Inhibition of enzymatic activity of phospholipases A 2 by minocycline and doxycycline

Abstract

Extracellular phospholipases A 2 play an important role in articular and extra-articular inflammatory processes. Secretory non-pancreatic phospholipase A 2 (PLA 2) has been implicated in the pathogenesis of articular inflammation in rheumatoid arthritis, whereas pancreatic PLA 2 contributes to the tissue damage associated with acute pancreatitis. Since in experimental models lipophilic tetracyclines such as minocycline and doxycycline are antiinflammatory, we examined their effects on PLA 2 activity using two assay systems in vitro. We found that minocycline and to a lesser degree doxycycline were markedly inhibitory to both pancreatic and non-pancreatic PLA 2. Using [ 14C]oleic acid labeled Escherichia coli membrane phospholipids as substrate, the IC 50 values for minocycline and doxycycline were 3.6 × 10 −50 M (18 μg/mL) and 0.98 × 10 −4 M (47 μ/mL), respectively. In a scooting mode assay using the synthetic phospholipid 1-palmitoyl-2-(10-pyrenedecanoyl)-3-L-phosphatidylmethanol as substrate, ic 50 values for minocycline were 5 muM (2.47 μg/mL) for non-pancreatic PLA 2 and 8muM (3.95 μg/mL) for pancreatic PLA 2. Addition of excess calcium up to 50 mM did not reverse the inhibitory activity of tetracyclines. We conclude that lipophilic tetracyclines inhibit PLA 2, probably by interaction with the substrate, and may be a useful adjunct in the therapy of inflammatory conditions in which PLA 2 is implicated pathogenetically.