Structurally distinct polycyclic aromatic hydrocarbons induce differential transcriptional responses in developing zebrafish.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment as components of fossil fuels and by-products of combustion. These multi-ring chemicals differentially activate the aryl hydrocarbon receptor (AHR) in a structurally dependent manner, and induce toxicity via both AHR-dependent and -independent mechanisms. PAH exposure is known to induce developmental malformations in zebrafish embryos, and recent studies have shown cardiac toxicity induced by compounds with low AHR affinity. Unraveling the potentially diverse molecular mechanisms of PAH toxicity is essential for understanding the hazard posed by complex PAH mixtures present in the environment. We analyzed transcriptional responses to PAH exposure in zebrafish embryos exposed to benz(a)anthracene (BAA), dibenzothiophene (DBT) and pyrene (PYR) at concentrations that induced developmental malformations by 120 h post-fertilization (hpf). Whole genome microarray analysis of mRNA expression at 24 and 48 hpf identified genes that were differentially regulated over time and in response to the three PAH structures. PAH body burdens were analyzed at both time points using GC-MS, and demonstrated differences in PAH uptake into the embryos. This was important for discerning dose-related differences from those that represented unique molecular mechanisms. While BAA misregulated the least number of transcripts, it caused strong induction of cyp1a and other genes known to be downstream of the AHR, which were not induced by the other two PAHs. Analysis of functional roles of misregulated genes and their predicted regulatory transcription factors also distinguished the BAA response from regulatory networks disrupted by DBT and PYR exposure. These results indicate that systems approaches can be used to classify the toxicity of PAHs based on the networks perturbed following exposure, and may provide a path for unraveling the toxicity of complex PAH mixtures.

AHR2 mutant reveals functional diversity of aryl hydrocarbon receptors in zebrafish.

The aryl hydrocarbon receptor (AHR) is well known for mediating the toxic effects of TCDD and has been a subject of intense research for over 30 years. Current investigations continue to uncover its endogenous and regulatory roles in a wide variety of cellular and molecular signaling processes. A zebrafish line with a mutation in ahr2 (ahr2(hu3335)), encoding the AHR paralogue responsible for mediating TCDD toxicity in zebrafish, was developed via Targeting Induced Local Lesions IN Genomes (TILLING) and predicted to express a non-functional AHR2 protein. We characterized AHR activity in the mutant line using TCDD and leflunomide as toxicological probes to investigate function, ligand binding and CYP1A induction patterns of paralogues AHR2, AHR1A and AHR1B. By evaluating TCDD-induced developmental toxicity, mRNA expression changes and CYP1A protein in the AHR2 mutant line, we determined that ahr2(hu3335) zebrafish are functionally null. In silico modeling predicted differential binding of TCDD and leflunomide to the AHR paralogues. AHR1A is considered a non-functional pseudogene as it does not bind TCCD or mediate in vivo TCDD toxicity. Homology modeling, however, predicted a ligand binding conformation of AHR1A with leflunomide. AHR1A-dependent CYP1A immunohistochemical expression in the liver provided in vivo confirmation of the in silico docking studies. The ahr2(hu3335) functional knockout line expands the experimental power of zebrafish to unravel the role of the AHR during development, as well as highlights potential activity of the other AHR paralogues in ligand-specific toxicological responses.

Stable carbon and nitrogen isotope ratios of sodium and potassium cyanide as a forensic signature.

Sodium and potassium cyanide are highly toxic, produced in large amounts by the chemical industry, and linked to numerous high-profile crimes. The U.S. Centers for Disease Control and Prevention has identified cyanide as one of the most probable agents to be used in a chemical terrorism event. We investigated whether stable C and N isotopic content of sodium and potassium cyanide could serve as a forensic signature for sample matching, using a collection of 65 cyanide samples. Upon analysis, a few of the cyanide samples displayed nonhomogeneous isotopic content associated with degradation to a carbonate salt and loss of hydrogen cyanide. Most samples had highly reproducible isotope content. Of the 65 cyanide samples, >95% could be properly matched based on C and N isotope ratios, with a false match rate <3%. These results suggest that stable C and N isotope ratios are a useful forensic signature for matching cyanide samples.

Separating the drivers from the driven: Integrative network and pathway approaches aid identification of disease biomarkers from high-throughput data.

The recent advances in high-throughput data acquisition have driven a revolution in the study of human disease and determination of molecular biomarkers of disease states. It has become increasingly clear that many of the most important human diseases arise as the result of a complex interplay between several factors including environmental factors, such as exposure to toxins or pathogens, diet, lifestyle, and the genetics of the individual patient. Recent research has begun to describe these factors in the context of networks which describe relationships between biological components, such as genes, proteins and metabolites, and have made progress towards the understanding of disease as a dysfunction of the entire system, rather than, for example, mutations in single genes. We provide a summary of some of the recent work in this area, focusing on how the integration of different kinds of complementary data, and analysis of biological networks and pathways can lead to discovery of robust, specific and useful biomarkers of disease and how these methods can help shed light on the mechanisms and etiology of the diseases being studied.

Nonclinical safety, pharmacokinetics, and pharmacodynamics of atacicept.

Atacicept, a soluble recombinant fusion protein of the human immunoglobulin (Ig) G(1) Fc and the extracellular domain of the human transmembrane activator and calcium modulator and cyclophylin ligand interactor receptor, acts as an antagonist of both B lymphocyte stimulator and a proliferating-inducing ligand. Here we determined the nonclinical safety, pharmacokinetics and pharmacodynamics of atacicept in mice and cynomolgus monkeys. Subcutaneous atacicept treatment (twice weekly in cynomolgus monkeys, three times weekly in mice) was generally safe and well tolerated safe and well tolerated with dosing up to 10 mg/kg every other day for up to 39 weeks or up to 80 mg/kg when dosed for 4 weeks. At a dose of 1 mg/kg subcutaneous (sc) bioavailability of atacicept in mice and monkeys was 76 and 92%, with a mean serum t(1/2) of 44 and 179 h, respectively. In accord with its anticipated mechanism of action, repeated administration of atacicept decreased serum IgG concentrations up to 50%, IgM concentrations >99%, and circulating mature B-cell concentrations up to 60%. These effects were dose-related but reversible, as determined in a 25-week follow-up period. Microscopically, B cells numbers were reduced in the follicular marginal zone of the spleen and the mantle surrounding germinal centers of the lymph nodes. These data confirm the preclinical safety and the pharmacological activity of atacicept and support its clinical development.

Risk factors associated with beta-amyloid(1-42) immunotherapy in preimmunization gene expression patterns of blood cells.

BACKGROUND: A phase 2a, double-blind, placebo-controlled, multicenter study was conducted to evaluate safety, tolerability, and pilot efficacy of immunization with beta-amyloid((1-42)) in patients with Alzheimer disease. Six immunizations were planned but were halted when meningoencephalitis was recognized as an adverse event in 6% of immunized patients. OBJECTIVE: To identify biomarkers associated with both the risk of meningoencephalitis and antibody responsiveness. PARTICIPANTS: One hundred fifty-three patients with mild to moderate Alzheimer disease.Main Outcome Measure Association between response to immunization and preimmunization expression levels of 8239 messenger RNA transcripts expressed in peripheral blood mononuclear cells that had been collected at the screening visit. RESULTS: Expression patterns of genes related to apoptosis and proinflammatory pathways (tumor necrosis factor pathway in particular) were identified as biomarkers of risk for the development of meningoencephalitis. Expression patterns of genes related to protein synthesis, protein trafficking, DNA recombination, DNA repair, and cell cycle were strongly associated with IgG response to immunization. CONCLUSIONS: Candidate biomarkers associated with risk of immunotherapy-related meningoencephalitis were detected in blood collected prior to treatment. In addition, a different set of biomarkers were identified that were associated with the desired outcome of IgG response.

A multinational study of alpha-lactalbumin concentrations in human milk.

Alpha-lactalbumin, a 14-kD protein, plays a central biochemical role in the mammary gland as the regulatory subunit of lactose synthase, and also plays a nutritional role for the rapidly growing neonate as the protein in highest concentration in human milk. The current study was undertaken to better characterize alpha-lactalbumin concentrations in human milk from a variety of countries. Mature human milk (lactation duration > or =1 month) was collected from at least 50 women from nine different countries on five continents. Alpha-lactalbumin concentration was determined by HPLC. The mean +/- SD for 452 samples was 2.44 +/- 0.64 g/L. The mean value of the samples from the United States was significantly higher than that from any other country, and the mean in Mexico was significantly lower than that from every country except China and Canada. Alpha-lactalbumin concentration decreased with increasing duration of lactation and was positively correlated with total nitrogen. On average, alpha-lactalbumin contributed 16% of the total nitrogen content of human milk and consequently an important part of the amino acid content.

Human respiratory tract cancer risks of inhaled formaldehyde: dose-response predictions derived from biologically-motivated computational modeling of a combined rodent and human dataset.

Formaldehyde inhalation at 6 ppm and above causes nasal squamous cell carcinoma (SCC) in F344 rats. The quantitative implications of the rat tumors for human cancer risk are of interest, since epidemiological studies have provided only equivocal evidence that formaldehyde is a human carcinogen. Conolly et al. (Toxicol. Sci. 75, 432-447, 2003) analyzed the rat tumor dose-response assuming that both DNA-reactive and cytotoxic effects of formaldehyde contribute to SCC development. The key elements of their approach were: (1) use of a three-dimensional computer reconstruction of the rat nasal passages and computational fluid dynamics (CFD) modeling to predict regional dosimetry of formaldehyde; (2) association of the flux of formaldehyde into the nasal mucosa, as predicted by the CFD model, with formation of DNA-protein cross-links (DPX) and with cytolethality/regenerative cellular proliferation (CRCP); and (3) use of a two-stage clonal growth model to link DPX and CRCP with tumor formation. With this structure, the prediction of the tumor dose response was extremely sensitive to cell kinetics. The raw dose-response data for CRCP are J-shaped, and use of these data led to a predicted J-shaped dose response for tumors, notwithstanding a concurrent low-dose-linear, directly mutagenic effect of formaldehyde mediated by DPX. In the present work the modeling approach used by Conolly et al. (ibid.) was extended to humans. Regional dosimetry predictions for the entire respiratory tract were obtained by merging a three-dimensional CFD model for the human nose with a one-dimensional typical path model for the lower respiratory tract. In other respects, the human model was structurally identical to the rat model. The predicted human dose response for DPX was obtained by scale-up of a computational model for DPX calibrated against rat and rhesus monkey data. The rat dose response for CRCP was used "as is" for the human model, since no preferable alternative was identified. Three sets of baseline parameter values for the human clonal growth model were obtained through separate calibrations against respiratory tract cancer incidence data for nonsmokers, smokers, and a mixed population of nonsmokers and smokers, respectively. Additional risks of respiratory tract cancer were predicted to be negative up to about one ppm for all three cases when the raw CRCP data from the rat were used. When a hockey-stick-shaped model was fit to the rat CRCP data and used in place of the raw data, positive maximum likelihood estimates (MLE) of additional risk were obtained. These MLE estimates were lower, for some comparisons by as much as 1,000-fold, than MLE estimates from previous cancer dose-response assessments for formaldehyde. Breathing rate variations associated with different physical activity levels did not make large changes in predicted additional risks. In summary, this analysis of the human implications of the rat SCC data indicates that (1) cancer risks associated with inhaled formaldehyde are de minimis (10(-6) or less) at relevant human exposure levels, and (2) protection from the noncancer effects of formaldehyde should be sufficient to protect from its potential carcinogenic effects.

Species and gender differences in the metabolism and distribution of tertiary amyl methyl ether in male and female rats and mice after inhalation exposure or gavage administration.

Tertiary amyl methyl ether (TAME) is a gasoline fuel additive used to reduce emissions. Understanding the metabolism and distribution of TAME is needed to assess potential human health issues. The effect of dose level, duration of exposure and route of administration on the metabolism and distribution of TAME were investigated in male and female F344 rats and CD-1 mice following inhalation or gavage administration. By 48 h after exposure, >96% of the administered radioactivity was expired in air (16-71%) or eliminated in urine and feces (28-72%). Following inhalation exposure, mice had a two- to threefold greater relative uptake of [14C]TAME compared with rats. Metabolites were excreted in urine of rats and mice that are formed by glucuronide conjugation of tertiary amyl alcohol (TAA), oxidation of TAA to 2,3-dihydroxy-2-methylbutane and glucuronide conjugation of 2,3-dihydroxy-2-methylbutane. A saturation in the uptake and metabolism of TAME with increased exposure concentration was indicated by a decreased relative uptake of total [14C]TAME equivalents and an increase in the percentage expired as volatiles. A saturation of P-450 oxidation of TAA was indicated by a disproportional decrease of 2,3-dihydroxy-2-methylbutane and its glucuronide conjugate with increased exposure concentration.

Blood pharmacokinetics of tertiary amyl methyl ether in male and female F344 rats and CD-1 mice after nose-only inhalation exposure.

Interest in understanding the biological behavior of aliphatic ethers has increased owing to their use as gasoline additives. The purpose of this study was to investigate the blood pharmacokinetics of the oxygenate tertiary amyl methyl ether (TAME), its major metabolite tertiary amyl alcohol (TAA) and acetone in rats and mice following inhalation exposure to TAME. Species differences in the area under the curve (AUC) for TAME were significant at each exposure concentration. For rats, the blood TAME AUC increased in proportion with an increase in exposure concentration. For mice, an increase in exposure concentration (100-500 ppm) resulted in a disproportional increase in the TAME AUC. Mice had greater (two- to threefold) blood concentrations of TAA compared with rats following exposure to 2500 or 500 ppm TAME. Mice had a disproportional increase in the TAA AUC with an increase in exposure concentration (100-500 ppm). This difference could result from saturation of a process (e.g. oxidation, glucuronide conjugation) that is involved in the further metabolism of TAA. For each species, gender and exposure concentration, acetone increased during exposure and returned to control values by 16 h following exposure. The source of acetone could be both as a metabolite of TAA or an effect on endogenous metabolism produced by exposure to TAME.

Benchmark dose risk assessment for formaldehyde using airflow modeling and a single-compartment, DNA-protein cross-link dosimetry model to estimate human equivalent doses.

Formaldehyde induced squamous-cell carcinomas in the nasal passages of F344 rats in two inhalation bioassays at exposure levels of 6 ppm and above. Increases in rates of cell proliferation were measured by T. M. Monticello and colleagues at exposure levels of 0.7 ppm and above in the same tissues from which tumors arose. A risk assessment for formaldehyde was conducted at the CIIT Centers for Health Research, in collaboration with investigators from Toxicological Excellence in Risk Assessment (TERA) and the U.S. Environmental Protection Agency (U.S. EPA) in 1999. Two methods for dose-response assessment were used: a full biologically based modeling approach and a statistically oriented analysis by benchmark dose (BMD) method. This article presents the later approach, the purpose of which is to combine BMD and pharmacokinetic modeling to estimate human cancer risks from formaldehyde exposure. BMD analysis was used to identify points of departure (exposure levels) for low-dose extrapolation in rats for both tumor and the cell proliferation endpoints. The benchmark concentrations for induced cell proliferation were lower than for tumors. These concentrations were extrapolated to humans using two mechanistic models. One model used computational fluid dynamics (CFD) alone to determine rates of delivery of inhaled formaldehyde to the nasal lining. The second model combined the CFD method with a pharmacokinetic model to predict tissue dose with formaldehyde-induced DNA-protein cross-links (DPX) as a dose metric. Both extrapolation methods gave similar results, and the predicted cancer risk in humans at low exposure levels was found to be similar to that from a risk assessment conducted by the U.S. EPA in 1991. Use of the mechanistically based extrapolation models lends greater certainty to these risk estimates than previous approaches and also identifies the uncertainty in the measured dose-response relationship for cell proliferation at low exposure levels, the dose-response relationship for DPX in monkeys, and the choice between linear and nonlinear methods of extrapolation as key remaining sources of uncertainty.

Biologically motivated computational modeling of formaldehyde carcinogenicity in the F344 rat.

Formaldehyde inhalation at 6 ppm and above causes nasal squamous cell carcinoma (SCC) in F344 rats. The human health implications of this effect are of significant interest since human exposure to environmental formaldehyde is widespread, though at lower concentrations than those that cause cancer in rats. In this article, which is part of a larger effort to predict the human cancer risks of inhaled formaldehyde, we describe biologically motivated quantitative modeling of the exposure-tumor response continuum in the rat. An anatomically realistic, three-dimensional fluid dynamics model of the F344 rat nasal airways was used to predict site-specific flux of formaldehyde from inhaled air into tissue, since both SCC and preneoplastic lesions develop in a characteristic site-specific pattern. Flux into tissue was used as a dose metric for two modes of action, direct mutagenicity and cytolethality-regenerative cellular proliferation (CRCP), which in turn were linked to key parameters of a two-stage clonal growth model. The direct mutagenicity mode of action was represented by a low dose linear dose-response model of DNA-protein cross-link (DPX) formation. An empirical J-shaped dose-response model and a threshold model fit to the empirical data were used for CRCP. In the clonal growth model, the probability of mutation per cell generation was a function of the tissue concentration of DPX while the rate of cell division was calculated from the CRCP data. Maximum likelihood methods were used to estimate parameter values. Survivor (a nontumor outcome) and tumor data for controls from the National Toxicology Program database and from two formaldehyde inhalation bioassays were used for likelihood calculations. The J-shaped dose-response for CRCP provided a better description of the SCC data than did the threshold model. Sensitivity analyses indicated that the rodent tumor response is due to the CRCP mode of action, with the directly mutagenic pathway having little, if any, influence. When evaluated in light of modeling and database uncertainties, particularly the specification of the clonal growth model and the dose-response data for CRCP, this work provides suggestive though not definitive evidence for a J-shaped dose-response for formaldehyde-mediated nasal SCC in the F344 rat.

Long-term pulmonary responses of three laboratory rodent species to subchronic inhalation of pigmentary titanium dioxide particles.

Female mice, rats, and hamsters were exposed to 10, 50, or 250 mg/m(3) pigmentary titanium dioxide (p-TiO(2)) particles for 6 h per day and 5 days per week for 13 weeks with recovery groups held for an additional 4, 13, 26, or 52 weeks postexposure (46 weeks for the p-TiO(2)-exposed hamsters). At each time point p-TiO(2) burdens in the lung and lymph nodes and selected lung responses were examined. The responses studied were chosen to assess a variety of pulmonary parameters, including inflammation, cytotoxicity, lung cell proliferation, and histopathologic alterations. Burdens of p-TiO(2) in the lungs and in the lung-associated lymph nodes increased in a concentration-dependent manner. Retained lung burdens following exposure were greatest in mice. Rats and hamsters had similar lung burdens immediately postexposure when assessed as milligrams of p-TiO(2) per gram of dried lung. Particle retention data suggested that pulmonary overload was achieved in both rats and mice at the exposure levels of 50 and 250 mg/m(3). Under the conditions of the present study, hamsters were better able to clear p-TiO(2) particles than were similarly exposed mice and rats. Pulmonary histopathology revealed both species and concentration-dependent differences in p-TiO(2) particle retention patterns. Inflammation was noted in all three species at 50 and 250 mg/m(3), as evidenced by increases in macrophage and neutrophil numbers and in soluble indices of inflammation in bronchoalveolar lavage fluid (BALF; rats > mice, hamsters). In mice and rats, the BALF inflammatory responses remained elevated relative to controls throughout the entire postexposure recovery period in the most highly exposed animals. In comparison, inflammation in hamsters eventually disappeared, even at the highest exposure dose, due to the more rapid clearance of particles from the lung. Pulmonary lesions were most severe in rats, where progressive epithelial- and fibroproliferative changes were observed in the 250 mg/m(3) group. These epithelial proliferative changes were also manifested in rats as an increase in alveolar epithelial cell labeling in cell proliferation studies. Associated with these foci of epithelial proliferation were interstitial particle accumulation and alveolar septal fibrosis. In summary, there were significant species differences in pulmonary responses to inhaled p-TiO(2) particles. Under conditions in which the lung p-TiO(2) burdens were similar and likely to induce pulmonary overload, rats developed a more severe and persistent pulmonary inflammatory response than either mice or hamsters. Rats also were unique in the development of progressive fibroproliferative lesions and alveolar epithelial metaplasia in response to 90 days of exposure to a high concentration of p-TiO(2) particles.