Alterations of telomere length and DNA methylation in hairdressers: A cross-sectional study

Do hairdressers comprise a high risk group for genotoxicity? A systematic review

BACKGROUND AND OBJECTIVES

Nowadays, hair dye products are widely used for aesthetic purposes, in which it generates chemical exposure to customers and, mainly, hairdressers. The aim of this systematic review was designed to elucidate the following question: are hair dye products able to induce DNA damage in hairdressers?

METHODS

Studies were included in our analyses if they met the following criteria: (1) studies measuring genetic damage in vivo; (2) studies published in English; (3) studies that provided data clearly presented in scientific standards.

RESULTS

Full manuscripts from 13 studies were carefully selected in this setting. Our results demonstrate that hair dye products may contain chemical agents able to induce DNA strand breaks or chromosome damage since the majority of studies demonstrated positive findings for genotoxicity. A total of 7 studies (out of 13) had strong or moderate rates in the quality assessment. The type of genotoxicity assay and sample selection criteria time influenced the outcome.

CONCLUSION

In summary, our results reveal that hairdressers are occupationally exposed to genotoxic agents. Such findings are very important for protecting these professionals who are continuously exposed to chemicals for long periods.

Toxicomethylomics revisited: A state-of-the-science review about DNA methylation modifications in blood cells from workers exposed to toxic agents

Introduction

Epigenetic marks have been proposed as early changes, at the subcellular level, in disease development. To find more specific biomarkers of effect in occupational exposures to toxicants, DNA methylation studies in peripheral blood cells have been performed. The goal of this review is to summarize and contrast findings about DNA methylation in blood cells from workers exposed to toxicants.

Methods

A literature search was performed using PubMed and Web of Science. After first screening, we discarded all studies performed in vitro and in experimental animals, as well as those performed in other cell types other than peripheral blood cells. Results: 116 original research papers met the established criteria, published from 2007 to 2022. The most frequent investigated exposures/labor group were for benzene (18.9%) polycyclic aromatic hydrocarbons (15.5%), particulate matter (10.3%), lead (8.6%), pesticides (7.7%), radiation (4.3%), volatile organic compound mixtures (4.3%), welding fumes (3.4%) chromium (2.5%), toluene (2.5%), firefighters (2.5%), coal (1.7%), hairdressers (1.7%), nanoparticles (1.7%), vinyl chloride (1.7%), and others. Few longitudinal studies have been performed, as well as few of them have explored mitochondrial DNA methylation. Methylation platforms have evolved from analysis in repetitive elements (global methylation), gene-specific promoter methylation, to epigenome-wide studies. The most reported observations were global hypomethylation as well as promoter hypermethylation in exposed groups compared to controls, while methylation at DNA repair/oncogenes genes were the most studied; studies from genome-wide studies detect differentially methylated regions, which could be either hypo or hypermethylated.

Discussion

Some evidence from longitudinal studies suggest that modifications observed in cross-sectional designs may be transitory; then, we cannot say that DNA methylation changes are predictive of disease development due to those exposures.

Conclusion

Due to the heterogeneity in the genes studied, and scarcity of longitudinal studies, we are far away from considering DNA methylation changes as biomarkers of effect in occupational exposures, and nor can we establish a clear functional or pathological correlate for those epigenetic modifications associated with the studied exposures.

Filaggrin variations are associated with PAH metabolites in urine and DNA alterations in blood

Dermal chemical exposure is common in many professions. The filaggrin protein is important for the skin barrier and variations in the filaggrin gene (FLG) may influence the uptake of chemicals via the skin, and consequently, the degree of systemic effects. The aim of this study was to investigate, in chimney sweeps with occupational exposure to polycyclic aromatic hydrocarbons (PAH) from soot, the influence of variation in FLG on internal PAH dose and DNA alterations, including epigenetic, previously linked to cancer and cardiovascular disease. We used TaqMan PCR to genotype 151 chimney sweeps and 152 controls for four FLG null variants (R501X, R2447X, S3247X and 2282del4) which cause impaired skin barrier, and FLG copy number variation (12th repeat, CNV12) which potentially is beneficial for the skin barrier. The internal dose of PAH was represented by urinary PAH metabolites (e.g. 1-hydroxypyrene and 3-hydroxybenzo[a]pyrene) that we measured by LC-MS/MS. We measured epigenetic alterations (methylation of AHRR and F2RL3) in blood by pyrosequencing; and DNA alterations (telomere length and mitochondrial DNA copy number) by real-time PCR. Hypomethylation of AHRR or F2RL3 is a risk factor for lung cancer and shorter telomere length a risk factor for cardiovascular disease. The frequencies of FLG null were 8.6 and 11.8% (p = 0.35), and CNV12 27.8 and 19.7% (p = 0.09) in chimney sweeps and controls, respectively. We found that among chimney sweeps working predominately with soot sweeping (high PAH exposure), CNV12 carriers had lower concentrations of PAH metabolites in urine compared with non-carriers (median 1-hydroxypyrene = 0.37 vs 0.86 μg/g creatinine respectively; p = 0.025 by linear regression models adjusted for age, BMI and smoking) compared to sweeps not carrying CNV12. Further, FLG null was associated with approximately 2.5% higher methylation of F2RL3 (cg03636183, p = 0.019 after adjustment for exposure group, age, BMI and smoking). FLG null was associated with approximately 7% shorter telomere length (p = 0.015, adjusted model). Our results suggest that FLG variations may influence the dose of PAH in highly exposed workers, possibly via dermal uptake. It also suggests that FLG variation may influence the degree of (epi)genotoxicity in the body. FLG variation is common in the working population and should be considered in risk assessment.

Genetic variants of filaggrin are associated with occupational dermal exposure and blood DNA alterations in hairdressers

Hairdressers are exposed to high levels of chemicals, including possible carcinogens. For dermal exposure, the skin protects against the uptake of chemicals and the protein filaggrin (encoded by FLG) has a key role in skin barrier function. This study investigated if variants of FLG previously linked to impaired skin barrier function, i.e. null mutations and copy number variation (CNV) alleles (CNV10), are associated with cancer-related DNA changes. Blood and questionnaire data were collected from hairdressers (n = 295) and controls (n = 92). Exposure to aromatic amines was measured as hemoglobin adducts by gas chromatography tandem mass spectrometry. DNA from peripheral blood was used to test for FLG null mutations and CNV (10, 11, or 12 repeats), telomere length, and methylation of selected cancer-related genes. Hairdressers had a lower frequency of FLG null mutations (4.1 vs. 7.6%, P = 0.18) and CNV10 (43.2 vs. 56%, P = 0.0032) than controls. In hairdressers, CNV10 carriers had a decreased risk of high ortho-toluidine adducts in blood compared with non-carriers (odds ratio, OR = 0.49, 95% CI = 0.30-0.81). Further, telomere length was shorter for carriers of any FLG null allele (β = -0.18, 95% CI = -0.31 to -0.044) and CNV10 carriers (β = -0.054, 95% CI = -0.11 to -0.00051, linear regression adjusted for age, passive smoking, residence, and education) compared to non-carriers. Carriers of any FLG null allele showed higher methylation of the cyclin-dependent kinase inhibitor 2A gene CDKN2A (OR = 6.26, CI = 1.13-34.7), but not of the other genes analyzed. These associations were not found among the controls. Our study showed that the frequency of FLG CNV10 was lower among hairdressers than controls, which may indicate a healthy worker selection. Moreover, FLG null and CNV10 were associated with cancer-related DNA changes in hairdressers, which may influence their risk of cancer.

The Question on the Potential Cancerous Effects of Hair Dyes: The Monitoring of the Oxidative Stress Induced by the Hair Dyes with the Dosage of the Salivary Free Radicals

Background:

Many studies indicate the difficulty on assessing the possible carcinogenic effects of hair dyes, for their high time of the latence.

Objectives:

Our objective is to determine their prognostic index, by monitoring the oxidative stress, produced exposed to hair dyes, in hairdressers, and in consumers, by measuring the concentration of salivary malondialdehyde.

Materials and Methods:

Saliva samples are provided by the hairdressers, working in private (NP) or shopping center (CC), by users of hair dyes, for at least 10 years, and by a control group. The values of malondialdehyde are determined using the thiobarbituric acid method. The results are statistically analyzed by Kruskal–Wallis and Mann–Whitney test.

Results:

Comparing the three groups with tests for K-independent Kruskal–Wallis samples (dyed vs. control vs. dyed at least 10 years), there is a significant difference for the amount of MDA (P < 0.001). Proceeding for the median MDA in the subgroups by testing for two independent U-samples of Mann–Whitney: control versus dyed, P < 0.001; control versus CC, P = 0.013; control versus NP, P < 0.001; control versus 10 years, P = 0.111; CC versus NP, P = 0.001; CC versus 10 years, P = 0.462; and NP versus 10 years, P < 0.001.

Discussion:

In hairdressers, the increase of the salivary MDA versus control group is statistically significant (P ≤ 0.05), with an accentuation in small workplace, for age, probably for a more direct exposure to dyes' gas. Another statistically significant increase of salivary MDA is for the consumers versus control group, also function of the increasing age.

Conclusions:

The results of this study show a significant increase of oxidative stress in the hairdressers. This factor involves a potential carcinogenic risk, especially for the bladder, difficult to assess in the short term.

Role of PON1, SOD2, OGG1, XRCC1, and XRCC4 polymorphisms on modulation of DNA damage in workers occupationally exposed to pesticides

Tobacco farming has been proving to induce poor health outcomes in agricultural workers, genomic instability being the triggering one. This study evaluated influence of PON1 (paraoxonase 1), SOD2 (superoxide dismutase), OGG1 (8-oxoguanine glycosylase), XRCC1 (X-ray repair cross-complementing protein 1), and XRCC4 (X-ray repair cross-complementing protein 4) genes polymorphisms on DNA damage in 121 subjects occupationally exposed to pesticides mixtures and nicotine at tobacco fields and 121 non-exposed individuals. Inorganic elements (Cl, P, S and Zn) and cotinine levels were found increased in farmers, confirming exposure. Results show higher frequencies of buccal micronucleus (MN), nuclear buds (NBUD), binucleated cells (BN) and damage index (comet assay), reduced telomere length (TL), and increased parameters of oxidative stress in farmers compared to non-exposed individuals. PON1 Gln/Gln genotype was associated with increased MN frequency. SOD2 Val/Val showed association with increased frequency of MN and NBUD and decreased antioxidant activity. The XRCC1 Arg/Arg showed protective effect for MN, BN and TL, which was also positively influenced by OGG1 -/Cys. MN was decreased in XRCC4 -/Ile farmers. These genotypes also showed a risk for antioxidant activity. Our study proposes that PON1 and SOD2 variants play a role in xenobiotic-metabolizing system in farmers, while base excision repair (BER) pathway could be the repair mechanism involved in genomic instability suffered by tobacco farmers.

Chronic occupational exposure endured by tobacco farmers from Brazil and association with DNA damage

Tobacco farming is an important economic income in Brazil, although it has been challenged as regard the occupational exposure to both pesticides and nicotine endured by farmers. Chronic occupational exposure to complex mixtures can lead to health hazardous. We examined genomic instability and epigenetic changes in tobacco farmers occupationally exposed to pesticide mixtures and nicotine at tobacco fields. DNA damage was assessed by alkaline comet assay in blood cells. Genomic DNA was isolated, and telomere length was measured using quantitative polymerase chain reaction assay. We measured 5-methyl-2'-deoxycytidine, a marker of global DNA methylation, and p16 promoter methylation. The oxidative profile was evaluated by trolox equivalent antioxidant capacity and lipid peroxidation (thiobarbituric acid reactive substances) in serum. Exposure parameters, plasma cotinine and inorganic element levels, were also measured. DNA damage was significantly elevated for farmers in relation to unexposed group (P < 0.001; Mann-Whitney test) and positively associated with years of exposure. Inverse relationship between DNA damage and total equivalent antioxidant activity was demonstrated for exposed and unexposed groups. Exposed group showed significantly shorter telomeres (P < 0.001; unpaired t-test) and DNA hypomethylation (P < 0.001; unpaired t-test), as well as p16 hypermethylation (P = 0.003; Mann-Whitney test). Lipid peroxidation was increased for exposed group in relation to unexposed one (P = 0.02; Mann-Whitney test) and presented a positive correlation with global DNA methylation (P = 0.0264). Farmers have increased plasma cotinine levels (P < 0.001) and inorganic elements (phosphorus, sulphur and chlorine) in relation to unexposed group. Elevated oxidative stress levels due to chronic occupational pesticide mixtures and nicotine exposure in tobacco farmers were associated with higher DNA damage, shorter telomeres and altered DNA methylation. Telomere-accelerated attrition due to exposure may be potential intermediate step before a disease state.