Deficiency Of Fumarylacetoacetate Hydrolase Research Articles

A Case Report of a Very Rare Association of Tyrosinemia type I and Pancreatitis Mimicking Neurologic Crisis of Tyrosinemia Type I.

Tyrosinemia type I is an autosomal recessively inherited metabolic disease of tyrosine metabolism due to the deficiency of fumarylacetoacetate hydrolase. Clinical manifestations include hepatic failure, cirrhosis, hepatocellular carcinoma, renal fanconi syndrome, and neurologic crisis. With the introduction of 2-(2-nitro-4-trifluoro-methylbenzyol)-1.3 cyclohexanedione (NTBC) treatment, the prognosis improved with reduced rate of complications. Here, we report a 6-year-old girl with tyrosinemia type I who discontinued NTBC treatment six months prior to admission, presenting with complaints of abdominal pain, vomiting, anorexia, weakness, and restlessness, suggesting the clinical status of neurologic crisis. Further laboratory and radiologic evaluation revealed that indeed this is a pancreatitis. We report this case as tyrosinemia type I and pancreatitis was reported only in one case in the literature, emphasizing confusing clinical signs of neurological crisis, and pancreatitis in tyrosinemia type I.

Experience of a Single Center in NTBC Use in Management of Hereditary Tyrosinemia Type I in Libya.

Background:Hereditary Tyrosinemia type I (HTI) is a metabolic disease caused by deficiency of fumarylacetoacetate hydrolase enzyme.Objectives:This study reports beside its clinical and biochemical presentation, the outcome of NTBC [2- (2-nitro-4-trifloro-methylbenzoyl)-1, 3-cyclohexanedion] treatment of the disease and evaluates its biochemical markers in 16 pediatric Libyan patients.Patients and Methods:The diagnosis was based on presence of high tyrosine levels in blood and succinylacetone in urine.Results:The consanguinity rate was 81.2%, the median age at onset, at diagnosis and at starting treatment were 4.5, 8, and 9.5 months respectively. At presentation hepatomegaly, jaundice, rickets and high gamma glutamyl transferase (GGT) were observed in 87.5% of patients. All patients had extremely high alpha fetoprotein (AFP) and high alkaline phosphatase (ALP) levels. Fifteen patients were treated with NTBC, normalization of PT (Prothrombine time) was achieved in average in 14 days. The other biochemical parameters of liver function (transaminases, GGT, ALP, bilirubin and albumin) took longer to improve and several months to be normalized. Survival rate with NTBC was 86.6%. Patients who started treatment in a median of 3 months post onset observed a fast drop of AFP in 90.6% of patients (P = 0.003). Abnormal liver function and rickets were the common presentations, GGT was an early cholestatic sensitive test. ALP was constantly high even in asymptomatic patients.Conclusions:In HT1 a faster dropping of AFP is a marker of good prognosis.

Succinylacetone as primary marker to detect tyrosinemia type I in newborns and its measurement by newborn screening programs

Tyrosinemia type I (TYR I) is caused by autosomal recessive fumarylacetoacetate hydrolase deficiency and is characterized by development of severe liver disease in infancy and neurologic crises. If left untreated, most patients die of liver failure in the first years of life. Intervention with medication is effective when initiated during the first month of life. This improvement in the treatment of TYR I patients influenced the decision to include TYR I in the US Secretary of the Department of Health and Human Services' (HHS) Recommended Uniform Screening Panel. However, while tyrosine is routinely measured in newborn screening (NBS) by tandem mass spectrometry (MS/MS), elevated tyrosine levels are not specific to TYR I. To improve the specificity of NBS for TYR I, several assays were developed to measure succinylacetone (SUAC) in dried blood spots (DBS). SUAC is a pathognomonic marker of TYR I, and its detection by NBS MS/MS is possible. This review of the current status of NBS for TYR I in the US is the result of discussions at the HHS Secretary's (Discretionary) Advisory Committee on Heritable Disorders in Newborns and Children about the inconsistent implementation of effective NBS for TYR I in the US. We sought to understand the different TYR I screening practices in US NBS programs. Results indicate that 50 out of 51 NBS programs in the US screen for TYR I, and a successful SUAC performance evaluation scheme is available from the Centers for Disease Control and Prevention. Programmatic and methodological barriers were identified that prevent widespread adoption of SUAC measurements in NBS laboratories. However, since SUAC detection is currently the best approach to NBS for TYR I, a further delay of the addition of SUAC measurement into NBS procedures is discouraged. SUAC measurement should improve both the false positive and false negative rate in NBS for TYR I thereby yielding the desired benefits for affected patients at no expense to the overall population served.

Brief report: Parthenogenetic embryonic stem cells are an effective cell source for therapeutic liver repopulation.

Parthenogenesis is the development of an oocyte without fertilization. Mammalian parthenogenetic (PG) embryos are not viable, but can develop into blastocysts from which embryonic stem cells (ESCs) have been derived in mouse and human. PG ESCs are frequently homozygous for alleles encoding major histocompatibility complex (MHC) molecules. MHC homozygosity permits much more efficient immune matching than MHC heterozygosity found in conventional ESCs, making PG ESCs a promising cell source for cell therapies requiring no or little immune suppression. However, findings of restricted differentiation and proliferation of PG cells in developmental chimeras have cast doubt on the potential of PG ESC derivatives for organ regeneration. To address this uncertainty, we determined whether PG ESC derivatives are effective in rescuing mice with lethal liver failure due to deficiency of fumarylacetoacetate hydrolase (Fah). In developmental chimeras generated by injecting wild-type PG ESCs into Fah-deficient blastocysts, PG ESCs differentiated into hepatocytes that could repopulate the liver, provide normal liver function, and facilitate long-term survival of adult mice. Moreover, after transplantation into adult Fah-deficient mice, PG ESC-derived hepatocytes efficiently engrafted and proliferated, leading to high-level liver repopulation. Our results show that--despite the absence of a paternal genome--PG ESCs can form therapeutically effective hepatocytes.

Fumarylacetoacetate hydrolase deficient pigs are a novel large animal model of metabolic liver disease

Hereditary tyrosinemia type I (HT1) is caused by deficiency in fumarylacetoacetate hydrolase (FAH), an enzyme that catalyzes the last step of tyrosine metabolism. The most severe form of the disease presents acutely during infancy, and is characterized by severe liver involvement, most commonly resulting in death if untreated. Generation of FAH+/− pigs was previously accomplished by adeno-associated virus-mediated gene knockout in fibroblasts and somatic cell nuclear transfer. Subsequently, these animals were outbred and crossed to produce the first FAH−/− pigs.FAH-deficiency produced a lethal defect in utero that was corrected by administration of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3 cyclohexanedione (NTBC) throughout pregnancy. Animals on NTBC were phenotypically normal at birth; however, the animals were euthanized approximately four weeks after withdrawal of NTBC due to clinical decline and physical examination findings of severe liver injury and encephalopathy consistent with acute liver failure. Biochemical and histological analyses, characterized by diffuse and severe hepatocellular damage, confirmed the diagnosis of severe liver injury. FAH−/− pigs provide the first genetically engineered large animal model of a metabolic liver disorder. Future applications of FAH−/− pigs include discovery research as a large animal model of HT1 and spontaneous acute liver failure, and preclinical testing of the efficacy of liver cell therapies, including transplantation of hepatocytes, liver stem cells, and pluripotent stem cell-derived hepatocytes.

Functional analysis and in vitro correction of splicing FAH mutations causing tyrosinemia type I

Hereditary tyrosinemia type I (HT1) is a rare disease caused by a deficiency of fumarylacetoacetate hydrolase (FAH) in the tyrosine catabolic pathway, resulting mainly in hepatic alterations due to accumulation of the toxic metabolites fumarylacetoacetate, maleylacetoacetate and succinylacetone. We have characterized using minigenes four splicing mutations affecting exonic or intronic nucleotides of the FAH gene identified in two HT1 patients. Two of the mutations are novel, c.82-1G>A and c.913G>C and the other two have been previously associated with a splicing defect (c.836A>G and c.1062+5G>A). All mutations were confirmed to affect splicing in minigenes, resulting in exon skipping or activation of a cryptic splice site. We have analyzed the effect of different compounds known to modulate splicing (valproic acid, phenyl butyrate, M344, EIPA, and resveratrol) and the overexpression of splice factors of the SR protein family on the transcriptional profile of the mutant minigenes. For the c.836A>G mutation, a partial recovery of the correctly spliced transcript was observed. These results confirm the relevance of performing functional studies for mutations potentially affecting the splicing process and open the possibility of supplementary therapeutic approaches to diseases caused by splicing defects.

Disruption of Fumarylacetoacetate Hydrolase Causes Spontaneous Cell Death under Short-Day Conditions in Arabidopsis

Fumarylacetoacetate hydrolase (FAH) hydrolyzes fumarylacetoacetate to fumarate and acetoacetate, the final step in the tyrosine (Tyr) degradation pathway that is essential to animals. Deficiency of FAH in animals results in an inborn lethal disorder. However, the role for the Tyr degradation pathway in plants remains to be elucidated. In this study, we isolated an Arabidopsis (Arabidopsis thaliana) short-day sensitive cell death1 (sscd1) mutant that displays a spontaneous cell death phenotype under short-day conditions. The SSCD1 gene was cloned via a map-based cloning approach and found to encode an Arabidopsis putative FAH. The spontaneous cell death phenotype of the sscd1 mutant was completely eliminated by further knockout of the gene encoding the putative homogentisate dioxygenase, which catalyzes homogentisate into maleylacetoacetate (the antepenultimate step) in the Tyr degradation pathway. Furthermore, treatment of Arabidopsis wild-type seedlings with succinylacetone, an abnormal metabolite caused by loss of FAH in the Tyr degradation pathway, mimicked the sscd1 cell death phenotype. These results demonstrate that disruption of FAH leads to cell death in Arabidopsis and suggest that the Tyr degradation pathway is essential for plant survival under short-day conditions.

Effect of nitisinone (NTBC) treatment on the clinical course of hepatorenal tyrosinemia in Québec

BackgroundHepatorenal tyrosinemia (HT1, fumarylacetoacetate hydrolase deficiency, MIM 276700) can cause severe hepatic, renal and peripheral nerve damage. In Québec, HT1 is frequent and neonatal HT1 screening is practiced. Nitisinone (NTBC, Orfadin ®) inhibits tyrosine degradation prior to the formation of toxic metabolites like succinylacetone and has been offered to HT1 patients in Québec since 1994. MethodsWe recorded the clinical course of 78 Québec HT1 patients born between 1984 and 2004. There were three groups: those who never received nitisinone (28 patients), those who were first treated after 1month of age (26 patients) and those treated before 1month (24 patients). Retrospective chart review was performed for events before 1994, when nitisinone treatment began, and prospective data collection thereafter. FindingsNo hospitalizations for acute complications of HT1 occurred during 5731months of nitisinone treatment, versus 184 during 1312months without treatment (p<0.001). Liver transplantation was performed in 20 non-nitisinone-treated patients (71%) at a median age of 26months, versus 7 late-treated patients (26%, p<0.001), and no early-treated patient (p<0.001). No early-treated patient has developed detectable liver disease after more than 5years. Ten deaths occurred in non-nitisinone treated patients versus two in treated patients (p<0.01). Both of the latter deaths were from complications of transplantation unrelated to HT1. One probable nitisinone-related event occurred, transient corneal crystals with photophobia. InterpretationNitisinone treatment abolishes the acute complications of HT1. Some patients with established liver disease before nitisinone treatment eventually require hepatic transplantation. Patients who receive nitisinone treatment before 1month had no detectable liver disease after more than 5years.

Simple and Fast Quantification of Nitisone (NTBC) using Liquid Chromatography-Tandem Mass Spectrometry Method in Plasma of Tyrosinemia Type 1 Patients

Tyrosinemia type 1, which is caused by a deficiency in fumarylacetoacetate hydrolase, is successfully treatable with nitisone (NTBC), an inhibitor of 4-hydroxyphenyl pyruvate dioxygenase. The recommended average dose of NTBC is 1 mg/kg per day. A rapid liquid chromatography (LC) coupled with negative electrospray ionization tandem mass spectrometry method was developed and validated for the quantification of NTBC in heparinized human plasma. The plasma samples were prepared by precipitation in acetonitrile. NTBC and the internal standard (IS) were chromatographed on a BEH C18 column. Gradient elution was done with a mixture of 10 mM ammonium acetate and methanol. The analyte was analyzed by LC-tandem mass spectrometry with only 2 min run time. Selected reaction monitoring modes for detection of NTBC and the IS were achieved by using m/z 328 > 281 and 234 > 190, respectively. The LC retention times for NTBC and IS were 0.99 and 0.93 min, respectively. The method was linear in the concentration range of 0.75-150 µM with r ≥ 0.998. Thus, this method is suitable for follow-up of patients treated with NTBC, because the current therapeutical concentrations range from 20 to 120 µM.

LC-MS/MS Method for Simultaneous Determination on a Dried Blood Spot of Multiple Analytes Relevant for Treatment Monitoring in Patients with Tyrosinemia Type I

Tyrosinemia type 1 is caused by deficiency of fumarylacetoacetate hydrolase. The enzymatic defect impairs the conversion of fumarylacetoacetate to fumarate, causing accumulation of succinylacetone which induces severe liver and kidney dysfunction along with mutagenic changes and hepatocellular carcinoma. Treatment is based on nitisinone (NTBC), an enzymatic inhibitor which suppresses succinylacetone production. NTBC, which has dramatically changed the disease course improving liver and kidney functions and reducing risk of liver cancer, causes a side effect of the increase of tyrosine levels. Treatment is therefore based on the combination of NTBC with a protein-restricted diet to prevent the potential toxicity of excessive tyrosine accumulation. Long-term therapy requires a careful monitoring in blood of NTBC levels along with other disease biomarkers, which include succinylacetone, and a selected panel of circulating aminoacids. We have developed a straightforward and fast MS/MS method for the simultaneous determination of NTBC, succinylacetone, tyrosine, phenylalanine, and methionine on a dried blood spot requiring a 2 min run. A single assay suitable for quantitative evaluation of all biochemical markers is of great advance over conventional methods, especially in pediatric patients, since it reduces laboratory costs and blood sampling, is less invasive and particularly suitable for pediatric patients, and allows easier storage and shipping.

Grown Up Mice From Gene-Corrected iPS Cells

In 2008, Science named induced pluripotent stem cells (iPS) the breakthrough of the year.1 In 2009, Nature Methods called the process of generating iPS cells the “Method of the Year.“2 Two years later, although the use of iPS cells remains a bright promise for both research and regenerative medicine, concerns remain about how the epigenetic and genetic changes that occur in the creation of iPS cells will affect their utility in the treatment of heritable conditions. This summer, a team led by Tobias Cantz, at the Max-Planck-Institute for Molecular Biomedicine, published a proof-of-principle paper in PLoS Biology demonstrating that iPS cells remained pluripotent after correction of genetic defects.3 The authors chose fumarylacetoacetate hydrolase (FAH) deficiency as a disease model for an iPS-mediated correction. FAH deficiency leads to the rare clinical syndrome, tyrosinemia type I, characterized by the accumulation of succinylacetone in multiple organs, including the liver and kidneys, leading to organ failure and death. In this paper, Wu et al first generated iPS cells from FAH-deficient fibroblasts and then corrected the FAH deficiency by transducing the iPS cells with recombinant lentiviruses. Subsequently they used the genetically corrected iPS cells to produce mice that expressed FAH (Figure). Figure. Diagram demonstrating the process described by Wu et al for creating mice from gene-corrected disease-specific iPS cells. (Illustration credit: Cosmocyte/Ben Smith, adapted from an image provided by Tobias Cantz). “The study clearly showed that the gene correction procedures did not impair the full pluripotentiality of iPS cells,” said Shinya Yamanaka (director of the Center for iPS Cell Research and Application at Kyoto University). Yamanaka is the father of the iPS field. In 2006 his laboratory was the first to coax adult mouse fibroblasts into an undifferentiated state through the expression of 4 transcription factors: Oct4, Sox2, Klf4, and c-Myc.4 …

Neuropsychological outcome of NTBC-treated patients with tyrosinaemia type 1

Corinne De Laet, Vanessa Terrones Munoz, Jaak Jaeken, Baudouin FranAois, Dietbrandt Carton, Etienne M Sokal, Bernard Dan, Philippe J Goyens 1 Nutrition and Metabolism Unit, H pital Universitaire des Enfants Reine Fabiola, Universit Libre de Bruxelles (ULB), Brussels, Belgium. 2 Centre for Metabolic Diseases, University Hospital Gasthuisberg, Leuven, Belgium. 3 Pinocchio Centre for Inborn Metabolic Diseases, Esperance Hospital, Li ge, Belgium. 4 Centre for Metabolic Diseases, Ghent University Hospital, Ghent, Belgium. 5 Paediatric Department, St Luc Clinics, Brussels, Belgium. Correspondence to: corinne.delaet@huderf.be

Modeling and therapy of human liver diseases using induced pluripotent stem cells: How far have we come?

Rashid ST, Corbineau S, Hannan N, Marciniak SJ, Miranda E, Alexander G, Huang-Doran I, Griffin J, Ahrlund-Richter L, Skepper J, Semple R, Weber A, Lomas DA, Vallier L. Modeling inherited metabolic disorders of the liver using human induced pluripotent stem cells. J Clin Invest. 2010 Sep 1;120(9):3127–36. Human induced pluripotent stem (iPS) cells hold great promise for advancements in developmental biology, cell-based therapy, and modeling of human disease. Here, we examined the use of human iPS cells for modeling inherited metabolic disorders of the liver. Dermal fibroblasts from patients with various inherited metabolic diseases of the liver were used to generate a library of patient-specific human iPS cell lines. Each line was differentiated into hepatocytes using what we believe to be a novel 3-step differentiation protocol in chemically defined conditions. The resulting cells exhibited properties of mature hepatocytes, such as albumin secretion and cytochrome P450 metabolism. Moreover, cells generated from patients with 3 of the inherited metabolic conditions studied in further detail (alpha1-antitrypsin deficiency, familial hypercholesterolemia, and glycogen storage disease type 1a) were found to recapitulate key pathological features of the diseases affecting the patients from which they were derived, such as aggregation of misfolded alpha1-antitrypsin in the endoplasmic reticulum, deficient LDL receptor-mediated cholesterol uptake, and elevated lipid and glycogen accumulation. Therefore, we report a simple and effective platform for hepatocyte generation from patient-specific human iPS cells. These patient-derived hepatocytes demonstrate that it is possible to model diseases whose phenotypes are caused by pathological dysregulation of key processes within adult cells. Espejel S, Roll GR, McLaughlin KJ, Lee AY, Zhang JY, Laird DJ, Okita K, Yamanaka S, Willenbring H. Induced pluripotent stem cell-derived hepatocytes have the functional and proliferative capabilities needed for liver regeneration in mice. J Clin Invest. 2010 Sep 1;120(9):3120–6. The ability to generate induced pluripotent stem (iPS) cells from a patient’s somatic cells has provided a foundation for organ regeneration without the need for immune suppression. However, it has not been established that the differentiated progeny of iPS cells can effectively reverse failure of a vital organ. Here, we examined whether iPS cell-derived hepatocytes have both the functional and proliferative capabilities needed for liver regeneration in mice with fumarylacetoacetate hydrolase deficiency. To avoid biases resulting from random genomic integration, we used iPS cells generated without viruses. To exclude compensation by hepatocytes not derived from iPS cells, we generated chimeric mice in which all hepatocytes were iPS cell derived. In vivo analyses showed that iPS cells were intrinsically able to differentiate into fully mature hepatocytes that provided full liver function. The iPS cell-derived hepatocytes also replicated the unique proliferative capabilities of normal hepatocytes and were able to regenerate the liver after transplantation and two-thirds partial hepatectomy. Thus, our results establish the feasibility of using iPS cells generated in a clinically acceptable fashion for rapid and stable liver regeneration.

Hepatic Differentiation of Murine Disease-Specific Induced Pluripotent Stem Cells Allows Disease ModellingIn Vitro

Direct reprogramming of somatic cells into pluripotent cells by retrovirus-mediated expression of OCT4, SOX2, KLF4, and C-MYC is a promising approach to derive disease-specific induced pluripotent stem cells (iPSCs). In this study, we focused on three murine models for metabolic liver disorders: the copper storage disorder Wilson's disease (toxic-milk mice), tyrosinemia type 1 (fumarylacetoacetate-hydrolase deficiency, FAH−/− mice), and alpha1-antitrypsin deficiency (PiZ mice). Colonies of iPSCs emerged 2-3 weeks after transduction of fibroblasts, prepared from each mouse strain, and were maintained as individual iPSC lines. RT-PCR and immunofluorescence analyses demonstrated the expression of endogenous pluripotency markers. Hepatic precursor cells could be derived from these disease-specific iPSCs applying an in vitro differentiation protocol and could be visualized after transduction of a lentiviral albumin-GFP reporter construct. Functional characterization of these cells allowed the recapitulation of the disease phenotype for further studies of underlying molecular mechanisms of the respective disease.

Induced pluripotent stem cell–derived hepatocytes have the functional and proliferative capabilities needed for liver regeneration in mice

The ability to generate induced pluripotent stem (iPS) cells from a patient's somatic cells has provided a foundation for organ regeneration without the need for immune suppression. However, it has not been established that the differentiated progeny of iPS cells can effectively reverse failure of a vital organ. Here, we examined whether iPS cell-derived hepatocytes have both the functional and proliferative capabilities needed for liver regeneration in mice with fumarylacetoacetate hydrolase deficiency. To avoid biases resulting from random genomic integration, we used iPS cells generated without viruses. To exclude compensation by hepatocytes not derived from iPS cells, we generated chimeric mice in which all hepatocytes were iPS cell derived. In vivo analyses showed that iPS cells were intrinsically able to differentiate into fully mature hepatocytes that provided full liver function. The iPS cell-derived hepatocytes also replicated the unique proliferative capabilities of normal hepatocytes and were able to regenerate the liver after transplantation and two-thirds partial hepatectomy. Thus, our results establish the feasibility of using iPS cells generated in a clinically acceptable fashion for rapid and stable liver regeneration.

Ploidy Reductions in Murine Fusion-Derived Hepatocytes

We previously showed that fusion between hepatocytes lacking a crucial liver enzyme, fumarylacetoacetate hydrolase (FAH), and wild-type blood cells resulted in hepatocyte reprogramming. FAH expression was restored in hybrid hepatocytes and, upon in vivo expansion, ameliorated the effects of FAH deficiency. Here, we show that fusion-derived polyploid hepatocytes can undergo ploidy reductions to generate daughter cells with one-half chromosomal content. Fusion hybrids are, by definition, at least tetraploid. We demonstrate reduction to diploid chromosome content by multiple methods. First, cytogenetic analysis of fusion-derived hepatocytes reveals a population of diploid cells. Secondly, we demonstrate marker segregation using ß-galactosidase and the Y-chromosome. Approximately 2–5% of fusion-derived FAH-positive nodules were negative for one or more markers, as expected during ploidy reduction. Next, using a reporter system in which ß-galactosidase is expressed exclusively in fusion-derived hepatocytes, we identify a subpopulation of diploid cells expressing ß-galactosidase and FAH. Finally, we track marker segregation specifically in fusion-derived hepatocytes with diploid DNA content. Hemizygous markers were lost by ≥50% of Fah-positive cells. Since fusion-derived hepatocytes are minimally tetraploid, the existence of diploid hepatocytes demonstrates that fusion-derived cells can undergo ploidy reduction. Moreover, the high degree of marker loss in diploid daughter cells suggests that chromosomes/markers are lost in a non-random fashion. Thus, we propose that ploidy reductions lead to the generation of genetically diverse daughter cells with about 50% reduction in nuclear content. The generation of such daughter cells increases liver diversity, which may increase the likelihood of oncogenesis.

Hepatic stress in hereditary tyrosinemia type 1 (HT1) activates the AKT survival pathway in the fah−/− knockout mice model

The AKT survival pathway is involved in a wide variety of human cancers. We investigated the implication of this pathway in hereditary tyrosinemia type 1 (HT1), a metabolic disease exhibiting hepatocellular carcinoma (HCC), despite treatment with 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexadione (NTBC) which prevents liver damage. HT1 is an autosomal recessive disorder caused by accumulation of toxic metabolites due to a deficiency in fumarylacetoacetate hydrolase (FAH), the last enzyme in the catabolism of tyrosine. NTBC withdrawal in the murine fah(-/-) knockout model was used to analyze in vivo the correlation between pathophysiological, biochemical and histological features consistent with hepatocarcinogenesis and activation of the AKT survival pathway. The HT1 stress initiated by NTBC discontinuation causes a progressive increase of liver and kidney pathophysiology. A stable activation of the AKT survival pathway is observed in the liver but not in kidneys of fah(-/-) mice. Hepatic survival is reinforced by inhibition of mitochondrial-mediated apoptosis through inactivation of Bad and induction of BCl-X(L) and BCl-2. The chronic stress induced by liver disease in HT1 activates the AKT survival signal and inhibits intrinsic apoptosis to confer cell death resistance in vivo and favor hepatocarcinogenesis.

Rescue from neonatal death in the murine model of hereditary tyrosinemia by glutathione monoethylester and vitamin C treatment

Hereditary tyrosinemia type 1 (HT1) is a recessive disease caused by a deficiency of the enzyme fumarylacetoacetate hydrolase (FAH) that catalyzes the conversion of fumarylacetoacetate (FAA) into fumarate and acetoacetate. In mice models of HT1, FAH deficiency causes death within the first 24 h after birth. Administration of 2-(2-nitro-4-trifluoro-methylbenzoyl)-1,3 cyclohexanedione (NTBC) prevents neonatal death in HT1 mice, ameliorates the HT1 phenotype but does not prevent development of hepatocellular carcinoma later on. FAA has been shown to deplete cells of glutathione by forming adducts. We tested whether a combination of a cell membrane permeable derivative of glutathione, glutathione monoethylester (GSH-MEE) and vitamin C could provide an alternative effective treatment for HT1. GSH-MEE (10 mmol/kg/j)/vitamin C (0.5 mmol/kg/j) treatment was given orally to pregnant/nursing female mice. While FAH −/− pups died in absence of treatment, all FAH −/− pups survived the critical first 24 h of life when the mothers were on the GSH-MEE/vitamin C treatment and showed normal growth until postnatal day 10 (P10). However, after P10, pups showed failure to thrive, lethargy and died around P17. Thus, GSH-MEE/vitamin C supplementation could rescue the mice model of HT1 from neonatal death but it did not prevent the appearance of a HT1 phenotype in the second week after birth.

The genetic tyrosinemias

The genetic tyrosinemias are characterized by the accumulation of tyrosine in body fluids and tissues. The most severe form of tyrosinemia, Type I, is a devastating disorder of childhood that causes liver failure, painful neurologic crises, rickets, and hepatocarcinoma. This disorder is caused by a deficiency of fumarylacetoacetate hydrolase (FAH). If untreated, death typically occurs at less than 2 years of age, with some chronic forms allowing longer survival. It has a prevalence of about 1 in 100,000 newborns in the general population. Oculocutaneous tyrosinemia, Type II, is caused by a deficiency of tyrosine aminotransferase (TAT). It clinically presents with hyperkeratotic plaques on the hands and soles of the feet and photophobia due to deposition of tyrosine crystals within the cornea. Tyrosinemia Type III is an extremely rare disorder caused by a deficiency of 4-hydroxyphenylpyruvic dioxygenase. It has been associated with ataxia and mild mental retardation. These disorders are diagnosed by observing elevated tyrosine by plasma amino acid chromatography and characteristic tyrosine metabolites by urine organic acid analysis. In tyrosinemia Type I, methionine is also elevated, reflecting impaired hepatocellular function. Urine organic acids show elevated p-hydroxy-phenyl organic acids in each type of tyrosinemia, and the pathognomic succinylacetone in tyrosinemia Type I. Diagnosis can be confirmed by enzyme or molecular studies in tyrosinemia Type I. Therapy consists of a diet low in phenylalanine and tyrosine for each of the tyrosinemias and 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC) for tyrosinemia Type I.

Evaluation of dichloroacetate treatment in a murine model of hereditary tyrosinemia type 1

Hereditary tyrosinemia type 1 (HT1) is an autosomal recessive disease severely affecting liver and kidney and is caused by a deficiency in fumarylacetoacetate hydrolase (FAH). Administration of 2-(2-nitro-4-trifluoro-methylbenzyol)-1,3 cyclohexanedione (NTBC) improves the HT1 phenotype but some patients do not respond to NTBC therapy. The objective of the present study was to evaluate whether administration of dichloroacetate, an inhibitor of maleyl acetoacetate isomerase (MAAI) to FAH-knockout mice could prevent acute pathological injury caused by NTBC withdrawal. DCA (0.5 and 5 g/L) was given in combination with a standard diet or with a tyrosine-restricted diet. With the low-tyrosine diet body weight loss and most of hepatic and renal injuries were prevented regardless the DCA dose. The administration of DCA with a standard diet did not prevent damage nor the oxidative stress response nor the AFP induction seen in FAH-knockout mice. DCA was shown to inhibit hepatic MAAI activity to 86% (0.5 g/L) and 94% (5 g/L) of untreated wild-type mice. Interestingly, FAH −/− mice deprived of NTBC (NTBC-OFF) and NTBC-treated FAH-knockout mice had similar low hepatic MAAI activity levels, corresponding to 10–20% of control. Thus the failure of DCA treatment in FAH −/− mice seems to be attributed to the residual MAAI activity, high enough to lead to FAA accumulation and HT1 phenotype.