Skin Sodium and Hypertension: a Paradigm Shift?

Pathophysiology of primary hypertension in children and adolescents

The progress in research on the physiology of the cardiovascular system made in the last 100 years allowed for the development of the pathogenesis not only of secondary forms of hypertension but also of primary hypertension. The main determinants of blood pressure are described by the relationship between stroke volume, heart rate, peripheral resistance, and arterial stiffness. The theories developed by Guyton and Folkow describe the importance of the volume factor and total peripheral resistance. However, none of them fully presents the pathogenesis of essential hypertension. The multifactorial model of primary hypertension pathogenesis developed by Irving Page in the 1940s, called Page's mosaic, covers most of the pathophysiological phenomena observed in essential hypertension. The most important pathophysiological phenomena included in Page's mosaic form a network of interconnected "nodes". New discoveries both from experimental and clinical studies made in recent decades have allowed the original Page mosaic to be modified and the addition of new pathophysiological nodes. Most of the clinical studies confirming the validity of the multifactorial pathogenesis of primary hypertension concern adults. However, hypertension develops in childhood and is even perinatally programmed. Therefore, the next nodes in Page's mosaic should be age and perinatal factors. This article presents data from pediatric clinical trials describing the most important pathophysiological processes associated with the development of essential hypertension in children and adolescents.

Trace Elements in Stenella coeruleoalba: Assessment of Marine Environmental Pollution and Dolphin Health Status

Heavy metals are environmental contaminants and can easily accumulate and biomagnify in various marine species (fishes and mammalians) at the top of the aquatic food chain. Among marine mammalians, the striped dolphin (Stenella coeruleoalba) is the most abundant cetacean in the Mediterranean Sea and is considered to be a sentinel species to monitor the environmental marine pollution. In this study, the contents of toxic metals and metalloids (Cd, Pb, Hg, and As), micro-elements (Ni, Cr, Cu, Fe, Co, Mn, Se and Zn) and macro-elements (Na, Ca, K, Mg and P) were evaluated by ICP-MS analysis in several organs/tissues (lung, skin, muscle and liver) of Stenella coeruleoalba. The assessment of marine environmental pollution and dolphins health status was carried out through further analysis of the same specific parameters such as the metal pollution index (MPI) and coefficient of condition (K). Finally, the correlation between toxic metals and metalloids and essential micro-elements, expressed as molar ratios, was analyzed to evaluate the detoxifying ability (effectiveness) of Zn, Se and Cu. Data obtained showed the presence of toxic metals and metalloids analyzed in the Stenella coeruleoalba samples but the MPI values suggested a low environmental contamination of the Mediterranean Sea where dolphins lived. The content of micro- and macro-elements was found to be in a normal range for this species and predictive of dolphins good health status, as confirmed by the coefficient of condition K. However, the correlation between toxic and essential metals, expressed as molar ratios, showed that the following toxic metals cannot be detoxified by the essential metals: 66Zn/201Hg, 82Se/201Hg, 63Cu/201Hg and 66Zn/52Cr, 82Se/52Cr, 63Cu/52Cr. Therefore, this study highlights the key role of dolphin Stenella coeruleoalba to assess marine pollution and the importance of analyzing the complete mineral profile to evaluate the animal health status.

Impact of homeostatic body hydration status, evaluated by hemodynamic measures, on different pain sensitization paths to a chronic pain syndrome

Contrasting findings on the mechanisms of chronic pain and hypertension development render the current conventional evidence of a negative relationship between blood pressure (BP) and pain severity insufficient for developing personalized treatments. In this interdisciplinary study, patients with fibromyalgia (FM) exhibiting clinically normal or elevated BP, alongside healthy participants were assessed. Different pain sensitization responses were evaluated using a dynamic 'slowly repeated evoked pain' (SREP) measure, as well as static pain pressure threshold and tolerance measures. Cardiovascular responses to clino-orthostatic (lying-standing) challenges were also examined as acute re- and de-hydration events, challenging cardiovascular and cerebrovascular homeostasis. These challenges involve compensating effects from various cardiac preload or afterload mechanisms associated with different homeostatic body hydration statuses. Additionally, hair cortisol concentration was considered as a factor with an impact on chronic hydration statuses. Pain windup (SREP) and lower pain threshold in FM patients were found to be related to BP rise during clinostatic (lying) rehydration or orthostatic (standing) dehydration events, respectively. These events were determined by acute systemic vasoconstriction (i.e., cardiac afterload response) overcompensating for clinostatic or orthostatic cardiac preload under-responses (low cardiac output or stroke volume). Lower pain tolerance was associated with tonic blood pressure reduction, determined by permanent hypovolemia (low stroke volume) decompensated by permanent systemic vasodilation. In conclusion, the body hydration status profiles assessed by (re)activity of systemic vascular resistance and effective blood volume-related measures can help predict the risk and intensity of different pain sensitization components in chronic pain syndrome, facilitating a more personalized management approach.

Muscle Sodium Accumulation in Kidney Failure: Physiological Impact and Mitigation Strategies

Skeletal muscle has recently been recognized as a nonosmotic sodium reservoir that buffers dietary sodium. The in-vivo quantification of muscle sodium is based on a novel technology, sodium magnetic resonance imaging. Studies using this technology have shown that muscle sodium accumulation may be a clinical complication of chronic kidney disease (CKD). This review aims to summarize existing evidence on muscle sodium accumulation in patients with CKD and to identify knowledge gaps and topics for further research. The literature examined in this review suggests that muscle sodium accumulation is associated with CKD progression and pathological conditions. However, the causalities between muscle sodium accumulation and its related pathological changes are still elusive mainly because it is still uncertain where and how sodium accumulates in the muscle. More research is needed to address these gaps and determine if muscle sodium is a new intervention target in CKD.

Sodium in the skin: a summary of the physiology and a scoping review of disease associations

A large and growing body of research suggests that the skin plays an important role in regulating total body sodium, challenging traditional models of sodium homeostasis that focused exclusively on blood pressure and the kidney. In addition, skin sodium may help to prevent water loss and facilitate macrophage-driven antimicrobial host defence, but may also trigger immune dysregulation via upregulation of proinflammatory markers and downregulation of anti-inflammatory processes. We performed a systematic search of PubMed for published literature on skin sodium and disease outcomes and found that skin sodium concentration is increased in patients with cardiometabolic conditions including hypertension, diabetes and end-stage renal disease; autoimmune conditions including multiple sclerosis and systemic sclerosis; and dermatological conditions including atopic dermatitis, psoriasis and lipoedema. Several patient characteristics are associated with increased skin sodium concentration including older age and male sex. Animal evidence suggests that increased salt intake results in higher skin sodium levels; however, there are conflicting results from small trials in humans. Additionally, limited data suggest that pharmaceuticals such as diuretics and sodium-glucose co-transporter-2 inhibitors approved for diabetes, as well as haemodialysis may reduce skin sodium levels. In summary, emerging research supports an important role for skin sodium in physiological processes related to osmoregulation and immunity. With the advent of new noninvasive magnetic resonance imaging measurement techniques and continued research on skin sodium, it may emerge as a marker of immune-mediated disease activity or a potential therapeutic target.

Hypertensive heart disease: risk factors, complications and mechanisms

Hypertensive heart disease constitutes functional and structural dysfunction and pathogenesis occurring primarily in the left ventricle, the left atrium and the coronary arteries due to chronic uncontrolled hypertension. Hypertensive heart disease is underreported and the mechanisms underlying its correlates and complications are not well elaborated. In this review, we summarize the current understanding of hypertensive heart disease, we discuss in detail the mechanisms associated with development and complications of hypertensive heart disease especially left ventricular hypertrophy, atrial fibrillation, heart failure and coronary artery disease. We also briefly highlight the role of dietary salt, immunity and genetic predisposition in hypertensive heart disease pathogenesis.

A profile of SGLT-2 inhibitors in hyponatremia: The evidence to date

Hyponatremia is the most common electrolyte disorder in clinical practice, which may lead to life-threatening complications. Several lines of evidence suggest that hyponatremia is associated not only with significant increases in length of stay, cost, and financial burden, but also with increased morbidity and mortality. Hyponatremia is also considered to be a negative prognostic factor in patients with heart failure and cancer. Although multiple therapeutic methods are available for treating hyponatremia, most have some limitations, such as poor compliance, rapid correction of serum Na⁺, other negative side effects and high cost. Given these limitations, identifying novel therapies for hyponatremia is essential. Recent clinical studies have shown that SGLT-2 inhibitors (SGLT 2i) significantly increased serum Na⁺ levels and were well tolerated by patients who underwent this treatment. Therefore, oral administration of SGLT 2i appears to be an effective treatment for hyponatremia. This article will briefly review the etiology of hyponatremia and integrated control of sodium within the kidney, current therapies for hyponatremia, potential mechanisms and efficacy of SGLT 2i for hyponatremia, and the benefits in cardiovascular, cancer, and kidney disease by regulating sodium and water balance.

Skin regulation of salt and blood pressure and potential clinical implications

Sodium chloride, as salt, gives rise to hypertension. Nevertheless, individual susceptibility to the ramifications of sodium chloride is heterogeneous. The conventional nephron-centric regulation of sodium with neurohormonal inputs and responses is now expanded to include an intricate extrarenal pathway including the endothelium, skin, lymphatics, and immune cells. An overabundance of sodium is buffered and regulated by the skin interstitium. Excess sodium passes through (and damages) the vascular endothelium and can be dynamically stored in the skin, modulated by skin immune cells and lymphatics. This excess interstitially stored sodium is implicated in hypertension, cardiovascular dysfunction, metabolic disruption, and inflammatory dysregulation. This extrarenal pathway of regulating sodium represents a novel target for better blood pressure management, rebalancing disturbed inflammation, and hence addressing cardiovascular and metabolic disease.

Salt, Not Always a Cardiovascular Enemy? A Mini-Review and Modern Perspective

Dietary salt intake is a long-debated issue. Increased sodium intake is associated with high blood pressure, leading to salt-sensitive hypertension. Excessive salt intake leads to arterial stiffness in susceptible individuals via impaired nitric oxide action and increased endothelin-1 expression, overactivity of the renal sympathetic nervous system and also via aldosterone-independent activation of the mineralocorticoid receptor. Salt restriction in such individuals reduces blood pressure (BP) values. The optimal level of salt restriction that leads to improved cardiovascular outcomes is still under debate. Current BP and dietary guidelines recommend low sodium intake for the general population. However, a specific category of patients does not develop arterial hypertension in response to sodium loading. In addition, recent research demonstrates the deleterious effects of aggressive sodium restriction, even in heart failure patients. This mini review discusses current literature data regarding the advantages and disadvantages of salt restriction and how it impacts the overall health status.

An Overview of the Latest Metabolomics Studies on Atopic Eczema with New Directions for Study

Atopic eczema (AE) is an inflammatory skin disorder affecting approximately 20% of children worldwide and early onset can lead to asthma and allergies. Currently, the mechanisms of the disease are not fully understood. Metabolomics, the analysis of small molecules in the skin produced by the host and microbes, opens a window to observe the mechanisms of the disease which then may lead to new drug targets for AE treatment. Here, we review the latest advances in AE metabolomics, highlighting both the lipid and non-lipid molecules, along with reviewing the metabolites currently known to reside in the skin.

Oxidative Stress Induced by High Salt Diet—Possible Implications for Development and Clinical Manifestation of Cutaneous Inflammation and Endothelial Dysfunction in Psoriasis vulgaris

Although oxidative stress is recognized as an important effector mechanism of the immune system, uncontrolled formation of reactive oxygen and nitrogen species promotes excessive tissue damage and leads to disease development. In view of this, increased dietary salt intake has been found to damage redox systems in the vessel wall, resulting in endothelial dysfunction associated with NO uncoupling, inflammation, vascular wall remodeling and, eventually, atherosclerosis. Several studies have reported increased systemic oxidative stress accompanied by reduced antioxidant capacity following a high salt diet. In addition, vigorous ionic effects on the immune mechanisms, such as (trans)differentiation of T lymphocytes are emerging, which together with the evidence of NaCl accumulation in certain tissues warrants a re-examination of the data derived from in vitro research, in which the ionic influence was excluded. Psoriasis vulgaris (PV), as a primarily Th17-driven inflammatory skin disease with proven inflammation-induced accumulation of sodium chloride in the skin, merits our interest in the role of oxidative stress in the pathogenesis of PV, as well as in the possible beneficial effects that could be achieved through modulation of dietary salt intake and antioxidant supplementation.

Beyond the Gastrointestinal Tract: Oral and Sex-Specific Skin Microbiota Are Associated with Hypertension in Rats with Genetic Disparities

Current knowledge of the link between microbiota and hypertension is limited to the gut. Besides the gut, oral cavity and skin are other locations where sodium chloride (NaCl) is in direct contact with microbiota. While oral nitrate reducing-bacteria generate nitric oxide, which lead to vasodilation and lowering of blood pressure (BP), the skin excretes sodium via sweat glands and is an important site for sodium and BP homeostasis. However, knowledge on the contributions of oral and skin microbiota to BP regulation, is limited. Therefore, the current study was conducted to compare the tripartite relationship between site, sex, and genetic effects on the composition of oral, skin and gut microbiota impacting hypertension. Microbiota were profiled from the oral cavity, skin and feces of both male and female hypertensive Dahl salt-sensitive (S) and congenic rats with genomic substitutions on rat chromosomes (RNO) 1, 5, 9 and 10, demonstrating disparate BP effects. Sex-specific differences in β-diversity were observed only in skin microbiota. The most abundant taxa of the oral and skin microbiota were Actinobacteria and Cyanobacteria, respectively. Oral Actinobacteria were inversely associated with BP. While the abundance of oral Actinobacteria was upregulated by the BP locus on RNO10 in both sexes, depletion of skin Cyanobacteria decreased the protection from hypertension in the RNO5 female, but not male, congenic strain. In conclusion, this is the first study to identify specific microbiota in sites other than gut as contributors to BP regulation. Notably, both oral Actinobacteria and skin Cyanobacteria were beneficial for lowering BP.

Tissue Sodium Accumulation: Pathophysiology and Clinical Implications

Excessive sodium intake has been well established as a risk factor for the development and progression of cardiovascular and renal diseases. Its adverse effects are achieved by renal sodium retention and related volume expansion and by inducing low-grade inflammation and oxidative stress (OS) in the target tissues. This review presents the recent concept of nonosmotic sodium storage in the skin interstitium, the subsequent dissociation of sodium and volume homeostasis, and the cellular response to the increased tissue sodium concentration. Furthermore, data are shown on the sodium barrier and buffering potential of the endothelial glycocalyx that may protect the functional integrity of the endothelium when it is challenged by an increased sodium load. Finally, examples will be given of the involvement of oxygen free radicals (OFR) in sodium-induced tissue damage, and some clinical entities will be mentioned that are causally associated with sodium/volume retention and OS.

Dietary sodium and health: How much is too much for those with orthostatic disorders?

High dietary salt (NaCl) increases blood pressure (BP) and can adversely impact multiple target organs including the vasculature, heart, kidneys, brain, autonomic nervous system, skin, eyes, and bone. However, patients with orthostatic disorders are told to increase their NaCl intake to help alleviate symptoms. While there is evidence to support the short-term benefits of increasing NaCl intake in these patients, there are few studies assessing the benefits and side effects of long-term high dietary NaCl. The evidence reviewed suggests that high NaCl can adversely impact multiple target organs, often independent of BP. However, few of these studies have been performed in patients with orthostatic disorders. We conclude that the recommendation to increase dietary NaCl in patients with orthostatic disorders should be done with care, keeping in mind the adverse impact on dietary NaCl in people without orthostatic disorders. Modest, rather than robust, increases in NaCl intake may be sufficient to alleviate symptoms but also minimize any long-term negative effects.

Ode to Salt: Commentary on "Skin Sodium Accumulates in Psoriasis and Reflects Disease Severity"

"Skin Sodium Accumulates in Psoriasis and Reflects Disease Severity" (Maifeld et al., 2021) showed that skin sodium ion (Na+) is increased in patients with a PASI > 5. Na+ concentration as well as its content were increased in these patients, supporting the proposed mechanism that increased Na+ concentrations enhance IL-17 expression from CD4+ cells. These data initially were generated using a noninvasive technique, sodium (23Na) magnetic resonance imaging, and then were verified using 23Na spectroscopy and atomic absorption spectrometry in ashed-skin biopsies in humans and also using mouse models of psoriasis. These findings suggest a novel pathologic mechanism for psoriasis development and target for treatment.

Ageing attenuates the effect of extracellular hyperosmolality on whole-body heat exchange during exercise-heat stress

KEY POINTS

In humans, hypohydration attenuates sweat secretion and attenuates whole-body heat loss, probably to mitigate further fluid losses and thereby support blood pressure regulation. Recently, however, we demonstrated that the hypohydration-mediated reduction in net whole-body heat exchange (evaporative heat loss - dry heat gain) was blunted in middle-aged compared to younger men during moderate exercise in dry heat; albeit, the underpinning mechanisms could not be determined. Here we evaluated the hypothesis that those findings stemmed from a diminished influence of extracellular hyperosmolality on net whole-body heat exchange in middle-aged-to-older compared to young men. Consistent with that hypothesis, extracellular hyperosmolality induced by an intravenous infusion of hypertonic saline (3% NaCl) reduced net heat exchange and augmented rectal temperature to a greater extent in the young compared to middle-aged-to-older men. Thus, age-related differences in the influence of hypohydration on thermoregulatory function appear to be due to blunted sensitivity to hyperosmolality with ageing.

ABSTRACT

We recently demonstrated that sweating-induced hypohydration attenuated whole-body heat dissipation to a greater extent in young compared to middle-aged men during exercise-heat stress. Here, we evaluated whether this divergent response stemmed from an attenuated influence of extracellular hyperosmolality on heat exchange with ageing. To achieve this, ten young (mean (SD): 25 (5) years) and ten middle-aged-to-older (61 (5) years) men completed two trials involving a 90-min intravenous infusion of isosmotic saline (0.9% NaCl; ISO) or hyperosmotic saline (3.0% NaCl; HYP) followed by 60 min of cycling at a fixed metabolic heat production of 250 W/m² (∼50% peak aerobic power) in dry heat (40°C, ∼17% relative humidity). Whole-body net heat exchange (evaporative heat loss - dry heat gain) was measured via direct calorimetry. Rectal temperature was monitored continuously. Heat exchange was attenuated in HYP compared to ISO in the young (233 (20) vs. 251 (17) W/m² ; P = 0.002) but not older group (229 (16) vs. 227 (20) W/m² ; P = 0.621). Further, heat exchange was lower in the middle-aged-to-older vs. young men in ISO (P = 0.034) but not in HYP (P = 0.623). Similarly, end-exercise rectal temperature was greater in HYP relative to ISO in the young (38.3 (0.4)°C vs. 37.9 (0.3)°C; P = 0.015) but not the middle-aged-to-older men (38.3 (0.3)°C vs. 38.2 (0.2)°C; P = 0.652). Compared to the young, rectal temperature was greater in the middle-aged-to-older during ISO (P = 0.035) whereas no between-group difference was observed in HYP (P = 0.746). Our findings indicate that ageing blunts the effect of extracellular hyperosmolality on thermoregulatory function during exercise-heat stress.

Salt sensitivity and hypertension

Salt sensitivity refers to the physiological trait present in mammals, including humans, by which the blood pressure (BP) of some members of the population exhibits changes parallel to changes in salt intake. It is commoner in elderly, females, Afro-Americans, patients with chronic kidney disease (CKD) and insulin resistance. Increased salt intake promotes an expansion of extracellular fluid volume and increases cardiac output. Salt-sensitive individuals present an abnormal kidney reaction to salt intake; the kidneys retain most of the salt due to an abnormal over-reactivity of sympathetic nervous system and a blunted suppression of renin-angiotensin axis. Moreover, instead of peripheral vascular resistance falling, salt-sensitive subjects present increased vascular resistance due mainly to impaired nitric oxide synthesis in endothelium. Recent studies have shown that part of the dietary salt loading accumulates in skin. Hypertensive and patients with CKD seem to have more sodium in skin comparing to healthy ones. However, we still have not fully explained the link between skin sodium, BP and salt sensitivity. Finally, although salt sensitivity plays a meaningful role in BP pathophysiology, it cannot be used by the physician in everyday patient's care, mainly due to lack of a simple and practical diagnostic test.

A Role of Inflammation and Immunity in Essential Hypertension-Modeled and Analyzed Using Petri Nets

Recent studies have shown that the innate and adaptive immune system, together with low-grade inflammation, may play an important role in essential hypertension. In this work, to verify the importance of selected factors for the development of essential hypertension, we created a Petri net-based model and analyzed it. The analysis was based mainly on t-invariants, knockouts of selected fragments of the net and its simulations. The blockade of the renin-angiotensin (RAA) system revealed that the most significant effect on the emergence of essential hypertension has RAA activation. This blockade affects: (1) the formation of angiotensin II, (2) inflammatory process (by influencing C-reactive protein (CRP)), (3) the initiation of blood coagulation, (4) bradykinin generation via the kallikrein-kinin system, (5) activation of lymphocytes in hypertension, (6) the participation of TNF alpha in the activation of the acute phase response, and (7) activation of NADPH oxidase-a key enzyme of oxidative stress. On the other hand, we found that the blockade of the activation of the RAA system may not eliminate hypertension that can occur due to disturbances associated with the osmotically independent binding of Na in the interstitium. Moreover, we revealed that inflammation alone is not enough to trigger primary hypertension, but it can coexist with it. We believe that our research may contribute to a better understanding of the pathology of hypertension. It can help identify potential subprocesses, which blocking will allow better control of essential hypertension.

Sodium Intake and Hypertension

The close relationship between hypertension and dietary sodium intake is widely recognized and supported by several studies. A reduction in dietary sodium not only decreases the blood pressure and the incidence of hypertension, but is also associated with a reduction in morbidity and mortality from cardiovascular diseases. Prolonged modest reduction in salt intake induces a relevant fall in blood pressure in both hypertensive and normotensive individuals, irrespective of sex and ethnic group, with larger falls in systolic blood pressure for larger reductions in dietary salt. The high sodium intake and the increase in blood pressure levels are related to water retention, increase in systemic peripheral resistance, alterations in the endothelial function, changes in the structure and function of large elastic arteries, modification in sympathetic activity, and in the autonomic neuronal modulation of the cardiovascular system. In this review, we have focused on the effects of sodium intake on vascular hemodynamics and their implication in the pathogenesis of hypertension.

The Influence of Dietary Salt Beyond Blood Pressure

PURPOSE OF REVIEW

Excess sodium from dietary salt (NaCl) is linked to elevations in blood pressure (BP). However, salt sensitivity of BP varies widely between individuals and there are data suggesting that salt adversely affects target organs, irrespective of BP.

RECENT FINDINGS

High dietary salt has been shown to adversely affect the vasculature, heart, kidneys, skin, brain, and bone. Common mediators of the target organ dysfunction include heightened inflammation and oxidative stress. These physiological alterations may contribute to disease development over time. Despite the adverse effects of salt on BP and several organ systems, there is controversy surrounding lower salt intakes and cardiovascular outcomes. Our goal here is to review the physiology contributing to BP-independent effects of salt and address the controversy around lower salt intakes and cardiovascular outcomes. We will also address the importance of background diet in modulating the effects of dietary salt.

Interplay of Na+ Balance and Immunobiology of Dendritic Cells

Local Na⁺ balance emerges as an important factor of tissue microenvironment. On the one hand, immune cells impact on local Na⁺ levels. On the other hand, Na⁺ availability is able to influence immune responses. In contrast to macrophages, our knowledge of dendritic cells (DCs) in this state of affair is rather limited. Current evidence suggests that the impact of increased Na⁺ on DCs is context dependent. Moreover, it is conceivable that DC immunobiology might also be influenced by Na⁺-rich-diet-induced changes of the gut microbiome.