Influence of lipophilicity of anthracyclines on the interactions with cholesterol in the model cell membranes - Langmuir monolayer and SEIRAS studies

The effect of trans-resveratrol on the physicochemical properties of lipid membranes with different cholesterol content

Resveratrol is one of the most popular phytoalexins, which naturally occurs in grapes and red wine. This compound not only has beneficial effects on the human body, especially on the cardiovascular system, but also has antiviral, antibacterial and antifungal properties. In addition, resveratrol may have therapeutic effects against various types of cancer. The mechanism of action of resveratrol is not fully understood, but it is suspected that one of the most important steps is its interaction with the cell membrane and changing its molecular organization. Therefore, in the present study, we investigated the effects of resveratrol at different concentrations (0-75 μM) on model membranes composed of POPC, SM and cholesterol, in systems with different cholesterol contents and a constant POPC/SM molar ratio (1:1). Our tests included systems containing 5, 15 and 33.3 mol% cholesterol. Tests were carried out for monolayers using the Langmuir monolayer technique supported by Brewster angle microscopy and penetration experiments. Bilayer (liposome) experiments included calcein release, steady-state DPH fluorescence anisotropy and partition coefficients. The results showed that resveratrol interacts with model cell membranes (lipid monolayers and lipid bilayers), and its incorporation into membranes is accompanied by changes in their physicochemical parameters, such as lipid packing, fluidity and permeability. Furthermore, we showed that the cholesterol content of the membrane significantly affects the degree of incorporation of resveratrol into the model membrane, which may indicate that the molecular mechanism of action of this compound is closely related to its interactions with lipid rafts, domains responsible for regulating various cellular functions.

Statin Action Targets Lipid Rafts of Cell Membranes: GIXD/PM-IRRAS Investigation of Langmuir Monolayers

Lipid rafts are condensed regions of cell membranes rich in cholesterol and sphingomyelin, which constitute the target for anticholesterolemic drugs - statins. In this work, we use for the first time a combined grazing-incidence X-ray diffraction (GIXD)/polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS)/Brewster angle microscopy (BAM) approach to show the statin effect on model lipid rafts and its components assembled in Langmuir monolayers at the air-water interface. Two representatives of these drugs, fluvastatin (FLU) and cerivastatin (CER), of different hydrophobicity were chosen, while cholesterol (Chol) and sphingomyelin (SM), and their 1:1 mixture were selected to form condensed monolayers of lipid rafts. The effect of statins on the single components of lipid rafts indicated that both the hydrophobicity of the drugs and the organization of the layer determined the drug-lipid interaction. For cholesterol monolayers, only the most hydrophobic CER was effectively changing the film structure, while for the less organized sphingomyelin, the biggest effect was observed for FLU. This drug affected both the polar headgroup region as shown by PM-IRRAS results and the 2D crystalline structure of the SM monolayer as evidenced by GIXD. Measurements performed for Chol/SM 1:1 models proved also that the statin effect depends on the presence of Chol-SM complexes. In this case, the less hydrophobic FLU was not able to penetrate the binary layer at all, while exposure to the hydrophobic CER resulted in the phase separation and formation of ordered assemblies. The changes in the membrane properties were visualized by BAM images and GIXD patterns and confirmed by thermodynamic parameters of hysteresis in the Langmuir monolayer compression-decompression experiments.

Site of the Hydroxyl Group Determines the Surface Behavior of Bipolar Chain-Oxidized Cholesterol Derivatives─Langmuir Monolayer Studies Supplemented with Theoretical Calculations

Cholesterol oxidation products (called oxysterols) are involved in many biological processes, showing both negative (e.g., neurodegenerative) and positive (e.g., antiviral and antimicrobial) effects. The physiological activity of oxysterols is undoubtedly closely related to their structure (i.e., the type and location of the additional polar group in the cholesterol skeleton). In this paper, we focus on determining how a seemingly minor structural change (introduction of a hydroxyl moiety at C(24), C(25), or C(27) in the isooctyl chain of cholesterol) affects the organization of the resulting molecules at the phase boundary. In our research, we supplemented the classic Langmuir monolayer technique, based on the surface pressure and electric surface potential isotherms, with microscopic (BAM) and spectroscopic (PM-IRRAS) techniques, as well as theoretical calculations (DFT and MD). This allowed us to show that 24-OH behaves more like cholesterol and forms stable, rigid monolayers. On the other hand, 27-OH, similar to 25-OH, undergoes the phase transition from monolayer to bilayer structures. Theoretical calculations enabled us to conclude that the formation of bilayers from 27-OH or 25-OH is possible due to the hydrogen bonding between adjacent oxysterol molecules. This observation may help to understand the factors responsible for the unique biological activity (including antiviral and antimicrobial) of 27-OH and 25-OH compared to other oxysterols.

Revealing the structure and mechanisms of action of a synthetic opioid with model biological membranes at the air-water interface

Synthetic opioids such as piperazine derivative called MT-45 interact with opioid receptors in a manner similar to morphine leading to euphoria, a sense of relaxation and pain relief and are commonly used as substituents of natural opioids. In this study we show the changes in the surface properties of nasal mucosa and intestinal epithelial model cell membranes formed at the air - water interface using Langmuir technique upon the exposure to MT-45. Both membranes constitute the first barrier to absorb this substance into the human body. The presence of the piperazine derivative affects the organization of both DPPC and ternary DMPC:DMPE:DMPS monolayers treated as simple models of nasal mucosa and intestinal cell membranes, respectively. This novel psychoactive substance (NPS) leads to the fluidization of the model layers, which may indicate their increased permeability. MT-45 has a greater influence on the ternary monolayers characteristic of the intestinal epithelial cells than nasal mucosa. It might be attributed to the increased attractive interactions between the components of the ternary layer, which in turn increase the interactions with a synthetic opioid. Additionally, the crystal structures of MT-45 determined by single-crystal and powder X-ray diffraction methods allowed us to both provide useful data for facilitating the identification of synthetic opioids as well as to attribute the effect of MT-45 to the ionic interactions between protonated nitrogen atoms and negatively charged parts of the polar heads of the lipids.

Interfacial Dynamics of Adsorption Layers as Supports for Biomedical Research and Diagnostics

The input of chemical and physical sciences to life sciences is increasingly important. Surface science as a complex multidisciplinary research area provides many relevant practical tools to support research in medicine. The tensiometry and surface rheology of human biological liquids as diagnostic tools have been very successfully applied. Additionally, for the characterization of pulmonary surfactants, this methodology is essential to deepen the insights into the functionality of the lungs and for the most efficient administration of certain drugs. Problems in ophthalmology can be addressed using surface science methods, such as the stability of the wetting films and the development of artificial tears. The serious problem of obesity is fast-developing in many industrial countries and must be better understood, while therapies for its treatment must also be developed. Finally, the application of fullerenes as a suitable system for detecting cancer in humans is discussed.

Model Lipid Raft Membranes for Embedding Integral Membrane Proteins: Reconstitution of HMG-CoA Reductase and Its Inhibition by Statins

For the first time, HMG-CoA reductase, the membrane protein responsible for cholesterol synthesis, was incorporated into a lipid membrane consisting of DOPC:Chol:SM at a 1:1:1 molar ratio, which mimics the lipid rafts of cell membranes. The membrane containing the protein was generated in the form of either a proteoliposomes or a film obtained by spreading the proteoliposomes at the air-water interface to prepare a protein-rich and stable lipid layer over time. The lipid vesicle parameters were characterized using dynamic light scattering (DLS) and fluorescence microscopy. The incorporation of HMG-CoA reductase was reflected in the increased size of the proteoliposomes compared to that of the empty liposomes of model rafts. Enzyme reconstitution was confirmed by measuring the activity of NADPH, which participates in the catalytic process. The thin lipid raft films formed by spreading liposomes and proteoliposomes at the air-water interface were investigated using the Langmuir technique. The activities of the HMG-CoA reductase films were preserved over time, and the two lipid raft systems, nanoparticles and films, were exposed to solutions of fluvastatin, a HMG-CoA reductase inhibitor commonly used in the treatment of hypercholesterolemia. Both lipid raft systems constructed were useful membrane models for the determination of reductase activity and for monitoring the statin inhibitory effects and may be used for investigating other integral membrane proteins during exposure to inhibitors/activators considered to be potential drugs.

Influence of cytochrome P450 3A4 and membrane lipid composition on doxorubicin activity

Drug resistance is known to depend on the interactions with cell membranes and other molecules such as human cytochromes P450 (CYPs) which are anchored on the endoplasmic reticulum (ER) membrane and involved in the metabolism of anticancer drugs. In this study, we determined the influence from cytochrome P450 3A4 (CYP3A4) on the interaction between the drug doxorubicin (DOX) and Langmuir monolayers mimicking cell membranes. The lipid composition was varied by changing the relative concentrations of cholesterol (Chol), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), and L-α-phosphatidylinositol (PI). Three compositions were studied in detail which represented a healthy cell membrane and cancerous cell membranes. DOX induced an expansion in the surface pressure isotherms for all monolayers, with stronger effect for the composition of cancerous cell with a high Chol content, thus confirming the relevance of lipid composition. This effect decreased considerably when CYP3A4 was incorporated with the formation of CYP3A4-DOX complexes, according to results from polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) measurements. Taken together, these results support the hypothesis of CYP3A4 being involved in drug resistance, which may be exploited to design strategies to enhance chemotherapy efficacy.