Taurine Regulates The Vascular Function And Artery Blood Pressure By Inhibiting Transient Receptor Potential Channel3

Background and Objectives:Hypertension is a major public health issue that is estimated to affect 20% of the adult population worldwide, and its aetiology has yet to be clearly identified. In 2003, the Joint National Committee 7（JNC7） proposed a new blood pressure category of 120 to 139 mm Hg systolic blood pressure（SBP） or 80 to 89 mmHg diastolic blood pressure（DBP） and delegated it as “prehypertension”. Generally, prehypertension progresses to hypertension within a period of 4 years, particularly in older adults. Now, it is estimated that about 30% to 50% of the population have this condition. Prehypertension frequently complicates other cardiometabolic risk factors and is closely associated with the increased risk of coronary heart disease, stroke, and renal dysfunction. Early intervention in prehypertension substantially prevents the incidence of hypertension and related damage to target organs. Currently, several strategies are used to treat prehypertension, including the incorporation of therapeutic lifestyle changes, such as healthy dietary intake and regular physical activity, as well as the use of antihypertensive drugs, such as an angiotensin II receptor blocker. Although these treatments improve prehypertension, poor compliance and limitations associated with antihypertensive medications prevent their application in the general population. Thus, there is an urgent need to identify reliable and accurate measures to prevent the development of prehypertension.Sulfur amino acid is the indispensable amino acid in mammals, and its smetabolites include Taurine, Hydrogen sulfide（H₂S） and sulfur dioxide（SO2）. Taurine was first isolated more than 150 years ago from ox（Taurus） bile. Although the taurine can be synthesized in vivo by cysteine in the presence of cysteine dioxygenase, it is mainly acquired from dietary sources, such as eggs, meat, and seafood. H₂ S is a biologically relevant mediator and plays potential roles in several physiological processes and disease states in the body. H₂ S is synthesized from 2 sulfur-containing amino acids, l-cysteine and l-methionine, by the 3 enzymes, cystathionine-γ-lyase（CSE）, cystathionine-β-synthetase（CBS）, and 3-mercaptopyruvate sulfurtransferase（3-MST）. Previous studies have demonstrated that Taurine and H₂ S may play important roles in the development of the hypertension. For instance, Mozaffari et al. found that taurine depletion accelerates the development of high salt–induced hypertension. Furthermore, van den Berg et al. showed that in renal transplant recipients, an increased blood pressure（BP） level may be associated with a low level of metabolite of H₂ S in urine. But how does the sulfur amino acid work in the development of the hypertension? The detailed mechanisms are still unclear.Transient receptor potential channels（TRPCs） are a superfamily of structurally homologous cation channels. Several studies demonstrated that transient receptor potential canonical channel 3（TRPC3）-mediated calcium signaling contributes to the development of hypertension. In addition, a recent study has found that H₂ S could affect TRPCs in mesenchymal stem cells and regulates calcium homeostasis. Although there was no direct relationship between the sulfur amino acid, TRPC3, calcium signaling and hypertension based on the current results, it still suggested their important roles in the process of the hypertension. Along these findings, in the present study we investigated the effects of chronic taurine supplementation on BP and vascular function in prehypertension by performing a randomized, doubleblind, placebo-controlled clinical trial.Materials and Methods:In the present study, clinical trials and animal experiments were performed simultaneously. In the first clinical trials part, the research programme was approved by the Ethnics Committee of The Third Military Medical University and registered in www.ClinicalTrials.gov with the uniue identifier NCT01816698. All participants were signed with informed consent. One hundred and twenty eligible prehypertensive individuals and 58 age-matched normotensive control subjects were included in the clinical trials. In the second basic research part, mesenteric arteries（MAs） from human and Trpc3-/- mice, and aortas from mice and spontaneously hypertensive rats were used in the animal experiments.1. The conventional mercury sphygmomanometer was applied to measure the BP every four weeks, and the ambulatory BP monitoring was recorded using Spacelabs 90217 monitor before and after intervention.2. The high-resolution ultrasonography using a 7.5-MHz linear transducer on an HY 6000 system（Wuxi Haiying Electronic Medical System Co. Ltd., Jiangsu, China） was applied to measure the flow-mediated（endothelium-dependent） and nitroglycerin-mediated（endothelium-independent） vasodilation.3. The reverse-phase high-performance liquid chromatography was applied to detect the plasma taurine and H₂ S levels.4. Immunofluorescence and western blot were applied to detect the expressions of CBS, CSE and TRPC3.5. The wire myograph（Danish Myo Technology, Denmark） was applied to measure the vascular reactivity（constriction and relaxation）.6. Fura-2AM using a PTI Fluorescence Master System（Photon Technology International, Birmingham, NJ, USA） was applied to detect the intracellular Ca²⁺ concentrations.Results:1. Compared with the normotensive control subjects, the enrolled prehypertensive individuals had higher clinic and ambulatory BPs and increased pulse wave velocity and postprandial blood glucose values. In addition, there were no significant differences in the baseline characteristics between the enrolled prehypertensive individuals in placebo and taurine groups.2. Administration of taurine for 12 weeks significantly reduced the clinic BP and the 24-hour ambulatory BP compared with the baseline values in prehypertensive individuals. Further analysis revealed that taurine treatment reduced the daytime ambulatory BP compared with the baseline values, but not the nighttime ambulatory BP. Chonic taurine intervention reduced BP levels more in high-normal prehypertensive participants.3. Chronic taurine supplementation significantly improved both endothelium-dependent vasodilation（flow-mediated dilation, FMD） and endotheliumindependent vasodilation（nitroglycerin-mediated dilation, NMD）, respectively in the prehypertensive individuals. On the contrary, the beneficial effect of taurine supplementation on vasodilation was absent in the prehypertensive individuals treated with placebo.4. After treatment for 12 weeks, the plasma taurine and H₂ S levels were significantly higher in the prehypertensive individuals treated with taurine. Furthermore, the changes in BP were negatively correlated with both the plasma H₂ S and taurine levels in the taurine-treated prehypertensive individuals.5. CBS, CSE and TRPC3 were co-expressed in human MAs and aortas from WT mice. The expression levels of CBS and CSE were enhanced in Trpc3-/- mice compared with Trpc3+/+ mice.6. Administration of taurine significantly upregulated CBS/CSE expression but inhibited TRPC3 expression in both aortas from spontaneously hypertensive rats treated with taurine and cultured human vascular tissues. In vitro experiments indicated that taurine incubation could upregulate the expression levels of CBS and CSE while inhibit the levels of TRPC3 in dose-dependent manner.7. After depletion of intracellular calcium storage using thapsigargin, a sarcoplasmic reticulum Ca²⁺-ATPase inhibitor, KCl-induced vasoconstriction was dose dependently relaxed by sodium hydrosulfide（NaHS）, a H₂ S donor; besides, this effect was enhanced by a TRPC3 inhibitor, Pyr3, or by Trpc3 gene knockout.8. Na HS could inhibit the calcium influx induced by phenylephrine. TRPC3 deficiency of TRPC3 inhibitor Pyr3 could significantly reduce thapsigargin induced calcium influx. NaHS significantly diminished the thapsigargin-induced increase in calcium influx in Trpc3 WT mice, while this effect of absent in TRPC3 knockout mice.Conclusions:1. Chonic administration of taurine significantly reduced the clinic BP and 24-hour ambulatory BP in prehypertensive individuals. The daytime ambulatory BP levels and those with high-normal BP prehypertensive participants. were reduced more significantly.2. Chonic taurine intervention significantly improve the FMD and NMD in prehypertensive participants.3. The plasma taurine and H₂ S levels were significantly higher in the prehypertensive individuals long-term treated with taurine. Those participants with higher plasma taurine and H₂ S levels were accompanied with higher BP reductions.4. CBS, CSE and TRPC3 were co-expressed in MAs from human / mice and aortas from WT mice. TRPC3 knockout or taurine intervention increase CBS and CSE expression levels while inhibit TRPC3 expression levels. The reduction of BP levels with taurine intervention were correlated with reduced expression of TRPC3 and Ca²⁺ concentration in vascular smooth mucle cells. Chonic taurine intervention upregulated CBS and CSE expression, promoted H₂ S synthesis and improved BP and vascular functions.