Differential Effects of an Anti-Oxidant Intervention on Cardiomyocyte Expression of Adrenomedullin and Intermedin and their Receptor Components in Chronic Nitric Oxide Deficiency

Abstract

Background: Chronic inhibition of nitric oxide (NO) synthesis is associated with hypertension, myocardial oxidative stress and hypertrophic remodeling. Upregulation of the cardiomyocyte adrenomedullin (AM) / intermedin (IMD) receptor signaling cascade is also apparent in NO-deficient cardiomyocytes: augmented expression of AM and receptor activity modifying proteins RAMP2 and RAMP3 is prevented by blood pressure normalization while that of RAMP1 and intermedin (IMD) is not, indicating that the latter is regulated by a pressure-independent mechanism. Aims: to verify the ability of an anti-oxidant intervention to normalize cardiomyocyte oxidant status and to investigate the influence of such an intervention on expression of AM, IMD and their receptor components in NO-deficient cardiomyocytes. Methods: NO synthesis inhibitor, N G -nitro-L-arginine methyl ester (L-NAME, 35mg/kg/day) was given to rats for 8 weeks, with/without con-current administration of antioxidants (Vitamin C (25mg/kg/day) and Tempol (25mg/kg/day)). Results: In left ventricular cardiomyocytes isolated from L-NAME treated rats, increased oxidative stress was indicated by augmented (3.6 fold) membrane protein oxidation, enhanced expression of catalytic and regulatory subunits of pro-oxidant NADPH oxidases (NOX1, NOX2) and compensatory increases in expression of anti-oxidant glutathione peroxidase and Cu/Zn superoxide dismutases (SOD1, SOD3). Vitamin C plus Tempol did not reduce systolic blood pressure but normalized augmented plasma levels of IMD, but not of AM, and in cardiomyocytes: (i) abolished increased membrane protein oxidation; (ii) normalized augmented expression of prepro-IMD and RAMP1, but not prepro-AM, RAMP2 and RAMP3; (iii) attenuated (by 42%) increased width and normalized expression of hypertrophic markers, skeletal-α-actin and prepro-endothelin-1 similarly to blood pressure normalization but in contrast to blood pressure normalization did not attenuate augmented brain natriuretic peptide (BNP) expression. Conclusion: normalization specifically of augmented IMD/RAMP1

Protection of Angiotensin II–Induced Vascular Hypertrophy in Vascular Smooth Muscle–Targeted Receptor Activity-Modifying Protein 2 Transgenic Mice

“…21 However, it should be noted that the levels of the AM-related peptide intermedin, which is an agonist at the CGRP family of receptors (including the AM1 receptor), is also raised in a rat model of pressure overload. 25 Thus, AM1 receptor activity may be influenced by Ͼ1 agonist.…”

Influence of Atenolol and Nifedipine on Nitric-Oxide Deficient Cardiomyocyte Hypertrophy and Expression of the Cardio-Endocrine Peptide Intermedin and its Receptor Components

“…L-NAME-induced expression of AM and RAMP2 and RAMP3 was normalized by blood pressure normalization by hydralazine / hydrocholorothiazide [10] but not by antioxidant therapy with Tempol/ Vitamin C in the absence of blood pressure reduction [11], despite a similar reduction in the extent of cardiomyocyte hypertrophy indicating that pressureloading exerts a direct influence on expression of these genes independently of any ability to prevent cardiomyocyte hypertrophy. Unlike Tempol and Vitamin C [11], hydralazine and hydrochlorothiazide were unable to attenuate augmented IMD and RAMP1 expression [10] despite attenuation of cardiomyocyte hypertrophic parameters to a similar extent. This observation strongly supports a direct influence of oxidative stress upon expression of IMD and RAMP1, independent of any indirect influence associated with the contribution of oxidative stress to development of cardiomyocyte hypertrophy.…”

“…Previous studies in our laboratory indicate two important findings relating to cardiomyocytes subjected to chronic NO deficiency. Firstly, pressure loading and oxidative stress, exerted directly on the myocardium, both contribute to cardiomyocyte hypertrophy since antihypertensive therapy (smooth muscle relaxant hydralazine given concurrently with the diuretic hydrochlorothiazide, [10]) and antioxidant therapy in the absence of blood pressure reduction (Vitamin C in combination with Tempol, [11]) each partially, but incompletely, attenuated increased cardiomyocyte width despite normalizing blood pressure and cardiomyocyte membrane oxidant status, respectively. Furthermore, L-NAME induced expression of the hypertrophic markers, sk-α-actin and prepro-ET1, was abolished either by blood pressure lowering agents [10] or by antioxidants in the absence of blood pressure reduction [11]; in contrast, however, augmented expression of the natriuretic peptides, ANP and BNP, was normalized by blood pressure lowering [10] but not by antioxidants in the absence of blood pressure reduction [11].…”

“…Systolic blood pressure was assessed to confirm that this combination normalized L-NAME induced hypertension. The results relating specifically to the atenolol/nifedipine arm of a larger study are presented here and these have been compared and contrasted in discussion with those of the hydrochlorothiazide / hydralazine [10] and Tempol / Vitamin C [11] arms of the study which have been reported recently elsewhere.…”

Toward revealing the roles for intermedin in the community of vasoactive peptides

“…For example, the actions of ADM against ischemia-reperfusion injury are strongly influenced by pressure loading, 10 while expression of IMD is regulated by the extent of myocardial oxidative stress and is reduced by antioxidant therapy. 11 It has also been observed that IMD and ADM may be differentially affected by regulating factors; furthermore, the two peptides have distinct effects on arterial endothelial cells in vitro. 12 Although both IMD and ADM interact with all the three RAMPs, the ranked affinities between them differ: ADM has higher agonist activity with RAMP2 or RAMP3 than does IMD.…”