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Biomedical subjects

R Johnson

Publications and source records attributed to R Johnson.

At least 181 records · Page 10Linked to original sources
PubMed1996

Effects of cationic diamidines on polyamine content and uptake on Leishmania infantum in in vitro cultures.

The effect of a series of cationic diamidines recently synthesized by Ciba Geigy, bearing diarylic (CGP040215A and CGP039937A) or monoarylic moieties (CGP033829A, CGP035537A and CGP036958A), was analyzed on some metabolic targets and cell proliferation of in vitro cultures of Leishmania infantum promastigotes (insect form). The action of these compounds on intracellular polyamine pools and putrescine transport suggests that diarylic structures were more effective than their monoarylic counterparts in depleting polyamine levels and inhibiting putrescine transport, although these processes correlate poorly with the antiproliferative rate of these compounds. Finally, the displacement of cationic diamidines to kDNA observed in the presence of several concentrations of spermidine suggests a possible combined mode of action of these molecules, first depleting intracellular polyamine pools and, then, displacing spermidine from its site of interaction to kDNA.

Animals↗
PubMed1996

Phosphorylation of SLP-76 by the ZAP-70 protein-tyrosine kinase is required for T-cell receptor function.

Two families of tyrosine kinases, the Src and Syk families, are required for T-cell receptor activation. While the Src kinases are responsible for phosphorylation of receptor-encoded signaling motifs and for up-regulation of ZAP-70 activity, the downstream substrates of ZAP-70 are unknown. Evidence is presented herein that the Src homology 2 (SH2) domain-containing leukocyte protein of 76 kDa (SLP-76) is a substrate of ZAP-70. Phosphorylation of SLP-76 is diminished in T cells that express a catalytically inactive ZAP-70. Moreover, SLP-76 is preferentially phosphorylated by ZAP-70 in vitro and in heterologous cellular systems. In T cells, overexpression of wild-type SLP-76 results in a hyperactive receptor, while expression of a SLP-76 molecule that is unable to be tyrosine-phosphorylated attenuates receptor function. In addition, the SH2 domain of SLP-76 is required for T-cell receptor function, although its role is independent of the ability of SLP-76 to undergo tyrosine phosphorylation. As SLP-76 interacts with both Grb2 and phospholipase C-gamma1, these data indicate that phosphorylation of SLP-76 by ZAP-70 provides an important functional link between the T-cell receptor and activation of ras and calcium pathways.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Direct regulation of ZAP-70 by SHP-1 in T cell antigen receptor signaling.

The threshold at which antigen triggers lymphocyte activation is set by the enzymes that regulate tyrosine phosphorylation. Upon T cell activation, the protein tyrosine phosphatase SHP-1 was found to bind to the protein tyrosine kinase ZAP-70. This interaction resulted in an increase in SHP-1 phosphatase activity and a decrease in ZAP-70 kinase activity. Expression of a dominant negative mutant of SHP-1 in T cells increased the sensitivity of the antigen receptor. Thus, SHP-1 functions as a negative regulator of the T cell antigen receptor and in setting the threshold of activation.

Animals↗
PubMed1996

Rapid determination of chloroprocaine and its major metabolite, 2-chloroaminobenzoic acid, in plasma by high-performance liquid chromatography.

A sensitive and specific high-performance liquid chromatographic method for determination of the 2-chloroprocaine, local anesthetic of ester type, and its major metabolite 2-chloroaminobenzoic acid, has been developed and validated. A single-step extraction procedure is employed followed by high-performance liquid chromatographic separation using reversed-phase column and analysis using variable length UV detection. Lidocaine was used as internal standard for 2-chloroprocaine measurement and p-aminobenzoic acid was used as internal standard for 2-chloroaminobenzoic acid analysis. The analysis of spiked plasma demonstrated good accuracy and precision of the method with limit of detection 0.1 microgram/ml for 2-chloroprocaine and 0.5 microgram/ml for 2-chloroaminobenzoic acid. The method has been used for pharmacokinetic studies in laboratory animals.

Anesthetics, Local↗
PubMed1996

DNA exposure and condensation in the X and 21 chromosomes.

Fluorescence in situ hybridization (FISH) whole chromosome painting probe studies have been carried out with X and 21 chromosomes on normal human fibroblasts grown in tissue culture. The majority of the cells were in G1 phase (including G0). The X chromosome, which exhibits differential inactivation, displays an active form which is most commonly in the nuclear periphery, is diffused over a large area with dark regions interspersed with bright regions, and exhibits punctate bright spots at its edges. The inactive X, which contains a small fraction of active genes, is also most often at the nuclear periphery, is highly condensed and also exhibits punctate labeling around its outer edge. Occasional nuclei exhibit X chromosomal material adjacent to a nucleolus. These observations fit the pattern proposed by the genome exposure theory in which inactive gene regions are sequestered by chromosome condensation, and become exposed by decondensation into a condition invisible by the video-imaging technique employed. Such exposed genes can then be activated by appropriate molecular messengers. In accordance with this theory, the total fluorescence observed from the active X is appreciably less than that of the inactive. The FISH pattern from chromosome 21 is very different, displaying two fluorescent bodies usually connected with the nucleoli. Both bodies contain condensed and decondensed regions, and both are much more similar in their degree of decondensation than was the case with the X chromosomes, although a small difference cannot be ruled out. Use of DNase I treatment of nuclei reveals the existence of exposed DNA. The use of FISH as demonstrated here can indicate sequestered DNA. Together the two techniques promise elucidation of gene regions of various chromosomes which are active and inactive in particular tissues and in normal and pathologic conditions.

Cell Nucleus↗
PubMed1996

Intelligence and the frontal lobe: the organization of goal-directed behavior.

Basic to the study of individual differences is the concept of 'general intelligence' or Spearman's g. In this article we suggest that g is largely a reflection of the control functions of the frontal lobe. A series of experiments investigates a phenomenon we call goal neglect: disregard of a task requirement event though it has been understood and remembered. Subjectively it is as though the neglected requirement "slips the subject's mind." Previously described in frontal patients, we show that goal neglect can also be seen in some members of the normal population. In line with conventional distinctions between controlled and automatic processing, eliciting conditions for goal neglect include novelty, weak error feedback, and multiple concurrent task requirements. Under these conditions neglect is linked closely to g and extremely common after frontal lesions. Following many other models, we suggest that behavior in any task is structured by a set of action constraints or requirements, derived in part from verbal instructions and specified at multiple levels of abstraction. A frontal process of constraint or requirement activation is fundamental to Spearman's g.

Adult↗
PubMed1996

Effects of interleukin 6 administration on platelets and haemopoietic progenitor cells in peripheral blood.

Platelet numbers and circulating haemopoietic progenitor cells were examined in 12 patients with advanced malignancies who were receiving recombinant human interleukin-6 (rhIL-6) as part of an investigation of its thrombopoietic effects. Patients received recombinant glycosylated IL-6 by daily subcutaneous injection for 7 consecutive days in doses of 1, 3 or 10 micrograms/kg/day. Platelet numbers increased reaching a peak on days 12-15 with a mean on day 15 of 198.1% of pre-treatment values. This was accompanied by a significant fall in the mean platelet volume (mean decrease of 10.6%, P = 0.0044). No significant correlation was seen between the IL-6 dose and the change in platelet number. No significant differences were observed between pre- and post-treatment levels of circulating erythroid burst-forming units (E-BFU) and granulocyte macrophage colony-forming units (GM-CFU) but a small significant increase was seen in circulating primitive progenitor cells measured in a plastic-adherent (P delta) assay (P = 0.025). As positive controls, a group of patients treated with cyclophosphamide/G-CSF showed significant increases in GM-CFU (P = 0.018), E-BFU (P = 0.018) and P delta progenitors (P = 0.028). These data suggest that the thrombopoietic effects of IL-6 are mediated at a relatively late stage via effects on megakaryocyte differentiation, with a relatively small effect on circulating haemopoietic progenitors.

Adult↗
PubMed1996

Quinolone arthropathy in immature rabbits treated with the fluoroquinolone, PD 117596.

To study the potential of the fluorquinolone, PD 117596 to cause arthropathy in experimental animals, immature rabbits were orally administered the drug for five days at 0, 100, 350, 500 and 750 mg/kg. Characterization of changes induced in major synovial joints was based on: macroscopic and histopathologic observations, transmission electron microscopic examinations and magnetic resonance imaging. Preferentially targeting the knee, PD 117596 produced vesicles and erosions in articular cartilage which resembled, morphologically, those described in other laboratory species. Lesion incidence was not clearly dose-related. In the perivesicular region, degenerate chondrocytes were intermixed with hypertrophic cartilage cells and chondrocyte clusters. Ultrastructurally, hypertrophic chondrocytes were the consequence of karyomegaly and RER proliferation. Matrix density was reduced due to collagen and proteoglycan loss. Joint structures were readily visualized by magnetic resonance imaging which identified thickened articular cartilage, surface irregularities consistent with ruptured vesicles and separation of opposing articular surfaces secondary to synovival effusions. The immature rabbit, although less sensitive than the juvenile dog to the arthropathic effects of quinolones, was nonetheless a good model to study this experimental osteoarticular disease.

Animals↗
PubMed1996

Mefloquine tolerability during chemoprophylaxis: focus on adverse event assessments, stereochemistry and compliance.

This longitudinal study of travellers to Africa taking mefloquine (MQ) chemoprophylaxis aimed to quantify and assess non-serious adverse events (AE) occurring during short-term prophylaxis and relate these to concentrations of racemic MQ, its enantiomers and metabolite. A total of 420 volunteers (52% F) participated. AEs with some impact on activities were reported by 11.2% of participants including 7.9% of neurological/psychiatric symptoms. Women were more likely to report AEs (P = 0.02). The standardized questionnaires used showed more pathological indicators in travellers who reported subjective AE with significantly more dizziness, distress, sleep disturbances and a high total mood disturbance (TMD) in the AE group. There was, however, no significant performance deficit in computerized psychomotor tests in those experiencing AE. Furthermore, no significant differences were observed in enantiomer ratios, metabolite concentrations, or racemic MQ levels in participants with or without AEs suggesting that these factors are not the main predictors of mefloquine intolerability.

Adolescent↗
PubMed1996

Cross-calibration of body-composition techniques against dual-energy X-ray absorptiometry in young children.

Using dual-energy X-ray absorptiometry (DXA) as a standard method for determining body composition in children, we evaluated the accuracy of skinfold-thickness measurements (with the Slaughter et al equations, which are based on triceps and calf skinfold-thickness measurements), bioelectrical resistance (BR; with the Kushner el al equations and age-specific hydration constants), and other clinical measurements (individual skinfold thicknesses and body mass index) for the assessment of body fat in children. We studied a heterogenous group of 49 boys and 49 girls, aged 6.6 +/- 1.4 y and weighing 24.1 +/- 5.9 kg. Fat mass estimated by DXA was significantly lower than fat mass measured by skinfold thickness, even though fat mass measurements by these two techniques were strongly related to each other. Fat mass estimated by DXA was also significantly lower than fat mass measured by BR, and the model R2 and SEE were not as strong as for the skinfold-thickness technique. Fat mass estimated by DXA also correlated with other clinical indexes such as triceps skinfold thickness, body mass index, body weight, and subscapular skinfold thickness. In forward-regression analysis, subscapular skinfold thickness, body weight, triceps skinfold thickness, sex, and height2/resistance estimated the value for fat mass measured by DXA with a model R2 of 0.91 and an SEE of 0.94 kg fat mass. These studies suggest that existing techniques for assessing body fat in children may be inaccurate. We provide new anthropometric equations based on the use of DXA as a criterion that provide accurate and precise measures of body fat and fat-free mass in white children aged 4-9 y. This approach provides estimates of body fat standardized to a known laboratory standard of chemical analysis of carcasses.

Absorptiometry, Photon↗
PubMed1996

Semantide- and chemotaxonomy-based analyses of some problematic phenotypic clusters of slowly growing mycobacteria, a cooperative study of the International Working Group on Mycobacterial Taxonomy.

During previous cooperative numerical taxonomic studies of slowly growing mycobacteria, the International Working Group on Mycobacterial Taxonomy described a number of strains whose taxonomic status was ambiguous. A new study of DNA, RNA, and proteins from 66 of these organisms was performed to correlate their properties with phenotypic clustering behavior; the results of this study permitted 51 of the strains studied to be assigned to known species. The methods used to characterize the semantides included nucleotide sequencing and assessment of levels of semantide relatedness by affinity binding techniques, including whole DNA-DNA hybridization, probe hybridization, and antibody binding. There was good overall agreement between the phenotypic and chemotaxonomic clusters and the groups of organisms identified by semantide analyses. Our results supported the conclusion that we should continue to rely on polyphasic taxonomy to provide satisfactory systematic resolution of members of the genus Mycobacterium. We identified no single 16S rRNA interstrain nucleotide sequence difference value that unequivocally defined species boundaries. DNA-DNA hybridization remains the gold standard, but common resources are needed to permit DNA-DNA hybridization analyses to be made available to laboratories that are not prepared to use this technology. One of the large novel clusters which we studied corresponds to the recently described species Mycobacterium interjectum, a pathogen that resembles the nonpathogen Mycobacterium gordonae phenotypically. We also identified strains that appear to represent ribovars of Mycobacterium intracellulare which do not react with the commercial diagnostic probes that are currently used for identification of this species. Other branches or clusters consisted of too few strains to permit a decision about their taxonomic status to be made.

Bacterial Proteins↗
PubMed1996

Impedance of pacemaker leads: correlation of different methods.

This study compares three different pacing system analyzers, which measure impedance at different points during an impulse, with measurements telemetered from implanted pacemakers from four different manufacturers. Measurements were obtained at the time of implantation in a group of 103 patients. The measurements obtained by these different methods differ significantly from each other; the later during the impulse the impedance is measured, the higher in general its value. Interpretation of impedance values should take into account the technique of measurement.

Cardiac Pacing, Artificial↗
PubMed1996

PUVA treatment selectively induces a cell cycle block and subsequent apoptosis in human T-lymphocytes.

Psoralen plus UVA (320-400 nm radiation; PUVA) is a highly effective therapy for cutaneous diseases caused by skin infiltration with normal or neoplastic T-lymphocytes. In comparing the effects of pharmacologically relevant, low-dose PUVA treatment on growth of human keratinocytes, peripheral blood leukocytes (PBMC), and T-lymphocyte cell lines, we determined that PBMC or T-lymphocytes were > 50-fold more sensitive to cytotoxic effects of PUVA, while antiproliferative effects were produced by similar PUVA levels in all cell types. Low doses of PUVA (10 ng/mL 8-methoxypsoralen and 1-2 J/cm2) were highly cytotoxic for phytohemagglutinin-activated normal lymphocytes or transformed T-lymphocytes as assessed by two viability assays and by flow cytofluorometry. Altered lymphocyte morphology, nuclear fragmentation, TUNEL+ nuclei or nuclear fragments, and the appearance of a sub-G1 DNA peak indicated that cell death occurred by apoptosis, beginning about 1 day after PUVA treatment and continuing for several days thereafter. From assessment of cell cycle progression in mimosine-synchronized cells, PUVA treatment markedly slowed cell cycle progression, eventually producing cell cycle arrest and apoptotic entry. We propose that the probable basis for disease remissions (psoriasis, cutaneous T-cell lymphoma) produced by PUVA treatment is through selective cytotoxic effects on clonal T-lymphocyte populations that are concentrated in diseased skin.

Apoptosis↗
PubMed1996

A sagittal plane model of the knee and cruciate ligaments with application of a sensitivity analysis.

In this investigation the complex multi-bundle structure of the cruciate ligaments and their interaction with the tibiofemoral joint was modeled analytically by representing the different regions of the cruciates with ligament elements. A sensitivity analysis was then performed to describe the effect that variations of the model input parameters had on the model variables (outputs). The effect that the cruciate ligament bundles had in controlling joint kinematics was dependent on knee flexion angle, and the load applied to the tibiofemoral joint. For passive range of knee motion with the thigh in the horizontal plane (a common rehabilitation activity), all cruciate ligament bundles were strained with the joint positioned between 0 and 10 deg of knee flexion, between 10 and 50 deg only the anterior bundle of the posterior cruciate ligament A-PCL was strained, and from 50 to 90 deg both the anteromedial portion of the anterior cruciate ligament A-ACL and the A-PCL were strained. This finding indicates that a strain distribution about a transverse cross section of the cruciates exists, and demonstrates the importance of differentiating between the strained and unstrained (unloaded) states of these ligaments. The strain value of a cruciate ligament bundle was an indication of how the bundle controls joint kinematics, while the unstrained values describe how much the ligament bundle must deform before it becomes strained and a restraint to tibiofemoral joint motion. In response to anterior and posterior directed loads, applied parallel to the tibial plateau, the respective, ACL and PCL load values were larger in magnitude. The sensitivity of the model outputs to the input parameters was highly dependent on knee flexion angle. The geometrical input parameters of the model (including the ligament insertion site locations and articular surface geometry) had the most pronounced effect on the model output quantities, while the stiffness and initial strain conditions of the ligament bundles had less of an effect on the model outputs. When loaded, the strain values of the ligament bundles were sensitive to the ligament insertion site position. The greatest sensitivity of the model outputs was the femoral insertion of the ACL; supporting clinical impressions and previous experimental findings. Changes in the anterior-posterior dimension of the femoral articular surface did not produce a substantial effect on the model outputs, while changes in the proximal-distal dimension created a large effect; similar results were found for the tibial surface dimensions. These findings indicate that rigid body contact between the articular surfaces may not be a realistic assumption particularly with application to the prediction of tibiofemoral compressive loading and the force/strain values of the cruciate ligament elements. This also has important implications for the design and clinical application of total knee replacements (that function as rigid bodies), particularly those that spare the PCL.

Anterior Cruciate Ligament↗
PubMed1996

Cellular transformation and malignancy induced by ras require c-jun.

ras is an important oncogene in experimental animals and humans. In addition, activated ras proteins are potent inducers of the transcription factor AP-1, which is composed of heterodimeric complexes of Fos and Jun proteins. Together with the fact that deregulated expression of some AP-1 proteins can cause neoplastic transformation, this finding suggests that AP-1 may function as a critical ras effector. We have tested this hypothesis directly by analyzing the response to activated ras in cells that harbor a null mutation in the c-jun gene. The transcriptional response of AP-1-responsive genes to activated ras is severely impaired in c-jun null fibroblasts. Compared with wild-type cells, the c-jun null cells lack many characteristics of ras transformation, including loss of contact inhibition, anchorage independence, and tumorigenicity in nude mice; these properties are restored by forced expression of c-jun. Rare tumorigenic variants of ras-expressing c-jun null fibroblasts do arise. Analysis of these variants reveals a consistent restoration of AP-1 activity. The results provide genetic evidence that c-jun is a crucial effector for transformation by activated ras proteins.

Animals↗
PubMed1996

Decreased muscle cell proliferation in chicks with a deletion in the GH receptor gene.

The increase in muscle weight in neonatal animals is a consequence of increased protein accretion and DNA content. GH increases protein accretion but direct effects of GH on myogenic cell proliferation have not been demonstrated. Sex-linked dwarfism in the chick is caused by mutation or deletion in the GH receptor gene and has provided a useful model to study the physiological consequences of GH insensitivity. This study determined the consequences of GH receptor gene mutation on muscle cell proliferation in vivo. Northern and Southern blotting and PCR analysis revealed restriction fragment length polymorphism patterns and a 1.7 kb deletion of the intracellular domain of the GH receptor gene in commercial dwarf broiler chicks, similar to the Connecticut strain in which there is a dysfunctional GH receptor. Cell proliferation was measured in muscle sections from normal and dwarf chicks after incorporation of 5-bromo-2'-deoxyuridine (BrdU; 25 mg/kg) in vivo at 2, 5 and 13 days of age. Incorporation of BrdU into nuclei was measured in frozen sections, counterstained with propidium iodide to estimate the total number of nuclei by quantitative image analysis, and the labelling index was calculated. Paraffin-embedded sections of breast muscle were stained using an anti-human IGF-I polyclonal antibody. Expression of IGF-I mRNA in muscle from each genotype at 5 days of age was measured by RNAse protection assay. The labelling index was similar in 2-day-old chicks from both genotypes (normal, 20.14 +/- 2.39%; dwarf, 19.79 +/- 5.83%). By day 5 the labelling index had decreased but was significantly higher (P < 0.02) in normal (12.53 +/- 3.36%) compared with the dwarf (6.25 +/- 1.39%). By 13 days of age, there was a further decrease in labelling index but no difference between the groups (normal, 4.92 +/- 1.28%; dwarf, 4.96 +/- 1.51%). IGF-I mRNA was expressed and IGF-I peptide was identified in muscle sections but there was no difference between genotypes. The results show that cell division in breast muscle in vivo is high in neonatal chicks but it declines with increasing age. The absence of a functional GH receptor in the dwarf is associated with a greater decline in DNA synthesis and suggests that GH may directly affect a proportion of cells, since there was no difference in IGF-I mRNA or peptide.

Animals↗