Antihypertensive Effects of Gynura divaricata (L.) DC in Rats with Renovascular Hypertension

Abstract

Gynura divaricata (L.) DC (Compositae) (GD) could be found in various parts of Asia. It has been used as a traditional medicine to treat diabetes, high blood pressure, and other diseases, but its effects have not yet been scientifically confirmed. Therefore, we aimed at determining whether GD could affect renal function regulation, blood pressure, and the renin-angiotensin-aldosterone system (RAAS). Cardio-renal syndrome (CRS) is a disease caused by the interaction between the kidney and the cardiovascular system, where the acute or chronic dysfunction in one organ might induce acute or chronic dysfunction of the other. This study investigated whether GD could improve cardio-renal mutual in CRS type 4 model animals, two-kidney one-clip (2K1C) renal hypertensive rats. The experiments were performed on the following six experimental groups: control rats (CONT); 2K1C rats (negative control); OMT (Olmetec, 10 mg/kg/day)-treated 2K1C rats (positive control); and 2K1C rats treated with GD extracts in three different doses (50, 100, and 200 mg/kg/day) for three weeks by oral intake. Each group consisted of 10 rats. We measured the systolic blood pressure weekly using the tail-cuff method. Urine was also individually collected from the metabolic cage to investigate the effect of GD on the kidney function, monitoring urine volume, electrolyte, osmotic pressure, and creatinine levels from the collected urine. We observed that kidney weight and urine volume, which would both display typically increased values in non-treated 2K1C animals, significantly decreased following the GD treatment (^###p < 0.001 vs. 2K1C). Osmolality and electrolytes were measured in the urine to determine how renal excretory function, which is reduced in 2K1C rats, could be affected. We found that the GD treatment improved renal excretory function. Moreover, using periodic acid-Schiff staining, we confirmed that the GD treatment significantly reduced fibrosis, which is typically increased in 2K1C rats. Thus, we confirmed that the GD treatment improved kidney function in 2K1C rats. Meanwhile, we conducted blood pressure and vascular relaxation studies to determine if the GD treatment could improve cardiovascular function in 2K1C rats. The heart weight percentages of the left atrium and ventricle were significantly lower in GD-treated 2K1C rats than in non-treated 2K1C rats. These results showed that GD treatment reduced cardiac hypertrophy in 2K1C rats. Furthermore, the acetylcholine-, sodium nitroprusside-, and atrial natriuretic peptide-mediated reduction of vasodilation in 2K1C rat aortic rings was also ameliorated by GD treatment (GD 200 mg/kg/day; p < 0.01, p < 0.05, and p < 0.05 vs. 2K1C for vasodilation percentage in case of each compound). The mRNA expression in the 2K1C rat heart tissue showed that the GD treatment reduced brain-type natriuretic peptide and troponin T levels (p < 0.001 and p < 0.001 vs. 2K1C). In conclusion, this study showed that GD improved the cardiovascular and renal dysfunction observed in an innovative hypertension model, highlighting the potential of GD as a therapeutic agent for hypertension. These findings indicate that GD shows beneficial effects against high blood pressure by modulating the RAAS in the cardio-renal syndrome. Thus, it should be considered an effective traditional medicine in hypertension treatment.

Keywords: Gynura divaricata (L.) DC; cardio-renal syndrome; renin-angiotensin-aldosterone system (RAAS); renovascular hypertension.

Figure 1

Structural identification of compounds isolated from Gynura divaricata (L.) DC (GD) using HPLC.

Figure 2

Effect of Gynura divaricata (L.) DC on systolic blood pressure (mmHg). The GD treatments at different concentrations (50, 100, 200 mg/kg/day) decreased systolic blood pressure (SBP) in 2K1C hypertensive rats. The values are expressed as the mean ± standard error (n = 10 per group). *** p < 0.001, vs. CONT and ^### p < 0.001, vs. 2K1C. 2K1C, two-kidney one-clip.

Figure 3

Vasorelaxation effect of Gynura divaricata (L.) DC (GD) following acetylcholine (ACh), sodium nitroprusside (SNP), and atrial natriuretic peptide (ANP) treatments. (A) Dose-response curves of ACh relaxation in the thoracic aorta of the 2K1C model; (B) The final ACh dose was changed in % change expression with each group; (C) Dose-response curves of SNP relaxation in the thoracic aorta of the 2K1C model; (D) Effect of GD on the ANP relaxation of the 2K1C model. Responses are expressed as the percentage of relaxations relative to the PE-induced pre-contractions. Each value shows the mean ± standard error (n = 10 per group). ** p < 0.01, *** p < 0.001, vs. CONT and ^# p < 0.05, ^## p < 0.01, ^### p < 0.0001 vs. 2K1C.

Figure 4

Effect of Gynura divaricata (L.) DC on endothelial nitric oxide synthase (eNOS) and endothelin-1 (ET-1) expressions in the blood vessels. (A) Immunohistochemical expression of eNOS in the aorta (magnification × 200); (C) Immunohistochemical expression of ET-1 in the aorta. Quantitative analysis of eNOS (B) and ET-1 (D) area. ** p < 0.01, *** p < 0.001, vs. CONT and ^# p < 0.05, ^## p < 0.01, ^### p < 0.0001 vs. 2K1C.

Figure 5

Effects of Gynura divaricata (L.) DC (GD) on heart weight and shape. (A) Effects of GD on the left atrial and left ventricular weight (expressed as % of control); (B) Photographs of the heart size in each group. Each value represents the mean ± standard error (n = 10 per group). *** p < 0.001 vs. CONT and ^## p < 0.01, ^### p < 0.001 vs. 2K1C.

Figure 6

Effects of Gynura divaricata (L.) DC (GD) on the biomarkers on cardiac dysfunction. (A) Effects of GD on the expression of troponin T (TnT) mRNA. Real time quantitative polymerase chain reaction of TnT mRNA was performed from the left ventricle; (B) Effects of GD on the expression of brain natriuretic peptide mRNA. Each value shows the mean ± standard error (n = 10 per group). *** p < 0.001, vs. CONT and ^## p < 0.01 ^### p < 0.0001 vs. 2K1C.

Figure 7

Effect of Gynura divaricata (L.) DC (GD) on fibrosis in the kidney tissue. (A) Periodic acid-Schiff (PAS) staining in the kidney cortex (magnification × 200); (B) Quantitative assessments representing the results of five independent experiments. The values are expressed as the mean ± standard error (n = 5 per group). *** p < 0.001, vs. CONT and ^# p < 0.05, ^### p < 0.0001 vs. 2K1C.

Figure 8

Effects of Gynura divaricata (L.) DC (GD) on kidney fibrosis in the outer medulla. (A) Periodic acid-Schiff staining of the kidney in the outer medulla. (magnification × 200); (B) Quantitative assessments representing the results of five independent experiments. The values are expressed as the mean ± standard error (n = 5 per group). *** p < 0.001, vs. CONT and ^### p < 0.0001 vs. 2K1C.