We recently showed that mucus from patients with ulcerative colitis, a chronic inflammatory disorder of the colon, is characterized by a low level of phosphatidylcholine (PC) while clinical studies reveal that therapeutic addition of PC using slow release preparations is beneficial. The positive role of PC in this disease is still elusive. Here we tested the hypothesis that exogenous application of PC has anti-inflammatory properties using three model systems. First, human Caco-2 cells were treated with tumor necrosis factor-␣ (TNF-␣) to induce a pro-inflammatory response via activation of NF-B. Second, latex bead phagosomes were analyzed for their ability to assemble actin in vitro, a process linked to pro-inflammatory signaling and correlating with the growth versus killing of mycobacteria in macrophages. The third system used was the rapid assembly of plasma membrane actin in macrophages in response to sphingosine 1-phosphate. TNF-␣ induced a pro-inflammatory response in Caco-2 cells, including 1) assembly of plasma membrane actin; 2) activation of both MAPKs ERK and p38; 3) transport of NF-B subunits to the nucleus; and 4) subsequent up-regulation of the synthesis of pro-inflammatory gene products. Exogenous addition of most PCs tested significantly inhibited these processes. Other phospholipids like sphingomyelin or phosphatidylethanolamine showed no effects in these assays. PC also inhibited latex bead phagosome actin assembly, the killing of Mycobacterium tuberculosis in macrophages, and the sphingosine 1-phosphate-induced actin assembly in macrophages. TNF-␣ induces the activation of signaling molecules and the reorganization of the actin cytoskeleton in human intestinal cells. Exogenous application of PC blocks pro-inflammatory signaling in Caco-2 cells, in phagosomes in vitro and facilitates intracellular survival of mycobacteria. We provide further evidence that actin assembly by membranes is part of the pro-inflammatory response. Collectively, these results provide a molecular foundation for the clinical studies showing a beneficial effect of PC therapy in ulcerative colitis.

Surfactant protein B (SP-B) is essential for normal lung surfactant function. Theoretical models predict that the disulfide cross-linked, N- and C-terminal domains of SP-B fold as charged amphipathic helices, and suggest that these adjacent helices participate in critical surfactant activities. This hypothesis is tested using a disulfide-linked construct (Mini-B) based on the primary sequences of the N- and C-terminal domains. Consistent with theoretical predictions of the full-length protein, both isotope-enhanced Fourier transform infrared (FTIR) spectroscopy and molecular modeling confirm the presence of charged amphipathic alpha-helices in Mini-B. Similar to that observed with native SP-B, Mini-B in model surfactant lipid mixtures exhibits marked in vitro activity, with spread films showing near-zero minimum surface tensions during cycling using captive bubble surfactometry. In vivo, Mini-B shows oxygenation and dynamic compliance that compare favorably with that of full-length SP-B. Mini-B variants (i.e. reduced disulfides or cationic residues replaced by uncharged residues) or Mini-B fragments (i.e. unlinked N- and C-terminal domains) produced greatly attenuated in vivo and in vitro surfactant properties. Hence, the combination of structure and charge for the amphipathic alpha-helical N- and C-terminal domains are key to SP-B function.

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.

Cholestatic liver disease (CLD) is a major cause of progressive liver damage and liver failure. Several forms of biliary cirrhosis are caused by mutations in specific genes. We sought to identify a genetic defect in a family with CLD impossible to assign to a distinct pathogenic entity. Clinical and histopathological characterization of the family members, microarraybased single-nucleotide polymorphism genotyping, and analysis of candidate genes were performed. Among six of 11 siblings severely affected by idiopathic CLD in a family from a population isolate in Transylvania, three died of cirrhosis (aged 5, 7, and 43 years) and three had adult-onset disease with small duct cholangiopathy, including ductopenia. Others were mildly affected and experienced intrahepatic cholestasis of pregnancy, miscarriages, or stillbirth. Pedigree studies revealed distant parental consanguinity. Genome-wide linkage analysis and autozygosity mapping yielded a single maximal lod-score of 3.88 on chromosome 7q21.1-7q22, excluding other genomic loci. Sequencing of ABCB4 at this locus revealed a novel missense mutation c.2362C>T (p.Arg788Trp) which cosegregated with severity of disease. Bile from a mutation homozygote showed a reduced phosphatidylcholine/bile acid ratio, consistent with reduced ABCB4 phosphatidylcholine transport activity. Conclusion: We show that a missense mutation in ABCB4 is a cause for ductopenic CLD in adulthood. Allelic status correlated with severity of liver disease ranging from intrahepatic cholestasis of pregnancy through fibrosis to cirrhosis and death in childhood and adulthood. Mutational analysis of ABCB4 should be generally considered in all patients with cholestatic liver disease of unknown etiology regardless of age and onset of disease. (HEPATOLOGY 2008;48:1157-1166

BackgroundPhosphatidylcholine (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.MethodsPC 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).ResultsThe 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.ConclusionPC 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.

Ulcerative colitis (UC) is the result of an inappropriate colonic inflammatory response triggered by environmental and genetic factors. We have recently shown that mucus from UC patients has a decreased phosphatidylcholine (PC) content, while clinical trials revealed that therapeutic addition of PC to the colonic mucus alleviated the inflammatory activity. The mechanisms behind this are still unclear. We hypothesized that PC has at least two possible functions in the intestine: First, it establishes the surface hydrophobicity of the mucus and therefore protects the underlying tissue against intraluminal aggressors; recent experiments on surgical specimens revealed reduced surface tension and hydrophobicity in UC patients. Second, mucus phospholipids might also be integrated into the plasma membranes of enterocytes and thereby influence the signaling state of the mucosa. PC has been shown to inhibit TNF-α induced pro-inflammatory responses including: (1) assembly of plasma membrane actin; (2) activation of MAP kinases ERK and p38; and (3) activation of NF-κB and synthesis of pro-inflammatory gene products. Other phospholipids like phosphatidylethanolamine or sphingomyelin had no effect. PC also inhibited latex bead phagosome actin assembly, killing of M. tuberculosis in macrophages, and sphingosine-1-phosphate induced actin assembly in macrophages. Collectively, these results provide a molecular foundation that shows PC, firstly, as an anti-inflammatory, and secondly, as a surface hydrophobicity increasing compound with promising therapeutic potential in the treatment of inflammatory bowel disease.

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Colonic mucus protects against attacks from bacteria in stool. One component of mucus is phosphatidylcholine (PC) which is thought to be arranged as continuous lamellar layer in the apical mucus and to be responsible for establishing a protective hydrophobic surface. This ‘intestinal surfactant’ plays a key role in mucosal defense. Thus, a defective PC layer contributes to the development of inflammation. Analysis of rectoscopically acquired mucus aliquots revealed a 70% decrease in PC content in ulcerative colitis (UC) compared to Crohn´s disease (CD) and healthy controls – independent of disease activity. Accordingly, we propose that lack of mucus PC is a key pathogenetic factor in UC. In clinical studies a delayed-release oral PC preparation (rPC) was found to substitute the lack of PC in rectal mucus. Indeed, in non-steroid-treated active UC, 53% of rPC patients reached remission [clinical activity index (CAI) ≤3] compared to 10% of placebo patients (p ≤ 0.001). Endoscopic and histologic findings improved concomitantly. A second trial with 60 chronic-active, steroid-dependent UC patients was conducted to test for steroid-sparing effects. Complete steroid withdrawal with a concomitant achievement of remission (CAI ≤3) or clinical response (≧50% CAI improvement) was reached in 15 PC-treated patients (50%) but only in 3 (10%) placebo patients (p = 0.002). In conclusion, intrinsic reduction of PC (lecithin) in colonic mucus may be a key pathogenetic feature of UC. Topical supplement of PC by a delayed-released oral PC preparation is effective in resolving inflammatory activity of UC and may develop to a first-choice therapy for this disease.