Dysregulated
glucagon drives hyperfunction in hepatic
glucose output, which is the main cause of persistent
hyperglycemia in
type 2 diabetes.
Berberine (Zhang et al., 2010) has been used as a
hypoglycemic agent, yet the mechanism by which BBR inhibits hepatic gluconeogenesis remains incompletely understood. In this study, we treated diabetic mice with BBR, tested
blood glucose levels, and then performed
insulin,
glucose lactate, and
glucagon tolerance tests. Intracellular cAMP levels in hepatocytes were determined by ELISA, hepatic gluconeogenetic genes were assayed by RT-qPCR, and the phosphorylation of CREB, which is the transcriptional factor controlling the expression of gluconeogenetic genes, was detected by western blot. BBR reduced
blood glucose levels, improved
insulin and
glucose tolerance, and suppressed
lactate- and
glucagon-induced hepatic gluconeogenesis in ob/ob and STZ-induced diabetic mice. Importantly, BBR blunted
glucagon-induced
glucose production and gluconeogenic gene expression in hepatocytes, presumably through reducing cAMP, which resulted in the phosphorylation of CREB. By utilizing a cAMP analogue,
adenylate cyclase (AC), to activate cAMP
synthetase, and an inhibitor of the cAMP degradative
enzyme,
phosphodiesterase (PDE), we revealed that BBR accelerates intracellular cAMP degradation. BBR reduces the intracellular cAMP level by activating PDE, thus blocking activation of downstream CREB and eventually downregulating gluconeogenic genes to restrain hepatic
glucose production.