Human HDL-associated paraoxonase (PON1) hydrolyzes a number of toxic organophosphorous compounds and reduces oxidation of LDLs and HDLs. These properties of PON1 account for its ability to protect against pesticide poisonings and atherosclerosis. PON1 also hydrolyzes a number of lactone and cyclic-carbonate drugs. Among individuals in a population, PON1 levels vary widely. We previously identified three polymorphisms in the PON1 regulatory region that affect expression levels in cultured human hepatocytes. In this study, we determined the genotypes of three regulatory-region polymorphisms for 376 white individuals and examined their effect on plasma-PON1 levels, determined by rates of phenylacetate hydrolysis. The -108 polymorphism had a significant effect on PON1-activity level, whereas the -162 polymorphism had a lesser effect. The -909 polymorphism, which is in linkage disequilibrium with the other sites, appears to have little or no independent effect on PON1-activity level in vivo. Other studies have found that the L55M polymorphism in the PON1-coding region is associated with differences in both PON1-mRNA and PON1-activity levels. The results presented here indicate that the L55M effect of lowered activity is not due to the amino acid change but is, rather, largely due to linkage disequilibrium with the -108 regulatory-region polymorphism. The codon 55 polymorphism marginally appeared to account for 15.3% of the variance in PON1 activity, but this dropped to 5% after adjustments for the effects of the -108 and Q192R polymorphisms were made. The -108C/T polymorphism accounted for 22.8% of the observed variability in PON1-expression levels, which was much greater than that attributable to the other PON1 polymorphisms. We also identified four sequence differences in the 3' UTR of the PON1 mRNA.

Abstract-The paraoxonase (PON1) PON1-Q192R and PON1-L55M polymorphisms have been inconsistently associated with vascular disease. Plasma PON1 activity phenotypes vary markedly within genotypes and were, therefore, expected to add to the informativeness of genotype for predicting vascular disease. The case-control sample included 212 ageand race-matched men (mean age 66.4 years). The 106 carotid artery disease (CAAD) cases had Ͼ80% carotid stenosis, and the 106 controls had Ͻ15%. [15][16][17] The cardioprotective role of HDL, the inhibition or reduction of atherogenic LDL oxidation, appears to be, in large part, a function of PON1, which is associated with HDL. 18 -22 PON1 metabolizes mildly oxidized phospholipids, presumably by eliminating hydroperoxy derivatives of unsaturated fatty acids. 20 Thus, the PON1-CVD association is expected to result from the role of PON1 in the metabolism of bioactive lipid molecules and protection against damage due to oxidized LDL.PON1 hydrolyzes a variety of substrates, including the toxic components of the pesticides parathion, chlorpyrifos, and diazinon; aryl esters, such as phenyl acetate; and the nerve agents soman and sarin. There is 10-to 40-fold interindividual variability in rates of paraoxon hydrolysis. 23 The PON1 192Q allele has the higher rate of in vitro hydrolysis of diazoxon, sarin, and soman, 24 whereas the PON1 192R allele has higher activity for the hydrolysis of paraoxon and chlorpyrifos oxon. 24,25 These rates of substrate hydrolysis are quite variable within PON1 genotypes (at least 13-fold) and represent phenotypes that can add information about PON1 status beyond genotyping alone. 24 Paraoxon hydrolysis activity is lost in the plasma of the PON1 knockout mouse, and these mice are more susceptible to atherosclerosis. 26 We compared the PON1 192 and PON1 55 genotypes with PON1 rates of hydrolysis of paraoxon (POase activity) and diazoxon (DZOase activity) for their predictiveness in vascular disease of the carotid arteries. These 2 substrates were chosen because, relative to the other isoform, the PON1 192Q isoform has a higher DZOase activity and the PON1 192R isoform has a higher POase activity in the in vitro assays. The resulting 2D plot (Figure 1) allows an accurate inference of PON1 192 genotype, in addition to providing PON1 phenotype information. 27 Methods Sample

Objective-Paraoxonase (PON1), an esterase physically associated with high density lipoprotein, has been shown to inhibit atherogenic low density lipoprotein and high density lipoprotein oxidation. PON1 activity appears to be primarily under genetic control with some environmental modification and is a predictor of vascular disease. Vitamins C and E, dietary antioxidants, scavenge free-oxygen radical products that may depress PON1 activity. Therefore, we evaluated the relationship between dietary vitamin C and E intake and PON1 activity. Methods and Results-The vitamin C and E intakes of male white subjects (nϭ189) were estimated by using a standardized food frequency survey. With covariates, vitamin C or E intakes were found to be significant positive predictors of PON1 activity for the hydrolysis of paraoxon and diazoxon with the use of linear regression. Smoking and use of statins were independent predictors of PON1 activity. Conclusions-PON1 activity, which is primarily genotype dependent, varies with antioxidant vitamins, cigarette smoking, and statin drug use. Because PON1 activity is a better predictor of vascular disease than is the currently described genetic variation in PON1, further studies of the environmental influences on PON1 activity and additional PON1 genetic variants are warranted.