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

Stability of blood lead levels in children with low-level lead absorption

Current child blood lead (Pb) screening guidelines assume that blood lead levels (BLLs) are relatively stable over time, and that only youngest children are vulnerable to the damaging effects of lower-range BLLs. This study aimed to test the stability of lower-range (≤ 10 μg/dL) child BLLs over time, and whether lower-range BLLs diminished with age among children aged 6 months to 16 years living in a lower-income neighborhood with a density of pre-1986 housing and legacy contamination. Age, sex, family income, age of residence, and/or residence proximity to point sources of Pb, were tested as potential additional factors. Capillary blood samples from 193 children were analyzed by inductively coupled plasma mass spectrometry (ICPMS). Multiple imputation was used to simulate missing data for 3 blood tests for each child. Integrated Growth Curve models with Test Wave as a random effect were used to test BLL variability over time. Among N = 193 children tested, at Time 1 testing, 8.7% had the BLLs ≥ 5 μg/dL (CDC "elevated" BLL reference value at the time of data collection) and 16.8% had BLLs ≥ 3.5 μg/dL (2021 CDC "elevated" BLL reference value). Modeling with time as a random effect showed that the variability of BLLs were attributable to changes within children. Moreover, time was not a significant predictor of child BLLs over 18 months. A sex by age interaction suggested that BLLs diminished with age only among males. Of the additional environmental factors tested, only proximity to a major source of industrial or vehicle exhaust pollution predicted child BLL variability, and was associated with a small, but significant BLL increase (0.22 μg/dL). These findings suggest that one or two BLL tests for only infants or toddlers are insufficient for identifying children with Pb poisoning.

Improving Equitability and Inclusion for Testing and Detection of Lead Poisoning in US Children

Policy Points Child lead poisoning is associated with socioeconomic inequity and perpetuates health inequality. Methods for testing and detection of child lead poisoning are ill suited to the current demographics and characteristics of the problem. A three-pronged revision of current testing approaches is suggested. Employing the suggested revisions can immediately increase our national capacity for equitable, inclusive testing and detection. ABSTRACT: Child lead poisoning, the longest-standing child public health epidemic in US history, is associated with socioeconomic inequity and perpetuates health inequality. Removing lead from children's environments ("primary prevention") is and must remain the definitive solution for ending child lead poisoning. Until that goal can be realized, protecting children's health necessarily depends on the adequacy of our methods for testing and detection. Current methods for testing and detection, however, are no longer suited to the demographics and magnitude of the problem. We discuss the potential deployment and feasibility of a three-pronged revision of current practices including: 1) acceptance of capillary samples for final determination of lead poisoning, with electronic documentation of "clean" collection methods submitted by workers who complete simple Centers for Disease Control and Prevention-endorsed online training and certification for capillary sample collection; 2) new guidance specifying the analysis of capillary samples by inductively coupled plasma mass spectrometry or graphite furnace atomic absorption spectrometry with documented limit of detection ≤0.2 μg/dL; and 3) adaptive "census tract-specific" universal testing and monitoring guidance for children from birth to 10 years of age. These testing modifications can bring child blood lead level (BLL) testing into homes and communities, immediately increasing our national capacity for inclusive and equitable detection and monitoring of dangerous lower-range BLLs in US children.

Early-life low-level lead exposure alters anxiety-like behavior, voluntary alcohol consumption and AC5 protein content in adult male and female C57BL/6 J mice

Despite efforts to eradicate sources of environmental lead (Pb), children, predominately in lower socioeconomic areas, are still frequently exposed to unsafe levels of Pb from soils, dust, and water. Human studies suggest that Pb exposure is associated with altered drug consumption in adults; however, there is limited research at comparable exposure levels (blood Pb levels <10 μg/dL). To model how early-life, low-level Pb exposure affects alcohol consumption in adulthood, we exposed postnatal day (PND) 21 C57Bl/6 J mice to either 30 ppm or 0 ppm Lead (IV) Acetate in distilled water until PND 42, and testing began in adulthood. We predicted that mice with early-life Pb exposure would exhibit greater anxiety-like behavior and consume more alcohol in a three-week Drinking-in-the-Dark procedure (20% v/v) and a 24-h two-bottle choice procedure (10% v/v). We also predicted that Pb exposure would decrease whole-brain content of Adenylate Cyclase-5 (AC5), a protein linked to anxiety-like behaviors and alcohol drinking. There was no difference in limited-access binge-like consumption between exposure groups; however, Pb-exposed mice displayed higher two-bottle choice alcohol intake and preference. Furthermore, Pb-exposed mice exhibited greater anxiety-like behaviors in experiments conducted before an alcohol drinking history but not after. Finally, Pb-exposed mice exhibited an upregulation of whole-brain AC5 protein content. However, this difference was not found in the nucleus accumbens, dorsomedial or dorsolateral striatum. These findings conclude that early-life Pb exposure alters voluntary alcohol consumption and whole-brain AC5 protein content in adulthood. Future studies are necessary to further understand the mechanism behind how Pb exposure alters alcohol intake.

Effect of exposure to endocrine disrupting chemicals in obesity and neurodevelopment: The genetic and microbiota link

Current evidence highlights the importance of the genetic component in obesity and neurodevelopmental disorders (attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD) and intellectual disability (ID)), given that these diseases have reported an elevated heritability. Additionally, environmental stressors, such as endocrine disrupting chemicals (EDCs) have been classified as obesogens, neuroendocrine disruptors, and microbiota disrupting chemicals (MDCs). For this reason, the importance of this work lies in examining two possible biological mechanistic pathways linking obesity and neurodevelopmental/behavioural disorders: EDCs - gene and EDCs - microbiota interactions. First, we summarise the shared mechanisms of action of EDCs and the common genetic profile in the bidirectional link between obesity and neurodevelopment. In relation to interaction models, evidence from the reviewed studies reveals significant interactions between pesticides/heavy metals and gene polymorphisms of detoxifying and neurotransmission systems and metal homeostasis on cognitive development, ASD and ADHD symptomatology. Nonetheless, available literature about obesity is quite limited. Importantly, EDCs have been found to induce gut microbiota changes through gut-brain-microbiota axis conferring susceptibility to obesity and neurodevelopmental disorders. In view of the lack of studies assessing the impact of EDCs - gene interactions and EDCs - mediated dysbiosis jointly in obesity and neurodevelopment, we support considering genetics, EDCs exposure, and microbiota as interactive factors rather than individual contributors to the risk for developing obesity and neurodevelopmental disabilities at the same time.

Delta-Aminolevulinic Acid Dehydratase, Low Blood Lead Levels, Social Factors, and Intellectual Function in an Afro-Brazilian Children Community

Delta-aminolevulinic acid dehydratase (ALAD) enzyme catalyzes the second phase of the heme biosynthesis and is involved in lead toxicokinetics. This research aimed to evaluate its influence on the relationship between blood lead (PbB) levels and intellectual performance in Afro-Brazilian children. PbB, hemoglobin concentration, ALAD activity, and polymorphism were determined in whole blood. Anthropometric, socioeconomic, and family environment stimuli data were collected with appropriate instruments. The non-verbal intelligence of children and their mothers or guardians was assessed using the correspondent Raven's Progressive Matrix versions. The medians (range) of PbB levels and ALAD activity were 1.0 μg/dL (0.1-21.3) and, 71 U/L (31-113), respectively. ALAD G177C was distributed as follows: 97.9% for ALAD1/1 and 2.1% for ALAD1/2 genotypes. The mean of Raven raw score was 19.3 (± 5.6) points and there were no differences according to sex or environmental Pb exposure. No statistically significant association was observed between PbB level and children's IQ. However, ALAD activity presented an inverse significant association with PbB levels, children's percentile IQ, and children's IQ/Age ratio, suggesting a neuroprotective role of ALAD1 genotype in those with low PbB level.

Kidney Involvement in Acute Hepatic Porphyrias: Pathophysiology and Diagnostic Implications

Porphyrias are a group of rare disorders originating from an enzyme dysfunction in the pathway of heme biosynthesis. Depending on the specific enzyme involved, porphyrias manifest under drastically different clinical pictures. The most dramatic presentation of the four congenital acute hepatic porphyrias (AHPs: acute intermittent porphyria-AIP, ALAD deficiency, hereditary coproporphyria-HCP, and porphyria variegata-VP) consists of potentially life-threatening neurovisceral attacks, for which givosiran, a novel and effective siRNA-based therapeutic, has recently been licensed. Nonetheless, the clinical manifestations of acute porphyrias are multifaceted and do not limit themselves to acute attacks. In particular, porphyria-associated kidney disease (PAKD) is a distinct, long-term degenerating condition with specific pathological and clinical features, for which a satisfactory treatment is not available yet. In PAKD, chronic tubule-interstitial damage has been most commonly reported, though other pathologic features (e.g., chronic fibrous intimal hyperplasia) are consistent findings. Given the relevant role of the kidney in porphyrin metabolism, the mechanisms possibly intervening in causing renal damage in AHPs are different: among others, δ-aminolevulinic acid (ALA)-induced oxidative damage on mitochondria, intracellular toxic aggregation of porphyrins in proximal tubular cells, and derangements in the delicate microcirculatory balances of the kidney might be implicated. The presence of a variant of the human peptide transporter 2 (PEPT2), with a greater affinity to its substrates (including ALA), might confer a greater susceptibility to kidney damage in patients with AHPs. Furthermore, a possible effect of givosiran in worsening kidney function has been observed. In sum, the diagnostic workup of AHPs should always include a baseline evaluation of renal function, and periodic monitoring of the progression of kidney disease in patients with AHPs is strongly recommended. This review outlines the role of the kidney in porphyrin metabolism, the available evidence in support of the current etiologic and pathogenetic hypotheses, and the known clinical features of renal involvement in acute hepatic porphyrias.

Long-term consequences of early postnatal lead exposure on hippocampal synaptic activity in adult mice

INTRODUCTION

Lead (Pb) exposure yielding blood lead levels (BLL) as low as 2 µg/dl in children is an international problem. More common in US low-income neighborhoods, childhood Pb exposure can cause behavioral and cognitive deficits, including working memory impairments, which can persist into adulthood. So far, studies characterized short-term effects of high Pb exposure on neuronal structure and function. However, long-term consequences of early chronic Pb exposure on neuronal activity are poorly documented.

METHODS

Here, we exposed male and female mice (PND [postnatal day] 0 to PND 28) to one of three Pb treatments: 0 ppm (sodium-treated water, control), 30 ppm (low dose), and 330 ppm (high dose) lead acetate. Once the male and female mice were 9-12 months old, extracellular field recordings on hippocampal slices were performed.

RESULTS

We show that at CA3 to CA1 synapses, synaptic transmission was decreased and neuronal fiber activity was increased in males exposed to lowest level Pb. In contrast, both synaptic transmission and neuronal fiber activity were increased in females exposed to high Pb. The ventral hippocampus-medial prefrontal cortex (vHPC-mPFC) synapses are crucial for working memory in rodents. The lowest level Pb decreased vHPC-mPFC synaptic transmission, whereas high Pb decreased short-term synaptic depression.

CONCLUSIONS

Overall, we show for the first time that early exposure to either high or lowest level Pb has long-term consequences on different synaptic properties of at least two hippocampal synapses. Such consequences of early Pb exposure might worsen the cognitive decline observed in aging men and women. Our results suggest that additional efforts should focus on the consequences of early Pb exposure especially in at-risk communities.

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.

A Comparison of Child Blood Lead Levels in Urban and Rural Children Ages 5-12 Years Living in the Border Region of El Paso, Texas

Lead exposure is an unresolved pediatric health risk and disproportionately affects children in lower-income neighborhoods. Residences with children younger than age 5 years are the focus of mitigation policies; however, studies have shown that older children between the ages of 5 and 12 years also are at risk of central nervous system effects. Whether historically contaminated neighborhoods present ongoing risk to older children also is of concern. This study compared the blood lead levels (BLLs) of older children from an historically contaminated urban neighborhood to those of demographically matched children from a nearby rural locale and predicted significantly higher BLLs in the urban children. The study included 222 children aged 5-12 years, 111 from the urban neighborhood and 111 from local rural townships, matched for age, sex, race/ethnicity, and family income. Blood lead, cadmium, and mercury were measured using inductively coupled plasma mass spectrometry. General linear models tested whether geographic location (urban vs. rural) predicted child heavy metal levels, controlling for sex and age. Only location predicted only child BLL (R²= 0.36); children living in the urban setting had significantly higher BLLs as compared with matched rural township children (F = 125, df_220,2, p <0.001). Neighborhoods with a history of lead contamination can present current risk of lead exposure for older children between the ages of 5 and 12 years, as well as for infants and toddlers. More studies are needed to better characterize the risk of lead exposure to older children, particularly in lower-income neighborhoods with a history of lead contamination.

Early chronic exposure to low-level lead alters total hippocampal microglia in pre-adolescent mice

Developmental lead (Pb) exposure alters brain function through mechanisms that are not yet understood. A previous study showed that early lead exposure reduced microglia number in the dentate gyrus region of the hippocampus. Given the critical role of microglia in brain development, it is important to determine whether these differences are unique to the dentate gyrus, or occur throughout the hippocampus. Unbiased stereology was used to quantify microglia mean cell body number in total hippocampus, and compare the proportion of microglia in the ventral vs. dorsal regions. Total hippocampal volume was also measured and compared. The study included brain tissue from 30 pre-adolescent C57BL/6 J mice, exposed to 30 ppm Pb acetate (n = 10, mean BLL 3.4 μg/dL at sacrifice), 330 ppm Pb acetate (n = 10, mean BLL 14.1 μg/dL at sacrifice), or 0 ppm Pb acetate (n = 10, negative controls). In lead exposed animals, microglia mean cell body number was reduced in total hippocampus; total hippocampal volume was reduced. Importantly, effects in low- and high-dose exposure groups did not differ. Contrary to study hypotheses, the distribution of hippocampal microglia in the ventral vs. dorsal hippocampal regions did not differ. Overall, lowest and higher levels of lead exposure during development had strikingly similar disruptive effects in the neuroimmune system. Studies are needed to determine the immune and other mechanisms responsible for these effects. Future studies would benefit from larger samples to determine whether in fact there is a group by sex interaction driving the effects of early lead exposure on microglia.

Low blood lead levels impair intellectual and hematological function in children from Cartagena, Caribbean coast of Colombia

Lead produces numerous biochemical and physiological changes in humans, including hematological disorders, toxic effects on the central nervous system and in the function of several organs. The aim of this study was to determine blood lead levels (BLL) in children from Cartagena, Colombia, associating those with hematological and liver damage markers, the intelligence quotient (IQ), as well as with gene expression of the aminolevulinate dehydratase (ALAD), superoxide dismutase 1 (SOD1), gamma interferon (INF-γ), tumor necrosis factor (TNF) and tumor protein (p53). To achieve this purpose, 118 blood samples were collected from children 5-16 years old, with their respective informed consent from their parents. BLL was measured by atomic absorption; hematological parameters were obtained with automated systems; plasma was utilized to analyze hepatic toxicity markers, alanine aminotransferase (ALT), gamma-glutamyltransferase (γ-GT) and alkaline phosphatase (ALP); the Kaufman Brief Intelligence Test (K-BIT) was administered to measure the IQ; and gene expression was quantified from blood RNA. The mean BLL was 1.7±0.3μg/dL. A low proportion of the children (3.4%) had BLL above the CDC recommended limit (5μg/dL). BLL were correlated weakly, but negatively with child age, weight, height, body mass index, platelets wide distribution, mean platelet volume, γ-GT and IQ. There were not significant changes in the expression of evaluated genes. These results support the hypothesis that BLL below 5μg/dL may still be a detrimental factor on children's cognitive abilities, development and hematology, in line with recent concerns that there is no safe level of pediatric lead exposure.

Influence of peptide transporter 2 (PEPT2) on the distribution of cefadroxil in mouse brain: A microdialysis study

Peptide transporter 2 (PEPT2) is a high-affinity low-capacity transporter belonging to the proton-coupled oligopeptide transporter family. Although many aspects of PEPT2 structure-function are known, including its localization in choroid plexus and neurons, its regional activity in brain, especially extracellular fluid (ECF), is uncertain. In this study, the pharmacokinetics and regional brain distribution of cefadroxil, a β-lactam antibiotic and PEPT2 substrate, were investigated in wildtype and Pept2 null mice using in vivo intracerebral microdialysis. Cefadroxil was infused intravenously over 4h at 0.15mg/min/kg, and samples obtained from plasma, brain ECF, cerebrospinal fluid (CSF) and brain tissue. A permeability-surface area experiment was also performed in which 0.15mg/min/kg cefadroxil was infused intravenously for 10min, and samples obtained from plasma and brain tissues. Our results showed that PEPT2 ablation significantly increased the brain ECF and CSF levels of cefadroxil (2- to 2.5-fold). In contrast, there were no significant differences between wildtype and Pept2 null mice in the amount of cefadroxil in brain cells. The unbound volume of distribution of cefadroxil in brain was 60% lower in Pept2 null mice indicating an uptake function for PEPT2 in brain cells. Finally, PEPT2 did not affect the influx clearance of cefadroxil, thereby, ruling out differences between the two genotypes in drug entry across the blood-brain barriers. These findings demonstrate, for the first time, the impact of PEPT2 on brain ECF as well as the known role of PEPT2 in removing peptide-like drugs, such as cefadroxil, from the CSF to blood.

Early chronic low-level Pb exposure alters global exploratory behaviors but does not impair spatial and object memory retrieval in an object-in-place task in pre-adolescent C57BL/6J mice

The mechanisms by which early chronic low-level lead (Pb) exposure disrupts the developing brain are not yet understood. Rodent models have provided promising results however behavioral tests sensitive to effects at lowest levels of exposure during development are needed. Preadolescent animals (N=52) exposed to low and higher levels of Pb via lactation from birth to PND 28 completed the Object-in-Place Task of visual spatial and visual object memory retrieval (at PND 28). Generalized linear mixed models were used, controlling for sex and litter as a random effect. As compared with controls, global vertical exploratory behavior (rearing) markedly increased during memory retrieval. The findings suggested that early chronic Pb exposure altered the development of critical exploratory functions needed for learning and survival. Behaviors exhibited in novel spatial and novel object zone perimeters suggested that the Object-in-Place task is a valid measure of visual spatial and visual object memory in pre-adolescent C57BL/6J mice. Additional studies are needed to understand how early chronic low-level lead exposure disrupts the trajectory and possible linkages of critical exploratory and perceptual systems during development.

A Variant of Peptide Transporter 2 Predicts the Severity of Porphyria-Associated Kidney Disease

CKD occurs in most patients with acute intermittent porphyria (AIP). During AIP, δ-aminolevulinic acid (ALA) accumulates and promotes tubular cell death and tubulointerstitial damage. The human peptide transporter 2 (PEPT2) expressed by proximal tubular cells mediates the reabsorption of ALA, and variants of PEPT2 have different affinities for ALA. We tested the hypothesis that PEPT2 genotypes affect the severity and prognosis of porphyria-associated kidney disease. We analyzed data from 122 individuals with AIP who were followed from 2003 to 2013 and genotyped for PEPT2 At last follow-up, carriers of the PEPT2*1*1 genotype (higher affinity variant) exhibited worse renal function than carriers of the lower affinity variants PEPT2*1/*2 and PEPT2*2/*2 (mean±SD eGFR: 54.4±19.1, 66.6±23.8, and 78.1±19.9 ml/min per 1.73 m², respectively). Change in eGFR (mean±SD) over the 10-year period was -11.0±3.3, -2.4±1.9, and 3.4±2.6 ml/min per 1.73 m² for PEPT2*1/*1, PEPT2*1*2, and PEPT*2*2*2 carriers, respectively. At the end of follow-up, 68% of PEPT2*1*1 carriers had an eGFR<60 ml/min per 1.73 m², compared with 37% of PEPT2*1*2 carriers and 15% of PEPT2*2*2 carriers. Multiple regression models including all confounders indicated that the PEPT2*1*1 genotype independently associated with an eGFR<60 ml/min per 1.73 m² (odds ratio, 6.85; 95% confidence interval, 1.34 to 46.20) and an annual decrease in eGFR of >1 ml/min per 1.73 m² (odds ratio, 3.64; 95% confidence interval, 1.37 to 9.91). Thus, a gene variant is predictive of the severity of a chronic complication of AIP. The therapeutic value of PEPT2 inhibitors in preventing porphyria-associated kidney disease warrants investigation.

The Impact of Low-Level Lead Toxicity on School Performance among Hispanic Subgroups in the Chicago Public Schools

BACKGROUND

Environmental lead exposure detrimentally affects children's educational performance, even at very low blood lead levels (BLLs). Among children in Chicago Public Schools (CPS), the severity of the effects of BLL on reading and math vary by racial subgroup (White vs. Hispanic vs. non-Hispanic Black). We investigated the impact of BLL on standardized test performance by Hispanic subgroup (Mexican, Puerto Rican, and Other Hispanic).

METHODS

We examined 12,319 Hispanic children born in Chicago between 1994 and 1998 who were tested for BLL between birth and 2006 and enrolled in the 3rd grade at a CPS school between 2003 and 2006. We linked the Chicago birth registry, the Chicago Blood Lead Registry, and 3rd grade Illinois Standard Achievement Test (ISAT) scores to examine associations between BLL and school performance. Primary analyses were restricted to children with BLL below 10 µg/dL (0.483 µmol/L).

RESULTS

BLLs below 10 µg/dL (0.483 µmol/L) were inversely associated with reading and math scores in all Hispanic subgroups. Adjusted Relative Risks (RRadj) and 95% confidence intervals (CI) for reading and math failure were 1.34 (95% CI = 1.25, 1.63) and 1.53 (95% CI = 1.32, 1.78), respectively, per each additional 5 µg/dL of lead exposure for Hispanic children; RRadj did not differ across subgroups. We estimate that 7.0% (95% CI = 1.8, 11.9) of reading and 13.6% (95% CI = 7.7, 19.2) of math failure among Hispanic children can be attributed to exposure to BLLs of 5-9 µg/dL (0.242 to 0.435 µmol/L) vs. 0-4 µg/dL (0-0.193 µmol/L). The RRadj of math failure for each 5 µg/dL (0.242 µmol/L) increase in BLL was notably (p = 0.074) stronger among black Puerto Rican children (RRadj = 5.14; 95% CI = 1.65-15.94) compared to white Puerto Rican children (RRadj = 1.50; 95% CI = 1.12-2.02).

CONCLUSIONS

Early childhood lead exposure is associated with poorer achievement on standardized reading and math tests in the 3rd grade for Mexican, Puerto Rican, and Other Hispanic children enrolled in Chicago Public Schools. While we did not see interactions between BLL and ISAT performance by Hispanic subgroup, the stronger association between BLL and math failure for Black Puerto Rican children is intriguing and warrants further study.

Association between δ-aminolevulinate dehydratase G177C polymorphism and blood lead levels in brain tumor patients

As the δ-aminolevulinic acid dehydratase (ALAD) G177C polymorphism affects the toxicokinetics of lead in the body, and the corresponding exposure to lead may increase the risk of adult brain tumors, we hypothesize that there is a possible association of the ALAD G177C genotype and the risk of brain tumors in human. Therefore, the aim of the present study was to clarify the role of the ALAD enzyme gene polymorphism at position G177C in the pathogenesis of brain tumors and its correlation to lead exposure. The ALAD gene polymorphism at position G177C was genotyped using the polymerase chain reaction with restriction fragment length polymorphism method and measured the blood lead level by atomic absorption in 81 brain tumor patients and compared the results with 81 controls. The frequency of the GC genotype (ALAD1-2) was significantly increased in primary brain tumor patients compared to the control group. The genotype frequency of ALAD2 (ALAD1-2 and ALAD2-2) was significantly higher in the meningioma patients but was not significant in glioma patients. There was no significant difference in the number of patients and blood lead level when compared with the control. There was a significant increase when compared to ALAD1 regarding a mean value of the lead level. The genotyping of the ALAD G177C polymorphism in the present study revealed a significant association between ALAD2 and brain tumors. The ALAD G177C polymorphism may modify the lead kinetics in the blood, is associated with higher blood lead burden and may provide a biomarker of neurotoxic risk.

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.

Proton-coupled oligopeptide transporter family SLC15: physiological, pharmacological and pathological implications

Mammalian members of the proton-coupled oligopeptide transporter family (SLC15) are integral membrane proteins that mediate the cellular uptake of di/tripeptides and peptide-like drugs. The driving force for uphill electrogenic symport is the chemical gradient and membrane potential which favors proton uptake into the cell along with the peptide/mimetic substrate. The peptide transporters are responsible for the absorption and conservation of dietary protein digestion products in the intestine and kidney, respectively, and in maintaining homeostasis of neuropeptides in the brain. They are also responsible for the absorption and disposition of a number of pharmacologically important compounds including some aminocephalosporins, angiotensin-converting enzyme inhibitors, antiviral prodrugs, and others. In this review, we provide updated information on the structure-function of PepT1 (SLC15A1), PepT2 (SLC15A2), PhT1 (SLC15A4) and PhT2 (SLC15A3), and their expression and localization in key tissues. Moreover, mammalian peptide transporters are discussed in regard to pharmacogenomic and regulatory implications on host pharmacology and disease, and as potential targets for drug delivery. Significant emphasis is placed on the evolving role of these peptide transporters as elucidated by studies using genetically modified animals. Whenever possible, the relevance of drug-drug interactions and regulatory mechanisms are evaluated using in vivo studies.

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.

Associations of iron metabolism genes with blood manganese levels: a population-based study with validation data from animal models

BACKGROUND

Given mounting evidence for adverse effects from excess manganese exposure, it is critical to understand host factors, such as genetics, that affect manganese metabolism.

METHODS

Archived blood samples, collected from 332 Mexican women at delivery, were analyzed for manganese. We evaluated associations of manganese with functional variants in three candidate iron metabolism genes: HFE [hemochromatosis], TF [transferrin], and ALAD [δ-aminolevulinic acid dehydratase]. We used a knockout mouse model to parallel our significant results as a novel method of validating the observed associations between genotype and blood manganese in our epidemiologic data.

RESULTS

Percentage of participants carrying at least one copy of HFE C282Y, HFE H63D, TF P570S, and ALAD K59N variant alleles was 2.4%, 17.7%, 20.1%, and 6.4%, respectively. Percentage carrying at least one copy of either C282Y or H63D allele in HFE gene was 19.6%. Geometric mean (geometric standard deviation) manganese concentrations were 17.0 (1.5) μg/l. Women with any HFE variant allele had 12% lower blood manganese concentrations than women with no variant alleles (β = -0.12 [95% CI = -0.23 to -0.01]). TF and ALAD variants were not significant predictors of blood manganese. In animal models, Hfe(-/-) mice displayed a significant reduction in blood manganese compared with Hfe(+/+) mice, replicating the altered manganese metabolism found in our human research.

CONCLUSIONS

Our study suggests that genetic variants in iron metabolism genes may contribute to variability in manganese exposure by affecting manganese absorption, distribution, or excretion. Genetic background may be critical to consider in studies that rely on environmental manganese measurements.

Exploring potential sources of differential vulnerability and susceptibility in risk from environmental hazards to expand the scope of risk assessment

Genetic factors, other exposures, individual disease states and allostatic load, psychosocial stress, and socioeconomic position all have the potential to modify the response to environmental exposures. Moreover, many of these modifiers covary with the exposure, leading to much higher risks in some subgroups. These are not theoretical concerns; rather, all these patterns have already been demonstrated in studies of the effects of lead and air pollution. However, recent regulatory impact assessments for these exposures have generally not incorporated these findings. Therefore, differential risk and vulnerability is a critically important but neglected area within risk assessment, and should be incorporated in the future.

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.

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.

MicroRNA expression as a predictive marker for gemcitabine response after surgical resection of pancreatic cancer

Background

To improve the prognosis of patients after resection of pancreatic cancer, the most appropriate and efficient treatment should be provided to specific subsets of patients. Our aim was to identify promising microRNAs as markers to predict responses to gemcitabine in patients with resected pancreatic cancer.

Methods

Two gemcitabine-resistant pancreatic cancer cell lines were established, and global microRNA expression analyses was performed by quantitative reverse transcription–polymerase chain reaction (qRT-PCR). Eleven miRNAs were selected as putative predictive markers and analyzed by means of macrodissected formalin-fixed, paraffin-embedded samples obtained from 90 patients with or without gemcitabine treatment after resection of pancreatic cancer.

Results

We identified 24 microRNAs whose expression was altered in gemcitabine-resistant cells. qRT-PCR analyses showed that patients with high miR-142-5p and miR-204 expression had significantly longer survival times than those with low miR-142-5p (P = 0.0077) and miR-204 (P = 0.0054) expression in the gemcitabine-treated group. This was not seen in the nontreated group. Multivariate analyses showed that miR-142-5p expression was an independent prognostic marker only in patients treated with gemcitabine (P = 0.034).

Conclusions

miR-142-5p is a promising predictive marker for gemcitabine response in patients with resected pancreatic cancer.

Distribution of glycylsarcosine and cefadroxil among cerebrospinal fluid, choroid plexus, and brain parenchyma after intracerebroventricular injection is markedly different between wild-type and Pept2 null mice

The purpose of this study was to define the cerebrospinal fluid (CSF) clearance kinetics, choroid plexus uptake, and parenchymal penetration of PEPT2 substrates in different regions of the brain after intracerebroventricular administration. To accomplish these objectives, we performed biodistribution studies using [(14)C]glycylsarcosine (GlySar) and [(3)H]cefadroxil, along with quantitative autoradiography of [(14)C]GlySar, in wild-type and Pept2 null mice. We found that PEPT2 deletion markedly reduced the uptake of GlySar and cefadroxil in choroid plexuses at 60 mins by 94% and 82% (P<0.001), respectively, and lowered their CSF clearances by about fourfold. Autoradiography showed that GlySar concentrations in the lateral, third, and fourth ventricle choroid plexuses were higher in wild-type as compared with Pept2 null mice (P<0.01). Uptake of GlySar by the ependymal-subependymal layer and septal region was higher in wild-type than in null mice, but the half-distance of penetration into parenchyma was significantly less in wild-type mice. The latter is probably because of the clearance of GlySar from interstitial fluid by brain cells expressing PEPT2, which stops further penetration. These studies show that PEPT2 knockout can significantly modify the spatial distribution of GlySar and cefadroxil (and presumably other peptides/mimetics and peptide-like drugs) in brain.