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Biomedical subjects

G Johnson

Publications and source records attributed to G Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1998

A domain flip as a result of a single amino-acid substitution.

BACKGROUND: The self-assembly properties of beta domains are important features of diverse classes of proteins that include cell-adhesion molecules, surface receptors and the immunoglobulin superfamily. Immunoglobulin light-chain variable domains are well suited to the study of structural factors that determine dimerization, including how residues at the interface influence the preferred dimer arrangement. RESULTS: Single-site mutants of light-chain variable domain Len, designated LenQ38E and LenK30T, formed 'flipped' dimers in which one domain was rotated by about 180 degrees compared with the native protein. The dimer in the native protein is similar to that found between variable domains in Fab immunoglobulin fragments. When compared to the native dimer, more surface area is buried, and more hydrogen bonds and salt bridges are formed between the monomers in the flipped conformation. CONCLUSIONS: Immunoglobulin light-chain variable domains can form a minimum of two distinct quaternary structures. Single-site mutations resulting from changes of one base, such as the exchange of Gln38 to Glu or Lys30 to Thr, change the 'conventional' dimer of protein Len to a flipped arrangement. Native Len is not found in the flipped-domain dimer conformation because it would have excess positive electrostatic potential at the dimer interface that is not compensated by other forces. Excess negative or positive electrostatic potential at the dimer interface can have a determining effect on the mode of dimerization.

Crystallography, X-Ray↗
PubMed1998

Rat oligodendrocyte O-2A precursor cells and the CG-4 oligodendrocyte precursor cell line express cadherins, beta-catenin and the neural cell adhesion molecule, NCAM.

Oligodendrocyte precursor cell migration throughout the developing central nervous system (CNS) and cessation of migration are poorly understood but are likely to involve cell adhesion molecules. The expression and distribution of neural cell adhesion molecule (NCAM), cadherins and beta-catenin were investigated in the CG-4 cell line and primary rat oligodendrocyte progenitor cells (O-2A) by immunofluorescence and Western blotting. NCAM was expressed by both cell types and was found all over the surface of both CG-4 cells and O-2A progenitor glia. The presence of a cadherin was detected in both CG-4 cells and O-2A progenitor glia, and this molecule was distributed all over the cell body and cell processes at different stages of differentiation. Beta-catenin showed a very similar distribution to that of the cadherin. We conclude that CG-4 cells are a valid model system to study cell adhesion molecule expression and function in oligodendrocyte progenitor cells.

Animals↗
PubMed1998

Production of interleukin-10 by granulocyte colony-stimulating factor-mobilized blood products: a mechanism for monocyte-mediated suppression of T-cell proliferation.

Previous reports showed that granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood mononuclear cells (G-PBMC) are hyporesponsive to alloantigen compared with control PBMC. In the current study, neutralizing antibodies to interleukin-10 (IL-10) increased the proliferative response of G-PBMC to alloantigen by 50. 14% (+/- 12.79%; n = 8), whereas the proliferative response of control PBMC was not affected. The inhibition of OKT3-stimulated CD4 cell proliferation by G-PBMC-derived CD14(+) cells could also be abrogated by the addition of IL-10 neutralizing antibodies. Further, IL-10 levels correlated with the number of CD14 cells in these cultures. Constitutive IL-10 mRNA levels detected by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) were 10-fold higher in G-PBMC compared with control PBMC. This translated into significantly higher IL-10 levels after 24-hour lipopolysaccharide (LPS) stimulation of G-PBMC compared with control PBMC (P = .036). IL-10 mRNA levels were also fivefold higher in isolated G-PBMC-derived CD14 cells compared with control CD14 cells. This corresponded to increased constitutive production of IL-10 by isolated G-PBMC-derived CD14 cells compared with control CD14 cells (357.2 +/- 104.5 v 51.7 +/- 30.5, P = .051). In conclusion, these data suggest that monocytes contained within G-PBMC, which, in comparison to marrow, are increased in absolute number and relative proportion to T cells, may suppress T-cell responsiveness by secretion of IL-10.

Antibodies, Blocking↗
PubMed1998

99mTc-HL91: "hot spot" detection of ischemic myocardium in vivo by gamma camera imaging.

BACKGROUND: 99mTc-HL91 is a new hypoxia imaging agent that demonstrates increased uptake and retention in globally hypoxic myocardium in vitro. The purpose of this study was to determine whether 99mTc-HL91 could detect regional ischemia in vivo by gamma camera imaging. METHODS AND RESULTS: Eight open-chest dogs with left circumflex (LCx) stenoses were studied. Injection of 5 mCi of 99mTc-HL91 and microspheres was followed by imaging over 4 hours. Heart slices were imaged, then stained with triphenyltetrazolium chloride (TTC), and tissues were well-counted. TTC staining demonstrated no injury. Mean LCx blood flow was 0.32+/-0.04 mL x min(-1) x g(-1), and mean left anterior descending coronary artery (LAD) flow was 0.96+/-0.02 mL x min(-1) x g(-1) (ratio, 0.33). "Hot spots" were detected in 8 of 8 experiments in vivo within 60 minutes and improved over 4 hours. Region of interest analysis of LCx/LAD activity ratios demonstrated significant increases within 30 minutes (final ratio, 3.0; P<0.05). LCx and LAD washout curves demonstrated significant differences within 15 minutes. Washout curves were biexponential over 1 hour, followed by linear retention from 1 to 4 hours. Four-hour fractional retention was 0.12 for LAD and 0.44 for LCx (P<0.01). Myocardial flow versus tracer uptake demonstrated 2 phases: phase 1 (flow, 0.05 to 0.7 mL x min(-1) x g(-1)) had an inverse linear correlation (r= -0.80); phase 2, (flow, >0.7 mL x min(-1) x g(-1)) had no correlation. Ischemic heart/liver ratios remained near 1.0 for 4 hours. CONCLUSIONS: 99mTc-HL91 positively identifies regional myocardial ischemia in a canine model using 99mTc imaging. Quantitative techniques allowed identification of ischemic myocardium within 15 minutes of tracer administration.

Animals↗
PubMed1998

Examination for heat-labile, heat-stable, and Shiga-like toxins and for the eaeA gene in Escherichia coli isolates obtained from dogs dying with diarrhea: 122 cases (1992-1996).

OBJECTIVE: To examine Escherichia coli isolates obtained from dogs dying with diarrhea for heat-labile, heat-stable, and Shiga-like toxins and for the eaeA gene, which is associated with attaching and effacing lesions. DESIGN: Retrospective study. ANIMALS: 122 dogs. PROCEDURE: E coli isolates were tested by means of dot-blot hybridization of DNA extracts of cultured bacteria. Medical records of dogs from which E coli isolates with virulence genes had been isolated were examined, and histologic findings and evidence of intercurrent bacterial and viral infections were recorded. RESULTS: None of the E coli isolates obtained from these dogs produced heat-labile, heat-stable, or Shiga-like toxins; however, E coli isolates from 44 of 122 dogs were found to have the eaeA gene. Histologically, multifocal bacterial adherence to the epithelium and epithelial necrosis and detachment were seen in colonic specimens from 20 of 44 (45%) dogs. Escherichia coli was the sole pathogen identified in 15 of 44 (34%) dogs. Intercurrent pathogens, including canine parvovirus (n = 19), Clostridium perfringens (8), rotavirus (5), hookworms (3), coccidia (3), and Salmonella agona (1), were identified in the remaining 29 (66%) dogs. CLINICAL IMPLICATIONS: Attaching and effacing E coli can be a primary or secondary pathogen in dogs with diarrhea. Antibiotic treatment is indicated in dogs with diarrhea because of the possibility that it is primarily bacterial in origin and because, even if it is primarily viral in origin, there may be secondary bacterial infection.

Adhesins, Bacterial↗
PubMed1998

Determination of phosphatidylethanol in blood from alcoholic males using high-performance liquid chromatography and evaporative light scattering or electrospray mass spectrometric detection.

The 'pathologic' phospholipid, phosphatidylethanol (PEth), formed only in the presence of ethanol, was determined in extracts of human blood using high-performance liquid chromatography with evaporative light scattering detection (ELSD) or electrospray (ES) mass spectrometry. Separation was performed using a diol column and a normal-phase binary gradient system. Decreasing concentrations of PEth (15 to 1 nmol/ml blood) could be detected by ELSD in three male alcoholics, up to 3 weeks after the beginning of an alcohol-free period. Using ES, levels down to 100 pmol/ml blood was detected. The molecular species of PEth were similar to those of phosphatidylcholine found in the same blood sample. The method provides a rapid quantitative and qualitative determination of PEth in blood. The limits of detection were 200 pmol (approximately 125 ng) using ELSD and 140 fmol (approximately 100 pg) using ES, total amounts injected. ON

Alcoholism↗
PubMed1998

Surface topography can interfere with epithelial tissue migration.

Corneal epithelial tissue migration over the surface of a synthetic polymer can be inhibited by pores in the substrate. The effects of this substrate topography upon epithelial tissue migration were studied in vitro. Membranes of different porosities and structures were used to provide two series of surfaces having a graded increase in discontinuities: cellulose nitrate/acetate membranes with a tortuous network of pores, and track-etched polycarbonate membranes with columnar pores. Corneal epithelial tissue outgrowth was inhibited by increased pore size, and for both series of membranes, outgrowth was completely halted on membranes with mean diameter of the pores 0.9 microm at the pore densities measured. On the track-etched membranes with pores of <0.9 microm diameter, tissue outgrowth could be partially "rescued" by coating with fibronectin or collagen, but above this size, the inhibition predominated. The effect of porosity of the track-etched membranes upon the migration of dissociated epithelial cells was also examined. Although migration of these cells was reduced on membranes having pore sizes larger than 0.9 microm, it was not completely inhibited even on membranes of 2.3-microm pore diameter. Therefore, tissue movement of adult stratified epithelium may be inhibited by specific surface topographies, and in this assay system, epithelial tissue outgrowth was more affected than was the migration of dissociated epithelial cells.

Animals↗
PubMed1998

Double-blind, multicenter trial to compare the efficacy of intramuscular dihydroergotamine plus hydroxyzine versus intramuscular meperidine plus hydroxyzine for the emergency department treatment of acute migraine headache.

STUDY OBJECTIVE: To evaluate intramuscular dihydroergotamine in direct comparison with opioid analgesia in the treatment of acute migraine headache. METHODS: This was a prospective, multicenter, double-blind trial performed in the emergency departments of 11 general hospitals in the United States. One hundred seventy-one patients between the ages of 18 and 60 years who presented to the ED with acute migraine headache were enrolled. Patients were randomly assigned to receive either 1 mg dihydroergotamine (DHE) or 1.5 mg/kg meperidine (MEP) by intramuscular injection. The anti-nauseant hydroxyzine (H) was coadministered in both treatment groups. RESULTS: One hundred fifty-six patients were evaluable. Treatment groups were comparable in sample size, demographics, and baseline measurements of headache pain. Reduction of headache pain as measured on a 100-mm visual analog scale was 41+/-33 mm (53.5% reduction) for the DHE group, and 45+/-30 mm (55.7% reduction) for the MEP group at 60 minutes after treatment (difference=2.2%; 95% confidence interval [CI] -10%, 14.5%; P=.81). Reduction in the severity of nausea and improvement in functional ability were similar between treatment groups. Central nervous system adverse events were less common in the DHE group (DHE 23.5% versus MEP 37.6%, difference-14.1%: 95% CI -28%, 0%). In particular, dizziness was reported less commonly with DHE than MEP (2% versus 15%, difference=-13%: 95% CI -21%, -5%). CONCLUSION: In this prospective, double-blind trial of a convenience sample of ED patients randomly assigned to one of two treatment regimens, DHE and MEP were comparable therapies for acute migraine. The use of DHE avoids several problems associated with opioid analgesia, including dizziness.

Acute Disease↗
PubMed1998

Lithium--early development, toxicity, and renal function.

The report of the effectiveness of lithium in the treatment of mania by John Cade was followed by a number of studies confirming his observations and developing guidelines for safe and effective use. Premature rejection of lithium on safety grounds denied many patients the benefit of treatment and may have cost more lives than it saved. A similar safety alarm was triggered by reports of kidney damage in the late 1970s. Subsequent reports have questioned the significance of anatomical findings, and functional impairment and relationship to lithium treatment. Recent findings support the conclusion that progressive impairment of glomerular and tubular function in patients during lithium maintenance is the exception rather than the rule and is related more to lithium intoxication, maintenance plasma lithium levels, concurrent medications, somatic illness, and age than on time on lithium. Guidelines for lithium use and monitoring of renal function are outlined.

Antimanic Agents↗
PubMed1998

Can preoperative psychological defensive strategies, mood and type of lower urinary tract reconstruction predict psychosocial adjustment after cystectomy in patients with bladder cancer?

OBJECTIVES: To assess if there is relationship between: (i) preoperative psychological defensive strategies, mood and type of lower urinary tract reconstruction, and (ii) psychosocial adaptation after radical cystectomy for bladder cancer. PATIENTS AND METHODS: Fifty-seven consecutive patients (44 men and 13 women, mean age 62 years, range 34-81) undergoing radical cystectomy (ileal conduit urinary diversion in 17, continent cutaneous diversion in 22 and orthotopic bladder replacement in 18) were assessed preoperatively using the meta-contrast technique (MCT), a projective test to reveal individual defensive strategies. From the results the patients were classified as hypothetical 'at risk' or 'no risk' patients for postoperative psychosocial complications. An 'at risk' patient was designated as one who showed neurotic defensive strategies in coping with threats, i.e. primitive, immature or regressive strategies or even lack of defence in connection with pronounced anxiety. All patients completed a questionnaire and were interviewed; 10 questions dealt with mood, five reflecting anxiety and five the depressive states. The questionnaire and the interview were repeated 3 and 12 months, and 5 years after surgery. RESULTS: The remembered difficulties during the first month after discharge from hospital differed between the 'risk' and 'no risk' groups after 1 and 5 years. On a visual analogue scale (VAS) the 'risk' patients had very low scores (less difficulty) or very high, while the 'no risk' patients had intermediate scores. VAS score were also higher, although not significantly so, in patients using primitive defence strategies. The psychosocial situation did not differ between the groups in the first year, but at 5 years there were differences in self-esteem and interpersonal contact-seeking. High depression scores before surgery were associated with high VAS scores at 3 months when recalling the first month after discharge, but the anxiety score was not predictive. Men with orthotopic bladder replacement adapted less well throughout the 5 year follow-up. Elderly patients with stereotypy (the commonest defensive strategy at these ages) adapted relatively well to ileal conduit diversion. About 20% of patients had difficulty in accepting the postoperative situation, regardless of urinary diversion modes. CONCLUSION: The combination of defensive strategies assessed using the MCT and selected on hypothetical grounds was less discriminatory than expected for those at risk of postoperative psychosocial problems. However, those with primitive strategies apparently had a long-term risk of poor adaptation. The search for an optimal instrument for the identification of patients at risk is warranted. In this study, patients with a 'wet' stoma did not seem to fare less well than those with a continent reconstruction.

Adaptation, Psychological↗
PubMed1998

Possible assortment of a1 and a2 region gene segments in human MHC class I molecules.

Using pair-wise comparison of aligned nucleotide sequences of distinct and complete human MHC class I molecules, we have constructed triangular tables to study the similarities and differences of various a1 (exon 2) and a2 (exon 3) region sequences. There are two HLA-A (A*6901 and A*6601) and 13 HLA-B (B*4201, B*8101, B*4102, B*4801, B*4007, B*4001, B*4802, Dw53, B*4406, B*4402, B*3901, B*1514 and B*3702) sequences that have identical a1 sequences with other known MHC class I molecules, while their a2 sequences are the same as those of different ones. Of these 15, A*6901, B*4001 and B*4802 have previously been suggested as the results of recombination between A*6801 and A*0201, B*4101 and B*8101, and B*4801 and B*3501, respectively. However, many other sequences can also be used to generate them by recombination. Furthermore, their reciprocal products have never been identified. Thus, gene conversion has subsequently been suggested as an alternative. Another possible genetic mechanism for generating these nucleotide sequence similarities can be assortment, or that some gene segments can be duplicated or multiplicated to be used in different human MHC class I molecules. Interestingly, this genetic mechanism is probably absent for the generation of different mouse MHC class I molecules.

Alleles↗
PubMed1998

Suppression of peroxisomal membrane protein defects by peroxisomal ATP binding cassette (ABC) proteins.

X-Linked adrenoleukodystrophy (X-ALD) is a neurodegenerative disorder characterized by reduced peroxisomal very long chain fatty acid (VLCFA) beta-oxidation. The X - ALD gene product (ALDP) is a peroxisomal transmembrane protein with an ATP binding cassette (ABC). ALDP and three other ABC proteins (PMP70, ALDR, P70R) localize to the peroxisomal membrane. The function of this family of peroxisomal membrane proteins is unknown. We used complementation studies to begin analysis of their role in VLCFA beta-oxidation and on the peroxisomal membrane. Expression of either ALDP or PMP70 restores VLCFA beta-oxidation in X-ALD fibroblasts, indicating overlapping functions. Their expression also restores peroxisome biogenesis in cells that are deficient in the peroxisomal membrane protein Pex2p. Thus it is likely that complex protein interactions are involved in the function and biogenesis of peroxisomal membranes that may contribute to disease heterogeneity.

ATP Binding Cassette Transporter, Subfamily D, Mem↗
PubMed1998

Preferred CDRH3 lengths for antibodies with defined specificities.

The third complementarity determining regions of heavy chain variable regions (CDRH3) confer the fine specificities of antibodies. The CDRH3 length distribution of all human or all mouse antibodies appears to be more or less random, with the human distribution having a wider spread. Since the Kabat database of aligned amino and nucleotide sequences of proteins of immunological interest has grown at least 4 times during the past 7 years, we attempt to study CDRH3 length distributions of human and mouse antibodies with defined specificities, where enough complete and distinct CDRH3 sequences are available. For mouse antibodies against small haptens or carbohydrates, a preferred length usually dominates for a given specificity. There are not enough human sequences of small hapten or carbohydrate antibodies for a similar study. Both human and mouse anti-protein antibodies have wider ranges of CDRH3 length distributions, probably due to the presence of different antigenic epitopes on the protein molecules, and thus many different antibodies. For anti-DNA antibodies, both humans and mice exhibit even wider length distributions, since DNA can be double stranded, single stranded, supercoiled, etc.

Animals↗
PubMed1998

Detection of Ureaplasma urealyticum in endotracheal tube aspirates from neonates by PCR.

A PCR-based test was optimized for the detection of Ureaplasma urealyticum from neonatal respiratory specimens, with primers directed against the multiple-banded antigen gene (L. J. Teng, X. Zheng, J. I. Glass, H. Watson, J. Tsai, and G. H. Cassell, J. Clin. Microbiol. 32:1464-1469, 1994). Endotracheal tube aspirates (225) from 103 low-birth-weight neonates (<1,250 g) were taken, when possible, at days 0, 4, and 14 after birth and examined by culture and by PCR. Of 77 specimens positive by either method, 73 were detected by PCR and 60 were detected by culture. Overall, 36% of the neonates were positive for U. urealyticum by either method. Of 16 patients with PCR-positive-culture-negative results, 13 had positive cultures at another sampling point, and one additional patient had a twin with positive cultures. Of 11 patients with day 0 specimens positive by PCR alone, 9 subsequently became culture positive, demonstrating the utility of this test in early detection. Multiple serovars were present in over 50% of positive specimens, with serovars 3 and 14 in combination being most prevalent. The amplicon size generated from the specimen by PCR correctly predicted the biovars isolated in over 85% of positive specimens. Thus, this PCR test was valuable in allowing early detection of U. urealyticum in neonatal respiratory specimens, as well as in providing biovar information.

Humans↗
PubMed1998

A role for potassium channels in smooth muscle cells and platelets in the etiology of primary pulmonary hypertension.

Plasma serotonin levels are markedly elevated in patients with primary pulmonary hypertension (PPH) and platelet levels of serotonin are low. Furthermore, plasma serotonin levels remain elevated after bilateral lung transplantation, in the absence of any pulmonary hypertension. Dexfenfluramine can cause the anorexigen-induced form of PPH that is clinically and histologically indistinguishable from PPH. We find that dexfenfluramine releases serotonin from platelets and inhibits its reuptake. These observations suggest that serotonin might be involved in, or be a marker for, the mechanism responsible for both forms of PPH. Dexfenfluramine causes inhibition of voltage-sensitive potassium (Kv) channels, membrane depolarization, and calcium entry in pulmonary artery smooth muscle cells and vasoconstriction in isolated perfused rat lungs. We have recently found that dexfenfluramine also inhibits Kv channels in megakaryocytes, the stem cell for platelets. In smooth muscle cells, taken from the pulmonary arteries of PPH patients, Kv channels appear to be dysfunctional. The underlying defect in PPH is likely to be an abnormality of one or more Kv channels in both pulmonary artery smooth muscle cells and platelets. Relatively few patients exposed to dexfenfluramine develop PPH. The factors responsible for susceptibility might be a difference in expression of potassium channels and/or a decrease in the endogenous production of nitric oxide.

Animals↗