Dental methacrylates may exert genotoxic effects via the oxidative induction of DNA double strand breaks and the inhibition of their repair

Methacrylate monomers used in dentistry have been shown to induce DNA double strand breaks (DSBs), one of the most serious DNA damage. In the present work we show that a model dental adhesive consisting of 45% 2-hydroxyethyl methacrylate (HEMA) and 55% bisphenol A-diglycidyl dimethacrylate (Bis-GMA) at concentrations up to 0.25 mM Bis-GMA induced oxidative DNA in cultured primary human gingival fibroblasts (HGFs) as evaluated by the comet assay and probed with human 8-hydroxyguanine DNA-glycosylase 1. HEMA/Bis-GMA induced DSBs in HGFs as assessed by the neutral comet assay and phosphorylation of the H2AX histone and sodium ascorbate or melatonin (5-methoxy-N-acetyltryptamine) both at 50 μM reduced the DSBs, they also inhibited apoptosis induced by HEMA/Bis-GMA. The adhesive slowed the kinetics of the repair of DNA damage induced by hydrogen peroxide in HGFs, while sodium ascorbate or melatonin improved the efficacy of H2O2-induced damage in the presence of the methacrylates. The adhesive induced a rise in the G2/M cell population, accompanied by a reduction in the S cell population and an increase in G0/G1 cell population. Sodium ascorbate or melatonin elevated the S population and reduced the G2/M population. In conclusion, HEMA/Bis-GMA induce DSBs through, at least in part, oxidative mechanisms, and these compounds may interfere with DSBs repair. Vitamin C or melatonin may reduce the detrimental effects induced by methacrylates applied in dentistry

B-11N-15 redor and B-11 spin echo studies for structural characterization of Si-B-C-N precursor ceramics

Solid-state NMR spectroscopy is employed for the structural characterization of precursor-derived Si-B-C-N ceramics. Particular emphasis is given to the structural composition of the BNCx phase which plays a key role for the unusual high temperature stability of these materials. In the present work B-11N-15 REDOR and B-11 spin echo experiments are presented for two N-15 enriched precursor systems, made from substituted polysilazanes and polysilylcarbodiimides, which provide interatomic boron-boron and boron-nitrogen distances. The obtained results are compatible with the presence of layered structures as reported for hexagonal boron nitride (h-BN). The derived boron-nitrogen and boron-boron distances, however, are larger than in h-BN, reflecting some layer distortions. The boron-boron distances are found to decrease with increasing pyrolysis temperature, whereas the boron-nitrogen distances remain practically unaltered at elevated pyrolysis temperatures. On the basis of the present results it is concluded that intercalated BN and sp(2)-carbon layers most likely constitute the BNCx phase. The graphite-like carbon layers are assumed to create some internal pressure, which in turn is responsible for the observed interatomic distance increase in the BN layers. However, other scenarios, like the direct incorporation of small sp(2)-carbon domains into the BN-sheets, cannot be ruled out completely. Further work along this line appears to be necessary to develop a comprehensive structural model for the BNCx phase in such quarternary ceramic systems

Zinc thiolate complexes ZnLn(SR)(+) with azamacrocyclic ligands, part II: Mechanism of the reaction with CS2

The thiolate complexes Zn(15]aneN(4))(S-CH2-C6H5)]ClO4 (1) (15aneN(4) = 1,4,8,12-tetraazacyclopentadecane) and Zn(i-14]aneN(4))(S-CH2-C6H5)ICIO4 (2) (i-14aneN(4) = 1, 4,7, 11 -tetraazacyclotetradecane) have been reacted with carbon disulfide. The trithiocarbonate complexes Zn(15]aneN(4))S-C(S)-S-CH2-C6H5]CIO4 1a, monoclinic, space group P2(1)/n, Z = 8, a = 13,2338(1) angstrom, b = 12.9251(2) angstrom, c = 30.1669(4) angstrom, beta = 101.463(1)degrees, V = 5057.1(1) angstrom(3) and Zn(i14]aneN(4))S-C(S)-S-CH2-C6H5]CIO4 2a, orthorhombic, space group P2(1)2(1)2(1), Z = 8, a = 9.9936(1) angstrom, b 22.1261(4) angstrom, c = 22.3192(4) angstrom, V = 4935.2(l) angstrom(3) were obtained. The reaction of 1 with CS2 is second order with a rate constant of k = (57.6 +/- 2.4) x 10(-3) m(-1.)s(-1) at 25 degrees C. The experimentally determined Eyring activation barrier is Delta H-exp(double dagger) = 65.3 +/- 0.7 kJ(.)mol(-1) (Delta S-exp(double dagger) = -49.9 +/- 2.5 J(.)mol(-1.)K(-1)) and a free energy of activation of Delta G* = 80.2 +/- 1.5 kJ(.)mol(-1) at 25 degrees C. To discriminate between an associative and a dissociative mechanism the barriers for both processes were calculated using density functional theory at the C-PCM(B98/G3MP2Large)//B3LYP/ 6-311+G(d) level. The associative mechanism is clearly favored with a difference in free energies of activation of delta Delta G(double dagger) approximate to 80kJ(.)mol(-1). Its calculated barrier Delta G(theor)(double dagger) = 114.3 kJ(.)mol(-1) is in reasonable agreement with the experimental value. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The serine-rich N-terminal region of Arabidopsis phytochrome A is required for protein stability.

Deletion or substitution of the serine-rich N-terminal stretch of grass phytochrome A (phyA) has repeatedly been shown to yield a hyperactive photoreceptor when expressed under the control of a constitutive promoter in transgenic tobacco or Arabidopsis seedlings retaining their native phyA. These observations have lead to the proposal that the serine-rich region is involved in negative regulation of phyA signaling. To re-evaluate this conclusion in a more physiological context we produced transgenic Arabidopsis seedlings of the phyA-null background expressing Arabidopsis PHYA deleted in the sequence corresponding to amino acids 6-12, under the control of the native PHYA promoter. Compared to the transgenic seedlings expressing wild-type phyA, the seedlings bearing the mutated phyA showed normal responses to pulses of far-red (FR) light and impaired responses to continuous FR light. In yeast two-hybrid experiments, deleted phyA interacted normally with FHY1 and FHL, which are required for phyA accumulation in the nucleus. Immunoblot analysis showed reduced stability of deleted phyA under continuous red or FR light. The reduced physiological activity can therefore be accounted for by the enhanced destruction of the mutated phyA. These findings do not support the involvement of the serine-rich region in negative regulation but they are consistent with a recent report suggesting that phyA turnover is regulated by phosphorylation

Promoter elements of the mustard CHS1 gene are sufficient for light regulation in transgenic plants

Kaiser T, Emmler K, Kretsch T, Weisshaar B, Schäfer E, Batschauer A. Promoter elements of the mustard CHS1 gene are sufficient for light regulation in transgenic plants. PLANT MOLECULAR BIOLOGY. 1995;28(2):219-229.The expression of chalcone synthase (CHS) genes, which encode the first enzyme of the flavonoid pathway, is under developmental control as well as affected by external stimuli such as light. Varying fragments of the 1 kb upstream region of the CHS1 gene from white mustard (Sinapis alba L.) were fused to the GUS-coding region, and the light-regulated expression of these constructs was analysed in transgenic Arabidopsis and tobacco plants. Studies performed with Arabidopsis seedlings indicate the presence of two elements within the CHS1 promoter mediating light responses via different photoreceptors. One element, located about 150 bp upstream of the transcription start site, is homologous to Unit 1 of the parsley CHS gene, the second, far more upstream element carries sequences similar to Unit 2 of the same gene. Detailed studies on Unit 1-driven expression indicate that this element transfers the expression characteristics of the original gene to both Arabidopsis and tobacco. Although the expression characteristics of Unit 1 are indistinguishable from those of the full-length promoter within the same species, we observed differences in mustard CHS promoter regulation between Arabidopsis and tobacco plants transgenic for the identical construct. The difference in photoreceptor usage by the same promoter element in different transgenic species (Unit 1 from mustard in Arabidopsis vs. tobacco) was also observed for different but homologous promoter elements in the same transgenic species (Unit 1 from mustard and parsley in tobacco). We therefore conclude that the same promoter and even the same promoter element (Unit 1) can mediate different spatial patterns of expression and modes of light regulation in different transgenic species