Activation of N-methyl-D-aspartate receptors in rat brain in vivo following acute ammonia intoxication: characterization by in vivo brain microdialysis

Establishing In-vivo brain microdialysis for comparing concentrations of a variety of cortical neurotransmitters in the awake rhesus macaque between different cognitive states

BACKGROUND

Neuronal activity is modulated by behavior and cognitive processes. The combination of several neurotransmitter systems, acting directly or indirectly on specific populations of neurons, underlie such modulations. Most studies with non-human primates (NHPs) fail to capture this complexity, partly due to the lack of adequate methods for reliably and simultaneously measuring a broad spectrum of neurotransmitters while the animal engages in behavioral tasks.

NEW METHOD

To address this gap, we introduce a novel implementation of brain microdialysis (MD), employing semi-chronically implanted guides and probes in awake, behaving NHPs facilitated by removable insets within a standard recording chamber over extrastriate visual cortex (here, the visual middle temporal area (MT)). This approach allows flexible access to diverse brain regions, including areas deep within the sulcus.

RESULTS

Reliable concentration measurements of GABA, glutamate, norepinephrine, epinephrine, dopamine, serotonin, and choline were achieved from small sample volumes (<20 µl) using ultra-performance liquid chromatography with electrospray ionization-mass spectrometry (UPLC-ESI-MS). Comparing two behavioral states - 'active' and 'inactive', we observe subtle concentration variations between the two behavioral states and a greater variability of concentrations in the active state. Additionally, we find positively and negatively correlated concentration changes for neurotransmitter pairs between the behavioral states.

CONCLUSIONS

Therefore, this MD setup allows insights into the neurochemical dynamics in awake primates, facilitating comprehensive investigations into the roles and the complex interplay of neurotransmitters in cognitive and behavioral functions.

Biomimetic Nanomotors for Deep Ischemia Penetration and Ferroptosis Inhibition in Neuroprotective Therapy of Ischemic Stroke

Nerve injury represents the primary reason of mortality and disability in ischemic stroke, but effective drug delivery to the region of cerebral ischemia and hypoxia poses a significant challenge in neuroprotective treatment. To address these clinical challenges, a biomimetic nanomotor, Pt@LF is designed, to facilitate deep delivery of neuroprotective agents and inhibit ferroptosis in ischemic stroke. Pt@LF traverses the blood-brain barrier (BBB) and penetrates into deep cerebral ischemic-hypoxic areas due to the active targeting capacity of apo-lactoferrin (Apo-LF) and the self-propelling motion properties of nanomotors. Subsequently, Pt@LF loosens thrombus and alleviates the "no reflow" phenomenon via mechanical thrombolysis. Thanks to the various enzyme-like abilities and multi-target ferroptosis inhibition capability, Pt@LF ameliorates the inflammatory microenvironment and rescues dying neurons. In conclusion, Pt@LF demonstrates efficiently deep penetration and neuroprotective effects in vitro and vivo. And this study provides a promising therapeutic platform for the treatment of ischemic stroke.

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.

Brain reserve in hepatic encephalopathy: Pathways of damage and preventive strategies through lifestyle and therapeutic interventions

Brain reserve is an important concept to understand the variability of damage associated with brain-related diseases and includes the adaptation of cognitive processes to preserve brain function. A good cognitive reserve might delay the onset of clinical manifestations of neurodegenerative diseases as well as hepatic encephalopathy, improving the quality of life in patients with chronic liver diseases. By stimulating activities and maintaining overall health, individuals may be able to enhance their brain's resilience to age-related changes and pathology. This review aims to collect all the data available on the role of brain reserve in hepatic encephalopathy development, and the potential effect of a good brain reserve in slowing down hepatic encephalopathy progression and frequency.

Ammonia-induced stress response in liver disease progression and hepatic encephalopathy

Ammonia levels are orchestrated by a series of complex interrelated pathways in which the urea cycle has a central role. Liver dysfunction leads to an accumulation of ammonia, which is toxic and is strongly associated with disruption of potassium homeostasis, mitochondrial dysfunction, oxidative stress, inflammation, hypoxaemia and dysregulation of neurotransmission. Hyperammonaemia is a hallmark of hepatic encephalopathy and has been strongly associated with liver-related outcomes in patients with cirrhosis and liver failure. In addition to the established role of ammonia as a neurotoxin in the pathogenesis of hepatic encephalopathy, an increasing number of studies suggest that it can lead to hepatic fibrosis progression, sarcopenia, immune dysfunction and cancer. However, elevated systemic ammonia levels are uncommon in patients with metabolic dysfunction-associated steatotic liver disease. A clear causal relationship between ammonia-induced immune dysfunction and risk of infection has not yet been definitively proven. In this Review, we discuss the mechanisms by which ammonia produces its diverse deleterious effects and their clinical relevance in liver diseases, the importance of measuring ammonia levels for the diagnosis of hepatic encephalopathy, the prognosis of patients with cirrhosis and liver failure, and how our knowledge of inter-organ ammonia metabolism is leading to the development of novel therapeutic approaches.

Seizure as the main presenting manifestation of three patients with acute glufosinate-ammonium poisoning

Glufosinate-ammonium herbicides are the most widely used broad-spectrum, non-selective herbicides in the world. Glufosinate-ammonium is a structural analogue of glutamate (Glu) which can irreversibly inhibit the activity of glutamine synthetase (GS) and Glu decarboxylase in plants, thereby blocking the synthesis of glutamine (Gln) from Glu and ammonia (Hoerlein, 1994). This causes the plants to die because of the nitrogen metabolism disorder and subsequent intracellular accumulation of ammonia. In humans, the characteristic features of glufosinate-ammonium herbicide poisoning include gastrointestinal symptoms and neurotoxicity (Watanabe and Sano, 1998). Currently, there are no antidotes for glufosinate-ammonium herbicide poisoning, and thus supportive care is the key treatment.

Dietary N-carbamylglutamate supplementation improves ammonia tolerance of juvenile yellow catfish Pelteobagrus fulvidraco

Introduction: Ammonia has been of concern for its high toxicity to animals. N-carbamylglutamate (NCG) can reduce blood ammonia levels in mammals, but studies on ammonia tolerance in fish are insufficient. Methods: Juvenile yellow catfish were fed two levels of NCG (0.00% and 0.05%) for 84 days under three ammonia levels (0.00, 0.08, and 0.16 mg/L NH₃). Results and Discussion: The results showed that survival rate (SUR), final body weight (FBW), weight gain (WG), and serum total protein (TP), triglycerides (TG), glucose (Glu), ornithine (Orn), citrulline (Cit) contents, and liver superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), arginase (ARG), ornithine transcarbamylase (OTC) activities decreased with the increase of ammonia levels, on the contrary, feed conversion ratio (FCR), hepatosomatic index (HSI), and serum ammonia, urea, alanine aminotransferase (ALT), aspartate aminotransferase (AST), glutamine (Gln), arginine (Arg) contents, and liver malondialdehyde (MDA), tumor necrosis factor (TNF), interleukin (IL) 1, IL 8 contents, and mRNA expressions of cu/zn sod, cat, gpx, gr, tnf ɑ, il 1, and il 8 were significantly increased. Dietary 0.05% NCG supplementation had higher SUR, FBW, WG, feed intake (FI), whole-body protein, and serum TP, total cholesterol (TC), Glu, citrulline (Cit) contents, and liver SOD, GPx, argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL), inducible nitric oxide synthase (iNOS) activities compared to 0.00% NCG group, but had lower serum ammonia, urea, ALT, AST, Gln, Arg contents, and liver MDA, TNF, IL 1, IL 8 contents, and neuronal nitric oxide synthase activity. At the end of bacterial challenge, cumulative mortality (CM) increased with ammonia levels increased, but serum antibody titer (AT), lysozyme (LYZ) activity, 50% hemolytic complement, immunoglobulin (Ig) contents, respiratory burst (RB), phagocytic indices decreased with ammonia levels increased. CM in 0.05% NCG group was lower than that in 0.00% NCG group, but serum AT, LYZ activity, Ig content, RB in 0.05% NCG group were significantly higher. The correlation analysis found that iNOS was positively correlated with ASS activity. This study indicates that dietary NCG supplementation can improve the ammonia tolerance of yellow catfish, and ASS may also be the target of NCG to activate the urea cycle.

Establishment of hyperammonemia mode in yellow catfish and the mitigation of exogenous L-ornithine-L-aspartate

Ammonia stress can lead to fish ammonia poisoning. The l-ornithine-l-aspartate (LoLa) has potential value in treating fish hyperammonemia. This study tried to establish a hyperammonemia mode of yellow catfish, which was used to evaluate the effect of LoLa on hyperammonemia. Fish were injected with ammonium acetate and sodium chloride for 3 d to establish model, respectively. Then ammonium acetate group was divided into two groups: one group was further injected with ammonium acetate, another group was injected with LoLa. Sodium chloride group was also divided into two groups: one group was further injected with sodium chloride, another group was injected with LoLa. The experiment continued for 96 h. The results showed that ammonia poisoning could induce serum ammonia content elevated, liver damage (serum aminotransferase activity elevated and liver malondialdehyde accumulation), and up-regulation of cytokine (IL 1, IL 8 and TNFɑ), apoptosis (P53, Bax, Cytochrome c, Caspase 3 and Caspase 9) and autophagy (Dynein, Beclin 1, AKT and PTEN) genes transcription, but LoLa could mitigate the adverse effect of ammonia poisoning. Our results suggesting that LoLa can detoxify ammonia into glutamine and stores it in muscle.

Hyperammonemia Alters the Function of AMPA and NMDA Receptors in Hippocampus: Extracellular cGMP Reverses Some of These Alterations

Chronic hyperammonemia alters membrane expression of AMPA and NMDA receptors subunits in hippocampus leading to impaired memory and learning. Increasing extracellular cGMP normalizes these alterations. However, it has not been studied whether hyperammonemia alters the function of AMPA and NMDA receptors. The aims of this work were: (1) assess if hyperammonemia alters AMPA and NMDA receptors function; (2) analyze if extracellular cGMP reverses these alterations. A multielectrode array device was used to stimulate Schäffer collaterals and record postsynaptic currents in the CA1 region in hippocampal slices from control and hyperammonemic rats and analyze different features of the excitatory postsynaptic potentials. Hyperammonemia reduces the amplitude and delays appearance of AMPA EPSPs, whereas increases amplitude, hyperpolarization, depolarization and desensitization area of the NMDA EPSPs. These alterations in AMPA and NMDA function are accentuated as the stimulation intensity increases. Adding extracellular cGMP reverses the alteration in amplitude in both, AMPA and NMDA EPSPs. In control slices extracellular cGMP decreases the AMPA and NMDA EPSPs amplitude and delays the response of neurons and the return to the resting potential at all stimulation intensities. In conclusion, hyperammonemia decreases the AMPA response, whereas increases the NMDA response and extracellular cGMP reverses these alterations.

Intracellular and extracelluar cyclic GMP in the brain and the hippocampus

Cyclic Guanosine-Monophosphate (cGMP) is implicated as second messenger in a plethora of pathways and its effects are executed mainly by cGMP-dependent protein kinases (PKG). It is involved in both peripheral (cardiovascular regulation, intestinal secretion, phototransduction, etc.) and brain (hippocampal synaptic plasticity, neuroinflammation, cognitive function, etc.) processes. Stimulation of hippocampal cGMP signaling have been proved to be beneficial in animal models of aging, Alzheimer's disease or hepatic encephalopathy, restoring different cognitive functions such as passive avoidance, object recognition or spatial memory. However, even when some inhibitors of cGMP-degrading enzymes (PDEs) are already used against peripheral pathologies, their utility as neurological treatments is still under clinical investigation. Additionally, it has been demonstrated a list of cGMP roles as not second but first messenger. The role of extracellular cGMP has been specially studied in hippocampal function and cognitive impairment in animal models and it has emerged as an important modulator of neuroinflammation-mediated cognitive alterations and hippocampal synaptic plasticity malfunction. Specifically, it has been demonstrated that extracellular cGMP decreases hippocampal IL-1β levels restoring membrane expression of glutamate receptors in the hippocampus and cognitive function in hyperammonemic rats. The mechanisms implicated are still unclear and might involve complex interactions between hippocampal neurons, astrocytes and microglia. Membrane targets for extracellular cGMP are still poorly understood and must be addressed in future studies.

Antibiotics and Liver Cirrhosis: What the Physicians Need to Know

The liver is the primary site of drug metabolism, which can be altered by a variety of diseases affecting the liver parenchyma, especially in patients with liver cirrhosis. The use of antibiotics in patients with cirrhosis is usually a matter of concern for physicians, given the lack of practical knowledge for drug choice and eventual dose adjustments in several clinical scenarios. The aim of the current narrative review is to report, as broadly as possible, basic, and practical knowledge that any physician should have when approaching a patient with liver cirrhosis and an ongoing infection to efficiently choose the best antibiotic therapy.

Impact of non-hepatic hyperammonemia on mortality in intensive care unit patients: a retrospective cohort study

BACKGROUND/AIMS

The effect of hyperammonemia on the mortality in patients with liver cirrhosis is well documented. However, little is known about the impact of hyperammonemia on mortality among intensive care unit patients without hepatic disease. We aimed to investigate factors associated with non-hepatic hyperammonemia among intensive care unit patients and to evaluate the factors related to the 7- and 90-day mortality.

METHODS

Between February 2016 and February 2020, 948 patients without hepatic disease who had 972 episodes of admission to the intensive care unit were retrospectively enrolled and classified as hyperammonemia grades 0 (≤ 80 µg/dL; 585 [60.2%]), 1 (≤ 160 µg/dL; 291 [29.9%]), 2 (≤ 240 µg/dL; 55 [5.7%]), and 3 (> 240 µg/dL; 41 [4.2%]). Factors associated with hyperammonemia and the 7- and 90-day mortality were evaluated by multivariate logistic regression analysis and Cox regression analysis, respectively. Kaplan-Meier survival curves for the 7- and 90-day mortality were constructed.

RESULTS

The independent risk factors for hyperammonemia were male sex (odds ratio, 1.517), age (0.984/year), acute brain failure (2.467), acute kidney injury (1.437), prothrombin time-international normalized ratio (2.272/unit), and albumin (0.694/g/dL). The 90-day mortality rate in the entire cohort was 24.3% and gradually increased with increasing hyperammonemia grade at admission (17.9%, 28.2%, 43.6%, and 61.0% in patients with grades 0, 1, 2, and 3, respectively). Additionally, non-hepatic hyperammonemia was an independent predictor of the 90- day mortality in intensive care unit patients.

CONCLUSION

Non-hepatic hyperammonemia is common (39.8%) and associated with the 90-day mortality among intensive care unit patients.

Hepatic Encephalopathy: From Metabolic to Neurodegenerative

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome of both acute and chronic liver disease. As a metabolic disorder, HE is considered to be reversible and therefore is expected to resolve following the replacement of the diseased liver with a healthy liver. However, persisting neurological complications are observed in up to 47% of transplanted patients. Several retrospective studies have shown that patients with a history of HE, particularly overt-HE, had persistent neurological complications even after liver transplantation (LT). These enduring neurological conditions significantly affect patient's quality of life and continue to add to the economic burden of chronic liver disease on health care systems. This review discusses the journey of the brain through the progression of liver disease, entering the invasive surgical procedure of LT and the conditions associated with the post-transplant period. In particular, it will discuss the vulnerability of the HE brain to peri-operative factors and post-LT conditions which may explain non-resolved neurological impairment following LT. In addition, the review will provide evidence; (i) supporting overt-HE impacts on neurological complications post-LT; (ii) that overt-HE leads to permanent neuronal injury and (iii) the pathophysiological role of ammonia toxicity on astrocyte and neuronal injury/damage. Together, these findings will provide new insights on the underlying mechanisms leading to neurological complications post-LT.

The Cerebral Effect of Ammonia in Brain Aging: Blood-Brain Barrier Breakdown, Mitochondrial Dysfunction, and Neuroinflammation

Aging occurs along with multiple pathological problems in various organs. The aged brain, especially, shows a reduction in brain mass, neuronal cell death, energy dysregulation, and memory loss. Brain aging is influenced by altered metabolites both in the systemic blood circulation and the central nervous system (CNS). High levels of ammonia, a natural by-product produced in the body, have been reported as contributing to inflammatory responses, energy metabolism, and synaptic function, leading to memory function in CNS. Ammonia levels in the brain also increase as a consequence of the aging process, ultimately leading to neuropathological problems in the CNS. Although many researchers have demonstrated that the level of ammonia in the body alters with age and results in diverse pathological alterations, the definitive relationship between ammonia and the aged brain is not yet clear. Thus, we review the current body of evidence related to the roles of ammonia in the aged brain. On the basis of this, we hypothesize that the modulation of ammonia level in the CNS may be a critical clinical point to attenuate neuropathological alterations associated with aging.

Decreased Expression and Uncoupling of Endothelial Nitric Oxide Synthase in the Cerebral Cortex of Rats with Thioacetamide-Induced Acute Liver Failure

Acute liver failure (ALF) is associated with deregulated nitric oxide (NO) signaling in the brain, which is one of the key molecular abnormalities leading to the neuropsychiatric disorder called hepatic encephalopathy (HE). This study focuses on the effect of ALF on the relatively unexplored endothelial NOS isoform (eNOS). The cerebral prefrontal cortices of rats with thioacetamide (TAA)-induced ALF showed decreased eNOS expression, which resulted in an overall reduction of NOS activity. ALF also decreased the content of the NOS cofactor, tetrahydro-L-biopterin (BH4), and evoked eNOS uncoupling (reduction of the eNOS dimer/monomer ratio). The addition of the NO precursor L-arginine in the absence of BH4 potentiated ROS accumulation, whereas nonspecific NOS inhibitor L-NAME or EDTA attenuated ROS increase. The ALF-induced decrease of eNOS content and its uncoupling concurred with, and was likely causally related to, both increased brain content of reactive oxidative species (ROS) and decreased cerebral cortical blood flow (CBF) in the same model.

The effects of thymoquinone on memory impairment and inflammation in rats with hepatic encephalopathy induced by thioacetamide

Hepatic encephalopathy (HE) is a prevalent complication of the central nervous system (CNS) that is caused by acute or chronic liver failure. This study was designed to evaluate the effects of thymoquinone (TQ) on thioacetamide (TAA)-induced HE in rats, and determine the consequential behavioral, biochemical, and histological changes. HE was induced in male Wistar rats by intraperitoneal (i.p.) injection of 200 mg/kg TAA once every 48 h for 14 consecutive days. Control groups received the normal saline containing 5 % DMSO. Thymoquinone (5, 10, and 20 mg/kg) was administered for ten consecutive days intraperitoneally (i.p.) after HE induction and it was continued until the end of the tests. Then, the passive avoidance memory, extracellular single unit, BBB permeability, and brain water content were evaluated. Moreover, hippocampal tissues were used for evaluation of oxidative stress index, inflammatory biomarkers, and histological parameters following HE. As result of the treatment, TQ improved passive avoidance memory, increased the average number of simultaneous firing of spikes/bins, improved the integrity of BBB, and decreased brain water content in the animal model of HE. Furthermore, the results indicated that treatment with TQ decreased the levels of inflammatory cytokines (TNF-α and IL-1β) but increased the levels of glutathione (GSH) and anti-inflammatory cytokine (IL-10) of the surviving cells in the hippocampal tissues. This study demonstrates that TQ may have beneficial therapeutic effects on cognitive, oxidative stress, neuroinflammatory, and histological complications of HE in rat.

Heteromeric Amino Acid Transporters in Brain: from Physiology to Pathology

In humans, more than 50 transporters are responsible for the traffic and balance of amino acids within and between cells and tissues, and half of them have been associated with disease [1]. Covering all common amino acids, Heteromeric Amino acid Transporters (HATs) are one class of such transporters. This review first highlights structural and functional studies that solved the atomic structure of HATs and revealed molecular clues on substrate interaction. Moreover, this review focuses on HATs that have a role in the central nervous system (CNS) and that are related to neurological diseases, including: (i) LAT1/CD98hc and its role in the uptake of branched chain amino acids trough the blood brain barrier and autism. (ii) LAT2/CD98hc and its potential role in the transport of glutamine between plasma and cerebrospinal fluid. (iii) y⁺LAT2/CD98hc that is emerging as a key player in hepatic encephalopathy. xCT/CD98hc as a potential therapeutic target in glioblastoma, and (iv) Asc-1/CD98hc as a potential therapeutic target in pathologies with alterations in NMDA glutamate receptors.

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.

Ammonia exposition during gestation induces neonatal oxidative damage in the brain and long-term cognitive alteration in rats

Ammonia is involved in the pathogenesis of neurological conditions associated with hyperammonemia, including hepatic encephalopathy. Few is known about the effects of gestational exposition to ammonia in the developing brain, and the possible long-term consequences of such exposure. We aimed to evaluate the effects of ammonia exposure during the gestation and the possible long-term cognitive alterations on pups. Eight female rats were divided into two groups: (1) control (saline solution); (2) ammonia (ammonium acetate, 2,5mmol/Kg). Each rat received a single subcutaneous injection during all gestational period. The brains from 1-day-old rats were obtained to the determination of thiobarbituric acid reactive species (TBARS), protein carbonyl and nitrite/nitrate levels. Some animals were followed 30 days after delivery and were subjected to the step-down inhibitory avoidance task. It was observed a significant increase in protein carbonyl, but not TBARS or nitrite/nitrate levels, in pups exposed to ammonia. Rats exposed to ammonia presented long-term cognitive impairment. Gestational exposition to ammonia induces protein oxidative damage in the neonatal rat brain, and long-term cognitive impairment.

Curcumin prevents cognitive deficits in the bile duct ligated rats

RATIONALE

Bile duct ligation (BDL) in rodents can cause impaired liver function and cognition deficits. Curcumin has shown a preventive and therapeutic role in memory impairment.

OBJECTIVES

Therefore, this study aimed to explore the effect of curcumin on the performance of male adult Wistar rats that underwent BDL, a model of hepatic encephalopathy (HE) in the Morris water maze (MWM).

METHODS

Four weeks after surgery, sham (manipulation of common bile duct without ligation) and BDL rats underwent the MWM test.

RESULTS

The representative data showed that BDL rats exhibited impairments in spatial learning and reference memory in the MWM compared with the sham rats. Treatment of BDL rats with curcumin (40 mg/kg, i.p., for 4 weeks) prevented these impairments, while it did not affect spatial learning and memory in the sham rats, by itself. Curcumin increased expression levels of the pro-survival B cell lymphoma extra-large (Bcl-xL) gene and two genes involved in mitochondrial function, peroxisome proliferative-activated receptor-γ co-activator 1α (PGC-1α) and mitochondrial transcription factor A (TFAM), in the hippocampus of BDL rats compared with the vehicle-treated sham or BDL rats, while it decreased the pro-apoptotic Bcl-2-associated X protein (Bax) gene expression level. BDL up-regulated Bax and down-regulated TFAM, by itself. Furthermore, curcumin reduced the mRNA level of Bax, while it increased Bcl-2 and TFAM mRNA levels.

CONCLUSIONS

These findings demonstrate the beneficial effect of curcumin on cognitive function in BDL rats of the HE model. The curcumin effect may be related to mitochondrial function improvement in the HE.

Mechanisms of ammonium-induced neurotoxicity. Neuroprotective effect of alpha-2 adrenergic agonists

Here we report the effects of ammonium on the main biophysical features of neurons and astrocytes during the first minutes of exposure. We found that ammonium causes the depolarization of neurons, which leads to the generation of high-frequency action potentials (APs). The initial alkalization and subsequent acidification of the intracellular medium in neurons occur along with the generation of calcium oscillations. Moreover, although the kinetics of calcium response of neurons and astrocytes is different, the dynamics of changes in the intracellular pH (pH_i) is similar. The rate of superoxide production and mitochondrial membrane potential do not change in most neurons and astrocytes during ammonium exposure. At the same time, we observed an increased superoxide production and a decrease in the mitochondrial potential in some neurons in response to ammonium application. However, in both cases, the amplitude of the calcium response in these neurons is significantly higher compared to other neurons. Application of UK 14,304, an agonist of alpha-2 adrenergic receptors (A-2ARs), decreased the frequency of APs upon ammonium-induced high-frequency spike activity. Moreover, we also observed periods of hyperpolarization occurred in individual neurons. We suppose that this hyperpolarization contributes to the suppression of activity and can be mediated by astrocytic GABA release, which is stimulated upon activation of A-2ARs. Thus, our findings reveal a new possible mechanism of the protective action of alpha-2 adrenergic agonists against ammonium-induced hyperexcitation and demonstrate the correlation between intracellular calcium concentration, mitochondrial membrane potential, pH_i, the intensity of superoxide production in hippocampal cells under acute hyperammonemia.

Giant African snail genomes provide insights into molluscan whole-genome duplication and aquatic-terrestrial transition

Whole-genome duplication (WGD), contributing to evolutionary diversity and environmental adaptability, has been observed across a wide variety of eukaryotic groups, but not in molluscs. Molluscs are the second largest animal phylum in terms of species numbers, and among the organisms that have successfully adapted to the nonmarine realm through aquatic-terrestrial (A-T) transition. We assembled a chromosome-level reference genome for Achatina immaculata, a globally invasive species, and compared the genomes of two giant African snails (A. immaculata and Achatina fulica) to other available mollusc genomes. Macrosynteny, colinearity blocks, Ks peak and Hox gene clusters collectively suggested a WGD event in the two snails. The estimated WGD timing (~70 million years ago) was close to the speciation age of the Sigmurethra-Orthurethra (within Stylommatophora) lineage and the Cretaceous-Tertiary (K-T) mass extinction, indicating that the WGD may have been a common event shared by all Sigmurethra-Orthurethra species and conferred ecological adaptability allowing survival after the K-T extinction event. Furthermore, the adaptive mechanism of WGD in terrestrial ecosystems was confirmed by the presence of gene families related to the respiration, aestivation and immune defence. Several mucus-related gene families expanded early in the Stylommatophora lineage, and the haemocyanin and phosphoenolpyruvate carboxykinase families doubled during WGD, and zinc metalloproteinase genes were highly tandemly duplicated after WGD. This evidence suggests that although WGD may not have been the direct driver of the A-T transition, it played an important part in the terrestrial adaptation of giant African snails.

Role of Oxidative Stress in Hepatic and Extrahepatic Dysfunctions during Nonalcoholic Fatty Liver Disease (NAFLD)

Nonalcoholic fatty liver disease (NAFLD) is a pathology that contains a broad liver dysfunctions spectrum. These alterations span from noninflammatory isolated steatosis until nonalcoholic steatohepatitis (NASH), a more aggressive form of the disease characterized by steatosis, inflammatory status, and varying liver degrees fibrosis. NAFLD is the most prevalent chronic liver disease worldwide. The causes of NAFLD are diverse and include genetic and environmental factors. The presence of NASH is strongly associated with cirrhosis development and hepatocellular carcinoma, two conditions that require liver transplantation. The liver alterations during NAFLD are well described. Interestingly, this pathological condition also affects other critical tissues and organs, such as skeletal muscle and even the cardiovascular, renal, and nervous systems. Oxidative stress (OS) is a harmful state present in several chronic diseases, such as NAFLD. The purpose of this review is to describe hepatic and extrahepatic dysfunctions in NAFLD. We will also review the influence of OS on the physiopathological events that affect the critical function of the liver and peripheral tissues.

Acute ammonia poisoning in dolly varden char (Salvelinus malma) and effect of methionine sulfoximine

Ammonia is toxic to most bony fishes. However, little information is available on the toxicology mechanisms induced by ammonia and the means to mitigate the effects by various fishes. In this study, four groups of experiments were designed and carried out to test the response of dolly varden char to ammonia toxicity and their mitigation through methionine sulfoximine (MSO). NaCl group was injected with NaCl, NH₃ group was injected with ammonium acetate, NH₃+MSO group was injected with ammonium acetate and MSO, MSO group was injected with MSO. Results showed that ammonia toxicity could lead to blood deterioration (elevation in white blood cell and blood ammonia), free amino acid imbalance (elevation in glutamine, glutamate, arginine and ornithine, coupled with reduction of citrulline and aspartate), ammonia metabolism enzyme activity inhibition (reduction in carbamyl phosphate synthetase, ornithine transcarbamylase and arginase), oxidative stress (reduction in superoxide dismutase, catalase and glutathione peroxidase) and immunosuppression (reduction in lysozyme, 50% hemolytic complement, total immunoglobulin and phagocytic index), but the MSO can eliminate fatal effect of oxidative damage. In addition, ammonia poisoning could induce down-regulation of antioxidant enzymes coding genes (SOD, CAT and GPx) and up-regulation of inflammatory cytokine genes (TNFα, IL-1β and IL-8) transcription, suggesting that immunosuppression and inflammation may relate to oxidative stress in fish.

Acute Liver Failure Induces Glial Reactivity, Oxidative Stress and Impairs Brain Energy Metabolism in Rats

Acute liver failure (ALF) implies a severe and rapid liver dysfunction that leads to impaired liver metabolism and hepatic encephalopathy (HE). Recent studies have suggested that several brain alterations such as astrocytic dysfunction and energy metabolism impairment may synergistically interact, playing a role in the development of HE. The purpose of the present study is to investigate early alterations in redox status, energy metabolism and astrocytic reactivity of rats submitted to ALF. Adult male Wistar rats were submitted either to subtotal hepatectomy (92% of liver mass) or sham operation to induce ALF. Twenty-four hours after the surgery, animals with ALF presented higher plasmatic levels of ammonia, lactate, ALT and AST and lower levels of glucose than the animals in the sham group. Animals with ALF presented several astrocytic morphological alterations indicating astrocytic reactivity. The ALF group also presented higher mitochondrial oxygen consumption, higher enzymatic activity and higher ATP levels in the brain (frontoparietal cortex). Moreover, ALF induced an increase in glutamate oxidation concomitant with a decrease in glucose and lactate oxidation. The increase in brain energy metabolism caused by astrocytic reactivity resulted in augmented levels of reactive oxygen species (ROS) and Poly [ADP-ribose] polymerase 1 (PARP1) and a decreased activity of the enzymes superoxide dismutase and glutathione peroxidase (GSH-Px). These findings suggest that in the early stages of ALF the brain presents a hypermetabolic state, oxidative stress and astrocytic reactivity, which could be in part sustained by an increase in mitochondrial oxidation of glutamate.

Exchange-mode glutamine transport across CNS cell membranes

CNS cell membranes possess four transporters capable of exchanging Lglutamine (Gln) for other amino acids: the large neutral amino acid (LNAA) transporters LAT1 and LAT2, the hybrid basic amino acid (L-arginine (Arg), L-leucine (Leu)/LNAA transporter y⁺LAT2, and the L-alanine/L-serine/L-cysteine transporter 2 (ASCT2). LAT1/LAT2 and y⁺LAT2 are present in astrocytes, neurons and the blood brain barrier (BBB) - forming cerebral vascular endothelial cells (CVEC), while the location of ASCT2 in the individual cell types is a matter of debate. In the healthy brain, contribution of the exchangers to Gln shuttling from astrocytes to neurons and thus their role in controlling the conversion of Gln to the amino acid neurotransmitters l-glutamate (Glu) and γ-aminobutyric acid (GABA) and Gln flux across the BBB appears negligible as compared to the system A and system N uniporters. Insofar, except for the contribution of LAT1 to the maintenance of Gln homeostasis in the interstitial fluid (ISF), no well-defined CNS-specific function has been established for either of the three transporters in the healthy brain. The Gln-accepting amino acid exchangers appear to gain significance under conditions of excessive brain Gln load (glutaminosis). Excess Gln efflux across the BBB enhances influx into the brain of L-tryptophan (Trp). Excess of Trp is responsible for overloading the brain with neuroactive compounds: serotonin, kynurenic acid, quinolinic acid and/or oxindole, which contribute to neurotransmission imbalance accompanying hyperammonemia. In turn, alterations of y⁺LAT2-mediated Gln/Arg exchange and Arg uptake in astrocyte, modulate astrocytic nitric oxide synthesis and oxidative/nitrosative stress in ammonia-overexposed brain. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

Modulation of lipid metabolism in juvenile yellow catfish (Pelteobagrus fulvidraco) as affected by feeding frequency and environmental ammonia

In the intensive culture systems, excessive feeding leads to ammonia accumulation, which results in lipid metabolism disorder. However, little information is available on the modulation of lipid metabolism in fish as affected by feeding frequency and ammonia stress. In this study, weight gain increased as feeding frequency increased from one to four times daily, but feed conversion ratio is opposite. The highest survival was found in ammonia group when fish was fed two times daily. Liver ammonia content increased as feeding frequency increased from one to four times daily, and the highest brain ammonia content was found when fish was fed four times daily. The highest liver 6-phospho-gluconate dehydrogenase (6PGD), fatty acid synthase (FAS), carnitine palmitoyltransferase (CPT), and lipoprotein lipase (LPL) contents were found in control group when fish was fed four times daily; in comparison, the highest liver 6PGD, FAS, CPT, and LPL contents were found in ammonia group when fish was fed two times daily. Liver 6PGD, FAS, CPT 1, SREBP-1, and PPARα mRNA expression in control group increased significantly as feeding frequency increased from one to four times daily, and the highest expression of 6PGD, G6PD, and FAS was observed in ammonia group when fish was fed two times daily. This study indicated that the optimal feeding frequency is two times daily when yellow catfish exposed to ammonia.

Pathogenesis of Hepatic Encephalopathy in Chronic Liver Disease

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome that occurs during chronic liver disease (CLD). While ammonia and other precipitating factors in liver disease including inflammation, bile acids, oxidative stress, and lactate play a role in the pathogenesis of HE, the exact mechanism that leads to HE is not fully understood. Notably, accumulating evidence points toward a synergic effect rather than independent actions among precipitating factors that contributes to the development and severity of HE in CLD. Hence, this review is aimed to briefly discuss the single and synergic interplay of pathological factors in the progression and severity of HE.

Effects of acute ammonia toxicity on oxidative stress, immune response and apoptosis of juvenile yellow catfish Pelteobagrus fulvidraco and the mitigation of exogenous taurine

Ammonia can easily form in intensive culture systems due to ammonification of uneaten food and animal excretion, which usually brings detrimental health effects to fish. However, little information is available on the mechanisms of the detrimental effects of ammonia stress and mitigate means in fish. In this study, the four experimental groups were carried out to test the response of yellow catfish to ammonia toxicity and their mitigation through taurine: group 1 was injected with NaCl, group 2 was injected with ammonium acetate, group 3 was injected with ammonium acetate and taurine, and group 4 was injected taurine. The results showed that ammonia poisoning could induce ammonia, glutamine, glutamate and malondialdehyde accumulation, and subsequently lead to blood deterioration (red blood cell, hemoglobin and serum biochemical index reduced), oxidative stress (superoxide dismutase and catalase activities declined) and immunosuppression (lysozyme, 50% hemolytic complement, total immunoglobulin, phagocytic index and respiratory burst reduced), but the exogenous taurine could mitigate the adverse effect of ammonia poisoning. In addition, ammonia poisoning could induce up-regulation of antioxidant enzymes (Cu/Zn-SOD, CAT, GPx and GR), inflammatory cytokines (TNF, IL-1 and IL-8) and apoptosis (p53, Bax, caspase 3 and caspase 9) genes transcription, suggesting that cell apoptotic and inflammation may relate to oxidative stress. This result will be helpful to understand the mechanism of aquatic toxicology induced by ammonia in fish.

Umbelliferone prevents oxidative stress, inflammation and hematological alterations, and modulates glutamate-nitric oxide-cGMP signaling in hyperammonemic rats

Hepatic encephalopathy (HE) is a serious neuropsychiatric complication that occurs as a result of liver failure. Umbelliferone (UMB; 7-hydroxycoumarin) is a natural product with proven hepatoprotective activity; however, nothing has yet been reported on its protective effect against hyperammonemia, the main culprit behind the symptoms of HE. Here, we evaluated the effect of UMB against ammonium chloride (NH₄Cl)-induced hyperammonemia, oxidative stress, inflammation and hematological alterations in rats. We demonstrated the modulatory role of UMB on the glutamate-nitric oxide (NO)-cGMP pathways in the cerebrum of rats. Rats received intraperitoneal injections of NH₄Cl (3 times/week) for 8 weeks and concomitantly received 50 mg/kg UMB. NH₄Cl-induced rats showed significantly elevated blood ammonia and liver function markers. Lipid peroxidation and NO were increased in the liver and cerebrum of rats while the antioxidant defenses were declined. UMB significantly reduced blood ammonia, liver function markers, lipid peroxidation and NO, and enhanced the antioxidant defenses in NH₄Cl-induced rats. UMB significantly prevented anemia, leukocytosis, thrombocytopenia and prolongation of PT and aPTT. Hyperammonemic rats showed elevated levels of cerebral TNF-α, IL-1β and glutamine as well as increased activity and expression of Na⁺/K⁺-ATPase, effects that were significantly reversed by UMB. In addition, UMB down-regulated nitric oxide synthase and soluble guanylate cyclase in the cerebrum of hyperammonemic rats. In conclusion, this study provides evidence that UMB protects against hyperammonemia via attenuation of oxidative stress and inflammation. UMB prevents hyperammonemia associated hematological alterations and therefore represents a promising protective agent against the deleterious effects of excess ammonia.

Extracellular Cyclic GMP Modulates Membrane Expression of The GluA1 and GluA2 Subunits of AMPA Receptor in Cerebellum: Molecular Mechanisms Involved

There is increasing evidence that extracellular cGMP modulates glutamatergic neurotransmission and some forms of learning. However, the underlying mechanisms remain unknown. We proposed the hypotheses that extracellular cGMP may regulate membrane expression of AMPA receptors. To do this extracellular cGMP should act on a membrane protein and activate signal transduction pathways modulating phosphorylation of the GluA1 and/or GluA2 subunits. It has been shown that extracellular cGMP modulates glycine receptors. The aims of this work were to assess: 1) whether extracellular cGMP modulates membrane expression of GluA1 and GluA2 subunits of AMPA receptors in cerebellum in vivo; 2) whether this is mediated by glycine receptors; 3) the role of GluA1 and GluA2 phosphorylation and 4) identify steps of the intracellular pathways involved. We show that extracellular cGMP modulates membrane expression of GluA1 and GluA2 in cerebellum in vivo and unveil the mechanisms involved. Extracellular cGMP reduced glycine receptor activation, modulating cAMP, protein kinases and phosphatases, and GluA1 and GluA2 phosphorylation, resulting in increased GluA1 and reduced GluA2 membrane expression. Extracellular cGMP therefore modulates membrane expression of AMPA receptors and glutamatergic neurotransmission. The steps identified may be therapeutic targets to improve neurotransmission and neurological function in pathological situations with abnormal glutamatergic neurotransmission.

Perfusion with carbon monoxide does not affect extracellular glutamate in dialysates of the hippocampus of freely moving mice

Carbon monoxide (CO) produces several neurological effects, including cognitive, mood, and behavioral disturbance. Glutamate is thought to play a particularly important role in learning and memory. Thus, the present study was aimed at investigating the local effect of CO on the glutamate level in the hippocampus of mice using in vivo reverse microdialysis. Mice were perfused with Ringer's solution (control) or CO (60-125 μM) in Ringer's solution into the hippocampus via microdialysis probe. Dialysate samples were collected every 20 min, and then analyzed with high-performance liquid chromatography coupled to an electrochemical detector. The result revealed that the perfusion with CO had no significant effect on glutamate levels (p = 0.316) as compared to the control group. This finding does not support a local CO rise as the cause of the increased glutamate level in the hippocampus of mice.

TNFα induced up-regulation of Na+,K+,2Cl- cotransporter NKCC1 in hepatic ammonia clearance and cerebral ammonia toxicity

The devastating consequences of hepatic failure include hepatic encephalopathy, a severe, life threatening impairment of neuronal function. Hepatic encephalopathy is caused by impaired hepatic clearance of NH₄⁺. Cellular NH₄⁺ uptake is accomplished mainly by the Na⁺,K⁺,2Cl⁻ cotransporter. Here we show that hepatic clearance of NH₄⁺ is impaired in TNFα deficient as well as TNFR1&TNFR2 double knockout mice, which both develop hyperammonemia. Despite impaired hepatic clearance of NH₄⁺, TNFα deficient mice and TNFR1 deficient mice were protected against acute ammonia intoxication. While 54% of the wild-type mice and 60% of TNFR2 deficient mice survived an NH₄⁺ load, virtually all TNFα deficient mice and TNFR1 deficient mice survived the treatment. Conversely, TNFα treatment of wild type mice sensitized the animals to the toxic effects of an NH₄⁺ load. The protection of TNFα-deficient mice against an NH₄⁺ load was paralleled by decreased cerebral expression of NKCC1. According to the present observations, inhibition of TNFα formation and/or NKCC1 may be strategies to favorably influence the clinical course of hepatic encephalopathy.

Commiphora molmol Modulates Glutamate-Nitric Oxide-cGMP and Nrf2/ARE/HO-1 Pathways and Attenuates Oxidative Stress and Hematological Alterations in Hyperammonemic Rats

Hyperammonemia is a serious complication of liver disease and may lead to encephalopathy and death. This study investigated the effects of Commiphora molmol resin on oxidative stress, inflammation, and hematological alterations in ammonium chloride- (NH₄Cl-) induced hyperammonemic rats, with an emphasis on the glutamate-NO-cGMP and Nrf2/ARE/HO-1 signaling pathways. Rats received NH₄Cl and C. molmol for 8 weeks. NH₄Cl-induced rats showed significant increase in blood ammonia, liver function markers, and tumor necrosis factor-alpha (TNF-α). Concurrent supplementation of C. molmol significantly decreased circulating ammonia, liver function markers, and TNF-α in hyperammonemic rats. C. molmol suppressed lipid peroxidation and nitric oxide and enhanced the antioxidant defenses in the liver, kidney, and cerebrum of hyperammonemic rats. C. molmol significantly upregulated Nrf2 and HO-1 and decreased glutamine and nitric oxide synthase, soluble guanylate cyclase, and Na⁺/K⁺-ATPase expression in the cerebrum of NH₄Cl-induced hyperammonemic rats. Hyperammonemia was also associated with hematological and coagulation system alterations. These alterations were reversed by C. molmol. Our findings demonstrated that C. molmol attenuates ammonia-induced liver injury, oxidative stress, inflammation, and hematological alterations. This study points to the modulatory effect of C. molmol on glutamate-NO-cGMP and Nrf2/ARE/HO-1 pathways in hyperammonemia. Therefore, C. molmol might be a promising protective agent against hyperammonemia.

Xanthine dehydrogenase-1 silencing in Aedes aegypti mosquitoes promotes a blood feeding-induced adulticidal activity

Aedesaegypti has 2 genes encoding xanthine dehydrogenase (XDH). We analyzed XDH1 and XDH2 gene expression by real-time quantitative PCR in tissues from sugar- and blood-fed females. Differential XDH1 and XDH2 gene expression was observed in tissues dissected throughout a time course. We next exposed females to blood meals supplemented with allopurinol, a well-characterized XDH inhibitor. We also tested the effects of injecting double-stranded RNA (dsRNA) against XDH1, XDH2, or both. Disruption of XDH by allopurinol or XDH1 by RNA interference significantly affected mosquito survival, causing a disruption in blood digestion, excretion, oviposition, and reproduction. XDH1-deficient mosquitoes showed a persistence of serine proteases in the midgut at 48 h after blood feeding and a reduction in the uptake of vitellogenin by the ovaries. Surprisingly, analysis of the fat body from dsRNA-XDH1-injected mosquitoes fell into 2 groups: one group was characterized by a reduction of the XDH1 transcript, whereas the other group was characterized by an up-regulation of several transcripts, including XDH1, glutamine synthetase, alanine aminotransferase, catalase, superoxide dismutase, ornithine decarboxylase, glutamate receptor, and ammonia transporter. Our data demonstrate that XDH1 plays an essential role and that XDH1 has the potential to be used as a metabolic target for Ae.aegypti vector control.-Isoe, J., Petchampai, N., Isoe, Y. E., Co, K., Mazzalupo, S., Scaraffia, P. Y. Xanthine dehydrogenase-1 silencing in Aedes aegypti mosquitoes promotes a blood feeding-induced adulticidal activity.

Cortical Synaptic Transmission and Plasticity in Acute Liver Failure Are Decreased by Presynaptic Events

Neurological symptoms of acute liver failure (ALF) reflect decreased excitatory transmission, but the status of ALF-affected excitatory synapse has not been characterized in detail. We studied the effects of ALF in mouse on synaptic transmission and plasticity ex vivo and its relation to distribution of (i) synaptic vesicles (sv) and (ii) functional synaptic proteins within the synapse. ALF-competent neurological and biochemical changes were induced in mice with azoxymethane (AOM). Electrophysiological characteristics (long-term potentiation, whole-cell recording) as well as synapse ultrastructure were evaluated in the cerebral cortex. Also, sv were quantified in the presynaptic zone by electron microscopy. Finally, presynaptic proteins in the membrane-enriched (P2) and cytosolic (S2) fractions of cortical homogenates were quantitated by Western blot. Slices derived from symptomatic AOM mice presented a set of electrophysiological correlates of impaired transmitter release including decreased field potentials (FPs), increased paired-pulse facilitation (PPF), and decreased frequency of spontaneous and miniature excitatory postsynaptic currents (sEPSCs/mEPSCs) accompanied by reduction of the spontaneous transmitter release-driving protein, vti1A. Additionally, an increased number of sv per synapse and a decrease of P2 content and/or P2/S2 ratio for sv-associated proteins, i.e. synaptophysin, synaptotagmin, and Munc18–1, were found, in spite of decreased content of the sv-docking protein, syntaxin-1. Slices from AOM-treated asymptomatic mice showed impaired long-term potentiation (LTP) and increased PPF but no changes in transmitter release or presynaptic protein composition. Our findings demonstrate that a decrease of synaptic transmission in symptomatic ALF is associated with inefficient recruitment of sv proteins and/or impaired sv trafficking to transmitter release sites.

Intracerebral Administration of S-Adenosylhomocysteine or S-Adenosylmethionine Attenuates the Increases in the Cortical Extracellular Levels of Dimethylarginines Without Affecting cGMP Level in Rats with Acute Liver Failure

Alterations in brain nitric oxide (NO)/cGMP synthesis contribute to the pathogenesis of hepatic encephalopathy (HE). An increased asymmetrically dimethylated derivative of L-arginine (ADMA), an endogenous inhibitor of NO synthases, was observed in plasma of HE patients and animal models. It is not clear whether changes in brain ADMA reflect its increased local synthesis therefore affecting NO/cGMP pathway, or are a consequence of its increased peripheral blood content. We measured extracellular concentration of ADMA and symmetrically dimethylated isoform (SDMA) in the prefrontal cortex of control and thioacetamide (TAA)-induced HE rats. A contribution of locally synthesized dimethylarginines (DMAs) in their extracellular level in the brain was studied after direct infusion of the inhibitor of DMAs synthesizing enzymes (PRMTs), S-adenosylhomocysteine (AdoHcy, 2 mM), or the methyl donor, S-adenosylmethionine (AdoMet, 2 mM), via a microdialysis probe. Next, we analyzed whether locally synthesized ADMA attains physiological significance by determination of extracellular cGMP. The expression of PRMT-1 was also examined. Concentration of ADMA and SDMA, detected by positive mode electrospray LC-DMS-MS/MS, was greatly enhanced in TAA rats and was decreased (by 30 %) after AdoHcy and AdoMet infusion. TAA-induced increase (by 40 %) in cGMP was unaffected after AdoHcy administration. The expression of PRMT-1 in TAA rat brain was unaltered. The results suggest that (i) the TAA-induced increase in extracellular DMAs may result from their effective synthesis in the brain, and (ii) the excess of extracellular ADMA does not translate into changes in the extracellular cGMP concentration and implicate a minor role in brain NO/cGMP pathway control.

Characterization of seizures induced by acute exposure to an organophosphate herbicide, glufosinate-ammonium

Glufosinate-ammonium (GLA), the active component of a widely used herbicide, induces convulsions in rodents and humans. In mouse, intraperitoneal treatment with 75 mg/kg GLA generates repetitive tonic-clonic seizures associated with 100% mortality within 72 h after treatment. In this context, we characterized GLA-induced seizures, their histological consequences and the effectiveness of diazepam treatment. Epileptic discharges on electroencephalographic recordings appeared simultaneously in the hippocampus and the cerebral cortex. Diazepam treatment at 6 h immediately stopped the seizures and prevented animal death. However, intermittent seizures were recorded on electroencephalogram from 6 h after diazepam treatment until 24 h, but had disappeared after 15 days. In our model, neuronal activation (c-Fos immunohistochemistry) was observed 6 h after GLA exposure in the dentate gyrus, CA1, CA3, amygdala, piriform and entorhinal cortices, indicating the activation of the limbic system. In these structures, Fluoro-Jade C and Cresyl violet staining did not show neuronal suffering. However, astroglial activation was clearly observed at 24 h and 15 days after GLA treatment in the amygdala, piriform and entorhinal cortices by PCR quantitative, western blot and immunohistochemistry. Concomitantly, glutamine synthetase mRNA expression (PCR quantitative), protein expression (western blot) and enzymatic activity were upregulated. In conclusion, our study suggests that GLA-induced seizures: (a) involved limbic structures and (b) induced astrocytosis without neuronal degeneration as an evidence of a reactive astrocyte beneficial effect for neuronal protection.

Acute ammonia toxicity in crucian carp Carassius auratus and effects of taurine on hyperammonemia

The four experimental groups were carried out to test the response of crucian carp Carassius auratus to ammonia toxicity and taurine: group 1 was injected with NaCl, group 2 was injected with ammonium acetate, group 3 was injected with ammonium acetate and taurine, and group 4 was injected with taurine. Fish in group 2 had the highest ammonia and glutamine contents, and the lowest glutamate content in liver and brain. Serum superoxide dismutase (SOD), glutathione (GSH) activities, red cell count (RBC), white cell count (WBC), lysozyme (LYZ) activity, complement C3 content of fish in group 2 reflected the lowest, but malondialdehyde content was the highest. Importantly, serum SOD and GSH activites, RBC, WBC, and LYZ activity, C3, C4 and total immunoglobulin contents of fish in group 3 were significantly higher than those of fish in group 2. This study indicates that ammonia exerts its toxic effects by interfering with amino acid transport, inducing ROS generation, leading to malondialdehyde accumulation and immunosuppression of crucian carp. The exogenous taurine could mitigate the adverse effect of high ammonia level on fish physiological disorder.

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

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

Asymmetric Dimethylarginine and Hepatic Encephalopathy: Cause, Effect or Association?

The methylated derivative of l-arginine, asymmetric dimethylarginine (ADMA) is synthesized in different mammalian tissues including the brain. ADMA acts as an endogenous, nonselective, competitive inhibitor of all three isoforms of nitric oxide synthase (NOS) and may limit l-arginine supply from the plasma to the enzyme via reducing its transport by cationic amino acid transporters. Hepatic encephalopathy (HE) is a relatively frequently diagnosed complex neuropsychiatric syndrome associated with acute or chronic liver failure, characterized by symptoms linked with impaired brain function leading to neurological disabilities. The l-arginine—nitric oxide (NO) pathway is crucially involved in the pathomechanism of HE via modulating important cerebral processes that are thought to contribute to the major HE symptoms. Specifically, activation of this pathway in acute HE leads to an increase in NO production and free radical formation, thus, contributing to astrocytic swelling and cerebral edema. Moreover, the NO-cGMP pathway seems to be involved in cerebral blood flow (CBF) regulation, altered in HE. For this reason, depressed NO-cGMP signaling accompanying chronic HE and ensuing cGMP deficit contributes to the cognitive and motor failure. However, it should be remembered that ADMA, a relatively little known element limiting NO synthesis in HE, may also influence the NO-cGMP pathway regulation. In this review, we will discuss the contribution of ADMA to the regulation of the NO-cGMP pathway in the brain, correlation of ADMA level with CBF and cognitive alterations observed during HE progression in patients and/or animal models of HE.

Naringin regulates glutamate-nitric oxide cGMP pathway in ammonium chloride induced neurotoxicity

Naringin, plant bioflavonoid extracted mainly from grapefruit and other related citrus species. This study was designed to assess the neuroprotective effect of naringin on ammonium chloride (NH₄Cl) induced hyperammonemic rats. Experimental hyperammonemia was induced by intraperitonial injection (i.p) of NH₄Cl (100mg/kg body weight (b.w.)) thrice a week for 8 consecutive weeks. Hyperammonemic rats were treated with naringin (80mg/kg b.w.) via oral gavage. Naringin administration drastically restored the levels of blood ammonia, plasma urea, nitric oxide (NO), glutamate, glutamine, lipid peroxidation, lipid profile, activities of liver marker enzymes, antioxidant status and sodium/potassium-ATPase (Na⁺/K⁺-ATPase). In addition, naringin supplementation reverted back the pathological changes of liver, brain and kidney tissues, the expressions of Glutamine synthetase (GS), Na⁺/K⁺-ATPase, neuronal nitric oxide (nNOS) and soluble guanylate cyclase (sGC) in hyperammonemic rats. Hence, this study suggested that nargingin exhibited their protective effect against NH₄Cl induced toxicity via enhancing the activities of antioxidant enzymes and inhibiting the lipid peroxidation process. Take together, this study provides data that naingin effectively reduced neurotoxicity by attenuating hyperammonemia, suggesting that naringin act as a potential therapeutic agent to treat hyperammonemic rats.

Neurotoxicity of Ammonia

Abnormal liver function has dramatic effects on brain functions. Hyperammonemia interferes profoundly with brain metabolism, astrocyte volume regulation, and in particular mitochondrial functions. Gene expression in the brain and excitatory and inhibitory neurotransmission circuits are also affected. Experiments with a number of pertinent animal models have revealed several potential mechanisms which could underlie the pathological phenomena occurring in hepatic encephalopathy.

Novel effect of Daflon and low-dose γ-radiation in modulation of thioacetamide-induced hepatic encephalopathy in male albino rats

This study was designed to evaluate the hepato and neuroprotective activity of Daflon and low-dose γ radiation on thioacetamide (TAA)-induced liver damage and hepatic encephalopathy (HE) in rats. Effect of daily Daflon treatment (100 mg/kg body weight, Per OS (p.o.) for consecutive 3 days) and/or fractionated low-dose γ-radiation (LDR; 0.25 Gy, twice the total dose of 0.5 Gy at the 1st and 3rd day, respectively) was evaluated against TAA (300 mg/kg, intraperitoneal × 3) induced liver damage and HE in rats. Serum aspartate transaminase, alanine transaminase, γ-glutamyltransferase, total bilirubin, ammonia, and manganese were estimated to evaluate liver function. In addition, malondialdehyde (MDA) as well as reduced glutathione (GSH), glutathione peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT) were determined to assess antioxidant capacity in liver tissue. Moreover, hepatic apoptotic markers (cysteine-dependent aspartate-directed proteases 3, 8 (caspase-3, 8) and cytochrome C) were estimated to indicate hepatic apoptosis. HE was evaluated through the determination of whole brain ammonia, manganese, MDA, GSH, GPX, SOD, CAT, and caspase-3. The cognitive and locomotor deficits were assessed via step through passive avoidance test, activity cage (actophotometer), γ-aminobutyric acid, and N-methyl-d-aspartate/adenosine triphosphate-neuronal nitric oxide synthase/nitric oxide-cyclic guanosine monophosphate axis in rats' cerebella and hippocampi. The involvement of hypoxia inducible factor-1α, aquaporine-4, and matrix metalloproteinase 9 in association with the brain water content (%) in the whole brain as an index for brain edema was also evaluated. The obtained results showed a marked amelioration of the aforementioned biochemical parameters and behavioral tasks which is supported by histopathological and immunohistochemical examination. It could be concluded that Daflon and LDR afforded hepatoprotection and neuroprotection against TAA-induced acute liver damage and HE.

Multifactorial Effects on Different Types of Brain Cells Contribute to Ammonia Toxicity

Effects of ammonia on astrocytes play a major role in hepatic encephalopathy, acute liver failure and other diseases caused by increased arterial ammonia concentrations (e.g., inborn errors of metabolism, drug or mushroom poisoning). There is a direct correlation between arterial ammonia concentration, brain ammonia level and disease severity. However, the pathophysiology of hyperammonemic diseases is disputed. One long recognized factor is that increased brain ammonia triggers its own detoxification by glutamine formation from glutamate. This is an astrocytic process due to the selective expression of the glutamine synthetase in astrocytes. A possible deleterious effect of the resulting increase in glutamine concentration has repeatedly been discussed and is supported by improvement of some pathologic effects by GS inhibition. However, this procedure also inhibits a large part of astrocytic energy metabolism and may prevent astrocytes from responding to pathogenic factors. A decrease of the already low glutamate concentration in astrocytes due to increased synthesis of glutamine inhibits the malate-aspartate shuttle and energy metabolism. A more recently described pathogenic factor is the resemblance between NH₄⁺ and K⁺ in their effects on the Na⁺,K⁺-ATPase and the Na⁺,K⁺, 2 Cl^- and water transporter NKCC1. Stimulation of the Na⁺,K⁺-ATPase driven NKCC1 in both astrocytes and endothelial cells is essential for the development of brain edema. Na⁺,K⁺-ATPase stimulation also activates production of endogenous ouabains. This leads to oxidative and nitrosative damage and sensitizes NKCC1. Administration of ouabain antagonists may accordingly have therapeutic potential in hyperammonemic diseases.

Ammonia toxicity induces glutamine accumulation, oxidative stress and immunosuppression in juvenile yellow catfish Pelteobagrus fulvidraco

A study was carried to test the response of yellow catfish for 28 days under two ammonia concentrations. Weight gain of fish exposure to high and low ammonia abruptly increased at day 3. There were no significant changes in fish physiological indexes and immune responses at different times during 28-day exposure to low ammonia. Fish physiological indexes and immune responses in the treatment of high ammonia were lower than those of fish in the treatment of low ammonia. When fish were exposed to high ammonia, the ammonia concentration in the brain increased by 19-fold on day 1. By comparison, liver ammonia concentration reached its highest level much earlier at hour 12. In spite of a significant increase in brain and liver glutamine concentration, there was no significant change in glutamate level throughout the 28-day period. The total superoxide dismutase (SOD), glutathione peroxidase (GPX) and glutathione reductase (GR) activities in the brain gradually decreased from hour 0 to day 28. Liver SOD, GPX and GR activities reached the highest levels at hour 12, and then gradually decreased. Thiobarbituric acid reactive substance brain and liver content gradually increased throughout the 28-day period. Lysozyme, acid phosphatase and alkaline phosphatase activities in the liver reached exceptionally low levels after day 14. This study indicated that glutamine accumulation in the brain was not the major cause of ammonia poisoning, the toxic reactive oxygen species is not fully counter acted by the antioxidant enzymes and immunosuppression is a process of gradual accumulation of immunosuppressive factors.