Characterization of FKGK18 as Inhibitor of Group VIA Ca(2+)-Independent Phospholipase A(2) (iPLA(2)β): Candidate Drug for Preventing Beta-Cell Apoptosis and Diabetes

Ongoing studies suggest an important role for iPLA(2)β in a multitude of biological processes and it has been implicated in neurodegenerative, skeletal and vascular smooth muscle disorders, bone formation, and cardiac arrhythmias. Thus, identifying an iPLA(2)βinhibitor that can be reliably and safely used in vivo is warranted. Currently, the mechanism-based inhibitor bromoenol lactone (BEL) is the most widely used to discern the role of iPLA(2)β in biological processes. While BEL is recognized as a more potent inhibitor of iPLA(2) than of cPLA(2) or sPLA(2), leading to its designation as a “specific” inhibitor of iPLA(2), it has been shown to also inhibit non-PLA(2) enzymes. A potential complication of its use is that while the S and R enantiomers of BEL exhibit preference for cytosol-associated iPLA(2)β and membrane-associated iPLA(2)γ, respectively, the selectivity is only 10-fold for both. In addition, BEL is unstable in solution, promotes irreversible inhibition, and may be cytotoxic, making BEL not amenable for in vivo use. Recently, a fluoroketone (FK)-based compound (FKGK18) was described as a potent inhibitor of iPLA(2)β. Here we characterized its inhibitory profile in beta-cells and find that FKGK18: (a) inhibits iPLA(2)β with a greater potency (100-fold) than iPLA(2)γ, (b) inhibition of iPLA(2)β is reversible, (c) is an ineffective inhibitor of α-chymotrypsin, and (d) inhibits previously described outcomes of iPLA(2)β activation including (i) glucose-stimulated insulin secretion, (ii) arachidonic acid hydrolysis; as reflected by PGE2 release from human islets, (iii) ER stress-induced neutral sphingomyelinase 2 expression, and (iv) ER stress-induced beta-cell apoptosis. These findings suggest that FKGK18 is similar to BEL in its ability to inhibit iPLA(2)β. Because, in contrast to BEL, it is reversible and not a non-specific inhibitor of proteases, it is suggested that FKGK18 is more ideal for ex vivo and in vivo assessments of iPLA(2)β role in biological functions.