Sunday, October 16, 2005 3:00 PM-5:00 PM Exhibit Hall

(PP075) Modification of radiation-induced bystander effect with melanin.

Marozik, Pavel*,1, 2, Mosse, Irma2, Seymour, Colin3, Mothersill, Carmel3, 1 Radiation and Environmental Science Centre, Dublin, Dublin, Ireland2 Laboratory of Radiation Genetics, Minsk, Minsk, Belarus3 Science, Hamilton, Ontario, Canada

ABSTRACT- Radiation-induced bystander effect (RIBE) describes biological consequences in surrounding cells not directly targeted by radiation. Over the last decade, there has been an increase of interest in studying this phenomenon. Huge advances have been made in this area, although the specific nature of the factor and the mechanism of RIBE have yet to be elucidated. In our research, we studied possible ways to decrease the effects of bystander factor influence on non-irradiated cells. For this purpose, we used a radioprotective substance, melanin, known as a photoprotective pigment and antioxidant. Melanin, a natural non-toxic substance, was shown to be effective protector against genetic consequences of acute and chronic radiation and it exerts its protective action at the initial stage of irradiation, preventing DNA damages. In our research we used the HPV-G-cell line (which are human keratinocytes immortalized by the transfection with the HPV-virus, rendering the cells p53 null). Donor cells were irradiated using 60Cobalt teletherapy source, their medium containing bystander factor was removed, filtered and transferred to unirradiated (bystander recipient) cells. The results show that the addition of melanin to the bystander recipient cells medium increased the colony forming ability of the cells compared with the ones without melanin. The addition of melanin to bystander donor medium before transfer to recipients lead to the same result, thus proving that melanin decreases not the direct irradiation effect, but the bystander donor medium effect. It was also shown that melanin is not present in the filtered bystander medium. Possibly, melanin has a double effect: neutralization of free radicals during irradiation and neutralization of secondary biochemical processes, connected with formation of free radicals. It is well known that melanin is able to catch all type physical energy. That is why it is possible to conclude that RIBE signal has physical nature or physical component.

Key words: bystander effect, melanin, radioprotection

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2005 RRS