Browsing by Author "Hollmann, Axel"
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- 25-hydroxycholesterol effect on membrane structure and mechanical propertiesPublication . Domingues, Marco; Gomes, Bárbara; Hollmann, Axel; Santos, Nuno C.Cholesterol is responsible for the plasticity of plasma membranes and is involved in physiological and pathophysiological responses. Cholesterol homeostasis is regulated by oxysterols, such as 25-hydroxycholesterol. The presence of 25-hydroxycholesterol at the membrane level has been shown to interfere with several viruses' entry into their target cells. We used atomic force microscopy to assess the effect of 25-hydroxycholesterol on different properties of supported lipid bilayers with controlled lipid compositions. In particular, we showed that 25-hydroxycholesterol inhibits the lipid-condensing effects of cholesterol, rendering the bilayers less rigid. This study indicates that the inclusion of 25-hydroxycholesterol in plasma membranes or the conversion of part of their cholesterol content into 25-hydroxycholesterol leads to morphological alterations of the sphingomyelin (SM)-enriched domains and promotes lipid packing inhomogeneities. These changes culminate in membrane stiffness variations.
- Antiviral lipopeptide-cell membrane Interaction Is Influenced by PEG linker lengthPublication . Augusto, Marcelo T.; Hollmann, Axel; Porotto, Matteo; Moscona, Anne; Santos, Nuno C.A set of lipopeptides was recently reported for their broad-spectrum antiviral activity against viruses belonging to the Paramyxoviridae family, including human parainfluenza virus type 3 and Nipah virus. Among them, the peptide with a 24-unit PEG linker connecting it to a cholesterol moiety (VG-PEG24-Chol) was found to be the best membrane fusion inhibitory peptide. Here, we evaluated the interaction of the same set of peptides with biomembrane model systems and isolated human peripheral blood mononuclear cells (PBMC). VG-PEG24-Chol showed the highest insertion rate and it was among the peptides that induced a larger change on the surface pressure of cholesterol rich membranes. This peptide also displayed a high affinity towards PBMC membranes. These data provide new information about the dynamics of peptide-membrane interactions of a specific group of antiviral peptides, known for their potential as multipotent paramyxovirus antivirals.
- Biological activity of antibacterial peptides matches synergism between electrostatic and non electrostatic forcesPublication . Bouchet, Ana M.; Iannucci, Nancy B.; Pastrian, María B.; Cascone, Osvaldo; Santos, Nuno C.; Disalvo, Edgardo A.; Hollmann, AxelSubstitution of Ala 108 and Ala 111 in the 107–115 human lysozyme (hLz) fragment results in a 20-fold increased anti-staphylococcal activity while its hemolytic activity becomes significant (30%) at veryhigh concentrations. This analog displays an additional positive charge near the N-terminus (108) and anextra Trp residue at the center of the molecule (111), indicating that this particular amino acid sequenceimproves its interaction with the bacterial plasma membrane. In order to understand the role of thisarrangement in the membrane interaction, studies with model lipid membranes were carried out.The interactions of peptides, 107–115 hLz and the novel analog ([K108W111]107–115 hLz) with lipo-somes and lipid monolayers were evaluated by monitoring the changes in the fluorescence of the Trpresidues and the variation of the monolayers surface pressure, respectively. Results obtained with bothtechniques revealed a significant affinity increase of [K108W111]107–115 hLz for lipids, especially whenthe membranes containing negatively charged lipids, such as phosphatidylglycerol. However, there is alsoa significant interaction with zwitterionic lipids, suggesting that other forces in addition to electrostaticinteractions are involved in the binding. The analysis of adsorption isotherms and the insertion kineticssuggest that relaxation processes of the membrane structure are involved in the insertion process ofnovel peptide [K108W111]107–115 hLz but not in 107–115 hLz, probably by imposing a reorganization ofwater at the interphases.In this regard, the enhanced activity of peptide [K108W111]107–115 hLz may be explained by a syner-gistic effect between the increased electrostatic forces as well as the increased hydrophobic interactions.
- Cell surface damage and morphological changes in Oenococcus oeni after freeze-drying and incubation in synthetic winePublication . Bravo-Ferrada, Bárbara Mercedes; Abreu, Sónia Gonçalves; Semorile, Liliana; Santos, Nuno C.; Brizuela, Natalia S.; Elizabeth Tymczyszyn, E.; Hollmann, AxelThe aim of the present study was to evaluate the effects of freeze-drying in the presence of trehalose as a cryoprotectant, followed by incubation in synthetic wine, on surface damage, viability and l-malic acid consumption of the oenological strain Oenococcus oeni UNQOe 73.2. After freeze-drying, no significant differences were observed in the number of viable cells (for both acclimated and non-acclimated cultures) respect to the fresh culture. In contrast, loss of viability was observed after wine incubation for 24 h, being acclimated freeze-dried cells the best conditions for this. After the preservation process, small changes in cell morphology were observed by Atomic Force Microscopy (AFM). The Zeta potential and AFM showed that 24 h of wine incubation was enough to induce several cell surface modifications. Plate count data allowed us to establish that surface damage is an important factor for loss of viability, regardless of the acclimation treatment. Although the number of surviving O. oeni cells decreased dramatically after incubation in synthetic wine for 15 days, the consumption of l-malic acid was higher than 70%, with freeze-dried cells showing a better performance than fresh cultures. These results demonstrate that O. oeni freeze-dried cultures could be applied to direct wine inoculation, to conduct malolactic fermentation, maintaining its technological properties and reducing the time and costs of the winemaking process.
- Conjugation of cholesterol to HIV-1 fusion inhibitor C34 increases peptide-membrane interactions potentiating its actionPublication . Hollmann, Axel; Matos, Pedro M.; Augusto, Marcelo T.; Castanho, Miguel A. R. B.; Santos, Nuno C.Recently, the covalent binding of a cholesterol moiety to a classical HIV-1 fusion inhibitor peptide, C34, was shown to potentiate its antiviral activity. Our purpose was to evaluate the interaction of cholesterol-conjugated and native C34 with membrane model systems and human blood cells to understand the effects of this derivatization. Lipid vesicles and monolayers with defined compositions were used as model membranes. C34-cholesterol partitions more to fluid phase membranes that mimic biological membranes. Importantly, there is a preference of the conjugate for liquid ordered membranes, rich in cholesterol and/or sphingomyelin, as observed both from partition and surface pressure studies. In human erythrocytes and peripheral blood mononuclear cells (PBMC), C34-cholesterol significantly decreases the membrane dipole potential. In PBMC, the conjugate was 14- and 115-fold more membranotropic than T-1249 and enfuvirtide, respectively. C34 or cholesterol alone did not show significant membrane activity. The enhanced interaction of C34-cholesterol with biological membranes correlates with its higher antiviral potency. Higher partitions for lipid-raft like compositions direct the drug to the receptor-rich domains where membrane fusion is likely to occur. This intermediary membrane binding step may facilitate the drug delivery to gp41 in its pre-fusion state.
- Coordination forces between lipid bilayers produced by ferricyanide and Ca2+Publication . Frías, Maria A.; Contis, Griselda; Hollmann, Axel; Disalvo, E. AnibalAttractive forces usually invoked to take place in membrane–membrane contact in aggregation are hydrogen bonding cross-linkings and hydrophobic interactions between opposing surfaces. However, little is known in relation to the presence of coordination forces in the membrane–membrane interaction. These are understood as those that may be favoured by the formation or the participation of coordination complexes between surface specific groups. In this work, we have analyzed the formation of this type of aggregates between phosphatidylcholine vesicles mediated by a coadsorption of ferricyanide and Ca2+ ions to the interface. The results obtained by surface potential measures, optical and electronic microscopy, FTIR and 1H NMR spectroscopies indicate that ferricyanide [Fe(CN)6]3− but not of ferrocyanide [Fe(CN)6]4− can form the complex when Ca2+ has been adsorbed previously to the membrane surface. In this condition, the anion is likely to act as a bridge between two opposing membranes causing a tight aggregation in which geometry and the polarizability of the ligands to Fe3+ play a role.
- Designing improved active peptides for therapeutic approaches against infectious diseasesPublication . Gomes, Bárbara; Augusto, Marcelo T.; Felício, Mário Romão; Hollmann, Axel; Franco, Octávio L.; Abreu, Sónia Gonçalves; Santos, Nuno C.Infectious diseases are one of the main causes of human morbidity and mortality. In the last few decades, pathogenic microorganisms' resistance to conventional drugs has been increasing, and it is now pinpointed as a major worldwide health concern. The need to search for new therapeutic options, as well as improved treatment outcomes, has therefore increased significantly, with biologically active peptides representing a new alternative. A substantial research effort is being dedicated towards their development, especially due to improved biocompatibility and target selectivity. However, the inherent limitations of peptide drugs are restricting their application. In this review, we summarize the current status of peptide drug development, focusing on antiviral and antimicrobial peptide activities, highlighting the design improvements needed, and those already being used, to overcome the drawbacks of the therapeutic application of biologically active peptides.
- Effect of 25-hydroxycholesterol in viral membrane fusion : insights on HIV inhibitionPublication . Gomes, Bárbara; Abreu, Sónia Gonçalves; Disalvo, Anibal; Hollmann, Axel; Santos, Nuno C.Recently, it was demonstrated that 25-hydroxycholesterol (25HC), an oxidized cholesterol derivative, inhibits human immunodeficiency virus type 1 (HIV) entry into its target cells. However, the mechanisms involved in this action have not yet been established. The aim of this work was to study the effects of 25HC in biomembrane model systems and at the level of HIV fusion peptide (HIV-FP). Integration of different biophysical approaches was made in the context of HIV fusion process, to clarify the changes at membrane level due to the presence of 25HC that result in the suppressing of viral infection. Lipid vesicles mimicking mammalian and HIV membranes were used on spectroscopy assays and lipid monolayers in surface pressure studies. Peptide-induced lipid mixing assays were performed by Förster resonance energy transfer to calculate fusion efficiency. Liposome fusion is reduced by 50% in the presence of 25HC, comparatively to cholesterol. HIV-FP conformation was assessed by infrared assays and it relies on sterol nature. Anisotropy, surface pressure and dipole potential assays indicate that the conversion of cholesterol in 25HC leads to a loss of the cholesterol modulating effect on the membrane. With different biophysical techniques, we show that 25HC affects the membrane fusion process through the modification of lipid membrane properties, and by direct alterations on HIV-FP structure. The present data support a broad antiviral activity for 25HC.
- Effects of singlet oxygen generated by a broad-spectrum viral fusion inhibitor on membrane nanoarchitecturePublication . Hollmann, Axel; Gonçalves, Sónia; Augusto, Marcelo T.; Castanho, Miguel A. R. B.; Lee, Benhur; Santos, Nuno C.Targeting membranes of enveloped viruses represents an exciting new paradigm to explore on the development of broad-spectrum antivirals. Recently, broad-spectrum small-molecule antiviral drugs were described, preventing enveloped virus entry at an intermediate step, after virus binding but before virus–cell fusion. Those compounds, including an oxazolidine-2,4-dithione named JL103 that presented the most promissing results, act deleteriously on the virus envelope but not at the cell membrane level. In this work, by using atomic force microscopy (AFM), we aimed at unraveling the effects that JL103 is able to induce in the lipid membrane architecture at the nanoscale. Our results indicate that singlet oxygen produced by JL103 decreases membrane thickness, with an expansion of the area per phospholipid, by attacking the double bonds of unsaturated phospholipids. This membrane reorganization prevents the fusion between enveloped virus and target cell membranes, resulting in viral entry inhibition.
- Improvement of HIV fusion inhibitor C34 efficacy by membrane anchoring and enhanced exposurePublication . Augusto, Marcelo T.; Hollmann, Axel; Castanho, Miguel A. R. B.; Porotto, Matteo; Pessi, Antonello; Santos, Nuno C.Objectives: The aim of the present work was to evaluate the interaction of two new HIV fusion inhibitors {HIVP3 [C34–polyethylene glycol (PEG)4–cholesterol] and HIVP4 [(C34–PEG4)2–cholesterol]} with membrane model systems and human blood cells in order to clarify where and how the fusion inhibitors locate, allowing us to understand their mechanism of action at the molecular level, and which strategies may be followed to increase efficacy. Methods: Lipid vesicles with defined compositions were used for peptide partition and localization studies, based on the intrinsic fluorescence of HIVP3 and HIVP4. Lipid monolayers were employed in surface pressure studies. Finally, human erythrocytes and peripheral blood mononuclear cells (PBMCs) isolated from blood samples were used in dipole potential assays. Results: Membrane partition, dipole potential and surface pressure assays indicate that the new fusion inhibitors interact preferentially with cholesterol-rich liquid-ordered membranes, mimicking biological membrane microdomains known as lipid rafts. HIVP3 and HIVP4 are able to interact with human erythrocytes and PBMCs to a similar degree as a previously described simpler drug with monomeric C34 and lacking the PEG spacer, C34–cholesterol. However, the pocket-binding domain (PBD) of both HIVP3 and HIVP4 is more exposed to the aqueous environment than in C34–cholesterol. Conclusions: The present data allow us to conclude that more efficient blocking of HIV entry results from the synergism between the membranotropic behaviour and the enhanced exposure of the PBD.
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