Inhibition of intestinal and renal Na+-glucose cotransporter by naringenin

Quercetin in anti-diabetic research and strategies for improved quercetin bioavailability using polymer-based carriers – a review

With numerous pharmacological and biological functions bio-flavonoids gain appreciable attention in diabetes and other therapeutic research.

In vitro α-amylase inhibitory activity and in vivo hypoglycemic effect of methanol extract of Citrus macroptera Montr. fruit

OBJECTIVE

To investigate the therapeutic effects of methanol extract of Citrus macroptera Montr.fruit in α-amylase inhibitory activity (in vitro) and hypoglycemic activity in normal and glucose induced hyperglycemic rats (in vivo).

METHODS

Fruits of Citrus macroptera without rind was extracted with pure methanol following cold extraction and tested for presence of phytochemical constituents, α-amylase inhibitory activity, and hypoglycemic effect in normal rats and glucose induced hyperglycemic rats.

RESULTS

Presence of saponin, steroid and terpenoid were identified in the extract. The results showed that fruit extract had moderate α-amylase inhibitory activity [IC50 value=(3.638±0.190) mg/mL] as compared to acarbose. Moreover at 500 mg/kg and 1 000 mg/kg doses fruit extract significantly (P<0.05 and P<0.01 respectively) reduced fasting blood glucose level in normal rats as compared to glibenclamide (5 mg/kg). In oral glucose tolerance test, 500 mg/kg dose significantly reduced blood glucose level (P<0.05) at 2 h but 1 000 mg/kg dose significantly reduced blood glucose level at 2 h and 3 h (P<0.05 and P<0.01 respectively) whereas glibenclamide (5 mg/kg) significantly reduced glucose level at every hour after administration. Overall time effect is also considered extremely significant with F value=23.83 and P value=0.0001 in oral glucose tolerance test.

CONCLUSION

These findings suggest that the plant may be a potential source for the development of new oral hypoglycemic agent.

Phytotherapy in diabetes: Review on potential mechanistic perspectives

Diabetes mellitus (DM) is a widely spread epidemic disease that results from the absence of insulin, decreased secretion and/or impaired function. Since DM is a multi-factorial disease, the available pharmaceuticals, despite their sensible treatment, target mostly one pathway to control hyperglycemia and encounter several side effects. Therefore, new therapeutic paradigms aim to hit several pathways using only one agent. Traditionally, antidiabetic plants and/or their active constituents may fulfill this need. More than 200 species of plants possess antidiabetic properties which were evaluated mostly by screening tests without digging far for the exact mode of action. Searching among the different literature resources and various database and in view of the above aspects, the present article provides a comprehensive review on the available antidiabetic plants that have been approved by pharmacological and clinical evaluations, and which their mechanism(s) of action is assured. These plants are categorized according to their proved mode of action and are classified into those that act by inhibiting glucose absorption from intestine, increasing insulin secretion from the pancreas, inhibiting glucose production from hepatocytes, or enhancing glucose uptake by adipose and muscle tissues. The current review also highlights those that mimic in their action the new peptide analogs, such as exenatide, liraglutide and dipeptidylpeptidase-4 inhibitors that increase glucagon-like peptide-1 serum concentration and slow down the gastric emptying.

Metabolic Stimulation of Plant Phenolics for Food Preservation and Health

Plant phenolics as secondary metabolites are key to a plant's defense response against biotic and abiotic stresses. These phytochemicals are also increasingly relevant to food preservation and human health in terms of chronic disease management. Phenolic compounds from different food crops with different chemical structures and biological functions have the potential to act as natural antioxidants. Plant-based human foods are rich with these phenolic phytochemicals and can be used effectively for food preservation and bioactive enrichments through metabolic stimulation of key pathways. Phenolic metabolites protect against microbial degradation of plant-based foods during postharvest storage. Phenolics not only provide biotic protection but also help to counter biochemical and physical food deteriorations and to enhance shelf life and nutritional quality. This review summarizes the role of metabolically stimulated plant phenolics in food preservation and their impact on the prevention of oxidative stress–induced human diseases.

Flavonoid-membrane interactions: involvement of flavonoid-metal complexes in raft signaling

Flavonoids are polyphenolic compounds produced by plants and delivered to the human body through food. Although the epidemiological analyses of large human populations did not reveal a simple correlation between flavonoid consumption and health, laboratory investigations and clinical trials clearly demonstrate the effectiveness of flavonoids in the prevention of cardiovascular, carcinogenic, neurodegenerative and immune diseases, as well as other diseases. At present, the abilities of flavonoids in the regulation of cell metabolism, gene expression, and protection against oxidative stress are well-known, although certain biophysical aspects of their functioning are not yet clear. Most flavonoids are poorly soluble in water and, similar to lipophilic compounds, have a tendency to accumulate in biological membranes, particularly in lipid rafts, where they can interact with different receptors and signal transducers and influence their functioning through modulation of the lipid-phase behavior. In this study, we discuss the enhancement in the lipophilicity and antioxidative activity of flavonoids after their complexation with transient metal cations. We hypothesize that flavonoid-metal complexes are involved in the formation of molecular assemblies due to the facilitation of membrane adhesion and fusion, protein-protein and protein-membrane binding, and other processes responsible for the regulation of cell metabolism and protection against environmental hazards.

Naringenin inhibits α-glucosidase activity: a promising strategy for the regulation of postprandial hyperglycemia in high fat diet fed streptozotocin induced diabetic rats

Obesity and the onset of diabetes are two closely linked medical complications prevalent globally. Postprandial hyperglycemia is one of the earliest abnormalities of glucose homeostasis associated with type 2 diabetes (T2D). Postprandial glucose levels can be regulated through α-glucosidase inhibition. The present study aims to demonstrate the potent inhibitory role of naringenin against α-glucosidase activity. The mode of inhibition of naringenin was examined by measuring enzyme activity in vitro with different concentrations of substrate using Lineweaver-Burk plot analysis. It shows competitive inhibition towards mammalian α-glucosidase thereby competing with α-limit dextrins and oligosaccharide residues for binding in the active site. Similar results have been obtained from the molecular docking analyses, where naringenin shows preferential binding for the active sites in each of the evaluated human intestinal α-glucosidase enzymes. Post-docking intramolecular hydrogen bonding analysis shows water molecule mediated hydrogen bonding for N-terminal maltase glucoamylase and N-terminal sucrase isomaltase. Naringenin's docked pose in the C-terminal maltase glucoamylase active site does not show any particular water mediated interaction similar to the co-crystallized acarbose. Further, our results suggest that naringenin (25 mg/kg) exerts significant inhibition of intestinal α-glucosidase activity in vivo thereby delaying the absorption of carbohydrates in T2D rats, thus resulting in significant lowering of postprandial blood glucose levels. Both in vitro and in vivo results were compared to the commercially available α-glucosidase inhibitor acarbose. Our findings clearly indicate that naringenin dampens postprandial glycemic response and offers a potential complementary approach in the management of T2D.

1-deoxynojirimycin inhibits glucose absorption and accelerates glucose metabolism in streptozotocin-induced diabetic mice

We investigated the role of 1-deoxynojirimycin (DNJ) on glucose absorption and metabolism in normal and diabetic mice. Oral and intravenous glucose tolerance tests and labeled ¹³C₆-glucose uptake assays suggested that DNJ inhibited intestinal glucose absorption in intestine. We also showed that DNJ down-regulated intestinal SGLT1, Na⁺/K⁺-ATP and GLUT2 mRNA and protein expression. Pretreatment with DNJ (50 mg/kg) increased the activity, mRNA and protein levels of hepatic glycolysis enzymes (GK, PFK, PK, PDE1) and decreased the expression of gluconeogenesis enzymes (PEPCK, G-6-Pase). Assays of protein expression in hepatic cells and in vitro tests with purified enzymes indicated that the increased activity of glucose glycolysis enzymes was resulted from the relative increase in protein expression, rather than from direct enzyme activation. These results suggest that DNJ inhibits intestinal glucose absorption and accelerates hepatic glucose metabolism by directly regulating the expression of proteins involved in glucose transport systems, glycolysis and gluconeogenesis enzymes.

Bergamot polyphenolic fraction enhances rosuvastatin-induced effect on LDL-cholesterol, LOX-1 expression and protein kinase B phosphorylation in patients with hyperlipidemia

BACKGROUND

Statins are the most commonly prescribed drugs to reduce cardiometabolic risk. Besides the well-known efficacy of such compounds in both preventing and treating cardiometabolic disorders, some patients experience statin-induced side effects. We hypothesize that the use of natural bergamot-derived polyphenols may allow patients undergoing statin treatment to reduce effective doses while achieving target lipid values. The aim of the present study is to investigate the occurrence of an enhanced effect of bergamot-derived polyphenolic fraction (BPF) on rosuvastatin-induced hypolipidemic and vasoprotective response in patients with mixed hyperlipidemia.

METHODS

A prospective, open-label, parallel group, placebo-controlled study on 77 patients with elevated serum LDL-C and triglycerides was designed. Patients were randomly assigned to a control group receiving placebo (n=15), two groups receiving orally administered rosuvastatin (10 and 20mg/daily for 30 days; n=16 for each group), a group receiving BPF alone orally (1000 mg/daily for 30 days; n=15) and a group receiving BPF (1000 mg/daily given orally) plus rosuvastatin (10mg/daily for 30 days; n=15).

RESULTS

Both doses of rosuvastatin and BPF reduced total cholesterol, LDL-C, the LDL-C/HDL-C ratio and urinary mevalonate in hyperlipidemic patients, compared to control group. The cholesterol lowering effect was accompanied by reductions of malondialdehyde, oxyLDL receptor LOX-1 and phosphoPKB, which are all biomarkers of oxidative vascular damage, in peripheral polymorphonuclear cells.

CONCLUSIONS

Addition of BPF to rosuvastatin significantly enhanced rosuvastatin-induced effect on serum lipemic profile compared to rosuvastatin alone. This lipid-lowering effect was associated with significant reductions of biomarkers used for detecting oxidative vascular damage, suggesting a multi-action enhanced potential for BPF in patients on statin therapy.

Cooperative anti-diabetic effects of deoxynojirimycin-polysaccharide by inhibiting glucose absorption and modulating glucose metabolism in streptozotocin-induced diabetic mice

We had previously shown that deoxynojirimycin-polysaccharide mixture (DPM) not only decreased blood glucose but also reversed the damage to pancreatic β-cells in diabetic mice, and that the anti-hyperglycemic efficacy of this combination was better than that of 1-deoxynojirimycin (DNJ) or polysachharide alone. However, the mechanisms behind these effects were not fully understood. The present study aimed to evaluate the therapeutic effects of DPM on streptozotocin (STZ)-induced diabetic symptoms and their potential mechanisms. Diabetic mice were treated with DPM (150 mg/kg body weight) for 90 days and continued to be fed without DPM for an additional 30 days. Strikingly, decrease of blood glucose levels was observed in all DPM treated diabetic mice, which persisted 30 days after cessation of DPM administration. Significant decrease of glycosylated hemoglobin and hepatic pyruvate concentrations, along with marked increase of serum insulin and hepatic glycogen levels were detected in DPM treated diabetic mice. Results of a labeled (13)C6-glucose uptake assay indicated that DPM can restrain glucose absorption. Additionally, DPM down-regulated the mRNA and protein expression of jejunal Na(+)/glucose cotransporter, Na(+)/K(+)-ATPase and glucose transporter 2, and enhanced the activities as well as mRNA and protein levels of hepatic glycolysis enzymes (glucokinase, phosphofructokinase, private kinase and pyruvate decarboxylas E1). Activity and expression of hepatic gluconeogenesis enzymes (phosphoenolpyruvate carboxykinase and glucose-6-phosphatase) were also found to be attenuated in diabetic mice treated with DPM. Purified enzyme activity assays verified that the increased activities of glucose glycolysis enzymes resulted not from their direct activation, but from the relative increase in protein expression. Importantly, our histopathological observations support the results of our biochemical analyses and validate the protective effects of DPM on STZ-induced damage to the pancreas. Thus, DPM has significant potential as a therapeutic agent against diabetes.

Possible effects of dietary polyphenols on sugar absorption and digestion

Excessive post-prandial glucose excursions are a risk factor for developing diabetes, associated with impaired glucose tolerance. One way to limit the excursion is to inhibit the activity of digestive enzymes for glucose production and of the transporters responsible for glucose absorption. Flavonols, theaflavins, gallate esters, 5-caffeoylqunic acid and proanthocyanidins inhibit α-amylase activity. Anthocyanidins and catechin oxidation products, such as theaflavins and theasinsensins, inhibit maltase; sucrase is less strongly inhibited but anthocyanidins seem somewhat effective. Lactase is inhibited by green tea catechins. Once produced in the gut by digestion, glucose is absorbed by SGLT1 and GLUT2 transporters, inhibited by flavonols and flavonol glycosides, phlorizin and green tea catechins. These in vitro data are supported by oral glucose tolerance tests on animals, and by a limited number of human intervention studies on polyphenol-rich foods. Acarbose is a drug whose mechanism of action is only through inhibition of α-amylases and α-glucosidases, and in intervention studies gives a 6% reduction in diabetes risk over 3 years. A lifetime intake of dietary polyphenols, assuming the same mechanism, has therefore a comparable potential to reduce diabetes risk, but more in vivo studies are required to fully test the effect of modulating post-prandial blood glucose in humans.

Anti-inflammatory and antifibrotic effects of naringenin in diabetic mice

Renal protective effects of naringenin at 0.5, 1, and 2% of the diet in diabetic mice were examined. Naringenin supplemented at 1 and 2% increased its deposit in liver and kidney of diabetic mice. Compared with the diabetic control group, naringenin treatments at 1 and 2% lowered plasma levels of glucose and blood urea nitrogen, as well as increased insulin level and creatinine clearance (P < 0.05). Naringenin treatments dose-dependently reduced renal tumor necrosis factor-α level and expression (P < 0.05) but only at 1 and 2% significantly decreased production and expression of interleukin (IL)-1β, IL-6, and monocyte chemoattractant protein-1 (P < 0.05). Naringenin intake at 2% decreased renal formation and expression of type IV collagen, fibronectin, and transforming growth factor-β1 (P < 0.05). This compound at 1 and 2% lowered protein kinase C activity and suppressed nuclear factor κB (NF-κB) p65 activity, mRNA expression, and protein production in kidney. However, this agent only at 2% diminished NF-κB p50 activity, mRNA expression, and protein production (P < 0.05). These results indicate that naringenin could attenuate diabetic nephropathy via its anti-inflammatory and antifibrotic activities.

Foods for the prevention of diabetes: how do they work?

With the diabetes epidemic reaching menacing proportions worldwide, there is an urgent need for the development of cost-efficient prevention strategies to be effective at the population level. Great potential in this direction lies in properly designed, large-scale dietary interventions. The macronutrient composition and the caloric content of our diet are major determinants of glucose homeostasis and there is a continuously growing list of foods, nutrients or individual compounds that have been associated with an increased or reduced incidence of diabetes mellitus. These include fat, carbohydrates, fibre, alcohol, polyphenols and other micronutrients or individual dietary compounds, which have been shown to either promote or prevent a progression towards a (pre-)diabetic state. This review aims to briefly summarize relevant epidemiological data linking foods to diabetes and to provide insights into the mechanisms through which these effects are mediated. These include improvement of insulin sensitivity or promotion of insulin resistance, regulation of inflammatory pathways, regulation of glucose transport and tissue glucose uptake, aggravation or attenuation of postprandial glycaemia/insulinaemia, interactions with hormonal responses and β-cell-dependent mechanisms.

Citrus fruit extracts reduce advanced glycation end products (AGEs)- and H₂O₂-induced oxidative stress in human adipocytes

Diabetes is a reactive oxygen species (ROS)-mediated pathology, with a worldwide prevalence estimated to double by 2030. A major effort has been launched to find therapeutic means to improve health conditions of diabetic patients. Recent data show that supplemental natural antioxidants represent a potential strategy as adjunct therapy. Despite the major role of adipocytes in the etiology of diabetes, little is known about the effect of natural antioxidants on adipocyte response to oxidative stress. Using a diabetes-like oxidative stress model, the potential protective effect of antioxidative flavedo, albedo, and pulp extracts of (1) tangor Elendale (Citrus reticulata × Citrus sinensis) and (2) tangelo Minneola (C. reticulata × Citrus paradisis) was investigated on human adipocytes. Besides the retardation of free-radical-induced hemolysis of human erythrocytes, non-cytotoxic concentrations of tangelo and tangor flavedo extracts significantly reduced the levels of protein carbonyls in response to advanced glycation end products (AGEs) generated by albumin glycation in SW872 cells. Flavedo extracts lowered carbonyl accumulation in H2O2-treated adipocytes, while tangelo and tangor flavedo, albedo, and pulp extracts suppressed ROS production in SW872 cells with or without the addition of H2O2. Our results clearly show that Mauritian Citrus fruit extracts represent an important source of antioxidants, with a novel antioxidative role at the adipose tissue level.

Inhibition of glucose intestinal absorption by kaempferol 3-O-α-rhamnoside purified from Bauhinia megalandra leaves

Glucose intestinal absorption (GIA) is one of the factors that increase glycemia. Its reduction could be an important factor in decreasing hyperglycemia in diabetic patients. It has been shown that the aqueous extract of Bauhinia megalandra leaves inhibits GIA. In the present study we identified a compound present in the extract of B. megalandra responsible for the biological effect. The methanol extract of B. megalandra leaves was fractionated using different solvents, and high-speed counter-current chromatography yielding two pure compounds identified by (1)H NMR and (13)C NMR as kaempferol 3-O-α-rhamnoside and quercetin 3-O-α-rhamnoside. The first one increased the K(M) without changes in the V(MAX) of GIA. In addition it exerted an additive inhibitory effect, on GIA, when combined with phlorizin. We suggest that kaempferol 3-O-α-rhamnoside is a competitive inhibitor of intestinal SGLT1 cotransporter.

Naringenin, a citrus flavonoid, increases muscle cell glucose uptake via AMPK

Naringenin, a flavonoid found in high concentrations in grapefruit, has been reported to have antioxidant, antiatherogenic, and anticancer effects. Effects on lipid and glucose metabolism have also been reported. Naringenin is structurally similar to the polyphenol resveratrol, that has been reported to activate the SIRT1 protein deacetylase and to have antidiabetic properties. In the present study we examined the direct effects of naringenin on skeletal muscle glucose uptake and investigated the mechanism involved. Naringenin stimulated glucose uptake in L6 myotubes in a dose- and time-dependent manner. Maximum stimulation was seen with 75 microM naringenin for 2 h (192.8+/-24%, p<0.01), a response comparable to maximum insulin response (190.1+/-13%, p<0.001). Similar to insulin, naringenin did not increase glucose uptake in myoblasts indicating that GLUT4 glucose transporters may be involved in the naringenin-stimulated glucose uptake. In addition, naringenin did not have a significant effect on basal or insulin-stimulated Akt phosphorylation while significantly increased AMPK phosphorylation/activation. Furthermore, silencing of AMPK, using siRNA approach, abolished the naringenin-stimulated glucose uptake. The SIRT1 inhibitors nicotinamide and EX527 did not have an effect on naringenin-stimulated AMPK phosphorylation and glucose uptake. Our data show that naringenin increases glucose uptake by skeletal muscle cells in an AMPK-dependent manner.

Impact of dietary polyphenols on carbohydrate metabolism

Polyphenols, including flavonoids, phenolic acids, proanthocyanidins and resveratrol, are a large and heterogeneous group of phytochemicals in plant-based foods, such as tea, coffee, wine, cocoa, cereal grains, soy, fruits and berries. Growing evidence indicates that various dietary polyphenols may influence carbohydrate metabolism at many levels. In animal models and a limited number of human studies carried out so far, polyphenols and foods or beverages rich in polyphenols have attenuated postprandial glycemic responses and fasting hyperglycemia, and improved acute insulin secretion and insulin sensitivity. The possible mechanisms include inhibition of carbohydrate digestion and glucose absorption in the intestine, stimulation of insulin secretion from the pancreatic β–cells, modulation of glucose release from the liver, activation of insulin receptors and glucose uptake in the insulin-sensitive tissues, and modulation of intracellular signalling pathways and gene expression. The positive effects of polyphenols on glucose homeostasis observed in a large number of in vitro and animal models are supported by epidemiological evidence on polyphenol-rich diets. To confirm the implications of polyphenol consumption for prevention of insulin resistance, metabolic syndrome and eventually type 2 diabetes, human trials with well-defined diets, controlled study designs and clinically relevant end-points together with holistic approaches e.g., systems biology profiling technologies are needed.

Naringenin protects against cadmium-induced oxidative renal dysfunction in rats

Cadmium (Cd) is an environmental and industrial pollutant that affects various organs in human and experimental animals. Naringenin is a naturally occurring plant bioflavonoid found in citrus fruits, which has been reported to have a wide range of pharmacological properties. A body of evidence has accumulated implicating the free radical generation with subsequent oxidative stress in the biochemical and molecular mechanisms of cadmium toxicity. Since kidney is the critical target organ of chronic Cd toxicity, we carried out this study to investigate the effects of naringenin on Cd-induced toxicity in the kidney of rats. In experimental rats, oral administration of cadmium chloride (5mg/(kgday)) for 4 weeks significantly induced the renal damage which was evident from the increased levels of serum urea, uric acid, creatinine with a significant (p<0.05) decrease in creatinine clearance. Cadmium also significantly decreased the levels of urea, uric acid and creatinine in urine. A markedly increased levels of lipid peroxidation markers (thiobarbituric acid reactive substances and lipid hydroperoxides) and protein carbonyl contents with significant (p<0.05) decrease in non-enzymatic antioxidants (total sulfhydryl groups, reduced glutathione, vitamin C and vitamin E) and enzymatic antioxidants (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST)) as well as glutathione metabolizing enzymes (glutathione reductase (GR) and glutathione-6-phosphate dehydrogenase (G6PD)) were also observed in cadmium-treated rats. Co-administration of naringenin (25 and 50mg/(kgday)) along with Cd resulted in a reversal of Cd-induced biochemical changes in kidney accompanied by a significant decrease in lipid peroxidation and an increase in the level of renal antioxidant defense system. The histopathological studies in the kidney of rats also showed that naringenin (50mg/(kgday)) markedly reduced the toxicity of Cd and preserved the normal histological architecture of the renal tissue. The present study suggest that the nephroprotective potential of naringenin in Cd toxicity might be due to its antioxidant and metal chelating properties, which could be useful for achieving optimum effects in Cd-induced renal damage.

Antidiabetic and toxicological evaluations of naringenin in normoglycaemic and NIDDM rat models and its implications on extra-pancreatic glucose regulation

AIM

The present investigation was designed to determine the in vivo antidiabetic effect of naringenin (NG) in normoglycaemic and diabetic rat models through blood glucose (GLU) measurements following acute and subchronic time periods. Possible modes of action of NG were investigated and its acute toxicity determined.

METHODS

Normoglycaemic and non-insulin-dependent diabetes mellitus (NIDDM) rat models were treated for acute and subchronic (5 days) time periods with 50 mg/kg/day of NG. Blood biochemical profiles were determined after 5 days of the treatment in normoglycaemic and NIDDM rats using commercial kits for GLU, triglycerides (TG), total cholesterol (CHOL) and high-density lipoprotein (HDL). In order to elucidate its antidiabetic mode of action, NG was administered intragastrically and an oral glucose tolerance test performed using GLU and sucrose (2 g/kg) as substrates. The inhibitory effect of a single concentration of NG (10 microM) on 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) activity in vitro was determined. Finally, the preclinical safety and tolerability of NG was determined by toxicological evaluation in mice and rats using Organization for Economic Cooperation and Development (OECD) protocols.

RESULTS

Intragastrically administered NG (50 mg/kg) induced a significant decrease in plasma GLU in normoglycaemic and NIDDM rat models (p < 0.05) following acute and subchronic time periods. After 5 days of administration, NG produced significant diminished blood GLU and TG levels in streptozotocin-nicotinamide-induced diabetic rats. The administration of NG to normal rats significantly increased the levels of TG, CHOL and HDL (p < 0.05). NG (5 and 50 mg/kg) induced a total suppression in the increase of plasma GLU levels after administration of substrates (p < 0.01), but NG did not produce inhibition of alpha-glucosidase activity in vitro. However, NG (10 microM) was shown to inhibit 11beta-HSD1 activity by 39.49% in a cellular enzyme assay. Finally, NG showed a Medium Lethal Dose LD(50) > 5000 mg/kg and ranking at level five based on OECD protocols.

CONCLUSION

Our findings suggest that NG may exert its antidiabetic effect by extra-pancreatic action and by suppressing carbohydrate absorption from intestine, thereby reducing the postprandial increase in blood GLU levels.

Preventive effect of naringin on isoproterenol-induced cardiotoxicity in Wistar rats: an in vivo and in vitro study

This study was aimed to evaluate the preventive role of naringin on heart weight, blood glucose, total proteins, albumin/globulin (A/G) ratio, serum uric acid, serum iron, plasma iron binding capacity and membrane bound enzymes such as sodium potassium-dependent adenosine triphosphatase (Na(+)/K(+) ATPase), calcium-dependent adenosine triphosphatase (Ca(2+) ATPase) and magnesium-dependent adenosine triphosphatase (Mg(2+) ATPase) and glycoproteins such as hexose, hexosamine, fucose and sialic acid in isoproterenol (ISO)-induced myocardial infarction (MI) in rats and in vitro free radical scavenging assay. Male albino Wistar rats were pretreated with naringin (10, 20 and 40 mg/kg, respectively) for a period of 56 days. After the treatment period, ISO (85 mg/kg) was subcutaneously injected to rats at an interval of 24 h for 2 days. ISO-induced rats showed a significant (P<0.05) increase in the heart weight, blood glucose, serum uric acid, serum iron and a significant (P<0.05) decrease in the levels of total proteins, A/G ratio and iron binding capacity. A significant (P<0.05) decrease in the activity of Na(+)/K(+) ATPase and increase in the activities of Ca(2+) and Mg(2+) ATPase in the heart and a significant (P<0.05) increase in the levels of glycoproteins in serum and the heart were also observed in ISO-induced rats. Pretreatment with naringin for a period of 56 days exhibited a significant (P<0.05) effect and altered these biochemical parameters positively in ISO-induced rats. Naringin also scavenges 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azinobis-(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) and nitric oxide (NO) radicals in vitro. Thus, our study shows that naringin has cardioprotective role in ISO-induced MI in rats.

alpha-Glucosidase inhibitory activity of the methanolic extract from Tournefortia hartwegiana: an anti-hyperglycemic agent

Tournefortia hartwegiana is a Mexican medicinal plant that is used for the treatment of diabetes, diarrhea and kidney pain. In a previous investigation, the methanolic extract of Tournefortia hartwegiana (METh) showed significant hypoglycemic and anti-diabetic properties on normoglycemic and alloxanized rats. In this context, the purpose of the present study was to establish one of the possible modes of action of METh to induce anti-diabetic activity. METh (310mg/kg) effect on alpha-glucosidase activity was investigated. METh intragastric administration was conducted to determine oral glucose tolerance test (OGTT), using different substrates: glucose, sucrose and maltose. The increase in plasma glucose level was significantly suppressed (P<0.05) by the extract after substrates administration. On the other hand, METh inhibited alpha-glucosidase activity in vitro, in a concentration-dependent manner (IC(50) of 3.16mg/mL). These results suggest that METh might exert its anti-diabetic effect by suppressing carbohydrate absorption from intestine, and thereby reducing the post-prandial increase of blood glucose. On the other hand, the bio-guided fractionation of this extract led to the isolation of: beta-sitosterol (1), stigmasterol (2), lupeol (3), ursolic acid (4), oleanolic acid (5), saccharose (6) and myo-inositol (7), using various chromatographic techniques.