Reiner Wiest

Bacterial translocation (BT) in cirrhosis

Gut flora and bacterial translocation (BT) play an important role in the pathogenesis of the complications of cirrhosis. Research on the pathogenesis of BT and its clinical significance transcends established boundaries between microbiology, cell biology, intestinal pathophysiology, and immunology. This review delineates multiple mechanisms involved in the process of BT, with an emphasis on alterations in intestinal flora and mucosal barrier function, particularly immunological defense mechanisms. Current knowledge on the innate and adaptive immune response that allows a “friendly” communication between bacteria and host is summarized, and alterations occurring in cirrhosis that may facilitate BT are discussed. In addition, definition of a “pathological” BT is proposed together with an analysis of the anatomical site and route of BT. Finally, therapeutic approaches for the prevention of BT in experimental and human cirrhosis are reviewed. Future research in the field of BT in cirrhosis will allow the development of new therapeutic targets in the prevention of infections and other complications of cirrhosis. (HEPATOLOGY 2005;41:422–433.)

Bacterial infections in cirrhosis: A position statement based on the EASL Special Conference 2013

Bacterial infections are very common and represent one of the most important reasons of progression of liver failure, development of liver-related complications, and mortality in patients with cirrhosis. In fact, bacterial infections may be a triggering factor for the occurrence of gastrointestinal bleeding, hypervolemic hyponatremia, hepatic encephalopathy, kidney failure, and development of acute-on-chronic liver failure. Moreover, infections are a very common cause of repeated hospitalizations, impaired health-related quality of life, and increased healthcare costs in cirrhosis. Bacterial infections develop as a consequence of immune dysfunction that occurs progressively during the course of cirrhosis. In a significant proportion of patients, infections are caused by gram-negative bacteria from intestinal origin, yet gram-positive bacteria are a frequent cause of infection, particularly in hospitalized patients. In recent years, infections caused by multidrug-resistant bacteria are becoming an important clinical problem in many countries. The reduction of the negative clinical impact of infections in patients with cirrhosis may be achieved by a combination of prophylactic measures, such as administration of antibiotics, to reduce the occurrence of infections in high-risk groups together with early identification and management of infection once it has developed. Investigation on the mechanisms of altered gut microflora, translocation of bacteria, and immune dysfunction may help develop more effective and safe methods of prevention compared to those that are currently available. Moreover, research on biomarkers of early infection may be useful in early diagnosis and treatment of infections. The current manuscript reports an in-depth review and a position statement on bacterial infections in cirrhosis.

Pathological bacterial translocation in liver cirrhosis

Humans harbor nearly 100 trillion intestinal bacteria, which in terms of numbers, represents around ten times more microbial cells than eukaryotic cells. The gastrointestinal (GI) tract, the largest surface area of the body with an epithelial surface of approximately 400 m, is in constant exposure to these live microorganisms. Their peaceful coexistence demonstrated by the lack of pro-inflammatory responses against commensal bacteria implicates the presence of clearly defined lines of communication. In fact, bacterial translocation (BT), being defined as translocation of bacteria and/or bacterial products (lipopolysaccharides, peptidoglycans, muramyl-dipeptides, bacterial DNA, etc.) from the gut to mesenteric lymph nodes (MLN) [1], is a physiological process in healthy conditions and crucial for host immunity. In contrast, in cirrhosis ‘‘pathological’’ BT develops with a sustained increase in quantity (rate and/or degree) of BT. However, at least in humans, lack of access to MLN and/or upstream compartments towards the mucosal barrier until now hamper establishment of ‘‘cut-off’’ levels for physiological levels of BT in individual patients. Nonetheless, there appears to exist a hierarchy of three barriers against pathological BT, each of which encompasses a distinct set of mechanisms (Fig. 1). First, there are mediators that limit direct contact between the intestinal bacteria and the epithelial cell surface. Secondly, a layer of immune protection involves the rapid detection and killing of bacteria that manage to penetrate. Finally, a set of immune responses minimizes exposure of bacteria to the systemic immune system. In advanced liver cirrhosis, at each of these

Bacterial translocation in the gut

The human gastrointestinal tract is colonized by a dense population of microorganisms, referred to as the bacterial flora. Although the gut provides a functional barrier between these organisms and the host, bacterial translocation is a common event in the healthy person. However, in critically ill patients, with various underlying diseases, this bacterial translocation may lead to infections and consequently to a further reduction in general health status. The mechanism of bacterial translocation is widely, and somehow controversially investigated in vitro and in animal models. In human studies, several diseases have been associated with bacterial translocation. However, methodological shortcomings, insufficient populations and conflicting results leave many open questions. This is also reflected in the various published therapeutic strategies. To overcome this problem more investigations in humans are needed, especially in techniques for detecting bacterial translocation.

The role of the sympathetic nervous system in intestinal inflammation

The nervous system in the intestine controls motility, secretion, sensory perception, and immune function. Peptidergic neurones with neurotransmitters such as substance P and nerve growth factors have been the main focus of neuroimmunomodulation research in the gut. This review summarises the present knowledge concerning the role of the sympathetic nervous system (SNS) in modulating intestinal inflammation. The role of the SNS for gut inflammation is compared with its role in rheumatoid arthritis which demonstrates notable similarities. Nerve fibres of the SNS not only enter the enteric plexuses but also innervate the mucosa and gut associated lymphoid tissue (GALT). The SNS has pro- and anti-inflammatory functions. Neurotransmitters such as norepinephrine, adenosine, and others can evoke remarkably different opposing effects depending on concentration (presence of sympathetic nerve fibres and extent of neurotransmitter release), receptor affinity at different receptor subtypes, expression of adrenoceptors, availability of cotransmitters, and timing of SNS activity in relation to the inflammatory course. This review attempts to integrate the different perspectives of the pro- and anti-inflammatory effects of the SNS on inflammatory disease of the gut.

Role of TLR9 in hepatic stellate cells and experimental liver fibrosis

Accumulating evidence indicates that bacteria and bacterial products promote hepatic fibrogenesis. The activation of hepatic stellate cells (HSC) plays a central role in hepatic fibrosis. Here, we demonstrate that HSC express toll-like receptor 9 (TLR9), a pattern recognition receptor that is activated by CpG motifs present specifically in bacterial DNA. Upon CpG stimulation human as well as murine HSC isolated from wild-type (TLR9+/+) mice express increased levels of the profibrogenic chemokine monocyte chemotactic protein 1 (MCP-1). In contrast, HSC isolated from TLR9 deficient (TLR9-/-) mice lacked CpG motif induced MCP-1 expression indicating the functionality of TLR9 in HSC. Bile duct ligation revealed significantly lower hepatic MCP-1 and collagen expression and less hepatic fibrosis in TLR9-/- compared to TLR9+/+ mice. In addition, the expression of hepatic alpha-smooth-muscle actin, a known marker for HSC activation, was reduced in TLR9-/- mice indicating that bacterial DNA induces the activation of HSC and therefore promotes hepatic fibrosis.

Prevention of Rebleeding From Esophageal Varices in Patients With Cirrhosis Receiving Small-Diameter Stents Versus Hemodynamically Controlled Medical Therapy

BACKGROUND & AIMSnPatients with cirrhosis and variceal hemorrhage have a high risk of rebleeding. We performed a prospective randomized trial to compare the prevention of rebleeding in patients given a small-diameter covered stent vs those given hepatic venous pressure gradient (HVPG)-based medical therapy prophylaxis.nnnMETHODSnWe performed an open-label study of patients with cirrhosis (92% Child class A or B, 70% alcoholic) treated at 10 medical centers in Germany. Patients were assigned randomly more than 5 days after variceal hemorrhage to groups given a small covered transjugular intrahepatic portosystemic stent-shunt (TIPS) (8 mm; n = 90), or medical reduction of portal pressure (propranolol and isosorbide-5-mononitrate; n = 95). HVPG was determined at the time patients were assigned to groups (baseline) and 2 weeks later. In the medical group, patients with an adequate reduction in HVPG (responders) remained on the drugs whereas nonresponders underwent only variceal band ligation. The study was closed 10 months after the last patient was assigned to a group. The primary end point was variceal rebleeding. Survival, safety (adverse events), and quality of life (based on the Short Form-36 health survey) were secondary outcome measures.nnnRESULTSnA significantly smaller proportion of patients in the TIPS group had rebleeding within 2 years (7%) than in the medical group (26%) (P = .002). A slightly higher proportion of patients in the TIPS group experienced adverse events, including encephalopathy (18% vs 8% for medical treatment; P = .05). Rebleeding occurred in 6 of 23 patients (26%) receiving medical treatment before hemodynamic control was possible. Per-protocol analysis showed that rebleeding occurred in a smaller proportion of the 32 responders (18%) than in nonresponders who received variceal band ligation (31%) (P = .06). Fifteen patients from the medical group (16%) underwent TIPS placement during follow-up evaluation, mainly for refractory ascites. Survival time and quality of life did not differ between both randomized groups.nnnCONCLUSIONSnPlacement of a small-diameter, covered TIPS was straightforward and prevented variceal rebleeding in patients with Child A or B cirrhosis more effectively than drugs, which often required step-by-step therapy. However, TIPS did not increase survival time or quality of life and produced slightly more adverse events. Clinical Trial no: ISRCTN 16334693.

NOD2 gene variants are a risk factor for culture-positive spontaneous bacterial peritonitis and monomicrobial bacterascites in cirrhosis.

Background: Spontaneous bacterial peritonitis (SBP) is considered as result of bacterial translocation from the gastrointestinal lumen to the mesenteric lymph nodes and subsequent circulation. Variants of the NOD2 gene contribute to bacterial translocation and were associated with SBP in a recent study.

Splanchnic sympathectomy prevents translocation and spreading of E coli but not S aureus in liver cirrhosis

Introduction Spontaneous bacterial peritonitis (SBP) is mainly caused by bacterial translocation of enteric Gram-negative bacteria, predominantly Escherichia coli. The sympathetic nervous system (SNS) is activated in advanced cirrhosis, particularly in the splanchic circulation, and exerts potent immunosuppressive actions. However, the role of splanchnic SNS activity in bacterial translocation and bacterial spreading in cirrhosis remains unclear. Methods E coli or Stapylococcus aureus (106 CFU) were given intraperitoneally. After 6u2005h, mesenteric lymph nodes (MLN), liver, spleen, lung and peripheral blood were harvested from ascitic cirrhotic rats (LC) and healthy controls with and without splanchnic sympathectomy (SE). The bacterial tissue burden was determined by standard microbiological culture techniques. In vitro phagocytic activity of peritoneal polymorphonuclear leucocytes was assessed by FACS analysis. Results Under basal conditions SE reduced bacterial translocation to MLN in LC rats from 45% to 17%. LC rats had a marked increase in bacteraemia after E coli and S aureus challenge and an increased incidence and degree of E coli translocation to MLN, liver, spleen and lung compared with control rats. SE prevented bacteraemia in LC rats after E coli but not after S aureus challenge. Prior SE abolished the difference in incidence as well as the bacterial tissue burden in each organ after E coli application in LC rats, being no longer significantly different from control rats with or without SE. The protective effects of SE against E coli were associated with a greater influx of mononuclear cells into the peritoneal cavity and increased phagocytic activity of peritoneal polymorphonuclear leucocytes. Conclusions In cirrhosis with bacterial peritonitis, hyperactivity of the splanchnic sympathetic nervous system contributes to the translocation of E coli but not S aureus to MLN and extraintestinal sites. This indicates a key role for sympathetic drive in the impairment in host defence against Gram-negative bacteria in cirrhosis.

Genetic susceptibility to increased bacterial translocation influences the response to biological therapy in patients with Crohn's disease

Objective The aetiology of Crohns disease (CD) has been related to nucleotide-binding oligomerisation domain containing 2 (NOD2) and ATG16L1 gene variants. The observation of bacterial DNA translocation in patients with CD led us to hypothesise that this process may be facilitated in patients with NOD2/ATG16L1-variant genotypes, affecting the efficacy of anti-tumour necrosis factor (TNF) therapies. Design 179 patients with Crohns disease were included. CD-related NOD2 and ATG16L1 variants were genotyped. Phagocytic and bactericidal activities were evaluated in blood neutrophils. Bacterial DNA, TNFα, IFNγ, IL-12p40, free serum infliximab/adalimumab levels and antidrug antibodies were measured. Results Bacterial DNA was found in 44% of patients with active disease versus 23% of patients with remitting disease (p=0.01). A NOD2-variant or ATG16L1-variant genotype was associated with bacterial DNA presence (OR 4.8; 95% CI 1.1 to 13.2; p=0.001; and OR 2.4; 95% CI 1.4 to 4.7; p=0.01, respectively). This OR was 12.6 (95% CI 4.2 to 37.8; p=0.001) for patients with a double-variant genotype. Bacterial DNA was associated with disease activity (OR 2.6; 95% CI 1.3 to 5.4; p=0.005). Single and double-gene variants were not associated with disease activity (p=0.19). Patients with a NOD2-variant genotype showed decreased phagocytic and bactericidal activities in blood neutrophils, increased TNFα levels in response to bacterial DNA and decreased trough levels of free anti-TNFα. The proportion of patients on an intensified biological therapy was significantly higher in the NOD2-variant groups. Conclusions Our results characterise a subgroup of patients with CD who may require a more aggressive therapy to reduce the extent of inflammation and the risk of relapse.