Figen Zihnioglu

Inhibition of alpha-glucosidase by aqueous extracts of some potent antidiabetic medicinal herbs.

Abstract Diabetes mellitus is one of the most prevalant diseases of adults. Agents with α‐glucosidase inhibitory activity have been useful as oral hypoglycemic drugs for the control of hyperglycemia in patients with type 2; noninsulin‐dependent, diabetes mellitus (NIDDM). Investigation of some medicinal herbs: Urtica dioica, Taraxacum officinale, Viscum album, and Myrtus communis with α‐glucosidase inhibitor activity was conducted to identify a prophylactic effect for diabetes in vitro. All plants showed differing potent α‐glucosidase inhibitory activity. However, Myrtus communis strongly inhibited the enzyme (IC50 = 38 µg/mL). The inhibitory effect of these plants and some common antidiabetic drugs against the enzyme source (bakers yeast, rabbit liver, and small intestine) were also searched. Approximately all inhibitors used in this study showed quite different inhibitory activities, according to α‐glucosidase origins. Furthermore, subsequent separation of the active material from Myrtus communis by HPLC showed that only one fraction acted as an α‐glucosidase inhibitor.

Biosensing approach for glutathione detection using glutathione reductase and sulfhydryl oxidase bienzymatic system

Chitosan membrane with glutathione reductase and sulfhydryl oxidase (SOX) was subsequently integrated onto the surface of spectrographic graphite rods for obtaining a glutathione biosensor. The working principle was based on the monitoring of O(2) consumption that correlates the concentration of glutathione during the enzymatic reaction. A linear relationship between sensor response and concentration was obtained between 0.5 and 2.0 mM for oxidized glutathione (GSSG), and 0.2-1.0 mM for reduced glutathione (GSH) in the presence of 2 microM nicotinamide adenine dinucleotide phosphate (NADPH) under the optimum working conditions. Also, reduced/oxidized glutathione were separated by HPLC and utility of bienzymatic system was investigated as an electrochemical detector for the analysis of these compounds. All data were given as a comparison of two systems: biosensor and diode array detector (DAD).

ENCAPSULATION OF INSULIN IN CHITOSAN-COATED ALGINATE BEADS: ORAL THERAPEUTIC PEPTIDE DELIVERY

Insulin was encapsulated in calcium alginate beads coated with chitosan. Its release from alginate-chitosan and alginate-chitosan-glutaraldehyde beads was studied in artificial gastric (pH 1.2) and intestinal (pH 7.5) fluids. By comparing the release amounts, the ionic interaction between alginate-chitosan matrix with the medium pHs, intestinal fluid was found to be the better. The degradation of released insulin was also searched, even after 6 h incubation, the beads remained stable and the undegraded insulin seemed to be sufficient for the physiological conditions. Consequently, it can be said that the system can be offered for oral delivery of the therapeutic peptide drug insulin.Insulin was encapsulated in calcium alginate beads coated with chitosan. Its release from alginate-chitosan and alginate-chitosan-glutaraldehyde beads was studied in artificial gastric (pH 1.2) and intestinal (pH 7.5) fluids. By comparing the release amounts, the ionic interaction between alginate-chitosan matrix with the medium pHs, intestinal fluid was found to be the better. The degradation of released insulin was also searched, even after 6 h incubation, the beads remained stable and the undegraded insulin seemed to be sufficient for the physiological conditions. Consequently, it can be said that the system can be offered for oral delivery of the therapeutic peptide drug insulin.

Covalent immobilization of trypsin on glutaraldehyde-activated silica for protein fragmentation

Abstract Trypsin was immobilized by covalent binding to glutaraldehyde-activated silica with and without a spacer arm; 1,6-diaminohexane and polyethyleneglycol as well. The addition of polyethyleneglycol (PEG) to the immobilization media increased the activity of immobilized trypsin in organic solvents, whilst free trypsin activity disappeared under the same conditions. Thermal, pH, storage, and operational stabilities of the free and immobilized enzyme were found to be better than the free enzyme. Furthermore, use of immobilized enzyme for protein fragmentation was achieved by solid-phase, on-line, protein digestion in organic solvents. Reaction times were reduced to a few minutes and the sample handling was minimized.

Immobilization of α‐Glucosidase in Chitosan Coated Polygalacturonic Acid

Abstract Crude α‐glucosidase from Bakers yeast was immobilized in polygalacturonic acid beads and coated with chitosan. Chemical and physical characterization were performed by using p‐nitrophenyl‐α‐D‐glucopyranoside (pNPG) as an artificial substrate. Operation, thermal, pH, and strorage stabilities of the free and immobilized enzyme were also examined. The stabilities of immobilized enzyme were found to be better than that of the free enzyme. Furthermore, the hydrolysis rate of the chitosan coated α‐glucosidase polygalacturonic acid beads were studied. In conclusion, the enzyme beads appear to have good characteristics and offer the prospect that this system may find application in enzyme immobilization, in addition to controlled drug release studies.

Caffeic Acid Detection Using an Inhibition-Based Lipoxygenase Sensor

An inhibition based biosensing system was developed for the caffeic acid as lipoxygenase (LOX) inhibitor. LOX was immobilized in carbon paste electrode and the amperometric detection of hydroperoxy linoleic acid due to the enzymatic reaction using linoleic acid as a substrate was monitored at +0.9 V versus Ag/AgCl. The decrease in biosensor response in the presence of caffeic acid was found to be correlated with the inhibitor concentration. Diode array detector and LOX biosensor was used as an electrochemical detector for the analysis of this compound. All data were given as a comparison of two systems.

Preparation of glutathione imprinted polymer.

Glutathione imprinted polymer was prepared using 1-vinyl imidazole and ethylene glycol dimethacrylate as the functional monomer and crosslinker, respectively, in dimethyl sulfoxide. The adsorption selectivity of glutathione-imprinted polymer was tested by reduced glutathione, oxidized glutathione, and L-Gly-Leu-Tyr in 30% phosphate buffer (0.01 M, pH 5.0)–70% acetonitrile and binding affinity values were compared. Reusability of molecularly imprinted polymer particles was also investigated. Molecularly imprinted polymer particles were found to be stable and to maintain glutathione adsorption capacity at 95% when washed with methanol–acetic acid (10%) after seven usages. Functional monomer 1-vinyl imidazole and cross linker ethylene glycol dimethacrylate-based glutathione imprinted polymer could be used as solid phase extraction material for recognition of glutathione in biological samples.

Preparation and Characterization of Chitosan-Entrapped Microsomal UDP-Glucuronyl Transferase

The hepatic microsomal UDP-Glucuronyl transferase which catalyze the glucuronidation of drugs, pesticides, carcinogens and other xenobiotics, was immobilized by entrappment in chitosan. Chemical and physical characterization were made by using 1-naphthol as substrate. Thermal, storage and operational stabilities of the immobilized enzyme was also searched and found to be better in comparison with the free enzyme. In conclusion, chitosan gel beads appear to have good characteristics for use as UDPGT immobilization support suitable for large scale use and offer the prospect that immobilized UDPGT may become an important form of catalyst in medicine.

Differentially displayed proteins as a tool for the development of type 2 diabetes

Background Type 2 diabetes is a complex disease that still requires a great deal of work to be carried out to understand the pathophysiology. Recently, researchers have focused on studying the organs and tissues known to be involved in the development of the type 2 phenotype using a proteomic approach. Little work has been reported on plasma of type 2 diabetics in whom the clinical status has been well characterized. In this study, changes in plasma proteins of type 2 diabetics were investigated by proteomic analysis in well-characterized individuals with type 2 diabetes (early and late stage) and control groups (with or without a family history of diabetes). Methods Samples were analysed by two-dimensional gel electrophoresis and significantly differentiated proteins were identified by nano-LC-ESI-MS. Results A total of 12 protein signatures that were differentially displayed with high significance compared with controls were selected. Four of the differentially displayed proteins were identified as haptoglobin alpha2, haptoglobin Hp2(fragment) and transthyretin and Chain A (formerly prealbumin), and all were up-regulated. Thiol-specific antioxidant protein, Chain A, tertiary structures of three amyloidogenic transthretin variants and haptoglobin-related protein precursor were all down-regulated in controls with a family history of diabetes, early and late diabetic patients in comparison with the control. Conclusion A proteomic-based approach was used to discover and identify the differentially expressed proteins in various states of type 2 diabetes.

A Novel Catechol Oxidase Enzyme Electrode for the Specific Determination of Catechol

An enzyme electrode for the specific determination of catechol was developed by using catechol oxidase (EC 1.10.3.1) from eggplant (Solanum melangena L.) in combination with a dissolved oxygen probe. Optimization studies of the prepared catechol oxidase enzyme electrode established a phosphate buffer 50 mM at pH 7.0 and 35°C to provide the optimum conditions for affirmative electrode response. The enzyme electrode response depended linearly on a catechol concentration range of 5•10(-7)-30•10(-5) M with a response time of 25 sec and substrate specificity of the catechol oxidase electrode of 100%. The biosensor retained its enzyme activity for at least 70 days.