Erythrocyte acetylcholinesterase as biomarker of pesticide exposure: new and forgotten insights

Chronic exposures to cholinesterase-inhibiting pesticides adversely affects the health of agricultural workers in India

Biomonitoring of pesticide exposure has become a public concern because of its potential health effects. The present study investigated the acetylcholinesterase (AChE) inhibitory levels and their associated health effects in agricultural areas in Telangana, India. This cross-sectional included 341 exposed participants and 152 control participants from agricultural areas. A structured questionnaire was completed and blood and urine samples were collected to measure pesticides, dialkyle phosphate (DAP) metabolites, and AChE activity using liquid chromatography-tandem mass spectrometry and reversed-phase high-performance liquid chromatography. twenty-eight pesticides were detected in blood samples at concentrations ranging 0.42-45.77 ng/mL. Six DAP metabolites were also measured in urine, and all DAP metabolites were significantly higher in the exposed group. AChE activity is significantly reduced in individuals exposed for >10 years, raising concerns regarding possible neurological disorders. These results emphasise the urgent need to investigate the health effects of pesticides exposure, especially in agriculture.

Organic contamination and multi-biomarker assessment in watersheds of the southern Brazil: an integrated approach using fish from the Astyanax genus

We aimed to examine the responses of pollution biomarkers in feral fish from Astyanax genus collected at three hydrographic regions in southern Brazil and the capacity of these tools to differentiate between various levels of contamination. To achieve this, levels of organochlorine pesticides (liver), as well as the biomarkers AChE (muscle and brain), TBARS (liver), and EROD (liver) were assessed. Collections were conducted in four municipalities (Alegrete, Caraá, Lavras, and Santa Vitória) during 1 year, encompassing winter and summer. Fish from Alegrete were the most contaminated overall, but animals sampled in Caraá, and Lavras also displayed elevated levels of current-use pesticides. Elevated levels of endosulfans, DDTs, HCHs, and current-use pesticides were accompanied by elevated levels of TBARS in the liver. Conversely, fish from Santa Vitória exhibited the highest levels of PAHs, accompanied by elevated levels of EROD in the liver and reduced levels of AChE in muscle and brain. TBARS proved to be a reliable biomarker for assessing impacts arising from pesticide accumulation, while EROD and AChE served as valuable indicators of impacts resulting from PAHs accumulation. Ultimately, the results obtained in this study demonstrate the reliable use of the proposed biomarkers for tracking biological impacts stemming from aquatic pollution using feral Astyanax as biomonitoring species.

Emerging significance of butyrylcholinesterase

Butyrylcholinesterase (BChE; EC 3.1.1.8), an enzyme structurally related to acetylcholinesterase, is widely distributed in the human body. It plays a role in the detoxification of chemicals such as succinylcholine, a muscle relaxant used in anesthetic practice. BChE is well-known due to variant forms of the enzyme with little or no hydrolytic activity which exist in some endogamous communities and result in prolonged apnea following the administration of succinylcholine. Its other functions include the ability to hydrolyze acetylcholine, the cholinergic neurotransmitter in the brain, when its primary hydrolytic enzyme, acetylcholinesterase, is absent. To assess its potential roles, BChE was studied in relation to insulin resistance, type 2 diabetes mellitus, cognition, hepatic disorders, cardiovascular and cerebrovascular diseases, and inflammatory conditions. Individuals who lack the enzyme activity of BChE are otherwise healthy, until they are given drugs hydrolyzed by this enzyme. Therefore, BChE is a candidate for the study of loss-of-function mutations in humans. Studying individuals with variant forms of BChE can provide insights into whether they are protected against metabolic diseases. The potential utility of the enzyme as a biomarker for Alzheimer's disease and the response to its drug treatment can also be assessed.

Biochemical and teratogenic effects of a mixture of pyriproxyfen and glyphosate

The mixture of agrochemicals can be made to improve pest control or accidentally. In this way, the effects on non-target organisms are a critical aspect of the environment and heath. Thus, this work aimed to show how a mixture of pyriproxyfen, and glyphosate can impair biochemical routes and embryonic development. Zebrafish embryos 0-72 hpf were exposed to 0.001-1 μg/mL of pyriproxyfen, glyphosate, and a mixture of both pesticides. The ADMETox was evaluated in silico. The FET-test was used to estimate teratogenic effects. The biochemical effects were estimated using AChE, SOD, and CAT as parameters. ROS generation was estimated using 30 μM H2DCF-DA and 5 μM DHE. The ADMETox reveals that intestinal absorption and P-glycoprotein are the main sites for PPx and Gly adsorption. The distribution parameters were diverse. PPx + Gly at 0.1 μg/mL leads to 50 % of lethality and at 1 μg/mL 100 % of lethality. PPx + Gly leads to a 22 % of lack of somite formation at 1 μg/mL. The heart rate was reduced by >10 % in all concentrations tested. The AChE has a decrease with IC20 19.6 μM and IC50 261.5 μM. SOD showed a reduction of 28 % to PPx and CAT was reduced by 58 % to PPx + Gly and Gly at 1 μg/mL. Glyphosate does not increase unspecific ROS generation. The superoxide generation was 2× higher in the PPx + Gly at 1 μg/mL. Summarily, was observed that the mixture of PPx + Gly potentiated the toxic effects. This finding suggests a possible synergism between the PPx and Gly even at lower concentrations.

Could pesticide exposure be implicated in the high incidence rates of depression, anxiety and suicide in farmers? A systematic review

Pesticide exposure and poisoning may rise the risk of mental health problems and suicidal tendencies. To explore the potential connection between chronic occupational exposure to pesticides and depression, anxiety, and suicide-related outcomes in farmers, a systematic review was performed. Systematic review protocol is available in PROSPERO registration number CRD42022316285. A total of fifty-seven studies met inclusion criteria: twenty-nine on depression or other mental disorders, twelve on suicide (two of them on both depression and suicide), and fourteen on pesticide poisoning or self-poisoning and death. Among the fifty-seven selected studies, eighteen were conducted in Asia, seventeen in North America, fourteen in South America, seven in European Union, one in Africa, and one in Australia/Oceania. Selected studies demonstrated an increased prevalence of depressive disorders in farmworkers exposed to pesticides as well as an increased self-reported prevalence of depression in this population. Moreover, previous pesticide poisoning increased the risk estimates for depression or other mental disorders as compared with chronic pesticide exposure. Severe pesticide poisoning and multiple poisoning showed increased risks of depressive symptoms compared with milder cases. In addition, financial difficulties and poor health were positively correlated with depression. Among studies on suicide, nine of them found that suicide rates increased in areas devoted to agriculture with intensive pesticide consumption. Moreover, studies demonstrate a higher suicide risk among farmers. The present review suggests more attention to the farmer's mental health and more detailed studies on occupational exposure to the mixture of these compounds.

Organophosphorus Poisoning: Acute Respiratory Distress Syndrome (ARDS) and Cardiac Failure as Cause of Death in Hospitalized Patients

Industrial production of food for animals and humans needs increasing amounts of pesticides, especially of organophosphates, which are now easily available worldwide. More than 3 million cases of acute severe poisoning are estimated to occur worldwide every year, and even more cases remain unreported, while 200,000–350,000 incidentally or intentionally poisoned people die every year. Diagnostic and therapeutic procedures in organophosphate poisoning have, however, remained unchanged. In addition to several neurologic symptoms (miosis, fasciculations), hypersecretion of salivary, bronchial, and sweat glands, vomiting, diarrhea, and loss of urine rapidly induce dehydration, hypovolemia, loss of conscience and respiratory distress. Within hours, signs of acidosis due to systemic hypoxia can be observed at first laboratory investigation after hospitalization. While determination of serum-cholinesterase does not have any diagnostic value, it has been established that hypoalbuminemia alone or accompanied by an increase in creatinine, lactate, or C-reactive protein serum levels has negative prognostic value. Increased serum levels of C-reactive protein are a sign of systemic ischemia. Protective mechanical ventilation should be avoided, if possible. In fact, acute respiratory distress syndrome characterized by congestion and increased weight of the lung, accompanied by heart failure, may become the cause of death. As the excess of acetylcholine at the neuronal level can persist for weeks until enough newly, locally synthesized acetylcholinesterase becomes available (the value of oximes in reducing this time is still under debate), after atropine administration, intravenous albumin and fluid infusion should be the first therapeutic interventions to reestablish normal blood volume and normal tissue oxygenation, avoiding death by cardiac arrest.

A meta-analysis of normal human blood cholinesterase activities determined by a modified electrometric method

Measurements of blood cholinesterase (ChE) activities, including those of erythrocytes (EChE), plasma or serum (PChE), and whole blood (WBChE), are used to assess exposure to ChE-inhibiting pesticides. The purpose of this review was to report normal reference ChE activities in the blood of healthy adult humans, as determined by a modified electrometric method. We performed a systematic review following PRISMA guidelines. Single-group meta-analysis of means of PChE, EChE, and WBChE activities of adult healthy subjects was conducted using the random effects model. The programs used were Open-Meta Analyst and Meta-Essentials Version 1.5. Studies selected for analysis comprised 21, 19, and 4 reports of normal reference/baseline PChE, EChE, and WBChE activities in 690, 635, and 121 healthy adult males and/or females, respectively. The meta-analysis showed normal reference values of the means (effect sizes) with 95% CI of PChE, EChE, and WBChE activities of healthy adult subjects, which were 1.078 (1.015, 1.142), 1.075 (1.024, 1.125) and 1.331 (1.226, 1.436), respectively. By the subgroup analysis, heterogeneity (I2>89%) was considerably reduced in females to 4.4% and 30.1% for PChE and EChE, respectively. Funnel plots indicated no publication bias. However, Egger's regression confirmed the symmetry of the data points for PChE and WBChE activities with a significant effect on EChE. This meta-analysis showed normal reference values of PChE, EChE, and WBChE activities, measured by a modified electrometric method, in healthy adult humans.

Silver and copper-oxide nanoparticles prepared with GA3 induced defense in rice plants and caused mortalities to the brown planthopper, Nilaparvata lugens (Stål)

BACKGROUND

Nanoparticles have been employed as nanopesticides for pest control in agriculture. However, the harmful effects of their chemical synthesis on human and environmental health have resulted in increased use of green synthetic approaches, including the use of plant extracts. The brown planthopper, Nilaparvata lugens (Stål) (BPH), is a severe pest of rice plants (Oryza sativa L.), especially in Asia. It is usually controlled chemically but has developed resistance against many insecticides.

RESULTS

In this study, we synthesized metallic silver (Ag-NPs) and copper-oxide (CuO-NPs) nanoparticles using the exogenous phytohormone, gibberellic acid (GA₃), as a reducing agent. We then sprayed them separately on rice plants and BPH together and evaluated their effects on the plants and insects. SEM and TEM images showed that the synthesis was successful, indicated by the sizes (25-60 nm), uniform shape and spherical and cubical structures of Ag-NPs, as well as by the rugby sheet-like of CuO-NPs with lateral sizes of 150-340 nm and thickness of 30-70 nm. Independent applications of the nanoparticles and GA₃ on rice plants induced different volatile profiles, of which the highest number emitted was under Ag-NPs, including the highest emission of linalool. Transcriptome analysis showed that Ag-NPs-treated rice plants showed different transcriptome profiles compared to the control, 24 h after treatment, including the upregulation of the linalool synthase gene, genes of plants transcription factors such as WRKY, bHLH and NAC and other genes involved in plant defense responses. In all treatments, the mortality rate of BPH increased with an increase in NPs concentrations over time but was prominent under Ag-NPs treatment. The LC₅₀ values for Ag-NPs and CuO-NPs decreased with an increase in time. Also, the nanoparticles increased the activities of protective enzymes (POD, SOD and CAT), inhibited that of detoxification enzymes (A-CHE, ACP and AKP), and reduced total protein concentrations in the BPH.

CONCLUSIONS

These results show that synthesizing nanoparticles using phytohormones may be a safer and environmentally friendly option, which also holds promise for controlling the BPH in rice production.

Acetylcholinesterase from the charru mussel Mytella charruana: kinetic characterization, physicochemical properties and potential as in vitro biomarker in environmental monitoring of mollusk extraction areas

Acetylcholinesterase (AChE; EC 3.1.1.7) from aquatic organisms have been used to evaluate the exposure of specimens to pesticides and heavy metals at sublethal levels in environmental samples. AChE of Mytella charruana was extracted to characterize its physicochemical and kinetic properties as well as the effect of organophosphate (dichlorvos, diazinon, chlorpyrifos, methyl-parathion and temephos), carbamates (carbaryl, carbofuran and aldicarb), benzoylureas (diflubenzuron and novaluron), pyrethroid (cypermethrin) and juvenile hormone analog - JHA (pyriproxyfen) and the effect of metal ions: Hg²⁺, Cd²⁺, Pb²⁺, As³⁺, Cu²⁺ and Zn²⁺, in order to evaluate the potential of the enzyme as biomarker. The optimum pH of M. charruana AChE was 8.5 and the maximum activity peak occurred at 48 °C, being highly thermostable maintaining 97.8% of its activity after incubation at 60 °C. The Michaelis-Menten constants (k_m) for the substrates acetylthiocholine and propionylthiocholine were 2.8 ± 1.26 and 4.94 ± 6.9 mmol·L^-1, respectively. The V_max values for the same substrates were 22.6 ± 0.90 and 10.2 ± 4.94 mU·mg^-1, respectively. Specific inhibition results suggest an AChE presenting active site with dimensions between those of AChE and butyrylcholinesterase (BChE). The IC₂₀ values related to the effect of the pesticides on the enzyme showed higher inhibitory power of temephos (0.17 μmol·L^-1), followed by aldicarb (0.19 μmol·L^-1) and diflubenzuron (0.23 μmol·L^-1). Metal ions inhibited M. charruana enzyme in the following order: Hg²⁺ > Pb²⁺ > Cd²⁺ > As³⁺ > Cu²⁺ > Zn²⁺. These data suggest that the enzyme showed potential as in vitro biomarker of the exposure to temephos, mercury, zinc and copper.

Dip-and-Fold Device: A Paper-Based Testing Platform for Rapid Assessment of Insecticides in Water Samples

The contamination of water and food in agricultural areas, where an enormous volume of pesticides is widely employed to enhance crop production, is a challenging reality. The rapid assessment of these contaminants is fundamental to assure water and food quality and safety, particularly for local community members. This work presents a nonexpensive and easy-operational paper-based testing device for the fast detection of insecticides (carbamates and organophosphates) in water samples. The structural design "dip-and-fold" allows us to carry out the analysis without introducing reagents or samples. The device is prepared using different high-quality papers to support the active acetylcholinesterase (AChE) and the customized chemical formulation for colorimetric detection. The chemical principle is based on the AChE inhibition reaction and Ellman's method. The experiments using standard solutions of carbofuran, propoxur, and chlorpyriphos indicated satisfactory detection at concentrations between 0.1 and 0.0001 mM, and the color results are revealed within 10 min. Therefore, this technique represents a promising alternative for implementing low-cost and efficient water monitoring and management solutions.

Modulatory effect of opioid administration on the activity of cholinesterase enzyme: a systematic review of mice/rat models

We aimed to review the literature to find the specific effect of opioids on the activity of cholinesterase (ChE) enzyme which plays a substantial role in the functioning of cholinergic system. Literature search was performed by two independent reviewers in order to find relevant articles about the changes in the activity of ChE in mice or rat following opioid administration. Based on findings from literature review, opioid administration is able to induce cholinergic modulation via decreasing or increasing the activity of ChE enzyme. However, the degree of variation of ChE in various brain regions is different. No gender differences was reported in the effect of opioids on ChE activity. Although chronic opioid administration may decrease enzyme function, ChE activity might be unchanged following opioid withdrawal using naloxone or the development of tolerance. Opioid type affects whether or not naloxone can reverse the changes of ChE. Direct inhibitory action of morphine and the other opioid ligands believed responsible for the decrease in the ChE activity. Moreover, the potency of codeine to induce allosteric enhancement of acetylcholine receptor signaling might be involved in the cholinergic modulation of codeine and other opioids. Animal studies on rat and mice showed that opioids may change the activity of ChE. These changes can pertain an increase or decrease in enzyme activity; as there might be no change. The type of opioid used may have an effect on the cholinergic modulation. It is beneficial to conduct cross-sectional and cohort studies on addicted individuals, especially opium abusers, to find the precise association of opioids with alterations in human acetyl cholinesterase or butyrylcholinesterase. Simulation studies can also examine the structure-function relationships and provide important details to better understand the mechanism of action of opioid compounds on ChE activity. In addition, understanding how opioids impact ChE activity may help perform proper interventions for drug abstinence.

Plasma cholinesterase activity is influenced by interactive effect between omethoate exposure and CYP2E1 polymorphisms

The aim of this study was to explore the association between metabolizing enzyme gene polymorphisms and the decrease in cholinesterase activity induced by omethoate exposure. A total of 180 workers exposed to omethoate over an extended period were recruited along with 115 healthy controls. Cholinesterase activity in whole blood, erythrocyte, and plasma was detected using acetylthiocholine and the dithio-bis-(nitrobenzoic acid) method. Six polymorphic loci of GSTT1(+/-), GSTM1(+/-), GSTP1 rs1695, CYP2E1 rs6413432, CYP2E1 rs3813867, and PON2 rs12026 were detected by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP). The gene-environment interactions were analyzed using the generalized linear model method. The cholinesterase activity of erythrocyte and plasma in the exposure group was significantly lower than that in the control group (P < 0.001) in general. The plasma cholinesterase activity in the TT + AT genotype in CYP2E1 rs6413432 was lower than that in the AA genotype in the exposure group (P = 0.016). Interaction between the AA genotype in CYP2E1 rs6413432 and omethoate exposure had a significant effect on plasma cholinesterase activity (P = 0.079). The decrease in plasma cholinesterase activity was associated with interaction between the AA genotypes in rs6413432 and omethoate exposure.

Effects of pyriproxyfen on zebrafish brain mitochondria and acetylcholinesterase

Pyriproxyfen is an insecticide used worldwide that acts as a biomimetic of juvenile hormone. This study investigated metabolic and synaptic impairments triggered by pyriproxyfen using zebrafish acetylcholinesterase (zbAChE) and mitochondria as markers. A brain zbAChE assay was performed in vitro and in vivo covering a range of pyriproxyfen concentrations (0.001-10 μmol/L) to assess inhibition kinetics. Docking simulations were performed to characterize inhibitory interactions. Zebrafish male adults were acutely exposed to 0.001, 0.01 and 0.1 μg/mL pyriproxyfen for 16 h. Mitochondrial respiration of brain tissues was assessed. ROS generation was estimated using H₂DCF-DA and MitoSOX. Calcium transport was monitored by Calcium Green™ 5 N. NO synthesis activity was estimated using DAF-FM-DA. Brain acetylcholinesterase showed an in vivo IC₂₀ of 0.30 μmol/L pyriproxyfen, and an IC₅₀ of 92.5 μmol/L. The inhibitory effect on zbAChE activity was competitive-like. Respiratory control of Complex I/II decreased significantly after insecticide exposure. The MitoSOX test showed that O₂^- generation had a pyriproxyfen dose-dependent effect. Brain tissue lost 50% of Ca²⁺ uptake capacity at 0.1 μg/mL pyriproxyfen. Ca²⁺ release showed a clear mitochondrial impairment at lower pyriproxyfen exposures. Thus, Ca²⁺ transport imbalance caused by pyriproxyfen may be a novel deleterious mechanism of action. Overall, the results showed that pyriproxyfen can compromise multiple and interconnected pathways: (1) zbAChE impairment and (2) the functioning of the electron transport chain, ROS generation and calcium homeostasis in zebrafish brain mitochondria. Considering the many similarities between zebrafish and human, more caution is needed when pyriproxyfen is used in both urban and agricultural pest control.

High level of methylmercury exposure causes persisted toxicity in Nauphoeta cinerea

Methylmercury (MeHg⁺) is a neurotoxicant abundantly present in the environment. The long-term effects of MeHg⁺ have been investigated in rodents, yet data on the long-term or persisted toxicity of MeHg⁺ in invertebrates is scanty. Here, we examined the acute, intermediate, and chronic effects upon dietary administration of MeHg⁺ in nymphs of Nauphoeta cinerea. Besides, the potential reversibility of the toxic effects of MeHg⁺ after a detoxification period was evaluated. Nymphs were exposed to diets containing 0 (control), 2.5, 25, and 100 μg MeHg⁺/g of diet for 10, 30, and 90 days. Additional groups of nymphs were fed with the same dose of MeHg⁺ for 30 days and then were subjected to a detoxification period for 60 days. The nymphs exposed to 100 μg MeHg⁺/g succumbed to a high mortality rate, along with multiple biochemical (increase of reactive oxygen species production and glutathione S-transferase activity, as well as decrease in the acetylcholinesterase activity) and behavioral alterations. We observed delayed mortality rate and behavioral alterations in nymphs exposed to 100 μg MeHg⁺/g for 30 days and subsequently subjected to 60 days of detoxification. However, the biochemical alterations did not persist throughout the detoxification period. In conclusion, our results established the persistent toxic effect of MeHg⁺ even after a prolonged detoxification period and evidenced the use of N. cinerea as an alternative model to study the toxicity of MeHg⁺.

The acetylcholinesterase (AChE) inhibitor and anti-Alzheimer drug donepezil interacts with human erythrocytes

Donepezil is used to treat symptomatically the Alzheimer's disease (AD). This drug is a specific inhibitor of the enzyme acetylcholinesterase (AChE), whose main physiological function is to hydrolyze the neurotransmitter acetylcholine. The main objective of this work was to study the effect of donepezil on human erythrocytes as AChE is present in its membrane. For this purpose, human erythrocytes and molecular model of its membrane built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were used. The latter correspond to classes of phospholipids present in the outer and inner monolayers of the human erythrocyte membrane, respectively. Our experimental evidences obtained from X-ray diffraction and differential scanning calorimetry (DSC) analysis indicated that donepezil was capable of interacting with both phospholipids. Fluorescence spectroscopy results showed a moderate increase in the fluidity of the hydrophobic tails of DMPC and isolated unsealed human erythrocyte membranes (IUM). On the other hand, results by scanning electron microscopy (SEM) and optical defocusing microscopy (DM) showed that the drug changed the normal biconcave shape of the erythrocytes inducing the formation of stomatocytes (cup-shaped cells). This effect was explained by the incorporation of donepezil molecules into the erythrocyte membrane and interactions with AChE.

Characterization of brain acetylcholinesterase of bentonic fish Hoplosternum littorale: Perspectives of application in pesticides and metal ions biomonitoring

Acetylcholinesterase (AChE; EC 3.1.1.7) is a serine hydrolase, whose main function is to modulate neurotransmission at cholinergic synapses. It is, therefore, the primary target of some pesticides and heavy metals. Its inhibition in aquatic organisms has been used as an indicator of the presence of these pollutants in water bodies. The present study aimed to characterize physicochemical and kinetic parameters of brain AChE in the benthic fish Hoplosternum littorale and to analyze the in vitro effects of pesticides (dichlorvos, diazinon, chlorpyrifos, parathion-methyl, temephos, carbaryl, carbofuran, aldicarb, diflubenzuron, novaluron and pyriproxyfen) and metal ions (As³⁺, Cd²⁺, Cu²⁺, Fe²⁺, Mn²⁺, Mg²⁺, K⁺, Pb²⁺, Hg²⁺, Zn²⁺) investigating the potential of this enzyme as environmental biomarker based on current regulations. Specific substrates and inhibitors have indicated AChE to be the predominant cholinesterase (ChE) in the brain of H. littorale. Peak activity was observed at pH 8.0 and 30 °C. The enzymatic activity is otherwise moderately thermostable (≈ 50% activity at 45 °C). The enzyme can reduce the activation energy of acetylthiocholine hydrolysis reaction to 8.34 kcal mol^-1 while reaching a rate enhancement of 10⁶. Among the pesticides under study, dichlorvos presented an IC₅₀ value below the maximum concentrations allowed by legislation. This study presents the first report on the inhibition of brain AChE activity from Siluriformes by the pesticides novaluron and pyriproxyfen. Mercury ion also exerted a strong inhibitory effect on its enzymatic activity. The H. littorale enzyme thus has the potential to function as an in vitro biomarker for the presence of the pesticide dichlorvos as well as mercury in areas of mining and industrial discharge.

Paraoxonase-1 genetic polymorphisms in organophosphate metabolism

Organophosphates (OPs) are a class of chemicals commonly used in agriculture as pesticides, that can often lead to severe toxicity in humans. Paraoxonase-1 (PON1) belongs to a family of A-esterases and hydrolyses several OPs while also serving other biological roles. Two main genetic polymorphisms have been shown to affect enzymatic ability; an A > G transition in the 192nd position (192 Q/R, rs662), and an A > T at codon 55 (55 M/L, rs854560). In this review, we searched PubMed for relevant articles published from its inception till June 2018 and included publications from 1996 to 2018. We aimed to address the distribution of the polymorphisms in various populations, the way they affect enzymatic activity and the possible use of PON1 as a biomarker. The polymorphisms present great heterogeneity between populations, with the data being clearer over 192 Q/R, and this heterogeneity is related to the phylogenetic origins of each population. Concerning enzymatic activity, the different genotypes react better or worse to different OP substrates, with studies presenting a variety of findings. Detecting the "paraoxonase status" of an individual -referring to PON1 function- seems to be important in predicting OP toxicity, as studies have shown that some specific-genotype individuals present symptoms of toxicity in higher rates than others. We are strongly convinced that in order for the scientific community to reach a consensus over which polymorphisms confer susceptibility to toxicity and whether PON1 can eventually be used as a biomarker, more studies need to be carried out, since the data thus far does not seem to reach a universal conclusion.