Effect of lactitol on blood ammonia response to oral glutamine challenge in cirrhotic patients: evidence for an effect of nonabsorbable disaccharides on small intestine ammonia generation

Sarcopenia in cirrhosis: Prospects for therapy targeted to gut microbiota

Decreased muscle mass and function, also known as sarcopenia, is common in patients with cirrhosis and is associated with a poor prognosis. Although the pathogenesis of this disorder has not been fully elucidated, a disordered gut-muscle axis probably plays an important role. Decreased barrier function of the gut and liver, gut dysbiosis, and small intestinal bacterial overgrowth (SIBO) can lead to increased blood levels of ammonia, lipopolysaccharides, pro-inflammatory mediators, and myostatin. These factors have complex negative effects on muscle mass and function. Drug interventions that target the gut microbiota (long-term use of rifaximin, lactulose, lactitol, or probiotics) positively affect most links of the compromised gut-muscle axis in patients with cirrhosis by decreasing the levels of hyperammonemia, bacterial translocation, and systemic inflammation and correcting gut dysbiosis and SIBO. However, although these drugs are promising, they have not yet been investigated in randomized controlled trials specifically for the treatment and prevention of sarcopenia in patients with cirrhosis. No data exist on the effects of fecal transplantation on most links of gut-muscle axis in cirrhosis; however, the results of animal experimental studies are promising.

Oral glutamine challenge is a marker of altered ammonia metabolism and predicts the risk of hepatic encephalopathy

BACKGROUND

The current therapies for hepatic encephalopathy (HE) are not completely effective in all patients, probably due to the physiopathological heterogeneity and the different conditions underlying the bout of HE. We hypothesized that oral glutamine challenge (OGC) is able to predict the risk of HE through the identification of various features and types of HE.

METHODS

We included 238 cirrhotic patients (198 without and 40 with a previous HE episode) that underwent OGC, obtaining baseline and 60 minutes post-load ammonia levels. Combined evaluation of baseline hyperammonemia (>78 mcg/dL) and impaired OGC (Δ >32 mcg/dL) defined low-, intermediate- and high-risk groups. Patients were censored at HE, liver transplantation and death or 6 years of follow-up.

RESULTS

The 28.3% (56/198) of the main cohort suffered from HE during the follow-up. In the competing risk analysis, both intermediate- (subhazard ratio (sHR) 2.01 (95% CI 1.00-4.14); P = .048) and high-risk groups (sHR 4.67 (95% CI 2.19-9.98); P = .0001) were associated with the first HE episode, together with age and albumin. Similar results were found for repeated HE events. The cumulative incidence for HE of the high-risk group was two and four times greater than the intermediate- and low-risk groups, respectively. The HE grade was also higher in individuals with the greatest risk (P = .035). The most common precipitant factor was diuretics in the high-risk group, while infections and electrolyte imbalance predominated in the rest of patients.

CONCLUSION

Oral glutamine challenge identified patients at risk of HE and defined specific features of the episodes. This tool could be useful in the decision-making process for the adequate management of HE.

Use Of Quantitative Modelling To Elucidate The Roles Of The Liver, Gut, Kidney, And Muscle In Ammonia Homeostasis And How Lactulose And Rifaximin Alter This Homeostasis

Humans must eliminate approximately 1M of ammonia per day while maintaining the blood concentration of this potent neurotoxin at a concentration of only about 30 µM. The mechanisms producing such effective ammonia homeostasis are poorly understood by clinicians due to the multiple organs (liver, gut, kidney and muscle) involved in ammonia homeostasis. Based on literature values we present a novel, simplified description of normal and disordered ammonia and the potential mechanisms whereby the drugs used to treat hepatic encephalopathy, lactulose and rifaximin, lower the blood ammonia concentration. Concepts discussed include the following: 1) only about 44 mmol of ammonia/day (4.4% of total production) reaches the peripheral circulation due to the efficient linkage of amino deamination and the urea cycle in hepatic mitochondria; 2) the gut and kidney contribute roughly equally to delivery of this 44 mmol/day to systemic blood; 3) the bulk of gut ammonia production seemingly originates in the small bowel from bacterial deamination of urea by bacteria and mucosal deamination of circulating and ingested glutamine; 4) the apparent production of ammonia in the small bowel markedly exceeds that quantity that enters the portal blood, indicating that ammonia disposal mechanisms in the small bowel play a major role in ammonia homeostasis. With regard to the hyperammonemia of chronic liver disease: 1) shunting of portal blood around the liver, by itself, can account for commonly observed ammonia elevations; 2) severe portal hypertension causes an increased release of ammonia by the kidney; 3) high blood ammonia is associated with an unexplained massive increase in the muscle uptake of ammonia that could play an important role in limiting hyperammonemia; and 4) a major action of lactulose administration may be the enhancement of ammonia uptake by small bowel bacteria, while the mechanism of action of rifaximin is unclear.

Update on management of patients with overt hepatic encephalopathy

Hepatic encephalopathy (HE) is a multifactorial neuropsychiatric disease that affects patients with cirrhosis. We review the clinical impact, pathogenesis, evaluation, management, and prevention of overt HE in patients with cirrhosis. Articles published between January 1960 and November 2012 were acquired through a MEDLINE search of different combinations of the terms hepatic encephalopathy, pathophysiology, treatment, prophylaxis, prevention, prognosis, and recurrence. The Healthcare Cost and Utilization Project database was used to obtain prevalence and cost information related to hospitalizations of patients with HE. The literature describes significant morbidity and mortality of HE in patients with cirrhosis. Overt HE develops in 30% to 45% of patients with cirrhosis and is associated with a substantial pharmacoeconomic burden, particularly HE-related hospitalizations. The development of HE in patients with cirrhosis portends a worsened prognosis and is incorporated into the Child-Pugh classification of the severity of liver disease. In the hospitalized patient, the development of HE is associated with precipitating events (eg, gastrointestinal bleeding, dehydration, infection), and in some patients, its course is characterized by frequent and severe relapses. In addition, hospitalized patients with overt HE have a 3.9-fold increased mortality risk. Patient management employs nonabsorbable disaccharides, the nonsystemic antibiotic rifaximin, or both, to treat acute HE episodes and prevent HE relapse. In open-label trials, use of the nonabsorbable disaccharide lactulose reduced the risk of overt HE recurrence in patients compared with no-lactulose control groups for ≤ a median of 14 months. In a randomized, placebo-controlled trial, rifaximin 550 mg twice daily was more effective in maintaining HE remission compared with placebo and was associated with a reduction in HE-related hospitalizations. Recent advances in treatment and preventative therapies may reduce the personal, societal, and economic impact of this disorder.

Pathogenesis of hepatic encephalopathy: lessons from nitrogen challenges in man

Induction of hyperammonaemia with nitrogen challenge in man can be used to study the pathogenesis and treatment of hepatic encephalopathy complicating cirrhosis. Initially 20 g of glutamine was given orally as a flavored solution which resulted in doubling of blood ammonia concentration and this was associated with a deterioration in performance of the choice reaction time. The effect could have been due to a direct effect of glutamine rather than the ammonia generated so in subsequent experiments a glutamine free mixture of amino acids resembling the composition of haemoglobin was used (gastrointestinal bleeding is a known precipitant of hepatic encephalopathy). In Child grade B and C patients, 2-3 h after 54 g, slowing of the EEG was observed. The cerebral effects of induced hyperammonaemia were studied with diffusion weighted imaging and MR spectroscopy after giving 54 g of a mixture of threonine, serine and glycine when apparent diffusion coefficient increased. Also the change in ammonia levels correlated with the change in cerebral glutamine levels (r = 0.78, p = 0.002) suggesting intra cerebral formation of glutamine from ammonia and this may have accounted for the fall in cerebral myoinositol concentrations observed. Finally a colonic source for ammonia was confirmed by administering urea using colon coated capsules when ammonia concentrations slowly increased from 5 h after administration and rapidly after 10 h. In two patients the hyperammonaemia was ameliorated by pre treatment with Rifaximin 1200 mg per day for 1 week. Nitrogen challenge studies are thus a valuable model for studying new treatments for hepatic encephalopathy without the need to simultaneously treat precipitating factors.

A capillary blood ammonia bedside test following glutamine load to improve the diagnosis of hepatic encephalopathy in cirrhosis

Background

Hepatic encephalopathy (HE) is a frequent and severe complication of cirrhosis. A single determination of ammonia in venous blood correlates poorly with neurological symptoms. Thus, a better biological marker is needed.

Aim

To make a diagnosis of HE, we explored the value of ammonia in capillary blood, an equivalent to arterial blood, measured at bedside following an oral glutamine challenge.

Methods

We included 57 patients (age 56 yrs; M/F: 37/20) with cirrhosis (alcoholic = 42; MELD score 13.8 [7-29], esophageal varices = 38) and previous episodes of HE (n = 19), but without neurological deficits at time of examination, and 13 healthy controls (age 54 yrs). After psychometric tests and capillary (ear lobe) blood ammonia measurements, 20 gr of glutamine was administered orally. Tests were repeated at 60 minutes (+ blood ammonia at 30'). Minimal HE was diagnosed if values were > 1.5 SD in at least 2 psychometric tests. Follow-up lasted 12 months.

Results

The test was well tolerated (nausea = 1; dizziness = 1). Patients showed higher values of capillary blood ammonia over time as compared to controls (0'-30'-60 minutes: 75, 117, 169 versus 52, 59, 78 umol/L, p < 0.05). At baseline, 25 patients (44%) had minimal HE, while 38 patients (67%) met the criteria for HE at 60 minutes (chi²: p < 0.01). For the diagnosis of minimal HE, using the ROC curve analysis, baseline capillary blood ammonia showed an AUC of 0.541 (CI: 0.38-0.7, p = 0.6), while at 60 minutes the AUC was 0.727 (CI: 0.58-0.87, p < 0.006). During follow-up, 18 patients (31%) developed clinical episodes of HE. At multivariate analysis, the MELD score (1.12 [1.018-1.236]), previous episodes of HE (3.2[1.069-9.58]), but not capillary blood ammonia, were independent predictors of event.

Conclusions

In patients with cirrhosis and normal neurological examination, bedside determination of ammonia in capillary blood following oral glutamine load is well tolerated and achieves a better diagnostic performance for minimal HE than basal capillary ammonia levels. However, capillary blood ammonia is a poor predictor of development of clinically overt HE.

New assessment of hepatic encephalopathy

Hepatic encephalopathy (HE) is a common complication of cirrhosis that requires careful appraisal of the clinical manifestations, evaluation of the underlying neurological disorders, and assessment of liver function and the portal-systemic circulation. This article reviews recent developments in the assessment of HE and discusses the controversy regarding the use of a categorical or a continuous approach in measuring the severity of this condition. New scales facilitate effective monitoring and assessment of episodic HE. Neuropsychological test batteries and neurophysiological tests are of value for evaluating cognitive function in outpatients and can establish the diagnosis of minimal HE, and the severity of low-grade HE. These tools allow better evaluation of the origin of cognitive complaints and help in estimating the risk of accidents. It is now possible to complete the evaluation with measurement of the effects of cognitive impairment on daily living. In difficult cases, imaging of the brain and portal-systemic circulation with magnetic resonance imaging is especially helpful. Based on these studies, neurological signs and symptoms can be attributed to HE in patients with mild liver disease and in those with complex neurological manifestations. The new methods presented are also valuable for investigating the neurological manifestations occurring after liver transplantation.

Pharmacotherapy of hepatic encephalopathy in cirrhosis

IMPORTANCE OF THE FIELD

Hepatic encephalopathy (HE) is a major complication encountered in nearly half of the patients with liver cirrhosis.

AREAS COVERED IN THIS REVIEW

A review of the safety and efficacy of current therapies for HE that seek to pre-empt ammonia production and/or to increase its elimination, reducing inflammation, blocking benzodiazepine-like compound production, and supporting systemic hemodynamics.

WHAT THE READER WILL GAIN

Insight into some recent advances in the management of HE that could modify our therapeutic approach to end-stage liver disease. Cirrhotic individuals during an overt HE episode require careful management, focusing on precipitant factors as well as metabolic and hemodynamic derangements.

TAKE HOME MESSAGE

Intestinal ammoniagenesis requires flora modification by antibiotics, prebiotics and probiotics; glutaminase inhibition as well as antibiotics to pre-empt systemic inflammation. Hemodynamic/fluid support is essential. Nutritional support is crucial and hypoproteinemic diets should be avoided. Blocking benzodiazepine-like compounds by the use of flumazenil could be useful in patients with severe, benzodiazepine-induced HE. Long-term rifaximin is well tolerated, does not promote resistance and could decrease overt HE bouts in patients with previous episodes of overt HE. Lactulose is better than no treatment in improving quality of life in patients with minimal HE; it also acts as secondary prophylaxis following overt HE.

Combination of polydextrose and lactitol affects microbial ecosystem and immune responses in rat gastrointestinal tract

The effects of various dietary fibres on gut health have been studied extensively but their combined effects are scarcely documented. In the present study the effects of 2 % (w/w) polydextrose (PDX), 2 % (w/w) disaccharide lactitol, or 2 % (w/w) PDX+2 % (w/w) lactitol on gut microflora, microbial metabolism and gut immune responses were investigated in rats. Both PDX and lactitol alone had an effect on many of the studied parameters, but their combination had stronger than additive effects in some parameters. The PDX+lactitol combination altered the microbial community structure as seen by a culture-independent method, percentage guanine+cytosine (%G+C) profiling, increasing the areas of %G+C 35–39 (P<0·0001) and %G+C 45–49 (P=0·0002), and decreasing %G+C 65–74 (P<0·0003). These changes were also reflected in the microbial metabolism so that the production of biogenic amines and branched volatile fatty acids was significantly reduced, by 12 (P=0·03) and 50 % (P=0·002), respectively, indicating a shift from putrefactive towards saccharolytic metabolism. PDX increased the secretion of IgA in the caecum (P=0·007). Secretion of IgA increased even more, almost ten-fold, with the combination of PDX+lactitol (P<0·0001) when compared with the control group. Lactitol increased the production of butyrate by caecal microbes by two- to three-fold when compared with the PDX or control group (P<0·0001). Butyrate is a preferred energy source for mucosal cells; thus a boost in the availability of energy for immune cells may have still added to the synergistic effects of PDX and lactitol on immune cells. It is noteworthy that improvement in the IgA secretion occurred without signs of mucosal inflammation.

Amino acid challenge in patients with cirrhosis and control subjects: ammonia, plasma amino acid and EEG changes

BACKGROUND/AIMS

The pathogenesis of hepatic encephalopathy (HE) is controversial. We have therefore studied the effect of induced hyperammonaemia in man.

PATIENTS AND METHODS

108 g of an amino acid mixture was given orally to 18 cirrhotics and 11 control subjects and changes in blood ammonia, EEG and plasma amino acids were observed.

RESULTS

Basal (39+/-6 versus 14+/-2 micromol/l) and 120-min post amino acid (77+/-10 versus 27+/-4) blood ammonia concentrations in cirrhotics were significantly increased compared to healthy controls (p < 0.001). Associated with these changes there was a significant increase in the ratio of slow-to-fast wave activity indicating EEG slowing (+0.41+/-0.16; N=13 versus -0.05+/-0.08; N=8; p=0.036). As expected in cirrhotics, basal valine and leucine concentrations were decreased while phenylalanine, tyrosine and methionine were significantly increased. Although the basal molar ratio of branched chain amino acids to the aromatic amino acids phenylalanine and tyrosine was significantly decreased in cirrhotics (1.5+/-0.2 versus 3.2+/-0.2; p < 0.0001), after the challenge when EEG changes were apparent in cirrhotics, the ratio significantly increased (p < 0.005) in both groups to 2.7+/-0.3 versus 4.1+/-0.3 (p=0.002). In the combined groups, there were significant correlations between EEG ratio change and the 120-min blood ammonia concentration (r=0.498; p=0.022).

CONCLUSION

The alterations in plasma amino acid patterns do not support a specific role for any of the amino acid groups in the pathogenesis of hepatic encephalopathy. They are however more in keeping with the direct or indirect role of ammonia.

Intestinal glutaminase activity is increased in liver cirrhosis and correlates with minimal hepatic encephalopathy

BACKGROUND/AIMS

We performed the current study to assess the intestinal activity of enterocyte phosphate-activated glutaminase (PAG) in cirrhosis.

METHODS

Forty-nine cirrhotic patients and 36 control subjects underwent endoscopic duodenal biopsies. Minimal hepatic encephalopathy (MHE) was evaluated using three psychometric tests. Oral glutamine challenge (OGC) was performed and MELD, Child-Pugh and the presence of esophageal varices were recorded. PAG was measured by enzymatic methods. Cerebral magnetic resonance spectroscopy was performed in 10 cirrhotics.

RESULTS

PAG was found to be higher in cirrhotics than control subjects 2.4+/-1.51 vs. 0.68+/-0.57IU/mg protein (P<0.001). PAG was also increased in patients with MHE and correlated with MELD, INR, esophageal varices and serum bile acids. A negative correlation was observed between PAG activity and intra-cerebral choline/creatine ratio (r=-0.67; P=0.035) and a positive correlation with glutamine plus glutamate/creatine ratio (r=0.78; P=0.007). In multivariate analysis using backward logistic regression, presence of MHE was the only variable independently related to altered enterocyte PAG.

CONCLUSIONS

Enterocyte PAG is increased in cirrhotic patients and correlates with MHE. These data support a possible role for intestinal glutaminase in the pathogenesis of hepatic encephalopathy (HE) and could be a new target for future therapies.

Prognostic value of altered oral glutamine challenge in patients with minimal hepatic encephalopathy

Oral glutamine challenge (OGC) has been found to be safe, and an altered response predicts elevated risk of overt hepatic encephalopathy (HE) in patients with minimal hepatic encephalopathy (MHE). We assessed the survival prognosis of patients with cirrhosis, but without current overt HE, who have an altered OGC and MHE. MHE was inferred using 3 neuropsychological tests. Venous ammonia concentrations were measured pre- and post-60 minutes of a 10 g oral glutamine load. The median follow-up was 25.2 months, by which time 22 patients had had bouts of overt HE and 18 had died from liver-related causes. The results in 126 patients with cirrhosis, indicated 25 with MHE and abnormal OGC response. Survival among patients who developed overt HE was 59% at 1 year and 38% at 3 years. In patients without HE, survival was 96% and 86% at 1 and 3 years, respectively (log-rank 50.9, P <.0001). The presence of MHE was not related to survival (log-rank 2.21, P =.23). Patients with MHE and abnormal OGC test had elevated mortality risk (log-rank 13.1, P =.0003). Multivariate analyses indicated Child-Pugh score (hazard ratio [HR] 1.46; 95% CI, 1.46-2.08), and MHE plus altered OGC response (HR 5.5; 95% CI, 1.81-16.6) were predictors of mortality, whether from liver-related or non-liver-related causes. In conclusion, a pathological OGC response in patients with MHE appears to be associated with lower survival rate and may prove useful in the selection of candidates for liver transplantation.

Oral glutamine challenge and magnetic resonance spectroscopy in three patients with congenital portosystemic shunts

BACKGROUND/AIMS

Congenital portosystemic shunts are rare abnormalities of liver vasculature that can cause neurological symptoms, probably secondarily to the effects of the metabolism of ammonia in the brain. Our aim was to investigate the relationship between capillary blood ammonia after oral glutamine challenge and magnetic resonance spectroscopy in three patients with congenital portosystemic shunts.

METHODS

Neuropsychological tests, oral glutamine challenge and magnetic resonance spectroscopy were performed at baseline and after 6 months of follow-up in three patients with congenital portosystemic shunts. The results were compared to those obtained in a group of six cirrhotic patients with prior episodes of hepatic encephalopathy and healthy controls.

RESULTS

Patients with congenital portosystemic shunts exhibited abnormalities of neuropsychological tests, magnetic resonance spectroscopy and a response to the oral glutamine challenge similar to those observed in patients with cirrhosis. The intensity of the rise of brain glutamine was correlated to the area under the curve of ammonia after the oral glutamine challenge (R=0.72).

CONCLUSIONS

Neurological manifestations of patients with congenital portosystemic shunts are mediated through similar mechanisms that are involved in the pathogenesis of hepatic encephalopathy. The area under the curve appears to be the better parameter that defines the response to the oral glutamine challenge.

Altered response to oral glutamine challenge as prognostic factor for overt episodes in patients with minimal hepatic encephalopathy

BACKGROUND/AIMS

We assessed the usefulness of oral glutamine challenge (OGC) and minimal hepatic encephalopathy in evaluating risk of overt hepatic encephalopathy in cirrhotic patients.

METHODS

Minimal hepatic encephalopathy (MHE) was inferred using neuro-psychological tests. Venous ammonia concentrations were measured pre- and post-60 min (NH(3)-60m) of a 10 g oral glutamine load. Receiver-operating-characteristic curve analysis indicated a pathological glutamine tolerance cut-off value of NH(3)-60m >128 microg/dl.

RESULTS

In healthy control subjects (n=10) ammonia concentrations remained unchanged but increased significantly in cirrhotic patients (from 70.41+/-45.2 to 127.43+/-78.6; P<0.001). In multiple logistic regression analysis, altered OGC was related to Child-Pugh (odds ratio, OR=7.69; 95% confidence interval, CI=1.72-33.3; P<0.01) and MHE (OR=5.45; 95% CI=1.17-25.4; P<0.05). In the follow-up 11 patients (15%) developed overt hepatic encephalopathy (HE). In multivariate analysis OGC (OR=14.5; 95% CI=1.26-126.3) and MHE (OR=1.56; 95% CI=1.02-21.9) were independently related with HE in the follow-up. Patients with MHE and altered OGC showed significantly higher risk of overt HE in the follow-up (60%) than patients without MHE and normal OGC (2.8%) (Log rank test=21.60; P<0.0001).

CONCLUSIONS

A pathological OGC in patients with MHE appears to be a prognostic factor for the development of overt hepatic encephalopathy, whereas a normal OGC in patients without MHE could exclude risk of overt HE.

Amino acid challenge in patients with cirrhosis: a model for the assessment of treatments for hepatic encephalopathy

BACKGROUND/AIMS

To mimic episodic hepatic encephalopathy after gastrointestinal bleeding under controlled conditions, cirrhotic patients were challenged with an amino acid mixture of comparable composition to haemoglobin.

METHODS

Basal EEG, psychometric score (HE test), reaction times and venous blood ammonia were recorded. Following a 54 or 108 gm oral amino acid challenge, blood ammonia levels and EEG were recorded at 30-min intervals, and psychometric testing was repeated at 180 min. Ten controls (57 +/- 2) and 31 cirrhotics (52 +/- 2) of which 21 were Child's grade A or B and 10 grade C underwent the challenge. Nine had a transjugular intrahepatic porta-systemic shunt in situ.

RESULTS

Seventeen patients had abnormal baseline HE scores. Basal blood ammonia and reaction time A were significantly greater in patients (52 +/- 5 micromol/l and 478 +/- 20 ms, respectively) than controls (19 +/- 2 micromol/l and 372 +/- 14 ms) (P < 0.001). Following the challenge, in patients with advanced liver disease (Child's grade B and C) the slowing of reaction time A (+85 +/- 38 and +71 +/- 31 ms, respectively; P < 0.03) and EEG (ratio of slow to fast wave activity +0.31 +/- 0.12 and +0.58 +/- 0.19; P < 0.02) were significantly greater than in controls (-3.3 +/- 8 ms and 0.00 +/- 0.03, respectively). Patients with an abnormal basal HE score had the most pronounced changes (reaction time A +110 +/- 39 ms, P < 0.01, EEG +0.52 +/- 13, P < 0.01, respectively). The change in EEG ratio correlated with the dose of amino acid administered (r = 0.96; P < 0.008).

CONCLUSION

The amino acid challenge constitutes a reproducible human model of episodic, Type C hepatic encephalopathy unaffected by the complications usually encountered in clinical practice.