Measurement of the Attachment and Assembly of Small Amyloid-β Oligomers on Live Cell Membranes at Physiological Concentrations Using Single-Molecule Tools

It is thought that the pathological cascade in Alzheimer's disease is initiated by the formation of amyloid-β (Aβ) peptide complexes on cell membranes. However, there is considerable debate about the nature of these complexes and the type of solution-phase Aβ aggregates that may contribute to their formation. Also, it is yet to be shown that Aβ attaches strongly to living cell membranes, and that this can happen at low, physiologically relevant Aβ concentrations. Here, we simultaneously measure the aggregate size and fluorescence lifetime of fluorescently labeled Aβ_1-40 on and above the membrane of cultured PC12 cells at near-physiological concentrations. We find that at 350 nM Aβ concentration, large (>>10 nm average hydrodynamic radius) assemblies of codiffusing, membrane-attached Aβ molecules appear on the cell membrane together with a near-monomeric species. When the extracellular concentration is 150 nM, the membrane contains only the smaller species, but with a similar degree of attachment. At both concentrations, the extracellular solution contains only small (∼2.3 nm average hydrodynamic radius) Aβ oligomers or monomers. We conclude that at near-physiological concentrations only the small oligomeric Aβ species are relevant, they are capable of attaching to the cell membrane, and they assemble in situ to form much larger complexes.     

Linear Mixed Model Selection for False Discovery Rate Control in Microarray Data Analysis

Summary In a microarray experiment, one experimental design is used to obtain expression measures for all genes. One popular analysis method involves fitting the same linear mixed model for each gene, obtaining gene‐specific p‐values for tests of interest involving fixed effects, and then choosing a threshold for significance that is intended to control false discovery rate (FDR) at a desired level. When one or more random factors have zero variance components for some genes, the standard practice of fitting the same full linear mixed model for all genes can result in failure to control FDR. We propose a new method that combines results from the fit of full and selected linear mixed models to identify differentially expressed genes and provide FDR control at target levels when the true underlying random effects structure varies across genes.     

Quinone and oxyradical scavenging properties of N-acetylcysteine prevent dopamine mediated inhibition of Na+, K+-ATPase and mitochondrial electron transport chain activity in rat brain: implications in the neuroprotective therapy of Parkinson's disease

Dopamine oxidation products such as H2O2 and reactive quinones have been held responsible for various toxic actions of dopamine, which have implications in the aetiopathogenesis of Parkinson's disease. This study has shown that N-acetylcysteine (0.25-1 mm) is a potent scavenger of both H2O2 and toxic quinones derived from dopamine and it further prevents dopamine mediated inhibition of Na+,K+-ATPase activity and mitochondrial respiratory chain function. The quinone scavenging ability of N-acetylcysteine is presumably related to its protective effect against dopamine mediated inhibition of mitochondrial respiratory chain activity. However, both H2O2 scavenging and quinone scavenging properties of N-acetylcysteine probably account for its protective effect against Na+,K+-ATPase inhibition induced by dopamine. The results have important implications in the neuroprotective therapy of sporadic Parkinson's disease since inactivation of mitochondrial respiratory activity and Na+,K+-ATPase may trigger intracellular damage pathways leading to the death of nigral dopaminergic neurons.     

Molecular recognition of plant DNA: Does it differ from conventional animal DNA?

The recognition mechanism of DNA with small drugs/ligands is an important field of research from pharmacological point of view. Such studies are ample with DNAs extracted from animal cells, but are rare for those extracted from plant cells. However, such a study is strongly demanding for the formulation of pesticides and other agrochemicals. In this contribution, for the first time, we report the interaction of two well-known DNA binder ethidium bromide (EB) and Hoechst 33258 (H33258) with two genomic DNAs extracted from the leaves of Ricinus communis L. (castor bean) and Mangifera indica (mango) using steady-state and picosecond-resolved fluorescence spectroscopy. The purity of the extracted DNAs is confirmed from gel electrophoresis and optical absorption studies. As evidenced from the circular dichroism (CD) measurements the DNAs retain physiologically relevant B forms. The well-known DNA intercalator EB has been found to show an additional electrostatic mode of binding with the DNAs, which is not present in the conventional animal DNAs. The binding affinity of EB is found to be even weaker for the DNA extracted from M. indica compared to that in R. communis L. On the other hand, the binding affinity of H33258 with the plant DNAs is found to be comparable to that of animal DNAs. The difference in interaction could be rationalized from the possible differences in the base sequences.     

Characterization and evaluation of methyl methacrylate-acetylated Saccharum spontaneum L. graft copolymers prepared under microwave

Hybridization of the natural polymers with synthetic polymers is of great interest because of its application to biomedical and biodegradable materials. Synthesis of graft copolymers of methyl methacrylate (MMA) onto acetylated Saccharum spontaneum L. fiber using ferrous ammonium sulphate–potassium per sulphate (FAS–KPS) redox initiator under the influence of microwave radiation (MWR) was carried-out. Different reaction parameters such as time, initiator molar ratio, monomer concentration, microwave power, pH and solvent were optimized to get maximum graft yield (72.2%). On grafting, percentage crystallinity decreases rapidly with reduction in its stiffness and hardness. The graft copolymers thus formed were characterized by FTIR, SEM, XRD, TGA, DTA and DTG techniques. Moreover, graft copolymers have been found to be more moisture resistant and also showed higher chemical and thermal resistance.     

Structural characterization of an immunoenhancing cytotoxic heteroglycan isolated from an edible mushroom Calocybe indica var. APK2

A water-soluble polysaccharide of an edible mushroom Calocybe indica var. APK2 showed immunoenhancing (macrophage, splenocyte, thymocyte, and bone marrow activation) and cytotoxic activity toward HeLa cell lines and found to consist of d-glucose, d-galactose, and l-fucose in a molar ratio of nearly 3:1:1. On the basis of acid hydrolysis, methylation analysis, and NMR studies (¹H, ¹³C, DEPT-135, TOCSY, DQF–COSY, NOESY, ROESY, HMQC, and HMBC), the structure of the repeating unit of the fuco-galacto-glucan was established as:     

Synthesis of β-arabinofuranoside glycolipids, studies of their binding to surfactant protein-A and effect on sliding motilities of M. smegmatis

Surfactant protein A (SP-A), which is a lung innate immune system component, is known to bind glycolipids present at the cell surface of a mycobacterial pathogen. Lipoarabinomannan (LAM), a component of mycobacterial thick, waxy cell wall, is one of the glycolipid ligands for SP-A. In order to assess binding of synthetic glycolipids with SP-A and the glycosidic linkage preferences for the interaction, β-arabinofuranoside trisaccharide glycolipids constituted with β-(1→2), β-(1→3) and β-(1→2), β-(1→5) linkages relevant to LAM were synthesized through chemical glycosylations. The efficacies of synthetic glycolipids to interact with SP-A were assessed by using the surface plasmon resonance (SPR) technique, from which association-dissociation rate constants and equilibrium binding constants were derived. The equilibrium binding constants of the interaction of two constitutionally varying β-arabinofuranoside glycolipids with SP-A were found to be in the millimolar range. A comparison of the results with few α-anomeric arabinofuranoside glycolipids showed that glycolipids with β-anomeric linkages were having relatively lower equilibrium binding constants than those with α-anomeric linkages in binding to the protein, whereas oligosaccharides alone, without lipidic chains, exhibited higher equilibrium binding constants. Further, the synthetic compounds inhibited the growth of mycobacteria and affected sliding motilities of the bacteria, although to an extent relatively lesser than that of synthetic compounds constituted with α-anomeric linkages.     

Study on the diuretic activity of Strychnos potatorum Linn. seed extract in albino rats.

Methanol extract of Strychnos potatorum Linn. seeds (SPSE) was evaluated for its diuretic activity in Wistar albino rats. The SPSE was administered at the graded doses of 200, 400, and 600 mg/kg body weight. The parameters which were taken into account during the experimental on each rat were: total urine volume (corrected for water intake during the test period), body weight before and after the experiment, and the concentration of sodium, potassium, and chloride ions in urine. The total urine volumes of the SPSE (600 mg/kg)-treated rats were evaluated nearly two and half fold then compared with the control (saline treated) group. Excretion of cations (sodium and potassium ions) and anions (chloride ions) also increased significantly with respect to the control group. The diuretic effect was comparable with that of the standard drug Furosemide. The increase of cations in the urine on treatment with Strychnos potatorum seed extract (SPSE) was dose-dependent. This effect supports the use of the Strychnos potatorum seeds as a diuretic in folk remedies.