Oleic Acid Could Act as a Channel Blocker in the Inhibition of nAChR: Insights from Molecular Dynamics Simulations.

The activation of the muscular nicotinic acetylcholine receptor (nAChR) produces the opening of the channel, with the consequent increase in the permeability of cations, triggering an excitatory signal. Free fatty acids (FFA) are known to modulate the activity of the receptor as noncompetitive antagonists, acting at the membrane-AChR interface. We present molecular dynamics simulations of a model of nAChR in a desensitized closed state embedded in a lipid bilayer in which distinct membrane phospholipids were replaced by two different monounsaturated FFA that differ in the position of a double bond.

New Multitarget Molecules Derived from Caffeine as Potentiators of the Cholinergic System.

Cholinergic deficit is a characteristic factor of several pathologies, such as myasthenia gravis, some types of congenital myasthenic syndromes, and Alzheimer's Disease. Two molecular targets for its treatment are acetylcholinesterase (AChE) and nicotinic acetylcholine receptor (nAChR). In previous studies, we found that caffeine behaves as a partial nAChR agonist and confirmed that it inhibits AChE.

Carlos Gutiérrez-Merino: Synergy of Theory and Experimentation in Biological Membrane Research.

Professor Carlos Gutiérrez-Merino, a prominent scientist working in the complex realm of biological membranes, has made significant theoretical and experimental contributions to the field. Contemporaneous with the development of the fluid-mosaic model of Singer and Nicolson, the Förster resonance energy transfer (FRET) approach has become an invaluable tool for studying molecular interactions in membranes, providing structural insights on a scale of 1-10 nm and remaining important alongside evolving perspectives on membrane structures. In the last few decades, Gutiérrez-Merino's work has covered multiple facets in the field of FRET, with his contributions producing significant advances in quantitative membrane biology.

New Synthetic Caffeine Analogs as Modulators of the Cholinergic System.

Alzheimer's disease is a multifactorial neurodegenerative disorder. Since cholinergic deficit is a major factor in this disease, two molecular targets for its treatment are the acetylcholinesterase (AChE) and the nicotinic acetylcholine receptors (nAChRs). Given that caffeine is a natural compound that behaves as an AChE inhibitor and as a partial agonist of nAChRs, the aim of this work was to synthetize more potent bifunctional caffeine analogs that modulate these two molecular targets.

Cholesterol and desmosterol incorporation into ram sperm membrane before cryopreservation: Effects on membrane biophysical properties and sperm quality.

Ram sperm are particularly sensitive to freeze-thawing mainly due to their lipid composition, limiting their use in artificial insemination programs. We evaluated the extent of cholesterol and desmosterol incorporation into ram sperm through incubation with increasing concentrations of methyl-β-cyclodextrin (MβCD)-sterol complexes, and its effect on membrane biophysical properties, membrane lateral organization and cryopreservation outcome. Sterols were effectively incorporated into the sperm membrane at 10 and 25 mM MβCD-sterols, similarly increasing membrane lipid order at physiological temperature and during temperature decrease.

Alzheimer's Disease as a Membrane Disorder: Spatial Cross-Talk Among Beta-Amyloid Peptides, Nicotinic Acetylcholine Receptors and Lipid Rafts.

Biological membranes show lateral and transverse asymmetric lipid distribution. Cholesterol (Chol) localizes in both hemilayers, but in the external one it is mostly condensed in lipid-ordered microdomains (raft domains), together with saturated phosphatidyl lipids and sphingolipids (including sphingomyelin and glycosphingolipids). Membrane asymmetries induce special membrane biophysical properties and behave as signals for several physiological and/or pathological processes.

Molecular Modulation of Human α7 Nicotinic Receptor by Amyloid-β Peptides.

Amyloid β peptide (Aβ) is a key player in the development of Alzheimer's disease (AD). It is the primary component of senile plaques in AD patients and is also found in soluble forms. Cholinergic activity mediated by α7 nicotinic receptors has been shown to be affected by Aβ soluble forms.

A novel pharmacological activity of caffeine in the cholinergic system.

Cholinergic deficit is regarded as an important factor responsible for Alzheimer's disease (AD) symptoms. Acetylcholinesterase (AChE) and nicotinic receptor (AChR) are two molecular targets for the treatment of this disease. We found here that methanolic extracts of Camellia sinensis exhibited anticholinesterase activity and induced AChR conformational changes.

Membrane Restructuring Events during the Enzymatic Generation of Ceramides with Very Long-Chain Polyunsaturated Fatty Acids.

In rat sperm heads, sphingomyelin (SM) species that contain very long-chain polyunsaturated fatty acid (V-SM) become ceramides (V-Cer) after inducing in vitro the acrosomal reaction. The reason for such a specific location of this conversion, catalyzed by a sphingomyelinase (SMase), has received little investigation so far. Here, the effects of SMase were compared in unilamellar vesicles (large unilamellar vesicles (LUVs), giant unilamellar vesicles (GUVs)) containing phosphatidylcholine, and either V-SM or a palmitate-rich SM (P-SM).

Free cholesterol and cholesterol esters in bovine oocytes: Implications in survival and membrane raft organization after cryopreservation.

Part of the damage caused by cryopreservation of mammalian oocytes occurs at the plasma membrane. The addition of cholesterol to cell membranes as a strategy to make it more tolerant to cryopreservation has been little addressed in oocytes. In order to increase the survival of bovine oocytes after cryopreservation, we proposed not only to increase cholesterol level of oocyte membranes before vitrification but also to remove the added cholesterol after warming, thus recovering its original level.

Fatty Acid Regulation of Voltage- and Ligand-Gated Ion Channel Function.

Free fatty acids (FFA) are essential components of the cell, where they play a key role in lipid and carbohydrate metabolism, and most particularly in cell membranes, where they are central actors in shaping the physicochemical properties of the lipid bilayer and the cellular adaptation to the environment. FFA are continuously being produced and degraded, and a feedback regulatory function has been attributed to their turnover. The massive increase observed under some pathological conditions, especially in brain, has been interpreted as a protective mechanism possibly operative on ion channels, which in some cases is of stimulatory nature and in other cases inhibitory.

Phosphoinositides: Two-Path Signaling in Neuronal Response to Oligomeric Amyloid β Peptide.

We have previously demonstrated that oligomeric amyloid β peptide (oAβ) together with iron overload generates synaptic injury and activation of several signaling cascades. In this work, we characterized hippocampal neuronal response to oAβ. HT22 neurons exposed to 500 nM oAβ showed neither increased lipid peroxidation nor altered mitochondrial function.

Transbilayer asymmetry and sphingomyelin composition modulate the preferential membrane partitioning of the nicotinic acetylcholine receptor in Lo domains.

We have previously shown that the intact nicotinic acetylcholine receptor (AChR) lacks preference for Lo domains when reconstituted in a sphingomyelin (SM), cholesterol (Chol) and POPC (1:1:1) model system (Bermúdez V, Antollini SS, Fernández-Nievas GA, Aveldaño MI, Barrantes FJ. J. Lipid Res.

Lipid Biochemical and Biophysical Changes in Rat Spermatozoa During Isolation and Functional Activation In Vitro.

In spermatozoa isolated from rat epididymis, lipids are differentially modified after in vitro induction of capacitation (Cap) and the acrosomal reaction (AR). This study uses Laurdan fluorescence generalized polarization values (GPv) to evaluate the effect of lipid changes occurring after isolation and functional activation on sperm membrane biophysical properties. In gametes isolated in the presence of a divalent cation chelator, no lipid changes occurred and the GPv were the lowest recorded, indicating maximal membrane lipid mobility.

Study of the influence of ascorbyl palmitate and amiodarone in the stability of unilamellar liposomes.

Amiodarone (AMI) is a low water-solubility drug, which is very useful in the treatment of severe cardiac disease. Its adverse effects are associated with toxicity in different tissues. Several antioxidants have been shown to reduce, and prevent AMI toxicity.

Atypical surface behavior of ceramides with nonhydroxy and 2-hydroxy very long-chain (C28-C32) PUFAs.

Unique species of ceramide (Cer) with very-long-chain polyunsaturated fatty acid (VLCPUFA), mainly 28-32 carbon atoms, 4-5 double bonds, in nonhydroxy and 2-hydroxy forms (n-V Cer and h-V Cer, respectively), are generated in rat spermatozoa from the corresponding sphingomyelins during the acrosomal reaction. The aim of this study was to determine the properties of these sperm-distinctive ceramides in Langmuir monolayers. Individual Cer species were isolated by HPLC and subjected to analysis of surface pressure, surface potential, and Brewster angle microscopy (BAM) as a function of molecular packing.

Unique thermal behavior of sphingomyelin species with nonhydroxy and 2-hydroxy very-long-chain (C28-C32) PUFAs.

In rat germ cells and spermatozoa, sphingomyelin (SM) contains molecular species with nonhydroxy (n) and 2-hydroxy (h) very-long-chain polyunsaturated fatty acids (V), the most abundant being SMs with (n- and h-) 28:4n-6, 30:5n-6, and 32:5n-6 as acyl chains. The aim of this study was to gain information about their thermotropic behavior and interactions with other lipids. After isolation from rat testis, multilamellar and giant unilamellar vesicles from these SMs were examined using fluorescent probes.

The position of the double bond in monounsaturated free fatty acids is essential for the inhibition of the nicotinic acetylcholine receptor.

Free fatty acids (FFAs) are non-competitive antagonists of the nicotinic acetylcholine receptor (AChR). Their site of action is supposedly located at the lipid-AChR interface. To elucidate the mechanism involved in this antagonism, we studied the effect that FFAs with a single double-bond at different positions (ω6, ω9, ω11 and ω13 cis-18:1) have on different AChR properties.

alpha 7-type acetylcholine receptor localization and its modulation by nicotine and cholesterol in vascular endothelial cells.

The neuronal-type α7 nicotinic acetylcholine receptor (α7AChR) is also found in various non-neural tissues, including vascular endothelium, where its peculiar ionotropic properties (high Ca(2+) permeability) and its supervening Ca(2+) -mediated intracellular cascades may play important roles in physiology (angiogenesis) and pathology (inflammation and atherogenesis). Changes in molecular (up-regulation, affinity, and conformational states) and cellular (distribution, association with membranes) properties of the α7AChR related to angiogenesis (wound-repair cell migration) and atherogenesis (alterations in cholesterol content) were studied in living endothelial cells, with the aim of determining whether such changes constitute early markers of inflammatory response. The combination of pharmacological, biochemical, and fluorescence microscopy tools showed that α7AChRs in rat arterial endothelial (RAEC) and human venous endothelial (HUVEC) cells occur at extremely low expression levels (∼50 fmol/mg protein) but undergo agonist-induced up-regulation at relatively high nicotine concentrations (∼300-fold with 50 µM ligand), increasing their cell-surface exposure.

Nongenomic steroid- and ceramide-induced maturation in amphibian oocytes involves functional caveolae-like microdomains associated with a cytoskeletal environment.

Stimulation of full-grown amphibian oocytes with progesterone initiates a nontranscriptional signaling pathway that converges in the activation of Cdc2/cyclin B and reentry into meiosis. We observed that cholesterol depletion mediated by methyl-beta-cyclodextrin (MbetaCD) inhibited meiotic maturation, suggesting involvement of membrane rafts. In the present study, we further characterized caveolae-like membranes from Rhinella arenarum oocytes biochemically and functionally.

Partition profile of the nicotinic acetylcholine receptor in lipid domains upon reconstitution.

The nicotinic acetylcholine receptor (AChR) is in intimate contact with the lipids in its native membrane. Here we analyze the possibility that it is the intrinsic properties of the AChR that determine its partition into a given lipid domain. Torpedo AChR or a synthetic peptide corresponding to the AChR M4 segment (the one in closer contact with lipids) was reconstituted into "raft"-containing model membranes.

A novel agonist effect on the nicotinic acetylcholine receptor exerted by the anticonvulsive drug Lamotrigine.

The anticonvulsive drug Lamotrigine (LTG) is found to activate adult muscle nicotinic acetylcholine receptors (AChR). Single-channel patch-clamp recordings showed that LTG (0.05-400 microM) applied alone is able to open AChR channels.

Modulation of nicotinic acetylcholine receptor conformational state by free fatty acids and steroids.

Steroids and free fatty acids (FFA) are noncompetitive antagonists of the nicotinic acetylcholine receptor (AChR). Their site of action is purportedly located at the lipid-AChR interface, but their exact mechanism of action is still unknown. Here we studied the effect of structurally different FFA and steroids on the conformational equilibrium of the AChR in Torpedo californica receptor-rich membranes.

Laurdan studies of membrane lipid-nicotinic acetylcholine receptor protein interactions.

The extrinsic fluorescent probe Laurdan (6-dodecanoyl-2-dimethylamino naphthalene) exhibits extreme sensitivity to the polarity and to the molecular dynamics of the dipoles in its environment. Dipolar relaxation processes are reflected as relatively large spectral shifts. Steady-state measurements of the so-called general polarization (GP) of Laurdan exploit the advantageous spectral properties of Laurdan.

Very long-chain polyunsaturated fatty acids are the major acyl groups of sphingomyelins and ceramides in the head of mammalian spermatozoa.

Very long-chain (C24 to C34) polyunsaturated fatty acids (VLCPUFA) are important constituents of sphingomyelin (SM) and ceramide (Cer) in testicular germ cells. In the present paper we focused on the SM and Cer and their fatty acids in spermatozoa and their main regions, heads and tails. In bull and ram spermatozoa, SM was the third most abundant phospholipid and VLCPUFA were the major acyl groups ( approximately 70%) of SM and Cer.