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PubMed2001

Radioprotective Effects Against Chromosomal Damage Induced in Human Lymphocytes by gamma-Rays as a Function of Polymerization Grade of Grape Seed Extracts.

The quantitative distribution of flavan-3-ols was determined using high-performance liquid chromatography in several grape seed extracts (GSEs). In all GSEs, polymers of four or more carbon units were the group of procyanidins present in the highest concentration, the real quantity ranging between 60% and 99.5%. In a previous paper we established a relation between antioxidant and anticlastogenic activity of GSEs. A higher grade of polymerization in GSEs allows the existence of a higher number of conjugated structures and higher antioxidant activity. The radioprotective effects of GSEs with various grades of polymerization were determined by use of the micronucleus test for anticlastogenic activity, evaluating the reduction in the frequency of micronuclei in cytokinesis-blocked cells of human lymphocytes exposed to gamma-rays. The radioprotective efficiency of GSEs was according to their grade of polymerization: GSE3 > GSE2 > GSE1 > dimethylsulfoxide. The higher antioxidant capacity and anticlastogenic activity of GSEs can be explained, structurally, by the high number of conjugated structures between the catechol groups in the B-rings and the 3-OH free groups of the polymeric polyphenolic skeleton and, in addition, by the stability of the aroxyl flavonoid radical generated in the processes.

Journal Article↗
PubMed2005

Bond strength of a dentin bonding system using two techniques of polymerization: visible-light and argon laser.

OBJECTIVE: The aim of this work was to study one dentin-bonding system associated with posterior teeth restorative composite resin by means of tensile bond strength tests varying the technique of polymerization: visible light and argon laser. BACKGROUND DATA: Previous studies have demonstrated the ability of the argon laser to polymerize light-activated materials. METHODS: Sixty specimens were prepared by grinding the labial surface of bovine teeth embedded in acrylic resin. The dentin bonding system used was Single Bond (3M), which has a poliacenoic acid copolimer, associated with a posterior teeth restorative composite resin (Filtek P60, 3M). The bonding sites were treated according to the instruction of the manufacturers. The 60 teeth, duly embedded and ground, were assigned to four groups with 15 teeth each: group 1, the adhesive was light cured during 10 sec with visible light (Curing Light, 3M) with power density of 410 mW/cm2 and the composite resin was light cured during 20 sec with visible light; group 2, the adhesive and the composite resin were cured during 10 seconds with argon laser with 150 mW of power; group 3, the adhesive and the composite resin were cured during 10 sec with argon laser with 200 mW of power; and group 4, the adhesive and the composite resin were cured during 10 sec with argon laser with 250 mW of power. The composite resin was light cured in layers of 1 mm of thickness until the model of teflon with 3 mm in height was completely filled. RESULTS: The tensile bond strength test was performed in a Mini-Instron (model 4442) and the results for group 1 were 19.75 MPa (+/-4.65), group 2 were 16.09 MPa (+/-7.27), group 3 were 11.56 MPa (+/-4.50), and group 4 were 11.90 MPa (+/-5.78). CONCLUSIONS: One can conclude that the tensile bond strength promoted by the polymerization with visible light presented greater tensile bond strength than the polymerization with argon laser with 200 mW and 250 mW, but there was no significant difference between visible light and argon laser with 150 mW. There was no significant difference between argon laser with 150 mW and argon laser with 200 mW or 250 mW.

Animals↗
PubMed2004

A comparative study of polymerization lamps to determine the degree of cure of composites using infrared spectroscopy.

The aim of this study was to compare polymerization lamps of various technologies (halogen, high performance halogen, xenon, i.e. plasma arc, as well as diode lamps) to determine the degree of polymerization of composite probes using Fourier-transform infrared (FTIR) spectroscopy. To observe the light-induced curing reaction under a bracket, an attenuated total reflection (ATR)-FTIR was used. The results showed that the recommended curing times for all the polymerization lamps tested were adequate for successful polymerization of the composite used (degree of conversion approximately 60 per cent, which did not exceed 66 per cent after longer curing times). However, even after very long curing times, delayed curing of the composite must be taken into consideration as there was a decrease of approximately 10 per cent in FTIR band intensities (1637 and 3104 cm(-1)). ATR-FTIR spectroscopy showed that when bonding brackets with materials cured by light, uncured areas remain in the centre of the lowest layer of the adhesive.

Acrylic Resins↗
PubMed1997

DNA polymerization catalysed by a group II intron RNA in vitro.

The excised group II intron bI1 from Saccharomyces cerevisiae can act as a ribozyme catalysing various chemical reactions with different substrate RNAs in vitro . Recently, we have described an editing-like RNA polymerization reaction catalysed by the bI1 intron lariat that proceeds in the 3'-->5'direction. Here we show that the bI1 lariat RNA can also catalyse successive deoxyribonucleotide polymerization reactions on exogenous substrate molecules. The basic mechanism of the reaction involved interacting cycles between an alternative version of partial reverse splicing (lariat charging) and canonical forward splicing (lariat discharging by exon ligation). With an overall chain growth in the 3'-->5' direction, the 5' exon RNAs (IBS1dN) were elongated by successive insertion of deoxyribonucleotides derived from single deoxyribonucleotide substitutions (dA, dG, dC or dT). All four deoxyribonucleotides were used as substrates, although with different efficiencies. Our findings extend the catalytic repertoire of group II intron RNAs not only by a novel DNA polymerization activity, but also by a DNA-DNA ligation capacity, supporting the idea that ribozymes might have been part of the first primordial polymerization machinery for both RNA and DNA.

Biopolymers↗
PubMed1996

Abundance of Gal beta 1,3GalNAc in O-linked oligosaccharide on hinge region of polymerized IgA1 and heat-aggregated IgA1 from normal human serum.

Gas-phase hydrazinolysis was used to analyze the glycoform of the O-linked oligosaccharide of human serum IgA1. In our previous report, only one glycoform was obtained from the IgA1 of healthy individuals. However, it was found to be composed of heterogeneous IgA1 components having mutually different glycoforms. First, the IgA1 was separated into two subfractions having different affinities toward jacalin. Among them, the high-affinity subfraction was mainly composed of polymerized IgA1. Comparative study of the carbohydrate chain showed a relative abundance of Gal beta 1,3GalNAc in the polymerized form. A simultaneous analysis of the N-glycan of these subfractions was also carried out. Three major components, two biantennary and one triantennary oligosaccharides, were obtained from both subfractions and the relative contents of these components were almost the same. On the other hand, IgA1 was artificially polymerized by heating at 63 degrees C for 2 h. The heat-stable IgA1 was separated from the heat-aggregated material on a Sephacryl S-300 column. The obtained heat-stable IgA1 (approximately 20%) was not further aggregated by more heating under the same conditions. The heat-stable IgA1 contained a much higher amount of the sialylated Gal beta 1,3GalNAc. Thus, it was shown that the degree of completeness of the hinge O-linked oligosaccharide might be correlated with the stability and polymerization process of the IgA1 molecule.

Acetylgalactosamine↗
PubMed2000

Functional interdependence of DNA polymerizing and 3'-->5' exonucleolytic activities in Pyrococcus furiosus DNA polymerase I.

Pyrococcus furiosus DNA polymerase I (Pol BI) belongs to the family B (alpha-like) DNA polymerases and has a strong 3'-->5' exonucleolytic activity, in addition to its DNA polymerizing activity. To understand the relationship between the structure and function of this DNA polymerase, three deletion mutants, Delta1 (DeltaLeu746-Ser775), Delta2 (DeltaLeu717-Ser775) and Delta3 (DeltaHis672-Ser775), and two substituted mutants of Asp405, D405A and D405E, were constructed. These substitutions affected both the DNA polymerizing and the 3'-->5' exonucleolytic activities. The Delta1 mutant protein had DNA polymerizing activity with higher specific activity than that of the wild-type Pol BI, but retained only 10% of the exonucleolytic activity of the wild-type. The other two deletion mutants lost most of both activities. These results suggest that the DNA polymerizing and exonucleolytic activities are closely related to each other in the folded structure of this DNA polymerase, as proposed in the family B DNA polymerases.

DNA Polymerase I↗
PubMed2002

Pressure-induced actin polymerization in vascular smooth muscle as a mechanism underlying myogenic behavior.

We hypothesize that actin polymerization within vascular smooth muscle (VSM) in response to increased intravascular pressure is a novel and previously unrecognized mechanism underlying arterial myogenic behavior. This hypothesis is based on the following observations. 1) Unlike skeletal or cardiac muscle, VSM contains a substantial pool of unpolymerized globular (G) actin whose function is not known. 2) The cytosolic concentration of G-actin is significantly reduced by an elevation in intravascular pressure, demonstrating the dynamic nature of actin within VSM and implying a shift in the F:G equilibrium in favor of F-actin. 3) Agents that inhibit actin polymerization and stabilize the cytoskeleton (cytochalasins and latrunculin) inhibit the development of myogenic tone and decrease the effectiveness of myogenic reactivity. 4) Depolymerization of F-actin with cytochalasin D causes VSM relaxation and increased G-actin content, whereas polymerization of F-actin with jasplakinolide causes VSM contraction and decreased G-actin content. These results are consistent with observations in other cell types in which actin dynamics have been implicated in contractility and/or motility. Actin filament formation in VSM may therefore underlie mechanotransduction and, by providing additional sites for interaction with myosin, enhance force production in response to pressure. Although the mechanism by which actin polymerization is stimulated by pressure is not known, it likely occurs via integrin-mediated activation of signal transduction pathways previously associated with VSM contraction (e.g., PKC activation, Rho A, and tyrosine phosphorylation).

Actins↗
PubMed1999

Radiopaque polymeric materials for medical applications. Current aspects of biomaterial research.

The aim of this review is to give an overview and some insight into different radiopaque polymeric materials that are currently used as medical implants or inserts. The advantages and limitations of each radiopaque polymeric material are summarized. The main method used to make medical implants radiologically visible is based on blending polymers with conventional radiopaque agents, blends which usually are a physical mixture of acrylic derivatives and inorganic salts. Other methods reported involve either the formation of single-phase radiopaque polymer salt complexes somehow preventing the release of the radiopacifying element by entrapment of the complex in a crosslinked network, or radiopaque polymerized monomers characterized by a radiopacifying element associated with the monomer unit prior to polymerization. In the near future, research will certainly concentrate on biocompatible radiopaque polymers with covalently bound opaque elements leading to stable polymers with properties equivalent to the nonopaque, parent polymer.

Biocompatible Materials↗
PubMed2000

Effect of a vegetable-protein-rich polymeric diet treatment on body composition and energy metabolism in inactive Crohn's disease.

OBJECTIVE: Since malnutrition and lactose intolerance are frequently reported in Crohn's disease (CD), we evaluated the differences in terms of compliance-to-treatment and nutritional status in inactive CD patients after two different treatments using either a standard polymeric diet or a vegetable-protein-rich and lactose-free diet. STUDY DESIGN: A case-control study. SUBJECTS: Forty CD patients with inactive disease were randomly divided into two groups. Group A (10 men; aged 33.9+/-7.2 years; BMI, 21.8+/-1.7 kg/m2) received a conventional polymeric enteral diet, while group B (10 men; aged 35.6+/-6.8 years; BMI, 21.4+/-1.8 kg/m2) was administered a soy-rich and lactose-free polymeric diet, over a 4-week period. METHODS: All the patients had a clinical and laboratory examination. Body composition was assessed by isotopic dilution and resting metabolic rate (RMR), and substrate oxidation rates were measured by indirect calorimetry. RESULTS: Body weight significantly increased after treatment in both groups (A, P<0.05; and B, P<0.01), as well as fat-free mass (A, P<0.05; and B, P<0.05) and fat mass (A, P<0.05; and B, P<0.01). RMR slightly increased, although it did not reach statistical significance. Treatment did not influence substrate oxidation rates. Group B lactose-intolerant patients reported a greater compliance-to-treatment than those in group A. CONCLUSIONS: This study showed that a polymeric enteral diet rich in vegetable protein and not containing milk protein, eaten at home, with no need for positioning a nasogastric tube, significantly improved body composition in inactive and lactose-intolerant CD patients, with no effect on energy metabolism, suggesting that it could be useful in improving nutritional status in these patients.

Adult↗
PubMed1993

Unique functional characteristics of the polymerization and MAP binding regulatory domains of plant tubulin.

An understanding of the regulation of microtubule polymerization and dynamics in plant cells requires biochemical information on the structures, functions, and molecular interactions of plant tubulin and microtubule-associated proteins (MAPs) that regulate microtubule function. We have probed the regulatory domain and polymerization domain of purified maize tubulin using MAP2, an extensively characterized mammalian neuronal MAP. MAP2 bound to the surface of preformed, taxol-stabilized maize microtubules, with binding saturation occurring with one MAP2 molecule per five to six tubulin dimers, as it does with mammalian microtubules. MAP2 binding and dissociation analyses revealed two affinity classes of binding sites on maize microtubules: a high-affinity site 12 dimers apart that may be homologous to the mammalian MAP2 binding site and an additional low-affinity site also 12 dimers apart that may be homologous to the mammalian tau binding site. MAP2 corrected in vitro folding errors in taxol-stabilized maize microtubules and reduced the critical concentration of maize tubulin polymerization eightfold, from 8.3 to 1.0 microM. However, MAP2 dissociated much more readily from maize microtubules than from mammalian microtubules and induced the assembly of maize tubulin into aberrant helical ribbon polymers that remained stable for prolonged periods. Our results indicated that MAP2 binds to maize tubulin via a partially specific, low-fidelity interaction that reflects unique structural and functional properties of the polymerization and regulatory domains of plant tubulin and possibly of the tubulin binding domains of undocumented MAPs that regulate microtubule function in plant cells.

Amino Acid Sequence↗
PubMed1994

Polymeric nutrition as the primary therapy in children with small bowel Crohn's disease.

BACKGROUND: Recent studies in adults have shown that polymeric (whole protein) diets are as effective as semi-elemental and elemental formulae for the induction of remission in small bowel Crohn's disease. Whole protein diets are more palatable and cheaper. There have been no studies confirming efficacy in children. PATIENTS AND METHODS: We report our experience with seven children with active small bowel Crohn's disease given a casein-based, polymeric feed rich in TGF-beta 2 (Specific Polymeric Diet; Nestle-Clintec; Vevey, Switzerland) as complete nutrition for 8 weeks. RESULTS: Initial and follow-up assessments were performed. All children showed a significant improvement in disease activity, with C-reactive protein returning to normal, an increase in serum albumin and a good weight gain. Initial and follow-up ileal biopsies were assessed and showed reduced mucosal inflammation in six of seven children, with complete healing in two. CONCLUSION: In an uncontrolled descriptive study we have shown that a polymeric (whole protein) diet is a therapeutic option for small bowel Crohn's disease in children. By comprehensive follow-up we have demonstrated clinical and biochemical remission, with an improved endoscopic appearance and a reduction of mucosal inflammation in the terminal ileum.

Adolescent↗
PubMed2005

Effect of LED and halogen light curing on polymerization of resin-based composites.

The clinical performance of light polymerized resin-based composites (RBCs) is greatly influenced by the quality of the light curing unit (LCU). A commonly used unit for polymerization of RBC material is the halogen LCUs. However, they have some drawbacks. Development of new blue superbright light emitting diodes (LED LCU) of 470 nm wavelengths with high light irradiance offers an alternative to standard halogen LCU. The aim of this study is compared the effectiveness of LED LCU and halogen LCU on the degree of conversion (DC) of different resin composites [two hybrid (Esthet-X, Filtek Z 250), four packable (Filtek P60, Prodigy Condensable, Surefil, Solitaire), one ormocer-based resin composite (Admira)]. The DC values of RBCs polymerized by LED LCU and halogen LCU ranged approximately from 61.1 +/- 0.4 to 50.6 +/- 0.6% and from 55.6 +/- 0.7 to 47.4 +/- 0.5%, respectively. Significantly higher DC of RBCs except Surefil and Filtek Z 250 was obtained for LED LCU compared with halogen LCU (P < 0.05). Surefil and Filtek Z 250 exhibited no statistically significant difference values between LED LCU and halogen LCU (P > 0.05). As a result, it was observed that the performance of LED LCU used in the study was satisfactory clinically and had sufficient irradiance to polymerize RBCs (hybrid, packable and ormocer based) at 2 mm depth with a curing time of 40 s.

Composite Resins↗
PubMed2005

In vitro evaluation of the bonding of auto-polymerizing soft denture liner to cobalt-chromium alloy.

This study evaluated the effects of surface pre-treatments on the bonding of auto-polymerizing silicone soft denture liner to a Co-Cr alloy denture base after cyclic thermal stressing. The bonding surfaces of Co-Cr alloy cylinders (8 mm diameter and 4 mm high) were polished with a 600-grit silicon carbide paper. The bonding surfaces received one of three pre-treatments, which included either the application of a metal primer, a metal primer after air abrasion, or a resin primer after adhesive resin coating. Tensile specimens were fabricated by polymerizing a 2-mm thickness of soft denture liner between a pair of pre-treated denture base cylinders. Failure loads were measured by tensile testing after subjecting the specimen to 0, 5, 10, 20, and 30 thousand thermal cycles. Seven specimens were fabricated for 15 groups, including three pre-treatments and five thermal cycle groups. Failure loads of resin-bonded specimens, which were formerly reported, were used as references. All data were statistically analysed by two-way anova and Bonferroni test at the 95% confidence level. Adhesive resin coating of the metal surface was effective in enhancing the failure loads up to 5000 thermal cycles. However, failure loads of all metal-bonded groups were significantly lower than those of resin-bonded groups at all thermal cycling intervals. The results of this in vitro study implied that polymerizing adhesive resin on the Co-Cr alloy might be a promising method, when the clinicians need to acquire improved bonding of an auto-polymerizing soft denture liner to Co-Cr alloy denture bases.

Air Abrasion, Dental↗
PubMed1981

Polymeric 2-mercaptopyridine and 2-mercapto-nitrobenzene derivatives. New reagents for peptide synthesis.

Insoluble 2-mercaptopyridine and 2-mercapto-nitrobenzene derivatives were prepared by modification of commercially available polystyrene. Applicability of these polymers as reagents for the thiolytic removal of the 2-nitrophenylsulphenyl amino-protecting group and as supports for preparation of polymeric active esters was evaluated. Polymeric 2-mercaptopyridine (PMP) was found efficient for both purposes. It was used in the stepwise synthesis of Leu-enkephalin via the polymeric reagent approach, serving as an Nps-cleaver. Polymeric esters derived from PMP and Boc-amino acids proved to be excellent acylators. Their usefulness is exemplified in the preparation of two dipeptides, which were produced rapidly and in high yields and purity.

Endorphins↗
PubMed1996

Opioid receptor affinity of multivalent ligand system consisting of polymerized liposome.

A multivalent ligand system, in which enkephalin/phospholipid conjugates were immobilized on a polymerized liposome, has been prepared. A hydrophilic spacer chain, -(Sar-Sar-Pro)2-, was placed between Tyr-D-Ala-Gly-Trp-Leu (an enkephalin part) and a phospholipid part to diminish steric hindrance of the liposome against receptor binding of the enkephalin unit. The affinity of the immobilized enkephalin conjugate for opioid receptor was dependent on the density of the enkephalin unit on the surface of polymerized liposome, indicating that more than two enkephalin units on a liposome simultaneously bind to receptors in the membrane. IC50 values for the delta- and mu-receptors were 15 and 26 nM, respectively, when the conjugate was immobilized at the molar ratio of [enkephalin]/[phospholipid] of 340. The latter affinity is better than that of Tyr-D-Ala-Gly-Trp-Leu (50 nM). The enkephalin part was located at the membrane surface, as indicated by fluorescence spectroscopy. When 12% cerebroside sulfate was mixed in the polymerized liposome, delta-receptor affinity of the immobilized enkephalin conjugate was improved to 7.4 nM. The environment around the enkephalin part became hydrophilic upon incorporation of cerebroside sulfate into the polymerized liposome, resulting in changes in the receptor affinities.

Animals↗
PubMed1978

Polyamine-induced actin polymerization.

Muscle actin has been found to polymerize reversibly upon addition of low concentrations of polyamines. This polymerization, studied by centrifugation, has shown a linear relationship between the actin polymerization yield and the chain length of the polyamine. Among the biological polyamines tested, spermidine and spermine are the most efficient. The polymerization of actin can also be induced by the corresponding mono or diguanidine derivatives of these polyamines but monoamines or amino acids are inactive at the same concentration. The transformation of actin from a globular to a fibrous from upon addition of spermidine is also demonstrated by the changes in the near-ultraviolet circular dichoroic spectrum of this protein. Moreover, the polyamine-induced F -actin exhibits the same properties as the salt-induced F -actin: it strongly activates the Mg2+ -ATPase of myosin, its specific viscosity is enhanced to the same extent and electron micrographs show homogeneous thin filaments.

Actins↗
PubMed1980

Microtubule-associated-protein MAP1 is not implicated in the polymerization of microtubules.

Addition of DNA to microtubule protein solutions results in a decrease of the amount of the high-molecular-weight microtubule-associated proteins (MAP1 and MAP2) available for polymerization. Complete removal of MAP1 from microtubules requires lower concentrations of DNA compared to MAP2. Removal of MAP1 from microtubules has little or no effect on microtubule polymerization (nucleation and propagation). In contrast, removal of MAP2 produces a marked decrease in microtubule polymerization. Incubation of microtubular protein with DNA results in complete disappearance of the 30-S ring-shaped oligomers at concentrations of DNA which are not markedly inhibitory of polymerization.

Animals↗
PubMed1988

[Influence of polymerization of D-amino acid oxidase on the behavior of the enzyme immobilized on chitosan by covalent fixation].

D-Amino-acid oxidase is a flavoprotein using FAD as cofactor. The enzyme has been immobilized in the presence of FAD on a non-porous matrix: chitosan. This support is covalently bound to the enzyme with glutaraldehyde as cross-linking reagent. It is characterized by a good mechanical resistance to mechanical stirring. The enzymatic assays have been performed in batch reactor with D-phenylglycine as substrate by a spectrophotometric method which is based on the variation of the absorbance at 252 or 280 nm. The behaviour of the biocatalysts has been studied during repeated assays of 1 h at 25 degrees C in the absence of exogenous FAD. The experimental results have been compared with those obtained with the soluble enzyme tested in the presence or in the absence of FAD. The dependence of D-amino-acid oxidase on FAD concentration has been studied. Immobilized enzyme on chitosan appears to be less sensitive to the association-dissociation equilibrium of FAD. This property and the capacity of the enzyme to polymerize spontaneously in solution according to the experimental conditions have been established. The fact that the enzyme can exist in various oligomeric forms is of major importance because its catalytic expression is dependent of this phenomenon. The polymerization is known to be responsible for a decrease of the maximal rate V of the enzyme. It has also been shown that in the same way this decrease was accompanied by an improvement of the affinity of enzyme for substrates. Furthermore, the value of the dissociation constant of the apoenzyme-FAD complex is significantly smaller as the degree of polymerization is high. The conclusion is that the dissociation of the cofactor can be avoided if the immobilization step is carried out at high concentration of enzyme which is favourable to its polymerization.

Chitin↗