L-Ornithine phenylacetate reduces ammonia in pigs with acute liver failure through phenylacetylglycine formation: a novel ammonia-lowering pathway

Associations between serum taurine concentrations in mothers and neonates and the children's anthropometrics and early neurodevelopment: Results from the Seychelles Child Development Study, Nutrition Cohort 2

BACKGROUND

High concentrations of taurine are present in the developing human brain and maternal breast milk. Taurine is thought to influence fetal growth and brain development based on experimental rodent studies. As fish is an important dietary source of taurine, we investigated associations between taurine concentrations and child outcomes in a high fish consuming population.

OBJECTIVE

To examine associations between maternal and cord serum taurine concentrations and birth anthropometric measures and cognitive development in children at 20 months of age.

METHODS

Pregnant women were recruited between 2008 and 2011 as part of Nutrition Cohort 2 (NC2) of the Seychelles Child Development Study (SCDS). Maternal taurine serum concentrations were measured at 28 week's gestation and in cord serum. Child weight, length and head circumference were measured at birth and neurodevelopment was assessed using Bayley Scales of Infant Development II (BSID-II) at 20 months of age. Associations between taurine status, birth measures and neurodevelopmental outcomes were examined (n = 300) using regression models and adjusted for relevant covariates.

RESULTS

Mean (SD) maternal and cord taurine concentrations were 124.9 (39.2) µmol/L (range 28.2-253.9 µmol/L) and 187.6 (60.0) µmol/L (range 55.0-417.4 µmol/L) respectively. We found no associations between maternal taurine concentrations and child anthropometric and neurodevelopmental measures (weight β = -0.001, SE=0.001; length β = -0.006, SE=0.006; head circumference β = -0.002, SE=0.002; MDI β = -0.005, SE=0.015; PDI β = -0.004, SE=0.016; all P > 0.05), or between cord taurine concentrations and outcomes (weight β = -0.001, SE<0.000; length β = -0.001, SE=0.004; head circumference β < 0.000, SE=0.002; MDI β = 0.004, SE=0.010; PDI β = -0.015, SE=0.012; all P > 0.05).

CONCLUSION

The Seychellois population have high maternal and cord taurine concentrations owing to their high fish intake and may be considered taurine replete compared to individuals who consume a Westernised diet. This high taurine status may explain why there were no significant associations between maternal and cord taurine concentrations and outcomes after adjusting for covariates.

A metabolomic study on the anti-depressive effects of two active components from Chrysanthemum morifolium

Chrysanthemum morifolium (Chr) is a traditional Chinese medicine (TCM) that has been used in the treatment of inflammation-linked diseases for hundreds of years. Naringenin (Nar) and apigenin (Api) are the major active components in aqueous extracts of C. morifolium. The aim of our study was to clarify the roles of Chr, Nar and Api in ameliorating depression-like behaviour induced by corticosterone. First, the behavioural and biochemical indicators closely related to depression were examined to evaluate the therapeutic effects of Chr/Nar/Api on a depression model. Then, a metabolomics approach was utilized to screen for biomarkers and related pathways between a control group and Chr/Nar/Api groups. The comprehensive results revealed that Chr/Nar/Api exerted anti-depressant effects through interfering with tryptophan metabolism, arginine and prolinemetabolism, citrate cycle, niacin and niacinamide metabolism, phenylalanine metabolism, and alanine, aspartate and glutamate metabolism. The mechanism of Chr/Api/Nar in the treatment of depression was elucidated based on material and energy metabolism. Moreover, Nar could be used as a substitute for Chr for reversing depression-like behaviour, and Api was similar to a positive drug in terms of function on depression. The integrated metabolomics approach demonstrated here should be an effective method for interpreting the function of herbs from TCM and clarifying the mechanism of their components in future studies.

Integrative Analysis of Vaginal Microorganisms and Serum Metabolomics in Rats With Estrous Cycle Disorder Induced by Long-Term Heat Exposure Based on 16S rDNA Gene Sequencing and LC/MS-Based Metabolomics

Long term heat exposure (HE) leads to estrous cycle disorder (ECD) in female rats and damages reproductive function. However, the regulation mechanism of vaginal microorganisms and serum metabolomics remains unclear. This study aimed to explore the effects of microbes on the vaginal secretions of rats with ECD and describe the serum metabolomics characteristics and their relationship with vaginal microorganisms. The alterations in the serum levels of neurotransmitters were used to verify the possible regulatory pathways. The relative abundance, composition, and colony interaction network of microorganisms in the vaginal secretions of rats with ECD changed significantly. The metabolomics analysis identified 22 potential biomarkers in the serum including lipid metabolism, amino acid metabolism, and mammalian target of rapamycin and gonadotropin-releasing hormone (GnRH) signaling pathways. Further, 52 pairs of vaginal microbiota–serum metabolites correlations (21 positive and 31 negative) were determined. The abundance of Gardnerella correlated positively with the metabolite L-arginine concentration and negatively with the oleic acid concentration. Further, a negative correlation was found between the abundance of Pseudomonas and the L-arginine concentration and between the metabolite benzoic acid concentration and the abundance of Adlercreutzia. These four bacteria–metabolite pairs had a direct or indirect relationship with the estrous cycle and reproduction. The glutamine, glutamate, and dopamine levels were significantly uncontrolled. The former two were closely related to GnRH signaling pathways involved in the development and regulation of HE-induced ECD in rats. Serum neurotransmitters partly reflected the regulatory effect of vaginal microorganisms on the host of HE-induced ECD, and glutamatergic neurotransmitters might be closely related to the alteration in vaginal microorganisms. These findings might help comprehend the mechanism of HE-induced ECD and propose a new intervention based on vaginal microorganisms.

Bile-duct ligation renders the brain susceptible to hypotension-induced neuronal degeneration: Implications of ammonia

Hepatic encephalopathy (HE) is a debilitating neurological complication of cirrhosis. By definition, HE is considered a reversible disorder, and therefore HE should resolve following liver transplantation (LT). However, persisting neurological complications are observed in as many as 47% of LT recipients. LT is an invasive surgical procedure accompanied by various perioperative factors such as blood loss and hypotension which could influence outcomes post-LT. We hypothesize that minimal HE (MHE) renders the brain frail and susceptible to hypotension-induced neuronal cell death. Six-week bile duct-ligated (BDL) rats with MHE and respective SHAM-controls were used. Several degrees of hypotension (mean arterial pressure of 30, 60 and 90 mm Hg) were induced via blood withdrawal from the femoral artery and maintained for 120 min. Brains were collected for neuronal cell count and apoptotic analysis. In a separate group, BDL rats were treated for MHE with the ammonia-lowering strategy ornithine phenylacetate (OP; MNK-6105), administered orally (1 g/kg) for 3 weeks before induction of hypotension. Hypotension 30 and 60 mm Hg (not 90 mm Hg) significantly decreased neuronal marker expression (NeuN) and cresyl violet staining in the frontal cortex compared to respective hypotensive SHAM-operated controls as well as non-hypotensive BDL rats. Neuronal degeneration was associated with an increase in cleaved caspase-3, suggesting the mechanism of cell death was apoptotic. OP treatment attenuated hyperammonaemia, improved anxiety and activity, and protected the brain against hypotension-induced neuronal cell death. Our findings demonstrate that rats with chronic liver disease and MHE are more susceptible to hypotension-induced neuronal cell degeneration. This highlights MHE at the time of LT is a risk factor for poor neurological outcome post-transplant and that treating for MHE pre-LT might reduce this risk.

Hepatic encephalopathy: Novel insights into classification, pathophysiology and therapy

Hepatic encephalopathy (HE) is a frequent and serious complication of both chronic liver disease and acute liver failure. HE manifests as a wide spectrum of neuropsychiatric abnormalities, from subclinical changes (mild cognitive impairment) to marked disorientation, confusion and coma. The clinical and economic burden of HE is considerable, and it contributes greatly to impaired quality of life, morbidity and mortality. This review will critically discuss the latest classification of HE, as well as the pathogenesis and pathophysiological pathways underlying the neurological decline in patients with end-stage liver disease. In addition, management strategies, diagnostic approaches, currently available therapeutic options and novel treatment strategies are discussed.

Ammonia Scavenging Prevents Progression of Fibrosis in Experimental Nonalcoholic Fatty Liver Disease

BACKGROUND AND AIMS

In nonalcoholic fatty liver disease (NAFLD), fibrosis is the most important factor contributing to NAFLD-associated morbidity and mortality. Prevention of progression and reduction in fibrosis are the main aims of treatment. Even in early stages of NAFLD, hepatic and systemic hyperammonemia is evident. This is due to reduced urea synthesis; and as ammonia is known to activate hepatic stellate cells, we hypothesized that ammonia may be involved in the progression of fibrosis in NAFLD.

APPROACH AND RESULTS

In a high-fat, high-cholesterol diet-induced rodent model of NAFLD, we observed a progressive stepwise reduction in the expression and activity of urea cycle enzymes resulting in hyperammonemia, evidence of hepatic stellate cell activation, and progressive fibrosis. In primary, cultured hepatocytes and precision-cut liver slices we demonstrated increased gene expression of profibrogenic markers after lipid and/or ammonia exposure. Lowering of ammonia with the ammonia scavenger ornithine phenylacetate prevented hepatocyte cell death and significantly reduced the development of fibrosis both in vitro in the liver slices and in vivo in a rodent model. The prevention of fibrosis in the rodent model was associated with restoration of urea cycle enzyme activity and function, reduced hepatic ammonia, and markers of inflammation.

CONCLUSIONS

The results of this study suggest that hepatic steatosis results in hyperammonemia, which is associated with progression of hepatic fibrosis. Reduction of ammonia levels prevented progression of fibrosis, providing a potential treatment for NAFLD.

Effects of a blend of Saccharomyces cerevisiae-based direct-fed microbial and fermentation products on plasma carbonyl-metabolome and fecal bacterial community of beef steers

BACKGROUND

Previous studies have evaluated the metabolic status of animals fed direct-fed microbial (DFM) using enzyme-based assays which are time-consuming and limited to a few metabolites. In addition, little emphasis has been placed on investigating the effects of DFM on hindgut microbiota. We examined the effects of dietary supplementation of a blend of Saccharomyces cerevisiae-based DFM and fermentation products on the plasma concentrations of carbonyl-containing metabolites via a metabolomics approach, and fecal bacterial community, via 16S rRNA gene sequencing, of beef steers during a 42-day receiving period. Forty newly weaned steers were randomly assigned to receive a basal diet with no additive (CON; n = 20) or a basal diet supplemented with 19 g of Commence™ (PROB; n = 20) for a 42-day period. Commence™ (PMI, Arden Hills, MN) is a blend of 6.2 × 1011 cfu/g of S. cerevisiae, 3.5 × 1010 cfu/g of a mixture of Enterococcus lactis, Bacillus subtilis, Enterococcus faecium, and Lactobacillus casei, and the fermentation products of these aforementioned microorganisms and those of Aspergillus oryzae and Aspergillus niger. On d 0 and 40, rectal fecal samples were collected randomly from 10 steers from each treatment group. On d 42, blood was collected for plasma preparation.

RESULTS

A total number of 812 plasma metabolites were detected. Up to 305 metabolites [fold change (FC) ≥ 1.5, FDR ≤ 0.01] including glucose, hippuric acid, and 5-hydroxykynurenamine were increased by PROB supplementation, whereas 199 metabolites (FC ≤ 0.63, FDR ≤ 0.01) including acetoacetate were reduced. Supplementation of PROB increased (P ≤ 0.05) the relative abundance of Prevotellaceae UCG-003, Megasphaera, Dorea, Acetitomaculum, and Blautia. In contrast, the relative abundance of Elusimicrobium, Moheibacter, Stenotrophomonas, Comamonas, and uncultured bacterium belonging to family p-2534-18B5 gut group (phylum Bacteroidetes) were reduced (P ≤ 0.05).

CONCLUSIONS

The results of this study demonstrated that supplementation of PROB altered both the plasma carbonyl metabolome towards increased glucose concentration suggesting an improved energy status, and fecal bacterial community, suggesting an increased hindgut fermentation of the beef steers.

Generation of carbamoyl phosphate synthetase 1 reporter cell lines for the assessment of ammonia metabolism

Both primary hepatocytes and stem cells-derived hepatocyte-like cells (HLCs) are major sources for bioartificial liver (BAL). Maintenance of hepatocellular functions and induction of functional maturity of HLCs are critical for BAL's support effect. It remains difficult to assess and improve detoxification functions inherent to hepatocytes, including ammonia clearance. Here, we aim to assess ammonia metabolism and identify ammonia detoxification enhancer by developing an imaging strategy. In hepatoma cell line HepG2, and immortalized hepatic cell line LO2, carbamoyl phosphate synthetase 1 (CPS1) gene, the first enzyme of ammonia-eliminating urea cycle, was labelled with fluorescence protein via CRISPR/Cas9 system. With the reporter-based screening approach, cellular detoxification enhancers were selected among a collection of 182 small molecules. In both CPS1 reporter cell lines, the fluorescence intensity is positively correlated with cellular CPS1 mRNA expression, ammonia elimination and secreted urea, and reflected ammonia detoxification in a dose-dependent manner. Surprisingly, high-level CPS1 reporter clones also reserved many other critical hepatocellular functions, for example albumin secretion and cytochrome 450 metabolic functions. Sodium phenylbutyrate and resveratrol were identified to enhance metabolism-related gene expression and liver-enriched transcription factors C/EBPα, HNF4α. In conclusion, the CPS1-reporter system provides an economic and effective platform for assessment of cellular metabolic function and high-throughput identification of chemical compounds that improve detoxification activities in hepatic lineage cells.

SHYCD induces APE1/Ref-1 subcellular localization to regulate the p53-apoptosis signaling pathway in the prevention and treatment of acute on chronic liver failure

Background & Aims: San huang yin chi decoction(SHYCD) is derived from the yin chen hao decoction, a well-known and canonical Chinese medicine formula from the “Treatise on Febrile Diseases”. Over the past decade, SHYCD has been used to treat and prevent the liver cirrhosis and liver failure. In the present study, we investigated the effects of SHYCD for acute on chronic liver failure(ACLF) and explored its potential mechanism. an ACLF rat model, which induced by carbon tetrachloride (CCl4) combined with D-galactosamine (D-GalN) and lipopolysaccharide(LPS), was used and confirmed by B-ultrasound analysis. Rats were randomly divided into control group, model group, SHYCD-H group, SHYCD-M group, SHYCD-L group, AGNHW group. Compared with the ACLF model group, High, medium, and low doses of SHYCD reduced ALT, AST, TBIL, NH3, IL-1β, IL-6, and TNFα expression levels in the serum, Shorten PT and INR time,and increased Fbg content in the whole blood, increased survival rate of the rats, improved liver pathological changes. APE1 / Ref-1 was mainly expressed in the nucleus, but the nucleus and cytoplasm were co-expressed after hepatocyte injury. SHYCD significantly downregulated APE1/Ref-1 expression in the cytoplasm. Increased APE1/Ref-1, Bcl-2, reduced p53, caspase-3, Bax, and Cyt-c in the total protein. Base on the results, we conclused that High, medium, and low doses of SHYCD could be applied in prevention and treatment of ACLF, and dose-dependent. The possible mechanism is to promote the APE1 / Ref-1 from the cytoplasm to the nuclear transfer, regulation of p53 apoptosis signal pathway prevention and treatment of ACLF.

A morphological method for ammonia detection in liver

Hyperammonemia is a metabolic condition characterized by elevated levels of ammonia and a common event in acute liver injury/failure and chronic liver disease. Even though hepatic ammonia levels are potential predictive factors of patient outcome, easy and inexpensive methods aiming at the detection of liver ammonia accumulation in the clinical setting remain unavailable. Thus, herein we have developed a morphological method, based on the utilization of Nessler´s reagent, to accurately and precisely detect the accumulation of ammonia in biological tissue. We have validated our method against a commercially available kit in mouse tissue samples and, by using this modified method, we have confirmed the hepatic accumulation of ammonia in clinical and animal models of acute and chronic advanced liver injury as well as in the progression of fatty liver disease. Overall, we propose a morphological method for ammonia detection in liver that correlates well with the degree of liver disease severity and therefore can be potentially used to predict patient outcome.

Establishment of a Novel Simplified Surgical Model of Acute Liver Failure in the Cynomolgus Monkey

Models using large animals that are suitable for studying artificial liver support system (ALSS) are urgently needed. Presently available acute liver failure (ALF) models mainly involve pigs or dogs. Establishment of current surgical ALF models (hepatectomy/devascularization) requires either very good surgical skills or multistep processes—even multiple stages of surgery. Therefore, it is necessary to develop a simplified surgical method. Here we report a novel simplified surgical ALF model using cynomolgus monkeys. Six monkeys underwent portal-right renal venous shunt combined with common bile duct ligation and transection (PRRS + CBDLT). Postoperatively, the monkeys had progressively increased listlessness, loss of appetite, and obvious jaundice. Blood biochemistry levels (Amm, ALT, AST, TBiL, DBiL, ALP, LDH, CK, and Cr) and prothrombin time (PT) were significantly increased (all P < 0.01) and albumin (ALB) was markedly reduced (P < 0.01) compared with baseline values. Histological examination of liver specimens on postoperative day 10 revealed cholestasis and inflammation. PRRS + CBDLT produced ALF that closely correlated with clinical situations. Compared with other surgical or drug ALF models, ours was simplified and animals were hemodynamically stable. This model could provide a good platform for further research on ALSS, especially regarding their detoxification functions.

Current state of knowledge of hepatic encephalopathy (part I): newer treatment strategies for hyperammonemia in liver failure

Alterations in interorgan metabolism of ammonia play an important role in the onset of hyperammonemia in liver failure. Glutamine synthetase (GS) in muscle is an important target for ammonia removal strategies in hyperammonemia. Ornithine Phenylacetate (OP) is hypothesized to remove ammonia by providing glutamate as a substrate for increased GS activity and hence glutamine production. The newly generated glutamine conjugates with phenylacetate forming phenylacetylglutamine which can be excreted in the urine, providing an excretion pathway for ammonia. We have also shown that OP targets glycine metabolism, providing an additional ammonia reducing effect.

Glycine and hyperammonemia: potential target for the treatment of hepatic encephalopathy

Hepatic encephalopathy (HE) is a neuropsychiatric disorder caused by hepatic dysfunction. Numerous studies dictate that ammonia plays an important role in the pathogenesis of HE, and hyperammonemia can lead to alterations in amino acid homeostasis. Glutamine and glycine are both ammoniagenic amino acids that are increased in liver failure. Modulating the levels of glutamine and glycine has shown to reduce ammonia concentration in hyperammonemia. Ornithine Phenylacetate (OP) has consistently been shown to reduce arterial ammonia levels in liver failure by modulating glutamine levels. In addition to this, OP has also been found to modulate glycine concentration providing an additional ammonia removing effect. Data support that glycine also serves an important role in N-methyl D-aspartate (NMDA) receptor mediated neurotransmission in HE. This potential important role for glycine in the pathogenesis of HE merits further investigations.

Impact of ornithine phenylacetate (OCR-002) in lowering plasma ammonia after upper gastrointestinal bleeding in cirrhotic patients

BACKGROUND

Ornithine phenylacetate (OP) has been proven effective in lowering ammonia plasma levels in animals, and to be well tolerated in cirrhotic patients. A trial to assess OP efficacy in lowering plasma ammonia levels versus placebo in cirrhotic patients after an upper gastrointestinal bleeding was performed. The primary outcome was a decrease in venous plasma ammonia at 24 hours.

METHODS

A total of 38 consecutive cirrhotic patients were enrolled within 24 hours of an upper gastrointestinal bleed. Patients were randomized (1:1) to receive OP (10 g/day) or glucosaline for 5 days.

RESULTS

The primary outcome was not achieved. A progressive decrease in ammonia was observed in both groups, being slightly greater in the OP group, with significant differences only at 120 hours. The subanalysis according to Child-Pugh score showed a statistically significant ammonia decrease in Child-Pugh C-treated patients at 36 hours, as well as in the time-normalized area under the curve (TN-AUC) 0-120 hours in the OP group [40.16 μmol/l (37.7-42.6); median (interquartile range) (IQR)] versus placebo group [65.5 μmol/l (54-126);p = 0.036]. A decrease in plasma glutamine levels was observed in the treated group compared with the placebo group, and was associated with the appearance of phenylacetylglutamine in urine. Adverse-event frequency was similar in both groups. No differences in hepatic encephalopathy incidence were observed.

CONCLUSIONS

OP failed to significantly decrease plasma ammonia at the given doses (10 g/day). Higher doses of OP might be required in Child-Pugh A and B patients. OP appeared well tolerated.

Metabolic Profiling of Impaired Cognitive Function in Patients Receiving Dialysis

Retention of uremic metabolites is a proposed cause of cognitive impairment in patients with ESRD. We used metabolic profiling to identify and validate uremic metabolites associated with impairment in executive function in two cohorts of patients receiving maintenance dialysis. We performed metabolic profiling using liquid chromatography/mass spectrometry applied to predialysis plasma samples from a discovery cohort of 141 patients and an independent replication cohort of 180 patients participating in a trial of frequent hemodialysis. We assessed executive function with the Trail Making Test Part B and the Digit Symbol Substitution test. Impaired executive function was defined as a score ≥2 SDs below normative values. Four metabolites-4-hydroxyphenylacetate, phenylacetylglutamine, hippurate, and prolyl-hydroxyproline-were associated with impaired executive function at the false-detection rate significance threshold. After adjustment for demographic and clinical characteristics, the associations remained statistically significant: relative risk 1.16 (95% confidence interval [95% CI], 1.03 to 1.32), 1.39 (95% CI, 1.13 to 1.71), 1.24 (95% CI, 1.03 to 1.50), and 1.20 (95% CI, 1.05 to 1.38) for each SD increase in 4-hydroxyphenylacetate, phenylacetylglutamine, hippurate, and prolyl-hydroxyproline, respectively. The association between 4-hydroxyphenylacetate and impaired executive function was replicated in the second cohort (relative risk 1.12; 95% CI, 1.02 to 1.23), whereas the associations for phenylacetylglutamine, hippurate, and prolyl-hydroxyproline did not reach statistical significance in this cohort. In summary, four metabolites related to phenylalanine, benzoate, and glutamate metabolism may be markers of cognitive impairment in patients receiving maintenance dialysis.

The Role of Sarcopenia and Frailty in Hepatic Encephalopathy Management

Normal regulation of total body and circulating ammonia requires a delicate interplay in ammonia formation and breakdown between several organ systems. In the setting of cirrhosis and portal hypertension, the decreased hepatic clearance of ammonia leads to significant dependence on skeletal muscle for ammonia detoxification; however, cirrhosis is also associated with muscle depletion and decreased functional muscle mass. Thus, patients with diminished muscle mass and sarcopenia may have a decreased ability to compensate for hepatic insufficiency and a higher likelihood of developing physiologically significant hyperammonemia and hepatic encephalopathy.

Recent advances in the treatment of hyperammonemia

Ammonia is a neurotoxic agent that is primarily generated in the intestine and detoxified in the liver. Toxic increases in systemic ammonia levels predominantly result from an inherited or acquired impairment in hepatic detoxification and lead to potentially life-threatening neuropsychiatric symptoms. Inborn deficiencies in ammonia detoxification mainly affect the urea cycle, an endogenous metabolic removal system in the liver. Hepatic encephalopathy, on the other hand, is a hyperammonemia-related complication secondary to acquired liver function impairment. A range of therapeutic options is available to target either ammonia generation and absorption or ammonia removal. Therapies for hepatic encephalopathy decrease intestinal ammonia production and uptake. Treatments for urea cycle disorders eliminate ammoniagenic amino acids through metabolic transformation, preventing ammonia generation. Therapeutic approaches removing ammonia activate the urea cycle or the second essential endogenous ammonia detoxification system, glutamine synthesis. Recent advances in treating hyperammonemia include using synergistic combination treatments, broadening the indication of orphan drugs, and developing novel approaches to regenerate functional liver tissue. This manuscript reviews the various pharmacological treatments of hyperammonemia and focuses on biopharmaceutical and drug delivery issues.

A(a)LS: Ammonia-induced amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a dreadful, devastating and incurable motor neuron disease. Aetiologically, it is a multigenic, multifactorial and multiorgan disease. Despite intense research, ALS pathology remains unexplained. Following extensive literature review, this paper posits a new integrative explanation. This framework proposes that ammonia neurotoxicity is a main player in ALS pathogenesis. According to this explanation, a combination of impaired ammonia removal- mainly because of impaired hepatic urea cycle dysfunction-and increased ammoniagenesis- mainly because of impaired glycolytic metabolism in fast twitch skeletal muscle-causes chronic hyperammonia in ALS. In the absence of neuroprotective calcium binding proteins (calbindin, calreticulin and parvalbumin), elevated ammonia-a neurotoxin-damages motor neurons. Ammonia-induced motor neuron damage occurs through multiple mechanisms such as macroautophagy-endolysosomal impairment, endoplasmic reticulum (ER) stress, CDK5 activation, oxidative/nitrosative stress, neuronal hyperexcitability and neuroinflammation. Furthermore, the regional pattern of calcium binding proteins' loss, owing to either ER stress and/or impaired oxidative metabolism, determines clinical variability of ALS. Most importantly, this new framework can be generalised to explain other neurodegenerative disorders such as Huntington's disease and Parkinsonism.

Is it time to target gut dysbiosis and immune dysfunction in the therapy of hepatic encephalopathy?

The development of overt hepatic encephalopathy (HE) in a patient with cirrhosis confers a damning prognosis with a 1-year mortality approaching 64%. This complex neuropsychiatric syndrome arises as a consequence of a dysfunctional gut-liver-brain axis. HE has been largely neglected over the past 30 years, with the reliance on therapies aimed at lowering ammonia production or increasing metabolism following the seminal observation that the hepatic urea cycle is the major mammalian ammonia detoxification pathway and is key in the pathogenesis of HE. The relationship with ammonia is more clear-cut in acute liver failure; but in cirrhosis, it has become apparent that inflammation is a key driver and that a disrupted microbiome resulting in gut dysbiosis, bacterial overgrowth and translocation, systemic endotoxemia and immune dysfunction may be more important drivers. Therefore, it is important to re-focus our efforts into developing therapies that modulate the disrupted microbiome or alleviating its downstream consequences.