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.

Risk characterization of human exposure to polycyclic aromatic hydrocarbons in vulnerable groups.

Nowadays, anthropogenic activities are a significant source of environmental pollutants at an alarming rate. Polycyclic aromatic hydrocarbons (PAHs) are widely spread and well-known mutagenic and carcinogenic legacy pollutants of public health concern. In underdeveloped countries like Brazil, limited data are available in the scientific literature on the risk assessment of exposure to PAHs, leading to a risk underestimation, especially in the vulnerable groups of the population. In the current investigation, we have measured seven PAH metabolites in healthy vulnerable groups (n = 400), including pregnant and lactating women, newborns, and children. Besides, according to the United States Environmental Protection Agency (US.EPA) guidelines, the risk characterization of this exposure was performed by calculating estimated daily intake, hazard quotient, hazard index, and cancer risk. The highest levels and detection rates for all metabolites were found in pregnant women, with 15.71 ng/mL for the ∑OH-PAHs, presumably due to the increased metabolic rate related to pregnancy. The lowest ∑OH-PAHs were detected in infants, with 2.33 ng/mL due to unmatured metabolism. When analyzing the health hazards, the non-carcinogenic risk - as a sum of all PAH metabolites, we observed a health risk (in all groups) above the limit that the US.EPA considers without significant potential health risk. Regarding cancer risks, benzo[a]pyrene levels in all the groups indicated a potential risk. In general, higher levels of potential cancer risk were observed for lactating women, which implies risks to them and their infants. Low molecular weight PAHs (naphthalene, fluorene, and phenanthrene) are associated with acute toxic effects. Their high detection rate (i.e., naphthalene: 100 %) demonstrates their extensive exposure, making these PAHs a priority for human biomonitoring. Besides, benzo[a]pyrene is carcinogenic to humans, being also important to monitor its levels since our risk assessment showed a high cancer risk to this PAH.

ALAD and APOE polymorphisms are associated with lead and mercury levels in Italian pregnant women and their newborns with adequate nutritional status of zinc and selenium.

The impacts of single-nucleotide polymorphisms (SNPs) in ALAD and VDR genes on Pb health effects and/or kinetics are inconclusive at low exposure levels, while studies including APOE SNPs are rare. In this study, we examined the associations of ALAD, VDR and APOE SNPs with exposure biomarkers of Pb and other trace elements (TEs) in Italian pregnant women (N = 873, aged 18-44 years) and their newborns (N = 619) with low-level mixed-element exposure through diet, the environment or endogenously. DNA from maternal peripheral venous blood (mB), sampled during the second and third trimesters, was genotyped for ALAD (rs1800435, rs1805313, rs1139488, rs818708), VDR (rs2228570, rs1544410, rs7975232, rs731236) and APOE (rs429358, rs7421) using TaqMan SNP assays. Personal and lifestyle data and TE levels (mB, maternal plasma, hair and mixed umbilical cord blood [CB]) from the PHIME project were used. Multiple linear regression models, controlling for confounding variables, were performed to test the associations between SNPs and TEs. The geometric means of mB-Pb, mB-Hg, mB-As and mB-Cd (11.0 ng/g, 2.16 ng/g, 1.38 ng/g and 0.31 ng/g, respectively) indicated low exposure levels, whereas maternal plasma Zn and Se (0.72 µg/mL and 78.6 ng/g, respectively) indicated adequate micronutritional status. Variant alleles of ALAD rs1800435 and rs1805313 were negatively associated with mB-Pb levels, whereas a positive association was observed for rs1139488. None of the VDR SNPs or their haplotypes had any association with Pb levels. Regarding APOE, the ϵ4 allele was associated with lower mB-Hg and CB-Hg, while a positive association was found with the ϵ2 allele and CB-Pb when the model included only newborn girls. The observed associations indicate possible modification effects of ALAD and APOE SNPs on Pb or Hg kinetics in women and their newborns with low exposure to non-essential TEs, as well as an adequate nutritional status of Zn and Se.

Identification of enzymes involved in oxidation of phenylbutyrate.

In recent years the short-chain fatty acid, 4-phenylbutyrate (PB), has emerged as a promising drug for various clinical conditions. In fact, PB has been Food and Drug Administration-approved for urea cycle disorders since 1996. PB is more potent and less toxic than its metabolite, phenylacetate (PA), and is not just a pro-drug for PA, as was initially assumed. The metabolic pathway of PB, however, has remained unclear. Therefore, we set out to identify the enzymes involved in the ß-oxidation of PB. We used cells deficient in specific steps of fatty acid ß-oxidation and ultra-HPLC to measure which enzymes were able to convert PB or its downstream products. We show that the first step in PB oxidation is catalyzed solely by the enzyme, medium-chain acyl-CoA dehydrogenase. The second (hydration) step can be catalyzed by all three mitochondrial enoyl-CoA hydratase enzymes, i.e., short-chain enoyl-CoA hydratase, long-chain enoyl-CoA hydratase, and 3-methylglutaconyl-CoA hydratase. Enzymes involved in the third step include both short- and long-chain 3-hydroxyacyl-CoA dehydrogenase. The oxidation of PB is completed by only one enzyme, i.e., long-chain 3-ketoacyl-CoA thiolase. Taken together, the enzymatic characteristics of the PB degradative pathway may lead to better dose finding and limiting the toxicity of this drug.