Assessment of genotoxic effects of lead in occupationally exposed workers

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.

Lead toxicity and potential therapeutic effect of plant-derived polyphenols

BACKGROUND

Due to its unique physical and chemical properties, lead is still used worldwide in several applications, especially in industry. Both environmental and industrial lead exposures remain a public health problem in many developing and rapidly industrializing countries. Plant polyphenols are pleiotropic in their function and have historically made a major contribution to pharmacotherapy.

PURPOSE

To summarize available pre-clinical and limited clinical evidence on plant polyphenols as potential antidotes against lead poisoning and discuss toxic mechanisms of lead.

METHOD

A comprehensive search of peer-reviewed publications was performed from core collections of electronic databases such as PubMed, Web of Science, Google Scholar, and Science Direct. Articles written in English-language from inception until December 2022 were selected.

RESULTS

In this review, we review key toxic mechanisms of lead and its pathological effects on the neurological, reproductive, renal, cardiovascular, hematological, and hepatic systems. We focus on plant polyphenols against lead toxicity and involved mechanisms. Finally, we address scientific gaps and challenges associated with translating these promising preclinical discoveries into effective clinical therapies.

CONCLUSION

While preclinical evidence suggests that plant polyphenols exhibit bioprotective effects against lead toxicity, scant and equivocal clinical data highlight a need for clinical trials with those polyphenols.

First Report of Mitochondrial DNA Copy Number Variation in Opsius heydeni (Insecta, Hemiptera, Cicadellidae) from Polluted and Control Sites

Mitochondrial DNA easily undergoes alterations due to exposure to stress factors. In particular, mitochondrial DNA copy number (mtDNAcn) variation can be used as a biomarker of the effect of exposure to various environmental contaminants. In this study, a molecular investigation based on the evaluation of mtDNAcn variation was applied for the first time to individuals belonging to the species Opsius heydeni. A total of 20 samples were collected from two sites in eastern Sicily: Priolo Gargallo, a site with a strong anthropic impact, and the Simeto river Oasis, a control site. Specimens identified based on morphological traits were used to obtain COI gene sequences from this species that were not previously available in GenBank. After processing, the relative mtDNAcn was evaluated using real-time PCR of a portion of the COI and 18S genes. A decrease in the mtDNAcn in the specimens from the polluted site was observed. These results highlight how environmental contaminants can alter the mitochondrial genome and how Opsius heydeni can be considered a potential bioindicator species of environmental quality.

Impact of DNA repair polymorphisms on DNA instability biomarkers induced by lead (Pb) in workers exposed to the metal

Although the mechanisms of Pb-induced genotoxicity are well established, a wide individual's variation response is seen in biomarkers related to Pb toxicity, despite similar levels of metal exposure. This may be related to intrinsic variations, such as genetic polymorphisms; moreover, very little is known about the impact of genetic variations related to DNA repair system on DNA instability induced by Pb. In this context, the present study aimed to assess the impact of SNPs in enzymes related to DNA repair system on biomarkers related to acute toxicity and DNA damage induced by Pb exposure, in individuals occupationally exposed to the metal. A cross-sectional study was run with 154 adults (males, >18 years) from an automotive batteries' factory, in Brazil. Blood lead levels (BLL) were determined by ICP-MS; biomarkers related to acute toxicity and DNA instability were monitored by the buccal micronucleus cytome (BMNCyt) assay and genotyping of polymorphisms of MLH1 (rs1799977), OGG1 (rs1052133), PARP1 (rs1136410), XPA (rs1800975), XPC (rs2228000) and XRCC1 (rs25487) were performed by TaqMan assays. BLL ranged from 2.0 to 51 μg dL^-1 (mean 20 ± 12 μg dL^-1) and significant associations between BLL and BMNCyt biomarkers related to cellular proliferation and cytokinetic, cell death and DNA damage were observed. Furthermore, SNPs from the OGG1, XPA and XPC genes were able to modulate interactions in nuclear bud formation (NBUDs) and micronucleus (MNi) events. Taken together, our data provide further evidence that polymorphisms related to DNA repair pathways may modulate Pb-induced DNA damage; studies that investigate the association between injuries to genetic material and susceptibilities in the workplace can provide additional information on the etiology of diseases and the determination of environmentally responsive genes.

F, Barcelos GRM. Association between Polymorphisms of Hemochromatosis (HFE), Blood Lead (Pb) Levels, and DNA Oxidative Damage in Battery Workers

Occupational exposure to lead (Pb) continues to be a serious public health concern and may pose an elevated risk of genetic oxidative damage. In Brazil, car battery manufacturing and recycling factories represent a great source of Pb contamination, and there are no guidelines on how to properly protect workers from exposure or to dispose the process wastes. Previous studies have shown that Pb body burden is associated with genetic polymorphisms, which consequently may influence the toxicity of the metal. The aim of this study was to assess the impact of Pb exposure on DNA oxidative damage, as well as the modulation of hemochromatosis (HFE) polymorphisms on Pb body burden, and the toxicity of Pb, through the analysis of 8-hydroxy-2'-deoxyguanosine (8-OHdG), in subjects occupationally exposed to the metal. Male Pb-exposed workers (n = 236) from car battery manufacturing and recycling factories in Brazil participated in the study. Blood and plasma lead levels (BLL and PLL, respectively) were determined by ICP-MS and urinary 8-OHdG levels were measured by LC-MS/MS, and genotyping of HFE SNPs (rs1799945, C → G; and 1800562, G → A) was performed by TaqMan assays. Our data showed that carriers of at least one variant allele for HFE rs1799945 (CG + GG) tended to have higher PLL than those with the non-variant genotype (β = 0.34; p = 0.043); further, PLL was significantly correlated with the levels of urinary 8-OHdG (β = 0.19; p = 0.0060), while workers that carry the variant genotype for HFE rs1800562 (A-allele) showed a prominent increase in 8-OHdG, as a function of PLL (β = 0.78; p = 0.046). Taken together, our data suggest that HFE polymorphisms may modulate the Pb body burden and, consequently, the oxidative DNA damage induced by the metal.

"Blood lead level among battery factory workers in low and middle-income countries: Systematic review and meta-analysis"

Introduction

Lead is one of the most health-hazardous causes of acute and chronic poisoning at workplaces. A limited study was conducted on the blood lead concentration among battery factory workers in low and middle-income countries. Therefore, this study will improve workplace health and safety conditions of workers in this sector and serve as baseline data for further studies in this segment of the working setup.

Objective

This review aims to identify the pooled mean blood lead level among battery factory workers in low and middle-income countries.

Methods

The search methods considered the following electronic bibliographic databases: google scholar, PubMed, and other gray literature. A funnel plot and Begg test were used to see the publication bias. The heterogeneity of studies was checked using I-square statistics with a cut of point 75% and the Joanna Briggs Institute (JBI) quality assessment tool was applied to ensure the quality of the included articles. A random-effect model was applied to pool the blood lead level intoxication. The sub-group analysis and Meta-regression analysis were conducted by country and year of publication to control heterogeneity and to show variation. We included the articles published from 2000 to 2021 year in the English language.

Results

Through the search strategies, 135 articles were identified and 43 full-text articles were selected for evaluation, and finally, eighteen (18) articles fit the inclusion criteria. From the 18 studies included in the meta-analysis, the mean pooled blood lead level of workers was 37.996 μg/dl (95% CI: 30.680-45.312) which is higher than the threshold limit value set by American conference of governmental industrial hygienists (20 μg/dl). In subgroup analysis by year in the random effect model, the pooled mean of blood lead level from 2006 to 2011= 43.20 μg/dL (35.91-50.50), 2012-2015 = 37.78 μg/dl (25.23-50.29), and 2016-2020 = 36.53 μg/dl (19.44-53.62).

Conclusions

This review showed that the pooled mean blood lead level of workers exposed to lead battery factories was (37.996 μg/dl) which is above the threshold limit value (20 μg/dl). Therefore, attention should be given by employers, government, and researchers to improve the health of working populations exposed to lead exposure in low and middle-income countries through the provision of occupational health and safety services like periodical medical checkups, treatments, and provision of training and adequate and appropriate personal protective equipment.Systematic review registration: Identifier: CRD42022322827.

Association between lead source exposure and blood lead levels in some lead manufacturing countries: A systematic review and meta-analysis

Lead is one of the 10 most toxic chemicals of greatest concern for its effects on public health. Predominantly, in undeveloped countries, high blood lead levels (BLLs) persist in the population. To develop intervention strategies that may reduce lead exposure in populations, it is a priority to know the sources of lead pollution. The objective of this critical review and meta-analysis is to assess whether there is an association between different sources of lead exposure and the mean difference in blood lead levels in people exposed. To identify the major lead source exposure, a statistical analysis was performed on selection studies. This investigation reveals the limited information available on the sources of lead in Mexico and other lead producer countries, such as Croatia, Ecuador, Brazil, South Korea, India, Nigeria, Turkey, and China. Meta-analysis could be performed only in battery, smelting mining, and glazed ceramic workers. Battery manufacturing workers have the highest mean difference level of lead in their blood worldwide. Mexico has the second highest mean difference BLL in battery workers in the world. An interesting difference between the mean difference in BLL in mining workers from uncontrolled industry (-39.38) and controlled industry (-5.68) was found. This difference highlighted the success of applying strict control of lead sources and community education to reduce BLL and its potential harmful effects on human health and the environment. Children living near mining sites have the highest mean difference BLL (-11.1). This analysis may aid in assessing the source of lead exposure associated with a range of BLLs in people. Furthermore, this review highlights several social and cultural patterns associated with lead exposure and lead levels in control populations. These results could help to develop international lead regulations and appropriate public health guidelines to protect people around the world.

Ameliorative role of naringenin against lead-induced genetic damage and oxidative stress in cultured human lymphocytes

Lead (Pb) is a ubiquitous toxic heavy metal that is known to induce damage to major macromolecules (lipids, proteins, and nucleic acids) by enhancing the level of reactive oxygen species (ROS). Naringenin, a predominant flavonoid primarily found in citrus fruits has attained increasing attention due to its various pharmacological properties. Thus, the present investigation aimed to explore the ameliorative role of naringenin against Pb-induced toxicity in human peripheral blood lymphocytes (PBLs) under in vitro conditions. For this purpose, PBLs were exposed to Pb (350 µg/ml) alone as well in combination with naringenin (10 and 30 µg/ml). Sister chromatid exchange (SCE) and alkaline comet assay were used as genotoxic indices to evaluate the genotoxic and antigenotoxic activity of Pb and naringenin, respectively. Lipid peroxidation (LPO), glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD), and reduced glutathione (GSH) assays were used as oxidative damage markers. The results revealed that Pb induced a significant (p < 0.05) increase in genetic and oxidative damage as compared with the untreated sample whereas the treatment of cells along with naringenin (10 and 30 µg/ml) and Pb (350 µg/ml) caused a significant reduction in genetic damage and elevation in SOD, GPx, and CAT activities and GSH level, accompanied by a significant reduction in LPO level as compared with Pb alone treated sample. So, the present investigation revealed that naringenin might be used as a protective agent against Pb-induced toxicity due to its antigenotoxic and antioxidative properties.

Environmental exposures associated with elevated risk for autism spectrum disorder may augment the burden of deleterious de novo mutations among probands

Although the full aetiology of autism spectrum disorder (ASD) is unknown, familial and twin studies demonstrate high heritability of 60-90%, indicating a predominant role of genetics in the development of the disorder. The genetic architecture of ASD consists of a complex array of rare and common variants of all classes of genetic variation usually acting additively to augment individual risk. The relative contribution of heredity in ASD persists despite selective pressures against the classic autistic phenotype; a phenomenon thought to be explained, in part, by the incidence of spontaneous (or de novo) mutations. Notably, environmental exposures attributed as salient risk factors for ASD may play a causal role in the emergence of deleterious de novo variations, with several ASD-associated agents having significant mutagenic potential. To explore this hypothesis, this review article assesses published epidemiological data with evidence derived from assays of mutagenicity, both in vivo and in vitro, to determine the likely role such agents may play in augmenting the genetic liability in ASD. Broadly, these exposures were observed to elicit genomic alterations through one or a combination of: (1) direct interaction with genetic material; (2) impaired DNA repair; or (3) oxidative DNA damage. However, the direct contribution of these factors to the ASD phenotype cannot be determined without further analysis. The development of comprehensive prospective birth cohorts in combination with genome sequencing is essential to forming a causal, mechanistic account of de novo mutations in ASD that links exposure, genotypic alterations, and phenotypic consequences.

Derivation of a biological limit value (BLV) for inorganic lead based on lead-induced genotoxicity in workers using the benchmark dose approach (BMD)

BACKGROUND

Safe exposure levels for industrial chemicals are a prerequisite to the safety of workers in occupational settings.

METHODS

The application areas of the benchmark dose (BMD) approach have tremendously increased in recent years. Quantitative analyzes of dose-response relationships of genotoxic chemicals are among these application areas too. This study investigates the applicability of sister chromatid exchange (SCE) frequencies in lymphocytes of lead-exposed workers to derive a biological limit value (BLV) for inorganic lead. To this end, our previously published occupational lead exposure data were pooled and re-examined by using the BMD approach. Subsequently, we determined the point of departure (POD) value for lead-induced SCE frequencies in lymphocytes. Accordingly, the blood lead concentrations and SCE frequencies in lymphocytes of 26 control and 108 lead-exposed male voluntary workers employed in a battery manufacturing plant were subjected to BMD modeling to determine the BMD confidence interval (BMD-CI).

RESULTS

According to our data set, benchmark dose lower bound (BMDL) of 6.55 μg Pb/dL blood for the SCE frequencies in lymphocytes of lead-exposed workers has been obtained.

CONCLUSION

The blood lead concentration of 6.55 μg/dL might be proposed as the BLV for lead and its inorganic lead compounds based on our dataset.

Lead (Pb)-induced oxidative stress mediates sex-specific autistic-like behaviour in Drosophila melanogaster

Autism spectrum disorder (ASD) is a highly prevalent neurodevelopmental disorder characterised by three main behavioural symptoms: abnormal social interaction, verbal and non-verbal communication impairments, and repetitive and restricted activities or interests. Even though the exact aetiology of ASD remains unknown, studies have shown a link between genetics and environmental pollutants. Heavy metal lead (Pb), the environmental pollutant, is associated with ASD. Pb may also exhibit sex-specific ASD behaviour, as has been demonstrated in the global human populations. Drosophila melanogaster as a model has been used in the present study to understand the involvement of Pb-induced oxidative stress in developing ASD behaviour. The larval feeding technique has been employed to administer different Pb concentrations (0.2-0.8 mM) to Oregon-R (ORR), superoxide dismutase (Sod), or catalase (Cat) antioxidants overexpressed or knockdown flies. Adult Drosophila (5-day old) were used for Pb content, biochemical, and behavioural analysis.Pb accumulated in the Drosophila brain induces oxidative stress and exhibited a human autistic-like behaviour such as reduced climbing, increased grooming, increased social spacing, and decreased learning and memory in a sex-specific manner.Pb-induced autistic-like behaviour was intensified in Sod or Cat-knockdown flies, whereas Sod or Cat-overexpressed flies overcome that behavioural alterations. These results unequivocally proved that Pb-induced oxidative stress causes ASD behaviour of humans in Drosophila. Thus, Drosophila is used as a model organism to analyse ASD-like human behaviour and underlines the importance of using antioxidant therapy in alleviating ASD symptoms in children.

Early occupational exposure to lead on neutrophil-to-lymphocyte ratio and genotoxicity

BACKGROUND

Lead (Pb) is known to induce detrimental health effects in exposed populations, including hematotoxicity and genotoxicity. Complete blood count (CBC) is a cost-effective and easy way to determine toxicity, and variations in proportion of different types of leukocytes: neutrophil-to-lymphocyte ratio (NLR) and lymphocyte-to-monocyte ratio (LMR) are further evidence of hematotoxicity. However, few studies have been conducted to systematically evaluate effects of occupational Pb exposure on NLR and LMR, and their associations with genotoxicity.

OBJECTIVES

Our study was aimed to systematically assess the effects of current occupational Pb exposure on NLR and LMR, and their associations with genotoxicity.

METHODS

Our investigation was performed on 1176 workers from a newly built battery factory in North China. The workers had just entered their current job position in recent years and most of them had no previous history of occupational exposure to Pb. Blood lead levels (BLLs) and leukocytes indices were detected for all participants. Cytokinesis-blocked micronucleus assay (MN; n = 675) and alkaline comet assay (% tail DNA; n = 869) were used to assess genotoxicity. Multivariate linear and Poisson regression analyses were conducted to examine associations between leukocytes indices, genotoxic biomarkers and BLLs with adjustment for covariates. Spearman correlation and mediation analyses were used to investigate relationships between NLR and genotoxicity.

RESULTS

Among all the exposed workers, NLR increased with increasing BLLs. However, WBC and LMR did not change significantly. Significant and dose-dependent increases in both MN frequencies and % tail DNA were observed among groups with different exposure doses. Compared with the normal NLR group (1.48 ≤ NLR < 4.58), the high NLR group (NLR ≥ 4.58) had higher % tail DNA. In addition, there was a significant and positive association between NLR and % tail DNA among all the workers, and % tail DNA mediated 15% of the effect of Pb on increasing NLR.

CONCLUSION

Our large-scale population study shows that Pb exposure increased NLR and induced genotoxicity. There was an association between elevated NLR and DNA damage. In addition, the mediation effect of % tail DNA on the relationship between BLLs and NLR provided mechanistic evidence that certain mechanisms, e.g. inflammation, may be involved in elevation of NLR from Pb exposure. Therefore, NLR may be a convenient and sensitive biomarker for indication of Pb toxicity. Further studies are needed to validate the proposed mechanism and NLR as a biomarker.

Adaptive epigenetic response of glutathione (GSH)-related genes against lead (Pb)-induced toxicity, in individuals chronically exposed to the metal

It is well known that one of the most outstanding adverse effects related to lead (Pb) exposure is oxidative stress; moreover, recent findings suggest that disturbances of the redox status of cells are associated with epigenetic responses, and metabolism of glutathione (GSH) plays an important role in this process. This study aimed to assess Pb exposure on % methylation of GSH-related genes' promoter regions (%CH₃-CpG) and their influence on biomarkers of oxidative stress, in workers exposed to the metal. One hundred nine male workers participated in the study; ICP-MS determined blood lead levels (BLL); biochemical parameters related to redox status, named GSH, glutathione peroxidase (GPX) and glutathione-S-transferase (GST) were quantified by UV/Vis spectrophotometry. Determination of %CH₃-CpG of genes GCLC, GPX1, GSR, and GSTP1 were done by pyrosequencing. Inverse associations were seen between BLL and %CH₃-CpG-GCLC, and %CH₃-CpG-GSTP1. Moreover, metal exposure did not impact GSH, GPX, and GST; however, negative associations were observed between %CH₃-CpG-GPX1 and %CH₃-CpG-GSTP1, and the activities of GPX and GST, respectively. Taken together, our results give further evidence about adaptive epigenetic response to avoid oxidative damage induced by Pb exposure, allowing a better understanding of the molecular mechanisms related to the metal toxicity.

Development of a benchmark dose for lead-exposure based on its induction of micronuclei, telomere length changes and hematological toxicity

BACKGROUND

Excessive lead exposure is associated with adverse health effects. However, there is a lack of systematic investigation using large populations to ascertain acceptable exposure limits.

OBJECTIVES

Our study was aimed to identify human exposure-response relationships between lead exposure and health-related outcomes, and to determine a benchmark dose (BMD).

METHODS

A total of 1896 participants from a lead-acid battery plant were recruited. Blood lead levels (BLLs) were detected for all participants. Hematological parameters (n = 1896), micronuclei (MN) frequencies (n = 934), and relative telomere length (rTL) (n = 757) were also determined. Multivariate linear/Poisson regression analyses were performed to examine associations between BLLs and these health outcomes. Restricted cubic splines were used to identify dose-response relationships. Three BMD approaches were used to calculate BMD and its 95% lower confidence limit (BMDL).

RESULTS

Among all participants, BLLs show a right-skewed distribution (median, 185.40 μg/L; 25th - 75th percentile, 104.63-271.70 μg/L). There existed significant differences for red blood cell (RBC), hemoglobin (Hb), MN and rTL among different BLL dose groups. After adjusting for possible confounders, all indicators were significantly associated with BLLs. Restricted cubic splines show that there were linear dose-response relationships for RBC and Hb with BLLs, while non-linear for MN and rTL. Results from the three BMD approaches indicate that the dichotomous models were better than continuous models to calculate BMD and BMDL of BLLs. The conservative BMDL obtained from RBC data was 135 for total, 104 for male and 175 μg/L for female. The corresponding BMDL obtained from Hb data was 105 for total, 116 for male and 70 μg/L for female. As for MN data, the BMDL estimate was 66 for total, 69 for male and 64 μg/L for female. Finally, the BMDL from rTL data was 35 for total, 32 for male and 43 μg/L for female.

CONCLUSIONS

Our data show significant dose-response relationships between lead exposure and expressions of hematological toxicity and genotoxicity. The new BMDLs of 135 and 105 μg/L based on RBC and Hb, and even more strict level of 66 and 35 μg/L based on MN and rTL are lower than current exposure limits in China. Therefore, the four values can be considered as novel exposure limits. In addition, sex effect should be taken into account when setting occupational health standard. Considering that different biomarkers have different sensitivities, better understanding their relationships will certainly improve the current emphasis on precision health risk assessment.

Associations of blood lead levels with multiple genotoxic biomarkers among workers in China: A population-based study

Carcinogenic effects from low doses of lead (Pb) exposure to populations have been suspected but not concluded. Therefore, a large-scale cross-sectional study was conducted by us to investigate genotoxic effects from Pb exposure during 2016-2018 in North China. Blood lead levels (BLLs) and cumulative blood lead levels (CBLLs) were measured. Multiple relevant biomarkers were used to assess genotoxicity of Pb: mitochondrial DNA copy number (mtDNAcn, n = 871), Comet Tail Intensity (n = 872), γ-H2AX (n = 345), relative telomere length (rTL, n = 757), micronuclei (MN, n = 934) and phosphatidylinositol glycan class A mutation (PIG-A, n = 362). The BLL data show right-skewed distribution, with increase of the median (P25, P75) from 17.4 (8.9, 26.4) μg/dl in 2016 to 18.5 (10.5, 27.2) μg/dl in 2017, and to 20.8 (11.3, 31.0) μg/dl in 2018. Multivariate regression analyses show that mtDNAcn was non-linearly associated with BLLs or CBLLs, i.e. decreased at low levels but increased at the higher levels. Comet and Micronuclei data show positive dose-response relationships with BLLs as well as CBLLs. γ-H2AX data show an overall increased trend with BLLs while rTL data show a shortening trend. No associations were found for PIG-A mutation with Pb exposure. Our findings indicate that current low dose exposure to Pb can still cause health hazards to occupational populations, and the mechanism may be via the induction of DNA & chromosome damage rather than via the mutagenesis pathway.

Assessment of Bone Turnover Biomarkers in Lead-Battery Workers with Long-Term Exposure to Lead

BACKGROUND

The major portion of lead in the body resides in skeletal system. The bone turnover affects the release of lead into the circulation from bones. The bone turnover biomarkers (BTM) in lead-battery workers with long-term exposure to lead have not been explored yet.

OBJECTIVE

To evaluate the BTM (formation and resorption) in lead-battery workers with long-term exposure to lead in lead-battery manufacturing plant.

METHODS

176 male lead-exposed workers and 80 matched comparison group were studied. All participants were examined for blood lead levels (BLLs), bone formation biomarkers- serum osteocalcin (OC), alkaline phosphatase (ALP), bone-specific alkaline phosphatase (BALP)-and bone resorption biomarkers-serum pyridinoline (PYD), deoxypyridinoline (DPYD), tartarate-resistant acid phosphatase-5b (TRACP-5b), and urinary hydroxyproline (UHYP).

RESULTS

We found a significantly higher bone formation biomarkers such as BALP (p=0.007) and bone resorption biomarkers, eg, PYD (p=0.048), TRCAP-5b (p=0.001), and UHYP (p=0.001) in lead-exposed workers. A significant (p=0.041) negative correlation (ρ ‑0.128) was noted between BLLs and OC. A significant positive correlation was noted between BLLs and TRACP-5b (ρ 0.176, p=0.005) and UHYP (ρ 0.258, p=0.004). Serum OC (p=0.040) and UHYP (p=0.015) levels changed significantly with BLL level. Bone resorption biomarkers levels- PYD, TRACP-5b, and BALP-were higher among those with higher BLLs levels. The duration of exposure was significantly associated with BALP (p=0.037), DPYD (p=0.016), TRACP-5b (p=0.001), and UHYP (p=0.002) levels.

CONCLUSION

Long-term lead exposure affects the bone turnover.

Leukocyte apoptosis, TNF-α concentration and oxidative damage in lead-exposed workers

Lead intoxication can generate pro-inflammatory conditions that have been proposed to be associated with cell injuries and oxidative stress. The pro-inflammatory state can participate in the pathophysiology of this toxicity to generate immune response dysfunctions, which could condition the presence of clinical manifestations and susceptibility to infections already described in lead-exposed patients. In the present work, we study workers of a battery recycler factory (n = 24) who are chronically exposed to lead and compared them with non-lead exposed workers (n = 17). Lead-exposed workers had high lead concentrations in blood (med 69.8 vs. 1.7 μg/dL), low δ-ALAD activity (med 149 vs. 1100 nmol PBG/h/mL), high lipid peroxidation (med 0.86 vs. 0.69 nmol/mL) and high erythrocytes apoptosis (med 0.81 vs. 0.50% PS externalization) in relation to non-lead exposed workers. Also, lead-exposed workers had a high incidence of signs and symptoms related to lead intoxication and a higher frequency of infections. The higher leukocyte apoptosis (med 18.3 vs. 8.2% PS externalization) and lower basal TNF-α concentration (med 0.38 vs. 0.94 pg/mL) in lead-exposed workers imply an immune response dysfunction; however, there was no difference in the TNF-α concentration when leukocytes were stimulated with lipopolysaccharide in whole blood (med 44 vs. 70 pg/mL), suggesting that lead-exposed workers might develop adaptation mechanisms to reduce basal TNF-α release through downregulation processes proposed for this cytokine.

Evaluation of possible molecular toxicity induced by occupational exposure to lead and concomitant effect of smoking

One of the most toxic heavy metals in the environment nowadays is lead (Pb). Even though exposure to lead has been reduced in some developed countries, individuals working in certain occupations are still exposed to lead at dangerous levels. Occupational exposure is of great concern and is also the main cause of lead poisoning. Although experts in various fields have been investigating the toxic effects of lead and its compounds for many years now, the association between chronic lead exposure and geno-toxicity is still an interesting point of research. The study aims to evaluate the possible DNA damage and the oxidative stress status induced by occupational exposure to lead and the role of concomitant smoking. The study was conducted on 60 subjects divided into two groups: an exposed group (40 male workers exposed to lead in their workplaces). This group was further divided into two subgroups; 20 workers were cigarette smokers and the other 20 workers were non-smokers. The other control group consists of 20 healthy males, not exposed to lead and matched by age to the exposed group (10 were smokers and the rest were non-smokers). Venous blood samples were collected from each participant for the determination of the following: blood lead level (BLL), plasma malondialdehyde (MDA) levels, and DNA damage using agarose gel electrophoresis. The exposed workers had significantly higher levels of lead and MDA, as well as a high frequency of DNA fragmentation. Smoking workers showed a greater frequency of DNA fragmentation than non-smokers. A significant relation was revealed between the BLL, as well as the MDA level, and the degree of DNA fragmentation among the lead-exposed workers. The study has shown additional evidence proving the association between Pb exposure and oxidative stress. The results further reinforced the role of cigarette smoking in augmenting such oxidative damage in the Pb-exposed population. However, further studies are recommended to evaluate the effect of cigarette smoking on Pb-exposed workers.

Participation of phospholipase-A2 and sphingomyelinase in the molecular pathways to eryptosis induced by oxidative stress in lead-exposed workers

The increment of eryptosis in lead-exposed workers has been associated with oxidative stress, having as the main mediator [Ca²⁺]_i. However, other molecules could participate as signals, such as PLA₂ and SMase, which have been proposed to increase PGE₂ and ceramides, both involved in the increment of PS externalization due to osmotic stress. To study the role of these enzymes in lead intoxication, we studied 30 lead exposed workers and 27 non-lead exposed individuals. We found, compared to non-exposed subjects, lead intoxication characterized by high blood lead concentration (median = 39.1 μg/dL), and low δ-ALAD activity (median = 348 nmol of porphobilinogen/h/mL); oxidative stress with high lipid peroxidation (median = 1.31 nmol of malondialdehyde/mL) and low TAC (median = 370 mM Trolox equivalents); a higher enzymatic activity of PLA₂ (median = 518 AFU/mg) and SMase (median = 706 AFU/mg) and higher eryptosis (median = 0.92% PS externalization). Correlation and conditional probability analyses permit to associate oxidative stress and eryptosis with high PLA₂ activity. However, high SMase activity was only associated with PLA₂ activity. The role of these enzymes in the signal path to eryptosis induced by oxidative stress in lead-exposed workers is discussed.

Genotoxic and Cytotoxic Effects in Exfoliated Buccal and Nasal Cells of Chromium and Cobalt Exposed Electroplaters

Results of a number of studies indicate that electroplaters have increased cancer risks as a consequence of exposure to genotoxic metals such as chromium (VI) and nickel. These effects may be due to induction of damage of the genetic material which plays a key role in the etiology of cancer, and it was found that workers in galvanization factories exhibited increased levels of DNA damage. The aim of the present study was to investigate genetic stability in workers of a bright plating factory who are exposed to chromium (Cr) and cobalt (Co). Exfoliated cells were collected from the buccal and nasal mucosa of workers (n = 42) and matched controls (n = 43) and analyzed for induction of micronuclei (MN) which are formed as a consequence of chromosomal aberrations. In addition, other nuclear anomalies namely nuclear buds (Nbuds) which are formed as a consequence of gene amplification and markers indicating different stages of cell death (condensed chromatin, karyorrhexis, karyolysis, and pyknosis) were also assessed. No evidence was noted for induction of MN, but significantly increased rates of Nbuds in cells from both, buccal and nasal mucosa, were found. Parameters which are indicative for cytotoxic effects were more pronounced in nasal cells and rose with duration of employment period. Overall, our findings indicated that no apparent chromosomal damage occurred in bright electroplaters. However, data demonstrated that acute cytotoxic effects may lead to inflammations and/or lesions in epithelia of the respiratory tract of the workers.

Alleviation of lead-induced oxidative stress and immune damage by selenium in chicken bursa of Fabricius

We investigated lead (Pb)-induced oxidative stress and immune damage in the chicken bursa of Fabricius (BF) and the ameliorative effect of selenium (Se). Seven-day-old male chickens were randomly divided into four groups and were provided standard diet and drinking water, Na₂SeO₃ added to the standard diet and drinking water, standard diet and (CH₃COO)₂Pb added to drinking water, and Na₂SeO₃ added to the standard diet and (CH₃COO)₂Pb added to drinking water for 30, 60, and 90 days. The presence of Pb inhibited total antioxidant capacity (T-AOC), glutathione peroxidase (GPx), glutathione S-transferase (GST), superoxide dismutase (SOD), and catalase (CAT) activities; decreased glutathione (GSH) content; increased malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents; inhibited interleukin (IL)-2 and interferon-γ (IFN-γ) messenger RNA (mRNA) expression; and increased IL-4, IL-6, IL-10, IL-12β, and IL-17 mRNA expression. The presence of Se relieved all of the above Pb-induced changes. There were close correlations among GSH, CAT, T-AOC, SOD, GPx, MDA, and H₂O₂ and among IL-2, IL-4, IL-6, IL-12β, IL-17, and IFN-γ. Our data showed that Pb caused oxidative stress and immune damage in the chicken BF. Se alleviated Pb-induced oxidative stress and immune damage in the chicken BF.

Lead (Pb) exposure induces disturbances in epigenetic status in workers exposed to this metal

Previous studies showed that lead (Pb) exposure may modulate gene expression by changes in the epigenetic status. However, little is known about the impact of Pb exposure and alterations on DNA methylation patterns in humans exposed to this metal. The aim of this study was to assess the consequences of exposure to Pb on DNA global methylation, in order to gain a better understanding of the interactions between Pb exposure and epigenetic effects. The study included 100 male workers employed in automotive battery factories from Paraná State, Brazil. Concentrations of Pb in blood (B-Pb) and plasma (P-Pb) were determined by ICP-MS, the percentage (%) of global DNA methylation was determined by quantification of 5-methylcytosine using indirect ELISA, and sociodemographic data collected by questionnaire by trained interviewers. The mean age was 37 ± 10 (18-67 years); 18% of participants were smokers, while 32% reported consumption of alcoholic beverages. The B-Pb and P-Pb levels were 20 ± 11 and 0.56 ± 0.64 µg/dl, respectively; % global DNA methylation was 2.8 ± 1.1% (ranging from 1.1 to 6.5%). B-Pb and P-Pb concentrations were significantly correlated. Furthermore, a marked association was noted between Pb biomarkers and DNA global methylation. Taken together, our data demonstrated that Pb exposure induced alterations on DNA global methylation in workers who were exposed to the metal and consequently may result in disturbances in the regulation of gene expression, leading to potentially several health adverse effect outcomes.

Effect of Lead Exposure on the Status of Reticulocyte Count Indices among Workers from Lead Battery Manufacturing Plant

Earlier studies conducted on lead-exposed workers have determined the reticulocyte count (RC) (%), but the parameters of Absolute Reticulocyte Count (ARC), Reticulocyte Index (RI), and Reticulocyte Production Index (RPI) were not reported. This study assessed the effect of lead (Pb) exposure on the status of reticulocyte count indices in workers occupied in lead battery plants. The present cross-sectional study was carried out on 391 male lead battery workers. The blood lead levels (BLL) were determined by using an Atomic Absorption Spectrophotometer. The RC (%) was estimated by using the supravital staining method. The parameters, such as ARC, RI, and RPI, were calculated by using the RC (%) with the red cell indices (RBC count and hematocrit). The levels of RBC count and hematocrit were determined by using an ABX Micros ES-60 hematology analyzer. The levels of reticulocyte count indices - RC (%), ARC, RI, and RPI significantly increased with elevated BLL. The association between BLL and reticulocyte count indices was positive and significant. The results of linear multiple regression analysis showed that the reticulocyte count (β = 0.212, P < 0.001), ARC (β = 0.217, P < 0.001), RI (β = 0.194, P < 0.001), and RPI (β = 0.208, P < 0.001) were positively associated with BLL. The variable, smoking habits, showed a significant positive association with reticulocyte count indices: RC (%) (β = 0.188, P < 0.001), ARC (β = 0.174, P < 0.001), RI (β = 0.200, P < 0.001), and RPI (β = 0.151, P < 0.005). The study results revealed that lead exposure may cause reticulocytosis with an increase of reticulocyte count indices.

Oxidative DNA damage and oxidative stress in lead-exposed workers

There are many discrepancies among the results of studies on the genotoxicity of lead. The aim of the study was to explore lead-induced DNA damage, including oxidative damage, in relation to oxidative stress intensity parameters and the antioxidant defense system in human leukocytes. The study population consisted of 100 male workers exposed to lead. According to the blood lead (PbB) levels, they were divided into the following three subgroups: a group with PbB of 20-35 μg/dL (low exposure to lead (LE) group), a group with a PbB of 35-50 µg/dL (medium exposure to lead (ME) group), and a group with a PbB of >50 μg/dL (high exposure to lead (HE) group). The control group consisted of 42 healthy males environmentally exposed to lead (PbB < 10 μg/dL). A comet assay was used to measure the DNA damage in leukocytes. We measured the activity of superoxide dismutase (SOD), catalase, glutathione reductase (GR), glucose-6-phosphate dehydrogenase (G6PD), and glutathione-S-transferase (GST) as well as the concentration of malondialdehyde (MDA), and the value of the total antioxidant capacity. The level of PbB was significantly higher in the examined subgroups than in the control group. The percentage of DNA in the tail was significantly higher in the LE, ME, and HE subgroups than in the control group by 10% ( p = 0.001), 15% ( p < 0.001), and 20% ( p < 0.001), respectively. The activity of GR was significantly lower in the LE and ME subgroups than in the control group by 25% ( p = 0.007) and 17% ( p = 0.028), respectively. The activity of G6PD was significantly lower in the ME subgroup by 25% ( p = 0.022), whereas the activity of GST was significantly higher in the HE subgroup by 101% ( p = 0.001) than in the control group. Similarly, the activity of SOD was significantly higher in the LE and ME subgroups by 48% ( p = 0.026) and 34% ( p = 0.002), respectively. The concentration of MDA was significantly higher in the LE, ME, and HE subgroups than in the control group by 43% ( p = 0.016), 57% ( p < 0.001), and 108% ( p < 0.001), respectively. Occupational lead exposure induces DNA damage, including oxidative damage, in human leukocytes. The increase in DNA damage was accompanied by an elevated intensity of oxidative stress.

Results of micronucleus assays with individuals who are occupationally and environmentally exposed to mercury, lead and cadmium

Millions of humans are exposed occupationally and environmentally to lead, mercury and cadmium compounds. Mercury compounds are less abundant but some of them belong to the most toxic chemicals which are known. We evaluated the literature to find out if these metals act in humans as genotoxic carcinogens and if their health effects can be predicted by use of micronucleus (MN) assays with lymphocytes and/or with other genotoxicity tests. Numerous studies showed that lead and mercury induce cancer in humans and also in animals, in vitro experiments with cultured cells indicate that they cause DNA damage via different molecular mechanisms including release of reactive oxygen species and interactions with DNA repair processes. Also in most human studies, positive results were obtained in MN tests with lymphocytes (all 15 occupational studies with lead yielded positive results, with mercury 6 out of 7 investigations were positive). For cadmium, there is clear evidence that it causes cancer in humans; however, induction of chromosomal damage was only seen in high dose experiments with mammalian cells while results of animal and human studies yielded conflicting results (only in 2 of 5MN trials with humans positive findings were reported). Possibly, non-genotoxic mechanisms such as inhibition of apoptosis and interaction with signaling pathways account for the carcinogenic properties of cadmium species. The findings of MN studies with lead and mercury are in excellent agreement with results which were obtained with other endpoints (e.g. chromosomal aberrations and comet formations) and it is evident that this approach can be used for occupational and environmental monitoring of exposed individuals. Important future tasks will be the realization of larger studies with a uniform standardized protocol, the additional evaluation of anomalies other than MN (nuclear buds and bridges) and the combination of such trials with investigations which allow to define the molecular mechanisms relevant for exposed humans.