Endothelium-dependent and -independent vasorelaxant actions and mechanisms induced by total flavonoids of Elsholtzia splendens in rat aortas

Endothelium-independent vasorelaxant effects of Curcuma phaeocaulis essential oil and its representative compound isocurcumenol

ETHNOPHARMACOLOGICAL RELEVANCE

The rhizomes of Curcuma phaeocaulis Val. are a Rhizoma curcumae source in Chinese pharmacopoeia, and this traditional Chinese medicine has been extensively used in China to promote blood circulation and remove blood stasis. However, little is known regarding the vasodilatory effects and underlying mechanisms.

AIM OF THE STUDY

This study investigated the vasorelaxant effects and mechanisms of C. phaeocaulis essential oil (CPEO) and its representative compound, isocurcumenol.

MATERIALS AND METHODS

The effects of CPEO and isocurcumenol on the contractile tension of isolated rat thoracic aortic rings in a resting state and a KCl or phenylephrine (PHE) preincubation state in the tissue organ bath system were studied. The potential vasodilatory mechanisms of CPEO and isocurcumenol were investigated using a series of experiments that included endothelium removal, CPEO and isocurcumenol preincubation, extracellular Ca2+-induced contraction and intracellular Ca2+ release, and incubation with various blockers. Laser confocal microscopy was used to evaluate the effect of isocurcumenol on the intracellular Ca2+ fluorescence intensity in A7r5 cells. The influence of isocurcumenol on the myosin light chain (MLC) protein expression and phosphorylation was determined using a Western blot assay. Furthermore, the whole-cell patch clamp technique was used to investigate the effect of isocurcumenol on voltage-dependent K⁺ channel (Kv) current cells.

RESULTS

CPEO (0.25-25 mg/L) and isocurcumenol (0.25-25 μM) exhibited concentration-dependent vasodilatory effects on endothelial intact vascular rings that were pre-contracted using KCl or PHE. These vasodilatory effects did not significantly change after the endothelium was removed. Notably, the vasodilatory effects of the CPEO and isocurcumenol were attenuated when preincubation was performed using with 4-aminopyridine (4-AP, a Kv channel blocker) or verapamil hydrochloride (an L-type calcium channel blocker). In the cell experiments, isocurcumenol suppressed an increase in the Ca2+ fluorescence intensity and inhibited the phosphorylation of the MLC protein in A7r5 cells. The results of the whole-cell patch clamp assay indicated that 25 μM of isocurcumenol enhanced Kv channel currents.

CONCLUSIONS

In this study, we confirmed that CPEO and isocurcumenol had significant endothelium-independent vasorelaxant effects. The underlying mechanism was attributed to the activation Kv channels and the suppression of L-type calcium channels. This resulted in a Ca2+ influx decrease in vascular smooth muscle cells and subsequent vascular contraction inhibition.

Antioxidant Properties and Vasorelaxant Mechanism of Aqueous Extract of Ricinodendron heudelotii (Euphorbiaceae)

Ricinodendron heudelotii is a plant of the Euphorbiaceae family, used in traditional medicine to treat numerous diseases, including high blood pressure. The aim of this study is to evaluate the antioxidant and vasorelaxant effects of the aqueous extract of the stem bark of R. heudelotii. The pharmacological studies were carried out using the aqueous extract obtained by infusion. The antioxidant capacity of R. heudelotii was assessed by in vitro tests with DPPH (2,2-diphenyl-1-picryl-hydrazyl), ABTS (2,2'-azino-bis (3-ethylbenz-thiazoline-6-sulfonic acid), iron-reducing capacity (FRAP), and inhibition of nitric oxide (NO) release. In vitro studies, the aortic rings obtained from adult Wistar albino rats of both sexes were used to determine the vasorelaxant effects of the extract of R. heudelotii on the NO and prostacyclin (PGI2) pathways as well as its involvement on various potassium channels were determined on intact or naked fragments of rat aorta precontracted with phenylephrine (10-6 M) or KCl (60 mM). The aqueous extract of R. heudelotii exhibited a remarkable DPPH (EC50: 1.68 μg/mL) and ABTS (EC50: 106.30 μg/mL) and nitric oxide (53.71% inhibition at 1000 μg/mL) radical scavenging activities as well as reducing power (absorbance of 1.56 at 1000 μg/mL). The nitric oxide inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and prostacyclin inhibitor, indomethacin, significantly attenuated the vasodilatory effect of R. heudelotii. Tetraethylammonium could not inhibit the vasodilatory effect of the extract, unlike glibenclamide and barium chloride. Ricinodendron heudelotii extract possesses antioxidant properties and vasorelaxing effect linked to endothelium-related factors, and this relaxation was partially mediated mainly through the inhibition of Kir and KATP channels.

Carissa edulis Vahl (Apocynaceae) extract, a medicinal plant of Benin pharmacopoeia, induces potent endothelium-dependent relaxation of coronary artery rings involving nitric oxide

BACKGROUND

Hypertension is a major cardiovascular risk factor that affects most countries including those of Africa. Although Carissa edulis Vahl, Diodia scandens Sw. and Cleome gynandra L. are traditionally used in Benin as antihypertensive treatments with some efficacy mentioned by the local population, their biological activity on the cardiovascular system remains poorly studied.

AIM

The study investigated the vasoreactivity of the plants and assessed the underlying mechanisms using isolated arteries.

STUDY DESIGN

Aqueous-ethanolic extracts of aerial parts of C. edulis, D. scandens and C. gynandra were prepared by maceration before being subjected to multi-step liquid-liquid fractionation with solvents of increasing polarity. The vasoreactivity of the extracts and fractions were assessed on isolated porcine coronary artery and rat aorta using organ chambers, the role of nitric oxide (NO) using N^G-nitro-L-arginine (NO synthase inhibitor), prostanoids using indomethacin (cyclooxygenases inhibitor) and endothelium-dependent hyperpolarization using TRAM-34 plus UCL 1684 (inhibitors of calcium-dependent K⁺ channels), and the vascular uptake of polyphenols using Neu reagent.

RESULTS

The aqueous-ethanolic crude extract of C. edulis (CECE) induced potent relaxations that were exclusively endothelium-dependent and more pronounced than those to D. scandens and C. gynandra. The n-butanolic fraction of C. edulis (CEBF) was more active than the cyclohexane, dichloromethane, and ethyl acetate fractions. The relaxation induced by CECE and CEBF were inhibited by N^G-nitro-L-arginine and affected neither by TRAM-34 plus UCL 1684 nor by indomethacin. CEBF induced sustained endothelium-dependent relaxations for at least 60 min, and inhibited, in a concentration-dependent manner, contractions to KCl, CaCl₂, U46619 and serotonin in rings with endothelium. Analysis of CEBF by LCHRMS indicated the presence of polyphenols, terpenes, and alkaloids. Exposure of coronary artery and aorta rings to CEBF caused the accumulation of polyphenols predominantly in the endothelium.

CONCLUSION

C. edulis leaf extract induced pronounced endothelium-dependent relaxations and inhibited contractile responses by stimulating the endothelial formation of NO. LCHRMS analysis of the most active fraction, the butanolic fraction, revealed the presence of numerous compounds including polyphenols, terpenes, and alkaloids. The polyphenols of CEBF accumulated preferentially in the endothelium of the arterial wall. Thus, these observations support the folkloric use of C. edulis in hypertension.

Vasorelaxant effect of curcubisabolanin A isolated from Curcuma longa through the PI3K/Akt/eNOS signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Curcuma longa L. (Zingiberaceae) is a known blood-activating and stasis-removing traditional Chinese medicine and has relevant pharmacological properties. The rhizomes of C. longa have been used for the treatment of cardiovascular disease (CVD) in China. Previous studies have shown that sesquiterpenoids from C. longa have significant vasorelaxant effects, which are closely associated with the prevention and treatment of CVD.

AIM OF THE STUDY

To explore the sesquiterpenoids with vasorelaxant effects from C. longa and investigate the underlying mechanisms.

MATERIALS AND METHODS

The compound was isolated from C. longa by multiple chromatography technologies. Its structure was determined by extensive spectroscopic analyses, nuclear magnetic resonance (NMR) data calculations, electronic circular dichroism (ECD) data calculations, and optical rotation (OR) data calculations. The vasorelaxant effect of the isolated compound was evaluated by KCl- or phenylephrine (PHE)-inducing contraction of the rat thoracic aortic rings. Endothelial removal and L-NAME pretreatment experiments were used to verify the endothelium-dependent vasorelaxant effect of the isolated compound in rat thoracic aortic rings. NO production was monitored in human umbilical vein endothelial cells (HUVECs). Western blot was carried out in HUVECs to elucidate the potential mechanisms.

RESULTS

A new bisabolane-type sesquiterpenoid, curcubisabolanin A [(+)-(1S,7S,9E)-bisabola-2(3),4(15),9(10)-trien-11-ol], was isolated from the rhizomes of C. longa. curcubisabolanin A exhibited endothelium-dependent relaxation on rat thoracic aortic rings, while pre-treatment of intact aortic rings with an eNOS inhibitor (L-NAME) attenuated the vasorelaxant response of curcubisabolanin A. In addition, curcubisabolanin A induced intracellular NO production and significantly increased the levels of phosphorylated PI3K (p-PI3K), phosphorylated Akt (p-Akt), and phosphorylated eNOS (p-eNOS) in HUVECs. LY294002 (a blocker of PI3K) and MK-2206 (a highly selective inhibitor of Akt) significantly decreased these effects of curcubisabolanin A.

CONCLUSIONS

These findings demonstrated that the vasorelaxant effect of curcubisabolanin A was partially endothelium-dependent and was related to regulation of NO production in vascular endothelial cells through the PI3K/Akt/eNOS signaling pathway.

Secondary Metabolites of Plants as Modulators of Endothelium Functions

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.

Characterization of ethyl acetate and n-butanol extracts of Cymbopogon schoenanthus and Helianthemum lippii and their effect on the smooth muscle of the rat distal colon

ETHNOPHARMACOLOGY RELEVANCE

Cymbopogon schoenanthus (C. schoenanthus) and Helianthemum lippii (H. lippii) are Saharan species found in the South West of Algeria, in the region of Bechar. Both plants are used in traditional medicine to treat gastrointestinal disorders.

OBJECTIVE

The aim of our study was to characterize the composition of the ethyl acetate (EtOAc) and n-Butanol (n-BuOH) extracts of C. schoenanthus and H. lippii, and to elucidate and compare their effect on the reactivity of the rat distal colon.

MAIN METHODS

The plants were macerated in a hydroalcoholic solution. After concentration, the aqueous solutions of the residues were submitted to liquid-liquid extractions to obtain EtOAc and n-BuOH extracts. The phenolic and flavonoid content of the extracts was determined by high performance liquid chromatography coupled with mass spectrometry with a time of flight analyzer (HPLC-TOF/MS). The effect of the extracts was tested on the rat distal colon, namely on the basal tone and on KCl- and Ach-induced precontracted preparations.

RESULTS

HPLC-TOF/MS identified 32 phenols and flavonoids in the extracts. The four extracts relaxed the rat distal colon, the effect being noticed on the basal tone and on the KCl- and Ach-induced precontractions. The EtOAc and the n-BuOH extracts of H. lippii decreased the basal tone of the rat distal colon more markedly than the correspondent extracts of C. schoenanthus. Moreover, the n-BuOH extract of C. schoenanthus decreased the basal tone more markedly than the EtOAc extract of this plant but there was no difference between extracts of H. lippii. The EtOAc extracts of both C. schoenanthus and H. lippii totally reverted both the KCl- and the Ach-induced precontraction of the rat distal colon. However, the n-BuOH extracts of the two plants reverted the Ach-precontracted colon but not the colon that has been precontracted with KCl.

CONCLUSION

Extracts of H. lippii contain a higher level of phenols compared to the extracts of C. schoenanthus. All extracts of C. schoenanthus and H. lippii caused marked relaxation of the isolated rat distal colon, either when applied directly or when tested over KCl- and Ach-induced precontraction. These results give support to the use of C. shoenanthus and H. lippii in traditional medicine, namely for gastrointestinal diseases.

Cardiovascular Effects of Flavonoids

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Cardiovascular Disease (CVD) is the major cause of death worldwide, especially in Western society. Flavonoids are a large group of polyphenolic compounds widely distributed in plants, present in a considerable amount in fruit and vegetable. Several epidemiological studies found an inverse association between flavonoids intake and mortality by CVD. The antioxidant effect of flavonoids was considered the main mechanism of action of flavonoids and other polyphenols. In recent years, the role of modulation of signaling pathways by direct interaction of flavonoids with multiple protein targets, namely kinases, has been increasingly recognized and involved in their cardiovascular protective effect. There are strong evidence, in in vitro and animal experimental models, that some flavonoids induce vasodilator effects, improve endothelial dysfunction and insulin resistance, exert platelet antiaggregant and atheroprotective effects, and reduce blood pressure. Despite interacting with multiple targets, flavonoids are surprisingly safe. This article reviews the recent evidence about cardiovascular effects that support a beneficial role of flavonoids on CVD and the potential molecular targets involved.

Antioxidant and Anti-inflammatory Activities of Cynaroside from Elsholtiza bodinieri

The flavonoid fraction was obtained from Elsholtiza bodinieri Vaniot (EBV) by ethanol-reflux and liquid-liquid extraction. The total content of flavonoid was 179.55 mg/g, and the purity was 64.6%. Then cynaroside with the purity of 94% was isolated from the fraction by preparative HPLC and characterized by the combined usage of HPLC, ESI-MS, and NMR. The antioxidant activity of cynaroside was determined using 2 complementary methods, namely, 2,2- diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and reducing power assay. The anti-inflammatory effect of cynaroside was investigated based on in-vitro and in-vivo experiment. The results showed that cynaroside from EBV scavenged DPPH radical and reduced Fe3+ to Fe2+ effectively, inhibited NO and ROS production in LPS-stimulated RAW264.7 cells and attenuated the inflammation in the mouse model significantly ( p < 0.01), which showed it to be a nutraceutical product in the food industry.

Vasorelaxant properties of Vernonia amygdalina ethanol extract and its possible mechanism

CONTEXT

Vernonia amygdalina Del. (VA) (Asteraceae) is commonly used to treat hypertension in Malaysia.

OBJECTIVE

This study investigates the vasorelaxant mechanism of VA ethanol extract (VAE) and analyzes its tri-step FTIR spectroscopy fingerprint.

MATERIALS AND METHODS

Dried VA leaves were extracted with ethanol through maceration and concentrated using rotary evaporator before freeze-dried. The vasorelaxant activity and the underlying mechanisms of VAE using the cumulative concentration (0.01-2.55 mg/mL at 20-min intervals) were evaluated on aortic rings isolated from Sprague Dawley rats in the presence of antagonists.

RESULTS

The tri-step FTIR spectroscopy showed that VAE contains alkaloids, flavonoids, and saponins. VAE caused the relaxation of pre-contracted aortic rings in the presence and absence of endothelium with EC₅₀ of 0.057 ± 0.006 and 0.430 ± 0.196 mg/mL, respectively. In the presence of Nω-nitro-l-arginine methyl ester (EC₅₀ 0.971 ± 0.459 mg/mL), methylene blue (EC₅₀ 1.203 ± 0.426 mg/mL), indomethacin (EC₅₀ 2.128 ± 1.218 mg/mL), atropine (EC₅₀ 0.470 ± 0.325 mg/mL), and propranolol (EC₅₀ 0.314 ± 0.032 mg/mL), relaxation stimulated by VAE was significantly reduced. VAE acted on potassium channels, with its vasorelaxation effects significantly reduced by tetraethylammonium, 4-aminopyridine, barium chloride, and glibenclamide (EC₅₀ 0.548 ± 0.184, 0.158 ± 0.012, 0.847 ± 0.342, and 0.304 ± 0.075 mg/mL, respectively). VAE was also found to be active in reducing Ca²⁺ released from the sarcoplasmic reticulum and blocking calcium channels.

CONCLUSIONS

The vasorelaxation effect of VAE involves upregulation of NO/cGMP and PGI₂ signalling pathways, and modulation of calcium/potassium channels, and muscarinic and β₂-adrenergic receptor levels.

Diosmin reduces chronic constriction injury-induced neuropathic pain in mice

Injury or dysfunction of somatosensory system induces a complex syndrome called neuropathic pain, which still needs adequate pharmacological control. The current pharmacological treatments were in part developed from natural compounds. Flavonoids are natural polyphenolic molecules presenting varied biological activities and low toxicity. The flavonoid diosmin is a safe compound with good tolerability and low toxicity. This study evaluated the antinociceptive effect of diosmin in the sciatic nerve chronic constriction injury (CCI)-induced neuropathic pain model. Male Swiss mice were submitted to CCI and 7 days after, diosmin at 1 or 10 mg/kg was administrated intraperitoneally. Mechanical (electronic analgesimeter) and thermal (hot plate) hyperalgesia were evaluated 1-24 h after treatment. The role of the NO/cGMP/PKG/KATP channel signaling pathway in the analgesic effect of diosmin was evaluated using the pretreatment with L-NAME (an inhibitor of NOS), ODQ (an inhibitor of soluble guanylate cyclase), KT5823 (an inhibitor of PKG), or glibenclamide (an ATP-sensitive K+ channels blocker). Single treatment with diosmin inhibited in a dose-dependent manner CCI-induced mechanical and thermal hyperalgesia by activating the NO/cGMP/PKG/KATP channel signaling pathway and inhibiting spinal cord cytokine (Il-1β and Il-33/St2) and glial cells activation (microglia - Iba-1, oligodendrocytes - Olig2) mRNA expression markers. Daily treatment during 7 days with diosmin inhibited CCI-induced mechanical and thermal hyperalgesia by inhibiting spinal cord cytokine (Il-1β, Tnfα, and Il-33/St2) and glial cells activation (astrocytes - Gfap, Iba-1, and Olig2) markers mRNA expression. In conclusion, diosmin inhibits neuropathic spinal cord nociceptive mechanisms suggesting this flavonoid as a potential therapeutic molecule to reduce nerve lesion-induced neuropathic pain.

Apigenin-7-O-β-D-glycoside isolation from the highly copper-tolerant plant Elsholtzia splendens

Elsholtzia splendens (Lamiaceae) is a copper-tolerant plant species growing on copper deposits in the south of China. Chromatographic separation of n-BuOH extracts from the flowering aerial biomass afforded apigenin-7-O-β-D-glycoside, using macroporous resin, Sephadex™ LH-20 gel, polyamide resin as well as preparative high-performance liquid chromatography (P-HPLC) columns. Chemical structure was elucidated using HPLC/ESI-MS (electrospray ionization-mass spectrometry), Fourier transform infrared (FTIR), and (1)D- and (2)D-nuclear magnetic resonance (NMR). Apigenin-7-O-β-D-glycoside could be the post-harvesting product from E. splendens biomass.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.