Gérard Cros

Quercetin potentiates insulin secretion and protects INS-1 pancreatic β-cells against oxidative damage via the ERK1/2 pathway

BACKGROUND AND PURPOSE Quercetin lowers plasma glucose, normalizes glucose tolerance tests and preserves pancreatic β‐cell integrity in diabetic rats. However, its mechanism of action has never been explored in insulin‐secreting β‐cells. Using the INS‐1 β‐cell line, the effects of quercetin were determined on glucose‐ or glibenclamide‐induced insulin secretion and on β‐cell dysfunctions induced by hydrogen peroxide (H2O2). These effects were analysed along with the activation of the extracellular signal‐regulated kinase (ERK)1/2 pathway. N‐acetyl‐L‐cysteine (NAC) and resveratrol, two antioxidants also known to exhibit some anti‐diabetic properties, were used for comparison.

Chicoric acid, a new compound able to enhance insulin release and glucose uptake

Caffeic acid and chlorogenic acid (CGA), a mono-caffeoyl ester, have been described as potential antidiabetic agents. Using in vitro studies, we report the effects of a dicaffeoyl ester, chicoric acid (CRA) purified from Cichorium intybus, on glucose uptake and insulin secretion. Our results show that CRA and CGA increased glucose uptake in L6 muscular cells, an effect only observed in the presence of stimulating concentrations of insulin. Moreover, we found that both CRA and CGA were able to stimulate insulin secretion from the INS-1E insulin-secreting cell line and rat islets of Langerhans. In the later case, the effect of CRA is only observed in the presence of subnormal glucose levels. Patch clamps studies show that the mechanism of CRA and CGA was different from that of sulfonylureas, as they did not close K(ATP) channels. Chicoric acid is a new potential antidiabetic agent carrying both insulin sensitizing and insulin-secreting properties.

Leaf methanol extract of Bidens pilosa prevents and attenuates the hypertension induced by high-fructose diet in Wistar rats

Chronic fructose treatment in rats has repeatedly been shown to elevate blood pressure in association with insulin resistance and hyperinsulinemia. The purpose of the current study was to investigate the effect of the leaf methanol extract of Bidens pilosa on systolic blood pressure (SBP) and plasma glucose, insulin, cholesterol, triglycerides and creatinine levels in rats with fructose-induced hypertension. Wistar rats that drank a 10% fructose solution for 3-6 weeks showed significant increase not only in plasma insulin and cholesterol levels but also in SBP. B. pilosa extract was able to prevent the establishment of hypertension and lower elevated blood pressure levels. The extract also reduced the highly elevated plasma insulin levels provoked by the high fructose diet. These results suggest that the leaf methanol extract of B. pilosa exerts its antihypertensive effect in part by improving insulin sensitivity.

In vivo antidiabetic actions of naglivan, an organic vanadyl compound in streptozotocin-induced diabetes☆☆☆

The vanadyl (+IV) form of vanadium has been demonstrated to have insulin-mimetic activity in vivo. In an effort to improve the poor gastrointestinal absorption of the ion, an organic complex of vanadyl (naglivan) was synthesized. We tested the antidiabetic effects of naglivan in rats made diabetic with streptozotocin (55 mg/kg, i.v.). Four days after the streptozotocin injection, one diabetic group (DVI) and a control group (CV) were treated with naglivan (50 mg/kg/day, equivalent to 0.06 mmol vanadium/kg/day) by oral gavage. Treatment in the DVI group was supplemented with daily insulin while a second diabetic group (DI) was administered daily titrated doses of insulin alone (Protamine Zinc, s.c.) to achieve stable euglycemia. The dose of exogenous insulin required to maintain normal glucose was significantly lower in the DVI group compared to the DI throughout the treatment period. At the end of week 3, exogenous insulin was withdrawn from both the DVI and DI groups, while naglivan treatment was continued in the CV and DVI groups for an additional 5 weeks. At termination, hearts were isolated and cardiac function (+dP/dt, -dP/dt and left ventricular developed pressure) was assessed in all the animals. After insulin was withdrawn, 4/8 DVI animals which continued to receive naglivan had consistent normoglycemia (as determined by % glycosylated hemoglobin) and an improved cardiac function. All the DI animals and 4/8 DVI rats were hyperglycemic and had depressed heart function despite having similar plasma insulin levels to the euglycemic DVI animals. As with vanadyl sulfate, there were no signs of long-term toxicity with regards to renal or liver function after 8 weeks of treatment. Thus, naglivan is an orally effective form of vanadyl with an oral potency 7.6 times greater than that of vanadyl sulfate (minimum effective dose: 0.06 mmol vanadium.kg-1.day-1) as compared to vanadyl sulfate (0.46 mmol vanadium.kg-1.day-1). The lack of incidence of diarrhea in either control or diabetic animals demonstrates that naglivan could be a more therapeutically desirable form of vanadyl.

Chicoric Acid Is an Antioxidant Molecule That Stimulates AMP Kinase Pathway in L6 Myotubes and Extends Lifespan in Caenorhabditis elegans

Chicoric acid (CA) is a caffeoyl derivative previously described as having potential anti-diabetic properties. As similarities in cellular mechanism similarities between diabetes and aging have been shown, we explored on L6 myotubes the effect of CA on the modulation of intracellular pathways involved in diabetes and aging. We also determined its influence on lifespan of Caenorhabditis elegans worm (C. elegans). In L6 myotubes, CA was a potent reactive oxygen species (ROS) scavenger, reducing ROS accumulation under basal as well as oxidative stress conditions. CA also stimulated the AMP-activated kinase (AMPK) pathway and displayed various features associated with AMPK activation: CA (a) enhanced oxidative enzymatic defences through increase in glutathion peroxidase (GPx) and superoxide dismutase (SOD) activities, (b) favoured mitochondria protection against oxidative damage through up-regulation of MnSOD protein expression, (c) increased mitochondrial biogenesis as suggested by increases in complex II and citrate synthase activities, along with up-regulation of PGC-1α mRNA expression and (d) inhibited the insulin/Akt/mTOR pathway. As AMPK stimulators (e.g. the anti-diabetic agent meformin or polyphenols such as epigallocatechingallate or quercetin) were shown to extend lifespan in C. elegans, we also determined the effect of CA on the same model. A concentration-dependant lifespan extension was observed with CA (5–100 μM). These data indicate that CA is a potent antioxidant compound activating the AMPK pathway in L6 myotubes. Similarly to other AMPK stimulators, CA is able to extend C. elegans lifespan, an effect measurable even at the micromolar range. Future studies will explore CA molecular targets and give new insights about its possible effects on metabolic and aging-related diseases.

Antihypertensive effects of Dorstenia psilurus extract in fructose-fed hyperinsulinemic, hypertensive rats

We examined the effect of methanol/methylene chloride extract of Dorstenia psilurus given by gastric intubation on systolic blood pressure, plasma glucose, insulin, cholesterol, triglycerides and creatinine in rats with fructose-induced hypertension. Male Wistar rats in groups of 6 animals each were fed fructose-rich diets or standard chow for 3 weeks and treated with 100 mg/kg/day or 200 mg/kg/day of plant extract or vehicle for 3 subsequent weeks. Systolic blood pressure was measured every three days using the indirect tail cuff method. Systolic blood pressure was higher in fructose-fed rats (142+/-2 mm Hg, p < 0.01) compared with the controls (112+/-2 mm Hg), and was lower in Dorstenia psilurus-treated groups (127+/-2 and 119+/-1 mm Hg for the dose of 100 and 200 mg/kg, respectively) compared with the fructose-fed rats. Plasma insulin, cholesterol and triglycerides were higher on the fructose-rich diet compared with the controls. Plasma insulin and cholesterol were lower in the Dorstenia psilurus-treated groups. These results suggest that, Dorstenia psilurus treatment could prevent and reverse high blood pressure induced by a diet rich in fructose probably by improvement of plasma insulin levels. The plant extract might prove useful in the treatment and/or prevention of hypertension.

Development and validation of a liquid chromatography-electrospray ionization-tandem mass spectrometry method for the determination of urolithin C in rat plasma and its application to a pharmacokinetic study

Urolithins are microflora human metabolites of dietary ellagic acid derivatives. There is now a growing interest in the biological activities of these compounds. Several studies suggest that urolithins have potential antioxidant, anti-inflammatory, anticancer and anti-glycative activities. Recently, our group investigated the role of urolithins as potential anti-diabetic treatments; among the four urolithins, urolithin C was the most promising compound. The purpose of this paper was to develop a rapid, sensitive and specific liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method for the determination of urolithin C in rat plasma. To date, no method is reported for the quantification of urolithin C in any of the matrices. Plasma samples were extracted with ethyl acetate. Urolithin D was selected as the internal standard. The separation was carried out on a C18 Kinetex EVO column (2.1mm×150mm, 2.6μm) using a mobile phase of acetonitrile-1% aqueous formic acid solution (30:70, v/v). A triple quadrupole mass spectrometer in the negative ion mode was used for the determination of the target analyte. The monitored ion transitions were m/z 243→187 for urolithin C and m/z 259→213 for the internal standard. The calibration curve range was 4.95-1085μg/L (r2>0.994). The intra- and inter-day precisions were less than 10%; accuracies ranged from 96.6 to 109%. The mean extraction recovery of urolithins C and D was greater than 91%. No significant matrix effects and no carryover effects were observed. Small changes in LC-ESI-MS/MS conditions did not have significant effect on the determination of urolithin C. Stability tests under various conditions were also investigated. This highly specific and sensitive method was used to analyze samples collected during preclinical pharmacokinetic studies in rats. Glucuronyl and sulfate conjugates of urolithin C were the main metabolites detected in plasma.

Protection of pancreatic β-cell function by dietary polyphenols

Abstract Diabetes mellitus is a complex metabolic disorder and is considered a fast-growing global health problem. Type 2 diabetes (T2D) represents the majority of total diabetes prevalence and β-cell dysfunction has been described as a crucial point for this disease development and progression. To date, all of the common anti-hyperglycaemic drugs used for diabetes management cause undesirable side effects or problems with long-term efficacy or safety and the development of alternative approaches for the prevention as well as for the treatment of T2D might be a valuable solution to meet this rising demand. In this regards, numerous epidemiological studies indicate that exposure to certain polyphenol compounds is associated with the prevention of chronic diseases, including diabetes. Here, we review growing evidence suggesting that polyphenols can modulate the activity of various molecular targets, which are known to control β-cell function, involved in the development and the progression of this diabetes. The protective effects of polyphenols on β-cell function is reported with a particular focus on the mechanism of action behind polyphenol putative bioactivity. Animal and in vitro studies selected in this review, reporting about both flavonoid and non-flavonoid compounds, highlight the direct action of polyphenols on pancreatic β-cells, stimulating insulin secretion through the activation of specific cellular targets and protecting these cells from damages mediated by oxidative stress and inflammation, both typically elevated in diabetes. Some of the reviewed studies describe polyphenol effects comparable to those exerted by many drugs commonly used in diabetes treatment, and, in some occasions, synergistic polyphenol-drug interactions. Finally, future studies need to be addressed to the effects of specific polyphenol human and microbial metabolites, which are still poorly studied, in order to better define the preventive and therapeutic approach to contrast β-cell failure and diabetes progression.

A Total Red Wine Polyphenolic Extract Prevents a Pathological Phenotype Manifested on Cardiomyocytes Isolated from Rats with Nutritionally-induced Metabolic Syndrome

Isolated cardiomyocyte contractility was explored in a model of metabolic syndrome (the fructose-fed rat) and the effect of a treatment by a total red wine polyphenolic extract (RWPE) determined. Fructose-enriched diet impaired cardiomyocyte maximal shortening and velocities of contraction and relaxation, while RWPE was able to prevent those changes. Those studies suggest that red wine polyphenols are able to prevent the development of a cardiac phenotype commonly observed at an early stage of heart failure.

P76 La correction rapide de l’hyperglycémie chronique par l’insuline réduit l’expression d’une sous-unité de la NADPH oxydase chez le diabétique de type 2

Introduction L’hyperglycemie chronique induit un stress oxydant implique dans la pathogenie des complications vasculaires du diabete. Nos objectifs etaient d’analyser, chez des patients diabetiques de type 2 (DT2) mal controles sous antidiabetiques oraux (ADO), l’expression d’une enzyme cle du stress oxydant, la NADPH oxydase (NADPHox), et sa regulation apres correction rapide de l’hyperglycemie. Materiels et Methodes L’expression des transcrits de deux sous-unites de la NADPHox, p22 phox (membranaire) et p47 phox (cytosolique), a ete etudiee par Q-PCR (Lightcycler-Roche) dans des monocytes isoles de patients non diabetiques (ND, n = 6), DT2 controles sous ADO (C, n = 6) et DT2 non controles sous ADO (NC, n = 12). Dans ce dernier groupe, l’expression a ete evaluee avant (J0) et apres trois jours (J3) d’insulinotherapie IV normalisant la glycemie. L’expression des transcrits a ete normalisee par la β-2-microglobuline. Resultats Les patients des groupes C et NC sont âges de 56,4 ± 7,9 et 64,0 ± 4,5 ans, ont un DT2 connu depuis 8,3 ± 2,9 et 9,1 ± 3,3 ans et presentent une HbA1c de 7,1 ± 0,4 % et 10,26 ± 1,0 %, respectivement. Dans les monocytes, les niveaux d’expression de la p47 phox sont : 2,14 ± 0,83 (ND) ; 2,57 ± 1,16 (C) ; 3,52 ± 1,86 (NC, J0). Nous observons une tendance a l’augmentation non significative de l’expression de la p47 phox dans le groupe NC a J0 vs . ND et C. En revanche, pour la p22 phox , aucune difference d’expression n’est constatee entre les groupes. Dans le groupe NC, apres normalisation des glycemies (J3), nous observons une diminution significative de l’expression de la p47 phox : 2,57 ± 1,58 vs . 3,52 ± 1,86 (p phox . Conclusion Nos resultats montrent une tendance a l’augmentation de l’expression de la p47 phox de la NADPHox chez des patients DT2 en hyperglycemie chronique et une diminution significative de cette expression lors de la correction rapide de l’hyperglycemie par une insulinotherapie IV. Ces variations d’expression, a confirmer dans des populations plus importantes, sont en faveur de la gluco-dependance du stress oxydant dans le DT2, et suggerent la possibilite de sa suppression rapide lors de la correction glycemique par l’insuline.