Paraoxonase-1: How a xenobiotic detoxifying enzyme has become an actor in the pathophysiology of infectious diseases and cancer

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.

PON-1 and PON-2 Polymorphisms and PON-1 Paraoxonase Activity in People Living with HIV-1

Antiretroviral therapy (ART) has significantly improved the life expectancy of people living with HIV-1 (PLWH). However, prolonged ART use is linked to metabolic alterations and oxidative stress. The paraoxonase (PON) enzymes, especially PON-1 and PON-2, are critical in maintaining antioxidant balance. Their activity can be influenced by polymorphisms such as Q192R and L55M in PON-1 and A148G and S311C in PON-2. This study examines the impact of these polymorphisms on paraoxonase activity, lipid metabolism, and infection markers in PLWH under various ART regimens. This is a case-control study with 525 participants, 175 healthy controls (HC) and 350 PLWH divided into subgroups: T0 (ART-naïve, n = 48), T1 (ART with reverse transcriptase inhibitors, n = 159), and T2 (ART with protease inhibitors, n = 143). Paraoxonase activity was higher in PLWH (123.0; IQR: 62.0-168.0) compared to HC (91.0; IQR: 48.0-136.0, p < 0.001) but similar between HC and T0 (p = 0.594). T1 (125.0; IQR: 65.5-166.0) and T2 (123.0; IQR: 61.0-182.0) showed higher activity than HC (p = 0.002 and 0.003). Among 61 complete genotypes, 13 were unique to PLWH and 6 to HC (p < 0.001). L55L was more frequent in HC (49.7% vs. 36.9% in PLWH), while M55M was higher in PLWH (p = 0.004). The S311C genotype was more frequent in HC (39.2%) than PLWH (24.9%) (p = 0.003). The L55L genotype conferred 59.9% protection against HIV-1 (OR: 0.401; 95% CI: 0.228-0.704), while the M allele increased susceptibility by ~69% (OR: 1.694; 95% CI: 1.173-2.446). The M55M genotype and/or M allele may be linked to HIV-1 susceptibility. Prolonged ART use elevates PON-1 activity in PLWH.

J, Ahmad SF, Attia SM, Emran TB, Patil RB, Ahmed SSSJ. Structural Characteristics of PON1 with Leu55Met and Gln192Arg Variants Influencing Oxidative-Stress-Related Diseases: An Integrated Molecular Modeling and Dynamics Study

Background and Objectives: PON1 is a multi-functional antioxidant protein that hydrolyzes a variety of endogenous and exogenous substrates in the human system. Growing evidence suggests that the Leu55Met and Gln192Arg substitutions alter PON1 activity and are linked with a variety of oxidative-stress-related diseases. Materials and Methods: We implemented structural modeling and molecular dynamics (MD) simulation along with essential dynamics of PON1 and molecular docking with their endogenous (n = 4) and exogenous (n = 6) substrates to gain insights into conformational changes and binding affinity in order to characterize the specific functional ramifications of PON1 variants. Results: The Leu55Met variation had a higher root mean square deviation (0.249 nm) than the wild type (0.216 nm) and Gln192Arg (0.202 nm), implying increased protein flexibility. Furthermore, the essential dynamics analysis confirms the structural change in PON1 with Leu55Met vs. Gln192Arg and wild type. Additionally, PON1 with Leu55Met causes local conformational alterations at the substrate binding site, leading to changes in binding affinity with their substrates. Conclusions: Our findings highlight the structural consequences of the variants, which would increase understanding of the role of PON1 in the pathogenesis of oxidative-stress-related diseases, as well as the management of endogenous and exogenous chemicals in the treatment of diseases.