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LE Magazine November 2001


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Effects of radiation on endothelial function.

PURPOSE: The response of endothelium to ionizing radiation was studied. METHODS AND MATERIALS: The abdominal aorta in different experimental groups of rats was irradiated, and the response of arterial rings from the irradiated segments to norepinephrine, acetylcholine (ACh), and nitroglycerin (NTG) was studied. Nonirradiated thoracic segments in the same experimental animals were used as as a control for comparisons. Two age-matched nonirradiated control groups were also studied. RESULTS: A poor endothelium-dependent vasodilator response was obtained with ACh in the irradiated rings and also in those not directly irradiated; the endothelium-independent vasodilator response to NTG was preserved during the first 3 days after irradiation. By 6 months, both the endothelium-dependent response and endothelium-independent response were impaired. CONCLUSIONS: Alterations in nitric oxide synthesis and/or release by the endothelium were observed during the early phase of radiation in irradiated and nonirradiated segments. In the delayed phase of radiation, endothelium-independent muscular relaxation was also affected.

Int J Radiat Oncol Biol Phys 1998 Jul 1;41(4):905-913

Enhancement of prostate cancer xenograft growth with whole-body radiation and vascular endothelial growth factor.

Prostate cancer research has been limited by the slow growth of human prostate tumors In athymic rodent models. This study sought to determine if low-dose radiation and vascular endothelial growth factor (VEGF) could enhance the development of PC-3 human prostate adenocarcinoma xenotransplanted into nude mice. Whole body radiation (2 Gy) was delivered only once, whereas VEGF (39 ng total/mouse) was injected subcutaneously over a 17-day period. The combination of the two agents, compared to nontreated controls, resulted in significantly higher tumor incidence (100% versus 50%) and more-rapid tumor progression (1288 mm3 versus 190 mm3 by day 60). Treatment-associated changes were observed in body weights and assays of blood and spleen cells. In addition, 3H-thymidine uptake by PC-3 cells cultured in the presence of VEGF and transforming growth factor-beta 1 was compared. These results show that low-dose, whole-body radiation and VEGF can be used in concert safely and effectively to facilitate growth of PC-3 prostate tumor and that the mechanisms of interaction may involve leukocyte modulation.

Anticancer Res 1997 Mar;17(2A):923-928

Ionizing radiation enhances platelet adhesion to the extracellular matrix of human endothelial cells by an increase in the release of von Willebrand factor.

The effect of radiation on the secretion of von Willebrand factor by endothelial cells was studied in a three-compartment culture system. The release of von Willebrand factor was significantly increased at 48 h after a single gamma-radiation dose of 20 Gy in both the luminal and abluminal direction by 23 (P < 0.05) and 41% (P < 0.02), respectively. To establish whether the enhanced production of von Willebrand factor affected the thrombogenicity of the extracellular matrix, platelet adhesion to the matrix produced by a monolayer of cultured endothelial cells during 48 h after irradiation was analyzed in a perfusion chamber at high shear rate (1300 s-1). Platelet adhesion was significantly increased by irradiation both in the presence and in the absence of plasmatic von Willebrand factor by 65 (P < 0.05) and 34.5% (P < 0.005), respectively. Incubation of the perfusate with a monoclonal antibody that blocks the binding of von Willebrand factor to platelet GPIb (CLB-RAg 35) resulted in an almost complete inhibition of platelet adhesion. These data indicate that radiation enhances platelet adhesion to the the extracellular matrix by an increase in the release of von Willebrand factor by endothelial cells. This event may be important in early radiation-induced vascular pathology.

Radiat Res 1994 Feb;137(2):202-207

Targeted cytoplasmic irradiation with alpha particles induces mutations in mammalian cells.

Ever since x-rays were shown to induce mutation in Drosophila more than 70 years ago, prevailing dogma considered the genotoxic effects of ionizing radiation, such as mutations and carcinogenesis, as being due mostly to direct damage to the nucleus. Although there was indication that alpha particle traversal through cellular cytoplasm was innocuous, the full impact remained unknown. The availability of the microbeam at the Radiological Research Accelerator Facility of Columbia University made it possible to target and irradiate the cytoplasm of individual cells in a highly localized spatial region. By using dual fluorochrome dyes (Hoechst and Nile Red) to locate nucleus and cellular cytoplasm, respectively, thereby avoiding inadvertent traversal of nuclei, we show here that cytoplasmic irradiation is mutagenic at the CD59 (S1) locus of human-hamster hybrid (AL) cells, while inflicting minimal cytotoxicity. The principal class of mutations induced are similar to those of spontaneous origin and are entirely different from those of nuclear irradiation. Furthermore, experiments with radical scavenger and inhibitor of intracellular glutathione indicated that the mutagenicity of cytoplasmic irradiation depends on generation of reactive oxygen species. These findings suggest that cytoplasm is an important target for genotoxic effects of ionizing radiation, particularly radon, the second leading cause of lung cancer in the United States. In addition, cytoplasmic traversal by alpha particles may be more dangerous than nuclear traversal, because the mutagenicity is accomplished by little or no killing of the target cells.

Proc Natl Acad Sci U S A 1999 Apr 27;96(9):4959-4964

Mutagenic effects of a single and an exact number of alpha particles in mammalian cells.

One of the main uncertainties in risk estimation for environmental radon exposure using lung cancer data from underground miners is the extrapolation from high- to low-dose exposure where multiple traversal is extremely rare. The biological effects of a single alpha particle are currently unknown. Using the recently available microbeam source at the Radiological Research Accelerator Facility at Columbia University, we examined the frequencies and molecular spectrum of S1- mutants induced in human-hamster hybrid (A(L)) cells by either a single or an exact number of alpha particles. Exponentially growing cells were stained briefly with a nontoxic concentration of Hoechst dye for image analysis, and the location of individual cells was computer-monitored. The nucleus of each cell was irradiated with either 1,2,4 or 8 alpha particles at a linear energy transfer of 90 keV/microm consistent with the energy spectrum of domestic radon exposure. Although single-particle traversal was only slightly cytotoxic to A(L) cells (survival fraction approximately 0.82), it was highly mutagenic, and the induced mutant fraction averaged 110 mutants per 10(5) survivors. In addition, both toxicity and mutant induction were dose-dependent. Multiplex PCR analysis of mutant DNA showed that the proportion of mutants with multilocus deletions increased with the number of particle traversals. These data provide direct evidence that a single a particle traversing a nucleus will have a high probability of resulting in a mutation and highlight the need for radiation protection at low doses.

Proc Natl Acad Sci U S A 1997 Apr 15;94(8):3765-3770

Direct evidence for the participation of gap junction-mediated intercellular communication in the transmission of damage signals from alpha-particle irradiated to nonirradiated cells.

It has generally been considered that important biological effects of ionizing radiation arise as a direct consequence of DNA damage occurring in irradiated cells. We have examined this hypothesis by exposing cells to very low fluences of alpha-particles, similar to those emitted by radon gas, such that as few as 1% of the cells in a population are traversed by a particle and thus receive any radiation exposure. By using the endpoints of changes in gene expression and induction of DNA damage, we show that nonirradiated “bystander” cells participate in the overall response of confluent density-inhibited populations of cultured fibroblast and epithelial cells. By in situ immunofluorescence techniques and the use of cells genetically compromised in their ability to perform gap junction intercellular communication, we present direct evidence for the involvement of connexin43-mediated intercellular communication in the transmission of damage signals to nonirradiated cells. Induction of the stress-inducible p21(Waf1) protein in aggregates of neighboring cells far exceeding the fraction of cells whose nucleus has been traversed occurred in gap junction-competent cells only. These changes in p21(Waf1) expression correlated with both the induction of DNA damage (as measured by micronucleus formation) as well as increased Ser-15 phosphorylation of p53.

Proc Natl Acad Sci U S A 2001 Jan 16;98(2):473-478

Differential radiation response of cultured endothelial cells and smooth myocytes.

In vivo observations have suggested that endothelial cells are the most radiosensitive elements of the vascular wall. To test whether this represents an intrinsic differential sensitivity, the response of bovine aortic endothelial cells and smooth myocytes was investigated in confluent cell cultures exposed to single doses of gamma radiation (250, 500, 1,000 or 2,000 rad). Both cell types showed a dose-dependent decrease in attachment efficiency when dissociated and replated at six hours after radiation. However, the attachment efficiency in both cell types was similar when a 72-hour postirradiation incubation period was used prior to dissociation of the cells. Growth inhibition was significantly greater (7- to 10-fold) in endothelial cells than in myocytes when examined four days after attachment. Confluent endothelial monolayers showed a dose-dependent, progressive cell loss during the 72-hour postirradiation period (70% after 1,000 rad); the myocyte cultures showed no radiation effect on the cell numbers. In spite of the reduction in number, the endothelial cells maintained the continuity of their monolayer by compensation with an increase in mean cell size. Endothelial cells developed multiple structural lesions, including an increase in the number and size of residual and lysosomal bodies, electron-lucent cytoplasmic defects, interruptions in the plasma membrane and irregular aggregation of chromatin, causing electron-lucent nuclei. These changes increased in severity with time and dose and were most pronounced 24 to 72 hours after 1,000 rad. No significant ultrastructural alterations were detected in myocytes four days after 2,000 rad.

Anal Quant Cytol 1982 Sep;4(3):188-198

Incidence of female breast cancer among atomic bomb survivors, 1950 to 1985.

An incidence survey among atomic bomb survivors identified 807 breast cancer cases, and 20 second breast cancers. As in earlier surveys of the Life Span Study population, a strongly linear radiation dose response was found, with the highest dose-specific excess relative risk (ERR) among survivors under 20 years old at the time of the bombings. Sixty-eight of the cases were under 10 years old at exposure, strengthening earlier reports of a marked excess risk associated with exposure during infancy and childhood. A much lower, but marginally significant, dose response was seen among women exposed at 40 years and older. It was not possible, however, to discriminate statistically between age at exposure and age at observation for risk as the more important determinant of ERR per unit dose. A 13-fold ERR at 1 Sv was found for breast cancer occurring before age 35, compared to a 2-fold excess after age 35, among survivors exposed before age 20. This a posteriori finding, based on 27 exposed, known-dose, early-onset cases, suggests the possible existence of a susceptible genetic subgroup. Further studies, involving family histories of cancer and investigations at the molecular level, are suggested to determine whether such a subgroup exists.

Radiat Res 1994 May;138(2):209-223

Endothelial alkaline phosphatase activity loss as an early stage in the development of radiation-induced heart disease in rats.

Alkaline phosphatase activity of capillary endothelial cells in the heart of Wistar and Sprague-Dawley rats was studied sequentially after single doses of 10, 15, 20 or 25 Gy. Following irradiation capillary density and alkaline phosphatase activity were focally lost before myocardial degeneration or clinical symptoms of heart disease developed. Recovery from both changes took place after doses of 10 or 15 Gy. The decrease in capillary density and enzyme activity showed the same strain difference in latency times and in the extent of the lesions as previously described for pathological and clinical signs of heart disease.

Radiat Res 1987 Apr;110(1):118-128

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