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Biomedical subjects

M Palmer

Publications and source records attributed to M Palmer.

At least 145 records · Page 8Linked to original sources
PubMed1994

Recovery of human fibroblasts from attack by the pore-forming alpha-toxin of Staphylococcus aureus.

When applied at low concentrations (< 10 micrograms/ml), staphylococcal alpha-toxin generates a small channel in keratinocyte and lymphocyte membranes that permits selective transmembrane flux of monovalent ions. Here we show that a moderate concentration (1-50 micrograms/ml) of alpha-toxin similarly produces a small pore in membranes of human fibroblasts. This process leads to rapid leakage of K+ and to a drop in cellular ATP to 10-20% of normal levels in 2 h. In the presence of medium supplemented with serum and at pH 7.4, the cells are able to recover from toxin attack, so that normal levels of K+ and ATP are reached after 6-8 h at 37 degrees C. The repair process is dependent on the presence of serum in the medium and is very sensitive towards pH. Decreases of pH in the medium to < or = 7.0 as well as increases to > or = 7.8 causes the repair mechanism to fail. The fate of cell-bound toxin molecules was investigated by using a radiolabelled tracer and by immunological detection of toxin exposed at the cell surface. The results indicated that 50-70% of the toxin was shed from cell membranes. However, there was no clear correlation between shedding and recovery, and shedding was also observed in cells that died at pH 7.8. Shedding was not decisive for repair, since cells that had recovered from toxin attack continued to carry 30-40% of initially bound toxin on their cell surface. Blockade of Na+/K(+)-ATPases with ouabain evoked similar kinetics of K(+)-depletion in control cells, compared with cells that had just recuperated from toxin attack and that still carried 30-40% alpha-toxin on their surface. We therefore tentatively concluded that repair of alpha-toxin lesions was due to closure of small pores, rather than from compensation of membrane leaks by up-regulation of Na+/K(+)-ATPase activity. We speculate that repair of small membrane lesions may extend to other agents that produce channels of similar nature in nucleated cells. Larger pores created by E. coli hemolysin or streptolysin O, both of which form larger functional transmembrane lesions, could not be repaired by fibroblasts.

Adenosine Triphosphate↗
PubMed1994

The quantitative distribution of nebulized antibiotic in the lung in cystic fibrosis.

Nebulized antibiotic therapy in cystic fibrosis is an established procedure. The present study was designed to quantitate deposition, and assess its relation to the disease state. Twenty seven children and young adults with cystic fibrosis (mean 11.6 years, range 4-23 years, 12 females) were studied to establish the quantity and pattern of deposition of nebulized tobramycin in the respiratory tract. A single (120 mg) dose of nebulized 99 m technetium-labelled tobramycin was administered, and imaged with a gamma-camera. The mean penetration index (which compares the distribution of 81 m-Krypton gas with Tc-radioaerosol) was also used to measure peripheral deposition efficiency. The aerosol mass median diameter (MMAD) for the compressor-nebulizer system used was 5.3 u, measured with the Malvern Mastersizer. Serial sputum samples were fluroimmunoassayed for tobramycin in nine patients. A mean of 8.0 (SEM 1.0) mg tobramycin reached the lungs. There was no relationship between the total pulmonary deposition and indices of pulmonary damage in cystic fibrosis. Sixteen percent of the lung tobramycin reached the periphery. The greater the lung damage as indicated by FEV1 and Chrispin-Norman scores, the smaller the proportion of pulmonary tobramycin that reached the periphery. The mean penetration index increased with increase in the FRC, but bore no relation to other respiratory function tests or to chest X-ray scores. Sputum tobramycin concentrations reached levels bactericidal for Pseudomonas aeruginosa. Airway obstruction and damage affected the proportion of pulmonary tobramycin reaching the periphery. The proportion of tobramycin reaching the lungs was small and variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Induction of rhythm abnormalities in the fetal rat heart. A tentative mechanism for the embryotoxic effect of the class III antiarrhythmic agent almokalant.

OBJECTIVES: The aim was to test the hypothesis that the recently reported embryotoxic effect of class III antiarrhythmic agents may be a result of electrophysiological disturbances induced by these agents. METHODS: Comparative studies of drug effects in the adult and fetal rat were performed using three experimental models: (1) effects of almokalant upon pregnancy and fetal mortality in rats given daily doses of 0, 10, 50, 100, or 400 mumol.kg-1 orally in the diet on days 6-15 of pregnancy; (2) effects of d-sotalol (1-1000 microM), almokalant (0.1-100 microM) and dofetilide (0.01-10 microM) on the adult and fetal cardiac action potential in vitro; (3) voltage clamp recordings in single fetal and adult ventricular myocytes superfused with almokalant (0.5 microM). RESULTS: In the groups of rats treated with 100 and 400 mumol.kg-1, respectively, the body weight gain was decreased from day 12 of gestation, and there were no viable fetuses at termination of pregnancy. In atrial as well as ventricular tissue, the class III agents induced a concentration dependent prolongation of the fetal action potential duration, accompanied by a reduction in heart rate and eventually the appearance of rhythm abnormalities and/or early afterdepolarisations. The adult action potential duration remained unaffected. An almokalant sensitive current (probably the delayed rectifier, IK) could be evoked both in the fetal and in the adult ventricular cells. CONCLUSIONS: Class III antiarrhythmic agents were shown to induce fetal mortality and rhythm abnormalities in the rat heart. Although they do not prove a causal relationship between these effects, our observations may have implications for the clinical use of class III antiarrhythmic agents in women of childbearing potential.

Action Potentials↗
PubMed1994

Novel path to apoptosis: small transmembrane pores created by staphylococcal alpha-toxin in T lymphocytes evoke internucleosomal DNA degradation.

Peripheral-blood human T lymphocytes were treated with Staphylococcus aureus alpha-toxin. Membrane permeabilization was assessed by measuring efflux of K+ and Rb+ and influx of Na+, Ca2+, and propidium iodide. Cellular ATP and [3H]thymidine incorporation following lectin stimulation were measured as parameters for cell viability. Internucleosomal cleavage characteristic of programmed cell death was assessed by agarose gel electrophoresis and by quantifying low-molecular-weight, [3H]thymidine-labeled DNA fragments. Nanomolar concentrations of alpha-toxin evoked protracted, irreversible ATP depletion in both activated and resting T lymphocytes. Toxin-damaged cells also lost their ability to incorporate [3H]thymidine upon subsequent stimulation with phytohemagglutinin. These cells carried toxin hexamers, and their plasma membranes became permeable for monovalent ions but not for Ca2+ and propidium iodide. The permeabilization event was followed by internucleosomal DNA degradation characteristic of programmed cell death. Membranes of cells treated with high toxin doses (> 300 nM) became permeable to both Ca2+ and propidium iodide. In this case, ATP depletion occurred within minutes and no DNA degradation was observed. When cells were suspended in Na(+)-free buffer, alpha-toxin applied at low doses still bound and formed hexamers. However, these cells displayed neither DNA degradation nor loss of viability. The data indicate that formation of very small but not of large alpha-toxin pores may trigger programmed cell death in lymphocytes and that uncontrolled flux of Na+ ions may be an important event precipitating the suicide cascade.

Adenosine Triphosphate↗
PubMed1994

Effect of schedule and maintenance on the antiemetic efficacy of ondansetron combined with dexamethasone in acute and delayed nausea and emesis in patients receiving moderately emetogenic chemotherapy: a phase III trial by the National Cancer Institute of Canada Clinical Trials Group.

PURPOSE: This study examines whether the schedule of ondansetron significantly influences its antiemetic efficacy in the first 24 hours after chemotherapy, whether the administration of oral ondansetron after 24 hours is effective in preventing delayed emesis, and whether the efficacy of ondansetron is preserved over multiple courses of moderately emetogenic chemotherapy. PATIENTS AND METHODS: A multicenter double-blind study randomized 302 cancer patients to one of three treatment arms. Arm A received dexamethasone 10 mg intravenously (i.v.) plus ondansetron (Zofran; Glaxo Canada Inc, Toronto, Canada) 8 mg i.v. prechemotherapy plus ondansetron 8 mg orally every 12 hours postchemotherapy for nine doses. Arm B received dexamethasone 10 mg i.v. plus ondansetron 16 mg i.v. prechemotherapy plus placebo orally postchemotherapy in the same schedule as arm A. Arm C received dexamethasone 10 mg i.v. plus ondansetron 8 mg prechemotherapy plus ondansetron 8 mg orally postchemotherapy for one dose followed by placebo orally every 12 hours for eight more doses. Response was assessed by the number of reported episodes of vomiting and by severity of nausea measured on a visual analog scale (VAS). RESULTS: The two schedules of ondansetron used in the first 24 hours were no different in their antiemetic efficacy, with similar rates for complete responses (76.7% v 72.0%, P = .472), complete plus major responses (90.2% v 82.0%, P = .135), and severity of nausea (P = .348). Oral ondansetron after 24 hours was more effective than placebo in preventing delayed nausea and emesis, with superior rates of complete responses (59.6% v 42.1%, P = .012 by one-sided test), complete plus major responses (80.9% v 66.3%, P = .018 by one-sided test), and less severe nausea (9.2 mm v 18.6 mm on a 100-mm VAS, P = .002). The efficacy of ondansetron was maintained over subsequent courses of chemotherapy. CONCLUSION: The schedule of ondansetron in the first 24 hours does not influence its efficacy. The use of oral maintenance ondansetron is effective in preventing delayed maintenance ondansetron is effective in preventing delayed nausea and emesis after moderately emetogenic chemotherapy.

Antineoplastic Agents↗
PubMed1993

Staphylococcus aureus alpha-toxin. Production of functionally intact, site-specifically modifiable protein by introduction of cysteine at positions 69, 130, and 186.

Staphylococcal alpha-toxin, the prototype of an oligomerizing, pore-forming cytotoxin, is sensitive to biochemical modifications and cannot be labeled with biotin or fluorescein under preservation of its biological activity. In this study, we have used site-directed mutagenesis to introduce cysteine residues at positions 69, 130, and 186. Each mutant was fully and rapidly reactive with several sulfhydryl-specific reagents, indicating superficial location. Coupling of SH-groups with fluorescein-maleimide or biotin-maleimide was tolerated without loss of hemolytic activity at position 130, and the formed hexamers were visible on target cells by fluorescence microscopy and could be detected on electroblots by reaction with streptavidin-peroxidase. At the two other positions, modification caused significant loss of activity. However, the labeled proteins still bound to red cells, as shown by fluorescence microscopy and electroblotting. Intrinsically labeled alpha-toxin represents a novel tool to study the interaction of this pore-former with target membranes.

Amino Acid Sequence↗
PubMed1993

Altered pore-forming properties of proteolytically nicked staphylococcal alpha-toxin.

Staphylococcal alpha-toxin is a single-chain polypeptide with a molecular weight of 34,000 that hexamerizes in lipid bilayers to form pores of 1-1.5 nm effective diameter in membranes. We demonstrate that limited proteolysis of purified alpha-toxin with proteinase K generates a hemolytically active product that yields one major protein band of 17-18 kDa in SDS-polyacrylamide gel electrophoresis. The 17-18-kDa protein band harbors two major fragments of similar size representing the N- and C-terminal halves, which remain associated with each other in non-denaturing buffers but dissociate in 6 M urea. Dissociation in urea leads to loss of hemolytic activity. In contrast, unnicked alpha-toxin is not inactivated by urea. Nicked, hemolytically active alpha-toxin forms hexamers on erythrocyte membranes and on lymphocytes and monocytes. However, the nicked toxin can only lyse erythrocytes and fails to permeabilize nucleated cells. Osmotic protection experiments indicate that the size of pores generated by the nicked toxin is considerably smaller (0.6-0.9 nm effective diameter) than that generated by native toxin. The collective results do not support a previous proposal that different functions of alpha-toxin are contained in separate domains of the molecule.

Bacterial Toxins↗
PubMed1993

A guide to the use of pore-forming toxins for controlled permeabilization of cell membranes.

Depending on the size of the pores one wishes to produce in plasma membranes, the choice will probably fall on one of the three toxins discussed above. S. aureus alpha-toxin should be tried first when pores of 1-1.5 nm diameter are required. This is generally the case when Ca2+ and nucleotide dependence of a given process is being studied. If alpha-toxin does not work, this is probably due to the fact that the toxin either does not produce pores, or that the pores are too small. In this case, high concentrations of alpha-toxin should be tried. If this still does not work, we recommend the use of HlyA. When very large pores are to be created, e.g. for introduction of antibodies into the cells, SLO or another member of this toxin family are the agents of choice. SLO preparations need to be checked for presence of protease contaminants. Tetanolysin currently offers advantages since it is protease-free, and the size of the pores can probably be controlled by varying the toxin dose. Methods for assessing the size of pores created by such agents have been published in the recent literature, and the appropriate papers can be consulted whenever the need arises.

Bacterial Proteins↗
PubMed1993

Problems encountered in teaching the use of the 65 cm flexible sigmoidoscope in a surgical oncology training program.

Flexible sigmoidoscopy after age 50 has been recommended by the American Cancer Society for colorectal cancer screening. A questionnaire to assess the difficulties encountered in learning to perform this procedure was given to 19 surgical oncology fellows after a 3-month rotation in the Division of Colorectal Surgery. Sixteen (84%) trainees related that between 10-20 flexible sigmoidoscopies were necessary before they felt competent. The most difficult aspect of learning flexible sigmoidoscopy was the torquing technique followed by the ability to determine the location of the proximal bowel lumen. All 19 trainees rated the ability to recognize pathology as not difficult. In this group of surgical trainees, the mean number of flexible sigmoidoscopy performed before competency was established was 15; torquing the shaft of the sigmoidoscope was the most difficult aspect to learn. The majority of the trainees recorded that following the performance of 15-20 endoscopies, torquing became easier.

Clinical Competence↗
PubMed1993

Survival with colorectal cancer in ulcerative colitis. A study of 102 cases.

OBJECTIVE: This study was undertaken to correlate postoperative survival of patients with ulcerative colitis-associated colorectal cancer with the stage, configuration, size, and mucin content of the tumor. SUMMARY BACKGROUND DATA: The factors influencing prognosis in colorectal cancer in the general population are well accepted, but less is known about their influence in cases of colorectal cancer associated with ulcerative colitis. METHODS: The authors reviewed the records of 102 patients with ulcerative colitis-associated colorectal cancer admitted to The Mount Sinai Hospital between 1959 and 1988. Tumors were classified on independent pathologic review according to histologic stage, configuration, size, and mucin content. Comparisons among survival curves were tested by the generalized Wilcoxon test. Cox regression models were used to examine the joint effects of selected clinicopathologic features on postoperative survival rates. RESULTS: Complete follow-up was obtained for 93 patients (92%). Overall 5-year actuarial survival was 52%. When factors were analyzed one at a time, survival was significantly poorer among patients with advanced cancer stage, larger tumor size, infiltrating and ulcerating configuration, and high mucin concentration. On multivariate analysis by the Cox regression model, however, only cancer stage emerged as a factor independently predicting survival. CONCLUSIONS: For colitis-associated colorectal cancers, as for noncolitic cancers, histologic stage is the most important variable determining postoperative survival. The distribution of stages in our series and the survival rates within each stage did not differ appreciably from the distributions and survival rates reported for noncolitic colorectal cancers.

Adult↗
PubMed1992

The utility of squamous cell carcinoma antigen for the follow-up of patients with squamous cell carcinoma of the anal canal.

BACKGROUND: Thirty-three patients with histologic documentation of squamous cell carcinoma (SCC) of the anal canal underwent prospective serial collection of 234 serum samples for radioimmunoassay of SCC tumor-associated antigen. METHODS: There were 23 female and 10 male patients, with a median age of 55 years. Twenty-two of the 33 patients had multimodality therapy with radiation therapy and chemotherapy as initial treatment. RESULTS: The median follow-up was 22 months (range, 4-52 months), with a median of 13 serum specimens per patient (range, 1-23 specimens). Twenty-eight patients currently have no evidence of disease, 4 patients are alive with disease, and 1 patient died with disease. CONCLUSION: In these 33 patients, the sensitivity of the SCC tumor-associated antigen was 76%, specificity 86%, and positive predictive value 62%.

Adult↗
PubMed1992

Quality-of-life assessment: patient compliance with questionnaire completion.

BACKGROUND: Previous investigators have found that compliance with quality-of-life data collection on cancer clinical trials is poor. There is general belief that collecting complete quality-of-life data is at present an unachievable goal. PURPOSE: We assessed the completeness of quality-of-life data collection on trials instituted by the National Cancer Institute of Canada Clinical Trials Group (NCIC CTG), since incorporation of quality-of-life outcomes into trials became mandatory for the group. METHODS: Data from three NCIC CTG trials in which quality of life was a study end point were examined to determine the extent to which protocol specifications were met with respect to questionnaire completion. Two of the studies examined adjuvant therapies, and one examined anti-emetics. In two trials, the quality-of-life questionnaire of the European Organization for Research and Treatment of Cancer was used; in the other, the Breast Cancer Chemotherapy Questionnaire. RESULTS: Patient compliance with questionnaire completion was unexpectedly high: More than 95% of the scheduled questionnaires were returned, and more than 99% of the questions were answered. CONCLUSIONS: We attribute this success to a comprehensive set of measures taken to enhance compliance on these studies. Which of these measures was most contributory requires further investigation, as does the issue of whether similar results can be obtained in other circumstances. IMPLICATIONS: It seems that the commonly held belief that quality-of-life data cannot be successfully collected in multicenter cancer trials is incorrect.

Clinical Trials as Topic↗
PubMed1992

Prediction of survival of patients with primary biliary cirrhosis. Examination of the Mayo Clinic model on a group of patients with known endpoint.

Increasing use of liver transplantation and new treatment regimens necessitate an accurate estimate of prognosis in primary biliary cirrhosis. To test the usefulness of the Mayo model for this purpose, the R value of the model was calculated for a group of 28 patients after each patient encounter and plotted against time. The data were best described by two linear regressions. For the period 10-2 years before death, the average increase in R value was 0.23 annually [R = 7.1-0.23 x time (in years)]. In the last 2 years of life, the average increase in R value was 1.4. This period could be fit by the expression R = 8.2-1.4 x time (in years). The increase in R value represents the natural progression of primary biliary cirrhosis and can be used for evaluating treatment of patients.

Forecasting↗
PubMed1992

Decision tree for the management of substance-abusing psychiatric patients.

This paper describes a short-term approach developed at a time of numerous drug-related incidents occurring at a large VA Hospital to help staff manage psychiatric patients abusing alcohol or drugs during hospitalization. This was accomplished through the development of a decision tree designed to improve the clinical problem-solving process by identifying key decision points. Prior to this, staff responded emotionally either by prematurely discharging patients or by not recognizing the problem at all. Decision Trees have widespread applicability for resolving complex clinical problems.

Adult↗
PubMed1992

The chemiluminescent detection of leptospiral antigen.

The aim of this study was to investigate the feasibility of using enhanced chemiluminescence for the rapid detection of leptospiral antigen (L. interrogans serovar hardjo) in biological fluids, and to assess the suitability of such an assay for the early diagnosis of human leptospiral infections. The limit of detection for homologous antigen in phosphate buffered saline was 9 x 10(4) leptospires/ml. In human blood the sensitivity remained unchanged throughout the sampling time, (1.8 x 10(5) leptospires/ml), but decreased with time in human urine. The assay did not cross-react with other members of the Leptospira interrogans species, was unaffected by the presence of biological fluids but the sensitivity was reduced by contaminating bacteria. The assay was both rapid and sensitive, when compared with current cultural techniques, and offers a potentially valuable aid to the early diagnosis of leptospirosis.

Antigens, Bacterial↗