Evidence of luminal phosphatidylcholine secretion in rat ileum

Gastrointestinal diseases and their impact on drug solubility: Ulcerative Colitis

For poorly soluble compounds, drug product performance in patients with Ulcerative Colitis (UC) compared to healthy subjects can be affected due to differences in drug solubility in GI fluids. A risk assessment tool was developed to identify compounds with a high risk of altered solubility in the GI fluids of UC patients. Pathophysiological changes impacting on the composition of GI fluids in UC patients were considered and UC biorelevant media representative of the stomach, intestine and colon were developed based on biorelevant media based on healthy subjects and literature data using a Design of Experiment approach. The UC media were characterised and revealed differences in surface tension, osmolality and buffer capacity compared to media based on healthy subjects. The solubility of six drugs was investigated in UC biorelevant media and results were related to media- and drug-dependent factors. A lower drug solubility in UC intestinal media was observed for compounds with a high lipophilicity. In UC simulated colonic fluids, drug solubility was altered for ionisable compounds. Additionally, a higher solubility of neutral lipophilic drugs was observed in UC fasted state colonic media with increased concentrations of soluble proteins. The developed UC biorelevant media offer the possibility to identify the risk of altered drug solubilisation in UC patients without conducting expensive clinical trials. A high risk was related to drug ionization properties and lipophilicity in the current study with all investigated drugs showing differences in solubility in biorelevant media based on UC patients compared to healthy subjects.

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.

Nonclassical Interactions of Phosphatidylcholine with Mucin Protect Intestinal Surfaces: A Microinterferometry Study

Albeit many studies demonstrated that the accumulation of phospholipids in the intestinal mucosal surfaces is essential for the protection of colon epithelia against pathogenic bacteria, the mechanism of interactions between phospholipids and the surface protein mucin is not well understood. In this study, the significance of interfacial interactions between phospholipids and mucin proteins was quantified by the combination of an in vitro intestinal surface model and label-free microinterferometry. The model of intestinal surfaces consists of planar lipid membranes deposited on solid substrates (supported membranes) that display mucin proteins at defined surface densities. Following the quantitative characterization of the systems, we monitored the vertical fluctuation of 10 μm-large particles on model intestinal surfaces by using microinterferometry, and calculated the effective interfacial interaction potentials by analytically solving the Langevin equation. We found that the spring constant of interfacial potentials calculated based on a harmonic approximation increased concomitantly with the increase in surface potentials, indicating the dominant role of electrostatic interactions. Intriguingly, the spring constants of particles coated with phospholipids do not follow electrostatic interactions. The spring constant of particles coated with zwitterionic phosphatidylcholine was larger compared to membranes incorporating positively or negatively charged lipids. Our data suggested the presence of another underlying molecular level interaction, such as phosphocholine-saccharide interactions. The fact that phosphatidylcholine sustains the binding capability to enzymatically degraded mucin suggests that the direct delivery of phosphatidylcholine to the damaged mucus is a promising strategy for the better treatment of patients affected by inflammatory bowel diseases.

The Detergent Effect of Mesalazine Interferes with Phosphatidylcholine Binding to Mucin 2

Objectives

Therapeutically applied delayed-release phosphatidylcholine (PC) revealed mucosa protection and clinical improvement of ulcerative colitis. However, a recent trial with simultaneous application of delayed-release PC and mesalazine showed lack of efficacy. It is hypothesized that mesalazine acts as detergent to prohibit PC integration into mucus as target compartment, thus preventing topical mucus protection.

Methods

In vitro PC-binding studies with mucin 2 and intestinally differentiated CaCo2 cells as well as outcome analysis of a therapeutic trial with delayed-release PC and additional mesalazine.

Results

Choline-containing phospholipids, in particular PC, bind to mucin 2 as main scaffold protein of intestinal mucus to establish a hydrophobic barrier towards microbiota in the intestinal lumen. PC also binds to the apical surface of polarized CaCo2 cells with membrane-anchored mucin 3. Mesalazine removes mucin-bound PC and, thus, reduces transepithelial resistance. A post hoc analysis of patients from a previous multicenter phase IIB trial with delayed-release PC revealed that those without mesalazine showed a PC dose-dependent outcome with regard to achievement of partial and complete remission (p < 0.05 for 1.6 and 3.2 g PC daily) whereas those treated simultaneously with mesalazine showed no PC dose dependency.

Conclusion

Mesalazine solubilizes PC and, thus, prevents the protective action of therapeutically applied delayed-release PC within mucus.

Phospholipase A2 of Microbiota as Pathogenetic Determinant to Induce Inflammatory States in Ulcerative Colitis: Therapeutic Implications of Phospholipase A2 Inhibitors

Background

Attack by commensal microbiota is one component of induction of inflammatory episodes in ulcerative colitis (UC). In UC, the mucus layer is intrinsically devoid of phosphatidylcholine (PC) resulting in low hydrophobicity which facilitates bacterial invasion. Colonic ectophospholipase-carrying bacterial strains are likely candidates to further thinning the PC mucus barrier and to precipitate inflammatory episodes.

Objective

To evaluate the effect of phospholipase A₂ (PLA₂) inhibitors on inflammation in a genetic UC mouse model.

Methods

As PLA₂ inhibitor, we applied the bile acid-phospholipid conjugate ursodeoxycholate-lysophosphatidylethanolamide (UDCA-LPE) or as control 5% Tween 80 by oral gavage to intestine-specific kindlin 2 knockout mice.

Results

Luminal UDCA-LPE reduced the PLA₂ activity in stool by 36 ± 8%. Concomitantly no inflammatory phenotype was observed when compared to kindlin 2^(-/-) mice not treated with UDCA-LPE. The improvement was documented in regard to stool consistency, calprotectin levels in stool, and macroscopic/endoscopic as well as histologic features of the mucosa. The pattern of colonic microbiota distribution obtained in the UC phenotype mice was reversed by UDCA-LPE to the control mice pattern.

Conclusion

The inhibition of the bacterial ectophospholipase A₂ activity improves mucosal inflammation in a genetic mouse model of UC. It is assumed that the remaining mucus PC shield is better preserved when luminal PLA₂ is suppressed.

Genetic Mouse Models with Intestinal-Specific Tight Junction Deletion Resemble an Ulcerative Colitis Phenotype

BACKGROUND AND AIMS

A key pathogenetic feature of ulcerative colitis [UC] is an intrinsic low mucus phosphatidylcholine[PC] content. Recently, a paracellular transport for PC across tight junctions[TJs] was described, suggesting TJ disturbance as a cause of diminished luminal PC transport. Therefore, we aimed to generate mutant mice with TJ deletion to evaluate whether a UC phenotype developed.

METHODS

CL57BL/6 control wild-type mice were compared to mutant mice with tamoxifen-induced villin-Cre-dependent intestinal deletion of kindlin 1 and 2.

RESULTS

Electron microscopy of mucosal biopsies obtained from both mutants before overt inflammation following only 2 days of tamoxifen exposure revealed a defective TJ morphology with extended paracellular space and, by light microscopy, expanded mucosal crypt lumina. PC secretion into mucus was reduced by >65% and the mucus PC content dropped by >50%, causing a >50 % decrease of mucus hydrophobicity in both mutants. Consequently, the microbiota was able to penetrate the submucosa. After 3 days of tamoxifen exposure, intestinal inflammation was present in both mutants, with loose bloody stools as well as macroscopic and histological features of colitis. Oral PC supplementation was able to suppress inflammation. By analogy, colonic biopsies obtained from patients with UC in remission also showed a defective epithelium with widened intercellular clefts, and enlarged crypt luminal diameters with functionally impaired luminal PC secretion.

CONCLUSIONS

Genetic mouse models with intestinal deletion of kindlin 1 and 2 resulted in TJ deletion and revealed pathophysiological features of impaired PC secretion to the mucus leading to mucosal inflammation compatible with human UC.

Phosphatidylcholine passes through lateral tight junctions for paracellular transport to the apical side of the polarized intestinal tumor cell-line CaCo2

Phosphatidylcholine (PC) is the most abundant phospholipid in intestinal mucus, indicative of a specific transport system across the mucosal epithelium to the intestinal lumen. To elucidate this transport mechanism, we employed a transwell tissue culture system with polarized CaCo2 cells. It was shown that PC could not substantially be internalized by the cells. However, after basal application of increasing PC concentrations, an apical transport of 47.1±6.3nmolh(-1)mMPC(-1) was observed. Equilibrium distribution studies with PC applied in equal concentrations to the basal and apical compartments showed a 1.5-fold accumulation on the expense of basal PC. Disruption of tight junctions (TJ) by acetaldehyde or PPARγ inhibitors or by treatment with siRNA to TJ proteins suppressed paracellular transport by at least 50%. Transport was specific for the choline containing the phospholipids PC, lysoPC and sphingomyelin. We showed that translocation is driven by an electrochemical gradient generated by apical accumulation of Cl(-) and HCO3(-) through CFTR. Pretreatment with siRNA to mucin 3 which anchors in the apical plasma membrane of mucosal cells inhibited the final step of luminal PC secretion. PC accumulates in intestinal mucus using a paracellular, apically directed transport route across TJs.

Therapeutic Potential to Modify the Mucus Barrier in Inflammatory Bowel Disease. Nutrients. 2016;8. [PMID: 26784223 PMCID: PMC4728657 DOI: 10.3390/nu8010044]

Recently, numerous studies have shown that disruption of the mucus barrier plays an important role in the exacerbation of inflammatory bowel disease, particularly in ulcerative colitis. Alterations in the mucus barrier are well supported by published data and are widely accepted. The use of fluorescence in situ hybridization and Carnoy’s fixation has revealed the importance of the mucus barrier in maintaining a mutualistic relationship between host and bacteria. Studies have raised the possibility that modulation of the mucus barrier may provide therapies for the disease, using agents such as short-chain fatty acids, prebiotics and probiotics. This review describes changes in the mucus barrier of patients with inflammatory bowel disease and in animal models of the disease. We also review the involvement of the mucus barrier in the exacerbation of the disease and explore the therapeutic potential of modifying the mucus barrier with short-chain fatty acids, prebiotics, probiotics, fatty acid synthase, H₂S, neutrophil elastase inhibitor and phophatidyl choline.

Inducing effect of clofibric acid on stearoyl-CoA desaturase in intestinal mucosa of rats

Fibrates have been reported to elevate the hepatic proportion of oleic acid (18:1n-9) through inducing stearoyl-CoA desaturase (SCD). Despite abundant studies on the regulation of SCD in the liver, little is known about this issue in the small intestine. The present study aimed to investigate the effect of clofibric acid on the fatty acid profile, particularly monounsaturated fatty acids (MUFA), and the SCD expression in intestinal mucosa. Treatment of rats with a diet containing 0.5% (w/w) clofibric acid for 7 days changed the MUFA profile of total lipids in intestinal mucosa; the proportion of 18:1n-9 was significantly increased, whereas those of palmitoleic (16:1n-7) and cis-vaccenic (18:1n-7) acids were not changed. Upon the treatment with clofibric acid, SCD was induced and the gene expression of SCD1, SCD2, and fatty acid elongase (Elovl) 6 was up-regulated, but that of Elovl5 was unaffected. Fat-free diet feeding for 28 days increased the proportions of 16:1n-7 and 18:1n-7, but did not effectively change that of 18:1n-9, in intestinal mucosa. Fat-free diet feeding up-regulated the gene expression of SCD1, but not that of SCD2, Elovl6, or Elovl5. These results indicate that intestinal mucosa significantly changes its MUFA profile in response to challenges by clofibric acid and a fat-free diet and suggest that up-regulation of the gene expression of SCD along with Elovl6 is indispensable to elevate the proportion of 18:1n-9 in intestinal mucosa.

Novel concepts in inflammatory bowel disease

INTRODUCTION

Clinical management in inflammatory bowel disease (IBD) is constantly changing. Although improvement in symptoms is of paramount importance, using this as the only surrogate marker of disease activity might underestimate disease burden.

SOURCES OF DATA

New data from randomized clinical trials are now available. Treatment paradigms are constantly changing leading to an evolution in the therapeutic approach in routine IBD practice.

AREAS OF AGREEMENT

Patients with an aggressive disease phenotype should be identified at the onset and treated more intensely in order to achieve long-lasting mucosal remission.

AREAS OF CONTROVERSY

Patients who have mild and indolent disease need to be identified and not over treated.

GROWING POINTS

The primary endpoint in IBD management should ideally be mucosal healing. Ample data are now available that correlates mucosal healing with surgical-free outcomes with minimal intestinal damage and patient disability. However, the exact degree of mucosal healing that will lead to improved long-term remission, decreased hospital and surgical rates remains unknown.

AREAS TIMELY FOR DEVELOPING RESEARCH

Clinical translational work is needed to identify novel pathways in IBD pathogenesis that sub-select patients who would benefit by specific-cytokine pathway modulation.

Lecithin as a therapeutic agent in ulcerative colitis

Lecithin [phosphatidylcholine (PC)] was shown to account for more than 70% of total phospholipids within the intestinal mucus layer. It is arranged in lamellar membranes (surfactant-like particles) and establishes a hydrophobic barrier preventing invasion of the colonic commensal microbiota. In ulcerative colitis (UC), the mucus PC content was demonstrated to be reduced by about 70%, irrespective of the presence of inflammation. This may be of primary pathogenetic significance allowing bacteria to enter the mucus and induce mucosal inflammation. Therefore, a new therapeutic strategy is being developed to substitute the missing mucus PC content in UC. Indeed, a delayed-release PC formulation was able to compensate the lack of PC and improve the inflammatory activity. In randomized controlled studies, delayed-release PC was proven to be clinically and endoscopically effective, which now awaits a phase III authority approval trial.

Comparison of lysophospholipid levels in rat feces with those in a standard chow

Although lysophospholipids have attracted much attention due to their diverse physiological activities through their specific receptors, little is known about their metabolic fates in mammalian digestive systems after their ingestion as a minor food component. In this study, we analyzed five lysophospholipids in lipid extracts of a standard rat chow and feces of rats fed the chow by two-dimensional thin layer chromatography and liquid chromatography-tandem mass spectrometry. The most abundant lysophospholipid in the rat chow was lysophosphatidylcholine followed by lysophosphatidylethanolamine, lysophosphatidic acid (LPA), lysophosphatidylinositol and lysophosphatidylserine (LPS) in an increasing order, but their concentrations were very low in rat feces. Among the molecular species of LPS in the chow, only saturated species were detected in the feces in significant amounts. In addition, several molecular species of LPA remained in the feces in variable portions (saturated > monounsaturated > polyunsaturated). These results suggest that a portion of ingested LPA and LPS reach the rat large intestine, affecting physiological colon functions.

Overexpression of CD36 and acyl-CoA synthetases FATP2, FATP4 and ACSL1 increases fatty acid uptake in human hepatoma cells

BACKGROUND

Understanding the mechanisms of long chain fatty acid (LCFA) uptake in hepatic cells is of high medical importance to treat and to prevent fatty liver disease (FLD). ACSs (Acyl-CoA synthetases) are a family of enzymes that catalyze the esterification of fatty acids (FA) with CoA. Recent studies suggest that ACS enzymes drive the uptake of LCFA indirectly by their enzymatic activity and could promote special metabolic pathways dependent on their localization.The only protein located at the plasma membrane which has consistently been shown to enhance FA uptake is CD36.

AIMS

The current study investigated whether ACSs and CD36 could regulate hepatic LCFA uptake.

METHODS AND RESULTS

FATP2 and FATP4 were both localized to the ER of HuH7 and HepG2 cells as shown by double immunofluorescence in comparison to marker proteins. ACSL1 was located at mitochondria in both cell lines. Overexpression of FATP2, FATP4 and ACSL1 highly increased ACS activity as well as the uptake of [3H]-oleic acid and fluorescent Bodipy-C12 (B12) fatty acid. Quantitative FACS analysis showed a correlation between ACS expression levels and B12 uptake. FATP2 had the highest effect on B12 uptake of all proteins tested. CD36 was mainly localized at the plasma membrane. Whereas [3H]-oleic acid uptake was increased after overexpression, CD36 had no effect on B12 uptake.

CONCLUSION

Uptake of LCFA into hepatoma cells can be regulated by the expression levels of intracellular enzymes. We propose that ACS enzymes drive FA uptake indirectly by esterification. Therefore these molecules are potential targets for treatment of nonalcoholic fatty liver disease (NAFLD) or steatohepatitis (NASH).

Specificity and rate of human and mouse liver and plasma phosphatidylcholine synthesis analyzed in vivo

Phosphatidylcholine (PC) synthesis by the direct cytidine diphosphate choline (CDP-choline) pathway in rat liver generates predominantly mono- and di-unsaturated molecular species, while polyunsaturated PC species are synthesized largely by the phosphatidylethanolamine-N-methyltransferase (PEMT) pathway. Although altered PC synthesis has been suggested to contribute to development of hepatocarcinoma and nonalcoholic steatohepatitis, analysis of the specificity of hepatic PC metabolism in human patients has been limited by the lack of sensitive and safe methodologies. Here we incorporated a deuterated methyl-D(9)-labled choline chloride, to quantify biosynthesis fluxes through both of the PC synthetic pathways in vivo in human volunteers and compared these fluxes with those in mice. Rates and molecular specificities of label incorporated into mouse liver and plasma PC were very similar and strongly suggest that label incorporation into human plasma PC can provide a direct measure of hepatic PC synthesis in human subjects. Importantly, we demonstrate for the first time that the PEMT pathway in human liver is selective for polyunsaturated PC species, especially those containing docosahexaenoic acid. Finally, we present a multiple isotopomer distribution analysis approach, based on transfer of deuterated methyl groups to S-adenosylmethionine and subsequent sequential methylations of PE, to quantify absolute flux rates through the PEMT pathway that are applicable to studies of liver dysfunction in clinical studies.

Phosphatidylcholine as a constituent in the colonic mucosal barrier--physiological and clinical relevance

Phosphatidylcholine (PC) is an important constituent of the gastrointestinal tract. PC molecules are not only important in intestinal cell membranes but also receiving increasing attention as protective agents in the gastrointestinal barrier. They are largely responsible for establishing the hydrophobic surface of the colon. Decreased phospholipids in colonic mucus could be linked to the pathogenesis of ulcerative colitis, a chronic inflammatory bowel disease. Clinical studies revealed that therapeutic addition of PC to the colonic mucus of these patients alleviated the inflammatory activity. This positive role is still elusive, however, we hypothesized that luminal PC has two possible functions: first, it is essential for surface hydrophobicity, and second, it is integrated into the plasma membrane of enterocytes and it modulates the signaling state of the mucosa. The membrane structure and lipid composition of cells is a regulatory component of the inflammatory signaling pathways. In this perspective, we will shortly summarize what is known about the localization and protective properties of PC in the colonic mucosa before turning to its evident medical importance. We will discuss how PC contributes to our understanding of the pathogenesis of ulcerative colitis and how reinforcing the luminal phospholipid monolayer can be used as a therapeutic concept in humans.

Delayed release phosphatidylcholine in chronic-active ulcerative colitis: a randomized, double-blinded, dose finding study

BACKGROUND

In 2 preceding studies, delayed release phosphatidylcholine (rPC) was found to (a) improve disease activity and (b) withdraw steroids in patients with chronic-active ulcerative colitis.

GOAL

Objective of the study was to determine the most effective rPC dose with least adverse events.

STUDY

A randomized, dose-controlled, double-blinded study. Four groups of 10 patients each with nonsteroid-treated, chronic-active ulcerative pancolitis with a clinical activity index (CAI) and endoscopic activity index (EAI) >or=7. Patients were treated with oral rPC at doses of 0.5, 1, 3, and 4 g daily over 12 weeks.

RESULTS

The CAI changes from baseline to the end of the study were 2.5 (0.5 g), 7.0 (1 g), 5.5 (3 g), and 6.0 (4 g dose arm). Significant improvement of the CAI was registered between the lowest rPC dose of 0.5 g (control group) and all higher doses of 1.0, 3.0, and 4.0-g rPC (P<or=0.05). Remission (CAI <or=3) was reached in 5/10 and 6/10 patients in the 3 and 4-g dose groups compared with no patients in the 0.5-g arm (P=0.033). In the 1-g dose group only 3/10 patients reached remission (P=0.21). The rates of clinical response (>or=50% CAI improvement) were 70% in all of the effective dose groups (1 to 4 g, P=0.003). This was paralleled by the EAI improvement and by the rates of mucosal healing. Median time to clinical response was 5 (IQR 2 to 8) weeks. Bloating was registered in 40% of the patients irrespective of the treatment dose. Three of the 10 patients in the 4 g dose group reported nausea.

CONCLUSION

We found a saturable dose response of rPC in the treatment of chronic-active ulcerative colitis with effective doses >or=1 g per day; doses of 3 and 4 g seem to be superior in achieving remission.

Intestinal absorption of gamma-tocotrienol is mediated by Niemann-Pick C1-like 1: in situ rat intestinal perfusion studies

gamma-Tocotrienol (gamma-T3) is a member of the vitamin E family that displays potent anticancer activity and other therapeutic benefits. The objective of this study was to evaluate gamma-T3 intestinal uptake and metabolism using the in situ rat intestinal perfusion model. Isolated segments of rat jejunum and ileum were perfused with gamma-T3 solution, and measurements were made as a function of concentration (5-150 microM). Intestinal permeability (P(eff)) and metabolism were studied by measuring total compound disappearance and major metabolite, 2,7,8-trimethyl-2-(beta-carboxy-ethyl)-6-hydroxychroman, appearance in the intestinal lumen. gamma-T3 and metabolite levels were also determined in mesenteric blood. The P(eff) of gamma-T3 was similar in both intestinal segments and significantly decreased at concentrations > or =25 microM in jejunum and ileum (p < 0.05), whereas metabolite formation was minimal and mesenteric blood concentrations of gamma-T3 and metabolite remained very low. These results indicate that gamma-T3 intestinal uptake is a saturable carrier-mediated process and metabolism is minimal. Results from subsequent in situ inhibition studies with ezetimibe, a potent and selective inhibitor of Niemann-Pick C1-like 1 (NPC1L1) transporter, suggested gamma-T3 intestinal uptake is mediated by NPC1L1. Comparable findings were obtained when Madin-Darby canine kidney II cells that express endogenous NPC1L1 were incubated with increasing concentrations of gamma-T3 or gamma-T3 with increasing concentrations of ezetimibe. The present data show for the first time that gamma-T3 intestinal absorption is partly mediated by NPC1L1.

Separate basolateral and apical phosphatidylcholine secretion routes in intestinally differentiated tumor cells

AIM: To investigate whether the secretion of phosphatidylcholine (PC) in intestinal mucus occurs by apical secretion or via basolateral excretion and to determine its subsequent passage across the tight junctions to the apical mucus.

METHODS: We addressed this question using the polarized intestinally differentiated tumor cell line CaCo-2 grown on filters to confluence in Transwell culture chambers. The released PC and sphingomyelin (Sph) from apical and basolateral media were analyzed by mass spectrometry.

RESULTS: The secreted PC species were identical in both compartments indicating the same intracellular origin of PC. However, PC secretion into the basolateral compartment was more effective, and the PC:Sph ratio in the basolateral compartment was significantly higher than that in the apical compartment (8.18 ± 1.84 vs 4.31 ± 1.22, P = 0.01). Both pathways were temperature sensitive and were unaltered in the presence of cyclosporine.

CONCLUSION: The data demonstrate the PC secretion capacity of CaCo-2 cells and indicate two separated apical and basolateral release mechanisms.

Alterations of phospholipid concentration and species composition of the intestinal mucus barrier in ulcerative colitis: a clue to pathogenesis

BACKGROUND

Phospholipids are essential for the normal function of the intestinal mucus barrier. The objective of this study was to systematically investigate phospholipids in the intestinal mucus of humans suffering from inflammatory bowel diseases, where a barrier defect is strongly supposed to be pathogenetic.

METHODS

Optimal mucus recovery was first validated in healthy mice and the method was then transferred to the endoscopic acquisition of ileal and colonic mucus from 21 patients with ulcerative colitis (UC), 10 patients with Crohn's disease (CD), and 29 healthy controls. Nano-electrospray ionization tandem mass spectrometry (ESI-MS/MS) was used to determine phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and sphingomyelin (SM) in lipid extracts of mucus specimens.

RESULTS

Human and rodent mucus contained very similar phospholipid species. In the ileal and colonic mucus from patients suffering from UC, the concentration of PC was highly significantly lower (607 +/- 147 pmol/100 microg protein and 745 +/- 148 pmol/100 microg protein) compared to that of patients with CD (3223 +/- 1519 pmol/100 microg protein and 2450 +/- 431 pmol/100 microg protein) and to controls (3870 +/- 760 pmol/100 microg protein and 2790 +/- 354 pmol/100 microg protein); overall, P = 0.0002 for ileal specimens and P < 0.0001 for colonic specimens. Independent of disease activity, patients suffering from UC showed an increased saturation grade of PC fatty acid residues and a higher LPC-to-PC ratio.

CONCLUSIONS

The intestinal mucus barrier of patients with UC is significantly altered concerning its phospholipid concentration and species composition. These alterations may be very important for the pathogenesis of this disease and underline new therapeutic strategies.

TNF-alpha-induced up-regulation of pro-inflammatory cytokines is reduced by phosphatidylcholine in intestinal epithelial cells

Background

Phosphatidylcholine (PC) is a major lipid of the gastrointestinal mucus layer. We recently showed that mucus from patients suffering from ulcerative colitis has low levels of PC. Clinical studies reveal that the therapeutic addition of PC to the colonic mucus using slow release preparations is beneficial. The positive role of PC in this disease is still unclear; however, we have recently shown that PC has an intrinsic anti-inflammatory property. It could be demonstrated that the exogenous application of PC inhibits membrane-dependent actin assembly and TNF-α-induced nuclear NF-κB activation. We investigate here in more detail the hypothesis that the exogenous application of PC has anti-inflammatory properties.

Methods

PC species with different fatty acid side chains were applied to differentiated and non-differentiated Caco-2 cells treated with TNF-α to induce a pro-inflammatory response. We analysed TNF-α-induced NF-κB-activation via the transient expression of a NF-κB-luciferase reporter system. Pro-inflammatory gene transcription was detected with the help of a quantitative real time (RT)-PCR analysis. We assessed the binding of TNF-α to its receptor by FACS and analysed lipid rafts by isolating detergent resistant membranes (DRMs).

Results

The exogenous addition of all PC species tested significantly inhibited TNF-α-induced pro-inflammatory signalling. The expression levels of IL-8, ICAM-1, IP-10, MCP-1, TNF-α and MMP-1 were significantly reduced after PC pre-treatment for at least two hours. The effect was comparable to the inhibition of NF-kB by the NF-kB inhibitor SN 50 and was not due to a reduced binding of TNF-α to its receptor or a decreased surface expression of TNF-α receptors. PC was also effective when applied to the apical side of polarised Caco-2 cultures if cells were stimulated from the basolateral side. PC treatment changed the compartmentation of the TNF-α-receptors 1 and 2 to DRMs.

Conclusion

PC induces a prolonged inhibition of TNF-α-induced pro-inflammatory signalling. This inhibition may be caused by a shift of the TNF-α receptors at the surface to lipid rafts. Our results may offer a potential molecular explanation for the positive role of PC seen in clinical studies for the treatment of ulcerative colitis.

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.

Isolation of lipids from photosystem I complex and its characterization with high performance liquid chromatography/electrospray ionization mass spectrometry

A method for simultaneous analysis of lipids extracted from photosystem I complex was developed with high performance liquid chromatography/electrospray ionization mass spectrometry. The photosystem I complex was firstly solubilized and separated using deoxycholate polyacrylamide gel electrophoresis method after ultrasonic treatment of the sample (leaves of pea, Pisum sativum L.). The Photosystem I complexes were electrophoretically eluted from the deoxycholate polyacrylamide gel electrophoresis bands containing them, and the electron transport activity of the eluent measured as confirmation. Lipids, which were isolated from the complex having photosystem I activity, were separated and characterized with high performance liquid chromatography/electrospray ionization mass spectrometry. Five lipids, monogalactosyldiacylglycerol, digalactosyldiacylglycerol, phosphatidylglycerol, sulphoquinovosyldiacylglycerol and phosphaditylcholine were found combining with photosystem I complex. Different species of these lipids were found in the ESI mass spectra and the compositions of the acyl groups in them were determined.

Zebrafish fat-free is required for intestinal lipid absorption and Golgi apparatus structure

The zebrafish fat-free (ffr) mutation was identified in a physiological screen for genes that regulate lipid metabolism. ffr mutant larvae are morphologically indistinguishable from wild-type sibling larvae, but their absorption of fluorescent lipids is severely impaired. Through positional cloning, we have identified a causative mutation in a highly conserved and ubiquitously expressed gene within the ffr locus. The Ffr protein contains a Dor-1 like domain typical of oligomeric Golgi complex (COG) gene, cog8. Golgi complex ultrastructure is disrupted in the ffr digestive tract. Consistent with a possible role in COG-mediated Golgi function, wild-type Ffr-GFP and COG8-mRFP fusion proteins partially colocalize in zebrafish blastomeres. Enterocyte retention of an endosomal lipid marker in ffr larvae support the idea that altered vesicle trafficking contributes to the ffr mutant defect. These data indicate that ffr is required for both Golgi structure and vesicular trafficking, and ultimately lipid transport.

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.

ABC lipid transporters: extruders, flippases, or flopless activators?

Many mammalian ABC transporters move membrane lipids to acceptor lipid assemblies in the extracellular aqueous milieu. Because the desorption from the membrane costs more energy than provided by two ATPs, the transporter probably only translocates the lipid to a partially hydrophilic site on its extracellular face. From this high-energy site, the lipid may efficiently move to the acceptor, which ideally is bound to the transporter, or, in the absence of an acceptor, fall back into the membrane. If the lipid originated from the cytosolic membrane surface, this represents lipid flop and is probably a side activity of the transporters.