Determination of paraoxonase 1 status and genotypes at specific polymorphic sites.

The procedures for determining paraoxonase (PON1) status and for determining PON1 genotypes for polymorphisms in coding and important regulatory regions are described. PON1 status is determined by a functional two-substrate analysis of plasma PON1 activities. Differences in catalytic efficiency of the PON1192Q and PON1192R alloforms result in the clear separation of all three phenotypes at position 192 (Q/Q, Q/R, R/R) and at the same time, the two-substrate analysis indicates activity levels of PON1. Because the enzyme activity levels are as important as the polymorphic genotypes, this two-substrate analysis of PON1 status provides the most relevant information for investigating the association of PON1 genetics with susceptibilities to disease, organophosphorus insecticide sensitivity, and pharmacokinetic status of drug metabolism. Genotyping of polymorphic sites alone fails to provide this important information but can be useful for gene frequency determination and forensic analysis. Analytical procedures for determining PON1 status and genotypes are described.

Paraoxonase activity, but not haplotype utilizing the linkage disequilibrium structure, predicts vascular disease.

OBJECTIVE: The effects of paraoxonase (PON1) activity and of genetic variation in the PON1 promoter and coding region on carotid artery disease (CAAD) were investigated. METHODS AND RESULTS: We identified functional promoter polymorphisms and examined their effects in a cohort with and without CAAD. We used the full sequences in 23 white subjects to determine the linkage disequilibrium (LD) structure of the PON1 region and to direct the grouping of haplotypes for disease association testing. There are several discrete regions of the PON1 gene with strong local LD, but the useful levels of LD do not extend across the entire gene. Indeed, PON1-162/-108/55/192 haplotype did not predict additional variation in PON1 activities compared with the 4 genotypes separately. PON1 hydrolysis activity predicted CAAD status, but this was not attributable to the promoter or coding region polymorphisms or haplotype or to the effects of smoking or statin use on PON1 activity. CONCLUSIONS: PON1 does not have LD across the gene, and use of haplotypes in association studies should consider the LD structure. PON1 activity predicts CAAD, yet 4 functional polymorphisms do not. Additional investigations of genetic and environmental factors that influence PON1 activity as a risk factor for vascular disease are warranted.

Expression of human paraoxonase (PON1) during development.

BACKGROUND: Paraoxonase (PON1), a HDL-associated enzyme, protects against toxicity from specific organophosphorus compounds and oxidized lipids. Common polymorphisms in the PON1 gene have been identified and characterized in the coding region, 5' regulatory region and 3' UTR. The Q192R coding region polymorphism determines substrate-dependent differences in catalytic efficiency of hydrolysis. The -108CT polymorphism in the 5' regulatory region has a significant effect on PON1 expression, with the -108C allele expressing on average twice the level of plasma PON1 as the -108T allele. In addition to the effects of regulatory and coding region polymorphisms on PON1 levels and activity, plasma PON1 levels are also developmentally regulated. Since PON1 levels are important in determining resistance to specific organophosphorus compounds, the time course of appearance of PON1 in newborns is of great interest. RESULTS: We report here that PON1 levels plateau between 6 to 15 months of age, and that variability in the age at which PON1 levels plateau is quite variable among individuals. In mice and rats, plasma PON1 activity reaches a plateau at 3 weeks of age. In mice that lack endogenous PON1, human transgenes encoding either PON1(Q192) or PON1(R192) under the control of the human PON1 regulatory sequences exhibited a similar time course of expression as that seen in wild-type mice, indicating conservation of the developmental regulatory elements between mouse and human PON1.

Novel paraoxonase (PON1) nonsense and missense mutations predicted by functional genomic assay of PON1 status.

Paraoxonase (PON1) has been termed an environmental response enzyme for its function in the detoxification of organophosphate pesticides, nerve agents and pharmaceuticals such as glucocorticoids and statins, as well as its cardioprotective role in breaking down oxidized LDL. PON1(192) genotype can be predicted with high accuracy from an examination of the two-dimensional plot of paraoxon and diazoxon hydrolysis rates [ 1]. Individuals for whom this functional genomic assay failed to predict PON1(192) genotype, or who had a low PON activity relative to others with the same genotype, were predicted to have genetic alterations that explained the inconsistency. Sequencing of the PON1 region of 23 Caucasian individuals detected a nonsense mutation changing amino acid 194 from a Trp to a stop codon (PON1(Trp194stop)). It was predicted that subjects who genotyped as PON1(192QR) but phenotyped as PON1(192QQ) or PON1(192RR) might carry the protein truncation mutation for which the defective product failed to be detected by the phenotyping assay. Screening of the five discordant subjects resulted in the detection of a single Caucasian carrying the stop codon, and determined its phasing on the PON1(192R) allele. Sequencing confirmed the change and revealed an additional subject with a likely deletion of the 5' end of the PON1 gene. Additional sequencing of 25 subjects with low PON1 activities identified two additional previously undescribed PON1 mutations, which may affect PON1 function: PON1(Pro90Leu) associated with the PON1(192Q) allele and PON1(Asp124missplice) associated with the PON1(192R) allele.