Arterial ammonia levels in cirrhosis are determined by systemic and hepatic hemodynamics, and by organ function: a quantitative modelling study

Novel Serum Biomarkers Associated With Pediatric Hepatic Encephalopathy: A Systematic Review

BACKGROUND

The pathophysiology of pediatric hepatic encephalopathy (HE) is not well understood. Various serum biomarkers associated with HE may provide insight into its pathology, but their use and interpretation in clinical practice for diagnosis and prognostication remain undetermined. We sought to investigate reported correlations of serum biomarkers with presence and degree of HE in children.

METHODS

We conducted a systematic review of studies examining novel serum biomarkers and cytokines in association with HE that included children on PubMed, Embase, Lilacs, and Scopus. We utilized Covidence for abstract and text review by 2 independent reviewers for each study.

RESULTS

We reviewed 2824 unique publications; 15 met criteria for inclusion. Categories of biomarkers reported were inflammatory cytokines, products of amino acid metabolism, trace elements and vitamins, and hepatic and neuro biomarkers. Of 19 individual biomarkers, only 5 were measured in more than 1 study. Elevations in interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were most commonly reported as associated with HE. Notably, we observed lower average IL-6 and TNF-alpha levels in pediatric-only studies compared to mixed age studies. Overall, high bias and poor applicability to our review question was observed. We encountered low numbers of studies with pediatric focus, and few conducted with low bias study designs.

CONCLUSION

Investigated biomarkers span a large range of categories and suggest potentially useful correlations with HE. Further well-designed prospective biomarker research is necessary to better elucidate the pathogenesis of HE in children and improve early detection and clinical care.

Russian Consensus “Hyperammonemia in Adults” (Version 2021)

Justification Given the large number of reports on the peculiarities of liver lesions during the Sars-Cov-2 infection [1], a team of experts who participated in the 23rd Congress of the Scientific Society of Gastroenterologists of Russia and 15 National Congress of Therapists of November 19, 2020 decided to make additions to the Russian Consensus of “Hyperammonemia in Adults” published early 2020 [2, 3].

Important Unresolved Questions in the Management of Hepatic Encephalopathy: An ISHEN Consensus

Management of hepatic encephalopathy (HE) remains challenging from a medical and psychosocial perspective. Members of the International Society for Hepatic Encephalopathy and Nitrogen Metabolism recognized 5 key unresolved questions in HE management focused on (i) driving, (ii) ammonia levels in clinical practice, (iii) testing strategies for covert or minimal HE, (iv) therapeutic options, and (v) nutrition and patient-reported outcomes. The consensus document addresses these topical issues with a succinct review of the literature and statements that critically evaluate the current science and practice, laying the groundwork for future investigations.

A model of blood-ammonia homeostasis based on a quantitative analysis of nitrogen metabolism in the multiple organs involved in the production, catabolism, and excretion of ammonia in humans

Increased blood ammonia (NH₃) is an important causative factor in hepatic encephalopathy, and clinical treatment of hepatic encephalopathy is focused on lowering NH₃. Ammonia is a central element in intraorgan nitrogen (N) transport, and modeling the factors that determine blood-NH₃ concentration is complicated by the need to account for a variety of reactions carried out in multiple organs. This review presents a detailed quantitative analysis of the major factors determining blood-NH₃ homeostasis – the N metabolism of urea, NH₃, and amino acids by the liver, gastrointestinal system, muscle, kidney, and brain – with the ultimate goal of creating a model that allows for prediction of blood-NH₃ concentration. Although enormous amounts of NH₃ are produced during normal liver amino-acid metabolism, this NH₃ is completely captured by the urea cycle and does not contribute to blood NH₃. While some systemic NH₃ derives from renal and muscle metabolism, the primary site of blood-NH₃ production is the gastrointestinal tract, as evidenced by portal vein-NH₃ concentrations that are about three times that of systemic blood. Three mechanisms, in order of quantitative importance, release NH₃ in the gut: 1) hydrolysis of urea by bacterial urease, 2) bacterial protein deamination, and 3) intestinal mucosal glutamine metabolism. Although the colon is conventionally assumed to be the major site of gut-NH₃ production, evidence is reviewed that indicates that the stomach (via Helicobacter pylori metabolism) and small intestine and may be of greater importance. In healthy subjects, most of this gut NH₃ is removed by the liver before reaching the systemic circulation. Using a quantitative model, loss of this “first-pass metabolism” due to portal collateral circulation can account for the hyperammonemia observed in chronic liver disease, and there is usually no need to implicate hepatocyte malfunction. In contrast, in acute hepatic necrosis, hyperammonemia results from damaged hepatocytes. Although muscle-NH₃ uptake is normally negligible, it can become important in severe hyperammonemia. The NH₃-lowering actions of intestinal antibiotics (rifaximin) and lactulose are discussed in detail, with particular emphasis on the seeming lack of importance of the frequently emphasized acidifying action of lactulose in the colon.

Large-scale computational models of liver metabolism: How far from the clinics?

Understanding the dynamics of human liver metabolism is fundamental for effective diagnosis and treatment of liver diseases. This knowledge can be obtained with systems biology/medicine approaches that account for the complexity of hepatic responses and their systemic consequences in other organs. Computational modeling can reveal hidden principles of the system by classification of individual components, analyzing their interactions and simulating the effects that are difficult to investigate experimentally. Herein, we review the state-of-the-art computational models that describe liver dynamics from metabolic, gene regulatory, and signal transduction perspectives. We focus especially on large-scale liver models described either by genome scale metabolic networks or an object-oriented approach. We also discuss the benefits and limitations of each modeling approach and their value for clinical applications in diagnosis, therapy, and prevention of liver diseases as well as precision medicine in hepatology. (Hepatology 2017;66:1323-1334).

The Measurement of Ammonia in Human Breath and its Potential in Clinical Diagnostics

Ammonia is an important component of metabolism and is involved in many physiological processes. During normal physiology, levels of blood ammonia are between 11 and 50 µM. Elevated blood ammonia levels are associated with a variety of pathological conditions such as liver and kidney dysfunction, Reye's syndrome and a variety of inborn errors of metabolism including urea cycle disorders (UCD), organic acidaemias and hyperinsulinism/hyperammonaemia syndrome in which ammonia may reach levels in excess of 1 mM. It is highly neurotoxic and so effective measurement is critical for assessing and monitoring disease severity and treatment. Ammonia is also a potential biomarker in exercise physiology and studies of drug metabolism. Current ammonia testing is based on blood sampling, which is inconvenient and can be subject to significant analytical errors due to the quality of the sample draw, its handling and preparation for analysis. Blood ammonia is in gaseous equilibrium with the lungs. Recent research has demonstrated the potential use of breath ammonia as a non-invasive means of measuring systemic ammonia. This requires measurement of ammonia in real breath samples with associated temperature, humidity and gas characteristics at concentrations between 50 and several thousand parts per billion. This review explores the diagnostic applications of ammonia measurement and the impact that the move from blood to breath analysis could have on how these processes and diseases are studied and managed.

Hyperammonemia Is Associated with Increasing Severity of Both Liver Cirrhosis and Hepatic Encephalopathy

Background. Hyperammonemia resulting from chronic liver disease (CLD) can potentially challenge and damage any organ system of the body, particularly the brain. However, there is still some controversy regarding the diagnostic or prognostic values of serum ammonia in patients with over hepatic encephalopathy, especially in the setting of acute-on-chronic or chronic liver failure. Moreover, the association of serum ammonia with worsening Child-Pugh grade of liver cirrhosis has not been studied. Objective. This study was conducted to solve the controversy regarding the association between hyperammonemia and cirrhosis, especially hepatic encephalopathy in chronically failed liver. Material and Methods. In this study, 171 cirrhotic patients had their serum ammonia measured and analyzed by SPSS version 16. Chi-squared test and one-way ANOVA were applied. Results. The study had 110 male and 61 female participants. The mean age of all the participants in years was 42.33 ± 7.60. The mean duration (years) of CLD was 10.15 ± 3.53 while the mean Child-Pugh (CP) score was 8.84 ± 3.30. Chronic viral hepatitis alone was responsible for 71.3% of the cases. Moreover, 86.5% of participants had hepatic encephalopathy (HE). The frequency of hyperammonemia was 67.3%, more frequent in males (N = 81, z-score = 2.4, and P < 0.05) than in females (N = 34, z-score = 2.4, and P < 0.05), and had a statistically significant relationship with increasing CP grade of cirrhosis (χ²(2) = 27.46, P < 0.001, Phi = 0.40, and P < 0.001). Furthermore, serum ammonia level was higher in patients with hepatic encephalopathy than in those without it; P < 0.001. Conclusion. Hyperammonemia is associated with both increasing Child-Pugh grade of liver cirrhosis and hepatic encephalopathy.

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.

Correlation between hepatic blood flow and liver function in alcoholic liver cirrhosis

AIM: To elucidate the correlation between hepatic blood flow and liver function in alcoholic liver cirrhosis (AL-LC).

METHODS: The subjects included 35 patients with AL-LC (34 men, 1 woman; mean age, 58.9 ± 10.7 years; median age, 61 years; range: 37-76 years). All patients were enrolled in this study after obtaining written informed consent. Liver function was measured with tests measuring albumin (Alb), prothrombin time (PT), brain natriuretic peptide (BNP), branched amino acid and tyrosine ratio (BTR), branched chain amino acid (BCAA), tyrosine, ammonia (NH₃), cholinesterase (ChE), immunoreactive insulin (IRI), total bile acid (TBA), and the retention rate of indocyanine green 15 min after administration (ICG R15). Hepatic blood flow, hepatic arterial tissue blood flow (HATBF), portal venous tissue blood flow (PVTBF), and total hepatic tissue blood flow (THTBF) were simultaneously calculated using xenon computed tomography.

RESULTS: PVTBF, HATBF and THTBF were 30.2 ± 10.4, 20.0 ± 10.7, and 50.3 ± 14.9 mL/100 mL/min, respectively. Alb, PT, BNP, BTR, BCAA, tyrosine, NH₃, ChE, IRI, TBA, and ICG R15 were 3.50 ± 0.50 g/dL, 72.0% ± 11.5%, 63.2 ± 56.7 pg/mL, 4.06 ± 1.24, 437.5 ± 89.4 μmol/L, 117.7 ± 32.8 μmol/L, 59.4 ± 22.7 μg/dL, 161.0 ± 70.8 IU/L, 12.8 ± 5.0 μg/dL, 68.0 ± 51.8 μmol/L, and 28.6% ± 13.5%, respectively. PVTBF showed a significant negative correlation with ICG R15 (r = -0.468, P <0.01). No significant correlation was seen between ICG 15R, HATBF and THTBF. There was a significant correlation between PVTBF and Alb (r = 0.2499, P < 0.05), and NH₃ tended to have an inverse correlation with PVTBF (r = -0.2428, P = 0.0894). There were also many significant correlations between ICG R15 and liver function parameters, including Alb, NH3, PT, BNP, TBA, BCAA, and tyrosine (r = -0.2156, P < 0.05; r = 0.4318, P < 0.01; r = 0.4140, P < 0.01; r = 0.3610, P < 0.05; r = 0.5085, P < 0.001; r = 0.4496, P < 0.01; and r = 0.4740, P < 0.05, respectively).

CONCLUSION: Our investigation showed that there is a close correlation between liver function and hepatic blood flow.

Treatment to improve nutrition and functional capacity evaluation in liver transplant candidates

OPINION STATEMENT

Liver transplantation is the definitive therapy for cirrhosis, and malnutrition is the most frequent complication in these patients. Sarcopenia or loss of muscle mass is the major component of malnutrition in cirrhotics and adversely affects their outcome. In addition to the metabolic consequences, functional consequences of sarcopenia include reduced muscle strength and deconditioning. Despite nearly universal occurrence of sarcopenia and its attendant complications, there are no established therapies to prevent or reverse the same. Major reasons for this deficiency include the lack of established standardized definitions or measures to quantify muscle mass, as well as paucity of mechanistic studies or identified molecular targets to develop specific therapeutic interventions. Anthropometric evaluation, bioelectrical impedance analysis, and DEXA scans are relatively imprecise measures of muscle mass, and recent data on imaging measures to determine muscle mass accurately are likely to allow well-defined outcome responses to treatments. Resurgence of interest in the mechanisms of muscle loss in liver disease has been directly related to the rapid advances in the field of muscle biology. Metabolic tracer studies on whole body kinetics have been complemented by direct studies on the skeletal muscle of cirrhotics. Hypermetabolism and anabolic resistance contribute to sarcopenia. Reduced protein synthesis and increased autophagy have been reported in cirrhotic skeletal muscle, while the contribution of the ubiquitin-proteasome pathway is controversial. Increased plasma concentration and skeletal muscle expression of myostatin, a TGFβ superfamily member that causes reduction in muscle mass, have been reported in cirrhosis. Hyperammonemia and TNFα have been reported to increase myostatin expression and may be responsible for sarcopenia in cirrhosis. Nutriceutical interventions with leucine enriched amino acid mixtures, myostatin antagonists and physical activity hold promise as measures to reverse sarcopenia. There is even less data on muscle function and deconditioning in cirrhosis and studies in this area are urgently needed. Even though macronutrient replacement is a major therapeutic goal, micronutrient supplementation, specifically vitamin D, is expected to improve outcomes.