High and low doses of ionizing radiation induce different secretome profiles in a human skin model

Anticancer effects of phytol against Sarcoma (S-180) and Human Leukemic (HL-60) cancer cells

Phytol (Pyt), a diterpenoid, possesses many important bioactivities. This study evaluates the anticancer effects of Pyt on sarcoma 180 (S-180) and human leukemia (HL-60) cell lines. For this purpose, cells were treated with Pyt (4.72, 7.08, or 14.16 μM) and a cell viability assay was performed. Additionally, the alkaline comet assay and micronucleus test with cytokinesis were also performed using doxorubicin (6 μM) and hydrogen peroxide (10 mM) as positive controls and stressors, respectively. Results revealed that Pyt significantly reduced the viability and rate of division in S-180 and HL-60 cells with IC50 values of 18.98 ± 3.79 and 1.17 ± 0.34 μM, respectively. Pyt at 14.16 μM exerted aneugenic and/or clastogenic effects in S-180 and HL-60 cells, where the number of micronuclei and other nuclear abnormalities (e.g., nucleoplasmic bridges and nuclear buds) were frequently observed. Moreover, Pyt at all concentrations induced apoptosis and showed necrosis at 14.16 μM, suggesting its anticancer effects on the tested cancer cell lines. Taken together, Pyt showed promising anticancer effects, possibly through inducing apoptosis and necrosis mechanisms, and it exerted aneugenic and/or clastogenic effects on the S-180 and HL-60 cell lines.

Bystander signals from low- and high-dose irradiated human primary fibroblasts and keratinocytes modulate the inflammatory response of peripheral blood mononuclear cells

Irradiated cells can propagate signals to neighboring cells. Manifestations of these so-called bystander effects (BEs) are thought to be relatively more important after exposure to low- vs high-dose radiation and can be mediated via the release of secreted molecules, including inflammatory cytokines, from irradiated cells. Thus, BEs can potentially modify the inflammatory environment of irradiated cells. To determine whether these modifications could affect the functionality of bystander immune cells and their inflammatory response, we analyzed and compared the in vitro response of primary human fibroblasts and keratinocytes to low and high doses of radiation and assessed their ability to modulate the inflammatory activation of peripheral blood mononuclear cells (PBMCs). Only high-dose exposure resulted in either up- or down-regulation of selected inflammatory genes. In conditioned culture media transfer experiments, radiation-induced bystander signals elicited from irradiated fibroblasts and keratinocytes were found to modulate the transcription of inflammatory mediator genes in resting PBMCs, and after activation of PBMCs stimulated with lipopolysaccharide (LPS), a strong inflammatory agent. Radiation-induced BEs induced from skin cells can therefore act as a modifier of the inflammatory response of bystander immune cells and affect their functionality.

Radiation Type- and Dose-Specific Transcriptional Responses across Healthy and Diseased Mammalian Tissues

Ionizing radiation (IR) is a genuine genotoxic agent and a major modality in cancer treatment. IR disrupts DNA sequences and exerts mutagenic and/or cytotoxic properties that not only alter critical cellular functions but also impact tissues proximal and distal to the irradiated site. Unveiling the molecular events governing the diverse effects of IR at the cellular and organismal levels is relevant for both radiotherapy and radiation protection. Herein, we address changes in the expression of mammalian genes induced after the exposure of a wide range of tissues to various radiation types with distinct biophysical characteristics. First, we constructed a publicly available database, termed RadBioBase, which will be updated at regular intervals. RadBioBase includes comprehensive transcriptomes of mammalian cells across healthy and diseased tissues that respond to a range of radiation types and doses. Pertinent information was derived from a hybrid analysis based on stringent literature mining and transcriptomic studies. An integrative bioinformatics methodology, including functional enrichment analysis and machine learning techniques, was employed to unveil the characteristic biological pathways related to specific radiation types and their association with various diseases. We found that the effects of high linear energy transfer (LET) radiation on cell transcriptomes significantly differ from those caused by low LET and are consistent with immunomodulation, inflammation, oxidative stress responses and cell death. The transcriptome changes also depend on the dose since low doses up to 0.5 Gy are related with cytokine cascades, while higher doses with ROS metabolism. We additionally identified distinct gene signatures for different types of radiation. Overall, our data suggest that different radiation types and doses can trigger distinct trajectories of cell-intrinsic and cell-extrinsic pathways that hold promise to be manipulated toward improving radiotherapy efficiency and reducing systemic radiotoxicities.

The intercellular communications mediating radiation-induced bystander effects and their relevance to environmental, occupational, and therapeutic exposures

PURPOSE

The assumption that traversal of the cell nucleus by ionizing radiation is a prerequisite to induce genetic damage, or other important biological responses, has been challenged by studies showing that oxidative alterations extend beyond the irradiated cells and occur also in neighboring bystander cells. Cells and tissues outside the radiation field experience significant biochemical and phenotypic changes that are often similar to those observed in the irradiated cells and tissues. With relevance to the assessment of long-term health risks of occupational, environmental and clinical exposures, measurable genetic, epigenetic, and metabolic changes have been also detected in the progeny of bystander cells. How the oxidative damage spreads from the irradiated cells to their neighboring bystander cells has been under intense investigation. Following a brief summary of the trends in radiobiology leading to this paradigm shift in the field, we review key findings of bystander effects induced by low and high doses of various types of radiation that differ in their biophysical characteristics. While notable mechanistic insights continue to emerge, here the focus is on the many means of intercellular communication that mediate these effects, namely junctional channels, secreted molecules and extracellular vesicles, and immune pathways.

CONCLUSIONS

The insights gained by studying radiation bystander effects are leading to a basic understanding of the intercellular communications that occur under mild and severe oxidative stress in both normal and cancerous tissues. Understanding the mechanisms underlying these communications will likely contribute to reducing the uncertainty of predicting adverse health effects following exposure to low dose/low fluence ionizing radiation, guide novel interventions that mitigate adverse out-of-field effects, and contribute to better outcomes of radiotherapeutic treatments of cancer. In this review, we highlight novel routes of intercellular communication for investigation, and raise the rationale for reconsidering classification of bystander responses, abscopal effects, and expression of genomic instability as non-targeted effects of radiation.

The Protein Secretome Is Altered in Rectal Cancer Tissue Compared to Normal Rectal Tissue, and Alterations in the Secretome Induce Enhanced Innate Immune Responses

Locally advanced rectal cancer is treated with neoadjuvant-chemoradiotherapy; however, only ~22% of patients achieve a complete response, and resistance mechanisms are poorly understood. The role of inflammation and immune cell biology in this setting is under-investigated. In this study, we profiled the inflammatory protein secretome of normal (non-cancer) (n = 8) and malignant rectal tissue (n = 12) pre- and post-radiation in human ex vivo explant models and examined the influence of these untreated and treated secretomes on dendritic cell biology (n = 8 for cancer and normal). These resultant profiles were correlated with patient clinical characteristics. Nineteen factors were secreted at significantly higher levels from the rectal cancer secretome when compared to the normal rectal secretome; Flt-1, P1GF, IFN-γ, IL-6, IL-10, CCL20, CCL26, CCL22, CCL3, CCL4, CCL17, GM-CSF, IL-12/IL-23p40, IL-17A, IL-1α, IL-17A/F, IL-1RA, TSLP and CXCL10 (p < 0.05). Radiation was found to have differential effects on normal rectal tissue and rectal cancer tissue with increased IL-15 and CCL22 secretion following radiation from normal rectal tissue explants (p < 0.05), while no significant alterations were observed in the irradiated rectal cancer tissue. Interestingly, however, the irradiated rectal cancer secretome induced the most potent effect on dendritic cell maturation via upregulation of CD80 and PD-L1. Patient's visceral fat area correlated with secreted factors including CCL20, suggesting that obesity status may alter the tumour microenvironment (TME). These results suggest that radiation does not have a negative effect on the ability of the rectal cancer TME to induce an immune response. Understanding these responses may unveil potential therapeutic targets to enhance radiation response and mitigate normal tissue injury. Tumour irradiation in this cohort enhances innate immune responses, which may be harnessed to improve patient treatment outcome.

Human epidermal stem cells: Role in adverse skin reactions and carcinogenesis from radiation

In human skin, keratinopoiesis is based on a functional hierarchy among keratinocytes, with rare slow-cycling stem cells responsible for the long-term maintenance of the tissue through their self-renewal potential, and more differentiated daughter progenitor cells actively cycling to permit epidermal renewal and turn-over every month. Skin is a radio-responsive tissue, developing all types of radiation damage and pathologies, including early tissue reactions such as dysplasia and denudation in epidermis, and later fibrosis in the dermis and acanthosis in epidermis, with the TGF-beta 1 pathway as a known master switch. Also there is a risk of basal cell carcinoma, which arises from epidermal keratinocytes, notably after oncogenic events in PTCH1 or TP53 genes. This review will cover the mechanisms of adverse human skin reactions and carcinogenesis after various types of exposures to ionizing radiation, with comparison with animal data when necessary, and will discuss the possible role of stem cells and their progeny in the development of these disorders. The main endpoints presented are basal cell intrinsic radiosensitivity, genomic stability, individual factors of risk, dose specific responses, major molecular pathways involved and the cellular origin of skin reactions and cancer. Although major advances have been obtained in recent years, the precise implications of epidermal stem cells and their progeny in these processes are not yet fully characterized.

S-Nitrosylation in Organs of Mice Exposed to Low or High Doses of γ-Rays: The Modulating Effect of Iodine Contrast Agent at a Low Radiation Dose

The covalent addition of nitric oxide (NO^•) onto cysteine thiols, or S-nitrosylation, modulates the activity of key signaling proteins. The dysregulation of normal S-nitrosylation contributes to degenerative conditions and to cancer. To gain insight into the biochemical changes induced by low-dose ionizing radiation, we determined global S-nitrosylation by the “biotin switch” assay coupled with mass spectrometry analyses in organs of C57BL/6J mice exposed to acute 0.1 Gy of ¹³⁷Cs γ-rays. The dose of radiation was delivered to the whole body in the presence or absence of iopamidol, an iodinated contrast agent used during radiological examinations. To investigate whether similar or distinct nitrosylation patterns are induced following high-dose irradiation, mice were exposed in parallel to acute 4 Gy of ¹³⁷Cs γ rays. Analysis of modulated S-nitrosothiols (SNO-proteins) in freshly-harvested organs of animals sacrificed 13 days after irradiation revealed radiation dose- and contrast agent-dependent changes. The major results were as follows: (i) iopamidol alone had significant effects on S-nitrosylation in brain, lung and liver; (ii) relative to the control, exposure to 0.1 Gy without iopamidol resulted in statistically-significant SNO changes in proteins that differ in molecular weight in liver, lung, brain and blood plasma; (iii) iopamidol enhanced the decrease in S-nitrosylation induced by 0.1 Gy in brain; (iv) whereas a decrease in S-nitrosylation occurred at 0.1 Gy for proteins of ~50 kDa in brain and for proteins of ~37 kDa in liver, an increase was detected at 4 Gy in both organs; (v) mass spectrometry analyses of nitrosylated proteins in brain revealed differential modulation of SNO proteins (e.g., sodium/potassium-transporting ATPase subunit beta-1; beta tubulins; ADP-ribosylation factor 5) by low- and high-dose irradiation; and (vi) ingenuity pathway analysis identified major signaling networks to be modulated, in particular the neuronal nitric oxide synthase signaling pathway was differentially modulated by low- and high-dose γ-irradiation.

Epidermis-dermis junction as a novel location for bone marrow-derived cells to reside in response to ionizing radiation

Bone marrow-derived cells (BMDCs) can migrate into the various organs in the mice irradiated by ionizing radiation (IR). However, it may not be the case in the skin. While IR is used for bone marrow (BM) transplantation, studying with the epidermal sheets demonstrated that the BMDC recruitment is extraordinarily rare in epidermis in the mouse. Herein, using the chimera mice with BM from green fluorescent protein (GFP) transgenic mice, we simply examined if BMDCs migrate into any layers in the total skin, as opposed to the epidermal sheets, in response to IR. Interestingly, we identified the presence of GFP-positive (GFP(+)) cells in the epidermis-dermis junction in the total skin sections although the epidermal cell sheets failed to have any GFP cells. To examine a possibility that the cells in the junction could be mechanically dissociated during separating epidermal sheets, we then salvaged such dissociated cells and examined its characteristics. Surprisingly, some GFP(+) cells were found in the salvaged cells, indicating that these cells could be derived from BM. In addition, such BMDCs were also associated with inflammation in the junction. In conclusion, BMDCs can migrate to and reside in the epidermis-dermis junction after IR.

Proteomic overview and perspectives of the radiation-induced bystander effects

Radiation proteomics is a recent, promising and powerful tool to identify protein markers of direct and indirect consequences of ionizing radiation. The main challenges of modern radiobiology is to predict radio-sensitivity of patients and radio-resistance of tumor to be treated, but considerable evidences are now available regarding the significance of a bystander effect at low and high doses. This "radiation-induced bystander effect" (RIBE) is defined as the biological responses of non-irradiated cells that received signals from neighboring irradiated cells. Such intercellular signal is no more considered as a minor side-effect of radiotherapy in surrounding healthy tissue and its occurrence should be considered in adapting radiotherapy protocols, to limit the risk for radiation-induced secondary cancer. There is no consensus on a precise designation of RIBE, which involves a number of distinct signal-mediated effects within or outside the irradiated volume. Indeed, several cellular mechanisms were proposed, including the secretion of soluble factors by irradiated cells in the extracellular matrix, or the direct communication between irradiated and neighboring non-irradiated cells via gap junctions. This phenomenon is observed in a context of major local inflammation, linked with a global imbalance of oxidative metabolism which makes its analysis challenging using in vitro model systems. In this review article, the authors first define the radiation-induced bystander effect as a function of radiation type, in vitro analysis protocols, and cell type. In a second time, the authors present the current status of protein biomarkers and proteomic-based findings and discuss the capacities, limits and perspectives of such global approaches to explore these complex intercellular mechanisms.

Donor-specific cell-based assays in studying sensitivity to low-dose radiation: a population-based perspective

Currently, a linear no-threshold model is used to estimate health risks associated with exposure to low-dose radiation, a prevalent exposure in the general population, because the direct estimation from epidemiological studies suffers from uncertainty. This model has been criticized based on unique biology of low-dose radiation. Whether the departure from linearity is toward increased or decreased risk is intensely debated. We present an approach based on individual radiosensitivity testing and discuss how individual radiosensitivity can be assessed with the goal to develop a quantifiable measure of cellular response that can be conducted via high-throughput population testing.