Effects of Bee Bread Extract on Fasting Glycaemia and Irs-1 Gene Expression in a Streptozotocin-Nicotinamide Model of Diabetes in Male Rats

Abstract

Background and Objective: Bee bread contains nutrients and phytochemicals that may influence metabolic homeostasis, but its effects on insulin-signalling-related outcomes in experimental diabetes remain incompletely characterised. This study evaluated the effects of ethanolic bee bread extract on fasting blood glucose (FBG), serum insulin, glucagon, an assay-derived serum GLUT4 concentration, pancreatic histology, and skeletal-muscle insulin receptor substrate-1 (IRS-1) gene expression in a streptozotocin-nicotinamide model of diabetes in male rats. Methods: Twenty-seven rats were included in the efficacy experiment and allocated to six groups: non-diabetic control (n = 5), untreated diabetic control (n = 4), metformin 100 mg/kg (n = 4), and bee bread extract at 150 mg/kg (n = 5), 300 mg/kg (n = 4), or 600 mg/kg (n = 5). Treatments were administered orally once daily for 3 weeks. A separate eight-animal acute oral toxicity observation preceded the efficacy experiment. IRS-1 expression was assessed by RT-qPCR and expressed relative to GAPDH using the 2^-DeltaDeltaCt method. Results: Mean FBG increased from 10.13 +/- 0.31 to 18.84 +/- 0.68 mmol/L in untreated diabetic rats, whereas final FBG was 5.71 +/- 0.47 mmol/L with metformin and 5.78 +/- 0.43, 5.20 +/- 0.50, and 4.84 +/- 0.31 mmol/L with 150, 300, and 600 mg/kg bee bread, respectively. Serum insulin remained similar among groups. Glucagon was higher in untreated diabetic rats (67.49 +/- 1.72 ng/mL) than in the non-diabetic group (29.71 +/- 1.41 ng/mL) and was lower in all bee-bread groups (39.73 +/- 0.63 to 33.94 +/- 1.50 ng/mL). The serum GLUT4 assay concentration was lowest in untreated diabetic rats (0.49 +/- 0.08 ng/L) and higher after bee bread treatment (1.70 +/- 0.11 to 3.04 +/- 0.04 ng/L). Relative IRS-1 expression was 0.50 in untreated diabetic rats and 1.10, 1.18, and 1.31 in the 150, 300, and 600 mg/kg groups, respectively. Pancreatic histology showed no major qualitative architectural differences across groups. Conclusion: Bee bread administration was associated with lower fasting glycaemia and glucagon, higher assay-derived GLUT4 concentrations, and higher skeletal-muscle IRS-1 expression in this experimental model. These findings support an association with altered insulin-signalling-related outcomes but do not establish IRS-1 upregulation as the causal mediator of the glycaemic response.