Acetylcholinesterase/paraoxonase interactions ... - The FASEB Journal

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Jan 3, 2005 - *The Life Sciences Institute, The Hebrew University of Jerusalem, Israel;†Departments of ... Center of Neuroscience, Ben Gurion University and.
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The FASEB Journal express article 10.1096/fj.04-2106fje. Published online January 3, 2005.

Acetylcholinesterase/paraoxonase interactions increase the risk of insecticide-induced Parkinson’s disease. Liat Benmoyal-Segal,* Tatiana Vander,† Sagiv Shifman,* Boris Bryk,* Richard Ebstein,§ Esther-Lee Marcus,§ Jochanan Stessman,║ Ariel Darvasi,* Yuval Herishanu,† Alon Friedman,‡ and Hermona Soreq* *The Life Sciences Institute, The Hebrew University of Jerusalem, Israel; †Departments of Neurology and ‡Neurosurgery; Zlotowsky Center of Neuroscience, Ben Gurion University and Soroka Medical Center, BeerSheva, Israel; §Herzog Hospital, Jerusalem, Israel; and ║Mount Scopus Hadassah University Hospital, Jerusalem, Israel Corresponding author: Hermona Soreq, The Life Sciences Institute, The Hebrew University of Jerusalem, Israel 91904. E-mail: [email protected] ABSTRACT Exposure to agricultural insecticides, together with yet incompletely understood predisposing genotype/phenotype elements, notably increase the risk of Parkinson's disease. Here, we report findings attributing the increased risk in an insecticide-exposed rural area in Israel to interacting debilitating polymorphisms in the ACHE/PON1 locus and corresponding expression variations. Polymorphisms that debilitate PON1 activity and cause impaired AChE overproduction under anticholinesterase exposure were strongly overrepresented in patients from agriculturally exposed areas, indicating that they confer risk of Parkinson's disease. Supporting this notion, serum AChE and PON1 activities were both selectively and significantly lower in patients than in healthy individuals and in carriers of the risky polymorphisms as compared with other Parkinsonian patients. Our findings suggest that inherited interactive weakness of AChE and PON1 expression increases the insecticide-induced occurrence of Parkinson's disease. Key words: association study • environmental exposure • gene-environment interactions • genotyping neuroprotection

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arkinson’s disease (PD) affects about 1% of the population older than 65 years (1). Both genetic and environmental factors play a role in the aetiology of PD. Living in a rural area, drinking of well water or exposure to insecticides significantly increase the risk of PD (2– 4). The insecticides-induced risk of PD was found to be associated with polymorphisms in the Paraoxonase (PON1) gene, the protein product of which degrades organophosphate (OP) compounds and therefore protects against them (5–7). Interestingly, distinct ethnic populations are protected by distinct PON1 alleles, suggesting trait-dependent gene-environment interactions with other PD-associated elements. The primary target for OP inhibition is acetylcholinesterase (AChE), and the ACHE gene is located 5.5 Mb upstream to PON1 on Chromosome 7q21-22. An

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activating deletion (∆ACHE) in the ACHE promoter induces constitutive transcriptional overproduction associated with acute sensitivity to OPs and other anti-acetylcholinestreases (anti-AChEs) (8). Anti-AChEs exposure increases ACHE gene expression in carriers of the normal—but not the mutated—gene (8, 9). We hypothesized that this transient increase in AChE reduces acetylcholine (ACh) concentrations to normal levels, restoring the balance between the cholinergic and dopaminergic systems, which is crucial for proper basal ganglia function (10). Both failure to hydrolyze OPs by PON1, or failure to increase AChE expression following OP exposure would result in failure to restore ACh levels following exposure. This, in turn, will lead to basal ganglia dysfunction and increase the risk for PD. For residents of rural areas in Israel the incidence of PD is increased to 5% (11), with unknown genetic and/or phenotypic origin(s). The aim of this study was to test whether specific ACHE/PON1 allele combinations are correlated with their exposure-induced PD risk. MATERIALS AND METHODS Subjects A total of 101 sporadic PD patients were recruited from the PD clinic of Soroka University Medical Center in Beer-Sheva, Israel. Of these, 38 patients (average age 71±11.1) live in rural areas and are therefore exposed to relatively high levels of different anti-AChEs, especially organophosphates, such as parathion, and to carbamates (11). Most of the PD patients that were included in this study lived in the same rural communities for approximately 40 years, and a minority of them for at least 20 years (38). They were subjected to chronic passive exposure to a large variety of pesticides (39). Herbicides (paraquat and diquat) as well as pesticides (mancozeb, organic phosphorus compounds) were detected in the soil of the fields around their communities and in the soil of their residential areas, unrelated to the time of the aerial spread (11). The remaining 63 patients (average age 71.5±10.2) live in urban areas. Although urban living does not necessarily imply non-exposure to pesticides, the composition of pesticides to which these groups of rural-living patients had been exposed, and the continuous nature of such exposure, are likely to be distinct from those of urban life. 232 healthy unrelated control subjects (average age 50.8±21.14) were randomly selected from the Soroka Medical Center, Herzog Geriatric Center (Jerusalem) and healthy adult volunteers, all Israeli Jews. These have been defined as “apparently healthy” because the average age of onset of PD is 65 (1). Age differences between the control group and the two PD groups were statistically significant (P10%) and three are rare (the PON1 promoter polymorphism –126PON1 = 3%; the ∆ACHE = 2%; and the H322N substitution in AChE that yields the YTb blood group phenotype (12), YTACHE = 8%). D' and r2 calculations showed three main LD blocks with a certain degree of disequilibrium within the PON1 gene (Fig. 1B), especially for the following SNP pairs: –108PON1 and –162PON1 (r2=0.28), 192PON1 and 55PON1 (r2=0.27); and 55PON1 and – 108PON1 (r2=0.21). 55PON1 was correlated to both –108 PON1 and 192 PON1, which reflect the total protein amount (assessed by measuring the arylesterase activity of PON) and paraoxonase efficacy, respectively (5). Within the ACHE gene, the Middle East frequent ∆ACHE and the H322NACHE polymorphisms expectedly presented D' = 0.8 and r2 = 0.15 (8) (Fig 1B). Thus, LD levels in the PON1 and ACHE genes generally repeated the intragenic LD patterns described in previous studies (5, 8). No LD was found between the ACHE and PON1 genes. Apparent association with exposure-induced PD risk Allelic composition of the ACHE/PON1 locus from insecticide-exposed and non-exposed PD patients was substantially similar to that of healthy individuals, allowing comparison between patients and controls despite the age differences. Three of the analyzed polymorphisms showed a nonsignificant trend for association with exposure-induced PD (–162PON1, –108PON1, ∆ACHE, P