14.    C-type natriuretic peptide exerts cardiac protective effects in hypertensive cardiac                 remodeling

Background and Question: C-type natriuretic peptide (CNP) is expressed in cardiac tissue at both genomic and protein levels. Even though the expression of the peptide has been demonstrated in both cardiac myocytes and fibroblasts, the functional relevance of CNP signalling in the heart remains unclear. Interestingly, the expression of the peptide is higher in patients with heart failure and some clinical studies have shown that plasma and/or urinary CNP levels also increase with age, hypertension and cardiac hypertrophy, suggesting a pathophysiological
role and a potential clinical utility of CNP as diagnostic and prognostic biomarker of cardiac diseases. In this study, we used a suitable model of experimental essential hypertension to characterize synthetic CNP actions on cardiac remodeling of spontaneously hypertensive rats (SHR). Methods: 12-week-old male SHR and their normotensive Wistar (W) controls were infused with CNP (0,75 μg/hr) or saline (S) (osmotic pumps, 14 days). Systolic blood pressure (SBP) was recorded by tail-cuff method. After the infusion period, animals were euthanized and the left ventricle (LV) was extracted to determine: left ventricle mass index (LVMI) and cross sectional area (CSA) of myocytes in Hematoxylin-Eosin (HE) staining as hypertrophy parameters and collagen content in Picrosirius-Red (PSR) staining, TGF-b content by Western Blot (WB) and Immunohistochemistry (IHC) and initiator Smad proteins content by IHC as fibrosis indicators. Finally, the content of proinflammatory cytokines IL-1b, IL-6 and TNF-α was measured by ELISA and by IHC as inflammation markers. Statistics: Two-way ANOVA, Bonferroni post-test. Results: SHR showed increased SBP levels accompanied by a marked LV hypertrophy, interstitial and perivascular fibrosis and inflammatory cytokine levels when compared to their normotensive controls. CNP attenuated hypertension and also significantly prevented myocyte hypertrophy and cardiac fibrosis and inflammation in SHR animals. No changes were observed in Wistar rats. Conclusion: CNP largely attenuated the deleterious structural cardiac changes present in SHR. These antiremodeling effects plus the mitigation of an inflammatory environment combined with the drop in blood pressure we observed, is evidence of an important pathophysiological role of CNP in preventing or even reversing cardiac fibrosis and inflammation in this model of arterial hypertension. Our observations suggest that CNP signalling may represent a target for heart-protecting therapies.