Rutin與EGCG作用於大鼠胰臟β細胞之抗糖毒性機制探討

Abstract

第二型糖尿病，此後天慢性疾病對於現今人類有著重大的威脅，目前以周邊組織產生胰島素抗性與胰臟胰島β細胞功能喪失為主要探討之對象。在長時間因飲食等因素導致肥胖產生下，當體內為因應高代謝負荷量時，胰島β細胞會大量釋出胰島素促使糖類代謝，過去研究發現在肥胖個體上胰島β細胞因應體內代謝需求，產生代償性β細胞增生之現象，如此達到應對體內代謝之需求。但在長期負荷環境下可導致胰島β細胞失去對糖份感受性，最終可促使β細胞走向細胞凋亡一途，當胰島β細胞失去代償作用，同時合併周邊組織胰島素抗性之情況下，往往成為糖尿病致死之因素。過往研究中已顯示茶中富含之EGCG對於抗癌與身體能量之代謝有著顯著之功效。此外，已有研究顯示，蕎麥濃縮萃取物可有效降低於糖尿病模式動物之血糖濃度。因而針對天然物質中茶多酚物EGCG與蕎麥富含之類黃酮Rutin，對於胰島β細胞於高糖濃度的環境下，是否能提供實質上保護作用與其分子機制為何，進行相關研究與探討。 於本實驗研究顯示，EGCG與Rutin皆可以有效增加β細胞對於高糖環境培育下之胰島素釋放，並對長時間培育於高糖環境下之β細胞維持對糖份之感受性，並有效減緩β細胞長期培育於高糖環境下所導致之細胞衰亡之發生，有助於細胞生長與存活。進一步探討其分子機制，Rutin與EGCG可有效促進其PDX-1轉錄因子進入細胞核，並促進其活化。PDX-1為對於胰島發育與β細胞維持正常功能之重要因子，有效活化PDX-1可幫助β細胞生長、胰島素生成與第二型葡萄糖運輸蛋白(Glucose transporter 2)等蛋白質表現，同時發現EGCG於長時間的作用下，更可有效增加PDX-1蛋白質表現量。胰島素接受器受質IRS-2在過去研究顯示，對於β細胞生長、維持糖份感受性和胰島素生成等相關生理功能皆扮演重要角色，而β細胞長期處於高糖環境下會降低IRS-2表現而影響細胞正常功能，在同時給予細胞Rutin與合併於高糖的環境下，發現對於胰島素接受器受質(IRS-2)蛋白質表現量有顯著增加的效果，對於其活性的增加也藉由Rutin與EGCG之給予有著顯著的效果，並有效影響至下游訊號，包括Akt與FoxO1活性之表現。過去研究顯示β細胞在長期高糖環境下會促進細胞內脂肪堆積，造成對細胞的損傷與破壞，直接影響其正常功能運作。EGCG及Rutin於高糖之環境下對於β細胞皆能快速促進活化細胞內之AMPK(AMP-activated protein kinase)此激酶活性，並能有效抑制脂肪酸合成酶FAS(Fatty acid synthase)之生成，同時也抑制乙醯輔酶A羧化酶ACC(Acetyl-CoA carboxylase)活性之上升與脂質合成相關之轉錄因子SREBP1的表現，並有效減緩細胞於高糖環境下細胞內脂肪之囤積。Rutin與EGCG有效幫助胰島β細胞於調控醣類與脂質類代謝，此外，也可藉由影響細胞週期相關之蛋白質表現幫助維持細胞活性與增生，如Cyclin D1與p21，同時也作用於BAX與Bcl-2等蛋白質表現，幫助抑制高糖下導致之細胞凋亡現象。 胰島β細胞於長期高糖環境下，促使其逐漸失去正常生理功能與反應，而EGCG與Rutin兩種物質則可幫助β細胞面對於高糖所誘導產生之毒性，延續其細胞活性與存活能力，可望有效延緩糖尿病致病過程之發展。

Pancreatic β cell is a fundamental element for the development of diabetes. Chronic hyperglycemia is associated with insulin insufficiency and peripheral insulin resistance, in which β cells have to meet overloaded metabolic demands, but gradually will cause the deteriorating cell function, even leading to irreversible damage, cell death. The decompensation of pancreatic β cell followed by adaptation of increased demand represents the onset of diabetic progression. Therefore, how to maintain the intact cellular function under long term glucose induced toxicity could be strategies for detaining the progression of diabetes. Rutin and EGCG, natural occurring compounds, have been abundantly found in buckwheat and tea separately, which have been shown the potential of anti-diabetes and anti-obesity in past studies. The actions of Rutin and EGCG on pancreatic β cell are discussed in this study, manifesting the underlying molecular mechanism in regulating the cellular glucose and lipid metabolism. Rutin and EGCG preserved the glucose sensing and glucose-stimulated insulin secretion ability under high glucose incubation. IRS2 signaling was enhanced in the actions of Rutin and EGCG, facilitating the delivery to downstream signals Akt, FoxO1, and PDX-1, which have been implicated as crucial factors in pancreatic β cell growth and function. AMPK is considered as a fuel sensor that enables to response the cellular energy expenditure, and also exerts numerous regulations in metabolism. AMPK was activated in the treatment and effectively suppressed the cellular lipogenesis via inhibition of FAS expression, inactivation of ACC, and manipulation of SREBP1 maturation. Cyclin D1, p21, Bcl-2, and BAX expression levels are also affected in the treatment of Rutin and EGCG, which enhance the cell viability to deal with chronic exposure of elevated glucose. Long term action of glucose caused multiple abnormalities in metabolism, however, Rutin and EGCG presented comprehensive protection on pancreatic β cell against glucotoxicity, and exhibited the potential to be candidates for anti-diabetes.