Exploring the antileishmanial activity of dicentrine from Ocotea puberula (Lauraceae) using biomembrane models.

This study aimed to assess the antiprotozoal efficacy of dicentrine, an aporphine alkaloid isolated from Ocotea puberula, against amastigote forms of Leishmania (L.) infantum. Our findings reveal that dicentrine demonstrated a notable EC50 value of 10.3 µM, comparable to the positive control miltefosine (EC50 of 10.4 µM), while maintaining moderate toxicity to macrophages (CC50 of 51.9 µM). Utilizing an in silico methodology, dicentrine exhibited commendable adherence to various parameters, encompassing lipophilicity, water solubility, molecule size, polarity, and flexibility. Subsequently, we conducted additional investigations to unravel the mechanism of action, employing Langmuir monolayers as models for protozoan cell membranes. Tensiometry analyses unveiled that dicentrine disrupts the thermodynamic and mechanical properties of the monolayer by expanding it to higher areas and increasing the fluidity of the film. The molecular disorder was further corroborated through dilatational rheology and infrared spectroscopy. These results contribute insights into the role of dicentrine as a potential antiprotozoal drug in its interactions with cellular membranes. Beyond elucidating the mechanism of action at the plasma membrane's external surface, our study sheds light on drug-lipid interface interactions, offering implications for drug delivery and other pharmaceutical applications.

Exploring the antileishmanial activity of dicentrine from Ocotea puberula (Lauraceae) using biomembrane models

This study aimed to assess the antiprotozoal efficacy of dicentrine, an aporphine alkaloid isolated from Ocotea puberula, against amastigote forms of Leishmania (L.) infantum. Our findings reveal that dicentrine demonstrated a notable EC50 value of 10.3 μM, comparable to the positive control miltefosine (EC50 of 10.4 μM), while maintaining moderate toxicity to macrophages (CC50 of 51.9 μM). Utilizing an in silico methodology, dicentrine exhibited commendable adherence to various parameters, encompassing lipophilicity, water solubility, molecule size, polarity, and flexibility. Subsequently, we conducted additional investigations to unravel the mechanism of action, employing Langmuir monolayers as models for protozoan cell membranes. Tensiometry analyses unveiled that dicentrine disrupts the thermodynamic and mechanical properties of the monolayer by expanding it to higher areas and increasing the fluidity of the film. The molecular disorder was further corroborated through dilatational rheology and infrared spectroscopy. These results contribute insights into the role of dicentrine as a potential antiprotozoal drug in its interactions with cellular membranes. Beyond elucidating the mechanism of action at the plasma membrane's external surface, our study sheds light on drug-lipid interface interactions, offering implications for drug delivery and other pharmaceutical applications.

Study of the interactions of gold nanoparticles functionalized with aminolevulinic acid in membrane models.

Gold nanoparticles have been intensively studied in cancer therapy to improve drug release, increasing therapeutic action and reducing adverse effects. The interaction between gold nanoparticles and cell membranes can give information about the cell internalization. In this study, gold nanoparticles with aminolevulinic acid (5-ALA) were synthesized using the photoreduction method (5-ALA: AuNPs). The prodrug 5-ALA is responsible for protoporphyrin IX synthesis inside the cell and allows the use of therapies as photodynamic and sonodynamic therapies. The cytotoxicity test was performed on a breast cancer tumor line (MCF-7), and high Content Screening assay was applied to evaluate the entry of nanoparticles into cells. DPPS Langmuir monolayers were assembled at the air/water interface and employed as a simplified membrane model for half of a tumorigenic cell membrane. We assessed the molecular interactions between 5-ALA: AuNPs and phospholipids using tensiometry (π-A isotherms) and vibrational spectroscopy (PM-IRRAS) experiments. We found that the functionalized gold nanoparticles strongly interact with DPPS polar head groups (especially phosphate and carbonyl), changing the phospholipid hydration and leading to a general decrease in the monolayer conformational order. This work then probes that specific interaction between 5-ALA: AuNPs and the negatively charged phospholipid can be assessed using Langmuir monolayers as simplified biomembrane models.

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.

Interaction between 17 α-ethynylestradiol hormone with Langmuir monolayers: The role of charged headgroups.

The persistence of steroid hormones disposed of in the environment may pose risks to the health of humans and wildlife, which brings the need of understanding their mode of action, believed to occur in cell membranes. In this study, we investigate the molecular-level interactions between the synthetic hormone 17 α-ethynylestradiol (EE2) and Langmuir monolayers that represent simplified cell membranes. In surface pressure isotherms, EE2 was found to expand the monolayers at low surface pressures of the positively charged dimethyldioctadecylammonium bromide (DODAB), zwitterionic 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), negatively charged 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), and partially anionized stearic acid (StAc). The largest effects were observed for the charged DODAB and DPPG. At the pressure (30mN.m-1) corresponding to the molecular packing of a cell membrane, EE2 caused the compressibility modulus to decrease, again with the largest changes occurring for DODAB and DPPG. The effects from EE2 on the packing of the lipid molecules at this high pressure depended essentially on the size of the headgroups, with EE2 contributing to the area per lipid for StAc and DODAB, whose headgroups are small. EE2 interacted with the headgroups of all lipids and StAc, also affecting the ordering of the tails for DODAB, DPPG and DPPC, according to in situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS). Based on the analysis with the two characterization methods, we propose a model for the EE2 positioning and molecular groups involved in the interaction, which should be relevant to unveil the endocrine disrupting action of EE2.

Interaction of acylated and unacylated forms of E. coli alpha-hemolysin with lipid monolayers: a PM-IRRAS study.

Uropathogenic strains of Escherichia coli produce virulence factors, such as the protein toxin alpha-hemolysin (HlyA), that enable the bacteria to colonize the host and establish an infection. HlyA is synthetized as a protoxin (ProHlyA) that is transformed into the active form in the bacterial cytosol by the covalent linkage of two fatty-acyl moieties to the polypeptide chain before the secretion of HlyA into the extracellular medium. The aim of this work was to investigate the effect of the fatty acylation of HlyA on protein conformation and protein-membrane interactions. Polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS) experiments were performed at the air-water interface, and lipid monolayers mimicking the outer leaflet of red-blood-cell membranes were used as model systems for the study of protein-membrane interaction. According to surface-pressure measurements, incorporation of the acylated protein into the lipid films was faster than that of the nonacylated form. PM-IRRAS measurements revealed that the adsorption of the proteins to the lipid monolayers induced disorder in the lipid acyl chains and also changed the elastic properties of the films independently of protein acylation. No significant difference was observed between HlyA and ProHlyA in the interaction with the model lipid monolayers; but when these proteins became adsorbed on a bare air-water interface, they adopted different secondary structures. The assumption of the correct protein conformation at a hydrophobic-hydrophilic interface could constitute a critical condition for biologic activity.

Langmuir films of dipalmitoyl phosphatidylethanolamine grafted poly(ethylene glycol). In-situ evidence of surface aggregation at the air-water interface.

The molecular packing-dependent interfacial organization of polyethylene glycol grafted dipalmitoylphosphatidylethanolamine (PE-PEGs) Langmuir films was studied. The PEG chains covered a wide molecular mass range (350, 1000 and 5000Da). In surface pressure-area (π-A), isotherms PE-PEG1000 and PE-PEG5000 showed transitions (midpoints at πm,t1∼11mN/m, "t1"), which appeared as a long non-horizontal line region. Thus, t1 cannot be considered a first-order phase transition but may reflect a transition within the polymer, comprising its desorption from the air-water interface and compaction upon compression. This is supported by the increase in the νs(C-O-C) PM-IRRAS signal intensity and the increasing surface potentials at maximal compression, which reflect thicker polymeric layers. Furthermore, changes in hydrocarbon chain (HC) packing and tilt with respect to the surface led to reorientation in the PO2- group upon compression, indicated by the inversion of the νasym(PO2-) PM-IRRAS signal around t1. The absence of a t1 in PE-PEG350 supports the requisite of a critical polymer chain length for this transition to occur. In-situ epifluorescence microscopy revealed 2D-domain-like structures in PE-PEG1000 and PE-PEG5000 around t1, possibly associated with gelation/dehydration of the polymeric layer and appearing at decreasing π as the polymeric tail became longer. Another transition, t2, appearing in PE-PEG350 and PE-PEG1000 at πm,t2=29.4 and 34.8mN/m, respectively, was associated with HC condensation and was impaired in PE-PEG5000 due to steric hindrance imposed by the large size of its polymer moiety. Two critical lengths of polymer chains were found, one of which allowed the onset of polymeric-tail gelation and the other limited HC compaction.

The interaction of mefloquine hydrochloride with cell membrane models at the air-water interface is modulated by the monolayer lipid composition.

The antiparasitic properties of antiparasitic drugs are believed to be associated with their interactions with the protozoan membrane, encouraging research on the identification of membrane sites capable of drug binding. In this study, we investigated the interaction of mefloquine hydrochloride, known to be effective against malaria, with cell membrane models represented by Langmuir monolayers of selected lipids. It is shown that even small amounts of the drug affect the surface pressure-area isotherms as well as surface vibrational spectra of some lipid monolayers, which points to a significant interaction. The effects on the latter depend on the electrical charge of the monolayer-forming molecules, with the drug activity being particularly distinctive for negatively charged lipids. Therefore, the lipid composition of the monolayer modulates the interaction with the lipophilic drug, which may have important implications in understanding how the drug acts on specific sites of the protozoan membrane.

Homologous Hevea brasiliensis REF (Hevb1) and SRPP (Hevb3) present different auto-assembling.

HbREF and HbSRPP are two Hevea brasiliensis proteins present on rubber particles, and probably involved in the coagulation of latex. Their function is unclear, but we previously discovered that REF had amyloid properties, which could be of particular interest during the coagulation process. First, we confirmed that REF and SRPP, homologous and principal proteins in hevea latex, are not glycoproteins. In this work, we investigated various aspects of protein interactions: aggregation, auto-assembling, yeast and erythrocyte agglutination, co-interactions by various biochemical (PAGE, spectroscopy, microscopy), biophysical (DLS, ellipsometry) and structural (TEM, ATR-FTIR, PM-IRRAS) approaches. We demonstrated that both proteins are auto-assembling into different aggregative states: REF polymerizes as an amyloid rich in ß-sheets and forms quickly large aggregates (>µm), whereas SRPP auto-assembles in solution into stable nanomultimers of a more globular nature. Both proteins are however able to interact together, and SRPP may inhibit the amyloidogenesis of REF. REF is also able to interact with the membranes of yeasts and erythrocytes, leading to their agglutination. In addition, we also showed that both REF and SRPP did not have antimicrobial activity, whereas their activity on membranes has been clearly evidenced. We may suspect that these aggregative properties, even though they are clearly different, may occur during coagulation, when the membrane is destabilized. The interaction of proteins with membranes could help in the colloidal stability of latex, whereas the protein-protein interactions would contribute to the coagulation process, by bringing rubber particles together or eventually disrupting the particle monomembranes.