An endogenous steroid marinobufagenin (MBG) induces fibrosis via inhibition of Fli1, a nuclear transcription factor and a negative regulator of collagen synthesis. Because immunization against MBG reduced cardiac fibrosis but minimally affected blood pressure (BP) in uremic rats (Hypertension, 2007;49:215–24), we hypothesized that MBG induces cardiovascular fibrosis via BP-independent mechanism.

We measured BP, urinary MBG, aortic collagen-1, and vascular function in NaCl-loaded male Wistar rats with type 2 diabetes mellitus (DM-NaCl) and in non-diabetic control rats (Ctrl). DM was induced by administration of 65 mg/kg streptozotocin to neonatal animals. At three months, 24 diabetic rats were dietary supplemented with 1.8% NaCl added to the drinking water for four weeks following which rats were twice administered monoclonal anti-MBG antibody (mAb) (n=12), or vehicle (n=12). Isolated rings of thoracic aortae were tested for their responsiveness to endothelin-1 and to sodium nitroprusside (SNP) following endothelin-1-induced constriction.

DM-NaCl rats exhibited a 3.5-fold increase in MBG excretion (25.4±4.5 vs. 7.7±1.5 nmoles in Ctrl; P<0.001) and 2.5-fold increase in collagen-1 in thoracic aortae in the absence of changes of BP or renal function. Compared to Ctrl, in aortic rings from DM-NaCl the responsiveness to endothelin-1 was unaltered (EC₅₀=2.2 and 3.2 nmol/L, respectively), but the response to the relaxant effect of SNP was impaired (EC₅₀=29 vs. EC₅₀=7 nmol/L P<0.001). In vivo administration of mAb to DM-NaCl rats did not affect BP, but reduced aortic collagen-1, and restored sensitivity of aortic rings to SNP (EC₅₀=9 nmol/L). Thus, MBG induces vascular fibrosis and increases vascular stiffness without affecting BP.