Paraoxanase-1 Modulates Cardiotonic Steroid Induced Cardiac Inflammation And Fibrosis In Dahl Salt Sensitive Model Of Chronic Kidney Disease

Objective: Cardiotonic steroids (CTS) are known ligands of the Na+/K+-ATPase (NKA) and chronic elevations in volume expanded conditions such as hypertension and chronic kidney disease (CKD) can mediate a pro-inflammatory and pro-fibrotic phenotype. Paraoxonase1 (PON1) is a lactonase enzyme that circulates bound to HDL and possesses antioxidant, anti-inflammatory and anti-atherogenic properties. PON1 can hydrolyze CTS to inactive open-ring forms making them incapable of stimulating NKA and initiating pro-inflammatory signaling cascades. Diminished PON1 activity results in detrimental clinical outcomes in the context of CKD but whether reduced PON1 activity is mechanistically linked to adverse cardiovascular events in CKD remains unknown. We hypothesized that PON-1 can attenuate progression of cardiac inflammation in CKD via modulating the pathogenic pathways induced by CTS signaling using a well characterized Dahl salt-sensitive rat model of hypertensive renal disease and elevated CTS. Methods: Dahl salt-sensitive wild type ( SS-WT ), PON1 knockout ( SS-PON1KO ), and PON1 knockout rats treated with 3E9 anti-CTS antibody (3E9 mAb,50μg/kg i.p. every week for a total of 4 injections) were fed a high salt (8%) diet for five weeks to induce hypertensive renal disease and elevate CTS levels. H&E staining was performed on hearts to analyze immune cell infiltration. Real-time PCR (RT-PCR) analysis was performed for markers of inflammation (IL6, IL1β, and CCL2), hypertrophy (Myh7, NPPA, and Slc8a), and fibrosis (Timp1). Results: RT-PCR analysis revealed significantly increased (≥1.5 fold) expression of cardiac inflammatory (p<0.005), hypertrophy (p<0.0005), and fibrotic markers (p<0.05) in SS-PON1 KO compared to SS-WT rats after high salt feeding. Treatment of SS-PON1 KO rats with 3E9 mAb significantly decreased (≥ 2.5 fold) expression of Timp1, IL6, Ccl2, IL1β, NPPA, Myh7 and Slc8a (all p<0.005). H&E analysis of hearts revealed significantly decreased immune cell infiltration in SS-PON1KO rats treated with 3E9 mAb compared to SS-PON-1 KO rats (3.5±0.5 VS1.813±0.4094,p<0.005). Conclusion: Our findings suggest that PON-1 via its counter-regulatory mechanism of the CTS signaling axis exhibits a cardioprotective role in chronic kidney disease.