Ammonia In Hepatic Encephalopathy Research Articles

The Ongoing Debate of Serum Ammonia Levels in Cirrhosis: the Good, the Bad, and the Ugly.

Serum ammonia testing in hepatic encephalopathy (HE) has been long debated in the field of hepatology. Although central to the pathophysiology of HE, serum ammonia testing is fraught with complexities that can lead to challenges in laboratory collection and interpretation. Although there is some disagreement across guideline organizations regarding routine testing of ammonia in HE, all acknowledge that normal values, although possible in HE, may warrant reconsideration of the diagnosis. In this study, we propose a nuanced approach to ammonia testing in HE. Serum ammonia testing provides little additional benefit in clinical scenarios with a high or low pretest probability for HE. However, if the pretest probability for HE is uncertain, a low ammonia level may reduce the posttest probability of HE. In this scenario, other etiologies of altered mental status should be explored. Future research should focus on developing a standardized approach to serum ammonia collection, processing, and interpretation.

Role of ammonia for brain abnormal protein glycosylation during the development of hepatitis B virus-related liver diseases

BackgroundAmmonia is the most typical neurotoxin in hepatic encephalopathy (HE), but the underlying pathophysiology between ammonia and aberrant glycosylation in HE remains unknown.ResultsHere, we used HBV transgenic mice and astrocytes to present a systems-based study of glycosylation changes and corresponding enzymes associated with the key factors of ammonia in HE. We surveyed protein glycosylation changes associated with the brain of HBV transgenic mice by lectin microarrays. Upregulation of Galβ1-3GalNAc mediated by core 1 β1,3-galactosyltransferase (C1GALT1) was identified as a result of ammonia stimulation. Using in vitro assays, we validated that upregulation of C1GALT1 is a driver of deregulates calcium (Ca2+) homeostasis by overexpression of inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) in astrocytes.ConclusionsWe demonstrated that silencing C1GALT1 could depress the IP3R1 expression, an effective strategy to inhibit the ammonia-induced upregulation of Ca2+ activity, thereby C1GALT1 and IP3R1 may serve as therapeutic targets in hyperammonemia of HE.

Is NMDA-Receptor-Mediated Oxidative Stress in Mitochondria of Peripheral Tissues the Essential Factor in the Pathogenesis of Hepatic Encephalopathy?

Background: Hepatic encephalopathy (HE) is a neuropsychiatric syndrome of increased ammonia-mediated brain dysfunction caused by impaired hepatic detoxification or when the blood bypasses the liver. Ammonia-activated signal transduction pathways of hyperactivated NMDA receptors (NMDAR) are shown to trigger a cascade of pathological reactions in the brain, leading to oxidative stress. NMDARs outside the brain are widely distributed in peripheral tissues, including the liver, heart, pancreas, and erythrocytes. To determine the contribution of these receptors to ammonia-induced oxidative stress in peripheral tissues, it is relevant to investigate if there are any ammonia-related changes in antioxidant enzymes and free radical formation and whether blockade of NMDARs prevents these changes. Methods: Hyperammonemia was induced in rats by ammonium acetate injection. Oxidative stress was measured as changes in antioxidant enzyme activities and O2•− and H2O2 production by mitochondria isolated from the tissues and cells mentioned above. The effects of the NMDAR antagonist MK-801 on oxidative stress markers and on tissue ammonia levels were evaluated. Results: Increased ammonia levels in erythrocytes and mitochondria isolated from the liver, pancreas, and heart of hyperammonemic rats are shown to cause tissue-specific oxidative stress, which is prevented completely (or partially in erythrocyte) by MK-801. Conclusions: These results support the view that the pathogenesis of HE is multifactorial and that ammonia-induced multiorgan oxidative stress-mediated by activation of NMDAR is an integral part of the disease and, therefore, the toxic effects of ammonia in HE may be more global than initially expected.

Carnosine protects brain mitochondria under hyperammonemic conditions: Relevance to hepatic encephalopathy treatment

Elevated brain ammonia in hepatic encephalopathy (HE) is a serious and potentially fatal complication. Ammonia-induced oxidative stress, mitochondrial dysfunction, and energy crisis are known as the major mechanisms of ammonia-induced brain injury. Hence, targeting mitochondria seems to be a therapeutic point of intervention in the treatment of HE. Carnosine is abundantly found in human body. Several biological functions including the mitochondrial protective properties are attributed to this peptide. The current investigation was designed to evaluate the effect of carnosine on brain mitochondria exposed to toxic ammonia concentrations. Isolated brain mitochondria were exposed to ammonia (5 and 10mM). It was found that ammonia inhibited mitochondrial dehydrogenases activity (MTT test), caused mitochondrial membrane potential (MMP) collapse, induced mitochondrial swelling (MPP), and increased reactive oxygen species (ROS) in isolated brain mitochondria. Furthermore, a significant amount of lipid peroxidation (LPO), along with glutathione (GSH) and ATP depletion were detected in ammonia-treated mitochondria. It was found that carnosine (1, 5, 10 and 20mM) alleviated ammonia-induced mitochondrial dysfunction. The current investigation demonstrates that carnosine preserved brain mitochondrial function in a hyperammonemic environment. The data suggest this peptide as a potential protective agent with therapeutic capability against hyperammonemia-induced energy metabolism failure and brain injury.

Elevated Ammonia Level as a Diagnostic Marker of Hepatic Encephalopathy

Objectives: Hepatic encephalopathy (HE) is a common and prognostic complication of cirrhosis. It may reflect either a reversible metabolic encephalopathy, brain atrophy, edema or any combination of these conditions. The mechanisms causing brain dysfunction in liver failure are still unknown. Ammonia is the best-characterized neurotoxin that precipitates HE. The purpose of this study was to ascertain the role of ammonia in HE. Methods: A hospital-based prospective study on HE was carried out at the First Central Hospital of Mongolia and the Chingeltei-Uul District Hospital in 2011-2013. Patients with hepatic failure were subdivided into the three following groups: (1) patients without HE, (2) patients with grade l-ll HE, (3) patients with grade lll-IV HE. We took liver function tests, Model for End-Stage Liver Disease (MELD) score and blood ammonia and correlated them with the severity of encephalopathy. The mean variables ±SD, p-values, and Pearson coefficients were calculated by SPSS 17.0. Results: The total sample size was 120 and the mean age was 36.8 ±15.4 years. Elevated ammonia level was observed in every stage of HE and increased by stage (p< 0.0001) MELD score and elevated ammonia level had a strong positive correlation (r = 0.54, p = 0.0001). In patients with any infection, the ammonia level was higher (p< 0.0001) than other groups. Conclusion: Ammonia is one of the diagnostic biomarkers of HE.

Evaluation of Serum Ammonia in Hepatic Encephalopathy Patients and Its Correlation with Clinical Severity

AIM: To study serum ammonia levels and its correlation with clinical status in patients of hepatic encephalopathy. METHODS: A total number of 84 patients diagnosed clinically as Hepatic encephalopathy (HE) were grouped into 3 groups, due to cirrhosis of liver (n = 40), due to acute viral hepatitis (n = 34), due to drug induced hepatitis (n = 10). The diagnosis of HE was based on clinical criteria, and its severity was graded according to the West Haven Criteria for grading of mental status. Serum ammonia levels were estimated using enzymatic UV-method (RANDOX LABS). Ammonia levels were correlated with the severity of hepatic encephalopathy in all the three groups. All data obtained were assessed and statistically analyzed. ANOVA (ANalysis Of VAriance between groups) was used to find the statistical significance between the groups. TUKEY–KRAMER multiple comparison testswere used to compare meanbetween the groups. RESULTS: The mean serum ammonia levels in each study group were found to be as follows [(μg/dL) ± SD]: 118.12 ± 48.87 in cirrhosis, 222.76 ± 74.73 in acute viral hepatitis, 134.6 ± 37.8 in drug induced hepatitis. Serum ammonia levels in acute viral hepatitis group were significantly higher than cirrhosis group (q= 10.59, p ≤ 0.001).In all 3 groups, an increase in mean serum ammonia levels were associated with worsening clinical status. Out of 84 patients, 12 patients (14.29%) of cirrhosis group, 18(21.43%) of acute viral hepatitis group, 4 (4.76%) of drug induced hepatitis expired during the course of illness. A higher risk of mortality was observed with an increase in serum ammonia levels. In cirrhosis group, 100% mortality was found with serum ammonia > 200 µg/dL. In acute viral hepatitis, 70% mortality was observed with serum ammonia levels > 200µg/dL. In drug induced hepatitis, 100% mortality was observed with serum ammonia values > 150 µg/dL. CONCLUSION: An elevated serum ammonia level is an important laboratory abnormality in patients with HE. Both the mortality and severity of HE increases with an increase in serum ammonia levels. This could be useful in identifying patientswith higher grades of HE, suggesting that estimation of serum ammonia could be a useful tool in assessing the severity of illness and to plan for aggressive detoxification measures.

Clinical utility of breath ammonia for evaluation of ammonia physiology in healthy and cirrhotic adults

Blood ammonia is routinely used in clinical settings to assess systemic ammonia in hepatic encephalopathy and urea cycle disorders. Despite its drawbacks, blood measurement is often used as a comparator in breath studies because it is a standard clinical test. We sought to evaluate sources of measurement error and potential clinical utility of breath ammonia compared to blood ammonia.We measured breath ammonia in real time by quartz enhanced photoacoustic spectrometry and blood ammonia in 10 healthy and 10 cirrhotic participants. Each participant contributed 5 breath samples and blood for ammonia measurement within 1 h. We calculated the coefficient of variation (CV) for 5 breath ammonia values, reported medians of healthy and cirrhotic participants, and used scatterplots to display breath and blood ammonia.For healthy participants, mean age was 22 years (±4), 70% were men, and body mass index (BMI) was 27 (±5). For cirrhotic participants, mean age was 61 years (±8), 60% were men, and BMI was 31 (±7). Median blood ammonia for healthy participants was within normal range, 10 μmol L−1 (interquartile range (IQR), 3–18) versus 46 μmol L−1 (IQR, 23–66) for cirrhotic participants. Median breath ammonia was 379 pmol mL−1 CO2 (IQR, 265–765) for healthy versus 350 pmol mL−1 CO2 (IQR, 180–1013) for cirrhotic participants. CV was 17 ± 6%.There remains an important unmet need in the evaluation of systemic ammonia, and breath measurement continues to demonstrate promise to fulfill this need. Given the many differences between breath and blood ammonia measurement, we examined biological explanations for our findings in healthy and cirrhotic participants. We conclude that based upon these preliminary data breath may offer clinically important information this is not provided by blood ammonia.

Clinical science workshop: targeting the gut-liver-brain axis.

A clinical science workshop was held at the ISHEN meeting in London on Friday 11th September 2014 with the aim of thrashing out how we might translate what we know about the central role of the gut-liver-brain axis into targets which we can use in the treatment of hepatic encephalopathy (HE). This review summarises the integral role that inter-organ ammonia metabolism plays in the pathogenesis of HE with specific discussion of the roles that the small and large intestine, liver, brain, kidney and muscle assume in ammonia and glutamine metabolism. Most recently, the salivary and gut microbiome have been shown to underpin the pathophysiological changes which culminate in HE and patients with advanced cirrhosis present with enteric dysbiosis with small bowel bacterial overgrowth and translocation of bacteria and their products across a leaky gut epithelial barrier. Resident macrophages within the liver are able to sense bacterial degradation products initiating a pro-inflammatory response within the hepatic parenchyma and release of cytokines such as tumour necrosis factor alpha (TNF-α) and interleukin-8 into the systemic circulation. The endotoxemia and systemic inflammatory response that are generated predispose both to the development of infection as well as the manifestation of covert and overt HE. Co-morbidities such as diabetes and insulin resistance, which commonly accompany cirrhosis, may promote slow gut transit, promote bacterial overgrowth and increase glutaminase activity and may need to be acknowledged in HE risk stratification assessments and therapeutic regimens. Therapies are discussed which target ammonia production, utilisation or excretion at an individual organ level, or which reduce systemic inflammation and endotoxemia which are known to exacerbate the cerebral effects of ammonia in HE. The ideal therapeutic strategy would be to use an agent that can reduce hyperammonemia and reduce systemic inflammation or perhaps to adopt a combination of therapies that can address both.

Systemic inflammation and ammonia in hepatic encephalopathy

Infection and inflammation have been associated with the development of delirium for many centuries and there is a rapidly growing evidence base supporting the role of inflammation in exacerbating the neurological manifestations of both acute and chronic liver failure. Inflammation in the context of hepatic encephalopathy (HE) can arise directly within the brain itself resulting in astrocytic, microglial and neuronal dysfunction, impacting on the development of 'brain failure'. Inflammation may also develop systemically and indirectly influence brain function. Systemic inflammation develops following liver injury, resulting in hyperammonemia and a 'cytotoxic soup' of pro-inflammatory mediators which are released into the circulation and modulate the impact of ammonia on the brain. The aim of this review is to summarise the current evidence base supporting the synergistic role of systemic inflammation and hyperammonemia in the pathogenesis of hepatic encephalopathy. Systemic inflammation and ammonia induce neutrophil degranulation and release reactive oxygen species into the peripheral circulation that may ultimately cross the blood brain barrier. Circulating endotoxin arising from the gut (bacterial translocation), superimposed sepsis, and hyperammonemia upregulate the expression of microbial pattern recognition receptors such as Toll-like receptors. The early recognition and management of systemic inflammation may not only facilitate improved outcomes in HE but supports the development of novel therapeutic strategies that reduce circulating endotoxemia and immune cell dysfunction.

Direct Exposure to Ammonia and Hyperammonemia Increase the Extracellular Accumulation and Degradation of Astroglia-Derived Glutathione in the Rat Prefrontal Cortex

We endeavored here to shed light on the supply of glutathione (GSH) precursors from glial cells to neurons and on the interference of ammonia with this process. Administration of ammonium chloride (ammonia) via a microdialysis probe to the rat prefrontal cortex rapidly increased GSH content in the microdialysates. The increase was abrogated by the inhibitor of astrocytic energy metabolism fluoroacetate and the inhibitor of glutathione synthesis buthionine sulfoximine. GSH in the microdialysates was significantly elevated in rats with simple hyperammonemia (HA) or hepatic encephalopathy (HE) (three ip administrations of ammonium acetate or thioacetamide, respectively, at 24-h intervals), only when microdialysis was carried out in the presence of a gamma-glutamyltranspeptidase (gammaGT) inhibitor acivicin. Extracellular GSH increased in cultured rat cortical astrocytes treated with 5mM ammonia for 1 h, but not for 3-72 h, which was the period of increased gammaGT activity. GSH remained increased during the whole 72-h incubation with 5 or 10mM ammonia in C6 glioma cells, where gammaGT activity is intrinsically low and was not increased by ammonia. Collectively, the results suggest that in rats with HA or HE ammonia specifically promote GSH synthesis and export from astrocytes and increase its extracellular degradation, which may improve the availability of precursors for GSH synthesis in neurons and their resistance to ammonia toxicity.

Clinical Management of Hepatic Encephalopathy

The number of patients with cirrhosis in the United States continues to rise, and 30-45% of these patients are expected to develop hepatic encephalopathy. A broad spectrum of clinical manifestations is seen with the disorder, including mental or personality changes, asterixis, decreased energy level, impaired cognition, impaired sleep-wake cycle, decreased hand-eye coordination, psychomotor retardation, and incessant talking. Hepatic encephalopathy is a clinical diagnosis, and several scoring systems have been used to determine the severity of hepatic encephalopathy. The West Haven Criteria appear to be the scoring system most frequently used. Minimal hepatic encephalopathy has been reported to affect 60-70% of patients with cirrhosis and is predictive of the development of overt hepatic encephalopathy. An estimated 10-50% of patients who have undergone a transjugular intrahepatic portosystemic shunt for variceal bleeding develop hepatic encephalopathy. A great amount of attention has centered on the role of ammonia in hepatic encephalopathy, but that role is still largely hypothetical. Lactulose has been used for many years to minimize the effects of hepatic encephalopathy; however, noncompliance with lactulose is a common cause of rehospitalization. The pathophysiology of hepatic encephalopathy is extremely complex, and formal treatment guidelines are grossly outdated. The survival rate after 3 years among patients with hepatic encephalopathy is only 25%.

Experimental ammonia encephalopathy in the primate.

The role of ammonia in hepatic encephalopathy has never been clearly defined. We have approached the problem by constant infusion of macaques with ammonium acetate. Controls consisted of non-infused and sodium-acetate-infused animals, as well as animals with a portacaval shunt. Achieving blood ammonia levels of 200μg to 400mμg 100 ml for periods of 2 to 44 days, we have produced a clinicopathologic syndrome reasonably similar to that seen in patients dying of hepatic encephalopathy. Pathologic changes in the brain consisted of a proliferation of astrocytes in gray matter, mainly of the protoplasmic variety. Lethargy and stupor occurred for short periods in some animals. The electroencephalographic abnormality consisted of diffuse symmetrical slow activity and could be related to the presence of gliosis. We conclude that ammonia is toxic to the brain at levels ordinarily seen in the clinic.