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Biomedical subjects

R A Beck

Publications and source records attributed to R A Beck.

At least 19 recordsLinked to original sources
PubMed2000

Picomolar quantitation of free sulfite in foods by means of [57Co]hydroxocobalamin and radiometric chromatography of [57Co]sulfitocobalamin. Method, applications and significance of coexisting sulfides.

The concentration dependent reaction of sulfite with 57Co-labeled hydroxocobalamin (OH57CoCbl) to produce a sulfitocobalamin (SO(3)57CoCbl) adduct served as a quantification strategy for foodborne sulfite residues freely extracted into pH 5.2, 0.05 M acetate buffer. SO(3)57CoCbl was then resolved using SP-Sephadex C-25 gel chromatography and its radiometric detection allowed calculation of a standard logit plot from which unknown sulfite concentrations could be determined. The sulfite detection range was 6.0 nM-0.3 pM with respective relative standard deviations of 4.4-29.4% for 50-microl samples. Individual incidences of foodborne sulfite intolerances provoked by L-cysteine or sulfite additive use in bakery products, which remained undetected using conventional sulfite analytical methods, underscored the quantitative value of the method. The analytical significance and occurrences of detectable sulfides coexisting with foodborne sulfite residues was also addressed.

Chromatography, Gel↗
PubMed1996

Ligands for the affinity chromatography of mammalian thymidine kinase. 1: Strategy, synthesis and evaluation.

Selected thymidine derivatives were synthesized with various spacers and fixed as model compounds at position N-3', C-5, C-3' and C-5', respectively, to simulate the preparation of an affinity gel matrix. Compounds 3, 6, 7 and 9 were evaluated for their effect on pure human cytosolic thymidine kinase (TK). All four compounds showed competitive inhibition with respect to thymidine, with Ki-values between 80 and 1000 microM. In the same positions as the model compounds were bound to the spacers thymidine derivatives were coupled with different Sepharose gel matrices. These affinity matrices were tested for isolation of thymidine kinase out of placental enzyme material. Except for one matrix, more than 98% of the applied activity was retained by the affinity matrices tested. The strongest binding to the enzyme resulted from a fixation at C-5' of the thymidine molecule to the gel matrix.

Binding Sites↗
PubMed1995

Different affinity of the two forms of human cytosolic thymidine kinase towards pyrimidine analogs.

Recent results showed that ATP enables a kinetically slow shift from a low affinity form to a high affinity form of human cytosolic thymidine kinase (TK1), as reflected by the respective apparent Km values for thymidine of 15 microM and 0.7 microM. The shift is dependent on the concentration of enzyme protein, and calculations indicate that the low affinity form is predominant in G1 cells, and the high affinity form is predominant in S-phase cells. Here, we report that the two forms of TK1 differ manyfold in affinity to the substrate ATP, to the inhibitor dTTP and to various analogs of thymidine substituted in the pyrimidine or sugar. Furthermore, the kinetic reaction mechanisms suggest that the nucleoside analog. 3'-azidothymidine, used for treatment of infections with human immune deficiency virus (HIV), is not a substrate for the low affinity form of TK1.

Adenosine Triphosphate↗
PubMed1994

Nitritocobalamin and nitrosocobalamin may be confused with sulfitocobalamin using cation-exchange chromatography.

The previously reported ability of SP-Sephadex C25 column chromatography for partitioning biologically important cobalamins has been modified to include analytical separation of nitritocobalamin (NO2-Cbl) and nitrosocobalamin (NO-Cbl). Gel column dimensions (1.5 x 11.0 cm), a low eluent flow-rate (125 microliters/min), collection of small eluate fractions (160 microliters) plus maintenance of He saturated mobile and gel phases all combined to eliminate ordinarily confusing proximal elution of NO2-Cbl and NO-Cb1 with sulfitocobalamin (SO3-Cbl) and cyanocobalamin. Cobalamin elution profiles from the gel column were monitored by direct radiometric analysis of 57Co-labelled cobalamin standards or competitive intrinsic factor radioassays for cobalamin sample sizes up to 10.0 ng. Failure to implement the chromatographic conditions detailed here totally obscured analysis of NO2-Cbl coexisting with SO3-Cbl in brain tissues for chicks exposed to dietary sulfites and caused oversight of NO-Cb1 normally coexisting in prepared NO2-Cbl standards.

Animals↗
PubMed1994

Bacterial meningitis in the pediatric population: paradigm shifts and ramifications for otolaryngology-head and neck surgery.

Various population-based studies have suggested that the incidence and epidemiology of bacterial meningitis is changing. No studies have been published which examine a sample population of the United States at large. Records of pediatric patients age 5 and under who were treated for bacterial meningitis (n = 470) at all US Army medical facilities between 1986 and 1991 were reviewed. The incidence of bacterial meningitis declined by 75% in the study group during this period. The largest decrease occurred in infants less than 1 year of age. The bacterial organisms isolated most commonly, in decreasing frequency were: Haemophilus influenza type b (HIB), pneumococcal, streptococcal, and staphylococcal. The most dramatic abatement occurred in Haemophilus meningitis following the introduction of HIB vaccinations. Neurologic sequelae were identified in 10% of meningitis survivors. The 2 most common impairments were hearing loss and speech/language delay. Economic modeling demonstrates tremendous savings in health care dollars from the decrease in disease incidence. These changes will have substantial bearing on training programs and practitioners, since the management of neurologic sequelae requires the expertise of multiple subspecialists. In the face of a medical onslaught, once devastating diseases are in retreat.

Child, Preschool↗
PubMed1993

The retreat of Hemophilus influenzae type B invasive disease: analysis of an immunization program and implications for OTO-HNS.

Hemophilus influenzae type b (Hib) is the most common cause of bacterial meningitis among children under 5 years old. Hib is also responsible for other invasive diseases including epiglottitis, cellulitis, sepsis, pneumonia, and osteomyelitis. A child's cumulative risk of systemic Hib disease during the first 5 years of life is approximately 1 in 200. A polysaccharide Hib vaccine was first marketed in 1985, and newer, more effective conjugated vaccines have been licensed since 1987. Immunization schedules have included increasingly younger children. No studies have been published that analyze the effects of a vigorous immunization program on a sample population representative of the United States at large. Records of pediatric patients ages 5 years and younger who were treated for Hib meningitis or epiglottitis (N = 373) at all U.S. Army medical facilities between 1986 and 1991 were reviewed. The combined incidence of these diseases declined by more than 86% in the study group during this period. The largest decrease occurred in infants less than 1 year old, before vaccines were licensed for use in this group. Meanwhile, the number of cases of bacterial meningitis due to other organisms in this cohort remained unchanged. Economic modeling validates the cost-effectiveness of vaccination. The impact of these preliminary trends on health care systems and otolaryngology-head and neck surgery will be significant. Almost two thirds of Hib disease has involved infants under 15 months old, for whom a conjugated vaccine has been available only since October 1990. The change in disease frequency will have substantial bearing on training programs, because management of neurologic sequelae and the emergent airway require the expertise of otolaryngologists. In the face of medical onslaught, Hib invasive disease is in retreat.

Child, Preschool↗
PubMed1992

Cardiovascular effects of pseudoephedrine in medically controlled hypertensive patients.

BACKGROUND: Oral sympathomimetics are effective in the treatment of nasal congestion through stimulation of alpha-adrenergic receptors in the blood vessels of the nasal mucosa. This vasoconstrictor activity has resulted in the general recommendation that such pressor amines not be used in patients with hypertension. No prospective studies have examined the safety of sustained-release pseudoephedrine in hypertensive patients. METHODS: Volunteers (N = 28) with controlled hypertension participated in a randomized, double-blind, placebo-controlled, crossover study that examined the cardiovascular effects of 120 mg of sustained-release pseudoephedrine taken on a twice daily basis. Physician-investigators measured blood pressure and heart rate using mercurial sphygmomanometers during acute and steady-state phases. Compliance was verified with pill counts and serum drug levels. Symptom questionnaires were completed by the volunteers. RESULTS: While a strong statistical correlation was found over time, with minimal increases in mean arterial pressure and heart rate, pseudoephedrine administration did not result in statistically significant changes in any cardiovascular parameter. Mild disturbances in sleeping pattern and urinary retention in some male subjects were the only significant symptoms detected. CONCLUSIONS: We conclude that while sustained-release pseudoephedrine appears safe for the majority of medically controlled hypertensive patients without statistically significant effects on blood pressure or heart rate our studies did show an upward trend in these parameters which, in a larger population of hypertensive patients, may prove to be clinically significant.

Adult↗
PubMed1989

The changing picture of facial fractures. 5-Year review.

A decline in the overall number and severity of facial fractures has been observed at Madigan Army Medical Center, Tacoma, Wash. Hospital records of patients (N = 262) who were treated for fractures of the zygoma, maxilla, and mandible between 1983 and 1987 were reviewed. The three leading causes of facial fractures were assault (35%), vehicular accidents (26%), and sports (12%). The preferred treatment modality consisted of open reduction and internal fixation with plates. Societal influences have been responsible for this declining trend in the number and severity of facial fractures. This pattern will impact on training programs that necessitate physician rotations at large trauma centers to provide necessary exposure to maxillofacial injuries.

Adult↗