Associations between PON1 enzyme activities in human ovarian follicular fluid and serum specimens.

Keewan Kim,Victor Y Fujimoto,Michael S Bloom,Richard W Browne,Wan-Xi Yang

doi:10.1371/journal.pone.0172193

Abstract

The importance of high-density lipoprotein (HDL) particle components to reproduction is increasingly recognized, including the constituent paraoxonase 1 (PON1). However, the reliability characteristics of PON1 enzymes in ovarian follicular fluid (FF) as biomarkers for clinical and epidemiologic studies have not been described. Therefore, we characterized PON1 enzymes in FF and serum and assessed the impact of the PON1 Q192R polymorphism on associations between enzyme activities in two compartments. We also evaluated associations between HDL particle size and enzyme activities. We collected FF and serum from 171 women undergoing in vitro fertilization. PON1 activities were measured as paraoxonase and arylesterase activities, and HDL particle size was determined by 1H NMR spectrometry. Reliability indices for PON1 activities were characterized and we evaluated HDL particle sizes as predictors of PON1 enzyme activities. We found that PON1 enzyme activities were correlated between compartments, but higher in serum than in FF. For FF, the index of individuality (II) was low and the coefficient of variation (CV%) was high for paraoxonase activity overall (0.12 and 11.51%, respectively). However, IIs increased (0.33–1.30) and CV%s decreased (5.58%-8.52%) when stratified by PON1 Q192R phenotype. The intraclass correlation coefficient (ICC) for FF paraoxonase activity was high overall (0.89) but decreased when stratified by PON1 Q192R phenotype (0.43–0.75). We found similar, although more modest, patterns for FF arylesterase activity. For enzyme activities in serum, ICCs were close to 1.00 across all phenotypes. Additionally, different HDL particle sizes predicted PON1 enzyme activities according to PON1 Q192R phenotype. Overall, stratification by PON1 Q192R phenotype improved the reliability characteristics of FF PON1 enzymes as biomarkers for use in clinical investigations but diminished usefulness for epidemiologic studies. Thus, we recommend stratification by PON1 Q192R phenotype for clinical but not epidemiologic investigations, when employing FF PON1 enzyme activity biomarkers.

Highlights

High-density lipoprotein (HDL) provides the cholesterol substrate for steroid hormone synthesis in the human pre-ovulatory ovarian follicle [1], and has well-recognized anti-oxidant and anti-inflammatory properties likely to be of importance for reproduction [2]
Using 27 size-specific HDL particles measured in follicular fluid (FF), we identified that different individual HDL particles sizes predicted different paraoxonase 1 (PON1) enzyme activities according to PON1 Q192R phenotypes (Table 4)
We describe the distribution of PON1 enzyme activities in FF and serum by PON1 Q192R phenotype, calculate reliability indices, and identify PON1 Q192R phenotype-specific HDL-particle sizes associated with enzyme activities in a cohort of women undergoing in vitro fertilization (IVF)

Summary

Introduction

High-density lipoprotein (HDL) provides the cholesterol substrate for steroid hormone synthesis in the human pre-ovulatory ovarian follicle [1], and has well-recognized anti-oxidant and anti-inflammatory properties likely to be of importance for reproduction [2]. HDL functionality is driven, at least in part, by particle composition [3,4,5]. The HDL-particle comprises a dynamic micelle in which apolipoproteins frame a core of cholesteryl esters and triglycerides surrounded by a phospholipid monolayer; cholesterol, lipid-soluble micronutrients, and paraoxonase 1 (PON1) are integrated within [2]. PON1 is subject to several polymorphisms, the most studied of which is an arginine (R)-glutamine (Q) substitution at the 192nd amino acid [3]. This PON1 Q192R polymorphism is functional (meaning it affects enzyme activity) and the mutant R allele is prevalent among Asians [6, 7]. Our group previously reported associations between the activity of follicular fluid (FF) PON1 and embryo quality among women undergoing in vitro fertilization (IVF) [8], presumably due to reduced lipid peroxidation [9]

Methods

Results

Discussion

Conclusion