Received on May 7, 2009
Accepted on September 28, 2009

Proteomics and Protein Markers

Cerebrospinal Fluid Secretory Ca²⁺-Dependent Phospholipase A₂ Activity Is Increased in Alzheimer Disease

¹ New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York
² Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Mölndal, Sweden
³ Department of Neurology, Akershus University Hospital, Lørenskog, Norway, and Department of Neurology, Faculty Division Akershus University Hospital, University of Oslo, Oslo, Norway

^* To whom correspondence should be addressed. E-mail: khalid.iqbal.ibr{at}gmail.com.

BACKGROUND: The phospholipase A₂ (PLA2) family comprises multiple isoenzymes that vary in their physicochemical properties, cellular localizations, calcium sensitivities, and substrate specificities. Despite these differences, PLA2s share the ability to catalyze the synthesis of the precursors of the proinflammatory mediators. To investigate the potential of PLA2 as a biomarker in screening neuroinflammatory disorders in both clinical and research settings, we developed a PLA2 assay and determined the predominant types of PLA2 activity in cerebrospinal fluid (CSF).

METHODS: We used liposomes composed of a fluorescent probe (bis-Bodipy® FL C11-PC [1,2-bis-(4,4- difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-undecanoyl)-sn-glycero-3-phosphocholine]) and 1,2-dioleoyl-l--phosphatidylcholine as a substrate to measure CSF PLA2 activity in a 96-well microtiter plate format. We established the type of CSF PLA2 activity using type-specific inhibitors of PLA2.

RESULTS: Using 5 μL CSF per assay, our PLA2 activity assay was reproducible with CVs <15% in 2 CSF samples and for recombinant secretory Ca²⁺-dependent PLA2 (sPLA2) in concentrations ranging from 0.25 to 1 μmol/L. This PLA2 assay allowed identification of sPLA2 activity in lumbar CSF from healthy individuals 20–77 years old that did not depend on either sex or age. Additionally, CSF sPLA2 activity was found to be increased (P = 0.0008) in patients with Alzheimer disease.

CONCLUSIONS: Adult human CSF has sPLA2 activity that can be measured reliably with the assay described. This enzyme activity in the CSF is independent of both sex and age and might serve as a valuable biomarker of neuroinflammation, as we demonstrated in Alzheimer disease.