Screening polyoxometalates as aquaporin inhibitors for cancer therapeutics

Aquaporins (AQPs) are transmembrane protein channels that facilitate the diffusion of water and glycerol across cell membranes, crucial for water and energy homeostasis. These proteins were found overexpressed in different cancer cells and tissues, being involved in cell proliferation and migration, tumor formation, and angiogenesis, suggesting their great potential as novel drug targets for cancer treatment. Identification of potent and selective aquaporin inhibitors to be used in cancer therapeutics is of utmost importance. Polyoxometalates (POMs) are transition metal complexes that exhibit a broad diversity of structures and properties.info:eu-repo/semantics/publishedVersio

Insights into solute carriers: physiological functions and implications in disease and pharmacokinetics

SLCs transport many endogenous and exogenous compounds including drugs; SLCs dysfunction has implications in pharmacokinetics, drug toxicity or lack of efficacy

Differential mesenteric fat deposition in bovines fed on silage or concentrate is independent of glycerol membrane permeability

© The Animal Consortium 2011In the meat industry, the manipulation of fat deposition in cattle is of pivotal importance to improve production efficiency, carcass composition and ultimately meat quality. There is an increasing interest in the identification of key factors and molecular mechanisms responsible for the development of specific fat depots. This study aimed at elucidating the influence of breed and diet on adipose tissue membrane permeability and fluidity and their interplay on fat deposition in bovines. Two Portuguese autochthonous breeds, Alentejana and Barrosã, recognized as late- and early-maturing breeds, respectively, were chosen to examine the effects of breed and diet on fat deposition and on adipose membrane composition and permeability. Twenty-four male bovines from these breeds were fed on silage-based or concentrate-based diets for 11 months. Animals were slaughtered to determine their live slaughter and hot carcass weights, as well as weights of subcutaneous and visceral adipose depots. Mesenteric fat depots were excised and used to isolate adipocyte membrane vesicles where cholesterol content, fatty acid profile as well as permeability and fluidity were determined. Total accumulation of neither subcutaneous nor visceral fat was influenced by breed. In contrast, mesenteric and omental fat depots weights were higher in concentrate-fed bulls relative to silage-fed animals. Membrane fluidity and permeability to water and glycerol in mesenteric adipose tissue were found to be independent of breed and diet. Moreover, the deposition of cholesterol and unsaturated fatty acids, which may influence membrane properties, were unchanged among experimental groups. Adipose membrane lipids from the mesenteric fat depot of ruminants were rich in saturated fatty acids, and unaffected by polyunsaturated fatty acids dietary levels. Our results provide evidence against the involvement of cellular membrane permeability to glycerol on fat accumulation in mesenteric fat tissue of concentrate-fed bovines, which is consistent with the unchanged membrane lipid profile found among experimental groups.This study was supported by Fundação para a Ciência e a Tecnologia (FCT) through grant PTDC/CVT/2006/66114 and individual fellowships to Ana P. Martins (SFRH/BD/2009/65046), Ana S. H. Costa (SFRH/BD/2009/61068) and Susana V. Martins (SFRH/BPD/2009/63019). Paula A. Lopes is a researcher from the program ‘‘Ciência 2008’’ from FC

Targeting Aquaporin Function:Potent Inhibition of Aquaglyceroporin-3 by a Gold-Based Compound

Aquaporins (AQPs) are membrane channels that conduct water and small solutes such as glycerol and are involved in many physiological functions. Aquaporin-based modulator drugs are predicted to be of broad potential utility in the treatment of several diseases. Until today few AQP inhibitors have been described as suitable candidates for clinical development. Here we report on the potent inhibition of AQP3 channels by gold(III) complexes screened on human red blood cells (hRBC) and AQP3-transfected PC12 cells by a stopped-flow method. Among the various metal compounds tested, Auphen is the most active on AQP3 (IC(50) = 0.8±0.08 µM in hRBC). Interestingly, the compound poorly affects the water permeability of AQP1. The mechanism of gold inhibition is related to the ability of Au(III) to interact with sulphydryls groups of proteins such as the thiolates of cysteine residues. Additional DFT and modeling studies on possible gold compound/AQP adducts provide a tentative description of the system at a molecular level. The mapping of the periplasmic surface of an homology model of human AQP3 evidenced the thiol group of Cys40 as a likely candidate for binding to gold(III) complexes. Moreover, the investigation of non-covalent binding of Au complexes by docking approaches revealed their preferential binding to AQP3 with respect to AQP1. The high selectivity and low concentration dependent inhibitory effect of Auphen (in the nanomolar range) together with its high water solubility makes the compound a suitable drug lead for future in vivo studies. These results may present novel metal-based scaffolds for AQP drug development

Leptin administration restores the altered adipose and hepatic expression of aquaglyceroporins improving the non-alcoholic fatty liver of ob/ob mice

Glycerol is an important metabolite for the control of lipid accumulation in white adipose tissue (WAT) and liver. We aimed to investigate whether exogenous administration of leptin improves features of non-alcoholic fatty liver disease (NAFLD) in leptin-deficient ob/ob mice via the regulation of AQP3 and AQP7 (glycerol channels mediating glycerol efflux in adipocytes) and AQP9 (aquaglyceroporin facilitating glycerol influx in hepatocytes). Twelve-week-old male wild type and ob/ob mice were divided in three groups as follows: control, leptin-treated (1 mg/kg/d) and pair-fed. Leptin deficiency was associated with obesity and NAFLD exhibiting an AQP3 and AQP7 increase in WAT, without changes in hepatic AQP9. Adipose Aqp3 and and hepatic Aqp9 transcripts positively correlated with markers of adiposity and hepatic steatosis. Chronic leptin administration (4 weeks) was associated with improved body weight, whole-body adiposity, and hepatosteatosis of ob/ob mice and to a down-regulation of AQP3, AQP7 in WAT and an up-regulation of hepatic AQP9. Acute leptin stimulation in vitro (4 h) induced the mobilization of aquaglyceroporins towards lipid droplets (AQP3) and the plasma membrane (AQP7) in murine adipocytes. Our results show that leptin restores the coordinated regulation of the fat-specific AQP7 and the liver-specific AQP9, a step which might prevent the lipid overaccumulation in WAT and liver in obesity

Assessment of Haemodynamic Remodeling in Fetal Aortic Coarctation Using a Lumped Model of the Circulation

Introduction: Aortic coarctation is one of the most difficult cardiac defects to diagnose before birth, and it accounts for 8% of congenital heart diseases. Antenatal diagnosis is crucial for early treatment of the neonate and to decrease the risk of morbidity and mortality; however the fetal hemodynamic changes are not fully understood and current imaging methods are limited to accurately diagnosis this congenital defect. Objective: We propose to use a lumped model of the fetal circulation to provide insights into the hemodynamic changes in fetuses with aortic coarctation, and thus helping to improve its diagnosis. Methods: To achieve this goal a patient-specific lumped model of the fetal circulation was implemented in OpenCOR, including the modeling of different types and degrees of aortic coarctation. A parametric study of degree and type of coarctation was performed, where blood flow distribution, cerebroplacental ratio, pressure drop over the coarctation and left ventricular pressure were quantified. Results: Obvious changes in the fetal hemodynamics were observed only from 80% of coarctation, corresponding to the clinically used cut-off for pressure drop of 20 mmHg. Furthermore, the observed hemodynamic changes were different depending on the location and degree of the coarctation

The grapevine uncharacterized intrinsic protein 1 (VvXIP1) is regulated by drought stress and transports glycerol, hydrogen peroxide, heavy metals but not water

A MIP (Major Intrinsic Protein) subfamily called Uncharacterized Intrinsic Proteins (XIP) was recently described in several fungi and eudicot plants. In this work, we cloned a XIP from grapevine, VvXIP1, and agrobacterium-mediated transformation studies in Nicotiana benthamiana revealed that the encoded aquaporin shows a preferential localization at the endoplasmic reticulum membrane. Stopped-flow spectrometry in vesicles from the aqy-null yeast strain YSH1172 overexpressing VvXIP1 showed that VvXIP1 is unable to transport water but is permeable to glycerol. Functional studies with the ROS sensitive probe CM-H(2)DCFDA in intact transformed yeasts showed that VvXIP1 is also able to permeate hydrogen peroxide (H2O2). Drop test growth assays showed that besides glycerol and H2O2, VvXIP1 also transports boric acid, copper, arsenic and nickel. Furthermore, we found that VvXIP1 transcripts were abundant in grapevine leaves from field grown plants and strongly repressed after the imposition of severe water-deficit conditions in potted vines. The observed downregulation of VvXIP1 expression in cultured grape cells in response to ABA and salt, together with the increased sensitivity to osmotic stress displayed by the aqy-null yeast overexpressing VvXIP1, corroborates the role of VvXIP1 in osmotic regulation besides its involvement in H2O2 transport and metal homeostasis.This work was supported by European Union Funds (FEDER/COMPETE Operational Competitiveness Programme) and Portuguese national Funds (FCT-Portuguese Foundation for Science and Technology): KBBE-2012-6-3117 "Inovinne", FCOMP-01-0124-FEDER-022692 and PTDC/AGR-ALI/100636/2008. HN (SFRH/BD/74257/2010) and APM (SFRH/BD/65046/2009) were supported by PhD grants from FCT. The Interuniversity Attraction Poles Programme-Belgian Science Policy (IAP7/29) and the Belgian French community ARC11/16-036 project.info:eu-repo/semantics/publishedVersio

Exploring the three PIPs and three TIPs of grapevine for transport of water and atypical substrates through heterologous expression in aqy-null yeast

Aquaporins are membrane channels that facilitate the transport of water and other small molecules across the cellular membranes. We examined the role of six aquaporins of Vitis vinifera (cv. Touriga nacional) in the transport of water and atypical substrates (other than water) in an aqy-null strain of Saccharomyces cerevisiae. Their functional characterization for water transport was performed by stopped-flow fluorescence spectroscopy. The evaluation of permeability coefficients (Pf) and activation energies (Ea) revealed that three aquaporins (VvTnPIP2;1, VvTnTIP1;1 and VvTnTIP2;2) are functional for water transport, while the other three (VvTnPIP1;4, VvTnPIP2;3 and VvTnTIP4;1) are non-functional. TIPs (VvTnTIP1;1 and VvTnTIP2;2) exhibited higher water permeability than VvTnPIP2;1. All functional aquaporins were found to be sensitive to HgCl2, since their water conductivity was reduced (24–38%) by the addition of 0.5 mM HgCl2. Expression of Vitis aquaporins caused different sensitive phenotypes to yeast strains when grown under hyperosmotic stress generated by KCl or sorbitol. Our results also indicate that Vitis aquaporins are putative transporters of other small molecules of physiological importance. Their sequence analyses revealed the presence of signature sequences for transport of ammonia, boron, CO2, H2O2 and urea. The phenotypic growth variations of yeast cells showed that heterologous expression of Vitis aquaporins increased susceptibility to externally applied boron and H2O2, suggesting the contribution of Vitis aquaporins in the transport of these speciesinfo:eu-repo/semantics/publishedVersio

An atherogenic diet disturbs aquaporin 5 expression in liver and adipocyte tissues of apolipoprotein e-deficient mice: new insights into an old model of experimental atherosclerosis

The dysfunction of vascular endothelial cells is profoundly implicated in the pathogenesis of atherosclerosis and cardiovascular disease, the global leading cause of death. Aquaporins (AQPs) are membrane channels that facilitate water and glycerol transport across cellular membranes re-cently implicated in the homeostasis of the cardiovascular system. Apolipoprotein-E deficient (apoE−/−) mice are a common model to study the progression of atherosclerosis. Nevertheless, the pattern of expression of AQPs in this atheroprone model is poorly characterized. In this study, apoE−/− mice were fed an atherogenic high-fat (HF) or a control diet. Plasma was collected at multiple time points to assess metabolic disturbances. At the endpoint, the aortic atherosclerotic burden was quantified using high field magnetic resonance imaging. Moreover, the transcriptional levels of several AQP isoforms were evaluated in the liver, white adipocyte tissue (WAT), and brown adipocyte tissue (BAT). The results revealed that HF-fed mice, when compared to controls, presented an ex-acerbated systemic inflammation and atherosclerotic phenotype, with no major differences in systemic methylation status, circulating amino acids, or plasma total glutathione. Moreover, an over-expression of the isoform AQP5 was detected in all studied tissues from HF-fed mice when compared to controls. These results suggest a novel role for AQP5 on diet-induced atherosclerosis that warrants further investigation

Crystal Structure of a Yeast Aquaporin at 1.15 Å Reveals a Novel Gating Mechanism

Atomic-resolution X-ray crystallography, functional analyses, and molecular dynamics simulations suggest a novel mechanism for the regulation of water flux through the yeast Aqy1 water channel