Association between aminolevulinate dehydrase genotypes and blood lead levels in children from a lead-contaminated area in Antofagasta, Chile

Effects of ALAD genotype on the relationship between lead exposure and anthropometry in a Cohort of Mexican children

OBJECTIVES

Lead exposure is associated with children's growth, but this relationship may depend on the presence of susceptibility factors, including genetic variation. Blood lead levels (BLL) differ by ALAD (aminolevulinic acid dehydratase) genotype. We investigated the association between BLL and growth in Mexican first-graders with different ALAD genotypes.

METHODS

Children between the ages of 6-8 years (n = 602) attending first grade in schools within the vicinity of a metal foundry in Torreón, Mexico were enrolled into a randomized controlled trial (RCT) testing the efficacy of iron and/or zinc supplementation on blood lead levels (BLL) and cognition. BLL and anthropometry were assessed at baseline (height, height-for-age z-score (HAZ), knee height, head circumference), after 6 (head circumference) and 12 months (height, HAZ, knee height). Children with ALAD_1-1 and ALAD_1-2/2-2 were compared. The study sample included 538 and 470 participants who had complete data at baseline and follow-up, respectively. Separate multivariable linear regression models adjusted for covariates were used to test the association between BLL at baseline and each anthropometric measure. Covariates included age, sex, hemoglobin, crowding, and maternal education. BLL x ALAD genotype interaction term was tested.

RESULTS

Median BLL (10.1 μg/dL) did not differ by ALAD genotype. After covariate adjustment, baseline BLL was inversely associated with baseline height, HAZ, and knee height. The association (β [95% CI]) between BLL and baseline height (-0.38[-0.68, -0.09]), HAZ (-0.07[-0.12, -0.02]) and knee height (-0.14[-0.25, -0.02]), was somewhat stronger in children with ALAD_1-2/2-2 than ALAD_1-1 (-0.09[-0.16, -0.02], -0.02[-0.03, -0.004] and -0.04[-0.06, -0.01], respectively). No associations between BLL and growth at 6 or 12 months were detected irrespective of ALAD genotype.

CONCLUSIONS

BLL was adversely associated with anthropometric measures among Mexican children. ALAD genotype may be a susceptibility factor for the effects of lead on child growth.

Investigation and Evaluation of Children's Blood Lead Levels around a Lead Battery Factory and Influencing Factors

Lead pollution incidents have occurred frequently in mainland China, which has caused many lead poisoning incidents. This paper took a battery recycling factory as the subject, and focused on measuring the blood lead levels of environmental samples and all the children living around the factory, and analyzed the relationship between them. We collected blood samples from the surrounding residential area, as well as soil, water, vegetables. The atomic absorption method was applied to measure the lead content in these samples. The basic information of the generation procedure, operation type, habit and personal protect equipment was collected by an occupational hygiene investigation. Blood lead levels in 43.12% of the subjects exceeded 100 μg/L. The 50th and the 95th percentiles were 89 μg/L and 232 μg/L for blood lead levels in children, respectively, and the geometric mean was 94 μg/L. Children were stratified into groups by age, gender, parents' occupation, distance and direction from the recycling plant. The difference of blood lead levels between groups was significant (p < 0.05). Four risk factors for elevated blood lead levels were found by logistic regression analysis, including younger age, male, shorter distance from the recycling plant, and parents with at least one working in the recycling plant. The rate of excess lead concentration in water was 6.25%, 6.06% in soil and 44.44% in leaf vegetables, which were all higher than the Chinese environment standards. The shorter the distance to the factory, the higher the value of BLL and lead levels in vegetable and environment samples. The lead level in the environmental samples was higher downwind of the recycling plant.

Delta-aminolevulinic acid dehydratase (ALAD) polymorphism in lead exposed Bangladeshi children and its effect on urinary aminolevulinic acid (ALA)

BACKGROUND AND OBJECTIVE

Lead has long been recognized as a harmful environmental pollutant. People in developing countries like Bangladesh still have a higher risk of lead exposure. Previous research has suggested that the delta-aminolevulinic acid dehydratase (ALAD) genotype can modify lead toxicity and individual susceptibility. As children are more susceptible to lead-induced toxicity, this study investigated whether the ALAD genotype influenced urinary excretion of delta-aminolevulinic acid (U-ALA) among children exposed to environmental lead in Bangladesh.

METHODS

Subjects were elementary schoolchildren from a semi-urban industrialized area in Bangladesh. A total of 222 children were studied. Blood and urine were collected to determine ALAD genotypes, blood lead levels and urinary aminolevulinic acid (U-ALA).

RESULTS

The mean BPb level was 9.7 µg/dl for the study children. BPb was significantly positively correlated with hemoglobin (p<0.01). In total, allele frequency for ALAD 1 and 2 was 0.83 and 0.17 respectively. The mean U-ALA concentration was lower in ALAD1-2/2-2 carriers than ALAD1-1 carriers for boys (p=0.001). But for girls, U-ALA did not differ significantly by genotype (p=0.26). When U-ALA was compared by genotype at the same exposure level in a multiple linear regression analysis, boys who were ALAD1-2/2-2 carriers still had a lower level of U-ALA compared to ALAD1-1 carriers.

CONCLUSION

This study provides information about the influence of ALAD polymorphism and its association with U-ALA in Bangladeshi children. Our results indicate that the ALAD1-2/2-2 genotype may have a protective effect in terms of U-ALA for environmentally lead exposed boys.

δ-Aminolevulinic acid dehydratase single nucleotide polymorphism 2 (ALAD2) and peptide transporter 2*2 haplotype (hPEPT2*2) differently influence neurobehavior in low-level lead exposed children

Delta-aminolevulinic acid dehydratase single nucleotide polymorphism 2 (ALAD2) and peptide transporter haplotype 2*2 (hPEPT2*2) through different pathways can increase brain levels of delta-aminolevulinic acid and are associated with higher blood lead burden in young children. Past child and adult findings regarding ALAD2 and neurobehavior have been inconsistent, and the possible association of hPEPT2*2 and neurobehavior has not yet been examined. Mean blood lead level (BLL), genotype, and neurobehavioral function (fine motor dexterity, working memory, visual attention and short-term memory) were assessed in 206 males and 215 females ages 5.1-11.8years. Ninety-six percent of children had BLLs<5.0μg/dl. After adjusting for covariates (sex, age and mother's level of education) and sibling exclusion (N=252), generalized linear mixed model analyses showed opposite effects for the ALAD2 and hPEPT2*2 genetic variants. Significant effects for ALAD2 were observed only as interactions with BLL and the results suggested that ALAD2 was neuroprotective. As BLL increased, ALAD2 was associated with enhanced visual attention and enhanced working memory (fewer commission errors). Independent of BLL, hPEPT2*2 predicted poorer motor dexterity and poorer working memory (more commission errors). BLL alone predicted poorer working memory from increased omission errors. The findings provided further substantiation that (independent of the genetic variants examined) lowest-level lead exposure disrupted early neurobehavioral function, and suggested that common genetic variants alter the neurotoxic potential of low-level lead. ALAD2 and hPEPT2*2 may be valuable markers of risk, and indicate novel mechanisms of lead-induced neurotoxicity. Longitudinal studies are needed to examine long-term influences of these genetic variants on neurobehavior.

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.

Influence of delta-aminolevulinic acid dehydratase gene polymorphism on selected lead exposure biomarkers in a cohort of ex-smelter workers

Lead (Pb) body burden and toxicity may be influenced by genetic polymorphisms. The aim of this study was to investigate the influence of G177C delta-aminolevulinic acid dehydratase (ALAD) polymorphism (rs1800435) on selected Pb exposure biomarkers in a population of workers highly exposed to this metal in the past. A cross-sectional survey was conducted between 2007 and 2009 within the cohort of ex-employees of a smelter in the north of France that closed down in 2003. A questionnaire was completed by each participant and blood samples enabled determination of Pb levels and ALAD polymorphism. Five parameters estimating the Pb body burden and its variations were studied: last blood lead level (BLL) during activity, cumulative blood Pb index, BLL at the time of the study, and absolute and percent changes in BLL after cessation of metal exposure. Multiple regression models were used to evaluate links between ALAD polymorphism and the selected Pb exposure biomarkers. Two hundred and four men were included. At the time of inclusion, the median age was 53.5 yr. The median duration of Pb exposure was 25 yr and the median latency since end of exposure was 5.6 yr. The frequency of ALAD-2 allele was 9.3%, with 34 subjects being heterozygous (ALAD1-2) and 2 homozygous (ALAD2-2). According to genotype, there was no significant difference for any of the five selected Pb exposure biomarkers. These results lend support to the notion that ALAD polymorphism exerts no marked impact on Pb body burden.

Genotyping an ALAD polymorphism with real-time PCR in two populations from the Iberian Peninsula

Lead-induced toxicity varies among individuals partly because of genetic differences in their susceptibility to the metal's effects. One genetic polymorphism associated with lead toxicity is a G-to-C transversion at position 177 in the coding region of delta-aminolevulinic acid dehydratase (ALAD), originating from two codominant alleles (ALAD1 and ALAD2). We examined the distribution of this single nucleotide polymorphism in two populations from the Iberian Peninsula. Genomic DNA was extracted from whole blood, and a real-time PCR assay was designed to determine ALAD polymorphic distribution. The distribution of MspI polymorphism was similar in the two populations studied, and allelic frequencies were comparable to those obtained in other studies of Caucasians. Further studies are needed to assess fully the functional significance of this polymorphism and its influence on the toxicokinetics of lead.

δ-Aminolevulinic acid dehydratase single nucleotide polymorphism 2 and peptide transporter 2*2 haplotype may differentially mediate lead exposure in male children

Child low-level lead (Pb) exposure is an unresolved public health problem and an unaddressed child health disparity. Particularly in cases of low-level exposure, source removal can be impossible to accomplish, and the only practical strategy for reducing risk may be primary prevention. Genetic biomarkers of increased neurotoxic risk could help to identify small subgroups of children for early intervention. Previous studies have suggested that, by way of a distinct mechanism, δ-aminolevulinic acid dehydratase single nucleotide polymorphism 2 (ALAD(2)) and/or peptide transporter 2*2 haplotype (hPEPT2*2) increase Pb blood burden in children. Studies have not yet examined whether sex mediates the effects of genotype on blood Pb burden. Also, previous studies have not included blood iron (Fe) level in their analyses. Blood and cheek cell samples were obtained from 306 minority children, ages 5.1 to 12.9 years. (208)Pb and (56)Fe levels were determined with inductively coupled plasma-mass spectrometry. General linear model analyses were used to examine differences in Pb blood burden by genotype and sex while controlling for blood Fe level. The sample geometric mean Pb level was 2.75 μg/dl. Pb blood burden was differentially higher in ALAD(2) heterozygous boys and hPEPT2*2 homozygous boys. These results suggest that the effect of ALAD(2) and hPEPT2*2 on Pb blood burden may be sexually dimorphic. ALAD(2) and hPEPT2*2 may be novel biomarkers of health and mental health risks in male children exposed to low levels of Pb.

Lead-binding proteins: a review

Lead-binding proteins are a series of low molecular weight proteins, analogous to metallothionein, which segregate lead in a nontoxic form in several organs (kidney, brain, lung, liver, erythrocyte). Whether the lead-binding proteins in every organ are identical or different remains to be determined. In the erythrocyte, delta-aminolevulinic acid dehydratase (ALAD) isoforms have commanded the greatest attention as proteins and enzymes that are both inhibitable and inducible by lead. ALAD-2, although it binds lead to a greater degree than ALAD-1, appears to bind lead in a less toxic form. What may be of greater significance is that a low molecular weight lead-binding protein, approximately 10 kDa, appears in the erythrocyte once blood lead exceeds 39 μg/dL and eventually surpasses the lead-binding capacity of ALAD. In brain and kidney of environmentally exposed humans and animals, a cytoplasmic lead-binding protein has been identified as thymosin β4, a 5 kDa protein. In kidney, but not brain, another lead-binding protein has been identified as acyl-CoA binding protein, a 9 kDa protein. Each of these proteins, when coincubated with liver ALAD and titrated with lead, diminishes the inhibition of ALAD by lead, verifying their ability to segregate lead in a nontoxic form.

Avaliação dos fatores de risco relacionados à exposição ao chumbo em crianças e adolescentes do Rio de Janeiro

A importância do chumbo atmosférico na contaminação global do ambiente tem recebido crescente atenção científica. A principal forma de monitorização da exposição é biológica, mas a ambiental tem um papel importante, já que o ambiente é a principal fonte de exposição ao chumbo. O estudo transversal busca identificar fontes de contaminação e potenciais fatores de risco da exposição em 64 crianças de zero a dezesseis anos de uma comunidade economicamente desfavorecida do Rio de Janeiro. Foram determinadas as concentrações de chumbo em solo, água, poeira e ar e calculados os fatores de risco neurológico e carcinogênico de inalação e ingestão. O sangue coletado foi utilizado para análise de Pb-S, ALA-D% e genotipagem da ALA-D. O fator de risco neurológico observado foi 549 vezes superior à dose de referência para poeira e 554 vezes superior no caso de ingestão. O fator de risco carcinogênico para ingestão foi de quatro vezes. A média de Pb-S foi 5,6μg/dL e 40% das crianças apresentaram valores de Pb-S acima do ponto de corte de 6μg/dL. A média de ALA-D% foi 40,3% e foi observada correlação entre Pb-S e ALA-D%. O genótipo ALAD1-2 foi identificado em 10% das crianças. Os resultados deste estudo permitirão o conhecimento da nossa realidade, subsidiando os órgãos de saúde pública e meio ambiente nas ações de controle e vigilância ambiental integrada

Polymorphisms of delta-aminolevulinic acid dehydratase (ALAD) and peptide transporter 2 (PEPT2) genes in children with low-level lead exposure

Low-level lead exposure during early childhood has long been associated with altered neurocognitive development and diminished cognitive functions. Over nine thousand U.S. industrial facilities annually emit significant amounts of lead, creating exposure risk particularly for minority children. The mechanisms by which low-level lead exerts neurotoxic effects are poorly understood. Once absorbed, the only intervention is source removal, thus primary prevention is key. Genetic biomarkers could provide an efficient means of identifying children at greatest risk. Common functional variants of genes that alter lead's neurotoxic potential have been identified and include delta-aminolevulinic acid dehydratase (ALAD(2)) and peptide transporter 2 (PEPT2*2). These polymorphisms have not been examined previously in Hispanic minority samples, or with regard to lowest level lead exposure. In 116 children of Mexican-American/Hispanic descent residing in zip codes previously designated as "high risk" for lead exposure (mean age=8.1, S.D.=1.9), blood lead level was measured at three time points over a 3-month period and averaged. DNA extraction was completed using buccal swab samples. The frequencies of the ALAD(2) and PEPT2*2 polymorphisms observed in this sample closely approximated those previously reported for Anglo, European and Asian samples. As compared to children heterozygous for the PEPT2*2 polymorphism, and without the PEPT2*2 polymorphism, the geometric mean blood lead level of children homozygous for the PEPT2*2 polymorphism was significantly higher. In contrast to past studies, mean blood lead level of children heterozygous and homozygous for the ALAD2 polymorphism in this sample did not differ from that of children without the ALAD2 polymorphism. Higher blood lead burden in children with the PEPT2*2 mutation may suggest that this common genetic variant is a biomarker of increased vulnerability to the neurotoxic effects of lowest level lead exposure.

Lack of association of delta-aminolevulinic acid dehydratase genotype with blood lead levels in environmentally exposed children of Uygur and Han populations

AIM

A cross-section study was conducted to explore the association between polymorphism of delta-aminolevulinic acid dehydratase (ALAD) and lead poisoning in Uygur and Han children in China.

METHODS

The ALAD genotyping was determined by PCR-RFLP in 443 Uygur and 469 Han children aged 6-10 years from Urumqi in Xinjiang province.

RESULTS

The blood lead levels of 912 environmentally exposed children ranged from 0.5 to 48.2 microg/dL, with a mean of 5.45 microg/dL and a standard deviation of 0.22 microg/dL, and 23. Thirty-one percent individuals were with blood lead level > or =10 microg/dL. The mean and standard deviation of blood lead levels were 5.57 +/- 0.223 microg/dL and 5.30 +/- 0.224 microg/dL in Uygur and Han children, respectively. The frequencies of the allele ALAD1 and ALAD2 in Uygur subjects were 90.52% and 9.48%, and in Han subjects were 95.73% and 4.27%, respectively (chi-square = 19.55, p < 0.05). No statistic correlation between the distribution of ALAD alleles and the blood lead level was found in both populations.

CONCLUSION

A significant difference was seen in the frequency distribution of ALAD genotype between the different races. The genetic susceptibility of ALAD polymorphism to lead toxicity may exhibit in a lead dose-dependent manner.

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.

Lead and delta-aminolevulinic acid dehydratase polymorphism: where does it lead? A meta-analysis

BACKGROUND

Lead poisoning affects many organs in the body. Lead inhibits delta-aminolevulinic acid dehydratase (ALAD), an enzyme with two co-dominantly expressed alleles, ALAD1 and ALAD2.

OBJECTIVE

Our meta-analysis studied the effects of the ALAD polymorphism on a) blood and bone lead levels and b) indicators of target organ toxicity.

DATA SOURCE

We included studies reporting one or more of the following by individuals with genotypes ALAD1-1 and ALAD1-2/2-2: blood lead level (BLL), tibia or trabecular lead level, zinc protoporphyrin (ZPP), hemoglobin, serum creatinine, blood urea nitrogen (BUN), dimercaptosuccinic acid-chelatable lead, or blood pressure.

DATA EXTRACTION

Sample sizes, means, and standard deviations were extracted for the genotype groups.

DATA SYNTHESIS

There was a statistically significant association between ALAD2 carriers and higher BLL in lead-exposed workers (weighted mean differences of 1.93 microg/dL). There was no association with ALAD carrier status among environmentally exposed adults with BLLs < 10 microg/dL. ALAD2 carriers were potentially protected against adverse hemapoietic effects (ZPP and hemoglobin levels), perhaps because of decreased lead bioavailability to heme pathway enzymes.

CONCLUSION

Carriers of the ALAD2 allele had higher BLLs than those who were ALAD1 homozygous and higher hemoglobin and lower ZPP, and the latter seems to be inversely related to BLL. Effects on other organs were not well delineated, partly because of the small number of subjects studied and potential modifications caused by other proteins in target tissues or by other polymorphic genes.

A polymorphism in the delta-aminolevulinic acid dehydratase gene modifies plasma/whole blood lead ratio

Delta aminolevulinic acid dehydratase (ALAD) plays an important role in lead poisoning. This study was carried out to examine the effects of ALAD gene polymorphism (G177C) on %Pb-P(plasma lead)/Pb-B(whole blood) ratio in 142 subjects environmentally exposed to lead. Genotypes for the ALAD G177C polymorphism were determined by PCR and restriction fragment length digestion. Pb-P and Pb-B were determined by inductively coupled plasma mass spectrometry and by graphite furnace atomic absorption spectrometry, respectively. The allele frequencies for ALAD1 and ALAD2 alleles were 0.897 and 0.103, respectively. We combined both ALAD 1-2 and ALAD 2-2 genotypes together (ALAD 1-2/2-2 group) and compared with the ALAD 1-1 genotype group. While no significant differences were found in Pb-B, subjects from the ALAD 1-2/2-2 genotype group presented significantly higher Pb-P concentrations and %Pb-P/Pb-B ratios (0.89+/-0.07 microg/l, and 1.45+/-0.10%, respectively) when compared with subjects from the ALAD 1-1 genotype group (0.44+/-0.05 microg/l, and 0.48+/-0.02, respectively; both P<0.0001). The higher %Pb-P/Pb-B ratios in carriers of the ALAD-2 allele compared with noncarriers indicate that ALAD 1-2/2-2 subjects are probably at increased health risks associated with lead exposure.