Brain edema and inflammatory activation in bile duct ligated rats with diet-induced hyperammonemia: A model of hepatic encephalopathy in cirrhosis

The effect of rifaximin and lactulose treatments to chronic hepatic encephalopathy rats: An [18F]PBR146 in-vivo neuroinflammation imaging study

INTRODUCTION

Hepatic encephalopathy (HE) is a severe neuropsychiatric complication of liver diseases characterized by neuroinflammation. The efficacies of nonabsorbable rifaximin (RIF) and lactulose (LAC) have been well documented in the treatment of HE. [18F]PBR146 is a translocator protein (TSPO) radiotracer used for in vivo neuroinflammation imaging. This study investigated anti-neuroinflammation effect of RIF or/and LAC in chronic HE rats by [18F]PBR146 micro-PET/CT.

METHODS

Bile duct ligation (BDL) operation induced chronic HE models, and this study included Sham+normal saline (NS), BDL+NS, BDL+RIF, BDL+LAC, and BDL+RIF+LAC groups. Behavioral assessment was performed to analyze the motor function, and fecal samples were collected after successfully established the chronic HE model (more than 28 days post-surgery). In addition, fecal samples collection and micro-PET/CT scans were performed sequentially. And we also collected the blood plasma, liver, intestinal, and brain samples after sacrificing the rats for further biochemical and pathological analyses.

RESULTS

The RIF- and/or LAC-treated BDL rats showed similar behavioral results with Sham+NS group, while the treatment could not reverse the biliary obstruction resulting in sustained liver injury. The RIF or/and LAC treatments can inhibit IFN-γ and IL-10 productions. The global brain uptake values of [18F]PBR146 in BDL+NS group was significantly higher than other groups (p < .0001). The brain regions analysis showed that the basal ganglia, hippocampus, and cingulate cortex had radiotracer uptake differences among groups (all p < .05), which were consistent with the brain immunohistochemistry results. Sham+NS group was mainly enriched in Christensenella, Coprobacillus, and Pseudoflavonifractor. BDL+NS group was mainly enriched in Barnesiella, Alloprevotella, Enterococcus, and Enterorhabdus. BDL+RIF+LAC group was enriched in Parabacteroides, Bacteroides, Allobaculum, Bifidobacterium, and Parasutterella.

CONCLUSIONS

RIF or/and LAC had anti-neuroinflammation in BDL-induced chronic HE rats with gut microbiota alterations. The [18F]PBR146 could be used for monitoring RIF or/and LAC treatment efficacy of chronic HE rats.

Parkinsonism in liver diseases or dysfunction

Parkinsonism in liver diseases or dysfunction, mainly including neurological manifestations in hereditary liver diseases and neurological complications of advanced liver diseases, occur in isolation or in combination with other movement disorders, and progress along disease course. Prominent akinetic-rigidity syndrome, various onset and progression, poor levodopa response and metabolism abnormalities reflected by serum biomarkers and neuroimaging, make this atypical parkinsonism recognizable and notable in clinical practice. Different susceptibility of brain areas, especially in basal ganglia, to manganese, iron, copper, ammonia overload, together with subsequent oxidative stress, neurotransmitter alterations, disturbed glia-neuron homeostasis and eventually neurotoxicity, contribute to parkinsonism under the circumstances of insufficient liver clearance ability. These mechanisms are interrelated and may interact collectively, adding to the complexity of clinical manifestations and treatment responses. This review summarizes shared clinical features of parkinsonism in liver diseases or dysfunction, depicts their underlying mechanisms and suggests practical flowchart for differential diagnosis.

Hyperactivation of MEK1 in cortical glutamatergic neurons results in projection axon deficits and aberrant motor learning

Abnormal extracellular signal-regulated kinase 1/2 (ERK1/2, encoded by Mapk3 and Mapk1, respectively) signaling is linked to multiple neurodevelopmental diseases, especially the RASopathies, which typically exhibit ERK1/2 hyperactivation in neurons and non-neuronal cells. To better understand how excitatory neuron-autonomous ERK1/2 activity regulates forebrain development, we conditionally expressed a hyperactive MEK1 (MAP2K1) mutant, MEK1S217/221E, in cortical excitatory neurons of mice. MEK1S217/221E expression led to persistent hyperactivation of ERK1/2 in cortical axons, but not in soma/nuclei. We noted reduced axonal arborization in multiple target domains in mutant mice and reduced the levels of the activity-dependent protein ARC. These changes did not lead to deficits in voluntary locomotion or accelerating rotarod performance. However, skilled motor learning in a single-pellet retrieval task was significantly diminished in these MEK1S217/221E mutants. Restriction of MEK1S217/221E expression to layer V cortical neurons recapitulated axonal outgrowth deficits but did not affect motor learning. These results suggest that cortical excitatory neuron-autonomous hyperactivation of MEK1 is sufficient to drive deficits in axon outgrowth, which coincide with reduced ARC expression, and deficits in skilled motor learning. Our data indicate that neuron-autonomous decreases in long-range axonal outgrowth may be a key aspect of neuropathogenesis in RASopathies.

Decreased muscle strength in adjuvant-induced rheumatoid arthritis animal model: A relationship to behavioural assessments

Rheumatoid arthritis (RA) is an autoimmune disorder with unknown aetiology. Patients suffering from RA face persistent pain due to joint inflammation, and tissue destruction. Behavioural phenotyping is an approach to target the role of different behavioural traits associated with disease progression. The study aimed to assess behavioural patterns associated with decreased muscle strength in the adjuvant-induced rheumatoid arthritis animal model. The study was conducted on male Albino Wister rats (n = 30) [Control, Vehicle, and Disease groups]. After taking ethical approvals RA was induced by complete Freund's adjuvant (CFA) intradermally base of tail. The weight of animals, macroscopic analysis of inflammatory signs, and arthritic scores were measured weekly. Grip strength, ganglia-based movement, cataleptic activity, and motor-coordination-related behaviours were assessed among the groups. Radiographs and spleen index assay were performed followed by data analysis using one-way and two-way ANOVA (Analysis of Variance). A significant decrease in weight and an increase in arthritic scores among the diseased group was observed. Behavioural analyses confirmed that diseased animals had significantly decreased grip strength and increased cataleptic activity with less motor coordination. Radiographic images and spleen index assay confirmed the pattern of RA. Therefore, it can be suggested that the development of the disease animal model is an effective approach to identifying the disease progression and associated behavioural changes. Moreover, this prepared laboratory animal model may be utilised for pathway analyses to understand the key role of immune regulators and genetic insight into molecular pathways associated with acute and chronic phases of RA.

Multiple ammonia-induced episodes of hepatic encephalopathy provoke neuronal cell loss in bile-duct ligated rats

Background & Aims

Hepatic encephalopathy (HE) is defined as a reversible syndrome and therefore should resolve following liver transplantation (LT). However, neurological complications have been reported in up to 47% of LT recipients, which have been documented to be associated with a history of overt HE pre-LT. We hypothesise that multiple episodes of HE lead to permanent cell injury and exacerbate neurological dysfunction. Our goal was to evaluate the impact of cumulative HE episodes on neurological status and brain integrity in rats with chronic liver disease.

Methods

Episodes of overt HE (loss of righting reflex) were induced following injection of ammonium acetate in bile duct ligation (BDL) rats (BDL-Ammonia) every 4 days starting at week 3 post-BDL. Neurobehaviour was evaluated after the last episode. Upon sacrifice, plasma ammonia, systemic oxidative stress, and inflammation markers were assessed. Neuronal markers including neuron-specific nuclear antigen and SMI311 (anti-neurofilament marker) and apoptotic markers (cleaved caspase-3, Bax, and Bcl2) were measured. Total antioxidant capacity, oxidative stress marker (4-hydroxynonenal), and proinflammatory cytokines (tumour necrosis factor-alpha and interleukin-1β) were measured in brain (hippocampus, frontal cortex, and cerebellum). Proteomic analysis was conducted in the hippocampus.

Results

In hippocampus of BDL-Ammonia rats, cleaved caspase-3 and Bax/Bcl2 ratio were significantly increased, whereas NeuN and SMI311 were significantly decreased compared with BDL-Vehicle rats. Higher levels of oxidative stress-induced post-translational modified proteins were found in hippocampus of BDL-Ammonia group which were associated with a lower total antioxidant capacity.

Conclusions

Ammonia-induced episodes of overt HE caused neuronal cell injury/death in BDL rats. These results suggest that multiple bouts of HE can be detrimental on the integrity of the brain, translating to irreversibility and hence neurological complications post-LT.

Impact and implications

Hepatic encephalopathy (HE) is defined as a reversible neuropsychiatric syndrome resolving following liver transplantation (LT); however, ∼47% of patients demonstrate neurological impairments after LT, which are associated with a previous history of overt HE pre-LT. Our study indicates that multiple episodes of overt HE can cause permanent neuronal damage which may lead to neurological complications after LT. Nevertheless, preventing the occurrence of overt HE episodes is critical for reducing the risk of irreversible neuronal injury in patients with cirrhosis.

Flaxseed Oil (Linum usitatissimum) Prevents Cognitive and Motor Damage in Rats with Hyperammonemia

Hyperammonemia is characterized by the excessive accumulation of ammonia in the body as a result of the loss of liver detoxification, leading to the development of hepatic encephalopathy (HE). These metabolic alterations carry cognitive and motor deficits and cause neuronal damage, with no effective treatment at present. In this study, we aimed to evaluate the effect of two subacute oral administrations of flaxseed oil (0.26 and 0.52 mL/kg) on short- and long-term memory, visuospatial memory, locomotor activity, motor coordination, and the neuronal morphology of the prefrontal cortex (PFC) via tests on Wistar rats with hyperammonemia. The goal was to identify its role in the regulation of cerebral edema, without liver damage causing cerebral failure. In contrast with an ammonium-rich diet, flaxseed oil and normal foods did not cause cognitive impairment or motor alterations, as evidenced in the short-term and visuospatial memory tests. Furthermore, the flaxseed oil treatment maintained a regular neuronal morphology of the prefrontal cortex, which represents a neuroprotective effect. We conclude that the oral administration of flaxseed oil prevents cognitive and motor impairments as well as neuronal alterations in rats with hyperammonemia, which supports the potential use of this oil to ameliorate the changes that occur in hepatic encephalopathy.

Novel insights into non-alcoholic fatty liver disease and dementia: insulin resistance, hyperammonemia, gut dysbiosis, vascular impairment, and inflammation

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disease characterized by multiple pathologies. The progression of dementia with NAFLD may be affected by various risk factors, including brain insulin resistance, cerebrovascular dysfunction, gut dysbiosis, and neuroinflammation. Many recent studies have focused on the increasing prevalence of dementia in patients with NAFLD. Dementia is characterized by cognitive and memory deficits and has diverse subtypes, including vascular dementia, Alzheimer’s dementia, and diabetes mellitus-induced dementia. Considering the common pathological features of NAFLD and dementia, further studies on the association between them are needed to find appropriate therapeutic solutions for diseases. This review summarizes the common pathological characteristics and mechanisms of NAFLD and dementia. Additionally, it describes recent evidence on association between NAFLD and dementia progression and provides novel perspectives with regard to the treatment of patients with dementia secondary to NAFLD.

A mouse model of hepatic encephalopathy: bile duct ligation induces brain ammonia overload, glial cell activation and neuroinflammation

Hepatic encephalopathy (HE) is a common complication of chronic liver disease, characterized by an altered mental state and hyperammonemia. Insight into the brain pathophysiology of HE is limited due to a paucity of well-characterized HE models beyond the rat bile duct ligation (BDL) model. Here, we assess the presence of HE characteristics in the mouse BDL model. We show that BDL in C57Bl/6j mice induces motor dysfunction, progressive liver fibrosis, liver function failure and hyperammonemia, all hallmarks of HE. Swiss mice however fail to replicate the same phenotype, underscoring the importance of careful strain selection. Next, in-depth characterisation of metabolic disturbances in the cerebrospinal fluid of BDL mice shows glutamine accumulation and transient decreases in taurine and choline, indicative of brain ammonia overload. Moreover, mouse BDL induces glial cell dysfunction, namely microglial morphological changes with neuroinflammation and astrocyte reactivity with blood-brain barrier (BBB) disruption. Finally, we identify putative novel mechanisms involved in central HE pathophysiology, like bile acid accumulation and tryptophan-kynurenine pathway alterations. Our study provides the first comprehensive evaluation of a mouse model of HE in chronic liver disease. Additionally, this study further underscores the importance of neuroinflammation in the central effects of chronic liver disease.

The Link between Gut Microbiota and Hepatic Encephalopathy

Hepatic encephalopathy (HE) is a serious complication of cirrhosis that causes neuropsychiatric problems, such as cognitive dysfunction and movement disorders. The link between the microbiota and the host plays a key role in the pathogenesis of HE. The link between the gut microbiome and disease can be positively utilized not only in the diagnosis area of HE but also in the treatment area. Probiotics and prebiotics aim to resolve gut dysbiosis and increase beneficial microbial taxa, while fecal microbiota transplantation aims to address gut dysbiosis through transplantation (FMT) of the gut microbiome from healthy donors. Antibiotics, such as rifaximin, aim to improve cognitive function and hyperammonemia by targeting harmful taxa. Current treatment regimens for HE have achieved some success in treatment by targeting the gut microbiota, however, are still accompanied by limitations and problems. A focused approach should be placed on the establishment of personalized trial designs and therapies for the improvement of future care. This narrative review identifies factors negatively influencing the gut–hepatic–brain axis leading to HE in cirrhosis and explores their relationship with the gut microbiome. We also focused on the evaluation of reported clinical studies on the management and improvement of HE patients with a particular focus on microbiome-targeted therapy.

Protective role of VEGF/VEGFR2 signaling against high fatality associated with hepatic encephalopathy via sustaining mitochondrial bioenergetics functions

Background

The lack of better understanding of the pathophysiology and cellular mechanisms associated with high mortality seen in hepatic encephalopathy (HE), a neurological complication arising from acute hepatic failure, remains a challenging medical issue. Clinical reports showed that the degree of baroreflex dysregulation is related to the severity of HE. Furthermore, mitochondrial dysfunction in the rostral ventrolateral medulla (RVLM), a key component of the baroreflex loop that maintains blood pressure and sympathetic vasomotor tone, is known to underpin impairment of baroreflex. Realizing that in addition to angiogenic and vasculogenic effects, by acting on its key receptor (VEGFR2), vascular endothelial growth factor (VEGF) elicits neuroprotection via maintenance of mitochondrial function, the guiding hypothesis of the present study is that the VEGF/VEGFR2 signaling plays a protective role against mitochondrial dysfunction in the RVLM to ameliorate baroreflex dysregulation that underpins the high fatality associated with HE.

Methods

Physiological, pharmacological and biochemical investigations were carried out in proof-of-concept experiments using an in vitro model of HE that involved incubation of cultured mouse hippocampal neurons with ammonium chloride. This was followed by corroboratory experiments employing a mouse model of HE, in which adult male C57BL/6 mice and VEGFR2 wild-type and heterozygous mice received an intraperitoneal injection of azoxymethane, a toxin used to induce acute hepatic failure.

Results

We demonstrated that VEGFR2 is present in cultured neurons, and observed that whereas recombinant VEGF protein maintained cell viability, gene-knockdown of vegfr2 enhanced the reduction of cell viability in our in vitro model of HE. In our in vivo model of HE, we found that VEGFR2 heterozygous mice exhibited shorter survival rate and time when compared to wild-type mice. In C57BL/6 mice, there was a progressive reduction in VEGFR2 mRNA and protein expression, mitochondrial membrane potential and ATP levels, alongside augmentation of apoptotic cell death in the RVLM, accompanied by a decrease in baroreflex-mediated sympathetic vasomotor tone and hypotension. Immunoneutralization of VEGF exacerbated all those biochemical and physiological events.

Conclusions

Our results suggest that, acting via VEGFR2, the endogenous VEGF plays a protective role against high fatality associated with HE by amelioration of the dysregulated baroreflex-mediated sympathetic vasomotor tone through sustaining mitochondrial bioenergetics functions and eliciting antiapoptotic action in the RVLM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00831-0.

Cholestasis alters brain lipid and bile acid composition and compromises motor function in neonatal piglets

Infants with neonatal cholestasis are prone to neurodevelopmental deficits, however, the underlying pathogenesis is unclear. Lipid malabsorption and accumulation of potentially neurotoxic molecules in the blood such as bile acids are important yet relatively unexplored pathways. Here, we developed a translational piglet model to understand how the molecular bile acid and lipid composition of the brain is affected by this disease and relates to motor function. Piglets (8-days old) had bile duct ligation or sham surgery and were fed a formula diet for 3 weeks. Alongside sensory-motor deficits observed in bile duct-ligated animals, we found a shift toward a more hydrophilic and conjugated bile acid profile in the brain. Additionally, comprehensive lipidomics of the cerebellum revealed a decrease in total lipids including phosphatidylinositols and phosphatidylserines and increases in lysophospholipid species. This was paralleled by elevated cerebellar expression of genes related to inflammation and tissue damage albeit without significant impact on the brain transcriptome. This study offers new insights into the developing brain's molecular response to neonatal cholestasis indicating that bile acids and lipids may contribute in mediating motor deficits.

The mechanistic and prognostic implications of heart rate variability analysis in patients with cirrhosis

Chronic liver damage leads to scarring of the liver tissue and ultimately a systemic illness known as cirrhosis. Patients with cirrhosis exhibit multi-organ dysfunction and high mortality. Reduced heart rate variability (HRV) is a hallmark of cirrhosis, reflecting a state of defective cardiovascular control and physiological network disruption. Several lines of evidence have revealed that decreased HRV holds prognostic information and can predict survival of patients independent of the severity of liver disease. Thus, the aim of this review is to shed light on the mechanistic and prognostic implications of HRV analysis in patients with cirrhosis. Notably, several studies have extensively highlighted the critical role systemic inflammation elicits in conferring the reduction in patients' HRV. It appears that IL-6 is likely to play a central mechanistic role, whereby its levels also correlate with manifestations, such as autonomic neuropathy and hence the partial uncoupling of the cardiac pacemaker from autonomic control. Reduced HRV has also been reported to be highly correlated with the severity of hepatic encephalopathy, potentially through systemic inflammation affecting specific brain regions, involved in both cognitive function and autonomic regulation. In general, the prognostic ability of HRV analysis holds immense potential in improving survival rates for patients with cirrhosis, as it may indeed be added to current prognostic indicators, to ultimately increase the accuracy of selecting the recipient most in need of liver transplantation. However, a network physiology approach in the future is critical to delineate the exact mechanistic basis by which decreased HRV confers poor prognosis.

Novel Drugs for the Management of Hepatic Encephalopathy: Still a Long Journey to Travel

Hepatic encephalopathy (HE) is one of the reversible complications of chronic liver disease, associated with a higher mortality rate. In current clinical practice, treatment with rifaximin and lactulose/lactitol is the first line of treatment in HE. With the advance in pathophysiology, a new class of ammonia lowering drugs has been revealed to overcome the hurdle and disease burden. The mechanism of the novel agents differs significantly and includes the alteration in intestinal microbiota, intestinal endothelial integrity, oxidative stress, inflammatory markers, and modulation of neurotoxins. Most of the trials have reported promising results in the treatment and prevention of HE with fecal microbiota transplantation, albumin, probiotics, flumazenil, polyethylene glycol, AST-120, glycerol phenylbutyrate, nitazoxanide, branched-chain amino acid, naloxone, and acetyl-l-carnitine. However, their clinical use is limited due to the presence of major drawbacks in their study design, sample size, safety profile, bias, and heterogenicity. This study will discuss the novel therapeutic targets for HE in liver cirrhosis patients with supporting clinical trial data.

Understanding the Role of the Gut Microbiome and Microbial Metabolites in Non-Alcoholic Fatty Liver Disease: Current Evidence and Perspectives

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. NAFLD begins as a relatively benign hepatic steatosis which can evolve to non-alcoholic steatohepatitis (NASH); the risk of cirrhosis and hepatocellular carcinoma (HCC) increases when fibrosis is present. NAFLD represents a complex process implicating numerous factors—genetic, metabolic, and dietary—intertwined in a multi-hit etiopathogenetic model. Recent data have highlighted the role of gut dysbiosis, which may render the bowel more permeable, leading to increased free fatty acid absorption, bacterial migration, and a parallel release of toxic bacterial products, lipopolysaccharide (LPS), and proinflammatory cytokines that initiate and sustain inflammation. Although gut dysbiosis is present in each disease stage, there is currently no single microbial signature to distinguish or predict which patients will evolve from NAFLD to NASH and HCC. Using 16S rRNA sequencing, the majority of patients with NAFLD/NASH exhibit increased numbers of Bacteroidetes and differences in the presence of Firmicutes, resulting in a decreased F/B ratio in most studies. They also present an increased proportion of species belonging to Clostridium, Anaerobacter, Streptococcus, Escherichia, and Lactobacillus, whereas Oscillibacter, Flavonifaractor, Odoribacter, and Alistipes spp. are less prominent. In comparison to healthy controls, patients with NASH show a higher abundance of Proteobacteria, Enterobacteriaceae, and Escherichia spp., while Faecalibacterium prausnitzii and Akkermansia muciniphila are diminished. Children with NAFLD/NASH have a decreased proportion of Oscillospira spp. accompanied by an elevated proportion of Dorea, Blautia, Prevotella copri, and Ruminococcus spp. Gut microbiota composition may vary between population groups and different stages of NAFLD, making any conclusive or causative claims about gut microbiota profiles in NAFLD patients challenging. Moreover, various metabolites may be involved in the pathogenesis of NAFLD, such as short-chain fatty acids, lipopolysaccharide, bile acids, choline and trimethylamine-N-oxide, and ammonia. In this review, we summarize the role of the gut microbiome and metabolites in NAFLD pathogenesis, and we discuss potential preventive and therapeutic interventions related to the gut microbiome, such as the administration of probiotics, prebiotics, synbiotics, antibiotics, and bacteriophages, as well as the contribution of bariatric surgery and fecal microbiota transplantation in the therapeutic armamentarium against NAFLD. Larger and longer-term prospective studies, including well-defined cohorts as well as a multi-omics approach, are required to better identify the associations between the gut microbiome, microbial metabolites, and NAFLD occurrence and progression.

Time dependent alteration of locomotor behavior in rat with acute liver failure induced cerebellar neuroinflammation and neuro-astroglial damage

Hepatic encephalopathy (HE) is a neurophysiological syndrome secondary to acute or chronic liver failure. Studies showed that HE patients exhibit a deficit in motor coordination, which may result from cerebellar functional impairment. The aim of this study is to assess the time-dependent alteration of locomotor behavior and the glial and neuronal alteration in rat with acute HE induced chemically. The study was carried out in male Sprague-Dawley rats with thioacetamide (TAA) induced acute liver failure at different stages 12 h, 24 h and 36 h. Hepatic and renal functions were assessed via various biochemical and histopathological examinations, while the cerebellum and the midbrain were examined using histology and immunohistochemistry for tyrosine hydroxylase (TH), cyclooxygenase-2 (COX-2) and glial fibrillary acidic protein (GFAP). We used as well, the open field test and the Rotarod test for assessing the locomotor activity and coordination. Our data showed a progressive loss of liver function and a progressive alteration in locomotor behavior and motor coordination in acute HE rats. In the cerebellum, we noted an increase in the degeneration of cerebellar Purkinje neurons parallel to increased COX-2 immunoreactivity together with astrocytic morphology and density changes. Likewise, in substantia nigra pars compacta, TH levels were reduced. We showed through the current study, a progressive deterioration in locomotor behavior in acute HE rats, as a result of Purkinje neurons death and a deficient dopaminergic neurotransmission, together with the morpho-functional astroglial modifications involving the oxidative stress and neuroinflammation.

Quercetin exhibits potent antioxidant activity, restores motor and non-motor deficits induced by rotenone toxicity

The rotenone-induced animal model of Parkinson's disease (PD) has been used to investigate the pathogenesis of PD. Oxidative stress is one of the main contributors of neurodegeneration in PD. Flavonoids have the potential to modulate neuronal function and combat various neurodegenerative diseases. The pre- and post-supplementation of quercetin (50 mg/kg, p.o) was done in rats injected with rotenone (1.5 mg/kg, s.c). After the treatment, behavioral activities were monitored for motor activity, depression-like behavior, and cognitive changes. Rats were decapitated after behavioral analysis and the brain samples were dissected out for neurochemical and biochemical estimation. Results showed that supplementation of quercetin significantly (p<0.01) restored rotenone-induced motor and non-motor deficits (depression and cognitive impairments), enhanced antioxidant enzyme activities (p<0.01), and attenuated neurotransmitter alterations (p<0.01). It is suggested that quercetin supplementation improves neurotransmitter levels by mitigating oxidative stress via increasing antioxidant enzyme activity and hence improves motor activity, cognitive functions, and reduces depressive behavior. The results of the present study showed that quercetin pre-supplementation produced more significant results as compared to post-supplementation. These findings show that quercetin can be a potential therapeutic agent to reduce the risk and progression of PD.

Hepatic encephalopathy and depression in chronic liver disease: is the common link systemic inflammation?

Hepatic encephalopathy and depression share a number of clinical features, such as cognitive impairment and psychomotor retardation, and are highly prevalent in patients with chronic liver disease. Both conditions signify a poor prognosis, carry an increased mortality and are major determinants of reduced health related quality of life. The pathophysiology of hepatic encephalopathy is complex. Whilst cerebral accumulation of ammonia is well-recognised as being central to the development of hepatic encephalopathy, systemic inflammation, which acts in synergy with hyperammonaemia, is emerging as a key driver in its development. The pro-inflammatory state is also widely documented in depression, and peripheral to brain communication occurs resulting in central inflammation, behavioural changes and depressive symptoms. Gut dysbiosis, with a similar reduction in beneficial bacteria, increase in pathogens and decreased bacterial diversity, has been observed in both hepatic encephalopathy and depression, and it may be that the resultant increased bacterial translocation causes their shared inflammatory pathophysiology. Whilst the literature on a positive association between hepatic encephalopathy and depression in cirrhosis remains to be substantiated, there is evolving evidence that treatment with psychobiotics may be of dual benefit, improving cognition and mood in cirrhosis.

Possible Association Between DHEA and PKCε in Hepatic Encephalopathy Amelioration: A Pilot Study

Objective: Hepatic encephalopathy (HE) is a neuropsychiatric syndrome caused by liver failure and by an impaired neurotransmission and neurological function caused by hyperammonemia (HA). HE, in turn, decreases the phosphorylation of protein kinase C epsilon (PKCε), contributing to the impairment of neuronal functions. Dehydroepiandrosterone (DHEA) exerts a neuroprotective effect by increasing the GABAergic tone through GABA_A receptor stimulation. Therefore, we investigated the protective effect of DHEA in an animal model of HE, and the possible modulation of PKCε expression in different brain area.

Methods: Fulminant hepatic failure was induced in 18 male, Sprague–Dawley rats by i.p. administration of 3 g/kg D-galactosamine, and after 30 min, a group of animals received a subcutaneous injection of 25 mg/kg (DHEA) repeated twice a day (3 days). Exploratory behavior and general activity were evaluated 24 h and 48 h after the treatments by the open field test. Then, brain cortex and cerebellum were used for immunoblotting analysis of PKCε level.

Results: DHEA administration showed a significant improvement of locomotor activity both 24 and 48 h after D-galactosamine treatment (^****p < 0.0001) but did not ameliorate liver parenchymal degeneration. Western blot analysis revealed a reduced immunoreactivity of PKCε (^*p < 0.05) following D-galactosamine treatment in rat cortex and cerebellum. After the addition of DHEA, PKCε increased in the cortex in comparison with the D-galactosamine-treated (^***p < 0.001) and control group (^*p < 0.05), but decreased in the cerebellum (^*p < 0.05) with respect to the control group. PKCε decreased after treatment with NH₄Cl alone and in combination with DHEA in both cerebellum and cortex (^****p < 0.0001). MTS assay demonstrated the synergistic neurotoxic action of NH₄Cl and glutamate pretreatment in cerebellum and cortex along with an increased cell survival after DHEA pretreatment, which was significant only in the cerebellum (^*p < 0.05).

Conclusion: An association between the DHEA-mediated increase of PKCε expression and the improvement of comatose symptoms was observed. PKCε activation and expression in the brain could inhibit GABA-ergic tone counteracting HE symptoms. In addition, DHEA seemed to ameliorate the symptoms of HE and to increase the expression of PKCε in cortex and cerebellum.

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.

[18F]PBR146 and [18F]DPA-714 in vivo Imaging of Neuroinflammation in Chronic Hepatic Encephalopathy Rats

Neuroinflammation is an important pathogenesis of hepatic encephalopathy (HE). The upregulation of translocator protein (TSPO) during neuroinflammation provides an imaging molecular target to evaluate the severity of neuroinflammation in chronic HE rats. [18F]DPA-714 and [18F]PBR146 targeting TSPO are often used for neuroinflammation imaging. This study performed bile duct ligation (BDL) in rats to simulate chronic HE model, tested the behavioral experiments, and conducted [18F]PBR146 and [18F]DPA-714 micro-PET/CT scans followed analyzing the average %ID/g values of the whole brain, brain regions and main organs of subjects. After sacrifice the rats, the blood plasma samples were taken for blood biochemical indexes and plasma inflammatory factor levels examination, the liver and brain specimens were obtained for pathological analysis. The BDL rats showed chronic liver failure with defects in cognition, motor coordination ability and mental state. [18F]PBR146 and [18F]DPA-714 micro-PET/CT imaging results were similar in whole brain of BDL group and Sham group. Besides, some regional brain areas in BDL rats were found abnormal uptakes mainly located in basal ganglia area, auditory cortex, motor cortex, cingulate gyrus, somatosensory cortex, hippocampus, thalamus, midbrain, and medulla oblongata, and these regions also correlated with behavioral alterations. In conclusion, both [18F]PBR146 and [18F]DPA-714 had the similar imaging effects in hepatic encephalopathy models could quantitatively evaluate neuroinflammation load and distribution. The difference brain regions with higher uptake values of radiotracers in BDL rats were correlated with behavioral alterations.

The Effect of NeuroAid (MLC901) on Cholestasis-Induced Spatial Memory Impairment with Respect to the Expression of BAX, BCL-2, BAD, PGC-1α and TFAM Genes in the Hippocampus of Male Wistar Rats

Cholestasis is a bile flow reduction that is induced following Bile Duct Ligation (BDL). Cholestasis impairs memory and induces apoptosis. Apoptosis consists of two pathways: intrinsic and extrinsic. The intrinsic pathway is modulated by BCL-2 (B cell lymphoma-2) family proteins. BCL-2 (a pro-survival BCL-2 protein) has anti-apoptotic effect, while BAD (BCL-2-associated death) and BAX (BCL-2-associated X), the other members of BCL-2 family have pro-apoptotic effect. Furthermore, TFAM (mitochondrial transcriptional factor A) is involved in transcription and maintenance of mitochondrial DNA and PGC-1α (peroxisome proliferator-activated receptor γ coactivator-1α) is a master regulator of mitochondrial biogenesis. On the other hand, NeuroAid is a Traditional Chinese Medicine with neuroprotective and anti-apoptosis effects. In this study, we evaluated the effect of cholestasis on spatial memory and expression of BCL-2, BAD, BAX, TFAM, and PGC-1α in the hippocampus of rats. Additionally, we assessed the effect of NeuroAid on cholestasis-induced cognitive and genetic alterations. Cholestasis was induced by BDL surgery and NeuroAid was injected intraperitoneal at the dose of 0.4 mg/kg. Furthermore, spatial memory was evaluated using Morris Water Maze (MWM) apparatus. The results showed cholestasis impaired spatial memory, increased the expression of BAD and BAX, decreased the expression of TFAM and PGC-1α, and did not alter the expression of BCL-2. Also, NeuroAid decreased the expression of BAD and BAX and increased the expression of TFAM, PGC-1α, and BCL-2. In conclusion, cholestasis impaired spatial memory and increased the expression of pro-apoptotic genes. Also, cholestasis decreased the expression of TFAM and PGC-1α. Interestingly, NeuroAid restored the effects of cholestasis.

2021 ISHEN guidelines on animal models of hepatic encephalopathy

This working group of the International Society of Hepatic Encephalopathy and Nitrogen Metabolism (ISHEN) was commissioned to summarize and update current efforts in the development and characterization of animal models of hepatic encephalopathy (HE). As defined in humans, HE in animal models is based on the underlying degree and severity of liver pathology. Although hyperammonemia remains the key focus in the pathogenesis of HE, other factors associated with HE have been identified, together with recommended animal models, to help explore the pathogenesis and pathophysiological mechanisms of HE. While numerous methods to induce liver failure and disease exist, less have been characterized with neurological and neurobehavioural impairments. Moreover, there still remains a paucity of adequate animal models of Type C HE induced by alcohol, viruses and non-alcoholic fatty liver disease; the most common etiologies of chronic liver disease.

Hepatic Encephalopathy: From Metabolic to Neurodegenerative

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

Genetically engineered E. coli Nissle attenuates hyperammonemia and prevents memory impairment in bile-duct ligated rats

Hyperammonemia associated with chronic liver disease (CLD) is implicated in the pathogenesis of hepatic encephalopathy (HE). The gut is a major source of ammonia production that contributes to hyperammonemia in CLD and HE and remains the primary therapeutic target for lowering hyperammonemia. As an ammonia-lowering strategy, Escherichia coli Nissle 1917 bacterium was genetically modified to consume and convert ammonia to arginine (S-ARG). S-ARG was further modified to additionally synthesize butyrate (S-ARG + BUT). Both strains were evaluated in bile-duct ligated (BDL) rats; experimental model of CLD and HE.

METHODS

One-week post-surgery, BDLs received non-modified EcN (EcN), S-ARG, S-ARG + BUT (3x10¹¹ CFU/day) or vehicle until sacrifice at 3 or 5 weeks. Plasma (ammonia/pro-inflammatory/liver function), liver fibrosis (hydroxyproline), liver mRNA (pro-inflammatory/fibrogenic/anti-apoptotic) and colon mRNA (pro-inflammatory) biomarkers were measured post-sacrifice. Memory, motor-coordination, muscle-strength and locomotion were assessed at 5 weeks.

RESULTS

In BDL-Veh rats, hyperammonemia developed at 3 and further increased at 5 weeks. This rise was prevented by S-ARG and S-ARG + BUT, whereas EcN was ineffective. Memory impairment was prevented only in S-ARG + BUT vs BDL-Veh. Systemic inflammation (IL-10/MCP-1/endotoxin) increased at 3 and 5 weeks in BDL-Veh. S-ARG + BUT attenuated inflammation at both timepoints (except 5-week endotoxin) vs BDL-Veh, whereas S-ARG only attenuated IP-10 and MCP-1 at 3 weeks. Circulating ALT/AST/ALP/GGT/albumin/bilirubin and gene expression of liver function markers (IL-10/IL-6/IL-1β/TGF-β/α-SMA/collagen-1α1/Bcl-2) were not normalized by either strain. Colonic mRNA (TNF-α/IL-1β/occludin) markers were attenuated by synthetic strains at both timepoints vs BDL-Veh.

CONCLUSION

S-ARG and S-ARG + BUT attenuated hyperammonemia, with S-ARG + BUT additional memory protection likely due to greater anti-inflammatory effect. These innovative strategies, particularly S-ARG + BUT, have potential to prevent HE.

Potassium deficiency decreases the capacity for urea synthesis and markedly increases ammonia in rats

Our study provides novel findings of experimental hypokalemia reducing urea cycle functionality and thereby severely increasing plasma ammonia. This is pathophysiologically interesting because plasma ammonia increases during hypokalemia by a hitherto unknown mechanism, which may be particular important in relation to the unexplained link between hypokalemia and hepatic encephalopathy. Potassium deficiency decreases gene expression, protein synthesis, and growth. The urea cycle maintains body nitrogen homeostasis including removal of toxic ammonia. Hyperammonemia is an obligatory trait of liver failure, increasing the risk for hepatic encephalopathy, and hypokalemia is reported to increase ammonia. We aimed to clarify the effects of experimental hypokalemia on the in vivo capacity of the urea cycle, on the genes of the enzymes involved, and on ammonia concentrations. Female Wistar rats were fed a potassium-free diet for 13 days. Half of the rats were then potassium repleted. Both groups were compared with pair- and free-fed controls. The following were measured: in vivo capacity of urea-nitrogen synthesis (CUNS); gene expression (mRNA) of urea cycle enzymes; plasma potassium, sodium, and ammonia; intracellular potassium, sodium, and magnesium in liver, kidney, and muscle tissues; and liver sodium/potassium pumps. Liver histology was assessed. The diet induced hypokalemia of 1.9 ± 0.4 mmol/L. Compared with pair-fed controls, the in vivo CUNS was reduced by 34% (P < 0.01), gene expression of argininosuccinate synthetase 1 (ASS1) was decreased by 33% (P < 0.05), and plasma ammonia concentrations were eightfold elevated (P < 0.001). Kidney and muscle tissue potassium contents were markedly decreased but unchanged in liver tissue. Protein expressions of liver sodium/potassium pumps were unchanged. Repletion of potassium reverted all the changes. Hypokalemia decreased the capacity for urea synthesis via gene effects. The intervention led to marked hyperammonemia, quantitatively explainable by the compromised urea cycle. Our findings motivate clinical studies of patients with liver disease.

Enhanced Meningeal Lymphatic Drainage Ameliorates Neuroinflammation and Hepatic Encephalopathy in Cirrhotic Rats

BACKGROUND & AIMS

Hepatic encephalopathy (HE) is a serious neurologic complication in patients with liver cirrhosis. Very little is known about the role of the meningeal lymphatic system in HE. We tested our hypothesis that enhancement of meningeal lymphatic drainage could decrease neuroinflammation and ameliorate HE.

METHODS

A 4-week bile duct ligation model was used to develop cirrhosis with HE in rats. Brain inflammation in patients with HE was evaluated by using archived GSE41919. The motor function of rats was assessed by the rotarod test. Adeno-associated virus 8-vascular endothelial growth factor C (AAV8-VEGF-C) was injected into the cisterna magna of HE rats 1 day after surgery to induce meningeal lymphangiogenesis.

RESULTS

Cirrhotic rats with HE showed significantly increased microglia activation in the middle region of the cortex (P < .001) as well as increased neuroinflammation, as indicated by significant increases in interleukin 1β, interferon γ, tumor necrosis factor α, and ionized calcium binding adaptor molecule 1 (Iba1) expression levels in at least 1 of the 3 regions of the cortex. Motor function was also impaired in rats with HE (P < .05). Human brains of patients with cirrhosis with HE also exhibited up-regulation of proinflammatory genes (NFKB1, IbA1, TNF-α, and IL1β) (n = 6). AAV8-VEGF-C injection significantly increased meningeal lymphangiogenesis (P = .035) and tracer dye uptake in the anterior and middle regions of the cortex (P = .006 and .003, respectively), their corresponding meninges (P = .086 and .006, respectively), and the draining lymph nodes (P = .02). Furthermore, AAV8-VEGF-C decreased microglia activation (P < .001) and neuroinflammation and ameliorated motor dysfunction (P = .024).

CONCLUSIONS

Promoting meningeal lymphatic drainage and enhancing waste clearance improves HE. Manipulation of meningeal lymphangiogenesis could be a new therapeutic strategy for the treatment of HE.

Cognitive Dysfunction in Non-Alcoholic Fatty Liver Disease-Current Knowledge, Mechanisms and Perspectives

Non-alcoholic fatty liver disease (NAFLD) has emerged as the hepatic component of the metabolic syndrome and now seemingly affects one-fourth of the world population. Features associated with NAFLD and the metabolic syndrome have frequently been linked to cognitive dysfunction, i.e. systemic inflammation, vascular dysfunction, and sleep apnoea. However, emerging evidence suggests that NAFLD may be a cause of cognitive dysfunction independent of these factors. NAFLD in addition exhibits dysbiosis of the gut microbiota and impaired urea cycle function, favouring systemic ammonia accumulation and further promotes systemic inflammation. Such disruption of the gut–liver–brain axis is essential in the pathogenesis of hepatic encephalopathy, the neuropsychiatric syndrome associated with progressive liver disease. Considering the growing burden of NAFLD, the morbidity from cognitive impairment is expected to have huge societal and economic impact. The present paper provides a review of the available evidence for cognitive dysfunction in NAFLD and outlines its possible mechanisms. Moreover, the clinical challenges of characterizing and diagnosing cognitive dysfunction in NAFLD are discussed.

Characterization of brain microstructural abnormalities in cirrhotic patients without overt hepatic encephalopathy using diffusion kurtosis imaging

Cirrhosis is a major public health concern. However, little is known about the neurobiological mechanisms underlying brain microstructure alterations in cirrhotic patients. The purpose of this prospective study was to investigate brain microstructural alterations in cirrhosis with or without minimal hepatic encephalopathy (MHE) and their relationship with patients’ neurocognitive performance and disease duration using voxel-based analysis of diffusion kurtosis imaging (DKI). DKI data were acquired from 30 cirrhotic patients with MHE, 31 patients without MHE (NMHE) and 59 healthy controls. All DKI-derived parametric maps were compared across the three groups to investigate their group differences. Correlation analyses were further performed to assess relationships between altered imaging parameters and clinical data. Voxel-based analysis of DKI data results showed that MHE/NMHE patients had increased radial diffusivity, axial diffusivity (AD) and mean diffusivity in addition to decreased axial kurtosis (AK) and fractional anisotropy of kurtosis in several regions. Compared to controls, these regions were primarily the cingulum, temporal and frontal cortices. The DKI metrics (i.e., AK and AD) were correlated with clinical variables in the two patient groups. In conclusion, DKI is useful for detecting brain microstructural abnormalities in MHE and NMHE patients. Abnormal DKI parameters suggest alterations in brain microstructural complexity in cirrhotic patients, which may contribute to the neurobiological basis of neurocognitive impairment. These results may provide additional information on the pathophysiology of cirrhosis.

Longitudinal osmotic and neurometabolic changes in young rats with chronic cholestatic liver disease

Type C hepatic encephalopathy (type C HE) is increasingly suspected in children with chronic liver disease (CLD), and believed to underlie long-term neurocognitive difficulties. The molecular underpinnings of type C HE in both adults and children are incompletely understood. In the present study we combined the experimental advantages of in vivo high field ¹H magnetic resonance spectroscopy with immunohistochemistry to follow longitudinally over 8 weeks the neurometabolic changes in the hippocampus of animals having undergone bile duct ligation as pups. Rats who develop CLD early in life displayed pronounced neurometabolic changes in the hippocampus characterized by a progressive increase in glutamine concentration which correlated with plasma ammonia levels and a rapid decrease in brain myo-inositol. Other neurometabolic findings included a decrease in other organic osmolytes (taurine, choline-containing compounds and creatine), ascorbate and glutamate. At the cellular level, we observed an increase in glial fibrillary acidic protein (GFAP) and aquaporin 4 (AQP4) expression in the hippocampus at 4 weeks post bile duct ligation (BDL), together with astrocytic morphological alterations. These findings differ from observations in the brain of adult rats following BDL, and are in keeping with the commonly accepted theory of age-dependent vulnerability.

Possible involvement of the opioidergic system in the modulation of body temperature, jumping behavior and memory process in cholestatic and addicted mice

Cholestasis is related to an increased plasma level of endogenous opioid levels. Naloxone-induced withdrawal syndrome has been reported in a mouse model of cholestasis. Moreover, studies revealed that the memory process is affected by cholestasis. Thus, we aimed at determining whether pharmacological manipulation of the opioidergic system is involved in signs of cholestasis disease such as hypothermia and withdrawal behaviors such as jumping behavior as well as memory process in mice. Cholestasis was induced by bile duct resection in mice and physical dependence was induced by administration of morphine and/or tramadol three times daily (8, 12 and 16 h) at the doses of 25, 50 and 75 mg/kg during three consecutive days. The memory process was assessed by a step-down passive avoidance test. Our results indicated that cholestatic mice showed hypothermia whereas cholestatic- and drug dependent mice indicated hyperthermia. Moreover, administration of morphine (50 mg/kg) and/or tramadol (50 mg/kg) on the 4th day, 2 h before naloxone injection significantly decreased latency to first jumping but increased the number of jumping and rearing behavior as well as locomotor activity in BDL-vs. sham-operated mice. In addition, the latency time of the step-down test decreased in BDL-vs. sham-operated group, showing impairment of memory in BDL mice. The results of this study support the evidence that (1) the opioidergic system involved in thermoregulation of cholestasis mice, (2) μ-opioid receptors play an important role in withdrawal behaviors, and (3) memory process is affected by cholestasis and addiction in mice.

Anxiety in rats with bile duct ligation is associated with activation of JNK3 mitogen-activated protein kinase in the hippocampus

We examine the anxiety-like behaviors in rats with bile duct ligation (BDL), as well as its relationship with the expression of JNK3 and P38 MAPKs in rat hippocampus. Male Wistar rats undergo either sham operation or BDL as a rat model of cirrhotic HE. The anxiety-like behaviors are determined using a light/dark box test two hours befor the surgery on day 1 and on days 7, 14, 21 and 28 of BDL. The gene and protein expression levels of JNK3 and p38 in the hippocampus were examined respectively with qPCR and western blotting methods on day 28 of BDL. The results revealed that anxiety was increased in the cirrhotic HE model rats during 28 days of BDL. The molecular data indicated that the gene expression of Jnk3 and protein levels of JNK3, as well as phospho-JNK3, significantly increased in the hippocampus of the cirrhotic HE model rats compared to the sham control group. However, the results revealed no significant changes in the gene expression and the protein levels of p38 as well as phospho-p38 in the hippocampus of the cirrhotic HE model rats compared to the sham control group. We conclude that the increases in the expression and activation of JNK3 MAPK in the hippocampus may underlie, at least partly, the anxiety-like behaviors in rats with cirrhotic HE.

Histamine-induced plasticity and gene expression in corticostriatal pathway under hyperammonemia

Aims

Histamine H3 receptor (H3R) antagonists/inverse agonists increase vigilance. We studied brain histaminergic pathways under hyperammonemia and the transcriptome of receptors and their signaling cascades to provide a rationale for wake‐promoting therapies.

Methods

We analyzed histamine‐induced long‐lasting depression of corticostriatal synaptic transmission (LLDhist). As the expression of dopamine 1 receptors (D1R) is upregulated in LGS‐KO striatum where D1R‐H3R dimers may exist, we investigated actions of H3R and D1R agonists and antagonists. We analyzed transcription of selected genes in cortex and dorsal striatum in a mouse model of inborn hyperammonemia (liver‐specific glutamine synthetase knockout: LGS‐KO) and compared it with human hepatic encephalopathy.

Results

LGS‐KO mice showed significant reduction of the direct depression (DD) but not the long‐lasting depression (LLD) by histamine. Neither pharmacological activation nor inhibition of D1R significantly affected DDhist and LLDhist in WT striatum, while in LGS‐KO mice D1R activation suppressed LLDhist. Histaminergic signaling was found unchanged at the transcriptional level except for the H2R. A study of cAMP‐regulated genes indicated a significant reduction in the molecular signature of wakefulness in the diseased cortex.

Conclusions

Our findings provide a rationale for the development of aminergic wake‐promoting therapeutics in hyperammonemic disorders.

Longitudinal neurometabolic changes in the hippocampus of a rat model of chronic hepatic encephalopathy

BACKGROUND & AIMS

The sequence of events in hepatic encephalopathy (HE) remains unclear. Using the advantages of in vivo 1H-MRS (9.4T) we aimed to analyse the time-course of disease in an established model of type C HE by analysing the longitudinal changes in a large number of brain metabolites together with biochemical, histological and behavioural assessment. We hypothesized that neurometabolic changes are detectable very early, and that these early changes will offer insight into the primary events underpinning HE.

METHODS

Wistar rats underwent bile-duct ligation (BDL) and were studied before BDL and at post-operative weeks 2, 4, 6 and 8 (n = 26). In vivo short echo-time ¹H-MRS (9.4T) of the hippocampus was performed in a longitudinal manner, as were biochemical (plasma), histological and behavioural tests.

RESULTS

Plasma ammonium increased early after BDL and remained high during the study. Brain glutamine increased (+47%) as early as 2-4 weeks post-BDL while creatine (-8%) and ascorbate (-12%) decreased. Brain glutamine and ascorbate correlated closely with rising plasma ammonium, while brain creatine correlated with brain glutamine. The increases in brain glutamine and plasma ammonium were correlated, while plasma ammonium correlated negatively with distance moved. Changes in astrocyte morphology were observed at 4 weeks. These early changes were further accentuated at 6-8 weeks post-BDL, concurrently with the known decreases in brain organic osmolytes.

CONCLUSION

Using a multimodal, in vivo and longitudinal approach we have shown that neurometabolic changes are already noticeable 2 weeks after BDL. These early changes are suggestive of osmotic/oxidative stress and are likely the premise of some later changes. Early decreases in cerebral creatine and ascorbate are novel findings offering new avenues to explore neuroprotective strategies for HE treatment.

LAY SUMMARY

The sequence of events in chronic hepatic encephalopathy (HE) remains unclear, therefore using the advantages of in vivo proton magnetic resonance spectroscopy at 9.4T we aimed to test the hypothesis that neurometabolic changes are detectable very early in an established model of type C HE, offering insight into the primary events underpinning HE, before advanced liver disease confounds the findings. These early, previously unreported neurometabolic changes occurred as early as 2 to 4 weeks after bile-duct ligation, namely an increase in plasma ammonium and brain glutamine, a decrease in brain creatine and ascorbate together with behavioural and astrocyte morphology changes, and continued to progress throughout the 8-week course of the disease.

Brain Edema in Chronic Hepatic Encephalopathy

Brain edema is a common feature associated with hepatic encephalopathy (HE). In patients with acute HE, brain edema has been shown to play a crucial role in the associated neurological deterioration. In chronic HE, advanced magnetic resonance imaging (MRI) techniques have demonstrated that low-grade brain edema appears also to be an important pathological feature. This review explores the different methods used to measure brain edema ex vivo and in vivo in animal models and in humans with chronic HE. In addition, an in-depth description of the main studies performed to date is provided. The role of brain edema in the neurological alterations linked to HE and whether HE and brain edema are the manifestations of the same pathophysiological mechanism or two different cerebral manifestations of brain dysfunction in liver disease are still under debate. In vivo MRI/magnetic resonance spectroscopy studies have allowed insight into the development of brain edema in chronic HE. However, additional in vivo longitudinal and multiparametric/multimodal studies are required (in humans and animal models) to elucidate the relationship between liver function, brain metabolic changes, cellular changes, cell swelling, and neurological manifestations in chronic HE.

Effects of erythropoietin on bile duct ligation-induced neuro-inflammation in male rats

Hepatic encephalopathy (HE) is a brain disorder as a result of liver failure. Previous studies have indicated that erythropoietin (EPO) has neuroprotective effects in different neurological diseases. This study addressed the therapeutic effect of a four-week treatment with EPO on neuronal damages in bile duct-ligated rats. Forty male Wistar rats (250-280 g) were used in the present study. The animals were randomly divided into four groups consisting of 10 animals each, including sham, sham + EPO, bile duct ligation (BDL), and BDL + EPO. EPO was intraperitoneally administered every other day (5,000 U/Kg) in the last four weeks after BDL. Biochemical and histological studies were performed to evaluate neurodegeneration. The results revealed that BDL increases the level of hepatic enzymes and total bilirubin. Furthermore, neurodegeneration was significantly increased in the BDL group compared to sham groups. EPO preserved hepatic enzymes and total bilirubin in the treated group. In addition, EPO significantly decreased the neurodegeneration in BDL + EPO compared to the BDL group. Results of this study showed that EPO has neuroprotective effects in the rat model of HE, possibly due to its anti-inflammatory and anti-oxidant properties. Complementary studies are required to clarify the exact mechanisms.

Hepatic encephalopathy: Lessons from preclinical studies

Hepatic encephalopathy (HE) is a major complication that is closely related to the progression of end-stage liver disease. Metabolic changes in advanced liver failure can promote cognition impairment, attention deficits and motor dysfunction that may result in coma and death. HE can be subdivided according to the type of hepatic injury, namely, type A, which results from acute liver failure, type B, which is associated with a portosystemic shunting without intrinsic liver disease, and type C, which is due to chronic liver disease. Several studies have investigated the pathogenesis of the disease, and most of the mechanisms have been explored using animal models. This article aimed to review the use of preclinical models to investigate HE. The most used animal species are rats and mice. Experimental models of type A HE include surgical procedures and the administration of hepatotoxic medications, whereas models of types B and C HE are generally surgically induced lesions in liver tissue, which evolve to hepatic cirrhosis. Preclinical models have allowed the comprehension of the pathways related to HE.

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.

Gene Therapy for Treatment of Chronic Hyperammonemia in a Rat Model of Hepatic Encephalopathy

INTRODUCTION AND AIM

Hepatic encephalopathy (HE), caused by hyperammonemia resulting from liver disease, is a spectrum of neuropsychiatric and motor disorders that can lead to death. Existing therapies are deficient and alternative treatments are needed. We have shown that gene therapy with a baculovirus vector containing the glutamine synthetase (Bac-GS) gene is efficient for reducing ammonia levels in an acute hyperammonemia rat model. However, the most common condition resulting from liver disease is chronic hyperammonemia. In this work, Bac-GS was evaluated in bile-duct ligated rats, a chronic liver disease model with hyperammonemia and some characteristics of Type C HE.

MATERIAL AND METHODS

Bac-GS was tested for mediating GS overexpression in HeLa cells and H9C2 myotubes. For determining the utility of Bac-GS for the reduction of ammonia levels in a chronic hyperammonemia animal model, four groups of rats were treated: control, sham, ligated with Bac-GS and ligated with Bac-GFP. Baculoviruses were injected i.m. 18 days post-surgery. Blood was drawn 2, 3 and 4 weeks post-surgery and plasma ammonia concentrations were quantified.

RESULTS

In protein lysates of cells and myotubes transduced with Bac-GS, a 44 kDa band corresponding to GS was detected. Significant results were obtained in the hyperammonemic bile-duct ligated rat model, as plasma ammonia was reduced to normal levels 3 days after treatment with Bac-GS. Furthermore, a transitory effect of Bac-GS was observed.

CONCLUSION

Our results show that gene therapy by delivering GS is a promising alternative for treatment of hyperammonemia in acute-on-chronic liver failure patients with HE.

Neuroinflammation in acute hepatic encephalopathy rats: imaging and therapeutic effectiveness evaluation using 11C-PK11195 and 18F-DPA-714 micro-positron emission tomography

Neuroinflammation has an important influence in pathogenesis of acute hepatic encephalopathy (AHE). ¹¹C-PK11195 and ¹⁸F-DPA-714 targeted to translocator protein (TSPO) have potential application in positron emission tomography (PET) as a molecular probe of neuroinflammation. The aim of this study was to compare these two radiotracers and their effectiveness in detecting neuroinflammation for the imaging of AHE rat models. Furthermore, using the new radiotracer ¹⁸F-DPA-714, we analyzed the effectiveness of therapeutic treatment for neuroinflammation in AHE. First, we performed a comparative study of ¹¹C-PK1195 and ¹⁸F-DPA-714 PET to image neuroinflammation in AHE rats induced by thioacetamide. Twenty-four rats were divided into either control group (n = 12) or AHE group (n = 12). Next, each group was subdivided depending on the radiotracer used during PET imaging (n = 6). Radiotracer uptake values encompassing the whole brain were compared. Lastly, we used the optimized tracer to monitor anti-neuroinflammation effects in AHE-induced rats. Forty-six rats were divided into four groups: [normal saline (NS) group (n = 13), minocycline (MINO) group (n = 11), dexamethasone (DEXA) group (n = 11), MINO+DEXA group (n = 11)]. ¹⁸F-DPA-714 PET was performed and the uptake values were calculated. The rotarod test, biochemical indices, and histopathological examinations were quantitatively measured and compared. AHE rats showed reduced motor ability, elevated ammonia levels, and higher liver function indices (all P < 0.05) with unchanged inflammatory factors (all P > 0.05), compared to control group. Both ¹¹C-PK11195 and ¹⁸F-DPA-714 PET can detect neuroinflammation of AHE rats. Behavioral studies showed that MINO and/or DEXA improved the motor ability in AHE rats (P < 0.05); however, no differences were found for liver function or inflammatory markers among the four groups (all P > 0.05). The average uptake values of whole brain and multiple brain areas in the MINO+DEXA group were lower compared to all other groups (all P < 0.05), which was demonstrated by CD11b stains of microglia. Our results show that both ¹¹C-PK11195 and ¹⁸F-DPA-714 PET can detect neuroinflammation in AHE-induced rat models. Additionally, the combined use of minocycline and dexamethasone can effectively inhibit neuroinflammation in AHE-induced rats, which can be sensitively monitored by ¹⁸F-DPA-714 PET.

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.

Systemic inflammation without gliosis mediates cognitive deficits through impaired BDNF expression in bile duct ligation model of hepatic encephalopathy

Chronic liver disease per se induces neuroinflammation that contributes to cognitive deficits in hepatic encephalopathy (HE). However, the processes by which pro-inflammatory molecules result in cognitive impairment still remains unclear. In the present study, a significant increase in the activity of liver function enzymes viz. alanine transaminase (ALT), aspartate transaminase (AST) and alkaline phosphatase (ALP) was observed along with increase in plasma ammonia levels after four weeks of bile duct ligation (BDL) in rats suggesting hepatocellular damage. A significant increase was observed in mRNA expression of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α) and monocyte chemoattractant protein-1 (MCP-1) in brain regions and liver of BDL rats. Concomitantly, IL-6, TNF-α and MCP-1 protein levels were also increased in brain regions, liver and serum of BDL rats suggesting the involvement of blood-brain-axis in inflammatory response. However, a significant decrease was observed in glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule-1 (Iba-1) expression at transcriptional and translation level in brain of BDL rats. Immunohistochemical and flowcytometric analysis revealed reduced number of GFAP-immunopositive astrocytes and Iba1-immunopositive microglia in the brain regions of BDL rats. Further, a significant decline was observed in cognitive functions in BDL rats assessed using Morris water maze and novel object recognition tests. Expression of pro and mature form of brain derived neurotrophic factor (BDNF) and its upstream transcription element showed significant reduction in brain of BDL rats. Taken together, the results of the present study suggest that systemic inflammation and reduced expression of BDNF and its upstream transcription factor plays a key role in cognitive decline in HE.

Hyperthermia associated with biliary obstruction during living donor liver transplantation

Intraoperative hypothermia occurs frequently, but hyperthermia is relatively rare during general anesthesia. We experienced a case of hyperthermia during living donor liver transplantation that appeared to be significantly associated with biliary obstruction. A 65-year-old male patient was diagnosed with intrahepatic cholangiocarcinoma, and living donor liver transplantation was planned after confirmation of no metastasis via intraoperative frozen biopsy. Following resection of a segment of common bile duct for frozen biopsy, the surgeon clamped the common bile duct, and the patient’s body temperature increased gradually to 39.5°C. As the congested bile was drained, the body temperature decreased to the normal range. This case report suggests that when a patient develops unexplained hyperthermia during hepatobiliary surgery or in a chance of biliary obstruction, clinicians should consider bile congestion as a possible reason for hyperthermia.

Effect of sirolimus on liver cirrhosis and hepatic encephalopathy of common bile duct-ligated rats

Cirrhosis is often associated with portal hypertension and portal-systemic collateral vessels formation attributed to angiogenesis, which leads to severe complications as hepatic encephalopathy. Sirolimus has anti-fibrosis and anti-angiogenesis effects, but whether it influences the severity of portal-systemic collaterals and hepatic encephalopathy is unknown. This study was thus designed to address this issue in rats with common bile duct ligation-induced liver cirrhosis. Sham-operated rats were surgical controls. Rats were intraperitoneally administered with 0.5 and 2 mg/kg/day sirolimus or vehicle for 2 weeks. Four weeks post operations, motor activities, body weight, biochemistry and hemodynamic data were measured. The liver was dissected for histopathology, immunohistochemical stains and protein analysis. On the parallel cirrhotic groups, the portal-systemic shunting was determined. The results showed that the body weight gain was significantly lower in sirolimus-treated rats. Sirolimus reduced portal pressure and plasma levels of alanine aminotransferase, aspartate aminotransferase and ammonia, and attenuated hepatic inflammation and fibrosis in cirrhotic rats. In addition, the hepatic phosphorylated mammalian target of rapamycin (mTOR) and P70S6K protein expressions were significantly downregulated and endothelial nitric oxide synthase (eNOS) expression upregulated by sirolimus. Sirolimus did not influence portal-systemic shunting and motor activities of cirrhotic rats. In conclusion, sirolimus significantly improved hepatic inflammation and fibrosis accompanied by portal pressure reduction in cirrhotic rats, in which down-regulated mTOR/P70S6K and up-regulated eNOS expressions might play a role. However, sirolimus did not significantly change the severity of portal-systemic collaterals and motor activities, suggesting that the multifactorial pathogenesis of hepatic encephalopathy could not be fully overcome by sirolimus.

Lactulose decreases neuronal activation and attenuates motor behavioral deficits in hyperammonemic rats

Lactulose is a nonabsorbable disaccharide commonly used in clinical practice to treat hepatic encephalopathy. However, its effects on neuropsychiatric disorders and motor behavior have not been fully elucidated. Male Wistar rats were bile-duct ligated, and 3 weeks after surgery, treated with lactulose administrated by gavage (1.43 or 3.57 g/kg), once a day for seven days. Plasma levels of ammonia, aspartate aminotransferase, total bilirubin, and creatinine were quantified and histopathological analysis of the livers was performed. Locomotor activity measurements were performed in an open field. The expression of water channel aquaporin-4 was investigated and the analysis of Fos protein immunoreactivity was used to evaluate the pattern of neural activation in brain areas related to motor behavior. Bile-duct ligated rats showed hyperammonemia, loss of liver integrity and function, impaired locomotor activity, reduced aquaporin-4 protein expression, and neuronal hyperactivity. Lactulose treatment was able to reduce ammonia plasma levels, despite not having an effect on biochemical parameters of liver function, such as aspartate aminotransferase activity and total bilirubin levels, or on the cirrhotic hepatic architecture. Lactulose was also able to reduce the locomotor activity impairments and to mitigate or reverse most changes in neuronal activation. Lactulose had no effect on reduced aquaporin-4 protein expression. Our findings confirm the effectiveness of lactulose in reducing hyperammonemia and neuronal hyperactivity in brain areas related to motor behavior, reinforcing the importance of its clinical use in the treatment of the symptoms of cirrhosis-associated encephalopathy.