Molecular dynamics investigations of drug-cell membrane interactions

2011 - 2012The cell membrane functions as a platform for the assembly of many signal transduction pathways and provides an additional level of regulation in cell signaling networks. The complex dynamic structure of the plasma membrane allows lipid–lipid and lipid–protein interactions, as well as the interaction of lipid–protein complexes with the submembrane cytoskeleton. The existence of membrane microdomains adds further complexity to such interactions, as well as the messages propagated in cells through G proteins and other non-permanent (extrinsic) membrane proteins. Each G protein can simultaneously bear a myristoyl, palmitoyl and isoprenyl moiety and therefore, many lipid molecules associated with G proteins may arise in G protein coupled receptor (GPCR)-rich membrane microdomains. These lipids can regulate the biophysical properties of membranes, which in turn modulate the interaction and activity of G proteins. The aim of the first part of my work was to understand the effect of these moieties on membrane structure and G protein-membrane interactions. Although recent studies found that the Gβγ dimer drives the interaction of G-proteins with nonlamellar-prone membranes, little is known about the molecular basis of this interaction. For this reason, I also investigated the interaction of the C-terminus of the Gγ protein with model membranes with or without the isoprenyl moieties. From the very beginning of my work, my studies have focused on the interaction of saturated and unsaturated fatty acids with cell membranes. Many of these molecules, in fact, have proven to be active against certain types of cancers and other diseases. Among all these molecules it is important to remember the Minerval, an analogue of oleic acid developed in the laboratory of Prof. Escribà, which has led to a reduction of up to 80% in the development of lung cancer and glioma cells. A promising molecule with high anti-inflammatory activity and synthesized by the group of Prof. Escribà like the previous one, is a modification of arachidonic acid: the 2-hydroxy arachidonic acid (AAOH). Due to the similarity with arachidonic acid (AA), that is the natural substrate of cyclooxygenase (COX), the second part of my work consisted in the investigation of the interaction of AAOH with COX-1 and COX-2. The results, in terms of free energy of binding and the Fukui function, demonstrated the potential of AAOH as non-toxic non-steroidal anti-inflammatory drug (NSAID). Recent findings pointed unambiguously to membranes as additional cellular sensors in activating a stress protein response, from prokaryotes to mammalian cells, at the beginning of temperature rise or other stresses. Aging or pathophysiological conditions can also be linked to the development of subtle membrane changes or “membrane-defects”, responsible for a dysregulated expression of heat shock proteins (HSPs). Chaperone co-inducers, among which can be mentioned the hydroxylamines such as BGP-15 and NG-094, are substances that cannot induce HSPs by itself, but can enhance HSP induction in combination with other mild stresses. A chaperone co-inducer also has the ability to lower the temperature threshold of the heat shock response and may provide suitable therapeutic candidates for many disease states since they are capable of affecting stressed rather than unstressed cells. The third part of my work consisted in molecular dynamics investigations of BGP-15 and NG-094 on membranes made of sphingomyelin and cholesterol at different composition to understand some aspects of membrane functioning. BGP-15 and NG-094 can induce an alteration in membrane’s fluidity similar to those induced by heat and a strong reorganization of sphingomyelin headgroups with an increased penetration of water. Taken together, all the results suggested that hydroxylamines have a strong effect on microdomains reorganization showing a great potential to become a new class of pharmaceuticals to combat most various protein-misfolding diseases and aging. All these investigations are relevant in the context of the physiology of cells, whose alterations may lead to pathologies whose treatment could be addressed by modifying membrane lipid composition and structure through so-called “Membrane-lipid therapy”. [edited by author]XI n.s

Two new catalogs of blazar candidates in the WISE infrared sky

We present two catalogs of radio-loud candidate blazars whose WISE mid-infrared colors are selected to be consistent with the colors of confirmed gamma-ray emitting blazars. The first catalog is the improved and expanded release of the WIBRaLS catalog presented by D'Abrusco et al. (2014): it includes sources detected in all four WISE filters, spatially cross-matched with radio source in one of three radio surveys and radio-loud based on their q22 spectral parameter. WIBRaLS2 includes 9541 sources classified as BL Lacs, FSRQs or mixed candidates based on their WISE colors. The second catalog, called KDEBLLACS, based on a new selection technique, contains 5579 candidate BL Lacs extracted from the population of WISE sources detected in the first three WISE passbands ([3.4], [4.6] and [12]) only, whose mid-infrared colors are similar to those of confirmed, gamma-ray BL Lacs. KDBLLACS members area also required to have a radio counterpart and be radio-loud based on the parameter q12, defined similarly to q22 used for the WIBRaLS2. We describe the properties of these catalogs and compare them with the largest samples of confirmed and candidate blazars in the literature. We crossmatch the two new catalogs with the most recent catalogs of gamma-ray sources detected by Fermi LAT instrument. Since spectroscopic observations of candidate blazars from the first WIBRaLS catalog within the uncertainty regions of gamma-ray unassociated sources confirmed that ~90% of these candidates are blazars, we anticipate that these new catalogs will play again an important role in the identification of the gamma-ray sky.Comment: 20 pages, 7 figures. Accepted for publication in The Astrophysical Journal Supplement Serie

Nonconvulsive Seizures and Dementia: A Case Report

Nonconvulsive status epilepticus (NCSE) is a severe medical condition that shows increased incidence in the elderly and is frequently underdiagnosed because of its pleomorphic presentation. We report an NCSE in a 76-year-old woman affected by dementia with acute change of cognitive status and behavior. Intravenous diazepam solved clinical and electroencephalographic manifestations. Neuropsychological assessment after NCSE conclusion showed impairment of several fields that remained unchanged at 3-month followup. NCSE should be considered when sudden and transient cognitive fluctuations appear in the elderly. Epileptic events in dementia occur frequently and are often underrecognized; this could be a misleading factor when considering a quick progression of mnesic performances. Moreover, recent findings both in animal models and in humans demonstrated the deep link between epilepsy and dementia, also supporting the hypothesis that epileptiform activity could contribute to cognitive impairment

Rapamycin Re-Directs Lysosome Network, Stimulates ER-Remodeling, Involving Membrane CD317 and Affecting Exocytosis, in Campylobacter Jejuni-Lysate-Infected U937 Cells.

The Gram-negative Campylobacter jejuni is a major cause of foodborne gastroenteritis in humans worldwide. The cytotoxic effects of Campylobacter have been mainly ascribed to the actions of the cytolethal distending toxin (CDT): it is mandatory to put in evidence risk factors for sequela development, such as reactive arthritis (ReA) and Guillain-Barré syndrome (GBS). Several researches are directed to managing symptom severity and the possible onset of sequelae. We found for the first time that rapamycin (RM) is able to largely inhibit the action of C. jejuni lysate CDT in U937 cells, and to partially avoid the activation of specific sub-lethal effects. In fact, we observed that the ability of this drug to redirect lysosomal compartment, stimulate ER-remodeling (highlighted by ER-lysosome and ER-mitochondria contacts), protect mitochondria network, and downregulate CD317/tetherin, is an important component of membrane microdomains. In particular, lysosomes are involved in the process of the reduction of intoxication, until the final step of lysosome exocytosis. Our results indicate that rapamycin confers protection against C. jejuni bacterial lysate insults to myeloid cells

Membrane-Lipid Therapy in Operation: The HSP Co-Inducer BGP-15 Activates Stress Signal Transduction Pathways by Remodeling Plasma Membrane Rafts

Aging and pathophysiological conditions are linked to membrane changes which modulate membrane-controlled molecular switches, causing dysregulated heat shock protein (HSP) expression. HSP co-inducer hydroxylamines such as BGP-15 provide advanced therapeutic candidates for many diseases since they preferentially affect stressed cells and are unlikely have major side effects. In the present study in vitro molecular dynamic simulation, experiments with lipid monolayers and in vivo ultrasensitive fluorescence microscopy showed that BGP-15 alters the organization of cholesterol-rich membrane domains. Imaging of nanoscopic long-lived platforms using the raft marker glycosylphosphatidylinositol-anchored monomeric green fluorescent protein diffusing in the live Chinese hamster ovary (CHO) cell plasma membrane demonstrated that BGP-15 prevents the transient structural disintegration of rafts induced by fever-type heat stress. Moreover, BGP-15 was able to remodel cholesterol-enriched lipid platforms reminiscent of those observed earlier following non-lethal heat priming or membrane stress, and were shown to be obligate for the generation and transmission of stress signals. BGP-15 activation of HSP expression in B16-F10 mouse melanoma cells involves the Rac1 signaling cascade in accordance with the previous observation that cholesterol affects the targeting of Rac1 to membranes. Finally, in a human embryonic kidney cell line we demonstrate that BGP-15 is able to inhibit the rapid heat shock factor 1 (HSF1) acetylation monitored during the early phase of heat stress, thereby promoting a prolonged duration of HSF1 binding to heat shock elements. Taken together, our results indicate that BGP-15 has the potential to become a new class of pharmaceuticals for use in ‘membrane-lipid therapy’ to combat many various protein-misfolding diseases associated with aging

Target genes, variants, tissues and transcriptional pathways influencing human serum urate levels.

Elevated serum urate levels cause gout and correlate with cardiometabolic diseases via poorly understood mechanisms. We performed a trans-ancestry genome-wide association study of serum urate in 457,690 individuals, identifying 183 loci (147 previously unknown) that improve the prediction of gout in an independent cohort of 334,880 individuals. Serum urate showed significant genetic correlations with many cardiometabolic traits, with genetic causality analyses supporting a substantial role for pleiotropy. Enrichment analysis, fine-mapping of urate-associated loci and colocalization with gene expression in 47 tissues implicated the kidney and liver as the main target organs and prioritized potentially causal genes and variants, including the transcriptional master regulators in the liver and kidney, HNF1A and HNF4A. Experimental validation showed that HNF4A transactivated the promoter of ABCG2, encoding a major urate transporter, in kidney cells, and that HNF4A p.Thr139Ile is a functional variant. Transcriptional coregulation within and across organs may be a general mechanism underlying the observed pleiotropy between urate and cardiometabolic traits.The Genotype-Tissue Expression (GTEx) Project was supported by the Common Fund of the Office of the Director of the National Institutes of Health, and by NCI, NHGRI, NHLBI, NIDA, NIMH, and NINDS. Variant annotation was supported by software resources provided via the Caché Campus program of the InterSystems GmbH to Alexander Teumer

Multi-messenger searches via IceCube’s high-energy neutrinos and gravitational-wave detections of LIGO/Virgo

We summarize initial results for high-energy neutrino counterpart searches coinciding with gravitational-wave events in LIGO/Virgo\u27s GWTC-2 catalog using IceCube\u27s neutrino triggers. We did not find any statistically significant high-energy neutrino counterpart and derived upper limits on the time-integrated neutrino emission on Earth as well as the isotropic equivalent energy emitted in high-energy neutrinos for each event