A clinical single-pass perfusion investigation of the dynamic in vivo secretory response to a dietary meal in human proximal small intestine

Nanoemulsion delivery systems for enhanced efficacy of antimicrobials and essential oils

The ever-growing threat of new and existing infectious diseases in combination with antimicrobial resistance requires the need for innovative and effective forms of drug delivery. Optimal drug delivery systems for existing and newly developed antimicrobials can enhance drug bioavailability, enable site-specific drug targeting, and overcome current limitations of drug formulations such as short elimination half-lives, poor drug solubility, and undesirable side effects. Nanoemulsions (NE) consist of nanometer-sized droplets stabilized by emulsifiers and are typically more stable and permeable due to their smaller particle sizes and higher surface area compared to conventional emulsions. NE have been identified as a promising means of antimicrobial delivery due to their intrinsic antimicrobial properties, ability to increase drug solubility, stability, bioavailability, organ and cellular targeting potentials, capability of targeting biofilms, and potential to overcome antimicrobial resistance. Herein, we discuss non-drug loaded essential oil-based NE that can confer antimicrobial actions through predominantly physical or biochemical mechanisms without drug payloads. We also describe drug-loaded NE for enhanced antimicrobial efficacy by augmenting the potency of existing antimicrobials. We highlight the versatility of NE to be administered through multiple different routes (oral, parenteral, dermal, transdermal, pulmonary, nasal, ocular, and rectal). We summarize recent advances in the clinical translation of antimicrobial NE and shed light on future development of effective antimicrobial therapy to combat infectious diseases.

Using naso- and oro-intestinal catheters in physiological research for intestinal delivery and sampling in vivo: practical and technical aspects to be considered

Intestinal catheters have been used for decades in human nutrition, physiology, pharmacokinetics, and gut microbiome research, facilitating the delivery of compounds directly into the intestinal lumen or the aspiration of intestinal fluids in human subjects. Such research provides insights about (local) dynamic metabolic and other intestinal luminal processes, but working with catheters might pose challenges to biomedical researchers and clinicians. Here, we provide an overview of practical and technical aspects of applying naso- and oro-intestinal catheters for delivery of compounds and sampling luminal fluids from the jejunum, ileum, and colon in vivo. The recent literature was extensively reviewed, and combined with experiences and insights we gained through our own clinical trials. We included 60 studies that involved a total of 720 healthy subjects and 42 patients. Most of the studies investigated multiple intestinal regions (24 studies), followed by studies investigating only the jejunum (21 studies), ileum (13 studies), or colon (2 studies). The ileum and colon used to be relatively inaccessible regions in vivo. Custom-made state-of-the-art catheters are available with numerous options for the design, such as multiple lumina, side holes, and inflatable balloons for catheter progression or isolation of intestinal segments. These allow for multiple controlled sampling and compound delivery options in different intestinal regions. Intestinal catheters were often used for delivery (23 studies), sampling (10 studies), or both (27 studies). Sampling speed decreased with increasing distance from the sampling syringe to the specific intestinal segment (i.e., speed highest in duodenum, lowest in ileum/colon). No serious adverse events were reported in the literature, and a dropout rate of around 10% was found for these types of studies. This review is highly relevant for researchers who are active in various research areas and want to expand their research with the use of intestinal catheters in humans in vivo.

Impact of gastrointestinal tract variability on oral drug absorption and pharmacokinetics: An UNGAP review

The absorption of oral drugs is frequently plagued by significant variability with potentially serious therapeutic consequences. The source of variability can be traced back to interindividual variability in physiology, differences in special populations (age- and disease-dependent), drug and formulation properties, or food-drug interactions. Clinical evidence for the impact of some of these factors on drug pharmacokinetic variability is mounting: e.g. gastric pH and emptying time, small intestinal fluid properties, differences in pediatrics and the elderly, and surgical changes in gastrointestinal anatomy. However, the link of colonic factors variability (transit time, fluid composition, microbiome), sex differences (male vs. female) and gut-related diseases (chronic constipation, anorexia and cachexia) to drug absorption variability has not been firmly established yet. At the same time, a way to decrease oral drug pharmacokinetic variability is provided by the pharmaceutical industry: clinical evidence suggests that formulation approaches employed during drug development can decrease the variability in oral exposure. This review outlines the main drivers of oral drug exposure variability and potential approaches to overcome them, while highlighting existing knowledge gaps and guiding future studies in this area.

Therapeutic Nanoemulsion: Concept to Delivery

Nanoemulsions (NEs) or nanometric-scaled emulsions are transparent or translucent, optically isotropic and kinetically stable heterogeneous system of two different immiscible liquids namely, water and oil stabilized with an amphiphilic surfactant having droplet size ranges up to 100 nm. They offer a variety of potential interests for certain applications: improved deep-rooted stability; excellent optical clarity; and, enhanced bioavailability due to its nanoscale of particles. Though there is still comparatively narrow insight apropos design, development, and optimization of NEs, which mainly stems from the fact that conventional characteristics of emulsion development and stabilization only partly apply to NEs. The contemporary article focuses on the nanoemulsion dosage form journey from concept to key application in drug delivery. In addition, industrial scalability of the nanoemulsion, as well as its presence in commercial and clinical practice, are also addressed.

A Non-Lipolysis Nanoemulsion Improved Oral Bioavailability by Reducing the First-Pass Metabolism of Raloxifene, and Related Absorption Mechanisms Being Studied

Objective

A non-lipolysis nanoemulsion (NNE) was designed to reduce the first-pass metabolism of raloxifene (RAL) by intestinal UDP-glucuronosyltransferases (UGTs) for increasing the oral absorption of RAL, coupled with in vitro and in vivo studies.

Methods

In vitro stability of NNE was evaluated by lipolysis and the UGT metabolism system. The oral bioavailability of NNE was studied in rats and pigs. Finally, the absorption mechanisms of NNE were investigated by in situ single-pass intestinal perfusion (SPIP) in rats, Madin-Darby canine kidney (MDCK) cells model, and lymphatic blocking model.

Results

The pre-NNE consisted of isopropyl palmitate, linoleic acid, Cremophor RH40, and ethanol in a weight ratio of 3.33:1.67:3:2. Compared to lipolysis nanoemulsion of RAL (RAL-LNE), the RAL-NNE was more stable in in vitro gastrointestinal buffers, lipolysis, and UGT metabolism system (p < 0.05). The oral bioavailability was significantly improved by the NNE (203.30%) and the LNE (205.89%) relative to the suspension group in rats. However, 541.28% relative bioavailability was achieved in pigs after oral NNE intake compared to the suspension and had two-fold greater bioavailability than the LNE (p < 0.05). The RAL-NNE was mainly absorbed in the jejunum and had high permeability at the intestine of rats. The results of both SPIP and MDCK cell models demonstrated that the RAL-NNE was absorbed via endocytosis mediated by caveolin and clathrin. The other absorption route, the lymphatic transport (cycloheximide as blocking agent), was significantly improved by the NNE compared with the LNE (p < 0.05).

Conclusion

A NNE was successfully developed to reduce the first-pass metabolism of RAL in the intestine and enhance its lymphatic transport, thereby improving the oral bioavailability. Altogether, NNE is a promising carrier for the oral delivery of drugs with significant first-pass metabolism.

A Novel Oral Astaxanthin Nanoemulsion from Haematococcus pluvialis Induces Apoptosis in Lung Metastatic Melanoma

Astaxanthin (AST) is a naturally occurring xanthophyll carotenoid having the potential to be used as an anticancer agent; however, the human body has a low bioavailability of AST due to its poor solubility in the water phase. Therefore, we applied D-α-tocopheryl polyethylene glycol succinate (TPGS) as an emulsifier and natural edible peanut oil to form a steady oil-in-water (O/W) nanoemulsion loaded with AST (denoted as TAP-nanoemulsion). TAP-nanoemulsions were stable without the droplet coalescence against thermal treatments (30-90°C), pH value changes (over a range of 2.0-8.0), and ionic strength adjustments (at NaCl concentrations of 100-500 mM) measured by dynamic light scattering (DLS). AST within TAP-nanoemulsion was released up to 80% in a simulated intestinal enzymatic fluid in vitro, and the overall recovery rate was fairly consistent in the Caco-2 cellular model. In order to further evaluate in vivo melanoma inhibitory experiments, we injected the fluorescent-stained B16F10 cells into female C57BL/6 mouse tail veins and treated TAP-nanoemulsion in an oral gavage. qRT-PCR and Western blot demonstrated that TAP-nanoemulsion triggered effectively the apoptosis pathway, including enhancements of cleaved caspase-3 and caspase-9, ataxia-telangiectasia mutated kinase (ATM), and p21WAF1/CIP1 (p21) and decreases of B-cell lymphoma 2 (Bcl-2); cyclins D, D1, and E; mitogen-activated protein kinase (MEK); extracellular signal-regulated kinases (ERK); nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB); and matrix metallopeptidase-1 and metallopeptidase-9 (MMP-1 and MMP-9) in both gene and protein expressions. In conclusion, this study suggests that TAP-nanoemulsion with the oral treatment has a positive chemotherapy effect in melanoma with lung metastases in vivo. As far as we know, this is the first time to demonstrate that an antioxidant in nanoparticle administration cures lung metastatic melanoma.

Pancreatic and mucosal enzymes in choline phospholipid digestion

The digestion of choline phospholipids is important for choline homeostasis, lipid signaling, postprandial lipid and energy metabolism, and interaction with intestinal bacteria. The digestion is mediated by the combined action of pancreatic and mucosal enzymes. In the proximal small intestine, hydrolysis of phosphatidylcholine (PC) to 1-lyso-PC and free fatty acid (FFA) by the pancreatic phospholipase A₂ IB coincides with the digestion of the dietary triacylglycerols by lipases, but part of the PC digestion is extended and must be mediated by other enzymes as the jejunoileal brush-border phospholipase B/lipase and mucosal secreted phospholipase A₂ X. Absorbed 1-lyso-PC is partitioned in the mucosal cells between degradation and reacylation into chyle PC. Reutilization of choline for hepatic bile PC synthesis, and the reacylation of 1-lyso-PC into chylomicron PC by the lyso-PC-acyl-CoA-acyltransferase 3 are important features of choline recycling and postprandial lipid metabolism. The role of mucosal enzymes is emphasized by sphingomyelin (SM) being sequentially hydrolyzed by brush-border alkaline sphingomyelinase (alk-SMase) and neutral ceramidase to sphingosine and FFA, which are well absorbed. Ceramide and sphingosine-1-phosphate are generated and are both metabolic intermediates and important lipid messengers. Alk-SMase has anti-inflammatory effects that counteract gut inflammation and tumorigenesis. These may be mediated by multiple mechanisms including generation of sphingolipid metabolites and suppression of autotaxin induction and lyso-phosphatidic acid formation. Here we summarize current knowledge on the roles of pancreatic and mucosal enzymes in PC and SM digestion, and its implications in intestinal and liver diseases, bacterial choline metabolism in the gut, and cholesterol absorption.

The impact of food intake on the luminal environment and performance of oral drug products with a view to in vitro and in silico simulations: a PEARRL review

Objectives

Using the type of meal and dosing conditions suggested by regulatory agencies as a basis, this review has two specific objectives: first, to summarize our understanding on the impact of food intake on luminal environment and drug product performance and second, to summarize the usefulness and limitations of available in vitro and in silico methodologies for the evaluation of drug product performance after food intake.

Key findings

Characterization of the luminal environment and studies evaluating product performance in the lumen, under conditions suggested by regulatory agencies for simulating the fed state, are limited. Various in vitro methodologies have been proposed for evaluating drug product performance in the fed state, but systematic validation is lacking. Physiologically based pharmacokinetic (PBPK) modelling approaches require the use of in vitro biorelevant data and, to date, have been used primarily for investigating the mechanisms via which an already observed food effect is mediated.

Summary

Better understanding of the impact of changes induced by the meal administration conditions suggested by regulatory agencies on the luminal fate of the drug product is needed. Relevant information will be useful for optimizing the in vitro test methods and increasing the usefulness of PBPK modelling methodologies.

Characterization of colloidal structures during intestinal lipolysis using small-angle neutron scattering

HYPOTHESIS

Bile micelles are thought to mediate intestinal absorption, in part by providing a phase into which compounds can partition. Solubilizing capacity of bile micelles is enhanced during the digestion of fat rich food. We hypothesized that the intestinal digestion of triglycerides causes an increase in volume of micelles that can be quantitatively monitored over the course of digestion using small-angle neutron scattering (SANS), and that SANS can enable evaluation of the contribution of each of the components present during digestion to the size of micelles.

EXPERIMENTS

SANS was used to characterize the size and shape of micelles present prior to and during the in vitro simulated intestinal digestion of a model food-associated lipid, triolein.

FINDINGS

Pre-lipolysis mixtures of a bile salt and phospholipid simulating bile concentrations in fed conditions were organized in micelles with an average volume of 40 nm³. During lipolysis, the micelle volume increased 2.5-fold over a 2-h digestion period due to growth in one direction as a result of insertion of monoglycerides and fatty acids. These efforts represent a basis for quantitative mechanistic understanding of changes in solubilizing capacity of the intestinal milieu upon ingestion of a fat-rich meal.

Nanoemulsion: Concepts, development and applications in drug delivery

Nanoemulsions are biphasic dispersion of two immiscible liquids: either water in oil (W/O) or oil in water (O/W) droplets stabilized by an amphiphilic surfactant. These come across as ultrafine dispersions whose differential drug loading; viscoelastic as well as visual properties can cater to a wide range of functionalities including drug delivery. However there is still relatively narrow insight regarding development, manufacturing, fabrication and manipulation of nanoemulsions which primarily stems from the fact that conventional aspects of emulsion formation and stabilization only partially apply to nanoemulsions. This general deficiency sets up the premise for current review. We attempt to explore varying intricacies, excipients, manufacturing techniques and their underlying principles, production conditions, structural dynamics, prevalent destabilization mechanisms, and drug delivery applications of nanoemulsions to spike interest of those contemplating a foray in this field.

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.

Intestinal alkaline phosphatase: a summary of its role in clinical disease

Over the past few years, there is increasing evidence implicating a novel role for Intestinal Alkaline Phosphatase (IAP) in mitigating inflammatory mediated disorders. IAP is an endogenous protein expressed by the intestinal epithelium that is believed to play a vital role in maintaining gut homeostasis. Loss of IAP expression or function is associated with increased intestinal inflammation, dysbiosis, bacterial translocation and subsequently systemic inflammation. As these events are a cornerstone of the pathophysiology of many diseases relevant to surgeons, we sought to review recent research in both animal and humans on IAP's physiologic function, mechanisms of action and current research in specific surgical diseases.

The 2-monoacylglycerol moiety of dietary fat appears to be responsible for the fat-induced release of GLP-1 in humans

BACKGROUND

Dietary triglycerides can, after digestion, stimulate the intestinal release of incretin hormones through activation of G protein-coupled receptor (GPR) 119 by 2-monoacylglycerol and by the activation of fatty acid receptors for long- and short-chain fatty acids. Medium-chain fatty acids do not stimulate the release of intestinal hormones.

OBJECTIVE

To dissect the mechanism of fat-induced glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) release in humans, we compared the effects of tributyrin (containing short-chain fatty acids; i.e., butyric acid), olive oil [containing long-chain fatty acids; e.g., oleic acid plus 2-oleoyl glycerol (2-OG)], and 1,3-dioctanoyl-2-oleoyl glycerol (C8-dietary oil), which is digested to form medium-chain fatty acids : i.e., octanoic acid : and 2-OG.

DESIGN

In a randomized, single-blinded crossover study, 12 healthy white men [mean age: 24 y; BMI (in kg/m(2)): 22] were given the following 4 meals on 4 different days: 200 g carrots + 6.53 g tributyrin, 200 g carrots + 13.15 g C8-dietary oil, 200 g carrots + 19 g olive oil, or 200 g carrots. All of the lipids totaled 0.0216 mol. Main outcome measures were incremental areas under the curve for total GLP-1, GIP, and cholecystokinin (CCK) in plasma.

RESULTS

C8-dietary oil and olive oil showed the same GLP-1 response [583 ± 101 and 538 ± 71 (pmol/L) × 120 min; P = 0.733], whereas the GIP response was higher for olive oil than for C8-dietary oil [3293 ± 404 and 1674 ± 270 (pmol/L) × 120 min; P = 0.002]. Tributyrin and carrots alone resulted in no increase in any of the measured hormones. Peptide YY (PYY) and neurotensin responses resembled those of GLP-1. Only olive oil stimulated CCK release.

CONCLUSIONS

Under our study conditions, 2-OG and GPR119 activation can fully explain the olive oil-induced secretion of GLP-1, PYY, and neurotensin. In contrast, both oleic acid and 2-OG contributed to the GIP response. Dietary butyrate did not stimulate gut hormone secretion. Olive oil-derived oleic acid seems to be fully responsible for olive oil-induced CCK secretion. This trial was registered at clinicaltrials.gov as NCT02264951.

Intestinal solubility and absorption of poorly water soluble compounds: predictions, challenges and solutions

We have explored for which type of compounds biorelevant dissolution profiling in simulated intestinal fluids would accurately predict solubility in human intestinal fluid. In total, 474 solubility values in simulated and aspirated human intestinal fluid for 78 drugs were compiled and analyzed. Significant solubilization in the colloidal structures was obtained in fasted and fed state fluids for drug compounds with a logD(oct)>3. Highly lipophilic compounds with high melting points (Tm > 200 °C) could also be significantly solubilized, but typically such compounds had solubility values in the lower µg/ml range also in the presence of the colloidal structures. On the basis of our analysis, compounds with a logD(oct)>3 should be explored in biorelevant dissolution media to better predict in vivo performance after oral dosing.

Serum cholesterol reduction efficacy of biscuits with added plant stanol ester

This study's aim was to test the low-density lipoprotein cholesterol- (LDL-c-) lowering efficacy of biscuits containing 2 g of plant stanols, which corresponded to 3.4 g of plant stanol esters. The biscuit is a new food format that can be consumed as a snack. In a double-blind, placebo-controlled parallel design study, 119 mildly to moderately hypercholesterolemic volunteers were randomized to plant stanol or control groups. Subjects were comparable in age, gender, lipid profiles, and body mass index. They consumed a control biscuit once a day for a two-week period, followed by a four-week intervention period that either had a plant stanol ester biscuit or a control. During the habitual diet, one biscuit per day was consumed at any time that subjects wished. Serum lipid profiles were measured at the first day of run-in, at baseline, and at the study's end. Compared to the control, the total cholesterol (TC), LDL-c, and the LDL-to-high-density lipoprotein (LDL/HDL) ratio had serum reductions of 4.9%, 6.1%, and 4.3%, respectively, and were observed after 4 weeks of biscuit consumption with added plant stanols (P < 0.05). A significantly higher reduction in LDL-c (8.9%) and LDL/HDL ratio (11.4%) was measured in those taking a plant stanol biscuit with a meal compared to those who consumed a plant stanol biscuit without other food. In conclusion, incorporating plant stanols into a biscuit is an attractive, convenient, and acceptable way to modestly lower elevated cholesterol concentrations. For optimal efficacy, biscuits should be consumed with a meal as part of a healthy diet.

Composition and physicochemical properties of fasted-state human duodenal and jejunal fluid: a critical evaluation of the available data

Various methods of sampling and analyzing intestinal fluids have been applied over the years. In this report, data that have been published to date about the composition of fasted-state human intestinal fluid (HIF) and its physicochemical properties are summarized and the influence of the methods used to generate the data is discussed. Key physiological parameters summarized include pH, buffer capacity, osmolarity, and ionic strength in both the fasted duodenum and jejunum. Furthermore, the bile salts and phospholipids in the fasted small intestine are addressed in terms of both qualitative and quantitative composition with respect to the different types and degrees of hydroxylation of bile salts. Taurocholate, glycocholate, and glycochenodeoxycholate were identified as the main bile salts. Lysolecithin was identified as the predominant phospholipid species in fasted HIF because of the enzymatic degradation of lecithin. Together with other intestinal surfactants, such as cholesterol and free fatty acids, the influence of bile acids and phospholipids on the surface tension of fasted HIF was evaluated. A good working knowledge of all the above-mentioned parameters is important to optimize the composition of biorelevant media, with a view to improving the prediction of in vivo dissolution and release performance of drugs and dosage forms.

PBPK models for the prediction of in vivo performance of oral dosage forms

Drug absorption from the gastrointestinal (GI) tract is a highly complex process dependent upon numerous factors including the physicochemical properties of the drug, characteristics of the formulation and interplay with the underlying physiological properties of the GI tract. The ability to accurately predict oral drug absorption during drug product development is becoming more relevant given the current challenges facing the pharmaceutical industry. Physiologically-based pharmacokinetic (PBPK) modeling provides an approach that enables the plasma concentration-time profiles to be predicted from preclinical in vitro and in vivo data and can thus provide a valuable resource to support decisions at various stages of the drug development process. Whilst there have been quite a few successes with PBPK models identifying key issues in the development of new drugs in vivo, there are still many aspects that need to be addressed in order to maximize the utility of the PBPK models to predict drug absorption, including improving our understanding of conditions in the lower small intestine and colon, taking the influence of disease on GI physiology into account and further exploring the reasons behind population variability. Importantly, there is also a need to create more appropriate in vitro models for testing dosage form performance and to streamline data input from these into the PBPK models. As part of the Oral Biopharmaceutical Tools (OrBiTo) project, this review provides a summary of the current status of PBPK models available. The current challenges in PBPK set-ups for oral drug absorption including the composition of GI luminal contents, transit and hydrodynamics, permeability and intestinal wall metabolism are discussed in detail. Further, the challenges regarding the appropriate integration of results from in vitro models, such as consideration of appropriate integration/estimation of solubility and the complexity of the in vitro release and precipitation data, are also highlighted as important steps to advancing the application of PBPK models in drug development. It is expected that the "innovative" integration of in vitro data from more appropriate in vitro models and the enhancement of the GI physiology component of PBPK models, arising from the OrBiTo project, will lead to a significant enhancement in the ability of PBPK models to successfully predict oral drug absorption and advance their role in preclinical and clinical development, as well as for regulatory applications.

Effects of various food ingredients on gall bladder emptying

Background/objectives:

The emptying of the gall bladder in response to feeding is pivotal for the digestion of fat, but the role of various food ingredients in contracting the gall bladder postprandially is not well understood. We hypothesized that different food ingredients, when consumed, will have a different effect on stimulating gall bladder emptying. To investigate this we designed two randomized, investigator-blind, cross-over studies in healthy subjects using magnetic resonance imaging (MRI) to measure gall bladder volumes serially and non-invasively.

Subjects/methods:

Study 1: exploratory study evaluating the effects of 10 different food ingredients on gall bladder emptying in eight healthy subjects. The choice of ingredients varied from common items like coffee, tea and milk to actives like curcumin and potato protease inhibitor. Study 2: mechanistic study investigating the cholecystokinin (CCK) dose response to the best performer ingredient from Study 1 in 21 healthy subjects four ways.

Results:

The largest gall bladder volume change in Study 1 was observed with fat, which therefore became the dose-response ingredient in Study 2, where the maximum % gall bladder volume change correlated well with CCK.

Conclusions:

These serial test-retest studies showed that the fasted gall bladder volume varied remarkably between individuals and that individual day-to-day variability had wide coefficients of variation. Improved knowledge of how to stimulate bile release using food ingredients will be useful to improve in vitro–in vivo correlation of bioavailability testing of hydrophobic drugs. It could improve performance of cholesterol-lowering plant stanol and sterol products and possibly aid understanding of some cholesterol gallstone disease.

Characterising the behaviour of poorly water soluble drugs in the intestine: application of biorelevant media for solubility, dissolution and transport studies

OBJECTIVES

Based on the knowledge of human intestinal fluids, compositions of biorelevant media and their impact on solubility, dissolution and permeability studies of poorly soluble drug compounds are discussed.

KEY FINDINGS

Human intestinal fluids show large variations with regard to composition and pH, which complicate the selection of biorelevant media. The influence of concentration and ratio of bile salts, phospholipids and hydrolysis products, such as monoglycerides and free fatty acids, in well characterised media, on the solubility, dissolution and permeability of a given drug provides valuable information on the behaviour of the drug in the intestine, thus enabling the prediction of the in-vivo absorption.

SUMMARY

This review discusses the implications of biorelevant media composition on the solubility, dissolution and permeability of poorly soluble drug compounds. Biorelevant media contain bile salts and phospholipids and when simulating the fed state also monoglycerides and free fatty acids. Solubility of some poorly soluble drugs increase independently of the type of surfactants included in the biorelevant media, while others have a higher solubility in monoglyceride- and fatty acid-containing media. This is independent of the log P (the octanol-water partition coefficient) of the drug. The use of biorelevant dissolution media improves the correlation to in-vivo data, compared with compendial media, and although the field of permeability studies is complex the use of biorelevant media in this setting shows promise with respect to a better prediction of absorption.

Finasteride metabolism and pharmacogenetics: new approaches to personalized prevention of prostate cancer

Incidences of prostate cancer in most countries are increasing owing to better detection methods; however, prevention with the use of finasteride, a very effective steroid 5α-reductase type II inhibitor, has been met with mixed success. A wide interindividual variation in response exists and is thought to be due to heritable factors. This article summarizes the literature that attempts to elucidate the molecular mechanisms of finasteride in terms of its metabolism, excretion and interaction with endogenous steroid molecules. We describe previously reported genetic variations of steroid-metabolizing genes and their potential association with finasteride efficacy. Based on the literature, we outline directions of research that may contribute to understanding the interindividual variation in finasteride prevention and to the future development of personalized medicine.

In vitro lipolysis models as a tool for the characterization of oral lipid and surfactant based drug delivery systems

With the increasing interest in lipid and surfactant based drug delivery systems (LSBDDS) for oral delivery of poorly soluble drugs, the need for efficient development tools is emerging. In vitro lipolysis models, simulating the digestion in the small intestine, is a promising tool in this regard. Several different in vitro lipolysis models have been used for characterization of LSBDDS, all using porcine pancreatin as lipase source, and primarily differing in the addition scheme of calcium and the kind of bile acids employed. Both calcium and bile influence the lipolysis. Calcium have been used both as fixed addition at the beginning of the experiment and with a continuous addition during lipolysis. Both pure bile acids and crude porcine bile extract have been used. Lipolysis of LSBDDS will generate mixed micelles, as well as lamellar and hexagonal phases. These have been characterized by dynamic light scattering, cryogenic transmission electron microscopy and small angle X-ray scattering. The faith of drug during in vitro digestion of a LSBDDS is often studied by ultracentrifugation and quantification of drug in the different phases formed. Further, drug precipitated during in vitro lipolysis has been characterized by X-ray powder diffraction and polarized light microscopy.

Intestinal alkaline phosphatase: multiple biological roles in maintenance of intestinal homeostasis and modulation by diet

The diverse nature of intestinal alkaline phosphatase (IAP) functions has remained elusive, and it is only recently that four additional major functions of IAP have been revealed. The present review analyzes the earlier literature on the dietary factors modulating IAP activity in light of these new findings. IAP regulates lipid absorption across the apical membrane of enterocytes, participates in the regulation of bicarbonate secretion and of duodenal surface pH, limits bacterial transepithelial passage, and finally controls bacterial endotoxin-induced inflammation by dephosphorylation, thus detoxifying intestinal lipopolysaccharide. Many dietary components, including fat, protein, and carbohydrate, modulate IAP expression or activity and may be combined to sustain a high level of IAP activity. In conclusion, IAP has a pivotal role in intestinal homeostasis and its activity could be increased through the diet. This is especially true in pathological situations (e.g., inflammatory bowel diseases) in which the involvement of commensal bacteria is suspected and when intestinal AP is too low to detoxify a sufficient amount of bacterial lipopolysaccharide.

Gastrointestinal metabolism of a vegetable-oil emulsion in healthy subjects

BACKGROUND

Given the growing prevalence of overweight and obesity, weight-management strategies could be developed based on the effect of specific food ingredients on the gastrointestinal system to reduce food intake.

OBJECTIVE

The aim of this study was to investigate the mechanisms by which a vegetable-oil emulsion may exert its effect on satiety by applying a multilumen tube to investigate digestion and absorption of lipids in the stomach and proximal jejunum.

DESIGN

We gave 16 healthy, normal-weight subjects (in a double-blind, placebo-controlled crossover design) a test product (yogurt with a vegetable-oil emulsion) or an equal-calorie control by intragastric administration on 2 separate occasions. Gastric and intestinal samples were collected from the proximal jejunum during 180 min.

RESULTS

We observed almost double amounts (P < 0.05) of total lipids, mainly as free fatty acids, from the test product (450 +/- 119 mg) in the proximal jejunum compared with amounts of total lipids from the control product (230 +/- 50 mg), and an over-time difference of free fatty acid concentrations was observed between the products (P < 0.05). To our knowledge, a novel and unexpected finding was the appearance of needle-shaped crystals in the jejunal samples that originated from the vegetable-oil emulsion and consisted of saturated fatty acids. Crystals were only rarely seen in the control samples.

CONCLUSION

The higher amount of lipids in the proximal jejunum and the recovery of crystals in the intestinal samples after test-product infusion provide a plausible physiologic explanation for the ileal brake mechanism that leads to the increased satiety observed for this test product.

Lysophosphatidylcholine for efficient intestinal lipid absorption and lipoprotein secretion in caco-2 cells

Phosphatidylcholine (PC) and its hydrolysates are considered to stimulate intestinal lipid absorption, however, their exact effects on lipoproteins and apolipoprotein (apo) metabolism remain ambiguous. This study aimed to further differentiate the effects of them using fully differentiated enterocyte-like Caco-2 cells. Lipid micelles (oleic acid 0.6, cholesterol 0.05, monooleylglycerol 0.2, taurocholate 2 in mmol/l) with or without choline, PC, and lysoPC (0.2 mmol/l each) were applied apically to Caco-2 cells. ³H-oleic acid and ¹⁴C-cholesterol were added to the micelles when necessary. Secreted lipoproteins were analyzed by a HPLC method. LysoPC had the most potent promoting effect on lipid uptake, and lipoprotein and apolipoprotein B-48 secretion among the molecules tested. LysoPC doubled the output of cholesterol and triglyceride as the lipoprotein component, but PC did not. On the other hand, PC only increased the secretion of apoA-IV in the presence of lipid micelles. These findings confirm that the alteration of PC by PLA₂ hydrolysis is intrinsically involved in the intestinal lipid absorption process and suggest that PC and its hydrolysis are coordinately associated with not only lipid absorption efficiency but also lipoprotein output and metabolism.

A possible role of lysophospholipids produced by calcium-independent phospholipase A(2) in membrane-raft budding and fission

Phospholipase A(2) (PLA(2)) not only plays a role in the membrane vesiculation system but also mediates membrane-raft budding and fission in artificial giant liposomes. This study aimed to demonstrate the same effects in living cells. Differentiated Caco-2 cells were cultured on filter membranes. MDCK cells were challenged with Influenza virus. The MDCK cultures were harvested for virus titration with a plaque assay. Alkaline phosphatase (ALP), a membrane-raft associated glycosylphosphatidylinositol (GPI)-anchored protein, was 70% released by adding 0.2 mmol/l lysophosphatidylcholine, which was abolished by treatment with a membrane-raft disrupter, methyl-beta-cyclodextrin. Activation of calcium-independent PLA(2) (iPLA(2)) by brefeldin A increased the apical release of ALP by approximately 1.5-fold (p<0.01), which was blocked by PLA(2) inhibitor bromoenol lactone (BEL). BEL also reduced Influenza virus production into the media (<10%) in the MDCK culture. These results suggest that cells utilize inverted corn-shaped lysophospholipids generated by PLA(2) to modulate plasma membrane structure and assist the budding of raft-associated plasma membrane particles, which virus utilizes for its budding. Brush borders are enriched with membrane-rafts and undergo rapid turnover; thus, PLA(2) may be involved in the regulatory mechanism in membrane dynamism. Further, iPLA(2) may provide a therapeutic target for viral infections.

Role of lysophosphatidylcholine in brush-border intestinal alkaline phosphatase release and restoration

Intestinal alkaline phosphatase (IAP) is a brush-border membrane ectoenzyme (BBM-IAP) that is released into the lumen (L-IAP) after a high-fat diet. We examined the effects of oil feeding and the addition of mixed-lipid micelles on the formation of L-IAP in oil-fed rat intestine, Caco-2 cell monolayers, and mouse intestinal loops. We localized IAP in the duodenum of rats fed corn oil using fluorescence microscopy with enzyme-labeled fluorescence-97 as substrate. Four hours after oil feeding, L-IAP increased approximately 10-fold accompanied by the loss of BBM-IAP, consistent with BBM-IAP release. Rat IAP isozyme mRNAs progressively increased 4-6 h after oil feeding, followed by the increase of IAP activity in the subapical location at 6 h, consistent with the restoration of IAP protein. Postprandial lipid-micelle components, sodium taurocholate with or without oleic acid, mono-oleylglycerol, cholesterol, or lysophosphatidylcholine (lysoPC) were applied singly or as mixed-lipid micelles to the apical surface of polarized Caco-2 cell monolayers. LysoPC increased L-IAP >10-fold over basal release. LysoPC released IAP into the apical medium more than other intestinal brush-border enzymes, 5'-nucleotidase, sucrase, aminopeptidase N, and lactase, without comparable lactate dehydrogenase release or cell injury. LysoPC increased human IAP mRNA levels by 1.5-fold in Caco-2 cells. Luminally applied lysoPC also increased release of IAP preferentially in mouse intestinal loops. These data show that lysoPC accelerates the formation of L-IAP from BBM-IAP, followed by enhanced IAP synthesis, suggesting the role that lysoPC might play in the turnover of brush-border proteins.

Postprandial evolution in composition and characteristics of human duodenal fluids in different nutritional states

The purpose of this study was to assess the changes in duodenal composition in three nutritional states: fasted, fed, and fat-enriched fed state. Two isocaloric meals were administered to healthy subjects on nonconsecutive days. Subsequently, duodenal samples were collected every 30 min after which they were characterized with respect to pH, lipolytic products, bile salts, phospholipids, osmolality, and surface tension. The resulting time profiles displayed fluctuating patterns, which reflect high inter- and intrasubject variability. Duodenal composition was not altered by the higher fat percentage of the fat-enriched liquid meal. Monoglycerides, amounting from 5% to 88% of total lipids, were the dominant lipolytic species, followed by free fatty acids. Within 30 min after meal administration, individual intraduodenal concentrations of lipid products were 0.0-5.5, 1.0-14.9, and 3.1-22.4 mg/mL in fasted, fed, and fat-enriched fed state, respectively. The corresponding values for bile salts were 2.0-9.0, 6.9-9.3, and 4.4-30.3 mM and for phospholipids 0.06-2.4, 2.6-5.7, and 1.4-9.3 mM, respectively. Specific trends though, were not detected. This study illustrates the variable intraluminal conditions that can result after food intake. As intraduodenal events (e.g., intraduodenal dissolution) affect absorption of poorly water soluble and/or highly lipophilic drugs, this variability may possibly contribute to the highly variable drug plasma-time profiles often observed.

Predicting drug disposition, absorption/elimination/transporter interplay and the role of food on drug absorption

The ability to predict drug disposition involves concurrent consideration of many chemical and physiological variables and the effect of food on the rate and extent of availability adds further complexity due to postprandial changes in the gastrointestinal (GI) tract. A system that allows for the assessment of the multivariate interplay occurring following administration of an oral dose, in the presence or absence of meal, would greatly benefit the early stages of drug development. This is particularly true in an era when the majority of new molecular entities are highly permeable, poorly soluble, extensively metabolized compounds (BDDCS Class 2), which present the most complicated relationship in defining the impact of transporters due to the marked effects of transporter-enzyme interplay. This review evaluates the GI luminal environment by taking into account the absorption/transport/elimination interplay and evaluates the physiochemical property issues by taking into account the importance of solubility, permeability and metabolism. We concentrate on the BDDCS and its utility in predicting drug disposition. Furthermore, we focus on the effect of food on the extent of drug availability (F), which appears to follow closely what might be expected if a significant effect of high fat meals is inhibition of transporters. That is, high fat meals and lipidic excipients would be expected to have little effect on F for Class 1 drugs; they would increase F of Class 2 drugs, while decreasing F for Class 3 drugs.

Development of simulated intestinal fluids containing nutrients as transport media in the Caco-2 cell culture model: Assessment of cell viability, monolayer integrity and transport of a poorly aqueous soluble drug and a substrate of efflux mechanisms

The purpose of this study was to identify simulated intestinal fluids (SIFs) containing nutrients compatible with the Caco-2 cell culture model and to examine the impact of the identified medium on the transport of a poorly aqueous soluble model compound, estradiol, and a substrate of efflux mechanisms, etoposide. Monolayer integrity was evaluated by transepithelial electrical resistance and cellular viability by release of lactate dehydrogenase to the apical compartment and cellular protein content. It was shown that the viability of Caco-2 cells was enhanced by use of the CO(2) independent nutritional medium, Leibovitz's L-15 compared to Hanks' balanced salt solution. SIF containing 5mM sodium taurocholate and 1.25 mM phosphatidylcholine or lysophosphatidylcholine in Leibovitz's L-15 induced less release of lactate dehydrogenase than the traditional transport medium, HBSS. Addition of lipolysis products, 0.5mM oleic acid and 0.25 mM monoolein, did only cause increase in lactate dehydrogenase in 3 of 12 comparisons. The presence of SIFs in the apical compartment was shown to decrease flux of estradiol due to incorporation of estradiol in micelles and hence a decreased fraction of free estradiol. Further, a concentration dependent increase in the apparent permeability of etoposide was observed from apical to basolateral compartment, which indicated that components in the SIFs affects efflux mechanisms.