Antihypertrophic effect of hemin in deoxycorticosterone acetate-salt-induced hypertensive rat model
Jadhav, Ashok B.
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The application of the synthetic mineralocorticoid, deoxycorticosterone acetate (DOCA)-salt, to unilaterally nephrectomised rats induces severe hypertension due to volume-overload, and mimics human primary aldosteronism. Importantly, DOCA-salt hypertension is characterized by severe cardiac and renal lesions triggered by nuclear factor kappa B (NF-kappaB), activating protein (AP-1), and transforming growth factor beta1 (TGF-beta1) leading to end-stage organ damage. Although DOCA-salt hypertension is a low renin model, local production of angiotensin-II and aldosterone in cardiac and renal tissues stimulate TGF-beta1, fibronectin and collagen-1 causing fibrosis and hypertrophy. Since TGF-beta1 gene promoter contains binding sites for NF-kappaB and AP-1, cross-talk between TGF-beta1, NF-kappaBƒnand AP-1 can be envisaged. Accordingly, the activation of TGF-beta1, fibronectin, collagen, NF-kappaB and AP-1 may constitute a potent destructive force in hypertension. Emerging evidence indicates that upregulation of the heme oxygenase (HO) system is cytoprotective with antioxidant, antihypertensive and antihypertrophic effects. Interestingly, the promoter region of HO-1 gene harbors consensus-binding sites for NF-kappaB and AP-1; therefore, the HO system may regulate these transcription factors to counteract tissue insults. However, the multifaceted interactions between the HO system, NF-kappaB, AP-1, TGF-beta1, fibronectin and collagen in mineralocorticoid-induced end-stage-organ damage have not been fully characterized. Similarly, the effect of the HO system on tissue angiotensin-II and aldosterone levels in mineralocorticoid-induced hypertension remains unclear. Therefore, the present study was designed to investigate the antihypertrophic effect of the HO system in cardiac and renal tissue of DOCA-salt hypertensive rats. In this study, the HO inducer, hemin, lowered blood pressure and attenuated cardiac/renal hypertrophy, whereas the HO inhibitor, chromium mesoporphyrin (CrMP), nullified the effects of hemin and exacerbated cardiac/renal injury the DOCA-salt hypertensive rats. The protective effect of hemin was associated with increased HO-1, HO activity, cyclic guanosine monophosphate (cGMP), superoxide dismutase activity, ferritin and the total antioxidant capacity in the cardiac and renal tissue. In contrast, angiotensin-II, aldosterone, 8-isoprostane, NF-kappaB and AP-1 were significantly downregulated. Furthermore, hemin therapy attenuated TGF-beta1 and extracellular matrix (ECM) proteins such as fibronectin and collagen, with corresponding reduction of cardiac histopathological lesions, including longitudinal/cross-sectional muscle fiber thickness, scarring, muscular hypertrophy, coronary arteriolar thickening and collagen deposition. Similarly, hemin attenuated structural lesions in the kidney such as glomerular hypertrophy, glomerular sclerosis, mononuclear cell infiltration, tubular cast formation, tubular dilation and renal arteriolar thickening with concomitant improvement of kidney function as evidenced by reduction of plasma creatinine, proteinuria, but enhanced creatinine clearance. Collectively, these results suggest that the HO system suppressed hypertension, cardiac and renal fibrosis, and hypertrophy in the DOCA-salt hypertensive rat by downregulating transcription factors such as NF-kappaB and AP-1, reducing ECM proteins such as fibronectin and collagen, decreasing local tissue production of angiotensin-II and aldosterone, and improved renal functional capacity.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorNdisang, Joseph Fomusi