Literaturberichte

Ohne Zusammenfassung     

Microcystin-LR, a cyanobacterial toxin, induces growth inhibition and histological alterations in common reed (Phragmites australis) plants regenerated from embryogenic calli

The aim of this study was to establish the histological effects of exposure to microcystin-LR (MC-LR), a cyanotoxin, on axenic Phragmites australis plantlets. Plantlets were regenerated from embryogenic reed calli by tissue culture methods. Microcystin-LR inhibited the growth and development of embryogenic calli and the growth of reed plantlets. The 50% plantlet growth inhibitory concentration value (IC50) of MC-LR was 12 microg ml(-1) (12.07 microM) on mineral medium and 36 microg ml(-1) (36.22 microM) on Murashige-Skoog medium. In the case of roots, the IC50 value was 4.1 microg ml(-1) (4.12 microM) on both media. Microcystin-LR induced aerenchyma obturation, altered lignification of cell walls in the axial organs, root necrosis and the capture of lateral or adventitious roots in the tissues of axial organs of reed plantlets. Cyanotoxin induced the premature development of lateral roots, root coalescence and early aerenchyma formation. Our data suggest that microcystin-LR, a cyanotoxin, induced developmental and histological alterations leading to growth inhibition of reed, and the induced harms have an impact on understanding reed decay in eutrophic fresh waters.     

Structure-activity study on the LH- and FSH-releasing and anticancer effects of gonadotropin-releasing hormone (GnRH)-III analogs

GnRH-III was reported to have selective FSH-releasing activity in rats and significant anticancer potency on human breast cancer cells. To improve either of these effects, 14 analogs were synthesized and investigated for FSH/LH stimulation and breast cancer inhibition. Analogs with single amino acid changes in positions 5-7 or 10 showed small or no difference in the FSH- or LH-releasing activity compared with GnRH-III but their anticancer potency decreased significantly. Modification of the terminal amino acids, side chain cyclization at the 6-8 regions, or combined amino acid changes at positions 4, 6 and/or 8 resulted in the decrease of both effects. Gonadotropin-releasing activity of Arg(8)-GnRH-III was improved 3-11-fold. A copolymer conjugate of GnRH-III showed 2-3-fold anticancer activity while losing endocrine potency. CONCLUSION: The activation of GnRH-receptors on pituitary and breast cancer cells requires a specific structure and/or conformation that makes possible to improve the anticancer selectivity of GnRH analogs.     

Synthesis of ketopyranosyl glycosides and determination of their anomeric configuration on the basis of the three-bond carbon-proton couplings

Anomeric pairs of ketopyranosyl glycosides with various substituents at C(alpha), C(beta) and C(gamma) were synthesized from the corresponding thioglycosides, and the influence of the C(alpha)-C(beta)-C(gamma)-H(gamma) torsion angle and substituent effects on the three-bond carbon-proton couplings was studied. The cis coupling constants range from 1 to 2Hz. The trans couplings are generally as small as 2.3-2.6Hz; however, for compounds bearing an unsubstituted gamma-carbon, a relatively large trans coupling was measured (4.8Hz). An S-ethyl group at the beta-position increases the cis coupling (up to 3.2Hz) compared to the corresponding O-glycosides.     

Stereoselective (2-naphthyl)methylation of sugar hydroxyls by the hydrogenolysis of diastereoisomeric dioxolane-type (2-naphthyl)methylene acetals

The cis axial/equatorial OH groups of methyl alpha-L- and ethyl 1-thio-alpha-L-rhamnopyranoside, 1,6-anhydro-beta-D-mannopyranose, and 1,6-anhydro-beta-D-galactopyranose were reacted with 2-naphthaldehyde dimethyl acetal to diastereomeric dioxolane-type 2,3-O-(2-naphthyl)methylene or 3,4-O-(2-naphthyl)methylene acetals. The glycosides yielded the exo- and endo-isomers in nearly 1:1 ratio, 1,6-anhydro-beta-D-mannopyranose gave predominantly the endo-, and 1,6-anhydro-beta-D-galactopyranose exclusively endo-isomer. The acetals and some of their fully protected derivatives bearing benzyl or tert-butyldimethylsilyl groups were hydrogenolised with AlH(3) (3LiAlH(4)-AlCl(3)) or with Me(3)N.BH(3)-AlCl(3) reagents. The endo-isomers were cleaved by both reagents to give axial NAP ethers, the exo-isomers of pyranosides furnished equatorial NAP ethers. However, the exo-isomers of pyranoses gave irregular axial ethers with a > 30-fold enhancement of the reaction rates with respect to the endo-isomer.     

Characterization of a ribonuclease from Anacystis nidulans infected with cyanophage as-1

In Anacystis nidulans the ribonuclease (RNase) activity is very low but is greatly increased upon phage-infection. A RNase was isolated and purified over 300-fold from A. nidulans cells infected by cyanophage AS-1. The enzyme did not attack single- or double-stranded DNA, was inactive on p-nitrophenyl phosphate or bis-p-nitrophenyl phosphate as substrates, and had neither 3′- nor 5′-nucleotidase activity. The approximate MW of the enzyme was 12000. Maximal enzyme activity was at pH 7.5. No absolute requirement for metal ions was observed, but Fe³⁺ stimulated and Co²⁺ and Ni²⁺ inhibited enzyme activity. The enzyme is an endonuclease which, upon exhaustive hydrolysis, produces mainly oligonucleotides (average chain-length: 3) with 3′-P termini. Analysis of the base composition of these oligonucleotides and determination of their 3′-terminal nucleosides, together with the investigation of the rate of hydrolysis of synthetic polyribonucleotides, have shown that the enzyme has a relative specificity for uridylic acid.     

Inhibition of Colorado potato beetle larvae by a locust proteinase inhibitor peptide expressed in potato

The cDNA for a 73-mer peptide containing two locust serine proteinase inhibitors was cloned, fused to the constitutive CaMV35S promoter and introduced into potato by Agrobacterium-mediated transformation. From 23 independent transgenic lines, three with high mRNA level and proteinase inhibitory activity were propagated in vitro and transferred to pots. The peptide from the leaves was identified by its N-terminal sequence and by K_i values against chymotrypsin and trypsin. Colorado potato beetle larvae reared on transgenic plants grew slightly but significantly more slowly than those on control plants. This supports the notion that expression of multifunctional proteinase inhibitors of insect origin might be a good strategy to improve insect resistance in plants.     

Clinical significance of serum thyroglobulin and antithyroglobulin antibody in differentiated thyroid cancer after thyroid ablation

Serum thyroglobulin (Tg) is a suitable marker for differentiated thyroid carcinoma following total thyroid ablation. Between 1998 and 2003, serum samples from 715 papillary and 179 follicular tumor patients treated with total/nearly total thyroidectomy and radioiodine ablation therapy were collected. According to the "Guidelines for Oncotherapy in Hungary", serum Tg, antithyroglobulin antibody (TgAb), TSH and FT4 levels were measured in periods of 3 months following the first treatment and of 6 months after 2 years. In the present work the prognostic value of Tg and TgAb data of cancer patients with hormone substitution therapy were evaluated individually and retrospectively. Serum Tg and TgAb concentrations were measured with a highly sensitive immunoradiometric (IRMA) method, and with a second generation, broad epitope specificity competitive radioimmunoassay, respectively. TSH levels determined by fourth generation LIAISON kit were in a range of 0.05-0.10 mIU/L. Accuracy of measuring of Tg <1 ng/ml made it possible to select the low cut-off level (Tg <2 ng/ml) following total thyroidectomy. In the predominant part of TSH-suppressed patients (746/774, 96%) the serum Tg concentration was below the cut-off level of 2 ng/ml. The sensitivity of Tg determination in 59 TSH-suppressed thyroid cancer patients with lung and bone metastases was as high as 86 to 100%. On the contrary, the number of false negative data was high in cases with lymph node metastases of papillary cancer, and sensitivity did not exceed 62%. Specificity and sensitivity of Tg in TgAb negative patients were 91 to 100%. Based on our results it could be concluded that measuring of Tg and TgAb, using a current IRMA method and a second generation RIA kit, proved to be effective tools for the postoperative monitoring of differentiated thyroid tumours. It has to be noted that determination of TgAb is highly recommended for the adequate interpretation of serum Tg levels. Persistently high and/or increasing serum TgAb concentration with low Tg result had a diagnostic value during the follow-up and can be connected with the recurrence or persistence of the differentiated thyroid cancer.