Biomedical subjects

E L Alpen

Publications and source records attributed to E L Alpen.

At least 19 recordsLinked to original sources

PubMed1994

Radiation effects on late cytopathological parameters in the murine lens relative to particle fluence.

Lenses of mice irradiated with 250 MeV protons, 670 MeV/amu 20Ne, 600 MeV/amu 56Fe, 600 MeV/amu 93Nb and 593 MeV/amu 139La ions were evaluated by analyzing cytopathological indicators which have been implicated in the cataractogenic process. The LETs ranged from 0.40 keV/micrometer to 953 keV/micrometer and fluences from 1.31 10(3)/mm2 to 4.99 x 10(7)/mm2. 60Co gamma-rays were used as the reference radiation. The doses ranged from 10 to 40 cGy. The lenses were assessed 64 weeks post irradiation in order to observe the late effects of LET and dose on the target cell population of the lens epithelium. Our study shows that growth dependent pathological changes occur at the cellular level as a function of dose and LET. The shapes of the RBE-LET and RBE-dose curves are consistent with previous work on eye and other biological systems done in both our laboratory and others. The RBEmax's were estimated, for the most radiation cataract related cytological changes, MN frequency and MR disorganization, by calculating the ratio of the initial slopes of dose effect curve for various heavy ions to that of 60Co gamma-ray. For each ion studied, the RBEmax derived from micronucleus (MN) frequency is similar to that derived from meridional row (MR) disorganization, suggesting that heavy ions are equally efficient at producing each type of damage. Furthermore, on a per particle basis (particle/cell nucleus), both MN frequency and MR disorganization are LET dependent indicating that these classic precataractogenic indicators are multi-gene effects. Poisson probability analysis of the particle number traversing cell nuclei (average area = 24 micrometers2) suggested that single nuclear traversals determine these changes. By virtue of their precataractogenic nature the data on these endpoints intimate that radiation cataract may also be the consequence of single hits. In any case, these observations are consistent with the current theory of the mechanism of radiation cataractogenesis, which proposes that genomic damage to the epithelial cells surviving the exposure is responsible for opacification.

Animals↗

PubMed1994

Fluence-based relative biological effectiveness for charged particle carcinogenesis in mouse Harderian gland.

Neoplasia in the rodent Harderian gland has been used to determine the carcinogenic potential of irradiation by HZE particles. Ions from protons to lanthanum at energies up to 670 MeV/a have been used to irradiate mice, and prevalence of Harderian gland tumors has been measured 16 months after irradiation. The RBE for tumor induction has been expressed as the RBEmax, which is the ratio of the initial slopes of the dose vs prevalence curve. The RBEmax has been found to be approximately 30 for ions with LET values in excess of 100 keV/micrometer. Analysis on the basis of fluence as a substitute for dose has shown that on a per particle basis all of the ions with LET values in excess of 100 keV/micrometer have equal effectiveness. An analysis of the probabilities of ion traversals of the nucleus has shown that for these high stopping powers that a single hit is effective in producing neoplastic transformation.

Animals↗

PubMed1993

Accelerated heavy ions and the lens. IX. Late effects of LET and dose on cellular parameters in the murine lens.

Lenses of mice irradiated with 250 MeV protons, 670 MeV/amu 20Ne, 600 MeV/amu 56Fe, 350 MeV/amu 56Fe, 600 MeV/amu 93Nb or 593 MeV/amu 139La ions were evaluated by analysing cytopathological indicators which have been implicated in the cataractogenic process. The LETs ranged from 0.39 to 953 keV/microns and the fluences from 1.31 x 10(3)/mm2 to 5.12 x 10(7)/mm2. The lenses were assessed 64 weeks post-irradiation in order to observe the late effects of LET and dose on the target cell population of the lens' epithelium. Our studies showed that growth-dependent pathological changes occurred at the cellular level as a function of dose and LET. For a given particle dose, as the LET rose, the number of abnormal mitotic figures, micronuclei frequency, and the disorganization of meridional rows increased to a maximum and then reached a plateau or decreased. For particles of the same LET, the severity of meridional rows disorganization and micronuclei frequency increased with increasing dose. The numbers of cells surviving at late times post-irradiation were comparable with those of controls. In addition, the cellular density was similarly unaffected. These observations are consistent with the current theory of the mechanism of radiation cataractogenesis which posits that genomic damage to the epithelial cells surviving the exposure is responsible for opacification.

Acceleration↗

PubMed1993

Tumorigenic potential of high-Z, high-LET charged-particle radiations.

The potential for radiogenic neoplasia from charged-particle irradiation has been estimated using the Harderian gland of the mouse as a test system. Particles ranging in Z from Z = 1 (proton) to Z = 41 (niobium), in energy from 228 to 670A MeV, and in LET from 0.4 to 464 keV/microns were produced at the Lawrence Berkeley Laboratory BEVALAC. Expression of the tumorigenic potential of the initiated cells was enhanced by hormones from isogeneic grafts of pituitaries. The goal of the studies was to estimate the initial slope of the relationship between increased tumor prevalence at 16 months after irradiation and the dose received. Initial slopes were measured with good precision for 60Co gamma rays and the Bragg plateau beams of 228A MeV 4He ions, 600A MeV 56Fe ions, and 350A MeV 56Fe ions. The ratio of the initial slope for these ions to that of 60Co gamma rays give an estimate of the maximum RBE for radiogenic neoplasia. These values were 2.3 for the 4He ions, 40 for 600A MeV 56Fe, and 20 for 350A MeV 56Fe. In the studies reported here the prevalence of tumors as the result of pituitary isografts was not enhanced after irradiation with 56Fe ions. It remains to be seen how effective pituitary isografts are for enhancement of radiogenic neoplasia from other ions at different LET values. A risk analysis was undertaken using particle fluence rather than dose as the independent variable. This analysis provides a value for a "cross section" expressed in microns 2. This parameter expresses as the increase in proportion of mice with one or more Harderian gland tumors per unit increase in particle fluence. The plot of the cross section (risk coefficient) as a function of LET is monotonic, with no clear evidence of a maximum value of the risk coefficient for even the highest LET particle used.

Animals↗

PubMed1992

Fluence-related risk coefficients using the Harderian gland data as an example.

The risk of radiation-induced cancer to space travelers outside the earth's magnetosphere will be of concern on missions to the Moon and beyond to Mars. High energy galactic cosmic rays with high charge (HZE particles) will penetrate the spacecraft and the bodies of the astronauts, sometimes fragmenting into nuclear secondary species of lower charge but always ionizing densely, thus causing cellular damage which may lead to malignant transformation. To quantitate this risk, the concept of dose equivalent (in which a quality factor Q as a function of LET is assumed) may not be adequate, since different particles of the same LET may have different efficiencies for tumor induction. Also, RBE values on which quality factors are based depend on response to low-LET radiation at low doses, a very difficult region for which to obtain reliable experimental data. Thus, we introduce a new concept, a fluence-related risk coefficient (F), which is the risk of a cancer per unit particle fluence and which we call the risk cross section. The total risk is the sum of the risk from each particle type: sigma i integral Fi(Li) phi i(Li) dLi, where Li is the LET and phi i(Li) is the fluence-LET spectrum of the ith particle type. As an example, tumor prevalence data in mice are used to estimate the probability of mouse Harderian gland tumor induction per year on an extra-magnetospheric mission inside an idealized shielding configuration of a spherical aluminum shell 1 g/cm2 thick. The combined shielding code BRYNTRN/GCR is used to generate the LET spectra at the center of the sphere. Results indicate a yearly prevalence at solar minimum conditions of 0.06, with 60% of this arising from charge components with Z between 10 and 28, and two-thirds of the contribution arising from LET components between 10 and 200 keV/micrometers.

Animals↗

PubMed1992

The RBE-LET relationship for rodent intestinal crypt cell survival, testes weight loss, and multicellular spheroid cell survival after heavy-ion irradiation.

This report presents data for survival of mouse intestinal crypt cells, mouse testes weight loss as an indicator of survival of spermatogonial stem cells, and survival of rat 9L spheroid cells after irradiation in the plateau region of unmodified particle beams ranging in mass from 4He to 139La. The LET values range from 1.6 to 953 keV/microns. These studies examine the RBE-LET relationship for two normal tissues and for an in vitro tissue model, multicellular spheroids. When the RBE values are plotted as a function of LET, the resulting curve is characterized by a region in which RBE increases with LET, a peak RBE at an LET value of 100 keV/microns, and a region of decreasing RBE at LETs greater than 100 keV/microns. Inactivation cross sections (sigma) for these three biological systems have been calculated from the exponential terminal slope of the dose-response relationship for each ion. For this determination the dose is expressed as particle fluence and the parameter sigma indicates effect per particle. A plot of sigma versus LET shows that the curve for testes weight loss is shifted to the left, indicating greater radiosensitivity at lower LETs than for crypt cell and spheroid cell survival. The curves for cross section versus LET for all three model systems show similar characteristics with a relatively linear portion below 100 keV/microns and a region of lessened slope in the LET range above 100 keV/microns for testes and spheroids. The data indicate that the effectiveness per particle increases as a function of LET and, to a limited extent, Z, at LET values greater than 100 keV/microns. Previously published results for spread Bragg peaks are also summarized, and they suggest that RBE is dependent on both the LET and the Z of the particle.

Animals↗

PubMed1991

An experimental compartmental flow model for assessing the hemodynamic response of intracranial arteriovenous malformations to stereotactic radiosurgery.

Stereotactic radiosurgery has proven to be an effective method of treating selected inaccessible or inoperable arteriovenous malformations (AVMs) of the brain. Radiation-induced obliteration of successfully-treated AVMs, however, occurs only after some latent period after treatment, depending on size, location, and dose. An experimental compartmental flow model is proposed to describe the hemodynamic alterations in the AVM as a result of the pathophysiological changes after radiosurgery, and to analyze temporal alterations in AVM blood flow rates and pressure gradients before complete obliteration. In representative small (low-flow, 150 ml/min) and large (high-flow, 440 ml/min) AVMs, it is found that increases in pressure gradients across certain vascular structures within the AVM occur during the normal course of radiation-induced flow decrease and AVM obliteration. The magnitude of these pressure alterations, however, may be within the normal physiological variations in cerebrovascular blood pressure. The effects of partial-volume irradiation of the AVM is examined by limiting radiosurgical treatment to varying portions of the flow compartments within the model. It is found that alterations in pressure gradients persist in unirradiated vascular shunts, even after complete obliteration of the treated AVM volume. These pressure alterations may increase the probability of hemorrhage from the untreated shunts of the AVM and cause redistribution of regional cerebral blood flow resulting in increased flow through these untreated shunts.

Cerebrovascular Circulation↗

PubMed1991

The historical background for large-animal studies with neutrons of various energies.

Studies of the biological effects of fast neutrons were started as soon as adequate sources became available, and the first of these was the cyclotron at Berkeley. Limitations on methods for physical dosimetry render most of the earliest studies nearly useless, and the first landmark studies with modern methodology were done at Berkeley in the 1950s. This report is an attempt to review and summarize all the work that took place from 1950 to 1965. The RBE for fast neutrons in the dog is generally in the range of 1.0 or less, depending upon reference radiation, the biological end point chosen, and the exposure geometry. Also the RBE seems to be relatively independent of the fast-neutron spectrum, at least for the range of values that has been studied. Mean after-survival times in irradiated dogs and goats indicate that the bone marrow syndrome usually predominates in large animals irradiated with fast neutrons. The gastrointestinal threshold for the dog is around 1200 cGy, and for neutrons the biological effectiveness for the GI syndrome still does not bring the GI threshold down to the point where it predominates over the bone marrow syndrome. As expected from biological first principles, for dose rates in excess of a few tens of centigrays per minute, dose rate seems to have no effect on the outcome with either neutron, gamma or X irradiations when the end point is lethality.

Animals↗

PubMed1990

Differential repair of potentially lethal damage in exponentially growing and quiescent 9L cells.

The alteration of potentially lethal damage repair by postirradiation treatment with hypertonic saline (0.5 M PBS) was investigated in exponentially growing and quiescent 9L cells in vitro. A single dose of X rays (8.5 Gy) immediately followed by a 30-min treatment with hypertonic PBS at 37 degrees C reduced the survival of exponentially growing 9L cells by a factor of 13-18 compared to survival of irradiated immediately and delayed-plated cells, while the survival of quiescent cells was reduced by only a factor of 5-8. Survival curves confirmed the relative resistance of the quiescent 9L cells versus exponentially growing 9L cells to X rays plus hypertonic treatment. Both the slope and the shoulder of the survival curve were reduced to a greater extent in exponentially growing cells than in the quiescent cells by hypertonic treatment. The response of quiescent cells cannot be explained by either the duration of hypertonic treatment or the redistribution of the cells into G1 phase. We show that quiescent 9L cells can recover from hypertonically induced potentially lethal damage when incubated under conditions which have been found to delay progression through the cell cycle, and postulate that an altered chromatin structure or an enhanced repair capacity of quiescent 9L cells may be responsible for their resistance.

Animals↗

PubMed1989

Radiation damage to glucose concentrating capacity and cell survival in kidney tubule cells: effects of fractionation.

The glucose concentrating capacity of cultured LLC-PK1 kidney epithelial cells has been measured after single and fractionated doses of X-rays. Steady-state glucose concentrating capacity (ratio of glucose concentration inside to outside cell) can be measured using radiolabelled analogues of glucose which are actively transported but not metabolized. These cells can be stimulated to increase their glucose concentrating capacity (up-regulation) by a reduction in the glucose concentration of the growth medium. However, after X-ray irradiation the cells have a reduced capacity to respond to up-regulation. This effect can be measured 7 days after irradiation and before radiation-induced cell killing affects the cell population. The previously reported radiosensitivity of this function to single doses of X-rays (in the range 1-16 Gy) was confirmed. Surprisingly, no significant sparing of this effect could be measured by fractionation of the X-ray dose into two or four fractions. However, the cells showed a significant fractionation effect if clonogenic survival was measured using the standard cell survival assay. These early effects have different fractionation response from the later phases of tissue damage, measured months to years after irradiation, which do show sparing due to fractionation and are thought to be mainly due to changes in cell survival. The lack of sparing by fractionation to the functional damage may suggest a different target from that which determines cell survival. These results support the hypothesis that radiation damages cellular functions, separately from cell replication.

Biological Transport↗

PubMed1989

Quiescence in 9L cells and correlation with radiosensitivity and PLD repair.

The onset of quiescence, changes in X-ray sensitivity, and changes in capacity for potentially lethal damage (PLD) repair of unfed plateau-phase 9L44 cell cultures have been systematically investigated. The quiescent plateau phase in 9L cells was the result of nutrient deprivation and was not a cell contact effect. Eighty-five to 90% of the plateau-phase cells had a G1 DNA content and a growth fraction less than or equal to 0.15. The cell kinetic shifts in the population were temporally correlated with a developing radioresistance, which was characterized by a larger shoulder in the survival curve of the quiescent cells (Dq = 5.71 Gy) versus exponentially growing cells (Dq = 4.48 Gy). When the quiescent plateau-phase cells were refed, an increase in radiosensitivity resulted which approached that of exponentially growing 9L cells. Delayed plating experiments after irradiation of exponentially growing cells, quiescent plateau-phase cells, and synchronized early to mid-G1-phase cells indicated that while significant PLD repair was evident in all three populations, the quiescent 9L cells had a higher PLD repair capacity. Although data for immediate plating indicated that 9L cells may enter quiescence in the relatively radioresistant mid-G1 phase, the enhanced PLD repair capacity of quiescent cells cannot be explained by redistribution into G1 phase. When the unfed quiescent plateau-phase 9L cells were stimulated to reenter the cell cycle by replating into fresh medium, the first G1 was extended by 6 h compared with the G1 of exponentially growing or refed plateau-phase 9L cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Line↗

PubMed1988

Joint oxygen-glucose deprivation as the cause of necrosis in a tumor analog.

The sandwich system was recently developed as an in vitro tumor analog. Like spheroids, sandwiches are organized, multicellular systems in which the interplay between diffusion and consumption leads to the formation of spatial gradients; a necrotic center and a viable cell border subsequently develop. Using sandwiches of the 9L and V79 cell lines, the effects of oxygen and glucose deprivation on the onset and formation of necrosis were investigated. The data indicate that in sandwiches necrosis is a result of a shortage of both substances. Complementary cell monolayer experiments to determine a number of consumption parameters were performed. On the basis of the data, we propose a joint oxygen-glucose deprivation model for V79 cell necrosis. It is assumed a cell dies when oxygen deprivation in conjunction with glucose deprivation lowers the cell's ATP production rate below a critical value. Interactions of the concentrations and consumptions of oxygen and glucose are analyzed theoretically; concentration profiles are obtained by numerically solving coupled non-linear integral equations arising from the diffusion equation. The predicted viable border widths are in good agreement with the observed values.

Animals↗

PubMed1988

Recovery from potentially lethal damage and recruitment time of noncycling clonogenic cells in 9L confluent monolayers and spheroids.

Cells that have been grown as multicell tumor spheroids exhibit radioresistance compared to the same cells grown in monolayers. Comparison of potentially lethal damage (PLD) repair and its kinetics was made between 9L cells grown as spheroids and confluent monolayers. Survival curves of cells plated immediately after irradiation showed the typical radioresistance associated with spheroid culture compared to plateau-phase monolayers. The dose-modification factor for spheroid cell survival is 1.44. Postirradiation incubations in normal phosphate-buffered saline (PBS), conditioned media, or 0.5 M NaCl in PBS reduced the differences in radiosensitivity between the two culture conditions. Postirradiation treatment in PBS or conditioned medium promoted repair of potentially lethal damage, and 0.5 M NaCl prevented the removal of PLD and allowed the fixation of damage resulting in lower survival. Survival of spheroid and monolayer cells after hypertonic NaCl treatment was identical. NaCl treatment reduced Do more than it did the shoulder (Dq) of the survival curve. PLD repair kinetics measured after postirradiation incubation in PBS followed by hypertonic NaCl treatment was the same for spheroids and for plateau-phase monolayers. The kinetics of PLD repair indicates a biphasic phenomenon. There is an initial fast component with a repair half-time of 7.9 min and a slow component with a repair half-time of 56.6 min. Most of the damage (59%) is repaired slowly. Since the repair capacity and kinetics are the same for spheroids and monolayers, the radioresistance of spheroids cannot be explained on this basis. Evidence indicates that the time to return from a Go (noncycling G1 cells) state to a proliferative state (recruitment) for cells from confluent monolayers and from spheroids after dissociation by protease treatment may be the most important determinant of the degree of PLD repair that occurs. Growth curves and flow cytometry cell cycle analysis indicate that spheroid cells have a lag period for reentry into a proliferative state. Since plating efficiency remains high and unchanging during this period, one cannot account for the delay on the basis of the existence of a large fraction of Go cells which are not potentially clonogenic. The cell cycle progression begins in 6-8 h for monolayer cells and in 14-15 h for spheroids. It is hypothesized that the slower reentry of spheroid cells into a cycling phase allows more time for repair than for the rapidly proliferating monolayer cells.

Animals↗

PubMed1987

The relative biological effectiveness of 670 MeV/A neon as a function of depth in water for a tissue model.

Linear energy transfer (LET infinity) spectra of identified charge fragments and primaries, produced by nuclear interactions of 670 MeV/A neon in water, were measured along the unmodulated Bragg curve of the neon beam. The relative biological effectiveness (RBE) values for spermatogonial cell killing, as reported on the basis of weight loss assay of mouse testes irradiated with beams of approximately constant single LET infinity, were summed over the particle LET infinity spectra to obtain an effective RBE for each charged-particle species, as a function of water absorber thickness. The resultant values of effective RBE were combined to obtain an effective RBE for the mixed radiation field. The RBE calculated in this way was compared with experimental RBEs obtained for spermatogonial cell killing in the mixed radiation field produced by neon ions traversing a thick water absorber. Discrepancies of 10-40% were observed between the calculated RBE and the RBE measured in the mixed radiation field. Part of this discrepancy can be attributed to undetected low-Z fragments, whose contribution is not included in the calculation, leading to an overestimated value for the calculated RBE. On the other hand, calculated values 10% greater than the measured RBE are explained as track structure effects due to the higher radial ionization density near neon tracks relative to the ionization density near the silicon tracks used to fit the RBE vs LET infinity data.

Animals↗

PubMed1987

Radiation-induced division delay in 9L spheroid versus monolayer cells.

The technique of percentage labeled mitoses was used to compare radiation-induced division delay in 9L rat gliosarcoma cells growing as spheroids or as exponential monolayers. The length of delay induced by each of five X-ray doses was determined as the difference between control and irradiated cultures in the time required to reach the half-height of the first peak of labeled mitoses. Spheroid cells were delayed significantly longer than monolayer cells; the slopes of the dose responses were 32 and 13 min/Gy, respectively. Cells in small spheroids (150 micron diameter) were delayed to the same extent as cells in large spheroids (800 micron diameter). Like the contact effect previously observed as enhanced radiation survival of cells grown as spheroids, the increased radiation-induced delay may be a consequence of the growth of cells in three-dimensional contact.

Animals↗

PubMed1986

Dynamics of cell kinetic parameters during 9L spheroid growth.

Cell population kinetics were followed in 9L tumour spheroids as they grew from aggregates of about 80 micron in diameter to over 800 micron. The kinetic parameters measured were cell cycle time, spheroid-doubling time, and growth fraction; from these the cell loss factor phi was calculated. The rate of cell shedding from the surface was also measured, so that the contribution of shedding to the overall cell loss could be evaluated. The major findings include significant elongation of the cell cycle, a low rate of cell death in spheroids below 500 micron in diameter, and a relatively high GF in large spheroids. The results also indicated that 9L spheroid kinetic parameters may be strongly influenced by the culture methodology.

Cell Cycle↗

PubMed1986

Differences in the X-ray sensitivity of cells in different regions of the sandwich, a diffusion-limited system for cell growth.

The sandwich system was recently developed as a tumor analog; like spheroids, sandwiches are diffusion-limited multicellular systems which exhibit a necrotic center and a viable cell border. Using sandwiches of the 9L cell line, we compared the X-ray sensitivity of cells in the inner half of the viable border, adjacent to the necrotic center, with that of cells in the outer half of the viable border, adjacent ot the medium. No cells were hypoxic at the time of irradiation. The cells in the inner half of the viable border exhibited an increased radioresistance over cells in the outer half. The effect was dose multiplying with a multiplying factor of 1.5. Besides the sandwich studies, the X-ray sensitivity of 9L plateau monolayer cultures (induced by starvation) was compared to exponentially growing monolayer cultures. The plateau cultures exhibited an increased radioresistance over the exponentially growing cultures. The effect was also dose multiplying with a multiplying factor of 1.5.

Animals↗

PubMed1985

Two-dimensional diffusion limited system for cell growth.

A new cell system, designed to supplement multicellular spheroids as tumour analogues, was analysed theoretically and experimentally. This 'sandwich' system is a single layer of cells, subject to self-created gradients of nutrients and metabolic products. Due to these gradients the sandwich system develops a border of viable cells and an inner region of necrotic cells corresponding to the viable rim and the necrotic center of a spheroid. However, sandwiches differ from spheroids in several ways. All the cells in the sandwich can be microscopically viewed during the entire experiment. In sandwiches there is no three-dimensional cell to cell contact. Also, the gradients are less steep in our sandwich system, so the width of the viable region in a sandwich is about 10 times as large as the width of the viable rim in a spheroid. Indeed, in sandwiches the experimenter has some control over the steepness of the gradients and thus can vary the width of this viable border. We used DNA labelling studies and flow cytometry along with visual observation to analyse the system. Our experiments show that the observed cell necrosis, similar to that found in spheroids, is due to diffusion limitations. The results are consistent with the idea that oxygen deprivation stops cell cycling and, when extreme and prolonged, leads to necrosis. The possibility that substances other than oxygen are involved is not excluded by the data. The data also suggests that in the final, near-equilibrium state the average overall oxygen consumption rate for the viable sandwich population may be about one-quarter of that for an exponentially growing population of the same cell line.

Animals↗