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Biomedical subjects

P Johnson

Publications and source records attributed to P Johnson.

At least 19 recordsLinked to original sources
PubMed1992

Mutational analysis of CD45. A leukocyte-specific protein tyrosine phosphatase.

The cytoplasmic domain of murine CD45 has been expressed using an in vitro transcription/translation system. The recombinant protein was isolated by immunoprecipitation with a specific rabbit antiserum and was shown to have protein tyrosine phosphatase (PTPase) activity. Oligonucleotide-directed mutagenesis was then used to investigate the structural requirements for PTPase activity. Although the cysteine crucial for PTPase activity resides in domain I, this domain was not active alone. Both PTPase domains of CD45 and the membrane proximal region of 77 amino acids were required for enzymatic activity. Deletion of 78 residues at the carboxyl terminus of the cytoplasmic region did not influence activity, but an additional deletion of 13 amino acids from PTPase domain II totally abolished activity. Excision of the 21-residue acidic insert in the second PTPase domain resulted in a decrease of activity of approximately 4-fold. Nine conserved residues around the critical cysteine in the first domain were found to be important for activity. Of the 3 conserved tyrosine residues in domain I, only Tyr729 was specifically required for activity.

Amino Acid Sequence↗
PubMed1992

Monosomy 7 myeloproliferative disease in children with neurofibromatosis, type 1: epidemiology and molecular analysis.

Loss of constitutional heterozygosity is a common molecular feature of cancers in which inactivation of one or more tumor suppressor genes is thought to contribute to tumorigenesis. Recent evidence suggests that the gene responsible for neurofibromatosis, type 1 (NF-1), belongs to this class of heritable cancer genes. Children with NF-1 show an increased incidence of myeloid leukemia, including juvenile chronic myelogenous leukemia (JCML) and, perhaps, the myeloproliferative syndrome (MPS) associated with bone marrow monosomy 7 (Mo 7). We have investigated five children with Mo 7: three with NF-1 and two others with suggestive evidence of NF-1. Southern blotting experiments performed in four patients showed no loss of heterozygosity in bone marrow specimens using probes linked to the NF-1 locus on the long arm of chromosome 17. Both of our patients with familial NF-1 inherited the disease from their mothers, as did 14 of 19 other cases of myeloid leukemia in children with familial NF-1. Seventeen of these 21 children were boys. Myeloid leukemia developed in 12 boys and four girls who inherited NF-1 from their mothers, and in five boys who inherited the disease from their fathers. Father-to-daughter transmission was not observed. Taken together, the presence of chromosome 7 deletions in the leukemias of children with NF-1, a pattern of inheritance favoring maternal transmission of NF-1, and the marked predilection for boys to develop JCML and Mo 7 suggest a multistep mechanism of oncogenesis in which epigenetic factors might play a role. Further investigation is required to determine if the NF-1 genes in the leukemic bone marrows of these patients have acquired point mutations or small deletions.

Blotting, Southern↗
PubMed1992

Expression of variable exon A-, B-, and C-specific CD45 determinants on peripheral and thymic T cell populations.

A mAb (I/24) has been generated that is specific for a determinant on mouse CD45 molecules. Reactivity of this mAb with a panel of CD45 transfected cell lines demonstrated that the determinant recognized is dependent upon expression of one or more CD45 variable exons and that exon C is sufficient for its expression. The exon C-specific epitope detected by I/24 is expressed at high density on essentially all B lymphocytes and at an intermediate density on the vast majority of CD8+ splenic T cells. Two distinct subpopulations of CD4+ splenic T cells were detected, a minor subpopulation that expresses this exon determinant at high density and a major subpopulation that expresses it at a much lower density. This first identification of a CD45RC-specific reagent allowed a comparison of the expression of exon A-, exon B-, and exon C-specific determinants on peripheral and thymic lymphoid populations. When splenic lymphocytes were analyzed for expression of CD45RA (reactive with mAb 14.8), CD45RB (reactive with mAb 23G2 or mAb 16.A), and CD45RC (reactive with mAb I/24) determinants, it was found that each of these CD45 determinants had a distinct pattern of expression on CD4+ and CD8+ T cells and B cells. CD45RB and RC epitopes were also detected at high density on a small proportion (0.7 to 4.1%) of thymocytes. Both CD45RB and RC epitopes were found predominantly on CD4-CD8- and CD4-CD8+ thymocytes but were also found on small numbers of CD4+CD8+ and CD4+CD8- cells. The population of thymocytes that expressed CD45RB and CD45RC determinants displayed a novel TCR CD3 phenotype characterized by a level of expression that was intermediate between that seen in the larger CD3 bright and CD3 dull populations of thymocytes.

Animals↗
PubMed1992

Assessment of skeletal muscle damage in successive biopsies from strength-trained and untrained men and women.

The effects of repeated biopsy sampling on muscle morphology was qualitatively and quantitatively assessed in strength-trained and untrained men and women. College-age men (13) and women (8) resistance trained twice a week for 8 weeks. A progressive resistance-training program was performed consisting of squats, leg presses, and leg extensions. Nontraining men (7) and women (5) served as controls. Muscle biopsy specimens and fasting bloods were obtained at the beginning and every 2 weeks and histochemical, biochemical, and ultrastructural methods were employed to assess the type and amount of damage. Except for a few scattered atrophic fibers in 2 of the 33 biopsy samples, all initial specimens were normal. In contrast, many of the subsequent biopsy samples from both untrained and resistance-trained men and women contained evidence of damage. Ultrastructural analysis confirmed that degenerative-regenerative processes were occurring in both groups. However, training subjects had a four-fold greater number of damaged fibers than nontraining subjects (8.53% vs 2.08%). In addition, only biopsy samples from training individuals contained fibers with internal disorganization (e.g., Z-line streaming, myofibrillar disruption). Calpain II levels in the biopsy samples and serum creatine kinase activity were not significantly affected supporting the light and electron microscopic observations that most of the damaged fibers were normal in appearance except for their small diameter. In summary, focal damage induced by the biopsy procedure is not completely repaired after 2 weeks and could affect the results, particularly cross-sectional area measurements. Moreover, resistance training appears to cause additional damage to the muscle and may delay repair of the biopsied region.

Adult↗
PubMed1992

Phase II trial of fludarabine phosphate for adenocarcinoma of the pancreas. An Illinois Cancer Center study.

We have conducted a phase II trial of fludarabine phosphate for advanced measurable adenocarcinoma of the pancreas. The drug was administered every 4 weeks by a daily-times-5 bolus schedule beginning at 20 mg/m2/day. No responses were observed in 20 evaluable patients, 18 of whom were previously untreated. Dose-limiting toxicity was leukopenia, and gastroenterologic side effects were frequent. Life-threatening or fatal renal dysfunction occurred in 3 patients. In this schedule fludarabine phosphate is ineffective against adenocarcinoma of the pancreas and appears to have unpredictable severe renal toxicity.

Adenocarcinoma↗
PubMed1992

Does amniotic fluid analysis reflect acid-base balance in fetal blood?

OBJECTIVE: The purpose of the study was to examine whether the acid-base balance in amniotic fluid reflects the acid-base state in fetal blood. STUDY DESIGN: The pH, PCO2, PO2, bicarbonate, and base excess concentrations were measured in umbilical venous, umbilical arterial, and maternal venous blood and in amniotic fluid samples obtained at fetoscopy. This was performed before intraamniotic termination of 16 normal pregnancies (mean gestation 19.4 weeks), as well as in 14 red blood cell isoimmunized pregnancies (mean gestation 28.4 weeks) undergoing fetoscopy for the diagnosis and treatment of fetal anemia. RESULTS: In normal pregnancies, amniotic fluid pH and bicarbonate were significantly lower than umbilical venous and umbilical arterial blood concentrations, and this was due to the high concentration of base deficit in amniotic fluid. Whereas amniotic fluid PCO2 did correlate significantly with fetal umbilical venous PCO2 values, there was no correlation between other acid-base characteristics. CONCLUSION: Simultaneous sampling of human fetal umbilical blood and amniotic fluid under the acute conditions of this study did not show significant correlations in acid-base values.

Acid-Base Equilibrium↗
PubMed1992

Differential effects of aluminum ion on smooth muscle calpain I and calpain II activities.

1. In millimolar Ca2+, smooth muscle calpains I and II were inhibited by aluminum ion. 2. At sub-millimolar Ca2+, calpain II, but not calpain I, was activated by low millimolar aluminum ion. 3. Calpastatin inhibited aluminum ion-activated calpain II. 4. Aluminum ion-activated and Ca(2+)-activated calpain II gave almost identical patterns of desmin cleavage. 5. Aluminum-activated calpain II, unlike the Ca(2+)-activated enzyme, did not autolyze and retained its proteolytic activity over extended periods of time.

Aluminum↗
PubMed1992

Histidine dipeptide levels in ageing and hypertensive rat skeletal and cardiac muscles.

1. In rat skeletal muscles (longissimus dorsi and quadriceps femoris), carnosine and anserine levels decreased 35-50% during senescence, and were 35-45% lower in hypertensive rats compared to normotensive levels. 2. In rat left ventricular cardiac muscle, although no free carnosine and anserine were detected, the total level of histidine dipeptides declined 22% during senescence and in hypertensive animals decreased 35% compared to normotensive levels. 3. The significance of these changes in relation to the possible antioxidant roles of histidine dipeptides in muscle is discussed.

Aging↗
PubMed1992

Umbilical venous pressure in nonimmune hydrops fetalis: correlation with cardiac size.

OBJECTIVES: Our objectives were to examine the relationship between umbilical venous pressure and cardiac size in nonimmune hydrops fetalis and to assess the role of cardiac failure in the pathogenesis of the disease. STUDY DESIGN: Fourteen fetuses with nonimmune hydrops fetalis were investigated in a tertiary referral unit with high-resolution ultrasonography, echocardiography, and fetal blood sampling. Fetal heart size was assessed by measurement of the cardiothoracic ratio. Umbilical venous pressure was measured at the time of fetal blood sampling with a fluid-filled system. RESULTS: The 10 fetuses with elevated umbilical venous pressures had significantly increased cardiothoracic ratios (p = 0.02). These fetuses also had ascites. Four other fetuses had normal-sized hearts, normal umbilical venous pressures, and no ascites. There was a linear relationship between cardiothoracic ratio and umbilical venous pressure (r = 0.75, p = 0.003). CONCLUSION: Measurement of umbilical venous pressure validates cardiothoracic ratio as a noninvasive assessment of cardiac function in nonimmune hydrops.

Female↗
PubMed1992

Linkage of the Indiana kindred of Gerstmann-Sträussler-Scheinker disease to the prion protein gene.

The Indiana kindred variant of Gerstmann-Sträussler-Scheinker disease has amyloid plaques that contain prion protein (PrP), but is atypical because neurofibrillary tangles like those of Alzheimer disease are present. To map the position of the disease causing gene, we used three markers for linkage analyses. A missense mutation at codon 198 of the PrP gene (PRNP) is found in all definitely affected individuals and yields a maximum lod score of 6.37 (theta = 0). The disease also is concordant with the two other PRNP-region markers. These results demonstrate tight linkage of the disease-causing gene to PRNP and support the hypothesis that the codon 198 mutation is the cause of IK-GSS. Our studies also suggest that methionine/valine heterozygotes at PRNP codon 129 have a later age of onset of the disease than codon 129 valine/valine homozygotes.

Adult↗
PubMed1992

Impact of specimen handling and storage on detection of hepatitis C virus RNA.

Direct detection of hepatitis C virus (HCV) RNA in serum or plasma is useful for validating the performance of anti-HCV assays and for the discrimination of persons with persistent HCV infections from those with resolved infections. Quantitation of HCV RNA may also be useful for disease prognosis and therapeutic monitoring. Previous studies have reported detection of HCV RNA in 50 to 70 percent of blood donors who were positive on anti-HCV supplemental tests. There is concern that specimen processing and storage conditions might influence the stability, and hence the detectability, of HCV RNA. To address this concern, the rate of detection of HCV RNA by the polymerase chain reaction (PCR) using donor pilot tube sera (PTS) previously subjected to routine donor screening and supplemental testing was compared with HCV PCR results obtained with fresh-frozen plasma (FFP) derived from the same donations. All 16 anti-HCV supplemental test-positive donations evaluated were HCV RNA positive with FFP, whereas only 10 (62.5%) were positive with PTS (p = 0.024). None of 11 FFP or PTS samples from HCV enzyme immunoassay-reactive donations not confirmed by supplemental anti-HCV assays tested positive for HCV RNA. Direct comparison of sample type (serum vs. plasma) and various storage conditions using specimens from two seropositive donors showed that room-temperature storage results in marked reduction in HCV RNA signal, while replicate freezing and thawing caused a moderate reduction. These data indicate that well-controlled sample processing and storage conditions are critical to the sensitive and potentially quantitative analysis of HCV RNA.

Blood Preservation↗
PubMed1992

Detecting malnutrition at age 6-12 months: international comparisons of arm circumference v. standard anthropometry.

Growth faltering, which may herald protein-energy malnutrition (PEM) usually begins between ages 6 and 12 months. However, arm circumference (AC or MUAC) has mainly been used to screen for PEM between 12 and 60 months of age, when AC is age-independent. This study of 378 infants aged 6-12 months in Pakistan, Nepal, Sierra Leone, and Papua New Guinea showed that a cut-off 12.5 cm AC selects infants < 80 per cent weight-for-age (WA) with 76 per cent sensitivity and 90 per cent specificity. Of the 378 infants studied 131 (35 per cent) had WA < 80 per cent and 126 (33 per cent) had AC < 12.5 cm. Weight-for-length agreed less well with AC. The inter-regional prevalence range of AC < 12.5 cm was 29-40 per cent, while the WA < 80 per cent range was 27-45 per cent. When AC is plotted against age, a flat 'plateau' (slope = 0.04) shows age-independence between 6 and 12 months in these 378; this contrasts to the 10 per cent AC increase in European reference populations. Because this AC plateau parallels the WA plateau seen between 6 and 12 months of age in most developing nations, AC < 12.5 cm may provide a simple and valid screening test for early PEM in this crucial age bracket. Conformatory studies elsewhere are indicated.

Anthropometry↗
PubMed1992

Benefits provided by an integrated education and clinical diabetes centre: a follow-up study.

The effects of a new integrated system of diabetes care with an enhanced role of the diabetes specialist nurse based in a purposed design diabetes centre, on diabetes control, attendance and cancellation rates, and admission for diabetic emergencies have been reviewed. Glycaemic control was examined in: (a) a cohort of 163 insulin-treated and 47 non-insulin treated diabetic subjects (age < 65 years) studied prospectively before and 3 years following the introduction of a new system of care; (b) a second cohort of more elderly patients aged greater than 65 years studied for the 3 years after the change over; (c) a cross-sectional study of the clinic population (n = 700) the year before and 3 years after the changeover; (d) a group of patients attending standard unaltered clinics in the same district (n = 157). Significant and sustained falls in HbA1 were observed in all groups of subjects attending the centre, with the means for those aged less than 65 falling from 11.9 +/- 2.3% to 9.9 +/- 1.9% and for those aged over 65 from a mean of 11.7 +/- 2.0% to 10.3 +/- 2.3%, 3 years later. The cross-sectional study provided similar results with a mean HbA1 of 12.2 +/- 3.0% prior to changeover and 10.4 +/- 4.4%, 3 years later. Smaller but significant changes were observed in patients continuing to attend the routine clinic (from 12.2 +/- 2.3% to 11.3 +/- 2.6%) over a similar period. Yearly admission rates for ketoacidosis and hypoglycaemia fell from 44 and 23, to 33 and 5 per annum, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗