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Biomedical subjects

D C Hooper

Publications and source records attributed to D C Hooper.

159 records · Page 9Linked to original sources
PubMed1981

Haptoglobin and albumin synthesis in isolated rat hepatocytes. Response to potential mediators of the acute-phase reaction.

Incorporation of [3H]leucine into haptoglobin and albumin by isolated rat hepatocyte suspensions was studied to assess the role of potential mediators of the acute-phase reaction in promoting haptoglobin synthesis. In vitro, in the presence of insulin, the addition of a hormone mixture containing hydrocortisone, glucagon, somatotropin, and triiodothyronine resulted in a 70% increase in leucine incorporation into haptoglobin relative to albumin at 48 h incubation. A variety of agents, selected because they are considered to play some part in the acute-phase reaction, were added to the medium, and similar measurements of leucine incorporation were made. The specific binding to hepatocytes by asialo- and asialo, agalacto-derivatives of haptoglobin or orosomucoid did not affect synthesis of haptoglobin or albumin. Epinephrine, prostaglandins E1 and E2, bacterial lipopolysaccharide, and sera containing active complement components also failed to stimulate relative haptoglobin synthesis. A partially purified preparation of human leukocytic pyrogen, however, caused a 70% increase in leucine incorporation into haptoglobin relative to albumin in the present of the hormone mixture, suggesting that this substance may affect acute-phase protein synthesis.

Albumins↗
PubMed1976

Determination of the subunit composition of haptoglobin 2-1 polymers using quantitative densitometry of polyacrylamide gels.

Human haptoglobin (Hp), a hemoglobin-binding glycoprotein containing two types of polypeptide chains, alpha and beta, in equimolar amounts linked by disulfide bonds, exists in three major phenotypes determined by the properties of the alpha chain: Hp 1-1 (alpha1), Hp 2-2 (alpha2), and Hp 2-1 (alpha1 and alpha2). Hp 2-2 and Hp 2-1 form a series of alpha-disulfide-linked polymers. The subunit composition of the Hp 2-1 series was studied by isolation of single Hp 2-1 polymers by polyacrylamide gel electrophoresis. After reductive disulfide cleavage and alkylation the relative content of alpha2 and alpha1 polypeptide chains was determined by quantitative densitometry of acid/urea polyacrylamide gels stained with Coomassie brilliant blue R250. The molar ratios alpha2/alpha1 for the Hp 2-1 polymers. P1 through P5 (in order of decreasing electrophoretic mobility), were found to be: P1, 0.0 (alpha1 only); P2, 0.48; P3, 0.97; P4, 1.6; P5, 2.0. Since one alphabeta-Hb half-molecule is known to bind to each Hp beta chain, the beta polypeptide chain content of each of the Hp 2-1 polymers could be estimated by by counting the number of Coomassie blue bands formed after electrophoresis of isolated Hp 2-1 polymers fractionally saturated with cyanmethemoglobin (Hb). The number of beta chains present in Hp 2-1 polymers P1 through P4 was determined to be: P1, 2; P2, 3; P3, 4 and P4, 5. Molecular weights of the Hp 2-1 polymers were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresus using as standards the almost homologous Hp 2-2 polymer series whose molecular weights are known from ultracentrifugation studies. Molecular weights for the first five Hp 2-1 polymers were estimated to be 107,000; 162,000; 217,000, 274,000; and 331,000, respectively. These data are consistent with the previously proposed model for the subunit composition of the Hp 2-1 polymer series when P1 = (alpha1 beta)2 and the subsequent polymers in order are represented as (alpha1 beta)2(alpha2 beta)n where n = 1,2,3,4...

Densitometry↗
PubMed1973

Characterization of ileal vitamin B12 Binding using homogeneous human and hog intrinsic factors.

Elucidation of the mechanism of intrinsic factor (IF)-mediated vitamin B(12) (B(12)) binding to ileal binding sites has been hampered by the use of crude or only partially purified preparations of IF in previous studies. We have used homogeneous human IF and hog IF isolated by affinity chromatography to study [(57)Co]B(12) binding to ileal mucosal homogenates. The following observations were made: (a) Human IF-B(12) and hog IF-B(12) were bound to human, monkey, hog, dog, rabbit, mouse, hamster, and guinea pig ileal, but not jejunal, homogenates in amounts significantly greater than free B(12) or B(12) bound to five other homogeneous B(12)-binding proteins; (b) only IF-mediated B(12) binding was localized to ileal homogenates and was inhibited by EDTA; (c) values for the association constant (K(a)) for the various ileal homogenates mentioned above and human IF-B(12) and hog IF-B(12) ranged from 0.3 x 10(9) M(-1) to 13.0 x 10(9) M(-1). Apparent differences in the K(a) for human IF-B(12) and hog IF-B(12) existed in most species; (d) the number of ileal IF-B(12) binding sites per gram (wet weight) of ileal mucosa ranged from 0.3 x 10(12) to 4.9 x 10(12). The same value was always obtained with human IF-B(12) and hog IF-B(12) for any given homogenate preparation; (c) 100-fold excesses of free B(12) or human IF and hog IF devoid of B(12) did not significantly inhibit human IF-B(12) and hog IF-B(12) binding to human and hog ileal homogenates. THESE EXPERIMENTS PERFORMED WITH HOMOGENEOUS IF INDICATE THAT: (a) gastric factors other than IF are not required for B(12) binding to ileal IF-B(12)-binding sites: (b) the mechanism of ileal IF-B(12) binding is different from that of free B(12) or of B(12) bound to non-IF-B(12)-binding proteins; (c) human IF and hog IF have different structures; (d) human IF-B(12) and hog IF-B(12) bind to the same ileal binding sites; and (c) human and hog ileal IF-B(12) binding sites bind free B(12) and human and hog IF devoid of B(12) poorly, if at all.

Animals↗
PubMedDate not supplied

Nongenitourinary infections caused by Mycoplasma hominis in adults.

Eleven new cases of Mycoplasma hominis infection occurring outside the genitourinary tract in adults not in the puerperium were evaluated in relation to the 25 cases previously reported. Cases of bacteremia (n = 14) were commonly associated with trauma or manipulation of the genitourinary tract and were often self-limited. Wound infections (n = 14) followed surgery by 4-14 days in most cases and may have arisen from contamination from the genitourinary or respiratory tract. Joint infections (n = 5) appeared to have resulted from bacteremic seeding in some cases and affected prosthetic joints in particular. Least frequent were central nervous system infections (one case of meningitis and two of brain abscess) and respiratory tract infections (three cases of empyema). The large majority of patients had fever, and infected fluid collections were commonly purulent. The response to therapy was difficult to assess in many cases, but responses to tetracycline, clindamycin, and drainage alone were observed. Identification of M. hominis requires clinical suspicion and alertness on the part of the bacteriology laboratory.

Adolescent↗
PubMedDate not supplied

Mode of action of the quinolone antimicrobial agents.

The newer quinolone antimicrobial agents are more potent antibacterial agents than is the older analog nalidixic acid. For many of the quinolone agents, increased antibacterial potency correlates with increased potency in inhibiting the essential bacterial enzyme DNA gyrase. Studies with mutants resistant to drug action have identified the A subunit of this enzyme as a drug target. Other drug-resistance mutations are associated with pleiotropic drug resistance and decreased amounts of porin outer-membrane proteins and appear to involve alterations in permeability of the bacterium to the drug. Structure-activity studies of a large number of quinolone analogs have identified the importance to drug action of substituents at positions 1, 3, 4, 6, and 7 of the quinolone ring. Uncertainties remain, however, about the details of the molecular interactions of quinolones, DNA gyrase, and DNA and about the specific events that lead to quinolone-mediated bacterial killing.

Anti-Bacterial Agents↗
PubMedDate not supplied

Mode of action of the quinolone antimicrobial agents: review of recent information.

Recent studies concerning the mechanism of action of quinolones against DNA gyrase are reviewed. DNA gyrase is an essential bacterial enzyme known to be a primary target of quinolone agents. Quinolone-resistant alleles of both the gyrA and gyrB genes of DNA gyrase have been sequenced, and domains that affect the action of quinolones have been identified within the amino terminus of the gyrase A peptide and the midportion of the gyrase B peptide. In addition, an ATP-induced structural transition of DNA complexed with DNA gyrase was shown to be blocked by norfloxacin, but the means by which quinolones effect this change and the molecular site of quinolone binding remain unclear. Studies of structure-activity relationships of the quinolone molecule have been expanded and have included effects of quinolones on DNA gyrase. Stereochemical effects at positions 1 and 7 have been found. Substitutions at position 7 that improve potency against gram-positive bacteria have also been identified. Novel mono- and three-ring structures and an isothiazolo substitution at position 3 have broadened the range of structures known to have activity. Studies of bacterial killing by quinolones have revealed additional correlations with markers of DNA damage and additional alterations in bacteria and growth conditions that affect bacterial killing. The exact events responsible for quinolone-mediated lethality, however, remain undefined.

4-Quinolones↗
PubMedDate not supplied

Bacterial resistance to quinolones: mechanisms and clinical importance.

An overview of bacterial resistance to new quinolones is presented with a consideration of mechanisms, clinical importance, and approaches to suppression of the emergence of resistance. Single-step mutation to high-level resistance occurs at a frequency of less than or equal to 10(-10) for many bacterial species but can be readily selected by serial exposure of cells to increasing drug concentrations. Two mechanisms of resistance have been identified: alteration in the target enzyme DNA gyrase and decreased drug permeation. Emergence of resistance to clinically useful quinolones thus far has been uncommon. Superinfection has been documented but also has been uncommon. Emergence of resistance appears to occur more often with certain bacterial species, including Pseudomonas aeruginosa and Staphylococcus aureus. In the special setting of cystic fibrosis, patients with P. aeruginosa infections often respond favorably despite emergence of resistance. Methods to minimize the emergence of quinolone resistance should be evaluated in an effort to preserve the clinical utility of these drugs.

4-Quinolones↗
PubMedDate not supplied

Novobiocin-induced ultrastructural changes and antagonism of DNA synthesis in Trypanosoma cruzi amastigotes growing in cell-free medium.

The antimicrobial agent novobiocin, an inhibitor of the bacterial enzyme topoisomerase II (DNA gyrase), is known to antagonize Trypanosoma cruzi amastigotes growing in cell-free medium. To determine sites of antagonism of novobiocin, the effects of drug on parasite ultrastructure and incorporation of radiolabeled precursors of DNA, RNA and protein into macromolecules were determined. The predominant ultrastructural abnormality seen after exposure to 0.40 mM novobiocin for 24 h was the presence of electron-dense clumps in the mitochondrion-kinetoplast organelle in 95 of 257 (37%) of cells, in comparison to no clumps seen in 110 drug-free cells. In addition, in the nucleus, the karyosome was less distinct than in control cells and appeared to merge with the chromatin. In the radiolabeling studies, incorporation of thymidine was inhibited in a dose-dependent fashion by novobiocin (0.16-0.80 mM) in a range of drug concentrations that also inhibited parasite growth. For 0.16 and 0.24 mM novobiocin, incorporation of thymidine was inhibited up to 65% relative to drug-free control cells while uptake of uridine and leucine was unaltered. We interpret these ultrastructure and precursor-incorporation studies as suggesting that (i) the mitochondrion-kinetoplast and possibly the nucleus are sites of novobiocin antagonism of T. cruzi amastigotes and (ii) that novobiocin appears to antagonize DNA synthesis within these organisms. Whether the drug target is topoisomerase II, however, is as yet unknown.

Animals↗
PubMedDate not supplied

Emerging mechanisms of fluoroquinolone resistance.

Broad use of fluoroquinolones has been followed by emergence of resistance, which has been due mainly to chromosomal mutations in genes encoding the subunits of the drugs' target enzymes, DNA gyrase and topoisomerase IV, and in genes that affect the expression of diffusion channels in the outer membrane and multidrug-resistance efflux systems. Resistance emerged first in species in which single mutations were sufficient to cause clinically important levels of resistance (e.g., Staphylococcus aureus and Pseudomonas aeruginosa). Subsequently, however, resistance has emerged in bacteria such as Campylobacter jejuni, Escherichia coli, and Neisseria gonorrhoeae, in which multiple mutations are required to generate clinically important resistance. In these circumstances, the additional epidemiologic factors of drug use in animals and human-to-human spread appear to have contributed. Resistance in Streptococcus pneumoniae, which is currently low, will require close monitoring as fluoroquinolones are used more extensively for treating respiratory tract infections.

Anti-Infective Agents↗
PubMedDate not supplied

Genotypic and phenotypic diversity of rabies virus variants involved in human rabies: implications for postexposure prophylaxis.

OBJECTIVES: Rabies virus variants associated with silver-haired bats (SHBRV) are responsible for most recent human rabies cases in the United States, which are not associated with a history of exposure. We compared their genotype and phenotype with those of dog rabies virus (DRV) variants, the classic cause of rabies in humans, to determine whether differences in these strains might have ramifications for therapeutic intervention, particularly vaccination. METHODS: Eleven silver-haired bat and 8 dog rabies virus isolates were characterized by sequencing the glycoprotein gene, by assessing their ability to replicate in neuronal versus nonneuronal cultures at optimal and suboptimal temperatures, by assessing their pathogenicity in mice, and by determining the resistance of these viruses to therapeutic immunization with commercial vaccines. RESULTS: SHBRV isolates were less genetically diverse, less neuronal cell specific, more temperature sensitive, but as pathogenic, on average, as DRV isolates. Immune protection was equivalent for SHBRV and DRV strains of similar pathogenicity. CONCLUSIONS: SHBRV strains have unique characteristics that may explain their exceptional association with human rabies but have little bearing on their lethality in mice. The pathogenicity of a particular virus, rather than its antigenic makeup, determines the outcome of immunization.

Amino Acid Sequence↗
PubMedDate not supplied

Circadian distribution of hematology variables in subjects with multiple sclerosis.

Hematology variables were measured in blood samples obtained every 3h (8/24h) from 10 multiple sclerosis (MS) patients and 34 healthy subjects and analyzed for circadian characteristics using the population multiple-components method. Red blood cell (RBC) and hemoglobin levels as well as hematocrits exhibited circadian rhythms with minimal amplitudes in healthy individuals and insignificant variability in the smaller group of MS patients. In contrast the total white blood cell (WBC) and platelet counts for MS patients and healthy individuals both showed significant circadian characteristics while the mean 24h WBC and platelet levels did not significantly differ between the two groups. When the different WBC subsets were examined independently, statistically significant circadian rhythms were seen for lymphocytes and eosinophils for both MS patients and healthy individuals and for neutrophils only in the latter. Moreover, the 24h mean levels of lymphocytes, basophils, and eosinophils were significantly higher for the healthy controls while those of monocytes were higher for the MS patients. However, of all the variables tested with significant circadian rhythms in both groups of individuals, only those of lymphocyte numbers exhibited different patterns with somewhat higher amplitude in healthy individuals and a peak level occurring over an hour after that of MS patients. These changes may be the reflection of a disturbance in the regulation of patterns of lymphocyte activity and migration in MS patients. In addition, the elevation in circulating monocytes in MS patients is consistent with the inflammatory nature of the disease.

Adult↗