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

Role of astrocytes and microglia in hepatic encephalopathy associated with advanced chronic liver disease: lessons from animal studies

Hepatic encephalopathy, defined as neuropsychiatric dysfunction secondary to liver disease, is a frequent decompensating event in cirrhosis. Its clinical impact is highlighted by a notable increase in patient mortality rates and a concomitant reduction in overall quality of life. Systemically, liver disease, liver function failure, portosystemic shunting, and associated multi-organ dysfunction result in the increase of disease-causing neurotoxins in the circulation, which impairs cerebral homeostasis. Key circulating neurotoxins are ammonia and inflammatory mediators. In the brain, pathophysiology is less well understood, but is thought to be driven by glial cell dysfunction. Astrocytes are the only brain resident cells that have ammonia-metabolizing machinery and are therefore putatively most susceptible to ammonia elevation. Based on a large body of mostly in vitro evidence, ammonia-induced cellular and molecular disturbances include astrocyte swelling and oxidative stress. Microglia, the brain resident macrophages, have been linked to the translation of systemic inflammation to the brain microenvironment. Recent evidence from animal studies has provided novel insights into old and new downstream effects of astrocyte and microglial dysfunction such as toxin clearance disruption and myeloid cell attraction to the central nervous system parenchyma. Furthermore, state of the art research increasingly implicates neuronal dysfunction and possibly even irreversible neuronal cell death. Cell-type specific investigation in animal models highlights the need for critical revision of the contribution of astrocytes and microglia to well-established and novel cellular and molecular alterations in hepatic encephalopathy. In this review, we therefore give a current and comprehensive overview of causes, features, and consequences of astrocyte and microglial dysfunction in hepatic encephalopathy, including areas of interest for future investigation.

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

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

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

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

Brain imaging in children with neonatal cholestatic liver disease: A systematic review

AIM

To determine if children with neonatal cholestatic liver disease had concurrent and later findings on brain imaging studies that could be attributed and the cholestasis to contribute to the understanding of the impaired neuropsychological development.

METHODS

Ovid MEDLINE and EMBASE were searched on July 21, 2022, and updated on March 26, 2023. Studies with children under 18 years of age with neonatal cholestasis and a brain scan at the time of diagnosis or later in life were included. Excluded studies were non-English, non-human, reviews or conference abstracts. Data were extracted on demographics, brain imaging findings, treatment and outcome. The results were summarised by disease categories. Risk of bias was assessed using JBI critical appraisal tools.

RESULTS

The search yielded 12 011 reports, of which 1261 underwent full text review and 89 were eligible for inclusion. Haemorrhage was the most common finding, especially in children with bile duct obstruction, including biliary atresia. Some findings were resolved after liver transplantation.

CONCLUSION

Children with neonatal cholestasis had changes in brain imaging, which might play a role in impaired neuropsychological development, but longitudinal clinical research with structured assessment is needed to better qualify the aetiology of the impairment.

Inhibition of urease-mediated ammonia production by 2-octynohydroxamic acid in hepatic encephalopathy

Hepatic encephalopathy is a neuropsychiatric complication of liver disease which is partly associated with elevated ammonemia. Urea hydrolysis by urease-producing bacteria in the colon is often mentioned as one of the main routes of ammonia production in the body, yet research on treatments targeting bacterial ureases in hepatic encephalopathy is limited. Herein we report a hydroxamate-based urease inhibitor, 2-octynohydroxamic acid, exhibiting improved in vitro potency compared to hydroxamic acids that were previously investigated for hepatic encephalopathy. 2-octynohydroxamic acid shows low cytotoxic and mutagenic potential within a micromolar concentration range as well as reduces ammonemia in rodent models of liver disease. Furthermore, 2-octynohydroxamic acid treatment decreases cerebellar glutamine, a product of ammonia metabolism, in male bile duct ligated rats. A prototype colonic formulation enables reduced systemic exposure to 2-octynohydroxamic acid in male dogs. Overall, this work suggests that urease inhibitors delivered to the colon by means of colonic formulations represent a prospective approach for the treatment of hepatic encephalopathy.

Lessons on brain edema in HE: from cellular to animal models and clinical studies

Brain edema is considered as a common feature associated with hepatic encephalopathy (HE). However, its central role as cause or consequence of HE and its implication in the development of the neurological alterations linked to HE are still under debate. It is now well accepted that type A and type C HE are biologically and clinically different, leading to different manifestations of brain edema. As a result, the findings on brain edema/swelling in type C HE are variable and sometimes controversial. In the light of the changing natural history of liver disease, better description of the clinical trajectory of cirrhosis and understanding of molecular mechanisms of HE, and the role of brain edema as a central component in the pathogenesis of HE is revisited in the current review. Furthermore, this review highlights the main techniques to measure brain edema and their advantages/disadvantages together with an in-depth description of the main ex-vivo/in-vivo findings using cell cultures, animal models and humans with HE. These findings are instrumental in elucidating the role of brain edema in HE and also in designing new multimodal studies by performing in-vivo combined with ex-vivo experiments for a better characterization of brain edema longitudinally and of its role in HE, especially in type C HE where water content changes are small.

Neurometabolism and brain morphometry in an adolescent female with an extra-hepatic congenital portosystemic shunt

Background

Chronic hepatic encephalopathy (CHE) has been reported both in patients with congenital porto-systemic shunts (CPSS) and chronic liver disease. CHE is difficult to recognize in children as there is no clear definition and its manifestations are highly variable. CHE is associated with variations in brain volumes and metabolites that have already been demonstrated using 1.5-3T MRI systems. However, the in-depth study of brain metabolism requires the high spectral resolution of high magnetic fields.

Objectives and Methods

We analyzed the neurometabolic profile, brain volumes and T1 relaxation times of a child with a CPSS using high field proton magnetic resonance spectroscopy (1H MRS, 7T) combined with MRI and compared it to an age-matched control group. We also evaluated the impact of shunt closure on neurocognitive symptoms using adapted neuropsychological tests.

Results

7T MRS revealed a significant increase in glutamine compared to controls, a decrease in brain osmolytes, and a slight elevation in NAA concentrations. 7T MRI scans showed morphological abnormalities but no changes in the signal intensity of the globus pallidus. Neurocognitive testing revealed attention deficit disorder, language difficulties, and mild intellectual disability. Most of these areas improved after shunt closure.

Conclusions

In this paediatric case of type B HE with normal fasting ammonia, neurometabolic profile was compatible with what has been previously shown in chronic liver disease, while also demonstrating an isolated glutamine peak. In addition, neurocognitive function partially improved after shunt closure, arguing strongly for shunt closure in both presymptomatic and symptomatic patients.

Neurometabolic changes in a rat pup model of type C hepatic encephalopathy depend on age at liver disease onset

Chronic liver disease (CLD) is a serious condition where various toxins present in the blood affect the brain leading to type C hepatic encephalopathy (HE). Both adults and children are impacted, while children may display unique vulnerabilities depending on the affected window of brain development.We aimed to use the advantages of high field proton Magnetic Resonance Spectroscopy (1H MRS) to study longitudinally the neurometabolic and behavioural effects of Bile Duct Ligation (animal model of CLD-induced type C HE) on rats at post-natal day 15 (p15) to get closer to neonatal onset liver disease. Furthermore, we compared two sets of animals (p15 and p21-previously published) to evaluate whether the brain responds differently to CLD according to age onset.We showed for the first time that when CLD was acquired at p15, the rats presented the typical signs of CLD, i.e. rise in plasma bilirubin and ammonium, and developed the characteristic brain metabolic changes associated with type C HE (e.g. glutamine increase and osmolytes decrease). When compared to rats that acquired CLD at p21, p15 rats did not show any significant difference in plasma biochemistry, but displayed a delayed increase in brain glutamine and decrease in total-choline. The changes in neurotransmitters were milder than in p21 rats. Moreover, p15 rats showed an earlier increase in brain lactate and a different antioxidant response. These findings offer tentative pointers as to which neurodevelopmental processes may be impacted and raise the question of whether similar changes might exist in humans but are missed owing to 1H MRS methodological limitations in field strength of clinical magnet.

High field brain proton magnetic resonance spectroscopy and volumetry in children with chronic, compensated liver disease - A pilot study

BACKGROUND

and rationale: There is increasing evidence that children or young adults having acquired liver disease in childhood display neurocognitive impairment which may become more apparent as they grow older. The molecular, cellular and morphological underpinnings of this clinical problem are incompletely understood.

AIM

Therefore, we used the advantages of highly-resolved proton magnetic resonance spectroscopy at ultra-high magnetic field to analyze the neurometabolic profile and brain morphometry of children with chronic, compensated liver disease, hypothesizing that with high field spectroscopy we would identify early evidence of rising brain glutamine and decreased myoinositol, such as has been described both in animals and humans with more significant liver disease.

METHODS

Patients (n = 5) and age-matched controls (n = 19) underwent 7T MR scans and short echo time ¹H MR spectra were acquired using the semi-adiabatic SPECIAL sequence in two voxels located in gray and white matter dominated prefrontal cortex, respectively. A 3D MP2RAGE sequence was also acquired for brain volumetry and T₁ mapping. Liver disease had to have developed at least 6 months before entering the study. Subjects underwent routine blood analysis and neurocognitive testing using validated methods within 3 months of MRI and MRS.

RESULTS

Five children currently aged 8-16 years with liver disease acquired in childhood were included. Baseline biological characteristics were similar among patients. There were no statistically significant differences between subjects and controls in brain metabolite levels or brain volumetry. Finally, there were minor neurocognitive fluctuations including attention deficit in one child, but none fell in the statistically significant range.

CONCLUSION

Children with chronic, compensated liver disease did not display an abnormal neurometabolic profile, neurocognitive abnormalities, or signal intensity changes in the globus pallidus. Despite the absence of neurometabolic changes, it is an opportunity to emphasize that it is only by developing the use of ¹H MRS at high field in the clinical arena that we will understand the significance and generalizability of these findings in children with CLD. Attention deficit was observed in one child. Healthy children displayed neurometabolic regional differences as previously reported in adult subjects.

Corrected cerebral blood flow and reduced cerebral inflammation in berk sickle mice with higher fetal hemoglobin

Fetal hemoglobin (HbF) is known to lessen the severity of sickle cell disease (SCD), through reductions in peripheral vaso-occlusive disease and reduced risk for cerebrovascular events. However, the influence of HbF on oxygen delivery to high metabolism tissues like the brain, or its influence on cerebral perfusion, metabolism, inflammation or function have not been widely studied. We employed a Berkley mouse model (BERK) of SCD with gamma transgenes q3 expressing exclusively human α- and β^S-globins with varying levels of γ globin expression to investigate the effect of HbF expression on the brain using magnetic resonance imaging (MRI), MRI diffusion tensor imaging (DTI) and spectroscopy (MRS) and hematological parameters. Hematological parameters improved with increasing γ level expression, as did markers for brain metabolism, perfusion and inflammation. Brain microstructure assessed by DTI fractional anisotropy improved, while myo-inositol levels increased, suggesting improved microstructural integrity and reduced cell loss. Our results suggest that increasing γ levels not only improves sickle peripheral disease, but also improves brain perfusion and oxygen delivery while reducing brain inflammation while protecting brain microstructural integrity.

Impaired Neurocognitive Performance in Children after Liver Transplantation

OBJECTIVES

To assess longitudinal neurocognitive development after liver transplantation and evaluate factors associated with neurocognitive performance.

STUDY DESIGN

Data from neurocognitive testing of 65 children (aged <18 years) who underwent liver transplantation at Oslo University Hospital between 1995 and 2018 were collected from the testing program after transplantation. The parent-reported version of the Behavior Rating Inventory of Executive Function was used to assess executive function.

RESULTS

A total of 104 neurocognitive tests were conducted on 65 patients. At the first test, conducted at a median of 4.1 years (IQR, 1.5-5.3 years) after transplantation and at a median age of 6.7 years (IQR, 5.4-10.5 years), the mean full-scale IQ (FSIQ) was 91.7 ± 14, and the mean verbal comprehension index was 92.0 ± 14.5. In the 30 patients tested more than once, there was no significant difference in FSIQ between the first test at a median age of 5.8 years (IQR, 5.2-8.5 years) and the last test at a median age of 10.8 years (IQR, 9.8-12.9 years) (87.4 ± 12.9 vs 88.5 ± 13.2; P = .58). Compared with the patients who underwent transplantation a age >1 year (n = 35), those who did so at age <1 year (n = 30) had a lower FSIQ (87.1 ± 12.6 vs 96.6 ± 13.8; P = .005) and lower verbal comprehension index (87.3 ± 13.8 vs 95.4 ± 13.0; P = .020). Age at transplantation (P = .005; adjusted for cholestasis: P = .038) and transfusion of >80 mL/kg (P = .004; adjusted for age at transplantation: P = .046) were associated with FSIQ.

CONCLUSIONS

Young age at transplantation and large blood transfusions during transplantation are risk factors for poor neurocognitive performance later in life. Children who undergo transplantation before 1 year of age have significantly lower neurocognitive performance compared with those who do so later in childhood. Cognitive performance did not improve over time after transplantation.

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.

Probiotics combined with rifaximin influence the neurometabolic changes in a rat model of type C HE

Type C hepatic encephalopathy (HE) is a neuropsychiatric disease caused by chronic liver disease. Management of type C HE remains an important challenge because treatment options are limited. Both the antibiotic rifaximin and probiotics have been reported to reduce the symptoms of HE, but longitudinal studies assessing their effects on brain metabolism are lacking and the molecular mechanisms underpinning their effects are not fully understood. Therefore, we evaluated in detail the effects of these different treatments on the neurometabolic changes associated with type C HE using a multimodal approach including ultra-high field in vivo ¹H MRS. We analyzed longitudinally the effect of rifaximin alone or in combination with the probiotic Vivomixx on the brain metabolic profile in the hippocampus and cerebellum of bile duct ligated (BDL) rats, an established model of type C HE. Overall, while rifaximin alone appeared to induce no significant effect on the neurometabolic profile of BDL rats, its association with the probiotic resulted in more attenuated neurometabolic alterations in BDL rats followed longitudinally (i.e. a smaller increase in Gln and milder decrease in Glu and Cr levels). Given that both rifaximin and some probiotics are used in the treatment of HE, the implications of these findings may be clinically relevant.

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.