Quantitative Analysis of the Plasma Proteome in Pre-eclampsia

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Abstract

There is currently no clinically useful screening test available to identify nulliparous women at high risk of developing pre-eclampsia. This study aimed to identify novel biomarkers using hypothesis generating proteomic methods applied to plasma samples obtained prior to clinical diagnosis of pre-eclampsia.Plasma samples taken at 15 weeks gestation from women who subsequently developed late pre-eclampsia (>34 weeks), early pre-eclampsia (<34 weeks) and two distinct groups of women with uncomplicated pregnancies (each n=12) were pooled. Pooled plasma was immunodepleted, labelled using iTRAQ-8 plex reagent and separated into fractions using high pH reverse phase chromatography. Fractions were analysed by LC-MS/MS and data interrogated using ProteinPilot 3.0.The merits of two immunodepletion systems were compared; the Seppro® IgY 14 -SuperMix LC column system removes up to 100 highly abundant plasma proteins and the Multiple Affinity Removal LC column depletes 14 highly abundant plasma proteins. Removal of more high abundance proteins allowed identification of more, potentially interesting, low abundance proteins, but was less reproducible than removing fewer proteins. Two methods of LC-MS/MS analysis were assessed; the QStar XL qTOF and 5800 MALDI–TOF-TOF. The protein identifications and the quantification data acquired by each method was comparable and complementary and increased the total number of proteins identified.A total of 502 proteins were identified. A stringent two stage analysis was developed to identify candidate proteins which changed in abundance in plasma from women who later developed pre-eclampsia compared to women with uncomplicated pregnancies. Analysis identified a total of 113 proteins which were both reproducibly quantified and changed by more than the expected range of biological variation. Six candidate proteins changed in abundance in the plasma taken from women who subsequently developed early pre-eclampsia were selected for further validation. A high throughput, low cost, method of multiple reaction monitoring which allows relative quantitation without the use of costly isotopically labelled peptides was developed to validate candidate proteins. Candidate proteins were also assessed by western blot and ELISA. Only one candidate protein; platelet basic protein, was validated by all three methods and demonstrated similar increases in the abundance.This investigation suggests that measurement of platelet basic protein at 15 weeks gestation is a novel candidate predictive marker for pre-eclampsia. Validation of platelet basic protein in a large, independent, sample set is required to confirm changes in protein expression and to evaluate potential, alongside other factors, to identify nulliparous women at high risk of developing pre-eclampsia later in pregnancy.

Keyword(s)

Biomarker; Pre-eclampsia; Proteomics

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