Transition in Survival From Low-Dose Hyper-Radiosensitivity to Increased Radioresistance Is Independent of Activation of ATM SER1981 Activity

AbstractAt high doses, the current recommended radiation weighting factors advise a significantly higher effectiveness of alpha particles relative to gamma radiation. However, at lower doses, the ratio of effectiveness between radiations of varying linear energy transfer values is complicated due to the relative importance of low dose phenomena such as genomic instability, bystander effects, low dose hyper-radiosensitivity and increased radioresistance (HRS/IRR). Radium is the most common source of alpha radiation exposure to humans, but the dosimetry is complicated by the decay chain which involves gamma exposure due to radon daughters. This study aimed to isolate the relative biological effect of alpha particles after low doses of radium to cells and their progeny. This was done by subtracting the survival values of a human keratinocyte cell line (HaCaT) and an embryonic Chinook salmon cell line (CHSE-214) exposed to gamma irradiation, from survival of the same cell lines exposed to mixed alpha and gamma radiation through chronic exposure to Ra-226 and its decay products. The human cell line showed increased radioresistance when exposed to low doses of alpha particles. In contrast the fish cell line, which demonstrated radioresistance to low dose gamma energy, demonstrated increased lethality when exposed to low doses of alpha particles. The results confirm the need to consider the dose-response relationship when developing radiation weighting factors for low dose exposures, as well as the need to be aware of possible cell line and species differences.

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Ovarian Dysfunction in Fetally Irradiated Beagles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100080717 ◽

1977 ◽

Vol 35 ◽

pp. 658-659

Author(s):

T. M. Seed ◽

M. H. Sanderson ◽

D. L. Gutzeit ◽

T. E. Fritz ◽

D. V. Tolle ◽

...

Keyword(s):

Gamma Rays ◽

Low Dose ◽

Long Term Effects ◽

Ovarian Dysfunction ◽

Dose Rates ◽

Highly Sensitive ◽

Microscopic Evaluation ◽

Ovarian Pathology ◽

Normal Offspring

The developing mammalian fetus is thought to be highly sensitive to ionizing radiation. However, dose, dose-rate relationships are not well established, especially the long term effects of protracted, low-dose exposure. A previous report (1) has indicated that bred beagle bitches exposed to daily doses of 5 to 35 R 60Co gamma rays throughout gestation can produce viable, seemingly normal offspring. Puppies irradiated in utero are distinguishable from controls only by their smaller size, dental abnormalities, and, in adulthood, by their inability to bear young.We report here our preliminary microscopic evaluation of ovarian pathology in young pups continuously irradiated throughout gestation at daily (22 h/day) dose rates of either 0.4, 1.0, 2.5, or 5.0 R/day of gamma rays from an attenuated 60Co source. Pups from non-irradiated bitches served as controls. Experimental animals were evaluated clinically and hematologically (control + 5.0 R/day pups) at regular intervals.

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High Resolution Microscopy of Multi-Layered Biological Crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010005319x ◽

1982 ◽

Vol 40 ◽

pp. 80-83

Author(s):

H.A. Cohen ◽

T.W. Jeng ◽

W. Chiu

Keyword(s):

High Resolution ◽

Low Dose ◽

Three Dimensional ◽

Data Interpretation ◽

Two Dimensional ◽

Biological Objects ◽

Density Maps ◽

Density Map ◽

Complex Crystal ◽

High Resolution Microscopy

This tutorial will discuss the methodology of low dose electron diffraction and imaging of crystalline biological objects, the problems of data interpretation for two-dimensional projected density maps of glucose embedded protein crystals, the factors to be considered in combining tilt data from three-dimensional crystals, and finally, the prospects of achieving a high resolution three-dimensional density map of a biological crystal. This methodology will be illustrated using two proteins under investigation in our laboratory, the T4 DNA helix destabilizing protein gp32*I and the crotoxin complex crystal.

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