Endothelium-dependent and endothelium-independent vasorelaxant effects of tiliacorinine 12′-O-acetate and mechanisms on isolated rat aorta

Antihypertensive effect of the stem bark aqueous extract of Garcinia lucida Vesque (Clusiaceae) in L-NAME-treated rats: Contribution of endothelium-dependent and -independent vasorelaxation

Garcinia lucida is used in Cameroonian folk medicine to handle a variety of ailments, including arterial hypertension. This study aimed at determining the phytochemical profile and the antihypertensive effect of the stem bark aqueous extract of G. lucida (AEGL). AEGL was subjected to LC-MS analysis, and its effect (75, 150, and 300 mg/kg/day; by gavage) was evaluated against Nω-nitro-L-arginine methyl ester (L-NAME; 40 mg/kg)-induced hypertension in adult male Wistar rats for four consecutive weeks. Blood pressure and heart rate were monitored weekly using tail-cuff plethysmography. The vasorelaxant effect of cumulative concentrations (3-10-30-100-300 μg/mL) of AEGL was examined on endothelium-intact and denuded thoracic aorta rings which were precontracted with KCl (90 mM) or norepinephrine (NE; 10-5 M), and in the absence or presence of L-NAME (10-4 M), indomethacin (10-5 M), methylene blue (10-6 M), tetraethylammonium (TEA, 5 × 10-6 M), glibenclamide (10 × 10-6 M) or propranolol (5 × 10-6 M). The influence of AEGL on the response to NE, KCl, and CaCl2 was also investigated. Six compounds, including Garcinia biflavonoids GB1 and GB2, were identified. AEGL prevented the development of hypertension (p < 0.01 and p < 0.001) without affecting the heart rate. AEGL induced a concentration-dependent relaxation of aortic rings precontracted with NE (EC50 = 7.915 μg/mL) that was significantly inhibited by the removal of the endothelium, L-NAME, or methylene blue (p < 0.05-0.001). Indomethacin, propranolol, TEA, and glibenclamide did not affect AEGL-evoked vasorelaxation. Preincubation of aortic rings with AEGL reduced the magnitude of contraction elicited by CaCl2 but did not alter that of KCl or NE. AEGL possesses an antihypertensive effect that is mediated by both endothelium-dependent and endothelium-independent mechanisms. The activation of the NO/sGC/cGMP pathway accounts for the endothelium-dependent vasorelaxation. These pharmacological effects of AEGL could be attributed to the presence of the Garcinia biflavonoids GB1 and GB2.

ELABELA RELAXES RAT PULMONARY ARTERY AND TRACHEA VIA BKCa, KV, and KATP CHANNELS

OBJECTIVE

Elabela is a newly discovered peptide hormone. This study aimed to determine the functional effects and mechanisms of action of elabela in rat pulmonary artery and trachea.

MATERIALS AND METHODS

Vascular rings isolated from the pulmonary arteries of male Wistar Albino rats were placed in chambers in the isolated tissue bath system. The resting tension was set to 1g. After the equilibration period, the pulmonary artery rings were contracted with 10^-6M phenylephrine. Once a stable contraction was achieved, elabela was applied cumulatively (10^-10-10^-6M) to the vascular rings. To determine the vasoactive effect mechanisms of elabela, the specified experimental protocol was repeated after the incubation of signaling pathway inhibitors and potassium channel blockers. The effect and mechanisms of action of elabela on tracheal smooth muscle were also determined by a similar protocol.

RESULTS

Elabela exhibited a concentration-dependent relaxation in the precontracted rat pulmonary artery rings (p<.001). Maximal relaxation level was 83% (pEC₅₀: 7.947 CI95(7.824-8.069)). Removal of the endothelium, indomethacin incubation, and dideoxyadenosine incubation significantly decreased the vasorelaxant effect levels of elabela (p<.001). Elabela-induced vasorelaxation levels were significantly reduced after iberiotoxin, glyburide, and 4-Aminopyridine administrations (p<.001). L-NAME, methylene blue, apamin, TRAM-34, anandamide, and BaCl₂ administrations did not cause a significant change in the vasorelaxant effect level of elabela (p=1.000). Elabela showed a relaxing effect on precontracted tracheal rings (p<.001). Maximal relaxation level was 73% (pEC₅₀: 6.978 CI95(6.791-7.153)). The relaxant effect of elabela on tracheal smooth muscle was decreased significantly after indomethacin, dideoxyadenosine, iberiotoxin, glyburide, and 4-Aminopyridine incubations (p<.001).

CONCLUSIONS

Elabela exerted a prominent relaxant effect in the rat pulmonary artery and trachea. Intact endothelium, prostaglandins, cAMP signaling pathway, and potassium channels (BK_Ca, K_V, and K_ATP channels) are involved in the vasorelaxant effect of elabela. Prostaglandins, cAMP signaling pathway, BK_Ca channels, K_V channels, and K_ATP channels also contribute to elabela-induced tracheal smooth muscle relaxant effect.

New insights on mode of action of vasorelaxant activity of simvastatin

Simvastatin is a semisynthetic inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and is used extensively to treat atherosclerotic cardiovascular disease. Apart from the lipid-lowering effect, simvastatin has been documented to offer impressive vasorelaxant activity. However, the mechanism associated with this vasorelaxant activity has yet not been substantially explored. Thus, the present study has aimed to elucidate the mechanism(s) associated with simvastatin-induced vasorelaxation using an established rat aortic ring model. The results from the study depicted that simvastatin caused significant relaxation in aortic rings pre-contracted with phenylephrine and potassium chloride (KCl). The vasorelaxant effect of simvastatin was attenuated by methylene blue (sGC-dependent cyclic guanosine monophosphate (cGMP) inhibitor), N^G-nitro-L-arginine methyl ester (L-NAME; NO synthase inhibitor), 4-aminopyridine (K_v blocker), glibenclamide (K_ATP blocker), and barium chloride (K_ir blocker). In addition, the vasorelaxant effect of simvastatin was slightly reduced by PD123319 (angiotensin II type 2 receptor (AT₂R) antagonist). However, indomethacin (COX inhibitor), 1H-[1,2,4]Ox adiazolol [4,3-α]quinoxalin-1-one (ODQ; selective soluble guanylate cyclase (sGC) inhibitor), losartan (angiotensin II type 1 receptor (AT₁R) antagonist), atropine (muscarinic receptor blocker), and tetraethyl ammonium (TEA; K_Ca blocker) did not affect the vasorelaxant effect of simvastatin. Furthermore, simvastatin was found to attenuate the release of calcium (Ca²⁺) from intracellular stores in the presence of ruthenium red (ryanodine receptor, RyR inhibitor) and extracellular stores via nifedipine (voltage-operated Ca²⁺ channels, VOCC blocker) and SK&F96365 (receptor-operated Ca²⁺ channel, ROCC blocker). Thus, it can be concluded that the vasorelaxant effect of simvastatin involves NO/cGMP pathways, AT₂R receptors, Ca²⁺ channels, and K⁺ channels.

Blood pressure-lowering and cardiovascular effects of plumbagin in rats: An insight into the underlying mechanisms

Background

Plumbagin, a natural phenolic compound is investigated for response against blood pressure and vascular reactivity.

Methodology

Blood pressure lowering effects were observed by in-vivo invasive evaluation in normotensive rats, and in-vitro experimentation to measure changes of tension in isolated rat aorta and contractility in atria.

Results

The percentage decrease in mean arterial pressure (MAP) observed with plumbagin intravenously at doses of 0.1, 0.5, 1, 5, 10 ​μg/kg in normotensive rats was 7.16 ​± ​2.35, 15.5 ​± ​5.62, 19.5 ​± ​5.27, 26 ​± ​6.67, 34.33 ​± ​8.80, respectively. Plumbagin exerted vasorelaxant effects in rat aorta, unaffected by the removal of vascular endothelium, and L-NAME and methylene blue pretreatment. Plumbagin completely inhibited phenylephrine (1 ​μM) and High K+ (80 ​mM) induced contractions. Similar to a Ca+2 channel antagonist, plumbagin caused a rightward shift in the Ca+2 concentration-response-curves (CRCs), resembling nifedipine. Pre-incubation with plumbagin, significantly suppressed contractions induced by phenylephrine in Ca+2-free medium via disrupting Ca+2 release from intracellular stores. No change in vasorelaxant response was observed with the addition of potassium channel blockers, TEA and BaCl2. In rat atrial strips, plumbagin exerted significant negative inotropic and chronotropic effects. No significant change was observed with atropine and atenolol pretreatment, so the effect appeared independent of muscarinic and beta-adrenergic receptors.

Conclusion

This study suggests the blood pressure lowering effects of plumbagin. That could be contributed by a decrease in vascular resistance via calcium antagonism, interferences in calcium efflux, and depressive effects on the rate and force of cardiac contraction. Further studies would be necessary to probe deeper into the underlying mechanisms.

Study of Traditional Uses, Extraction Procedures, Phytochemical Constituents, and Pharmacological Properties of Tiliacora triandra

Tiliacora triandra (Colebr.) Diels (Menispermaceae family) is a Southeast Asian angiosperm herb. Traditional medicine in these areas often includes the use of plant parts. Plant extracts are highly effective against various infections including bacterial, fungal, viral, and parasitic. The leaves and root extracts are used to treat gastrointestinal diseases, hypertension, diabetes, skin diseases, and malaria as an antipyretic, detoxification agent, anti-inflammatory, anticancer, and immunomodulator. Bioactive compounds contained in T. triandra include phenolic compounds, alkaloids, flavonoids, terpenoids, fatty acids, essential amino acids, peptides, carbohydrates, vitamins, and nucleic acid precursors. Despite the plant species’ abundance of bioactive compounds, there is very little in vivo and clinical proof of its pharmacological significance. The present review focuses on the phytochemical configurations, extraction methods for major bioactive compounds, and pharmacology of T. triandra, in light of its potent medicinal values.

Large Cardamom Extract Enhances Ramipril's Vasoprotective Action in the Aorta by Modulating Endothelial Redox Biology. An Evaluation based on In-silico and In-vitro Research

BACKGROUND

The mechanisms that cause a patient's blood pressure to rise are diverse. Controlling blood pressure with monotherapy acting through a single pathway may be unachievable. Combining a clinically used medication with herbal medicine can result in an antihypertensive effect that is two to five times greater than monotherapy.

METHOD

This study examined the effects of aqueous extracts of large cardamom and ramipril on the redox biology of nitric oxide and vascular reactivity in the isolated aorta incubated with a nitro-L-arginine methyl ester. Molecular docking study was performed to predict the affinity of constituents of large cardamom extracts with the NOX 2 gene.

RESULTS

Nitric oxide (NO) levels, disordered antioxidant enzymes (glutathione and catalase), NADPH oxidase and lipid peroxidation were recovered when aqueous extract of large cardamom and ramipril were combined. A gradual increase in the percentage relaxation of acetylcholine in phenylephrine pre-contracted aorta indicates that the combination therapy prevents endothelial damage. The molecular docking study reveals the important phytoconstituents present in the large cardamom that can effectively bind with the NADPH oxidase for its antioxidant activity. Consculsion: According to our findings, it was evidenced that the large cardamom extract's vasoprotective action was mostly related to its ability to restore endothelial redox biology by suppressing NADPH oxidase activity. Our findings suggest that ramipril's direct impact on the eNOS/NO system, along with the antioxidant properties of AELC, could have a synergetic benefit in the treatment of hypertension, as well as lessen ramipril's existing side effects.

Vascular Functional Effect Mechanisms of Elabela in Rat Thoracic Aorta

BACKGROUND

Elabela is a recently discovered peptide hormone. The present study aims to investigate the vasorelaxant effect mechanisms of elabela in the rat thoracic aorta.

METHODS

The vascular rings obtained from the thoracic aortas of the male Wistar albino rats were placed in the isolated tissue bath system. Resting tension was set to 1 gram. After the equilibration period, the vessel rings were contracted with phenylephrine or potassium chloride. Once a stable contraction was achieved, elabela-32 was applied cumulatively (10-9-10-6 molar) to the vascular rings. The experimental protocol was repeated in the presence of specific signaling pathway inhibitors or potassium channel blockers to determine the effect mechanisms of elabela.

RESULTS

Elabela showed a significant vasorelaxant effect in a concentration-dependent manner (P < 0.001). The vasorelaxant effect level of elabela was significantly reduced by the apelin receptor antagonist F13A, cyclooxygenase inhibitor indomethacin, adenosine monophosphate-activated protein kinase inhibitor dorsomorphin, protein kinase C inhibitor bisindolmaleimide, large-conductance calcium-activated potassium channel blocker iberiotoxin, and intermediate-conductance calcium-activated potassium channel blocker TRAM-34 (P < 0.001). However, the vasorelaxant effect level of elabela was not significantly affected by the endothelial nitric oxide synthase inhibitor nitro-L-arginine methyl ester and mitogen-activated protein kinase inhibitor U0126.

CONCLUSIONS

Elabela exhibits a prominent vasodilator effect in rat thoracic aorta. Apelin receptor, prostanoids, adenosine monophosphate-activated protein kinase, protein kinase C, and calcium-activated potassium channels are involved in the vasorelaxant effect mechanisms of elabela.

Autocrine Activity of Extracellular Vesicles Induced by Icariin and Its Effectiveness in Glucocorticoid-Induced Injury of Bone Microvascular Endothelial Cells

Glucocorticoids could induce injury and apoptosis of bone microvascular endothelial cells (BMECs) in the femoral head, which is associated with the development of osteonecrosis and osteoporosis. Icariin is a prenylated flavonol glycoside isolated from Epimedium brevicornum, serving as the main active pharmaceutical constituent to treat bone loss. Currently, the impact of the autocrine activity of extracellular vesicles (EVs) induced by icariin on the glucocorticoid-induced injury of BMECs is still to be confirmed. In this study, EVs were isolated from BMECs treated with and without icariin by super-speed centrifugation. Although icariin treatment would not significantly change the size and total protein content of BMECs-derived EVs, expression of EVs-carried vascular endothelial growth factor (VEGF) and transforming growth factor β1 (TGF-β1) was enhanced and numerous miRNAs involved in cell proliferation and apoptosis were upregulated (e.g., hsa-miR-1469 and hsa-miR-133a-5p) or downregulated (e.g., hsa-miR-10b-5p) (p < 0.05). A total of 29 differentially expressed inflammatory factors were detected between the EVs secreted by BMECs from the Icariin-treated group and the Model group. The EVs secreted by BMECs could improve cell viability, decrease cell apoptosis, and promote cell migration and angiogenesis under the intervention of glucocorticoids. Meanwhile, icariin intervention could reinforce these protective effects of BMECs-derived EVs. To sum up, the present study indicates that icariin acts as a promising candidate for treating glucocorticoid-induced injury of BMECs and bone diseases, partially through the autocrine activity of EVs. In vivo or animal studies are still required to better understand the function of BMECs-derived EVs.

Potassium Channels Contributes to Apelin-induced Vasodilation in Rat Thoracic Aorta

Background:

Apelin is a newly discovered peptide hormone and originally discovered endogenous apelin receptor ligand.

Objective:

In this study, we aimed to investigate the possible roles of potassium channel subtypes in the vasorelaxant effect mechanisms of apelin.

Methods:

The vascular rings obtained from the thoracic aortas of the male Wistar Albino rats were placed into the isolated tissue bath system. The resting tension was set to 2 g. After the equilibration period, the aortic rings were precontracted with 10-5 M phenylephrine (PHE) or 45 mM KCl. Pyroglutamyl-apelin-13 ([Pyr1]apelin-13), which is the dominant apelin isoform in the human cardiovascular tissues and human plasma, was applied cumulatively (10-10-10-6 M) to the aortic rings in the plateau phase. The experimental protocol was repeated in the presence of specific K+ channel subtype blockers to determine the role of K+ channels in the vasorelaxant effect mechanisms of apelin.

Results:

[Pyr1]apelin-13 induced a concentration-dependent vasorelaxation (p < 0.001). The maximum relaxation level was approximately 52%, according to PHE-induced contraction. Tetraethylammonium, iberiotoxin, 4-Aminopyridine, glyburide, anandamide, and BaCl2 statistically significantly decreased the vasorelaxant effect level of [Pyr1]apelin-13 (p < 0.001). However, apamin didn’t statistically significantly change the vasorelaxant effect level of [Pyr1]apelin-13.

Conclusion:

In conclusion, our findings suggest that BKCa, IKCa, Kv, KATP, Kir, and K2P channels are involved in the vasorelaxant effect mechanisms of apelin in the rat thoracic aorta.

The role of potassium channels on vasorelaxant effects of elabela in rat thoracic aorta

Background

This study aims to investigate the roles of potassium channel subtypes in the vasorelaxant effect mechanism of elabela, which is a recently discovered endogenous apelin receptor ligand.

Methods

The vascular rings (4-mm) obtained from the thoracic aortas of 20 male Wistar Albino rats were placed into the isolated tissue bath system. The resting tension was set to 1 g. The aortic rings were contracted with 10-5 molar phenylephrine after the equilibration period (90 min). Elabela was applied cumulatively (10-10-10-6 molar) to the aortic rings in the plateau phase. The experimental protocol was repeated in the presence of specific potassium channel subtype inhibitors to determine the role of potassium channels in the vasorelaxant effect mechanism of elabela.

Results

Elabela induced a concentration-dependent vasorelaxation (p<0.001). The maximum relaxation level was approximately 51% according to phenylephrineinduced contraction. Vasorelaxant effect level of elabela statistically significantly decreased after removal of the endothelium (p<0.05). Tetraethylammonium (1 milimolar), 4-Aminopyridine (1 milimolar), glyburide (10 micromolar), and barium chloride (30 micromolar) statistically significantly decreased the vasorelaxant effect level of elabela (p<0.001, p<0.001, p<0.01, and p<0.05 respectively). However, anandamide (10 micromolar) and apamin (100 nanomolar) did not statistically significantly change the vasorelaxant effect level of elabela.

Conclusion

Our results suggest that large-conductance calciumactivated, voltage-gated, adenosine triphosphate-sensitive, and inward-rectifier potassium channels are involved in the vasorelaxant effect mechanism of elabela in the rat thoracic aorta.

Tiliacora triandra extract and its major constituent attenuates diabetic kidney and testicular impairment by modulating redox imbalance and pro-inflammatory responses in rats

BACKGROUND

Literature has demonstrated that diabetes is associated with renal complication and testicular dysfunctions. The current study explored the potential of Tiliacora triandra extract and its major component against diabetic kidney and testicular damages in rats.

METHODS

Diabetes was induced by high fat diet/streptozotocin (HFD/STZ) and treated orally with Tiliacora triandra extract (TTE, 100 and 400 mg kg^-1 body weight) and its major component, 5,7-dihydroxy-6-oxoheptadecanoic acid (DHA, 25 mg kg^-1 body weight) for 30 consecutive days. Testicular activities of testicular enzymes, serum levels of testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), sperm parameters and urinalysis for protein and albumin levels were evaluated. Renal and testicular biomarkers of oxidative stress and pro-inflammation were analysed along with histology.

RESULTS

The experimental diabetes induced significant alterations in the levels and activities of indices evaluated compared to non-diabetic normal rats. The 28-day treatment of diabetic rats with TTE and DHA markedly improved activities of testicular enzymes, restored levels of testosterone, LH and FSH and sperm parameters compared to untreated diabetic rats. TTE and DHA abrogated proteinuria and reversed urine albumin level. Testicular and renal oxidative stress and pro-inflammation were attenuated in diabetic rats treated with TTE and DHA. The diabetes-mediated histopathological damage was alleviated in the kidney and testis.

CONCLUSION

The protective effect of TTE and DHA against diabetes induced kidney and testicular damages may be related to its antioxidant and anti-inflammatory activities. © 2020 Society of Chemical Industry.

Schisantherin A causes endothelium-dependent and -independent vasorelaxation in isolated rat thoracic aorta

AIMS

Schisandra is a good choice in Traditional Chinese Medicine for the therapy of cardiovascular diseases, but whether it contains a or some specific component (s) responsible these effects are still unclear. In the present study, we explored whether Schisantherin A (SCA) causes vasorelaxation in isolated rat thoracic aorta.

MAIN METHODS

We selected SCA, one of the main monomers of lignans from Schisandra, to examine its vasorelaxant effect on the isolated rat thoracic aorta and also exploited several tool inhibitors to probe its underlying mechanisms.

KEY FINDINGS

SCA produced relaxation concentration-dependently on the endothelium-intact (43.56 ± 2.17%) and endothelium-denuded thoracic aorta strips (18.76 ± 3.95%) pre-contracted by phenylephrine (PE). However, after treated with indomethacin or L-NAME, SCA showed only partial vasorelaxant effects. Whereas, this vasorelaxation by SCA was not changed with specific K⁺-channel inhibitors, i.e. barium chloride (BaCl₂), 4-aminopyridine (4-AP), tetraethylamine (TEA), and glibenclamide. SCA had no effect on the aorta strips pre-contracted by PE in neither Ca²⁺-free nor CaCl₂ conditions. But, in the Ca²⁺ free and high K⁺ environment, SCA partly abolished the vasocontraction induced by CaCl₂.

SIGNIFICANCE

It was the first report to demonstrate that SCA had endothelium-dependent and -independent vasorelaxant effects on the isolated rat thoracic aorta, and the underlying mechanisms might be involved into its promoting the production of nitric oxide (NO) and prostacyclin (PGI₂), and inhibiting the voltage-dependent calcium channels (VDCCs) opening. This study may partially explain the use of Schisandra in cardiovascular diseases and facilitate further drug development as well.