Covert hepatic encephalopathy: elevated total glutathione and absence of brain water content changes

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.

J-difference GABA-edited MRS reveals altered cerebello-thalamo-cortical metabolism in patients with hepatic encephalopathy

Hepatic encephalopathy (HE) is a common neurological manifestation of liver cirrhosis and is characterized by an increase of ammonia in the brain accompanied by a disrupted neurotransmitter balance, including the GABAergic and glutamatergic systems. The aim of this study is to investigate metabolic abnormalities in the cerebello-thalamo-cortical system of HE patients using GABA-edited MRS and links between metabolite levels, disease severity, critical flicker frequency (CFF), motor performance scores, and blood ammonia levels. GABA-edited MRS was performed in 35 participants (16 controls, 19 HE patients) on a clinical 3 T MRI system. MRS voxels were placed in the right cerebellum, left thalamus, and left motor cortex. Levels of GABA+ and of other metabolites of interest (glutamine, glutamate, myo-inositol, glutathione, total choline, total NAA, and total creatine) were assessed. Group differences in metabolite levels and associations with clinical metrics were tested. GABA+ levels were significantly increased in the cerebellum of patients with HE. GABA+ levels in the motor cortex were significantly decreased in HE patients, and correlated with the CFF (r = 0.73; p < .05) and motor performance scores (r = -0.65; p < .05). Well-established HE-typical metabolite patterns (increased glutamine, decreased myo-inositol and total choline) were confirmed in all three regions and were closely linked to clinical metrics. In summary, our findings provide further evidence for alterations in the GABAergic system in the cerebellum and motor cortex in HE. These changes were accompanied by characteristic patterns of osmolytes and oxidative stress markers in the cerebello-thalamo-cortical system. These metabolic disturbances are a likely contributor to HE motor symptoms in HE. In patients with hepatic encephalopathy, GABA+ levels in the cerebello-thalamo-cortical loop are significantly increased in the cerebellum and significantly decreased in the motor cortex. GABA+ levels in the motor cortex strongly correlate with critical flicker frequency (CFF) and motor performance score (pegboard test tPEG), but not blood ammonia levels (NH3).

Formaldehyde in Hospitals Induces Oxidative Stress: The Role of GSTT1 and GSTM1 Polymorphisms

Despite the toxicity and health risk characteristics of formaldehyde (FA), it is currently used as a cytological fixative and the definition of safe exposure levels is still a matter of debate. Our aim was to investigate the alterations in both oxidative and inflammatory status in a hospital working population. The 68 workers recruited wore a personal air-FA passive sampler, provided a urine sample to measure 15-F_2t-Isoprostane (15-F_2t-IsoP) and malondialdehyde (MDA) and a blood specimen to measure tumour necrosis factor α (TNFα). Subjects were also genotyped for GSTT1 (Presence/Absence), GSTM1 (Presence/Absence), CYP1A1 exon 7 (A > G), and IL6 (−174, G > C). Workers were ex post split into formalin-employers (57.3 μg/m³) and non-employers (13.5 μg/m³). In the formalin-employers group we assessed significantly higher levels of 15-F_2t-IsoP, MDA and TNFα (<0.001) in comparison to the non-employers group. The air-FA levels turned out to be positively correlated with 15-F_2t-IsoP (p = 0.027) and MDA (p < 0.001). In the formalin-employers group the MDA level was significantly higher in GSTT1 Null (p = 0.038), GSTM1 Null (p = 0.031), and CYP1A1 exon 7 mutation carrier (p = 0.008) workers, compared to the wild type subjects. This study confirms the role of FA in biomolecular profiles alterations, highlighting how low occupational exposure can also result in measurable biological outcomes.

Pathomechanisms in hepatic encephalopathy

Hepatic encephalopathy (HE) is a frequent neuropsychiatric complication in patients with acute or chronic liver failure. Symptoms of HE in particular include disturbances of sensory and motor functions and cognition. HE is triggered by heterogeneous factors such as ammonia being a main toxin, benzodiazepines, proinflammatory cytokines and hyponatremia. HE in patients with liver cirrhosis is triggered by a low-grade cerebral edema and cerebral oxidative/nitrosative stress which bring about a number of functionally relevant alterations including posttranslational protein modifications, oxidation of RNA, gene expression changes and senescence. These alterations are suggested to impair astrocyte/neuronal functions and communication. On the system level, a global slowing of oscillatory brain activity and networks can be observed paralleling behavioral perceptual and motor impairments. Moreover, these changes are related to increased cerebral ammonia, alterations in neurometabolite and neurotransmitter concentrations and cortical excitability in HE patients.

Impaired brain glucose metabolism in cirrhosis without overt hepatic encephalopathy: a retrospective 18F-FDG PET/CT study

OBJECTIVES

There are subclinical neurologic deficits in cirrhotic patients without overt hepatic encephalopathy. We aimed to use F-fluorodeoxyglucose PET/computed tomography to explore the impaired brain glucose metabolism of subclinical hepatic encephalopathy in cirrhosis.

METHODS

Thirty-seven patients with hepatitis B virus-related cirrhosis without overt hepatic encephalopathy and 49 controls were enrolled in the study. The patients' Model for End-Stage Liver Disease scores were calculated. All participants underwent resting state F-fluorodeoxyglucose PET/computed tomography. Between-group comparisons of brain PET/computed tomography data were conducted with two-sample t-tests and multivariate tests with Statistical Parametric Mapping 8 software.

RESULTS

Most of the patients (30/37) had a Model for End-Stage Liver Disease score of less than 20. The patients and controls did not significantly differ in baseline characteristics, such as sex, age, plasma glucose level, smoking history or BMI, but they did significantly differ in blood uric acid level and serum levels of bilirubin, albumin, total protein, alkaline phosphatase, alanine aminotransferase and aspartate aminotransferase (P <  0.0001). Relative to brain glucose metabolism in the controls, that in the patients involved both hyper- and hypometabolic regions (P <  0.001). The relative hypometabolic regions included the parietal, occipital and limbic lobes, and the hypermetabolic regions included the hippocampus, parahippocampal gyri, right basal ganglia and circumventricular organs.

CONCLUSION

Patients with cirrhosis have characteristic patterns of brain glycometabolic impairment. F-fluorodeoxyglucose PET/computed tomography may serve as a preclinical biomarker for brain damage in cirrhosis.

Chemical exchange saturation transfer imaging in hepatic encephalopathy

Hepatic encephalopathy (HE) is a common complication in liver cirrhosis and associated with an invasion of ammonia into the brain through the blood-brain barrier. Resulting higher ammonia concentrations in the brain are suggested to lead to a dose-dependent gradual increase of HE severity and an associated impairment of brain function. Amide proton transfer-weighted (APT_w) chemical exchange saturation transfer (CEST) imaging has been found to be sensitive to ammonia concentration. The aim of this work was to study APT_w CEST imaging in patients with HE and to investigate the relationship between disease severity, critical flicker frequency (CFF), psychometric test scores, blood ammonia, and APT_w signals in different brain regions.

Whole-brain APT_w CEST images were acquired in 34 participants (14 controls, 20 patients (10 minimal HE, 10 manifest HE)) on a 3 T clinical MRI system accompanied by T₁ mapping and structural images. T₁ normalized magnetization transfer ratio asymmetry analysis was performed around 3 ppm after B₀ and B₁ correction to create APT_w images. All APT_w images were spatially normalized into a cohort space to allow direct comparison. APT_w images in 6 brain regions (cerebellum, occipital cortex, putamen, thalamus, caudate, white matter) were tested for group differences as well as the link to CFF, psychometric test scores, and blood ammonia.

A decrease in APT_w intensities was found in the cerebellum and the occipital cortex of manifest HE patients. In addition, APT_w intensities in the cerebellum correlated positively with several psychometric scores, such as the fine motor performance scores MLS1 for hand steadiness / tremor (r = 0.466; p = .044) and WRT2 for motor reaction time (r = 0.523; p = .022). Moreover, a negative correlation between APT_w intensities and blood ammonia was found for the cerebellum (r = −0.615; p = .007) and the occipital cortex (r = −0.478; p = .045). An increase of APT_w intensities was observed in the putamen of patients with minimal HE and correlated negatively with the CFF (r = −0.423; p = .013).

Our findings demonstrate that HE is associated with regional differential alterations in APT_w signals. These variations are most likely a consequence of hyperammonemia or hepatocerebral degeneration processes, and develop in parallel with disease severity.

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Ammonia is suggested to play a key role in the emergence of HE.

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Increase of ammonia in HE patients might be studied with APT_w CEST.

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HE leads to regionally decreasing APT_w CEST signal.

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APT_w CEST correlates with blood ammonia levels and psychometric test scores.

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APT_w CEST is possibly linked to hyperammonemia or hepatocerebral degeneration.

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.

Combined diffusion tensor imaging and magnetic resonance spectroscopy to predict neurological outcome before transjugular intrahepatic portosystemic shunt

BACKGROUND

Hepatic encephalopathy (HE) may occur after transjugular intrahepatic portosystemic shunt (TIPSS) placement. Multimodal magnetic resonance imaging (MRI), combining anatomical sequences, diffusion tensor imaging (DTI) and ¹ H magnetic resonance spectroscopy, is modified in cirrhotic patients.

AIMS

To describe multimodal MRI images before TIPSS, to assess if TIPSS induces changes in multimodal MRI, and to find predictors of HE after TIPSS in patients with cirrhosis.

METHODS

Consecutive cirrhotic patients with an indication for TIPSS were prospectively screened. Diagnosis of minimal HE was performed using psychometric HE test score. Multimodal MRI was performed before and 3 months after TIPSS placement.

RESULTS

Twenty-five consecutive patients were analysed (median age = 59, male gender 76%, median Child-Pugh score = 8 [5-8], MELD score = 12 [9-17], indication for TIPSS placement: ascites/secondary prophylaxis of variceal bleeding/other 20/3/2), no HE/minimal HE/overt HE: 21/4/0. 8/25 patients developed HE after TIPSS. Before TIPSS placement, metabolite concentrations were different in patients with or without minimal HE (lower myo-inositol, mI, higher glutamate/glutamine), but there were no differences in DTI data. TIPSS placement induced changes in metabolite concentrations even in asymptomatic patients, but not in DTI metrics. Baseline fractional anisotropy was significantly lower in patients who developed HE after TIPSS in five regions of interest.

CONCLUSIONS

TIPSS placement induced significant changes in cerebral metabolites, even in asymptomatic patients. Patients who developed HE after TIPSS displayed lower fractional anisotropy before TIPSS. Brain MRI with DTI acquisition may help selecting patients at risk of HE.

Ammonia-weighted imaging by chemical exchange saturation transfer MRI at 3 T

Hepatic encephalopathy (HE) is triggered by liver cirrhosis and is associated with an increased ammonia level within the brain tissue. The goal of this study was to investigate effects of ammonia on in vitro amide proton transfer (APT)-weighted chemical exchange saturation transfer (CEST) imaging in order to develop an ammonia-sensitive brain imaging method. APT-weighted CEST imaging was performed on phantom solutions including pure ammonia, bovine serum albumin (BSA), and tissue homogenate samples doped with various ammonia concentrations. All CEST data were assessed by magnetization transfer ratio asymmetry. In addition, optical methods were used to determine possible structural changes of the proteins in the BSA phantom. In vivo feasibility measurements were acquired in one healthy participant and two patients suffering from HE, a disease associated with increased brain ammonia levels. The CEST effect of pure ammonia showed a base-catalyzed behavior. At pH values greater than 5.6 no CEST effect was observed. The APT-weighted signal was significantly reduced for ammonia concentrations of 5mM or more at fixed pH values within the different protein phantom solutions. The optical methods revealed no protein aggregation or denaturation for ammonia concentrations less than 5mM. The in vivo measurements showed tissue specific and global reduction of the observed CEST signal in patients with HE, possibly linked to pathologically increased ammonia levels. APT-weighted CEST imaging is sensitive to changes in ammonia concentrations. Thus, it seems useful for the investigation of pathologies with altered tissue ammonia concentrations such as HE. However, the underlying mechanism needs to be explored in more detail in future in vitro and in vivo investigations.