Assessment of genotoxic effects and changes in gene expression in humans exposed to formaldehyde by inhalation under controlled conditions

Assessment of associations between inhaled formaldehyde and lymphohematopoietic cancer through the integration of epidemiological and toxicological evidence with biological plausibility

Formaldehyde is recognized as carcinogenic for the portal of entry sites, though conclusions are mixed regarding lymphohematopoietic (LHP) cancers. This systematic review assesses the likelihood of a causal relationship between formaldehyde and LHP cancers by integrating components recommended by NASEM. Four experimental rodent bioassays and 16 observational studies in humans were included following the implementation of the a priori protocol. All studies were assessed for risk of bias (RoB), and meta-analyses were conducted on epidemiological studies, followed by a structured assessment of causation based on GRADE and Bradford Hill. RoB analysis identified systemic limitations precluding confidence in the epidemiological evidence due to inadequate characterization of formaldehyde exposure and a failure to adequately adjust for confounders or effect modifiers, thus suggesting that effect estimates are likely to be impacted by systemic bias. Mixed findings were reported in individual studies; meta-analyses did not identify significant associations between formaldehyde inhalation (when measured as ever/never exposure) and LHP outcomes, with meta-SMRs ranging from 0.50 to 1.51, depending on LHP subtype. No associations with LHP-related lesions were reported in reliable animal bioassays. No biologically plausible explanation linking the inhalation of FA and LHP was identified, supported primarily by the lack of systemic distribution and in vivo genotoxicity. In conclusion, the inconsistent associations reported in a subset of the evidence were not considered causal when integrated with the totality of the epidemiological evidence, toxicological data, and considerations of biological plausibility. The impact of systemic biases identified herein could be quantitatively assessed to better inform causality and use in risk assessment.

The Comet Assay as a Tool in Human Biomonitoring Studies of Environmental and Occupational Exposure to Chemicals-A Systematic Scoping Review

Biomonitoring of human populations exposed to chemical substances that can act as potential mutagens or carcinogens, may enable the detection of damage and early disease prevention. In recent years, the comet assay has become an important tool for assessing DNA damage, both in environmental and occupational exposure contexts. To evidence the role of the comet assay in human biomonitoring, we have analysed original research studies of environmental or occupational exposure that used the comet assay in their assessments, following the PRISMA-ScR method (preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews). Groups of chemicals were designated according to a broad classification, and the results obtained from over 300 original studies (n = 123 on air pollutants, n = 14 on anaesthetics, n = 18 on antineoplastic drugs, n = 57 on heavy metals, n = 59 on pesticides, and n = 49 on solvents) showed overall higher values of DNA strand breaks in the exposed subjects in comparison with the unexposed. In summary, our systematic scoping review strengthens the relevance of the use of the comet assay in assessing DNA damage in human biomonitoring studies.

Is micronucleus assay in nasal mucosa cells an appropriate technique for detecting genotoxins by inhalation in humans? A systematic review

This study aimed to evaluate the scientific literature on the micronucleus assay in nasal mucosa as an appropriate method for evaluating genotoxicity caused by chemical agents. According to the PRISMA guidelines, only in vivo human studies with micronucleus assays using nasal cells were considered. Reviews, case reports, editorials, letters to the editor, and articles not written in English were excluded. The following scientific databases/search engines were used: PubMed/MEDLINE, Scopus, and Web of Science. Results: This review included 13 studies. Four articles detected no statistical significance regarding the frequency of micronuclei while nine articles showed an increase in micronuclei in nasal cells. In the qualitative analysis, two articles were considered strong, eight were moderate and three were weak. The micronucleus assay using nasal mucosa cells is a sensitive and effective technique for assessing DNA damage and an appropriate method for monitoring humans continuously exposed to chemicals.

An updated mode of action and human relevance framework evaluation for Formaldehyde-Related nasal tumors

Formaldehyde is a reactive aldehyde naturally present in all plant and animal tissues and a critical component of the one-carbon metabolism pathway. It is also a high production volume chemical used in the manufacture of numerous products. Formaldehyde is also one of the most well-studied chemicals with respect to environmental fate, biology, and toxicology-including carcinogenic potential, and mode of action (MOA). In 2006, a published MOA for formaldehyde-induced nasal tumors in rats concluded that nasal tumors were most likely driven by cytotoxicity and regenerative cell proliferation, with possible contributions from direct genotoxicity. In the past 15 years, new research has better informed the MOA with the publication of in vivo genotoxicity assays, toxicogenomic analyses, and development of ultra-sensitive methods to measure endogenous and exogenous formaldehyde-induced DNA adducts. Herein, we review and update the MOA for nasal tumors, with particular emphasis on the numerous studies published since 2006. These new studies further underscore the involvement of cytotoxicity and regenerative cell proliferation, and further inform the genotoxic potential of inhaled formaldehyde. The data lend additional support for the use of mechanistic data for the derivation of toxicity criteria and/or scientifically supported approaches for low-dose extrapolation for the risk assessment of formaldehyde.

Formaldehyde exposure and leukemia risk: a comprehensive review and network-based toxicogenomic approach

Formaldehyde is a widely used but highly reactive and toxic chemical. The International Agency for Research on Cancer classifies formaldehyde as a Group 1 carcinogen, based on nasopharyngeal cancer and leukemia studies. However, the correlation between formaldehyde exposure and leukemia incidence is a controversial issue. To understand the association between formaldehyde exposure and leukemia, we explored biological networks based on formaldehyde-related genes retrieved from public and commercial databases. Through the literature-based network approach, we summarized qualitative associations between formaldehyde exposure and leukemia. Our results indicate that oxidative stress-mediated genetic changes induced by formaldehyde could disturb the hematopoietic system, possibly leading to leukemia. Furthermore, we suggested major genes that are thought to be affected by formaldehyde exposure and associated with leukemia development. Our suggestions can be used to complement experimental data for understanding and identifying the leukemogenic mechanism of formaldehyde.

Using mechanistic information to support evidence integration and synthesis: a case study with inhaled formaldehyde and leukemia

Formaldehyde is one of the most comprehensively studied chemicals, with over 30 years of research focused on understanding the development of cancer following inhalation. The causal conclusions regarding the potential for leukemia are largely based on the epidemiological literature, with little consideration of cancer bioassays, dosimetry studies, and mechanistic research, which challenge the biological plausibility of the disease. Recent reanalyzes of the epidemiological literature have also raised significant questions related to the purported associations between formaldehyde and leukemia. Because of this, considerable scientific debate and uncertainty remain on whether there is a causal association between formaldehyde inhalation exposure and leukemia. Further complexity in evaluating this association is related to the endogenous production of formaldehyde. Multiple modes of action (MOA) have been postulated for the development of leukemia following formaldehyde inhalation that includes unsupported hypotheses of direct or indirect toxicity to the target cell population. Herein, the available evidence relevant to evaluating the postulated MOAs for leukemia following formaldehyde inhalation exposure is organized in the IPCS MOA Framework. The integration of all the available evidence clearly highlights the limited amount of data that support any of the postulated MOAs and demonstrates a significant amount of research supporting the null hypothesis that there is no causal association between formaldehyde inhalation exposure and leukemia. These analyses result in a lack of confidence in any of the postulated MOAs, increasing confidence in the conclusion that there is a lack of biological plausibility for a causal association between formaldehyde inhalation exposure and leukemia.

Oxidative and radiation stress induces transposable element transcription in Drosophila melanogaster

It has been shown that stressors are capable of activating transposable elements (TEs). Currently, there is a hypothesis that stress activation of TEs may be involved in adaptive evolution, favouring the increase in genetic variability when the population is under adverse conditions. However, TE activation under stress is still poorly understood. In the present study, we estimated the fraction of differentially expressed TEs (DETEs) under ionizing radiation (144, 360 and 864 Gy) and oxidative stress (dioxin, formaldehyde and toluene) treatments. The stress intensity of each treatment was estimated by measuring the number of differentially expressed genes, and we show that several TEs families are activated by stress whereas others are repressed. The proportion of DETEs was positively related to stress intensity. However, even under the strongest stress, only a small fraction of TE families were activated (9.28%) and 17.72% were repressed. Considering all treatments together, the activated proportion was 19.83%. Nevertheless, as several TEs are incomplete or degenerated, only 10.55% of D. melanogaster mobilome is, at same time, activated by the stressors and able to transpose or at least code a protein. Thus, our study points out that although stress activates TEs, it is not a generalized activation process, and for some families, the stress induces repression.

Human anatomy education and management of anatomic specimens during and after COVID-19 pandemic: Ethical, legal and biosafety aspects

COVID-19 is an infection caused by the SARS-CoV-2 virus, initially identified in the city of Wuhan, China, in December 2019. Since then, the virus has spread to the continents, causing a major pandemic. The impacts of this pandemic on the education of human anatomy interfere in at least two aspects: (1) receiving and managing anatomical specimens in anatomy laboratories and (2) adaptations for classes on remote virtual teaching. Therefore, this study reviewed and discussed the legal and bioethical aspects, considering the scenario of a South American Country, aiming to stimulate the debate on these two relevant themes in the international community. Because of the COVID-19 pandemic and the impossibility of mass testing, anatomists and other workers in the field must deal with the risk of receiving bodies infected with SARS-CoV-2. In this situation, additional care measures in biosafety practices are essential to protect the staff. Such measures are: the bodies must be preserved by the perfusion of formaldehyde or other fixative solutions; embalming must be performed in ventilated rooms with a good air exhaust system; to avoid excessive manipulation of bodies and procedures such as pulmonary insufflation or craniotomy; and proper use of personal protective equipment, including lab coat, gloves and masks. As for exposure of body images in online classes, this review showed that there are no legal impediments to this end. However, anatomists must adopt measures aimed at protecting the memory of the deceased, such as using secure digital platforms with restricted access; family authorization/consent and student awareness.

Mode of action-based risk assessment of genotoxic carcinogens

The risk assessment of chemical carcinogens is one major task in toxicology. Even though exposure has been mitigated effectively during the last decades, low levels of carcinogenic substances in food and at the workplace are still present and often not completely avoidable. The distinction between genotoxic and non-genotoxic carcinogens has traditionally been regarded as particularly relevant for risk assessment, with the assumption of the existence of no-effect concentrations (threshold levels) in case of the latter group. In contrast, genotoxic carcinogens, their metabolic precursors and DNA reactive metabolites are considered to represent risk factors at all concentrations since even one or a few DNA lesions may in principle result in mutations and, thus, increase tumour risk. Within the current document, an updated risk evaluation for genotoxic carcinogens is proposed, based on mechanistic knowledge regarding the substance (group) under investigation, and taking into account recent improvements in analytical techniques used to quantify DNA lesions and mutations as well as "omics" approaches. Furthermore, wherever possible and appropriate, special attention is given to the integration of background levels of the same or comparable DNA lesions. Within part A, fundamental considerations highlight the terms hazard and risk with respect to DNA reactivity of genotoxic agents, as compared to non-genotoxic agents. Also, current methodologies used in genetic toxicology as well as in dosimetry of exposure are described. Special focus is given on the elucidation of modes of action (MOA) and on the relation between DNA damage and cancer risk. Part B addresses specific examples of genotoxic carcinogens, including those humans are exposed to exogenously and endogenously, such as formaldehyde, acetaldehyde and the corresponding alcohols as well as some alkylating agents, ethylene oxide, and acrylamide, but also examples resulting from exogenous sources like aflatoxin B1, allylalkoxybenzenes, 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx), benzo[a]pyrene and pyrrolizidine alkaloids. Additionally, special attention is given to some carcinogenic metal compounds, which are considered indirect genotoxins, by accelerating mutagenicity via interactions with the cellular response to DNA damage even at low exposure conditions. Part C finally encompasses conclusions and perspectives, suggesting a refined strategy for the assessment of the carcinogenic risk associated with an exposure to genotoxic compounds and addressing research needs.

Penalized negative binomial models for modeling an overdispersed count outcome with a high-dimensional predictor space: Application predicting micronuclei frequency

Chromosomal aberrations, such as micronuclei (MN), have served as biomarkers of genotoxic exposure and cancer risk. Guidelines for the process of scoring MN have been presented by the HUman MicroNucleus (HUMN) project. However, these guidelines were developed for assay performance but do not address how to statistically analyze the data generated by the assay. This has led to the application of various statistical methods that may render different interpretations and conclusions. By combining MN with data from other high-throughput genomic technologies such as gene expression microarray data, we may elucidate molecular features involved in micronucleation. Traditional methods that can model discrete (synonymously, count) data, such as MN frequency, require that the number of explanatory variables (P) is less than the number of samples (N). Due to this limitation, penalized models have been developed to enable model fitting for such over-parameterized datasets. Because penalized models in the discrete response setting are lacking, particularly when the count outcome is over-dispersed, herein we present our penalized negative binomial regression model that can be fit when P > N. Using simulation studies we demonstrate the performance of our method in comparison to commonly used penalized Poisson models when the outcome is over-dispersed and applied it to MN frequency and gene expression data collected as part of the Norwegian Mother and Child Cohort Study. Our countgmifs R package is available for download from the Comprehensive R Archive Network and can be applied to datasets having a discrete outcome that is either Poisson or negative binomial distributed and a high-dimensional covariate space.

Re-evaluation of the WHO (2010) formaldehyde indoor air quality guideline for cancer risk assessment

In 2010, the World Health Organization (WHO) established an indoor air quality guideline for short- and long-term exposures to formaldehyde (FA) of 0.1 mg/m3 (0.08 ppm) for all 30-min periods at lifelong exposure. This guideline was supported by studies from 2010 to 2013. Since 2013, new key studies have been published and key cancer cohorts have been updated, which we have evaluated and compared with the WHO guideline. FA is genotoxic, causing DNA adduct formation, and has a clastogenic effect; exposure-response relationships were nonlinear. Relevant genetic polymorphisms were not identified. Normal indoor air FA concentrations do not pass beyond the respiratory epithelium, and therefore FA's direct effects are limited to portal-of-entry effects. However, systemic effects have been observed in rats and mice, which may be due to secondary effects as airway inflammation and (sensory) irritation of eyes and the upper airways, which inter alia decreases respiratory ventilation. Both secondary effects are prevented at the guideline level. Nasopharyngeal cancer and leukaemia were observed inconsistently among studies; new updates of the US National Cancer Institute (NCI) cohort confirmed that the relative risk was not increased with mean FA exposures below 1 ppm and peak exposures below 4 ppm. Hodgkin's lymphoma, not observed in the other studies reviewed and not considered FA dependent, was increased in the NCI cohort at a mean concentration ≥0.6 mg/m3 and at peak exposures ≥2.5 mg/m3; both levels are above the WHO guideline. Overall, the credibility of the WHO guideline has not been challenged by new studies.

Is it possible to use biomonitoring for the quantitative assessment of formaldehyde occupational exposure?

The European classification, labeling and packaging classified formaldehyde as human carcinogen Group 1B and mutagen 2, fostering the re-evaluation of the exposure risk in occupational settings. Although formaldehyde exposure is traditionally measured in air, many efforts were made to identify specific exposure biomarkers: urinary formaldehyde, formic acid and DNA damage indicators. Though used in combination, none of these seems satisfactory. The influence of the metabolism on exogenous formaldehyde levels, the exposure to other xenobiotics, the difference in genetic background and metabolism efficiency, misled the relationship between genotoxicity and exposure data. Nevertheless, the limitation of adverse effects to the local contact sites hampers biomonitoring. Here we discuss the feasibility of formaldehyde biomonitoring and the use of DNA, DNA-protein cross-links and protein adducts as potential biomarkers.

Functional Toxicogenomic Profiling Expands Insight into Modulators of Formaldehyde Toxicity in Yeast

Formaldehyde (FA) is a commercially important chemical with numerous and diverse uses. Accordingly, occupational and environmental exposure to FA is prevalent worldwide. Various adverse effects, including nasopharyngeal, sinonasal, and lymphohematopoietic cancers, have been linked to FA exposure, prompting designation of FA as a human carcinogen by U.S. and international scientific entities. Although the mechanism(s) of FA toxicity have been well studied, additional insight is needed in regard to the genetic requirements for FA tolerance. In this study, a functional toxicogenomics approach was utilized in the model eukaryotic yeast Saccharomyces cerevisiae to identify genes and cellular processes modulating the cellular toxicity of FA. Our results demonstrate mutant strains deficient in multiple DNA repair pathways-including homologous recombination, single strand annealing, and postreplication repair-were sensitive to FA, indicating FA may cause various forms of DNA damage in yeast. The SKI complex and its associated factors, which regulate mRNA degradation by the exosome, were also required for FA tolerance, suggesting FA may have unappreciated effects on RNA stability. Furthermore, various strains involved in osmoregulation and stress response were sensitive to FA. Together, our results are generally consistent with FA-mediated damage to both DNA and RNA. Considering DNA repair and RNA degradation pathways are evolutionarily conserved from yeast to humans, mechanisms of FA toxicity identified in yeast may be relevant to human disease and genetic susceptibility.

Reassessment of MTBE cancer potency considering modes of action for MTBE and its metabolites

A 1999 California state agency cancer potency (CP) evaluation of methyl tert-butyl ether (MTBE) assumed linear risk extrapolations from tumor data were plausible because of limited evidence that MTBE or its metabolites could damage DNA, and based such extrapolations on data from rat gavage and rat and mouse inhalation studies indicating elevated tumor rates in male rat kidney, male rat Leydig interstitial cells, and female rat leukemia/lymphomas. More recent data bearing on MTBE cancer potency include a rodent cancer bioassay of MTBE in drinking water; several new studies of MTBE genotoxicity; several similar evaluations of MTBE metabolites, formaldehyde, and tert-butyl alcohol or TBA; and updated evaluations of carcinogenic mode(s) of action (MOAs) of MTBE and MTBE metabolite's. The lymphoma/leukemia data used in the California assessment were recently declared unreliable by the U.S. Environmental Protection Agency (EPA). Updated characterizations of MTBE CP, and its uncertainty, are currently needed to address a variety of decision goals concerning historical and current MTBE contamination. To this end, an extensive review of data sets bearing on MTBE and metabolite genotoxicity, cytotoxicity, and tumorigenicity was applied to reassess MTBE CP and related uncertainty in view of MOA considerations. Adopting the traditional approach that cytotoxicity-driven cancer MOAs are inoperative at very low, non-cytotoxic dose levels, it was determined that MTBE most likely does not increase cancer risk unless chronic exposures induce target-tissue toxicity, including in sensitive individuals. However, the corresponding expected (or plausible upper bound) CP for MTBE conditional on a hypothetical linear (e.g., genotoxic) MOA was estimated to be ∼2 × 10(-5) (or 0.003) per mg MTBE per kg body weight per day for adults exposed chronically over a lifetime. Based on this conservative estimate of CP, if MTBE is carcinogenic to humans, it is among the weakest 10% of chemical carcinogens evaluated by EPA.

Formaldehyde-induced toxicity in the nasal epithelia of workers of a plastic laminate plant

Formaldehyde is a ubiquitous volatile organic compound widely used for various industrial purposes. Formaldehyde was reclassified by the International Agency for Research on Cancer as a human carcinogen, based on sufficient evidence for a casual role for nasopharyngeal cancer. However, the mechanisms by which this compound causes nasopharyngeal cancer are not completely understood. Therefore, we have examined the formaldehyde-induced toxicity in the nasal epithelia of the workers of a plastic laminate plant in Bra, Cuneo, Piedmont region, North-Western Italy, hence in the target site for formaldehyde-related nasal carcinogenesis. We have conducted a cross-sectional study aimed at comparing the frequency of 3-(2-deoxy-β-d-erythro-pentafuranosyl)pyrimido[1,2-α]purin-10(3H)-one deoxyguanosine (M1dG) adducts, a biomarker of oxidative stress and lipid peroxidation, in 50 male exposed workers and 45 male controls using 32P-DNA post-labeling. The personal levels of formaldehyde exposure were analysed by gas-chromatography mass-spectrometry. The smoking status was estimated by measuring the concentrations of urinary cotinine by gas-chromatography mass-spectrometry. The air monitoring results showed that the exposure levels of formaldehyde were significantly greater for the plastic laminate plant workers, 211.4 ± 14.8 standard error (SE) μg m-3, than controls, 35.2 ± 3.4 (SE) μg m-3, P < 0.001. The levels of urinary cotinine were 1064 ± 118 ng ml-1 and 14.18 ± 2.5 ng ml-1 in smokers and non-smokers, respectively, P < 0.001. The M1dG adduct frequency per 108 normal nucleotides was significantly higher among the workers of the plastic laminate plant exposed to formaldehyde, 111.6 ± 14.3 (SE), compared to controls, 49.6 ± 3.4 (SE), P < 0.001. This significant association persisted also when personal dosimeters were used to measure the extent of indoor levels of formaldehyde exposure. No influences of smoking and age were observed across the study population. However, after categorization for occupational exposure, a significant effect was found in the controls, P = 0.018, where the levels of DNA damage were significantly correlated with the levels of urinary cotinine, regression coefficient (β) = 0.494 ± 0.000 (SE), P < 0.002. Our findings indicated that M1dG adducts constitute a potential mechanism of formaldehyde-induced toxicity. Persistent DNA damage contributes to the general decline of the physiological mechanisms designed to maintain cellular homeostasis.

Induction and repair of DNA damage measured by the comet assay in human T lymphocytes separated by immunomagnetic cell sorting

The comet assay is widely used in human biomonitoring to measure DNA damage in whole blood or isolated peripheral blood mononuclear cells (PBMC) as a marker of exposure to genotoxic agents. Cytogenetic assays with phytohemagglutinin (PHA)-stimulated cultured T lymphocytes are also frequently performed in human biomonitoring. Cytogenetic effects (micronuclei, chromosome aberrations, sister chromatid exchanges) may be induced in vivo but also occur ex vivo during the cultivation of lymphocytes as a consequence of DNA damage present in lymphocytes at the time of sampling. To better understand whether DNA damage measured by the comet assay in PBMC is representative for DNA damage in T cells, we comparatively investigated DNA damage and its repair in PBMC and T cells obtained by immunomagnetic cell sorting. PBMC cultures and T cell cultures were exposed to mutagens with different modes of genotoxic action and DNA damage was measured by the comet assay after the end of a 2h exposure and after 18h post-incubation. The mutagens tested were methyl methanesulfonate (MMS), (±)-anti-B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), 4-nitroquinoline-1-oxide (4NQO), styrene oxide and potassium bromate. MMS and potassium bromate were also tested by the modified comet assay with formamido pyrimidine glycosylase (FPG) protein. The results indicate that the mutagens tested induce DNA damage in PBMC and T cells in the same range of concentrations and removal of induced DNA lesions occurs to a comparable extent. Based on these results, we conclude that the comet assay with PBMC is suited to predict DNA damage and its removal in T cells.

Oxidative DNA damage and formalin-fixation procedures

An experimental study on how formaldehyde-fixation is capable of inducing excess oxidative DNA damage in formalin-fixed paraffin-embedded tissues.

Investigations on potential co-mutagenic effects of formaldehyde

The genotoxicity and mutagenicity of formaldehyde (FA) has been well-characterized during the last years. Besides its known direct DNA-damaging and mutagenic activity in sufficiently exposed cells, FA at low concentrations might also enhance the mutagenic and carcinogenic effects of other environmental mutagens by interfering with the repair of DNA lesions induced by these mutagens. To further assess potential co-mutagenic effects of FA, we exposed A549 human lung cells to FA in combination with various mutagens and measured the induction and removal of DNA damage by the comet assay and the production of chromosomal mutations by the cytokinesis-block micronucleus assay (CBMN assay). The mutagens tested were ionizing radiation (IR), (±)-anti-B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), N-nitroso-N-methylurea (methyl nitrosourea; MNU) and methyl methanesulfonate (MMS). FA (10-75μM) did not enhance the genotoxic and mutagenic activity of these mutagens under the test conditions applied. FA alone and in combination with MNU or MMS did not affect the expression (mRNA level) of the gene of the O(6)-methylguanine-DNA methyltransferase (MGMT) in A549 cells. The results of these experiments do not support the assumption that low FA concentrations might interfere with the repair of DNA damage induced by other mutagens.

Amended Safety Assessment of Formaldehyde and Methylene Glycol as Used in Cosmetics

Formaldehyde and methylene glycol may be used safely in cosmetics if established limits are not exceeded and are safe for use in nail hardeners in the present practices of use and concentration, which include instructions to avoid skin contact. In hair-smoothing products, however, in the present practices of use and concentration, formaldehyde and methylene glycol are unsafe. Methylene glycol is continuously converted to formaldehyde, and vice versa, even at equilibrium, which can be easily shifted by heating, drying, and other conditions to increase the amount of formaldehyde. This rapid, reversible formaldehyde/methylene glycol equilibrium is distinguished from the slow, irreversible release of formaldehyde resulting from the so-called formaldehyde releaser preservatives, which are not addressed in this safety assessment (formaldehyde releasers may continue to be safely used in cosmetics at the levels established in their individual Cosmetic Ingredient Review safety assessments).

Formaldehyde-associated changes in microRNAs: tissue and temporal specificity in the rat nose, white blood cells, and bone marrow

MicroRNAs (miRNAs) are critical regulators of gene expression, yet much remains unknown regarding their changes resulting from environmental exposures as they influence cellular signaling across various tissues. We set out to investigate miRNA responses to formaldehyde, a critical air pollutant and known carcinogen that disrupts miRNA expression profiles. Rats were exposed by inhalation to either 0 or 2 ppm formaldehyde for 7, 28, or 28 days followed by a 7-day recovery. Genome-wide miRNA expression profiles were assessed within the nasal respiratory epithelium, circulating white blood cells (WBC), and bone marrow (BM). miRNAs showed altered expression in the nose and WBC but not in the BM. Notably in the nose, miR-10b and members of the let-7 family, known nasopharyngeal carcinoma players, showed decreased expression. To integrate miRNA responses with transcriptional changes, genome-wide messenger RNA profiles were assessed in the nose and WBC. Although formaldehyde-induced changes in miRNA and transcript expression were largely tissue specific, pathway analyses revealed an enrichment of immune system/inflammation signaling in the nose and WBC. Specific to the nose was enrichment for apoptosis/proliferation signaling, involving let-7a, let-7c, and let-7f. Across all tissues and time points assessed, miRNAs were predicted to regulate between 7% and 35% of the transcriptional responses and were suggested to play a role in signaling processes including immune/inflammation-related pathways. These data inform our current hypothesis that formaldehyde-induced inflammatory signals originating in the nose may drive WBC effects.

Distinguishing between genotoxic and non-genotoxic hepatocarcinogens by gene expression profiling and bioinformatic pathway analysis

A rapid and sensitive method to determine the characteristics of carcinogens is needed. In this study, we used a microarray-based genomics approach, with a short-term in vivo model, in combination with insights from statistical and mechanistic analyses to determine the characteristics of carcinogens. Carcinogens were evaluated based on the different mechanisms involved in the responses to genotoxic carcinogens and non-genotoxic carcinogens. Gene profiling was performed at two time points after treatment with six training and four test carcinogens. We mapped the DEG (differentially expressed gene)-related pathways to analyze cellular processes, and we discovered significant mechanisms that involve critical cellular components. Classification results were further supported by Comet and Micronucleus assays. Mechanistic studies based on gene expression profiling enhanced our understanding of the characteristics of different carcinogens. Moreover, the efficiency of this study was demonstrated by the short-term nature of the animal experiments that were conducted.

In vitro effects of aldehydes present in tobacco smoke on gene expression in human lung alveolar epithelial cells

Tobacco smoke consists of thousands of harmful components. A major class of chemicals found in tobacco smoke is formed by aldehydes, in particular formaldehyde, acetaldehyde and acrolein. The present study investigates the gene expression changes in human lung alveolar epithelial cells upon exposure to formaldehyde, acrolein and acetaldehyde at sub-cytotoxic levels. We exposed A549 cells in vitro to aldehydes and non-aldehyde chemicals (nicotine, hydroquinone and 2,5-dimethylfuran) present in tobacco smoke and used microarrays to obtain a global view of the transcriptomic responses. We compared responses of the individual aldehydes with that of the non-aldehydes. We also studied the response of the aldehydes when present in a mixture at relative concentrations as present in cigarette smoke. Formaldehyde gave the strongest response; a total of 66 genes were more than 1.5-fold differentially expressed mostly involved in apoptosis and DNA damage related processes, followed by acetaldehyde (57 genes), hydroquinone (55 genes) and nicotine (8 genes). For acrolein and the mixture only one gene was upregulated involved in oxidative stress. No gene expression effect was found for exposure to 2,5-dimethylfuran. Overall, aldehyde responses are primarily indicative for genotoxicity and oxidative stress. These two toxicity mechanisms are linked to respiratory diseases such as cancer and COPD, respectively. The present findings could be important in providing further understanding of the role of aldehydes emitted from cigarette smoke in the onset of pulmonary diseases.

New results on formaldehyde: the 2nd International Formaldehyde Science Conference (Madrid, 19-20 April 2012)

The toxicology and epidemiology of formaldehyde were discussed on the 2nd International Formaldehyde Science Conference in Madrid, 19-20 April 2012. It was noted that a substantial amount of new scientific data has appeared within the last years since the 1st conference in 2007. Progress has been made in characterisation of genotoxicity, toxicokinetics, formation of exogenous and endogenous DNA adducts, controlled human studies and epidemiology. Thus, new research results are now at hand to be incorporated into existing evaluations on formaldehyde by official bodies.

Recent trend in risk assessment of formaldehyde exposures from indoor air

Studies about formaldehyde (FA) published since the guideline of 0.1 mg/m(3) by the World Health Organization (WHO) in 2010 have been evaluated; critical effects were eye and nasal (portal-of-entry) irritation. Also, it was considered to prevent long-term effects, including all types of cancer. The majority of the recent toxicokinetic studies showed no exposure-dependent FA-DNA adducts outside the portal-of-entry area and FA-DNA adducts at distant sites were due to endogenously generated FA. The no-observed-adverse-effect level for sensory irritation was 0.5 ppm and recently reconfirmed in hypo- and hypersensitive individuals. Investigation of the relationship between FA exposure and asthma or other airway effects in children showed no convincing association. In rats, repeated exposures showed no point mutation in the p53 and K-Ras genes at ≤15 ppm neither increased cell proliferation, histopathological changes and changes in gene expression at 0.7 ppm. Repeated controlled exposures (0.5 ppm with peaks at 1 ppm) did not increase micronucleus formation in human buccal cells or nasal tissue (0.7 ppm) or in vivo genotoxicity in peripheral blood lymphocytes (0.7 ppm), but higher occupational exposures were associated with genotoxicity in buccal cells and cultivated peripheral blood lymphocytes. It is still valid that exposures not inducing nasal squamous cell carcinoma in rats will not induce nasopharyngeal cancer or lymphohematopoietic malignancies in humans. Reproductive and developmental toxicity are not considered relevant in the absence of sensory irritation. In conclusion, the WHO guideline has been strengthened.

Analysis of leukemia-specific aneuploidies in cultured myeloid progenitor cells in the absence and presence of formaldehyde exposure

A recently published human study suggested that exposure to formaldehyde (FA) at the workplace might induce leukemia-specific aneuploidies (monosomy 7 and trisomy 8) in cultured myeloid progenitor cells. Despite its preliminary character, this study was considered by the International Agency for Research on Cancer to be a potential mechanistic explanation for the induction of leukemia by FA. To further evaluate the reliability of these findings, chromosome preparations from cultured myeloid progenitor cells (obtained from blood samples of five healthy subjects) were analyzed by fluorescence in situ hybridization (FISH) for spontaneously occurring numerical aberrations after cultivation for 9 days. FISH analysis with probes for chromosomes 6, 7, and 8 revealed that the baseline frequency of aneuploid metaphases is similar and rather low for all three chromosomes tested. More monosomies than trisomies were measured. We also exposed myeloid progenitor cells during the whole cultivation period to FA and determined the frequency of aneuploidies after 9 days of cultivation. The results clearly indicate that FA did not induce aneuploidy under these experimental conditions. In contrast, aneuploidy was induced under these conditions by the known aneugen vincristine. Myeloid progenitor cells from healthy subjects were not particularly sensitive toward the cytotoxic action of FA. Colony forming ability in the presence of FA was not reduced to a higher degree than in cultured cell lines (A549; V79). Our results do not support the assumption of a specific effect of FA on myeloid progenitor cells as a potential mechanism for the induction of leukemia.

Investigations of potential susceptibility toward formaldehyde-induced genotoxicity

Blood samples were taken from three groups of volunteers (30 male smokers, 30 female non-smokers, and 30 school children) and tested for ex vivo susceptibility toward formaldehyde (FA)-induced genotoxicity. Blood samples were exposed to 150 μM FA for 2 h, and the induction of DNA-protein crosslinks (DPX) in leukocytes was measured by a modification of the alkaline comet assay (i.e., reduction of γ-irradiation induced DNA migration). Removal of DPX was determined by the abolition of FA-induced reduction in DNA migration within 4 h after the end of the exposure. Induction and persistence of FA-induced DNA lesions was also measured by the sister chromatid exchange (SCE) test with cultured lymphocytes after treatment of whole blood cultures with FA (150 μM). Furthermore, the expression (mRNA level) of the GSH-dependent formaldehyde dehydrogenase (FDH, identical to alcohol dehydrogenase 5; ADH5) was measured in leukocytes by quantitative real-time RT-PCR with TaqMan probes. The subjects were also analyzed for the GSTM1 and GSTT1 metabolic gene polymorphisms and a correlation analysis with the investigated genetic endpoints for FA-induced genotoxicity was performed. The results indicate that there are no biologically relevant differences between the three study groups with regard to the various indicators of cellular sensitivity toward FA-induced genotoxic effects and the expression of FDH. The induced genotoxic effects were not associated with polymorphisms in GSTM1 and GSTT1. None of the study groups showed particular mutagen sensitivity toward FA-induced genotoxicity. These results suggest that a low scaling factor to address possible human inter-individual differences in FA-induced genotoxicity could be reasonable.

Re-evaluation of a reported increased micronucleus frequency in lymphocytes of workers occupationally exposed to formaldehyde

A replicate evaluation of increased micronucleus (MN) frequencies in peripheral lymphocytes of workers occupationally exposed to formaldehyde (FA) was undertaken to verify the observed effect and to determine scoring variability. May-Grünwald-Giemsa-stained slides were obtained from a previously performed cytokinesis-block micronucleus test (CBMNT) with 56 workers in anatomy and pathology laboratories and 85 controls. The first evaluation by one scorer (scorer 1) had led to a highly significant difference between workers and controls (3.96 vs 0.81 MN per 1000 cells). The slides were coded before re-evaluation and the code was broken after the complete re-evaluation of the study. A total of 1000 binucleated cells (BNC) were analysed per subject and the frequency of MN (in ‰) was determined. Slides were distributed equally and randomly between two scorers, so that the scorers had no knowledge of the exposure status. Scorer 2 (32 exposed, 36 controls) measured increased MN frequencies in exposed workers (9.88 vs 6.81). Statistical analysis with the two-sample Wilcoxon test indicated that this difference was not significant (p=0.17). Scorer 3 (20 exposed, 46 controls) obtained a similar result, but slightly higher values for the comparison of exposed and controls (19.0 vs 12.89; p=0.089). Combining the results of the two scorers (13.38 vs 10.22), a significant difference between exposed and controls (p=0.028) was obtained when the stratified Wilcoxon test with the scorers as strata was applied. Interestingly, the re-evaluation of the slides led to clearly higher MN frequencies for exposed and controls compared with the first evaluation. Bland-Altman plots indicated that the agreement between the measurements of the different scorers was very poor, as shown by mean differences of 5.9 between scorer 1 and scorer 2 and 13.0 between scorer 1 and scorer 3. Calculation of the intra-class correlation coefficient (ICC) revealed that all scorer comparisons in this study were far from acceptable for the reliability of this assay. Possible implications for the use of the CBMNT in human biomonitoring studies are discussed.

Exposure study to examine chemosensory effects of formaldehyde on hyposensitive and hypersensitive males

OBJECTIVE

Main objective of this study was to examine the chemosensory effects of formaldehyde on hyposensitive and hypersensitive males at concentrations relevant to the workplace. Attention focused on objective effects on and subjective symptoms of the mucous membranes of the eyes, the nose, the upper respiratory tract and olfactory function.

METHODS

Forty-one male volunteers were exposed for 5 days (4 h per day) in a randomised schedule to the control condition (0 ppm) and to formaldehyde concentrations of 0.5 and 0.7 ppm and to 0.3 ppm with peak exposures of 0.6 ppm, and to 0.4 ppm with peak exposures of 0.8 ppm, respectively. Peak exposures were carried out four times a day over a 15-min period of time. Subjective pain perception induced by nasal application of carbon dioxide served as indicator for sensitivity to sensory nasal irritation. The following parameters were examined before and after exposure: subjective rating of symptoms and complaints (Swedish Performance Evaluation System), conjunctival redness, eye-blinking frequency, self-reported tear film break-up time and nasal flow rates. In addition, the influence of personality factors on the volunteer's subjective scoring was examined (Positive And Negative Affect Schedule).

RESULTS

Formaldehyde exposures to 0.7 ppm for 4 h and to 0.4 ppm for 4 h with peaks of 0.8 ppm for 15 min caused no significant sensory irritation of the measured conjunctival and nasal parameters. No differences between hypo- and hypersensitive subjects were seen. Nevertheless, statistically significant differences were noted for olfactory symptoms, especially for the 'perception of impure air'. These subjective complaints were more pronounced in hypersensitive subjects.

CONCLUSIONS

Formaldehyde concentrations of 0.7 ppm for 4 h and of 0.4 ppm for 4 h with peaks of 0.8 ppm for 15 min did not cause adverse effects related to irritation, and no differences between hypo- and hypersensitive subjects were observed.