Person: TOKSOY ÖNER, EBRU
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TOKSOY ÖNER
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Publication Metadata only Investigation of anti-cancer activity of linear and aldehyde-activated levan from Halomonas smyrnensis AAD6(T)(ELSEVIER, 2014) TOKSOY ÖNER, EBRU; Sarilmiser, Hande-Kazak; Oner, Ebru ToksoyThe main aim of this study was to investigate the potential role of levan polysaccharide in developing polysaccharide-based anticancer therapeutics. Moreover, by periodate oxidation, chemically modified forms of levan harboring increasing amounts of aldehyde groups were obtained and characterized. All the samples were found to be biocompatible when treated with the mouse fibroblast cell line L929. Anticancer activities of levan and its derivatives were investigated in A549 (human lung adenocarcinoma), HepG2/C3A (human liver hepatocellular carcinoma), AGS (human gastric adenocarcinoma), and MCF-7 (human breast adenocarcinoma) cell lines and were found to depend on the dose as well as on the cell type. The observed decrease in cancer cell viability was shown to be due to apoptosis via luminogenic-based caspase-3/7 activity assay. This study established the high potential of these levan-based polymers in developing polysaccharide-based nanocarrier systems for anti-cancer drugs. (C) 2014 Elsevier B.V. All rights reserved.Publication Metadata only Formation of new, cytocompatible hydrogels based on photochemically crosslinkable levan methacrylates(ELSEVIER, 2018) TOKSOY ÖNER, EBRU; Berg, Albrecht; Oner, Ebru Toksoy; Combie, Joan; Schneider, Bernd; Ellinger, Renate; Weisser, Juergen; Wyrwa, Ralf; Schnabelrauch, MatthiasLevan is a high molecular weight fructose-based biotechnologically available polysaccharide with a range of interesting properties qualifying this molecule for applications in biomedicine. In this study, new levan derivatives containing methacrylate groups attached either via ester or urethane linkages to the fructan backbone could be synthesized and structurally characterized by conventional analytical techniques. The photochemical crosslinking of these substances applying different photoinitiator systems and reaction conditions resulted in hydrogels of diverse properties which were investigated with regard to mechanical behaviour, hydrolytic degradability, and cytocompatibility. It was found that crosslinkable levan derivatives represent a new class of promising biopolymer-based macromers broadening the spectrum of available biomaterials to facilitate the adaption to the requirements of specific applications. (C) 2017 Elsevier B.V. All rights reserved.Publication Metadata only Sulfated levan from Halomonas smyrnensis as a bioactive, heparin-mimetic glycan for cardiac tissue engineering applications(ELSEVIER SCI LTD, 2016) TOKSOY ÖNER, EBRU; Erginer, Merve; Akcay, Ayca; Coskunkan, Binnaz; Morova, Tunc; Rende, Deniz; Bucak, Seyda; Baysal, Nihat; Ozisik, Rahmi; Eroglu, Mehmet S.; Agirbasli, Mehmet; Oner, Ebru ToksoyChemical derivatives of levan from Halomonas smyrnensis AAD6T with low, medium and high levels of sulfation were synthesized and characterized by FTIR and 2D-NMR. Sulfated levan samples were found to exhibit anticoagulation activity via the intrinsic pathway like heparin in a dose-dependent manner. Exceptionally high heparin equivalent activity of levan sulfate was shown to proceed via thrombin inhibition where decreased Factor Xa activity with increasing concentration was observed in antithrombin tests and above a certain concentration, levan sulfate showed a better inhibitor activity than heparin. In vitro experimental results were then verified in silico by docking studies using equilibrium structures obtained by molecular dynamic simulations and results suggested a sulfation dependent binding mechanism. With its high biocompatibility and heparin mimetic activity, levan sulfate can be considered as a suitable functional biomaterial to design biologically active, functionalized, thin films and engineered smart scaffolds for cardiac tissue engineering applications. (C) 2016 Elsevier Ltd. All rights reserved.Publication Metadata only Comprehensive characterization of chitosan/PEO/levan ternary blend films(ELSEVIER SCI LTD, 2014) TOKSOY ÖNER, EBRU; Bostan, Muge Sennaroglu; Mutlu, Esra Cansever; Kazak, Hande; Keskin, S. Sinan; Oner, Ebru Toksoy; Eroglu, Mehmet S.Ternary blend films of chitosan, PEO (300,000) and levan were prepared by solution casting method and their phase behavior, miscibility, thermal and mechanical properties as well as their surface energy and morphology were characterized by different techniques. FT-IR analyses of blend films indicated intermolecular hydrogen bonding between blend components. Thermal and XRD analysis showed that chitosan and levan suppressed the crystallinity of PEO up to nearly 25% of PEO content in the blend, which resulted in more amorphous film structures at higher PEO/(chitosan + levan) ratios. At more than 30% of PEO concentration, contact angle (CA) measurements showed a surface enrichment of PEO whereas at lower PEO concentrations, chitosan and levan were enriched on the surfaces leading to more amorphous and homogenous surfaces. This result was further confirmed by atomic force microscopy (AFM) images. Cell proliferation and viability assay established the high biocompatibility of the blend films. (C) 2013 Elsevier Ltd. All rights reserved.Publication Metadata only Development and optimization of a novel PLGA-Levan based drug delivery system for curcumin, using a quality-by-design approach(ELSEVIER, 2019) TOKSOY ÖNER, EBRU; Bahadori, Fatemeh; Eskandari, Zahra; Ebrahimi, Nabiallah; Bostan, Muge Sennaroglu; Eroglu, Mehmet Sayip; Oner, Ebru ToksoyThis study aimed to develop a PLGA, Levan-based drug delivery system (DDS) of Curcumin using a quality-by-design (QbD) approach to reveal how formulation parameters affect the critical quality attributes (CQAs) of this DDS and to present an optimal design. First, a risk assessment was conducted to determine the impact of various process parameters on the CQAs of the DDS (i.e., average particle size, ZP, encapsulation efficiency and polydispersity index). Plackett-Burman design revealed that potential risk factors were Levan molecular weight, PLGA amount and acetone amount. Then, the optimization of the DDS was achieved through a Box-Behnken Design. The optimum formulation was prepared using low molecular weight Levan (134 kDa), 51.51 mg PLGA and 10 ml acetone. The model was validated and the optimized formulation was further characterized using different physic-chemical methods. The study resulted in the most stable NP with a spherical and uniform shape and physical stability tests indicated its stability for at least 60 days at room temperature. In conclusion, this study was an effort for developing a DDS which solubilizes Curcumin in clinically applicable concentrations.Publication Metadata only Molasses as fermentation substrate for levan production by Halomonas sp.(SPRINGER, 2011) TOKSOY ÖNER, EBRU; Kucukasik, Faruk; Kazak, Hande; Guney, Dilvin; Finore, Ilaria; Poli, Annarita; Yenigun, Orhan; Nicolaus, Barbara; Oner, Ebru ToksoyLevan is a homopolymer of fructose with many outstanding properties like high solubility in oil and water, strong adhesiveness, good biocompatibility, and film-forming ability. However, its industrial use has long been hampered by costly production processes which rely on mesophilic bacteria and plants. Recently, Halomonas sp. AAD6 halophilic bacteria were found to be the only extremophilic species producing levan at high titers in semi-chemical medium containing sucrose, and in this study, pretreated sugar beet molasses and starch molasses were both found to be feasible substitutes for sucrose. Five different pretreatment methods and their combinations were applied to both molasses types. Biomass and levan concentrations reached by the Halomonas sp. AAD6 cells cultivated on 30 g/L of pretreated beet molasses were 6.09 g dry cells/L and 12.4 g/L, respectively. When compared with literature, Halomonas sp. was found to stand out with its exceptionally high levan production yields on available fructose. Molecular characterization and monosaccharide composition studies confirmed levan-type fructan structure of the biopolymers. Rheological properties under different conditions pointed to the typical characteristics of low viscosity and pseudoplastic behaviors of the levan polymers. Moreover, levan polymer produced from molasses showed high biocompatibility and affinity with both cancerous and non-cancerous cell lines.Publication Metadata only Effective stimulating factors for microbial levan production by Halomonas smyrnensis AAD6(T)(SOC BIOSCIENCE BIOENGINEERING JAPAN, 2015) TOKSOY ÖNER, EBRU; Sarilmiser, Hande Kazak; Ates, Ozlem; Ozdemir, Gonca; Arga, Kazim Yalcin; Oner, Ebru ToksoyLevan is a bioactive fructan polymer that is mainly associated with high-value applications where exceptionally high purity requirements call for well-defined cultivation conditions. In this study, microbial levan production by the halophilic extremophile Halomonas smyrnensis AAD6(T) was investigated systematically. For this, different feeding strategies in fed-batch cultures were employed and fermentation profiles of both shaking and bioreactor cultures were analyzed. Initial carbon and nitrogen source concentrations, production pH, NaCl and nitrogen pulses, nitrogen and phosphorous limitations, trace elements and thiamine contents of the basal production medium were found to affect the levan yields at different extends. Boric acid was found to be the most effective stimulator of levan production by increasing the sucrose utilization three-fold and levan production up to five-fold. This significant improvement implied the important role of quorum sensing phenomenon and its regulatory impact on levan production mechanism. Levan produced by bioreactor cultures under conditions optimized within this study was found to retain its chemical structure. Moreover, its biocompatibility was assessed for a broad concentration range. Hence H. smyrnensis AAD6(T) has been firmly established as an industrially important resource microorganism for high-quality levan production. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.Publication Metadata only Levan-based nanocarrier system for peptide and protein drug delivery: Optimization and influence of experimental parameters on the nanoparticle characteristics(ELSEVIER SCI LTD, 2011) SEZER, ALİ DEMİR; Sezer, Ali Demir; Kazak, Hande; Oner, Ebru Toksoy; Akbuga, JulideMicrobial levans are biopolymers produced from sucrose-based substrates by a variety of microorganisms. There is very limited information related to the levan-based drug delivery systems. In this study, bovine serum albumin (BSA) encapsulated-levan nanoparticles were prepared using levan produced by a new Halomonas sp. Effects of polymer and BSA concentrations and rotating speed on in vitro characterization of the nanoparticles were investigated. The size of levan nanoparticles, with the surface charges +4.3 mV to +7.6 mV, changed between 200 nm and 537 nm. The encapsulation capacity of the particles changed between 49.3% and 71.3% depending on the levan concentration used in the formulation. The cumulative in vitro release of protein from the particles was shown to be controlled release of BSA. This study affirmed the suitability of levan by Halomonas sp. to be used as a nanocarrier system for potential delivery of macromolecular drugs such as peptides and proteins. (C) 2010 Elsevier Ltd. All rights reserved.Publication Metadata only Halomonas smyrnensis as a cell factory for co-production of PHB and levan(ELSEVIER SCIENCE BV, 2018) KASAVİ, CEYDA; Tohme, Souha; Haciosmanoglu, Gul Gulenay; Eroglu, Mehmet Sayip; Kasavi, Ceyda; Genc, Seval; Can, Zehra Semra; Oner, Ebru ToksoyLevan is a fructan type polysaccharide that has long been considered as an industrially important biopolymer however its limited availability is mainly due to the bottlenecks associated with its large-scale production. To overcome such bottlenecks in the commercialization of this very promising polysaccharide, co-production of levan with polyhydroxyalkanoates (PHAs) by halophilic Halomonas smyrnensis cultures has been proposed in this study for the first time. After in silico and in vitro assessment of PHA accumulation, fermentation profiles for levan and PHA concentrations were obtained in the presence of sucrose and glucose and the PHA granules observed by TEM were found to be poly(3-hydroxybutyrate) (PHB) after detailed structural characterization by GC-MS, DSC, FTIR and NMR. Six nutrient limitation strategies based on nitrogen (N) and phosphorus (P) were tested but highest levan and PHB yields were obtained under unlimited conditions. H. smyrnensis is proved to co-produce PHB and levan while using inexpensive carbon sources which is a commercially successful microbial cell factory system showing a great potential in lowering manufacturing costs and aiming for a zero waste policy within the biorefinery concept. (C) 2018 Elsevier B.V. All rights reserved.Publication Metadata only Novel levan and pNIPA temperature sensitive hydrogels for 5-ASA controlled release(ELSEVIER SCI LTD, 2017) TOKSOY ÖNER, EBRU; Osman, Asila; Oner, Ebru Toksoy; Eroglu, Mehmet S.Levan based cross-linker was successfully synthesized and used to prepare a series of more biocompatible and temperature responsive levan/N-isopropyl acrylamide (levan/pNIPA) hydrogels by redox polymerization at room temperature. Volume phase transition temperature (VPTT) of the hydrogels were precisely determined by derivative differential scanning calorimetry (DDSC). Incorporation of levan into the pNIPA hydrogel increased the VPTT from 32.8 degrees C to 35.09 degrees C, approaching to body temperature. Swelling behavior and 5-aminosalicylic acid (5-ASA) release of the hydrogels were found to vary significantly with temperature and composition. Moreover, a remarkable increase in thermal stability of levan within hydrogel with increase of pNIPA content was recorded. The biocompatibility of the hydrogels were tested against mouse fibroblast L929 cell line in phosphate buffer saline (PBS, pH 7.4). The hydrogels showed increasing biocompatibility with increasing Levan ratio, indicating levan enhanced the hydrogel surface during swelling. (C) 2017 Elsevier Ltd. All rights reserved.