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Biomedical subjects

D A Johnson

Publications and source records attributed to D A Johnson.

At least 55 records · Page 3Linked to original sources
PubMed2000

Molecular signals for development of neuronal circuitry in the retina.

In this review article, we summarize recently accumulated knowledge regarding the molecular mechanisms, which control retinal development. Retinal neurons are born in two waves of cytogenesis. In the first wave, neurons of cone circuitry are generated, whereas in the second wave, rod circuitry is added. Neurons generated in these two waves of cytogenesis differ in many respects, including the molecular cues used for migrational guidance. The neurons generated in the second phase of proliferation are arranged in radial columns associated with Müller cells, whereas those of the first phase are often found outside the radial columns. Certain early born cone photoreceptors may form templates for the arrangement of additional mosaics of other cell types. These mosaic arrangements of cell bodies are subsequently refined by lateral displacement of cells and apoptosis. Müller cells may play an important role in directing migration of second phase neurons within groups of radial columns and also in guiding the projections of these neurons so that specific connections are formed. The Müller cell's ability to exert these influences perhaps resides in a variety of cell adhesion molecules such as L1/NgCAM, F11, and 5A11, which are expressed on the surface of Müller cells and retinal neurons. CAMs also promote neurite outgrowth through second messenger pathways.

Animals↗
PubMed2000

Salivary alterations in type 2 (non-insulin-dependent) diabetes mellitus and hypertension.

OBJECTIVES: The aim of this study was to determine whether saliva output and composition are altered in type 2 diabetes mellitus by comparison with a healthy, non-medicated control group, and also a group of hypertensives. METHODS: From a community-dwelling cohort of Mexican American and European American subjects enrolled in the OH:SALSA oral aging study, we identified 233 subjects with type 2 diabetes mellitus, 227 with hypertension, and 240 healthy control subjects. We collected unstimulated whole (UW) and submandibular/ sublingual (US) saliva, as well as stimulated parotid (SP) and submandibular/ sublingual (SS) saliva. Flow rates were determined, yeast carriage was assayed in UW saliva, and SP and SS saliva samples were analyzed for protein composition. ELISA was used to determine concentrations of an array of specific protein components, with both antimicrobial and other activities. RESULTS: Both diabetic and hypertensive subjects had reduced output of both stimulated and unstimulated submandibular/sublingual saliva. 30% of the diabetic subjects had high oral yeast counts (> or =1000 cfu/mL) compared with 17% of the healthy subjects and 20% of the hypertensives. Significant increases in the concentrations of a number of the protein components were found in the diabetic subjects, specifically, SP lactoferrin, myeloperoxidase (MPO), and salivary peroxidase (SPO), as well as SS total protein, albumin, lactoferrin and secretory IgA. CONCLUSIONS: The pattern of decreased flow rates and increased protein concentrations were similar, but consistently greater in diabetics than hypertensives, suggesting that disease-specific mechanisms may be responsible. Diabetics may be more prone to oral dryness and infections than non-diabetics.

Adult↗
PubMed2000

Esomeprazole improves healing and symptom resolution as compared with omeprazole in reflux oesophagitis patients: a randomized controlled trial. The Esomeprazole Study Investigators.

BACKGROUND: The pharmacologic profile of the new proton pump inhibitor esomeprazole has demonstrated advantages over omeprazole that suggest clinical benefits for patients with acid-related disease. METHODS: 1960 patients with endoscopy-confirmed reflux oesophagitis (RO) were randomized to once daily esomeprazole 40 mg (n=654) or 20 mg (n=656), or omeprazole 20 mg (n=650), the standard recommended dose for RO, for up to 8 weeks in a US, multicentre, double-blind trial. The primary efficacy variable was the proportion of patients healed at week 8. Secondary variables included healing and heartburn resolution at week 4, time to first resolution and sustained resolution of heartburn, and per cent of heartburn-free days and nights. Safety and tolerability were also evaluated. RESULTS: Significantly more patients were healed at week 8 with esomeprazole 40 mg (94.1%) and 20 mg (89.9%) vs. omeprazole 20 mg (86.9%), using cumulative life table estimates, ITT analysis (each P < 0.05). Esomeprazole 40 mg was also significantly more effective than omeprazole for healing at week 4 and for all secondary variables evaluating heartburn resolution. The most common adverse events in all treatment groups were headache, abdominal pain and diarrhoea. CONCLUSION: Esomeprazole was more effective than omeprazole in healing and symptom resolution in GERD patients with reflux oesophagitis, and had a tolerability profile comparable to that of omeprazole.

Adult↗
PubMed2000

Propionibacterium acnes as a cause of visually significant corneal ulcers.

PURPOSE: To report Propionibacterium acnes as a cause of vision-threatening infectious keratitis and to discuss culture isolation and antibiotic treatment. METHODS: Retrospective case series presentation collected from three academic medical centers. RESULTS: Six cases of P. acnes infectious keratitis are presented, all of which were associated with a compromised corneal barrier or environment. All cases were culture-positive on thioglycolate broth; none became positive before 7 days of growth. No other organisms were isolated from any culture, and the growth of P. acnes occurred in some cases despite negative gram stains. CONCLUSION: P. acnes can produce vision-debilitating keratitis when the cornea is compromised. Growth in culture should be monitored for at least 10 days to ensure isolation of this fastidious organism. P. acnes may respond to several different antibiotics that have gram-positive coverage, but it should be treated with vancomycin to enhance clearance of the organism.

Adult↗
PubMed2000

Association of salivary flow rates with maximal bite force.

Mean salivary secretion and bite force decrease with advancing age. Previous studies have shown that salivary flow rates are influenced by mastication. In the present study, we examined the relationship between salivary flow rates and maximal bite force in a community-based sample of men and women 35 years of age or older. Salivary flow rates for unstimulated whole and unstimulated submandibular/sublingual (SMSL) saliva as well as citrate-stimulated parotid and SMSL saliva were measured in 399 subjects. Bite force was assessed with a bilateral force transducer. Pearson correlation analysis yielded significant positive correlations between bite force and flow rates for unstimulated whole saliva (r = 0.24, p < 0.0001), stimulated parotid saliva (r = 0.13, p < 0.03), unstimulated SMSL (r = 0.14, p < 0.0001), and stimulated SMSL (r = 0.16, p < 0.003). When adjusted for age and gender, the partial correlations between bite force and salivary flow rates remained significant for unstimulated whole saliva (r = 0.10, p < 0.05), stimulated parotid saliva (r = 0.13, p < 0.02), and stimulated SMSL saliva (r = 0.14, p < 0.006). Subjects were divided into four groups based on their maximal bite force score (low, medium low, medium high, and high). For each saliva type, the flow rate of the high-bite-force group was significantly greater than that of the low-bite-force group as well as that of the medium-high-bite-force group. These results confirm an age-related decrease in bite force and salivary flow rates and show that, regardless of age or gender, bite force is correlated with salivary flow.

Adult↗
PubMed2000

Cloning and molecular characterisation of the trout (Oncorhynchus mykiss) vacuolar H(+)-ATPase B subunit.

The current model of transepithelial ion movements in the gill of freshwater fish incorporates an apically oriented vacuolar H(+)-ATPase (H(+)V-ATPase; proton pump) that is believed to facilitate both acid excretion and Na(+) uptake. To substantiate this model, we have cloned and sequenced a cDNA encoding the B subunit of the rainbow trout (Oncorhynchus mykiss) H(+)V-ATPase. The cloning of the B subunit enabled an examination by northern analysis of its tissue distribution and expression during external hypercapnia. Degenerate oligonucleotide primers to the B subunit of the H(+)V-ATPase were designed and used in a semi-nested polymerase chain reaction (PCR) to amplify an 810 base pair (bp) product from a trout gill/kidney cDNA library. This PCR product was cloned and sequenced and then used to screen the same cDNA library. The assembled 2262 bp cDNA included an open reading frame coding for a deduced protein of 502 amino acid residues. A BLAST search of the GenBank nucleotide database revealed numerous matches to other vertebrate and invertebrate H(+)V-ATPase B subunits. Protein alignment demonstrated that the trout H(+)V-ATPase B subunit is more than 85 % identical and more than 90 % similar to those in other vertebrate species. An initial analysis of H(+)V-ATPase mRNA tissue distribution revealed significant expression in blood. Although a comparison of perfused tissues (blood removed) with non-perfused tissues demonstrated no obvious contribution of the blood to total tissue H(+)-ATPase mRNA levels, all subsequent experiments were performed using perfused tissues. Levels of H(+)V-ATPase mRNA expression were high in the gill, kidney (anterior or posterior), intestine, heart and spleen, but lower in liver and white muscle. Exposure of the fish to 12 h of external hypercapnia (water P(CO2)=7. 5 mmHg; 1 kPa) was associated with a transient increase (at 2 h) in the levels of H(+)V-ATPase B subunit mRNA in gill and kidney; liver mRNA levels were unaffected. These results are consistent with the hypothesis of an apically localised plasma membrane H(+)V-ATPase in the freshwater trout gill and that the expression of this proton pump is increased during periods of acidosis, at least in part because of an increased steady-state level of H(+)V-ATPase mRNA.

Amino Acid Sequence↗
PubMed1999

3-O-Desacyl monophosphoryl lipid A derivatives: synthesis and immunostimulant activities.

The synthesis of a series of novel analogues of lipid A, the active principle of lipopolysaccharide, is reported. In these compounds, the 1-O-phosphono and (R)-3-hydroxytetradecanoyl moieties of native Salmonella minnesota R595 lipid A have been replaced with hydrogen and the length of the normal fatty acyl residues has been systematically varied. Normal fatty acid chain length in the 3-O-desacyl monophosphoryl lipid A (MLA) series is shown to be a critical determinant of iNOS gene expression in activated mouse macrophages and the induction of proinflammatory cytokines in human peripheral monocytes. Examination of pyrogenicity in rabbits and lethal toxicity in D-galactosamine-treated mice shows that toxic effects in the MLA series can be ameliorated by modifying fatty acid chain length. When used as an adjuvant for tetanus toxoid vaccines, certain MLA derivatives enhance the production of tetanus toxoid-specific antibodies in mice.

Adjuvants, Immunologic↗
PubMed1999

Mobilization of the A-kinase N-myristate through an isoform-specific intermolecular switch.

Although the catalytic (C) subunit of cAMP-dependent protein kinase is N-myristylated, it is a soluble protein, and no physiological role has been identified for its myristyl moiety. To determine whether the interaction of the two regulatory (R) subunit isoforms (R(I) and R(II)) with the N-myristylated C subunit affects its ability to target membranes, the effect of N-myristylation and the R(I) and R(II) subunit isoforms on C subunit binding to phosphatidylcholine/phosphatidylserine liposomes was examined. Only the combination of N-myristylation and R(II) subunit interaction produced a dramatic increase in the rate of liposomal binding. To assess whether the R(II) subunit also increased the conformational flexibility of the C subunit N terminus, the effect of N-myristylation and the R(I) and R(II) subunits on the rotational freedom of the C subunit N terminus was measured. Specifically, fluorescein maleimide was conjugated to Cys-16 in the N-terminal domain of a K16C mutant of the C subunit, and the time-resolved emission anisotropy was determined. The interaction of the R(II) subunit, but not the R(I) subunit, significantly increased the backbone flexibility around the site of mutation and labeling, strongly suggesting that R(II) subunit binding to the myristylated C subunit induced a unique conformation of the C subunit that is associated with an increase in both the N-terminal flexibility and the exposure of the N-myristate. R(II) subunit thus appears to serve as an intermolecular switch that disrupts of the link between the N-terminal and core catalytic domains of the C subunit to expose the N-myristate and poise the holoenzyme for interaction with membranes.

Cyclic AMP-Dependent Protein Kinases↗
PubMed1999

Mitomycin resistance in mammalian cells expressing the bacterial mitomycin C resistance protein MCRA.

The mitomycin C-resistance gene, mcrA, of Streptomyces lavendulae produces MCRA, a protein that protects this microorganism from its own antibiotic, the antitumor drug mitomycin C. Expression of the bacterial mcrA gene in mammalian Chinese hamster ovary cells causes profound resistance to mitomycin C and to its structurally related analog porfiromycin under aerobic conditions but produces little change in drug sensitivity under hypoxia. The mitomycins are prodrugs that are enzymatically reduced and activated intracellularly, producing cytotoxic semiquinone anion radical and hydroquinone reduction intermediates. In vitro, MCRA protects DNA from cross-linking by the hydroquinone reduction intermediate of these mitomycins by oxidizing the hydroquinone back to the parent molecule; thus, MCRA acts as a hydroquinone oxidase. These findings suggest potential therapeutic applications for MCRA in the treatment of cancer with the mitomycins and imply that intrinsic or selected mitomycin C resistance in mammalian cells may not be due solely to decreased bioactivation, as has been hypothesized previously, but instead could involve an MCRA-like mechanism.

Aerobiosis↗
PubMed1999

Synthesis and biological evaluation of a new class of vaccine adjuvants: aminoalkyl glucosaminide 4-phosphates (AGPs).

A novel series of acylated omega-aminoalkyl 2-amino-2-deoxy-4-phosphono-beta-D-glucopyranosides (aminoalkyl glucosaminide 4-phosphates) was synthesized and screened for immunostimulant activity. Several of these compounds enhance the production of tetanus toxoid-specific antibodies in mice and augment vaccine-induced cytotoxic T cells against EG.7-ova target cells.

Adjuvants, Immunologic↗
PubMed1999

Binding-dependent disorder-order transition in PKI alpha: a fluorescence anisotropy study.

The conformational flexibility of peptidyl ligands may be an essential element of many peptide-macromolecular interactions. Consequently, the alpha-carbonyl backbone flexibility of the 8 kDa protein kinase inhibitor (PKI alpha) peptide of cAMP-dependent protein kinase (cAPK) free in solution and bound to cAPK was assessed by time-resolved fluorescence anisotropy. Specifically, three full-length, single-site PKI alpha mutants (V3C, S28C, and S59C) were prepared, and fluorescein iodoacetamide (FI) was selectively conjugated to the side chains of each substituted cysteine. The time-resolved anisotropy decay profiles of the labeled mutants were well fit to a model-free nonassociative biexponential equation. Free in solution, the three labeled proteins had very similar anisotropy decays arising primarily from local alpha-carbonyl backbone movements. Only a small fraction of the anisotropy decay was associated with slower, whole-body tumbling, confirming that PKI alpha is highly disordered at all three locations. Complexation of the mutants with the catalytic (C) subunit of cAPK decreased the rate of whole-body tumbling for all three mutants. The effects on the rapid decay processes, however, were dependent upon the site of conjugation. The anisotropy decay profiles of both FI-V3C- and FI-S28C-PKI alpha were associated with significantly reduced contributions from the fast decay processes, while that of FI-S59C-PKI alpha was largely unaffected by binding to the C-subunit. The results suggest that the cAPK-binding domain of PKI alpha extends from the its N-terminus to residues beyond Ser28 but does not include the segment around Ser59, which is still part of a highly flexible domain when bound to the C-subunit.

Amino Acid Sequence↗
PubMed1999

Paramagnetic fluorescence quenching in a model membrane: a consideration of lifetime and temperature.

To expand our understanding of paramagnetic quenching in membranes, the relationship between fluorophore excited-state lifetime (tau), temperature, and the collisional quenching was studied. Specifically, the ability of tempo to quench the steady-state and time-resolved emission from five lipophilic fluorophores (diphenylhexatriene, perylene, phenanthrene, pyrene, and triphenylene) partitioned into egg phosphatidylcholine (EggPC) liposomes was examined. Also, the temperature dependence of spin-labeled androstane to quench the emission (steady-state and time-resolved) from perylene in EggPC liposomes was determined. Unexpectedly, in EggPC liposomes, the apparent quenching efficiency decreased with increasing tau until the effect leveled off above approximately 20 ns. Moreover, in EggPC liposomes, dynamic quenching decreased with increasing temperature. The results suggest that in membranes, paramagnetic quenching is more complex than generally recognized.

Journal Article↗
PubMed1999

Subcellular localization and partial purification of prelamin A endoprotease: an enzyme which catalyzes the conversion of farnesylated prelamin A to mature lamin A.

The nuclear lamina protein, lamin A is produced by proteolytic cleavage of a 74 kDa precursor protein, prelamin A. The conversion of this precursor to mature lamin A is mediated by a specific endoprotease, prelamin A endoprotease. Subnuclear fractionation indicates that the prelamin A endoprotease is localized at the nuclear membrane. The enzyme appears to be an integral membrane protein, as it can only be removed from the nuclear envelope with detergent. It is effectively solubilized by the detergent n-octyl-beta-D-glucopyranoside and can be partially-purified (approximately 1200-fold) by size exclusion and cation exchange (Mono S) chromatography. Prelamin A endoprotease from HeLa cells was eluted from Mono S with 0.3 M sodium chloride as a single peak of activity. SDS-PAGE analysis of this prelamin A endoprotease preparation shows that it contains one major polypeptide at 65 kDa and smaller amounts of a second 68 kDa polypeptide. Inhibition of the enzyme activity in this preparation by specific serine protease inhibitors is consistent with the enzyme being a serine protease.

Acrylic Resins↗
PubMed1999

Improving cognitive function after brain injury: the use of exercise and virtual reality.

OBJECTIVE: To assess the impact of exercise and virtual reality (VR) on the cognitive rehabilitation of persons with traumatic brain injury (TBI). DESIGN: Before-after trial assessed cognitive function after a 4-week intervention program. A random allocation crossover assessed changes in reaction and movement times after a single bout of VR exercise and a no-exercise control condition. SETTING: Brain injury rehabilitation unit in Edinburgh, Scotland. PATIENTS: (1) Four-week intervention: a consecutive sample of 13 suitable TBI adults were compared to control populations (n > 25) of previous TBI patients of similar age, severity, and time postinjury. (2) Single-bout intervention: a consecutive sample of 13 suitable adults with moderate TBI, 6.29 to 202.86 weeks postinjury. INTERVENTION: Nonimmersive VR exercise. MAIN OUTCOME MEASURES: (1) Tests of attention, information processing, learning, and memory. (2) Reaction and movement times. RESULTS: After the 4-week intervention patients performed significantly better than controls on the digit symbol (p < .01). verbal (p < .01), and visual learning tasks (p < .05). Significant improvements in reaction times (p < .01) and movement times (p < .05) were gained following a single bout of VR exercise. CONCLUSION: Exercising in a virtual environment offers the potential for significant gains in cognitive function.

Adolescent↗
PubMed1999

Peripheral steroid sulfatase inhibition potentiates improvement of memory retention for hippocampally administered dehydroepiandrosterone sulfate but not pregnenolone sulfate.

Dehydroepiandrosterone sulfate (DHEAS) improves memory retention when administered peripherally. Estrone-3-O-sulfamate (EMATE), a steroid sulfatase inhibitor, potentiates the effect of DHEAS on memory retention such that lower doses of DHEAS improve memory retention. It is not clear if this effect is mediated by both compounds entering the central nervous system. In the current studies, mice were trained to avoid footshock in a T-maze and memory retention was tested 1 week later. DHEAS, injected into the hippocampus after training, improved memory retention in a dose-dependent manner. In previous studies, pregnenolone sulfate (PREGS) improved memory retention when injected into the hippocampus. EMATE, administered peripherally, potentiated the effect of centrally administered DHEAS on memory retention. However, EMATE did not potentiate the effect of centrally administered PREGS. It was concluded that EMATE, acting peripherally, increased plasma levels of DHEAS which entered the brain and added to the effect of centrally administered DHEAS. The failure of EMATE to potentiate PREGS is discussed.

Animals↗