Chitosan effects on monolayers of zwitterionic, anionic and a natural lipid extract from E. coli at physiological pH.

Langmuir monolayers are used to simulate the biological membrane environment, acting as a mimetic system of the outer or the inner membrane leaflet. Herein, we analyze the interaction of membrane models with a partially N-acetylated chitosan (Ch35%) possessing a quasi-ideal random pattern of acetylation, full water solubility up to pH ≈ 8.5 and unusually high weight average molecular weight. Lipid monolayers containing dipalmitoyl phosphatidyl choline (DPPC), dipalmitoyl phosphatidyl ethalonamine (DPPE), dipalmitoyl phosphatidyl glycerol (DPPG) or E. coli total lipid extract were spread onto subphases buffered at pH 4.5 or 7.4. The incorporation of Ch35% chitosan caused monolayer expansion and a general trend of decreasing monolayer rigidity with Ch35% concentration. Due to its relatively high content of N-acetylglucosamine (GlcNAc) units, Ch35% interactions with negatively charged monolayers and with E. coli extract were weaker than those involving zwitterionic monolayers or lipid rafts. While the smaller interaction with negatively charged lipids was unexpected, this finding can be attributed to the degree of acetylation (35%) which imparts a small number of charged groups for Ch35% to interact. Chitosan properties are therefore determinant for interactions with model cell membranes, which explains the variability in chitosan bactericide activity in the literature. This is the first study on the effects from chitosans on realistic models of bacterial membranes under physiological pH.

On the role of surrounding regions in the fusion peptide in dengue virus infection.

Dengue virus infection depends on its fusion with the host membrane, where the binding occurs through interaction between proteins on the virus cell surface and specific viral receptors on target membranes. This process is mediated by the fusion peptide located between residues 98 and 112 (DRGWGNGCGLFGKGG) that forms a loop in domain II of dengue E glycoprotein. In this study, we evaluated the role of fusion peptide surrounding regions (88-97 and 113-123) of the Dengue 2 subtype on its interaction with the membrane and fusion activity. These sequences are important to stabilize the fusion peptide loop and increase fusion activity. Three peptides, besides the fusion peptide, were synthesized by SPPS using the Fmoc chemical approach. The first contains the fusion peptide and the C-terminal region of the loop (sequence 98-123); another contains the N-terminal region (88-112) and the larger peptide contains both regions (88-123). The peptides were able to interact with a model membrane. Differences in morphology of the monolayer promoted by the peptides were assessed by Brewster Angle Microscopy (BAM). Our data indicated that the C-terminal region of fusion peptide loop is more efficient in promoting fusion and interacting with the membrane than the N-terminal sequence, which is responsible for the electrostatic initial interaction. We propose a 2-step mechanism for the interaction of the dengue virus fusion peptide with the host membrane, where the N-terminal sequence docks electrostatically on the headgroups and then the C-terminal interacts via hydrophobic forces in the acyl chains.

Salmonella Membrane Structural Remodeling Increases Resistance to Antimicrobial Peptide LL-37.

Gram-negative bacteria are protected from their environment by an outer membrane that is primarily composed of lipopolysaccharides (LPSs). Under stress, pathogenic serotypes of Salmonella enterica remodel their LPSs through the PhoPQ two-component regulatory system that increases resistance to both conventional antibiotics and antimicrobial peptides (AMPs). Acquired resistance to AMPs is contrary to the established narrative that AMPs circumvent bacterial resistance by targeting the general chemical properties of membrane lipids. However, the specific mechanisms underlying AMP resistance remain elusive. Here we report a 2-fold increase in bacteriostatic concentrations of human AMP LL-37 for S. enterica with modified LPSs. LPSs with and without chemical modifications were isolated and investigated by Langmuir films coupled with grazing-incidence X-ray diffraction (GIXD) and specular X-ray reflectivity (XR). The initial interactions between LL-37 and LPS bilayers were probed using all-atom molecular dynamics simulations. These simulations suggest that initial association is nonspecific to the type of LPS and governed by hydrogen bonding to the LPS outer carbohydrates. GIXD experiments indicate that the interactions of the peptide with monolayers reduce the number of crystalline domains but greatly increase the typical domain size in both LPS isoforms. Electron densities derived from XR experiments corroborate the bacteriostatic values found in vitro and indicate that peptide intercalation is reduced by LPS modification. We hypothesize that defects at the liquid-ordered boundary facilitate LL-37 intercalation into the outer membrane, whereas PhoPQ-mediated LPS modification protects against this process by having innately increased crystallinity. Since induced ordering has been observed with other AMPs and drugs, LPS modification may represent a general mechanism by which Gram-negative bacteria protect against host innate immunity.

The cyclic peptide labaditin does not alter the outer membrane integrity of Salmonella enterica serovar Typhimurium.

Antimicrobial peptides are a promising class of new antibiotics with the ability to kill bacteria by disrupting their cell membrane, which is especially difficult for Gram-negative bacteria whose cell wall contains an outer layer of lipopolysaccharides (LPS). Here we show that the cyclic decapeptide Labaditin (Lo), with proven activity against the Gram-positive Staphylococcus aureus and Streptococcus mutans, is not able to kill the Gram-negative Salmonella enterica serovar Typhimurium (S.e.s. Typhimurium). We found that Lo induced significant changes in the surface pressure isotherms of Langmuir monolayers representing the Salmonella enterica serovar Typhimurium inner membrane (S.e.s. Typhimurium IM), and caused leakage in large unilamellar vesicles made with this IM lipid composition. On the basis of these results one should expect bactericidal activity against S.e.s. Typhimurium. However, Lo could not interact with a monolayer of LPS, causing no significant changes in either the surface pressure isotherms or in the polarization-modulated infrared reflection absorption spectra (PM-IRRAS). Therefore, the failure of Lo to kill S.e.s. Typhimurium is associated with the lack of interaction with LPS from the outer bacteria membrane. Our approach with distinct monolayer compositions and combined techniques to investigate molecular-level interactions is useful for drug design to fight antibiotic-resistant bacteria.

Evidence of photoinduced lipid hydroperoxidation in Langmuir monolayers containing Eosin Y.

Photodynamic therapy (PDT) efficiency depends on many factors including the incorporation of the photosensitizer (PS) in cell membranes and possible lipid hydroperoxidation. In this study, we show that hydroperoxidation may be photoinduced when eosin Y is incorporated into Langmuir monolayers that serve as cell membrane models. This occurs for Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), which have unsaturation in their hydrophobic chains. In contrast, light irradiation had no effect on monolayers of saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Evidence of hydroperoxidation was obtained from the area increase in eosin-containing DOPC and POPC monolayers upon irradiation, which was accompanied by a decrease in monolayer thickness according to grazing incidence X-ray off-specular scattering (GIXOS) data. Furthermore, the changes in polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) induced by irradiation were consistent with hydroperoxide migration toward the lipid hydrophilic heads.. In summary, this combination of experimental methods allowed us to determine the effects of eosin Y interaction with cell membrane models under irradiation, which may be associated with the underlying mechanisms of eosin Y as photosensitizer in PDT.

The "pre-assembled state" of magainin 2 lysine-linked dimer determines its enhanced antimicrobial activity.

Antimicrobial peptides (AMPs) are alternatives to conventional antibiotics against multi-drug resistant bacteria with low potential for developing microbial resistance. The design of such molecules requires understanding of the mechanisms of action, particularly the interaction with bacteria cell membranes. In this work, we determine the mechanism responsible for the higher activity against Escherichia coli of the C-terminal lysine dimer of magainin 2, (MG2)2K, in comparison to the monomeric peptide magainin 2 (MG2). Langmuir monolayers and vesicles made with the E. coli lipid extract were used to address the two possible states for the peptide-membrane interaction, namely the "binding state" and "pore state", respectively. The incorporation of MG2 and (MG2)2K in lipid monolayers at the air-water interface caused slight differences in surface pressure isotherms and polarization-modulated infrared reflection absorption (PM-IRRAS) spectra, and therefore the difference in activity is not associated with the binding state. In contrast, large differences were observed in the leakage experiments where (MG2)2K was shown to disrupt the large unilamellar vesicles to a much higher extent owing to efficient pore formation. The binding and penetration of MG2 and (MG2)2K were also probed with molecular dynamics (MD) simulations for bilayers made with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine:1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPE:POPG). (MG2)2K forms disordered toroidal pores at a significant lower concentration than for MG2. In summary, the combination of experimental and computational simulation results indicated that the "pre-assembling state" of (MG2)2K dimer leads to a reduced number of molecules and shorter time being required to kill E. coli.

The importance of cyclic structure for Labaditin on its antimicrobial activity against Staphylococcus aureus.

Antimicrobial resistance has reached alarming levels in many countries, thus leading to a search for new classes of antibiotics, such as antimicrobial peptides whose activity is exerted by interacting specifically with the microorganism membrane. In this study, we investigate the molecular-level mechanism of action for Labaditin (Lo), a 10-amino acid residue cyclic peptide from Jatropha multifida with known bactericidal activity against Streptococcus mutans. We show that Lo is also effective against Staphylococcus aureus (S. aureus) but this does not apply to its linear analogue (L1). Using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), we observed with that the secondary structure of Lo was preserved upon interacting with Langmuir monolayers from a phospholipid mixture mimicking S. aureus membrane, in contrast to L1. This structure preservation for the rigid, cyclic Lo is key for the self-assembly of peptide nanotubes that induce pore formation in large unilamellar vesicles (LUVs), according to permeability assays and dynamic light scattering measurements. In summary, the comparison between Labaditin (Lo) and its linear analogue L1 allowed us to infer that the bactericidal activity of Lo is more related to its interaction with the membrane. It does not require specific metabolic targets, which makes cyclic peptides promising for antibiotics without bacteria resistance.

Acylated Carrageenan Changes the Physicochemical Properties of Mixed Enzyme-Lipid Ultrathin Films and Enhances the Catalytic Properties of Sucrose Phosphorylase Nanostructured as Smart Surfaces.

Control over the catalytic activity of enzymes is important to construct biosensors with a wide range of detectability and higher stability. For this, immobilization of enzymes on solid supports as nanostructured films is a current approach that permits easy control of the molecular architecture as well as tuning of the properties. In this article, we employed acylated carrageenan (AC) mixed with phospholipids at the air-water interface to facilitate the adsorption of the enzyme sucrose phosphorylase (SP). AC stabilized the adsorption of SP at the phospholipid monolayer, as detected by tensiometry, by which thermodynamic parameters could be inferred from the surface pressure-area isotherm. Also, infrared spectroscopy applied in situ over the monolayer showed that the AC-phospholipid system not only permitted the enzyme to be adsorbed but also helped conserve its secondary structure. The mixed monolayers were then transferred onto solid supports as Langmuir-Blodgett (LB) films and investigated with transfer ratio, quartz crystal microbalance, fluorescence spectroscopy, and atomic force microscopy. The enzyme activity of the LB film was then determined, revealing that although there was an expected reduction in activity in relation to the homogeneous environment the activity could be better preserved after 1 month, revealing enhanced stability.

Molecular-Level Modifications Induced by Photo-Oxidation of Lipid Monolayers Interacting with Erythrosin.

Incorporation into cell membranes is key for the action of photosensitizers in photomedicine treatments, with hydroperoxidation as the prominent pathway of lipid oxidation. In this paper, we use Langmuir monolayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as cell membrane models to investigate adsorption of the photosensitizer erythrosin and its effect on photoinduced lipid oxidation. From surface pressure isotherms and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) data, erythrosin was found to adsorb mainly via electrostatic interaction with the choline in the head groups of both DOPC and DPPC. It caused larger monolayer expansion in DOPC, with possible penetration into the hydrophobic unsaturated chains, while penetration into the DPPC saturated chains was insignificant. Easier penetration is due to the less packed DOPC monolayer, in comparison to the more compact DPPC according to the monolayer compressibility data. Most importantly, light irradiation at 530 nm made the erythrosin-containing DOPC monolayer become less unstable, with a relative surface area increase of ca. 19%, in agreement with previous findings for bioadhesive giant vesicles. The relative area increase is consistent with hydroperoxidation, supporting the erythrosin penetration into the lipid chains, which favors singlet oxygen generation close to double bonds, an important requirement for photodynamic efficiency.

Extent of shielding by counterions determines the bactericidal activity of N,N,N-trimethyl chitosan salts.

In this study, we show that the bactericidal activity of quaternized chitosans (TMCs) with sulfate, acetate, and halide counterions against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) correlates with the "availability" of N-quaternized groups [-(+)N(CH3)3] in the TMCs backbones. N,N,N-trimethyl chitosan sulfate (TMCS) and N,N,N-trimethyl chitosan acetate (TMCAc) displayed the highest activities, probably due to their delocalized π system. Among TMCs with halide counterions, activity was higher for N,N,N-trimethyl chitosan chloride (TMCCl), whereas N,N,N-trimethyl chitosan iodide (TMCI) and N,N,N-trimethyl chitosan bromide (TMCBr) exhibited lower, similar values to each other. This is consistent with the shielding of -(+)N(CH3)3 groups inferred from chemical shifts for halide counterions in (1)HNMR spectra. We also demonstrate that TMCs with distinct bactericidal activities can be classified according to their vibrational spectra using principal component analysis. Taken together, these physicochemical characterization approaches represent a predictive tool for the bactericidal activity of chitosan derivatives.

Modification of Salmonella Lipopolysaccharides Prevents the Outer Membrane Penetration of Novobiocin.

Small hydrophilic antibiotics traverse the outer membrane of Gram-negative bacteria through porin channels. Large lipophilic agents traverse the outer membrane through its bilayer, containing a majority of lipopolysaccharides in its outer leaflet. Genes controlled by the two-component regulatory system PhoPQ modify lipopolysaccharides. We isolate lipopolysaccharides from isogenic mutants of Salmonella sp., one lacking the modification, the other fully modified. These lipopolysaccharides were reconstituted as monolayers at the air-water interface, and their properties, as well as their interaction with a large lipophilic drug, novobiocin, was studied. X-ray reflectivity showed that the drug penetrated the monolayer of the unmodified lipopolysaccharides reaching the hydrophobic region, but was prevented from this penetration into the modified lipopolysaccharides. Results correlate with behavior of bacterial cells, which become resistant to antibiotics after PhoPQ-regulated modifications. Grazing incidence x-ray diffraction showed that novobiocin produced a striking increase in crystalline coherence length, and the size of the near-crystalline domains.

Deconstructing the DGAT1 enzyme: Binding sites and substrate interactions.

Diacylglycerol acyltransferase 1 (DGAT1) is a microsomal membrane enzyme responsible for the final step in the synthesis of triacylglycerides. Although DGATs from a wide range of organisms have nearly identical sequences, there is little structural information available for these enzymes. The substrate binding sites of DGAT1 are predicted to be in its large luminal extramembranous loop and to include common motifs with acyl-CoA cholesterol acyltransferase enzymes and the diacylglycerol binding domain found in protein kinases. In this study, synthetic peptides corresponding to the predicted binding sites of DGAT1 enzyme were examined using synchrotron radiation circular dichroism spectroscopy, fluorescence emission and adsorption onto lipid monolayers to determine their interactions with substrates associated with triacylglyceride synthesis (oleoyl-CoA and dioleoylglycerol). One of the peptides, Sit1, which includes the FYxDWWN motif common to both DGAT1 and acyl-CoA cholesterol acyltransferase, changes its conformation in the presence of both substrates, suggesting its capability to bind their acyl chains. The other peptide (Sit2), which includes the putative diacylglycerol binding domain HKWCIRHFYKP found in protein kinase C and diacylglycerol kinases, appears to interact with the charged headgroup region of the substrates. Moreover, in an extended-peptide which contains Sit1 and Sit2 sequences separated by a flexible linker, larger conformational changes were induced by both substrates, suggesting that the two binding sites may bring the substrates into close proximity within the membrane, thus catalyzing the formation of the triacylglyceride product.

Effect of carrageenans of different chemical structures in biointerfaces: a Langmuir film study.

Carrageenans have unique properties in the pharmaceutical and food industries that involve interactions with lipid interfaces, which may be accessed if surface chemistry techniques are employed. The interaction between three different types of carrageenans with dipalmitoylphosphatidylcholine (DPPC) was investigated using Langmuir monolayers as biointerface models. With a combination of data on Surface Pressure-Area Isotherms and Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRRAS), the effect of different fractions on DPPC monolayers was compared by considering the chemical and structural differences as well as the anticoagulant activity of each fraction. Thus, a model is proposed in which carrageenans can encompass interactions that are maximized due to geometrical adaptations on behalf of the interactions between polysaccharide sulfate groups and lipid polar heads.

Lipid interaction triggering Septin2 to assembly into ß-sheet structures investigated by Langmuir monolayers and PM-IRRAS.

The molecular mechanisms responsible for protein structural changes in the central nervous system leading to Alzheimer's disease are unknown, but there is evidence that a family of proteins known as septins may be involved. Septins are a conserved group of GTP-binding proteins which participate in various cellular processes, including polarity determination and membrane dynamics. SEPT1, SEPT4, and SEPT2 have been found in deposits known as neurofibrillary tangles and glial fibrils in Alzheimer's disease. In this study, we provide molecular-level information for the interaction of SEPT2 with Langmuir monolayers at the air/water interface, which are used as simplified membrane models. The high surface activity of SEPT2 causes it to adsorb onto distinct types of lipid Langmuir monolayers, namely dipalmitoylphosphatidylcholine and PtdIns(4,5)P2. However, the interaction with PtdIns(4,5)P2 is much stronger, not only leading to a higher adsorption, but also to SEPT2 remaining inserted within the membrane at high surface pressures. Most importantly, in situ polarization-modulated infrared reflection absorption spectroscopy results indicated that the native secondary structure of SEPT2 is preserved upon interacting with PtdIns(4,5)P2, but not when dipalmitoylphosphatidylcholine is at the air/water interface. Taken together, the results presented here suggest that the interaction between SEPT2 and the cell membrane may play an important role in the assembly of SEPT2 into amyloid-like fibers.

Low molecular-weight chitosans are stronger biomembrane model perturbants.

The influence from the chitosan molecular weight on its interaction with cell membrane models has been studied. A low molecular weight chitosan (LMWChi) adsorbed from the subphase expanded the surface pressure-area and surface potential-area isotherms of dimyristoyl phosphatidic acid (DMPA) monolayers and decreased the compressional modulus. The expansion in the monolayers and the decrease in the compressional modulus were larger for LMWChi than for a high molecular weight chitosan (Chi). The polymeric nature is still essential for the interaction though, which was demonstrated by measuring negligible changes in the mechanical properties of the DMPA monolayer when the subphase contained glucosamine and acetyl-glucosamine. The results were rationalized in a model through which chitosan interacted with the membrane via electrostatic and hydrophobic interactions, with the smaller chains of LMWChi having less steric hindrance to be accommodated in the membrane. In summary, the activity based on membrane interactions depends on the distribution of molar mass, with lower molecular weight chitosan more likely to have stronger effects.

A new strategy to investigate the toxicity of nanomaterials using Langmuir monolayers as membrane models.

Nanomaterials such as carbon nanotubes (CNTs) and nanoparticles have received enormous attention in analytical areas for their potential applications as new tools for biotechnology and life sciences. Most of these possible applications involve the use of CNTs and related materials as vehicles for drug delivery and/or gene therapy. In this study, we introduce a methodology to evaluate the interactions between CNTs/dendrimers nanoconjugates and phospholipid biomembrane models, using the Langmuir film balance technique. Our main goal was to elucidate the action of engineered nanomaterials in cell membranes, at the molecular level, using a membrane model system. The penetration of single-walled carbon nanotubes (SWCNTs)/polyamidoamine dendrimer nanocomplexes into dipalmitoylphosphatidylcholine monolayers was pronounced, as revealed by adsorption kinetics and surface pressure measurements. These findings suggest that SWCNTs were able to interact even at high surface pressure values, ∼30 mN/m. Therefore, the results confirm that the presence of the nanomaterial affects the packing of the synthetic membranes. We believe the methodology introduced here may be of great importance for further nanotoxicity studies.

Interaction of chitosan and mucin in a biomembrane model environment.

Chitosans have been widely exploited in biological applications, including drug delivery and tissue engineering, especially owing to their mucoadhesive properties, but the molecular-level mechanisms for the chitosan action are not known in detail. It is believed that chitosan could affect the mucus by interacting with the proteins mucins, in a process mediated by the cell membrane. In this study we used Langmuir monolayers of dimyristoylphosphatidic acid (DMPA) as simplified membrane models to investigate the interplay between the activity of mucins and chitosan. Surface pressure and surface potential measurements were performed with DMPA monolayers onto which chitosan and/or mucin was adsorbed. We found that the expanding effect from mucin was considerably reduced when chitosan was injected after mucin had been adsorbed on the DMPA monolayer. The results were consistent with the formation of complexes between mucin and chitosan, thus highlighting the importance of electrostatic interactions. Furthermore, chitosan could remove mucin that was co-deposited along with DMPA in Langmuir-Blodgett (LB) films, which could be ascribed to molecular-level interactions between chitosan and mucin inferred from the FTIR spectra of the LB films. In conclusion, the results with Langmuir and LB films suggest that electrostatic interactions are crucial for the mucoadhesive mechanism, which is affected by the complexation between chitosan and mucin.

The role of the C-terminal region of pulchellin A-chain in the interaction with membrane model systems.

Pulchellin is a Ribosome Inactivating Protein containing an A-chain (PAC), whose toxic activity requires crossing the endoplasmic reticulum (ER) membrane. In this paper, we investigate the interaction between recombinant PAC (rPAC) and Langmuir monolayers of dipalmitoyl phosphatidyl glycerol (DPPG), which served as membrane model. Three catalytically active, truncated PACs with increasing deletion of the C-terminal region, possessing 244, 239 and 236 residues (rPAC(244), rPAC(239) and rPAC(236)), were studied. rPAC had the strongest interaction with the DPPG monolayer, inducing a large expansion in its surface pressure-area isotherm. The affinity to DPPG decreased with increased deletion of the C-terminal region. When the C-terminal region was deleted completely (rPAC(236)), the interaction was recovered, probably because other hydrophobic regions were exposed to the membrane. Using Polarization Modulated-Infrared Reflection Absorption Spectroscopy (PM-IRRAS) we observed that at a bare air/water interface rPAC comprised mainly α-helix structures, the C-terminal region had unordered structures when interacting with DPPG. For rPAC(236) the α-helices were preserved even in the presence of DPPG. These results confirm the importance of the C-terminal region for PAC-ER membrane interaction. The partial unfolding only with preserved C-terminal appears a key step for the protein to reach the cytosol and develop its toxic activity.

Dermaseptin 01 as antimicrobial peptide with rich biotechnological potential: study of peptide interaction with membranes containing Leishmania amazonensis lipid-rich extract and membrane models.

This article addresses the interactions of the synthetic antimicrobial peptide dermaseptin 01 (GLWSTIKQKGKEAAIAAA- KAAGQAALGAL-NH(2) , DS 01) with phospholipid (PL) monolayers comprising (i) a lipid-rich extract of Leishmania amazonensis (LRE-La), (ii) zwitterionic PL (dipalmitoylphosphatidylcholine, DPPC), and (iii) negatively charged PL (dipalmitoylphosphatidylglycerol, DPPG). The degree of interaction of DS 01 with the different biomembrane models was quantified from equilibrium and dynamic liquid-air interface parameters. At low peptide concentrations, interactions between DS 01 and zwitterionic PL, as well as with the LRE-La monolayers were very weak, whereas with negatively charged PLs the interactions were stronger. For peptide concentrations above 1 µg/ml, a considerable expansion of negatively charged monolayers occurred. In the case of DPPC, it was possible to return to the original lipid area in the condensed phase, suggesting that the peptide was expelled from the monolayer. However, in the case of DPPG, the average area per lipid molecule in the presence of DS 01 was higher than pure PLs even at high surface pressures, suggesting that at least part of DS 01 remained incorporated in the monolayer. For the LRE-La monolayers, DS 01 also remained in the monolayer. This is the first report on the antiparasitic activity of AMPs using Langmuir monolayers of a natural lipid extract from L. amazonensis.

Chitosan as a bioadhesive agent between porphyrins and phospholipids in a biomembrane model.

Porphyrins are currently used in photodynamic therapy as photosensitizers. In this paper we studied the interaction of two charged porphyrins, 5, 10, 15, 20-mesotetrakis(N-metyl-4-pyridyl) porphyrin, (TMPyP/chloride salt) cationic, and 5, 10, 15, 20-meso-tetrakis(sulfonatophenyl) porphyrin, (TPPS4/sodium salt) anionic, nanoassembled in phospholipid Langmuir monolayers and Langmuir-Blodgett films. Furthermore, we used chitosan to mediate the interaction between the porphyrins and the model membrane, aiming to understand the role of the polysaccharide in a molecular level. The effect of the interaction of the photosensitizers on the fluidity of the lipid monolayer was investigated by using dilatational surface elasticity. We also used photoluminescence (PL) spectroscopy to identify the porphyrins adsorbed in the phospholipid films. We observed an expansion of the monolayer promoted by the adsorption of the porphyrins into the lipid-air interface which was more pronounced in the case of TMPyP, as a consequence of a strong electrostatic interaction with the anionic monolayer. The chitosan promoted a higher adsorption of the porphyrins on the phospholipid monolayers and enabled the porphyrin to stay in its monomeric form (as confirmed by PL spectroscopy), thus demonstrating that chitosan can be pointed out as a potential photosensitizer delivery system in photodynamic therapy.