A new colorimetric method for determining the isomerization activity of sucrose isomerase

Tailor-Made α-Glucans by Engineering the Processivity of α-Glucanotransferases via Tunnel-Cleft Active Center Interconversions

The function of polysaccharides is intimately associated with their size, which is largely determined by the processivity of transferases responsible for their synthesis. A tunnel active center architecture has been recognized as a key factor that governs processivity of several glycoside hydrolases (GHs), e.g., cellulases and chitinases. Similar tunnel architecture is also observed in the Limosilactobacillus reuteri 121 GtfB (Lr121 GtfB) α-glucanotransferase from the GH70 family. The molecular element underpinning processivity of these transglucosylases remains underexplored. Here, we report the synthesis of the smallest (α1 → 4)-α-glucan interspersed with linear and branched (α1 → 6) linkages by a novel 4,6-α-glucanotransferase from L. reuteri N1 (LrN1 GtfB) with an open-clefted active center instead of the tunnel structure. Notably, the loop swapping engineering of LrN1 GtfB and Lr121 GtfB based on their crystal structures clarified the impact of the loop-mediated tunnel/cleft structure at the donor subsites -2 to -3 on processivity of these α-glucanotransferases, enabling the tailoring of both product sizes and substrate preferences. This study provides unprecedented insights into the processivity determinants and evolutionary diversification of GH70 α-glucanotransferases and offers a simple route for engineering starch-converting α-glucanotransferases to generate diverse α-glucans for different biotechnological applications.

A practical approach to producing the single-arm linear dextrin, a chimeric glucosaccharide containing an (α-1 → 4) linked portion at the nonreducing end of an (α-1 → 6) glucochain

How to improve the solubility of linear dextrins (LD) and retain their characteristic helix amphiphilic cavities with flexible embedding capability, is a question worth exploring without adding new chemical groups. The strategy presented in this study is to attach a highly flexible (α-1 → 6) glucochain at the reducing end of LD by preparing a new type of dextrin, referred to as single-arm linear dextrin (SLD). In the actual synthesis, an (α-1 → 6) linked oligosaccharide of DP¯ 10.7 (PDI = 1.28) was formed by extension of glucose units onto sucrose (2 M) by using L940W mutant of the glucansucrase GTF180-ΔN firstly. Next using γ-CD as glucosylation donor γ-CGTase extended this (α-1 → 6) glucochain with (α-1 → 4) bonds. SLD is a chimeric glucosaccharide comprising an (α-1 → 4) linked part (DP¯ 10.5) attached to the nonreducing end of an (α-1 → 6) glucochain as verified by enzyme fingerprinting and ¹H NMR. Furthermore, SLD was validated to show greatly improved solubility and dispersibility of resveratrol in water, as indicated by a 3.12-fold enhancement over the solubility in the presence of 0.014 M SLD. This study provided a new strategy for solving the solubility problem of LD and opens possibilities for new design of the fine structure of starch-like materials.

Site-Directed Mutagenic Engineering of a Bifidobacterium Amylosucrase toward Greater Efficiency of Turanose Synthesis

The aim of this study was to establish one of the most efficient biocatalytic processes for turanose production by applying a robust Bifidobacterium thermophilum (BtAS) mutant developed through site-directed mutagenesis. A gene encoding the amylosucrase of B. thermophilum (BtAS) was cloned and used as a mutagenesis template. Among the BtAS variants generated by the site-directed point mutation, four different single-point mutants (P200R, V202I, Y265F, and Y414F) were selected to create double-point mutants, among which BtAS_Y414F/P200R displayed the greatest turanose productivity without losing the thermostability of native BtAS. The turanose yield of BtAS_Y414F/P200R reached 89.3% at 50 °C after 6 h with 1.0 M sucrose + 1.0 M fructose. BtAS_Y414F/P200R produced significantly more turanose than BtAS-wild type (WT) by 2 times and completed the reaction faster by another 2 times. Thus, turanose productivity (82.0 g/(L h)) by BtAS_Y414F/P200R was highly improved from 28.1 g/(L h) of BtAS-WT with 2.0 M sucrose + 0.75 M fructose.

Beneficial effects of combination therapy of phloretin and metformin in streptozotocin-induced diabetic rats and improved insulin sensitivity in vitro

Phloretin combined with metformin ameliorates glucose and lipid metabolism in STZ-induced T2D rats via AKT/GLUT4 signaling pathways.

Sucrose-based biosynthetic process for chain-length-defined α-glucan and functional sweetener by Bifidobacterium amylosucrase

A unique thermostable amylosucrase from Bifidobacterium thermophilum was produced as a recombinant protein with the half-life of 577 h at 50 °C. By adding 1.0 M fructose, turanose yield was improved from 22.7% to 43.3% with 1.0 M sucrose, and from 23.7% to 39.4% with 1.5 M sucrose. Sucrose consumption rate was greatest at 55 °C, but the lowest amount of turanose was produced. Thus, turanose yield from sucrose biomass was inversely proportional to reaction temperature and was highly dependent on [fructose]. Meanwhile, insoluble α-glucan yield was clearly reduced as [fructose] increased. With 1.0 M fructose + 1.0 M sucrose, glucan byproduct yield significantly decreased from 29.4% to 1.1%. Molecular weights of linear glucans were almost identical among various [sucrose]s and were homogenous with very low polydispersity. This unique dual reaction patterns of amylosucrase enzyme would be very useful for massive productions of two different biomaterials simply by changing sucrose biomass concentration.

Phloretin exerts hypoglycemic effect in streptozotocin-induced diabetic rats and improves insulin resistance in vitro

The present study investigated the possible antiobesity and hypoglycemic effects of phloretin (Ph). In an attempt to discover the hypoglycemic effect and potential mechanism of Ph, we used the streptozotocin-induced diabetic rats and (L6) myotubes. Daily oral treatment with Ph for 4 weeks significantly (P<0.05) reduced postprandial blood glucose and improved islet injury and lipid metabolism. Glucose consumption and glucose tolerance were improved by Ph via GOD–POD method. Western blot results revealed that the expression of Akt, PI3K, IRS-1, and GLUT4 were upregulated in skeletal muscle of type 2 diabetes (T2D) rats and in L6 myotubes by Ph. The immunofluorescence studies confirmed that Ph improved the translocation of GLUT4 in L6 myotubes. Ph exerted hypoglycemic effects in vivo and in vitro, hence it may play an important role in the management of diabetes.

Antidiabetic andantioxidant properties, and α-amylase and α-glucosidase inhibition effects of triterpene saponins from Piper auritum

Bioactivity-guided fractionation of methanol extracts from leaves of Piper auritum produced four triterpenoid saponin compounds 1-4. Structures were established based on interpretation of mass spectrometry (MS), nuclear magnetic resonance (NMR) data. 21-(p-methoxycinnamoyl)-olean-12-ene-28oic cid-3-O-α-L-arabinopyranosyl-(1→2)-β-D-glucopyranoside (1) and olean-12-ene-28 methyl ester-3-O-α-L-arabinofuranosyl-(1→2)-β-D-glucopyranoside (2) were orally administered to diabetic mice at dosage of 10 mg/kg of body weight per day for 30 days and resultant biochemical parameters were studied. Both compounds significantly (p<0.05) decreased serum glucose, total cholesterol, and triglyceride levels, compared with controls. Low density lipoprotein and high density lipoprotein cholesterol levels were ameliorated. The effects of lipid peroxidation and oxidative stress in the liver, pancreas, and kidney were reversed, with reductions insulin resistance and stimulation of insulin production. β-Glucosidase activities were studied in vitro. Compounds 1 and 2 can be used to improve glucose and lipid metabolism and to reduce the imbalance between generation of reactive oxygen species and scavenging enzyme activities for prevention of diabetic complications.

Antidiabetic activity of Piper auritum leaves in streptozotocin-induced diabetic rat, beneficial effect on advanced glycation endproduct

OBJECTIVE

To investigate the effect of hypoglycaemic, hypolipidemic, oxidative stress, insulin resistance and advanced glycation endproducts (AGEs) formation of hexane extract from Piper auritum.

METHODS

The streptozotocin (STZ)-induced diabetic Wistar rats were treated with the hexane extract from Piper auritum leaves for 28 days and a set of biochemical parameters were studied including glucose level, total cholesterol, triglycerides, lipid peroxidation, liver and muscle glycogen, superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase. The liver function was observed by determining glucose-6-phosphatase, glucokinase and hexokinase activities, and the effect of the hexane extract on insulin level and protein glycation.

RESULTS

There was a significant increase in blood glucose level (P<0.05) in diabetic rats after 24 h of STZ injection. There was a significantly decreased in blood glucose in diabetic rats with hexane extract treatment (P<0.05). The serum biochemical parameters, hepatic enzymes, thiobarbituric acid reactive substances, glycosylated hemoglobin, AGEs, and insulin level (P<0.01 or P<0.05) were restored to normal levels in STZ-diabetic rats treated with hexane extract.

CONCLUSION

The hexane extract from Piper auritum leaves can efficiently inhibit insulin resistance, AGEs formation, improvement of renal function, lipid abnormalities and oxidative stress, indicating that its therapeutic properties may be due to the interaction of hexane extract components with multiple targets involved in diabetes pathogenesis.

Effect of chronic administration of hexane extract of Byrsonima crassifolia seed on B-cell and pancreatic oxidative parameters in streptozotocin-induced diabetic rat

BACKGROUND

In Mexican traditional medicine, the seeds of Byrsonima crassifolia have been used in the treatment of diabetes, rheumatism and for wound healing. The aim was to evaluate the effect of seeds of B. crassifolia on insulin release from the pancreatic beta cells in streptozotocininduced diabetic rats.

MATERIALS AND METHODS

In the present study, we evaluated the beneficial effect of seeds B. crassifolia streptozotocin-induced type 1 diabetic rats. Insulin level; insulin sensitivity index, insulin content in pancreas, malonaldehyde, nitric oxide contents, oxidative stress parameters were assayed. Serum glucose levels were determined by the glucose oxidase method. To determine the insulin releasing activity, after extract treatment, the pancreas was excised. Pancreatic sections were processed for examination of insulin-releasing activity using an imunocytochemistry kit.

RESULTS

Administration of the hexane extract (200 and 400 mg/kg), exhibited a significant reduction in serum glucose. Administration of streptozotocin decreased the number of beta cells with insulin secretory activity in comparison with intact rats; but treatment with the B. crassifolia seed extract increased significantly the activity of the beta cells in comparison with the diabetic control rats. The extract decreased serum glucose in streptozotocin-induced diabetic rats and increased insulin release from the beta cells of the pancreas.

CONCLUSION

These finding suggest that B. crassifolia seed has beneficial effect for diabetes through decreasing blood glucose and lipid levels, increasing insulin sensitivity index and insulin content, up-regulating antioxidant enzyme activity and decreasing lipid peroxidation.

Ameliorative Effect of Hexane Extract of Phalaris canariensis on High Fat Diet-Induced Obese and Streptozotocin-Induced Diabetic Mice

Obesity is one of the major factors to increase various disorders like diabetes. The present paper emphasizes study related to the antiobesity effect of Phalaris canariensis seeds hexane extract (Al-H) in high-fat diet- (HFD-) induced obese CD1 mice and in streptozotocin-induced mild diabetic (MD) and severely diabetic (SD) mice.AL-H was orally administered to MD and SD mice at a dose of 400 mg/kg once a day for 30 days, and a set of biochemical parameters were studied: glucose, cholesterol, triglycerides, lipid peroxidation, liver and muscle glycogen, ALP, SGOT, SGPT, glucose-6-phosphatase, glucokinase, hexokinase, SOD, CAT, GSH, GPX activities, and the effect on insulin level. HS-H significantly reduced the intake of food and water and body weight loss as well as levels of blood glucose, serum cholesterol, triglyceride, lipoprotein, oxidative stress, showed a protective hepatic effect, and increased HDL-cholesterol, serum insulin in diabetic mice. The mice fed on the high-fat diet and treated with AL-H showed inhibitory activity on the lipid metabolism decreasing body weight and weight of the liver and visceral adipose tissues and cholesterol and triglycerides in the liver. We conclude that AL-H can efficiently reduce serum glucose and inhibit insulin resistance, lipid abnormalities, and oxidative stress in MD and SD mice. Our results demonstrate an antiobesity effect reducing lipid droplet accumulation in the liver, indicating that its therapeutic properties may be due to the interaction plant components soluble in the hexane extract, with any of the multiple targets involved in obesity and diabetes pathogenesis.

Effect of the hexane extract of Piper auritum on insulin release from β-cell and oxidative stress in streptozotocin-induced diabetic rat

Background:

The large-leafed perennial plant Piper auritum known as Hoja Santa, is used for its leaves that because of their spicy aromatic scent and flavor have an important presence in Mexican cuisine, and in many regions, this plant is known for its therapeutic properties.

Materials and Methods:

In the present study, we investigated the effect of hexane, chloroform and methanol extracts from Piper auritum on cell culture system and the effect in streptozotocin-induced type 1 diabetic rats treated by 28 days on the physiological, metabolic parameters and oxidative stress.

Results:

The hexane extract of P. auritum (HS) treatment significantly reduced the intake of both food, water and body weight loss as well as levels of blood glucose, serum cholesterol, triglycerides and increase HDL-cholesterol. After 4-week administration of HS antioxidant enzyme as SOD, CAT, GSH, GPx in pancreas were determined. These enzyme increased significantly compared with those of the diabetic rats control and normal animals. For all estimated, the results of HS treated groups leading to a restoration of the defense mechanism. The treatment also improves pancreatic TBARS–reactive substance level and serum NO and iNOS. To determine the insulin releasing activity, after extract treatment the serum and pancreatic sections were processed for examination of insulin-releasing activity using an immunocytochemistry kit. The results showed that administration of the hexane extract (200 and 400 mg/kg) exhibited a significant increase in serum and pancreas tissue insulin. Administration of streptozotocin decreased the insulin secretory activity in comparison with intact rats, but treatment with the HS extract increased significantly the activity of the beta cells in comparison with the diabetic control rats. The extract decreased serum glucose in streptozotocin-induced diabetic rats and increased insulin release from the beta cells of the pancreas. In cultured RIN-5F cells, we examined whether hexane extract of P. auritum would protect the pancreas-derived β-cells from oxidative stress. Moreover, HS could protect pancreatic β-cells from advanced glycation end products-induced oxidative stress.

Conclusion:

From these results, HS is suggested to show anti-diabetic effect by stimulating insulin-dependent and by protecting pancreatic β-cells from advanced glycation end products-induced oxidative stress.

Evaluation of hypoglycemic activity of the leaves of Malva parviflora in streptozotocin-induced diabetic rats

Malva parviflora (MP), known in Mexico by the name of "quesitos" or "malva", is popular due to its culinary and medicinal properties. Diabetic rats were treated with the hexane, chloroform and methanol extracts of the M. parviflora leaves for 28 days and a set of biochemical parameters were studied including: glucose level, total cholesterol, triglycerides, lipid peroxidation, liver and muscle glycogen, superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase. We also looked into liver function by determining glucose-6-phosphatase, glucokinase and hexokinase activities, and the effect of the extracts on insulin level and protein glycation. As a result we found that with the hexane extract the blood glucose level, serum biochemical parameters, hepatic enzymes, thiobarbituric acid reactive substances, glycosylated hemoglobin, advanced glycation end products, and insulin level were restored in streptozotocin induced diabetic rats to nearly normal levels. We conclude that the hexane extract of M. parviflora leaves can efficiently inhibit insulin resistance, lipid abnormalities and oxidative stress, indicating that its therapeutic properties may be due to the interaction plant components soluble in the hexane extract, with any of the multiple targets involved in diabetes pathogenesis.

Hypoglycemic activity of constituents from Astianthus viminalis in normal and streptozotocin-induced diabetic mice

Astianthus viminalis has been used as a medicinal plant for a long time owing to its many physiological actions such as anti-inflammatory and antidiabetic activities. A new tetracyclic triterpenoid 3beta,19alpha-dihydroxyurs-12,20(21)-diene-28-oic acid (1), known constituents oleanolic acid (2) and ursolic acid (3), and the coumarins 7,8-dimethoxycoumarin (4) and 7-methoxycoumarin (5) were isolated from the chloroform extract of the leaves of A. viminalis. The structure and relative configurations of 1 were determined by spectroscopic methods (1H- and 13C-NMR, IR, and MS) and 2D-NMR experiments. The hypoglycemic ingredients of A. viminalis were characterized as compounds 1-3. The hypoglycemic effect of the isolated natural product 1 was investigated in normoglycemic and streptozotocin (STZ)-induced diabetic mice. All effects were compared with those of tolbutamide. Triterpenoid 1 showed potent hypoglycemic and hypolipidemic effects in the STZ-induced diabetic mice. Continuous administration of 1 (30 mg/kg, orally) led to significant decrease in the level of glucose, triglycerides, total cholesterol, LDL, and VLDL in the diabetic mice, whereas the level of HDL did not alter significantly in any of the groups studied.