PAF-receptor antagonists, lovastatin, and the PTK inhibitor genistein inhibit H₂O₂ secretion by macrophages cultured on oxidized-LDL matrices

Adhesion of mononuclear phagocytes (Macs) to extracellular matrices containing oxidized low-density lipoproteins (oxLDL) stimulates these cells to secrete reactive oxygen species (e.g., O₂^-, H ₂O₂) that are believed to promote atherogenesis. Current in vitro systems designed to measure Mac H₂O₂ secretion in response to oxLDL show that these cells secrete H₂O₂ for only a few hours after plating. The slow onset and chronicity of atherogenesis, however, suggested to us that Mac ROS secretion might be sustained for much longer periods when Macs are maintained in an environment resembling that in the intima of arteries undergoing atherogenesis. The findings reported here confirm this suggestion. They show that Macs maintained on collagen IV matrices containing oxLDL in medium containing human plasma-derived serum secrete H ₂O₂ continuously and in large amounts for at least 11 days. Using this system we tested the effects of compounds known to attenuate atherogenesis in vivo. Platelet-activating factor (PAF) receptor antagonists, lovaslatin, and the isoflavone protein tyrosine kinase (PTK) inhibitor genistein each reduced H₂O₂ secretion by Macs maintained on oxLDL-containing matrices by ∼60%. Lovastatin's inhibitory effect was blocked completely by addition of geranylgeranyl pyrophosphate to the medium. We conclude that matrix-bound and oxidized lipoproteins stimulate Macs to produce H₂O₂ continuously and in large quantities via a pathway that involves PAF receptors and PTK and is reversibly blocked by inhibitors of protein prenylation.