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Biomedical subjects

P Simpson

Publications and source records attributed to P Simpson.

At least 37 records · Page 2Linked to original sources
PubMed1998

All three surface tryptophans in Type IIa cellulose binding domains play a pivotal role in binding both soluble and insoluble ligands.

The three surface tryptophans of the Type IIa cellulose binding domain of Pseudomonas fluorescens subsp. cellulosa xylanase A (CBD(XYLA)) were independently mutated to alanine, to create the mutants W13A, W49A and W66A. The three mutant proteins were purified, and their capacity to bind to a variety of ligands was determined. The mutant proteins have native-like structures but exhibited much weaker affinity for crystalline and amorphous cellulose and for cellohexaose than the wild type. These data indicate that all three tryptophans are important for binding to cellulose, and support a model in which the three tryptophans form an aromatic strip on the surface of the protein that binds to a single cellulose.

Bacterial Proteins↗
PubMed1998

Pseudomonas cellulose-binding domains mediate their effects by increasing enzyme substrate proximity.

To investigate the mode of action of cellulose-binding domains (CBDs), the Type II CBD from Pseudomonas fluorescens subsp. cellulosa xylanase A (XYLACBD) and cellulase E (CELECBD) were expressed as individual entities or fused to the catalytic domain of a Clostridium thermocellum endoglucanase (EGE). The two CBDs exhibited similar Ka values for bacterial microcrystalline cellulose (CELECBD, 1.62x10(6) M-1; XYLACBD, 1.83x10(6) M-1) and acid-swollen cellulose (CELECBD, 1.66x10(6) M-1; XYLACBD, 1.73x10(6) M-1). NMR spectra of XYLACBD titrated with cello-oligosaccharides showed that the environment of three tryptophan residues was affected when the CBD bound cellohexaose, cellopentaose or cellotetraose. The Ka values of the XYLACBD for C6, C5 and C4 cello-oligosaccharides were estimated to be 3.3x10(2), 1.4x10(2) and 4.0x10(1) M-1 respectively, suggesting that the CBD can accommodate at least six glucose molecules and has a much higher affinity for insoluble cellulose than soluble oligosaccharides. Fusion of either the CELECBD or XYLACBD to the catalytic domain of EGE potentiated the activity of the enzyme against insoluble forms of cellulose but not against carboxymethylcellulose. The increase in cellulase activity was not observed when the CBDs were incubated with the catalytic domain of either EGE or XYLA, with insoluble cellulose and a cellulose/hemicellulose complex respectively as the substrates. Pseudomonas CBDs did not induce the extension of isolated plant cell walls nor weaken cellulose paper strips in the same way as a class of plant cell wall proteins called expansins. The XYLACBD and CELECBD did not release small particles from the surface of cotton. The significance of these results in relation to the mode of action of Type II CBDs is discussed.

Bacterial Proteins↗
PubMed1998

Prevalence of microalbuminuria in children with sickle cell disease.

Renal involvement is common in homozygous sickle cell disease (HbSS), including glomerular hypertension and hypertrophy similar to that seen in rodent models of ablative nephrectomy and stage I diabetic nephropathy (DN). The proteinuria in the rodent models is attenuated by angiotensin converting enzyme inhibition (ACEI). Microalbuminuria (MA) is a sensitive marker for renal involvement in DN prior to the development of proteinuria, and is also attenuated with ACEI. Elevated urinary microalbumin/creatinine ratios (U Alb/Cr) >20 mg/g Cr are reported in 39%-43% of adults with HbSS, and studies are ongoing in this age group to assess the effect of attenuated proteinuria by ACEI on long-term renal function. The purpose of this study was to prospectively investigate the prevalence of MA in children with HbSS and determine factors which affect its expression. U Alb/Cr values were measured on spot urine samples in 102 children (aged 2-18 years, mean 9.47+/-4.62, M:F=53:49) by rate nephelometry. Children with prior known proteinuria, hypertension, or fever/pain episode in the last 15 days were excluded. MA was present in 26.5% of all children with HbSS. However, in children between the ages of 10 and 18 years, the prevalence was 46% (similar to the prevalence in adults). There was a strong correlation between patient age and prevalence of MA (P<0.0001) by both univariate and multivariate analysis. However, pain frequency, hospitalization, transfusion program, ferritin levels, and Cr clearance (C(Cr)) did not correlate with prevalence, although C(Cr) (as estimated by Schwartz formula) was elevated in all. We conclude that the prevalence of MA in the 2nd decade of life is similar to that in adults.

Adolescent↗
PubMed1998

Impaired exercise capacity late after cardiac transplantation: influence of chronotropic incompetence, hypertension, and calcium channel blockers.

BACKGROUND AND METHODS: Patients undergoing orthotopic cardiac transplantation manifest reduced exercise capacity during the first postoperative year, which is related primarily to chronotropic incompetence of the denervated heart. To determine whether exercise capacity improves during the long term after transplantation, we prospectively studied 45 patients from 1 month to 6 years after cardiac transplantation by use of maximal treadmill exercise testing for measurement of exercise duration, peak heart rate, and peak VO2. All had normal left ventricular ejection fractions. Patients were categorized according to length of time since transplant and compared to 14 untrained normal subjects. RESULTS: Peak exercise heart rate and exercise duration were progressively higher as time after transplantation increased. However, patients who had undergone transplantation more than 2 years earlier continued to manifest a significant reduction in peak exercise heart rate (157+/-3 beats/min vs 178+/-14 beats/min) and reduced exercise duration (8.6+/-0.5 minutes vs 13.2+/-2.0 minutes) compared with controls. In contrast, peak VO2 was similar at all times after transplant and remained markedly reduced in patients who underwent transplantation more than 2 years earlier as compared with controls (22.1+/-0.7 mL/kg/min vs 42.1+/-9.1 mL/kg/min). The potential effects of 14 clinical variables on exercise performance were evaluated by regression modeling. Patients with poorly controlled hypertension had a shorter median exercise duration (7.4 minutes vs 9.7 minutes) and a lower median peak VO2 (20.3 mL/kg/min vs 23.2 mL/kg/min) compared with patients with normal or well-controlled blood pressure. Patients treated with calcium channel blockers for hypertension had greater chronotropic incompetence during exercise (peak heart rate 139 beats/min vs 158 beats/min). There was no relation between exercise capacity and recipient age, donor age, recipient sex, donor ischemic time, pretransplant diagnosis, length of peritransplant hospitalization, percentage of ideal body weight, left ventricular ejection fraction, frequency or severity of allograft rejection, or long-term use of oral prednisone therapy. CONCLUSIONS: Exercise capacity, as measured by treadmill exercise time and peak heart rate, improves in the first 2 years after transplantation, but does not reach normal values in patients up to 6 years after transplant. Peak VO2 remains significantly reduced at all times after transplantation despite the presence of normal resting left ventricular systolic function.

Adult↗
PubMed1998

Use of Emergency Medical Service transport system in medical patients up to 36 months of age.

OBJECTIVES: To determine the frequency of inappropriate transport by Emergency Medical Service (EMS). DESIGN: A retrospective study. SUBJECTS: Patients up to 36 months of age with medical complaints transported by EMS to an urban pediatric emergency department (ED). INTERVENTIONS: None. MEASUREMENTS: Arbitrary criteria for appropriate use of EMS transport system were developed. The age, triage status, number of previous uses of EMS, health insurance status, time of calls, chief complaint, and clinical management of patients in the ED were determined. The frequency of inappropriate use of EMS was determined and also the percentage of patients up to 36 months of age who used EMS transport system on more than one occasion. RESULTS: Charts of 341 patients were reviewed of which 126 patients (37%) could have been transported by nonemergent vehicles according to our arbitrary criteria. In addition 97 (28%) of these patients had used the EMS transport system on at least one other occasion. CONCLUSIONS: EMS is utilized for inappropriate transportation in approximately 37% of our pediatric patients less than 36 months of age with medical complaints. In addition, 28% of these same patients utilized the EMS system on more than one occasion. It would appear that education of care providers in the appropriate use of EMS and use of alternate means of transportation would make the system more efficient and productive.

Ambulances↗
PubMed1998

Use of topical lidocaine in pediatric laceration repair: a review of topical anesthetics.

OBJECTIVE: To determine whether application of topical aqueous lidocaine to a laceration attenuates the pain from the subsequent lidocaine injection in children. DESIGN: Prospective, double-blind study. SETTING: A large, urban, tertiary care children's hospital emergency department. PATIENTS: A convenience sample of 100 children, five to 16 years of age, presenting with simple lacerations over a six-month period. INTERVENTIONS: An unlabelled 3-ml solution of either 1% lidocaine or placebo (saline) was used to soak a Telfa pad (Kendall, Mansfield, MA) and then placed onto the laceration for 10 minutes. The wound was then injected with 1% lidocaine, irrigated, and sutured per standard emergency department protocol. Independent pain response was elicited from the patient and parent four times: before any intervention, after the soak, after the injection, and at the end of the procedure. Blood pressure and heart rates were recorded at the same intervals. RESULTS: Four patients were excluded. Of the 96 remaining patients, 46 received the placebo and 50 received lidocaine. Age, sex, race, and laceration length and location were similar between groups. Physiologic parameters did not differ between groups. For all four pain ratings, the independent variables of age, sex, race, and laceration length or location did not differ between groups. Topical lidocaine was ineffective in relieving pain from the injection. When groups were combined, a significant negative correlation was noted for age versus injection pain (P = .035), with older children reporting less pain from injection than younger children. CONCLUSION: For children, soaking a simple laceration with 1% lidocaine does not decrease pain from the subsequent lidocaine injection.

Adolescent↗
PubMed1997

Requirement for dynamin during Notch signaling in Drosophila neurogenesis.

Singling out of a unique neural precursor from a group of equivalent cells, during Drosophila neurogenesis, involves Notch-mediated lateral signaling. During this process, activation of the Notch signaling pathway leads to repression of neural development. Disruption of this signaling pathway results in the development of an excess of neural cells. The loss of activity of dynamin, which is encoded by the gene shibire and is required for endocytosis, results in a similar phenotype. Here we have investigated the requirement of shibire function for Notch signaling during the segregation of sensory bristles on the notum of the fly. Overexpression of different constitutively active forms of Notch in shibire mutant flies indicates that shibire function is not necessary for transduction of the signal downstream of Notch, even when the receptor is integrated in the plasma membrane. However, when wild-type Notch is activated by its ligand Delta, dynamin is required in both signaling and receiving cells for normal singling out of precursors. This suggests an active role of the signaling cell for ligand-mediated receptor endocytosis in the case of transmembrane ligands. We discuss the possible implications of these results for normal functioning of Notch-mediated lateral signaling.

Animals↗
PubMed1997

u-shaped encodes a zinc finger protein that regulates the proneural genes achaete and scute during the formation of bristles in Drosophila.

The pattern of the large sensory bristles on the notum of Drosophila arises as a consequence of the expression of the achaete and scute genes. The gene u-shaped encodes a novel zinc finger that acts as a transregulator of achaete and scute in the dorsal region of the notum. Viable hypomorphic u-shaped mutants display additional dorsocentral and scutellar bristles that result from overexpression of achaete and scute. In contrast, overexpression of u-shaped causes a loss of achaete-scute expression and consequently a loss of dorsal bristles. The effects on the dorsocentral bristles appear to be mediated through the enhancer sequences that regulate achaete and scute at this site. The effects of u-shaped mutants are similar to those of a class of dominant alleles of the gene pannier with which they display allele-specific interactions, suggesting that the products of both genes cooperate in the regulation of achaete and scute. A study of the sites at which the dorsocentral bristles arise in mosaic u-shaped nota, suggests that the levels of the u-shaped protein are crucial for the precise positioning of the precursors of these bristles.

Amino Acid Sequence↗
PubMed1997

Transcriptional activity of pannier is regulated negatively by heterodimerization of the GATA DNA-binding domain with a cofactor encoded by the u-shaped gene of Drosophila.

The genes pannier (pnr) and u-shaped (ush) are required for the regulation of achaete-scute during establishment of the bristle pattern in Drosophila. pnr encodes a protein belonging to the GATA family of transcription factors, whereas ush encodes a novel zinc finger protein. Genetic interactions between dominant pnr mutants bearing lesions situated in the amino-terminal zinc finger of the GATA domain and ush mutants have been described. We show here that both wild-type Pannier and the dominant mutant form activate transcription from the heterologous alpha globin promoter when transfected into chicken embryonic fibroblasts. Furthermore, Pnr and Ush are found to heterodimerize through the amino-terminal zinc finger of Pnr and when associated with Ush, the transcriptional activity of Pnr is lost. In contrast, the mutant pnr protein with lesions in this finger associates only poorly with Ush and activates transcription even when cotransfected with Ush. These interactions have been investigated in vivo by overexpression of the mutant and wild-type proteins. The results suggest an antagonistic effect of Ush on Pnr function and reveal a new mode of regulation of GATA factors during development.

Animals↗
PubMed1997

Notch signalling in development: on equivalence groups and asymmetric developmental potential.

Notch-mediated lateral signalling takes place between equivalent cells that then adopt alternative fates. An example is the epidermal-neural choice in the Drosophila neuro-ectoderm. Sometimes this choice is random. Sometimes it is biased to a preferred cell by an extrinsic signal. Sometimes the neural precursor is predetermined. A stochastic outcome is probably older in evolutionary terms.

Animals↗
PubMed1997

The LIN-12/Notch signaling pathway and its regulation.

Notch, LIN-12, and GLP-1 are receptors that mediate a broad range of cell interactions during Drosophila and nematode development. Signaling by these receptors relies on a conserved pathway with three core components: DSL ligand, LNG receptor, and a CSL effector that links the receptor to its transcriptional response. Although key functional regions have been identified in each class of proteins, the mechanism for signal transduction is not yet understood. Diverse regulatory mechanisms influence signaling by the LIN-12/Notch pathway. Inductive signaling relies on the synthesis of ligand and receptor in distinct but neighboring cells. By contrast, lateral signaling leads to the transformation of equivalent cells that express both ligand and receptor into nonequivalent cells that express either ligand or receptor. This transformation appears to rely on regulatory feedback loops within the LIN-12/Notch pathway. In addition, the pathway can be regulated by intrinsic factors that are asymmetrically segregated during cell division or by extrinsic cues via other signaling pathways. Specificity in the pathway does not appear to reside in the particular ligand or receptor used for a given cell-cell interaction. The existence of multiple ligands and receptors may have evolved from the stringent demands placed upon the regulation of genes encoding them.

Animals↗
PubMed1997

Transcriptional regulation of Notch and Delta: requirement for neuroblast segregation in Drosophila.

Segregation of a single neural precursor from each proneural cluster in Drosophila relies on Notch-mediated lateral signalling. Studies concerning the spacing of precursors for the microchaetes of the peripheral nervous system suggested the existence of a regulatory loop between Notch and its ligand Delta within each cell that is under transcriptional control. Activation of Notch leads to repression of the achaete-scute genes which themselves regulate transcription of Delta, perhaps directly. Here we have tested a requirement for transcriptional regulation of Notch and/or Delta during neuroblast segregation in embryos, by providing Notch and Delta ubiquitously at uniform levels. Neuroblast segregation occurs normally under conditions of uniform Notch expression. Under conditions of uniform Delta expression, a single neuroblast segregates from each proneural group in 80% of the cases, more than one in the remaining 20%. Thus transcriptional regulation of Delta is largely dispensable. We discuss the possibility that segregation of single precursors in the central nervous system may rely on a heterogeneous distribution of neural potential between different cells of the proneural group. Notch signalling would enable all cells to mutually repress each other and only a cell with an elevated neural potential could overcome this repression.

Animals↗
PubMed1997

Experience with gastrojejunal feeding tubes in children.

OBJECTIVE: Assessment of untoward symptomatic outcomes and major/minor complications occurring in children with percutaneous gastrojejunal tubes (GJT) in place. METHODS: A retrospective chart review of 28 patients with GJTs was performed. The diagnoses for these patients were: neurological diseases, 23; respiratory diseases, two; and gastrointestinal tract disorders, three. Twenty-three tubes were placed radiologically, four endoscopically, and one surgically. Patients' age range was between 1.5 and 180 months (mean 47.2 months), and weight at the time of tube insertion was between 2.28 and 42.7 kg. (mean 11.7 kg.). Duration of follow-up was from 1 to 49 months (mean 17.3 months). The patients were evaluated for the persistence or new development of the following symptoms: vomiting, hematemesis, abdominal pain, constipation, diarrhea, pain at the site of gastrostomy tube insertion, stridor with feeds, and dumping. Minor complications (including breakage, partial/total displacement, or dislodgement of GJT, tube occlusion, tube leakage, transient infection and/or granuloma at the gastrostomy site, and continued gastroesophageal reflux post-GJT conversion), as well as major complications (requiring surgical intervention) and mortality, were assessed. RESULTS: One or more symptoms either persisted or developed de novo in 20 children after tube insertion. Vomiting was the most common symptom, being present in 16 patients. One or more minor complication occurred in 21 patients; the most common was the accidental dislodgement of the jejunal feeding catheter. Major complications occurred in 11 patients (e.g., fundoplication in seven patients). Five patients died. Six patients had no complications; at the time of GJT placement, their mean age (93.3 months) was significantly older (p = 0.0269) and mean weight (21.3 kg.) significantly heavier (p = 0.0067) than those of children reporting major complications. CONCLUSIONS: We conclude that ongoing or new gastrointestinal symptoms and minor complications are common in children with GJT. However, GJT placement in larger children is associated with fewer complications than in smaller children.

Abdominal Pain↗
PubMed1997

Distribution of astigmatism among Sioux Indians in South Dakota.

BACKGROUND: Previous studies have reported a greater prevalence of high astigmatism and vision disorders among Native Americans than occurs in the general U.S. population. The majority of these studies, however, have focused on Native American schoolchildren. This study assessed the distribution of astigmatism in a general clinic population at the Rosebud Indian Reservation in South Dakota. METHODS: From examination of 174 patients, demographic information, visual acuities, refractive error, binocular vision status, and eye health were recorded. RESULTS: The data showed more high astigmatism than would be expected in a general U.S. population. Three or more diopters of astigmatism were found in 9.2% of the right eyes and 10.8% of the left eyes in the study population. High astigmatism was noted less frequently among those ages 40 years and older (3.3% right eyes, 6.3% left eyes). Most of the astigmatism was with-the-rule, but a shift toward against-the-rule and oblique astigmatism was found in older individuals. No significant gender differences were noted. CONCLUSIONS: The results suggest an ethnic difference in astigmatism and emphasize thee need for continued and expanded vision services for Native American populations.

Adolescent↗
PubMed1997

Juvenile rheumatoid arthritis in African Americans.

OBJECTIVE: To examine racial differences in disease expression in African American and Caucasian children with pauciarticular and polyarticular juvenile rheumatoid arthritis (JRA). METHODS: A retrospective chart review was conducted of 35 African American and 137 Caucasian children with pauciarticular and polyarticular JRA. RESULTS: African American children were significantly older than Caucasian children at the time of presentation. This was true both for the group as a whole and for each of the disease onset subtypes. African American children were less likely to have positive antinuclear antibody tests than Caucasian children. This finding paralleled a low incidence of uveitis in African American children. African American children were also more likely to have IgM rheumatoid factors (detected by latex agglutination) than Caucasian children. This was true even for African American children with pauciarticular JRA. CONCLUSION: There are significant phenotypic differences between African American and Caucasian children with JRA.

Adolescent↗
PubMed1996

A prepattern for sensory organs. Drosophila development.

The sensory bristles of Drosophila arise in stereotyped positions from small clusters of cells that express achaete-scute genes. A set of genes has now been identified that regulate achaete-scute expression and form a prepattern for sensory bristle development.

Animals↗