**Author details**

The absence of increase in the frequency of apoptosis after treatment in other terms of cultivation both under the influence of only ionizing radiation and under the combined action of γ-radiation and astaxanthin can be explained by either insufficient time for realization of apoptosis or existence of contingent on the stage of the cell cycle apoptotic pathways, which

Since the increase in the level of apoptosis is not a reason for the decline of the pool of high damaged cells under the astaxanthin influence after irradiation at 40 and 46 h of cultivation,

It is generally accepted that reactive oxygen species, which are formed by ionizing radiation exposure, cause DNA breaks [40]. Astaxanthin is a power antioxidant and capable to scavenge and quench free radicals and ipso facto to reduce the overall level of DNA damages [3]. According to the data presented in **Figure 7**, the results obtained after irradiation of cells at 46 h of cultivation can be explained by the antioxidant properties of astaxanthin: reducing of oxidative stress leads to a decrease in the number of "comets" of the ten groups and increasing (although not always statistically significant) in the frequencies of cells belonging to other

However, such impact of astaxanthin was not observed when cells were irradiated at 40 h of cultivation. It is noteworthy that in this experiment the increase in the frequency of the "comets" of group 1 (from 11.18 ± 1.46 to 17.54 ± 1.62%, p < 0.01) was detected. It can be explained by the fact that this group may include cells having a sufficiently large number of lesions enough to trigger mechanisms for the cell cycle arrest on the S phase. Probably, astaxanthin activates


data concerning the effects of astaxanthin on the proliferation of tumor cells [7, 17, 41].

The obtained results enable us to resume the following astaxanthin effects on irradiated cells that may be clearly observed depending on the phase of the cell cycle and the duration of cells

**1.** Stimulation of apoptosis in the irradiated cells resulting in a decrease in the level of cells

**2.** Stimulation of the processes that lead to the activation of the checkpoints on the S phase and, accordingly, arrest the division of the most damaged cell population (irradiation on

**3.** Scavenge of reactive oxygen species resulting in reduction in the total level of DNA breaks

phase of the cell cycle and cultivation after irradiation for 2 h)

phase of the cell cycle and

with a large number of DNA damages (irradiation on the G<sup>0</sup>

the S phase of the cell cycle and cultivation after irradiation for 8 h)

astaxanthin is unable to activate on the S and G<sup>2</sup> phases of the cell cycle.

the question remains: what is the cause of such effect of astaxanthin?

groups (except 3 and 9).

134 Progress in Carotenoid Research

S-/G<sup>2</sup>

**4. Conclusion**

cultivation after irradiation:

(irradiation on the G<sup>2</sup>

cultivation after irradiation for 48 h)

Denys Кurinnyi<sup>1</sup> \*, Stanislav Rushkovsky<sup>2</sup> , Olena Demchenko<sup>1</sup> and Mariya Pilinska<sup>1</sup>

\*Address all correspondence to: kurinnyi.d@gmail.com

1 State Institution "National Research Center for Radiation Medicine of the National Academy of Medical Sciences of Ukraine", Kyiv, Ukraine

2 Educational and Research Center "Institute of Biology and Medicine" Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
