New antifungal flavonoid glycoside from Vitex negundo

Flavonoids are ubiquitous in photosynthesizing cells and are common part of human diet. For centuries, preparations containing these compounds as the principal physiologically active constituents have been used to treat human diseases. Increasingly, this class of natural products is becoming the subject of anti-infective research. Our bioactivity guided fractionation of ethanolic extract of leaves of Vitex negundo resulted in the isolation of new flavone glycoside (4) along with five known compounds 1-3, 5 and 6. All the isolated compounds were evaluated for their antimicrobial activities. The new flavone glycoside 4 and compound 5 were found to have significant antifungal activity against Trichophyton mentagrophytes and Cryptococcus neoformans at MIC 6.25 microg/ml.     

New liver cell mutants defective in the endocytic pathway

To isolate mutant liver cells defective in the endocytic pathway, a selection strategy using toxic ligands for two distinct membrane receptors was utilized. Rare survivors termed trafficking mutants (Trf2-Trf7) were stable and more resistant than the parental HuH-7 cells to both toxin conjugates. They differed from the previously isolated Trf1 HuH-7 mutant as they expressed casein kinase 2 α″ (CK2α″) which is missing from Trf1 cells and which corrects the Trf1 trafficking phenotype. Binding of ¹²⁵I-asialoorosomucoid (ASOR) and cell surface expression of asialoglycoprotein receptor (ASGPR) were reduced approximately 20%-60% in Trf2-Trf7 cells compared to parental HuH-7, without a reduction in total cellular ASGPR. Based on ¹²⁵I-transferrin binding, cell surface transferrin receptor activity was reduced between 13% and 88% in the various mutant cell lines. Distinctive phenotypic traits were identified in the differential resistance of Trf2-Trf7 to a panel of lectins and toxins and to UV light-induced cell death. By following the endocytic uptake and trafficking of Alexa₄₈₈-ASOR, significant differences in endosomal fusion between parental HuH-7 and the Trf mutants became apparent. Unlike parental HuH-7 cells in which the fusion of endosomes into larger vesicles was evident as early as 20 min, ASOR endocytosed into the Trf mutants remained within small vesicles for up to 60 min. Identifying the biochemical and genetic mechanisms underlying these phenotypes should uncover novel and unpredicted protein-protein or protein-lipid interactions that orchestrate specific steps in membrane protein trafficking.     

Mouse recombinant leptin protects human hepatoma HepG2 against apoptosis, TNF-alpha response and oxidative stress induced by the hepatotoxin-ethanol

Obesity is a risk factor for hepatocellular carcinoma (HCC) complicated with alcoholic liver disease (ALD) and cryptogenic cirrhosis. Leptin is a 16-kDa antiobesity hormone secreted mainly by adipocytes. The role of leptin on alcohol-mediated effects in cell line is yet to be unraveled. Therefore, we investigated the effect of leptin against ethanol-elicited cytoxicity in human hepatoma cell lines (HepG2). HepG2 cells were treated with leptin (31.2 nM), ethanol (500 mM), ethanol+leptin and untreated cells served as control. 48 h after treatment, cell viability, apoptosis, TNF-alpha secretory response and oxidative damage were analysed. Our results suggest that leptin at a concentration of 31.2 nM prevents ethanol elicited cytotoxicity as evidenced by MTT and trypan blue dye exclusion assay. Leptin also inhibited ethanol-induced apoptosis, which was confirmed by [(3)H] thymidine uptake and cell cycle analysis using propidium iodide (PI) staining. Further, simultaneous leptin treatment along with ethanol showed protection against ethanol mediated cellular damage as indicated by significantly decreased levels of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS) and significantly increased levels of reactive nitrogen species (RNS), reduced glutathione (GSH) and elevated activities of superoxide dismutase (SOD) and catalase (CAT). In addition, leptin downregulated the secretion of tumor necrosis factor-alpha (TNF-alpha) by ethanol-induced HepG2 cells. Our results demonstrate that simultaneous leptin treatment along with ethanol could be useful in preventing the damage produced by ethanol, which might be of therapeutic interest.     

On the Neighbourhood Relationships of Two Common Understorey Trees of a Shorea robusta Community

The two common understorey tree species, Mallotus philippensisand Holarrhena antidysenterica of a Shorea-dominated forestshowed significant differences in their near neighbours. Thespatial pattern of the understorey community has been discussedin relation to the form and growth features of co-occurringspecies. The observations suggest that in a common physicalenvironment, the local organization of a community is conditionedby mutual architectural adjustment of neighbouring species.Species which are ubiquitous in the community generally showplastic architecture.Copyright 1995, 1999 Academic Press Mallotus, Holarrhena, neighbours, spatial organization, architectural plasticity     

Drosophila Sirtuin 6 mediates developmental diet‐dependent programming of adult physiology and survival

Organisms in the wild experience unpredictable and diverse food availability throughout their lifespan. Over‐/under‐nutrition during development and in adulthood is known to dictate organismal survival and fitness. Studies using model systems have also established long‐term effects of developmental dietary alterations on life‐history traits. However, the underlining genetic/molecular factors, which differentially couple nutrient inputs during development with fitness later in life are far less understood. Using Drosophila and loss/gain of function perturbations, our serendipitous findings demonstrate an essential role of Sirtuin 6 in regulating larval developmental kinetics, in a nutrient‐dependent manner. The absence of Sirt6 affected ecdysone and insulin signalling and led to accelerated larval development. Moreover, varying dietary glucose and yeast during larval stages resulted in enhanced susceptibility to metabolic and oxidative stress in adults. We also demonstrate an evolutionarily conserved role for Sirt6 in regulating physiological homeostasis, physical activity and organismal lifespan, known only in mammals until now. Our results highlight gene‐diet interactions that dictate thresholding of nutrient inputs and physiological plasticity, operative across development and adulthood. In summary, besides showing its role in invertebrate ageing, our study also identifies Sirt6 as a key factor that programs macronutrient‐dependent life‐history traits.     

Sustainable hydrogen production in the Cyanobacterium Nostoc sp. ARM 411 grown in fructose- and magnesium sulphate-enriched culture

We show that high levels of both carbon sources (sugars) and cations (notably magnesium) in the growth medium enhance the frequency of heterocyst formation by three-fold over the control in Nostoc sp. Such an alteration in the frequency and in enzyme activity (hydrogenase and nitrogenase), induced a proportional increase in hydrogen evolution capacity under a variety of conditions. Nitrogenase and hydrogenase activity also showed an increase in the enriched cultures. Our results therefore suggest that enriching the Nostoc culture with some selected carbon source or a low cost inorganic source like magnesium would result in a high yield of heterocysts in heterocystous cyanobacteria which would be helpful in the production of sustainable bio-fuels.     

A novel role for 3-O-sulfated heparan sulfate in herpes simplex virus 1 entry.

Herpes simplex virus type 1 (HSV-1) binds to cells through interactions of viral glycoproteins gB and gC with heparan sulfate chains on cell surface proteoglycans. This binding is not sufficient for viral entry, which requires fusion between the viral envelope and cell membrane. Here, we show that heparan sulfate modified by a subset of the multiple D-glucosaminyl 3-O-sulfotransferase isoforms provides sites for the binding of a third viral glycoprotein, gD, and for initiation of HSV-1 entry. We conclude that susceptibility of cells to HSV-1 entry depends on (1) presence of heparan sulfate chains to which virus can bind and (2) 3-O-sulfation of specific glucosamine residues in heparan sulfate to generate gD-binding sites or the expression of other previously identified gD-binding receptors.