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1.
The Transporter-Mediated Cellular Uptake and Efflux of Pharmaceutical Drugs and Biotechnology Products: How and Why Phospholipid Bilayer Transport Is Negligible in Real Biomembranes.
Kell, DB
Molecules (Basel, Switzerland). 2021;(18)
Abstract
Over the years, my colleagues and I have come to realise that the likelihood of pharmaceutical drugs being able to diffuse through whatever unhindered phospholipid bilayer may exist in intact biological membranes in vivo is vanishingly low. This is because (i) most real biomembranes are mostly protein, not lipid, (ii) unlike purely lipid bilayers that can form transient aqueous channels, the high concentrations of proteins serve to stop such activity, (iii) natural evolution long ago selected against transport methods that just let any undesirable products enter a cell, (iv) transporters have now been identified for all kinds of molecules (even water) that were once thought not to require them, (v) many experiments show a massive variation in the uptake of drugs between different cells, tissues, and organisms, that cannot be explained if lipid bilayer transport is significant or if efflux were the only differentiator, and (vi) many experiments that manipulate the expression level of individual transporters as an independent variable demonstrate their role in drug and nutrient uptake (including in cytotoxicity or adverse drug reactions). This makes such transporters valuable both as a means of targeting drugs (not least anti-infectives) to selected cells or tissues and also as drug targets. The same considerations apply to the exploitation of substrate uptake and product efflux transporters in biotechnology. We are also beginning to recognise that transporters are more promiscuous, and antiporter activity is much more widespread, than had been realised, and that such processes are adaptive (i.e., were selected by natural evolution). The purpose of the present review is to summarise the above, and to rehearse and update readers on recent developments. These developments lead us to retain and indeed to strengthen our contention that for transmembrane pharmaceutical drug transport "phospholipid bilayer transport is negligible".
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2.
Roles for Selenoprotein I and Ethanolamine Phospholipid Synthesis in T Cell Activation.
Ma, C, Martinez-Rodriguez, V, Hoffmann, PR
International journal of molecular sciences. 2021;(20)
Abstract
The selenoprotein family includes 25 members, many of which are antioxidant or redox regulating enzymes. A unique member of this family is Selenoprotein I (SELENOI), which does not catalyze redox reactions, but instead is an ethanolamine phosphotransferase (Ept). In fact, the characteristic selenocysteine residue that defines selenoproteins lies far outside of the catalytic domain of SELENOI. Furthermore, data using recombinant SELENOI lacking the selenocysteine residue have suggested that the selenocysteine amino acid is not directly involved in the Ept reaction. SELENOI is involved in two different pathways for the synthesis of phosphatidylethanolamine (PE) and plasmenyl PE, which are constituents of cellular membranes. Ethanolamine phospholipid synthesis has emerged as an important process for metabolic reprogramming that occurs in pluripotent stem cells and proliferating tumor cells, and this review discusses roles for upregulation of SELENOI during T cell activation, proliferation, and differentiation. SELENOI deficiency lowers but does not completely diminish de novo synthesis of PE and plasmenyl PE during T cell activation. Interestingly, metabolic reprogramming in activated SELENOI deficient T cells is impaired and this reduces proliferative capacity while favoring tolerogenic to pathogenic phenotypes that arise from differentiation. The implications of these findings are discussed related to vaccine responses, autoimmunity, and cell-based therapeutic approaches.
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3.
From Bench to Biomolecular Simulation: Phospholipid Modulation of Potassium Channels.
Pipatpolkai, T, Quetschlich, D, Stansfeld, PJ
Journal of molecular biology. 2021;(17):167105
Abstract
Potassium (K+) ion channels are crucial in numerous cellular processes as they hyperpolarise a cell through K+ conductance, returning a cell to its resting potential. K+ channel mutations result in multiple clinical complications such as arrhythmia, neonatal diabetes and migraines. Since 1995, the regulation of K+ channels by phospholipids has been heavily studied using a range of interdisciplinary methods such as cellular electrophysiology, structural biology and computational modelling. As a result, K+ channels are model proteins for the analysis of protein-lipid interactions. In this review, we will focus on the roles of lipids in the regulation of K+ channels, and how atomic-level structures, along with experimental techniques and molecular simulations, have helped guide our understanding of the importance of phospholipid interactions.
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4.
Transferosomes as nanocarriers for drugs across the skin: Quality by design from lab to industrial scale.
Fernández-García, R, Lalatsa, A, Statts, L, Bolás-Fernández, F, Ballesteros, MP, Serrano, DR
International journal of pharmaceutics. 2020;:118817
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Abstract
Transferosomes, also known as transfersomes, are ultradeformable vesicles for transdermal applications consisting of a lipid bilayer with phospholipids and an edge activator and an ethanol/aqueous core. Depending on the lipophilicity of the active substance, it can be encapsulated within the core or amongst the lipid bilayer. Compared to liposomes, transferosomes are able to reach intact deeper regions of the skin after topical administration delivering higher concentrations of active substances making them a successful drug delivery carrier for transdermal applications. Most transferosomes contain phosphatidylcholine (C18) as it is the most abundant lipid component of the cell membrane, and hence, it is highly tolerated for the skin, decreasing the risk of undesirable effects, such as hypersensitive reactions. The most common edge activators are surfactants such as sodium deoxycholate, Tween® 80 and Span® 80. Their chain length is optimal for intercalation within the C18 phospholipid bilayer. A wide variety of drugs has been successfully encapsulated within transferosomes such as phytocompounds like sinomenine or apigenin for rheumatoid arthritis and leukaemia respectively, small hydrophobic drugs but also macromolecules like insulin. The main factors to develop optimal transferosomal formulations (with high drug loading and nanometric size) are the optimal ratio between the main components as well as the critical process parameters for their manufacture. Application of quality by design (QbD), specifically design of experiments (DoE), is crucial to understand the interplay among all these factors not only during the preparation at lab scale but also in the scale-up process. Clinical trials of a licensed topical ketoprofen transferosomal gel have shown promising results in the alleviation of symptons in orthreothritis with non-severe skin and subcutaneous tissue disorders. However, the product was withdrawn from the market which probably was related to the higher cost of the medicine linked to the expensive manufacturing process required in the production of transferosomes compared to other conventional gel formulations. This example brings out the need for a careful formulation design to exploit the best properties of this drug delivery system as well as the development of manufacturing processes easily scalable at industrial level.
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Myocardial contrast echocardiography in the diagnosis of postoperative takotsubo myocardiopathy: case report and literature review.
Zeng, JH, Li, W, Yao, FJ, Liu, DH, Li, CL, Liu, YQ, Fan, R, Ye, M, Lin, H
BMC cardiovascular disorders. 2019;(1):9
Abstract
BACKGROUND Takotsubo cardiomyopathy (TCM) is a brief ventricular dysfunction that usually occurs after emotional or physical stress. Here, we report a patient who underwent cardiac surgery and then developed TCM during the postoperative period. CASE PRESENTATION A 51-year-old woman was admitted to our hospital complaining of chest tightness, palpitations and dyspnoea after activity. An echocardiogram performed by our hospital showed rheumatic heart disease (severe mitral stenosis and regurgitation) with normal cardiac function and wall motion. After mitral valve replacement, this patient developed heart failure with low blood pressure and tachycardia. Urgent bedside echocardiography demonstrated akinesis in the middle and apical segments of the left ventricle and a depressed ejection fraction (EF) of 36%. Myocardial contrast echocardiography (MCE) showed similar enhancement intensity in the basal, middle and apical segments. Quantitative analysis showed approximately equivalent maximum intensity in these regions. The diagnosis was considered TCM instead of myocardial infarction. Then, an intra-aortic balloon pump was inserted to maintain effective circulation and reduce the postcardiac load. Given ventilation therapy, postoperative anticoagulation therapy and anti-infection treatment, the patient recovered quickly. In the follow-up examination, the patient remained asymptomatic and showed normalization of ventricular wall motion in the apical segment. CONCLUSION This report presents a case of TCM in which MCE was used to demonstrate intact microvascular perfusion despite apical akinesis. This report might support the use of MCE as a substitute for invasive coronary angiography.
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6.
Lipid trafficking across the Gram-negative cell envelope.
Shrivastava, R, Chng, SS
The Journal of biological chemistry. 2019;(39):14175-14184
Abstract
The outer membrane (OM) of Gram-negative bacteria exhibits unique lipid asymmetry, with lipopolysaccharides (LPS) residing in the outer leaflet and phospholipids (PLs) in the inner leaflet. This asymmetric bilayer protects the bacterium against intrusion of many toxic substances, including antibiotics and detergents, yet allows acquisition of nutrients necessary for growth. To build the OM and ensure its proper function, the cell produces OM constituents in the cytoplasm or inner membrane and transports these components across the aqueous periplasmic space separating the two membranes. Of note, the processes by which the most basic membrane building blocks, i.e. PLs, are shuttled across the cell envelope remain elusive. This review highlights our current understanding (or lack thereof) of bacterial PL trafficking, with a focus on recent developments in the field. We adopt a mechanistic approach and draw parallels and comparisons with well-characterized systems, particularly OM lipoprotein and LPS transport, to illustrate key challenges in intermembrane lipid trafficking. Pathways that transport PLs across the bacterial cell envelope are fundamental to OM biogenesis and homeostasis and are potential molecular targets that could be exploited for antibiotic development.
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7.
The ins and outs of Ca2+ in plant endomembrane trafficking.
Himschoot, E, Pleskot, R, Van Damme, D, Vanneste, S
Current opinion in plant biology. 2017;:131-137
Abstract
Trafficking of proteins and lipids within the plant endomembrane system is essential to support cellular functions and is subject to rigorous regulation. Despite this seemingly strict regulation, endomembrane trafficking needs to be dynamically adjusted to ever-changing internal and environmental stimuli, while maintaining cellular integrity. Although often overlooked, the versatile second messenger Ca2+ is intimately connected to several endomembrane-associated processes. Here, we discuss the impact of electrostatic interactions between Ca2+ and anionic phospholipids on endomembrane trafficking, and illustrate the direct role of Ca2+ sensing proteins in regulating endomembrane trafficking and membrane integrity preservation. Moreover, we discuss how Ca2+ can control protein sorting within the plant endomembrane system. We thus highlight Ca2+ signaling as a versatile mechanism by which numerous signals are integrated into plant endomembrane trafficking dynamics.
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8.
The role of human phospholipid scramblases in apoptosis: An overview.
Sivagnanam, U, Palanirajan, SK, Gummadi, SN
Biochimica et biophysica acta. Molecular cell research. 2017;(12):2261-2271
Abstract
Human phospholipid scramblases (hPLSCRs) are a family of four homologous single pass transmembrane proteins (hPLSCR1-4) initially identified as the proteins responsible for Ca2+ mediated bidirectional phospholipid translocation in plasma membrane. Though in-vitro assays had provided evidence, the role of hPLSCRs in phospholipid translocation is still debated. Recent reports revealed a new class of proteins, TMEM16 and Xkr8 to exhibit scramblase activity challenging the function of hPLSCRs. Apart from phospholipid scrambling, numerous reports have emphasized the multifunctional roles of hPLSCRs in key cellular processes including tumorigenesis, antiviral defense, protein and DNA interactions, transcriptional regulation and apoptosis. In this review, the role of hPLSCRs in mediating cell death through phosphatidylserine exposure, interaction with death receptors, cardiolipin exposure, heavy metal and radiation induced apoptosis and pathological apoptosis followed by their involvement in cancer cells are discussed. This review aims to connect the multifunctional characteristics of hPLSCRs to their decisive involvement in apoptotic pathways.
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9.
Alkylphospholipids: An update on molecular mechanisms and clinical relevance.
Ríos-Marco, P, Marco, C, Gálvez, X, Jiménez-López, JM, Carrasco, MP
Biochimica et biophysica acta. Biomembranes. 2017;(9 Pt B):1657-1667
Abstract
Alkylphospholipids (APLs) represent a new class of drugs which do not interact directly with DNA but act on the cell membrane where they accumulate and interfere with lipid metabolism and signalling pathways. This review summarizes the mode of action at the molecular level of these compounds. In this sense, a diversity of mechanisms has been suggested to explain the actions of clinically-relevant APLs, in particular, in cancer treatment. One consistently reported finding is that APLs reduce the biosynthesis of phosphatidylcholine (PC) by inhibiting the rate-limiting enzyme CTP:phosphocholine cytidylyltransferase (CT). APLs also alter intracellular cholesterol traffic and metabolism in human tumour-cell lines, leading to an accumulation of cholesterol inside the cell. An increase in cholesterol biosynthesis associated with a decrease in the synthesis of choline-containing phospholipids and cholesterol esterification leads to a change in the free-cholesterol:PC ratio in cells exposed to APLs. Akt phosphorylation status after APL exposure shows that this critical regulator for cell survival is modulated by changes in cholesterol levels induced in the plasma membrane by these lipid analogues. Furthermore, APLs produce cell ultrastructural alterations with an abundant autophagic vesicles and autolysosomes in treated cells, indicating an interference of autophagy process after APL exposure. Thus, antitumoural APLs interfere with the proliferation of tumour cells via a complex mechanism involving phospholipid and cholesterol metabolism, interfere with lipid-dependent survival-signalling pathways and autophagy. Although APLs also exert antiparasitic, antibacterial, and antifungal effects, in this review we provide a summary of the antileishmanial activity of these lipid analogues. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.
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Oral and I.V. contrast enhanced ultrasonography of the digestive tract--a useful completion of the B-mode examination: a literature review and an exhaustive illustration through images.
Neciu, C, Badea, R, Chiorean, L, Badea, AF, Opincariu, I
Medical ultrasonography. 2015;(1):62-73
Abstract
Contrast enhanced ultrasonography, using i.v. and/or oral/rectal contrast agents, represents a technical development of the US method, which has proved its applicability in the qualitative and quantitative assessment of the normal and pathological circulatory bed, as well as of the digestive lumen. The use of microbubbles and harmonics opens a new horizon in the detection and characterization of the inflammatory and tumoral conditions of the digestive tract. The interpretation of the data requires corroboration with the grey scale aspect of the examined lesion/area, as well as with the clinical context of the case and the results of other diagnosis techniques. The purpose of this paper is to review the main applications of CEUS in digestive tract pathology by analyzing the significant literature and guidelines in the light of our personal experience and demonstrating it through suggestive images.