The response of mouse embryonic stem cells to low doses of γ-radiation: Evidence for an adaptive response

DNA double-strand break repair and adaptive responses of low-dose radiation in normal and tumor lung cell lines

The adaptive response (AR), which can be induced by low-dose ionizing radiation (LD), may influence the therapeutic ratio of cancer treatment. We investigated the AR and the DNA double-strand break (DSB) repair pathway in human lung tumor cells and normal cells. We measured viability and proliferation of normal lung cells (MRC-5) and lung cancer cells (QU-DB) using the MTT and colony formation assays. Flow cytometric analysis of γ-H2AX was used to measure DNA-DSBs induction, repair, and residual damages. AR was seen in the normal cells but not in the cancer cells. Our findings suggest that LD stimulates DSB repair and that this may contribute to distinctive AR in normal vs. cancer cells.

Hormesis and embryonic stem cells

This paper provides an identification and detailed assessment of hormetic dose responses of embryonic stem cells (ESCs) with particular emphasis on cell renewal (proliferation) and differentiation, underlying mechanistic foundations and potential therapeutic implications. Hormetic dose responses were commonly reported, being induced by a broad range of chemicals, including pharmaceuticals (e.g., atorvastatin, isoproterenol, lithium, nicotine, ouabain), dietary supplements (e.g., curcumin, multiple ginsenosides, resveratrol), endogenous agents (e.g., estrogen, hydrogen peroxide, melatonin), and physical stressor agents (e.g., hypoxia, ionizing radiation). ESC-hormetic dose responses are similar for other stem cell types (e.g., adipose-derived stem cells, apical papilla, bone marrow stem cells, dental pulp stem cells, endothelial stem cells, muscle stem cells, periodontal ligament stem cells, neural stem cells), indicating a high degree of generality for the hormetic-stem cells response. The widespread occurrence of hormetic dose responses shown by ESCs and other stem cells suggests that the hormetic dose response may represent a fundamental and highly conserved evolutionary strategy.

Low-dose ionizing irradiation triggers apoptosis of undifferentiated spermatogonia in vivo and in vitro

Background

The present study aimed to investigate the mechanism of low-dose ionizing radiation (IR) induced apoptosis of undifferentiated spermatogonia in vivo and in vitro.

Methods

Following 50 mGy IR, testicular tissues were collected from the adult DBA/2 mice at 1, 2 and 24 h; mice in the control group received pseudo-irradiation. Immunofluorescence (IF) staining and TUNEL were performed to assess DNA damage and apoptosis, respectively, in the irradiated testicular tissues. Furthermore, the spermatogonia were also irradiated in vitro, and the expression of apoptosis-related proteins was detected by Western blotting. TUNEL and flow cytometry were applied to assess cell apoptosis.

Results

γH2AX (a marker of DNA damage) was up-regulated in the seminiferous tubules at 1 and 2 h after IR, but it was reduced following the DNA repair. This was consistent with the finding that apoptosis of germline cells was present in the seminiferous tubules after IR, especially at 1 h (IF and TUNEL). Apoptosis was also present in the PLZF(+) spermatogonia, particularly at 1 h after IR. Apoptotic cells decreased with the increase in DNA repair time after IR. Moreover, the caspase-3 protein was expressed in the undifferentiated spermatogonia following IR. The expression of caspase-3, P53, Ku70 and DNA-PKcs in the cultured spermatogonia was also up-regulated following IR in vitro, but their expression decreased gradually over time after IR, which was supported by the findings from flow cytometry, and the apoptosis of spermatogonia peaked at 24 h post IR.

Conclusions

IR may induce the apoptosis of spermatogonia at early stage in vivo, but the apoptosis of spermatogonia secondary to IR occurs at a relatively later time point (24 h) in vitro mainly. The apoptosis of spermatogonia is improved over time after IR.

Cyclic-RGDyC functionalized liposomes for dual-targeting of tumor vasculature and cancer cells in glioblastoma: An in vitro boron neutron capture therapy study

The efficacy of boron neutron capture therapy depends on the selective delivery of ¹⁰B to the target. Integrins αvβ3 are transmembrane receptors over-expressed in both glioblastoma cells and its neovasculature. In this study, a novel approach to dual-target glioblastoma vasculature and tumor cells was investigated. Liposomes (124 nm) were conjugated with a αvβ3 ligand, cyclic arginine-glycine-aspartic acid-tyrosine-cysteine peptide (c(RGDyC)-LP) (1% molar ratio) through thiol-maleimide coupling. Expression of αvβ3 in glioblastoma cells (U87) and human umbilical vein endothelial cells (HUVEC), representing tumor angiogenesis, was determined using Western Blotting with other cells as references. The results showed that both U87 and HUVEC had stronger expression of αvβ3 than other cell types, and the degree of cellular uptake of c(RGDyC)-LP correlated with the αvβ3-expression levels of the cells. In contrast, control liposomes without c(RGDyC) showed little cellular uptake, regardless of cell type. In an in vitro boron neutron capture therapy study, the c(RGDyC)-LP containing sodium borocaptate generated more rapid and significant lethal effects to both U87 and HUVEC than the control liposomes and drug solution. Interestingly, neutron irradiated U87 and HUVEC showed different types of subsequent cell death. In conclusion, this study has demonstrated the potential of a new dual-targeting strategy using c(RGDyC)-LP to improve boron neutron capture therapy for glioblastoma.

The paradox of adaptive responses and iso-effect per fraction

PURPOSE

Despite decades of research into radiation-induced adaptive responses, where prior irradiation changes the response to subsequent irradiations, the field of radiation oncology relies upon models of tumor control that assume that each radiation therapy fraction reproduces the same effect, known as iso-effect per fraction. Can these radiobiology principles both be true, forming a paradox or is only one of them right? Here, the apparent coexistence of these two contradictory observations is considered, examining how adaptive responses might apply in radiotherapy scenarios that are inconsistent with the majority of adaptive response experimental designs.

CONCLUSION

While the iso-effect per fraction assumption would preclude the observation of adaptive responses for cells survival after radiotherapy fractions, this does not preclude the observation of adaptive responses for other endpoints. Adaptive responses for cell survival might also manifest without invalidating the iso-effect principle in practical terms. It may also be the case that instances of both phenomena can be observed under different conditions, but not at the same time.

Ionizing radiation-induced adaptive response in fibroblasts under both monolayer and 3-dimensional conditions

To observe the adaptive response (AR) induced by ionizing radiation in human fibroblasts under monolayer and 3-dimensional (3-D) condition. Three kinds of fibroblasts were cultured under both monolayer and 3-D condition. Immunofluorescent staining was used to detect the γ-H2AX foci and the morphological texture. Trypan blue staining was used to detect the cell death. Western blot was used to detect the expressions of γ-H2AX, p53 and CDKN1A/p21 (p21). We found that DNA damage increased in a dose-dependent and time-dependent manner after high doses of radiation. When cells were pretreated with a priming low dose of radiation followed by high dose radiation, DNA damage was attenuated under both monolayer and 3-D condition, and the adaptive response (AR) was induced. Additionally, the morphology of cells under monolayer and 3-D conditions were different, and radiation also induced AR according to morphological texture analysis. Priming low dose radiation induced AR both under monolayer and 3-D condition. Interestingly, 3-D microenvironment made cells more sensitive to radiation. The expression of p53 and p21 was changed and indicated that they might participate in the regulation of AR.