Inhibition of the activity of pro-inflammatory secretory phospholipase A₂ by acute phase proteins

Abstract

Pro-Inflammatory non-pancreatic phospholipase A₂ (sPLA₂) is markedly over-expressed in acute systemic and chronic local inflammatory processes. Since in acute phase reaction sPLA₂ is often over-expressed simultaneously with acute phase proteins (APP), it is important to determine whether APP interacts with sPLA₂. We tested ten APPs for interaction with sPLA₂ using as a substrate multilamellar Hposomes composed either of PC:Lyso PC or PE:Lyso PE. Using PC:Lyso PC substrate, CRP, lactoferrin and SAP were found to inhibit sPLA₂ activity with an IC₅₀ of 25 μg/ml, 7.5 μg/ml and 50 μg/ml, respectively, corresponding to 0.21 μM, 0.1 μM and 0.21 μM respectively. Using PE:Lyso PE substrate only SAP was inhibitory, with an IC₅₀ of 10 μg/ml (0.04 μM). Phosphorylcholine abolished the inhibitory activity of CRP but not of SAP or lactoferrin. Addition of phosphorylethanolamine or of excess calcium had no effect on the inhibitory activity of APP. Limulin, lysozyme, transferrin, β₂-microglobulin, α₂-macroglobulin, human and bovine albumins had no effect on sPLA2 activity. Therefore neither the structure of pentraxins, or ironbinding, bacteriostatic property or amyloidogenic property preclude whether APP modulates sPLA₂ activity. Inhibition of pro-inflammatory sPLA₂ by APP may be one of the protective mechanisms of the acute phase reaction.