Further evidence for an association of the paraoxonase 1 (PON1) Met-54 allele with Parkinson's disease

Role of PON1 L55M Gene Polymorphism in Parkinson's Disease among North Indian Population

BACKGROUND AND OBJECTIVES

The role of various genetic markers including alpha synuclein, Parkin, etc., is known in the pathogenesis of Parkinson's disease (PD). Novel genetic markers including paraoxonase 1 (PON1) have also been linked to PD pathogenesis in recent studies. The PON1 L55M allele carriers may have defective clearance of environmental toxins and may result in increased susceptibility to PD. Hence, we studied the role of PON1 L55M polymorphism in PD among a North Indian population.

MATERIALS AND METHOD

Seventy-four PD patients and 74 age- and sex-matched controls were recruited in this hospital-based case-control study. Baseline characteristics were recorded using structured questionnaire. DNA was extracted from 3-4 ml of venous blood, followed by PCR and restriction digestion. PON1 L55M genotypes were visualized as bands: LL (177 bp), LM (177, 140 bp) and MM (140,44 bp) on 3% agarose gel. Mann-Whitney U test and Chi-squared test were used for comparing two groups of skewed and categorical variables, respectively. Measures of strength of association were calculated by binary regression analysis. P value < 0.05 was considered as significant.

RESULTS

Parkinson's disease patients had significantly higher exposure to pesticides (12.2%; P (organophosphate exposure) < 0.001) and well water drinking (28.4%; P = 0.006) compared to controls. Frequency distribution of LL, LM, MM genotypes was 67.5% (50/74), 28.4% (21/74), and 4.1% (3/74), respectively, for cases and 72.6% (54/74), 26% (19/74) and 1.4% (1/74), respectively, for controls. PON1 L55M genotype distribution between Parkinson's disease cases and controls was not significant (P = 0.53). PON1 L55M polymorphism was not associated with PD after adjusting for confounders by binary regression analysis.

CONCLUSION

There was no significant association between PON1 L55M polymorphism and PD. Larger population-based studies would be required from India before drawing any definite conclusions.

Involvement of antioxidant enzymes in Parkinson's disease

Similar to many other diseases, the etiology of Parkinson's disease (PD) is multifactorial and includes both genetic and environmental factors. Exposure to pesticides and the production of reactive oxygen species (ROS) in the body, mainly in electron transporter complexes 1 and 2 in the inner mitochondrial membrane, are two primary environmental risk factors for this disease. Increased accumulation of ROS and oxidative stress (OS) trigger a series of reactions that can lead to the aggregation of misfolded proteins, DNA damage, autophagy, and apoptosis, which may adversely affect cell function. These processes cause diseases such as coronary artery disease (CAD), Alzheimer's disease (AD), and PD. As indicated in previous studies, ROS is considered a critical regulator in the progression of PD. The human body contains several antioxidant molecules, such as vitamin A, vitamin C, bilirubin, and uric acid, as well as antioxidant enzymes including paraoxonase (PON), glutathione reductase (GR), glutathione peroxidase (GPx), catalase (CAT), and superoxide dismutase (SOD). Therefore, based on the canonical function of the antioxidant enzymes in PD, In the present review, we attempted to examine the function of antioxidant enzymes in PD.

Paraoxonases at the Heart of Neurological Disorders

Paraoxonase enzymes serve as an important physiological redox system that participates in the protection against cellular injury caused by oxidative stress. The PON enzymes family consists of three members (PON-1, PON-2, and PON-3) that share a similar structure and location as a cluster on human chromosome 7. These enzymes exhibit anti-inflammatory and antioxidant properties with well-described roles in preventing cardiovascular disease. Perturbations in PON enzyme levels and their activity have also been linked with the development and progression of many neurological disorders and neurodegenerative diseases. The current review summarizes the available evidence on the role of PONs in these diseases and their ability to modify risk factors for neurological disorders. We present the current findings on the role of PONs in Alzheimer's disease, Parkinson's disease, and other neurodegenerative and neurological diseases.

Investigation of Paraoxonase-1 Genotype and Enzyme-Kinetic Parameters in the Context of Cognitive Impairment in Parkinson's Disease

Cognitive impairment is a common non-motor symptom of Parkinson's disease (PD), which often progresses to PD dementia. PD patients with and without dementia may differ in certain biochemical parameters, which could thus be used as biomarkers for PD dementia. The enzyme paraoxonase 1 (PON1) has previously been investigated as a potential biomarker in the context of other types of dementia. In a cohort of PD patients, we compared a group of 89 patients with cognitive impairment with a group of 118 patients with normal cognition. We determined the kinetic parameters K_m and V_max for PON1 for the reaction with dihydrocoumarin and the genotype of four single nucleotide polymorphisms in PON1. We found that no genotype or kinetic parameter correlated significantly with cognitive impairment in PD patients. However, we observed associations between PON1 rs662 and PON1 K_m (p < 10^-10), between PON1 rs662 and PON1 V_max (p = 9.33 × 10^-7), and between PON1 rs705379 and PON1 V_max (p = 2.21 × 10^-10). The present study is novel in three main aspects. (1) It is the first study to investigate associations between the PON1 genotype and enzyme kinetics in a large number of subjects. (2) It is the first study to report kinetic parameters of PON1 in a large number of subjects and to use time-concentration progress curves instead of initial velocities to determine K_m and V_max in a clinical context. (3) It is also the first study to calculate enzyme-kinetic parameters in a clinical context with a new algorithm for data point removal from progress curves, dubbed iFIT. Although our results suggest that in the context of PD, there is no clinically useful correlation between cognitive status on the one hand and PON1 genetic and enzyme-kinetic parameters on the other hand, this should not discourage future investigation into PON1's potential associations with other types of dementia.

Quantitative and causal analysis for inflammatory genes and the risk of Parkinson's disease

Background

The dysfunction of immune system and inflammation contribute to the Parkinson's disease (PD) pathogenesis. Cytokines, oxidative stress, neurotoxin and metabolism associated enzymes participate in neuroinflammation in PD and the genes involved in them have been reported to be associated with the risk of PD. In our study, we performed a quantitative and causal analysis of the relationship between inflammatory genes and PD risk.

Methods

Standard process was performed for quantitative analysis. Allele model (AM) was used as primary outcome analysis and dominant model (DM) and recessive model (RM) were applied to do the secondary analysis. Then, for those genes significantly associated with the risk of PD, we used the published GWAS summary statistics for Mendelian Randomization (MR) to test the causal analysis between them.

Results

We included 36 variants in 18 genes for final pooled analysis. As a result, IL-6 rs1800795, TNF-α rs1799964, PON1 rs854560, CYP2D6 rs3892097, HLA-DRB rs660895, BST1 rs11931532, CCDC62 rs12817488 polymorphisms were associated with the risk of PD statistically with the ORs ranged from 0.66 to 3.19 while variants in IL-1α, IL-1β, IL-10, MnSOD, NFE2L2, CYP2E1, NOS1, NAT2, ABCB1, HFE and MTHFR were not related to the risk of PD. Besides, we observed that increasing ADP-ribosyl cyclase (coded by BST1) had causal effect on higher PD risk (OR[95%CI] =1.16[1.10-1.22]) while PON1(coded by PON1) shown probably protective effect on PD risk (OR[95%CI] =0.81[0.66-0.99]).

Conclusion

Several polymorphisms from inflammatory genes of IL-6, TNF-α, PON1, CYP2D6, HLA-DRB, BST1, CCDC62 were statistically associated with the susceptibility of PD, and with evidence of causal relationships for ADP-ribosyl cyclase and PON1 on PD risk, which may help understand the mechanisms and pathways underlying PD pathogenesis.

Pon1 Deficiency Promotes Trem2 Pathway-Mediated Microglial Phagocytosis and Inhibits Pro-inflammatory Cytokines Release In Vitro and In Vivo

Paraoxonase 1 (PON1) plays an anti-inflammatory role in the cardiovascular system. Levels of serum PON1 and polymorphisms in this gene were linked to Alzheimer's disease (AD) and Parkinson disease (PD), but its function in the neuroimmune system and AD is not clear. To address this issue, we used Pon1 knockout rats previously generated by our lab to investigate the role of Pon1 in microglia. Knockout of Pon1 in rat brain tissues protected against LPS-induced microglia activation. Pon1 deficiency in rat primary microglia increased Trem2 (triggering receptor expressed in myeloid cells 2) expression, phagocytosis, and IL-10 (M2-phenotype marker) release, but decreased production of pro-inflammatory cytokines such as IL-1β, IL-6, and IL-18 especially TNF-α (M1-phenotype markers) induced by LPS. Pon1 deficiency in rat primary microglia activated Trem2 pathway but decreased LPS-induced ERK activation. The phagocytosis-promoting effect of Pon1 knockout could be reversed by administration of recombinant PON1 protein. The interaction between PON1 and TREM2 was verified by co-immunoprecipitation (co-IP) using rat brain tissues or over-expressed BV2 cell lysates, which might be involved in lysosomal localization of TREM2. Furthermore, Pon1 knockout also enhanced microglial phagocytosis and clearance of exogenous Aβ by an intrahippocampal injection and decrease the transcription of cytokines such as IL-1β, IL-6, and TNF-α in vivo. These results suggest that Pon1 knockout facilitates microglial phagocytosis and inhibits the production of proinflammatory cytokines both in vivo and in vitro, in which the interaction between Pon1 and Trem2 may be involved. These findings provide novel insights into the role of PON1 in neuroinflammation and highlight TREM2 as a potential target for Alzheimer's disease therapy.

HDL Accessory Proteins in Parkinson’s Disease—Focusing on Clusterin (Apolipoprotein J) in Regard to Its Involvement in Pathology and Diagnostics—A Review

Parkinson’s disease (PD)—a neurodegenerative disorder (NDD) characterized by progressive destruction of dopaminergic neurons within the substantia nigra of the brain—is associated with the formation of Lewy bodies containing mainly α-synuclein. HDL-related proteins such as paraoxonase 1 and apolipoproteins A1, E, D, and J are implicated in NDDs, including PD. Apolipoprotein J (ApoJ, clusterin) is a ubiquitous, multifunctional protein; besides its engagement in lipid transport, it modulates a variety of other processes such as immune system functionality and cellular death signaling. Furthermore, being an extracellular chaperone, ApoJ interacts with proteins associated with NDD pathogenesis (amyloid β, tau, and α-synuclein), thus modulating their properties. In this review, the association of clusterin with PD is delineated, with respect to its putative involvement in the pathological mechanism and its application in PD prognosis/diagnosis.

Human Paraoxonase-2 (PON2): Protein Functions and Modulation

PON1, PON2, and PON3 belong to a family of lactone hydrolyzing enzymes endowed with various substrate specificities. Among PONs, PON2 shows the highest hydrolytic activity toward many acyl-homoserine lactones (acyl-HL) involved in bacterial quorum-sensing signaling. Accordingly, defense against pathogens, such as Brevundimonas aeruginosa (B. aeruginosa), was postulated to be the principal function of PON2. However, recent findings have highlighted the importance of PON2 in oxidative stress control, inhibition of apoptosis, and the progression of various types of malignancies. This review focuses on all of these aspects of PON2.

Paraoxonase Role in Human Neurodegenerative Diseases

The human body has biological redox systems capable of preventing or mitigating the damage caused by increased oxidative stress throughout life. One of them are the paraoxonase (PON) enzymes. The PONs genetic cluster is made up of three members (PON1, PON2, PON3) that share a structural homology, located adjacent to chromosome seven. The most studied enzyme is PON1, which is associated with high density lipoprotein (HDL), having paraoxonase, arylesterase and lactonase activities. Due to these characteristics, the enzyme PON1 has been associated with the development of neurodegenerative diseases. Here we update the knowledge about the association of PON enzymes and their polymorphisms and the development of multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and Parkinson's disease (PD).

An Enriched Environment Ameliorates Oxidative Stress and Olfactory Dysfunction in Parkinson's Disease with α-Synucleinopathy

Parkinson’s disease (PD) features nonmotor symptoms such as olfactory dysfunction referred to as hyposmia, an initial sign of disease progression. Metabolic dysfunction can contribute to neurodegenerative diseases, and various xenobiotics and endogenous compounds are also involved in the pathogenesis of PD. Although aerobic exercise was found to induce preservation or improvement in olfactory function in PD patients in a recent study, the exact underlying mechanism for this effect is not clear. We aimed to investigate the influence of an enriched environment (EE) on olfactory dysfunction especially via metabolic pathways related to detoxification enzymes. Eight-month-old transgenic (Tg) PD mice that overexpress human A53T α-synuclein (α-syn) were randomly allocated to an EE or standard conditions for 2 mo. The buried food test showed that EE group had significantly improved olfactory function compared to the control group. Reverse transcription polymerase chain reaction (PCR) and real-time quantitative PCR showed that expression of the detoxification enzymes––cytochrome P450 family 1 subfamily A member 2, paraoxonase 1, alcohol dehydrogenase 1, UDP glucuronosyltransferase family 2 member A1 complex locus, aldehyde oxidase homolog 2, and aldehyde glutathione peroxidase 6––was significantly increased in the olfactory bulb (OB) of the PD control group, but these enzymes were normalized in the EE group. Immunohistochemical staining of the OB showed that oxidative stress and nitrated α-syn were significantly increased in the control group but decreased in the EE group. In conclusion, we suggest that exposure to an EE decreases both oxidative stress and nitrated α-syn, resulting in normalized detoxification enzymes and amelioration of olfactory dysfunction.

Environmental Exposures and Parkinson's Disease

Parkinson’s disease (PD) affects millions around the world. The Braak hypothesis proposes that in PD a pathologic agent may penetrate the nervous system via the olfactory bulb, gut, or both and spreads throughout the nervous system. The agent is unknown, but several environmental exposures have been associated with PD. Here, we summarize and examine the evidence for such environmental exposures. We completed a comprehensive review of human epidemiologic studies of pesticides, selected industrial compounds, and metals and their association with PD in PubMed and Google Scholar until April 2016. Most studies show that rotenone and paraquat are linked to increased PD risk and PD-like neuropathology. Organochlorines have also been linked to PD in human and laboratory studies. Organophosphates and pyrethroids have limited but suggestive human and animal data linked to PD. Iron has been found to be elevated in PD brain tissue but the pathophysiological link is unclear. PD due to manganese has not been demonstrated, though a parkinsonian syndrome associated with manganese is well-documented. Overall, the evidence linking paraquat, rotenone, and organochlorines with PD appears strong; however, organophosphates, pyrethroids, and polychlorinated biphenyls require further study. The studies related to metals do not support an association with PD.

Total oxidative stress, paraoxonase and arylesterase levels at patients with pseudoexfoliation syndrome and pseudoexfoliative glaucoma

AIM

To investigate the oxidative stress status of the aqueous humor and serum of patients with pseudoexfoliation (PEX) syndrome and pseudoexfoliative glaucoma (PEG) and to measure paraoxonase (PON) and arylesterase (ARE) levels.

METHODS

A total of 78 patients were enrolled in the study, with 26 patients in each separate group. The patients were divided into three groups: the first group entailed PEX syndrome patients, while the second group consisted of patients with PEG and the third group involved patients with no additional systemic diseases, other than the diagnosis of cataract as control. Total oxidative stress (TOS), total antioxidant capacity (TAC), PON, and ARE levels in aqueous humor and serum were measured.

RESULTS

TAC, PON and arylesterase levels in aqueous humor and serum of the PEX syndrome and PEG patients were significantly decreased compared with control group (P<0.05). TOS values were higher in patients with PEX syndrome and PEG than controls (P<0.05). TAC, PON and ARE levels of aqueous humor did not differ significantly between the PEX syndrome and PEG groups.

CONCLUSION

These findings are potentially of significance and add to the growing body of evidence for oxidative stress in PEX syndrome and PEG. Decreased antioxidant defense and increased oxidative stress system may play an important role in the pathogenesis of PEX syndrome and PEG.

DJ-1 interacts with and regulates paraoxonase-2, an enzyme critical for neuronal survival in response to oxidative stress

Loss-of-function mutations in DJ-1 (PARK7) gene account for about 1% of all familial Parkinson's disease (PD). While its physiological function(s) are not completely clear, DJ-1 protects neurons against oxidative stress in both in vitro and in vivo models of PD. The molecular mechanism(s) through which DJ-1 alleviates oxidative stress-mediated damage remains elusive. In this study, we identified Paraoxonase-2 (PON2) as an interacting target of DJ-1. PON2 activity is elevated in response to oxidative stress and DJ-1 is crucial for this response. Importantly, we showed that PON2 deficiency hypersensitizes neurons to oxidative stress induced by MPP⁺ (1-methyl-4-phenylpyridinium). Conversely, over-expression of PON2 protects neurons in this death paradigm. Interestingly, PON2 effectively rescues DJ-1 deficiency-mediated hypersensitivity to oxidative stress. Taken together, our data suggest a model by which DJ-1 exerts its antioxidant activities, at least partly through regulation of PON2.

Shared mechanisms of neurodegeneration in Alzheimer's disease and Parkinson's disease

Alzheimer's disease (AD) and Parkinson's disease (PD) have markedly different clinical and pathological features, but these two diseases are the most common neurodegenerative disorders. Previous studies have showed that there are common mechanisms in AD and PD. Several genetic studies have revealed mutations in genes associated with the risk of AD and PD. Circumstantial evidences have shown that dysregulation of brain iron homeostasis leads to abnormal iron accumulation and results in AD as well as PD. α-Synuclein and tau take part in the mechanisms of these diseases by oxidative stress and mitochondrial dysfunction. Some studies indicated that the loss of LC noradrenergic neurons may occur early in the progression of AD and PD. Nicotinic acetylcholine receptors (nAChRs) are members of the Cys-loop superfamily of pentameric ligand-gated ion channels; some evidence showed that nicotinic receptors may be associated with AD and PD. These experimental and clinical studies may provide a scientific foundation for common shared mechanisms in AD and PD.

Paraoxonase 1 in neurological disorders

Paroxonase 1 displays multiple physiological activities that position it as a putative player in the pathogenesis of neurological disorders. Here we reviewed the literature focusing on the role of paraoxonase 1 (PON1) as a factor in the risk of stroke and the major neurodegenerative diseases. PON1 activity is reduced in stroke patients, which significantly correlates inversely with carotid and cerebral atherosclerosis. The presence of the R allele of the Q192R PON1 polymorphism seems to potentiate this risk for stroke. PON1 exerts peroxidase activities that may be important in neurodegenerative disorders associated with oxidative stress. PON1 is also a key detoxifier of organophosphates and organophosphate exposure has been linked to the development of neurological disorders in which acetylcholine plays a significant role. In Parkinson's disease most of the studies suggest no participation of either L55M or the Q192R polymorphisms in its pathogenesis. However, many studies suggest that the MM55 PON1 genotype is associated with a higher risk for Parkinson's disease in individuals exposed to organophosphates. In Alzheimer's disease most studies have failed to find any association between PON1 polymorphisms and the development of the disease. Some studies show that PON1 activity is decreased in patients with Alzheimer's disease or other dementias, suggesting a possible protective role of PON1. No links between PON1 polymorphisms or activity have been found in other neurodegenerative diseases such as multiple sclerosis and amyotrophic lateral sclerosis. PON1 is a potential player in the pathogenesis of several neurological disorders. More research is warranted to ascertain the precise pathogenic links and the prognostic value of its measurement in neurological patients.

Paraoxonase and arylesterase activity and total oxidative/anti-oxidative status in patients with idiopathic Parkinson's disease

This study investigated serum paraoxonase (PON1) and arylesterase activity along with determination of oxidative status via measurement of total oxidant status (TOS), total anti-oxidant status (TAS) and oxidative stress index (OSI) in patients with Parkinson's disease (PD) and compared results with data from healthy controls. A total of 82 subjects, including 42 patients with idiopathic PD, newly diagnosed and untreated (24 men, 18 women, aged 47-66 years) and 40 healthy controls were enrolled in this study. We aimed to evaluate the oxidative status of PD patients via measurement of serum TOS and TAS and estimation of OSI using new automated methods. PON1 and arylesterase activities were measured spectrophotometrically. Serum total cholesterol, high density lipoprotein cholesterol, low density lipoprotein (LDL) cholesterol and triglyceride levels were measured using routine methods. TAS levels of PD patients were significantly lower than that of controls (p<0.05). TOS levels of PD patients were higher than those of controls (p<0.05). PON1 and arylesterase activities of PD were lower than those of controls (p<0.05). Serum levels of total and LDL cholesterol were significantly reduced in PD patients. In conclusion, the presence of high TOS and OSI levels together with low levels of TAS in PD patients supports the important role of oxidative stress in the pathophysiology of PD. Since oxidative stress is involved in neurodegeneration, selecting anti-oxidants, metal chelators or other compounds boosting endogenous enzymatic and non-enzymatic defense mechanisms seems to be an obvious choice as treatment for PD.

Association of paraoxonase 1 L55M and Q192R single-nucleotide polymorphisms with age-related macular degeneration

PURPOSE

To determine if paraoxonase 1 (PON1) gene polymorphisms have an effect on the risk of having age-related macular degeneration (AMD).

METHODS

The study population consisted of 142 patients who were diagnosed with either exudative or atrophic AMD and 138 sex- and age-matched controls without AMD. Genotyping of the PON1 L55M and Q192R single-nucleotide polymorphisms was performed using real-time polymerase chain reaction and commercially produced kits. A full ophthalmic evaluation was performed in each subject, and all subjects were screened for hypertension, diabetes, hypercholesterolemia, and smoking history.

RESULTS

The PON1 MM and QQ genotypes were less frequent in patients with AMD than in control subjects (MM: 4 vs. 13%, P = 0.015; QQ: 15 vs. 27%, P = 0.020). A multivariate logistic regression analysis was also conducted. After adjusting for age, gender, and the prevalence of smoking, hypertension, diabetes, and hypercholesterolemia, the MM and QQ genotypes (MM/QQ vs. LL + LM/QR + RR) were found to be associated with a decreased risk of AMD (MM: odds ratio = 0.24, P = 0.007, 95% confidence interval: 0.09-0.68; QQ: odds ratio = 0.46, P = 0.013, 95% confidence interval: 0.25-0.85).

CONCLUSION

The authors found that subjects with the PON1 MM and QQ genotypes had a lower risk of AMD.

Novel common and rare genetic determinants of paraoxonase activity: FTO, SERPINA12, and ITGAL

HDL-associated paraoxonase 1 (PON1) activity is associated with cardiovascular and other human diseases. As the role of genetic variants outside of the PON gene cluster on PON1 activity is unknown, we sought to identify common and rare variants in such loci. We typed 33,057 variants on the CVD chip in 1,362 subjects to test for their effects on adjusted-PON1 activity. Three novel genes (FTO, ITGAL, and SERPINA12) and the PON gene cluster had SNPs associated with PON1 arylesterase (AREase) activity. These loci were carried forward for rare-variant analysis using Exome chip genotypes in an overlapping subset of 1,051 subjects using sequence kernel association testing. PON1 (P = 2.24 × 10(-4)), PON3 (P = 0.022), FTO (P = 0.019), and SERPINA12 (P = 0.039) had both common and rare variants associated with PON1 AREase. ITGAL variants were associated with PON1 activity when using weighted sequence kernel association testing (SKAT) analysis (P = 2.63 × 10(-3)). When adjusting for the initial common variants, SERPINA12 became marginally significant (P = 0.09), whereas all other findings remained significant (P < 0.05), suggesting independent rare-variant effects. We present novel findings that common and rare variants in FTO, SERPINA12, and ITGAL predict PON1 activity. These results further link PON1 to diabetes and inflammation and may inform the role of HDL in human disease.

Dietary cholesterol increases paraoxonase 1 enzyme activity

HDL-associated paraoxonase 1 (PON1) activity has been consistently associated with cardiovascular and other diseases. Vitamins C and E intake have previously been positively associated with PON1 in a subset of the Carotid Lesion Epidemiology and Risk (CLEAR) cohort. The goal of this study was to replicate these findings and determine whether other nutrient intake affected PON1 activity. To predict nutrient and mineral intake values, 1,402 subjects completed a standardized food frequency survey of their dietary habits over the past year. Stepwise regression was used to evaluate dietary and covariate effects on PON1 arylesterase activity. Five dietary components, cholesterol (P < 2.0 × 10(-16)), alcohol (P = 8.51 × 10(-8)), vitamin C (P = 7.97 × 10(-5)), iron (P = 0.0026), and folic acid (0.037) were independently predictive of PON1 activity. Dietary cholesterol was positively associated and predicted 5.5% of PON1 activity, second in variance explained. This study presents a novel finding of dietary cholesterol, iron, and folic acid predicting PON1 activity in humans and confirms prior reported associations, including that with vitamin C. Identifying and understanding environmental factors that affect PON1 activity is necessary to understand its role and that of HDL in human disease.

Polymorphisms in genes involved in oxidative stress response in patients with sudden sensorineural hearing loss and Ménière's disease in a Japanese population

The etiologies of idiopathic sudden sensorineural hearing loss (SSNHL) and Ménière's disease remain unclear. Recently, accumulating evidence has demonstrated that oxidative stress is related to the pathology of inner ear disease. Because genetic factors may contribute partly to the etiologies of SSNHL and Ménière's disease, we investigated the associations between genetic polymorphisms located in oxidative stress response genes and susceptibility to SSNHL and Ménière's disease. We compared 84 patients affected by SSNHL, 82 patients affected by Ménière's disease, and 2107 adults (1056 men and 1051 women; mean age, 59.2 years; range, 40-79 years) who participated in the National Institute for Longevity Sciences, Longitudinal Study of Aging. Multiple logistic regression was used to calculate odds ratios for SSNHL and Ménière's disease in individuals with polymorphisms in the genes glutathione peroxidase 1 (GPX1) (Pro198Leu, rs1050450), paraoxonase 1 (PON1) (Gln192Arg, rs662; and Met55Leu, rs854560), PON2 (Ser311Cys, rs7493), and superoxide dismutase 2 (SOD2) (Val16Ala, rs4880), with adjustment for age and gender. No significant differences in the distribution of the genotypes at these polymorphisms were observed among individuals with SSNHL and Ménière's disease and controls. No significant risk for SSNHL and Ménière's disease was observed in the additive genetic model, regardless of moderating variables. The C allele of SOD2 (rs4880) was more frequent in Ménière's disease cases with a hearing level over 50 dB compared with cases with a hearing level below 50 dB, suggesting that this polymorphism is associated with progression of a hearing loss in Ménière's disease. In conclusion, no significant associations between the polymorphisms of GPX1, PON1, PON2, and SOD2 and risk of SSNHL and Ménière's disease were observed in this Japanese case-control study.

Additional Common Polymorphisms in the PON Gene Cluster Predict PON1 Activity but Not Vascular Disease

Background. Paraoxonase 1 (PON1) enzymatic activity has been consistently predictive of cardiovascular disease, while the genotypes at the four functional polymorphisms at PON1 have not. The goal of this study was to identify additional variation at the PON gene cluster that improved prediction of PON1 activity and determine if these variants predict carotid artery disease (CAAD). Methods. We considered 1,328 males in a CAAD cohort. 51 tagging single-nucleotide polymorphisms (tag SNPs) across the PON cluster were evaluated to determine their effects on PON1 activity and CAAD status. Results. Six SNPs (four in PON1 and one each in PON2/3) predicted PON1 arylesterase (AREase) activity, in addition to the four previously known functional SNPs. In total, the 10 SNPs explained 30.1% of AREase activity, 5% of which was attributable to the six identified predictive SNPs. We replicate rs854567 prediction of 2.3% of AREase variance, the effects of rs3917510, and a PON3 haplotype that includes rs2375005. While AREase activity strongly predicted CAAD, none of the 10 SNPs predicting AREase predicted CAAD. Conclusions. This study identifies new genetic variants that predict additional PON1 AREase activity. Identification of SNPs associated with PON1 activity is required when evaluating the many phenotypes associated with genetic variation near PON1.

Paraoxonase 1 polymorphisms L55M and Q192R were not risk factors for Parkinson's disease: a HuGE review and meta-analysis

PURPOSE

The Paraoxonase 1 (PON1) has been studied as a potential candidate gene for Parkinson's disease risk, but direct evidence from genetic association studies remains inconclusive. We performed a meta-analysis pooling data from all relevant studies in order to determine the effects of two PON 1 polymorphisms (L55M and Q192R) on Parkinson's disease.

METHODS

We applied a random effects to combine odds ratio (OR) and 95% confidence intervals. Q statistic was used to evaluate the homogeneity, and Egger's test and Funnel plot were used to assess publication bias. In secondary analyses, we examined dominant and recessive models as well.

RESULTS

Concerning the PON1 L55M polymorphism, we identified 9 eligible studies (a total of 2582 cases and 3997 controls). The random effects pooled OR was OR=1.29, (0.90, 1.84). Concerning the Q192R polymorphism, we identified 7 eligible studies (a total of 2582 cases and 3997 controls). The random effects pooled OR was OR=1.08(0.81, 1.43). Analysis with dominant and recessive genetic models yielded the same inferences as genotype-based comparisons for both of the two polymorphisms.

CONCLUSION

The results of this meta-analysis suggested that both PON1 L55M and Q192R were not responsible for PD.

Polymorphic genes of detoxification and mitochondrial enzymes and risk for progressive supranuclear palsy: a case control study

Background

There are no known causes for progressive supranuclear palsy (PSP). The microtubule associated protein tau (MAPT) H1 haplotype is the major genetic factor associated with risk of PSP, with both oxidative stress and mitochondrial dysfunction also implicated. We investigated whether specific single nucleotide polymorphisms (SNPs) in genes encoding enzymes of xenobiotic detoxification, mitochondrial functioning, or oxidative stress response, including debrisoquine 4-hydroxylase, paraoxonase 1 and 2, N-acetyltransferase 1 and 2 (NAT2), superoxide dismutase 1 and 2, and PTEN-induced putative kinase are associated with PSP.

Methods

DNA from 553 autopsy-confirmed Caucasian PSP cases (266 females, 279 males; age at onset 68 ± 8 years; age at death 75 ± 8) from the Society for PSP Brain Bank and 425 clinical control samples (197 females, 226 males; age at draw 72 ± 11 years) from healthy volunteers were genotyped using Taqman PCR and the SequenomiPLEX Gold assay.

Results

The proportion of NAT2 rapid acetylators compared to intermediate and slow acetylators was larger in cases than in controls (OR = 1.82, p < 0.05). There were no allelic or genotypic associations with PSP for any other SNPs tested with the exception of MAPT (p < 0.001).

Conclusions

Our results show that NAT2 rapid acetylator phenotype is associated with PSP, suggesting that NAT2 may be responsible for activation of a xenobiotic whose metabolite is neurotoxic. Although our results need to be further confirmed in an independent sample, NAT2 acetylation status should be considered in future genetic and epidemiological studies of PSP.

Role of paraoxonase 1 (PON1) in organophosphate metabolism: implications in neurodegenerative diseases

Organophosphate pesticides are a class of compounds that are widely used in agricultural and rural areas. Paraoxonase 1 (PON1) is a phase-I enzyme that is involved in the hydrolysis of organophosphate esters. Environmental poisoning by organophosphate compounds has been the main driving force of previous research on PON1 enzymes. Recent discoveries in animal models have revealed the important role of the enzyme in lipid metabolism. However although PON1 function is well established in experimental models, the contribution of PON1 in neurodegenerative diseases remains unclear. In this minireview we summarize the involvement of PON1 genotypes in the occurrence of Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis. A brief overview of latest epidemiological studies, regarding the two most important PON1 coding region polymorphisms PON1-L55M and PON1-Q192R is presented. Positive and negative associations of PON1 with disease occurrence are reported. Notably the MM and RR alleles contribute a risk enhancing effect for the development of some neurodegenerative diseases, which may be explained by the reduced lipoprotein free radical scavenging activity that may give rise to neuronal damage, through distinct mechanism. Conflicting findings that fail to support this postulate may represent the human population ethnic heterogeneity, different sample size and environmental parameters affecting PON1 status. We conclude that further epidemiological studies are required in order to address the exact contribution of PON1 genome in combination with organophosphate exposure in populations with neurodegenerative diseases.

Human PON1, a biomarker of risk of disease and exposure

Human paraoxonase 1 (PON1) is a high-density lipoprotein (HDL)-associated serum enzyme that exhibits a broad substrate specificity. In addition to protecting against exposure to some organophosphorus (OP) pesticides by hydrolyzing their toxic oxon metabolites, PON1 is important in protecting against vascular disease by metabolizing oxidized lipids. Recently, PON1 has also been shown to play a role in inactivating the quorum sensing factor N-(3-oxododecanoyl)-l-homoserine lactone (3OC12-HSL) of Pseudomonas aeruginosa. Native, untagged engineered recombinant human PON1 (rHuPON1) expressed in Escherichia coli and purified by conventional column chromatographic purification is stable, active, and capable of protecting PON1 knockout mice (PON1(-/-)) from exposure to high levels of the OP compound diazoxon. The bacterially derived rHuPON1 can be produced in large quantities and lacks the glycosylation of eukaryotic systems that can produce immunogenic complications when inappropriately glycosylated recombinant proteins are used as therapeutics. Previous studies have shown that the determination of PON1 status, which reveals both PON1(192) functional genotype and serum enzyme activity level, is required for a meaningful evaluation of PON1's role in risk of disease or exposure. We have developed a new two-substrate assay/analysis protocol that provides PON1 status without use of toxic OP substrates, allowing for use of this protocol in non-specialized laboratories. Factors were also determined for inter-converting rates of hydrolysis of different substrates. PON1 status also plays an important role in revealing changes in HDL-associated PON1 activities in male patients with Parkinson disease (PD). Immunolocalization studies of PONs 1, 2 and 3 in nearly all mouse tissues suggest that the functions of PONs 1 and 3 extend beyond the plasma and the HDL particle.

Paraoxonase 1, agricultural organophosphate exposure, and Parkinson disease

BACKGROUND

Human, animal and cell models support a role for pesticides in the etiology of Parkinson disease. Susceptibility to pesticides may be modified by genetic variants of xenobiotic enzymes, such as paraoxonase, that play a role in metabolizing some organophosphates.

METHODS

We examined associations between Parkinson disease and the organophosphates diazinon, chlorpyrifos, and parathion, and the influence of a functional polymorphism at position 55 in the coding region of the PON1 gene (PON1-55). From 1 January 2001 through 1 January 2008, we recruited 351 incident cases and 363 controls from 3 rural California counties in a population-based case-control study. Participants provided a DNA sample, and residential exposure to organophosphates was determined from pesticide usage reports and a geographic information system (GIS) approach. We assessed the main effects of both genes and pesticides in unconditional logistic regression analyses, and evaluated the effect of carrying a PON1-55 MM variant on estimates of effects for diazinon, chlorpyrifos, and parathion exposures.

RESULTS

Carriers of the variant MM PON1-55 genotype exposed to organophosphates exhibited a greater than 2-fold increase in Parkinson disease risk compared with persons who had the wildtype or heterozygous genotype and no exposure (for diazinon, odds ratio = 2.2 [95% confidence interval = 1.1-4.5]; for chlorpyrifos, 2.6 [1.3-5.4]). The effect estimate for chlorpyrifos, was more pronounced in younger-onset cases and controls (<or=60 years) (5.3 [1.7-16]). No increase in risk was noted for parathion.

CONCLUSION

The increase in risk we observed among PON1-55 variant carriers for specific organophosphates metabolized by PON1 underscores the importance of considering susceptibility factors when studying environmental exposures in Parkinson disease.

Paraoxonase 1 polymorphisms are not related with the risk for multiple sclerosis

It has been suggested a possible role of oxidative stress and lipid peroxidation in the inflammatory processes and in the pathogenesis of multiple sclerosis. Human serum paraoxonase 1 is a polymorphic enzyme encoded by the gene PON1, located in chromosome 7q21.3, that plays a major role in the metabolism of organophosporus compounds, and in the protection against oxidative stress. Paraoxonase-1 activity has been found decreased in the plasma of multiple sclerosis patients. An association between PON1 polymorphism and the risk of multiple sclerosis has been described in Italians. To investigate the possible association between the PON1 genotype and allelic variants of the polymorphisms L55M and Q192R and the risk for multiple sclerosis in the Spanish Caucasian population; we studied the frequency of the PON1 genotypes and allelic variants in 228 patients with multiple sclerosis and 220 healthy controls using a PCR-RLFP method. The frequencies of the PON1 genotypes and allelic variants did not differ significantly between patients and controls, and were unrelated with gender, age of onset, and course of the disease. The OR (95% confidence intervals) for the variant alleles PON1-55L and PON1-192R were 0.96 (0.73-1.26) and 1.01 (0.76-1.35), respectively. The results of the present study suggest that PON1 polymorphism is not related with the risk for multiple sclerosis in our population.

The paraoxonases: role in human diseases and methodological difficulties in measurement

Research into the paraoxonase (PON) gene family has flourished over the past few years. In the 1970s and 1980s, only PON1 was known, and the investigations were conducted, essentially, by toxicologists focusing on protection against organophosphate poisoning. Since then, two new members of the family, PON2 and PON3, have been identified, both being shown to play antioxidant and anti-inflammatory roles. Evidence exists indicating that the PON family is central to a wide variety of human illnesses such as cardiovascular disease, diabetes mellitus, metabolic syndrome, obesity, non-alcoholic steatohepatitis, and several mental disorders. However, research is hampered considerably by the methods currently available to measure the activity of these enzymes. In this review, we summarize the state of knowledge on PON biochemistry and function, the influence of genetic variations, and the involvement of PON in several diseases. The problems associated with PON measurement, such as sample acquisition, lack of reference methods, and variety of substrates, will be presented. Also, we cover some of the present lines of research and propose some others for future progress in this field.

Impact of low-level exposure to organophosphates on human reproduction and survival

Despite their widespread and longstanding use for the public good, organophosphate (OP) pesticides have led to many adverse effects on human health. Environmental exposure to OPs and adverse reproductive outcomes in men and women working on or living near farms are increasingly reported worldwide. The aim of the current review is to determine whether exposure to OPs, at levels lower than that which results in clinical manifestations of acute OP poisoning, leads to an adverse impact on fertility, growth and development, and to highlight possible effects for further investigation. There is evidence of impaired fertility due to a reduction in semen quality and possibly lower testosterone levels in exposed males. There is also evidence of impairment of fetal growth and development brought about by prenatal exposure to OPs. Paraoxonase gene (PON1) activity in the fetus and during early childhood makes the fetus and child more vulnerable to OP poisoning, suggesting that OP exposure has a greater impact on fetal and infant growth and development than on adults when exposed to the same concentrations of pesticides. This review raises concerns that exposure to OP pesticides at levels currently regarded as safe adversely affect human reproductive function and survival.

Polymorphisms and the expression of genes encoding enzymes involved in cardiovascular diseases

BACKGROUND

Atherosclerosis, a multi-factorial disease, is the main determinant of cardiovascular disease (CVD) leading to high mortality and morbidity in westernized countries. Gene polymorphisms and gene expression related to the atherosclerosis process can be identified using a genome-wide approach or looking for candidate disease-causing genes.

METHODS

Using genome wide strategy or candidate gene approach various genes, including paraoxonase genes, which are involved in lipid metabolism, oxidation, inflammation and coagulation, have been associated to atherosclerosis.

CONCLUSION

Evaluation of gene polymorphisms, together with traditional and novel biochemical parameters, may help identify individuals at a high risk for CVD. Genetic characterization of susceptibility genes may also lead to new drugs for atherosclerosis prevention and treatment. In addition, gene expression studies can provide novel insights into the molecular mechanism of lesion development and progression.

Polymorphisms in the genes of citohrom oxidase P450 2D6 (CYP2D6), paraoxonase 1 (PON1) and apolipoproteine E (APOE) as risk factors for Parkinson's disease

Background/Aim. The presence of Parkinson's disease (PD) among the members of a family is a clear indication of the significance of genetics in its development. In spite of that, the majority of patients with PD shows a sporadic form of the disease induced as a result of interaction of both environmental and genetic factors. The aim of this study was to examine the effects of polymorphisms in the genes of cytohrome P450 2D6(CYP2D6), paraoxonase 1 (PON 1) and apolipoprotein E (APOE), as risk factors for PD. Methods. We examined 106 patients with PD (65 men and 41 women) and 75 ethnically matched control subjects. The mean age at onset of PD in the patients was 46.9?9.4 years (ranging from 30 to 70 years). Genotyping was performed using standard PCR amplification and restriction endonuclease digestion protocols described for known polymorphism in the candidate genes under study. Results. The genotype A/A polymorphisms 2D6* gene of CYP2D6 and genotype M/M polymorphisms L54M gene of PON1 were significantly more frequent in the patients with PD than in the control group. The patients with genotypes A/A and M/M had 3.4 and 3.2 higher risk of PD, respectively than the control group (p = 0.01). The relation between genotypes A/A gene of CYP2D6 and M/M gene of PON1 was modified by the age at onset. The genotypes were associated with early onset of PD (p = 0.001, p = 0.004). The carriers of the A and M alleles in homozygote had 2.4 and 4.2 years respectively earlier onset of PD than carriers of other genotypes with these polymorphisms. The frequency allele ?4 gene of APOE was higher in the PD patients with early onset (20%) than in PD with later onset (7.4%), while the genotype ?3/?3 was associated with PD late onset (p = 0.024). Combined genotype I (carriers of the two risk allels in homozygote and one alleles risk in heterozygote) and combined genotype II (carriers of the three alleles risk in homozygote) caused early PD. Combined genotype II was detected in 12.7% of the patients in the group of early onset, and in 2.4% of the patients with the onset after 45 years. Conclusion. The results of our study suggest that the genotypes A/A and M/M genes of CYP2D6 and PON1, and allele ?4 gene are an important risk for the development of PD, causing its early onset. The cumulative effects of the risk genes cause an early onset of PD.

Gene-environment interactions in sporadic Parkinson's disease

Much has been learned in recent years about the genetics of familial Parkinson's disease. However, far less is known about those malfunctioning genes which contribute to the emergence and/or progression of the vast majority of cases, the 'sporadic Parkinson's disease', which is the focus of our current review. Drastic differences in the reported prevalence of Parkinson's disease in different continents and countries suggest ethnic and/or environmental-associated multigenic contributions to this disease. Numerous association studies showing variable involvement of multiple tested genes in these distinct locations support this notion. Also, variable increases in the risk of Parkinson's disease due to exposure to agricultural insecticides indicate complex gene-environment interactions, especially when genes involved in protection from oxidative stress are explored. Further consideration of the brain regions damaged in Parkinson's disease points at the age-vulnerable cholinergic-dopaminergic balance as being involved in the emergence of sporadic Parkinson's disease in general and in the exposure-induced risks in particular. More specifically, the chromosome 7 ACHE/PON1 locus emerges as a key region controlling this sensitive balance, and animal model experiments are compatible with this concept. Future progress in the understanding of the genetics of sporadic Parkinson's disease depends on globally coordinated, multileveled studies of gene-environment interactions.

LRRK2 expression linked to dopamine-innervated areas

OBJECTIVE

Leucine-rich repeat kinase 2 (LRRK2) has been linked to Parkinson's disease. Our study explores the expression of LRRK2 in human and rodent brain tissue.

METHODS

We analyzed LRRK2 gene activity at the cellular level using in situ hybridization.

RESULTS

We found a high and strikingly specific expression of LRRK2 mRNA in rodent striatum and parts of cortex and no signals in dopamine neurons. In human tissue, LRRK2 mRNA was found in the corresponding brain areas caudatus and putamen at lower levels and dopamine neurons were also devoid of LRRK2 mRNA. Expression levels in striatal tissue did not differ between Parkinson's disease patients and control subjects.

INTERPRETATION

Unlike all other genes so far linked to Parkinson's disease, our results demonstrate that LRRK2 expression is particularly high in brain dopaminoceptive areas.

Paraoxonase and superoxide dismutase gene polymorphisms and noise-induced hearing loss

BACKGROUND

Noise-induced cochlear epithelium damage can cause hearing loss in industrial workers. In experimental systems, noise induces the release of free radicals and may damage the cochlear sensorial epithelium. Therefore, genes involved in regulating the reactive oxygen species manganese-superoxide dismutase (SOD2) and the antioxidant paraoxonase (PON) could influence cochlea vulnerability to noise. We evaluated whether susceptibility to noise-induced hearing loss (NIHL) is associated with SOD2, PON1, and PON2 polymorphisms in workers exposed to prolonged loud noise.

METHODS

We enrolled 94 male workers from an aircraft factory in the study. The SOD2 gene was screened by denaturing reversed-phase HPLC, and the PON1 (Q192R and M55L) and PON2 (S311C) polymorphisms were analyzed by PCR amplification followed by digestion with restriction endonucleases.

RESULTS

Three known (A16V, IVS3-23T/G, and IVS3-60T/G) and two new SOD2 polymorphisms (IVS1+ 8A/G and IVS3+107T/A) were identified. Regression analysis showed that PON2 (SC+CC) [odds ratio (OR) = 5.01; 95% confidence interval (CI), 1.11-22.54], SOD2 IVS3-23T/G and IVS3-60T/G (OR = 5.09; 95% CI, 1.27-20.47), age (OR = 1.22; 95% CI, 1.09-1.36), and smoking (OR = 49.49; 95% CI, 5.09-480.66) were associated with NIHL. No association was detected for PON1 (QQ+RR) and PON1 (LL) genotypes.

CONCLUSIONS

Our data suggest that SOD2 and PON2 polymorphisms, by exerting variable local tissue antioxidant roles, could predispose to NIHL. However, caution should be exercised in interpreting these data given the small sample size and the difficulty in matching cases to controls regarding the overwhelming risk factor, i.e., smoking at least 10 cigarettes/day.

Paraoxonase 1 (PON1) gene polymorphisms and Parkinson’s disease in a Finnish population

Paraoxonase 1 (PON1) is involved in the metabolism and detoxification of insecticides and pesticides. Two polymorphisms within the gene affect the enzyme activity. One is a methionine to leucine change at position 54 (M54L) and the other is a glutamine to arginine variant at position 192 (Q192R). There are contrasting reports assessing the role of these variants in Parkinson's disease (PD). We performed a case--control association study in order to elucidate the possible contribution of variability within PON1 to the risk of sporadic PD in a Finnish population. There was no statistically significant association of the allele, genotype or haplotype distribution with PD (all P values > 0.75). Our results suggest that the M54L and Q192R polymorphisms are not major risk factors for PD in the Finnish population.

Association of paraoxonase 1 gene polymorphisms with risk of Parkinson's disease: a meta-analysis

Paraoxonase1 (PON1) gene polymorphisms were implicated as risk factors for Parkinson's disease (PD), but the results of case-control studies that investigated these associations were controversial. In order to provide an answer to these contradictory results, a meta-analysis of all available studies relating the PON1-55M/L and PON1-192Q/R polymorphisms to the risk of developing PD was conducted. The racial descent of the populations in these studies was Caucasian and Asian. The meta-analysis revealed that there was an association of the PON1-55M allele and the risk of developing PD relative to the L allele: fixed effects pooled odds ratio (OR)=1.32 [95%CI (1.10-1.59)]. In addition, there was evidence of association for the genotypic contrast PON1-55MM+LM relative to PON1-55LL: fixed effects OR=1.50 [95%CI (1.16-1.95)]. There was no significant association between PON1-192Q/R alleles and risk of developing PD: OR=1.09 [95%CI (0.93-1.26)]. There was no evidence for an association between the genotypic contrasts of PON1-192 and development of PD. The heterogeneity between studies and the publication bias were not significant ( P> or =0.10) in either polymorphism. Therefore, the pooled results of the meta-analysis supported that there was an association between PON1-55M/L polymorphism and PD and that PON1-192Q/R polymorphism was unlikely to be a major risk factor for susceptibility to PD.

Genetic contributions to Parkinson's disease

Sporadic Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the loss of midbrain dopamine neurons and Lewy body inclusions. It is thought to result from a complex interaction between multiple predisposing genes and environmental influences, although these interactions are still poorly understood. Several causative genes have been identified in different families. Mutations in two genes [alpha-synuclein and nuclear receptor-related 1 (Nurr1)] cause the same pathology, and a third locus on chromosome 2 also causes this pathology. Other familial PD mutations have identified genes involved in the ubiquitin-proteasome system [parkin and ubiquitin C-terminal hydroxylase L1 (UCHL1)], although such cases do not produce Lewy bodies. These studies highlight critical cellular proteins and mechanisms for dopamine neuron survival as disrupted in Parkinson's disease. Understanding the genetic variations impacting on dopamine neurons may illuminate other molecular mechanisms involved. Additional candidate genes involved in dopamine cell survival, dopamine synthesis, metabolism and function, energy supply, oxidative stress, and cellular detoxification have been indicated by transgenic animal models and/or screened in human populations with differing results. Genetic variation in genes known to produce different patterns and types of neurodegeneration that may impact on the function of dopamine neurons are also reviewed. These studies suggest that environment and genetic background are likely to have a significant influence on susceptibility to Parkinson's disease. The identification of multiple genes predisposing to Parkinson's disease will assist in determining the cellular pathway/s leading to the neurodegeneration observed in this disease.

The effects of occupational exposure to chlorpyrifos on the neurologic examination of central nervous system function: a prospective cohort study

Questions persist about adverse effects such as impaired cognition and attention, incoordination, spasticity, or parkinsonism from chronic, low-level exposures to organophosphate (OP) compounds. In a prospective cohort study, we evaluated chlorpyrifos-manufacturing workers and a referent group on 2 occasions, 1 year apart, to determine whether occupational exposure to chlorpyrifos produced clinically evident central nervous system (CNS) dysfunction. Chlorpyrifos subjects had significantly higher TCP excretion and lower average BuChE activity than referents in a range in which physiological effects on B-esterases exist. Few subjects had neurologic symptoms or signs, and there were no significant group differences in terms of signs at baseline or second examinations. Chronic chlorpyrifos exposure produced no clinical evidence of cortical, pyramidal tract, extrapyramidal, or other CNS dysfunction among chlorpyrifos subjects compared with referents, either at baseline or after 1 year of additional chlorpyrifos exposure.

Paraoxonase gene polymorphisms, oxidative stress, and diseases

The paraoxonase (PON) gene cluster contains at least three members, including PON1, PON2, and PON3, located on chromosome 7q21.3-22.1. Until now there has been little insight into the role of the respective gene products in human physiology and pathology. However, emerging evidence from biochemical and genetic experiments is providing clues about the role(s) of the products of these genes, which indicates that PON(s) acts as important guardians against cellular damage from toxic agents, such as organophosphates, oxidized lipids in the plasma low-density lipoproteins. In parallel, substantial data have been published on the association between the polymorphisms of PON(s) and coronary heart disease. It has become clear that the polymorphisms significantly affect the prevalence of coronary heart disease. However, the associations between the PON(s) polymorphisms and most of these conditions were found to be inconsistent when additional populations were investigated. This contribution provides an overview of the status of research of each of the three genes and the available association studies and the potential problems in interpreting the data. We also review the current evidence on the association between PON(s) polymorphisms and diseases other than coronary heart disease and some metabolic quantitative phenotypes, such as plasma lipoproteins, plasma glucose, and birthweight. Finally, we suggest directions for the future that might elucidate the role of the PON genetic polymorphisms in this potentially important function of PON(s) and the role in coronary heart disease and other related diseases.