Biomedical subjects

S H Benedict

Publications and source records attributed to S H Benedict.

At least 37 records · Page 2Linked to original sources

PubMed1998

Accelerated radiotherapy regimen for malignant gliomas using stereotactic concomitant boosts for dose escalation.

The purpose of this pilot study was to determine the feasibility and toxicities of an accelerated treatment program by using a concomitant stereotactic radiotherapy boost given weekly during a course of standard external-beam irradiation (EBXRT) in patients with malignant gliomas. Twelve patients underwent biopsy or subtotal resection of a malignant glioma and were enrolled on the protocol, which delivered 44 Gy-EBXRT and a 12-Gy stereotactic radiotherapy boost given on 3 consecutive weeks of treatment for a total dose of 80 Gy over 33 days. Three patients with anaplastic astrocytoma and nine patients with glioblastoma multiforme had median survival times of 33 months and 16 months, respectively. All of the tumor recurrences were within or were closely adjacent to the region of high-dose irradiation. None of the patients required a treatment break, and there were no acute complications. Two patients developed seizures in the follow-up period, and four patients were diagnosed with radionecrosis at the time of the second operation. The treatment program was found to be feasible and was well tolerated, and it resulted in a rate of late complications similar to those of radiosurgery or interstitial brachytherapy.

Adult↗

PubMed1997

The biological effectiveness of intermittent irradiation as a function of overall treatment time: development of correction factors for linac-based stereotactic radiotherapy.

PURPOSE: Continuous irradiation of relatively short duration as administered in gamma-ray stereotactic radiosurgery (SRS) is biologically not equivalent to the more protracted intermittent exposures during accelerator-based radiosurgery with multiple arcs. Accelerator-based SRS and fractionated stereotactic radiotherapy (SRT) is currently performed with a high degree of variability in equipment and techniques resulting in highly variable treatment delivery times. The present work is designed to quantify the effects of radiation delivery times on biological effectiveness. For this, the intermittent radiation delivery schemes, typical for linac-based SRS/SRT, have been simulated in vitro to derive biological correction factors. METHODS AND MATERIALS: The experiments were carried out using U-87MG human glioma cells in suspension at 37 degrees C irradiated with 6 MV X-rays to clinically relevant doses ranging from 6 to 18 Gy, delivered over total irradiation times from 16 min to 3 h. The resulting cell survival data was used to calculate dose correction factors to compensate for wide variations in dose delivery times. RESULTS: At each total dose level, cell survival increased with increasing total irradiation time. The increase in survival was more pronounced at higher dose levels. At a total dose of 12 Gy, cell survival increased by a factor of 4.7 when irradiation time was increased from 16 to 112 min. Dose correction factors were calculated to allow biologically equivalent irradiations over the range of exposure times. Cells irradiated with corrected total doses of 11.5 Gy delivered incrementally in 16 min up to 13.3 Gy in 112 min were found to exhibit the same survival within the experimental limits of accuracy. CONCLUSIONS: For a given total dose, variations in dose delivery time typical of SRS/SRT techniques will result in significant changes in cell survival. In the dose range studied, an isoeffect dose correction factor of 2 to 3 cGy/min was shown to compensate for the change in delivery time for U-87 MG human gloma cells in vitro.

Brain Neoplasms↗

PubMed1997

Early phosphorylation of the retinoblastoma gene product regulates protein binding to the c-fos retinoblastoma control element during T cell activation.

Function of the retinoblastoma tumor suppressor protein [pRb] is regulated by phosphorylation during the G1 and S phases of the cell cycle. pRb regulates transcription of several genes, including c-fos. However, since c-fos is regulated during exit from G0, it has remained unclear how pRb participates in c-fos regulation. We have identified a protein complex, the retinoblastoma control factor A [RCF-A] which binds to the c-fos retinoblastoma control element [RCE] and is regulated by pRb within 10 min after T cell activation. We demonstrate that pRb control of RCF-A is dependent upon the state of phosphorylation of pRb. pRb becomes hyperphosphorylated on specific peptides at 10 min after mitogenic stimulation and pRb is dephosphorylated by 30 min. This time course coincides with RCF-A DNA binding. RCF-A binds RCE DNA longer when cells are treated with okadaic acid, and okadaic acid prevents pRb dephosphorylation. Dephosphorylated pRb inhibits RCF-A binding in vitro but phosphorylated pRb does not. Thus, in addition to the described G1/S regulation of pRb, transient inactivation by phosphorylation of pRb in T cells may also be important as resting cells leave G0.

Adult↗

PubMed1997

Inhibition of homotypic adhesion of T-cells: secondary structure of an ICAM-1-derived cyclic peptide.

The objective of this study was to elucidate the solution conformation of cyclo-(1,12) Pen1-Pro2-Ser3-Lys4-Val5-Ile6-Leu7-Pro8-Ar g9-Gly10-Gly11-Cys12 (1) derived from the intercellular adhesion molecule-1 (ICAM-1). Cyclic peptide 1 inhibits homotypic adhesion of T-cells (Molt-3) mediated by ICAM-1 and the leukocyte function-associated antigen-1 (LFA-1) on the surface of T-cells. Cyclic peptide 1 is more potent than is the linear peptide Pen1-Pro2-Ser3-Lys4-Val5-Ile6-Leu7-Pro8-Ar g9-Gly10-Gly11-Cys12 (2) in inhibiting homotypic adhesion. The difference in biological activity of peptides 1 and 2 may be due to the more stable conformation of cyclic peptide 1 compared to linear peptide 2 or because cyclization prevents the peptide from adopting non-productive conformation. Therefore, conformational studies of cyclic peptide 1 will give a better understanding of its biological active conformation. The conformational studies of cyclic peptide 1 were done by NMR, CD and molecular dynamics simulations. NMR studies indicated that the major conformation of cyclic peptide 1 contained trans-configuration at both X-Pro peptide bonds. Type I beta-turns at Lys4-Val5-Ile6-Leu7 and Leu7-Pro8-Arg9-Gly10 were found in cyclic peptide 1. The C- and N-terminal regions of this peptide were stabilized by antiparallel beta-sheet-like structure with the presence of intramolecular hydrogen bonds. The overall structure of this peptide exposed the hydrophobic side chains on one face of the molecule and the hydrophilic side chains on the other.

Amino Acid Sequence↗

PubMed1996

A kinase/phosphatase system involving the protooncogene Lck is necessary for inducible modulation of Sob 1 during T cell activation.

The phosphotyrosine containing protein Sob 1 regulates inducibility of a DNA binding complex (Band A) at the SRE of c-fos during T cell activation. In the present study, Sob 1 was regulated by activation of T cells through the T cell antigen receptor. Inhibition of protein tyrosine kinases (PTK) inactivated Sob 1 function and allowed the Band A DNA-protein complex to form. Inhibition of protein tyrosine phosphatases (PTP) caused constitutive activation of Sob 1 function and prevented induction of Band A at the SRE. Thus, Sob 1 is regulated by a constitutive PTP/PTK system. J.CaM 1 cells that lack a functional form of the PTK Lck are unable to induce Band A through the T cell antigen receptor. J.CaM 1 cells reconstituted with Lck seem to induce Band A normally. Thus, functional Lck is required for regulation of Sob 1.

Base Sequence↗

PubMed1995

Cross-linking of ICAM-1 on T cells induces transient tyrosine phosphorylation and inactivation of cdc2 kinase.

Intercellular adhesion molecules (ICAM)-1 and -3 coexist on T lymphocytes and are counter-receptors for the integrin LFA-1. Signaling through ICAM-3 stimulates a number of T cell functions and involves phosphorylation of Fyn, Lck, CD45, and other proteins. In contrast, this type of specific signaling event has not been described for signaling through ICAM-1. Here, tyrosine phosphorylation of cellular proteins was examined after cross-linking of ICAM-1. Tyrosine phosphorylation of the 34-kDa cdc2 protein kinase was induced transiently after stimulation of the leukemic T cell line, Molt-3, or peripheral blood T cells. Stimulation through ICAM-1 had no effect on constitutive presence of cdc2 or phosphorylation of cdc2 on threonine. cdc2 kinase activity was constitutive in peripheral blood T cells, and transient inhibition of kinase activity after ICAM-1 stimulation correlated kinetically with phosphorylation of cdc2 on tyrosine.

Antibodies, Monoclonal↗

PubMed1995

Modulation of T cell morphology and induction of homotypic adhesion by a protein tyrosine kinase inhibitor.

T cells are spherical in culture and during travel through the bloodstream. They depart from this shape as part of the adhesion cascade by which they penetrate endothelium, interact with the extracellular matrix, and migrate through tissues. The mechanisms by which shape changes and altered adhesive properties are regulated are largely uncharacterized; however, they involve modulation of protein phosphorylation on tyrosine. Here, an inhibitor (MDHC) of protein tyrosine kinases (PTK) caused a shift in the morphology of a human T cell line from spherical to spread. This involved cytoskeletal components and was preceded by altered tyrosyl-phosphorylation and accompanied by an increased capacity for homotypic adhesion involving LFA-1 and CD2. Examples exist demonstrating prevention of morphological alteration or cell adhesion by PTK inhibitors, and thus MDHC differed from these other inhibitors. This suggests differential sites of action for PTK inhibitors and perhaps that MDHC accessed different steps in the adhesion cascade.

Cell Adhesion↗

PubMed1994

Inducible binding to the c-fos serum response element during T cell activation is regulated by a phosphotyrosine-containing protein.

The proto-oncogene c-fos is an immediate-early gene, and one of the first genes transcribed after stimulation of most cells with a variety of ligands. Fos expression may be a pivotal event in converting ligand-receptor interactions at the membrane into functional modulation of cell phenotype. The serum response element (SRE) in the c-fos regulatory region participates in induction of transcription by various growth factors and by phorbol esters and subsequent squelching of transcription. We show that an inducible protein complex (Band A) binds to SRE DNA within 10 min after mitogenic stimulation of human PBL-T, and becomes nondetectable by 60 min. Band A contains the serum response factor plus additional factor(s). A protein that is phosphorylated on a tyrosine residue in resting PBL-T suppresses binding of a component of Band A to the SRE motif. Upon stimulation of the cells, this protein no longer prevents binding of DNA by Band A, and suppression of binding is restored within 30 min. The phosphorylated tyrosine residue itself is important for the protein-protein interaction.

Base Sequence↗

PubMed1994

Anti-IgM and anti-IgG modulate c-fos RNA levels differently in human B lymphocytes.

One component of the B cell activation cascade is the induction of the protooncogene c-fos. Data presented here demonstrate that stimulation of mIgM-bearing cells with either anti-IgM or the combination of PDB plus ionomycin generated comparable levels of c-fos RNA. Furthermore, a synergistic response was observed when the cells were treated with selected concentrations of anti-IgM plus either PDB or ionomycin. In contrast, stimulation of mIgG-bearing B cells with anti-IgG did not induce the c-fos RNA levels that were seen when these cells were treated with the combination of PDB plus ionomycin. Treatment of mIgG-bearing cells with only the combination of anti-IgG plus ionomycin yielded a synergistic response and anti-IgG plus PDB did not. Thus, induction of c-fos RNA appears to be different in mIgM- and mIgG-bearing B cells after stimulation through mIg.

Antibodies, Anti-Idiotypic↗

PubMed1991

Assessment of 18F gaseous releases during the production of 18F-fluorodeoxyglucose.

Fluorodeoxyglucose labeled with 18F (18F-FDG) is the most commonly used radiopharmaceutical in positron emission tomography (PET). Fluorine-18-labeled FDG is used as a diagnostic tool in PET studies to monitor the physiology of the brain, diagnose heart function and disease, and to image cancerous tumors. At the University of California, Los Angeles (UCLA), three cyclotrons produce [18F]-fluoride ion using 18O-enriched water targets. Fluorine-18, which has a half-life of 109.8 min, is produced using an 18O(p.n.)18F reaction and is chemically processed to yield 18F-FDG. This study presents data which demonstrate that during the radiochemical processes involved in the production of 18F-FDG, gaseous effluent containing 18F is released. Forty cyclotron production runs with average end of cyclotron bombardment activities of 15.9 +/- 1.88 GBq (430 +/- 50.8 mCi) and end of radiochemical synthesis activities of 5.40 +/- 1.27 GBq (146 +/- 34.3 mCi) yield 18F gaseous effluent releases ranging from 0 to 2560 MBq (0 to 69.2 mCi) with a mean of 437 MBq (11.8 mCi). Temporal correlation of the 18F gaseous releases during 18F-FDG radiochemical production has tied the 18F release to the addition of the glucose precursor (mannotriflate) and ethyl ether in the radiochemical processing. The results are presented in terms of activities released and dilution factors required from the release stack point to maintain controlled (occupational) and uncontrolled (public) area limits in accordance with the recommendations of the International Commission on Radiological Protection and the regulatory requirements of the federal government.

Air Pollutants, Radioactive↗

PubMed1991

Exposure rates in high-level-control fluoroscopy for image enhancement.

High-level fluoroscopic boost options that exceed conventional exposure limits are available as a means of reducing quantum mottle during angiography. Federal law does not specify exposure limits for such high-level controls but requires specific means of activation to safeguard against inadvertent use. The American Association of Physicists in Medicine recently recommended that high-level exposure rates not exceed 2.58 mC/kg/min (10R/min). At six institution surveyed, maximum exposure rates ranged from 5.42 to 24 mC/kg/min (21-93 R/min). Activation of high-level capability varied from a simple foot switch to a keyed interlock requiring a second operator to engage. There appears to be no industry coherence in high-level control exposure limits as yet, although the Center for Devices and Radiological Health recently initiated an investigatory program.

Environmental Exposure↗

PubMed1991

Pathogenesis of pulmonary fibrosis in interstitial lung disease. Alveolar macrophage PDGF(B) gene activation and up-regulation by interferon gamma.

Alveolar macrophages are believed to be central in orchestrating the fibrotic response in interstitial lung disease (ILD). To test the hypothesis that macrophages from patients with ILD were dedicated to growth factor production and that this was independent of other indices of macrophage activation, we measured the mRNA of the B chain of PDGF and TGF-beta, as well as HLA-DR-alpha in alveolar macrophages from patients with ILD and from normal control subjects. When alveolar macrophages were examined immediately after lavage, cells from patients with ILD had increased PDGF(B) but similar TGF-beta and HLA-DR-alpha mRNA when compared with control subjects. Discoordinate regulation of these genes was observed when alveolar macrophage PDGF(B) mRNA increased while TGF-beta and HLA-DR-alpha mRNA decreased after culture for 24 h. This response was not disease-related as these changes were similar in cells from patients with ILD and from control subjects. Because a lymphocytic alveolitis is present in many cases of ILD, we asked whether interferon gamma (IFN-gamma) modulated the activation of these genes. In both the patients and the control subjects, PDGF(B) and HLA-DR-alpha, but not TGF-beta, mRNA were increased after incubation with IFN-gamma. These results indicate that PDGF(B) mRNA may be increased in alveolar macrophages in ILD and that PDGF(B), TGF-beta, and HLA-DR-alpha are independently regulated genes in alveolar macrophages, but that IFN-gamma increases both PDGF(B) and HLA-DR-alpha mRNA. We speculate that IFN-gamma induced PDGF(B) gene activation may be an important mechanism by which lymphocytes promote pulmonary fibrosis.

Adult↗

PubMed1990

Expression of IgE from a nonrearranged epsilon locus in cloned B-lymphoblastoid cells that also express IgM.

During development, B lymphocytes have the ability to switch from synthesis of IgM to immunoglobulins of another isotype such as IgG, IgA, or IgE. This class switching mechanism has been shown to involve DNA rearrangement and concomitant deletion of intervening CH genes. In our report, an EBV-transformed B lymphoblastoid cloned cell line is described that simultaneously expressed and secreted both IgM and IgE. DNA analysis showed the (nonproductive) rearrangement of one allele to gamma and (productive) rearrangement of the other allele to mu. Germ-line arrangement of the C epsilon gene was preserved on both alleles.

B-Lymphocytes↗

PubMed1990

Physician exposure to ionizing radiation during trauma resuscitation: a prospective clinical study.

A prospective study of emergency physician whole body and extremity exposure to ionizing radiation during trauma resuscitation over a three-month period was conducted. Radiation film badges and thermoluminescent dosimeter finger rings were permanently attached to leaded aprons worn by emergency medicine residents during all trauma resuscitations. One set of apron and finger ring dosimeters was designated for the resident who managed the airway and stabilized the neck, when necessary, during cervical spine radiography (A-CS resident). A separate set of dosimeters was designated for the resident supervising the resuscitation. During the study period, 150 major trauma patients requiring 481 radiographic studies were treated. The mean monthly cumulative whole body exposures were 136.7 +/- 85.0 and 103.3 +/- 60.3 mrem for A-CS and supervising residents, respectively. The mean weekly cumulative extremity exposures were 523.3 +/- 611.0 and 46.7 +/- 18.6 mrem for A-CS and supervising residents, respectively. Calculated whole body exposures per patient were 2.7 mrem for the A-CS resident and 2.1 mrem for the supervising resident. Calculated extremity exposures per patient were 41.9 +/- 48.9 and 3.7 +/- 1.5 mrem, respectively. To exceed the annual whole body exposure limit established by the National Council of Radiologic Protection, the A-CS resident, working 200 shifts per year, would have to treat 9.2 trauma patients per shift. To exceed the annual extremity exposure limit, the A-CS resident would have to treat 5.9 trauma patients per shift. Of note, European exposure limits are 10% of current US limits. We conclude that significant exposures may occur to physicians working in trauma centers and that the use of shielding devices is indicated.

Emergency Medicine↗

PubMed1990

Adherence-dependent increase in human monocyte PDGF(B) mRNA is associated with increases in c-fos, c-jun, and EGR2 mRNA.

Adherence is an important initial step in the transition of a circulating monocyte to a tissue macrophage. This differentiation is accompanied by an augmented capacity to generate growth factors. We hypothesized that adherence itself might be an important trigger for a sequence of gene activation culminating in cells with increased mRNA encoding profibrotic growth factors such as platelet-derived growth factor B subunit (PDGF[B]) and transforming growth factor-beta (TGF-beta). After in vitro adherence, human monocytes had a biphasic increase in PDGF(B) mRNA with peaks at 6 h and 13 d. No increase in TGF-beta mRNA was observed. The 6-h increase in PDGF(B) mRNA was adherence dependent, and in addition, was abrogated when the cytoskeletal integrity was compromised by cytochalasin D. The 6-h increase in PDGF(B) mRNA was unaltered by adherence in the presence of the monocyte stimulus lipopolysaccharide. Adherence to either fibronectin or collagen-coated plastic had little consistent effect on PDGF(B) mRNA accumulation. The increased PDGF(B) mRNA observed in adherent monocytes was accompanied by increases in mRNAs of the early growth response genes c-fos (maximal at 20 min), c-jun, and EGR2 (maximal at 6-24 h). The increase in c-jun and EGR2, but not c-fos, mRNA was also abrogated by cytochalasin D. These observations suggest that adherence results in increases of c-fos, c-jun, EGR2, and PDGF(B) mRNA. In addition, the increases in c-jun, EGR2, and PDGF(B) may depend on cytoskeletal rearrangement. Modulation of these events at the time of adherence offers a mechanism by which differential priming of the cells may be accomplished.

Cell Adhesion↗

PubMed1990

Expansion of B lymphocytes with an unusual immunoglobulin rearrangement associated with atypical lymphocytosis and cigarette smoking.

Persistent polyclonal lymphocytosis has been described in a group of female patients who all have the HLA-DR7 antigen in common and who are all heavy cigarette smokers. Immunoglobulin heavy chain gene rearrangement was analyzed by hybridization with specific immunoglobulin heavy chain genes to restriction enzyme-digested genomic DNA samples. The results in two of these patients showed that the lymphocytosis was associated with an expanded subpopulation of B-lineage cells represented by the presence of an unusual immunoglobulin gene rearrangement pattern. Expansion of this subpopulation of B cells appeared to be linked to cigarette smoking since the intensity of the cell population harboring the rearranged gene was much stronger in patients who were smoking heavily compared with the same patients who were temporarily not smoking.

B-Lymphocytes↗

PubMed1989

Phorbol ester activation of phospholipase D in human monocytes but not peripheral blood lymphocytes.

Previous reports have shown that 12-0-tetradecanoylphorbol-13-acetate can activate phospholipase D in human peripheral blood mononuclear cells as measured by an enzyme-catalyzed transphosphatidylation reaction (phosphatidylethanol formation). In the present study, the mononuclear cells were fractionated by two procedures to identify the responsive cells. Contrary to earlier suggestions, the results indicate that phorbol ester does not stimulate phospholipase D activity in normal lymphocytes. Thus, phosphatidylethanol was not produced by T lymphocytes (isolated by sheep erythrocyte rosette formation) or by a mixture of T and B lymphocytes (isolated by centrifugal elutriation). Under the same conditions, phorbol ester was able to activate phospholipse D in fractions that contained predominately monocytes. Preliminary experiments have further shown that phorbol ester does not induce phospholipase D activity in human T cell leukemic lines (MOLT-3, CEM, JURKAT, PEER) but can do so in some, but not all, B cell lines that have been infected with Epstein-Barr virus.

B-Lymphocytes↗

PubMed1989

Exposure of emergency medicine personnel to ionizing radiation during cervical spine radiography.

We studied the potential hazard of ionizing radiation exposure to health care workers who routinely stabilize the necks of trauma patients during cervical spine radiography. A clinical trauma model was developed using an Alderson RANDO Phantom artificial torso to simulate an actual patient. A radiation monitor was placed where a health care worker's fingers, hands, arms, and thyroid gland would be, and standard cervical spine radiographs were taken. The exposures to the finger positions then were repeated with the monitor inside a 0.5 mm lead-equivalent glove. The mean exposure to the finger for a single cross-table lateral radiograph was 174.5 mrem. The use of leaded gloves reduced this exposure to 0.3 mrem a 99.9% reduction). For a single series of lateral, anteroposterior, odontoid, and swimmer's views, the total mean measured unprotected exposure to the finger of the hand positioned nearest the radiographic tube was 681 mrem and the exposure to the finger of the opposite hand was 230 mrem. If these simulated exposures are indicative of actual patient situations, a health care worker who holds the head of a trauma patient four times each week with unshielded hands would receive more than twice the maximum allowable annual occupational radiation exposure to the extremities recommended by the National Council of Radiation Protection and Measurements. We conclude that health care workers who routinely stabilize the necks of trauma patients during cervical spine radiography may incur a radiation exposure risk and that 0.5-mm lead-equivalent gloves provide an effective barrier to ionizing radiation.

Cervical Vertebrae↗