| Diabetes mellitus is a serious, complex metabolic disorder affecting approximately 4% of the population worldwide and is expected to increase by 5.4% in 2025. Despite continuing introduction of hypoglycemic drugs, intervention of diabetes and related complications still remain a major global medical problem. The traditional Chinese medicine has become the new concern on developing hypoglycemic drugs.Berberine (BER) is an isoquinoline alkaloid extracted from the genera Berberis and Coptis which have been commonly used as an oral drug to treat gastroenteritis and secretory diarrhea as traditional Chinese medicines for more than 1400 years. Its therapeutic potential for the treatment of diabetes and its complications, such as hyperlipidemia and cardiovascular diseases in human and animal models has been widely reported. Berberine has no adverse effect, and the price is very cheap. Because of this advantage of berberine, lots of experts pay close attention to the anti-diabetic function.Even the hypoglycemic effect of berberine is very perfect, it also not used in clinical as a hypoglycemic drugs. The major reason is the poor intestinal absorption, and the bioavailability is low. High dose oral administration usually causes gastrointestinal side effects, which greatly limit its clinical application. So how to improve the bioavailability of berberine is important. In our previous study, we have observed that Berberine co-administrated with sodium caprate, an absorption enhancer, to improve its absorption in intestine.The in vitro and in vivo models were used to observe the effect of sodium caprate on the intestinal absorption of berberine. The results showed that the absorption of berberine was poor, and the Papp was only 2.82×10-7 cm·s-1. Sodium caprate could significantly stimulated mucosal-to-serosal transport of berberine in the duodenum, jejunum and ileum, and increase the Papp of berberine. The absorption enhancement in ileum was the best and enhancement ratio was 3.49. In vivo experiment showed that after co-administration of sodium caprate, the area under the plasma concentration–time curve (AUC) of berberine was increased. The data showed that sodium caprate could significantly increase the bioavailability of berberine.Low dose of STZ(30mg/kg)twice and the high fat diet feed induced T2DM diabetic animals. After 4 weeks treatment, low dose of berberine showed no significant effect on FBG and glucose tolerance, while high dose of berberine group could significantly decrease the body weight, FBG, triglyceride, and total cholesterol. It also increased ISI and improved the glucose tolerance. Compared with berberine treatment groups, the therapeutic action of berberine co-administrated with sodium caprate groups were even better in these indexes. What's more, the low dose of berberine co-administrated with sodium caprate could also depress the FBG and improve the glucose tolerance. These findings demonstrated that co-administrated with sodium caprate could notably enhance the anti-diabetic effect of berberine. It shows no significant change in sodium caprate group.Hepatic gluconeogenesis is an important part of glucose metabolism in the liver, and gluconeogenesis disorders was closely related with insulin resistance diseases, such as diabetes, obesity, non-alcoholic fatty liver and other diseases. Inhibit excessive hepatic gluconeogenesis, reducing endogenous glucose production, will be one of the important target in the treatment of type 2 diabetes. Hepatic gluconeogenesis is regulated by a series of transcription factors. The PGC-1α, FOXO1, HNF4α, GR interacted with hormone and gluconeogenesis key enzyme G-6-Pase and PEPCK gene encoding crosstalk is the key point to determine the start of gluconeogenesis. Presently the antidiabetic effects of BER were mostly focus on glucose uptake and utilization in tissues. However, there is few studies exploring its effect on gluconeogenesis capabilities and its mechanisms remain uncertain. In this subject, we firstly studied the effect of berberine on hepatic gluconeogenesis, and further explore its molecular mechanism and action target.The results showed that compared with the control group, the G-6-Pase and PEPCK protein and mRNA expressions increased in liver of type 2 diabetes rat models and the gluconeogenesis was excess. Berberine could significantly reduce G-6-Pase and PEPCK mRNA and protein levels, and also reduce expression of PGC-1αprotein in liver tissues. Berberine reduced glucose production in HepG2 hepatocytes, meanwhile dose dependently inhibited PEPCK expression. These results suggest that berberine significantly inhibited the abnormal excess gluconeogenesis in type 2 diabetes, and the inhibition may regulate by the transcription factors of key enzymes in gluconeogenesis.We further observed the expression of AMPK and its active form p-AMPK in liver tissue. The results suggest compared with control group, the expression of p-AMPK was decreased in diabetic model group. After treatment of berberine, total AMPK was significantly reduced, while the p-AMPK expression was increased, p-AMPK / total AMPK ratio was also increased significantly, indicating that berberine could effectively activate AMPK in liver tissues. In HepG2 cells, both berberine and AMPK agonist AICAR may reduce the expression of PEPCK. After added the AMPK inhibitor Compound C, the effect of berberine reduced PEPCK expression was partially blocked. Berberine also reduces the key nuclear transcription factor FOXO1 and HNF4αprotein expression, and the effects were more or less diminished or disappeared in the presence of Compound C. These results suggest that berberine inhibited hepatic gluconeogenesis is at least in part through activation of AMPK signaling pathway.Type 1 11β-hydroxy steroid dehydrogenase enzyme (11β-HSD1) is a key enzyme to catalyzed glucocorticoid (GC) synthesis and transformation. It regulates the local activity of glucocorticoid levels, thereby to influence insulin sensitivity and regulate the expression of key enzymes in gluconeogenesis, thus regulate activities of hepatic gluconeogenesis. In our study, the result showed that the 11β-HSD1 and GR expression in liver were significantly increased in type 2 diabetic model rats, and berberine treatment could reversed the overexpression of 11β-HSD1 and GR. Cortisone (1×10-6mol/L) incubated 24h could induce expression of 11β-HSD1 increased and abnormal gluconeogenesis in HepG2 cells. Berberine could dose-dependently decrease the cortisone -induced high levels of 11β-HSD1 and GR, and the inhibition degree is familiar with CBX, the 11β-HSD1 inhibitor. Meanwhile, berberine could also reverse the cortisone-induced high levels of PEPCK and G-6-Pase. These results show that berberine significantly inhibit 11β-HSD1, prevented the inactive cortisone into active hydrocortisone, and then prevented excess gluconeogenesis mediated by GR. Berberine shows no effect on H6PDH, the upstream regulatory enzyme of 11β-HSD1.We future set up a computer model for screening the 11β-HSD1 inhibitor and to analysis the ability of berberine to direct binding with 11β-HSD1. The result showed that the combination of berberine and 11β-HSD1 are weak, indicating that 11β-HSD1 is not the direct targets of berberine.Berberine can be issued of yellow-green fluorescence in the UV excitation spectrum. Using confocal laser we can see berberine was quickly through the cell membrane and distributed in the cytoplasm and the nucleus.In summary, sodium caprate, the intestinal absorption enhancer, could significantly improve the bioavailability of berberine. Combined with sodium caprate could significantly enhance the role of berberine on reducing blood glucose, blood lipids, improve glucose tolerance and insulin resistance in type 2 diabetic rats. Abnormal hepatic gluconeogenesis is a major aspect of the pathogenesis of type 2 diabetes .Berberine is a multi-target drug, and it inhibits the gene expression of gluconeogenesis key enzyme through activating AMPK signaling pathway and inhibiting 11β-HSD1 signaling pathway, respectively. Berberine effectively prevents excessive hepatic gluconeogenesis, reducing endogenous glucose production, is the important mechanism for treatment of type 2 diabetes.
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