Role of TRPV4 on vascular tone regulation in pathophysiological states

Vascular tone regulation is a key event in controlling blood flow in the body. Endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) help regulate the vascular tone. Abnormal vascular responsiveness to various stimuli, including constrictors and dilators, has been observed in pathophysiological states although EC and VSMC coordinate to maintain the exquisite balance between contraction and relaxation in vasculatures. Thus, investigating the mechanisms underlying vascular tone abnormality is very important in maintaining vascular health and treating vasculopathy. Increased intracellular free Ca2+ concentration ([Ca2+]i) is one of the major triggers initiating each EC and VSMC response. Transient receptor potential vanilloid family member 4 (TRPV4) is a Ca2+-permeable non-selective ion channel, which is activated by several stimuli, and is presented in both ECs and VSMCs. Therefore, TRPV4 plays an important role in vascular responses. Emerging evidence indicates the role of TRPV4 on the functions of ECs and VSMCs in various pathophysiological states, including hypertension, diabetes, and obesity. This review focused on the link between TRPV4 and the functions of ECs/VSMCs, particularly its role in vascular tone and responsiveness to vasoactive substances.

Crotonaldehyde-induced vascular relaxation and toxicity: Role of endothelium and transient receptor potential ankyrin-1 (TRPA1)

INTRODUCTION

Crotonaldehyde (CR) is an electrophilic α,β-unsaturated aldehyde present in foods and beverages and is a minor metabolite of 1,3-butadiene. CR is a product of incomplete combustion, and is at high levels in smoke of cigarettes and structural fires. Exposure to CR has been linked to cardiopulmonary toxicity and cardiovascular disease.

OBJECTIVE

The purpose of this study was to examine the direct effects of CR in murine blood vessels (aorta and superior mesenteric artery, SMA) using an in vitro system.

METHODS AND RESULTS

CR induced concentration-dependent (1-300 μM) relaxations (75-80%) in phenylephrine (PE) precontracted aorta and SMA. Because the SMA was 20× more sensitive to CR than aorta (SMA EC50 3.8 ± 0.5 μM; aorta EC50 76.0 ± 2.0 μM), mechanisms of CR relaxation were studied in SMA. The CR-induced relaxation at low concentrations (1-30 μM) was inhibited by: 1) mechanically-impaired endothelium; 2) Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME); 3) guanylyl cyclase (GC) inhibitor (ODQ); 4) transient receptor potential ankyrin-1 (TRPA1) antagonist (A967079); and, 5) by non-vasoactive level of nicotine (1 μM). Similarly, a TRPA1 agonist, allyl isothiocyanate (AITC; mustard oil), stimulated SMA relaxation dependent on TRPA1, endothelium, NO, and GC. Consistent with these mechanisms, TRPA1 was present in the SMA endothelium. CR, at higher concentrations (100-300 μM), induced tension oscillations (spasms) and irreversibly impaired contractility (a vasotoxic effect enhanced by impaired endothelium).

CONCLUSIONS

CR relaxation depends on a functional endothelium and TRPA1, whereas vasotoxicity is enhanced by endothelium dysfunction. Thus, CR is both vasoactive and vasotoxic along a concentration continuum.

Acetaldehyde Induces an Endothelium-Dependent Relaxation of Superior Mesenteric Artery: Potential Role in Postprandial Hyperemia

Acetaldehyde (AA) is a small, ubiquitous compound present in foods, beverages, as a gas phase combustion product, and also endogenously generated from metabolism as from ethanol (EtOH). Acetate is a short chain fatty acid derived from AA oxidation, and acetate levels were significantly higher in urine collected overnight with food provided ad libitum compared with urine collected after 9 h fasting. Feeding increases gastrointestinal blood flow, and thus, we explored the direct effects of AA (and acetate) in isolated murine superior mesenteric artery (SMA). Over the concentration range of 1–100 mM, AA strongly, and reversibly relaxed agonist-induced contractions of SMA including phenylephrine (PE), thromboxane A₂ analog (U46,619) and high potassium (High K⁺) without toxicity. The sensitivity (EC₅₀) but not the efficacy (>90% relaxation of PE-precontraction) of AA-induced relaxations was dependent on blood vessel (SMA was 3× more sensitive than aorta) and contractile agonist (PE EC₅₀ = 3.3 ± 0.4 mM; U46,619 EC₅₀ = 14.9 ± 1.5 mM; and High K⁺ EC₅₀ = 17.7 ± 0.5 mM) yet independent of circadian cycle and sex. The most sensitive component of the AA-induced relaxation was inhibited significantly by: (1) a mechanically impaired endothelium; (2) nitric oxide synthase (NOS) inhibitor (L-NAME); and (3) a guanylyl cyclase (GC) inhibitor (ODQ). Both acetate and EtOH stimulated much weaker relaxations in SMA than did AA, yet these relaxations were significantly inhibited by L-NAME as well. Neither EtOH nor acetate relaxed pre-contracted aorta. Although neither cyanamide, a non-specific aldehyde dehydrogenase (ALDH) enzyme inhibitor, nor Alda-1, a specific activator of ALDH2 activity, had any effect on either sensitivity or efficacy of AA-induced relaxation in SMA, cyanamide significantly blocked both EtOH- and acetate-induced relaxations in SMA implicating a role of ALDH activity in vasorelaxation. These data show that AA relaxes SMA via an endothelium- and NO-dependent mechanism indicating that AA may be one component of the complex post-prandial hyperemia reflex via vasodilatation of mesenteric vasculature.

Formaldehyde Induces Mesenteric Artery Relaxation via a Sensitive Transient Receptor Potential Ankyrin-1 (TRPA1) and Endothelium-Dependent Mechanism: Potential Role in Postprandial Hyperemia

Formaldehyde (FA), the smallest aldehyde, is generated endogenously, and is widespread in the environment in foods, beverages and as a gas phase product of incomplete combustion. The main metabolite of FA, formate, was increased significantly in murine urine (∼3×) after overnight feeding. Because feeding increases mesenteric blood flow, we explored the direct effects of FA in isolated murine superior mesenteric artery (SMA). Over the concentration range of 30–1,200 μM, FA strongly and reversibly relaxed contractions of SMA induced by three different agonists: phenylephrine (PE), thromboxane A₂ analog (U46,619) and high potassium (60K, 60 mM K⁺). Formate (to 1.5 mM) induced a modest relaxation. FA (>1,500 μM) irreversibly depressed vascular function in SMA indicating vasotoxicity. The sensitivity (EC₅₀) but not the efficacy (% relaxation) of FA-induced relaxations was dependent on blood vessel type (SMA << aorta) and contractile agonist (PE, EC₅₀= 52 ± 14 μM; U46,619, EC₅₀= 514 ± 129 μM; 60K, EC₅₀= 1,093 ± 87 μM). The most sensitive component of FA vasorelaxation was within physiological levels (30–150 μM) and was inhibited significantly by: (1) mechanically impaired endothelium; (2) Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME); (3) transient receptor potential ankyrin-1 (TRPA1) antagonist (A967079); (4) guanylyl cyclase (GC) inhibitor (ODQ); and, (5) K⁺ channel inhibitor (BaCl₂). A similar mechanism of SMA vasorelaxation was stimulated by the TRPA1 agonist cinnamaldehyde. Positive TRPA1 immunofluorescent staining and gene-specific sequence were present in SMA but not in aorta. These data indicate FA, but not formate, robustly relaxes SMA via a sensitive TRPA1- and endothelium-dependent mechanism that is absent in aorta. Thus, as FA levels increase with feeding, FA likely contributes to the physiological reflex of post-prandial hyperemia via SMA vasodilatation.

Involvement of histamine in endothelium-dependent relaxation of mesenteric lymphatic vessels

OBJECTIVES

The knowledge of the basic principles of lymphatic function, still remains, to a large degree, rudimentary and will require significant research efforts. Recent studies of the physiology of the MLVs suggested the presence of an EDRF other than NO. In this study, we tested the hypothesis that lymphatic endothelium-derived histamine relaxes MLVs.

METHODS

We measured and analyzed parameters of lymphatic contractility in isolated and pressurized rat MLVs under control conditions and after pharmacological blockade of NO by L-NAME (100 μM) or/and histamine production by α-MHD (10 μM). Effectiveness of α-MHD was confirmed immunohistochemically. We also used immunohistochemical labeling and Western blot analysis of the histamine-producing enzyme, HDC. In addition, we blocked HDC protein expression in MLVs by transient transfection with vivo-morpholino oligos.

RESULTS

We found that only combined pharmacological blockade of NO and histamine production completely eliminates flow-dependent relaxation of lymphatic vessels, thus confirming a role for histamine as an EDRF in MLVs. We also confirmed the presence of HDC and histamine inside lymphatic endothelial cells.

CONCLUSIONS

This study supports a role for histamine as an EDRF in MLVs.

Nitric oxide scavenging by red cell microparticles

Red cell microparticles form during the storage of red blood cells and in diseases associated with red cell breakdown and asplenia, including hemolytic anemias such as sickle cell disease. These small phospholipid vesicles that are derived from red blood cells have been implicated in the pathogenesis of transfusion of aged stored blood and hemolytic diseases, via activation of the hemostatic system and effects on nitric oxide (NO) bioavailability. Red cell microparticles react with the important signaling molecule NO almost as fast as cell-free hemoglobin, about 1000 times faster than red-cell-encapsulated hemoglobin. The degree to which this fast reaction with NO by red cell microparticles influences NO bioavailability depends on several factors that are explored here. In the context of stored blood preserved in ADSOL, we find that both cell-free hemoglobin and red cell microparticles increase as a function of duration of storage, and the proportion of extra erythrocytic hemoglobin in the red cell microparticle fraction is about 20% throughout storage. Normalized by hemoglobin concentration, the NO-scavenging ability of cell-free hemoglobin is slightly higher than that of red cell microparticles as determined by a chemiluminescence NO-scavenging assay. Computational simulations show that the degree to which red cell microparticles scavenge NO will depend substantially on whether they enter the cell-free zone next to the endothelial cells. Single-microvessel myography experiments performed under laminar flow conditions demonstrate that microparticles significantly enter the cell-free zone and inhibit acetylcholine, endothelial-dependent, and NO-dependent vasodilation. Taken together, these data suggest that as little as 5 μM hemoglobin in red cell microparticles, an amount formed after the infusion of one unit of aged stored packed red blood cells, has the potential to reduce NO bioavailability and impair endothelial-dependent vasodilation.

Nitric oxide scavenging by red cell microparticles. Free Radic Biol Med. 2013;65:1164-1173. [PMID: 24051181 DOI: 10.1016/jfreeradbiomed.2013.09.002]

Red cell microparticles form during the storage of red blood cells and in diseases associated with red cell breakdown and asplenia, including hemolytic anemias such as sickle cell disease. These small phospholipid vesicles that are derived from red blood cells have been implicated in the pathogenesis of transfusion of aged stored blood and hemolytic diseases, via activation of the hemostatic system and effects on nitric oxide (NO) bioavailability. Red cell microparticles react with the important signaling molecule NO almost as fast as cell-free hemoglobin, about 1000 times faster than red-cell-encapsulated hemoglobin. The degree to which this fast reaction with NO by red cell microparticles influences NO bioavailability depends on several factors that are explored here. In the context of stored blood preserved in ADSOL, we find that both cell-free hemoglobin and red cell microparticles increase as a function of duration of storage, and the proportion of extra erythrocytic hemoglobin in the red cell microparticle fraction is about 20% throughout storage. Normalized by hemoglobin concentration, the NO-scavenging ability of cell-free hemoglobin is slightly higher than that of red cell microparticles as determined by a chemiluminescence NO-scavenging assay. Computational simulations show that the degree to which red cell microparticles scavenge NO will depend substantially on whether they enter the cell-free zone next to the endothelial cells. Single-microvessel myography experiments performed under laminar flow conditions demonstrate that microparticles significantly enter the cell-free zone and inhibit acetylcholine, endothelial-dependent, and NO-dependent vasodilation. Taken together, these data suggest that as little as 5 μM hemoglobin in red cell microparticles, an amount formed after the infusion of one unit of aged stored packed red blood cells, has the potential to reduce NO bioavailability and impair endothelial-dependent vasodilation.

Oxygen binding to partially nitrosylated hemoglobin

Reactions of nitric oxide (NO) with hemoglobin (Hb) are important elements in protection against nitrosative damage. NO in the vasculature is depleted by the oxidative reaction with oxy Hb or by binding to deoxy Hb to generate partially nitrosylated Hb (Hb-NO). Many aspects of the formation and persistence of Hb-NO are yet to be clarified. In this study, we used a combination of EPR and visible absorption spectroscopy to investigate the interactions of partially nitrosylated Hb with O2. Partially nitrosylated Hb samples had predominantly hexacoordinate NO-heme geometry and resisted oxidation when exposed to O2 in the absence of anionic allosteric effectors. Faster oxidation occurred in the presence of 2,3-diphosphoglycerate (DPG) or inositol hexaphosphate (IHP), where the NO-heme derivatives had higher levels of pentacoordinate heme geometry. The anion-dependence of the NO-heme geometry also affected O2 binding equilibria. O2-binding curves of partially nitrosylated Hb in the absence of anions were left-shifted at low saturations, indicating destabilization of the low O2 affinity T-state of the Hb by increasing percentages of NO-heme, much as occurs with increasing levels of CO-heme. Samples containing IHP showed small decreases in O2 affinity, indicating shifts toward the low-affinity T-state and formation of inert α-NO/β-met tetramers. Most remarkably, O2-equilibria in the presence of the physiological effector DPG were essentially unchanged by up to 30% NO-heme in the samples. As will be discussed, under physiological conditions the interactions of Hb with NO provide protection against nitrosative damage without impairing O2 transport by Hb's unoccupied heme sites. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.

Vascular pharmacology of mokuboito (mu-fang-yi-tang) and its constituents on the smooth muscle and the endothelium in rat aorta

Pharmacological actions of Mokuboito and its constituents (Sinomenium acutum and sinomenine) on rat aorta were examined. Mokuboito and S. acutum at lower concentrations (0.03-1 mg ml(-1)) contracted the non-loaded aorta, but at higher concentrations (1-3 mg ml(-1)), reversed to dilate it. The vasoconstriction was blocked by phentolamine (10 muM). Sinomenine failed to exhibit the vasoconstriction. On the other hand, Mokuboito and S. acutum dilated the NE (5 muM)-induced vasoconstriction: at 3 mg ml(-1), by 98.9 +/- 2.5% (n = 6, P < 0.01) and 97.0 +/- 4.8% (n = 6, P < 0.01). Vasorelaxation induced by Mokuboito and S. acutum was attenuated by indomethacin, L-NMMA and nicardipine. Propranolol decreased the vasorelaxation induced by Mokuboito, but not by S. acutum. Sinomenine also relaxed the constriction and at 100 muM, by 68.8 +/- 5.1% (n = 7, P < 0.01). This vasorelaxation was attenuated by indomethacin, L-NMMA and nicardipine, and also by propranolol. Therefore, these results indicate that Mokuboito and its constituents exert both vasodilating actions mediated by endothelium-dependent mechanisms (PGI(2) and NO from endothelium) and by endothelium-independent mechanisms (Ca(2+) influx control on smooth muscle cells). Simultaneously, Mokuboito and S. acutum cause the vasoconstrictions mediated through alpha-adrenoceptor stimulation, but not sinomenine. Also, Mokuboito and sinomenine possess beta-adrenoreceptor stimulating action, but not S. acutum.

Hydrogen sulfide as a gasotransmitter

Nitric oxide (NO) and carbon monoxide (CO) are well established as messenger molecules throughout the body, gasotransmitters, based on striking alterations in mice lacking the appropriate biosynthetic enzymes. Hydrogen sulfide (H(2)S) is even more chemically reactive, but until recently there was little definitive evidence for its physiologic formation. Cystathionine beta-synthase (EC 4.2.1.22), and cystathionine gamma-lyase (CSE; EC 4.4.1.1), also known as cystathionine, can generate H(2)S from cyst(e)ine. Very recent studies with mice lacking these enzymes have established that CSE is responsible for H(2)S formation in the periphery, while in the brain cystathionine beta-synthase is the biosynthetic enzyme. Endothelial-derived relaxing factor activity is reduced 80% in the mesenteric artery of mice with deletion of CSE, establishing H(2)S as a major physiologic endothelial-derived relaxing factor. H(2)S appears to signal predominantly by S-sulfhydrating cysteines in its target proteins, analogous to S-nitrosylation by NO. Whereas S-nitrosylation typically inhibits enzymes, S-sulfhydration activates them. S-nitrosylation basally affects 1-2% of its target proteins, while 10-25% of H(2)S target proteins are S-sulfhydrated. In summary, H(2)S appears to be a physiologic gasotransmitter of comparable importance to NO and carbon monoxide.