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Biomedical subjects

P John

Publications and source records attributed to P John.

At least 37 records · Page 2Linked to original sources
PubMed2001

Thoracic interventional radiology in children.

Significant technological advancements have been achieved in radiology with the introduction of a branch speciality known as interventional radiology. Radiology has moved into the therapeutic arena, performing minimally invasive diagnostic and therapeutic procedures. The interventional radiologist can treat certain vascular and non-vascular conditions with "keyhole" or perhaps more correctly "pinhole" techniques using catheter-based technology directed under image guidance with X-ray (including computed tomography), ultrasound and magnetic resonance imaging. Interventional radiology can provide new treatment options for children not possible a few years ago.

Age Factors↗
PubMed2000

Identification of P gene mutations in individuals with oculocutaneous albinism in sub-Saharan Africa.

Oculocutaneous albinism (OCA) is an inherited disorder resulting in hypopigmentation of the skin, hair, and eyes. OCA type 2 (tyrosinase-positive) is the most common recessively inherited disorder among southern African Blacks. OCA2 is also seen in southern African Caucasoids, but is less frequent. The gene responsible for this type of albinism, P, is the human homolog of the mouse pink-eyed dilution gene. Mutations at this locus are also responsible for the milder hypopigmentation phenotype seen in individuals with brown oculocutaneous albinism (BOCA). A common African P mutation was identified in Black OCA2 individuals, and has since been shown to occur in Black individuals with brown OCA as well. This mutation is a 2.7 kb interstitial deletion. In this study, we undertook to screen the coding region of the P gene for mutations in the non-2.7 kb deletion alleles of OCA2 patients who did not carry the deletion allele in either one or both of their P genes. We identified four mutations (A334V, 614delA, 683insG [corrected], 727insG) in a group of 39 unrelated Black OCA2 patients with a total of 52 non-2.7 kb deletion OCA2 genes. When taking all OCA2 cases into consideration, including those homozygous for the 2.7 kb deletion mutation, these account for a further 1.7% of OCA2 mutations in southern African Blacks, increasing the overall mutation detection rate to 78.7%. Three mutations (E678K, L688F, I370T) were identified in a group of 15 Black patients with an initially unclassified type of OCA and another three mutations (IVS 14-2 (a-->g), V350M, P743L) were identified in nine Caucasoid OCA patients. Relatively few mutations, all with low frequency, were identified in the non-2.7 kb deletion OCA genes. We propose that other mutations may lie either within intronic sequence or within the promoter region of the gene.

Africa South of the Sahara↗
PubMed2000

Intraventricular haemorrhage due to ruptured posterior inferior cerebellar artery aneurysm in tuberculous meningitis.

A 9-year-old Asian boy with known miliary tuberculosis, tuberculous meningitis and hydrocephalus was successfully treated with chemotherapy and ventriculoperitoneal shunting, but re-presented 7 months later with an intraventricular haemorrhage secondary to a ruptured left posterior inferior cerebellar artery mycotic aneurysm. The aneurysm was successfully treated by craniotomy and clipping. Tuberculous mycotic intracranial aneurysms are rare, but they should be considered in patients with tuberculous meningitis, particularly when there is a rapid neurological deterioration which may represent rupture.

Aneurysm, Infected↗
PubMed2000

Superior vena cava thrombosis causing respiratory obstruction successfully resolved by stenting in a small bowel transplant candidate.

A 4 year old child was referred for small bowel transplantation. He had superior vena cava obstruction secondary to numerous central venous line placements; alternative routes for long term central venous access were compromised by extensive venous occlusive disease. Patency for the superior vena cava was re-established with stenting, which allowed for radiological placement of another central venous line. Long term survival in infants and young children with intestinal failure is dependent on adequate central venous access for the administration of parenteral nutrition. Line sepsis and physical damage to the catheter often necessitates multiple central venous catheter placements during their early life and these children are at risk of catheter related veno-occlusive disease. Recurrent sepsis and the loss of satisfactory venous access for the administration of parenteral nutrition is life threatening and is an indication for intestinal transplantation in up to 41% of patients reported by the small bowel registry.

Catheterization↗
PubMed1999

Shorter turn-around-time and improved patient care in peripheral blood progenitor cell collection procedures.

The collection of peripheral blood progenitor cells (PBPC) requires the combined efforts of the Transfusion Medicine/Hemapheresis and Hematology/Oncology services and HLA/Progenitor Cell and Immunology laboratories. Coordination and communication among these different services and laboratories are key to attaining an optimal collection in a timely manner for the patient undergoing PBPC collection. In an effort to improve patient care by same-day decision to cease or continue collections avoiding unnecessary collections, needless patient trips to the hospital and ultimately increasing patient satisfaction, a flow chart was used to capture the sequence of events. The flow chart served as a powerful tracking tool that defined system process and steps to attain enumeration of CD34+ cells the same day of collection. It provided documentation of work flow from each of the independent operations involved in progenitor cell collection and enumeration turn-around-time including attending and staff time involvement. By using the flow chart, potential and actual problem areas were demonstrated and this allowed for creative thinking and problem solving by individual sections rather than recriminations. Finally, it focused all the staff involved in the common goal of a shorter turn-around-time for CD34+ cell enumeration the same day of collection. This allowed a prompt decision for subsequent leukapheresis as improved service to oncology patients and their physicians.

Adult↗
PubMed1999

Orthotopic liver transplantation for unresectable hepatoblastoma: a single center's experience.

BACKGROUND/PURPOSE: Complete surgical resection after chemotherapy is the definitive treatment for hepatoblastoma. However, orthotopic liver transplantation (OLT) is now accepted as a treatment modality for patients with unresectable tumours. The aim of this study was to review a single center's experience of OLT for unresectable hepatoblastoma. METHODS: A retrospective review of 8 patients with unresectable hepatoblastoma who were referred for liver transplantation was conducted. RESULTS: The patients assessed had an age range of 5 to 105 months at presentation; median, 24 months, (5 boys; 3 girls). Two patients have familial adenomatous polyposis, and one has right hemihypertrophy. All 8 patients had received standard chemotherapy according to SIOP (International Society of Pediatric Oncology) protocols. Extrahepatic metastases were found in 3 patients at diagnosis, but none had detectable metastases at the time of OLT. Four patients continued chemotherapy while awaiting OLT. Three patients received whole grafts, and 5 received reduced grafts. The median follow-up period was 22 months (range, 2 to 78 months). Five patients are alive and well, although 1 patient had a second OLT for biliary cirrhosis secondary to biliary stricture at 6 years. Three patients died: one 26 days post OLT of sepsis and two of disease recurrence at 22 months and 70 months posttransplant. The actuarial survival rate is 88% and 65% at 1 and 5 years, respectively, whereas the overall survival rate is 62.5%. CONCLUSION: OLT for unresectable hepatoblastoma without extra hepatic metastases is highly successful with a low recurrence rate.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1999

An indigo-reducing moderate thermophile from a woad vat, Clostridium isatidis sp. nov.

A Gram-positive, anaerobic, moderate thermophile, strain Wv6T, capable of reducing indigo dye, was isolated from a fermenting woad vat prepared essentially as in medieval Europe. Strain Wv6T formed rod-shaped cells, which occurred singly, in pairs or in chains and produced terminal oval endospores. Strain Wv6T was saccharolytic. Growth occurred at pH 5.9-9.9 (initial pH) with an optimum at 50 degrees C of pH 7.2 +/- 0.2 (constant pH). At pH 7.8, the temperature range for growth was 30-55 degrees C with the optimum at 49-52 degrees C. Comparative 16S rRNA gene sequence analysis demonstrated that the bacterium represents a hitherto unknown subline within rRNA cluster I Clostridium. Based on the results of the phylogenetic analysis and phenotypic criteria, it is proposed that the unknown moderate thermophile should be classified as Clostridium isatidis sp. nov., a new species of the genus Clostridium. The type strain of Clostridium isatidis is strain Wv6T (= NCFB 3071T).

Bacterial Typing Techniques↗
PubMed1997

Inactivation of 1-aminocyclopropane-1-carboxylate oxidase involves oxidative modifications.

1-Aminocyclopropane-1-carboxylate (ACC) oxidase catalyzes the final step in the biosynthesis of the plant signaling molecule ethylene. It is a member of the ferrous iron dependent family of oxidases and dioxygenases and is unusual in that it displays a very short half-life under catalytic conditions, typically less than 20 min, and a requirement for CO2 as an activator. The rates of inactivation of purified, recombinant ACC oxidase from tomato under various combinations of substrates and cofactors were measured. Inactivation was relatively slow in the presence of buffer alone (t1/2 > 1 h), but fast in the presence of ferrous iron and ascorbate (t1/2 approximately 10 min). The rate of iron/ascorbate-mediated inactivation was increased by the addition of ACC, unaffected by the addition of CO2 at saturation (supplied as bicarbonate) but decreased by the addition of catalase or ACC + CO2 at saturation (supplied as bicarbonate). Iron/ascorbate-mediated inactivation was accompanied by partial proteolysis as observed by SDS-PAGE analysis. The fragmentation pattern was altered when ACC was also included, suggesting that ACC can bind to ACC oxidase in the absence of bicarbonate. N-terminal sequencing of fragments resulted in identification of an internal cleavage site which we propose is proximate to active-site bound iron. Thus, ACC oxidase inactivates via relatively slow partial unfolding of the catalytically active conformation, oxidative damage mediated via hydrogen peroxide which is catalase protectable and oxidative damage to the active site which results in partial proteolysis and is not catalase protectable.

Amino Acid Oxidoreductases↗
PubMed1997

29Si chemical shift tensors of silyl silicate cages.

Static and 29Si CP MAS spectra (spinning rates of 2000 and 500 Hz) of six silyl silicate cages are analyzed by deconvolution and simulation. The principal values of the various 29Si chemical shift tensors provide information about the point symmetry of the Si sites. The intensities of the signals correspond sufficiently well with the stoichiometries.

Isotopes↗
PubMed1996

Heterologous expression and site-directed mutagenesis of the 1-aminocyclopropane-1-carboxylate oxidase from kiwi fruit.

A system has been developed for the expression in Escherichia coli of 1-aminocyclopropane-1-carboxylate (ACC) oxidase from kiwi fruit. In this first report of site-directed mutagenesis of ACC oxidase, seven different mutants of the enzyme have been expressed, and their activities compared to that of the heterologoulsy expressed wild-type enzyme. No great loss of activity was observed when Lys172 was substituted by either Ala or Cys, or when Gly137 was substituted by Pro. However, the mutant proteins showed only 1% of the wild-type activity when substitutions were made of Asp179, His177, and Lys158. The results are discussed in terms of possible mechanisms by which ACC oxidase is activated by carbon dioxide, and in terms of structural motifs suggested by the known structure of isopenicillin N-synthase, an enzyme related by mechanism and sequence similarity to ACC oxidase. It is concluded that Lys172, a putative carbon dioxide binding site, has no role to play in the catalytic activity of the enzyme. The results support a previous suggestion that ACC oxidase shares important structural features with isopenicillin N-synthase.

Amino Acid Oxidoreductases↗
PubMed1996

Detachable balloon occlusion of vascular malformations in young patients.

Two patients (11 and 23 months old, respectively) had successful transcatheter occlusion of congenital arterio-venous or veno-venous malformations using detachable silicone balloons. Patient 1 with a cervicofacial hemangioma had selective embolization of the feeding artery with two balloons. Patient 2, with a veno-venous malformation between a systemic vein and pulmonary vein also had selective embolization of the lesion with two balloons. Follow-up examinations confirm a successful outcome in both cases.

Brachiocephalic Veins↗
PubMed1996

The value of colour Doppler imaging in assessing flow through ventriculo-peritoneal shunts.

So far, Doppler ultrasonography has had little application in paediatric neurosurgery. The incidental observation of normally invisible CSF flow from the peritoneal end of a ventriculo-peritoneal (V-P) shunt on colour Doppler during a conventional abdominal ultrasound examination in one of our patients suggested that colour Doppler imaging might be of potential interest. Using a 10-5 MHz broad-band linear array transducer, conventional 2D and Doppler (spectral and colour-coded) ultrasonography was performed in 17 patients with V-P shunts, who were aged 3 months to 12 years. In all, 20 examinations were performed, because 2 patients had repeat examinations before and after shunt revision. In 13 examinations (65%) CSF flow was identified through the shunt tube. Flow velocities between 5 and 7 cm/s were measured. No flow was seen in 7 examinations (35%), 3 of which (15%) were performed before revisions for a blocked shunt. Further in vitro studies with simulated shunt/ventricular system model demonstrated that although clear CSF is not ultrasonically visible, the presence of particulate matter, such as choroid plexus debris, can generate a satisfactory Doppler signal with the probe insonating over the length of the tubing. In the presence of clear CSF, turbulence generated at junction points of the shunt system or at the exit of the peritoneal tube can be visualised well with Doppler ultrasonography, presumably due to generation of microbubbles. The clinical implications for the management of shunt obstruction are discussed.

Cerebrospinal Fluid↗
PubMed1996

Partially selective semiconductor redox electrodes.

Redox electrodes made of passivated metals of the subgroups IV to VI of the periodic system with a surface coating of n-conducting metal oxides, generated by oxidizing agents or anodic oxidation, are well suited for measuring the concentration of oxidizing agents. Neither oxygen nor reducing agents affect the measurements. There is a correlation between the mean conductivity of the passive layer and its selectivity. The aged n-conducting passive layers permit reproducible potential settings, and the occurring changes in potential are greater than what is to be expected according to the Nernst equation. The potentiometric measuring of nitrosyl ions and chlorine is used as an example to demonstrate the selectivity of these electrodes.

Journal Article↗
PubMed1995

Expression, purification and characterization of 1-aminocyclopropane-1-carboxylate oxidase from tomato in Escherichia coli.

1-Aminocyclopropane-1-carboxylate (ACC) oxidase catalyses the final step in the biosynthesis of the plant hormone ethylene. The successful overexpression and characterization of active ACC oxidase from tomato has been achieved. PCR was used to insert the corrected cDNA coding for the tomato ACC oxidase into the pET-11a expression vector. Cloning of the resultant construct in Escherichia coli BL21(DE3)pLysE gave transformants which expressed ACC oxidase at levels greater than 30% of soluble protein under optimized conditions. When induced by addition of isopropyl-beta-D-thiogalactopyranoside (IPTG) at 37 degrees C the ACC oxidase expressed was less soluble and less active than when induced at 27 degrees C. The enzyme was purified to near homogeneity by a three-step chromatographic procedure. The specific activity of the purified recombinant ACC oxidase was typically 1.3-1.9 mol of ethylene/mol of enzyme per min, higher than values reported for native enzyme. Like the native enzyme it displayed a requirement for ferrous iron and ascorbate, and CO2 was an activator. The ability to discriminate between racemic diastereomers of 1-amino-2-ethyl cyclopropane-1-carboxylic acid was demonstrated. The enzyme was found to have a loose specificity for ascorbate, showing apparent preference for D-ascorbate and 5,6-O-isopropylidene L-ascorbate rather than L-ascorbate. The addition of catalase, dithiothreitol and BSA to incubation mixtures all resulted in significant increases in activity. When treated with diethylpyrocarbonate (DEPC) under mildly acidic conditions, the enzyme rapidly lost activity. Comparison of the rate of inactivation with the increase in absorbance at 240 nm gave results consistent with the modification of two to three histidine residues at the active site, although the possibility of additional modification of other nucleophilic residues cannot be excluded. Inactivation was largely prevented by the addition of substrates and ferrous iron, implying that DEPC treatment results in the modification of active-site histidines, which act as ligands for ferrous iron. CO2 offered no protection against DEPC inactivation, either in the absence or presence of substrates and/or ferrous iron.

Amino Acid Oxidoreductases↗
PubMed1995

Biliary complications after paediatric liver transplantation: Birmingham's experience.

Between 1983 and 1992, 112 children underwent liver transplantation. Of 138 grafts, 60 (43.4%) were whole livers, 77 (55.6%) were reduced livers, and 1 (0.7%) was a split liver. Biliary complications (BC) were defined as any abnormality, even minor, related to the biliary tract. Results were analysed with a minimum follow-up of 9 months. Some 36 grafts (26.1%) in 34 patients (30.4%) presented with BC: bile leaks (17 grafts), biliary obstructions or dilatations (16 grafts), and other complications (3 grafts). Management was mainly surgical with biliary reconstruction via a Roux-en-Y loop. Interventional radiology had an increasing role in recent years. BC were associated with a mortality of 1.8% (2/112), a graft loss rate of 4.3% (6/138), and significant morbidity. Among the various factors whose association with BC was studied, the date of transplantation, the use of reduced grafts and the use of gallbladder conduits appeared to be the main determining factors for BC. From multivariate analysis the use of reduced grafts emerged as the most important factor in reducing BC. We therefore conclude that BC are associated with significant morbidity, but general improvements in both surgical and medical management seem to account for better results in recent years.

Adolescent↗