Xinting Wang

Modulation of glucagon-like peptide-1 release by berberine: in vivo and in vitro studies.

Glucagon-like peptide (GLP)-1 is a potent glucose-dependent insulinotropic gut hormone released from intestinal L cells. Our previous studies showed that berberine increased GLP-1 secretion in streptozotocin-induced diabetic rats. The aim of this study was to investigate whether berberine affected GLP-1 release in normal rats and in NCI-H716 cells. Proglucagon and prohormone convertase 3 genes regulating GLP-1 biosynthesis were analyzed by RT-PCR. Effects of pharmacological inhibitors on berberine-mediated GLP-1 release were studied. In vivo, 5-week treatment of berberine enhanced GLP-1 secretion induced by glucose load and promoted proglucagon mRNA expression as well as L cell proliferation in intestine. In vitro, berberine concentration-dependently stimulated GLP-1 release in NCI-H716 cells. Berberine also promoted both prohormone convertase 3 and proglucagon mRNA expression. Chelerythrine (inhibitor of PKC) concentration-dependently suppressed berberine-mediated GLP-1 secretion. Compound C (inhibitor of AMPK) also inhibited berberine-mediated GLP-1 secretion. But only low concentrations of H89 (inhibitor of PKA) showed inhibitory effects on berberine-mediated GLP-1 release. The present results demonstrated that berberine showed its modulation on GLP-1 via promoting GLP-1 secretion and GLP-1 biosynthesis. Some signal pathways including PKC-dependent pathway were involved in this process. Elucidation of mechanisms controlling berberine-mediated GLP-1 secretion may facilitate the understanding of berberines antidiabetic effects.

Increased glucagon-like peptide-1 secretion may be involved in antidiabetic effects of ginsenosides

Panax ginseng is one of the most popular herbal remedies. Ginsenosides, major bioactive constituents in P. ginseng, have shown good antidiabetic action, but the precise mechanism was not fully understood. Glucagon-like peptide-1 (GLP1) is considered to be an important incretin that can regulate glucose homeostasis in the gastrointestinal tract after meals. The aim of this study was to investigate whether ginseng total saponins (GTS) exerts its antidiabetic effects via modulating GLP1 release. Ginsenoside Rb1 (Rb1), the most abundant constituent in GTS, was selected to further explore the underlying mechanisms in cultured NCI-H716 cells. Diabetic rats were developed by a combination of high-fat diet and low-dose streptozotocin injection. The diabetic rats orally received GTS (150 or 300u200amg/kg) daily for 4 weeks. It was found that GTS treatment significantly ameliorated hyperglycemia and dyslipidemia, accompanied by a significant increase in glucose-induced GLP1 secretion and upregulation of proglucagon gene expression. Data from NCI-H716 cells showed that both GTS and Rb1 promoted GLP1 secretion. It was observed that Rb1 increased the ratio of intracellular ATP to ADP concentration and intracellular Ca2+ concentration. The metabolic inhibitor azide (3u200amM), the KATP channel opener diazoxide (340u200aμM), and the Ca2+ channel blocker nifedipine (20u200aμM) significantly reversed Rb1-mediated GLP1 secretion. All these results drew a conclusion that ginsenosides stimulated GLP1 secretion both in vivo and in vitro. The antidiabetic effects of ginsenosides may be a result of enhanced GLP1 secretion.

Increased plasma exposures of five protoberberine alkaloids from Coptidis Rhizoma in streptozotocin-induced diabetic rats: is P-GP involved?

Our previous study showed a higher exposure of berberine, palmatine, coptisine, epiberberine and jatrorrhizine in 6-week streptozotocin (STZ)-induced diabetic rats, after oral administration of Coptidis Rhizoma extract. The aim of the present study was to investigate whether the function and expression of intestinal P-glycoprotein (P-GP) was downregulated in STZ-induced diabetic rats and if the impairment of P-GP function and expression contributed to the exposure increase of the five protoberberine alkaloids. Plasma concentration-time profiles of the drugs in the portal vein were obtained after oral administration of Coptidis Rhizoma extract. The effective permeability of the drug across duodenum and ileum were measured using in situ single-pass intestine perfusion. P-GP function in the rat intestine was assessed by measuring the absorption of rhodamine 123 (Rho123). P-GP levels were evaluated using Western blots. It was found that the C(max) and AUC(0-8) values of five alkaloids in the portal vein of diabetic rats were significantly higher than those in the control rats. Diabetic rats also exhibitd a higher level of Rho123 in the portal vein, which showed impairment of P-GP function. A higher effective permeability of the tested drug was found in the duodenum of diabetic rats using in situ single-pass intestine perfusion, indicating that berberine and Rho123 transported more easily across the intestinal barrier of diabetic rats. A lower level of P-GP protein was found in the duodenum, jejunum and ileum of the diabetic rats as compared with age-matched control rats. All these results suggested that the function and expression of P-GP were impaired in the intestine of STZ-induced diabetic rats which, at least partly, contributed to the exposure increase of the five protoberberine alkaloids.

Opposite Effect of Diabetes Mellitus Induced by Streptozotocin on Oral and Intravenous Pharmacokinetics of Verapamil in Rats

The aim of this study was to report the effect of diabetes mellitus on the pharmacokinetics of verapamil in a route-dependent manner. Diabetes in rats was induced by streptozotocin. Plasma concentrations of verapamil and its metabolite, norverapamil, were measured after oral (10 mg/kg) or intravenous (1 mg/kg) administration. The concentrations of verapamil in portal plasma after oral administration were also determined. Norverapamil formation was used for assessing CYP3A activity in hepatic and intestinal microsomes of diabetic rats. The protein levels of CYP3A1 and CYP3A2 in liver and intestine were measured by Western blot. It was found that diabetes significantly increased the plasma concentration of verapamil and norverapamil after oral administration, which resulted in a 74% increase in the area under the concentration-time curve (AUC) of verapamil, but the ratio of AUC(norverapamil)/AUC(verapamil) was significantly decreased by 38%. In contrast, diabetes significantly decreased the AUC of verapamil by 22% after intravenous administration. Diabetes also resulted in increased AUC of verapamil in portal vein by 3.8-fold compared with that in control rats. The absolute bioavailability of verapamil was higher than that of control rats. An in vitro study showed that increased CYP3A activity in the hepatic microsome and decreased CYP3A activity in the intestinal microsome were accompanied by an increase and decrease in the protein expression of CYP3A1/2 in liver and intestine of diabetic rats, respectively. In conclusion, diabetes mellitus revealed a tissue-specific effect on CYP3A activity and expression (induced in liver and inhibited in intestine), resulting in opposite pharmacokinetic behaviors of verapamil after oral and intravenous administration to diabetic rats.

Insulin deficiency induces abnormal increase in intestinal disaccharidase activities and expression under diabetic states, evidences from in vivo and in vitro study

Structural and functional alterations in the gastrointestinal tract of diabetic patients are often accompanied by increase in absorption of intestinal glucose and activities of brush-border disaccharidases. The purpose of this study was to investigate the role of insulin in regulating intestinal disaccharidases using in vivo and in vitro experiments. Streptozotocin-induced diabetic rats and normal rats received protamine zinc insulin (10 IU/kg) subcutaneously twice daily for 5 weeks. Disaccharidase activities and sucrase-isomaltase (SI) complex protein and mRNA expression in intestinal regions were assessed. In addition, Caco-2 cells were cultured in medium containing glucose, insulin or insulin plus some pharmacological inhibitors for 7 days, disaccharidase activities, sucrase-isomaltase (SI) complex and Cdx2 mRNA levels were measured. The animal experiments showed that diabetes increased intestinal disaccharidase activities, accompanied by high mRNA and protein expression of SI complex. Insulin treatment reversed the increases induced by diabetes. The cellular results showed that insulin suppressed disaccharidase activities and down-regulated SI complex and Cdx2 mRNA expression in a concentration-dependent manner. The inhibitor of MAPK signal pathway PD-98059 blocked the suppression of disaccharidase activities and expression of SI complex and Cdx2 mRNA induced by insulin. In conclusion, insulin deficiency induces abnormal increase in intestinal disaccharidase activities and expression under diabetic states. Insulin plays an essential role in regulation disaccharidase activities and expression, at least in part, via the MAPK-dependent pathway.

P-glycoprotein and multidrug resistance-associated protein 2 are oppositely altered in brain of rats with thioacetamide-induced acute liver failure

P‐glycoprotein (P‐GP) and multidrug resistance‐associated protein 2 (MRP2) are involved in transport of many drugs across blood–brain barrier (BBB). The function and expression of P‐GP and MRP2 may be modulated by different pathologies. Acute liver failure (ALF) was reported to impair BBB function, resulting in the increased BBB permeability.

Induction of multidrug resistance-associated protein 2 in liver, intestine and kidney of streptozotocin-induced diabetic rats

Many studies have demonstrated that Mrp2 is highly regulated in some physiopathological situations. The aim of this study was to investigate effects of diabetes mellitus on function and expression of multidrug resistance-associated protein 2 (Mrp2) in rat liver, kidney and intestine. Diabetic rats were induced by an intraperitoneal administration of streptozotocin (65u2009mg/kg) and randomly divided into diabetic (DM) rats and insulin-treated diabetic rats. Sulfobromophthalein (BSP), a substrate of Mrp2, was used to evaluate Mrp2 function in vivo. Data from excretion experiments demonstrated that compared with normal rats, diabetes markedly enhanced BSP excretion via bile, urine and intestinal perfusate, which contributed to the elevated plasma clearance of BSP after intravenous administration of 45 μmol/kg BSP. Western blot results showed higher levels of hepatic, renal and intestinal Mrp2 protein in DM rats, although no difference was observed in renal Mrp2. Insulin treatment partly reversed these alterations. Induction of Mrp2 by diabetes was in parallel with the increase in bile flow, levels of biliary and plasma total bile acid (TBA), and plasma conjugated bilirubin in DM rats. Diabetes may enhance Mrp2 function and expression in liver, kidney and intestine, which might be due to insulin deficiency, increased TBA and conjugated bilirubin.

Combined contributions of over-secreted glucagon-like peptide 1 and suppressed insulin secretion to hyperglycemia induced by gatifloxacin in rats

Accumulating evidences have showed that gatifloxacin causes dysglycemia in both diabetic and non-diabetic patients. Our preliminary study demonstrated that gatifloxacin stimulated glucagon-like peptide 1 (GLP-1) secretion from intestinal cells. The aim of the study was to investigate the association between gatifloxacin-stimulated GLP-1 release and dysglycemia in both normal and streptozotocin-induced diabetic rats and explore the possible mechanisms. Oral administration of gatifloxacin (100 mg/kg/day and 200 mg/kg/day) for 3 and 12 days led to marked elevation of GLP-1 levels, accompanied by significant decrease in insulin levels and increase in plasma glucose. Similar results were found in normal rats treated with 3-day gatifloxacin. Gatifloxacin-stimulated GLP-1 release was further confirmed in NCI-H716 cells, which was abolished by diazoxide, a K(ATP) channel opener. QT-PCR analysis showed that gatifloxacin also upregulated expression of proglucagon and prohormone convertase 3 mRNA. To clarify the contradiction on elevated GLP-1 without insulinotropic effect, effects of GLP-1 and gatifloxacin on insulin release were investigated using INS-1 cells. We found that short exposure (2h) to GLP-1 stimulated insulin secretion and biosynthesis, whereas long exposure (24 h and 48 h) to high level of GLP-1 inhibited insulin secretion and biosynthesis. Moreover, we also confirmed gatifloxacin acutely stimulated insulin secretion while chronically inhibited insulin biosynthesis. All the results gave an inference that gatifloxacin stimulated over-secretion of GLP-1, in turn, high levels of GLP-1 and gatifloxacin synergistically impaired insulin release, worsening hyperglycemia.

Impaired hepatic and intestinal ATP-binding cassette transporter G5/8 was associated with high exposure of β-sitosterol and the potential risks to blood-brain barrier integrity in diabetic rats.

Plant sterols are thought to treat hypercholesterolemia via inhibiting intestinal cholesterol absorption. The aim of this study was to evaluate the contribution of impaired ATP‐binding cassette transporter G5/8 (ABCG5/8) expression by diabetes to the increased β‐sitosterol (BS) exposure and impact of increased BS on integrity of blood–brain barrier (BBB).

Sodium-dependent Glucose Transporter Was Involved in Salidroside Absorption in Intestine of Rats

Aim nTo report saturable absorption process of salidroside in rat intestine and investigate whether Na+-dependent glucose transporter (SGLT1) was involved in the absorption of salidroside.