key: cord-0837325-siewh7vt authors: Bartáková, Anna; Nováková, Marie title: Secondary Metabolites of Plants as Modulators of Endothelium Functions date: 2021-03-03 journal: Int J Mol Sci DOI: 10.3390/ijms22052533 sha: 5c89ae31ca2b3c458b4c252a82e2f0e89a0f04a6 doc_id: 837325 cord_uid: siewh7vt According to the World Health Organization, cardiovascular diseases are the main cause of death worldwide. They may be caused by various factors or combinations of factors. Frequently, endothelial dysfunction is involved in either development of the disorder or results from it. On the other hand, the endothelium may be disordered for other reasons, e.g., due to infection, such as COVID-19. The understanding of the role and significance of the endothelium in the body has changed significantly over time—from a simple physical barrier to a complex system encompassing local and systemic regulation of numerous processes in the body. Endothelium disorders may arise from impairment of one or more signaling pathways affecting dilator or constrictor activity, including nitric oxide–cyclic guanosine monophosphate activation, prostacyclin–cyclic adenosine monophosphate activation, phosphodiesterase inhibition, and potassium channel activation or intracellular calcium level inhibition. In this review, plants are summarized as sources of biologically active substances affecting the endothelium. This paper compares individual substances and mechanisms that are known to affect the endothelium, and which subsequently may cause the development of cardiovascular disorders. According to the World Health Organization (WHO), almost 18 million people died worldwide in 2017 due to cardiovascular disorders. Numerous experimental and clinical studies are, therefore, focused on the cardiovascular system under both physiological and pathological conditions. The cardiovascular system consists of the heart and vessels of various types. Three layers form a typical vessel: the tunica intima, tunica media, and tunica adventitia. The thickness ratio of a vessel wall depends on the functional requirements of that particular part of circulation system. Nevertheless, endothelial cells are a standard part of the tunica intima in any vessel. A single layer of flat endothelial cells covers the inner surface of a vessel, which is in direct contact with the blood. Thus, this inner lining provides an anticoagulant barrier between the vessel wall and blood. All endothelial cells form a large organ consisting of approximately 1-6 × 10 13 of cells, a mass of almost one kilogram [1] . The endothelium originates from the splanchnopleuric mesoderm [1] . Vascular endothelial growth factor (VEGF) and its high-affinity flk-1 and flt-1 receptor tyrosine kinases represent a paracrine signaling system that is critical for endothelial cell differentiation and vascular system development [2, 3] . It has been proven that VEGF is the only specific mitogen for endothelial cells. It stimulates their growth, inhibits apoptosis, increases vascular permeability in various tissues, and promotes vasculogenesis and angiogenesis. Angiogenesis plays a protective role in coronary artery disease and myocardial infarction [4] . Endothelial cells consist of four basic compartments: the glycocalyx, cell cortex, cytoplasm, and nucleus ( Figure 1 ). The structure and mechanical properties of these compartments directly affect physiological processes [1] . The endothelial glycocalyx is a thick, carbohydrate-rich layer that surrounds the endothelial lumen surface; it is composed of proteoglycans and glycoproteins. On the inner side of a cell membrane, the cell cortex is found, containing actin organized in a dynamic net. Actin fibers represent a support network for the plasma membrane and membrane proteins. The cell is also penetrated by actin microtubules and intermediate filaments. All components of the cell cytoskeleton are associated with the nucleus. Mechanical stimuli perceived by actin fibers, microtubules, or intermediate filaments are integrated in the nucleus [5] . Endothelial cells contain so-called Weibel-Palade bodies, measuring 0.1 µm wide and 0.3 µm long. These membrane-bound structures are a kind of storage organelle for von Willebrand's factor (vWf) (Figure 1 ) [1] . For a long time, the role of the simple barrier was attributed to the endothelium. Since then, its concept has changed significantly and new functions of endothelial cells have been reported. It is now considered a specialized organ with numerous physiological functions [1] . First of all, the barrier function of the endothelium is viewed in a less static way than in the original concept, where the endothelium was believed to simply separate blood from the surrounding tissues. Nowadays, it is considered a dynamic barrier, the integrity of which is essential for maintaining physiological blood flow. On the other hand, endothelial cells communicate among themselves on one side and with circulating blood elements on the other side; the latter involves thrombocytes and leukocytes. Communication with other cells, even distant ones, via various paracrine and endocrine substances has also been described. All of these cells, cooperatively with the blood flow, affect the behavior of the endothelium [6] . Based on the above, it can be presumed that both endothelial cell injury and its dysfunction may lead to a number of pathological situations. Endothelial dysfunction results in various seemingly unrelated pathological processes, such as loss of semipermeable membrane function, hyperlipoproteinemia (often accompanied by atherogenesis), diabetes mellitus, vascular spasms, and arterial hypertension. Together with certain risk factors (e.g., smoking), these processes progress to uniform vascular changes. Subsequent organ hypoperfusion leads to failure in the target structure, for example heart failure [1] . The basic humoral and metabolic functions of the endothelium are summarized in Figure 2 . Various types of autocrine, paracrine, and endocrine communication systems are presented. The basic humoral and metabolic functions of the endothelium. ACE: angiotensin converting enzyme; CSF: colony-stimulating factor; ECM: extracellular matrix; EDH: endothelium-derived hyperpolarization; IGF: insulin-like growth factor; LDL receptor: low-density lipoprotein receptor; MHC II: major histocompatibility complex type 2; PAF: platelet-activating factor; PAI: plasminogen activator inhibitor; ROS: reactive oxygen species; TGF: transforming growth factor; vWf: von Willebrand's factor. Purple arrow: paracrine communication, red arrow: endocrine communication. The endothelium is a site of production or modification of numerous vasodilatory and vasoconstrictory substances, which regulate the vascular tone via several pathways, namely nitric oxide-cyclic guanosine monophosphate (NO-cGMP) activation, prostacyclincyclic adenosine monophosphate (PGI 2 -cAMP) activation, inhibition of phosphodiesterase (PDE), and activation of K + channels or inhibition of intracellular Ca 2+ levels ( Figure 3 ). The endothelial cell reacts to physical and chemical stimuli from the circulation. Physical (hemodynamic) factors increase the sensory tension of endothelial cells, which depends on the blood flow velocity in the vessels. Chemical stimuli are represented by vasoactive substances (e.g., adenosine monophosphate, bradykinin, histamine), neurotransmitters (e.g., acetylcholine), hormones (e.g., antidiuretic hormone, angiotensin), coagulation factors, and substances produced by platelets (e.g., thrombin) [1] . In cases of locally increased blood flow, the local regulatory system is activated, which results in endothelium-mediated vasodilation. Nitric oxide (NO), prostacyclin (PGI 2 ), or endothelium-derived hyperpolarization (EDH) is secreted from the endothelium due to the increased shear stress. This may be a form of endothelium protection, resulting from increased blood flow. In the case of a turbulent flow, the risk of damage to the endothelium and consequent thrombus formation increases. NO mainly regulates the tonus of relatively large conduit vessels. On the contrary, EDH mediates vasodilation, especially in small resistance vessels in the microcirculation. Prostacyclins play a small but constant role, independent of vessel size. Furthermore, metabolic regulation can occur when substances (e.g., O 2 ) that are necessary to ensure metabolism or emerging catabolites (CO 2 , lactic acid, adenosine, and others) act on vascular smooth muscle and affect its tone, either directly or more often through endothelial receptors [7] [8] [9] . A detailed view of the intracellular mediation of the effects of vasoactive substances brings about a thought-provoking idea: a key player in this game is angiotensin-converting enzyme (ACE), also known as kininase II. It is produced by the vascular endothelium and plays a central role in the renin-angiotensin-aldosterone system (RAAS). ACE converts angiotensin I (AT I) to octapeptide angiotensin II (AT II), which is a very potent vasoconstrictor ( Figure 4 ) [10] . AT II increases the production of reactive oxygen species (ROS) via increasing NADPH oxidase activity. Increased levels of endothelial ROS lead to rapid inactivation or degradation of NO, and at the same time to endothelial nitric oxide synthase (eNOS) and prostacyclin synthase (PGIS) inhibition [10] [11] [12] [13] [14] . It is important to mention that NADPH oxidase activation is one of the pathways involved in production of endothelium-derived H 2 O 2 (E-D H 2 O 2 ) hyperpolarizing factor, a substance with high vasodilating potency [7] . AT II itself increases blood pressure, not only through vasoconstriction, but also through stimulation of the sympathetic system via the synthesis of aldosterone. AT II also acts as an inducer of growth, cell migration, and cell mitosis in vascular smooth muscle. It also increases the synthesis of type I and III collagen in fibroblasts, resulting in thickening of the blood vessel wall and myocardium and fibrosis. These effects are mediated by receptor type I for angiotensin II (AT 1 R) and can be blocked by AT 1 R blockers known as the "sartan" family [15, 16] . Receptor type II for AT II mediates the opposite effect, e.g., inhibition of cell proliferation in coronary endothelial cells [17] . AT II may trigger endothelial cell apoptosis, mediated either by generation of ROS or by inhibiting the function of the antiapoptotic protein B-cell lymphoma 2 [11] . The regulation of its effect is an essential part of the clinical practice of treating hypertension [10] . Moreover, ACE degrades kinins. Bradykinin stimulates NO and PGI 2 release [10] [11] [12] 14] and increases vascular permeability [18] . The effect of bradykinin on NO release is mediated by B 2 receptor [10] [11] [12] 14] . Angiotensin-converting enzyme inhibitors (iACEs) potentiate the actions of bradykinin by reducing its degradation [11] , which leads to higher bradykinin levels. On the contrary, blocking the effect of AT II through AT 1 R does not affect the level of bradykinin [19] . At this point, we would like to emphasize that iACEs affect the delicate physiological balance between NO and EDH [7] . Nitric Oxide-Cyclic Guanosine Monophosphate Activation Pathway Endothelium-derived relaxing factor (NO) is produced from the amino acid arginine, which is transferred into the amino acid citrulline. This reaction is catalyzed by the enzyme nitric oxide synthase (NOS). Nitric oxide is one of the three gasotransmitters, along with carbon monoxide (CO) and hydrogen sulphide (H 2 S), which are critical for cardiovascular homeostasis [20] . NO acts as a mediator, having a local vasodilatory effect on vascular smooth muscle. NOS exists in three isoforms: endothelial (eNOS), neural (nNOS), and inducible (iNOS). Vascular tone regulation is primarily dependent on NO produced in the reaction catalyzed by eNOS [21, 22] . Its production is regulated either at the level of its activity (increased by agonists such as CO, bradykinin, acetylcholine, substance P, thrombin, insulin, and shear stress) or gene expression [6, [21] [22] [23] [24] [25] . NO stimulates the soluble receptor with guanylate cyclase activity (sGC) in a neighboring cell. This leads to an increase in the cyclic guanosine monophosphate (cGMP) concentration, and consequently to vasodilation ( Figure 5 ). Another possible way to affect the NO-cGMP pathway is to modulate the activity or gene expression of sGC. Some substances activate the sGC [21, 22] . Inhibitors of both eNOS and sGC are used in studies focusing on the NO-cGMP pathway. In the case of eNOS, NG-nitro-L-arginine methyl esters or NG-monomethyl-L-arginine are most often used; in the case of sGC, methylene blue or 1H- [1, 2, 4] oxadiazole[4,3-a]quinoxalin-1-one can be employed [21, 22] . Another possible approach is the use of NO scavengers, e.g., hydroxocobalamin [26] . The plants are summarized in Table 1 , the vasodilation effects of which are mediated via the NO-cGMP pathway. As examples, Cynara scolymus L. [27] , Panax ginseng C. A. Meyer [28] , and Theobroma cacao L. [29] can be mentioned. Prostacyclin is an endogenous eicosanoid that relaxes vascular smooth muscle by stimulating the G-protein-coupled receptor. It is a vasodilator and platelet aggregation inhibitor, which activates adenylyl cyclase (AC), thereby increasing cyclic adenosine monophosphate (cAMP) levels. It also counterbalances the vasoconstrictor effect of thromboxane A 2 (TXA 2 ). Arachidonic acid (ARA) is metabolized by cyclooxygenase (COX) to form unstable prostaglandin H 2 (PGH 2 ). PGI 2 release is further catalyzed by PGIS ( Figure 6 ) [30] [31] [32] . Production of PGI 2 is activated by endogenous substances, such as histamine, serotonin, bradykinin, and acetylcholine [32, 33] . PGIS is activated by thrombin, cytokines, growth factors, and shear stress [31] . On the contrary, increased concentration of ROS inhibits PGIS activity, resulting in decreased PGI 2 synthesis [30] [31] [32] . Numerous natural substances have been studied for their vasodilation effects mediated via the PGI2-cAMP pathway. Both AC inhibitor SQ22536 and protein kinase A inhibitor KT5720 can be employed to study this pathway. Another possibility is the use of analogues and antagonists of cyclic nucleotides or COX inhibitor indomethacin [26, 32, 33] . The plants' vasodilation effects, which are mediated via the PGI2-cAMP pathway, are summarized in Table 2 . A frequently mentioned representative of this group is Piper truncatum Vell [34, 35] . Cyclic nucleotide phosphodiesterases (PDEs) are enzymes regulating cellular cAMP and cGMP levels by regulation of their degradation rate. Inhibition of the PDE enzyme leads to an increase of cyclic nucleotide levels and induces vasodilation ( Figure 7 ). The change in PDE activity, as measured by radioenzymatic assays, can elucidate the role of PDEs in the vasodilation effects of compounds in this pathway [33] . The plant metabolites that cause vasodilation via inhibition of PDE are summarized in Table 3 Vascular smooth muscle cell (VSMC) relaxation can be directly regulated by specific ionic channels. An important role is played by K + channels. In VSMC, four different types of K + channels were characterized: voltage-dependent, Ca 2+ -activated, ATP-dependent, and inward rectifier [33, 38] . K + channels control the membrane potential in VSMC, thereby determining the activity of voltage-dependent Ca 2+ channels (VDCC). A K + channel opening leads to membrane hyperpolarization ( Figure 8 ), resulting in closing of VDCC and preventing Ca 2+ influx. The concentration of cytosolic Ca 2+ is reduced, which leads to VSMC relaxation and consequent vasodilation [39] . A significant number of natural vasodilators at least partially utilize the mechanism of Ca 2+ -activated K + channel activation [33, 38] . Decreasing of the intracellular Ca 2+ concentration is another possibility to induce vasodilation. Ca 2+ enters cells through a receptor-operated Ca 2+ channel (ROCC) or VDCC. Obstructing these channels or inhibition of Ca 2+ release from intracellular stores lead to vasodilation [33] . Endothelium-derived hyperpolarization (EDH) represents a vasodilation system that is particularly important in small arteries, which are mostly dependent on Ca 2+ influx during contraction. EDH is used to describe the endothelium-dependent relaxation that is non-NO and non-prostanoid in nature. This results in VSMC hyperpolarization via opening of K + -channels or activation of Na + -K + -ATPase [38,40]. Since 1988, several candidates have been identified as the driver of EDH, including H 2 O 2 [7] , H2S [20, 41, 42] , epoxyeicosatrienoic acids, metabolites of ARA, K + ions, electrical communication through gap junctions, and P450 epoxygenase pathway. Nowadays, E-D H 2 O 2 is one of the major EDH in human vessels. It is generated by the dismutation of superoxide anions derived from various sources in the endothelium, including NADPH oxidase and eNOS [7] . Despite the fact that EDH evokes hyperpolarization and subsequent vasodilation (especially of small resistance vessels), higher concentrations of E-D H 2 O 2 induce vasoconstriction by releasing COX-derived TXA 2 [7, 43] . As mentioned above, although a lot of attention is paid to NO-targeted therapy and ROS elimination (including iACEs), the evidence indicates the importance of maintaining the delicate balance between NO and EDH. Moreover, despite the fact that ROS have been considered primarily harmful for cells and tissues, physiological levels of ROS can serve as crucial signaling molecules [7] . The vasodilation is caused by either K + channel activation or based on decreasing intracellular Ca 2+ levels, which can be studied by using selective activators or blockers of specific ionic channels. Voltage-clamp or patch-clamp techniques help to elucidate the roles of particular channels and their activation or blocking in vasodilation processes. Another possibility is to study the vasodilation or vasoconstriction effect of a particular substance on isolated vessels or isolated aortic rings. Most of the present knowledge of the roles of ionic channels in vasodilation was gained in experiments using non-selective K + channel blockers chloride tetraethylammonium and BaCl 2 , ATP-dependent K + channel blocker glibenclamide, and voltage-dependent K + channel blocker 4-aminopyridine. Various compounds affecting either Ca 2+ influx across the plasmatic membrane via Ca 2+ channels (such as cobalt or verapamil) or its release or re-uptake from or to the sarcoplasmic reticulum (SR Ca 2+ channel opener ryanodine or SR Ca 2+ -ATPase blockers cyclopiazonic acid and thapsigargin) can be used in studies focusing on the changes of cytosolic Ca 2+ availability and its impact on vascular tone [33] . The plants and their primary or secondary metabolites that lead to vasodilation via this pathway are summarized in Table 4 . All of the abovementioned substances are vasodilatory ones. Contrary to this, ET-1 and TXA 2 are endothelium-produced vasoconstrictors. Next to them, AT II-mediated vasoconstriction is worth mentioning [32] . In addition to the previously described functions, other endothelium functions should be mentioned, such as its role in hemostasis and coagulation. Endothelial and smooth muscle cells express a variety of proteins that act both pro-and antithrombotically (intact non-wettable endothelium is an important factor in preventing intravascular hemocoagulation). Endothelial cells also participate in the regulation of inflammation [6, 44] . Another endothelium function is the transport of numerous substances dissolved in blood to the subendothelial space to meet the metabolic needs of the surrounding tissues [6] . Finally, the endothelium participates in lipid metabolism on one side, while circulating lipids (fatty acids, lipoproteins) alter endothelial function on the other side. This leads to certain endothelial changes that exacerbate inflammatory processes and may promote certain diseases, such as atherogenesis [45]. Most research is focused on substances with vasodilatory potential, since these are of high clinical relevance. Although there are also some substances with vasoconstriction activity, research studies focus on them quite rarely. In folk medicine, some plants are used for their vasoconstriction activity, e.g., Thromboxane A 2 (as well as PGI 2 ) is a metabolite of ARA. For a long time, TXA 2 was known to be released from platelets. Nowadays, it is known to be released by a variety of cells, including the endothelial ones. It stimulates platelet activation, aggregation, and proliferation, as well as vasoconstriction [53, 54] . It counterbalances the effects of PGI 2 , especially in pathological situations, such as tissue injury and inflammation [54] . ARA is metabolised by COX to form unstable PGH 2 . PGH 2 is further converted into TXA 2 by thromboxane synthase (TXAS) [53] . TXA 2 binds to TXA 2 -prostanoid receptor (TPR), resulting in an influx of Ca 2+ ions and VSMC contraction [53, 54] . Production of TXA 2 can be evoked by acetylcholine, among others. TXA 2 level reduction and TPR antagonism may be promising therapeutic targets to prevent cardiovascular disease [53,55]. As mentioned above, the production of synergic TXA 2 and PGI 2 is catalyzed by COX enzymes. The two COX isoforms, cyclooxygenase 1 (COX-1) and cyclooxygenase 2 (COX-2), metabolise ARA to PGH 2 , the common substrate for TXA 2 and PGI 2 synthesis. TXA 2 is the predominant COX-1-derived product, in contrast to PGI 2 , which is synthetized as a result of COX-2 activation [32,56]. The common name endothelin (ET) is used for three peptides, namely endothelin-1, -2, and -3 (ET-1, ET-2, and ET-3). ET-1 is the most examined endothelin and is considered the most potent vasoconstrictive substance to date. Its expression is stimulated by shear stress, thrombin, insulin, adrenaline, AT II, cortisol, and also by hypoxia; it is inhibited by NO and natriuretic peptides. ET-1 is produced by endothelial cells, smooth muscle cells, macrophages, fibroblasts, cardiomyocytes, neurons, and endocrine pancreas cells. ET-2 is formed in the ovaries and intestinal epithelial cells. ET-3 is expressed in endothelial cells, placenta, brain neurons, melanocytes, and renal tubular epithelial cells [57] [58] [59] [60] [61] . Formation of the final, biologically active ET-1 is catalyzed by endothelin-converting enzymes 1-3 (ECE 1-3), each occurring in several isoforms. ECE-1 is the major enzyme, which catalyzes all endothelin isoform formation. Endothelin receptors ET A , ET B1 , ET B2 , and ET C are G-protein-coupled receptors, differing in their affinity for individual ETs. ET-1 via ET A mediates vasoconstriction (ET A is expressed mainly in smooth muscle cells). Moreover, bronchoconstriction and secretion of aldosterone are mediated via ET A . ET B1 and ET B2 occur in both endothelial and smooth muscle cells. ET B1 agonist causes vasodilation by stimulating NO, PGI 2 , and EDH. On the contrary, ET B2 mediates vasoconstriction [57-61]. Platelet-activating factor (PAF) is a phospholipid mediator, synthesis and degradation of which are catalyzed enzymatically. PAF plays a role in numerous pathophysiological reactions-it potentiates aggregation and chemotaxis, as well as formation of neutrophils, eosinophils, and monocytes. In other words, by increasing vascular permeability, it induces local inflammatory processes and edema [62]. Endogenous substances with vasodilatory potential were overviewed in previous chapters. This chapter is focused on plants with a potential vasodilating effect. Table 1 to Table 4 summarize plants and their primary or secondary metabolites, in which certain effects dominate a particular signaling pathway-in Table 1 it is the NO-cGMP activation pathway, in Table 2 it is the PGI2-cAMP activation pathway, in Table 3 it is inhibition of PDE, and in Table 4 it is activation of K + channels or inhibition of intracellular Ca 2+ levels. Numerous plants exhibiting vasodilatory effects are reported to use more than one signaling pathway. In Table 5 , plant metabolites with combined mechanisms and without a dominant mechanism are summarized. Table 6 presents the plant metabolites, the effects of which have not yet been fully elucidated. Most metabolites with vasodilatory activity belong to alkaloids, flavonoids, or terpenes; additionally, stilbenes, lignans, xanthones, and coumarins are reported to have vasoactive effects. Numerous studies suggest that the most common mechanisms are interactions with the NO-cGMP pathway [33] . Table 4 . Activation of K + channels or inhibition of intracellular Ca 2+ levels. Alchemilla vulgaris L. (Rosaceae L.) quercetin aerial parts [133, 134] Ammi visnaga (L.) Lam. (Apiaceae Lindl.) visnagin fruits [135] Calea glomerata Klatt. (Asteraceae Martinov) flavonoids, terpenoids aerial parts [83, 136] Cistus populifolius L. (Cistaceae Juss.) diterpenoids, luteolin leaves [137, 138] Cymbopogon martini (Roxb.) W.Watson (Poaceae Barnhart) geraniol leaves [139] Trachyspermum ammi (L.) Sprague (Apiaceae Lindl.) thymol, gamma-terpinene, p-cymene seeds [161] Uncaria rhynchophylla (Miquel) Jack (Rubiaceae Juss.) rhynchophylline, isorhynchophylline, hirsutine hooks [162, 163] Andrographis paniculata (burm. F.) Nees (Acanthaceae Juss.) 14-deoxyandrographolide, 14-deoxy-11,12-dihydroandrographolide leaves [171] [172] [173] [174] Angelica dahurica Benthman et Hooker (Apiaceae Lindl.) pyranocoumarin, biscoumarin, isoimperatorin, imperatorin, phellopterin, isodemethylfuropinarine, demethylfuropinarine, decursinol roots, rhizomes [175] [176] [177] [178] Angelica gigas Nakai (Apiaceae Lindl.) ferulic acid roots [179] Angelica keiskei Koidz. (Apiaceae Lindl.) xanthoangelol, 4-hydroxyderricin, xanthoangelol B, xanthoangelol E, xanthoangelol F roots [180] Apium graveolens L. var. dulce DC (Apiaceae Lindl.) apigenin leaves, roots [181] [182] [183] Bacopa monnieri (L.) Pennel (Plantaginaceae Juss.) bacoside A, bacopaside I, luteolin, apigenin whole plants [184] [185] [186] [187] Berberis vulgaris L. (Berberidaceae Juss.) berberine fruits, stems bark, roots [188, 189] Camellia sinensis (L.) Kunzte (Theaceae D. Don) epigallocatechin-3-gallate, epicatechin, epigallocatechin, epicatechin-3-gallate green tea (leaves) [190] [191] [192] [193] [194] Chenopodium ambrosioides L. (Amaranthaceae Juss.) kaempferol, quercetin, isorhamnetin, catechins, delphinidin leaves [195] Chrysanthemum morifolium Ramat (Asteraceae Martinov) luteolin-7-O-β-D-glucoside, apigenin-7-O-β-D-glucoside, acacetin-7-O-β-D-glucoside flowers [196] Coptis chinensis Franch. (Ranunculaceae Arnott) berberine, coptisine rhizomes [197] [198] [199] [200] Curcuma longa L. (Zingiberaceae Lindl.) curcumane C, curcumane D, 4,5-seco-cadinane sesquiterpenoid rhizomes [201] Dalbergia odorifera T. Chen (Fabaceae Lindl.) butein, isoliquiritigenin, biochanin A roots, leaves [202] [203] [204] [205] [206] [207] [208] Table 6 . Not fully elucidated/not specified. Calpurnia aurea (Ait.) Benth. (Fabaceae Lindl.) seeds [240] Vitex negundo L. (Lamiaceae Lindl.) aerial parts [241] Ficcus saussureana DC (Moraceae Dumort.) root bark [242] Prunus persica (L.) (Rosaceae L.) branches [243] Satureja obovata Lag. (Lamiaceae Lindl.) eriodictyol [244, 245] Vernonia amygdalina Del. (Asteraceae Martinov) alkaloids, flavonoids, saponins leaves [246] The clinical relevance of endothelial dysfunction in patients with (not only) cardiovascular disorders remains subject to investigation. Although a number of vascular and non-vascular markers of endothelial dysfunction have been proposed, inexpensive, clinically accessible, optimal, and reproducible indicators still have not been found [247] . Nevertheless, it should always be considered that numerous plants and their metabolites may impact on the endothelium and affect its physiological functions. This may become even more important if the endothelium is disordered, as can be observed in numerous diseases. Therefore, patients should be actively informed about possible interactions between the prescribed medication and various dietary supplements or folk medicines containing substances with the potential to affect endothelial functions. Further basic science and clinical studies are needed to better inform us about the therapeutic potential of and drug interferences from plant metabolites. No new data were created or analyzed in this study. Data sharing is not applicable to this article. The authors wish to thank Petr Babula for creating a supportive atmosphere and for fruitful discussions over the manuscript. The authors declare no conflict of interest. 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Can Vasorelaxant effect of the rootbark extract of Paeonia moutan on isolated rat thoracic aorta Water extract of Korean red ginseng stimulates angiogenesis by activating the PI3K/Akt-dependent ERK1/2 and eNOS pathways in human umbilical vein endothelial cells Signaling pathway of ginsenoside-Rg1 leading to nitric oxide production in endothelial cells Upregulates eNOS expression in human endothelial cells Chemical constituents of Prunella vulgaris A review of the phytochemistry and pharmacological activities of raphani semen The antihypertensive effect of ethyl acetate extract of radish leaves in spontaneously hypertensive rats Vasodilatory and anti-inflammatory effects of the aqueous extract of rhubarb via a NO-cGMP pathway Large conductance Ca 2+ -activated K + (BKCa) channels are involved in the vascular relaxations elicited by piceatannol isolated from Rheum undulatum rhizome Vasorelaxant effect of stilbenes from rhizome extract of rhubarb (Rheum undulatum) on the contractility of rat aorta Cardiovascular effects of lignans isolated from Saururus chinensis Vasorelaxation by amentoflavone isolated from Selaginella tamariscina Review on the Phytochemistry, Pharmacology, and Pharmacokinetics of Amentoflavone, a Naturally-Occurring Biflavonoid. Molecules Vasodilatory properties of Solanum crispum Ruiz & Pav. a South American native plant Vasorelaxant activity of indole alkaloids from Tabernaemontana dichotoma Phytochemical Study of Tapirira guianensis Leaves Guided by Vasodilatory and Antioxidant Activities Epicatechin mediates beneficial effects of flavanol-rich cocoa on vascular function in humans Cocoa reduces blood pressure and insulin resistance and improves endothelium-dependent vasodilation in hypertensives Acute dark chocolate and cocoa ingestion and endothelial function: A randomized controlled crossover trial Effects of cocoa extracts on endothelium-dependent relaxation Endothelium-dependent vasodilatory effect of vitisin C, a novel plant oligostilbene from Vitis plants (Vitaceae), in rabbit aorta Antihypertensive, vasodilator and antioxidant effects of a vinifera grape skin extract Cardioprotective actions of grape polyphenols Absolute structures of new hydroxystilbenoids, vitisin C and viniferal, from Vitis vinifera 'Kyohou' Grape Skin Extract Prevents Development of Hypertension and Altered Lipid Profile in Spontaneously Hypertensive Rats: Role of Oxidative Stress Mechanism of endothelial nitric oxide-dependent vasorelaxation induced by wine polyphenols in rat thoracic aorta Reciprocal regulation of endothelial nitric-oxide synthase and NADPH oxidase by betulinic acid in human endothelial cells Vasorelaxant effects of ethyl cinnamate isolated from Kaempferia galanga on smooth muscles of the rat aorta Calcium channel blockade as a target for the cardiovascular effects induced by the The (8)17,12E,14-labdatrien-18-oic acid (labdane302), labdane-type diterpene isolated from Xylopia langsdorffiana St. Hil. & Tul. (Annonaceae) relaxes the guinea-pig trachea Ácido (8)17,12E,14-labdatrieno-18-óico (labdano302), diterpeno tipo labdano isolado de Xylopia langsdorffiana St. Hil. & Tul. (Annonaceae) relaxa a traquéia isolada de cobaia Caffeine and other phosphodiesterase inhibitors are potent inhibitors of the promotional effect of TPA on morphological transformation of hamster embryo cells Phosphodiesterase inhibitors Phytochemical overview and medicinal importance of Coffea species from the past until now. Asian Pac Erectogenic and neurotrophic effects of icariin, a purified extract of horny goat weed (Epimedium spp.) in vitro and in vivo Icariin enhances endothelial nitric-oxide synthase expression on human endothelial cells in vitro Vasorelaxant effects of icariin on isolated canine coronary artery Uydeş-Dogan, B.S. Endothelium-dependent vasorelaxant effect of Alchemilla vulgaris methanol extract: A comparison with the aqueous extract in rat aorta Uydeş-Doǧan, B.S. Vasorelaxant and blood pressure lowering effects of alchemilla vulgaris: A comparative study of methanol and aqueous extracts Vasodilator effects of visnagin in isolated rat vascular smooth muscle The genus Calea L.: A review on traditional uses, phytochemistry, and biological activities Vasodilator effects of the extract of the leaves of Cistus populifolius on rat thoracic aorta Luteolin induces vasorelaxion in rat thoracic aorta via calcium and potassium channels Bronchodilator, vasodilator and spasmolytic activities of Cymbopogon martinii Endothelium-independent vasodilation induced by kolaviron, a biflavonoid complex from Garcinia kola seeds, in rat superior mesenteric arteries The xanthones gentiacaulein and gentiakochianin are responsible for the vasodilator action of the roots of Gentiana kochiana Vasodilatory actions of xanthones isolated from a Tibetan herb, Halenia elliptica Hibiscus acid from Hibiscus sabdariffa (Malvaceae) has a vasorelaxant effect on the rat aorta Xanthorrhizol induces endotheliumindependent relaxation of rat thoracic aorta Endothelium-Independent Vasorelaxant Effect of Ligusticum jeholense Root and Rhizoma on Rat Thoracic Aorta The vasorelaxant activity of marrubenol and marrubiin from Marrubium vulgare Characterisation of marrubenol, a diterpene extracted from Marrubium vulgare, as an L-type calcium channel blocker Ex vivo study of the vasorelaxant activity induced by phenanthrene derivatives isolated from Maxillaria densa Antispasmodic and vasodilator activities of Morinda citrifolia root extract are mediated through blockade of voltage dependent calcium channels Xeronine structure and function: Computational comparative mastery of its mystery Vasorelaxant effects on rat aortic artery by two types of indole alkaloids, naucline and cadamine Relaxant activity of methanolic extract from seeds of Peganum harmala on isolated rat aorta Comparative study on the vasorelaxant effects of three harmala alkaloids in vitro Vasorelaxant effects of harmine and harmaline extracted from Peganum harmala L. seeds in isolated rat aorta Xanthones from the roots of Polygala caudata and their antioxidation and vasodilatation activities in vitro Vasorelaxant effect of euxanthone in the rat thoracic aorta Vasorelaxant effect of Prunus yedoensis bark Prunetin Relaxed Isolated Rat Aortic Rings by Blocking Calcium Channels Studies on cardio-suppressant, vasodilator and tracheal relaxant effects of Sarcococca saligna Endothelium-independent vasorelaxant activity of Trachyspermum ammi essential oil on rat aorta In vitro vasodilator mechanisms of the indole alkaloids rhynchophylline and isorhynchophylline, isolated from the hook of Uncaria rhynchophylla (Miquel) Effects of hirsutine, an antihypertensive indole alkaloid from Uncaria rhynchophylla, on intracellular calcium in rat thoracic aorta Antihypertensive and vasorelaxant effects of tilianin isolated from Agastache mexicana are mediated by NO/cGMP pathway and potassium channel opening Vasorelaxant mode of action of dichloromethane-soluble extract from Agastache mexicana and its main bioactive compounds Vasorelaxant effects of cardamonin and alpinetin from Alpinia henryi K. Schum Cardamonin is a bifunctional vasodilator that inhibits Ca(v)1.2 current and stimulates K(Ca)1.1 current in rat tail artery myocytes Evaluation of Alstonia scholaris leaves for broncho-vasodilatory activity Mechanisms underlying the antihypertensive effect of Alstonia scholaris Alstiphyllanines I-O, ajmaline type alkaloids from Alstonia macrophylla showing vasorelaxant activity Some characteristic relaxant effects of aqueous leaf extract of Andrographis paniculata and andrographolide on guinea pig tracheal rings Hypotensive activity of aqueous extract of Andrographis paniculata in rats Vasorelaxation of rat thoracic aorta caused by 14-deoxyandrographolide Cardiovascular activity of labdane diterpenes from Andrographis paniculata in isolated rat hearts Investigation of the mechanisms of Angelica dahurica root extract-induced vasorelaxation in isolated rat aortic rings New coumarins from the roots of Angelica dahurica var. formosana cv. Chuanbaizhi and their inhibition on NO production in LPS-activated RAW264.7 cells Imperatorin induces vasodilatation possibly via inhibiting voltage dependent calcium channel and receptor-mediated Ca2+ influx and release Imperatorin is responsible for the vasodilatation activity of Angelica Dahurica var. Formosana regulated by nitric oxide in an endothelium-dependent manner Radix angelica elicits both nitric oxide-dependent and calcium influx-mediated relaxation in rat aorta Artery relaxation by chalcones isolated from the roots of Angelica keiskei Endothelium-dependent vasorelaxant and antiproliferative effects of apigenin Vasodilatory action mechanisms of apigenin isolated from Apium graveolens in rat thoracic aorta Apigenin, a plant-derived flavone, activates transient receptor potential vanilloid 4 cation channel Calcium antagonistic activity of Bacopa monniera on vascular and intestinal smooth muscles of rabbit and guinea-pig Broncho-vasodilatory activity of fractions and pure constituents isolated from Bacopa monniera Vasodilatory Effects and Mechanisms of Action of Bacopa monnieri and its constituents is hypotensive in anaesthetized rats and vasodilator in various artery types Vasorelaxant and antiproliferative effects of berberine Berberine: Botanical Occurrence, Traditional Uses, Extraction Methods, and Relevance in Cardiovascular, Metabolic, Hepatic, and Renal Disorders Green tea (Camellia sinensis) catechins and vascular function Antispasmodic, bronchodilator and vasodilator activities of (+)-catechin, a naturally occurring flavonoid Endothelium/nitric oxide mechanism mediates vasorelaxation and counteracts vasoconstriction induced by low concentration of flavanols Study of the mechanisms involved in the vasorelaxation induced by (-)-epigallocatechin-3-gallate in rat aorta Epigallocatechin-3-gallate relaxes the isolated bovine ophthalmic artery: Involvement of phosphoinositide 3-kinase-Akt-nitric oxide/cGMP signalling pathway Chenopodium ambrosioides induces an endothelium-dependent relaxation of rat isolated aorta Endothelium-dependent and direct relaxation induced by ethyl acetate extract from Flos Chrysanthemi in rat thoracic aorta Cardiovascular and metabolic effects of Berberine Berberine prevents hyperglycemiainduced endothelial injury and enhances vasodilatation via adenosine monophosphate-activated protein kinase and endothelial nitric oxide synthase Analysis of the mechanisms underlying the vasorelaxant action of coptisine in rat aortic rings Rhizoma Coptidis: A Potential Cardiovascular Protective Agent Curcumane C and (±)-curcumane D, an unusual secocadinane sesquiterpenoid and a pair of unusual nor-bisabolane enantiomers with significant vasorelaxant activity from Curcuma longa Endothelium-dependent relaxation of rat aorta by butein, a novel cyclic AMP-specific phosphodiesterase inhibitor Vasorelaxant effect of isoliquiritigenin, a novel soluble guanylate cyclase activator, in rat aorta Simple and efficient preparation of biochanin A and genistein from Dalbergia odorifera T. Chen leaves using macroporous resin followed by flash chromatography Biochanin-A elicits relaxation in coronary artery of goat through different mechanisms Endothelium-independent Vasorelaxant Effect of the Phyto-oestrogen Biochanin A on Rat Thoracic Aorta Mechanisms of phytoestrogen biochanin A-induced vasorelaxation in renovascular hypertensive rats Biochanin A, the Most Potent of 16 Isoflavones, Induces Relaxation of the Coronary Artery Through the Calcium Channel and cGMP-dependent Pathway Pharmaceutical properties and toxicology of Dioclea grandiflora Endothelium-independent vasorelaxant effect of dioclein, a new flavonoid isolated from Dioclea grandiflora, in the rat aorta Pharmacological evidence for the activation of potassium channels as the mechanism involved in the hypotensive and vasorelaxant effect of dioclein in rat small resistance arteries The flavonoid dioclein is a selective inhibitor of cyclic nucleotide phosphodiesterase type 1 (PDE1) and a cGMP-dependent protein kinase (PKG) vasorelaxant in human vascular tissue Structure and vasorelaxant activity of floranol, a flavonoid isolated from the roots of Dioclea grandiflora Echinodorus grandiflorus: Ethnobotanical, phytochemical and pharmacological overview of a medicinal plant used in Brazil Pharmacological mechanisms involved in the vasodilator effects of extracts from Echinodorus grandiflorus Involvement of bradykinin B2 and muscarinic receptors in the prolonged diuretic and antihypertensive properties of Echinodorus grandiflorus Simultaneous separation of apigenin, luteolin and rosmarinic acid from the aerial parts of the copper-tolerant plant Elsholtzia splendens Endothelium-dependent and -independent vasorelaxant actions and mechanisms induced by total flavonoids of Elsholtzia splendens in rat aortas Endothelium-dependent vasodilation induced by Hancornia speciosa in rat superior mesenteric artery Mechanisms underlying the vasorelaxing effects of butylidenephthalide, an active constituent of Ligusticum chuanxiong, in rat isolated aorta Ligustilide induces vasodilatation via inhibiting voltage dependent calcium channel and receptor-mediated Ca2+ influx and release Relaxation effects of ligustilide and senkyunolide A, two main constituents of Ligusticum chuanxiong, in rat isolated aorta Endothelium-independent vasorelaxation by Ligusticum wallichii in isolated rat aorta: Comparison of a butanolic fraction and tetramethylpyrazine, the main active component of Ligusticum wallichii Endothelium-dependent hypotensive and vasorelaxant effects of the essential oil from aerial parts of Mentha x villosa in rats Muscarinic agonist properties involved in the hypotensive and vasorelaxant responses of rotundifolone in rats Calcium antagonism and the vasorelaxation of the rat aorta induced by rotundifolone. Braz Rotundifolone-induced relaxation is mediated by BK(Ca) channel activation and Ca(v) channel inactivation Vasodilating properties of the stem bark extract of Mitragyna ciliata in rats and guinea pigs Vasorelaxant effect of isoquinoline derivatives from two species of Popowia perakensis and Phaeanthus crassipetalus on rat aortic artery New insights into the mechanisms of the vasorelaxant effects of apocynin in rat thoracic aorta Apocynin reduces blood pressure and restores the proper function of vascular endothelium in SHR Role of Nitric Oxide and Hydrogen Sulfide in the Vasodilator Effect of Ursolic Acid and Uvaol from Black Cherry Prunus serotina Fruits The mechanism of vasorelaxation induced by Schisandra chinensis extract in rat thoracic aorta Gomisin A induces Ca2+-dependent activation of eNOS in human coronary artery endothelial cells Gomisin A from Schisandra chinensis induces endothelium-dependent and direct relaxation in rat thoracic aorta Baicalin relaxes vascular smooth muscle and lowers blood pressure in spontaneously hypertensive rats Baicalin, a flavonoid from Scutellaria baicalensis Georgi, activates large-conductance Ca 2+ -activated K + channels via cyclic nucleotide-dependent protein kinases in mesenteric artery Hydroalcoholic extract and pure compounds from Senecio nutans Sch. Bip (Compositae) induce vasodilation in rat aorta through endothelium-dependent and independent mechanisms Mechanisms underlying vasorelaxation induced in the porcine coronary arteries by Thymus linearis Antihypertensive activity of 80% methanol seed extract of Calpurnia aurea (Ait.) Benth. subsp. aurea (Fabaceae) is mediated through calcium antagonism induced vasodilation Studies on Blood Pressure Lowering, Vasodilator and Cardiac Suppressant Activities of Vitex negundo: Involvement of K+ Channel Activation and Ca++ Channel Blockade Vasodilating effect of the root bark extract of Ficus saussureana on guinea pig aorta Endothelium-dependent vasorelaxant effect of Prunus persica branch on isolated rat thoracic aorta Vasodilatory effect in rat aorta of eriodictyol obtained from Satureja obovata Pharmacological activity of the extracts of 2 Satureja obovata varieties on isolated smoothmuscle preparations Vasorelaxant properties of Vernonia amygdalina ethanol extract and its possible mechanism Clinical Significance of Endothelial Dysfunction in Essential Hypertension