Preglomerular and postglomerular resistance responses to different levels of sympathetic activation by hypoxia

Where do you live and what do you do? Two questions that might impact your kidney health

In many cases the social determinants of health need to be assessed through their interaction with environmental factors. This review looks at the impact of physical location and occupation of individuals on their kidney health. It examines the effect of living at high altitude on kidney function and the relationship between extreme cold or hot temperatures and the incidence of kidney injury. It reviews as well the many occupations that have been linked to kidney disease in high-income and low-and-middle-income countries. As a conclusion, this overview proposes preventive recommendations that could be individualized based on weather, altitude, socio-economic level of the country and occupation of the individual.

Association of insomnia and short sleep duration, alone or with comorbid obstructive sleep apnea, and the risk of chronic kidney disease

STUDY OBJECTIVES

Obstructive sleep apnea (OSA), sleep fragmentation, and short sleep duration (SD) have been associated with chronic kidney disease (CKD). However, these potential mechanisms for CKD have not been compared in the same cohort. This study investigated the independent and combined impact of OSA and insomnia with short sleep duration on the risk of CKD progression in a sleep clinic population.

METHODS

In a cross-sectional study design, adults with suspected OSA completed an overnight sleep study and a questionnaire that included the Insomnia Severity Index (ISI) and Pittsburgh Sleep Quality Index (PSQI). They also provided blood and urine samples for measurement of the glomerular filtration rate and urine albumin:creatinine ratio, from which the risk of CKD progression was determined.

RESULTS

Participants (n = 732, 41% female, 55 ± 13 years) were categorized into four groups: no/mild OSA without insomnia (NM-OSA, n = 203), insomnia with SD without OSA (Insomnia-SD, n = 104), moderate-to-severe OSA without insomnia (MS-OSA, n = 242), and comorbid insomnia and OSA with SD (COMISA-SD, n = 183). After stratification, 12.8% of NM-OSA, 15.4% of Insomnia-SD, 28.9% of MS-OSA, and 31.7% of the COMISA-SD participants had an increased risk of CKD progression. Compared to NM-OSA, the odds ratio (OR) for an increased risk of CKD progression was not increased in Insomnia-SD (OR 0.95, confidence interval [CI]: 0.45-1.99) and was increased to the same degree in MS-OSA (OR 2.79, CI: 1.60-4.85) and COMISA-SD (OR 3.04, CI: 1.69-5.47). However, the ORs were similar between the MS-OSA and COMISA-SD groups across all statistical models (p ≥ .883).

CONCLUSIONS

In a sleep clinic population, insomnia with short sleep duration does not increase the risk of CKD progression; nor does it further increase the risk of CKD progression associated with moderate-to-severe OSA.

Nocturnal hypoxemia severity influences the effect of CPAP therapy on renal renin-angiotensin-aldosterone system activity in humans with obstructive sleep apnea

STUDY OBJECTIVES

Nocturnal hypoxemia (NH) in obstructive sleep apnea (OSA) is associated with renal renin-angiotensin-aldosterone system (RAAS) up-regulation and loss of kidney function. Continuous positive airway pressure (CPAP) therapy is associated with RAAS down-regulation, though the impact of NH severity remains unknown. We sought to determine whether NH severity alters the effect of CPAP on renal hemodynamics and RAAS activity in humans.

METHODS

Thirty sodium-replete, otherwise healthy, OSA participants (oxygen desaturation index ≥ 15 h-1) with NH (SpO2 < 90% ≥ 12%/night) were studied pre- and post-CPAP (>4 h/night∙4 weeks). NH severity was characterized as moderate (mean SpO2[MSpO2] ≥ 90%; N = 15) or severe (MSpO2 < 90%; N = 15). Glomerular filtration rate (GFR), renal plasma flow (RPF), and filtration fraction (FF) were measured at baseline and in response to angiotensin-II (3 ng/kg/min∙30 min, 6 ng/kg/min∙30 min), a marker of RAAS activity.

RESULTS

Pre-CPAP, baseline renal hemodynamics did not differ by NH severity. Pre-CPAP, severe NH participants demonstrated blunted GFR (Δ30 min, -9 ± 4 vs 1 ± 3 mL/min, p = 0.021; Δ60 min, -5 ± 5 vs 8 ± 5 mL/min, p = 0.017) and RPF (Δ30 min, -165 ± 13 vs -93 ± 19 mL/min, p = 0.003; Δ60 min, -208 ± 18 vs -112 ± 22 mL/min, p = 0.001; moderate vs severe) responses to angiotensin-II. Post-CPAP, severe NH participants demonstrated maintained GFR (112 ± 5 vs 108 ± 3 mL/min, p = 0.9), increased RPF (664 ± 35 vs 745 ± 34 mL/min, p = 0.009), reduced FF (17.6 ± 1.4 vs 14.9 ± 0.6%, p = 0.009), and augmented RPF responses to Angiotensin-II (Δ30 min, -93 ± 19 vs -138 ± 16 mL/min, p = 0.009; Δ60 min, -112 ± 22 vs -175 ± 20 mL/min, p = 0.001; pre- vs post-CPAP), while moderate participants were unchanged.

CONCLUSIONS

Correction of severe, but not moderate, NH with CPAP therapy was associated with improved renal hemodynamics and decreased renal RAAS activity in humans with OSA.

Renal Physiological Adaptation to High Altitude: A Systematic Review

Background: Under normal physiological conditions, renal tissue oxygen is tightly regulated. At high altitude, a physiological challenge is imposed by the decrease in atmospheric oxygen. At the level of the kidney, the physiological adaptation to high altitude is poorly understood, which might relate to different integrated responses to hypoxia over different time domains of exposure. Thus, this systematic review sought to examine the renal physiological adaptation to high altitude in the context of the magnitude and duration of exposure to high altitude in the healthy kidney model.

Methods: To conduct the review, three electronic databases were examined: OVID, PubMed, and Scopus. Search terms included: Altitude, renal, and kidney. The broad, but comprehensive search, retrieved 1,057 articles published between 1997 and April 2020. Fourteen studies were included in the review.

Results: The inconsistent effect of high altitude on renal hemodynamic parameters (glomerular filtration rate, renal blood flow, and renal plasma flow), electrolyte balance, and renal tissue oxygen is difficult to interpret; however, the data suggest that the nature and extent of renal physiological adaptation at high altitude appears to be related to the magnitude and duration of the exposure.

Conclusion: It is clear that renal physiological adaptation to high altitude is a complex process that is not yet fully understood. Further research is needed to better understand the renal physiological adaptation to hypoxia and how renal oxygen homeostasis and metabolism is defended during exposure to high altitude and affected as a long-term consequence of renal adaptation at high altitude.

Anemia and Incident End-Stage Kidney Disease

BACKGROUND

Chronic kidney disease (CKD) progression can be a cause and potentially a consequence of anemia. Previous studies suggesting that anemia is associated with CKD progression have not utilized methodologic approaches to address time-dependent confounding.

METHODS

We evaluated the association of anemia (defined using World Health Organization criteria of hemoglobin <12 g/dL in women and <13 g/dL in men) with incident ESRD and all-cause death in individuals with CKD using data from the Chronic Renal Insufficiency Cohort Study. Marginal structural models were used to account for time-dependent confounding.

RESULTS

Among 3919 participants, 1859 (47.4%) had anemia at baseline. Over median follow up of 7.8 years, we observed 1,010 ESRD events and 994 deaths. In multivariable analyses, individuals with anemia had higher risk for ESRD compared to those without (HR 1.62, 95% CI 1.24-2.11). In stratified analyses, the increased risk for incident ESRD with anemia was observed in males (HR 2.15, 95% CI: 1.53-3.02) but not females (HR 1.20, 95% CI 0.82-1.78. The association between anemia and ESRD was significant among all racial/ethnic groups except non-Hispanic blacks (non-Hispanic white, HR 2.16, 95% CI 1.53-3.06; Hispanic, HR 1.92, 1.04-3.51; others, HR 2.94; 95% CI 1.16-7.44; non-Hispanic black, HR 1.39; 95% CI 0.95-2.02). There was no association between anemia and all-cause death.

CONCLUSIONS

In this cohort, anemia was independently associated with increased risk for incident ESRD. Future work is needed to evaluate the mechanisms by which anemia leads to CKD progression as well as the impact of novel therapeutic agents to treat anemia.

Reversibility of microalbuminuria with continuous positive airway pressure treatment in obstructive sleep apnea syndrome

INTRODUCTION

Microalbuminuria is an early marker of kidney damage and an early predictor and risk factor for cardiovascular diseases. We aimed to evaluate the association between albuminuria levels in different severity obstructive sleep apnea syndrome (OSAS) cases and to find out the efficacy of CPAP treatment on microalbuminuria.

MATERIALS AND METHODS

We conducted a prospective study on subjects who underwent polysomnography. The polysomnographic data were recorded to establish the presence and severity of OSAS. The blood and urine samples were taken both at the time of diagnosis and 3 months after CPAP therapy. The relationship between the severity of OSAS and microalbuminuria and the effect of CPAP treatment on microalbuminuria were evaluated.

RESULTS

The study population consisted of 449 subjects. Better compliance to CPAP was associated with significantly reduced levels of microlbuminuria. Urinary albumin/creatinine was increased in severe cases, but the difference was not statistically significant. In the non-compliant group, microalbumin/creatinine ratio was 25.24 prior to initiation of CPAP treatment and 28.36 at the third month control visit (p = 0.25). In the compliant group, microalbumin/creatinine ratio was 49.71 prior to initiation of CPAP treatment and 22.30 at the third month control visit (p = 0.04).

CONCLUSION

Our study demonstrated that good compliance to CPAP therapy is associated with a decrease in microalbuminuria. Patients who used CPAP regularly had a significant decline in albumin/creatinine ratio after 3 months of CPAP therapy.

Cardiorenal Syndrome: Pathophysiology

Cardiorenal syndrome commonly refers to the collective dysfunction of heart and kidney resulting in a cascade of feedback mechanism causing damage to both the organs and is associated with adverse clinical outcomes. The pathophysiology of cardiorenal syndrome is complex, multifactorial, and dynamic. Improving the understanding of disease mechanisms will aid in developing targeted pharmacologic and nonpharmacologic therapies for the management of this syndrome. This article discusses the various mechanisms involved in the pathophysiology of the cardiorenal syndrome.

Effect of CPAP therapy on kidney function in patients with obstructive sleep apnoea and chronic kidney disease: a protocol for a randomised controlled clinical trial

INTRODUCTION

Obstructive sleep apnoea (OSA) is common in patients with chronic kidney disease (CKD) and may contribute to the progression of kidney disease either through direct effects of hypoxia on the kidney or indirectly through hypoxaemia-induced oxidative stress, endothelial dysfunction, inflammation, activation of the renin-angiotensin and sympathetic nervous systems, and hypertension. Treatment of OSA with continuous positive airway pressure (CPAP) improves many of these physiological abnormalities in patients with normal renal function, though to date there are no trials evaluating the effect of OSA treatment on kidney function in patients with CKD. The purpose of this study is to test the feasibility and efficacy of CPAP therapy in CKD patients with OSA.

METHODS AND ANALYSIS

The study is a randomised, controlled, non-blinded, parallel clinical trial in which patients with established CKD are screened for OSA. Patients with OSA are randomised to either conventional medical therapy (control group) or medical therapy and CPAP (CPAP group) and followed for 1 year. The primary outcome is the change in estimated glomerular filtration rate. Secondary outcomes are the change in the urinary albumin/creatinine ratio, the Epworth Sleepiness Scale , Pittsburgh Sleep Quality Index and Kidney Disease Quality of Life questionnaire.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from the Conjoint Health Research Ethics Board (ID: REB15-0055). Results from this study will be disseminated through presentations at scientific conferences and publication in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT02420184; Pre-results.

The role of the Nox4-derived ROS-mediated RhoA/Rho kinase pathway in rat hypertension induced by chronic intermittent hypoxia

BACKGROUND

Obstructive sleep apnea syndrome, which is a risk factor for resistant hypertension, is characterized by chronic intermittent hypoxia (CIH) and is associated with many cardiovascular diseases. CIH elicits systemic oxidative stress and sympathetic hyperactivity, which lead to hypertension. Rho kinases (ROCKs) are considered to be major effectors of the small GTPase RhoA and have been extensively studied in the cardiovascular field. Upregulation of the RhoA/ROCK signaling cascade is observed in various cardiovascular disorders, such as atherosclerosis, pulmonary hypertension, and stroke. However, the exact molecular function of RhoA/ROCK in CIH remains unclear and requires further study.

OBJECTIVE

This study aimed to investigate the role of the NADPH oxidase 4 (Nox4)-induced ROS/RhoA/ROCK pathway in CIH-induced hypertension in rats.

METHODS

Male Sprague-Dawley rats were exposed to CIH for 21 days (intermittent hypoxia of 21% O₂ for 60 s and 5% O₂ for 30 s, cyclically repeated for 8 h/day). We randomly assigned 56 male rats to groups of normoxia (RA) or vertically implemented CIH together with vehicle (CIH-V), GKT137831 (CIH-G), N-acetyl cysteine (NAC) (CIH-N), or Y27632 (CIH-Y). The rats in the RA group were continuously exposed to room air, whereas the rats in the other groups were exposed to CIH. Systolic blood pressure (BP) was monitored at the beginning of each week. After the experiment, renal sympathetic nerve activity (RSNA) was recorded, and serum and renal tissues were subjected to molecular biological and biochemical analyses.

RESULTS

Compared with the BP of RA rats, the BP of CIH-V rats started to increase 2 weeks after the beginning of the experiment, subsequently stabilizing at a high level at the end of the third week. CIH increased both RSNA and oxidative stress. This response was attenuated by treatment of the rats with GKT137831 or NAC. Inhibiting Nox4 activity or ROS production reduced RhoA/ROCK expression. Treatment with Y27632 reduced both BP and RSNA in rats exposed to CIH.

CONCLUSION

Hypertension can be induced by CIH in SD rats. The CIH-induced elevation of BP is at least partially mediated via the Nox4-induced ROS/RhoA/ROCK pathway.

Intrarenal hemodynamic and oxidative stress in patients with obstructive sleep apnea syndrome

BACKGROUND

Oxygen desaturation and reoxygenation, related to intermittent hypoxia cycles due to upper airway obstruction, are major pathophysiologic features of obstructive sleep apnea syndrome (OSAS) and are thought to be responsible for an increased risk of cardiovascular diseases. Continuous positive airway pressure (CPAP) is therefore considered the gold standard in the management of OSAS. Further data demonstrated a high prevalence of OSAS in patients with altered renal function despite the underlying pathophysiological mechanisms that have not been clarified. This study aims to provide evidence on the reported high prevalence of endothelial dysfunction and alterations of the intrarenal hemodynamic in patients affected by OSAS. Furthermore, we evaluated the effect of a CPAP therapy on these endpoints.

METHODS

Twenty patients were enrolled in a prospective study and underwent ultrasound examination to assess endothelial dysfunction, by collecting brachial flow-mediated dilation (FMD) and intrarenal artery stiffness, pre- and post a 30-day treatment with CPAP.

RESULTS

Endothelial dysfunction and intrarenal artery stiffness significantly improved in all patients after a month of CPAP. In particular, we observed a significant reduction in the renal resistance index (RI) (p < 0.001) and systolic/diastolic ratio (S/D) ratio (p < 0.001) and a significant increase of FMD (p < 0.001). The apnea-hypopnea index (AHI) showed a negative correlation with Δ FMD (p < 0.05, r = -0.46). Conversely, a positive correlation exists between Δ RI and the oxygen desaturation index (ODI) (specificare la sigla) (p < 0.05, r = 0.46).

CONCLUSIONS

Our study firstly showed a significant effect of CPAP on renal perfusion and endothelial function in OSAS patients without concomitant cardiovascular comorbidities.

Impact of tubulointerstitial lesions on anaemia in patients with biopsy-proven diabetic nephropathy

AIMS

To investigate the relationship between the progression of anaemia and renal pathological findings in patients with diabetic nephropathy.

METHODS

A total of 223 patients with diabetes underwent renal biopsy from 1985 to 2010 and were confirmed to have pure diabetic nephropathy according to the recent classification, of whom 113 (baseline haemoglobin ≥ 11 g/dl) were enrolled in the study. Linear regression analysis was used to estimate the changes in haemoglobin levels during the follow-up period.

RESULTS

In a multivariate model adjusted for clinical and histopathological variables, higher interstitial fibrosis and tubular atrophy scores were more strongly associated with a decrease in haemoglobin levels than were lower scores. Compared with an interstitial fibrosis and tubular atrophy score of 0, the standardized coefficients for interstitial fibrosis and tubular atrophy scores of 1, 2 and 3 were 0.20 (95% CI -0.31 to 0.93), 0.34 (95% CI -0.22 to 1.34) and 0.47 (95% CI 0.07 to 1.96), respectively, whereas a higher glomerular class, a higher vascular lesion score and the presence of exudative lesions were not strongly correlated with the decrease in haemoglobin.

CONCLUSIONS

Tubulointerstitial lesions that are more advanced are significantly associated with the progression of anaemia in patients with diabetic nephropathy after adjustment for numerous covariates. This finding suggests that tubulointerstitial lesions may be a useful prognostic indicator for anaemia in patients with diabetic nephropathy, and that decreased erythropoietin production attributable to the progression of tubulointerstitial lesions is a major cause of anaemia in these patients.

Effects of renal denervation on regional hemodynamics and kidney function in experimental hyperdynamic sepsis

OBJECTIVE

To determine the influence of the renal sympathetic nerves on the pathogenesis of septic acute kidney injury.

DESIGN

Interventional control study to determine the effects of renal denervation in ovine hyperdynamic sepsis.

SETTING

Research Institute.

SUBJECTS

Twenty-four adult Merino ewes.

INTERVENTIONS

The effects of infusion of angiotensin II and norepinephrine and induction of hyperdynamic sepsis by administration of live Escherichia coli were examined in control sheep and in sheep at 2 weeks after bilateral renal denervation (n = 10/group).

MEASUREMENTS AND MAIN RESULTS

Systemic hemodynamics and renal function were measured in conscious sheep instrumented with flow probes on the pulmonary and renal arteries. Angiotensin II, but not norepinephrine, had a greater pressor effect in denervated animals. Sepsis increased cardiac output by 60%, renal blood flow by 35%, and arterial lactate by approximately four-fold. The denervated compared with the control group had a greater degree of hypotension during sepsis (68 vs 81 mm Hg; p = 0.003) and a reduction in the early polyuric response (from 496 to 160 mL at 2-8 hr of sepsis; p < 0.001). Creatinine clearance decreased similarly in both groups.

CONCLUSIONS

In experimental hyperdynamic sepsis, renal denervation was associated with greater hypotension and a loss of the initial diuresis, but no significant change in creatinine clearance. In sepsis, the renal nerves help support arterial pressure and determine the initial diuretic response, but septic acute kidney injury developed similarly in the innervated and denervated groups.

Tamoxifen resistance in breast cancer

Tamoxifen is a central component of the treatment of estrogen receptor (ER)-positive breast cancer as a partial agonist of ER. It has been clinically used for the last 30 years and is currently available as a chemopreventive agent in women with high risk for breast cancer. The most challenging issue with tamoxifen use is the development of resistance in an initially responsive breast tumor. This review summarizes the roles of ER as the therapeutic target of tamoxifen in cancer treatment, clinical values and issues of tamoxifen use, and molecular mechanisms of tamoxifen resistance. Emerging knowledge on the molecular mechanisms of tamoxifen resistance will provide insight into the design of regimens to overcome tamoxifen resistance and discovery of novel therapeutic agents with a decreased chance of developing resistance as well as establishing more efficient treatment strategies.

Guanosine regulates adenosine levels in the kidney

In cell culture, extracellular guanosine increases extracellular adenosine by attenuating the disposition of extracellular adenosine (American Journal of Physiology – Cell Physiology 304: C406–C421, 2013). The goal of this investigation was to determine whether this “guanosine–adenosine mechanism” is operative in an intact organ. Twenty‐seven isolated, perfused mouse kidneys were subjected to metabolic poisons (iodoacetate plus 2,4‐dinitrophenol) to cause energy depletion and thereby stimulate renal adenosine production. Adenosine levels in the renal venous perfusate increased from a baseline of 36 ± 8 to 499 ± 96, 258 ± 50, and 71 ± 13 nmol/L at 15, 30, and 60 min, respectively, after administering metabolic poisons (% of basal; 1366 ± 229, 715 ± 128, and 206 ± 33, respectively). Changes in renal venous levels of guanosine closely mirrored the time course of changes in adenosine: baseline of 15 ± 2 to 157 ± 13, 121 ± 8, and 50 ± 5 nmol/L at 15, 30, and 60 min, respectively (% of basal; 1132 ± 104, 871 ± 59, and 400 ± 51, respectively). Freeze‐clamp experiments in 12 kidneys confirmed that metabolic poisons increased kidney tissue levels of adenosine and guanosine. In eight additional kidneys, we examined the ability of guanosine to reduce the renal clearance of exogenous adenosine; and these experiments revealed that guanosine significantly decreased the renal extraction of adenosine. Because guanosine is metabolized by purine nucleoside phosphorylase (PNPase), in another set of 16 kidneys we examined the effects of 8‐aminoguanine (PNPase inhibitor) on renal venous levels of adenosine and inosine (adenosine metabolite). Kidneys treated with 8‐aminoguanine showed a more robust increase in both adenosine and inosine in response to metabolic poisons. We conclude that in the intact kidney, guanosine regulates adenosine levels.

In cell culture, extracellular guanosine increases extracellular adenosine by attenuating the disposition of extracellular adenosine (American Journal of Physiology – Cell Physiology 304: C406–C421, 2013). The goal of this study was to determine whether the “guanosine–adenosine mechanism” is operative in an intact organ. In isolated, perfused mouse kidneys, inhibition of energy production induced changes in renal venous levels of guanosine that closely mirrored the time course of changes in adenosine, and freeze‐clamp experiments confirmed that metabolic poisons similarly increased kidney tissue levels of adenosine and guanosine. Moreover, exogenous guanosine significantly decreased the renal extraction of exogenous adenosine, and inhibition of purine nucleoside phosphorylase (metabolizes guanosine) augmented the effects of energy depletion on renal levels of both guanosine and adenosine. We conclude that in the intact kidney, guanosine regulates adenosine levels.

Elevated serum cystatin C in severe OSA younger men without complications

PURPOSE

Serum cystatin C is a promising new biomarker of glomerular filtration rate and cardiovascular events, but few studies focused on serum cystatin C levels in obstructive sleep apnea (OSA) patients. The aim of our study was to evaluate the association between serum cystatin C and OSA in younger men (≤40 years old of age) without complications.

METHODS

We prospectively recruited consecutive participants without comorbidities who underwent polysomnography. Fasting blood samples were obtained from all subjects for biological profile measurements. Statistical analysis was used to evaluate the relationship between serum cystatin C and other parameters.

RESULTS

The population consisted of 98 subjects (mean age = 32.5 years, mean body mass index = 27.93 kg/m(2)) that were divided according to polysomnographic finding into control group (n = 23), mild (n = 15), moderate (n = 24), and severe (n = 36) OSA group. Compared with the control group, patients with severe OSA were significantly heavier (body mass index, 29.69 ± 3.81 vs. 26.42 ± 3.10) and presented significantly higher levels of high sensitive C-reactive protein (hsCRP) (1.10 ± 0.28 vs. 0.88 ± 0.20 mg/l) and serum cystatin C (0.87 ± 0.12 vs. 0.74 ± 0.10 mg/l) (p < 0.05 for all comparisons). Cystatin C was correlated with Apnea Hypopnea Index (AHI), Oxygen Desaturation Index, hsCRP, creatinine, and estimated glomerular filtration rate (r = 0.319, 0.279, 0.321, 0.233, -0.241, p = 0.001, 0.005, 0.001, 0.021, 0.017, respectively). After adjustment for confounding factors, AHI was significantly and positively associated with serum cystatin C levels (β = 0.284, p = 0.007).

CONCLUSIONS

Our finding indicated that serum cystatin C was associated with the severity of OSA in younger men. Further study is needed to find out whether OSA patients with increased serum cystatin C levels are prone to subclinical cardiovascular and renal diseases.

Azelnidipine attenuates glomerular damage in Dahl salt-sensitive rats by suppressing sympathetic nerve activity

Dihydropyridine-type calcium channel blockers (CCBs) exert potent antihypertensive effects. The CCB azelnidipine decreases heart rate by suppressing sympathetic nerve activity, which affects afferent and efferent arterioles in the glomeruli. We examined whether azelnidipine can improve progressive glomerular injury in comparison with amlodipine by suppressing renal sympathetic nerve activity in Dahl salt-sensitive rats. Glomerular circulation in Dahl salt-sensitive rats was monitored with a charge-coupled device camera before and after administration of amlodipine (0.5 mg kg(-1), bolus injection) or azelnidipine (0.1 mg kg(-1), bolus injection). Systemic sympathetic nerve activity was also compared by analysis of heart rate variability with a telemetry blood pressure monitoring system after crossover administration of amlodipine (1.0 mg kg(-1) per day) and azelnidipine (3.0 mg kg(-1) per day) for 1 week. To investigate renoprotective effects, rats were treated with amlodipine (1.0 mg kg(-1) per day) or azelnidipine (3.0 mg kg(-1) per day) for 3 weeks with or without renal denervation. The efferent arteriole contracted in response to acute amlodipine but not azelnidipine treatment. The low frequency/high frequency ratio, an index of parasympathetic nerve activity, decreased in response to azelnidipine but not amlodipine treatment. In response to chronic treatment, proteinuria and glomerular injury improved to a greater extent with azelnidipine compared with amlodipine. The renoprotective effects of azelnidipine were diminished by renal denervation. Azelnidipine decreased glomerular damage in Dahl salt-sensitive rats to a greater extent than amlodipine. Azelnidipine appeared to decrease intraglomerular pressure by suppressing sympathetic nerve activity.

Renal programming: cause for concern?

Development of the kidney can be altered in utero in response to a suboptimal environment. The intrarenal factors that have been most well characterized as being sensitive to programming events are kidney mass/nephron endowment, the renin-angiotensin system, tubular sodium handling, and the renal sympathetic nerves. Newborns that have been subjected to an adverse intrauterine environment may thus begin life at a distinct disadvantage, in terms of renal function, at a time when the kidney must take over the primary role for extracellular fluid homeostasis from the placenta. A poor beginning, causing renal programming, has been linked to increased risk of hypertension and renal disease in adulthood. However, although a cause for concern, increasingly, evidence demonstrates that renal programming is not a fait accompli in terms of future cardiovascular and renal disease. A greater understanding of postnatal renal maturation and the impact of secondary factors (genes, sex, diet, stress, and disease) on this process is required to predict which babies are at risk of increased cardiovascular and renal disease as adults and to be able to devise preventative measures.

Obstructive sleep apnoea syndrome promotes reversal albuminuria during sleep

INTRODUCTION

Sleep apnoea syndrome (OSAS) may induce albuminuria during sleep which could reflect one of the possible pathogenetic mechanisms regarding cardiovascular risk.

MATERIALS AND METHODS

We studied 224 patients with newly diagnosed OSAS, free of any chronic disease, and any regular drug therapy. The levels of urine albumin/creatinine ratio (ACR) before (ACR-bsleep) and immediately after (ACR-asleep) a sleep study were determined. The same procedure was repeated during the first night on CPAP treatment (n = 121) and in 46 reevaluated patients, after 3 months, on CPAP therapy. Ambulatory blood pressure was monitored in 133 of the patients.

RESULTS

ACR-asleep was significantly higher in patients (17.82 ± 31.10 mg/g) compared with controls (6.54 ± 6.53 mg/g, p < 0.001). The mean percent change in ACR levels between after and before sleep (%dACR) was increased by 8.82% ± 61.06 in OSAS patients and reduced by 26.87% ± 18.95 in controls (p < 0.001). During the first sleep study on CPAP, the %dACR was reduced by 21.40% ± 24.59, in contrast to the increase observed during the initial study (10.73% ± 69.93, p < 0.001). This beneficial effect of CPAP treatment was preserved in the reevaluated patients. The %dACR was +29.33% ± 57.67 in nondippers (44% of the patients) and -5.57% ± 40.81 in dippers (p < 0.001). It was negatively correlated to the percent change of systolic (rho = -0.284, p = 0.003) and diastolic (rho = -0.341, p < 0.001) blood pressure between wakefulness and sleep. Contrary to normal people, ACR is increased in OSAS patients during sleep, at least partially, related to the nondipping phenomenon observed in these patients. Following CPAP treatment, urinary albumin excretion is reduced.

Impact of mild hypoxemia on renal function and renal resistive index during mechanical ventilation

RATIONALE

Short-term hypoxemia affects diuresis and natriuresis in healthy individuals. No data are available on the impact of the mild hypoxemia levels usually tolerated in critically ill patients receiving mechanical ventilation.

OBJECTIVES

To assess the renal effects of mild hypoxemia during mechanical ventilation for acute lung injury (ALI).

METHODS

Prospective, physiological study in 12 mechanically ventilated patients with ALI. Patients were studied at baseline with an arterial saturation (SaO(2)) of 96% [94-98] then a comparison was performed between SaO(2) values of 88-90% (mild hypoxemia) and 98-99% (high oxygenation).

MAIN RESULTS

FiO(2) was set at 0.25 [0.23-0.32] and 0.7 [0.63-0.8], respectively, to obtain SaO(2) of 89 [89-90] and 99% [98-99]. Hemodynamic or respiratory parameters were not significantly affected by FiO(2) levels. Compared with high oxygenation level, mild hypoxemia using low FiO(2) was associated with increase in diuresis (median [interquartile range], 67 [55-105] vs. 55 [45-60] ml/h; P = 0.003) and in doppler-based renal resistive index (RI) (0.78 [0.66-0.85] vs. 0.72 [0.60-0.78]; P = 0.003). The 2-h calculated creatinine clearance also increased (63 [46-103] vs. 35 [30-85] ml/min; P = 0.005) without change in urinary creatinine (P = 0.13). No significant change in natriuresis was observed. Half of the patients were under norepinephrine infusion and the renal response did not differ according to the presence of vasopressors.

CONCLUSION

In patients with ALI, mild hypoxemia related to short-term low FiO(2) induce increases in diuresis and in renal RI. This latter point suggests intra-renal mechanisms that need to be further investigated.

Altered responsiveness of the kidney to activation of the renal nerves in fat-fed rabbits

We tested whether mild adiposity alters responsiveness of the kidney to activation of the renal sympathetic nerves. After rabbits were fed a high-fat or control diet for 9 wk, responses to reflex activation of renal sympathetic nerve activity (RSNA) with hypoxia and electrical stimulation of the renal nerves (RNS) were examined under pentobarbital anesthesia. Fat pad mass and body weight were, respectively, 74% and 6% greater in fat-fed rabbits than controls. RNS produced frequency-dependent reductions in renal blood flow, cortical and medullary perfusion, glomerular filtration rate, urine flow, and sodium excretion and increased renal plasma renin activity (PRA) overflow. Responses of sodium excretion and medullary perfusion were significantly enhanced by fat feeding. For example, 1 Hz RNS reduced sodium excretion by 79 +/- 4% in fat-fed rabbits and 46 +/- 13% in controls. RNS (2 Hz) reduced medullary perfusion by 38 +/- 11% in fat-fed rabbits and 9 +/- 4% in controls. Hypoxia doubled RSNA, increased renal PRA overflow and medullary perfusion, and reduced urine flow and sodium excretion, without significantly altering mean arterial pressure (MAP) or cortical perfusion. These effects were indistinguishable in fat-fed and control rabbits. Neither MAP nor PRA were significantly greater in conscious fat-fed than control rabbits. These observations suggest that mild excess adiposity can augment the antinatriuretic response to renal nerve activation by RNS, possibly through altered neural control of medullary perfusion. Thus, sodium retention in obesity might be driven not only by increased RSNA, but also by increased responsiveness of the kidney to RSNA.

The effect of losartan on hemoglobin concentration and renal outcome in diabetic nephropathy of type 2 diabetes

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers can decrease hemoglobin, causing anemia and this may be an independent risk factor for chronic kidney disease progression. We studied the relationship between a decline in hemoglobin and outcome in 1513 patients with type 2 diabetes and kidney disease by a post hoc analysis of the RENAAL Study (Reduction of Endpoints in NIDDM with the Angiotensin II Antagonist Losartan) with an average follow-up of 3.4 years. The relationship between baseline and year-1 hemoglobin and treatment on end-stage renal disease (ESRD) and ESRD or death was evaluated using multivariate Cox models (covariates: baseline hemoglobin, proteinuria, serum albumin, serum creatinine, and year-1 hemoglobin). Compared with placebo, losartan treatment was associated with a significant decrease of hemoglobin, with the largest between-group difference at 1 year. After adjustment, there were significant relative risk reductions for losartan compared with placebo for ESRD and for ESRD or death regardless of the baseline hemoglobin even in those patients with a baseline hemoglobin below 120 g l(-1). Hence, the renoprotective properties of losartan were maintained despite a significant lowering of the hemoglobin concentration.

Sex differences in postnatal growth and renal development in offspring of rabbit mothers with chronic secondary hypertension

Previously, we demonstrated that adult blood pressure was increased in offspring of rabbit mothers with chronic secondary renal hypertension. Our study identified sex-specific differences in the programming of hypertension, with female, not male, offspring, having increased blood pressure at 30 wk of age. The aim of this study was to characterize the maternal hypertension during pregnancy to determine potential programming stimuli. Further, we examined the impact of chronic maternal hypertension on offspring birth weight, nephron number, and renal noradrenaline content (as an index of renal innervation density). Three groups of mothers and their offspring were studied: two-kidney, one-wrap (2K-1W, n = 9 mothers) hypertensive, two-kidney, two-wrap (2K-2W, n = 8) hypertensive, and a sham-operated group (n = 9). Mean arterial blood pressure was increased by approximately 20 mmHg throughout pregnancy in both hypertensive groups compared with sham mothers (P(G) < 0.001). Plasma renin activity (PRA; P(G) < 0.05) and aldosterone (P(G) < 0.05) levels were increased during gestation in the 2K-1W, but not the 2K-2W mothers. Birth weight was increased by approximately 20% in offspring of both groups of hypertensive mothers (P(T) < 0.001), though this was associated with a reduction in litter size. Renal noradrenaline content was increased ( approximately 40%, P < 0.05) at 5 wk of age in female 2K-1W offspring compared with sham offspring. Glomerular number was not reduced in female offspring of either group of hypertensive mothers; however, glomerular tuft volume was reduced in female 2K-2W offspring (P < 0.05), indicative of a reduction in glomerular filtration surface area. In conclusion, the two models of renal hypertension produced differential effects on the offspring. The impact of a stimulated maternal renin-angiotensin system in the 2K-1W model of hypertension may influence development of the renal sympathetic nerves and contribute to programming of adult hypertension.

Lower haemoglobin level and subsequent decline in kidney function in type 2 diabetic adults without clinical albuminuria

AIMS/HYPOTHESIS

Anaemia has been suggested to be an independent risk factor for subsequent progression of advanced diabetic nephropathy; however, the relationship between haemoglobin levels and progression of nephropathy in patients without clinical albuminuria is unknown.

METHODS

We conducted this prospective hospital-based cohort study of 464 type 2 diabetic patients (149 women and 315 men, 55+/-13 [mean+/-SD] years of age) with serum creatinine <177 micromol/l (2.00 mg/dl) and urinary albumin : creatinine ratio <300 mg/g creatinine. GFR was estimated using the equation formulated by the Modification of Diet in Renal Disease Study group, refitted for Japanese individuals. Most patients had haemoglobin concentrations in the normal range (144+/-15 g/l), only modest renal impairment (GFR: 74.8+/-14.5 ml min(-1) 1.73 m(-2)), and normal urinary albumin levels (81.5/18.5% with normo-/microalbuminuria). The primary outcome measurement was the rate of change in GFR determined by regression analysis with GFR as a function of time. Patients were followed up for a mean observation period of 5.0+/-0.9 (range: 2.5 to 6.2) years.

RESULTS

Univariate and multiple regression analyses yielded a significant association between the rate of change in GFR and baseline haemoglobin concentration. After adjusting for covariates, the rate of decline in GFR was significantly greater in patients in the lowest haemoglobin quartile (-3.27 ml min(-1) 1.73 m(-2) year(-1)) than in the third (-2.71 ml min(-1) 1.73 m(-2) year(-1), p = 0.024) and highest quartiles (-2.78 ml min(-1) 1.73 m(-2) year(-1), p = 0.046).

CONCLUSIONS/INTERPRETATION

Lower haemoglobin concentrations in type 2 diabetic patients without clinical albuminuria may be a significant predictor of subsequent decline in GFR.

Long-term mathematical model involving renal sympathetic nerve activity, arterial pressure, and sodium excretion

This paper presents a physiological long-term model of the cardiovascular system. It integrates the previous models developed by Guyton, Uttamsingh and Coleman. Additionally it introduces mechanisms of direct effects of the renal sympathetic nerve activity (rsna) on tubular sodium reabsorption and renin secretion in accordance with experimental data from literature. The resulting mathematical model constitutes the first long-term model of the cardiovascular system accounting for the effects of rsna on kidney functions in such detail. The objective of developing such a model is to observe the consequences of long-term rsna increase and impairment of rsna inhibition under volume loading. This model provides an understanding of the rsna-related mechanisms, which cause mean arterial pressure increase in hypertension and total sodium amount increase (sodium retention) in congestive heart failure, nephrotic syndrome and cirrhosis.

Percutaneous coronary interventions in the high-risk renal patient: strategies for renal protection and vascular protection

CKD is the most important factor in predict-ing adverse short- and long-term outcomes after PCI. Hence, the rationale for renal end-organ protection is based on chronic renal protection,avoidance of additive renal insults, and a comprehensive CIN prophylaxis. The pathogenesis of CIN goes beyond serum creatinine and involves a unique vascular pathobiology in which interrelates renal and CVD outcomes are interrelated. Attempts at PCI in patients with CKD and ESRD are high-risk procedures, but the risks involved seem to be warranted given comparative outcomes in conservatively treated patients. The benefits of short- and long-term vascular protective therapies in CKD patients have been confirmed, and these therapies are an important component of PCI care.

Contrast-induced nephropathy

Contrast-induced nephropathy (CIN) is a leading cause of in-hospital acute renal failure in critically ill patients who undergo radiographic procedures. Critical care patients are at particular risk, often because of baseline renal dysfunction, older age, and the presence of diabetes. In addition, there are superimposed risks, including volume depletion, sepsis, and use of nephrotoxic drugs. The rates of CIN (defined as an increase in serum creatinine by >25% or 0.5 mg/dL) can be predicted by using multivariate tools. Prevention measures include adequate hydration, use of N-acetylcysteine and iso-osmolar contrast, and for patients who are at the highest risk, prophylactic hemofiltration.

Anemia and end-stage renal disease in patients with type 2 diabetes and nephropathy

BACKGROUND

Diabetic nephropathy is the leading cause of end-stage renal disease (ESRD). Anemia is common in diabetics with nephropathy; however, the impact of anemia on progression to ESRD has not been carefully examined.

METHODS

We studied the relationship between baseline hemoglobin concentration (Hb) and progression of diabetic nephropathy to ESRD in 1513 participants enrolled in Reduction in Endpoints in NIDDM with the Angiotensin II Antagonist Losartan study and followed for an average of 3.4 years. Multivariate Cox proportional hazards models were used to analyze the relationship between Hb and ESRD, after adjusting for predictors for ESRD. Analyses were performed with Hb stratified by quartile: first quartile <11.3 g/dL, second quartile 11.3 to 12.5 g/dL, third quartile 12.6 to 13.8 g/dL, and fourth quartile >/=13.8 g/dL (reference) and as a continuous variable.

RESULTS

Baseline hemoglobin concentration was correlated with subsequent development of ESRD. After adjustment for predictors of ESRD, the hazard ratios for the first, second, and third Hb quartiles were 1.99 (95% CI, 1.34-2.95), 1.61 (95% CI 1.08-2.41), and 1.87 (95% CI 1.25-2.80). With hemoglobin as a continuous variable, the adjusted hazard ratio was 0.90 (95% CI 0.84-0.96, P= 0.0013). The average increase in adjusted relative risk was 11% for each 1 g/dL decrease in hemoglobin concentration.

CONCLUSION

Our data suggest that even mild anemia, Hb <13.8 g/dL increases risk for progression to ESRD. Hemoglobin is an independent risk factor for progression of nephropathy to ESRD in type 2 diabetes.

Short-term use of continuous positive airway pressure ameliorates glomerular hyperfiltration in patients with obstructive sleep apnoea syndrome

Patients with OSAS (obstructive sleep apnoea syndrome) demonstrate renal signs such as proteinuria, glomerular hypertrophy and focal glomerular sclerosis. We performed a clinical study to investigate the glomerular function in OSAS patients and the short-term effect of CPAP (continuous positive airway pressure) on it. OSAS patients underwent a sodium thiosulphate and p-aminohippurate double clearance test, polysomnography and ambulatory blood pressure monitoring before and a week after the induction of CPAP. Twenty-seven consecutive patients (24 males) with moderate-to-severe OSAS admitted to our hospital for the induction of CPAP, and 32 healthy donors for renal transplantation as controls participated in the study. Before treatment, the glomerular filtration rate, estimated by the sodium thiosulphate clearance test, was within normal range, and the renal plasma flow was significantly lower than normal in the OSAS patients, thus the FF (filtration fraction) value was much higher than normal. FF before CPAP was not significantly correlated with age, body mass index or blood pressure; however, indices of increased hypoxaemia correlated with increased FF values. Polysomnographic variables after CPAP showed significant improvements in all patients, and only the nocturnal blood pressures were slightly lower than before CPAP. In 21 patients who underwent the clearance test after CPAP, FF significantly decreased from 0.26 +/- 0.04 to 0.23 +/- 0.03 (P < 0.001). OSAS patients were generally in a glomerular-hyperfiltrating condition that appeared to cause the renal findings associated with OSAS. CPAP might prevent nephropathy by ameliorating the glomerular hyperfiltration in OSAS patients.

Predominant postglomerular vascular resistance response to reflex renal sympathetic nerve activation during ANG II clamp in rabbits

We have shown previously that a moderate reflex increase in renal sympathetic nerve activity (RSNA) elevated glomerular capillary pressure, whereas a more severe increase in RSNA decreased glomerular capillary pressure. This suggested that the nerves innervating the glomerular afferent and efferent arterioles could be selectively activated, allowing differential control of glomerular capillary pressure. A caveat to this conclusion was that intrarenal actions of neurally stimulated ANG II might have contributed to the increase in postglomerular resistance. This has now been investigated. Anesthetized rabbits were prepared for renal micropuncture and RSNA recording. One group (ANG II clamp) received an infusion of an angiotensin-converting enzyme inhibitor (enalaprilat, 2 mg/kg bolus plus 2 mg·kg−1·h−1) plus ANG II (∼20 ng·kg−1·min−1), the other vehicle. Measurements were made before (room air) and during 14% O2. Renal blood flow decreased less during ANG II clamp compared with vehicle [9 ± 1% vs. 20 ± 4%, interaction term (PGT) < 0.05], despite a similar increase in RSNA in response to 14% O2in the two groups. Arterial pressure and glomerular filtration rate were unaffected by 14% O2in both groups. Glomerular capillary pressure increased from 33 ± 1 to 37 ± 1 mmHg during ANG II clamp and from 33 ± 2 to 35 ± 1 mmHg in the vehicle group before and during 14% O2, respectively (PGT< 0.05). During ANG II clamp, postglomerular vascular resistance was still increased in response to RSNA during 14% O2, demonstrating that the action of the renal nerves on the postglomerular vasculature was independent of the renin-angiotensin system. This further supports our hypothesis that increases in RSNA can selectively control pre- and postglomerular vascular resistance and therefore glomerular ultrafiltration.

Anaemia as a risk factor for the progression of chronic kidney disease

PURPOSE OF REVIEW

About a dozen controlled clinical trials examined the effect of anaemia correction on the progression of chronic kidney disease. None of these studies fulfilled the stringent criteria of a randomized controlled trial as suggested by the CONSORT statement, yet evidence emerged that anaemia sustains mitogenic and fibrogenic stimuli by lowering local partial oxygen tension. This review addresses the question of why and how anaemia could possibly enhance the progression of chronic kidney disease, and summarizes relevant clinical trials.

RECENT FINDINGS

The discovery of hypoxia-inducible factor, a transcription factor stabilized under hypoxic conditions, with DNA-binding properties towards about 50 target genes including erythropoietin, has largely encouraged the hypothesis that tissue hypoxia may serve as another common mechanism for the progression of chronic kidney disease besides hypertension or proteinuria. In addition, anaemia-mediated alterations of renal sympathetic nerve activity and anaemia-related increments of oxidative stress may contribute to a progressive nephron loss. Conclusive evidence from clinical trials is scarce.

SUMMARY

Pathophysiological concepts suggest some impact of anaemia on the progression of chronic kidney disease. The urge for more sound clinical intervention trials is met by the ongoing ECAP study (Effect of early Correction of Anaemia on the Progression of chronic kidney disease).