Is there a role for alpha-glucosidase inhibitors in the prevention of type 2 diabetes mellitus?

Biosynthesis of the anti-diabetic metabolite montbretin A: glucosylation of the central intermediate mini-MbA

Type 2 diabetes (T2D) affects over 320 million people worldwide. Healthy lifestyles, improved drugs and effective nutraceuticals are different components of a response against the growing T2D epidemic. The specialized metabolite montbretin A (MbA) is being developed for treatment of T2D and obesity due to its unique pharmacological activity as a highly effective and selective inhibitor of the human pancreatic α-amylase. MbA is an acylated flavonol glycoside found in small amounts in montbretia (Crocosmia × crocosmiiflora) corms. MbA cannot be obtained in sufficient quantities for drug development from its natural source or by chemical synthesis. To overcome these limitations through metabolic engineering, we are investigating the genes and enzymes of MbA biosynthesis. We previously reported the first three steps of MbA biosynthesis from myricetin to myricetin 3-O-(6'-O-caffeoyl)-glucosyl rhamnoside (mini-MbA). Here, we describe the sequence of reactions from mini-MbA to MbA, and the discovery and characterization of the gene and enzyme responsible for the glucosylation of mini-MbA. The UDP-dependent glucosyltransferase CcUGT3 (UGT703E1) catalyzes the 1,2-glucosylation of mini-MbA to produce myricetin 3-O-(glucosyl-6'-O-caffeoyl)-glucosyl rhamnoside. Co-expression of CcUGT3 with genes for myricetin and mini-MbA biosynthesis in Nicotiana benthamiana validated its biological function and expanded the set of genes available for metabolic engineering of MbA.

Sugar-Lowering Drugs for Type 2 Diabetes Mellitus and Metabolic Syndrome-Review of Classical and New Compounds: Part-I

Diabetes mellitus (DM) is a metabolic disorder characterized by chronic hyperglycemia together with disturbances in the metabolism of carbohydrates, proteins and fat, which in general results from an insulin availability and need imbalance. In a great number of patients, marketed anti-glycemic agents have shown poor effectiveness in maintaining a long-term glycemic control, thus being associated with severe adverse effects and leading to an emerging interest in natural compounds (e.g., essential oils and other secondary plant metabolites, namely, flavonoid-rich compounds) as a novel approach for prevention, management and/or treatment of either non-insulin-dependent diabetes mellitus (T2DM, type 2 DM) and/or Metabolic Syndrome (MS). In this review, some of these promising glucose-lowering agents will be comprehensively discussed.

Magnificamide, a β-Defensin-Like Peptide from the Mucus of the Sea Anemone Heteractis magnifica, Is a Strong Inhibitor of Mammalian α-Amylases

Sea anemones’ venom is rich in peptides acting on different biological targets, mainly on cytoplasmic membranes and ion channels. These animals are also a source of pancreatic α-amylase inhibitors, which have the ability to control the glucose level in the blood and can be used for the treatment of prediabetes and type 2 diabetes mellitus. Recently we have isolated and characterized magnificamide (44 aa, 4770 Da), the major α-amylase inhibitor of the sea anemone Heteractis magnifica mucus, which shares 84% sequence identity with helianthamide from Stichodactyla helianthus. Herein, we report some features in the action of a recombinant analog of magnificamide. The recombinant peptide inhibits porcine pancreatic and human saliva α-amylases with Ki’s equal to 0.17 ± 0.06 nM and 7.7 ± 1.5 nM, respectively, and does not show antimicrobial or channel modulating activities. We have concluded that the main function of magnificamide is the inhibition of α-amylases; therefore, its functionally active recombinant analog is a promising agent for further studies as a potential drug candidate for the treatment of the type 2 diabetes mellitus.

MiR-26a and miR-26b downregulate the expression of sucrase-isomaltase enzyme: A new chapter in diabetes treatment

Type II diabetes is a metabolic disease that has affected 460 million people around the globe and become a heavy burden on health care system. Diabetic patients suffer from hyperglycemia and hyperinsulinemia which can damage vital organs in body like heart, kidneys, eyes and nervous system. Different strategies have been introduced to control or lessen these diabetic complications in which one of the most promising approaches is the inhibition of intestinal sucrase-isomaltase (SI). Inhibition of this enzyme will block the release of glucose into bloodstream and lead to reduced postprandial hyperglycemia. MicroRNAs are small regulatory molecules that play critical roles in different cellular pathways and molecular mechanisms. It is proved that microRNAs have significant effects on cellular mechanisms involved in diabetes and can be used as biomarkers for diagnosis of this metabolic disease. Based on bioinformatics analysis miR-26a and miR-26b can interact with a conserved 3'-UTR region of SI mRNA which lead to a hypothesis that these miRs may have negative regulatory effect on this enzyme. In this study, we investigated the impact of high glucose conditions on expression of sucrase-isomaltase, miR-26a and miR-26b in caco-2 cell line. It is proved that in a simulated diabetic condition there is a reverse correlation between the expression pattern of these miRs and SI. QRT-PCR method was used to evaluate the expression of our target molecules. Interestingly, transfection of miR-26a and miR-26b in caco-2 cell line reduced the transcription of SI mRNA and decreased the sucrase and maltase activity of its active sites. To sum up, our results demonstrate the first evidence of the significant effect of miR-26a and miR-26b on SI expression and activity. We proved that these microRNAs may directly inhibit this enzyme and can be used as a new scaffold in search of finding novel treatments for type II diabetes.

Coumarin tethered cyclic imides as efficacious glucose uptake agents and investigation of hit candidate to probe its binding mechanism with human serum albumin

A series of novel coumarin-cyclic imide conjugates (1a-1j) were designed and synthesized to evaluate their glucose uptake activity by insulin resistant liver hepatocyte carcinoma (HepG2) cells through 2-NBDG uptake assay. Compounds (1a-1j) were characterised using various analytical methods such as ¹H NMR, ¹³C NMR, IR, GC-MS, elemental and single-crystal X-ray diffraction techniques. Compounds (1a-1j) exhibited 85.21 - 65.80% of glucose uptake and showed low level of cytotoxicity towards human embryonic kidney cells (HEK-293) indicating good selectivity and safety profile. Compound 1f was identified as a hit candidate exhibiting 85.21% of glucose uptake which was comparable with standard antidiabetic drug Metformin (93.25% glucose uptake). Solution stability study under physiological pH conditions ≈ (3.4 - 8.7), indicates that compound 1f is sufficiently stable at varied pH conditions and thereby compatible with bio-physiological environments. Interaction of 1f with human serum albumin (HSA) were also studied which quantifies that compound 1f binds with HSA efficiently through facile binding reaction in solution. Fluorescence, UV-vis spectrophotometry and molecular modeling methodologies were employed for studying the interaction mechanism of compound 1f with protein.

Plant-Derived Bioactive Peptides: A Treatment to Cure Diabetes

ABSTRACT

Recent advances in analytical techniques have opened new opportunities for plant-based drug discovery in the field of peptide and proteins. Enzymatic hydrolysis of plant parent proteins forms bioactive peptides which are explored in the treatment of various diseases. In this review, we will discuss the identified plant-based bioactive proteins and peptides and the in vitro, in vivo results for the treatment of diabetes. Extraction, isolation, characterization and commercial utilization of plant proteins is a challenge for the pharmaceutical industry as plants contain several interfering secondary metabolites. The market of peptide drugs for the treatment of diabetes is growing at a fast rate. Plant-based bioactive peptides might open up new opportunities to discover economic lead for the management of various diseases.

GRAPHIC ABSTRACT

Maltase-glucoamylase inhibition potency and cytotoxicity of pyrimidine-fused compounds: An in silico and in vitro approach

The prevalence of diabetes mellitus has been incremented in the current century and the need for novel therapeutic compounds to treat this disease has been significantly increased. One of the most promising approaches is to inhibit intestinal alpha glucosidases. Based on our previous studies, four pyrimidine-fused heterocycles (PFH) were selected as they revealed satisfactory inhibitory action against mammalian α-glucosidase. The interaction of these compounds with both active domains of human maltase-glucoamylase (MGAM) and their effect on human Caco-2 cell line were investigated. The docking assessments suggested that binding properties of these ligands were almost similar to that of acarbose by establishing hydrogen bonds especially with Tyr1251 and Arg526 in both C-terminal and N-terminal MGAM, respectively. Also, these compounds indicated a stronger affinity for C-terminal of MGAM. L2 and L4 made tightly complexes with both terminals of MGAM which in turn revealed the importance of introducing pyrimidine scaffold and its hinge compartment. The results of molecular dynamics simulation analyses confirmed the docking data and showed deep penetration of L2 and L4 into the active site of MGAM. Based on cell cytotoxicity assessments, no significant cell death induction was observed. Hence, these functional MGAM inhibitors might be considered as new potential therapeutic compounds in treatment of diabetes and its complications.

Effect of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes

OBJECTIVE

We investigated the effects of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes (T2DM).

METHODS

Empagliflozin (OLETF-EMPA) or voglibose (OLETF-VOG) was administered to Otsuka Long-Evans Tokushima fatty (OLETF) rats once daily for 12 weeks. Control Long-Evans Tokushima Otsuka (LETO) and OLETF (OLETF-C) rats received saline.

RESULTS

Blood glucose levels were significantly suppressed in OLETF-EMPA and OLETF-VOG compared with the OLETF-C group. The liver fat content was significantly higher in the OLETF-C group than in the OLETF-EMPA and OLETF-VOG. Hepatic gene expressions involved in gluconeogenesis (glucose 6-phosphatase [G6Pase], fructose-1,6-bisphosphatase [FBP1], and phosphoenolpyruvate carboxykinase [PEPCK]) and lipogenesis (acetyl-CoA carboxylase [ACC], fatty acid synthase [FAS], and sterol regulatory element-binding transcription factor 1c [SREBP-1c]) were significantly decreased in the OLETF-EMPA group compared with other OLETF groups (OLETF-C and OLETF-VOG). Sirtuin 1 (SIRT1) expression level and SIRT1 activity were markedly reduced in OLETF-C rats; however, its expression increased in the OLETF-EMPA and OLETF-VOG. AMP-activated protein kinase (AMPK) phosphorylation level was remarkably increased by empagliflozin treatment in OLETF rats compared with other OLETF groups. Long-term empagliflozin and voglibose treatment reduced hepatic steatosis with suppression of gluconeogenesis and lipogenesis pathway in OLETF rats.

CONCLUSION

We suggest that this metabolic improvement might be related to SIRT1 and AMPK pathway in T2DM. But empagliflozin is thought to have more advantage to prevent hepatic steatosis than voglibose in T2DM.

Proteins with Evolutionarily Hypervariable Domains are Associated with Immune Response and Better Survival of Basal-like Breast Cancer Patients

Maltase-glucoamylase (MGAM) and MGAM2 both belong to the glycoside hydrolase family 31. MGAM, a therapeutic target for type 2 diabetes, is α-1,4-glucosidase and expressed in the intestine to catalyze starch digestion. MGAM2, however, is largely uncharacterized. By investigating The Cancer Genome Atlas data, we found that among breast cancer subtypes, MGAM2 expression is nearly exclusive to basal-like breast cancers (BLBCs), whereas MGAM tends to express in luminal A breast cancers. Moreover, MGAM2 expression is associated with better patient survival and correlated with immune genes/signatures, unlike MGAM. Both genes have emerged in mammals, but diverged after the placental-marsupial split. In placentals, MGAM2 has likely lost its α-1,4-glucosidase activity due to mutations in key catalytic sites, and has acquired a large domain that is extracellular, threonine-rich and evolutionarily hypervariable (EHV). Guided by MGAM2 findings, our genome-wide search identified >1000 human proteins with EHV regions. These proteins are enriched in immune functions and molecules, including major histocompatibility complex proteins. Their genes are expressed higher in BLBCs and are associated with better patient survival, like MGAM2. Their EHV-coding sequences are rich in simple repeats and harbor more cancer passenger mutations. In conclusion, MGAM2 diverges from MGAM structurally and likely functionally in placentals. MGAM2 is among >1000 human proteins with EHV regions and associated with immune response. We propose that these EHV molecules may have significant implication in cancer immunotherapy and BLBC treatment.

Enzyme immobilized on polyamidoamine-coated magnetic microspheres for α-glucosidase inhibitors screening from Radix Paeoniae Rubra extracts accompanied with molecular modeling

In this study, a method for direct screening and identification of α-glucosidase inhibitors (AGIs) from extracts of natural products was established based on polyamidoamine (PAMAM) coated magnetic microspheres. A facile route to synthesize the magnetic PAMAM was employed and α-glucosidase was successfully covalently attached to its surface through cross linking of glutaraldehyde. Using the enzyme-loaded magnetic microspheres, potential inhibitors were fished out from crude extracts directly, followed by structure confirmation. The inhibitory activities of the screened components were further investigated by the enzyme-loaded magnetic microspheres. The Fe₃O₄ @PAMAM@α-Glu microspheres displayed favorable dispersibility, fast magnetic separation, large enzyme binding amount (42.9 μg•mg^-1) and high enzyme activity. Moreover, the α-glucosidase on the surface of PAMAM coating maintained high storage stability and remarkable reusability. Taking advantage of specific interaction of the α-glucosidase with AGIs, the materials could selectively capture a known AGI (+)-catechin under the interference of an inactive compound salicylic acid, with a binding capacity as high as 15.4%. Additionally, using the Fe₃O₄ @PAMAM@α-Glu microspheres in the inhibition assay, the enzymatic reaction could be stopped by magnetic separation instead of the traditional addition of Na₂CO₃ solution, which not only eliminated the disturbance of termination reagent to the results, but also reused the immobilized α-glucosidase. The screening and inhibitory activity verification of potential ligands in Radix Paeoniae Rubra ("Chi-shao" in Chinese) extracts were achieved by using Fe₃O₄ @PAMAM@α-Glu microspheres, demonstrating practical applicability of our method. Therefore, the magnetic PAMAM-based screening approach could be a feasible and alternative strategy for discovering enzyme inhibitors from natural product extracts.

Phase 1 Study of the Pharmacology of BTI320 Before High-Glycemic Meals

BTI320 is a proprietary fractionated mannan polysaccharide being studied for attenuation of postprandial glucose excursion. The apparent blood glucose‐lowering effect of this compound is effective in lowering postprandial hyperinsulinemia, participating in the metabolic regulation of other lipid molecules; the consequence of this activity is yet to be validated with BTI320 with respect to the risk of cardiovascular disease. The primary objective of the study was to determine the postprandial glucose and insulin responses to 3 test meals containing rice alone or consumed with BTI320 (study A) or 3 test meals (Sprite^TM) alone or consumed with BTI320 (study B). Twenty overweight but otherwise healthy volunteers, 4 female and 6 male (mean age 29 years, BMI 27–28 kg/m²) in study A and 6 female and 4 male (mean age 32 years, BMI 25‐32 kg/m²) in study B participated in the BTI320 evaluations. Standardized postprandial response methodology was utilized. In study A the addition of 6‐ and 12‐g BTI320 tablets reduced postprandial glucose responses to white rice by 19% and 32% and reduced postprandial insulin responses by 16% and 24%, respectively (P ≤ .05). In study B 2.6 and 5.2 g BTI320 reduced the glycemic index by 10% and 14%, respectively, and led to 14% and 18% decreases in the insulinemic index of the soft drink (P ≤ .05). These 2 studies demonstrated that the consumption of BTI320 before carbohydrate food or sugary beverage significantly reduced postprandial glucose levels and insulin responses to that meal or beverage in a dose‐dependent manner.

Synthesis of furostanol glycosides: discovery of a potent α-glucosidase inhibitor

A convenient approach to the synthesis of furostanol glycosides has been developed with the features of both highly efficient incorporation of a 26-O-β-d-glucopyranosyl unit and ready formation of hemiketal ring E. The total syntheses of seven furostanol saponins including funlioside B, lilioglycoside, protobioside I, protodioscin, pallidifloside I, coreajaponins A and parisaponin I are efficiently achieved using an easily available 16β-acetoxy-22-oxo-26-hydroxy-cholestanic derivative as a powerful building block. The α-glucosidase inhibitory activity of the synthesized saponins is also evaluated, which reveals that funlioside B is a highly potential lead for developing α-glucosidase inhibitors.

Flaxseed: its bioactive components and their cardiovascular benefits

Cardiovascular disease remains the leading cause of mortality and morbidity worldwide. The inclusion of functional foods and natural health products in the diet are gaining increasing recognition as integral components of lifestyle changes in the fight against cardiovascular disease. Several preclinical and clinical studies have shown the beneficial cardiovascular effects of dietary supplementation with flaxseed. The cardiovascular effects of dietary flaxseed have included an antihypertensive action, antiatherogenic effects, a lowering of cholesterol, an anti-inflammatory action, and an inhibition of arrhythmias. Its enrichment in the ω-3 fatty acid α-linolenic acid and the antioxidant lignan secoisolariciresinol diglucoside as well as its high fiber content have been implicated primarily in these beneficial cardiovascular actions. Although not as well recognized, flaxseed is also composed of other potential bioactive compounds such as proteins, cyclolinopeptides, and cyanogenic glycosides, which may also produce biological actions. These compounds could also be responsible for the cardiovascular effects of flaxseed. This article will not only summarize the cardiovascular effects of dietary supplementation with flaxseed but also review its bioactive compounds in terms of their properties, biological effects, and proposed mechanisms of action. It will also discuss promising research directions for the future to identify additional health-related benefits of dietary flaxseed.

Towards Tuneable Retaining Glycosidase-Inhibiting Peptides by Mimicry of a Plant Flavonol Warhead

Retaining glycosidases are an important class of enzymes involved in glycan degradation. To study better the role of specific enzymes in deglycosylation processes, and thereby the importance of particular glycosylation patterns, a set of potent inhibitors, each specific to a particular glycosidase, would be an invaluable toolkit. Towards this goal, we detail here a more in-depth study of a prototypical macrocyclic peptide inhibitor of the model retaining glycosidase human pancreatic α-amylase (HPA). Notably, incorporation of l-DOPA into this peptide affords an inhibitor of HPA with potency that is tenfold higher (K_i =480 pm) than that of the previously found consensus sequence. This represents a first successful step in converting a recently discovered natural-product-derived motif, already specific for the catalytic side-chain arrangement conserved in the active sites of retaining glycosidases, into a tuneable retaining glycosidase inhibition warhead.

Saponins and Flavonoids from Adzuki Bean (Vigna angularis L.) Ameliorate High-Fat Diet-Induced Obesity in ICR Mice

Background and purpose: As an herbal medicine, adzuki bean has been practiced since the Tang Dynasty of China to maintain health and control weight; this practice is still very popular in China nowadays. However, it is still lack of sufficient scientific basis to explain scientific principle of this popular civil practice in weight control using adzuki bean. The purpose of this study was to verify and explain the anti-obesity effects of adzuki bean through in vitro enzymatic assays, in vitro lipolysis and in vivo study of obese mice model.

Methods: Inhibitory effects of flavonoids and saponins from adzuki bean (Vigna angularis) on pancreatic lipase, α-glucosidase activities, and noradrenaline-induced lipolysis were assessed. High-fat diet-induced obesity model was created to study anti-obesity effects of adzuki bean. Both serum and liver lipid parameters were determined after 8 weeks intervention.

Results: Adzuki bean extracts enhanced lipolysis. Compared to the final body weight of high-fat diet group, oral administration of adzuki bean significantly (p < 0.05) reduced the final body weight of mice and adipose tissue accumulation. The adzuki bean intervention also significantly reduced the levels of serum triglyceride, total cholesterol, low density lipoprotein-cholesterol, and liver lipid.

Conclusion: Adzuki bean demonstrated the anti-obesity effects on mice, such effects may mediated through the inhibitory effects of flavonoids and saponins from adzuki bean on α-glucosidase and pancreatic lipase activities, and lipolysis enhancement effect of active components from adzuki bean.

1,6-Cyclophellitol Cyclosulfates: A New Class of Irreversible Glycosidase Inhibitor

The essential biological roles played by glycosidases, coupled to the diverse therapeutic benefits of pharmacologically targeting these enzymes, provide considerable motivation for the development of new inhibitor classes. Cyclophellitol epoxides and aziridines are recently established covalent glycosidase inactivators. Inspired by the application of cyclic sulfates as electrophilic equivalents of epoxides in organic synthesis, we sought to test whether cyclophellitol cyclosulfates would similarly act as irreversible glycosidase inhibitors. Here we present the synthesis, conformational analysis, and application of novel 1,6-cyclophellitol cyclosulfates. We show that 1,6-epi-cyclophellitol cyclosulfate (α-cyclosulfate) is a rapidly reacting α-glucosidase inhibitor whose ⁴C₁ chair conformation matches that adopted by α-glucosidase Michaelis complexes. The 1,6-cyclophellitol cyclosulfate (β-cyclosulfate) reacts more slowly, likely reflecting its conformational restrictions. Selective glycosidase inhibitors are invaluable as mechanistic probes and therapeutic agents, and we propose cyclophellitol cyclosulfates as a valuable new class of carbohydrate mimetics for application in these directions.

Coumarins as potential antidiabetic agents

OBJECTIVES

Even with great advances in modern medicine and therapeutic agent development, the search for effective antidiabetic drugs remains challenging. Coumarins are secondary metabolites found widely in nature plants and used mainly in anticoagulation and antithrombotic therapy. Over the past two decades, however, there has been an increasing body of literatures related to the effects of coumarins and their derivatives on diabetes and its complications. This review aimed to focus on research findings concerning the effects of coumarins against diabetes and its complications using in-vitro and in-vivo animal models, and also to discuss cellular and molecular mechanisms underlying these effects.

KEY FINDINGS

The search for new coumarins against diabetes and it complications, either isolated from traditional medicine or chemically synthesized, has been constantly expanding. The cellular and molecular mechanisms involved include protecting pancreatic beta cells from damage, improving abnormal insulin signalling, reducing oxidative stress/inflammation, activating AMP-activated protein kinase (AMPK), inhibiting α-glucosidases and ameliorating diabetic complications.

CONCLUSIONS

The effects and mechanisms of coumarins and their derivatives upon diabetes and its complications are discussed in current review. Further investigations remain to be carried out to develop a promising antidiabetic agent based on coumarin cores.

Potential of rooibos, its major C-glucosyl flavonoids, and Z-2-(β-D-glucopyranosyloxy)-3-phenylpropenoic acid in prevention of metabolic syndrome

Risk factors of type 2 diabetes mellitus (T2D) and cardiovascular disease (CVD) cluster together and are termed the metabolic syndrome. Key factors driving the metabolic syndrome are inflammation, oxidative stress, insulin resistance (IR), and obesity. IR is defined as the impairment of insulin to achieve its physiological effects, resulting in glucose and lipid metabolic dysfunction in tissues such as muscle, fat, kidney, liver, and pancreatic β-cells. The potential of rooibos extract and its major C-glucosyl flavonoids, in particular aspalathin, a C-glucoside dihydrochalcone, as well as the phenolic precursor, Z-2-(β-D-glucopyranosyloxy)-3-phenylpropenoic acid, to prevent the metabolic syndrome, will be highlighted. The mechanisms whereby these phenolic compounds elicit positive effects on inflammation, cellular oxidative stress and transcription factors that regulate the expression of genes involved in glucose and lipid metabolism will be discussed in terms of their potential in ameliorating features of the metabolic syndrome and the development of serious metabolic disease. An overview of the phenolic composition of rooibos and the changes during processing will provide relevant background on this herbal tea, while a discussion of the bioavailability of the major rooibos C-glucosyl flavonoids will give insight into a key aspect of the bioefficacy of rooibos.

α-Glucosidase inhibitory effect of resveratrol and piceatannol

Dietary polyphenols have been shown to inhibit α-glucosidase, an enzyme target of some antidiabetic drugs. Resveratrol, a polyphenol found in grapes and wine, has been reported to inhibit the activity of yeast α-glucosidase. This triggered our interest to synthesize analogs and determine their effect on mammalian α-glucosidase activity. Using either sucrose or maltose as substrate resveratrol, piceatannol and 3'-hydroxypterostilbene showed strong inhibition of mammalian α-glucosidase activity; pinostilbene, cis-desoxyrhapontigenin and trans-desoxyrhapontigenin had moderate inhibition. Compared to acarbose (IC₅₀ 3-13 μg/ml), piceatannol and resveratrol inhibited mammalian α-glucosidase to a lesser extent (IC₅₀ 14-84 and 111-120 μg/ml, respectively). 3'-Hydroxypterostilbene (IC₅₀ 105-302 μg/ml) was 23-35-fold less potent than acarbose. We investigated the effect of piceatannol and resveratrol on postprandial blood glucose response in high-fat-fed C57Bl/6 mice. Animals administered resveratrol (30 mg/kg body weight [BW]) or piceatannol (14 mg/kg BW) 60 min prior to sucrose or starch loading had a delayed absorption of carbohydrates, resulting in significant lowering of postprandial blood glucose concentrations, similar to the antidiabetic drug acarbose, while no significant effect was observed with the glucose-loaded animals. Our studies demonstrate that the dietary polyphenols resveratrol and piceatannol lower postprandial hyperglycemia and indicate that inhibition of intestinal α-glucosidase activity may be a potential mechanism contributing to their antidiabetic property.

Rapid Discovery of Potent and Selective Glycosidase-Inhibiting De Novo Peptides

Human pancreatic α-amylase (HPA) is responsible for degrading starch to malto-oligosaccharides, thence to glucose, and is therefore an attractive therapeutic target for the treatment of diabetes and obesity. Here we report the discovery of a unique lariat nonapeptide, by means of the RaPID (Random non-standard Peptides Integrated Discovery) system, composed of five amino acids in a head-to-side-chain thioether macrocycle and a further four amino acids in a 3₁₀ helical C terminus. This is a potent inhibitor of HPA (K_i = 7 nM) yet exhibits selectivity for the target over other glycosidases tested. Structural studies show that this nonapeptide forms a compact tertiary structure, and illustrate that a general inhibitory motif involving two phenolic groups is often accessed for tight binding of inhibitors to HPA. Furthermore, the work reported here demonstrates the potential of this methodology for the discovery of de novo peptide inhibitors against other glycosidases.

Agrimoniin, an Active Ellagitannin from Comarum palustre Herb with Anti-α-Glucosidase and Antidiabetic Potential in Streptozotocin-Induced Diabetic Rats

Naturally existing α-glucosidase inhibitors from traditional herbal medicines have attracted considerable interest to treat type 2 diabetes mellitus (DM). The present study aimed to evaluate the anti-α-glucosidase activity of extracts from marsh cinquefoil (Comarum palustre L.), their hypoglycaemic action and detection of the responsible compounds. A 60% ethanol extract from C. palustre herb revealed the highest inhibitory activity against α-glucosidase (IC50 52.0 μg/mL). The HPLC analysis of the major compounds resulted in detection of 15 compounds, including ellagitannins, flavonoids, catechin and other compounds. Using HPLC activity-based profiling a good inhibitory activity of agrimoniin-containing eluates against α-glucosidase was demonstrated. The removal of ellagitannins from the C. palustre extract significantly decreased α-glucosidase inhibition (IC50 204.7 μg/mL) due to the high enzyme-inhibiting activity of the dominant agrimoniin (IC50 21.8 μg/mL). The hypoglycaemic effect of C. palustre extracts before and after ellagitannin removal, agrimoniin and insulin was evaluated on streptozotocin-induced experimental model. Diabetic rats treated with agrimoniin and C. palustre extract before ellagitannin removal showed significant increases in the levels of plasma glucose and glycosylated hemoglobin and significant decreases in the levels of plasma insulin and hemoglobin. The data obtained confirm the leading role of agrimoniin in the antidiabetic activity of the herb C. palustre and allows us to suggest the use of this plant as a possible dietary adjunct in the treatment of DM and a source of new oral hypoglycaemic agents.

Cost-Effectiveness of Saxagliptin versus Acarbose as Second-Line Therapy in Type 2 Diabetes in China

Objective

This study assessed the long-term cost-effectiveness of saxagliptin+metformin (SAXA+MET) versus acarbose+metformin (ACAR+MET) in Chinese patients with type 2 diabetes mellitus (T2DM) inadequately controlled on MET alone.

Methods

Systematic literature reviews were performed to identify studies directly comparing SAXA+MET versus ACAR+MET, and to obtain diabetes-related events costs which were modified by hospital surveys. A Cardiff Diabetes Model was used to estimate the long-term economic and health treatment consequences in patients with T2DM. Costs (2014 Chinese yuan) were calculated from the payer’s perspective and estimated over a patient’s lifetime.

Results

SAXA+MET predicted lower incidences of most cardiovascular events, hypoglycemia events and fatal events, and decreased total costs compared with ACAR+MET. For an individual patient, the quality-adjusted life-years (QALYs) gained with SAXA+MET was 0.48 more than ACAR+MET at a cost saving of ¥18,736, which resulted in a cost saving of ¥38,640 per QALY gained for SAXA+MET versus ACAR+MET. Results were robust across various univariate and probabilistic sensitivity analyses.

Conclusion

SAXA+MET is a cost-effective treatment alternative compared with ACAR+MET for patients with T2DM in China, with a little QALYs gain and lower costs. SAXA is an effective, well-tolerated drug with a low incidence of adverse events and ease of administration; it is anticipated to be an effective second-line therapy for T2DM treatment.

Caloric restriction ameliorates cardiomyopathy in animal model of diabetes

BACKGROUND

The db/db mouse is an animal model of diabetes in which leptin receptor activity is deficient resulting accelerated cardiomyopathy when exposed to angiotensin (AT). Toll-like receptors 4 and 2 (TLR4, TLR2) are pattern recognition receptors, that recognize pathogen-associated molecular patterns and exacerbate and release inflammatory cytokines. Fetuin A (Fet A) is a fatty acid carrier which affects inflammation and insulin resistance in obese humans and animals through TLRs. The aim of this study was to investigate the effect of caloric restriction (CR) on free fatty acids (FFA) level and the inflammatory response in diabetic cardiomyopathy.

METHODS AND RESULTS

Left ventricular hypertrophy, increased fibrosis and leukocytes infiltration were observed in db/db AT treated hearts. Serum glucose, FFA, and cholesterol levels were elevated in db/db AT treated mice. Cardiac expression of PPARα increased while AKT phosphorylation was decreased.

CONCLUSIONS

Cumulatively, CR elevated cardiac PPARα improved the utilization of fatty acids, and reduced myocardial inflammation as seen by reduced levels of Fet A. Thus CR negated cardiomyopathy associated with AT in an animal model of diabetes suggesting that CR is an effective therapeutic approach in the treatment of diabetes and associated cardiomyopathy.

Effects of linagliptin monotherapy compared with voglibose on postprandial blood glucose responses in Japanese patients with type 2 diabetes: Linagliptin Study of Effects on Postprandial blood glucose (L-STEP)

AIMS

To compare the efficacy on glycemic parameters between a 12-week administration of once-daily linagliptin and thrice-daily voglibose in Japanese patients with type 2 diabetes.

METHODS

In a multi-center, randomized, parallel-group study, 382 patients with diabetes were randomized to the linagliptin group (n=192) or the voglibose group (n=190). A meal tolerance test was performed at weeks 0 and 12. Primary outcomes were the change from baseline to week 12 in serum glucose levels at 2h during the meal tolerance test, HbA1c levels, and serum fasting glucose levels, which were compared between the 2 groups.

RESULTS

Whereas changes in serum glucose levels at 2h during the meal tolerance test did not differ between the groups, the mean change in HbA1c levels from baseline to week 12 in the linagliptin group (-0.5±0.5% [-5.1±5.4mmol/mol]) was significantly larger than in the voglibose group (-0.2±0.5% [-2.7±5.4mmol/mol]). In addition, there was significant difference in changes in serum fasting glucose levels (-0.51±0.95mmol/L in the linagliptin group vs. -0.18±0.92mmol/L in the voglibose group, P<0.001). The incidences of hypoglycemia, serious adverse events (AEs), and discontinuations due to AEs were low and similar in both groups. However, gastrointestinal AEs were significantly lower in the linagliptin group (1.05% vs. 5.85%; P=0.01).

CONCLUSIONS

These data suggested that linagliptin monotherapy had a stronger glucose-lowering effect than voglibose monotherapy with respect to HbA1c and serum fasting glucose levels, but not serum glucose levels 2h after the start of the meal tolerance test.

The Physiological Effects of Dandelion (Taraxacum Officinale) in Type 2 Diabetes

The tremendous rise in the economic burden of type 2 diabetes (T2D) has prompted a search for alternative and less expensive medicines. Dandelion offers a compelling profile of bioactive components with potential anti-diabetic properties. The Taraxacum genus from the Asteraceae family is found in the temperate zone of the Northern hemisphere. It is available in several areas around the world. In many countries, it is used as food and in some countries as therapeutics for the control and treatment of T2D. The anti-diabetic properties of dandelion are attributed to bioactive chemical components; these include chicoric acid, taraxasterol (TS), chlorogenic acid, and sesquiterpene lactones. Studies have outlined the useful pharmacological profile of dandelion for the treatment of an array of diseases, although little attention has been paid to the effects of its bioactive components on T2D to date. This review recapitulates previous work on dandelion and its potential for the treatment and prevention of T2D, highlighting its anti-diabetic properties, the structures of its chemical components, and their potential mechanisms of action in T2D. Although initial research appears promising, data on the cellular impact of dandelion are limited, necessitating further work on clonal β-cell lines (INS-1E), α-cell lines, and human skeletal cell lines for better identification of the active components that could be of use in the control and treatment of T2D. In fact, extensive in-vitro, in-vivo, and clinical research is required to investigate further the pharmacological, physiological, and biochemical mechanisms underlying the effects of dandelion-derived compounds on T2D.

Fermentation of purple Jerusalem artichoke extract to improve the α-glucosidase inhibitory effect in vitro and ameliorate blood glucose in db/db mice

BACKGROUND/OBJECTIVES

Jerusalem artichoke has inhibitory activity against α-glucosidase and decreases fasting serum glucose levels, which may be related to its fructan content. The biological activity of fructan can be influenced by the degree of polymerization. Thus, in this study, the inhibitory effects of original and fermented purple Jerusalem artichoke (PJA) on α-glucosidase were compared in vitro. Additionally, the anti-diabetes effect of Lactobacillus plantarum-fermented PJA (LJA) was studied in a non-insulin-dependent diabetes mellitus animal model (C57BIKsJ db/db).

MATERIALS/METHODS

The water extract of PJA was fermented by L. plantarum, and two strains of Bacillus subtilis to compare their anti-α-glucosidase activities in vitro by α-glucosidase assays. The anti-diabetes effect of LJA was studied in a non-insulin-dependent diabetes mellitus animal model (C57BIKsJ db/db) for seven weeks. During the experiment, food intake, body weight, and fasting blood glucose were measured every week. At the end of the treatment period, several diabetic parameters and the intestinal α-glucosidase activity were measured.

RESULTS

The LJA showed the highest α-glucosidase inhibitory activity in vitro. In the in vivo study, it resulted in a significantly lower blood glucose concentration than the control. Serum insulin and HDL cholesterol levels were significantly higher and the concentrations of triglycerides, non-esterified fatty acids, and total cholesterol were significant lower in mice treated with LJA after seven weeks. In addition, the intestinal α-glucosidase activity was partially inhibited.

CONCLUSIONS

These results suggested that LJA regulates blood glucose and has potential use as a dietary supplement.

Phenolic group on A-ring is key for dracoflavan B as a selective noncompetitive inhibitor of α-amylase

A high throughput assay was applied to guide the isolation of a new pancreatic α-amylase inhibitor, dracoflavan B, from the dragon's blood resin from Daemonorops draco. Applying C18 column, we successfully isolated both diastereomers and their structures verified by (1)H NMR spectra in comparison with the literature values. Their activity in inhibition of pancreatic α-amylase with comparable IC50 values of 23μM (A type) and 27μM (B type) that are similar to that of acarbose. Dracoflavan B shows much weaker activity in inhibiting bacterial α-amylase and no activity towards fungal α-amylase. Moreover, both isomers show no inhibitory activity towards mammalian α-glucosidase. Kinetic analysis revealed that using starch as the substrate, dracoflavan B was a non-competitive α-amylase inhibitor with a Ki value of 11.7μM. Lack of α-amylase inhibition for proanthocyanidin A2 dimer demonstrated that dracoflavan B hydrophobic nature of the B, A', C' and B' rings are important for its α-amylase inhibition. In addition, selective chemical modification studies revealed that the phenolic group is also vital to dracoflavan B for its pancreatic α-amylase inhibition activity. Without the A ring phenolic hydrogen bond donor, the derivatives of dracoflavan B showed detrimental α-amylase inhibition. On the contrary, galloylation on the A ring phenolic OH group enhanced the activity as shown by the low IC50 (12μM) against α-amylase which is 56% more potent as compared to dracoflavan B.

Synthesis of novel flavone hydrazones: in-vitro evaluation of α-glucosidase inhibition, QSAR analysis and docking studies

Thirty derivatives of flavone hydrazone (5-34) had been synthesized through a five-step reaction and screened for their α-glucosidase inhibition activity. Chalcone 1 was synthesized through aldol condensation then subjected through oxidative cyclization, esterification, and condensation reaction to afford the final products. The result for baker's yeast α-glucosidase (EC 3.2.1.20) inhibition assay showed that all compounds are active with reference to the IC50 value of the acarbose (standard drug) except for compound 3. Increase in activity observed for compounds 2 to 34 clearly highlights the importance of flavone, hydrazide and hydrazone linkage in suppressing the activity of α-glucosidase. Additional functional group on N-benzylidene moiety further enhances the activity significantly. Compound 5 (15.4 ± 0.22 μM), a 2,4,6-trihydroxy substituted compound, is the most active compound in the series. Other compounds which were found to be active are those having chlorine, fluorine, and nitro substituents. Compounds with methoxy, pyridine, and methyl substituents are weakly active. Further studies showed that they are not active in inhibiting histone deacetylase activity and do not possess any cytotoxic properties. QSAR model was being developed to further identify the structural requirements contributing to the activity. Using Discovery Studio (DS) 2.5, various 2D descriptors were being used to develop the model. The QSAR model is able to predict the pIC50 and could be used as a prediction tool for compounds having the same skeletal framework. Molecular docking was done for all compounds using homology model of α-glucosidase to identify important binding modes responsible for inhibition activity.

High-resolution bioactivity profiling combined with HPLC-HRMS-SPE-NMR: α-Glucosidase inhibitors and acetylated ellagic acid rhamnosides from Myrcia palustris DC. (Myrtaceae)

Type 2 diabetes (T2D) is an endocrine metabolic disease with a worldwide prevalence of more than 8%, and an expected increase close to 50% in the next 15-20years. T2D is associated with severe and life-threatening complications like retinopathy, neuropathy, nephropathy, and cardiovascular diseases, and therefore improved drug leads or functional foods containing α-glucosidase inhibitors are needed for management of blood glucose. In this study, leaves of Myrcia palustris were investigated by high-resolution α-glucosidase inhibition profiling combined with HPLC-HRMS-SPE-NMR. This led to identification of casuarinin, myricetin 3-O-β-d-(6″-galloyl)galactopyranoside, kaempferol 3-O-β-d-galactopyranoside, myricetin, and quercetin as α-glucosidase inhibitors. In addition, four acetylated ellagic acid rhamnosides, i.e., 4-O-(2″,4″-O-diacetyl-α-l-rhamnopyranosyl)ellagic acid, 4-O-(2″,3″-O-diacetyl-α-l-rhamnopyranosyl)ellagic acid, 4-O-(3″,4″-O-diacetyl-α-l-rhamnopyranosyl)ellagic acid, and 4-O-(2″,3″,4″-O-triacetyl-α-l-rhamnopyranosyl)ellagic acid were identified.

Effects of Miglitol, Acarbose, and Sitagliptin on Plasma Insulin and Gut Peptides in Type 2 Diabetes Mellitus: A Crossover Study

INTRODUCTION

Both dipeptidyl peptidase-4 inhibitors and α-glucosidase inhibitors (α-GI) have been reported to change the incretin and insulin secretion. To examine the effects of acarbose, miglitol, and sitagliptin on glucose metabolism and secretion of gut peptides, we conducted a crossover study in patients with type 2 diabetes mellitus (T2DM).

METHODS

Eleven Japanese patients with T2DM underwent four meal tolerance tests with single administration of acarbose, miglitol, sitagliptin, or nothing. Fasting and postprandial plasma levels of glucose, insulin, glucagon, active glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), ghrelin, and des-acyl ghrelin were measured.

RESULTS

Early-phase insulin secretion was reduced following acarbose and miglitol, and the areas under the curve (AUC) of insulin at 180 min following acarbose and miglitol were significantly lower than sitagliptin. AUC of plasma glucose at 180 min after acarbose, miglitol, and sitagliptin tended to be lower than in controls, and plasma glucose levels at 30-60 min following miglitol were significantly lower than in controls. Plasma glucagon, ghrelin, and des-acyl ghrelin levels did not differ among the four conditions. Postprandial plasma active GLP-1 levels and AUC of GLP-1 increased significantly in both the sitagliptin and miglitol groups compared to control. Postprandial plasma total GIP levels increased following sitagliptin but decreased after acarbose and miglitol. Changes in incretin levels tended to be greater with miglitol than acarbose.

CONCLUSION

These results showed that sitagliptin and α-GIs, miglitol more so than acarbose, improved hyperglycemia in patients with T2DM after single administration, and had different effects on insulin and incretin secretion.

TRIAL REGISTRATION

UMIN-CTR number, UMIN000009981.

Investigation of antihyperglycaemic activity of banana (Musa sp. var. Nanjangud rasa bale) pseudostem in normal and diabetic rats

BACKGROUND

Postprandial hyperglycaemia in diabetes could be ameliorated by inhibiting intestinal α-glucosidases, responsible for starch hydrolysis and its absorption. Different parts of banana have been in use in conventional medicinal formulations since ancient times. Its role as an antihyperglycaemic agent has also been studied. This study was aimed at explaining the mechanism of hypoglycaemic effect by ethanol extract of banana pseudostem (EE). Additionally, studies on the active components involved in the effect have also been attempted.

RESULTS

EE significantly inhibited mammalian intestinal α-glucosidases and yeast α-glucosidase (IC50 , 8.11 ± 0.10 µg mL(-1) ). The kinetic studies showed that EE inhibited sucrase, maltase and and p-nitrophenyl-α-d-glucopyranoside hydrolysis by mixed-type inhibition. Further, in vivo studies identified that the oral administration (100-200 mg kg(-1) body weight) of EE significantly suppressed the maltose/glucose-induced postprandial plasma glucose elevation and wielded an antihyperglycaemic effect in normal and alloxan-induced diabetic rats. GC-MS analysis of EE revealed high levels of β-sitosterol (29.62%), stigmasterol (21.91%), campesterol (10.85%) and other compounds.

CONCLUSION

These findings suggest that EE might exert an anti-diabetic effect by inhibition of α-glucosidases from the intestine, in turn suppressing the carbohydrate absorption into the bloodstream. Hence the results extend a foundation to the future prospects of the food-derived enzyme inhibitors in treatment of diabetes.

Historical cohort analysis of treatment patterns for patients with type 2 diabetes initiating metformin monotherapy

OBJECTIVE

To describe treatment regimen changes of patients with type 2 diabetes mellitus (T2DM) initiating metformin monotherapy, and assess factors associated with those changes 12 months post-initiation.

METHODS

Retrospective cohort analysis of medical, pharmacy and laboratory claims of 17,527 Medicare Advantage (MAPD) Humana members aged 18-89, who had ≥1 medical claim with primary diagnosis or ≥2 medical claims with secondary diagnosis of T2DM (ICD-9-CM code 250.x0 or 250.x2) who filled an initial prescription for metformin (GPI code 2725) between 1 January 2008 and 30 September 2011. The main outcome measure was change in metformin monotherapy during the 12 months following initiation. Factors associated with treatment changes during follow-up were examined using Cox proportional hazards regression models.

RESULTS

Fifty-nine percent of patients (mean age 69.6 years) remained on metformin monotherapy with no changes. Discontinuation was the most common treatment change (33%), followed by addition (5%), and switching (2%) to other antidiabetics. Of patients who discontinued treatment (median time to discontinuation = 90 days), 61% did not reinitiate any diabetic treatment during the follow-up period. Among patients who added or switched to other antidiabetics, sulfonylureas were the most common addition or replacement agent. Predictors of discontinuation were being female, Black or Hispanic, low-income subsidy eligible, having higher initial out-of-pocket metformin costs, or a diagnosis of depression. Discontinuation was less likely during follow-up if patients had higher pre-index pill burdens or records of a pre-index A1C screening test. A higher risk of discontinuation was observed for patients with low baseline A1C. One study limitation was that exact discontinuation dates could not be determined using claims.

CONCLUSIONS

The findings suggest that gender, race, ethnicity, depression, and low income status were contributory factors to metformin discontinuation. More intensive monitoring and treatment adjustments may be warranted for patients newly initiated on metformin. This could ultimately improve morbidity, mortality, and costs associated with poor glycemic control.

Additive effects of miglitol and anagliptin on insulin-treated type 2 diabetes mellitus: a case study

The aim of this case study was to examine the efficacy of a dipeptidyl peptidase-4 inhibitor (anagliptin) and an α-glucosidase inhibitor (miglitol) when added to ongoing insulin treatment in patients with type 2 diabetes mellitus. Continuous glucose monitoring was performed in four Japanese insulin-treated inpatients with type 2 diabetes. Baseline data were collected on day 1. Miglitol was administered on days 2 and 3. On day 4, miglitol and anagliptin were coadministered before breakfast. On days 1, 3, and 5, blood was drawn for plasma glucose, serum C-peptide, plasma glucagon, total and active glucagon-like peptide-1 (GLP-1), and total and active glucose-dependent insulinotropic peptide (GIP) measurements. Coadministration of anagliptin with miglitol resulted in additional improvements in glycemic control over the entire day in three of the four patients. The C-peptide, glucagon, and total and active GLP-1 and GIP responded differently to the medications for each patient, suggesting interindividual differences in hormonal responses, which may be complicated by multifactorial effects.

Safety and efficacy of acarbose in the treatment of diabetes in Chinese patients

Acarbose is an α-glucosidase inhibitor that is commonly used to control postprandial blood glucose. It functions as a competitive and reversible inhibitor of small intestinal brush border glucosidase, blocks the degradation of starch and sucrose, and delays the absorption of glucose and fructose in the alimentary tract. The starch content of a diet might alter the hypoglycemic effects of acarbose because of its mechanism of action. Chinese individuals consume a typical Eastern diet, which is characterized by a high intake of whole grains, legumes, vegetables, fruits, and fish. These dietary habits allow acarbose to be used extensively in the People’s Republic of China. Several Chinese-based studies have demonstrated that the use of acarbose as a monotherapy had similar effects on other anti-diabetes agents in decreasing glycosylated hemoglobin (HbA_1c) and blood glucose levels, and acarbose in combination with other anti-diabetic drugs could further reduce blood glucose and decrease the mean amplitude of glycemic excursions. Importantly, acarbose is safe and well tolerated, with a low incidence of adverse effects. This article provides a comprehensive review of the safety and efficacy of acarbose for the treatment of diabetes in Chinese patients.

Efficacy of voglibose in type 2 diabetes

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is currently at epidemic proportions and the forecast is for a continued sharp increase in global prevalence. An even larger proportion of the population has prediabetes (impaired glucose tolerance [IGT]) underscoring the urgent need for preventive strategies. Even in the presence of adequate glycosylated hemoglobin (HbA1c) levels, postprandial hyperglycemia can occur and is known to have a stronger association with cardiovascular morbidity than fasting glucose. The α-glucosidase inhibitor voglibose is widely used in Japan to improve postprandial hyperglycemia.

AREAS COVERED

This review examines the literature for the pharmacology, pharmacokinetics, clinical efficacy and safety of voglibose in patients with T2DM. Particular focus is on its efficacy in preventing T2DM in individuals with IGT and its efficacy as add-on therapy or in combination with other oral antidiabetic agents in patients with T2DM.

EXPERT OPINION

As the relationship between glucose levels and cardiovascular risk extends below the diabetic threshold, postprandial hyperglycemia is recognized as a key therapeutic target in the treatment of T2DM. Strategies to prevent the progression of IGT to overt T2DM have enormous potential to reduce the individual and societal burden of disease. Voglibose is the first oral antidiabetic agent to gain approval in Japan for this indication.

Rhinacanthus nasutus Improves the Levels of Liver Carbohydrate, Protein, Glycogen, and Liver Markers in Streptozotocin-Induced Diabetic Rats

The present study was designed to investigate the total carbohydrate, total protein, and glycogen levels in the liver and to measure functional liver markers such as aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in streptozotocin-(STZ-) induced diabetic rats after treatment with methanolic extract of Rhinacanthus nasutus (R. nasutus). The methanolic extract of R. nasutus was orally administered at 200 mg/kg/day while glibenclamide was administered at 50 mg/kg/day. All animals were treated for 30 days before being sacrificed. The amounts of carbohydrate, glycogen, proteins, and liver markers (AST and ALT) were measured in the liver tissue of the experimental animals. The levels of carbohydrate, glycogen, and proteins were significantly reduced in the diabetic rats but were augmented considerably after 30 days of R. nasutus treatment. The elevated AST and ALT levels in diabetic rats showed a significant decline after treatment with R. nasutus for 30 days. These results show that the administration of R. nasutus ameliorates the altered levels of carbohydrate, glycogen, proteins, and AST and ALT observed in diabetic rats and indicate that R. nasutus restores overall metabolism and liver function in experimental diabetic rats. In conclusion, the outcomes of the present study support the traditional belief that R. nasutus could ameliorate the diabetic state.

The effect of polyhydroxylated alkaloids on maltase-glucoamylase

One of the most important carbohydrate-splitting enzymes is themaltase-glucoamylase which catalyzes the hydrolysis of alpha-glucosidic linkages. Maltase-glucoamylase inhibitors during the last few years have aroused medical interests in the treatment of diabetes. They contribute to a better understanding of the mechanism of maltase-glucoamylase. At present there are many different classes of maltase-glucoamylase inhibitors. This paper focuses on alkaloidal inhibitors of maltase-glucoamylase and structure-activity relationship (SAR) studies between them in order to discover some drugs with better efficiency and lower toxicity for treating diabetes.

Antidiabetic effect of the Chrysobalanus icaco L. aqueous extract in rats

Chrysobalanus icaco L. is a medicinal plant popularly known in Brazil as "Grageru" or "Abageru." It is used in African and American continents as medicinal food in the treatment of several diseases, including diabetes. This study used phytochemical screening to determine the antioxidant and α-amylase inhibitor activities of the aqueous extract (AECI) of C. icaco, and evaluated its antidiabetic potential in rodents. Phytochemical screening was performed using colorimetric tests with specific reagents. The in vitro antioxidant activity was evaluated by the scavenging activity of 2,2-diphenyl-1-picril-hydrazyl. The lethality test and behavioral screening was performed using an oral administration of 5 g/kg of AECI. The antidiabetic potential of AECI was evaluated through the oral glucose tolerance test (OGTT) and chronic hypoglycemic test at the doses of 100, 200, and 400 mg/kg (orally). Metformin was used as a reference drug in all tests. Diabetes was induced by injection of alloxan (40 mg/kg; intravenously). Phytochemical screening showed the presence of various compounds, including tannins, flavones, triterpenoids, steroids, saponins, and alkaloids. The in vitro antioxidant test demonstrated that AECI presented potent antioxidant activity. The lethality test and behavioral screening did not show lethality signs. In the OGTT test, AECI administration was not able to inhibit the elevation of glycemia. However, chronically administrated, it was able to cause a significant (P<.05) reduction of glycemia from 335±27 up to 197±15 mg/dL. These results demonstrate that the AECI presents a potential beneficial effect for diabetes.