Selenomethionine modulates insulin secretion in the MIN6-K8 mouse insulinoma cell line.

Selenium is an essential trace element of interest for its potential role in glucose homeostasis. The present study investigated the impact of selenium supplementation as selenomethionine (SeMet) on insulin secretion in MIN6-K8 cells, a pancreatic ß-cell model. We found that SeMet enhanced percent glucose-induced insulin secretion, while also increasing tolbutamide- and KCl-induced percent insulin secretion. RNA-sequencing showed that SeMet supplementation altered expression of several selenoproteins, including glutathione peroxidase 3 (Gpx3) and selenoprotein P (SelP). Targeted knockdown of Gpx3 increased both percent and total insulin release, while SelP knockdown increased insulin content and insulin release. Collectively, these studies support a putative role for selenium and selenoproteins in the regulation of insulin secretion, glucose homeostasis, and diabetes risk.

Influences of Corydalis decumbens on the Activities of CYP450 Enzymes in Rats with a Cocktail Approach.

Corydalis decumbens, a Traditional Chinese Medicine, has been widely used for the alternative and/or complementary therapy of hypertension, arrhythmias rheumatoid arthritis, sciatica, stroke, hemiplegia, paraplegia, and vascular embolism. The aim of this study was to determinate the potential effects of Corydalis decumbens on the five cytochrome P450 (CYP) enzyme activities (CYP1A2, CYP3A4, CYP2C9, CYP2C19, and CYP2D6) by cocktail approach. To evaluate whether concurrent use of Corydalis decumbens interferes with the effect of several prescription drugs, saline (control group) or Corydalis decumbens (XTW group) were administrated via gavage for 7 successive days. A probe cocktail solution (phenacetin, omeprazole, metoprolol, tolbutamide, and midazolam) was given 24 h after the last dose of saline or Corydalis decumbens. A specific and sensitive UHPLC-MS/MS method was validated for the determination of five substrates and their metabolites in control group and XTW group. Our results indicated that Corydalis decumbens could have inductive effects of CYP2C19 and inhibit the activities of CYP1A2 and CYP3A4. However, Corydalis decumbens had no significant influence on CYP2C9 and CYP2D6. The herb-drug interaction should require more attention by careful monitoring and appropriate drug dosing adjustments to the concurrent use of western medications which were metabolized by CYP1A2, CYP2C19, and CYP3A4 in human-Corydalis decumbens, Cytochrome P450, Cocktail, Pharmacokinetics, herb-drug interactions.

Influence of Shenxiong Glucose Injection on the Activities of Six CYP Isozymes and Metabolism of Warfarin in Rats Assessed Using Probe Cocktail and Pharmacokinetic Approaches.

Shenxiong glucose injection (SGI), a traditional Chinese medicine (TCM) preparation, has been widely used for the treatment of various cardiovascular and cerebrovascular diseases for many years. We assessed the potential influences of SGI on the activities of six CYP enzymes (CYP1A2, CYP2C11, CYP2C19, CYP2D4, CYP2E1, and CYP3A2) and on the pharmacokinetics of warfarin in rats. We compared plasma pharmacokinetics of six probe drugs (caffeine/CYP1A2, tolbutamide/CYP2C11, omeprazole/CYP2C19, metoprolol/CYP2D4, chlorzoxazone/CYP2E1, and midazolam/CYP3A2) and of warfarin between control and SGI-pretreated groups, to estimate the effect on the relative activities of the six isozymes and warfarin metabolism. There were no significant differences in the pharmacokinetic parameters of caffeine, omeprazole, metoprolol, chlorzoxazone, and midazolam between the SGI-pretreated and control groups. However, many pharmacokinetic parameters of tolbutamide in SGI-pretreated rats were affected significantly (p < 0.05), and indicated tolbutamide metabolism in the former group was markedly slower. Moreover, SGI reduced the clearance of warfarin. These results suggested SGI showed no effects on the enzyme activities of rat CYP1A2, CYP2C19, CYP2D4, CYP2E1, and CYP3A2, but inhibited the enzyme activity of CYP2C11, and improved the blood concentration of warfarin. This suggests that the dose of warfarin may need be adjusted when co-administrated with SGI.

An ex vivo approach to botanical-drug interactions: a proof of concept study.

ETHNOPHARMACOLOGICAL RELEVANCE: Botanical medicines are frequently used in combination with therapeutic drugs, imposing a risk for harmful botanical-drug interactions (BDIs). Among the existing BDI evaluation methods, clinical studies are the most desirable, but due to their expense and protracted time-line for completion, conventional in vitro methodologies remain the most frequently used BDI assessment tools. However, many predictions generated from in vitro studies are inconsistent with clinical findings. Accordingly, the present study aimed to develop a novel ex vivo approach for BDI assessment and expand the safety evaluation methodology in applied ethnopharmacological research. MATERIALS AND METHODS: This approach differs from conventional in vitro methods in that rather than botanical extracts or individual phytochemicals being prepared in artificial buffers, human plasma/serum collected from a limited number of subjects administered botanical supplements was utilized to assess BDIs. To validate the methodology, human plasma/serum samples collected from healthy subjects administered either milk thistle or goldenseal extracts were utilized in incubation studies to determine their potential inhibitory effects on CYP2C9 and CYP3A4/5, respectively. Silybin A and B, two principal milk thistle phytochemicals, and hydrastine and berberine, the purported active constituents in goldenseal, were evaluated in both phosphate buffer and human plasma based in vitro incubation systems. RESULTS: Ex vivo study results were consistent with formal clinical study findings for the effect of milk thistle on the disposition of tolbutamide, a CYP2C9 substrate, and for goldenseal׳s influence on the pharmacokinetics of midazolam, a widely accepted CYP3A4/5 substrate. Compared to conventional in vitro BDI methodologies of assessment, the introduction of human plasma into the in vitro study model changed the observed inhibitory effect of silybin A, silybin B and hydrastine and berberine on CYP2C9 and CYP3A4/5, respectively, results which more closely mirrored those generated in clinical study. CONCLUSIONS: Data from conventional buffer-based in vitro studies were less predictive than the ex vivo assessments. Thus, this novel ex vivo approach may be more effective at predicting clinically relevant BDIs than conventional in vitro methods.

Coleus forskohlii extract attenuates the hypoglycemic effect of tolbutamide in vivo via a hepatic cytochrome P450-mediated mechanism.

This in vivo study in rats evaluated whether Coleus forskohlii extract (CFE) taken orally interacted with tolbutamide, a hypoglycemic drug metabolized by CYP2C enzymes. Rats were fed 0%, 0.3%, 1% (w/w) CFE diet for 2 weeks, followed by 0% CFE diet for 1 day. They were then given 40 mg/kg tolbutamide by intragastric gavage. Blood glucose level was determined up to 6 h after tolbutamide administration. CFE treatment increased total CYP content and various CYP subtypes in the liver. In particular, increases in activity and protein expression were noted for the CYP2B, CYP2C, and CYP3A subtypes. CFE treatment dose-dependently attenuated both the hypoglycemic action of tolbutamide at 6 h and the plasma concentration of tolbutamide. The activity of (S)-warfarin 7-hydroxylase, a CYP2C enzyme was negatively correlated with plasma tolbutamide level, which also showed a negative correlation with the reduction of blood glucose level. These results indicate that CFE induced hepatic CYPs in rats and attenuated the hypoglycemic action of tolbutamide via a hepatic CYP2C-mediated mechanism.

Effects of eleutheroside B and eleutheroside E on activity of cytochrome P450 in rat liver microsomes.

BACKGROUND: Chemicals of herbal products may cause unexpected toxicity or adverse effect by the potential for alteration of the activity of CYP450 when co-administered with other drugs. Eleutherococcus senticosus (ES), has been widely used as a traditional herbal medicine and popular herbal dietary supplements, and often co-administered with many other drugs. The main bioactive constituents of ES were considered to be eleutherosides including eleutheroside B (EB) and eleutheroside E (EE). This study was to investigate the effects of EB and EE on CYP2C9, CYP2D6, CYP2E1 and CYP3A4 in rat liver microsomes in vitro. METHOD: Probe drugs of tolbutamide (TB), dextromethorphan (DM), chlorzoxazone (CLZ) and testosterone (TS) as well as eleutherosides of different concentrations were added to incubation systems of rat liver microsomes in vitro. After incubation, validated HPLC methods were used to quantify relevant metabolites. RESULTS: The results suggested that EB and EE exhibited weak inhibition against the activity of CYP2C9 and CYP2E1, but no effects on CYP2D6 and CYP3A4 activity. The IC50 values for EB and EE were calculated to be 193.20 µM and 188.36 µM for CYP2E1, 595.66 µM and 261.82 µM for CYP2C9, respectively. Kinetic analysis showed that inhibitions of CYP2E1 by EB and EE were best fit to mixed-type with Ki value of 183.95 µM and 171.63 µM, respectively. CONCLUSIONS: These results indicate that EB and EE may inhibit the metabolism of drugs metabolized via CYP2C9 and CYP2E1, and have the potential to increase the toxicity of the drugs.

Effects of aescin on cytochrome P450 enzymes in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Aescin, the main active component found in extracts of horse chestnut (Aesculus hippocastanum) seed a traditional medicinal herb, is a mixture of triterpene saponins. It has been shown to be effective in inflammatory, chronic venous and edematous treatment conditions in vitro and in vivo, and is broadly used to treat chronic venous insufficiency. The purpose of this study was to find out whether aescin influences the effect on rat cytochrome P450 (CYP) enzymes (CYP1A2, CYP2C9, CYP2E1 and CYP3A4) by using cocktail probe drugs in vivo; the influence on the levels of CYP mRNA was also studied. MATERIALS AND METHODS: A cocktail solution at a dose of 5mL/kg, which contained phenacetin (20mg/kg), tolbutamide (5mg/kg), chlorzoxazone (20mg/kg) and midazolam (10mg/kg), was given as oral administration to rats treated with a single dose or multiple doses of intravenous aescin via the caudal vein. Blood samples were collected at a series of time-points and the concentrations of probe drugs in plasma were determined by HPLC-MS/MS. The corresponding pharmacokinetic parameters were calculated by the software of DAS 2.0. In addition, real-time RT-PCR was performed to determine the effects of aescin on the mRNA expression of CYP1A2, CYP2C9, CYP2E1 and CYP3A4 in rat liver. RESULTS: Treatment with a single dose or multiple doses of aescin had inductive effects on rat CYP1A2, while CYP2C9 and CYP3A4 enzyme activities were inhibited. Moreover, aescin has no inductive or inhibitory effect on the activity of CYP2E1. The mRNA expression results were in accordance with the pharmacokinetic results. CONCLUSIONS: Aescin can either inhibit or induce activities of CYP1A2, CYP2C9 and CYP3A4. Therefore, caution is needed when aescin is co-administration with some CYP1A2, CYP2C9 or CYP3A4 substrates in clinic, which may result in treatment failure and herb-drug interactions.

Development of in vitro 3D TissueFlex® islet model for diabetic drug efficacy testing.

Increasing individuals diagnosed with type II diabetes pose a strong demand for the development of more effective anti-diabetic drugs. However, expensive, ethically controversial animal-based screening for anti-diabetic compounds is not always predictive of the human response. The use of in vitro cell-based models in research presents obviously ethical and cost advantages over in vivo models. This study was to develop an in vitro three-dimensional (3D) perfused culture model of islets (Islet TF) for maintaining viability and functionality longer for diabetic drug efficacy tests. Briefly fresh isolated rat islets were encapsulated in ultrapure alginate and the encapsulated islets were cultured in TissueFlex(®), a multiple, parallel perfused microbioreactor system for 7 days. The encapsulated islets cultured statically in cell culture plates (3D static) and islets cultured in suspension (2D) were used as the comparisons. In this study we demonstrate for the first time that Islet TF model can maintain the in vitro islet viability, and more importantly, the elevated functionality in terms of insulin release and dynamic responses over a 7-day culture period. The Islet TF displays a high sensitivity in responding to drugs and drug dosages over conventional 2D and 3D static models. Actual drug administration in clinics could be simulated using the developed Islet TF model, and the patterns of insulin release response to the tested drugs were in agreement with the data obtained in vivo. Islet TF could be a more predictive in vitro model for routine short- and long-term anti-diabetic drug efficacy testing.

The mechanisms of insulin secretion and calcium signaling in pancreatic ß-cells exposed to fluoroquinolones.

Fluoroquinolones reportedly induce hypoglycemia through stimulation of insulin secretion from pancreatic ß-cells via inhibition of K(ATP) channels and activation of L-type voltage-dependent Ca(2+) channels. In physiological condition, the cytosolic Ca(2+) concentration ([Ca(2+)](c)) is also regulated by release of Ca(2+) from intracellular Ca(2+) stores. In this study, we investigated the mechanism of insulin secretion induced by fluoroquinolones, with respect to intracellular Ca(2+) stores. Even where the absence of supplemental extracellular Ca(2+), insulin secretion and [Ca(2+)](c) were increased by gatifloxacin, levofloxacin or tolbutamide. Insulin secretion and the rise of [Ca(2+)](c) induced by fluoroquinolones were reduced by depleting of Ca(2+) in endoplasmic reticumum (ER) by thapsigargin, and inhibiting ryanodine receptor of ER by dantrolene. Inhibition of inositol 1,4,5-triphosphate receptor of ER by xestospongin C suppressed insulin secretion induced by fluoroquinolones, whereas it did not affect [Ca(2+)](c). Destruction of acidic Ca(2+) stores such as lysosome and lysosome-related organelles by glycyl-L-phenylalanine-2-nephthylamide (GPN) did not affect insulin secretion and the rise of [Ca(2+)](c) induced by fluoroquinolones. The increase in insulin and [Ca(2+)](c) induced by tolbutamide were reduced by thapsigargin, dantrolene, and GPN but not by xestospongin C. In conclusion, fluoroquinolones induces Ca(2+) release from ER mediated by the ryanodine receptor, and the reaction might involve in insulin secretion. Sulfonylureas induce Ca(2+) release from GPN-sensitive acidic Ca(2+) stores, but fluoroquinolones did not.

Activation of glibenclamide-sensitive ATP-sensitive K+ channels during ß-adrenergically induced metabolic stress produces a substrate for atrial tachyarrhythmia.

BACKGROUND: Cardiac ATP-sensitive K(+) channels have been suggested to contribute to the adaptive physiological response to metabolic challenge after ß-adrenoceptor stimulation. However, an increased atrial K(+)-conductance might be expected to be proarrhythmic. We investigated the effect of ATP-sensitive K(+) channel blockade on the electrophysiological responses to ß-adrenoceptor-induced metabolic challenge in intact atria. METHODS AND RESULTS: Atrial electrograms were recorded from the left atrial epicardial surface of Langendorff-perfused rat hearts using a 5×5 electrode array. Atrial effective refractory period and conduction velocity were measured using an S(1)-S(2) protocol. The proportion of hearts in which atrial tachyarrhythmia was produced by burst-pacing was used as an index of atrial tachyarrhythmia-inducibility. Atrial nucleotide concentrations were measured by high performance liquid chromatography. Perfusion with ≥10(-9) mol/L of the ß-adrenoceptor agonist, isoproterenol (ISO), resulted in a concentration-dependent reduction of atrial effective refractory period and conduction velocity. The ISO-induced changes produced a proarrhythmic substrate such that atrial tachyarrhythmia could be induced by burst-pacing. Atrial [ATP] was significantly reduced by ISO (10(-6) mol/L). Perfusion with either of the ATP-sensitive K(+) channel blockers, glibenclamide (10(-5) mol/L) or tolbutamide (10(-3) mol/L), in the absence of ISO had no effect on basal atrial electrophysiology. On the other hand, the proarrhythmic substrate induced by 10(-6) mol/L ISO was abolished by either of the sulfonylureas, which prevented induction of atrial tachyarrhythmia. CONCLUSIONS: Atrial ATP-sensitive K(+) channels activate in response to ß-adrenergic metabolic stress in Langendorff-perfused rat hearts, resulting in a proarrhythmic substrate.

Effects of Ginkgo biloba extract on the pharmacokinetics and pharmacodynamics of tolbutamide in protein-restricted rats.

OBJECTIVES: Effects of repeated administration of Ginkgo biloba extract on pharmacokinetics and pharmacodynamics of tolbutamide were examined in rats fed a low-protein diet. METHODS: Rats were given a low (7% casein) or control (20% casein) protein diet for 21 days and administered Ginkgo biloba extract (100mg/kg per day) for the last 5 days. Tolbutamide was co-administered on the last day. Blood glucose and plasma tolbutamide concentrations were determined over the subsequent 12h and the activity of hepatic cytochrome P450s were determined at 12h after dosing. KEY FINDINGS: There were significant decreases in body weight, the ratio of liver to body weight, and plasma albumin concentrations in rats on the low-protein diet compared with controls. The hypoglycaemic effect of tolbutamide was significantly greater and the concentration of the drug in plasma was higher in the former group. The repeated administration of Ginkgo biloba extract had little influence on the hypoglycaemic effect of tolbutamide, but tended to decrease the drug concentration in plasma of control rats, while it reduced significantly the hypoglycaemic action and plasma concentration of tolbutamide in the protein-restricted rats. CONCLUSIONS: The effects of Ginkgo biloba extract on the pharmacokinetics and pharmacodynamics of tolbutamide were significantly enhanced in rats on the low-protein diet.

Polysaccharide peptides from Coriolus versicolor competitively inhibit tolbutamide 4-hydroxylation in specific human CYP2C9 isoform and pooled human liver microsomes.

Polysaccharide peptide (PSP), isolated from COV-1 strain of Coriolus versicolor, is commonly used as an adjunct in cancer chemotherapy in China. Previous studies have shown that PSP decreased antipyrine clearance and inhibited CYP2C11-mediated tolbutamide 4-hydroxylation in the rat both in vitro and in vivo. In this study, the effects of water extractable fraction of PSP on tolbutamide 4-hydroxylation was investigated in pooled human liver microsomes and in specific human CYP2C9 isoform. PSP (2.5-20µM) dose-dependently decreased the biotransformation of tolbutamide to 4-hydroxy-tolbutamide. Enzyme kinetics studies showed inhibition of tolbutamide 4-hydroxylase activity was competitive and concentration-dependent. In pooled human liver microsomes, PSP had a K(i) value of 14.2µM compared to sulfaphenazole, a human CYP2C9 inhibitor, showed a K(i) value of 0.32µM. In human CYP2C9 isoform, the K(i) value of PSP was 29.5µM and the K(i) value of sulfaphenazole was 0.04µM. This study demonstrated that PSP can competitively inhibit tolbutamide 4-hydroxylation in both pooled human liver microsomes and specific human CYP2C9 in vitro. This study compliments previous findings in the rat that PSP can inhibit human tolbutamide 4-hydroxylase, but the relatively high K(i) values in human CYP2C9 would suggest a low potential for PSP to cause herb-drug interaction.

Exendin-4 upregulates the expression of Wnt-4, a novel regulator of pancreatic ß-cell proliferation.

The Wnt-signaling pathway regulates ß-cell functions. It is not known how the expression of endogenous Wnt-signaling molecules is regulated in ß-cells. Therefore, we investigated the effect of antidiabetic drugs and glucose on the expression of Wnt-signaling molecules in ß-cells. Primary islets were isolated and cultured. The expression of Wnt-signaling molecules (Wnt-4, Wnt-10b, Frizzled-4, LRP5, TCF7L2) and TNFα was analyzed by semiquantitative PCR and Western blotting. Transient transfections were carried out and proliferation assays of INS-1 ß-cells performed using [(3)H]thymidine uptake and BrdU ELISA. Insulin secretion was quantified. A knockdown (siRNA) of Wnt-4 in ß-cells was carried out. Exendin-4 significantly increased the expression of Wnt-4 in ß-cells on the mRNA level (2.8-fold) and the protein level (3-fold) (P < 0.001). The effect was dose dependent, with strongest stimulation at 10 nM, and it was maintained after long-term stimulation over 4 wk. Addition of exd-(9-39), a GLP-1 receptor antagonist, abolished the effect of exendin-4. Treatment with glucose, insulin, or other antidiabetic drugs had no effect on the expression of any of the examined Wnt-signaling molecules. Functionally, Wnt-4 antagonized the activation of canonical Wnt-signaling in ß-cells. Wnt-4 had no effect on glucose-stimulated insulin secretion or insulin gene expression. Knocking down Wnt-4 decreased ß-cell proliferation to 45% of controls (P < 0.05). In addition, Wnt-4 and exendin-4 treatment decreased the expression of TNFaα mRNA in primary ß-cells. These data demonstrate that stimulation with exendin-4 increases the expression of Wnt-4 in ß-cells. Wnt-4 modulates canonical Wnt signaling and acts as regulator of ß-cell proliferation and inflammatory cytokine release. This suggests a novel mechanism through which GLP-1 can regulate ß-cell proliferation.

Calcium-activated and voltage-gated potassium channels of the pancreatic islet impart distinct and complementary roles during secretagogue induced electrical responses.

Glucose-induced ß-cell action potential (AP) repolarization is regulated by potassium efflux through voltage gated (Kv) and calcium activated (K(Ca)) potassium channels. Thus, ablation of the primary Kv channel of the ß-cell, Kv2.1, causes increased AP duration. However, Kv2.1(-/-) islet electrical activity still remains sensitive to the potassium channel inhibitor tetraethylammonium. Therefore, we utilized Kv2.1(-/-) islets to characterize Kv and K(Ca) channels and their respective roles in modulating the ß-cell AP. The remaining Kv current present in Kv2.1(-/-) ß-cells is inhibited with 5 µM CP 339818. Inhibition of the remaining Kv current in Kv2.1(-/-) mouse ß-cells increased AP firing frequency by 39.6% but did not significantly enhance glucose stimulated insulin secretion (GSIS). The modest regulation of islet AP frequency by CP 339818 implicates other K(+) channels, possibly K(Ca) channels, in regulating AP repolarization. Blockade of the K(Ca) channel BK with slotoxin increased ß-cell AP amplitude by 28.2%, whereas activation of BK channels with isopimaric acid decreased ß-cell AP amplitude by 30.6%. Interestingly, the K(Ca) channel SK significantly contributes to Kv2.1(-/-) mouse islet AP repolarization. Inhibition of SK channels decreased AP firing frequency by 66% and increased AP duration by 67% only when Kv2.1 is ablated or inhibited and enhanced GSIS by 2.7-fold. Human islets also express SK3 channels and their ß-cell AP frequency is significantly accelerated by 4.8-fold with apamin. These results uncover important repolarizing roles for both Kv and K(Ca) channels and identify distinct roles for SK channel activity in regulating calcium- versus sodium-dependent AP firing.

2-hydroxy 4-methoxy benzoic acid isolated from roots of Hemidesmus indicus ameliorates liver, kidney and pancreas injury due to streptozotocin-induced diabetes in rats.

Protective effect was evaluated in streptozoticin (STZ)-induced diabetes rats. 2-Hydroxy 4-methoxy benzoic acid (HMBA) was isolated from the roots of Hemidesmus indicus and administered (500 microg/kg body weight) orally for 7 weeks to STZ-induced diabetic and non-diabetic rats to study its effect on protein metabolism, serum electrolytes and on liver and kidney lipid peroxides. Oral administration of HMBA restored the altered biochemical parameters such as urea, uric acid, creatinine, plasma proteins and serum electrolytes to near-normal levels. HMBA treatment significantly decreased lipid peroxidation and malondialdehyde levels in diabetic liver and kidney. Effect of HMBA was equivalent to that of the standard drug, tolbutamide (100 mg/kg body wt). The histological changes were also in correlation with the biochemical findings. The present study showed that HMBA isolated from H. indicus roots had ameliorative effect on liver, kidney and pancreatic injury in STZ-induced diabetic rats.

Facilitation of ß-cell K(ATP) channel sulfonylurea sensitivity by a cAMP analog selective for the cAMP-regulated guanine nucleotide exchange factor Epac.

Clinical studies demonstrate that combined administration of sulfonylureas with exenatide can induce hypoglycemia in type 2 diabetic subjects. Whereas sulfonylureas inhibit ß-cell K(ATP) channels by binding to the sulfonylurea receptor-1 (SUR1), exenatide binds to the GLP-1 receptor, stimulates ß-cell cAMP production and activates both PKA and Epac. In this study, we hypothesized that the adverse in vivo interaction of sulfonylureas and exenatide to produce hypoglycemia might be explained by Epac-mediated facilitation of K(ATP) channel sulfonylurea sensitivity. We now report that the inhibitory action of a sulfonylurea (tolbutamide) at K(ATP) channels was facilitated by 2'-O-Me-cAMP, a selective activator of Epac. Thus, under conditions of excised patch recording, the dose-response relationship describing the inhibitory action of tolbutamide at human ß-cell or rat INS-1 cell K(ATP) channels was left-shifted in the presence of 2'-O-Me-cAMP, and this effect was abolished in INS-1 cells expressing a dominant-negative Epac2. Using an acetoxymethyl ester prodrug of an Epac-selective cAMP analog (8-pCP T-2'-O-Me-cAMP-AM), the synergistic interaction of an Epac activator and tolbutamide to depolarize INS-1 cells and to raise [Ca²(+)](i) was also measured. This effect of 8-pCP T-2'-O-Me-cAMP-AM correlated with its ability to stimulate phosphatidylinositol 4,5-bisphosphate hydrolysis that might contribute to the changes in K(ATP) channel sulfonylurea-sensitivity reported here. On the basis of such findings, we propose that the adverse interaction of sulfonylureas and exenatide to induce hypoglycemia involves at least in part, a functional interaction of these two compounds to close K(ATP) channels, to depolarize ß-cells and to promote insulin secretion.

Influence of Helicteres isora administration for diabetes mellitus: Its effect on erythrocyte membrane and antioxidant status.

In this study the effect of Helicteres isora L. on erythrocyte membrane bound enzymes and antioxidants activity in plasma and erythrocytes of streptozotocin (STZ) induced diabetic model was investigated. The aqueous bark extract of H. isora was administered orally for 30 days to control and STZ induced diabetic rats. The effect of bark extract on glucose, insulin, haemoglobin, glycosylated haemoglobin, TBARS, hydroperoxide, superoxide dismutase (SOD), catalase (CAT), glutathione peroxide (GPx), glutathione-S-transferase (GST), vitamins C and E, reduced glutathione (GSH) and membrane bound enzymes were studied. The levels of glucose, glycosylated haemoglobin, TBARS, hydroperoxide, and vitamin E were increased significantly whereas the level of insulin, haemoglobin, as well as antioxidants, membrane bound total ATPase, Na(+)/K(+)-ATPase, Ca(2+)-ATPase and Mg(2+)-ATPase were decreased significantly in STZ diabetic rats. Administration of bark extract to diabetic rats showed a decrease in the levels of glucose, glycosylated haemoglobin, lipid peroxidation markers and vitamin E. In addition the levels of insulin, haemoglobin, enzymatic antioxidants, vitamin C, and GSH and the activities of membrane bound enzymes also were increased in H. isora treated diabetic rats. The present study indicates that the H. isora possesses a significant favourable effect on erythrocyte membrane bound enzymes and antioxidants defense system in addition to its antidiabetic effect.

Antidiabetic activities of Tecoma stans (L.) Juss. ex Kunth.

ETHNOPHARMACOLOGICAL RELEVANCE: Tecoma stans aqueous extract (TAE) is widely used as a traditional antidiabetic remedy in Mexico; its rational use is controversial. We provide evidence of its main antidiabetic activities. AIM OF THE STUDY: To evaluate in vivo and in vitro intestinal alpha-glucosidases inhibition as the possible mode of action of TAE on type 2 diabetes mellitus (DM2) animal models, and to test the effects of its sub-chronic administration on lipids and glucose blood levels. MATERIALS AND METHODS: In healthy and streptozotocin (STZ)-induced diabetic male Sprague-Dawley rats, glucose or cornstarch was administered after an oral dose of TAE, acarbose, tolbutamide or vehicle, in order to build starch and glucose tolerance curves (STC and GTC). An intestinal brush border preparation was used to evaluate the TAE alpha-glucosidases inhibitory activity. Moreover, in STZ-induced diabetic rats TAE, tolbutamide or vehicle was administered for 21 days for evaluate their effects on fasting glucose cholesterol and triglycerides. Also, TAE total phenolic compounds were quantified. RESULTS: In STC, TAE decreased hyperglycemic peak values in both healthy and STZ-treated rats, in a magnitude similar to that of acarbose. The in vitro preparation showed a dose-dependent inhibition of glucose release from starch. Sub-chronic administration of TAE significantly reduced cholesterol and triglycerides levels. Moreover, we confirmed that acute and sub-chronic administration of TAE (500mg/kg) in both rat models did not diminish fasting glucose and did not modify the GTC. CONCLUSIONS: The study present evidence that the main antidiabetic effect of TAE is due to intestinal alpha-glucosidase inhibition by decreasing the postprandial hyper-glycaemia peak; in addition, TAE sub-chronic administration reduces triglycerides and cholesterol, without modifying fasting glucose.

Hypoglycemic effect of Mucuna pruriens seed extract on normal and streptozotocin-diabetic rats.

The hypoglycemic effect of the aqueous extract of the seeds of Mucuna pruriens was investigated in normal, glucose load conditions and streptozotocin (STZ)-induced diabetic rats. In normal rats, the aqueous extract of the seeds of Mucuna pririens (100 and 200 mg/kg body weight) significantly (P<0.001) reduced the blood glucose levels after an oral glucose load from 127.5+/-3.2 to 75.6+/-4.8 mg% 2 h after oral administration of seed extract. It also significantly lowered the blood glucose in STZ diabetic rats from 240.5+/-7.2 to 90.6+/-5.6 mg% after 21 days of daily oral administration of the extract (P<0.001). Thus, this study shows that M. pruriens has an anti-hyperglycemic action and it could be a source of hypoglycemic compounds.

Elevation in intracellular long-chain acyl-coenzyme A esters lead to reduced beta-cell excitability via activation of adenosine 5'-triphosphate-sensitive potassium channels.

Closure of pancreatic beta-cell ATP-sensitive potassium (K(ATP)) channels links glucose metabolism to electrical activity and insulin secretion. It is now known that saturated, but not polyunsaturated, long-chain acyl-coenyzme A esters (acyl-CoAs) can potently activate K(ATP) channels when superfused directly across excised membrane patches, suggesting a plausible mechanism to account for reduced beta-cell excitability and insulin secretion observed in obesity and type 2 diabetes. However, reduced beta-cell excitability due to elevation of endogenous saturated acyl-CoAs has not been confirmed in intact pancreatic beta-cells. To test this notion directly, endogenous acyl-CoA levels were elevated within primary mouse beta-cells using virally delivered overexpression of long-chain acyl-CoA synthetase-1 (AdACSL-1), and the effects on beta-cell K(ATP) channel activity and cell excitability was assessed using the perforated whole-cell and cell-attached patch-clamp technique. Data indicated a significant increase in K(ATP) channel activity in AdACSL-1-infected beta-cells cultured in medium supplemented with palmitate/oleate but not with the polyunsaturated fat linoleate. No changes in the ATP/ADP ratio were observed in any of the groups. Furthermore, AdACSL-1-infected beta-cells (with palmitate/oleate) showed a significant decrease in electrical responsiveness to glucose and tolbutamide and a hyperpolarized resting membrane potential at 5 mm glucose. These results suggest a direct link between intracellular fatty ester accumulation and K(ATP) channel activation, which may contribute to beta-cell dysfunction in type 2 diabetes.