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Biomedical subjects

R J Leeming

Publications and source records attributed to R J Leeming.

At least 19 recordsLinked to original sources
PubMed1998

The origin of red blood cell biopterin.

Data are presented to support the hypothesis that the biopterin content of red blood cells arises during erythropoiesis. Only when the plasma concentration rises above the erythrocyte concentration of biopterin is there likely to be diffusion into the cell.

Adult↗
PubMed1994

5-Methyltetrahydrofolate level in the serum of depressed subjects and its relationship to the outcome of ECT.

Serum 5-MeTHF levels are reported in 26 subjects, before and after completing a course of ECT, and compared to 21 healthy volunteers. 5-MeTHF levels of depressed subjects were significantly lower than controls before and after ECT. There was no difference in 5-MeTHF levels between ECT responders and non-responders but folate deficiency was related to severity of depression before ECT. Serum 5-MeTHF was not related to treatment response and values remained markedly low even after a good response to treatment.

Aged↗
PubMed1993

A microtitre plate method for measuring biopterin with cryopreserved Crithidia fasciculata.

The assay of biopterin derivatives in dried blood spots is used by us in initial screening for inherited defects in tetrahydrobiopterin synthesis. The previously described method (1) required aseptic technique and microbiological facilities. The modification detailed here has the advantages of antibiotic cover, which overcomes these needs and microtitre plate technology allowing the incubation time to be halved with precision and accuracy retained. Data reduction facilities may be applied.

Adult↗
PubMed1992

Radioimmunoassay that measures serum vitamin B12.

AIMS: To develop a specific radioimmunoassay for the routine determination of serum vitamin B12. METHODS: Antisera were raised in rabbits by immunisation with the monocarboxylic acid derivative of cyanocobalamin coupled to human serum albumin. Antibody titres and affinities were determined and the antiserum giving the highest binding affinity constant, Ka, was used to develop the assay protocol. Donkey-anti-rabbit gamma globulin-coated magnetisable particles were used to separate the bound from free vitamin B12. The considerable cobalamin binding capacity of human serum was destroyed by autoclaving in acetate-cyanide buffer. Sixty samples were assayed by the radioimmunoassay (RIA) and the Lactobacillus leichmannii assay. Recovery and cross-reactivity experiments were performed. RESULTS: Final rabbit antibody titres varied from 1/20,000 to 1/188,000. Scatchard plots did not correlate with the antibody titres. The Ka values varied from 2.6 to 6.7 x 10(10) litres/mol. For maximum sensitivity the highest Ka (titre 1/66,000) was chosen. A tracer concentration of 22 pmol/l, an antiserum dilution of 1/100,000, and a sample volume of 0.1 ml were used. At an antiserum dilution of 1 in 100,000 the cyanocobalamin binding of the rabbit serum was diluted out. The assay showed excellent correlation with the microbiological assay, with 100% recovery of added vitamin B12. Levels of cross-reactivity for dicyanide cobinamide and hydroxocobalamin were 9.8 and 8.1%, respectively. CONCLUSIONS: The development of this immunoassay permits the measurement of serum vitamin B12 without important interference from cobalamin analogues, related corrinoids, and non-specific binders.

Animals↗
PubMed1992

The significance of neopterin and biopterin concentrations at presentation in haematological malignancies.

Urinary neopterin and biopterin concentrations were measured in 32 healthy controls and 53 patients with newly diagnosed haematological malignancies classified and staged by accepted criteria. The neopterin concentrations were only significantly raised in chronic lymphocytic leukaemia at stages III-IV. Total biopterin concentrations after oxidation with iodine at acid pH were decreased in chronic lymphocytic leukaemia stages O-II, multiple myeloma, and acute myeloid leukaemia but not in chronic lymphocytic leukaemia stages III-IV. Although of research interest, neopterin concentrations proved of little prognostic value at presentation, but taken with the biopterin concentration they may be useful for the assessment of tumour activity.

Biomarkers, Tumor↗
PubMed1990

Dihydropteridine reductase activity in eluates from dried blood spots: automation of an assay for a national screening service.

We describe the automation, using a Cobas Bio centrifugal analyser, of a method for dihydropteridine reductase (DHPR) assay in eluates from dried blood spots. This is used as part of a routine screening service of neonates with hyperphenylalaninaemia in the United Kingdom. Automation reduced reagent volumes and analysis time by about 80% and improved the precision of the assay. Relating DHPR activity to haemoglobin concentration of the eluate further improved the precision of the assay and removed some differences in 'apparent' DHPR activity between samples from different countries and different age groups.

Age Factors↗
PubMed1990

Relationship between plasma and red cell biopterins in acute and chronic hyperphenylalaninaemia.

Biopterin concentrations in red blood cells were higher in patients with chronic hyperphenylalaninaemia than following a single oral dose of phenylalanine, although the plasma concentrations were similar. These findings suggest that tetrahydrobiopterin is synthesized in immature red blood cells in response to hyperphenylalaninaemia. The less marked increase in plasma biopterin suggests slow release from a tissue reservoir. The maintenance of a differential between erythrocyte and plasma biopterin concentrations suggests that some mechanism retains biopterin intracellularly.

Acute Disease↗
PubMed1990

Neuroblastoma in a patient with dihydropteridine reductase deficiency.

Tetrahydrobiopterin (BH4) deficiency is a rare cause of hyperphenylalaninaemia (HPA) and usually leads to progressive neurological deterioration despite early dietary control of plasma phenylalanine concentrations. Dihydropteridine reductase (DHPR) deficiency is the most severe cause with respect to a fatal outcome. We report a 7-year-old girl with HPA diagnosed on neonatal Guthrie screening who at the age of 6 months had cytotoxic therapy for an adrenal neuroblastoma which secreted catecholamines. When 4 years old she was found to have DHPR deficiency. Although developmentally retarded and microcephalic she has failed to develop the florid neurological features often associated with the condition.

Adrenal Gland Neoplasms↗