A critical analysis of studies assessing L-ornithine-L-aspartate (LOLA) in hepatic encephalopathy treatment

The Story of Ammonia in Liver Disease: An Unraveling Continuum

Hyperammonemia and liver disease are closely linked. Most of the ammonia in our body is produced by transamination and deamination activities involving amino acid, purine, pyrimidines, and biogenic amines, and from the intestine by bacterial splitting of urea. The only way of excretion from the body is by hepatic conversion of ammonia to urea. Hyperammonemia is associated with widespread toxicities such as cerebral edema, hepatic encephalopathy, immune dysfunction, promoting fibrosis, and carcinogenesis. Over the past two decades, it has been increasingly utilized for prognostication of cirrhosis, acute liver failure as well as acute on chronic liver failure. The laboratory assessment of hyperammonemia has certain limitations, despite which its value in the assessment of various forms of liver disease cannot be negated. It may soon become an important tool to make therapeutic decisions about the use of prophylactic and definitive treatment in various forms of liver disease.

Efficacy and Safety of Variable Treatment Options in the Prevention of Hepatic Encephalopathy: A Systematic Review and Network Meta-Analysis

There are no guidelines for the most effective medication to reduce hepatic encephalopathy (HE) or the associated mortality. The purpose of this study is to determine the most effective possible treatment among the single treatment options or the combined treatment options for decreasing the morbidity and mortality of HE. We evaluated the outcomes by various parameters such as the quality of life, reduction in ammonia, all causes of mortality, adverse events, reversal of minimal HE, and development of overt HE. We systematically searched PubMed, Cochrane, Web of Science, and Scopus till the 19th of January 2023 for studies that assess various treatment options for HE. Data were extracted from eligible studies and pooled in a frequentist network meta-analysis as standardized mean difference (SMD) and their 95% confidence interval (CI) using the MetaInsight web-based tool. The Cochrane Tool was used to assess the randomized controlled trials' quality (RCT), while the NIH tool was used to assess the quality of the included cohort studies. Utilizing the R software, the network meta-analysis was conducted. In addition to a significant variation in cases of (Lactulose and Rifaximin) compared with Rifaximin (RR= 0.39, 95% CI [0.17; 0.89]), the results demonstrated a significantly lower incidence of overt HE in (Lactulose and Rifaximin) compared with placebo (RR=0.19, 95% CI [0.09; 0.40]). Most arms demonstrated a statistically significant reduction in the incidence of overt HE compared to albumin and placebo. The results also demonstrated a significant reduction in ammonia between L-ornithine-L-aspartate (LOLA) and probiotics (MD= -19.17, 95% CI [-38.01; -0.32]), as well as a significant difference in the incidence of LOLA compared to placebo (MD= -22.62, 95% CI [-39.16; -6.07]). This network meta-analysis has significant data for managing subclinical HE in people without a history of overt HE. Our analysis showed that (Lactulose and Rifaximin), followed by (Rifaximin and L-carnitine), followed by (Lactulose and Rifaximin with zinc) were the best combinations regarding overt HE. LOLA reduced ammonia best, followed by Nitazoxanide and finally Lactulose. (Lactulose and Nitazoxanide) have the least adverse effects, followed by (Rifaximin and L-carnitine), then Probiotics. Yet, all mortality outcomes and quality of life changes yielded no useful findings. Future studies like RCTs must be done to compare our therapies directly.

An orally deliverable ornithine-based self-assembling polymer nanomedicine ameliorates hyperammonemia in acetaminophen-induced acute liver injury

l-Ornithine (Orn) is a core amino acid responsible for ammonia detoxification in the body via the hepatic urea cycle. Clinical studies in Orn therapy have focused on interventions for hyperammonemia-associated diseases, such as hepatic encephalopathy (HE), a life-threatening neurological symptom affecting more than 80% of patients with liver cirrhosis. However, its low molecular weight (LMW) causes Orn to diffuse nonspecifically and be rapidly eliminated from the body after oral administration, resulting in unfavorable therapeutic efficacy. Hence, Orn is constantly supplied by intravenous infusion in many clinical settings; however, this treatment inevitably decreases patient compliance and limits its application in long-term management. To improve the performance of Orn, we designed self-assembling polyOrn-based nanoparticles for oral administration through ring-opening polymerization of Orn-N-carboxy anhydride initiated with amino-ended poly(ethylene glycol), followed by acylation of free amino groups in the main chain of the polyOrn segment. The obtained amphiphilic block copolymers, poly(ethylene glycol)-block-polyOrn(acyl) (PEG-block-POrn(acyl)), enabled the formation of stable nanoparticles (NanoOrn(acyl)) in aqueous media. We employed the isobutyryl (iBu) group for acyl derivatization in this study (NanoOrn(iBu)). In the healthy mice, daily oral administration of NanoOrn(iBu) for one week did not induce any abnormalities. In the mice exhibiting acetaminophen (APAP)-induced acute liver injury, oral pretreatment with NanoOrn(iBu) effectively reduced systemic ammonia and transaminases levels compared to the LMW Orn and untreated groups. The results suggest that the application of NanoOrn(iBu) is of significant clinical value with the feasibility of oral delivery and improvement in APAP-induced hepatic pathogenesis. STATEMENT OF SIGNIFICANCE: Liver injury is often accompanied by hyperammonemia, a life-threatening condition characterized by elevated blood ammonia levels. Current clinical treatments for reducing ammonia typically entail the invasive approach of intravenous infusion, involving the administration of l-ornithine (Orn) or a combination of Orn and L-aspartate. This method is employed due to the poor pharmacokinetics associated with these compounds. In our pursuit of enhancing therapy, we have developed an orally administrable nanomedicine based on Orn-based self-assembling nanoparticle (NanoOrn(iBu)), which provides sustained Orn supply to the injured liver. Oral administration of NanoOrn(iBu) to healthy mice did not cause any toxic effects. In a mouse model of acetaminophen-induced acute liver injury, oral administration of NanoOrn(iBu) surpassed Orn in reducing systemic ammonia levels and liver damage, thereby establishing NanoOrn(iBu) as a safe and effective therapeutic option.

L-ornithine L-aspartate for prevention and treatment of hepatic encephalopathy in people with cirrhosis

BACKGROUND

Hepatic encephalopathy is a common complication of cirrhosis and has high associated morbidity and mortality. The condition is classified as overt if it is clinically apparent or minimal if only evident though psychometric testing. The exact pathogenesis of this syndrome is unknown although ammonia is thought to play a key role. L-ornithine L-aspartate has ammonia-lowering properties and may, therefore, benefit people with cirrhosis and hepatic encephalopathy.

OBJECTIVES

To evaluate the beneficial and harmful effects of L-ornithine L-aspartate versus placebo, no intervention, or other active interventions in people with cirrhosis and hepatic encephalopathy.

SEARCH METHODS

We undertook electronic searches of The Cochrane Hepato-Biliary Group Controlled Trials Register, CENTRAL, MEDLINE, Embase, LILACS and Science Citation Index Expanded to December 2017 and manual searches of meetings and conference proceedings; checks of bibliographies; and corresponded with investigators and pharmaceutical companies.

SELECTION CRITERIA

We included randomised clinical trials, irrespective of publication status, language, or blinding. We included participants with cirrhosis who had minimal or overt hepatic encephalopathy or who were at risk for developing hepatic encephalopathy. We compared: L-ornithine L-aspartate versus placebo or no intervention; and L-ornithine L-aspartate versus other active agents such as non-absorbable disaccharides, antibiotics, probiotics, or branched-chain amino acids.

DATA COLLECTION AND ANALYSIS

Two review authors, working independently, retrieved data from published reports and correspondence with investigators and pharmaceutical companies. The primary outcomes were mortality, hepatic encephalopathy, and serious adverse events. We undertook meta-analyses and presented the results as risk ratios (RR) and mean differences (MD) with 95% confidence intervals (CI). We assessed bias control using the Cochrane Hepato-Biliary Group domains; we evaluated the risk of publication bias and other small trial effects in regression analyses; conducted subgroup and sensitivity analyses; and performed Trial Sequential Analyses. We determined the quality of the evidence using GRADE.

MAIN RESULTS

We identified 36 randomised clinical trials, involving at least 2377 registered participants, which fulfilled our inclusion criteria including 10 unpublished randomised clinical trials. However, we were only able to access outcome data from 29 trials involving 1891 participants. Five of the included trials assessed prevention, while 31 trials assessed treatment. Five trials were at low risk of bias in the overall assessment of mortality; one trial was at low risk of bias in the assessment of the remaining outcomes.L-ornithine L-aspartate had a beneficial effect on mortality compared with placebo or no intervention when including all trials (RR 0.42, 95% CI 0.24 to 0.72; I² = 0%; 19 trials; 1489 participants; very low quality evidence), but not when the analysis was restricted to the trials at low risk of bias (RR 0.47, 95% CI 0.06 to 3.58; 4 trials; 244 participants). It had a beneficial effect on hepatic encephalopathy compared with placebo or no intervention when including all trials (RR 0.70, 95% CI 0.59 to 0.83; 22 trials; 1375 participants; I² = 62%; very low quality evidence), but not in the one trial at low risk of bias (RR 0.96, 95% CI 0.85 to 1.07; 63 participants). The analysis of serious adverse events showed a potential benefit of L-ornithine L-aspartate when including all randomised clinical trials (RR 0.63, 95% CI 0.45 to 0.90; 1 trial; 1489 participants; I² = 0%; very low quality evidence), but not in the one trial at low risk of bias for this outcome (RR 0.83, 95% CI 0.15 to 4.65; 63 participants). The Trial Sequential Analyses of mortality, hepatic encephalopathy, and serious adverse events found insufficient evidence to support or refute beneficial effects. Subgroup analyses showed no difference in outcomes in the trials evaluating evaluating the prevention or treatment of either overt or minimal hepatic encephalopathy or trials evaluating oral versus intravenous administration We were unable to undertake a meta-analysis of the three trials involving 288 participants evaluating health-related quality of life. Overall, we found no difference between L-ornithine L-aspartate and placebo or no intervention in non-serious adverse events (RR 1.15, 95% CI 0.75 to 1.77; 14 trials; 1076 participants; I² = 40%). In comparison with lactulose, L-ornithine L-aspartate had no effect on mortality (RR 0.68, 95% CI 0.11 to 4.17; 4 trials; 175 participants; I² = 0%); hepatic encephalopathy (RR 1.13, 95% CI 0.81 to 1.57); serious adverse events (RR 0.69, 95% CI 0.22 to 2.11); or non-serious adverse events (RR 0.05, 95% CI 0.01 to 0.18). In comparison with probiotics, L-ornithine L-aspartate had no effect on mortality (RR 1.01, 95% CI 0.11 to 9.51); serious adverse events (RR 1.07, 95% CI 0.23 to 4.88); or changes in blood ammonia concentrations from baseline (RR -2.30 95% CI -6.08 to 1.48), but it had a possible beneficial effect on hepatic encephalopathy (RR 0.71, 95% CI 0.56 to 0.90). Finally, in comparison with rifaximin, L-ornithine L-aspartate had no effect on mortality (RR 0.33, 95% CI 0.04 to 3.03; 2 trials; 105 participants); hepatic encephalopathy (RR 1.06, 95% CI 0.57 to 1.96); serious adverse events (RR 0.32, 95% CI 0.01 to 7.42), or non-serious adverse events (RR 0.32, 95% CI 0.01 to 7.42).

AUTHORS' CONCLUSIONS

The results of this review suggest a possible beneficial effect of L-ornithine L-aspartate on mortality, hepatic encephalopathy, and serious adverse events in comparisons with placebo or no-intervention, but, because the quality of the evidence is very low, we are very uncertain about these findings. There was very low quality evidence of a possible beneficial effect of L-ornithine L-aspartate on hepatic encephalopathy, when compared with probiotics, but no other benefits were demonstrated in comparison with other active agents. Additional access to data from completed, but unpublished trials, and new randomised placebo-controlled, double-blind clinical trials are needed.

The Pharmabiotic Approach to Treat Hyperammonemia

Ammonia is constantly produced as a metabolic waste from amino acid catabolism in mammals. Ammonia, the toxic waste metabolite, is resolved in the liver where the urea cycle converts free ammonia to urea. Liver malfunctions cause hyperammonemia that leads to central nervous system (CNS) dysfunctions, such as brain edema, convulsions, and coma. The current treatments for hyperammonemia, such as antibiotics or lactulose, are designed to decrease the intestinal production of ammonia and/or its absorption into the body and are not effective, besides being often accompanied by side effects. In recent years, increasing evidence has shown that modifications of the gut microbiota could be used to treat hyperammonemia. Considering the role of the gut microbiota and the physiological characteristics of the intestine, the removal of ammonia from the intestine by modulating the gut microbiota would be an ideal approach to treat hyperammonemia. In this review, we discuss the significance of hyperammonemia and its related diseases and the efficacy of the current management methods for hyperammonemia to understand the mechanism of ammonia transport in the human body. The possibility to use the gut microbiota as pharmabiotics to treat hyperammonemia and its related diseases is also explored.

Microbial Production of Amino Acid-Related Compounds

Corynebacterium glutamicum is the workhorse of the production of proteinogenic amino acids used in food and feed biotechnology. After more than 50 years of safe amino acid production, C. glutamicum has recently also been engineered for the production of amino acid-derived compounds, which find various applications, e.g., as synthons for the chemical industry in several markets including the polymer market. The amino acid-derived compounds such as non-proteinogenic ω-amino acids, α,ω-diamines, and cyclic or hydroxylated amino acids have similar carbon backbones and functional groups as their amino acid precursors. Decarboxylation of amino acids may yield ω-amino acids such as β-alanine, γ-aminobutyrate, and δ-aminovalerate as well as α,ω-diamines such as putrescine and cadaverine. Since transamination is the final step in several amino acid biosynthesis pathways, 2-keto acids as immediate amino acid precursors are also amenable to production using recombinant C. glutamicum strains. Approaches for metabolic engineering of C. glutamicum for production of amino acid-derived compounds will be described, and where applicable, production from alternative carbon sources or use of genome streamline will be referred to. The excellent large-scale fermentation experience with C. glutamicum offers the possibility that these amino acid-derived speciality products may enter large-volume markets.

Branched-chain amino acid supplementation in treatment of liver cirrhosis: Updated views on how to attenuate their harmful effects on cataplerosis and ammonia formation

Branched-chain amino acid (BCAA; valine, leucine, and isoleucine) supplementation is common for patients with liver cirrhosis due to decreased levels of BCAA in the blood plasma of these patients, which plays a role in pathogenesis of hepatic encephalopathy and cachexia. The unique pharmacologic properties of BCAA also are a factor for use as supplementation in this population. In the present article, BCAA is shown to provide nitrogen to alpha-ketoglutarate (α-KG) for synthesis of glutamate, which is a substrate for ammonia detoxification to glutamine (GLN) in the brain and muscles. The article also demonstrates that the favorable effects of BCAA supplementation might be associated with three adverse effects: draining of α-KG from tricarboxylic acid cycle (cataplerosis), increased GLN content and altered glutamatergic neurotransmission in the brain, and activated GLN catabolism to ammonia in the gut and kidneys. Cataplerosis of α-KG can be attenuated by dimethyl-α-ketoglutarate, l-ornithine-l-aspartate, and ornithine salt of α-KG. The pros and cons of GLN elimination from the body using phenylbutyrate (phenylacetate), which may impair liver regeneration and decrease BCAA levels, should be examined. The therapeutic potential of BCAA might be enhanced also by optimizing its supplementation protocol. It is concluded that the search for strategies attenuating adverse and increasing positive effects of the BCAA is needed to include the BCAA among standard medications for patients with cirrhosis of the liver.

L‐ornithine L‐aspartate for people with cirrhosis and hepatic encephalopathy

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

To assess the beneficial and harmful effects of L‐ornithine L‐aspartate versus placebo, no intervention, or other active interventions for people with cirrhosis and hepatic encephalopathy.

Ammonia metabolism and hyperammonemic disorders

Human adults produce around 1000 mmol of ammonia daily. Some is reutilized in biosynthesis. The remainder is waste and neurotoxic. Eventually most is excreted in urine as urea, together with ammonia used as a buffer. In extrahepatic tissues, ammonia is incorporated into nontoxic glutamine and released into blood. Large amounts are metabolized by the kidneys and small intestine. In the intestine, this yields ammonia, which is sequestered in portal blood and transported to the liver for ureagenesis, and citrulline, which is converted to arginine by the kidneys. The amazing developments in NMR imaging and spectroscopy and molecular biology have confirmed concepts derived from early studies in animals and cell cultures. The processes involved are exquisitely tuned. When they are faulty, ammonia accumulates. Severe acute hyperammonemia causes a rapidly progressive, often fatal, encephalopathy with brain edema. Chronic milder hyperammonemia causes a neuropsychiatric illness. Survivors of severe neonatal hyperammonemia have structural brain damage. Proposed explanations for brain edema are an increase in astrocyte osmolality, generally attributed to glutamine accumulation, and cytotoxic oxidative/nitrosative damage. However, ammonia neurotoxicity is multifactorial, with disturbances also in neurotransmitters, energy production, anaplerosis, cerebral blood flow, potassium, and sodium. Around 90% of hyperammonemic patients have liver disease. Inherited defects are rare. They are being recognized increasingly in adults. Deficiencies of urea cycle enzymes, citrin, and pyruvate carboxylase demonstrate the roles of isolated pathways in ammonia metabolism. Phenylbutyrate is used routinely to treat inherited urea cycle disorders, and its use for hepatic encephalopathy is under investigation.

Recent insights into the pathogenesis of hepatic encephalopathy and treatments

Hepatic encephalopathy (HE) encompasses a spectrum of neuropsychiatric disorders related to liver failure. The development of HE can have a profound impact on mortality as well as quality of life for patients and carers. Ammonia is central in the disease process contributing to alteration in neurotransmission, oxidative stress, and cerebral edema and astrocyte swelling in acute liver failure. Inflammation in the presence of ammonia coactively worsens HE. Inflammation can result from hyperammonemic responses, endotoxemia, innate immune dysfunction or concurrent infection. This review summarizes the current processes implicated in the pathogenesis of HE, as well as current and potential treatments. Treatments currently focus on reducing inflammation and/or blood ammonia levels and provide varying degrees of success. Optimization of current treatments and initial testing of novel therapies will provide the basis of improvement of care in the near future.

Metabolic engineering of Corynebacterium glutamicum aimed at alternative carbon sources and new products

Corynebacterium glutamicum is well known as the amino acid-producing workhorse of fermentation industry, being used for multi-million-ton scale production of glutamate and lysine for more than 60 years. However, it is only recently that extensive research has focused on engineering it beyond the scope of amino acids. Meanwhile, a variety of corynebacterial strains allows access to alternative carbon sources and/or allows production of a wide range of industrially relevant compounds. Some of these efforts set new standards in terms of titers and productivities achieved whereas others represent a proof-of-principle. These achievements manifest the position of C. glutamicum as an important industrial microorganism with capabilities far beyond the traditional amino acid production. In this review we focus on the state of the art of metabolic engineering of C. glutamicum for utilization of alternative carbon sources, (e.g. coming from wastes and unprocessed sources), and construction of C. glutamicum strains for production of new products such as diamines, organic acids and alcohols