The pathogenesis of molybdenum cofactor deficiency, its delay by maternal clearance, and its expression pattern in microarray analysis

Fosdenopterin: a First-in-class Synthetic Cyclic Pyranopterin Monophosphate for the Treatment of Molybdenum Cofactor Deficiency Type A

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Molybdenum cofactor deficiency type A: Prenatal monitoring using MRI

Molybdenum cofactor deficiency type A (MoCD-A) is an inborn error of metabolism presenting early after birth with severe seizures. Recently, experimental substitution treatment with cyclic pyranopterin monophosphate (cPMP) has become available. Because prenatal data is scarce, we report data of prenatal Magnetic Resonance Imaging (MRI) in two cases with MoCD-A demonstrating signs of possible early brain injury. Prenatal MRI can be used for monitoring in MoCD-A to guide decision-making in timing of delivery.

Sulfite Oxidase Activity of Cytochrome c: Role of Hydrogen Peroxide

In humans, sulfite is generated endogenously by the metabolism of sulfur containing amino acids such as methionine and cysteine. Sulfite is also formed from exposure to sulfur dioxide, one of the major environmental pollutants. Sulfite is used as an antioxidant and preservative in dried fruits, vegetables, and beverages such as wine. Sulfite is also used as a stabilizer in many drugs. Sulfite toxicity has been associated with allergic reactions characterized by sulfite sensitivity, asthma, and anaphylactic shock. Sulfite is also toxic to neurons and cardiovascular cells. Recent studies suggest that the cytotoxicity of sulfite is mediated by free radicals; however, molecular mechanisms involved in sulfite toxicity are not fully understood. Cytochrome c (cyt c) is known to participate in mitochondrial respiration and has antioxidant and peroxidase activities. Studies were performed to understand the related mechanism of oxidation of sulfite and radical generation by ferric cytochrome c (Fe³⁺cyt c) in the absence and presence of H₂O₂. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with sulfite, Fe³⁺cyt c, and H₂O₂. An EPR spectrum corresponding to the sulfite radical adducts of DMPO (DMPO-SO₃^-) was obtained. The amount of DMPO-SO3- formed from the oxidation of sulfite by the Fe³⁺cyt c increased with sulfite concentration. In addition, the amount of DMPO-SO3- formed by the peroxidase activity of Fe³⁺cyt c also increased with sulfite and H₂O₂ concentration. From these results, we propose a mechanism in which the Fe³⁺cyt c and its peroxidase activity oxidizes sulfite to sulfite radical. Our results suggest that Fe³⁺cyt c could have a novel role in the deleterious effects of sulfite in biological systems due to increased production of sulfite radical. It also shows that the increased production of sulfite radical may be responsible for neurotoxicity and some of the injuries which occur to humans born with molybdenum cofactor and sulfite oxidase deficiencies.

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Cytochrome c oxidizes sulfite to sulfite radical.

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In the presence of H₂O₂, sulfite radical generation from cyt c increases.

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The formation of sulfite radical is sulfite concentration dependent.

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This mechanism of sulfite radical formation may be important in sulfite toxicity.

Neuroprotective and antioxidant activities of bamboo salt soy sauce against H2O2-induced oxidative stress in rat cortical neurons

Bamboo salt (BS) and soy sauce (SS) are traditional foods in Asia, which contain antioxidants that have cytoprotective effects on the body. The majority of SS products contain high levels of common salt, consumption of which has been associated with numerous detrimental effects on the body. However, BS may be considered a healthier substitute to common salt. The present study hypothesized that SS made from BS, known as bamboo salt soy sauce (BSSS), may possess enhanced cytoprotective properties; this was evaluated using a hydrogen peroxide (H₂O₂)-induced neuronal cell death rat model. Rat neuronal cells were pretreated with various concentrations (0.001, 0.01, 0.1, 1 and 10%) of BSSS, traditional soy sauce (TRSS) and brewed soy sauce (BRSS), and were subsequently exposed to H₂O₂ (100 µM). The viability of neuronal cells, and the occurrence of DNA fragmentation, was subsequently examined. Pretreatment of neuronal cells with TRSS and BRSS reduced cell viability in a concentration-dependent manner, whereas neuronal cells pretreated with BSSS exhibited increased cell viability, as compared with non-treated neuronal cells. Furthermore, neuronal cells pretreated with 0.01% BSSS exhibited the greatest increase in viability. Exposure of neuronal cells to H₂O₂ significantly increased the levels of reactive oxygen species (ROS), B-cell lymphoma 2-associated X protein, poly (ADP-ribose), cleaved poly (ADP-ribose) polymerase, cytochrome c, apoptosis-inducing factor, cleaved caspase-9 and cleaved caspase-3, in all cases. Pretreatment of neuronal cells with BSSS significantly reduced the levels of ROS generated by H₂O₂, and increased the levels of phosphorylated AKT and phosphorylated glycogen synthase kinase-3β. Furthermore, the observed effects of BSSS could be blocked by administration of 10 µM LY294002, a phosphatidylinositol 3-kinase inhibitor. The results of the present study suggested that BSSS may exert positive neuroprotective effects against H₂O₂-induced cell death by reducing oxidative stress, enhancing survival signaling, and inhibiting death signals.

Elucidating how bamboo salt interacts with supported lipid membranes: influence of alkalinity on membrane fluidity

Bamboo salt is a traditional medicine produced from sea salt. It is widely used in Oriental medicine and is an alkalizing agent with reported antiinflammatory, antimicrobial and chemotherapeutic properties. Notwithstanding, linking specific molecular mechanisms with these properties has been challenging to establish in biological systems. In part, this issue may be related to bamboo salt eliciting nonspecific effects on components found within these systems. Herein, we investigated the effects of bamboo salt solution on supported lipid bilayers as a model system to characterize the interaction between lipid membranes and bamboo salt. The atomic composition of unprocessed and processed bamboo salts was first analyzed by mass spectrometry, and we identified several elements that have not been previously reported in other bamboo salt preparations. The alkalinity of hydrated samples was also measured and determined to be between pH 10 and 11 for bamboo salts. The effect of processed bamboo salt solutions on the fluidic properties of a supported lipid bilayer on glass was next investigated by fluorescence recovery after photobleaching (FRAP) analysis. It was demonstrated that, with increasing ionic strength of the bamboo salt solution, the fluidity of a lipid bilayer increased. On the contrary, increasing the ionic strength of near-neutral buffer solutions with sodium chloride salt diminished fluidity. To reconcile these two observations, we identified that solution alkalinity is critical for the effects of bamboo salt on membrane fluidity, as confirmed using three additional commercial bamboo salt preparations. Extended-DLVO model calculations support that the effects of bamboo salt on lipid membranes are due to the alkalinity imparting a stronger hydration force. Collectively, the results of this work demonstrate that processing of bamboo salt strongly affects its atomic composition and that the alkalinity of bamboo salt solutions contributes to its effect on membrane fluidity.

Molybdopterin biosynthesis-Mechanistic studies on a novel MoaA catalyzed insertion of a purine carbon into the ribose of GTP

The first step in the biosynthesis of the molybdopterin cofactor involves an unprecedented insertion of the purine C8 carbon between the C2' and C3' carbons of the ribose moiety of GTP. Here we review mechanistic studies on this remarkable transformation. This article is part of a Special Issue entitled: Cofactor-dependent proteins: evolution, chemical diversity and bio-applications.

Early features in neuroimaging of two siblings with molybdenum cofactor deficiency

We report the features of neuroimaging within 24 hours after birth in 2 siblings with molybdenum cofactor deficiency. The first sibling was delivered by emergency cesarean section because of fetal distress and showed pedaling and crawling seizures soon after birth. Brain ultrasound revealed subcortical multicystic lesions in the frontal white matter, and brain MRI at 4 hours after birth showed restricted diffusion in the entire cortex, except for the area adjacent to the subcortical cysts. The second sibling was delivered by elective cesarean section. Cystic lesions were seen in the frontal white matter on ultrasound, and brain MRI showed low signal intensity on T1-weighted image and high signal intensity on T2-weighted image in bifrontal white matter within 24 hours after birth, at which time the infant sucked sluggishly. Clonic spasm appeared at 29 hours after birth. The corpus callosum could not be seen clearly on ultrasound or MRI in both infants. Cortical atrophy and white matter cystic lesions spread to the entire hemisphere and resulted in severe brain atrophy within ~1 month in both infants. Subcortical multicystic lesions on ultrasound and a cortex with nonuniform, widespread, restricted diffusion on diffusion-weighted images are early features of neuroimaging in patients with molybdenum cofactor deficiency type A.

Distinctive pattern of restricted diffusion in a neonate with molybdenum cofactor deficiency

We present a neonate with molybdenum cofactor deficiency imaged at presentation during the first month of life and at 5 months with diffusion-weighted brain MRI. While the imaging features of this disease have previously been reported, this case highlights a distinctive initial pattern of widespread restricted diffusion involving cortex at the depths of sulci. Other case series have published diffusion-weighted images (DWI) with this pattern but never specifically commented on this finding. This distinct DWI pattern also accounts for the configuration of ulegyria frequently described on later imaging. Early recognition of this unique initial DWI pattern could avoid misdiagnosis and better direct counseling and management.

The molybdenum cofactor

The transition element molybdenum needs to be complexed by a special cofactor to gain catalytic activity. Molybdenum is bound to a unique pterin, thus forming the molybdenum cofactor (Moco), which, in different variants, is the active compound at the catalytic site of all molybdenum-containing enzymes in nature, except bacterial molybdenum nitrogenase. The biosynthesis of Moco involves the complex interaction of six proteins and is a process of four steps, which also require iron, ATP, and copper. After its synthesis, Moco is distributed, involving Moco-binding proteins. A deficiency in the biosynthesis of Moco has lethal consequences for the respective organisms.

Molybdenum cofactor deficiency mimics cerebral palsy: differentiating factors for diagnosis

We describe an infant with molybdenum cofactor deficiency, initially diagnosed as cerebral palsy. Clinical features of molybdenum cofactor deficiency, e.g., neonatal seizures, hypertonus/hypotonus, and feeding and respiratory difficulties, resemble those of neonatal hypoxic-ischemic encephalopathy. Our patient, a 2-year-old boy, presented with spastic quadriplegia and mental retardation. He manifested intractable neonatal seizures and diffuse cerebral atrophy. When admitted with bronchitis at age 18 months, his uric acid levels in blood and urine were undetectable. A urinary sulfite test revealed positive results. Further tests revealed elevated urinary levels of xanthine, hypoxanthine, and S-sulfocystein. Sequencing of the MOCS2A gene revealed heterozygosity for c.[265T>C] + [266A>G], diagnosed as molybdenum cofactor deficiency type B. Neonatal seizures, progressive cerebral atrophy, and low serum levels of uric acid may provide diagnostic clues in patients with cerebral palsy of undetermined cause.

Clinical neuroimaging features and outcome in molybdenum cofactor deficiency

Molybdenum cofactor deficiency predominantly affects the central nervous system. There are limited data on long-term outcome or brain magnetic resonance imaging (MRI) features. We examined the clinical, brain MRI, biochemical, genetic, and electroencephalographic features and outcome in 8 children with a diagnosis of molybdenum cofactor deficiency observed in our institution over 10 years. Two modes of presentation were identified: early (classical) onset with predominantly epileptic encephalopathy in 6 neonates, and late (atypical) with global developmental impairment in 2 children. Children in both groups had varying degrees of motor, language, and visual impairment. There were no deaths. Brain MRI demonstrated cerebral infarction in all but one child in the atypical group. Distinctive features were best observed on early brain MRI: acute symmetrical involvement of the globus pallidi and subthalamic regions coexisting with older cerebral hemisphere infarction, chronic lesions suggestive of a prenatal insult, pontocerebellar hypoplasia with retrocerebellar cyst, and presence of a distinctive band at the cortical/subcortical white matter. Sequential imaging revealed progressive pontine atrophy and enlargement of retrocerebellar cyst. The brain MRI of one child with atypical presentation (verbal dyspraxia, lens dislocation) showed symmetrical cerebellar deep nuclei signal abnormality without cerebral infarction. Imaging pattern on early brain MRI (<1 week) may prompt the diagnosis, potentially allowing early treatment and disease modifications.

Arachnomelia syndrome in Simmental cattle is caused by a homozygous 2-bp deletion in the molybdenum cofactor synthesis step 1 gene (MOCS1)

Background

Arachnomelia syndrome is an autosomal recessive inherited disease in cattle. Affected calves die around birth and show malformations of the skeleton mainly affecting the legs, the spinal column and the skull. A number of arachnomelia syndrome affected Simmental calves were recently detected by a surveillance system of anomalies with a peak of more than 120 recorded cases in the year 2006. The causative mutation was previously mapped to a 9 cM-region on bovine chromosome 23. We herein report the fine-mapping and identification of the gene causing arachnomelia syndrome in Simmental cattle.

Results

By using a dense set of markers, the arachnomelia syndrome linked region could be refined to 1.5 cM harbouring three protein coding genes. Comparative sequencing of these genes revealed a two-bp-deletion in the bovine MOCS1 gene resulting in a frame-shift and a premature termination codon. We genotyped affected calves and their ancestors and found that all affected were homozygous for the deletion whereas all carriers were heterozygous. Furthermore, cattle from the same population, but not directly related to known carriers mostly showed the wild type genotype.

Conclusions

MOCS1 encodes two proteins that are involved in the first synthesis step of molybdenum cofactor. A non functional sulfite-oxydase, one of the enzymes requiring molybdenum cofactor, leads to a similar pathology in Brown Swiss cattle. In combination the perfect association of the mutation with the phenotype and the obvious disruption of protein translation provide strong evidence for the causality of the MOCS1 mutation. Our results are the first example for an oligogenic lethal inherited disease in cattle. Furthermore, they show the potential involvement of sulfite metabolism in aberrant bone development.

Chronological changes of the amplitude-integrated EEG in a neonate with molybdenum cofactor deficiency

Molybdenum cofactor (Moco) deficiency is a rare neurometabolic disorder, characterized by neurological impairment and refractive seizures, due to toxic accumulation of sulfite in the brain. Earlier it was suggested that in Moco-deficient humans maternal clearance of neurotoxic metabolites prevents prenatal brain damage. However, limited data are available about the time profile in which neurophysiologic deterioration occurs after birth. The amplitude-integrated electroencephalography (aEEG) is a bedside method in neonates to monitor cerebral recovery after hypoxic-ischemic insults, detect epileptic activity, and evaluate antiepileptic drug treatment. We describe a chronological series of changes in aEEG tracings in a neonate with Moco deficiency. He presented with myoclonic spasms and hypertonicity a few hours after birth, however, the aEEG pattern was still normal. Within 2 days, the aEEG rapidly changed into a burst suppression pattern with repetitive seizures. After antiepileptic treatment, the aEEG remained abnormal. In this patient, the normal aEEG pattern at birth may have been due to maternal clearance of sulfite in utero. After birth, accumulation of sulfite causes progressive brain damage, reflected by the progressive depression of the aEEG tracings. This is in agreement with the results from a Moco-deficient mouse model, suggesting that maternal sulfite clearance suppresses prenatal brain damage. To our knowledge, this is the first case report describing the chronological changes in the aEEG pattern in a Moco-deficient patient. Insight into the time profile in which neurologic deterioration in Moco-deficient humans occurs is essential, especially when potential treatment strategies are being evaluated.

Maternal uniparental isodisomy is responsible for serious molybdenum cofactor deficiency

Molybdenum cofactor (MoCo) deficiency is a rare autosomal recessive inherited metabolic disorder resulting in the combined deficiency of aldehyde oxidase, xanthine dehydrogenase, and sulfite oxidase. We report a male infant with MoCo deficiency whose clinical findings consisted of microcephaly, intractable seizures soon after birth, feeding difficulties, and developmental delay. Sequencing of MOCS1, MOCS2, and GEPH genes, and single nucleotide polymorphism genotyping array analysis showed, to our knowledge, unusual inheritance of MoCo deficiency/maternal uniparental isodisomy for the first time in the literature. At 10 months of age, he now has microcephaly and developmental delay, and his seizures are controlled with phenobarbital, clonozepam, and vigabatrin therapy.

Molybdenum cofactor deficiency: clinical features in a Turkish patient

The molybdenum cofactor is essential for the function of sulphite oxidase, xanthine dehydrogenase, and aldehyde oxidase enzymes. Molybdenum cofactor deficiency (MoCD) is a fatal disease resulting in severe neurological damage and death in early childhood. MoCD is an autosomal recessive condition which may mimic ischaemic encephalopathy. Although milder cases with later onset and less severe symptoms have been identified, the classic presentation involves neonatal seizures, progressive encephalopathy and death at an early age. There is currently no effective therapy, and the prognosis is poor. The disorder should be considered in all cases of intractable seizures in the newborn period and infants with clinical and radiological features of ischaemic encephalopathy, especially when no obvious lesion is detected. Blood uric acid measurement should be included in the battery of tests to be performed in all neonates' refractory seizures. We reported here an infant with MoCD who presented with hypoxic ischaemic encephalopathy and identified a novel mutation, c.130C>T in cDNA of the MOCS2 gene from the infant.

Long-term rescue of a lethal inherited disease by adeno-associated virus-mediated gene transfer in a mouse model of molybdenum-cofactor deficiency

Molybdenum cofactor (MoCo) deficiency is a progressive neurological disorder that inevitably leads to early childhood death because of the lack of any effective therapy. In a mouse model of MoCo deficiency type A, the most frequent form of this autosomal recessively inherited disease, the affected animals show the biochemical characteristics of sulphite and xanthine intoxication and do not survive >2 wk after birth. We have constructed a recombinant-expression cassette for the gene MOCS1, which, via alternative splicing, facilitates the expression of the proteins MOCS1A and MOCS1B, both of which are necessary for the formation of a first intermediate, cyclic pyranopterin monophosphate (cPMP), within the biosynthetic pathway leading to active MoCo. A recombinant adeno-associated virus (AAV) vector was used to express the artificial MOCS1 minigene, in an attempt to cure the lethal MOCS1-deficient phenotype. The vector was used to transduce Mocs1-deficient mice at both 1 and 4 d after birth or, after a pretreatment with purified cPMP, at 40 d after birth. We report here that all Mocs1-deficient animals injected with a control AAV-enhanced green fluorescent protein vector died approximately 8 d after birth or after withdrawal of cPMP supplementation, whereas AAV-MOCS1-transduced animals show significantly increased longevity. A single intrahepatic injection of AAV-MOCS1 resulted in fertile adult animals without any pathological phenotypes.

Individualized markers optimize class prediction of microarray data

Background

Identification of molecular markers for the classification of microarray data is a challenging task. Despite the evident dissimilarity in various characteristics of biological samples belonging to the same category, most of the marker – selection and classification methods do not consider this variability. In general, feature selection methods aim at identifying a common set of genes whose combined expression profiles can accurately predict the category of all samples. Here, we argue that this simplified approach is often unable to capture the complexity of a disease phenotype and we propose an alternative method that takes into account the individuality of each patient-sample.

Results

Instead of using the same features for the classification of all samples, the proposed technique starts by creating a pool of informative gene-features. For each sample, the method selects a subset of these features whose expression profiles are most likely to accurately predict the sample's category. Different subsets are utilized for different samples and the outcomes are combined in a hierarchical framework for the classification of all samples. Moreover, this approach can innately identify subgroups of samples within a given class which share common feature sets thus highlighting the effect of individuality on gene expression.

Conclusion

In addition to high classification accuracy, the proposed method offers a more individualized approach for the identification of biological markers, which may help in better understanding the molecular background of a disease and emphasize the need for more flexible medical interventions.

Ten novel mutations in the molybdenum cofactor genes MOCS1 and MOCS2 and in vitro characterization of a MOCS2 mutation that abolishes the binding ability of molybdopterin synthase

Molybdenum cofactor deficiency (MIM#252150) is a severe autosomal-recessive disorder with a devastating outcome. The cofactor is the product of a complex biosynthetic pathway involving four different genes (MOCS1, MOCS2, MOCS3 and GEPH). This disorder is caused almost exclusively by mutations in the MOCS1 or MOCS2 genes. Mutations affecting this biosynthetic pathway result in a lethal phenotype manifested by progressive neurological damage via the inactivation of the molybdenum cofactor-dependent enzyme, sulphite oxidase. Here we describe a total of ten novel disease-causing mutations in the MOCS1 and MOCS2 genes. Nine out of these ten mutations were classified as pathogenic in nature, since they create a stop codon, affect constitutive splice site positions, or change strictly conserved motifs. The tenth mutation abolishes the stop codon of the MOCS2B gene, thus elongating the corresponding protein. The mutation was expressed in vitro and was found to abolish the binding affinities of the large subunit of molybdopterin synthase (MOCS2B) for both precursor Z and the small subunit of molybdopterin synthase (MOCS2A).