The discovery of hypertension: evolving views on the role of the kidneys, and current hot topics

Role of hypertension in progression of pediatric CKD

Hypertension is frequent in children with chronic kidney disease (CKD). Its prevalence varies according to CKD stage and cause. It is relatively uncommon in children with congenital kidney disease, while acquired kidney disease is associated with a higher prevalence of hypertension. Studies in children with CKD utilizing ambulatory blood pressure monitoring also showed a high prevalence of masked hypertension. Uncontrolled and longstanding hypertension in children is associated with progression of CKD. Aggressive treatment of high blood pressure should be an essential part of care to delay CKD progression in children.

Ambulatory blood pressure as risk factor for long-term kidney function decline in the general population: a distributional regression approach

The results of randomized controlled trials are unclear about the long-term effect of blood pressure (BP) on kidney function assessed as the glomerular filtration rate (GFR) in persons without chronic kidney disease or diabetes. The limited duration of follow-up and use of imprecise methods for assessing BP and GFR are important reasons why this issue has not been settled. Since a long-term randomized trial is unlikely, we investigated the association between 24-h ambulatory BP (ABP) and measured GFR in a cohort study with a median follow-up of 11 years. The Renal Iohexol Clearance Survey (RENIS) cohort is a representative sample of persons aged 50 to 62 years without baseline cardiovascular disease, diabetes, or kidney disease from the general population of Tromsø in northern Norway. ABP was measured at baseline, and iohexol clearance at baseline and twice during follow-up. The study population comprised 1589 persons with 4127 GFR measurements. Baseline ABP or office BP components were not associated with the GFR change rate in multivariable adjusted conventional regression models. In generalized additive models for location, scale, and shape (GAMLSS), higher daytime systolic, diastolic, and mean arterial ABP were associated with a slight shift of the central part of the GFR distribution toward lower GFR and with higher probability of GFR < 60 mL/min/1.73 m2 during follow-up (p < 0.05). The use of a distributional regression method and precise methods for measuring exposure and outcome were necessary to detect an unfavorable association between BP and GFR in this study of the general population.

Epigenetics of the blood pressure reactivity to salt: Is the salt sensitive phenotype correctable?

Salt sensitivity defines a state characterized by a highly reactive blood pressure to changes in salt intake. The salt-sensitive phenotype is strongly associated with hypertension, visceral adiposity/metabolic syndrome, and ageing. Obesity accounts for around 70% of hypertension in young adults, and 30% to 50% of adult hypertensives carry the salt-sensitive phenotype. It is estimated that the salt-sensitive phenotype is responsible for high blood pressure in over 600 million adults. But is the salt-sensitive phenotype correctable? Interventional, controlled, clinical trials in obese adolescents and young obese adults, demonstrated that weight-reducing lifestyle modifications revert the salt-sensitive to the salt-resistant phenotype, and restored the faulty production of nitric oxide. Correction of the salt-sensitive phenotype lowers the blood pressure by reducing its reactivity to dietary salt. In a random sample of obese adults subjected to lifestyle modifications, those who were salt-resistant at baseline, were also normotensive and failed to further lower their blood pressure despite a 12% drop in body weight. The salt-resistant phenotype protects the metabolically healthy obese from hypertension, even if their salt consumption is comparable to that of salt-sensitive obese. In summary, at early stages, the elevated blood pressure of obesity, is determined by epigenetic changes leading to a state of salt-sensitivity.

Diversified Shifts in the Cross Talk between Members of the Gut Microbiota and Development of Coronary Artery Diseases

Coronary artery disease (CAD) is one of leading causes of mortality worldwide. Studies on roles that the gut microbiota plays in development of atherosclerosis or acute myocardial infarction (AMI) have been widely reported. However, the gut microbiota is affected by many factors, including age, body mass index (BMI), and hypertension, that lead to high CAD risk. However, the associations between gut microbiota and CAD development or other CAD risk factors remain unexplored. Here, we performed a 16S RNA gene sequencing analysis of 306 fecal samples collected from patients with mild coronary stenosis (MCS; n = 36), stable angina (SA; n = 91), unstable angina (UA; n = 48), and acute myocardial infarction (AMI; n = 66) and 65 non-CAD controls. Using a noise-corrected method based on principal-component analysis (PCA) and the random forest algorithm, we identified the interference with gut microbial profiling of multiple factors (including age, gender, BMI, and hypertension) that potentially contributed significantly to the development of CAD. After correction of noise interference from certain interfering factors, we found consistent indicator microbiota organisms (such as Vampirovibrio, Ruminococcus, and Eisenbergiella) associated with the presence of MCS, SA, and AMI. Establishment of a diagnostic model revealed better performance in early CAD than clinical indexes with indicator microbes. Furthermore, indicator microbes can improve the accuracy of clinical indexes for the diagnosis of AMI. Additionally, we found that the microbial indicators of AMI Sporobacter and Eisenbergiella showed consistent positive and negative correlations to the clinical indexes creatine kinase (CK) and hemoglobin (Hb), respectively. As a control indicator of AMI, Dorea was negatively correlated with CK but positively correlated with Hb. IMPORTANCE Our study discovered the effect of confounding factors on gut microbial variations and identified gut microbial indicators possibly associated with the CAD development after noise correction. Our discovered indicator microbes may have potential for diagnosis or therapy of cardiovascular disorders.

One-third of patients with lupus nephritis classified as complete responders continue to accrue progressive renal damage despite resolution of proteinuria

OBJECTIVE

Treatment response in lupus nephritis (LN) is defined based on proteinuria, yet protocol kidney biopsy studies have shown that patients with lupus can have active nephritis in the absence of proteinuria. Using estimated glomerular filtration rate (eGFR) trajectories, we characterised early chronic kidney disease in LN and examined whether certain patients continue to accrue renal damage despite proteinuric response.

METHODS

We conducted a single-centre study of patients diagnosed with their first episode of biopsy-proven class III, IV, and/or V LN (n=37). For each patient, eGFR trajectory was graphed over 5 years following renal biopsy. Participants were divided into those with progressive eGFR loss (eGFR slope <-5 mL/min/1.73 m2/year) versus those with stable eGFR. Participant demographics, renal biopsy features and response status at 1 year (urine protein to creatinine ratio <500 mg/g) were compared between eGFR trajectory groups.

RESULTS

Overall, 30% (n=11) of participants accrued progressive eGFR loss despite standard of care therapy over the first 5 years following renal biopsy. There were no significant differences in baseline renal biopsy features, medication regimens or comorbidities between eGFR trajectory groups. Resolution of proteinuria at 1 year did not differentiate between groups: 6 of 18 (33%) of complete responders continued to accrue renal damage compared with 5 of 17 (29%) of non-responders. Response status could not be assigned for two participants in the stable eGFR group due to missing clinical information at 1 year.

CONCLUSIONS

We identified an understudied category of patients with LN who accrue progressive renal damage despite apparent response to standard of care therapy. Better definitions and biomarkers of response are needed to improve renal outcomes and trial design.

Sir George Johnson FRCP (1818-96), high blood pressure and the continuing altercation about its origins

NEW FINDINGS

What is the topic of this review? The review takes a historical approach to examining where in the body it might be possible to identify the most common cause, or causes, of long-term hypertension. It gathers evidence from histology, human and animal physiology, and computational modelling. The burden of decades of controversy is noted. What advances does it highlight? The review highlights the distinctive pathology of the afferent renal circulation and what its consequences are for the widespread view that essential hypertension is caused by elevated peripheral vascular resistance.

ABSTRACT

The widely promulgated notion that long-term elevation in mean arterial blood pressure (MAP) can be caused by raised peripheral vascular resistance remains a subject of vigorous debate. According to the 1967 mathematical model of Guyton and Coleman, such a causal relationship is impossible, kidney function being the determining factor. We explore this altercation starting with Sir George Johnson's 19th-century renal vascular histological observations in patients with Bright's disease. We note the striking physiological measurements in hypertensives by Gómez and Bolomey in the 1950s, moving on to the mathematical modelling of the circulation from the 1960s up to the ∼100-parameter computer models of the present day. Confusion has been generated by the fact that peripheral resistance is raised in hypertension in close proportion to MAP whilst cardiac output often stays normal, an apparent autoregulation, the mechanism of which is poorly understood. All models allowing for the circulation to be an open system show that isolated changes in peripheral resistance cannot lead to long-term hypertension, but models fail so frequently to account for results from experiments such as salt loading that their credibility with regard to this key finding is compromised. Laboratory animal models of adrenergic renal actions resonate with a contemporary emphasis on the sympathetic nerve supply to the kidney as contributing to the characteristically markedly elevated renal afferent resistance that appears to be the most common cause of hypertension. Remarkably, there remains no account of the way in which the fixed structural changes in vessels observed by Johnson relate to this sympathetic overactivity, which can itself be modified by drugs in the medium term. In this account, we seek to locate the crime scene and identify a smoking gun.

Role of Klotho in the Development of Essential Hypertension

Klotho has antiaging properties, and serum levels decrease with physiological aging and aging-related diseases, such as hypertension, cardiovascular, and chronic kidney disease. Klotho deficiency in mice results in accelerated aging and cardiovascular injury, whereas Klotho supplementation slows down the progression of aging-related diseases. The pleiotropic functions of Klotho include, but are not limited to, inhibition of insulin/IGF-1 (insulin-like growth factor 1) and WNT (wingless-related integration site) signaling pathways, suppression of oxidative stress and aldosterone secretion, regulation of calcium-phosphate homeostasis, and modulation of autophagy with inhibition of apoptosis, fibrosis, and cell senescence. Accumulating evidence shows an interconnection between Klotho deficiency and hypertension, and Klotho gene polymorphisms are associated with hypertension in humans. In this review, we critically review the current understanding of the role of Klotho in the development of essential hypertension and the most important underlying pathways involved, such as the FGF23 (fibroblast growth factor 23)/Klotho axis, aldosterone, Wnt5a/RhoA, and SIRT1 (Sirtuin1). Based on this critical review, we suggest avenues for further research.

HIV-positive demonstrate more salt sensitivity and nocturnal non-dipping blood pressure than HIV-negative individuals

Background

High dietary salt and a lack of reduced blood pressure (BP) at night (non-dipping) are risk factors for the development of hypertension which may result in end-organ damage and death. The effect of high dietary salt on BP in black people of sub-Saharan Africa living with HIV is not well established. The goal of this study was to explore the associations between salt sensitivity and nocturnal blood pressure dipping according to HIV and hypertension status in a cohort of adult Zambian population.

Methods

We conducted an interventional study among 43 HIV-positive and 42 HIV-negative adults matched for age and sex. Study participants were instructed to consume a low (4 g) dietary salt intake for a week followed by high (9 g) dietary salt intake for a week. Salt resistance and salt sensitivity were defined by a mean arterial pressure difference of ≤5 mmHg and ≥ 8 mmHg, respectively, between the last day of low and high dietary salt intervention. Nocturnal dipping was defined as a 10–15% decrease in night-time blood pressure measured with an ambulatory blood pressure monitor.

Results

The median age was 40 years for both the HIV-positive and the HIV-negative group with 1:1 male to female ratio. HIV positive individuals with hypertension exhibited a higher BP sensitivity to salt (95%) and non-dipping BP (86%) prevalence compared with the HIV negative hypertensive (71 and 67%), HIV positive (10 and 24%) and HIV-negative normotensive (29 and 52%) groups, respectively (p < 0.05). Salt sensitivity was associated with non-dipping BP and hypertension in both the HIV-positive and HIV-negative groups even after adjustment in multivariate logistic regression (< 0.001).

Conclusions

The results of the present study suggest that high dietary salt intake raises blood pressure and worsens nocturnal BP dipping to a greater extent in hypertensive than normotensive individuals and that hypertensive individuals have higher dietary salt intake than their normotensive counterparts. Regarding HIV status, BP of HIV-positive hypertensive patients may be more sensitive to salt intake and demonstrate more non-dipping pattern compared to HIV-negative hypertensive group. However, further studies with a larger sample size are required to validate this.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40885-020-00160-0.

Physiological factors characterizing heat-vulnerable older adults: A narrative review

More frequent and intense periods of extreme heat (heatwaves) represent the most direct challenge to human health posed by climate change. Older adults are particularly vulnerable, especially those with common age-associated chronic health conditions (e.g., cardiovascular disease, hypertension, obesity, type 2 diabetes, chronic kidney disease). In parallel, the global population is aging and age-associated disease rates are on the rise. Impairments in the physiological responses tasked with maintaining homeostasis during heat exposure have long been thought to contribute to increased risk of health disorders in older adults during heatwaves. As such, a comprehensive overview of the provisional links between age-related physiological dysfunction and elevated risk of heat-related injury in older adults would be of great value to healthcare officials and policy makers concerned with protecting heat-vulnerable sectors of the population from the adverse health impacts of heatwaves. In this narrative review, we therefore summarize our current understanding of the physiological mechanisms by which aging impairs the regulation of body temperature, hemodynamic stability and hydration status. We then examine how these impairments may contribute to acute pathophysiological events common during heatwaves (e.g., heatstroke, major adverse cardiovascular events, acute kidney injury) and discuss how age-associated chronic health conditions may exacerbate those impairments. Finally, we briefly consider the importance of physiological research in the development of climate-health programs aimed at protecting heat-vulnerable individuals.

Effect of febuxostat on renal function in patients from South China with CKD3 diabetic nephropathy

OBJECTIVE

To investigate the efficacy and safety of febuxostat on renal function in CKD stage 3 diabetic nephropathy patients.

METHODS

Patients in our hospital with chronic kidney disease (CKD) stage 3 diabetic nephropathy (DN) complicated by high serum uric acid (360 µmol/L) were recruited. Patients were then divided into treatment group and control group according to the random number table method. All the patients received low purine diet, renin-angiotensin-aldosterone system (RAAS) inhibitors, and adequate routine hypoglycemic treatment. Febuxostat was employed only in the treatment group. The levels of blood uric acid (sUA), serum creatinine (Scr), cystatin C (cys-c), eGFR, 24-hour urine protein quantification, albuminuria, and creatinine ratio (ACR) were evaluated in all patients before and after treatment at 4, 8, 12, and 24 week.

RESULTS

No difference was found before treatment between the two groups. After treatment at 4, 8, 12, and 24 week, the levels of sUA, SCr, cys-c, and eGFR between the two groups were significant different (P<0.05). There was no difference in 24-hour urine protein quantification, albuminuria, and creatinine ratio between two groups before treatment, and significant differences were observed after treatment. Fifty percent of patients from the treatment group achieved the treatment goal with 20 mg febuxostat at 4 weeks. Tubular markers were also decreased with the treatment.

CONCLUSIONS

Febuxostat can reduce uric acid and improve renal function effectively in patients with CKD stage 3 diabetic nephropathy, while being well tolerated. However, the conclusion is still uncertain due to the short term of the study.

Epoxy Fatty Acids: From Salt Regulation to Kidney and Cardiovascular Therapeutics: 2019 Lewis K. Dahl Memorial Lecture

Epoxyeicosatrienoic acids (EETs) are epoxy fatty acids that have biological actions that are essential for maintaining water and electrolyte homeostasis. An inability to increase EETs in response to a high-salt diet results in salt-sensitive hypertension. Vasodilation, inhibition of epithelial sodium channel, and inhibition of inflammation are the major EET actions that are beneficial to the heart, resistance arteries, and kidneys. Genetic and pharmacological means to elevate EETs demonstrated antihypertensive, anti-inflammatory, and organ protective actions. Therapeutic approaches to increase EETs were then developed for cardiovascular diseases. sEH (soluble epoxide hydrolase) inhibitors were developed and progressed to clinical trials for hypertension, diabetes mellitus, and other diseases. EET analogs were another therapeutic approach taken and these drugs are entering the early phases of clinical development. Even with the promise for these therapeutic approaches, there are still several challenges, unexplored areas, and opportunities for epoxy fatty acids.

Mechanisms in fluid retention - towards a mutual concept

Fluid retention is a common and challenging condition in daily clinical practice. The normal fluid homoeostasis in the human body is based on accurately counter-balanced physiological mechanisms. When compromised fluid retention occurs and is seen in pathophysiologically different conditions such as liver cirrhosis, heart and kidney failure, and in preeclampsia. These conditions may share pathophysiological mechanisms such as functional arterial underfilling, which seems to be a mutual element in cirrhosis, cardiac failure, cardiorenal and hepatorenal syndromes, and in pregnancy. However, there are also distinct differences and it is still unclear whether kidney dysfunction or arterial underfilling is the initiating factor of fluid retention or if they happen simultaneously. This review focuses on similarities and differences in water retaining conditions and points to areas where important knowledge is still needed.

Effects of Sleeve Gastrectomy on Blood Pressure and the Renal Renin-Angiotensin System in Rats with Diet-Induced Obesity

OBJECTIVE

Sleeve gastrectomy (SG) has been reported to decrease blood pressure (BP), although the reason has not been revealed. The present study aimed to establish the reason why SG decreases BP.

METHODS

Male Sprague-Dawley rats were subjected to surgical (sham operation or SG) and dietary interventions (fed a normal diet or high-fat diet ad libitum or fed by pair-feeding [PF]). Systolic BP (SBP), urinary sodium excretion, and endocrine parameters were examined 4 weeks after surgery.

RESULTS

Both SG and PF rats had reduced body weight compared with SO rats fed normal diet or high-fat diet ad libitum. SG rats exhibited a reduction in SBP compared with PF, which was associated with a reduction in renal renin, angiotensin II, and catechol-O-methyltransferase levels (P < 0.01 for each). SG increased plasma cholecystokinin (CCK) levels compared with PF (P < 0.0001 for each), whereas glucagon-like peptide 1 and peptide YY were not changed in fasting. Exogenous administration of CCK reduced renal catechol-O-methyltransferase (P = 0.0233), renin (P < 0.0001), and angiotensin II (P < 0.0001) levels and SBP (P = 0.0053).

CONCLUSIONS

SG reduced SBP, at least in part, through suppression of sympathetic nerve action by elevation of CCK, which was followed by suppression of the intrarenal renin-angiotensin system.

Effect of cocoa powder on hypertension and antioxidant status in uninephrectomized hypertensive rats

BACKGROUND AND AIM

High salt diet and uninephrectomy are associated with high blood pressure with attendant cardiovascular disease conditions such as hypertension, renal damage, myocardial infarction, and stroke. The aim of this study was to investigate the beneficial effects of consumption of cocoa and cocoa-containing products in the management of high blood pressure in uninephrectomized hypertensive rats.

MATERIALS AND METHODS

The effect of cocoa powder on blood pressure, markers of inflammation, oxidative stress, and histopathology were investigated in uninephrectomized animals fed with cocoa feed alone or in combination with a high salt diet. Male rats were randomly divided into five groups: Group A was the control group and fed with normal feed alone, Group B was fed with cocoa feed alone, Group C was fed with high salt diet (8% salt), GroupD was fed with cocoa-feed compounded with 8% salt for 4weeks after uninephrectomy, and GroupE was uninephrectomized rats on a normal diet. The left kidneys of animals in GroupsC, D, and E were removed by surgery. After 4weeks of treatment, the systolic, diastolic, and mean arterial blood pressure was measured. The serum markers of renal damage and oxidative stress were determined. Histological examination was also performed on renal and cardiac tissues.

RESULTS

Results showed significant increases in biomarkers of oxidative stress, inflammation, and renal damage with a concomitant decrease in antioxidant status in hypertensive uninephrectomized rats. Cocoa feed, however, significantly improved blood pressure and nitric oxide bioavailability, antioxidant status and reduced markers of inflammation and oxidative stress.

CONCLUSION

These findings show that cocoa powder could be used to maintain blood pressure levels in hypertensive rats through its antioxidant capacity.

Oxidative stress and vascular stiffness in hypertension: A renewed interest for antioxidant therapies?

Since the first successful launch of the Veterans Administration(VA) cooperative studies in the late 1960s, the increasing access to blood pressure lowering medications has significantly contributed to improving longevity and quality of life in hypertensive patients. Since then, insights into the pathogenesis of hypertension have shown a mechanistic role for reactive oxygen species (ROS) in all phases of disease progression, suggesting the potential utility of antioxidant therapies to counteract symptoms and, at the same time, treat a fundamental mechanism of the disease. Despite these progresses, hypertension still remains the main contributor to the global incidence of cardiovascular disease and the leading cause of morbidity and mortality worldwide. We here briefly review and update the role of ROS and ROS-dependent metalloproteinase activation in the maladaptive remodeling of the vascular wall in hypertension. Such understanding should provide new Potential sites of action for antioxidant therapies as an integrated therapeutic approach to hypertension and its consequences.

Perirenal Fat: A Unique Fat Pad and Potential Target for Cardiovascular Disease

Although visceral obesity is recognized as a risk factor for cardiovascular diseases (CVDs), the efficacy of omental fat removal in CVD treatment is still controversial. There is a need to identify other visceral fat depots for CVD management. This review aims to provide a summary on perirenal fat as an important risk factor for CVD. Studies on epidemiology, anatomy, and function of perirenal fat were reviewed. Observational studies in humans suggest that excessive perirenal fat increases the risk of hypertension and coronary heart disease. Anatomy studies prove that perirenal fat is unique compared to other connective tissues in that it is well vascularized, innervated, and drains into the lymphatic system. Other special morphological features include a complete fascia border, sympathetic-independent development of architecture, and proximity to the kidneys. Based on these anatomical features, perirenal fat regulates the cardiovascular system presumably via neural reflex, adipokine secretion, and fat-kidney interaction. These new insights suggest that perirenal fat may constitute a promising target for CVD management.

Analogy between non-alcoholic steatohepatitis (NASH) and hypertension: a stepwise patient-tailored approach for NASH treatment

Non-alcoholic steatohepatitis (NASH) is a common liver disorder worldwide. Although there has been improvement in our understanding of the natural history and pathogenesis of the disease, there is still no approved therapy for NASH. NASH shares many similarities with primary hypertension, in that both are extremely common disorders that can easily lead to serious complications if left untreated. Both conditions are viewed as "silent killers", because the disease can progress over a period of time prior to the occurrence of potentially deadly outcomes. While attempts to find the "miracle pill" for NASH are unrealistic, we can make an analogy with the "stepwise combination" approach developed over the last few decades for the treatment of hypertension. In the present review, we summarize some of the similarities in the concepts that underlie NASH and hypertension. The development of a stepwise patient-tailored method for the treatment of NASH is presented.

Blood pressure and age-related GFR decline in the general population

BACKGROUND

Hypertension is one of the most important causes of end-stage renal disease, but it is unclear whether elevated blood pressure (BP) also accelerates the gradual decline in the glomerular filtration rate (GFR) seen in the general population with increasing age. The reason may be that most studies have considered only baseline BP and not the effects of changes in BP, antihypertensive treatment and other determinants of GFR during follow-up. Additionally, the use of GFR estimated from creatinine or cystatin C instead of measurements of GFR may have biased the results because of influence from non-GFR related confounders. We studied the relationship between BP and GFR decline using time-varying variables in a cohort representative of the general population using measurements of GFR as iohexol clearance.

METHODS

We included 1594 subjects aged 50 to 62 years without baseline diabetes, kidney-, or cardiovascular disease in the Renal Iohexol-clearance Survey in Tromsø 6 (RENIS-T6). GFR, BP, antihypertensive medication and all adjustment variables were ascertained at baseline, and at follow-up after a median observation time of 5.6 years in 1299 persons (81%). The relationship between GFR decline and BP was analyzed in linear mixed models.

RESULTS

The mean (standard deviation) GFR decline rate was 0.95 (2.23) mL/min/year. The percentage of persons with hypertension (systolic BP ≥ 140 mmHg, diastolic BP ≥ 90 mmHg or antihypertensive medication) increased from 42 to 52% between baseline and follow-up. In multivariable adjusted linear mixed models using time-varying independent variables measured at baseline and follow-up, higher systolic and diastolic BP were associated with slower GFR decline rates by 0.10 and 0.20 mL/min/year/10 mmHg, respectively (p < 0.05). The association was stronger in persons on antihypertensive medication than in others (p < 0.05 for the interaction between BP and antihypertensive medication).

CONCLUSIONS

In the medium-term, elevated BP is not associated with accelerated GFR decline in the general middle-aged population. In persons using antihypertensive medication, elevated BP is associated with a paradoxical slower GFR decline. Studies with even longer observation periods are needed to evaluate the ultimate effect of BP on kidney function.

Urinary Exosomes and Their Cargo: Potential Biomarkers for Mineralocorticoid Arterial Hypertension?

Arterial hypertension (AHT) currently affects approximately 40% of adults worldwide, and its pathological mechanisms are mainly related to renal, vascular, and endocrine systems. Steroid hormones as aldosterone and cortisol are highly relevant to human endocrine physiology, and also to endocrine hypertension. Pathophysiological conditions, such as primary aldosteronism, affect approximately 10% of patients diagnosed with AHT and are secondary to a high production of aldosterone, increasing the risk also for cardiovascular damage and heart diseases. Excess of aldosterone or cortisol increases the activity of the mineralocorticoid receptor (MR) in epithelial and non-epithelial cells. Current research in this field highlights the potential regulatory mechanisms of the MR pathway, including pre-receptor regulation of the MR (action of 11BHSD2), MR activating proteins, and the downstream genes/proteins sensitive to MR (e.g., epithelial sodium channel, NCC, NKCC2). Mineralocorticoid AHT is present in 15-20% of hypertensive subjects, but the mechanisms associated to this condition have been poorly described, due mainly to the absence of reliable biomarkers. In this way, steroids, peptides, and lately urinary exosomes are thought to be potential reporters of biological processes. This review highlight exosomes and their cargo as potential biomarkers of metabolic changes associated to mineralocorticoid AHT. Recent reports have shown the presence of RNA, microRNAs, and proteins in urinary exosomes, which could be used as biomarkers in physiological and pathophysiological conditions. However, more studies are needed in order to benefit from exosomes and the exosomal cargo as a diagnostic tool in mineralocorticoid AHT.

Gut microbiota in hypertension

PURPOSE OF REVIEW

Hypertension, which is present in about one quarter of the world's population, is responsible for about 41% of the number one cause of death - cardiovascular disease. Not included in these statistics is the effect of sodium intake on blood pressure, even though an increase or a marked decrease in sodium intake can increase blood pressure. This review deals with the interaction of gut microbiota and the kidney with genetics and epigenetics in the regulation of blood pressure and salt sensitivity.

RECENT FINDINGS

The abundance of the gut microbes, Firmicutes and Bacteroidetes, is associated with increased blood pressure in several models of hypertension, including the spontaneously hypertensive and Dahl salt-sensitive rats. Decreasing gut microbiota by antibiotics can increase or decrease blood pressure that is influenced by genotype. The biological function of probiotics may also be a consequence of epigenetic modification, related, in part, to microRNA. Products of the fermentation of nutrients by gut microbiota can influence blood pressure by regulating expenditure of energy, intestinal metabolism of catecholamines, and gastrointestinal and renal ion transport, and thus, salt sensitivity.

SUMMARY

The beneficial or deleterious effect of gut microbiota on blood pressure is a consequence of several variables, including genetics, epigenetics, lifestyle, and intake of antibiotics. These variables may influence the ultimate level of blood pressure and control of hypertension.

Perinatal programming of renal function

PURPOSE OF REVIEW

Perinatal programming of renal function reflects the epigenetic alteration of genetically determined development by environmental factors. These include intrauterine malnutrition, pre and postnatal overnutrition, glucocorticoids, and certain toxins such as smoking. This review aims to summarize the most important findings.

RECENT FINDINGS

Human studies may show an increased susceptibility toward the general prevalence of renal failure in already small for gestational age children and adolescents. In particular, glomerular diseases present with a more severe clinical course. Partially related, partially independently, arterial hypertension is found in this at-risk group. The findings can mostly be confirmed in animal models. Both intrauterine nutrient deprived and overfed rodents show a tendency toward developing glomerulosclerosis and other renal disorders. Animal studies attempt to imitate clinical conditions, however, there are difficulties in transferring the findings to the human setting. The reduction of nephron number, especially in intrauterine growth-restricted humans and animals, is one mechanism of perinatal programming in the kidneys. In addition, vascular and endocrine alterations are prevalent. The molecular changes behind these mechanisms include epigenetic changes such as DNA-methylation, microRNAs, and histone modifications.

SUMMARY

Future research will have to establish clinical studies with clear and well defined inclusion criteria which also reflect prenatal life. The use of transgenic animal models might help to obtain a deeper insight into the underlying mechanisms.

Role of the kidney in the pathogenesis of hypertension: time for a neo-Guytonian paradigm or a paradigm shift?

The "Guytonian paradigm" places the direct effect of arterial pressure, on renal excretion of salt and water, at the center of long-term control of blood pressure, and thus the pathogenesis of hypertension. It originated in the sixties and remains influential within the field of hypertension research. However, the concept of one central long-term feedback loop, through which arterial pressure is maintained by its influence on renal function, has been questioned. Furthermore, some concepts in the paradigm are undermined by experimental observations. For example, volume retention and increased cardiac output induced by high salt intake do not necessarily lead to increased arterial pressure. Indeed, in multiple models of salt-sensitive hypertension the major abnormality appears to be failure of the vasodilator response to increased cardiac output, seen in salt-resistant animals, rather than an increase in cardiac output itself. There is also evidence that renal control of extracellular fluid volume is driven chiefly by volume-dependent neurohumoral control mechanisms rather than through direct or indirect effects of changes in arterial pressure, compatible with the concept that renal sodium excretion is controlled by parallel actions of different feedback systems, including hormones, reflexes, and renal arterial pressure. Moreover, we still do not fully understand the sequence of events underlying the phenomenon of "whole body autoregulation." Thus the events by which volume retention may develop to hypertension characterized by increased peripheral resistance remain enigmatic. Finally, by definition, animal models of hypertension are not "essential hypertension;" progress in our understanding of essential hypertension depends on new results on system functions in patients.

Inhibition of cyclooxygenase-2 in hematopoietic cells results in salt-sensitive hypertension

Inhibition of prostaglandin (PG) production with either nonselective or selective inhibitors of cyclooxygenase-2 (COX-2) activity can induce or exacerbate salt-sensitive hypertension. This effect has been previously attributed to inhibition of intrinsic renal COX-2 activity and subsequent increase in sodium retention by the kidney. Here, we found that macrophages isolated from kidneys of high-salt-treated WT mice have increased levels of COX-2 and microsomal PGE synthase-1 (mPGES-1). Furthermore, BM transplantation (BMT) from either COX-2-deficient or mPGES-1-deficient mice into WT mice or macrophage-specific deletion of the PGE2 type 4 (EP4) receptor induced salt-sensitive hypertension and increased phosphorylation of the renal sodium chloride cotransporter (NCC). Kidneys from high-salt-treated WT mice transplanted with Cox2-/- BM had increased macrophage and T cell infiltration and increased M1- and Th1-associated markers and cytokines. Skin macrophages from high-salt-treated mice with either genetic or pharmacologic inhibition of the COX-2 pathway expressed decreased M2 markers and VEGF-C production and exhibited aberrant lymphangiogenesis. Together, these studies demonstrate that COX-2-derived PGE2 in hematopoietic cells plays an important role in both kidney and skin in maintaining homeostasis in response to chronically increased dietary salt. Moreover, these results indicate that inhibiting COX-2 expression or activity in hematopoietic cells can result in a predisposition to salt-sensitive hypertension.

Targeting T helper 17 by mycophenolate mofetil attenuates diabetic nephropathy progression

Proinflammatory T helper 1 (Th1) and T helper 17 (Th17) cell subsets have been reported to have an immunopathogenic role in metabolic disease. We previously demonstrated that CD4(+) T cells are increased in kidneys in type 2 diabetic patients. However, the role of Th1 and Th17 cells in the development and progression of diabetic nephropathy is unclear. In this study, we examined the hypothesis that mycophenolate mofetil (MMF) attenuates diabetic kidney injury by the suppression of renal T-cell proliferation and related cytokines. Four groups of male C57/BL6 mice (8-weeks-old) were studied: (1) untreated controls, (2) MMF-treated controls (30 mg/kg of body weight per day), (3) streptozotocin (STZ)-induced diabetes, and (4) MMF-treated STZ-induced diabetes. The interferon gamma (IFN-γ) and interleukin 17 (IL-17) from renal CD4(+) T cells were analyzed in kidney mononuclear cells by flow cytometry. We found proliferating CD4(+) T cells were significantly increased in the kidney compared with the spleen. There were increases in IFN-γ(+) CD4(+) and IL-17A(+) CD4(+) T cells from the initiation of albuminuria in the kidneys of diabetic mice. We found MMF suppresses only the intrarenal IL-17A(+) CD4(+) T cells from early diabetic nephropathy and improves albuminuria, tubulointerstitial fibrosis independent of glycemic control. Our study results suggest that Th17 may play an independent role in the progression of diabetic nephropathy and modulation of IL-17 has potential as an immunologic therapeutic target.