Nanomechanics and sodium permeability of endothelial surface layer modulated by hawthorn extract WS 1442

Advances in the study of the vascular protective effects and molecular mechanisms of hawthorn (Crataegus anamesa Sarg.) extracts in cardiovascular diseases

Hawthorn belongs to the rose family and is a type of functional food. It contains various chemicals, including flavonoids, terpenoids, and organic acid compounds. This study aimed to review the vascular protective effects and molecular mechanisms of hawthorn and its extracts on cardiovascular diseases (CVDs). Hawthorn has a wide range of biological functions. Evidence suggests that the active components of HE reduce oxidative stress and inflammation, regulate lipid levels to prevent lipid accumulation, and inhibit free cholesterol accumulation in macrophages and foam cell formation. Additionally, hawthorn extract (HE) can protect vascular endothelial function, regulate endothelial dysfunction, and promote vascular endothelial relaxation. It has also been reported that the effective components of hawthorn can prevent age-related endothelial dysfunction, increase cellular calcium levels, cause antiplatelet aggregation, and promote antithrombosis. In clinical trials, HE has been proved to reduce the adverse effects of CVDs on blood lipids, blood pressure, left ventricular ejection fraction, heart rate, and exercise tolerance. Previous studies have pointed to the benefits of hawthorn and its extracts in treating atherosclerosis and other vascular diseases. Therefore, as both medicine and food, hawthorn can be used as a new drug source for treating cardiovascular diseases.

Effects of Chronic Kidney Disease on Nanomechanics of the Endothelial Glycocalyx Are Mediated by the Mineralocorticoid Receptor

Endothelial mechanics control vascular reactivity and are regulated by the mineralocorticoid receptor (MR) and its downstream target, the epithelial Na⁺ channel (ENaC). Endothelial dysfunction is a hallmark of chronic kidney disease (CKD), but its mechanisms are poorly understood. We hypothesized that CKD disrupts endothelial mechanics in an MR/ENaC-dependent process.

METHODS

Primary human endothelial cells were cultured with uremic serum derived from children with stage 3-5 (predialysis) CKD or adult hemodialysis (HD) patients or healthy controls. The height and stiffness of the endothelial glycocalyx (eGC) and cortex were monitored by atomic force microscopy (AFM) using an ultrasensitive mechanical nanosensor.

RESULTS

In a stage-dependent manner, sera from children with CKD induced a significant increase in eGC and cortex stiffness and an incremental reduction of the eGC height. AFM measurements were significantly associated with individual pulse wave velocity and serum concentrations of gut-derived uremic toxins. Serum from HD patients increased MR expression and mechanical stiffness of the endothelial cortex, an effect reversed by MR and ENaC antagonists, decreased eNOS expression and NO bioavailability, and augmented monocyte adhesion.

CONCLUSION

These data indicate progressive structural damage of the endothelial surface with diminishing kidney function and identify the MR as a mediator of CKD-induced endothelial dysfunction.

Hawthorn fruit acid consumption attenuates hyperlipidemia-associated oxidative damage in rats

Context

Hyperlipidemia is a highly prevalent risk factor for atherosclerosis and stroke. The currently available medications used to treat Hyperlipidemia cannot improve its oxidative stress damage. Consumption of hawthorn can regulate blood sugar and blood lipids, and its rich fruit acid is a natural antioxidant that can improve oxidative stress damage.

Objective

The present research aimed to investigate the protective effect of hawthorn fruit acid (HFA) on hyperlipidemia and to determine its potential molecular mechanism.

Materials and methods

Sprague-Dawley rats were fed a high-fat diet (HFD) to induce hyperlipidemia and treated orally with hawthorn fruit acids (HFA). Serum and liver levels of total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), superoxide dismutase (SOD), hydrogen peroxide (CAT), and malondialdehyde (MDA) were measured. Human hepatocellular carcinoma cell lines (HepG2) cells were treated with 0.1 mM oleic acid and HFA (0.125, 0.25 mg/mL), and intracellular TC, TG, HDL-C, SOD, CAT and MDA were measured. Changes in LDLR, HMGCR, Nrf2, HO-1, NQO1 protein and gene expression were analyzed by Western blot and qPCR.

Results

This study found that HFA treatment effectively reduced the level of triglyceride, cholesterol, and glucose, and attenuated hepatic steatosis in rats. Additionally, oxidative stress damage of rats was effectively reduced by treatment with HFA. Western blot and qPCR analysis indicated that HFA treatment inhibited fat accumulation in HepG2 cells by upregulating LDLR and downregulating HMGCR gene expression. HFA inhibits oleic acid (OA)-induced oxidative damage to HepG2 by activating the Nrf2/HO-1 signaling pathway.

Conclusion

HFA administration can provide health benefits by counteracting the effects of hyperlipidemia caused by an HFD in the body, and the underlying mechanism of this event is closely related to the activation of the Nrf2/HO-1 signaling pathway.

Herbs and their bioactive ingredients in cardio-protection: Underlying molecular mechanisms and evidences from clinical studies

BACKGROUND

Medicinal plants or herbs produce a bounty of bioactive phytochemicals. These phytochemicals can influence a variety of physiological events related to cardiovascular health through multiple underlying mechanisms, such as their role as antioxidative, anti-ischemic, anti-proliferative, hypotensive, anti-thrombotic, and anti-hypercholesterolemic agents.

PURPOSE

The purpose of this review is to summarize and connect evidences supporting the use of phytotherapy in the management of some of the most common cardiovascular impairments, molecular mechanisms underlying cardio-protection mediated by herbs, and clinical studies which are positively linked with the use of herbs in cardiovascular biology. Additionally, we also describe several adverse effects associated with some of the herbal plants and their products to provide a balanced set of studies in favor or against phytotherapy in cardiovascular health that may help global discourses on this matter.

METHODS

Studies relating to the use of medicinal plants were mined by strategically searching scientific databases including Google Scholar, PubMed and Science Direct. Investigations involving approximately 175 articles including reviews, research articles, meta-analyses, and cross-sectional and observational studies were retrieved and analyzed in line with the stated purpose of this study.

RESULTS

A positive correlation between the use of medicinal plants and cardiovascular health was observed. While maintaining cardiovascular physiology, medicinal plants and their derivatives seem to govern a variety of cellular mechanisms involved in vasoconstriction and vasorelaxation, which in turn, are important aspects of cardiovascular homeostasis. Furthermore, a variety of studies including clinical trials, cross-sectional studies, and meta-analyses have also supported the anti-hypertensive and thus, cardio-protective effects, of medicinal plants. Apart from this, evidence is also available for the potential drawbacks of several herbs and their products indicating that the unsupervised use of many herbs may lead to severe health issues.

CONCLUSIONS

The cardio-protective outcomes of medicinal plants and their derivatives are supported by ever-increasing studies, while evidences exist for the potential drawbacks of some of the herbs. A balanced view about the use of medicinal plants and their derivative in cardiovascular biology thus needs to be outlined by researchers and the medical community. The novelty and exhaustiveness of the present manuscript is reflected by the detailed outline of the molecular basis of "herbal cardio-protection", active involvement of several herbs in ameliorating the cardiovascular status, adverse effects of medicinal plants, and the clinical studies considering the use of phytotherapy, all on a single platform.

Detrimental or beneficial: Role of endothelial ENaC in vascular function

In the past, it was believed that the expression of the epithelial sodium channel (ENaC) was restricted to epithelial tissues, such as the distal nephron, airway, sweat glands, and colon, where it is critical for sodium homeostasis. Over the past two decades, this paradigm has shifted due to the finding that ENaC is also expressed in various nonepithelial tissues, notably in vascular endothelial cells. In this review, the recent findings of the expression, regulation, and function of the endothelial ENaC (EnNaC) are discussed. The expression of EnNaC subunits is reported in a variety of endothelial cell lines and vasculatures, but this is controversial across different species and vessels and is not a universal finding in all vascular beds. The expression density of EnNaC is very faint compared to ENaC in the epithelium. To date, little is known about the regulatory mechanism of EnNaC. Through it can be regulated by aldosterone, the detailed downstream signaling remains elusive. EnNaC responds to increased extracellular sodium with the feedforward activation mechanism, which is quite different from the Na⁺ self-inhibition mechanism of ENaC. Functionally, EnNaC was shown to be a determinant of cellular mechanics and vascular tone as it can sense shear stress, and its activation or insertion into plasma membrane causes endothelial stiffness and reduced nitric oxide production. However, in some blood vessels, EnNaC is essential for maintaining the integrity of endothelial barrier function. In this context, we discuss the possible reasons for the distinct role of EnNaC in vasculatures.

SAFETY AND EFFECTS OF CRATAEGUS EXTRACT WS 1442 AND NORDIC WALKING ON LIPID PROFILE AND ENDOTHELIAL FUNCTION: A RANDOMIZED, PARTIALLY BLINDED PILOT STUDY IN OVERWEIGHT VOLUNTEERS

Overweight and physical inactivity adversely affect endothelial function and are risk factors for atherosclerosis and cardiovascular disease. Both Crataegus extract WS 1442 and physical exercise exert beneficial effects on endothelial function. We investigated whether WS 1442 and Nordic walking (NW) had comparable effects on endothelial function and lipid profile in overweight subjects. In this partially blinded pilot study, overweight, otherwise healthy volunteers aged 45-75 years were randomized into four groups as follows: WS 1442 2x450 mg/day (WS-standard), WS 1442 2x900 mg/day (WS-double), exercise 2x30 minutes/week (NW-low), and exercise 4x45 minutes/week (NW-high) for 12 weeks. Safety was assessed based on adverse events. Endothelial function testing (EndoPAT^®), assessment of endothelial progenitor cells, lipid profiles, and treadmill testing were performed. Sixty subjects participated in the study. At baseline, subjects in WS-standard/-double groups had higher lipid levels and greater impairment of endothelial function. Subjects with impaired endothelial function showed improvement regardless of the type of intervention. Subjects in WS-standard and WS-double groups showed a trend towards modest decrease in triglycerides and modest increase in HDL-cholesterol; most changes were within the normal limits. In NW-low/-high groups, values also remained within the normal range. Exercise capacity improved in both NW groups. WS-double showed no additional benefits over WS-standard. All adverse events were unrelated or improbably related to treatment. In conclusion, WS 1442 and exercise training were safe and showed beneficial effects on endothelial function and lipid profile in overweight but otherwise healthy volunteers; exercise capacity improved only by Nordic walking.

Roles and Mechanisms of Hawthorn and Its Extracts on Atherosclerosis: A Review

Cardiovascular disease (CVD), especially atherosclerosis, is a leading cause of morbidity and mortality globally; it causes a considerable burden on families and caregivers and results in significant financial costs being incurred. Hawthorn has an extensive history of medical use in many countries. In China, the use of hawthorn for the treatment of CVD dates to 659 AD. In addition, according to the theory of traditional Chinese medicine, it acts on tonifying the spleen to promote digestion and activate blood circulation to dissipate blood stasis. This review revealed that the hawthorn extracts possess serum lipid-lowering, anti-oxidative, and cardiovascular protective properties, thus gaining popularity, especially for its anti-atherosclerotic effects. We summarize the four principal mechanisms, including blood lipid-lowering, anti-oxidative, anti-inflammatory, and vascular endothelial protection, thus providing a theoretical basis for further utilization of hawthorn.

Application of a layered model for determination of the elasticity of biological systems

Elasticity of biological systems is considered to be an important property that might be related to functional or pathological changes. Therefore, careful study and detailed understanding of cell and tissue elasticity is crucial for correct description of their functioning. Atomic Force Microscopy (AFM) is a powerful technique, which allows for determination of the physical properties, such as elasticity, of soft-matter systems in nano-scale. An important step in AFM elasticity studies is a proper interpretation of experimental data. Two most frequently used theoretical schemes applied to determine elasticity are due to Hertz and Sneddon, which are effectively one-parameter models. In this work, we go beyond this approach. Firstly, as elasticity is a local property, we extract from the slope of experimental force-indentation curve an elasticity parameter, which varies with indentation depth. Then secondly, we find best approximation of this parameter by applying the two-layer model with four effective parameters, as proposed by Kovalev. This method is employed to the experimental data taken on murine liver sinusoidal endothelial cells in non-alcoholic fatty liver disease model. The obtained results show additional effects, not seen within the traditional, simplified scheme. Namely, the elasticity of the first layer does not change its value in the model of non-alcoholic fatty liver disease, but the increase of stiffness is noticed in second layer. The second goal of this article is to reveal and discuss the differences between traditional approaches and the one being presented. The deviations from the original assumptions are analysed and the corresponding restrictions on utility of theoretical models are presented.

Endothelial Nanomechanics in the Context of Endothelial (Dys)function and Inflammation

SIGNIFICANCE

Stiffness of endothelial cells is closely linked to the function of the vasculature as it regulates the release of vasoactive substances such as nitric oxide (NO) and reactive oxygen species. The outer layer of endothelial cells, consisting of the glycocalyx above and the cortical zone beneath the plasma membrane, is a vulnerable compartment able to adapt its nanomechanical properties to any changes of forces exerted by the adjacent blood stream. Sustained stiffening of this layer contributes to the development of endothelial dysfunction and vascular pathologies. Recent Advances: The development of specific techniques to quantify the mechanical properties of cells enables the detailed investigation of the mechanistic link between structure and function of cells.

CRITICAL ISSUES

Challenging the mechanical stiffness of cells, for instance, by inflammatory mediators can lead to the development of endothelial dysfunction. Prevention of sustained stiffening of the outer layer of endothelial cells in turn improves endothelial function.

FUTURE DIRECTIONS

The mechanical properties of cells can be used as critical marker and test system for the proper function of the vascular system. Pharmacological substances, which are able to improve endothelial nanomechanics and function, could take a new importance in the prevention and treatment of vascular diseases. Thus, detailed knowledge acquisition about the structure/function relationship of endothelial cells and the underlying signaling pathways should be promoted.

[Significance of hawthorn extract in general practice - a current positioning]

BACKGROUND

Traditionally, hawthorn extract has been used for preventive and curative support in mild forms of age-related cardiovascular problems. There are now solid data demonstrating pre-clinical effects and mechanisms of action on a molecular-biological and cellular level that appear to be of particular interest in influencing vascular ageing and in arterial vascular disorders.

METHOD

The review presents the results of a meeting of experts that took place to work out a current assessment of the therapeutic suitability of hawthorn extract in the treatment of cardiovascular disease.

RESULTS AND CONCLUSIONS

Although currently no general recommendation can be given on the use of hawthorn extract in cardiac insufficiency, its use is indicated for typical challenges arising in general practice, where particularly patients with functional cardiorespiratory complaints present, possibly those with cardiac insufficiency with preserved heart function for whom there has thus far been no effective therapy apart from exercise. This recommendation is supported by the findings of studies on the safety and very good tolerability of hawthorn extract, particularly for therapy adjuvant to standard practice.

Laminar shear stress modulates endothelial luminal surface stiffness in a tissue-specific manner

OBJECTIVE

Endothelial cells form vascular beds in all organs and are exposed to a range of mechanical forces that regulate cellular phenotype. We sought to determine the role of endothelial luminal surface stiffness in tissue-specific mechanotransduction of laminar shear stress in microvascular mouse cells and the role of arachidonic acid in mediating this response.

METHODS

Microvascular mouse endothelial cells were subjected to laminar shear stress at 4 dynes/cm² for 12 hours in parallel plate flow chambers that enabled real-time optical microscopy and atomic force microscopy measurements of cell stiffness.

RESULTS

Lung endothelial cells aligned parallel to flow, while cardiac endothelial cells did not. This rapid alignment was accompanied by increased cell stiffness. The addition of arachidonic acid to cardiac endothelial cells increased alignment and stiffness in response to shear stress. Inhibition of arachidonic acid in lung endothelial cells and embryonic stem cell-derived endothelial cells prevented cellular alignment and decreased cell stiffness.

CONCLUSIONS

Our findings suggest that increased endothelial luminal surface stiffness in microvascular cells may facilitate mechanotransduction and alignment in response to laminar shear stress. Furthermore, the arachidonic acid pathway may mediate this tissue-specific process. An improved understanding of this response will aid in the treatment of organ-specific vascular disease.

Benefit-Risk Assessment of Crataegus Extract WS 1442: An Evidence-Based Review

Preparations from Crataegus (hawthorn) have a long history in the treatment of heart failure. WS 1442 is a dry extract from hawthorn leaves with flowers (4–6.6:1), extraction solvent of ethanol 45% (w/w), adjusted to 17.3–20.1% of oligomeric procyanidins. Nonclinical studies show that WS 1442 has positive inotropic and antiarrhythmic properties and protects the myocardium from ischemic damage, reperfusion injury, and hypertension-related hypertrophy, improves endothelial functions such as NO synthesis, and delays endothelial senescence. Randomized, controlled trials in patients with heart failure have demonstrated that the herbal medicinal product increases functional capacity, alleviates disabling symptoms, and improves health-related quality of life, all of which have become important targets of heart failure therapy according to current disease management guidelines. Clinical trials (including a 2-year mortality study with polypharmacy and > 1300 patients exposed) and post-marketing surveillance studies have shown that WS 1442 has a very favorable safety profile both as monotherapy and as add-on therapy, where no drug interactions have been observed. No specific adverse reactions to WS 1442 are known to date. WS 1442 may thus help to close the therapeutic gap between systolic and diastolic heart failure for which evidence of efficacy for other cardioactive drugs is sparse. Scientific evidence shows that WS 1442 is safe and has a beneficial effect in patients with heart failure corresponding to New York Heart Association classes II or III. The benefit-risk assessment for WS 1442 is therefore positive.

The glycocalyx and its significance in human medicine

Cells are covered by a surface layer of glycans that is referred to as the 'glycocalyx'. In this review, we focus on the role of the glycocalyx in vascular diseases (atherosclerosis, stroke, hypertension, kidney disease and sepsis) and cancer. The glycocalyx and its principal glycosaminoglycans [heparan sulphate (HS) and hyaluronic acid (HA)] and core proteins (syndecans and glypicans) are degraded in vascular diseases, leading to a breakdown of the vascular permeability barrier, enhanced access of leucocytes to the arterial intima that propagate inflammation and alteration of endothelial mechanotransduction mechanisms that protect against disease. By contrast, the glycocalyx on cancer cells is generally robust, promoting integrin clustering and growth factor signalling, and mechanotransduction of interstitial flow shear stress that is elevated in tumours to upregulate matrix metalloproteinase release which enhances cell motility and metastasis. HS and HA are consistently elevated on cancer cells and are associated with tumour growth and metastasis. Later, we will review the agents that might be used to enhance or protect the glycocalyx to combat vascular disease, as well as a different set of compounds that can degrade the cancer cell glycocalyx to suppress cell growth and metastasis. It is clear that what is beneficial for either vascular disease or cancer will not be so for the other. The overarching conclusions are that (i) the importance of the glycocalyx in human medicine is only beginning to be recognized, and (ii) more detailed studies of glycocalyx involvement in vascular diseases and cancer will lead to novel treatment modalities.

Sodium renders endothelial cells sticky for red blood cells

Negative charges in the glycocalyx of red blood cells (RBC) and vascular endothelial cells (EC) facilitate frictionless blood flow through blood vessels. Na⁺ selectively shields these charges controlling surface electronegativity. The question was addressed whether the ambient Na⁺ concentration controls RBC-EC interaction. Using atomic force microscopy (AFM) adhesion forces between RBC and endothelial glycocalyx were quantified. A single RBC, mounted on an AFM cantilever, was brought in physical contact with the endothelial surface and then pulled off. Adhesion forces were quantified (i) after enzymatic removal of negative charges in the glycocalyx, (ii) under different ambient Na⁺ and (iii) after applying the intracellular aldosterone receptor antagonist spironolactone. Removal of negative surface charges increases RBC-EC interaction forces. A stepwise increase of ambient Na⁺ from 133 to 140 mM does not affect them. However, beyond 140 mM Na⁺ adhesion forces increase sharply (10% increase of adhesion force per 1 mM increase of Na⁺). Spironolactone prevents this response. It is concluded that negative charges reduce adhesion between RBC and EC. Ambient Na⁺ concentration determines the availability of free negative charges. Na⁺ concentrations in the low physiological range (below 140 mM) allow sufficient amounts of vacant negative charges so that adhesion of RBC to the endothelial surface is small. In contrast, Na⁺ in the high physiological range (beyond 140 mM) saturates the remaining negative surface charges thus increasing adhesion. Aldosterone receptor blockade by spironolactone prevents Na⁺ induced RBC adhesion to the endothelial glycocalyx. Extrapolation of in vitro experiments to in vivo conditions leads to the hypothesis that high sodium intake is likely to increase the incidence of thrombotic events.

Herbal drugs against cardiovascular disease: traditional medicine and modern development

Herbal products have been used as conventional medicines for thousands of years, particularly in Eastern countries. Thousands of clinical and experimental investigations have focused on the effects and mechanisms-of-action of herbal medicine in the treatment of cardiovascular diseases (CVDs). Considering the history of clinical practice and the great potentials of herb medicine and/or its ingredients, a review on this topic would be helpful. This article discusses possible effects of herbal remedies in the prevention and treatment of CVDs. Crucially, we also summarize some underlying pharmacological mechanisms for herb products in cardiovascular regulations, which might provide interesting information for further understanding the effects of herbal medicines, and boost the prospect of new herbal products against CVDs.

Cystic fibrosis transmembrane conductance regulator is involved in polyphenol-induced swelling of the endothelial glycocalyx

Previous studies show that polyphenol-rich compounds can induce a swelling of the endothelial glycocalyx (eGC). Our goal was to reveal the mechanism behind the eGC-swelling. As polyphenols are potent modulators of fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel, the hypothesis was tested whether polyphenol-induced increase in CFTR activity is responsible for the eGC-swelling. The impact of the polyphenols resveratrol, (-)-epicatechin, and quercetin on nanomechanics of living endothelial GM7373 cells was monitored by AFM-nanoindentation. The tested polyphenols lead to eGC-swelling with a simultaneous decrease in cortical stiffness. EGC-swelling, but not the change in cortical stiffness, was prevented by the inhibition of CFTR. Polyphenol-induced eGC-swelling could be mimicked by cytochalasin D, an actin-depolymerizing agent. Thus, in the vascular endothelium, polyphenols induce eGC-swelling by softening cortical actin and activating CFTR. Our findings imply that CFTR plays an important role in the maintenance of vascular homeostasis and may explain the vasoprotective properties of polyphenols.

FROM THE CLINICAL EDITOR

Many vascular problems clinically can be attributed to a dysregulation of endothelial glycocalyx (eGC). The underlying mechanism however remains unclear. In this article, the authors used nanoindentation and showed that polyphenols could swell the endothelial glycocalyx and alter its function. This investigative method can lead to further mechanistic studies of other molecular pathways.

Sodium selective erythrocyte glycocalyx and salt sensitivity in man

Negatively charged surfaces of erythrocytes (RBC) reflect properties of the endothelial glycocalyx. Plasma electrolytes counteract these charges and thus control the repulsive forces between RBC and endothelium. Although Na⁺ is supposed to exert a rather high affinity to the RBC surface, a direct comparison between Na⁺ and K⁺ in counteracting the RBC surface has been never made. Therefore, we measured Na⁺/K⁺ selectivity of the RBC surface in 20 healthy volunteers applying the previously published salt blood test (SBT). It turned out that the Na⁺/K⁺ selectivity ratio of the RBC glycocalyx is on average 6.1 ± 0.39 (ranging from 3 to 9 in different individuals). Considering standard plasma Na⁺ and K⁺ concentrations, binding probability of Na⁺/K⁺ at the RBC surface is about 180:1. The SBT reveals that plasma K⁺ counteracts only about 7 % of the negative charges in the RBC glycocalyx. As an in vivo proof of principle, a volunteer’s blood was continuously tested over 6 months while applying a glycocalyx protective polyphenol-rich natural compound (hawthorn extract). It turned out that RBC Na⁺ sensitivity (the inverse of Na⁺ buffer capacity) decreased significantly by about 25 % while Na⁺/K⁺ selectivity of the RBC glycocalyx declined only slightly by about 8 %. Taken together, (i) plasma Na⁺ selectively buffers the negative charges of the RBC glycocalyx, (ii) the contribution of K⁺ in counteracting these negative surface charges is small, and (iii) natural polyphenols applied in vivo increase RBC surface negativity. In conclusion, low plasma Na⁺ is supposed to favor frictionless RBC-slipping through blood vessels.

Nanomechanics of vascular endothelium

The mechanical characteristics of endothelial cells reveal four distinct compartments, namely glycocalyx, cell cortex, cytoplasm and nucleus. There is accumulating evidence that endothelial nanomechanics of these individual compartments control vascular physiology. Depending on protein composition, filament formation and interaction with cross-linker proteins, these four compartments determine endothelial stiffness. Structural organization and mechanical properties directly influence physiological processes such as endothelial barrier function, nitric oxide release and gene expression. This review will focus on endothelial nanomechanics and its impact on vascular function.

Vascular endothelium: a vulnerable transit zone for merciless sodium

In humans, when plasma sodium concentration rises slightly beyond 140 mM, vascular endothelium sharply stiffens and nitric oxide release declines. In search of a vascular sodium sensor, the endothelial glycocalyx was identified as being a negatively charged biopolymer capable of selectively buffering sodium ions. Sodium excess damages the glycocalyx and renders vascular endothelium increasingly permeable for sodium. In the long term, sodium accumulates in the interstitium and gradually damages the organism. It was discovered that circulating red blood cells (RBC) 'report' surface properties of the vascular endothelium. To some extent, the RBC glycocalyx mirrors the endothelial glycocalyx. A poor (charge-deprived) endothelial glycocalyx causes a poor RBC glycocalyx and vice versa. This observation led to the assumption that the current state of an individual's vascular endothelium in terms of electrical surface charges and sodium-buffering capabilities could be read simply from a blood sample. Recently, a so-called salt blood test was introduced that quantifies the RBC sodium buffer capacity and thus characterizes the endothelial function. The arguments are outlined in this article spanning a bridge from cellular nano-mechanics to clinical application.

Nanomechanics of the endothelial glycocalyx in experimental sepsis

The endothelial glycocalyx (eGC), a carbohydrate-rich layer lining the luminal side of the endothelium, regulates vascular adhesiveness and permeability. Although central to the pathophysiology of vascular barrier dysfunction in sepsis, glycocalyx damage has been generally understudied, in part because of the aberrancy of in vitro preparations and its degradation during tissue handling. The aim of this study was to analyze inflammation-induced damage of the eGC on living endothelial cells by atomic-force microscopy (AFM) nanoindentation technique. AFM revealed the existence of a mature eGC on the luminal endothelial surface of freshly isolated rodent aorta preparations ex vivo, as well as on cultured human pulmonary microvascular endothelial cells (HPMEC) in vitro. AFM detected a marked reduction in glycocalyx thickness (266 ± 12 vs. 137 ± 17 nm, P<0.0001) and stiffness (0.34 ± 0.03 vs. 0.21 ± 0.01 pN/mn, P<0.0001) in septic mice (1 mg E. coli lipopolysaccharides (LPS)/kg BW i.p.) compared to controls. Corresponding in vitro experiments revealed that sepsis-associated mediators, such as thrombin, LPS or Tumor Necrosis Factor-α alone were sufficient to rapidly decrease eGC thickness (-50%, all P<0.0001) and stiffness (-20% P<0.0001) on HPMEC. In summary, AFM nanoindentation is a promising novel approach to uncover mechanisms involved in deterioration and refurbishment of the eGC in sepsis.

The role of ENaC in vascular endothelium

Once upon a time, the expression of the epithelial sodium channel (ENaC) was mainly assigned to the kidneys, colon and sweat glands where it was considered to be the main determinant of sodium homeostasis. Recent, though indirect, evidence for the possible existence of ENaC in a non-epithelial tissue was derived from the observation that the vascular endothelium is a target for aldosterone. Inhibitory actions of the intracellular aldosterone receptors by spironolactone and, more directly, by ENaC blockers such as amiloride supported this view. Shortly after, direct data on the expression of ENaC in vascular endothelium could be demonstrated. There, endothelial ENaC (EnNaC) could be defined as a major regulator of cellular mechanics which is a critical parameter in differentiating between vascular function and dysfunction. Foremost, the mechanical stiffness of the endothelial cell cortex, a layer 50-200 nm beneath the plasma membrane, has been shown to play a crucial role as it controls the production of the endothelium-derived vasodilator nitric oxide (NO) which directly affects the tone of the vascular smooth muscle cells. In contrast to soft endothelial cells, stiff endothelial cells release reduced amounts of NO, the hallmark of endothelial dysfunction. Thus, the combination of endothelial stiffness and myogenic tone might increase the peripheral vascular resistance. An elevation of arterial blood pressure is supposed to be the consequence of such functional changes. In this review, EnNaC is discussed as an aldosterone-regulated plasma membrane protein of the vascular endothelium that could significantly contribute to maintaining of an appropriate arterial blood pressure but, if overexpressed, could participate in the pathogenesis of arterial hypertension.

Determination of erythrocyte sodium sensitivity in man

Sodium buffer capacity of vascular endothelium depends on an endothelial glycocalyx rich in negatively charged heparan sulfate. It has been shown recently that after the mechanical interaction of blood with heparan sulfate-depleted endothelium, erythrocytes also lose this glycocalyx constituent. This observation led to the conclusion that the vascular sodium buffer capacity of an individual could be derived from a blood sample. A test system (salt blood test (SBT)) was developed based upon the sodium-dependent erythrocyte zeta potential. Erythrocyte sedimentation velocity was measured in isosmotic, biopolymer-supplemented electrolyte solutions of different sodium concentrations. Erythrocyte sodium sensitivity (ESS), inversely related to erythrocyte sodium buffer capacity, was expressed as the ratio of the erythrocyte sedimentation velocities of 150 mM over 125 mM Na⁺ solutions (ESS = Na⁺₁₅₀/Na⁺₁₂₅). In 61 healthy individuals (mean age, 23 ± 0.5 years), ESS ranged between 2 and 8. The mean value was 4.3 ± 0.19. The frequency distribution shows two peaks, one at about 3 and another one at about 5. To test whether ESS reflects changes of the endothelial glycocalyx, a cultured endothelial monolayer was exposed for 3 hours to a rhythmically moving blood layer (drag force experiment). When applying this procedure, we found that ESS was reduced by about 21 % when the endothelium was pretreated for 4 days with the glycocalyx protective agent WS 1442. In conclusion, the SBT could possibly serve as an in vitro test system for the evaluation of erythrocyte/vascular salt sensitivity allowing follow-up measurements in the prevention and treatment of vascular dysfunctions.

Vascular endothelium leaves fingerprints on the surface of erythrocytes

Gliding of red blood cells (RBC) through blood vessels is mediated by the negatively charged glycocalyx located on the surfaces of both RBC and endothelial cells (EC). In various vasculopathies, EC gradually lose this protective surface layer. As a consequence, RBC come into close physical contact with the vascular endothelium. It is hypothesized that the RBC glycocalyx could be adversely affected by a poor EC glycocalyx. This hypothesis was tested by evaluating the RBC and EC surface layers with atomic force microscopy techniques. In the first series of experiments, EC monolayers grown in culture were exposed to rhythmic drag forces exerted from a blood overlay (drag force treatment), and thereafter, the EC surface was investigated in terms of thickness and adhesiveness. In the second series, the glycocalyx of the EC monolayers was disturbed by enzymatic cleavage of negatively charged heparan sulfates before drag force treatment, and thereafter, the RBC surface was evaluated. In the third series, the RBC glycocalyx of the blood overlay was enzymatically disturbed before drag force treatment, and thereafter, the EC surface was evaluated. A strong positive correlation between the RBC and EC surface properties was found (r (2) = 0.95). An enzymatically affected EC glycocalyx lead to the shedding of the RBC glycocalyx and vice versa. It is concluded that there is physical interaction between the blood and endothelium. Apparently, the RBC glycocalyx reflects properties of the EC glycocalyx. This observation could have a significant impact on diagnosis and treatment of cardiovascular diseases.

Grape seed proanthocyanidin extracts enhance endothelial nitric oxide synthase expression through 5'-AMP activated protein kinase/Surtuin 1-Krüpple like factor 2 pathway and modulate blood pressure in ouabain induced hypertensive rats

Grape seed proanthocyanidin extracts (GSPE) belonging to polyphenols, possess various biological effects including anti-inflammation, anti-oxidant, anti-aging, anti-atherosclerosis, etc. GSPE is potential in regulating endothelial function. However, the underlying mechanism is not clear yet. In this study, by small interfering RNA (siRNA) knocking down, we proved that GSPE increase endothelial nitric oxide synthase (eNOS) expression in human umbilical vessel cells (HUVECs) in vitro, which was attributed to its transcription factor Krüpple like factor 2 (KLF2) induction. Furthermore, GSPE activate 5'-AMP activated protein kinase (AMPK) and increase surtuin 1 (SIRT1) protein level, critical for KLF2 induction. We also illuminated the role of GSPE in hypertension treatment. By chronic administration of GSPE in ouabain induced hypertensive rats model, we access the effect of GSPE on blood pressure regulation and the possible mechanisms involved. After 5 weeks feeding, GSPE significantly block the ouabain induced blood pressure increase. The aortic NO production impaired by ouabain was improved. In conclusion, GSPE increase eNOS expression and NO production in an AMPK/SIRT1 dependent manner through KLF2 induction, and attenuate ouabain induced hypertension.

A physiological concept unmasking vascular salt sensitivity in man

About one third of the population worldwide is supposed to be salt sensitive which is a major cause for arterial hypertension later in life. For preventive actions it is thus desirable to identify salt-sensitive individuals before the appearance of clinical symptoms. Recent observations suggest that the vascular endothelium consists of two salt-sensitive barriers in series, the glycocalyx that buffers sodium and the endothelial cell membrane that contains sodium channels. Glycocalyx sodium buffer capacity and sodium channel activity are conversely related to each other. For proof of concept, a so-called salt provocation test (SPT) was developed that should unmask vascular salt sensitivity in humans at virtually any age. Nineteen healthy subjects, ranging from 25 to 63 years of age, underwent two series of 1-h blood pressure measurements after acute ingestion of a salt cocktail with or without addition of a sodium channel blocker effective in vascular endothelium. Differential analysis of the changes in diastolic blood pressure (net ∆DP) identified 12 individuals (63 %) as being salt resistant (net ∆DP = −0.05 ± 0.62 mmHg) and seven individuals (37 %) as being salt sensitive (net ∆DP = +6.98 ± 0.75 mmHg). Vascular salt sensitivity was not related to the age of the study participants. It is concluded that the SPT could be useful for identifying vascular salt sensitivity in humans already early in life.

Two barriers for sodium in vascular endothelium?

Vascular endothelium plays a key role in blood pressure regulation. Recently, it has been shown that a 5% increase of plasma sodium concentration (sodium excess) stiffens endothelial cells by about 25%, leading to cellular dysfunction. Surface measurements demonstrated that the endothelial glycocalyx (eGC), an anionic biopolymer, deteriorates when sodium is elevated. In view of these results, a two-barrier model for sodium exiting the circulation across the endothelium is suggested. The first sodium barrier is the eGC which selectively buffers sodium ions with its negatively charged proteoglycans. The second sodium barrier is the endothelial plasma membrane which contains sodium channels. Sodium excess, in the presence of aldosterone, leads to eGC break-down and, in parallel, to an up-regulation of plasma membrane sodium channels. The following hypothesis is postulated: Sodium excess increases vascular sodium permeability. Under such conditions (e.g. high-sodium diet), day-by-day ingested sodium, instead of being readily buffered by the eGC and then rapidly excreted by the kidneys, is distributed in the whole body before being finally excreted. Gradually, the sodium overload damages the organism.