Endothelium-dependent nitric oxide and hyperpolarization-mediated venous relaxation pathways in rat inferior vena cava

Sulodexide Inhibits Arterial Contraction via the Endothelium-Dependent Nitric Oxide Pathway

Background/Objectives: Sulodexide (SDX) is a drug known for restoring the glycocalyx, thereby offering endothelial protection and regulating permeability. Additionally, it has antithrombotic and anti-inflammatory properties and has shown arterial vasodilatory effects. Endothelial cells play a crucial role in maintaining homeostasis, with their dysfunction being a key contributor to loss in vasodilatory response, especially in arterial pathologies. The aim of this study was to investigate the effects of SDX on stimulated vascular tonus in human arterial samples and to assess the function of the endothelial layer as a source of nitric oxide (NO). Methods: A total of 16 internal mammary artery remnants from coronary artery bypass graft surgeries were dissected into endothelium-intact and endothelium-denuded groups (n = 8 each). The arterial rings were equilibrated under tension, with their basal tonus recorded before and after phenylephrine stimulation. SDX's impact on arterial contraction was assessed through cumulative dose-response curves. NO synthase inhibitor (Nω-nitro-L-arginine methyl ester) was used to assess SDX's vasodilatory effect over the NO pathway. Results: SDX application resulted in concentration-dependent vasorelaxation in both endothelium-intact and endothelium-denuded groups at certain doses. However, the inhibitory effect of SDX was more pronounced in endothelium-intact rings at higher doses compared to endothelium-denuded rings (p < 0.05). Similar inhibition of contraction curves was achieved for both endothelium-intact and endothelium-denuded rings after L-NAME pre-incubation, suggesting a necessity for NO-related endothelial pathways. Conclusions: SDX exerts a concentration-dependent inhibition on arterial contraction, emphasizing the critical role of an intact endothelium and NO-mediated pathways in this process. This underscores SDX's potential in treating endothelial dysfunction-related pathologies.

Channelopathy of small- and intermediate-conductance Ca2+-activated K+ channels

Small- and intermediate-conductance Ca2+-activated K+ (KCa2.x/KCa3.1 also called SK/IK) channels are gated exclusively by intracellular Ca2+. The Ca2+ binding protein calmodulin confers sub-micromolar Ca2+ sensitivity to the channel-calmodulin complex. The calmodulin C-lobe is constitutively associated with the proximal C-terminus of the channel. Interactions between calmodulin N-lobe and the channel S4-S5 linker are Ca2+-dependent, which subsequently trigger conformational changes in the channel pore and open the gate. KCNN genes encode four subtypes, including KCNN1 for KCa2.1 (SK1), KCNN2 for KCa2.2 (SK2), KCNN3 for KCa2.3 (SK3), and KCNN4 for KCa3.1 (IK). The three KCa2.x channel subtypes are expressed in the central nervous system and the heart. The KCa3.1 subtype is expressed in the erythrocytes and the lymphocytes, among other peripheral tissues. The impact of dysfunctional KCa2.x/KCa3.1 channels on human health has not been well documented. Human loss-of-function KCa2.2 mutations have been linked with neurodevelopmental disorders. Human gain-of-function mutations that increase the apparent Ca2+ sensitivity of KCa2.3 and KCa3.1 channels have been associated with Zimmermann-Laband syndrome and hereditary xerocytosis, respectively. This review article discusses the physiological significance of KCa2.x/KCa3.1 channels, the pathophysiology of the diseases linked with KCa2.x/KCa3.1 mutations, the structure-function relationship of the mutant KCa2.x/KCa3.1 channels, and potential pharmacological therapeutics for the KCa2.x/KCa3.1 channelopathy.

Sulodexide Develops Contraction in Human Saphenous Vein via Endothelium-Dependent Nitric Oxide Pathway

Chronic venous disease (CVD) is a proqgressive and underestimated condition related to a vicious circle established by venous reflux and endothelial inflammation, leading to vein dilation and histology distortion, including loss of media tone. Sulodexide (SDX) is a drug restoring the glycocalyx that demonstrated endothelial protection and permeability regulation, together with anti-thrombotic and anti-inflammatory roles. In the lab it also exhibited vein contractility function. The aim of the present study was to show the possible role of endothelium and nitric oxide pathway on SDX's veno-contractile effect on human saphenous veins. The remnants of great saphenous vein (GSV) segments (n = 14) were harvested during coronary artery bypass graft surgery. They were dissected as endothelium-intact (n = 8) and denuded rings (n = 6). First, a viability test was carried out in bath with Krebs-Henseleit solution to investigate a control and basal tension value. After this, cumulative doses of SDX were applied to rings and contraction values were studied in endothelium-intact phenylephrine (PheE, 6 × 10^-7 M) pre-contracted vein rings. Finally, endothelium-intact PheE pre-contacted vein rings were treated by nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME, 10^-4 M) for 10 min. Contraction protocol was applied, and contraction values were measured in cumulative doses of SDX. The same protocol was applied to endothelium-denuded vein rings to investigate the effect of SDX. Saphenous vein rings showed an increase in contraction to cumulative doses of SDX. In endothel-intact rings, KCL-induced contraction from 92.6% ± 0.3 to 112.9% ± 0.4 with cumulative SDX doses. However, SDX did not show any veno-contractile effect on endothel-denuded rings. In denuded rings contraction responses measured from 94.9% ± 0.3 to 85.2% ± 0.3 with increasing doses of SDX, indicating no significant change. Nitric oxide synthase inhibitor (L-NAME) prohibited the contraction response of the sulodexide in all dosages, indicating that the contractile function of SDX was mediated by endothelial derived nitric oxide. Results of endothel-intact and denuded rings with L-NAME showed a similar incline with denuded rings with SDX only. The results confirmed SDX's veno-contractile effect in human samples, by means of nitric oxide synthase pathways involvement.

Venous endothelial function in cardiovascular disease

The essential role of the endothelium in vascular homeostasis is associated with the release of endothelium-dependent relaxing and contractile factors (EDRF and EDCF, respectively). Different from arteries, where these factors are widely studied, the vasoactive factors derived from the venous endothelium have been given less attention. There is evidence for a role of the nitric oxide (NO), endothelium-dependent hyperpolarization (EDH) mechanism, and cyclooxygenase (COX)-derived metabolites as EDRFs; while the EDCFs need to be better evaluated since no consensus has been reached about their identity in venous vessels. The imbalance between the synthesis, bioavailability, and/or action of EDRFs and/or EDCFs results in a pathological process known as endothelial dysfunction, which leads to reduced vasodilation and/or increased vasoconstriction. In the venous system, endothelial dysfunction is relevant since reduced venodilation may increase venous tone and decrease venous compliance, thus enhancing mean circulatory filling pressure, which maintains or modify cardiac workload contributing to the etiology of cardiovascular diseases. Interestingly, some alterations in venous function appear at the early stages (or even before) the establishment of these diseases. However, if the venous endothelium dysfunction is involved in these alterations is not yet fully understood and requires further studies. In this sense, the present study aims to review the current knowledge on venous endothelial function and dysfunction, and the general state of the venous tone in two important cardiovascular diseases of high incidence and morbimortality worldwide: hypertension and heart failure.

Vena cava presents endothelial dysfunction prior to thoracic aorta in heart failure: the pivotal role of nNOS uncoupling/oxidative stress

Arterial endothelial dysfunction has been extensively studied in heart failure (HF). However, little is known about the adjustments shown by the venous system in this condition. Considering that inferior vena cava (VC) tone could influence cardiac performance and HF prognosis, the aim of the present study was to assess the VC and thoracic aorta (TA) endothelial function of HF-post-myocardial infarction (MI) rats, comparing both endothelial responses and signaling pathways developed. Vascular reactivity of TA and VC from HF post-MI and sham operated (SO) rats was assessed with a wire myograph, 4 weeks after coronary artery occlusion surgery. Nitric oxide (NO), H2O2 production and oxidative stress were evaluated in situ with fluorescent probes, while protein expression and dimer/monomer ratio was assessed by Western blot. VC from HF rats presented endothelial dysfunction, while TA exhibited higher acetylcholine (ACh)-induced vasodilation when compared with vessels from SO rats. TA exhibited increased ACh-induced NO production due to a higher coupling of endothelial and neuronal NO synthases isoforms (eNOS, nNOS), and enhanced expression of antioxidant enzymes. These adjustments, however, were absent in VC of HF post-MI rats, which exhibited uncoupled nNOS, oxidative stress and higher H2O2 bioavailability. Altogether, the present study suggests a differential regulation of endothelial function between VC and TA of HF post-MI rats, most likely due to nNOS uncoupling and compromised antioxidant defense.

A Review of the Actions of Endogenous and Exogenous Vasoactive Substances during the Estrous Cycle and Pregnancy in Rats

Vascular endothelium plays a key role in regulating cardiovascular homeostasis by controlling the vascular tone. Variations in sex hormones during the reproductive cycle of females affect the homeostasis of the cardiovascular system. Also, the evidence shows that estrogens show a cardioprotective effect. On this basis, this study describes some vascular responses induced by vasoactive substances during the estrous cycle in rats. We obtained the information available on this topic from the online databases that included scientific articles published in the Web of Science, PubMed, and Scielo. Many investigations have evaluated the vasoactive response of substances such as acetylcholine and norepinephrine during the estrous cycle. In this review, we specifically described the vascular response to vasoactive substances in rats during the estrous cycle, pregnancy, and in ovariectomized rats. In addition, we discussed the existence of different signaling pathways that modulate vascular function. The knowledge of these effects is relevant for the optimization and development of new treatments for some vascular pathologies.

Endothelium-dependent relaxation mechanisms involve nitric oxide and prostanoids in the isolated bovine digital vein

Endothelial dysfunction contributes to the development of ungulate's laminitis. Although extensively studied in equines, the endothelial function is not fully examined in bovine digital veins (BDVs). BDVs were studied under isometric conditions to describe the acetylcholine (ACh) endothelium-dependent relaxation. Concentration-response curves were constructed to phenylephrine, ACh, and sodium nitroprusside (SNP). Relaxation responses were evaluated using either phenylephrine or depolarizing high-potassium Krebs solution (DKS) as precontraction agents. Endothelium denudation and incubation with L-NAME (300 μM), indomethacin (10 μM) or both were used to explore endothelial-mediated mechanisms. Endothelium denudation did not modify phenylephrine and SNP responses, however, significantly (p < 0.05) converted a relaxation (63.2 ± 5%) response to ACh into a contraction (30.3±9%). The ACh-evoked relaxation was significantly (p < 0.05) reduced in the presence of indomethacin (37.5 ± 6%) and L-NAME (6.40 ± 2%). The presence of both inhibitors abolished the ACh-evoked relaxation. Although DKS caused a higher precontraction than phenylephrine, ACh-evoked relaxation (22.4 ± 3.4%) was still observed and was reduced by the combination of inhibitors (7.0 ± 1.0%). The ACh endothelium-dependent relaxation in BDVs is essentially mediated by nitric oxide and endothelium-derived prostanoids. The BDV endothelium function is a dynamic component in the control of the bovine digital blood flow, particularly under endothelial dysfunction conditions when venoconstriction might lead to postcapillary resistance increase.

Venous endothelium reactivity to Angiotensin II: A study in primary endothelial cultures of rat vena cava and portal vein

The role of the vascular endothelium in modulating the arterial system has been widely investigated, but poorly explored at the venous site. In the present work, primary cultures of venous endothelium from rat Vena Cava (VC) and Portal Vein (PV) were established, characterized and analyzed according to their growth pattern and ability to produce nitric oxide (NO) and prostanoids (PGF_{2 α} and PGI₂), at basal state and after stimulation with Angiotensin II (Ang II, 1μmol/L). Basal NO was detected in all examined cells in culture. Pre-incubation with Ang II increased NO production in cells from VC (but not in PV cultures), through activation of both AT₁ and AT₂ receptors. Both cultures exhibited detectable levels of PGF_{2 α} at resting conditions, which were similarly enhanced by Ang II. Basal PGI₂ levels were higher in PV, but increased after Ang II treatment in VC, with no further effect on PV cells. We conclude that endothelial cells from VC and PV exhibit important properties and react to Ang II, probably influencing the whole circulatory system. This experimental cell model gives support to further studies concerning intracellular pathways of the venous endothelium, analyzed in separate from the vascular smooth muscle wall.

A de novo mutation in KCNN3 associated with autosomal dominant idiopathic non-cirrhotic portal hypertension

Non-cirrhotic portal hypertension is characterized by histopathological abnormalities in the liver, mostly affecting small intrahepatic portal veins that cause portal hypertension in the absence of cirrhosis. It can be secondary to coagulation disorders or toxic agents. However, most cases are idiopathic non-cirrhotic portal hypertension (INCPH) and familial cases are rare. We report a family in which a father and three of his four children conceived with three different mothers are affected by INCPH. Whole exome and Sanger sequencing showed the father to have a de novo single nucleotide substitution c.1348G>C in the KCNN3 gene that was transmitted to all three of his affected offspring. The KCNN3 gene encodes small conductance calcium-activated potassium (SK) channel 3. SK channels are involved in the regulation of arterial and venous vascular tone by causing smooth muscle relaxation on activation. No data exist on the expression and function of SK channels in portal veins. The autosomal dominant inheritance in this unique pedigree and the single de novo mutation identified, strongly suggests that KCNN3 mutations have a pathogenetic role in INCPH.

Adenosine-associated delivery systems

Adenosine is a naturally occurring purine nucleoside in every cell. Many critical treatments such as modulating irregular heartbeat (arrhythmias), regulation of central nervous system (CNS) activity and inhibiting seizural episodes can be carried out using adenosine. Despite the significant potential therapeutic impact of adenosine and its derivatives, the severe side effects caused by their systemic administration have significantly limited their clinical use. In addition, due to adenosine's extremely short half-life in human blood (<10 s), there is an unmet need for sustained delivery systems to enhance efficacy and reduce side effects. In this article, various adenosine delivery techniques, including encapsulation into biodegradable polymers, cell-based delivery, implantable biomaterials and mechanical-based delivery systems, are critically reviewed and the existing challenges are highlighted.

Enhancing vascular relaxing effects of nitric oxide-donor ruthenium complexes

Ruthenium-derived complexes have emerged as new nitric oxide (NO) donors that may help circumvent the NO deficiency that impairs vasodilation. NO in vessels can be produced by the endothelial cells and/or released by NO donors. NO interacts with soluble guanylyl-cyclase to produce cGMP to activate the kinase-G pathway. As a result, conductance arteries, veins and resistance arteries dilate, whereas the cytosolic Ca2+ levels in the smooth muscle cells decrease. NO also reacts with oxygen or the superoxide anion, to generate reactive oxygen species that modulate NO-induced vasodilation. In this article, we focus on NO production by NO synthase and discuss the vascular changes taking place during hypertension originating from endothelial dysfunction. We will describe how the NO released from ruthenium-derived complexes enhances the vascular effects arising from failed NO generation or lack of NO bioavailability. In addition, how ruthenium-derived NO donors induce the hypotensive effect by vasodilation is also discussed.