Dantrolene is an HDL-associated paraoxonase-1 activator with immunosuppressive and atheroprotective properties

Human paraoxonase 1 (PON1), an enzyme bound to high-density lipoprotein (HDL), hydrolyzes oxidized lipids and contributes to HDL atheroprotective functions. Decreased serum paraoxonase and arylesterase activities of PON1 have been reported in patients at increased atherosclerosis risk, such as rheumatoid arthritis patients, and associated with arthritis severity and cardiovascular risk. Agents that can modulate PON1 activity and HDL-mediated effects have not been discovered. Aiming to discover chemical tools that enhance PON1 activity, we screened a library of marketed drugs (956 compounds) to identify small molecules that can increase HDL-associated PON1 activity. Screening was performed by a kinetic absorbance assay using human HDL as a source of PON1, and paraoxon and phenyl acetate as substrates to measure paraoxonase and arylesterase activities, respectively. Screening identified the drug dantrolene as a potential PON1 activator, which was confirmed by enzymatic kinetic assays using recombinant wild-type PON1, as well as the PON1[L55M] variant displaying decreased enzyme activity in humans. Furthermore, we used the collagen-induced arthritis (CIA) mouse model to examine the effect of dantrolene on HDL properties and arthritis in vivo. Administration of dantrolene in CIA mice increased paraoxonase and arylesterase activities of PON1, as well as the antioxidant capacity of HDL, and reduced arthritis severity by inhibition of naïve CD4⁺ T cell differentiation to effector memory cells and generation of Th1 cells. Collectively, our in vitro and in vivo findings indicate using small molecules to enhance HDL-associated PON1 activity is a tractable approach that could lead to novel therapeutics targeting immune responses and atherosclerosis.