Impact of aluminum on the oxidation of lipids and enzymatic lipolysis in monomolecular films at the air/water interface

Insights into Transfer of Supramolecular Doxorubicin/Congo Red Aggregates through Phospholipid Membranes

Doxorubicin (DOX) is a commonly used chemotherapeutic drug, from the anthracycline class, which is genotoxic to neoplastic cells via a DNA intercalation mechanism. It is effective and universal; however, it also causes numerous side effects. The most serious of them are cardiotoxicity and a decrease in the number of myeloid cells. For this reason, targeted DOX delivery systems are desirable, since they would allow lowering the drug dose and therefore limiting systemic side effects. Recently, synthetic dyes, in particular Congo red (CR), have been proposed as possible DOX carriers. CR is a planar molecule, built of a central biphenyl moiety and two substituted naphthalene rings, connected with diazo bonds. In water, it forms elongated ribbon-shaped supramolecular structures, which are able to selectively interact with immune complexes. In our previous studies, we have shown that CR aggregates can intercalate DOX molecules. In this way, they preclude DOX precipitation in water solutions and increase its uptake by MCF7 breast cancer cells. In the present work, we further explore the interactions between DOX, CR, and their aggregates (CR/DOX) with phospholipid membranes. In addition to neutral molecules, the protonated doxorubicin form, DXP, is also studied. Molecular dynamics simulations are employed to study the transfer of CR, DOX, DXP, and their aggregates through POPC bilayers. Interactions of CR, DOX, and CR/DOX with model monolayers are studied with Langmuir trough measurements. This study shows that CR may support the transfer of doxorubicin molecules into the bilayer. Both electrostatic and van der Waals interactions with lipids are important in this respect. The former promote the initial stages of the insertion process, the latter keep guest molecules inside the bilayer.

Simultaneous action of microbial phospholipase C and lipase on model bacterial membranes - Modeling the processes crucial for bioaugmentation

Bioaugmentation is a promising method of the remediation of soils polluted by persistent organic pollutants (POP). Unfortunately, it happens frequently that the microorganisms inoculated into the soil die out due to the presence of enzymes secreted by autochthonous microorganisms. Especially destructive are here phospholipases C (PLC) and lipases which destruct the microorganism's cellular membrane. The composition of bacterial membranes differs between species, so it is highly possible that depending on the membrane constitution some bacteria are more resistant to PLCs and lipases than other. To shed light on these problems we applied phospholipid Langmuir monolayers as model microbial membranes and studied their interactions with α-toxin (model bacterial PLC) and the lipase isolated from soil fungus Candida rugosa. Membrane phospholipids differing in their headgroup (phosphatidylcholines, phosphatidylethanolamines, phosphatidylglycerols and cardiolipins) and in their tail structure were applied. The monolayers were characterized by the Langmuir technique, visualized by Brewster angle microscopy, and the packing mode of the phospholipid molecules was verified by the application of the diffraction of synchrotron radiation. We also studied the mutual miscibility of diacylglycerols and the native phospholipids as their interaction is crucial for the understanding of the PLC and lipase activity. It turned out that all the investigated phospholipid classes can be hydrolyzed by PLC; however, they differ profoundly in the hydrolysis degree. Depending on the effects of the initial PLC action and the mutual organization of the diacylglycerol and phospholipid molecules the lipase can ruin the model membranes or can be completely neutral to them.

Two antibacterial nalidixate calixarene derivatives in cholesterol monolayers: Molecular dynamics and physicochemical effects

The interaction of two antibacterial calixarene derivatives with cholesterol, a eukaryotic cell membrane lipid, was investigated with the aim to get more insight in the potential advers effects on our cells. The derivatives used had one or two nalidixic acid arms grafted on the lower rim of the calixarene aromatic crown. Monomolecular films spread at the air-water interface were used as model lipid membranes. Pure cholesterol and pure calixarene derivatives, as well as binary cholesterol - calixarene derivative mixtures were studied using surface pressure measurements, polarization-modulation infrared reflection absorption spectroscopy and molecular dynamics simulations. The properties of the mixed monolayers were described quantitatively using thermodynamic models. The analysis of surface pressure-area isotherms of mixed monolayers shows that cholesterol may form homogenous but metastable domains with both nalidixate derivatives. This phenomenon is more clearly observed with mono-substituted calixarene. A detailed modeling analysis indicates that cholesterol favors dehydration of the calixarene polar headgroups and transfer of the derivatives from the aqueous to the gas phase. This effect, more pronounced in the case of the monosubstituted calixarene, can be linked to the hydrophobic interaction with cholesterol. This observation may be useful for developing new calixarene derivatives allowing us to control disease-causing bacteria without harming our own cells.

Impact of two different saponins on the organization of model lipid membranes

Saponins, naturally occurring plant compounds are known for their biological and pharmacological activity. This activity is strongly related to the amphiphilic character of saponins that allows them to aggregate in aqueous solution and interact with membrane components. In this work, Langmuir monolayer techniques combined with polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and Brewster angle microscopy were used to study the interaction of selected saponins with lipid model membranes. Two structurally different saponins were used: digitonin and a commercial Merck Saponin. Membranes of different composition, namely, cholesterol, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol) were formed at the air/water and air/saponin solution interfaces. The saponin-lipid interaction was characterized by changes in surface pressure, surface potential, surface morphology and PM-IRRAS signal. Both saponins interact with model membranes and change the physical state of membranes by perturbing the lipid acyl chain orientation. The changes in membrane fluidity were more significant upon the interaction with Merck Saponin. A higher affinity of saponins for cholesterol than phosphatidylglycerols was observed. Moreover, our results indicate that digitonin interacts strongly with cholesterol and solubilize the cholesterol monolayer at higher surface pressures. It was shown, that digitonin easily penetrate to the cholesterol monolayer and forms a hydrogen bond with the hydroxyl groups. These findings might be useful in further understanding of the saponin action at the membrane interface and of the mechanism of membrane lysis.

Cytotoxicity of environmentally relevant concentrations of aluminum in murine thymocytes and lymphocytes

The effects of low concentrations of aluminum chloride on thymocytes and lymphocytes acutely dissociated from young mice were studied using flow cytometry with a DNA-binding dye. We demonstrate a rapid and dose-dependent injury in murine thymocytes and lymphocytes resulting from exposure to aluminum, as indicated by an increase in the entry into the cell of the DNA-binding dye, propidium iodine. A 60-minute exposure to 10 μM AlCl₃ caused damage of about 5% of thymocytes, while 50% were injured after 10 minutes at 20 μM. Nearly all thymocytes showed evidence of damage at 30 μM AlCl₃ after only 5 minutes of incubation. In lymphocytes, injury was observed at 15 μM AlCl₃ and less than 50% of cells were injured after a 60-minute exposure to 20 μM. Injury only rarely proceeded to rapid cell death and was associated with cell swelling. These results suggest that aluminum has cytotoxic effects on cells of the immune system.

Meloxicam and meloxicam-beta-cyclodextrin complex in model membranes: effects on the properties and enzymatic lipolysis of phospholipid monolayers in relation to anti-inflammatory activity

Meloxicam, a nonsteroidal anti-inflammatory drug (NSAID), is known as a selective cyclooxygenase-2 inhibitor. Cyclooxygenase-2 is a membrane protein, functionally coupled to an interfacial enzyme, phospholipase A2. Consequently, it may be supposed that the interactions of NSAIDs with lipid membranes play a role in the anti-inflammatory process. In order to investigate the mechanism of this process, Langmuir films formed with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dilauroyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, or 1,2-myristoyl-sn-glycero-3-phosphoethanolamine were exposed to meloxicam and its beta-cyclodextrin inclusion complex. The monolayers were studied by measuring surface pressure, electric surface potential, Brewster angle micrographs, polarization-modulation infrared reflection-absorption spectra, and phospholipase A2 activity; the inclusion complex was studied using molecular modeling. The results obtained show that the monolayers formed in the presence of meloxicam and its complex are expanded and more liquid-like compared to pure lipids. Both compounds modify hydration of the lipid polar heads, orientation of the molecules, morphology of the domains, and the rate of lipolysis catalyzed by phospholipase A2. The latter effect may be involved in the anti-inflammatory activity of meloxicam. Importantly, the effects observed with the meloxicam-beta-cyclodextrin complex are more pronounced compared to those of the free meloxicam. This observation may be relevant for developing new meloxicam preparations with increased bioavailability.

Interfacial approach to polyaromatic hydrocarbon toxicity: phosphoglyceride and cholesterol monolayer response to phenantrene, anthracene, pyrene, chrysene, and benzo[a]pyrene

Interactions of phenantrene, anthracene, pyrene, chrysene, and benzo[a]pyrene (polyaromatic hydrocarbons) with model phospholipid membranes were probed using the Langmuir technique. The lipid monolayers were prepared using 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol, 1,2-dipalmitoyl-sn-glycero-3-phosphoserine, 1,2-myristoyl-sn-glycero-3-phosphoethanolamine, 1,2-dilauroyl-sn-glycero-3-phosphocholine, and cholesterol. Surface pressure and electrical surface potential were measured on mixed phospholipid/PAH monolayers spread on a pure water subphase. The morphology of the mixed monolayers was followed with Brewster angle microscopy. Polarization-modulation infrared reflection-absorption spectroscopy spectra obtained on DPPE/benzo[a]pyrene showed that the latter interacts with the carbonyl groups of the phospholipid. On the other hand, the activity of phospholipase A2 toward DLPC used as a probe to locate benzo[a]pyrene in the monolayers indicates that the polyaromatic hydrocarbons are not accessible to the enzyme. The results obtained show that all PAHs studied affect the properties of the pure lipid, albeit in different ways. The most notable effects, namely, film fluidization and morphology changes, were observed with benzo[a]pyrene. In contrast, the complexity of mixed lipid monolayers makes the effect of PAHs difficult to detect. It can be assumed that the differences observed between PAHs in monolayers correlate with their toxicity.