Prophylactic melatonin significantly reduces Alzheimer's neuropathology and associated cognitive deficits independent of antioxidant pathways in AßPP(swe)/PS1 mice.

BACKGROUND: Alzheimer's disease (AD) underlies dementia for millions of people worldwide, and its occurrence is set to double in the next 20 years. Currently, approved drugs for treating AD only marginally ameliorate cognitive deficits, and provide limited symptomatic relief, while newer substances under therapeutic development are potentially years away from benefiting patients. Melatonin (MEL) for insomnia has been proven safe with >15 years of over-the-counter access in the US. MEL exerts multiple complementary mechanisms of action against AD in animal models; thus it may be an excellent disease-modifying therapeutic. While presumed to provide neuroprotection via activation of known G-protein-coupled melatonin receptors (MTNRs), some data indicate MEL acts intracellularly to protect mitochondria and neurons by scavenging reactive oxygen species and reducing free radical formation. We examined whether genetic deletion of MTNRs abolishes MEL's neuroprotective actions in the AßPP(swe)/PSEN1dE9 mouse model of AD (2xAD). Beginning at 4 months of age, both AD and control mice either with or without both MTNRs were administered either MEL or vehicle in drinking water for 12 months. RESULTS: Behavioral and cognitive assessments of 15-month-old AD mice revealed receptor-dependent effects of MEL on spatial learning and memory (Barnes maze, Morris Water Maze), but receptor-independent neuroprotective actions of MEL on non-spatial cognitive performance (Novel Object Recognition Test). Similarly, amyloid plaque loads in hippocampus and frontal cortex, as well as plasma Aß1-42 levels, were significantly reduced by MEL in a receptor-independent manner, in contrast to MEL's efficacy in reducing cortical antioxidant gene expression (Catalase, SOD1, Glutathione Peroxidase-1, Nrf2) only when receptors were present. Increased cytochrome c oxidase activity was seen in 16 mo AD mice as compared to non-AD control mice. This increase was completely prevented by MEL treatment of 2xAD/MTNR+ mice, but only partially prevented in 2xAD/MTNR- mice, consistent with mixed receptor-dependent and independent effects of MEL on this measure of mitochondrial function. CONCLUSIONS: These findings demonstrate that prophylactic MEL significantly reduces AD neuropathology and associated cognitive deficits in a manner that is independent of antioxidant pathways. Future identification of direct molecular targets for MEL action in the brain should open new vistas for development of better AD therapeutics.

Isolation and characterization of a cryptic plasmid from Erwinia citreus ATCC 31623.

A multiple-copy plasmid pPZG500 (3.8 kb) was isolated from a phytopathogenic bacterium Erwinia citreus ATCC 31623. This is the smallest plasmid so far isolated from the genus Erwinia. The plasmid was partially characterized by a set of restriction enzymes and the unique restriction sites were mapped for HindIII, EcoRI, EcoRV and XBaI, while three sites were found for BglII. Nineteen other enzymes did not cut pPZG500. By deletion analyses minimal regions required for replication (ori) and segregational stability (par) were localized on 1.4 kb EcoRV/BglII and 0.7 kb Bgl/II/EcoRI fragments, respectively. The erythromycin resistance marker (Emr) was cloned into pPZG500 and two plasmid derivatives, pPZG502 and pPZG503, were constructed expressing erythromycin resistance as a good selective marker for recombinant selection in Erw. citreus and Escherichia coli. The segregational stability of both constructed plasmids during 90 generations in E. coli JM109 and Erw. citreus C-4 showed that plasmid pPZG503 lacking the presumptive par region was lost from the population at a higher rate. The results of this study demonstrate that plasmid pPZG500 and derivatives are suitable prerequisites for the construction of useful cloning vector(s) in the genus Erwinia.

[Genetic and biochemical basis of microbial resistance to antibiotics]. / Geneticke i biokemijske osnove rezistencije mikroorganizama prema antibioticima.

Antibiotics affect different structures or metabolic processes in a bacterial cell inhibiting its growth and reproduction what results in the destruction of microorganisms. Microorganisms have developed some resistance mechanisms in order to survive in the presence of antibiotics. Recent advances in molecular biology of microorganisms Recent advances in molecular biology of microorganisms and technique of recombinant DNA have helped us to understand more clearly the molecular aspects of resistance of microorganisms against antibiotics. Some of the mechanisms of drug resistance include: change of the binding site of the antibiotic due to the mutation of genes being responsible for the synthesis of the target sites of the antibiotic (aminoglycosides, chloramphenicol, beta-lactams); change of the binding site of the antibiotic by the activity of methylase (macrolides); diminished patency of the cell membrane for the antibiotic (tetracyclines, chloramphenicol, macrolides, aminoglycosides); active transport of the antibiotic outside the cell (tetracyclines); synthesis of specific enzymes modifying and thus inactivating the molecule of the antibiotic (aminoglycosides, chloramphenicol); tolerance of microorganisms to the activity of the antibiotic (beta-lactams); inactivation of the antibiotic molecule by the enzymes such as beta-lactamase for the beta-lactam antibiotic and by esterase for the antibiotic with a lactone ring (macrolides).

Enhancement of bacitracin biosynthesis by branched-chain amino acids in a regulatory mutant of Bacillus licheniformis.

DL-4-Azaleucine-resistant mutant of Bacillus licheniformis azlr-1 isolated after N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis, was a better bacitracin producer than the parent strain. In the minimal medium, the antibiotic biosynthesis was 4 times higher in the mutant than in the parent strain and less dependent on L-leucine addition. In the complex fermentation medium, the yield was 18-20% higher in the mutant strain. Transaminase B activity measured in the crude extract revealed that the branched-chain amino acid biosynthetic enzymes were 5-10 times derepressed supplying bacitracin synthetase with enhanced quantity of isoleucine and leucine, the building units of bacitracin molecule.

Biochemical and genetic studies of a histidine regulatory mutant of Streptomyces coelicolor A3 (2).

The specific activities of three enzymes in a histidine regulatory mutant RF59 of Streptomyces coelicolor A3(2) resistant to the histidine analogue 1,2,4-triazolealanine (TRA) were measured and compared to the activity of the wild type strain. The first enzyme of the histidine pathway, phosphorybosyl-ATP-pyrophosphorylase (PR-ATP-pyrophosphorylase), of mutant RF59 and the wild type was sensitive to allosteric inhibition by L-histidine and hence feed-back inhibition was not affected by mutation, although the specific activity in the mutant was 2.9 fold higher than in the wild type. The other two enzymes coded by genes from the histidine operon were significantly derepressed. The enzyme D-erythroimidazoleglycerol phosphate dehydrase (IGP-dehydrase) in mutant RF59 had a 4.9 fold higher specific activity than in the wild type strain. The specific activity of the last enzyme of the pathway, histidinol-dehydrogenase (Hol-dehydrogenase), in the mutant was 4.7 fold derepressed compared to the wild type strain. The results of genetic crosses revealed the mapping of RF59 regulatory mutation between argA1 and cysD18 on S. coelicolor chromosome, suggesting that the mutant RF59 is a regulatory mutant unable to fully repress genes of the histidine pathway.

Histidine production by a regulatory mutant of Streptomyces coelicolor.

Streptomyces coelicolor mutant RF-59, isolated as a revertant of a histidine auxotroph after mutagenic treatment with N-methylN'-nitro-N-nitrosoguanidine, was found to accumulate L-histidine. The mutant was sensitive to 2-thiazo-lealanine and L-2,4-diaminobutyric acid and partially sensitive to alpha-methylhistidine but resistant to 1,2,4-triazolealanine, indicating that repression of the histidine operon was modified in the mutant. Culture conditions were investigated, and optimal media for L-histidine production were developed, resulting in L-histidine accumulation of 2.1 to 3.5 g/liter.

Mutagenic action of N-methyl-N'-nitro-N-nitrosoguanidine on Gaffkya tibisci at alkaline pH.

Good yields of mutants were obtained by incubating cells of Gaffkya tibisci with N-methyl-N'-nitro-N-nitrosoguanidine in alkaline buffer. Nearly 50% of the survivors were auxotrophic mutants under the conditions described.