High glucose stimulates glutamate uptakes in pancreatic β-cells

Abstract

Pancreatic β-cells are major cells responsible for glucose metabolism in the body. Hyperglycemia is known to be a primary factor in the induction of diabetes mellitus. Glutamate is also an excitatory neurotransmitter in diverse organs. Oxidative stress also plays a pivotal role in the development of diabetes mellitus. However, the effect of hyperglycemia in glutamate uptake in the pancreas is not clear. Furthermore, the relationship between high glucose-induced glutamate uptake and oxidative stress has not been investigated. Therefore, this study was conducted to investigate the effect of high glucose on glutamate uptake in pancreatic β-cells. In the present study, 25 mM glucose stimulated the glutamate uptake in HIT-15 cells of hamster pancreatic β-cells. The treatment of 25 mM glucose and 1 mM glutamate also decreased the cell viability in HIT-15 cells. In addition, the treatment of 25 mM glucose induced an increase of lipid peroxide formation. High glucose-induced increase of LPO formation was prevented by the treatment of antioxidants such as N-acetyl-L-cysteine and quercetin. Furthermore, high glucose-induced stimulation of glutamate uptake and decrease of cell viability were also blocked by the treatment of N-acetyl-L-cysteine and quercetin. In conclusion, high glucose stimulated glutamate uptake via oxidative stress in pancreatic β-cells.

Keywords: Pancreatic β-cells; glutamate uptake; hyperglycemia; oxidative stress.

Figure 1

Time and dose response of 25 mM glucose on D-[2,3-³H]-aspartate uptake. (A) Dose dependent effect of glucose and the effect of osmotic load on D-[2,3-³H]-aspartate uptake. Different dosages of glucose (10, 25 or 50 mM glucose), 25 mM mannitol, or 25 mM L-glucose were administered to HITT15 cells. (B) HIT-T15 cells were treated with 25 mM glucose at different time intervals (0-480 min). Then, D-[2,3-³H]-aspartate uptake was determined. Values are mean±SE of three independent experiments performed in triplicate. ^*P<0.05 vs control (Con: 5 mM glucose).

Figure 2

Dose response of 25 mM glucose on cell proliferation. Different dosages of glucose (25 or 50 mM glucose), 25 mM mannitol, or 1 mM L-glutamate were administered to HIT-T15 cells for 24 h and cell proliferation was determined using MTT assay. Values are mean±SE of three independent experiments performed in triplicate. ^*P<0.05 vs control (Control: 5 mM glucose).

Figure 3

Effect of N-acetyl-L-cysteine (NAC) and quercetin on high glucose-induced lipid peroxide formation (A) and D-[2,3-³H]-aspartate uptake (B). NAC (1 mM) and quercetin (100 µM) were used to treat the HIT-T15 cells for 30 min prior to the treatment of 25 mM glucose for 8 h. Then, lipid peroxides and D-[2,3-³H]-aspartate uptake were conducted. ^*P<0.05 vs control, ^**P<0.05 vs 25 mM glucose alone.

Figure 4

Effect of N-acetyl-L-cysteine (NAC) and quercetin on high glucose-induced cell proliferation. NAC (1 mM) and quercetin (100 µM) were used to treat the HIT-T15 cells for 30 min prior to the treatment of 25 mM glucose for 24 h. Then, cell proliferation was determined using MTT assay. ^*P<0.05 vs control, ^**P<0.05 vs 25 mM glucose alone.