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Yang YT, Ji MR, Lin ZJ, Li P, Wu RZ, Liu XD, Liu L. Bile duct ligation impairs visual acuity in rats by ammonia- and bilirubin-induced retinal degeneration. Acta Pharmacol Sin 2024:10.1038/s41401-024-01388-4. [PMID: 39294446 DOI: 10.1038/s41401-024-01388-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2024] [Accepted: 08/28/2024] [Indexed: 09/20/2024] Open
Abstract
Patients with hepatic failure are often accompanied by hepatic retinopathy, but the cellular and molecular mechanisms underlying the hepatic retinopathy remain unclear. In this study, we investigated how liver failure leads to hepatic retinopathy using bile duct ligation (BDL) rats as a cholestasis animal model. Light-dark box test was used to assess sensitivity to light, indexed as visual acuity. On D28 post-BDL, rats were subjected to light-dark box test and blood samples were collected for biochemical analyses. The rats then were euthanized. Liver, spleen and both side of eye were quickly harvested. We showed that BDL impaired rat sensitivity to light, significantly decreased the thickness of inner nuclear layer (INL), outer nuclear layer (ONL) and total retina, as well as the retinal cell numbers in ONL and ganglion cell layer (GCL). The expression of rhodopsin (RHO), brn-3a and GPX4 was significantly decreased in retina of BDL rats, whereas the expression of cleaved caspase 3, 8, 9, bax/bcl-2, RIP1, GFAP, and iba-1, as well as TUNEL-positive cells were significantly increased. In cultured retinal explant, we found that NH4Cl (0.2, 1, 5 mM) concentration-dependently impaired activity of retinal explant, decreased thickness of INL and ONL, downregulated expression of brn-3a, RHO and GFAP, increased expression of cl-caspase 3 and TUNEL-positive cell numbers, with NH4Cl (5 mM) almost completely disrupting the structure of the cultured retina; bilirubin (1 μM) significantly upregulated GFAP expression, whereas high level (10 μM) of bilirubin downregulated expression of GFAP. We further demonstrated in vivo that hyperammonemia impaired rat sensitivity to light, decreased thickness of INL and ONL, downregulated expression of RHO, brn-3a, GFAP and increased expression of cl-caspase 3; hyperbilirubinemia impaired rat sensitivity to light, upregulated expression of GFAP and iba-1. In conclusion, BDL impaired rat visual acuity due to the elevated levels of ammonia and bilirubin. Ammonia induced loss of retinal ganglion cells and rod photoreceptor cells via apoptosis-mediated cell death. Bilirubin impaired retinal function via activating microglia and Müller cells.
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Affiliation(s)
- Yi-Ting Yang
- Department of Pharmacology, China Pharmaceutical University, Nanjing, 210009, China
- Hangzhou Institute of Medicine (HIM), Zhejiang Cancer Hospital, Chinese Academy of Sciences, Hangzhou, 310022, China
| | - Ming-Rui Ji
- Department of Pharmacology, China Pharmaceutical University, Nanjing, 210009, China
| | - Zi-Jin Lin
- Department of Pharmacology, China Pharmaceutical University, Nanjing, 210009, China
| | - Ping Li
- Department of Pharmacy, Beijing Tongren Hospital, Capital Medical University, Beijing, 100176, China
| | - Run-Ze Wu
- Department of Pharmacology, China Pharmaceutical University, Nanjing, 210009, China
| | - Xiao-Dong Liu
- Department of Pharmacology, China Pharmaceutical University, Nanjing, 210009, China.
| | - Li Liu
- Department of Pharmacology, China Pharmaceutical University, Nanjing, 210009, China.
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van der Knaap MS, Bugiani M, Abbink TEM. Vanishing white matter. HANDBOOK OF CLINICAL NEUROLOGY 2024; 204:77-94. [PMID: 39322396 DOI: 10.1016/b978-0-323-99209-1.00015-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/27/2024]
Abstract
"Vanishing white matter" (VWM) is a leukodystrophy caused by autosomal recessive pathogenic variants in the genes encoding the subunits of eukaryotic initiation factor 2B (eIF2B). Disease onset and disease course are extremely variable. Onset varies from the antenatal period until senescence. The age of onset is predictive of disease severity. VWM is characterized by chronic neurologic deterioration and, additionally, episodes of rapid and major neurologic decline, provoked by stresses such as febrile infections and minor head trauma. The disease is dominated by degeneration of the white matter of the central nervous system due to dysfunction of oligodendrocytes and in particular astrocytes. Organs other than the brain are rarely affected, with the exception of the ovaries. The reason for the selective vulnerability of the white matter of the central nervous system and, less consistently, the ovaries is poorly understood. eIF2B is a central regulatory factor in the integrated stress response (ISR). Genetic variants decrease eIF2B activity and thereby cause constitutive activation of the ISR downstream of eIF2B. Strikingly, the ISR is specifically activated in astrocytes. Modulation of eIF2B activity and ISR activation in VWM mouse models impacts disease severity, revealing eIF2B-regulated pathways as potential druggable targets.
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Affiliation(s)
- Marjo S van der Knaap
- Department of Child Neurology, Amsterdam Leukodystrophy Center, Emma Children's Hospital, Amsterdam University Medical Center, and Amsterdam Neuroscience, Cellular & Molecular Mechanisms, Vrije Universiteit, Amsterdam, The Netherlands.
| | - Marianna Bugiani
- Department of Pathology, Amsterdam Leukodystrophy Center, Amsterdam University Medical Centers, Amsterdam, The Netherlands
| | - Truus E M Abbink
- Department of Child Neurology, Amsterdam Leukodystrophy Center, Emma Children's Hospital, Amsterdam UMC, Amsterdam, The Netherlands; Amsterdam Neuroscience, Cellular & Molecular Mechanisms, Vrije Universiteit, Amsterdam, The Netherlands
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The effect of induced hyperammonaemia on sleep and melanopsin-mediated pupillary light response in patients with liver cirrhosis: A single-blinded randomized crossover trial. PLoS One 2022; 17:e0275067. [PMID: 36170326 PMCID: PMC9518847 DOI: 10.1371/journal.pone.0275067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Accepted: 09/06/2022] [Indexed: 11/25/2022] Open
Abstract
Background & aims Sleep disturbances are related to hepatic encephalopathy and hyperammonaemia in patients with cirrhosis. The circadian rhythm is regulated by light stimulation of the retina via melanopsin-containing ganglion cells. The study aimed to investigate whether induced hyperammonaemia affects the pupillary light response and sleep efficiency in patients with cirrhosis. Methods The study was a single-blinded crossover trial including nine patients with cirrhosis. Sleep was evaluated by Pittsburgh Sleep Quality Index (PSQI) and monitored for twelve nights with wrist accelerometers and sleep diaries. On two experimental days, separated by one week, patients were randomized to ingest either an oral amino acid challenge (AAC) or an isocaloric glucose solution (GS). We measured pupillary light response, capillary ammonia, the Karolinska Sleepiness Scale (KSS), and two neuropsychological tests on both experimental days. Results The patients had poor self-assessed sleep quality. The amino acid challenge led to a significant increase in capillary ammonia and KSS. The time spent in bed sleeping after AAC was longer and with a reduced movement index compared to baseline but not different from GS. We found no difference in the pupillary light response or neuropsychiatric tests when comparing the effect of AAC with GS. Conclusions Patients with cirrhosis had impaired sleep quality. Induced hyperammonaemia led to increased sleepiness but had no acute effect on pupillary light response or the neuropsychiatric tests. Trial registration Registration number: NCT04771104.
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Li P, Yang Y, Lin Z, Hong S, Jiang L, Zhou H, Yang L, Zhu L, Liu X, Liu L. Bile Duct Ligation Impairs Function and Expression of Mrp1 at Rat Blood-Retinal Barrier via Bilirubin-Induced P38 MAPK Pathway Activations. Int J Mol Sci 2022; 23:7666. [PMID: 35887010 PMCID: PMC9318728 DOI: 10.3390/ijms23147666] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2022] [Revised: 07/04/2022] [Accepted: 07/07/2022] [Indexed: 11/29/2022] Open
Abstract
Liver injury is often associated with hepatic retinopathy, resulting from accumulation of retinal toxins due to blood-retinal barrier (BRB) dysfunction. Retinal pigment epithelium highly expresses MRP1/Mrp1. We aimed to investigate whether liver injury affects the function and expression of retinal Mrp1 using bile duct ligation (BDL) rats. Retinal distributions of fluorescein and 2,4-dinitrophenyl-S-glutathione were used for assessing Mrp1 function. BDL significantly increased distributions of the two substrates and bilirubin, downregulated Mrp1 protein, and upregulated phosphorylation of p38 and MK2 in the retina. BDL neither affected the retinal distribution of FITC-dextran nor expressions of ZO-1 and claudin-5, demonstrating intact BRB integrity. In ARPE-19 cells, BDL rat serum or bilirubin decreased MRP1 expression and enhanced p38 and MK2 phosphorylation. Both inhibiting and silencing p38 significantly reversed the bilirubin- and anisomycin-induced decreases in MRP1 protein. Apparent permeability coefficients of fluorescein in the A-to-B direction (Papp, A-to-B) across the ARPE-19 monolayer were greater than Papp, B-to-A. MK571 or bilirubin significantly decreased Papp, A-to-B of fluorescein. Bilirubin treatment significantly downregulated Mrp1 function and expression without affecting integrity of BRB and increased bilirubin levels and phosphorylation of p38 and MK2 in rat retina. In conclusion, BDL downregulates the expression and function of retina Mrp1 by activating the p38 MAPK pathway due to increased bilirubin levels.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Xiaodong Liu
- Center of Drug Metabolism and Pharmacokinetics, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China; (P.L.); (Y.Y.); (Z.L.); (S.H.); (L.J.); (H.Z.); (L.Y.); (L.Z.)
| | - Li Liu
- Center of Drug Metabolism and Pharmacokinetics, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China; (P.L.); (Y.Y.); (Z.L.); (S.H.); (L.J.); (H.Z.); (L.Y.); (L.Z.)
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Bugiani M, Vuong C, Breur M, van der Knaap MS. Vanishing white matter: a leukodystrophy due to astrocytic dysfunction. Brain Pathol 2019; 28:408-421. [PMID: 29740943 DOI: 10.1111/bpa.12606] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Accepted: 03/07/2018] [Indexed: 12/26/2022] Open
Abstract
VWM is one of the most prevalent leukodystrophies with unique clinical, pathological and molecular features. It mostly affects children, but may develop at all ages, from birth to senescence. It is dominated by cerebellar ataxia and susceptible to stresses that act as factors provoking disease onset or episodes of rapid neurological deterioration possibly leading to death. VWM is caused by mutations in any of the genes encoding the five subunits of the eukaryotic translation initiation factor 2B (eIF2B). Although eIF2B is ubiquitously expressed, VWM primarily manifests as a leukodystrophy with increasing white matter rarefaction and cystic degeneration, meager astrogliosis with no glial scarring and dysmorphic immature astrocytes and increased numbers of oligodendrocyte progenitor cells that are restrained from maturing into myelin-forming cells. Recent findings point to a central role for astrocytes in driving the brain pathology, with secondary effects on both oligodendroglia and axons. In this, VWM belongs to the growing group of astrocytopathies, in which loss of essential astrocytic functions and gain of detrimental functions drive degeneration of the white matter. Additional disease mechanisms include activation of the unfolded protein response with constitutive predisposition to cellular stress, failure of astrocyte-microglia crosstalk and possibly secondary effects on the oxidative phosphorylation. VWM involves a translation initiation factor. The group of leukodystrophies due to defects in mRNA translation is also growing, suggesting that this may be a common disease mechanism. The combination of all these features makes VWM an intriguing natural model to understand the biology and pathology of the white matter.
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Affiliation(s)
- Marianna Bugiani
- Departments of Pathology, Child Neurology, and Functional Genomics, VU University Medical Center, Amsterdam Neuroscience, Amsterdam, The Netherlands
| | - Caroline Vuong
- Departments of Pathology, Child Neurology, and Functional Genomics, VU University Medical Center, Amsterdam Neuroscience, Amsterdam, The Netherlands
| | - Marjolein Breur
- Departments of Pathology, Child Neurology, and Functional Genomics, VU University Medical Center, Amsterdam Neuroscience, Amsterdam, The Netherlands
| | - Marjo S van der Knaap
- Departments of Pathology, Child Neurology, and Functional Genomics, VU University Medical Center, Amsterdam Neuroscience, Amsterdam, The Netherlands
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Aloin Inhibits Müller Cells Swelling in a Rat Model of Thioacetamide-Induced Hepatic Retinopathy. Molecules 2018; 23:molecules23112806. [PMID: 30380640 PMCID: PMC6278412 DOI: 10.3390/molecules23112806] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 10/19/2018] [Accepted: 10/29/2018] [Indexed: 12/30/2022] Open
Abstract
Swelling of retinal Müller cells is implicated in retinal edema and neuronal degeneration. Müller cell swelling is observed in patients with liver failure and is referred to as hepatic retinopathy. In the present study, we evaluated the effects of aloin, an anthraquinone-C-glycoside present in various Aloe species, on Müller cell dysfunction in a rat model of thioacetamide (TAA)-induced hepatic retinopathy. Experimental hepatic retinopathy was induced by three injections of TAA (200 mg/kg/day, intraperitoneal injection) for 3 days in rats. After the last injection of TAA, aloin (50 and 100 mg/kg) was orally gavaged for 5 days. The effects of aloin on the liver injury, serum ammonia levels, Müller cell swelling, glial fibrillary acidic protein (GFAP) expression, and gene expression of Kir4.1 and aquaporin-4 were examined. TAA-injected rats exhibited liver failure and hyperammonemia. In the TAA-injected rats, Müller cell bodies were highly enlarged, and GFAP, an indicator of retinal stress, was highly expressed in the retinas, indicating a predominant Müller cell gliosis. However, administration of aloin suppressed liver injury as well as Müller cell swelling through the normalization of Kir4.1 and aquaporin-4 channels, which play a key role in potassium and water transport in Müller cells. These results indicate that aloin may be helpful to protect retinal injury associated with liver failure.
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Feltracco P, Cagnin A, Carollo C, Barbieri S, Ori C. Neurological disorders in liver transplant candidates: Pathophysiology and clinical assessment. Transplant Rev (Orlando) 2017; 31:193-206. [DOI: 10.1016/j.trre.2017.02.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2016] [Revised: 12/29/2016] [Accepted: 02/20/2017] [Indexed: 12/14/2022]
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Maier M, Brückmann A, Schleußner E, Schlembach D. Using critical flicker frequency in the evaluation of visual impairment in preeclamptic women. Eur J Obstet Gynecol Reprod Biol 2017; 211:188-193. [PMID: 28292692 DOI: 10.1016/j.ejogrb.2017.02.029] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2016] [Revised: 02/20/2017] [Accepted: 02/28/2017] [Indexed: 11/15/2022]
Abstract
OBJECTIVE To assess critical flicker frequency (CFF) in normal uneventful pregnancy and preeclampsia. STUDY-DESIGN Case-control observational study at the University Hospital Jena and Outpatient Institute for Prenatal Diagnosis and Preventive Medicine. 25 non-pregnant women, 75 uncomplicated pregnant women in first, second and third trimester, and 15 women with overt preeclampsia. For comparison with preeclamptic patients we matched 15 normal pregnant women (mNP) for age, parity, body mass index, current smoking and family history of cardiovascular disease (CVD). We measured CFF using the portable HEPAtonorm Analyzer (nevoLAB GmbH, Germany). This device generates a flickering red light, starting with a frequency of 60Hz, giving the subjective an impression of a steady light. The participant signifies once the impression of a flickering light is recognized, and this CFF is recorded. Mean CFF and standard deviation is automatically calculated. Statistical analysis was performed using SPSS Version 22 for Windows. Following assessment of normal distribution with Kolmogorov-Smirnow test, comparisons were made with univariate and multivariate ANOVA and with unpaired and paired t test for continuous data and with χ2 test for categorical data. RESULTS Critical flicker frequency in healthy pregnant women does not differ from nonpregnant women. No significant differences in CFF measurements exist in first, second, and third trimester. In preeclampsia, CFF is significantly decreased compared to normal pregnant women (PE 38.80±2.16 vs. mNP 46.23±3.37; p=0.000). This alteration persists even some weeks postpartum (PE 41.17±1.13 vs. mNP 46.45±3.44; p=0.003). CONCLUSION In preeclamptic women, CFF is decreased indicating an altered endothelial situation. The finding that CFF remains reduced postpartum may be explained by either the effect of preeclampsia on maternal endothelium causing longer lasting damage or indicate a preexisting endothelial disorder. Up to this point, precise responsible mechanisms for altered CFF in preeclampsia are currently unclear and further studies are needed.
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Affiliation(s)
- Marina Maier
- Department of Obstetrics, Jena University Hospital, Friedrich-Schiller-University, 07744 Jena, Germany
| | - Andreas Brückmann
- Department of Prenatal Diagnosis and Preventive Medicine, GesaTal Medical Center, 99089 Erfurt, Germany
| | - Ekkehard Schleußner
- Department of Obstetrics, Jena University Hospital, Friedrich-Schiller-University, 07744 Jena, Germany
| | - Dietmar Schlembach
- Department of Obstetrics, Jena University Hospital, Friedrich-Schiller-University, 07744 Jena, Germany; Clinic of Obstetrics, Vivantes Hospital Berlin-Neukoelln, 12351 Berlin, Germany.
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Dooves S, Bugiani M, Postma NL, Polder E, Land N, Horan ST, van Deijk ALF, van de Kreeke A, Jacobs G, Vuong C, Klooster J, Kamermans M, Wortel J, Loos M, Wisse LE, Scheper GC, Abbink TEM, Heine VM, van der Knaap MS. Astrocytes are central in the pathomechanisms of vanishing white matter. J Clin Invest 2016; 126:1512-24. [PMID: 26974157 DOI: 10.1172/jci83908] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 01/28/2016] [Indexed: 11/17/2022] Open
Abstract
Vanishing white matter (VWM) is a fatal leukodystrophy that is caused by mutations in genes encoding subunits of eukaryotic translation initiation factor 2B (eIF2B). Disease onset and severity are codetermined by genotype. White matter astrocytes and oligodendrocytes are almost exclusively affected; however, the mechanisms of VWM development remain unclear. Here, we used VWM mouse models, patients' tissue, and cell cultures to investigate whether astrocytes or oligodendrocytes are the primary affected cell type. We generated 2 mouse models with mutations (Eif2b5Arg191His/Arg191His and Eif2b4Arg484Trp/Arg484Trp) that cause severe VWM in humans and then crossed these strains to develop mice with various mutation combinations. Phenotypic severity was highly variable and dependent on genotype, reproducing the clinical spectrum of human VWM. In all mutant strains, impaired maturation of white matter astrocytes preceded onset and paralleled disease severity and progression. Bergmann glia and retinal Müller cells, nonforebrain astrocytes that have not been associated with VWM, were also affected, and involvement of these cells was confirmed in VWM patients. In coculture, VWM astrocytes secreted factors that inhibited oligodendrocyte maturation, whereas WT astrocytes allowed normal maturation of VWM oligodendrocytes. These studies demonstrate that astrocytes are central in VWM pathomechanisms and constitute potential therapeutic targets. Importantly, astrocytes should also be considered in the pathophysiology of other white matter disorders.
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Goldbecker A, Weissenborn K, Hamidi Shahrezaei G, Afshar K, Rümke S, Barg-Hock H, Strassburg CP, Hecker H, Tryc AB. Comparison of the most favoured methods for the diagnosis of hepatic encephalopathy in liver transplantation candidates. Gut 2013; 62:1497-504. [PMID: 23297006 DOI: 10.1136/gutjnl-2012-303262] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
OBJECTIVE Hepatic encephalopathy (HE) is a common complication of liver insufficiency. While there is widespread acceptance of its importance, there is no consensus on how best to diagnose and monitor HE. OBJECTIVE To compare the four most favoured methods for the diagnosis of HE. DESIGN 170 patients who were on the waiting list for liver transplantation as well as 86 healthy controls were included in the study. All patients and controls underwent the portosystemic encephalopathy syndrome test yielding the psychometric hepatic encephalopathy score (PHES), the repeatable battery for the assessment of neuropsychological status (RBANS), the inhibitory control test (ICT) and critical flicker frequency (CFF) measurement. RESULTS PHES and ICT targets had the best sensitivity (85.7% vs 85.7%) and specificity (96.5% vs 97.6%) for the diagnosis of overt HE. CFF showed inferior sensitivity (40.9%) for the diagnosis of HE and dependency from previous alcohol abuse (p=0.015). Multiple regression analysis showed that all test results apart from PHES were influenced by secondary diagnoses such as diabetes mellitus and renal insufficiency. CONCLUSIONS In the German population of patients awaiting liver transplantation, PHES is the most robust method for the diagnosis and follow-up of HE.
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Affiliation(s)
- Annemarie Goldbecker
- Integrated Research and Treatment Center (IFB) Transplantation, Hannover Medical School, , Hannover, Germany
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Götz T, Huonker R, Kranczioch C, Reuken P, Witte OW, Günther A, Debener S. Impaired evoked and resting-state brain oscillations in patients with liver cirrhosis as revealed by magnetoencephalography. NEUROIMAGE-CLINICAL 2013; 2:873-82. [PMID: 24179838 PMCID: PMC3777687 DOI: 10.1016/j.nicl.2013.06.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 05/21/2013] [Accepted: 06/05/2013] [Indexed: 10/26/2022]
Abstract
A number of studies suggest that the clinical manifestation of neurological deficits in hepatic encephalopathy results from pathologically synchronized neuronal oscillations and altered oscillatory coupling. In the present study spontaneous and evoked oscillatory brain activities were analyzed jointly with established behavioral measures of altered visual oscillatory processing. Critical flicker and fusion frequencies (CFF, FUF) were measured in 25 patients diagnosed with liver cirrhosis and 30 healthy controls. Magnetoencephalography (MEG) data were collected at rest and during a visual task employing repetitive stimulation. Resting MEG and evoked fields were analyzed. CFF and FUF were found to be reduced in patients, providing behavioral evidence for deficits in visual oscillatory processing. These alterations were found to be related to resting brain activity in patients, namely that the lower the dominant MEG frequency at rest, the lower the CFF and FUF. An analysis of evoked fields at sensor level indicated that in comparison to normal controls, patients were not able to dynamically adapt to flickering visual stimulation. Evoked activity was also analyzed based on independent components (ICs) derived by independent component analysis. The similarity between the shape of each IC and an artificial sine function representing the stimulation frequency was tested via magnitude squared coherence. In controls, we observed a small number of components that correlated strongly with the sine function and a high number of ICs that did not correlate with the sine function. Interestingly, patient data were characterized by a high number of moderately correlating components. Taken together, these results indicate a fundamental divergence of the cerebral resonance activity in cirrhotic patients.
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Key Words
- CFF, critical flicker frequency
- CON, control
- CSI, component similarity index
- Critical flicker and fusion frequency
- EEG, electroencephalography
- EMG, electromyogram
- ERA, event related averages
- FUF, fusion frequency
- GSI, general similarity index
- GW, Gabor wavelet
- HE, hepatic encephalopathy
- HESA, hepatic encephalopathy scoring algorithm
- ICA, independent component analysis
- Impaired neuronal oscillations
- Liver cirrhosis
- MEG, magnetoencephalography
- MELD score, model of end-stage liver disease-score
- MSC, magnitude squared coherence
- PCA, principal component analysis
- Resting frequency
- SSVEF/SSVEP/SSVER, steady state visual evoked field/potential/response
- SW, sine wave
- Visual steady state evoked fields
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Affiliation(s)
- Theresa Götz
- Biomagnetic Center, Department of Neurology, University Hospital Jena, Erlanger Allee 101, 07747 Jena, Germany ; CSCC, Center for Sepsis Control and Care, Erlanger 101, 07747 Jena, Germany
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Kappus MR, Bajaj JS. Covert hepatic encephalopathy: not as minimal as you might think. Clin Gastroenterol Hepatol 2012; 10:1208-19. [PMID: 22728384 DOI: 10.1016/j.cgh.2012.05.026] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Revised: 05/30/2012] [Accepted: 05/31/2012] [Indexed: 02/07/2023]
Abstract
Hepatic encephalopathy (HE) is a serious neuropsychiatric and neurocognitive complication of acute and chronic liver disease. Symptoms are often overt (confusion, disorientation, ataxia, or coma) but can also be subtle (difficulty with cognitive abilities such as executive decision-making and psychomotor speed). There is consensus that HE is characterized as a spectrum of neuropsychiatric symptoms in the absence of brain disease, ranging from overt HE (OHE) to minimal HE (MHE). The West Haven Criteria are most often used to grade HE, with scores ranging from 0-4 (4 being coma). However, it is a challenge to diagnose patients with MHE or grade 1 HE; it might be practical to combine these entities and name them covert HE for clinical use. The severity of HE is associated with the stage of liver disease. Although the pathologic mechanisms of HE are not well understood, they are believed to involve increased levels of ammonia and inflammation, which lead to low-grade cerebral edema. A diagnosis of MHE requires dedicated psychometric tests and neurophysiological techniques rather than a simple clinical assessment. Although these tests can be difficult to perform in practice, they are cost effective and important; the disorder affects patients' quality of life, socioeconomic status, and driving ability and increases their risk for falls and the development of OHE. Patients with MHE are first managed by excluding other causes of neurocognitive dysfunction. Therapy with gut-specific agents might be effective. We review management strategies and important areas of research for MHE and covert HE.
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Affiliation(s)
- Matthew R Kappus
- Division of Gastroenterology, Hepatology and Nutrition, Virginia Commonwealth University and McGuire VA Medical Center, Richmond, Virginia 23249, USA
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Montoliu C, Gonzalez-Escamilla G, Atienza M, Urios A, Gonzalez O, Wassel A, Aliaga R, Giner-Duran R, Serra MA, Rodrigo JM, Belloch V, Felipo V, Cantero JL. Focal cortical damage parallels cognitive impairment in minimal hepatic encephalopathy. Neuroimage 2012; 61:1165-75. [PMID: 22465844 DOI: 10.1016/j.neuroimage.2012.03.041] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2011] [Revised: 03/11/2012] [Accepted: 03/13/2012] [Indexed: 01/12/2023] Open
Abstract
Little attention has been paid to cortical integrity in patients with minimal hepatic encephalopathy (MHE), although cognitive functions affected in early stages of liver disease are mainly allocated in different neocortical structures. Here we used cortical surface-based analysis techniques to investigate if patterns of cortical thinning accompany the mildest form of HE. To aim this goal, cortical thickness obtained from high-resolution 3T magnetic resonance imaging (MRI) was measured in patients with no MHE (NMHE), MHE, and healthy controls. Further correlation analyses were performed to examine whether scores in the critical flicker frequency (CFF) test, and blood ammonia levels accounted for the loss of cortical integrity in different stages of liver disease. Finally, we assessed group differences in volume of different subcortical regions and their potential relationships with CFF scores/blood ammonia levels. Results showed a focal thinning of the superior temporal cortex and precuneus in MHE patients when compared with NMHE and controls. Relationships between blood ammonia levels and cortical thickness of the calcarine sulcus accounted for impaired visual judgment in patients with MHE when compared to NMHE. Regression analyses between cortical thickness and CFF predicted differences between controls and the two groups of HE patients, but failed to discriminate between patients with NMHE and MHE. Taking together, these findings provide the first report of cortical thinning in MHE patients, and they yield novel insights into the neurobiological basis of cognitive impairment associated with early stages of liver diseases.
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Affiliation(s)
- Carmina Montoliu
- Fundación Investigación Hospital Clínico Universitario de Valencia-INCLIVA, Spain
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Kappus MR, Bajaj JS. Assessment of minimal hepatic encephalopathy (with emphasis on computerized psychometric tests). Clin Liver Dis 2012; 16:43-55. [PMID: 22321464 PMCID: PMC3312030 DOI: 10.1016/j.cld.2011.12.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Minimal hepatic encephalopathy (MHE) is associated with a high risk of development of overt hepatic encephalopathy, impaired quality of life, and driving accidents. The detection of MHE requires specialized testing because it cannot, by definition, be diagnosed on standard clinical examination. Psychometric and neurophysiologic techniques are often used to test for MHE. Paper-pencil psychometric batteries and computerized tests have proved useful in diagnosing MHE and predicting its outcomes. Neurophysiologic tests also provide useful information. The diagnosis of MHE is an important issue for clinicians and patients alike. Testing strategies depend on the normative data available, patient comfort, and local expertise.
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Affiliation(s)
- Matthew R Kappus
- Division of Gastroenterology, Hepatology and Nutrition, McGuire VA Medical Center, Virginia Commonwealth University, 1201 Broad Rock Boulevard, Richmond, VA 23249, USA
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15
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Reversible retinal edema in an infant with neonatal hemochromatosis and liver failure. J AAPOS 2011; 15:91-3. [PMID: 21397814 PMCID: PMC3059895 DOI: 10.1016/j.jaapos.2010.11.016] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2010] [Revised: 11/05/2010] [Accepted: 11/08/2010] [Indexed: 11/23/2022]
Abstract
We present a case of bilateral severe retinal edema with subretinal fluid in an infant diagnosed with neonatal hemochromatosis and liver failure. A macular cherry-red spot in each eye mimicked the clinical appearance of many metabolic storage diseases. Both the clinical retinal appearance and the anatomic abnormalities observed on spectral domain optical coherence tomography resolved after successful liver transplant.
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Abstract
Hepatic encephalopathy (HE) is caused by liver impairment and has a multitude of symptoms in affected patients, including change in level of consciousness, intellectual function, and neuromuscular function. Pharmacologic therapy includes use of nonabsorbable disaccharides (lactulose and lactitol), and antibiotics such as neomycin, paromycin, metronidazole, and rifaximin. Probiotics, acarbose, and drugs such as L-carnitine and flumazenil, may also be helpful in treating HE.
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Abstract
OBJECTIVES Plasma melatonin profile abnormalities have been described in patients with cirrhosis and generally attributed to impaired hepatic melatonin metabolism. The possibility that they might reflect circadian clock dysfunction has not been explored. In addition, the relationship between plasma melatonin profiles and the sleep disturbances observed in these patients remains unclear. The aims of this study were: (i) to evaluate circadian clock function and hepatic melatonin metabolism in cirrhotic patients, and (ii) to study the relationship between plasma melatonin profiles and sleep-wake behavior. METHODS The study population comprised 20 patients with cirrhosis (mean (range) age, 59 (39-77) years) and 9 healthy volunteers (60 (38-84) years). Plasma melatonin/cortisol concentrations were measured hourly, for 24 h, in light/posture-controlled conditions. Urinary 6-sulfatoxymelatonin, the main melatonin metabolite, was measured simultaneously to determine clearance. The ability of light to suppress nocturnal melatonin synthesis was assessed. Habitual sleep quality/timing was evaluated using a questionnaire, actigraphy, and sleep diaries. RESULTS There was evidence of central circadian disruption in patients compared with healthy controls: peak plasma melatonin/cortisol times were delayed (04:48+/-02:36 vs. 02:48+/-00:54, P=0.01; 10:18+/-02:54 vs. 08:54+/-01:24, P=0.06) and the plasma melatonin response to light was reduced (12%+/-19% vs. 24%+/-15%, P=0.09). However, the mean 24 h plasma melatonin clearance did not differ significantly between patients and healthy volunteers (0.22+/-0.10 vs. 0.28+/-0.17 l/kg per h, P=0.36). Finally, although patients showed a degree of misalignment between sleep and circadian timings, there was no association between circadian abnormalities and impaired sleep quality. CONCLUSIONS Plasma melatonin profile abnormalities, predominantly central in origin, are observed in patients with mild to moderately decompensated cirrhosis. However, they are substantially unrelated to the sleep disturbances prevalent in this population.
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Timmermann L, Butz M, Gross J, Kircheis G, Häussinger D, Schnitzler A. Neural synchronization in hepatic encephalopathy. Metab Brain Dis 2005; 20:337-46. [PMID: 16382344 DOI: 10.1007/s11011-005-7916-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Hepatic encephalopathy (HE) is clinically characterized by a large variety of symptoms including motor symptoms, cognitive deficits, as well as changes in the level of alertness up to hepatic coma. A number of pathological processes affecting glial and neuronal function have been identified, including hyper-ammonia, changes within the excitatory and inhibitory transmitter systems, as well as osmolytic changes with consecutive cell swelling. One explanation how these pathological processes result in neurological deficits in HE is the concept of pathologically synchronized oscillations within and between relevant brain regions. A number of studies suggest that the cognitive deficits and the reduced level of alertness in patients with HE can be attributed to a significantly slowed and pathologically synchronized spontaneous oscillatory brain activity, depending on the grade of HE. Moreover, HE motor symptoms, like postural tremor called"mini asterixis," have recently been shown to be associated with abnormal thalamo-cortical and cortico-muscular synchronization. Indirect evidence exists from studies of processing and recognition of flicker stimuli that in HE slowing of oscillations also occurs in the visual system. Taken together, pathological synchronization of neuronal activity may turn out to be a promising pathophysiological concept for linking neuronal dysfunction to the diversity of clinical deficits in HE.
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Affiliation(s)
- Lars Timmermann
- Department of Neurology, University Hospital Düsseldorf, Heinrich-Heine University, Düsseldorf, Germany
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Montagnese S, Gordon HM, Jackson C, Smith J, Tognella P, Jethwa N, Sherratt RM, Morgan MY. Disruption of smooth pursuit eye movements in cirrhosis: relationship to hepatic encephalopathy and its treatment. Hepatology 2005; 42:772-81. [PMID: 16175619 DOI: 10.1002/hep.20855] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Smooth pursuit eye movements (SPEM) are the conjugate movements used to track the smooth trajectory of small dots. Jerky or 'saccadic' ocular pursuit has been reported in patients with cirrhosis, but no formal assessment of SPEM has ever been undertaken. The aim of this study was to evaluate SPEM in patients with cirrhosis and varying degrees of hepatic encephalopathy. The patient population comprised 56 individuals (31 men, 25 women) of mean age 51.1 (range, 25-70) years, with biopsy-proven cirrhosis, classified, using clinical, electroencephalographic, and psychometric variables, as either neuropsychiatrically unimpaired or as having minimal or overt hepatic encephalopathy; patients were further categorized in relation to their treatment status. The reference population comprised 28 healthy volunteers (12 men, 16 women) of mean age 47.3 (range, 26-65) years. SPEM was assessed using an electro-oculographic technique. Visual inspection of the SPEM recordings showed clear disruption of smooth pursuit in the patients with minimal hepatic encephalopathy, and more pronounced disruption, if not complete loss, of smooth pursuit in patients with overt hepatic encephalopathy. The differences observed in quantifiable SPEM indices between the healthy volunteers/unimpaired patients and those with overt hepatic encephalopathy were significant (P < .05). In conclusion, SPEM performance is impaired in patients with hepatic encephalopathy in parallel with the degree of neuropsychiatric disturbance: the pathophysiology of these changes is unknown, but retinal, extrapyramidal, and attentional abnormalities are likely to play a role. Treatment status confounds the classification of neuropsychiatric status and should be taken into account when categorizing these patients.
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Affiliation(s)
- Sara Montagnese
- Centre for Hepatology, Department of Medicine, Hampstead Campus, Royal Free & University College Medical School, Rowland Hill Street, Hampstead, London, United Kingdom
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20
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Chapter 7 Oscillatory responses and gamma band activity. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/s1567-4231(09)70204-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
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Abstract
The term minimal hepatic encephalopathy refers to the subtle changes in cognitive function, electrophysiological parameters, cerebral neurochemical/neurotransmitter homeostasis, cerebral blood flow, metabolism, and fluid homeostasis that can be observed in patients with cirrhosis who have no clinical evidence of hepatic encephalopathy. Use of this term emphasizes the fact that the entity of hepatic encephalopathy is a single syndrome with quantitatively distinct features relating to severity. The absence of clinical evidence of hepatic encephalopathy is key to the diagnosis and can only be determined by a detailed assessment of the patients' history and a comprehensive neurological assessment of consciousness, cognitive, and motor function. The neuropsychological features of minimal hepatic encephalopathy point to a disorder of executive functioning, particularly selective attention and psychomotor speed, but other abnormalities may be observed. Alterations in electrophysiological variables have been described; endogenous evoked potentials are, in principle, more likely to reflect the presence of minimal hepatic encephalopathy, since they reflect cognitive phenomena rather than mere stimulus conduction but the specificity of the changes observed is unclear at present. Changes have also been described in the execution of diadochokinetic movements and in the capacity to discriminate flickering light, both of which may have diagnostic potential. The changes observed in cerebral blood flow and metabolism in SPET, PET, and 1H and 31P MRS studies reflect the pathogenic process that underlies the condition rather than providing diagnostic information. Similarly, the morphological brain abnormalities identified in this population, including mild brain oedema, hyperintensity of the globus pallidus and other subcortical nuclei observed in cerebral MR studies, and the central and cortical atrophy observed in neural imaging studies, are unlikely to have diagnostic utility. The presence of minimal hepatic encephalopathy is not without clinical consequence; it has a detrimental effect on health-related quality of life, the ability to perform complex tasks such as driving, and on outcome.
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Affiliation(s)
- Piero Amodio
- Clinica Medica 5, CIRMANMEC, University of Padova, Italy.
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Izumi Y, Matsukawa M, Benz AM, Izumi M, Ishikawa M, Olney JW, Zorumski CF. Role of ammonia in reversal of glutamate-mediated Müller cell swelling in the rat retina. Glia 2004; 48:44-50. [PMID: 15326614 DOI: 10.1002/glia.20052] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Glutamate is thought to participate in a variety of retinal degenerative disorders. However, when exposed to glutamate at concentrations up to 1 mM, ex vivo rat retinas typically exhibit Müller cell swelling, but not excitotoxic neuronal damage. This Müller cell swelling is reversible following glutamate washout, indicating that the glial edema is not required for glutamate-induced neuronal injury. It is unclear whether glutamate directly induces the Müller cell swelling or whether a metabolite of glutamate such as glutamine acts as an osmolyte to generate the cellular edema. To examine this issue, ex vivo rat retinas were exposed to 1 mM glutamate or 1 mM glutamine and were evaluated histologically. Glutamate was also combined with 1 mM ammonia or with methionine sulfoximine (MSO), an inhibitor of glutamine synthetase, the enzyme that catalyzes the synthesis of glutamine from glutamate and ammonia. Glutamate-mediated Müller cell swelling was blocked by co-administration of ammonia and the reversibility of Müller cell swelling was inhibited by MSO administered following glutamate exposure. Glutamine alone failed to induce Müller cell swelling. These results indicate that glutamate-mediated Müller cell swelling is unlikely to result from glutamine accumulation. Rather, conversion of glutamate to glutamine in a reaction involving ammonia helps reverse Müller cell swelling following exposure to exogenous glutamate.
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Affiliation(s)
- Yukitoshi Izumi
- Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri
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Affiliation(s)
- M Lewis
- Academic Unit of Medicine, St James's University Hospital, Leeds, UK.
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Guérit JM, Amodio P, Hafner H, Litscher G, Van Huffelen AC. Neuromonitoring in the operating room and intensive care unit: an update. SUPPLEMENTS TO CLINICAL NEUROPHYSIOLOGY 2003; 53:61-71. [PMID: 12740978 DOI: 10.1016/s1567-424x(09)70139-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/02/2023]
Affiliation(s)
- J M Guérit
- Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, B-1200 Brussels, Belgium.
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Kircheis G, Wettstein M, Timmermann L, Schnitzler A, Häussinger D. Critical flicker frequency for quantification of low-grade hepatic encephalopathy. Hepatology 2002; 35:357-66. [PMID: 11826409 DOI: 10.1053/jhep.2002.30957] [Citation(s) in RCA: 255] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Subclinical hepatic encephalopathy (SHE) is currently diagnosed by psychometric tests or neurophysiologic techniques. In view of its sociomedical relevance, simple and reproducible tests for routine diagnosis are required. This study evaluates critical flicker-frequency thresholds for quantification of low-grade hepatic encephalopathy. A total of 115 patients (92 with cirrhosis, 23 controls) were analyzed for HE severity (mental state, computerized psychometric tests), and the threshold frequencies at which light pulses are perceived as fused (fusion frequency) or flickering light (critical flicker frequency [CFF]). CFF was a highly reproducible parameter with little age, day-time, and training dependency. CFFs in cirrhotic patients without HE (HE 0) were not different from those found in noncirrhotic controls. Significantly lower CFFs were found in cirrhotic patients with subclinical or manifest HE, and the various HE groups separated from each other at a high level of significance (P <.01). By using a CFF cut-off value of 39 Hz, a 100% separation of patients with manifest HE from noncirrhotic controls and HE 0 cirrhotic patients was obtained. SHE patients separated from HE 0 cirrhotic patients with high sensitivity (55%) and specificity (100%). The HE severity-dependent differences were found in both, alcoholic and posthepatitic cirrhosis. Statistically significant correlations (P <.01) were found between CFFs and individual psychometric tests. Aggravation of preexisting HE after transjugular intrahepatic portosystemic stent shunt (TIPS) implantation was accompanied by a corresponding decrease of CFF, whereas improvement of HE increased CFF. In conclusion, CFF is a sensitive, simple, and reliable parameter for quantification of low-grade HE severity in cirrhotic patients and may be useful for the detection and monitoring of SHE.
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Affiliation(s)
- Gerald Kircheis
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
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Abstract
Electrophysiological research on acquired retinal disorders, both common and rare, is reviewed. Age is a major factor influencing electroretinogram (ERG) and electro-oculogram (EOG) findings. Bipolar or Müller cell death in the aging retina could account for much of the amplitude decline that is observed with age. In diabetic retinopathy, the oscillatory potentials can monitor the progression of the disease and indicate neuronal alterations rather than diabetic angiopathy of the retina. Human ERG studies on glaucoma concentrated on ERG measures that are dominated by inner retinal contributions. It has been shown that the pattern ERG can serve as a predictor of ocular hypertension's progression to glaucoma. In retinal disorders caused by endogenous intoxication, such as hepatic retinopathy, or exogenous intoxication from chronic lead exposure, ERG changes give an objective measure of the damage and allow to study the pathophysiological mechanisms that are involved. Inflammations of the choroid and the retina affect the standard ERG when they are diffuse. In central serous chorioretinopathy, functional disturbances can be revealed not only in the photoreceptors but also in the middle and inner retinal layers with the use of focal stimuli. Choroidal melanoma leads to large reductions of the EOG light peak-to-dark trough ratio through its influence on the transepithelial potential of the retinal pigment epithelium (RPE). In cancer-associated retinopathy, both the rod and cone ERGs are reduced. However, selective cone dysfunction has been described. In melanoma-associated retinopathy, the long flash ERG may reveal a specific pathophysiological mechanism, namely the affection of the ON-pathway with preservation of the OFF-pathway. ERG measurements can reveal vitamin A deficiency and are altered in cases with a mutation in the gene for the retinol binding protein in which other organs are not affected. Photochemical damage to the retina from light emission by the operating microscope can be assessed by electrophysiological methods.
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Affiliation(s)
- H P Scholl
- Department of Pathophysiology of Vision and Neuro-Ophthalmology, University Eye Hospital, Tübingen, Germany.
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Abstract
It is widely assumed that neurones have sufficient metabolic reserves to allow them to function independently of glial cells for extended periods. The present study investigates the length of time taken before retinal neurones no longer respond normally to light after the inhibition of glial enzymes that are involved in the synthesis of precursors of neuronal glutamate. The glutamine synthetase inhibitor methionine sulfoximine, when injected intraocularly in Wistar rats, caused a time- and dose-dependent suppression of the scotopic electroretinogram b-wave. At the highest dosage (40 mM) the b-wave was significantly reduced within 2 min of injection. Because the b-wave is an indicator of neurotransmission in the retina, it is deduced that inhibition of glutamine synthetase rapidly blocks glutamatergic neurotransmission. Immunohistochemistry revealed a depletion of neuronal glutamate and an accumulation of glutamate in Müller glial cells, in a time course that matched the b-wave suppression. The b-wave was quickly restored by injection of glutamine (4 mM). The rapid reduction of glutamatergic transmission after methionine sulfoximine administration challenges the view that neurones have sufficient reserves to allow them to function independently for extended periods; instead, it indicates that glia are essential for the moment-to-moment sustenance of neuronal function.
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Affiliation(s)
- N L Barnett
- Vision, Touch & Hearing Research Centre, The University of Queensland, Brisbane, Australia.
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Affiliation(s)
- A T Blei
- Department of Medicine, Lakeside VAMC and Northwestern University, Chicago, IL 60611, USA
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