Biomedical subjects
Publications and source records attributed to L R Berkowitz.
The hemostatic abnormalities commonly encountered in patients with renal disease can significantly threaten the well-being of the patient and pose difficult management issues for the clinician. In this review, we explore the pathophysiology underlying the bleeding diathesis and hypercoagulability that can occur. Current therapeutic interventions are also discussed.
OBJECTIVE: To develop reliable scale measures of factors most important to applicants when they select internal medicine residencies and to assess their validity by comparing scores from these measures with responses to open-ended questions. DESIGN: All 353 applicants ranked by the University of North Carolina at Chapel Hill (UNC-CH) for the 1988 National Residency Match Program received a questionnaire after submitting their match lists. First, they listed the three most important factors considered in ranking residency programs and starred the single most important factor out of the three. Then, they rated 41 items on a five-point Likert scale ranging from 1 (not important) to 5 (extremely important). SETTING: Categorical internal medicine residency program at an academic medical center. MEASUREMENTS AND MAIN RESULTS: 315 (88%) applicants responded to the survey. Three reliable scales, Interpersonal Issues (7 items, alpha = 0.78), Reputation (5 items, alpha = 0.77), and Work Issues (11 items, alpha = 0.89), were developed using exploratory factor analysis of applicants' responses to the 41 items. Applicants felt interpersonal issues were very important (mean score = 4.2 +/- 0.5), academic reputation was important (3.3 +/- 0.8), and work issues were less important (2.8 +/- 0.7). The differences between these scores were significant (F = 3.76, p < 0.05). The ratings for the top five items not in these scales also indicated that education and location were very important. These results were corroborated by applicants' responses to the open-ended request to list the three most important factors in ranking residencies. CONCLUSION: These findings suggest that work issues are important, but greater emphasis is placed on interpersonal issues, education, location, and a program's reputation when applicants select residency programs. Furthermore, this study provides evidence supporting the reliability and validity of the three scales.
Explore the source record for details and available documents.
The thioalkylating agent N-ethylmaleimide (NEM) causes ouabain-insensitive K loss from human red blood cells. This K loss is inhibited when intracellular Cl is replaced by another permeant anion or when loop diuretics are placed in the incubation medium after NEM exposure. In this report, we have tested the possibility that Cl replacement or loop diuretics not only influence the transport of K induced by NEM but also the interaction of NEM with its target sulfhydryl group. This possibility was examined by replacing intracellular Cl or exposing the cells to loop diuretics before NEM exposure, then measuring K loss in a Cl medium free of loop diuretics. We found that such pretreatment with either Cl substitution or loop diuretics stimulated, rather than inhibited, NEM-induced K loss. This enhancement was not additive in that the increase in K loss induced by anion substitution was not increased further when loop diuretics were also present. These data suggest that anion substitution and loop diuretics enhance the interaction of NEM with its cellular target but inhibit the K loss induced by NEM.
Explore the source record for details and available documents.
The elevated calcium content found in red cells from patients with sickle cell anemia may be of pathophysiologic importance in the hemolysis and vasoocclusion which characterize this disorder. Cetiedil, an antisickling agent, has been reported to inhibit the activity of enzymes that are stimulated by the calcium regulatory protein calmodulin. To investigate the mechanism by which cetiedil modifies calcium-mediated erythrocyte function, the effect of the drug on the active transport of calcium into inside-out erythrocyte vesicles was examined and its influence on the activities of phosphodiesterase and Ca-ATPase studied. Cetiedil, in the presence of calmodulin, significantly inhibited calcium transport into inside-out vesicles that were prepared with erythrocytes from normal controls and from patients with sickle cell anemia. However, in the absence of calmodulin, no inhibition was observed. Likewise, cetiedil inhibited calmodulin-stimulated, but not basal, activities of phosphodiesterase and Ca-ATPase. These data, along with previous reports, suggest that cetiedil does not act by lowering the intracellular calcium content. It is, therefore, likely that the beneficial effect of cetiedil is due to its ability to protect the red cell from the deleterious consequences of an elevated concentration of intracellular calcium.
A variety of thiol reactive agents have been found to have antisickling properties thought to be due to the ability of these drugs to bind to hemoglobin, resulting in increased hemoglobin-oxygen affinity. Because thiol reactive agents also influence K movements in red cells and deoxygenation leads to K loss and Na gain in sickle erythrocytes, the authors investigated the possibility that deoxygenation-induced K loss could be influenced by thiol agents, independent of an effect on hemoglobin-oxygen affinity. Experiments were performed with the thiol crosslinking agent N,N'-p-phenylenedimaleimide (PMD). The authors found that PMD inhibited deoxygenation-induced K loss in sickle erythrocytes. This effect was not due to sickling inhibition as PMD-treated cells gained Na with deoxygenation, nor could the effect be explained by monofunctional PMD binding to membrane sulfhydryl groups, as a monofunctional analogue of PMD was not able to retard deoxygenation-induced K loss. These findings support a role for membrane sulfhydryl groups in deoxygenation-induced K movements in sickle red cells and suggest that this K loss may be prevented by crosslinking of certain membrane sulfhydryl groups.
The susceptibility of 31 strains of Nocardia asteroides to various quinolones and beta-lactams, as well as coumermycin, amikacin, and minocycline, was determined by the agar dilution technique. Ciprofloxacin was the most active fluoroquinolone tested on a weight basis, as it inhibited approximately 50% of the isolates at achievable drug levels in serum. Ceftriaxone and cefpirome were the most active cephalosporins in this system with MICs of 8 micrograms/ml for 80% of strains tested. Imipenem, amikacin, and minocycline were the most effective agents tested.
Swelling hemoglobin CC erythrocytes stimulates a ouabain-insensitive K flux that restores original cell volume. This volume regulatory pathway was characterized for its anion dependence, sensitivity to loop diuretics, and requirement for Na. The swelling-induced K flux was eliminated if intracellular chloride was replaced by nitrate and both swelling-activated K influx and efflux were partially inhibited by 1 mM furosemide or bumetanide. K influx in swollen hemoglobin CC cells was not diminished when Na in the incubation medium was replaced with choline, indicating Na independence of the swelling-induced flux. Identical experiments with hemoglobin AA cells also demonstrated a swelling-induced increase in K flux, but the magnitude and duration of this increase were considerably less than that seen with hemoglobin CC cells. The increased K flux in hemoglobin AA cells was likewise sensitive to anion replacement and to loop diuretics and did not require the presence of Na. These data indicate that a volume-activated K pathway with similar transport characteristics exists in both hemoglobin CC and AA red cells.
N-ethylmaleimide (NEM) is a sulfhydryl-reacting agent known to stimulate chloride-dependent K transport in a variety of red cells. In high K sheep red cells, NEM-induced K movements are greater in magnitude in young cells compared with old cells. We hypothesized that human red cells might respond to NEM like high K sheep red cells. To test this idea, cells of various age were exposed to 0.5 mM NEM. We found that, after a 4-h incubation, young cells lost 50% of cell K, compared with 10% K loss in older cells. K loss in all fractions was inhibited by chloride replacement or furosemide.
In this study, we used a recently developed nuclear magnetic resonance (NMR) technique to measure ionized calcium in sickle erythrocytes. The NMR technique, which involves 19F NMR studies of a fluorinated calcium chelator quinMF, [2-(2-amino-4-methyl-5-fluorophenoxy)methyl-8-aminoquinoline-N,N,N',N'- tetraacetic acid] provides a novel approach to the study of ionized calcium in erythrocytes since the presence of hemoglobin precludes the use of fluorescent calcium indicators. The mean value for ionized calcium in oxygenated sickle erythrocytes was 18 +/- 2 nmol/L (SE). Experiments with normal RBCs gave a mean value of 21 +/- 2 nmol/L (SE). After 1 hour of deoxygenation, mean values for ionized calcium in sickle erythrocytes did not increase as compared with values obtained under oxygen. To investigate whether deoxygenation stimulated endocytosis, sickle erythrocytes were deoxygenated for 1 hour in the presence of impermeant FBAPTA (1,2 bis-(2-amino-5-fluorophenoxy) ethane N,N,N',N'-tetraacetic acid). Cells were then separated from the extracellular medium and assayed for the presence of FBAPTA; they had incorporated significant quantities of the extracellular FBAPTA. This incorporation was not observed with normal erythrocytes. These data are consistent with at least a portion of the elevation in total cell calcium in sickle erythrocytes arising as a consequence of an endocytotic process in which extracellular calcium ions are incorporated into vesicles. Additional experiments show that these intracellular vesicles accumulate Ca2+ on further deoxygenation, consistent with a transient increase in ionized cell calcium. These studies represent the first use of NMR spectroscopy to evaluate endocytotic processes.
Cetiedil citrate is an antisickling agent shown to be effective in reducing the severity and duration of acute sickle cell crisis. With the use of a sensitive GC/MS assay, the pharmacokinetic profile of cetiedil was studied in normal men and in men with sickle cell anemia who were not in crisis at the time of study. A peak cetiedil concentration of 70 to 200 ng/ml was found immediately after a 30-minute drug infusion. The plasma level then gradually declined to approximately 10 ng/ml during a 3-hour distributive phase. Computer analysis of the data was most consistent with a three-compartment model. No pharmacokinetic differences were found between the normal men and the subjects with sickle cell. Because the cetiedil plasma levels achieved during this in vivo study are well below concentrations that exhibit antisickling activity in vitro, additional clinical studies will be necessary before an optimal dosing regimen can be established.
Gallstones are frequently found in patients with sickle cell anemia. The differentiation between acute calculous biliary tract disease and sickle cell crisis can be difficult and should be based on the clinical presentation, comparison with previous episodes of abdominal pain, and judicious use of hepatobiliary radionuclide scanning. Emergency cholecystectomy is associated with a high morbidity and should be avoided if possible. Elective cholecystectomy is associated with a lower but still significant risk of complications. We believe patients with sickle cell anemia and symptomatic cholelithiasis should have elective cholecystectomy. Careful management is essential to minimize the danger of postoperative complications.
Red blood cells were loaded with 1,2-bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid (FBAPTA) by incubation with 50 microM of the acetoxymethyl ester (FBAPTA-AM), and cytosolic free Ca2+ was monitored with 19F-nuclear magnetic resonance (NMR). Loading with 50 microM FBAPTA-AM, which results in a final FBAPTA level of approximately 0.5 mM, caused only a 25-30% fall in cell ATP as measured by 31P-NMR when 5 mM pyruvate was present. Leakage of the NMR active Ca2+ indicator, which results from cell lysis, was corrected for with the addition of extracellular Eu3+ ions, extracellular ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA), or washing. With this method, we have found basal levels of cytosolic free Ca2+ averaging 61 +/- 6 nM (means +/- SE, n = 19). When the intracellular level of FBAPTA was varied from 0.1 to 1.0 mM, there was no correlation between the level of cytosolic free Ca2+ and the level of loading with FBAPTA. Addition of 10 microM of the Ca2+ ionophore A23187 with extracellular Ca2+ set at different levels by Ca2+-EGTA buffers caused an increase in cytosolic free Ca2+ as expected. Furthermore, ATP depletion caused a two- to three-fold increase in cytosolic free Ca2+, consistent with inhibition of Ca2+ efflux via that Ca2+-ATPase.
Explore the source record for details and available documents.
We have recently completed a double-blind, placebo-controlled, noncrossover study, the goal of which was to determine whether cetiedil citrate (cetiedil) could affect the course of vaso-occlusive crises in sickle cell disease. Patients, who presented to the emergency room at least 4 but no more than 24 hours after the onset of a painful vasoocclusive crisis severe enough to require hospitalization, were considered candidates for the study. Each patient received either placebo or cetiedil at one of the following three dosages: 0.2, 0.3, or 0.4 mg/kg body weight. The assigned drug dosage was given as a 30 minute intravenous infusion every 8 hours for 4 consecutive days. A total of 67 patients was enrolled in the study. Cetiedil, at its highest dosage (0.4 mg/kg body weight), was found to be significantly superior to placebo both in reducing the number of painful sites present on all 4 treatment days and in shortening the total time in crisis. No serious adverse reactions were observed during the course of the study. We conclude that cetiedil, given at a dosage of 0.4 mg/kg body weight, is therapeutically advantageous for sickle cell crisis.
Hemolytic anemia occurred in a 70-year-old female after a five-day course of intravenous cefamandole. The patient's serum contained an IgG antibody which was reactive with red blood cells which had been coated in vitro with cefamandole but not with uncoated cells. An in vitro assay of allogeneic mononuclear phagocytosis of cefamandole-coated red cells sensitized with the patient's anti-cefamandole indicated that the anti-cefamandole could induce significant phagocytosis. The anti-cefamandole was easily inhibited in vitro by cefamandole as well as by a variety of related cephalosporins indicating broad cross-reactivity, with the antigenic site primarily the 7-amino-cephalosporanic acid nucleus. Penicillins could inhibit the anti-cefamandole but only when using concentrations 3-10 X those of cephalosporins. Eleven examples of anti-penicillin tested failed to react with cefamandole-coated red cells. Screening of 344 random sera from hospitalized patients found only five (1.5%) reactive with cefamandole-coated red cells; three of these sera were also reactive with penicillin-coated red cells. The patient's hemolysis subsided following cessation of the drug. This is the first report of anti-cefamandole-induced hemolytic anemia.
Deoxygenation causes an increase in passive Na and K movements across the membrane of the sickle erythrocyte. Some investigators find that these ion movements are accompanied by cell dehydration, while others find no evidence for cell water loss with sickling. Because gelation of hemoglobin S would be enhanced by cell water loss, we reinvestigated Na and K movements in sickle cells to define further the role that ion movements might play in the pathogenesis of sickling. With deoxygenation, we found that sickle cells gained Na and lost K without losing cell water. These net ion movements were not seen in control red blood cells. For sickle cells, deoxygenation also increased passive unidirectional influxes of Na and K, effects not observed when control red blood cells were deoxygenated. The deoxygenation-induced passive influxes of Na and K in sickle cells were not diminished by anion substitution or by the addition of the diuretic furosemide. We also found differences in passive Na and K fluxes between oxygenated sickle cells and normal red blood cells. The addition of furosemide or replacement of Cl with NO3 or SCN, maneuvers that largely reduced passive Na and K movements in oxygenated normal cells, had no effect on Na and K movements in oxygenated sickle cells. These findings militate against the idea that solute and water loss occur as a consequence of deoxygenation but do indicate that there are acquired membrane abnormalities in sickle red blood cells.