Preparation and anticoagulant activity of carboxybutyrylated hydroxyethyl chitosan sulfates

Marine Biological Macromolecules and Chemically Modified Macromolecules; Potential Anticoagulants

Coagulation is a potential defense mechanism that involves activating a series of zymogens to convert soluble fibrinogen to insoluble fibrin clots to prevent bleeding and hemorrhagic complications. To prevent the extra formation and diffusion of clots, the counterbalance inhibitory mechanism is activated at levels of the coagulation pathway. Contrariwise, this system can evade normal control due to either inherited or acquired defects or aging which leads to unusual clots formation. The abnormal formations and deposition of excess fibrin trigger serious arterial and cardiovascular diseases. Although heparin and heparin-based anticoagulants are a widely prescribed class of anticoagulants, the clinical use of heparin has limitations due to the unpredictable anticoagulation, risk of bleeding, and other complications. Hence, significant interest has been established over the years to investigate alternative therapeutic anticoagulants from natural sources, especially from marine sources with good safety and potency due to their unique chemical structure and biological activity. This review summarizes the coagulation cascade and potential macromolecular anticoagulants derived from marine flora and fauna.

N-octyl chitosan derivatives as amphiphilic carrier agents for herbicide formulations

This study investigates the potential of N-octyl chitosan derivatives, namely N-octyl-O-sulfate chitosan (NOOSC), N-octyl-N-succinyl chitosan (NONSC) and N-octyl-O-glycol chitosan (NOOGC) as amphiphilic carrier agents for atrazine in water-insoluble herbicide formulations. The N-octyl chitosan derivatives were characterised using several analytical instruments such as Fourier Transform Infrared (FTIR) Spectrometer, CHNS-O Elemental Analyser (CHNS-O), Transmission Electron Microscope (TEM), Thermogravimetric Analyser (TGA), Differential Scanning Calorimeter (DSC) and Fluorescence Spectrometer. The encapsulation of atrazine by N-octyl chitosan derivatives was studied using a High Performance Liquid Chromatography (HPLC). The FTIR spectra of N-octyl chitosan derivatives confirmed the presence of hydrophobic and hydrophilic groups on chitosan backbone. TEM images revealed that N-octyl chitosan derivatives have formed self-aggregates with a spherical shape. The CMC values for N-octyl chitosan derivatives were between 0.06 and 0.09 mg/mL. The encapsulation efficiency (EE) values for amphiphilic chitosan were greater than 90%. The release profiles showed different release behaviour of pure herbicide in solution as compared to atrazine-loaded N-octyl chitosan derivatives. Results suggest that the chitosan derivatives offer promising characteristics that enable them to act as effective carrier agents for atrazine. In conclusion, the application of N-octyl chitosan derivatives could reduce the use of organic solvents in herbicide formulations by 37.5%.

Dehydroabietyl Glycidyl Ether Grafted Hydroxyethyl Chitosan: Synthesis, Characterization and Physicochemical Properties

A series of novel polymeric nonionic surfactants based on water-soluble N,O-hydroxyethyl chitosan (N,O-HECTS) and dehydroabietyl glycidyl ether (DAGE), DAGE-g-N,O-HECTSs, were synthesized by an additive reaction between N,O-HECTS and DAGE. The structures of DAGE-g-N,O-HECTSs were characterized by FT-IR and 1H NMR. The substitution degree of hydroxyethylation (DSHE) of N,O-HECTS and the grafting degree (DG) of DAGE onto N,O-HECTS for DAGE-g-N,O-HECTSs were determined by elemental analysis. The surface activities of DAGE-g-N,O-HECTSs in aqueous solution were investigated by measuring the surface tension. The experimental results showed that the degree of grafting (DG) of DAGE-gN,O-HECTSs could have a significant impact on their critical micelle concentrations (CMCs) and surface tensions at the CMC (γCMC), but the DG of DAGE-g-N,O-HECTSs had almost no effect on the minimum of surface tensions (γmin). When using the DAGE-g-N,O-HECTSs as emulsifier, the increase in DG had a favorable influence on the stability of an emulsion of water and benzene. At a DG greater than 40.45%, the emulsifying power of DAGE-g-N,O-HECTS exceeded that of Tween-60.

Chemical synthesis of glycosaminoglycan-mimetic polymers

This review describes several general chemical approaches for the preparation of glycosaminoglycan (GAG)-mimetic polymers based on different backbones and sidechains, and highlights the importance of these synthetic GAG-mimetic polymers in controlling key biofunctions.

Optimization of the preparation conditions of thermo-sensitive chitosan hydrogel in heterogeneous reaction using response surface methodology

A thermo-sensitive hydroxybutyl chitosan (HBC) hydrogel was prepared by using 1,2‑butene oxide as an etherification modifying agent. To obtain the maximum yield of HBC, response surface methodology (RSM) was applied to optimize its preparation conditions. Key factors were chosen firstly by Plackett-Burman design (PBD) experiments, such as the concentration of NaOH, the ratio of isopropanol to water and reaction temperature. Steepest ascent experiments were employed to reach the top region of the response and determine the appropriate levels of three key factors. A three-level-three-variable Box-Behnken design (BBD) was used to further optimize the synthesis parameters. The results indicated that when the concentration of NaOH and the ratio of isopropyl alcohol to water were 40.65% and 2.68:1 at reaction temperature of 59 °C, respectively, the yield of HBC production was 5.897 ± 0.112 g and close to the predicted value (6.002 g), which demonstrated that the effectiveness of BBD model and the controllability for the yield of HBC in the heterogeneous reaction system.

Heparin mimetics with anticoagulant activity

Heparin, a sulfated polysaccharide belonging to the glycosaminoglycan family, has been widely used as an anticoagulant drug for decades and remains the most commonly used parenteral anticoagulant in adults and children. However, heparin has important clinical limitations and is derived from animal sources which pose significant safety and supply problems. The ever growing shortage of the raw material for heparin manufacturing may become a very significant issue in the future. These global limitations have prompted much research, especially following the recent well-publicized contamination scandal, into the development of alternative anticoagulants derived from non-animal and/or totally synthetic sources that mimic the structural features and properties of heparin. Such compounds, termed heparin mimetics, are also needed as anticoagulant materials for use in biomedical applications (e.g., stents, grafts, implants etc.). This review encompasses the development of heparin mimetics of various structural classes, including synthetic polymers and non-carbohydrate small molecules as well as sulfated oligo- and polysaccharides, and fondaparinux derivatives and conjugates, with a focus on developments in the past 10 years.

Bioactive TGF-β1/HA Alginate-Based Scaffolds for Osteochondral Tissue Repair: Design, Realization and Multilevel Characterization

Background

The design of an appropriate microenvironment for stem cell differentiation constitutes a multitask mission and a critical step toward the clinical application of tissue substitutes. With the aim of producing a bioactive material for orthopedic applications, a transforming growth factor-β (TGF- β1)/hydroxyapatite (HA) association within an alginate-based scaffold was investigated. The bioactive scaffold was carefully designed to offer specific biochemical cues for an efficient and selective cell differentiation toward the bony and chondral lineages.

Methods

Highly porous alginate scaffolds were fabricated from a mixture of calcium cross-linked alginates by means of a freeze-drying technique. In the chondral layer, the TGF in citric acid was mixed with an alginate/alginate-sulfate solution. In the bony layer, HA granules were added as bioactive signal, to offer an osteoinductive surface to the cells. Optical and scanning electron microscopy analyses were performed to assess the macro-micro architecture of the biphasic scaffold. Different mechanical tests were conducted to evaluate the elastic modulus of the grafts. For the biological validation of the developed prototype, mesenchymal stem cells were loaded onto the samples; cellular adhesion, proliferation and in vivo biocompatibility were evaluated.

Results and conclusions

The results successfully demonstrated the efficacy of the designed osteochondral graft, which combined interesting functional properties and biomechanical performances, thus becoming a promising candidate for osteochondral tissue-engineering applications.

A Direct Sulfation Process of a Marine Polysaccharide in Ionic Liquid

GY785 is an exopolysaccharide produced by a mesophilic bacterial strain Alteromonas infernus discovered in the deep-sea hydrothermal vents. GY785 highly sulfated derivative (GY785 DRS) was previously demonstrated to be a promising molecule driving the efficient mesenchymal stem cell chondrogenesis for cartilage repair. This glycosaminoglycan- (GAG-) like compound was modified in a classical solvent (N,N′-dimethylformamide). However, the use of classical solvents limits the polysaccharide solubility and causes the backbone degradation. In the present study, a one-step efficient sulfation process devoid of side effects (e.g., polysaccharide depolymerization and/or degradation) was developed to produce GAG-like derivatives. The sulfation of GY785 derivative (GY785 DR) was carried out using ionic liquid as a reaction medium. The successful sulfation of this anionic and highly branched heteropolysaccharide performed in ionic liquid would facilitate the production of new molecules of high specificity for biological targets such as tissue engineering or regenerative medicine.

Engineering the regenerative microenvironment with biomaterials

Modern synthetic biomaterials are being designed to integrate bioactive ligands within hydrogel scaffolds for cells to respond and assimilate within the matrix. These advanced biomaterials are only beginning to be used to simulate the complex spatio-temporal control of the natural healing microenvironment. With increasing understanding of the role of growth factors and cytokines and their interactions with components of the extracellular matrix, novel biomaterials are being developed that more closely mimic the natural healing environments of tissues, resulting in increased efficacy in applications of tissue repair and regeneration. Herein, the important aspects of the healing microenvironment, and how these features can be incorporated within innovative hydrogel scaffolds, are presented.

Preparation and anticoagulant activity of N-succinyl chitosan sulfates

In order to develop a promising substitute for heparin, N-succinyl chitosan (NSC) was chemically modified by sulfating agent N(SO(3)Na)(3), which were synthesized with sodium bisulfite and sodium nitrite in aqueous solution. The N-succinyl chitosan sulfates (NSCS) products were characterized by infrared spectroscopy (FT-IR) and (13)C NMR. The degree of substitution (DS) of NSCS depended on the ratio of sulfating agent to N-succinyl chitosan, reaction temperature, reaction time and pH of sulfation agent. N-succinyl chitosan sulfates with DS of 1.97 were obtained under optimal conditions. The in vitro coagulation assay of NSCS was determined by activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) assays. The results showed that NSCS obviously prolonged APTT. The anticoagulant activity strongly depended on DS, molecular weight (M(w)) and concentration of NSCS. The anticoagulant activity of NSCS promoted with the increase of DS and concentration, and NSCS exhibited the best anticoagulant activity with the M(w) of 1.37×10(4).

Coordination properties of N,O-carboxymethyl chitosan (NOCC). Synthesis and equilibrium studies of some metal ion complexes. Ternary complexes involving Cu(II) with (NOCC) and some biorelevant ligand

In the present study, the acid-base equilibria of N,O-carboxymethy chitosan abbreviated as (NOCC), is investigated. The complex formation equilibria with the metal ions Cu(II), Ni(II), Co(II), Mn(II), and Zn(II) are investigated potentiometrically. The stability constant values of the binary and ternary complexes formed in solution were determined and the binding centers of the ligands were assigned. The relationships between the properties of the studied central metal ions as ionic radius, electronegativity, atomic number, and ionization potential, and the stability constants of the formed complexes were investigated in an effort to give information about the nature of chemical bonding in complexes and make possible the calculation of unknown stability constants. Cu(II), Ni(II), and U(VI) complexes with NOCC are isolated as solid complexes and characterized by conventional chemical and physical methods. The structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies. The ternary copper(II) complexes involving NOCC and various biologically relevant ligands containing different functional groups, as amino acids and DNA constituents are investigated. The stability constants of the complexes are determined and the concentration distribution diagrams of the complexes are evaluated.

Preparation, characterization and anticoagulant activity in vitro of heparin-like 6-carboxylchitin derivative

A series of heparin-like 6-carboxylchitin derivatives with different N-acetyl group and sulfate group contents were prepared. Their structures were characterized by element analysis, FT-IR, (13)C NMR, and gel permeation chromatography. Their anticoagulant activity in vitro was investigated for human plasma with respect to activated partial thromboplastin time (APTT). The results showed all 6-carboxylchitin derivatives prolonged APTT within the scope of studied degree of sulfation (0.28-1.03) and Mws (4.3-13.7 kDa). Their anticoagulant activity strongly depended on their structures. 3,6-O-sulfated group promoted the anticoagulant activity. Only incorporation of N-sulfated group into deacetylated 6-carboxylchitin could not improve the anticoagulant activity. But, N-sulfated group and O-sulfated group had the synergistic action, and N-sulfated group could promote the anticoagulant activity for the N,O-sulfated chitin derivatives. In addition, acetyl group took a role in the anticoagulant activity, too.

Synthesis and Characterization of an Alendronate-Chitosan Conjugate

The biomineral-binding alendronate-chitosan conjugate (Scheme 1) was developed as a novel drug delivery system. Alendronate was conjugated to the hydroxyl groups of chitosan, thereby maintaining the amino groups of chitosan intact. By means of FT-IR and 1H NMR, the characterization was conducted to confirm the successful synthesis of alendronate-chitosan conjugate.

Inhibition of inducible nitric oxide synthase and cyclooxygenase-2 in lipopolysaccharide-stimulated RAW264.7 cells by carboxybutyrylated glucosamine takes place via down-regulation of mitogen-activated protein kinase-mediated nuclear factor-kappaB signaling

Glucosamine (GlcN) has been reported to possess several biomedical properties, and currently a great deal of attention has been focused on improving the functional properties of GlcN for different applications. Therefore, this study was conducted to introduce a carboxybutyryl functional group to GlcN and to find out the inhibitory mechanism of a novel GlcN derivative, carboxybutyrylated GlcN (CGlcN), on the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in bacterial lipopolysaccharide (LPS)-induced mouse macrophages (RAW264.7 cells). In the initial experiments, the production of NO and prostaglandin E(2) (PGE(2)) was inhibited by CGlcN pretreatment and suggested the possibility of down-regulating their respective genes, iNOS and COX-2. Reverse transcription-polymerase chain reaction and Western blot analysis revealed that CGlcN can affect both transcriptional and translational levels of iNOS and COX-2 expression. The data from the nuclear factor-kappaB (NF-kappaB) promoter gene transfection experiment supported the idea that inhibition of iNOS and COX-2 is caused by the down-regulation of their transcription factor, NF-kappaB. Following stimulation with LPS, p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinase (JNK) present upstream of NF-kappaB signaling were also inhibited by CGlcN treatment. However, the protein level of another MAPK, extracellular signal-regulated kinase (ERK), remained unaffected. Moreover, following treatment with CGlcN, the protein expression of I-kappaB kinase (IKK) clearly confirmed that its down-regulation directly inhibited the degradation of IkappaB and release of NF-kappaB. Therefore, it can be concluded that CGlcN is capable of inhibiting iNOS and COX-2 expression in LPS-induced RAW264.7 cells via attenuation of NF-kappaB signaling by p38 MAPK and JNK, but not by ERK.

Polyelectrolyte complexes based on (quaternized) poly[(2-dimethylamino)ethyl methacrylate]: behavior in contact with blood

Polyelectrolyte complexes (PECs) between (quaternized) poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) and (crosslinked) N-carboxyethylchitosan (CECh) or poly(2-acrylamido-2-methylpropane sodium sulfonate) (PAMPSNa) were prepared and characterized in terms of their stability, equilibrium water content, and surface morphology. The evaluation of the behavior of the studied PECs in contact with blood revealed that the (crosslinked) CECh/(quaternized) PDMAEMA complexes had lost the inherent PDMAEMA cytotoxicity but still preserved haemostatic activity. In contrast, the complex formation between (quaternized) PDMAEMA and PAMPSNa allowed the preparation of materials with improved blood compatibility.

Sulfated glucosamine inhibits oxidation of biomolecules in cells via a mechanism involving intracellular free radical scavenging

Although, several effects of glucosamine and its sulfated form (sulfated glucosamine) have been proposed for the suppression of osteoarthritis, their exact mechanisms have not been completely elucidated. This study explains the novel possibility of involvement of sulfated glucosamine in improving cellular antioxidant potential and thereby controlling oxidative damage that could be effective for its therapeutic potential in osteoarthritis. Treatment with sulfated glucosamine to human chondrocytes and macrophages inhibited radical simulated oxidation of membrane lipids, proteins and DNA in a dose-dependent manner. Moreover, detection of reactive oxygen species by electron spin resonance (ESR) spectroscopy and 2',7'-dichlorodihydrofluororescein diacetate (DCFH-DA) fluorescence probe clearly confirmed effective radical scavenging potential of sulfated glucosamine in cellular and non-cellular systems. More importantly, NF-kappaB reporter gene assay and western blot analysis revealed that sulfated glucosamine inhibits radical mediated expression and activation of nuclear factor kappaB (NF-kappaB) proteins (transcription factor involves in expression of a number of genes related to osteoarthritis). Further, sulfated glucosamine enhanced reduced glutathione (GSH) level in oxidatively stressed human chondrocytes improving cellular redox balance. In conclusion, it is suggested that potential effects of sulfated glucosamine in controlling osteoarthritis might be partly via mechanisms involving direct scavenging of cellular radical species and alteration of oxidation mediated destructive events.

Sulfated glucosamine inhibits MMP-2 and MMP-9 expressions in human fibrosarcoma cells

In the present study, sulfated glucosamine (SGlc) that has been reported to relieve joint pain and inflammation in many arthritis patients was studied for its inhibitory effects on MMP-2 and MMP-9 in human fibrosarcoma cells. Expression and activity of above MMPs studied using gelatin zymography suggested SGlc as a potent MMP inhibitor. Further, transfection of promoter genes of MMPs and their transcription factors clearly exhibited that inhibition of MMP-2 and MMP-9 was due to down-regulation of transcription factor, NF-kappaB. However expression of activator protein-1 (AP-1), another important transcription factor of MMPs, was not affected by SGlc treatment. In addition, protein expression results of Western blot analysis were also in agreement with the results of gene transfection experiments. Moreover, down-regulation of NF-kappaB resulted in production of low levels of both NF-kappaB p50 and p65 proteins and directly affected activation process of MMP-2 and MMP-9 expressions. Since MMPs involve in joint inflammation, it can be presumed that inhibition of MMP-2 and MMP-9 can be one of the mechanisms of SGlc to be an effective drug in relieving the symptoms of osteoarthritis.

Glucosamine sulfate promotes osteoblastic differentiation of MG-63 cells via anti-inflammatory effect

Glucosamine sulfate (SGlc) has been known to be effective in controlling osteoarthritis (OA) symptoms in several clinical studies. However, the mechanisms of this positive effect of SGlc in human OA still remain elusive. Therefore, first, the effects of SGlc on the differentiation of osteoblast-like MG-63 cells were investigated. Our results demonstrate that SGlc can increase ALP activity, collagen synthesis, osteocalcin secretion, and mineralization in osteoblastic cells in vitro. Furthermore, it was observed that SGlc exhibited anti-inflammatory effect on production of TNF-alpha, IL-1beta, and PGE(2) in macrophage, RAW264.7 cells. In conclusion, these results suggest that SGlc can promote cell differentiation in cultured MG-63 osteoblast cells via anti-inflammatory effect.

Inhibition of free radical-mediated oxidation of cellular biomolecules by carboxylated chitooligosaccharides

The objective of this study was to identify the cellular antioxidant effects of carboxylated chitooligosaccharides (CCOS), a chemically modified derivative of chitooligosaccharides (COS), by assessing oxidation inhibition potential on cellular biomolecules such as lipids, proteins, and direct scavenging of reactive oxygen species (ROS). Radical-mediated oxidation of cell membrane lipids and proteins was dose-dependently inhibited by CCOS, assessed by amount of lipid hydroperoxides and carbonyl carbon content in mouse macrophages, RAW264.7 cells. Further, CCOS inhibited myeloperoxidase (MPO) activity in human myeloid cells (HL60) suggesting indirect possibility of inhibiting generation of reactive oxygen species (ROS) such as superoxide radicals, H(2)O(2) and HOCl. Direct radical scavenging studies carried out with DCFH-DA fluorescence probe concluded that CCOS can act as a potent radical scavenger in cells.

Carboxylated chitooligosaccharides (CCOS) inhibit MMP-9 expression in human fibrosarcoma cells via down-regulation of AP-1

Matrix metalloproteinases (MMPs) play a fundamental role in invasion and metastasis of tumor and, recent advances in medicinal chemistry have approached designing of MMP inhibitors with desired structural properties, selectivity and bioavailability. In the present study, novel low-molecular-weight carboxylated chitooligosaccharides (CCOS) were evaluated for their MMP-9 inhibitory effect on human fibrosarcoma cell line (HT1080). In zymography experiments, a clear dose-dependent inhibition on MMP-9 mediated gelatinolytic activities were observed in HT1080 cells following treatment with CCOS. Further, transfection studies carried out with MMP-9 and AP-1 reporter constructs suggested that the observed reduction in MMP-9 expression was due to down-regulation of MMP-9 transcription that mediated via inhibition of AP-1. Moreover, expression of c-Fos protein levels in cytoplasm and nucleus confirmed that CCOS could inhibit AP-1 expression but not its translocation. However, in the presence of CCOS, NF-kappaB and TIMP-1 expression levels remained constant. More importantly, inhibition of MMP-9 expression clearly led to inhibit tumor invasiveness that was studied with reconstituted basement membrane matrix proteins coated synthetic membranes. Taken together, this study discusses MMP-9 inhibition potential of CCOS and their involvement to demote degradation and cellular invasion of extracellular matrix (ECM) and basement membrane. Thus, control of MMP-9 expression by CCOS has considerable significance for the regulation of tumor progression.

Carboxy derivatized glucosamine is a potent inhibitor of matrix metalloproteinase-9 in HT1080 cells

Experimental evidences have confirmed that matrix metalloproteinases (MMPs) play a fundamental role in a wide variety of pathologic conditions and recent advances in medicinal chemistry approach to the design of MMP inhibitors with desired structural and functional properties. Among MMPs, MMP-9 has demonstrated to play a major role in the establishment of metastases and it is substantially increased in the majority of malignant tumors. Inhibition of MMP-9 is thought to have a therapeutic benefit to cancer. Results of this study present a novel synthetic MMP-9 inhibitor that downregulates MMP-9 expression level in HT1080, human fibrosarcoma cells.

Preparation and antimicrobial activity of hydroxypropyl chitosan

Water-soluble hydroxypropyl chitosan (HPCS) derivatives with different degrees of substitution (DS) and weight-average molecular weight (Mw) were synthesized from chitosan and propylene epoxide under basic conditions. Their structure was characterized by IR spectroscopy, NMR spectroscopy, and elemental analysis, which showed that both the OH groups at C-6 and C-3 and the NH2 group of chitosan were alkylated. The DS value of HPCS ranged from 1.5 to 3.1 and the Mw was between 2.1x10(4) and 9.2x10(4). In vitro antimicrobial activities of the HPCS derivatives were evaluated by the Kirby-Bauer disc diffusion method and the macrotube dilution broth method. The HPCS derivatives exhibited no inhibitory effect on two bacterial strains (Escherichia coli and Staphylococcus aureus); however, some inhibitory effect was found against four of the six pathogenic fruit fungi investigated. Some derivatives (HPCS1, HPCS2, HPCS3, HPCS3-1, and HPCS4) were effective against C. diplodiella and F. oxysporum. HPCS3-1 is the most effective one with MIC values of 5.0, 0.31, 0.31, and 0.16mg/mL against A. mali, C. diplodiella, F. oxysporum, and P. piricola, respectively. Antifungal effects were also observed for HPCS2 and HPCS3-1 against A. mali, as well as HPCS3 and HPCS3-1 against P. piricola. The results suggest that relatively lower DS and higher Mw value enhances the antifungal activity of HPCS derivatives.

Strong electronic charge as an important factor for anticancer activity of chitooligosaccharides (COS)

Even though several studies report the importance of chitosan derivatives for their anticancer activity, no clear information is available to describe the relationship between their charge properties and observed activities. In this research, differently charged chitooligosaccharide (COS) derivatives were synthesized and their anticancer activities were studied using three cancer cell lines, HeLa, Hep3B and SW480. Neutral red and MTT cell viability studies revealed that, highly charged COS derivatives could significantly reduce cancer cell viability, regardless to the positive or negative charge. Further, fluorescence microscopic observations and DNA fragmentation studies confirmed that the anticancer effect of these highly charged COS derivatives were due to necrosis. However, the exact molecular mechanism for anticancer activity of strongly charged COS compared to their poorly charged counterparts is not clear.

Improvement of ACE inhibitory activity of chitooligosaccharides (COS) by carboxyl modification

In the present research, chitooligosaccharides (COS) were carboxylated with -COCH(2)CH(2)COO(-) groups to obtain specific structural features similar to Captopril. Angiotensin I converting enzyme (ACE) inhibitory activity of carboxylated COS was studied and observed to enhance its activity with increased substitution degree. Further, Lineweaver-Burk plot analysis revealed that inhibition was competitive via obligatory binding site of the enzyme. This was accompanied with substitution of positively charged quarternized amino groups to COS with different substitution degrees, in which negative impact on ACE inhibition was observed.

Factors affecting the free radical scavenging behavior of chitosan sulfate

Scavenging activity of hydroxyethyl chitosan sulfate (HCS) against 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl and carbon-centered radical species were studied using electron spin resonance (ESR) spectroscopy. In addition, its antioxidant activity to retard lipid peroxidation was also evaluated in a linoleic acid model system. HCS could scavenge DPPH (33.78%, 2.5 mg/mL) and carbon-centered radicals (67.74%, 0.25 mg/mL) effectively. However, chitosan sulfate did not exhibit any scavenging activity against hydroxyl radicals, but increased its generation. This was different from the published literature and was presumed due to the loss of chelating ability on Fe2+. This assumption could further confirm from the results obtained for Fe2+-ferrozine method that upon sulfation chitooligosaccharides lost its chelation properties. Therefore, HCS can be identified as antioxidant that effectively scavenges carbon centered radicals to retard lipid peroxidation.

Study of graft copolymerization of N-maleamic acid-chitosan and butyl acrylate by γ-ray irradiation

N-maleamic acid-chitosan was synthesized and characterized by Fourier transform infrared spectra analysis (FT-IR) and 1H NMR. The graft copolymerization of N-maleamic acid-chitosan and butyl acrylate (BA) in acetic acid aqueous solution was investigated, using the gamma-ray of 60Co gamma-irradiation method. DSC (differential scanning calorimetry) trace of N-maleamic acid-chitosan-g-PBA has a glass-transition temperature (Tg) at -42 degrees C. The thermal stabilities of the graft copolymer were studied by the thermal gravimetric analysis (TGA). The effect of synthesis variables in the graft copolymerization have been discussed in the light of grafting efficiency, grafting percentage, and homopolymer percentage. Increasing grafting percentage was observed when the monomer concentration and total dose were increased or when the reaction temperature was decreased.

The structure–anticoagulant activity relationships of sulfated lacquer polysaccharide

Regiospecific oxidation of the primary hydroxyl groups in lacquer polysaccharide (LPL, Mw 6.85 x 10(4)) and its NaIO4 oxidation derivatives (LPLde) to C-6 carboxy groups was achieved with NaOCl in the presence of Tempo and NaBr. Sulfate groups were incorporated into the oxidated polysaccharides using Py.SO3 complex as a reagent. Reactivity of polysaccharide hydroxyl group was C-6 > C-2 > C-4. Sulfate groups were mainly linked to the second hydroxy at C-2 in the products. The results of APTT assay showed after incorporation of carboxyl groups into lacquer polysaccharides, the intrinsic coagulation pathway was promoted, and all sulfated polysaccharides had very weak anticoagulant activity within the scope of studied DS (0.39-1.11). These indicated that carboxyl groups and sulfate groups had the synergistic action. At the same time, the anticoagulant activity increased very slowly with the DS in the second hydroxy. This indicated that 6-O-SO3- in the side chains took an important role in the anticoagulant activity.