Dose-Response: An International Journal: Volume 6, Issue 1
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2008-31-03
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Dose-Response Vol 6, no 1, Table of Contents
(2008-03-01)
HORMESIS [BIOLOGICAL EFFECTS OF LOW LEVEL EXPOSURES (BELLE)] AND DERMATOLOGY
(2008-03-01) Thong, Haw-Yueh; Maibach, Howard I
Hormesis, or biological effects of low level exposures (BELLE), is characterized by nonmonotonic dose response which is biphasic, displaying opposite effects at low and high dose. Its occurrence has been documented across a broad range of biological models and diverse type of exposure. Since hormesis appears to be a relatively common phenomenon in many areas, the objective of this review is to explore its occurrence related to dermatology and its public health and risk assessment implication. Hormesis appears to be a common phenomenon in in-vitro skin biology. However, in vivo data are lacking and the clinical relevance of hormesis has yet to be determined. Better understanding of this phenomenon will likely lead to different strategies for risk assessment process employed in the fields of dermatologic toxicology and pharmacology. We believe that hormesis is a common phenomenon and should be given detailed consideration to its concept and its risk assessment implications, and how these may be incorporated into the experimental and regulatory processes in dermatology. The skin, with its unique characteristics, its accessibility, and the availability of non-invasive bioengineering and DNA microarray technology, will be a good candidate to extend the biology of hormesis.
EFFECTS OF SPECIFIC DOSAGES OF MAGNESIUM AND ZINC ON THE TERATOGENICITY OF CADMIUM, NICKEL, AND COBALT IN XENOPUS EMBRYOS, AS ASSESSED BY THE FETAX TEST
(2008-03-01) Boga, Ayper; Erdogan, Seref; Sertdemir, Yasar
The objective of this study was to determine if exposure to divalent cations, Cd2+, Ni2+, and Co2+ would lead to malformations in Xenopus laevis embryos, and whether addition of Mg2+and Zn2+; separately and in combination, would reduce their toxicity and teratogenicity on the embryos of Xenopus laevis as assessed by 96-h FETAX tests. Results indicate that exposure to Cd2+, Ni2+ or Co2+ lead to an increase in toxicity and teratogenicity in embryos, whereas Mg2+, Zn2+, or a combination of them reduced the toxic and teratogenic effects of these divalent cations. Modulation of Cd2+, Ni2+ or Co2+ toxicity and teratogenicity by Mg2+ and Zn2+, varied with the metal. Zn2+ was observed to be a better suppressor of Co2+ toxicity and teratogenicity than Mg2+. In contrast, Ni2+, and Cd2+ teratogenicity was reduced more prominently by Mg2+. On the other hand, combination of Mg2+ and Zn2+ showed potentialization effect on all divalent cation toxicity and teratogenicity. We concluded that Mg2+ and Zn2+ reduced the toxicity and teratogenicity of Cd2+, Ni2+, Co2+.
NON-PROBLEMATIC RISKS FROM LOW-DOSE RADIATION-INDUCED DNA DAMAGE CLUSTERS
(2008-03-01) Hayes, Daniel P
Radiation-induced DNA damage clusters have been proposed and are usually considered to pose the threat of serious biological damage. This has been attributed to DNA repair debilitation or cessation arising from the complexity of cluster damage. It will be shown here, contrary to both previous suggestions and perceived wisdom, that radiation induced damage clusters contribute to non-problematic risks in the low-dose, low-LET regime. The very complexity of cluster damage which inhibits and/or compromises DNA repair will ultimately be responsible for the elimination and/or diminution of precancerous and cancerous cells.
SMOKING AND HORMESIS AS CONFOUNDING FACTORS IN RADIATION PULMONARY CARCINOGENESIS
(2008-03-01) Sanders, Charles L.; Scott, Bobby R
Confounding factors in radiation pulmonary carcinogenesis are passive and active cigarette smoke exposures and radiation hormesis. Significantly increased lung cancer risk from ionizing radiation at lung doses < 1 Gy is not observed in never smokers exposed to ionizing radiations. Residential radon is not a cause of lung cancer in never smokers and may protect against lung cancer in smokers. The risk of lung cancer found in many epidemiological studies was less than the expected risk (hormetic effect) for nuclear weapons and power plant workers, shipyard workers, fluoroscopy patients, and inhabitants of highdose background radiation. The protective effect was noted for low- and mixed high- and low-linear energy transfer (LET) radiations in both genders. Many studies showed a protection factor (PROFAC) > 0.40 (40% avoided) against the occurrence of lung cancer. The ubiquitous nature of the radiation hormesis response in cellular, animal, and epidemiological studies negates the healthy worker effect as an explanation for radiation hormesis. Low-dose radiation may stimulate DNA repair/apoptosis and immunity to suppress and eliminate cigarette-smoke-induced transformed cells in the lung, reducing lung cancer occurrence in smokers.