Neuroinflammation in hepatic encephalopathy: mechanistic aspects

Management of hepatic encephalopathy following transjugular intrahepatic portosystemic shunts: Current strategies and future directions

Transjugular intrahepatic portosystemic shunts (TIPSs) are generally used for the management of complications of portal hypertension in patients with decompensated cirrhosis. However, hepatic encephalopathy (HE), which impairs neuropsychiatric function and motor control, remains the primary adverse effect of TIPS, limiting its utility. Prompt prevention and treatment of post-TIPS HE are critical, as they are strongly associated with readmission rates and poor quality of life. This review focuses on the main pathophysiological mechanisms underlying post-TIPS HE, explores advanced biomarkers and predictive tools, and discusses current management strategies and future directions to prevent or reverse HE following TIPS. These strategies include preoperative patient assessment, individualized shunt diameter optimization, spontaneous portosystemic shunt embolization during the TIPS procedure, postoperative preventive and therapeutic measures such as nutrition management, medical therapy, fecal microbiota transplantation, and stent reduction.

Linking KATP channel activation to p-AKT/mTORC1/eEF2/BDNF axis unravels Nicorandil's promise in countering acetaminophen-induced hepatic encephalopathy in mice

Nicorandil (NIC), an antianginal agent that acts both as an opener of adenosine triphosphate-sensitive potassium (KATP) channels and a nitric oxide donor, has demonstrated protective and curative effects in various diseases. The predominance of these mechanisms varies based on the dose of NIC and the specific organ affected. This study scrutinized the possible beneficial effects of NIC in acetaminophen (APAP)-induced hepatic encephalopathy (HE) model through highlighting the role of KATP channels in mediating these effects. Forty-eight mice were randomly subdivided into four groups: control (saline), APAP model (1 g/kg, i.p.), NIC treatment (15 mg/kg/day p.o. for 14 days), and glibenclamide (GLIB "KATP blocker", 5 mg/kg/day, p.o. 1 h before NIC for 14 days). NIC significantly mitigated APAP-induced liver injury, hyperammonemia, and cognitive deficits, as evidenced by reduced serum alanine aminotransferase, aspartate aminotransferase, ammonia levels, and improved performance in Y-maze and Morris Water Maze tests. Mechanistically, NIC suppressed hippocampal glutamate, activated phosphoserine 473 protein kinase B (p-AKT(Ser473))/mammalian target of rapamycin complex 1 (mTORC1) pathway, lessened the inactive phosphorylation of eukaryotic elongation factor 2 (eEF2), upsurged brain-derived neurotrophic factor (BDNF), leading to reduced neuroinflammation proved by nuclear factor-kappa B and tumor necrosis factor-alpha suppression. Histopathological analyses revealed improved liver and hippocampal morphology, while immunohistochemistry showed reduced astrocyte activation with NIC treatment. These effects were abolished by GLIB pre-treatment, indicating the crucial role of KATP channel. Accordingly, NIC could alleviate APAP-induced liver injury and HE mainly dependent on KATP channel opening, with resultant inhibition of glutamate signaling, activation of p-AKT/mTORC1/eEF2/BDNF trajectory, and abating hippocampal inflammation.

Cell-cell communications in the brain of hepatic encephalopathy: The neurovascular unit

Many patients with liver diseases are exposed to the risk of hepatic encephalopathy (HE). The incidence of HE in liver patients is high, showing various symptoms ranging from mild symptoms to coma. Liver transplantation is one of the ways to overcome HE. However, not all patients can receive liver transplantation. Moreover, patients who have received liver transplantation have limitations in that they are vulnerable to hepatocellular carcinoma, allograft rejection, and infection. To find other therapeutic strategies, it is important to understand pathological factors and mechanisms that lead to HE after liver disease. Oxidative stress, inflammatory response, hyperammonaemia and metabolic disorders seen after liver diseases have been reported as risk factors of HE. These are known to affect the brain and cause HE. These peripheral pathological factors can impair the blood-brain barrier, cause it to collapse and damage the neurovascular unit component of multiple cells, including vascular endothelial cells, astrocytes, microglia, and neurons, leading to HE. Many previous studies on HE have suggested the impairment of neurovascular unit and cell-cell communication in the pathogenesis of HE. This review focuses on pathological factors that appear in HE, cell type-specific pathological mechanisms, miscommunication/incorrect relationships, and therapeutic candidates between brain cells in HE. This review suggests that regulating communications and interactions between cells may be important in overcoming HE.

Edaravone reduces brain injury in hepatic encephalopathy by upregulation of Nrf2/HO-1 and inhibition of NF-κB, iNOS/NO and inflammatory cytokines

BACKGROUND

Brain damage is the most important complication in patients with hepatic encephalopathy (HE). Oxidative stress and inflammation are essential factors in the progression of brain injury caused by HE. The aim of this study was to investigate the potential therapeutic effect of edaravone and its underlying mechanisms against brain injury associated with HE in mice.

METHODS AND RESULTS

HE was induced by the injection of thioacetamide (200 mg/kg) for 2 days and then mice treated with edaravone (10 or 20 mg/kg/day, ip) for four consecutive days. The brain tissues were dissected for histopathological, biochemical, ELISA, RT-qPCR and immunofluorescence analysis. The results showed that edaravone improved the locomotor function and ameliorated brain histopathological changes in mice with HE. Edaravone inhibited oxidative stress markers by increasing the levels of glutathione, catalase, superoxide dismutase, glutathione reductase and the upregulation of nuclear erythroid 2-related factor (Nrf2)/HO-1 pathway in the brain tissue. Administration of edaravone significantly decreased the expression of p-NF-κB and iNOS. Edaravone treatment reduced the levels of NO, MPO and MMP-9 in the brain of mice. Additionally, the brain levels and expressions of inflammatory cytokines IL-1β, IL-6, TNF-α and IFN-γ were downregulated in mice treated with edaravone.

CONCLUSIONS

These results suggest that edaravone exerts significant neuroprotection by modulating of inflammatory and oxidative responses in HE and may serve as a promising agent for the treatment of brain injury associated with HE.

Clinical Implications of Inflammation in Patients With Cirrhosis

Cirrhosis-associated immune dysfunction refers to the concurrent systemic inflammation and immunoparesis evident across the disease spectrum of chronic liver disease, ranging from the low-grade inflammatory plasma milieu that accompanies compensated disease to the intense high-grade inflammatory state with coexistent severe immune paralysis that defines acute decompensation and acute-on-chronic liver failure. Systemic inflammation plays a crucial role in the disease course of cirrhosis and is a key driver for acute decompensation and the progression from compensated to decompensated cirrhosis. Severe systemic inflammation is fundamental to the development of organ dysfunction and failure and, in its most extreme form, acute-on-chronic liver failure. Systemic inflammation propagates the development of hepatic encephalopathy and hepatorenal syndrome-acute kidney injury. It may also be involved in the pathogenesis of further complications such as hepatocellular carcinoma and mental illness. Those patients with the most profound systemic inflammation have the worst prognosis. Systemic inflammation exerts its negative clinical effects through a number of mechanisms including nitric oxide-mediated increased splanchnic vasodilation, immunopathology, and metabolic reallocation.

Activation of the kynurenine pathway identified in individuals with covert hepatic encephalopathy

BACKGROUND

HE is a neuropsychiatric complication of liver disease characterized by systemic elevation in ammonia and proinflammatory cytokines. These neurotoxins cross the blood-brain barrier and cause neuroinflammation, which can activate the kynurenine pathway (KP). This results in dysregulated production of neuroactive KP metabolites, such as quinolinic acid, which is known to cause astrocyte and neuronal death. Our aim was to compare KP activity between patients with covert HE (CHE), patients without encephalopathic cirrhosis (NHE), and healthy controls (HCs).

METHODS

This was a single-center prospective cohort study conducted between 2018 and 2021 at St Vincent's Hospital, Sydney. Overall, 13 patients with CHE, 10 patients with NHE, and 12 with HC were recruited. Patients with cirrhosis were diagnosed with CHE if they scored ≤-4 on the Psychometric Hepatic Encephalopathy Score. KP metabolite levels were quantified on plasma samples via HPLC and gas chromatography/mass spectrometry. One-way Kruskal-Wallis test was used to compare the expression levels of KP enzymes.

RESULTS

KP was highly activated in patients with cirrhosis, demonstrated by higher levels of activity in the rate-limiting enzymes, indoleamine 2,3-dioxygenase, and tryptophan-2,3-dioxygenase in both CHE (65.04±20.72, p=0.003) and patients with NHE (64.85±22.10, p=0.015) compared to HC (40.95±7.301). Higher quinolinic acid concentrations were demonstrated in CHE (3726 nM±3385, p<0.001) and patients with NHE (1788 nM±632.3, p=0.032) compared to HC (624 nM±457). KP activation was positively correlated with inflammatory marker C-reactive protein in patients with CHE (Rs=0.721, p≤0.01).

CONCLUSIONS

KP is highly activated in patients with CHE, resulting in heightened production of neurotoxic metabolites. Dysregulation of the pathway is demonstrable in patients who do not yet show clinical signs of neurocognitive impairment. Therapeutic agents that modulate KP activity may be able to alleviate symptoms of patients with CHE.

Mechanism of Alzheimer type II astrocyte development in hepatic encephalopathy

Type C hepatic encephalopathy (Type C HE) is a major and complex neurological condition that occurs following chronic liver failure. The molecular basis of Type C HE remains elusive. Type C HE is characterized by mental confusion, cognitive and motor disturbances. The presence of Alzheimer type II astrocytes (AT2A) is the key histopathological finding observed in Type C HE. However, nothing is currently known regarding AT2A development and its involvement in cognitive, and motor deficits in Type C HE. We, therefore, examined in rats the mechanisms by which liver failure contributes to the progression of AT2A, and its role in the development of cognitive and motor deficits in thioacetamide (TAA) model of Type C HE. We and others earlier reported increased oxidative/nitrosative stress (ONS), JNK1/2, and cMyc activation in ammonia-treated astrocyte cultures, as well as in brains from chronic liver failure. We now found increased levels of astrocytic glia maturation factor (GMF, a factor strongly implicated in neuroinflammation), as well as various inflammatory factors (IL-1β, TNF-α, IL-6, MMP-3, COX2, CXCL1, and PGE2), and reduced levels of GFAP and increased levels of aggregated nuclear protein Lamin A/C in rat brain cortex post-chronic liver failure. We also found increased levels of GMF and inflammatory factors (MMP-3, COX2, CXCL1, and PGE2) in astrocytes post-ammonia treatment in vitro. Additionally, pharmacological inhibition of upstream signaling of GMF (ONS, JNK1/2, and cMyc) or GMF inhibitors W-7 and trifluoperazine significantly reduced the levels of inflammatory factors, the number of AT2A cells, as well as the cognitive and motor deficits in TAA-treated rats. Increased levels of GMF were also identified in human post-mortem brain sections. These findings strongly suggest that increased levels of astrocytic GMF due to elevated levels of ONS, JNK1/2, and cMyc and the subsequent inflammation contribute to the development of AT2A and the consequent cognitive, and motor deficits in chronic liver failure.

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.

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.

Therapeutic Effect of Levetiracetam Against Thioacetamide-Induced Hepatic Encephalopathy Through Inhibition of Oxidative Stress and Downregulation of NF-κB, NLRP3, iNOS/NO, Pro-Inflammatory Cytokines and Apoptosis

Hepatic encephalopathy (HE) is a serious brain disorder which associated with neurological and psychiatric manifestations. Oxidative stress and neuroinflammation and apoptosis play main roles in the development of brain damage in HE. Levetiracetam is an antiseizure drug with established antioxidant and anti-inflammatory activities. In the present study we investigated the therapeutic effects of levetiracetam against brain injury in HE and its underlying mechanisms of action. Male C57BL/6 mice were subjected to the induction of HE by the injection of thioacetamide (200 mg/kg) for 2 days. Mice were treated with levetiracetam at two doses (50 or 100 mg/kg/day) for 3 days in the treatment groups. Animals were subjected to a behavioral test and the brain tissues were dissected for histopathological, biochemical, gene expression and immunofluorescence analysis. The results showed that levetiracetam alleviated body weight loss and improved locomotor activity of mice with HE. Levetiracetam treatment decreased the histopathological changes, lipid peroxidation and protein carbonylation while restored the antioxidants (GSH, SOD and CAT) in the brain. Levetiracetam decreased the expression and activity of NF-κB, NOD-like receptor pyrin domain-containing protein 3 (NLRP3) and pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IFN-γ) in the brain tissue. Administration of levetiracetam inhibited iNOS/NO pathway and myeloperoxidase (MPO) activity in the brain. Moreover, caspase-3 was decreased and the ratio of Bcl2/Bax was increased in the brain of mice treated with levetiracetam. These findings suggest that levetiracetam may be a promising therapeutic agent for brain injury in HE through inhibiting the oxidative, inflammatory and apoptotic pathways.

Effect of an Autotaxin Inhibitor, 2-(4-Chlorophenyl)-7-methyl-8-pentylimidazo[1,2-a] Pyrimidin-5(8H)-one (CBT-295), on Bile Duct Ligation-Induced Chronic Liver Disease and Associated Hepatic Encephalopathy in Rats

The role of autotaxin (ATX)-lysophosphatidic acid (LPA) is yet to be explored in the context of liver cirrhosis and associated encephalopathy. Our objective of this study was to evaluate the role of an ATX inhibitor in biliary cirrhosis and associated hepatic encephalopathy in rats. The preliminary investigation revealed significant impairment in liver function, which eventually led to the development of hepatic encephalopathy. Interestingly, LPA levels were significantly increased in the plasma, liver, and brain of rats following bile duct ligation. Subsequently, we tested the efficacy of an ATX inhibitor, CBT-295, in bile duct-induced biliary cirrhosis and neuropsychiatric symptoms associated with hepatic encephalopathy. CBT-295 showed good oral bioavailability and favorable pharmacokinetic properties. CBT-295 exhibited a significant reduction in inflammatory cytokines like TGF-β, TNF-α, and IL-6 levels, also reduced bile duct proliferation marker CK-19, and lowered liver fibrosis, as evident from reduced collagen deposition. The reversal of liver fibrosis with CBT-295 led to a reduction in blood and brain ammonia levels. Furthermore, CBT-295 also reduced neuroinflammation induced by ammonia, which is characterized by a significant reduction in brain cytokine levels. It improved neuropsychiatric symptoms such as locomotor activities, cognitive impairment, and clinical grading scores associated with hepatic encephalopathy. The improvement in hepatic encephalopathy observed with the ATX inhibitor could be the result of its hepatoprotective action and its ability to attenuate neuroinflammation. Therefore, inhibition of ATX-LPA signaling can be a multifactorial approach for the treatment of chronic liver diseases.

Gut microbiome-brain-cirrhosis axis

Cirrhosis is characterized by inflammation, degeneration, and fibrosis of liver tissue. Along with being the most common cause of liver failure and liver transplant, cirrhosis is a significant risk factor for several neuropsychiatric conditions. The most common of these is HE, which is characterized by cognitive and ataxic symptoms, resulting from the buildup of metabolic toxins with liver failure. However, cirrhosis patients also show a significantly increased risk for neurodegenerative diseases such as Alzheimer and Parkinson diseases, and for mood disorders such as anxiety and depression. In recent years, more attention has been played to communication between the ways the gut and liver communicate with each other and with the central nervous system, and the way these organs influence each other's function. This bidirectional communication has come to be known as the gut-liver-brain axis. The gut microbiome has emerged as a key mechanism affecting gut-liver, gut-brain, and brain-liver communication. Clinical studies and animal models have demonstrated the significant patterns of gut dysbiosis when cirrhosis is present, both with or without concomitant alcohol use disorder, and have provided compelling evidence that this dysbiosis also influences the cognitive and mood-related behaviors. In this review, we have summarized the pathophysiological and cognitive effects associated with cirrhosis, links to cirrhosis-associated disruption of the gut microbiome, and the current evidence from clinical and preclinical studies for the modulation of the gut microbiome as a treatment for cirrhosis and associated neuropsychiatric conditions.

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

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

Bacterial DNA Translocation Is Associated With Overt Hepatic Encephalopathy and Mortality in Patients With Cirrhosis

INTRODUCTION

Data on the relationship between bacterial translocation, hepatic encephalopathy (HE), and mortality are scarce. This study aimed to assess the association between bacterial DNA (bactDNA) translocation, inflammatory response, ammonia levels, and severity of HE in patients with cirrhosis, as well as the role of bactDNA translocation in predicting mortality.

METHODS

Cirrhotic patients without bacterial infection were prospectively enrolled between June 2022 and January 2023. Grading of HE was classified by the West Haven Criteria and Psychometric Hepatic Encephalopathy Score ≤ -5.

RESULTS

Overall, 294 cirrhotic patients were enrolled, with 92 (31.3%) and 58 (19.7%) having covert and overt HE, respectively. BactDNA translocation was detected in 36.1% of patients (n = 106). Patients with overt HE had more bactDNA translocation and higher serum lipopolysaccharide-binding protein (LBP), tumor necrosis factor-α, interleukin-6 (IL-6), and ammonia levels than those without HE. Patients with detectable bactDNA had higher white cell counts and serum LBP and IL-6 levels than those without. By contrast, bactDNA, serum LBP, and soluble CD14 levels were comparable between patients with covert HE and those without HE. The multivariate Cox regression analysis revealed that bactDNA translocation (hazard ratio [HR] = 2.49, 95% confidence interval [CI]: 1.22-5.11), Model for End-Stage Liver Disease score (HR = 1.12, 95% CI: 1.09-1.16), age (HR = 1.05, 95% CI: 1.000-1.002), and baseline IL-6 (HR = 1.001, 95% CI: 1.000-1.002) were independent factors associated with 6-month mortality.

DISCUSSION

Apart from hyperammonemia, bactDNA translocation is a possible factor associated with overt HE in cirrhotic patients. BactDNA translocation and IL-6 are independent factors associated with 6-month mortality.

Cinnamaldehyde/lactulose combination therapy alleviates thioacetamide-induced hepatic encephalopathy via targeting P2X7R-mediated NLRP3 inflammasome signaling

AIMS

Cinnamaldehyde (CA), the main active constituent of cinnamon oil, is reported to have neuroprotective effects. However, the potential benefits of CA for brain protection in hepatic encephalopathy (HE) are still not understood. Thus, the present study investigates the possible ameliorative effect of CA (70 mg/kg/day, I.P.) either alone or in combination with lactulose (Lac) (5.3 g/kg/day, oral) against thioacetamide (TAA)-induced hepatic encephalopathy in rats.

MATERIALS AND METHODS

For induction of HE, TAA (200 mg/kg) was intraperitoneally administered for 1 week at alternative days. CA, Lac and Lac+CA were administered for 14 days prior to and for further 7 days together with TAA injection.

KEY FINDINGS

CA, Lac and Lac+CA combination effectively attenuated TAA-induced HE; as indicated by the improvement in behavioral tests, mitigation of pathological abnormalities in both liver and brain, the significant reduction in serum hyperammonemia and amelioration in liver function biomarkers; ALT and AST. This was accompanied with a substantial restoration of redox state in liver and brain; MDA and GSH levels. Moreover, CA, Lac and Lac+CA combination reduced neuroinflammation as demonstrated by the notable attenuation of P2X7R, NLRP3, caspase-1, IL-1β, GFAP and Iba1 brain levels, as well as the amelioration of brain edema as manifested by reduction in AQP4 levels in brain.

SIGNIFICANCE

Our study has demonstrated that CA in combination with Lac possesses a superior neuroprotective effect over Lac alone against TAA-induced HE by attenuation of P2X7R/NLRP3 mediated neuroinflammation and relieving brain edema.

Short Working Memory Impairment Associated with Hippocampal Microglia Activation in Chronic Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a major neuropsychological condition that occursas a result of impaired liver function. It is frequently observed in patients with advanced liver disease or cirrhosis. Memory impairment is among the symptoms of HE; the pathophysiologic mechanism for this enervating condition remains unclear. However, it is possible that neuroinflammation may be involved, as recent studies have emphasized such phenomena. Therefore, the aim of the present study is to assess short working memory (SWM) and examine the involvement of microglia in a chronic model of HE. The study was carried out with male Wistar rats that were induced by repeated thioacetamide (TAA) administration (100 mg/kg i.p injection for 10 days). SWM function was assessed through Y-maze, T-Maze, and novel object recognition (NOR) tests, together with an immunofluorescence study of microglia activation within the hippocampal areas. Our data showed impaired SWM in TAA-treated rats that was associated with microglial activation in the three hippocampal regions, and which contributed to cognitive impairment.

Unveiling thioacetamide-induced toxicity: Multi-organ damage and omitted bone toxicity

Thioacetamide (TAA), a widely employed hepatotoxic substance, has gained significant traction in the induction of liver failure disease models. Upon administration of TAA to experimental animals, the production of potent oxidative derivatives ensues, culminating in the activation of oxidative stress and subsequent infliction of severe damage upon multiple organs via dissemination through the bloodstream. This review summarized the various organ damages and corresponding mechanistic explanations observed in previous studies using TAA in toxicological animal experiments. The principal pathological consequences arising from TAA exposure encompass oxidative stress, inflammation, lipid peroxidation, fibrosis, apoptosis induction, DNA damage, and osteoclast formation. Recent in vivo and in vitro studies on TAA bone toxicity have confirmed that long-term high-dose use of TAA not only induces liver damage in experimental animals but also accompanies bone damage, which was neglected for a long time. By using TAA to model diseases in experimental animals and controlling TAA dosage, duration of use, and animal exposure environment, we can induce various organ injury models. It should be noted that TAA-induced injuries have a time-dependent effect. Finally, in our daily lives, especially for researchers, we should take precautions to minimize TAA exposure and reduce the probability of related organ injuries.

The contributions of bacteria metabolites to the development of hepatic encephalopathy

Over 20% of mortality during acute liver failure is associated with the development of hepatic encephalopathy (HE). Thus, HE is a complication of acute liver failure with a broad spectrum of neuropsychiatric abnormalities ranging from subclinical alterations to coma. HE is caused by the diversion of portal blood into systemic circulation through portosystemic collateral vessels. Thus, the brain is exposed to intestinal-derived toxic substances. Moreover, the strategies to prevent advancement and improve the prognosis of such a liver-brain disease rely on intestinal microbial modulation. This is supported by the findings that antibiotics such as rifaximin and laxative lactulose can alleviate hepatic cirrhosis and/or prevent HE. Together, the significance of the gut-liver-brain axis in human health warrants attention. This review paper focuses on the roles of bacteria metabolites, mainly ammonia and bile acids (BAs) as well as BA receptors in HE. The literature search conducted for this review included searches for phrases such as BA receptors, BAs, ammonia, farnesoid X receptor (FXR), G protein-coupled bile acid receptor 1 (GPBAR1 or TGR5), sphingosine-1-phosphate receptor 2 (S1PR2), and cirrhosis in conjunction with the phrase hepatic encephalopathy and portosystemic encephalopathy. PubMed, as well as Google Scholar, was the search engines used to find relevant publications.

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.

Hepatic encephalopathy complications are diminished by piracetam via the interaction between mitochondrial function, oxidative stress, inflammatory response, and locomotor activity

Background

of the study: Hepatic encephalopathy (HE) is a complication in which brain ammonia (NH4+) levels reach critically high concentrations because of liver failure. HE could lead to a range of neurological complications from locomotor and behavioral disturbances to coma. Several tactics have been established for subsiding blood and brain NH4+. However, there is no precise intervention to mitigate the direct neurological complications of NH4+.

Purpose

It has been found that oxidative stress, mitochondrial damage, and neuro-inflammation play a fundamental role in NH4+ neurotoxicity. Piracetam is a drug used clinically in neurological complications such as stroke and head trauma. Piracetam could significantly diminish oxidative stress and improve brain mitochondrial function.

Research methods

In the current study, piracetam (100 and 500 mg/kg, oral) was used in a mice model of HE induced by thioacetamide (TA, 800 mg/kg, single dose, i.p).

Results

Significant disturbances in animals' locomotor activity, along with increased oxidative stress biomarkers, including reactive oxygen species formation, protein carbonylation, lipid peroxidation, depleted tissue glutathione, and decreased antioxidant capacity, were evident in the brain of TA-treated mice. Meanwhile, mitochondrial permeabilization, mitochondrial depolarization, suppression of dehydrogenases activity, and decreased ATP levels were found in the brain of the TA group. The level of pro-inflammatory cytokines was also significantly high in the brain of HE animals.

Conclusion

It was found that piracetam significantly enhanced mice's locomotor activity, blunted oxidative stress biomarkers, decreased inflammatory cytokines, and improved mitochondrial indices in hyperammonemic mice. These data suggest piracetam as a neuroprotective agent which could be repurposed for the management of HE.

Hyperammonemia induces microglial NLRP3 inflammasome activation via mitochondrial oxidative stress in hepatic encephalopathy

BACKGROUND

The role of nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome in the pathogenesis of hepatic encephalopathy (HE) is unclear. Mitochondrial reactive oxygen species (mtROS) is a signal for NLRP3 inflammasome activation. Therefore, we aimed to determine whether mtROS-dependent NLRP3 inflammasome activation is involved in HE, using in vivo and in vitro models.

METHODS

Bile duct ligation (BDL) in C57/BL6 mice was used as an in vivo HE model. NLRP3 activation was assessed in the hippocampus. Immunofluorescence staining was performed to determine the cellular source of NLRP3 in the hippocampal tissue. For the in vitro experiment, BV-2 microglial cells were primed with lipopolysaccharide (LPS), followed by ammonia treatment. NLRP3 activation and mitochondrial dysfunction were measured. Mito-TEMPO was used to suppress mtROS production.

RESULTS

BDL mice showed cognitive impairment with hyperammonemia. Both the priming and activation steps of NLRP3 inflammasome activation were processed in the hippocampus of BDL mice. Moreover, intracellular ROS levels increased in the hippocampus, and NLRP3 was mainly expressed in the microglia of the hippocampus. In LPS-primed BV-2 cells, ammonia treatment induced NLRP3 inflammasome activation and pyroptosis, with elevation of mtROS and altered mitochondrial membrane potential. Pretreatment with Mito-TEMPO suppressed mtROS production and the subsequent NLRP3 inflammasome activation and pyroptosis under LPS and ammonia treatment in BV-2 cells.

CONCLUSIONS

Hyperammonemia in HE may be involved in mtROS overproduction and subsequent NLRP3 inflammasome activation. Further studies using NLRP3-specific inhibitor or NLRP3 knockout mice are needed to elucidate the important role of NLRP3 inflammasome in HE development.

Gut Microbiota and Neuroinflammation in Acute Liver Failure and Chronic Liver Disease

Acute liver failure and chronic liver disease are associated with a wide spectrum of neurological changes, of which the best known is hepatic encephalopathy (HE). Historically, hyperammonemia, causing astrocyte swelling and cerebral oedema, was considered the main etiological factor in the pathogenesis of cerebral dysfunction in patients with acute and/or chronic liver disease. However, recent studies demonstrated a key role of neuroinflammation in the development of neurological complications in this setting. Neuroinflammation is characterized by activation of microglial cells and brain secretion of pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6, which alter neurotransmission, leading to cognitive and motor dysfunction. Changes in the gut microbiota resulting from liver disease play a crucial role in the pathogenesis of neuroinflammation. Dysbiosis and altered intestinal permeability, resulting in bacterial translocation and endotoxemia, are responsible for systemic inflammation, which can spread to brain tissue and trigger neuroinflammation. In addition, metabolites derived from the gut microbiota can act on the central nervous system and facilitate the development of neurological complications, exacerbating clinical manifestations. Thus, strategies aimed at modulating the gut microbiota may be effective therapeutic weapons. In this review, we summarize the current knowledge on the role of the gut-liver-brain axis in the pathogenesis of neurological dysfunction associated with liver disease, with a particular focus on neuroinflammation. In addition, we highlight emerging therapeutic approaches targeting the gut microbiota and inflammation in this clinical setting.

Regulation of mild cognitive impairment associated with liver disease by humoral factors derived from the gastrointestinal tract and MRI research progress: a literature review

Patients with liver disease are prone to various cognitive impairments. It is undeniable that cognitive impairment is often regulated by both the nervous system and the immune system. In this review our research focused on the regulation of mild cognitive impairment associated with liver disease by humoral factors derived from the gastrointestinal tract, and revealed that its mechanisms may be involved with hyperammonemia, neuroinflammation, brain energy and neurotransmitter metabolic disorders, and liver-derived factors. In addition, we share the emerging research progress in magnetic resonance imaging techniques of the brain during mild cognitive impairment associated with liver disease, in order to provide ideas for the prevention and treatment of mild cognitive impairment in liver disease.

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

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

Rifaximin Improves Liver Functional Reserve by Regulating Systemic Inflammation

Rifaximin, a non-absorbable antibiotic, has been demonstrated to be effective against hepatic encephalopathy (HE); however, its efficacy on liver functional reserve remains unknown. Here, we evaluated the efficacy of rifaximin on the liver functional reserve and serological inflammation-based markers in patients with cirrhosis. A retrospective study was conducted on patients who received rifaximin for more than three months at our hospital between November 2016 and October 2021. The recurrence and grade of HE, serological ammonia levels, Child–Pugh score (CPS), and serological inflammation-based markers such as the neutrophil–lymphocyte ratio (NLR), lymphocyte–monocyte ratio (LMR), platelet–lymphocyte ratio (PLR), C-reactive protein (CRP), and CRP to albumin ratio (CAR) were evaluated. The correlations between serological inflammation-based markers and liver functional reserve were evaluated. HE grades, serum ammonia levels, and inflammation-based markers significantly improved at three months compared with those at baseline. Patients with improved albumin levels showed significantly higher CRP improvement rates at both 3 and 12 months. Patients with an improvement in CAR at 3 months demonstrated a significant improvement in CPS at 12 months. Rifaximin improved the liver functional reserve in patients with cirrhosis. Improvements in inflammation-based markers, particularly CRP and albumin, may be involved in this process.

New Insight Into Mechanisms of Hepatic Encephalopathy: An Integrative Analysis Approach to Identify Molecular Markers and Therapeutic Targets

Hepatic encephalopathy (HE) is a set of complex neurological complications that arise from advanced liver disease. The precise molecular and cellular mechanism of HE is not fully understood. Differentially expressed genes (DEGs) from microarray technologies are powerful approaches to obtain new insight into the pathophysiology of HE. We analyzed microarray data sets of cirrhotic patients with HE from Gene Expression Omnibus to identify DEGs in postmortem cerebral tissues. Consequently, we uploaded significant DEGs into the STRING to specify protein-protein interactions. Cytoscape was used to reconstruct the genetic network and identify hub genes. Target genes were uploaded to different databases to perform comprehensive enrichment analysis and repurpose new therapeutic options for HE. A total of 457 DEGs were identified in 2 data sets totally from 12 cirrhotic patients with HE compared with 12 healthy subjects. We found that 274 genes were upregulated and 183 genes were downregulated. Network analyses on significant DEGs indicated 12 hub genes associated with HE. Enrichment analysis identified fatty acid beta-oxidation, cerebral organic acidurias, and regulation of actin cytoskeleton as main involved pathways associated with upregulated genes; serotonin receptor 2 and ELK-SRF/GATA4 signaling, GPCRs, class A rhodopsin-like, and p38 MAPK signaling pathway were related to downregulated genes. Finally, we predicted 39 probable effective drugs/agents for HE. This study not only confirms main important involved mechanisms of HE but also reveals some yet unknown activated molecular and cellular pathways in human HE. In addition, new targets were identified that could be of value in the future study of HE.

The effects of Ibuprofen and 1, 8- cineol on anxiety and spatial memory in hyperammonemic rats

In hepatic encephalopathy, hyperammonemia (HA) causes cognitive impairment and anxiety by causing neuroinflammation. Ibuprofen and 1,8- cineol have anti-inflammatory and antioxidant properties, respectively. The aim of this study was to evaluate the effects of ibuprofen alone and in combination with 1,8- cineol on anxiety and oxidative stress in a HA rat animal model. For this purpose, 36 rats were divided into six groups (n = 6) including the HA (received intraperitoneally (IP) ammonium acetate 2.5 mg/kg for four week), ibuprofen (induced HA rats that received 15 mg/kg, IP), cineol (induced HA rats that received 5 and 10 mg/kg, IP), Ib + cineol (induced HA rats that received 15 and 10 mg/kg, respectively, IP), and the control groups (received normal saline, IP). Except the HA group, all other groups received the aforementioned treatment for two weeks.. The Morris water maze and elevated plus maze were used to assess cognitive function and anxiety in the animals, respectively. Superoxide dismutase (SOD) activity was measured to evaluate oxidative stress. The mRNA expression levels of interleukin (IL)-6 and IL-1β was assessed by real-time PCR in the animal's brain. The results showed a significant improvement in spatial memory and anxiety of the Ib group compared to the HA group (P < 0.01), but no significant change was observed in SOD activity (P > 0.05). There was a significant improvement in spatial memory and anxiety as well as a significant increase in SOD activity in the Ib + cineol group (P < 0.01) compared to the HA group. These results indicate that the Ib + cineol, not only improve cognitive function and reduce anxiety, also reduce oxidative stress, therefore, the simultaneous use of these two compounds may be useful in improving HA-induced cognitive disorders and anxiety.

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

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

Host-microbiome interactions: Gut-Liver axis and its connection with other organs

An understanding of connections between gut microbiome and liver has provided important insights into the pathophysiology of liver diseases. Since gut microbial dysbiosis increases gut permeability, the metabolites biosynthesized by them can reach the liver through portal circulation and affect hepatic immunity and inflammation. The immune cells activated by these metabolites can also reach liver through lymphatic circulation. Liver influences immunity and metabolism in multiple organs in the body, including gut. It releases bile acids and other metabolites into biliary tract from where they enter the systemic circulation. In this review, the bidirectional communication between the gut and the liver and the molecular cross talk between the host and the microbiome has been discussed. This review also provides details into the intricate level of communication and the role of microbiome in Gut-Liver-Brain, Gut-Liver-Kidney, Gut-Liver-Lung, and Gut-Liver-Heart axes. These observations indicate a complex network of interactions between host organs influenced by gut microbiome.

Inhibition of Autotaxin Ameliorates LPA-Mediated Neuroinflammation and Alleviates Neurological Dysfunction in Acute Hepatic Encephalopathy

Growing evidence suggests an essential role of neuroinflammation in behavioral abnormalities associated with hepatic encephalopathy (HE). Here, we report the involvement of autotaxin-lysophosphatidic acid (LPA) signaling in HE's pathogenesis. We demonstrate that the autotaxin (ATX) inhibitor PF-8380 attenuates neuroinflammation and improves neurological dysfunction in the mouse model of HE. In the thioacetamide (TAA)-induced model of HE, we found a twofold increase in the levels of ammonia in the brain and in plasma along with a significant change in HE-related behavioral parameters. Mice with HE show an increased brain weight, increased levels of tumor necrosis factor-α (TNF-α), IL-1β (interleukin-1β), interleukin-6 (IL-6), and LPA 18:0 in the cerebral cortex and hippocampus, and increased levels of LPA 18:0 in plasma. Treatment with the autotaxin inhibitor (ATXi) did not affect liver injury, as we observed no change in liver function markers including aspartate aminotransferase (AST), alanine aminotransferase (ALT), and total bilirubin (TBIL) and no change in ammonia levels in the brain and plasma. However, ATXi treatment significantly ameliorated the neuroinflammation, reduced the levels of LPA 18:0 in the cerebral cortex and hippocampus in the brain and plasma, and reduced brain edema and the levels of IL1β, IL-6, and TNF-α. The neurobehavioral symptoms for HE such as the cognitive and motor function deficit and overall clinical grading score were significantly improved in ATXi-treated mice. Mouse astrocytes and microglia stimulated with NH₄CL with or without ATXi showed significant attenuation of oxidative stress and the neuroinflammatory effect of NH4CL in ATXi-treated cells.

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

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

Carvedilol attenuates brain damage in mice with hepatic encephalopathy

Brain injury is the most common and serious consequence of hepatic encephalopathy (HE), and its pathophysiology is poorly understood. Excessive inflammatory, oxidative and apoptotic responses are the major mechanisms involved in the progression of brain injury induced by HE. Carvedilol is an adrenergic receptor antagonist with pronouncedantioxidant and anti-inflammatory activity. The present study aimed to investigatethe effects and underlying mechanisms of carvedilol on HE-induced brain damage in mice. Experimental model of HE was induced by the injection of thioacetamide (200 mg/kg) for two consecutive days and then mice were treated with carvedilol (10 or 20 mg/kg/day, orally) for 3 days in treatment groups. After the behavioral test, animals were sacrificed and the brain tissues were collected for biochemical, real time PCR and immunohistochemical analysis. The results showed that carvedilol improved locomotor impairment and reduced mortality rate in mice with HE. Carvedilol treatment decreased the brain levels of oxidative stress markers and induced Nrf2/HO-1 pathway. Carvedilol inhibited the activity of nuclear factor kappa B (NF-κB) and the expression of pro-inflammatory cytokines TNF-α, IL1β and IL-6 in the brain tissues. Treatment of mice with carvedilol caused a significant reduction in the brain levels of iNOS/NO, myeloperoxidase (MPO), cyclooxygenase (COX)-2 and chemokine MCP-1 as proinflammatory mediators in HE. Moreover, the ratio of Bcl2/Bax was increased and apoptotic cell death was decreased in the brain of mice treated with carvedilol. In conclusion, carvedilol exerted protective effect against HE-induced brain injury through increasing antioxidant defense mechanisms and inhibitionof inflammatory and apoptotic pathways.

Overview of oxidative stress findings in hepatic encephalopathy: From cellular and ammonium-based animal models to human data

Oxidative stress is a natural phenomenon in the body. Under physiological conditions intracellular reactive oxygen species (ROS) are normal components of signal transduction cascades, and their levels are maintained by a complex antioxidants systems participating in the in-vivo redox homeostasis. Increased oxidative stress is present in several chronic diseases and interferes with phagocytic and nervous cell functions, causing an up-regulation of cytokines and inflammation. Hepatic encephalopathy (HE) occurs in both acute liver failure (ALF) and chronic liver disease. Increased blood and brain ammonium has been considered as an important factor in pathogenesis of HE and has been associated with inflammation, neurotoxicity, and oxidative stress. The relationship between ROS and the pathophysiology of HE is still poorly understood. Therefore, sensing ROS production for a better understanding of the relationship between oxidative stress and functional outcome in HE pathophysiology is critical for determining the disease mechanisms, as well as to improve the management of patients. This review is emphasizing the important role of oxidative stress in HE development and documents the changes occurring as a consequence of oxidative stress augmentation based on cellular and ammonium-based animal models to human data.

Dysregulation of Astrocytic Glutamine Transport in Acute Hyperammonemic Brain Edema

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

Hepatic Encephalopathy and Melatonin

Hepatic encephalopathy (HE) is a severe metabolic syndrome linked with acute/chronic hepatic disorders. HE is also a pernicious neuropsychiatric complication associated with cognitive decline, coma, and death. Limited therapies are available to treat HE, which is formidable to oversee in the clinic. Thus, determining a novel therapeutic approach is essential. The pathogenesis of HE has not been well established. According to various scientific reports, neuropathological symptoms arise due to excessive accumulation of ammonia, which is transported to the brain via the blood-brain barrier (BBB), triggering oxidative stress and inflammation, and disturbing neuronal-glial functions. The treatment of HE involves eliminating hyperammonemia by enhancing the ammonia scavenging mechanism in systemic blood circulation. Melatonin is the sole endogenous hormone linked with HE. Melatonin as a neurohormone is a potent antioxidant that is primarily synthesized and released by the brain's pineal gland. Several HE and liver cirrhosis clinical studies have demonstrated impaired synthesis, secretion of melatonin, and circadian patterns. Melatonin can cross the BBB and is involved in various neuroprotective actions on the HE brain. Hence, we aim to elucidate how HE impairs brain functions, and elucidate the precise molecular mechanism of melatonin that reverses the HE effects on the central nervous system.

Effect of a specific Escherichia coli Nissle 1917 strain on minimal/mild hepatic encephalopathy treatment

BACKGROUND

Hepatic encephalopathy (HE) can be considered a result of dysregulated gut-liver-brain axis function, where cognitive impairment can be reversed or prevented by the beneficial effects induced by "gut-centric" therapies, such as the administration of nonabsorbable disaccharides, nonabsorbable antibiotics, probiotics and prebiotics.

AIM

To assess the short-term efficacy and safety of the probiotic Escherichia coli Nissle (EcN) 1917 strain compared to lactulose and rifaximin in patients with minimal/mild HE.

METHODS

From January 2017 to March 2020, a total of 45 patients with HE were enrolled in this prospective, single-centre, open-label, randomized study. Participants were randomly assigned at a ratio of 1:1:1 to one of the treatment groups: The EcN group (n = 15), lactulose group (n = 15) or rifaximin group (n = 15) for a 1 mo intervention period. The main primary outcomes of the study were changes in serum ammonia and Stroop test score. The secondary outcomes were markers of a chronic systemic inflammatory response (ІL-6, ІL-8, and IFN-γ) and bacteriology of the stool flora evaluated by specialized nonculture techniques after a 1 mo intervention period.

RESULTS

Patients who were given rifaximin or EcN showed a more significant reduction in serum ammonia and normalization of Bifidobacteria and Lactobacilli abundance compared to the lactulose group. However, the most pronounced restoration of the symbiotic microflora was associated with EcN administration and characterized by the absence of E. coli with altered properties and pathogenic enterobacteria in patient faeces. In the primary outcome analysis, improvements in the Stroop test parameters in all intervention groups were observed. Moreover, EcN-treated patients performed 15% faster on the Stroop test than the lactulose group patients (P = 0.017). Both EcN and rifaximin produced similar significant reductions in the proinflammatory cytokines INF-γ, IL-6 and IL-8. EcN was more efficient than lactulose in reducing proinflammatory cytokine levels.

CONCLUSION

The use of the probiotic EcN strain was safe and quite efficient for HE treatment. The probiotic reduced the ammonia content and the level of serum proinflammatory cytokines, normalized the gut microbiota composition and improved the cognitive function of patients with HE. The application of the EcN strain was more effective than lactulose treatment.

Phytochemical constituents and protective efficacy of Schefflera arboricola L. leaves extract against thioacetamide-induced hepatic encephalopathy in rats

Context: Hepatic encephalopathy (HE) is a severe neuropsychiatric syndrome resulting from liver failure. Objective: To evaluate the protective effect of Schefflera arboricola L. leaves methanol extract against thioacetamide (TAA) induced HE in rats. Materials and methods: GC/MS, LC-ESI-MS and the total phenolic and flavonoid contents were determined. The methanol extract was orally administrated (100 and 200 mg/kg) for 21 days. TAA (200 mg/kg) was given intraperitoneally on day 19 and continued for three days. The evaluation was done by measuring alanine aminotransferases (ALT), alkaline phosphatase (ALP), ammonia, reduced glutathione (GSH), malondialdehyde (MDA), nitric oxide (NO) alpha tumor necrotic factor (TNFα), toll like receptor (TLR4), interleukin 1 beta (IL-1β), interlukin 6 (IL-6), cyclooxygenase 2(COX2), B cell lymphoma (BCL2), alpha smooth muscle actin (α-SMA) and cluster of differentiation 163 (CD163). The histological features of liver and brain were conducted. Results: Forty five compounds were identified from the n-hexane fraction, while twenty nine phenolic compounds were determined from the methanol extract. Pretreatment with the plant extract returned most of the measurements under investigation to nearly normal. Conclusion: Due to its richness with bioactive compounds, Schefflera arboricola L. leaves extract succeeded to exert anti-fibrotic, anti-inflammatory and antioxidants properties in TAA-induced HE in rats with more efficacy to its high protective dose.

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.

Hepatic Encephalopathy: Thinking Beyond Ammonia

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Central nervous system and systemic oxidative stress interplay with inflammation in a bile duct ligation rat model of type C hepatic encephalopathy

The role and coexistence of oxidative stress (OS) and inflammation in type C hepatic encephalopathy (C HE) is a subject of intense debate. Under normal conditions the physiological levels of intracellular reactive oxygen species are controlled by the counteracting antioxidant response to maintain redox homeostasis. Our previous in-vivo¹H-MRS studies revealed the longitudinal impairment of the antioxidant system (ascorbate) in a bile-duct ligation (BDL) rat model of type C HE. Therefore, the aim of this work was to examine the course of central nervous system (CNS) OS and systemic OS, as well as to check for their co-existence with inflammation in the BDL rat model of type C HE. To this end, we implemented a multidisciplinary approach, including ex-vivo and in-vitro electron paramagnetic resonance spectroscopy (EPR) spin-trapping, which was combined with UV-Vis spectroscopy, and histological assessments. We hypothesized that OS and inflammation act synergistically in the pathophysiology of type C HE. Our findings point to an increased CNS- and systemic-OS and inflammation over the course of type C HE progression. In particular, an increase in the CNS OS was observed as early as 2-weeks post-BDL, while the systemic OS became significant at week 6 post-BDL. The CNS EPR measurements were further validated by a substantial accumulation of 8-Oxo-2'-deoxyguanosine (Oxo-8-dG), a marker of oxidative DNA/RNA modifications on immunohistochemistry (IHC). Using IHC, we also detected increased synthesis of antioxidants, glutathione peroxidase 1 (GPX-1) and superoxide dismutases (i.e.Cu/ZnSOD (SOD1) and MnSOD (SOD2)), along with proinflammatory cytokine interleukin-6 (IL-6) in the brains of BDL rats. The presence of systemic inflammation was observed already at 2-weeks post-surgery. Thus, these results suggest that CNS OS is an early event in type C HE rat model, which seems to precede systemic OS. Finally, our results suggest that the increase in CNS OS is due to enhanced formation of intra- and extra-cellular ROS rather than due to reduced antioxidant capacity, and that OS in parallel with inflammation plays a significant role in type C HE.

Hepatitis C Virus-Related Central and Peripheral Nervous System Disorders

Hepatitis C Virus (HCV), despite being a hepatotropic virus, is the causative agent of many systemic disorders, such as vasculitis, autoimmune diseases, lymphoproliferative disorders, and a broad spectrum of neurological and psychiatric manifestations. Although symptoms have been misdiagnosed or underdiagnosed, only recently, evidence of direct (inflammatory) or indirect (immune-mediated) HCV-dependent cerebral effects has been established. HCV infection can promote acute inflammatory response, pro-coagulative status and ischemic disorders, and neurodegeneration. These effects rely on cerebral HCV replication, possibly mediated by blood-brain barrier alterations. Further study is needed to better understand the HCV-related mechanisms of brain damage.

Role of SIRT1 in Hepatic Encephalopathy: In Vivo and In Vitro Studies Focusing on the NLRP3 Inflammasome

Hepatic encephalopathy (HE) is a neuropsychiatric disorder resulting from acute or chronic liver failure. This study is aimed at investigating the therapeutic effects and mechanisms of SIRT1 in thioacetamide- (TAA-) induced rat HE models. A selective activator (CAY10602) and inhibitor (EX527) of SIRT1 were used in this study. All male rats were separated into control, TAA, CAY10602+TAA, and EX527+TAA groups. Histological damage, liver function, serum ammonia, behavioral changes, and brain oxidative stress were measured in each group. Western blotting was used to measure SIRT1, NLRP3, ASC, and IL-1β protein expression. The results showed that CAY10602 alleviated liver injury, improved neurological decline, reduced microglial activation and brain oxidative stress, and improved the survival rates of HE rats. Moreover, CAY10602 inhibited activation of the NLRP3 inflammasome in microglia of the brain cortex in HE rats. Next, cell experiments confirmed that CAY10602 inhibited activation of the NLRP3 inflammasome in BV2 microglial cells. However, inhibition of SIRT1 by EX527 or lentivirus could enhance activation of the NLRP3 inflammasome in this process. Finally, CAY10602 reduced the neurotoxicity induced by high levels of ammonia in HT22 cells. Taken together, CAY10602 alleviates TAA-induced HE by suppressing microglial activation and the NLRP3 inflammasome and reducing the neurotoxicity of NH₄Cl in HT22 cells. A pharmacologic activator of SIRT1 may be a promising approach for the treatment of HE.

Electroacupuncture Synergistically Inhibits Proinflammatory Cytokine Production and Improves Cognitive Function in Rats with Cognitive Impairment due to Hepatic Encephalopathy through p38MAPK/STAT3 and TLR4/NF-κB Signaling Pathways

Objective

To investigate the effect of electroacupuncture (EA) on cognitive dysfunction in rats with hepatic encephalopathy and its underlying mechanism.

Methods

Fifty Wistar rats were randomly divided into a normal group (n = 10) and model group (n = 40). Rat models of hepatic encephalopathy were established by administration of carbon tetrachloride and thioacetamide for a total of 12 weeks. At the 9th week after modeling, rats with cognitive impairment in the model group were identified by conducting the Morris water maze test, which were then randomly divided into a control group (CCl₄) and treatment groups including EA group (CCl₄ + EA), lactulose group (CCl₄ + Lac), and EA plus lactulose group (CCl₄ + CM), with 9 rats in each group. At the end of the 9th week, rats in CCl₄ + Lac and CCl₄ + CM groups had lactulose gavage at a dose of 10 mL/kg body weight, while normal control and CCl₄ groups had gavage with the same volume of normal saline once a day for 21 days until the end of the experiment. Rats in CCl₄ + EA and CCl₄ + CM groups underwent acupuncture at Baihui (GV[DU]20), Shenting (GV[DU]24), and Zusanli (ST36) acupoints, among which EA at Baihui and Shenting acupoints were given once daily for 30 min lasting for 21 consecutive days. The effect of the treatment was measured by the Morris water maze test for learning and memory ability and magnetic resonance spectroscopy (MRS) for neuronal metabolism in the hippocampus of rats with hepatic encephalopathy. Pathological change in the rat hippocampus was observed by HE staining, while serum ammonia and liver function markers were detected. Western blot and real-time fluorescent quantitative PCR were used to detect the expressions of specific genes and proteins in the brain tissue.

Results

Compared with those in the control group, rats undergoing EA had significantly shortened escape latency and increased number of platform crossing. H&E staining confirmed that EA improved brain tissue necrosis and ameliorated nuclear pyknosis in rats with hepatic encephalopathy. Significantly decreased levels of serum ammonia, alanine aminotransferase (ALT), aspartate transaminase (AST), total bilirubin (TBil), and total bile acid (TBA) were observed in rats undergoing EA, as well as improved levels of total protein (TP) and albumin (ALB). In addition, EA inhibited the brain expressions of TNF-α, IL-1β, IL-6, iNOS, TLR4, MyD88, NF-κB, p38MAPK, phosphorylated (p)-p38MAPK, STAT3, and p-STAT3 genes, as well as protein expressions of TNF-α, IL-6, TLR4, MyD88, NF-κB, p38MAPK, p-p38MAPK, STAT3, and p-STAT3. MRS showed increased Glx/Cr and decreased NAA/Cr, Cho/Cr and mI/Cr in the control group, and EA significantly reversed such changes in Glx/Cr and mI/Cr values.

Conclusion

EA ameliorated the production of excessive proinflammatory cytokines in the hippocampus of rats with cognitive dysfunction secondary to hepatic encephalopathy, which also gave rise to subsequent changes such as reduced blood ammonia level, brain-protective activated astrocytes, and lower degree of brain tissue injury. The p38MAPK/STAT3 and TLR4/MyD88/NF-κB signaling pathways may be involved. EA can also improve the metabolism of NAA and Cho in the rat hippocampus and thereby improve learning and memory abilities.

The neurogliovascular unit in hepatic encephalopathy

Hepatic encephalopathy (HE) is a neurological complication of hepatic dysfunction and portosystemic shunting. It is highly prevalent in patients with cirrhosis and is associated with poor outcomes. New insights into the role of peripheral origins in HE have led to the development of innovative treatment strategies like faecal microbiota transplantation. However, this broadening of view has not been applied fully to perturbations in the central nervous system. The old paradigm that HE is the clinical manifestation of ammonia-induced astrocyte dysfunction and its secondary neuronal consequences requires updating. In this review, we will use the holistic concept of the neurogliovascular unit to describe central nervous system disturbances in HE, an approach that has proven instrumental in other neurological disorders. We will describe HE as a global dysfunction of the neurogliovascular unit, where blood flow and nutrient supply to the brain, as well as the function of the blood-brain barrier, are impaired. This leads to an accumulation of neurotoxic substances, chief among them ammonia and inflammatory mediators, causing dysfunction of astrocytes and microglia. Finally, glymphatic dysfunction impairs the clearance of these neurotoxins, further aggravating their effect on the brain. Taking a broader view of central nervous system alterations in liver disease could serve as the basis for further research into the specific brain pathophysiology of HE, as well as the development of therapeutic strategies specifically aimed at counteracting the often irreversible central nervous system damage seen in these patients.

Intestinal Permeability Is a Mechanical Rheostat in the Pathogenesis of Liver Cirrhosis

Recent studies have suggested that an alteration in the gut microbiota and their products, particularly endotoxins derived from Gram-negative bacteria, may play a major role in the pathogenesis of liver diseases. Gut dysbiosis caused by a high-fat diet and alcohol consumption induces increased intestinal permeability, which means higher translocation of bacteria and their products and components, including endotoxins, the so-called "leaky gut". Clinical studies have found that plasma endotoxin levels are elevated in patients with chronic liver diseases, including alcoholic liver disease and nonalcoholic liver disease. A decrease in commensal nonpathogenic bacteria including Ruminococaceae and Lactobacillus and an overgrowth of pathogenic bacteria such as Bacteroidaceae and Enterobacteriaceae are observed in cirrhotic patients. The decreased diversity of the gut microbiota in cirrhotic patients before liver transplantation is also related to a higher incidence of post-transplant infections and cognitive impairment. The exposure to endotoxins activates macrophages via Toll-like receptor 4 (TLR4), leading to a greater production of proinflammatory cytokines and chemokines including tumor necrosis factor-alpha, interleukin (IL)-6, and IL-8, which play key roles in the progression of liver diseases. TLR4 is a major receptor activated by the binding of endotoxins in macrophages, and its downstream signal induces proinflammatory cytokines. The expression of TLR4 is also observed in nonimmune cells in the liver, such as hepatic stellate cells, which play a crucial role in the progression of liver fibrosis that develops into hepatocarcinogenesis, suggesting the importance of the interaction between endotoxemia and TLR4 signaling as a target for preventing liver disease progression. In this review, we summarize the findings for the role of gut-derived endotoxemia underlying the progression of liver pathogenesis.

Prevalence of Hepatic Encephalopathy from a Commercial Medical Claims Database in the United States

INTRODUCTION

Hepatic encephalopathy (HE), a complication of cirrhosis, is associated with increased healthcare resource utilization and mortality, and impaired quality of life. Information on the prevalence of HE in the US general population is limited.

METHODS

Prevalence of HE was estimated by sequential stepwise data analysis of the Symphony Health anonymized patient-level data (APLD) claims database. First, patients ≥ 18 years with International Classification of Diseases ninth/tenth edition, clinical modification (ICD-9/10-CM), and codes for cirrhosis from 2018 medical and hospital claims were used to estimate prevalence of cirrhosis within the data set and number of patients with cirrhosis in the US general population. Second, patients diagnosed with cirrhosis in the APLD data set from 2015-2016 with an HE ICD-9/10-CM code within 1 year of cirrhosis diagnosis were used to deduce the prevalence of HE within the data set and estimate the number of patients with HE in the US general population. Last, US DiagnosticSource data on serum ammonia level laboratory results measured within ±2 days of a confirmed HE event were merged with the APLD HE data set, then applied to the US general population.

RESULTS

Medical and hospital claims data were available for 272,256 patients with cirrhosis in 2018. An estimated 536,856 US adults had a diagnosis of cirrhosis (prevalence of 0.21%) in 2018. This proportion applied to the estimated number of patients with cirrhosis in the United States resulted in a prevalence estimate of 201,858 cirrhosis patients with HE in 2018. When factoring in serum ammonia data, prevalence was conservatively estimated as approximately 196,000 cirrhosis patients with HE and serum ammonia levels > 21 μmol/L.

CONCLUSIONS

In this longitudinal cohort-based study, it was estimated that ≈202,000 patients had HE in the United States in 2018, representing a considerable burden to society and payers.

Drug-induced-acute liver failure: A critical appraisal of the thioacetamide model for the study of hepatic encephalopathy

Hepatic encephalopathy (HE) following acute and chronic liver failure is defined as a complex of neuropsychiatric abnormalities, such as discrete personal changes, sleep disorder, forgetfulness, confusion, and decreasing the level of consciousness to coma. The use and design of suitable animal models that represent clinical features and pathological changes of HE are valuable to map the molecular mechanisms that result in HE. Among different types of animal models, thioacetamide (TAA) has been used extensively for the induction of acute liver injury and HE. This agent is not directly hepatotoxic but its metabolites induce liver injury through the induction of oxidative stress and produce systemic inflammation similar to that seen in acute HE patients. In this short review article, we shortly review the most important pathological findings in animal models of acute HE following the administration of TAA.

Elevation of Autoantibodies to Cerebral Proteins in Hepatic Encephalopathy: Another Pathogenic Factor?

BACKGROUND

The pathophysiology of hepatic encephalopathy (HE) is incompletely understood. It remains elusive how the contributing factors of neuronal ammonia accumulation, cell swelling, and inflammation interact.

OBJECTIVE

The objective of this study was to find the correlation between neuronal autoantibody levels and the degree of HE as first indication of immune-mediated pathogenesis.

METHODS

We investigated serum autoantibody levels of representative brain proteins in patients with HE as well as in an experimental rat model with cirrhosis and HE after carbon tetrachloride exposure. They were examined in relation to presence of HE and the degree of neurological impairment evaluated by quantitative scores.

RESULTS

In HE, an increase in all of the examined antibodies was observed in serum. The grade of antibody elevation correlated to the degree of encephalopathy registered by quantitative evaluation of brain dysfunction.

CONCLUSION

The degree of HE parallels neuronal autoantibody elevation. In case a causal relationship could finally be established, it adds to the understanding of HE and may open a new perspective for treatment of this handicapping condition by immunosuppressive strategies.

Association between serum albumin and cognitive dysfunction in hepatic encephalopathy: An exploratory data analysis

Background and Aim

Because covert hepatic encephalopathy (CHE) has been shown to affect the prognosis of cirrhotic patients, early diagnosis of hepatic encephalopathy (HE) is a prerequisite for the preservation of patients' quality of life and for prophylaxis of overt HE. The aim of this study was to identify a clinical parameter to predict impairment of cognitive function in cirrhotic patients with early‐stage HE.

Methods

We investigated the data from 172 patients with cirrhotic or idiopathic portosystemic shunt (PSS) in phase II/III trials of rifaximin in Japan. Classification and regression trees (CARTs) were constructed to identify clinical profiles related to cognitive dysfunction as indicated by the prolongation of time required for the Number Connection Test (NCT‐B).

Results

CART analysis detected age 65 years as the variable for the initial split, and serum albumin level was selected as the variable for the second split among patients aged ≤65 years. In 27 cirrhotic patients aged ≤65 years without PSS, receiver operating characteristic curve analysis revealed that the optimal albumin level cutoff point was 3.05 g/dL, and the area under the curve was 0.80 for the prolongation of NCT‐B time, which was higher than that of the branched‐chain amino acids‐to‐tyrosine ratio (0.46), the prothrombin time–international normalized ratio (PT‐INR) (0.68), serum ammonia (0.61), and total bilirubin (0.69).

Conclusions

Lower serum albumin level as a clinical biomarker associated with impaired cognitive function may be available as a screening examination for early‐stage HE in cirrhotic patients aged ≤65 years without PSS before undergoing neuropsychological tests.

Interplay of cardiovascular mediators, oxidative stress and inflammation in liver disease and its complications

The liver is a crucial metabolic organ that has a key role in maintaining immune and endocrine homeostasis. Accumulating evidence suggests that chronic liver disease might promote the development of various cardiac disorders (such as arrhythmias and cardiomyopathy) and circulatory complications (including systemic, splanchnic and pulmonary complications), which can eventually culminate in clinical conditions ranging from portal and pulmonary hypertension to pulmonary, cardiac and renal failure, ascites and encephalopathy. Liver diseases can affect cardiovascular function during the early stages of disease progression. The development of cardiovascular diseases in patients with chronic liver failure is associated with increased morbidity and mortality, and cardiovascular complications can in turn affect liver function and liver disease progression. Furthermore, numerous infectious, inflammatory, metabolic and genetic diseases, as well as alcohol abuse can also influence both hepatic and cardiovascular outcomes. In this Review, we highlight how chronic liver diseases and associated cardiovascular effects can influence different organ pathologies. Furthermore, we explore the potential roles of inflammation, oxidative stress, vasoactive mediator imbalance, dysregulated endocannabinoid and autonomic nervous systems and endothelial dysfunction in mediating the complex interplay between the liver and the systemic vasculature that results in the development of the extrahepatic complications of chronic liver disease. The roles of ageing, sex, the gut microbiome and organ transplantation in this complex interplay are also discussed.