A robust immunoassay for pregnancy-associated plasma protein-A2 based on analysis of circulating antigen: establishment of normal ranges in pregnancy

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  • Søren Kløverpris, Danmark
  • Ervinas Gaidamauskas, Danmark
  • Louise Carøe Vohlander Rasmussen, Danmark
  • Michael Toft Overgaard, Institut for Kemi og Bioteknologi, Danmark
  • Christian Kronborg
  • Ulla Breth Knudsen
  • Michael Christiansen, Danmark
  • A Kumar, Ansh Labs, USA
  • Claus Oxvig
Pregnancy-associated plasma protein-A (PAPP-A) and PAPP-A2, two homologous metzincin metalloproteases, are both tightly linked to regulation within the insulin-like growth factor (IGF) system because of their specific cleavage of IGF binding proteins. Recent studies suggest that PAPP-A may be involved in clinical conditions related to unwanted cellular growth, and the circulating levels of PAPP-A is an established biomarker in prenatal screening for chromosomal abnormalities. Microarray data indicate that PAPP-A2 has potential as a biomarker for pre-eclampsia. However, well-characterized immunological methods of quantification are not available. We therefore developed monoclonal antibodies against recombinant PAPP-A2. The antibodies were epitope mapped against recombinantly expressed chimeras between PAPP-A2 and PAPP-A. Furthermore, circulating PAPP-A2 was immunoaffinity purified and characterized by sequence analysis and mass spectrometry. Unlike PAPP-A, PAPP-A2 is a noncovalent dimer in which each subunit of 1558 amino acids originates from all of the 22 predicted coding exons. A previously hypothesized variant (PAPP-E) does not exist, but low amounts of a C-terminally truncated PAPP-A2 variant was detected. A sensitive and robust ELISA for full-length PAPP-A2 was developed and used to establish normal ranges of PAPP-A2 through pregnancy. The functional sensitivity of this ELISA at 20% CV was 0.08 ng/ml, and the serum concentration of PAPP-A2 was found to increase during pregnancy in agreement with placental synthesis. The existence of this assay will enable an assessment of the biomarker potential of PAPP-A2 in pre-eclampsia as well as other clinical conditions.
OriginalsprogEngelsk
TidsskriftMolecular Human Reproduction
Vol/bind19
Nummer11
Sider (fra-til)756-763
Antal sider8
ISSN1360-9947
DOI
StatusUdgivet - nov. 2013

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