L-carnitine prevents ammonia-induced cytotoxicity and disturbances in intracellular amino acid levels in human astrocytes

Branched chain amino acids in hepatic encephalopathy and sarcopenia in liver cirrhosis: Evidence and uncertainties

Liver cirrhosis is commonly associated with nutritional alterations, reported in 20% of patients with compensated disease and over 60% of patients with decompensated cirrhosis. Nutritional disturbances are associated with a worse prognosis and increased risk of complication. Serum levels of branched-chain amino acids (BCAAs) are decreased in patients with liver cirrhosis. The imbalance of amino acids levels has been suggested to be associated with the development of complications, such as hepatic encephalopathy and sarcopenia, and to affect the clinical presentation and prognosis of these patients. Several studies investigated the efficacy of BCAAs supplementation as a therapeutic option in liver cirrhosis, but uncertainties remain about the real efficacy, the best route of administration, and dosage.

Cellular Pathogenesis of Hepatic Encephalopathy: An Update

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome derived from metabolic disorders due to various liver failures. Clinically, HE is characterized by hyperammonemia, EEG abnormalities, and different degrees of disturbance in sensory, motor, and cognitive functions. The molecular mechanism of HE has not been fully elucidated, although it is generally accepted that HE occurs under the influence of miscellaneous factors, especially the synergistic effect of toxin accumulation and severe metabolism disturbance. This review summarizes the recently discovered cellular mechanisms involved in the pathogenesis of HE. Among the existing hypotheses, ammonia poisoning and the subsequent oxidative/nitrosative stress remain the mainstream theories, and reducing blood ammonia is thus the main strategy for the treatment of HE. Other pathological mechanisms mainly include manganese toxicity, autophagy inhibition, mitochondrial damage, inflammation, and senescence, proposing new avenues for future therapeutic interventions.

Non-hepatic Hyperammonemia: A Potential Therapeutic Target for Sepsis-associated Encephalopathy

Sepsis-Associated Encephalopathy (SAE) is a common complication in the acute phase of sepsis, and patients who develop SAE have a higher mortality rate, longer hospital stay, and worse quality of life than other sepsis patients. Although the incidence of SAE is as high as 70% in sepsis patients, no effective treatment is available for this condition. To develop an effective treatment for SAE, it is vital to explore its pathogenesis. It is known that hyperammonemia is a possible factor in the pathogenesis of hepatic encephalopathy as ammonia is a potent neurotoxin. Furthermore, our previous studies indicate that non-hepatic hyperammonemia seems to occur more often in sepsis patients; it was also found that >50% of sepsis patients with non-hepatic hyperammonemia exhibited encephalopathy and delirium. Substatistical analyses indicate that non-hepatic hyperammonemia is an independent risk factor for SAE. This study updates the definition, clinical manifestations, and diagnosis of SAE; it also investigates the possible treatment options available for non-hepatic hyperammonemia in patients with sepsis and the mechanisms by which non-hepatic hyperammonemia causes encephalopathy.

Survival benefit of L-carnitine supplementation in patients with cirrhosis

BACKGROUND

L-carnitine supplementation is effective in improving muscle cramps, hyperammonemia, and hepatic encephalopathy in patients with cirrhosis. However, limited evidence is available on the effect of L-carnitine supplementation on the survival of patients with cirrhosis.

METHODS

In this retrospective study, 674 patients with cirrhosis admitted to Gifu University Hospital or Chuno Kosei Hospital between October 2011 and December 2018 were enrolled. L-carnitine supplementation was defined as the use of L-carnitine for more than 30 consecutive days during the follow-up period. Propensity score matching was applied to create comparable groups between L-carnitine-treated and untreated patients. Mortality was evaluated using the Cox proportional hazards model.

RESULTS

Among the patients, 93 were excluded. Of the remaining 581 patients, 71 (12%) received L-carnitine supplementation. Propensity matching identified 189 patients (63 L-carnitine-treated and 126 untreated patients) with comparable baseline characteristics in both groups. Of the matched patients, 33 (52%) L-carnitine-treated and 74 (59%) untreated patients died during the median follow-up period of 36.3 months. Overall survival was significantly higher in L-carnitine-treated patients than in untreated patients (hazard ratio [HR], 0.66; 95% confidence interval [CI], 0.43-0.99). A subgroup analysis showed that the survival benefit of L-carnitine supplementation was prominent in patients with Child-Pugh class B or C (HR, 0.39; 95% CI, 0.23-0.68), albumin levels ≤3.5 g/dL (HR, 0.59; 95% CI, 0.37-0.95), and ammonia levels ≥90 μg/dL (HR, 0.50; 95% CI, 0.26-0.97) and those without sarcopenia (HR, 0.56; 95% CI, 0.35-0.90).

CONCLUSION

L-carnitine supplementation may improve survival in patients with cirrhosis.

CLINICAL RELEVANCY STATEMENT

Carnitine is a vitamin-like compound that regulates lipid and energy metabolism. Although it has been recognized that L-carnitine supplementation improves hyperammonemia, hepatic encephalopathy, sarcopenia, and frailty in patients with cirrhosis, the relationship between L-carnitine supplementation mortality remains unknown. The results of our study provide the first evidence that L-carnitine supplementation may improve survival in patients with cirrhosis. L-carnitine supplementation may shed a new light on the nutritional intervention for patients with cirrhosis. This article is protected by copyright. All rights reserved.

Supplementation with Branched-Chain Amino Acids Induces Unexpected Deleterious Effects on Astrocyte Survival and Intracellular Metabolism with or without Hyperammonemia: A Preliminary In Vitro Study

INTRODUCTION

Ammonia is a key component in the pathogenesis of hepatic encephalopathy. Branched-chain amino acids (BCAA) have been reported to improve the symptoms of HE induced by hyperammonemia; however, we recently reported that ammonia increases intracellular levels of BCAA and exerts toxic effects on astrocytes.

OBJECTIVES

This follow-up study was designed to confirm the direct effects of BCAA on human astrocytes and clarify their underlying mechanisms using metabolome analysis and evaluation of associated signaling.

METHODS

We performed cytotoxicity and cell proliferation tests on astrocytes following BCAA treatment with and without ammonium chloride (NH4Cl) and then compared the results with the effects of BCAA on hepatocytes and neurons. Subsequently, we used metabolomic analysis to investigate intracellular metabolite levels in astrocytes with and without BCAA treatment.

RESULTS

The astrocytes showed increased leakage of intracellular lactate dehydrogenase and reduced proliferation rate upon BCAA treatment. Interestingly, our analysis showed a BCAA-induced impairment of intracellular glycolysis/glyconeogenesis as well as amino acid and butyric acid metabolism. Furthermore, BCAA treatment was found to cause decreased levels of Glut-1 and phosphorylated GSK-3β and mTOR in astrocytes.

CONCLUSIONS

Although further investigations of the effect of BCAA on human astrocytes with hyperammonemia are needed, our work demonstrates that BCAA supplementation has direct negative effects on astrocyte survival and intracellular metabolism.

REVIEW: Practical strategies to maintain anabolism by intravenous nutritional management in children with inborn metabolic diseases

One of the most vital elements of management for patients with inborn errors of intermediary metabolism is the promotion of anabolism, the state in which the body builds new components, and avoidance of catabolism, the state in which the body breaks down its own stores for energy. Anabolism is maintained through the provision of a sufficient supply of substrates for energy, as well as critical building blocks of essential amino acids, essential fatty acids, and vitamins for synthetic function and growth. Patients with metabolic diseases are at risk for decompensation during prolonged fasting, which often occurs during illnesses in which enteral intake is compromised. During these times, intravenous nutrition must be supplied to fully meet the specific nutritional needs of the patient. We detail our approach to intravenous management for metabolic patients and its underlying rationale. This generally entails a combination of intravenous glucose and lipid as well as early introduction of protein and essential vitamins. We exemplify the utility of our approach in case studies, as well as scenarios and specific disorders which require a more careful administration of nutritional substrates or a modification of macronutrient ratios.

Neuroprotective Effects of Carnitine and Its Potential Application to Ameliorate Neurotoxicity

Carnitine is an essential metabolite that is absorbed from the diet and synthesized in the kidney, liver, and brain. It ferries fatty acids across the mitochondrial membrane to undergo β-oxidation. Carnitine has been studied as a therapy or protective agent for many neurological diseases and neurotoxicity (e.g., prolonged anesthetic exposure-induced developmental neurotoxicity in preclinical models). Preclinical and clinical data support the notion that carnitine or acetyl carnitine may improve a patient's quality of life through increased mitochondrial respiration, release of neurotransmitters, and global gene expression changes, showing the potential of carnitine beyond its approved use to treat primary and secondary carnitine deficiency. In this review, we summarize the beneficial effects of carnitine or acetyl carnitine on the central nervous system, highlighting protective effects against neurotoxicity-induced damage caused by various chemicals and encouraging a thorough evaluation of carnitine use as a therapy for patients suffering from neurotoxicant exposure.

Update on pharmacotherapy of hepatic encephalopathy

Hepatic encephalopathy (HE) is a central nervous system disease caused by serious liver diseases or various portal vein systemic circulation abnormalities. The pathogenesis and pathophysiology of HE have not been fully elucidated yet, and among others, the most important is still the theory of ammonia intoxication proposed in the 1930s. Therefore, reducing blood ammonia is currently the main therapeutic strategy for HE, along with improving nervous system function. Thanks to the clarification of the mechanism underlying ammonia-induced brain cell injury in recent years, researchers have proposed some novel therapeutic targets and related drugs. This work will make a brief summary regarding the update of HE drugs with regard to ammonia reduction, nervous system improvement, and intervention of ammonia toxicity targets.

Disturbance of the Glutamate-Glutamine Cycle, Secondary to Hepatic Damage, Compromises Memory Function

Glutamate fulfils many vital functions both at a peripheral level and in the central nervous system (CNS). However, hyperammonemia and hepatic failure induce alterations in glutamatergic neurotransmission, which may be the main cause of hepatic encephalopathy (HE), an imbalance which may explain damage to both learning and memory. Cognitive and motor alterations in hyperammonemia may be caused by a deregulation of the glutamate-glutamine cycle, particularly in astrocytes, due to the blocking of the glutamate excitatory amino-acid transporters 1 and 2 (EAAT1, EAAT2). Excess extracellular glutamate triggers mechanisms involving astrocyte-mediated inflammation, including the release of Ca2+-dependent glutamate from astrocytes, the appearance of excitotoxicity, the formation of reactive oxygen species (ROS), and cell damage. Glutamate re-uptake not only prevents excitotoxicity, but also acts as a vital component in synaptic plasticity and function. The present review outlines the evidence of the relationship between hepatic damage, such as that occurring in HE and hyperammonemia, and changes in glutamine synthetase function, which increase glutamate concentrations in the CNS. These conditions produce dysfunction in neuronal communication. The present review also includes data indicating that hyperammonemia is related to the release of a high level of pro-inflammatory factors, such as interleukin-6, by astrocytes. This neuroinflammatory condition alters the function of the membrane receptors, such as N-methyl-D-aspartate (NMDA), (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) AMPA, and γ-aminobutyric acid (GABA), thus affecting learning and spatial memory. Data indicates that learning and spatial memory, as well as discriminatory or other information acquisition processes in the CNS, are damaged by the appearance of hyperammonemia and, moreover, are associated with a reduction in the production of cyclic guanosine monophosphate (cGMP). Therefore, increased levels of pharmacologically controlled cGMP may be used as a therapeutic tool for improving learning and memory in patients with HE, hyperammonemia, cerebral oedema, or reduced intellectual capacity.

Hydrogen Sulfide Protects Against Ammonia-Induced Neurotoxicity Through Activation of Nrf2/ARE Signaling in Astrocytic Model of Hepatic Encephalopathy

Objective: Hepatic encephalopathy (HE) characterized by neuropsychiatric abnormalities is a major complication of cirrhosis with high mortality. However, the pathogenesis of HE has not been fully elucidated. This study aimed to determine endogenous hydrogen sulfide (H₂S) in the blood of HE patients and investigate the role of H₂S in an astrocytic model of HE.

Methods: Patients with and without HE were recruited to determine plasma H₂S levels and blood microbial 16S rRNA gene. Rat astrocytes were employed as a model of HE by treatment of NH₄Cl. Exogenous H₂S was preadded. Cell viability was measured by Cell Counting Kit-8 (CCK-8) assay, and cell death was evaluated by lactate dehydrogenase (LDH) release. Apoptosis was determined by Hoechst 33342/Propidium Iodide (PI) Double Staining and Western blot analysis of apoptosis-related protein expression. Intracellular reactive oxygen species (ROS) levels were assessed by flow cytometer. Expressions of Nrf2 and its downstream regulated genes were examined by immunofluorescence staining and Western blot, respectively. Nrf2 gene knockdown was performed by antisense shRNA of Nrf2 gene.

Results: There was a significant decrease in H₂S levels in cirrhotic patients with HE compared with without HE. Blood microbiota analyses revealed that certain strains associated with H₂S production were negatively correlated with HE. In vitro, H₂S markedly attenuated NH₄Cl-induced cytotoxicity, oxidative stress, and apoptosis. This effect was mediated by Nrf2/ARE signaling, and knockdown of Nrf2 expression abolished the antagonistic effect of H₂S on NH₄Cl-induced neurotoxicity in astrocytes.

Conclusion: Levels of H₂S and bacteria associated with H₂S production are decreased in HE, and H₂S functions as the neuroprotector against NH₄Cl-induced HE by activating Nrf2/ARE signaling of astrocytes.

l-Carnitine protects against 1,4-benzoquinone-induced apoptosis and DNA damage by suppressing oxidative stress and promoting fatty acid oxidation in K562 cells

Widespread occupational and environmental exposure to benzene is unavoidable and poses a public health threat. Studies of potential interventions to prevent or relieve benzene toxicity are, thus, essential. Research has shown l-carnitine (LC) has beneficial effects against various pathological processes and diseases. LC possesses antioxidant activities and participates in fatty acid oxidation (FAO). In this study, we investigated whether 1,4-benzoquinone (1,4-BQ) affects LC levels and the FAO pathway, as well as analyzed the influence of LC on the cytotoxic effects of 1,4-BQ. We found that 1,4-BQ significantly decreased LC levels and downregulated Cpt1a, Cpt2, Crat, Hadha, Acaa2, and Acadvl mRNA expression in K562 cells. Subsequent assays confirmed that 1,4-BQ decreased cell viability and increased apoptosis and caspase-3, -8, and -9 activities. It also induced obvious oxidative stress and DNA damage, including an increase in the levels of reactive oxygen species and malondialdehyde, tail DNA%, and olive tail moment. Additionally, the mitochondrial membrane potential was significantly reduced. Cotreatment with LC (500 μmol/L) relieved these alterations by reducing oxidative stress and increasing the protein expression levels of Cpt1a and Hadha, particularly in the 20 μmol/L 1,4-BQ group. Thus, our results demonstrate that 1,4-BQ causes cytotoxicity, reduces LC levels, and downregulates the FAO genes. In contrast, LC exhibits protective effects against 1,4-BQ-induced apoptosis and DNA damage by decreasing oxidative stress and promoting the FAO pathway.

1H NMR-Based Metabolic Signatures in the Liver and Brain in a Rat Model of Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a debilitating neuropsychiatric complication associated with acute and chronic liver failure. It is characterized by diverse symptoms with variable severity that includes cognitive and motor deficits. The aim of the study is to assess metabolic alterations in the brain and liver using nuclear magnetic resonance (NMR) spectroscopy and subsequent multivariate analyses to characterize metabolic signatures associated with HE. HE was developed by bile duct ligation (BDL) that resulted in hepatic dysfunctions and cirrhosis as shown by liver function tests. Metabolic profiles from control and BDL rats indicated increased levels of lactate, branched-chain amino acids (BCAAs), glutamate, and choline in the liver, whereas levels of glucose, phenylalanine, and pyridoxine were decreased. In brain, the levels of lactate, acetate, succinate, citrate, and malate were increased, while glucose, creatine, isoleucine, leucine, and proline levels were decreased. Furthermore, neurotransmitters such as glutamate and GABA were increased, whereas choline and myo-inositol were decreased. The alterations in neurotransmitter levels resulted in cognitive and motor defects in BDL rats. A significant correlation was found among alterations in NAA/choline, choline/creatine, and NAA/creatine with behavioral deficits. Thus, the data suggests impairment in metabolic pathways such as the tricarboxylic acid (TCA) cycle, glycolysis, and ketogenesis in the liver and brain of animals with HE. The study highlights that metabolic signatures could be potential markers to monitor HE progression and to assess therapeutic interventions.

Impaired brain function improved by L-carnitine in patients with cirrhosis: evaluation using near-infrared spectroscopy

To evaluate the effects of l-carnitine on impaired brain function in patients with liver cirrhosis. We conducted a retrospective cohort study that included sequential 80 liver cirrhosis patients with impaired brain function evaluated using near-infrared spectroscopy (NIRS). Among them, l-carnitine was administered to 48 patients. The NIRS data and blood ammonia level at baseline and after 8 weeks of treatment were compared between patients administered with l-carnitine (l-carnitine group) and those who were not (control group). The NIRS data at baseline were similar between the l-carnitine and control groups (0.04 ± 0.04 vs. 0.04 ± 0.05 mMmm, p = n.s), whereas those in the l-carnitine group (n = 48) were significantly better than that of the control group at 8 weeks of treatment (n = 32) (0.103 ± 0.081 vs. 0.040 ± 0.048 mMmm, p < 0.001). In the l-carnitine group, 35.4% (17/48) of patients had hyperammonemia. The NIRS data of the l-carnitine group at 8 weeks of treatment were significantly improved than that of the control group, irrespective of baseline ammonia levels (0.11 ± 0.09 vs. 0.04 ± 0.05 mMmm, p = 0.005, and 0.10 ± 0.06 vs. 0.02 ± 0.03 mMmm, p = 0.003, for normal baseline ammonia and elevated ammonia levels, respectively). In the multivariate analysis, l-carnitine administration (odds ratio [OR] 3.51, 95% confidence interval [CI] 1.23–9.99, p = 0.019) and baseline NIRS data of ≤ 0.07 mMmm (OR 5.21, 95% CI 1.69–16.0, p = 0.0041) were found as independent significant factors. l-carnitine improves impaired brain function in patients with liver cirrhosis.

Astrocyte swelling in hepatic encephalopathy: molecular perspective of cytotoxic edema

Hepatic encephalopathy (HE) may occur in patients with liver failure. The most critical pathophysiologic mechanism of HE is cerebral edema following systemic hyperammonemia. The dysfunctional liver cannot eliminate circulatory ammonia, so its plasma and brain levels rise sharply. Astrocytes, the only cells that are responsible for ammonia detoxification in the brain, are dynamic cells with unique phenotypic properties that enable them to respond to small changes in their environment. Any pathological changes in astrocytes may cause neurological disturbances such as HE. Astrocyte swelling is the leading cause of cerebral edema, which may cause brain herniation and death by increasing intracranial pressure. Various factors may have a role in astrocyte swelling. However, the exact molecular mechanism of astrocyte swelling is not fully understood. This article discusses the possible mechanisms of astrocyte swelling which related to hyperammonia, including the possible roles of molecules like glutamine, lactate, aquaporin-4 water channel, 18 KDa translocator protein, glial fibrillary acidic protein, alanine, glutathione, toll-like receptor 4, epidermal growth factor receptor, glutamate, and manganese, as well as inflammation, oxidative stress, mitochondrial permeability transition, ATP depletion, and astrocyte senescence. All these agents and factors may be targeted in therapeutic approaches to HE.