Unleashing the Potential of Nrf2: A Novel Therapeutic Target for Pulmonary Vascular Remodeling

Pulmonary vascular remodeling, characterized by the thickening of all three layers of the blood vessel wall, plays a central role in the pathogenesis of pulmonary hypertension (PH). Despite the approval of several drugs for PH treatment, their long-term therapeutic effect remains unsatisfactory, as they mainly focus on vasodilation rather than addressing vascular remodeling. Therefore, there is an urgent need for novel therapeutic targets in the treatment of PH. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a vital transcription factor that regulates endogenous antioxidant defense and emerges as a novel regulator of pulmonary vascular remodeling. Growing evidence has suggested an involvement of Nrf2 and its downstream transcriptional target in the process of pulmonary vascular remodeling. Pharmacologically targeting Nrf2 has demonstrated beneficial effects in various diseases, and several Nrf2 inducers are currently undergoing clinical trials. However, the exact potential and mechanism of Nrf2 as a therapeutic target in PH remain unknown. Thus, this review article aims to comprehensively explore the role and mechanism of Nrf2 in pulmonary vascular remodeling associated with PH. Additionally, we provide a summary of Nrf2 inducers that have shown therapeutic potential in addressing the underlying vascular remodeling processes in PH. Although Nrf2-related therapies hold great promise, further research is necessary before their clinical implementation can be fully realized.

Phosphodiesterase 5 and Arginase Inhibitory Activities of the Extracts from Some Members of Nelumbonaceae and Nymphaeaceae Families

The objectives of this study were (1) to investigate the effect of extracts from some plants in the families Nelumbonaceae and Nymphaeaceae on phosphodiesterase 5 (PDE5) and arginase, which have been used in erectile dysfunction treatment, and (2) to isolate and identify the compounds responsible for such activities. The characterization and quantitative analysis of flavonoid constituents in the active extracts were performed by HPLC. Thirty-seven ethanolic extracts from different parts of plants in the genus Nymphaea and Victoria of Nymphaeaceae and genus Nelumbo of Nelumbonaceae were screened for PDE5 and arginase inhibitory activities. The ethanolic extracts of the receptacles and pollens of Nelumbo nucifera Gaertn., petals of Nymphaea cyanea Roxb. ex G.Don, Nymphaea stellata Willd., and Victoria amazonica (Poepp.) Sowerby and the petals and receptacles of Nymphaea pubescens Willd. showed IC50 values on PDE5 of less than 25 μg/mL while none of the extracts showed effects on arginase. The most active extract, N. pubescens petal extract, was fractionated to isolate and identify the PDE5 inhibitors. The results showed that six flavonoid constituents including quercetin 3'-O-β-xylopyranoside (1), quercetin 3-methyl ether 3'-O-β-xylopyranoside (2), quercetin (3), 3-O-methylquercetin (4), kaempferol (5) and 3-O-methylkaempferol (6) inhibited PDE5 with IC50 values at the micromolar level.

Natural Products for the Treatment of Pulmonary Hypertension: Mechanism, Progress, and Future Opportunities

Pulmonary hypertension (PH) is a lethal disease due to the remodeling of pulmonary vessels. Its pathophysiological characteristics include increased pulmonary arterial pressure and pulmonary vascular resistance, leading to right heart failure and death. The pathological mechanism of PH is complex and includes inflammation, oxidative stress, vasoconstriction/diastolic imbalance, genetic factors, and ion channel abnormalities. Currently, many clinical drugs for the treatment of PH mainly play their role by relaxing pulmonary arteries, and the treatment effect is limited. Recent studies have shown that various natural products have unique therapeutic advantages for PH with complex pathological mechanisms owing to their multitarget characteristics and low toxicity. This review summarizes the main natural products and their pharmacological mechanisms in PH treatment to provide a useful reference for future research and development of new anti-PH drugs and their mechanisms.

Benefits of Curcumin in the Vasculature: A Therapeutic Candidate for Vascular Remodeling in Arterial Hypertension and Pulmonary Arterial Hypertension?

Growing evidence suggests that hypertension is one of the leading causes of cardiovascular morbidity and mortality since uncontrolled high blood pressure increases the risk of myocardial infarction, aortic dissection, hemorrhagic stroke, and chronic kidney disease. Impaired vascular homeostasis plays a critical role in the development of hypertension-induced vascular remodeling. Abnormal behaviors of vascular cells are not only a pathological hallmark of hypertensive vascular remodeling, but also an important pathological basis for maintaining reduced vascular compliance in hypertension. Targeting vascular remodeling represents a novel therapeutic approach in hypertension and its cardiovascular complications. Phytochemicals are emerging as candidates with therapeutic effects on numerous pathologies, including hypertension. An increasing number of studies have found that curcumin, a polyphenolic compound derived from dietary spice turmeric, holds a broad spectrum of pharmacological actions, such as antiplatelet, anticancer, anti-inflammatory, antioxidant, and antiangiogenic effects. Curcumin has been shown to prevent or treat vascular remodeling in hypertensive rodents by modulating various signaling pathways. In the present review, we attempt to focus on the current findings and molecular mechanisms of curcumin in the treatment of hypertensive vascular remodeling. In particular, adverse and inconsistent effects of curcumin, as well as some favorable pharmacokinetics or pharmacodynamics profiles in arterial hypertension will be discussed. Moreover, the recent progress in the preparation of nano-curcumins and their therapeutic potential in hypertension will be briefly recapped. The future research directions and challenges of curcumin in hypertension-related vascular remodeling are also proposed. It is foreseeable that curcumin is likely to be a therapeutic agent for hypertension and vascular remodeling going forwards.

Natural ingredients from Chinese materia medica for pulmonary hypertension

Pulmonary hypertension (PH) is a severe pathophysiological condition characterized by pulmonary artery remodeling and continuous increases in pulmonary artery pressure, which may eventually develop to right heart failure and death. Although newly discovered and incredible treatment strategies in recent years have improved the prognosis of PH, limited types of effective and economical drugs for PH still makes it as a life-threatening disease. Some drugs from Chinese materia medica (CMM) have been traditionally applied in the treatment of lung diseases. Accumulating evidence suggests active pharmaceutical ingredients (APIs) derived from those medicines brings promising future for the prevention and treatment of PH. In this review, we summarized the pharmacological effects of APIs derived from CMM which are potent in treating PH, so as to provide new thoughts for initial drug discovery and identification of potential therapeutic strategies in alternative medicine for PH.

Demethoxycurcumin: A naturally occurring curcumin analogue for treating non-cancerous diseases

Turmeric extracts contain three primary compounds, which are commonly referred to as curcuminoids. They are curcumin, demethoxycurcumin (DMC), and bisdemethoxycurcumin. While curcumin has been the most extensively studied of the curcuminoids, it suffers from low overall oral bioavailability due to extremely low absorption as a result of low water solubility and instability at acidic pH, as well as rapid metabolism and clearance from the body. However, DMC, which lacks the methoxy group on the benzene ring of the parent structure, has much greater chemical stability at physiological pH and has been recently reported to exhibit antitumor properties. However, the treatment of noncancerous diseases with DMC has not been comprehensively reviewed. Therefore, here we evaluate published scientific literature on the therapeutic properties of DMC. The beneficial pharmacological actions of DMC include anti-inflammatory, neuroprotective, antihypertensive, antimalarial, antimicrobial, antifungal, and vasodilatory properties. In addition, DMC's ability to ameliorate the effects of free radicals and an environment characterized by oxidative stress caused by the accumulation of advanced glycation end-products associated with diabetic nephropathy, as well as DMC's capacity to inhibit the migration and proliferation of vascular smooth muscle cells following balloon angioplasty are also addressed. This review collates the available literature regarding the therapeutic possibilities of DMC in noncancerous conditions.

Elucidation of Vasodilation Response and Structure Activity Relationships of N²,N⁴-Disubstituted Quinazoline 2,4-Diamines in a Rat Pulmonary Artery Model

Pulmonary arterial hypertension (PAH) is a rare and progressive disease arising from various etiologies and pathogenesis. PAH decreases life expectancy due to pulmonary vascular remodeling, elevation of mean pulmonary arterial pressure, and ultimately progresses to heart failure. While clinical treatments are available to reduce the associated symptoms, a complete cure has yet to be found. Phosphodiesterase-5 (PDE-5) inhibition has been identified as a possible intervention point in PAH treatment. The functional vasodilation response to N²,N⁴-diamino quinazoline analogues with differing PDE-5 inhibitory activities and varying physicochemical properties were assessed in both endothelium-intact and denuded rat pulmonary arteries to gain greater insight into their mode of action. All analogues produced vasorelaxant effects with EC50s ranging from 0.58 ± 0.22 µM to ˃30 µM. It was observed that vasodilation response in intact vessels was highly correlated with that of denuded vessels. The ~10% drop in activity is consistent with a loss of the nitric oxide mediated cyclic guanosine monophosphate (NO/cGMP) pathway in the latter case. A moderate correlation between the vasodilation response and PDE-5 inhibitory activity in the intact vessels was observed. Experimental protocol using the alpha-adrenergic (α₁) receptor agonist, phenylephrine (PE), was undertaken to assess whether quinazoline derivatives showed competitive behavior similar to the α₁ receptor blocker, prazosin, itself a quinazoline derivative, or to the PDE-5 inhibitor, sildenafil. Competitive experiments with the α₁-adrenergic receptor agonist point to quinazoline derivatives under investigation here act via PDE-5 inhibition and not the former. The pre-incubation of pulmonary arterial rings with quinazoline test compounds (10 μM) reduced the contractile response to PE around 40–60%. The most promising compound (9) possessed ~32 folds higher selectivity in terms of vasodilation to its mammalian A549 cell cytotoxicity. This study provides experi0 0mental basis for PDE-5 inhibition as the mode of action for vasodilation by N²,N⁴-diamino quinazoline analogues along with their safety studies that may be beneficial in the treatment of various cardiovascular pathologies.

Eulophia macrobulbon extract relaxes rat isolated pulmonary artery and protects against monocrotaline-induced pulmonary arterial hypertension

BACKGROUND

Extract of the wild orchid, Eulophia macrobulbon (EM) inhibits phosphodiesterase5 (PDE5) suggesting it could preferentially dilate the pulmonary vasculature.

PURPOSE AND STUDY DESIGN

To pharmacologically characterize the vascular actions of EM ethanolic extract and its active compound, 1-(4'-hydroxybenzyl)-4,8-dimethoxyphenanthrene-2,7-diol using isolated pulmonary arteries (PA) from rats having pulmonary arterial hypertension (PAH) induced by monocrotaline (MCT). PA were fixed and prepared for histology.

RESULTS

EM extract relaxed PA (EC₅₀ = 0.17  mg/ml, E_max ∼ 94%) but less so for aorta (EC₅₀ = 0.51 mg/ml, E_max ∼ 62%), suggesting some selectivity towards the pulmonary circulation. PA vasorelaxation was reduced by endothelial removal or N^G-nitro-L-arginine methyl ester, but unaffected by indomethacin, apamin +charybdotoxin, 4-aminopyridine, glibenclamide, iberiotoxin, or 1H - [1,2,4]oxadiazolo[4,3-a]quinoxalin -1- one. Sodium nitroprusside-induced relaxation was enhanced by EM extract, probably via PDE5 inhibition. EM extract reduced contractions evoked by extracellular Ca²⁺application, and inhibited intracellular Ca²⁺release activated by phenylephrine. The phenanthrene relaxed PA independently of the endothelium. MCT thickened walls and decreased lumens of PA, and hypertrophied right ventricular myocytes, effects ameliorated by 3 weeks of oral sildenafil (20  mg/kg) or EM extract (15, 450 or 1000  mg/kg).

CONCLUSION

PAH is improved by EM extract acting through PA relaxation mediated through endothelial NO, reduced Ca²⁺-mobilization, and reduced PA wall thickness and right ventricular hypertrophy.

Endothelium-independent and calcium channel-dependent relaxation of the porcine cerebral artery by different species and strains of turmeric

Objective

To clarify the underlying mechanism of turmeric, which is traditionally used as a medicinal plant for the treatment of cardiovascular disorders, such as hypertension, and palpitations.

Methods

Methanol extracts of different turmeric were used. A tissue-organ-bath system was used to investigate the vasoactive effects of methanol extracts from 5 kinds of turmeric on isolated porcine basilar arteries. The arterial rings were suspended in physiological solution that was maintained at 37 °C temperature with a continuous supply of 95% O₂ and 5% CO₂.

Results

All turmeric extracts (20–800 μg/mL) induced concentration-dependent relaxation of the isolated porcine basilar artery pre-contracted with U46619 (1-5 × 10⁻⁹ M) in arterial rings with or without endothelium. There were no significant differences in the relaxation induced by different turmeric or between the endothelium-intact and denuded arteries. In depolarized, Ca²⁺-free medium, the turmeric extracts inhibited CaCl₂-induced contractions and caused a concentration-dependent rightward shift of the response curves. In addition, propranolol (a non-specific β-adrenoceptor antagonist) slightly inhibited the relaxation induced by turmeric. In contrast, Nω-nitro-l-arginine, indomethacin, tetraethylammonium, glibenclamide and 4-aminopyridine did not affect turmeric-induced relaxation.

Conclusion

These results demonstrated that turmeric induced endothelium-independent relaxation of the porcine basilar artery, which may be due to the inhibition of extracellular and intracellular Ca²⁺ receptors and the partial inhibition of β-adrenergic receptors in vascular smooth muscle cells.

Extract of Aquilaria crassna leaves and mangiferin are vasodilators while showing no cytotoxicity

The leaves of Aquilaria spp. promote “physiological balance”, and are “cardiotonic and provide blood nourishment”. In Asia, these leaves are increasingly consumed as tea and claimed to provide benefits to cardiovascular function, albeit without any scientific proof. Therefore, this study sought to evaluate the action of Aquilaria crassna leaf aqueous extract (AE) on vascular function and vascular smooth muscle cytotoxicity. AE and a main constituent, mangiferin were investigated for their vasorelaxation of rat mesenteric arteries and aortae in vitro. Acute cytotoxicity of AE (0.1–1000 μg/ml) and mangiferin (0.1–100 μM) on rat enzymatically isolated vascular smooth muscle cells was assayed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide. AE dilated rat mesenteric arteries (EC₅₀∼107 μg/ml, E_max∼95%) more than aorta (EC₅₀∼265 μg/ml, E_max∼76%, p < 0.05).

AE-induced vasodilation in mesenteric artery was reduced by endothelial removal (EC₅₀∼202 μg/ml, p < 0.05), incubation with endothelial nitric oxide synthase (eNOS) (100 μM, L-NAME) (EC₅₀∼309 μg/ml, p < 0.05), and partly reduced by L-type Ca²⁺ channel blockade at higher concentrations. Likewise, mangiferin (1–100 μM) dilated the mesenteric artery more potently than the aorta. However, its maximum relaxation was less than with AE (41% in the mesenteric artery and <10% in the aorta). Isolated vascular smooth muscle cells incubated in AE or mangiferin for 1 h showed no cytotoxicity. Thus, AE is a vasorelaxant while being free of acute cytotoxicity towards vascular smooth muscle, thus potentially ameliorating human vascular dysfunction.

Role of curcumin in PLD activation by Arf6-cytohesin1 signaling axis in U46619-stimulated pulmonary artery smooth muscle cells

Phospholipase D (PLD) catalyzes the hydrolysis of phosphatidylcholine to produce phosphatidic acid (PA) which in some cell types play a pivotal role in agonist-induced increase in NADPH oxidase-derived [Formula: see text]production. Involvement of ADP ribosylation factor (Arf) in agonist-induced activation of PLD is known for smooth muscle cells of systemic arteries, but not in pulmonary artery smooth muscle cells (PASMCs). Additionally, role of cytohesin in this scenario is unknown in PASMCs. We, therefore, determined the involvement of Arf and cytohesin in U46619-induced stimulation of PLD in PASMCs, and the probable mechanism by which curcumin, a natural phenolic compound, inhibits the U46619 response. Treatment of PASMCs with U46619 stimulated PLD activity in the cell membrane, which was inhibited upon pretreatment with SQ29548 (Tp receptor antagonist), FIPI (PLD inhibitor), SecinH3 (inhibitor of cytohesins), and curcumin. Transfection of the cells with Tp, Arf-6, and cytohesin-1 siRNA inhibited U46619-induced activation of PLD. Upon treatment of the cells with U46619, Arf-6 and cytohesin-1 were translocated and associated in the cell membrane, which were not inhibited upon pretreatment of the cells with curcumin. Cytohesin-1 appeared to be necessary for in vitro binding of GTPγS with Arf-6; however, addition of curcumin inhibited binding of GTPγS with Arf-6 even in the presence of cytohesin-1. Our computational study suggests that although curcumin to some extent binds with Tp receptor, yet the inhibition of Arf6_GDP to Arf6_GTP conversion appeared to be an important mechanism by which curcumin inhibits U46619-induced increase in PLD activity in PASMCs.

A comprehensive review on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases

Phosphodiesterases are a group of enzymes that hydrolyze cyclic nucleotides, which assume a key role in directing intracellular levels of the second messengers' cAMP and cGMP, and consequently cell function. The disclosure of 11 isoenzyme families and our expanded knowledge of their functions at the cell and molecular level stimulate the improvement of isoenzyme selective inhibitors for the treatment of various diseases, particularly cardiovascular diseases. Hence, future and new mechanistic investigations and carefully designed clinical trials could help reap additional benefits of natural/synthetic PDE inhibitors for cardiovascular disease in patients. This review has concentrated on the potential therapeutic benefits of phosphodiesterase inhibitors on cardiovascular diseases.

Demethoxycurcumin Preserves Renovascular Function by Downregulating COX-2 Expression in Hypertension

Hypertension-associated endothelial dysfunction is largely due to the exaggerated vasoconstrictor generation by cyclooxygenase-2 (COX-2). COX-2 is induced under inflammatory condition. Demethoxycurcumin (DMC) is a major component of Curcuma longa L, which possesses anti-inflammatory action. This study aimed to examine whether DMC protects endothelial function in hypertension by modulating COX-2. Changes in isometric tension showed that in vivo and ex vivo treatment with DMC rescued the attenuated endothelium-dependent relaxations (EDRs) and elevated endothelium-dependent contractions (EDCs) in the renal arteries of SHR, which were also corrected by acute usage of the COX-2 inhibitor celecoxib. The restoration of renovascular activity by DMC was accompanied by the normalization of COX-2 expression. The enhanced COX-2 expression observed in the renal arteries of hypertensive patients was suppressed by incubation of excised arteries with DMC for 12 hrs. In the renal arteries of Wistar-Kyoto rats (WKY), DMC prevented the endothelial dysfunction caused by angiotensin II. The reduction in the generation of nitric oxide (NO) and expression of eNOS phosphorylation (Ser1177) in human umbilical vein endothelial cells caused by angiotensin II (Ang II) were restored by DMC or celecoxib. Our findings suggest that DMC may decrease COX-2 expression and improve endothelial function in hypertension.