Toxicogenomics Article Increased Influence of Genetic Variation on PON1 Activity in Neonates Jia Chen,1,2,3 Madhu Kumar,4 Wendy Chan,2 Gertrud Berkowitz,2 and James G. Wetmur4,5 1The Derald H. Ruttenberg Cancer Center, and Departments of 2Community and Preventive Medicine, 3Pediatrics, 4Microbiology, and 5Human Genetics, Mount Sinai School of Medicine, New York, New York, USA James 2000; Brophy et al. 2001a, 2001b). PON1 (paraoxonase-1) detoxifies organophosphates by cleavage of active oxons before they have a Promoter variants in PON1 affect the level chance to inhibit cholinesterases. The corresponding gene PON1 has common polymorphisms in of expression by more than 2-fold (Boright both the promoter (–909, –162, –108) and the coding region (L55M, Q192R). The five PON1 et al. 1998; Brophy et al. 2001a, 2001b). genotypes were determined for maternal blood (n = 402) and cord blood (n = 229) as part of a Q192R affects the relative rate of hydrolysis study of the effects of organophosphate pesticide exposure on infant growth and neurodevelop- of certain organophosphate substrates com- ment. PON1 enzymatic activities were determined for a majority of subjects. The population pared with phenyl acetate by as much as an contained Caucasians, Caribbean Hispanics, and African Americans. PON1 activity was strongly order of magnitude but has only a small dependent upon the promoter alleles in both maternal and cord blood. For example, PON1 activ- effect on chlorpyrifos oxon/phenylacetate ities for position –108CC, CT, and TT mothers were 146, 128, and 109 arylesterase U/mL rate of hydrolysis (Davies et al. 1996). The (analysis of variance, p < 0.0001), whereas the same PON1 activities for the respective cord L55M polymorphism has been found to bloods were 49.0, 32.4, and 23.2 U/mL (p < 0.0001). Compared with adults, neonates had lower affect lipid peroxidation (Malin et al. 2001) PON1 activity, implying reduced capacity to detoxify organophosphates. In addition there was a and PON1 protein stability (Leviev et al. larger difference in activity between genotype groups in neonates than in adults. Because the five 2001), although the recent work on pro- polymorphisms in PON1 occur in a short stretch of DNA, they were tested for linkage disequilib- moter mutations has suggested that the rium (LD). Significant LD was found among all three promoter polymorphisms as well as apparent effect of the L55M polymorphism between promoter polymorphisms and L55M, with the strongest LD for Caucasians and the on enzyme concentration also may be due to weakest for African Americans. The Caribbean Hispanics fall between these two groups. linkage disequilibrium (LD) with one of the Surprisingly, significant LD also was observed between the promoter polymorphisms and C311S promoter variants (Brophy et al. 2001b). in PON2. LD between the promoter polymorphisms and Q192R was not significant. Key words: Toxicity of chlorpyrifos is inversely children, chlorpyrifos, linkage disequilibrium, neonate, pesticide, polymorphism, PON1, preg- related to serum PON1 activity. Intravenous nancy. Environ Health Perspect 111:1403–1410 (2003). doi:10.1289/ehp.6105 available via injection of PON1 before challenge by http://dx.doi.org/ [Online 7 May 2003] chlorpyrifos is protective in the rat (Costa et al. 1990). PON1 knockout mice were more susceptible to chlorpyrifos toxicity (Shih et Chlorpyrifos, an insecticide implicated as a diverse mothers and their neonates. In this al. 1998), and the toxicity was alleviated by developmental neurotoxin in animals (Shih study, we examined the hypothesis that intraperitoneal injection of purified PON1, et al. 1998), has been used routinely in the genetic factors may be more crucial in with the 192RR (homozygous) enzyme pro- homes of urban populations in the United determining risk in neonates than in adults viding better protection than 192QQ (Li et States. The biochemical contributions of of various ethnicities. al. 2000). Using the rat model, Attenberry metabolizing enzymes to the neurotoxic The PON1 gene has been fully et al. (1997) have demonstrated that the potential of chlorpyrifos and other characterized (Clendenning et al. 1996) age-related decrease in susceptibility to organophosphates remain subjects of active and has been found to be a member of a chlorpyrifos CNS toxicity is not due to investigation (Sams et al. 2000; Costa et al. multigene family of three linked genes, either the rate of activation to the oxon or to 1999; Furlong et al. 2000). Specifically, PON1 (MIM 168820), PON3 (MIM the reactivity of the oxon in the CNS but is after activation of chlorpyrifos to the reac- 602720), and PON2 (MIM 602447) entirely due to age-related differences in the tive oxon, the oxon may be detoxified by (OMIM 2002), in that order (Primo- detoxification of the oxon. Developing PON1 (paraoxonase-1) before it has the Parmo et al. 1996; Entrez Chromosome human fetuses have much lower protective chance to inactivate acetylcholinesterase in Map 2002). Human PON1 had long been PON1 activities than do adults, with the the peripheral nervous system (PNS) and recognized to be polymorphic based both level in cord blood being severalfold lower central nervous system (CNS). PON1, on large differences in serum PON1 activ- (Mueller et al. 1983). Furthermore, both which is associated with high-density lipid ity (Geldmacher-von Mallinckrodt et al. chlorpyrifos and chlorpyrifos oxon can cross lipoprotein (HDL), also functions to cleave 1983) and on the phosphodiesterase/ the placenta. Subcutaneous delivery of a oxidized lipids in low-density lipid lipo- arylesterase activity ratio for different sub- high dose of chlorpyrifos to pregnant rats protein (LDL) as well as in HDL (Aviram strates, including organophosphate oxons et al. 1998, 2000). PON1 also has an derived from pesticides and direct-acting arylesterase activity (Gan et al. 1991). cholinesterase inhibitors such as the nerve Address correspondence to J.G. Wetmur, HDL levels and PON1 activities are some- gas sarin (Davies et al. 1996). The purified Microbiology, Box 1124, Mount Sinai School of Medicine, 1 Gustave L. Levy Place, New York, NY what elevated during pregnancy (Roy et al. isozymes retained these differences in 10029-6574 USA. Telephone: (212) 241-7685. Fax: 1994). As part of the continuing effort of organophosphate hydrolysis activity nor- (212) 534-1684. E-mail: [email protected] the Mount Sinai Children’s Environmental malized to arylesterase activity (Smolen et This work was supported by grants ES09584 Health Center to prospectively assess the al. 1991). PON1 contains two common and ES11643 from the National Institute of neurodevelopmental risks associated with polymorphisms in the coding region, Environmental Sciences and R827039 from the U.S. chlorpyrifos exposure in an inner-city pop- Q192R (Adkins et al. 1993; Humbert et al. Environmental Protection Agency. J.C. was sup- ported by a Career Development Award CA81750 ulation in New York City, we investigated 1993) and L55M (Garin et al. 1997), and from the National Cancer Institute. the genetic determinants of chlorpyrifos three common polymorphisms in the pro- The authors declare they have no conflict of interest. metabolism in a population of ethnically moter at –909, –162 and –108 (Leviev and Received 12 November 2002; accepted 7 May 2003. Environmental Health Perspectives • VOLUME 111 | NUMBER 11 | August 2003 1403 Toxicogenomics | Chen et al. led to significant (30–49%) inhibition of maternal plasma and three aliquots of cord PON1 Assay fetal acetylcholinesterase activity (Chanda blood plasma were frozen at –70°C, one for The hydrolysis of phenylacetate to acetic and Pope 1996). Thus, both fetuses and determination of PON1. The buffy coat acid and phenol, measured by absorbance very young children may be more suscepti- was separated from the red blood cells, and maximum A270, was used to determine ble to pesticide exposure compared with DNA was extracted and purified using a human plasma PON1 activity using the adults. Lower PON1 activities may reflect QIAamp blood kit (Qiagen, Valencia, CA) standard definition of units (Furlong et al. increased risk after acute or chronic expo- as described by the manufacturer. 1989). The molar extinction coefficient of sure to chlorpyrifos in utero and in the phenol is 1,310. On the order of 5% of neonatal period. Genotyping the PON1 activity in plasma may be due Using maternal and cord blood, we have All PCR reactions were assembled using to serum cholinesterase and serum albu- carried out a systematic study of the origin standard precautions in an ultraviolet- min (Gan et al. 1991). This contribution and extent of variation in PON1 activities in irradiated hood in a room dedicated to this was minimized by performing the assays our population of three racial/ethnic groups purpose to prevent carryover contamina- at high pH. A cholinesterase inhibitor, in comprising the majority of many inner-city tion. The PON1 –909G→C, L55M, and this case eserine sulfate, is also necessary populations: Caucasians, African Americans, Q192R and the PON2 C311S genotypes for specificity. The assay was first per- and Caribbean Hispanics. Specifically, we were determined by the clamp-dependent formed as described in a Hewlett-Packard address genotype–phenotype relationships allele-specific PCR (CD-ASPCR) method diode array spectrophotometer (Agilent, for all five polymorphisms and note differ- of Germer and Higuchi (1999). Real-time Palo Alto, CA) equipped with a cell ences among these three racial/ethnic PCR methods was selected because it is a holder equipped with a thermostat. The groups, highlighting the differences between single-tube assay and offers high through- assay was then adapted to 96-well format mothers and neonates. We also address LD put. The primer sequences for genotyping for high throughput and replication. A among the five polymorphisms, noting dif- were as follows: buffer solution (1.2×) was prepared as 12 ferences among of three racial/ethnic groups –909G→C: G (sense), 5´-TGCCTCT- mM Tris–HCl (pH 8.0), 1.2 mM CaCl2, that will affect inference of haplotypes.