Hepatobiliary injury associated with experimental small-bowel bacterial overgrowth in rats

The gut-liver axis: impact of a mouse model of small-bowel bacterial overgrowth

BACKGROUND

The mechanisms by which intestinal bacteria impact liver diseases remain poorly understood. The aim of this study was to develop a mouse model of small-bowel bacterial overgrowth and to determine its impact on hepatobiliary injury.

MATERIALS AND METHODS

A jejunal self-filling blind loop (SFBL) was created in C57BL/6 mice. Three weeks after surgery, the mice were euthanized, and bacterial cultures of luminal content of the loop and extraintestinal tissues were performed. Liver and jejunum were collected for histological grading of inflammation and injury. Serum liver biochemistry assays were performed. Hepatobiliary transporter mRNA expression in liver was measured by quantitative real-time polymerase chain reaction. Bile and blood were collected for measurement of total bile acids, phospholipid, and cholesterol. Mice undergoing jejunal transection and reanastomosis and laparotomy only served as control groups.

RESULTS

SFBL induced a dramatic increase in intraluminal bacterial counts, mesenteric lymph node bacterial translocation, and evidence of jejunal and hepatobiliary injury. Significant reductions in hepatic expression of hepatobiliary transporters involved in biliary canalicular export and basolateral uptake were observed in SFBL mice. SFBL resulted in a significant increase in biliary total bile acid concentration, decreases in bile phospholipid and cholesterol output, and an increase in the bile acid/phospholipid ratio.

CONCLUSIONS

We have developed a reproducible mouse model of small-bowel bacterial overgrowth with evidence of liver inflammation, altered hepatobiliary transporter expression, and alterations in bile composition. This model may help to elucidate the mechanisms by which gut-derived bacterial factors impact the liver and contribute to the exacerbation of liver diseases and biliary injury.

Is intestinal inflammation linking dysbiosis to gut barrier dysfunction during liver disease?

Changes in the intestinal microbiota composition contribute to the pathogenesis of many disorders including gastrointestinal and liver diseases. Recent studies have broadened our understanding of the "gut-liver" axis. Dietary changes, other environmental and genetic factors can lead to alterations in the microbiota. Dysbiosis can further disrupt the integrity of the intestinal barrier leading to pathological bacterial translocation and the initiation of an inflammatory response in the liver. In this article, the authors dissect the different steps involved in disease pathogenesis to further refine approaches for the medical management of liver diseases. The authors will specifically discuss the role of dysbiosis in inducing intestinal inflammation and increasing intestinal permeability.

Characterization of animal models for primary sclerosing cholangitis (PSC)

Primary sclerosing cholangitis (PSC) is a chronic cholangiopathy characterized by biliary fibrosis, development of cholestasis and end stage liver disease, high risk of malignancy, and frequent need for liver transplantation. The poor understanding of its pathogenesis is also reflected in the lack of effective medical treatment. Well-characterized animal models are utterly needed to develop novel pathogenetic concepts and study new treatment strategies. Currently there is no consensus on how to evaluate and characterize potential PSC models, which makes direct comparison of experimental results and effective exchange of study material between research groups difficult. The International Primary Sclerosing Cholangitis Study Group (IPSCSG) has therefore summarized these key issues in a position paper proposing standard requirements for the study of animal models of PSC.

Chronic cholestatic liver diseases: clues from histopathology for pathogenesis

Chronic cholestatic liver diseases include fibrosing cholangiopathies such as primary biliary cirrhosis or primary sclerosing cholangitis. These and related cholangiopathies clearly display pathologies associated with (auto)immunologic processes. As the cholangiocyte's apical membrane is exposed to the toxic actions of the bile fluid, the interaction of bile with cholangiocytes and the biliary tree in general must be considered to completely understand the pathogenesis of cholangiopathies. While the molecular processes involved in the hepatocellular formation of bile are well understood in both normal and pathophysiologic conditions, those in the bile ducts of normal liver and in livers with cholangiopathies lag behind. This survey highlights key mechanisms known to date that are important for the formation of bile by hepatocytes and its modification by the biliary tree. It also delineates the clinical pathophysiologic findings for cholangiopathies and puts them in perspective with current experimental models to reveal the pathogenesis of cholangiopathies and develop novel therapeutic approaches.

Pathogenesis of primary sclerosing cholangitis and advances in diagnosis and management

Primary sclerosing cholangitis (PSC), first described in the mid-1850s, is a complex liver disease that is heterogeneous in its presentation. PSC is characterized by chronic cholestasis associated with chronic inflammation of the biliary epithelium, resulting in multifocal bile duct strictures that can affect the entire biliary tree. Chronic inflammation leads to fibrosis involving the hepatic parenchyma and biliary tree, which can lead to cirrhosis and malignancy. The etiology of PSC is not fully understood, which in part explains the lack of effective medical therapy for this condition. However, we have begun to better understand the molecular pathogenesis of PSC. The recognition of specific clinical subtypes and their pattern of progression could improve phenotypic and genotypic classification of the disease. We review our current understanding of this enigmatic disorder and discuss important topics for future studies.

Randomised clinical trial: vancomycin or metronidazole in patients with primary sclerosing cholangitis - a pilot study

BACKGROUND

Emerging data suggest that oral antibiotics may have therapeutic effects in primary sclerosing cholangitis (PSC), but published studies are limited.

AIMS

To investigate the safety and efficacy of oral vancomycin and metronidazole in patients with PSC.

METHODS

Thirty-five patients with PSC were randomised in a double-blind manner into four groups: vancomycin 125 mg or 250 mg four times/day, or metronidazole 250 mg or 500 mg three times/day for 12 weeks. The primary endpoint was decrease in alkaline phosphatase (ALK) at 12 weeks. Secondary end points included serum bilirubin and Mayo PSC risk score; pruritus; and adverse effects (AEs). Nonparametric tests were used for analysis.

RESULTS

The primary endpoint was reached in the low-dose (-43% change in ALK, P = 0.03) and high-dose (-40%, P = 0.02) vancomycin groups, with two patients in the former experiencing ALK normalisation. Bilirubin decreased significantly in the low-dose metronidazole group (-20%, P = 0.03) and trended towards significance in the low-dose vancomycin group (-33%, P = 0.06). Mayo PSC risk score decreased significantly in the low-dose vancomycin (-0.55, P = 0.02) and low-dose metronidazole group (-0.16, P = 0.03). Pruritus decreased significantly in the high-dose metronidazole group (-3.4, P = 0.03). AEs led to medication discontinuation in six patients, four of whom were receiving metronidazole.

CONCLUSIONS

Both vancomycin and metronidazole demonstrated efficacy; however, only patients in the vancomycin groups reached the primary endpoint, and with less adverse effects. Larger, longer-term studies are needed to further examine the safety and efficacy of antibiotics as a potential treatment for patients with primary sclerosing cholangitis (clinicaltrials.gov NCT01085760).

Pathogenesis of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) represents a chronic cholestatic liver disease with fibroobliterative sclerosis of intra- and/or extrahepatic bile ducts, eventually leading to biliary cirrhosis. The association with human leukocyte antigen (HLA) and non-HLA haplotypes and the presence of autoantibodies in sera of PSC patients support a crucial role for immune-mediated mechanisms in the initiation and progression of PSC. The strong clinical association between PSC and inflammatory bowel diseases led to intriguing pathogenetic concepts, in which the inflamed gut with translocation of bacterial products and homing of gut-primed memory T lymphocytes via aberrantly expressed adhesion molecules plays a fundamental role. Genetically or chemically modified bile composition was shown to induce sclerosing cholangitis and liver fibrosis in a number of animal models ("toxic bile concept"). The potential role of vascular injury with ischemia of bile duct epithelium cells in the development of sclerosing cholangitis is supported by animal models of endothelial cell injury showing close morphological similarities with human PSC.

Will we ever model PSC? - "it's hard to be a PSC model!"

Cholangiopathies such as primary sclerosing cholangitis (PSC) represent an important group of liver diseases of the intra- and extrahepatic bile ducts frequently causing end-stage liver disease with significant morbidity and mortality due to limited treatment options. The relatively low incidence of PSC and the difficult accessibility of the human bile duct system for longitudinal studies may represent some of the critical reasons for the lack of profound knowledge in regard to PSC pathophysiology. Therefore, there is an urgent need for reliable, well-defined and easily reproducible animal models to learn more about the pathophysiology of PSC and to test novel treatment modalities. In an ideal world, immunogenetically predisposed animals would develop fibrous-obliterative cholangitis of the intra- and extrahepatic bile ducts in association with inflammation of the gut (especially colitis) in a highly reproducible manner allowing to test new drugs. To date, however, no such animal model is available. We aimed to provide a systematic overview of current available rodent models for sclerosing cholangitis and biliary fibrosis and therefore critically analyzed the characteristics of models for chemically-induced cholangitis, knock-out mouse models with cholangitis, cholangitis induced by infectious agents, models of experimental biliary obstruction, models involving enteric bacterial cell-wall components or colitis, and models of primary biliary epithelial and endothelial cell injury.

Risk factors for small bowel bacterial overgrowth in cystic fibrosis

OBJECTIVES

The purpose of this study was to determine the prevalence of small bowel bacterial overgrowth in patients with pancreatic-insufficient cystic fibrosis (CF) compared with age-matched controls and to identify potential risk factors for small bowel bacterial overgrowth.

PATIENTS AND METHODS

Fifty patients, 25 pancreatic-insufficient CF study patients (mean age, 17 y) and 25 gastrointestinal clinic control patients (mean age, 15 y), completed a glucose-hydrogen breath test after an overnight fast. Study patients completed a quality-of-life questionnaire modified from the Cystic Fibrosis Questionnaire. The medical history of each patient was compared with breath test results. A positive breath test was defined as a fasting hydrogen > or =15 ppm or a rise of > or =10 ppm hydrogen over baseline during the test.

RESULTS

The prevalence of positive breath tests was higher in the CF study group (56%) than in the control group (20%) (P = 0.02). The mean fasting hydrogen levels of patients in the study and control groups were 22 and 5 ppm (P = 0.0001). The mean questionnaire scores were not significantly different between breath test-positive and -negative study patients. The use of azithromycin was associated with an increased risk of a positive breath test. Use of laxatives and inhaled ipratropium was associated with a decreased risk of a positive breath test.

CONCLUSIONS

Patients with CF were more likely to have elevated fasting hydrogen levels compared with controls. This suggests a high prevalence of small bowel bacterial overgrowth in CF patients. Medications commonly used by CF patients may influence intestinal health.

Animal models for primary sclerosing cholangitis

Since the aetiopathogenesis of primary sclerosing cholangitis (PSC) in humans remains undefined, investigators have studied a variety of animal models to gain insights into immunopathogenetic mechanisms associated with obliterative fibrous cholangitis of intra- and extra-hepatic bile ducts. To date, no animal model has been developed that exhibits all of the attributes of PSC. Rodent models instigated by bacterial cell components or colitis are promising because they may help to explain the strong association between PSC and inflammatory bowel disease (IBD). Other models of direct injury to biliary epithelia, peribiliary vascular endothelia or portal venous endothelia indicate that inflammation, chemokines and cytokines can produce diffuse sclerosis of bile ducts. Models of toxic, infectious or intra-luminal injury of the biliary tract also exhibit focal biliary sclerosis mediated by inflammation and cytokines. The histopathology of several models suggests a sequence of events beginning with secretion of proinflammatory cytokines by activated hepatic macrophages followed by peribiliary infiltration with CD4 and CD8 T cells with a T helper 1 phenotype. These results strongly suggest co-ordinated, pathogenetic roles for both the innate and adaptive immune responses. However, the stimuli that initiate and perpetuate peribiliary fibrosis remain unknown. Interestingly, several models are also associated with the development of anti-neutrophil cytoplasmic antibodies that react in a perinuclear and cytoplasmic pattern similar to that observed in patients with ulcerative colitis and/or PSC. Finally, models of extra-hepatic biliary obstruction continue to provide important information about the pathogenesis of portal fibrosis and secondary biliary cirrhosis that occurs in PSC and other diseases with obstruction of bile flow. Future studies in either existing or new animal models should advance our understanding of the pathogenesis of PSC, the major prerequisite for the development of effective therapies.

Factors impacting the survival of children with intestinal failure referred for intestinal transplantation

PURPOSE

The aim of this study was to analyze factors impacting on the survival of pediatric patients with intestinal failure referred for intestinal transplantation (ITx).

METHODS

Two hundred fifty-seven children (mean age, 3.4+/-0.26 years) with intestinal failure were evaluated for ITx between 1990 and 1998. All patients were dependent on total parenteral nutrition (TPN) for a mean of 31+/-2.7 months. The mean follow-up time from the date of evaluation was 9.2+/-0.9 months.

RESULTS

Eighty-two (32%) children underwent ITx with a mean waiting time of 10.1+/-1.3 months (simultaneous liver-intestinal allograft in 68% instances). Of the 175 patients who did not undergo transplantation, 120 died, 23 were lost to follow-up, and 32 are alive. Younger patients (< or =1 year) had poorer survival rates than patients older than 1 year (P<.0001). The patients with the worse prognosis were those with necrotizing enterocolitis, and those with the best prognosis were those with Hirschsprung's disease. Patients with "surgical" causes had poorer survival rates than those with "nonsurgical" causes (P<.04). Patients with bridging fibrosis or established cirrhosis had an earlier mortality than patients with portal fibrosis (P<.003). The worst survival rate was found for patients with bilirubin levels of greater than 3 mg/dL (P<.0001), plateletcounts less than 100.000/mL (P<.0001), prothrombin time greater than 15 seconds (P = .03) or partial thromboplastin time greater than 40 seconds (P<.04). Children who at the time of evaluation needed only an isolated intestinal allograft had a better prognosis than those who required a combined liver-intestine allograft (P<.00001). With multivariate analysis independent prognosis risk factors of poor outcome were hyperbilirubinemia and severity of histopathologic damage.

CONCLUSIONS

Early referral for ITx should occur before the development of liver dysfunction, taking into consideration the aforementioned risk factors that would facilitate the development and ominous evolution to liver failure.