Magnesium Improves Cardiac Function in Experimental Uremia by Altering Cardiac Elastin Protein Content

Abstract

Cardiovascular complications are accompanied by life-threatening complications and represent the major cause of death in patients with chronic kidney disease (CKD). Magnesium is important for the physiology of cardiac function, and its deficiency is common in CKD. In the present study, we investigated the impact of oral magnesium carbonate supplementation on cardiac function in an experimental model of CKD induced in Wistar rats by an adenine diet. Echocardiographic analyses revealed restoration of impaired left ventricular cardiac function in animals with CKD. Cardiac histology and real-time PCR confirmed a high amount of elastin protein and increased collagen III expression in CKD rats supplemented with dietary magnesium as compared with CKD controls. Both structural proteins are crucial in maintaining cardiac health and physiology. Aortic calcium content increased in CKD as compared with tissue from control animals. Magnesium supplementation numerically lowered the increases in aortic calcium content as it remained statistically unchanged, compared with controls. In summary, the present study provides evidence for an improvement in cardiovascular function and aortic wall integrity in a rat model of CKD by magnesium, as evidenced by echocardiography and histology.

Keywords: adenine nephropathy; cardiac function; chronic kidney disease; echocardiography; magnesium.

Figure 1

Time schedule and diet plans of adenine nephropathy in rats. Wistar rats received either a standardized control diet or an initial 2 weeks of phosphate-rich diet, followed by 4 weeks of an adenine diet—either alone or supplemented with MgCO₃, followed by 2 weeks of a phosphate-rich diet, with or without MgCO₃. BP: blood pressure; CKD: chronic kidney disease; MgCO₃: magnesium carbonate; PO₄: phosphate.

Figure 2

Decreased cardiac function was measured by echocardiography and Millar catheter at the end of the experiment. (A) Ejection fraction, (B) stroke volume, (C) pulse wave velocity (PVW) inside the common carotid artery, (D) left ventricular developed pressure (DP), (E) minimal developed pressure over time (Dpmin); and (F) maximal developed pressure over time (DPmax). Ad: adenine; Ctrl: control; MG: magnesium. * p < 0.05.

Figure 3

Histological analysis revealed cardiac hypertrophy but absent remarkable fibrosis in cardiac sections from adenine rats, whereas magnesium supplementation to the adenine diet increased green-emitting fibrils enhanced by polarized light after picrosirius red staining. (a) PAS staining in cardiac tissue from control rats; (b) PAS staining in cardiac tissue from adenine-fed rats; (c) PAS staining in cardiac tissue from adenine + magnesium-fed rats; (d) PAS staining in kidney tissue from control rats; (e) PAS staining in kidney tissue from adenine-fed rats; (f) PAS staining in kidney tissue from adenine + magnesium-fed rats; (g) picrosirius red staining in cardiac tissue from control rats, brightfield image; (h) sirius red staining in cardiac tissue from adenine-fed rats, brightfield image; (i) picrosirius red staining in cardiac tissue from adenine + magnesium fed-rats, brightfield image; (j) picrosirius red staining in cardiac tissue from control rats, polarized light; (k) picrosirius red staining in cardiac tissue from adenine-fed rats, polarized light; (l) picrosirius red staining in cardiac tissue from adenine + magnesium- fed rats, polarized light; (m) cardiomyocyte size, measured from PAS-stained sections (mean, SD); and (n) percentage of green-positive area in picrosirius-red-stained sections under polarized light (mean, SD). Scale = 50 µM; Ad: adenine; Ctrl: control; MG: magnesium. * p < 0.05, ** p < 0.01.

Figure 4

Cardiac immunohistochemistry presented an increase in elastin protein by magnesium supplementation to the adenine diet. (a) Collagen III staining in cardiac tissue from control rats; (b) collagen III staining in cardiac tissue from adenine-fed rats; (c) collagen III staining in cardiac tissue from adenine + magnesium-fed rats; (d) elastin staining in cardiac tissue from control rats; (e) elastin staining in cardiac tissue from adenine-fed rats; (f) elastin staining in cardiac tissue from adenine + magnesium-fed rats; (g) planimetric quantification of collagen III staining in heart tissue; (h) relative expression of collagen III mRNA to GAPDH, measured by semiquantitative real-time PCR; (i) planimetric quantification of elastin staining in hearts; (j) relative expression of elastin mRNA to GAPDH, measured by semiquantitative real-time PCR. Scale bar = 50 µM; Ad: adenine; Ctrl: control; MG: magnesium; *: p < 0.05.

Figure 5

Von Kossa staining of aortas and hearts visualized an increase in soft tissue calcification with adenine diet. (a) Cardiac tissue from control rats; (b) cardiac tissue from adenine-fed rats; (c) cardiac tissue from adenine + magnesium-fed rats; (d) heart valves from control rats; (e) heart valves from adenine-fed rats; (f) heart valves from adenine + magnesium-fed rats; (g) aorta from control rats; (h) aorta from adenine-fed rats; (i) aorta from adenine + magnesium-fed rats; (j) total calcium content of cardiac tissue (mg/g) normalized to total cardiac protein; (k) total calcium content of aortic tissue (mg/g) normalized to total aortic protein; and (l) intima media thickness, measured in von Kossa-stained aortas. Scale bar = 50 µM; Ad: adenine; Ca: calcium Ctrl: control; MG: magnesium; *: p < 0.05.