Induction of frameshift mutations in cultured mammalian cells within a transfected sequence containing a poly(dC-dA) · poly(dT-dG) microsatellite

A cultured mouse cell line with an integrated copy of a plasmid that contains a short dinucleotide repeat sequence (microsatellite) has been used to determine the frequencies and types of mutation induced by two frameshift mutagens. The presence of the microsatellite, which consists of 17 repeats of a poly(dC-dA) · poly(dT-dG) sequence, disrupts the reading frame of a gene coding for neomycin resistance. Revertants were selected in G418, and mutations were analyzed by PCR. ICR-170 was found to increase the reversion frequency by ten- to 15-fold at its LD₅₀, although most of the frameshifts that it induced were single-base insertions outside the microsatellite sequence. NA-AAF brought about a more modest increase in mutation frequency, but nearly all of the revertants in the NA-AAF-treated cultures had insertions or deletions of multiples of two base pairs within the DNA segment that included the microsatellite. This system can be modified to include different short tandem repeat sequences as targets for testing of compounds that are suspected of having frameshift-inducing activities. © 1996 Wiley-Liss, Inc.     

Functional monomers and polymers, 56. Effects of ionic strength on the structure of Cu(II)· poly(vinylimidazole) and Cu(II)· imidazole complexes in aqueous solution

The effect of ionic strength on the structure of Cu(II) complexes of imidazole and poly(4(5)-vinylimidazole) in aqueous solution was studied by viscometric, spectrophotometric, and electron spin resonance (ESR) techniques. Frequency of the center of the absorption band in visible region (λ_max) and ESR spectra of the polymeric Cu(II) complex were different from those of the low-molecular-weight Cu(II) complex. The spectra of polymeric Cu(II) complex were different in the presence of sodium perchlorate, but it was not the case for the low-molecular-weight Cu(II) complex. The reduced viscosity of the polymeric Cu(II) complex and the polymeric ligand decreased with a rise of the concentration of sodium perchlorate. It was proposed that the conformational change in the polymeric ligand resulted in a structural change of the Cu(II). poly(4(5)-vinylimidazole) complex.     

Interaction between polynucleotides in aqueous NaCl solution, 5. Temperature dependence of the heat of formation of poly(I) · poly(C) duplex

The heat of mixing of equimolar solutions of poly(I) and poly(C) containing various NaCl concentrations was measured at 288 and 308 K, and the heat of formation of Poly(I) · poly(C) duplex from the randomly coiled constituents, poly(I) and poly(C), was estimated from the heat of mixing with the aid of CD measurements. The temperature dependence of this heat of formation, ΔH, differs at lower and higher NaCl concentrations: In the region of NaCl concentration less than 0,5 mol · dm^-3, ΔH increases with temperature, while in the region of NaCl concentrations higher than 0,5 mol · dm^-3, ΔH decreases with temperature. The free energy change, ΔG, of the formation of poly(I) · poly(C) duplex decreases as the NaCl concentration increases, that is, the stability of poly(I) · poly(C) duplex increases with NaCl concentration. Moreover, the conformation of poly(I) · poly(C) duplex seems to differ at lower and higher NaCl concentration as derived from the CD spectra and the thermodynamic quantities.     

Morphological studies on a novel poly(aryl ether ketone)

The morphology of a novel poly(aryl ether ketone) [PEDEKmK] was investigated via polarizing optical microscopy (POM), TEM, DSC, SAXS and electron diffraction (ED). A distinct change in lamellar thickness, orientation, and spherulitic morphology was observed due to crystal melting and recrystallization. However, the crystal packing mode is found to be identical before and after the recrystallization process.     

The F···H Hydrogen Bonding Effect on the Dynamic Mechanical and Shape‐Memory Properties of a Fluorine‐Containing Polybenzoxazine

A fluorine‐containing difunctional benzoxazine is synthesized by hydrosilylation of a monofunctional benzoxazine based on o‐allylphenol and p‐fluoroaniline. Besides the intramolecular and intermolecular hydrogen bonding associated with the nitrogen and oxygen atoms in the oxazine ring, specific self‐complementary intermolecular Ar F···HO hydrogen bonding is formed in the polymerization of the benzoxazine, which leads to the resultant polybenzoxazine possessing a broad glass transition temperature range and showing two not well‐separated transitions. Based on the two glass transition temperatures, the polybenzoxazine exhibits triple‐shape‐memory behaviors by manipulating temperature and strain in the shape fixing process under tensile and bending modes. The dynamic mechanical and shape‐memory properties of the polybenzoxazine are influenced by the combined effect of the cross‐linking density and the Ar F···HO hydrogen bonding.

     

Light scattering and viscosity studies of poly(2-vinylpyridine 1-oxide) in some organic solvents at 25°C

Light scattering in 2-propanol and viscosity measurements in six good solvents were carried out at 25°C for fourteen fractions of poly(2-vinylpyridine 1-oxide) (P2VPO) with molar mass of (1,3–34,4) · 10⁴ g · mol^?1, which were synthesized by oxidizing poly(2-vinylpyridine) with H₂O₂. The numerical values of the Mark-Houwink-Sakurada constants K′ and a and of the parameters K and B from the plots of Kamide-Kawai, Kurata-Stockmayer and Inagaki-Ptitsyn as well as Stockmayer-Fixman, were determined as well. The averaged characteristic ratio C∞ and steric factor σ for this polymer are 8,58 and 2,07, evaluated from K in each solvent except benzyl alcohol with the last plot. The value in benzyl alcohol is rather large and clearly shows the solvent dependence in K. Comparing this average value with those of similar polymers, it is concluded that the P2VPO chain acquires a compact coil structure. The solvent power was found to increase in the following sequence: chloroform < 2-propanol < 1-propanol < methanol ≤ 1-butanol < benzyl alcohol, as judged from the B values.     

B6.g7 mice reconstituted with BDC2·5 non‐obese diabetic (BDC2·5NOD) stem cells do not develop autoimmune diabetes

In BDC2·5 non‐obese diabetic (BDC2·5NOD) mice, a spontaneous model of type 1 diabetes, CD4⁺ T cells express a transgene‐encoded T cell receptor (TCR) with reactivity against a pancreatic antigen, chromogranin. This leads to massive infiltration and destruction of the pancreatic islets and subsequent diabetes. When we reconstituted lethally irradiated, lymphocyte‐deficient B6.g7 (I‐A^g7+) Rag^–/– mice with BDC2·5NOD haematopoietic stem and progenitor cells (HSPC; ckit⁺Lin^–Sca‐1^hi), the recipients exhibited hyperglycaemia and succumbed to diabetes. Surprisingly, lymphocyte‐sufficient B6.g7 mice reconstituted with BDC2·5NOD HSPCs were protected from diabetes. In this study, we investigated the factors responsible for attenuation of diabetes in the B6.g7 recipients. Analysis of chimerism in the B6.g7 recipients showed that, although B cells and myeloid cells were 98% donor‐derived, the CD4⁺ T cell compartment contained ～50% host‐derived cells. These host‐derived CD4⁺ T cells were enriched for conventional regulatory T cells (T_regs) (CD25⁺forkhead box protein 3 (FoxP3)⁺] and also for host‐ derived CD4⁺CD25^–FoxP3^– T cells that express markers of suppressive function, CD73, FR4 and CD39. Although negative selection did not eliminate donor‐derived CD4⁺ T cells in the B6.g7 recipients, these cells were functionally suppressed. Thus, host‐derived CD4⁺ T cells that emerge in mice following myeloablation exhibit a regulatory phenoytpe and probably attenuate autoimmune diabetes. These cells may provide new therapeutic strategies to suppress autoimmunity.     

Vinyl polymerization by metal complexes, 20. Initiation by vinylamine/vinyl alcohol copolymer · copper(II) systems

The polymerization of acrylonitrile (AN) and of methyl methacrylate (MMA) initiated by various copper(II) chelates was studied in the presence of carbon tetrachloride. Several vinylamine (VAm)/vinyl alcohol (VA) copolymers with different contents of NH₂ and OH bearing monomeric units were chosen as polymer ligands as well as polyvinylamine (PVAm)/poly(vinyl alcohol) (PVA) mixtures (of equal NH₂ and OH group contents as the corresponding copolymers), PVAm, and PVA. The activity of the used polymer chelates to initiate the AN and the MMA polymerization was compared at various pH values of the reaction systems. For the polymerization of MMA, the VAm/VA copolymer systems showed a higher activity than the PVAm chelate containing the same amount of NH₂ groups, contrary to the case of the polymerization of AN, where the polymerization activity showed a reverse behavior. The initiation mechanism is discussed.     

RNA synthesis in activated macrophages I. Poly(I) · poly(C)-induced triggering of cytolytic activity is associated with decrease in RNA synthesis

The effects of polyinosinic, polycytidylic acid [poly(I) · poly(C)] on the activation and RNA metabolism in murine peritoneal macrophages (MΦ) elicited by proteose-peptone (pMΦ) was investigated. Poly(I) · poly(C) triggered the cytolytic activity of pMΦ and augmented their glucose oxidation. In contrast, a profound depression of [³H]uridine incorporation into RNA was observed in poly(I) · poly(C)-activated pMΦ. The degree of depression of RNA labeling paralleled the dose of poly(I) · poly(C) used to activate the pMΦ and the expression of tumoricidal activity. This decrease in [³H]uridine incorporation into MΦ RNA could not be accounted for by decreased permeability of the activated MΦ to [³H]uridine, or by instability of the labeled RNA. Moreover, analysis of the specific activity of the intracellular uridine triphosphate (UTP) pool and studies on the labeling of MΦ RNA with [³²P] orthophosphate indicated that the decreased RNA labeling was not due to changes in the specific activity of UTP. We concluded that poly(I) · poly(C)-activated pMΦ exhibit a depressed rate of RNA synthesis. We suggest that the rate of RNA synthesis may be investigated as a potential new indicator for MΦ activation.     

Investigation of poly(arylenevinylene)s, 40. Electrochemical studies on poly(p-phenylenevinylene)s

Differential pulse polarography (DPP) and cyclovoltammetry (CV) were conducted to study the redox behaviour of poly(p-phenylenevinylene) (PPV; E = 0,76 V; E = ?1,74 V) as well as of three insoluble PPV-derivatives and four soluble aryl-substituted PPV's. Oxidation studies of DP-PPV, DMOP-PPV and DPOP-PPV in comparison with two series of the oligomeric model compounds 1a–e and 2a–d lead to the conclusion that for DMOP-PPV (E = 0,98, 1,24,1,31 V) and DPOP-PPV (E = 1,10, 1,29, 1,44 V) three distinct oxidation stages exist, which are reversibly occupied and represent 1/2, 1 and 2 positive charges per repeating unit. In DP-PPV two oxidation stages representing 1/2 and 1 positive charges were found to be reversibly occupied (E = 1,17, 1,69 V), whereas at higher potentials irreversible dehydrocyclization occurred.     

Conductivity studies on living poly(methyl methacrylate) in tetrahydrofuran

The change in conductivity with concentration has been studied for living poly(methyl methacrylate) at ?78°C in tetrahydrofuran as solvent and using lithium, sodium, and potassium as gegen-ions. The experimental conditions of MMA polymerizations have been similar to those used to prepare monodisperse samples. Biphenyl-alkali metal complexes have been used as initiators. Their dissociation constants have been determined at 25°C with values 2.7·10^?6, 0.83·10^?6, and 0.18·10^?6 mole/l., for Li^⊕, Na^⊕, and K^⊕ as gegen-ions, respectively. Log Λ vs. log c plots for living polymers yield straight lines with slopes varying between ?0.17 and ?0.28, depending on the cation. At dilute concentrations the slopes sharply jump up to ?0.50. The values for the dissociation constants, calculated by FUOSS method, are 4.4·10^?10 and 2.1·10^?10 mole/l., with Li^⊕ and K^⊕ as gegen-ions, respectively. In the case of Na^⊕ a quantitative estimation of K_d was not possible, but, qualitatively, it appears to be intermediate between those for Li^⊕ and K^⊕.     

Decay studies of poly(vinyl chloride) electrets

Thermoelectrets of poly(vinyl chloride) were prepared at 4, 14, 20 kV/cm and 105, 115, 125 and 135°C. The final charge is always homocharge, though the initial one depends upon the polarizing parameters. With 4 and 14 kV/cm, up to 125°C, the initial charge is homo, increasing with the polarizing temperature T_p. At 135°C, it is heterocharge tending to increase with the polarizing field E_p. From the thermally stimulated depolarization glow curves, the number of dipoles per monomeric unit of the material is calculated; it is seen that this number cannot account for the heterocharge. A mica spacer placed between the dielectric and one electrode suppresses the peak current. A model is proposed to explain the electret behaviour.     

Translocations t(X;7) and t(7;14) in a synovial sarcoma.

Cytogenetic analysis of a metastatic biphasic synovial sarcoma showed two structural abnormalities: t(X;7)(q11 or 12;q32) and t(7;14)(q22;q11.2). This is the first report of a synovial sarcoma without the involvement of either Xp11 or 18q11.     

Platelet adhesion studies on nanostructured poly(lactic-co-glycolic-acid)-carbon nanotube composite

Design of blood-compatible surfaces is required to minimize platelet-surface interactions and increase the thromboresistance of foreign surfaces. Poly(lactic-co-glycolic-acid)-carbon nanotube (PLGA-CNT) composite is studied as a building material to fabricate artificial blood prostheses. This nanocomposite-based biomaterial is prepared by an electrostatic Layer-by-Layer (LbL) deposition technique, in which layers of CNTs are adsorbed onto a PLGA film. Before incubation in nonstimulated platelet-rich plasma (PRP) for platelet studies, fibrinogen is immobilized on PLGA-CNT composite. Interactions between the plasma proteins, e.g. fibrinogen and PRP, are investigated on the prepared PLGA-CNT composite. Contact angle measurements on the PLGA-CNT composite displayed a good resistance of platelets adhesion on a hydrophilic surface with an angle of 64.94 degrees as compared to pristine PLGA control with an angle of 93.43 degrees . A significant reduction of adhesion is observed on the PLGA-CNT composite, as well as the absence of platelet activation. On the contrary, both platelet adhesion and activation are observed on control samples. We inferred this suppression in secretion of granule contents in the platelet by the presence of the CNTs that resulted in the absence of platelet activation and its subsequent inhibition in the release of adhesive membrane receptors on the PLGA-CNT composite.     

New poly(ester-carbonate) multi-block copolymers based on poly(lactic-glycolic acid) and poly(ϵ-caprolactone) segments

A new family of multi-block copolymers having the structure of poly(ester-carbonate)s was obtained by a chain-extension reaction involving poly(lactic-glycolic acid) oligomers (PLGA) and oligomeric α,ω-bishydroxy-terminated poly(ϵ-caprolactone)s (PCDT). The latter were first transformed into α,ω-bis(chloroformate)s, which were subsequently condensed in the presence of amines with both the hydroxylic and the carboxylic end-groups of PLGA oligomers. Several samples differing in the length of the PCDT segments and in the composition of the PLGA segments were prepared and characterized for their physico-chemical properties. All of them had high molecular weight, good solubility in organic solvents, and modest swellability in aqueous media. As regards their thermal behaviour, some samples showed evidence of the presence of a crystalline phase. Since these products are potentially useful as bioerodible materials in drug delivery systems, some preliminary results on their degradation behaviour under conditions mimicking those found in biological fluids are reported.     

Resonance Raman spectroscopic studies on dehydrochlorinated stretched poly(vinyl chloride)

Resonance Raman spectroscopy has been used to assess the effect of streching on the formation of conjugated polyenes during the thermal dehydrochlorination of poly(vinyl chloride). Two samples, a commerical mass polymer and a material prepared at ?30°C, have been examined, unplasticised and plasticised, at different draw ratios. Stretching prior to dehydrochlorination leads to an increase in the length of the polyene sequences, the effect being more marked with the low temperature polymer and with increasing draw ratio. Stretching after dehydrochlorination has no significant effect on the polyene distribution. These observations are consistent with the occurrence of chain orientation and alignment during stretching; this reduces the incidence of cross-linking between polyene sequences in adjacent chains and leads to an increase in the average sequence length.     

Thermodynamic studies on hemoglobin solutions

The heat of solution and the osmotic pressure of bovin hemoglobin in aqueous solution have been measured at 298 K using a twin microcalorimeter and an osmometer. The heat of association, ΔH, from calorimetric measurement and the association equilibrium constant, K, from osmometric measurement have been estimated, respectively. Also the thermodynamic quantities of the hemoglobin molecule which associates from 2αβ to the original α₂β₂ form are calculated. In all systems of the hemoglobin solutions, the value of dissociation equilibrium constant, K', calculated as the reciprocal of K, and that of ΔH seem to be of comparable order to those determined by the other investigators.     

Translocation (7;21) in a lipoma

Cytogenetic analysis was performed on a solitary lipoma from the flank of a 38-year-old male. A translocation t(7;21)(p22;q11.2) was found as the sole clonal chromosomal abnormality. The results are discussed in relation to other cytogenetic abnormalities found in benign adipose tumors.     

Thermodynamic studies on DNA-dye complexes

The interaction between DNA and dyes such as acridine orange ( 1 ), proflavine ( 2 ), and 3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide ( 3 ) were studied by means of the heat of mixing and UV spectra. From the results obtained, the thermodynamic quantities of DNA-dye complexes were estimated. It is concluded that the intercalation process forms a more stable binding than the stacking process does. Further, in each process, ΔG of DNA- 2 and DNA- 3 systems is nearly equal to that of the DNA- 1 system, but their — ΔH and — ΔS values are higher than those of the DNA- 1 system. The stability of binding in DNA- 2 and DNA- 3 systems may be governed largely by ΔH, while in the DNA- 1 system ΔS may contribute largely to the stability of binding.