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PubMed2001

Inhalation toxicity of 1,6-hexamethylene diisocyanate homopolymers (HDI-IC and HDI-BT): results of subacute and subchronic repeated inhalation exposure studies.

This article addresses results of two 13-wk inhalation toxicity studies in Wistar rats with aerosolized 1,6-hexamethylene diisocyanate (HDI) homopolymers using either the isocyanurate (HDI-IC) type or biuret (HDI-BT) type. Groups of 10 rats/sex/level were exposed nose-only to breathing zone concentrations of 0.5, 3.3, and 26.4 mg HDI-IC/m(3) or 0.4, 3.4, and 21.0 mg HDI-BT/m(3) (MMAD = 1.4-3.3 microm). The exposure regimen was 6 h/day, 5 days/wk for 13 wk. Two control groups were used in each study; one was exposed to filtered air, and the other to the vehicle acetone. In subacute pilot studies, groups of rats were exposed under identical conditions for 3 consecutive weeks using concentrations of approximately 4, 15-18, and 77-90 mg homopolymer/m(3). All studies demonstrated that adverse effects were caused by irritation-related responses occurring predominantly in the lower respiratory tract. Following subchronic exposure, compound-related effects were found only at the highest concentrations used and were confined to mild respiratory distress, marginally decreased body weights, and increased lung weights. Hematological evaluation showed a marginal increase in leukocyte counts. Pulmonary function testing revealed minimal changes indicative of increases in functional residual capacity and total lung capacity but without evidence of increased bronchial hyperreactivity to acetylcholine aerosol. Histopathology demonstrated an increased recruitment of alveolar macrophages, focal interstitial fibrosis with round-cell infiltrations, and bronchiolo-alveolar proliferations at the high-level exposure groups. The no-observable-adverse-effect levels (NOAELs) of both the 3- and 13-wk studies were in the range of 3-4 mg/m(3). Appreciable differences between the two types of polyisocyanates were not observed.

Administration, Inhalation↗
PubMed1992

Stimulation of calcium influx in HL60 cells by cholesteryl-modified homopolymer oligodeoxynucleotides.

Cholesteryl-modified 15-mer homopolymers of cytidine and thymidine phosphodiester oligodeoxynucleotides (chol-OdC15 and chol-OdT15), but not chol-modified heteropolymeric oligos or chol-modified phosphorothioate oligos, were found to increase cytosolic free Ca2+ in HL60 cells. A flow cytometer and the calcium-sensitive dye indo-1 were used to make multiparameter measurements on the HL60 cells. Chol-OdC15 (5-10 microM) triggered a rapid increase (within 1 min) in [Ca2+]i, with a subsequent slow decline to baseline over 15 min in the continuous presence of agonist. The effect was preserved after unloading the intracellular Ca2+ stores with caffeine and ryanodine. The effect was not sensitive to membrane depolarization by KCl (60 mM) or nimodipine, a dihydropyridine calcium channel antagonist. An increase in [Ca2+]i was absent in a Ca(2+)-free solution and was inhibited by the inorganic Ca2+ channel blocker Cd2+. The results suggest that Ca2+ influx activated by the chol-oligomer is probably mediated by receptor-operated Ca2+ channels. This effect may be due to direct binding of the chol-oligo to the channel or to induced conformational changes due to modification of the local microenvironment.

Base Sequence↗
PubMed1997

Inhibitory nonsequence-specific effects of cytidine homopolymers on in vivo neointimal formation.

Phosphorothioate oligodeoxynucleotides (PS oligos) manifest both antisense and G-quartet aptameric inhibitory effects on vascular smooth muscle cell (SMC) proliferation. In this study, we examined the effects of three cytidine (S-dC) homopolymers lacking any guanosines of various chain length-S-dC28, S-dC18 and S-dC12-on in vitro SMC proliferation and in vivo neointimal formation. S-dC18 significantly inhibited human vascular SMC proliferation, although it had only half the potency as the same dose of S-dC28. Furthermore, S-dC12 at the same concentrations as S-dC18 did not significantly inhibit vascular SMC proliferation. S-dC28 and S-dC18 inhibited PDGF-induced in vitro SMC migration, whereas D-dC12 had no significant effect on PDGF-induced in vitro SMC migration. We determined the effects of S-dC28, S-dC18, and S-dC12 on neointimal SMC formation in the rat carotid balloon injury model. Rat carotid artery neointimal formation after balloon injury was significantly attenuated by S-dC28 treatment compared with the control group and by S-dC18 treatment compared with the control group. S-dC28 and S-dC18 treatment significantly reduced the intima/media area ratio compared with the values of the control groups. However, S-dC12 did not significantly inhibit neointimal formation. We investigated the time course of the inhibitory effects of S-dC28 on rat carotid artery neointimal formation. S-dC28 significantly inhibited rat carotid artery intimal area and intima/media area ratio at 4 weeks and 8 weeks. Fluoresceinated S-dC28 (FITC-S-dC28) was found to be present throughout the rat carotid arterial wall within 6 hours after balloon injury. Taken together, the potent non-G-quartet, nonsequence-specific inhibitory effects of S-dC compounds on in vitro SMC proliferation and in vivo neointimal formation in the rat carotid balloon injury model are chain length dependent and long lasting.

Angioplasty, Balloon↗
PubMed1994

In-situ polymerized PLOT columns III: divinylbenzene copolymers and dimethacrylate homopolymers.

Studies of divinylbenzene copolymers and dimethacrylate homopolymers indicate that the polymer pore size controls the separation of water and ammonia on porous-layer-open-tubular (PLOT) columns. To a lesser degree, the polarity of the polymers also affects the separation of a water-ammonia gas mixture. Our results demonstrate that the pore size can be regulated by controlling the cross-linking density or the chain length between the cross-linking functional groups. An optimum pore size will provide the best separation of water and ammonia.

Ammonia↗
PubMed2004

Sinorhizobium meliloti strain 1021 produces a low-molecular-mass capsular polysaccharide that is a homopolymer of 3-deoxy-D-manno-oct-2-ulosonic acid harboring a phospholipid anchor.

Sinorhizobium meliloti strain 1021 possesses the particularity to synthesize biologically inefficient capsular polysaccharides (KPS). It has been assumed that this class of compounds is not produced in high-molecular-mass (HMM) forms, even if many genetic analyses show the existence of expression of genes involved in the biosynthesis of capsular polysaccharides. The expression of these genes that are involved in the export of a KPS throughout the membrane and in the attachment of a lipid moiety has never been related to a structurally characterized surface polysaccharide. It is now reported that S. meliloti strain 1021 produces low-molecular-mass polysaccharides (4-4.5 kDa) that are exclusively composed of beta-(2-->7)-linked 3-deoxy-d-manno-oct-2-ulopyranosonic acid (Kdo) residues. These compounds are considered precursor molecules of HMM KPS, whose biosynthesis is arrested in the case of S. meliloti strain 1021. For the first time, the phospholipid anchor of a rhizobial KPS has been found, and its structure could be partially identified-namely, a phosphoglycerol moiety bearing a hydroxy-octacosanoic acid. When compared to other rhizobial KPS (composed of dimeric hexose-Kdo-like sugar repeating units), the Kdo homopolymer described here may explain why a complementation of S. meliloti strain 1021 Exo B mutant with an effective rkpZ gene restoring an active higher KPS size does not completely lead to the fully effective nitrogen fixing phenotype.

Biopolymers↗
PubMed2006

The truncated prelamin A in Hutchinson-Gilford progeria syndrome alters segregation of A-type and B-type lamin homopolymers.

Hutchinson-Gilford progeria syndrome (HGPS) is a dominant autosomal premature aging syndrome caused by the expression of a truncated prelamin A designated progerin (Pgn). A-type and B-type lamins are intermediate filament proteins that polymerize to form the nuclear lamina network apposed to the inner nuclear membrane of vertebrate somatic cells. It is not known if in vivo both type of lamins assemble independently or co-assemble. The blebbing and disorganization of the nuclear envelope and adjacent heterochromatin in cells from patients with HGPS is a hallmark of the disease, and the ex vivo reversal of this phenotype is considered important for the development of therapeutic strategies. Here, we investigated the alterations in the lamina structure that may underlie the disorganization caused in nuclei by Pgn expression. We studied the polymerization of enhanced green fluorescent protein- and red fluorescent protein-tagged wild-type and mutated lamins in the nuclear envelope of living cells by measuring fluorescence resonance energy transfer (FRET) that occurs between the two fluorophores when tagged lamins interact. Using time domain fluorescence lifetime imaging microscopy that allows a quantitative analysis of FRET signals, we show that wild-type lamins A and B1 polymerize in distinct homopolymers that further interact in the lamina. In contrast, expressed Pgn co-assembles with lamin B1 and lamin A to form a mixed heteropolymer in which A-type and B-type lamin segregation is lost. We propose that such structural lamina alterations may be part of the primary mechanisms leading to HGPS, possibly by impairing functions specific for each lamin type such as nuclear membrane biogenesis, signal transduction, nuclear compartmentalization and gene regulation.

Animals↗
PubMed1986

CD of homopolymer DNA-RNA hybrid duplexes and triplexes containing A-T or A-U base pairs.

CD spectra and difference-CD spectra of (a) two DNA X RNA hybrid duplexes (poly[r(A) X d(U)] and poly[r(A) X d(T)]) and (b) three hybrid triplexes (poly-[d(T) X r(A) X d(T)], poly[r(U) X d(A) X r(U)], and poly[r(T) X d(A) X r(T)]) were obtained and compared with CD spectra of six A X U- and A X T-containing duplex and triplex RNAs and DNAs. We found that the CD spectra of the homopolymer duplexes above 260 nm were correlated with the type of base pair present (A-U or A-T) and could be interpreted as the sum of the CD contributions of the single strands plus a contribution due to base pairing. The spectra of the duplexes below 235 nm were related to the polypurine strands present (poly-[r(A)] or poly[d(A)]). We interpret the CD intensity in the intermediate 255-235 nm region of these spectra to be mainly due to stacking of the constituent polypurine strands. Three of the five hybrids (poly[r(A) X d(U)], poly[r(A) X d(T)], and poly[d(T) X r(A) X d(T)]) were found to have heteronomous conformations, while poly[r(U) X d(A) X r(U)] was found to be the most A-like and poly[r(T) X d(A) X r(T)], the least A-like.

Adenine↗
PubMed1991

Vacuum UV CD spectra of homopolymer duplexes and triplexes containing A.T or A.U base pairs.

Vacuum UV circular dichroism (CD) spectra were measured down to 174 nm for five homopolymers, five duplexes, and four triplexes containing adenine, uracil, and thymine. Near 190 nm, the CD bands of poly[d(A)] and poly[r(A)] were larger than the CD bands of the polypyrimidines, poly[d(T)], poly[d(U)], and poly[r(U)]. Little change was observed in the 190 nm region upon formation of the duplexes (poly[d(A).d(T)], poly[d(A).d(U)], poly[r(A).d(T)], poly[r(A).d(U)], and poly[r(A).r(U)]) or upon formation of two of the triplexes (poly[d(T).d(A).d(T)] and poly[d(U).d(A).d(U)]). This showed that the purine strand had the same or a similar structure in these duplexes and triplexes as when free in solution. Both A.U and A.T base pairing induced positive bands at 177 and 202 nm. For three triplexes containing poly[d(A)], the formation of a triplex from a duplex and a free pyrimidine strand induced a negative band centered between 210 and 215 nm. The induction of a band between 210 and 215 nm indicated that these triplexes had aspects of the A conformation.

Base Composition↗
PubMed1981

An improved procedure for utilizing terminal transferase to add homopolymers to the 3' termini of DNA.

Terminal deoxynucleotidyl transferase (E.C.2.7.7.3.1.) from calf thymus was used to add homopolymer tails to duplex DNA with 3' protruding, even, or 3' recessive ends. A gel electrophoresis method was employed to analyze the tail length and the percent of DNA with tails. In all the tailing reactions, dA, dT, and dC tails from CoCl2-containing buffer were longer than those from MnCl2 - or MgCl2 - containing buffers, whereas dG tails from MnCl2 -containing buffer were the longest. By varying the ratio of dNTP over DNA terminus and the concentration of terminal transferase, optimal conditions were found for adding dG or dC tails of 10-25 nucleotides in length and dA and dT tails of 20-40 nucleotides in length to duplex DNA with all types of 3' termini.

Animals↗
PubMed2000

Inhalation toxicity of 1,6-hexamethylene diisocyanate homopolymer (HDI-IC) aerosol: results of single inhalation exposure studies.

The early acute pulmonary response of female Wistar rats exposed nose-only to a mixture of 1,6-hexamethylene diisocyanate homopolymer (HDI-IC) aerosol was examined. This study was designed to investigate the time course of the relationship between acute pulmonary irritation and ensuing disturbances of the air/blood barrier in rats exposed to concentrations of 3.9, 15.9, 54.3, or 118. 1 mg HDI-IC/m(3). The duration of exposure was 6 h, followed by serial sacrifices 0 h, 3 h, 1 day, 3 days, and 7 days postexposure. Concentrations were selected based on the results of a 4-h acute inhalation study in rats (LC(50) = 462 mg/m(3)). Bronchoalveolar lavage (BAL) fluid was analyzed for markers indicative of injury of the bronchoalveolar region, including phospholipids as proxy of altered surfactant homeostasis. Glutathione (GSH) was determined in BAL fluid and lung tissue. BAL cells with increased intracellular phospholipids were observed on day 1 and especially day 3, with some residual increase on day 7. Increased intracellular phospholipids and activity of acid phosphatases appear to suggest that phagocytized phospholipids may transiently affect lysosomal function. Following exposure to 15.9 mg/m(3), changes returned almost entirely to the level of the air-exposed control on day 7. Especially at higher exposure concentrations, lung weights and total number of cells in BAL were still statistically significantly elevated at this time point. Experimental evidence suggests that markers indicative of a dysfunction of the air/blood barrier, such as angiotensin-converting enzyme, total protein, and phospholipids engulfed by alveolar macrophages, were most sensitive to probe this type of changes. Although GSH in BALF was increased following exposure, there was an apparent depletion of tissue GSH immediately after cessation of exposure. In summary, this study suggests that respirable HDI-IC aerosol appears to cause a transient dysfunction of the air/blood barrier indicated by an increased extravasation of plasma constituents. Despite the remarkable extent of effects observed, most changes were reversible within a postexposure period as short as 7 days. First evidence of increased leakage of pulmonary epithelial barrier was observed at 3.9 mg/m(3). With respect to changes of early markers of pulmonary epithelial barrier dysfunction, approximately 3 mg HDI-IC/m(3) was considered to be the threshold concentration for acute pulmonary irritation.

Acid Phosphatase↗
PubMed1990

The Drosophila neurogenic locus mastermind encodes a nuclear protein unusually rich in amino acid homopolymers.

The neurogenic loci of Drosophila are required for proper partitioning of ectodermal cells into epidermal versus neural lineages. The loci appear to encode components of a developmental pathway involving cellular communication. In an effort to understand the role of the neurogenic locus mastermind in these processes, we have characterized its expression and sequence. The locus produces a number of transcripts that accumulate ubiquitously during early embryogenesis but more specifically in the central nervous system during later stages. Sequence analysis of a major cDNA product predicts an unusual protein containing an abundance of amino acid homopolymers and charge clusters typical of regulatory molecules. Nearly half of the mass of the predicted protein derives from only three amino acids: glutamine, glycine, and asparagine. Immunohistochemical studies of the protein in cell culture and early embryos show that the protein accumulates predominantly in the nucleus.

Amino Acid Sequence↗
PubMed2001

Single homopolymers in the relative density representation.

A single symmetric homopolymer is studied in the grand ensemble of its monomeric units. For an arbitrary external field but next neighbor interactions alone, such a system is represented as a functional of the local density to local fugacity ratio, conjugate to the fugacity, with the excess grand potential as thermodynamic generating function. A sample case in a spherical enclosure is solved, where a complementary exclusion from a spherical volume requires an extension to a grand ensemble of polymers. A preliminary extension is also made in mean field form to non-neighbor interactions, as well as to nonsymmetric interactions.

Journal Article↗
PubMed2002

Glassy behavior of a homopolymer from molecular dynamics simulations.

We study at- and out-of-equilibrium dynamics of a single homopolymer chain at low temperature using molecular dynamics. The main quantities of interest are the average root mean square displacement of the monomers below the theta point, and the structure factor, as a function of time. The observation of these quantities show a close resemblance to those measured in structural glasses and suggest that the polymer chain in its low temperature phase is in a glassy phase, with its dynamics dominated by traps. In equilibrium, at low temperature, we observe the trapping of the monomers and a slowing down of the overall motion of the polymer as well as nonexponential relaxation of the structure factor. Out of equilibrium, at low temperatures, we compute the two-time quantities and observe breaking of ergodicity in a range of waiting times, with the onset of aging.

Biophysics↗
PubMed2004

Stretching of homopolymers and contact order.

Mechanical stretching of self-interacting homopolymers is studied through molecular dynamics simulations in which the polymers are pulled with constant speed. At temperatures below the compactification temperature, the force-extension curves show a plateau that corresponds to the situation in which the polymer adopts "ball-string" configurations. The dependence of rupture distances on contact order and the effects of temperature are similar to those found in the case of model proteins. The dependence of behavior on the pulling speed is logarithmic. In the entropic limit, above the compactification temperature, the rupturing of contacts shows a monotonic decrease of extension with the contact order. The attainment of this limit depends on the system size and the pulling speed.

Biopolymers↗
PubMed2005

Dynamic self-consistent field theory for unentangled homopolymer fluids.

We present a lattice formulation of a dynamic self-consistent field (DSCF) theory that is capable of resolving interfacial structure, dynamics, and rheology in inhomogeneous, compressible melts and blends of unentangled homopolymer chains. The joint probability distribution of all the Kuhn segments in the fluid, interacting with adjacent segments and walls, is approximated by a product of one-body probabilities for free segments interacting solely with an external potential field that is determined self-consistently. The effect of flow on ideal chain conformations is modeled with finitely extensible, nonlinearly elastic dumbbells in the Peterlin approximation, and related to stepping probabilities in a random walk. Free segment and stepping probabilities generate statistical weights for chain conformations in a self-consistent field, and determine local volume fractions of chain segments. Flux balance across unit lattice cells yields mean field transport equations for the evolution of free segment probabilities and of momentum densities on the Kuhn length scale. Diffusive and viscous contributions to the fluxes arise from segmental hops modeled as a Markov process, with transition rates reflecting changes in segmental interaction, kinetic energy, and entropic contributions to the free energy under flow. We apply the DSCF equations to study both transient and steady-state interfacial structure, flow, and rheology in a sheared planar channel containing either a one-component melt or a phase-separated, two-component blend.

Journal Article↗
PubMed2006

Globule transitions of a single homopolymer: a Wang-Landau Monte Carlo study.

The temperature-independent Wang-Landau Monte Carlo approach is implemented for an off-lattice model of flexible homopolymers and applied to the coil-globule and solidification transitions based on chain sizes up to N=300. An intermediate transformation from low-density liquid globule to high-density liquid globule is suggested. A scheme for identifying polymer structures representative of particular temperatures in the course of the simulation is presented and applied to illustrate intermediate states in the coil-globule transition. Transition temperatures are calculated and used to obtain a theta point of at least Theta=1.96, distinctly higher than the solid-liquid transition temperature T(M)=1.26.

Journal Article↗
PubMed2004

Symmetric-to-asymmetric transition in triblock copolymer-homopolymer blends.

In blends of a symmetric poly(styrene-ethylene/butylene-styrene) tri-block-copolymer with a polystyrene homopolymer, small-angle x-ray scattering and cryotransmission electron microscopy measurements reveal a microstructure consisting of a disordered arrangement of poly(ethylene/butylene) membranes suspended in polystyrene. For triblock volume fractions less than 0.22, the membranes form an asymmetric sponge or L4 phase, consisting predominantly of equilibrium vesicles. For volume fractions greater than 0.22, they form a symmetric sponge-phase (L3 phase), separated from the L4 phase by a first-order transition.

Journal Article↗
PubMed2005

Ginzburg number of a homopolymer-diblock copolymer mixture covering the 3D-Ising, isotropic Lifshitz, and Brasovskii classes of critical universality.

The Ginzburg number Gi of deuterated poly(butadiene) (dPB) and poly(styrene) (PS) homopolymer blend of critical composition mixed with a dPB-PS symmetric diblock copolymer was determined from small angle neutron scattering. A 3 orders of magnitude change of Gi was determined between binary polymer blend and diblock copolymer melt. The strongest change of Gi is observed within the isotropic Lifshitz regime of critical universality occurring over a 3% range of diblock concentration and interpolates the corresponding Gi of the 3D-Ising and Brasovskii regimes. A Lifshitz critical point was not observed consistent with the proposed lower critical dimension d(LCP)=4.

Journal Article↗