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Biomedical subjects

D A Johnson

Publications and source records attributed to D A Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1999

Diagnostic evaluation in gastroesophageal reflux disease.

Gastroesophageal reflux disease (GERD) describes the clinical manifestations of reflux of gastric contents and the associated symptoms and patterns of tissue injury. Although its exact prevalence is difficult to determine, there is no doubt the GERD is the most common esophageal disease and probably among the most prevalent conditions seen in the primary care setting. GERD has a wide clinical spectrum, making the diagnostic evaluation challenging and complicated at times. Confirmatory test are rarely needed in patients with typical symptoms of heartburn or regurgitation who have a good clinical response to GERD therapy. This article describes the diagnostic tests necessary for some cases of GERD.

Esophagoscopy↗
PubMed1999

The spectrum of spontaneous and iatrogenic esophageal injury: perforations, Mallory-Weiss tears, and hematomas.

Esophageal perforations, Mallory-Weiss tears, and esophageal hematoma involve traumatic injury to the esophagus. These can be iatrogenic, in particular due to esophageal instrumentation, but can also occur spontaneously. The remarkable increase in diagnostic and therapeutic endoscopy as well as esophageal surgery has made instrumentation the most common cause of esophageal perforation. In many instances, spontaneous perforations are associated with retching and vomiting, which causes a sudden increase in intraesophageal pressure. A high index of suspicion leading to rapid diagnosis and appropriate therapy are needed to optimize clinical outcomes. This article focuses on esophageal perforations, Mallory-Weiss tears, and esophageal hematomas, with emphasis on etiology, pathogenesis, clinical presentation, diagnosis, management, and prevention.

Esophageal Diseases↗
PubMed1999

Further characterization of human salivary anticandidal activities in a human immunodeficiency virus-positive cohort by use of microassays.

Salivary anticandidal activities play an important role in oral candidal infection. R. P. Santarpia et al. (Oral Microbiol. Immunol. 7:38-43, 1992) developed in vitro anticandidal assays to measure the ability of saliva to inhibit the viability of Candida albicans blastoconidia and the formation of germ tubes by C. albicans. In this report, we describe modifications of these assays for use with small volumes of saliva (50 to 100 microl). For healthy subjects, there is strong inhibition of blastoconidial viability in stimulated parotid (75%), submandibular-sublingual (74%), and whole (97%) saliva, as well as strong inhibition of germ tube formation (>80%) for all three saliva types. The susceptibility of several Candida isolates to inhibition of viability by saliva collected from healthy subjects is independent of body source of Candida isolation (blood, oral cavity, or vagina) or the susceptibility of the isolate to the antifungal drug fluconazole. Salivary anticandidal activities in human immunodeficiency virus (HIV)-infected patients were significantly lower than those in healthy controls for inhibition of blastoconidial viability (P < 0.05) and germ tube formation (P < 0. 001). Stimulated whole-saliva flow rates were also significantly lower (P < 0.05) for HIV-infected patients. These results show that saliva of healthy individuals has anticandidal activity and that this activity is reduced in the saliva of HIV-infected patients. These findings may help explain the greater incidence of oral candidal infections for individuals with AIDS.

AIDS-Related Opportunistic Infections↗
PubMed1999

The 5S rRNA gene in wall barley (Hordeum murinum L. sensu lato): sequence variation among repeat units and relationship to the Y haplome in the genus Hordeum (Poaceae: Triticeae).

The molecular diversity of the 5S rDNA units in 13 accessions of wall barley, which include Hordeum murinum, H. leporinum, and H. glaucum, is reported. Our analyses, based on 54 sequenced clones, indicate the presence of two sequence classes not previously seen in other barley species; namely, the long Y1 unit class and the short Y1 unit class. In addition, the accumulation of new sequence information has allowed us to refine previous groups. Using these new results, along with previously published work, we present a summary of all the unit classes described to date and potential correspondences between 5S rDNA unit classes and haplomes identified previously. In H. murinum, we found the long H1 and long X2 unit classes, and in one of six accessions referable to H. glaucum we found the unique short Y1 unit class. Our cladistic analyses, using orthologous sequences, provide support for the current model for the relationships among several species within the Triticeae.

Base Sequence↗
PubMed1999

Congenital esophageal stenosis: clinical and endoscopic features in adults.

BACKGROUND: Congenital esophageal stenosis (CES) is an uncommon anomaly that reportedly rarely goes undiagnosed until adulthood. One variant of CES includes patients with multiple cartilaginous rings described usually in the mid-distal esophagus. METHODS: Ten patients with CES seen over the past 7 years were interviewed and their clinical and endoscopic records reviewed. RESULTS: Eight patients were male and age at time of diagnosis ranged from 21 to 75 years. Meat impaction was the presenting symptom in 8 patients and 3 patients reported a relapsing history. Intermittent solid food dysphagia over extended duration (10-40 years) was reported in all patients with an estimated onset of symptoms at a mean age of 27 years (11-52 years). Endoscopically, all patients had segmental esophageal stenosis (length 2-8 cm, mean = 4.7 cm) due to 'trachea-like' multiple submucosal rings. Pseudodiverticulosis and distal reflux esophagitis were evident in 1 patient. Nine of 10 patients had no macroscopic esophagitis. Dilatation was performed by balloon insufflation (18 mm in 5 patients, 15 mm in 3 patients, 12 mm followed by 15 mm in a patient with a tight stricture) and by Savary dilators in 1 patient, without any complications. No patient had recurrent meat impaction on follow-up (1-7 years, mean = 3 years) after education about the condition. CONCLUSION: (1) We suspect CES is an under-recognized cause for intermittent, long-standing dysphagia in adults. (2) Food impaction is a frequent initial presentation. Recognition of CES is critical for appropriate patient education and planning.

Adult↗
PubMed1998

Backbone flexibility of five sites on the catalytic subunit of cAMP-dependent protein kinase in the open and closed conformations.

To develop an alternative approach to measure peptidyl backbone flexibility and to expand our understanding of the segmental flexibility of cAMP-dependent protein kinase (cAPK), the effect of protein kinase inhibitor peptide, PKIalpha(5-24), and MgATP on the mobility of fluorescein selectively conjugated to five sites on the catalytic subunit of cAPK was examined. Specifically, five full-length, single-site catalytic subunit mutants (K16C, K81C, I244C, C199A, and N326C) were prepared, and fluorescein maleimide was selectively attached to the side chains of each substituted cysteine or, in the case of the C199A mutant, to the unprotected native C343. The time-resolved anisotropy decay profiles of the five fluorescein maleimide-conjugated mutants were well fit to a biexponential equation. The fast rotational correlation times of the fluorescein conjugates ranged between 1.9 and 2.8 ns and were inversely correlated (r = -0.87) to the averaged crystallographic main-chain atom B factors around each site of conjugation. The slow correlation times ranged between 25 and 28 ns and were about the same magnitude as the value of 21 ns estimated from the Stokes-Einstein equation. The presence of MgATP and PKIalpha(5-24), which induces the closed conformation of cAPK, was associated with a reduction of the fast rotational correlation time of the K81C conjugate, indicating that the peptidyl backbone around K81 is measurably less flexible when the C subunit is in the closed compared with the open conformation. The results suggest (i) that time-resolved fluorescence anisotropy can assess the nanosecond flexibility of short segments of the peptidyl backbone around each site of labeling and (ii) that the substrate/pseudosubstrate binding differentially affects the backbone flexibility of cAPK.

Animals↗
PubMed1998

Synthesis and evaluation of diphenyl phosphonate esters as inhibitors of the trypsin-like granzymes A and K and mast cell tryptase.

Thirty-six new amino acid and peptidyl diphenyl phosphonate esters were synthesized and evaluated to identify potent and selective inhibitors for four trypsin-like proteases: lymphocyte granzymes A and K, human mast cell tryptase, and pancreatic trypsin. Among five Cbz derivatives of Lys and Arg homologues, Z-(4-AmPhe)P(OPh)2 is the most potent inhibitor for granzyme A, and Z-LysP(OPh)2 is the best inhibitor for granzyme K, mast tryptase, and trypsin. The amidino P1 residue D,L-(4-AmPhGly)P(OPh)2 was utilized in a series of compounds with several different N-protecting groups and systematic substitutions at P2 in Cbz-AA derivatives and at P3 in Cbz-AA-Ala derivatives. Generally, these phosphonates inhibit granzyme A and trypsin more potently than granzyme K and tryptase. The P2 Thr and Ala dipeptide phosphonates, Cbz-AA-(4-AmPhGly)P(OPh)2, are the most potent inhibitors for granzyme A, and Cbz-Thr-(4-AmPhGly)P(OPh)2 (kobs/[I] = 2220 M-1 s-1) was quite specific with much lower inhibition rates for granzyme K and trypsin (kobs/[I] = 3 and 97 M-1 s-1, respectively) and no inhibition with tryptase. The most effective inhibitor of granzyme A was Ph-SO2-Gly-Pro-(4-AmPhGly)P(OPh)2 with a second-order rate constant of 3650 M-1 s-1. The most potent inhibitor for granzyme K was 3, 3-diphenylpropanoyl-Pro-(4-AmPhGly)P(OPh)2 with a kobs/[I] = 1830 M-1 s-1; all other phosphonates inhibited granzyme K weakly (kobs/[I] < 60 M-1 s-1). Human mast cell tryptase was inhibited slowly by these phosphonates with Cbz-LysP(OPh)2 as the best inhibitor (kobs/[I] = 89 M-1 s-1). The overall results suggest that scaffolds of Phe-Thr-(4-AmPhe) and Phe-Pro-Lys will be useful to create selective phosphonate inhibitors for granzymes A and K, respectively, and that P4 substituents offer opportunities to further enhance selectivity and reactivity.

Amino Acids↗
PubMed1998

Human mast cell tryptase fibrinogenolysis: kinetics, anticoagulation mechanism, and cell adhesion disruption.

Tryptase is a 31 kDa, glycosylated, trypsin-like enzyme stored in and released from mast cell granules. Human tryptase exists as a tetramer, binds heparin, and has a limited substrate specificity, yet it displays remarkable resistance to inhibition by blood plasma proteinase inhibitors. In this study we have examined the cleavage of human fibrinogen by tryptase. alpha chain cleavage was shown to occur in the carboxyl terminal region at Arg572 and beta chain cleavage was found to occur at Lys21. Kinetic analyses of these reactions yielded Km values of 0.2 microM for alpha chain cleavage and 0.26 microM for beta chain cleavage, as well as kcat/KM values of 7 x 10(5) and 4.6 x 10(5) M-1 s-1 for alpha and beta chain reactions, respectively. Proteolysis at Arg572 destroyed the Arg-Gly-Asp (RGD) sequence motif recognized by cell surface alphavbeta3 integrins, and endothelial cell binding to tryptase-modified fibrinogen was significantly reduced, consistent with loss of the RGD motif. Tryptase competed with thrombin in clotting assays using pure fibrinogen with heparin or blood plasma in the absence of heparin. Thrombin failed to initiate the clotting of fibrinogen following modification by tryptase, and fibrin clotting initiated with Ancrod was stopped and partially reversed by tryptase. These data provide insight concerning the mechanism by which tryptase renders fibrinogen unclottable by thrombin and suggests a novel role for tryptase in the modulation of cellular interactions with fibrin(ogen).

Amino Acid Sequence↗
PubMed1998

Estrogen replacement attenuates effects of scopolamine and lorazepam on memory acquisition and retention.

A multiple-trial passive avoidance paradigm was used to examine and compare the ability for estrogen replacement to attenuate learning and memory deficits produced by the muscarinic antagonist scopolamine and the benzodiazepine lorazepam. The multiple-trial paradigm was used in order to distinguish effects on acquisition from effects on retention. Estrogen replacement significantly attenuated a scopolamine-induced deficit on passive avoidance acquisition, but not retention. The ability for estrogen to attenuate the effect of scopolamine on acquisition was observed only when the analysis was limited to animals with serum levels of estradiol <200 pg/ml, suggesting that higher levels of estradiol were ineffective. This observation is consistent with at least one recent study showing dose-related effects of estrogen on ChAT-like immunoreactivity in the basal forebrain and supports the hypothesis that effects of estrogen on basal forebrain cholinergic neurons can help to reduce cognitive deficits associated with cholinergic impairment. Estrogen replacement was also observed to protect against a lorazepam-induced impairment on passive avoidance retention. This effect was observed specifically in animals that received estrogen prior to and during training and was not due to any effect of estrogen on serum levels of lorazepam following acute lorazepam administration. Collectively, these data demonstrate the ability for estrogen replacement to attenuate specific pharmacologically induced impairments in learning and retention and provide additional clues as to potential mechanisms by which estrogen replacement may help to reduce cognitive deficits associated with aging and Alzheimer's disease in postmenopausal women.

Animals↗
PubMed1998

Proteoglycan gene expression is decreased in abdominal aortic aneurysms.

BACKGROUND: Abdominal aortic aneurysms (AAA) are characterized by both increases in proteolysis and changes in the biosynthesis of the extracellular matrix (ECM) proteins. Proteoglycans are important components of the ECM, particularly the small proteoglycans, biglycan and decorin. Biglycan and decorin regulate cell proliferation and collagen assembly. Therefore, the purpose of this study is to quantify the levels of mRNA for biglycan and decorin in normal aorta (Na) and AAA. MATERIALS AND METHODS: Northern blot hybridization and competitive polymerase chain reaction using gene-specific external standards were used to quantify mRNA levels of bigylcan and decorin in RNA derived from AAA and NA. Results are expressed as a percentage of glyceraldehyde-3-phosphate dehydrogenase or normalized to ribosomal RNA content and compared using the unpaired t test. RESULTS: A statistically significant 15-fold decrease in biglycan mRNA expression was observed in AAA compared to NA (176.9% vs 11.8%, P < 0.001). In contrast to biglycan, the decorin mRNA expression is unchanged in AAA compared to NA. CONCLUSIONS: The marked decrease in biglycan mRNA levels is unique to aneurysmal disease of the aorta. In atherosclerosis and restenosis, biglycan expression is increased in comparison with normal artery. This decrease in biglycan expression may reflect important regulatory changes specific for the AAA. Furthermore, a decrease in biglycan gene expression and biosynthesis could have a broad impact on the physiology and matrix architecture of the aorta.

Adult↗
PubMed1998

Purification and activation of recombinant p38 isoforms alpha, beta, gamma, and delta.

p38 is a proline-directed serine/threonine kinase that is activated by inflammatory cytokines and cellular stress. At present, four isoforms of p38 have been identified and termed alpha, beta, gamma, and delta. We expressed each p38 homolog in Escherichia coli and purified the recombinant isoforms. p38alpha and C-terminal Flag-tagged p38beta were purified by Q-Sepharose fast flow, hydroxyapatite, and Q-Sepharose high-performance chromatography. His-tagged p38gamma was purified using Ni2+-NTA resin followed by Mono Q chromatography. Glutathione S-transferase-Flag p38delta was purified using M2 affinity agarose and gel-filtration chromatography. Upstream activators of p38, constitutively active (ca) MKK3 and MKK6, were also cloned, purified, and used to activate each p38 isoform. p38 alpha, gamma, and delta were phosphorylated by both MKK6 and caMKK3. p38beta was phosphorylated only by MKK6. Mass spectrometry analysis and kinase assays showed that MKK6 was the superior reagent for phosphorylating and activating all p38 isoforms.

Activating Transcription Factor 2↗
PubMed1998

Impact of aging on human salivary gland function: a community-based study.

A comprehensive evaluation of salivary flow rates and composition was undertaken in an age- and community-stratified population. A nonmedicated subpopulation was used to assess the effect of "primary aging" on salivary gland function. Unstimulated whole, parotid and submandibular/sublingual (SMSL) saliva, as well as citrate-stimulated parotid and SMSL saliva were collected from 1006 subjects. Flow rates were determined, and the total protein concentrations measured. Height and caloric intake were documented. Subjects were divided into six age groups from 35 to 75+ years old. Significant age-related decreases in the secretion rates of unstimulated whole (p < 0.001), stimulated parotid (p < 0.01) and unstimulated and stimulated SMSL (both p < 0.0001) saliva were observed in the total population. In the non-medicated subpopulation, age-related decreases in salivary secretions were observed in unstimulated whole (p < 0.01) and unstimulated and stimulated SMSL (p < 0.01 and p < 0.0001, respectively). Multiple regression analysis revealed that, as well as age, caloric intake was related to unstimulated SMSL and stimulated SMSL saliva in the whole population, and height was a contributor to unstimulated whole saliva and unstimulated parotid saliva flow rate variances. In the non-medicated population, caloric intake was the significant independent variable for unstimulated and stimulated parotid secretion, as was height for unstimulated whole and SMSL flow rates. Age-related increases in the total protein concentration of unstimulated parotid (p < 0.001) and unstimulated SMSL (p < 0.05) saliva were evident in the whole population, but not in the non-medicated subgroup. These data suggest that there are significant age-related alterations in salivary function.

Adult↗
PubMed1998

Mechanisms and pathways from recent deoxysugar biosynthesis research.

In the past few years, there have been many important advances in our understanding of the biosynthesis of deoxysugars. Mechanistic studies have shed light on how enzymes can cleave C-O bonds, epimerize the configuration of substituents and reduce keto groups to make deoxysugars. Exciting progress has also been made in our comprehension of the genetics of deoxysugar biosynthesis in antibiotics. All this information is important for potential medical and biotechnological applications, such as drug discovery based on combinatorial biology.

Deoxyribose↗
PubMed1998

Social and behavioural effects of traumatic brain injury in children.

Traumatic brain injury (TBI) is the leading cause of death and permanent disability in children and adolescents. Although cognitive and behavioural effects have now been reported for all degrees of TBI severity in children, other aspects of functioning which might be related (such as psychosocial adjustment), have been neglected. In the present study the social and behavioural effects of TBI were assessed by comparing 27 TBI children with 27 controls. TBI children demonstrated significantly lower levels of self-esteem and adaptive behaviour, and higher levels of loneliness, maladaptive behaviour and aggressive/antisocial behaviour. These findings confirm the previously demonstrated detrimental effects of TBI on children's behavioural functioning and offer new evidence for the detrimental effects of TBI on children's social functioning.

Adaptation, Psychological↗
PubMed1998

A multiplex ARMS test for 10 cystic fibrosis (CF) mutations: evaluation in a prenatal CF screening program.

In Maine, prenatal screening for cystic fibrosis (CF) is offered through primary care providers. Cheekbrush (buccal) samples are routinely tested for eight mutations by multiplex PCR amplification of five exons, followed by dot-blot hybridization with pooled allele-specific oligonucleotides (ASO). The ASO methodology is widely used and effective, but somewhat time and labor intensive when applied to CF carrier testing or couple-based prenatal screening in the general pregnant population. Amplification Refractory Mutation System (ARMS) is an improvement of the PCR that allows rapid detection of mutations involving single base changes or small deletions/insertions. In this study, two multiplex ARMS reactions are used to test for 10 common CF mutations. Clinical evaluation of the ARMS test includes a retrospective study of 140 banked samples (54 cell line, proficiency testing, and buccal controls; 86 clinical buccal samples) with known CF genotype (57 with CF mutations, 83 no mutation), followed by a prospective trial in which 309 buccal samples are analyzed con-currently using both methods. The success rate of the ARMS test in buccal lysates is comparable to the ASO method; all CF mutations are successfully identified. For testing nonsterile buccal lysates with low DNA concentrations, optimized performance in the ARMS method is obtained using Amplitaq Gold polymerase. The ARMS method developed is easy, rapid (1 day), and avoids the need for ASO probe labeling, dot-blotting and autoradiography. This study provides further evidence that ARMS methodology is suitable for clinical CF mutation analysis.

Cheek↗
PubMed1998

Lacquer cracks following laser treatment of choroidal neovascularization in pathologic myopia.

BACKGROUND: Lacquer cracks are breaks in the retinal pigment epithelial-Bruch's membrane-choriocapillaris complex and are manifestations of pathologic myopia. Progressive posterior segment elongation, uveal scleral thinning, and retinal pigment epithelial degeneration are thought to create a predisposition for crack formation in these eyes. In turn, choroidal neovascularization (CNV) may develop within the cracks to produce disciform scarring of the macula. This study examined lacquer cracks as a possible consequence of laser photocoagulation of CNV. METHODS: From the files of two retinal referral practices, five patients were located in whom lacquer cracks developed or expanded after laser photocoagulation for macular CNV in pathologic myopia. The mean age of the patients was 54.8 years. Four patients were treated with krypton red laser and one with an argon laser. Laser settings were available for only one of the patients. RESULTS: After laser photocoagulation, lacquer cracks were noted to expand in one or two directions from the laser scar between 10 days and 3 months of the treatment. The cracks also served as a pathway for progressive or recurrent neovascularization. CONCLUSIONS: Although lacquer cracks occur spontaneously in pathologic myopia, expansion, elongation, or simple development of a crack may occur as a result of laser photocoagulation of CNV. The new cracks also serve as a potential risk for recurrent neovascularization. This potential adverse complication should be considered in the management of CNV in pathologic myopia with laser treatment.

Adult↗
PubMed1998

The relationship between salivary histatin levels and oral yeast carriage.

Candida species are common commensal inhabitants of the oral cavity. Human saliva contains antifungal proteins called histatins. We tested the hypothesis that oral yeast status is related to salivary histatin levels. Thirty subjects were divided into two groups based on the presence (n = 15) or absence (n = 15) of yeast on oral mucosa surfaces. Unstimulated and stimulated submandibular and sublingual and parotid saliva was collected from each subject. Salivary flow rates were measured and histatin concentrations were determined in the stimulated saliva samples. The yeast colony positive group showed lower median unstimulated parotid saliva flow rates as well as lower median concentrations of total histatins in submandibular and sublingual saliva. There was a negative correlation between yeast colony-forming units and unstimulated parotid saliva flow rates and between yeast colony-forming units and submandibular and sublingual saliva histatin concentration and secretion. The results suggest that oral yeast status may be influenced by unstimulated parotid saliva flow rates and by submandibular and sublingual histatin concentration and secretion.

Aged↗