Processing of abasic DNA clusters in hApeI-silenced primary fibroblasts exposed to low doses of X-irradiation.

Clustered damage in DNA includes two or more closely spaced oxidized bases, strand breaks or abasic sites that are induced by high- or low-linear-energy-transfer (LET) radiation, and these have been found to be repair-resistant and potentially mutagenic. In the present study we found that abasic clustered damages are also induced in primary human fibroblast cells by low-LET X-rays even at very low doses. In response to the induction of the abasic sites, primary fibroblasts irradiated by low doses of X-rays in the range 10–100 cGy showed dose-dependent up-regulation of the DNA repair enzyme, ApeI. We found that the abasic clusters in primary fibroblasts were more lethal to cells when hApeI enzyme expression was down-regulated by transfecting primary fibroblasts with hApeI siRNA as determined by clonogenic survival assay. Endonuclease activity of hApeI was found to be directly proportional to hApeI gene-silencing efficiency. The DNA repair profile showed that processing of abasic clusters was delayed in hApeI-siRNA-silenced fibroblasts, which challenges the survival of the cells even at very low doses of X-rays. Thus, the present study is the first to attempt to understand the induction of cluster DNA damage at very low doses of low- LET radiation in primary human fibroblasts and their processing by DNA repair enzyme ApeI and their relation with the survival of the cells.

ETM study of electroporation influence on cell morphology in human malignant melanoma and human primary gingival fibroblast cells

Objective:To estimate electroporation (EP) influence on malignant and normal cells.Methods:Two cell lines including human malignant melanoma (Me-45) and normal human gingival fibroblast (HGFs) were used. EP parameters were the following:250,1000,1750,2500 V/cm;50 μs by5 impulses for every case. The viability of cells after EP was estimated byMTT assay. The ultrastructural analysis was observed by transmission electron microscope (ZeissEM900). Results:In the current study we observed the intracellular effect followingEP on Me-45 and HGF cells. At the conditions applied, we did not observe any significant damage of mitochondrial activity in both cell lines treated byEP. Conversely, we showed thatEP in some conditions can stimulate cells to proliferation. Some changes induced byEP were only visible in electron microscopy. In fibroblast cells we observed significant changes in lower parameters ofEP (250 and1000 V/cm). After applying higher electric field intensities (2500 V/cm) we detected many vacuoles, myelin-like bodies and swallowed endoplasmic reticulum. In melanoma cells such strong pathological modifications afterEP were not observed, in comparison with control cells. The ultrastructure of both treated cell lines was changed according to the applied parameters ofEP.Conclusions:We can claim thatEP conditions are cell line dependent. In terms of the intracellular morphology, human fibroblasts are more sensitive to electric field as compared with melanoma cells. Optimal conditions should be determined for each cell line. Summarizing our study, we can conclude thatEP is not an invasive method for human normal and malignant cells. This technique can be safely applied in chemotherapy for delivering drugs into tumor cells.