Linear Dose Dependence Research Articles

Spectroscopic detection of thrombin with peptides self-assembled on gold nanoparticles hybridized graphene oxide

Thrombin is an important kind of proteases that can cleavage specific peptide bonds and plays a crucial role in numerous diseases, which leads to large amounts of efforts on its detection. In this study, a novel peptide self-assembled biosensor was developed based on gold nanoparticles functionalized graphene oxide (GO) for specific detection of thrombin. Through sulfhydryl design, peptides containing thrombin cleavage sites could self-assemble with the nanocomposites of the graphene material and gold particles, which brought the biosensor unique optoelectronic properties and high biological sensitivity to transduce bio-molecular interactions into optical signals. Spectroscopic measurements were carried out in the presence of thrombin to observe an increase of the absorption peak at ∼528nm and a decrease of the absorbance at wavelength larger than 600nm. The biosensor showed a linear dose-dependence and stable response to thrombin. And with a 528–680nm absorbance ratio as the sensitive detection parameter, the self-assembled biosensor exhibited high sensitivity and specificity for the thrombin detection. Thus, it revealed convenient and sensitive detection abilities for protease of thrombin, indicating a promising prospect for other related proteases, such as matrix metalloproteinases to cancer related diseases.

DNA damage by the sulfate radical anion: hydrogen abstraction from the sugar moiety versus one-electron oxidation of guanine

ABSTRACTThe products of oxidative damage to double-stranded (ds) DNA initiated by photolytically generated sulfate radical anions SO4•− were analyzed using reverse-phase (RP) high-performance liquid chromatography (HPLC). Relative efficiencies of two major pathways were compared: production of 8-oxoguanine (8oxoG) and hydrogen abstraction from the DNA 2-deoxyribose moiety (dR) at C1,′ C4,′ and C5′ positions. The formation of 8oxoG was found to account for 87% of all quantified lesions at low illumination doses. The concentration of 8oxoG quickly reaches a steady state at about one 8oxoG per 100 base pairs due to further oxidation of its products. It was found that another guanine oxidation product identified as 2-amino-5-(2′-alkylamino)-4H-imidazol-4-one (X) was released in significant quantities from its tentative precursor 2-amino-5-[(2′-deoxy-β-d-erythro-pentofuranosyl)amino]-4H-imidazol-4-one (dIz) upon treatment with primary amines in neutral solutions. The linear dose dependence of X release points to the formation of dIz directly from guanine and not through oxidation of 8oxoG. The damage to dR was found to account for about 13% of the total damage, with majority of lesions (33%) originating from the C4′ oxidation. The contribution of C1′ oxidation also turned out to be significant (17% of all dR damages) despite of the steric problems associated with the abstraction of the C1′-hydrogen. However, no evidence of base-to-sugar free valence transfer as a possible alternative to direct hydrogen abstraction at C1′ was found.

CYTOGENETIC EFFECTS OF LOW NEUTRON DOSES IN MAMMALIAN CELLS

Актуальность. В связи с облучением больших групп людей в малых дозах при лечебных и диагностических процедурах и потребностью прогнозирования канцерогенного риска облучения представляется актуальным изучение закономерностей биологических эффектов малых доз радиации. Относительно мало исследованы особенности биологического действия нейтронного излучения и его эффекты на цитогенетическом уровне в области малых доз, при этом они могут быть важны при проведении нейтронной терапии и разработке нормативных документов по радиационной защите на ускорителях ионов, в том числе терапевтического назначения.Цель – изучение закономерностей образования структурных повреждений хромосом в клетках млекопитающих при действии быстрых нейтронов в области доз до 1 Гр.Материал и методы. Цитогенетическую эффективность нейтронов с энергией 14,5 МэВ исследовали на лимфоцитах крови человека и клетках китайского хомячка СНО-К1. Диапазон доз нейтронов составлял 0,1–1,2 Гр, мощностей доз – 0,3–60 мГр/мин, частота следования импульсов – 50, 5, и 0,017 Гц. Приготовление препаратов хромосом проводили по общепринятым стандартным методикам. При анализе учитывали весь спектр аберраций хромосом. Результаты. В исследованном диапазоне доз нейтронов для обеих клеточных культур наблюдалась одинаковая закономерность: резкий подъем выхода аберраций хромосом при дозах 0,12–0,15 Гр, замедление роста числа аберраций с увеличением дозы нейтронов до 0,3–0,5 Гр, далее стандартная дозовая зависимость. Указанная закономерность выявлена как по суммарной частоте аберраций хромосом, так и по частоте дицентриков (лимфоциты) и парных фрагментов (СНО-К1). Заключение. Полученные результаты свидетельствуют о проявлении феномена гиперчувствительности и индуцированной радиорезистентности в клетках лимфоцитов человека и китайского хомячка при действии нейтронов с энергией 14,5 МэВ.

Study of thermoluminescence (TL) and optically stimulated luminescence (OSL) from α-keratin protein found in human hairs and nails: potential use in radiation dosimetry.

The thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of human nails and hairs containing α-keratin proteins have been investigated. For the present studies, black hairs and finger nails were selectively collected from individuals with ages between 25 and 35 years. The collected hairs/nails were cut to a size of < 1 mm and cleaned with distilled water to remove dirt and other potential physical sources of contamination. All samples were optically beached with 470 nm of LED light at 60 mW/cm(2) intensity and irradiated by a (60)Co γ source. The hair and nail samples showed overlapping multiple TL glow peaks in the temperature range from 70 to 210 ° C. Continuous wave (CW)-OSL measurements of hair samples at a wavelength of 470 nm showed the presence of two distinct OSL components with photoionization cross section (PIC) values of about 1.65 × 10(-18) cm(2) and about 3.48 × 10(-19) cm(2), while measurements of nail samples showed PIC values of about 6.98 × 10(-18) cm(2) and about 8.7 × 10(-19) cm(2), respectively. This difference in PIC values for hair and nail samples from the same individual is attributed to different arrangement of α-keratin protein concentrations in the samples. The OSL sensitivity was found to vary ± 5 times among nail and hair samples from different individuals, with significant fading (60% in 11 h) at room temperature. The remaining signal (after fading) can be useful for dose estimation when a highly sensitive OSL reader is used. In the absorbed dose range of 100 mGy-100 Gy, both the TL and OSL signals of hair and nail samples showed linear dose dependence. The results obtained in the present study suggest that OSL using hair and nail samples may provide a supplementary method of dose estimation in radiological and nuclear emergencies.

SU‐E‐T‐497: Initial Characterization of a Novel 2D Computed Radiography (CR) Dosimeter for SBRT

PurposeFor 2D, sub‐mm resolution dose measurements Gafchromic™ film is currently a standard in radiotherapy; mainly because of its energy independence and water equivalence. However, EBT film is disposable. Therefore, the dosimetric and uniformity characteristics needs to be estimated from a second, possibly different, (calibration) film. Moreover, EBT has a post‐irradiation coloration and a non‐linear dose dependence with saturation, which limits the applicable time interval and dose range. CR technology forms an interesting alternative for EBT. Dose dependent CRplates have a sub‐mm resolution, and additionally a linear dose dependence over decades of dose. But, CR has an inherent signal fading and energy dependence. Here, for the first time, a radiotherapy 2D CR prototype was characterized for an extended dose range (up to 35Gy), signal fading, and basic energy dependence.MethodsThe prototype was irradiated with a standard 10×10cm 6MV photon beam, and scanned with a commercial CR 15‐X(R) scanner. The time between the start of irradiation and scanning (T_Scan) was monitored. The linearity of the dose response was evaluated between 0 and 35Gy using a fixed T_Scan of 4min, if possible (i.e. ≤10Gy). Next, the signal fading was characterized for a T_Scan‐range of 4 to 20min. The energy dependence was assessed by a comparison of out‐of‐field measurements of CR, EBT, and TLD.ResultsThe radiotherapy CR prototype has a linear response over the complete SBRT dose range (0– 35Gy). The prototype had a small (5%), but linear signal fading over the time interval of interest (4–20min). Out‐of‐field, the prototype has a 8% over response due to an increased amount of low energy photons. The impact of the over response on intensity modulated radiotherapy remains to be evaluated.ConclusionCR technology is promising for SBRT dose measurements up to 35Gy. It is a reusable linear alternative for film dosimetry.

Photoluminescence and radioluminescence properties of MnO-doped SnO–ZnO–P2O5 glasses

In this study, the photoluminescence and radioluminescence properties of MnO-doped SnO–ZnO–P2O5 glasses are examined. We have confirmed that linear dose-dependence and radioluminescence emission decay depend on Mn2+ concentration. Energy transfer from donor Sn2+ center to acceptor Mn2+ center is observed in both photoluminescence and radioluminescence processes, and the energy transfer efficiency is more than 90% when the Mn2+/Sn2+ ratio is 5. Since emission intensity of Mn2+ is higher than that of Sn2+ in radioluminescence compared to photoluminescence, it is suggested that energy transfer from the host matrix to Mn2+ center by X-ray occurred preferentially over energy transfer to Sn2+ center. The present results suggest that the conventional parity rule for photoluminescence is not always adaptable for radioluminescence, although emission-related energy levels are the same for both the processes.

Characterization of a commercially-produced chemically stable Fricke gel dosimeter

The successful manufacturing of a modified Fricke gel with increased shelf life in a pilot scale (20-liter) commercial production facility is reported. The gels remained chemically stable and usable for over 30 days. Linear dose dependence was observed for cumulative doses up to 30 Gy. Dose-depth studies showed a good correlation between the experimental data and theoretical expectations, but the dose response appeared to be energy-dependent.

Significant disparity in base and sugar damage in DNA resulting from neutron and electron irradiation.

In this study, a comparison of the effects of neutron and electron irradiation of aqueous DNA solutions was investigated to characterize potential neutron signatures in DNA damage induction. Ionizing radiation generates numerous lesions in DNA, including base and sugar lesions, lesions involving base–sugar combinations (e.g. 8,5′-cyclopurine-2′-deoxynucleosides) and DNA–protein cross-links, as well as single- and double-strand breaks and clustered damage. The characteristics of damage depend on the linear energy transfer (LET) of the incident radiation. Here we investigated DNA damage using aqueous DNA solutions in 10 mmol/l phosphate buffer from 0–80 Gy by low-LET electrons (10 Gy/min) and the specific high-LET (∼0.16 Gy/h) neutrons formed by spontaneous 252Cf decay fissions. 8-hydroxy-2′-deoxyguanosine (8-OH-dG), (5′R)-8,5′-cyclo-2′-deoxyadenosine (R-cdA) and (5′S)-8,5′-cyclo-2′-deoxyadenosine (S-cdA) were quantified using liquid chromatography–isotope-dilution tandem mass spectrometry to demonstrate a linear dose dependence for induction of 8-OH-dG by both types of radiation, although neutron irradiation was ∼50% less effective at a given dose compared with electron irradiation. Electron irradiation resulted in an exponential increase in S-cdA and R-cdA with dose, whereas neutron irradiation induced substantially less damage and the amount of damage increased only gradually with dose. Addition of 30 mmol/l 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS), a free radical scavenger, to the DNA solution before irradiation reduced lesion induction to background levels for both types of radiation. These results provide insight into the mechanisms of DNA damage by high-LET 252Cf decay neutrons and low-LET electrons, leading to enhanced understanding of the potential biological effects of these types of irradiation.

Thermoluminescence and linear thermal expansion of MgAl2O4

The co-efficient of linear thermal expansion (αav) and dose dependence of thermoluminescence (TL) in MgAl2O4(s) were measured. The change in length per unit length was recorded as a function of temperature between room temperature to 1,273 K at a heating rate of 8 K min−1, in flowing argon atmosphere. The average of three measurements was quoted as the αav for MgAl2O4(s). The linear thermal expansion was measured to an accuracy of ±3 %. The dose dependence of the TL was found to be super linear in the dose range of 0–10 kGy with a k value of 0.503 indicating that the MgAl2O4(s) ceramic is ideally suited for the dose estimation of self-irradiated inert matrix fuel in a once through fuel cycle for actinide burning.

Chromium(VI) Causes Interstrand DNA Cross-Linking in Vitro but Shows No Hypersensitivity in Cross-Link Repair-Deficient Human Cells

Hexavalent chromium is a human carcinogen activated primarily by direct reduction with cellular ascorbate and to a lesser extent, by glutathione. Cr(III), the final product of Cr(VI) reduction, forms six bonds allowing intermolecular cross-linking. In this work, we investigated the ability of Cr(VI) to cause interstrand DNA cross-links (ICLs) whose formation mechanisms and presence in human cells are currently uncertain. We found that in vitro reduction of Cr(VI) with glutathione showed a sublinear production of ICLs, the yield of which was less than 1% of total Cr-DNA adducts at the optimal conditions. Formation of ICLs in fast ascorbate-Cr(VI) reactions occurred during a short reduction interval and displayed a linear dose dependence with the average yield of 1.3% of total adducts. In vitro production of ICLs was strongly suppressed by increasing buffer molarity, indicating inhibitory effects of ligand-Cr(III) binding on the formation of cross-linking species. The presence of ICLs in human cells was assessed from the impact of ICL repair deficiencies on Cr(VI) responses. We found that ascorbate-restored FANCD2-null and isogenic FANCD2-complemented cells showed similar cell cycle inhibition and toxicity by Cr(VI). XPA-null cells are defective in the repair of Cr-DNA monoadducts, but stable knockdowns of ERCC1 or XPF in these cells with extended time for the completion of cross-linking reactions did not produce any sensitization to Cr(VI). Our results together with chemical and steric considerations of Cr(III) reactivity suggest that ICL generation by chromate is probably an in vitro phenomenon occurring at conditions permitting the formation of Cr(III) oligomers.

Intravenous infusions of glucose stimulate key lipogenic enzymes in adipose tissue of dairy cows in a dose-dependent manner

The present study was investigated whether increasing amounts of glucose supply have a stimulatory effect on the mRNA abundance and activity of key lipogenic enzymes in adipose tissue of midlactation dairy cows. Twelve Holstein-Friesian dairy cows in midlactation were cannulated in the jugular vein and infused with either a 40% glucose solution (n=6) or saline (n=6). For glucose infusion cows, the infusion dose increased by 1.25%/d relative to the initial net energy for lactation (NEL) requirement until a maximum dose equating to a surplus of 30% NEL was reached on d 24. This maximum dose was maintained until d 28 and stopped thereafter (between d 29–32). Cows in the saline infusion group received an equivalent volume of 0.9% saline solution. Samples of subcutaneous adipose tissue were taken on d 0, 8, 16, 24, and 32 when surplus glucose reached 0, 10, 20, and 30% of the NEL requirement, respectively. The mRNA abundance of fatty acid synthase, cytoplasmic acetyl-coenzyme A synthetase, cytoplasmic glycerol 3-phosphate dehydrogenase-1, and glucose 6-phosphate dehydrogenase showed linear treatment × dose interactions with increasing mRNA abundance with increasing glucose dose. The increased mRNA abundance was paralleled by a linear treatment × dose interaction for fatty acid synthase and acetyl-coenzyme A synthetase enzymatic activities. The mRNA abundance of ATP-citrate lyase showed a tendency for linear treatment × dose interaction with increasing mRNA abundance with increasing glucose dose. The mRNA abundance of all tested enzymes, as well as the activities of fatty acid synthase and acetyl-coenzyme A synthetase, correlated with plasma glucose and serum insulin levels. In a multiple regression model, the predictive value of insulin was dominant over that of glucose. In conclusion, gradual increases in glucose supply upregulate key lipogenic enzymes in adipose tissue of midlactating dairy cows with linear dose dependency. Insulin appears to be critically involved in this regulation.

Highly sensitive detection of urinary cadmium to assess personal exposure

A series of Boron-Doped Diamond (BDD) ultramicroelectrode arrays were fabricated and investigated for their performance as electrochemical sensors to detect trace level metals such as cadmium. The steady-state diffusion behavior of these sensors was validated using cyclic voltammetry followed by electrochemical detection of cadmium in water and in human urine to demonstrate high sensitivity (>200μAppb−1cm−2) and low background current (<4nA). When an array of ultramicroelectrodes was positioned with optimal spacing, these BDD sensors showed a sigmoidal diffusion behavior. They also demonstrated high accuracy with linear dose dependence for quantification of cadmium in a certified reference river water sample from the U.S. National Institute of Standards and Technology (NIST) as well as in a human urine sample spiked with 0.25–1ppb cadmium.

Physiological characterization of lipid accumulation and in vivo ester formation inGordoniasp. KTR9

Previous work has demonstrated the feasibility of in vivo biodiesel synthesis in Escherichia coli, however, ethyl ester formation was dependent on an external fatty acid feedstock. In contrast to E. coli, actinomycetes may be ideal organisms for direct biodiesel synthesis because of their capacity to synthesize high levels of triacylglcerides (TAGs). In this study, we investigated the physiology and associated TAG accumulation along with the in vivo ability to catalyze ester formation from exogenous short chain alcohol sources in Gordonia sp. KTR9, a strain that possesses a large number of genes dedicated to fatty acid and lipid biosynthesis. Total lipid fatty acids content increased by 75% and TAG content increased by 50% under nitrogen starvation conditions in strain KTR9. Strain KTR9 tolerated the exogenous addition of up to 4% methanol, 4% ethanol and 2% propanol in the media. Increasing alcohol concentrations resulted in a decrease in the degree of saturation of recovered fatty acid alcohol esters and a slight increase in the fatty acid chain length. A linear dose dependency in fatty alcohol ester synthesis was observed in the presence of 0.5-2% methanol and ethanol compared to control KTR9 strains grown in the absence of alcohols. An inspection of the KTR9 genome revealed the presence of several putative wax ester synthase/acyl-coenzyme A : diacylglycerol acyltransferase (WS/DGAT) enzymes, encoded by atf gene homologs, that may catalyze the in vivo synthesis of fatty acid esters from short chain alcohols. Collectively, these results indicate that Gordonia sp. KTR9 may be a suitable actinomycete host strain for in vivo biodiesel synthesis.

Radiation-induced double strand breaks and subsequent apoptotic DNA fragmentation in human peripheral blood mononuclear cells

In case of accidental radiation exposure or a nuclear incident, physical dosimetry is not always complete. Therefore, it is important to develop tools that allow dose estimates and determination that are based on biological markers of radiation exposure. Exposure to ionizing radiation triggers a large-scale activation of specific DNA signaling and repair mechanisms. This includes the phosphorylation of γH2AX in the vicinity of a double-strand break (DSB). A DNA DSB is a cytotoxic form of DNA damage, and if not correctly repaired can initiate genomic instability, chromosome aberrations, mutations or apoptosis. Measurements of DNA DSBs and their subsequent repair after invitro irradiation has been suggested to be of potential use to monitor cellular responses. The bone marrow and the blood are known to be the most radiosensitive tissues of the human body and can therefore be of particular importance to find radiation-induced biological markers. In the present study, changes in H2AX phosphorylation and apoptosis of irradiated human peripheral blood mononuclear cells (PBMCs) were analyzed. Freshly isolated PBMCs from healthy donors were irradiated with X-rays (0.1, 0.25, 0.5, 1, 2 and 4Gy). The phosphorylation of γH2AX was measured at different time points (0, 0.25, 1, 2, 4, 6 and 24h) after irradiation. We detected a linear dose-dependency of γH2AX phosphorylation measured by γH2AX foci scoring using immunofluorescence microscopy as well as by γH2AX fluorescence detection using flow cytometry. Apoptosis was detected by measuring DNA fragmentation at different time points (0, 24, 48, 72, 96h) after X-irradiation using DNA ladder gel electrophoresis. The apoptotic DNA fragmentation increased in a dose-dependent manner. In conclusion, DNA DSBs and subsequent apoptotic DNA fragmentation monitoring have potential as biomarkers for assessing human exposure in radiation biodosimetry.

Luminescence properties of CaS:Ce, Sm nanophosphors

CaS:Ce, Sm nanophosphors were synthesized via solid state diffusion method. X-Ray diffraction confirmed the cubic crystalline phase of CaS:Ce, Sm nanoparticles. The particle size calculated using Debye–Scherrer formula was found to be 52 nm. The morphological investigations of the nanoparticles were made using TEM and found to have nearly spherical morphology with diameter 45–50 nm, which is in close agreement with the XRD result. The PL emission characteristics of CaS:Ce, Sm as a function of cerium and samarium concentrations have been studied and CaS:Ce 0.6Sm 0.4 system has maximum emission intensity, hence it was opted for further studies. The CaS:Ce 0.6Sm 0.4 system showed independent emission of Sm and Ce when excited at 330 and 450 nm, respectively. To study the energy transfer between cerium and samarium, the CaS:Ce 0.6Sm 0.4 was excited at wavelengths other than the excitation wavelengths of Ce (450 nm) and Sm (330 nm). The existence of Ce emission (at an excitation of 390 nm) even in the absence of Ce excitation band and Sm emission at an excitation of 405 nm, which is the excitation band of Ce, indicates the energy transfer at these two wavelengths. Thermoluminescence characteristics of 60Co irradiated CaS:Ce 0.6Sm 0.4 have been investigated for different doses of 0.14–125 Gy. All the glow curves show a single peak at 475 K. With increasing dose, the intensity of this peak increases and a shoulder is formed on the lower temperature side at 415 K at 21 Gy of exposure. CaS:Ce 0.6Sm 0.4 shows almost linear dose dependence up to 125 Gy.

Feasibility of radiation dosimetry with phosphorus-doped optical fibers in the ultraviolet and visible domain

We investigated the feasibility of using phosphorus-doped optical fibers to monitor the levels of deposited dose during an irradiation. For this, we characterized their spectral and time dependence of the steady state 10 keV X-ray radiation-induced attenuation in the ultraviolet and visible range of wavelengths (200 nm–900 nm). Their radiation sensitivity is very high with losses exceeding 10 dB m −1 for doses larger than 10 Gy and wavelengths shorter than 550 nm. Our results reveal a sub linear dose dependence of the induced losses that also depends on the dose rate (1 Gy s −1–50 Gy s −1) between 350 nm and 900 nm. For this spectral domain, excess of attenuation is due to the phosphorus oxygen-hole centers. P 2 defects are responsible for the induced losses around 300 nm that linearly increase with the dose at least until 1 kGy and without dose rate effect. We measured no noticeable influence of the temperature (5 °C–50 °C) on the radiation-induced attenuation in the studied spectral domain. Our study shows that dosimetry with phosphorus-doped fibers seems possible in the ultraviolet (around 300 nm) with a sensitivity enhanced by a factor > 100 compared to the one observed in the infrared region (> 900 nm).

Simulation of the Nonlinear Dose Dependence of Stabilized Point Defects

The dose dependence of the concentration of point defects in alkali-halides as well as other crystals, as exhibited by the dependence of the thermoluminescence (TL), optical absorption and ESR on the dose of non-ionizing UV excitation is studied using numerical simulation. The relevant set of coupled rate equations are first written and plausible sets of trapping parameters are chosen. Instead of using simplifying assumptions previously used for reaching conclusions concerning this dose behavior, exact numerical solutions have now been reached. Depending on the parameters chosen, different dose dependencies are seen. In some cases, linear dose dependence is reached in a broad range. Sublinear dose dependence, close to a D1/2 dependence when D is the dose of excitation can be reached when retrapping is stronger than trapping in other traps stabilizing the defects. When strong competition between stabilizing traps takes place, an initial linear range is observed followed by strong superlinearity and an approach to saturation. All these behaviors have been observed experimentally in TL measurements as well as ESR and optical absorption in different materials. Similarities and dissimilarities to linear and non-linear dose dependencies obtained experimentally and by simulations when ionizing irradiation is used for excitation are discussed.

In vitro tools for photobiological testing: molecular responses to simulated solar UV of keratinocytes growing as monolayers or as part of reconstructed skin

Epidermal keratinocytes are critical targets for UV-induced genotoxicity as their transformation by sunlight overexposure can lead to skin cancer such as basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Therefore, assessment of photoprotection should involve early markers associated with DNA photodamage. Here, the same normal human keratinocytes either in monoculture (KC) or in full thickness reconstructed skin (RS) were compared with respect to their response to simulated solar UV (SSUV) exposure. Irradiation conditions (spectral power distribution and doses) were designed to mimic environmental zenithal UV from sunlight. At doses where survival was higher than 80%, comet assay showed more single strand breaks (SSB) and cyclobutane pyrimidine dimers (CPD) in keratinocytes in RS than in KC one hour post-exposure. The transcription factor p53 was activated in both models. While in KC p53 accumulation displayed a linear dose-dependency up to 24 h post-exposure, in RS it followed a bell-shaped profile and reverted to its basal rate. QRT-PCR demonstrated that among genes controlled by p53, P21 and MDM2 were clearly induced by SSUV in KC, whereas GADD45 expression was strongly and almost exclusively up-regulated in RS. Nrf2-dependent antioxidant genes (Ferritin light chain, NQO1) were only induced in RS, yet at low doses for NQO1. In vitro models such as KC or RS allowing the development of quantitative methodologies should be used as surrogates for in vivo tests assessing photogenotoxicity.

PSL study of irradiated food: NaCl as possible reference material

Gamma-irradiated NaCl samples of different origin were studied with the aim to find a reliable, easy-to-use, low-cost standard for the PSL technique, an increasingly used screening method for irradiated food identification. Five different natural salt types (rock and sea salts) purchased in the local markets were studied along with a laboratory-grade NaCl. High sensitivity and reproducibility of the PSL response are good properties of salt, but the pronounced fading of the signal may be a severe limitation of its use as a reference material. The high sensitivity along with the linear dose dependence of the PSL response opens up the interesting possibility of salt as suitable material for retrospective and environmental dosimetry, especially in the case of accidental irradiation or malevolent use of ionizing radiation. Again, the extreme sensitivity of the PSL signal to light and the pronounced fading must be considered limiting factors, and further basic research is required before practical applications of salt be feasible.

Relevance of laser irradiance threshold in the induction of alkaline phosphatase in human osteoblast cultures

Induction of matrix synthesis by low-level laser has been demonstrated extensively. However, the question of dose- or power intensity-dependency is under-investigated. To address this issue we chose human osteoblast cell cultures and measured their alkaline phosphatase (ALP) activity after laser irradiation. The cell cultures were irradiated periodically by 690 nm radiation via optical transmission fiber-based laser needles, reaching into the culture dishes. The osteoblasts showed no induction of ALP activity when we used a single laser needle stimulation with a laser irradiance of 51 mW/cm(2), an increase of approximately 43% at 102 mW/cm(2) irradiance (two needles per well) and a ninefold increase at 204 mW/cm(2) irradiance (four needles per well), leaving the temperature of the culture medium unaffected. We concluded that the osteoblastic response in ALP activity to a laser stimulus shows a logarithmic relationship, with a distinct threshold, rather than a linear dose-dependency. Secondly, the laser irradiance, rather than the dose, is relevant for the impact of the laser.