title: Measurement of apo(a) kinetics in human subjects using a microfluidic device with tandem mass spectrometry.
abstract: BACKGROUND
  Apolipoprotein(a) [apo(a)] is the defining protein component of lipoprotein(a) [Lp(a)], an independent risk factor for cardiovascular disease. The regulation of Lp(a) levels in blood is poorly understood in part due to technical challenges in measuring Lp(a) kinetics. Improvements in the ability to readily and reliably measure the kinetics of apo(a) using a stable isotope labeled tracer is expected to facilitate studies of the role of Lp(a) in cardiovascular disease. Since investigators typically determine the isotopic labeling of protein-bound amino acids following acid-catalyzed hydrolysis of a protein of interest [e.g., apo(a)], studies of protein synthesis require extensive protein purification which limits throughput and often requires large sample volumes. We aimed to develop a rapid and efficient method for studying apo(a) kinetics that is suitable for use in studies involving human subjects.
  
  
  METHODS
  Microfluidic device and tandem mass spectrometry were used to quantify the incorporation of [(2)H3]-leucine tracer into protein-derived peptides.
  
  
  RESULTS
  We demonstrated that it is feasible to quantify the incorporation of [(2)H3]-leucine tracer into a proteolytic peptide from the non-kringle repeat region of apo(a) in human subjects. Specific attention was directed toward optimizing the multiple reaction monitoring (MRM) transitions, mass spectrometer settings, and chromatography (i.e., critical parameters that affect the sensitivity and reproducibility of isotopic enrichment measurements). The results demonstrated significant advantages with the use of a microfluidic device technology for studying apo(a) kinetics, including enhanced sensitivity relative to conventional micro-flow chromatography, a virtually drift-free elution profile, and a stable and robust electrospray.
  
  
  CONCLUSIONS
  The technological advances described herein enabled the implementation of a novel method for studying the kinetics of apo(a) in human subjects infused with [(2)H3]-leucine.
authors.affiliation: Molecular Biomarkers-PPDM, Merck Sharp & Dohme Corp., Whitehouse Station, NJ, USA.
authors.forename: Haihong
authors.initials: H
authors.lastname: Zhou
authors.forename: Jose
authors.initials: J
authors.lastname: Castro-Perez
authors.forename: Michael E
authors.initials: ME
authors.lastname: Lassman
authors.forename: Tiffany
authors.initials: T
authors.lastname: Thomas
authors.forename: Wenyu
authors.initials: W
authors.lastname: Li
authors.forename: Theresa
authors.initials: T
authors.lastname: McLaughlin
authors.forename: Xie
authors.initials: X
authors.lastname: Dan
authors.forename: Patricia
authors.initials: P
authors.lastname: Jumes
authors.forename: John A
authors.initials: JA
authors.lastname: Wagner
authors.forename: David E
authors.initials: DE
authors.lastname: Gutstein
authors.forename: Brian K
authors.initials: BK
authors.lastname: Hubbard
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Rader
authors.forename: John S
authors.initials: JS
authors.lastname: Millar
authors.forename: Henry N
authors.initials: HN
authors.lastname: Ginsberg
authors.forename: Gissette
authors.initials: G
authors.lastname: Reyes-Soffer
authors.forename: Michele
authors.initials: M
authors.lastname: Cleary
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Previs
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Roddy
mesh_terms: D001054:Apolipoproteins A / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D046210:Microfluidic Analytical Techniques / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D001054:Apolipoproteins A