Possible influence of delta-aminolevulinic acid dehydratase polymorphism and susceptibility to renal toxicity of lead: a study of a Vietnamese population

Genetic susceptibility to low-level lead exposure in men: Insights from ALAD polymorphisms

The genetic susceptibility to low-level lead (Pb) exposure in general populations has been poorly investigated and is limited to the single nucleotide polymorphism (SNP) rs1800435 in the delta-aminolevulinic acid dehydratase gene (ALAD). This study explored associations between ten selected ALAD SNPs with Pb concentrations in blood (BPb) and urine (UPb) among 281 men aged 18-49 years from Slovenia, including 20 individuals residing in a Pb-contaminated area. The geometric mean (range) of BPb and UPb were 19.6 (3.86-84.7) μg/L and 0.69 (0.09-3.82) μg/L SG, respectively. The possible genetic influence was assessed by examining SNP haplotypes, individual SNPs, and the combination of two SNPs using multiple linear regression analyses. While no significant associations were found for haplotypes, the presence of variant alleles of rs1800435 and rs1805312 resulted in an 11% and 13% decrease in BPb, respectively, while the presence of variant allele of rs1139488 (homozygous only) exhibited significant 20% increase in BPb, respectively. Additionally, variant allele of rs1800435 resulted in lower UPb. Individual SNPs in the model explained only around 1 additional percentage point of BPb variability. In contrast, combination analyses identified six combinations of two SNPs, which significantly explained 3-22 additional percentage points of BPb variability, with the highest explanatory power observed for the rs1800435-rs1139488 and rs1139488-rs1805313 combinations. Moreover, excluding participants from the Pb-contaminated area indicated that exposure level influenced SNPs-Pb associations. Our results confirm the importance of the ALAD gene in Pb kinetics even at low exposure levels. Additionally, we demonstrated that identifying individuals with specific combinations of ALAD SNPs explained a larger part of Pb variability, suggesting that these combinations, pending confirmation in other populations and further evaluation through mechanistic studies, may serve as superior susceptibility biomarker in Pb exposure compared to individual SNPs.

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.

Ecogenetics of lead toxicity and its influence on risk assessment

Lead (Pb) toxicity is a public health problem affecting millions worldwide. Advances in 'omic' technology have paved the way to toxico-genomics which is currently revolutionizing the understanding of interindividual variations in susceptibility to Pb toxicity and its functional consequences to exposure. Our objective was to identify, comprehensively analyze, and curate all the potential genetic and epigenetic biomarkers studied to date in relation to Pb toxicity and its association with diseases. We screened a volume of research articles that focused on Pb toxicity and its association with genetic and epigenetic signatures in the perspective of occupational and environmental Pb exposure. Due to wide variations in population size, ethnicity, age-groups, and source of exposure in different studies, researchers continue to be skeptical on the topic of the influence of genetic variations in Pb toxicity. However, surface knowledge of the underlying genetic factors will aid in elucidating the mechanism of action of Pb. Moreover, in recent years, the application of epigenetics in Pb toxicity has become a promising area in toxicology to understand the influence of epigenetic mechanisms such as DNA methylation, chromatin remodeling, and small RNAs for the regulation of genes in response to Pb exposure during early life. Growing evidences of ecogenetic understanding (both genetic and epigenetic processes) in a dose-dependent manner may help uncover the mechanism of action of Pb and in the identification of susceptible groups. Such studies will further help in refining uncertainty factors and in addressing risk assessment of Pb poisoning.

Lead exposure: a summary of global studies and the need for new studies from Saudi Arabia

Lead poisoning (plumbism) can cause irreversible genetic and reproductive toxicity, hematological effects, neurological damage, and cardiovascular effects. Despite many efforts to minimize lead poisoning, it continues to be a major health concern in many developing and developed countries. Despite efforts to control lead exposure and toxicity, serious cases of lead poisoning increasingly occur as a result of higher vehicular traffic and industrialization. The biomarkers for identification of genetic susceptibility to a particular disease are useful to identify individuals who are at risk for lead poisoning. Although many such studies have been taken up elsewhere, very few studies were performed in Saudi Arabia to assess susceptibility to lead poisoning. This indicates an urgent need for testing of susceptible individuals. The present paper was planned to understand the genetic susceptibility to lead toxicity in the various population studies conducted worldwide and also to correlate it with the current scenario in Saudi Arabia. Such studies are necessary for appropriate precautions in terms of diet and avoiding exposure to be used in order to prevent adverse health effects.

δ-Aminolevulinic acid dehydratase genotype predicts toxic effects of lead on workers' peripheral nervous system

There is a wide variation in sensitivity to lead (Pb) exposure, which may be due to genetic susceptibility towards Pb. We investigated whether a polymorphism (rs1800435) in the δ-aminolevulinic acid dehydratase (ALAD) gene affected the toxicokinetics and toxicodynamics of Pb. Among 461 Chinese Pb-exposed storage battery and 175 unexposed workers, allele frequencies for the ALAD1 and ALAD2 alleles were 0.968 and 0.032, respectively. The Pb-exposed workers had a higher fraction of the ALAD1-2/2-2 genotype than unexposed workers (7.8% vs. 2.3%, p=0.01). The Pb levels in blood (B-Pb) and urine (U-Pb) were higher in Pb-exposed workers carrying the ALAD2 allele compared to homozygotes for ALAD1 (median B-Pb: 606 vs. 499 μg/L; U-Pb: 233 vs. 164 μg/g creatinine), while there was no statistically significant difference in the unexposed controls (median: 24 vs. 37 μg/L, and 3.9 vs. 6.4μg/g creatinine, respectively). High B-Pb and U-Pb were associated with statistically significantly lower sensory and motor conduction velocities in the median, ulnar and peroneal nerves. At the same B-Pb and U-Pb, ALAD1 homozygotes had lower conduction velocities than the ALAD2 carriers. There were similar trends for toxic effects on haem synthesis (zinc protoporphyrin and haemoglobin in blood) and renal function (albumin and N-acetyl-d-β-acetylglucosaminidase in urine), but without statistical significance. There was no difference in Pb toxicokinetics and toxicodynamics associated with VDR BsmI polymorphism. Our results show that the ALAD genotype modifies the relationship between Pb and its toxic effects on the peripheral nervous system. This must be considered in the assessment of risks at Pb exposure.

Association between delta-aminolevulinic acid dehydratase (ALAD) polymorphism and blood lead levels: a meta-regression analysis

A meta-regression analysis was undertaken to evaluate the association between delta-aminolevulinic acid dehydratase (ALAD) genotypes and blood lead levels obtained from data published in various journals. In total, 15 studies were included in the final analysis. Both fixed effects and random effects models were used to undertake the pooled analysis. Using a fixed effects model, pooled estimates of mean differences of various ALAD genotypes was significant at 0.61 microg/dl. Using a random effects model, the pooled estimate was also significant at 1.51 microg/dl. Data indicated that certain ALAD genotypes may affect the susceptibility of humans to lead.