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Biomedical subjects

Stephen D Cederbaum

Publications and source records attributed to Stephen D Cederbaum.

17 recordsLinked to original sources
PubMed2006

Diagnostic yield of chromosome analysis in patients with developmental delay or mental retardation who are otherwise nondysmorphic.

There is a standard recommendation that chromosomes be obtained in any patient who presents with developmental delay (DD) or mental retardation (MR) regardless of whether or not they have dysmorphic features. Increasingly, if patients are physically well-formed, the option to perform a karyotype is questioned because of the presumed low yield of a chromosomal abnormality. We hypothesize that patients with DD/MR who are non-dysmorphic do not have abnormal chromosomes at a rate high enough to warrant obtaining a karyotype on all patients in this population. A retrospective analysis of patients with DD/MR who were non-dysmorphic was performed. The total number of subjects was 134. Of these, 120 patients were recommended to have high-resolution chromosomes performed, among whom seven were lost to follow-up. In the remaining 113 patients, all had normal karyotypes. Three subjects were found to have fragile X syndrome, accounting for 3% of the males. One subject had a pathological mutation in MECP2. Our yield of chromosome analysis in non-dysmorphic patients with DD/MR is less than that previously described. The role of array-comparative genomic hybridization (array-CGH) as an auxiliary or alternative procedure in this patient population will be discussed.

Child↗
PubMed2006

Clinical and functional characterization of a human ORNT1 mutation (T32R) in the hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome.

We studied two related families (HHH013 and HHH015) with the hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, a disorder of the urea cycle and ornithine degradation pathway, who have the same novel ornithine transporter (ORNT1) genotype (T32R) but a variable phenotype. Both HHH015 patients are doing well in school and are clinically stable; conversely, the three affected HHH013 siblings had academic difficulties and one suffered recurrent episodes of hyperammonemia and ultimately died. Overexpression studies revealed that the product of the ORNT1-T32R allele has residual function. Ornithine transport studies in HHH015 fibroblasts, however, showed basal activity similar to fibroblasts carrying nonfunctional ORNT1 alleles. We also examined two potential modifying factors, the ORNT2 gene and the mitochondrial DNA lineage (haplogroup). Haplogroups, associated with specific diseases, are hypothesized to influence mitochondrial function. Results demonstrated that both HHH015 patients are heterozygous for an ORNT2 gain of function polymorphism and belong to haplogroup A whereas the HHH013 siblings carry the wild-type ORNT2 and are haplogroup H. These observations suggest that the ORNT1 genotype cannot predict the phenotype of HHH patients. The reason for the phenotypic variability is unknown, but factors such as redundant transporters and mitochondrial lineage may contribute to the neuropathophysiology of HHH patients.

Adolescent↗
PubMed2006

Ornithine deficiency in the arginase double knockout mouse.

Knockout mouse models have been created to study the consequences of deficiencies in arginase AI and AII, both individually and combined. The AI knockout animals die by 14 days of age from hyperammonemia, while the AII knockout has no obvious phenotype. The double knockout (AI(-/-)/AII(-/-)) exhibits the phenotype of the AI-deficient mice, with the additional absence of AII not exacerbating the observed phenotype of the AI knockout animals. Plasma amino acid measurements in the double knockout have shown arginine levels increased roughly 100-fold and ornithine decreased roughly 10-fold as compared to wildtype. Liver ornithine levels were reduced to 2% of normal in the double knockout with arginine very highly elevated. Arginine and ornithine were also altered in other tissues in the double knockout mice, such as kidney, brain, and small intestine. This is the first demonstration that the fatal hyperammonemia in the AI knockout mouse is almost certainly due to ornithine deficiency, the amino acid needed to drive the urea cycle. Others have shown that the expression of ornithine aminotransferase (OAT) rapidly decreases in the intestine at the same age when the AI-deficient animals die, indicating that this enzyme is critical to the maintenance of ornithine homeostasis, at least at this early stage of mouse development. Although most human AI-deficient patients have no symptomatic hyperammonemia at birth, it is possible that clinically significant ornithine deficiency is already present.

Animals↗
PubMed2006

Loss of arginase I results in increased proliferation of neural stem cells.

Loss of arginase I (AI) results in a metabolic disorder characterized by growth retardation, increased mental impairment and spasticity, and potentially fatal hyperammonemia. This syndrome plus a growing body of evidence supports a role for arginase and arginine metabolites in normal neuronal development and function. Here we report our initial observations of the effects of AI loss on proliferation and differentiation of neural stem cells (NSCs) isolated from the germinal zones of embryonic and newborn AI knockout (KO) mice compared with heterozygous (HET) and wild-type (WT) control animals. By using both short and long-term proliferation assays (3 and 10 days, respectively), we found a 1.5-2-fold increase in the number of KO cells compared with WT. FACS analysis showed an increase in KO cells in the synthesis phase of the cell cycle vs. WT cells. After NSC differentiation, AI-deficient cells expressed beta-tubulin, SMI81 (SNAP25), glial fibrillary acidic protein, and CNPase, which are markers consistent with neurons, astrocytes, and oligodendrocytes. Many KO cells exhibited a more mature morphology and expressed mature neuronal markers that were decreased or not present in HET or WT cells. Limited, comparative expression array and quantitative RT-PCR analysis identified differences in the levels of several mRNAs encoding structural, signaling, and arginine metabolism proteins between KO and WT cells. The consequence of these changes may contribute to the differential phenotypes of KO vs. WT cells. It appears that AI may play an important and unanticipated role in growth and development of NSCs.

Animals↗
PubMed2005

Clinical, pathological, and biochemical studies in a patient with propionic acidemia and fatal cardiomyopathy.

A patient diagnosed at 9 months with a milder form of propionic acidemia was functioning at a near normal intellectual level and a normal neurological level at age 8. After 2-week history of feeling "poorly" but functioning normally, she became acutely ill and succumbed to heart failure and ventricular fibrillation in 12 h. At post-mortem the heart was hypertrophied and had low carnitine levels, despite carnitine supplementation and repeatedly normal plasma carnitine levels. The findings in this patient provide a possible mechanism for the cardiac complications that are becoming more apparent in propionic acidemia.

Amino Acid Metabolism, Inborn Errors↗
PubMed2004

Hyperargininemia due to liver arginase deficiency.

The urea cycle is a series of six reactions necessary to rid the body of the nitrogen generated by the metabolism, primarily of amino acids, from the diet or released as the result of endogenous protein catabolism. Arginase is the sixth and final enzyme of this cycle. Arginase catalyzes the conversion of arginine to urea and ornithine, the latter recycled to continue the cycle. Hyperargininemia due to arginase deficiency is inherited in an autosomal recessive manner and gene for arginase, designated AI, has been cloned. Unlike the other urea cycle enzymes, a second gene encoding arginase, with similar structural properties and enzyme characteristics, exists and has been named Arginase II (AII). Comprehensive histories and physical examinations confirm a strikingly uniform clinical picture and one notably different from patients with other urea cycle disorders. This condition rarely presents in the neonatal period and first symptoms typically present in children between 2 and 4 years of age. First symptoms are often neurologically based. If untreated, symptoms are progressive with a gradual loss of developmental milestones. With adherence to a dietary and drug regimen, a favorable outcome can be expected, with cessation of further neurological deterioration and in some instances, of improvement. This article summarizes the clinical course of selected patients who represent the full spectrum of presentations of arginase deficiency. In addition to the clinical characterization of this disorder; the biochemical, enzymatic, and molecular evidence of disease is summarized. Treatment and prenatal diagnosis are also discussed.

Arginase↗
PubMed2004

Arginases I and II: do their functions overlap?

Arginase, often perceived solely as the last of the now six enzymes of the urea cycle, exists in two forms and has a broad tissue distribution. A cytosolic form, AI, is highly expressed in the liver and is thought to be primarily involved in ureagenesis. A mitochondrial form, AII, has been thought to be more widely expressed and to be involved in the biosynthesis of polyamines, the amino acids ornithine, proline, and glutamate and in the inflammatory process, among others. This paper will address recent experiments that cast some doubt on the validity of these distinctions. Studies have now suggested that macrophages may express AI or AII in different experimental conditions, both in vivo and in vitro. In contrast, most studies, at least in cell culture, suggest that AII may be most highly expressed in cancers of a number of different types. Inhibition of arginase activity in vivo and in vitro has implicated this activity in maintaining ornithine levels for polyamine synthesis. In situ and "quantitative" PCR studies in mouse have demonstrated that AI and not AII is the predominant isoform expressed during development and in the majority of organs. Mouse knockout models for both AI and AII have been produced and are available to address their functions. Surprisingly, the AII knockout animal has no apparent phenotype except for some diminished fertility in homozygous males, consistent with the belief that AII, highly expressed in prostate, is important for sperm function in semen. The AI knockout animal has a more dramatic phenotype and dies at 10-12 days of life of hyperammonemia. The reason for the prolonged survival, as compared to other urea cycle knockout animals, may be due to the later occurrence of hypo-ornithinemia, a contention not yet proven. Transgenic manipulation of the AI knockout animal and breeding the AI and AII knockouts into single animals may address the ability of AII to rescue animals from some of the metabolic consequences of AI deficiency, as appears to happen in man. Newborn screening has given particular hope to patients affected by arginase (AI) deficiency. Increased arginine appears to be detectable by newborn screening with tandem mass spectrometry and the past years continue to demonstrate the therapeutic effectiveness of dietary management of the disorder, with patients treated from birth remaining normal and those treated late, ceasing to deteriorate and even improving in cognitive and physical functioning. Finally, prenatal diagnosis appears to be possible as was predicted, but never proven, some years ago.

Animals↗
PubMed2003

Widespread expression of arginase I in mouse tissues. Biochemical and physiological implications.

Arginase I (AI), the fifth and final enzyme of the urea cycle, detoxifies ammonia as part of the urea cycle. In previous studies from others, AI was not found in extrahepatic tissues except in primate blood cells, and its roles outside the urea cycle have not been well recognized. In this study we undertook an extensive analysis of arginase expression in postnatal mouse tissues by in situ hybridization (ISH) and RT-PCR. We also compared arginase expression patterns with those of ornithine decarboxylase (ODC) and ornithine aminotransferase (OAT). We found that, outside of liver, AI was expressed in many tissues and cells such as the salivary gland, esophagus, stomach, pancreas, thymus, leukocytes, skin, preputial gland, uterus and sympathetic ganglia. The expression was much wider than that of arginase II, which was highly expressed only in the intestine and kidney. Several co-localization patterns of AI, ODC, and OAT have been found: (a) AI was co-localized with ODC alone in some tissues; (b) AI was co-localized with both OAT and ODC in a few tissues; (c) AI was not co-localized with OAT alone in any of the tissues examined; and (d) AI was not co-localized with either ODC or OAT in some tissues. In contrast, AII was not co-localized with either ODC or OAT alone in any of the tissues studied, and co-localization of AII with ODC and OAT was found only in the small intestine. The co-localization patterns of arginase, ODC, and OAT suggested that AI plays different roles in different tissues. The main roles of AI are regulation of arginine concentration by degrading arginine and production of ornithine for polyamine biosynthesis, but AI may not be the principal enzyme for regulating glutamate biosynthesis in tissues and cells.

Animals↗
PubMed2002

Helicobacter pylori induces macrophage apoptosis by activation of arginase II.

Helicobacter pylori infection induces innate immune responses in macrophages, contributing to mucosal inflammation and damage. Macrophage apoptosis is important in the pathogenesis of mucosal infections but has not been studied with H. pylori. NO derived from inducible NO synthase (iNOS) can activate macrophage apoptosis. Arginase competes with iNOS by converting L-arginine to L-ornithine. Since we reported that H. pylori induces iNOS in macrophages, we now determined whether this bacterium induces arginase and the effect of this activation on apoptosis. NF-kappa B-dependent induction of arginase II, but not arginase I, was observed in RAW 264.7 macrophages cocultured with H. pylori. The time course of apoptosis matched those of both arginase and iNOS activities. Surprisingly, apoptosis was blocked by the arginase inhibitors N(omega)-hydroxy-L-arginine or N(omega)-hydroxy-nor-L-arginine, but not by the iNOS inhibitor N-iminoethyl-L-lysine. These findings were confirmed in peritoneal macrophages from iNOS-deficient mice and were not dependent on bacterial-macrophage contact. Ornithine decarboxylase (ODC), which metabolizes L-ornithine to polyamines, was also induced in H. pylori-stimulated macrophages. Apoptosis was abolished by inhibition of ODC and was restored by the polyamines spermidine and spermine. We also demonstrate that arginase II expression is up-regulated in both murine and human H. pylori gastritis tissues, indicating the likely in vivo relevance of our findings. Therefore, we describe arginase- and ODC-dependent macrophage apoptosis, which implicates polyamines in the pathophysiology of H. pylori infection.

Animals↗
PubMed2002

Cloning and characterization of human agmatinase.

Arginine decarboxylase (ADC) and agmatinase are part of an operon in Escherichia coli, which constitutes the primary pathway of polyamine synthesis from arginine. This pathway is also known to exist in plants, but until recently, neither agmatine nor ADC, the enzyme that synthesizes it, nor agmatinase the enzyme that is responsible for conversion of agmatine to putrescine, were known to exist in man or other mammals. We describe here the cloning of the agmatinase gene and the tissue distribution of its transcription product. Human agmatinase contains 352 amino acid residues and has a calculated molecular weight of 37,688 kDa. It has 56% similarity to E. coli agmatinase and 42% similarity to human arginases I and II and shares highly conserved substrate-binding domains with these well-characterized enzymes.

Amino Acid Sequence↗
PubMed2002

Arginase expression in mouse embryonic development.

We are using the model of the developing mouse embryo to elucidate the pattern of arginase expression in mammalian cells in normal animals and in arginase I (AI) deficiency during development by digoxigenin-labeled RNA in situ hybridization. Our goal is to understand the regulation of these isozymes, with the expectation that this knowledge will help patients suffering from AI deficiency. We found that AI mRNA was widely and strongly expressed in the normal developing mouse embryo; in contrast, a relatively strong AII mRNA signal was found only in the intestine. In the AI knockout mouse embryo, no AII overexpression was found. These results indicated that arginases are needed in mouse embryonic development and AI is the principal form required. The strong AI expression in the peripheral nervous system suggests that the pathogenesis of the neurological retardation in AI deficiency may be conditioned by AI deficiency in the nervous system during embryonic development.

Animals↗
PubMed2002

Expression of the liver form of arginase in erythrocytes.

Arginase I (AI) has a critical function in mammalian liver as the final enzyme in the urea cycle responsible for the disposal of ammonia from protein catabolism. AI is also expressed in various extrahepatic tissues and may play a role in regulating arginine levels and in providing ornithine for biosynthetic reactions that generate various critical intermediary metabolites such as glutamate, glutamine, GABA, agmatine, polyamines, creatine, proline, and nitric oxide. AI is expressed in red blood cells (RBCs) only in humans and certain higher primates. Macaca fascicularis has been identified as an evolutionary transition species in which RBC-AI expression is co-dominantly regulated. The M. fascicularis AI gene was analyzed to understand AI expression in erythrocytes. Erythroid progenitor cells [nucleated red blood cells (nRBCs)] isolated from cord blood were utilized to demonstrate AI expression by immunocytochemical staining using anti-AI antibody. Introduction of EGFP reporter vectors into nRBC showed that the proximal 1.2 kbp upstream of the AI gene is sufficient for AI expression. Expression of a second arginase isoform, AII, in nRBCs was discovered by cDNA profiling. This contrasts with mature fetal or adult RBCs which contain only the AI protein. In addition, an alternatively spliced AI (AI(')) variant was observed from erythroid mRNA analysis with an alternative splice acceptor site located within intron 2, causing the insertion of eight additional amino acids yet retaining significant enzymatic activity.

Alternative Splicing↗
PubMed2002

Carnitine membrane transporter deficiency: a long-term follow up and OCTN2 mutation in the first documented case of primary carnitine deficiency.

Three older patients were diagnosed with systemic carnitine deficiency in childhood nearly a generation ago and have together been treated for more than 50 patient years. Treatment improved tissue carnitine stores (proven in two) and eliminated most of the signs and symptoms of carnitine deficiency. All three have continued to respond to carnitine therapy and remain well except for the irreversible sequelae of the pretreatment illnesses. We demonstrate here that transformed lymphocytes from the first documented case of plasma membrane carnitine transporter deficiency fail to take up carnitine from the medium. The analysis of the cDNA of this patient and his parents revealed a homozygous frameshift mutation, 1027delT in exon 4. The resulting polypeptide terminates after amino acid 295. His parents are heterozygous for this mutation. The deletion resulted in predominately abnormal mRNA splicing with either a 13 or 19bp insertion between the junction of exons 3 and 4. The 13/19bp insertions were found in both parents, predominantly in cis with the deletion, and rarely seen with normal alleles from either parents or controls.

Adolescent↗
PubMed2002

Mouse model for human arginase deficiency.

Deficiency of liver arginase (AI) causes hyperargininemia (OMIM 207800), a disorder characterized by progressive mental impairment, growth retardation, and spasticity and punctuated by sometimes fatal episodes of hyperammonemia. We constructed a knockout mouse strain carrying a nonfunctional AI gene by homologous recombination. Arginase AI knockout mice completely lacked liver arginase (AI) activity, exhibited severe symptoms of hyperammonemia, and died between postnatal days 10 and 14. During hyperammonemic crisis, plasma ammonia levels of these mice increased >10-fold compared to those for normal animals. Livers of AI-deficient animals showed hepatocyte abnormalities, including cell swelling and inclusions. Plasma amino acid analysis showed the mean arginine level in knockouts to be approximately fourfold greater than that for the wild type and threefold greater than that for heterozygotes; the mean proline level was approximately one-third and the ornithine level was one-half of the proline and ornithine levels, respectively, for wild-type or heterozygote mice--understandable biochemical consequences of arginase deficiency. Glutamic acid, citrulline, and histidine levels were about 1.5-fold higher than those seen in the phenotypically normal animals. Concentrations of the branched-chain amino acids valine, isoleucine, and leucine were 0.4 to 0.5 times the concentrations seen in phenotypically normal animals. In summary, the AI-deficient mouse duplicates several pathobiological aspects of the human condition and should prove to be a useful model for further study of the disease mechanism(s) and to explore treatment options, such as pharmaceutical administration of sodium phenylbutyrate and/or ornithine and development of gene therapy protocols.

Animals↗
PubMedDate not supplied

Identification of isobutyryl-CoA dehydrogenase and its deficiency in humans.

The acyl-CoA dehydrogenases (ACDs) are a family of related enzymes that catalyze the alpha,beta-dehydrogenation of acyl-CoA esters. Two homologues active in branched chain amino acid metabolism have previously been identified. We have used expression in Escherichia coli to produce a previously uncharacterized ACD-like sequence (ACAD8) and define its substrate specificity. Purified recombinant enzyme had a k(cat)/K(m) of 0.8, 0.23, and 0.04 (microM(-1)s(-1)) with isobutyryl-CoA, (S) 2-methylbutyryl-CoA, and n-propionyl-CoA, respectively, as substrates. Thus, this enzyme is an isobutyryl-CoA dehydrogenase. A single patient has previously been described whose fibroblasts exhibit a specific deficit in the oxidation of valine. Amplified ACAD8 cDNA made from patient fibroblast mRNA was homozygous for a single nucleotide change (905G>A) in the ACAD8 coding region compared to the sequence from control cells. This encodes an Arg302Gln substitution in the full-length protein (position 280 in the mature protein), a position predicted by molecular modeling to be important in subunit interactions. The mutant enzyme was stable but inactive when expressed in E. coli. It was also stable and appropriately targeted to mitochondria, but inactive when expressed in mammalian cells. These data confirm further the presence of a separated ACD in humans specific to valine catabolism (isobutyryl-CoA dehydrogenase, IBDH), along with the first enzymatic and molecular confirmation of a deficiency of this enzyme in a patient.

Amino Acid Metabolism, Inborn Errors↗