Cholesterol depletion of human immunodeficiency virus type 1 and simian immunodeficiency virus with beta-cyclodextrin inactivates and permeabilizes the virions: evidence for virion-associated lipid rafts

Help or Hinder: Protein Host Factors That Impact HIV-1 Replication

Interactions between human immunodeficiency virus type 1 (HIV-1) and the host factors or restriction factors of its target cells determine the cell's susceptibility to, and outcome of, infection. Factors intrinsic to the cell are involved at every step of the HIV-1 replication cycle, contributing to productive infection and replication, or severely attenuating the chances of success. Furthermore, factors unique to certain cell types contribute to the differences in infection between these cell types. Understanding the involvement of these factors in HIV-1 infection is a key requirement for the development of anti-HIV-1 therapies. As the list of factors grows, and the dynamic interactions between these factors and the virus are elucidated, comprehensive and up-to-date summaries that recount the knowledge gathered after decades of research are beneficial to the field, displaying what is known so that researchers can build off the groundwork of others to investigate what is unknown. Herein, we aim to provide a review focusing on protein host factors, both well-known and relatively new, that impact HIV-1 replication in a positive or negative manner at each stage of the replication cycle, highlighting factors unique to the various HIV-1 target cell types where appropriate.

Hydroxypropyl-Beta Cyclodextrin Barrier Prevents Respiratory Viral Infections: A Preclinical Study

The emergence and mutation of pathogenic viruses have been occurring at an unprecedented rate in recent decades. The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has developed into a global public health crisis due to extensive viral transmission. In situ RNA mapping has revealed angiotensin-converting enzyme 2 (ACE2) expression to be highest in the nose and lower in the lung, pointing to nasal susceptibility as a predominant route for infection and the cause of subsequent pulmonary effects. By blocking viral attachment and entry at the nasal airway using a cyclodextrin-based formulation, a preventative therapy can be developed to reduce viral infection at the site of entry. Here, we assess the safety and antiviral efficacy of cyclodextrin-based formulations. From these studies, hydroxypropyl beta-cyclodextrin (HPBCD) and hydroxypropyl gamma-cyclodextrin (HPGCD) were then further evaluated for antiviral effects using SARS-CoV-2 pseudotypes. Efficacy findings were confirmed with SARS-CoV-2 Delta variant infection of Calu-3 cells and using a K18-hACE2 murine model. Intranasal pre-treatment with HPBCD-based formulations reduced viral load and inflammatory signaling in the lung. In vitro efficacy studies were further conducted using lentiviruses, murine hepatitis virus (MHV), and influenza A virus subtype H1N1. These findings suggest HPBCD may be used as an agnostic barrier against transmissible pathogens, including but not limited to SARS-CoV-2.

Conversion of raltegravir carrying a 1,3,4-oxadiazole ring to a hydrolysis product upon pH changes decreases its antiviral activity

Raltegravir (RAL), a human immunodeficiency virus (HIV)-1 integrase inhibitor, has been administered as part of antiretroviral therapy. Studies in patients with HIV-1 have shown high variability in the pharmacokinetics of RAL, and in healthy volunteers, coadministration of proton-pump inhibitors has been shown to increase the plasma RAL concentrations. Here, we found that RAL containing a 1,3,4-oxadiazole ring is converted to a hydrolysis product (H-RAL) with a cleaved 1,3,4-oxadiazole ring at pH 1.0 and 13.0 conditions in vitro, thereby reducing the anti-HIV activity of the drug. The inclusion of cyclodextrins (beta-cyclodextrin [βCD], random methyl-βCD [RAM-βCD], and hydroxypropyl-βCD [HP-βCD]) can protect RAL from pH-induced changes. The conversion of RAL to H-RAL was detected by using various mass spectrometry analyses. The chromatogram of H-RAL increased in a time-dependent manner similar to another 1,3,4-oxadiazole-containing drug, zibotentan, using high-performance liquid chromatography. Oral bioavailability and target protein interactions of H-RAL were predicted to be lower than those of RAL. Moreover, H-RAL exhibited significantly reduced anti-HIV-1 activity, whereas combinations with βCD, RAM-βCD, and HP-βCD attenuated this effect in cell-based assays. These findings suggest that βCDs can potentially protect against the conversion of RAL to H-RAL under acidic conditions in the stomach, thereby preserving the anti-HIV-1 effect of RAL. Although clinical trials are needed for evaluation, we anticipate that protective devices such as βCDs may improve the pharmacokinetics of RAL, leading to better treatment outcomes, including reduced dosing, long-term anti-HIV-1 activity, and deeper HIV-1 suppression.

Validation of nuclear receptor RORγ isoform 1 as a novel host-directed antiviral target based on the modulation of cholesterol levels

Currently, the clinically approved repertoire of antiviral drugs predominantly comprises direct-acting antivirals (DAAs). However, the use of DAAs is frequently limited by adverse effects, restriction to individual virus species, or the induction of viral drug resistance. These issues will likely be resolved by the introduction of host-directed antivirals (HDAs) targeting cellular proteins crucial for viral replication. However, experiences with the development of antiviral HDAs and clinical applications are still in their infancy. With the present study, we explored the human nuclear receptor and transcription factor RORγ isoform 1 (RORγ1), a member of the retinoic acid receptor-related orphan receptor (ROR) family, as a putative target of antiviral HDAs. To this end, cell culture models were used to investigate major viral human pathogens, i.e. the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), human cytomegalovirus (HCMV), varicella zoster virus (VZV) and human immunodeficiency virus 1 (HIV-1). Our results demonstrated (i) an antiviral activity of the clinically relevant RORγ modulators cedirogant and others, (ii) that isoform RORγ1 acts as the responsible determinant and drug target in the analyzed cell culture-based models, (iii) a selectivity of the antiviral effect for RORγ1 over related receptors RORα and RORβ, (iv) a late-phase inhibition exerted by cedirogant in HCMV replication and (v) a mechanistic link to the cellular cholesterol biosynthesis. Combined, the data highlight this novel RORγ-specific antiviral targeting concept and the developmental potential of RORγ-directed small molecules.

CD-MOFs: From preparation to drug delivery and therapeutic application

Cyclodextrin metal-organic frameworks (CD-MOFs) show considerable advantages of edibility, degradability, low toxicity, and high drug loading, which have attracted enormous interest, especially in drug delivery. This review summarizes the typical synthesis approaches of CD-MOFs, the drug loading methods, and the mechanism of encapsulation and release. The influence of the structure of CD-MOFs on their drug encapsulation and release is highlighted. Finally, the challenges CD-MOFs face are discussed regarding biosafety assessment systems, stability in aqueous solution, and metal ion effect.

2-Hydroxypropyl-β-Cyclodextrin Treatment Induces Modest Immune Activation in Healthy Rhesus Macaques

Experimental simian immunodeficiency virus (SIV) infection of Asian macaques is an excellent model for HIV disease progression and therapeutic development. Recent coformulations of nucleoside analogs and an integrase inhibitor have been used for parenteral antiretroviral (ARV) administration in SIV-infected macaques, successfully resulting in undetectable plasma SIV RNA. In a cohort of SIVmac239-infected macaques, we recently observed that administration of coformulated ARVs resulted in an unexpected increase in plasma levels of soluble CD14 (sCD14), associated with stimulation of myeloid cells. We hypothesized that the coformulation solubilizing agent Kleptose (2-hydroxypropyl-β-cyclodextrin [HPβCD]) may induce inflammation with myeloid cell activation and the release of sCD14. Herein, we stimulated peripheral blood mononuclear cells (PBMCs) from healthy macaques with HPβCD from different commercial sources and evaluated inflammatory cytokine production in vitro. Treatment of PBMCs resulted in increased sCD14 release and myeloid cell interleukin-1β (IL-1β) production-with stimulation varying significantly by HPβCD source-and destabilized lymphocyte CCR5 surface expression. We further treated healthy macaques with Kleptose alone. In vivo, we observed modestly increased myeloid cell activation in response to Kleptose treatment without significant perturbation of the immunological transcriptome or epigenome. Our results demonstrate a need for vehicle-only controls and highlight immunological perturbations that can occur when using HPβCD in pharmaceutical coformulations. IMPORTANCE SIV infection of nonhuman primates is the principal model system for assessing HIV disease progression and therapeutic development. HPβCD has recently been incorporated as a solubilizing agent in coformulations of ARVs in SIV-infected nonhuman primates. Although HPβCD has historically been considered inert, recent findings suggest that HPβCD may contribute to inflammation. Herein, we investigate the contribution of HPβCD to healthy macaque inflammation in vitro and in vivo. We observe that HPβCD causes an induction of sCD14 and IL-1β from myeloid cells in vitro and demonstrate that HPβCD stimulatory capacity varies by commercial source. In vivo, we observe modest myeloid cell activation in blood and bronchoalveolar lavage specimens absent systemic immune activation. From our findings, it is unclear whether HPβCD stimulation may improve or diminish immune reconstitution in ARV-treated lentiviral infections. Our results demonstrate a need for vehicle-only controls and highlight immunological perturbations that can occur when using HPβCD in pharmaceutical coformulations.

Neutral sphingomyelinase 2 is required for HIV-1 maturation

HIV-1 assembly occurs at the inner leaflet of the plasma membrane (PM) in highly ordered membrane microdomains. The size and stability of membrane microdomains is regulated by activity of the sphingomyelin hydrolase neutral sphingomyelinase 2 (nSMase2) that is localized primarily to the inner leaflet of the PM. In this study, we demonstrate that pharmacological inhibition or depletion of nSMase2 in HIV-1-producer cells results in a block in the processing of the major viral structural polyprotein Gag and the production of morphologically aberrant, immature HIV-1 particles with severely impaired infectivity. We find that disruption of nSMase2 also severely inhibits the maturation and infectivity of other primate lentiviruses HIV-2 and simian immunodeficiency virus, has a modest or no effect on nonprimate lentiviruses equine infectious anemia virus and feline immunodeficiency virus, and has no effect on the gammaretrovirus murine leukemia virus. These studies demonstrate a key role for nSMase2 in HIV-1 particle morphogenesis and maturation.

Transport Across Cell Membranes is Modulated by Lipid Order

This study measures the uptake of various dyes into HeLa cells and determines simultaneously the degree of membrane lipid chain order on a single cell level by spectral analysis of the membrane-embedded dye Laurdan. First, this study finds that the mean generalized polarization (GP) value of single cells varies within a population in a range that is equivalent to a temperature variation of 9 K. This study exploits this natural variety of membrane order to examine the uptake as a function of GP at constant temperature. It is shown that transport across the cell membrane correlates with the membrane phase state. Specifically, higher membrane transport with increasing lipid chain order is observed. As a result, hypothermal-adapted cells with reduced lipid membrane order show less transport. Environmental factors influence transport as well. While increasing temperature reduces lipid order, it is found that locally high cell densities increase lipid order and in turn lead to increased dye uptake. To demonstrate the physiological relevance, membrane state and transport during an in vitro wound healing process are analyzed. While the uptake within a confluent cell layer is high, it decreases toward the center where the membrane lipid chain order is lowest.

Pillararenes as Promising Carriers for Drug Delivery

Since their discovery in 2008 by N. Ogoshi and co-authors, pillararenes (PAs) have become popular hosts for molecular recognition and supramolecular chemistry, as well as other practical applications. The most useful property of these fascinating macrocycles is their ability to accommodate reversibly guest molecules of various kinds, including drugs or drug-like molecules, in their highly ordered rigid cavity. The last two features of pillararenes are widely used in various pillararene-based molecular devices and machines, stimuli-responsive supramolecular/host-guest systems, porous/nonporous materials, organic-inorganic hybrid systems, catalysis, and, finally, drug delivery systems. In this review, the most representative and important results on using pillararenes for drug delivery systems for the last decade are presented.

Analysis of HIV-1 envelope cytoplasmic tail effects on viral replication

Trimers of the HIV-1 envelope (Env) protein perform receptor binding and virus-cell fusion functions during the virus life cycle. The cytoplasmic tail (CT) of Env forms an unusual baseplate structure, and is palmitoylated, rich in arginines, carries trafficking motifs, binds cholesterol, and interacts with host proteins. To dissect CT activities, we examined a panel of Env variants, including CT truncations, mutations, and an extension. We found that whereas all variants could replicate in permissive cells, viruses with CT truncations or baseplate mutations were defective in restrictive cells. We also identified a determinant in HIV-1 amphotericin sensitivity, and characterized variants that escape amphotericin inhibition via viral protease-mediated CT cleavage. Results additionally showed that full-length, his tagged Env can oligomerize and be co-assembled with CT truncations that delete portions of the baseplate, host protein binding sites, and trafficking signals. Our observations illuminate novel aspects of HIV-1 CT structure, interactions, and functions.

Aminotransferasas y perfil lipídico en pacientes ecuatorianos con infección activa por virus dengue

El dengue es la arbovirosis con mayor incidencia a nivel mundial. Aproximadamente 100 millones de casos de dengue con signos de alarma y entre 250.000 y 500.000 casos de dengue grave, se registran anualmente. En Ecuador, en los últimos cuatro años se han registrado 83.472 casos de dengue. Estudios previos evidencian un incremento de los casos que cursan con disfunción hepática. El objetivo de este estudio fue analizar la asociación entre los niveles séricos de las enzimas aspartato aminotransferasa y alanino aminotransferasa y el perfil lipídico en pacientes con infección confirmada de Dengue. Se estudiaron 110 pacientes seleccionados sin distingo de edad, género o procedencia, cuyo diagnóstico fue confirmado virológica y serológicamente. Se incluyó un grupo control seronegativo al virus. En el perfil lipídico se evidenciaron diferencias significativas (p<0,003) en los valores de colesterol total y en infecciones secundarias; mientras que la frecuencia de elevación de ambas aminotransferasas fue alta en pacientes con dengue, no obstante, al comparar cuantitativamente los valores séricos no arrojaron cambios significativos, ni asociación. Se confirma la endemicidad del dengue, los cambios en el perfil lipídico, sin embargo, es evidente la necesidad de estudios poblacionales tomando en cuenta la genética de las poblaciones

Dose-Response Effects of 7-Dehydrocholesterol Reductase Inhibitors on Sterol Profiles and Vesicular Stomatitis Virus Replication

Cholesterol is ubiquitous in cells; it plays a critical role in membrane structure and transport as well as in intracellular trafficking processes. There are suggestions that cholesterol metabolism is linked to innate immunity with inhibitors of DHCR7, the last enzyme in the cholesterol pathway, suggested to have potential as viral therapeutics nearly a decade ago. In fact, there are a number of highly prescribed pharmaceuticals that are off-target inhibitors of DHCR7, causing increased cellular levels of 7-dehydrodesmosterol (7-DHD) and 7-dehydrocholesterol (7-DHC). We report here dose-response studies of six such inhibitors on late-stage cholesterol biosynthesis in Neuro2a cells as well as their effect on infection of vesicular stomatitis virus (VSV). Four of the test compounds are FDA-approved drugs (cariprazine, trazodone, metoprolol, and tamoxifen), one (ifenprodil) has been the object of a recent Phase 2b COVID trial, and one (AY9944) is an experimental compound that has seen extensive use as a DHCR7 inhibitor. The three FDA-approved drugs inhibit replication of a GFP-tagged VSV with efficacies that mirror their effect on DHCR7. Ifenprodil and AY9944 have complex inhibitory profiles, acting on both DHCR7 and DHCR14, while tamoxifen does not inhibit DHCR7 and is toxic to Neuro2a at concentrations where it inhibits the Δ7-Δ8 isomerase of the cholesterol pathway. VSV itself affects the sterol profile in Neuro2a cells, showing a dose-response increase of dehydrolathosterol and lathosterol, the substrates for DHCR7, with a corresponding decrease in desmosterol and cholesterol. 7-DHD and 7-DHC are orders of magnitude more vulnerable to free radical chain oxidation than other sterols as well as polyunsaturated fatty esters, and the effect of these sterols on viral infection is likely a reflection of this fact of Nature.

Bioactive Compounds from Elderberry: Extraction, Health Benefits, and Food Applications

Elderberries are appreciated for their antioxidant properties. Sambucus nigra L. is an extremely abundant plant in the wild flora of Romania, but it is underutilized. Elderberry is used in modern and traditional medicine due to the complex chemical composition of the fruit. The content of phenolic compounds is high (516–8974 mg/100 g DW), of which the most abundant are anthocyanins. Phenolic compounds are known for their beneficial effects on the body. Numerous studies have demonstrated the antioxidant capacity, antibacterial, antiviral, antidiabetic, and anticancer properties of the fruit. It is considered that most of the therapeutic properties of elderberries can be correlated with the antioxidant activity they have. S. nigra fruits are also used in the food industry. Some studies have shown that the therapeutic properties of elderberries can also be found in the products obtained from them. Therefore, this review aimed to describe the chemical composition of elderberries and products obtained from them, the positive effects on the body, and the methods by which the bioactive compounds can be extracted from the fruits and analyzed. This manuscript is useful for extraction optimization and characterization in order to valorize new functional foods, food supplements, and also in new pharmaceutical products.

Broad-Spectrum Extracellular Antiviral Properties of Cucurbit[n]urils

Viruses are microscopic pathogens capable of causing disease and are responsible for a range of human mortalities and morbidities worldwide. They can be rendered harmless or destroyed with a range of antiviral chemical compounds. Cucurbit[n]urils (CB[n]s) are a family of macrocycle chemical compounds existing as a range of homologues; due to their structure, they can bind to biological materials, acting as supramolecular "hosts" to "guests", such as amino acids. Due to the increasing need for a nontoxic antiviral compound, we investigated whether cucurbit[n]urils could act in an antiviral manner. We have found that certain cucurbit[n]uril homologues do indeed have an antiviral effect against a range of viruses, including herpes simplex virus 2 (HSV-2), respiratory syncytial virus (RSV) and SARS-CoV-2. In particular, we demonstrate that CB[7] is the active homologue of CB[n], having an antiviral effect against enveloped and nonenveloped species. High levels of efficacy were observed with 5 min contact times across different viruses. We also demonstrate that CB[7] acts with an extracellular virucidal mode of action via host-guest supramolecular interactions between viral surface proteins and the CB[n] cavity, rather than via cell internalization or a virustatic mechanism. This finding demonstrates that CB[7] acts as a supramolecular virucidal antiviral (a mechanism distinct from other current extracellular antivirals), demonstrating the potential of supramolecular interactions for future antiviral disinfectants.

Identification of a βCD-Based Hyper-Branched Negatively Charged Polymer as HSV-2 and RSV Inhibitor

Cyclodextrins and cyclodextrin derivatives were demonstrated to improve the antiviral potency of numerous drugs, but also to be endowed with intrinsic antiviral action. They are suitable building blocks for the synthesis of functionalized polymer structures with potential antiviral activity. Accordingly, four water-soluble hyper-branched beta cyclodextrin (βCD)-based anionic polymers were screened against herpes simplex virus (HSV-2), respiratory syncytial virus (RSV), rotavirus (HRoV), and influenza virus (FluVA). They were characterized by FTIR-ATR, TGA, elemental analyses, zeta-potential measurements, and potentiometric titrations, while the antiviral activity was investigated with specific in vitro assays. The polymer with the highest negative charge, pyromellitic dianhydride-linked polymer (P_PMDA), showed significant antiviral action against RSV and HSV-2, by inactivating RSV free particles and by altering HSV-2 binding to the cell. The polymer fraction with the highest molecular weight showed the strongest antiviral activity and both P_PMDA and its active fractions were not toxic for cells. Our results suggest that the polymer virucidal activity against RSV can be exploited to produce new antiviral materials to counteract the virus dissemination through the air or direct contact. Additionally, the strong HSV-2 binding inhibition along with the water solubility of P_PMDA and the acyclovir complexation potential of βCD are attractive features for developing new therapeutic topical options against genital HSV-2 infection.

An Ultrasound-Responsive Theranostic Cyclodextrin-Loaded Nanoparticle for Multimodal Imaging and Therapy for Atherosclerosis

Atherosclerosis is a major cause of mortality and morbidity worldwide. Left undiagnosed and untreated, atherosclerotic plaques can rupture and cause cardiovascular complications such as myocardial infarction and stroke. Atherosclerotic plaques are composed of lipids, including oxidized low-density lipoproteins and cholesterol crystals, and immune cells, including macrophages. 2-Hydroxypropyl-beta-cyclodextrin (CD) is FDA-approved for capturing, solubilizing, and delivering lipophilic drugs in humans. It is also known to dissolve cholesterol crystals and decrease atherosclerotic plaque size. However, its low retention time necessitates high dosages for successful therapy. This study reports CD delivery via air-trapped polybutylcyanoacrylate nanoparticles (with diameters of 388 ± 34 nm) loaded with CD (CDNPs). The multimodal contrast ability of these nanoparticles after being loaded with IR780 dye in mice is demonstrated using ultrasound and near-infrared imaging. It is shown that CDNPs enhance the cellular uptake of CD in murine cells. In an ApoE^-/- mouse model of atherosclerosis, treatment with CDNPs significantly improves the anti-atherosclerotic efficacy of CD. Ultrasound triggering further improves CD uptake, highlighting that CDNPs can be used for ultrasound imaging and ultrasound-responsive CD delivery. Thus, CDNPs represent a theranostic nanocarrier for potential application in patients with atherosclerosis.

Galectin-3 facilitates cell-to-cell HIV-1 transmission by altering the composition of membrane lipid rafts in CD4 T cells

Galectin-3 (GAL3) is a β-galactoside-binding lectin expressed in CD4 T cells infected with human immunodeficiency virus-1 (HIV-1). GAL3 promotes HIV-1 budding by associating with ALIX and Gag p6. GAL3 has been shown to localize in membrane lipid rafts in dendritic cells and positively regulate cell migration. HIV-1 spreads between T cells by forming supramolecular structures (virological synapses [VSs]), whose integrity depends on lipid rafts. Here, we addressed the potential role of GAL3 in cell-to-cell transmission of HIV-1 in CD4 T cells. GAL3 expressed in donor cells was more important for facilitating HIV-1 cell-to-cell transfer than GAL3 expressed in target cells. GAL3 was found to be co-transferred with Gag from HIV-1-positive donor to HIV-1-negative target T cells. HIV-1 infection induced translocation of GAL3 together with Gag to the cell-cell interfaces and colocalize with GM1, where GAL3 facilitated VS formation. GAL3 regulated the coordinated transfer of Gag and flotillin-1 into plasma membrane fractions. Finally, depletion of GAL3 reduced the cholesterol levels in membrane lipid rafts in CD4 T cells. These findings provide evidence that endogenous GAL3 stimulates lipid raft components and facilitates intercellular HIV-1 transfer among CD4 T cells, offering another pathway by which GAL3 regulates HIV-1 infection. These findings may inform the treatment of HIV-1 infection based on targeting GAL3 to modulate lipid rafts.

Hydroxypropyl-beta-cyclodextrin (HP-BCD) inhibits SARS-CoV-2 replication and virus-induced inflammatory cytokines

COVID-19 is marked by extensive damage to the respiratory system, often accompanied by systemic manifestations, due to both viral cytopathic effects and hyperinflammatory syndrome. Therefore, the development of new therapeutic strategies or drug repurposing aiming to control virus replication and inflammation are required to mitigate the impact of the disease. Hydroxypropyl-beta-cyclodextrin (HP-BCD) is a cholesterol-sequestering agent with antiviral activity that has been demonstrated against enveloped viruses in in vitro and in vivo experimental models. We also demonstrated that HP-BCD has an immunomodulatory effect, inhibiting the production of selected proinflammatory cytokines induced by microbial products. Importantly, this drug has been used in humans for decades as an excipient in drug delivery systems and as a therapeutic agent in the treatment of Niemann pick C disease. The safety profile for this compound is well established. Here, we investigated whether HP-BCD would affect SARS-CoV-2 replication and virus-induced inflammatory response, using established cell lines and primary human cells. Treating virus or cells with HP-BCD significantly inhibited SARS-CoV-2 replication with a high selective index. A broad activity against distinct SARS-CoV-2 variants was evidenced by a remarkable reduction in the release of infectious particles. The drug did not alter ACE2 surface expression, but affected cholesterol accumulation into intracellular replication complexes, lowering virus RNA and protein levels, and reducing virus-induced cytopathic effects. Virus replication was also impaired by HP-BCD in Calu-3 pulmonary cell line and human primary monocytes, in which not only the virus, but also the production of proinflammatory cytokines were significantly inhibited. Given the pathophysiology of COVID-19 disease, these data indicate that the use HP-BCD, which inhibits both SARS-CoV2 replication and production of proinflammatory cytokines, as a potential COVID-19 therapeutic warrants further investigation.

The constellation of cholesterol-dependent processes associated with SARS-CoV-2 infection

The role of cholesterol in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other coronavirus-host cell interactions is currently being discussed in the context of two main scenarios: i) the presence of the neutral lipid in cholesterol-rich lipid domains involved in different steps of the viral infection and ii) the alteration of metabolic pathways by the virus over the course of infection. Cholesterol-enriched lipid domains have been reported to occur in the lipid envelope membrane of the virus, in the host-cell plasma membrane, as well as in endosomal and other intracellular membrane cellular compartments. These membrane subdomains, whose chemical and physical properties distinguish them from the bulk lipid bilayer, have been purported to participate in diverse phenomena, from virus-host cell fusion to intracellular trafficking and exit of the virions from the infected cell. SARS-CoV-2 recruits many key proteins that participate under physiological conditions in cholesterol and lipid metabolism in general. This review analyses the status of cholesterol and lipidome proteins in SARS-CoV-2 infection and the new horizons they open for therapeutic intervention.

Coronavirus Infection and Cholesterol Metabolism

Host cholesterol metabolism remodeling is significantly associated with the spread of human pathogenic coronaviruses, suggesting virus-host relationships could be affected by cholesterol-modifying drugs. Cholesterol has an important role in coronavirus entry, membrane fusion, and pathological syncytia formation, therefore cholesterol metabolic mechanisms may be promising drug targets for coronavirus infections. Moreover, cholesterol and its metabolizing enzymes or corresponding natural products exert antiviral effects which are closely associated with individual viral steps during coronavirus replication. Furthermore, the coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 infections are associated with clinically significant low cholesterol levels, suggesting cholesterol could function as a potential marker for monitoring viral infection status. Therefore, weaponizing cholesterol dysregulation against viral infection could be an effective antiviral strategy. In this review, we comprehensively review the literature to clarify how coronaviruses exploit host cholesterol metabolism to accommodate viral replication requirements and interfere with host immune responses. We also focus on targeting cholesterol homeostasis to interfere with critical steps during coronavirus infection.

Global Increases in Human Immunodeficiency Virus Neutralization Sensitivity Due to Alterations in the Membrane-Proximal External Region of the Envelope Glycoprotein Can Be Minimized by Distant State 1-Stabilizing Changes

Binding to the receptor, CD4, drives the pretriggered, "closed" (State-1) conformation of the human immunodeficiency virus (HIV-1) envelope glycoprotein (Env) trimer ([gp120/gp41]₃) into more "open" conformations. HIV-1 Env on the viral membrane is maintained in a State-1 conformation that resists binding and neutralization by commonly elicited antibodies. Premature triggering of Env before the virus engages a target cell typically leads to increased susceptibility to spontaneous inactivation or ligand-induced neutralization. Here, we showed that single amino acid substitutions in the gp41 membrane-proximal external region (MPER) of a primary HIV-1 strain resulted in viral phenotypes indicative of premature triggering of Env to downstream conformations. Specifically, the MPER changes reduced viral infectivity and globally increased virus sensitivity to poorly neutralizing antibodies, soluble CD4, a CD4-mimetic compound, and exposure to cold. In contrast, the MPER mutants exhibited decreased sensitivity to the State 1-preferring inhibitor, BMS-806, and to the PGT151 broadly neutralizing antibody. Depletion of cholesterol from virus particles did not produce the same State 1-destabilizing phenotypes as MPER alterations. Notably, State 1-stabilizing changes in Env distant from the MPER could minimize the phenotypic effects of MPER alteration but did not affect virus sensitivity to cholesterol depletion. Thus, membrane-proximal gp41 elements contribute to the maintenance of the pretriggered Env conformation. The conformationally disruptive effects of MPER changes can be minimized by distant State 1-stabilizing Env modifications, a strategy that may be useful in preserving the native pretriggered state of Env. IMPORTANCE The pretriggered shape of the human immunodeficiency virus (HIV-1) envelope glycoprotein (Env) is a major target for antibodies that can neutralize many strains of the virus. An effective HIV-1 vaccine may need to raise these types of antibodies, but this goal has proven difficult. One reason is that the pretriggered shape of Env is unstable and dependent on interactions near the viral membrane. Here, we showed that the membrane-proximal external region (MPER) of Env plays an important role in maintaining Env in a pretriggered shape. Alterations in the MPER resulted in global changes in Env conformation that disrupted its pretriggered shape. We also found that these disruptive effects of MPER changes could be minimized by distant Env modifications that stabilized the pretriggered shape. These modifications may be useful for preserving the native shape of Env for structural and vaccine studies.

Porous surfaces: stability and recovery of coronaviruses

The role of indirect contact in the transmission of SARS-CoV-2 is not clear. SARS-CoV-2 persists on dry surfaces for hours to days; published studies have largely focused on hard surfaces with less research being conducted on different porous surfaces, such as textiles. Understanding the potential risks of indirect transmission of COVID-19 is useful for settings where there is close contact with textiles, including healthcare, manufacturing and retail environments. This article aims to review current research on porous surfaces in relation to their potential as fomites of coronaviruses compared to non-porous surfaces. Current methodologies for assessing the stability and recovery of coronaviruses from surfaces are also explored. Coronaviruses are often less stable on porous surfaces than non-porous surfaces, for example, SARS-CoV-2 persists for 0.5 h-5 days on paper and 3-21 days on plastic; however, stability is dependent on the type of surface. In particular, the surface properties of textiles differ widely depending on their construction, leading to variation in the stability of coronaviruses, with longer persistence on more hydrophobic materials such as polyester (1-3 days) compared to highly absorbent cotton (2 h-4 days). These findings should be considered where there is close contact with potentially contaminated textiles.

SARS-CoV-2 requires cholesterol for viral entry and pathological syncytia formation

Many enveloped viruses induce multinucleated cells (syncytia), reflective of membrane fusion events caused by the same machinery that underlies viral entry. These syncytia are thought to facilitate replication and evasion of the host immune response. Here, we report that co-culture of human cells expressing the receptor ACE2 with cells expressing SARS-CoV-2 spike, results in synapse-like intercellular contacts that initiate cell-cell fusion, producing syncytia resembling those we identify in lungs of COVID-19 patients. To assess the mechanism of spike/ACE2-driven membrane fusion, we developed a microscopy-based, cell-cell fusion assay to screen ~6000 drugs and >30 spike variants. Together with quantitative cell biology approaches, the screen reveals an essential role for biophysical aspects of the membrane, particularly cholesterol-rich regions, in spike-mediated fusion, which extends to replication-competent SARS-CoV-2 isolates. Our findings potentially provide a molecular basis for positive outcomes reported in COVID-19 patients taking statins and suggest new strategies for therapeutics targeting the membrane of SARS-CoV-2 and other fusogenic viruses.

Fusogenic Effect of Cholesterol Prevails over the Inhibitory Effect of a Peptide-Based Membrane Fusion Inhibitor

Membrane fusion is the primary step in the entry of enveloped viruses into the host cell. Membrane composition modulates the membrane fusion by changing the organization dynamics of the fusion proteins, peptides, and membranes. The asymmetric lipid compositions of the viral envelope and the host cell influence the membrane fusion. Cholesterol is an important constituent of mammalian cells and plays a vital role in the entry of several viruses. In our pursuit of developing peptide-based general fusion inhibitors, we have previously shown that a coronin 1-derived peptide, TG-23, inhibited polyethylene glycol-induced fusion between symmetric membranes without cholesterol. In this work, we have studied the effect of TG-23 on the polyethylene glycol-mediated fusion between 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG) (60/30/10 mol %) and DOPC/DOPE/DOPG/CH (50/30/10/10 mol %) membranes and between DOPC/DOPE/DOPG (60/30/10 mol %) and DOPC/DOPE/DOPG/CH (40/30/10/20 mol %) membranes. Our results demonstrate that the TG-23 peptide inhibited the fusion between membranes containing 0 and 10 mol % cholesterol though the efficacy is less than that of symmetric fusion between membranes devoid of cholesterol, and the inhibitory efficacy becomes negligible in the fusion between membranes containing 0 and 20 mol % cholesterol. Several steady-state and time-resolved fluorescence spectroscopic techniques have been successfully utilized to evaluate the organization, dynamics, and membrane penetration of the TG-23 peptide. Taken together, our results demonstrate that the reduction of the inhibitory effect of TG-23 in asymmetric membrane fusion containing cholesterol of varying concentrations is not due to the altered peptide structure, organization, and dynamics, rather owing to the intrinsic negative curvature-inducing property of cholesterol. Therefore, the membrane composition is an added complexity in the journey of developing peptide-based membrane fusion inhibitors.

Cyclodextrins in Antiviral Therapeutics and Vaccines

The present review describes the various roles of cyclodextrins (CDs) in vaccines against viruses and in antiviral therapeutics. The first section describes the most commonly studied application of cyclodextrins—solubilisation and stabilisation of antiviral drugs; some examples also refer to their beneficial taste-masking activity. The second part of the review describes the role of cyclodextrins in antiviral vaccine development and stabilisation, where they are employed as adjuvants and cryopreserving agents. In addition, cyclodextrin-based polymers as delivery systems for mRNA are currently under development. Lastly, the use of cyclodextrins as pharmaceutical active ingredients for the treatment of viral infections is explored. This new field of application is still taking its first steps. Nevertheless, promising results from the use of cyclodextrins as agents to treat other pathologies are encouraging. We present potential applications of the results reported in the literature and highlight the products that are already available on the market.

Roles of Cholesterol in Early and Late Steps of the Nipah Virus Membrane Fusion Cascade

Cholesterol has been implicated in various viral life cycle steps for different enveloped viruses, including viral entry into host cells, cell-cell fusion, and viral budding from infected cells. Enveloped viruses acquire their membranes from their host cells. Although cholesterol has been associated with the binding and entry of various enveloped viruses into cells, cholesterol's exact function in the viral-cell membrane fusion process remains largely elusive, particularly for the paramyxoviruses. Furthermore, paramyxoviral fusion occurs at the host cell membrane and is essential for both virus entry (virus-cell fusion) and syncytium formation (cell-cell fusion), central to viral pathogenicity. Nipah virus (NiV) is a deadly member of the Paramyxoviridae family, which also includes Hendra, measles, mumps, human parainfluenza, and various veterinary viruses. The zoonotic NiV causes severe encephalitis, vasculopathy, and respiratory symptoms, leading to a high mortality rate in humans. We used NiV as a model to study the role of membrane cholesterol in paramyxoviral membrane fusion. We used a combination of methyl-beta cyclodextrin (MβCD), lovastatin, and cholesterol to deplete or enrich cell membrane cholesterol outside cytotoxic concentrations. We found that the levels of cellular membrane cholesterol directly correlated with the levels of cell-cell fusion induced. These phenotypes were paralleled using NiV/vesicular stomatitis virus (VSV)-pseudotyped viral infection assays. Remarkably, our mechanistic studies revealed that cholesterol reduces an early F-triggering step but enhances a late fusion pore formation step in the NiV membrane fusion cascade. Thus, our results expand our mechanistic understanding of the paramyxoviral/henipaviral entry and cell-cell fusion processes.IMPORTANCE Cholesterol has been implicated in various steps of the viral life cycle for different enveloped viruses. Nipah virus (NiV) is a highly pathogenic enveloped virus in the Henipavirus genus within the Paramyxoviridae family, capable of causing a high mortality rate in humans and high morbidity in domestic and agriculturally important animals. The role of cholesterol for NiV or the henipaviruses is unknown. Here, we show that the levels of cholesterol influence the levels of NiV-induced cell-cell membrane fusion during syncytium formation and virus-cell membrane fusion during viral entry. Furthermore, the specific role of cholesterol in membrane fusion is not well defined for the paramyxoviruses. We show that the levels of cholesterol affect an early F-triggering step and a late fusion pore formation step during the membrane fusion cascade. Thus, our results expand our mechanistic understanding of the viral entry and cell-cell fusion processes, which may aid the development of antivirals.

Ceramide synthase 2 deletion decreases the infectivity of HIV-1

The lipid composition of HIV-1 virions is enriched in sphingomyelin (SM), but the roles that SM or other sphingolipids (SLs) might play in the HIV-1 replication pathway have not been elucidated. In human cells, SL levels are regulated by ceramide synthase (CerS) enzymes that produce ceramides, which can be converted to SMs, hexosylceramides, and other SLs. In many cell types, CerS2, which catalyzes the synthesis of very long chain ceramides, is the major CerS. We have examined how CerS2 deficiency affects the assembly and infectivity of HIV-1. As expected, we observed that very long chain ceramide, hexosylceramide, and SM were reduced in CerS2 knockout cells. CerS2 deficiency did not affect HIV-1 assembly or the incorporation of the HIV-1 envelope (Env) protein into virus particles, but it reduced the infectivites of viruses produced in the CerS2-deficient cells. The reduced viral infection levels were dependent on HIV-1 Env, since HIV-1 particles that were pseudotyped with the vesicular stomatitis virus glycoprotein did not exhibit reductions in infectivity. Moreover, cell-cell fusion assays demonstrated that the functional defect of HIV-1 Env in CerS2-deficient cells was independent of other viral proteins. Overall, our results indicate that the altered lipid composition of CerS2-deficient cells specifically inhibit the HIV-1 Env receptor binding and/or fusion processes.

Are statins beneficial for the treatment of SARS-CoV-2 infection?

Novel coronavirus disease 2019 (COVID-19) is a highly infectious, rapidly spreading viral disease and has emerged as a public health emergency of international concern. As of this time, there are no specific antiviral therapies available for the treatment of COVID-19. However, it is possible that some existing drugs, usually used for other conditions, may have some benefits. Statins have been widely reported to exert antiviral activity against many enveloped viruses by inhibiting the cholesterol biosynthesis pathway. Cholesterol likewise contributes to the coronavirus's life cycle, including viral entry, fusion and budding. In addition, statins have been ascribed beneficial anti-inflammatory, immunomodulatory effects and promote haemodynamic stability. Therefore, statins, which are cholesterol-lowering drugs with anti-inflammatory, immunomodulatory and antiviral properties, may play a role in SARS-CoV-2 therapy. The aim of the present minireview was to delineate the potential beneficial therapeutic effects of statins in treating SARS-CoV-2 infections. Nevertheless, large, randomised trials are needed to confirm the beneficial effects and safety profile of the statins in patients with SARS-CoV-2.

Current Understanding of the Role of Cholesterol in the Life Cycle of Alphaviruses

Enveloped viruses rely on different lipid classes present in cell membranes to accomplish several steps of their life cycle in the host. Particularly for alphaviruses, a medically important group of arboviruses, which are part of the Togaviridae family, cholesterol seems to be a critical lipid exploited during infection, although its relevance may vary depending on which stage of the virus life cycle is under consideration and whether infection takes place in vertebrate or invertebrate hosts. In this review, the role of cholesterol in both early and late events of alphavirus infection and how viral replication may affect cholesterol metabolism are summarized, taking into account studies on Old World and New World alphaviruses in different cell lines. Moreover, the importance of cholesterol for the structural stability of alphavirus particles is also discussed, shedding light on the role played by this lipid when they leave the host cell.

Membrane Heterogeneity Beyond the Plasma Membrane

The structure and organization of cellular membranes have received intense interest, particularly in investigations of the raft hypothesis. The vast majority of these investigations have focused on the plasma membrane of mammalian cells, yielding significant progress in understanding membrane heterogeneity in terms of lipid composition, molecular structure, dynamic regulation, and functional relevance. In contrast, investigations on lipid organization in other membrane systems have been comparatively scarce, despite the likely relevance of membrane domains in these contexts. In this review, we summarize recent observations on lipid organization in organellar membranes, including endoplasmic reticulum, Golgi, endo-lysosomes, lipid droplets, and secreted membranes like lung surfactant, milk fat globule membranes, and viral membranes. Across these non-plasma membrane systems, it seems that the biophysical principles underlying lipid self-organization contribute to lateral domains.

Cyclic Oligosaccharides as Active Drugs, an Updated Review

There have been many reviews of the cyclic oligosaccharide cyclodextrin (CD) and CD-based materials used for drug delivery, but the capacity of CDs to complex different agents and their own intrinsic properties suggest they might also be considered for use as active drugs, not only as carriers. The aim of this review is to summarize the direct use of CDs as drugs, without using its complexing potential with other substances. The direct application of another oligosaccharide called cyclic nigerosyl-1,6-nigerose (CNN) is also described. The review is divided into lipid-related diseases, aggregation diseases, antiviral and antiparasitic activities, anti-anesthetic agent, function in diet, removal of organic toxins, CDs and collagen, cell differentiation, and finally, their use in contact lenses in which no drug other than CDs are involved. In the case of CNN, its application as a dietary supplement and immunological modulator is explained. Finally, a critical structure-activity explanation is provided.

Super-Resolution Fluorescence Imaging Reveals That Serine Incorporator Protein 5 Inhibits Human Immunodeficiency Virus Fusion by Disrupting Envelope Glycoprotein Clusters

Serine incorporator protein 5 (SERINC5) is the host antiretroviral factor that reduces HIV-1 infectivity by incorporating into virions and inhibiting the envelope glycoprotein (Env) mediated virus fusion with target cells. We and others have shown that SERINC5 incorporation into virions alters the Env structure and sensitizes the virus to broadly neutralizing antibodies targeting cryptic Env epitopes. We have also found that SERINC5 accelerates the loss of Env function over time compared to control viruses. However, the exact mechanism by which SERINC5 inhibits HIV-1 fusion is not understood. Here, we utilized 2D and 3D super-resolution microscopy to examine the effect of SERINC5 on the distribution of Env glycoproteins on single HIV-1 particles. We find that, in agreement with a previous report, Env glycoproteins form clusters on the surface of mature virions. Importantly, incorporation of SERINC5, but not SERINC2, which lacks antiviral activity, disrupted Env clusters without affecting the overall Env content. We also show that SERINC5 and SERINC2 also form clusters on single virions. Unexpectedly, Env and SERINC molecules exhibited poor codistribution on virions, as evidenced by much greater Env-SERINC pairwise distances compared to Env-Env distances. This observation is inconsistent with the previously reported interaction between Env and SERINC5 and suggests an indirect effect of SERINC5 on Env cluster formation. Collectively, our results reveal a multifaceted mechanism of SERINC5-mediated restriction of HIV-1 fusion that, aside from the effects on individual Env trimers, involves disruption of Env clusters, which likely serve as sites of viral fusion with target cells.

The Lord of the NanoRings: Cyclodextrins and the battle against SARS-CoV-2

A handful of singular structures and laws can be observed in nature. They are not always evident but, once discovered, it seems obvious how to take advantage of them. In chemistry, the discovery of reproducible patterns stimulates the imagination to develop new functional materials and technological or medical applications. Two clear examples are helical structures at different levels in biological polymers as well as ring and spherical structures of different size and composition. Rings are intuitively observed as holes able to thread elongated structures. A large number of real and fictional stories have rings as inanimate protagonists. The design, development or just discovering of a special ring has often been taken as a symbol of power or success. Several examples are the Piscatory Ring wore by the Pope of the Catholic Church, the NBA Championship ring and the One Ring created by the Dark Lord Sauron in the epic story The Lord of the Rings. In this work, we reveal the power of another extremely powerful kind of rings to fight against the pandemic which is currently affecting the whole world. These rings are as small as ~1 nm of diameter and so versatile that they are able to participate in the attack of viruses, and specifically SARS-CoV-2, in a large range of different ways. This includes the encapsulation and transport of specific drugs, as adjuvants to stabilize proteins, vaccines or other molecules involved in the infection, as cholesterol trappers to destabilize the virus envelope, as carriers for RNA therapies, as direct antiviral drugs and even to rescue blood coagulation upon heparin treatment.

“One ring to rule them all. One ring to find them. One ring to bring them all and in the darkness bind them.” J. R. R. Tolkien.

Fluorescence Microscopy of the HIV-1 Envelope

Human immunodeficiency virus (HIV) infection constitutes a major health and social issue worldwide. HIV infects cells by fusing its envelope with the target cell plasma membrane. This process is mediated by the viral Env glycoprotein and depends on the envelope lipid composition. Fluorescent microscopy has been employed to investigate the envelope properties, and the processes of viral assembly and fusion, but the application of this technique to the study of HIV is still limited by a number of factors, such as the small size of HIV virions or the difficulty to label the envelope components. Here, we review fluorescence imaging studies of the envelope lipids and proteins, focusing on labelling strategies and model systems.

Cellular evasion strategies of Helicobacter pylori in regulating its intracellular fate

Helicobacter pylori colonizes human stomach mucosa and its infection causes gastrointestinal diseases with variable severity. Bacterial infection stimulates autophagy, which is a part of innate immunity used to eliminate intracellular pathogens. Several intracellular bacteria have evolved multipronged strategies to circumvent this conserved system and thereby enhance their chance of intracellular survival. Nonetheless, studies on H. pylori have produced inconsistent results, showing either elevated or reduced clearance efficiency of intracellular bacteria through autophagy. In this review, we summarize recent studies on the mechanisms involved in autophagy induced by H. pylori and the fate of intracellular bacteria.

Cyclodextrins: Emerging Medicines of the New Millennium

Cyclodextrins, since their discovery in the late 19th century, were mainly regarded as excipients. Nevertheless, developments in cyclodextrin research have shown that some of these hosts can capture and include biomolecules, highlighting fatty acids and cholesterol, which implies that they are not inert and that their action may be used in specific medicinal purposes. The present review, centered on literature reports from the year 2000 until the present day, presents a comprehensive description of the known biological activities of cyclodextrins and their implications for medicinal applications. The paper is divided into two main sections, one devoted to the properties and applications of cyclodextrins as active pharmaceutical ingredients in a variety of pathologies, from infectious ailments to cardiovascular dysfunctions and metabolic diseases. The second section is dedicated to the use of cyclodextrins in a range of biomedical technologies.

Quantification of phosphoinositides reveals strong enrichment of PIP2 in HIV-1 compared to producer cell membranes

Human immunodeficiency virus type 1 (HIV-1) acquires its lipid envelope during budding from the plasma membrane of the host cell. Various studies indicated that HIV-1 membranes differ from producer cell plasma membranes, suggesting budding from specialized membrane microdomains. The phosphoinositide PI(4,5)P₂ has been of particular interest since PI(4,5)P₂ is needed to recruit the viral structural polyprotein Gag to the plasma membrane and thus facilitates viral morphogenesis. While there is evidence for an enrichment of PIP₂ in HIV-1, fully quantitative analysis of all phosphoinositides remains technically challenging and therefore has not been reported, yet. Here, we present a comprehensive analysis of the lipid content of HIV-1 and of plasma membranes from infected and non-infected producer cells, resulting in a total of 478 quantified lipid compounds, including molecular species distribution of 25 different lipid classes. Quantitative analyses of phosphoinositides revealed strong enrichment of PIP₂, but also of PIP₃, in the viral compared to the producer cell plasma membrane. We calculated an average of ca. 8,000 PIP₂ molecules per HIV-1 particle, three times more than Gag. We speculate that the high density of PIP₂ at the HIV-1 assembly site is mediated by transient interactions with viral Gag polyproteins, facilitating PIP₂ concentration in this microdomain. These results are consistent with our previous observation that PIP₂ is not only required for recruiting, but also for stably maintaining Gag at the plasma membrane. We believe that this quantitative analysis of the molecular anatomy of the HIV-1 lipid envelope may serve as standard reference for future investigations.

The lipid membrane of HIV-1 stabilizes the viral envelope glycoproteins and modulates their sensitivity to antibody neutralization

The envelope glycoproteins (Envs) of HIV-1 are embedded in the cholesterol-rich lipid membrane of the virus. Chemical depletion of cholesterol from HIV-1 particles inactivates their infectivity. We observed that diverse HIV-1 strains exhibit a range of sensitivities to such treatment. Differences in sensitivity to cholesterol depletion could not be explained by variation in Env components known to interact with cholesterol, including the cholesterol-recognition motif and cytoplasmic tail of gp41. Using antibody-binding assays, measurements of virus infectivity, and analyses of lipid membrane order, we found that depletion of cholesterol from HIV-1 particles decreases the conformational stability of Env. It enhances exposure of partially cryptic epitopes on the trimer and increases sensitivity to structure-perturbing treatments such as antibodies and cold denaturation. Substitutions in the cholesterol-interacting motif of gp41 induced similar effects as depletion of cholesterol. Surface-acting agents, which are incorporated into the virus lipid membrane, caused similar effects as disruption of the Env-cholesterol interaction. Furthermore, substitutions in gp120 that increased structural stability of Env (i.e. induced a "closed" conformation of the trimer) increased virus resistance to cholesterol depletion and to the surface-acting agents. Collectively, these results indicate a critical contribution of the viral membrane to the stability of the Env trimer and to neutralization resistance against antibodies. Our findings suggest that the potency of poorly neutralizing antibodies, which are commonly elicited in vaccinated individuals, may be markedly enhanced by altering the lipid composition of the viral membrane.

The Incorporation of Host Proteins into the External HIV-1 Envelope

The incorporation of biologically active host proteins into HIV-1 is a well-established phenomenon, particularly due to the budding mechanism of viral egress in which viruses acquire their external lipid membrane directly from the host cell. While this mechanism might seemingly imply that host protein incorporation is a passive uptake of all cellular antigens associated with the plasma membrane at the site of budding, this is not the case. Herein, we review the evidence indicating that host protein incorporation can be a selective and conserved process. We discuss how HIV-1 virions displaying host proteins on their surface can exhibit a myriad of altered phenotypes, with notable impacts on infectivity, homing, neutralization, and pathogenesis. This review describes the canonical and emerging methods to detect host protein incorporation, highlights the well-established host proteins that have been identified on HIV-1 virions, and reflects on the role of these incorporated proteins in viral pathogenesis and therapeutic targeting. Despite many advances in HIV treatment and prevention, there remains a global effort to develop increasingly effective anti-HIV therapies. Given the broad range of biologically active host proteins acquired on the surface of HIV-1, additional studies on the mechanisms and impacts of these incorporated host proteins may inform the development of novel treatments and vaccine designs.

A Polycationic Brush Mediated Co-Delivery of Doxorubicin and Gene for Combination Therapy

The combination of drug and gene strategies for cancer therapy, has exhibited greater effectiveness than drug or gene therapy alone. In this paper, a coil-comb shaped polycationic brush was used as a multifunctional carrier for co-delivery of drug and gene. The side chains of the comb block of the brush were composed of cyclodextrin (CD)-containing cationic star polymers, with a super-high density of positive charge. Doxorubicin (DOX) could be loaded into the cavity of CD polymers to form DOX-loaded nanoparticles (DOX-NPs) and the p53 gene could be subsequently condensed by DOX-NPs. The obtained DOX-NPs/pDNA complexes were less than 150 nm in size, and so could transport DOX and the gene into the same cell. The complexes performed well with regards to their transfection efficiency on MCF-7 cancer cells. As a result, enhanced cell growth inhibition, with decreased DOX dosage was achieved due to the synergistic effect of co-delivery of DOX and the p53 gene. This finding provides an efficient approach for the development of a co-delivery system in combination therapy.

Hydroxypropyl-Beta-Cyclodextrin Reduces Inflammatory Signaling from Monocytes: Possible Implications for Suppression of HIV Chronic Immune Activation

Monocytes from HIV-infected patients produce increased levels of inflammatory cytokines, which are associated with chronic immune activation and AIDS progression. Chronic immune activation is often not restored even in patients showing viral suppression under ART. Therefore, new therapeutic strategies to control inflammation and modulate immune activation are required. Hydroxypropyl-beta-cyclodextrin (HP-BCD) is a cholesterol-sequestering agent that has been reported to be safe for human use in numerous pharmaceutical applications and that has been shown to inactivate HIV in vitro and to control SIV infection in vivo Since cellular cholesterol content or metabolism has been related to altered cellular activation, we evaluated whether HP-BCD treatment could modulate monocyte response to inflammatory stimuli. Treatment of monocytes isolated from HIV-positive and HIV-negative donors with HP-BCD inhibited the expression of CD36 and TNF-α after LPS stimulation, independent of raft disruption. Accordingly, HP-BCD-treated cells showed significant reduction of TNF-α and IL-10 secretion, which was associated with lower mRNA expression. LPS-induced p38MAPK phosphorylation was dampened by HP-BCD treatment, indicating this pathway as a target for HP-BCD-mediated anti-inflammatory response. The expression of HLA-DR was also reduced in monocytes and dendritic cells treated with HP-BCD, which could hinder T cell activation by these cells. Our data suggest that, besides its well-known antiviral activity, HP-BCD could have an immunomodulatory effect, leading to decreased inflammatory responses mediated by antigen-presenting cells, which may impact HIV pathogenesis and AIDS progression.IMPORTANCE Chronic immune activation is a hallmark of HIV infection and is often not controlled even in patients under antiretroviral therapy. Indeed, chronic diseases with inflammatory pathogenesis are being reported as major causes of death for HIV-infected persons. Hydroxypropyl-beta cyclodextrin (HP-BCD) is a cholesterol-sequestering drug that inhibits HIV replication and infectivity in vitro and in vivo Recent studies have demonstrated the importance of cholesterol metabolism and content in different inflammatory conditions; therefore, we investigated the potential of HP-BCD as an immunomodulatory drug, regulating the activation of cells from HIV-infected patients. Treatment of monocytes with HP-BCD inhibited the expression and secretion of receptors and mediators that are usually enhanced in HIV patients. Furthermore, we investigated the molecular mechanisms associated with the immunomodulatory effect of HP-BCD. Our results indicate that, besides reducing viral replication, HP-BCD treatment may contribute to modulation of chronic immune activation associated with AIDS.

Dynamic pattern generation in cell membranes: Current insights into membrane organization

It has been two decades since the lipid raft hypothesis was first presented. Even today, whether these nanoscale cholesterol-rich domains are present in cell membranes is not completely resolved. However, especially in the last few years, a rich body of literature has demonstrated both the presence and the importance of non-random distribution of biomolecules on the membrane, which is the focus of this review. These new developments have pushed the experimental limits of detection and have brought us closer to observing lipid domains in the plasma membrane of live cells. Characterization of biomolecules associated with lipid rafts has revealed a deep connection between biological regulation and function and membrane compositional heterogeneities. Finally, tantalizing new developments in the field have demonstrated that lipid domains might not just be associated with the plasma membrane of eukaryotes but could potentially be a ubiquitous membrane-organizing principle in several other biological systems. This article is part of a Special Issue entitled: Emergence of Complex Behavior in Biomembranes edited by Marjorie Longo.

HIV-1 Matrix Protein Interactions with tRNA: Implications for Membrane Targeting

The N-terminally myristoylated matrix (MA) domain of the HIV-1 Gag polyprotein promotes virus assembly by targeting Gag to the inner leaflet of the plasma membrane. Recent studies indicate that, prior to membrane binding, MA associates with cytoplasmic tRNAs (including tRNA^Lys3), and in vitro studies of tRNA-dependent MA interactions with model membranes have led to proposals that competitive tRNA interactions contribute to membrane discrimination. We have characterized interactions between native, mutant, and unmyristylated (myr-) MA proteins and recombinant tRNA^Lys3 by NMR spectroscopy and isothermal titration calorimetry. NMR experiments confirm that tRNA^Lys3 interacts with a patch of basic residues that are also important for binding to the plasma membrane marker, phosphatidylinositol-4,5-bisphosphate [PI(4,5)P₂]. Unexpectedly, the affinity of MA for tRNA^Lys3 (K_d = 0.63 ± 0.03 μM) is approximately 1 order of magnitude greater than its affinity for PI(4,5)P₂-enriched liposomes (K_d(apparent) = 10.2 ± 2.1 μM), and NMR studies indicate that tRNA^Lys3 binding blocks MA association with liposomes, including those enriched with PI(4,5)P₂, phosphatidylserine, and cholesterol. However, the affinity of MA for tRNA^Lys3 is diminished by mutations or sample conditions that promote myristate exposure. Since Gag-Gag interactions are known to promote myristate exposure, our findings support virus assembly models in which membrane targeting and genome binding are mechanistically coupled.

Cyclodextrins and Iatrogenic Hearing Loss: New Drugs with Significant Risk

Cyclodextrins are a family of cyclic oligosaccharides with widespread usage in medicine, industry and basic sciences owing to their ability to solubilize and stabilize guest compounds. In medicine, cyclodextrins primarily act as a complexing vehicle and consequently serve as powerful drug delivery agents. Recently, uncomplexed cyclodextrins have emerged as potent therapeutic compounds in their own right, based on their ability to sequester and mobilize cellular lipids. In particular, 2-hydroxypropyl-β-cyclodextrin (HPβCD) has garnered attention because of its cholesterol chelating properties, which appear to treat a rare neurodegenerative disorder and to promote atherosclerosis regression related to stroke and heart disease. Despite the potential health benefits, use of HPβCD has been linked to significant hearing loss in several species, including humans. Evidence in mice supports a rapid onset of hearing loss that is dose-dependent. Ototoxicity can occur following central or peripheral drug delivery, with either route resulting in the preferential loss of cochlear outer hair cells (OHCs) within hours of dosing. Inner hair cells and spiral ganglion cells are spared at doses that cause ~85% OHC loss; additionally, no other major organ systems appear adversely affected. Evidence from a first-to-human phase 1 clinical trial mirrors animal studies to a large extent, indicating rapid onset and involvement of OHCs. All patients in the trial experienced some permanent hearing loss, although a temporary loss of function can be observed acutely following drug delivery. The long-term impact of HPβCD use as a maintenance drug, and the mechanism(s) of ototoxicity, are unknown. β-cyclodextrins preferentially target membrane cholesterol, but other lipid species and proteins may be directly or indirectly involved. Moreover, as cholesterol is ubiquitous in cell membranes, it remains unclear why OHCs are preferentially susceptible to HPβCD. It is possible that HPβCD acts upon several targets—for example, ion channels, tight junctions (TJ), membrane integrity, and bioenergetics—that collectively increase the sensitivity of OHCs over other cell types.

Exacerbating and reversing lysosomal storage diseases: from yeast to humans

Lysosomal storage diseases (LSDs) arise from monogenic deficiencies in lysosomal proteins and pathways and are characterized by a tissue-wide accumulation of a vast variety of macromolecules, normally specific to each genetic lesion. Strategies for treatment of LSDs commonly depend on reduction of the offending metabolite(s) by substrate depletion or enzyme replacement. However, at least 44 of the ~50 LSDs are currently recalcitrant to intervention. Murine models have provided significant insights into our understanding of many LSD mechanisms; however, these systems do not readily permit phenotypic screening of compound libraries, or the establishment of genetic or gene-environment interaction networks. Many of the genes causing LSDs are evolutionarily conserved, thus facilitating the application of models system to provide additional insight into LSDs. Here, we review the utility of yeast models of 3 LSDs: Batten disease, cystinosis, and Niemann-Pick type C disease. We will focus on the translation of research from yeast models into human patients suffering from these LSDs. We will also discuss the use of yeast models to investigate the penetrance of LSDs, such as Niemann-Pick type C disease, into more prevalent syndromes including viral infection and obesity.

Improvement of De Novo Cholesterol Biosynthesis Efficiently Promotes the Production of Human Immunodeficiency Virus Type 1-Derived Lentiviral Vectors

The use of lentiviral vectors (LVs) for gene transfer in research, technological, or clinical applications requires the production of large amounts of vector. Mass production of clinical-grade LVs remains a challenge and limits certain perspectives for therapeutic use. Some improvements in LV production protocols have been possible by acting on multiple steps of the production process. The addition of animal-derived cholesterol to the culture medium of producer cells is known to increase the infectivity of LVs. To avoid the use of this animal-derived product in clinical settings, an alternative approach is to increase de novo the production of cholesterol by overexpressing a crucial cholesterogenic enzyme, namely, 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). This project evaluates the impact of such an approach on the production, infectivity, and stability of LVs. We demonstrated that the overexpression of human HMGCR isoform 1 (hHMGCR1) in LV producer cells efficiently increased de novo cholesterol biosynthesis and enhanced by 2- to 3-fold the physical and infectious titers of LVs. We also observed that LVs produced in hHMGCR1-overexpressing cells were comparable in stability to LVs produced under classical conditions and were capable of transducing human CD34⁺ hematopoietic stem/progenitor cells efficiently. Interestingly, we also showed that LV production in the absence of fetal calf serum (FCS) but under hHMGCR1-overexpressing conditions allowed a viral production yield comparable to that achieved under classical conditions in high FCS content, leading the way to the establishment of new LV production protocols on adherent cells without serum.

Characterization and Role of Lentivirus-Associated Host Proteins

Enveloped viruses obtain their envelopes during the process of budding from infected cells. During this process, however, these viruses acquire parts of the host cell membranes and host cell-derived proteins as integral parts of their mature envelopes. These host-derived components of viral envelopes may subsequently exhibit various effects on the life cycle of the virus; virus cell interactions, especially host response to virus-incorporated self-proteins; and the pathogenesis of the disease induced by these viruses. Although it was known for some time that various viruses incorporate host cell-derived proteins, the issue of the role of these proteins has received increased attention, specifically in connection with human immunodeficiency virus (HIV) infection and development of acquired immunodeficiency syndrome (AIDS) in humans. The aim of this review is to summarize our current knowledge of the analysis and role of host-derived proteins associated with enveloped viruses, with emphasis on the potential role of these proteins in the pathogenesis of AIDS. Clearly, differences in the clinical outcome of those nonhuman primates infected with simian immunodeficiency virus (SIV) that are disease resistant compared with SIV-infected species that are disease susceptible provide a unique opportunity to determine whether differences in the incorporation of distinct sets of host proteins play a role with distinct clinical outcomes.

Use of a Cholesterol Recognition Amino Acid Consensus Peptide To Inhibit Binding of a Bacterial Toxin to Cholesterol

Recognition of and binding to cholesterol on the host cell membrane is an initial step in the mechanism of numerous pathogens, including viruses, bacteria, and bacterial toxins; however, a viable method of inhibiting this interaction has not yet been uncovered. Here, we describe the mechanism by which a cholesterol recognition amino acid consensus peptide interacts with cholesterol and inhibits the activity of a cholesterol-binding bacterial leukotoxin (LtxA). Using a series of biophysical techniques, we have shown that the peptide recognizes the hydroxyl group of cholesterol with nanomolar affinity and does not disrupt membrane packing, suggesting that it sits primarily near the membrane surface. As a result, LtxA is unable to bind to cholesterol or subsequently become internalized in host cells. Additionally, because cholesterol is not being removed from the cell membrane, the peptide-treated target cells remain viable over extended periods of time. We have demonstrated the use of this peptide in the inhibition of toxin activity for an antivirulence approach to the treatment of bacterial disease, and we anticipate that this approach might have broad utility in the inhibition of viral and bacterial pathogenesis.