Gut flora and bacterial translocation in chronic liver disease

Increasing evidence suggests that derangement of gut flora is of substantial clinical relevance to patients with cirrhosis. Intestinal bacterial overgrowth and increased bacterial translocation of gut flora from the intestinal lumen, in particular, predispose to an increased potential for bacterial infection in this group. Recent studies suggest that, in addition to their role in the pathogenesis of overt infective episodes and the clinical consequences of sepsis, gut flora contributes to the pro-inflammatory state of cirrhosis even in the absence of overt infection. Furthermore, manipulation of gut flora to augment the intestinal content of lactic acid-type bacteria at the expense of other gut flora species with more pathogenic potential may favourably influence liver function in cirrhotic patients. Here we review current concepts of the various inter-relationships between gut flora, bacterial translocation, bacterial infection, pro-inflammatory cytokine production and liver function in this group.     

肝硬化细菌移位及其后果

随着人们对细菌移位（bacterial translocation，BT）后果研究的不断深入，BT的概念已从传统的有活性的肠道菌群通过肠道屏障到达肠系膜淋巴结和肠腔外其他器官或部位，延伸到细菌释放产物（如内毒素和细菌DNA）的移位。现就细菌移位过程中的多种机制，特别是肠内菌群和黏膜屏障功能的改变及免疫防御机制综述如下。     

Management of bacterial infection in the liver transplant candidate

Bacterial infection(BI) is a common cause of impairment of liver function in patients with cirrhosis, especially in the liver transplant candidates. These patients share an immunocompromised state and increased susceptibility to develop community and hospital-acquired infections. The changing epidemiology of BI, with an increase of multidrug resistant strains, especially in healthcareassociated settings, represents a critical issue both in the waiting list and in the post-operative management. This review focused on the role played by BI in patients awaiting liver transplantation, evaluating the risk of drop-out from the waiting list, the possibility to undergo liver transplantation after recovery from infection or during a controlled infection.     

Gut microbiota-related complications in cirrhosis

Gut microbiota plays an important role in cirrhosis. The liver is constantly challenged with commensal bacteria and their products arriving through the portal vein in the so-called gut-liver axis. Bacterial translocation from the intestinal lumen through the intestinal wall and to mesenteric lymph nodes is facilitated by intestinal bacterial overgrowth, impairment in the permeability of the intestinal mucosal barrier, and deficiencies in local host immune defences. Deranged clearance of endogenous bacteria from portal and systemic circulation turns the gut into the major source of bacterial-related complications. Liver function may therefore be affected by alterations in the composition of the intestinal microbiota and a role for commensal flora has been evidenced in the pathogenesis of several complications arising in end-stage liver disease such as hepatic encephalopathy, splanchnic arterial vasodilatation and spontaneous bacterial peritonitis. The use of antibiotics is the main therapeutic pipeline in the management of these bacteria-related complications. However, other strategies aimed at preserving intestinal homeostasis through the use of pre-, pro- or symbiotic formulations are being studied in the last years. In this review, the role of intestinal microbiota in the development of the most frequent complications arising in cirrhosis and the different clinical and experimental studies conducted to prevent or improve these complications by modifying the gut microbiota composition are summarized.     

Starring role of toll-like receptor-4 activation in the gut-liver axis

Since the introduction of the term “gut-liver axis”, many studies have focused on the functional links of intestinal microbiota, barrier function and immune responses to liver physiology. Intestinal and extra-intestinal diseases alter microbiota composition and lead to dysbiosis, which aggravates impaired intestinal barrier function via increased lipopolysaccharide translocation. The subsequent increased passage of gut-derived product from the intestinal lumen to the organ wall and bloodstream affects gut motility and liver biology. The activation of the toll-like receptor 4 (TLR-4) likely plays a key role in both cases. This review analyzed the most recent literature on the gut-liver axis, with a particular focus on the role of TLR-4 activation. Findings that linked liver disease with dysbiosis are evaluated, and links between dysbiosis and alterations of intestinal permeability and motility are discussed. We also examine the mechanisms of translocated gut bacteria and/or the bacterial product activation of liver inflammation and fibrogenesis via activity on different hepatic cell types.     

Bacterial translocation and changes in the intestinal microbiome associated with alcoholic liver disease

Alcoholic liver disease progresses through several stages of tissue damage, from simple steatosis to alcoholic hepatitis, fibrosis, or cirrhosis. Alcohol also affects the intestine, increases intestinal permeability and changes the bacterial microflora. Liver disease severity correlates with levels of systemic bacterial products in patients, and experimental alcoholic liver disease is dependent on gut derived bacterial products in mice. Supporting evidence for the importance of bacterial translocation comes from animal studies demonstrating that intestinal decontamination is associated with decreased liver fibrogenesis. In addition, mice with a gene mutation or deletion encoding receptors for either bacterial products or signaling molecules downstream from these receptors, are resistant to alcohol-induced liver disease. Despite this strong association, the exact molecular mechanism of bacterial translocation and of how changes in the intestinal microbiome contribute to liver disease progression remains largely unknown. In this review we will summarize evidence for bacterial translocation and enteric microbial changes in response to alcoholic liver injury and chronic alcoholic liver disease. We will further describe consequences of intestinal dysbiosis on host biology. We finally discuss how therapeutic interventions may modify the gastrointestinal microflora and prevent or reduce alcoholic liver disease progression.     

Gut-liver axis signaling in portal hypertension

Portal hypertension(PHT) in advanced chronic liver disease(ACLD) results from increased intrahepatic resistance caused by pathologic changes of liver tissue composition(structural component) and intrahepatic vasoconstriction(functional component). PHT is an important driver of hepatic decompensation such as development of ascites or variceal bleeding. Dysbiosis and an impaired intestinal barrier in ACLD facilitate translocation of bacteria and pathogen-associated molecular patterns(PAMPs) that promote disease progression via immune system activation with subsequent induction of proinflammatory and profibrogenic pathways. Congestive portal venous blood flow represents a critical pathophysiological mechanism linking PHT to increased intestinal permeability: The intestinal barrier function is affected by impaired microcirculation, neoangiogenesis, and abnormal vascular and mucosal permeability. The close bidirectional relationship between the gut and the liver has been termed "gut-liver axis". Treatment strategies targeting the gut-liver axis by modulation of microbiota composition and function, intestinal barrier integrity, as well as amelioration of liver fibrosis and PHT are supposed to exert beneficial effects. The activation of the farnesoid X receptor in the liver and the gut was associated with beneficial effects in animal experiments, however,further studies regarding efficacy and safety of pharmacological FXR modulation in patients with ACLD are needed. In this review, we summarize the clinical impact of PHT on the course of liver disease, discuss the underlying pathophysiological link of PHT to gut-liver axis signaling, and provide insight into molecular mechanisms that may represent novel therapeutic targets.     

胆汁酸对失代偿期肝硬化大鼠肠道细菌过度生长和细菌移位的影响

目的观察胆汁酸对失代偿期肝硬化大鼠肠道细菌过度生长和移位的影响,为其临床应用提供依据。方法将37只伴有腹水的肝硬化大鼠及30只健康大鼠随机分为三组,分别采用结合胆汁酸甘氨胆酸(CG)、非结合胆汁酸熊去氧胆酸(UDCA)[均为70mg/(kg·d)]和安慰剂治疗2周。测定胆汁分泌速度、回肠细菌总数、细菌移位率。结果安慰剂组肝硬化大鼠胆汁分泌速度显著低于健康大鼠(P<0.001);胆汁酸治疗后速度增至正常水平。肝硬化大鼠回肠细菌总量显著高于健康大鼠(P<0.001),予胆汁酸治疗后降至正常水平。予胆汁酸的肝硬化大鼠细菌移位发生率显著低于安慰剂治疗组(P<0.01),存活率显著高于安慰剂组。结论失代偿期肝硬化大鼠应用结合或非结合胆汁酸可增加胆汁分泌、抑制肠道细菌过度生长,减少细菌移位的发生率,提高存活率。     

Intestinal bacterial overgrowth and bacterial translocation in cirrhotic rats with ascites

Background/Aims: Translocation of indigenous bacterial from the gut lumen of cirrhotic animals to mesenteric lymph nodes appears to be an important step in the pathogenesis of spontaneous bacterial peritonitis. However, the sequence of events leading to translocation remains unclear. One of the most predictable risk factors for translocation is overgrowth of gut bacterial flora. The present study was designed to compare the intestinal aerobic bacterial flora of cecal stools at the time of sacrifice between cirrhotic and normal rats and to evaluate the role of intestinal aerobic bacterial overgrowth in bacterial translocation in cirrhotic rats.Methods: Thirty-five male Sprague-Dawley rats with carbon tetrachloride-induced cirrhosis and ascites and 10 normal rats were included in this study. Cirrhotic rats were sacrificed when ill and samples of ascitic fluid, mesenteric lymph nodes and cecal stool were taken for detecting quantitatively aerobic bacteria.Results: Total intestinal aerobic bacterial count in cecal stool at the time of sacrifice was significantly increased in cirrhotic rats with bacterial translocation with or without spontaneous bacterial peritonitis compared to cirrhotic rats without bacterial translocation (p<0.001 and p<0.001, respectively) and to normal rats (p<0.001 and p<0.001, respectively). Of the 42 species of bacteria translocating to the mesenteric lymph nodes, 41 (97.6%) were found in supranormal numbers in the stool at the time of sacrifice.Conclusions: Carbon tetrachloride-induced cirrhotic rats with bacterial translocation have increased total intestinal aerobic bacteria count, and intestinal bacterial overgrowth appears to play an important role in bacterial translocation in this experimental model of cirrhosis in rats.     

Intestinal barrier dysfunction in cirrhosis: Current concepts in pathophysiology and clinical implications

The intestinal lumen is a host place for a wide range of microbiota and sets a unique interplay between local immune system, inflammatory cells and intestinal epithelium, forming a physical barrier against microbial invaders and toxins. Bacterial translocation is the migration of viable or nonviable microorganisms or their pathogen-associated molecular patterns, such as lipopolysaccharide, from the gut lumen to the mesenteric lymph nodes, systemic circulation and other normally sterile extraintestinal sites. A series of studies have shown that translocation of bacteria and their products across the intestinal barrier is a commonplace in patients with liver disease. The deterioration of intestinal barrier integrity and the consulting increased intestinal permeability in cirrhotic patients play a pivotal pathophysiological role in the development of severe complications as high rate of infections, spontaneous bacterial peritonitis, hepatic encephalopathy, hepatorenal syndrome, variceal bleeding, progression of liver injury and hepatocellular carcinoma. Nevertheless, the exact cellular and molecular mechanisms implicated in the phenomenon of microbial translocation in liver cirrhosis have not been fully elucidated yet.     

肝硬化大鼠模型肠壁结构及细菌移位的研究

目的 研究肝硬化大鼠模型肠黏膜结构的改变及细菌移位.方法 采用皮下注射40%四氯化碳诱导大鼠肝硬化模型,比较肝硬化大鼠模型与正常对照组小肠组织结构及超微结构的变化;将肝、脾和肠系膜淋巴结组织匀浆进行细菌培养,了解肠道细菌移位情况;采用鲎实验检测血浆内毒素水平.结果 与正常对照组相比,肝硬化模型组小肠绒毛表面积显著下降(P<0.01),而肠隐窝深度无明显变化(P>0.05),肠黏膜上皮细胞微绒毛明显缩短、稀疏,上皮细胞间紧密连接结构模糊,细胞间隙增大;肝硬化模型组肝、脾、肠系膜淋巴结细菌移位发生率分别为16.67%、16.67%和41.67%,正常对照组未发现细菌生长;肝硬化模型组血浆内毒素水平明显高于正常对照组(P<0.01).结论 肝硬化大鼠模型肠黏膜上皮组织及超微结构发生改变,从而导致肠道细菌移位和血浆内毒素水平的升高.     

内源性大麻素系统对肝硬化的影响

内源性大麻素系统包括内源性大麻素物质、特异性大麻素受体1(cannabinoid receptor1,CB1)和大麻素受体2(cannabinoid receptor2,CB2).许多研究已经证实在慢性肝病发展过程中,肝脏肌成纤维细胞和血管内皮细胞的CB1和CB2表达升高,内源性大麻素系统与肝纤维化及肝硬化关系密切.本文就内源性大麻素系统、内源性大麻素系统和脂肪性肝病、内源性大麻素系统和肝纤维化、内源性大麻素系统和肝硬化并发症等作一综述.     

Prognostic significance of hepatic encephalopathy in patients with cirrhosis treated with current standards of care

BACKGROUND Hepatic encephalopathy(HE) is a reversible neuropsychiatric complication of liver cirrhosis and occurs in up to 50% of cirrhotic patients. Studies examining the prognostic significance of HE are limited despite the high prevalence in cirrhosis.AIM To define the clinical outcomes of patients after an episode of HE treated with current standards-of-care.METHODS All patients hospitalised with HE requiring Rifaximin to 3 tertiary centres over46-mo(2012–2016) were identified via pharmacy dispensing records. Patients with hepatocellular carcinoma and those prescribed Rifaximin prior to admission were excluded. Medical records were reviewed to determine baseline characteristics and survival. The Kaplan-Meier method was used to calculate survival probability. Univariate survival analysis was performed with variables reaching statistical significance included in a multivariate analysis. The primary outcome was 12-mo mortality following commencement of Rifaximin.RESULTS188 patients were included. Median age was 57 years(IQR 50-65), 71% were male and median model for end stage liver disease and Child Pugh scores were 25(IQR 18-31) and 11(IQR 9-12) respectively. The most common causes of cirrhosis were alcohol(62%), hepatitis C(31%) and non-alcoholic fatty liver disease(20%).A precipitating cause for HE was found in 92% patients with infection(43%), GI bleeding(16%), medication non-compliance(15%) and electrolyte imbalance(14%) the most common. During a mean follow up period of 12 ± 13 mo 107(57%) patients died and 32(17%) received orthotopic liver transplantation. Themost common causes of death were decompensated chronic liver disease(57%)and sepsis(19%). The probability of survival was 44% and 35% at 12-and 24-mo respectively. At multivariate analysis a model for end stage liver disease 15 and international normalised ratio reached statistical significance in predicting mortality.CONCLUSION Despite advances made in the management of HE patients continue to have poor survival. Thus, in all patients presenting with HE the appropriateness of orthotopic liver transplantation should be considered.     

Bacterial translocation in patients with liver cirrhosis: physiology,clinical consequences,and practical implications

Introduction: The gut liver axis is an operative unit that works to protect the human body against potentially harmful substances and microorganisms, maintaining the homeostasis of the immune system. Liver cirrhosis profoundly alters this complex system. The intestine becomes more permeable allowing the translocation of bacteria, bacterial products and fragments into the portal circulation, triggering an abnormal local and systemic inflammatory response and a condition of perpetual immunologic alarm. This immune-inflammatory disorder related to dysbiosis is involved in the development of liver damage and liver cirrhosis complications and increases intestinal permeability in a vicious circle.

Areas covered: The most relevant studies on bacterial translocation, the mechanism of intestinal barrier dysfunction and its consequences in patients with liver cirrhosis have been revised through a PubMed search. Data have been discussed with particular regard to their significance in clinical practice.

Expert commentary: The assessment of bacterial translocation and intestinal permeability is not currently used in clinical practice but may be useful to stratify patients’ prognosis.     

Role of vaptans in the management of hydroelectrolytic imbalance in liver cirrhosis

Ascites and hyponatremia are the most common complications in patients with liver cirrhosis and develop as a consequence of a severe impairment of liver function and portal hypertension. Increasing evidences support the central role of renal function alterations in the pathogenesis of hydroelectrolytic imbalances in cirrhotic patients, thus implying a dense cross-talk between liver and kidney in the systemic and splanchnic vascular homeostasis in such subjects. Since Arginin Vasopressin (AVP) hyperincretion occurs at late stage of cirrhosis and plays an important role in the development of refractory ascites, dilutional hyponatremia and finally hepato-renal syndrome, selective antagonists of AVP receptors V₂ (vaptans) have been recently introduced in the therapeutic algorithm of advanced cirrhotic patients. Despite the promising results of earlier phase-two studies, randomized controlled trials failed to find significant results in terms of efficacy of such drugs both in refractory ascites and hyponatremia. Moreover, concerns on their safety profile arise, due to the number of potentially severe side effects of vaptans in the clinical setting, such as hypernatremia, dehydration, renal impairment, and osmotic demyelination syndrome. More robust data from randomized controlled trials are needed in order to confirm the potential role of vaptans in the management of advanced cirrhotic patients.     

Effect of artesunate supplementation on bacterial translocation and dysbiosis of gut microbiota in rats with liver cirrhosis

AIM: To evaluate the effect of artesunate(AS) supplementation on bacterial translocation(BT) and gut microbiota in a rat model of liver cirrhosis. METHODS: Fifty-four male Sprague-Dawley rats were randomly divided into a normal control group(N), a liver cirrhosis group(M) and a liver cirrhosis group intervened with AS(MA). Each group was sampled at 4, 6 and 8 wk. Liver cirrhosis was induced by injection of carbon tetrachloride(CCl4), intragastric administration of 10% ethanol, and feeding a high fat diet. Rats in the MA group were intragastrically administered with AS(25 mg/kg body weight, once daily). Injuries of the liver and intestinal mucosa were assessed by hematoxylineosin or Masson's trichrome staining. Liver index was calculated as a ratio of the organ weight(g) to body weight(g). The gut microbiota was examined by automated ribosomal intergenic-spacer analysis of fecal DNA. BT was assessed by standard microbiological techniques in the blood, mesenteric lymph nodes(MLNs), liver, spleen, and kidney. RESULTS: Compared to group N, the body weight was reduced significantly in groups M and MA due to the development of liver cirrhosis over the period of 8 wk. The body weight was higher in group MA than in group M. The liver indices were significantly elevated at 4, 6 and 8 wk in groups M and MA compared to group N. AS supplementation partially decreased the liver indices in group MA. Marked histopathologic changes in the liver and small intestinal mucosa in group M were observed, which were alleviated in group MA. Levels of pro-inflammatory interleukin-6 and tumor necrosis factor-α were significantly elevated at 8 wk in ileal homogenates in group M compared to group N, which were decreased after AS supplementation in group MA. The dysbiosis of gut microbiota indicated by the mean diversity(Shannon index) and mean similarity(Sorenson index) was severe as the liver cirrhosis developed, and AS supplementation had an apparent intervention effect on the dysbiosis of gut microbiota at 4 wk. The occurrence of BT was increased in the liver of group M compared to that of group N. AS supplementation reduced BT in group MA at 8 wk. BT also occurred in the MLNs, spleen, and kidney, which was reduced by AS supplementation. BT was not detected in the blood in any group.CONCLUSION: Dysbiosis of gut microbiota, injury of intestinal mucosal barrier and BT occurred as liver cirrhosis progressed, which might enhance inflammation and aggravate liver injury. AS may have other nonantimalarial effects that modulate gut microbiota,inhibit BT and alleviate inflammation, resulting in a reduction in CCl4, alcohol and high fat-caused damages to the liver and intestine.     

Liver surgery in cirrhosis and portal hypertension

The prevalence of hepatic cirrhosis in Europe and the United States, currently 250 patients per 100000 inhabitants, is steadily increasing. Thus, we observe a significant increase in patients with cirrhosis and portal hypertension needing liver resections for primary or metastatic lesions. However, extended liver resections in patients with underlying hepatic cirrhosis and portal hypertension still represent a medical challenge in regard to perioperative morbidity, surgical management and postoperative outcome. The Barcelona Clinic Liver Cancer classification recommends to restrict curative liver resections for hepatocellular carcinoma in cirrhotic patients to early tumor stages in patients with Child A cirrhosis not showing portal hypertension. However, during the last two decades, relevant improvements in preoperative diagnostic, perioperative hepatologic and intensive care management as well as in surgical techniques during hepatic resections have rendered even extended liver resections in higher-degree cirrhotic patients with portal hypertension possible. However, there are few standard indications for hepatic resections in cirrhotic patients and risk stratifications have to be performed in an interdisciplinary setting for each individual patient. We here review the indications, the preoperative risk-stratifications, the morbidity and the mortality of extended resections for primary and metastatic lesions in cirrhotic livers. Furthermore, we provide a review of literature on perioperative management in cirrhotic patients needing extrahepatic abdominal surgery and an overview of surgical options in the treatment of hepatic cirrhosis.     

70例肝硬化门脉高压症患者术前评估及术后生存率分析

目的研究门脉高压症患者术前肝功能及病毒复制状况对其预后的影响。方法按改良Child肝功能分级法对70例肝硬化门脉高压症接受手术治疗者作术前肝功能评估,并对术后并发症、肝炎再活动、1年和5年生存率进行分析。结果肝功能分级与手术时机的选择是影响预后的独立因素,5年生存率依次为A级〉B级〉C级;活动性肝硬化术后并发症发生率显著高于静止期肝硬化（P〈0．01）;急症手术者术后死亡率显著高于择期手术者（P〈0．01）;术前病毒复制指标阳性者术后半年内肝炎活动率显著高于病毒复制指标阴性者（P〈0．01）。结论肝硬化门脉高压症患者术后5年生存率与术前肝功能贮备密切相关,急症手术的风险较之择期手术的风险为大。     

Rifaximin has minor effects on bacterial composition,inflammation, and bacterial translocation in cirrhosis: A randomized trial

Background and Aim

Decompensated cirrhosis is characterized by disturbed hemodynamics, immune dysfunction, and high risk of infections. Translocation of viable bacteria and bacterial products from the gut to the blood is considered a key driver in this process. Intestinal decontamination with rifaximin may reduce bacterial translocation (BT) and decrease inflammation. A randomized, placebo‐controlled trial investigated the effects of rifaximin on inflammation and BT in decompensated cirrhosis.

Methods

Fifty‐four out‐patients with cirrhosis and ascites were randomized, mean age 56 years (± 8.4), and model for end‐stage liver disease score 12 (± 3.9). Patients received rifaximin 550‐mg BD (n = 36) or placebo BD (n = 18). Blood and fecal (n = 15) sampling were conducted at baseline and after 4 weeks. Bacterial DNA in blood was determined by real‐time qPCR 16S rRNA gene quantification. Bacterial composition in feces was analyzed by 16S rRNA gene sequencing.

Results

Circulating markers of inflammation, including tumor necrosis factor alpha, interleukins 6, 10, and 18, stromal cell‐derived factor 1‐α, transforming growth factor β‐1, and high sensitivity C‐reactive protein, were unaltered by rifaximin treatment. Rifaximin altered abundance of bacterial taxa in blood marginally, only a decrease in Pseudomonadales was observed. In feces, rifaximin decreased bacterial richness, but effect on particular species was not observed. Subgroup analyses on patients with severely disturbed hemodynamics (n = 34) or activated lipopolysaccharide binding protein (n = 37) revealed no effect of rifaximin.

Conclusion

Four weeks of treatment with rifaximin had no impact on the inflammatory state and only minor effects on BT and intestinal bacterial composition in stable, decompensated cirrhosis (NCT01769040).