Adaptive responses to low doses of radiation or chemicals: their cellular and molecular mechanisms.

This article reviews the current knowledge on the mechanisms of adaptive response to low doses of ionizing radiation or chemical exposure. A better knowledge of these mechanisms is needed to improve our understanding of health risks at low levels of environmental or occupational exposure and their involvement in cancer or non-cancer diseases. This response is orchestrated through a multifaceted cellular program involving the concerted action of diverse stress response pathways. These evolutionary highly conserved defense mechanisms determine the cellular response to chemical and physical aggression. They include DNA damage repair (p53, ATM, PARP pathways), antioxidant response (Nrf2 pathway), immune/inflammatory response (NF-κB pathway), cell survival/death pathway (apoptosis), endoplasmic response to stress (UPR response), and other cytoprotective processes including autophagy, cell cycle regulation, and the unfolded protein response. The coordinated action of these processes induced by low-dose radiation or chemicals produces biological effects that are currently estimated with the linear non-threshold model. These effects are controversial. They are difficult to detect because of their low magnitude, the scarcity of events in humans, and the difficulty of corroborating associations over the long term. Improving our understanding of these biological consequences should help humans and their environment by enabling better risk estimates, the revision of radiation protection standards, and possible therapeutic advances.

Concerted Uranium Research in Europe (CURE): toward a collaborative project integrating dosimetry, epidemiology and radiobiology to study the effects of occupational uranium exposure.

The potential health impacts of chronic exposures to uranium, as they occur in occupational settings, are not well characterized. Most epidemiological studies have been limited by small sample sizes, and a lack of harmonization of methods used to quantify radiation doses resulting from uranium exposure. Experimental studies have shown that uranium has biological effects, but their implications for human health are not clear. New studies that would combine the strengths of large, well-designed epidemiological datasets with those of state-of-the-art biological methods would help improve the characterization of the biological and health effects of occupational uranium exposure. The aim of the European Commission concerted action CURE (Concerted Uranium Research in Europe) was to develop protocols for such a future collaborative research project, in which dosimetry, epidemiology and biology would be integrated to better characterize the effects of occupational uranium exposure. These protocols were developed from existing European cohorts of workers exposed to uranium together with expertise in epidemiology, biology and dosimetry of CURE partner institutions. The preparatory work of CURE should allow a large scale collaborative project to be launched, in order to better characterize the effects of uranium exposure and more generally of alpha particles and low doses of ionizing radiation.

Low to moderate dose 137Cs (γ) radiation promotes M2 type macrophage skewing and reduces atherosclerotic plaque CD68+ cell content in ApoE(-/-) mice.

The effects of low doses of ionizing radiation on atherosclerosis remain uncertain, particularly as regards the generation of pro- or anti-inflammatory responses, and the time scale at which such effects can occur following irradiation. To explore these phenomena, we exposed atheroprone ApoE(-/-) mice to a single dose of 0, 0.05, 0.5 or 1 Gy of 137Cs (γ) administered at a 10.35 mGy min-1 dose rate and evaluated short-term (1-10 days) and long-term consequences (100 days). Bone marrow-derived macrophages were derived from mice 1 day after exposure. Irradiation was associated with a significant skewing of M0 and M2 polarized macrophages towards the M2 phenotype, as demonstrated by an increased mRNA expression of Retnla, Arg1, and Chil3 in cells from mice exposed to 0.5 or 1 Gy compared with non-irradiated animals. Minimal effects were noted in M1 cells or M1 marker mRNA. Concurrently, we observed a reduced secretion of IL-1ß but enhanced IL-10 release from M0 and M2 macrophages. Effects of irradiation on circulating monocytes were most marked at day 10 post-exposure, when the 1 Gy dose was associated with enhanced numbers of both Ly6CHigh and Ly6Low cells. By day 100, levels of circulating monocytes in irradiated and non-irradiated mice were equivalent, but anti-inflammatory Ly6CLow monocytes were significantly increased in the spleen of mice exposed to 0.05 or 1 Gy. Long term exposures did not affect atherosclerotic plaque size or lipid content, as determined by Oil red O staining, whatever the dose applied. Similarly, irradiation did not affect atherosclerotic plaque collagen or smooth muscle cell content. However, we found that lesion CD68+ cell content tended to decrease with rising doses of radioactivity exposure, culminating in a significant reduction of plaque macrophage content at 1 Gy. Taken together, our results show that short- and long-term exposures to low to moderate doses of ionizing radiation drive an anti-inflammatory response, skewing bone marrow-derived macrophages towards an IL-10-secreting M2 phenotype and decreasing plaque macrophage content. These results suggest a low-grade athero-protective effect of low and moderate doses of ionizing radiation.

Effects of moderate doses of ionizing radiation on experimental abdominal aortic aneurysm.

BACKGROUND: Exposure to ionizing radiation has been linked to cardiovascular diseases. However, the impact of moderate doses of radiation on abdominal aortic aneurysm (AAA) remains unknown. METHODS: Angiotensin II-infused Apoe-/- mice were irradiated (acute, 1 Gray) either 3 days before (Day-3) or 1 day after (Day+1) pomp implantation. Isolated primary aortic vascular smooth muscle cells (VSMCs) were irradiated (acute 1 Gray) for mechanistic studies and functional testing in vitro. RESULTS: Day-3 and Day+1 irradiation resulted in a significant reduction in aorta dilation (Control: 1.39+/-0.12; Day-3: 1.12+/-0.11; Day+1: 1.15+/-0.08 mm, P<0.001) and AAA incidence (Control: 81.0%; Day-3: 33.3%, Day+1: 53.3%) compared to the non-irradiated group. Day-3 and Day+1 irradiation led to an increase in collagen content in the adventitia (Thickness control: 23.64+/-2.9; Day-3: 54.39+/-15.5; Day+1 37.55+/-10.8 mm, P = 0.006). However, the underlying protective mechanisms were different between Day-3 and Day+1 groups. Irradiation before Angiotensin II (AngII) infusion mainly modulated vascular smooth muscle cell (VSMC) phenotype with a decrease in contractile profile and enhanced proliferative and migratory activity. Irradiation after AngII infusion led to an increase in macrophage content with a local anti-inflammatory phenotype characterized by the upregulation of M2-like gene and IL-10 expression. CONCLUSION: Moderate doses of ionizing radiation mitigate AAA either through VSCM phenotype or inflammation modulation, depending on the time of irradiation.

Plasminogen activator inhibitor-1 controls bone marrow-derived cells therapeutic effect through MMP9 signaling: role in physiological and pathological wound healing.

We assessed the role of plasminogen activator inhibitor-1 (PAI-1) and matrix metalloproteinase 9 (MMP9) in wound healing process and in the bone marrow mononuclear cells (BMMNC)-related effects on physiological and pathological wound healing. A full thickness excision wound was created by removal of the skin on the midback of irradiated and nonirradiated animals. Angiogenesis and re-epithelialization were markedly increased in PAI-1-/- mice compared to wild-type (WT) animals. We revealed high MMP activity in tissue of PAI-1-/- animals. Of interest, the wound healing process was reduced in PAI-1-/-:MMP9-/- animals compared to PAI-1-/- mice, suggesting a key role of MMP9 in beneficial effect of PAI-1 deficiency on wound closure. To unravel the role of PAI-1 in BMMNC relative effects, mice were treated with or without local injection of BMMNC isolated from WT, PAI-1-/-, and PAI-1-/-: MMP9-/- animals for 14 days (10(6) cells, n = 6 per group). In WT nonirradiated mice, transplantation of BMMNC isolated from PAI-1-/- animals enhanced wound formation when compared with WT BMMNC. BMMNC differentiation into cells with endothelial phenotype was enhanced by PAI-1 deficiency. These effects were abrogated in PAI-1-/-:MMP9-/- and MMP9-/- BMMNC. In addition, using chimeric mice, we demonstrated that PAI-1 deficiency environment increased the BMMNC-GFP recruitment to the wound site, whereas this effect was abrogated when using PAI-1-/-:MMP9-/- BMMNC. PAI-1 deficiency, at least through MMP9 upregulation, enhanced wound healing and BMMNC therapeutic potential in irradiated and nonirradiated animals.

alpha2beta1 integrin controls association of Rac with the membrane and triggers quiescence of endothelial cells.

Integrin receptors and their extracellular matrix ligands provide cues to cell proliferation, survival, differentiation and migration. Here, we show that alpha2beta1 integrin, when ligated to the basement membrane component laminin-1, triggers a proliferation arrest in primary endothelial cells. Indeed, in the presence of strong growth signals supplied by growth factors and fibronectin, alpha2beta1 engagement alters assembly of mature focal adhesions by alpha5beta1 and leads to impairment of downstream signaling and cell-cycle arrest in the G1 phase. Although the capacity of alpha5beta1 to signal for GTP loading of Rac is preserved, the joint engagement of alpha2beta1 interferes with membrane anchorage of Rac. Adapting the 'split-ubiquitin' sensor to screen for membrane-proximal alpha2 integrin partners, we identified the CD9 tetraspanin and further establish its requirement for destabilization of focal adhesions, control of Rac subcellular localization and growth arrest induced by alpha2beta1 integrin. Altogether, our data establish that alpha2beta1 integrin controls endothelial cell commitment towards quiescence by triggering a CD9-dependent dominant signaling.

A systems radiation biology approach to unravel the role of chronic low-dose-rate gamma-irradiation in inducing premature senescence in endothelial cells.

PURPOSE: The aim of this study was to explore the effects of chronic low-dose-rate gamma-radiation at a multi-scale level. The specific objective was to obtain an overall view of the endothelial cell response, by integrating previously published data on different cellular endpoints and highlighting possible different mechanisms underpinning radiation-induced senescence. MATERIALS AND METHODS: Different datasets were collected regarding experiments on human umbilical vein endothelial cells (HUVECs) which were chronically exposed to low dose rates (0, 1.4, 2.1 and 4.1 mGy/h) of gamma-rays until cell replication was arrested. Such exposed cells were analyzed for different complementary endpoints at distinct time points (up to several weeks), investigating cellular functions such as proliferation, senescence and angiogenic properties, as well as using transcriptomics and proteomics profiling. A mathematical model was proposed to describe proliferation and senescence. RESULTS: Simultaneous ceasing of cell proliferation and senescence onset as a function of time were well reproduced by the logistic growth curve, conveying shared equilibria between the two endpoints. The combination of all the different endpoints investigated highlighted a dose-dependence for prematurely induced senescence. However, the underpinning molecular mechanisms appeared to be dissimilar for the different dose rates, thus suggesting a more complex scenario. CONCLUSIONS: This study was conducted integrating different datasets, focusing on their temporal dynamics, and using a systems biology approach. Results of our analysis highlight that different dose rates have different effects in inducing premature senescence, and that the total cumulative absorbed dose also plays an important role in accelerating endothelial cell senescence.

Exposure to Low to Moderate Doses of Ionizing Radiation Induces A Reduction of Pro-Inflammatory Ly6chigh Monocytes and a U-Curved Response of T Cells in APOE -/- Mice.

Low dose ionizing radiation (LDIR) is known to have a protective effect on atherosclerosis in rodent studies, but how it impacts different cells types involved in lesion formation remains incompletely understood. We investigated the immunomodulatory response of different doses and dose-rates of irradiation in ApoE-/- mice. Mice were exposed to external γ rays at very low (1.4 mGy.h-1) or low (50 mGy.h-1) dose-rates, with cumulative doses spanning 50 to 1000 mGy. Flow cytometry of circulating cells revealed a significant decrease in pro-inflammatory Ly6CHi monocytes at all cumulative doses at low dose-rate, but more disparate effects at very low dose-rate with reductions in Ly6CHi cells at doses of 50, 100 and 750 mGy only. In contrast, Ly6CLo monocytes were not affected by LDIR. Similarly, proportions of CD4+ T cell subsets in the spleen did not differ between irradiated mice and non-irradiated controls, whether assessing CD25+FoxP3+ regulatory or CD69+ activated lymphocytes. In the aorta, gene expression of cytokines such as IL-1 and TGF-ß and adhesion molecules such as E-Selectin, ICAM-1, and VCAM-1 were reduced at the intermediate dose of 200 mGy. These results suggest that LDIR may reduce atherosclerotic plaque formation by selectively reducing blood pro-inflammatory monocytes and by impairing adhesion molecule expression and inflammatory processes in the vessel wall. In contrast, splenic T lymphocytes were not affected by LDIR. Furthermore, some responses to irradiation were nonlinear; reductions in aortic gene expression were significant at intermediate doses, but not at either highest or lowest doses. This work furthers our understanding of the impact of LDIR with different dose-rates on immune system response in the context of atherosclerosis.

Expert consultation is vital for adverse outcome pathway development: a case example of cardiovascular effects of ionizing radiation.

BACKGROUND: The circulatory system distributes nutrients, signaling molecules, and immune cells to vital organs and soft tissues. Epidemiological, animal, and in vitro cellular mechanistic studies have highlighted that exposure to ionizing radiation (IR) can induce molecular changes in cellular and subcellular milieus leading to long-term health impacts, particularly on the circulatory system. Although the mechanisms for the pathologies are not fully elucidated, endothelial dysfunction is proven to be a critical event via radiation-induced oxidative stress mediators. To delineate connectivities of events specifically to cardiovascular disease (CVD) initiation and progression, the adverse outcome pathway (AOP) approach was used with consultation from field experts. AOPs are a means to organize information around a disease of interest to a regulatory question. An AOP begins with a molecular initiating event and ends in an adverse outcome via sequential linkages of key event relationships that are supported by evidence in the form of the modified Bradford-Hill criteria. Detailed guidelines on building AOPs are provided by the Organisation for Economic Cooperation and Development (OECD) AOP program. Here, we report on the questions and discussions needed to develop an AOP for CVD resulting from IR exposure. A recent workshop jointly organized by the MELODI (Multidisciplinary European Low Dose Initiative) and the ALLIANCE (European Radioecology Alliance) associations brought together experts from the OECD to present the AOP approach and tools with examples from the toxicology field. As part of this workshop, four working groups were formed to discuss the identification of adverse outcomes relevant to radiation exposures and development of potential AOPs, one of which was focused on IR-induced cardiovascular effects. Each working group comprised subject matter experts and radiation researchers interested in the specific disease area and included an AOP coach. CONCLUSION: The CVD working group identified the critical questions of interest for AOP development, including the exposure scenario that would inform the evidence, the mechanisms of toxicity, the initiating event, intermediate key events/relationships, and the type of data currently available. This commentary describes the four-day discussion of the CVD working group, its outcomes, and demonstrates how collaboration and expert consultation is vital to informing AOP construction.

Microparticles from ischemic muscle promotes postnatal vasculogenesis.

BACKGROUND: We hypothesized that microparticles (MPs) released after ischemia are endogenous signals leading to postischemic vasculogenesis. METHODS AND RESULTS: MPs from mice ischemic hind-limb muscle were detected by electron microscopy 48 hours after unilateral femoral artery ligation as vesicles of 0.1- to 1-microm diameter. After isolation by sequential centrifugation, flow cytometry analyses showed that the annexin V(+) MP concentration was 3.5-fold higher in ischemic calves than control muscles (1392+/-406 versus 394+/-180 annexin V(+) MPs per 1 mg; P<0.001) and came mainly from endothelial cells (71% of MPs are CD(144+)). MPs isolated from ischemic muscles induced more potent in vitro bone marrow-mononuclear cell (BM-MNC) differentiation into cells with endothelial phenotype than those isolated from control muscles. MPs isolated from atherosclerotic plaques were ineffective, whereas those isolated from apoptotic or interleukin-1beta-activated endothelial cells also promoted BM-MNC differentiation. Interestingly, MPs from ischemic muscles produced more reactive oxygen species and expressed significantly higher levels of NADPH oxidase p47 (6-fold; P<0.05) and p67 subunits (16-fold; P<0.001) than controls, whereas gp91 subunit expression was unchanged. BM-MNC differentiation was reduced by 2-fold with MPs isolated from gp91-deficient animals compared with wild-type mice (P<0.05). MP effects on postischemic revascularization were then examined in an ischemic hind-limb model. MPs isolated from ischemic muscles were injected into ischemic legs in parallel with venous injection of BM-MNCs. MPs increased the proangiogenic effect of BM-MNC transplantation, and this effect was blunted by gp91 deficiency. In parallel, BM-MNC proangiogenic potential also was reduced in ABCA1 knockout mice with impaired vesiculation. CONCLUSIONS: MPs produced during tissue ischemia stimulate progenitor cell differentiation and subsequently promote postnatal neovascularization.

PSGL-1-mediated activation of EphB4 increases the proangiogenic potential of endothelial progenitor cells.

Endothelial progenitor cell (EPC) transplantation has beneficial effects for therapeutic neovascularization; however, only a small proportion of injected cells home to the lesion and incorporate into the neocapillaries. Consequently, this type of cell therapy requires substantial improvement to be of clinical value. Erythropoietin-producing human hepatocellular carcinoma (Eph) receptors and their ephrin ligands are key regulators of vascular development. We postulated that activation of the EphB4/ephrin-B2 system may enhance EPC proangiogenic potential. In this report, we demonstrate in a nude mouse model of hind limb ischemia that EphB4 activation with an ephrin-B2-Fc chimeric protein increases the angiogenic potential of human EPCs. This effect was abolished by EphB4 siRNA, confirming that it is mediated by EphB4. EphB4 activation enhanced P selectin glycoprotein ligand-1 (PSGL-1) expression and EPC adhesion. Inhibition of PSGL-1 by siRNA reversed the proangiogenic and adhesive effects of EphB4 activation. Moreover, neutralizing antibodies to E selectin and P selectin blocked ephrin-B2-Fc-stimulated EPC adhesion properties. Thus, activation of EphB4 enhances EPC proangiogenic capacity through induction of PSGL-1 expression and adhesion to E selectin and P selectin. Therefore, activation of EphB4 is an innovative and potentially valuable therapeutic strategy for improving the recruitment of EPCs to sites of neovascularization and thereby the efficiency of cell-based proangiogenic therapy.

Adiponectinemia controls pro-angiogenic cell therapy.

Angiogenic cell therapy with the transplantation of endothelial progenitor cells (EPC) or bone marrow mononuclear cells (BM-MNC) receives considerable attention as an approach to revascularize ischemic tissues. Adiponectin is a circulating hormone produced by the apM1 gene in adipocytes. Adiponectin modulates lipid metabolism and obesity, and it was recently found to promote physiological angiogenesis in response to ischemia. Patients with multiple cardiovascular disease risk factors or myocardial infarction may benefit from progenitor cell therapy, but they display depressed adiponectinemia. We hypothesized that adiponectin stimulation of transplanted cells is critical for their pro-angiogenic function. We aimed to establish whether adiponectinemia in the cell donor or in the cell recipient determines the success of pro-angiogenic cell therapy. In vitro, we found that conditioned media derived from wild-type adipocytes (adipo-CM) or purified adiponectin strongly enhanced BM-MNC survival and proliferation and stimulated EPC differentiation, whereas adipo-CM from apM1-/- adipocytes was one-half less effective. On the other hand, wild-type and apM1-/- BM-MNC displayed similar resistance to apoptosis and proliferation rates. In vivo, wild-type, and apM1-/- BM-MNC induced similar angiogenic reactions in wild-type ischemic hindlimbs. In contrast, wild-type BM-MNC had much diminished effects in apM1-/- ischemic hindlimbs. We concluded that adiponectin enhances BM-MNC survival and proliferation, and adiponectinemia in the cell therapy recipient is essential for the pro-angiogenic benefits of cell therapy. These observations imply that progenitor cell transplantation might only induce angiogenesis in patients with high adiponectinemia.

Preconditioning by mitochondrial reactive oxygen species improves the proangiogenic potential of adipose-derived cells-based therapy.

OBJECTIVE: Transplantation of adipose-derived stroma cells (ADSCs) stimulates neovascularization after experimental ischemic injury. ADSC proangiogenic potential is likely mediated by their ability to differentiate into endothelial cells and produce a wide array of angiogenic and antiapoptotic factors. Mitochondrial reactive oxygen species (ROS) have been shown to control ADSC differentiation. We therefore hypothesized that mitochondrial ROS production may change the ADSC proangiogenic properties. METHODS AND RESULTS: The use of pharmacological strategies (mitochondrial inhibitors, antimycin, and rotenone, with or without antioxidants) allowed us to specifically and precisely modulate mitochondrial ROS generation in ADSCs. We showed that transient stimulation of mitochondrial ROS generation in ADSCs before their injection in ischemic hindlimb strongly improved revascularization and the number of ADSC-derived CD31-positive cells in ischemic area. Mitochondrial ROS generation increased the secretion of the proangiogenic and antiapoptotic factors, VEGF and HGF, but did not affect ADSC ability to differentiate into endothelial cells, in vitro. Moreover, mitochondrial ROS-induced ADSC preconditioning greatly protect ADSCs against oxidative stress-induced cell death. CONCLUSIONS: Our study demonstrates that in vitro preconditioning by moderate mitochondrial ROS generation strongly increases in vivo ADSC proangiogenic properties and emphasizes the crucial role of mitochondrial ROS in ADSC fate.

Effect of repetitive potassium iodide on thyroid and cardiovascular functions in elderly rats.

BACKGROUND: To date, paediatric thyroid cancer has been the most severe health consequence of the Chernobyl accident, caused by radioactive iodine (131I) aerosol's dispersion. WHO recommends a single dose of potassium iodide (KI) to reduce this risk. Following the Fukushima accident, it became obvious that repetitive doses of KI may be necessary due to multiple exposures to 131I. Knowledge about the effects of repeated ITB (Iodine Thyroid Blocking) is scarce and controversial. KI may affect the thyroid hormones synthesis; which is crucial for the cardiovascular function. Furthermore, myocardial and vascular endothelial tissues are sensitizes to subtle changes at the concentration of circulating pituitary and/or thyroid hormones. OBJECTIVE: In this preclinical study, we aimed to assess the effects of repeated ITB in elderly male rats. METHODS: Twelve months old male Wistar rats were subjected to either KI or saline solution for eight days. Analyses were performed 24 h and 30 days after the treatment discontinuation. FINDINGS: We reported a significant increase (18%) in some urinary parameters related to renal function, a subtle decrease of plasma TSH level, a significant increase (379%) in renin and a significant decrease (50%) in aldosterone upon KI administration. At the molecular level, the expression of thyroid and cardiovascular genes was significantly affected by the treatment. However, in our experimental settlement, animal heart rate was not significantly affected thirty days after KI discontinuation. ECG patterns did not change after administration of KI, and arrhythmia was not observed in these conditions despite the PR-intervals decreased significantly. Cardiovascular physiology was preserved. CONCLUSION: Our results indicate that repeated ITB in elderly rats is characterized by molecular modifications of cardiovascular key actors, particularly the Renin-angiotensin-aldosterone axis with a preserved physiological homeostasis. This new scientific evidence may be useful for the maturation of ITB guidelines especially for elderly sub-population.

Evaluation of the Nose-to-Brain Transport of Different Physicochemical Forms of Uranium after Exposure via Inhalation of a UO4 Aerosol in the Rat.

BACKGROUND: Health-risk issues are raised concerning inhalation of particulate pollutants that are thought to have potential hazardous effects on the central nervous system. The brain is presented as a direct target of particulate matter (PM) exposure because of the nose-to-brain pathway involvement. The main cause of contamination in nuclear occupational activities is related to exposure to aerosols containing radionuclides, particularly uranium dust. It has been previously demonstrated that instilled solubilized uranium in the rat nasal cavity is conveyed to the brain via the olfactory nerve. OBJECTIVE: The aim of this study was to analyze the anatomical localization of uranium compounds in the olfactory system after in vivo exposure to a polydisperse aerosol of uranium tetraoxide (UO4) particles. METHODS: The olfactory neuroepithelium (OE) and selected brain structures-olfactory bulbs (OB), frontal cortex (FC), hippocampus (HIP), cerebellum (Cer), and brainstem (BS)-were microdissected 4 h after aerosol inhalation via a nose-only system in adult rats. Tissues were subjected to complementary analytical techniques. RESULTS: Uranium concentrations measured by inductively coupled plasma mass spectrometry (ICP-MS) were significantly higher in all brain structures from exposed animals compared with their respective controls. We observed that cerebral uranium concentrations followed an anteroposterior gradient with typical accumulation in the OB, characteristic of a direct olfactory transfer of inhaled compounds. Secondary ion mass spectrometry (SIMS) microscopy and transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (TEM-EDX) were used in order to track elemental uranium in situ in the olfactory epithelium. Elemental uranium was detected in precise anatomical regions: olfactory neuron dendrites, paracellular junctions of neuroepithelial cells, and olfactory nerve tracts (around axons and endoneural spaces). CONCLUSION: These neuroanatomical observations in a rat model are consistent with the transport of elemental uranium in different physicochemical forms (solubilized, nanoparticles) along olfactory nerve bundles after inhalation of UO4 microparticles. This work contributes to knowledge of the mechanistic actions of particulate pollutants on the brain. https://doi.org/10.1289/EHP4927.

Gamma Low-Dose-Rate Ionizing Radiation Stimulates Adaptive Functional and Molecular Response in Human Aortic Endothelial Cells in a Threshold-, Dose-, and Dose Rate-Dependent Manner.

A central question in radiation protection research is whether low-dose and low-dose-rate (LDR) exposures to ionizing radiation play a role in progression of cardiovascular disease. The response of endothelial cells to different LDR exposures may help estimate risk of cardiovascular disease by providing the biological mechanism involved. We investigated the effect of chronic LDR radiation on functional and molecular responses of human aorta endothelial cells (HAoECs). Human aorta endothelial cells were continuously irradiated at LDR (6 mGy/h) for 15 days and analyzed at time points when the cumulative dose reached 0.05, 0.5, 1.0, and 2.0 Gy. The same doses were administered acutely at high-dose rate (HDR; 1 Gy/min). The threshold for the loss of angiogenic capacity for both LDR and HDR radiations was between 0.5 and 1.0 Gy. At 2.0 Gy, angiogenic capacity returned to normal only for HAoEC exposed to LDR radiation, associated with increased expression of antioxidant and anti-inflammatory genes. Pre-LDR, but not pre-HDR, radiation, followed by a single acute 2.0 Gy challenge dose sustained the expression of antioxidant and anti-inflammatory genes and stimulated angiogenesis. Our results suggest that dose rate is important in cellular response and that a radioadaptive response is involved for a 2.0 Gy dose at LDR.

Effects of repeated potassium iodide administration on genes involved in synthesis and secretion of thyroid hormone in adult male rat.

BACKGROUND: A single dose of potassium iodide (KI) is recommended to reduce the risk of thyroid cancer during nuclear accidents. However in case of prolonged radioiodine exposure, more than one dose of KI may be necessary. This work aims to evaluate the potential toxic effect of repeated administration of KI. METHODS: Adult Wistar rats received an optimal dose of KI 1 mg/kg over a period of 1, 4 or 8 days. RESULTS: hormonal status (TSH, FT4) of treated rats was unaffected. Contrariwise, a sequential Wolff-Chaikoff effect was observed, resulting in a prompt decrease of NIS and MCT8 mRNA expression (-58% and -26% respectively), followed by a delayed decrease of TPO mRNA expression (-33%) in conjunction with a stimulation of PDS mRNA expression (+62%). CONCLUSION: we show for the first time that repeated administration of KI at 1 mg/kg/24h doesn't cause modification of thyroid hormones level, but leads to a reversible modification of the expression of genes involved in the synthesis and secretion of thyroid hormones.

In vivo animal studies help achieve international consensus on standards and guidelines for health risk estimates for chronic exposure to low levels of tritium in drinking water.

Existing and future nuclear fusion technologies involve the production and use of large quantities of tritium, a highly volatile, but low toxicity beta-emitting isotope of hydrogen. Tritium has received international attention because of public and scientific concerns over its release to the environment and the potential health impact of its internalization. This article provides a brief summary of the current state of knowledge of both the biological and regulatory aspects of tritium exposure; it also explores the gaps in this knowledge and provides recommendations on the best ways forward for improving our understanding of the health effects of low-level exposure to it. Linking health effects specifically to tritium exposure is challenging in epidemiological studies due to high uncertainty in tritium dosimetry and often suboptimal cohort sizes. We therefore argued that limits for tritium in drinking water should be based on evidence derived from controlled in vivo animal tritium toxicity studies that use realistically low levels of tritium. This article presents one such mouse study, undertaken within an international collaboration, and discusses the implications of its main findings, such as the similarity of the biokinetics of tritiated water (HTO) and organically bound tritium (OBT) and the higher biological effectiveness of OBT. This discussion is consistent with the position expressed in this article that in vivo animal tritium toxicity studies carried out within large, multi-partner collaborations allow evaluation of a great variety of health-related endpoints and essential to the development of international consensus on the regulation of tritium levels in the environment. Environ. Mol. Mutagen. 59:586-594, 2018. © 2018 The Authors Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Increase in vascular permeability and vasodilation are critical for proangiogenic effects of stem cell therapy.

BACKGROUND: Proangiogenic cell therapy based on administration of bone marrow-derived mononuclear cells (BMCs) or endothelial progenitor cells (EPCs) is now under investigation in humans for the treatment of ischemic diseases. However, mechanisms leading to the beneficial effects of BMCs and EPCs remain unclear. METHODS AND RESULTS: BMC- and CD34+-derived progenitor cells interacted with ischemic femoral arteries through SDF-1 and CXCR4 signaling and released nitric oxide (NO) via an endothelial nitric oxide synthase (eNOS)-dependent pathway. BMC-induced NO production promoted a marked vasodilation and disrupted vascular endothelial-cadherin/beta-catenin complexes, leading to increased vascular permeability. NO-dependent vasodilation and hyperpermeability were critical for BMC infiltration in ischemic tissues and their proangiogenic potential in a model of hindlimb ischemia in mice. CONCLUSIONS: Our results propose a new concept that proangiogenic progenitor cell activity does not rely only on their ability to differentiate into endothelial cells but rather on their capacity to modulate the function of preexisting vessels.

Tetrapeptide AcSDKP induces postischemic neovascularization through monocyte chemoattractant protein-1 signaling.

BACKGROUND: We investigated the putative proangiogenic activity and molecular pathway(s) of the tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (AcSDKP) in a model of surgically induced hindlimb ischemia. METHODS AND RESULTS: Hindlimb ischemia was induced by femoral artery ligature and an osmotic minipump was implanted subcutaneously to deliver low (0.12 mg/kg per day) or high (1.2 mg/kg per day) doses of AcSDKP, for 7 or 21 days. Angiography scores, arteriole density, capillary number, and foot perfusion were increased at day 21 in the high-dose AcSDKP-treated mice (by 1.9-, 1.8-, 1.3-, and 1.6-fold, respectively) compared with control animals (P<0.05, P<0.01, P<0.01, respectively). AcSDKP treatment for 24 hours upregulated the monocyte chemoattractant protein-1 (MCP-1) mRNA and protein levels by 1.5-fold in cultured endothelial cells (P<0.01). In the ischemic hindlimb model, administration of AcSDKP also enhanced MCP-1 mRNA levels by 90-fold in ischemic leg (P<0.001) and MCP-1 plasma levels by 3-fold (P<0.001 versus untreated ischemic control mice). MCP-1 levels upregulation were associated with a 2.3-fold increase in the number of Mac3-positive cells in ischemic area of AcSDKP-treated mice (P<0.001 versus untreated animals). Interestingly, AcSDKP-induced monocyte/macrophage infiltration and postischemic neovascularization was fully blunted in MCP-1-deficient animals. CONCLUSIONS: AcSDKP stimulates postischemic neovascularization through activation of a proinflammatory MCP-1-related pathway.