Ordered-disordered domain coexistence in ternary lipid monolayers activates sphingomyelinase by clearing ceramide from the active phase

Perfluorocarbons Therapeutics in Modern Cancer Nanotechnology for Hypoxiainduced Anti-tumor Therapy

With an estimated failure rate of about 90%, immunotherapies that are intended for the treatment of solid tumors have caused an anomalous rise in the mortality rate over the past decades. It is apparent that resistance towards such therapies primarily occurs due to elevated levels of HIF-1 (Hypoxia-induced factor) in tumor cells, which are caused by disrupted microcirculation and diffusion mechanisms. With the advent of nanotechnology, several innovative advances were brought to the fore; and, one such promising direction is the use of perfluorocarbon nanoparticles in the management of solid tumors. Perfluorocarbon nanoparticles enhance the response of hypoxia-based agents (HBAs) within the tumor cells and have been found to augment the entry of HBAs into the tumor micro-environment. The heightened penetration of HBAs causes chronic hypoxia, thus aiding in the process of cell quiescence. In addition, this technology has also been applied in photodynamic therapy, where oxygen self-enriched photosensitizers loaded perfluorocarbon nanoparticles are employed. The resulting processes initiate a cascade, depleting tumour oxygen and turning it into a reactive oxygen species eventually to destroy the tumour cell. This review elaborates on the multiple applications of nanotechnology based perfluorocarbon formulations that are being currently employed in the treatment of tumour hypoxia.

Clearly Detectable, Kinetically Restricted Solid-Solid Phase Transition in cis-Ceramide Monolayers

Sphingosine [(2 S,3 R,4 E)-2-amino-4-octadecene-1,3-diol] is the most common sphingoid base in mammals. Ceramides are N-acyl sphingosines. Numerous small variations on this canonical structure are known, including the 1-deoxy, the 4,5-dihydro, and many others. However, whenever there is a Δ4 double bond, it adopts the trans (or E) configuration. We synthesized a ceramide containing 4 Z-sphingosine and palmitic acid ( cis-pCer) and studied its behavior in the form of monolayers extended on an air-water interface. cis-pCer acted very differently from the trans isomer in that, upon lateral compression of the monolayer, a solid-solid transition was clearly observed at a mean molecular area ≤44 Ų·molecule^-1, whose characteristics depended on the rate of compression. The solid-solid transition, as well as states of domain coexistence, could be imaged by atomic force microscopy and by Brewster-angle microscopy. Atomistic molecular dynamics simulations provided results compatible with the experimentally observed differences between the cis and trans isomers. The data can help in the exploration of other solid-solid transitions in lipids, both in vitro and in vivo, that have gone up to now undetected because of their less obvious change in surface properties along the transition, as compared to cis-pCer.

A Robust Liposomal Platform for Direct Colorimetric Detection of Sphingomyelinase Enzyme and Inhibitors

The enzyme sphingomyelinase (SMase) is an important biomarker for several diseases such as Niemann Pick's, atherosclerosis, multiple sclerosis, and HIV. We present a two-component colorimetric SMase activity assay that is more sensitive and much faster than currently available commercial assays. Herein, SMase-triggered release of cysteine from a sphingomyelin (SM)-based liposome formulation with 60 mol % cholesterol causes gold nanoparticle (AuNP) aggregation, enabling colorimetric detection of SMase activities as low as 0.02 mU/mL, corresponding to 1.4 pM concentration. While the lipid composition offers a stable, nonleaky liposome platform with minimal background signal, high specificity toward SMase avoids cross-reactivity of other similar phospholipases. Notably, use of an SM-based liposome formulation accurately mimics the natural in vivo substrate: the cell membrane. We studied the physical rearrangement process of the lipid membrane during SMase-mediated hydrolysis of SM to ceramide using small- and wide-angle X-ray scattering. A change in lipid phase from a liquid to gel state bilayer with increasing concentration of ceramide accounts for the observed increase in membrane permeability and consequent release of encapsulated cysteine. We further demonstrated the effectiveness of the sensor in colorimetric screening of small-molecule drug candidates, paving the way for the identification of novel SMase inhibitors in minutes. Taken together, the simplicity, speed, sensitivity, and naked-eye readout of this assay offer huge potential in point-of-care diagnostics and high-throughput drug screening.

Regulation of phase boundaries and phase-segregated patterns in model membranes

Demixing of components has long been described in model membranes. It is a consequence of non-ideal lateral interactions between membrane components, and it causes the presence of segregated phases, forming patches (domains) of different properties, thus introducing heterogeneity into the membrane. In the present review we first describe the processes through which domains are generated, how they grow, and why they are rounded, striped or fractal-like, as well as why they get distributed forming defined patterns. Next, we focus on the effect of an additive on a lipid mixture, which usually induces shifts in demixing points, thus stabilizing or destabilizing the phase-segregated state. Results found for different model membranes are summarized, detailing the ways in which phase segregation and the generated patterns may be modulated. We focus on which are, from our viewpoint, the most relevant regulating factors affecting the surface texture observed in model membranes. This article is part of a Special Issue entitled: Emergence of Complex Behavior in Biomembranes edited by Marjorie Longo.

The many faces (and phases) of ceramide and sphingomyelin II - binary mixtures

A rather widespread idea on the functional importance of sphingolipids in cell membranes refers to the occurrence of ordered domains enriched in sphingomyelin and ceramide that are largely assumed to exist irrespective of the type of N-acyl chain in the sphingolipid. Ceramides and sphingomyelins are the simplest kind of two-chained sphingolipids and show a variety of species, depending on the fatty acyl chain length, hydroxylation, and unsaturation. Abundant evidences have shown that variations of the N-acyl chain length in ceramides and sphingomyelins markedly affect their phase state, interfacial elasticity, surface topography, electrostatics, and miscibility, and that even the usually conceived "condensed" sphingolipids and many of their mixtures may exhibit liquid-like expanded states. Their lateral miscibility properties are subtlety regulated by those chemical differences. Even between ceramides with different acyl chain length, their partial miscibility is responsible for a rich two-dimensional structural variety that impacts on the membrane properties at the mesoscale level. In this review, we will discuss the miscibility properties of ceramide, sphingomyelin, and glycosphingolipids that differ in their N-acyl or oligosaccharide chains. This work is a second part that accompanies a previous overview of the properties of membranes formed by pure ceramides or sphingomyelins, which is also included in this Special Issue.

Applications of Brewster angle microscopy from biological materials to biological systems

Brewster angle microscopy (BAM) is a powerful technique that allows for real-time visualization of Langmuir monolayers. The lateral organization of these films can be investigated, including phase separation and the formation of domains, which may be of different sizes and shapes depending on the properties of the monolayer. Different molecules or small changes within a molecule such as the molecule's length or presence of a double bond can alter the monolayer's lateral organization that is usually undetected using surface pressure-area isotherms. The effect of such changes can be clearly observed using BAM in real-time, under full hydration, which is an experimental advantage in many cases. While previous BAM reviews focused more on selected compounds or compared the impact of structural variations on the lateral domain formation, this review provided a broader overview of BAM application using biological materials and systems including the visualization of amphiphilic molecules, proteins, drugs, extracts, DNA, and nanoparticles at the air-water interface.

Cholesterol interactions with ceramide and sphingomyelin

Sphingolipids contain in their polar heads chemical groups allowing them to establish a complex network of H-bonds (through different OH and NHgroups) with other lipids in the bilayer. In the recent years the specific interaction of sphingomyelin (SM) with cholesterol (Chol) has been examined, largely in the context of the "lipid raft" hypothesis. Formation of SM-Ceramide (Cer) complexes, proposed to exist in cell membranes in response to stress, has also been described. More recently, a delicate balance of phase formation and transformation in ternary mixtures of SM, Chol and Cer, with mutual displacement of Chol and Cer from their interaction with SM is considered to exist. In addition, data demonstrating direct Chol-Cer interaction are becoming available.

Sirolimus-loaded polymeric micelles with honokiol for oral delivery

Objectives

The aims of the present study were to design polymeric micelles loading sirolimus with honokiol to increase drug solubility and to gain an insight into the effect of honokiol on oral transport of P-glycoprotein substrate (P-gp).

Methods

Particle size distribution, encapsulation efficiency, drug-loading content and in-vitro release of sirolimus-loaded micelles with honokiol were determined. Transport of sirolimus-loaded micelles across Caco-2 cell monolayers and jejunum segment of rats were investigated. In-vitro cytotoxicity experiments and the cellular uptake study were carried out via sulforhodamine B assay and flow cytometry, respectively.

Key findings

A coadministration of honokiol with sirolimus in micelles did not significantly modify the particle size, polydispersity index and release of drugs demonstrating successful loading within the micelles. The apparent transport coefficients (Papp) and effective permeability (Peff) of sirolimus were increased with more amount of honokiol loaded in micelles. Cellular uptake study demonstrated that rhodamine123 uptake rate was enhanced by honokiol-loaded micelles, indicating substantial P-gp inhibition action by honokiol and mPEG-PLA-based micelles.

Conclusion

Oral transport of sirolimus was significantly improved by coadministration with honokiol, an inhibitor of the P-gp, in polymeric micelles formulation.

The Presence of Sterols Favors Sticholysin I-Membrane Association and Pore Formation Regardless of Their Ability to Form Laterally Segregated Domains

Sticholysin I (St I) is a pore-forming toxin (PFT) produced by the Caribbean Sea anemone Stichodactyla helianthus belonging to the actinoporin protein family, a unique class of eukaryotic PFT. As for actinoporins, it has been proposed that the presence of cholesterol (Chol) and the coexistence of lipid phases increase binding to the target membrane and pore-forming ability. However, little is known about the role of membrane structure and dynamics (phase state, fluidity, and the presence of lipid domains) on the activity of actinoporins or which regions of the membrane are the most favorable for protein insertion, oligomerization, and eventually pore formation. To gain insight into the role of membrane properties on the functional activity of St I, we studied its binding to monolayers and vesicles of phosphatidylcholine (PC), sphingomyelin (SM), and sterols inducing (ergosterol -Erg and cholesterol -Chol) or not (cholestenone - Cln) membrane phase segregation in liquid ordered (Lo) and liquid disordered (Ld) domains. This study revealed that St I binds and permeabilizes with higher efficiency sterol-containing membranes independently of their ability to form domains. We discuss the results in terms of the relevance of different membrane properties for the actinoporins mechanism of action, namely, molecular heterogeneity, specially potentiated in membranes with sterols inducers of phase separation (Chol or Erg) or Cln, a sterol noninducer of phase separation but with a high propensity to induce nonlamellar phase. The role of the Ld phase is pointed out as the most suitable platform for pore formation. In this regard, such regions in Chol-containing membranes seem to be the most favored due to its increased fluidity; this property promotes toxin insertion, diffusion, and oligomerization leading to pore formation.

Direct observation by using Brewster angle microscopy of the diacetylene polimerization in mixed Langmuir film

Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) and amphiphilic hemicyanine (HSP) have been fabricated at the air-water interface. The mixed monolayer has been proved to be completely homogeneous. The DA molecules are arranged in a single monolayer within the mixed Langmuir monolayer, as opposed to the typical trilayer architecture for the pure DA film. Brewster angle microscopy has been used to reveal the mesoscopic structure of the mixed Langmuir monolayer. Flower shape domains with internal anisotropy due the ordered alignment of hemicyanine groups have been observed. Given the absorption features of the hemicyanine groups at the wavelength used in the BAM experiments, the enhancement of reflection provoked by the absorption process leads to the observed anisotropy. The ordering of such groups is promoted by their strong self-aggregation tendency. Under UV irradiation at the air-water interface, polydiacetylene (PDA) has been fabricated. In spite a significant increase in the domains reflectivity has been observed owing to the modification in the mentioned enhanced reflection, the texture of the domains remains equal. The PDA polymer chain therefore grows in the same direction in which the HSP molecules are aligned. This study is expected to enrich the understanding and design of fabrication of PDA at interfaces.

Polymeric micelles, a promising drug delivery system to enhance bioavailability of poorly water-soluble drugs

Oral administration is the most commonly used and readily accepted form of drug delivery; however, it is find that many drugs are difficult to attain enough bioavailability when administered via this route. Polymeric micelles (PMs) can overcome some limitations of the oral delivery acting as carriers able to enhance drug absorption, by providing (1) protection of the loaded drug from the harsh environment of the GI tract, (2) release of the drug in a controlled manner at target sites, (3) prolongation of the residence time in the gut by mucoadhesion, and (4) inhibition of efflux pumps to improve the drug accumulation. To explain the mechanisms for enhancement of oral bioavailability, we discussed the special stability of PMs, the controlled release properties of pH-sensitive PMs, the prolongation of residence time with mucoadhesive PMs, and the P-gp inhibitors commonly used in PMs, respectively. The primary purpose of this paper is to illustrate the potential of PMs for delivery of poorly water-soluble drugs with bioavailability being well maintained.