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David A Johnson

Publications and source records attributed to David A Johnson.

At least 55 records · Page 3Linked to original sources
PubMed2003

Tail profile: a more accurate system for analyzing DNA damage using the Comet assay.

The Comet assay (single cell gel electrophoresis assay) measures DNA strand breaks in individual cells. In the assay cells are embedded in agarose, lysed, and electrophoresed under low voltage, allowing migration of damaged DNA. The DNA is stained and subsequently viewed with an epifluorescent microscope. If DNA damage has occurred the electrophoresed DNA fragments appear as a diffuse tail behind the nucleus known as a "comet". Many computer-aided analysis systems are currently in use to quantify the amount of DNA damage that is represented by a comet image. Here, we present a novel method of analysis known as "tail profile". This method of analysis provides several advantages over currently employed methods, which rely primarily on the "tail moment" method of analysis. We compared the amount of DNA damage reported from both the tail profile and tail moment methods of analysis and observed a 26% (P<0.0001) increase in damage detected by tail profile across the 10-25 microm range of tail length, where the majority of the relevant comet data is concentrated. We further report that this increase in sensitivity is not only limited to assessing DNA damage, but also to gathering data from DNA repair assays. Furthermore, we demonstrate increased functionality and extended data analysis capabilities with the use of a compressed collection of images called a "comet chip" and through a visual representation of data called a "profile plot". Use of the custom macros enabled us to detect an unexpected characteristic of the electrophoretic profile, giving us novel insight into the nature of comet analysis. In addition to the increased analytical sensitivity proffered by this system, the tail profile macros are upgradeable and platform independent.

Comet Assay↗
PubMed2003

Estrogen enhances potassium-stimulated acetylcholine release in the rat hippocampus.

Short-term estrogen replacement has been shown to enhance basal forebrain cholinergic function. Whether or not long-term estrogen replacement can enhance basal forebrain cholinergic function has been questioned in light of recent studies showing that several cholinergic measures which are increased following short-term treatment are not increased following longer-term (>30 days) treatment. In the present study, in vivo microdialysis was used to assess the effects of continuous estradiol replacement on basal forebrain cholinergic function. Our data show that 6-7 weeks of continuous estradiol replacement significantly enhanced potassium-stimulated acetylcholine release in the hippocampus of ovariectomized rats, and that this effect was reversed following discontinuation of the estrogen treatment. These data are consistent with the hypothesis that estrogen-mediated effects on cholinergic neurons can contribute to the effects of long-term estrogen replacement on cognitive performance recently described.

Acetylcholine↗
PubMed2003

Endoscopic, deep mural implantation of Enteryx for the treatment of GERD: 6-month follow-up of a multicenter trial.

OBJECTIVES: This prospective, multicenter, single-arm study evaluated the safety and efficacy of the endoscopic implantation of Enteryx, a biocompatible, non-biodegradable liquid polymer for the treatment of GERD. METHODS: Eighty-five patients with heartburn symptoms responsive to proton pump inhibitor (PPI) use were enrolled. Inclusion requirements were HRQL score < or = 11 on PPI and > or = 20 off PPI, and 24-hour PH probe with > or = 5% total time at PH < or = 4. Patients with a hiatus hernia > 3 cm, grade 3 or 4 esophagitis, or esophageal motility disorder were excluded. Using a 4-mm needle tipped catheter during standard endoscopy, implants were made in 3-4 quadrants deep into the wall of the cardia. Use of PPI medications, pH-metry, manometry, GERD symptoms, and patient quality of life were assessed over a 6-month follow-up period. RESULTS: At 6 months, PPI use was eliminated in 74% and reduced by > 50% in 10% of patients. The median HRQL score improved from 24.0 pre-implant (baseline off PPIs) to 4.0 at 6 months (p < 0.001). Mean total esophageal acid exposure time was 9.5% pretherapy and 6.7% at 6 months (p < 0.001). Mean LES length increased from 2.0 cm at baseline to 3.0 cm posttherapy (p = 0.003). There were no clinically serious adverse events. Transient mild-to-moderate chest pain commonly occurred after implantation. CONCLUSIONS: The endoscopic implantation of Enteryx is a safe and effective therapy for eliminating or decreasing the need for PPI medications, improving GERD symptoms and patient quality of life, and decreasing esophageal acid exposure among patients suffering from GERD.

Biopolymers↗
PubMed2003

Endoscopic implantation of enteryx for treatment of GERD: 12-month results of a prospective, multicenter trial.

OBJECTIVES: This study aimed to assess the efficacy and safety of endoscopically implanting a nonresorbable biocompatible polymer (Enteryx) in the distal esophagus and proximal gastric cardia for the treatment of gastroesophageal reflux disease (GERD). METHODS: In a prospective, multicenter, international trial, 85 well-controlled GERD patients who were receiving chronic proton pump inhibitor (PPI) therapy underwent Enteryx implantation under fluoroscopic visualization, without general anesthesia. After the procedure, patients were discharged within approximately 2-4 h. Patients were judged to be treatment responders if after implantation they reduced PPI dosage by >/=50%. Follow-up evaluations were conducted at 1, 3, 6, and 12 months and included medication usage, symptoms, quality of life, endoscopy, pH monitoring, manometry, and documentation of adverse events. RESULTS: At 12 months, 80.3% (95% CI = 69.9%-88.3%) of 81 evaluable patients were treatment responders. Of the responders, 87.7% completely discontinued PPIs, and 12.3% reduced PPI dosage by >/=50%. Treatment response was more likely in patients with residual implant volume of >/=5 mL (p = 0.027). Other patient and treatment variables were not predictive. Both GERD heartburn and regurgitation symptom scores significantly improved at 12 months compared with baseline (p < 0.001). There were significant reductions in median supine, upright, and total percent time of esophageal exposure to pH <4. Endoscopically assessed esophagitis grades were unchanged. No serious adverse events were encountered. Transient retrosternal chest pain was experienced by 91.8% of patients. This pain was seldom severe and was typically successfully managed with prescription pain medication. CONCLUSIONS: Enteryx implantation allows most patients to discontinue PPI therapy, improves their symptoms, and reduces esophageal acid exposure. The effects of implantation are long-lasting, and morbidity is transient and minimal. The procedure requires basic endoscopic skills and seems to provide a useful option in the effective clinical management of GERD.

Adult↗
PubMed2003

Review of esomeprazole in the treatment of acid disorders.

Esomeprazole (Nexium, AstraZeneca) is the (S)-isomer of omeprazole and the first proton pump inhibitor to be developed as an optical isomer. Esomeprazole has an improved pharmacokinetic profile, resulting in increased systemic exposure and less interindividual variability compared with omeprazole, and more effective suppression of gastric acid production compared with other proton pump inhibitors. In several large, double-blind, randomised trials, significantly higher rates of endoscopically-confirmed healing of erosive oesophagitis and resolution of heartburn have been achieved in patients with gastro-oesophageal reflux disease receiving 8 weeks of esomeprazole 40 mg o.d. compared with those receiving omeprazole 20 mg o.d. or lansoprazole 30 mg o.d. In the maintenance of healed erosive oesophagitis, esomeprazole 10, 20 or 40 mg o.d. was significantly more effective than placebo in two 6-month, randomised, double-blind trials. Additionally, esomeprazole 20 mg o.d. was more effective than lansoprazole 15 mg in the maintenance of healed erosive oesophagitis in another 6-month, randomised, double-blind trial. Healing of oesophagitis was also effectively maintained by esomeprazole 40 mg o.d. in a 12-month non-comparative trial. Esomeprazole 20 or 40 mg o.d. effectively relieved heartburn in patients with gastro-oesophageal reflux disease without oesophagitis in two 4-week, placebo-controlled trials. Clinical trials have shown that triple therapy with esomeprazole 40 mg o.d. in combination with amoxicillin and clarithromycin produced Helicobacter pylori eradication rates similar to those obtained using triple therapy involving twice-daily dosing with other proton pump inhibitors. Esomeprazole is well-tolerated, with a spectrum and incidence of adverse events similar to those associated with omeprazole.

Anti-Ulcer Agents↗
PubMed2003

Enhancement of antigen-specific immunity via the TLR4 ligands MPL adjuvant and Ribi.529.

MPL (Corixa) adjuvant is a chemically modified derivative of lipopolysaccharide that displays greatly reduced toxicity while maintaining most of the immunostimulatory activity of lipopolysaccharide. MPL adjuvant has been used extensively in clinical trials as a component in prophylactic and therapeutic vaccines targeting infectious disease, cancer and allergies. With over 33,000 doses administered to date, MPL adjuvant has emerged as a safe and effective vaccine adjuvant. Recently, scientists at Corixa Corporation have developed a library of synthetic lipid A mimetics (aminoalkyl glucosaminide 4-phosphates) with demonstrated immunostimulatory properties. Similar to MPL adjuvant, these synthetic compounds signal through Toll-like receptor 4 to stimulate the innate immune system. One of these compounds, Ribi.529 (RC-529), has emerged as a leading adjuvant with a similar efficacy and safety profile to MPL adjuvant in both preclinical and clinical studies.

Adjuvants, Immunologic↗
PubMed2003

Stability of esomeprazole capsule contents after in vitro suspension in common soft foods and beverages.

STUDY OBJECTIVE: To determine the in vitro stability of esomeprazole pellets from an opened capsule after suspension in various common soft foods and beverages. DESIGN: In vitro study. SETTING: Pharmaceutical company research laboratory. MEASUREMENTS AND MAIN RESULTS: Pellets from opened esomeprazole 20-mg capsules were suspended in 100 ml of tap water, milk (1.5% fat), orange juice, apple juice, yogurt, or cultured milk for 30 minutes, then added to 500 ml of hydrochloric acid to simulate gastric acid exposure. After a 2-hour incubation, the mixture was filtered through a sieve, and the collected pellets were dissolved in an alkaline solution. Esomeprazole concentrations were measured using reverse-phase liquid chromatography The stability of the esomeprazole pellets exceeded 98% in all beverages and soft foods except milk. CONCLUSION: Administration of the pellets from an opened esomeprazole capsule shortly after suspending them in tap water, yogurt, cultured milk, orange juice, or apple juice may be a practical alternative for patients who cannot swallow an intact capsule. Bioavailability studies comparing esomeprazole administered as an intact capsule to that of the pellets from an opened capsule suspended in these beverages or soft foods are recommended to confirm these findings.

Animals↗
PubMed2003

Endoscopic therapy for GERD--baking, sewing, or stuffing: an evidence-based perspective.

The concept of using endoscopic therapy for the treatment of symptomatic gastroesophageal reflux disease (GERD) is a relatively recent development. Currently, three basic techniques are approved for use in the United States. To date, clinical trials have examined either a thermal approach, endoscopic suturing, or injection intervention in the area of the lower esophageal sphincter. However, the trials for each type of endoscopically directed therapy have varied in methodologic design and data analysis. It is important to recognize these differences when attempting to compare the efficacy and outcomes for each endoscopic therapy. Additionally, the risk/benefit profile must be carefully evaluated for each of these interventions before considering it a viable treatment strategy.

Catheter Ablation↗
PubMed2003

Alternative dosing for PPI therapy: rationale and options.

The target goal for all acid suppressive therapy is to optimize control of intragastric pH over extended periods of time. A somewhat axiomatic paradigm has been that effective control of gastric acid production is associated with optimal outcome in acid-related diseases. The proton pump inhibitor (PPI) class of therapy has shown superiority for effective control of acid and healing of related diseases. Traditional delivery of PPIs may not be a viable option for all patients. Therefore, a clear understanding of alternative dosing formulations and related efficacies is key in order for the clinician to select the most appropriate agent and strategy to optimize outcomes and cost-effectiveness for each patient.

Antacids↗
PubMed2002

Selective lesion of cholinergic neurons in the medial septum by 192 IgG-saporin impairs learning in a delayed matching to position T-maze paradigm.

This study examined whether selective destruction of cholinergic neurons in the medial septum impairs acquisition of a delayed matching-to-position (DMP) spatial memory task. Either the selective immunotoxin 192 IgG-saporin (SAP; 0.22 or 1.0 microg) or the non-selective excitatory neurotoxin ibotenate (IBO; 5 microg), was infused directly into the medial septum of rats. Both doses of SAP, but not IBO, significantly impaired acquisition of the DMP task and blunted the initial alternating behavior of the rats in the T-maze. Histochemical staining revealed that both doses of SAP produced a near complete depletion of choline acetyltransferase (ChAT)-positive neurons in the medial septum. Some loss of parvalbumin staining was observed following administration of the higher dose, but not the lower dose, of SAP. In contrast, IBO produced a nearly complete depletion of parvalbumin-positive staining throughout the medial septum. IBO also produced a loss of ChAT-positive neurons and considerable local damage in the medial septum around the area of injection; however, many ChAT-positive neurons in the medial septum distal to the injection remained. A significant correlation between the number of days to reach criterion and ChAT activity in the frontal cortex and hippocampus was observed. The results suggest that low doses of SAP can be used to selectively destroy cholinergic neurons in the medial septum, and that selective destruction of these neurons significantly impairs acquisition of the DMP task. We propose that acquisition of the DMP task is a sensitive behavioral assay for the selective loss of basal forebrain cholinergic projections.

Animals↗
PubMed2002

Evidence for an internal entropy contribution to phosphoryl transfer: a study of domain closure, backbone flexibility, and the catalytic cycle of cAMP-dependent protein kinase.

While there is no question that ligands can induce large-scale domain movements that narrow (close) the active-site cleft of the catalytic (C) subunit of cAMP-dependent protein kinase (cAPK), the results from small-angle X-ray scattering, protein footprinting, and thermostability studies are inconsistent with regard to which ligands induce these movements. This inconsistency suggests a greater complexity of cAPK conformational dynamics than is generally recognized. As an initial step to study this issue in relation to the catalysis, a new method to measure cAPK domain closure was developed, and the state of domain closure and the local segmental flexibility at major steps of the cAPK catalytic cycle were examined with site-directed labeling and fluorescence spectroscopy. To achieve this, a C subunit mutant (F239C/C199A) was engineered that allowed for fluorescein 5-maleimide (donor) conjugation of F239C in the large lobe and tetramethylrhodamine (acceptor) conjugation of C343 in the small lobe. Domain closure was assessed as an increase in the efficiency of energy transfer between donor and acceptor. The anisotropy decay of fluoroscein 5-maleimide, conjugated to a site of cysteine substitution (K81C) in the small lobe of the C subunit was used to assess the local backbone flexibility around the B helix. The effects of substrate/pseudosubstrate (ATP and PKI(5-24)), a fragment of protein kinase inhibitor) and products (ADP and phosphorylated PKS) on domain closure and B helix flexibility were measured. The results show that domain closure is not tightly coupled to the flexibility around K81C. Moreover, although substrates/pseudosubstrate and products independently close the active-site cleft, only the substrates substantially decreased the backbone flexibility around the B helix. Because this order-to-disorder transition coincides with the phosphoryl transfer transition, the results suggest the existence of an internal entropy contribution to catalysis.

Amino Acid Substitution↗
PubMed2002

Taking toll: lipid A mimetics as adjuvants and immunomodulators.

Vaccine adjuvants based on the structure of lipid A, such as monophosphoryl lipid A (MLA), have proven to be safe and effective in inducing immune responses to heterologous proteins in animal and human vaccines. Recent work on the development of a recombinant vaccine for leishmaniasis has demonstrated that a clinical grade MLA formulation - MPL(R) adjuvant - is essential in the development of a protective response. Preliminary evidence suggests that MLA and a chemically distinct family of lipid A mimetics - the aminoalkyl glucosaminide 4-phosphates - act on Toll-like receptor 4 (TLR4). As TLR4 agonists, they have potent immunomodulatory effects when used both as vaccine adjuvants and as stand-alone products. Novel approaches to vaccine development could benefit from taking full advantage of the effects of these compounds on innate and adaptive responses.

Adjuvants, Immunologic↗
PubMed2002

Hypnosis treatment for severe irritable bowel syndrome: investigation of mechanism and effects on symptoms.

Hypnosis improves irritable bowel syndrome (IBS), but the mechanism is unknown. Possible physiological and psychological mechanisms were investigated in two studies. Patients with severe irritable bowel syndrome received seven biweekly hypnosis sessions and used hypnosis audiotapes at home. Rectal pain thresholds and smooth muscle tone were measured with a barostat before and after treatment in 18 patients (study I), and treatment changes in heart rate, blood pressure, skin conductance, finger temperature, and forehead electromyographic activity were assessed in 24 patients (study II). Somatization, anxiety, and depression were also measured. All central IBS symptoms improved substantially from treatment in both studies. Rectal pain thresholds, rectal smooth muscle tone, and autonomic functioning (except sweat gland reactivity) were unaffected by hypnosis treatment. However, somatization and psychological distress showed large decreases. In conclusion, hypnosis improves IBS symptoms through reductions in psychological distress and somatization. Improvements were unrelated to changes in the physiological parameters measured.

Abdominal Pain↗
PubMed2002

Esomeprazole (40 mg) compared with lansoprazole (30 mg) in the treatment of erosive esophagitis.

OBJECTIVES: Esomeprazole, the S isomer of omeprazole, has been shown to have higher healing rates of erosive esophagitis than omeprazole. This study compared esomeprazole with lansoprazole for the healing of erosive esophagitis and resolution of heartburn. METHODS: This United States multicenter, randomized, double blind, parallel group trial was performed in 5241 adult patients (intent-to-treat population) with endoscopically documented erosive esophagitis, which was graded by severity at baseline (Los Angeles classification). Patients received 40 mg of esomeprazole (n = 2624) or 30 mg of lansoprazole (n = 2617) once daily before breakfast for up to 8 wk. The primary efficacy endpoint was healing of erosive esophagitis at week 8. Secondary assessments included proportion of patients healed at week 4, resolution of investigator-recorded heartburn, time to first and time to sustained resolution of patient diary-recorded heartburn, and proportion of heartburn-free days and nights. RESULTS: Esomeprazole (40 mg) demonstrated significantly higher healing rates (92.6%, 95% CI = 91.5-93.6%) than lansoprazole (30 mg) (88.8%, 95% CI = 87.5-90.0%) at week 8 (p = 0.0001, life-table estimates, intent-to-treat analysis). A significant difference in healing rates favoring esomeprazole was also observed at week 4. The difference in healing rates between esomeprazole and lansoprazole increased as baseline severity of erosive esophagitis increased. Sustained resolution of heartburn occurred faster and in more patients treated with esomeprazole. Sustained resolution of nocturnal heartburn also occurred faster with esomeprazole. Both treatments were well tolerated. CONCLUSIONS: Esomeprazole (40 mg) is more effective than lansoprazole (30 mg) in healing erosive esophagitis and resolving heartburn. Healing rates are consistently high with esomeprazole, irrespective of baseline disease severity.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed2002

Immunostimulatory activity of aminoalkyl glucosaminide 4-phosphates (AGPs): induction of protective innate immune responses by RC-524 and RC-529.

Earlier we showed that the structural requirements for adjuvanticity among the aminoalkyl glucosaminide 4-phosphate (AGP) class of synthetic immunostimulants may be less strict than those for other endotoxic activities, including the induction of nitric oxide synthase in murine macrophages and cytokine production in human whole blood. The known role of nitric oxide and pro-inflammatory cytokines in the activation of host defenses against infection prompted us to examine the ability of certain AGPs to enhance non-specific resistance in mice to Listeria monocytogenes and influenza infections as well as to stimulate the production of pro-inflammatory cytokines in mouse splenocytes, human PBMCs, and human U937 histiocytic lymphoma cells. Intranasal administration of RC-524 or RC-529 to mice 2 days prior to a lethal influenza challenge provided significant protection in each case. Similarly, the intravenous administration of these AGPs induced resistance to L. monocytogenes infection as measured by survival or reduction of bacteria in the spleen. Activation of the innate immune response by AGPs appears to involve activation of Toll-like receptor 4 (TLR4) because RC-524 failed to elicit a protective effect in C3H/HeJ mice which have a defect in TLR4 signaling or induce significant cytokine levels in C3H/HeJ splenocytes. Both AGPs also stimulated pro-inflammatory cytokine release in human cell cultures in a dose-dependent manner.

Administration, Intranasal↗
PubMed2002

Readership survey. Reviews in Gastroenterological Disorders.

The readership survey demonstrates that Reviews in Gastroenterological Disorders has been extremely well received by the gastroenterological community. It is through readership surveys that we are able to assess our progress and identify future opportunities for improvement. We are grateful to the 191 gastroenterologists who took the time to complete the survey. The information and insights gained from the survey will help us to deliver an even better product in the future. We hope that our readership will continue providing their feedback in years to come.

Gastroenterology↗
PubMedDate not supplied

Rehabilitation and development after childhood cancer: can the need for physical exercise be met?

Clinical and experimental evidence attests to the neurological and psychological benefits of physical exercise. Prescribing exercise for children after cancer has the potential to facilitate recovery, performance and development, with consequent improvement in quality of life and long-term outcome. However, could a school take up the prescription for a child's individual exercise programme? As a preliminary to an intervention study, all primary and secondary schools in two Scottish regions were surveyed. The aim was to evaluate the utility of prescribing exercise as part of a child's individual rehabilitation plan and to investigate awareness in schools of the potential benefits of exercise for cognition and behaviour. Approximately half the respondents indicated that extra physical exercise sessions could be incorporated into the school day. The main difficulties preventing such inclusion were identified as a lack of staff for supervision and timetabling problems. However, there was also a high level (>70%) of lack of information about what a child could be expected to do after cancer. Further, more respondents (approximately 60%) anticipated benefits of exercise for social development than for academic progress (approximately 35%). These results emphasize the necessity of clear and specific liaison with a school when planning and implementing a child's long-term rehabilitation programme.

Child↗