Protein adducts as dosimeters of human exposure to styrene, styrene-7,8-oxide, and benzene

Integration of various protein similarities using random forest technique to infer augmented drug-protein matrix for enhancing drug-disease association prediction

Identifying new therapeutic indications for existing drugs is a major challenge in drug repositioning. Most computational drug repositioning methods focus on known targets. Analyzing multiple aspects of various protein associations provides an opportunity to discover underlying drug-associated proteins that can be used to improve the performance of the drug repositioning approaches. In this study, machine learning models were developed based on the similarities of diversified biological features, including protein interaction, topological network, sequence alignment, and biological function to predict protein pairs associating with the same drugs. The crucial set of features was identified, and the high performances of protein pair predictions were achieved with an area under the curve (AUC) value of more than 93%. Based on drug chemical structures, the drug similarity levels of the promising protein pairs were used to quantify the inferred drug-associated proteins. Furthermore, these proteins were employed to establish an augmented drug-protein matrix to enhance the efficiency of three existing drug repositioning techniques: a similarity constrained matrix factorization for the drug-disease associations (SCMFDD), an ensemble meta-paths and singular value decomposition (EMP-SVD) model, and a topology similarity and singular value decomposition (TS-SVD) technique. The results showed that the augmented matrix helped to improve the performance up to 4% more in comparison to the original matrix for SCMFDD and EMP-SVD, and about 1% more for TS-SVD. In summary, inferring new protein pairs related to the same drugs increase the opportunity to reveal missing drug-associated proteins that are important for drug development via the drug repositioning technique.

Metabolomics and adductomics of newborn bloodspots to retrospectively assess the early-life exposome

PURPOSE OF REVIEW

Exposomics studies can measure health-relevant chemical exposures during a lifetime and estimate the 'internal' environment. However, sampling limitations make these features difficult to capture directly during the critical neonatal time period.

RECENT FINDINGS

We review the use of newborn dried bloodspots (DBS) archived from newborn screening programs for exposomic analysis in epidemiological children's health studies. Emerging 'omics technologies such as adductomics and metabolomics have been adapted for DBS analysis, and these technologies can now provide valuable etiological information on the complex interplay between exposures, biological response, and population phenotypes.

SUMMARY

Adductomics and metabolomics of DBS can provide robust measurements for retrospective epidemiological investigations. With extensive bioarchiving programs in the United States and other countries, DBS are poised to substantially aid epidemiological studies, particularly for rare and low-frequency childhood diseases and disorders.

Critical review of styrene genotoxicity focused on the mutagenicity/clastogenicity literature and using current organization of economic cooperation and development guidance

Styrene is an important high production volume chemical used to manufacture polymeric products. In 2018, International Agency for Research on Cancer classified styrene as probably carcinogenic to humans; National Toxicology Program lists styrene as reasonably anticipated to be a human carcinogen. The genotoxicity literature for styrene and its primary metabolite, styrene 7,8-oxide (SO), begins in the 1970s. Organization of Economic Cooperation and Development (OECD) recently updated most genotoxicity test guidelines, making substantial new recommendations for assay conduct and data evaluation for the standard mutagenicity/clastogenicity assays. Thus, a critical review of the in vitro and in vivo rodent mutagenicity/clastogenicity studies for styrene and SO, based on the latest OECD recommendations, is timely. This critical review considered whether a study was optimally designed, conducted, and interpreted and provides a critical assessment of the evidence for the mutagenicity/clastogenicity of styrene/SO. Information on the ability of styrene/SO to induce other types of genotoxicity endpoints is summarized but not critically reviewed. We conclude that when styrene is metabolized to SO, it can form DNA adducts, and positive in vitro mutagenicity/clastogenicity results can be obtained. SO is mutagenic in bacteria and the in vitro mouse lymphoma gene mutation assay. No rodent in vivo mutation studies were identified. SO is clastogenic in cultured mammalian cells. Although the in vitro assays gave positive responses, styrene/SO is not clastogenic/aneugenic in vivo in rodents. In addition to providing updated information for styrene, this review demonstrates the application of the new OECD guidelines for chemicals with large genetic toxicology databases where published results may or may not be reliable. Environ. Mol. Mutagen. 2019. © 2019 Wiley Periodicals, Inc.

Biomonitoring of styrene occupational exposures: Biomarkers and determinants

INTRODUCTION

High styrene exposures are still experienced in various occupational settings, requesting regular exposure assessments. The aims of this study were to study occupational exposures in various industrial sectors and to determine factors influencing styrene urinary metabolites levels.

METHODS

Biomonitoring was conducted in 141 workers from fiberglass-reinforced plastic (FRP) manufacture, thermoplastic polymers production, vehicle repair shops and cured-in-place pipe lining (CIPP). Urinary styrene (StyU) as well as Mandelic (MA) / Phenyglyoxylic Acids (PGA) were quantified at the beginning and at the end of week, and multivariate linear regression models were used.

RESULTS

StyU levels revealed very low, rarely exceeding 3 μg.L^-1. Highest concentrations of MA + PGA were observed in FRP sector, with levels reaching up to 1100 mg.g^-1 of creatinine. Factors influencing end-of-week MA + PGA concentrations were levels at the beginning of week, open molding processes, proximity to the emission source, respiratory protection, styrene content in raw materials. Elevated levels were also observed during CIPP process, whereas thermoplastic injection and vehicle repair shop workers exhibited much lower exposures.

CONCLUSIONS

Intervention on process (decreasing styrene proportion, using closed molding), protective equipment (local exhaust ventilation, respiratory protection) and individual practices (stringent safety rules) are expected to decrease occupational exposures. Urinary MA + PGA remain the most appropriate biomarkers for occupational biomonitoring.

The application of mass spectrometry in molecular dosimetry: ethylene oxide as an example

Mass spectrometry plays an increasingly important role in the search for and quantification of novel chemically specific biomarkers. The revolutionary advances in mass spectrometry instrumentation and technology empower scientists to specifically analyze DNA and protein adducts, considered as molecular dosimeters, derived from reactions of a carcinogen or its active metabolites with DNA or protein. Analysis of the adducted DNA bases and proteins can elucidate the chemically reactive species of carcinogens in humans and can serve as risk-associated biomarkers for early prediction of cancer risk. In this article, we review and compare the specificity, sensitivity, resolution, and ease-of-use of mass spectrometry methods developed to analyze ethylene oxide (EO)-induced DNA and protein adducts, particularly N7-(2-hydroxyethyl)guanine (N7-HEG) and N-(2-hydroxyethyl)valine (HEV), in human samples and in animal tissues. GC/ECNCI-MS analysis after HPLC cleanup is the most sensitive method for quantification of N7-HEG, but limited by the tedious sample preparation procedures. Excellent sensitivity and specificity in analysis of N7-HEG can be achieved by LC/MS/MS analysis if the mobile phase, the inlet (split or splitless), and the collision energy are properly optimized. GC/ECNCI-HRMS and GC/ECNCI-MS/MS analysis of HEV achieves the best performance as compared with GC/ECNCI-MS and GC/EI-MS. In conclusion, future improvements in high-throughput capabilities, detection sensitivity, and resolution of mass spectrometry will attract more scientists to identify and/or quantify novel molecular dosimeters or profiles of these biomarkers in toxicological and/or epidemiological studies.

Toward an "omic" physiopathology of reactive chemicals: thirty years of mass spectrometric study of the protein adducts with endogenous and xenobiotic compounds

Cancer and degenerative diseases are major causes of morbidity and death, derived from the permanent modification of key biopolymers such as DNA and regulatory proteins by usually smaller, reactive molecules, present in the environment or generated from endogenous and xenobiotic components by the body's own biochemical mechanisms (molecular adducts). In particular, protein adducts with organic electrophiles have been studied for more than 30 [see, e.g., Calleman et al., 1978] years essentially for three purposes: (a) as passive monitors of the mean level of individual exposure to specific chemicals, either endogenously present in the human body or to which the subject is exposed through food or environmental contamination; (b) as quantitative indicators of the mean extent of the individual metabolic processing which converts a non-reactive chemical substance into its toxic products able to damage DNA (en route to cancer induction through genotoxic mechanisms) or key proteins (as in the case of several drugs, pesticides or otherwise biologically active substances); (c) to relate the extent of protein modification to that of biological function impairment (such as enzyme inhibition) finally causing the specific health damage. This review describes the role that contemporary mass spectrometry-based approaches employed in the qualitative and quantitative study of protein-electrophile adducts play in the discovery of the (bio)chemical mechanisms of toxic substances and highlights the future directions of research in this field. A particular emphasis is given to the measurement of often high levels of the protein adducts of several industrial and environmental pollutants in unexposed human populations, a phenomenon which highlights the possibility that a number of small organic molecules are generated in the human organism through minor metabolic processes, the imbalance of which may be the cause of "spontaneous" cases of cancer and of other degenerative diseases of still uncharacterized etiology. With all this in mind, it is foreseen that a holistic description of cellular functions will take advantage of new analytical methods based on time-integrated metabolomic measurements of a new biological compartment, the "adductome," aimed at better understanding integrated organism response to environmental and endogenous stressors.

Styrene-oxide N-terminal valine haemoglobin adducts in reinforced plastic workers: Possible influence of genetic polymorphism of drug-metabolising enzymes

Styrene is one of the most important organic chemicals used worldwide. In humans, styrene metabolism involves oxidation by cytochrome P450 monooxygenases (CYPs) to styrene-7,8-oxide, an epoxide thought to be responsible for the genotoxic effects of styrene exposure, and detoxification by means of epoxide hydrolase (mEH) and glutathione S-transferases (GSTs). The objective of this study was to investigate if genetic polymorphisms of metabolic enzymes modulate the level of urinary styrene metabolites and styrene oxide adducts with N-terminal valine of human globin (SO-Hb) in 75 workers occupationally exposed to styrene and 77 unexposed controls. The mean air concentration of styrene in the breathing zone of workers (30.4ppm) was higher than the threshold limit value of 20ppm recommended by the American Conference of Governmental Industrial Hygienists (ACGIH), and the biological exposure index adopted by the ACGIH for exposure to styrene prior to the next shift (MA+PGA=400mg/g creatinine) was exceeded, indicating that styrene exposure for this group of workers was higher than recommended. A highly significant correlation was observed between styrene concentration in the breathing zone and the MA+PGA in urine of workers (r=0.85, P<0.001). The levels of SO-Hb adducts in exposed workers were significantly increased as compared with controls, although no difference was observed between subjects stratified as high and medium exposure categories based on MA+PGA excretion. Regarding the effect of the genetic polymorphisms we found that the level of SO-Hb adducts might be modulated by the predicted mEH enzymatic activity in the exposed workers. From our data we conclude that SO-Hb adduct measurement is a complementary method to MA+PG measurement for assessing exposure to styrene at occupational and environmental levels, which reflects a more extensive exposure period.

Biological monitoring of exposure: trends and key developments

The concept of biological monitoring (BM) has gained the special interest of individual scientists and international organizations. Today, when analytical problems have almost ceased due to new laboratory techniques and quality assurance systems, the methods for interpretation of results have become the most important issue. There are important discrepancies regarding the role of biological monitoring of occupational exposure between Europe and the United States. BM has been an important tool of medical health surveillance in the European countries. In the United States it belongs rather to the field of occupational hygiene. It seems that both the approaches can be accepted. More attention should be paid to the development of the truly health-based biomarkers of exposure based on the dose-effect and dose-response relationships. New areas of application of BM of occupational exposure include determination of DNA and protein adducts, unchanged volatile organic compounds in urine, monitoring of exposure to pesticides, antineoplastic drugs, hard metals, and polycyclic aromatic hydrocarbons. In the general environment BM is the most valuable tool for acquiring knowledge of current levels of internal exposure to xenobiotics, identifying the hot spots and developments in trends of exposure. BM can provide policy makers with more accurate information on the control measures undertaken. At present, the main areas include heavy metals, persistent organic pollutants and pesticides. BM of chemical exposure has become increasingly important in the assessment of the health risk in occupational and environmental medicine. Therefore it would be worthwhile to include BM in the curricula for the training of occupational hygienists.

Albumin adducts of naphthalene metabolites as biomarkers of exposure to polycyclic aromatic hydrocarbons

We investigated the utility of adducts formed by the reaction of the naphthalene metabolites naphthalene-1,2-oxide, 1,2-naphthoquinone (1,2-NPQ), and 1,4-naphthoquinone (1,4-NPQ) with serum albumin (Alb) as biomarkers of exposure to polycyclic aromatic hydrocarbons. Cysteinyl serum Alb adducts of 1,2- and 1,4-NPQ (1,2-NPQ-Alb and 1,4-NPQ-Alb, respectively) but not of naphthalene-1,2-oxide were detected in 28 coke oven workers and 22 controls from the steel industry of northern China. The median level of 1,2-NPQ-Alb in coke oven workers (76.6 pmol/g) was significantly higher than that observed in controls (44.9 pmol/g; P = 0.0027). However, the median level of 1,4-NPQ-Alb in exposed subjects was not significantly different from that of controls (48.6 versus 44.2 pmol/g; P = 0.296). Levels of 1,2-NPQ-Alb were significantly correlated with exposure category (controls, side and bottom workers, and top-of-oven workers) as well as with previously measured levels of urinary naphthalene, 1- and 2-naphthol, and 1-pyrenol in these subjects. Multiple linear regression analysis revealed that 35% of the variation in 1,2-NPQ-Alb could be explained by the work category and age. A negative relationship between 1,2-NPQ-Alb and age was observed, suggesting that cytochrome P450 c metabolism diminished with age at approximately 3%/year of life.

Assessment of biotransformation of the arene moiety of styrene in volunteers and occupationally exposed workers

Styrene is a chemical widely used in the plastic industry. The main pathway of styrene metabolism in humans occurs via the oxidation to styrene-7,8-oxide (7,8-SO). The aim of this study was the investigation of a minor metabolic route, involving the oxidation of the arene moiety of styrene, by means of the characterization of the conjugated urinary metabolites of 4-vinylphenol (4-VP). 4-vinylphenol-glucuronide (4-VP-G) and -sulfate (4-VP-S), were measured by liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS/MS) from 174 workers belonging to three cohorts recruited in European countries and from 26 volunteers exposed to 50 mg/m(3) (11.8 ppm) of styrene for 8 h. The 4-VP conjugates represented about 0.5-1% of the total excretion of styrene metabolites. Both 4-VP-G and 4-VP-S are eliminated with a monophasic kinetic, the glucuronide being excreted faster (half-time, 2.2 +/- 0.2 h) than the sulfate (half-time 9.7 +/- 1.7 h). The urinary 4-VP was found to be significantly correlated both with airborne styrene (r = 0.607, p < 0.001) and the sum of MA and PGA (r = 0.903, p < 0.001 in "end-of-shift" samples). Apart from 7,8-SO, 4-VP is the only styrene metabolite not shared with ethylbenzene and therefore thought to be a highly specific marker of styrene exposure. However, a measurable background excretion of 4-VP was also found in all urine samples from controls not occupationally exposed to styrene. This background appears to be highly correlated to smoking (p < 0.001) and possibly also to the dietary intake of styrene or 4-VP. Consequently, the use of 4-VP as a biomarker of styrene exposure is recommended for exposures exceeding 1 ppm.

Pharmacokinetic modeling of disposition and time-course studies with [14C]atrazine

A physiological pharmacokinetic (PPK) model, with blood, body, and brain compartments, was developed to estimate total plasma chlorotriazine (CI-TRI) time courses (i.e., atrazine [ATRA] and its three chlorinated metabolites) after oral dosing with ATRA. The model, based on disposition data for 14C-ATRA, tracked two pools of compounds: (1) ATRA and chlorinated metabolites (i.e., the CI-TRIs) and (2) glutathione conjugates. The PPK model developed from total radioactivity was valuable for assessing total plasma CI-TRI concentrations, estimating blood protein binding rates of CI-TRIs, and inferring relationships between tissue exposures of CI-TRIs and administered dose. Absorption of radioactivity into plasma was slow with a rate constant of 0.2 h-1. 14C-disposition data indicated that CI-TRIs react with red blood cells (presumably hemoglobin) and plasma proteins. Second-order rates of reaction of CI-TRIs with hemoglobin and plasma protein were estimated to be 0.008 L/mmol/h and 1.14 x 10(-7) L/mg/h, respectively. A time-course study, conducted as part of this study, evaluated the absorption, disposition, and elimination characteristics of individual CI-TRIs in plasma after a single oral dose of 90 mg ATRA/kg and indicated (1) that slow uptake into blood reflected both absorption and slow dissolution of the ATRA slurry and (2) that diaminochloro-s-triazine (DACT) was the major, persistent plasma CI-TRI after oral dosing. Optimally, PK model development for pesticide compounds like atrazine should include a combination of radiolabeled studies for residues and speciation studies of important metabolites.

Bleomycin genotoxicity and amifostine (WR-2721) cell protection in normal leukocytes vs. K562 tumoral cells

Recent advances in chemotherapy have focused on the benefit of high dose regimens, increasing the dose intensity of conventional chemotherapy. However, unacceptable cytotoxicity and genotoxicity on normal cells often impairs the proper management of patients. Phosphoaminothiol WR-1065, the active metabolite of amifostine, appears to protect normal cells and tissues against cytotoxic exposure to radiation or chemotherapeutic agents. Nevertheless, there is disagreement in findings on amifostine protection against bleomycin-induced severe side effects which have suggested that amifostine effectiveness against bleomycin-induced genotoxicity in normal leukocytes and tumour line cells K562 be studied. DNA damage was detected by single cell gel electrophoresis (or Comet) assay, a technique able to detect DNA strand breaks, alkali-labile sites and incomplete excision repair events in individual cells and which appears to be an ideal tool for assessing variability in response of different cell types in vitro. WR-2721 appears to selectively protect healthy leukocytes but not K562 tumoral cells. On the other hand, data on the inter- and intra-individual sensitivity to bleomycin and amifostine suggest that individual metabolic/genetic differences and other factors relating to lifestyle may be responsible for response variability. Application of the Comet assay in appropriate clinical settings to test the sensitivity of patients when undergoing chemotherapy appears possible.

Amifostine (WR-2721) selective protection against melphalan genotoxicity

Amifostine (WR-2721) is an aminothiol compound dephosphorylated at the tissue site by alkaline phosphatase to the active metabolite, which is able to inactivate electrophilic substances and scavenge free radicals. Amifostine effects against melphalan-induced DNA strand breaks were studied in normal human white blood cells (WBC) and K562 leukemic cells using the single cell gel electrophoresis (SCGE) or Comet assay, a reported method for measuring DNA damage in individual cells. Prior to treatment (1 h, 37 degrees C) with increasing doses of melphalan, with or without S9, the cells were treated (15 min, 37 degrees C) with a control medium or amifostine (3 mg/ml). Treatment of normal and leukemic cells with melphalan induced a dose-dependent 'comet formation'. Melphalan-induced DNA damage follows a normal distribution in WBC. On the other hand, in K562, a significant proportion of undamaged cells remains even with doses at which mean DNA damage is serious. Pretreatment with WR-2721 protects WBC, but not K562, against the genotoxic effect of melphalan. Amifostine might even strengthen the action of the antiblastic drug against K562 cells. S9 addition appears to enhance melphalan effectiveness. SCGE appears as a suitable primary screening method for in vitro and in vivo studies on drug-DNA interactions and their modulations by endogenous/exogenous factors.