Gamma-irradiation produces active chlorine species (ACS) in physiological solutions: Secoisolariciresinol diglucoside (SDG) scavenges ACS - A novel mechanism of DNA radioprotection.
Secoisolariciresinol diglucoside (SDG), the main lignan in whole grain flaxseed, is a potent antioxidant and free radical scavenger with known radioprotective properties. However, the exact mechanism of SDG radioprotection is not well understood. The current study identified a novel mechanism of DNA radioprotection by SDG in physiological solutions by scavenging active chlorine species (ACS) and reducing chlorinated nucleobases.



The ACS scavenging activity of SDG was determined using two highly specific fluoroprobes: hypochlorite-specific 3'-(p-aminophenyl) fluorescein (APF) and hydroxyl radical-sensitive 3'-(p-hydroxyphenyl) fluorescein (HPF). Dopamine, an SDG structural analog, was used for proton (1)H NMR studies to trap primary ACS radicals. Taurine N-chlorination was determined to demonstrate radiation-induced generation of hypochlorite, a secondary ACS. DNA protection was assessed by determining the extent of DNA fragmentation and plasmid DNA relaxation following exposure to ClO(-) and radiation. Purine base chlorination by ClO(-) and γ-radiation was determined by using 2-aminopurine (2-AP), a fluorescent analog of 6-aminopurine.



Chloride anions (Cl(-)) consumed >90% of hydroxyl radicals in physiological solutions produced by γ-radiation resulting in ACS formation, which was detected by (1)H NMR. Importantly, SDG scavenged hypochlorite- and γ-radiation-induced ACS. In addition, SDG blunted ACS-induced fragmentation of calf thymus DNA and plasmid DNA relaxation. SDG treatment before or after ACS exposure decreased the ClO(-) or γ-radiation-induced chlorination of 2-AP. Exposure to γ-radiation resulted in increased taurine chlorination, indicative of ClO(-) generation. NMR studies revealed formation of primary ACS radicals (chlorine atoms (Cl) and dichloro radical anions (Cl2¯)), which were trapped by SDG and its structural analog dopamine.



We demonstrate that γ-radiation induces the generation of ACS in physiological solutions. SDG treatment scavenged ACS and prevented ACS-induced DNA damage and chlorination of 2-aminopurine. This study identified a novel and unique mechanism of SDG radioprotection, through ACS scavenging, and supports the potential usefulness of SDG as a radioprotector and mitigator for radiation exposure as part of cancer therapy or accidental exposure.
Department of Medicine, Pulmonary, Allergy and Critical Care Division, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, United States. Electronic address: mishra.o@gmail.com.
Om P
OP
Mishra
Department of Radiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, United States. Electronic address: avpopov@mail.med.upenn.edu.
Anatoliy V
AV
Popov
Department of Medicine, Pulmonary, Allergy and Critical Care Division, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, United States. Electronic address: ralphp@mail.med.upenn.edu.
Ralph A
RA
Pietrofesa
Department of Medicine, Pulmonary, Allergy and Critical Care Division, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, United States. Electronic address: melpo@mail.med.upenn.edu.
Melpo
M
Christofidou-Solomidou
D015075:2-Aminopurine / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002072:Butylene Glycols / Q000494:pharmacology*; D002417:Cattle; D002713:Chlorine / Q000378:metabolism*; D004247:DNA / Q000187:drug effects*; D053938:DNA Fragmentation / Q000187:drug effects; D019597:Flax / Q000737:chemistry; D016166:Free Radical Scavengers / Q000494:pharmacology*; D005720:Gamma Rays / Q000009:adverse effects*; D005960:Glucosides / Q000494:pharmacology*; D017665:Hydroxyl Radical / Q000378:metabolism; D017705:Lignans / Q000494:pharmacology; D015227:Lipid Peroxidation / Q000187:drug effects; D010957:Plasmids / Q000235:genetics; D011837:Radiation-Protective Agents / Q000494:pharmacology*
D000975:Antioxidants; D002072:Butylene Glycols; D016166:Free Radical Scavengers; D005960:Glucosides; D017705:Lignans; D011837:Radiation-Protective Agents; D017665:Hydroxyl Radical; D015075:2-Aminopurine; D002713:Chlorine; D004247:DNA; C427203:calf thymus DNA; C090142:secoisolariciresinol diglucoside
2-Aminopurine; Active chlorine species; Chlorine atoms; DNA fragmentation; Dichloro radical anion; Hydroxyl radical; Hypochlorite ion; Mitigation; Radicals; Radioprotection; Secoisolariciresinol diglucoside; Taurine chloramine; γ-Radiation