Biomonitoring findings for occupational lead exposure in battery and ceramic tile workers using biochemical markers, alkaline comet assay, and micronucleus test coupled with fluorescence in situ hybridisation

Manufacture of lead-containing products has long been associated with various health risks. To get an insight into the related genotoxic risks, we conducted a biomonitoring study in 50 exposed workers and 48 matched controls using a battery of endpoints that sensitively detect the extent of genome instability in peripheral blood lymphocytes. The levels of primary DNA damage were estimated with the alkaline comet assay, while cytogenetic abnormalities were determined with the cytokinesis-block micronucleus (CBMN) cytome assay. Additionally, CBMN slides of 20 exposed and 16 control participants were subjected to fluorescence in situ hybridisation (FISH), coupled with pancentromeric probes to establish the incidence of centromere-positive micronuclei, nuclear buds, and nucleoplasmic bridges. Blood lead levels (B-Pb) were measured with atomic absorption spectrometry. To further characterise cumulative effects of occupational exposure, we measured erythrocyte protoporphyrin (EP) concentrations and delta-aminolevulinic acid dehydratase (ALAD) activity in blood. We also assessed the influence of serum folate (S-folate) and vitamin B12 (S-B12) on genome stability. Compared to controls, occupationally exposed workers demonstrated significantly higher B-Pb (298.36±162.07 vs 41.58±23.02), MN frequency (18.71±11.06 vs 8.98±7.50), centromere positive MN (C+ MN) (8.15±1.8 vs 3.69±0.47), and centromere negative MN (C- MN) (14.55±1.80 vs 4.56±0.89). Exposed women had significantly higher comet tail intensity (TI) and length (TL) than control women. Furthermore, workers showed a positive correlation between age and nuclear buds and MN, between MN and years of exposure, and between S-B12 levels and TI and ALAD activity, while a negative correlation was found between TI and B-Pb. These findings suggest that occupational settings in the manufacture of lead-containing products pose significant genotoxic risks, which calls for developing more effective work safety programmes, including periodical monitoring of B-Pb and genetic endpoints.

Influence of VDR and HFE polymorphisms on blood lead levels of occupationally exposed workers

Lead is a ubiquitous heavy metal toxin of significant public health concern. Every individual varies in their response to lead’s toxic effects due to underlying genetic variations in lead metabolizing enzymes or proteins distributed in the population. Earlier studies, including our lab, have attributed the influence of ALAD (δ-Aminolevulinate dehydratase) polymorphism on blood lead retention and ALAD activity. The present study aimed to investigate the influence of VDR (Vitamin D receptor) and HFE (Hemochromatosis) polymorphisms in modulating blood lead levels (BLLs) of occupationally exposed workers. 164 lead-exposed subjects involved in lead alloy manufacturing and battery breaking and recycling processes and 160 unexposed controls with BLLs below 10 µg/dL recruited in the study. Blood lead levels, along with a battery of biochemical assays and genotyping, were performed. Regression analysis revealed a negative influence of BLLs on ALAD activity ( p < 0.0001) and a positive influence on smokeless tobacco use ( p < 0.001) in lead-exposed subjects. A predicted haplotype of the three VDR polymorphisms computed from genotyping data revealed that T-A-A haplotype increased the BLLs by 0.93 units ( p ≤ 0.05) and C-C-A haplotype decreased the BLLs by 7.25 units ( p ≤ 0.05). Further analysis revealed that the wild-type CC genotype of HFE H63D presented a higher median BLL, indicating that variant C allele may have a role in increasing the concentration of lead. Hence, the polymorphism of genes associated with lead metabolism might aid in predicting genetic predisposition to lead and its associated effects.

Use of Generalized Additive Model to Detect the Threshold of δ-Aminolevulinic Acid Dehydratase Activity Reduced by Lead Exposure

Background: Lead inhibits the enzymes in heme biosynthesis, mainly reducing δ-aminolevulinic acid dehydratase (ALAD) activity, which could be an available biomarker. The aim of this study was to detect the threshold of δ-aminolevulinic acid dehydratase activity reduced by lead exposure. Methods: We collected data on 121 lead workers and 117 non-exposed workers when annual health examinations were performed. ALAD activity was determined by the standardized method of the European Community. ALAD G177C (rs1800435) genotyping was conducted using the polymerase chain reaction and restricted fragment length polymorphism (PCR-RFLP) method. In order to find a threshold effect, we used generalized additive models (GAMs) and scatter plots with smoothing curves, in addition to multiple regression methods. Results: There were 229 ALAD1-1 homozygotes and 9 ALAD1-2 heterozygotes identified, and no ALAD2-2 homozygotes. Lead workers had significantly lower ALAD activity than non-exposed workers (41.6 ± 22.1 vs. 63.3 ± 14.0 U/L, p < 0.001). The results of multiple regressions showed that the blood lead level (BLL) was an important factor inversely associated with ALAD activity. The possible threshold of BLL affecting ALAD activity was around 5 μg/dL. Conclusions: ALAD activity was inhibited by blood lead at a possible threshold of 5 μg/dL, which suggests that ALAD activity could be used as an indicator for lead exposure regulation.

Towards Initial Indications for a Thiol-Based Redox Control of Arabidopsis 5-Aminolevulinic Acid Dehydratase

Thiol-based redox control is one of the important posttranslational mechanisms of the tetrapyrrole biosynthesis pathway. Many enzymes of the pathway have been shown to interact with thioredoxin (TRX) and Nicotinamide adenine dinucleotide phosphate (NADPH)-dependent thioredoxin reductase C (NTRC). We examined the redox-dependency of 5-aminolevulinic acid dehydratase (ALAD), which catalyzed the conjugation of two 5-aminolevulinic acid (ALA) molecules to porphobilinogen. ALAD interacted with TRX f, TRX m and NTRC in chloroplasts. Consequently, less ALAD protein accumulated in the trx f1, ntrc and trx f1/ntrc mutants compared to wild-type control resulting in decreased ALAD activity. In a polyacrylamide gel under non-reducing conditions, ALAD monomers turned out to be present in reduced and two oxidized forms. The reduced and oxidized forms of ALAD differed in their catalytic activity. The addition of TRX stimulated ALAD activity. From our results it was concluded that (i) deficiency of the reducing power mainly affected the in planta stability of ALAD; and (ii) the reduced form of ALAD displayed increased enzymatic activity.

The threshold of the delta-aminolevulinic acid dehydratase (ALAD) activities reduced by lead (Pb) exposure could be 10 μg/dL without modification of ALAD G177C genotypes in Chinese Han Taiwanese.

Background: Lead inhibits the enzymes in the heme biosynthesis, mainly the δ-aminolevulinic acid dehydratase (ALAD) activities. The aims of this study was to establish ALAD activity assay in Taiwan and analyzed the effects of lead exposure on hematological system and the ALAD activity with the modification of the ALAD genotypes. Methods: Among 121 lead workers and 117 non-exposed workers, the data were from health examination. ALAD activity was determined by the standardized method of the European Community. ALAD genotyping was using a method of PCR-RFLP. For finding a threshold effect, we used generalized additive models (GAM) and scatter plots with smoothing curve, in addition to multiple regression methods. Results: There were 229 ALAD1-1 homozygotes, 9 ALAD1-2 heterozygotes were identified, and none of ALAD2-2 homozygote. Lead workers had significantly lower ALAD activity than non-exposed group (41.6 ± 22.1 vs. 63.3 ± 14.0 U/L, p-value &lt; 0.001). The results of multiple regressions showed the blood lead level (BLL) was profound factor associated with ALAD activity inversely. The possible threshold of BLL affecting ALAD activity was around 10 μg/dL. Conclusions: ALAD activity was inhibited by blood lead, which could be a threshold of 10 ug/dL, which ALAD activity may be adopted as a biomarker of health examination for lead workers.

Inhibition of δ-aminolevulinic acid dehydratase activity by cadmium in excised etiolated maize leaf segments during greening

Supply of 0.1&ndash;0.5 mmol CdCl₂ inhibited &delta;-aminolevulinic acid dehydratase (EC 4.2.1.24, ALAD) activity and total chlorophylls in excised etiolated segments of maize leaves during greening. Due to cadmium supply &delta;-aminolevulinic acid (ALA) content was reduced significantly at 0.5 mmol Cd only. Also the Cd treatment decreased the protein content and accumulated significantly the Cd in the tissue. Significant correlation between Cd accumulation in the leaves and various parameters measured is observed, with the R-squared values being 0.727 with ALAD activity, 0.885 with ALA content, 0.902 with total chlorophylls and 1.00 with proteins. The % inhibition of ALAD activity by Cd was decreased in the presence of nitrogenous compounds, glutamine and NH₄NO₃ and the observed inhibition was 25% and 16%, respectively. More substantial reduction in % inhibition of enzyme activity by Cd was observed during treatment with glutathione, a ubiquitous thiol and levulinic acid, a competitive inhibitor of ALAD, with the inhibition being only 2% and 4%, respectively. Supply of some essential metal ions, such as Mg, Zn, and Mn, also reduced the % inhibition of enzyme activity by Cd. Inclusion of varying concentrations of ALA during assay also affected the % inhibition of enzyme activity by Cd showing an increased inhibition from 17% to 53% with increasing ALA concentration. It is suggested that Cd inhibits ALAD activity by affecting the ALA binding to the enzyme and/or disrupting thiol interaction.