Immobilised lipase for in vitro lipolysis experiments

Lipidic drug delivery systems are responsive to the human microbiome

In vitro and in vivo tests for therapeutic agents are typically conducted in sterile environments, but many target areas for drug delivery are home to thousands of microbial species. Here, we examine the behaviour of lipidic nanomaterials after exposure to representative strains of four bacterial species found in the gastrointestinal tract and skin. Small angle X-ray scattering measurements show that the nanostructure of monoolein cubic and inverse hexagonal phases are transformed, respectively, into inverse hexagonal and inverse micellar cubic phases upon exposure to a strain of live Staphylococcus aureus often present on skin and mucosa. Further investigation demonstrates that enzymatic hydrolysis and cell membrane lipid transfer are both likely responsible for this effect. The structural responses to S. aureus are rapid and significantly reduce the rate of drug release from monoolein-based nanomaterials. These findings are the first to demonstrate how a key species in the live human microbiome can trigger changes in the structure and drug release properties of lipidic nanomaterials. The effect appears to be strain specific, varies from patient to patient and body region to body region, and is anticipated to affect the bioapplication of monoglyceride-based formulations.

Developing an in vitro lipolysis model for real-time analysis of drug concentrations during digestion of lipid-based formulations

Understanding the effect of digestion on oral lipid-based drug formulations is a critical step in assessing the impact of the digestive process in the intestine on intraluminal drug concentrations. The classical pH-stat in vitro lipolysis technique has traditionally been applied, however, there is a need to explore the establishment of higher throughput small-scale methods. This study explores the use of alternative lipases with the aim of selecting digestion conditions that permit in-line UV detection for the determination of real-time drug concentrations. A range of immobilised and pre-dissolved lipases were assessed for digestion of lipid-based formulations and compared to digestion with the classical source of lipase, porcine pancreatin. Palatase® 20000 L, a purified liquid lipase, displayed comparable digestion kinetics to porcine pancreatin and drug concentration determined during digestion of a fenofibrate lipid-based formulation were similar between methods. In-line UV analysis using the MicroDISS ProfilerTM demonstrated that drug concentration could be monitored during one hour of dispersion and three hours of digestion for both a medium- and long-chain lipid-based formulations with corresponding results to that obtained from the classical lipolysis method. This method offers opportunities exploring the real-time dynamic drug concentration during dispersion and digestion of lipid-based formulations in a small-scale setup avoiding artifacts as a result of extensive sample preparation.

Controlling drug release by introducing lipase inhibitor within a lipid formulation

Drug overdose connected to marketed pharmaceutical products, particularly opioids, occurs at an alarming rate. Novel strategies through innovative formulation approaches that reduce the likelihood of overdose while allowing safe therapeutic outcomes are urgently required. The current study provides a proof-of-concept for a new formulation approach by co-formulating drug with a lipase inhibitor within a solid lipid formulation in order to prevent or reduce the harmful effects of taking multiple doses of an oral solid dose form. Lipase inhibitor controlled-release (LICR) formulations were created using a simple hot melt method to co-formulate the inhibitor (orlistat) and ibuprofen, as the model drug, within the lipid matrix. The digestion and drug release kinetics were determined using an in vitro lipolysis model. Above a threshold level of orlistat there was decreased digestibility of multiple doses of the LICR formulations, leading to reduced drug release. Upon administration of the formulations in capsules to rats, the LICR formulation displayed the lowest exposure of ibuprofen during the pharmacokinetic studies. This novel formulation approach shows promise in preventing accidental drug overdose after oral administration of multiple doses of formulation.

Emulsions containing optimum cow milk fat and canola oil mixtures replicate the lipid self-assembly of human breast milk during digestion

HYPOTHESIS

The digestion of different milks and milk substitutes leads to the formation of a variety of self-assembled lipid structures, with the structuring of human milk being paramount for infant nutrition. It was hypothesised that mixing cow milk fat rich in medium/long-chain lipids with canola oil rich in long-chain unsaturated lipids would replicate the structuring of human milk by balancing lipid chain lengths and saturation levels.

EXPERIMENTS

Emulsions of cow milk fat/canola oil mixtures were prepared in two ways - by pre-mixing ghee and canola oil before dispersing them and by dispersing canola oil directly into commercial cow milk. Small angle X-ray scattering combined with titration of the fatty acids produced during digestion allowed for the correlation of dynamic lipid self-assembly with the extent of lipid digestion. Laser light scattering was used to show that the particle sizes in the digesting mixtures were similar and coherent anti-Stokes Raman spectroscopy (CARS) microscopy was used to confirm the mixing of canola oil into cow milk fat globules.

FINDINGS

As the amount of long-chain unsaturated canola oil lipids in the mixtures increased, the lipid self-assembly tended towards colloidal structures of greater interfacial curvature. When the ratio of cow milk fat to canola oil lipids was 1:1 (w/w), the digesting lipids assembled themselves into the same liquid crystalline structures as human breast milk. This observation was independent of the method used to mix the lipids, with CARS microscopy indicating uniform mixing of the canola oil into cow milk upon ultrasonication.

Correlating Digestion-Driven Self-Assembly in Milk and Infant Formulas with Changes in Lipid Composition

Lipids in mammalian milks such as bovine milk and human breast milk have been shown to self-assemble into various liquid crystalline materials during digestion. In this study, the direct correlation between the composition of the lipids from three types of mammalian milk, three brands of infant formulas (IFs), and soy milk and the liquid crystalline structures that form during their digestion was investigated to link the material properties to the composition. The self-assembly behavior was assessed using in vitro digestion coupled with in situ small-angle X-ray scattering (SAXS). Lipid composition was determined during in vitro digestion using ex situ liquid chromatography–mass spectrometry. All tested milks self-assembled into ordered structures during digestion, with the majority of milks displaying nonlamellar phases. Milks that released mostly long-chain fatty acids (>95 mol % of the top 10 fatty acids released) with more than 47 mol % unsaturation predominantly formed a micellar cubic phase during digestion. Other milks released relatively more medium-chain fatty acids and medium-chain monoglycerides and produced a range of ordered liquid crystalline structures including the micellar cubic phase, the hexagonal phase, and the bicontinuous cubic phase. One infant formula did not form liquid crystalline structures at all as a consequence of differences in fatty acid distributions. The self-assembly phenomenon provides a powerful discriminator between different classes of nutrition and a roadmap for the design of human milklike systems and is anticipated to have important implications for nutrient transport and the delivery of bioactives.

Comparison of bulk and microfluidic methods to monitor the phase behaviour of nanoparticles during digestion of lipid-based drug formulations using in situ X-ray scattering

The performance of orally administered lipid-based drug formulations is crucially dependent on digestion, and understanding the colloidal structures formed during digestion is necessary for rational formulation design. Previous studies using the established bulk pH-stat approach (Hong et al. 2015), coupled to synchrotron small angle X-ray scattering (SAXS), have begun to shed light on this subject. Such studies of digestion using in situ SAXS measurements are complex and have limitations regarding the resolution of intermediate structures. Using a microfluidic device, the digestion of lipid systems may be monitored with far better control over the mixing of the components and the application of enzyme, thereby elucidating a finer understanding of the structural progression of these lipid systems. This work compares a simple T-junction microcapillary device and a custom-built microfluidic chip featuring hydrodynamic flow focusing, with an equivalent experiment with the full scale pH-stat approach. Both microfluidic devices were found to be suitable for in situ SAXS measurements in tracking the kinetics with improved time and signal sensitivity compared to other microfluidic devices studying similar lipid-based systems, and producing more consistent and controllable structural transformations. Particle sizing of the nanoparticles produced in the microfluidic devices were more consistent than the pH-stat approach.

Effect of lipids on absorption of carvedilol in dogs: Is coadministration of lipids as efficient as a lipid-based formulation?

Lipid-based formulations (LBFs) is a formulation strategy for enabling oral delivery of poorly water-soluble drugs. However, current use of this strategy is limited to a few percent of the marketed products. Reasons for that are linked to the complexity of LBFs, chemical instability of pre-dissolved drug and a limited understanding of the influence of LBF intestinal digestion on drug absorption. The aim of this study was to explore intestinal drug solubilization from a long-chain LBF, and evaluate whether coadministration of LBF is as efficient as a lipid-based drug formulation containing the pre-dissolved model drug carvedilol. Thus, solubility studies of this weak base were performed in simulated intestinal fluid (SIF) and aspirated dog intestinal fluid (DIF). DIF was collected from duodenal stomas after dosing of water and two levels (1 g and 2 g) of LBF. Similarly, the in vitro SIF solubility studies were conducted prior to, and after addition of, undigested or digested LBF. The DIF fluid was further characterized for lipid digestion products (free fatty acids) and bile salts. Subsequently, carvedilol was orally administered to dogs in a lipid-based drug formulation and coadministered with LBF, and drug plasma exposure was assessed. In addition to these studies, in vitro drug absorption from the different formulation approaches were evaluated in a lipolysis-permeation device, and the obtained data was used to evaluate the in vitro in vivo correlation. The results showed elevated concentrations of free fatty acids and bile salts in the DIF when 2 g of LBF was administered, compared to only water. As expected, the SIF and DIF solubility data revealed that carvedilol solubilization increased by the presence of lipids and lipid digestion products. Moreover, coadministration of LBF and drug demonstrated equal plasma exposure to the lipid-based drug formulation. Furthermore, evaluation of in vitro absorption resulted in the same rank order for the LBFs as in the in vivo dog study. In conclusion, this study demonstrated increased intestinal solubilization from a small amount of LBF, caused by lipid digestion products and bile secretion. The outcomes also support the use of coadministration of LBF as a potential dosing regimen in cases where it is beneficial to have the drug in the solid form, e.g. due to chemical instability in the lipid vehicle. Finally, the in vitro lipolysis-permeation used herein established IVIVC for carvedilol in the presence of LBFs.

Lipolysis-Permeation Setup for Simultaneous Study of Digestion and Absorption in Vitro

Lipid-based formulations (LBFs) are a delivery strategy to enhance intestinal absorption of poorly water-soluble drugs. LBF performance is typically evaluated by in vitro lipolysis studies, but these do not accurately predict the in vivo performance. One possible reason is the absence of an absorptive membrane driving sink conditions in the serosal compartment. To explore the impact of absorption under sink conditions on the performance evaluation, we developed a lipolysis-permeation setup that allows simultaneous investigation of intestinal digestion of an LBF and drug absorption. The setup consists of two chambers, an upper one for digestion (luminal), and a lower, receiving one (serosal), separated by a Caco-2 monolayer. Digestions were performed with immobilized lipase, instead of the pancreatic extract typically used during lipolysis, since the latter has proven incompatible with Caco-2 cells. Danazol-loaded LBFs were used to develop the setup, and fenofibrate-loaded LBFs were used to establish an in vitro in vivo correlation. As in regular lipolysis studies, our setup allows for the evaluation of (i) the extent of digestion and (ii) drug distribution in different phases present during lipolysis of drug-loaded LBFs (i.e., oil, aqueous, and solid phase). In addition, our setup can determine drug permeation across Caco-2 monolayers and hence, the absorptive flux of the compound. The presence of the absorptive monolayer and sink conditions tended to reduce aqueous drug concentrations and supersaturation in the digestion chamber. The drug transfer across the Caco-2 membrane accurately reflected in vivo drug exposure upon administration of three different LBFs loaded with fenofibrate, where the traditional lipolysis setup failed to predict in vivo performance. As the new setup reflects the dynamic processes occurring in the gastrointestinal tract, it is a valuable tool that can be used in the development of LBFs prior to in vivo studies.

Solubilisation behaviour of poorly water-soluble drugs during digestion of solid SMEDDS

Lipid based-formulations can enhance the bioavailability of poorly water-soluble lipophilic drugs through enhanced solubilisation of drugs in the gastrointestinal (GI) tract during digestion. This study investigates the solubilisation behaviour of poorly water-soluble drugs upon digestion of solid self-microemulsifying drug delivery system (S-SMEDDS). The S-SMEDDS were prepared using two different core lipids, Gelucire® 44/14 (GEL) or glyceryl monooleate (GMO), and were loaded with two model drugs, fenofibrate (FEN) and cinnarizine (CINN). S-SMEDDS formulations were characterized using wide-angle X-ray scattering (WAXS) and Raman spectroscopy, and their structural behaviour and drug solubilisation behaviour were monitored using drug-related diffraction peaks during digestion under fasted and fed simulated intestinal conditions using time-resolved small and wide-angle X-ray scattering (SAXS/WAXS). The concentrations of FEN and CINN released into the aqueous phase (AP) during digestion were quantified using high-performance liquid chromatography (HPLC). Both model drugs, FEN and CINN, had greater solubility in the GMO-based S-SMEDDS formulations and were partially solubilised into lipid matrix and uniformly distributed in solid formulations. The extent of digestion was greater for the GEL-based systems (92-94%) than GMO-based systems (65-75%) as was the rate of digestion. GEL-based S-SMEDDS formulations formed a lamellar phase during digestion in the fasted state and formed mixed micelles in the fed state. In contrast, the GMO-based system formed the mixed micelles in both intestinal conditions. The time-resolved SAXS profiles revealed solubilisation of crystalline drugs into the lipolysis products. Synchrotron SAXS results were in correlation with the HPLC measurements, confirming the ability of the SAXS technique to monitor drug behaviour and showing that the digestion of S-SMEDDS can enhance drug solubilisation.

Caco-2 Cell Conditions Enabling Studies of Drug Absorption from Digestible Lipid-Based Formulations

Purpose

To identify conditions allowing the use of cell-based models for studies of drug absorption during in vitro lipolysis of lipid-based formulations (LBFs).

Methods

Caco-2 was selected as the cell-based model system. Monolayer integrity was evaluated by measuring mannitol permeability after incubating Caco-2 cells in the presence of components available during lipolysis. Pure excipients and formulations representing the lipid formulation classification system (LFCS) were evaluated before and after digestion. Porcine mucin was evaluated for its capacity to protect the cell monolayer.

Results

Most undigested formulations were compatible with the cells (II-LC, IIIB-LC, and IV) although some needed mucin to protect against damaging effects (II-MC, IIIB-MC, I-LC, and IIIA-LC). The pancreatic extract commonly used in digestion studies was incompatible with the cells but the Caco-2 monolayers could withstand immobilized recombinant lipase. Upon digestion, long chain formulations caused more damage to Caco-2 cells than their undigested counterparts whereas medium chain formulations showed better tolerability after digestion.

Conclusions

Most LBFs and components thereof (undigested and digested) are compatible with Caco-2 cells. Pancreatic enzyme is not tolerated by the cells but immobilized lipase can be used in combination with the cell monolayer. Mucin is beneficial for critical formulations and digestion products.

Electronic supplementary material

The online version of this article (10.1007/s11095-017-2327-8) contains supplementary material, which is available to authorized users.

Self-emulsifying drug delivery systems (SEDDS): Proof-of-concept how to make them mucoadhesive

AIM

The objective of this study was to provide a proof-of-concept that self-emulsifying drug delivery systems can be made mucoadhesive by the incorporation of hydrophobic mucoadhesive polymers.

METHODS

In order to obtain such a hydrophobic mucoadhesive polymer, Eudragit® S100 was thiolated by covalent attachment of cysteamine. After determination of the thiol group content, in vitro mucoadhesion studies (rotating cylinder and rheological measurements) were performed. Then, synthesized conjugate was incorporated into self-emulsifying drug delivery systems (SEDDS) and their toxic potential as well as that of unmodified and thiolated Eudragit® S100 was examined on Caco-2 cell line. Lastly, the mucoadhesiveness of developed SEDDS on porcine intestinal mucosa was determined.

RESULTS

Generated thiolated Eudragit® S100 displaying 235±14μmol of free thiol groups and 878±101μmol of disulfide bonds per gram polymer showed a great improvement in both: dynamic viscosity with mucus and adhesion time on mucosal tissue compared to the unmodified polymer. Resazurin assay revealed that unmodified and thiolated polymers and also SEDDS dispersions were non-toxic over Caco-2 cells. Furthermore, the incorporation of 1.5% (w/w) of such thiomer into SEDDS led to remarkably improved mucoadhesiveness. Blank SEDDS were completely removed from the mucosa within 15min, whereas >60% of SEDDS containing thiolated Eudragit® S100 were still attached to it.

CONCLUSION

These results provide evidence that SEDDS can be made mucoadhesive by the incorporation of hydrophobic mucoadhesive polymers.