The effect of a shift in sodium intake on renal hemodynamics is determined by body mass index in healthy young men

Sodium and water dynamics in the progression of chronic kidney disease: mechanisms and clinical significance

AIM

Lifestyle modifications can postpone the progression of chronic kidney disease toward its terminal stage. This mini-review aims to explore the impact of salt and water intake on the progression of chronic kidney disease (CKD) and provide insights into the optimal consumption levels to preserve the glomerular filtration rate.

METHODS

We reviewed relevant literature to examine the association between salt and water consumption and CKD progression. Our analysis includes discussions on the pathophysiology, findings from clinical trials, and recommended intake guidelines.

RESULTS

Sodium intake, often linked to cardiovascular risk and CKD progression, has shown a complex J-shaped association in some studies, leading to uncertainty about the ideal salt intake level. Sodium and fluid retention are key factors contributing to hypertension, a well-established risk factor for CKD progression. Low-sodium diets have demonstrated promise in reducing blood pressure and enhancing the effects of renin-angiotensin-aldosterone system inhibitors in non-dialysis CKD patients. However, a debate persists regarding the independent effect of salt restriction on CKD progression. Despite medical recommendations, salt consumption remains high among CKD patients. Additionally, the role of water consumption in CKD remains controversial despite its established benefits for CKD prevention in the general population.

CONCLUSION

Lifestyle modifications involving salt and water intake can influence the progression of CKD. While low-sodium diets have shown potential for mitigating hypertension and proteinuria in non-dialysis CKD patients, their independent impact on CKD progression warrants further investigation. The role of water consumption in CKD remains uncertain, and there is a need for additional research in this area. Clinicians should consider individualized dietary recommendations for CKD patients to help preserve the glomerular filtration rate and improve overall outcomes.

High dietary salt intake attenuates nitric oxide mediated endothelium-dependent vasodilation and increases oxidative stress in pregnancy

OBJECTIVE

This study aimed to investigate the impact of dietary salt intake during normal pregnancy on maternal microvascular and macrovascular endothelium-dependent reactivity and oxidative stress level.

MATERIALS AND METHODS

In this cross-sectional study, based on their 24-h urinary sodium excretion, pregnant women (37-40 weeks of gestation) were divided into three groups: normal salt (<5.75 g/day, N  = 12), high salt (5.75-10.25 g/day, N  = 36), and very high salt (VHS;>10.25 g/day, N  = 17). Forearm skin microvascular reactivity in response to vascular occlusion, local heating (LTH) and iontophoresis of acetylcholine (AChID), as well as brachial artery flow mediated dilation (FMD) were measured. Serum nitric oxide, endocan, 8-iso-prostaglandin F2α (8-iso-PGF2α), thiobarbituric acid reactive substances (TBARS), and ferric-reducing ability of plasma assay were measured as biomarkers of endothelial function/activation and oxidative stress.

RESULTS

Brachial artery FMD, microvascular AChID, and LTH were significantly decreased in VHS compared with NS group, while LTH was also decreased in normal salt compared with high salt group. Nitric oxide was significantly decreased in both high salt and VHS groups compared with normal salt. Endocan, 8-iso-PGF2α, and TBARS were significantly increased in VHS compared with the normal salt group.

CONCLUSION

High dietary salt intake is associated with decreased nitric oxide mediated endothelium-dependent vasodilation in peripheral microcirculation and macrocirculation of healthy pregnant women due to increased oxidative stress.

Management of traditional risk factors for the development and progression of chronic kidney disease

Chronic kidney disease (CKD) and its downstream complications (i.e. cardiovascular) are a major source of morbidity worldwide. Additionally, deaths due to CKD or CKD-attributable cardiovascular disease account for a sizeable proportion of global mortality. However, the advent of new pharmacotherapies, diagnostic tools, and global initiatives are directing greater attention to kidney health in the public health agenda, including the implementation of effective strategies that (i) prevent kidney disease, (ii) provide early CKD detection, and (iii) ameliorate CKD progression and its related complications. In this Review, we discuss major risk factors for incident CKD and CKD progression categorized across cardiovascular (i.e. hypertension, dyslipidemia, cardiorenal syndrome), endocrine (i.e. diabetes mellitus, hypothyroidism, testosterone), lifestyle (i.e. obesity, dietary factors, smoking), and genetic/environmental (i.e. CKDu/Mesoamerican nephropathy, APOL1, herbal nephropathy) domains, as well as scope, mechanistic underpinnings, and management.

Anemia and Hypoxia Impact on Chronic Kidney Disease Onset and Progression: Review and Updates

Chronic kidney disease (CKD) is caused by hypoxia in the renal tissue, leading to inflammation and increased migration of pathogenic cells. Studies showed that leukocytes directly sense hypoxia and respond by initiating gene transcription, encoding the 2-integrin adhesion molecules. Moreover, other mechanisms participate in hypoxia, including anemia. CKD-associated anemia is common, which induces and worsens hypoxia, contributing to CKD progression. Anemia correction can slow CKD progression, but it should be cautiously approached. In this comprehensive review, the underlying pathophysiology mechanisms and the impact of renal tissue hypoxia and anemia in CKD onset and progression will be reviewed and discussed in detail. Searching for the latest updates in PubMed Central, Medline, PubMed database, Google Scholar, and Google search engines were conducted for original studies, including cross-sectional studies, cohort studies, clinical trials, and review articles using different keywords, phrases, and texts such as "CKD progression, anemia in CKD, CKD, anemia effect on CKD progression, anemia effect on CKD progression, and hypoxia and CKD progression". Kidney tissue hypoxia and anemia have an impact on CKD onset and progression. Hypoxia causes nephron cell death, enhancing fibrosis by increasing interstitium protein deposition, inflammatory cell activation, and apoptosis. Severe anemia correction improves life quality and may delay CKD progression. Detection and avoidance of the risk factors of hypoxia prevent recurrent acute kidney injury (AKI) and reduce the CKD rate. A better understanding of kidney hypoxia would prevent AKI and CKD and lead to new therapeutic strategies.

Protein intake and risk of urolithiasis and kidney diseases: an umbrella review of systematic reviews for the evidence-based guideline of the German Nutrition Society

PURPOSE

Changes in dietary protein intake metabolically affect kidney functions. However, knowledge on potential adverse consequences of long-term higher protein intake (HPI) for kidney health is lacking. To summarise and evaluate the available evidence for a relation between HPI and kidney diseases, an umbrella review of systematic reviews (SR) was conducted.

METHODS

PubMed, Embase and Cochrane Database of SRs published until 12/2022 were searched for the respective SRs with and without meta-analyses (MA) of randomised controlled trials or cohort studies. For assessments of methodological quality and of outcome-specific certainty of evidence, a modified version of AMSTAR 2 and the NutriGrade scoring tool were used, respectively. The overall certainty of evidence was assessed according to predefined criteria.

RESULTS

Six SRs with MA and three SRs without MA on various kidney-related outcomes were identified. Outcomes were chronic kidney disease, kidney stones and kidney function-related parameters: albuminuria, glomerular filtration rate, serum urea, urinary pH and urinary calcium excretion. Overall certainty of evidence was graded as 'possible' for stone risk not to be associated with HPI and albuminuria not to be elevated through HPI (above recommendations (> 0.8 g/kg body weight/day)) and graded as 'probable' or 'possible' for most other kidney function-related parameters to be physiologically increased with HPI.

CONCLUSION

Changes of the assessed outcomes may have reflected mostly physiological (regulatory), but not pathometabolic responses to higher protein loads. For none of the outcomes, evidence was found that HPI does specifically trigger kidney stones or diseases. However, for potential recommendations long-term data, also over decades, are required.

High dietary salt intake increases urinary NGAL excretion and creatinine clearance in healthy young adults

In rodents and older patients with elevated blood pressure (BP), high dietary sodium increases excretion of biomarkers of kidney injury, but it is unclear whether this effect occurs in healthy young adults. The purpose of this study was to determine whether short-term high dietary salt increases urinary excretion of the kidney injury biomarkers neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) in healthy young adults. Twenty participants participated in a double-blind, placebo-controlled, randomized crossover study. For 10 days each, participants were asked to consume salt (3,900 mg sodium) or placebo capsules. We measured BP during each visit, obtained 24-h urine samples for measurements of electrolytes, NGAL, and KIM-1, and assessed creatinine clearance. Compared with placebo, salt loading increased daily urinary sodium excretion (placebo: 130.3 ± 62.4 mmol/24 h vs. salt: 287.2 ± 72.0 mmol/24 h, P < 0.01). There was no difference in mean arterial BP (placebo: 77 ± 7 mmHg vs. salt: 77 ± 6 mmHg, P = 0.83) between conditions. However, salt loading increased the urinary NGAL excretion rate (placebo: 59.8 ± 44.4 ng/min vs. salt: 80.8 ± 49.5 ng/min, P < 0.01) and increased creatinine clearance (placebo: 110.5 ± 32.9 mL/min vs. salt: 145.0 ± 24.9 mL/min, P < 0.01). Urinary KIM-1 excretion was not different between conditions. In conclusion, in healthy young adults 10 days of dietary salt loading increased creatinine clearance and increased urinary excretion of the kidney injury biomarker marker NGAL but not KIM-1.NEW & NOTEWORTHY In healthy young adults, 10 days of dietary salt loading increased creatinine clearance and increased urinary excretion of the kidney injury biomarker marker neutrophil gelatinase-associated lipocalin despite no change in resting blood pressure.

Effect of a low-salt diet on chronic kidney disease outcomes: a systematic review and meta-analysis

OBJECTIVE

The benefits of a low-salt diet for patients with chronic kidney disease (CKD) are controversial. We conducted a systematic review and meta-analysis of the effect of a low-salt diet on major clinical outcomes.

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

MEDLINE by Ovid, EMBASE and the Cochrane Library databases.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

We included randomised controlled trials (RCTs) and cohort studies that assessed the effect of a low-salt diet on the renal composite outcomes (more than 50% decline in estimated glomerular filtration rate (eGFR) during follow-up, doubling of serum creatinine or end-stage renal disease), rate of eGFR decline, change in proteinuria, all-cause mortality events, cardiovascular (CV) events, and changes in systolic blood pressure and diastolic blood pressure.

DATA EXTRACTION AND SYNTHESIS

Two independent researchers extracted data and evaluated their quality. Relative risks (RRs) with 95% CIs were used for dichotomous data. Differences in means (MDs) or standardised mean differences (SMDs) with 95% CIs were used to pool continuous data. We used the Cochrane Collaboration risk-of-bias tool to evaluate the quality of RCTs, and Newcastle-Ottawa Scale to evaluate the quality of cohort studies.

RESULTS

We found 9948 potential research records. After removing duplicates, we reviewed the titles and abstracts, and screened the full text of 230 publications. Thirty-three studies with 101 077 participants were included. A low-salt diet produced a 28% reduction in renal composite outcome events (RR: 0.72; 95% CI: 0.58 to 0.89). No significant effects were found in terms of changes in proteinuria (SMD: -0.71; 95% CI: -1.66 to 0.24), rate of eGFR (decline MD: 1.16; 95% CI: -2.02 to 4.33), risk of all-cause mortality (RR: 0.92; 95% CI: 0.58 to 1.46) and CV events (RR: 1.01; 95% CI: 0.46 to 2.22).

CONCLUSION

A low-salt diet seems to reduce the risk for renal composite outcome events in patients with CKD. However, no compelling evidence indicated that such a diet would reduce the eGFR decline rate, proteinuria, incidence of all-cause mortality and CV events. Further, more definitive studies are needed.

PROSPERO REGISTRATION NUMBER

CRD42017072395.

Plasma sodium, extracellular fluid volume, and blood pressure in healthy men

In the general population we recently reported a consistent association between plasma sodium and volume markers, suggesting that individuals with higher plasma sodium have higher extracellular fluid volume (ECFV). To test this hypothesis, we analyzed the association between plasma sodium and directly measured ECFV (iothalamate distribution volume) in healthy men. Second, we studied whether plasma sodium is associated with blood pressure. We analyzed data from 70 men (age 24 ± 7 years) at the end of two 7-day periods on a low-sodium diet (LS, 50 mmol Na/24 h) and a high-sodium diet (HS, 200 mmol Na/24 h), respectively. The association of plasma sodium with blood pressure was assessed in the combined data of the different sodium intakes by linear mixed effects models. A positive univariable association between plasma sodium and ECFV was found during HS (β = 0.24, p = 0.042) and LS (β = 0.23, p = 0.058), respectively. Individual values of plasma sodium on LS and HS diet were strongly correlated (β = 0.68, p < 0.001), as were values for ECFV (β = 0.54, p < 0.001). In the combined data set plasma sodium level was significantly associated with ECFV (B [SE] = 0.10 [0.04], p = 0.02), and systolic blood pressure (SBP, B [SE] = 0.73 [0.26], p = 0.006), independent of ECFV. In conclusion, plasma sodium concentration is positively associated with ECFV on both LS and HS intake. Our data confirm and extend prior data on individual regulation of plasma sodium and suggest that this is associated with individuality of the regulation of ECFV. Finally, plasma sodium level is associated with SBP, independent of ECFV and diet.

Effects of a Behavioral Weight Loss Intervention and Metformin Treatment on Serum Urate: Results from a Randomized Clinical Trial

Background: Lower body mass index (BMI) has been associated with lower serum urate (SU), but only in observational studies. We sought to determine the effects of behavioral weight loss and metformin treatment on SU in a randomized trial. Methods and Findings: The Survivorship Promotion In Reducing IGF-1 Trial (SPIRIT) was a parallel three-arm randomized controlled trial of overweight/obese adult cancer survivors without gout at a single center in Maryland, United States. Participants were randomized to: (1) coach-directed weight loss (behavioral telephonic coaching), (2) metformin (up to 2000 mg daily), or (3) self-directed weight loss (informational brochures; reference group). SU and BMI were assessed at baseline and at 3, 6, and 12 months post-randomization. The 121 participants had a mean ± standard deviation (SD) age of 60 ± 9 years, 79% were female, and 45% were Black. At baseline, BMI was 35 ± 5 kg/m², and SU was 5.6 ± 1.3 mg/dL. Compared to the self-directed group, at 12 months, the coach-directed group reduced BMI by 0.9 kg/m² (95% confidence interval (CI): -1.5, -0.4) and metformin reduced BMI by 0.6 kg/m² (95% CI: -1.1, -0.1). However, compared to the self-directed group, the coach-directed group unexpectedly increased SU by 0.3 mg/dL (95% CI: 0.05, 0.6), and metformin non-significantly increased SU by 0.2 mg/dL (95% CI: -0.04, 0.5); these effects were attenuated when analyses included change in estimated glomerular filtration rate (eGFR). Conclusions: In this randomized trial of cancer survivors without gout, reductions in BMI either increased or did not change SU, potentially due to effects on eGFR. These results do not support a focus on BMI reduction for SU reduction; however, long-term studies are needed. ClinicalTrials.gov Registration: NCT02431676.

The Forgotten Antiproteinuric Properties of Diuretics

BACKGROUND

Although diuretics are one of the most widely used drugs by nephrologists, their antiproteinuric properties are not generally taken into consideration.

SUMMARY

Thiazide diuretics have been shown to reduce proteinuria by >35% in several prospective controlled studies, and these values are markedly increased when combined with a low-salt diet. Thiazide-like diuretics (indapamide and chlorthalidone) have shown similar effectiveness. The antiproteinuric effect of mineralocorticoid receptor antagonists (spironolactone, eplerenone, and finerenone) has been clearly established through prospective and controlled studies, and treatment with finerenone reduces the risk of chronic kidney disease progression in type-2 diabetic patients. The efficacy of other diuretics such as amiloride, triamterene, acetazolamide, or loop diuretics has been less explored, but different investigations suggest that they might share the same antiproteinuric properties of other diuretics that should be evaluated through controlled studies. Although the inclusion of sodium-glucose cotransporter-2 inhibitors (SGLT2i) among diuretics is a controversial issue, their renoprotective and cardioprotective properties, confirmed in various landmark trials, constitute a true revolution in the treatment of patients with kidney disease. Recent subanalyses of these trials have shown that the early antiproteinuric effect induced by SGLT2i predicts long-term preservation of kidney function. Key Message: Whether the early reduction in proteinuria induced by diuretics other than finerenone and SGLT2i, as summarized in this review, also translates into long-term renoprotection requires further prospective and observational studies. In any case, it is important for the clinician to be aware of the antiproteinuric properties of drugs so often used in daily clinical practice.

[Effect of salt intake on residual renal function in rats receiving peritoneal dialysis]

OBJECTIVE

To assess the effect of salt intake on residual renal function in rats and explore the possible mechanism.

OBJECTIVE

SD rats were 5/6-nephrectomized to induce chronic renal failure followed by peritoneal dialysis for 4 weeks (n=18) or without dialysis treatment (control group; n=18). In both groups, the rats were divided into 3 subgroups and were given lowsalt diet (0.02% NaCl), normal salt diet (0.4% NaCl), and high-salt diet (4% NaCl). After 8 and 12weeks, blood pressure and creatinine and sodium levels in the blood, urine, and peritoneal dialysate of the rats were examined. Glomerular sclerosis, tubulointerstitial fibrosis, and protein expression levels of RAS components (ACE-1, AGT, and AT-1) in renal cortical tissue of the rats were evaluated.

OBJECTIVE

The residual renal function of the rats all decreased especially in rats with high salt intake for 8and 12 weeks. In peritoneal dialysis group, the rats with high-salt diet showed signficiantly increased renal interstitial fibrosis score (P=0.036), glomerular sclerosis index (P=0.045), systolic blood pressure (P=0.004), diastolic blood pressure (P=0.048), and renal expressions of AGT, ACE-1, and AT1 (P < 0.05) as compared with those with normal salt intake. In the rats fed the same high-salt diet, the renal interstitial fibrosis score, glomerular sclerosis index, diastolic blood pressure increase, and renal AGT and ACE-1 expression levels were significantly lower in the peritoneal dialysis group than in the control group (P < 0.05). A positive correlation was noted between the reduction of residual renal function and sodium intake in the rats.

OBJECTIVE

In rats with chronic renal failure, high salt intake promotes the activation of the renal RAS system, increases blood pressure, and agrevates renal fibrosis to accelerate the decline of residual renal function, and peritoneal dialysis partially reduces the damage of residual renal function induced by high-salt diets by removing excessive sodium.

Dietary sodium intake and cortisol measurements

OBJECTIVES

To assess the influence of a dietary sodium intake intervention on cortisol measurements within the general population.

DESIGN

Cross-over intervention.

PATIENTS

Six hundred thirty adults without known Cushing syndrome, cardiovascular or renal disease completed a restricted dietary sodium diet (10 mmol/d, 230 mg/d) followed by cross-over to a liberalized dietary sodium diet (200 mmol/d, 4600 mg/d). Twenty-four-hour urine collection and biochemical investigations were performed at the end of each dietary intervention.

RESULTS

Mean 24-hour urinary free cortisol increased with liberalized sodium intake when compared with restricted sodium intake (178.0 ± 89.7 vs 121.3 ± 65.6 nmol/d, P < .001). Nearly all participants (84%) had an increase in the urinary free cortisol following liberalized sodium intake. This translated to a substantial difference in the proportion of participants exceeding categorical thresholds of urinary cortisol on liberalized vs restricted sodium intake: 62% vs 27% for 138 nmol/d (50 mcg/d), 46% vs 17% for 166 nmol/d (60 mcg/d), 32% vs 10% for 193 nmol/d (70 mcg/d), 23% vs 6% for 221 nmol/d (80 mcg/d), 17% vs 4% for 248 nmol/d (90 mcg/d). In parallel, there was a small decrease in morning total serum cortisol with liberalized sodium intake (303.0 ± 117.3 vs 326.4 ± 162.5 nmol/L, P < .001).

CONCLUSIONS

Increased dietary sodium intake increases urinary free cortisol excretion and may increase the risk for false-positive results. Variations in dietary sodium intake may influence the interpretations of cortisol measurements performed to evaluate for hypercortisolism.

DASH Dietary Pattern: A Treatment for Non-communicable Diseases

Non-communicable diseases are the major inducer of mortality and morbidity in the Western world. In terms of nutrition, a diet high in fat (particularly saturated fat), salt and sugars have shown to be associated with innumerable incidence of diet- associated health diseases. Dietary modification is a central part of any treatment strategy. The Dietary Approach to Stop Hypertension (DASH) diet is one among such healthy dietary patterns, which emphasizes on the consumption of fruits, vegetables and low-fat dairy foods, including whole grains, poultry, fish, and small quantities of red meat, sweets and drinks containing sugar. This study provides certain practical evidence that prolonged adoption of DASH diet which can be a useful treatment for numerous non-communicable diseases with a sustained effect on the health that involves both accessibility and proximity to healthy eating choices. Long-term studies are required to assess whether these effects are maintained over time.

Results of the CARDIA study suggest that higher dietary potassium may be kidney protective

The association between dietary sodium and potassium intake with the development of kidney disease remains unclear, particularly among younger individuals. Here, we determined whether dietary sodium and potassium intake are associated with incident chronic kidney disease (CKD) using data from 1,030 adults (age 23-35 in 1990-1991) from the Coronary Artery Risk Development In Young Adults study, based on repeated measurements of estimated glomerular filtration rate (eGFR) and urinary albumin to creatinine ratio (ACR) from 1995 through 2015. Urinary sodium and potassium excretion (mg/day), calculated from three 24-hour urine collections in 1990-1991, were averaged to measure sodium and potassium intake. Serum creatinine was used to calculate eGFR using the CKD EPI equation; spot urine albumin and creatinine were used to calculate ACR, each at five visits from 1995-1996 through 2015-2016. CKD was defined as decreased eGFR (under 60 ml/min/1.73m2) or the development of albuminuria (ACR over 30 mg/g). We used log binomial regression models adjusted for socio-demographic, behavioral, and clinical factors to determine whether sodium and potassium intake were associated with incident CKD (decreased eGFR or developed albuminuria) among those free of CKD in 1995. Dietary sodium intake was not significantly associated with incident CKD. However, every 1,000 mg/day increment of potassium intake in 1990 was significantly associated with a 29% lower risk of incident albuminuria (relative risk 0.71, 95% confidence interval 0.53, 0.95), but not eGFR. Thus, higher dietary potassium intake may protect against the development of kidney damage, particularly albuminuria.

Impact of Moderate Sodium Restriction and Hydrochlorothiazide on Iodine Excretion in Diabetic Kidney Disease: Data from a Randomized Cross-Over Trial

Sodium restriction may potentially reduce iodine intake. This study aimed to determine the effect of sodium restriction (dietary counseling) on 24-h urinary iodine excretion. Diuretics provide an alternative to sodium restriction and are frequently added to sodium restriction, so the effects of hydrochlorothiazide (50 mg daily) and combined therapy were also studied. We performed a post-hoc analysis of a Dutch multi-center, randomized cross-over trial in 45 patients with diabetic kidney disease with a mean age of 65 ± 9 years, mean eGFR of 65 ± 27 mL/min/1.73 m², median albuminuria of 648 [230–2008] mg/24 h and 84% were male. During regular sodium intake with placebo, mean 24 h urinary sodium and iodine excretion were 224 ± 76 mmol/24 h and 252 ± 94 ug/24 h, respectively (r = 0.52, p < 0.001). Mean iodine excretion did not change significantly if sodium restriction and hydrochlorothiazide were applied separately; mean difference −8 ug/day (95% CI −38, 22; p = 0.6) and 14 ug/day (95% CI −24, 52; p = 0.5), respectively. Combined therapy induced a significant decrease in mean iodine excretion (−37 ug/day; 95% CI −67, −7; p = 0.02), yet this was not seen to a clinically meaningful level. The number of patients with an estimated intake below recommended daily allowances did not differ significantly between the four treatment periods (p = 0.3). These findings show that sodium restriction is not a risk factor for iodine deficiency.

Effect of high compared with low dairy intake on blood pressure in overweight middle-aged adults: results of a randomized crossover intervention study

BACKGROUND

Observational studies suggest that high dairy intake is associated with a lower blood pressure (BP).

OBJECTIVE

We aimed to investigate the effect of a high-dairy diet (HDD) as compared with a low-dairy diet (LDD) on BP in overweight middle-aged adults.

METHODS

Fifty-two overweight men and women were included in a randomized crossover intervention study. Each subject consumed 2 isocaloric diets for 6 wk, an LDD (≤1 dairy portion per day) and an HDD (6 or 5 reduced-fat dairy portions for men and women, respectively), with a 4-wk washout period in between the diets during which the subjects consumed their habitual diet. BP was measured at the start and at the end of the intervention diets. The effect of the intervention study was evaluated by 2-sample t tests. Mixed-model analyses were used for adjustment for the potential influence of changes in dietary protein and mineral intake and risk factors for hypertension including body weight and plasma cholesterol.

RESULTS

Consumption of an HDD as compared with an LDD resulted in a reduction of both systolic BP (mean ± SD: 4.6 ± 11.2 mm Hg, P < 0.01) and diastolic BP (3.0 ± 6.7 mm Hg, P < 0.01). In further analyses, these reductions appeared dependent on the concomitant increase in calcium intake.

CONCLUSIONS

This intervention study shows that an HDD results in a reduction of both systolic and diastolic BP in overweight middle-aged men and women. If the results of our study are reproduced by other studies, advice for high dairy intake may be added to treatment and prevention of high BP. This trial was registered at trialregister.nl as NTR4899.

[Effect of dietary sodium intake on residual renal function in patients undergoing peritoneal dialysis: a prospective study of 33 cases]

OBJECTIVE

To explore the impact of dietary sodium-intake on residual renal function in patients undergoing peritoneal dialysis (PD).

METHODS

Thirty-three patients on PD with stable dialysis were regularly followed up for 12 months. The daily sodium intake of the patients was calculated based on the 3-day dietary record. Based on the mean daily sodium intake, the patients enrolled were divided into low-salt group (sodium intake≤3.0 g/day, 19 patients) and high-salt group (sodium intake&gt;3.0 g/day, 14 patients). The baseline data of the patients were recorded, and the indicators of residual renal function and peritoneal function were regularly tested. The patients were followed-up at 3-month intervals, and their urine volume, peritoneal ultrafiltration volume and other clinical indicators were recorded and the biochemical indexes were detected to evaluate the changes in the residual renal function and peritoneal function.

RESULTS

There was a positive correlation between the total sodium excretion and dietary sodium intake in these patients (r=0.536, P=0.0013), and sodium excretion by dialysis was positively correlated with their sodium intake (r=0.901, P=0.000). Regression analysis suggested that the total sodium excretion was correlated with dietary sodium intake (β=0.416, 95% CI: 0.170-0.666; P &lt; 0.0018); sodium excretion by dialysis was associated with dietary sodium intake (β=0.489, 95% CI: 0.395-0.582; P &lt; 0.001). The residual renal function was reduced by 17.48±11.22 L /(w·1.73 m²) in the low-salt group, as compared to 30.20±18.30 L /(w·1.73 m²) in the high-salt group (P=0.032). The reduction in the residual renal function was correlated with sodium intake in the PD patients (r=0.409, P=0.018). Multivariate regression analysis showed that sodium intake was an independent factor contributing to the reduction of residual renal function (β=14.646, 95% CI 7.426-21.866, P &lt; 0.001).

CONCLUSIONS

Sodium excretion by PD in patients with continuous ambulatory PD is positively correlated with their dietary sodium intake, which contribute to the decrease of residual renal function. A high dietary sodium intake may accelerate the reduction of residual renal function in these patients.

Rapid weight loss with dietary salt restriction in hospitalized patients with chronic kidney disease

Dietary salt restriction is essential for managing fluid retention in patients with chronic kidney disease (CKD). In this retrospective cohort study, we investigated weight loss from the perspective of fluid status in CKD patients during a 7-day hospitalization period while consuming a low-salt diet (5 g/day). Among 311 patients, the median weight loss (interquartile range, maximum) was 0.7 (0.0–1.4, 4.7) kg on Day 4 and 1.0 (0.3–1.7, 5.9) kg on Day 7. Patients were classified into quartiles based on pre-hospital urinary salt excretion (quartile [Q] 1, 1.2–5.7; Q2, 5.8–8.4; Q3, 8.5–11.3; Q4, 11.4–29.2 g/day). Weight loss was significantly greater in Q3 and Q4 than in Q1. The body mass index (BMI) and urinary salt excretion in the first 24 hours after admission were independently associated with rapid weight loss on Day 4 by multivariate logistic regression analysis. In conclusion, CKD patients with a high salt intake or high BMI exhibit rapid weight loss within a few days of consuming a low-salt diet. Dietary salt restriction is effective for reducing proteinuria in these patients, but long-term observation is needed to confirm the sustained effects.

Lipid Accumulation and Chronic Kidney Disease

Obesity and hyperlipidemia are the most prevalent independent risk factors of chronic kidney disease (CKD), suggesting that lipid accumulation in the renal parenchyma is detrimental to renal function. Non-esterified fatty acids (also known as free fatty acids, FFA) are especially harmful to the kidneys. A concerted, increased FFA uptake due to high fat diets, overexpression of fatty acid uptake systems such as the CD36 scavenger receptor and the fatty acid transport proteins, and a reduced β-oxidation rate underlie the intracellular lipid accumulation in non-adipose tissues. FFAs in excess can damage podocytes, proximal tubular epithelial cells and the tubulointerstitial tissue through various mechanisms, in particular by boosting the production of reactive oxygen species (ROS) and lipid peroxidation, promoting mitochondrial damage and tissue inflammation, which result in glomerular and tubular lesions. Not all lipids are bad for the kidneys: polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) seem to help lag the progression of chronic kidney disease (CKD). Lifestyle interventions, especially dietary adjustments, and lipid-lowering drugs can contribute to improve the clinical outcome of patients with CKD.

Kidney Function Reserve Capacity in Early and Later Stage Autosomal Dominant Polycystic Kidney Disease

BACKGROUND AND OBJECTIVES

It is assumed that in autosomal dominant polycystic kidney disease (ADPKD), kidney function remains in the normal range for several decades because of hyperfiltration of remnant nephrons. In this study, we investigate the extent to which patients with ADPKD hyperfilter.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In this cross-sectional study, we measured GFR as urinary clearance using continuous infusion of 125I-iothalamate. Kidney function reserve capacity was determined as increase in measured GFR after adding a dopamine infusion of 4.4-6 mg/h. Potential kidney donors were used as healthy controls and matched by age and sex to patients with ADPKD for comparisons across age groups and CKD stages. Hyperfiltration was defined by a loss of kidney function reserve capacity compared with healthy controls.

RESULTS

A total of 300 participants were studied. In the youngest age group (18-29 years), measured GFR was not different between patients with ADPKD and healthy controls (103±21 versus 111±9 ml/min per 1.73 m2; P=0.14). In this age group kidney function reserve capacity was higher compared with healthy controls (11.1%±8.3% versus 5.3%±6.5%; P=0.04). Moreover, kidney function reserve capacity was similar to healthy controls in patients with ADPKD with early-stage disease (eGFR≥60 ml/min per 1.73 m2), either overall or when divided into fast or slow progressors according to their Mayo height-adjusted total kidney volume class. However, in patients with ADPKD, lower measured GFR was associated with lower kidney function reserve capacity (β=1.0 [95% confidence interval, 0.5 to 1.5] % per 10 ml/min per 1.73 m2; P<0.001). Kidney function reserve capacity was therefore lower compared with healthy controls at older age and later CKD stages.

CONCLUSIONS

Patients with early-stage ADPKD, either classified as having rapidly or slowly progressive disease, are able to increase their GFR in response to dopamine. Hyperfiltration, defined by a loss of kidney function reserve capacity, may therefore not be an early phenomenon in ADPKD.

The Effect of Diet on the Survival of Patients with Chronic Kidney Disease

The prevalence of chronic kidney disease (CKD) is high and it is gradually increasing. Individuals with CKD should introduce appropriate measures to hamper the progression of kidney function deterioration as well as prevent the development or progression of CKD-related diseases. A kidney-friendly diet may help to protect kidneys from further damage. Patients with kidney damage should limit the intake of certain foods to reduce the accumulation of unexcreted metabolic products and also to protect against hypertension, proteinuria and other heart and bone health problems. Despite the fact that the influence of certain types of nutrients has been widely studied in relation to kidney function and overall health in CKD patients, there are few studies on the impact of a specific diet on their survival. Animal studies demonstrated prolonged survival of rats with CKD fed with protein-restricted diets. In humans, the results of studies are conflicting. Some of them indicate slowing down of the progression of kidney disease and reduction in proteinuria, but other underline significant worsening of patients' nutritional state, which can be dangerous. A recent systemic study revealed that a healthy diet comprising many fruits and vegetables, fish, legumes, whole grains, and fibers and also the cutting down on red meat, sodium, and refined sugar intake was associated with lower mortality in people with kidney disease. The aim of this paper is to review the results of studies concerning the impact of diet on the survival of CKD patients.

Sodium and Its Role in Cardiovascular Disease - The Debate Continues

Guidelines have recommended significant reductions in dietary sodium intake to improve cardiovascular health. However, these dietary sodium intake recommendations have been questioned as emerging evidence has shown that there is a higher risk of cardiovascular disease with a low sodium diet, including in individuals with type 2 diabetes. This may be related to the other pleotropic effects of dietary sodium intake. Therefore, despite recent review of dietary sodium intake guidelines by multiple organizations, including the dietary guidelines for Americans, American Diabetes Association, and American Heart Association, concerns about the impact of the degree of sodium restriction on cardiovascular health continue to be raised. This literature review examines the effects of dietary sodium intake on factors contributing to cardiovascular health, including left ventricular hypertrophy, heart rate, albuminuria, rennin-angiotensin-aldosterone system activation, serum lipids, insulin sensitivity, sympathetic nervous system activation, endothelial function, and immune function. In the last part of this review, the association between dietary sodium intake and cardiovascular outcomes, especially in individuals with diabetes, is explored. Given the increased risk of cardiovascular disease in individuals with diabetes and the increasing incidence of diabetes worldwide, this review is important in summarizing the recent evidence regarding the effects of dietary sodium intake on cardiovascular health, especially in this population.

Underweight Is an Independent Risk Factor for Renal Function Deterioration in Patients with IgA Nephropathy

Studies on the relationship between body mass index (BMI) and renal progression in IgA Nephropathy (IgAN) were limited, especially for underweight patients with IgAN. To elucidate the clinical features and effect of underweight on renal function deterioration in this disease, we recruited IgAN patients with diagnostic age ≥18 years old and a baseline estimated glomerular filtration rate (eGFR) ≥15 ml/min/1.73m² from our center between 1985 and 2014. Patients secondary to systemic diseases or follow-up less than 6 months were excluded. All patients’ clinical data at renal biopsy and during follow-up were recorded. Renal outcome was defined as end-stage kidney disease (ESRD). Baseline body mass index (BMI) was calculated by weight (kg) over squared height (m²). According to WHO Asian guideline, BMI was categorized as follows: <18.5kg/m² (underweight), 18.5–22.99kg/m² (normal weight), 23–27.49kg/m² (overweight) and obese (≥27.5 kg/m²). Of 930 primary IgAN patients enrolled in this study, mean age at renal biopsy was 37.6 years and 49.2% were men. Totally, 114 (12.3%) ESRD occurred after a mean follow-up of 47.1 months. More ESRD happened in underweight patients (17.3%) compared to patients with normal weight (13.2%), overweight (11.0%) or obesity (9.5%). By multivariate Cox regression analysis, underweight was independently associated with a higher risk of ESRD after adjustment for demographic characteristics and clinical variables (HR: 3.5, 95% CI: 1.3–9.5, P = 0.01) comparing to normal weight. Underweight patients had lower hemoglobin, serum uric acid, triglycerides, cholesterol and lymphocyte counts than patients with normal weight. Furthermore, BMI was positively correlated with serum C3 (r = 0.25, p <0.001). Our research finds that underweight is an independent risk factor for kidney disease progression in IgAN, which might be associated with malnutrition status and decreased C3 levels.

The kidney in obesity

Body mass index has been found to be the second most important contributor to relative risk for developing end state renal disease (ESRD), after proteinuria. The impact of obesity on the kidney includes a wide spectrum, from characteristic pathologic lesions to increment in urinary albumin excretion (UAE) and proteinuria/or decrease in glomerular filtration rate (GFR). The cause of renal disease associated to obesity is not well understood, but two relevant elements emerge. The first is the presence of obesity-related glomerulopathy, and the second is the fat deposit in the kidney with impact on renal haemodynamics and intrarenal regulation. The mechanisms linking obesity and renal damage are complex and include haemodynamic changes, inflammation, oxidative stress, apoptosis, and finally renal scarring. The protection of kidney damage needs to combine weight reduction with the proper control of the cardiometabolic risk factors associated, hypertension, metabolic syndrome, diabetes and dyslipidaemia. The search for specific treatments merits future research.

Plasma Vitamin D Level and Change in Albuminuria and eGFR According to Sodium Intake

BACKGROUND AND OBJECTIVES

Low circulating 25-hydroxyvitamin D [25(OH)D] and high sodium intake are both associated with progressive albuminuria and renal function loss in CKD. Both vitamin D and sodium intake interact with the renin-angiotensin-aldosterone system. We investigated whether plasma 25(OH)D or 1,25-dihydroxyvitamin D [1,25(OH)2D] is associated with developing increased albuminuria or reduced renal function and whether these associations depend on sodium intake.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Baseline plasma 25(OH)D and 1,25(OH)2D were measured by liquid chromatography tandem mass spectrometry, and sodium intake was assessed by 24-hour urine collections in the general population-based Prevention of Renal and Vascular End-Stage Disease cohort (n=5051). Two primary outcomes were development of urinary albumin excretion >30 mg/24 h and eGFR (creatinine/cystatin C-based CKD Epidemiology Collaboration) <60 ml/min per 1.73 m(2). Participants with CKD at baseline were excluded. In Cox regression analyses, we assessed associations of vitamin D with developing increased albuminuria or reduced eGFR and potential interaction with sodium intake.

RESULTS

During a median follow-up of 10.4 (6.2-11.4) years, 641 (13%) participants developed increased albuminuria, and 268 (5%) participants developed reduced eGFR. Plasma 25(OH)D was inversely associated with increased albuminuria (fully adjusted hazard ratio [HR] per SD higher, 0.86; 95% confidence interval [95% CI], 0.78 to 0.95; P=0.003) but not reduced eGFR (HR, 0.99; 95% CI, 0.87 to 1.12; P=0.85). There was interaction between 25(OH)D and sodium intake for risk of developing increased albuminuria (P interaction =0.03). In participants with high sodium intake, risk of developing increased albuminuria was inversely associated with 25(OH)D (lowest versus highest quartile: adjusted HR, 1.81; 95% CI, 1.20 to 2.73, P<0.01), whereas this association was nonsignificant in participants with low sodium intake (HR, 1.29; 95% CI, 0.94 to 1.77; P=0.12). Plasma 1,25(OH)2D was not significantly associated with increased albuminuria or reduced eGFR.

CONCLUSIONS

Low plasma 25(OH)D is associated with higher risk of developing increased albuminuria, particularly in individuals with high sodium intake, but not of developing reduced eGFR. Plasma 1,25(OH)2D is not associated with risk of developing increased albuminuria or reduced eGFR.

Effect of Acetazolamide on Obesity-Induced Glomerular Hyperfiltration: A Randomized Controlled Trial

AIMS

Obesity is an important risk factor for the development of chronic kidney disease. One of the major factors involved in the pathogenesis of obesity-associated kidney disease is glomerular hyperfiltration. Increasing salt-delivery to the macula densa is expected to decrease glomerular filtration rate (GFR) by activating tubuloglomerular feedback. Acetazolamide, a carbonic anhydrase inhibitor which inhibits salt reabsorption in the proximal tubule, increases distal salt delivery. Its effects on obesity-related glomerular hyperfiltration have not previously been studied. The aim of this investigation was to evaluate whether administration of acetazolamide to obese non diabetic subjects reduces glomerular hyperfiltration.

MATERIALS AND METHODS

The study was performed using a randomized double-blind crossover design. Obese non-diabetic men with glomerular hyperfiltration were randomized to receive intravenously either acetazolamide or furosemide at equipotent doses. Twelve subjects received the allocated medications. Two weeks later, the same subjects received the drug which they had not received during the first study. Inulin clearance, p-aminohippuric acid clearance and fractional lithium excretion were measured before and after medications administration. The primary end point was a decrease in GFR, measured as inulin clearance.

RESULTS

GFR decreased by 21% following acetazolamide and did not decrease following furosemide. Renal vascular resistance increased by 12% following acetazolamide, while it remained unchanged following furosemide administration. Natriuresis increased similarly following acetazolamide and furosemide administration. Sodium balance was similar in both groups.

CONCLUSIONS

Intravenous acetazolamide decreased GFR in obese non-diabetic men with glomerular hyperfiltration. Furosemide, administered at equipotent dose, did not affect GFR, suggesting that acetazolamide reduced glomerular hyperfiltration by activating tubuloglomerular feedback.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01146288.

The relationship between renal volume and histology in obese and nonobese kidney donors

BACKGROUND

Obesity and related kidney diseases have become a global epidemic problem. However, the underlying pathogenesis of obesity-related renal diseases has not been clearly understood. In this study, we explored the link between renal volume (RV) determined by computed tomography (CT) and renal histology together with functional parameters in an obese population.

MATERIALS AND METHODS

Eighty-two kidney donors who underwent CT for the measurement of kidney volume and zero-hour renal biopsy for renal histology were included in this cross-sectional study. Protein creatinine clearance and eGFR were evaluated in 24-h urine specimens as indicators of renal function.

RESULTS

Mean body mass index (BMI) was 28 ± 4.2 kg/m(2); 32.9% (n = 27) were obese. Mean RV was 196 ± 36 cm(3). RV was positively correlated with BMI, body surface area and creatinine clearance and negatively with HDL-cholesterol in the whole population. Renal function parameters of obese subjects were better, and their renal volumes were higher compared with the nonobese subjects. In obese subjects, corrected RV was positively correlated with glomerular filtration rate (r = 0.46, P = 0.01) and negatively with sclerotic glomeruli (r = -0.38, P = 0.04) and chronicity index (r = -0.43, P = 0.02). In adjusted ordinal logistic regression analysis, corrected RV was significantly associated with chronicity index (OR: 0.96; P = 0.01).

CONCLUSIONS

In obese cases, decreased RV determined by CT is associated with worse renal histology. In this population, kidney imaging techniques may provide important clues about renal survival.

Association between obesity and glomerular hyperfiltration: the confounding effect of smoking and sodium and protein intakes

PURPOSE

Glomerular hyperfiltration has been suggested as a possible mechanism linking obesity and chronic kidney disease (CKD), independently of classical risk factors. We explored the association of overweight and obesity with glomerular hyperfiltration in a large sample of the Swiss adult population, accounting for several confounders including dietary factors.

METHODS

Data from a 2010 to 2012 cross-sectional population-based survey in Switzerland were used. Creatinine clearance (CrCl) was determined from 24-h urine collection; CrCl > 140 ml/min was used to define glomerular hyperfiltration. Participants were categorized into lean (<25 kg/m(2)), overweight (25-29.9 kg/m(2)) and obese (≥30 kg/m(2)) according to body mass index (BMI).

RESULTS

A total of 1339 participants were included in the analysis [median (IQR) age 49.4 (34.3-63.5) years, 48.9 % men]. The prevalences of overweight and obesity were 32.2 and 14.2 %, respectively. Median CrCl was 102[84-121] ml/min in lean, 110 [87-136] ml/min in overweight and 124 [97-150] ml/min in obese participants (p < 0.001). The prevalence of glomerular hyperfiltration increased across BMI categories (10.4, 20.8 and 34.7 %, respectively; p < 0.001). This positive association remained significant after adjusting for age, sex, hypertension, diabetes, smoking and dietary factors (sodium and protein intakes): odds ratio [95 %CI] 2.39 [1.52-3.76] (p < 0.001) for overweight versus lean and 4.10[2.31-7.27] (p < 0.001) for obesity versus lean.

CONCLUSIONS

BMI categories and glomerular hyperfiltration are positively associated, independently of other known CKD risk factors and dietary confounders, suggesting that glomerular hyperfiltration may represent an early renal phenotype in obesity. Our observations confirm the significant association of glomerular hyperfiltration with sodium and protein intakes and identify sodium intake as an important modifying factor of the association between hyperfiltration and obesity.

Higher filtration fraction in formerly early-onset preeclamptic women without comorbidity

Formerly preeclamptic women have an increased risk for developing end-stage renal disease, which has been attributed to altered renal hemodynamics and abnormalities in the renin-angiotensin-aldosterone system. Whether this is due to preeclampsia itself or to comorbid conditions is unknown. Renal hemodynamics and responsiveness to ANG II during low Na(+) intake (7 days, 50 mmol Na(+)/24 h) and high Na(+) (HS) intake (7 days, 200 mmol Na(+)/24 h) were studied in 18 healthy normotensive formerly early-onset preeclamptic women (fPE women) and 18 healthy control subjects (fHP women), all selected for absence of comorbidity. At the end of each diet, renal hemodynamics and blood pressure were measured before and during graded ANG II infusion. Both HS intake and former preeclampsia increased filtration fraction (FF) without an interaction between the two. FF was highest during HS intake in fPE women [0.31 ± 0.12 vs. 0.29 ± 0.11 in fHP women, generalized estimating equation analysis (body mass index corrected), P = 0.03]. The renal response to ANG II infusion was not different between groups. In conclusion, fPE women have a higher FF compared with fHP women. As this was observed in the absence of comorbidity, preeclampsia itself might exert long-term effects on renal hemodynamics. However, we cannot exclude the presence of prepregnancy alterations in renal function, which, in itself, lead to an increased risk for preeclampsia. In experimental studies, an elevated FF has been shown to play a pathogenic role in the development of hypertension and renal damage. Future studies, however, should evaluate whether the subtle differences in renal hemodynamics after preeclampsia contribute to the increased long-term renal risk after preeclampsia.

Dietary sodium restriction: a neglected therapeutic opportunity in chronic kidney disease

PURPOSE OF REVIEW

Restriction of dietary sodium is recommended at a population level as well as for groups at high cardiovascular risk, and chronic kidney disease (CKD). This review addresses recent evidence for the protective effect of dietary sodium restriction in CKD patients specifically.

RECENT FINDINGS

Sodium intake in CKD populations is generally high, and often above population average. Recent data demonstrated that moderately lower sodium intake in CKD patients is associated with substantially better long-term outcome of renin-angiotensin-aldosterone system (RAAS)-blockade, in diabetic and nondiabetic CKD, related to better effects of RAAS-blockade on proteinuria, independent of blood pressure. This is in line with better short-term efficacy of RAAS-blockade during moderate sodium restriction in diabetic and nondiabetic CKD. This effect of sodium restriction is likely mediated by its effects on volume status. Sustainable sodium restriction can be achieved by approaches on the basis of behavioral sciences.

SUMMARY

Moderate restriction of dietary sodium can substantially improve the protective effects of RAAS-blockade in CKD, by specific renal effects apparent from proteinuria reduction. The latter precludes straightforward extrapolation of data from nonrenal populations to CKD. Concerns regarding the adverse effects of a very low sodium intake should not distract from the protective effects of moderate sodium restriction. Prospective studies should assess the efficacy and sustainability of different strategies to target high sodium intake in CKD, along with measures at population level.

VIDEO ABSTRACT

http://links.lww.com/CONH/A14.

Body mass index and body fat distribution as renal risk factors: a focus on the role of renal haemodynamics

Weight excess and/or central body fat distribution are associated with increased long-term renal risk, not only in subjects with renal disease or renal transplant recipients, but also in the general population. As the prevalence of weight excess is rising worldwide, this may become a main renal risk factor on a population basis, even more so because the risk extends to the overweight range. Understanding the mechanisms of this detrimental effect of weight excess on the kidneys is needed in order to design preventive treatment strategies. The increased risk associated with weight excess is partly attributed to associated comorbid conditions, such as hypertension, dyslipidaemia, insulin resistance and diabetes; however, current evidence supports a direct pathogenetic role for renal haemodynamics as well. Weight excess is associated with an altered renal haemodynamic profile, i.e. an increased glomerular filtration rate relative to effective renal plasma flow, resulting in an increased filtration fraction (FF). This renal haemodynamic profile is considered to reflect glomerular hyperfiltration and glomerular hypertension, resulting from a dysbalance between afferent and efferent arterial vasomotor balance. This unfavorable renal haemodynamic profile was found to be associated with renal outcome in experimental models and in human renal transplant recipients, and is associated with a blunted sodium excretion, and reversible by weight loss, renin-angiotensin-aldosterone system blockade or by dietary sodium restriction. More recent evidence showed that a central body fat distribution is also associated with an increased FF, even independent of overall weight excess. In this review, we provide an overview on current literature on the impact of weight excess and central body fat distribution on the renal haemodynamic profile in humans, and its possible role in progressive renal damage.

Obesity in kidney disease: A heavyweight opponent

Obesity is an important worldwide challenge that must be faced in most developed and developing countries because of unhealthy nutritional habits. The consequences of obesity and being overweight are observed in different organs, but the kidney is one of the most affected. Excess adipose tissue causes hemodynamic alterations in the kidney that can result in renal disease. However, obesity is also commonly associated with other comorbidities such as chronic inflammation, hypertension and diabetes. This association of several aggravating factors is still a matter of concern in clinical and basic research because the pathophysiologic mechanisms surrounding chronic kidney disease development in obese patients remain unclear. This review will discuss the consequences of obesity in the context of renal injury.

Effects of sodium restriction and hydrochlorothiazide on RAAS blockade efficacy in diabetic nephropathy: a randomised clinical trial

BACKGROUND

Reduction of dietary sodium intake or diuretic treatment increases renin-angiotensin-aldosterone system (RAAS) blockade efficacy in non-diabetic nephropathy. We aimed to investigate the effect of sodium restriction and the diuretic hydrochlorothiazide, separately and in combination, added to RAAS blockade on residual albuminuria in patients with type 2 diabetic nephropathy.

METHODS

In this multicentre, double-blind, placebo-controlled, crossover randomised trial, we included patients with type 2 diabetic nephropathy. Main entry criteria were microalbuminaria or macroalbuminuria, and creatinine clearance of 30 mL/min or higher with less than 6 mL/min decline in the previous year. We tested the separate and combined effects of sodium restriction (dietary counselling in the outpatient setting) and hydrochlorothiazide (50 mg daily), added to standardised maximal angiotensin-converting enzyme (ACE) inhibition (lisinopril 40 mg daily), on albuminuria (primary endpoint). Patients were given hydrochlorothiazide (50 mg per day) or placebo during four treatment periods of 6 weeks. Both treatments were combined with regular sodium diet or sodium restriction (target sodium intake 50 mmol Na(+) per day). The 6-week treatment periods were done consecutively in a random order. Patients were randomised in blocks of two patients. The trial was analysed by intention to treat. The trial is registered with TrialRegister.nl, number 2366.

FINDINGS

Of 89 eligible patients, 45 were included in the study. Both sodium restriction and hydrochlorothiazide significantly reduced albuminuria, irrespective of treatment sequence. Residual geometric mean albuminuria with baseline treatment was 711 mg per day (95% CI 485-1043); it was significantly reduced by sodium restriction (393 mg per day [258-599], p=0·0002), by hydrochlorothiazide (434 mg per day [306-618], p=0·0003), and to the greatest extent by their combination (306 mg per day [203-461], p<0·0001). Orthostatic complaints were present in two patients (4%) during baseline treatment, five (11%) during addition of sodium restriction, five (11%) during hydrochlorothiazide treatment, and 12 (27%) during combination treatment. No serious adverse events occurred.

INTERPRETATION

We conclude that sodium restriction is an effective non-pharmacological intervention to increase RAAS blockade efficacy in type 2 diabetic nephropathy.

FUNDING

None.

Influence of dietary protein on glomerular filtration before and after bariatric surgery: a cohort study

BACKGROUND

Obesity-associated elevations in glomerular filtration rate (GFR) are common and may play a role in the development of kidney disease, so identifying the underlying mechanism is important. We therefore studied whether reductions in dietary protein intake, which is known to modulate GFR, explain why GFR decreases after bariatric surgery-induced weight loss.

STUDY DESIGN

Cohort study with participants as their own controls.

SETTING & PARTICIPANTS

8 severely obese patients with normal kidney function were recruited from bariatric surgery centers in Indianapolis, IN. All participants were placed on a fixed-protein (50-g/d) diet for 1 week before and after a minimum of a 20-kg weight loss by bariatric surgery and were followed up closely by dieticians for adherence.

PREDICTOR

Ad lib versus low-protein diet before versus after bariatric surgery.

OUTCOME

Measured GFR, using repeated-measures analysis, was used to estimate the independent effects of diet and surgery.

MEASUREMENT

GFR was measured using plasma iohexol clearance.

RESULTS

A median of 32.9 (range, 19.5-54.4)kg was lost between the first presurgery visit and first postsurgery visit. Dietetic evaluations and urinary urea excretion confirmed that patients generally adhered to the study diet. GFRs on an ad lib diet were significantly higher before compared to after surgery (GFR medians were 144 (range, 114-178) and 107 (range, 85-147) mL/min, respectively; P=0.01). Although bariatric surgery (-26mL/min; P=0.005) and dietary sodium intake (+7.5mL/min per 100mg of dietary sodium; P=0.001) both influenced GFR, consuming a low-protein diet did not (P=0.7).

LIMITATIONS

Small sample size; mostly white women; possible lack of generalizability.

CONCLUSIONS

The decrease in GFR observed after bariatric surgery is explained at least in part by the effects of surgery and/or dietary sodium intake, but not by low dietary protein consumption.

Obesity in CKD--what should nephrologists know?

Obesity, the epidemic of the 21st century, carries a markedly increased risk for comorbid complications, such as type 2 diabetes, cancer, hypertension, dyslipidemia, cardiovascular disease, and sleep apnea. In addition, obesity increases the risk for CKD and its progression to ESRD. Paradoxically, even morbid obesity associates with better outcomes in studies of ESRD patients on maintenance dialysis. Because the number of obese CKD and maintenance dialysis patients is projected to increase markedly in developed as well as low- and middle-income countries, obesity is a rapidly emerging problem for the international renal community. Targeting the obesity epidemic represents an unprecedented opportunity for health officials to ameliorate the current worldwide increase in CKD prevalence. Nephrologists need more information about assessing and managing obesity in the setting of CKD. Specifically, more precise estimation of regional fat distribution and the amount of muscle mass should be introduced into regular clinical practice to complement more commonly used practical markers, such as body mass index. Studies examining the effects of obesity on kidney disease progression and other clinical outcomes along with weight management strategies are much needed in this orphan area of research.

Proximal tubular hypertrophy and enlarged glomerular and proximal tubular urinary space in obese subjects with proteinuria

Background

Obesity is associated with glomerular hyperfiltration, increased proximal tubular sodium reabsorption, glomerular enlargement and renal hypertrophy. A single experimental study reported an increased glomerular urinary space in obese dogs. Whether proximal tubular volume is increased in obese subjects and whether their glomerular and tubular urinary spaces are enlarged is unknown.

Objective

To determine whether proximal tubules and glomerular and tubular urinary space are enlarged in obese subjects with proteinuria and glomerular hyperfiltration.

Methods

Kidney biopsies from 11 non-diabetic obese with proteinuria and 14 non-diabetic lean patients with a creatinine clearance above 50 ml/min and with mild or no interstitial fibrosis were retrospectively analyzed using morphometric methods. The cross-sectional area of the proximal tubular epithelium and lumen, the volume of the glomerular tuft and of Bowman’s space and the nuclei number per tubular profile were estimated.

Results

Creatinine clearance was higher in the obese than in the lean group (P=0.03). Proteinuria was similarly increased in both groups. Compared to the lean group, the obese group displayed a 104% higher glomerular tuft volume (P=0.001), a 94% higher Bowman’s space volume (P=0.003), a 33% higher cross-sectional area of the proximal tubular epithelium (P=0.02) and a 54% higher cross-sectional area of the proximal tubular lumen (P=0.01). The nuclei number per proximal tubular profile was similar in both groups, suggesting that the increase in tubular volume is due to hypertrophy and not to hyperplasia.

Conclusions

Obesity-related glomerular hyperfiltration is associated with proximal tubular epithelial hypertrophy and increased glomerular and tubular urinary space volume in subjects with proteinuria. The expanded glomerular and urinary space is probably a direct consequence of glomerular hyperfiltration. These effects may be involved in the pathogenesis of obesity-related renal disease.

Structural renal changes in obesity and diabetes

Overweight, obesity, and associated diseases represent an emerging problem, not only in Western countries but also in the developing world. They are now characterized as epidemic diseases. Obesity is particularly serious because its incidence in children and adolescents increased dramatically: it is estimated that in the United States every eighth adolescent suffers from obesity, which in the long run may reduce life expectancy in the population. Apart from cardiovascular disease (ie, blood pressure, stroke, and coronary heart disease), kidney diseases also have been shown to be associated with obesity. Epidemiologic studies have indicated that obesity can be a risk factor of chronic kidney disease irrespective of the presence or absence of diabetes, arterial hypertension, and other comorbidities. More evidence is accumulated on the link between chronic kidney disease in obesity and abnormalities in adipokine secretion (hyperleptinemia, lack of adiponectin), activation of the renin-angiotensin system, chronic inflammation, endothelial dysfunction, lipid accumulation, impaired renal hemodynamics, and diminished nephron number related to body mass. In general, obesity is known to aggravate the course of many primary renal diseases such as glomerulonephritides, but also impairs renal function after kidney transplantation. Microalbuminuria, proteinuria, hyperfiltration, and impaired renal function are associated with obesity. Histologically, secondary focal segmental sclerosis has been shown to be caused particularly by obesity. Of practical purpose for clinical nephrology, loss of body weight either by lifestyle modification or bariatric surgery improves albuminuria and hyperfiltration in obese patients, making renal disease in obesity accessible for prevention programs. This review specifically addresses the pathogenesis and morphology of renal functional and particularly structural changes in obesity and associated renal disease such as diabetic nephropathy.

Obesity and kidney disease: potential mechanisms

Assessment of adiposity should include measurements of both body mass index and waist circumference. The prevalence of obesity, based on a body mass index of 30 kg/m(2) or greater, has increased substantially over the past 2 decades in Western societies. Obesity remains the number one preventable risk factor for chronic kidney disease because obesity largely mediates diabetes and hypertension, the 2 most common etiologies for end-stage kidney disease. However, obesity itself likely has independent effects on renal hemodynamics and individuals with a low number of nephrons are likely to be the most susceptible to these changes. Multiple mechanisms have been postulated whereby obesity directly impacts kidney disease including hyperfiltration, increased glomerular capillary wall tension, and podocyte stress. Weight loss reduces glomerular filtration rate and effective renal plasma flow along with proteinuria, but these changes are most notable after bariatric surgery in adults with morbid obesity. Aside from adiposity itself, the high caloric intake that leads to obesity also may heighten chronic kidney disease risk via the circuitous loop between Sirt1 and adiponectin and podocyte effacement. Sirt1 is a nicotinamide adenine dinucleotide+dependent deacteylase that is up-regulated in the setting of caloric restriction. Sirt1 expression modulates adiponectin levels that in turn appear to influence podocyte effacement. Clinical trials are needed to assess the benefits and risks of intentional weight loss on kidney disease measures and progression.

Salt intake in kidney disease--a missed therapeutic opportunity?

Although significant progress has been made in the treatment of chronic kidney disease (CKD), treatment is not yet satisfactory, particularly when it is started in the late stages of the disease. Novel modes of intervention to mitigate the burden of disease are required. The reduction of dietary salt intake (which is high in the industrialized world) is one such option. Better understanding of the deleterious effects of salt on renal and cardiovascular health is necessary to raise awareness of the importance of reduction of the salt content in food products. Therefore, we (i) review pathways through which high salt intake exerts damaging effects, (ii) provide an assessment of recent observational studies linking dietary salt intake to the progression of renal and cardiovascular disease and (iii) discuss the interaction between salt intake and rennin-angiotensin-aldosterone-system inhibitors, i.e. the first choice antihypertensive agents for the treatment of CKD.

Central body fat distribution associates with unfavorable renal hemodynamics independent of body mass index

Central distribution of body fat is associated with a higher risk of renal disease, but whether it is the distribution pattern or the overall excess weight that underlies this association is not well understood. Here, we studied the association between waist-to-hip ratio (WHR), which reflects central adiposity, and renal hemodynamics in 315 healthy persons with a mean body mass index (BMI) of 24.9 kg/m(2) and a mean (125)I-iothalamate GFR of 109 ml/min per 1.73 m(2). In multivariate analyses, WHR was associated with lower GFR, lower effective renal plasma flow, and higher filtration fraction, even after adjustment for sex, age, mean arterial pressure, and BMI. Multivariate models produced similar results regardless of whether the hemodynamic measures were indexed to body surface area. Thus, these results suggest that central body fat distribution, independent of BMI, is associated with an unfavorable pattern of renal hemodynamic measures that could underlie the increased renal risk reported in observational studies.

Early improvement in albuminuria in non-diabetic patients after Roux-en-Y bariatric surgery

BACKGROUND

Obesity is a growing epidemic in the USA that has been shown to be associated with chronic kidney disease and albuminuria. Bariatric surgery is an effective means of achieving long-term weight loss and improvements in metabolic derangements including albumin excretion over the long term.

METHODS

We report changes in urinary albumin excretion levels in the early post-operative period for a euglycemic, predominantly Hispanic American cohort undergoing Roux-en-Y gastric bypass surgery.

RESULTS

Our cohort of 38 patients was largely female (89.5%) and predominantly Hispanic (76.3%) with a mean BMI of 46 ± 8.0 kg/m(2). Over half (53.3%) of the patients with significant preoperative albumin excretion in our cohort lowered their albumin excretion levels to <20 mg/g of creatinine. This early reduction in albumin excretion in our cohort correlated significantly with the level of albumin excretion preoperatively but not with the degree of weight loss experienced in this early post-operative period.

CONCLUSIONS

Improvements in microalbuminuria in the early post-operative period after Roux-en-Y surgery may result from an interplay between changes in gastrointestinal hormones, insulin sensitivity, blood pressure, and adipose tissue-and needs further study.

Short term dietary sodium restriction decreases HDL cholesterol, apolipoprotein A-I and high molecular weight adiponectin in healthy young men: relationships with renal hemodynamics and RAAS activation

BACKGROUND AND AIMS

We aimed to determine the effect of short-term dietary sodium restriction on plasma total cholesterol, LDL-C, HDL-C, triglycerides, apolipoprotein (apo) A-I, apo B and high molecular weight (HMW) adiponectin in non-obese, normotensive young men. Glomerular filtration rate (GFR), effective renal plasma flow (ERPF), plasma renin activity (PRA) and aldosterone were also measured.

METHODS AND RESULTS

Sixty-five men, aged 23 ± 7 years, were randomly studied on a high sodium intake (HS, 228 ± 77 mmol Na+/24 h) and a low sodium intake (LS, 36 ± 27 mmol Na+/24 h), each period lasting 1 week. LS decreased GFR and ERPF and increased PRA and aldosterone (p < 0.0001 for all). LS also induced a decrease in HDL-C (3.8 ± 10.8%), apo A-I (3.7 ± 6.5%) and HMW-adiponectin (13.6 ± 40.5%) (p < 0.05 for all), but plasma total cholesterol, LDL-C, triglycerides and apo B did not significantly change. The changes in HDL-C and apo A-I were correlated negatively to the changes in effective renal plasma flow (p < 0.05), whereas the changes in HMW adiponectin were correlated negatively to the changes in PRA and aldosterone (p < 0.05 for both).

CONCLUSION

Short term sodium restriction modestly decreases HDL-C, apo A-I and HMW-adiponectin in healthy men. Changes in GFR and ERPF and in the renin-angiotensin-aldosterone system as induced by LS may be involved in these responses.

Effects of dietary salt restriction on puromycin aminonucleoside nephrosis: preliminary data

Proteinuria is a major promoter that induces tubulointerstitial injury in glomerulopathy. Dietary salt restriction may reduce proteinuria, although the mechanism is not clear. We investigated the effects of dietary salt restriction on rat kidneys in an animal model of glomerular proteinuria. Male Sprague-Dawley rats were used and divided into 3 groups: vehicle-treated normal-salt controls, puromycin aminonucleoside (PA)-treated normal-salt rats, and PA-treated low-salt rats. PA was given at a dose of 150 mg/kg BW at time 0, followed by 50 mg/kg BW on days 28, 35, and 42. Sodium-deficient rodent diet with and without additional NaCl (0.5%) were provided for normal-salt rats and low-salt rats, respectively. On day 63, kidneys were harvested for histopathologic examination and immunohistochemistry. PA treatment produced overt proteinuria and renal damage. Dietary salt restriction insignificantly reduced proteinuria in PA-treated rats, and PA-treated low-salt rats had lower urine output and lower creatinine clearance than vehicle-treated normal-salt controls. When tubulointerstitial injury was semiquantitatively evaluated, it had a positive correlation with proteinuria. The tubulointerstitial injury score was significantly increased by PA treatment and relieved by low-salt diet. ED1-positive infiltrating cells and immunostaining for interstitial collagen III were significantly increased by PA treatment. These changes appeared to be less common in PA-treated low-salt rats, although the differences in PA-treated normal-salt versus low-salt rats did not reach statistical significance. Our results suggest that renal histopathology in PA nephrosis may potentially be improved by dietary salt restriction. Non-hemodynamic mechanisms induced by low-sodium diet might contribute to renoprotection.