Nanoparticle radiosensitization: from extended local effect modeling to a survival modification framework of compound Poisson additive killing and its carbon dots validation.

Objective. To construct an analytical model instead of local effect modeling for the prediction of the biological effectiveness of nanoparticle radiosensitization.Approach. An extended local effects model is first proposed with a more comprehensive description of the nanoparticles mediated local killing enhancements, but meanwhile puts forward challenging issues that remain difficult and need to be further studied. As a novel method instead of local effect modeling, a survival modification framework of compound Poisson additive killing is proposed, as the consequence of an independent additive killing by the assumed equivalent uniform doses of individual nanoparticles per cell under the LQ model. A compound Poisson killing (CPK) model based on the framework is thus derived, giving a general expression of nanoparticle mediated LQ parameter modification. For practical use, a simplified form of the model is also derived, as a concentration dependent correction only to theαparameter, with the relative correction (α″/α) dominated by the mean number, and affected by the agglomeration of nanoparticles per cell. For different agglomeration state, a monodispersion model of the dispersity factorη = 1, and an agglomeration model of 2/3 < Î· < 1, are provided for practical prediction of (α″/α) value respectively.Main results. Initial validation by the radiosensitization of HepG2 cells by carbon dots showed a high accuracy of the CPK model. In a safe range of concentration (0.003-0.03µgµl-1) of the carbon dots, the prediction errors of the monodispersion and agglomeration models were both within 2%, relative to the clonogenic survival data of the sensitized HepG2 cells.Significance. The compound Poisson killing model provides a novel approach for analytical prediction of the biological effectiveness of nanoparticle radiosensitization, instead of local effect modeling.

Follow-up study of abnormal biological indicators and gene expression in the peripheral blood of three accidentally exposed persons.

In order to identify biomarkers for early diagnosis and/or for therapeutic targets in the delayed health effects of ionizing radiation, we analyzed the subgroups of lymphocytes, serum protein levels and gene expression profiles in the peripheral blood of three 6°Co γ-ray accidentally exposed persons during the three years after irradiation. Flow cytometry analyses and agarose gel electrophoresis were applied to investigate the subgroups of lymphocytes and the composition of serum proteins, respectively. Gene expression profiling was obtained using a whole genome gene expression chip assay. Both the percentage of CD4+ T lymphocytes and the ratio of Th to Ts were reduced compared with the normal control values. The percentage of albumin decreased whereas beta globulin increased. There were 285 up-regulated and 446 down-regulated genes in irradiated samples relative to the control samples. The expression of KDR, CEACAM8 and OSM was validated by RT-PCR. The majority of the differentially expressed genes encode proteins associated with the immune response, inflammation, oncogenesis, cell structure, oxidative stress, neuro-hormone regulation, reproduction, susceptibility to psychiatric disorders, or transcriptional regulation. We have identified a number of promising novel candidates that have potential for serving as biomarkers for delayed damage. Furthermore, the changes in the immunological indicator CD4+ T cells, and the ratio of CD4+ T to CD8+ T cells may be biomarkers for the prediction of delayed damage by ionizing radiation. The findings of our study are useful for forming a comprehensive understanding of the mechanisms underlying the delayed effects of ionizing radiation.

Vitamin E-deficiency did not exacerbate partial skin reactions in mice locally irradiated with X-rays.

We previously showed that free radicals and oxidative stress are involved in radiation-induced skin reactions. Since vitamin E (VE) is a particularly important lipophilic antioxidant, VE-deficient mice were used to examine its effects on radiation-induced skin damage. The VE content of the skin was reduced to one fourth of levels of normal mice. Neither the time of onset nor the extent of the reactions quantified with a scoring system differed between normal and VE-deficient mice after local X-irradiation (50 Gy). Similarly, there was no difference in the levels of the ascorbyl radical between the groups, although they were higher in irradiated skin than non-irradiated skin. X-irradiation increased the amount of Bax protein in the skin of normal mice both in the latent and acute inflammatory stages, time- and dose-dependently. The increase was associated with an increase in cytochrome c in the cytosolic fraction, indicating that apoptosis was also promoted by the irradiation. The increase in Bax protein correlated well with the thickness of the skin. Although a deficiency in VE should lower resistance to free radicals in the mitochondrial membrane and thus enhance radiation-induced Bax expression and apoptosis, it actually attenuated the increase in Bax protein caused by irradiation.

In vivo generation of free radicals in the skin of live mice under ultraviolet light, measured by L-band EPR spectroscopy.

Although free radicals may be involved in various types of UV-induced injuries, only a few in vivo studies of the generation of free radicals, including oxygen radicals, during exposure to ultraviolet light (UV) have been reported. In this study, the nitroxyl probe 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl was intravenously injected into hairless mice, and its decay was monitored in the skin with an in vivo EPR spectrometer equipped with a surface-coil-type resonator. The rate of decay of the EPR signal increased during UV (UVA+B) irradiation. This increase in signal decay was suppressed by preadministration of a spin trap, N-tert-butyl-alpha-phenylnitrone (PBN). PBN did not change the rate of signal decay in nonirradiated mice. The correlation between signal decay rate and physiological parameters such as blood velocity, blood mass, or skin temperature was low. The decay rate responded rapidly and reversibly to starting and stopping the UV illumination. Hydroxyl and peroxyl radicals caused reduction of the probe signal in vitro, and PBN inhibited only the peroxyl radical-induced signal reduction. These observations suggest that peroxyl radicals are generated in the skin of live mice during UVA+B irradiation.

In vivo nitric oxide production and iNOS expression in X-ray irradiated mouse skin.

Inducible nitric oxide synthase (iNOS) and NO have been suggested to be involved in acute radiation response in tissues such as the liver, intestine, colon, and brain. However, direct measurement of NO and iNOS in ionizing radiation-induced skin inflammatory reactions is not reported yet. We show here for the first time, by in vivo experiments, that X-ray irradiated mouse skin generates NO with concomitant expression of iNOS at both the mRNA and protein levels. When irradiated at 50 Gy, iNOS mRNA appeared at day 8 post-irradiation, whereas iNOS protein could be detected only at day 14. No iNOS protein was detectable however for the mice receiving 5 or 15 Gy irradiation, even at day 14. Skin inflammatory reactions were observed at day 8 post-irradiation as an increase in skin thickness, which increased further by day 14. Histological observations showed acute inflammatory responses. The parallel relationship between iNOS induction and the onset of skin inflammatory reactions suggests the involvement of iNOS and NO in the skin damage. Immunohistochemical staining showed the localization of iNOS at skin erosion areas, exudate and infiltrating cells. Taken together, these findings suggest that iNOS induction and NO production in X-irradiated skin are relatively early events in skin inflammatory reactions and are probably secondary rather than primary reactions of irradiation.

Quantitative measurements of oxidative stress in mouse skin induced by X-ray irradiation.

To find efficient methods to evaluate oxidative stress in mouse skin caused by X-ray irradiation, several markers and methodologies were examined. Hairless mice were irradiated with 50 Gy X-rays and skin homogenates or skin strips were prepared. Lipid peroxidation was measured using the skin homogenate as the level of thiobarbituric acid reactive substances. The level of lipid peroxidation increased with time after irradiation and was twice that of the control at 78 h. ESR spectra of skin strips showed a clear signal for the ascorbyl radical, which increased with time after irradiation in a manner similar to that of lipid peroxidation. To measure levels of glutathione (GSH) and its oxidized forms (GSSG) simultaneously, two HPLC methods, sample derivatization with 1-fluoro-2,4-dinitrobenzene and detection with a UV detector (method A) and no derivatization and detection with an electrochemical detector (method B), were compared and the latter was found to be better. No significant change was observed within 24 h after irradiation in the levels of GSH and GSSG measured by method B. The GSH/GSSG ratio may be a less sensitive parameter for the evaluation of acute oxidative stress caused by X-ray irradiation in the skin. Monitoring the ascorbyl radical seems to be a good way to evaluate oxidative stress in skin in vivo.