Dietary Sodium Restriction Reduces Arterial Stiffness, Vascular TGF-β-Dependent Fibrosis and Marinobufagenin in Young Normotensive Rats

Urinary Marinobufagenin in Patients with Non-Advanced Chronic Kidney Disease: A Cross-Sectional Study

Background and Objectives: The global prevalence of chronic kidney disease (CKD) is on the rise, posing important challenges for healthcare systems. Thus, the search for new factors potentially involved in the pathogenesis, progression and complications of early CKD remains urgent. Marinobufagenin (MBG) is a natriuretic endogenous cardiotonic steroid, and increased circulating levels of it may accelerate kidney damage. In this study, we explored the possible clinical significance of measuring urinary marinobufagenin (uMBG) in patients with non-advanced CKD. Materials and Methods: One hundred and eight adult CKD patients (mean age 71.6 ± 10 years, 70.4% male; mean eGFR 40.54 ± 17 mL/min/1.73 m2) were enrolled in this cross-sectional study. uMBG was measured together with a series of clinical, anthropometric, laboratory and instrumental analyses. Twenty-five healthy matched subjects served as controls for the uMBG measurement. Results: The uMBG values were lower in the patients with CKD as compared to those of the controls (0.37 [IQR: 0.25-0.45] vs. 0.64 [0.46-0.78] nmol/L. p = 0.004), and a significant trend in eGFR levels was noticed across the decreasing uMBG tertiles (p = 0.03). Regarding the correlation analyses, the uMBG values remained robustly associated with the eGFR in multivariate models employing either uMBG or eGFR as the dependent variable (β = 0.248; p = 0.01 and β = 0.139; p = 0.04, respectively). Besides the eGFR, the independent predictors of uMBG values in this population were the use of statins (β = -0.326; p = 0.001), the presence of diabetes (β = 0.243; p = 0.009) and urine sodium (β = 0.204; p = 0.01). Conclusions: Reduced uMBG excretion may reflect impaired renal clearance, which may contribute to the detrimental effects attributed to this hormone due to systemic accumulation. Future studies are needed to clarify the biological mechanisms placing uMBG at the crossroad of sodium intake and the presence of diabetes in CKD-suffering individuals and to verify whether a statin treatment may somewhat limit the detrimental effects of MBG in the presence of impaired renal function.

New Insights on the Role of Marinobufagenin from Bench to Bedside in Cardiovascular and Kidney Diseases

Marinobufagenin (MBG) is a member of the bufadienolide family of compounds, which are natural cardiac glycosides found in a variety of animal species, including man, which have different physiological and biochemical functions but have a common action on the inhibition of the adenosine triphosphatase sodium-potassium pump (Na+/K+-ATPase). MBG acts as an endogenous cardiotonic steroid, and in the last decade, its role as a pathogenic factor in various human diseases has emerged. In this paper, we have collated major evidence regarding the biological characteristics and functions of MBG and its implications in human pathology. This review focused on MBG involvement in chronic kidney disease, including end-stage renal disease, cardiovascular diseases, sex and gender medicine, and its actions on the nervous and immune systems. The role of MBG in pathogenesis and the development of a wide range of pathological conditions indicate that this endogenous peptide could be used in the future as a diagnostic biomarker and/or therapeutic target, opening important avenues of scientific research.

Silencing of PKG1 Gene Mimics Effect of Aging and Sensitizes Rat Vascular Smooth Muscle Cells to Cardiotonic Steroids: Impact on Fibrosis and Salt Sensitivity

Background Marinobufagenin, NKA (Na/K-ATPase) inhibitor, causes vasoconstriction and induces fibrosis via inhibition of Fli1 (Friend leukemia integration-1), a negative regulator of collagen synthesis. In vascular smooth muscle cells (VSMC), ANP (atrial natriuretic peptide), via a cGMP/PKG1 (protein kinase G1)-dependent mechanism, reduces NKA sensitivity to marinobufagenin. We hypothesized that VSMC from old rats, due to downregulation of ANP/cGMP/PKG-dependent signaling, would exhibit heightened sensitivity to the profibrotic effect of marinobufagenin. Methods and Results Cultured VSMC from the young (3-month-old) and old (24-month-old) male Sprague-Dawley rats and young VSMC with silenced PKG1 gene were treated with 1 nmol/L ANP, or with 1 nmol/L marinobufagenin, or with a combination of ANP and marinobufagenin. Collagen-1, Fli1, and PKG1 levels were assessed by Western blotting analyses. Vascular PKG1 and Fli1 levels in the old rats were reduced compared with their young counterparts. ANP prevented inhibition of vascular NKA by marinobufagenin in young VSMC but not in old VSMC. In VSMC from the young rats, marinobufagenin induced downregulation of Fli1 and an increase in collagen-1 level, whereas ANP blocked this effect. Silencing of the PKG1 gene in young VSMC resulted in a reduction in levels of PKG1 and Fli1; marinobufagenin additionally reduced Fli1 and increased collagen-1 level, and ANP failed to oppose these marinobufagenin effects, similar to VSMC from the old rats with the age-associated reduction in PKG1. Conclusions Age-associated reduction in vascular PKG1 and the resultant decline in cGMP signaling lead to the loss of the ability of ANP to oppose marinobufagenin-induced inhibition of NKA and fibrosis development. Silencing of the PKG1 gene mimicked these effects of aging.

Effect of Cardiotonic Steroid Marinobufagenin on Vascular Remodeling and Cognitive Impairment in Young Dahl-S Rats

The hypertensive response in Dahl salt-sensitive (DSS) rats on a high-salt (HS) diet is accompanied by central arterial stiffening (CAS), a risk factor for dementia, and heightened levels of a prohypertensive and profibrotic factor, the endogenous Na/K-ATPase inhibitor marinobufagenin (MBG). We studied the effect of the in vivo administration of MBG or HS diet on blood pressure (BP), CAS, and behavioral function in young DSS rats and normotensive Sprague-Dawley rats (SD), the genetic background for DSS rats. Eight-week-old male SD and DSS rats were given an HS diet (8% NaCl, n = 18/group) or a low-salt diet (LS; 0.1% NaCl, n = 14-18/group) for 8 weeks or MBG (50 µg/kg/day, n = 15-18/group) administered via osmotic minipumps for 4 weeks in the presence of the LS diet. The MBG-treated groups received the LS diet. The systolic BP (SBP); the aortic pulse wave velocity (aPWV), a marker of CAS; MBG levels; spatial memory, measured by a water maze task; and tissue collection for the histochemical analysis were assessed at the end of the experiment. DSS-LS rats had higher SBP, higher aPWV, and poorer spatial memory than SD-LS rats. The administration of stressors HS and MBG increased aPWV, SBP, and aortic wall collagen abundance in both strains vs. their LS controls. In SD rats, HS or MBG administration did not affect heart parameters, as assessed by ECHO vs. the SD-LS control. In DSS rats, impaired whole-heart structure and function were observed after HS diet administration in DSS-HS vs. DSS-LS rats. MBG treatment did not affect the ECHO parameters in DSS-MBG vs. DSS-LS rats. The HS diet led to an increase in endogenous plasma and urine MBG levels in both SD and DSS groups. Thus, the prohypertensive and profibrotic effect of HS diet might be partially attributed to an increase in MBG. The prohypertensive and profibrotic functions of MBG were pronounced in both DSS and SD rats, although quantitative PCR revealed that different profiles of profibrotic genes in DSS and SD rats was activated after MBG or HS administration. Spatial memory was not affected by HS diet or MBG treatment in either SD or DSS rats. Impaired cognitive function was associated with higher BP, CAS, and cardiovascular remodeling in young DSS-LS rats, as compared to young SD-LS rats. MBG and HS had similar effects on the cardiovascular system and its function in DSS and SD rats, although the rate of change in SD rats was lower than in DSS rats. The absence of a cumulative effect of increased aPWV and BP on spatial memory can be explained by the cerebrovascular and brain plasticity in young rats, which help the animals to tolerate CAS elevated by HS and MBG and to counterbalance the profibrotic effect of heightened MBG.

High-Salt Attenuates the Efficacy of Dapagliflozin in Tubular Protection by Impairing Fatty Acid Metabolism in Diabetic Kidney Disease

High-salt intake leads to kidney damage and even limits the effectiveness of drugs. However, it is unclear whether excessive intake of salt affects renal tubular energy metabolism and the efficacy of dapagliflozin on renal function in diabetic kidney disease (DKD). In this study, we enrolled 350 DKD patients and examined the correlation between sodium level and renal function, and analyzed influencing factors. The results demonstrated that patients with macroalbuminuria have higher 24 h urinary sodium levels. After establishment of type 2 diabetes mellitus model, the animals received a high-salt diet or normal-salt diet. In the presence of high-salt diet, the renal fibrosis was aggravated with fatty acid metabolism dysregulation. Furthermore, Na+/K+-ATPase expression was up-regulated in the renal tubules of diabetic mice, while the fatty acid metabolism was improved by inhibiting Na+/K+-ATPase of renal tubular epithelial cells. Of note, the administration with dapagliflozin improved renal fibrosis and enhanced fatty acid metabolism. But high salt weakened the above-mentioned renal protective effects of dapagliflozin in DKD. Similar results were recapitulated in vitro after incubating proximal tubular epithelial cells in high-glucose and high-salt medium. In conclusion, our results indicate that high salt can lead to fatty acid metabolism disorders by increasing Na+/K+-ATPase expression in the renal tubules of DKD. High salt intake diminishes the reno-protective effect of dapagliflozin in DKD.

Multitargeted interventions to reduce dialysis-induced systemic stress

Hemodialysis (HD) is a life-sustaining therapy as well as an intermittent and repetitive stress condition for the patient. In ridding the blood of unwanted substances and excess fluid from the blood, the extracorporeal procedure simultaneously induces persistent physiological changes that adversely affect several organs. Dialysis patients experience this systemic stress condition usually thrice weekly and sometimes more frequently depending on the treatment schedule. Dialysis-induced systemic stress results from multifactorial components that include treatment schedule (i.e. modality, treatment time), hemodynamic management (i.e. ultrafiltration, weight loss), intensity of solute fluxes, osmotic and electrolytic shifts and interaction of blood with components of the extracorporeal circuit. Intradialytic morbidity (i.e. hypovolemia, intradialytic hypotension, hypoxia) is the clinical expression of this systemic stress that may act as a disease modifier, resulting in multiorgan injury and long-term morbidity. Thus, while lifesaving, HD exposes the patient to several systemic stressors, both hemodynamic and non-hemodynamic in origin. In addition, a combination of cardiocirculatory stress, greatly conditioned by the switch from hypervolemia to hypovolemia, hypoxemia and electrolyte changes may create pro-arrhythmogenic conditions. Moreover, contact of blood with components of the extracorporeal circuit directly activate circulating cells (i.e. macrophages-monocytes or platelets) and protein systems (i.e. coagulation, complement, contact phase kallikrein-kinin system), leading to induction of pro-inflammatory cytokines and resulting in chronic low-grade inflammation, further contributing to poor outcomes. The multifactorial, repetitive HD-induced stress that globally reduces tissue perfusion and oxygenation could have deleterious long-term consequences on the functionality of vital organs such as heart, brain, liver and kidney. In this article, we summarize the multisystemic pathophysiological consequences of the main circulatory stress factors. Strategies to mitigate their effects to provide more cardioprotective and personalized dialytic therapies are proposed to reduce the systemic burden of HD.

Endogenous Mammalian Cardiotonic Steroids-A New Cardiovascular Risk Factor?-A Mini-Review

The role of endogenous mammalian cardiotonic steroids (CTS) in the physiology and pathophysiology of the cardiovascular system and the kidneys has interested researchers for more than 20 years. Cardiotonic steroids extracted from toads or plants, such as digitalis, have been used to treat heart disease since ancient times. CTS, also called endogenous digitalis-like factors, take part in the regulation of blood pressure and sodium homeostasis through their effects on the transport enzyme called sodium–potassium adenosine triphosphatase (Na/K-ATPase) in renal and cardiovascular tissue. In recent years, there has been increasing evidence showing deleterious effects of CTS on the structure and function of the heart, vasculature and kidneys. Understanding the role of CTS may be useful in the development of potential new therapeutic strategies.

Association of central arterial stiffness with hippocampal blood flow and N-acetyl aspartate concentration in hypertensive adult Dahl salt sensitive rats

BACKGROUND

Central arterial stiffness (CAS) is associated with elevated arterial blood pressure (BP) and is likely associated with stiffening of cerebral artery walls, with attendant cerebral hypoperfusion, neuronal density loss and cognitive decline. Dahl salt-sensitive (Dahl-S) rats exhibit age-associated hypertension and memory loss, even on a normal salt intake.

METHOD

We sought to explore whether central arterial pulse wave velocity (PWV), a marker of CAS, is associated with hippocampal cerebral blood flow (CBF) and neuronal density in hypertensive Dahl-S rats. We measured systolic BP (by tail-cuff plethysmography), aortic PWV (by echocardiography) and CBF and N-acetyl aspartate (NAA) (by magnetic resonance imaging) in 6 month-old male Dahl-S rats (n = 12).

RESULTS

Greater PWV was significantly associated with lower CBF and lower NAA concentration in the hippocampus, supporting a role of CAS in cerebrovascular dysfunction and decline in cognitive performance with aging.

CONCLUSION

These findings implicate increased CAS in cerebral hypoperfusion and loss of neuronal density and function in the Dahl-S model of age-associated cardiovascular dysfunction.

Preeclampsia: Cardiotonic Steroids, Fibrosis, Fli1 and Hint to Carcinogenesis

Despite prophylaxis and attempts to select a therapy, the frequency of preeclampsia does not decrease and it still takes the leading position in the structure of maternal mortality and morbidity worldwide. In this review, we present a new theory of the etiology and pathogenesis of preeclampsia that is based on the interaction of Na/K-ATPase and its endogenous ligands including marinobufagenin. The signaling pathway of marinobufagenin involves an inhibition of transcriptional factor Fli1, a negative regulator of collagen synthesis, followed by the deposition of collagen in the vascular tissues and altered vascular functions. Moreover, in vitro and in vivo neutralization of marinobufagenin is associated with the restoration of Fli1. The inverse relationship between marinobufagenin and Fli1 opens new possibilities in the treatment of cancer; as Fli1 is a proto-oncogene, a hypothesis on the suppression of Fli1 by cardiotonic steroids as a potential anti-tumor therapeutic strategy is discussed as well. We propose a novel therapy of preeclampsia that is based on immunoneutralization of the marinobufagenin by monoclonal antibodies, which is capable of impairing marinobufagenin-Na/K-ATPase interactions.

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

The endogenous Na+/K+-ATPase inhibitor, marinobufagenin (MBG), strongly associates with salt intake and a greater left ventricular mass index (LVMi) in humans and was shown to promote cardiac fibrosis and hypertrophy in animals. The adverse effects of MBG on cardiac remodeling may be exacerbated with obesity, due to an increased sensitivity of Na+/K+-ATPase to MBG. This study determined whether MBG is related to the change in LVMi over time in adults with a body mass index (BMI) ≥30 kg/m2 (obese) and <30 kg/m2 (non-obese). The study followed 275 healthy participants (aged 20-30 years) from the African-Prospective study on the Early Detection and Identification of Cardiovascular disease and Hypertension (African-PREDICT) study over 4.5 years. At baseline, we measured 24 h urine MBG excretion. MBG levels were positively associated with salt intake. LVMi was determined by two-dimensional echocardiography at baseline and after >4.5 years. With multivariate adjusted analyses in obese adults (N = 56), we found a positive association of follow-up LVMi (Adjusted (Adj.) R2 = 0.35; Std. β = 0.311; p = 0.007) and percentage change in LVMi (Adj. R2 = 0.40; Std. β = 0.336; p = 0.003) with baseline MBG excretion. No association of LVMi (Adj. R2 = 0.37; p = 0.85) or percentage change in LVMi (Adj. R2 = 0.19; p = 0.68) with MBG excretion was evident in normal weight adults (N = 123). These findings suggest that obese adults may be more sensitive to the adverse cardiac effects of MBG and provide new insight into the potential role of dietary salt, by way of MBG, in the pathogenesis of cardiac remodeling in obese individuals.

Cardiotonic Steroids Induce Vascular Fibrosis Via Pressure-Independent Mechanism in NaCl-Loaded Diabetic Rats

Endogenous cardiotonic steroid, marinobufagenin (MBG), induces Fli1-dependent tissue fibrosis. We hypothesized that an increase in MBG initiates the development of aortic fibrosis in salt-loaded rats with type 2 diabetes mellitus (DM2) via pressure-independent mechanism. DM2 was induced by a single intraperitoneal administration of 65 mg/kg streptozotocin to neonatal (4-5 days) male Wistar rats. Eight-week-old DM2 rats received water or 1.8% NaCl (DM-NaCl) solution for 4 weeks (n = 16); half of DM-NaCl rats were treated with anti-MBG monoclonal antibody (mAb) (DM-NaCl-AB) during week 4 of salt loading; control intact rats received water (n = 8/group). Blood pressure, MBG, erythrocyte Na/K-ATPase activity, aortic weights, levels of fibrosis markers (Fli1, protein kinase Cδ, transforming growth factor-β1, receptors of the transforming growth factor beta5, fibronectin, collagen-1), and sensitivity of the aortic explants to the vasorelaxant effect of sodium nitroprusside were assessed. No changes in systolic blood pressure were observed while erythrocyte Na/K-ATPase was inhibited by 30%, plasma MBG was doubled, and aortic markers of fibrosis became elevated in DM-NaCl rats versus control. Treatment of DM-NaCl rats with anti-MBG mAb activated Na/K-ATPase, prevented increases in aortic weights, and the levels of fibrosis markers returned to the control levels. The responsiveness of the aortic rings from DM-NaCl rats to the relaxant effect of sodium nitroprusside was reduced (half maximal effective concentration (EC50) = 29 nmol/L) versus control rings (EC50 = 7 nmol/L) and was restored by anti-MBG mAb (EC50 = 9 nmol/L). Our results suggest that in salt-loaded diabetic rats, MBG stimulates aortic collagen synthesis in a pressure-independent fashion and that 2 profibrotic mechanisms, Fli1 dependent and transforming growth factor-β dependent, underlie its effects.

Antibody against Na/K-ATPase Inhibitor Lowers Blood Pressure and Increases Vascular Fli1 in Experimental Preeclampsia

BACKGROUND

Previous studies implicated cardiotonic steroids, including Na/K-ATPase inhibitor marinobufagenin (MBG), in the pathogenesis of preeclampsia (PE). We demonstrated that MBG induces fibrosis via mechanism involving inhibition of Fli1, a nuclear transcription factor and a negative regulator of collagen-1 synthesis. We hypothesized that PE blockade of increased MBG with antibody would lessen the fibrosis of umbilical arteries and lower the blood pressure in rats with PE.

METHODS

We tested 36 pregnant Sprague-Dawley rats in which 12 were made hypertensive by 1.8% Na supplementation (days 6-19 of gestation), 12 pregnant rats served controls. At day 19, PE rats received one intraperitoneal injection of polyclonal anti-MBG-4 antibody (0.5 ug/ml) for 4 hours.

RESULTS

PE was associated with higher blood pressure (117 ± 2 vs. 107 ± 2 mm Hg; P < 0.01), plasma MBG levels (1.54 ± 0.34 vs. 0.49 ± 0.11 nmol/L; P < 0.01), protein excretion (26 vs. 12 mg/24 hours), sFlt-1 (3-fold), decrease in Fli1 (7-fold) and increase in collagen-1 in aorta (4-fold) vs. control rats (all P < 0.01). In 12 rats treated with polyclonal anti-MBG-4 antibody blood pressure dropped (93 ± 3 mm Hg) and Fli1 was decreased much less (2-fold; P < 0.01 vs. nontreated rats).

CONCLUSIONS

These results demonstrate that in experimental PE elevated MBG level is implicated in umbilical fibrosis via suppression of Fli1.

Microvascular function in non-dippers: Potential involvement of the salt sensitivity biomarker, marinobufagenin-The African-PREDICT study

Suppressed nighttime blood pressure dipping is associated with salt sensitivity and may increase the hemodynamic load on the microvasculature. The mechanism remains unknown whereby salt sensitivity may increase the cardiovascular risk of non-dippers. Marinobufagenin, a novel steroidal biomarker, is associated with salt sensitivity and other cardiovascular risk factors independent of blood pressure. The authors investigated whether microvascular function in non-dippers is associated with marinobufagenin. The authors included 220 dippers and 154 non-dippers (aged 20-30 years) from the African-PREDICT study, with complete 24-hour urinary marinobufagenin and sodium data. The authors determined dipping status using 24-hour blood pressure monitoring and defined nighttime non-dipping <10%. The authors measured microvascular reactivity as retinal artery dilation in response to light flicker provocation. Young healthy non-dippers and dippers presented with similar peak retinal artery dilation, urinary sodium, and MBG excretion (P > .05). However, only in non-dippers did peak retinal artery dilation relate negatively to marinobufagenin excretion after single (r = -0.20; P = .012), partial (r = -0.23; P = .004), and multivariate-adjusted regression analyses (Adj. R²  = 0.34; β = -0.26; P < .001). The authors also noted a relationship between peak artery dilation and estimated salt intake (Adj. R²  = 0.30; β = -0.14; P = .051), but it was lost upon inclusion of marinobufagenin (Adj. R²  = 0.33; β = -0.015; P = .86). No relationship between microvascular reactivity and marinobufagenin was evident in dippers (P = .77). Marinobufagenin, representing salt sensitivity, may be involved in early microvascular functional changes in young non-dippers and thus contributes to the development of hypertension and cardiovascular disease later in life.

A novel methodology for rat aortic pulse wave velocity assessment by Doppler ultrasound: validation against invasive measurements

There is still lack of a simple, accurate, and noninvasive method for rat aortic pulse wave velocity (PWV) measurement, especially the transit distance cannot be accurately measured. Thus, we aimed to derive an equation for aortic transit distance as a function of the nose-to-rump length (L) and to test the hypothesis that aortic PWV measured by new equation combined with Doppler ultrasound (the "equation method") may have stronger correlation with invasive measurements than traditional "body surface method." Two-hundred male Sprague-Dawley (SD) rats (age ranged 5-24 wk) were included in protocol 1, and the aortic transit distances were measured postmortem. In protocol 2, heart-femoral PWV and carotid-femoral PWV were measured by equation method (hfPWV_E, cfPWV_E) and also by traditional body surface method (hfPWV_S, cfPWV_S) in another 30 young and 28 old rats. These measurements were then validated against invasively measured hfPWV_I and cfPWV_I from the same animal. Protocol 1 showed that the heart-femoral transit distance could be calculated by 0.6086 × L - 1.6523, and the carotid-femoral transit distance by 0.4614 × L + 1.8335. In protocol 2, in young rats, the Pearson r between hfPWV_E, cfPWV_E, hfPWV_S, and cfPWV_S and their corresponding invasive measurement were 0.8962, 0.8509, 0.8387, and 0.7828, respectively (all P < 0.0001). In the old group, the results were 0.8718, 0.7999, 0.8330, and 0.7112, respectively (all P < 0.0001). The hfPWV_E and cfPWV_E showed better agreement with hfPWV_I and cfPWV_I and lower intra- and interobserver variability compared with hfPWV_S and cfPWV_S in both groups. These findings demonstrate that this novel methodology provides a simple and reliable method for rat noninvasive aortic PWV measurement.NEW & NOTEWORTHY First, when measuring aortic PWV in SD rat models, the heart-femoral transit distance can be estimated by 0.6086 × L - 1.6523, and the carotid-femoral distance transit distance can be estimated by 0.4614 × L + 1.8335, where L (in mm) is nose-to-rump length. Second, this novel methodology for aortic PWV measurement was validated with a closer correlation with the invasive measurements than traditional approach in young and old rats. Third, this study provides a simple and reliable method for rat noninvasive aortic PWV measurement.

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

Background Elevated 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 Results Dahl-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. Conclusions Immunoneutralization 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 Na+K+-ATPase Inhibitor Marinobufagenin and Early Cardiovascular Risk in Humans: a Review of Recent Evidence

PURPOSE OF REVIEW

This review synthesizes recent findings in humans pertaining to the relationships between marinobufagenin (MBG), a steroidal Na⁺/K⁺-ATPase inhibitor and salt-sensitivity biomarker, and early cardiovascular risk markers.

RECENT FINDINGS

Twenty-four-hour urinary MBG strongly associates with habitual salt intake in young healthy adults (aged 20-30 years). Furthermore, in young healthy adults free of detected cardiovascular disease, MBG associates with increased large artery stiffness and left ventricular mass independent of blood pressure. These findings in human studies corroborate mechanistic data from rat studies whereby stimulation of MBG by a high salt intake or MBG infusion increased vascular fibrosis and cardiac hypertrophy. Twenty-four-hour urinary MBG may be a potential biomarker of early cardiovascular risk. Adverse associations between MBG-which increases with salt consumption-and early cardiovascular risk markers support the global efforts to reduce population-wide salt intake in an effort to prevent and control the burden of non-communicable diseases.

Acute salt loading and cardiotonic steroids in resistant hypertension

The study addresses the association of marinobufagenin (MBG), a natriuretic and vasoconstrictor steroid, and Na/K-ATPase (NKA) activity with pressor response to salt-loading and arterial stiffness in resistant hypertension (RH). Thirty-four patients (18 males and 16 females; 56±8 years) with RH on a combined (lisnopril/amlodipine/hydrochlorothiazide) therapy and 11 healthy age-matched normotensive subjects (7 males and 4 females; 54±2 years) were enrolled in this study. Salt-loading was performed via intravenous infusion of 1000mL saline (0.9% NaCl) for 1h. Arterial stiffness was measured by Sphygmocor Px device with a calculation of pulse-wave velocity (PWV). Activity of NKA was measured in erythrocytes. We demonstrated that plasma levels of MBG and magnitude of NaCl-induced MBG-dependent NKA inhibition are associated with PWV, and that this association has gender- and age-specific fashion in RH patients.

Cardiotonic Steroids-A Possible Link Between High-Salt Diet and Organ Damage

High dietary salt intake has been listed among the top ten risk factors for disability-adjusted life years. We discuss the role of endogenous cardiotonic steroids in mediating the dietary salt-induced hypertension and organ damage.