高血尿酸與第 2 型糖尿病及心血管疾病發展有關,但傳統的降尿酸藥物之副作用限縮了其臨床使用,故需積極尋找替代療法。已知台灣土肉桂葉精油 (TC) 及其活性成分枷羅木醇 (linalool, Lin) 及肉桂醛(cinnamaldehyde, Cin) 能抑制 xanthine oxidase 活性,且有抗發炎效果。本研究利用十週齡雄性 C57BL/6 小鼠隨機分為十組,其中一組給予一般飲食,其餘九組給予含有 2% potassium oxonate 及 3% uric acid 之高尿酸飲食,於開始實驗後第四十二天以隔日管餵一次的方式給予試劑,共灌食八次。一般飲食組及其中一組高尿酸飲食組灌食載劑玉米油 (2 ml/kg BW),其餘八組高尿酸飲食組則分別灌食 TC (13 mg/kg BW)、Lin 合併 Cin (Lin:5.2 mg/kg BW、Cin:0.9 mg/kgBW)、低劑量 Lin (2.6 mg/kg BW)、高劑量 Lin (5.2 mg/kg BW)、低劑量 Cin (0.45 mg/kgBW)、高劑量 Cin (0.9 mg/kg BW)、allopurinol (5 mg/kgBW)、colchicine (1.5 mg/kg BW)。於第六次灌食後執行口服葡萄糖耐受試驗及胰島素耐受試驗,在實驗開始後第五十六天的早上眼窩採血,備用於血尿酸濃度分析,並於灌食後禁食十五小時再以二氧化碳窒息犧牲,收集血液,備用於尿酸、fructosamime、IL-1β、CXCL1、ICAM、C-peptide、nitrate/nitrite 濃度分析,並收集組織/臟器,備用於nitrate/nitrite、IL-1β、TNF-α 含量分析、caspase-1 活性分析、西方墨點分析及/或組織學觀察。結果顯示,給予高尿酸飼料或灌食土肉桂精油成分後對於小鼠體重並無顯著影響。與控制組相較,此模式顯著提高飽食狀態下血尿酸濃度,且介入 TC 可顯著降低其濃度,但無論是單獨或合併給予 Lin、Cin 雖有降低尿酸值之趨勢,但不具統計學意義。在血糖調控方面,此模式雖未影響葡萄糖耐受性及周邊 fructosamine 濃度,但顯著增加血清中 C-peptide 濃度,且經過葡萄糖負荷兩小時,血清中 C-peptide 濃度也有增加之趨勢,顯示此模式雖然尚未影響血糖值及胰島素分泌能力,但可能有胰島素阻抗之現象以致需分泌較多胰島素來維持正常血糖;而介入 TC、單獨或合併給予 Lin 或 Cin 均可在不影響血糖的情況下顯著降低高尿酸所導致之 C-peptide 升高,顯示精油及其成分具有改善胰島素阻抗之效果,其機制可部分歸因於逆轉高血尿酸所造成之脂肪組織中 TLR2、MyD88、ASC、caspase-1 p20 的蛋白質表現量增加及 IL-1β 含量增加,及逆轉骨骼肌中 nitrate/nitrite 含量減少的情況。在血壓及血管內皮功能方面,與控制組相較,此模式造成血管內皮中 eNOS 蛋白質表現量減少,並伴隨周邊血中 nitrate/nitrite 濃度顯著下降,這可能造成血管內皮功能不良,進而導致血壓調控異常,而無論是介入 TC、IX合併或單獨給予 Lin 及 Cin 均顯著提升周邊血中 nitrate/nitrite 濃度,並伴隨回復血管內皮 eNOS 蛋白質表現量。綜合以上結果,TC 及其活性成分Lin 及 Cin 具有減緩高血尿酸所造成之脂肪組織發炎反應活化,並有助於回復骨骼肌及內皮細胞釋出 NO,進而改善高尿酸所導致之血糖調控不佳及血壓異常。
Recent studies suggest that hyperuricemia is an independent risk factor for type 2 diabetes mellitus and cardiovascular disease. However, the use of urate-lowering drugs is usually limited by the adverse effects. Hence, there is a need for alternative/complamentary treatments. Previous studies found the leaf essential oil of Cinnamomum osmophloeum Kanehira (TC) and its active ingredients linalool (Lin) and cinnamaldehyde (Cin) have inhibitory effect on xanthine oxidase and possess anti-inflammatory activity. In the present study, male C57BL/6 mice were randomly assigned to ten groups, one of which was given normal diet, and the others were given hyperuricemia-inducing (HU) diet containing 2% potassium oxonate and 3% uric acid and treated for 56 days. On the 42nd day, mice receiving HU diet were gavaged with vehicle (corn oil, 2 ml/kg BW), TC (13 mg/kg BW), Lin (5.2 mg/kg BW) plus Cin (0.9 mg/kg BW), Lin (2.6 or 5.2 mg/kg BW), Cin (0.4 or 0.9mg/kg BW), allopurinol (5 mg/kg BW) or colchicine (1.5 mg/kg BW) every other day until day 56. Mice receiving normal diet were gavaged with vehicle. Oral glucose tolerance test and insulin tolerance test were conducted on the 53th and 54th day, respectively. On the 56th day, blood samples were collected from orbital sinus and used for the determination of serum uric acid concentration. Subsequently, mice were starved overnight before sacrificed with CO2 which was followed by the collection of blood and tissues/organs for analysis. It was found that body weight of the animals was not affected by either the treatment with HU diet or the intervention with TC, Cin, or Lin. Compared with the normal diet-fed mice, HU diet-fed mice showed significantly elevated level of serum uric acid at fed satus but can be reversed by the treatment with TC. Although HU diet did not affect fasting peripheral fructosamine concentration or glucose tolerance, fasting serum C-peptide concentration was found to be significantly increased thus suggest insulin resistance may occur in mice receiving HU diet. In addition, the treatment with TC, Cin, and Lin reversed elevated fasting C-peptide level in mice receiving HU diet without affecting glucose tolerance of these animals, suggesting improved insulin-sensitivity by these agents. The protective effect of these agents is attributable to not only the reduced IL-1β content in epididymal adipose tissue which was associated with decreased expression of TLR2, MyD88, ASC and caspase-1 p20 in this tissue but also the reversed level of nitrate/nitrite in gastrocnemius muscle of these mice. The present study also found that fed mice with HU diet decreased eNOS expression in vascular endothelial along with significant reduction of serum nitrate/nitrite, suggesting endothelial dysfunction may occur in mice receiving HU diet. The treatment with TC, Cin, and Lin significantly reversed HU diet-induced reduction of serum nitrate/nitrite and showed to be associated with elevated expression of eNOS in vascular endothelial. In conclusion, the results of this study suggest that TC and its active ingredients Lin and Cin have preventive effects on HU diet-induced activation of inflammation in adipose tissue and help to restore physiological level of NO in skeletal muscle and in peripheral blood, thereby would benefit glycemic and blood pressure homeostasis under hyperurecemic condition.
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