Cholinesterase and paraoxonase (PON1) enzyme activities in Mexican-American mothers and children from an agricultural community

Evaluation of paraoxonase I and hemoglobin levels in farmers and agricultural workers in relation to organophosphorus and carbamate levels in their blood and urine samples: A cross sectional study

Background: Pesticides are chemicals that have become common household products in developing countries. The purpose of pesticides is to manage agricultural work. The majority of pesticides for indoor and agricultural use are carbamate and organophosphorus. Toxicity is caused due to excess and improper use or disposal of these chemical agents. Slow exposure to pesticides causes chronic poisoning whereas rapid exposure causes acute poisoning. The paraoxonase I (PON 1) enzyme has a role in detoxifying some of the oxon derivatives which thereby inhibit acetylcholinesterase and butyrylcholinesterase. Methods: This study analyzed farmers who were exposed intermittently to organophosphorus and carbamates pesticides during farming for more than five years. Serum paraoxonase I was evaluated by colorimetry method, and hemoglobin levels were evaluated using portable Fresenius Kabi haemoglobinometer. Results: The study showed that the pesticides were found in the blood and urine samples of farmers and there was an alteration of paraoxonase I and hemoglobin levels in them due to the exposure of pesticides in large quantities over some time. The present study showed around 81% of the participants who were intermittently exposed to pesticides for more than five years were detected with pesticide toxicity. The paraoxonase I level was altered in farmers who were positive for organophosphorus and carbamate pesticides. The hemoglobin level did not show much variation among the farmers exposed to pesticides. This may be due to the lifestyle of the subjects, climatic variations and also their eating habits. Conclusions: The study suggested that there was alteration in the levels of PON1 and hemoglobin in farmers and agricultural workers with positive organophosphorus and carbamates in their blood and urine samples. As our study was done without quantifying the amount of pesticides, further studies can be done by quantifying the pesticide level and comparing it with the paraoxonase I level.

Children Environmentally Exposed to Agrochemicals in Rural Areas Present Changes in Oxidative Status and DNA Damage

Rural children are exposed to several chemicals. This study evaluated the environmental co-exposure of rural children to cholinesterase inhibitor insecticides and metals/metalloids, and the resulting oxidative stress and DNA damage. Seventy-two children (5 to 16 years old) were studied at two different moments: period 1, when agrochemicals were less used, and period 2, when agrochemicals were extensively used in agriculture. Biomonitoring was performed by evaluating butyrylcholinesterase (BuChE) activity in serum; arsenic (As), chromium (Cr), lead (Pb), and nickel (Ni) levels in blood; malondialdehyde (MDA) in plasma; glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST) activities in whole blood; non-protein thiol levels in erythrocytes; and micronuclei (MN) assay in exfoliated buccal cells. Cr and As levels were higher than the reference values in both periods, and Ni levels were higher than the reference values in period 2 alone. BuChE activity was inhibited in period 2 compared with period 1. In period 2, there was an increase in endogenous antioxidants and a decrease in MDA, probably demonstrating a compensatory mechanism as a response to increasing xenobiotics. Also in period 2, the MN frequency increased and BuChE and As were positively associated, suggesting co-exposure. On the other hand, in period 1, it was observed that Cr, Ni, and Pb blood levels were negatively associated with GSH-Px and GST, while MDA was positively associated with As levels. Our findings demonstrated an imbalance in endogenous antioxidants, contributing to genotoxicity and lipoperoxidation, probably in response to exposure to xenobiotics, especially carcinogenic elements (Cr, As, and Ni).

Use of computational toxicology (CompTox) tools to predict in vivo toxicity for risk assessment

Computational Toxicology tools were used to predict toxicity for three pesticides: propyzamide (PZ), carbaryl (CB) and chlorpyrifos (CPF). The tools used included: a) ToxCast/Tox21 assays (AC₅₀ s μM: concentration 50% maximum activity); b) in vitro-to-in vivo extrapolation (IVIVE) using ToxCast/Tox21 AC₅₀s to predict administered equivalent doses (AED: mg/kg/d) to compare to known in vivo Lowest-Observed-Effect-Level (LOEL)/Benchmark Dose (BMD); c) high throughput toxicokinetics population based (HTTK-Pop) using AC₅₀s for endpoints associated with the mode of action (MOA) to predict age-adjusted AED for comparison with in vivo LOEL/BMDs. ToxCast/Tox21 active-hit-calls for each chemical were predictive of targets associated with each MOA, however, assays directly relevant to the MOAs for each chemical were limited. IVIVE AEDs were predictive of in vivo LOEL/BMD₁₀s for all three pesticides. HTTK-Pop was predictive of in vivo LOEL/BMD₁₀s for PZ and CPF but not for CB after human age adjustments 11-15 (PZ) and 6-10 (CB) or 6-10 and 11-20 (CPF) corresponding to treated rat ages (in vivo endpoints). The predictions of computational tools are useful for risk assessment to identify targets in chemical MOAs and to support in vivo endpoints. Data can also aid is decisions about the need for further studies.

Influence of nutritional factors and the PON1 C(-107)T polymorphism on paraoxonase-1 activity in childhood

OBJECTIVE

The cardioprotective enzyme paraoxonase-1 (PON1) suffers an important influence from genetic polymorphisms and nutritional factors. The aim of this study was to investigate the influence of diet, nutritional status, and the C(-107)T polymorphism on PON1 arylesterase activity in children.

METHODS

This was a cross-sectional study with 97 children, aged between 5 and 8 years, of both genders, from a pediatric outpatient clinic in southern Brazil. A sociodemographic, behavioral, and food consumption questionnaire was applied, and anthropometric measurements and laboratory blood samples were taken. PON1 arylesterase activity was measured by phenol extinction (U/mL), and DNA extraction and analysis of the PON1 C(-107)T polymorphism were performed. The Hardy-Weinberg equilibrium was tested with the chi-squared test and linear regression was used to estimate PON1 activity according to four adjustment models, with an acceptable error of 5%.

RESULTS

In the sample, the male gender accounted for 50.5%, 39.2% were 6 years of age, 54.5% had normal weight, and 51.5% had PON1 activity below the median (90.0, 15-30U/mL). Genotype frequency was 54.6% (53/97), 31.0% (30/97), and 14.4% (14/97), respectively, for CT, CC, and TT, consistent with the Hardy-Weinberg equilibrium (p=0.22). In the regression analysis, the model that included sociodemographic variables as well as frequency of consumption of fruits, vegetables, legumes, dairy products, and beans estimated a variability of 14.8% in PON1 activity combined with the PON1 C(-107)T polymorphism.

CONCLUSIONS

During childhood, a good-quality diet with greater inclusion of healthy foods was important to predict the activity of the cardioprotective enzyme PON1 combined with the C(-107)T polymorphism of the PON1 gene.

PON1 DNA methylation and neurobehavior in Mexican-American children with prenatal organophosphate exposure

PON1 is a multifunctional enzyme involved in oxidative stress and detoxification of some organophosphate (OP) pesticides. It has been associated with nervous system diseases like Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease, and autism. We previously found that PON1 susceptible genotypes were associated with lower IQ scores in children. Epigenetic marks, such as DNA methylation, can regulate gene expression. Yet, data on whether DNA methylation may influence the relationship between PON1 levels and neurobehavior are limited. In this study, we used Illumina 450K and EPIC BeadChip arrays to assess PON1 DNA methylation in blood specimens collected from children (n = 238) at birth (cord blood) and age 7 years and examined their relationship with cognitive outcomes. The Wechsler Intelligence Scale for Children was used to assess Full Scale IQ and four composite measures (Verbal Comprehension, Perceptual Reasoning, Working Memory, and Processing Speed Indexes) in 7-year-old children. We observed a consistent yet nonsignificant inverse relationship of methylation at several CpG sites close to the PON1 transcription start site with Full Scale IQ and other composite measures of cognition. We also found an inverse relationship between cord blood methylation at cg15887283 with working memory and a positive association of 7-year-old methylation at cg22798737 with processing speed, independent of OP exposure. However, none of the associations remained significant after accounting for multiple comparisons. This study provides some evidence of the role DNA methylation may play in the known relationship between PON1 and neurobehavior in children, however it appears to be only suggestive and warrants additional research.

Blood cholinesterase activity levels of farmers in winter and hot season of Mae Taeng District, Chiang Mai Province, Thailand

Organophosphate and carbamate pesticides have been widely used by farmers for crop protection and pest control. Inhibition of acetylcholinesterase (AChE) in erythrocyte and butyrylcholinesterase (BChE) in plasma is the predominant toxic effect of organophosphate and carbamate pesticides. Mae Taeng District, Chiang Mai Province, is one of the large areas of growing vegetables and fruits. Due to their regular exposure to these pesticides, the farmers are affected by this toxicity. The objective of the study was to examine the AChE and the BChE activity levels in the blood of 102 farmers for comparison of exposure in two cropping seasons, winter and hot. Blood samples were collected in December 2013 (winter) and April-June 2014 (hot). A total of 102 farmers joined the study, represented by 76 males (74.5 %) and 26 females (25.5 %). The age of most of the farmers was 53.4 ± 8.7 years. Out of 102, 21 farmers used carbamate pesticides. The results showed that the AChE and the BChE activity levels of all the farmers were 3.27 ± 0.84 Unit/mL and 2.15 ± 0.58 Unit/mL, respectively. The AChE and the BChE activity levels in males were 3.31 ± 0.88 Unit/mL and 1.97 ± 0.60 U/mL, respectively, during winter and 3.27 ± 0.82 Unit/mL and 2.15 ± 0.58 U/mL, respectively, during the hot season, and AChE and the BChE activity levels in females were 3.27 ± 0.82 U/mL and 2.44 ± 0.56 U/mL, respectively, during the hot season. The cholinesterase activity levels, both AChE and BChE, in the male farmers' blood had significant difference between the two seasons, while in the case of the female farmers, there was significant difference in the BChE activity levels, at p < 0.05. The BChE activity level was found to significantly correlate with self-spray (p < 0.05), which implies that the BChE activity decreased when they sprayed by themselves. The cholinesterase activity levels of the present study were lower than those of the other studies, which may be an indication of some chronic effect of exposure to anticholinesterase pesticides. Thus, it is recommended that the use of pesticides be decreased, together with increase in the awareness of the impact of pesticides on health; also recommended is regular monitoring of blood cholinesterase.

Relationship Between Paraoxonase-1 and Butyrylcholinesterase Activities and Nutritional Status in Mexican Children

BACKGROUND

The enzymes butyrylcholinesterase (BuChE) and paraoxonase-1 (PON1) are the primary bioscavenging enzymes in serum and exhibit antioxidant and anti-inflammatory activities. PON1 has been associated with diseases caused by high oxidative stress, whereas BuChE appears to be involved in the pathophysiology of the metabolic syndrome and related disorders. It has been suggested that children from rural communities in Mexico may have a predisposition to develop obesity or type 2 diabetes during adolescence or adulthood. The objective of this study was to determine whether associations exist between the paraoxonase (PONase)/arylesterase (AREase) activity of PON1, its PON1-Q192R and PON1-L55M polymorphisms, and BuChE activity with the nutritional status and lipid profiles in a group of children from rural communities in Mexico.

METHODS

A group of 97 boys and girls from a rural community in Mexico were assessed for body mass index, the enzymatic activities of BuChE, PONase, and AREase were measured in serum, and their lipid profiles were determined. Genetic polymorphisms of PON1-L55M and PON1-Q192R were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

The children were classified into four groups: thinness, normal weight, overweight, and obese. Of the children studied, 34.4% were overweight and obese. The mean age of the participants was 9.5 years (standard deviation = 1.8). The L allele of the PON1-L55M genotype was the most frequent (83.3%), and the R allele of the PON1-Q192R genotype was the most frequent (61.8%). Overweight and obese children had higher values of BuChE, total cholesterol, triglycerides (TG), and lower high-density lipoprotein (HDL-C) values than children with thinness or normal weight (P = 0.028, P = 0.019, P = 0.004, P = 0.069 and P = 0.021, respectively). The levels of AREase and PONase and the prevalence of PON1-L55M and PON1-Q192R genotypes were similar between groups (P = 0.484 and P = 0.380, respectively).

CONCLUSIONS

This study establishes a positive association of BuChE activity with nutritional status and serum TG.

Paraoxonase, arylesterase and lactonase activities of paraoxonase-1 (PON1) in obese and severely obese women

Obesity is independently associated with disturbances in lipid and lipoprotein metabolism, oxidative stress, and is a well-established independent risk factor for cardiovascular diseases (CVD). Human paraoxonase 1 (PON1) is a pleotropic high-density lipoprotein (HDL)-associated enzyme with antioxidant and anti-inflammatory proprieties that have been suggested to contribute to the athero-protective function of the lipoprotein. The aim of this study was to investigate whether obesity is associated with PON1 activity and whether this association is influenced by oxidative stress, inflammation and HDL cholesterol (HDL-C) concentration. The promiscuous activities, arylesterase and paraoxonase, and the putative physiological activity, lactonase, of PON1 were assessed in the serum of 214 obese and severely obese, 101 overweight and 129 normal-weight women. Levels of high-sensitivity C-reactive protein (hs-CRP), hydroperoxides (by-products of lipid oxidative damage) and lipid profiles were also evaluated. Arylesterase activity was the only activity that significantly differed across the groups (ANOVA, p < .01), with the greatest decrease observed in individuals with body mass index (BMI) > 40 kg/m² compared to controls (p < .001). This activity was also inversely, although weakly (r = -0.160, p < .001) correlated with the BMI, and the association was independent of age and levels of oxidative stress and inflammation, but not of HDL-C concentration. In conclusion, our results suggest that the apparent obesity-associated decrement of PON1 activity might simply reflect the decrease in concentration of its plasmatic carrier.

Environmental exposure and effects on health of children from a tobacco-producing region

Children may be environmentally exposed to several hazards. In order to evaluate the health of children living in a tobacco-producing region, different biomarkers of exposure and effect, as well as hematological parameters, were evaluated. Biomarkers of exposure to the following xenobiotics were assessed: pesticides, nicotine, toxic elements, and organic solvents. Oxidative damage markers malondialdehyde (MDA) and protein carbonyls (PCO), vitamin C, microalbuminuria (mALB) levels, and N-acetyl-β-D-glucosaminidase (NAG) activity were also evaluated. Peripheral blood samples and urine were collected from 40 children (6-12 years), at two different crop periods: in the beginning of pesticide applications (period 1) and in the leaf harvest (period 2). The Wilcoxon signed-rank test for paired data was used to evaluate the differences between both periods. Biomarkers of exposure cotinine in urine and blood chromium (Cr) levels were increased in period 1 when compared to period 2. Moreover, a significant reduced plasmatic activity of butyrylcholinesterase (BuChE) was observed in period 2 in relation to period 1. Blood Cr levels were above the recommended by WHO in both evaluations. The biomarkers MDA and PCO as well as the kidney dysfunction biomarker, mALB, presented levels significantly increased in period 1. Additionally, decreased lymphocytes and increased basophils were also observed. Cotinine was positively associated with PCO, and Cr was positively associated with PCO and MDA. The increased Cr levels were associated with decreased lymphocytes and increased basophils. Our findings demonstrate that children environmentally exposed to xenobiotics in rural area may present early kidney dysfunction, hematological alterations, as well as lipid and protein damages, associated with co-exposure to different xenobiotics involved in tobacco cultivation.

Mercury levels assessment and its relationship with oxidative stress biomarkers in children from three localities in Yucatan, Mexico

Mercury (Hg) is a global pollutant that is released into the environment from geologic and anthropogenic sources. Once it enters an organism, it generates several toxicity mechanisms and oxidative stress has been proposed as the main one. Metal susceptibility is greater in children, which is a result of their physiology and behavior. In Yucatan, Mexico, burning of unregulated garbage dumps and household trash, ingestion of top marine predators, and pottery manufacturing are among the conditions that could promote Hg exposure. However, for Yucatan, there are no published studies that report Hg levels and associated oxidative stress status in children. Therefore, this study aimed to assess Hg levels in blood and urine and oxidative stress biomarkers levels in a sample of 107 healthy children from three localities in Yucatan, Mexico, as well as investigate the relationship between these parameters. Hg was detected in 11 (10.28%) of blood samples and 38 (35.51%) of urine samples collected from the participating children. Fourteen subjects showed Hg above recommended levels. The oxidative stress biomarkers were slightly elevated in comparison with other studies and were statistically different between the sampling sites. No linear correlation between Hg levels and oxidative stress biomarkers was found. Nevertheless, exploratory univariate and multivariate analysis showed non-linear relations among the measured variables. Globally, the study provides, for the first time, information regarding Hg levels and their relationship with oxidative stress biomarkers in a juvenile population from Mexico's southeast (Yucatan) region. In agreement with worldwide concern about Hg, this study should stimulate studies on metal monitoring in humans (especially children) among scientists working in Mexico, the establishment of polices for its regulation, and the reduction of human health risks.

Chronic exposure to organophosphate (OP) pesticides and neuropsychological functioning in farm workers: a review

BACKGROUND

Previous studies have demonstrated that acute poisoning from exposure to organophosphate (OP) pesticides in agricultural workers causes adverse health effects. However, neuropsychological and cognitive effects of chronic occupational exposure to OP pesticides remain controversial.

OBJECTIVE

To identify, evaluate, and systematize existing evidence regarding chronic exposure to OP pesticides and neuropsychological effects in farmworkers.

METHODS

Using the PubMed search engine, a systematic review process was implemented and replicated according to the PRISMA statement. Eligibility criteria included workers over 18 years of age exposed to OP pesticides as well as assessment of neuropsychological and cognitive functioning. Search terms were in English and Spanish languages and included organophosphate and workers.

RESULTS

Of the search results, 33 of 1,256 articles meet eligibility criteria. Twenty-four studies found an association between chronic occupational exposure to OP pesticides and low neuropsychological performance in workers. We classified nine of the studies to have study design limitations. Studies indicated occupational exposure to OP pesticides is linked to difficulties in executive functions, psychomotor speed, verbal, memory, attention, processing speed, visual-spatial functioning, and coordination. Nine studies find no relationship between OP pesticides exposure and neuropsychological performance.

CONCLUSIONS

Overall, evidence suggests an association between chronic occupational exposure to OP pesticides and neuropsychological effects. However, there is no consensus about the specific cognitive skills affected.

Associations of maternal organophosphate pesticide exposure and PON1 activity with birth outcomes in SAWASDEE birth cohort, Thailand

Prenatal organophosphate (OP) pesticide exposure has been reported to be associated with adverse birth outcomes and neurodevelopment. However, the mechanisms of toxicity of OP pesticides on human fetal development have not yet been elucidated. Our pilot study birth cohort, the Study of Asian Women and Offspring's Development and Environmental Exposures (SAWASDEE cohort) aimed to evaluate environmental chemical exposures and their relation to birth outcomes and infant neurodevelopment in 52 pregnant farmworkers in Fang district, Chiang Mai province, Thailand. A large array of data was collected multiple times during pregnancy including approximately monthly urine samples for evaluation of pesticide exposure, three blood samples for pesticide-related enzyme measurements and questionnaire data. This study investigated the changes in maternal acetylcholinesterase (AChE) and paraoxonase 1 (PON1) activities and their relation to urinary diakylphosphates (DAPs), class-related metabolites of OP pesticides, during pregnancy. Maternal AChE, butyrylcholinesterase (BChE) and PON1 activities were measured three times during pregnancy and urinary DAP concentrations were measured, on average, 8 times from enrollment during pregnancy until delivery. Among the individuals in the group with low maternal PON1 activity (n=23), newborn head circumference was negatively correlated with log10 maternal ∑DEAP and ∑DAP at enrollment (gestational age=12±3 weeks; β=-1.0 cm, p=0.03 and β=-1.8 cm, p<0.01, respectively) and at 32 weeks pregnancy (β=-1.1cm, p=0.04 and β=-2.6 cm, p=0.01, respectively). Furthermore, among these mothers, newborn birthweight was also negatively associated with log10 maternal ∑DEAP and ∑DAP at enrollment (β=-219.7 g, p=0.05 and β=-371.3g, p=0.02, respectively). Associations between maternal DAP levels and newborn outcomes were not observed in the group of participants with high maternal PON1 activity. Our results support previous findings from US birth cohort studies. This is the first study to report the associations between prenatal OP pesticide exposure and birth outcomes in Thailand.

Recent progress in the genetics and epigenetics of paraoxonase: why it is relevant to children's environmental health

PURPOSE OF REVIEW

Children are more susceptible to exposures in utero and during early childhood that may result in developmental problems and chronic diseases. Novel discoveries in the field of molecular epidemiology that can help explain susceptibility to exposures and disease will be demonstrated using the multifunctional enzyme paraoxonase 1 (PON1) as an example.

RECENT FINDINGS

The broad PON1 variability in humans, partly due to differences in genetics and age, can confer differential susceptibility because this enzyme can detoxify organophosphate pesticides and has antioxidant properties. Epigenetics plays a significant role in the mediation of the effects of environmental exposure on human health and is hypothesized to be a major contributing factor to the early-life origins of adult disease. Studies highlighted in this review demonstrate the relationship of PON1 polymorphisms with microRNA binding in addition to a link between DNA methylation in the transcriptional regulatory region with changes in PON1 enzyme levels. Other important methodologies such as ancestry informative markers and lactonase activity can enhance studies involving PON1.

SUMMARY

This PON1 model demonstrates that integrating genetic and epigenetic factors, as well as other novel methodologies, can improve our understanding of important susceptibility factors linked to pediatric disease.

Variability in the take-home pathway: farmworkers and non-farmworkers and their children

Organophosphate pesticides (OPs) are related to ill health among adults, including farmworkers who are exposed to OPs as part of their regular work. Children of both farmworkers and non-farmworkers in agricultural communities may also be affected by pesticide exposure. Study groups of 100 farmworkers with a referent child (aged 2-6 years) and 100 non-farmworkers with a referent child were recruited to participate in three data collection periods over the course of a year. At each collection, participants provided three urine samples within 5 days, and homes and vehicles were vacuumed to collect pesticide residues in dust. In thinning and harvest seasons, farmworkers and their children had higher dimethyl urinary metabolites than non-farmworkers and their children. During the non-spray season, the urinary metabolites levels decreased among farmworkers to a level comparable to that of non-farmworkers. Farmworkers consistently had higher pesticide residues in their home and vehicle dust. Differences exist between farmworkers and non-farmworkers in urinary metabolites, and the differences extended throughout the agricultural seasons.OP metabolites are seen at much higher levels for farmworkers and their children than for non-farmworkers and their children during agricultural seasons when OPs are in use. These metabolite levels were significantly higher than the nationwide NHANES IV survey and up to 10-fold higher than other rural agricultural studies.

Neurodevelopmental effects in children associated with exposure to organophosphate pesticides: a systematic review

Many studies have investigated the neurodevelopmental effects of prenatal and early childhood exposures to organophosphate (OP) pesticides among children, but they have not been collectively evaluated. The aim of the present article is to synthesize reported evidence over the last decade on OP exposure and neurodevelopmental effects in children. The Data Sources were PubMed, Web of Science, EBSCO, SciVerse Scopus, SpringerLink, SciELO and DOAJ. The eligibility criteria considered were studies assessing exposure to OP pesticides and neurodevelopmental effects in children from birth to 18 years of age, published between 2002 and 2012 in English or Spanish. Twenty-seven articles met the eligibility criteria. Studies were rated for evidential consideration as high, intermediate, or low based upon the study design, number of participants, exposure measurement, and neurodevelopmental measures. All but one of the 27 studies evaluated showed some negative effects of pesticides on neurobehavioral development. A positive dose-response relationship between OP exposure and neurodevelopmental outcomes was found in all but one of the 12 studies that assessed dose-response. In the ten longitudinal studies that assessed prenatal exposure to OPs, cognitive deficits (related to working memory) were found in children at age 7 years, behavioral deficits (related to attention) seen mainly in toddlers, and motor deficits (abnormal reflexes) seen mainly in neonates. No meta-analysis was possible due to different measurements of exposure assessment and outcomes. Eleven studies (all longitudinal) were rated high, 14 studies were rated intermediate, and two studies were rated low. Evidence of neurological deficits associated with exposure to OP pesticides in children is growing. The studies reviewed collectively support the hypothesis that exposure to OP pesticides induces neurotoxic effects. Further research is needed to understand effects associated with exposure in critical windows of development.