Sitagliptin phosphate

DPP IV (lyophilized powder, ≥ 10 units/mg protein, D-7052), glucose, Gly-Pro p-nitroanilide, pepsin (3460 units/mg solid, P-6887), and sitagliptin phosphate were purchased from Sigma Chemical Co. (St. Louis, MO). The HF diet for obesity induction (fat composition provide 60% of total calories, D12942) was purchased from Research Diets, Inc. (NJ, USA). The standard mouse/rat chow (fat composition provide 12.137% of total calories, Prolab® RMH2500, 5P14 Diet; PMI Nutrition International, MO, USA).

RES was purchased from Sigma Chemical Co. Sitagliptin phosphate (Januvia) was produced by Merck Sharp Dohme Ltd. Rosiglitazone was produced by Chengdu Hengrui Pharmaceutical Co., Ltd. Fluoxetine hydrochloride (Prozac) was provided by Eli Lilly Pharmaceuticals. Donepezil hydrochloride (Haosen) was produced by Jiangsu Haosen Pharmaceutical Co., Ltd. All the drugs were dissolved in an aqueous solution of 0.5% sodium carboxymethyl cellulose for a mixed suspension.

Imperatorin (purity > 98%) and triamterene (Sigma-Aldrich Chemical Co., St. Louis, MO, USA) were diluted in dimethyl sulfoxide (DMSO) as the stock solution. Additionally, sitagliptin phosphate (Merck, Cramlington, Northumberland, UK), an inhibitor of dipeptidyl peptidase-4 (DPP-4), was diluted in normal saline.

QUE was purchased from Sigma Chemical Co. (Louis, MO, USA). Sitagliptin phosphate was produced by Merck Sharp Dohme Ltd. (New Jersey, USA). Donepezil hydrochloride was produced by Jiangsu Haosen Pharmaceutical Co., Ltd. (Jiangsu, China). All the drugs were dissolved in 0.5% sodium carboxymethyl cellulose aqueous solution to make a mixed suspension.

All experiments were conducted with the minimum number of animals and in obedience to the guidelines of the Animal Care Committee from the Sichuan Agricultural University. Male wistar rats (about 200 grams) were maintained in an enriched environment with a room-controlled temperature, 12 h light-dark cycle, food and water available ad libitum. HepG2 cell was a gift from Chengdu institute of biology, Chinese academy of science. Cells were maintained in RPMI-1640 or DMEM (high glucose) (Sigma, USA) containing 10% bovine calf serum (BCS) (Invitrogen, USA) and 100 U/mL penicillin-streptomycin at 37 °C with 5% CO₂. The Isoquercitrin (98% purity) was purchased from National Institutes for food and drug control of China. Sitagliptin phosphate (100 mg/pill) was produced by Merck sharp & Dohme Italia SPA (Italy).