Salt, water and nephron: Mechanisms of action and link to hypertension and chronic kidney disease

Hesperidin improves physiological outcomes in an arginine vasopressin rat model of pre-eclampsia

BACKGROUND

Hesperidin, a flavanone commonly found in citrus fruits and herbal formulations, has emerged as a potential new therapeutic agent for modulating several diseases. Since pre-eclampsia is a growing public health threat, it may negatively impact the economy and increase the disease burden of South Africa. Phytocompounds are easily accessible, demonstrate minimal side effects, and may confer novel medicinal options as a treatment and preventive preference.

OBJECTIVE

To investigate the physiological, biochemical, and hematological outcomes of hesperidin in an arginine vasopressin (AVP)-induced rodent model of pre-eclampsia.

METHODS

Female Sprague-Dawley rats were surgically implanted with mini-osmotic pumps to deliver AVP (200 ng/h) subcutaneously. Animals were treated with hesperidin at 200 mg/kg.b.w via oral gavage for 14 days. Systolic and diastolic blood pressures were measured on GD 7, 14, and 18 using a non-invasive tail-cuff method and were euthanized on GD 21.

RESULTS

The findings showed that hesperidin administration significantly decreased blood pressure (P < 0.05) and urinary protein levels in pregnant rats (P < 0.001). Placental and individual pup weight also increased significantly in the pregnant hesperidin-treated groups compared to AVP untreated groups (P < 0.001). Biochemical and hematological markers such as white blood cell count and lymphocyte levels differed significantly (P < 0.05) in AVP groups treated with and without hesperidin.

CONCLUSION

Our results suggest that hesperidin is an antihypertensive agent with modes of action associated with its diuretic and blood pressure lowering effects and reduction of proteinuria in AVP-induced pre-eclamptic rats.

When the tap runs dry: The multi-tissue gene expression and physiological responses of water deprived Peromyscus eremicus

The harsh and dry conditions of desert environments have resulted in genomic adaptations, allowing for desert organisms to withstand prolonged drought, extreme temperatures, and limited food resources. Here, we present a comprehensive exploration of gene expression across five tissues (kidney, liver, lung, gastrointestinal tract, and hypothalamus) and 19 phenotypic measurements to explore the whole-organism physiological and genomic response to water deprivation in the desert-adapted cactus mouse (Peromyscus eremicus). The findings encompass the identification of differentially expressed genes and correlative analysis between phenotypes and gene expression patterns across multiple tissues. Specifically, we found robust activation of the vasopressin renin-angiotensin-aldosterone system (RAAS) pathways, whose primary function is to manage water and solute balance. Animals reduce food intake during water deprivation, and upregulation of PCK1 highlights the adaptive response to reduced oral intake via its actions aimed at maintained serum glucose levels. Even with such responses to maintain water balance, hemoconcentration still occurred, prompting a protective downregulation of genes responsible for the production of clotting factors while simultaneously enhancing angiogenesis which is thought to maintains tissue perfusion. In this study, we elucidate the complex mechanisms involved in water balance in the desert-adapted cactus mouse, P. eremicus. By prioritizing a comprehensive analysis of whole-organism physiology and multi-tissue gene expression in a simulated desert environment, we describe the complex and successful response of regulatory processes.

Novel Therapeutic Approaches in the Management of Chronic Kidney Disease

Chronic kidney disease (CKD) is a progressive and incurable disease that impairs kidney function. Its prevalence is estimated to affect up to 800 million individuals within the general population, and patients with diabetes and hypertension are particularly at risk. This disorder disrupts the physiological mechanisms of the body, including water and electrolyte balance, blood pressure regulation, the excretion of toxins, and vitamin D metabolism. Consequently, patients are exposed to risks such as hyperkalemia, hyperphosphatemia, metabolic acidosis, and blood pressure abnormalities. These risks can be reduced by implementing appropriate diagnostic methods, followed by non-pharmacological (such as physical activity, dietary, and lifestyle adjustment) and pharmacological strategies after diagnosis. Selecting the appropriate diet and suitable pharmacological treatment is imperative in maintaining kidney function as long as possible. Drugs such as finerenone, canakinumab, and pentoxifylline hold promise for improved outcomes among CKD patients. When these interventions prove insufficient, renal replacement therapy becomes essential. This is particularly critical in preserving residual renal function while awaiting renal transplantation or for patients deemed ineligible for such a procedure. The aim of this study is to present the current state of knowledge and recent advances, providing novel insights into the treatment of chronic kidney disease.

Association between CORIN methylation and hypertension in Chinese adults

Background

Corin, a physical activator of atrial natriuretic peptide, has been associated with hypertension with unclear mechanisms. Here, we aimed to examine whether CORIN gene methylation was involved in the underlying molecular mechanisms.

Methods

DNA methylation levels of CORIN were measured by target bisulfite sequencing using genomic DNA isolated from peripheral blood mononuclear cells in 2498 participants in the Gusu cohort (discovery sample) and 1771 independent participants (replication sample). We constructed a mediation model with DNA methylation as the predictor, serum corin as the mediator, and hypertension as the outcome, adjusting for covariates. Multiple testing was controlled by false discovery rate (FDR) approach.

Results

Of the 9 CpGs assayed, hypermethylation at all CpGs were significantly associated with a lower level of blood pressure in the discovery sample and eight associations were also significant in the replication sample (all FDR-adjusted p&lt;0.05). Serum corin mediated approximately 3.07% (p=0.004), 6.25% (p=0.002) and 10.11% (p=0.034) of the associations of hypermethylation at one CpG (Chr4:47840096) with systolic and diastolic blood pressure, and hypertension, respectively. All these mediations passed the causal inference test.

Conclusions

These results suggest that hypermethylation in the CORIN gene is associated with a lower odds of prevalent hypertension and may be involved in the role of corin in blood pressure regulation.

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.

Association between serum sodium level trajectories and survival in patients with heart failure

AIMS

The effect of changes in serum sodium levels on the survival of patients with heart failure (HF) is unclear. We aimed to analyse the impact of serum sodium level trajectories on survival in intensive care unit (ICU) patients with HF.

METHODS

A total of 4760 patients diagnosed with HF between 2001 and 2012 from the Medical Information Mart for Intensive Care III (MIMIC-III) database were extracted. Of these patients, 1132 patients who died within 48 h of ICU admission were excluded, and 3628 patients were included in this retrospective cohort study. Sodium levels were measured at baseline, 6, 12, 18, 24, 30, 36, 42, and 48 h. Patients were divided into hyponatremia, normal, and hypernatremia groups based on baseline sodium levels, and trajectory modelling was performed for each group separately. Group-based trajectory model (GBTM) method was utilized to identify serum sodium levels trajectories.

RESULTS

The number of patients with hyponatremia (<135 mmol/L), normal sodium levels (135-145 mmol/L), and hypernatremia (>145 mmol/L) at baseline were 594 (16.37%), 2,738 (75.47%), and 296 (8.16%), respectively. A total of seven trajectory groups were identified, including hyponatremia-slow rise group [initial levels (IL), 128.48 ± 5.42 mmol/L; end levels (EL), 131.23 ± 3.83 mmol/L], hyponatremia-rapid rise to normal group (IL, 132.13 ± 2.18 mmol/L; EL, 137.46 ± 3.68 mmol/L), normal-slow decline group (IL, 137.65 ± 2.15 mmol/L; EL, 134.50 ± 2.54 mmol/L), normal-steady-state group (IL, 139.20 ± 2.26 mmol/L; EL, 139.04 ± 2.58 mmol/L), normal-slow rise group (IL, 140.94 ± 2.37 mmol/L; EL, 143.43 ± 2.89 mmol/L), hypernatremia-rapid decline to normal group (IL, 146.31 ± 1.98 mmol/L; EL, 140.71 ± 3.61 mmol/L), and hypernatremia-slow decline group (IL, 148.89 ± 5.54 mmol/L; EL, 146.28 ± 3.90 mmol/L). The results showed that hyponatremia-slow rise group [hazard ratio (HR) = 1.35; 95% confidence interval (CI), 1.01-1.80, P = 0.040], hyponatremia-rapid rise to normal group (HR = 1.37; 95% CI, 1.11-1.71, P = 0.004), hypernatremia-rapid decline to normal group (HR = 1.46; 95% CI, 1.08-1.97, P = 0.014), and hypernatremia-slow decline group (HR = 1.49; 95% CI, 1.07-2.07, P = 0.018) trajectories were associated with an increased risk of 1-year mortality in HF patients compared with normal-steady-state group. After adjustment for all confounders, hyponatremia-rapid rise to normal group (HR = 1.26, 95% CI; 1.01-1.57, P = 0.038) and hypernatremia-rapid decline to normal group (HR = 1.36; 95% CI, 1.01-1.84, P = 0.047) trajectories were still related to an increased risk of 1-year mortality in patients with HF.

CONCLUSIONS

Serum sodium level trajectories were associated with mortality in patients with HF. Association between serum sodium level trajectories and prognosis in patients with HF deserve further study.

Association between CORIN methylation and hypertension in Chinese adults

BACKGROUND

Corin, a physical activator of atrial natriuretic peptide, has been associated with hypertension with unclear mechanisms. Here, we aimed to examine whether CORIN gene methylation was involved in the underlying molecular mechanisms.

METHODS

DNA methylation levels of CORIN were measured by target bisulfite sequencing using genomic DNA isolated from peripheral blood mononuclear cells in 2498 participants in the Gusu cohort (discovery sample) and 1771 independent participants (replication sample). We constructed a mediation model with DNA methylation as the predictor, serum corin as the mediator, and hypertension as the outcome, adjusting for covariates. Multiple testing was controlled by false discovery rate (FDR) approach.

RESULTS

Of the 9 CpGs assayed, hypermethylation at all CpGs were significantly associated with a lower level of blood pressure in the discovery sample and eight associations were also significant in the replication sample (all FDR-adjusted p<0.05). Serum corin mediated approximately 3.07% (p=0.004), 6.25% (p=0.002) and 10.11% (p=0.034) of the associations of hypermethylation at one CpG (Chr4:47840096) with systolic and diastolic blood pressure, and hypertension, respectively. All these mediations passed the causal inference test.

CONCLUSIONS

These results suggest that hypermethylation in the CORIN gene is associated with a lower odds of prevalent hypertension and may be involved in the role of corin in blood pressure regulation.

AVP-eGFP was significantly upregulated by hypovolemia in the parvocellular division of the paraventricular nucleus in the transgenic rats

Arginine vasopressin (AVP) is produced in the paraventricular (PVN) and supraoptic nuclei (SON). Peripheral AVP, which is secreted from the posterior pituitary, is produced in the magnocellular division of the PVN (mPVN) and SON. In addition, AVP is produced in the parvocellular division of the PVN (pPVN), where corticotrophin-releasing factor (CRF) is synthesized. These peptides synergistically modulate the hypothalamic-pituitary-adrenal (HPA) axis. Previous studies have revealed that the HPA axis was activated by hypovolemia. However, the detailed dynamics of AVP in the pPVN under hypovolemic state has not been elucidated. Here, we evaluated the effects of hypovolemia and hyperosmolality on the hypothalamus, using AVP-enhanced green fluorescent protein (eGFP) transgenic rats. Polyethylene glycol (PEG) or 3% hypertonic saline (HTN) was intraperitoneally administered to develop hypovolemia or hyperosmolality. AVP-eGFP intensity was robustly upregulated at 3 and 6 h after intraperitoneal administration of PEG or HTN in the mPVN. While in the pPVN, eGFP intensity was significantly increased at 6 h after intraperitoneal administration of PEG with significant induction of Fos-immunoreactive (-ir) neurons. Consistently, eGFP mRNA, AVP hnRNA, and CRF mRNA in the pPVN and plasma AVP and corticosterone were significantly increased at 6 h after intraperitoneal administration of PEG. The results suggest that AVP and CRF syntheses in the pPVN were activated by hypovolemia, resulting in the activation of the HPA axis.

Differential influences of dietary sodium on blood pressure regulation based on race and sex

There are clear differences between men and women, and differences among races, in the incidence and prevalence of hypertension. Furthermore, there is extensive inter-individual variability among humans in the extent to which sodium ingestion alters blood pressure. Orthostatic intolerance and orthostatic hypotension are more common in women; these are often treated with a high salt diet, which has variable efficacy in increasing blood volume and blood pressure. Conversely, people with certain forms of hypertension are often counseled to decrease their sodium intake. Non-Hispanic Black men and women have higher rates of hypertension compared to non-Hispanic White men and women and other racial/ethnic groups. In aggregate, Black women appear to have better orthostatic tolerance than White women. In the present paper, we summarize and evaluate the current evidence for mechanisms of blood pressure regulation in men and women, as well as differences between Black and White groups, with a focus on cardiovascular responses to salt and differences among these groups. We also provide a brief review of factors that are not traditionally considered to be "biological" - such as socio-economic disparities resulting from historic and contemporary inequity across racial groups. These non-biological factors have direct and substantial influences on cardiovascular mechanisms, as well as implications for the influences of salt and sodium intake on blood pressure and cardiovascular health. We conclude that both biological and socio-economic factors provide critical modulating influences when considering the impacts of sodium on cardiovascular health as functions of race and sex.

Physiological characterization of an arginine vasopressin rat model of preeclampsia

Rodent models have contributed greatly to our understanding of preeclampsia (PE) progression in humans, however to-date no model has been able to effectively replicate the clinical presentation of the disease. This study aimed to provide a thorough physiological characterization of the arginine vasopressin (AVP)-induced rat model of PE to determine its applicability in studying the pathophysiology of PE. Female Sprague Dawley rats (n = 24) were separated into four groups (n = 6 per group) viz., pregnant AVP, pregnant saline, non-pregnant AVP, and non-pregnant saline. All animals received a continuous dose of either AVP (150 ng/h) or saline via subcutaneous mini osmotic pumps for 18 days. Full physiological characterization of the model included measuring systolic and diastolic blood pressure, and collecting urine and blood samples for biochemical analysis. AVP infusion significantly increased blood pressure and urinary protein levels in the pregnant rats (p < 0.05). Biochemical markers measured, differed significantly in the AVP-treated vs the pregnant saline groups (p < 0.05). Placental and individual pup weight decreased significantly in the pregnant AVP vs pregnant saline group (p < 0.05). The physiological and hematological data confirm the usefulness of this rat model in the study of PE, since AVP-induced vasoconstriction increases peripheral resistance and successfully mimics the pathological changes associated with PE development in humans.Abbreviations: PE: preeclampsia; AVP: arginine vasopressin; ISSHP: International Society for the Study of Hypertension in Pregnancy; ACOG: American College of Obstetricians and Gynecologists; RUPP: reduced uterine perfusion pressure; sFlt-1: soluble fms-like tyrosine kinase; VEGF: vascular endothelial growth factor; PlGF: placental growth factor; AVP: arginine vasopressin; PAVP: pregnant AVP-treated; PS: pregnant saline; GD: gestational day; ALT: alanine transaminase; NAVP: non-pregnant AVP-treated; NS: non-pregnant saline; AST: aspartate aminotransferase; HDL: high-density lipoprotein; RBC: red blood cell; RAAS: renin-angiotensin aldosterone system; HELLP: hemolysis, elevated liver enzymes, low platelet.

Complementary Role of Oxytocin and Vasopressin in Cardiovascular Regulation

The neurons secreting oxytocin (OXY) and vasopressin (AVP) are located mainly in the supraoptic, paraventricular, and suprachiasmatic nucleus of the brain. Oxytocinergic and vasopressinergic projections reach several regions of the brain and the spinal cord. Both peptides are released from axons, soma, and dendrites and modulate the excitability of other neuroregulatory pathways. The synthesis and action of OXY and AVP in the peripheral organs (eye, heart, gastrointestinal system) is being investigated. The secretion of OXY and AVP is influenced by changes in body fluid osmolality, blood volume, blood pressure, hypoxia, and stress. Vasopressin interacts with three subtypes of receptors: V1aR, V1bR, and V2R whereas oxytocin activates its own OXTR and V1aR receptors. AVP and OXY receptors are present in several regions of the brain (cortex, hypothalamus, pons, medulla, and cerebellum) and in the peripheral organs (heart, lungs, carotid bodies, kidneys, adrenal glands, pancreas, gastrointestinal tract, ovaries, uterus, thymus). Hypertension, myocardial infarction, and coexisting factors, such as pain and stress, have a significant impact on the secretion of oxytocin and vasopressin and on the expression of their receptors. The inappropriate regulation of oxytocin and vasopressin secretion during ischemia, hypoxia/hypercapnia, inflammation, pain, and stress may play a significant role in the pathogenesis of cardiovascular diseases.

Increased short-term and long-term mortality in community- and hospital-acquired hypernatraemia and in patients with delayed serum sodium correction

BACKGROUND

This study examined the short-term and long-term mortality of community- and hospital-acquired hypernatraemia in a large cohort of general hospitalised patients, and the impact of delayed serum sodium correction in hypernatraemic patients.

METHODS

Adult patients admitted to Mayo Clinic Rochester from 2011 to 2013 were examined. The patients with admission serum sodium ≥138 mEq/L and at least 2 serum sodium measurements during hospitalisation were included. Hypernatraemia was defined as serum sodium ≥143 mEq/L. The patients were categorised into three groups based on serum sodium at admission and during hospitalisation: (a) normal serum sodium, (b) community-acquired hypernatraemia and (c) hospital-acquired hypernatraemia. Outcomes included hospital mortality and 1-year mortality after hospital discharge amongst hospital survivors.

RESULTS

Of 25 781 eligible patients, 45% had normal serum sodium, 20% had community-acquired hypernatraemia and 35% had hospital-acquired hypernatraemia. In adjusted analysis, odds ratios (ORs) of community- and hospital-acquired hypernatraemia for hospital mortality were 4.91 (95% CI 3.47-6.94) and 4.11 (95% CI 2.94-5.73), whereas hazard ratio (HR) for 1-year mortality was 1.76 (95% CI 1.56-1.98) and 1.61 (95% CI 1.45-1.79), respectively. Hospital-acquired hypernatraemia had a higher hospital mortality but not 1-year mortality than community-acquired hypernatraemia. In patients with community-acquired hypernatraemia, 36% remained hypernatraemic by hospital day 3. Hospital mortality (OR 3.01; 95% CI 2.71-5.83) and 1-year mortality (HR 1.51; 95% CI 1.26-1.81) were significantly increased in patients with persistent hypernatraemia, compared with those with serum sodium correction into optimal range of 138-142 mEq/L.

CONCLUSION

Hypernatraemia, regardless of acquisition origin, is associated with elevated short-term and long-term mortality. Hospital-acquired hypernatraemia was more common and had a higher short-term mortality than community-acquired hypernatraemia. Failure to correct hypernatraemia by hospital day 3 is associated with increased mortality.

Association between ultrapocessed food and chronic kidney disease

The modern diet is closely linked to the consumption of processed foods, causing an increase in the intake of salt, simple sugars, phosphorus and added potassium. This excess intake is associated with an increased risk of obesity, diabetes, hypertension and chronic kidney disease (CKD). CKD, which according to data from the ENRICA study affects 15% of the population, magnifies its impact due to the higher prevalence of diabetes and hypertension and due to limitations in the management of sodium and phosphorus. The intake of these products far exceeds the established recommendations, assuming 72% of total sodium, 25%-35% of phosphorus, 12%-18% of potassium and exceeding 10% of the caloric intake in simple sugars. Measures are necessary to reduce their contribution through nutritional advice, labeling review, education campaigns on healthy habits, fees and institutional actions that involve food safety agencies, industry, distribution and scientific societies.

Altered dietary salt intake for people with chronic kidney disease

BACKGROUND

Evidence indicates that reducing dietary salt may reduce the incidence of heart disease and delay decline in kidney function in people with chronic kidney disease (CKD). This is an update of a review first published in 2015.

OBJECTIVES

To evaluate the benefits and harms of altering dietary salt for adults with CKD.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to 6 October 2020 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Register (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

Randomised controlled trials comparing two or more levels of salt intake in adults with any stage of CKD.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed studies for eligibility, conducted risk of bias evaluation and evaluated confidence in the evidence using GRADE. Results were summarised using random effects models as risk ratios (RR) for dichotomous outcomes or mean differences (MD) for continuous outcomes, with 95% confidence intervals (CI).

MAIN RESULTS

We included 21 studies (1197 randomised participants), 12 in the earlier stages of CKD (779 randomised participants), seven in dialysis (363 randomised participants) and two in post-transplant (55 randomised participants). Selection bias was low in seven studies, high in one and unclear in 13. Performance and detection biases were low in four studies, high in two, and unclear in 15. Attrition and reporting biases were low in 10 studies, high in three and unclear in eight. Because duration of the included studies was too short (1 to 36 weeks) to test the effect of salt restriction on endpoints such as death, cardiovascular events or CKD progression, changes in salt intake on blood pressure and other secondary risk factors were examined. Reducing salt by mean -73.51 mmol/day (95% CI -92.76 to -54.27), equivalent to 4.2 g or 1690 mg sodium/day, reduced systolic/diastolic blood pressure by -6.91/-3.91 mm Hg (95% CI -8.82 to -4.99/-4.80 to -3.02; 19 studies, 1405 participants; high certainty evidence). Albuminuria was reduced by 36% (95% CI 26 to 44) in six studies, five of which were carried out in people in the earlier stages of CKD (MD -0.44, 95% CI -0.58 to -0.30; 501 participants; high certainty evidence). The evidence is very uncertain about the effect of lower salt intake on weight, as the weight change observed (-1.32 kg, 95% CI -1.94 to -0.70; 12 studies, 759 participants) may have been due to fluid volume, lean tissue, or body fat. Lower salt intake may reduce extracellular fluid volume in the earlier stages of CKD (-0.87 L, 95% CI -1.17 to -0.58; 3 studies; 187 participants; low certainty evidence). The evidence is very uncertain about the effect of lower salt intake on reduction in antihypertensive dose (RR 2.45, 95% CI 0.98 to 6.08; 8 studies; 754 participants). Lower salt intake may lead to  symptomatic hypotension (RR 6.70, 95% CI 2.40 to 18.69; 6 studies; 678 participants; moderate certainty evidence). Data were sparse for other types of adverse events.

AUTHORS' CONCLUSIONS

We found high certainty evidence that salt reduction reduced blood pressure in people with CKD, and albuminuria in people with earlier stage CKD in the short-term. If such reductions could be maintained long-term, this effect may translate to clinically significant reductions in CKD progression and cardiovascular events. Research into the long-term effects of sodium-restricted diet for people with CKD is warranted.

Higher volume of water intake is associated with lower risk of albuminuria and chronic kidney disease

Increased water intake correlated to lower vasopressin level and may benefit kidney function. However, results of previous studies were conflicted and inconclusive. We aimed to investigate the association between water intake and risk of chronic kidney disease (CKD) and albuminuria.In this cross-sectional study, the study population were adult participants of 2011-2012 National Health and Nutrition Examination Survey (NHANES) whose estimated glomerular filtration rate (eGFR) were ≥30 ml/min/1.73 m2. Data of water intake were obtained from the NHANES 24-h dietary recall questionnaire. Participants were divided into three groups based on volume of water intake: <500 (low, n = 1589), ≥500 to <1200 (moderate, n = 1359), and ≥1200 ml/day (high, n = 1685). CKD was defined as eGFR <60 ml/min/1.73 m2, and albuminuria as albumin-to-creatinine ratio (ACR) ≥30 mg/g.Our results showed that 377 out of 4633 participants had CKD; the prevalence inversely correlated to volume of water intake: 10.7% in low, 8.2% in moderate, and 5.6% in high intake groups (P < .001). Prevalence of albuminuria was also lower in high (9.5%) compared with moderate (12.8%) and low intake groups (14.1%), P < .001. Additionally, water intake positively correlated to eGFR and negatively correlated to urinary ACR, as well as plasma and urine osmolality. Multivariable logistic regression showed that low water intake group had higher risk of CKD (OR 1.35, 95% CI 1.01-1.82) and albuminuria when compared to high water intake group (OR 1.42, 95% CI 1.13-1.79).In conclusion, increased water intake was associated lower risk of CKD and albuminuria. Meticulous studies are needed to elucidate the underlying mechanisms.

Association between ultrapocessed food and chronic kidney disease

The modern diet is closely linked to the consumption of processed foods, causing an increase in the intake of salt, simple sugars, phosphorus and added potassium. This excess intake is associated with an increased risk of obesity, diabetes, hypertension and chronic kidney disease (CKD). CKD, which according to data from the ENRICA study affects 15% of the population, magnifies its impact due to the higher prevalence of diabetes and hypertension and due to limitations in the management of sodium and phosphorus. The intake of these products far exceeds the established recommendations, assuming 72% of total sodium, 25-35% of phosphorus, 12-18% of potassium and exceeding 10% of the caloric intake in simple sugars. Measures are necessary to reduce their contribution through nutritional advice, labeling review, education campaigns on healthy habits, fees and institutional actions that involve food safety agencies, industry, distribution and scientific societies.

Increased mortality risk associated with serum sodium variations and borderline hypo- and hypernatremia in hospitalized adults

Background

This study aimed to evaluate short-term and long-term mortalities in a cohort of unselected hospitalized patients with serum sodium concentration ([Na⁺]) variations within and outside of reference range.

Methods

All adult patients admitted to the Mayo Clinic, Rochester, MN, USA from January 2011 to December 2013 (n = 147358) were retrospectively screened. Unique patients admitted during the study period were examined. The main exposure was serum [Na⁺] variation. Outcome measures were hospital and 1-year all-cause mortalities.

Results

A total of 60944 patients, mean age 63 ± 17 years, were studied. On admission, 17% (n = 10066) and 1.4% (n = 852) had hypo- and hypernatremia, respectively. During the hospital stay, 11044 and 4128 developed hypo- and hypernatremia, respectively, accounting for 52.3 and 82.9% of the total hypo- and hypernatremic patients. Serum [Na⁺] variations of ≥6 mEq/L occurred in 40.6% (n = 24 740) of the 60 944 patients and were significantly associated with hospital and 1-year mortalities after adjusting potential confounders (including demographics, comorbidities, estimated glomerular filtration rate, admission serum [Na⁺], number of [Na⁺] measurements and length of hospital stay). Adjusted odds ratios for hospital and 1-year mortalities increased with increasing [Na⁺] variations in a dose-dependent manner, from 1.47 to 5.48 (all 95% confidence intervals >1.0). Moreover, in fully adjusted models, [Na⁺] variations (≥6 mEq/L) within the reference range (135–145 mEq/L) or borderline hypo- or hypernatremia (133–137 and 143–147 mEq/L, respectively) compared with 138–142 mEq/L were associated with increased hospital and 1-year mortalities.

Conclusion

In hospitalized adults, [Na⁺] fluctuation (≥6 mEq/L) irrespective of admission [Na⁺] and borderline hypo- or hypernatremia are independent predictors of progressively increasing short- and long-term mortality burdens.

Differential roles of VPS and RAAS in water homeostasis and a risk for kidney dysfunction in rats undergoing rapid fasting/dehydration with regular exercise

Purpose

We examined the effects of rapid restriction of food and fluid intake on the pathways of water homeostasis, the vasopressinergic system (VPS), and the renin–angiotensin–aldosterone system (RAAS), in rats with or without regular exercise.

Methods

Sprague Dawley rats were divided into the following groups: no intervention, rapid restriction, regular exercise, and rapid restriction combined with regular exercise. Rats in the exercise group performed climbing exercise for 4 weeks. All rats consumed food ad libitum, and those in the rapid restriction group fasted for the last 3 days with no water on the last 1 day.

Results

Despite no significant differences in body weight among the groups, the kidney weight was decreased when rapid restriction and regular exercise were combined. Rapid restriction reduced the urine volume and increased the urine osmolality, whereas regular exercise did not. Rapid restriction but not regular exercise increased the levels of circulating aldosterone and the renal expression levels of the ion channel SGK‐1 compared to those without rapid restriction, indicating the stimulation of RAAS. Conversely, VPS showed no significant response to these interventions. Moreover, rapid restriction combined with regular exercise induced the renal expression levels of proinflammatory cytokines and increased the active forms of apoptotic effector caspase‐3 compared with the no intervention group.

Conclusions

Functional significance may differ between VPS and RAAS in water homeostasis in response to rapid restriction. Moreover, the combination of rapid restriction and regular exercise has potentially deleterious effects on the kidney.

Evolutionary genetics and acclimatization in nephrology

Evolutionary processes, including mutation, migration and natural selection, have influenced the prevalence and distribution of various disorders in humans. However, despite a few well-known examples, such as the APOL1 variants - which have undergone positive genetic selection for their ability to confer resistance to Trypanosoma brucei infection but confer a higher risk of chronic kidney disease - little is known about the effects of evolutionary processes that have shaped genetic variation on kidney disease. An understanding of basic concepts in evolutionary genetics provides an opportunity to consider how findings from ancient and archaic genomes could inform our knowledge of evolution and provide insights into how population migration and genetic admixture have shaped the current distribution and landscape of human kidney-associated diseases. Differences in exposures to infectious agents, environmental toxins, dietary components and climate also have the potential to influence the evolutionary genetics of kidneys. Of note, selective pressure on loci associated with kidney disease is often from non-kidney diseases, and thus it is important to understand how the link between genome-wide selected loci and kidney disease occurs in relation to secondary nephropathies.

Eight Days of Water-Only Fasting Promotes Favorable Changes in the Functioning of the Urogenital System of Middle-Aged Healthy Men

The aim of this study was to determine whether, after 8 days of water-only fasting, there are changes in the efficiency of the lower urinary tract, the concentration of sex hormones, and the symptoms of prostate diseases in a group of middle-aged men (n = 14). For this purpose, before and after 8 days of water-only fasting (subjects drank ad libitum moderately mineralized water), and the following somatic and blood concentration measurements were made: total prostate specific antigen (PSA-T), free prostate specific antigen (PSA-F), follicle stimulating hormone (FSH), luteotropic hormone (LH), prolactin (Pr), total testosterone (T-T), free testosterone (T-F), dehydroepiandrosterone (DHEA), sex hormone globulin binding (SHGB), total cholesterol (Ch-T), β-hydroxybutyrate (β-HB). In addition, prostate volume (PV), volume of each testis (TV), total volume of both testes (TTV), maximal urinary flow rate (Qmax), and International Prostate Symptom Score (IPSS) values were determined. The results showed that after 8 days of water-only fasting, Qmax and IPSS improved but PV and TTV decreased significantly. There was also a decrease in blood levels of PSA-T, FSH, P, T-T, T-F, and DHEA, but SHGB concentration increased significantly. These results indicate that 8 days of water-only fasting improved lower urinary tract functions without negative health effects.

An Increase in SNAP Benefits Did Not Impact Food Security or Diet Quality in Youth

BACKGROUND

Low diet quality during childhood and adolescence is associated with adverse health outcomes later in life. Diet quality is generally poor in American youth, particularly in youth of low socioeconomic status. The Supplemental Nutrition Assistance Program (SNAP) is the primary safety net to help low-income households afford a healthy diet. Yet self-selection into the program creates challenges in estimating the relationship between SNAP and diet outcomes.

OBJECTIVE

This study examined how the increase in SNAP benefits during the American Recovery and Reinvestment Act (ARRA) affected food security and diet quality in low-income youth.

DESIGN

This analysis used a difference-in-differences design and data from the National Health and Nutrition Examination Survey 2007-2008 to 2011-2012 waves.

PARTICIPANTS/SETTING

The sample included children and adolescents aged 2 to 18 years with household income ≤250% of the Federal Poverty Line. Food security and diet outcomes in SNAP-eligible youth (n = 2,797) were examined, with children in nearly SNAP-eligible households serving as a comparison group (n = 1,169). The diet quality analysis stratified the sample by age range.

MAIN OUTCOME MEASURES

The study assessed food security and 6 dietary outcomes: 2 nutrients (sodium and fiber), 3 food categories (fruit, vegetables, and sugar-sweetened beverages), and 1 measure of overall diet quality (Healthy Eating Index 2010).

STATISTICAL ANALYSIS PERFORMED

Logistic regression and linear regression were used to estimate the relationship between SNAP eligibility and child food security and diet.

RESULTS

In unadjusted analysis, approximately 64% of SNAP-eligible children were food secure before ARRA and 73% were food secure while ARRA was in effect. Using logistic regression in a difference-in-differences framework, the ARRA SNAP benefit increase was not significantly associated with food security (odds ratio 1.37, P = 0.43). Diet quality of SNAP-eligible children was low, scoring a 46 out of 100 on the Healthy Eating Index 2010. Measures of diet quality did not significantly change from the pre-ARRA period to the ARRA period; this did not differ by age range.

CONCLUSIONS

The increase in SNAP benefits during ARRA did not significantly impact food security or diet quality in low-income children and adolescents. Additional research to better understand how SNAP benefits impact dietary choice is warranted.

Salt-sensitive hypertension in chronic kidney disease: distal tubular mechanisms

Chronic kidney disease (CKD) causes salt-sensitive hypertension that is often resistant to treatment and contributes to the progression of kidney injury and cardiovascular disease. A better understanding of the mechanisms contributing to salt-sensitive hypertension in CKD is essential to improve these outcomes. This review critically explores these mechanisms by focusing on how CKD affects distal nephron Na+ reabsorption. CKD causes glomerulotubular imbalance with reduced proximal Na+ reabsorption and increased distal Na+ delivery and reabsorption. Aldosterone secretion further contributes to distal Na+ reabsorption in CKD and is not only mediated by renin and K+ but also by metabolic acidosis, endothelin-1, and vasopressin. CKD also activates the intrarenal renin-angiotensin system, generating intratubular angiotensin II to promote distal Na+ reabsorption. High dietary Na+ intake in CKD contributes to Na+ retention by aldosterone-independent activation of the mineralocorticoid receptor mediated through Rac1. High dietary Na+ also produces an inflammatory response mediated by T helper 17 cells and cytokines increasing distal Na+ transport. CKD is often accompanied by proteinuria, which contains plasmin capable of activating the epithelial Na+ channel. Thus, CKD causes both local and systemic changes that together promote distal nephron Na+ reabsorption and salt-sensitive hypertension. Future studies should address remaining knowledge gaps, including the relative contribution of each mechanism, the influence of sex, differences between stages and etiologies of CKD, and the clinical relevance of experimentally identified mechanisms. Several pathways offer opportunities for intervention, including with dietary Na+ reduction, distal diuretics, renin-angiotensin system inhibitors, mineralocorticoid receptor antagonists, and K+ or H+ binders.

Molecular Mechanisms of SGLT2 Inhibitor on Cardiorenal Protection

The development of sodium-glucose transporter 2 inhibitor (SGLT2i) broadens the therapeutic strategies in treating diabetes mellitus. By inhibiting sodium and glucose reabsorption from the proximal tubules, the improvement in insulin resistance and natriuresis improved the cardiovascular mortality in diabetes mellitus (DM) patients. It has been known that SGLT2i also provided renoprotection by lowering the intraglomerular hypertension by modulating the pre- and post- glomerular vascular tone. The application of SGLT2i also provided metabolic and hemodynamic benefits in molecular aspects. The recent DAPA-CKD trial and EMPEROR-Reduced trial provided clinical evidence of renal and cardiac protection, even in non-DM patients. Therefore, the aim of the review is to clarify the hemodynamic and metabolic modulation of SGLT2i from the molecular mechanism.

High-salt diet decreases mechanical thresholds in mice that is mediated by a CCR2-dependent mechanism

Background

Though it is well-known that a high-salt diet (HSD) is associated with many chronic diseases, the effects of long-term high-salt intake on physiological functions and homeostasis remain elusive. In this study, we investigated whether and how an HSD affects mouse nociceptive thresholds, and myeloid cell trafficking and activation.

Methods

Healthy C57BL/6 male and female mice were fed an HSD (containing 4% NaCl in chow and 1% NaCl in water) from the time of weaning for 3 to 4 months. Circulating monocytes, nerve macrophages, spinal microglia, and associated inflammatory responses were scrutinized using flow cytometry, immunohistochemistry, and quantitative real-time polymerase chain reaction (qPCR) approaches. Mouse pain sensitivity to mechanical stimuli was monitored with von Frey tests along the experimental duration.

Results

Mice on an HSD have reduced mechanical thresholds. They feel more pain than those on a normal diet (ND), e.g., regular laboratory chow (0.3% NaCl in chow). An HSD induced not only a remarkable expansion of circulating monocytes, CCR2⁺Ly6C^hi inflammatory monocytes in particular, but also an accumulation of CD11b⁺F4/80⁺ macrophages in the peripheral nerves and an activation of Iba-1⁺ spinal microglia. Replacing an HSD with a ND was unable to reverse the HSD-induced mechanical hypersensitivity or rescue the altered immune responses. However, treating HSD-fed mice with a chemokine receptor CCR2 antagonist effectively normalized the pain thresholds and immune cell profile in the periphery and spinal cord. An HSD failed to alter pain thresholds and myeloid cell activation in CCR2-deficient mice. Spinal microglial activation is required for HSD-induced mechanical hypersensitivity in male, but not in female mice.

Conclusion

Overall, this study provides evidence that an HSD has a long-term impact on physiological function. CCR2-mediated cellular response, including myeloid cell trafficking and associated inflammation, plays pivotal roles in salt-dietary modulation of pain sensitivity.

Sodium Intake and Target Organ Damage in Hypertension-An Update about the Role of a Real Villain

Salt intake is too high for safety nowadays. The main active ion in salt is sodium. The vast majority of scientific evidence points out the importance of sodium restriction for decreasing cardiovascular risk. International Guidelines recommend a large reduction in sodium consumption to help reduce blood pressure, organ damage, and cardiovascular risk. Regulatory authorities across the globe suggest a general restriction of sodium intake to prevent cardiovascular diseases. In spite of this seemingly unanimous consensus, some researchers claim to have evidence of the unhealthy effects of a reduction of sodium intake, and have data to support their claims. Evidence is against dissenting scientists, because prospective, observational, and basic research studies indicate that sodium is the real villain: actual sodium consumption around the globe is far higher than the safe range. Sodium intake is directly related to increased blood pressure, and independently to the enlargement of cardiac mass, with a possible independent role in inducing left ventricular hypertrophy. This may represent the basis of myocardial ischemia, congestive heart failure, and cardiac mortality. Although debated, a high sodium intake may induce initial renal damage and progression in both hypertensive and normotensive subjects. Conversely, there is general agreement about the adverse role of sodium in cerebrovascular disease. These factors point to the possible main role of sodium intake in target organ damage and cardiovascular events including mortality. This review will endeavor to outline the existing evidence.

Renal Dopamine Oxidation and Inflammation in High Salt Fed Rats

Background

Oxidative stress and high salt intake could be independent or intertwined risk factors in the origin of hypertension. Kidneys are the major organ to regulate sodium homeostasis and blood pressure and the renal dopamine system plays a pivotal role in sodium regulation during sodium replete conditions. Oxidative stress has been implicated in renal dopamine dysfunction and development of hypertension, especially in salt‐sensitive animal models. Here we show the nexus between high salt intake and oxidative stress causing renal tubular dopamine oxidation, which leads to mitochondrial and lysosomal dysfunction and subsequently causes renal inflammation and hypertension.

Methods and Results

Male Sprague Dawley rats were divided into the following groups, vehicle (V)—tap water, high salt (HS)—1% NaCl, L‐buthionine‐sulfoximine (BSO), a prooxidant, and HS plus BSO without and with antioxidant resveratrol (R) for 6 weeks. Oxidative stress was significantly higher in BSO and HS+BSO–treated rat compared with vehicle; however, blood pressure was markedly higher in the HS+BSO group whereas an increase in blood pressure in the BSO group was modest. HS+BSO–treated rats had significant renal dopamine oxidation, lysosomal and mitochondrial dysfunction, and increased renal inflammation; however, HS alone had no impact on organelle function or inflammation. Resveratrol prevented oxidative stress, dopamine oxidation, organelle dysfunction, inflammation, and hypertension in BSO and HS+BSO rats.

Conclusions

These data suggest that dopamine oxidation, especially during increased sodium intake and oxidative milieu, leads to lysosomal and mitochondrial dysfunction and renal inflammation with subsequent increase in blood pressure. Resveratrol, while preventing oxidative stress, protects renal function and mitigates hypertension.

Identification and classification of epithelial cells in nephron segments by actin cytoskeleton patterns

The basic functional unit in a kidney is the nephron, which is a long and morphologically segmented tubule. The nephron begins with a cluster of capillaries called glomerulus through which the blood is filtered into the Bowman's space. The filtrate flows through the nephron segments. During this flow, electrolytes and solutes are reabsorbed by channels and transport systems into the capillaries wrapped around the nephron. Many questions related to renal function focus on identifying the sites of expression of these systems. In this study, we mapped whole kidney sections by confocal microscopic imaging of fluorescent phalloidin, which binds to actin filaments. In tile scans (composed of hundreds of images) of these sections, the cortex and the medullary regions (outer and inner stripes of the outer medulla, and inner medulla) could be easily identified by their cytoskeletal patterns. At a higher resolution, we identified distinct features of the actin cytoskeleton in the apical, basal, and lateral borders of the cells. These features could be used to identify segments of a nephron (the proximal tubule, thin and thick segments of Henle's loop, and distal tubule), the collecting duct system, the papillary ducts in the papilla, and the urothelium that covers the pelvis. To verify our findings, we used additional markers, including aquaporin isoforms, cytokeratin 8‐18, and WGA lectin. This study highlights the power of high‐resolution confocal microscopy for identifying specific cell types using the simple probe of F‐actin‐binding phalloidin.

Dietary Influence on Body Fluid Acid-Base and Volume Balance: The Deleterious "Norm" Furthers and Cloaks Subclinical Pathophysiology

The popular modern diet, characterized by an excess of animal protein and salt but insufficient in fruits, vegetables and water, is a poor fit for human physiological and homeostatic regulatory systems. Sustained net acid and sodium retention, coupled with an insufficient intake of cardiovascular protective potassium-rich foods and hydration in the modern diet can give rise to debilitating chronic organ dysfunction and ultimately, mortality. This holds true, especially in our aging population who are already facing inevitable decline in organ functional reserve. Importantly, in most cases, despite the mismatch and adverse effects to multiple organ systems, plasma electrolyte and acid-base parameters can, on the surface, be maintained within a “normal” reference range, primarily by activating (often maximally activating) compensatory homeostatic mechanisms. These diet-induced effects can thus be clinically silent for decades. Embodied in the chronic corrective homeostatic processes, however, are real risks for multiorgan damage. According to the Dietary Guideline Advisory Committee (DGAC), half of American adults have one or more chronic diseases that are preventable with dietary modification. Here, homeostasis of body fluid acid-base, sodium, potassium and water is examined. Our current dietary habits and their required regulatory adaptation, maladaptation and relevant physiology and pathophysiology are discussed. A framework of dietary modifications to avoid a propensity for maladaptation and thus lowers the risks of common modern diseases (primary prevention) and minimizes the risk of chronic and age-related disease progression (secondary prevention) is emphasized. Although there are other variables at play, a key to restoring the all-important dietary potassium to sodium ratio is greater consumption of vegetables/fruits and adopting salt temperance. Dietary and nutritional optimization is an under-emphasized area of health care that has an enormous potential to temper the epidemics of prevalent chronic diseases in modern society and improve population health.