Effect of 5-[125I]iodo-2′-deoxyuridine uptake on the proliferation and pluripotency of human embryonic stem cells

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Abstract
Purpose: Human embryonic stem cells (hESC) hold a great potential for regenerative medicine because, in principle, they can differentiate into any cell type found in the human body. In addition, studying the effect of ionizing radiation (IR) on hESC may provide valuable information about the response of human cells to IR exposure in their most naive state, as well as the consequences of IR exposure on the development of organisms. However, the effect of IR, in particular radionuclide uptake, on the pluripotency, proliferation and survival of hESC has not been extensively studied. Methods: In this study we treated cultured hESC with 5-[125I]iodo-2′-deoxyuridine (125IdU), a precursor of DNA synthesis. Then we measured the expansion of colonies and expression of pluripotency markers in hESC. Results: We found that uptake of 125IdU was similar in both hESC and HT1080 human fibrosarcoma cells. However, treatment with 0.1 μCi/ml 125IdU for 24 hours resulted in complete death of the hESC population; whereas HT1080 cancer cells continued to grow. Treatment with a 10-fold lower dose 125IdU (0.01 μCi/ml) resulted in colonies of hESC becoming less defined with numerous cells growing in monolayer outside of the colonies showing signs of differentiation. Then we analyzed the expression of pluripotency markers (octamer-binding transcription factor 4 [Oct-4] and stage-specific embryonic antigen-4 [SSEA4]) in the surviving hESC. We found that hESC in the surviving colonies expressed pluripotency markers at levels comparable with those in the non-treated controls. Conclusions: Our results provide important initial insights into the sensitivity of hESC to IR, and especially that produced by the decay of an internalized radionuclide.

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