Nanostructured lipid carriers: effect of solid phase fraction and distribution on the release of encapsulated materials

Liposome bilayer stability: emphasis on cholesterol and its alternatives

Liposomes are spherical lipidic nanocarriers composed of natural or synthetic phospholipids with a hydrophobic bilayer and aqueous core, which are arranged into a polar head and a long hydrophobic tail, forming an amphipathic nano/micro-particle. Despite numerous liposomal applications, their use encounters many challenges related to the physicochemical properties strongly affected by their constituents, colloidal stability, and interactions with the biological environment. This review aims to provide a perspective and a clear idea about the main factors that regulate the liposomes' colloidal and bilayer stability, emphasising the roles of cholesterol and its possible alternatives. Moreover, this review will analyse strategies that offer possible approaches to provide more stable in vitro and in vivo liposomes with enhanced drug release and encapsulation efficiencies.

Mannose-Anchored Nano-Selenium Loaded Nanostructured Lipid Carriers of Etravirine for Delivery to HIV Reservoirs

The present investigation aims to develop and explore mannosylated lipid-based carriers to deliver an anti-HIV drug, Etravirine (TMC) and Selenium nanoparticles (SeNPs), to the HIV reservoirs via the mannose receptor. The successful mannosylation was evaluated by the change in zeta potential and lectin binding assay using fluorescence microscopy. Electron microscopy and scattering studies were employed to study the structure and surface of the nanocarrier system. The presence of selenium at the core-shell of the nanocarrier system was confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis. Further, the in vitro anti-HIV1 efficacy was assessed using HIV1 infected TZM-bl cells followed by in vivo biodistribution studies to evaluate distribution to various reservoirs of HIV. The results exhibited higher effectiveness and a significant increase in the therapeutic index as against the plain drug. The confocal microscopy and flow cytometry studies exhibited the efficient uptake of the coumarin-6 tagged respective formulations. The protective effect of nano selenium toward oxidative stress was evaluated in rats, demonstrating the potential of the lipidic nanoparticle-containing selenium in mitigating oxidative stress in all the major organs. The in vivo biodistribution assessment in rats showed a 12.44, 8.05 and 9.83-fold improvement in the brain, ovary, and lymph node biodistribution, respectively as compared with plain TMC. Delivery of such a combination via mannosylated nanostructured lipid carriers could be an efficient approach for delivering drugs to reservoirs of HIV while simultaneously reducing the oxidative stress induced by such long-term therapies by co-loading Nano-Selenium.

Dual loaded nanostructured lipid carrier of nano-selenium and Etravirine as a potential anti-HIV therapy

There is a dire need for dual-long-acting therapy that could simultaneously target different stages of the HIV life cycle and providing a dual-prolonged strategy for improved anti-HIV therapy while reducing oxidative stress associated with the prolonged treatment. Thus, in the present work, nanostructured lipid carriers of Etravirine were developed and modified with nano-selenium. The dual-loaded nanocarrier system was fabricated using the double emulsion solvent evaporation method, further screened and optimized using the design of experiments methodology. The spherical core-shell type of a system was confirmed with an electron microscope and small-angle neutron scattering, while XPS confirmed the presence of selenium at the core-shell of the nanocarrier. In vitro assessment against HIV1 (R5 and X4 strains) infected TZM-bl cells exhibited higher efficacy for the dual-loaded nanocarrier system than the plain drug, which could be attributed to the synergistic effect of the nano-selenium. Confocal microscopy and flow cytometry results exhibited enhanced uptake in TZM-bl cells compared to plain drug. A significant increase of GSH, SOD, CAT was observed in animals administered with the dual-loaded nanocarrier system containing nano-selenium, suggesting the protective potential of the lipidic nanoparticle containing the nano-selenium. Improvement in the in vivo pharmacokinetic parameters was also observed, along with a higher accumulation of the dual-loaded nanocarrier in remote HIV reservoir organs like the brain, ovary, and lymph node. The results suggest the potential of a dual-loaded formulation for synergistically targeting the HIV1 infection while simultaneously improving the intracellular anti-oxidant balance for improving a prolonged anti-HIV therapy.

Molecular Mechanism of Ultrasound-Induced Structural Defects in Liposomes: A Nonequilibrium Molecular Dynamics Simulation Study

The use of ultrasound in combination with liposomes is a promising approach to improve drug delivery. To achieve an optimal drug release rate, it is important to understand how ultrasound induces pathways on the liposome surface where drugs can be released from the liposome. To this end, we carry out large-scale ultrasound-induced molecular dynamics simulations for three single lipid component liposomes formed from the commonly used phospholipids: 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoylphosphatidylcholine (DPPC), or phosphatidylcholine (POPC). The results show that ultrasound induces the detachment of two leaflets of the DOPC surface, suggesting that the drug release pathway may be through the low lipid packing areas on the stretched surface. In contrast, ultrasound induces pore formation on the surface of DPPC and DOPC, where drugs could escape from the liposomes. While the leaflet detachment and transient pore formation are the mechanisms of DOPC and DPPC, respectively, in both liquid-ordered and liquid-disordered phases, the leaflet detachment mechanism is switched to the transient pore formation mechanism on going from the liquid-ordered phase to the liquid-disordered phase in the POPC liposome. By adding 30% mol cholesterol, the leaflet detachment mechanism is observed in all liposomes. We found that the molecular origin that determines a mechanism is the competition between the intraleaflet and interleaflet interacting energy of lipids. The connection to experimental and theoretical modeling is discussed in some detail.

Multi-organ targeting of HIV-1 viral reservoirs with etravirine loaded nanostructured lipid carrier: An in-vivo proof of concept

The inadequate bioavailability and toxicity potential of antiretroviral therapy limit their effectiveness in the complete eradication of HIV from viral reservoirs. The penetration of these drugs into the brain is challenging because of the unfavorable physicochemical properties required to cross the membranes, limiting the transport of the drugs. Thus, in the current study, the authors report a nanocarrier-based drug delivery of a highly hydrophobic drug to overcome the existing limitations of the conventional therapies. An explicitly simple approach was used to overcome the limitations of existing anti-HIV therapies. The monophasic hot homogenized solution of lipid, drug, and solubilizer was diluted with the predetermined hot surfactant solution followed by the ultrasonication to generate the polydisperse nanoparticles with the size range of 50-1000 nm. The anti-HIV1 potential of nanostructured lipid carriers of Etravirine on HIV-infected cell lines showed efficacy with an appreciable increase in the therapeutic index as compared with the plain drug. Further, the results obtained from confocal microscopy along with flow cytometry exhibited efficient uptake of the nanocarrier loaded with coumarin-6 in cells. The pharmacokinetics of Etravirine nanostructured carriers was significantly better in all aspects compared to the plain drug solution, which could be attributed to molecular dispersion in the lipid matrix of the nanocarrier. A significant enhancement of Etravirine concentration of several-fold was also observed in the liver, ovary, lymph node, and brain, respectively, as compared to plain drug solution when assessed by biodistribution studies in rats. In conclusion, ETR-NLC systems could serve as a promising approach for simultaneous multi-site targeting and could provide therapeutic benefits for the efficient eradication of HIV/AIDS infections.

Quality by design (QbD)-based fabrication of atazanavir-loaded nanostructured lipid carriers for lymph targeting: bioavailability enhancement using chylomicron flow block model and toxicity studies

Atazanavir (ATV) is widely used as anti-HIV agent having poor aqueous solubility needs to modulate novel drug delivery system to enhance therapeutic efficiency and safety. The main objective of the present work was to fabricate ATV-loaded nanostructured lipid carriers (NLCs) employing quality by design (QbD) approach to address the challenges of bioavailability and their safety after oral administration. Herein, the main objective was to identify the influencing variables for the production of quality products. Considering this objective, quality target product profile (QTPP) was assigned and a systematic risk assessment study was performed to identify the critical material attributes (CMAs) and critical process parameter (CPP) having an influence on critical quality attributes (CQAs). Lipid concentrations, surfactant concentrations, and pressure of high-pressure homogenizer were identified as CMAs and CPP. ATV-NLCs were prepared by emulsification-high pressure homogenization method and further lyophilized to obtain solid-state NLCs. The effect of formulation variables (CMAs and CPP) on responses like particle size (Y₁), polydispersity index (Y₂), and zeta potential (Y₃) was observed by central composite rotatable design (CCRD). The data were statistically evaluated by ANOVA for confirmation of a significant level (p < 0.05). The optimal conditions of NLCs were obtained by generating design space and desirability value. The lyophilized ATV-NLCs were characterized by DSC, powder X-ray diffraction, and FT-IR analysis. The morphology of NLCs was revealed by TEM and FESEM. In vitro study suggested a sustained release pattern of drug (92.37 ± 1.03%) with a mechanism of Korsmeyer-Peppas model (r² = 0.925, and n = 0.63). In vivo evaluation in Wistar rats showed significantly higher (p < 0.001) plasma drug concentration of ATV-NLCs as compared to ATV-suspension using chylomicron flow block model. The relative bioavailability of ATV-NLCs was obtained to be 2.54 folds. Thus, a safe and promising drug targeting system was successfully developed to improve bioavailability and avoiding first-pass effect ensures to circumvent the acute-toxicity of liver.

Lipid-based nano-formulation platform for eplerenone oral delivery as a potential treatment of chronic central serous chorioretinopathy: in-vitro optimization and ex-vivo assessment

Purpose

Eplerenone (EPL) is a selective mineralocorticoid receptor antagonist used for treatment of chronic central serous chorioretinopathy which characterized by accumulation of subretinal fluid causing a localized area of retinal detachment. unfortunately, EPL suffers from poor oral bioavailability due to poor aqueous solubility in addition to high hepatic first pass metabolism.

Method

Aiming to improve its oral bioavailability, EPL-loaded nanostructured lipid carriers (NLCs) were prepared by the emulsification solvent evaporation method and in-vitro evaluated for particle size (PS), polydispersity index (PDI), zeta potential (ZP), and entrapment efficiency (EE%). A D-optimal design was used for study the effect of liquid lipid to solid lipid ratio, surfactant type and percentage on PS, PDI, EE%, and for data optimization. The optimized EPL-loaded NLCs system was further evaluated using in-vitro drug release and ex-vivo permeation studies through rabbit intestine in comparison to EPL aqueous suspension. The physicochemical properties of the drug in the optimized system were further examined using FT-IR and X-ray diffraction studies.

Results

The resultant NLCs showed small PS (100.85–346.60 nm), homogenous distribution (0.173–0.624), negatively charged particles (ZP −20.20 to −36.75 mV), in addition to EE% (34.31–70.64%). The optimized EPL-loaded NLCs system with a desirability value of 0.905 was suggested through the Design expert^® software, containing liquid to solid lipid ratio (2:1) in presence of 0.43%w/v Pluronic^® F127 as a surfactant. The optimized EPL-loaded NLCs system showed a PS of 134 nm and PDI of 0.31, in addition to high EE% (76 ± 6.56%w/w), and ZP (-32.37 mV). The ex-vivo permeation study showed two-fold higher drug permeation through rabbit intestine compared to that from the aqueous drug suspension after 24 h, confirming the ability of optimized EPL-loaded NLCs system as successful oral targeting delivery carrier.

Conclusion

Our results pave the way for a new oral nanotherapeutic approach toward CSCR treatment. In-vivo study is currently under investigation.

Influence of lipid nanoparticle physical state on β-carotene stability kinetics under different environmental conditions

Carotenoids are lipophilic compounds that provide important health-related benefits for human body functions. However, they have low water solubility and chemical stability, hence their incorporation in aqueous-based foods requires the use of emulsion-based lipid carriers. This work aimed at elucidating whether their inclusion in emulsion-based Solid Lipid Nanoparticles (SLNs) can provide a protective effect against β-carotene degradation under different environmental conditions in comparison to liquid lipid nanoemulsions. Glyceryl Stearate (GS) was mixed with Medium Chain Trygliceride (MCT) oil to formulate SLNs. SLNs presented a significantly enhanced β-carotene retention and a slower β-carotene degradation kinetics at increasing storage temperature, acidic conditions and light exposure. In fact, SLNs formulated with 5% GS in the lipid phase and stored at 4 °C and pH 7 retained almost 70% of the initially encapsulated β-carotene after 55 days of storage, while it was completely degraded when it was encapsulated in liquid nanoemulsions. Moreover, it was observed that the solid lipid type affects the protective effect that SLNs may confer to the encapsulated lipophilic bioactives. Saturated long chain triglycerides, such as hydrogenated palm oil (HPO) presented slower and lower β-carotene degradation kinetics in comparison to solid lipids composed of MCT, such as Coconut Oil (CNUT) or MCT + 5% of GS in the lipid phase. This work evidences that the incorporation of lipophilic bioactive compounds, such as β-carotene, into SLNs slows down their degradation kinetics which might be attributed to a reduced diffusion of the oxidative species due to the lipid crystalline structure.

Nanoparticles fabricated from bulk solid lipids: Preparation, properties, and potential food applications

Unlike conventional emulsions, solid lipids are used to prepare solid lipid nanoparticles (SLNs) with crystalline structures and nanostructured lipid carriers (NLCs) with imperfect crystals or amorphous structures to encapsulate various bioactive compounds significant to food applications. The solid lipid matrix can stabilize particle structures and control release properties of the encapsulated compounds that may not be possible for emulsions with liquid droplets. In this review, common approaches of preparing SLNs and NLCs are first presented, followed by parameters used to study lipid particles, including dimensional, morphological, charge, thermal, and crystalline properties. The structures of SLNs and NLCs with respect to the release mechanisms of encapsulated compounds are discussed in the context of lipid and emulsifier chemistry and preparation conditions. Lastly, possible applications of SLNs and NLCs in food systems are discussed.

A simulation environment for polymeric nanoparticles based on multi-agent systems

Production and characterization of polymeric nanoparticles, as colloidal dispersions, are processes that require time and technical skills to make the results accurate. Computational simulations in nanoscience have been used to help in these processes and provide agility and support to reach results: stability and quality in dispersions. Multi-Agent System for Polymeric Nanoparticles (MASPN) is an innovative and original simulation environment with features to demonstrate interactions of particles from physical-chemical parameters, ensuring Brownian motion of particles and attractive and repulsive behaviour. The MASPN environment has been designed and has been built according to the feature-driven development (FDD), as software methodology, and a multi-agent systems approach. In addition, we have used the event-driven simulation package algs4, the JASON agent building environment, all integrated by Java language. This paper aims to present the relation of the algs4 package and the JASON tool, both integrated into the MASPN environment to generate Brownian motion with elastic and inelastic collisions. The MASPN environment as a simulation tool emerges as a result, including the following features: graphical interface; integrated physical-chemical parameters; Brownian motion; JASON and algs4 integration; and distribution charts (size, zeta potential, and pH).

Nanoparticles for Detection and Treatment of Peripheral Arterial Disease

Peripheral arterial disease (PAD) is defined as a slow, progressive disorder of the lower extremity arterial vessels characterized by chronic narrowing that often results in occlusion and is associated with loss of functional capacity. Although the PAD occurrence rate is increasing in the elderly population, outcomes with current treatment strategies are suboptimal. Hence, there is an urgent need to develop new technologies that overcome limitations of traditional modalities for PAD detection and therapy. In this Review, the application of nanotechnology as a tool that bridges the gap in PAD diagnosis and therapy is in focus. Several materials including synthetic, natural, biodegradable, and biocompatible materials are used to develop nanoparticles for PAD diagnostic and/or therapeutic applications. Moreover, various recent research approaches are being explored to diagnose PAD through multimodality imaging with different nanoplatforms. Further efforts include targeted delivery of various therapeutic agents using nanostructures as carriers to treat PAD. Last, but not least, despite being a fairly new field, researchers are exploring the use of nanotheranostics for PAD detection and therapy.

Soft nanoparticles charge expression within lipid membranes: The case of amino terminated dendrimers in bilayers vesicles

Interactions of charged nanoparticles with model bio-membranes provide important insights about the soft interaction involved and the physico-chemical parameters that influence lipid bilayers stability, thus providing key features of their cytotoxicity effects onto cellular membranes. With this aim, the self-assembly processes between polyamidoamine dendrimers (generation G = 2.0 and G = 4.0) and dipalmitoylphosphatidylcholine (DPPC) lipids were investigated by means of Zeta potential analysis, x-rays, Raman and quasielastic light scattering experiments. Raman scattering data evidenced that dendrimers penetration produce a perturbation of the DPPC vesicles alkyl chains. A linear increase of liposome zeta-potential with increasing PAMAM concentration evidenced that only a fraction of the dendrimers effective charge contributes to the expression of the charge at the surface of the DPPC liposome. The linear region of the zeta-potential extends toward higher PAMAM concentrations as the dendrimer generation decreases from G = 4.0 to G = 2.0. Further increase in PAMAM concentration, outside of the linear region, causes a perturbation of the bilayer characterized by the loss in multilamellar correlation and the increase of DPPC liposome hydrodynamic radius. The findings of our investigation help to rationalize the effect of nanoparticles electrostatic interaction within lipid vesicles as well as to provide important insights about the perturbation of lipid bilayers membrane induced by nanoparticles inclusion.

Compound Stability in Nanoparticles: The Effect of Solid Phase Fraction on Diffusion of Degradation Agents into Nanostructured Lipid Carriers

The stability of active compounds encapsulated in nanoparticles depends on the resistance of the particles to diffusion of environmental degradation agents. In this paper, off-lattice Monte Carlo simulations are used to investigate a suspension of nanostructured lipid carriers (NLC) composed of interspaced liquid and solid lipid domains, immersed in a solution containing molecules representing oxidative or other degradation agents. The simulations examine the diffusion of the degradation agents into the nanoparticles as a function of nanoparticle size, solid domain fraction, and domain size. Two types of suspensions are studied: one (representing an infinitely dilute nanoparticle suspension) where the concentration of oxidative agents is constant in the solution around the particle and the other, finite system where diffusion into the nanoparticle causes depletion in the concentration of degradation agents in the surrounding solution. The total number of degradation agent molecules in the NLCs is found to decrease with the solid domain fraction, as may be expected. However, their concentration in the liquid domains is found to increase with the solid domain fraction. Since the degradation reaction depends on the concentration of the degradation agents, this suggests that compounds encapsulated in nanoparticles with high liquid content (such as emulsions) will degrade less and be more stable than those encapsulated in NLCs with high solid domain fraction, in agreement with previous experimental results.

Nanomaterials for In Vivo Imaging

In vivo imaging, which enables us to peer deeply within living subjects, is producing tremendous opportunities both for clinical diagnostics and as a research tool. Contrast material is often required to clearly visualize the functional architecture of physiological structures. Recent advances in nanomaterials are becoming pivotal to generate the high-resolution, high-contrast images needed for accurate, precision diagnostics. Nanomaterials are playing major roles in imaging by delivering large imaging payloads, yielding improved sensitivity, multiplexing capacity, and modularity of design. Indeed, for several imaging modalities, nanomaterials are now not simply ancillary contrast entities, but are instead the original and sole source of image signal that make possible the modality's existence. We address the physicochemical makeup/design of nanomaterials through the lens of the physical properties that produce contrast signal for the cognate imaging modality-we stratify nanomaterials on the basis of their (i) magnetic, (ii) optical, (iii) acoustic, and/or (iv) nuclear properties. We evaluate them for their ability to provide relevant information under preclinical and clinical circumstances, their in vivo safety profiles (which are being incorporated into their chemical design), their modularity in being fused to create multimodal nanomaterials (spanning multiple different physical imaging modalities and therapeutic/theranostic capabilities), their key properties, and critically their likelihood to be clinically translated.

Nanostructuring Biomaterials with Specific Activities towards Digestive Enzymes for Controlled Gastrointestinal Absorption of Lipophilic Bioactive Molecules

This review describes the development of novel lipid-based biomaterials that modulate fat digestion for the enhanced uptake of encapsulated lipophilic bioactive compounds (e.g. drugs and vitamins). Specific focus is directed towards analysing how key material characteristics affect the biological function of digestive lipases and manipulate lipolytic digestion. The mechanism of lipase action is a complex, interfacial process, whereby hydrolysis can be controlled by the ability for lipase to access and adsorb to the lipid-in-water interface. However, significant conjecture exists within the literature regarding parameters that influence the activities of digestive lipases. Important findings from recent investigations that strategically examined the interplay between the interfacial composition of the lipid microenvironment and lipolysis kinetics in simulated biophysical environments are presented. The correlation between lipolysis and the rate of solubilisation and absorption of lipophilic compounds in the gastrointestinal tract (GIT) is detailed. Greater insights into the mechanism of lipase action have provided a new approach for designing colloidal carriers that orally deliver poorly soluble compounds, directly impacting the pharmaceutical and food industries.

Computational and experimental approaches for investigating nanoparticle-based drug delivery systems

Most therapeutic agents suffer from poor solubility, rapid clearance from the blood stream, a lack of targeting, and often poor translocation ability across cell membranes. Drug/gene delivery systems (DDSs) are capable of overcoming some of these barriers to enhance delivery of drugs to their right place of action, e.g. inside cancer cells. In this review, we focus on nanoparticles as DDSs. Complementary experimental and computational studies have enhanced our understanding of the mechanism of action of nanocarriers and their underlying interactions with drugs, biomembranes and other biological molecules. We review key biophysical aspects of DDSs and discuss how computer modeling can assist in rational design of DDSs with improved and optimized properties. We summarize commonly used experimental techniques for the study of DDSs. Then we review computational studies for several major categories of nanocarriers, including dendrimers and dendrons, polymer-, peptide-, nucleic acid-, lipid-, and carbon-based DDSs, and gold nanoparticles. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.