血糖控制不良是糖尿病程進展的重要因素，高血糖之葡萄糖毒性會造成胰臟β細胞損傷，影響葡萄糖刺激之胰島素分泌(GSIS)功能。本實驗室過去研究發現，餵食大蒜精油(GO)及其有機含硫成分二烯丙基三硫化物Diallyltrisulfide(DATS)可在streptozotocin誘發的糖尿病大鼠增加空腹及葡萄糖負荷後血中胰島素含量；本研究觀察在正常及高糖濃度下，GO及DATS對於胰島β細胞株HIT-T15之GSIS功能之影響。實驗方法係將HIT-T15細胞培養於含有不同葡萄糖濃度(5.5、11.1、33.3mM)之培養基中並加入不同濃度之GO(1-10μg╱ml)或DATS(0.001-0.01mM)，培養24小時後觀察細胞存活率、胰島素分泌量、ATP含量及葡萄糖運輸動力學。此外，在高糖培養基的實驗中，亦觀察不同濃度之GO對於細胞抗氧化狀態之影響。結果發現，在正常培養基中添加GO不影響細胞存活率但顯著且呈劑量依賴性增加GSIS(最大增加率達33%)，且其效果與glibenclamide之作用相當；而細胞ATP含量及細胞葡萄糖運輸動力學研究結果顯示，GO促進GSIS之作用至少有部分可由促進細胞攝取葡萄糖及產生ATP來解釋。另一方面，DATS在不影響細胞存活率的最大劑量下可促進GSIS作用，並且增加細胞ATP含量及改善細胞葡萄糖運輸蛋白對於葡萄糖之親和力，但其效果不如GO。此結果顯示，正常下GO僅部分透過其中所含之DATS促進胰島素分泌。在高葡萄糖濃度(11.1、33.3mM)培養條件下，細胞存活率並未受影響且並未顯著發生apoptosis，但細胞GSIS顯著降低，伴隨細胞ATP含量降低且細胞最大攝取葡萄糖運輸速率亦下降。此外，高糖顯著增加細胞脂質過氧化程度並顯著降低細胞SOD活性影響，但是不影響總GSH含量或GPx與GR之活性。培養在高糖下之細胞可因添加GO而顯著增加細胞GSIS作用、ATP含量並增加葡萄糖運輸蛋白對於葡萄糖之親合力，且DATS在高糖下對於胰島素分泌、ATP含量或係葡萄糖運輸動力學之影響均與GO類似。而高糖下添加GO雖然增加細胞SOD活性，然而細胞脂質過氧化程度並未因而獲得改善。由本實驗結果可得知，HIT-T15細胞不論培養於正常培養基或含高葡萄糖之培養基，GO均呈現促進胰島素分泌之作用，且與增加細胞對於葡萄糖之利用及胞內ATP含量有關，但是與降低高糖所致之氧化傷害無關。而在高糖下GO促進胰島素分泌的作用中，DATS為作用成分之一。 Poorly controlled blood glucose level has been recognized a major factor responsible for the progressing of diabetes. Glucose toxicity resulting from hyperglycemia adversely affects glucose-stimulated insulin secretion (GSIS) from islet beta cell. We previously reported that both garlic oil (GO) and its organosulfur compound diallyl trisulfide (DATS) improved plasma insulin level in diabetes. With an islet beta cell line HIT-T15, the present study investigated the effect of GO and DATS on GSIS under normal- (5.5 mM glucose) and hyper-glycemic (11.1 or 33.3 mM glucose) condition. Cells were cultured in various concentrations of glucose with or without GO (1-10 .mu.g╱ml) or DATS (0.001-0.01 mM) for 24h followed by the determination of their validity, GSIS, cellular ATP content, and glucose transport kinetics. The effect of GO on oxidative condition of cells cultured under hyperglycemic condition was also investigated. When under normal condition, GO did not affect the validity while dose-dependently increased the GSIS to a level similar to that by glibenclamide. Studies on cellular ATP content and on glucose transport kinetics suggested that GO could improve GSIS through improving cellular glucose uptake and ATP production. Hyperglycemia affected neither the validity nor the apoptosis rate of cells while suppressed the GSIS and lowered cellular ATP content and the maximal glucose transport rate. Hyperglycemia also increased TBARS and decreased SOD activity in cells, although total GSH content, the activity of GPx and GR remained unaffected. GO reversed decreased GSIS and cellular ATP content in cells cultured under hyperglycemic condition, and improved Km of glucose transport in these cells. DATS showed similar effects on GSIS, cellular ATP and the kinetics of glucose transport to that of GO in cells cultured under both normal- and hyper-glycemic conditions. In addition, GO also improved SOD activity of cells cultured under hyperglycemic condition, however, did not ameliorate the increased TBARS in these cells. In conclusion, GO acutely improved GSIS in the beta cell line HIT-T15 cultured in normal and in hyperglycemic conditions in associate with increased glucose utilization by these cells while not through its antioxidant effect. DATS is a major functional compound in GO for its insulin secretogogues effect.
