Effect of antibiotic treatment on fat absorption in mice with cystic fibrosis

Impaired Intestinal Farnesoid X Receptor Signaling in Cystic Fibrosis Mice

BACKGROUND & AIMS

The bile acid (BA)-activated farnesoid X receptor (FXR) controls hepatic BA synthesis and cell proliferation via the intestinal hormone fibroblast growth factor 19. Because cystic fibrosis (CF) is associated with intestinal dysbiosis, anomalous BA handling, and biliary cirrhosis, we investigated FXR signaling in CF.

METHODS

Intestinal and hepatic expression of FXR target genes and inflammation markers was assessed in Cftr null mice and controls. Localization of the apical sodium-dependent BA transporter was assessed, and BAs in gastrointestinal tissues were analyzed. The CF microbiota was characterized and FXR signaling was investigated in intestinal tissue and organoids.

RESULTS

Ileal murine fibroblast growth factor 19 ortholog (Fgf15) expression was strongly reduced in CF mice, compared with controls. Luminal BA levels and localization of apical sodium-dependent BA transporter was not affected, and BAs induced Fgf15 up to normal levels in CF ileum, ex vivo, and CF organoids. CF mice showed a dysbiosis that was associated with a marked up-regulation of genes involved in host-microbe interactions, including those involved in mucin glycosylation, antimicrobial defense, and Toll-like receptor signaling. Antibiotic treatment reversed the up-regulation of inflammatory markers and restored intestinal FXR signaling in CF mice. Conversely, FXR-dependent gene induction in ileal tissue and organoids was repressed by bacterial lipopolysaccharide and proinflammatory cytokines, respectively. Loss of intestinal FXR activity was associated with a markedly blunted hepatic trophic response to oral BA supplementation, and with impaired repression of Cyp7a1, the gene encoding the rate-limiting enzyme in BA synthesis.

CONCLUSIONS

In CF mice, the gut microbiota represses intestinal FXR activity, and, consequently, FXR-dependent hepatic cell proliferation and feedback control of BA synthesis.

Defective FXR-FGF15 signaling and bile acid homeostasis in cystic fibrosis mice can be restored by the laxative polyethylene glycol

The gastrointestinal phenotype of cystic fibrosis (CF) features intestinal bile acid (BA) malabsorption, impaired intestinal farnesoid X receptor (FXR) activation, and consequently reduced fibroblast growth factor 19 (FGF19, FGF15 in mice) production. The osmotic laxative polyethylene glycol (PEG) has been shown to decrease intestinal mucus accumulation in CF mice and could, by doing so, improve BA reabsorption. Here we determined the effect of PEG on BA excretion and FXR-FGF15 signaling in CF mice. Male Cftr^-/-tm1Unc (CF) and wild-type (WT) littermates were administered PEG 4000 in drinking water and fed either chow or a semisynthetic diet. PEG was withdrawn for 3 days before termination. Fecal BA excretion was measured at PEG dosages of 37 g/l (100%) and 0 g/l (0%). Ileal FXR activation was assessed by gene expression of its downstream targets Fgf15 and small heterodimer partner ( Shp). In CF mice, PEG withdrawal increased fecal BA excretion on either diet compared with full PEG dosage (chow, 2-fold, P = 0.06; semisynthetic, 4.4-fold, P = 0.007). PEG withdrawal did not affect fecal BA excretion in WT mice on either diet. After PEG withdrawal, gene expression levels of intestinal FXR target genes Fgf15 and Shp were decreased in CF mice but unaffected in WT littermates. PEG did not affect the gene expression of the main intestinal BA transporter apical sodium-dependent bile acid transporter (ASBT). PEG treatment ameliorates intestinal BA malabsorption in CF mice and restores intestinal FXR-FGF15 signaling, independent from Asbt gene expression. These findings highlight the potential of PEG in the prevention and treatment of the gastrointestinal phenotype of CF. NEW & NOTEWORTHY A gastrointestinal feature of cystic fibrosis is bile acid malabsorption and consequent impairment of farnesoid X receptor (FXR)-fibroblast growth factor 15 (FGF15) signaling. FXR-FGF15 signaling regulates various metabolic processes and could be implicated in metabolic and gastrointestinal complications of cystic fibrosis, such as diabetes and liver disease. In cystic fibrosis mice, treatment with the osmotic laxative polyethylene glycol is associated with decreased fecal bile acid loss and restoration of FXR-FGF15 signaling.

Prevalence of Fecal Incontinence in Adults with Cystic Fibrosis

BACKGROUND

Patients with cystic fibrosis (CF) are deemed at risk of developing urinary incontinence (UI) due to repeated coughing and other factors causing increased pressure on the pelvic floor. Fecal incontinence (FI) is probably derived from the same mechanism, but only very few data are available on its frequency.

AIMS

The aim of this study was to determine the prevalence of FI in an adult population with CF.

METHODS

This retrospective study was conducted from January 2012 to June 2014. Patients were recruited from Marseille referral center for adult CF. They were asked to fill in a self-completed anonymous questionnaire for symptom assessment of UI and FI. Clinical data and a detailed history of CF were also recorded.

RESULTS

A total of 155 out of 190 patients (92 females) of mean age 30.5 ± 11 years completed the survey. Seventy-three patients (47%) were lung transplanted. Forty patients (25.8%) reported FI with a mean St Mark's score of 4.9 ± 2. Thirty-five patients (22.6%) reported UI. Eighteen patients (11.6%) reported both FI and UI. FI was significantly more frequent in older patients (34.27 vs. 29.54 years, p = 0.03) and in patients with associated UI (p = 0.001). No relationship was found between respiratory, bacterial, nutritional status, transplantation, pancreatic status, practice of physiotherapy, delivery history, and FI.

CONCLUSIONS

The high prevalence of FI in CF and its negative impacts need to integrate this symptom in the overall treatment of this pathology. The systematic early detection of FI may allow its rapid management and limit their consequences.

Intestinal PPARδ protects against diet-induced obesity, insulin resistance and dyslipidemia

Peroxisome proliferator-activated receptor δ (PPARδ) is a ligand-activated transcription factor that has an important role in lipid metabolism. Activation of PPARδ stimulates fatty acid oxidation in adipose tissue and skeletal muscle and improves dyslipidemia in mice and humans. PPARδ is highly expressed in the intestinal tract but its physiological function in this organ is not known. Using mice with an intestinal epithelial cell-specific deletion of PPARδ, we show that intestinal PPARδ protects against diet-induced obesity, insulin resistance and dyslipidemia. Furthermore, absence of intestinal PPARδ abolished the ability of PPARδ agonist GW501516 to increase plasma levels of HDL-cholesterol. Together, our findings show that intestinal PPARδ is important in maintaining metabolic homeostasis and suggest that intestinal-specific activation of PPARδ could be a therapeutic approach for treatment of the metabolic syndrome and dyslipidemia, while avoiding systemic toxicity.

Cholic acid induces a Cftr dependent biliary secretion and liver growth response in mice

The cause of Cystic fibrosis liver disease (CFLD), is unknown. It is well recognized that hepatic exposure to hydrophobic bile salts is associated with the development of liver disease. For this reason, we hypothesize that, CFTR dependent variations, in the hepatic handling of hydrophobic bile salts, are related to the development CFLD. To test our hypothesis we studied, in Cftr^-/- and control mice, bile production, bile composition and liver pathology, in normal feeding condition and during cholate exposure, either acute (intravenous) or chronic (three weeks via the diet). In Cftr^-/- and control mice the basal bile production was comparable. Intravenous taurocholate increased bile production to the same extent in Cftr^-/- and control mice. However, chronic cholate exposure increased the bile flow significantly less in Cftr^-/- mice than in controls, together with significantly higher biliary bile salt concentration in Cftr^-/- mice. Prolonged cholate exposure, however, did not induce CFLD like pathology in Cftr^-/- mice. Chronic cholate exposure did induce a significant increase in liver mass in controls that was absent in Cftr^-/- mice. Chronic cholate administration induces a cystic fibrosis-specific hepatobiliary phenotype, including changes in bile composition. These changes could not be associated with CFLD like pathological changes in CF mouse livers. However, chronic cholate administration induces liver growth in controls that is absent in Cftr^-/- mice. Our findings point to an impaired adaptive homeotrophic liver response to prolonged hydrophobic bile salt exposure in CF conditions.

Intestinal complications of cystic fibrosis

PURPOSE OF REVIEW

The article reviews advances in gastrointestinal aspects of cystic fibrosis (CF) published in the literature over the past year, and highlights new and interesting research.

RECENT FINDINGS

Animal models can be used to understand the pathophysiology of gastrointestinal complications in CF. The CF mouse is useful for studying distal intestinal obstruction, dysmotility and dysbiosis, and the CF pig model has helped us better understand meconium ileus and pancreatic and hepatobiliary secretory problems. Studies in humans help elucidate the evolution of pancreatic insufficiency, how reflux may lead to lung disease, problems with intestinal dysmotility, mechanisms leading to pancreatitis and the increased prevalence of gastrointestinal cancer. Biomarkers are shedding light on CF-related liver disease. Rectal biopsies can help in diagnosis and in studying new drugs for CF.

SUMMARY

Gastrointestinal complications of CF are likely to be seen with increasing frequency as patients with CF lead longer lives. CF animal models and modern research techniques are providing new insights into extrapulmonary complications. CF clinicians should be familiar with diagnosis and management of common gastrointestinal complications and should build bridges with specialists so that referrals can be made when needed.

Benefits of structured and free monoacylglycerols to deliver eicosapentaenoic (EPA) in a model of lipid malabsorption

In the present study, we used a preclinical model of induced lipolytic enzyme insufficiency, and hypothesized that the use of monoacylglycerols (MAG) will enhance their bioavailability and delivery to the tissues. Experimental diets containing 20% lipids were fed to rats for 21 days with or without Orlistat. The control diet of fish oil (FO), a source of EPA and DHA, was tested against: structured (A) vanillin acetal of sn-2 MAG (Vanil + O) and (B) diacetyl derivative of sn-2 MAG (Acetyl + O) and (C) free MAG (MAG + O). FA profiles with an emphasis on EPA and DHA levels were determined in plasma, red blood cells (RBC), liver, spleen, brain and retina. We observed significant reduction of lipid absorption when rats co-consumed Orlistat. As expected, the FO groups with and without Orlistat showed the biggest difference. The Vanil + O, Acetyl + O and MAG + O groups, demonstrated higher levels of EPA (5.5 ± 1.9, 4.6 ± 1.6 and 5.6 ± 0.6, respectively) in RBC compared with FO + O diets (3.3 ± 0.2, 2.6 ± 0.2). Levels of EPA incorporation, in plasma, were similar to those obtained for RBC, and similar trends were observed for the collected tissues and even with DHA levels. These observations with two MAG derivatives providing the fatty acid esterified in the sn-2 position, show that these molecules are efficient vehicles of EPA in malabsorption conditions which is in line with our hypothesis. Free MAG, characterized as having exclusively sn-1(3) isomers of EPA, demonstrated better absorption efficiencies and accretion to tissues when compared to structured MAG. The study demonstrated that structured and free MAG can be used efficiently as an enteral vehicle to supply bioactive fatty acids such as EPA and DHA in lipid malabsorption where diminished lipolytic activity is the underlying cause.

Altered de novo lipogenesis contributes to low adipose stores in cystic fibrosis mice

Cystic fibrosis (CF) mouse models exhibit exocrine pancreatic function, yet they do not develop adipose stores to the levels of non-CF mice. CF mice homozygous for the Cftr mutation (F508del) at 3 wk (postweaning) and 6 wk (young adult) of age had markedly less adipose tissue than non-CF mice. Food intake was markedly lower in 3-wk-old CF mice but normalized by 6 wk of age. Both 3- and 6-wk-old mice had dietary lipid absorption and fecal lipid excretion comparable to non-CF mice. Hepatic de novo lipogenesis (DNL), determined by (2)H incorporation, was reduced in CF mice. At 3 wk, F508del mice had significantly decreased DNL of palmitate and stearate, by 83% and 80%, respectively. By 6 wk, DNL rates in non-CF mice remained unchanged compared with 3-wk-old mice, while DNL rates of F508del mice were still reduced, by 33% and 40%, respectively. Adipose tissue fatty acid (FA) profiles were comparable in CF and non-CF mice, indicating that adipose differences are quantitative, not qualitative. A correspondingly lower content of (2)H-labeled FA was found in CF adipose tissue, consistent with reduced deposition of newly made hepatic triglycerides and/or decreased adipose tissue lipogenesis. Hepatic transcriptome analysis revealed lower mRNA expression from several genes involved in FA biosynthesis, suggesting downregulation of this pathway as a mechanism for the reduced lipogenesis. These novel data provide a model for altered lipid metabolism in CF, independent of malabsorption, and may partly explain the inability of pancreatic enzyme replacement therapy to completely restore normal body mass to CF patients.