Associations of subtypes of hemoglobin with delta-aminolevulinic acid dehydratase genotype and dimercaptosuccinic acid-chelatable lead levels

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.

Blood lead in the 21st Century: The sub-microgram challenge

In the US the dominant sources of lead through much of the 20th Century (eg, vehicular emissions, plumbing, household paint) have been significantly diminished. The reductions in adult and pediatric average blood lead levels in the US have been extraordinary. Progress continues: the US Environmental Protection Agency recently developed a new air standard for lead. In the 21st Century, the average blood lead level in a society may be seen as a marker of the status of their public's health. However, the threat of lead exposure remains a significant public health problem among subpopulation groups in the US and in many less developed countries. This paper examines some of the specific issues involved in the reduction of blood lead in a post-industrial era. These involve the control of the remaining exogenous primary sources, both general (eg, industrial emissions) and specific (eg, at-risk occupations), exogenous secondary sources (eg, contaminated urban soils, legacy lead-based paints), an endogenous source (ie, cumulative body lead burden) and emergent sources.

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.

Blood lead levels of the battery and exhaust workers and their pulmonary function tests

In an attempt to understand the impact of inhaled lead on the pulmonary functions, we assessed the blood lead levels and pulmonary functions of the battery and exhaust workers who are potential candidates for lead inhalation. The hospital staff served as control group. The measurements of lead levels were performed using atomic absorption spectrophotometry. Pulmonary function tests (PFTs) were performed using a portable spirometer. The blood lead levels of the battery workers, exhaust workers and controls were found to be 36.83, 26.94 and 14.81 microg/dl, respectively. The values of the workers were significantly higher than the controls (p < 0.001). The lead levels of the battery workers were also significantly higher than the exhaust workers (p < 0.001). PFT results (maximum voluntary ventilation, forced expiration flow and first forced expiration volume values of the workers) were significantly worse than the controls, and their pulmonary function test results were consistent with restrictive problems in the airways.

Influence of the delta-aminolevulinic acid dehydratase (ALAD) polymorphism on biomarkers of lead exposure in Turkish storage battery manufacturing workers

BACKGROUND

The relationship between delta-aminolevulinic acid dehydratase polymorphism (ALAD) and biomarkers of exposure was investigated in Turkish lead workers in this study.

METHODS

Seventy two male lead battery manufacturing workers were selected for the study. Blood lead (BPb) and urinary lead (UPb) concentrations were determined by atomic absorption spectrometry. Erythrocyte ALAD activity and urinary 5-aminolevulinic acid (UALA) were measured spectrophotometrically. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used to determine the genotype of the ALAD gene.

RESULTS

In total, 51 workers (70.8%) had the ALAD 1-1 genotype, whereas 21 workers (29.2%) had the ALAD 1-2 genotype. No significant relationships were found between the two genotypes and BPb, UPb, and ALAD activity. ALAD1 homozygotes showed significantly higher levels of UALA in comparison with those ALAD2 carriers.

CONCLUSIONS

ALAD 1-1 individuals might be an increased risk compared to ALAD2 carriers to disturbance in heme biosynthetic pathway in high lead exposure.

Lead binding to delta-aminolevulinic acid dehydratase (ALAD) in human erythrocytes

Over 99% of the lead present in blood is usually found in erythrocytes. To investigate the nature of this selective accumulation of lead in erythrocytes, the specific binding of lead to proteins in human erythrocytes was studied using liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC-ICP-MS). The principal lead-binding protein had a mass of approximately 240 kDa, and adsorption to specific antibodies showed that protein was delta-aminolevulinic acid dehydratase (ALAD). Thus, the previous notion that lead in erythrocytes was bound primarily to haemoglobin has to be revised. Furthermore, in lead-exposed workers, the percentage of lead bound to ALAD was influenced by a common polymorphism in the ALAD gene. Specifically, in seven carriers of the ALAD2 allele, 84% of the protein-bound lead recovered was bound to ALAD compared to 81% in seven homozygotes for the ALAD1 allele whose erythrocytes were matched for blood-lead concentration. The small difference was statistically significant in Wilcoxon matched-pairs signed-rank test (P = 0.03). No ALAD allele-specific difference in ALAD-bound lead was found among 20 unexposed controls. Perhaps the difference in ALAD-bound lead can provide an explanation for the previously reported finding of higher blood-lead levels among carriers of the ALAD2 allele than among ALAD1 homozygotes in lead-exposed populations.