Abstract 14650: A Monoclonal Antibody to a Sodium Pump Inhibitor Marinobufagenin Reversed Aortic Remodeling and Stiffness in Normotensive Rats on a High Salt Intake

Abstract

Background: Marinobufagenin (MBG), an endogenous cardiotonic steroid, is a Na/K-ATPase inhibitor and a vasoconstrictor. Previously it was demonstrated, that administration of 3E9 anti-MBG-antibody (mAb) reduced blood pressure (BP) and reversed left ventricular fibrosis in animal models of salt-sensitive hypertension and nephropathy. In the present study we investigated whether mAb alleviates BP and vascular remodeling in normotensive rats on a high salt intake. Methods: Wistar rats (5 months old) received normal salt diet (CTRL; n=8) or high salt intake (2% NaCl in drinking water) for 4 weeks. Rats on a high salt were administered vehicle (SALT; n=8) or mAb (50 ug/kg) (SALT-AB; n=8) 3 times during the last week of a high salt diet. BP was measured at baseline, after 3 and 4 weeks of experiment. Na/K-ATPase activity was measured in erythrocytes. Aortas were weighed, and were used to study sensitivity to the vasorelaxant effect of sodium nitroprusside (SNP), and for the histochemistry analysis of collagen deposition. Renal 24-hr MBG excretion was measured at week 4. Results: In SALT vs. CTRL, in the absence of BP changes, elevated levels of MBG (14.1±1.1 vs. 9.0±1.6 pmol/24hr, p<0.05) were associated with inhibition of erythrocyte Na/K-ATPase (12.6±0.3 vs. 14.2±0.35 μmol Pi/ml/hr, p<0.05), increased aortic weights (217±15 vs. 158±9 mg/kg BW, p<0.01), increased levels of collagen in aorta (2.5-fold; p<0.05), and compromised SNP vasorelaxant effect in aortic explants (EC50=167±19.3 nM vs. 99±2.0 nM; P<0.01). Antibody treatment in SALT-AB vs. SALT increased Na/K-ATPase activity (13.93±0.54 μmol Pi/ml/hr, p<0.05), reduced the aortic weight (180±12 mg/kg; P<0.05) and collagen deposition 3-fold (P<0.05), and restored the vasorelaxation of aortic rings by SNP to the levels in CTRL (70±1.5 nM, p<0.01). Conclusion: These findings for the first time demonstrated that in normotensive rats on a high salt intake heightened MBG levels induced vascular fibrosis and impairment of vasorelaxation in the absence of blood pressure changes. Immunoneutralization of MBG reversed these changes. Thus, high dietary NaCl intake in normotensive animals can stimulate vascular fibrosis via pressure-independent/ MBG-dependent mechanisms, and this remodeling is reversible.