Interaction of oxidative stress, astrocyte swelling and cerebral ammonia toxicity

Protective effect of menthol against thioacetamide-induced hepatic encephalopathy by suppressing oxidative stress and inflammation, augmenting expression of BDNF and α7-nACh receptor, and improving spatial memory

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome that can occur in people with acute or chronic liver disease. Here, we investigated the effects of menthol, a natural monoterpene, on HE induced by thioacetamide (TA) in male Wistar rats. The rats received 200 mg/kg of TA twice a week for four weeks and were administered 10 mg/kg of menthol intraperitoneally daily for the same period. The results showed that menthol treatment reduced oxidative stress and inflammation in the livers and hippocampi of the rats that received TA. It also lowered the levels of ammonium and liver enzymes AST, ALT, ALP, and GGT in the serum of these animals and prevented liver histopathological damage. In addition, the expression and activity of acetylcholinesterase in the hippocampus of HE model rats were decreased by menthol. Likewise, this monoterpene reduced the expression of TLR4, MyD88, and NF-κB in the hippocampus while increasing the expression of BDNF and α7-nACh receptor. Menthol also reduced neuronal death in the hippocampal cornu ammonis-1 and dentate gyrus regions and reduced astrocyte swelling, which led to improved learning and spatial memory in rats with HE. In conclusion, the study suggests that menthol may have strong protective effects on the liver and brain, making it a potential treatment for HE and neurodegenerative diseases.

The Contributions of Thrombospondin-1 to Epilepsy Formation

Epilepsy is a neural network disorder caused by uncontrolled neuronal hyperexcitability induced by an imbalance between excitatory and inhibitory networks. Abnormal synaptogenesis plays a vital role in the formation of overexcited networks. Recent evidence has confirmed that thrombospondin-1 (TSP-1), mainly secreted by astrocytes, is a critical cytokine that regulates synaptogenesis during epileptogenesis. Furthermore, numerous studies have reported that TSP-1 is also involved in other processes, such as angiogenesis, neuroinflammation, and regulation of Ca2+ homeostasis, which are closely associated with the occurrence and development of epilepsy. In this review, we summarize the potential contributions of TSP-1 to epilepsy development.

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.

The interaction of ammonia and manganese in abnormal metabolism of minimal hepatic encephalopathy: A comparison metabolomics study

This study was to investigate the effects of ammonia and manganese in the metabolism of minimal hepatic encephalopathy (MHE). A total of 32 Sprague-Dawley rats were divided into four subgroups: chronic hyperammonemia (CHA), chronic hypermanganese (CHM), MHE and control group (CON). 1H-NMR-based metabolomics was used to detect the metabolic changes. Sparse projection to latent structures discriminant analysis was used for identifying and comparing the key metabolites. Significant elevated blood ammonia were shown in the CHA, CHM, and MHE rats. Significant elevated brain manganese (Mn) were shown in the CHM, and MHE rats, but not in the CHA rats. The concentrations of γ-amino butyric acid (GABA), lactate, alanine, glutamate, glutamine, threonine, and phosphocholine were significantly increased, and that of myo-inositol, taurine, leucine, isoleucine, arginine, and citrulline were significantly decreased in the MHE rats. Of all these 13 key metabolites, 10 of them were affected by ammonia (including lactate, alanine, glutamate, glutamine, myo-inositol, taurine, leucine, isoleucine, arginine, and citrulline) and 5 of them were affected by manganese (including GABA, lactate, myo-inositol, taurine, and leucine). Enrichment analysis indicated that abnormal metabolism of glutamine and TCA circle in MHE might be affected by the ammonia, and abnormal metabolism of GABA might be affected by the Mn, and abnormal metabolism of glycolysis and branched chain amino acids metabolism might be affected by both ammonia and Mn. Both ammonia and Mn play roles in the abnormal metabolism of MHE. Chronic hypermanganese could lead to elevated blood ammonia. However, chronic hyperammonemia could not lead to brain Mn deposition.

SB332235, a CXCR2 antagonist, ameliorates thioacetamide-induced hepatic encephalopathy through modulation of the PI3K/AKT pathways in rats

RATIONALE

Hepatic encephalopathy (HE) is a neuropsychiatric disorder that results from either acute or chronic liver failure. CXCR2 plays an essential role in the pathophysiology of liver and brain diseases. In the present study, the potential beneficial effects of SB332235, a selective inhibitor of CXCR2, against HE were evaluated.

METHODS

HE was induced in male rats by thioacetamide injection (200 mg/kg, i.p.) at three alternative days. SB332235 was injected in rats 1 h before TAA at a dose of 1 and 3 mg/kg i.p.

RESULTS

SB332235 alleviated oxidative stress as shown by the decreased serum NO and reduced MDA, elevated GSH and SOD levels, and reduced TNF-α and NF-κB levels in both brain and liver tissues of rats. Additionally, SB332235 suppressed brain ASK-1, JNK, IL-8, and caspase-3 expression, and activated PI3K/AKT expression in brain tissues. Markers of brain dysfunction, such as ammonia, and markers of hepatic injury, such as LDH, albumin, bilirubin, γGT, AST, ALT, and ALP, were significantly ameliorated. Also, the protective effect of SB332235 was confirmed by histological examination of both brain and liver tissues.

CONCLUSIONS

Both doses (1 and 3 mg/kg) of SB332235 revealed significant hepatic/neuroprotective effects due to their anti-inflammatory, antioxidant, and antiapoptotic activities via activation of the PI3K/AKT pathway. Between the two, the 1 mg/kg dose provided significantly improved outcomes.

Protocatechuic acid protects against thioacetamide-induced chronic liver injury and encephalopathy in mice via modulating mTOR, p53 and the IL-6/ IL-17/ IL-23 immunoinflammatory pathway

Protocatechuic acid (PCA), a natural phenolic acid, is known for antioxidant, anti-inflammatory, anti-apoptotic, and anti-fibrotic activities. However, the protective mechanisms of PCA on thioacetamide (TAA)-induced liver/brain injury are not well addressed. Chronic liver injury was induced in mice by intraperitoneal injection of TAA (200 mg/kg, 3 times/week) for 8 weeks. Simultaneously, PCA (100, 150 mg/kg/day, p.o.) was given daily from the 4th week. Protocatechuic acid ameliorated liver and brain damage indicated by the decrease in serum activities of aminotransferases, gamma-glutamyl transferase, alkaline phosphatase, lactate dehydrogenase, levels of bilirubin, and ammonia concomitant with restoration of normal albumin levels. Additionally, PCA treatment ameliorated oxidative stress in liver and brain, confirmed by the decrease in malondialdehyde and nitric oxide levels and the increase in antioxidant activities. Moreover, PCA showed anti-inflammatory actions through downregulation of TNF-α expression in the liver and IL-6/IL-17/IL-23 levels in the brain, which is confirmed by the decrease in CD4⁺ T brain cell numbers. Most importantly, PCA treatment showed a significant decrease in mTOR level and number of LC3 positive cells in both liver and brain tissues. Consequently, PCA could inhibit mTOR-induced apoptosis, as it showed anti-apoptotic actions through downregulation of caspase-3 expression in liver and p53 expression in liver and brain. Furthermore, liver and brain tissues of treated mice showed restoration of normal histology. It can be concluded that, several mechanisms, including: antioxidant, anti-inflammatory, anti-autophagic and anti-apoptotic activities can be implicated in the hepato- and neuroprotective potentials of PCA.

Role of ammonia for brain abnormal protein glycosylation during the development of hepatitis B virus-related liver diseases

Background

Ammonia is the most typical neurotoxin in hepatic encephalopathy (HE), but the underlying pathophysiology between ammonia and aberrant glycosylation in HE remains unknown.

Results

Here, we used HBV transgenic mice and astrocytes to present a systems-based study of glycosylation changes and corresponding enzymes associated with the key factors of ammonia in HE. We surveyed protein glycosylation changes associated with the brain of HBV transgenic mice by lectin microarrays. Upregulation of Galβ1-3GalNAc mediated by core 1 β1,3-galactosyltransferase (C1GALT1) was identified as a result of ammonia stimulation. Using in vitro assays, we validated that upregulation of C1GALT1 is a driver of deregulates calcium (Ca²⁺) homeostasis by overexpression of inositol 1,4,5-trisphosphate receptor type 1 (IP3R1) in astrocytes.

Conclusions

We demonstrated that silencing C1GALT1 could depress the IP3R1 expression, an effective strategy to inhibit the ammonia-induced upregulation of Ca²⁺ activity, thereby C1GALT1 and IP3R1 may serve as therapeutic targets in hyperammonemia of HE.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00751-4.

Metabolic reprogramming during hyperammonemia targets mitochondrial function and postmitotic senescence

Ammonia is a cytotoxic metabolite with pleiotropic molecular and metabolic effects, including senescence induction. During dysregulated ammonia metabolism, which occurs in chronic diseases, skeletal muscle becomes a major organ for nonhepatocyte ammonia uptake. Muscle ammonia disposal occurs in mitochondria via cataplerosis of critical intermediary metabolite α-ketoglutarate, a senescence-ameliorating molecule. Untargeted and mitochondrially targeted data were analyzed by multiomics approaches. These analyses were validated experimentally to dissect the specific mitochondrial oxidative defects and functional consequences, including senescence. Responses to ammonia lowering in myotubes and in hyperammonemic portacaval anastomosis rat muscle were studied. Whole-cell transcriptomics integrated with whole-cell, mitochondrial, and tissue proteomics showed distinct temporal clusters of responses with enrichment of oxidative dysfunction and senescence-related pathways/proteins during hyperammonemia and after ammonia withdrawal. Functional and metabolic studies showed defects in electron transport chain complexes I, III, and IV; loss of supercomplex assembly; decreased ATP synthesis; increased free radical generation with oxidative modification of proteins/lipids; and senescence-associated molecular phenotype–increased β-galactosidase activity and expression of p16^INK, p21, and p53. These perturbations were partially reversed by ammonia lowering. Dysregulated ammonia metabolism caused reversible mitochondrial dysfunction by transcriptional and translational perturbations in multiple pathways with a distinct skeletal muscle senescence-associated molecular phenotype.

The Role of Nrf2 Transcription Factor and Sp1-Nrf2 Protein Complex in Glutamine Transporter SN1 Regulation in Mouse Cortical Astrocytes Exposed to Ammonia

Ammonia toxicity in the brain primarily affects astrocytes via a mechanism in which oxidative stress (OS), is coupled to the imbalance between glutamatergic and GABAergic transmission. Ammonia also downregulates the astrocytic N system transporter SN1 that controls glutamine supply from astrocytes to neurons for the replenishment of both neurotransmitters. Here, we tested the hypothesis that activation of Nrf2 is the process that links ammonia-induced OS formation in astrocytes to downregulation and inactivation of SN1 and that it may involve the formation of a complex between Nrf2 and Sp1. Treatment of cultured cortical mouse astrocytes with ammonia (5 mM NH₄Cl for 24 h) evoked Nrf2 nuclear translocation, increased its activity in a p38 MAPK pathway-dependent manner, and enhanced Nrf2 binding to Slc38a3 promoter. Nrf2 silencing increased SN1 mRNA and protein level without influencing astrocytic [³H]glutamine transport. Ammonia decreased SN1 expression in Nrf2 siRNA treated astrocytes and reduced [³H]glutamine uptake. In addition, while Nrf2 formed a complex with Sp1 in ammonia-treated astrocytes less efficiently than in control cells, treatment of astrocytes with hybrid-mode inactivated Sp1-Nrf2 complex (Nrf2 silencing + pharmacological inhibition of Sp1) did not affect SN1 protein level in ammonia-treated astrocytes. In summary, the results document that SN1 transporter dysregulation by ammonia in astrocytes involves activation of Nrf2 but does not require the formation of the Sp1-Nrf2 complex.

Differentiation of hepatic encephalopathy from delirium tremens: A case series and review

Hepatic encephalopathy (HE) is an important and potentially life threatening complication in alcoholic patients with decompensated liver function that develop even as they continue drinking. Delirium tremens, on the other hand, is an acute condition resulting from alcohol abstinence in a person dependent on alcohol, making it a life threatening diagnosis that requires intensive care and successful management of the withdrawal. Often in medical wards, these two conditions are mistaken and so is the management plan confused with each other. Making the right diagnosis early on during the hospital course is extremely important in these critical conditions so as to make an appropriate schedule for treatment and a better outcome for the same. A case series of patients who presented with a diagnostic dilemma is reported. Clinical examinations, diagnostic tools to measure the levels of ammonia and liver function tests and hemogram, West Haven criteria and Child-Pugh grading, and clinical scales of these patients are reported. Increased levels of ammonia were present in all the cases. The subtle similarities in the presentation of the two conditions often make it confusing for the clinician to distinguish between them. Using a simple test of measuring ammonia levels in the blood helps in such situations. The detection of raised levels of ammonia in cases of chronic liver disease helps in not just the diagnosis but also is an important prognostic indicator for development of HE.

Altered motor cortical plasticity in patients with hepatic encephalopathy: A paired associative stimulation study

OBJECTIVE

Hepatic encephalopathy (HE) is a potentially reversible brain dysfunction caused by liver failure. Altered synaptic plasticity is supposed to play a major role in the pathophysiology of HE. Here, we used paired associative stimulation with an inter-stimulus interval of 25 ms (PAS25), a transcranial magnetic stimulation (TMS) protocol, to test synaptic plasticity of the motor cortex in patients with manifest HE.

METHODS

23 HE-patients and 23 healthy controls were enrolled in the study. Motor evoked potential (MEP) amplitudes were assessed as measure for cortical excitability. Time courses of MEP amplitude changes after the PAS25 intervention were compared between both groups.

RESULTS

MEP-amplitudes increased after PAS25 in the control group, indicating PAS25-induced synaptic plasticity in healthy controls, as expected. In contrast, MEP-amplitudes within the HE group did not change and were lower than in the control group, indicating no induction of plasticity.

CONCLUSIONS

Our study revealed reduced synaptic plasticity of the primary motor cortex in HE.

SIGNIFICANCE

Reduced synaptic plasticity in HE provides a link between pathological changes on the molecular level and early clinical symptoms of the disease. This decrease may be caused by disturbances in the glutamatergic neurotransmission due to the known hyperammonemia in HE patients.

Glutamine synthetase as a central element in hepatic glutamine and ammonia metabolism: novel aspects

Glutamine synthetase (GS) in the liver is expressed in a small perivenous, highly specialized hepatocyte population and is essential for the maintenance of low, non-toxic ammonia levels in the organism. However, GS activity can be impaired by tyrosine nitration of the enzyme in response to oxidative/nitrosative stress in a pH-sensitive way. The underlying molecular mechanism as investigated by combined molecular simulations and in vitro experiments indicates that tyrosine nitration can lead to a fully reversible and pH-sensitive regulation of protein function. This approach was also used to understand the functional consequences of several recently described point mutations of human GS with clinical relevance and to suggest an approach to restore impaired GS activity.

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.

Amelioration of Hepatic Encephalopathy Using Dunaliella salina Microalgae in Rats: Modulation of Hyperammonemia/TLR4

Hepatic encephalopathy (HE) is a neuropsychiatric disease that is developed as a complication of both acute and chronic liver failure affecting psychomotor dysfunction, memory, and concentration. This study is aimed at evaluating the therapeutic effects of Dunaliella salina (D. salina) microalgae in thioacetamide- (TAA-) induced HE in rats. HE was induced by TAA (200 mg/kg; i.p.) for three successive days. Forty male Wister albino rats were divided into 4 groups; the first group was served as a normal, and the second group was injected with TAA and served as TAA control. The third and fourth groups were administered D. salina (100 and 200 mg/kg; p.o.), respectively, after TAA injection for 7 days. The behavioral and biochemical markers as well as histological aspects of HE were estimated. This study revealed that TAA caused behavioral changes, oxidative stress, neuroinflammation, nuclear pyknosis, and neurons degeneration. D. salina improved liver function and decreased oxidative stress and inflammatory mediator as TLR4 protein expression. Also, D. salina elevated HSP-25 and IGF-1 as well as improved brain histopathological alterations. In conclusion, D. salina exerted a therapeutic potential against HE via its antioxidant, antiinflammatory and cytoprotective effects.

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.

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

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

Systemic Oxidative Stress Markers in Cirrhotic Patients with Hepatic Encephalopathy: Possible Connections with Systemic Ammoniemia

Background and objectives: Oxidative stress shows evidence of dysregulation in cirrhotic patients with hepatic encephalopathy (HE), although there are still controversies regarding the connections between oxidative stress and ammonia in these patients. The aim of this study was to evaluate the oxidative stress implication in overt HE pathogenesis of cirrhotic patients. Materials and Methods: We performed a prospective case-control study, which included 40 patients divided into two groups: group A consisted of 20 cirrhotic patients with HE and increased systemic ammoniemia, and group B consisted of 20 cirrhotic patients with HE and normal systemic ammoniemia. The control group consisted of 21 healthy subjects matched by age and sex. The activity of superoxide dismutase (SOD), glutathione peroxidase (GPx), malondialdehyde (MDA) levels (lipid peroxidation marker), and ammoniemia were evaluated. Results: We found a significant decrease in SOD and GPx activity and also a significant increase of MDA levels in cirrhotic patients with HE as compared to the healthy age-matched control group (1.35 ± 0.08 vs. 0.90 ± 0.08 U/mL, p = 0.002; 0.093 ± 0.06 vs. 0.006 ± 0.008 U/mL, p = 0.001; and 35.94 ± 1.37 vs. 68.90 ± 5.68 nmols/mL, p = 0.0001, respectively). Additionally, we found significant correlations between the main oxidative stress markers and the levels of systemic ammonia (r = 0.452, p = 0.005). Patients from group A had a significant increase of MDA as compared with those from group B (76.93 ± 5.48 vs. 50.06 ± 5.60 nmols/mL, p = 0.019). Also, there was a compensatory increase in the activity of both antioxidant enzymes (SOD and GPx) in patients with increased systemic ammoniemia (group A), as compared to HE patients from group B. Conclusions: Our results demonstrated a significant decrease in antioxidants enzymes activities (SOD and GPx), as well as a significant increase in MDA concentrations, adding new data regarding the influence of oxidative stress in HE pathogenesis in cirrhotic patients.

The Direct Contribution of Astrocytes and Microglia to the Pathogenesis of Hepatic Encephalopathy

Hepatic encephalopathy is a neurological complication resulting from loss of hepatic function and is associated with poor clinical outcomes. During acute liver failure over 20% of mortality can be associated with the development of hepatic encephalopathy. In patients with liver cirrhosis, 1-year survival for those that develop overt hepatic encephalopathy is under 50%. The pathogenesis of hepatic encephalopathy is complicated due to the multiple disruptions in homeostasis that occur following a reduction in liver function. Of these, elevations of ammonia and neuroinflammation have been shown to play a significant contributing role to the development of hepatic encephalopathy. Disruption of the urea cycle following liver dysfunction leads to elevations of circulating ammonia, which enter the brain and disrupt the functioning of astrocytes. This results in dysregulation of metabolic pathways in astrocytes, oxidative stress and cerebral edema. Besides ammonia, circulating chemokines and cytokines are increased following liver injury, leading to activation of microglia and a subsequent neuroinflammatory response. The combination of astrocyte dysfunction and microglia activation are significant contributing factors to the pathogenesis of hepatic encephalopathy.

Increase in P-glycoprotein levels in the blood-brain barrier of partial portal vein ligation /chronic hyperammonemia rats is medicated by ammonia/reactive oxygen species/ERK1/2 activation: In vitro and in vivo studies

Liver failure altered P-glycoprotein (P-gp) function and expression at blood-brain barrier (BBB), partly owing to hyperammonemia. We aimed to examine the effects of partial portal vein ligation (PVL) plus chronic hyperammonemia (CHA) on P-gp function and expression at rat BBB. Experimental rats included sham-operation (SH), PVL, CHA and PVL+CHA. The PVL+CHA rats were developed by ammonia-containing diet for 2 weeks after operation. The brain-to-plasma concentration ratios (K_p) and apparent unidirectional influx constants (K_in) of rhodamine123 and sodium fluorescein were measured to assess function of P-gp and BBB integrity, respectively. Human cerebral microvascular endothelial cells (HCMEC/D3) were used to assess effects of ammonia on P-gp expression and function. It was found that PVL+CHA significantly decreased K_p and K_in of rhodamine123 without affecting brain distribution of fluorescein. The P-gp expressions in membrane protein in cortex and hippocampus were significantly increased in CHA and PVL +CHA rats, especially in PVL + CHA rats, while remarkably increased phosphorylated ERK1/2 was only found in PVL +CHA rats. Expressions of tight junction proteins claudin-5 and occluding in rat brain remained unchanged. In vitro data showed that NH₄Cl increased reactive oxygen species, membrane expression and function of P-gp as well as phosphorylated ERK1/2 levels in HCMEC/D3. The NH₄Cl-induced alterations were reversed by reactive oxygen species scavenger N-acetylcysteine and ERK1/2 inhibitor U0126. In conclusion, PVL+CHA increased function and membrane translocation of P-gp at rat BBB partly via ammonia. Reactive oxygen species/ERK1/2 pathway activation may be one of the reasons that ammonia upregulated P-gp expression and function at BBB.

The role of Branched Chain Amino Acids in the treatment of hepatic Encephalopathy

The relationship between intake of nutrients and Hepatic Encephalopathy (HE) dates back to the historical roots of experimental hepatology. Branched-Chain Amino Acids (BCAA; Isoleucine, leucine and valine) have attracted particular interest and in 1956 Müting described the amino acid pattern in patients with cirrhosis. The abnormal plasma pattern has been characterized by the ratio between BCAA and aromatic amino acids in plasma, the so called 'Fischer´s ratio'. This ratio has been associated with the grade of HE. Under normal conditions, ammonia detoxification predominantly takes place in the liver. When the liver fails, the homeostasis is altered and muscle tissue becomes the main alternative organ for at least temporary detoxification of ammonia. BCAA are believed to support this muscle ammonia detoxification and the ammonia lowering effect of BCAA has been intensely investigated. In this review the effect of BCAA on muscle ammonia metabolism and the protein sparing and anabolic effects of BCAA are discussed. A Cochrane metaanalysis showed that BCAA had beneficial effects on HE with a number needed to treat of 5 patients (RR 0.73, 95% CI 0.61 to 0.88). The combined evidence suggests that although the pathophysiology is poorly understood, there is evidence to support clinical benefits of BCAA. BCAAs enhance muscle mass and exert anabolic effects via stimulation of protein synthesis. The beneficial long-term effects of BCAA on HE could be related to these effects and not only related to Branched-Chain Amino Acid increased ammonia metabolism.

Air-breathing and excretory nitrogen metabolism in fishes

During water-land transition, ancient fishes acquired the ability to breathe air, but air-breathing engendered problems in nitrogenous waste excretion. Nitrogen is a fundamental component of amino acids, proteins, and nucleic acids, and the degradation of these nitrogen-containing compounds releases ammonia. Ammonia is toxic and must be removed. Fishes in water excrete ammonia as the major nitrogenous waste through gills, but gills of air-breathing fishes are modified for air-breathing or largely replaced by air-breathing organs. Notably, fishes emerged from water can no longer excrete ammonia effectively because of a lack of water to flush the gills. Hence, ancient fishes that participated in water-land transition must have developed means to deal with ammonia toxicity. Extant air-breathing fishes, particularly amphibious ones, can serve as models to examine adaptations which might have facilitated the emergence of ancient fishes from water. Some of these fishes can actively emerge from water and display complex behaviors on land, while a few can burrow into mud and survive for years during drought. Many of them are equipped with mechanisms to ameliorate ammonia toxicity during emersion. In this review, the mechanisms adopted by air-breathing fishes to deal with ammonia toxicity during emersion were organized into seven disparate strategies. In addition, eight extant air-breathing fishes with distinctive terrestrial behaviors and peculiar natural habitats were selected to describe in detail how these seven strategies could be adopted in disparate combinations to ameliorate ammonia toxicity during emersion.

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.

Hyperammonemia in Hepatic Encephalopathy

The precise mechanism underlying the neurotoxicity of Hepatic Encephalopathy (HE) is remains unclear. The dominant view has been that gut-derived nitrogenous toxins are not extracted by the diseased liver and thereby enter the brain. Among the various toxins proposed, the case for ammonia is most compelling. Events that lead to increased levels of blood or brain ammonia have been shown to worsen HE, whereas reducing blood ammonia levels alleviates HE. Clinical, pathological, and biochemical changes observed in HE can be reproduced by increasing blood or brain ammonia levels in experimental animals, while exposure of cultured astrocytes to ammonium salts reproduces the morphological and biochemical findings observed in HE. However, factors other than ammonia have recently been proposed to be involved in the development of HE, including cytokines and other blood and brain immune factors. Moreover, recent studies have questioned the critical role of ammonia in the pathogenesis of HE since blood ammonia levels do not always correlate with the level/severity of encephalopathy. This review summarizes the vital role of ammonia in the pathogenesis of HE in humans, as well as in experimental models of acute and chronic liver failure. It further emphasizes recent advances in the molecular mechanisms involved in the progression of neurological complications that occur in acute and chronic liver failure.

Taurine supplementation abates cirrhosis-associated locomotor dysfunction

AIM OF THE STUDY

Hepatic encephalopathy and hyperammonemia is a clinical complication associated with liver cirrhosis. The brain is the target organ for ammonia toxicity. Ammonia-induced brain injury is related to oxidative stress, locomotor activity dysfunction, and cognitive deficit, which could lead to permanent brain injury, coma and death if not appropriately managed. There is no promising pharmacological intervention against cirrhosis-associated brain injury. Taurine (TAU) is one of the most abundant amino acids in the human body. Several physiological and pharmacological roles have been attributed to TAU. TAU may act as an antioxidant and is an excellent neuroprotective agent. This study aimed to evaluate the effect of TAU supplementation on cirrhosis-associated locomotor activity disturbances and oxidative stress in the brain.

MATERIAL AND METHODS

Rats underwent bile duct ligation (BDL) surgery, and plasma and brain ammonia level, plasma biochemical parameters, and rats' locomotor function were monitored. Furthermore, brain tissue markers of oxidative stress were assessed.

RESULTS

It was found that plasma and brain ammonia was increased, and markers of liver injury were significantly elevated in the cirrhotic group. Impaired locomotor activity was also evident in BDL rats. Moreover, an increase in brain tissue markers of oxidative stress was detected in the brain of cirrhotic animals. It was found that TAU supplementation (50, 100, and 200 mg/kg, gavage) alleviated brain tissue markers of oxidative stress and improved animals' locomotor activity.

CONCLUSIONS

These data suggest that TAU is a potential protective agent against cirrhosis-associated brain injury.

Therapeutic Interference With Vascular Calcification-Lessons From Klotho-Hypomorphic Mice and Beyond

Medial vascular calcification, a major pathophysiological process associated with cardiovascular disease and mortality, involves osteo-/chondrogenic transdifferentiation of vascular smooth muscle cells (VSMCs). In chronic kidney disease (CKD), osteo-/chondrogenic transdifferentiation of VSMCs and, thus, vascular calcification is mainly driven by hyperphosphatemia, resulting from impaired elimination of phosphate by the diseased kidneys. Hyperphosphatemia with subsequent vascular calcification is a hallmark of klotho-hypomorphic mice, which are characterized by rapid development of multiple age-related disorders and early death. In those animals, hyperphosphatemia results from unrestrained formation of 1,25(OH)₂D₃ with subsequent retention of calcium and phosphate. Analysis of klotho-hypomorphic mice and mice with vitamin D₃ overload uncovered several pathophysiological mechanisms participating in the orchestration of vascular calcification and several therapeutic opportunities to delay or even halt vascular calcification. The present brief review addresses the beneficial effects of bicarbonate, carbonic anhydrase inhibition, magnesium supplementation, mineralocorticoid receptor (MR) blockage, and ammonium salts. The case is made that bicarbonate is mainly effective by decreasing intestinal phosphate absorption, and that carbonic anhydrase inhibition leads to metabolic acidosis, which counteracts calcium-phosphate precipitation and VSMC transdifferentiation. Magnesium supplementation, MR blockage and ammonium salts are mainly effective by interference with osteo-/chondrogenic signaling in VSMCs. It should be pointed out that the, by far, most efficient substances are ammonium salts, which may virtually prevent vascular calcification. Future research will probably uncover further therapeutic options and, most importantly, reveal whether these observations in mice can be translated into treatment of patients suffering from vascular calcification, such as patients with CKD.

The nature of early astroglial protection-Fast activation and signaling

Our present review is focusing on the uniqueness of balanced astroglial signaling. The balance of excitatory and inhibitory signaling within the CNS is mainly determined by sharp synaptic transients of excitatory glutamate (Glu) and inhibitory γ-aminobutyrate (GABA) acting on the sub-second timescale. Astroglia is involved in excitatory chemical transmission by taking up i) Glu through neurotransmitter-sodium transporters, ii) K⁺ released due to presynaptic action potential generation, and iii) water keeping osmotic pressure. Glu uptake-coupled Na⁺ influx may either ignite long-range astroglial Ca²⁺ transients or locally counteract over-excitation via astroglial GABA release and increased tonic inhibition. Imbalance of excitatory and inhibitory drives is associated with a number of disease conditions, including prevalent traumatic and ischaemic injuries or the emergence of epilepsy. Therefore, when addressing the potential of early therapeutic intervention, astroglial signaling functions combating progress of Glu excitotoxicity is of critical importance. We suggest, that excitotoxicity is linked primarily to over-excitation induced by the impairment of astroglial Glu uptake and/or GABA release. Within this framework, we discuss the acute alterations of Glu-cycling and metabolism and conjecture the therapeutic promise of regulation. We also confer the role played by key carrier proteins and enzymes as well as their interplay at the molecular, cellular, and organ levels. Moreover, based on our former studies, we offer potential prospect on the emerging theme of astroglial succinate sensing in course of Glu excitotoxicity.

PM2.5 Exposure Suppresses Dendritic Maturation in Subgranular Zone in Aged Rats

Detrimental effects of long-term inhalation of fine particulate matter (PM_2.5) on the pulmonary and cardiovascular systems have been widely reported. Recent studies have shown that exposure to PM_2.5 also causes adverse neurocognitive effects. This study investigates the effects of inhaled ammonium sulfate, which is a major compound of inorganic air pollutants in PM_2.5, on adult neurogenesis in aged Sprague-Dawley rats. A total of 20 rats were randomly assigned to experimental (n = 10) and control (n = 10) conditions, wherein they were exposed to either ammonium sulfate or sham air for 2 h per day and for 28 consecutive days. It was observed that ammonium sulfate inhibited the maturation process and diminished dendritic complexity of immature neurons in the subgranular zone (SGZ) of the hippocampus significantly, although the number of neural stem cells or the rates of differentiation were comparable between the two groups. Our findings provide clear evidence on the direct relationship between air quality and advantageous neurogenesis. Exposure to PM leads to specific adverse effects on the maturation process during neurogenesis.

Impaired novelty acquisition and synaptic plasticity in congenital hyperammonemia caused by hepatic glutamine synthetase deficiency

Genetic defects in ammonia metabolism can produce irreversible damage of the developing CNS causing an impairment of cognitive and motor functions. We investigated alterations in behavior, synaptic plasticity and gene expression in the hippocampus and dorsal striatum of transgenic mice with systemic hyperammonemia resulting from conditional knockout of hepatic glutamine synthetase (LGS-ko). These mice showed reduced exploratory activity and delayed habituation to a novel environment. Field potential recordings from LGS-ko brain slices revealed significantly reduced magnitude of electrically-induced long-term potentiation (LTP) in both CA3-CA1 hippocampal and corticostriatal synaptic transmission. Corticostriatal but not hippocampal slices from LGS-ko brains demonstrated also significant alterations in long-lasting effects evoked by pharmacological activation of glutamate receptors. Real-time RT-PCR revealed distinct patterns of dysregulated gene expression in the hippocampus and striatum of LGS-ko mice: LGS-ko hippocampus showed significantly modified expression of mRNAs for mGluR1, GluN2B subunit of NMDAR, and A1 adenosine receptors while altered expression of mRNAs for D1 dopamine receptors, the M1 cholinoreceptor and the acetylcholine-synthetizing enzyme choline-acetyltransferase was observed in LGS-ko striatum. Thus, inborn systemic hyperammonemia resulted in significant deficits in novelty acquisition and disturbed synaptic plasticity in corticostriatal and hippocampal pathways involved in learning and goal-directed behavior.

Impact of Exposure to Fenitrothion on Vital Organs in Rats

This study was designed to investigate the impact of oral administration of fenitrothion (10 mg/kg) on liver, kidney, brain, and lung function in rats. The effect was studied on days 7, 14, 21, 28, and 42. Our results have shown deterioration in liver function as evidenced by the elevation in serum ALT, AST, ALP, and bilirubin and reduction in albumin and hepatic glycogen. This was associated with a state of hyperglycemia and hyperlipidemia and increased prothrombin time, while hemoglobin content was reduced. In addition, the kidney function was reduced as indicated by the elevation in serum creatinine, uric acid, and BUN, while the serum levels of magnesium, potassium, and sodium were reduced. This study also showed an impairment in brain neurotransmitter (elevated 5-HT, glutamate, GABA, and reduced dopamine and norepinephrine level). This was associated with a reduction in the barrier capacity in brain and lung. Fenitrothion also caused a decrease in cholinesterase activity in serum, lung, and brain activity associated with a state of oxidative stress in all tested organs and hyperammonemia. These results support the hazards of pesticide use and shows the importance of minimizing pesticide use or discovering new safe pesticides.

Effect of taurine on chronic and acute liver injury: Focus on blood and brain ammonia

Hyperammonemia is associated with chronic and acute liver injury. There is no promising therapeutic agent against ammonia-induced complications. Hence, finding therapeutic molecules with safe profile of administration has clinical value. The present study was conducted to evaluate the role of taurine (TA) administration on plasma and brain ammonia and its consequent events in different models of chronic and acute liver injury and hyperammonemia. Bile duct ligated (BDL) rats were used as a model of chronic liver injury. Thioacetamide and acetaminophen-induced acute liver failure were used as acute liver injury models. A high level of ammonia was detected in blood and brain of experimental groups. An increase in brain ammonia level coincided with a decreased total locomotor activity of animals and significant changes in the biochemistry of blood and also liver tissue. TA administration (500 and 1000 mg/kg, i.p), effectively alleviated liver injury and its consequent events including rise in plasma and brain ammonia and brain edema. The data suggested that TA is not only a useful and safe agent to preserve liver function, but also prevented hyperammonemia as a deleterious consequence of acute and chronic liver injury.

Electrospun Nanofibers from a Tricyanofuran-Based Molecular Switch for Colorimetric Recognition of Ammonia Gas

A chromophore based on tricyanofuran (TCF) with a hydrazone (H) recognition moiety was developed. Its molecular-switching performance is reversible and has differential sensitivity towards aqueous ammonia at comparable concentrations. Nanofibers were fabricated from the TCF-H chromophore by electrospinning. The film fabricated from these nanofibers functions as a solid-state optical chemosensor for probing ammonia vapor. Recognition of ammonia vapor occurs by proton transfer from the hydrazone fragment of the chromophore to the ammonia nitrogen atom and is facilitated by the strongly electron withdrawing TCF fragment. The TCF-H chromophore was added to a solution of poly(acrylic acid), which was electrospun to obtain a nanofibrous sensor device. The morphology of the nanofibrous sensor was determined by SEM, which showed that nanofibers with a diameter range of 200-450 nm formed a nonwoven mat. The resultant nanofibrous sensor showed very good sensitivity in ammonia-vapor detection. Furthermore, very good reversibility and short response time were also observed.

SIRT5 regulation of ammonia-induced autophagy and mitophagy

In liver the mitochondrial sirtuin, SIRT5, controls ammonia detoxification by regulating CPS1, the first enzyme of the urea cycle. However, while SIRT5 is ubiquitously expressed, urea cycle and CPS1 are only present in the liver and, to a minor extent, in the kidney. To address the possibility that SIRT5 is involved in ammonia production also in nonliver cells, clones of human breast cancer cell lines MDA-MB-231 and mouse myoblast C2C12, overexpressing or silenced for SIRT5 were produced. Our results show that ammonia production increased in SIRT5-silenced and decreased in SIRT5-overexpressing cells. We also obtained the same ammonia increase when using a new specific inhibitor of SIRT5 called MC3482. SIRT5 regulates ammonia production by controlling glutamine metabolism. In fact, in the mitochondria, glutamine is transformed in glutamate by the enzyme glutaminase, a reaction producing ammonia. We found that SIRT5 and glutaminase coimmunoprecipitated and that SIRT5 inhibition resulted in an increased succinylation of glutaminase. We next determined that autophagy and mitophagy were increased by ammonia by measuring autophagic proteolysis of long-lived proteins, increase of autophagy markers MAP1LC3B, GABARAP, and GABARAPL2, mitophagy markers BNIP3 and the PINK1-PARK2 system as well as mitochondrial morphology and dynamics. We observed that autophagy and mitophagy increased in SIRT5-silenced cells and in WT cells treated with MC3482 and decreased in SIRT5-overexpressing cells. Moreover, glutaminase inhibition or glutamine withdrawal completely prevented autophagy. In conclusion we propose that the role of SIRT5 in nonliver cells is to regulate ammonia production and ammonia-induced autophagy by regulating glutamine metabolism.

Carnosine Reduces Oxidative Stress and Reverses Attenuation of Righting and Postural Reflexes in Rats with Thioacetamide-Induced Liver Failure

Cerebral oxidative stress (OS) contributes to the pathogenesis of hepatic encephalopathy (HE). Existing evidence suggests that systemic administration of l-histidine (His) attenuates OS in brain of HE animal models, but the underlying mechanism is complex and not sufficiently understood. Here we tested the hypothesis that dipeptide carnosine (β-alanyl-l-histidine, Car) may be neuroprotective in thioacetamide (TAA)-induced liver failure in rats and that, being His metabolite, may mediate the well documented anti-OS activity of His. Amino acids [His or Car (100 mg/kg)] were administrated 2 h before TAA (i.p., 300 mg/kg 3× in 24 h intervals) injection into Sprague–Dawley rats. The animals were thus tested for: (i) brain prefrontal cortex and blood contents of Car and His, (ii) amount of reactive oxygen species (ROS), total antioxidant capacity (TAC), GSSG/GSH ratio and thioredoxin reductase (TRx) activity, and (iii) behavioral changes (several models were used, i.e. tests for reflexes, open field, grip test, Rotarod). Brain level of Car was reduced in TAA rats, and His administration significantly elevated Car levels in control and TAA rats. Car partly attenuated TAA-induced ROS production and reduced GSH/GSSG ratio, whereas the increase of TRx activity in TAA brain was not significantly modulated by Car. Further, Car improved TAA-affected behavioral functions in rats, as was shown by the tests of righting and postural reflexes. Collectively, the results support the hypothesis that (i) Car may be added to the list of neuroprotective compounds of therapeutic potential on HE and that (ii) Car mediates at least a portion of the OS-attenuating activity of His in the setting of TAA-induced liver failure.

Induction of inducible nitric oxide synthase expression in ammonia-exposed cultured astrocytes is coupled to increased arginine transport by upregulated y(+)LAT2 transporter

One of the aspects of ammonia toxicity to brain cells is increased production of nitric oxide (NO) by NO synthases (NOSs). Previously we showed that ammonia increases arginine (Arg) uptake in cultured rat cortical astrocytes specifically via y(+)L amino acid transport system, by activation of its member, a heteromeric y(+)LAT2 transporter. Here, we tested the hypothesis that up-regulation of y(+)LAT2 underlies ammonia-dependent increase of NO production via inducible NOS (iNOS) induction, and protein nitration. Treatment of rat cortical astrocytes for 48 with 5 mM ammonium chloride ('ammonia') (i) increased the y(+)L-mediated Arg uptake, (ii) raised the expression of iNOS and endothelial NOS (eNOS), (iii) stimulated NO production, as manifested by increased nitrite+nitrate (Griess) and/or nitrite alone (chemiluminescence), and consequently, (iv) evoked nitration of tyrosine residues of proteins in astrocytes. Except for the increase of eNOS, all the above described effects of ammonia were abrogated by pre-treatment of astrocytes with either siRNA silencing of the Slc7a6 gene coding for y(+)LAT2 protein, or antibody to y(+)LAT2, indicating their strict coupling to y(+)LAT2 activity. Moreover, induction of y(+)LAT2 expression by ammonia was sensitive to Nf-κB inhibitor, BAY 11-7085, linking y(+)LAT2 upregulation to the Nf-κB activation in this experimental setting as reported earlier and here confirmed. Importantly, ammonia did not affect y(+)LAT2 expression nor y(+)L-mediated Arg uptake activity in the cultured cerebellar neurons, suggesting astroglia-specificity of the above described mechanism. The described coupling of up-regulation of y(+)LAT2 transporter with iNOS in ammonia-exposed astrocytes may be considered as a mechanism to ensure NO supply for protein nitration. Ammonia (NH4(+)) increases the expression and activity of the L-arginine (Arg) transporter (Arg/neutral amino acids [NAA] exchanger) y(+)LAT2 in cultured rat cortical astrocytes by a mechanism involving activation (nuclear translocation) of the transcription factor nuclear factor-Nuclear factor-κB (Nf-κB-p65). Up-regulation of y(+)LAT2 transporter is coupled with increased inducible nitric oxide synthase (iNOS) expression, which leads to increase nitric oxide (NO) synthesis and protein nitration.

Finasteride Has Regionally Different Effects on Brain Oxidative Stress and Acetylcholinesterase Activity in Acute Thioacetamide-Induced Hepatic Encephalopathy in Rats

Finasteride (FIN) inhibits neurosteroid synthesis and potentially improves the course of hepatic encephalopathy (HE). This study aimed to investigate the effects of FIN on brain oxidative stress and acetylcholinesterase (AchE) activity in acute thioacetamide-induced HE in rats. Male Wistar rats were divided into groups: 1. control; 2. thioacetamide-treated group (TAA; 900 mg/kg); 3. finasteride-treated group (FIN; 150 mg/kg); 4. group treated with FIN and TAA (FIN+TAA). Daily doses of FIN (50 mg/kg) and TAA (300 mg/kg) were administered intraperitoneally during three days and in FIN+TAA group FIN was administered 2h before every dose of TAA. FIN pretreatment prevented TAA-induced rise in malondialdehyde level in the cortex due to restoration of catalase activity and increased expression of superoxide dismutase 1 (SOD1) and induced an increase in malondialdehyde level in the thalamus due to reduction of glutathione peroxidase (GPx) and glutathione reductase (GR) activity. Although FIN pretreatment did not affect malondialdehyde level in hippocampus and caudate nucleus, hippocampal SOD1 expression was higher (p<0.05) and GR activity lower in FIN+TAA vs. TAA group (p<0.05). GPx activity was lower in caudate nucleus in FIN+TAA vs. TAA group (p<0.01). FIN pretreatment prevented TAA-induced rise in AchE activity in the thalamus and caudate nucleus and AchE activity correlates inversely in the thalamus (p<0.05) and positively in caudate nucleus (p<0.01) with malondialdehyde level. FIN has regionally selective effects on oxidative stress and AchE activity in the brain in acute TAA-induced HE in rats. The prooxidant role of FIN in the thalamus may be causally linked with inhibition of AchE.

To Break or to Brake Neuronal Network Accelerated by Ammonium Ions?

Purpose

The aim of present study was to investigate the effects of ammonium ions on in vitro neuronal network activity and to search alternative methods of acute ammonia neurotoxicity prevention.

Methods

Rat hippocampal neuronal and astrocytes co-cultures in vitro, fluorescent microscopy and perforated patch clamp were used to monitor the changes in intracellular Ca²⁺- and membrane potential produced by ammonium ions and various modulators in the cells implicated in neural networks.

Results

Low concentrations of NH₄Cl (0.1–4 mM) produce short temporal effects on network activity. Application of 5–8 mM NH₄Cl: invariably transforms diverse network firing regimen to identical burst patterns, characterized by substantial neuronal membrane depolarization at plateau phase of potential and high-amplitude Ca²⁺-oscillations; raises frequency and average for period of oscillations Ca²⁺-level in all cells implicated in network; results in the appearance of group of «run out» cells with high intracellular Ca²⁺ and steadily diminished amplitudes of oscillations; increases astrocyte Ca²⁺-signalling, characterized by the appearance of groups of cells with increased intracellular Ca²⁺-level and/or chaotic Ca²⁺-oscillations. Accelerated network activity may be suppressed by the blockade of NMDA or AMPA/kainate-receptors or by overactivation of AMPA/kainite-receptors. Ammonia still activate neuronal firing in the presence of GABA(A) receptors antagonist bicuculline, indicating that «disinhibition phenomenon» is not implicated in the mechanisms of networks acceleration. Network activity may also be slowed down by glycine, agonists of metabotropic inhibitory receptors, betaine, L-carnitine, L-arginine, etc.

Conclusions

Obtained results demonstrate that ammonium ions accelerate neuronal networks firing, implicating ionotropic glutamate receptors, having preserved the activities of group of inhibitory ionotropic and metabotropic receptors. This may mean, that ammonia neurotoxicity might be prevented by the activation of various inhibitory receptors (i.e. by the reinforcement of negative feedback control), instead of application of various enzyme inhibitors and receptor antagonists (breaking of neural, metabolic and signaling systems).

Multidrug resistance-associated protein 4 expression in ammonia-treated cultured rat astrocytes and cerebral cortex of cirrhotic patients with hepatic encephalopathy

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome frequently accompanying liver cirrhosis and reflects the clinical manifestation of a low grade cerebral edema associated with cerebral oxidative/nitrosative stress. The multidrug resistance-associated protein (Mrp) 4 is an export pump which transports metabolites that were recently suggested to play a major role in the pathogenesis of HE such as neurosteroids and cyclic nucleotides. We therefore studied Mrp4 expression changes in ammonia-exposed cultured astrocytes and postmortem human brain samples of cirrhotic patients with HE. NH₄ Cl increased Mrp4 mRNA and protein levels in astrocytes in a dose- and time-dependent manner up to threefold after 72 h of exposure and concurrently inhibited N-glycosylation of Mrp4 protein. Upregulation of Mrp4 mRNA and protein as well as impaired N-glycosylation of Mrp4 protein by ammonia were sensitive towards the glutamine-synthetase inhibitor l-methionine-S-sulfoximine and were not induced by CH₃ NH₃ Cl (5 mmol/L). Upregulation of Mrp4 mRNA required ammonia-induced activation of nitric oxide synthases or NADPH oxidase and p38^MAPK -dependent activation of PPARα. Inhibition of Mrp4 by ceefourin 1 synergistically enhanced both, inhibition of astrocyte proliferation as well as transcription of the oxidative stress surrogate marker heme oxygenase 1 by forskolin (10 µmol/L, 72 h) or NH₄ Cl (5 mmol/L, 72 h) in cultured rat astrocytes. Increased Mrp4 mRNA and protein levels were also found in postmortem brain samples from patients with liver cirrhosis with HE but not in those without HE. The data show that Mrp4 is upregulated in HE, which may be relevant for the handling of neurosteroids and cyclic nucleotides in response to ammonia. GLIA 2015;63:2092-2105.

NH4Cl Treatment Prevents Tissue Calcification in Klotho Deficiency

Klotho, a cofactor in suppressing 1,25(OH)2D3 formation, is a powerful regulator of mineral metabolism. Klotho-hypomorphic mice (kl/kl) exhibit excessive plasma 1,25(OH)2D3, Ca(2+), and phosphate concentrations, severe tissue calcification, volume depletion with hyperaldosteronism, and early death. Calcification is paralleled by overexpression of osteoinductive transcription factor Runx2/Cbfa1, Alpl, and senescence-associated molecules Tgfb1, Pai-1, p21, and Glb1. Here, we show that NH4Cl treatment in drinking water (0.28 M) prevented soft tissue and vascular calcification and increased the life span of kl/kl mice >12-fold in males and >4-fold in females without significantly affecting extracellular pH or plasma concentrations of 1,25(OH)2D3, Ca(2+), and phosphate. NH4Cl treatment significantly decreased plasma aldosterone and antidiuretic hormone concentrations and reversed the increase of Runx2/Cbfa1, Alpl, Tgfb1, Pai-1, p21, and Glb1 expression in aorta of kl/kl mice. Similarly, in primary human aortic smooth muscle cells (HAoSMCs), NH4Cl treatment reduced phosphate-induced mRNA expression of RUNX2/CBFA1, ALPL, and senescence-associated molecules. In both kl/kl mice and phosphate-treated HAoSMCs, levels of osmosensitive transcription factor NFAT5 and NFAT5-downstream mediator SOX9 were higher than in controls and decreased after NH4Cl treatment. Overexpression of NFAT5 in HAoSMCs mimicked the effect of phosphate and abrogated the effect of NH4Cl on SOX9, RUNX2/CBFA1, and ALPL mRNA expression. TGFB1 treatment of HAoSMCs upregulated NFAT5 expression and prevented the decrease of phosphate-induced NFAT5 expression after NH4Cl treatment. In conclusion, NH4Cl treatment prevents tissue calcification, reduces vascular senescence, and extends survival of klotho-hypomorphic mice. The effects of NH4Cl on vascular osteoinduction involve decrease of TGFB1 and inhibition of NFAT5-dependent osteochondrogenic signaling.

Brain edema in acute liver failure: mechanisms and concepts

Brain edema and associated increase in intracranial pressure continue to be lethal complications of acute liver failure (ALF). Abundant evidence suggests that the edema in ALF is largely cytotoxic brought about by swelling of astrocytes. Elevated blood and brain ammonia levels have been strongly implicated in the development of the brain edema. Additionally, inflammation and sepsis have been shown to contribute to the astrocyte swelling/brain edema in the setting of ALF. We posit that ammonia initiates a number of signaling events, including oxidative/nitrative stress (ONS), the mitochondrial permeability transition (mPT), activation of the transcription factor (NF-κB) and signaling kinases, all of which have been shown to contribute to the mechanism of astrocyte swelling. All of these factors also impact ion-transporters, including Na(+), K(+), Cl(-) cotransporter and the sulfonylurea receptor 1, as well as the water channel protein aquaporin-4 resulting in a perturbation of cellular ion and water homeostasis, ultimately resulting in astrocyte swelling/brain edema. All of these events are also potentiated by inflammation. This article reviews contemporary knowledge regarding mechanisms of astrocyte swelling/brain edema formation which hopefully will facilitate the identification of therapeutic targets capable of mitigating the brain edema associated with ALF.

O-GlcNAcylation as a novel ammonia-induced posttranslational protein modification in cultured rat astrocytes

Hepatic encephalopathy (HE) is a clinical manifestation of a low grade cerebral edema with a mutual interrelationship between osmotic- and oxidative stress. This leads to RNA oxidation and posttranslational protein modifications such as protein tyrosine nitration with pathophysiological relevance. Here, we report on O-GlcNAcylation as another ammonia-induced posttranslational protein modification in cultured rat astrocytes. NH4Cl induced O-GlcNAcylation of distinct proteins (25-250 kDa) in astrocytes in a dose- and time-dependent manner. Exposure of astrocytes to NH4Cl (5 mmol/l) for 48 h and 72 h significantly increased protein O-GlcNAcylation by about 2-fold and 4-fold, respectively. NH4Cl at a concentration of 1 mmol/l was sufficient to double protein O-GlcNAcylation in astrocytes after 72 h as compared to untreated controls. Ammonia-induced protein O-GlcNAcylation was sensitive towards glutamine-synthetase inhibition by methionine sulfoximine (MSO), but was not induced by hypoosmolarity (205 mosmol/l) or CH3NH3Cl (5 mmol/l). Increased protein O-GlcNAcylation in NH4Cl (5 mmol/l, 48 h)-treated astrocytes was fully reversible within 24 h after withdrawal of NH4Cl from culture medium. Amongst the proteins which are O-GlcNAcylated in response to ammonia, GAPDH was identified. It is concluded that ammonia induces reversible protein O-GlcNAcylation in astrocytes that depends on glutamine synthesis but not on astrocyte swelling per se or ammonia-induced pH-changes. In view of the complex involvement of O-GlcNAcylation in cell regulation, such as energy metabolism, apoptosis and circadian rhythmicity and in pathologies, such as neurodegenerative diseases, O-GlcNAcylation might contribute to the pathophysiology of hepatic encephalopathy.

Astroglial NMDA receptors inhibit expression of Kir4.1 channels in glutamate-overexposed astrocytes in vitro and in the brain of rats with acute liver failure

Astroglial inward rectifying Kir4.1 potassium channels are fundamental for the maintenance of ion and water homeostasis in the central nervous system (CNS). Down-regulation of Kir4.1 expression is observed in CNS disorders associated with excessive extracellular glutamate (Glu) accumulation, including hepatic encephalopathy related to acute liver failure (ALF). Here we demonstrate that prolonged (3 days) treatment of cultured rat cortical astrocytes with 2 mM Glu or 100 µM NMDA decreases the expression of Kir4.1 mRNA and protein. Inhibition by Glu of Kir4.1 mRNA expression was reversed by NMDA receptor antagonists MK-801 and AP-5 (each at 50 µM), and by a non-transportable inhibitor of Glu uptake TBOA (100 µM). MK-801 reversed the inhibitory effect of Glu on Kir4.1 protein expression. In contrast, transcription of Kir4.1 channels was not affected by: (i) a transportable Glu uptake inhibitor PDC (100 µM); (ii) by group I mGluR antagonist MTEP (100 µM); (iii) by antagonists of oxidative-nitrosative stress (ONS) in astrocytes, including the neuroprotective amino acid taurine (Tau; 10 mM), the NADPH oxidase inhibitor apocyanine (APO; 300 µM), the nitric oxide synthase inhibitor, L-NNA (100 µM), and a membrane permeable glutathione precursor, glutathione-diethyl ester (GEE; 3 mM). Down-regulation of Kir4.1 transcription in rats with ALF was attenuated by intraperitoneal administration of a competitive NMDA receptor antagonist memantine, but not by histidine, which reverses ONS associated with ALF. Collectively, the results indicate that over-activation of astroglial NMDA receptors, aided by as yet undefined effects of Glu entry to astrocytes, is a primary cause of the reduction of Kir4.1 expression in CNS disorders associated with increased exposure to Glu.

Ammonia-induced senescence in cultured rat astrocytes and in human cerebral cortex in hepatic encephalopathy

Hepatic encephalopathy (HE) is a frequent complication of liver cirrhosis and is due to a low-grade cerebral edema associated with oxidative/nitrosative stress. Recent reports suggest that cognitive impairment in cirrhotic patients may not resolve completely after an attack of manifest HE. As astrocyte dysfunction is central to the pathogenesis of HE and astrocytes are critically involved in synaptic plasticity, we tested for sustained impairment of astrocyte function by analyzing expression levels of senescence biomarkers in ammonia-treated cultured rat astrocytes and in postmortem brain samples from cirrhotic patients with or without HE. NH4 Cl time- and dose-dependently inhibited proliferation of cultured astrocytes by up to 45% (5 mmol/L, 72 h) and strongly increased senescence-associated β-galactosidase activity. Inhibition of astrocyte proliferation by ammonia was mediated by a l-methionine sulfoximine-, oxidative stress-, and p38(MAPK) -dependent activation of p53 associated with enhanced transcription of cell cycle inhibitory genes GADD45α and p21. Mitochondria and the nucleus were identified as sources of oxygen radical formation after prolonged NH4 Cl exposure. Concurrently, NH4 Cl (5 mmol/L) treatment inhibited both epidermal growth factor- and brain-derived neurotrophic factor (BDNF)-induced proliferation as well as BDNF-mediated astrocyte morphology changes through downregulation of the respective growth factor receptors epidermal growth factor receptor and truncated tyrosine receptor kinase B. Increased mRNA expression levels of senescence-associated genes were also found in post mortem brain samples from patients with liver cirrhosis with HE, but not in those without HE. The data suggest that ammonia toxicity and HE are associated with premature astrocyte senescence, which may impair neurotransmission and contribute to persistence of cognitive disturbances after resolution of episodes of overt HE.

Ephrin/Ephrin receptor expression in ammonia-treated rat astrocytes and in human cerebral cortex in hepatic encephalopathy

Hepatic encephalopathy (HE) represents a neuropsychiatric syndrome, which evolves as a consequence of a low grade cerebral edema and a concomitant oxidative/nitrosative stress response. Ephrin receptors (EphR) and their ligands (ephrins) regulate astrocytic glutamate uptake and gliotransmitter release thereby governing neurotransmission, but their role in HE and ammonia toxicity is unclear. We therefore tested effects of ammonia on expression levels of EphR/ephrin isoforms in cultured rat astrocytes and analysed underlying mechanisms. NH4Cl induced mRNA expression changes of several EphR/ephrin isoforms in a methionine sulfoximine-, NADPH oxidase- and NO synthase-dependent manner in cultured astrocytes. A prominent upregulation was noted for EphR A4 mRNA and protein in NH4Cl-treated astrocytes. NH4Cl-treatment decreased EphR A4 molecular mass to similar extent as found in astrocytes treated with the N-glycosylation inhibitor tunicamycin. Knockdown of EphR A4 by siRNA, or treating astrocytes with NH4Cl or tunicamycin abolished fibroblast growth factor-induced and EphR A4-dependent astrocyte proliferation. NH4Cl-treatment also decreased GLAST mRNA levels in cultured astrocytes. This effect was sensitive to inhibitors of NAPDH oxidase or glutamine synthetase, but was insensitive to siRNA-mediated EphR A4 knockdown. Eph/ephrin gene expression changes were also found in post mortem brain samples of cirrhotic patients without or with HE compared to controls suggesting a potential in vivo relevance of the present findings. The present study suggests that ammonia modulates EphR/ephrin signaling in astrocytes and in the brain of cirrhotic patients with HE with potential implications for deranged neurotransmission in HE.

Oxidative stress as a crucial factor in liver diseases

Redox state constitutes an important background of numerous liver disorders. The redox state participates in the course of inflammatory, metabolic and proliferative liver diseases. Reactive oxygen species (ROS) are primarily produced in the mitochondria and in the endoplasmic reticulum of hepatocytes via the cytochrome P450 enzymes. Under the proper conditions, cells are equipped with special molecular strategies that control the level of oxidative stress and maintain a balance between oxidant and antioxidant particles. Oxidative stress represents an imbalance between oxidant and antioxidant agents. Hepatocytic proteins, lipids and DNA are among the cellular structures that are primarily affected by ROS and reactive nitrogen species. The process results in structural and functional abnormalities in the liver. Thus, the phenomenon of oxidative stress should be investigated for several reasons. First, it may explain the pathogenesis of various liver disorders. Moreover, monitoring oxidative markers among hepatocytes offers the potential to diagnose the degree of liver damage and ultimately to observe the response to pharmacological therapies. The present report focuses on the role of oxidative stress in selected liver diseases.