Role of aldosterone on lung structural remodelling and right ventricular function in congestive heart failure

Pathophysiology and clinical relevance of pulmonary remodelling in pulmonary hypertension due to left heart diseases

Pulmonary hypertension (PH) in left heart disease, classified as group II, is the most common form of PH that occurs in approximately 60% of cases of reduced and preserved left ventricular ejection fraction. Although relatively much is known about hemodynamic stages (passive or reactive) and their consequences on the right ventricle (RV) there is no consensus on the best hemodynamic definition of group II PH. In addition, the main pathways that lead to lung capillary injury and impaired biology of small artery remodelling processes are largely unknown. Typical lung manifestations of an increased pulmonary pressure and progressive RV-pulmonary circulation uncoupling are an abnormal alveolar capillary gas diffusion, impaired lung mechanics (restriction), and exercise ventilation inefficiency. Of several classes of pulmonary vasodilators currently clinically available, oral phosphodiesterase 5 inhibition, because of its strong selectivity for targeting the cyclic guanosine monophosphate pathway in the pulmonary circulation, is increasingly emerging as an attractive opportunity to reach hemodynamic benefits, reverse capillary injury, and RV remodelling, and improve functional capacity. Guanylate cyclase stimulators offer an additional intriguing opportunity but the lack of selectivity and systemic effects might preclude some of the anticipated benefits on the pulmonary circulation. Future trials will determine whether new routes of pharmacologic strategy aimed at targeting lung structural and vascular remodelling might affect morbidity and mortality in left heart disease populations. We believe that this therapeutic goal rather than a pure hemodynamic effect might ultimately emerge as an important challenge for the clinician.

Upregulation of steroidogenic acute regulatory protein by hypoxia stimulates aldosterone synthesis in pulmonary artery endothelial cells to promote pulmonary vascular fibrosis

BACKGROUND

The molecular mechanism(s) regulating hypoxia-induced vascular fibrosis are unresolved. Hyperaldosteronism correlates positively with vascular remodeling in pulmonary arterial hypertension, suggesting that aldosterone may contribute to the pulmonary vasculopathy of hypoxia. The hypoxia-sensitive transcription factors c-Fos/c-Jun regulate steroidogenic acute regulatory protein (StAR), which facilitates the rate-limiting step of aldosterone steroidogenesis. We hypothesized that c-Fos/c-Jun upregulation by hypoxia activates StAR-dependent aldosterone synthesis in human pulmonary artery endothelial cells (HPAECs) to promote vascular fibrosis in pulmonary arterial hypertension.

METHODS AND RESULTS

Patients with pulmonary arterial hypertension, rats with Sugen/hypoxia-pulmonary arterial hypertension, and mice exposed to chronic hypoxia expressed increased StAR in remodeled pulmonary arterioles, providing a basis for investigating hypoxia-StAR signaling in HPAECs. Hypoxia (2.0% FiO2) increased aldosterone levels selectively in HPAECs, which was confirmed by liquid chromatography-mass spectrometry. Increased aldosterone by hypoxia resulted from enhanced c-Fos/c-Jun binding to the proximal activator protein-1 site of the StAR promoter in HPAECs, which increased StAR expression and activity. In HPAECs transfected with StAR-small interfering RNA or treated with the activator protein-1 inhibitor SR-11302 [3-methyl-7-(4-methylphenyl)-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraenoic acid], hypoxia failed to increase aldosterone, confirming that aldosterone biosynthesis required StAR activation by c-Fos/c-Jun. The functional consequences of aldosterone were confirmed by pharmacological inhibition of the mineralocorticoid receptor with spironolactone or eplerenone, which attenuated hypoxia-induced upregulation of the fibrogenic protein connective tissue growth factor and collagen III in vitro and decreased pulmonary vascular fibrosis to improve pulmonary hypertension in vivo.

CONCLUSION

Our findings identify autonomous aldosterone synthesis in HPAECs attributable to hypoxia-mediated upregulation of StAR as a novel molecular mechanism that promotes pulmonary vascular remodeling and fibrosis.

Lung capillary injury and repair in left heart disease: a new target for therapy?

The lungs are the primary organs affected in LHD (left heart disease). Increased left atrial pressure leads to pulmonary alveolar–capillary stress failure, resulting in cycles of alveolar wall injury and repair. The reparative process causes the proliferation of MYFs (myofibroblasts) with fibrosis and extracellular matrix deposition, resulting in thickening of the alveolar wall. Although the resultant reduction in vascular permeability is initially protective against pulmonary oedema, the process becomes maladaptive causing a restrictive lung syndrome with impaired gas exchange. This pathological process may also contribute to PH (pulmonary hypertension) due to LHD. Few clinical trials have specifically evaluated lung structural remodelling and the effect of related therapies in LHD. Currently approved treatment for chronic HF (heart failure) may have direct beneficial effects on lung structural remodelling. In the future, novel therapies specifically targeting the remodelling processes may potentially be utilized. In the present review, we summarize data supporting the clinical importance and pathophysiological mechanisms of lung structural remodelling in LHD and propose that this pathophysiological process should be explored further in pre-clinical studies and future therapeutic trials.

Perindopril treatment promote left ventricle remodeling in patients with heart failure screened positive for autoantibodies against angiotensin II type 1 receptor

Background

Autoantibodies specific to the angiotensin II type I receptor (anti-AT₁-AR) have been implicated in the pathology of congestive heart failure (CHF). Anti-AT₁-AR may be associated with left ventricular function in CHF patients treated with perindopril.

Methods

Synthetic angiotensin II type 1 receptor (AT₁-R) peptides served as the target antigen. ELISA was used to screen the sera of 156 CHF patients, which were divided into positive and negative groups based on their anti-AT₁-AR reactivity. Echocardiography and a 6-minute walk test were performed at baseline and after one year of perindopril therapy. The end-point events were compared over a 5-year follow-up.

Results

Final analysis covered 138 patients, including 82 positive and 56 negative. The frequency and geometric mean titre of anti-AT₁-AR were significantly lower in the positive group after one year of treatment (all P < 0.01, from 100% to 73.2% and from 1:125.3 ± 1.0 to 1:69.2 ± 1.1). Of these, 22 patients showed no antibodies. Both groups showed improvement in left ventricular end-diastole, end-systolic dimensions, ejection fraction, and a 6-minute walk test by perindopril in combination with standard treatment regime for one year (all P < 0.01). However, the 82 patients positive for anti-AT₁-AR showed more pronounced improvement than the 56 negative patients (all P < 0.05). However, after 5 years of follow-up, the rate of all causes and cardiovascular mortality attributable to any cause and the re-hospitalisation rate showed no significant differences between the two groups (all P > 0.05).

Conclusions

Perindopril treatment significantly decreased the frequency and geometric mean titre in patients positive for anti-AT₁-AR, even to complete ablation. These patients showed greater improvement in left ventricular remodeling and heart function than negative that in patients after one year of perindopril treatment in combination with standard treatment, but no significant differences in endpoint events were observed in the following 5 years. Anti-AT₁-AR might be a useful biomarker of over-activation of the renin-angiotensin-aldosterone system for clinical medication.

Evolving strategies for the use of spironolactone in cardiovascular disease

The evolution of strategies for the use of spironolactone and its analogue, eplerenone, has, over the years, encompassed favourable modification of the natural history of symptomatic heart failure in subjects with subnormal left ventricular ejection fraction (LVEF), and mitigation of the risk of new-onset atrial fibrillation in mildly symptomatic systolic heart failure. Given the fact that these benefits might be attributable, at least in part, to mitigation of severity of diastolic dysfunction when the latter co-exists with subnormal LVEF, what needs to be explored is the possibility of similar benefits from the use of these agents in patients such as those with hypertension, and aortic valve stenosis, in whom left ventricular dysfunction is of the predominantly diastolic subtype.

Mineralocorticoid receptor antagonism attenuates experimental pulmonary hypertension

Mineralocorticoid receptor (MR) activation stimulates systemic vascular and left ventricular remodeling. We hypothesized that MR contributes to pulmonary vascular and right ventricular (RV) remodeling of pulmonary hypertension (PH). We evaluated the efficacy of MR antagonism by spironolactone in two experimental PH models; mouse chronic hypoxia-induced PH (prevention model) and rat monocrotaline-induced PH (prevention and treatment models). Last, the biological function of the MR was analyzed in cultured distal pulmonary artery smooth muscle cells (PASMCs). In hypoxic PH mice, spironolactone attenuated the increase in RV systolic pressure, pulmonary arterial muscularization, and RV fibrosis. In rat monocrotaline-induced PH (prevention arm), spironolactone attenuated pulmonary vascular resistance and pulmonary vascular remodeling. In the established disease (treatment arm), spironolactone decreased RV systolic pressure and pulmonary vascular resistance with no significant effect on histological measures of pulmonary vascular remodeling, or RV fibrosis. Spironolactone decreased RV cardiomyocyte size modestly with no significant effect on RV mass, systemic blood pressure, cardiac output, or body weight, suggesting a predominantly local pulmonary vascular effect. In distal PASMCs, MR was expressed and localized diffusely. Treatment with the MR agonist aldosterone, hypoxia, or platelet-derived growth factor promoted MR translocation to the nucleus, activated MR transcriptional function, and stimulated PASMC proliferation, while spironolactone blocked these effects. In summary, MR is active in distal PASMCs, and its antagonism prevents PASMC proliferation and attenuates experimental PH. These data suggest that MR is involved in the pathogenesis of PH via effects on PASMCs and that MR antagonism may represent a novel therapeutic target for this disease.