title: A continuous fluorescence assay for the determination of calcium-dependent secretory phospholipase A2 activity in serum.
abstract: BACKGROUND
  Calcium-dependent secretory phospholipase A(2)-IIA (sPLA(2)-IIA) in the circulation is a marker of inflammation, associated with acute and chronic disease processes. We describe a quick, sensitive and reliable microplate continuous fluorescence assay for determining sPLA(2) activity in serum.
  
  
  METHODS
  Liposomes composed of a fluorescent probe and varying amounts of L-alpha-phosphatidylglycerol (PG) and 1,2-dioleoyl-L-alpha-phosphatidylcholine (DOPC) were used as substrates to determine the optimal protocol for sPLA(2) activity determination without interference from serum albumin and lipoproteins.
  
  
  RESULTS
  Hydrolysis of the labeled substrate by sPLA(2)-IIA, characterized by increase in fluorescence intensity (FI) and confirmed by end-product analysis, occurred in a time-, calcium-, and protein-dependent manner. Liposomes containing 100% PG were most suitable for measurement of sPLA(2) activity without interference from serum components; LDL produced a Ca(2+)-independent increase in FI when liposomes containing DOPC were used. The assay determined that sPLA(2) activity in serum spiked with sPLA(2)-IIA and illustrated that endogenous sPLA(2) activity was markedly higher in sera from patients with sepsis than in healthy subjects. Intra-assay and inter-assay CVs were in the ranges of 1.6-8.8% and 3.0-11.5%, respectively.
  
  
  CONCLUSIONS
  The described method has potential for rapid and sensitive screening of sPLA(2) activity in both clinical and research settings.
authors.affiliation: Department of Medicine, Section of Pulmonary and Critical Care Medicine, University of Wisconsin Medical School, Madison, WI 53792, USA. fhtao@wisc.edu
authors.forename: Francis H C
authors.initials: FH
authors.lastname: Tsao
authors.forename: Dhanansayan
authors.initials: D
authors.lastname: Shanmuganayagam
authors.forename: Derek K
authors.initials: DK
authors.lastname: Zachman
authors.forename: Mehdi
authors.initials: M
authors.lastname: Khosravi
authors.forename: John D
authors.initials: JD
authors.lastname: Folts
authors.forename: Keith C
authors.initials: KC
authors.lastname: Meyer
mesh_terms: D008078:Cholesterol, LDL / Q000097:blood; D054501:Group II Phospholipases A2; D006801:Humans; D010741:Phospholipases A / Q000097:blood*; D054467:Phospholipases A2; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence / Q000379:methods* / Q000592:standards*; D013379:Substrate Specificity
chemical_list: D008078:Cholesterol, LDL; D010741:Phospholipases A; D054501:Group II Phospholipases A2; D054467:Phospholipases A2