Direct Immunoassay for Free Pregnancy-Associated Plasma Protein A (PAPP-A)

Area of Science:

• Biochemistry
• Cardiology
• Assay Development

Background:

• Pregnancy-associated plasma protein A (PAPP-A), particularly its free form (fPAPP-A), is associated with vulnerable atherosclerotic plaques and increased cardiac event risk.
• A sensitive assay for detecting fPAPP-A has been a significant unmet need in clinical diagnostics.

Purpose of the Study:

• To develop and validate a direct assay for the sensitive and reliable measurement of free PAPP-A (fPAPP-A) in blood samples.
• To address the lack of a specific assay for fPAPP-A, crucial for assessing cardiovascular risk.

Main Methods:

• Development of monoclonal antibodies specific for fPAPP-A.
• Optimization of a direct immunoassay using an fPAPP-A-specific capture antibody and a labeled antibody recognizing all PAPP-A forms.
• Evaluation of the assay according to CLSI guidelines and comparison with a subtractive 2-assay method; clinical validation in acute coronary syndrome patients.

Main Results:

• The assay demonstrated high linearity (R2 = 0.999 up to 1000 mIU/L) with low limits of detection (0.4 mIU/L) and quantitation (1.3 mIU/L).
• The assay showed good performance in both serum and heparin plasma, with no significant interference from complexed PAPP-A.
• Higher fPAPP-A concentrations were observed in patients with myocardial infarction or 1-year mortality (1.13 mIU/L vs 0.82 mIU/L, P = 0.008), and the assay predicted clinical endpoints effectively.

Conclusions:

• A novel, direct assay for fPAPP-A has been successfully developed and validated.
• This assay provides sensitive and reliable quantification of fPAPP-A in blood, enabling better risk stratification for cardiac events.