In Vitro Gastrointestinal Lipolysis: Replacement of Human Digestive Lipases by a Combination of Rabbit Gastric and Porcine Pancreatic Extracts

The bile salt/phospholipid ratio determines the extent of in vitro intestinal lipolysis of triglycerides: Interfacial and emulsion studies

This study focused on the protein-stabilised triglyceride (TG)/water interfaces and oil-in-water emulsions, and explored the influence of varying molar ratios of bile salts (BSs) and phospholipids (PLs) on the intestinal lipolysis of TGs. The presence of these two major groups of biosurfactants delivered with human bile to the physiological environment of intestinal digestion was replicated in our experiments by using mixtures of individual BSs and PLs under in vitro small intestinal lipolysis conditions. Conducted initially, retrospective analysis of available scientific literature revealed that an average molar ratio of 9:4 for BSs to PLs (BS/PL) can be considered physiological in the postprandial adult human small intestine. Our experimental data showed that combining BSs and PLs synergistically enhanced interfacial activity, substantially reducing oil-water interfacial tension (IFT) during interfacial lipolysis experiments with pancreatic lipase, especially at the BS/PL-9:4 ratio. Other BS/PL molar proportions (BS/PL-6.5:6.5 and BS/PL-4:9) and an equimolar amount of BSs (BS-13) followed in IFT reduction efficiency, while using PLs alone as biosurfactants was the least efficient. In the following emulsion lipolysis experiments, BS/PL-9:4 outperformed other BS/PL mixtures in terms of enhancing the TG digestion extent. The degree of TG conversion and the desorption efficiency of interfacial material post-lipolysis correlated directly with the BS/PL ratio, decreasing as the PL proportion increased. In conclusion, this study highlights the crucial role of biliary PLs, alongside BSs, in replicating the physiological function of bile in intestinal lipolysis of emulsified TGs. Our results showed different contributions of PLs and BSs to lipolysis, strongly suggesting that any future in vitro studies aiming to simulate the human digestion conditions should take into account the impact of biliary PLs - not just BSs - to accurately mimic the physiological role of bile in intestinal lipolysis. This is particularly crucial given the fact that existing in vitro digestion protocols typically focus solely on applying specific concentrations and/or compositions of BSs to simulate the action of human bile during intestinal digestion, while overlooking the presence and concentration of biliary PLs under physiological gut conditions.

Current advances for in vitro protein digestibility

Protein is an essential macronutrient in our diet, source of nitrogen and essential amino acids, but the biological utilization of dietary protein depends on its digestibility and the absorption of amino acids and peptides in the gastrointestinal tract. The methods to define the amount and the quality of protein to meet human nutritional needs, such as the Digestible Indispensable Amino Acid Score (DIAAS), require the use of animal models or human studies. These in vivo methods are the reference in protein quality evaluation, but they are expensive and long-lasting procedures with significant ethical restrictions. Therefore, the development of rapid, reproducible and in vitro digestion methods validated with in vivo data is an old demand. This review describes the challenges of the in vitro digestion methods in the evaluation of the protein nutritional quality. In addition to the technical difficulties to simulate the complex and adaptable processes of digestion and absorption, these methods are affected by similar limitations as the in vivo procedures, i.e., analytical techniques to accurately determine bioavailable amino acids and the contribution of the endogenous nitrogen. The in vitro methods used for the evaluation of protein digestibility, with special attention on those showing comparative data, are revised, emphasizing their pros and cons. The internationally harmonized digestion protocol proposed by the INFOGEST network is being adapted to evaluate protein and amino acid digestibility. The inter-laboratory reproducibility of this protocol was demonstrated for dairy products. The in vivo/in vitro comparability results obtained to date with this protocol for several plant and animal sources are promising, but it requires an extensive validation with a wider range of foods and substrates with known in vivo digestibility. These in vitro methods will probably not be applicable to all foods, and therefore, it is important to identify their limitations, not to elude their use, but to apply them within the limits, by using the appropriate standards and references, and always as a complementary tool to in vivo tests to reduce their number.

Pancreatic lipase digestion: The forgotten barrier in oral administration of lipid-based delivery systems?

This review highlights the importance of controlling the digestion process of orally administered lipid-based delivery systems (LBDS) and their performance. Oral LBDS are prone to digestion via pancreatic lipase in the small intestine. Rapid or uncontrolled digestion may cause the loss of delivery system integrity, its structural changes, reduced solubilization capacity and physical stability issues. All these events can lead to uncontrolled drug release from the digested LBDS into the gastrointestinal environment, exposing the incorporated drug to precipitation or degradation by luminal proteases. To prevent this, the digestion rate of orally administered LBDS can be estimated by appropriate choice of the formulation type, excipient combinations and their ratios. In addition, in vitro digestion models like pH-stat are useful tools to evaluate the formulation digestion rate. Controlling digestion can be achieved by conventional lipase inhibitors like orlistat, sterically hindering of lipase adsorption on the delivery system surface with polyethylene glycol (PEG) chains, lipase desorption or saturation of the interface with surfactants as well as formulating LBDS with ester-free excipients. Recent in vivo studies demonstrated that digestion inhibition lead to altered pharmacokinetic profiles, where Cmax and Tmax were reduced in spite of same AUC compared to control or even improved oral bioavailability.

Evaluating the in vitro digestion of lipids rich in medium-chain fatty acids (MCFAs) using dynamic and static protocols

Investigating the digestion of lipids is paramount for developing new lipid-based products. This work evaluated the gastrointestinal (GI) digestion of medium-chain fatty acids (MCFAs) rich lipids. The dynamic GI in vitro system was used to simulate gastric, duodenal, jejunal, and ileal GI tract portions. Results from the dynamic protocol were compared against static in vitro assays and GC analyses were conducted to assess the FA profile of FFA released during digestion. Caprylic and capric acids released during the gastric digestion of MCT oil varied from 61-63% and 36-38% of total esterified FA, respectively. Lauric acid was the most representative FFA released (31-54%) during the gastric digestion of coconut oil samples. It was observed that the gastric digestion phase plays a crucial role in the MCFA lipolysis and the lipase activity restricted the amount of free MCFA liberated during the GI digestion, resulting in incomplete lipids hydrolysis.

Pre-duodenal lipid digestion of emulsions: Relevance, colloidal aspects and mechanistic insight

The digestion of lipids in the human body has several health and nutritional implications. Lipid digestion is an interfacial phenomenon meaning that water-soluble lipases need to first adsorb to the oil-water interface before enzymatic conversions can start. The digestion of lipids mainly occurs on colloidal structures dispersed in water, such as oil-in-water (o/w) emulsions, which can be designed during food formulation/processing or structured during digestion. From a food design perspective, different in vitro studies have demonstrated that the kinetics of lipid digestion can be influenced by emulsion properties. However, most of these studies have been performed with pancreatic enzymes to simulate lipolysis in the small intestine. Only few studies have dealt with lipid digestion in the gastric phase and its subsequent impact on intestinal lipolysis. In this aspect, this review compiles information on the physiological aspects of gastric lipid digestion. In addition, it deals with colloidal and interfacial aspects starting from emulsion design factors and how they evolve during in vitro digestion. Finally, molecular mechanisms describing gastric lipolysis are discussed.

Oligomer nanoparticle release from polylactic acid plastics catalysed by gut enzymes triggers acute inflammation

The health risks of exposure to 'eco-friendly' biodegradable plastics of anthropogenic origin and their effects on the gastrointestinal tract are largely unknown. Here we demonstrate that the enzymatic hydrolysis of polylactic acid microplastics generated nanoplastic particles by competing for triglyceride-degrading lipase during gastrointestinal processes. Nanoparticle oligomers were formed by hydrophobically driven self-aggregation. In a mouse model, polylactic acid oligomers and their nanoparticles bioaccumulated in the liver, intestine and brain. Hydrolysed oligomers caused intestinal damage and acute inflammation. A large-scale pharmacophore model revealed that oligomers interacted with matrix metallopeptidase 12. Mechanistically, high binding affinity (K_d = 13.3 μmol l^-1) of oligomers to the catalytic zinc-ion finger domain led to matrix metallopeptidase 12 inactivation, which might mediate the adverse bowel inflammatory effects after exposure to polylactic acid oligomers. Biodegradable plastics are considered to be a solution to address environmental plastic pollution. Thus, understanding the gastrointestinal fates and toxicities of bioplastics will provide insights into potential health risks.

Efficient in vitro digestion of lipids and proteins in bovine milk fat globule membrane ingredient (MFGMi) and whey-casein infant formula with added MFGMi

The relative immaturity of the infant digestive system has the potential to affect the bioavailability of dietary lipids, proteins, and their digested products. We performed a lipidomic analysis of a commercial bovine milk fat globule membrane ingredient (MFGMi) and determined the profile of lipids and proteins in the bioaccessible fraction after in vitro digestion of both the ingredient and whey-casein-based infant formula without and with MFGMi. Test materials were digested using a static 2-phase in vitro model, with conditions simulating those in the infant gut. The extent of digestion and the bioaccessibility of various classes of neutral and polar lipids were monitored by measuring a wide targeted lipid profile using direct infusion-mass spectrometry. Digestion of abundant proteins in the ingredient and whey-casein infant formula containing the ingredient was determined by denaturing PAGE with imaging of Coomassie Brilliant Blue stained bands. Cholesterol esters, diacylglycerides, triacylglycerides, phosphatidylcholines, and phosphatidylethanolamines in MFGMi were hydrolyzed readily during in vitro digestion, which resulted in marked increases in the amounts of free fatty acids and lyso-phospholipids in the bioaccessible fraction. In contrast, sphingomyelins, ceramides, and gangliosides were largely resistant to simulated digestion. Proteins in MFGMi and the infant formulas also were hydrolyzed efficiently. The results suggest that neutral lipids, cholesterol esters, phospholipids, and proteins in MFGMi are digested efficiently during conditions that simulate the prandial lumen of the stomach and small intestine of infants. Also, supplementation of whey-casein-based infant formula with MFGMi did not appear to alter the profiles of lipids and proteins in the bioaccessible fraction after digestion.

Effect of phospholipid matrix on emulsion stability, microstructure, proteolysis, and in vitro digestibility in model infant formula emulsion

The effects of adding different phospholipid (PL) matrices [milk sphingomyelin (SM) vs soy phosphatidylcholine (PC)] on emulsion stability, microstructure, and in vitro simulated lipid digestion were examined using a Model Infant Formula Emulsion (MIFE). The emulsion stability of MIFE increased significantly with PL addition (0.1 and 0.2 %). Compared to sole MIFE or MIFE + PC, the incorporation of SM resulted in increased emulsion stability (p < 0.05) and a greater amount of free fatty acid release (p < 0.05) during in vitro simulated digestion. This was mainly due to the reduction of intensive droplet aggregation, thus providing a large surface area and improved digestibility. This is further experimentally supported by the evolution of particle size distribution, zeta-potential, and microstructure analysis using confocal laser scanning microscopy. The incorporation of SM in the emulsion formation significantly delayed digestion of β-lactoglobulin during in vitro digestion. Lipid digestibility in MIFE was altered depending on the type of PL matrix, and SM displayed a superior effect to PC. Thus, the creation of a novel emulsion interface by the appropriate selection of emulsifiers can be used to improve lipid digestion in infants and obtain desirable nutritional consequences.

Exploration of suitable in vitro simulated digestion model for lipid oxidation of flaxseed oil emulsion during digestion

BACKGROUND

The INFOGEST model is a standardized general in vitro digestion study, but it cannot accurately simulate the fatty acid release process of lipids in the stomach and small intestine. In this study, the internationally universal INFOGEST 2019 was used as the basic model and flaxseed oil emulsion was used as the research object. In various improvement models, the effect of fatty acid release rate on the oxidation stability of flaxseed oil was assessed by adding rabbit stomach extract and changing the order of bile salts addition.

RESULTS

With the presence of rabbit gastric extract, flaxseed oil emulsion flocculation and coalescence in stomach were reduced, and the absolute value of ζ-potential increased. Moreover, the release rate of fatty acids in the small intestine increased by 12.14%. The amount of lipid oxidation product (i.e. hexanal) in the gastric and intestinal phases increased by 0.08 ppb. In addition, the fatty acid release rate in the small intestine phase increased by 5.85% and the hexanal content increased by 0.011 ppb in the digestion model of adding bile salts before adjusting the pH in the small intestine phase compared with the model of adjusting the pH first and then adding bile salts.

CONCLUSION

The results obtained from this study will contribute to finding the most suitable static digestion model for simulating digestion and oxidation of lipid during lipid gastrointestinal digestion. © 2022 Society of Chemical Industry.

Bio-enabling strategies to mitigate the pharmaceutical food effect: a mini review

The concomitant administration of oral drugs with food can result in significant changes in bioavailability, leading to variable pharmacokinetics and considerable clinical implications, such as over- or under-dosing. Consequently, there is increasing demand for bio-enabling formulation strategies to reduce variability in exposure between the fasted and fed state and/or mitigate the pharmaceutical food effect. The current review critically evaluates technologies that have been implemented to overcome the positive food effects of pharmaceutical drugs, including, lipid-based formulations, nanosized drug preparations, cyclodextrins, amorphisation and solid dispersions, prodrugs and salts. Additionally, improved insight into preclinical models for predicting the food effect is provided. Despite the wealth of research, this review demonstrates that application of optimal formulation strategies to mitigate the positive food effects and the evaluation in preclinical models is not a universal approach, and improved standardisation of models to predict the food effects would be desirable. Ultimately, the successful reformulation of specific drugs to eliminate the food effect provides a panoply of advantages for patients with regard to clinical efficacy and compliance.

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.

Potential benefits of structured lipids in bulk compound chocolate: Insights on bioavailability and effect on serum lipids

The bioavailability impact of serum lipids in compound chocolate products based on structured lipids was studied. Compound chocolate products containing fat with and without structured lipids were digested in vitro under simulated gastrointestinal lipolysis conditions and were studied in vivo in healthy C57BL/6J mice. The in vitro digestion results show that products containing structured lipids, milk compound chocolate filling and white compound coating, significantly reduced the release rate of Free Fatty Acids (FFA) and improved the caloric reduction between 12.49% and 13.71% compared to products without structured lipids, suggesting that FFA were not absorbed. Animal feeding studies revealed no adverse effects on the compound products intake; in fact, these products reduced total cholesterol, LDL-c, VLDL-c and triacylglycerols. The present work shows the relevance of developing functional compound chocolate as providing a potential healthy initiative through the biological effect of the bioactive ingredients incorporated.

Gastric lipase can significantly increase lipolysis and carotenoid bioaccessibility from plant food matrices in the harmonized INFOGEST static in vitro digestion model

Gastrointestinal digestion of carotenoids has received much attention, as these lipophilic compounds have been related to several health benefits. Most commonly, static digestion models such as the consensus INFOGEST model are employed to study their bioaccessibility from test matrices. However, an aspect that has been much neglected is the use of gastric lipase. Its inclusion to gastro-intestinal (GI) digestion is expected to foster emulsification of lipophilic constituents prior to their incorporation into mixed micelles. In this study, we compared the effect of various lipases from R. niveus, R. oryzae, and rabbit gastric extracts (RGE), at different concentrations (0, 30, and 60 U mL^-1), on carotenoid bioaccessibility from several food matrices (tomato juice, spinach, and carrot juice). We also investigated whether co-digestion of pure proteins (whey and soy protein isolates) at 0, 25, and 50% of the equivalent recommended dietary allowance, would interact with carotenoid bioaccessibility in presence or absence of RGE. Lipolysis was also studied. Considering all matrices combined, lipases significantly improved the bioaccessibility of carotenoids (p < 0.001). Compared to other lipases, RGE consistently increased carotenoid bioaccessibility in all tested matrices, by up to 182% (p < 0.001), this effect was partly maintained in the presence of co-digested proteins. Unexpectedly, all 3 lipases improved gastric lipolysis in all matrices, by an average of 10-fold (p < 0.001). In conclusion, only RGE contributed significantly to improving both lipolysis extent and carotenoid bioaccessibility in all tested matrices, while the presence of proteins mitigated the positive effect of lipases on carotenoid bioaccessibility.

Advances in static in vitro digestion models after the COST action Infogest consensus protocol

In vitro digestion models are essential to predictively evaluate the bioaccessibility and bioactivity of food molecules or natural products. Dynamic models better simulate the gastrointestinal conditions as they reproduce similar physiological environments. Despite this, static methods, also known as biochemical methods, represent a simple and useful approach for the study of different types of molecules, with a broad applicability in the nutritional, pharmaceutical, and toxicological fields. In addition, static models can be validated, avoiding the disadvantage of a difficult reproducibility of dynamic in vitro systems and inter-individual variations of in vivo experiments. A crucial point in the standardization of static models was the COST Action Infogest in 2014, which elaborated an international consensus static digestion method to harmonize experimental conditions and has general guidelines, thus allowing the comparison of studies and data. The aim of our review is to underline the impact of the Infogest consensus method and the development and evolution of in vitro static methods in the following years, with a focus on food applications.

Simulated In Vitro Infant Gastrointestinal Digestion of Infant Formulas Containing Different Fat Sources and Human Milk: Differences in Lipid Profiling and Free Fatty Acid Release

Simulated in vitro infant gastrointestinal digestion of human milk and four infant formulas containing different fat sources was analyzed and compared in this study. Although there are disadvantages brought about by its larger droplet size than infant formulas, human milk exhibited a higher lipolysis level due to the presence of MFGM interfacial layers. Higher hydrolysis efficiency of infant formulas (IFB, IFC, and IFM) was due to the presence of MFGM/phospholipid-enriched materials. Human milk released higher free fatty acid levels, especially long-chain fatty acid, and less undigested TAG molecules at the end of digestion than infant formulas. Human milk had a higher proportion of MAG and DAG linked to long-chain fatty acid. Furthermore, several lipids were identified as potential biomarkers that could be used to further analyze differences in the biological properties of human, bovine, and caprine milk. This comprehensive analysis might be fruitful to formulate an infant formula closest to human milk.

In vitro intestinal digestion of lipids from the marine diatom Porosira glacialis compared to commercial LC n-3 PUFA products

Marine sources of long chain omega-3 polyunsaturated fatty acids (LC n-3 PUFA) are in high demand for use in health supplements. Mass cultivated marine microalgae is a promising and sustainable source of LC n-3 PUFA, which relieves pressure on natural fish stocks. The lipid class profile from cultivated photosynthetic algae differ from the marine organisms currently used for the production of LC n-3 PUFA. The objective of this study was to compare in vitro intestinal digestion of oil extracted from the cold-adapted marine diatom Porosira glacialis with commercially available LC n-3 PUFA supplements; cod liver oil, krill oil, ethyl ester concentrate, and oil from the copepod Calanus finmarchicus (Calanus® oil). The changes in the free fatty acids and neutral and polar lipids during the enzymatic hydrolysis were characterized by liquid and gas chromatography. In Calanus® oil and the Ethyl ester concentrate, the free fatty acids increased very little (4.0 and 4.6%, respectively) during digestion. In comparison, free fatty acids in Krill oil and P. glacialis oil increased by 14.7 and 17.0%, respectively. Cod liver oil had the highest increase (28.2%) in free fatty acids during the digestion. Monounsaturated and saturated fatty acids were more easily released than polyunsaturated fatty acids in all five oils.

O/W Emulsion Stabilized by Bovine Milk Phospholipid-Protein Nanoemulsions: Preparation, Stability, and In Vitro Digestion

This study aims to prepare a stable oil-in-water (O/W) emulsion with droplets of approximately 3-5 μm and a structured phospholipid (PL)-protein membrane that is similar to human milk fat globules. A nanoemulsion with an average droplet size of 200 nm prepared with bovine milk PL-protein, a milk fat globule membrane (MFGM)-rich ingredient, was used as an emulsifier to form an O/W emulsion with an average droplet size of 3.96 μm. Stable O/W emulsions were formed with a low concentration (1 wt %) of the MFGM-rich ingredient. The nanoemulsion was adsorbed at the oil-water interface. The O/W emulsions stored at 4 °C did not show structural damage upon 7 days of storage. The deformation or partial deformation of nanoemulsion droplets attached to lipid droplets may contribute to the physical stability of the emulsion. In vitro digestion of the O/W emulsion showed a low lipolysis degree in gastric digestion, and the final hydrolysis efficiency of the O/W emulsion was 62.74%, which is higher than that of traditional infant formula.

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.

In vitro bioaccessibility of macular xanthophylls from commercial microalgal powders of Arthrospira platensis and Chlorella pyrenoidosa

The bioaccessibility of the major carotenoids present in two commercial microalgal supplements in powder form was investigated through a standardized in vitro digestion method. The dried biomass of Arthrospira platensis contained β-carotene (36.8 mg/100 g) and zeaxanthin (20.8 mg/100 g) as the main carotenoids as well as a high content of saturated fatty acids (61% of total fatty acids), whereas that of Chlorella pyrenoidosa was rich in lutein (37.8 mg/100 g) and had a high level of unsaturated fatty acids (65% of total fatty acids). In the case of the latter, lutein bioaccessibility was not statistically enhanced after the replacement of porcine bile extract with bovine bile extract in the in vitro digestion protocol and after the addition of coconut oil (17.8% as against to 19.2% and 19.2% vs. 18.5%, respectively). In contrast, the use of bovine bile extract along with co-digestion with coconut oil significantly enhanced the bioaccessibility of zeaxanthin from A. platensis, reaching the highest bioaccessibility of 42.8%.

Investigating the Impact of Crohn's Disease on the Bioaccessibility of a Lipid-Based Formulation with an In Vitro Dynamic Gastrointestinal Model

The aim of the study was to investigate the impact of Crohn's disease (CD) on the performance of a lipid-based formulation of ciprofloxacin in a complex gastrointestinal simulator (TIM-1, TNO) and to compare the luminal environment in terms of bile salt and lipid composition in CD and healthy conditions. CD conditions were simulated in the TIM-1 system with a reduced concentration of porcine pancreatin and porcine bile. The bioaccessibility of ciprofloxacin was similar in simulated CD and healthy conditions considering its extent as well as its time course in the jejunum and ileum filtrate. Differences were observed in terms of the luminal concentration of triglycerides, monoglycerides, and fatty acids in the different TIM-1 compartments, indicating a reduction and delay in the lipolysis of formulation excipients in CD. The quantitative analysis of bile salts revealed higher concentrations for healthy conditions (standard TIM-1 fasted-state protocol) in the duodenum and jejunum TIM-1 compartments compared to published data in human intestinal fluids of healthy subjects. The reduced concentrations of bile salts in simulated CD conditions correspond to the levels observed in human intestinal fluids of healthy subjects in the fasted state.A lipidomics approach with ultra performance liquid chromatography (UPLC)/mass spectrometry (MS) has proven to be a time-efficient method to semiquantitatively analyze differences in fatty acid and bile salt levels between healthy and CD conditions. The dynamic luminal environment in CD and healthy conditions after administration of a lipid-based formulation can be simulated using the TIM-1 system. For ciprofloxacin, an altered luminal lipid composition had no impact on its performance indicating a low risk of altered performance in CD patients.

Rapid screening of lipase inhibitors in licorice extract by using porcine pancreatic lipase immobilized on Fe3O4 magnetic nanoparticles

Chalcones, a class of natural lipase inhibitors, have received substantial attention from researchers in recent years. Although many kinds of chalcones are typically distributed in G. inflata, there is little literature about the anti-lipase activity of G. inflata extracts (GIEs). In the present study, a ligand fishing strategy for fast screening of lipase inhibitors from GIEs was thus proposed. Porcine pancreatic lipase (PPL) was firstly immobilized on carboxyl modified Fe3O4 magnetic nanoparticles (MNPs) to obtain PPL functionalized MNPs (PPL@MNPs), and then the PPL@MNPs were incubated with a bioactive fraction to fish out the ligands. Eight ligands were obtained and identified as one flavone together with seven chalcones. Licochalcone A, licochalcone D and licochalcone E inhibited pancreatic lipase (PL) with IC50 of 4.9, 3.2 and 5.8 μM, respectively. Meanwhile, investigation of the structure-activity relationship also revealed that isopentenyl and hydroxyl substituents at ring A were essential for the noncovalent inhibitory potency of the chalcones.

Addition of either gastric lipase or cholesterol esterase to improve both β-cryptoxanthin ester hydrolysis and micellarization during in vitro digestion of fruit pulps

Using the INFOGEST in vitro digestion protocol adapted to carotenoids, the impact of additional rabbit gastric lipase (RGL) on the hydrolysis extent of β-cryptoxanthin esters was evaluated for the first time, and compared with the addition of porcine cholesterol esterase (CEL). Both the modifications increased the hydrolysis of (all-E)-β-cryptoxanthin esters from mandarin and peach pulps, although the outcomes were different. Addition of RGL consistently increased the average hydrolysis extent from 55.2% to 59.5% in mandarin pulp and from 22.7% to 48.8% in peach pulp (p < 0.05). The addition of CEL produced lower hydrolysis extents, i.e., 58.5% in mandarin (not statistically significant) and 28.4% in peach (p < 0.05), compared to those obtained with RGL. The hydrolysis extent positively correlated with the carotenoid ester concentration in both matrices. Bioaccessibility values were higher in mandarin pulp (range 32-34%) compared to those in peach pulp (range 16-21%), and were associated with the hydrolysis extent of the carotenoid esters during digestion. Addition of RGL and CEL produced no significant (p < 0.05) effect on the overall carotenoid bioaccessibility values of mandarin, while positively affected those in peach. Altogether these results corroborate that the hydrolysis extent of xanthophyll esters limits bioaccessibility. Additionally, hydrophobicity of the carotenoid inversely correlates with micellarization, as free (all-E)-xanthophylls micellarized in a higher extent compared to (all-E)-β-carotene and xanthophyll esters. The new information of our results is that the addition of rabbit gastric lipase substantially contributes to the hydrolysis of β-cryptoxanthin esters from fruit pulps, and consequently, to increase carotenoid bioaccessibility, being even more effective than CEL.

Comparing the permeability of human and porcine small intestinal mucus for particle transport studies

The gastrointestinal mucus layer represents the last barrier between ingested food or orally administered pharmaceuticals and the mucosal epithelium. This complex gel structure plays an important role in the process of small intestinal absorption. It provides protection against hazardous particles such as bacteria but allows the passage of nutrients and drug molecules towards the intestinal epithelium. In scientific research, mucus from animal sources is usually used to simulate difficult-to-obtain human small intestinal mucus for investigating the intramucus transport of drug delivery systems or food nanoparticles. However, there is a lack of evidence the human mucus can be reliably substituted by animal counterparts for human-relevant transport models. In this report, a procedure for collecting human mucus has been described. More importantly, the permeability characteristics of human and porcine small intestinal mucus secretions to sub-micron sized particles have been compared under simulated intestinal conditions. Negatively charged, 500 nm latex beads were used in multiple-particle tracking experiments to examine the heterogeneity and penetrability of mucus from different sources. Diffusion of the probe particles in adult human ileal mucus and adult pig jejunal and ileal mucus revealed no significant differences in microstructural organisation or microviscosity between the three mucus types (P > 0.05). In contrast to this interspecies similarity, the intraspecies comparison of particle diffusivity in the mucus obtained from adult pigs vs. 2-week old piglets showed better penetrability of the piglet mucus. The mean Stokes–Einstein viscosity of the piglet jejunal mucus was approx. two times lower than the viscosity of the pig jejunal mucus (P < 0.05). All mucus structures were also visualised by scanning electron microscopy. This work validates the use of porcine small intestinal mucus collected from fully-grown pigs for studying colloidal transport of sub-micron sized particles in mucus under conditions mimicking the adult human small intestinal environment.

Adding a Gastric Step to the Intestinal In Vitro Digestion Model Improves the Prediction of Pharmacokinetic Data in Beagle Dogs of Two Lipid-Based Drug Delivery Systems

Drug release from a lipid-based drug delivery system (LbDDS) is typically studied in vitro using a one-step intestinal digestion model. However, lately the importance of incorporating gastric digestion has been stressed. The aim of the present study was to compare a two-step gastro-intestinal (GI) in vitro digestion model to the commonly used one-step intestinal digestion model. The models were evaluated by studying release of the model drug A1260 from two LbDDSs (F-I and F-II), for which in vivo pharmacokinetic data from oral administration to beagle dogs were available. The amount of A1260 recovered in the aqueous phases during and after the GI digestion of F-I and F-II was related to the C_max and AUC_0-48h of the plasma concentration-time profiles of each formulation and produced a rank order in vitro-in vivo (IVIV) relation. In comparison, a similar IVIV rank ordering was obtained when relating the amount of A1260 recovered in the aqueous phase prior (t = 0 min), and following 15 min of intestinal digestion, to the plasma concentration-time profiles. However, after 60 min of intestinal digestion, the LbDDSs performed equally in the one-step in vitro digestion model, contrary to what was observed in the two-step digestion model, and in vivo. As the GI digestion model produced a clearer distinction in terms of LbDDS rank ordering of the two LbDDSs, compared to the intestinal digestion model, it was found to be a promising in vitro model to study and estimate the LbDDS behavior in vivo.

Triacylglycerol Containing Medium-Chain Fatty Acids: Comparison of Human Milk and Infant Formulas on Lipolysis during In Vitro Digestion

Medium-chain triacylglycerol (MCT) is widely used in infant formulas (IFs) to provide medium-chain fatty acids (MCFAs) for infants with special fat absorption requirements. However, MCFAs naturally present in human milk are medium-and long-chain triacylglycerols (MLCTs). This study investigated the effect of triacylglycerol containing MCFAs (MLCT vs MCT) on lipolysis by comparison of human milk and IFs containing 0, 20, 30, and 55% of MCT (IF 1 to IF 4) using an in vitro digestion model. Rabbit gastric lipase showed an extent of digestion within the expected range, and was selected as the alternative to human gastric lipase. All IFs showed a lower lipolysis degree compared with human milk. There was no significant difference (p = 0.175) among IFs supplemented with MCT at the end of intestinal digestion. In addition, the digestion of IFs with different MCT contents led to different free fatty acid profiles, which may have health effects on infants.

Bile amount affects both the degree of micellarization and the hydrolysis extent of carotenoid esters during in vitro digestion

Carotenoid esters are present in considerable amounts in most fruits, such as in citrus. Although the bioavailability of carotenoid esters is similar or even higher compared to that of free carotenoids, these molecules are generally detected only in the free form in human plasma, suggesting that hydrolysis of carotenoid esters occurs in vivo. However, the available in vitro digestion methods were not able to achieve satisfactory carotenoid ester hydrolysis so far. As bile salts play an essential role in the hydrolytic action of lipolytic enzymes from pancreatin, we evaluated the effect of increasing the bile extract/food ratio from 0.045 to 0.12 (g g-1) on the hydrolysis of β-cryptoxanthin esters from mandarin pulp during in vitro digestion. Additionally, considering the positive effect of lipids on carotenoid bioavailability, the impact of soybean oil addition on carotenoid ester hydrolysis was studied. Finally, bioaccessibility and recovery of 33 carotenoids were assessed by LC-DAD-MS. The hydrolysis extent of β-cryptoxanthin esters enhanced from 29% to 55% by increasing the bile extract/food ratio, but reduced respectively to 28% and 11% by the addition of 1% and 10% oil (p < 0.05). The bioaccessibility of overall carotenoids improved from 19% to 35% by increasing the bile extract/food ratio, along with that of (all-E)-β-carotene (from 19 to 31%) and total (all-E)-β-cryptoxanthin (17% to 49%). Soybean oil addition reduced carotenoid micellarization, regardless of the concentration (p < 0.05). Irrespective of the bile extract amount and oil addition, the bioaccessibility of carotenoids was inversely related to its hydrophobicity, with respect to the following ranking: free xanthophylls > carotenes ≥ xanthophyll esters. Altogether, these results indicate that increasing the bile extract amount is a simple and inexpensive option to improve carotenoid ester hydrolysis in in vitro digestion protocols. Additionally, the constant amounts of bile (and possibly enzymes) of static methods, such as INFOGEST, should be further optimized for experiments involving lipid addition in which carotenoid bioaccessibility is evaluated.

Simulating human digestion: developing our knowledge to create healthier and more sustainable foods

The gold standard for nutrition studies is clinical trials but they are expensive and variable, and do not always provide the mechanistic information required, hence the increased use ofin vitroand increasinglyin silicosimulations of digestion.

A standardised semi-dynamic in vitro digestion method suitable for food – an international consensus

Standardised recommendations for a physiologically relevant, semi-dynamic in vitro simulation of upper GI tract digestion.

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.

Characterization of pepsin from rabbit gastric extract, its action on β-casein and the effects of lipids on proteolysis

Rabbit gastric extract (RGE) is a source of gastric enzymes for in vitro digestion studies. While its gastric lipase activity has been characterized and compared to other lipases, its pepsin activity has not been studied. We measured pepsin activity in RGE using both hemoglobin and azocoll as substrates, and identified the protein separated by SDS-PAGE as a type II-4 mature pepsin of 328 amino acid residues using Edman sequencing, LC-MS/MS analysis and intact mass measurement. As a proof-of-concept that RGE was suitable for in vitro digestion of both proteins and lipids, it was used for studying the proteolysis of β-casein under conditions mimicking the early stages of intragastric digestion. β-Casein was displayed either in solution or at the surface of a β-casein-stabilized rapeseed oil emulsion to investigate the impact of lipids and lipolysis on proteolysis. Proteolysis of β-casein was quantified based on the kinetics of β-casein disappearance, the identification of various peptides generated upon digestion and their variation with time. The results obtained with RGE were highly similar to those obtained with equivalent amounts of porcine pepsin used as a reference standard. Digestion of β-casein was slower when it was displayed at the oil-water interface and some degradation peptides were transiently observed at higher levels and for a longer time than with β-casein in solution, or accumulated upon digestion. N-terminal sequencing of the main isolated peptides revealed a sequential action of pepsin starting from the hydrophobic C-terminal end of β-casein, which was impaired by the interaction of β-casein with lipids.

INFOGEST static in vitro simulation of gastrointestinal food digestion

Developing a mechanistic understanding of the impact of food structure and composition on human health has increasingly involved simulating digestion in the upper gastrointestinal tract. These simulations have used a wide range of different conditions that often have very little physiological relevance, and this impedes the meaningful comparison of results. The standardized protocol presented here is based on an international consensus developed by the COST INFOGEST network. The method is designed to be used with standard laboratory equipment and requires limited experience to encourage a wide range of researchers to adopt it. It is a static digestion method that uses constant ratios of meal to digestive fluids and a constant pH for each step of digestion. This makes the method simple to use but not suitable for simulating digestion kinetics. Using this method, food samples are subjected to sequential oral, gastric and intestinal digestion while parameters such as electrolytes, enzymes, bile, dilution, pH and time of digestion are based on available physiological data. This amended and improved digestion method (INFOGEST 2.0) avoids challenges associated with the original method, such as the inclusion of the oral phase and the use of gastric lipase. The method can be used to assess the endpoints resulting from digestion of foods by analyzing the digestion products (e.g., peptides/amino acids, fatty acids, simple sugars) and evaluating the release of micronutrients from the food matrix. The whole protocol can be completed in ~7 d, including ~5 d required for the determination of enzyme activities.

In vitro digestion models to evaluate lipid based drug delivery systems; present status and current trends

During the past two decades, a range of in vitro models simulating the digestion processes occurring in the stomach and small intestine have been developed to characterize lipid based drug delivery systems (LbDDSs). This review describes the presently existing range of in vitro digestion models and their use in the field of oral drug delivery. The models are evaluated in terms of their suitability to assess LbDDSs, and their ability to produce in vitro - in vivo correlations (IVIVCs). While the pH-stat lipolysis model is by far the most commonly utilized in vitro digestion model in relation to characterizing LbDDSs, a series of recent studies have shown a lack of IVIVCs limiting its future use. Presently, no single in vitro digestion model exists which is able to predict the in vivo performance of various LbDDSs. However, recent research has shown the potential of combined digestion-permeation models as well as species specific digestion models.

Effects of interesterified lipid design on the short/medium chain fatty acid hydrolysis rate and extent (in vitro)

Short/medium chain fatty acids have well known health effects such as gut immune regulation and ketogenesis.

Screening of critical factors influencing the efficient hydrolysis of zeaxanthin dipalmitate in an adapted in vitro- digestion model

As hydrolysis of carotenoid esters is believed to be highly efficient in vivo, their insufficient hydrolysis in in vitro-digestion models, particularly, regarding zeaxanthin diesters, is a current issue. Therefore, in this study, several factors related to the enzymatic hydrolysis were investigated in an adapted version of the standardized INFOGEST in vitro-digestion model, using zeaxanthin dipalmitate (ZDP) as a substrate. The results showed that pancreatic lipase was able to hydrolyze ZDP, whereas carboxyl ester lipase (CEL) substantially contributed to ZDP cleavage. Replacement of commonly used porcine with bovine bile extracts and the substitution of coffee creamer for soybean oil at identical fat contents both significantly improved hydrolysis efficiency and bioaccessibility of total zeaxanthin to better mimic in vivo conditions. Thus, bile and lipids selection for in vitro digestion of carotenoid esters was crucial. The combined use of coffee creamer, pancreatin, CEL, and bovine bile led to the highest hydrolysis efficiency of 29.5%.

Comparison of lipases for in vitro models of gastric digestion: lipolysis using two infant formulas as model substrates

The aim of this study was to find a lipase suitable as a surrogate for Human Gastric Lipase (HGL), since the development of predictive gastrointestinal lipolysis models are hampered by the lack of a lipase with similar digestive properties as HGL. Three potential surrogates for HGL; Rhizopus Oryzae Lipase (ROL), Rabbit Gastric Lipase (RGL) and recombinant HGL (rHGL), were used to catalyze the in vitro digestion of two infant formulas (a medium-chain triacylglyceride enriched formula (MC-IF) and a predominantly long-chain triacylglyceride formula (LC-IF)). Digesta were withdrawn after 0, 5, 15, 30, 60 min of gastric digestion and after 90 or 180 min of intestinal digestion with or without the presence of pancreatic enzymes, respectively. The digesta were analyzed by scanning electron microscopy and gas chromatography to quantify the release of fatty acids (FAs). Digestions of both formulas, catalyzed by ROL, showed that the extent of gastric digestion was higher than expected from previously published in vivo data. ROL was furthermore insensitive to FA chain length and all FAs were released at the same pace. RGL and rHGL favoured the release of MC-FAs in both formulas, but rHGL did also release some LC-FAs during digestion of MC-IF, whereas RGL only released MC-FAs. Digestion of a MC-IF by HGL in vivo showed that MC-FAs are preferentially released, but some LC-FAs are also released. Thus of the tested lipase rHGL replicated the digestive properties of HGL the best and is a suitable surrogate for HGL for use in in vitro gastrointestinal lipolysis models.

Infant digestion physiology and the relevance of in vitro biochemical models to test infant formula lipid digestion

Lipids play an important role in the diet of preterm and term infants providing a key energy source and essential lipid components for development. While a lot is known about adult lipid digestion, our understanding of infant digestion physiology is still incomplete, the greatest gap being on the biochemistry of the small intestine, particularly the activity and relative importance of the various lipases active in the intestine. The literature has been reviewed to identify the characteristics of lipid digestion of preterm and term infants, but also to better understand the physiology of the infant gastrointestinal tract compared to adults that impacts the absorption of lipids. The main differences are a higher gastric pH, submicellar bile salt concentration, a far more important role of gastric lipases as well as differences at the level of the intestinal barrier. Importantly, the consequences of improper in vitro replication of gastric digestions conditions (pH and lipase specificity) are demonstrated using examples from the most recent of studies. It is true that some animal models could be adapted to study infant lipid digestion physiology, however the ethical relevance of such models is questionable, hence the development of accurate in vitro models is a must. In vitro models that combine up to date knowledge of digestion biochemistry with intestinal cells in culture are the best choice to replicate digestion and absorption in infant population, this would allow the adaptation of infant formula for a better digestion and absorption of dietary lipids by preterm and term infants.

In Vitro Model Simulating Gastro-Intestinal Digestion in the Pediatric Population (Neonates and Young Infants)

The focus on drug delivery for the pediatric population has been steadily increasing in the last decades. In terms of developing in vitro models simulating characteristics of the targeted pediatric population, with the purpose of predicting drug product performance after oral administration, it is important to simulate the gastro-intestinal conditions and processes the drug will encounter upon oral administration. When a drug is administered in the fed state, which is commonly the case for neonates, as they are typically fed every 3 h, the digestion of the milk will affect the composition of the fluid available for drug dissolution/solubilization. Therefore, in order to predict the solubilized amount of drug available for absorption, an in vitro model simulating digestion in the gastro-intestinal tract should be utilized. In order to simulate the digestion process and the drug solubilization taking place in vivo, the following aspects should be considered; physiologically relevant media, media volume, use of physiological enzymes in proper amounts, as well as correct pH and addition of relevant co-factors, e.g., bile salts and co-enzymes. Furthermore, physiological transit times and appropriate mixing should be considered and mimicked as close as possible. This paper presents a literature review on physiological factors relevant for digestion and drug solubilization in neonates. Based on the available literature data, a novel in vitro digestion model simulating digestion and drug solubilization in the neonate and young infant pediatric population (2 months old and younger) was designed.

Biological fate of food nanoemulsions and the nutrients they carry – internalisation, transport and cytotoxicity of edible nanoemulsions in Caco-2 intestinal cells

Internalisation of edible food nanoemulsions by CaCo-2 intestinal cells. The structure of edible nanoemulsions increases five times upon incorporation of reactive/ROS producing nutrients/APIs.

In vitro bioaccessibility of proteins and lipids of pH-shift processed Nannochloropsis oculata microalga

The pH-shift process fractionates biomass into soluble proteins and insoluble fractions, followed by precipitation and recovery of the solubilized proteins. Nannochloropsis oculata in seawater was subjected to the pH-shift process, followed by digestion of various intermediates and product fractions of the process, using the Infogest in vitro digestion model (Minekus et al., 2014) with added gastric lipase. As measures for protein and lipid accessibility, degrees of protein hydrolysis and fatty acid liberation were assessed post-digestion and compared to the amounts of peptide bonds and total fatty acids present in the raw materials. Results showed that neither proteins nor lipids of intact Nannochloropsis cells were accessible to the mammalian digestive enzymes used in the digestion model. Cell disruption, and to a lesser extent, further pH-shift processing with protein solubilisation at pH 7 or pH 10, increased the accessibility of lipids. For proteins, differences amongst the pH-shift processed materials were non-significant, though pre-freezing the product prior to digestion increased the accessibility from 32% to 47%. For fatty acids, pH-shift process-products gave rise to 43% to 52% lipolysis, with higher lipolysis for products solubilised at pH 10 as opposed to pH 7. Our results indicate the importance of processing to produce an algal product that has beneficial nutritional properties when applied as food or feed.

Lipid-associated oral delivery: Mechanisms and analysis of oral absorption enhancement

The majority of newly discovered oral drugs are poorly water soluble, and co-administration with lipids has proven effective in significantly enhancing bioavailability of some compounds with low aqueous solubility. Yet, lipid-based delivery technologies have not been widely employed in commercial oral products. Lipids can impact drug transport and fate in the gastrointestinal (GI) tract through multiple mechanisms including enhancement of solubility and dissolution kinetics, enhancement of permeation through the intestinal mucosa, and triggering drug precipitation upon lipid emulsion depletion (e.g., by digestion). The effect of lipids on drug absorption is currently not quantitatively predictable, in part due to the multiple complex dynamic processes that can be impacted by lipids. Quantitative mechanistic analysis of the processes significant to lipid system function and overall impact on drug absorption can aid in the understanding of drug-lipid interactions in the GI tract and exploitation of such interactions to achieve optimal lipid-based drug delivery. In this review, we discuss the impact of co-delivered lipids and lipid digestion on drug dissolution, partitioning, and absorption in the context of the experimental tools and associated kinetic expressions used to study and model these processes. The potential benefit of a systems-based consideration of the concurrent multiple dynamic processes occurring upon co-dosing lipids and drugs to predict the impact of lipids on drug absorption and enable rational design of lipid-based delivery systems is presented.

Relevant pH and lipase for in vitro models of gastric digestion

The development of in vitro digestion models relies on the availability of in vivo data such as digestive enzyme levels and pH values recorded in the course of meal digestion. The variations of these parameters along the GI tract are important for designing dynamic digestion models but also static models for which the choice of representative conditions of the gastric and intestinal conditions is critical. Simulating gastric digestion with a static model and a single set of parameters is particularly challenging because the variations in pH and enzyme concentration occurring in the stomach are much broader than those occurring in the small intestine. A review of the literature on this topic reveals that most models of gastric digestion use very low pH values that are not representative of the fed conditions. This is illustrated here by showing the variations in gastric pH as a function of meal gastric emptying instead of time. This representation highlights those pH values that are the most relevant for testing meal digestion in the stomach. Gastric lipolysis is still largely ignored or is performed with microbial lipases. In vivo data on gastric lipase and lipolysis have however been collected in humans and dogs during test meals. The biochemical characterization of gastric lipase has shown that this enzyme is rather unique among lipases: (i) stability and activity in the pH range 2 to 7 with an optimum at pH 4-5.4; (ii) high tensioactivity that allows resistance to bile salts and penetration into phospholipid layers covering TAG droplets; (iii) sn-3 stereospecificity for TAG hydrolysis; and (iv) resistance to pepsin. Most of these properties have been known for more than two decades and should provide a rational basis for the replacement of gastric lipase by other lipases when gastric lipase is not available.