RARE DISEASE
Argininosuccinic aciduria
Argininosuccinic aciduria
Argininosuccinic aciduria
Synonyms: ASA deficiency, ASL deficiency, Argininosuccinase deficiency, Argininosuccinatelyase deficiency, Argininosuccinic acid lyase deficiency
Synonyms: ASA deficiency, ASL deficiency, Argininosuccinase deficiency, Argininosuccinatelyase deficiency, Argininosuccinic acid lyase deficiency
Synonyms: ASA deficiency, ASL deficiency, Argininosuccinase deficiency, Argininosuccinatelyase deficiency, Argininosuccinic acid lyase deficiency
Drug discovery
10
drugs
With orphan designations
Overview
Argininosuccinic aciduria (ASA) is an autosomal recessive urea cycle disorder caused by argininosuccinate lyase deficiency, leading to impaired ammonia detoxification and hyperammonemia. It presents as neonatal-onset (lethargy, vomiting, seizures) or late-onset (stress-induced hyperammonemia, neurocognitive deficits). Chronic complications include liver dysfunction, hypertension, and trichorrhexis nodosa. Diagnosis involves elevated ammonia, citrulline, and argininosuccinic acid levels, confirmed by genetic testing [1][13][16].
Categories: rare genetic diseases, rare inborn errors of metabolism, rare neurological diseases
Research Papers
105 drug discovery papers about Argininosuccinic aciduria, with 2 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
105 drug discovery papers about Argininosuccinic aciduria, with 2 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
small molecules
2026-09-23 | Seizure due to Lamotrigine Underexposure During High-Volume CRRT for Hyperammonaemia: A Case Report.
Hyperammonaemic decompensation in urea cycle disorders (UCDs) is a medical emergency that requires prompt intervention. Continuous renal replacement therapy (CRRT) is an effective strategy for acute ammonia clearance, but it may significantly alter the pharmacokinetics of administered drugs. A woman in her 40s with argininosuccinate lyase (ASL) deficiency and long-standing, well-controlled epilepsy treated with lamotrigine presented with a hyperammonaemic crisis and was treated with high-volume continuous venovenous haemodialysis (CVVHD). She developed a generalised tonic-clonic seizure shortly after cessation of CVVHD. Serum lamotrigine declined from 12.7 to 6.0 mg/L over approximately 12 h, corresponding to an apparent elimination half-life of 11.5 h. Lamotrigine was measurable in the effluent (2.9 mg/L), giving a saturation coefficient of 0.48 and an extracorporeal clearance of 38.4 mL/min during the high-volume phase. The seizure was attributed to the abrupt underexposure of lamotrigine in a previously seizure-free patient. This case underscores the clinical significance of extracorporeal clearance of antiseizure medications during CRRT in patients with UCDs. Drug selection should consider both ammonia-modifying and dialysability profiles. Therapeutic drug monitoring and pre-emptive dose adjustment, or the addition of a second intravenously available agent, should be considered when high-volume dialysis is initiated in a patient receiving a dialysable antiseizure medication.
2024-03-11 | Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders.
Liver transplantation (LTx) is an intervention when medical management is not sufficiently preventing individuals with urea cycle disorders (UCDs) from the occurrence of hyperammonemic events. Supplementation with L-citrulline/arginine is regularly performed prior to LTx to support ureagenesis and is often continued after the intervention. However, systematic studies assessing the impact of long-term L-citrulline/arginine supplementation in individuals who have undergone LTx is lacking to date. Using longitudinal data collected systematically, a comparative analysis was carried out by studying the effects of long-term L-citrulline/arginine supplementation vs. no supplementation on health-related outcome parameters (i.e., anthropometric, neurological, and cognitive outcomes) in individuals with UCDs who have undergone LTx. Altogether, 52 individuals with male ornithine transcarbamylase deficiency, citrullinemia type 1 and argininosuccinic aciduria and a pre-transplant "severe" disease course who have undergone LTx were investigated by using recently established and validated genotype-specific in vitro enzyme activities. Long-term supplementation of individuals with L-citrulline/arginine who have undergone LTx (n = 16) does neither appear to alter anthropometric nor neurocognitive endpoints when compared to their severity-adjusted counterparts that were not supplemented (n = 36) after LTx with mean observation periods between four to five years. Moreover, supplementation with L-citrulline/arginine was not associated with an increase of disease-specific plasma arithmetic mean values for the respective amino acids when compared to the non-supplemented control cohort. Although supplementation with L-citrulline/arginine is often continued after LTx, this pilot study does neither identify altered long-term anthropometric or neurocognitive health-related outcomes nor does it find an adequate biochemical response as reflected by the unaltered plasma arithmetic mean values for L-citrulline or L-arginine. Further prospective analyses in larger samples and even longer observation periods will provide more insight into the usefulness of long-term supplementation with L-citrulline/arginine for individuals with UCDs who have undergone LTx.
2023-12-04 | Transition to glycerol phenylbutyrate for the management of urea cycle disorders: clinical experiences.
Urea cycle disorders (UCDs) are a group of rare inborn diseases caused by a deficiency in one of the six enzymes or one of the two transporters involved in the urea cycle. The most common biochemical feature is elevated blood ammonia levels, which can be toxic at high levels, especially to the brain and may manifest as encephalopathy if left untreated. Glycerol phenylbutyrate (GPB) is currently approved for use in the USA and Europe for patients of all ages with UCD who cannot be managed with protein restriction and/or amino acid supplementation alone. This article presents the author's experience in different exemplary settings and depicts the most efficient management of UCDs with GPB. Six patient histories are described. 4 had OCT, one citrullinemia, and one argininosuccinic aciduria. Treatment with GPB was started between 2 days and 14 years of age. Before GPB, one patient had not been treated, 4 had received sodium phenylbutyrate (NaPB), and one Na benzoate. Overall, treatment with GPB was followed by a relevant metabolic improvement, resulting in better therapeutic compliance, reduced hospitalization, and improved quality of life.
2023-12-04 | The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria.
Argininosuccinate lyase (ASL) is integral to the urea cycle detoxifying neurotoxic ammonia and the nitric oxide (NO) biosynthesis cycle. Inherited ASL deficiency causes argininosuccinic aciduria (ASA), a rare disease with hyperammonemia and NO deficiency. Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis. A neurodegenerative phenotype has been proposed in ASA. To better characterise this neurodegenerative phenotype in ASA, we conducted a retrospective study in six paediatric and adult metabolic centres in the UK in 2022. We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour. We analysed neuroimaging with diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) in an individual with ASA with movement disorders. We assessed conventional and DTI MRI alongside single photon emission computer tomography (SPECT) with dopamine analogue radionuclide 123I-ioflupane, in Asl-deficient mice treated by hASL mRNA with normalised ureagenesis. Movement disorders in ASA appear in the second and third decades of life, becoming more prevalent with ageing and independent from the age of onset of hyperammonemia. Neuroimaging can show abnormal DTI features affecting both grey and white matter, preferentially basal ganglia. ASA mouse model with normalised ureagenesis did not recapitulate these DTI findings and showed normal 123I-ioflupane SPECT and cerebral dopamine metabolomics. Altogether these findings support the pathophysiology of a late-onset movement disorder with cell-autonomous functional central catecholamine dysregulation but without or limited neurodegeneration of dopaminergic neurons, making these symptoms amenable to targeted therapy.
2021-05-03 | Naturally-occurring spinosyn A and its derivatives function as argininosuccinate synthase activator and tumor inhibitor.
Argininosuccinate synthase (ASS1) is a ubiquitous enzyme in mammals that catalyzes the formation of argininosuccinate from citrulline and aspartate. ASS1 genetic deficiency in patients leads to an autosomal recessive urea cycle disorder citrullinemia, while its somatic silence or down-regulation is very common in various human cancers. Here, we show that ASS1 functions as a tumor suppressor in breast cancer, and the pesticide spinosyn A (SPA) and its derivative LM-2I suppress breast tumor cell proliferation and growth by binding to and activating ASS1. The C13-C14 double bond in SPA and LM-2I while the Cys97 (C97) site in ASS1 are critical for the interaction between ASS1 and SPA or LM-2I. SPA and LM-2I treatment results in significant enhancement of ASS1 enzymatic activity in breast cancer cells, particularly in those cancer cells with low ASS1 expression, leading to reduced pyrimidine synthesis and consequently the inhibition of cancer cell proliferation. Thus, our results establish spinosyn A and its derivative LM-2I as potent ASS1 enzymatic activator and tumor inhibitor, which provides a therapeutic avenue for tumors with low ASS1 expression and for those non-tumor diseases caused by down-regulation of ASS1.
proteins
2026-03-19 | Impact of long-term nitrogen scavenger therapy on clinical outcome in individuals with urea cycle disorders.
Principles of long-term medical management in individuals with urea cycle disorders (UCDs) encompass (1) a low protein diet, (2) supplementation of arginine and/or citrulline along with essential amino acids, nutrients, vitamins and trace elements, and (3) use of nitrogen scavenging agents to reduce recurrent hyperammonemic events (HAEs). These principles aim at providing metabolic stability, elimimation of chronic complications, and achievement of normal development as well as growth. A retrospective comparative analysis was performed by studying 138 individuals with male ornithine transcarbamylase deficiency (mOTC-D), citrullinemia type 1 (CTLN1) and argininosuccinic aciduria (ASA) based on in vitro residual enzymatic activity for severity-adjustment. Results show that individuals with mOTC-D, CTLN1 and ASA are at risk of progressive linear growth impairment, recurrent annual HAEs and an unfavorable neurocognitive outcome despite being under long-term nitrogen scavenging pharmacotherapy. No overall superiority among existing nitrogen scavenging agents with regard to the individual's metabolic stability, linear growth impairment and poor neurocognitive outcome was observed. Novel therapeutic strategies are urgently needed to ultimately improve health outcomes in individuals with UCDs in order to sufficiently meet guideline-specific goals.
2022-07-06 | Characterisation of Expression the Arginine Pathway Enzymes in Childhood Brain Tumours to Determine Susceptibility to Therapeutic Arginine Depletion.
Despite significant improvements in treatment and survival in paediatric cancers, outcomes for children with brain tumours remain poor. Novel therapeutic approaches are needed to improve survival and quality of survival. Extracellular arginine dependency (auxotrophy) has been recognised in several tumours as a potential therapeutic target. This dependency is due to the inability of cancer cells to recycle or synthesise intracellular arginine through the urea cycle pathway compared to normal cells. Whilst adult glioblastoma exhibits this dependency, the expression of the arginine pathway enzymes has not been delineated in paediatric brain tumours. We used immunohistochemical (IHC) methods to stain for arginine pathway enzymes in paediatric high-grade glioma (pHGG), low-grade glioma (pLGG), ependymoma (EPN), and medulloblastoma (MB) tumour tissue microarrays (TMAs). The antibodies detected protein expression of the metaboliser arginase (Arg1 and Arg2); recycling enzymes ornithine transcarbamoylase (OTC), argininosuccinate synthetase (ASS1), and argininosuccinate lyase (ASL); and the transporter SLC7A1. Deficiency of OTC, ASS1, and ASL was seen in 87.5%, 94%, and 79% of pHGG samples, respectively, consistent with an auxotrophic signature. Similar result was obtained in pLGG with 96%, 93%, and 91% of tumours being deficient in ASL, ASS1, and OTC, respectively. 79%, 88%, and 85% of MB cases were ASL, ASS1, and OTC deficient whilst ASL and OTC were deficient in 57% and 91% of EPN samples. All tumour types highly expressed SLC7A1 and Arginase, with Arg2 being the main isoform, demonstrating that they could transport and utilise arginine. Our results show that pHGG, pLGG, EPN, and MB demonstrate arginine auxotrophy based on protein expression and are likely to be susceptible to arginine depletion. Pegylated arginase (BCT-100) is currently in phase I/II trials in relapsed pHGG. Our results suggest that therapeutic arginine depletion may also be useful in other tumour types and IHC analysis of patient tumour samples could help identify patients likely to benefit from this treatment.
2020-06-19 | A Phase I Study of Pegylated Arginine Deiminase (Pegargiminase), Cisplatin, and Pemetrexed in Argininosuccinate Synthetase 1-Deficient Recurrent High-grade Glioma.
Patients with recurrent high-grade gliomas (HGG) are usually managed with alkylating chemotherapy ± bevacizumab. However, prognosis remains very poor. Preclinically, we showed that HGGs are a target for arginine depletion with pegargiminase (ADI-PEG20) due to epimutations of argininosuccinate synthetase (ASS1) and/or argininosuccinate lyase (ASL). Moreover, ADI-PEG20 disrupts pyrimidine pools in ASS1-deficient HGGs, thereby impacting sensitivity to the antifolate, pemetrexed. We expanded a phase I trial of ADI-PEG20 with pemetrexed and cisplatin (ADIPEMCIS) to patients with ASS1-deficient recurrent HGGs (NCT02029690). Patients were enrolled (01/16-06/17) to receive weekly ADI-PEG20 36 mg/m2 intramuscularly plus pemetrexed 500 mg/m2 and cisplatin 75 mg/m2 intravenously once every 3 weeks for up to 6 cycles. Patients with disease control were allowed ADI-PEG20 maintenance. The primary endpoints were safety, tolerability, and preliminary estimates of efficacy. Ten ASS1-deficient heavily pretreated patients were treated with ADIPEMCIS therapy. Treatment was well tolerated with the majority of adverse events being Common Terminology Criteria for Adverse Events v4.03 grade 1-2. The best overall response was stable disease in 8 patients (80%). Plasma arginine was suppressed significantly below baseline with a reciprocal increase in citrulline during the sampling period. The anti-ADI-PEG20 antibody titer rose during the first 4 weeks of treatment before reaching a plateau. Median progression-free survival (PFS) was 5.2 months (95% confidence interval (CI), 2.5-20.8) and overall survival was 6.3 months (95% CI, 1.8-9.7). In this recurrent HGG study, ADIPEMCIS was well tolerated and compares favorably to historical controls. Additional trials of ADI-PEG20 in HGG are planned.
2019-03-13 | The Citrulline Recycling Pathway Sustains Cardiovascular Function in Arginine-Depleted Healthy Mice, but Cannot Sustain Nitric Oxide Production during Endotoxin Challenge.
The recycling of citrulline by argininosuccinate synthase 1 (ASS1) and argininosuccinate lyase (ASL) is crucial to maintain arginine availability and nitric oxide (NO) production. Pegylated arginine deiminase (ADI-PEG20) is a bacterial enzyme used to deplete circulating arginine. The goal of this research was to test the hypothesis that citrulline is able to sustain intracellular arginine availability for NO production in ADI-PEG20 arginine-depleted mice. Six- to 8-wk-old male C57BL/6J mice injected with ADI-PEG20 (5 IU) or saline (control) were used in 4 different studies. Arginine, citrulline, and NO kinetics were determined by using stable isotopes in unchallenged (study 1) and endotoxin-challenged (study 2) mice. Blood pressure was determined by telemetry for 6 d after ADI-PEG20 administration (study 3), and vasomotor activity and ASS1 and ASL gene expression were determined in mesenteric arteries collected from additional mice (study 4). ADI-PEG20 administration resulted in arginine depletion (<1 compared with 111 ± 37 µmol/L) but in greater plasma citrulline concentrations (900 ± 123 compared with 76 ± 8 µmol/L; P < 0.001) and fluxes (402 ± 17 compared with 126 ± 4 µmol ⋅ kg-1 ⋅ h-1; P < 0.001) compared with controls. Endotoxin-challenged ADI-PEG20-treated mice produced less NO than controls (13 ± 1 compared with 27 ± 2 µmol ⋅ kg-1 ⋅ h-1; P < 0.001). No differences (P > 0.50) were observed for cardiovascular variables (heart rate, blood pressure) between ADI-PEG20-treated and control mice. Furthermore, no ex vivo vasomotor differences were observed between the 2 treatments. ADI-PEG20 administration resulted in greater gene expression of ASS1 (∼3-fold) but lower expression of ASL (-30%). ADI-PEG20 successfully depleted circulating arginine without any effect on cardiovascular endpoints in healthy mice but limited NO production after endotoxin challenge. Therefore, the citrulline recycling pathway can sustain local arginine availability independently from circulating arginine, satisfying the demand of arginine for endothelial NO production; however, it is unable to do so when a high demand for arginine is elicited by endotoxin.
2019-02-05 | Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects
Abstract The first patients affected by argininosuccinic aciduria (ASA) were reported 60 years ago. The clinical presentation was initially described as similar to other urea cycle defects, but increasing evidence has shown overtime an atypical systemic phenotype with a paradoxical observation, that is, a higher rate of neurological complications contrasting with a lower rate of hyperammonaemic episodes. The disappointing long‐term clinical outcomes of many of the patients have challenged the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels. Interrogations have raised about the benefit of newborn screening or liver transplantation on the neurological phenotype. Over the last decade, novel discoveries enabled by the generation of new transgenic argininosuccinate lyase (ASL)‐deficient mouse models have been achieved, such as, a better understanding of ASL and its close interaction with nitric oxide metabolism, ASL physiological role outside the liver, and the pathophysiological role of oxidative/nitrosative stress or excessive arginine treatment. Here, we present a collaborative review, which highlights these recent discoveries and novel emerging concepts about ASL role in human physiology, ASA clinical phenotype and geographic prevalence, limits of current standard of care and newborn screening, pathophysiology of the disease, and emerging novel therapies. We propose recommendations for monitoring of ASA patients. Ongoing research aims to better understand the underlying pathogenic mechanisms of the systemic disease to design novel therapies.
cell therapies
2025-01-08 | Positive Clinical, Neuropsychological, and Metabolic Impact of Liver Transplantation in Patients With Argininosuccinate Lyase Deficiency.
Liver transplantation (LTx) is increasingly used in Urea Cycle Defects (UCDs) to prevent recurrent hyperammonemia and related neurological irreversible injury. Among UCDs, argininosuccinate lyase deficiency (ASLD) has a more complex phenotype than other UCDs, with long-term neurocognitive deficits. Therefore, the role of LTx in ASLD is still debated. The impact of LTx on nine patients with early-onset ASLD was assessed through pre- and post-LTx clinical, neuropsychological, MRI and biochemical evaluations. After LTx, no episodes of metabolic decompensations were reported. Neuropsychological evaluations documented significant improvement in cognitive/developmental functioning especially in patients transplanted in early childhood. Improvements were also highlighted in daily living skills and emotional-behavioral problems, with a reduction in attention disturbances and somatic complaints. Movement disorders resolved after LTx in patient transplanted in early childhood. Any patients developed epilepsy with stability of EEG alterations after LTx. A positive effect of LTx on other disease-related outcomes such as growth, diet, medications, hospitalizations, and long-term ASLD-related complications was highlighted. The primary biomarker argininosuccinic acid dramatically reduced in plasma after transplantation with a decreasing trend in CSF at long-term follow-up. Moreover, health-related quality of life improved after LTx, especially when assessed through MetabQoL, a tool designed for intoxication diseases such as ASLD. In conclusion, our study showed a global beneficial impact of LTx in early-onset ASLD patients to avoid episodes of hyperammonemia, and improve neurocognitive outcome, adaptive and behavioral deficits when performed in early childhood with a dramatic benefit in terms of quality of life.
2022-04-12 | Inborn error of metabolism patients after liver transplantation: Outcomes of 35 patients over 27 years in one pediatric quaternary hospital.
Liver transplantation (LT) has been used for many years as a therapeutic option for certain inborn errors of metabolism (IEMs). Here we present one institution's 27 years of experience with LT in IEMs. Our objective is to assess the outcomes of IEM patients who have undergone LT, which we hypothesize to be generally successful for prevention of metabolic decompensation. A retrospective chart review was performed on patients with urea cycle defects, organic acidemias, and amino acidopathies who underwent LT at the Children's Hospital of Philadelphia. Thirty-five patients with the following conditions have undergone LT: tyrosinemia (8), methylmalonic acidemia (7), maple syrup urine disease (6), citrullinemia (6), ornithine transcarbamylase deficiency (4), propionic acidemia (2), and argininosuccinate lyase deficiency (2). Average age at transplantation was 3.6 years. Three patients are now deceased. One patient suffered a metabolic stroke posttransplant. No episodes of metabolic decompensation have been noted. Thirty-five patients received LT with generally favorable outcome. None sustained metabolic decompensation posttransplant. As has been reported previously, LT does not ameliorate pre-existing developmental differences or risk to other organ systems. Further research is needed to aid in standardization of care and follow-up, as most patients no longer follow with a geneticist.
2021-08-01 | Liver Transplantation in Children with Urea Cycle Disorders: The Importance of Minimizing Waiting Time
Liver transplantation (LT) for children with urea cycle disorders (UCDs) is capable of correcting the enzymatic defect and preventing progressive neurologic injury. We describe the characteristics and outcomes of pediatric LT recipients with UCDs. We identified all pediatric (<18 years) LT candidates with UCDs in the United Network for Organ Sharing (UNOS) database (February 2002 to September 2020). Multivariable Cox and logistic regression were used to determine risk factors for graft loss and cognitive delay, respectively. Of 424 patients, 1.9% (8/424) experienced waitlist mortality and 95.0% underwent LT (403/424). The most frequently encountered UCDs in our cohort were ornithine transcarbamylase deficiency (46.2%), citrullinemia (20.3%), and argininosuccinic aciduria (ASA; 12.9%). The 1-, 3-, and 5-year graft survival rates were 90.4%, 86.3%, and 85.2%, respectively. Multivariable analysis showed a decreased risk of graft loss with increasing weight at LT (adjusted hazard ratio [aHR], 0.96; 95% confidence interval [CI], 0.94-0.99; P = 0.02), male sex (aHR, 0.49; 95% CI, 0.28-0.85; P = 0.01), and ASA diagnosis (aHR, 0.29; 95% CI, 0.09-0.98; P = 0.047), when adjusting for location (intensive care/hospital/home) and graft type (both P ≥ 0.65). In multivariable logistic regression, waitlist time (adjusted odds ratio [aOR], 1.10; 95% CI, 1.02-1.17; P = 0.009) and male sex (aOR, 1.71; 95% CI, 1.02-2.88; P = 0.04) were associated with increased odds of long-term cognitive delay. Waitlist duration is associated with a long-term risk of cognitive delay. Given excellent long-term outcomes, early LT evaluation should be considered in all children with UCDs to prevent progressive neurologic injury and optimize cognitive outcomes.
2020-09-14 | Differential Intraoperative Effect of Liver Transplant in Different Inborn Errors of Metabolism.
Liver transplant (LT) is a therapeutic option for a growing number of inborn errors of metabolism (IEM), including some disorders not confined to the liver. Clinical advantages of LT in maple syrup urine disease (MSUD), methylmalonic acidemia (MMA), and argininosuccinic aciduria (ASA) have been reported. However, no information on the early metabolic effect of LT after portal reperfusion is available in these disorders. Here we describe the intraoperative differential metabolic outcome of LT in MSUD, MMA, and ASA. In these IEM, LT promptly cleared toxic metabolites to safe concentrations. In MSUD, leucine concentration reached physiological concentration within 12 hours after portal reperfusion. In MMA and ASA, LT allowed faster clearance of methylmalonate and argininosuccinate, respectively, both dropping by ∼90% within the first hour after portal reperfusion. The early biochemical benefits of LT in MSUD, MMA, and ASA demonstrate its immediate effectiveness in protecting patients from intercurrent metabolic decompensations.
2019-12-02 | Intrahepatic Administration of Human Liver Stem Cells in Infants with Inherited Neonatal-Onset Hyperammonemia: A Phase I Study
Abstract Previous studies have shown that human liver stem-like cells (HLSCs) may undergo differentiation in vitro into urea producing hepatocytes and in vivo may sustain liver function in models of experimentally induced acute liver injury. The aim of this study was to assess the safety of HLSCs intrahepatic administration in inherited neonatal-onset hyperammonemia. The study was approved by the Agenzia Italiana del Farmaco on favorable opinion of the Italian Institute of Health as an open-label, prospective, uncontrolled, monocentric Phase I study (HLSC 01–11, EudraCT-No. 2012–002120-33). Three patients affected by argininosuccinic aciduria (patient 1) and methylmalonic acidemia (patients 2 and 3) and included in the liver transplantation list were enrolled. In all patients, HLSCs were administered by percutaneous intrahepatic injections (once a week for two consecutive weeks) within the first months of life. The first patient received 125,000 HLSCs x gram of liver/dose while the other two patients received twice this dose. No immunosuppression was administered since HLSCs possess immunomodulatory activities. None of the patients experienced infections, hyperammonemia decompensation, or other adverse events during the whole observation period. No donor specific antibodies (DSA) against HLSCs were detected. Patients were metabolic stable despite an increase (~30%) in protein intake. Two patients underwent liver transplantation after 19 and 11 months respectively, and after explantation, the native livers showed no histological alterations. In conclusion, percutaneous intrahepatic administration of HLSCs was safe in newborn with inherited neonatal-onset hyperammonemia. These data pave the way for Phase II studies in selected inherited and acquired liver disorders.
gene therapies
2024-04-08 | Genetic and functional correction of argininosuccinate lyase deficiency using CRISPR adenine base editors.
Argininosuccinate lyase deficiency (ASLD) is a recessive metabolic disorder caused by variants in ASL. In an essential step in urea synthesis, ASL breaks down argininosuccinate (ASA), a pathognomonic ASLD biomarker. The severe disease forms lead to hyperammonemia, neurological injury, and even early death. The current treatments are unsatisfactory, involving a strict low-protein diet, arginine supplementation, nitrogen scavenging, and in some cases, liver transplantation. An unmet need exists for improved, efficient therapies. Here, we show the potential of a lipid nanoparticle-mediated CRISPR approach using adenine base editors (ABEs) for ASLD treatment. To model ASLD, we first generated human-induced pluripotent stem cells (hiPSCs) from biopsies of individuals homozygous for the Finnish founder variant (c.1153C>T [p.Arg385Cys]) and edited this variant using the ABE. We then differentiated the hiPSCs into hepatocyte-like cells that showed a 1,000-fold decrease in ASA levels compared to those of isogenic non-edited cells. Lastly, we tested three different FDA-approved lipid nanoparticle formulations to deliver the ABE-encoding RNA and the sgRNA targeting the ASL variant. This approach efficiently edited the ASL variant in fibroblasts with no apparent cell toxicity and minimal off-target effects. Further, the treatment resulted in a significant decrease in ASA, to levels of healthy donors, indicating restoration of the urea cycle. Our work describes a highly efficient approach to editing the disease-causing ASL variant and restoring the function of the urea cycle. This method relies on RNA delivered by lipid nanoparticles, which is compatible with clinical applications, improves its safety profile, and allows for scalable production.
2021-03-01 | Nitric oxide and bone: The phoenix rises again
The involvement of nitric oxide (NO) in preventing bone loss has long been hypothesized, but despite decades of research the mechanisms remain obscure. In this issue of the JCI, Jin et al. explored NO deficiency using human cell and mouse models that lacked argininosuccinate lyase (ASL), the enzyme involved in synthesizing arginine and NO production. Osteoblasts that did not express ASL produced less NO and failed to differentiate. Notably, in the context of Asl deficiency, heterozygous deletion of caveolin 1, which normally inhibits NO synthesis, restored NO production, osteoblast differentiation, glycolysis, and bone mass. These experiments suggest that ASL regulates arginine synthesis in osteoblasts, which leads to enhanced NO production and increased glucose metabolism. After a period when research slowed, these studies, like the legendary phoenix, renew the exploration of NO in bone biology, and provide exciting translational potential.
2018-12-01 | Rapid Disruption of Genes Specifically in Livers of Mice Using Multiplex CRISPR/Cas9 Editing
Background & aimsDespite advances in gene editing technologies, generation of tissue-specific knockout mice is time-consuming. We used CRISPR/Cas9-mediated genome editing to disrupt genes in livers of adult mice in just a few months, which we refer to as somatic liver knockouts.MethodsIn this system, Fah–/– mice are given hydrodynamic tail vein injections of plasmids carrying CRISPR/Cas9 designed to excise exons in Hpd; the Hpd-edited hepatocytes have a survival advantage in these mice. Plasmids that target Hpd and a separate gene of interest can therefore be used to rapidly generate mice with liver-specific deletion of nearly any gene product.ResultsWe used this system to create mice with liver-specific knockout of argininosuccinate lyase, which develop hyperammonemia, observed in humans with mutations in this gene. We also created mice with liver-specific knockout of ATP binding cassette subfamily B member 11, which encodes the bile salt export pump. We found that these mice have a biochemical phenotype similar to that of Abcb11–/– mice. We then used this system to knock out expression of 5 different enzymes involved in drug metabolism within the same mouse.ConclusionsThis approach might be used to develop new models of liver diseases and study liver functions of genes that are required during development. Despite advances in gene editing technologies, generation of tissue-specific knockout mice is time-consuming. We used CRISPR/Cas9-mediated genome editing to disrupt genes in livers of adult mice in just a few months, which we refer to as somatic liver knockouts. In this system, Fah–/– mice are given hydrodynamic tail vein injections of plasmids carrying CRISPR/Cas9 designed to excise exons in Hpd; the Hpd-edited hepatocytes have a survival advantage in these mice. Plasmids that target Hpd and a separate gene of interest can therefore be used to rapidly generate mice with liver-specific deletion of nearly any gene product. We used this system to create mice with liver-specific knockout of argininosuccinate lyase, which develop hyperammonemia, observed in humans with mutations in this gene. We also created mice with liver-specific knockout of ATP binding cassette subfamily B member 11, which encodes the bile salt export pump. We found that these mice have a biochemical phenotype similar to that of Abcb11–/– mice. We then used this system to knock out expression of 5 different enzymes involved in drug metabolism within the same mouse. This approach might be used to develop new models of liver diseases and study liver functions of genes that are required during development.
small molecules
2026-09-23 | Seizure due to Lamotrigine Underexposure During High-Volume CRRT for Hyperammonaemia: A Case Report.
Hyperammonaemic decompensation in urea cycle disorders (UCDs) is a medical emergency that requires prompt intervention. Continuous renal replacement therapy (CRRT) is an effective strategy for acute ammonia clearance, but it may significantly alter the pharmacokinetics of administered drugs. A woman in her 40s with argininosuccinate lyase (ASL) deficiency and long-standing, well-controlled epilepsy treated with lamotrigine presented with a hyperammonaemic crisis and was treated with high-volume continuous venovenous haemodialysis (CVVHD). She developed a generalised tonic-clonic seizure shortly after cessation of CVVHD. Serum lamotrigine declined from 12.7 to 6.0 mg/L over approximately 12 h, corresponding to an apparent elimination half-life of 11.5 h. Lamotrigine was measurable in the effluent (2.9 mg/L), giving a saturation coefficient of 0.48 and an extracorporeal clearance of 38.4 mL/min during the high-volume phase. The seizure was attributed to the abrupt underexposure of lamotrigine in a previously seizure-free patient. This case underscores the clinical significance of extracorporeal clearance of antiseizure medications during CRRT in patients with UCDs. Drug selection should consider both ammonia-modifying and dialysability profiles. Therapeutic drug monitoring and pre-emptive dose adjustment, or the addition of a second intravenously available agent, should be considered when high-volume dialysis is initiated in a patient receiving a dialysable antiseizure medication.
2024-03-11 | Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders.
Liver transplantation (LTx) is an intervention when medical management is not sufficiently preventing individuals with urea cycle disorders (UCDs) from the occurrence of hyperammonemic events. Supplementation with L-citrulline/arginine is regularly performed prior to LTx to support ureagenesis and is often continued after the intervention. However, systematic studies assessing the impact of long-term L-citrulline/arginine supplementation in individuals who have undergone LTx is lacking to date. Using longitudinal data collected systematically, a comparative analysis was carried out by studying the effects of long-term L-citrulline/arginine supplementation vs. no supplementation on health-related outcome parameters (i.e., anthropometric, neurological, and cognitive outcomes) in individuals with UCDs who have undergone LTx. Altogether, 52 individuals with male ornithine transcarbamylase deficiency, citrullinemia type 1 and argininosuccinic aciduria and a pre-transplant "severe" disease course who have undergone LTx were investigated by using recently established and validated genotype-specific in vitro enzyme activities. Long-term supplementation of individuals with L-citrulline/arginine who have undergone LTx (n = 16) does neither appear to alter anthropometric nor neurocognitive endpoints when compared to their severity-adjusted counterparts that were not supplemented (n = 36) after LTx with mean observation periods between four to five years. Moreover, supplementation with L-citrulline/arginine was not associated with an increase of disease-specific plasma arithmetic mean values for the respective amino acids when compared to the non-supplemented control cohort. Although supplementation with L-citrulline/arginine is often continued after LTx, this pilot study does neither identify altered long-term anthropometric or neurocognitive health-related outcomes nor does it find an adequate biochemical response as reflected by the unaltered plasma arithmetic mean values for L-citrulline or L-arginine. Further prospective analyses in larger samples and even longer observation periods will provide more insight into the usefulness of long-term supplementation with L-citrulline/arginine for individuals with UCDs who have undergone LTx.
2023-12-04 | Transition to glycerol phenylbutyrate for the management of urea cycle disorders: clinical experiences.
Urea cycle disorders (UCDs) are a group of rare inborn diseases caused by a deficiency in one of the six enzymes or one of the two transporters involved in the urea cycle. The most common biochemical feature is elevated blood ammonia levels, which can be toxic at high levels, especially to the brain and may manifest as encephalopathy if left untreated. Glycerol phenylbutyrate (GPB) is currently approved for use in the USA and Europe for patients of all ages with UCD who cannot be managed with protein restriction and/or amino acid supplementation alone. This article presents the author's experience in different exemplary settings and depicts the most efficient management of UCDs with GPB. Six patient histories are described. 4 had OCT, one citrullinemia, and one argininosuccinic aciduria. Treatment with GPB was started between 2 days and 14 years of age. Before GPB, one patient had not been treated, 4 had received sodium phenylbutyrate (NaPB), and one Na benzoate. Overall, treatment with GPB was followed by a relevant metabolic improvement, resulting in better therapeutic compliance, reduced hospitalization, and improved quality of life.
2023-12-04 | The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria.
Argininosuccinate lyase (ASL) is integral to the urea cycle detoxifying neurotoxic ammonia and the nitric oxide (NO) biosynthesis cycle. Inherited ASL deficiency causes argininosuccinic aciduria (ASA), a rare disease with hyperammonemia and NO deficiency. Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis. A neurodegenerative phenotype has been proposed in ASA. To better characterise this neurodegenerative phenotype in ASA, we conducted a retrospective study in six paediatric and adult metabolic centres in the UK in 2022. We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour. We analysed neuroimaging with diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) in an individual with ASA with movement disorders. We assessed conventional and DTI MRI alongside single photon emission computer tomography (SPECT) with dopamine analogue radionuclide 123I-ioflupane, in Asl-deficient mice treated by hASL mRNA with normalised ureagenesis. Movement disorders in ASA appear in the second and third decades of life, becoming more prevalent with ageing and independent from the age of onset of hyperammonemia. Neuroimaging can show abnormal DTI features affecting both grey and white matter, preferentially basal ganglia. ASA mouse model with normalised ureagenesis did not recapitulate these DTI findings and showed normal 123I-ioflupane SPECT and cerebral dopamine metabolomics. Altogether these findings support the pathophysiology of a late-onset movement disorder with cell-autonomous functional central catecholamine dysregulation but without or limited neurodegeneration of dopaminergic neurons, making these symptoms amenable to targeted therapy.
2021-05-03 | Naturally-occurring spinosyn A and its derivatives function as argininosuccinate synthase activator and tumor inhibitor.
Argininosuccinate synthase (ASS1) is a ubiquitous enzyme in mammals that catalyzes the formation of argininosuccinate from citrulline and aspartate. ASS1 genetic deficiency in patients leads to an autosomal recessive urea cycle disorder citrullinemia, while its somatic silence or down-regulation is very common in various human cancers. Here, we show that ASS1 functions as a tumor suppressor in breast cancer, and the pesticide spinosyn A (SPA) and its derivative LM-2I suppress breast tumor cell proliferation and growth by binding to and activating ASS1. The C13-C14 double bond in SPA and LM-2I while the Cys97 (C97) site in ASS1 are critical for the interaction between ASS1 and SPA or LM-2I. SPA and LM-2I treatment results in significant enhancement of ASS1 enzymatic activity in breast cancer cells, particularly in those cancer cells with low ASS1 expression, leading to reduced pyrimidine synthesis and consequently the inhibition of cancer cell proliferation. Thus, our results establish spinosyn A and its derivative LM-2I as potent ASS1 enzymatic activator and tumor inhibitor, which provides a therapeutic avenue for tumors with low ASS1 expression and for those non-tumor diseases caused by down-regulation of ASS1.
proteins
2026-03-19 | Impact of long-term nitrogen scavenger therapy on clinical outcome in individuals with urea cycle disorders.
Principles of long-term medical management in individuals with urea cycle disorders (UCDs) encompass (1) a low protein diet, (2) supplementation of arginine and/or citrulline along with essential amino acids, nutrients, vitamins and trace elements, and (3) use of nitrogen scavenging agents to reduce recurrent hyperammonemic events (HAEs). These principles aim at providing metabolic stability, elimimation of chronic complications, and achievement of normal development as well as growth. A retrospective comparative analysis was performed by studying 138 individuals with male ornithine transcarbamylase deficiency (mOTC-D), citrullinemia type 1 (CTLN1) and argininosuccinic aciduria (ASA) based on in vitro residual enzymatic activity for severity-adjustment. Results show that individuals with mOTC-D, CTLN1 and ASA are at risk of progressive linear growth impairment, recurrent annual HAEs and an unfavorable neurocognitive outcome despite being under long-term nitrogen scavenging pharmacotherapy. No overall superiority among existing nitrogen scavenging agents with regard to the individual's metabolic stability, linear growth impairment and poor neurocognitive outcome was observed. Novel therapeutic strategies are urgently needed to ultimately improve health outcomes in individuals with UCDs in order to sufficiently meet guideline-specific goals.
2022-07-06 | Characterisation of Expression the Arginine Pathway Enzymes in Childhood Brain Tumours to Determine Susceptibility to Therapeutic Arginine Depletion.
Despite significant improvements in treatment and survival in paediatric cancers, outcomes for children with brain tumours remain poor. Novel therapeutic approaches are needed to improve survival and quality of survival. Extracellular arginine dependency (auxotrophy) has been recognised in several tumours as a potential therapeutic target. This dependency is due to the inability of cancer cells to recycle or synthesise intracellular arginine through the urea cycle pathway compared to normal cells. Whilst adult glioblastoma exhibits this dependency, the expression of the arginine pathway enzymes has not been delineated in paediatric brain tumours. We used immunohistochemical (IHC) methods to stain for arginine pathway enzymes in paediatric high-grade glioma (pHGG), low-grade glioma (pLGG), ependymoma (EPN), and medulloblastoma (MB) tumour tissue microarrays (TMAs). The antibodies detected protein expression of the metaboliser arginase (Arg1 and Arg2); recycling enzymes ornithine transcarbamoylase (OTC), argininosuccinate synthetase (ASS1), and argininosuccinate lyase (ASL); and the transporter SLC7A1. Deficiency of OTC, ASS1, and ASL was seen in 87.5%, 94%, and 79% of pHGG samples, respectively, consistent with an auxotrophic signature. Similar result was obtained in pLGG with 96%, 93%, and 91% of tumours being deficient in ASL, ASS1, and OTC, respectively. 79%, 88%, and 85% of MB cases were ASL, ASS1, and OTC deficient whilst ASL and OTC were deficient in 57% and 91% of EPN samples. All tumour types highly expressed SLC7A1 and Arginase, with Arg2 being the main isoform, demonstrating that they could transport and utilise arginine. Our results show that pHGG, pLGG, EPN, and MB demonstrate arginine auxotrophy based on protein expression and are likely to be susceptible to arginine depletion. Pegylated arginase (BCT-100) is currently in phase I/II trials in relapsed pHGG. Our results suggest that therapeutic arginine depletion may also be useful in other tumour types and IHC analysis of patient tumour samples could help identify patients likely to benefit from this treatment.
2020-06-19 | A Phase I Study of Pegylated Arginine Deiminase (Pegargiminase), Cisplatin, and Pemetrexed in Argininosuccinate Synthetase 1-Deficient Recurrent High-grade Glioma.
Patients with recurrent high-grade gliomas (HGG) are usually managed with alkylating chemotherapy ± bevacizumab. However, prognosis remains very poor. Preclinically, we showed that HGGs are a target for arginine depletion with pegargiminase (ADI-PEG20) due to epimutations of argininosuccinate synthetase (ASS1) and/or argininosuccinate lyase (ASL). Moreover, ADI-PEG20 disrupts pyrimidine pools in ASS1-deficient HGGs, thereby impacting sensitivity to the antifolate, pemetrexed. We expanded a phase I trial of ADI-PEG20 with pemetrexed and cisplatin (ADIPEMCIS) to patients with ASS1-deficient recurrent HGGs (NCT02029690). Patients were enrolled (01/16-06/17) to receive weekly ADI-PEG20 36 mg/m2 intramuscularly plus pemetrexed 500 mg/m2 and cisplatin 75 mg/m2 intravenously once every 3 weeks for up to 6 cycles. Patients with disease control were allowed ADI-PEG20 maintenance. The primary endpoints were safety, tolerability, and preliminary estimates of efficacy. Ten ASS1-deficient heavily pretreated patients were treated with ADIPEMCIS therapy. Treatment was well tolerated with the majority of adverse events being Common Terminology Criteria for Adverse Events v4.03 grade 1-2. The best overall response was stable disease in 8 patients (80%). Plasma arginine was suppressed significantly below baseline with a reciprocal increase in citrulline during the sampling period. The anti-ADI-PEG20 antibody titer rose during the first 4 weeks of treatment before reaching a plateau. Median progression-free survival (PFS) was 5.2 months (95% confidence interval (CI), 2.5-20.8) and overall survival was 6.3 months (95% CI, 1.8-9.7). In this recurrent HGG study, ADIPEMCIS was well tolerated and compares favorably to historical controls. Additional trials of ADI-PEG20 in HGG are planned.
2019-03-13 | The Citrulline Recycling Pathway Sustains Cardiovascular Function in Arginine-Depleted Healthy Mice, but Cannot Sustain Nitric Oxide Production during Endotoxin Challenge.
The recycling of citrulline by argininosuccinate synthase 1 (ASS1) and argininosuccinate lyase (ASL) is crucial to maintain arginine availability and nitric oxide (NO) production. Pegylated arginine deiminase (ADI-PEG20) is a bacterial enzyme used to deplete circulating arginine. The goal of this research was to test the hypothesis that citrulline is able to sustain intracellular arginine availability for NO production in ADI-PEG20 arginine-depleted mice. Six- to 8-wk-old male C57BL/6J mice injected with ADI-PEG20 (5 IU) or saline (control) were used in 4 different studies. Arginine, citrulline, and NO kinetics were determined by using stable isotopes in unchallenged (study 1) and endotoxin-challenged (study 2) mice. Blood pressure was determined by telemetry for 6 d after ADI-PEG20 administration (study 3), and vasomotor activity and ASS1 and ASL gene expression were determined in mesenteric arteries collected from additional mice (study 4). ADI-PEG20 administration resulted in arginine depletion (<1 compared with 111 ± 37 µmol/L) but in greater plasma citrulline concentrations (900 ± 123 compared with 76 ± 8 µmol/L; P < 0.001) and fluxes (402 ± 17 compared with 126 ± 4 µmol ⋅ kg-1 ⋅ h-1; P < 0.001) compared with controls. Endotoxin-challenged ADI-PEG20-treated mice produced less NO than controls (13 ± 1 compared with 27 ± 2 µmol ⋅ kg-1 ⋅ h-1; P < 0.001). No differences (P > 0.50) were observed for cardiovascular variables (heart rate, blood pressure) between ADI-PEG20-treated and control mice. Furthermore, no ex vivo vasomotor differences were observed between the 2 treatments. ADI-PEG20 administration resulted in greater gene expression of ASS1 (∼3-fold) but lower expression of ASL (-30%). ADI-PEG20 successfully depleted circulating arginine without any effect on cardiovascular endpoints in healthy mice but limited NO production after endotoxin challenge. Therefore, the citrulline recycling pathway can sustain local arginine availability independently from circulating arginine, satisfying the demand of arginine for endothelial NO production; however, it is unable to do so when a high demand for arginine is elicited by endotoxin.
2019-02-05 | Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects
Abstract The first patients affected by argininosuccinic aciduria (ASA) were reported 60 years ago. The clinical presentation was initially described as similar to other urea cycle defects, but increasing evidence has shown overtime an atypical systemic phenotype with a paradoxical observation, that is, a higher rate of neurological complications contrasting with a lower rate of hyperammonaemic episodes. The disappointing long‐term clinical outcomes of many of the patients have challenged the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels. Interrogations have raised about the benefit of newborn screening or liver transplantation on the neurological phenotype. Over the last decade, novel discoveries enabled by the generation of new transgenic argininosuccinate lyase (ASL)‐deficient mouse models have been achieved, such as, a better understanding of ASL and its close interaction with nitric oxide metabolism, ASL physiological role outside the liver, and the pathophysiological role of oxidative/nitrosative stress or excessive arginine treatment. Here, we present a collaborative review, which highlights these recent discoveries and novel emerging concepts about ASL role in human physiology, ASA clinical phenotype and geographic prevalence, limits of current standard of care and newborn screening, pathophysiology of the disease, and emerging novel therapies. We propose recommendations for monitoring of ASA patients. Ongoing research aims to better understand the underlying pathogenic mechanisms of the systemic disease to design novel therapies.
cell therapies
2025-01-08 | Positive Clinical, Neuropsychological, and Metabolic Impact of Liver Transplantation in Patients With Argininosuccinate Lyase Deficiency.
Liver transplantation (LTx) is increasingly used in Urea Cycle Defects (UCDs) to prevent recurrent hyperammonemia and related neurological irreversible injury. Among UCDs, argininosuccinate lyase deficiency (ASLD) has a more complex phenotype than other UCDs, with long-term neurocognitive deficits. Therefore, the role of LTx in ASLD is still debated. The impact of LTx on nine patients with early-onset ASLD was assessed through pre- and post-LTx clinical, neuropsychological, MRI and biochemical evaluations. After LTx, no episodes of metabolic decompensations were reported. Neuropsychological evaluations documented significant improvement in cognitive/developmental functioning especially in patients transplanted in early childhood. Improvements were also highlighted in daily living skills and emotional-behavioral problems, with a reduction in attention disturbances and somatic complaints. Movement disorders resolved after LTx in patient transplanted in early childhood. Any patients developed epilepsy with stability of EEG alterations after LTx. A positive effect of LTx on other disease-related outcomes such as growth, diet, medications, hospitalizations, and long-term ASLD-related complications was highlighted. The primary biomarker argininosuccinic acid dramatically reduced in plasma after transplantation with a decreasing trend in CSF at long-term follow-up. Moreover, health-related quality of life improved after LTx, especially when assessed through MetabQoL, a tool designed for intoxication diseases such as ASLD. In conclusion, our study showed a global beneficial impact of LTx in early-onset ASLD patients to avoid episodes of hyperammonemia, and improve neurocognitive outcome, adaptive and behavioral deficits when performed in early childhood with a dramatic benefit in terms of quality of life.
2022-04-12 | Inborn error of metabolism patients after liver transplantation: Outcomes of 35 patients over 27 years in one pediatric quaternary hospital.
Liver transplantation (LT) has been used for many years as a therapeutic option for certain inborn errors of metabolism (IEMs). Here we present one institution's 27 years of experience with LT in IEMs. Our objective is to assess the outcomes of IEM patients who have undergone LT, which we hypothesize to be generally successful for prevention of metabolic decompensation. A retrospective chart review was performed on patients with urea cycle defects, organic acidemias, and amino acidopathies who underwent LT at the Children's Hospital of Philadelphia. Thirty-five patients with the following conditions have undergone LT: tyrosinemia (8), methylmalonic acidemia (7), maple syrup urine disease (6), citrullinemia (6), ornithine transcarbamylase deficiency (4), propionic acidemia (2), and argininosuccinate lyase deficiency (2). Average age at transplantation was 3.6 years. Three patients are now deceased. One patient suffered a metabolic stroke posttransplant. No episodes of metabolic decompensation have been noted. Thirty-five patients received LT with generally favorable outcome. None sustained metabolic decompensation posttransplant. As has been reported previously, LT does not ameliorate pre-existing developmental differences or risk to other organ systems. Further research is needed to aid in standardization of care and follow-up, as most patients no longer follow with a geneticist.
2021-08-01 | Liver Transplantation in Children with Urea Cycle Disorders: The Importance of Minimizing Waiting Time
Liver transplantation (LT) for children with urea cycle disorders (UCDs) is capable of correcting the enzymatic defect and preventing progressive neurologic injury. We describe the characteristics and outcomes of pediatric LT recipients with UCDs. We identified all pediatric (<18 years) LT candidates with UCDs in the United Network for Organ Sharing (UNOS) database (February 2002 to September 2020). Multivariable Cox and logistic regression were used to determine risk factors for graft loss and cognitive delay, respectively. Of 424 patients, 1.9% (8/424) experienced waitlist mortality and 95.0% underwent LT (403/424). The most frequently encountered UCDs in our cohort were ornithine transcarbamylase deficiency (46.2%), citrullinemia (20.3%), and argininosuccinic aciduria (ASA; 12.9%). The 1-, 3-, and 5-year graft survival rates were 90.4%, 86.3%, and 85.2%, respectively. Multivariable analysis showed a decreased risk of graft loss with increasing weight at LT (adjusted hazard ratio [aHR], 0.96; 95% confidence interval [CI], 0.94-0.99; P = 0.02), male sex (aHR, 0.49; 95% CI, 0.28-0.85; P = 0.01), and ASA diagnosis (aHR, 0.29; 95% CI, 0.09-0.98; P = 0.047), when adjusting for location (intensive care/hospital/home) and graft type (both P ≥ 0.65). In multivariable logistic regression, waitlist time (adjusted odds ratio [aOR], 1.10; 95% CI, 1.02-1.17; P = 0.009) and male sex (aOR, 1.71; 95% CI, 1.02-2.88; P = 0.04) were associated with increased odds of long-term cognitive delay. Waitlist duration is associated with a long-term risk of cognitive delay. Given excellent long-term outcomes, early LT evaluation should be considered in all children with UCDs to prevent progressive neurologic injury and optimize cognitive outcomes.
2020-09-14 | Differential Intraoperative Effect of Liver Transplant in Different Inborn Errors of Metabolism.
Liver transplant (LT) is a therapeutic option for a growing number of inborn errors of metabolism (IEM), including some disorders not confined to the liver. Clinical advantages of LT in maple syrup urine disease (MSUD), methylmalonic acidemia (MMA), and argininosuccinic aciduria (ASA) have been reported. However, no information on the early metabolic effect of LT after portal reperfusion is available in these disorders. Here we describe the intraoperative differential metabolic outcome of LT in MSUD, MMA, and ASA. In these IEM, LT promptly cleared toxic metabolites to safe concentrations. In MSUD, leucine concentration reached physiological concentration within 12 hours after portal reperfusion. In MMA and ASA, LT allowed faster clearance of methylmalonate and argininosuccinate, respectively, both dropping by ∼90% within the first hour after portal reperfusion. The early biochemical benefits of LT in MSUD, MMA, and ASA demonstrate its immediate effectiveness in protecting patients from intercurrent metabolic decompensations.
2019-12-02 | Intrahepatic Administration of Human Liver Stem Cells in Infants with Inherited Neonatal-Onset Hyperammonemia: A Phase I Study
Abstract Previous studies have shown that human liver stem-like cells (HLSCs) may undergo differentiation in vitro into urea producing hepatocytes and in vivo may sustain liver function in models of experimentally induced acute liver injury. The aim of this study was to assess the safety of HLSCs intrahepatic administration in inherited neonatal-onset hyperammonemia. The study was approved by the Agenzia Italiana del Farmaco on favorable opinion of the Italian Institute of Health as an open-label, prospective, uncontrolled, monocentric Phase I study (HLSC 01–11, EudraCT-No. 2012–002120-33). Three patients affected by argininosuccinic aciduria (patient 1) and methylmalonic acidemia (patients 2 and 3) and included in the liver transplantation list were enrolled. In all patients, HLSCs were administered by percutaneous intrahepatic injections (once a week for two consecutive weeks) within the first months of life. The first patient received 125,000 HLSCs x gram of liver/dose while the other two patients received twice this dose. No immunosuppression was administered since HLSCs possess immunomodulatory activities. None of the patients experienced infections, hyperammonemia decompensation, or other adverse events during the whole observation period. No donor specific antibodies (DSA) against HLSCs were detected. Patients were metabolic stable despite an increase (~30%) in protein intake. Two patients underwent liver transplantation after 19 and 11 months respectively, and after explantation, the native livers showed no histological alterations. In conclusion, percutaneous intrahepatic administration of HLSCs was safe in newborn with inherited neonatal-onset hyperammonemia. These data pave the way for Phase II studies in selected inherited and acquired liver disorders.
gene therapies
2024-04-08 | Genetic and functional correction of argininosuccinate lyase deficiency using CRISPR adenine base editors.
Argininosuccinate lyase deficiency (ASLD) is a recessive metabolic disorder caused by variants in ASL. In an essential step in urea synthesis, ASL breaks down argininosuccinate (ASA), a pathognomonic ASLD biomarker. The severe disease forms lead to hyperammonemia, neurological injury, and even early death. The current treatments are unsatisfactory, involving a strict low-protein diet, arginine supplementation, nitrogen scavenging, and in some cases, liver transplantation. An unmet need exists for improved, efficient therapies. Here, we show the potential of a lipid nanoparticle-mediated CRISPR approach using adenine base editors (ABEs) for ASLD treatment. To model ASLD, we first generated human-induced pluripotent stem cells (hiPSCs) from biopsies of individuals homozygous for the Finnish founder variant (c.1153C>T [p.Arg385Cys]) and edited this variant using the ABE. We then differentiated the hiPSCs into hepatocyte-like cells that showed a 1,000-fold decrease in ASA levels compared to those of isogenic non-edited cells. Lastly, we tested three different FDA-approved lipid nanoparticle formulations to deliver the ABE-encoding RNA and the sgRNA targeting the ASL variant. This approach efficiently edited the ASL variant in fibroblasts with no apparent cell toxicity and minimal off-target effects. Further, the treatment resulted in a significant decrease in ASA, to levels of healthy donors, indicating restoration of the urea cycle. Our work describes a highly efficient approach to editing the disease-causing ASL variant and restoring the function of the urea cycle. This method relies on RNA delivered by lipid nanoparticles, which is compatible with clinical applications, improves its safety profile, and allows for scalable production.
2021-03-01 | Nitric oxide and bone: The phoenix rises again
The involvement of nitric oxide (NO) in preventing bone loss has long been hypothesized, but despite decades of research the mechanisms remain obscure. In this issue of the JCI, Jin et al. explored NO deficiency using human cell and mouse models that lacked argininosuccinate lyase (ASL), the enzyme involved in synthesizing arginine and NO production. Osteoblasts that did not express ASL produced less NO and failed to differentiate. Notably, in the context of Asl deficiency, heterozygous deletion of caveolin 1, which normally inhibits NO synthesis, restored NO production, osteoblast differentiation, glycolysis, and bone mass. These experiments suggest that ASL regulates arginine synthesis in osteoblasts, which leads to enhanced NO production and increased glucose metabolism. After a period when research slowed, these studies, like the legendary phoenix, renew the exploration of NO in bone biology, and provide exciting translational potential.
2018-12-01 | Rapid Disruption of Genes Specifically in Livers of Mice Using Multiplex CRISPR/Cas9 Editing
Background & aimsDespite advances in gene editing technologies, generation of tissue-specific knockout mice is time-consuming. We used CRISPR/Cas9-mediated genome editing to disrupt genes in livers of adult mice in just a few months, which we refer to as somatic liver knockouts.MethodsIn this system, Fah–/– mice are given hydrodynamic tail vein injections of plasmids carrying CRISPR/Cas9 designed to excise exons in Hpd; the Hpd-edited hepatocytes have a survival advantage in these mice. Plasmids that target Hpd and a separate gene of interest can therefore be used to rapidly generate mice with liver-specific deletion of nearly any gene product.ResultsWe used this system to create mice with liver-specific knockout of argininosuccinate lyase, which develop hyperammonemia, observed in humans with mutations in this gene. We also created mice with liver-specific knockout of ATP binding cassette subfamily B member 11, which encodes the bile salt export pump. We found that these mice have a biochemical phenotype similar to that of Abcb11–/– mice. We then used this system to knock out expression of 5 different enzymes involved in drug metabolism within the same mouse.ConclusionsThis approach might be used to develop new models of liver diseases and study liver functions of genes that are required during development. Despite advances in gene editing technologies, generation of tissue-specific knockout mice is time-consuming. We used CRISPR/Cas9-mediated genome editing to disrupt genes in livers of adult mice in just a few months, which we refer to as somatic liver knockouts. In this system, Fah–/– mice are given hydrodynamic tail vein injections of plasmids carrying CRISPR/Cas9 designed to excise exons in Hpd; the Hpd-edited hepatocytes have a survival advantage in these mice. Plasmids that target Hpd and a separate gene of interest can therefore be used to rapidly generate mice with liver-specific deletion of nearly any gene product. We used this system to create mice with liver-specific knockout of argininosuccinate lyase, which develop hyperammonemia, observed in humans with mutations in this gene. We also created mice with liver-specific knockout of ATP binding cassette subfamily B member 11, which encodes the bile salt export pump. We found that these mice have a biochemical phenotype similar to that of Abcb11–/– mice. We then used this system to knock out expression of 5 different enzymes involved in drug metabolism within the same mouse. This approach might be used to develop new models of liver diseases and study liver functions of genes that are required during development.
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Drug Discovery Landscape
10 orphan drug designations for Argininosuccinic aciduria, including 1 approved therapy.
10 orphan drug designations for Argininosuccinic aciduria, including 1 approved therapy.
Drug | Therapy type | Orphan designation | Clinical trial status | Sponsor |
|---|---|---|---|---|
sodium nitrite | small molecules | FDA | — | Bryan Therapeutics |
Heterologous human adult liver-derived stem cells | cell therapies | EMA | — | Unicyte S.R.L. |
Sodium benzoate, sodium phenylacetate | small molecules | EMA | — | Dipharma B.V. |
Modified messenger ribonucleic acid encoding human argininosuccinate lyase enzyme encapsulated into lipid nanoparticles | RNAs | EMA | — | PhaseRx Ireland, Ltd |
mRNA encoding human argininosuccinate lyase | RNAs | FDA | — | PhaseRx, Inc. |
Sodium benzoate | small molecules | EMA | — | Lucane Pharma SA |
Sodium benzoate | small molecules | EMA | — | Syri Pharma Limited |
Heterologous human adult liver-derived progenitor cells | cell therapies | EMA | Cellaion | |
Human heterologous liver cells (for infusion) | cell therapies | EMA | — | Promethera Biosciences |
Glyceryl tri-(4-phenylbutyrate) [Ravicti] | small molecules | EMA | Approved | Immedica Pharma AB |
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