Physical-chemical behavior of dietary and biliary lipids during intestinal digestion and absorption. 2. Phase analysis and aggregation states of luminal lipids during duodenal fat digestion in healthy adult human beings

Solubilization and Pharmacokinetic Behaviors of Sodium Cholate/Lecithin-Mixed Micelles Containing Cyclosporine A

The purpose of this study was to investigate the solubilization capacity of sodium cholate/lecithin-mixed micelles and to evaluate the potential of mixed micelles as a carrier of cyclosporine A for intravenous infusion. The mixed micelles were prepared by coprecipitation technique. The formulation components and preparation procedures, which may affect the solubilization of cyclosporine A, were studied. The dilution stability of cyclosporine A-containing mixed micelles was investigated. Pharmacokinetic behaviors of mixed micelles in rabbits after intravenous infusion were compared with Sandimmun. Results showed the strategies to increase the solubility of cyclosporine A include lowering the molar ratio of sodium cholate to lecithin, increasing the concentration of lecithin, and reducing the ionic strength of the dispersion medium and temperature. The largest solubility was found to be 5.42 +/- 0.16 mg/ml. The leakage of mixed micelles in 5% glucose (5.84%) was much less than that in saline solution (36.7%). The relative bioavailability of mixed micelles versus Sandimmun was 112 +/- 20%, and statistical analysis demonstrated both preparations were bioequivalent. Sodium cholate/lecithin-mixed micelles are promising carriers in the intravenous delivery of cyclosporine A, considering their capability of large-scale production and low-toxic property.

Possible degradation/biotransformation of lutein in vitro and in vivo: isolation and structural elucidation of lutein metabolites by HPLC and LC-MS (atmospheric pressure chemical ionization)

Metabolites of lutein are highly concentrated in the human macula and are known to provide protection against age-related macular degeneration. The aim of this investigation was to characterize the in vitro oxidation products of lutein obtained through photo-oxidation and to compare them with biologically transformed dietary lutein in intestine, plasma, liver, and eyes of rats. In vivo studies involved feeding rats a diet devoid of lutein for 2 weeks to induce deficiency. Rats were divided into two equal groups (n=6/group) and received either micellar lutein by gavage for 10 days or diet supplemented with fenugreek leaves as a lutein source for 4 weeks. Lutein metabolites/oxidation products obtained from in vivo and in vitro studies were characterized by HPLC and LC-MS (APCI) techniques to elucidate their structure. The characteristic fragmented ions resulting from photo-oxidation of lutein were identified as 523 (M(+)+H(+)-3CH(3)), 476 (M(+)+H(+)-6CH(3)), and 551 (M(+)+H(+)-H(2)O). In the eyes, the fragmented molecules resulting from lutein were 13-Z lutein, 13'-Z lutein, 13-Z zeaxanthin, all-E zeaxanthin, 9-Z lutein, 9'-Z lutein, and 3'-oxolutein. Epoxycarotenoids were identified in liver and plasma, whereas anhydrolutein was identified in intestine. This study emphasizes the essentiality of dietary lutein to maintain its status in the retina.

A new self-emulsifying drug delivery system (SEDDS) for poorly soluble drugs: characterization, dissolution, in vitro digestion and incorporation into solid pellets

The aim of the current study was the development of a new pellet based self-emulsifying (SE) drug delivery system for the oral delivery of poorly soluble drugs. Furthermore, we wanted to investigate the influence of physiological dilution media and enzymatic digestion on the solubilization capacity of the formulation for the model drug Progesterone. Lipid mixtures composed of Solutol HS 15 and medium chain glycerides were optimized with respect to their self-emulsifying properties. The liquid SE lipid was mixed with microcrystalline cellulose and transformed into pellets by extrusion/spheronization. The pellets were characterized for size, shape, surface characteristics and friability. In vitro dissolution and digestion experiments were carried out using physiological dissolution media. The droplet diameter of the dispersed SE mixtures was largely affected by changing the oil to Solutol HS 15 ratio. Moreover, digestion of SE mixtures changed the solubilization capacity for Progesterone. Pellets with good properties (size, shape and friability) have been produced through the incorporation of a selected SE mixture into MCC. In conclusion, extrusion/spheronization is a suitable process to produce solid self-emulsifying pellets with up to 40% load of a liquid SE mixture. Digestion induces a change in lipid composition which affects the solubilization capacity of the lipid phase.

ESR studies on the influence of physiological dissolution and digestion media on the lipid phase characteristics of SEDDS and SEDDS pellets

The aim of the current study is the evaluation of a recently optimized SEDDS, composed of Solutol HS15 and medium chain glycerides, and self-emulsifying pellets by means of ESR. Tempol-benzoate (TB)-loaded SEDDS were produced and electron spin resonance (ESR) spectroscopy was used to evaluate the diluted self-emulsifying mixtures. Moreover, ESR in vitro digestion experiments were carried out to have an insight on the characteristics of the different phases formed during the digestion process and to evaluate the distribution and the localization of TB in these phases. In addition, self-emulsifying pellets were produced using nitroxide-loaded SEDDS and the microenvironment within the pellets during release process was monitored in an online process using ESR spectroscopy. After dilution of nitroxide-loaded SEDDS, the percent of TB localized in the lipophilic compartment was decreasing with increasing the surfactant fraction in the mixture. Moreover, it was found that different phases with variable viscosity and polarity were produced as a result of the enzymatic digestion of SEDDS in physiologically relevant media. This change in lipid composition has largely affected the distribution and the localization of the spin probe during the digestion process. A rapid increase in the mobility of the spin probe inside the pellets was noticed after exposure to the release media. Additionally, TB was localized within the self-emulsifying mixture environment for the time of the experiment. ESR is considered a powerful non-invasive tool to assess the microenvironment of the diluted SEDDS and to monitor in vitro digestion process. Digestion induces a change in lipid composition which can affect the solubilization capacity of the administered drug. Therefore, monitoring in vitro digestion process using ESR spectroscopy will help in providing greater understanding of the interaction between the administered drug and the digested lipid vehicles.

Effect of interfacial protein cross-linking on the in vitro digestibility of emulsified corn oil by pancreatic lipase

The objective of this study was to investigate the influence of globular protein interfacial cross-linking on the in vitro digestibility of emulsified lipids by pancreatic lipase. 3% (wt/wt) corn oil-in-water emulsions stabilized by either lecithin or beta-lactoglobulin were prepared (pH 7). A portion of the beta-lactoglobulin stabilized emulsions was subjected to a heat treatment known to cross-link the adsorbed globular proteins (85 degrees C, 20 min). Pancreatic lipase and bile extract were then added to each emulsion at 37 degrees C (pH 7) and the evolution of the particle charge, particle size, appearance and free fatty acids released were measured over a period of 2 h. The rate and extent of lipid digestion did not differ greatly between lecithin and beta-lactoglobulin stabilized emulsions, nor did it differ greatly for unheated (BLG-U) or heated (BLG-H) beta-lactoglobulin stabilized emulsions. For example, the initial rate of lipid digestion was found to be 3.1, 3.4, and 2.3 mM fatty acids s(-1) m(-2) of lipid surface for droplets stabilized by BLG-U, BLG-H, and lecithin, respectively. Pancreatic lipase was able to adsorb to the droplet surfaces and access the emulsified lipids, regardless of the initial interfacial composition and the fact that some of the original emulsifier appeared to remain at the oil-water interface during digestion. These results help to explain why the human body is so efficient at digesting dietary triacylglycerols.

Fast and simple method for the simultaneous evaluation of the capacity and efficiency of food antioxidants in trapping peroxyl radicals in an intestinal model system

A simple oxygraphic method, for which the theoretical and experimental bases have been recently revised, has been successfully applied to evaluate the peroxyl radical chain-breaking characteristics of some typical food antioxidants in micelle systems, among which is a system that reproduces conditions present in the upper part of the digestive tract, where the absorption and digestion of lipids occur. This method permits one to obtain from a single experimental run the peroxyl radical trapping capacity (PRTC, that is, the number of moles of peroxyl radicals trapped by a given amount of food), the peroxyl radical trapping efficiency (PRTE, that is, the reciprocal of the amount of food that reduces to half the steady-state concentration of peroxyl radicals), and the half-life of the antioxidant ( t(1/2)) when only a small fraction of peroxyl radicals reacts with the antioxidants present in foods. Examples of application of the method to various types of foodstuffs have been reported, assessing the general validity of the method in the simple and fast evaluation of the above-reported fundamental antioxidant characteristics of foods.

Rapid throughput solubility screening method for BCS class II drugs in animal GI fluids and simulated human GI fluids using a 96-well format

A rapid solubility-screening assay was developed with a focus on Biopharmaceutic Classification Scheme (BCS) class II drug solubility in animal and simulated human gastrointestinal (GI) fluids. The assay enables biologically promising drug leads to be evaluated for solubility limitations earlier in the drug development process, minimizes GI fluid needs, and produces in vitro solubility information with potential in vivo implications. A number of BCS II drugs were dissolved in DMSO at approximately 40 mM, and robotically distributed to a 96-well plate. The DMSO was evaporated and drugs were equilibrated with selected GI fluids, both fed and fasted states. After equilibration, precipitated wells were subjected to HPLC analysis. A spreadsheet calculated solubility automatically from HPLC output. Intra-day, inter-day, and inter-plate reproducibility were within 15% RSTD for the tested drugs with the primary source of variability being injection precision of our injector system. The reported solubility from screening assays was well correlated with literature data (r(2) = 0.80) with a slope of 0.86 and (r(2) = 0.99) with a slope of 0.89. This screening assay converts conventional solubility measurements to a 96-well format for increased throughput (>12 samples/h), reduces fluid needs, and minimizes drug consumption.

NPC1L1 and SR-BI are involved in intestinal cholesterol absorption from small-size lipid donors

In the human intestinal content after a meal, cholesterol is dispersed in a complex mixture of emulsified droplets, vesicles, mixed micelles and precipitated material. The aim of this study was to determine the contribution of the main intestinal cholesterol transporters (NPC1L1, SR-BI) to the absorption processes, using different cholesterol-solubilizing donors. Cholesterol donors prepared with different taurocholate concentrations were added to an apical medium of differentiated TC7/Caco-2 cells. As the taurocholate concentrations increased, cholesterol donor size decreased (from 712 to 7 nm in diameter), which enhanced cholesterol absorption in a dose-dependent manner (38-fold). Two transport processes were observed: (1) absorption from large donors exhibited low-capacity transport with no noticeable transporter contribution; (2) efficient cholesterol absorption occurs from small lipid donors (<or=23 nm diameter), mainly due to NPC1L1 and SR-BI involvement. In addition, bile acids significantly increased mRNA and protein expression of NPC1L1, but not of SR-BI. In conclusion, bile acids present in the intestinal lumen and the micelles enhance intestinal cholesterol transport into the cell by two different regulatory processes: by reducing the lipid donor size, so that small-size mixed micelles can more easily access brush-border membrane transporters, and by increasing the expression level of the enterocyte NPC1L1. These mechanisms could account for the important inter-individual variations observed in cholesterol intestinal absorption.

Formulation of lipid-based delivery systems for oral administration: materials, methods and strategies

Oral lipid-based drug delivery systems may include a broad range of oils, surfactants, and cosolvents. This diversity makes comparison of lipid-based formulations difficult. Although the relationship between formulation and drug absorption is understood at a conceptual level, performance in vivo cannot be predicted with confidence at present. The Lipid Formulation Classification System (LFCS) identifies the factors which are likely to affect performance in vivo. There is now a need to establish performance criteria which will facilitate in vitro-in vivo correlation studies. In this review we discuss the properties of excipients, and identify criteria for selection of excipients for lipid-based formulations. Excipients are discussed in the context of the LFCS, our existing knowledge of the fate of these materials during dispersion and digestion, and the likely consequences of their use in formulations. We outline the formulation strategies that can be used for each type of lipid formulation, and suggest a framework for the in vitro testing of each type. Finally we address the choice of lipid formulations in relation to the physicochemical properties of the drug.

Enhancing intestinal drug solubilisation using lipid-based delivery systems

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

Oral vaccination of mice with lipid-encapsulated Mycobacterium bovis BCG: anatomical sites of bacterial replication and immune activity

Lipid microencapsulation of Mycobacterium bovis bacille Calmette-Guérin (BCG) produces an oral delivery vaccine that can establish systemic cell-mediated immune reactivity and protection against aerosol mycobacterial challenge in mice. Here, we describe the lymphatic and mucosal sites of bacterial replication, and location of Mycobacterium-specific IFN-gamma-secreting cell populations, following oral vaccination of BALB/c mice. Eight weeks following a single oral dose of lipid-encapsulated BCG, viable BCG organisms were recovered from the mesenteric lymph nodes (MLN) of 11/12 mice investigated (93%). Live bacteria were also occasionally recovered from the cervical lymph nodes (17%) and Peyer's patches (8%), but not from homogenates of the lungs or spleen. Strong Mycobacterium-specific IFN-gamma production was recorded among isolated splenocytes, but not among populations of mononuclear cells derived from the MLN or lungs. Oral vaccination of mice with lipid-encapsulated BCG thus appears to promote a state of systemic immunological reactivity more akin to that observed following parenteral rather than conventional oral vaccination, despite the fact that replicating bacilli are restricted to lymphatic tissues of the alimentary tract. Possible patterns of lymphocyte sensitization and trafficking are discussed.

Direct intestinal cholesterol secretion contributes significantly to total fecal neutral sterol excretion in mice

BACKGROUND & AIMS

Hepatobiliary secretion is generally believed to be an integral step in the pathway of cholesterol excretion from the body. Here we have investigated the validity of this paradigm in mice.

METHODS

Cholesterol balance was assessed by measuring intake, excretion, and biliary output in different mouse models. Direct secretion of cholesterol from the luminal side of enterocytes was studied by perfusion of isolated segments of the small intestine in mice.

RESULTS

Cholesterol input and output measurements in different mouse models revealed that fecal neutral sterol excretion was higher than the sum of dietary cholesterol intake and biliary cholesterol secretion indicating the existence of an alternative pathway. Here we show that substantial amounts of cholesterol can be secreted directly by enterocytes. Transintestinal cholesterol secretion is a specific process observed throughout the small intestine (proximal > medial > distal). Secretion depended on the presence of a cholesterol acceptor and was strongly stimulated by bile salts and phospholipids. The capacity of the pathway was sufficient to account for the missing cholesterol in the balance studies. The contribution of this pathway to cholesterol excretion in mice is approximately twice that of the biliary pathway.

CONCLUSIONS

In mice, the intestine plays a significant role in removal of cholesterol from the body.

Monolayers (Langmuir films) behavior of multi-component systems composed of a bile acid with different sterols and with their 1:1 mixtures

Different physicochemical properties of Langmuir films (monolayers) composed of 10 mixed systems of a bile acid, deoxycholic acid (DC) with various plant sterols, such as stigmasterol (Stig), beta-sitosterol (Sito) and campesterol (Camp) and a stanol, cholestanol (Chsta) in addition to an animal sterol, cholesterol (Ch) [these sterols and Chsta are abbreviated as St] and DC with 1:1 St mixtures; (Ch+Chsta), (Ch+Stig), (Stig+Chsta), (Ch+Sito) and (Ch+Camp) on the substrate of 5M aqueous NaCl solution (pH 1.2) at 25 degrees C, were investigated in terms of mean surface area per molecule (A(m)), the partial molecular area (PMA), surface excess Gibbs energy (DeltaG((ex))), interaction parameter (I(p)) as well as activity coefficients (f(1) and f(2)) in 2-D phase of each binary (or ternary) component system and elasticity (Cs(-1)) of formed films; these were analyzed on the basis of the respective surface pressure (pi) versus A(m) isotherms as a function of mole fraction of Sts (X(st)) in the DC/St(s) mixtures at discrete surface pressures. Notable findings are: (i) all the binary component systems did form patched film type monolayers consisting of (a) DC-dominant film solubilizing a trace amount of St molecules and (b) St dominant film dissolving a small amount of DC molecules, (ii) DC in 2-D phase exhibited a transition from LE film to LC film at a constant pressure (pi(C)(1)) accompanied by compression and (iii) DeltaG((ex)) as well as I(p) was found to be greatly dependent on (a) the combinations of DC with different St species and (b) to be markedly varied by a difference in mixing ratio of DC to Sts. Compressibility (or elasticity) analyses and fluorescence microscopy images could support the above findings as well as interpretation.

Oral lipid-based formulations

Poor drug solubility remains a significant and frequently encountered problem for pharmaceutical scientists. The ability of lipid-based formulations to facilitate gastrointestinal absorption of many poorly soluble drug candidates has been thoroughly documented in the published literature. However, a considerable gap exists between our knowledge of this technology and the know-how required for its application. This commentary provides a comprehensive summary of the development, characterization, and utilization of oral lipid-based formulations, from both physicochemical and biopharmaceutical perspectives. The characteristics of currently available lipid excipients are reviewed in context of their application to the basic lipid-based formulation modalities. The fundamental concepts of in vitro and in vivo evaluation of lipid-based formulations are summarized followed by a forward-looking summary of unrealized opportunities and potential limitations to more widespread use of this technology.

Estimating drug solubility in the gastrointestinal tract

Solubilities measured in water are not always indicative of solubilities in the gastrointestinal tract. The use of aqueous solubility to predict oral drug absorption can therefore lead to very pronounced underestimates of the oral bioavailability, particularly for drugs which are poorly soluble and lipophilic. Mechanisms responsible for enhancing the luminal solubility of such drugs are discussed. Various methods for estimating intra-lumenal solubilities are presented, with emphasis on the two most widely implemented methods: determining solubility in fluids aspirated from the human gastrointestinal tract, and determining solubility in so-called biorelevant media, composed to simulate these fluids. The ability of the biorelevant media to predict solubility in human aspirates and to predict plasma profiles is illustrated with case examples.

Low dose lipid formulations: effects on gastric emptying and biliary secretion

PURPOSE

Food stimulates changes to gastrointestinal secretion and motility patterns, however, the effect of smaller quantities of lipid, such as that contained in a lipid-based drug formulation, has not been detailed. This study aimed to examine the effects of small quantities of lipid on gastric emptying and biliary secretion.

METHODS

The influence of oral administration of three lipid-based formulations and a negative control formulation on gastric emptying and biliary secretion was evaluated in 16 healthy male subjects using gamma scintigraphy, ultrasonography and duodenal aspiration.

RESULTS

Low quantities (2 g) of long chain lipid stimulated gall bladder contraction and elevated intestinal bile salt, phospholipid and cholesterol levels. Changes in gastric emptying were also evident, although these did not reach statistical significance. Administration of a similar quantity of medium chain lipid, however, had little effect on gastric emptying and gallbladder contraction and did not stimulate appreciable increases in intestinal concentrations of biliary-derived lipids.

CONCLUSIONS

The quantities of long chain lipid that might be administered in a pharmaceutical formulation stimulate gallbladder contraction and elevate intestinal levels of bile salt and phospholipid. This effect is a likely contributor to the ability of lipid based formulations to enhance the absorption of poorly water-soluble drugs.

Platycodon grandiflorum extract represses up-regulated adipocyte fatty acid binding protein triggered by a high fat feeding in obese rats

AIM: To investigate the effect of Platycodon grandi-florum extract (PGE) on lipid metabolism and FABP mRNA expression in subcutaneous adipose tissue of high fat diet-induced obese rats.

METHODS: PGE was treated to investigate the inhibitory effect on the pre-adipocyte 3T3-L1 differentiation and pancreatic lipase activity. Male Sprague-Dawley rats with an average weight of 439.03 ± 7.61 g were divided into four groups: the control groups that fed an experimental diet alone (C and H group) and PGE treatment groups that administered PGE along with a control diet or HFD at a concentration of 150 mg/kg body weight (C + PGE and H + PGE group, respectively) for 7 wk. Plasma total cholesterol (TC) and triglycerol (TG) concentrations were measured from the tail vein of rats. Adipocyte cell area was measured from subcutaneous adipose tissue and the fatty acid binding protein (FABP) mRNA expression was analyzed by northern blot analysis.

RESULTS: PGE treatment inhibited 3T3-L1 pre-adipocyte differentiation and fat accumulation, and also decreased pancreatic lipase activity. In this experiment, PGE significantly reduced plasma TC and TG concentrations as well as body weight and subcutaneous adipose tissue weight. PGE also significantly decreased the size of subcutaneous adipocytes. Furthermore, it significantly repressed the up-regulation of FABP mRNA expression induced by a high-fat feeding in subcutaneous adipose tissue.

CONCLUSION: PGE has a plasma lipid lowering-effect and anti-obesity effect in obese rats fed a high fat diet. From these results, we can suggest the possibility that PGE can be used as a food ingredient or drug component to therapeutically control obesity.

A method to evaluate capacity and efficiency of water soluble antioxidants as peroxyl radical scavengers

In this paper, we report on a method to evaluate the activity of water soluble and H-atom donor antioxidants as peroxyl radical scavengers in a micelle system reproducing the conditions occurring in the upper small intestine in humans, during digestion and absorption of lipids. This method, which overcomes some of the problems of the total radical trapping antioxidant parameter (TRAP) assays, measures the peroxyl radical trapping capacity (n) and the peroxyl radical trapping efficiency IC50(-1) of antioxidants, that is the number "n" of peroxyl radicals trapped by one molecule of the studied antioxidant and the reciprocal of the antioxidant concentration that halves the steady-state concentration of peroxyl radicals, respectively. These two fundamental parameters characterizing the radical chain breaking of many water soluble antioxidants, among which dietary polyphenols, can be obtained with relatively good precision from a single experiment, on the basis of a rigorous treatment of the kinetic data.

Morphological observations on a lipid-based drug delivery system during in vitro digestion

The in vitro digestion of a self nano-emulsifying drug delivery system (SNEDDS) was visualized by cryogenic transmission electron microscopy (Cryo-TEM). The dynamic lipolysis model, simulating the environment of the gastrointestinal tract in fasted conditions, was used for this purpose. The results revealed that micelles are present during the entire lipolysis process. Oil droplets from the self nano-emulsifying drug delivery system are transformed to spherical or elongated unilamellar vesicles as lipolysis progresses. Low numbers of bilamellar and open vesicles were detected. After 50% hydrolysis a decrease in the number of unilamellar vesicles and oil droplets was observed. Furthermore, the electrical properties of the oil droplets were investigated by measuring their zeta-potential values as a function of time. An increase (in absolute values) to the zeta-potential of the hydrolyzing SNEDDS droplets observed versus time implying (binding or incorporation) of the micelles to the surface. The current data emphasize that Cryo-TEM combined with the in vitro dynamic lipolysis model can offer useful information on the formation of the various colloid phases during in vitro digestion of lipid-based formulations. Furthermore, it can provide a better understanding of the in vivo behavior of these systems, as well the solubilization of lipophilic drug compounds, offering new insights for designing and optimizing oral lipid-based formulations and possibly predicting their in vivo behavior. Such methodology can be a useful tool for the strategic development of lipid-based formulations.

Structural Development of Self Nano Emulsifying Drug Delivery Systems (SNEDDS) During In Vitro Lipid Digestion Monitored by Small-angle X-ray Scattering

PURPOSE

To investigate the structural development of the colloid phases generated during lipolysis of a lipid-based formulation in an in vitro lipolysis model, which simulates digestion in the small intestine.

MATERIALS AND METHODS

Small-Angle X-Ray scattering (SAXS) coupled with the in vitro lipolysis model which accurately reproduces the solubilizing environment in the gastrointestinal tract and simulates gastrointestinal lipid digestion through the use of bile and pancreatic extracts. The combined method was used to follow the intermediate digestion products of a self nano emulsified drug delivery system (SNEDDS) under fasted conditions. SNEDDS is developed to facilitate the uptake of poorly soluble drugs.

RESULTS

The data revealed that a lamellar phase forms immediately after initiation of lipolysis, whereas a hexagonal phase is formed after 60 min. The change of the relative amounts of these phases clearly demonstrates that lipolysis is a dynamic process. The formation of these phases is driven by the lipase which continuously hydrolyzes triglycerides from the oil-cores of the nanoemulsion droplets into mono- and diglycerides and fatty acids. We propose that this change of the over-all composition of the intestinal fluid with increased fraction of hydrolyzed nanoemulsion induces a change in the composition and effective critical packing parameter of the amphiphilic molecules, which determines the phase behavior of the system. Control experiments (only the digestion medium) or the surfactant (Cremophor RH 40) revealed the formation of a lamellar phase demonstrating that the hexagonal phase is due to the hydrolysis of the SNEDDS formulation.

CONCLUSIONS

The current results demonstrate that SAXS measurements combined with the in vitro dynamic lipolysis model may be used to elucidate the processes encountered during the digestion of lipid-based formulations of poorly soluble drugs for oral drug delivery. Thus the combined methods may act as an efficient screening tool.

A new standardized lipolysis approach for characterization of emulsions and dispersions

A new standardized lipolysis approach is presented where the focus is on the initial rate of lipolysis. An advantage is that data obtained in this way reflect degradation before growing amounts of lipolysis products retard the process. The method can be used to rank different lipase substrates. In particular, the method can be used to obtain information about the susceptibility to degradation of various emulsions and dispersions that are used in technical applications. We present how the method is standardized to facilitate comparison of various substrates. This involves (i) lipase substrate in excess, i.e., the amount of lipase is rate limiting, and (ii) expressing rate of degradation relative to that of a reference substrate, tributyrin. Under such conditions, with the amount of lipase substrate held constant, an increase in enzymatic activity will generate a proportional increase in the lipolysis rate. This enables comparison of results obtained from different enzyme batches and corrects for day-to-day variability. Examples illustrating the potential of the method to discriminate and rank different lipase substrates with regard to enzymatic degradation are presented.

Class B type I scavenger receptor is responsible for the high affinity cholesterol binding activity of intestinal brush border membrane vesicles

Recent studies have documented the importance of Niemann-Pick C1-like 1 protein (NPC1L1), a putative physiological target of the drug ezetimibe, in mediating intestinal cholesterol absorption. However, whether NPC1L1 is the high affinity cholesterol binding protein on intestinal brush border membranes is still controversial. In this study, brush border membrane vesicles (BBMV) from wild type and NPC1L1-/- mice were isolated and assayed for micellar cholesterol binding in the presence or absence of ezetimibe. Results confirmed the loss of the high affinity component of cholesterol binding when wild type BBMV preparations were incubated with antiserum against the class B type 1 scavenger receptor (SR-BI) in the reaction mixture similar to previous studies. Subsequently, second order binding of cholesterol was observed with BBMV from wild type and NPC1L1-/- mice. The inclusion of ezetimibe in these in vitro reaction assays resulted in the loss of the high affinity component of cholesterol interaction. Surprisingly, BBMVs from NPC1L1-/- mice maintained active binding of cholesterol. These results documented that SR-BI, not NPC1L1, is the major protein responsible for the initial high affinity cholesterol ligand binding process in the cholesterol absorption pathway. Additionally, ezetimibe may inhibit BBM cholesterol binding through targets such as SR-BI in addition to its inhibition of NPC1L1.

Lipids and lipid-based formulations: optimizing the oral delivery of lipophilic drugs

Highly potent, but poorly water-soluble, drug candidates are common outcomes of contemporary drug discovery programmes and present a number of challenges to drug development - most notably, the issue of reduced systemic exposure after oral administration. However, it is increasingly apparent that formulations containing natural and/or synthetic lipids present a viable means for enhancing the oral bioavailability of some poorly water-soluble, highly lipophilic drugs. This Review details the mechanisms by which lipids and lipidic excipients affect the oral absorption of lipophilic drugs and provides a perspective on the possible future applications of lipid-based delivery systems. Particular emphasis has been placed on the capacity of lipids to enhance drug solubilization in the intestinal milieu, recruit intestinal lymphatic drug transport (and thereby reduce first-pass drug metabolism) and alter enterocyte-based drug transport and disposition.

Supplementation of test meals with fat-free phytosterol products can reduce cholesterol micellarization during simulated digestion and cholesterol accumulation by Caco-2 cells

Phytosterols have been shown to reduce cholesterol absorption in humans. Supplementing phytosterols in fat-free formulations, however, has yielded controversial results. In the present study, we investigated the effect of supplementing test meals with different fat-free phytosterol products on cholesterol incorporation into mixed micelles during simulated digestion and accumulation of micellar cholesterol by Caco-2 cells: control orange juice (OJ), orange juice supplemented with either multivitamin/multimineral tablets (MVT), multivitamin/multimineral tablets containing phytosterols (MVT+P), and phytosterol powder (PP). These combinations were added to Ensure-based test meals and spiked with cholesterol of natural isotopic composition or 13C2-cholesterol to differentiate external from endogenous cholesterol. After simulated gastric/small intestinal digestion, micelle fractions were analyzed for cholesterol enzymatically (n = 6-20/product) and by high-performance liquid chromatography-tandem mass spectrometry (n = 12/product) and added to Caco-2 cells to determine the accumulation of 13C2-cholesterol (n = 10-24/product). As compared to OJ, PP and MVT+P significantly decreased cholesterol micellarization (determined enzymatically) by 70 +/- 39 (mean +/- SD) and 70 +/- 39%, respectively (P < 0.001, Bonferroni). The stable isotope experiments revealed that both PP and MVT+P reduced cholesterol micellarization [by 25 +/- 12 (P = 0.055) and 21 +/- 8% (P = 0.020), respectively, Fisher's protected LSD test] and Caco-2 cell accumulation (by 28 +/- 8 and 10 +/- 8%, respectively; P < 0.010, Bonferroni). OJ+P did not inhibit micellarization or accumulation of cholesterol by Caco-2 cells. This study shows that fat-free phytosterol-containing products can significantly inhibit cholesterol micellarization and Caco-2 cell bioaccessibility, albeit to different extents depending on individual formulations. This is most likely explained by inhibition of cholesterol micellarization.

Biliary secretion of rosuvastatin and bile acids in humans during the absorption phase

AIM

The aim of this study was to investigate the biliary secretion of rosuvastatin in healthy volunteers using an intestinal perfusion method after administration of 10mg rosuvastatin dispersion in the intestine.

METHODS

The Loc-I-Gut tube was positioned in the distal duodenum/proximal jejunum and a semi-open segment was created by inflating the proximal balloon in ten volunteers. A dispersion of 10mg rosuvastatin was administered below the inflated balloon and bile was collected proximally of the inflated balloon. Bile and plasma samples were withdrawn every 20 min during a 4h period (absorption phase) and additional plasma samples were collected 24 and 48 h post-dose.

RESULTS

The study showed that there is a substantial and immediate transport of rosuvastatin into the human bile, with the maximum concentration appearing 42 min after dosing, 39,000+/-31,000 ng/ml. Approximately 11% of the administered intestinal dose was recovered in the bile after 240 min. At all time points the biliary concentration exceeded the plasma concentration, and the average bile to plasma ratio was 5200+/-9200 (range 89-33,900, median 2000). We were unable to identify any bile-specific metabolites of rosuvastatin in the present study.

CONCLUSION

Rosuvastatin is excreted via the biliary route in humans, and the transport and accumulation of rosuvastatin in bile compared to that in plasma is rapid and extensive. This intestinal perfusion technique offers a successful way to estimate the biliary secretion for drugs, metabolites and endogenous substances during the absorption phase in healthy volunteers.

Monitoring of in vitro fat digestion by electron paramagnetic resonance spectroscopy

PURPOSE

The distribution of drugs between water, oil and mixed micelles after the oral application of lipid-based drug delivery systems affects their absorption rate. Since it has not been previously possible to monitor this process online during in vitro lipolysis, it was our aim to develop a suitable real-time method.

MATERIALS AND METHODS

To follow the fate of a co-administered drug during fat digestion, the spin probe tempol benzoate was incorporated as a lipophilic model drug into a long-chain triglyceride (olive oil) and an in vitro digestion test was combined with electron paramagnetic resonance (EPR) spectroscopy (X-Band). Additionally the progression of digestion was determined by means of high performance thin layer chromatography (HPTLC).

RESULTS

The spectral shape of the EPR spectrum changed significantly during the digestion process. EPR spectra at all times could be simulated with three species indicating a redistribution of the lipophilic model drug between olive oil, phosphate buffer and mixed micelles formed by bile salts and phospholipids.

CONCLUSION

This in vitro real-time analysis could be a very helpful tool to monitor the digestibility of novel lipid-based drug nanocarriers which is an important step to optimize and to predict drug delivery processes. In future the EPR monitoring of fat digestion will be transferred to in vivo experiments.

Micellar oleic and eicosapentaenoic acid but not linoleic acid influences the β-carotene uptake and its cleavage into retinol in rats

Improving the bioavailability of beta-carotene is vital to manage vitamin A deficiency. The influence of micellar oleic (OA), linoleic (LA) and eicosapentaenoic (EPA) acids on plasma beta-carotene response and its conversion to retinol has been studied in rats employing single (9 h time course) and repeated (10 days) dose administrations. After a single dose, the levels (area under the curve) of plasma beta-carotene and retinyl palmitate in OA and EPA groups were higher (p < 0.05) by 13, 7 and 11, 6 folds than LA group. The liver beta-carotene level in OA and EPA groups were higher (p < 0.05) by 3 and 1.2 folds than LA group. After repeated dose, the plasma beta-carotene and retinyl palmitate levels in OA (6.2%, 51.7%) and EPA (25.4%, 17.23%) groups were higher (p < 0.05) than LA group. The liver beta-carotene level in OA (21.2%) and EPA (17.6%) groups were higher (p < 0.05) than LA group. In both the experiments, the activity of beta-carotene 15,15'-dioxygenase in the intestinal mucosa and plasma triglyceride levels were also higher in OA and EPA groups than LA group. beta-Carotene excreted through urine and feces of OA and EPA groups was lower than the LA group. These results demonstrate an improved absorption and metabolism of beta-carotene when fed mixed micelles with OA or EPA compared with LA. Although the mechanism involved in selective absorption of fatty acids needs further studies, intestinal beta-carotene uptake and its conversion to vitamin A can be modulated using specific fatty acids.

Effects of chenodeoxycholic acid and deoxycholic acid on cholesterol absorption and metabolism in humans

Quantitative and qualitative differences in intralumenal bile acids may affect cholesterol absorption and metabolism. To test this hypothesis, 2 cross-over outpatient studies were conducted in adults with apo-A IV 1/1 or apo-E 3/3 genotypes. Study 1 included 11 subjects 24 to 37 years of age, taking 15 mg/kg/day chenodeoxycholic acid (CDCA) or no bile acid for 20 days while being fed a controlled diet. Study 2 included 9 adults 25 to 38 years of age, taking 15 mg/kg/day deoxycholic acid (DCA) or no bile acid, following the same experimental design and procedures as study 1. CDCA had no effect on plasma lipid concentrations, whereas DCA decreased (P < 0.05) plasma high-density lipoprotein (HDL)-cholesterol and tended to decrease (P = 0.15) low-density lipoprotein (LDL)-cholesterol. CDCA treatment enriched (P < 0.0001) bile with CDCA and increased cholesterol concentration in micelles, whereas meal-stimulated bile acid concentrations were decreased. DCA treatment enriched (P < 0.0001) bile with DCA and tended to increase intralumenal cholesterol solubilized in micelles (P = 0.06). No changes were found in cholesterol absorption, free cholesterol fractional synthetic rate (FSR), or 3-hydroxy-3 methylglutaryl (HMG) CoA reductase and LDL receptor messenger ribonucleic acid (mRNA) levels after CDCA treatment. DCA supplementation tended to decrease cholesterol absorption and reciprocally increase FSR and HMG CoA reductase and LDL receptor mRNA levels. Results of these 2 studies suggest that the solubilization of cholesterol in the intestinal micelles is not a rate-limiting step for its absorption.

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

PURPOSE

To investigate the gastrointestinal secretory and enzymatic responses to a liquid meal during in vivo perfusion of the proximal human jejunum.

METHODS

Human intestinal fluid was collected from the proximal jejunum by single-pass in vivo perfusion (Loc-I-Gut). The fluid was quantitatively collected at 10-min intervals during 90 min while perfusing a nutritional drink at 2 mL/min. Quantification of lipids in the fluid leaving the segment was performed by using novel chromatographic methods.

RESULTS

The overall bile acid concentration varied between 0.5 and 8.6 mM with a peak level 40 min after the start of the liquid meal perfusion. The total concentration of phospholipids was between 0.1 and 3.9 mM and there was a rapid degradation of phosphatidylcholine to lysophosphatidylcholine. The tri-, di-, monoglycerides and free fatty acid levels increased sharply in the beginning and reached steady-state levels between 7 and 9.5 mM.

CONCLUSIONS

There is a rapid secretion of bile in response to food. Most of the dietary lipids are found in the form of their degradation products in vivo in human jejunum. This novel in vivo characterization, based on direct and high-recovery sampling of intestinal fluids, forms a basis for further development of improved in vitro drug dissolution test media.

Indomethacin disrupts the protective effect of phosphatidylcholine against bile salt-induced ileal mucosa injury

BACKGROUND

Indomethacin (Indo) exerts local toxic effects on small intestinal mucosa, possibly in association with hydrophobic bile salts. We investigated the potential toxic effects of Indo on ileal mucosa and the role of phosphatidylcholine (PC).

MATERIALS AND METHODS

Transmucosal resistance and Na-fluorescein permeability of ileal mucosa segments from female Wistar rats were determined in Ussing chambers during a 30-min incubation with model systems containing: control-buffer, taurodeoxycholate (TDC), Indo, TDC-Indo, TDC-PC, or TDC-PC-Indo. Decrease of resistance and increase of permeability were considered as parameters for mucosal injury. After incubation in Ussing chambers, the histopathology was examined to quantify the extent of mucosal injury. Also, in CaCo-2 cells, LDH-release was determined as a measure of cytotoxicity, after incubation with various model systems.

RESULTS

Decrease of resistance and increase of permeability were highest in systems containing TDC-Indo (P < 0.01). Phosphatidylcholine protected against the cytotoxic effects of TDC in absence of Indo only. Extent of mucosal injury by histological examination was also highest in systems containing TDC-Indo (P = 0.006). Again, PC exhibited protective effects in absence of Indo only. The LDH-release by CaCo2-cells was strongest in TDC-Indo systems (P < 0.001).

CONCLUSIONS

Indomethacin disrupts protective effects of PC against bile salt-induced ileal mucosa injury. This finding is relevant for small intestinal injury induced by non-steroidal anti-inflammatory drugs.

Pancreatic lipase and pancreatic lipase-related protein 2, but not pancreatic lipase-related protein 1, hydrolyze retinyl palmitate in physiological conditions

The major sources of vitamin A in the human diet are retinyl esters (mainly retinyl palmitate) and provitamin A carotenoids. It has been shown that classical pancreatic lipase (PL) is involved in the luminal hydrolysis of retinyl palmitate (RP), but it is not known whether pancreatic lipase-related proteins 1 (PLRP1) and 2 (PLRP2), two other lipases recovered in the human pancreatic juice, are also involved. The aim of this study was to assess whether RP acts a substrate for these lipase-related proteins. Pure horse PL, horse PLRP2 and dog PLRP1 were incubated with RP solubilized in its physiological vehicles, i.e., triglyceride-rich lipid droplets, mixed micelles and vesicles. High performance liquid chromatography (HPLC) was used to assess RP hydrolysis by the free retinol released in the incubation medium. Incubation of RP-containing emulsions with horse PL and colipase resulted in RP hydrolysis (0.051+/-0.01 micromol/min/mg). This hydrolysis was abolished when colipase was not added to the medium. PLRP2 and PLRP1 were unable to hydrolyze RP solubilized in emulsions, regardless of whether colipase was added to the medium. PL hydrolyzed RP solubilized in mixed micelles as well (0.074+/-0.014 micromol/min/mg). Again, this hydrolysis was abolished in the absence of colipase. PLRP2 hydrolyzed RP solubilized in micelles but less efficiently than PL (0.023+/-0.005 micromol/min/mg). Colipase had no effect on this hydrolysis. PLRP1 was unable to hydrolyze RP solubilized in micelles, regardless of whether colipase was present or absent. Both PL and PLRP2 hydrolyzed RP solubilized in a vesicle rich-solution, and a synergic phenomenon between the two lipases was enlighten. Taken together, these results show that (1) PL hydrolyzes RP whether RP is solubilized in emulsions or in mixed micelles, (2) PLRP2 hydrolyzes RP only when RP is solubilized in mixed micelles, and (3) PLRP1 is unable to hydrolyze RP regardless of whether RP is solubilized in emulsions or in mixed micelles.

Enhanced lutein bioavailability by lyso-phosphatidylcholine in rats

The bioavailability of lutein solubilized in mixed micelles containing either phosphatidylcholine (PC) or lysophosphatidylcholine (lysoPC) was evaluated in male rats. Mixed micelles contained 2.5 mM monooleoylglycerol, 7.5 mM oleic acid, 12 mM sodium taurocholate and 200 microM lutein either with 3 mM PC or lysoPC. To study lutein bioavailability, single and repeated dose experiments were conducted. For single dose study, group of rats (n = 30/group) were fed single dose of lutein solubilized in lysoPC (LPC group), PC (PC group) and no phospholipids (NoPL group) in micellar form. Each group was further divided in to five sub-groups (n = 6/sub group) to measure lutein bioavailability over time up to 9 h. For repeated dose study, group of rats (n = 6/group) were fed daily for 10 days a dose of lutein in mixed micelles with NoPL, PC and LPC. A separate group (n = 6) not fed mixed micelles was considered as zero-time control. In both the experiments, mixed micelles (0.2 ml/rat) were fed to the rat by direct intubation to the stomach. Results of single dose studies showed that the mean lutein levels in the plasma and liver of the PC group was significantly lower (p < 0.05) than those of the other two groups. Moreover, the average lutein level in the plasma and liver was significantly (p < 0.05) different among the groups in the order LPC > NoPL > PC. But, repeated dose experiment followed the order LPC > PC > NoPL. The level of lutein excreted through urine and feces of PC group was significantly higher (p < 0.05) than those of the other two groups. Thus, the results indicate that the PC in the mixed micelles suppressed the intestinal uptake of lutein after single dose but not after repeated dose and that lysoPC enhanced the absorption. In both the experiments, plasma and liver level of lutein was higher in LPC compared with PC group. Results also suggest that the luminal hydrolysis of PC to lysoPC is necessary for intestinal uptake of lutein solubilized in mixed micelles.

Development of supersaturatable self-emulsifying drug delivery system formulations for improving the oral absorption of poorly soluble drugs

The supersaturatable self-emulsifying drug delivery system (S-SEDDS) represents a new thermodynamically stable formulation approach wherein it is designed to contain a reduced amount of a surfactant and a water-soluble cellulosic polymer (or other polymers) to prevent precipitation of the drug by generating and maintaining a supersaturated state in vivo. The S-SEDDS formulations can result in enhanced oral absorption as compared with the related self-emulsifying drug delivery systems (SEDDS) formulation and the reduced surfactant levels may minimise gastrointestinal surfactant side effects.

Oral delivery of lipid-encapsulated Mycobacterium bovis BCG extends survival of the bacillus in vivo and induces a long-term protective immune response against tuberculosis

The success of oral-route vaccination using Mycobacterium bovis bacille Calmette-Guérin (BCG) relies on delivery of live, actively metabolising bacilli to confer protection. Here, we describe that lipid-microencapsulation can extend the in vivo survival of bacilli when fed to mice, and can induce a long-lasting protective immune response. Feeding mice with lipid-encapsulated BCG (L-BCG) resulted in greater recovery of viable BCG bacilli from the mesenteric lymph nodes (MLN) compared to mice fed non-encapsulated BCG. A time-course study indicated persistence of viable BCG bacilli in MLN up to 30 weeks post-vaccination, similar to the duration of viable BCG recovery from the spleen following subcutaneous vaccination. The persistence of viable bacilli in the MLN of L-BCG mice invoked long-lasting systemic cell-mediated immune reactivity, with responses similar to those observed in subcutaneously-vaccinated mice. Further, L-BCG-vaccinated mice showed a high degree of protection against aerogenic challenge with virulent M. bovis at 30 weeks post-vaccination, with significant reductions in lung and spleen pathogen burdens. This study identifies that lipid-encapsulation of live BCG bacilli can facilitate increased in vivo survival and immunogenicity of the vaccine in orally-vaccinated mice, and highlights protection via this route for up to 7 months post-immunisation.

The effects of food on the dissolution of poorly soluble drugs in human and in model small intestinal fluids

PURPOSE

This study was conducted to determine the effect of food on drug solubility and dissolution rate in simulated and real human intestinal fluids (HIF).

METHODS

Dissolution rate obtained via the rotating disk method and saturation solubility studies were carried out in fed and fasted state HIF, fed dog (DIF), and simulated (FeSSIF) intestinal fluid for six aprotic low solubility drugs. The intestinal fluids were characterized with respect to physical-chemical characteristics and contents.

RESULTS

Fed HIF provided a 3.5- to 30-times higher solubility compared to fasted HIF and FeSSIF, whereas fed DIF corresponded well (difference of less than 30%) to fed HIF. The increased solubility of food could mainly be attributed to dietary lipids and bile acids. The dissolution rate was also 2 to 7 times higher in fed HIF than fasted HIF. This was well predicted by both DIF and FeSSIF (difference of less than 30%).

CONCLUSIONS

Intestinal solubility is higher in fed state compared to fasted state. However, the dissolution rate does not increase to the same extent. Dog seems to be a good model for man with respect to dissolution in the small intestine after intake of a meal, whereas FeSSIF is a poorer means of determining intestinal saturation solubility in the fed state.

Mechanisms of digestion and absorption of dietary vitamin A

Mechanisms involved in the digestion and absorption of dietary vitamin A require the participation of several proteins. Dietary retinyl esters are hydrolyzed in the intestine by the pancreatic enzyme, pancreatic triglyceride lipase, and intestinal brush border enzyme, phospholipase B. Unesterified retinol taken up by the enterocyte is complexed with cellular retinol-binding protein type 2 and the complex serves as a substrate for reesterification of the retinol by the enzyme lecithin:retinol acyltransferase (LRAT). The retinyl esters are then incorporated into chylomicrons, intestinal lipoproteins containing other dietary lipids, such as triglycerides, phospholipids, and free and esterified cholesterol, and apolipoprotein B. Chylomicrons containing newly absorbed retinyl esters are then secreted into the lymph. Although under normal dietary conditions much of the dietary vitamin A is absorbed via the chylomicron/lymphatic route, it is also clear that under some circumstances there is substantial absorption of unesterified retinol via the portal route. Evidence supports the idea that the cellular uptake and efflux of unesterified retinol by enterocytes is mediated by lipid transporters, but the exact number, identity, and role of these proteins is not known and is an active area of research.

Uptake of micellar long-chain fatty acid and sn-2-monoacylglycerol into human intestinal Caco-2 cells exhibits characteristics of protein-mediated transport

Long-chain fatty acid and sn-2-monoacylglycerol (2-MG) are the digestive products of dietary triacylglycerol (TG) hydrolysis. Although fatty acid uptake into the enterocyte has been examined widely, less is known about 2-MG uptake, and few studies have mimicked the physiologic conditions present in the postprandial situation. In this study, the cellular uptake of oleic acid and 2-monoolein, presented in taurocholate micellar solution, was examined in human intestinal Caco-2 cells to model the postprandial intestinal milieu. Initial uptake of oleic acid and 2-MG displayed a saturable function of their monomer concentrations, suggesting that fatty acid and 2-MG uptake may be protein-mediated processes at low unbound concentrations of lipid. The initial rate of oleate uptake was faster and the apparent Km was lower than values for 2-MG. Unlabeled oleic acid and, to a lesser extent, unlabeled 2-MG, inhibited the uptakes of both [3H]oleic acid and [3H]2-monoolein, suggesting competitive uptake. The nonphysiologic isomer sn-1-MG had effects similar to 2-MG, whereas the intermediate digestive product, diacylglycerol (DG), did not inhibit either oleate or 2-monoolein uptake. These results suggest that in the postprandial state, fatty acid and 2-MG derived from dietary TG are transported into the enterocyte, at least in part, via a protein-mediated pathway that is shared by both lipids, but not by the intermediate digestive product, DG.

Molecular mechanisms of cholesterol absorption and transport in the intestine

Many enzymes and transport proteins participate in cholesterol absorption. This review summarizes recent results on several proteins that are important for each step of the cholesterol absorption pathway, including the important roles of: (i) pancreatic triglyceride lipase (PTL), carboxyl ester lipase (CEL), and ileal bile acid transporter in determining the rate of cholesterol absorption; (ii) ATP binding cassette (ABC) transporters and the Niemann-Pick C-1 like-1 (NPC1L1) protein as intestinal membrane gatekeepers for cholesterol efflux and influx; and (iii) intracellular membrane vesicles and transport proteins in lipid trafficking through intracellular compartments prior to lipoprotein assembly and secretion to plasma circulation.

In vivo in vitro correlations for a poorly soluble drug, danazol, using the flow-through dissolution method with biorelevant dissolution media

The purpose of the study was to design dissolution tests that were able to distinguish between the behaviour of danazol under fasted and fed conditions, by using biorelevant media. In vitro dissolution of 100mg danazol capsules was performed using the flow-through dissolution method. Flow rates were 8, 16 or 32 ml/min, corresponding to total volumes dissolution medium of 960, 1920 and 3840 ml, respectively. The media used contained bile salt and phospholipid levels relevant for either fasted or fed conditions in vivo. Crude and inexpensive bile components, Porcine Bile Extract and soybean phospholipids, were used as the bile source. The effect of adding different concentrations and molar ratios of monoglycerides and fatty acids to the fed state media was investigated. In vivo release profiles under fasted and fed conditions were obtained from a previous study by deconvolution [Sunesen, V.H., Vedelsdal, R., Kristensen, H.G., Christrup, L., Müllertz, A. 2005. Effect of liquid volume and food intake on the absolute bioavailability of danazol, a poorly soluble drug, Eur. J. Pharm. Sci. 24, 297-303]. In the fasted state, the physiologically most relevant correlation with in vivo results was achieved with a medium containing 6.3 mM bile salts and 1.25 mM phospholipids (8 ml/min). A medium containing 18.8 mM bile salts, 3.75 mM phospholipids, 4.0 mM monoglycerides and 30 mM fatty acids (8 ml/min) gave the closest correlation with fed state in vivo results. By using the flow-through dissolution method it was possible to obtain correlations with in vivo release of danazol under fasted and fed conditions. Both hydrodynamics and medium composition were important for the dissolution of danazol. In the fed state an IVIVC could only be obtained by including monoglycerides and fatty acids in the medium.

Anti-obese action of raspberry ketone

Raspberry ketone (4-(4-hydroxyphenyl) butan-2-one; RK) is a major aromatic compound of red raspberry (Rubus idaeus). The structure of RK is similar to the structures of capsaicin and synephrine, compounds known to exert anti-obese actions and alter the lipid metabolism. The present study was performed to clarify whether RK helps prevent obesity and activate lipid metabolism in rodents. To test the effect on obesity, our group designed the following in vivo experiments: 1) mice were fed a high-fat diet including 0.5, 1, or 2% of RK for 10 weeks; 2) mice were given a high-fat diet for 6 weeks and subsequently fed the same high-fat diet containing 1% RK for the next 5 weeks. RK prevented the high-fat-diet-induced elevations in body weight and the weights of the liver and visceral adipose tissues (epididymal, retroperitoneal, and mesenteric). RK also decreased these weights and hepatic triacylglycerol content after they had been increased by a high-fat diet. RK significantly increased norepinephrine-induced lipolysis associated with the translocation of hormone-sensitive lipase from the cytosol to lipid droplets in rat epididymal fat cells. In conclusion, RK prevents and improves obesity and fatty liver. These effects appear to stem from the action of RK in altering the lipid metabolism, or more specifically, in increasing norepinephrine-induced lipolysis in white adipocytes.

Effect of phytosterols and phytostanols on the solubilization of cholesterol by dietary mixed micelles: an in vitro study

The effect of a plant sterol, beta-sitosterol (SI), and a plant stanol, sitostanol (SS), on the solubilization of cholesterol (CH) by model dietary mixed micelles was examined under in vitro conditions with the use of gas chromatography, isothermal titration calorimetry, NMR spectroscopy and cryogenic transmission electron microscopy techniques. Free SI and SS were shown to reduce the concentration of CH in dietary mixed micelles via a dynamic competition mechanism. CH, SI and SS affect the microstructure of lipid vesicles and influence the process of amphiphilic self-assembly of nutrients in the gut with the formation of dietary mixed micelles in a similar manner. Therefore, substitution of CH by phytosterols and phytostanols in the diet does not lead to the notable changes in the mechanism of dietary mixed micelle formation and does not affect the process of the intestinal transport of nutrients and drugs via the micellar diffusion mechanism. Our experimental findings demonstrate that the introduction of plant sterols and plant stanols into the diet is clearly beneficial for the reduction of the intestinal uptake of cholesterol. Due to the limited capacity of dietary mixed micelles to embody hydrophobic sterol/stanol molecules, the micellar concentration of cholesterol is reduced and hence, its transport towards the intestinal brush border membrane decreases.