Nonlinear Dose-response Curve Research Articles

SU-G-BRB-14: Uncertainty of Radiochromic Film Based Relative Dose Measurements

Purpose: Due to inherently non-linear dose response, measurement of relative dose distribution with radiochromic film requires measurement of absolute dose using a calibration curve following previously established reference dosimetry protocol. On the other hand, a functional form that converts the inherently non-linear dose response curve of the radiochromic film dosimetry system into linear one has been proposed recently [Devic et al, Med. Phys. 39 4850–4857 (2012)]. However, there is a question what would be the uncertainty of such measured relative dose. Methods: If the relative dose distribution is determined going through the reference dosimetry system (conversion of the response by using calibration curve into absolute dose) the total uncertainty of such determined relative dose will be calculated by summing in quadrature total uncertainties of doses measured at a given and at the reference point. On the other hand, if the relative dose is determined using linearization method, the new response variable is calculated as ζ=a(netOD)n/ln(netOD). In this case, the total uncertainty in relative dose will be calculated by summing in quadrature uncertainties for a new response function (σζ) for a given and the reference point. Results: Except at very low doses, where the measurement uncertainty dominates, the total relative dose uncertainty is less than 1% for the linear response method as compared to almost 2% uncertainty level for the reference dosimetry method. The result is not surprising having in mind that the total uncertainty of the reference dose method is dominated by the fitting uncertainty, which is mitigated in the case of linearization method. Conclusion: Linearization of the radiochromic film dose response provides a convenient and a more precise method for relative dose measurements as it does not require reference dosimetry and creation of calibration curve. However, the linearity of the newly introduced function must be verified. Dave Lewis is inventor and runs a consulting company for radiochromic films

TLD efficiency calculations for heavy ions: an analytical approach

The use of thermoluminescent dosimeters (TLDs) in heavy charged particles’ dosimetry is limited by their non-linear dose response curve and by their response dependence on the radiation quality. Thus, in order to use TLDs with particle beams, a model that can reproduce the behavior of these detectors under different conditions is needed. Here a new, simple and completely analytical algorithm for the calculation of the relative TL-efficiency depending on the ion charge Z and energy E is presented. The detector response is evaluated starting from the single ion case, where the computed effectiveness values have been compared with experimental data as well as with predictions from a different method. The main advantage of this approach is that, being fully analytical, it is computationally fast and can be efficiently integrated into treatment planning verification tools. The calculated efficiency values have been then implemented in the treatment planning code TRiP98 and dose calculations on a macroscopic target irradiated with an extended carbon ion field have been performed and verified against experimental data.

Dose–response curve of a microfluidic magnetic bead-based surface coverage sandwich assay

Magnetic micro- and nanoparticles ('magnetic beads') have been used to advantage in many microfluidic devices for sensitive antigen (Ag) detection. Today, assays that use as read-out of the signal the number count of immobilized beads on a surface for quantification of a sample's analyte concentration have been among the most sensitive and have allowed protein detection lower than the fgmL(-1) concentration range. Recently, we have proposed in this category a magnetic bead surface coverage assay (Tekin et al., 2013 [1]), in which 'large' (2.8μm) antibody (Ab)-functionalized magnetic beads captured their Ag from a serum and these Ag-carrying beads were subsequently exposed to a surface pattern of fixed 'small' (1.0μm) Ab-coated magnetic beads. When the system was exposed to a magnetic induction field, the magnet dipole attractive interactions between the two bead types were used as a handle to approach both bead surfaces and assist with Ag-Ab immunocomplex formation, while unspecific binding (in absence of an Ag) of a large bead was reduced by exploiting viscous drag flow. The dose-response curve of this type of assay had two remarkable features: (i) its ability to detect an output signal (i.e. bead number count) for very low Ag concentrations, and (ii) an output signal of the assay that was non-linear with respect to Ag concentration. We explain here the observed dose-response curves and show that the type of interactions and the concept of our assay are in favour of detecting the lowest analyte concentrations (where typically either zero or one Ag is carried per large bead), while higher concentrations are less efficiently detected. We propose a random walk process for the Ag-carrying bead over the magnetic landscape of small beads and this model description explains the enhanced overall capture probability of this assay and its particular non-linear dose response curves.

A new cytotoxicity assay for brevetoxins using fluorescence microscopy.

Brevetoxins are a family of ladder-framed polyether toxins produced during blooms of the marine dinoflagellate, Karenia brevis. Consumption of shellfish or finfish exposed to brevetoxins can lead to the development of neurotoxic shellfish poisoning. The toxic effects of brevetoxins are believed to be due to the activation of voltage-sensitive sodium channels in cell membranes. The traditional cytotoxicity assay for detection of brevetoxins uses the Neuro-2A cell line, which must first be treated with the neurotoxins, ouabain and veratridine, in order to become sensitive to brevetoxins. In this study, we demonstrate several drawbacks of the Neuro-2A assay, which include variability for the EC50 values for brevetoxin and non-linear triphasic dose response curves. Ouabain/veratridine-treated Neuro-2A cells do not show a typical sigmoidal dose response curve in response to brevetoxin, but rather, have a polynomial shaped curve, which makes calculating EC50 values highly variable. We describe a new fluorescence live cell imaging model, which allows for accurate calculation of cytotoxicity via nuclear staining and additional measurement of other viability parameters depending on which aspect of the cell is stained. In addition, the SJCRH30 cell line shows promise as an alternative to Neuro-2A cells for testing brevetoxins without the need for ouabain and veratridine.

Bayesian Semiparametric Predictive Modeling with Applications in Dose-Response Prediction

A framework is proposed for making quality predictions in situations for which only systematically inaccurate data are available. The predictions are based on the systematically inaccurate data, complete data from similar situations, and expert knowledge. The proposed predictive model is well suited to functional data and is computationally simple, fast, and stable. We focus primarily on a particular problem presenting itself in the pharmaceutical industry. Predicting both side effect and endpoint dose responses before the initiation of a clinical trial has enormous ethical and financial importance in the pharmaceutical industry. The proposed Bayesian semiparametric predictive model is used to predict unobserved clinical dose-response curves conditional on preclinical data, data from similar compounds, and prior knowledge. The model allows for nonlinear dose-response curves and the incorporation of relevant prior information. Posterior sampling is achieved through a simple and computationally efficient Gibbs sampler. The predictions from the model are drawn from the posterior distribution of the average dose-response curve for the candidate compound, allowing straightforward incorporation into a risk assessment model unlike the deterministic predictions often used currently. The model is used on actual data from the pharmaceutical industry, showing that the model is capable of predicting lack or presence of trend with appropriate uncertainty.

A Mode-of-Action Approach for the Identification of Genotoxic Carcinogens

Distinguishing between clastogens and aneugens is vital in cancer risk assessment because the default assumption is that clastogens and aneugens have linear and non-linear dose-response curves, respectively. Any observed non-linearity must be supported by mode of action (MOA) analyses where biological mechanisms are linked with dose-response evaluations. For aneugens, the MOA has been well characterised as disruptors of mitotic machinery where chromosome loss via micronuclei (MN) formation is an accepted endpoint used in risk assessment. In this study we performed the cytokinesis-block micronucleus assay and immunofluorescence mitotic machinery visualisation in human lymphoblastoid (AHH-1) and Chinese Hamster fibroblast (V79) cell lines after treatment with the aneugen 17-β-oestradiol (E2). Results were compared to previously published data on bisphenol-A (BPA) and Rotenone data. Two concentration-response approaches (the threshold-[Td] and benchmark-dose [BMD] approaches) were applied to derive a point of departure (POD) for in vitro MN induction. BMDs were also derived from the most sensitive carcinogenic endpoint. Ranking comparisons of the PODs from the in vitro MN and the carcinogenicity studies demonstrated a link between these two endpoints for BPA, E2 and Rotenone. This analysis was extended to include 5 additional aneugens, 5 clastogens and 3 mutagens and further concentration and dose-response correlations were observed between PODs from the in vitro MN and carcinogenicity. This approach is promising and may be further extended to other genotoxic carcinogens, where MOA and quantitative information from the in vitro MN studies could be used in a quantitative manner to further inform cancer risk assessment.

Abstract 1281: POLD3 is required for DNA damage response to endogenous and exogenous DNA damage in human cells.

Abstract Methyl methanesulfonate (MMS) induces mutations in a nonlinear (hockey-stick-shaped) dose-response curve in DT40 cells, about 55% of which are located at A:T sites with a high frequency of A to T mutations. We hypothesized that these transversion mutations are due to base excision repair (BER) intermediates, such as abasic sites and single strand breaks derived from N3-methyladenine. One candidate polymerase to bypass abasic sites is polymerase delta (POLD). POLD is responsible for the lagging strand during DNA replication. POLD is referred to as a high fidelity DNA polymerase because of its ability to discriminate deoxynucleotides and its 3’->5’ exo-nuclease activity. One of the POLD subunits, POLD3, is important to recruit PCNA binding to the POLD core enzyme and is implied to have critical roles for translesion DNA synthesis. In yeast, cells deficient in POLD3 homologous gene POL32 are sensitive to DNA damaging agents and resistant to mutations caused by mutagens, such as MMS and UV. Here we generated POLD3 knock-down (KD) cells via lentivirus based shRNA in three different human cell lines. All POLD3 KD cells grow slower than the control cells, suggesting POLD3 function tolerates endogenous DNA lesions. Furthermore, we found that POLD3 KD cells were sensitive to various genotoxic agents including MMS and potassium chromate. To further investigate the role of POLD3 in the DNA damage response, we introduced a series of deletion mutations of POLD3 in POLD3 deficient cells. We found that both the POLD2 binding domain and the middle linker domain are critical for the activity of POLD3 while the C-terminal PCNA binding domain is dispensable. While there is little homology between human POLD3 and yeast POL32, function of these two proteins appears to be quite similar in structure biology analysis. Our results also suggest that POLD3 plays important roles to bypass DNA lesions caused by endogenous and various exogenous genotoxic agents. Citation Format: Xu Tian, James Swenberg, Jun Nakamura. POLD3 is required for DNA damage response to endogenous and exogenous DNA damage in human cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1281. doi:10.1158/1538-7445.AM2013-1281

The Emerging Battlefield: Should the Use of a Nonmonotonic, Non-Threshold Dose-Response Curve for Alleged Endocrine-Disrupting Chemicals Survive aDaubert/FryeChallenge?

IN Hormones and Endocrine-Disrupting Chemicals: Low-Dose Effects and Nonmonotonic Dose Responses, (1) authors contend that toxicological significance of alleged endocrine-disrupting chemicals (EDCs) cannot be assessed using traditional monotonic threshold dose-response curve. In contrast, they suggest that EDCs can cause adverse human biological effects at low, regulatory-approved dose levels. Although this article only focuses on biological effects per se and not on whether effect is adverse or not, they contend that it is improper to extrapolate that harmful effects cannot occur at environmentally relevant, regulatory-approved low-dose levels just because no effects are seen at much higher regulatory-accepted no observable adverse effect level (NOAEL). Plaintiffs' attorneys and their retained experts will point to Vandenberg paper in support of position that EDC at issue proximately caused their plaintiff's cancer, reproductive or developmental problem, even when plaintiff only was exposed to alleged EDC at regulatory-approved safe level. Through a weight-of-the-evidence methodology, plaintiffs' experts may attempt to use some sort of nonmonotonic, non-threshold dose-response curve to opine that health condition at issue generally and specifically was caused by exposure to very low doses of alleged EDC at regulatory approved levels. Accordingly, defendants must mount a convincing Daubert/Frye argument to defeat this theory. This article demonstrates how-to construct a successful Daubert/Frye challenge against an expert's attempted use of a nonmonotonic, non-threshold dose-response curve to support an adverse causation opinion about an alleged EDC. I. Dose-Response Curves There are three dose-response curves that come into play in any personal injury environmental toxic tort case. First, traditional monotonic, nonlinear threshold dose-response curve provides that dose has to reach a recognized threshold level before chemical likely will have any adverse human health consequences. Once chemical exerts an adverse effect, adverse effect will continue to worsen as dose increases. The generally recognized phrase the dose makes poison is associated with a monotonic, nonlinear dose-response curve. Second, monotonic, linear non-threshold dose-response curve states that a chemical can have an adverse human health effect at any dose level. Thus, there is no safe dose level and no threshold dose level. As such, exposure to even molecule of chemical at issue puts an individual at risk for development of an adverse health condition. This concept is referred to as one hit theory because allegedly just dose of chemical at any level can start disease process. Third, nonmonotonic, non-threshold dose-response curve, suggested by Vandenberg article as being particularly applicable to EDCs, provides that a chemical can have effects at regulatory approved low dose levels; have no effects at moderately higher dose levels and have effects at highest dose levels. A nonmonotonic, non-threshold dose-response curve is described as either Ushaped or inverted U-shaped. Allowing a plaintiff's expert to opine that chemical on trial should be analyzed through use of a nonmonotonic, non-threshold dose-response curve would present significant problems for a defendant. Specifically, defendant's assertion of common regulatory compliance defense that plaintiffs dose level never exceeded applicable regulatory-acceptable safe dose level would be seriously questioned and could be disregarded completely by fact finder. Moreover, plaintiff would be able to raise a significant question in jurors' minds as to whether defendant was negligent for only testing alleged EDC at regulatory-accepted high levels instead of also including in its test protocol environmentally relevant low dose levels. …

Affinity Is an Important Determinant of the Anti-Trypanosome Activity of Nanobodies

BackgroundThe discovery of Nanobodies (Nbs) with a direct toxic activity against African trypanosomes is a recent advancement towards a new strategy against these extracellular parasites. The anti-trypanosomal activity relies on perturbing the highly active recycling of the Variant-specific Surface Glycoprotein (VSG) that occurs in the parasite's flagellar pocket.Methodology/Principal FindingsHere we expand the existing panel of Nbs with anti-Trypanosoma brucei potential and identify four categories based on their epitope specificity. We modified the binding properties of previously identified Nanobodies Nb_An05 and Nb_An33 by site-directed mutagenesis in the paratope and found this to strongly affect trypanotoxicity despite retention of antigen-targeting properties. Affinity measurements for all identified anti-trypanosomal Nbs reveal a strong correlation between trypanotoxicity and affinity (KD), suggesting that it is a crucial determinant for this activity. Half maximal effective (50%) affinity of 57 nM was calculated from the non-linear dose-response curves. In line with these observations, Nb humanizing mutations only preserved the trypanotoxic activity if the KD remained unaffected.Conclusions/SignificanceThis study reveals that the binding properties of Nanobodies need to be compatible with achieving an occupancy of >95% saturation of the parasite surface VSG in order to exert an anti-trypanosomal activity. As such, Nb-based approaches directed against the VSG target would require binding to an accessible, conserved epitope with high affinity.

Linearization of dose-response curve of the radiochromic film dosimetry system.

Despite numerous advantages of radiochromic film dosimeter (high spatial resolution, near tissue equivalence, low energy dependence) to measure a relative dose distribution with film, one needs to first measure an absolute dose (following previously established reference dosimetry protocol) and then convert measured absolute dose values into relative doses. In this work, we present result of our efforts to obtain a functional form that would linearize the inherently nonlinear dose-response curve of the radiochromic film dosimetry system. Functional form [ζ = (-1)[middle dot]netOD((2∕3))∕ln(netOD)] was derived from calibration curves of various previously established radiochromic film dosimetry systems. In order to test the invariance of the proposed functional form with respect to the film model used we tested it with three different GAFCHROMIC™ film models (EBT, EBT2, and EBT3) irradiated to various doses and scanned on a same scanner. For one of the film models (EBT2), we tested the invariance of the functional form to the scanner model used by scanning irradiated film pieces with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic film dosimetry system, verification tests have been performed in clinical applications: percent depth dose measurements, IMRT quality assurance (QA), and brachytherapy QA. Obtained R(2) values indicate that the choice of the functional form of the new argument appropriately linearizes the dose response of the radiochromic film dosimetry system we used. The linear behavior was insensitive to both film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMIC™ EBT3 film model are well within ±2% window of the local relative dose value when compared to the tabulated Cobalt-60 data. It was also found that criteria of 3%∕3 mm for an IMRT QA plan and 3%∕2 mm for a brachytherapy QA plan are passing 95% gamma function points. In this paper, we demonstrate the use of functional argument to linearize the inherently nonlinear response of a radiochromic film based reference dosimetry system. In this way, relative dosimetry can be conveniently performed using radiochromic film dosimetry system without the need of establishing calibration curve.

Cancer incidence and mortality after low-dosage radiation exposure: Epidemiological aspects

Current recommendations for limiting exposure to ionizing radiation are based on the linear no-threshold (LNT) model for radiation carcinogenesis under which every dose, no matter how low, bears some cancer risk. In this review, epidemiological evidence is discussed that the LNT hypothesis is incorrect at low doses. A large set of data was accumulated that show that cancer risk after ordinarily encountered radiation exposure (natural background radiation, medical X-rays, etc.) is much lower than estimates based on the LNT model. The discovery of low-level radiation hormesis (stimulating effect) implies a non-linear dose-response curve in the low-dosage region. Further studies in this field will provide new insights into the mechanisms of radiation carcinogenesis.

Strategies in case of positive in vivo results in genotoxicity testing

At the 2009 International Workshop on Genotoxicity Testing in Basel, an expert group gathered to provide guidance on suitable follow-up tests to describe risk when basic in vivo genotoxicity tests have yielded positive results. The working group agreed that non-linear dose-response curves occur in vivo with at least some DNA-reactive agents. Quantitative risk assessment in such cases requires the use of (1) adequate data, i.e., the use of all available data for the selection of reliable in vivo models to be used for quantitative risk assessment, (2) appropriate mathematical models and statistical analysis for characterizing the dose-response relationships and allowing the use of quantitative and dose-response information in the interpretation of results, (3) mode of action (MOA) information for the evaluation and analysis of risk, and (4) reliable assessments of the internal dose across species for deriving acceptable margins of exposure and risk levels. Hence, the elucidation of MOA and understanding of the mechanism underlying the dose-response curve are important components of risk assessment. The group agreed on the need for (i) the development of in vivo assays, especially multi-endpoint, multi-species assays, with emphasis on those applicable to humans, and (ii) consensus about the most appropriate mathematical models and statistical analyses for defining non-linear dose-responses and exposure levels associated with acceptable risk.

The DNA damage repair protein Ku70 interacts with FOXO4 to coordinate a conserved cellular stress response

In this study, we searched for proteins regulating the tumor suppressor and life-span regulator FOXO4. Through an unbiased tandem-affinity purification strategy combined with mass spectrometry, we identified the heterodimer Ku70/Ku80 (Ku), a DNA double-strand break repair component. Using biochemical interaction studies, we found Ku70 to be necessary and sufficient for the interaction. FOXO4 mediates its tumor-suppressive function in part through transcriptional regulation of the cell cycle arrest p27(kip1) gene. Immunoblotting, luciferase reporter assays, and flow cytometry showed that Ku70 inhibited FOXO4-mediated p27(kip1) transcription and cell cycle arrest induction by >40%. In contrast, Ku70 RNAi but not control RNAi significantly increased p27(kip1) transcription. In addition, in contrast to wild-type mouse embryonic stem (ES) cells, Ku70(-/-) ES cells showed significantly increased FOXO activity, which was rescued by Ku70 reexpression. Immunofluorescence studies demonstrated that Ku70 sequestered FOXO4 in the nucleus. Interestingly, the Ku70-FOXO4 interaction stoichiometry followed a nonlinear dose-response curve by hydrogen peroxide-generated oxidative stress. Low levels of oxidative stress increased interaction stoichiometry up to 75%, peaking at 50 μM, after which dissociation occurred. Because the Ku70 ortholog in the roundworm Caenorhabditis elegans was shown to regulate life span involving C. elegans FOXO, our findings suggest a conserved critical Ku70 role for FOXO function toward coordination of a survival program, regulated by the magnitude of oxidative damage.

IMMUNOMODULATORY EFFECTS UPON IN VITRO EXPOSURE OF CALIFORNIA SEA LION AND SOUTHERN SEA OTTER PERIPHERAL BLOOD LEUKOCYTES TO DOMOIC ACID

During red tide bloom events, the marine diatom Pseudo-nitzschia produces the toxin domoic acid (DA), which has been associated with stranding and mortality events involving California sea lions (Zalophus californianus) and southern sea otters (Enhydra lutris). In addition to these well-documented DA-induced neurotoxic events, there is increasing concern that DA may exert chronic effects, such as immunomodulation, which may potentially increase an individual's susceptibility to a number of opportunistic infections following nonlethal exposure. We investigated the effects of DA on innate (phagocytosis and respiratory burst) and adaptive (mitogen-induced lymphocyte proliferation) immune functions with the use of peripheral blood leukocytes collected from healthy California sea lions and southern sea otters upon in vitro exposure to 0 (unexposed control), 0.0001, 0.001, 0.01, 0.1, 1.0, 10, and 100 microM DA. Domoic acid did not significantly modulate phagocytosis or respiratory burst in either species. For California sea lions, DA significantly increased ConA-induced T-lymphocyte proliferation upon exposure to DA concentrations ranging from 0.0001 to 10 microM, resulting in a nonlinear dose-response curve. There was no effect on lymphocyte proliferation at the highest concentration of DA tested. No effects on lymphocyte proliferation were observed in southern sea otters. Importantly, the in vitro DA concentrations affecting T-cell proliferation were within or below the range of DA in serum measured in free-ranging California sea lions following natural exposure, suggesting a risk for immunomodulation in free-ranging animals. Understanding the risk for immunomodulation upon DA exposure will contribute in the health assessment and management of California sea lions and southern sea otters, as well as guide veterinarians and wildlife rehabilitators in caring for and treating afflicted animals.

Metabolic influences for mutation induction curves after exposure to Sudan-1 and para red

Sudan-1 and para red are industrial dyes that have been illegally added to some foodstuffs, leading to withdrawal of the adulterated products throughout the UK since 2003. This resulted in international concern that arose because Sudan-1 is classified by International Agency for Research on Cancer as a Category 3 carcinogen. However, little is known about the dose response of this chemical at low, more biologically relevant, doses. The study therefore aimed to characterize the dose response for gene mutation and chromosomal damage induced by two azo dyes, namely Sudan-1 and para red. Gene mutations were analysed using the hypoxanthine phosphoribosyltransferase forward mutation assay and chromosomal damage was measured using the cytokinesis-blocked micronucleus assay. Two cell lines were used in these investigations. These were the AHH-1 cell line, which inducibly expresses CYP1A1, and the MCL-5 cell line derived from a subpopulation of AHH-1 cells that expresses a particularly high level of CYP1A1 activity. The MCL-5 cell line has also been transfected with two plasmids that stably express CYP1A2, CYP2A6 and CYP3A4 and all four of these CYP enzymes are known to metabolically activate Sudan-1. AHH-1 cells were used to investigate the dose response of the azo dyes, and MCL-5 cells were used to see if the dose response changed with increased metabolism. Sudan-1 induced a non-linear dose-response curve for gene mutation and chromosomal damage in AHH-1 cells. The genotoxic activity of Sudan-1 was greatly increased in MCL-5 cells. This indicated that the oxidation metabolites from Sudan-1 were both more mutagenic and more clastogenic than the parent compound. Para red also demonstrated a non-linear dose response for both gene mutation and chromosome damage in AHH-1 cells, and an increase in micronuclei induction was observed after increased oxidative metabolism in MCL-5 cells. Sudan-1 and para red are genotoxic chemicals with non-linear dose responses in AHH-1 but not in MCL-5 cells, and oxidative metabolism increases the genotoxic effect of both compounds.

Insulin-like growth factor-I (IGF-I) serum concentrations in healthy children and adolescents: Relationship to level of contamination by DDT-derivative pesticides

Context Serum levels of Insulin-like growth factor I (IGF-I) play a critical role in children growth and in the pathogenesis of several diseases. In addition, recent studies suggest that DDT-derivative organochlorine pesticides (OC–DDTs) could influence IGF levels in human beings. Objective and design Because it has been suggested that IGF-I peak levels at puberty could determine IGF-I levels in adulthood, we developed a cross-sectional study of the potential association between serum levels of OC–DDTs and IGF system in 160 serum samples from young people (81 boys and 79 girls) living in the Canary Islands (Spain). Results Multivariate tests were used adjusting for confounding variables (age, height, and weight) and stratifying by gender and age: IGF-I serum levels were significantly lower in pre-pubertal male children (6–15 years) who showed detectable values of p, p′-DDE, and p, p′-DDD than in pre-pubertal male children with undetectable levels of these OC–DDTs-metabolites ( p = 0.023 and p = 0.049, respectively). In addition, in this multivariate model, a non-linear dose–response curve was observed between Total DDT body burden (sum of the three DDT-derivatives measured: p, p′-DDT, p, p′-DDE, and p, p′-DDD) and IGF-I in pre-pubertal male children (6–15 years; p = 0.043). Conclusion These findings suggest that OC–DDTs could modulate the IGF-system in a way that is highly influenced by gender and age. Improvements in our understanding of exogenous determinants of the IGF-system may provide new insights into the role played by environmental contaminants in IGF-related diseases.

Evaluating the use of 3'-(p-Aminophenyl) fluorescein for determining the formation of highly reactive oxygen species in particle suspensions.

BackgroundGiven the importance of highly reactive oxygen species (hROS) as reactants in a wide range of biological, photochemical, and environmental systems there is an interest in detection and quantification of these species. The extreme reactivity of the hROS, which includes hydroxyl radicals, presents an analytical challenge. 3'-(p-Aminophenyl) fluorescein (APF) is a relatively new probe used for measuring hROS. Here, we further evaluate the use of APF as a method for the detection of hydroxyl radicals in particle suspensions.ResultsParticle-generated hROS can be quantified with an estimated detection limit of 50 nM. Measurements of hROS in two National Institute of Standards and Technology (NIST 2709 and 2710) soil suspensions and a pyrite suspension show non-linear particle dose-response curves for hROS generation. APF can also be used in solutions containing no dissolved molecular oxygen (O2) to determine the role of O2 in the formation of hROS. Results confirm that O2 is mechanistically important in the formation of hROS by dissolved ferrous iron and in pyrite suspensions.ConclusionGiven the non-linear dose-response curves for particle generation of hROS, we recommend using several particle loadings in experiments aimed to compare particles for their hROS generation potential. The method presented here is specific to hROS and simple to perform. The analysis can be conducted in mobile labs as only basic laboratory equipment is required.

Effect of TRA-8 Anti-Death Receptor 5 Antibody in Combination With Chemotherapy in an Ex Vivo Human Ovarian Cancer Model

To investigate the cytotoxicity of TRA-8, an antibody that specifically binds death receptor 5, alone and in combination with chemotherapy, using an ex vivo human ovarian cancer model. Twenty-six ovarian cancer specimens were obtained during ovarian cancer debulking, and tumor slices were prepared with the Krumdieck tissue slicer. The tumor slices were exposed to varying concentrations of TRA-8, carboplatin/paclitaxel, or the combination of TRA-8 and chemotherapy. Using nonlinear modeling, dose-response curves and IC50 values were generated for specimens treated with TRA-8. The additive and synergistic cytotoxic effects of chemotherapy combination with TRA-8 were evaluated in specimens. In addition to adenosine triphosphate viability assays, the treated and untreated slices were assessed by immunohistochemistry to confirm apoptosis induction. Specimens from 13 patients yielded TRA-8-induced IC50 values. Of these specimens, 15% were found to be sensitive to TRA-8-induced cytotoxicity at IC50 doses less than 500 ng/mL. Specimens from 13 patients underwent combination treatment with TRA-8 and carboplatin/paclitaxel. Of these specimens, 77% exhibited additive cytotoxicity in comparison with those treated with either agent alone, whereas 15% exhibited synergistic cytotoxicity. Immunohistochemical analysis of terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling and cleaved caspase 3 staining demonstrated a dose-dependent increase in apoptosis with the combination treatment. This study demonstrates the efficacy of the death receptor monoclonal antibody TRA-8 in combination with conventional chemotherapy in an ex vivo human ovarian cancer model. This model can be used to assess cytotoxicity of novel agents in combination with chemotherapy in ovarian cancer.

Non-linear dose–response of DNA-reactive genotoxins: Recommendations for data analysis

Until recently, there has only been a limited amount of data available on the kinetics of mutation induction in the low dose region of exposure. In our publication Doak et al. [S.H. Doak, G.J. Jenkins, G.E. Johnson, E. Quick, E.M. Parry, J.M. Parry, Mechanistic influences for mutation induction curves after exposure to DNA-reactive carcinogens, Cancer Res. 67 (2007) 3904–3911] we showed that the two alkylating agents methyl-methanesulfonate (MMS) and ethyl-methanesulfonate (EMS) possess non-linear dose–response curves with no observed effect levels (NOEL) for mutation or chromosomal damage in vitro. These experiments were carried out in the AHH-1 human lymphoblastoid cell line, using the hypoxanthine phosphoribosyl transferase ( HPRT) assay and the cytokinesis-block micronucleus (CBMN) assay, respectively. We have now carried out more advanced statistical analyses to define threshold values, which is critical as it has a dramatic impact on hazard and risk assessment. To do this, we re-analysed the data to see if the linear model or a more complex model (hockey stick or quadratic) gave a significant better fit of the data. For both EMS and MMS cytokinesis-block micronucleus data sets, the hockey stick model gave the most significant fit. The same was true for EMS, MMS and surprisingly ethylnitrosourea (ENU) in the HPRT assay in human AHH-1 cells. However, methylnitrosourea (MNU) was linear in both assays. These further analyses have shown that EMS and MMS have clear thresholds for both gene mutation and chromosome damage, as does ENU for gene mutation in AHH-1 cells. MNU was linear for gene and chromosome mutation and so was ENU for chromosome mutations at the concentrations tested. These findings correlate closely with those in vivo findings of Gocke et al. [E. Gocke, L. Müller, In vivo studies in the mouse to define a threshold for the genotoxicity of EMS and ENU, Mutat. Res. (this issue)] and together these data show a true threshold for EMS both in vitro and in vivo. In this report, we will discuss the approaches that were taken to investigate potential threshold dose–response curves for DNA-reactive genotoxic compounds, with recommendations for further studies.

No-observed effect levels are associated with up-regulation of MGMT following MMS exposure

The alkylating agents methyl methanesulphonate (MMS) and ethyl methanesulphonate (EMS) have non-linear dose–response curves, with a no-observed effect level (NOEL) and a lowest observed effect level (LOEL) for both gross chromosomal damage and mutagenicity. However, the biological mechanism responsible for the NOEL has yet to be identified. A strong candidate is DNA repair as it may be able to efficiently remove alkyl adducts at low doses resulting in a NOEL, but at higher doses fails to fully remove all lesions due to saturation of enzymatic activity resulting in a LOEL and subsequent linear increases in mutagenicity. We therefore assessed the transcriptional status of N-methylpurine-DNA glycoslase (MPG) and O6-methylguanine DNA methyltransferase (MGMT), which represent the first line of defence following exposure to alkylating agents through the respective enzymatic removal of N7-alkylG and O6-alkylG. The relative MPG and MGMT gene expression profiles were assessed by real-time RT-PCR following exposure to 0–2μg/ml MMS for 1–24h. MPG expression remained fairly steady, but in contrast significant up-regulation of MGMT was observed when cells were treated with 0.5 and 1.0μg/ml MMS for 4h (2.5- and 6.5-fold increases respectively). These doses lie within the NOEL for MMS mutagenicity (LOEL is 1.25μg/ml), thus this boost in MGMT expression at low doses may be responsible for efficiently repairing O6methylG lesions and creating the non-linear response for mutations. However, as the LOEL for MMS clastogenicity is 0.85μg/ml, O6-alkylG is unlikely to be responsible for the clastogenicity observed at these concentrations. Consequently, at low doses N7-methylG is possibly the predominant cause of MMS clastogenicity, while O6-methylG is more likely to be responsible for MMS mutagenicity, with MGMT up-regulation playing a key role in removal of O6-alkylG lesions before they are fixed as permanent point mutations, resulting in non-linear dose–responses for direct acting genotoxins.