Naringenin protects pancreatic β cells in diabetic rat through activation of estrogen receptor β.

Naringenin is a citrus flavonoid that potently improves metabolic parameters in animal models of metabolic disorders, such as type 2 diabetes. Estrogen receptor (ER) activation promotes β cell function and survival, thereby improving systemic glucose metabolism. In this study, we used a luciferase reporter assay, isolated rat islets and a diabetic rat model to investigate the effects of naringenin on ER signaling and the underlying mechanism of naringenin-mediated improvement of islet function in diabetes. Naringenin specifically activated ERβ without affecting the activity of ERα, G protein-coupled estrogen receptor (GPER) or estrogen-related receptor (ERR) α/β/γ. Additionally, treatment with naringenin enhanced glucose-stimulated insulin secretion in isolated rat islets. This effect was abrogated by PHTPP, an ERβ antagonist. Transcriptomic analysis revealed that naringenin upregulated the expression of genes, such as Pdx1 and Mafa, which are closely linked to improved β-cell function. In consistence, single administration of naringenin to normal rats elevated plasma insulin levels and improved glucose responses. These beneficial effects were blocked by PHTPP. In streptozocin-nicotinamide induced diabetic rats, treatment for 2 weeks with naringenin alone, but not in combination with PHTPP, significantly restored pancreatic β cell mass and improved glucose metabolism. Collectively, these data support that naringenin specifically activate ERβ to improve insulin secretion in the primary rat islets. Furthermore, naringenin administration also protected β cell function and reversed glucose dysregulation in diabetic rats. These beneficial effects are at least partially dependent on the ERβ pathway.