Glutamine: a Trojan horse in ammonia neurotoxicity

Different cortical and subcortical astroglial responsiveness in rats with acute liver failure

Hepatic encephalopathy (HE) is a neuropsychiatric complication of liver failure. Previous studies described astroglia alterations in HE, but regional changes have not been well investigated. This study addresses regional astroglial response by exploring glial fibrillary acidic protein (GFAP) immunoreactivity in cortical structures including somatosensory (S1Tr and S1BF), piriform (Pir), and perirhinal (PRh) cortices, and subcortical regions including corpus callosum (CC), ventromedial thalamus (VMT), mammillothalamic tract (MTT), and dorsomedial hypothalamic nucleus (DHN) in rats with acute liver failure (ALF) sacrificed at coma stage. Our data showed decreased numbers of astrocytes in S1Tr, Pir, and CC in ALF rats. GFAP-immunoreactive cells were increased within other regions including PRh, VMT, MTT, and DHN. Cell morphometric analysis showed significant increase in GFAP-immunoreactive astrocyte processes and cell bodies in cortical and subcortical regions but not in CC and DHN. However, astrocyte perimeters were increased, particularly in S1Tr and VMT. Our study demonstrates regional specificity including (1) regions with astrocyte activation associated with an increase of GFAP-immunostaining and astrocyte cell counts, together with (2) unaltered GFAP components, and (3) regions characterized by presumably inactive astrocyte with a reduced GFAP-immunostaining. These findings may reflect either different regional alterations in HE, or stages of an alteration progressing differently in different regions.

The Glutamate/GABA-Glutamine Cycle: Insights, Updates, and Advances

Synaptic homeostasis of the principal neurotransmitters glutamate and GABA is tightly regulated by an intricate metabolic coupling between neurons and astrocytes known as the glutamate/GABA-glutamine cycle. In this cycle, astrocytes take up glutamate and GABA from the synapse and convert these neurotransmitters into glutamine. Astrocytic glutamine is subsequently transferred to neurons, serving as the principal precursor for neuronal glutamate and GABA synthesis. The glutamate/GABA-glutamine cycle integrates multiple cellular processes, including neurotransmitter release, uptake, synthesis, and metabolism. All of these processes are deeply interdependent and closely coupled to cellular energy metabolism. Astrocytes display highly active mitochondrial oxidative metabolism and several unique metabolic features, including glycogen storage and pyruvate carboxylation, which are essential to sustain continuous glutamine release. However, new roles of oligodendrocytes and microglia in neurotransmitter recycling are emerging. Malfunction of the glutamate/GABA-glutamine cycle can lead to severe synaptic disruptions and may be implicated in several brain diseases. Here, I review central aspects and recent advances of the glutamate/GABA-glutamine cycle to highlight how the cycle is functionally connected to critical brain functions and metabolism. First, an overview of glutamate, GABA, and glutamine transport is provided in relation to neurotransmitter recycling. Then, central metabolic aspects of the glutamate/GABA-glutamine cycle are reviewed, with a special emphasis on the critical metabolic roles of glial cells. Finally, I discuss how aberrant neurotransmitter recycling is linked to neurodegeneration and disease, focusing on astrocyte metabolic dysfunction and brain lipid homeostasis as emerging pathological mechanisms. Instead of viewing the glutamate/GABA-glutamine cycle as individual biochemical processes, a more holistic and integrative approach is needed to advance our understanding of how neurotransmitter recycling modulates brain function in both health and disease.

Oral Administration of L-Arginine Improves the Growth and Survival of Sow-Reared Intrauterine Growth-Restricted Piglets

Neonatal piglets with intrauterine growth restriction (IUGR) exhibit reduced rates of growth and survival. The present study tested the hypothesis that L-arginine supplementation can mitigate this problem. One hundred and twelve (112) IUGR piglets (with a mean birth weight of 0.84 kg) from 28 sows (four IUGR piglets/sow) were assigned randomly into one of four groups. Piglets were nursed by sows and orally administered 0, 0.1, 0.2, or 0.4 g L-arginine (in the form of L-arginine-HCl) per kg body weight (BW) twice daily between 0 and 14 days of age. The total doses of L-arginine were 0, 0.2, 0.4, or 0.8 g/kg BW/day. Appropriate amounts of L-alanine were added to L-arginine solutions so that all groups of piglets received the same amount of nitrogen. Piglets were weighed on days 0, 7, and 14 of age. On day 14, blood samples (5 mL) were obtained from the jugular vein of piglets at 1 h after suckling, and their milk consumption was measured over a 10-h period using the weigh-suckle-weigh technique. Milk intake did not differ (p > 0.05) among the four groups of piglets. Oral administration of 0.4 g L-arginine/kg BW/day increased (p < 0.05) the circulating levels of arginine, creatine, and anabolic hormones (insulin, growth hormone, and insulin-like growth factor-I), but decreased (p < 0.05) plasma concentrations of ammonia and cortisol (a catabolic hormone). Compared to the control group, IUGR piglets administered 0.2 and 0.4 g L-arginine/kg BW/day increased (p < 0.05) weight gain by 19% and 31%, respectively. Growth did not differ (p > 0.05) between the control and 0.8 g L-arginine/kg BW/day groups. The survival rates of IUGR piglets were 50%, 75%, 89%, and 89%, respectively, for the 0, 0.2, 0.4, and 0.8 g L-arginine/kg BW/day groups. Collectively, these results indicate that the growth and survival of IUGR piglets can be improved through L-arginine supplementation.

Neuroglia in hepatic encephalopathy

Neuroglia contribute to the pathophysiology of hepatic encephalopathy (HE) either beneficially or detrimentally. Pathogenesis of HE is linked to damage triggered by blood-derived toxins, with ammonia being the main causative factor. Neuroglial cells, especially astrocytes and microglia, respond to HE-associated systemic and central signals and undergo complex and variable changes in their metabolism, morphology, and function, which include ion and water dyshomeostasis in conjunction with neurotransmission imbalance and neuroinflammation. HE-induced alterations of astrocytes are defined as astrocytopathy, with aberrant astrocytes resulting in either gain or loss of functions. In the chronic HE, the presence of Alzheimer type II cells is a histologic hallmark, with asthenic astrocytes emerging as a newcomer. In acute HE, rapid swelling of astrocytes is a primary cause of cerebral edema and mortality. This chapter reviews the dominant role of astrocytes in the pathogenesis of HE resulting from acute and chronic liver failure, mainly in experimental models. The focus is on the loss of homeostatic function bearing upon the functioning of the glymphatic system, aberrant neurotransmission as a consequence of astrocyte-neuron miscommunication, and the concordant neuroinflammatory response of astrocytes and microglia. The chapter concludes with a delineation of concepts for future research.

The Balance of Ketoacids α-Ketoglutarate and α-Ketoglutaramate Reflects the Degree of the Development of Hepatoencephalopathy in Rats

Hepatoencephalopathy (HE) is a liver disease that can lead to brain pathology and the impairment of human cognitive abilities. The objective assessment of HE disease severity is difficult due to the lack of reliable diagnostic markers. This paper examines the background to the emergence of HE markers and provides a brief overview of research results indicating the diagnostic value of potential markers isolated from a wide range of metabolites analyzed. It has been suggested that metabolites of the glutamate-glutamine (Glu-Gln) cycle, α-ketoglutarate (αKG), and α-ketoglutaramate (αKGM) can act as such markers of HE. The informative value of these markers was revealed during a comparative analysis of the distribution of αKG and αKGM in samples of the blood plasma and tissues (liver, kidneys, and brain) of rats exposed to the strong hepatotoxin thioacetamide (TAA). A comparative analysis of the balance of αKG and αKGM, as well as their ratio (αKG/αKGM) in the examined samples of blood plasma and animal tissues in these models, revealed their diagnostic value for assessing the severity of HE and/or monitoring the recovery process.

Modulation of brain energy metabolism in hepatic encephalopathy: impact of glucose metabolic dysfunction

Cerebral function is linked to a high level of metabolic activity and relies on glucose as its primary energy source. Glucose aids in the maintenance of physiological brain activities; as a result, a disruption in metabolism has a significant impact on brain function, launching a chain of events that leads to neuronal death. This metabolic insufficiency has been observed in a variety of brain diseases and neuroexcitotoxicity disorders, including hepatic encephalopathy. It is a significant neurological complication that develops in people with liver disease, ranging from asymptomatic abnormalities to coma. Hyperammonemia is the main neurotoxic villain in the development of hepatic encephalopathy and induces a wide range of complications in the brain. The neurotoxic effects of ammonia on brain function are thought to be mediated by impaired glucose metabolism. Accordingly, in this review, we provide an understanding of deranged brain energy metabolism, emphasizing the role of glucose metabolic dysfunction in the pathogenesis of hepatic encephalopathy. We also highlighted the differential metabolic profiles of brain cells and the status of metabolic cooperation between them. The major metabolic pathways that have been explored are glycolysis, glycogen metabolism, lactate metabolism, the pentose phosphate pathway, and the Krebs cycle. Furthermore, the lack of efficacy in current hepatic encephalopathy treatment methods highlights the need to investigate potential therapeutic targets for hepatic encephalopathy, with regulating deficient bioenergetics being a viable alternative in this case. This review also demonstrates the importance of the development of glucose metabolism-focused disease diagnostics and treatments, which are now being pursued for many ailments.

Paediatric acute liver failure: a multidisciplinary perspective on when a critically ill child is unsuitable for liver transplantation

Paediatric acute liver failure is a devastating condition with high morbidity and mortality, which is challenging to manage for the hepatologist, intensivist, and associated specialists. Emergency liver transplantation is required for 10-20% of patients, but for 10% of critically ill children, liver transplantation is deemed unsuitable; the child might be too unwell, or the underlying cause might carry a poor prognosis. Other social, logistical, or ethical considerations are often relevant. Liver transplantation when a patient is too unwell creates perioperative risk to the child that could lead to morbidity, mortality, and potential graft wastage, which is detrimental for others on the waiting list. Donor liver scarcity should prompt an evaluation of whether a transplant is justified through a holistic multidisciplinary lens that considers medical, social, logistical, and ethical concerns. In this Review, we explore, from a multidisciplinary perspective, why a critically unwell child with paediatric acute liver failure might be unsuitable for liver transplantation.

Hepatic encephalopathy as a result of ammonia-induced increase in GABAergic tone with secondary reduced brain energy metabolism

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome caused by liver insufficiency and/or portosystemic shunting. HE is mostly episodic and as such reversible. Hyperammonemia clearly plays a key role in the pathophysiology, but the precise detrimental events in the brain leading to HE remain equivocal. Several pathogenic models have been proposed, but few have been linked to clinical studies and observations. Decreased oxygen metabolism is observed in both type A and C HE and in this review, we advocate that this reflects an actual reduced oxygen demand and not a primary cause of HE. As driving force, we propose that the hyperammonemia via astrocytic glutamine synthetase causes an increased γ-aminobutyric acid (GABA) mediated neuro-inhibition which subsequently leads to an overall decreased energy demand of the brain, something that can be enhanced by concomitant neuroinflammation. This also explains the reversibility of the condition.

Quo vadis ureagenesis disorders? A journey from 90 years ago into the future

The pathway of ammonia disposal in the mammalian organism has been described in 1932 as a metabolic cycle present in the liver in different compartments. In 1958, the first human disorder affecting this pathway was described as a genetic condition leading to cognitive impairment and constant abnormalities of amino acid metabolism. Since then, defects in all enzymes and transporters of the urea cycle have been described, referring to them as primary urea cycle disorders causing primary hyperammonemia. In addition, there is a still increasing list of conditions that impact on the function of the urea cycle by various mechanisms, hereby leading to secondary hyperammonemia. Despite great advances in understanding the molecular background and the biochemical specificities of both primary and secondary hyperammonemias, there remain many open questions: we do not fully understand the pathophysiology in many of the conditions; we do not always understand the highly variable clinical course of affected patients; we clearly appreciate the need for novel and improved diagnostic and therapeutic approaches. This study does look back to the beginning of the urea cycle (hi)story, briefly describes the journey through past decades, hereby illustrating advancements and knowledge gaps, and gives examples for the extremely broad perspective imminent to some of the defects of ureagenesis and allied conditions.

Ecological risks of high-ammonia environment with inhibited growth of Daphnia magna: Disturbed energy metabolism and oxidative stress

High ammonia pollution is a common problem in water bodies. However, research on the mechanisms underlying the toxic effects on organisms at different nutritional levels is still insufficient. Herein, based on the environmental concentration, the toxic effects of high ammonia pollution on Daphnia magna were investigated. Overall, the feeding and filtration rates of D. magna were significantly decreased by ammonia. Growth inhibition of D. magna by ammonia was confirmed by the decreased body length. After ammonia exposure, the metabolic status of D. magna changed, the correlation network weakened, and the correlations between metabolites were disrupted. Changes occurred in metabolites primarily involved in oxidative stress, fatty acid oxidation, tricarboxylic acid cycle, and protein digestion, absorption, and synthesis, which were validated through alterations in multiple biomarkers. In addition, mitochondrial function was evaluated and was found to inhibit mitochondrial activity, which was accompanied by a decreased marker of mitochondrial activity contents and ATPase activity. Thus, the results suggested that energy metabolism and oxidative stress were involved in ammonia-induced growth toxicity. This study provides new insights into the impact of ammonia on aquatic ecological health.

Bibliometrics and knowledge mapping of the pathogenesis of hepatic encephalopathy in patients with liver cirrhosis

Background

Hepatic encephalopathy is a common and serious complication of decompensated cirrhosis. It can considerably contribute to economic burden and impaired quality of life. However, its pathogenesis remains unclear.

Method

In this study, we aimed to visually analyse the research status and development trends in hepatic encephalopathy pathogenesis using bibliometrics and knowledge mapping. Information regarding publications between 1978 and 2022 were obtained from the Web of Science Core Collection. CiteSpace was used to analyse and present data by year, author, institution, country, journal, reference, and keyword.

Results

A total of 1578 publications on hepatic encephalopathy pathogenesis in patients with cirrhosis were retrieved from Web of Science Core Collection. A gradual increasing trend in annual publications has occurred. The collaborative network analysis results suggest the United States of America, the University of London, and Bajaj, Jasmohan S as the most influential country, institution, and author, respectively, in this research field. Notably, China appeariiuis to be the most promising country. Research on 'hepatology' garners the most significant papers in the field. Combined with reference co-citation and keyword co-occurrence analyses, we found that ammonia metabolism, gut microbiota, sarcopenia, and trace elements will become future research frontiers that are likely to be explored for a considerable length of time.

Conclusion

Future research directions in HE pathogenesis may target modulating the ammonia metabolism, the gut microbiota, sarcopenia, and trace elements.

Nutritional management for acute liver failure

Acute liver failure (ALF) induces increased energy expenditure and disrupts the metabolism of essential nutrients. Hepatic encephalopathy is a complication of ALF with a poor prognosis and mainly involves the metabolic disturbance of amino acids in its pathogenesis. In this review, we discuss the nutritional management for ALF in consideration of the pathophysiology of ALF with respect to the impairment of hepatocyte function. It is known that enteral nutrition is recommended for patients with ALF, while parenteral nutrition is recommended for patients who cannot tolerate enteral nutrition. As ALF leads to a hypermetabolic state, the energy intake is recommended to cover 1.3 times the resting energy expenditure. Because of the high risk of hypoglycemia associated with disturbances in glucose metabolism, substantial glucose intake is recommended. Along with the deterioration of glucose metabolism, protein metabolism is also disrupted. As patients with ALF have increased systemic protein catabolism together with decreased protein synthesis, appropriate amounts of amino acids or protein under monitoring serum ammonia levels are recommended. In conclusion, nutritional management based on the understanding of nutritional pathophysiology is a pivotal therapeutic approach for patients with ALF. The approach should be individualized in the acute phase, the recovery phase, and the pretransplant phase.

Feasibility exploration of GSH in the treatment of acute hepatic encephalopathy from the aspects of pharmacokinetics, pharmacodynamics, and mechanism

Our previous study highlighted the therapeutic potential of glutathione (GSH), an intracellular thiol tripeptide ubiquitous in mammalian tissues, in mitigating hepatic and cerebral damage. Building on this premise, we posited the hypothesis that GSH could be a promising candidate for treating acute hepatic encephalopathy (AHE). To verify this conjecture, we systematically investigated the feasibility of GSH as a therapeutic agent for AHE through comprehensive pharmacokinetic, pharmacodynamic, and mechanistic studies using a thioacetamide-induced AHE rat model. Our pharmacodynamic data demonstrated that oral GSH could significantly improve behavioral scores and reduce hepatic damage of AHE rats by regulating intrahepatic ALT, AST, inflammatory factors, and homeostasis of amino acids. Additionally, oral GSH demonstrated neuroprotective effects by alleviating the accumulation of intracerebral glutamine, down-regulating glutamine synthetase, and reducing taurine exposure. Pharmacokinetic studies suggested that AHE modeling led to significant decrease in hepatic and cerebral exposure of GSH and cysteine. However, oral GSH greatly enhanced the intrahepatic and intracortical GSH and CYS in AHE rats. Given the pivotal roles of CYS and GSH in maintaining redox homeostasis, we investigated the interplay between oxidative stress and pathogenesis/treatment of AHE. Our data revealed that GSH administration significantly relieved oxidative stress levels caused by AHE modeling via down-regulating the expression of NADPH oxidase 4 (NOX4) and NF-κB P65. Importantly, our findings further suggested that GSH administration significantly regulated the excessive endoplasmic reticulum (ER) stress caused by AHE modeling through the iNOS/ATF4/Ddit3 pathway. In summary, our study uncovered that exogenous GSH could stabilize intracerebral GSH and CYS levels to act on brain oxidative and ER stress, which have great significance for revealing the therapeutic effect of GSH on AHE and promoting its further development and clinical application.

Mitochondrial Changes in Rat Brain Endothelial Cells Associated with Hepatic Encephalopathy: Relation to the Blood-Brain Barrier Dysfunction

The mechanisms underlying cerebral vascular dysfunction and edema during hepatic encephalopathy (HE) are unclear. Blood-brain barrier (BBB) impairment, resulting from increased vascular permeability, has been reported in acute and chronic HE. Mitochondrial dysfunction is a well-documented result of HE mainly affecting astrocytes, but much less so in the BBB-forming endothelial cells. Here we review literature reports and own experimental data obtained in HE models emphasizing alterations in mitochondrial dynamics and function as a possible contributor to the status of brain endothelial cell mitochondria in HE. Own studies on the expression of the mitochondrial fusion-fission controlling genes rendered HE animal model-dependent effects: increase of mitochondrial fusion controlling genes opa1, mfn1 in cerebral vessels in ammonium acetate-induced hyperammonemia, but a decrease of the two former genes and increase of fis1 in vessels in thioacetamide-induced HE. In endothelial cell line (RBE4) after 24 h ammonia and/or TNFα treatment, conditions mimicking crucial aspects of HE in vivo, we observed altered expression of mitochondrial fission/fusion genes: a decrease of opa1, mfn1, and, increase of the fission related fis1 gene. The effect in vitro was paralleled by the generation of reactive oxygen species, decreased total antioxidant capacity, decreased mitochondrial membrane potential, as well as increased permeability of RBE4 cell monolayer to fluorescein isothiocyanate dextran. Electron microscopy documented enlarged mitochondria in the brain endothelial cells of rats in both in vivo models. Collectively, the here observed alterations of cerebral endothelial mitochondria are indicative of their fission, and decreased potential of endothelial mitochondria are likely to contribute to BBB dysfunction in HE.

The role of glutamate and glutamine metabolism and related transporters in nerve cells

BACKGROUND

Glutamate and glutamine are the most abundant amino acids in the blood and play a crucial role in cell survival in the nervous system. Various transporters found in cell and mitochondrial membranes, such as the solute carriers (SLCs) superfamily, are responsible for maintaining the balance of glutamate and glutamine in the synaptic cleft and within cells. This balance affects the metabolism of glutamate and glutamine as non-essential amino acids.

AIMS

This review aims to provide an overview of the transporters and enzymes associated with glutamate and glutamine in neuronal cells.

DISCUSSION

We delve into the function of glutamate and glutamine in the nervous system by discussing the transporters involved in the glutamate-glutamine cycle and the key enzymes responsible for their mutual conversion. Additionally, we highlight the role of glutamate and glutamine as carbon and nitrogen donors, as well as their significance as precursors for the synthesis of reduced glutathione (GSH).

CONCLUSION

Glutamate and glutamine play a crucial role in the brain due to their special effects. It is essential to focus on understanding glutamate and glutamine metabolism to comprehend the physiological behavior of nerve cells and to treat nervous system disorders and cancer.

Dietary manganese nano-particles improves gene regulation and biochemical attributes for mitigation of lead and ammonia toxicity in fish

In the present study, we explored the capability of manganese nanoparticles (Mn-NPs) to alleviate the toxicity induced by lead (Pb) and ammonia (NH3) toxicity in Oreochromis niloticus (GIFT strain). The experiment followed a completely randomized design, including a control group (Mn-NPs-0 mg kg-1 diet) and groups exposed to Pb and NH3 alongwith Mn-NPs at 2 and 3 mg kg-1. Cortisol levels were significantly elevated in Pb + NH3 group whereas reduced by Mn-NPs diets. Gene expressions of HSP 70, iNOS, CYP 450, and Cas 3a were notably upregulated by Pb + NH3 group and downregulated by Mn-NPs diets. The cellular metabolic enzymes were affected by Pb + NH3 exposure and mitigated by Mn-NPs diets. The liver and kidney exhibited reduced activities of catalase, superoxide dismutase, and glutathione-s-transferase with Mn-NPs diets. Concurrently, immune-related genes such as total immunoglobulin (Ig) and tumor necrosis factor (TNFα) were upregulated in the Mn-NPs-fed groups. Growth performance indicators, including weight gain %, feed conversion ratio, specific growth rate, protein efficiency ratio, and relative feed intake were adversely affected by Pb + NH3 stress but improvement with Mn-NPs diets. Genes associated with growth performance, such as growth hormone (GH), growth hormone regulatory (GHR1), and myostatin, exhibited enhancements in response to Mn-NPs diets. Digestive enzymes, including protease and amylase were also enhanced by Mn-NPs diets. Additionally, Mn-NPs diets led to a reduction in the bioaccumulation of lead. This study aims to investigate the role of Mn-NPs in mitigating the effects of lead and ammonia toxicity on fish by examining various biochemical and gene regulatory factors to enhance fish wellbeing.

A glimpse into multimodal neuromonitoring in acute liver failure: a case report

Introduction

Acute liver failure (ALF) is a rapidly progressing, life-threatening syndrome characterized by liver-related coagulopathy and hepatic encephalopathy (HE). Given that higher HE grades correlate with poorer outcomes, clinical management of ALF necessitates close neurological monitoring. The primary objective of this case report is to highlight the diagnostic value of utilizing multimodal neuromonitoring (MNM) in a patient suffering from ALF.

Case report

A 56-year-old male patient with a history of chronic alcoholism, without prior chronic liver disease, and recent acetaminophen use was admitted to the hospital due to fatigue and presenting with a mild flapping tremor. The primary hypothesis was an acute hepatic injury caused by acetaminophen intoxication. In the following hours, the patient's condition deteriorated, accompanied by neurological decline and rising ammonia levels. The patient's neurological status was closely monitored using MNM. Bilaterally altered pupillary light reflex assessed by decreasing in the Neurological Pupil Index values, using automated pupillometry, initially suggested severe brain oedema. However, ultrasound measurements of the optic nerve sheath diameter showed normal values in both eyes, P2/P1 noninvasive intracranial pressure waveform assessment was within normal ranges and the cerebral computed tomography-scan revealed no signs of cerebral swelling. Increased middle cerebral artery velocities measured by Transcranial Doppler and the initiation of electroencephalography monitoring yielded the presence of status epilepticus.

Discussion

The utilization of MNM facilitated a more comprehensive understanding of the mechanisms underlying the patient's clinical deterioration in the setting of HE. Nonetheless, future studies are needed to show feasibility and to yield valuable insights that can enhance the outcomes for patients with HE using such an approach. Given the absence of specific guidelines in this particular context, it is advisable for physicians to give further consideration to the incorporation of MNM in the management of unconscious patients with ALF.

Supraphysiological glutamine as a means of depleting intracellular amino acids to enhance pancreatic cancer chemosensitivity

Limited efficacy of systemic therapy for pancreatic ductal adenocarcinoma (PDAC) patients contributes to high mortality. Cancer cells develop strategies to secure nutrients in nutrient-deprived conditions and chemotherapy treatment. Despite the dependency of PDAC on glutamine (Gln) for growth and survival, strategies designed to suppress Gln metabolism have limited effects. Here, we demonstrated that supraphysiological concentrations of glutamine (SPG) could produce paradoxical responses leading to tumor growth inhibition alone and in combination with chemotherapy. Integrated metabolic and transcriptomic analysis revealed that the growth inhibitory effect of SPG was the result of a decrease in intracellular amino acid and nucleotide pools. Mechanistically, disruption of the sodium gradient, plasma membrane depolarization, and competitive inhibition of amino acid transport mediated amino acid deprivation. Among standard chemotherapies given to PDAC patients, gemcitabine treatment resulted in a significant enrichment of amino acid and nucleoside pools, exposing a metabolic vulnerability to SPG-induced metabolic alterations. Further analysis highlighted a superior anticancer effect of D-glutamine, a non-metabolizable enantiomer of the L-glutamine, by suppressing both amino acid uptake and glutaminolysis, in gemcitabine-treated preclinical models with no apparent toxicity. Our study suggests supraphysiological glutamine could be a means of inhibiting amino acid uptake and nucleotide biosynthesis, potentiating gemcitabine sensitivity in PDAC.

Low-dose ketamine improves animals' locomotor activity and decreases brain oxidative stress and inflammation in ammonia-induced neurotoxicity

Ammonium ion (NH4 + ) is the major suspected molecule responsible for neurological complications of hepatic encephalopathy (HE). No specific pharmacological action for NH4 + -induced brain injury exists so far. Excitotoxicity is a well-known phenomenon in the brain of hyperammonemic cases. The hyperactivation of the N-Methyl- d-aspartate (NMDA) receptors by agents such as glutamate, an NH4 + metabolite, could cause excitotoxicity. Excitotoxicity is connected with events such as oxidative stress and neuroinflammation. Hence, utilizing NMDA receptor antagonists could prevent neurological complications of NH4 + neurotoxicity. In the current study, C57BL6/J mice received acetaminophen (APAP; 800 mg/kg, i.p) to induce HE. Hyperammonemic animals were treated with ketamine (0.25, 0.5, and 1 mg/kg, s.c) as an NMDA receptor antagonist. Animals' brain and plasma levels of NH4 + were dramatically high, and animals' locomotor activities were disturbed. Moreover, several markers of oxidative stress were significantly increased in the brain. A significant increase in brain tissue levels of TNF-α, IL-6, and IL-1β was also detected in hyperammonemic animals. It was found that ketamine significantly normalized animals' locomotor activity, improved biomarkers of oxidative stress, and decreased proinflammatory cytokines. The effects of ketamine on oxidative stress biomarkers and inflammation seem to play a key role in its neuroprotective mechanisms in the current study.

A review of the toxic effects of ammonia on invertebrates in aquatic environments

Aquatic invertebrates are the organisms most susceptible to ammonia toxicity. However, the toxic effects of ammonia on invertebrates are still poorly understood. This study reviews the research progress in ammonia toxicology for the period from 1986 to 2023, focusing on the effects on invertebrates. Through examining the toxic effects of ammonia at different levels of organization (community, individual, tissue and physiology, and molecular) as well as the results from omics studies, we determined that the most significant effects were on the reproductive capacity of invertebrates and the growth of offspring, although different populations show variation in their tolerance to ammonia, and tissues have varied potential to respond to ammonia stress. A multicomponent analysis is an in-depth technique employed in toxicological studies, as it can be used to explore the enrichment pathways and functional genes expressed under ammonia stress. This study comprehensively discusses ammonia toxicity from multiple aspects in order to provide new insights into the toxic effects of ammonia on aquatic invertebrates.

Intravenous BCAA Infusion Does Not Lead to a Sustained Recovery From Overt HE in ACLF - An Open Label Randomized Clinical Trial

Background

Hepatic encephalopathy (HE) in acute-on-chronic liver failure (ACLF) is associated with significant morbidity and mortality. We conducted a prospective, randomized controlled clinical trial to study the efficacy of intravenous branched chain amino acids (IV-BCAA) with lactulose versus lactulose alone for improvement in HE at 24 h, day 3, and day 7. The primary outcome was an improvement in encephalopathy by ≥ 1 grade at 72 h.

Patients and methods

European association for study of liver (EASL) defined ACLF patients with overt HE were assessed and randomized into the experimental arm (IV-BCAA - 500 mL/day for 3 days + Lactulose; n = 39) and the comparator arm (Lactulose alone; n = 37). Six patients developed COVID-19 after randomization and were excluded (4-experimental arm and 2-comparator arm).

Results

Of 222 screened patients, 70 (35 in each arm) were included in the analysis. Baseline characteristics, including HE grade (2.9 ± 0.7 vs 2.8 ± 0.7; P = 0.86) and (chronic liver failure) CLIF-C ACLF score (54.2 ± 5.6 vs 54.8 ± 5.7; P = 0.65), were similar. Overall survival was 40% at 28 days (48.5% vs 31.4%; P = 0.14). Improvement in hepatic encephalopathy scoring algorithm (HESA) by ≥ 1 grade at 24 h occurred in 14 patients (40%) in the BCAA arm and 6 patients (17.1%) in the control group (P = 0.03) which translated to a shorter intensive care unit (ICU) stay. The median change in HESA at 24 h was greater in the BCAA arm than the control arm (P = 0.006), which was not sustained at days 3 or 7. Ammonia levels did not correlate with the grade of HE (Spearman's correlation coefficient (ρ) = - 0.0843; P = 0.29).

Conclusion

Intravenous BCAA does not lead to a sustained improvement in HE grade in ACLF.

Trial registration no

NCT04238416 (clinicaltrials.gov).

Astrocytes in human central nervous system diseases: a frontier for new therapies

Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.

Nanotoxicity of multifunctional stoichiometric cobalt oxide nanoparticles (SCoONPs) with repercussions toward apoptosis, necrosis, and cancer necrosis factor (TNF-α) at nano-biointerfaces

Introduction

Apoptosis, necrosis, and cancer necrosis factor (TNF-a) are all impacted by the nanotoxicity of multifunctional stoichiometric cobalt oxide nanoparticles (SCoONPs) at nano-biointerfaces. The creation of multi-functional nanoparticles has had a considerable impact on the transport of drugs and genes, nanotheranostics (in-vivo imaging, concurrent diagnostics), interventions for external healing, the creation of nano-bio interfaces, and the instigation of desired changes in nanotherapeutics.

Objectives

The quantitative structure-activity relationships, chemical transformations, biological interactions as well as toxicological analyses are considered as main objectives. Discrete dimensions of SCoNPs-cell interaction interfaces, their characteristic physical features (size, shape, shell structure, and surface chemistry), impact on cell proliferation and differentiation are the key factors responsible for nanotoxicity.

Methods

The development of multi-functional nanoparticles has been significant in drug/gene delivery, nanotheranostics (in-vivo imaging, coinciding diagnostics), and external healing interventions, designing a nano-bio interface, as well as inciting desired alterations in nanotherapeutics. Every so often, the cellular uptake of multi-functional cobalt [Co, CoO, Co2(CO)8 and Co3O4] nanoparticles (SCoONPs) influences cellular mechanics and initiates numerous repercussions (oxidative stress, DNA damage, cytogenotoxicity, and chromosomal damage) in pathways, including the generation of dysregulating factors involved in biochemical transformations.

Results

The concerns and influences of multifunctional SCoNPs on different cell mechanisms (mitochondria impermeability, hydrolysis of ATP, the concentration of Ca2+, impaired calcium clearance, defective autophagy, apoptosis, and necrosis), and interlinked properties (adhesion, motility, and internalization dynamics, role in toxicity, surface hydrophilic and hydrophobicity, biokinetics and biomimetic behaviors of biochemical reactions) have also been summarized. SCoONPs have received a lot of interest among the nanocarriers family because of its advantageous qualities such as biodegradability, biocompatibility, nontoxicity, and nonimmunogenicity.

Conclusion

Various applications, such as bio-imaging, cell labeling, gene delivery, enhanced chemical stability, and increased biocompatibility, concerning apoptosis, necrosis, and nano-bio interfaces, along with suitable examples. In this analysis, the multi-functional cobalt [Co, CoO, Co2(CO)8 and Co3O4] nanoparticles (SCoNPs) intricacies (cytogenotoxicity, clastogenicity, and immunomodulatory), nanotoxicity, and associated repercussions have been highlighted and explained.

Immunonutrition: facilitating mucosal immune response in teleost intestine with amino acids through oxidant-antioxidant balance

Comparative animal models generate fundamental scientific knowledge of immune responses. However, these studies typically are conducted in mammals because of their biochemical and physiological similarity to humans. Presently, there has been an interest in using teleost fish models to study intestinal immunology, particularly intestinal mucosa immune response. Instead of targeting the pathogen itself, a preferred approach for managing fish health is through nutrient supplementation, as it is noninvasive and less labor intensive than vaccine administrations while still modulating immune properties. Amino acids (AAs) regulate metabolic processes, oxidant-antioxidant balance, and physiological requirements to improve immune response. Thus, nutritionists can develop sustainable aquafeeds through AA supplementation to promote specific immune responses, including the intestinal mucosa immune system. We propose the use of dietary supplementation with functional AAs to improve immune response by discussing teleost fish immunology within the intestine and explore how oxidative burst is used as an immune defense mechanism. We evaluate immune components and immune responses in the intestine that use oxidant-antioxidant balance through potential selection of AAs and their metabolites to improve mucosal immune capacity and gut integrity. AAs are effective modulators of teleost gut immunity through oxidant-antioxidant balance. To incorporate nutrition as an immunoregulatory means in teleost, we must obtain more tools including genomic, proteomic, nutrition, immunology, and macrobiotic and metabonomic analyses, so that future studies can provide a more holistic understanding of the mucosal immune system in fish.

Intracranial pressure monitoring in the perioperative period of patients with acute liver failure undergoing orthotopic liver transplantation

Acute liver failure (ALF) may result in severe neurological complications caused by cerebral edema and elevated intracranial pressure (ICP). Multiple pathogenic mechanisms explain the elevated ICP, and newer hypotheses have been descri bed. While invasive ICP monitoring (ICPM) may have a role in ALF management, these patients are typically coagulopathic and at risk for intracranial hemorrhage. ICPM is the subject of much debate, and significant heterogeneity exists in clinical practice regarding its use. Contemporary ICPM techniques and coagulopathy reversal strategies may be associated with a lower risk of hemor rhage; however, most of the evidence is limited by its retrospective nature and relatively small sample size.

Hemocytes in blue mussel Mytilus edulis adopt different energy supply modes to cope with different BDE-47 exposures

The energetic response of blue mussel Mytilus edulis when coping with tetrabromodiphenyl ether (BDE-47) exposure was evaluated from the perspective of alterations in energy supply mode, and the possible regulating mechanism was discussed based on a 21-day bioassay. The results showed that the energy supply mode changed with concentration: 0.1 μg/L BDE-47 decreased the activity of isocitrate dehydrogenase (IDH), succinate dehydrogenase (SDH), malate dehydrogenase and oxidative phosphorylation, suggesting inhibition of the tricarboxylic (TCA) acid cycle and aerobic respiration. The coincident increase in phosphofructokinase and the decrease in lactate dehydrogenase (LDH) indicated that glycolysis and anaerobic respiration were increased. When exposed to 1.0 μg/L BDE-47, M. edulis mainly utilized aerobic respiration, but lowered glucose metabolism as indicated by the decrease in glutamine and l-leucine was suggested to be involved in this process, which was differed from that in the control. The reoccurrence of IDH and SDH inhibition as well as LDH elevation indicated attenuation of aerobic and anaerobic respiration when the concentration increased to 10 μg/L, but severe protein damage was evidenced based on the elevation of amino acids and glutamine. Under the 0.1 μg/L BDE-47, activation of the AMPK-Hif-1a signaling pathway promoted the expression of glut1, which was the potential mechanism for the improvement of anaerobic respiration, and further activated glycolysis and anaerobic respiration. This study shows that the energy supply mode experienced a conversion from aerobic respiration under normal conditions to anaerobic mode in the low BDE-47 treatment and back to aerobic respiration with increasing BDE-47 concentrations, which may represent a potential mechanism for mussel physiological responses when faced with different levels of BDE-47 stress.

Longitudinal Evaluation Using Preclinical 7T-Magnetic Resonance Imaging/Spectroscopy on Prenatally Dose-Dependent Alcohol-Exposed Rats

Prenatal alcohol exposure causes many detrimental alcohol-induced defects in children, collectively known as fetal alcohol spectrum disorders (FASD). This study aimed to evaluate a rat model of FASD, in which alcohol was administered at progressively increasing doses during late pregnancy, using preclinical magnetic resonance (MR) imaging (MRI) and MR spectroscopy (MRS). Wistar rats were orally administered 2.5 mL/day of ethanol (25% concentration) on gestational day 15, and postnatal fetuses were used as FASD models. Four groups were used: a control group (non-treatment group) and three groups of FASD model rats that received one, two, or four doses of ethanol, respectively, during the embryonic period. Body weight was measured every other week until eight weeks of age. MRI and MRS were performed at 4 and 8 weeks of age. The volume of each brain region was measured using acquired T₂-weighted images. At 4 weeks of age, body weight and cortex volume were significantly lower in the three FASD model groups (2.5 × 1: 304 ± 6 mm³, p < 0.05; 2.5 × 2: 302 ± 8 mm³, p < 0.01; 2.5 × 4: 305 ± 6 mm³, p < 0.05) than they were in the non-treatment group (non-treatment: 313 ± 6 mm³). The FASD model group that received four doses of alcohol (2.5 × 4: 0.72 ± 0.09, p < 0.05) had lower Taurine/Cr values than the non-treatment group did (non-treatment: 0.91 ± 0.15), an effect that continued at 8 weeks of age (non-treatment: 0.63 ± 0.09; 2.5 × 4: 0.52 ± 0.09, p < 0.05). This study is the first to assess brain metabolites and volume over time using MRI and MRS. Decreases in brain volume and taurine levels were observed at 4 and 8 weeks of age, suggesting that the effects of alcohol persisted beyond adulthood.

Lipocalin-2 Secreted by the Liver Regulates Neuronal Cell Function Through AKT-Dependent Signaling in Hepatic Encephalopathy Mouse Model

Hepatic encephalopathy (HE) associated with liver failure is accompanied by hyperammonemia, severe inflammation, depression, anxiety, and memory deficits as well as liver injury. Recent studies have focused on the liver-brain-inflammation axis to identify a therapeutic solution for patients with HE. Lipocalin-2 is an inflammation-related glycoprotein that is secreted by various organs and is involved in cellular mechanisms including iron homeostasis, glucose metabolism, cell death, neurite outgrowth, and neurogenesis. In this study, we investigated that the roles of lipocalin-2 both in the brain cortex of mice with HE and in Neuro-2a (N2A) cells. We detected elevated levels of lipocalin-2 both in the plasma and liver in a bile duct ligation mouse model of HE. We confirmed changes in cytokine expression, such as interleukin-1β, cyclooxygenase 2 expression, and iron metabolism related to gene expression through AKT-mediated signaling both in the brain cortex of mice with HE and N2A cells. Our data showed negative effects of hepatic lipocalin-2 on cell survival, iron homeostasis, and neurite outgrowth in N2A cells. Thus, we suggest that regulation of lipocalin-2 in the brain in HE may be a critical therapeutic approach to alleviate neuropathological problems focused on the liver-brain axis.

Glial Glutamine Homeostasis in Health and Disease

Glutamine is an essential cerebral metabolite. Several critical brain processes are directly linked to glutamine, including ammonia homeostasis, energy metabolism and neurotransmitter recycling. Astrocytes synthesize and release large quantities of glutamine, which is taken up by neurons to replenish the glutamate and GABA neurotransmitter pools. Astrocyte glutamine hereby sustains the glutamate/GABA-glutamine cycle, synaptic transmission and general brain function. Cerebral glutamine homeostasis is linked to the metabolic coupling of neurons and astrocytes, and relies on multiple cellular processes, including TCA cycle function, synaptic transmission and neurotransmitter uptake. Dysregulations of processes related to glutamine homeostasis are associated with several neurological diseases and may mediate excitotoxicity and neurodegeneration. In particular, diminished astrocyte glutamine synthesis is a common neuropathological component, depriving neurons of an essential metabolic substrate and precursor for neurotransmitter synthesis, hereby leading to synaptic dysfunction. While astrocyte glutamine synthesis is quantitatively dominant in the brain, oligodendrocyte-derived glutamine may serve important functions in white matter structures. In this review, the crucial roles of glial glutamine homeostasis in the healthy and diseased brain are discussed. First, we provide an overview of cellular recycling, transport, synthesis and metabolism of glutamine in the brain. These cellular aspects are subsequently discussed in relation to pathological glutamine homeostasis of hepatic encephalopathy, epilepsy, Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis. Further studies on the multifaceted roles of cerebral glutamine will not only increase our understanding of the metabolic collaboration between brain cells, but may also aid to reveal much needed therapeutic targets of several neurological pathologies.

The Glymphatic System May Play a Vital Role in the Pathogenesis of Hepatic Encephalopathy: A Narrative Review

Hepatic encephalopathy (HE) is a neurological complication of liver disease resulting in cognitive, psychiatric, and motor symptoms. Although hyperammonemia is a key factor in the pathogenesis of HE, several other factors have recently been discovered. Among these, the impairment of a highly organized perivascular network known as the glymphatic pathway seems to be involved in the progression of some neurological complications due to the accumulation of misfolded proteins and waste substances in the brain interstitial fluids (ISF). The glymphatic system plays an important role in the clearance of brain metabolic derivatives and prevents aggregation of neurotoxic agents in the brain ISF. Impairment of it will result in aggravated accumulation of neurotoxic agents in the brain ISF. This could also be the case in patients with liver failure complicated by HE. Indeed, accumulation of some metabolic by-products and agents such as ammonia, glutamine, glutamate, and aromatic amino acids has been reported in the human brain ISF using microdialysis technique is attributed to worsening of HE and correlates with brain edema. Furthermore, it has been reported that the glymphatic system is impaired in the olfactory bulb, prefrontal cortex, and hippocampus in an experimental model of HE. In this review, we discuss different factors that may affect the function of the glymphatic pathways and how these changes may be involved in HE.

Magnetic resonance spectroscopy and liquid chromatography-mass spectrometry metabolomics study may differentiate pre-eclampsia from gestational hypertension

OBJECTIVE

To investigate the findings of magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and serum metabolomics for differentiating pre-eclampsia (PE) from gestational hypertension (GH).

METHODS

This prospective study enrolled 176 subjects including a primary cohort with healthy non-pregnant women (HN, n = 35), healthy pregnant women (HP, n = 20), GH (n = 27), and PE (n = 39) and a validation cohort with HP (n = 22), GH (n = 22), and PE (n = 11). T1 signal intensity index (T1SI), apparent diffusion coefficient (ADC) value, and the metabolites on MRS were compared. The differentiating performances of single and combined MRI and MRS parameters for PE were evaluated. Serum liquid chromatography-mass spectrometry (LC-MS) metabolomics was investigated by sparse projection to latent structures discriminant analysis.

RESULTS

Increased T1SI, lactate/creatine (Lac/Cr), and glutamine and glutamate (Glx)/Cr and decreased ADC value and myo-inositol (mI)/Cr in basal ganglia were found in PE patients. T1SI, ADC, Lac/Cr, Glx/Cr, and mI/Cr yielded an area under the curves (AUC) of 0.90, 0.80, 0.94, 0.96, and 0.94 in the primary cohort, and of 0.87, 0.81, 0.91, 0.84, and 0.83 in the validation cohort, respectively. A combination of Lac/Cr, Glx/Cr, and mI/Cr yielded the highest AUC of 0.98 in the primary cohort and 0.97 in the validation cohort. Serum metabolomics analysis showed 12 differential metabolites, which are involved in pyruvate metabolism, alanine metabolism, glycolysis, gluconeogenesis, and glutamate metabolism.

CONCLUSIONS

MRS is expected to be a noninvasive and effective tool for monitoring GH patients to avoid the development of PE.

KEY POINTS

• Increased T1SI and decreased ADC value in the basal ganglia were found in PE patients than in GH patients. • Increased Lac/Cr and Glx/Cr, and decreased mI/Cr in the basal ganglia were found in PE patients than in GH patients. • LC-MS metabolomics showed that the major differential metabolic pathways between PE and GH were pyruvate metabolism, alanine metabolism, glycolysis, gluconeogenesis, and glutamate metabolism.

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.

Regulation of the Volume-Regulated Anion Channel Pore-Forming Subunit LRRC8A in the Intrahippocampal Kainic Acid Model of Mesial Temporal Lobe Epilepsy

Volume-regulated anion channels (VRACs) are a group of ubiquitously expressed outwardly-rectifying anion channels that sense increases in cell volume and act to return cells to baseline volume through an efflux of anions and organic osmolytes, including glutamate. Because cell swelling, increased extracellular glutamate levels, and reduction of the brain extracellular space (ECS) all occur during seizure generation, we set out to determine whether VRACs are dysregulated throughout mesial temporal lobe epilepsy (MTLE), the most common form of adult epilepsy. To accomplish this, we employed the IHKA experimental model of MTLE, and probed for the expression of LRRC8A, the essential pore-forming VRAC subunit, at acute, early-, mid-, and late-epileptogenic time points (1-, 7-, 14-, and 30-days post-IHKA, respectively). Western blot analysis revealed the upregulation of total dorsal hippocampal LRRC8A 14-days post-IHKA in both the ipsilateral and contralateral hippocampus. Immunohistochemical analyses showed an increased LRRC8A signal 7-days post-IHKA in both the ipsilateral and contralateral hippocampus, along with layer-specific changes 1-, 7-, and 30-days post-IHKA bilaterally. LRRC8A upregulation 1 day post-IHKA was observed primarily in astrocytes; however, some upregulation was also observed in neurons. Glutamate-GABA/glutamine cycle enzymes glutamic acid decarboxylase, glutaminase, and glutamine synthetase were also dysregulated at the 7-day timepoint post status epilepticus. The timepoint-dependent upregulation of total hippocampal LRRC8A and the possible subsequent increased efflux of glutamate in the epileptic hippocampus suggest that the dysregulation of astrocytic VRAC may play an important role in the development of epilepsy.

Decoding the contributions of gut microbiota and cerebral metabolism in acute liver injury mice with and without cognitive dysfunction

AIMS

Patients with acute liver injury (ALI) can develop cognitive dysfunction (CD). The study investigated the role of gut microbiota and cerebral metabolism in ALI mice with and without CD.

METHODS

Male C57BL/6 mice that received thioacetamide were classified into ALI mice with (susceptible) or without (unsusceptible) CD-like phenotypes by hierarchical cluster analysis of behavior. The role of gut microbiota was investigated by 16S ribosomal RNA gene sequencing and feces microbiota transplantation (FMT). ¹ H-[¹³ C] NMR and electrophysiology were used to detect the changes in cerebral neurotransmitter metabolic and synaptic transition in neurons or astrocytes.

RESULTS

Apromixlay 55% (11/20) of mice developed CD and FMT from the susceptible group transmitted CD to gut microbiota-depleted mice. Alloprevotella was enriched in the susceptible group. GABA production was decreased in the frontal cortex, while hippocampal glutamine was increased in the susceptible group. Altered Escherichia. Shigella and Alloprevotella were correlated with behaviors and cerebral metabolic kinetics and identified as good predictors of ALI-induced CD. The frequencies of both miniature inhibitory and excitatory postsynaptic currents in hippocampal CA1 and prefrontal cortex were decreased in the susceptible group.

CONCLUSION

Altered transmitter metabolism and synaptic transmission in the hippocampus and prefrontal cortex and gut microbiota disturbance may lead to ALI-induced CD.

Impact of broad-spectrum antibiotics on the gut-microbiota-spleen-brain axis

The spleen is a key immune-related organ that plays a role in communication between the brain and the immune system through the brain-spleen axis and brain-gut-microbiota axis. However, how the gut microbiota affects spleen and brain function remains unclear. Here, we investigated whether microbiome depletion induced by administration of an antibiotic cocktail (ABX) affects spleen and brain function. Treatment with ABX for 14 days resulted in a significant decrease in spleen weight and significant alterations in splenic functions, including the percentage of neutrophils, NK cells, macrophages, and CD8⁺ T cells. Furthermore, ABX treatment resulted in the depletion of a large portion of the gut microbiota. Untargeted metabolomics analysis showed that ABX treatment caused alterations in the levels of certain compounds in the plasma, spleen, and brain. Moreover, ABX treatment decreased the expression of microglia marker Iba1 in the cerebral cortex. Interestingly, correlations were found between the abundance of different microbiome components and metabolites in various tissues, as well as splenic cell populations and spleen weight. These findings suggest that ABX-induced microbiome depletion and altered metabolite levels may affect spleen and brain function through the gut-microbiota-spleen-brain axis.

Plasma ammonia levels predict hospitalisation with liver-related complications and mortality in clinically stable outpatients with cirrhosis

BACKGROUND & AIMS

Hyperammonaemia is central in the pathogenesis of hepatic encephalopathy. It also has pleiotropic deleterious effects on several organ systems, such as immune function, sarcopenia, energy metabolism and portal hypertension. This study was performed to test the hypothesis that severity of hyperammonaemia is a risk factor for liver-related complications in clinically stable outpatients with cirrhosis.

METHODS

We studied 754 clinically stable outpatients with cirrhosis from 3 independent liver units. Baseline ammonia levels were corrected to the upper limit of normal (AMM-ULN) for the reference laboratory. The primary endpoint was hospitalisation with liver-related complications (a composite endpoint of bacterial infection, variceal bleeding, overt hepatic encephalopathy, or new onset or worsening of ascites). Multivariable competing risk frailty analyses using fast unified random forests were performed to predict complications and mortality. External validation was carried out using prospective data from 130 patients with cirrhosis in an independent tertiary liver centre.

RESULTS

Overall, 260 (35%) patients were hospitalised with liver-related complications. On multivariable analysis, AMM-ULN was an independent predictor of both liver-related complications (hazard ratio 2.13; 95% CI 1.89-2.40; p <0.001) and mortality (hazard ratio 1.45; 95% CI 1.20-1.76; p <0.001). The AUROC of AMM-ULN was 77.9% for 1-year liver-related complications, which is higher than traditional severity scores. Statistical differences in survival were found between high and low levels of AMM-ULN both for complications and mortality (p <0.001) using 1.4 as the optimal cut-off from the training set. AMM-ULN remained a key variable for the prediction of complications within the random forests model in the derivation cohort and upon external validation.

CONCLUSION

Ammonia is an independent predictor of hospitalisation with liver-related complications and mortality in clinically stable outpatients with cirrhosis and performs better than traditional prognostic scores in predicting complications.

LAY SUMMARY

We conducted a prospective cohort study evaluating the association of blood ammonia levels with the risk of adverse outcomes in 754 patients with stable cirrhosis across 3 independent liver units. We found that ammonia is a key determinant that helps to predict which patients will be hospitalised, develop liver-related complications and die; this was confirmed in an independent cohort of patients.

Reactive Microgliosis in Sepsis-Associated and Acute Hepatic Encephalopathies: An Ultrastructural Study

Sepsis and acute liver failure are associated with severe endogenous intoxication. Microglia, which are the resident immune brain cells, play diverse roles in central nervous system development, surveillance, and defense, as well as contributing to neuroinflammatory reactions. In particular, microglia are fundamental to the pathophysiology of reactive toxic encephalopathies. We analyzed microglial ultrastructure, morphotypes, and phagocytosis in the sensorimotor cortex of cecal ligation and puncture (CLP) and acetaminophen-induced liver failure (AILF) Wistar rats. A CLP model induced a gradual shift of ~50% of surveillant microglia to amoeboid hypertrophic-like and gitter cell-like reactive phenotypes with active phagocytosis and frequent contacts with damaged neurons. In contrast, AILF microglia exhibited amoeboid, rod-like, and hypertrophic-like reactive morphotypes with minimal indications for efficient phagocytosis, and were mostly in contact with edematous astrocytes. Close interactions of reactive microglia with neurons, astrocytes, and blood-brain barrier components reflect an active contribution of these cells to the tissue adaptation and cellular remodeling to toxic brain damage. Partial disability of reactive microglia may affect the integrity and metabolism in all tissue compartments, leading to failure of the compensatory mechanisms in acute endogenous toxic encephalopathies.

Optic nerve sheath diameter in patients with hepatic encephalopathy

BACKGROUND

This study aims to reveal whether the optic nerve sheath diameter (ONSD) increases in hepatic encephalopathy (HE) patients, and to determine ONSD is associated with the poor prognosis of patients with HE.

METHODS AND MATERIAL

In this retrospective case-control study, HE patients who underwent cranial computerized tomography (CT) were included in the case group; and the patients who underwent CT for other reasons for the same age and gender and were normally interpreted were included in the control group. ONSD measurements in the case and control groups and clinical grades of HE with in-hospital mortality and ONSD measurements were compared in the case group.

RESULTS

This study was done with 74 acute HE patients and 74 control patients. The mean age was 62.9 ± 11.0 years and 67.6% of patients were male in both groups. The ONSD in the case group was higher than the control group (5.27-mm ± 0.82 vs 4.73 mm ± 0.57, p <0.001). In the case group, the ONSD was 5.30 mm ± 0.87 in survivors, and 5.21 ± 0.65 in non-survivors (P = 0.670). There was no significant difference between the West Haven HE grade (P = 0.348) and Child-Pugh Score (P = 0.505) with ONSD measurements.

CONCLUSION

We have shown that ONSD increases in HE patients compared to the control group. ONSD was not related to the Child-Pugh Score, HE grade, and in-hospital mortality.

Hyperammonemia in Inherited Metabolic Diseases

Ammonia is a neurotoxic compound which is detoxified through liver enzymes from urea cycle. Several inherited or acquired conditions can elevate ammonia concentrations in blood, causing severe damage to the central nervous system due to the toxic effects exerted by ammonia on the astrocytes. Therefore, hyperammonemic patients present potentially life-threatening neuropsychiatric symptoms, whose severity is related with the hyperammonemia magnitude and duration, as well as the brain maturation stage. Inherited metabolic diseases caused by enzymatic defects that compromise directly or indirectly the urea cycle activity are the main cause of hyperammonemia in the neonatal period. These diseases are mainly represented by the congenital defects of urea cycle, classical organic acidurias, and the defects of mitochondrial fatty acids oxidation, with hyperammonemia being more severe and frequent in the first two groups mentioned. An effective and rapid treatment of hyperammonemia is crucial to prevent irreversible neurological damage and it depends on the understanding of the pathophysiology of the diseases, as well as of the available therapeutic approaches. In this review, the mechanisms underlying the hyperammonemia and neurological dysfunction in urea cycle disorders, organic acidurias, and fatty acids oxidation defects, as well as the therapeutic strategies for the ammonia control will be discussed.

Advances in medical management of acute liver failure in children: promoting native liver survival

Paediatric acute liver failure (PALF) is defined as a biochemical evidence of acute liver injury in a child with no previous history of chronic liver disease characterised by an international normalised ratio (INR) of 1·5 or more unresponsive to vitamin K with encephalopathy, or INR of 2·0 or more with or without encephalopathy. PALF can rapidly progress to multiorgan dysfunction or failure. Although the transplant era has substantially changed the outlook for these patients, transplantation itself is not without risks, including those associated with life-long immunosuppression. Consequently, there has been an increased focus on improving medical management to prioritise bridging of patients to native liver survival, which is possible due to improved understanding of the underlying pathophysiology of multiorgan involvement in PALF. In this Review, we discuss recent advances in the medical management of PALF with an aim of reducing the need for liver transplantation. The Review will focus on the non-specific immune-mediated inflammatory response, extracorporeal support devices, neuromonitoring and neuroprotection, and emerging cellular and novel future therapeutic options.

Dysregulation of Astrocytic Glutamine Transport in Acute Hyperammonemic Brain Edema

Acute liver failure (ALF) impairs ammonia clearance from blood, which gives rise to acute hyperammonemia and increased ammonia accumulation in the brain. Since in brain glutamine synthesis is the only route of ammonia detoxification, hyperammonemia is as a rule associated with increased brain glutamine content (glutaminosis) which correlates with and contributes along with ammonia itself to hyperammonemic brain edema-associated with ALF. This review focuses on the effects of hyperammonemia on the two glutamine carriers located in the astrocytic membrane: Slc38a3 (SN1, SNAT3) and Slc7a6 (y + LAT2). We emphasize the contribution of the dysfunction of either of the two carriers to glutaminosis- related aspects of brain edema: retention of osmotically obligated water (Slc38a3) and induction of oxidative/nitrosative stress (Slc7a6). The changes in glutamine transport link glutaminosis- evoked mitochondrial dysfunction to oxidative-nitrosative stress as formulated in the “Trojan Horse” hypothesis.

Neurological monitoring and sedation protocols in the Liver Intensive Care Unit

Patients with liver disease often have alteration of neurological status which requires admission to an intensive care unit. Patients with acute liver failure (ALF), acute-on-chronic liver failure (ACLF) and rarely cirrhosis are at risk of cerebral edema. These patients require prompt assessment of neurological status including assessment of intra-cranial pressure (ICP) and monitoring metabolic parameters like arterial/venous ammonia levels, serum creatinine and serum electrolytes so that timely specific therapy for raised ICP can be instituted to prevent permanent neurological dysfunction. The overall aims of neuromonitoring and sedation protocols in a liver intensive care unit are to identify the level of multifactorial metabolic encephalopathy, individualize sedation and analgesia requirements for patients on mechanical ventilation, institute specific therapy to correct the neurological insult in ALF and ACLF, provide clear physiological data for guided therapy of drugs like muscle relaxants, antiepileptics, and cerebral edema reducing agents, and assist with overall prognostication. In this review article we will outline the clinical scenarios related to liver disease requiring intensive care and neuromonitoring, current techniques of neurological assessment, sedation protocols and point of care tests which enable the treating physician and intensivist guide therapy for raised ICP.

Enhanced intestinal protein fermentation in schizophrenia

BACKGROUND

Emerging findings highlighted the associations of mental illness to nutrition and dysbiosis in the intestinal microbiota, but the underlying mechanisms, especially in schizophrenia (SZ), remain unclarified.

METHODS

We conducted a case-control study of SZ patients (case to control=100:52) by performing sequencing of the gut metagenome; measurement of fecal and plasma non-targeted metabolome; including short-, medium-, and long-chain fatty acids; and targeted metabolites, along with recorded details of daily intakes of food.

RESULTS

The metagenome analysis uncovered enrichment of asaccharolytic species and reduced abundance of carbohydrate catabolism pathways and enzymes in the gut of SZ patients, but increased abundance of peptidases in contrast to their significantly reduced protein intake. Fecal metabolome analysis identified increased concentrations of many protein catabolism products, including amino acids (AAs), urea, branched short-chain fatty acids, and various nitrogenous derivates of aromatic AAs in SZ patients. Protein synthesis, represented by the abundance of AA-biosynthesis pathways and aminoacyl-tRNA transferases in metagenome, was significantly decreased. The AUCs (area under the curve) of the diagnostic random forest models based on their abundance achieved 85% and 91%, respectively. The fecal levels of AA-fermentative enzymes and products uniformly showed positive correlations with the severity of psychiatric symptoms.

CONCLUSIONS

Our findings revealed apparent dysbiosis in the intestinal microbiome of SZ patients, where microbial metabolism is dominated by protein fermentation and shift from carbohydrate fermentation and protein synthesis in healthy conditions. The aberrant macronutrient metabolism by gut microbes highlights the importance of nutrition care and the potential for developing microbiota-targeted therapeutics in SZ.

Saul Brusilow: Understanding and treating diseases of ammonia toxicity

This article reviews the scientific career and accomplishments of the late Dr. Saul Brusilow, Professor of Pediatrics at Johns Hopkins. Dr. Brusilow's career was focused on diseases involving hyperammonemia. He and his colleagues developed a set of drugs that could lower ammonia levels in patients with genetic disorders of the urea cycle by providing alternative pathways for the synthesis of excretable nitrogenous molecules. Those drugs and their derivatives represent one of the earliest and most successful drug therapies for genetic diseases. Turning their attention to brain swelling caused by liver disease, Dr. Brusilow and colleagues developed the Osmotic Gliopathy Hypothesis to help explain the mechanism of ammonia toxicity, postulating that high ammonia drives glutamine synthetase in astrocytes to produce elevated levels of glutamine that act as a potent osmolyte, drawing water into the cell and causing cerebral edema. This hypothesis suggests that inhibiting glutamine synthetase with its well-characterized inhibitor, methionine sulfoximine, might prove therapeutic in cases of hepatic encephalopathy, a conclusion supported by their subsequent studies in animals. But although the drugs developed to treat hyperammonemia resulting from urea cycle disorders were successfully developed and approved by the FDA, the compound suggested as a treatment for hepatic encephalopathy was unable to attract sufficient interest and investment to be tested for use in humans.

Oral glutamine supplementation increases seizure severity in a rodent model of mesial temporal lobe epilepsy

Background: Glutamine synthetase (GS) is the only enzyme known to synthesize significant amounts of glutamine in mammals, and loss of GS in the hippocampus has been implicated in the pathophysiology of medication refractory mesial temporal lobe epilepsy (MTLE). Moreover, loss-of-function mutations of the GS gene causes severe epileptic encephalopathy, and supplementation with glutamine has been shown to normalize EEG and possibly improve the outcome in these patients. Here we examined whether oral glutamine supplementation is an effective treatment for MTLE by assessing the frequency and severity of seizures after supplementation in a translationally relevant model of the disease.Methods: Male Sprague Dawley rats (380-400 g) were allowed to drink unlimited amounts of glutamine in water (3.6% w/v; n = 8) or pure water (n = 8) for several weeks. Ten days after the start of glutamine supplementation, GS was chronically inhibited in the hippocampus to induce MTLE. Continuous video-intracranial EEG was collected for 21 days to determine the frequency and severity of seizures.Results: While there was no change in seizure frequency between the groups, the proportion of convulsive seizures was significantly higher in glutamine treated animals during the first three days of GS inhibition.Conclusion: The results suggest that oral glutamine supplementation transiently increases seizure severity in the initial stages of an epilepsy model, indicating a potential role of the amino acid in seizure propagation and epileptogenesis.

Organ and brain crosstalk: The liver-brain axis in gastrointestinal, liver, and pancreatic diseases

The liver is the largest organ in the human body and is responsible for the metabolism and storage of the three principal nutrients: carbohydrates, fats, and proteins. In addition, the liver contributes to the breakdown and excretion of alcohol, medicinal agents, and toxic substances and the production and secretion of bile. In addition to its role as a metabolic centre, the liver has recently attracted attention for its function in the liver-brain axis, which interacts closely with the central nervous system via the autonomic nervous system, including the vagus nerve. The liver-brain axis influences the control of eating behaviour in the central nervous system through stimuli from the liver. Conversely, neural signals from the central nervous system influence glucose, lipid, and protein metabolism in the liver. The liver also receives a constant influx of nutrients and hormones from the intestinal tract and compounds of bacterial origin via the portal system. As a result, the intestinal tract and liver are involved in various immunological interactions. A good example is the co-occurrence of primary sclerosing cholangitis and ulcerative colitis. These heterogeneous roles of the liver-brain axis are mediated via the vagus nerve in an asymmetrical manner. In this review, we provide an overview of these interactions, mainly with the liver but also with the brain and gut.