Intestinal mucosal alterations in experimental cirrhosis in the rat: role of oxygen free radicals

Retinoid metabolism in the small intestine during development of liver cirrhosis

BACKGROUND AND AIMS

Retinoids are important mediators of cellular differentiation and proliferation in various epithelia of the body including the small intestine. Though alterations in intestinal epithelial cell proliferation have been noted in liver cirrhosis, mechanisms involved in the process are not well understood. This study examined the levels of various retinoids and retinoid-metabolizing enzymes in the small intestine during development of liver cirrhosis.

METHODS

Four groups of animals were used (control, phenobarbitone control, thioacetamide and carbon tetrachloride treatment). Twice-weekly intragastric or i.p. administration of carbon tetrachloride or thioacetamide, respectively, produced liver cirrhosis after 3 months, which was confirmed through histology and serum markers. Retinoid levels were measured by high-performance liquid chromatography.

RESULTS

A decrease in the levels of retinal, retinoic acid and retinol was evident in the intestine by 3 months, when cirrhosis was evident histologically, and these remained low until 6 months. A decrease in the activities of retinaldehyde oxidase, retinaldehyde reductase and retinol dehydrogenase was also seen in intestine from cirrhotic rats.

CONCLUSION

These results suggest that altered retinoid metabolism in the intestine of cirrhotic rats might have an influence on changes in intestinal epithelial cell differentiation, seen in liver cirrhosis.

Spontaneous bacterial peritonitis

Since its initial description in 1964, research has transformed spontaneous bacterial peritonitis (SBP) from a feared disease (with reported mortality of 90%) to a treatable complication of decompensated cirrhosis, albeit with steady prevalence and a high recurrence rate. Bacterial translocation, the key mechanism in the pathogenesis of SBP, is only possible because of the concurrent failure of defensive mechanisms in cirrhosis. Variants of SBP should be treated. Leucocyte esterase reagent strips have managed to shorten the ‘tap-to-shot’ time, while future studies should look into their combined use with ascitic fluid pH. Third generation cephalosporins are the antibiotic of choice because they have a number of advantages. Renal dysfunction has been shown to be an independent predictor of mortality in patients with SBP. Albumin is felt to reduce the risk of renal impairment by improving effective intravascular volume, and by helping to bind pro-inflammatory molecules. Following a single episode of SBP, patients should have long-term antibiotic prophylaxis and be considered for liver transplantation.

Glutamine inhibits over-expression of pro-inflammatory genes and down-regulates the nuclear factor kappaB pathway in an experimental model of colitis in the rat

We investigated the effects of glutamine on markers of oxidative stress, nuclear factor kappaB (NF-kappaB) activation, and pro-inflammatory mediators in a rat model of experimental colitis induced by intracolonic administration of 7% acetic acid. Glutamine (25 mg/kg) was given by rectal route 48 and 24h before acetic acid instillation. Glutamine significantly reduced gross damage and histopathological scores, and partially prevented the decrease of anal pressure observed in the animals receiving acetic acid. Increases in the cytosolic concentration of TBARS and hydroperoxide-initiated chemiluminescence were significantly prevented in glutamine-treated animals. Acetic acid instillation induced a marked increase of the NF-kappaB p65 subunit expression in the nucleus and resulted in significant changes in the cytosolic protein level of IkappaB kinases (IKKalpha and IKKbeta) and the non-phosphorylated form of the inhibitor IkappaBalpha. Protein levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) were significantly increased. All these effects were partially prevented by administration of glutamine. It is concluded that the anti-inflammatory activity of glutamine in a rat model of acetic acid-induced colitis may be mediated, at least in part, by inhibition of the expression of certain pro-inflammatory mediators which are regulated by the oxidative stress-sensitive NF-kappaB signalling pathway.

[Physiopathology of bacterial translocation and spontaneous bacterial peritonitis in cirrhosis]

The key pathogenic mechanism initiating spontaneous bacterial peritonitis (SBP) is bacterial translocation (BT), a process through which enteric bacteria cross the intestinal barrier and infect the mesenteric lymph nodes, thus entering the blood circulation and ascitic fluid. The high rate of bacterial translocation in cirrhosis is due to injury to the three pilars composing the intestinal mucosal barrier (the balance of intraluminal bacterial flora, the integrity of the intestinal epithelial barrier, and the local immune system). Blood dissemination and microbial growth in ascitic fluid resulting from SBP are a consequence of damage to the immune system in cirrhosis. Hyperproduction of proinflammatory cytokines and other vasoactive substances contributes to the arterial vasodilation and renal failure that frequently complicate the course of SBP. Even in the absence of SBP, translocation of bacteria and bacterial products from the intestinal lumen contribute to systemic inactivation of immune cells in cirrhosis.

Allopurinol, oxidative stress and intestinal permeability in patients with cirrhosis: an open-label pilot study

BACKGROUND

Cirrhosis is associated with intestinal barrier failure, related in part to enterocytes oxidative damage via xanthine oxidase overactivity. Experimentally, allopurinol, a xanthine oxidase inhibitor, reduces enterocytes' damage and bacterial translocation.

AIM

To assess the short-term effects of allopurinol on intestinal permeability, oxidative stress and endotoxin-dependent cytokines in patients with cirrhosis.

METHODS

Nineteen patients with cirrhosis, in a stable condition (age: 56 years; Child A/B/C: 6/7/6; ascites: 12; alcoholic cirrhosis: 16/19; abstinence >2 weeks), were included. At baseline and day 10 of allopurinol 400 mg/day, intestinal permeability [lactulose/mannitol (Lac/Man) ratio test], oxidative stress (serum malondialdehyde), as well as TNF-soluble receptor-1, IL-6 and lipopolysaccharide-binding protein (which reflects exposition to endotoxin) were measured.

RESULTS

Malondialdehyde decreased significantly (-23%, P<0.05), whereas no effects were seen on intestinal permeability and the endotoxin-associated systemic inflammatory response. At baseline, portal pressure correlated to the Lac/Man ratio (r=0.55, P<0.02). At day 10, changes in malondialdehyde correlated to changes in the Lac/Man ratio (r=0.51, P<0.05).

CONCLUSIONS

A 10-day course of allopurinol in patients with cirrhosis is associated with a significant reduction in oxidative stress but no effect on intestinal permeability and inflammatory markers. Whether intestinal damage in cirrhosis can be accessible to antioxidant therapy requires further study.

Intestinal barrier dysfunction in developing liver cirrhosis: An in vivo analysis of bacterial translocation

AIM

Transmucosal passage of bacteria across the intestine, the essential step for bacterial translocation, has been identified as a key event in the pathogenesis of life-threatening infections in cirrhosis. Existing animal models of liver cirrhosis only provide indirect information about the pathogenesis of such infections. The aim of this study has been to assess transmucosal passage and bacterial translocation directly in vivo using a rat model of developing liver cirrhosis.

METHODS

Male Sprague Dawley rats were randomly assigned to two groups: controls and animals with developing liver cirrhosis induced by s.c. injection of carbon tetrachloride. In anesthetized animals a suspension of green fluorescent protein (GFP)-tagged E. coli was administered into the terminal ileum. Time intervals necessary for translocation of E. coli into the mucosa and muscularis were assessed by intravital microscopy and translocation of E. coli in mesentery, liver and spleen was determined microbiologically.

RESULTS

Bacterial kinetics at the level of the mucosa and muscularis showed significant enhancement in cirrhotic rats compared to the controls (P < 0.001). GFP-expressing E. coli were detected in the mesentery, liver and spleen of animals with cirrhosis taken one hour after E. coli administration. However, cultures of control animals remained sterile.

CONCLUSION

Intravital microscopy of fluorescent bacteria represents a novel approach to studying bacterial translocation in vivo. Here we report that this technique can be used to visualize bacterial transit in in vivo and gives further support to the transmucosal passage of bacteria across the intestine correlating with bacterial translocation in CCl(4)-induced liver cirrhosis.

The effect of caffeic acid phenethyl ester on bacterial translocation and intestinal damage in cholestatic rats

We investigated the effect of caffeic acid phenethyl ester in rat ileum injury induced by chronic biliary obstruction. Swiss albino rats were divided into three groups: Group 1, sham (n = 7); Group 2, common bile duct ligation (n = 7); and Group 3, common bile duct ligation plus caffeic acid phenethyl ester (n = 7). In the caffeic acid phenethyl ester-treated rats, ileum tissue levels of malondialdehyde and myeloperoxidase were significantly lower than those of the bile duct-ligated rats (P < 0.001). The levels of tumor necrosis factor-alpha, interleukin-6, and interleukin-1alpha in the caffeic acid phenethyl ester group were significantly lower than those in the bile duct ligation group (P < 0.03, P < 0.01, and P < 0.02 respectively). The present study demonstrates that intraperitoneal administration of caffeic acid phenethyl ester in bile duct-ligated rats reduces intestinal oxidative stress. This effect may be useful in the preservation of intestinal damage in cholestasis.

Renal damage in experimentally-induced cirrhosis in rats: Role of oxygen free radicals

Cirrhosis with ascites is associated with impaired renal function accompanied by sodium and water retention. Although it has been suggested that mediators such as nitric oxide play a role in the development of renal failure in this situation, other mechanisms underlying the process are not well understood. This study examined the role of oxidative stress in mediating renal damage during the development of cirrhosis in order to understand mechanisms involved in the process. It was shown that carbon tetrachloride- or thioacetamide-induced cirrhosis in rats results in oxidative stress in the kidney as seen by increased lipid peroxidation and protein oxidation, accompanied by altered antioxidant status. Cirrhosis was also found to affect renal mitochondrial function, as assessed by measurement of the respiratory control ratio, the swelling of mitochondria, and calcium flux across mitochondrial membranes. Increased lipid peroxidation and changes in lipid composition were evident in the renal brush border membranes, with compromised transport of 14C glucose across these membranes. In conclusion, renal alterations produced as a result of cirrhosis in the rat are possibly mediated by oxidative stress.

Intestinal mucosal alterations in rats with carbon tetrachloride-induced cirrhosis: changes in glycosylation and luminal bacteria

Spontaneous bacterial peritonitis is a major cause of mortality after liver cirrhosis. Altered permeability of the mucosa and deficiencies in host immune defenses through bacterial translocation from the intestine due to intestinal bacterial overgrowth have been implicated in the development of this complication. Molecular mechanisms underlying the process are not well known. In order to understand mechanisms involved in translocation of bacteria, this study explored the role of oxidative stress in mediating changes in intestinal mucosal glycosylation and luminal bacterial content during cirrhosis. CCl4-induced cirrhosis in rats led to prolonged oxidative stress in the intestine, accompanied by increased sugar content of both intestinal brush border and surfactant layers. This was accompanied by changes in bacterial flora in the gut, which showed increased hydrophobicity and adherence to the mucosa. Inhibition of xanthine oxidase using sodium tungstate or antioxidant supplementation using vitamin E reversed the oxidative stress, changes in brush border membrane sugar content, and bacterial adherence. In conclusion, oxidative stress in the intestine during cirrhosis alters mucosal glycosylation, accompanied by an increased hydrophobicity of luminal bacteria, enabling increased bacterial adherence onto epithelial cells. This might facilitate translocation across the mucosa, resulting in complications such as spontaneous bacterial peritonitis.

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.

Perméabilité intestinale et cirrhose

Patients with cirrhosis are at increased risk of developing infections due to bacterial translocation. This process depends on three principal factors: bacterial overgrowth, immunodepression, and altered intestinal permeability. Intestinal barrier functions may be disturbed in cirrhosis, related to the toxic effects of alcohol (on mucosa and biological membranes) and portal hypertensive enteropathy. Few studies on the assessment of intestinal permeability in cirrhotic patients are available, and contradictory results may be explained by methodological differences. However, four studies using a differential sugar absorption test (lactulose-mannitol test, a combination of an oligosaccharide and a monosaccharide) showed an increased intestinal permeability in cirrhotic patients. The recurrence of spontaneous bacterial peritonitis can be appreciated only by one similar case history, a low rate of protides in ascites (<10 g/L), bilirubinemia > 55 micromol/L, and thrombocytopenia<98.000/mm3. These results suggest that primary antibiotherapy prophylaxis should be recommended, but this recommendation is limited by the risk of bacterial resistant selection and by the fact that no patient survival benefits was shown. Intestinal permeability could be another predictive factor to justify preventive antibiotherapy; but more studies are needed and methods should be standardized (technique used to measure permeability, patient groups involved).

Intestinal permeability in rats with CCl4-induced portal hypertension

AIM: To investigate the intestinal barrier changes in rats with CCl₄-induced portal hypertension.

METHODS: The permeability of intestinal barrier detected by Lanthanum as a tracer was evaluated in rats. Bacterial translocation and plasma endotoxin were also determined.

RESULTS: The incidence of bacterial translocation was 85% in rats with CCl₄-induced portal hypertension, which was significantly higher than that in control rats (20%, P<0.01). Plasma endotoxin level was significantly higher in experimental group than in control group. Permeability of the epithelial mucosa and pathological alteration were increased in the ileum and the microvilli became shorter and thinner in rats with portal hypertension.

CONCLUSION: Bacterial translocation occurs in rats with CCl₄-induced portal hypertension and increased permeability between epithelial cells contributes to the translocation.

Effects of Atractylodes macrocephalae on gastric emptying and nitrergic nerves in rats with hepatic cirrhosis

AIM: To observe the effects of atractylodes macrocephalae (AM) on gastric motility and nitrergic nerval system in rats with hepatic cirrhosis.

METHODS: Twenty-four Wister rats were randomly divided into control group, cirrhosis model group and AM treatment group. Dextran blue-2000 was used as an internal marker to assay the gastric emptying of the rats. The nitrergic nerves in the myenteric plexuses of gastric fundus, body and antrum were observed with NADPH-d histochemical staining.

RESULTS: Compared with those in control group, the gastric emptyings of rats were markedly delayed in model group (160.23±45.13 vs 100±17.78, P<0.01), and the distributions and densities of myenteric nitrergic nerves in the gastric body and antrum were significantly increased (7.35±0.95 vs 5.52±0.92, P<0.01; 6.26±0.79 vs 5.28±0.78, P<0.05). No significant changes were found in the fundus. After treatment with AM, the gastric motility of rats was markedly improved and the nitrergic nerves in antrum were significantly recovered. No significant differences were observed between the rats of AM and control group (96.12±16.25 vs 100±17.78, 5.39±0.84 vs 5.28±0.78, both P>0.05).

CONCLUSION: Atractylodes macrocephalae can improve the gastric motility and the mechanism may be related to its effect on the distributions of nitrigic nerves in the gastric body and antrum of rats with hepatic cirrhosis.

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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.

Nitric oxide and the hyperdynamic circulation in cirrhosis: is there a role for selective intestinal decontamination?

Abnormal vascular tone is responsible for many of the complications seen in cirrhosis making the identification of the pathophysiology of abnormal dilatation a major focus in hepatology research. The study of abnormal vascular tone is complicated by the multiple vascular beds involved (hepatic, splanchnic, peripheral, renal and pulmonary), the differences in the underlying cause of portal hypertension (hepatic versus pre-hepatic) and the slow evolution of the hyperdynamic state. The autonomic nervous system, circulating vasodilators and abnormalities in vascular smooth muscle cells (receptors, ion channels, signalling systems and contraction) have all been implicated. There is overwhelming evidence for an overproduction of NO (nitric oxide) contributing to the peripheral dilatation in both animal models of, and in humans with, cirrhosis and portal hypertension. This review focuses on the proposal that endotoxaemia, possibly from gut-derived bacterial translocation, causes induction of NOS (NO synthase) leading to increased vascular NO production, which is the primary stimulus for the development of vasodilatation in cirrhosis and its accompanying clinical manifestations. The current controversy lies not in whether NO production is elevated, but in which isoform of NOS is responsible. We review the evidence for endotoxaemia in cirrhosis and the factors contributing to gut-derived bacterial translocation, including intestinal motility and permeability, and finally discuss the possible role of selective intestinal decontamination in the management of circulatory abnormalities in cirrhosis.

Alteration of intestinal intraepithelial lymphocytes and increased bacterial translocation in a murine model of cirrhosis

Alterations in immunological defense in the gut may lead to the bacterial infection that is frequently associated with cirrhosis of the liver. The aim of this study was to investigate the changes in distribution and function of intestinal intraepithelial lymphocytes (IELs) in relation to intestinal barrier dysfunction in experimental cirrhosis. Cirrhosis was induced in mice by treatment with carbon tetrachloride (CCl4) intraperitoneally with 5% alcohol in drinking water for 12 weeks. Bacterial translocation was assessed in mesenteric lymph nodes (MLNs) by the transport of fluorescence-labeled latex beads and by bacteriological cultures. The lymphocyte subpopulation was compared in three groups (cirrhosis, alcohol alone and controls). IFN-gamma production from isolated IELs was determined by ELISA after stimulation with anti-CD3 or IL-12/IL-18. The total number of IELs significantly increased in the cirrhosis and alcohol groups. There was a preferential increase in TCRgammadelta+CD8+ population in the alcohol group, but no change in cirrhosis. Bacterial translocation was negative in the control group, and a small number was noted in the alcohol group, whereas it was significantly noted in the cirrhosis group. Although the number of IEL was significantly increased in the cirrhosis group, their proliferative response was decreased, and IFN-gamma production from each IEL was markedly diminished in either stimulation by anti-CD3 or IL-12/IL-18. These changes were more remarkable in the cirrhosis group than in the alcohol group. In conclusion, bacterial translocation due to intestinal barrier dysfunction in cirrhosis may be closely correlated with the alteration of the immune function in IELs.

Gut microflora in the pathogenesis of the complications of cirrhosis

The gut flora plays an important role in the pathogenesis of the complications of cirrhosis. Cirrhotic patients are prone to develop bacterial infections, mainly the 'spontaneous' infection of ascites or spontaneous bacterial peritonitis. Other complications of cirrhosis, such as variceal haemorrhage and ascites, occur mostly or solely as a consequence of portal hypertension. Portal pressure increases initially as a consequence of an increased intrahepatic resistance but, once collaterals have formed, high portal pressure is maintained by an increased splanchnic blood inflow secondary to vasodilatation. Splanchnic vasodilatation is the initiating event in the hyperdynamic circulatory state that aggravates the complications of cirrhosis. The gut flora plays a role in both the development of infections and in the hyperdynamic circulatory state of cirrhosis and, although less prominently, it also plays a role in the pathogenesis of hepatic encephalopathy. This chapter presents evidence regarding gut flora and its modification in the pathogenesis and management of these complications of cirrhosis.

Gastrointestinal disorders of the critically ill. 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.