title: Effect of Photon Hormesis on Dose Responses to Alpha Particles in Zebrafish Embryos.
abstract: Photon hormesis refers to the phenomenon where the biological effect of ionizing radiation with a high linear energy transfer (LET) value is diminished by photons with a low LET value. The present paper studied the effect of photon hormesis from X-rays on dose responses to alpha particles using embryos of the zebrafish (Danio rerio) as the in vivo vertebrate model. The toxicity of these ionizing radiations in the zebrafish embryos was assessed using the apoptotic counts at 20, 24, or 30 h post fertilization (hpf) revealed through acridine orange (AO) staining. For alpha-particle doses ≥ 4.4 mGy, the additional X-ray dose of 10 mGy significantly reduced the number of apoptotic cells at 24 hpf, which proved the presence of photon hormesis. Smaller alpha-particle doses might not have inflicted sufficient aggregate damages to trigger photon hormesis. The time gapTbetween the X-ray (10 mGy) and alpha-particle (4.4 mGy) exposures was also studied. Photon hormesis was present whenT≤ 30 min, but was absent whenT= 60 min, at which time repair of damage induced by alpha particles would have completed to prevent their interactions with those induced by X-rays. Finally, the drop in the apoptotic counts at 24 hpf due to photon hormesis was explained by bringing the apoptotic events earlier to 20 hpf, which strongly supported the removal of aberrant cells through apoptosis as an underlying mechanism for photon hormesis.
authors.affiliation: Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China. yuenpng3-c@my.cityu.edu.hk.
authors.forename: Candy Yuen Ping
authors.initials: CY
authors.lastname: Ng
authors.affiliation: Department of Biomedical Sciences, City University of Hong Kong, Hong Kong, China. bhcheng@cityu.edu.hk.|State Key Laboratory in Marine Pollution, City University of Hong Kong, Hong Kong, China. bhcheng@cityu.edu.hk.
authors.forename: Shuk Han
authors.initials: SH
authors.lastname: Cheng
authors.affiliation: Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China. peter.yu@cityu.edu.hk.|State Key Laboratory in Marine Pollution, City University of Hong Kong, Hong Kong, China. peter.yu@cityu.edu.hk.
authors.forename: Kwan Ngok
authors.initials: KN
authors.lastname: Yu
mesh_terms: D000512:Alpha Particles; D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D004625:Embryo, Nonmammalian / Q000528:radiation effects*; D059165:Hormesis; D017785:Photons; D011829:Radiation Dosage; D011839:Radiation, Ionizing; D014965:X-Rays; D015027:Zebrafish
keywords: ionizing radiation; photon hormesis; zebrafish embryos