FKGK 18 is an inhibitor of group VIA (GVIA) calcium-independent phospholipase A2 (iPLA2). It inhibits GVIA iPLA2 by 99.9% at 0.091 mole fraction in a mixed micelle activity assay and is selective for GVIA iPLA2 over GIVA cPLA2 and GV sPLA2 where it shows 80.8 and 36.8% inhibition, respectively. FKGK 18 inhibits iPLA2β activity in cytosolic extracts from INS-1 cells overexpressing iPLA2β (IC50 = ~50 nM) as well as iPLA2γ activity in mouse heart membrane fractions (IC50s = ~1-3 μM). It inhibits glucose-induced increases in prostaglandin E2 production and insulin secretion in human pancreatic islets when used at a concentration of 10 μM and inhibits thapsigargin-induced apoptosis in INS-1 cells overexpressing iPLA2β in a concentration-dependent manner. FKGK 18 (20 mg/kg, 3 times per week) reduces blood glucose levels in an intraperitoneal glucose tolerance test, decreases the incidence of diabetes, and increases serum insulin levels in non-obese diabetic (NOD) mice.
The phospholipases are an extensive family of lipid hydrolases that function in cell signaling, digestion, membrane remodeling, and as venom components. The calcium-independent phospholipases (iPLA2) are a PLA2 subfamily closely associated with the release of arachidonic acid in response to physiologic stimuli. (R)-Bromoenol lactone ((R)-BEL) is an irreversible, chiral, mechanism-based inhibitor of calcium-independent phospholipase γ (iPLA2γ). Unlike (S)-BEL, (R)-BEL does not inhibit iPLA2β except at high doses of 20-30 μM. (R)-BEL inhibits human recombinant iPLA2γ with an IC50 of approximately 0.6 μM.
Arachidonoyl Thio-PC is a substrate for many phospholipase A2s (PLA2s) including sPLA2, cPLA2, and iPLA2. Cleavage of the sn-2 fatty acid by PLA2 results in generation of a free thiol which reacts with chromogenic reagents such as DTNB (Ellman's reagent) and DTP to allow quantitation of PLA2 activity. Isozyme-specific cPLA2 activity can be measured by excluding or inhibiting sPLA2 and iPLA2 activities in the assay.
GSK563 is a potent GVIA iPLA2 inhibitor (XI(50) 0.0000021, IC50 1 nM). GSK563 is 22 000 times more active against GVIA iPLA2 than GIVA cPLA2. It was found to reduce β-cell apoptosis induced by proinflammatory cytokines, raising the possibility that it can be beneficial in countering autoimmune diseases, such as type 1 diabetes.