FXR modulates the gut-vascular barrier by regulating the entry sites for bacterial translocation in experimental cirrhosis

BACKGROUND & AIMS

Pathological bacterial translocation (PBT) in cirrhosis is the hallmark of spontaneous bacterial infections, increasing mortality several-fold. Increased intestinal permeability is known to contribute to PBT in cirrhosis, although the role of the mucus layer has not been addressed in detail. A clear route of translocation for luminal intestinal bacteria is yet to be defined, but we hypothesize that the recently described gut-vascular barrier (GVB) is impaired in experimental portal hypertension, leading to increased accessibility of the vascular compartment for translocating bacteria.

MATERIALS

Cirrhosis was induced in mouse models using bile-duct ligation (BDL) and CCl₄. Pre-hepatic portal-hypertension was induced by partial portal vein ligation (PPVL). Intestinal permeability was compared in these mice after GFP-Escherichia coli or different sized FITC-dextrans were injected into the intestine.

RESULTS

Healthy and pre-hepatic portal-hypertensive (PPVL) mice lack translocation of FITC-dextran and GFP-E. coli from the small intestine to the liver, whereas BDL and CCl₄-induced cirrhotic mice demonstrate pathological translocation, which is not altered by prior thoracic-duct ligation. The mucus layer is reduced in thickness, with loss of goblet cells and Muc2-staining and expression in cirrhotic but not PPVL mice. These changes are associated with bacterial overgrowth in the inner mucus layer and pathological translocation of GFP-E. coli through the ileal epithelium. GVB is profoundly altered in BDL and CCl₄-mice with Ileal extravasation of large-sized 150 kDa-FITC-dextran, but only slightly altered in PPVL mice. This pathological endothelial permeability and accessibility in cirrhotic mice is associated with augmented expression of PV1 in intestinal vessels. OCA but not fexaramine stabilizes the GVB, whereas both FXR-agonists ameliorate gut to liver translocation of GFP-E. coli.

CONCLUSIONS

Cirrhosis, but not portal hypertension per se, grossly impairs the endothelial and muco-epithelial barriers, promoting PBT to the portal-venous circulation. Both barriers appear to be FXR-modulated, with FXR-agonists reducing PBT via the portal-venous route.

LAY SUMMARY

For intestinal bacteria to enter the systemic circulation, they must cross the mucus and epithelial layer, as well as the gut-vascular barrier. Cirrhosis disrupts all 3 of these barriers, giving bacteria access to the portal-venous circulation and thus, the gut-liver axis. Diminished luminal bile acid availability, cirrhosis and the associated reduction in farnesoid x receptor (FXR) signaling seem, at least partly, to mediate these changes, as FXR-agonists reduce bacterial translocation via the portal-venous route to the liver in cirrhosis.

Regulatory role of PI3K-protein kinase B on the release of interleukin-1β in peritoneal macrophages from the ascites of cirrhotic patients

Great effort has been paid to identify novel targets for pharmaceutical intervention to control inflammation associated with different diseases. We have studied the effect of signalling inhibitors in the secretion of the proinflammatory and profibrogenic cytokine interleukin (IL)-1β in monocyte-derived macrophages (M-DM) obtained from the ascites of cirrhotic patients and compared with those obtained from the blood of healthy donors. Peritoneal M-DM were isolated from non-infected ascites of cirrhotic patients and stimulated in vitro with lipopolysaccharide (LPS) and heat-killed Candida albicans in the presence or absence of inhibitors for c-Jun N-terminal kinase (JNK), mitogen-activated protein kinase kinase 1 (MEK1), p38 mitogen-activated protein kinase (MAPK) and phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K). The IL1B and CASP1 gene expression were evaluated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The expression of IL-1β and caspase-1 were determined by Western blot. IL-1β was also assayed by enzyme-linked immunosorbent assay (ELISA) in cell culture supernatants. Results revealed that MEK1 and JNK inhibition significantly reduced the basal and stimulated IL-1β secretion, while the p38 MAPK inhibitor had no effect on IL-1β levels. On the contrary, inhibition of PI3K increased the secretion of IL-1β from stimulated M-DM. The activating effect of PI3K inhibitor on IL-1β release was mediated mainly by the enhancement of the intracellular IL-1β and caspase-1 content release to the extracellular medium and not by increasing the corresponding mRNA and protein expression levels. These data point towards the role of MEK1 and JNK inhibitors, in contrast to the PI3K-protein kinase B inhibitors, as potential therapeutic tools for pharmaceutical intervention to diminish hepatic damage by reducing the inflammatory response mediated by IL-1β associated with liver failure.

The existence of a relationship between increased serum alanine aminotransferase levels detected in premarketing clinical trials and postmarketing published hepatotoxicity case reports

BACKGROUND

Drug-induced liver injury (DILI) profile in most drugs' available information is based on both the incidence of alanine aminotansferase (ALT) elevations in clinical trials and published case reports.

AIM

To assess the relationship between ALT elevations in clinical trials and the number of published case reports in the postmarketing setting.

METHODS

Hepatotoxic drugs were identified from product labelling and classified in high-medium risk (Black Box Warning or Precautions section) or low risk (a statement in the Adverse Reactions section). Incidence of ALT elevations (> or = 3 x ULN) for drug (I(D)) and placebo (I(C)) treated patients in premarketing clinical trials and DILI published case reports were retrieved from product labelling and MEDLINE.

RESULTS

The median I(C) was 10/1000. The high-medium-risk drugs' median I(D) was significantly higher compared with low-risk drugs (17/1000 vs. 10/1000; P = 0.046). Chi-squared test, absolute difference and odds ratio comparing I(D) and I(C) identified 35%, 51% and 77% of high-medium-risk drugs respectively. Less number of case reports were associated with low- than high-medium-risk drugs (1 vs. 7; P = 0.001). A high odds ratio in clinical trials (I(D) vs. I(C)) was the strongest predictor of published DILI case reports.

CONCLUSION

A relationship between increased ALT incidence in premarketing clinical trials and postmarketing published case reports exists.

Translocation of bacterial DNA from Gram-positive microorganisms is associated with a species-specific inflammatory response in serum and ascitic fluid of patients with cirrhosis

Translocation of bacterial-DNA in patients with cirrhosis and ascites triggers an innate immune response. Identification of characteristics to which this response is sensitive is relevant from a clinical standpoint. The aim of this study has been to determine if the proinflammatory immune response established in vivo in cirrhotic patients with ascites as a consequence of bacterial-DNA translocation is related to the identified bacterial species and their frequency of cytosine-guanosine content in serum and ascitic fluid. Patients with advanced cirrhosis and ascites were included in the study and distributed into groups I and II according to the absence or presence of bacterial-DNA translocation, respectively. Serum and ascitic fluid levels of proinflammatory cytokines after normalization of bacterial-DNA concentration and the activated form of nuclear factor-kappa B in ascitic fluid pellets were measured by enzyme-linked immunosorbent assay techniques. Translocation of bacterial-DNA with higher cytosine-guanosine content induced the highest cytokine response, which was higher than that in patients without bacterial-DNA translocation. The activated form of nuclear factor-kappa B in ascitic fluid pellets of patients with bacterial-DNA translocation was greater in patients with higher bacterial-DNA cytosine-guanosine content, whereas the amount of total nuclear factor-kappa B remained unaltered. Bacterial-DNA translocation induces a marked immune reaction in vivo in patients with advanced cirrhosis and ascites which is related, among other factors, to the bacterial-DNA cytosine-guanosine content. Therefore, the host's immune response to bacterial-DNA translocation constitutes a species-specific phenomenon.

Detection and identification of bacterial DNA in serum from patients with acute pancreatitis

BACKGROUND AND AIMS

Bacterial infections are common complications in patients with acute pancreatitis, and translocation of bacteria from the intestinal lumen is probably the first step in the pathogenesis of these infections. As blood cultures in afebrile patients are usually negative, more sensitive methods to investigate this hypothesis in patients are needed. Our group has recently developed a method to detect the presence of bacterial DNA in biological fluids, and we aimed to detect bacterial DNA in patients with acute pancreatitis, as molecular evidences of bacterial translocation.

METHODS

Samples of blood were obtained on three consecutive days within the first six days after admission. Bacterial DNA was detected using a polymerase chain reaction based method, and an automated DNA nucleotide sequencing process allowed identification of bacteria species.

RESULTS

Thirty one consecutively admitted patients with acute pancreatitis were studied. Bacterial DNA was detected in six patients (19.3%), and the sequencing process allowed identification of Citrobacter freundii and Pseudomonas aeruginosa. In two patients the same bacteria detected at admission was detected 24 hours later (above 99.9% homology of nucleotide sequence). Basic clinical and biochemical characteristics were similar among patients with or without the presence of bacterial DNA.

CONCLUSION

Detection of gram negative bacteria derived bacterial DNA in our series supports the contention that bacterial translocation is a systemic process in approximately 20% of patients with acute pancreatitis that does not seem to be related to the severity of the episode or immediate development of infection.

Norfloxacin decreases bacterial adherence of quinolone-resistant strains of Escherichia coli isolated from patients with cirrhosis

BACKGROUND

Long-term administration of norfloxacin is recommended for secondary prophylaxis of spontaneous bacterial peritonitis in cirrhosis, but it may be associated with the development of quinolone-resistant bacteria in stools. However, these bacteria rarely cause infections.

AIM

To assess bacterial adherence of either quinolone-sensitive or -resistant Escherichia coli obtained from stools of cirrhotic patients, as one of the main virulence factors, and its variations when sub-minimum inhibitory concentration of norfloxacin were added to the medium.

METHODS

E. coli strains were co-cultured with oral epithelial cells obtained from patients in presence/absence of norfloxacin. Bacterial adherence was measured as percentage of cells exhibiting positive adherence and the number of bacteria attached to epithelial cells.

RESULTS

37 sensitive and 22 resistant E. coli strains were studied. Bacterial adherence was similar in both series (78% vs. 81%, P = N.S.), and these percentages were similarly and significantly reduced when subminimum inhibitory concentration of norfloxacin was added to the culture medium (P < 0.001).

CONCLUSIONS

Bacterial adherence of E. coli obtained from patients with cirrhosis is unrelated to the sensitivity/resistance to quinolones, and is similarly reduced in both cases when subminimum inhibitory concentration of norfloxacin is added to the medium.

Bacterial DNA activates cell mediated immune response and nitric oxide overproduction in peritoneal macrophages from patients with cirrhosis and ascites

BACKGROUND AND AIMS

Translocation of intestinal bacteria to ascitic fluid is probably the first step in the development of episodes of spontaneous bacterial peritonitis in patients with cirrhosis. We have recently reported the detection of bacterial DNA in blood and ascitic fluid from patients with advanced cirrhosis, what we consider as molecular evidence of bacterial translocation. Several studies have shown the immunogenic role of bacterial DNA in vitro, and we hypothesised that the presence of bacterial DNA could activate the type I immune response in peritoneal macrophages from these patients, leading to greater cytokine synthesis (interleukin (IL)-2 and IL-12, tumour necrosis factor alpha, and interferon gamma) and effector molecules such as nitric oxide.

METHODS

Peritoneal macrophages obtained from patients with cirrhosis and culture negative non-neutrocytic ascitic fluid were collected and characterised by flow cytometry. Inducible nitric oxide synthase, nitric oxide levels, and cytokine production were measured by immunoenzymometric assays in basal and harvested conditions according to the presence/absence of bacterial DNA.

RESULTS

The ability of peritoneal macrophages to synthesise nitric oxide and levels of all cytokines were significantly increased in patients with bacterial DNA. There was a positive correlation between inducible nitric oxide synthase and nitric oxide levels.

CONCLUSIONS

The presence of bacterial DNA in patients with decompensated cirrhosis is associated with marked activation of peritoneal macrophages, as evidenced by nitric oxide synthesising ability, together with enhanced cytokine production.