Salt Sensitivity and Nondippers in Chronic Kidney Disease

Dipping Status, Ambulatory Blood Pressure Control, Cardiovascular Disease, and Kidney Disease Progression: A Multicenter Cohort Study of CKD

RATIONALE & OBJECTIVE

Ambulatory blood pressure (BP) monitoring allows concurrent evaluation of BP control and nocturnal BP dipping status, both related to adverse outcomes. However, few studies have assessed the prognostic role of combining information on dipping status and achieved ambulatory BP in patients with chronic kidney disease (CKD).

STUDY DESIGN

Prospective observational cohort study.

SETTING & PARTICIPANTS

906 patients with hypertension and CKD attending 1 of 3 Italian nephrology clinics.

EXPOSURE

Four groups were defined by simultaneously classifying systolic ambulatory BP levels as being at goal (daytime SBP <135 and nighttime SBP <120 mm Hg) or above goal, and the presence or absence of nocturnal dipping (nighttime to daytime SBP ratio of <0.9 versus ≥0.9).

OUTCOME

The composite of time to initiation of maintenance dialysis or estimated glomerular filtration rate (eGFR) decline ≥50%, and the composite of fatal and nonfatal cardiovascular events.

ANALYTICAL APPROACH

Multivariable Cox proportional hazards models were used to estimate risks of kidney disease progression and cardiovascular disease in the 4 exposure groups where nocturnal dipping with systolic ambulatory BP at goal was the reference group.

RESULTS

The mean patient age was 63.8 years, 61% were male, and 26.4% had diabetes; eGFR was 41.1 ± 20.8 mL/min/1.73 m². The dipping prevalence in each of the 4 groups was as follows: nocturnal dipping with ambulatory BP at goal, 18.6%; no nocturnal dipping with ambulatory BP at goal, 20.5%; nocturnal dipping with ambulatory BP above goal, 11.8%; and no nocturnal dipping with ambulatory BP above goal, 49.1%. Among patients with ambulatory BP above goal, the risk of cardiovascular events was greater in the absence (HR, 2.79 [95% CI, 1.64-4.75]) and presence (HR, 2.05 [95% CI, 1.10-3.84]) of nocturnal dipping. The same held true for risk of kidney disease progression (HRs of 2.40 [95% CI, 1.58-3.65] and 2.11 [95% CI, 1.28-3.48] in the absence and presence of nocturnal dipping, respectively). Patients at the ambulatory BP goal but who did not experience nocturnal dipping had an increased risk of the cardiovascular end point (HR, 2.06 [95% CI, 1.15-3.68]) and the kidney disease progression outcome (HR, 1.82 [95% CI, 1.17-2.82]).

LIMITATIONS

Lack of a diverse cohort (all those enrolled were White). Residual uncontrolled confounding.

CONCLUSIONS

Systolic ambulatory BP above goal or the absence of nocturnal dipping, regardless of ambulatory BP, is associated with higher risks of cardiovascular disease and kidney disease progression among patients with CKD.

PLAIN-LANGUAGE SUMMARY

Among patients with chronic kidney disease (CKD), ambulatory blood pressure (BP) monitoring improves the identification of individuals at high risk of clinical disease outcomes. Those with uncontrolled ambulatory BP are known to have a higher risk of developing cardiovascular disease and kidney disease progression, particularly when their ambulatory BP does not decline by at least 10% at night. Whether this is also true for patients with presence of optimal ambulatory BP levels but a BP pattern of no nighttime decline is largely unknown. We measured ambulatory BP in 900 Italian patients with CKD and followed them for several years. We found that, independent of ambulatory BP level, the absence of nighttime reductions in BP was associated with worsening of CKD and more frequent cardiovascular events. The absence of nighttime declines in BP is an independent risk factor for adverse events among patients with CKD. Future studies are needed to examine whether treating the absence of nighttime declines in BP improves clinical outcomes.

Circadian Rhythm of Blood Pressure of Dipper and Non-dipper Patients With Essential Hypertension: A Mathematical Modeling Approach

Blood pressure in humans presents a circadian variation profile with a morning increase, a small postprandial valley, and a deeper descent during night-time rest. Under certain conditions, the nocturnal decline in blood pressure can be reduced or even reversed (non-dipper), which is related to a significantly worse prognosis than a normal fall pattern (dipper). Despite several advances in recent years, our understanding of blood pressure's temporal structure, its sources and mechanisms is far from complete. In this work, we developed an ordinary differential equation-based mathematical model capable of capturing the circadian rhythm of blood pressure in dipper and non-dipper patients with arterial hypertension. The model was calibrated by means of global optimization, using 24-h data of systolic and diastolic blood pressure, physical activity, heart rate, blood glucose and norepinephrine, obtained from the literature. After fitting the model, the mean of the normalized error for each data point was <0.2%, and confidence intervals indicate that all parameters were identifiable. Sensitivity analysis allowed identifying the most relevant parameters and therefore inferring the most important blood pressure regulatory mechanisms involved in the non-dipper status, namely, increase in sympathetic over parasympathetic nervous tone, lower influence of physical activity on heart rate and greater influence of physical activity and glucose on the systemic vascular resistance. In summary, this model allows explaining the circadian rhythm of blood pressure and deepening the understanding of the underlying mechanisms and interactions integrating the results of previous works.

Association of a Disrupted Dipping Pattern of Blood Pressure with Progression of Renal Injury during the Development of Salt-Dependent Hypertension in Rats

The aim of the present study is to investigate whether a disruption of the dipping pattern of blood pressure (BP) is associated with the progression of renal injury in Dahl salt-sensitive (DSS) hypertensive rats. Seven-week-old DSS rats were fed a high salt diet (HSD; 8% NaCl) for 10 weeks, followed by a transition to a normal salt diet (NSD; 0.3% NaCl) for 4 weeks. At baseline, NSD-fed DSS rats showed a dipper-type circadian rhythm of BP. By contrast, HSD for 5 days caused a significant increase in the difference between the active and inactive periods of BP with an extreme dipper type of BP, while proteinuria and renal tissue injury were not observed. Interestingly, HSD feeding for 10 weeks developed hypertension with a non-dipper pattern of BP, which was associated with obvious proteinuria and renal tissue injury. Four weeks after switching to an NSD, BP and proteinuria were significantly decreased, and the BP circadian rhythm returned to the normal dipper pattern. These data suggest that the non-dipper pattern of BP is associated with the progression of renal injury during the development of salt-dependent hypertension.

Proteasuria-The impact of active urinary proteases on sodium retention in nephrotic syndrome

Sodium retention and extracellular volume expansion are typical features of patients with nephrotic syndrome. In recent years, from in vitro data, endoluminal activation of the epithelial sodium channel (ENaC) by aberrantly filtered serine proteases has been proposed as an underlying mechanism. Recently, this concept was supported in vivo in nephrotic mice that were protected from proteolytic ENaC activation and sodium retention by the use of aprotinin for the pharmacological inhibition of urinary serine protease activity. These and other findings from studies in both rodents and humans highlight the impact of active proteases in the urine, or proteasuria, on ENaC-mediated sodium retention and edema formation in nephrotic syndrome. Targeting proteasuria could become a therapeutic approach to treat patients with nephrotic syndrome. However, pathophysiologically relevant proteases remain to be identified. In this review, we introduce the concept of proteasuria to explain tubular sodium avidity and conclude that proteasuria can be considered as a key mechanism of sodium retention in patients with nephrotic syndrome.

Clinical Conditions and Predictive Markers of Non-Dipper Profile in Hypertensive Patients

Hypertension remains one of the primary causes of premature cardiovascular mortality representing a major independent risk factor.

The importance of ambulatory blood pressure monitoring in clinical evaluation of hypertensive patients, beyond diagnosis, is the identification of circadian dipping/non-dipping profile. The non-dipper pattern in hypertensive and normotensive patients is associated with significant target organ damage and worse outcomes, as an increased cardiovascular risk condition. Non-dipping pattern has been found to be associated with specific clinical conditions. Obesity, diabetes mellitus, metabolic syndrome, obstructive sleep apnea syndrome, chronic kidney disease, autonomic and baroreflex dysfunctions, salt sensitivity, hormonal changes, gender and age were extensively studied. Research efforts are focused on recognizing and exploring predictive markers of abnormal blood pressure circadian pattern. Previous studies acknowledge that red cell distribution width, mean platelet volume, fibrinogen level, C-reactive protein, serum uric acid and gamma-glutamyltransferase, are independently significant and positive associated to non-dipping pattern. Moreover, research on new biomarkers are conducted: Chitinase 3-Like-Protein 1, atrial and B-type natriuretic peptide, brain-derived neurotrophic factor, chemerin, sphingomyelin and the G972R polymorphism of the insulin receptor substrate-1 gene. This review summarizes the current knowledge of different clinical conditions and biomarkers associated with the non-dipper profile in hypertensive patients.

Sodium balance, circadian BP rhythm, heart rate variability, and intrarenal renin-angiotensin-aldosterone and dopaminergic systems in acute phase of ARB therapy

We have revealed that even in humans, activated intrarenal renin–angiotensin–aldosterone system (RAAS) enhances tubular sodium reabsorption to facilitate salt sensitivity and nondipper rhythm of blood pressure (BP), and that angiotensin receptor blocker (ARB) could increase daytime urinary sodium excretion rate (U_NaV) to produce lower sodium balance and restore nondipper rhythm. However, the sympathetic nervous system and intrarenal dopaminergic system can also contribute to renal sodium handling. A total of 20 patients with chronic kidney disease (61 ± 15 years) underwent 24‐h ambulatory BP monitoring before and during two‐day treatment with ARB, azilsartan. Urinary angiotensinogen excretion rate (U_AGTV, μg/gCre) was measured as intrarenal RAAS; urinary dopamine excretion rate (U_DAV, pg/gCre) as intrarenal dopaminergic system; heart rate variabilities (HRV, calculated from 24‐h Holter‐ECG) of non‐Gaussianity index λ_25s as sympathetic nerve activity; and power of high‐frequency (HF) component or deceleration capacity (DC) as parasympathetic nerve activity. At baseline, glomerular filtration rate correlated inversely with U_AGTV (r = −0.47, P = 0.04) and positively with U_DAV (r = 0.58, P = 0.009). HF was a determinant of night/day BP ratio (β = −0.50, F = 5.8), rather than DC or λ_25s. During the acute phase of ARB treatment, a lower steady sodium balance was not achieved. Increase in daytime U_NaV preceded restoration of BP rhythm, accompanied by decreased U_AGTV (r = −0.88, P = 0.05) and increased U_DAV (r = 0.87, P = 0.05), but with no changes in HRVs. Diminished sodium excretion can cause nondipper BP rhythm. This was attributable to intrarenal RAAS and dopaminergic system and impaired parasympathetic nerve activity. During the acute phase of ARB treatment, cooperative effects of ARB and intrarenal dopaminergic system exert natriuresis to restore circadian BP rhythm.

Addition of hydrochlorothiazide to angiotensin receptor blocker therapy can achieve a lower sodium balance with no acceleration of intrarenal renin angiotensin system in patients with chronic kidney disease

Objective:

Angiotensin receptor blockers (ARBs) produce a lower sodium (Na) balance, and the natriuretic effect is enhanced under Na deprivation, despite falls in blood pressure (BP) and glomerular filtration rate (GFR).

Methods:

The effect of additional hydrochlorothiazide (HCTZ; 12.5 mg/day) to ARB treatment (valsartan; 80 mg/day) on glomerulotubular Na balance was evaluated in 23 patients with chronic kidney disease.

Results:

Add-on HCTZ decreased GFR, tubular Na load, and tubular Na reabsorption (t_Na), although 24-hour urinary Na excretion (U_NaV) remained constant. Daily urinary angiotensinogen excretion (U_AGTV, 152±10→82±17 μg/g Cre) reduced (p=0.02). Changes in tubular Na load (r²=0.26) and t_Na (r²=0.25) correlated with baseline 24-hour U_AGTV. Changes in filtered Na load correlated with changes in nighttime systolic BP (r²=0.17), but not with changes in daytime systolic BP. The change in the t_Na to filtered Na load ratio was influenced by the change in daytime U_NaV (β=−0.67, F=16.8), rather than the change in nighttime U_NaV.

Conclusions:

Lower Na balance was produced by add-on HCTZ to ARB treatment without an increase of intra-renal renin-angiotensin system activity, leading to restoration of nocturnal hypertension. A further study is needed to demonstrate that the reduction of U_AGTV by additional diuretics to ARBs prevents the progression of nephropathy or cardiovascular events.

Sodium intake and renal outcomes: a systematic review

BACKGROUND

Sodium intake is an important determinant of blood pressure; therefore, reduction of intake may be an attractive population-based target for chronic kidney disease (CKD) prevention. Most guidelines recommend sodium intake of < 2.3 g/day, based on limited evidence. We reviewed the association between sodium intake and renal outcomes.

METHODS

We reviewed cohort studies and clinical trials, which were retrieved by searching electronic databases, that evaluated the association between sodium intake/excretion and measures of renal function, proteinuria, or new need for dialysis.

RESULTS

Of 4,337 reviewed citations, seven (n = 8,129) were eligible, including six cohort studies (n = 7,942) and one clinical trial (n = 187). Four studies (n = 1,787) included patients with CKD. All four cohort studies reported that high intake (> 4.6 g/day) was associated with adverse outcomes (vs. moderate/low), while none reported an increased risk with moderate intake (vs. low). Three studies (n = 6,342) included patients without CKD. Two cohort studies (n = 6,155) reported opposing directions of association between low (vs. moderate) sodium intake and renal outcomes, and one clinical trial (n = 187) reported a benefit from low intake (vs. moderate) on proteinuria but an adverse effect on serum creatinine.

CONCLUSIONS

Available, but limited, evidence supports an association between high sodium intake (> 4.6g/day) and adverse outcomes. However, the association with low intake (vs. moderate) is uncertain, with inconsistent findings from cohort studies. There is urgent need to clarify the long-term efficacy and safety of currently recommended low sodium intake in patients with CKD.

The fixed-dose combination of losartan/hydrochlorothiazide elicits potent blood pressure lowering during nighttime in obese hypertensive patients

Background

Hypertension is one of the most powerful predictor of the future cardiovascular events, and antihypertensive therapy adopting multiple drug regimen is often needed to obtain the appropriate blood pressure (BP) control. To clarify the blood pressure-lowering effect of the fixed-dose combination (FDC) of an angiotensin receptor blocker (ARB) and diuretic agent in poorly controlled hypertensive patients, we intended a multicenter prospective observational study (Investigation for Normalized Blood pressure control with the Appropriate medication: INBA) by means of the sequential ambulatory blood pressure monitoring (ABPM).

Methods

One hundred and thirteen hypertensive patients who had not achieved the target BP control proposed in the guidelines with medication containing any ARB but without diuretic agents (54 men; mean age, 66 years old; mean office systolic/diastolic BP (SBP/DBP), 158/82 mmHg) were enrolled. Daytime and nighttime blood pressures were assessed with ABPM before and at 12 weeks after switching the ARB to the FDC of 50 mg of losartan, and 12.5 mg of hydrochlorothiazide (HCTZ).

Results

Daytime SBP/DBP (mean ± SD) decreased from 151 ± 14/88 ± 8 mmHg to 140 ± 11/82 ± 8 mmHg (P < 0.001, P < 0.001, respectively), and nocturnal SBP/DBP from 138 ± 18/78 ± 9 mmHg to 125 ± 14/72 ± 9 mmHg (P < 0.001, P < 0.001, respectively) during the 12 weeks treatment. Pulse rate did not change irrespective of the time window. Among various parameters (age, history of hypertension, body mass index (BMI), serum potassium, uric acid, estimated glomerular filtration rate, plasma B-type natriuretic peptide), BMI alone showed significant negative correlation with 12-weeks reduction in nocturnal SBP (r = -0.43, P < 0.05). No parameters correlated with reduction in daytime SBP during this period. Patients with BMI ≥ median (25.8 kg/m²) showed significantly greater reduction in nocturnal SBP for 12 weeks than patients with BMI < median (20.1 ± 15.6 mmHg vs 6.1 ± 10.9 mmHg, P < 0.001) although reduction in daytime SBP was comparable between the two groups (8.9 ± 13.5 mmHg vs 11.9 ± 12.7 mmHg).

Conclusions

The administration of the FDC of losartan/HCTZ lowers BP both in day- and nighttime, and the nocturnal antihypertensive potency is remarkable in obese patients.

Long-term control of ambulatory hypertension in children: improving with time but still not achieving new blood pressure goals

BACKGROUND

Short-term therapy can decrease blood pressure (BP) to less than the 95th percentile in only about 50% of children. The aim of our study was to investigate the long-term control of hypertension (HT) in children using ambulatory BP monitoring (ABPM).

METHODS

We analyzed data from all children who started ramipril monotherapy in our center. Controlled HT was defined according to the most current guidelines as systolic and diastolic BP at daytime and nighttime <90th percentile in primary HT and <75th percentile in renoparenchymal HT.

RESULTS

Thirty-eight children who were on therapy ≥1 year were included. Thirty-two children had renoparenchymal, and 6 had primary HT. The median age at the beginning of therapy was 13.6 years (range = 4.1-18.0 years), and the median time of antihypertensive therapy was 2.6 years (range = 1.0-11.8 years). Thirty-four percent of children received combination therapy; the median number of antihypertensive drugs was 1.5 drugs/patient (range = 1-4). Sixty-eight percent of children had BP <95th percentile, but only 34% of the children had controlled HT. Children with uncontrolled HT had a tendency to have a higher daytime diastolic BP index before the start of therapy than children with controlled HT (0.99±0.11 vs. 0.94±0.11; P = 0.09). There was a significant decrease in prevalence of nondipping (from 47% to 16%; P = 0.006) with therapy.

CONCLUSIONS

This first pediatric study focusing on long-term control of HT using ABPM showed that long-term control of HT is better than short-term control, but still only one-third of children achieve the new BP goals. The low control of HT might be improved by more intensive therapy.

Blood pressure variability in chronic kidney disease patients

'Usual' blood pressure (BP) levels are known to be directly related to cardiovascular (CV) risk in the general population and patients with essential hypertension. However, there is increasing evidence that, apart from usual BP, BP variability across visits may also be an important risk factor for death and CV events in healthy subjects and in essential hypertensive patients. In chronic kidney disease (CKD) patients the relationship between hypertension and clinical outcome is still controversial. Moreover, high visit-to-visit BP variability was very recently found to predict death and CV events in this high-risk patient population. This review focuses on the available evidence about the link between high visit-to-visit BP variability and clinical outcomes in CKD patients and describes some hypothetical mechanisms that could explain such a relationship.

Significance of estimated salt excretion as a possible predictor of the efficacy of concomitant angiotensin receptor blocker (ARB) and low-dose thiazide in patients with ARB resistance

The purpose of this study was to assess the factors affecting the efficacy of combination therapy with losartan and thiazide, with a focus on the significance of salt excretion, via a multicenter observational study. Adult patients with essential hypertension showing therapy resistance to angiotensin receptor blocker (ARB) as a monotherapy or in combination with Ca channel blockers (CCB) were enrolled, and their previously administered ARBs were replaced with the combination tablet containing losartan (50 mg per day) and hydrochlorothiazide (12.5 mg per day). Blood pressure and biochemical parameters were monitored for a year. The baseline blood pressure (153.4±14.8/86.4±11.3 mm Hg) was significantly lowered at the 3rd month (137.3±17.4/78.2±11.1 mm Hg, n=93) and was maintained at this lower level until the 12th month (135.3±14.0/76.4±11.1 mm Hg, n=74). The baseline value of estimated salt excretion (eSE), calculated using Tanaka's formula, differed significantly between the high and low treatment response groups, which were defined by the average change in mean blood pressure (MBP-C, -11.3 mm Hg; eSE=10.8±2.9 g per day in high responders vs. 9.2±2.3 g per day in low responders, P=0.004). Univariate and multivariate analyses showed a significant correlation between eSE and MBP-C (R=-0.288, P=0.007) and indicated the clinical effectiveness of eSE as a possible predictor for MBP-C (P=0.021). In addition, the urine Na-to-Cr ratio (NCR) demonstrated significant correlations with eSE (R=0.848, P<0.001) and MBP-C (R=-0.344, P<0.001). These results suggest that eSE or NCR could, to a certain extent, predict the efficacy of combination therapy with losartan and low-dose thiazide in patients demonstrating ARB resistance. Combination therapy with losartan and thiazide might thus be suitable for patients with a large amount of salt excretion.