Antidiabetic Effect of Black Bean Peptides through Reduction of Glucose Absorption and Modulation of SGLT1, GLUT2 and DPP‐IV in in vitro and in vivo Models
Authors: Mojica Luis , DE MEJIA ELVIRA GONZALEZ , Menjivar Marta , Granados‐Silvestre María Á. 
Published: November 2023

The aim was to determine the in vitro and in vivo effects of black bean peptides on glucose absorption and markers of diabetes in epithelial Caco‐2 cells, and in healthy and in diabetic Wistar rats. Peptide fractions (PF) were generated using an optimized hydrolysis process with alcalase for 120 min and an enzyme‐substrate ratio 1:20. In the in vitro model, glucose transporters SGLT1 and GLUT2 protein expression, dipeptidyl peptidase‐IV (DPP‐IV) activity, intracellular oxygen reactive species (ROS) and glucose absorption in Caco‐2 cells monolayer insert were evaluated. In the in vivo oral acute glucose tolerance test (OAGTT), the rats received a dose of 3.5 g of glucose/kg of body weight (BW) and were randomized into three groups: control (glucose load only), and glucose load plus either 30 or 50 mg PF/kg BW. Postprandial glucose was measured after treatments, during 0 to 150 min. The PF sub‐chronic effect was evaluated in the rats fed with a standard diet and corresponding treatments during eight days. The animals were randomized into five groups; hyperglycemia was induced in three of the groups with streptozotocin (ST, 45 mg/kg BW). Treatments were as follows: 1) ST+PF, 50 mg PF/kg BW twice a day; 2) ST+INS, 2 U insulin/kg BW twice a day, 3) ST, non‐treatment control; 4) CO+PF, non‐hyperglycemic rats fed 50 mg PF/kg BW twice daily, and 5) CO, nonhyperglycemic and non‐treatment control. Thirty‐three peptide sequences were identified by LC‐ESI‐MS/MS. PF reduced 28.2% SGLT1 and 25.2% GLUT2 of (p < 0.05) after 30 min of PF treatment (10 mg/mL). It also significantly inhibited DPP‐IV activity by 51.4% and 57.5% at 30 min and 24 h, respectively (p < 0.05). Glucose uptake was decreased by 8.0% and 14.6% after 30 min and 24 h of treatment, respectively, with 10 mg PF/mL (p < 0.05). PF reduced intracellular oxygen reactive species formation by 70%. For OAGTT, postprandial glucose significantly decreased in comparison to control (24% and 26%, respectively, p < 0.05). Glucose area under the curve (AUC) showed an overall reduction in glucose absorption in groups 30 mg PF (7,680 AUC) and 50 mg PF (5,640 AUC) compared to the control group (10,500 AUC). In the subchronic evaluation, there were no differences in animals body weight among groups (p > 0.05). Fasting glucose at day eight did not show significant differences between CO and CO+PF groups (p > 0.05). ST+PF group showed the lowest fasting glucose concentration (208.0 ± 42.3 mg/dL) compared to ST+INS (288.3 ± 69.0 mg/dL) and ST (383.8 ± 142.8 mg/dL) group (p < 0.05). ST+INS group showed a significant (p < 0.05) decrease in blood cholesterol 43.0 ± 6.6 mg/dL and LDL 1.76 ± 0.3 mg/dL. Renal profile, sera proteins profile and hepatic profile did not show significant differences among treatments. Insulin ranged from 0.72 ± 0.6 ng/mL (ST) to 2.9 ± 2.4 ng/Ml (CO). However, no significant differences in GLP‐1 levels were found among groups (p > 0.05). We report for the first time the potential of black bean peptides to reduce glucose absorption and concomitant lower postprandial glucose in a diabetic rat model.Support or Funding InformationInternational program UNAM‐UIUC