Biomedical subjects

B Greenberg

Publications and source records attributed to B Greenberg.

At least 109 records · Page 6Linked to original sources

PubMed1990

Genetic and structural characterization of endA. A membrane-bound nuclease required for transformation of Streptococcus pneumoniae.

The endA gene encoding the membrane nuclease of Streptococcus pneumoniae, which is necessary for DNA uptake in genetic transformation, was cloned in a streptococcal vector. This was accomplished by insertional mutagenesis of the gene, cloning of the mutant allele, and substitution of the wild-type allele by chromosomal facilitation of plasmid establishment. Plasmids carrying the endA+ gene complemented cells with endA- in the chromosome to restore DNAase activity and transformability. Determination of its DNA sequence showed the gene to encode a 30 kDa protein, EndA, with a typical signal sequence for membrane transport at its amino end. In vitro synthesis of EndA showed the initial translation product to be enzymatically active without further processing. Comparison with EndA found in cell membranes indicated that the enzyme retained its signal sequence, which apparently anchored the otherwise hydrophilic protein to the membrane. From the nucleotide sequence in the vicinity of endA and the effect of various insertions and deletions, it appears that endA is the last gene in an operon containing at least two other genes. Neither of these upstream genes, nor the downstream gene, are essential for either cell viability or transformability.

Amino Acid Sequence↗

PubMed1990

Nocturnal oviposition behavior of blow flies (Diptera: Calliphoridae).

It is widely held that blow flies, in general, and Phaenicia sericata (Meigen), in particular, are not active at night and do not lay eggs during that time. P. sericata is thought to require sunlight and warmth for oviposition. Three common and forensically important flies--Calliphora vicina (Robineau-Desvoidy), P. sericata, and Phormia regina (Meigen)--oviposited during the dark hours of the night during the summers of 1988 and 1989. Nocturnal oviposition can alter the usual estimate of the postmortem interval in homicide cases by as much as 12 h. Cases are presented that serve to change our concept of P. sericata from an obligate heliophile to a facultative heliophile that has a willingness to enter dim or dark places to oviposit.

Adult↗

PubMed1990

Neural networks in radiologic diagnosis. II. Interpretation of neonatal chest radiographs.

A neural network (NN) system was trained to choose one or more diagnoses from a list of 12 possible diagnoses, based on 21 radiographic observations made on each of a series of neonatal chest radiographs. Initially, an experienced pediatric radiologist provided both the radiographic observations and ranked differential diagnoses for each of 77 neonatal chest radiographs in the preliminary phase used to train the NN. Subsequently, two pediatric radiologists (one of whom provided the initial training-phase data) independently read a series of 103 neonatal chest radiographs (different from the training set) and compiled a list of radiographic findings and differential diagnoses for each radiograph. The trained NN was then asked to provide a list of differential diagnoses for each case from the radiologists' lists of findings. Agreement between the network and each radiologist independently was greater than between the two radiologists. Both the positive and negative agreement between the network and either radiologist was greater than the inter-radiologist agreements for most of the diagnostic endpoints.

Artificial Intelligence↗

PubMed1990

DNA sequence of folate biosynthesis gene sulD, encoding hydroxymethyldihydropterin pyrophosphokinase in Streptococcus pneumoniae, and characterization of the enzyme.

A cloned segment of the chromosome of Streptococcus pneumoniae, in which mutations to sulfonamide resistance occur, contains several genes encoding enzymes for folate biosynthesis. Determination of the DNA sequence of parts of this segment and identification of a putative promoter and terminator of transcription indicate an operon composed of four genes. The first, sulA, encodes the enzyme dihydropteroate synthase. The functions of the second and third possible genes, sulB and sulC, are not known. The last gene, sulD, encodes a 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase. The product of this enzyme is the substrate for dihydropteroate synthetase. The enzyme protein was partially purified and shown to consist of a single subunit of 31 kilodaltons, encoded by sulD. On the basis of gel filtration behavior, the native protein appears to be a trimer or tetramer. Subcloning of the sulD gene in an Escherichia coli expression vector increased expression of the pyrophosphokinase 1,000-fold over the level produced by a single copy of the chromosomal gene.

Amino Acid Sequence↗

PubMed1990

Cardiac contractility and conduction: a comparison of antihypertensives.

The four classes of first-line antihypertensive agents recommended in the 1988 report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure are reviewed here. Particular consideration is given to the effects of these agents on heart rate, atrioventricular nodal conduction, and myocardial contractility in patients with other cardiovascular diseases. Diuretics and angiotensin-converting enzyme inhibitors have no significant direct effects on cardiac function. beta-Blockers inhibit catecholamine stimulation of the heart and may be particularly beneficial in treating patients with a history of myocardial infarction. Calcium channel blockers reduce blood pressure by dilating arterial resistance vessels. They are structurally heterogeneous and highly selective in their sites of action. As a consequence, cardiac effects can be minimized by selecting a calcium channel blocker with more potent peripheral vasodilatory effects. A new calcium channel blocker, isradipine, currently undergoing clinical trials, is highly selective for arterial smooth muscle and appears to be a safe and effective antihypertensive agent.

Adrenergic beta-Antagonists↗

PubMed1990

Neuronal and microglial involvement in beta-amyloid protein deposition in Alzheimer's disease.

This study was undertaken to localize amyloid precursor protein (APP) and to determine how APP might be released and proteolyzed to yield the beta-amyloid protein deposits found in senile plaques in the brains of Alzheimer's disease patients. We found that antibodies to recombinantly expressed APP labeled many normal neurons and neurites. In addition, dystrophic neurites in different types of senile plaques and degenerating neurons in the temporal cortex and hippocampus of Alzheimer's disease patients were immunostained. We also detected small clusters of dystrophic APP immunoreactive neurites that were not associated with beta-amyloid protein deposits. Microglia was involved in different types of senile plaques and often were associated closely with APP immunoreactive neurites and neurons. The greatest concurrence of APP immunoreactivity and reactive microglia was seen in the subiculum and area CA1, regions with a high density of congophilic plaques and subject to intense Alzheimer's pathology. Our findings suggest that neuronally derived APP is the source for senile plaque beta-amyloid protein, while microglia may act as processing cells.

Aged↗

PubMed1989

Soluble derivatives of the beta amyloid protein precursor of Alzheimer's disease are labeled by antisera to the beta amyloid protein.

The amyloid deposited in Alzheimer's disease (AD) is composed primarily of a 39-42 residue polypeptide (beta AP) that is derived from a larger beta amyloid protein precursor (beta APP). In previous studies, we and others identified full-length, membrane-associated forms of the beta APP and showed that these forms are processed into soluble derivatives that lack the carboxyl-terminus of the full-length forms. In this report, we demonstrate that the soluble approximately 125 and approximately 105 kDa forms of the beta APP found in human cerebrospinal fluid are specifically labeled by several different antisera to the beta AP. This finding indicates that both soluble derivatives contain all or part of the beta AP sequence, and it suggests that one or both of these forms may be the immediate precursor of the amyloid deposited in AD.

Alzheimer Disease↗

PubMed1989

Chronic aortic insufficiency: factors associated with progression to aortic valve replacement.

STUDY OBJECTIVE: To determine whether the initial measurement of clinical variables in patients with chronic stable aortic insufficiency is helpful in identifying patients at risk for earlier progression to aortic valve replacement. DESIGN: Prospective analysis of a cohort of patients for a median follow-up time of 44 months (range, 8 to 57). SETTING: Referral-based cardiology clinics at two university hospitals and their affiliated Veterans Administration medical centers. PATIENTS: Cohort of 50 asymptomatic or minimally symptomatic patients with chronic aortic insufficiency and left ventricular enlargement. Patients had preserved left ventricular ejection fraction at rest and no evidence of coronary artery disease or significant noncardiac illness. INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: Baseline evaluation included a history and physical examination, chest roentgenogram. M-mode echocardiogram, treadmill test, and radionuclide angiogram done at rest and during supine bicycle exercise. Ten patients progressed to surgery because of the onset of limiting symptoms or objective evidence of left ventricular dysfunction, or both; the overall rate was 4% +/- 3% per year. The Breslow and Mantel-Cox statistics were used to compute survival (surgery-free) dichotomized by prognostic variables. The progression to surgery was earlier in patients with left ventricular end-diastolic volume indices of 150 cc/m2 or more, end-systolic volume indices of 60 cc/m2 or more, a left ventricular ejection fraction at maximal exercise of less than 0.50, or an end-systolic wall stress of 86 dynes/cm2 or more. CONCLUSIONS: Patients at higher and lower risk for early progression to aortic valve replacement can be identified through the measurement of left ventricular size and function. This information can be used to decide the frequency and intensity of follow-up evaluation in these patients.

Actuarial Analysis↗

PubMed1989

Laboratory investigations of the electrical characteristics of honey bees and their exposure to intense electric fields.

Bees exposed to 60-Hz electric (E) fields greater than 150 kV/m show field-induced vibrations of wings, antennae, and body hairs. They also show altered behavior if exposed while in contact with a conductive substrate. Measurements indicate that approximately 240 nA is coupled to a bee standing on a conductive substrate in a 100-kV/m E field. In lab experiments, bee disturbance and sting result from exposure to E field greater than 200 kV/m (bee current greater than 480 nA) and reduced voluntary movements at greater than 300 kV/m (greater than 720 nA bee current) only if the bee is on a conductive substrate. It is hypothesized that in the latter situation coupled bee current drains through the lower thorax and legs to the conductive substrate, and that the resulting enhanced current density in these regions is the cause of observed responses. The observation that bees exposed to intense E fields on an insulator show vibration of body parts but no behavioral response suggests that vibration contributes little to the disturbance of bees in intense E fields. Lab measurements of bee impedance from front-to-rear leg pairs were made on wet and dry conductors. Measurements validate the selection of 1 M omega as a middle value for bee impedance used in the design of devices used to generate step-potential-induced currents in bees.

Animals↗

PubMed1989

Value of color Doppler estimation of regurgitant volume in patients with chronic aortic insufficiency.

We studied 16 patients with chronic aortic insufficiency to compare a method for measuring regurgitant volume with color Doppler flow mapping to stroke count ratio determined by radionuclide ventriculography and to ventricular volumes assessed by two-dimensional echocardiography. A real-time color flow map of the left ventricular was obtained from an apical two- and five-chamber view and the maximal mosaic pattern of diastolic turbulent flow was planimetered as a reflection of the maximal regurgitant volume using biplane Simpson's rule. The maximal Doppler regurgitant volume evaluated by color Doppler flow mapping correlated with the stroke count ratio measured by scintigraphy (r = 0.86, SEE = 11 cc). There were significant relationships between maximal regurgitant volume measured by color Doppler and echocardiographic left ventricular end-diastolic volume (r = 0.88), left ventricular end-systolic volume (r = 0.77), and left ventricular mass (r = 0.71). Patients with larger regurgitant volumes tended to have a larger left ventricular end-diastolic volume-to-mass ratio (r = 0.56). Thus maximal aortic regurgitant volume can be estimated noninvasively with color Doppler flow mapping. The measurement appears to relate to left ventricular morphologic changes occurring in this condition and it may prove to be useful in assessing patients with chronic aortic insufficiency and in determining their long-term management.

Adult↗

PubMed1989

Phase II trial of fenretinide [N-(4-hydroxyphenyl) retinamide] in myelodysplasia: possible retinoid-induced disease acceleration.

To determine the activity of fenretinide in patients with myelodysplastic syndromes, 15 patients were treated (300 mg/d starting dose, escalated to 400 mg/d) for a 12-week course. No responses were observed in 14 evaluable patients. Exacerbation of thrombocytopenia occurred in one patient with chronic myelomonocytic leukemia, who succumbed to an intracerebral hemorrhage after 3 weeks of treatment. Two patients with long-standing stable sideroblastic anemia experienced interval leukemic progression. In one patient, clinical features of chronic myelomonocytic leukemia appeared, characterized by a striking rise in peripheral monocyte count (0.49 x 10(9)/l to 10.8 x 10(9)/l) and hepatosplenomegaly, which resolved promptly after cessation of treatment. The second patient experienced evolution into acute myelomonocytic leukemia with cytogenetic progression. The drug was well tolerated with no patient having to discontinue treatment because of toxicity. We conclude that fenretinide lacks clinical efficacy in the treatment of myelodysplasia and in some patients may enhance leukemic progression.

Acute Disease↗

PubMed1989

Salvage of jeopardized total-knee prosthesis: the role of the gastrocnemius muscle flap.

Total-knee arthroplasty has provided many patients with excellent long-term functional results. However, exposure of a total-knee replacement usually eventuates in failure. The relatively superficial location of the prosthesis, the need for early active motion, previous surgical incisions, and a variety of systemic factors may militate against early wound healing. Restoration of well-vascularized soft-tissue cover can salvage an otherwise disastrous situation. The authors recommend early operative intervention upon observation of wound breakdown, devitalized skin edges, or significant subcutaneous infection leading to necrotic overlying skin. The operative procedure found to salvage the majority of prostheses consists of adequate debridement, antibiotic irrigation (of the joint, if exposed), and coverage with a well-vascularized muscle flap, preferably the medial gastrocnemius muscle. The operative technique and ultimate long-term outcome are reviewed based on experience with 10 consecutive patients presenting with a jeopardized knee prosthesis. Follow-up ranged from 1 to 6 years. Representative case histories are presented.

Adult↗

PubMed1989

The exoA gene of Streptococcus pneumoniae and its product, a DNA exonuclease with apurinic endonuclease activity.

The gene encoding the major DNA exonuclease of Streptococcus pneumoniae, exoA, was cloned in a streptococcal host vector system. Its location was determined by subcloning and by insertion mutations. Transfer of a DNA segment containing the gene to an Escherichia coli expression vector showed that exoA was the structural gene for the enzyme and that it was adjacent to its promoter. DNA sequence determination indicated that the gene encoded a protein, ExoA, of molecular weight 31,263. Under hyperexpression conditions, the ExoA protein constituted 10% of total cellular protein. In addition to previously demonstrated 3' to 5' exonuclease and 3'-phosphatase activities, ExoA was shown to make single-strand breaks at apurinic sites in DNA. Its enzymatic activities are thus similar to those of exonuclease III of E. coli and other gram-negative bacteria. The nucleotide sequence of exoA revealed it to be homologous to xth of E. coli, with 26% identity of amino acid residues in the predicted proteins. So far, no null chromosomal mutants of exoA have been obtained, and the biological function of ExoA remains unknown.

Amino Acid Sequence↗

PubMed1988

The amyloid percursor protein of Alzheimer disease is expressed as a 130 kDa polypeptide in various cultured cell types.

The vascular and parenchymal amyloid deposits in Alzheimer disease (AD), normal aging and Down syndrome are mainly composed of a 4 kDa polypeptide (A4), which derives from a larger precursor protein (APP). There is evidence that APP is a transmembrane glycoprotein present in most tissues, but the characteristics of APP in intact cells are not yet known. In order to investigate this issue, we examined the immunoreactivity of fibroblasts of human and nonhuman cell lines with antisera raised to synthetic peptides corresponding to A4 and to two other domains of the APP. All three antisera recognized a 130 kDa polypeptide (APP-130) in immunoblots from all cell lines. In fibroblasts, an additional polypeptide of 228 kDa (APP-228) was recognized by the antiserum to A4. In immunoblots of two dimensional gels, APP-130 showed a pI of 6.2, while APP-228 failed to focus in the pH range of 4.7-7.0. Sequential extractions of cells with buffer and with Triton X-100 indicate that APP-130 is extractable with nonionic detergents at high ionic strength, whereas 228 kDa APP is a cystolic component. Immunofluorescence staining is consistent with an intracellular perinuclear and plasma membrane localization. It is concluded that APP-130 and APP-228 are two forms of the APP which result from extensive posttranslational modifications of a smaller original gene product. It is likely that APP undergoes similar posttranslational modifications in different cell types.

Alzheimer Disease↗

PubMed1988

Upstream sequences confer atrial-specific expression on the human atrial natriuretic factor gene.

5'-Flanking sequences from the human atrial natriuretic factor (hANF) gene were subcloned into a reporter plasmid (pSVOCAT) and transfected into primary cultures of neonatal rat atrial cardiocytes. Hybrid hANFCAT genes containing either 2500 or 409 base pairs of 5'-flanking sequence DNA were expressed at similar levels. When sequences between -409 and -332 were deleted, reporter gene (CAT) activity decreased significantly. Expression of the hANFCAT constructs was specific for atrial cells, as no expression was detected in primary cultures of ventricular cardiocytes or nonmyocardial cells derived from the neonatal hearts. Correct transcription start sites for the transfected hANF genes were confirmed by S1 nuclease mapping and RNase protection analysis. A "gel shift" assay was used to identify a specific cardiac nuclear protein which bound to the 5'-flanking sequence of the hANF gene. A 192-base pair PvuII fragment (-400 to -208) associated with a protein in these extracts in a tissue- and sequence-specific fashion. These findings indicate that the DNA sequence between -409 and -332 in the hANF gene harbors a tissue-specific element whose activity may involve association with a cardiac-specific nuclear protein.

Animals↗

PubMed1988

A new A4 amyloid mRNA contains a domain homologous to serine proteinase inhibitors.

The amyloid proteins isolated from neuritic plaques and the cerebrovasculature of Alzheimer's disease are self-aggregating moieties termed A4 protein and beta-protein, respectively. A putative A4 amyloid precursor (herein termed A4(695] has been characterized by analysis of a human brain complementary DNA. We report here the sequence of a closely related amyloid cDNA, A4(751), distinguished from A4(695) by the presence of a 168 base-pair (bp) sequence which adds 57 amino acids to, and removes one residue from, the predicted A4(695) protein. The peptide predicted from this insert is very similar to the Kunitz family of serine proteinase inhibitors. The two A4-specific messenger RNAs are differentially expressed: in a limited survey, A4(751) mRNA appears to be ubiquitous, whereas A4(695) mRNA has a restricted pattern of expression which includes cells from neuronal tissue. These data may have significant implications for understanding amyloid deposition in Alzheimer's disease.

Alzheimer Disease↗

PubMed1988

Exposure scheme separates effects of electric shock and electric field for honey bees, Apis mellifera L.

Mechanisms to explain disturbance of honey bee colonies under a 765-kV, 60-Hz transmission line [electric (E) field = 7 kV/m] fall into two categories: direct bee perception of enhanced in-hive E fields, and perception of shock from induced currents. The same adverse biological effects previously observed in honey bee colonies exposed under a 765-kV transmission line can be reproduced by exposing worker bees to shock or E field within elongated hive entranceways (= tunnels). Exposure to intense E field caused disturbance only if bees were in contact with a conductive substrate. E-field and shock exposure can be separated and precisely defined within tunnels, eliminating dosimetric vagaries that occur when entire hives are exposed to E field.

Animals↗

PubMed1988

Mechanism of biological effects observed in honey bees (Apis mellifera, L.) hived under extra-high-voltage transmission lines: implications derived from bee exposure to simulated intense electric fields and shocks.

This work explores mechanisms for disturbance of honey bee colonies under a 765 kV, 60-Hz transmission line [electric (E) field = 7 kV/m] observed in previous studies. Proposed mechanisms fell into two categories: direct bee perception of enhanced in-hive E fields and perception of shock from induced currents. The adverse biological effects could be reproduced in simulations where only the worker bees were exposed to shock or to E field in elongated hive entranceways (= tunnels). We now report the results of full-scale experiments using the tunnel exposure scheme, which assesses the contribution of shock and intense E field to colony disturbance. Exposure of worker bees (1,400 h) to 60-Hz E fields including 100 kV/m under moisture-free conditions within a nonconductive tunnel causes no deleterious affect on colony behavior. Exposure of bees in conductive (e.g., wet) tunnels produces bee disturbance, increased mortality, abnormal propolization, and possible impairment of colony growth. We propose that this substrate dependence of bee disturbance is the result of perception of shock from coupled body currents and enhanced current densities postulated to exist in the legs and thorax of bees on conductors. Similarly, disturbance occurs when bees are exposed to step-potential-induced currents. At 275-350 nA single bees are disturbed; at 600 nA bees begin abnormal propolization behavior; and stinging occurs at 900 nA. We conclude that biological effects seen in bee colonies under a transmission line are primarily the result of electric shock from induced hive currents. This evaluation is based on the limited effects of E-field exposure in tunnels, the observed disturbance thresholds caused by shocks in tunnels, and the ability of hives exposed under a transmission line to source currents 100-1,000 times the shock thresholds.

Animals↗