Monoclonal Antibody to Marinobufagenin Downregulates TGFβ Profibrotic Signaling in Left Ventricle and Kidney and Reduces Tissue Remodeling in Salt‐Sensitive Hypertension

Abstract

BackgroundElevated levels of an endogenous Na/K‐ATPase inhibitor marinobufagenin accompany salt‐sensitive hypertension and are implicated in cardiac fibrosis. Immunoneutralization of marinobufagenin reduces blood pressure in Dahl salt‐sensitive (Dahl‐S) rats. The effect of the anti‐marinobufagenin monoclonal antibody on blood pressure, left ventricular (LV) and renal remodeling, and gene expression were investigated in hypertensive Dahl‐S rats.Methods and ResultsDahl‐S rats were fed high NaCl (8%, HS; n=14) or low NaCl (0.1%, LS; n=14) diets for 8 weeks. Animals were administered control antibody (LS control antibody, LSC; HS control antibody, HSC; n=7 per group) or anti‐marinobufagenin antibody once on week 7 of diet intervention (n=7 per group). Levels of marinobufagenin, LV, and kidney mRNAs and proteins implicated in profibrotic signaling were assessed. Systolic blood pressure was elevated (211±8 versus 133±3 mm Hg, P<0.01), marinobufagenin increased 2‐fold in plasma (P<0.05) and 5‐fold in urine (P<0.01), LV and kidney weights increased, and levels of LV collagen‐1 rose 3.5‐fold in HSC versus LSC. Anti‐marinobufagenin antibody treatment decreased systolic blood pressure by 24 mm Hg (P<0.01) and reduced organ weights and level of LV collagen‐1 (P<0.01) in hypertensive Dahl salt‐sensitive rats with anti‐marinobufagenin antibody versus HSC. The expression of genes related to transforming growth factor‐β–dependent signaling was upregulated in the left ventricles and kidneys in HSC versus LSC groups and became downregulated following administration of anti‐marinobufagenin antibody to hypertensive Dahl‐S rats. Marinobufagenin also activated transforming growth factor‐β signaling in cultured ventricular myocytes from Dahl‐S rats.ConclusionsImmunoneutralization of heightened marinobufagenin levels in hypertensive Dahl‐S rats resulted in a downregulation of genes implicated in transforming growth factor‐β pathway, which indicates that marinobufagenin is an activator of profibrotic transforming growth factor‐β–dependent signaling in salt‐sensitive hypertension.

The Cardiotonic Steroid Marinobufagenin Is a Predictor of Increased Left Ventricular Mass in Obesity: The African-PREDICT Study

“…It is via the inhibition of cardiac Na + /K + -ATPase and the concurrent downward Src signaling cascade that MBG promotes cardiac remodeling [ 15 , 16 ]. Similarly, in the Dahl-S model of salt-sensitive hypertension, MBG-activated cardiovascular TGF-β pro-fibrotic signaling via Na + /K + -ATPase resulted in an increase in LVMi while also promoting the development of fibrosis and cardiac remodeling [ 17 ].…”

“…Dahl-S rats on a high salt intake also developed left ventricular hypertrophy, which was accompanied by an increased sensitivity of cardiac Na + /K + -ATPase to MBG [ 31 ]. An increased sensitivity of cardiovascular Na + /K + -ATPase to the endogenous inhibitors may contribute to the exaggerated effect of MBG on the Na + /K + -ATPase-initiated down-stream pro-fibrotic signaling [ 15 , 17 ].…”

“…Taken together, the activation of the Na + /K + -ATPase-Src signaling cascade may be promoted with obesity and contribute to early cardiac remodeling. The inhibition of cardiac Na + /K + -ATPase as a result of MBG is associated with oxidative stress [ 33 ], cardiac myocyte apoptosis [ 21 ], collagen synthesis [ 15 , 17 ], and cardiac myocyte hypertrophy [ 17 ], which are all factors of overall structural cardiac changes. Meanwhile, the endocytosis of Na + /K + -ATPase with obesity is proposed to play an important role in promoting a pro-inflammatory environment [ 34 ]; further studies are needed to investigate the role of MBG on macrophage adhesion and cytokines activation in the cardiac remodeling of obese individuals.…”

“…Subsequent investigations into the pathophysiological role of MBG have yielded strong evidence of an adverse effect of excessive MBG on the cardiovascular system. In animal and experimental studies, MBG was shown to promote cardiac myocyte apoptosis [ 21 ], cardiovascular fibrosis, and cardiac hypertrophy [ 15 , 16 , 17 , 39 ]. While in humans, MBG was found to be associated with autonomic activity [ 40 ], microvascular dysfunction [ 41 ], arterial stiffness [ 13 , 42 ], and increased LVMi [ 19 ].…”

“…The latter occurs via the MBG inhibition of cardiovascular Na + /K + -ATPase [ 14 ]. Elevated MBG promotes cardiac fibrosis and hypertrophy in animals by way of the Na + /K + -ATPase-Src and/or Na + /K + -ATPase-SMAD-transforming growth factor beta (TGFβ) signaling cascades [ 15 , 16 , 17 ], which may involve oxidative stress initiated via Na + /K + -ATPase [ 18 ]. In humans with excessive MBG excretion, an independent cross-sectional association of MBG with increased left ventricular mass index (LVMi) [ 19 ] was demonstrated, but it is unknown whether obesity would further exacerbate this relationship.…”