A new standardized lipolysis approach for characterization of emulsions and dispersions

Exploring LIPIDs for their potential to improves bioavailability of lipophilic drugs candidates: A review

This review aims to provide a thorough examination of the benefits, challenges, and advancements in utilizing lipids for more effective drug delivery, ultimately contributing to the development of innovative approaches in pharmaceutical science. Lipophilic drugs, characterized by low aqueous solubility, present a formidable challenge in achieving effective delivery and absorption within the human body. To address this issue, one promising approach involves harnessing the potential of lipids. Lipids, in their diverse forms, serve as carriers, leveraging their unique capacity to enhance solubility, stability, and absorption of these challenging drugs. By facilitating improved intestinal solubility and selective lymphatic absorption of porously permeable drugs, lipids offer an array of possibilities for drug delivery. This versatile characteristic not only bolsters the pharmacological efficacy of drugs with low bioavailability but also contributes to enhanced therapeutic performance, ultimately reducing the required dose size and associated costs. This comprehensive review delves into the strategic formulation approaches that employ lipids as carriers to ameliorate drug solubility and bioavailability. Emphasis is placed on the critical considerations of lipid type, composition, and processing techniques when designing lipid-based formulations. This review meticulously examines the multifaceted challenges that come hand in hand with lipid-based formulations for lipophilic drugs, offering an insightful perspective on future trends. Regulatory considerations and the broad spectrum of potential applications are also thoughtfully discussed. In summary, this review presents a valuable repository of insights into the effective utilization of lipids as carriers, all aimed at elevating the bioavailability of lipophilic drugs.

Investigation of lipolytic activity of the red king crab hepatopancreas homogenate by NMR spectroscopy

The digestive gland of craboids (hepatopancreas) is rich in a huge number of various enzymes (collagenases, nucleases, hyaluronidases, proteases), which are well studied at the moment. However, little is known about crustacean lipases. In this work, using ¹H NMR spectroscopy, it was found that the hepatopancreas homogenate of the red king crab Paralithodes camtschaticus demonstrates high lipolytic activity against triacetin in a wide pH range and shows moderate activity against the caprylic/capric triglyceride emulsion. Under the action of the hepatopancreas homogenate, triacylglycerols are converted into 1,2-diacylglycerol, and then into 2-monoacylglycerol and 1-monoacylglycerol. The 1-monoacylglycerol predominates in the reaction products. The use of NMR spectroscopy makes it possible to quickly detect hydrolysis products and evaluate the reaction direction.

Solid lipid matrix mediated nanoarchitectonics for improved oral bioavailability of drugs

Introduction: Solid matrix mediated lipid nanoparticle formulations (LNFs) retain some of the best features of ideal drug carriers necessary for improving the oral absorption and bioavailability (BA) of both hydrophilic and hydrophobic drugs. LNFs with solid matrices may be typically categorized into three major types of formulations, viz., solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs) and lipid-drug conjugate nanoparticles (LDC-NPs). Solid matrix based LNFs are, potentially, the most appropriate delivery systems for poorly water soluble drugs in need of improved drug solubility, permeability, absorption, or increased oral BA. In addition, LNFs as matrices are able to encapsulate both hydrophobic and hydrophilic drugs in a single matrix based on their excellent ability to form cores and shells. Interestingly, LNFs also act as delivery devices to impart chemical stability to various orally administered drugs. Areas covered: Aim of the review is to forecast the presentation of pharmacokinetic characteristics of solid lipid matrix based nanocarriers which are typically biocompatible, biodegradable and non-toxic carrier systems for efficient oral delivery of various drugs. Efficient delivery is broadly mediated by the fact that lipophilic drugs are readily soluble in lipidic substrates that are capable of permeating across the gut epithelium following oral administration, subsequently delivering the moiety of interest more efficiently across the gut mucosal membrane. This enhances the overall BA of many drugs facing oral delivery challenges by improving their pharmacokinetic profile. This article specifically focuses on the biopharmaceutical and pharmacokinetic aspects of such solid lipid matrix based nanoformulations and possible mechanisms for better drug absorption and improved BA following oral administration. It also briefly reviews methods to access the efficacy of LNFs for improving oral BA of drugs, regulatory aspects and some interesting lipid-derived commercial formulations, with a concluding remark. Expert opinion: LNFs enhance the overall BA of many drugs facing oral delivery challenges by improving their pharmacokinetic profile.

Development of a New Ex Vivo Lipolysis-Absorption Model for Nanoemulsions

The use of lipid-based formulations (LBFs) in improving the absorption of poorly water-soluble drugs has now well established. Because the in vivo evaluation of LBFs is labor-intensive, in vitro or ex vivo approaches could provide advantages. In this study, a new ex vivo lipolysis-absorption model (evLAM) composed of an intestinal digestion system and an intestinal tissue system was developed to evaluate and predict the in vivo absorption performances of LBFs. Model factors, including the pH of the system and concentrations of d-glucose and pancreatic lipase, were investigated and optimized by a Box-Behnken design. To evaluate this new model, a lipid formulation of indomethacin, which was chosen based on preliminary studies of pseudo-ternary phase diagrams, emulsion droplets, and solubility, was further investigated by an in vivo pharmacokinetic study of rats, the everted gut sac model, and the evLAM, respectively. The absorption percentages obtained from the evLAM were much more similar to the data of rats in vivo than those from the everted gut sac model, showing a preferable in vitro-in vivo correlation (r = 0.9772). Compared with the conventional in vitro and in vivo methods, the evLAM, which allowed precise insights into the in vivo absorption characteristics without much time or a complicated process, could be a better tool for assessing LBFs of poorly water-soluble drugs.

In vitro study of triglyceride lipolysis and phase distribution of the reaction products and cholesterol: effects of calcium and bicarbonate

We describe a relatively simple in vitro model for triglyceride (TG) lipolysis which mimics closely the conditions in the human stomach and small intestine. The main model advantages are: (1) as in vivo, sodium bicarbonate is used for buffering; (2) the pH-profile in the small intestine is closely matched; (3) the experimental procedure does not include complex equipment. To test its performance, the proposed in vitro model is applied to quantify the effects of Ca(2+), pH, and bicarbonate on the degree of TG lipolysis and on the solubilization of the lipolysis products and cholesterol in the aqueous phase. We found that TG lipolysis passes through a shallow minimum at 3.5 mM Ca(2+) when varying the calcium concentration between 1 and 11 mM, while the presence of bicarbonate and the increase of pH led to a higher degree of lipolysis. Centrifugation and filtration were used to separate the aqueous phase and to study the solubilisation of the lipophilic components in the aqueous phase. We found that the solubilized cholesterol increases linearly with the concentration of free fatty acids (FFA) which is evidence for co-solubilization of these two components in the bile micelles. At high Ca(2+) concentrations, aggregates larger than 300 nm were observed by cryo-microscopy and light scattering, which solubilize well cholesterol and saturated FFA. In contrast, the monoglycerides were always predominantly solubilized in the small bile micelles with diameters around 4 nm.

Design of lipid-based formulations for oral administration of poorly water-soluble drug fenofibrate: effects of digestion

Lipid-based drug carriers are likely to have influence on bioavailability through enhanced solubilization of the drug in the gastrointestinal tract. The study was designed to investigate the lipid formulation digestibility in the simulated gastro intestinal media. Fenofibrate was formulated in representative Type II, IIIA, IIIB and IV self-emulsifying/microemulsifying lipid delivery systems (SEDDS and SMEDDS designed for oral administration) using various medium-chain glyceride components, non-ionic surfactants and cosolvents as excipients. Soybean oil was used only as an example of long-chain triglycerides to compare the effects of formulation with their counterparts. The formulations were subjected to in vitro digestion specifically to predict the fate of the drug in the gastro intestinal tract after exposure of the formulation to pancreatic enzymes and bile. In vitro digestion experiments were carried out using a pH-stat maintained at pH 7.5 for 30 min using intestinal fluids simulating the fed and fasted states. The digestion rate was faster and almost completed in Type II and IIIA systems. Most of the surfactants used in the studies are digestible. However, the high concentration of surfactant and/or cosolvent used in Type IIIB or IV systems lowered the rate of digestion. The digestion of medium-chain triglycerides was faster than long-chain triglycerides, but kept comparatively less drug in the post digestion products. Medium-chain mixed glycerides are good solvents for fenofibrate as rapidly digested but to improve fenofibrate concentration in post digestion products the use of long-chain mixed glycerides are suggested for further investigations.

Review of in vitro digestion models for rapid screening of emulsion-based systems

There is increasing interest in understanding and controlling the digestion of emulsified lipids within the food and pharmaceutical industries. Emulsion-based delivery systems are being developed to encapsulate, protect, and release non-polar lipids, vitamins, nutraceuticals, and drugs. These delivery systems are also being used to control the stability and digestion of lipids within the human gastrointestinal tract so as to create foods that enhance satiety and reduce hunger. In vitro digestion models are therefore needed to test the efficacy of different approaches of controlling lipid digestion under conditions that simulate the human gastrointestinal tract. This article reviews the current status of in vitro digestion models for simulating lipid digestion, with special emphasis on the pH stat method. The pH stat method is particularly useful for the rapid screening of food emulsions and emulsion-based delivery systems with different compositions and structures. Successful candidates can then be tested with more rigorous in vitro digestion models, or using animal or human feeding studies.

Silica nanoparticles to control the lipase-mediated digestion of lipid-based oral delivery systems

We investigate the role of hydrophilic fumed silica in controlling the digestion kinetics of lipid emulsions, hence further exploring the mechanisms behind the improved oral absorption of poorly soluble drugs promoted by silica-lipid hybrid (SLH) microcapsules. An in vitro lipolysis model was used to quantify the lipase-mediated digestion kinetics of a series of lipid vehicles formulated with caprylic/capric triglycerides: lipid solution, submicrometer lipid emulsions (in the presence and absence of silica), and SLH microcapsules. The importance of emulsification on lipid digestibility is evidenced by the significantly higher initial digestion rate constants for SLH microcapsules and lipid emulsions (>15-fold) in comparison with that of the lipid solution. Silica particles exerted an inhibitory effect on the digestion of submicrometer lipid emulsions regardless of their initial location, i.e., aqueous or lipid phases. This inhibitory effect, however, was not observed for SLH microcapsules. This highlights the importance of the matrix structure and porosity of the hybrid microcapsule system in enhancing lipid digestibility as compared to submicrometer lipid emulsions stabilized by silica. For each studied formulation, the digestion kinetics is well correlated to the corresponding in vivo plasma concentrations of a model drug, celecoxib, via multiple-point correlations (R(2) > 0.97). This supports the use of the lipid digestion model for predicting the in vivo outcome of an orally dosed lipid formulation. SLH microcapsules offer the potential to enhance the oral absorption of poorly soluble drugs via increased lipid digestibility in conjunction with improved drug dissolution/dispersion.

Novel self-nanoemulsifying drug delivery system for enhanced solubility and dissolution of lutein

Self-nanoemulsifying drug delivery system (SNEDDS) containing oil (Phosal 53 MCT), surfactant (Labrasol), and cosurfactant (Transcutol-HP or Lutrol-E400) was prepared to enhance solubility and dissolution of lutein. Ternary phase diagram of the SNEDDS was constructed to identify the self-emulsifying regions following which the percentage of oil, surfactant, and cosurfactant in the SNEDDS were optimized in terms of emulsification time and mean emulsion droplet size. The optimized SNEDDS consists of 25% oil, 60% surfactant, and 15% cosurfactant. When measured using USP XXIII dissolution apparatus II, the emulsification time of the SNEDDS prepared with Transcutol-HP as cosurfactant was less than 20 sec, and it was 20-30 sec in the SNEDDS prepared with Lutrol-E400. Mean emulsion droplet size was slightly smaller when Transcutol-HP was used as cosurfactant (80 +/- 6 nm), compared to when Lutrol- E400 was used (93 +/- 6 nm). Dissolution of lutein from the solid SNEDDS (physical mixture of the optimized SNEDDS and Aerosil 200) took place immediately (less than 5 min) in distilled water, and, once dissolved, no precipitation or aggregation of the drug were observed. In contrast, no drug was released from lutein powder or from the commercial product (Eyelac(R)) until 3 h of the study duration.

Enhancing intestinal drug solubilisation using lipid-based delivery systems

Lipid-based delivery systems are finding increasing application in the oral delivery of poorly water-soluble, lipophilic drugs. Whilst lipidic dose forms may improve oral bioavailability via several mechanisms, enhancement of gastrointestinal solubilisation remains argueably the most important method of absorption enhancement. This review firstly describes the mechanistic rationale which underpins the use of lipid-based delivery systems to enhance drug solubilisation and briefly reviews the available literature describing increases in oral bioavailability after the administration of lipid solution, suspension and self-emulsifying formulations. The use of in vitro methods including dispersion tests and more complex models of in vitro lipolysis as indicators of potential in vivo performance are subsequently described, with particular focus on recent data which suggests that the digestion of surfactants present in lipid-based formulations may impact on formulation performance. Finally, a series of seven guiding principles for formulation design of lipid-based delivery systems are suggested based on an analysis of recent data generated in our laboratories and elsewhere.