Monascin 扮演天然 PPARγ 促效劑以改善甲基乙二 醛誘導發炎及糖尿病之機制探討

Abstract

本研究探討 monascin 對胰島素阻抗之改善作用，並評估 monascin 對血糖調節之可能機制。結果發現 monascin 為過氧化小體增生劑活化接受體 (peroxisome proliferator activated receptor-γ；PPARγ) 促效劑 (agonist) 而能活化 PPARγ，進而改善 tumor necrosis factor-α (TNF-α) 及 methylglyoxal 所造成 C2C12 肌肉細胞與 FL83B 肝臟細胞的胰島素抗性。此外，monascin 可透過活化核因子-紅血球之 2 相關因子-2 (nuclear factor-erythroid 2 related factor-2；Nrf2) 來減緩 THP-1 單核球細胞的過度糖化最終產物受器 (receptor for advanced glycation endproducts；RAGE) 訊號活化所造成的氧化壓力及發炎細胞激素產生。另外一方面，以連續 28 天口服方式給予 methylglyoxal (600 mg/kg bw) 來誘導 Wistar 大鼠產生糖尿病，在糖尿病誘導前，動物先被進行口服葡萄糖耐受試驗 (oral glucose tolerance test；OGTT)，結果發現 monascin 可較糖尿病用藥 (rosiglitazone；PPARγ agonist) 更有效減緩血糖上升，且此活性與胰島素分泌無關，顯示 monascin 可能不需胰島素存在下直接改善周邊組織對葡萄糖的利用；動物在經 methylglyoxal 誘導後可明顯造成高血糖 (hyperglycemia) 及高胰島素症 (hyperinsulinmia)，而 monascin 處理則可較 rosiglitazone 更有效抑制 methylglyoxal 所造成的發炎及高血糖現象。此外，monascin 可透過活化 Nrf2 而增加 glyoxalase 表現以代謝 methylglyoxal，減少過度糖化最終產物 (advanced glycation endproducts；AGEs) 含量，而 rosiglitazone 則無此活性。由於 monascin 對高血糖的改善優於 rosigltazone，故本研究進而探討 monascin 對肝臟之調節效應，結果發現 monascin 可透過增加動物肝臟 adenosine monophosphate (AMP) protein kinase (AMPK) 磷酸化而使其活化，進而改善肝細胞對葡萄糖之攝入效應，且此結果也於 FL83B 肝細胞中被確認；以上 monascin 對細胞與動物之改善效果均可因 GW9662 (PPARγ 抑制劑) 或 PPARγ siRNA 處理而被減弱，顯示 monascin 對糖尿病之改善效應對 PPARγ 具依賴性，而具備開發為抗糖尿病藥物之潛力。

The aim of this study is to investigate the improvement of monascin on insulin resistance and the mechanism of monascin for blood glucose regulation. Results indicated that monascin plays as a peroxisome proliferator activated receptor-γ (PPARγ) agonist to activate PPARγ, thereby attenuating insulin resistance in C2C12 cells induced by tumor necrosis factor-α (TNF-α) and FL83B hepatocytes induced by methylglyoxal. In addition, monascin activates nclear factor-erythroid 2 related factor -2 (Nrf2) to inhibit activation of receptor for advanced glycation endproducts (RAGE), lowering oxidative stress and pro-inflammatory cytokine production in THP-1 monocytes. On the other hand, Wistar rats were administered with methylglyoxal (600 mg/kg bw) for 28 days to induce diabetes, and the oral glucose tolerance test (OGTT) was carried out before methylglyoxal induction. Results indicated that the suppression of blood glucose elevation by monascin treatment was greater than rosiglitazone (PPARγ agonist), and this activity was not depended in insulin secretion, suggesting that monascin was able to promote glucose uptake in the absence of insulin. Methylglyoxal induction significantly resulted in hyperglycemia and hyperinsulinmia in Wistar rats, but monascin effectively inhibited inflammation and hyperglycemia caused by methylglyoxal comparing to rosiglitazone treatment. We also found that monascin increased glyoxalase expression to metabolize methylglyoxal via activating Nrf2, resulting in an attenuation of advanced glycation endproducts generation, but rosiglitazone treatment did not exert this effect in methylglyoxal-induced rats. As a result of monascin significantly down-regulated blood glucose than rosiglitazone, hence, this study investigated the effect of monascin on liver. Result demonstrated that monascin elevated AMP protein kinase (AMPK) phosphorylation to improve glucose uptake of hepatic cells, and this result was confirmed in FL83B hepatocytes. However, the anti-diabetic effects of monascin were attenuated by GW9662 or PPARγ siRNA treatment in vitro and in vivo. It suggested that improvements of monascin for hyperglycemia depended in PPARγ activation therefore monascin have potentials for development of anti-diabetic agent.