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Biomedical subjects

J D Johnson

Publications and source records attributed to J D Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1993

Application of the polymerase chain reaction to the diagnosis of human toxoplasmosis.

Toxoplasmosis may cause significant damage to the developing fetus and is a life-threatening opportunistic infection in immunocompromised persons. Serological investigation is unreliable, while isolation of the parasite is time consuming and may lack sensitivity. We have developed a system for detecting Toxoplasma gondii based on the amplification of the P30 gene using sequential rounds of PCR and nested primers. The clinical value of this technique was assessed by the investigation of a range of tissues taken from pregnant women, fetuses, neonates, AIDS patients and organ graft recipients. The PCR assay produced more positive reactions than isolation of the parasite by means of cell culture or animal inoculation. Extended autoradiography was found to be more sensitive than stained agarose gels for detecting the PCR product. Systematic contamination of PCR reactions was avoided but it was not possible to exclude sporadic contamination in certain cases. Detection of specific DNA is of clinical value in the investigation of the pregnant woman in order to assess the risk of transplacental passage of infection and in the fetus and neonate to identify congenital toxoplasmosis. Even so, PCR findings must be interpreted with caution because of the risk of a sample being contaminated. PCR may be the investigation of choice when brain biopsy is performed on a patient with AIDS and when toxoplasmosis associated with bone marrow transplantation is suspected.

AIDS-Related Opportunistic Infections↗
PubMed1993

Measurement of Toxoplasma IgM by a microparticle capture enzyme immuno-assay.

The microparticle capture enzyme immuno-assay (MEIA) is an automated system for measuring specific antibody by interaction with antigen-coated particles. An MEIA method for detecting toxoplasma-specific IgM was compared with established reference methods. The MEIA had an acceptable level of sensitivity and reproducibility and was easier to perform than conventional tests, but it required expensive, dedicated equipment and, in our study, false positive results were recorded with 7% of samples. MEIA could be used to investigate immunocompetent patients with suspected toxoplasmosis but positive findings should be confirmed by an alternative form of assay. The technique is not suitable for the investigation of neonates, for which a more sensitive method is required.

Agglutination Tests↗
PubMed1993

Differential cytokine gene expression and secretion after phagocytosis by a human monocytic cell line of Toxoplasma gondii compared with Mycobacterium tuberculosis.

Toxoplasma gondii infection may be clinically silent in immunocompetent individuals but may cause fatal disease in immunocompromised patients such as those with HIV infection. Proinflammatory cytokines are known to be important in murine resistance to T. gondii but there are no data from human models of infection. We have investigated whether phagocytosis of T. gondii, of Mycobacterium tuberculosis (a pathogen which elicits a granulomatous host immune response) and of inert latex particles by THP-1 cells, a human monocytic line, caused gene expression and secretion of tumour necrosis factor (TNF), IL-6 and IL-8. These cytokines are important in recruitment and activation of T lymphocytes, and both TNF and IL-6 may have direct antitoxoplasmacidal and antimycobacterial activity. Phagocytosis of T. gondii by THP-1 cells resulted in minimal gene expression and secretion of TNF, IL-6 and IL-8 similar to that following phagocytosis of inert latex particles. In contrast, phagocytosis of M. tuberculosis resulted in increased gene expression of TNF and IL-8 as well as increased secretion of all three cytokines, particularly IL-8. These observations may partially explain the frequency of non-inflammatory host responses to T. gondii in immunocompetent individuals.

Animals↗
PubMed1993

Insertion sequence elements in Bacillus thuringiensis subsp. darmstadiensis.

Two variants of insertion sequence IS231, named IS231G and H, were isolated from Bacillus thuringiensis subsp. darmstadiensis 73-E-10-2 (BTD2), an isolate toxic to dipteran insects, and characterized by DNA sequence analysis. They are encoded consecutively as direct repeats on an EcoRI fragment of 5.6 kilo base pairs. Direct tandem repeats of IS231 elements have not been previously reported. Both elements are closely related to other members of the IS231 family that have been isolated from B. thuringiensis strains toxic to lepidopteran as well as to dipteran insects. A close correlation exists between the evolutionary relationships of the IS231 sequences determined to data and the toxicity spectrum of the host cell. Probing of BTD2 DNA with a radiolabeled IS231G fragment demonstrated that IS231 elements are located on 55- and 34-MDa plasmids as well as on chromosomal DNA. Chromosomal DNA, but not plasmids, from BTD2 also hybridizes to another, unrelated insertion sequence, IS240, from B. thuringiensis subsp. israelensis, an isolate toxic to dipteran insects. BTD2, therefore, contains IS elements once thought to reside exclusively in either dipteran- or lepidopteran-specific subspecies of B. thuringiensis.

Bacillus thuringiensis↗
PubMed1993

Cancer-related channel selection: an extension for a sample of women who have had a mammogram.

This study examines the impact of three major classes of factors, triggers, impediments, and demographics, on the use of four different communication channels: doctors, friends/family, organizations, and media. A sample of women over forty (n = 209) who had a mammography were asked which channels they had turned to within the last year for cancer-related information. The most important variable in the significant discriminant functions was the degree of interpersonal influence within one's social network. These results are discussed in terms of their theoretic and pragmatic implications for the development of communication campaigns related to mammography screening.

Adult↗
PubMed1992

Characteristics of the F52 protein, a MARCKS homologue.

A recently cloned mouse cDNA designated F52 encodes a putative protein with striking sequence similarity to the MARCKS protein, a major cellular substrate for protein kinase C (PKC). Major regions of sequence similarity include the amino-terminal myristoylation consensus sequence and the central calmodulin-binding/PKC phosphorylation site domain. The F52 protein was expressed in Escherichia coli with apparent M(r) 50,000; it was a substrate for PKC and comigrated on two-dimensional electrophoresis with a myristoylated protein whose phosphorylation was stimulated by phorbol 12-myristate 13-acetate in mouse neuroblastoma cells. The F52 protein also was myristoylated in E. coli by co-expression with N-myristoyltransferase. A 24-amino acid peptide derived from the protein's phosphorylation site domain was a good substrate for PKC; like the cognate MARCKS peptide, it was phosphorylated with high affinity (S0.5 = 173 nM) and positive cooperativity (KH = 5.4). The F52 peptide also bound calmodulin with high affinity (Kd = less than 3 nM); this binding could be disrupted by phosphorylation of the peptide with PKC, with a half-time of 8 min. The F52 protein is clearly a member of the MARCKS family as defined by primary sequence; in addition, the two proteins share several key attributes that may be functionally important.

Amino Acid Sequence↗
PubMed1992

Differences in evaluations of communication channels for cancer-related information.

This study examined women's evaluations of communication channels which are major carriers of cancer-related information. A sample of women over 40 (n = 395) was asked which channels they had received cancer-related information from within the last year and what their evaluations were of these channels in terms of three dimensions: editorial tone (credibility), communication potential (presentation and style), and utility. Various statistical analyses revealed significant interactions between evaluations and channels and significant main effects for channels and for evaluations. Additional post hoc comparisons suggested that there was a general trend across channel characteristics to rate doctors and organizations more highly than friends/family and the media for providing cancer-related information, although the respondents did not perceive information received from doctors and organizations as more understandable or more novel than information obtained from the media. On the whole, friends and family were evaluated least positively. These results are discussed in terms of their relationship to other programmatic research in this area and their pragmatic implications for future cancer control efforts.

Adult↗
PubMed1992

Relative bioavailability of lead from mining waste soil in rats.

The purposes of this study were to determine the extent of absorption of lead (Pb) in mining waste soil from Butte, Montana, and to investigate the effect of mining waste soil dose (g soil/day) on tissue lead concentrations. Young, 7- to 8-week-old male and female Sprague-Dawley rats (5/sex/group) were given mining waste soil that contained 810 or 3908 ppm lead mixed in a purified diet (AIN-76) at four different dose levels (0.2, 0.5, 2, and 5% dietary soil) for 30 consecutive days. Standard groups included untreated controls and dosed feed soluble lead acetate groups (1, 10, 25, 100, and 250 micrograms Pb/g feed). The test soil dose levels bracketed a pica child's soil exposure level and the lead acetate concentrations bracketed the test soil dose levels of lead. Liver, blood, and femur were analyzed for total lead concentration using graphite furnace atomic absorption spectroscopy. Clinical signs, body weight, food consumption, and liver weights for test soil and standard groups were similar to control. Tissue lead concentrations from test soil animals were significantly lower than the tissue concentrations for the lead acetate group. Relative percentage bioavailability values, based on lead acetate as the standard, were independent of the two different test soils, dose levels, and sex and were only slightly dependent on the tissue (blood > bone, liver). Mean relative percentage bioavailability values of lead in the Butte mining waste soil were 20% based on the blood data, 9% based on the bone data, and 8% based on the liver data. The results of this study will provide the information needed to determine the significance of lead exposure from Butte soils in assessing human health risks as part of the Superfund Remedial Investigation/Feasibility Study process.

Animals↗
PubMed1992

Modulation of the Ca2+ channel voltage sensor and excitation-contraction coupling by silver.

Ag+ (0.5-10 microM) is known to produce a transient contraction of intact frog skeletal muscle fibers followed by complete inhibition of excitation-contraction (E-C) coupling. We have carried out physiological and biochemical experiments to investigate the basis of this effect. Dihydropyridine (DHP) Ca2+ channel blockers, which inhibit the voltage sensor of the Ca2+ channel, completely inhibit Ag+ contractions. Removal of extracellular Ca2+, or blockade of Ca2+ entry with cadmium, does not inhibit Ag+ contractions. Activation of the Ca2+ channel's voltage sensor with the Ca2+ channel agonists Bay K 8644 or with perchlorate, potentiates the Ag(+)-induced contraction. Ag+ binds to the partially purified rabbit skeletal muscle Ca2+ channel and inhibits DHP binding (IC50 = 1.1 microM) and sulfhydryl (SH) reactivity (IC50 = 0.11 microM) over the concentration range where it inhibits E-C coupling. Oxidation of free SH groups by H2O2 or their reaction with DTNB prevents Ag+ contractions, while DTT reduction of oxidized SH groups restores Ag+ contractions. These results suggest that Ag+ binds to critical SH groups on the DHP receptor Ca2+ channel, resulting in modification of the channel's voltage sensor and the failure of E-C coupling.

Animals↗
PubMed1992

Use of transvaginal endosonography in the evaluation of women with stress urinary incontinence.

Hypermobility of the bladder neck in response to increased intra-abdominal pressure is the anatomical cause of uncomplicated stress urinary incontinence in women. Transvaginal endosonography is a reliable, minimally invasive technique for demonstrating bladder neck hypermobility in patients with genuine stress urinary incontinence. Of 279 patients with genuine stress urinary incontinence evaluated during a 24-month period 271 (97%) had bladder neck hypermobility demonstrated by transvaginal endosonography. Resolution of stress urinary incontinence after surgical bladder neck suspension correlated with stabilization of bladder neck mobility on ultrasound examination. The technique is painless and easily performed in the office setting.

Female↗
PubMed1992

Cell swelling, blebbing, and death are dependent on ATP depletion and independent of calcium during chemical hypoxia in a glial cell line (ROC-1).

The morphological and biochemical changes that occur during chemical hypoxic injury in a neural cell line were studied in the presence and absence of calcium. Oligodendroglial-glioma hybrid cells (ROC-1) were subjected to inhibitors of glycolytic and oxidative ATP synthesis (chemical hypoxia). Complete respiratory inhibition depleted [ATP] to less than 5% of control by 4 min. Blebs appeared on the cell surfaces and cells began to swell within a few minutes of ATP depletion. A 200% increase in cell volume and bleb coalescence preceded irreversible cell injury (lactate dehydrogenase release) which began at approximately 20 min with 50% cell death by 40 min. In energized cells an equivalent degree of osmotic swelling induced by ouabain inhibition of the Na+, K(+)-ATPase pump did not produce blebbing or cell death. Partial inhibition of respiration decreased [ATP] to approximately 10% of control by 40 min. Blebbing and swelling began at 40 min and bleb coalescence preceded plasma membrane disruption which began at approximately 55 min. ATP depletion, blebbing, swelling, and death followed similar time courses in the presence or absence of extracellular calcium ([Ca2+]e). Intracellular calcium ([Ca2+]i) was measured using fura-2. In calcium-containing medium metabolic inhibition caused a transient increase in resting [Ca2+]i (100 +/- 17 nM) followed by a low steady-state level preceding plasma membrane disruption. Following deenergization in calcium-free medium, [Ca2+]i remained below 60 nM throughout injury and death. These data suggest that decreased ATP initiates a sequence of events including bleb formation and cell swelling that lead to irreversible cell injury in the absence of large increases in [Ca2+]i.

Adenosine Triphosphate↗
PubMed1992

Expanding health insurance coverage and the implications for dentistry.

Numerous proposals have been suggested for expanding health insurance coverage to the over 30 million Americans without health insurance. These proposals range from establishing a program of national health insurance modeled after the Canadian system to establishing statewide risk pools. Many of these proposals could have an impact on financial access to dental care for the approximately 120 million people without dental insurance. Dental insurance coverage has been shown to increase access to dental services and improve oral health status. Oral health professionals could facilitate discussions concerning health insurance expansion by informing policymakers about important preventive benefits to be gained by improving access to dental services. Dental public health professionals can serve as a bridge between organized dentistry and health policymakers by providing information to help formulate the priorities and characteristics of a dental health insurance program. This visibility and influence in the health policy arena would be beneficial to dentistry and could ultimately result in greater access to dental services and improved oral health for the uninsured.

Dental Health Services↗
PubMed1992

Effect of temperature on relaxation rate and Ca2+, Mg2+ dissociation rates from parvalbumin of frog muscle fibres.

1. Influence of temperature on relaxation rate as a function of isometric tetanus duration and on Ca2+ and Mg2+ dissociation rates from purified parvalbumin (PA) was examined to test the hypothesis that PA promotes relaxation in frog skeletal muscle. Single fibres and PA IVB from Rana temporaria skeletal muscle were utilized. 2. The magnitude of slowing of relaxation rate with increasing tetanus duration, relative to the final, steady value of relaxation rate, is 3-fold greater at O than at 10 degrees C. 3. In the 0-10 degrees C range, the Q10 for relaxation rate increases from 2.3 to 3.7 with increasing tetanus duration. 4. Dissociation of Ca2+ and Mg2+ from PA exhibited: (i) rate constants of 1.03 +/- 0.03 s-1 (mean +/- S.D., n = 5) and 3.42 +/- 0.14 s-1 (n = 5) at 20 degrees C and (ii) Q10 values of 2.3 and 1.9 in the 0-20 degrees C range, respectively. 5. Time courses of slowing of relaxation rate with increasing tetanus duration and recovery of relaxation rate with rest after a prolonged tetanus at 10 degrees C are similar to rates of dissociation of Mg2+ and Ca2+ from PA, respectively, as previously reported at 0 degree C. 6. Both the temperature dependence of the relative magnitude of slowing of relaxation rate and the increased Q10 of relaxation rate with increased tetanus duration can be explained if the Q10 for Ca2+ uptake by the sarcoplasmic reticulum is greater than the Q10 for Ca2+ sequestration by PA during relaxation. When Ca2+ and Mg2+ dissociation rates from PA at various temperatures are compared to other proposed indicators of PA function, it is concluded that PA facilitates relaxation of frog skeletal muscle in the 0-20 degrees C range.

Animals↗