease of the phosphorylation of ERK, AKT and GSK3β in pressure-overload mice heart. This study demonstrated the protective potential of chronic treatment of KS370G against the metabolic consequences in diabetes mellitus.