Abstract 13166: Paraoxonase-3 Regulation of Cardiotonic Steroids Mediates Renal Injury and Dysfunction in a Dahl Salt Sensitive Model of Chronic Kidney Disease

Abstract

Background: Paraoxonases (Pons) belong to a family of hydrolytic enzymes with 3 distinct isoforms: Pon 1, 2, and 3. While the physiologic substrates for Pons are unclear, their lactonase activity is considered central to their native physiological role. We have previously demonstrated an association between diminished Pon lactonase activity and worse clinical outcomes in volume expanded states such as chronic kidney disease (CKD). Furthermore, we have identified a novel reno-protective role for Pon3 in hypertensive renal disease. However, the underlying mechanism(s) are unknown. Cardiotonic steroids (CTS) are natriuretic hormones that are increased in CKD and promote renal inflammation and fibrosis via binding of their 17β-lactone ring to the alpha-1 subunit of the Na + /K + -ATPase (NKA-α-1). Therefore, we tested the hypothesis that reduction of Pon3 lactonase activity would lead to increased renal injury and dysfunction in a CTS induced rat model of CKD. Methods/Results: Experiments were performed on Dahl salt-sensitive rats (SS rats) and Pon3 knock-out rats on the Dahl salt-sensitive background (SS- Pon3 KO). First, CTS levels in the urine of SS control and SS- Pon3 KO rats were quantified using mass spectrometry. We found that SS- Pon3 KO rats had 59 times greater increase in 24-hour urine CTS levels vs SS rats. Next, to examine the role of Pon3 in mediating CTS induced renal injury, ten-week-old, age-matched male SS control and SS- Pon3 KO rats were administered the CTS telocinobufagin (TCB, 100 μg/kg/day s.q) for four weeks followed by assessment of blood pressure (tail cuff plethysmography) and renal function. We found that SS- Pon3 KO rats following TCB administration had significantly increased 24-hour urinary protein excretion (UPE) (50.73 ± 3.59vs 25.29 ± 2.07, p<0.0001), as well as decreased FITC-Sinistrin monitored glomerular filtration rate (GFR) (0.80 ± 0.10 vs 1.16 ± 0.05, p<0.01) compared to SS control rats, despite similar degrees of hypertension. Conclusion: These findings suggest that Pon3 plays a critical role in regulating CTS mediated renal dysfunction in vivo.