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Biomedical subjects

D A Mitchell

Publications and source records attributed to D A Mitchell.

At least 73 records · Page 4Linked to original sources
PubMed1989

Detection of kinetically abnormal argininosuccinate synthase in neonatal citrullinemia by conversion of citrulline to arginine in intact fibroblasts.

The apparent Km values of argininosuccinate synthase toward citrulline and aspartate were significantly increased in cultured skin fibroblasts from one patient with neonatal citrullinemia, whereas, those determined in cells from three other patients were within the normal range. The abnormal apparent Km of the mutant enzyme toward aspartate was determined by a ureagenesis assay system (0.14 mmol/l as compared with 0.010-0.018 mmol/l for the normal enzyme), and the abnormal values toward citrulline were measured by both arginine synthesis (6.1 mmol/l as compared with 0.21-0.26 mmol/l for the normal enzyme) and ureagenesis (0.63 as compared with 0.043-0.067) assay systems.

Amino Acid Metabolism, Inborn Errors↗
PubMed1989

Prenatal diagnosis of I-cell disease in the first and second trimesters.

First trimester prenatal diagnosis of I-cell disease (1 case) was based on demonstration of profound deficiency of N-acetylglucosamine 1-phosphotransferase in chorionic villi and in cultured trophoblasts derived from the chorionic villus specimen. Deficiency of this enzyme in cultured amniotic fluid cells obtained via amniocentesis was the basis for prenatal diagnosis of I-cell disease in the second trimester (2 cases). In both procedures, the diagnosis was corroborated by the finding of intracellular deficiency and extracellular elevation of multiple lysosomal enzymes in the fetal cell cultures (trophoblasts and amniotic fluid cells), as well as a significant increase in several lysosomal enzyme activities in the maternal serum.

Amniocentesis↗
PubMed1989

Leukocyte and plasma N-laurylsphingosine deacylase (ceramidase) in Farber disease.

Severe deficiency of acid ceramidase activity (4-5% of normal) was demonstrated in cultured skin fibroblasts, leukocytes and plasma from a 1-year-old boy who was diagnosed as being affected with Farber disease. Determination of ceramidase activity in plasma was achieved by a highly sensitive assay employing a ceramide substrate containing radiolabeled C12 N-acyl moiety (N-lauryl). The enzyme activity in the parents' leukocytes and plasma was found to be reduced to 18-47% of the respective normal values, and that determined in a plasma specimen from a patient with I-cell disease was about 4 times elevated above the normal level.

Acid Ceramidase↗
PubMed1989

Medial brachial fascial compartment syndrome: anatomic basis of neuropathy after transaxillary arteriography.

The authors reviewed their experience with 320 transaxillary arteriograms, as well as the English-language literature on neuropathy complicating transaxillary arteriography. Three of their patients had median and ulnar motor and sensory nerve injury, and six others had only sensory involvement. The occurrence or severity of nerve injury did not correlate well with the size or presence of an observable axillary or arm hematoma. Dissection of the axillae and arms of 25 human cadavers revealed a tough medial brachial fascial compartment (MBFC) outside a thin axillary sheath. The median and ulnar nerves were within the MBFC at an arterial puncture site just lateral to the anterior axillary fold. The radial and musculocutaneous nerves exited the MBFC more proximally. The different levels at which the major nerves of the brachial plexus exit the MBFC explain the anatomic distribution of the nerve injuries associated with compression by a hematoma after transaxillary arteriography.

Adult↗
PubMed1988

First trimester prenatal evaluation for I-cell disease by N-acetyl-glucosamine 1-phosphotransferase assay.

First trimester prenatal diagnosis was offered to a couple at risk for having a child with I-cell disease (mucolipidosis II). The prenatal evaluation was based for the first time on examination of N-acetylglucosamine 1-phosphotransferase activity, deficiency of which is the primary biochemical defect in both I-cell disease and pseudo-Hurler polydystrophy (mucolipidosis III). Heterozygote levels of this enzyme activity were determined in chorionic villi obtained at 9 weeks of gestation, as well as in cultured trophoblasts derived from this specimen, and led to the diagnosis of an unaffected fetus. This procedure has advantages over that based on detection of abnormal intracellular-extracellular distribution of lysosomal enzyme activities, which is expressed only in homozygotes and fully expressed only in cell culture specimens.

Adult↗
PubMed1987

Altered molecular size of N-acetylglucosamine 1-phosphotransferase in I-cell disease and pseudo-Hurler polydystrophy.

The size of the mutant N-acetylglucosamine 1-phosphotransferase in Golgi membranes from fibroblasts of patients with I-cell disease and classical pseudo-Hurler polydystrophy, which comprised one complementation group characterized by deficiency towards both artificial and natural acceptor substrates, was significantly smaller than the normal enzyme, 151-174 kDa compared with 225-278 kDa. The size of the mutant enzyme from cell lines of patients with variant forms of pseudo-Hurler polydystrophy, which comprised another complementation group characterized by normal activity towards mono- and oligo-saccharide substrates, was significantly larger than the normal enzyme, ranging from 321 to 356 kDa in two families and from 528 to 547 kDa in a third family. These findings suggest that the mutations in I-cell disease and classical pseudo-Hurler polydystrophy result in a missing enzyme component, which renders the enzyme catalytically inefficient toward any type of acceptor substrate. In contrast, the mutations in the variant forms of pseudo-Hurler polydystrophy produce a larger enzyme molecule which is active toward small substrates but is incapable of binding natural lysosomal glycoprotein substrates.

Cell Line↗
PubMed1987

Tinidazole or pivampicillin in third molar surgery.

There is an increasing body of evidence implicating oral anaerobic bacteria in the aetiology of post-surgical dentoalveolar infections. This information has lead to several studies demonstrating the usefulness of specific anaerobicidal drugs in the prevention and treatment of dento-alveolar infection. One such study utilised a single 2 g preoperative oral dose of tinidazole which was found to be significantly better than placebo in preventing infective sequelae after removal of impacted mandibular third molars. The present study was designed to compare a high-dose short-term broad spectrum penicillin, (pivampicillin), with the previously described regimen, using tinidazole in order to discern the existence or otherwise of any practical difference between an anaerobicidal and a broad spectrum antibiotic when local infection was considered.

Adolescent↗
PubMed1987

Detection of Krabbe disease using tritiated galactosylceramides with medium-chain fatty acids.

Galactocerebrosidase (galactosylceramidase) assays using tritiated galactosylceramides with saturated, medium-chain fatty acids (C6-C11) were found to be more sensitive and more reliable than the commonly used assays with long-chain and very long-chain substrates (C16-C26). Galactosylsphingosine (psychosine) was tritiated by a modification of the galactose oxidase-sodium borohydride method, and 19 galactosylceramides were synthesized by the direct coupling of galactosylsphingosine with fatty acids of varying lengths (C6 to C24). The highest specific activities of normal prenatal and postnatal enzyme preparations were obtained with the C6 and C8 derivatives, which were six and five times more sensitive, respectively, than the C16 substrate. The residual activities in enzyme preparations from fetuses and children with Krabbe disease were proportionally increased. Our experience indicates that these substrates can provide a sensitive and reliable means for the prenatal and postnatal detection of Krabbe disease.

Amnion↗
PubMed1986

Lysosomal enzyme activities in fresh and frozen chorionic villi and in cultured trophoblasts.

Fifteen lysosomal enzyme activities were compared in 14 presumed normal chorionic villus specimens that were each divided, processed and analyzed as fresh tissue, tissue frozen for 1 week, and cultures established from minced whole villi. Most of the activities determined in the chorionic villus tissue were not affected significantly by freezing. However, activities for most enzymes were significantly different from those determined in the cultured cells. Our experience with first trimester prenatal evaluations for several lysosomal disorders showed that the limited amount of tissue obtained is not always sufficient for thorough analysis and thus, cultured trophoblasts derived from the tissue specimen should also be examined. The results of this study stress the importance of using appropriate tissue-type and cell-type controls to establish the normal range in the respective analyses.

Arylsulfatases↗
PubMed1986

Molecular size of N-acetylglucosaminylphosphotransferase and alpha-N-acetylglucosaminyl phosphodiesterase as determined in situ in Golgi membranes by radiation inactivation.

The radiation inactivation method was used to determine the molecular size of the two enzymes that participate in the synthesis of the phosphomannosyl recognition marker of lysosomal proteins. The determinations were carried out in situ, in Golgi membranes isolated from normal human placenta and cultured skin fibroblasts. A molecular size of 228 +/- 29 kDa was found for placental N-acetylglucosaminyl-phosphotransferase, and 129 +/- 11 kDa for placental alpha-N-acetylglucosaminyl phosphodiesterase. The values for the fibroblast enzymes were about 20% higher, 283 +/- 27 kDa and 156 +/- 14 kDa for the transferase and phosphodiesterase respectively. Triton X-100 had no effect on the molecular size of these enzymes.

Cells, Cultured↗
PubMed1986

Characterization of the mutant N-acetylglucosaminylphosphotransferase in I-cell disease and pseudo-Hurler polydystrophy: complementation analysis and kinetic studies.

Complementation was examined among various types of I-cell disease and pseudo-Hurler polydystrophy by monitoring N-acetylglucosaminylphosphotransferase activity in multinucleated cells produced by fusing pair combinations of cultured skin fibroblasts. Patients with the classical forms of these disorders (5 I-cell disease and 3 pseudo-Hurler polydystrophy cell lines) comprised one complementation group and 5 cell lines from patients with variant forms of pseudo-Hurler polydystrophy comprised a distinct complementation group. In the first group, total or partial deficiency of the transferase activity was demonstrated with both natural (lysosomal enzymes) and artificial (alpha-methylmannoside) acceptor substrates with low Vmax but apparently normal Km values for the donor (UDP-GlcNAc) and acceptor (alpha-methylmannoside) substrates. The activity toward artificial substrate could be inhibited by adding exogenous lysosomal enzyme preparations to the reaction mixture. In the second group, the cells demonstrated deficiency of the transferase activity toward lysosomal enzyme acceptors but had normal activity toward alpha-methylmannoside acceptor and this activity could not be inhibited by the addition of exogenous lysosomal enzyme preparations. These findings suggest that N-acetylglucosaminylphosphotransferase is composed of at least two distinct subunits, a catalytic subunit which is absent or defective in the first complementation group, and a recognition subunit which is altered or deficient in the second group.

Cells, Cultured↗