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Biomedical subjects

L Zeitz

Publications and source records attributed to L Zeitz.

14 recordsLinked to original sources
PubMed1988

Free radical production by high energy shock waves--comparison with ionizing irradiation.

Fricke chemical dosimetry is used as an indirect measure of the free radical production of ionizing irradiation. We adapted the Fricke ferrous sulfate radiation dosimeter to examine the chemical effects of high energy shock waves. Significant free radical production was documented. The reaction was dose dependent, predictably increased by acoustic impedance, but curvilinear. A thousand shocks at 18 kilovolts induced the same free radical oxidation as 1100 rad cobalt-60 gamma ionizing irradiation, increasing to 2900 rad in the presence of an air-fluid zone of acoustic impedance. The biological effect of these free radicals was compared to that of cobalt-60 ionizing irradiation by measuring the affect on Chinese hamster cells by clonogenic assay. While cobalt-60 irradiation produced a marked decrease in clonogenic survivors, little effect was noted with high energy shock waves. This suggested that the chemical effects produced by shock waves were either absent or attenuated in the cells, or were inherently less toxic than those of ionizing irradiation.

Animals↗
PubMed1987

Increased radiation-induced transformation in C3H/10T1/2 cells after transfer of an exogenous c-myc gene.

C3H/10T1/2 cells were infected with a retroviral vector expressing a mouse c-myc oncogene and a drug-selection marker. The resulting cells, morphologically indistinguishable from C3H/10T1/2, displayed a greatly enhanced sensitivity to neoplastic transformation by ionizing radiation or by a chemical carcinogen. Constitutive expression of myc therefore appears to synergize with an initial carcinogenic event, providing a function analogous to a subsequent event that apparently is required for the neoplastic transformation of these cells. This cell system should prove useful in exploring early stages in radiation-induced transformation.

Animals↗
PubMed1986

Potentiation of growth factor activity by exogenous c-myc expression.

The c-myc oncogene has been implicated in deregulation of cell growth in neoplastic cells and response to "competence-inducing" growth factors in normal cells. In the latter case, expression of c-myc has been shown to be associated with the transition from the G0 to the G1 phase of the cell cycle induced by platelet-derived growth factor (PDGF). In the work reported here, we have introduced the c-myc coding region, in a retroviral vector, into mouse and rat cells. We show that under conditions of anchorage-independent growth, constitutive c-myc expression increases the response of rodent cells to PDGF, as well as to other growth factors of both the competence-inducing and "progression" classes. These effects of the myc product are observed whether or not an exogenous ras gene has also been introduced into the same cells. Possible models for the influence of myc on growth responses are discussed.

Cell Line↗
PubMed1975

Suppression of melanoma cell tyrosinase activity and tumorigenicity after incorporation of bromouracil for one or two cell divisions.

We have studied the kinetics of suppression of tyrosinase activity and tumorigenicity in unsynchronized B16 mouse melanoma cells (clone B559) exposed to 5-bromodeoxyuridine (BrdU, 3 mug/ml) for one or two cell divisions, then cultured in BrdU-free medium (RM) for five or six days. Bromouracil replaced about 23% of thymine residues after 24 hours (1 cell division) and almost 40% after 48 hours (2 cell divisions) in the presence of BrdU. Upon subsequent growth in RM the extent of replacement declined in a manner consistent with dilution by new DNA synthesis, reaching 5-10% substitution by day 7 of these experiments. Tyrosinase activity was significantly reduced after treatment with BrdU for 24 or 48 hours but continued to decline after the cultures were changed to RM, approaching undetectable levels on day 7. The time course of reduction was similar to that previously determined in cells grown continuously for seven days in the presence of BrdU. Therefore, suppression of tyrosinase activity can result from incorporation of BrdU during a single cell cycle, but requires about seven days for full manifestation of the effect. Tumorigenicity decreased to 55% after 24 hours and to 15% after 48 hours with BrdU but rapidly reversed to approach that of untreated melanoma cells when subsequently grown in RM for 5-6 days. The effects of BrdU on total RNA or protein synthesis, or on plating efficiency appeared insufficient to account for the degree of suppression observed. Our results indicate that substitution by bromouracil into either strand of DNA loci controlling tyrosinase activity or tumorigenic potential may be sufficient for suppression. In addition, they demonstrate that such brief treatment with BrdU may be used to probe the regulation of differentiated function and tumorigenicity in these melanoma cells.

Animals↗
PubMedDate not supplied

Improved "nonisolated-sensor" solid polystyrene calorimeter.

A "nonisolated-sensor" solid polystyrene calorimeter is described which permits absorbed dose measurements with precision of less than 0.3% (standard error of the mean). The accuracy for obtaining absolute absorbed dose was estimated by comparisons with cavity ionization measurements. The calculation of absorbed dose with ionization chambers was carried out based upon the TG-21 AAPM dosimetry protocol. Measurements in a 60Co gamma-ray field with three different polystyrene parallel-plate ion chambers in a polystyrene phantom did not differ by more than 1.5% from that obtained with the polystyrene calorimeter. Measurements taken over a period of 247 days are compared with the expected values on the basis of the decay 60Co. The calorimeter system, with its capability of acquiring, printing, storing, plotting, and analyzing the data by computer, is described.

Calorimetry↗
PubMedDate not supplied

Design of apparatus for precise x-ray dose chamber calibrations.

An apparatus for precision calibration of ion chambers in the x-ray region from 16 to 320 kV is described. The development of a fast-acting shutter with "opening" and "closing" times of less than 3-ms eliminates the requirement for operating time corrections. Controls from outside the radiation room permit changing x-ray filters and alternately positioning both test and standard ion chambers in the x-ray beam. Thus, the remote controls eliminate the need to enter the x-ray room in the course of a series of calibrations. The potential advantages resulting from the capabilities of this apparatus are described in this Technical Report.

Calibration↗