Elevated cerebral lactate: Implications in the pathogenesis of hepatic encephalopathy

Downregulated expression of lactate dehydrogenase in adult oligodendrocytes and its implication for the transfer of glycolysis products to axons

Oligodendrocytes and astrocytes are metabolically coupled to neuronal compartments. Pyruvate and lactate can shuttle between glial cells and axons via monocarboxylate transporters. However, lactate can only be synthesized or used in metabolic reactions with the help of lactate dehydrogenase (LDH), a tetramer of LDHA and LDHB subunits in varying compositions. Here we show that mice with a cell type-specific disruption of both Ldha and Ldhb genes in oligodendrocytes lack a pathological phenotype that would be indicative of oligodendroglial dysfunctions or lack of axonal metabolic support. Indeed, when combining immunohistochemical, electron microscopical, and in situ hybridization analyses in adult mice, we found that the vast majority of mature oligodendrocytes lack detectable expression of LDH. Even in neurodegenerative disease models and in mice under metabolic stress LDH was not increased. In contrast, at early development and in the remyelinating brain, LDHA was readily detectable in immature oligodendrocytes. Interestingly, by immunoelectron microscopy LDHA was particularly enriched at gap junctions formed between adjacent astrocytes and at junctions between astrocytes and oligodendrocytes. Our data suggest that oligodendrocytes metabolize lactate during development and remyelination. In contrast, for metabolic support of axons mature oligodendrocytes may export their own glycolysis products as pyruvate rather than lactate. Lacking LDH, these oligodendrocytes can also "funnel" lactate through their "myelinic" channels between gap junction-coupled astrocytes and axons without metabolizing it. We suggest a working model, in which the unequal cellular distribution of LDH in white matter tracts facilitates a rapid and efficient transport of glycolysis products among glial and axonal compartments.

Evaluation of G3BP1 in the prognosis of acute and acute-on-chronic liver failure after the treatment of artificial liver support system

BACKGROUND

The increased expression of G3BP1 was positively correlated with the prognosis of liver failure.

AIM

To investigate the effect of G3BP1 on the prognosis of acute liver failure (ALF) and acute-on-chronic liver failure (ACLF) after the treatment of artificial liver support system (ALSS).

METHODS

A total of 244 patients with ALF and ACLF were enrolled in this study. The levels of G3BP1 on admission and at discharge were detected. The validation set of 514 patients was collected to verify the predicted effect of G3BP1 and the viability of prognosis.

RESULTS

This study was shown that lactate dehydrogenase (LDH), alpha-fetoprotein (AFP) and prothrombin time were closely related to the prognosis of patients. After the ALSS treatment, the patient' amount of decreased G3BP1 index in difference of G3BP1 between the value of discharge and admission (difG3BP1) < 0 group had a nearly 10-fold increased risk of progression compared with the amount of increased G3BP1 index. The subgroup analysis showed that the difG3BP1 < 0 group had a higher risk of progression, regardless of model for end-stage liver disease high-risk or low-risk group. At the same time, compared with the inflammatory marks [tumor necrosis factor-α, interleukin (IL)-1β and IL-18], G3BP1 had higher discrimination and was more stable in the model analysis and validation set. When combined with AFP and LDH, concordance index was respectively 0.84 and 0.8 in training and validation cohorts.

CONCLUSION

This study indicated that G3BP1 could predict the prognosis of ALF or ACLF patients treated with ALSS. The combination of G3BP1, AFP and LDH could accurately evaluate the disease condition and predict the clinical endpoint of patients.

Combined Therapeutic Plasma Exchange and Continuous Renal Replacement Therapy in Children With Dengue-Associated Acute Liver Failure and Shock Syndrome: Single-Center Cohort From Vietnam

OBJECTIVES

Pediatric acute liver failure (PALF) is a fatal complication in patients with severe dengue. To date, clinical data on the combination of therapeutic plasma exchange (TPE) and continuous renal replacement therapy (CRRT) for managing dengue-associated PALF concomitant with shock syndrome are limited.

DESIGN

Retrospective cohort study (January 2013 to June 2022).

PATIENTS

Thirty-four children.

SETTING

PICU of tertiary Children's Hospital No. 2 in Vietnam.

INTERVENTIONS

We assessed a before-versus-after practice change at our center of using combined TPE and CRRT (2018 to 2022) versus CRRT alone (2013 to 2017) in managing children with dengue-associated acute liver failure and shock syndrome. Clinical and laboratory data were reviewed from PICU admission, before and 24 h after CRRT and TPE treatments. The main study outcomes were 28-day in-hospital mortality, hemodynamics, clinical hepatoencephalopathy, and liver function normalization.

MEASUREMENTS AND MAIN RESULTS

A total of 34 children with a median age of 10 years (interquartile range: 7-11 yr) underwent standard-volume TPE and/or CRRT treatments. Combined TPE and CRRT ( n = 19), versus CRRT alone ( n = 15), was associated with lower proportion of mortality 7 of 19 (37%) versus 13 of 15 (87%), difference 50% (95% CI, 22-78; p < 0.01). Use of combined TPE and CRRT was associated with substantial advancements in clinical hepatoencephalopathy, liver transaminases, coagulation profiles, and blood lactate and ammonia levels (all p values < 0.001).

CONCLUSIONS

In our experience of children with dengue-associated PALF and shock syndrome, combined use of TPE and CRRT, versus CRRT alone, is associated with better outcomes. Such combination intervention was associated with normalization of liver function, neurological status, and biochemistry. In our center we continue to use combined TPE and CRRT rather than CRRT alone.

The interaction of ammonia and manganese in abnormal metabolism of minimal hepatic encephalopathy: A comparison metabolomics study

This study was to investigate the effects of ammonia and manganese in the metabolism of minimal hepatic encephalopathy (MHE). A total of 32 Sprague-Dawley rats were divided into four subgroups: chronic hyperammonemia (CHA), chronic hypermanganese (CHM), MHE and control group (CON). 1H-NMR-based metabolomics was used to detect the metabolic changes. Sparse projection to latent structures discriminant analysis was used for identifying and comparing the key metabolites. Significant elevated blood ammonia were shown in the CHA, CHM, and MHE rats. Significant elevated brain manganese (Mn) were shown in the CHM, and MHE rats, but not in the CHA rats. The concentrations of γ-amino butyric acid (GABA), lactate, alanine, glutamate, glutamine, threonine, and phosphocholine were significantly increased, and that of myo-inositol, taurine, leucine, isoleucine, arginine, and citrulline were significantly decreased in the MHE rats. Of all these 13 key metabolites, 10 of them were affected by ammonia (including lactate, alanine, glutamate, glutamine, myo-inositol, taurine, leucine, isoleucine, arginine, and citrulline) and 5 of them were affected by manganese (including GABA, lactate, myo-inositol, taurine, and leucine). Enrichment analysis indicated that abnormal metabolism of glutamine and TCA circle in MHE might be affected by the ammonia, and abnormal metabolism of GABA might be affected by the Mn, and abnormal metabolism of glycolysis and branched chain amino acids metabolism might be affected by both ammonia and Mn. Both ammonia and Mn play roles in the abnormal metabolism of MHE. Chronic hypermanganese could lead to elevated blood ammonia. However, chronic hyperammonemia could not lead to brain Mn deposition.

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

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

Bile duct ligation differently regulates protein expressions of organic cation transporters in intestine, liver and kidney of rats through activation of farnesoid X receptor by cholate and bilirubin

Body is equipped with organic cation transporters (OCTs). These OCTs mediate drug transport and are also involved in some disease process. We aimed to investigate whether liver failure alters intestinal, hepatic and renal Oct expressions using bile duct ligation (BDL) rats. Pharmacokinetic analysis demonstrates that BDL decreases plasma metformin exposure, associated with decreased intestinal absorption and increased urinary excretion. Western blot shows that BDL significantly downregulates intestinal Oct2 and hepatic Oct1 but upregulates renal and hepatic Oct2. In vitro cell experiments show that chenodeoxycholic acid (CDCA), bilirubin and farnesoid X receptor (FXR) agonist GW4064 increase OCT2/Oct2 but decrease OCT1/Oct1, which are remarkably attenuated by glycine-β-muricholic acid and silencing FXR. Significantly lowered intestinal CDCA and increased plasma bilirubin levels contribute to different Octs regulation by BDL, which are confirmed using CDCA-treated and bilirubin-treated rats. A disease-based physiologically based pharmacokinetic model characterizing intestinal, hepatic and renal Octs was successfully developed to predict metformin pharmacokinetics in rats. In conclusion, BDL remarkably downregulates expressions of intestinal Oct2 and hepatic Oct1 protein while upregulates expressions of renal and hepatic Oct2 protein in rats, finally, decreasing plasma exposure and impairing hypoglycemic effects of metformin. BDL differently regulates Oct expressions via Fxr activation by CDCA and bilirubin.

Cerebrospinal fluid lactate levels along the Alzheimer’s disease continuum and associations with blood-brain barrier integrity, age, cognition, and biomarkers

Background

Cerebrospinal fluid (CSF) lactate levels have been suggested to be associated with disease severity and progression in several neurological diseases as an indicator of impaired energy metabolism, neuronal death, or microglial activation. Few studies have examined CSF lactate levels in dementia due to Alzheimer’s disease (AD) and found higher values in AD patients compared to healthy controls (HC). However, these studies were mostly small in size, the inclusion criteria were not always well defined, and the diagnostic value and pathophysiological significance of CSF lactate in AD remain unclear.

Methods

We examined CSF lactate levels and potentially associated factors in a large (n=312), biologically and clinically well-defined sample of patients with AD at the stage of mild cognitive impairment (MCI-AD) and dementia (ADD), HC, and patients with frontotemporal lobar degeneration (FTLD).

Results

Contrary to previous studies, patients with ADD and HC did not differ in CSF lactate levels. However, we found higher values for patients with MCI-AD compared to those with ADD and to HC in univariate analysis, as well as for MCI-AD compared to ADD when controlling for age and blood-brain barrier integrity. CSF lactate levels were associated with age and blood-brain barrier integrity but not with clinical severity or CSF biomarkers of AD.

Conclusions

CSF lactate does not indicate biological or clinical disease severity in AD, nor does it differentiate between patients with AD and HC or patients with FTLD. However, higher CSF lactate levels were found in earlier stages of AD, which might be interpreted in the context of inflammatory processes.

Therapeutic plasma exchange and continuous renal replacement therapy in pediatric dengue-associated acute liver failure: A case series from Vietnam

BACKGROUND AND OBJECTIVES

Paediatric dengue-associated acute liver failure (PALF) is a rare and fatal complication. To date, clinical data regarding the combination of therapeutic plasma exchange (TPE) and continuous renal replacement therapy (CRRT) for the treatment of dengue-associated PALF are limited.

METHODS

We conducted a single-center, retrospective study of all children with dengue-associated PALF admitted to the paediatric intensive care unit of Children Hospital No.2, Vietnam, who were treated with TPE+CRRT between January 2021 and March 2022. The main study outcomes were in-hospital survival, normalisation of hepatic function, and hepatic encephalopathy improvement.

RESULTS

Twelve patients aged from 06 to 12 years underwent TPE+CRRT procedures. Among them, three (25 %) patients died of severe sepsis and septic shock confirmed by Enterobacteriaceae spp. haemocultures (stable on maintenance treatment of COVID-19-associated MIS-C with low dose of oral steroids on hospital admission), acute respiratory distress syndrome (ARDS), and clinically apparent intracranial haemorrhage. Nine patients (75 %) survived. The paediatric mortality risk score improved significantly at discharge compared with PICU admission (P < 0.01). Markedly, all twelve patients were diagnosed with hepatoencephalopathy of grades III and IV on PICU admission. After the combined TPE+CRRT interventions, there were substantial improvements in liver transaminases levels, coagulation profiles, and metabolic biomarkers. Normal neurological functions were observed in nine alive patients at hospital discharge. Only one patient experienced an adverse event of slightly low blood pressure, which rapidly self-resolved.

INTERPRETATION AND CONCLUSIONS

Combined TPE+CRRT significantly improved survival outcome, neurological status, and rapid normalisation of liver functions in dengue-associated PALF.

Risk Factor Analysis of Hepatic Encephalopathy and the Establishment of Diagnostic Model

To identify laboratory diagnostic indicators of hepatic encephalopathy (HE), the present study established a HE diagnostic model to explore the diagnostic value of serum homocysteine, lactic acid, procalcitonin, and bile acid levels in HE identification. 371 patients with liver cirrhosis were selected as research objects, who were admitted to the Department of Hepatic Diseases, Affiliated Hospital of Northwest Minzu University from August 2019 to August 2020. The Spearman correlation results indicated that between lactic acid, procalcitonin, bile acid, serum homocysteine, and HE, the coefficients were -0.15, 0.41, 0.29, and -0.19, respectively. Univariate and multivariate analysis methods were adopted for inpatient analysis to identify the influencing factors of HE occurrence, and the diagnosis of the HE identification model was subsequently constructed. The univariate logistic regression showed that risk of developing HE increased as bile acid level (P = 0.00434) and serum homocysteine (P = 0.058) increased. Multivariate logistic regression diagnostic model of bile acid level and serum homocysteine revealed that the AUC value of the area under the ROC curve was 0.7201, indicating that the diagnostic model produced a satisfactory evaluation effect. The model formula referred logistic (P) = -2.4544 + 0.0117 bile acid levels + 0.0198 serum homocysteine. In this study, the HE diagnostic model was established using logistic regression analysis, which could benefit patients in early HE differential diagnosis. Particularly, combined detection of serum homocysteine and bile acid levels was considered to be more significant.

The neurogliovascular unit in hepatic encephalopathy

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

The Direct Contribution of Astrocytes and Microglia to the Pathogenesis of Hepatic Encephalopathy

Hepatic encephalopathy is a neurological complication resulting from loss of hepatic function and is associated with poor clinical outcomes. During acute liver failure over 20% of mortality can be associated with the development of hepatic encephalopathy. In patients with liver cirrhosis, 1-year survival for those that develop overt hepatic encephalopathy is under 50%. The pathogenesis of hepatic encephalopathy is complicated due to the multiple disruptions in homeostasis that occur following a reduction in liver function. Of these, elevations of ammonia and neuroinflammation have been shown to play a significant contributing role to the development of hepatic encephalopathy. Disruption of the urea cycle following liver dysfunction leads to elevations of circulating ammonia, which enter the brain and disrupt the functioning of astrocytes. This results in dysregulation of metabolic pathways in astrocytes, oxidative stress and cerebral edema. Besides ammonia, circulating chemokines and cytokines are increased following liver injury, leading to activation of microglia and a subsequent neuroinflammatory response. The combination of astrocyte dysfunction and microglia activation are significant contributing factors to the pathogenesis of hepatic encephalopathy.

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.

Metabolomic Analysis Identifies Lactate as an Important Pathogenic Factor in Diabetes-associated Cognitive Decline Rats

Diabetes mellitus causes brain structure changes and cognitive decline, and it has been estimated that diabetes doubles the risk for dementia. Until now, the pathogenic mechanism of diabetes-associated cognitive decline (DACD) has remained unclear. Using metabolomics, we show that lactate levels increased over time in the hippocampus of rats with streptozotocin-induced diabetes, as compared with age-matched control rats. Additionally, mRNA levels, protein levels, and enzymatic activity of lactate dehydrogenase-A (LDH-A) were significantly up-regulated, suggesting increased glycolysis activity. Importantly, by specifically blocking the glycolysis pathway through an LDH-A inhibitor, chronic diabetes-induced memory impairment was prevented. Analyzing the underlying mechanism, we show that the expression levels of cAMP-dependent protein kinase and of phosphorylated transcription factor cAMP response element-binding proteins were decreased in 12-week diabetic rats. We suggest that G protein-coupled receptor 81 mediates cognitive decline in the diabetic rat. In this study, we report that progressively increasing lactate levels is an important pathogenic factor in DACD, directly linking diabetes to cognitive dysfunction. LDH-A may be considered as a potential target for alleviating or treating DACD in the future.

Cerebral Blood Flow and Metabolism in Hepatic Encephalopathy-A Meta-Analysis

Hepatic Encephalopathy (HE) is associated with abnormalities in brain metabolism of glucose, oxygen and amino acids. In patients with acute liver failure, cortical lactate to pyruvate ratio is increased, which is indicative of a compromised cerebral oxidative metabolism. In this meta-analysis we have reviewed the published data on cerebral blood flow and metabolic rates from clinical studies of patients with HE. We found that hepatic encephalopathy was associated with reduced cerebral metabolic rate of oxygen, glucose, and blood flow. One exemption was in HE type B (shunt/by-pass) were a tendency towards increased cerebral blood flow was seen. We speculate that HE is associated with a disturbed metabolism-cytopathic hypoxia-and that type specific differences of brain metabolism is due to differences in pathogenesis of HE.

Pathogenesis of Hepatic Encephalopathy in Chronic Liver Disease

Hepatic encephalopathy (HE) is a complex neuropsychiatric syndrome that occurs during chronic liver disease (CLD). While ammonia and other precipitating factors in liver disease including inflammation, bile acids, oxidative stress, and lactate play a role in the pathogenesis of HE, the exact mechanism that leads to HE is not fully understood. Notably, accumulating evidence points toward a synergic effect rather than independent actions among precipitating factors that contributes to the development and severity of HE in CLD. Hence, this review is aimed to briefly discuss the single and synergic interplay of pathological factors in the progression and severity of HE.

Disruption of Intracellular ATP Generation and Tight Junction Protein Expression during the Course of Brain Edema Induced by Subacute Poisoning of 1,2-Dichloroethane

The aim of this study was to explore changes in intracellular ATP generation and tight junction protein expression during the course of brain edema induced by subacute poisoning of 1,2-dichloroethane (1,2-DCE). Mice were exposed to 1.2 g/m³ 1,2-DCE for 3.5 h per day for 1, 2, or 3 days, namely group A, B, and C. Na⁺-K⁺-ATPase and Ca²⁺-ATPase activity, ATP and lactic acid content, intracellular free Ca²⁺ concentration and ZO-1 and occludin expression in the brain were measured. Results of present study disclosed that Ca²⁺-ATPase activities in group B and C, and Na⁺/K⁺-ATPase activity in group C decreased, whereas intracellular free Ca²⁺ concentrations in group B and C increased significantly compared with control. Moreover, ATP content decreased, whereas lactic acid content increased significantly in group C compared with control. On the other hand, expressions of ZO-1 and occludin at both the protein and gene levels in group B and C decreased significantly compared with control. In conclusion, findings from this study suggest that calcium overload and depressed expression of tight junction associated proteins, such as ZO-1 and occludin might play an important role in the early phase of brain edema formation induced by subacute poisoning of 1,2-DCE.

Magnetic Resonance Spectroscopy for Evaluating Portal-Systemic Encephalopathy in Patients with Chronic Hepatic Schistosomiasis Japonicum

Portal-systemic encephalopathy (PSE) is classified as type B hepatic encephalopathy. Portal-systemic shunting rather than liver dysfunction is the main cause of PSE in chronic hepatic schistosomiasis japonicum (HSJ) patients. Owing to lack of detectable evidence of intrinsic liver disease, chronic HSJ patients with PSE are frequently clinically undetected or misdiagnosed, especially chronic HSJ patients with covert PSE (subclinical encephalopathy). In this study, we investigated whether magnetic resonance spectroscopy (MRS) could be a useful tool for diagnosing PSE in chronic HSJ patients. Magnetic resonance (MR) T1-weighted imaging, diffusion-weighted imaging, and MRS were performed in 41 chronic HSJ patients with suspected PSE and in 21 age-matched controls. The T1 signal intensity index (T1SI) and apparent diffusion coefficient (ADC) value were obtained in the Globus pallidus. Liver function was also investigated via serum ammonia and liver function tests. Higher T1SI and ADC values, increased lactate and glutamine levels, and decreased myo-inositol were found in the bilateral Globus pallidus in chronic HSJ patients with PSE. No significantly abnormal serum ammonia or liver function tests were observed in chronic HSJ patients with PSE. On the basis of these findings, we propose a diagnostic procedure for PSE in chronic HSJ patients. This study reveals that MRS can be useful for diagnosing PSE in chronic HSJ patients.

Portal-systemic encephalopathy (PSE) is classified as type B hepatic encephalopathy. Portal-systemic shunting rather than liver dysfunction is the main cause of PSE in chronic hepatic schistosomiasis japonicum (HSJ) patients. Chronic HSJ patients with PSE are frequently misdiagnosed as suffering from dementia, depression, and other psychiatric disorders. However, there are few studies of this type of encephalopathy. In this study, magnetic resonance spectroscopy (MRS) was used as a noninvasive tool to detect abnormalities in brain metabolism in chronic HSJ patient with PSE. The results demonstrate that MRS would be useful for the diagnosis of PSE in chronic HSJ patients. Based on the results, a diagnostic procedure for PSE has also been proposed.

What we know: the inflammatory basis of hepatic encephalopathy

Central Nervous System (CNS) degeneration appearing in patients with cirrhosis is responsible for cognitive and persistent motor impairments that lead to an important impact on life quality. Brain injury affects certain areas of the CNS that might affect two types of cells: neurons and astrocytes. The process leading to brain injury could be induced by portosystemic shunting accompanied by hyperammonemia and by the activation of peripheral inflammation, manifested as episodic encephalopathy. Hyperammonemia combined with a decrease on the BCA/AAA ratio induces alterations of energetic metabolism and the formation of free radicals in the CNS. This process would be stimulated by the activation of peripheral inflammatory mediators that could act on receptors of the blood brain barrier such as TLR4, activating inflammatory responses in the CNS. As a result, a persistent activation of microglia and an irreversible neuronal and astrocytic injury would be induced. A new knowledge of the mechanisms leading to brain injury in cirrhosis would develop protective strategies to correct changes of nitrogen metabolism and inflammation.

Lactate as a Metabolite and a Regulator in the Central Nervous System

More than two hundred years after its discovery, lactate still remains an intriguing molecule. Considered for a long time as a waste product of metabolism and the culprit behind muscular fatigue, it was then recognized as an important fuel for many cells. In particular, in the nervous system, it has been proposed that lactate, released by astrocytes in response to neuronal activation, is taken up by neurons, oxidized to pyruvate and used for synthesizing acetyl-CoA to be used for the tricarboxylic acid cycle. More recently, in addition to this metabolic role, the discovery of a specific receptor prompted a reconsideration of its role, and lactate is now seen as a sort of hormone, even involved in processes as complex as memory formation and neuroprotection. As a matter of fact, exercise offers many benefits for our organisms, and seems to delay brain aging and neurodegeneration. Now, exercise induces the production and release of lactate into the blood which can reach the liver, the heart, and also the brain. Can lactate be a beneficial molecule produced during exercise, and offer neuroprotection? In this review, we summarize what we have known on lactate, discussing the roles that have been attributed to this molecule over time.

Nitric oxide mediates effects of acute, not chronic, naltrexone on LPS-induced hepatic encephalopathy in cirrhotic rats

Recent studies suggest endogenous opioids and nitric oxide (NO) are involved in the pathophysiology of hepatic encephalopathy (HE). In this study, the interaction between the opioid receptor antagonist and NO was investigated on lipopolysaccharide (LPS)-induced HE in cirrhotic rats. Male rats were divided in the sham- and bile duct ligation (BDL)-operated groups. Animals were treated with saline; naltrexone (10 mg/kg, i.p.); or L-NAME (3 mg/kg, i.p.), alone or in combination with naltrexone. To induce HE, LPS (1 mg/kg, i.p.) was injected 1 h after the final drug treatment. HE scoring, hepatic histology, and plasma NO metabolites levels and mortality rate were recorded. Deteriorated level of consciousness and mortality after LPS administration significantly ameliorated following both acute and chronic treatment with naltrexone in cirrhotic rats. However, acute and chronic administration of L-NAME did not change HE scores in cirrhotic rats. The effects of acute but not chronic treatment of naltrexone on HE parameters were reversed by L-NAME. Plasma NO_x concentrations elevated in BDL rats, which were decreased after acute and chronic treatment by naltrexone or L-NAME, significantly. We suggest both acute and chronic treatment with naltrexone improved LPS-induced HE. But, only acute treatment with naltrexone may affect through NO pathway.

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

Recent pathophysiological models suggest that oxidative stress and hyperammonemia lead to a mild brain oedema in hepatic encephalopathy (HE). Glutathione (GSx) is a major cellular antioxidant and known to be involved in the interception of both. The aim of this work was to study total glutathione levels in covert HE (minimal HE and HE grade 1) and to investigate their relationship with local brain water content, levels of glutamine (Gln), myo-inositol (mI), neurotransmitter levels, critical flicker frequency (CFF), and blood ammonia. Proton magnetic resonance spectroscopy ((1)H MRS) data were analysed from visual and sensorimotor cortices of thirty patients with covert HE and 16 age-matched healthy controls. Total glutathione levels (GSx/Cr) were quantified with respect to creatine. Furthermore, quantitative MRI brain water content measures were evaluated. Data were tested for links with the CFF and blood ammonia. GSx/Cr was elevated in the visual (mHE) and sensorimotor (mHE, HE 1) MRS volumes and correlated with blood ammonia levels (both P < 0.001). It was further linked to Gln/Cr and mI/Cr (P < 0.01 in visual, P < 0.001 in sensorimotor) and to GABA/Cr (P < 0.01 in visual). Visual GSx/Cr correlated with brain water content in the thalamus, nucleus caudatus, and visual cortex (P < 0.01). Brain water measures did neither show group effects nor correlations with CFF or blood ammonia. Elevated total glutathione levels in covert HE (< HE 2) correlate with blood ammonia and may be a regional-specific reaction to hyperammonemia and oxidative stress. Brain water content is locally linked to visual glutathione levels, but appears not to be associated with changes of clinical parameters. This might suggest that cerebral oedema is only marginally responsible for the symptoms of covert HE.

Differences in cognitive function between patients with viral and alcoholic compensated liver cirrhosis

As alcohol induces change in frontal cortex primarily involved in cognition, cognitive function may be different between viral and alcoholic liver cirrhosis (LC). This study aimed to determine the differences of cognitive function between viral and alcoholic compensated LC. From October 2011 to March 2013, 80 patients (viral: 37; alcohol: 43) with compensated LC were prospectively enrolled. Neuropsychological functions including attention, language, visuospatial, verbal memory, visual memory, and frontal/executive function were evaluated between two groups and compared with age-matched normal group (n = 1000). Cumulative incidence rate of overt hepatic encephalopathy (HE) was calculated. In the comparison with normal group, both two groups showed decreased memory function, frontal/executive function, and Korea-Mini Mental Status Examination. In the analysis of two groups, memory function by Verbal Learning Test (recognition: 20.1 ± 3.6 and 17.8 ± 4.8, p = 0.022), visuospatial function by Ray-Complex Figure Copy Test (recognition: 19.0 ± 2.6 and 17.3 ± 4.0, p = 0.043), frontal/executive function by Controlled Oral Ward Association (semantic: 17.1 ± 6.9 and 12.7 ± 6.9, p = 0.004), and the Korea-Mini Mental Status Examination (27.5 ± 1.9 and 26.2 ± 3.1, p = 0.03) showed low scores in alcoholic compensated LC patients. The 1-, 2-, and 3-year cumulative incidence rates of overt HE were 23%, 26%, and 26% and 33%, 43%, and 49% in the viral and alcoholic compensated LC group, respectively (p = 0.033). Impaired memory and frontal lobe executive functions and early development of overt HE were more common in patients with alcoholic LC. For patients with alcoholic LC, more integrated tests for early detection of minimal HE and intensive treatment should be considered to prevent overt HE.