Taurine supplementation reduces blood pressure and prevents endothelial dysfunction and oxidative stress in post-weaning protein-restricted rats

Abstract

Introduction: Taurine is a sulfur-containing amino acid that exerts protective effects on vascular function and structure in several models of cardiovascular diseases through its antioxidant and anti-inflammatory properties. Early protein malnutrition reprograms the cardiovascular system and is linked to hypertension in adulthood. This study assessed the effects of taurine supplementation in vascular alterations induced by protein restriction in post-weaning rats.

Methods and results: Weaned male Wistar rats were fed normal- (12%, NP) or low-protein (6%, LP) diets for 90 days. Half of the NP and LP rats concomitantly received 2.5% taurine supplementation in the drinking water (NPT and LPT, respectively). LP rats showed elevated systolic, diastolic and mean arterial blood pressure versus NP rats; taurine supplementation partially prevented this increase. There was a reduced relaxation response to acetylcholine in isolated thoracic aortic rings from the LP group that was reversed by superoxide dismutase (SOD) or apocynin incubation. Protein expression of p47phox NADPH oxidase subunit was enhanced, whereas extracellular (EC)-SOD and endothelial nitric oxide synthase phosphorylation at Ser 1177 (p-eNOS) were reduced in aortas from LP rats. Furthermore, ROS production was enhanced while acetylcholine-induced NO release was reduced in aortas from the LP group. Taurine supplementation improved the relaxation response to acetylcholine and eNOS-derived NO production, increased EC-SOD and p-eNOS protein expression, as well as reduced ROS generation and p47phox expression in the aortas from LPT rats. LP rats showed an increased aortic wall/lumen ratio and taurine prevented this remodeling through a reduction in wall media thickness.

Conclusion: Our data indicate a protective role of taurine supplementation on the high blood pressure, endothelial dysfunction and vascular remodeling induced by post-weaning protein restriction. The beneficial vascular effect of taurine was associated with restoration of vascular redox homeostasis and improvement of NO bioavailability.

Figure 1. Taurine supplementation prevented the reduction in endothelium-dependent relaxation to acetylcholine induced by post-weaning protein restriction.

Concentration-response curves to acetylcholine (A) and sodium nitroprusside (B) in aortas from rats fed an isocaloric normal-protein (NP) or low-protein (LP) diets without or with taurine (T). Relaxation responses are expressed as a percentage of serotonin-induced contraction. Values represent the mean ± SEM. The number of rats included in each group is indicated into parentheses in the figure. 2-way ANOVA:Figure 1A showed significant main effects of groups and acetylcholine;Figure 1B showed significant main effects of groups and sodium nitroprusside. Bonferroni post-test (p<0.05): * LP vs. NP, ⁺ LPT vs. LP, ^# LPT vs. NPT.

Figure 2. Superoxide dismutase (SOD) and apocynin (Apo) restored the endothelium-dependent relaxation in aorta from low-protein-fed rats.

Concentration-response curves to acetylcholine were obtained in aortas from rats fed an isocaloric normal-protein (NP) (A) or low-protein (LP) (B) diets supplemented with taurine (T) in drinking water (C, D). Values represent the mean ± SEM. The number of rats included in each group is indicated into parenthesis in the figure. 2-way ANOVA:Figure 2B showed significant main effects of SOD/Apo and acetylcholine. Bonferroni post-test (p<0.05): * vs. LP.

Figure 3. Increased ROS generation and reduced NO bioavailability induced by low-protein diet is normalized by taurine.

Representative fluorographs and fluorescence intensity analysis of aortic sections labeled with NO-sensitive fluorescent dye 4,5-diaminofluorescein (DAF-2) (A, B) or with the dihydroethidine (DHE) (C, D) from rats fed an isocaloric normal-protein (NP) or low-protein (LP) diets without or with taurine (T). Fluorescence was quantified as intensity per vessel area (µm²); DAF-2 was evaluated in the presence of acetylcholine (ACh, 1 µM) and the results are expressed as a percentage of increase in relation to basal level. Effect of L-NAME incubation was evaluated in NO (A, B) and ROS production (C, D). Values represent the mean ± SEM. The number of rats (n) included in each group is indicated in parenthesis. 2-way ANOVA:Figure 3B showed significant main effects of groups and L-NAME;Figure 3D showed significant main effect of groups. Bonferroni post-test (p<0.05): * vs. NP, ⁺ vs. LP, ° vs. without L-NAME. Bar scale = 100 µm.

Figure 4. Taurine prevented the alterations in p47^phox, EC-SOD and eNOS phosphorylation induced by low-protein diet.

Protein expression of gp91^phox (A), p47^phox (B), EC-SOD (C), CuZn-SOD (D), Mn-SOD (E), catalase (F), glutathione peroxidase (GPx) (G), eNOS (H) and phosphorylated Ser1177 (p)eNOS (I) were analyzed by Western-blot in aorta from rats fed normal-protein (NP) or low-protein (LP), with or without taurine (T). α-actin content was used as internal control in each sample. Values represent the mean ± SEM (Number of animals in each group = 5–9). 2-way ANOVA:Figure 4B and 4C showed significant interaction (LP diet x taurine).Figure 4E showed main effect of LP diet;Figure 4I showed significant main effects of LP diet and taurine. Bonferroni post-test (p<0.05): * vs. NP, ⁺ vs. LP, ^# vs. NPT.

Figure 5. Effect of post-weaning protein restriction and taurine supplementation on the morphometric parameters of rat aorta.

Representative images of transversal aortic slices are shown in panel A. Aortic cross sectional area (CSA) (B) and wall/lumen ratio (C) were calculated in aortic slices of rats fed a normal-protein (NP) or low-protein (LP) diet, with or without taurine (T). Values represent the mean ± SEM (Number of animals in each group = 5–9). 2-way ANOVA: Figure 5B showed main effect of LP diet; Figure 5C showed significant interaction (LP diet x taurine). Bonferroni post-test (p<0.05): * vs. NP, ⁺ vs. LP, ^# vs. NPT.