title: Measurement of plasma vitamin K1 (phylloquinone) and K2 (menaquinones-4 and -7) using HPLC-tandem mass spectrometry.
abstract: BACKGROUND
  Given the growing interest in the health benefits of vitamin K, there is great need for development of new high-throughput methods for quantitative determination of vitamin K in plasma. We describe a simple and rapid method for measurement of plasma vitamin K1 (phylloquinone [PK]) and K2 (menaquinones [MK]-4 and -7). Furthermore, we investigated the association of fasting plasma vitamin K with functional vitamin K insufficiency in renal transplant recipients (RTR).
  
  
  METHODS
  We used HPLC-tandem mass spectrometry with atmospheric pressure chemical ionization for measurement of plasma PK, MK-4, and MK-7. Solid-phase extraction was used for sample clean-up. Mass spectrometric detection was performed in multiple reaction monitoring mode. Functional vitamin K insufficiency was defined as plasma desphospho-uncarboxylated matrix Gla protein (dp-ucMGP) >500 pmol/L.
  
  
  RESULTS
  Lower limits of quantitation were 0.14 nmol/L for PK and MK-4 and 4.40 nmol/L for MK-7. Linearity up to 15 nmol/L was excellent. Mean recoveries were >92%. Fasting plasma PK concentration was associated with recent PK intake (ρ=0.41, p=0.002) and with plasma MK-4 (ρ=0.49, p<0.001). Plasma PK (ρ=0.38, p=0.003) and MK-4 (ρ=0.46, p<0.001) were strongly correlated with plasma triglyceride concentrations. Furthermore, we found that MK-4-triglyceride ratio, but not PK-triglyceride ratio, was significantly associated with functional vitamin K insufficiency (OR 0.22 [0.07-0.70], p=0.01) in RTR.
  
  
  CONCLUSIONS
  The developed rapid and easy-to-use LC-MS/MS method for quantitative determination of PK, MK-4, and MK-7 in human plasma may be a good alternative for the labor-intensive and time-consuming LC-MS/MS methods and enables a higher sample throughput.
authors.forename: Ineke J
authors.identifier: http://orcid.org/0000-0001-5500-0145
authors.initials: IJ
authors.lastname: Riphagen
authors.forename: Jan C
authors.initials: JC
authors.lastname: van der Molen
authors.forename: Martijn
authors.initials: M
authors.lastname: van Faassen
authors.forename: Gerjan
authors.initials: G
authors.lastname: Navis
authors.forename: Martin H
authors.initials: MH
authors.lastname: de Borst
authors.forename: Frits A J
authors.initials: FA
authors.lastname: Muskiet
authors.forename: Wilhelmina H A
authors.initials: WH
authors.lastname: de Jong
authors.forename: Stephan J L
authors.initials: SJ
authors.lastname: Bakker
authors.forename: Ido P
authors.initials: IP
authors.lastname: Kema
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D053719:Tandem Mass Spectrometry / Q000379:methods*; D010837:Vitamin K 1 / Q000097:blood*; D024482:Vitamin K 2 / Q000097:blood*
chemical_list: D024482:Vitamin K 2; D010837:Vitamin K 1