Three-dimensional co-culture model employing silica nonwoven fabrics to enhance cell-to-cell communication of paracrine signaling between hepatocytes and fibroblasts.

The realization that soluble factors secreted by heterotypic cells play an importanta role in paracrine signaling, which facilitates intercellular communication, enabled the development of physiologically relevant co-culture models for drug screening and the engineering of tissues, such as hepatic tissues. The most crucial issues confronting the use of conventional membrane inserts in segregated co-culture models that are used to study paracrine signaling between heterotypic cells have been identified as long-term viability and retention of cell-specific functions, especially when isolated primary cells are used. Herein, we present an in vitro segregated co-culture model consisting of a well plate incubated with rat primary hepatocytes and normal human dermal fibroblasts which were segregated using a membrane insert with silica nonwoven fabric (SNF) on it. SNF, which mimics a physiological environment much more effectively than a two-dimensional (2D) one, promotes cell differentiation and resultant paracrine signaling in a manner that is not possible in a conventional 2D culture, owing to high mechanical strength generated by its inorganic materials and interconnected network structure. In segregated co-cultures, SNF clearly enhanced the functions of hepatocytes and fibroblasts, thereby showing its potential as a measure of paracrine signaling. These results may advance the understanding of the role played by paracrine signaling in cell-to-cell communication and provide novel insights into the applications of drug metabolism, tissue repair, and regeneration.

Modification and Validation of the DREIDING Force Field for Molecular Liquid Simulations (DREIDING-UT).

In this study, we modified Lennard-Jones (LJ) parameters and point-charge parameters of the DREIDING force field (the modified force-field model is named DREIDING-UT). While the original LJ parameters of DREIDING were derived through an analytical formula to reproduce the potential depths and the equilibrium lengths of the Buckingham potentials of DREIDING/X6, the modified LJ parameters were derived through the least square fitting of the Buckingham potentials. Because the Gasteiger-Marsili (GM) charges of the original DREIDING underestimated electrostatic interactions, we replaced it with the restrained electrostatic potential (RESP) charges calculated from the ab initio wavefunctions, taking the dynamic electron correlation and solvation effects into account. To confirm how the modified force field works, we conducted molecular dynamics (MD) simulations of typical liquids. It was found that the densities and self-diffusion coefficients of the DREIDING-UT model agreed with the experimental ones much better than those of the original model.

Improvement of Hepatic Functions by Spheroids Coculture with Fibroblasts in 3D Silica Nonwoven Fabrics.

In order to realize organ-on-a-chip as an effective tool for regenerative medicine and drug development, tissue-mimic cell culture methods which promote liver-specific function for long period have been developed. We have previously demonstrated that coculture of hepatocyte spheroids on fibroblasts using micropatterned substrate improved the hepatic functions due to the heterotypic cell-cell interactions and paracrine signaling from each other. In addition, hepatocyte function cultured as monolayer was also promoted in separately coculture with fibroblasts cultured as monolayer, and it is more improved in separately coculture with fibroblasts in 3D silica nonwoven fabrics. In this study, separately coculture of hepatocyte spheroids with fibroblasts cultured on 3D silica nonwoven fabrics was estimated for further improvement of hepatocyte functions. The hepatic function cocultured with fibroblast was more promoted than mono spheroids culture. The functional enhancement was significantly most improved in separately coculture with fibroblast in 3D silica nonwoven fabrics. Thus, these results were suggested that 3D culture of fibroblasts in 3D silica nonwoven fabrics increased the heterotypic secretion of paracrine factors, and it is essential for improved hepatic performance.

Topical application of polyethylenimine as a candidate for novel prophylactic therapeutics against genital herpes caused by herpes simplex virus.

Herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) cause genital herpes, which can enhance the acquisition of human immunodeficiency virus. The development of anti-HSV agents with novel mechanisms of action is urgently required in the topical therapy of genital herpes. In this study, the in vitro and in vivo anti-HSV effects of Epomin SP-012(®), a highly cationic polyethylenimine, were evaluated. When the in vitro antiviral effects of SP-012 were assessed, this compound showed potent activity against HSV-1 and HSV-2. It inhibited the attachment of HSV-2 to host cells and cell-to-cell spread of infection in a concentration-dependent manner and exerted a virucidal effect. No SP-012-resistant HSV-2 was found when the virus was successively passaged in the presence of SP-012. In a mouse genital herpes model, topically administered SP-012 inhibited the progression of the disease caused by HSV infection. These data illustrate that SP-012 may be a novel class of HSV inhibitor that would be acceptable for long-term topical application.

Micropatterned co-culture of hepatocyte spheroids layered on non-parenchymal cells to understand heterotypic cellular interactions.

Microfabrication and micropatterning techniques in tissue engineering offer great potential for creating and controlling cellular microenvironments including cell-matrix interactions, soluble stimuli and cell-cell interactions. Here, we present a novel approach to generate layered patterning of hepatocyte spheroids on micropatterned non-parenchymal feeder cells using microfabricated poly(ethylene glycol) (PEG) hydrogels. Micropatterned PEG-hydrogel-treated substrates with two-dimensional arrays of gelatin circular domains (ϕ = 100 µm) were prepared by photolithographic method. Only on the critical structure of PEG hydrogel with perfect protein rejection, hepatocytes were co-cultured with non-parenchymal cells to be led to enhanced hepatocyte functions. Then, we investigated the mechanism of the functional enhancement in co-culture with respect to the contributions of soluble factors and direct cell-cell interactions. In particular, to elucidate the influence of soluble factors on hepatocyte function, hepatocyte spheroids underlaid with fibroblasts (NIH/3T3 mouse fibroblasts) or endothelial cells (BAECs: bovine aortic endothelial cells) were compared with physically separated co-culture of hepatocyte monospheroids with NIH3T3 or BAEC using trans-well culture systems. Our results suggested that direct heterotypic cell-to-cell contact and soluble factors, both of these between hepatocytes and fibroblasts, significantly enhanced hepatocyte functions. In contrast, direct heterotypic cell-to-cell contact between hepatocytes and endothelial cells only contributed to enhance hepatocyte functions. This patterning technique can be a useful experimental tool for applications in basic science, drug screening and tissue engineering, as well as in the design of artificial liver devices.

In vitro and in vivo evaluation of a novel antiherpetic flavonoid, 4'-phenylflavone, and its synergistic actions with acyclovir.

The development of therapeutic agents for preventing herpes simplex virus (HSV) infections has become urgently necessary because of the increasing incidence of this virus and its role as a cofactor in the transmission of human immunodeficiency virus infection. We have evaluated the antiviral activities of a series of natural and synthetic flavonoids and found that a synthetic flavonoid, 4'-phenylflavone, showed the highest activity against acyclovir (ACV)-sensitive and ACV-resistant strains of HSV-1, as well as HSV-2, with a selectivity index of 213, 35 and 55, respectively. Although the attachment and penetration of HSV-1 to host cells and the synthesis of viral proteins were not inhibited, the infectivity of the virus and the amount of progeny virus released were reduced by 4'-phenylflavone treatment in a dose-dependent manner. 4'-Phenylflavone plus ACV synergistically inhibited the replication of HSV-1. This flavonoid also showed efficacy in vivo and potentiated the antiherpetic effect of ACV in a mouse model of genital herpes. Our results suggest that 4'-phenylflavone might be useful as a candidate for the development of novel antiherpetic therapeutics.

Development of hydroxyapatite-coated nonwovens for efficient isolation of somatic stem cells from adipose tissues.

Adipose-derived stem cells (ASCs) are an attractive cell source for cell therapy. Despite the increasing number of clinical applications, the methodology for ASC isolation is not optimized for every individual. In this study, we developed an effective material to stabilize explant cultures from small-fragment adipose tissues. Methods: Polypropylene/polyethylene nonwoven sheets were coated with hydroxyapatite (HA) particles. Adipose fragments were then placed on these sheets, and their ability to trap tissue was monitored during explant culture. The yield and properties of the cells were compared to those of cells isolated by conventional collagenase digestion. Results: Hydroxyapatite-coated nonwovens immediately trapped adipose fragments when placed on the sheets. The adhesion was stable even in culture media, leading to cell migration and proliferation from the tissue along with the nonwoven fibers. A higher fiber density further enhanced cell growth. Although cells on nonwoven explants could not be fully collected with cell dissociation enzymes, the cell yield was significantly higher than that of conventional monolayer culture without impacting stem cell properties. Conclusions: Hydroxyapatite-coated nonwovens are useful for the effective primary explant culture of connective tissues without enzymatic cell dissociation.

Metallic behavior of cyclotron relaxation time in two-dimensional systems.

Cyclotron resonance of two-dimensional electrons is studied at low temperatures down to 0.4 K for a high-mobility Si/SiGe quantum well which exhibits a metallic temperature dependence of dc resistivity ρ. The relaxation time τ(CR) shows a negative temperature dependence, which is similar to that of the transport scattering time τ(t) obtained from ρ. The ratio τ(CR)/τ(t) at 0.4 K increases as the electron density N(s) decreases, and exceeds unity when N(s) approaches the critical density for the metal-insulator transition.

High-dose-rate brachytherapy using inverse planning optimization with tandem and ovoid applicators for locally advanced cervical cancer: a simulation study.

The purpose of this study was to evaluate the dosimetric advantage of inverse planning optimization (IPO) in locally advanced cervical cancer using high-dose-rate (HDR) brachytherapy (BT). IPO was compared with point A plan and geometric optimization (GO). The three planning methods were evaluated using doses to the virtual organ-at-risk (OAR) and D90 (the minimum dose covering of 90% of the volume) to the virtual high-risk clinical target volume (HR-CTV) based on quantitative analysis. HR-CTV structures measuring 38.5 cm3 and 59.5 cm3 were created based on the outcomes of a European Group cohort study. The HR-CTVs were located either at the center of the cervix (cervical center model) or shifted toward the left (extensive disease model). The distances from the HR-CTVs to the rectum were set at 0 mm, 3 mm, 5 mm, 8 mm, 10 mm, and 15 mm. We analyzed 336 conditions in this study. All doses were evaluated by conversion to doses in 2-Gy fractions of conventional radiotherapy. The D90 of the HR-CTV using GO and IPO could achieve the desired dose in all conditions, providing better results than that of point A plan. IPO makes it possible to deliver a sufficient dose for the D90 of the HR-CTV while reducing OAR doses with smaller HR-CTV values (< 38.5 cm3) in HDR BT. However, taking into consideration the whole treatment planning time, IPO should be used only when the HR-CTV-to-rectum distance is ≤ 5 mm, and the use of GO cannot spare OARs.

Verification of KURBUC-based ion track structure mode for proton and carbon ions in the PHITS code.

The particle and heavy ion transport code system (PHITS) is a general-purpose Monte Carlo radiation transport simulation code. It has the ability to handle diverse particle types over a wide range of energy. The latest PHITS development enables the generation of track structure for proton and carbon ions (1H+, 12C6+) based on the algorithms in the KURBUC code, which is considered as one of the most verified track-structure codes worldwide. This ion track-structure mode is referred to as the PHITS-KURBUC mode. In this study, the range, radial dose distributions, and microdosimetric distributions were calculated using the PHITS-KURBUC mode. Subsequently, they were compared with the corresponding data obtained from the original KURBUC and from other studies. These comparative studies confirm the successful inclusion of the KURBUC code in the PHITS code. As results of the synergistic effect between the macroscopic and microscopic radiation transport codes, this implementation enabled the detailed calculation of the microdosimetric and nanodosimetric quantities under complex radiation fields, such as proton beam therapy with the spread-out Bragg peak.

A SNP in a Steroidogenic Enzyme Is Associated with Phenotypic Sex in Seriola Fishes.

Vertebrate sex development consists largely of two processes: "sex determination," the initial bifurcation of sexual identity, and "sex differentiation," which subsequently facilitates maleness or femaleness according to the sex determination signal. Steroid hormones promote multiple types of sexual dimorphism in eutherian mammals and avians [1-3], in which they are indispensable for proper sex differentiation. By contrast, in many poikilothermic vertebrates, steroid hormones have been proposed to be key players in sex determination as well as sex differentiation [4-8]. This hypothesis was introduced more than 50 years ago but has never been rigorously tested due to difficulties in discriminating the roles of steroids in sex determination and differentiation. We found that a missense SNP in the gene encoding the steroidogenic enzyme 17ß-hydroxysteroid dehydrogenase 1 (Hsd17b1) was perfectly associated with ZZ/ZW sex determination in Seriola fishes. Biochemical analyses revealed that a glutamate residue present specifically in Z-type HSD17B1 attenuated interconversion between 17-keto and 17ß-hydroxy steroids relative to the allelic product from the W chromosome, which harbors glycine at that position, by disrupting the hydrogen bond network between the steroid and the enzyme's catalytic residues. Hsd17b1 mRNA is constitutively expressed in undifferentiated and differentiating gonads of both genotypic sexes, whereas W-type mRNA is expressed only in genotypic females. Meanwhile, Cyp19a1 is predominantly expressed in differentiating ovary. We conclude that the combination of Hsd17b1 alleles determines sex by modulating endogenous estrogen levels in Seriola species. These findings strongly support the long-standing hypothesis on steroids in sex determination.

Estrogen agonistic/antagonistic activity of brominated parabens.

The estrogen agonistic/antagonistic activity of 16 brominated by-products of parabens was assessed by using a yeast two-hybrid assay transfected with the human estrogen receptor α. Characterization of synthetic compounds including novel brominated parabens was performed using 1H-NMR spectroscopy and high-resolution mass spectrometry. For the agonist assay, five C3-C4 alkylparabens exhibited significant activity (P < 0.05) relative to that of 17ß-estradiol, ranging from 3.7 × 10-5 to 7.1 × 10-4. In contrast, none of the brominated alkyl parabens exhibited agonistic activity. In the antagonist assay, 12 brominated alkylparabens and butylparaben exhibited significant antagonistic activity (P < 0.05). Their antagonistic activity relative to 4-hydroxytamoxifen ranged from 0.11 to 2.5. The antagonist activity of C1-C4 alkylparabens increased with the number of bromine substitutions. Benzylparaben exhibited both agonistic and antagonistic activity, and these activities dissipated or were weakened with increased bromination. Thus, increased bromination appeared to attenuate the estrogen agonistic activity of most parabens such that it resulted in increased antagonistic activity, a feature of parabens that had not been previously described.

Osteogenic Differentiation of Bone Marrow-Derived Mesenchymal Stem Cells in Electrospun Silica Nonwoven Fabrics.

Silica nonwoven fabrics (SNFs) with enough mechanical strength are candidates as implantable scaffolds. Culture of cells therein is expected to affect the proliferation and differentiation of the cells through cell-cell and cell-SNF interactions. In this study, we examined three-dimensional (3D) SNFs as a scaffold of mesenchymal stem cells (MSCs) for bone tissue engineering applications. The interconnected highly porous microstructure of 3D SNFs is expected to allow omnidirectional cell-cell interactions, and the morphological similarity of a silica nanofiber to that of a fibrous extracellular matrix can contribute to the promotion of cell functions. 3D SNFs were prepared by the sol-gel process, and their mechanical properties were characterized by the compression test and rheological analysis. In the compression test, SNFs showed a compressive elastic modulus of over 1 MPa and a compressive strength of about 200 kPa. These values are higher than those of porous polystyrene disks used for in vitro 3D cell culture. In rheological analysis, the elastic modulus and fracture stress were 3.27 ± 0.54 kPa and 25.9 ± 8.3 Pa, respectively. Then, human bone marrow-derived MSCs were cultured on SNFs, and the effects on proliferation and osteogenic differentiation were evaluated. The MSCs seeded on SNF proliferated, and the thickness of the cell layer became over 80 µm after 14 days of culture. The osteogenic differentiation of MSCs on SNFs was induced by the culture in the commercial osteogenic differentiation medium. The alkaline phosphatase activity of MSCs on SNFs increased rapidly and remained high up to 14 days and was much higher than that on two-dimensional tissue culture-treated polystyrene. The high expression of RUNX2 and intense staining by alizarin red s after differentiation supported that SNFs enhanced the osteogenic differentiation of MSCs. Furthermore, permeation analysis of SNFs using fluorescein isothiocyanate-dextran suggested a sufficient permeability of SNFs for oxygen, minerals, nutrients, and secretions, which is important for maintaining the cell viability and vitality. These results suggested that SNFs are promising scaffolds for the regeneration of bone defects using MSCs, originated from highly porous and elastic SNF characters.

Integrated Modelling of Cell Responses after Irradiation for DNA-Targeted Effects and Non-Targeted Effects.

Intercellular communication after ionizing radiation exposure, so-called non-targeted effects (NTEs), reduces cell survival. Here we describe an integrated cell-killing model considering NTEs and DNA damage along radiation particle tracks, known as DNA-targeted effects (TEs) based on repair kinetics of DNA damage. The proposed model was applied to a series of experimental data, i.e., signal concentration, DNA damage kinetics, cell survival curve and medium transfer bystander effects (MTBEs). To reproduce the experimental data, the model considers the following assumptions: (i) the linear-quadratic (LQ) function as absorbed dose to express the hit probability to emit cell-killing signals, (ii) the potentially repair of DNA lesions induced by NTEs, and (iii) lower efficiency of repair for the damage in NTEs than that in TEs. By comparing the model results with experimental data, we found that signal-induced DNA damage and lower repair efficiency in non-hit cells are responsible for NTE-related repair kinetics of DNA damage, cell survival curve with low-dose hyper-radiosensitivity (HRS) and MTBEs. From the standpoint of modelling, the integrated cell-killing model with the LQ relation and a different repair function for NTEs provide a reasonable signal-emission probability and a new estimation of low-dose HRS linked to DNA repair efficiency.

Investigation of dose-rate effects and cell-cycle distribution under protracted exposure to ionizing radiation for various dose-rates.

During exposure to ionizing radiation, sub-lethal damage repair (SLDR) competes with DNA damage induction in cultured cells. By virtue of SLDR, cell survival increases with decrease of dose-rate, so-called dose-rate effects (DREs). Here, we focused on a wide dose-rate range and investigated the change of cell-cycle distribution during X-ray protracted exposure and dose-response curves via hybrid analysis with a combination of in vitro experiments and mathematical modelling. In the course of flow-cytometric cell-cycle analysis and clonogenic assays, we found the following responses in CHO-K1 cells: (1) The fraction of cells in S phase gradually increases during 6 h exposure at 3.0 Gy/h, which leads to radio-resistance. (2) Slight cell accumulation in S and G2/M phases is observed after exposure at 6.0 Gy/h for more than 10 hours. This suggests that an increase of SLDR rate for cells in S phase during irradiation may be a reproducible factor to describe changes in the dose-response curve at dose-rates of 3.0 and 6.0 Gy/h. By re-evaluating cell survival for various dose-rates of 0.186-60.0 Gy/h considering experimental-based DNA content and SLDR, it is suggested that the change of S phase fraction during irradiation modulates the dose-response curve and is possibly responsible for some inverse DREs.

Modeling cell survival and change in amount of DNA during protracted irradiation.

Hyper-radiosensitivity (HRS) is a well-known bioresponse under low-dose or low-dose-rate exposures. Although disorder of the DNA repair function, non-targeted effects and accumulation of cells in G2 have been experimentally observed, the mechanism for inducing HRS by long-term irradiation is still unclear. On the basis of biological experiments and a theoretical study, we have shown that change in the amount of DNA associated with accumulation of cells in G2 enhances radiosensitivity. To demonstrate continuous irradiation with 250 kVp X-rays, we adopted a fractionated regimen of 0.186 or 1.00 Gy per fraction at intervals of 1 h (i.e. 0.186 Gy/h, 1.00 Gy/h on average) to Chinese Hamster Ovary (CHO)-K1 cells. The change in the amount of DNA during irradiation was quantified by flow cytometric analysis with propidium iodide (PI). Concurrently, we attempted a theoretical evaluation of the DNA damage by using a microdosimetric-kinetic (MK) model that was modified to incorporate the change in the amount of DNA. Our experimental results showed that the fraction of the cells in G2/M phase increased by 6.7% with 0.186 Gy/h and by 22.1% with 1.00 Gy/h after the 12th irradiation. The MK model considering the change in amount of DNA during the irradiation exhibited a higher radiosensitivity at a high dose range, which could account for the experimental clonogenic survival. The theoretical results suggest that HRS in the high dose range is associated with an increase in the total amount of DNA during irradiation.

In vitro and in vivo antiherpetic effects of (1R,2R)-1-(5'-methylful-3'-yl)propane-1,2,3-triol.

In this study, we demonstrated the in vitro and in vivo antiherpetic activities of a stable furan derivative, (1R,2R)-1-(5'-methylful-3'-yl)propane-1,2,3-triol (MFPT), which had originally been isolated from Streptomyces sp. strain FV60. In the present study, we synthesized MFPT from (5-methylfuran-3-yl)methanol in 6 steps for use in the experiments. MFPT showed potent in vitro antiviral activities against two acyclovir (ACV)-sensitive (KOS and HF) strains and an ACV-resistant (A4-3) strain of herpes simplex virus type 1 (HSV-1) and an ACV-sensitive HSV type 2 (HSV-2) UW 268 strain, their selectivity indices ranging from 310 to 530. By intravaginal application of MFPT to mice, the virus yields decreased dose-dependently against the three strains of HSV-1 and HSV-2. When MFPT was applied at a dose of 1.0 mg/day, the lesion scores, as clinical signs manifested by viral infection, were extensively suppressed in HSV-1-infected mice, whereas the lesion scores in HSV-2-infected mice were not markedly decreased. Interestingly, MFPT exerted an inhibitory effect against ACV-resistant HSV-1 in mice to a similar degree as in ACV-sensitive HSV-1-infected mice. Therefore, the compound might have potential for developing a topical antiviral agent that could be also applied to the infections caused by ACV-resistant viruses.

Evaluation of the cell survival curve under radiation exposure based on the kinetics of lesions in relation to dose-delivery time.

We have investigated the dose rate effects on cell damage caused by photon-beam irradiation. During a relatively long dose-delivery time with a low dose rate, lesions created in cells may undergo some reactions, such as DNA repair. In order to investigate these reactions quantitatively, we adopted the microdosimetric-kinetic (MK) model and deduced a cell surviving fraction (SF) formula for continuous irradiation. This model enabled us to estimate the SF from dose and dose rate. The parameters in the MK model were determined so as to generate the SF, and we attempted to evaluate the dose rate effects on the SF. To deduce the cell-specific parameters in the SF formula, including the dose rate, we performed a split-dose experiment and a single-dose experiment with a constant dose-delivery time (10 min) (to retain the condition for equivalent behavior of cell lesions) by means of a clonogenic assay. Then, using the MK model parameters, the SFs were reproduced for a variety of dose rates (1.0, 0.31, 0.18, 0.025 and 0.0031 Gy/min) and were compared with reported experimental data. The SF curves predicted by the MK model agreed well with the experimental data, suggesting that the dose rate effects appear in the kinetics of cell lesions during the dose-delivery time. From fitting the analysis of the model formula to the experimental data, it was shown that the MK model could illustrate the characteristics of log-SF in a rectilinear form at a high dose range with a relatively low dose rate.

Characterization of a novel mutation in NS1 protein of influenza A virus induced by a chemical substance for the attenuation of pathogenicity.

It is generally accepted that live attenuated influenza vaccine (LAIV) has the potential for use as a vaccination against flu. In this study, we demonstrated the nature of an influenza A virus (IAV) mutant induced by treating the IAV with a stable furan derivative, (1R,2R)-1-(5'-methylfur-3'-yl)propane-1,2,3-triol (MFPT), which had been isolated from Streptomyces sp. strain FV60 with the objective of it being an LAIV candidate. The resulting MFPT-resistant (MFPTr) IAVs possessed attenuated pathogenicity in vitro and in vivo when compared with that of the parent virus (H1N1 subtype, NWS strain). Sequencing analysis revealed that a novel mutation, C490U in ns gene (P164S in NS1), was detected in all MFPTr virus clones tested. Therefore, NS1 might be a main target of MFPT, and it was suggested that the P164S mutation contributed to the attenuated pathogenicity of the mutants. Although the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway is one of the targets of NS1, the MFPTr virus suppressed the phosphorylation of Akt when compared with the wild-type (WT) virus. It was suggested that this might lead to the subsequent inhibition of the cleavage of PARP-1 and caspase-3, which is important for the progression of apoptosis. At the same time, nucleoprotein (NP) was found to be retained in the nuclei in MFPTr virus-infected cells while nuclear export of NP was detected in WT virus-infected cells. In addition, the expression levels of interferon-ß transcripts were significantly decreased in MFPTr virus-infected cells. From these results it can be shown that the mutation, NS1P164S, might be one of the key residues to control NS1 function concerning the induction of apoptosis. In conclusion, MFPT induced favorable mutation in the ns gene for the attenuation of IAV, and therefore might provide the novel methodology for preparing LAIVs.

A formulation of cell surviving fraction after radiation exposure.

Local energy transfer from electrons generated in biotissues that are exposed to ionizing radiation is fundamental to cell damage. Our aim in this investigation was to quantify the probability of cell mortality associated with the damage by electrons and the repair processes in the cell nucleus, envisaging a new interpretation of the cell surviving fraction (SF). We introduced a SF formula for cells exposed to X-rays, which is given as a linear combination of the Poisson distributions about the number of long-lived lesions per nucleus and their "non-lethal probabilities", to show the non-linearity of log SF as a function of dose. The model selection was rated by a statistical index, Akaike's information criterion (AIC). It was shown that the new formula is suitable for describing cell survival and explicitly takes account of the non-lethality in damage-processing pathways of the cells.