Neurological implications of urea cycle disorders

Unraveling the Link: Seizure Characteristics and Ammonia Levels in Urea Cycle Disorder During Hyperammonemic Crises

BACKGROUND

This retrospective clinical study performed at a single clinical center aimed to identify the prevalence of seizures in individuals with urea cycle disorders (UCDs) with and without hyperammonemic (HA) crises. In addition, we sought to correlate the utility of biochemical markers and electroencephalography (EEG) in detecting subclinical seizures during HA.

METHODS

Medical records of individuals with UCDs enrolled in Urea Cycle Disorders Consortium Longitudinal Study (UCDC-LS) (NCT00237315) at Children's National Hospital between 2006 and 2022 were reviewed for evidence of clinical and subclinical seizuress during HA crises, and initial biochemical levels concurrently.

RESULTS

Eighty-five individuals with UCD were included in the analyses. Fifty-six of the 85 patients (66%) experienced HA crises, with a total of 163 HA events. Seizures are observed in 13% of HA events. Among all HA events with concomitant EEG, subclinical seizures were identified in 27% of crises of encephalopathy without clinical seizures and 53% of crises with clinical seizures. The odds of seizures increases 2.65 (95% confidence interval [CI], 1.51 to 4.66) times for every 100 μmol/L increase in ammonia and 1.14 (95% CI, 1.04 to 1.25) times for every 100 μmol/L increase in glutamine.

CONCLUSIONS

This study highlights the utility of EEG monitoring during crises for patients presenting with clinical seizures or encephalopathy with HA. During HA events, measurement of initial ammonia and glutamine can help determine risk for seizures and guide EEG monitoring decisions.

Severity-adjusted evaluation of initial dialysis on short-term health outcomes in urea cycle disorders

OBJECTIVE

In individuals with urea cycle disorders (UCDs) and neonatal disease onset, extracorporeal detoxification by continuous kidney replacement therapy is considered the therapeutic method of choice in addition to metabolic emergency treatment to resolve hyperammonemic decompensation. However, the indications for the initiation of dialysis are heterogeneously implemented transnationally, thereby hampering our understanding of (optimal) short-term health outcomes.

METHODS

We performed a retrospective comparative analysis evaluating the therapeutic effects of initial dialysis on survival as well as neurocognitive outcome parameters in individuals with UCDs in comparison to a severity-adjusted non-dialyzed control cohort. Overall, 108 individuals with a severe phenotype of male ornithine transcarbamylase deficiency (mOTC-D), citrullinemia type 1 (CTLN1) and argininosuccinic aciduria (ASA) were investigated by stratification based on a recently established and validated genotype-specific disease prediction model.

RESULTS

Mortality is associated with the height of initial peak plasma ammonium concentration, but appears to be independent from treatment with initial dialysis in mOTC-D. However, improved survival after initial dialysis was observed in CTLN1, while there was a trend towards improved survival in ASA. In survivors, annual frequency of (subsequent) metabolic decompensations did not differ between the dialyzed and non-dialyzed cohorts. Moreover, treatment with initial dialysis was not associated with improved neurocognitive outcomes.

INTERPRETATION

The present severity-adjusted comparative analysis reveals that general practice of initial dialysis is neither associated with improved survival in individuals with mOTC-D nor does it differ with regard to the neurocognitive outcome for the investigated UCD subtypes. However, initial dialysis might potentially prove beneficial for survival in CTLN1 and ASA.

CLINICAL TRIAL REGISTRATION

The UCDC database is recorded at the US National Library of Medicine (https://clinicaltrials.gov).

Single nuclei RNA-seq reveals a medium spiny neuron glutamate excitotoxicity signature prior to the onset of neuronal death in an ovine Huntington's disease model

Huntington's disease (HD) is a neurodegenerative genetic disorder caused by an expansion in the CAG repeat tract of the huntingtin (HTT) gene resulting in behavioural, cognitive, and motor defects. Current knowledge of disease pathogenesis remains incomplete, and no disease course-modifying interventions are in clinical use. We have previously reported the development and characterisation of the OVT73 transgenic sheep model of HD. The 73 polyglutamine repeat is somatically stable and therefore likely captures a prodromal phase of the disease with an absence of motor symptomatology even at 5-years of age and no detectable striatal cell loss. To better understand the disease-initiating events we have undertaken a single nuclei transcriptome study of the striatum of an extensively studied cohort of 5-year-old OVT73 HD sheep and age matched wild-type controls. We have identified transcriptional upregulation of genes encoding N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate receptors in medium spiny neurons, the cell type preferentially lost early in HD. Further, we observed an upregulation of astrocytic glutamate uptake transporters and medium spiny neuron GABAA receptors, which may maintain glutamate homeostasis. Taken together, these observations support the glutamate excitotoxicity hypothesis as an early neurodegeneration cascade-initiating process but the threshold of toxicity may be regulated by several protective mechanisms. Addressing this biochemical defect early may prevent neuronal loss and avoid the more complex secondary consequences precipitated by cell death.

CPS1 augments hepatic glucagon response through CaMKII/FOXO1 pathway

Introduction: Elevated glucagon levels are a characteristic feature of type 2 diabetes. This abnormal increase in glucagon can lead to an accelerated rate of gluconeogenesis. Glucagon also stimulates hepatic metabolism of amino acids, particularly promoting the formation of urea. The specific role of carbamoyl phosphate synthetase 1 (CPS1), a rate-limiting enzyme in the urea cycle, in the development versus the persistence of glucagon-induced hyperglycemia has not been previously established. Methods: The study employed both in vivo and in vitro approaches to assess the impact of CPS1 modulation on glucagon response. CPS1 was knockdown or overexpression to evaluate its influence on hepatic gluconeogenesis. In addition, an in-silico strategy was employed to identify a potential CPS1 inhibitor. Results: Knockdown of CPS1 significantly reduced the glucagon response both in vivo and in vitro. Conversely, overexpression of CPS1 resulted in an overactive hepatic gluconeogenic response. Mechanistically, CPS1 induced the release of calcium ions from the endoplasmic reticulum, which in turn triggered the phosphorylation of CaMKII. The activation of CaMKII then facilitated the dephosphorylation and nuclear translocation of FOXO1, culminating in the enhancement of hepatic gluconeogenesis. Furthermore, cynarin, a natural CPS1 inhibitor derived from the artichoke plant, had the capacity to attenuate the hepatic glucagon response in a CPS1-dependent manner. Discussion: CPS1 played a pivotal role in mediating glucagon-induced hepatic gluconeogenesis. The discovery of cynarin as a natural inhibitor of CPS1 suggested its potential as a therapeutic agent for diabetes treatment.

Proteomic profiling of interferon-responsive reactive astrocytes in rodent and human

Astrocytes are a heterogeneous population of central nervous system glial cells that respond to pathological insults and injury by undergoing a transformation called "reactivity." Reactive astrocytes exhibit distinct and context-dependent cellular, molecular, and functional state changes that can either support or disturb tissue homeostasis. We recently identified a reactive astrocyte sub-state defined by interferon-responsive genes like Igtp, Ifit3, Mx1, and others, called interferon-responsive reactive astrocytes (IRRAs). To further this transcriptomic definition of IRRAs, we wanted to define the proteomic changes that occur in this reactive sub-state. We induced IRRAs in immunopanned rodent astrocytes and human iPSC-differentiated astrocytes using TNF, IL1α, C1Q, and IFNβ and characterized their proteomic profile (both cellular and secreted) using unbiased quantitative proteomics. We identified 2335 unique cellular proteins, including IFIT2/3, IFITM3, OASL1/2, MX1/2/3, and STAT1. We also report that rodent and human IRRAs secrete PAI1, a serine protease inhibitor which may influence reactive states and functions of nearby cells. Finally, we evaluated how IRRAs are distinct from neurotoxic reactive astrocytes (NRAs). While NRAs are described by expression of the complement protein C3, it was not upregulated in IRRAs. Instead, we found ~90 proteins unique to IRRAs not identified in NRAs, including OAS1A, IFIT3, and MX1. Interferon signaling in astrocytes is critical for the antiviral immune response and for regulating synaptic plasticity and glutamate transport mechanisms. How IRRAs contribute to these functions is unknown. This study provides the basis for future experiments to define the functional roles of IRRAs in the context of neurodegenerative disorders.

Hyperammonemia in the Pediatric Emergency Department

ABSTRACT

Hyperammonemia is a serious clinical condition associated with significant morbidity and mortality. In the pediatric population, this is often caused by urea cycle disorders, acute liver failure, or other less common underlying etiologies. Children and teens with hyperammonemia can have a broad range of clinical findings, including vomiting, respiratory distress, and changes in mental status. As ammonia levels worsen, this presentation can progress to respiratory failure, encephalopathy, cerebral edema, seizures, and death. Given the risk of neurologic damage, timely identification and management of hyperammonemia is critical and includes initial resuscitation, early consultation with subspecialists, and initiation of appropriate therapies. It is important for pediatric emergency medicine providers to understand the clinical findings, causes, diagnosis, and management of hyperammonemia because they play a key role in the provision of effective, multidisciplinary care of these patients.

Maternal Exposure to Endocrine-Disrupting Chemicals: Analysis of Their Impact on Infant Gut Microbiota Composition

Endocrine disruptors (EDCs) are chemicals that interfere with the endocrine system. EDC exposure may contribute to the development of obesity, type 2 diabetes, and cardiovascular diseases by impacting the composition of an infant's gut microbiota during the first 1000 days of life. To explore the relationship between maternal urinary levels of Bisphenol-A and phthalates (UHPLC-MS/MS), and the composition of the infant gut microbiota (16S rDNA) at age 12 months (T3) and, retrospectively, at birth (T0), 1 month (T1), and 6 months (T2), stool samples from 20 infants breastfed at least once a day were analyzed. Metataxonomic bacteria relative abundances were correlated with EDC values. Based on median Bisphenol-A levels, infants were assigned to the over-exposed group (O, n = 8) and the low-exposed group (B, n = 12). The B-group exhibited higher gut colonization of the Ruminococcus torques group genus and the O-group showed higher abundances of Erysipelatoclostridium and Bifidobacterium breve. Additionally, infants were stratified as high-risk (HR, n = 12) or low-risk (LR, n = 8) exposure to phthalates, based on the presence of at least three phthalates with concentrations exceeding the cohort median values; no differences were observed in gut microbiota composition. A retrospective analysis of gut microbiota (T0-T2) revealed a disparity in β-diversity between the O-group and the B-group. Considering T0-T3, the Linear Discriminant Effect Size indicated differences in certain microbes between the O-group vs. the B-group and the HR-group vs. the LR-group. Our findings support the potential role of microbial communities as biomarkers for high EDC exposure levels. Nevertheless, further investigations are required to deeply investigate this issue.

The Potential of a Stratified Approach to Drug Repurposing in Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurodegenerative condition that is characterized by the build-up of amyloid-beta plaques and neurofibrillary tangles. While multiple theories explaining the aetiology of the disease have been suggested, the underlying cause of the disease is still unknown. Despite this, several modifiable and non-modifiable factors that increase the risk of developing AD have been identified. To date, only eight AD drugs have ever gained regulatory approval, including six symptomatic and two disease-modifying drugs. However, not all are available in all countries and high costs associated with new disease-modifying biologics prevent large proportions of the patient population from accessing them. With the current patient population expected to triple by 2050, it is imperative that new, effective, and affordable drugs become available to patients. Traditional drug development strategies have a 99% failure rate in AD, which is far higher than in other disease areas. Even when a drug does reach the market, additional barriers such as high cost and lack of accessibility prevent patients from benefiting from them. In this review, we discuss how a stratified medicine drug repurposing approach may address some of the limitations and barriers that traditional strategies face in relation to drug development in AD. We believe that novel, stratified drug repurposing studies may expedite the discovery of alternative, effective, and more affordable treatment options for a rapidly expanding patient population in comparison with traditional drug development methods.

Liver transplantation in ornithine transcarbamylase deficiency: A retrospective multicentre cohort study

Ornithine transcarbamylase deficiency (OTCD) is an X-linked defect of ureagenesis and the most common urea cycle disorder. Patients present with hyperammonemia causing neurological symptoms, which can lead to coma and death. Liver transplantation (LT) is the only curative therapy, but has several limitations including organ shortage, significant morbidity and requirement of lifelong immunosuppression. This study aims to identify the characteristics and outcomes of patients who underwent LT for OTCD. We conducted a retrospective study for OTCD patients from 5 UK centres receiving LT in 3 transplantation centres between 2010 and 2022. Patients' demographics, family history, initial presentation, age at LT, graft type and pre- and post-LT clinical, metabolic, and neurocognitive profile were collected from medical records. A total of 20 OTCD patients (11 males, 9 females) were enrolled in this study. 6/20 had neonatal and 14/20 late-onset presentation. 2/20 patients had positive family history for OTCD and one of them was diagnosed antenatally and received prospective treatment. All patients were managed with standard of care based on protein-restricted diet, ammonia scavengers and supplementation with arginine and/or citrulline before LT. 15/20 patients had neurodevelopmental problems before LT. The indication for LT was presence (or family history) of recurrent metabolic decompensations occurring despite standard medical therapy leading to neurodisability and quality of life impairment. Median age at LT was 10.5 months (6-24) and 66 months (35-156) in neonatal and late onset patients, respectively. 15/20 patients had deceased donor LT (DDLT) and 5/20 had living related donor LT (LDLT). Overall survival was 95% with one patient dying 6 h after LT. 13/20 had complications after LT and 2/20 patients required re-transplantation. All patients discontinued dietary restriction and ammonia scavengers after LT and remained metabolically stable. Patients who had neurodevelopmental problems before LT persisted to have difficulties after LT. 1/5 patients who was reported to have normal neurodevelopment before LT developed behavioural problems after LT, while the remaining 4 maintained their abilities without any reported issues. LT was found to be effective in correcting the metabolic defect, eliminates the risk of hyperammonemia and prolongs patients' survival.

Astrocytes as Drivers and Disruptors of Behavior: New Advances in Basic Mechanisms and Therapeutic Targeting

Astrocytes are emerging as key regulators of cognitive function and behavior. This review highlights some of the latest advances in the understanding of astrocyte roles in different behavioral domains across lifespan and in disease. We address specific molecular and circuit mechanisms by which astrocytes modulate behavior, discuss their functional diversity and versatility, and highlight emerging astrocyte-targeted treatment strategies that might alleviate behavioral and cognitive dysfunction in pathologic conditions. Converging evidence across different model systems and manipulations is revealing that astrocytes regulate behavioral processes in a precise and context-dependent manner. Improved understanding of these astrocytic functions may generate new therapeutic strategies for various conditions with cognitive and behavioral impairments.

Role of caveolin-1 in metabolic programming of fetal brain

Mice lacking caveolin-1 (Cav1), a key protein of plasma membrane, exhibit brain aging at an early adult stage. Here, integrative analyses of metabolomics, transcriptomics, epigenetics, and single-cell data were performed to test the hypothesis that metabolic deregulation of fetal brain due to the ablation of Cav1 is linked to brain aging in these mice. The results of this study show that lack of Cav1 caused deregulation in the lipid and amino acid metabolism in the fetal brain, and genes associated with these deregulated metabolites were significantly altered in the brain upon aging. Moreover, ablation of Cav1 deregulated several metabolic genes in specific cell types of the fetal brain and impacted DNA methylation of those genes in coordination with mouse epigenetic clock. The findings of this study suggest that the aging program of brain is confounded by metabolic abnormalities in the fetal stage due to the absence of Cav1.

From Pathogenesis to Therapeutics: A Review of 150 Years of Huntington's Disease Research

Huntington's disease (HD) is a debilitating neurodegenerative genetic disorder caused by an expanded polyglutamine-coding (CAG) trinucleotide repeat in the huntingtin (HTT) gene. HD behaves as a highly penetrant dominant disorder likely acting through a toxic gain of function by the mutant huntingtin protein. Widespread cellular degeneration of the medium spiny neurons of the caudate nucleus and putamen are responsible for the onset of symptomology that encompasses motor, cognitive, and behavioural abnormalities. Over the past 150 years of HD research since George Huntington published his description, a plethora of pathogenic mechanisms have been proposed with key themes including excitotoxicity, dopaminergic imbalance, mitochondrial dysfunction, metabolic defects, disruption of proteostasis, transcriptional dysregulation, and neuroinflammation. Despite the identification and characterisation of the causative gene and mutation and significant advances in our understanding of the cellular pathology in recent years, a disease-modifying intervention has not yet been clinically approved. This review includes an overview of Huntington's disease, from its genetic aetiology to clinical presentation and its pathogenic manifestation. An updated view of molecular mechanisms and the latest therapeutic developments will also be discussed.

Metabolomics and Self-Reported Depression, Anxiety, and Phobic Symptoms in the VA Normative Aging Study

Traditional approaches to understanding metabolomics in mental illness have focused on investigating a single disorder or comparisons between diagnoses, but a growing body of evidence suggests substantial mechanistic overlap in mental disorders that could be reflected by the metabolome. In this study, we investigated associations between global plasma metabolites and abnormal scores on the depression, anxiety, and phobic anxiety subscales of the Brief Symptom Inventory (BSI) among 405 older males who participated in the Normative Aging Study (NAS). Our analysis revealed overlapping and distinct metabolites associated with each mental health dimension subscale and four metabolites belonging to xenobiotic, carbohydrate, and amino acid classes that were consistently associated across all three symptom dimension subscales. Furthermore, three of these four metabolites demonstrated a higher degree of alteration in men who reported poor scores in all three dimensions compared to men with poor scores in only one, suggesting the potential for shared underlying biology but a differing degree of perturbation when depression and anxiety symptoms co-occur. Our findings implicate pathways of interest relevant to the overlap of mental health conditions in aging veterans and could represent clinically translatable targets underlying poor mental health in this high-risk population.

Clinical and radiological description of 120 pediatric stroke-like episodes

BACKGROUND AND PURPOSE

Stroke-like episodes (SLEs) are defined as acute onset of neurological symptoms mimicking a stroke and radiological lesions non-congruent to vascular territory. We aimed to analyze the acute clinical and radiological features of SLEs to determine their pathophysiology.

METHODS

We performed a monocenter retrospective analysis of 120 SLEs in 60 children over a 20-year period. Inclusion criteria were compatible clinical symptoms and stroke-like lesions on brain magnetic resonance imaging (MRI; performed for all 120 events) with focal hyperintensity on diffusion-weighted imaging in a non-vascular territory.

RESULTS

Three groups were identified: children with mitochondrial diseases (n = 22) involving mitochondrial DNA mutations (55%) or nuclear DNA mutations (45%); those with other metabolic diseases or epilepsy disorders (n = 22); and those in whom no etiology was found despite extensive investigations (n = 16). Age at first SLE was younger in the group with metabolic or epilepsy disorders (18 months vs. 128 months; p < 0.0001) and an infectious trigger was more frequent (69% vs. 20%; p = 0.0001). Seizures occurred in 75% of episodes, revealing 50% episodes of SLEs and mainly leading to status epilepticus (90%). Of the 120 MRI scans confirming the diagnosis, 28 were performed within a short and strict 48-h period and were further analyzed to better understand the underlying mechanisms. The scans showed primary cortical hyperintensity (n = 28/28) with decreased apparent diffusion coefficient in 52% of cases. Systematic hyperperfusion was found on spin labeling sequences when available (n = 18/18).

CONCLUSION

Clinical and radiological results support the existence of a vicious circle based on two main mechanisms: energy deficit and neuronal hyperexcitability at the origin of SLE.

Taste-masked formulation of sodium phenylbutyrate (ACER-001) for the treatment of urea cycle disorders

Urea cycle disorders (UCDs) are a group of rare inherited metabolic diseases caused by a deficiency of one of the enzymes or transporters that constitute the urea cycle. Defects in these enzymes lead to acute accumulation (hyperammonemic crises, HAC) or chronically elevated levels (hyperammonemia) of ammonia in the blood and/or various tissues including the brain, which can cause persistent neurological deficits, irreversible brain damage, coma, and death. Ongoing treatment of UCDs include the use of nitrogen-scavenging agents, such as sodium phenylbutyrate (salt of 4-phenylbutyric acid; NaPBA) or glycerol phenylbutyrate (GPB). These treatments provide an alternative pathway for nitrogen disposal through the urinary excretion of phenylacetylglutamine. ACER-001 is a novel formulation of NaPBA with polymer coated pellets in suspension, which is designed to briefly mask the unpleasant bitter taste of NaPBA and is being developed as a treatment option for patients with UCDs. Four Phase 1 studies were conducted to characterize the bioavailability (BA) and/or bioequivalence (BE) of ACER-001 (in healthy volunteers) and taste assessment relative to NaPBA powder (in taste panelists). ACER-001 was shown to be bioequivalent to NaPBA powder under both fed and fasting conditions. Lower systemic exposure of phenylacetate (PAA) and phenylbutyrate (PBA) was observed when ACER-001 was administered with a high-fat meal relative to a fasting state suggesting that the lower doses of PBA administered under fasting conditions may yield similar efficacy with potentially fewer dose dependent adverse effects relative to higher doses with a meal. ACER-001 appeared to be adequately taste-masked, staying below the aversive taste threshold for the first 3 min after the formulation was prepared and remaining palatable when taken within 5 min.

Three-Country Snapshot of Ornithine Transcarbamylase Deficiency

X-linked ornithine transcarbamylase deficiency (OTCD) is the most common urea cycle defect. The disease severity ranges from asymptomatic carrier state to severe neonatal presentation with hyperammonaemic encephalopathy. We audited the diagnosis and management of OTCD, using an online 12-question-survey that was sent to 75 metabolic centres in Turkey, France and the UK. Thirty-nine centres responded and 495 patients were reported in total. A total of 208 French patients were reported, including 71 (34%) males, 86 (41%) symptomatic and 51 (25%) asymptomatic females. Eighty-five Turkish patients included 32 (38%) males, 39 (46%) symptomatic and 14 (16%) asymptomatic females. Out of the 202 UK patients, 66 (33%) were male, 83 (41%) asymptomatic and 53 (26%) symptomatic females. A total of 19%, 12% and 7% of the patients presented with a neonatal-onset phenotype in France, Turkey and the UK, respectively. Vomiting, altered mental status and encephalopathy were the most common initial symptoms in all three countries. While 69% in France and 79% in Turkey were receiving protein restriction, 42% were on a protein-restricted diet in the UK. A total of 76%, 47% and 33% of patients were treated with ammonia scavengers in Turkey, France and the UK, respectively. The findings of our audit emphasize the differences and similarities in manifestations and management practices in three countries.

Novel pathogenic variant (c.2947C > T) of the carbamoyl phosphate synthetase 1 gene in neonatal-onset deficiency

Background

Carbamoyl phosphate synthetase 1 deficiency (CPS1D) is a rare autosomal recessive urea cycle disorder characterized by hyperammonaemia. The biochemical measurement of the intermediate metabolites is helpful for CPS1D diagnosis; it however cannot distinguish CPS1D from N-acetylglutamate synthetase deficiency. Therefore, next-generation sequencing (NGS) is often essential for the accurate diagnosis of CPS1D.

Methods

NGS was performed to identify candidate gene variants of CPS1D in a Asian neonatal patient presented with poor feeding, reduced activity, tachypnea, lethargy, and convulsions. The potential pathogenicity of the identified variants was predicted by various types of bioinformatical analyses, including evolution conservation, domain and 3D structure simulations.

Results

Compound heterozygosity of CPS1D were identified. One was in exon 24 with a novel heterozygous missense variant c.2947C > T (p.P983S), and another was previously reported in exon 20 with c.2548C > T (p.R850C). Both variants were predicted to be deleterious. Conservation analysis and structural modeling showed that the two substituted amino acids were highly evolutionarily conserved, resulting in potential decreases of the binding pocket stability and the partial loss of enzyme activity.

Conclusion

In this study, two pathogenic missense variants were identified with NGS, expanding the variants pectrum of the CPS1 gene. The variants and related structural knowledge of CPS enzyme demonstrate the applicability for the accurate diagnosis of CPS1D.

Modelling urea cycle disorders using iPSCs

The urea cycle is a liver-based pathway enabling disposal of nitrogen waste. Urea cycle disorders (UCDs) are inherited metabolic diseases caused by deficiency of enzymes or transporters involved in the urea cycle and have a prevalence of 1:35,000 live births. Patients present recurrent acute hyperammonaemia, which causes high rate of death and neurological sequelae. Long-term therapy relies on a protein-restricted diet and ammonia scavenger drugs. Currently, liver transplantation is the only cure. Hence, high unmet needs require the identification of effective methods to model these diseases to generate innovative therapeutics. Advances in both induced pluripotent stem cells (iPSCs) and genome editing technologies have provided an invaluable opportunity to model patient-specific phenotypes in vitro by creating patients' avatar models, to investigate the pathophysiology, uncover novel therapeutic targets and provide a platform for drug discovery. This review summarises the progress made thus far in generating 2- and 3-dimensional iPSCs models for UCDs, the challenges encountered and how iPSCs offer future avenues for innovation in developing the next-generation of therapies for UCDs.

Review of Applications of Near-Infrared Spectroscopy in Two Rare Disorders with Executive and Neurological Dysfunction: UCD and PKU

Studying rare diseases, particularly those with neurological dysfunction, is a challenge to researchers and healthcare professionals due to their complexity and small population with geographical dispersion. Universal and standardized biomarkers generated by tools such as functional neuroimaging have been forged to collect baseline data as well as treatment effects. However, the cost and heavily infrastructural requirement of those technologies have substantially limited their availability. Thus, developing non-invasive, portable, and inexpensive modalities has become a major focus for both researchers and clinicians. When considering neurological disorders and diseases with executive dysfunction, EEG is the most convenient tool to obtain biomarkers which can correlate the objective severity and clinical observation of these conditions. However, studies have also shown that EEG biomarkers and clinical observations alone are not sensitive enough since not all the patients present classical phenotypical features or EEG evidence of dysfunction. This article reviews disorders, including two rare disorders with neurological dysfunction and the usefulness of functional near-infrared spectroscopy (fNIRS) as a non-invasive optical modality to obtain hemodynamic biomarkers of diseases and for screening and monitoring the disease.

Neuropathological report of propionic acidemia

Propionic acidemia (PA) is an autosomal recessive inheritable metabolic disease caused by mutations in the propionyl CoA carboxylase gene (PCC) that affects multiple systems of the human body. Here, we report neuropathological findings of a PA patient. The patient was a male infant who presented with increasing lethargy and poor feeding from four days postpartum. He gradually became comatose and died from complications after liver transplantation at three months old. The results of laboratory examination were consistent with PA, and genetic analysis revealed compound heterozygous mutations in the gene for PCC subunit beta: c.838dupC (rs769968548) and c.1127G>T (rs142982097). Brain-restricted autopsy was performed 23 h after his death, and the neuropathological examination revealed distinct astrocytosis, oligodendrocytic loss, neuronal loss, and demyelination across the brainstem, motor cortex, basal ganglia, and thalamus. Spongiosis, vacuolization, and the appearance of Alzheimer type II astrocytes and activated microglia were observed as well. This is the first brain autopsy report of PA with a clear genetic cause.

Fecal microbiota transplantation can improve cognition in patients with cognitive decline and Clostridioides difficile infection

After fecal microbiota transplantation (FMT) to treat Clostridioides difficile infection (CDI), cognitive improvement is noticeable, suggesting an essential association between the gut microbiome and neural function. Although the gut microbiome has been associated with cognitive function, it remains to be elucidated whether fecal microbiota transplantation can improve cognition in patients with cognitive decline. The study included 10 patients (age range, 63-90 years; female, 80%) with dementia and severe CDI who were receiving FMT. Also, 10 patients (age range, 62-91; female, 80%) with dementia and severe CDI who were not receiving FMT. They were evaluated using cognitive function tests (Mini-Mental State Examination [MMSE] and Clinical Dementia Rating scale Sum of Boxes [CDR-SB]) at 1 month before and after FMT or antibiotics treatment (control group). The patients' fecal samples were analyzed to compare the composition of their gut microbiota before and 3 weeks after FMT or antibiotics treatment. Ten patients receiving FMT showed significantly improvements in clinical symptoms and cognitive functions compared to control group. The MMSE and CDR-SB of FMT group were improved compare to antibiotics treatment (MMSE: 16.00, median, 13.00-18.00 [IQR] vs. 10.0, median, 9.8-15.3 [IQR]); CDR-SB: 5.50, median, 4.00-8.00 [IQR]) vs. 8.0, median, 7.9-12.5, [IQR]). FMT led to changes in the recipient's gut microbiota composition, with enrichment of Proteobacteria and Bacteroidetes. Alanine, aspartate, and glutamate metabolism pathways were also significantly different after FMT. This study revealed important interactions between the gut microbiome and cognitive function. Moreover, it suggested that FMT may effectively delay cognitive decline in patients with dementia.

Metabolomic Analysis of Human Astrocytes in Lipotoxic Condition: Potential Biomarker Identification by Machine Learning Modeling

The association between neurodegenerative diseases (NDs) and obesity has been well studied in recent years. Obesity is a syndrome of multifactorial etiology characterized by an excessive accumulation and release of fatty acids (FA) in adipose and non-adipose tissue. An excess of FA generates a metabolic condition known as lipotoxicity, which triggers pathological cellular and molecular responses, causing dysregulation of homeostasis and a decrease in cell viability. This condition is a hallmark of NDs, and astrocytes are particularly sensitive to it, given their crucial role in energy production and oxidative stress management in the brain. However, analyzing cellular mechanisms associated with these conditions represents a challenge. In this regard, metabolomics is an approach that allows biochemical analysis from the comprehensive perspective of cell physiology. This technique allows cellular metabolic profiles to be determined in different biological contexts, such as those of NDs and specific metabolic insults, including lipotoxicity. Since data provided by metabolomics can be complex and difficult to interpret, alternative data analysis techniques such as machine learning (ML) have grown exponentially in areas related to omics data. Here, we developed an ML model yielding a 93% area under the receiving operating characteristic (ROC) curve, with sensibility and specificity values of 80% and 93%, respectively. This study aimed to analyze the metabolomic profiles of human astrocytes under lipotoxic conditions to provide powerful insights, such as potential biomarkers for scenarios of lipotoxicity induced by palmitic acid (PA). In this work, we propose that dysregulation in seleno-amino acid metabolism, urea cycle, and glutamate metabolism pathways are major triggers in astrocyte lipotoxic scenarios, while increased metabolites such as alanine, adenosine, and glutamate are suggested as potential biomarkers, which, to our knowledge, have not been identified in human astrocytes and are proposed as candidates for further research and validation.

Benefits of tailored disease management in improving tremor, white matter hyperintensities, and liver enzymes in a child with heterozygous X-linked ornithine transcarbamylase deficiency

We report the case of a 19-month-old girl with late-onset ornithine transcarbamylase (OTC) deficiency initially referred to gastroenterology for intermittent vomiting lasting a year and abnormal liver enzymes (AST 730 U/L [reference range 26-55 U/L]; ALT 1213 U/L [reference range 11-30 U/L]) without hepatomegaly. While the patient was hospitalized for liver biopsy, intermittent tremors of the upper extremities with varying severity were noted. The patient was presumed to have hyperammonemia secondary to acute liver failure and was discharged after 5 days; follow-up monitoring led to readmission 7 days later. A brain MRI showed nonspecific bilateral pericallosal and bifrontal white matter FLAIR hyperintensities. These findings raised suspicion for a metabolic disease and prompted a genetics consultation. After inconclusive biochemical testing and worsening clinical status, rapid whole genome sequencing results were obtained identifying a novel, de novo, likely pathogenic, variant c.608C > T (p.Ser203Phe) in the OTC gene. The patient was promptly started on an oral nitrogen scavenger, citrulline supplementation, and protein restriction. Ammonia and glutamine levels normalized within 1 month of treatment and have stayed within the goal ranges with continued tailoring of treatment. Her parents noted resolution of vomiting and improved mood stability. Liver enzymes normalized after 2 months of treatment. The tremor, identified as asterixis, improved and a repeat brain MRI 3 months after the initial imaging showed near-complete resolution of previous white matter hyperintensities.

Recommendations for the Diagnosis and Therapeutic Management of Hyperammonaemia in Paediatric and Adult Patients

Hyperammonaemia is a metabolic derangement that may cause severe neurological damage and even death due to cerebral oedema, further complicating the prognosis of its triggering disease. In small children it is a rare condition usually associated to inborn errors of the metabolism. As age rises, and especially in adults, it may be precipitated by heterogeneous causes such as liver disease, drugs, urinary infections, shock, or dehydration. In older patients, it is often overlooked, or its danger minimized. This protocol was drafted to provide an outline of the clinical measures required to normalise ammonia levels in patients of all ages, aiming to assist clinicians with no previous experience in its treatment. It is an updated protocol developed by a panel of experts after a review of recent publications. We point out the importance of frequent monitoring to assess the response to treatment, the nutritional measures that ensure not only protein restriction but adequate caloric intake and the need to avoid delays in the use of specific pharmacological therapies and, especially, extrarenal clearance measures. In this regard, we propose initiating haemodialysis when ammonia levels are >200−350 µmol/L in children up to 18 months of age and >150−200 µmol/L after that age.

A 36-year-old Man with Repeated Short-term Transient Hyperammonemia and Impaired Consciousness with a Confirmed Carbamoyl Phosphate Synthase 1 Gene Monoallelic Mutation

A 36-year-old man experienced severely impaired consciousness twice after drinking because of hyperammonemia. No abnormal blood tests were found other than ammonia levels. However, magnetic resonance imaging (MRI) showed atrophy of the brain parenchyma. One the second occasion, the patient suffered severe impairment of consciousness, and because of seizures and glossoptosis, mechanical ventilation was started. Urea cycle disorders (UCDs) were assumed to be involved. Genetic testing revealed a monoallelic mutation of the carbamoyl phosphate synthase 1 (CPS1) gene. When transient hyperammonemia of unknown cause occurs repeatedly in adults, an active investigation for UCDs should be conducted.

Comparison of Microflow and Analytical Flow Liquid Chromatography Coupled to Mass Spectrometry Global Metabolomics Methods Using a Urea Cycle Disorder Mouse Model

Microscale-based separations are increasingly being applied in the field of metabolomics for the analysis of small-molecule metabolites. These methods have the potential to provide improved sensitivity, less solvent waste, and reduced sample-size requirements. Ion-pair free microflow-based global metabolomics methods, which we recently reported, were further compared to analytical flow ion-pairing reagent containing methods using a sample set from a urea cycle disorder (UCD) mouse model. Mouse urine and brain homogenate samples representing healthy, diseased, and disease-treated animals were analyzed by both methods. Data processing was performed using univariate and multivariate techniques followed by analyte trend analysis. The microflow methods performed comparably to the analytical flow ion-pairing methods with the ability to separate the three sample groups when analyzed by partial least-squares analysis. The number of detected metabolic features present after each data processing step was similar between the microflow-based methods and the ion-pairing methods in the negative ionization mode. The observed analyte trend and coverage of known UCD biomarkers were the same for both evaluated approaches. The 12.5-fold reduction in sample injection volume required for the microflow-based separations highlights the potential of this method to support studies with sample-size limitations.

Fifteen years of urea cycle disorders brain research: Looking back, looking forward

Urea cycle disorders (UCD) are inherited diseases resulting from deficiency in one of six enzymes or two carriers that are required to remove ammonia from the body. UCD may be associated with neurological damage encompassing a spectrum from asymptomatic/mild to severe encephalopathy, which results in most cases from Hyperammonemia (HA) and elevation of other neurotoxic intermediates of metabolism. Electroencephalography (EEG), Magnetic resonance imaging (MRI) and Proton Magnetic resonance spectroscopy (MRS) are noninvasive measures of brain function and structure that can be used during HA to guide management and provide prognostic information, in addition to being research tools to understand the pathophysiology of UCD associated brain injury. The Urea Cycle Rare disorders Consortium (UCDC) has been invested in research to understand the immediate and downstream effects of hyperammonemia (HA) on brain using electroencephalogram (EEG) and multimodal brain MRI to establish early patterns of brain injury and to track recovery and prognosis. This review highlights the evolving knowledge about the impact of UCD and HA in particular on neurological injury and recovery and use of EEG and MRI to study and evaluate prognostic factors for risk and recovery. It recognizes the work of others and discusses the UCDC's prior work and future research priorities.

Perceptions and use of phenylbutyrate metabolite testing in urea cycle disorders: Results of a clinician survey and analysis of a centralized testing database

The nitrogen scavengers sodium and glycerol phenylbutyrate (PB), approved for chronic treatment of urea cycle disorders (UCDs), undergo hepatic conversion to phenylacetate (PAA), which conjugates glutamine to form phenylacetylglutamine for urinary nitrogen excretion. Elevated PAA has been associated with reversible neurological toxicity, with symptoms similar to hyperammonemia. Plasma PB metabolite analysis can assess for toxicity and therapeutic drug levels. An online survey was undertaken to assess US clinician perceptions and use of the test in addition to an analysis of centralized US laboratory records. Survey responses from 52 clinicians were analyzed, including 58% who reported using plasma PB metabolite testing. Test users reported managing more UCD patients than nonusers. Users rated the test as "often helpful" for ruling out PAA toxicity (44%), informing PB dosing decisions (42%), and assessing adherence (28%). Test results were reported as most often unremarkable (61%) or suggestive of poor adherence (13%); 46% of users had never encountered results indicative of PAA toxicity. Analyses of laboratory records for 1668 plasma metabolite tests determined that only 5% of samples had plasma PAA-to-phenylacetylglutamine ratios associated with increased risk of PAA toxicity. Nearly half of surveyed clinicians were unsure of metabolite targets; those conducting ad hoc (versus regular) testing were significantly more likely to be unsure of targets. One-fifth of test users identified uncertainties, including questions about test validation, timing, and interpretation. Increased awareness of published PB metabolite data and further clinician education on test interpretation may help to inform the use of metabolite testing to optimize UCD care.

Sodium Benzoate, a Metabolite of Cinnamon and a Food Additive, Improves Cognitive Functions in Mice after Controlled Cortical Impact Injury

Traumatic brain injury (TBI) is a major health concern, sometimes leading to long-term neurological disability, especially in children, young adults and war veterans. Although research investigators and clinicians have applied different treatment strategies or neurosurgical procedures to solve this health issue, we are still in need of an effective therapy to halt the pathogenesis of brain injury. Earlier, we reported that sodium benzoate (NaB), a metabolite of cinnamon and a Food and Drug Administration-approved drug against urea cycle disorders and glycine encephalopathy, protects neurons in animal models of Parkinson's disease and Alzheimer's disease. This study was undertaken to examine the therapeutic efficacy of NaB in a controlled cortical impact (CCI)-induced preclinical mouse model of TBI. Oral treatment with NaB, but not sodium formate (NaFO), was found to decrease the activation of microglia and astrocytes and to inhibit the expression of inducible nitric oxide synthase (iNOS) in the hippocampus and cortex of CCI-insulted mice. Further, administration of NaB also reduced the vascular damage and decreased the size of the lesion cavity in the brain of CCI-induced mice. Importantly, NaB-treated mice showed significant improvements in memory and locomotor functions as well as displaying a substantial reduction in depression-like behaviors. These results delineate a novel neuroprotective property of NaB, highlighting its possible therapeutic importance in TBI.

Nitric Oxide-Dependent Mechanisms Underlying MK-801- or Scopolamine-Induced Memory Dysfunction in Animals: Mechanistic Studies

MK-801, an NMDA receptor antagonist, and scopolamine, a cholinergic receptor blocker, are widely used as tool compounds to induce learning and memory deficits in animal models to study schizophrenia or Alzheimer-type dementia (AD), respectively. Memory impairments are observed after either acute or chronic administration of either compound. The present experiments were performed to study the nitric oxide (NO)-related mechanisms underlying memory dysfunction induced by acute or chronic (14 days) administration of MK-801 (0.3 mg/kg, i.p.) or scopolamine (1 mg/kg, i.p.). The levels of L-arginine and its derivatives, L-citrulline, L-glutamate, L-glutamine and L-ornithine, were measured. The expression of constitutive nitric oxide synthases (cNOS), dimethylaminohydrolase (DDAH1) and protein arginine N-methyltransferases (PMRTs) 1 and 5 was evaluated, and the impact of the studied tool compounds on cGMP production and NMDA receptors was measured. The studies were performed in both the cortex and hippocampus of mice. S-nitrosylation of selected proteins, such as GLT-1, APP and tau, was also investigated. Our results indicate that the availability of L-arginine decreased after chronic administration of MK-801 or scopolamine, as both the amino acid itself as well as its level in proportion to its derivatives (SDMA and NMMA) were decreased. Additionally, among all three methylamines, SDMA was the most abundant in the brain (~70%). Administration of either compound impaired eNOS-derived NO production, increasing the monomer levels, and had no significant impact on nNOS. Both compounds elevated DDAH1 expression, and slight decreases in PMRT1 and PMRT5 in the cortex after scopolamine (acute) and MK-801 (chronic) administration were observed in the PFC, respectively. Administration of MK-801 induced a decrease in the cGMP level in the hippocampus, accompanied by decreased NMDA expression, while increased cGMP production and decreased NMDA receptor expression were observed after scopolamine administration. Chronic MK-801 and scopolamine administration affected S-nitrosylation of GLT-1 transport protein. Our results indicate that the analyzed tool compounds used in pharmacological models of schizophrenia or AD induce changes in NO-related pathways in the brain structures involved in cognition. To some extent, the changes resemble those observed in human samples.

Late-onset argininosuccinic aciduria in a 72-year-old man presenting with fatal hyperammonemia

Argininosuccinate lyase deficiency (ASLD, MIM #207900) is an inherited urea cycle disorder. There are mainly two clinical forms, an acute neonatal form which manifests as life-threatening hyperammonemia, and a late-onset form characterised by polymorphic neuro-cognitive or psychiatric presentation with transient hyperammonemia episodes. Here, we report a late-onset case of ASLD in a 72-year-old man carrying a homozygous pathogenic variant in the exon 16 of the ASL gene, presenting for the first time with fatal hyperammonemic coma. This case report shows the need to systematically carry out an ammonia assay when faced with an unexplained coma.

Hyperammonemia in Inherited Metabolic Diseases

Ammonia is a neurotoxic compound which is detoxified through liver enzymes from urea cycle. Several inherited or acquired conditions can elevate ammonia concentrations in blood, causing severe damage to the central nervous system due to the toxic effects exerted by ammonia on the astrocytes. Therefore, hyperammonemic patients present potentially life-threatening neuropsychiatric symptoms, whose severity is related with the hyperammonemia magnitude and duration, as well as the brain maturation stage. Inherited metabolic diseases caused by enzymatic defects that compromise directly or indirectly the urea cycle activity are the main cause of hyperammonemia in the neonatal period. These diseases are mainly represented by the congenital defects of urea cycle, classical organic acidurias, and the defects of mitochondrial fatty acids oxidation, with hyperammonemia being more severe and frequent in the first two groups mentioned. An effective and rapid treatment of hyperammonemia is crucial to prevent irreversible neurological damage and it depends on the understanding of the pathophysiology of the diseases, as well as of the available therapeutic approaches. In this review, the mechanisms underlying the hyperammonemia and neurological dysfunction in urea cycle disorders, organic acidurias, and fatty acids oxidation defects, as well as the therapeutic strategies for the ammonia control will be discussed.

Reye Syndrome with Severe Hyperammonemia and a Good Neurological Outcome

Patient: Male, 4-year-old

Final Diagnosis: Reye syndrome

Symptoms: Hypoglycemia • disturbance of consciousness • diarrhoea • signs of respiratory infection • vomiting and nausea

Medication: —

Clinical Procedure: —

Specialty: Critical Care Medicine • Endocrinology and Metabolic • Pediatrics and Neonatology

Diagnostics of Inherited Metabolic Diseases in Newborns with the Hyperammonemia Syndrome at the Onset of Disease (Pilot Study)

The aim of the study was to develop a diagnostic model that allows with a high degree of probability predicting the development of inherited metabolic disease (IMD) in newborns with the hyperammonemia syndrome at the onset of disease and determine the adequate management tactics for such patients.

Creatine metabolism in patients with urea cycle disorders

The urea cycle generates arginine that is one of the major precursors for creatine biosynthesis. Here we evaluate levels of creatine and guanidinoacetate (the precursor in the synthesis of creatine) in plasma samples (n_s = 207) of patients (n_p = 73) with different types of urea cycle disorders (ornithine transcarbamylase deficiency (n_s = 22; n_p = 7), citrullinemia type 1 (n_s = 60; n_p = 22), argininosuccinic aciduria (n_s = 81; n_p = 31), arginase deficiency (n_s = 44; n_p = 13)). The concentration of plasma guanidinoacetate positively correlated (p < 0.001, R² = 0.64) with levels of arginine, but not with glycine in all patients with urea cycle defects, rising to levels above normal in most samples (34 out of 44) of patients with arginase deficiency. In contrast to patients with guanidinoacetate methyltransferase deficiency (a disorder of creatine synthesis characterized by elevated guanidinoacetate concentrations), creatine levels were normal (32 out of 44) or above normal (12 out of 44) in samples from patients with arginase deficiency. Creatine levels correlated significantly, but poorly (p < 0.01, R² = 0.1) with guanidinoacetate levels and, despite being overall in the normal range in patients with all other urea cycle disorders, were occasionally below normal in some patients with argininosuccinic acid synthase and lyase deficiency. Creatine levels positively correlated with levels of methionine (p < 0.001, R² = 0.16), the donor of the methyl group for creatine synthesis. The direct correlation of arginine levels with guanidinoacetate in patients with urea cycle disorders explains the increased concentration of guanidino compounds in arginase deficiency. Low creatine levels in some patients with other urea cycle defects might be explained by low protein intake (creatine is naturally present in meat) and relative or absolute intracellular arginine deficiency.

Hepatic Manifestations of Urea Cycle Disorders

Content available: Author Interview and Audio Recording.

Long-term outcome of urea cycle disorders: Report from a nationwide study in Japan

Urea cycle disorders (UCDs) are inherited metabolic disorders with impaired nitrogen detoxification caused by defects in urea cycle enzymes. They often manifest with hyperammonemic attacks resulting in significant morbidity or death. We performed a nationwide questionnaire-based study between January 2000 and March 2018 to document all UCDs in Japan, including diagnoses, treatments, and outcomes. A total of 229 patients with UCDs were enrolled in this study: 73 males and 53 females with ornithine transcarbamylase deficiency (OTCD), 33 patients with carbamoylphosphate synthetase 1 deficiency, 48 with argininosuccinate synthetase deficiency, 14 with argininosuccinate lyase deficiency, and 8 with arginase deficiency. Survival rates at 20 years of age of male and female patients with late-onset OTCD were 100% and 97.7%, respectively. Blood ammonia levels and time of onset had a significant impact on the neurodevelopmental outcome (P < .001 and P = .028, respectively). Hemodialysis and liver transplantation did not prevent poor neurodevelopmental outcomes. While treatment including medication, hemodialysis, and liver transplantation may aid in decreasing blood ammonia and/or preventing severe hyperammonemia, a blood ammonia level ≥ 360 μmol/L was found to be a significant indicator for a poor neurodevelopmental outcome. In conclusion, although current therapy for UCDs has advanced and helped saving lives, patients with blood ammonia levels ≥ 360 μmol/L at onset often have impaired neurodevelopmental outcomes. Novel neuroprotective measures should therefore be developed to achieve better neurodevelopmental outcomes in these patients.

Physiological and Pathological Factors Affecting Drug Delivery to the Brain by Nanoparticles

The prevalence of neurological/neurodegenerative diseases, such as Alzheimer's disease is known to be increasing due to an aging population and is anticipated to further grow in the decades ahead. The treatment of brain diseases is challenging partly due to the inaccessibility of therapeutic agents to the brain. An increasingly important observation is that the physiology of the brain alters during many brain diseases, and aging adds even more to the complexity of the disease. There is a notion that the permeability of the blood-brain barrier (BBB) increases with aging or disease, however, the body has a defense mechanism that still retains the separation of the brain from harmful chemicals in the blood. This makes drug delivery to the diseased brain, even more challenging and complex task. Here, the physiological changes to the diseased brain and aged brain are covered in the context of drug delivery to the brain using nanoparticles. Also, recent and novel approaches are discussed for the delivery of therapeutic agents to the diseased brain using nanoparticle based or magnetic resonance imaging guided systems. Furthermore, the complement activation, toxicity, and immunogenicity of brain targeting nanoparticles as well as novel in vitro BBB models are discussed.

Review of Multi-Modal Imaging in Urea Cycle Disorders: The Old, the New, the Borrowed, and the Blue

The urea cycle disorders (UCD) are rare genetic disorder due to a deficiency of one of six enzymes or two transport proteins that act to remove waste nitrogen in form of ammonia from the body. In this review, we focus on neuroimaging studies in OTCD and Arginase deficiency, two of the UCD we have extensively studied. Ornithine transcarbamylase deficiency (OTCD) is the most common of these, and X-linked. Hyperammonemia (HA) in OTCD is due to deficient protein handling. Cognitive impairments and neurobehavioral disorders have emerged as the major sequelae in Arginase deficiency and OTCD, especially in relation to executive function and working memory, impacting pre-frontal cortex (PFC). Clinical management focuses on neuroprotection from HA, as well as neurotoxicity from other known and yet unclassified metabolites. Prevention and mitigation of neurological injury is a major challenge and research focus. Given the impact of HA on neurocognitive function of UCD, neuroimaging modalities, especially multi-modality imaging platforms, can bring a wealth of information to understand the neurocognitive function and biomarkers. Such information can further improve clinical decision making, and result in better therapeutic interventions. In vivo investigations of the affected brain using multimodal neuroimaging combined with clinical and behavioral phenotyping hold promise. MR Spectroscopy has already proven as a tool to study biochemical aberrations such as elevated glutamine surrounding HA as well as to diagnose partial UCD. Functional Near Infrared Spectroscopy (fNIRS), which assesses local changes in cerebral hemodynamic levels of cortical regions, is emerging as a non-invasive technique and will serve as a surrogate to fMRI with better portability. Here we review two decades of our research using non-invasive imaging and how it has contributed to an understanding of the cognitive effects of this group of genetic conditions.

Stimulation of Dopamine Production by Sodium Benzoate, a Metabolite of Cinnamon and a Food Additive

BACKGROUND

Parkinson's disease (PD) is one of the most important neurodegenerative disorders in human in which recovery of functions could be achieved by improving the survival and function of residual dopaminergic neurons in the substantia nigra pars compacta. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the dopamine (DA) biosynthesis pathway.

OBJECTIVE

Earlier our laboratory has shown that sodium benzoate (NaB), a metabolite of cinnamon and an FDA-approved drug against urea cycle disorders and glycine encephalopathy, increases neuroprotective molecules and protects dopaminergic neurons in a mouse model of PD. Here, we examined whether NaB could stimulate the production of DA in dopaminergic neurons.

METHODS

We employed PCR, real-time PCR, western blot, immunostaining, and HPLC to study the signature function of dopaminergic neurons. Locomotor functions were monitored in mice by open-field.

RESULTS

NaB increased the mRNA and protein expression of TH to produce DA in mouse MN9D dopaminergic neuronal cells. Accordingly, oral feeding of NaB increased the expression of TH in the nigra, upregulated striatal DA, and improved locomotor activities in striatum of normal C57/BL6 and aged A53T-α-syn transgenic mice. Rapid induction of cAMP response element binding (CREB) activation by NaB in dopaminergic neuronal cells and the abrogation of NaB-induced expression of TH by siRNA knockdown of CREB suggest that NaB stimulates the transcription of TH in dopaminergic neurons via CREB.

CONCLUSION

These results indicate a new function of NaB in which it may be beneficial in PD via stimulation of DA production from residual dopaminergic neurons.

Outcome of Liver Transplantation for Neonatal-onset Citrullinemia Type I

BACKGROUND

We evaluated the outcome of liver transplantation (LT) in neonatal-onset citrullinemia type I patients, especially its impact on neurological deficits and developmental retardation.

METHODS

From October 2006 to October 2019, 5 of the 2003 children who received LT at Ren Ji Hospital had been diagnosed with citrullinemia type I. The primary indication for transplantation was repeated metabolic compensation and developmental retardation in 4 patients and prophylactic transplantation in the other. Among them, 3 patients received living donor LT and 2 received orthotopic LT.

RESULTS

All recipients had successfully recovered within the median follow-up period of 32 months (range, 6-54 mo). Transplantation restored citrulline metabolism and liver function. Plasma ammonia and citrulline concentration decreased to normal levels with no further hyperammonemic episodes being reported, even after normal diet intake began. Meanwhile, uracil-2 and orotic acid were not detected in urinary excretion. Strikingly, patients suffered developmental retardation before LT showed improved psychomotor ability and significant catch-up growth during the follow-up period. Cognitive ability, including language skills and academic performance, also greatly improved. Three patients had sustained brain injuries and exhibited severe neurological deficits before transplantation, especially repeated generalized tonic-clonic seizures. LT halted neurological deterioration and controlled seizure episodes, which further facilitated the intellectual development and improvement of life quality.

CONCLUSIONS

LT is an effective treatment for neonatal-onset citrullinemia type I patients, which reverses metabolism decompensation and improves quality of life. For patients who have suffered severe hyperammonemic insults, LT should be conducted at an early age to avoid further neurological or developmental deficits.

Arginase-1 deficiency in neural cells does not contribute to neurodevelopment or functional outcomes after sciatic nerve injury

Arginase-1 (Arg1) is an enzyme controlling the final step of the urea cycle, with highest expression in the liver and lower expression in the lungs, pancreas, kidney, and some blood cells. Arg1 deficiency is an inherited urea cycle disorder presenting with neurological dysfunction including spastic diplegia, intellectual and growth retardation, and encephalopathy. The contribution of Arg1 expression in the central and peripheral nervous system to the development of neurological phenotypes remains largely unknown. Previous studies have shown prominent arginase-1 expression in the nervous system and post-peripheral nerve injury in mice, but very low levels in the naïve state. To investigate neurobiological roles of Arg1, we created a conditional neural (n)Arg1 knockout (KO) mouse strain, with expression eliminated in neuronal and glial precursors, and compared them to littermate controls. Long-term analysis did not reveal any major differences in blood amino acid levels, body weight, or stride gait cycle from 8 to 26-weeks of age. Brain structure measured by magnetic resonance imaging at 16-weeks of age observed only a significant decrease in the volume of the mammillary bodies. We also assessed whether nArg1, which is expressed by sensory neurons after injury, may play a role in regeneration following sciatic nerve crush. Only subtle differences were observed in locomotor and sensory recovery between nArg1 KO and control mice. These results suggest that arginase-1 expression in central and peripheral neural cells does not contribute substantially to the phenotypes of this urea cycle disorder, nor is it likely crucial for post-injury regeneration in this mouse model.

The Application of Neurodiagnostic Studies to Inform the Acute Management of a Newborn Presenting With Sarbamoyl Shosphate Synthetase 1 Deficiency

Neonatal-onset urea cycle disorders (UCDs) may result in hyperammonemic (HA) encephalopathy presenting with several neurologic sequelae including seizures, coma, and death. However, no recommendations are given in how and when neurodiagnostic studies should be used to screen or assess for these neurologic complications. We present a case of carbamoyl phosphate synthetase 1 (CPS1) deficiency in a newborn female in which electroencephalogram monitoring to assess encephalopathy and seizures, and magnetic resonance imaging measurements of brain metabolites were used to guide care during her hyperammonemic crisis. Her neurologic course and response to treatment characterizes the significant neurologic impact of HA encephalopathy. Our group herein proposes a clinical neurodiagnostic pathway for managing acute HA encephalopathy.

Glucagon Receptor Inhibition Reduces Hyperammonemia and Lethality in Male Mice with Urea Cycle Disorder

The liver plays a critical role in maintaining ammonia homeostasis. Urea cycle defects, liver injury, or failure and glutamine synthetase (GS) deficiency result in hyperammonemia, serious clinical conditions, and lethality. In this study we used a mouse model with a defect in the urea cycle enzyme ornithine transcarbamylase (Otcspf-ash) to test the hypothesis that glucagon receptor inhibition using a monoclonal blocking antibody will reduce the hyperammonemia and associated lethality induced by a high-protein diet, which exacerbates disease. We found reduced expression of glutaminase, which degrades glutamine and increased expression of GS in livers of Otcspf-ash mice treated with the glucagon receptor blocking antibody. The gene expression changes favor ammonia consumption and were accompanied by increased circulating glutamine levels and diminished hyperammonemia. Otcspf-ash mice treated with the glucagon receptor-blocking antibody gained lean and body mass and had increased survival. These data suggest that glucagon receptor inhibition using a monoclonal antibody could reduce the risk for hyperammonemia and other clinical manifestations of patients suffering from defects in the urea cycle, liver injury, or failure and GS deficiency.

Increasing serum ammonia level is a risk factor for the prognosis of critically ill patients: A multicenter retrospective cohort study

PURPOSE

To assess the association between serum ammonia level upon admission during the initial intensive care unit (ICU) stay and mortality.

MATERIALS AND METHODS

This retrospective cohort study included 2703 adult patients in eICU Collaborative Research Database. The ICU mortality within ammonia deciles were assessed. Logistic regression analyses were performed to analyze the relationship between ammonia and mortality.

RESULTS

We defined three ammonia categories: <47, 47-111, and ≥111 μg/dL, corresponding to low, intermediate, and high ICU mortality. Increased ammonia was significantly associated with increased ICU mortality (per 10 μg/dL increase: odds ratio, 1.070 [95% confidence intervals, 1.05-1.09]; intermediate vs. low: 1.90 [1.41-2.56]; high vs. low: 4.38 [2.99-6.41]) and in-hospital mortality (1.06 [1.04-1.08]; 1.45 [1.13-1.87]; 3.41 [2.43-4.79]). Adding ammonia to the Acute Physiology and Chronic Health Evaluation (APACHE) IV score improved the area under the curve from 0.826 to 0.839 (P < 0.001) and from 0.806 to 0.813 (P = 0.001) for ICU and in-hospital mortality, respectively. Interaction and subgroup analyses demonstrated consistent results in patients with different APACHE IV scores, with or without hepatic diseases.

CONCLUSIONS

Elevated serum ammonia level in critically ill patients upon admission was an early risk factor for higher ICU and in-hospital mortality.

Status epilepticus as an initial manifestation of hepatic encephalopathy: A case report

BACKGROUND

Status epilepticus in patients with hepatic encephalopathy (HE) is a rare but serious condition that is refractory to antiepileptic drugs, and current treatment plans are vague. Diagnosis may be difficult without a clear history of cirrhosis. Liver transplantation (LT) is effective to alleviate symptoms, however, there are few reports about LT in the treatment of status epilepticus with HE. To our knowledge, this is the first report of status epilepticus present as initial manifestation of HE.

CASE SUMMARY

A 59-year-old woman with a 20-year history of heavy drinking was hospitalized for generalized tonic-clonic seizures. She reported no history of episodes of HE, stroke, spontaneous bacterial peritonitis, ascites or gastrointestinal bleeding. Neurological examination revealed a comatose patient, without papilledema. Laboratory examination suggested liver cirrhosis. Plasma ammonia levels upon admission were five times normal. Brain computed tomography (CT) was normal, while abdominal CT and ultrasound revealed mild ascites, liver cirrhosis and splenomegaly. Electroencephalography (EEG)showed diffuse slow waves rhythm, consistent with HE, and sharp waves during ictal EEG corresponding to clinical semiology of focal tonic seizures. The symptoms were reversed by continuous antiepileptic treatment and lactulose. She was given oral levetiracetam, and focal aware seizures occasionally affected her 10 mo after LT.

CONCLUSION

Status epilepticus could be an initial manifestation of HE. Antiepileptic drugs combined with lactulose are essential for treatment of status epilepticus with HE, and LT is effective to prevent the relapse.

Ammonia exposition during gestation induces neonatal oxidative damage in the brain and long-term cognitive alteration in rats

Ammonia is involved in the pathogenesis of neurological conditions associated with hyperammonemia, including hepatic encephalopathy. Few is known about the effects of gestational exposition to ammonia in the developing brain, and the possible long-term consequences of such exposure. We aimed to evaluate the effects of ammonia exposure during the gestation and the possible long-term cognitive alterations on pups. Eight female rats were divided into two groups: (1) control (saline solution); (2) ammonia (ammonium acetate, 2,5mmol/Kg). Each rat received a single subcutaneous injection during all gestational period. The brains from 1-day-old rats were obtained to the determination of thiobarbituric acid reactive species (TBARS), protein carbonyl and nitrite/nitrate levels. Some animals were followed 30 days after delivery and were subjected to the step-down inhibitory avoidance task. It was observed a significant increase in protein carbonyl, but not TBARS or nitrite/nitrate levels, in pups exposed to ammonia. Rats exposed to ammonia presented long-term cognitive impairment. Gestational exposition to ammonia induces protein oxidative damage in the neonatal rat brain, and long-term cognitive impairment.

Reshaping circadian metabolism in the suprachiasmatic nucleus and prefrontal cortex by nutritional challenge

Food is a powerful entrainment cue for circadian clocks in peripheral tissues, and changes in the composition of nutrients have been demonstrated to metabolically reprogram peripheral clocks. However, how food challenges may influence circadian metabolism of the master clock in the suprachiasmatic nucleus (SCN) or in other brain areas is poorly understood. Using high-throughput metabolomics, we studied the circadian metabolome profiles of the SCN and medial prefrontal cortex (mPFC) in lean mice compared with mice challenged with a high-fat diet (HFD). Both the mPFC and the SCN displayed a robust cyclic metabolism, with a strikingly high sensitivity to HFD perturbation in an area-specific manner. The phase and amplitude of oscillations were drastically different between the SCN and mPFC, and the metabolic pathways impacted by HFD were remarkably region-dependent. Furthermore, HFD induced a significant increase in the number of cycling metabolites exclusively in the SCN, revealing an unsuspected susceptibility of the master clock to food stress.