人類血清中ANGPTL6濃度與新生糖尿病的關係

Abstract

簡介 糖尿病是世界上最普遍的慢性疾病之一，可導致病人發生心血管疾病、腎病變、神經病變、視網膜病變等併發症，糖尿病的致病機轉除了眾所皆知的胰島素阻抗之外，肝臟與脂肪組織也被認為扮演重要的角色。肝臟會分泌hepatokines，脂肪細胞組織會分泌adipokines，均與調控生物體內營養素的代謝有關。Angiopoietin-like protein 6 (ANGPTL6) 是一個近幾年新發現的hepatokine，在動物實驗中發現其可增加能量消耗、改善胰島素敏感性以及減輕體重。然而，文獻中人類橫斷性研究中卻發現糖尿病受試者其血清中的ANGPTL6濃度較健康對照組高。本研究將利用前瞻性的縱貫性世代來探討人類血清中ANGPTL6濃度與新生糖尿病之間的關係，以釐清動物實驗與人類橫斷性研究看似衝突的結果。 目的 利用縱貫性的世代研究 (longitudinal cohort study)，探討血清中ANGPTL6濃度與未來新生糖尿病之間的關係。本研究的假說是 (1) 隨著血糖上升，血清中ANGPTL6濃度也隨之上升，可用以解釋文獻中人類橫斷性研究的結果。 (2) 血清中ANGPTL6濃度較高的受試者，未來發生糖尿病的機會較低。 方法 本研究採用的世代是一個以社區為基礎的世代，收錄2006年至2012年20歲以上且從未被診斷有糖尿病的台灣雲林地區居民。在此前瞻性世代中，每一至三年會追蹤一次，且接受詳盡的問卷受訪、身體理學檢查 (包括血壓、身高、體重、腰圍、臀圍等) 與抽血檢驗，檢測項目包括基礎生化值、口服葡萄糖測試、高密度及低密度膽固醇、三酸甘油酯及胰島素抗性指標等。 本研究利用ELISA (Enzyme-Linked Immunosorbent Assay) 來測量受試者初次進入本研究時血清中ANGPTL6濃度，藉此探討血清中ANGPTL6與新生糖尿病的關係，分析上利用Pearson’s correlation coefficient 來探討臨床上的特徵與ANGPTL6之關係。此外，採用Cox proportional hazard model，計算血中ANGPTL6濃度是否可以預測未來糖尿病的產生，並調整相關干擾因子，包括年齡、性別、糖尿病家族史、身體質量指標 (body mass index, BMI) 糖化血色素及胰島素分泌相關指標HOMA2-B (Homeostasis Model Assessment 2-beta cell function index) 與HOMA2-IR (Homeostasis Model Assessment 2-insulin resistance index)。 結果 此研究世代收錄1103位沒有糖尿病的社區民眾，平均追蹤時間為4.22年 (interquartile range 2.16-6.04年)，在追蹤期間，有113位受試者新發生糖尿病，990位受試者仍無罹患糖尿病。血清中ANGPTL6濃度與年齡、空腹血糖、葡萄糖耐受性測試後兩小時的血糖、糖化血色素呈現正相關，女性受試者血清中ANGPTL6的濃度較男性為高。利用Cox proportional hazard model，在調整過年齡、性別、糖尿病家族病史、身體質量指標、糖化血色素，HOMA2-B與HOMA2-IR之後，發現血中ANGPTL6越高，則新生糖尿病的風險越低 (Hazard ratio=0.77，95% confidence interval 0.60-0.98, p<0.05)，這結果與動物實驗的發現一致。 文獻中的橫斷面研究顯示，糖尿病以及代謝症侯群的受試者血清中ANGPTL6濃度比健康對照組為高；在本研究縱貫性世代追蹤前 (baseline) 的橫斷面分析，也發現糖尿病前期的受試者，血清中ANGPTL6濃度顯著地比血糖正常的受試者為高 (p=0.018)。此外，本研究中有89位受試者接受了75克口服葡萄糖耐性測試 (75gm oral glucose tolerance test)，並於空腹、30分鐘與120分鐘測定了血清中ANGPTL6的濃度。結果顯示血清中ANGPTL6濃度隨者血糖上升而顯著地上升 (p<0.001)，且空腹血清ANGPTL6濃度與接受口服葡萄糖耐性測試後30 分鐘 (r=0.5833, p<0.0001) 以及120分鐘 (r=0.05873, p<0.0001) 血清中之ANGPTL6濃度呈現正相關，也與血清中ANGPTL6 ROC曲線下方的面積 (area under curve) 呈現正相關 (r=0.7111, p<0.0001)。 討論 針對世代研究與橫斷面分析結果的不同，我們認為是因為兩者代表的意義不同。橫斷面分析代表的是，高血糖對於血清中ANGPTL6的影響；而縱貫性世代研究的結果，則是血中ANGPTL6對於血糖的作用。另外，針對世代研究的結果，我們的解釋如下：在追蹤過程中，當血糖因為年紀、肥胖或營養過剩等原因升高時，血中ANGPTL6會代償性的升高來維持血糖正常，當此代償機制越好，未來罹患糖尿病的風險較低。 結論 本研究證實血清中ANGPTL6濃度會隨者血糖上升而升高，同時，血清中ANGPTL6濃度較高的受試者，在調整年齡、性別、糖尿病家族史、身體質量指標、糖化血色素以及HOMA2-B與HOMA2-IR等變項後未來發生糖尿病的機會較低。

Introduction Type 2 diabetes mellitus is one of the most prevalent chronic diseases in the world and can result in multiple complications such as cardiovascular disease, nephropathy, neuropathy and retinopathy. Recently, liver is found to secrete various hepatokines to regulate energy homeostasis and glucose metabolism, which is similar to the concept of adipokines. Angiopoietin-like protein 6 (ANGPTL6) is a novel hepatokine which increases energy consumption, improve insulin sensitivity and lower body weight, as shown in animal studies. However, human cross-sectional studies in the literature showed that serum ANGPTL6 level is higher in subjects with diabetes than in healthy subjects. In this study, we used a prospective longitudinal cohort to investigate the relationship between serum ANGPTL6 and incident diabetes, in order to reconcile the findings from animal study and human cross-sectional studies. Methods and Materials In the present study, we used a longitudinal cohort study to analyze the relationship between serum ANGPTL6 level and the incidence of diabetes mellitus. This cohort is community-based, which enrolled residents from the Yunlin County, Taiwan, aged over 20 years old, who did not report the presence of diabetes during an interview. Subjects were invited to join this prospective study from 2006 to 2012 and followed visits were arranged every 1 to 3 years. Diabetes was diagnosed by the results of OGTT and hemoglobinA1c, or if the subject received anti-diabetic agents. Serum ANGPTL6 level was measured by ELISA (Enzyme-Linked Immunosorbent Assay). Results We recruited 1103 subjects without diabetes at baseline. Serum ANGPTL6 is higher in subjects with pre-diabetes, compared with that in normal controls (p=0.018). After glucose challenge, serum ANGPTL6 increased significantly (p<0.001). Besides, fasting serum ANGPTL6 concentration was positively associated with serum ANGPTL6 level at 30-minutes (r=0.5833, p<0.0001), serum ANGPTL6 level at 120-minutes after glucose challenge (r=0.05873, p<0.0001) and area under the curve of serum ANGPTL6 during an OGTT (r=0.7111, p<0.0001). During an average of 4.22 years (interquartile range 2.16-6.04 years) of follow-up, 113 subjects developed incident diabetes. High serum ANGPTL6 was associated with a lower incidence of diabetes (HR for 1 SD increase in serum ANGPTL6=0.77, 95% confidence interval: 0.60-0.98, p<0.05), adjusted for age, gender, family history of diabetes, BMI, hemoglobin A1C, HOMA2-B and HOMA2-IR. Discussion The seemingly conflict findings between longitudinal study and cross-sectional study may result from different meanings of the studies. Results from cross-sectional studies suggest the regulation of serum ANGPTL6 by hyperglycemia which is supported by the results of OGTT in the present study; whereas results from cohort study indicate the function of serum ANGPTL6 on glucose homeostasis which is in concordance with the findings of animal study. The secreted serum ANGPTL6 is increased to counteract increased plasma glucose developed by other mechanisms such as aging, obesity or nutrition excess. Therefore, a better compensatory effect of serum ANGPTL6, as indicated by a high fasting serum ANGPTL6 concentration, is associated with a lower incidence of new onset diabetes. Conclusion Serum ANGPTL6 increased in response to hyperglycemia. A high fasting serum ANGPTL6 level was associated with a better response to hyperglycemia and was a protective predictor for the incidence of diabetes.