Monoacyl phosphatidylcholine inhibits the formation of lipid multilamellar structures during in vitro lipolysis of self-emulsifying drug delivery systems

Tailoring Lipid-Based Drug Delivery Nanosystems by Synchrotron Small Angle X-ray Scattering

Thanks to specific physico-chemical properties, drug delivery systems based on nanoparticles have proven to effectively transport delicate molecules for therapeutic purposes, protecting them from degradation, increasing their stability in the blood circulation and allowing to convey and release the transported substances in specific areas of the body. Nanoparticles obtained from biopolymers for applications in medicine and pharmaceutics have become particularly popular in recent years due to the enormous research effort in the field of vaccines to respond to the pandemic emergency. Among the various types of biopolymers used to produce nanoparticles for therapeutics, lipids have characteristics that make them biocompatible, with low toxicity and ease of clearance. They can be synthesized by designing their characteristics according to the foreseen administration path, or to the target of the transported drug. The analytical methods mostly used to evaluate the characteristics of lipid nanosytems for drug delivery involve studying their effects on cells, in vitro and in vivo. Although it is often considered a "niche technique" for research in the bio-related sciences, Small Angle X-ray Scattering (SAXS) is a versatile tool to study the structure of nanosystems based on lipids, both ex situ and in situ. Therefore, it allows to evaluate both the effect of the different synthesis parameters and of the exposure of lipid nanoparticles to physiological conditions, which is of fundamental importance to design efficient drug delivery systems. In this mini-review, we will report some recent examples of characterization and design of nanoparticles based on lipids, where SAXS has been a fundamental step both to guide the synthesis of nanomaterials with tailored characteristics, and to understand the interaction between nanomaterials and cells.

Emulsion gels and oil-filled aerogels as curcumin carriers: Nanostructural characterization of gastrointestinal digestion products

Agar and κ-carrageenan emulsion gels and oil-filled aerogels were investigated as curcumin carriers and their structure and mechanical properties, as well as their structural changes upon in vitro gastrointestinal digestion were characterized. Agar emulsion gels presented stiffer behaviour, with smaller and more homogeneous oil droplets (ϕ ∼ 12 µm) than those from κ-carrageenan (ϕ ∼ 243 µm). The structure of κ-carrageenan gels was characterized by the presence of rigid swollen linear chains, while agar produced more branched networks. After simulated gastrointestinal digestion bile salt lamellae/micelles (∼5 nm) and larger vesicles of partially digested oil (R_g ∼ 20-50 nm) were the predominant structures, being their proportion dependent of the polysaccharide type and the physical state of the gel network. The presence of curcumin induced the formation of larger vesicles and limited the formation of mixed lamellae/micelles.

Estimating the Oral Absorption from Self-Nanoemulsifying Drug Delivery Systems Using an In Vitro Lipolysis-Permeation Method

The aim of this study was to design an in vitro lipolysis-permeation method to estimate drug absorption following the oral administration of self-nanoemulsifying drug delivery systems (SNEDDSs). The method was evaluated by testing five oral formulations containing cinnarizine (four SNEDDSs and one aqueous suspension) from a previously published pharmacokinetic study in rats. In that study, the pharmacokinetic profiles of the five formulations did not correlate with the drug solubilization profiles obtained during in vitro intestinal lipolysis. Using the designed lipolysis-permeation method, in vitro lipolysis of the five formulations was followed by in vitro drug permeation in Franz diffusion cells equipped with PermeaPad^® barriers. A linear in vivo–in vitro correlation was obtained when comparing the area under the in vitro drug permeation–time curve (AUC_0–3h), to the AUC_0–3h of the plasma concentration–time profile obtained from the in vivo study. Based on these results, the evaluated lipolysis-permeation method was found to be a promising tool for estimating the in vivo performance of SNEDDSs, but more studies are needed to evaluate the method further.

Current challenges and future perspectives in oral absorption research: An opinion of the UNGAP network

Although oral drug delivery is the preferred administration route and has been used for centuries, modern drug discovery and development pipelines challenge conventional formulation approaches and highlight the insufficient mechanistic understanding of processes critical to oral drug absorption. This review presents the opinion of UNGAP scientists on four key themes across the oral absorption landscape: (1) specific patient populations, (2) regional differences in the gastrointestinal tract, (3) advanced formulations and (4) food-drug interactions. The differences of oral absorption in pediatric and geriatric populations, the specific issues in colonic absorption, the formulation approaches for poorly water-soluble (small molecules) and poorly permeable (peptides, RNA etc.) drugs, as well as the vast realm of food effects, are some of the topics discussed in detail. The identified controversies and gaps in the current understanding of gastrointestinal absorption-related processes are used to create a roadmap for the future of oral drug absorption research.

Porous Nanostructure, Lipid Composition, and Degree of Drug Supersaturation Modulate In Vitro Fenofibrate Solubilization in Silica-Lipid Hybrids

The unique nanostructured matrix obtained by silica-lipid hybrids (SLHs) is well known to improve the dissolution, absorption, and bioavailability of poorly water-soluble drugs (PWSDs). The aim of this study was to investigate the impact of: (i) drug load: 3–22.7% w/w, (ii) lipid type: medium-chain triglyceride (Captex 300) and mono and diester of caprylic acid (Capmul PG8), and (iii) silica nanostructure: spray dried fumed silica (FS) and mesoporous silica (MPS), on the in vitro dissolution, solubilization, and solid-state stability of the model drug fenofibrate (FEN). Greater FEN crystallinity was detected at higher drug loads and within the MPS formulations. Furthermore, an increased rate and extent of dissolution was achieved by FS formulations when compared to crystalline FEN (5–10-fold), a commercial product; APO-fenofibrate (2.4–4-fold) and corresponding MPS formulations (2–4-fold). Precipitation of FEN during in vitro lipolysis restricted data interpretation, however a synergistic effect between MPS and Captex 300 in enhancing FEN aqueous solubilization was attained. It was concluded that a balance between in vitro performance and drug loading is key, and the optimum drug load was determined to be between 7–16% w/w, which corresponds to (200–400% equilibrium solubility in lipid S_eq). This study provides valuable insight into the impact of key characteristics of SLHs, in constructing optimized solid-state lipid-based formulations for the oral delivery of PWSDs.

Amelioration of lipophilic compounds in regards to bioavailability as self-emulsifying drug delivery system (SEDDS)

Background

High lipophilicity and poor aqueous solubility are the endemic problems of new drug molecules. Sixty to seventy percent of these drugs are unable to solubilize completely in aqueous media, or have very low permeability. This hampers their oral absorption and further leads to their poor bioavailability. Various researches are in progress to overcome these limitations. Novel technologies like nano-carrier systems have become popular for improving the solubility of drugs.

Main body

Lipid-based formulations, among nano systems, are taking pace for the enhancement of solubility, oral absorption, and hence the bioavailability of drugs. Among the lipid formulations, self-emulsification systems are gaining popularity by offering various advantages to delivery systems. Self-emulsifying drug delivery systems (SEDDS) are isotropic blends of oil and surfactant/co-surfactants. These ingredients upon gentle agitation in aqueous media results in the formation of o/w emulsion. In spite of many works published in SEDDS, the major concerns of this article are to discuss the various approaches to formulate a good lipid-based carrier system for poorly aqueous soluble drugs, role of various polymers, and their categories used in the formulation along-with the modern technologies used for enhancing the stability of liquid SEDDS. This review majorly focuses upon the problems related to the poor aqueous solubility of the newer lipid molecules and the solutions to overcome their solubility and in addition bioavailability.

Conclusion

As per the researches done in formulation and optimization of SEDDS for the enhancement of bioavailability of lipophilic molecules, it can be stated that the aqueous solubility as well as bioavailability can be increased by many folds compared to their marketed or other oral formulations.

Improvement of carotenoid bioaccessibility from spinach by co-ingesting with excipient nanoemulsions: impact of the oil phase composition

Many of the carotenoids found naturally in fruits and vegetables are beneficial to human health, but they often have low oral bioavailability because of their high hydrophobicity. In this study, the effects of varying the composition of the oil phase of excipient nanoemulsions on carotenoid bioaccessibility from spinach were investigated using a simulated gastrointestinal tract. Nanoemulsions containing different ratios of medium chain triglycerides (MCT) and long chain triglycerides (LCT) were prepared: (i) mixing MCT and LCT oils before homogenization and (ii) mixing MCT droplets with LCT droplets after homogenization. The release of carotenoids from spinach and their solubilization within the mixed micelles formed after lipid digestion depended strongly on the oil phase composition. As expected, carotenoid bioaccessibility was always higher in the presence of excipient nanoemulsions than in their absence. The total free fatty acids released in the small intestine increased as the MCT/LCT ratio increased, which can be attributed to the faster release of shorter chain fatty acids from the oil droplet surfaces during lipid digestion. As the MCT ratio increased, lutein bioaccessibility increased but β-carotene bioaccessibility decreased. This difference was attributed to the ability of the formed mixed micelles to accommodate the two different kinds of carotenoids in their hydrophobic domains. Interestingly, carotenoid bioaccessibility was significantly lower (P < 0.05) when the oil droplets were mixed after homogenization than when the oils were mixed before homogenization. These results have important implications for the design of excipient foods to improve the bioavailability of hydrophobic nutraceuticals in fruits and vegetables.

Successful oral delivery of poorly water-soluble drugs both depends on the intraluminal behavior of drugs and of appropriate advanced drug delivery systems

Poorly water-soluble drugs continue to be a problematic, yet important class of pharmaceutical compounds for treatment of a wide range of diseases. Their prevalence in discovery is still high, and their development is usually limited by our lack of a complete understanding of how the complex chemical, physiological and biochemical processes that occur between administration and absorption individually and together impact on bioavailability. This review defines the challenge presented by these drugs, outlines contemporary strategies to solve this challenge, and consequent in silico and in vitro evaluation of the delivery technologies for poorly water-soluble drugs. The next steps and unmet needs are proposed to present a roadmap for future studies for the field to consider enabling progress in delivery of poorly water-soluble compounds.

Colloidal aspects of dispersion and digestion of self-dispersing lipid-based formulations for poorly water-soluble drugs

Self-dispersing lipid-based formulations, particularly self-microemulsifying drug delivery systems (SMEDDS) have gained an increased interest in recent times as a means to enhance the oral bioavailability of poorly water-soluble lipophilic drugs. Upon dilution, SMEDDS self-emulsify in an aqueous fluid and usually form a kinetically stable oil-in-water emulsion or in some rare cases a true thermodynamically stable microemulsion. The digestion of the formulation leads to the production of amphiphilic digestion products that interact with endogenous amphiphilic components and form self-assembled colloidal phases in the aqueous environment of the intestine. The formed colloidal phases play a pivotal role in maintaining the lipophilic drug in the solubilised state during gastrointestinal transit prior to absorption. Thus, this review describes the structural characterisation techniques employed for SMEDDS and the recent literature studies that elucidated the colloidal aspects during dispersion and digestion of SMEDDS and solid SMEDDS. Possible future studies are proposed to gain better understanding on the colloidal aspects of SMEDDS and solid SMEDDS.

Exploring the utility of the Chasing Principle: influence of drug-free SNEDDS composition on solubilization of carvedilol, cinnarizine and R3040 in aqueous suspension

This study assessed the influence of the composition of drug-free SNEDDS co-dosed with aqueous suspensions of carvedilol (CAR), cinnarizine (CIN) or R3040 on drug solubilization in a two-compartment in vitro lipolysis model. Correlation of drug logP or solubility in SNEDDS with drug solubilization during in vitro lipolysis in the presence of drug-free SNEDDS was assessed. SNEDDS with varying ratios of soybean oil:Maisine 35-1 (1:1, w/w) and Kolliphor RH40, with ethanol at 10% (w/w) were used. SNEDDS were named F65, F55 and F20 (numbers refer to the percentage of lipids) and aqueous suspensions without drug-free SNEDDS (F0) were also analyzed. While the ranking order of drug solubilization was F65=F55=F20>F0 for CAR; F65=F55>F20>F0 for CIN and F65=F55=F20>F0 for R3040 - with higher CAR solubilization than for R3040 and CIN - the ranking of S eq of CAR, CIN and R3040 in SNEDDS was F65F20 and F65>F55>F20, respectively. Therefore, the composition of SNEDDS influenced the solubilization of CIN, but not CAR and R3040. Furthermore, high S eq in SNEDDS did not reflect high drug solubilization. As CAR (logP 3.8) showed higher solubilization than CIN (logP 5.8) and R3040 (logP 10.4), a correlation between drug logP and drug solubilization was observed.

Liquid Crystalline Nanostructures as PEGylated Reservoirs of Omega-3 Polyunsaturated Fatty Acids: Structural Insights toward Delivery Formulations against Neurodegenerative Disorders

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) are bioactive lipids with considerable impact in medicine and nutrition. These compounds exert structuring effects on the cellular membrane organization, regulate the gene expression, and modulate various signaling cascades and metabolic processes. The purpose of the present work is to demonstrate the structural features of ω-3 PUFA-containing three-dimensional supramolecular lipid assemblies suitable for pharmaceutical applications that require soft porous carriers. We investigate the liquid crystalline structures formed upon mixing of eicosapentaenoic acid (EPA, 20:5) with the lyotropic nonlamellar lipid monoolein and the formation of multicompartment assemblies. Starting with the monoolein-based lipid cubic phase, double membrane vesicles, cubosome precursors, sponge-type particles (spongosomes), mixed intermediate nonlamellar structures, and multicompartment assemblies are obtained through self-assembly at different amphiphilic compositions. The dispersions containing spongosomes as well as nanocarriers with oil and vesicular compartments are stabilized by PEGylation of the lipid/water interfaces using a phospholipid with a poly(ethylene glycol) chain. The microstructures of the bulk mixtures were examined by cross-polarized light optical microscopy. The dispersed liquid crystalline structures and intermediate states were studied by small-angle X-ray scattering, cryogenic transmission electron microscopy, and quasielastic light scattering techniques. They established that PUFA influences the phase type and the sizes of the aqueous compartments of the liquid crystalline carriers. The resulting multicompartment systems and stealth nanosponges may serve as mesoporous reservoirs for coencapsulation of ω-3 PUFA (e.g., EPA) with water-insoluble drugs and hydrophilic macromolecules toward development of combination treatment strategies of neurodegenerative and other diseases.