New tacrine-dihydropyridine hybrids that inhibit acetylcholinesterase, calcium entry, and exhibit neuroprotection properties

In this communication, we describe the synthesis and biological evaluation of tacripyrimedones 1-5, a series of new tacrine-1,4-dihydropyridine hybrids bearing the general structure of 11-amino-12-aryl-3,3-dimethyl-3,4,5,7,8,9,10,12-octahydrodibenzo[b,g][1,8]naphthyridine-1(2H)-one. These multifunctional compounds are moderately potent and selective AChEIs, with no activity toward BuChE. Kinetic analysis and molecular modeling studies point out that the new compounds preferentially bind the peripheral anionic site of AChE. In addition, compounds 1-5 show an excellent neuroprotective profile, and a moderate blocking effect of L-type voltage-dependent calcium channels due to the mitigation of [Ca(2+)] elevation elicited by K(+) depolarization. Therefore, they represent a new family of molecules with potential therapeutic application for the treatment of Alzheimer's disease.     

A Novel Model of Human Skin Pressure Ulcers in Mice

Introduction

Pressure ulcers are a prevalent health problem in today''s society. The shortage of suitable animal models limits our understanding and our ability to develop new therapies. This study aims to report on the development of a novel and reproducible human skin pressure ulcer model in mice.

Material and Methods

Male non-obese, diabetic, severe combined immunodeficiency mice (n = 22) were engrafted with human skin. A full-thickness skin graft was placed onto 4×3 cm wounds created on the dorsal skin of the mice. Two groups with permanent grafts were studied after 60 days. The control group (n = 6) was focused on the process of engraftment. Evaluations were conducted with photographic assessment, histological analysis and fluorescence in situ hybridization (FISH) techniques. The pressure ulcer group (n = 12) was created using a compression device. A pressure of 150 mmHg for 8 h, with a total of three cycles of compression-release was exerted. Evaluations were conducted with photographic assessment and histological analysis.

Results

Skin grafts in the control group took successfully, as shown by visual assessment, FISH techniques and histological analysis. Pressure ulcers in the second group showed full-thickness skin loss with damage and necrosis of all the epidermal and dermal layers (ulcer stage III) in all cases. Complete repair occurred after 40 days.

Conclusions

An inexpensive, reproducible human skin pressure ulcer model has been developed. This novel model will facilitate the development of new clinically relevant therapeutic strategies that can be tested directly on human skin.     

Budding yeast Rif1 binds to replication origins and protects DNA at blocked replication forks

Despite its evolutionarily conserved function in controlling DNA replication, the chromosomal binding sites of the budding yeast Rif1 protein are not well understood. Here, we analyse genome‐wide binding of budding yeast Rif1 by chromatin immunoprecipitation, during G1 phase and in S phase with replication progressing normally or blocked by hydroxyurea. Rif1 associates strongly with telomeres through interaction with Rap1. By comparing genomic binding of wild‐type Rif1 and truncated Rif1 lacking the Rap1‐interaction domain, we identify hundreds of Rap1‐dependent and Rap1‐independent chromosome interaction sites. Rif1 binds to centromeres, highly transcribed genes and replication origins in a Rap1‐independent manner, associating with both early and late‐initiating origins. Interestingly, Rif1 also binds around activated origins when replication progression is blocked by hydroxyurea, suggesting association with blocked forks. Using nascent DNA labelling and DNA combing techniques, we find that in cells treated with hydroxyurea, yeast Rif1 stabilises recently synthesised DNA. Our results indicate that, in addition to controlling DNA replication initiation, budding yeast Rif1 plays an ongoing role after initiation and controls events at blocked replication forks.     

Kinetic modelling and simulation of laccase catalyzed degradation of reactive textile dyes

A kinetic model based on Michaelis-Menten equation was developed to simulate the dye decolourisation of Reactive Black 5 (RB5), Reactive Blue 114 (RB114), Reactive Yellow 15 (RY15), Reactive Red 239 (RR239) and Reactive Red 180 (RR180) dyes by commercial laccase. The unusual kinetic behavior of some of these reactions suggests that the kinetic model must consider the activation of the laccase-mediator system. Several reactions at different concentrations of each dye were performed in batch reactors and time courses were obtained. A LSODE code to solve the differential equation obtained from the batch reactor was combined with an optimization Fortran program to obtain the theoretical time courses. The time courses obtained from the developed program were compared with the experimentally obtained ones to estimate the kinetic constants that minimized the difference between them. The close correlation between the predicted and the experimental results seems to support the reliability of the established models.     

Copper-induced calcium release from ER involves the activation of ryanodine-sensitive and IP3-sensitive channels in Ulva compressa

The marine alga Ulva compressa (Chlorophyta) showed a triphasic release of intracellular calcium with maximal levels at 2, 3 and 12 h and a biphasic accumulation of intracellular hydrogen peroxide with peaks at 3 and 12 h when cultivated with copper excess. Intracellular hydrogen peroxide originated exclusively in organelles. In this work, we analyzed the intracellular origin of calcium release and the type of calcium channels activated in response to copper excess. U. compressa was treated with thapsigargin, an inhibitor of endoplasmic reticulum (ER) calcium ATPase, ryanodine, an inhibitor of ryanodine-sensitive channels and xestospongin C, an inhibitor of inositol 1, 4, 5-triphosphate (IP₃)-sensitive channels. Thapsigargin induced the depletion of calcium stored in ER at 75 min and completely inhibited calcium release at 2, 3 and 12 h of copper exposure indicating that calcium release originated in ER. In addition, ryanodine and xestospogin C inhibited calcium release at 2 and 3 h of copper exposure whereas the peak at 12 h was only inhibited by ryanodine. Thus, copper induced the activation of ryanodine-sensitive and IP₃-sensitive calcium channels in ER of U. compressa.Key words: calcium release, endoplasmic reticulum, calcium channels, marine alga, Ulva compressaPlants showed common responses to biotic and abiotic stresses, mainly the accumulation of reactive oxygen species (ROS), in particular hydrogen peroxide, and the release of intracellular calcium.^1,2 Regarding abiotic stress, it has been shown that ozone triggers a NADPH oxidase-dependent biphasic oxidative burst in Arabidopsis thaliana that activates antioxidant and defense enzymes.^3,4 In addition, cadmium induced a NADPH oxidase-dependent monophasic accumulation of extracellular hydrogen peroxide in tobacco cells.⁵ On the other hand, ozone as well as absicic acid treatment, dessication, cold, heat, salinity, UV light and anoxia induce intracellular calcium release and the activation of antioxidant enzymes.^6–8 Regarding abiotic stress in algae, copper induced a monophasic increase of intracellular hydrogen peroxide at 2 h of copper exposure in the brown seaweeds Lessonia nigrecsens and Scytosiphon lomentaria.⁹ On the other hand, strontium induced calcium release in the green microalga Eremosphaera viridis as did osmotic stress in the zygote of the brown macroalga Fucus serratus.^10,11 U. compressa is a cosmopolitan marine macroalga (Chlorophyta) growing in copper-impacted coastal areas in northern Chile.¹² U. compressa cultivated in seawater with copper excess (10 µM) showed co-occuring increases of intracellular calcium and hydrogen peroxide.¹³ Copper induced a triphasic release of calcium with maximal levels at 2, 3 and 12 h and a biphasic production of hydrogen peroxide with peaks at 3 and 12 h. Interestingly, the production of hydrogen peroxide occurred exclusively in organelles, i.e., mitochondria and chloroplasts. In addition, calcium and hydrogen peroxide act as signals in the differential activation of antioxidant and defense enzymes.¹³ In this work, we analyzed the intracellular origin of copper-induced calcium release and the type of calcium channels activated in response to copper excess in U. compressa.     

Species traits and environmental characteristics together regulate ant‐associated biodiversity

Host‐associated organisms (e.g., parasites, commensals, and mutualists) may rely on their hosts for only a portion of their life cycle. The life‐history traits and physiology of hosts are well‐known determinants of the biodiversity of their associated organisms. The environmental context may strongly influence this interaction, but the relative roles of host traits and the environment are poorly known for host‐associated communities. We studied the roles of host traits and environmental characteristics affecting ant‐associated mites in semi‐natural constructed grasslands in agricultural landscapes of the Midwest USA. Mites are frequently found in ant nests and also riding on ants in a commensal dispersal relationship known as phoresy. During nonphoretic stages of their development, ant‐associated mites rely on soil or nest resources, which may vary depending on host traits and the environmental context of the colony. We hypothesized that mite diversity is determined by availability of suitable host ant species, soil detrital resources and texture, and habitat disturbance. Results showed that that large‐bodied and widely distributed ant species within grasslands support the most diverse mite assemblages. Mite richness and abundance were predicted by overall ant richness and grassland area, but host traits and environmental predictors varied among ant hosts: mites associated with Aphaenogaster rudis depended on litter depth, while Myrmica americana associates were predicted by host frequency and grassland age. Multivariate ordinations of mite community composition constructed with host ant species as predictors demonstrated host specialization at both the ant species and genus levels, while ordinations with environmental variables showed that ant richness, soil texture, and grassland age also contributed to mite community structure. Our results demonstrate that large‐bodied, locally abundant, and cosmopolitan ant species are especially important regulators of phoretic mite diversity and that their role as hosts is also dependent on the context of the interaction, especially soil resources, texture, site age, and area.     

The phylogeographic history of Megistostegium (Malvaceae) in the dry,spiny thickets of southwestern Madagascar using RAD‐seq data and ecological niche modeling

The spiny thicket of southwestern Madagascar represents an extreme and ancient landscape with extraordinary levels of biodiversity and endemism. Few hypotheses exist for explaining speciation in the region and few plant studies have explored hypotheses for species diversification. Here, we investigate three species in the endemic genus Megistostegium (Malvaceae) to evaluate phylogeographic structure and explore the roles of climate, soil, and paleoclimate oscillations on population divergence and speciation throughout the region. We combine phylogenetic and phylogeographic inference of RADseq data with ecological niche modeling across space and time. Population structure is concurrent with major rivers in the region and we identify a new, potentially important biogeographic break coincident with several landscape features. Our data further suggests that niches occupied by species and populations differ substantially across their distribution. Paleodistribution modeling provide evidence that past climatic change could be responsible for the current distribution, population structure, and maintenance of species in Megistostegium.