Journal of Hepatology
Volume 37, Issue 4 , Pages 523-526, October 2002

Multifactorial gut barrier failure in cirrhosis and bacterial translocation: working out the role of probiotics and antioxidants

  • Agustı́n Albillos

      Affiliations

    • Servicio de Gastroenterologı́a, Hospital Ramón y Cajal, Madrid, Spain
    • Laboratorio de Enfermedades del Sistema Inmune y Oncologı́a, Unidad I+D Asociada al Consejo Superior de Investigaciones Cientı́ficas, Spain
    • Departmento de Medicina, Facultad de Medicina-Campus Universitario, Universidad de Alcalá, Ctra. Madrid-Barcelona km. 33.600, 28871 Alcalá de Henares, Madrid, Spain
    • Corresponding Author InformationCorresponding author. Fax: +34-91-336-8085
    • ,
  • Antonio de la Hera

      Affiliations

    • Laboratorio de Enfermedades del Sistema Inmune y Oncologı́a, Unidad I+D Asociada al Consejo Superior de Investigaciones Cientı́ficas, Spain
    • Departmento de Medicina, Facultad de Medicina-Campus Universitario, Universidad de Alcalá, Ctra. Madrid-Barcelona km. 33.600, 28871 Alcalá de Henares, Madrid, Spain

See Article, pages 456–462

Article Outline

 

Under normal physiological conditions the gastrointestinal tract absorbs nutrients while maintaining bacteria within the intestinal lumen. Bacterial translocation (BT) is the process by which the normal microflora crosses the gut mucosa and reaches the local mesenteric lymph nodes and eventually the systemic circulation. BT has been studied in animal models and has been shown to occur in situations such as intestinal obstruction, hemorrhagic shock, sepsis, endotoxinemia, severe trauma, thermal injury and cirrhosis [1], [2], [3]. The results of these studies have shown the major mechanisms promoting BT to be intestinal bacterial overgrowth, altered permeability of the intestinal mucosa and deficiencies in host immune defenses. This shows the gut barrier is more of a functional than an anatomic concept. The operational definition of BT has relied upon the culture of viable bacteria in the mesenteric lymph nodes. However, the release of bacterial products such as endotoxin from non-viable bacteria can promote many of the physiopathological consequences attributed to BT [4].

The villi in the epithelial apical surface are covered in a layer of mucus coated with a biofilm of anaerobic bacteria [5]. This prevents the adherence to enterocytes and limits the overgrowth of aerobic gram-negative enteric bacilli (mainly Enterobacteria). Immunological factors such as secretory IgA further prevent the adherence of aerobic bacteria to the enterocytes. Any expansion of the enteric gram-negative bacteria or reduction in anaerobic microflora increases susceptibility to BT. Gastric acidity, pancreatobiliary secretion, intestinal immunological factors and (mainly) intestinal peristalsis are the endogenous factors that maintain the microbiological ecology of the gut. In this regard, probiotics have been proposed as a means of reequilibrating the level of potentially pathogenic Enterobacteria and protective anaerobic bacteria so that BT rate is reduced [6]. The cellular barrier of the gut is composed of a layer of simple columnar epithelial cells interspersed with specialized cells such as goblet cells, lymphocytes and M cells. The maintenance of normal epithelial cell structure and function, including the preservation of tight junctions, avoids the transepithelial or paracellular migration of bacteria. The contaminating bacteria are phagocytosed by the antigen-presenting cells; other immune mechanisms then contribute to rapid bacterial clearance. BT occurs at a low rate in normal individuals, and indigenous bacteria such as Escherichia coli continuously translocate when their levels exceed 108/g cecum [7]. A markedly increased BT rate and/or host immunocompromise leads to bacterial replication in the mesenteric lymph nodes and eventual dissemination through the lymphatic or vascular channels.

Increased BT by gram-negative enteric bacteria has been shown in experimental models of cirrhosis, and is postulated as a pathogenic mechanism for the spontaneous bacteriemia and peritonitis frequently observed in cirrhotic patients [2], [3], [8]. Most of the mechanisms mitigating BT in health are altered in cirrhosis. Patients and animal models of cirrhosis show abnormalities in the coordinated motor function of the small bowel that delay intestinal transit and favor intestinal overgrowth (IBO) of Enterobacteria [3], [9], [10], [11]. Indeed, intestinal motor anomalies are more severe in cirrhotic individuals that develop IBO [3], [10]. Oxidative damage to the intestinal wall, the increased activity of the sympathetic nervous system and the enhanced production of nitric oxide have all been proposed as possible factors underlying the intestinal dismotility of cirrhosis [3]. Cirrhosis is also associated with structural and functional alterations in intestinal mucosa, which may increase permeability to macromolecules and bacteria. Experimental cirrhosis results in oxidative stress in the mucosa of the small intestine, as seen by increased xanthine oxidase activity and altered antioxidant status, increased lipid peroxidation of the brush border membranes and abnormal intestinal transport [12], [13]. These lesions resemble those observed in ischemia/reperfusion injury, hemorrhagic shock and endotoxinemia, in which intestinal permeability and susceptibility to BT are increased [14]. However, it should be noted that with respect to cirrhosis the above concepts only form a working hypothesis since oxidative damage of the intestinal mucosa, increased permeability and BT have been separately studied, and firm links among them have not been formally established.

The immune defense in the mesenteric lymph nodes is defective in cirrhosis, and together with the marked increase in BT rate, allows the enteric bacteria and their products (such as endotoxin) to reach the blood. Several in vivo and in vitro experimental and human models of advanced cirrhosis have shown deficiencies in the bacteriostatic and opsonic capacity of serum, in phagocytosis by neutrophils, and in the effector function of immune cells circulating in blood [15], [16], [17]. The splanchnic hyperemia that follows portal hypertension impairs rolling, adherence and migration of phagocytic cells in mesenteric venules, providing another contributing mechanism to the impaired immune response in cirrhosis [18].

A remarkable aspect of cirrhosis is that there is a concurrent alteration of the three pillars (microflora content, mucosal integrity, immunity) that support the gut barrier [3], thus explaining the high rate of BT observed. Combined injury to the three gut barrier pillars results in greater susceptibility to BT than do clinical or experimental situations that affect one alone [19]. Moreover, the defective immunological clearance of the translocated gram-negative bacteria that occurs in cirrhosis is accompanied by pronounced endotoxin-driven proinflammatory cytokine release [3], [20]. The tumor necrosis factor alpha and nitric oxide production promoted by the endotoxin cascade causes further oxidative damage to the bowel wall [14], [21].

Decreasing the enteric bacterial load of aerobic bacilli by poorly absorbed antibiotics, such as quinolones, reduces the BT rate in experimental cirrhosis as well as that of spontaneous infections in cirrhotic patients [22], [23]. But the frequent emergence of fecal quinolone-resistant Enterobacteria has led to the search for alternatives to antibiotics. Encouraging results have been obtained with agents such as cisapride and propranolol, which reduce enteric bacterial load by decreasing the intestinal transit time of patients and animals with cirrhosis [3], [11]. Two articles recently published in the Journal report an alternative approach, that of modulating BT by using probiotics and/or antioxidants in CCl4 ascitic cirrhotic rats [24], [25]. In the study of Bauer et al., the BT rate, ascitic fluid infection and enteric bacterial load were unchanged after an 8–10 day course of Lactobacillus rhamnosus strain GG (LGG) [24]. In the current issue of the Journal, Chiva et al. report the oral administration to three groups of cirrhotic rats of either Lactobacillus johnsonii La1 with a vehicle of antioxidants (vitamin C and glutamate), antioxidants alone or water [25]. Antioxidants alone or in combination with L. johnsonii La1 suppressed BT to the mesenteric lymph nodes, and reduced ileal and cecal counts of Enterobacteria and Enterococci as well as intestinal malondialdehyde levels (used as an index of intestinal oxidative damage). Unfortunately, no group of cirrhotic rats received L. johnsonii La1 alone, precluding a direct comparison with the results of Bauer et al.

Probiotics are live-microbe food supplements thought to benefit the host by improving intestinal microbial balance. Lactobacillus, the most common probiotic used in humans, has favorably influenced the course of antibiotic-associated, Clostridium difficile and childhood forms of diarrhea [6]. LGG, the agent used by Bauer et al., has the ability to adhere to epithelial cells, to counteract the adherence of Enterobacteria and temporarily colonize the gut, and to improve immune defense by increasing the production of γ-interferon by isolated T cells [6]. Although the LGG adequately colonized the bowel of cirrhotic rats, it was unable to reduce the cecal content of aerobic bacteria and the rate of BT. The use of probiotics to reduce BT in experimental models of acute liver injury and of prehepatic portal hypertension have led to similarly discouraging results [26], [27]. LGG has also failed to improve gut permeability after NSAID ingestion in humans [28]. It is possible that probiotics may exert their beneficial effect in infectious diseases due to a primary disruption in intestinal microecology [6], [29], whereas they are ineffective in processes such as cirrhosis when damage affects the several pillars of the gut barrier. Interestingly, LGG itself translocated to mesenteric lymph nodes in a quarter of the rats [24], underlining the severity of gut barrier disruption and immunocompromise in cirrhosis.

Chiva et al. report an intriguing finding: the ability of the antioxidants vitamin C and glutamate to reduce BT, enteric bacterial load and oxidative stress of the bowel wall in cirrhotic rats [25]. In accordance with these results, attenuation of intestinal oxidative damage mediated by xanthine dehydrogenase/oxidase reduces BT in bile duct ligated cirrhotic rats [30]. Antioxidants (vitamins C and E, glutamate) have also been proposed to improve intestinal barrier function and to ameliorate the gut permeability that occurs after ischemia/reperfusion injury, radiation injury and parenteral nutrition [31], [32]. The mechanism by which antioxidants reduced the enteric bacterial load remains speculative. As suggested by the authors, it might be the consequence of intestinal transit acceleration after improving oxidative damage. Unfortunately, they investigated neither the permeability nor the transit time of the intestine, which would have given some clues. A further point that should be considered is the possibility that antioxidants might have improved CCl4 liver injury, a lesion mediated by lipid and protein oxidation [33], data on liver function would have helped clarify this. The role of oxidative damage of the bowel wall in the pathogenesis of BT in cirrhosis has attracted little attention. Whereas further studies on the mechanisms by which antioxidants reinforce the gut barrier are needed, the results of Chiva et al. should be regarded with interest since they may open new strategies to prevent BT and spontaneous infections in cirrhosis.

To date few studies have investigated the contribution of the naturally complex commensal biofilms to the prevention of BT, and the search has instead focused in the identification on ‘the’ clinically ideal probiotic strain. The experiments reported in the Journal underline that a single probiotic strain is unlikely to exert profound modifications in the gut microbiological ecology let alone to prevent BT in cirrhosis. This finding is not surprising since the interference between microorganisms is complex and involves several specific mechanisms with respect to the target bacteria implicated [34]. Moreover, bacterial antagonism might be only operative in a particular anatomical region or microenvironment in the intestinal tract where the probiotic and target organisms coexist at appropriate concentrations.

The ‘probiotic concept’ remains controversial, primarily because the mechanisms by which such commensal bacteria antagonize the translocation of unwanted gut microorganisms or exert other beneficial effects to the host have not been identified in vivo. The concept of bacterial interference has evolved from the notion of microbial competition for host epithelial cell binding sites, to include the stimulation of host immune defense, and the triggering of cell-signalling events that ‘silence’ pathogenic bacteria virulence factors that favor BT [35]. The available evidence shows a concurrent breakdown of the three pillars of the functional epithelial barrier is a remarkable aspect of BT in cirrhosis. Taken together with the paradigm shift regarding microbial antagonism, and the recent finding that drugs accelerating intestinal transit reduce BT in cirrhosis, the report in this issue of the Journal of the beneficial influence of probiotics administered in an anti-oxidant vehicle draws attention to the therapeutic consideration of the serial nature of the defects in the gut barrier in cirrhosis. It provides a rationale for the trial of novel therapies that concurrently attempt the repair of multiple gut barrier pillar defects.

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Acknowledgements 

Supported in part by grants from Plan Nacional de Investigación y Desarrollo SAF 2000-0219, SAF 2001-2453 y FEDER 2FD97-1950.

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References 

  1. Deitch EA. Gut failure: its role in the multiple organ failure syndrome. In:  Deitch EA editors. Multiple organ failure. New York: Thieme; 1990;p. 40–59
  2. Garcia-Tsao G, Lee FY, Barden GE, Cartun R, West B. Bacterial translocation to mesenteric lymph nodes is increased in cirrhotic rats with ascites. Gastroenterology. 1995;108:1835–1841
  3. Perez-Paramo M, Muñoz J, Albillos A, Portero F, Freire I, Santos M, et al.  Effect of propranolol on the factors promoting bacterial translocation in cirrhotic rats with ascites. Hepatology. 2000;1:43–48
  4. Albillos A, De-la-Hera A, González M, Moya JL, Calleja JL, Monserrat J, et al.  Increased lypolysaccharide binding protein in cirrhotic patients with marked immune and hemodynamic derangement. Hepatology. 2002; In press
  5. Davies DG, Parsek MR, Pearson JP, Iglewski BH, Costerton JW, Greenberg EP. The involvement of cell-to-cell signals in the development of a bacterial biofilm. Science. 1998;280:295–298
  6. Elmer GW, McFarland LV. Biotherapeutic agents in the treatment of infectious diarrhea. Gastroenterol Clin N Am. 2001;30:837–852
  7. Berg RD. Inhibition of Escherichia coli translocation from the gastrointestinal tract by the normal cecal flora in gnotobiotic or antibiotic-decontaminated mice. Infect Immun. 1980;29:1073–1081
  8. Runyon BA, Squier S, Borzio M. Translocation of gut bacteria in rats with cirrhosis to mesenteric lymph nodes partially explains the pathogenesis of spontaneous bacterial peritonitis. J Hepatol. 1994;21:792–796
  9. Chesta J, Defilippi C, Defilippi C. Abnormalities in proximal small bowel motility in patients with cirrhosis. Hepatology. 1993;17:828–832
  10. Chan CS, Chen GH, Lien HC, Yeh HZ. Small intestine dismotility and bacterial overgrowth in cirrhotic patients with spontaneous bacterial peritonitis. Hepatology. 1998;28:1187–1190
  11. Pardo A, Bartolı́ R, Lorenzo-Zuñiga V, Planas R, Vinado B, Riva J, et al.  Effect of cisapride on intestinal bacterial overgrowth and bacterial translocation in cirrhosis. Hepatology. 2000;31:858–863
  12. Castilla-Cortazar I, Picardi A, Tosar A, Ainzua J, Urdaneta E, Garcia M, et al.  Effect of insulin-like growth factor I on in vivo intestinal absorption of d-galactose in cirrhotic rats. Am J Physiol. 1999;276:G37–G42
  13. Ramachandran A, Prabhu R, Thomas S, Reddy JB, Pulimood A, Balasubramanian KA. Intestinal mucosal alterations in experimental cirrhosis in the rat: role of oxygen free radicals. Hepatology. 2002;35:622–629
  14. Chamulitrat W, Skrepnik NV, Spitzer JJ. Endotoxin-induced oxidative stress in the rat small intestine: role of nitric oxide. Shock. 1996;5:217–222
  15. Rajkovic IA, Williams R. Abnormalities of neutrophil phagocytosis, intracellular killing and metabolic activity in alcoholic cirrhosis and hepatitis. Hepatology. 1986;6:252–262
  16. Mellencamp MA, Preheim PC. Pneumococcal pneumonia in a rat model of cirrhosis: effects of cirrhosis on pulmonary defense mechanisms against Streptococcus pneumoniae. J Infect Dis. 1991;163:1102–1108
  17. Gomez F, Ruiz P, Schreiber AD. Impaired function of macrophage Fcy receptor and bacterial infection in alcoholic cirrhosis. N Engl J Med. 1994;331:1122–1128
  18. Panés J, Pérez-del-Pulgar S, Casadevall M, Salas A, Pizcueta P, Bosch J, et al.  Impaired mesenteric leukocyte recruitment in experimental portal hypertension in the rat. Hepatology. 1999;30:445–453
  19. O'Boyle CJ, McFie J, Dave K, Sagar PS, Poon P, Mitchell CJ. Alterations in intestinal barrier function do not predispose to translocation of enteric bacteria in gastroenterologic patients. Nutrition. 1998;14:358–362
  20. Wiest R, Das S, Cadelina G, Garcia-Tsao G, Milstien S, Groszmann RJ. Bacterial translocation in cirrhotic rats stimulates eNOS-derived NO production and impairs mesenteric vascular contractility. J Clin Invest. 1999;104:1223–1233
  21. Unno N, Wang H, Menconi MJ, Tytgat SH, Larkin V, Smith M, et al.  Inhibition of inducible nitric oxide synthase ameliorates endotoxin-induced gut mucosal barrier dysfunction in rats. Gastroenterology. 1997;113:1246–1257
  22. Llovet JM, Bartoli R, Planas R, Vinado B, Perez J, Cabre E, et al.  Selective intestinal decontamination with norfloxacin reduces bacterial translocation in ascitic cirrhotic rats exposed to hemorrhagic shock. Hepatology. 1996;23:781–787
  23. Ginès P, Rimola A, Planas R, Vargas V, Marco F, Almeda A, et al.  Norfloxacin prevents spontaneous bacterial peritonitis recurrence in cirrhosis: results of a double-blind, placebo controlled trial. Hepatology. 1990;12:716–724
  24. Bauer TM, Fernandez J, Navasa M, Vila J, Rodés J. Failure of Lactobacillus spp. to prevent bacterial translocation in a rat model of experimental cirrhosis. J Hepatol. 2002;36:501–506
  25. Chiva M, Soriano G, Rochat I, Peralta C, Rochat F, Llovet T, et al. Effect of Lactobacillus johnsonii La1 and antioxidants on intestinal flora and bacterial translocation in rats with experimental cirrhosis. J Hepatol 2002;37:456–462.
  26. Adawi D, Kasravi FB, Molin G, Jeppsson B. Effect of Lactobacillus supplementation with and without arginine on liver damage and bacterial translocation in an acute liver injury model in the rat. Hepatology. 1997;25:642–647
  27. Wiest R, Chen F, Das S, Cadelina G, Garcia-Tsao G. Effect of Lactobacillus acidophilus-fermented diet on intestinal flora and on bacterial translocation in experimental pre-hepatic portal hypertension. Hepatology. 1999;30:581A
  28. Gotteland M, Cruchet S, Verbeke S. Effect of Lactobacillus ingestion on the gastrointestinal mucosal barrier alterations induced by indometacin in humans. Aliment Pharmacol Ther. 2001;15:11–17
  29. Mattar AF, Drongowski RA, Coran AG, Harmon CM. Effect of probiotics on enterocyte bacterial translocation in vitro. Pediatr Surg Int. 2001;17:265–268
  30. Schimpl G, Pabst MA, Feierl G, Kuesz A, Ozbey H, Takahashi S, et al.  A tungsten supplemented diet attenuates bacterial translocation in chronic portal hypertensive and cholestatic rats: role of xanthine dehydrogenase and xanthine oxidase. Gut. 1999;45:904–910
  31. Mutlu-Turkoglu U, Erbil Y, Oztezcan S, Olgac V, Toker G, Uysal M. The effect of selenium and/or vitamin E treatments on radiation-induced intestinal injury in rats. Life Sci. 2000;66:1905–1913
  32. Ikeda S, Zarzaur BL, Johnson CD, Fukatsu K, Kudsk KA. Total parenteral nutrition supplementation with glutamine improves survival after gut ischemia/reperfusion. J Parenter Enteral Nutr. 2002;26:169–173
  33. Yao T, Degli Esposti S, Huang L, Arnon R, Spangenberger A, Zern MA. Inhibition of carbon tetrachloride-induced liver injury by liposomes containing vitamin E. Am J Physiol. 1994;267:G476–G484
  34. Hooper LV, Gordon JI. Commensal host-bacterial relationships in the gut. Science. 2001;292:1115–1118
  35. Strauss E. Fighting bacterial fire with bacterial fire. Science. 2000;290:2214–2215

PII: S0168-8278(02)00265-9

Journal of Hepatology
Volume 37, Issue 4 , Pages 523-526, October 2002

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