Potential Protective Effects of the Water-Soluble Chinese Propolis on Hypertension Induced by High-Salt Intake

Abstract

High-salt (HS) intake is closely associated with the ignition and progression of hypertension. The mechanisms might be involved in endothelial dysfunction, nitric oxide deficiency, oxidative stress, and proinflammatory cytokines. Propolis is widely used as a natural antioxidant and is a well-known functional food for its biological activities, which includes anti-inflammation, antimicrobial, and liver detoxification. In this study, we successfully replicated a HS diet-induced hypertensive rat model. We found that in the long-term HS diet group, the myocardial function of the rats was altered and led to a significant decrease (around 49%) in heart function. However, doses of Chinese water-soluble propolis (WSP) were found directly proportional (11%, 60%, 91%, respectively) to the myocardial function improvement in hypertensive rats. The results from the blood circulation test and hematoxylin-eosin stains showed that propolis had protective effects on myocardial functions and blood vessels in hypertensive rats. Also, based on the results of western blot and polymerase chain reaction, WSP effectively regulated Nox2 and Nox4 levels and was responsible for a decrease in reactive oxygen species synthesis. Our findings demonstrate that Chinese WSP has a significant effect on the blood pressure of hypertensive rats and their cardiovascular functions that improved significantly. The improvement in the cardiovascular functions might be related to the process of anti-oxidation, anti-inflammation, and the improvements of the endothelial function in hypertensive rats.

Figure 1

Detection of cardiac function and hemodynamics. (a) Changes of BP in each group. ( $\overline{x}\pm s$ , n = 6, **P < 0.01 vs. NC group; ^## P < 0.01 vs. HS group. (b) Changes of ±LV dp/dt _max index in each group ( $\overline{x}\pm s$ , n = 10). *P < 0.05, **P < 0.01 vs. NC group ^# P < 0.05, ^## P < 0.01 vs. HS group; ^△ P < 0.01 vs. HS + WSP‐H group; ^※ P < 0.01 vs. HS + CAP group. BP, blood pressure; HS, high salt; NC, normal control; WSP, Chinese water‐soluble propolis.

Figure 2

Direct measurement of endothelial function. (a) Effects of different concentrations of Phe on the arterial ring contraction rate in each group ( $\overline{x}\pm s$ , n = 6). *P < 0.05, **P < 0.01 vs. NC group; ^# P < 0.05, ^## P < 0.01 vs. HS group. (b) Differences in ACh relaxation effect on pre‐contracted vascular rings induced by Phe ( $\overline{x}\pm s$ , n = 6). *P < 0.05, **P < 0.01 vs. NC group; ^# P < 0.05, ^## P < 0.01 vs. HS group. (c) Effect of L‐NAME on the relaxation rate of the rat thoracic aorta ring ( $\overline{x}\pm s$ , n = 6). ACh, Acetylcholine; CAP, captopril; HS, high salt; NC, normal control; Phe, phenylephrine; WSP, Chinese water‐soluable propolis.

Figure 3

Detection of oxidative stress‐related indicators. (a) Serum NO content in each group ( $\overline{x}\pm s$ , n = 6). (b) Comparison of IL‐6 levels in each group ( $\overline{x}\pm s$ , n = 6). (c) Comparison of TNF‐α levels in each group ( $\overline{x}\pm s$ , n = 6). (d) Comparison of H₂O₂ levels of arterial homogenate in each group ( $\overline{x}\pm s$ , n = 6). (e) Comparison of CAT Levels in Vascular Tissues of Rats ( $\overline{x}\pm s$ , n = 6). *P < 0.05, **P < 0.01 vs. NC group; ^# P < 0.05, ^## P < 0.01 vs. HS group. ^△ P < 0.05, ^△△ P < 0.01 vs. WSP‐L group. (f) Detection of ROS content in vascular tissue using flow cytometry ( $\overline{x}\pm s$ , n = 6). CAP, captopril; CAT, catalase; HS, high salt; NC, normal control; ROS, reactive oxygen species; WSP, Chinese water‐soluble propolis.

Figure 4

Morphological changes of rat myocardium, vascular, and kidney tissues in each group (HE stains × 400). (a) In myocardial tissues. (b) In vascular tissue. (c) In kidney tissue. (A: NC group; B: HS group; C: HS + WSP‐L group; D: HS + WSP‐M group; E: HS + WSP‐H group; F: HS + CAP group). CAP, captopril; HE, hematoxylin‐eosin; HS, high salt; NC, normal control; WSP, Chinese water‐soluble propolis.

Figure 5

Determination of NADPH oxidase activity. (a) and (b) represent Nox2/Nox4 protein expression in myocardial, vascular and kidney tissues of each group, respectively. ( $\overline{x}\pm s$ , n = 6). *P < 0.05, **P < 0.01 vs. NC group; ^# P < 0.05, ^## P < 0.01 vs. HS group (A: Myocardial tissue; B: Vascular tissue; C: Kidney tissue). (c) The expression level of the Nox2 and Nox4 gene in each group by real‐time fluorescent PCR (A: Nox2 gene expression; B: Nox4 gene expression). (d) PCR statistical results of Nox2 and Nox4 gene expression ( $\overline{x}\pm s$ , n = 6). (ABC represents different gene expression sites; A: Heart, B: Vessel, C: Kidney). *P < 0.05, **P < 0.01 vs. NC group; ^# P < 0.05, ^## P < 0.01 vs. HS group. CAP, captopril; HS, high salt; NC, normal control; PCR, polymerase chain reaction; WSP, water‐soluable Chinese propolis.