Induction Methods of Type 2 Diabetic Models

Type 2 DM rats were induced by low dose STZ administration and high-fat-diet feeding (Gheibi et al., 2017). SD rats were randomly divided into “Control Rats” group (n = 15) and “T2DM Rats” group (n = 54).

After fasting for 10 h, rats in T2DM Rats were intraperitoneally injected with 1% STZ (Lot number WXBC3087V, Sigma-Aldrich, St. Louis, MO, United States) citrate buffer (pH = 4.2–4.5) at a dose of 30 mg/kg body weight in the first time (−3d, Figure 1). At 72 h after STZ injection, these rats fasted for 3 h before measurements of fasting blood glucose (FBG) were taken. The rats with FBG < 11.1 mmol/L were re-injected with the same dose of 1% STZ on the next day (1d, Figure 1). FBG was again measured after 72 h and continued to be measured for 20 weeks. Type 2 DM rats were fed with a high-fat diet (10% lard + 20% sucrose + 2.5% cholesterol + 1% cholate + 66.5% conventional chow) during the whole experimental process (Gheibi et al., 2017). Rats in the Control rats group were injected with the same amount of citrate buffer, and were fed with a normal diet.

Schematic representation of experimental design. Type 2 DM rats were induced by low dose STZ administration and high-fat-diet feeding. SD rats were randomly divided into Control rats group and T2DM rats group. After fasting for 10 h, rats in the T2DM rats group were intraperitoneally injected with 1% STZ citrate buffer at a dose of 30 mg/kg body weight in the first time (−3d). At 72 h after STZ injection, these rats were fasted for 3 h and subjected to measurements of FBG. The rats with FBG < 11.1 mmol/L were re-injected with the same dose of 1% STZ on the next day (1d). FBG was measured after 72 h and continued to be observed for 20 weeks. Type 2 DM rats were fed with high-fat-diet starting day 0. Rats in the Control rats group were injected with the same amount of citrate buffer, and were fed with normal diet. The KK-Ay mice model of spontaneous type 2 DM was established by feeding with high-fat-diet which was started at day 0, while the C57BL/6J control mice were fed with normal diet. The body weight and FBG for rats and mice were recorded every 2 weeks. Serum and urine samples were collected, and OGTT and ITT were performed, at the indicated time points after the initial of modeling. Animals were sacrificed at the indicated time points, and renal tissues were used for H&E staining. STZ, streptozotocin; FBG, fasting blood glucose; OGCT, oral glucose challenge test; ITT, insulin tolerance test.

Male C57BL/6J mice (n = 18) and KK-Ay mice (n = 18, SPF grade, 8 weeks old) were maintained in the individually ventilated cages (IVC) at the experimental animal center for 20 weeks (Figure 1). The KK-Ay mice model of spontaneous type 2 DM was established by feeding with high-fat diet (protein 16.5 kcal%, carbohydrate 37.9 kcal%, fat 45.6 kcal%) (Gheibi et al., 2017), while the C57BL/6J control mice were fed a normal diet. All feed was purchased from Beijing Huafukang Biotechnology Co. Ltd. with a license No. SCXK (Beijing) 2014-0008.