Understanding the effects of chronic kidney disease on cardiovascular risk: are there lessons to be learnt from healthy kidney donors?

A therapeutic target for CKD: activin A facilitates TGFβ1 profibrotic signaling

BACKGROUND

TGFβ1 is a major profibrotic mediator in chronic kidney disease (CKD). Its direct inhibition, however, is limited by adverse effects. Inhibition of activins, also members of the TGFβ superfamily, blocks TGFβ1 profibrotic effects, but the mechanism underlying this and the specific activin(s) involved are unknown.

METHODS

Cells were treated with TGFβ1 or activins A/B. Activins were inhibited generally with follistatin, or specifically with neutralizing antibodies or type I receptor downregulation. Cytokine levels, signaling and profibrotic responses were assessed with ELISA, immunofluorescence, immunoblotting and promoter luciferase reporters. Wild-type or TGFβ1-overexpressing mice with unilateral ureteral obstruction (UUO) were treated with an activin A neutralizing antibody.

RESULTS

In primary mesangial cells, TGFβ1 induces secretion primarily of activin A, which enables longer-term profibrotic effects by enhancing Smad3 phosphorylation and transcriptional activity. This results from lack of cell refractoriness to activin A, unlike that for TGFβ1, and promotion of TGFβ type II receptor expression. Activin A also supports transcription through regulating non-canonical MRTF-A activation. TGFβ1 additionally induces secretion of activin A, but not B, from tubular cells, and activin A neutralization prevents the TGFβ1 profibrotic response in renal fibroblasts. Fibrosis induced by UUO is inhibited by activin A neutralization in wild-type mice. Worsened fibrosis in TGFβ1-overexpressing mice is associated with increased renal activin A expression and is inhibited to wild-type levels with activin A neutralization.

CONCLUSIONS

Activin A facilitates TGFβ1 profibrotic effects through regulation of both canonical (Smad3) and non-canonical (MRTF-A) signaling, suggesting it may be a novel therapeutic target for preventing fibrosis in CKD.

Impact of the kidney transplantation on renalase and blood pressure levels in renal transplant donors and recipients

INTRODUCTION AND OBJECTIVES

Prevalence of hypertension increases as glomerular filtration rate (GFR) declines. Renalase metabolizes catecholamines and have an important role in blood pressure (BP) regulation. The purpose of the study was to evaluate the effect of kidney transplantation on renalase levels and BP in kidney donors and recipients.

MATERIALS AND METHODS

Twenty kidney transplant recipients and their donors were included in the study. Serum renalase levels and ambulatory BP values were measured in both donors and recipients before and after transplantation. Factor associated with change in renalase and BP levels were also evaluated.

RESULTS

In donors; mean GFR and hemoglobin levels decreased while night-time systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels and serum renalase levels increased simultaneously after nephrectomy. Day-time SBP and DBP levels did not changed and the night/day ratio of mean arterial pressure (MAP) increased significantly. In recipients, mean GFR increased, while mean serum renalase levels, creatinine and BP levels decreased after transplantation. Correlation analysis revealed that changes in MAP correlated with alteration in serum renalase levels and GFR.

CONCLUSIONS

After transplantation, serum renalase levels increased in donors and decreased in recipients. The renalase levels are associated with change in MAP and circadian rhythm of BP in donors and recipients.

Impact of the kidney transplantation on renalase and blood pressure levels in renal transplant donors and recipients

INTRODUCTION AND OBJECTIVES

Prevalence of hypertension increases as glomerular filtration rate (GFR) declines. Renalase metabolizes catecholamines and have an important role in blood pressure (BP) regulation. The purpose of the study was to evaluate the effect of kidney transplantation on renalase levels and BP in kidney donors and recipients.

MATERIALS AND METHODS

Twenty kidney transplant recipients and their donors were included in the study. Serum renalase levels and ambulatory BP values were measured in both donors and recipients before and after transplantation. Factor associated with change in renalase and BP levels were also evaluated.

RESULTS

In donors; mean GFR and hemoglobin levels decreased while night-time systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels and serum renalase levels increased simultaneously after nephrectomy. Day-time SBP and DBP levels did not changed and the night/day ratio of mean arterial pressure (MAP) increased significantly. In recipients, mean GFR increased, while mean serum renalase levels, creatinine and BP levels decreased after transplantation. Correlation analysis revealed that changes in MAP correlated with alteration in serum renalase levels and GFR.

CONCLUSIONS

After transplantation, serum renalase levels increased in donors and decreased in recipients. The renalase levels are associated with change in MAP and circadian rhythm of BP in donors and recipients.

Hyperuricemia, urate-lowering therapy, and kidney outcomes: a systematic review and meta-analysis

BACKGROUND

Contradictory evidence exists for association of hyperuricemia and kidney function. To investigate the association of hyperuricemia and kidney function decline (hyperuricemia question) and effect of urate-lowering therapies (ULTs) on kidney function (ULT question), we performed a systematic review and meta-analysis.

METHODS

MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and CINAHL were searched from inception to July 2020. We selected observational studies for the hyperuricemia question and controlled trials for the ULT question. Two investigators independently assessed study eligibility and abstracted the data. Risk of bias was assessed using the Newcastle-Ottawa Scale and Cochrane risk of bias tool. Meta-analysis was done using the inverse variance method and random effect model. We estimated odds ratio (OR), hazard ratio (HR), risk ratio (RR), and the mean difference (MD). Evidence certainty was evaluated using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system.

RESULTS

Of 12,037 studies screened, 131 studies with 3,414,226 patients were included. Hyperuricemia was associated with a significant risk of rapid estimated glomerula filtration rate (eGFR) decline ⩾3 ml/min per 1.73 m2 per year (OR 1.38, 95% CI 1.20-1.59; low certainty), albuminuria (OR/HR 1.94, 95% CI 1.34-2.79; very low certainty), chronic kidney disease (OR/HR 2.13, 95% CI 1.74-2.61; very low certainty), and kidney failure (HR 1.53, 95% CI 1.18-1.99; very low certainty). Compared with control, ULT use for ⩾1 year was associated with significantly more improved eGFR (MD 1.81 ml/min per 1.73 m2, 95% CI 0.26-3.35; very low certainty), serum creatinine (MD -0.33 mg/dl, 95% CI -0.47 to -0.19; low certainty), and proteinuria (MD -5.44 mg/day, 95% CI -8.49 to -2.39; low certainty), but no difference in kidney failure.

CONCLUSION

Hyperuricemia is associated with worsening eGFR, albuminuria, chronic kidney disease, and kidney failure. ULT use for ⩾1 year may improve kidney function.

REGISTRATION

The protocol was registered at PROSPERO database, CRD42015013859.

Changes in Blood Pressure and Arterial Hemodynamics following Living Kidney Donation

BACKGROUND AND OBJECTIVES

The Effect of a Reduction in GFR after Nephrectomy on Arterial Stiffness and Central Hemodynamics (EARNEST) study was a multicenter, prospective, controlled study designed to investigate the associations of an isolated reduction in kidney function on BP and arterial hemodynamics.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Prospective living kidney donors and healthy controls who fulfilled criteria for donation were recruited from centers with expertise in vascular research. Participants underwent office and ambulatory BP measurement, assessment of arterial stiffness, and biochemical tests at baseline and 12 months.

RESULTS

A total of 469 participants were recruited, and 306 (168 donors and 138 controls) were followed up at 12 months. In the donor group, mean eGFR was 27 ml/min per 1.73 m² lower than baseline at 12 months. Compared with baseline, at 12 months the mean within-group difference in ambulatory day systolic BP in donors was 0.1 mm Hg (95% confidence interval, -1.7 to 1.9) and 0.6 mm Hg (95% confidence interval, -0.7 to 2.0) in controls. The between-group difference was -0.5 mm Hg (95% confidence interval, -2.8 to 1.7; P=0.62). The mean within-group difference in pulse wave velocity in donors was 0.3 m/s (95% confidence interval, 0.1 to 0.4) and 0.2 m/s (95% confidence interval, -0.0 to 0.4) in controls. The between-group difference was 0.1 m/s (95% confidence interval, -0.2 to 0.3; P=0.49).

CONCLUSIONS

Changes in ambulatory peripheral BP and pulse wave velocity in kidney donors at 12 months after nephrectomy were small and not different from controls.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

NCT01769924 (https://clinicaltrials.gov/ct2/show/NCT01769924).

Anticoagulant strategies for the patient with chronic kidney disease

Chronic kidney disease (CKD) is a global health problem affecting up to 14% of the adult population in developed countries. On the basis of current guidelines, patients with CKD will often fulfil criteria for both short-term and long-term anticoagulation. Paradoxically, patients with CKD are not only at a higher risk of thrombosis, they are also at increased risk of bleeding. Furthermore, the pharmacokinetics and pharmacodynamics of many anticoagulant therapies are significantly affected by renal dysfunction. In addition, patients with advanced CKD are often systematically excluded from major clinical trials. As such, the decision on whether to anticoagulate or not, and if so with what agent, poses significant challenges. A solid understanding of the condition in question and the available treatments is required to make an informed judgement call. An in-depth appreciation of the advantages and disadvantages of the currently available anticoagulants is a key element in the decision-making process.

Incipient Albuminuria in Persons with Newly Diagnosed Type 2 Diabetes Mellitus: A 5-Year Retrospective Cohort Study

Introduction: This study aimed to determine the 5-year incidence of  albuminuria among Asian persons with newly diagnosed type 2 diabetes mellitus (DM), and to identify the risk factors at diagnosis for progression to albuminuria. Materials and Methods: A retrospective 5-year closed cohort study was conducted among 1016 persons aged ≥18 years old who were diagnosed with type 2 DM between 1 January 2007 and 31 December 2009 at primary care facilities in Singapore. The cumulative incidence of  progression from normoalbuminuria to albuminuria—termed “progression”—was determined. The risk factors associated with progression were evaluated using multiple logistic regression analysis. Results: A total of 541 (53.2%) participants were men. The mean (SD) onset age of type 2 DM was 54 (11) years. From diagnosis of type 2 DM, the 5-year cumulative incidence of  progression was 17.3% and mean (SD) duration to progression was 2.88 (1.23) years. Higher onset age (OR 1.02; 95% CI, 1.00-1.04), history of  hypertension (OR, 1.88; 95% CI, 1.32-2.70) and higher glycated haemoglobin (HbA1c) (OR, 1.17; 95% CI, 1.09-1.26) at diagnosis were associated with progression. In addition, being on angiotensin converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) treatment at baseline modified the effect of hypertension on progression. Conclusion: This study highlighted the importance of early screening and treatment of diabetes as well as prevention of hypertension, which could potentially delay the onset of  microalbuminuria in persons with type 2 DM. Persons on ACEI or ARB treatment should continue to be monitored regularly for progression to albuminuria. Key words: Incidence, New onset, Proteinuria, Risk factors

Arterial stiffness alone does not explain arteriovenous fistula outcomes

INTRODUCTION

Marked arterial adaptation is critical in permitting and sustaining the increased blood flow within an arteriovenous fistula (AVF). The aim of this investigation was to evaluate markers of arterial disease and their association with the early post-operative AVF outcomes.

METHODS

We included all patients in whom an AVF had been performed after enrolment to the Renal Impairment In Secondary Care (RIISC) study. Primary AVF failure (PFL) was defined as thrombosis at six-week review. All patients underwent BP Tru and Vicorder pulse wave analysis assessments and also had assays of advanced glycation end-products prior to AVF formation. These were correlated with the short-term AVF outcomes.

RESULTS

One hundred and eight AVFs were created in 86 patients. The primary patency (PPT) group were found to have significantly higher body mass index (BMI) (p = 0.01). Intraluminal vein diameter was significantly greater in the PPT group than the PFL group (p≤0.01). Mean augmentation index and augmentation index 75 was significantly higher in the PPT group than the PFL group (p = 0.03 and 0.03, respectively). Aortic pulse wave velocity was slower in the PPT group at 10.2 m/s than the PFL group at 10.8 m/s (p = 0.32). Advanced glycation end-product measurements did not vary significantly between the PPT and PFL groups (p = 0.4). Logistic regression analysis provided a predictive model, which demonstrated a predictive value of 78.1% for AVF patency at 6 weeks.

CONCLUSIONS

All patients in this end-stage renal disease cohort have significant aortic stiffness. The results for pulse wave velocity were slower in the PPT group suggesting a tendency towards stiffer vessels and PFL.

Apolipoprotein L1 and Chronic Kidney Disease Risk in Young Potential Living Kidney Donors

OBJECTIVE

The aim of this study was to develop a novel chronic kidney disease (CKD) risk prediction tool for young potential living kidney donors.

SUMMARY OF BACKGROUND DATA

Living kidney donor selection practices have evolved from examining individual risk factors to a risk calculator incorporating multiple characteristics. Owing to limited long-term data and lack of genetic information, current risk tools lack precision among young potential living kidney donors, particularly African Americans (AAs).

METHODS

We identified a cohort of young adults (18-30 years) with no absolute contraindication to kidney donation from the longitudinal cohort study Coronary Artery Risk Development in Young Adults. Risk associations for CKD (estimated glomerular filtration rate <60 mL/min/1.73 m) were identified and assigned weighted points to calculate risk scores.

RESULTS

A total of 3438 healthy adults were identified [mean age 24.8 years; 48.3% AA; median follow-up 24.9 years (interquartile range: 24.5-25.2)]. For 18-year olds, 25-year projected CKD risk varied by ethnicity and sex even without baseline clinical and genetic abnormalities; risk was 0.30% for European American (EA) women, 0.52% for EA men, 0.52% for AA women, 0.90% for AA men. Among 18-year-old AAs with apolipoprotein L1 gene (APOL1) renal-risk variants without baseline abnormalities, 25-year risk significantly increased: 1.46% for women and 2.53% for men; among those with 2 APOL1 renal-risk variants and baseline abnormalities, 25-year risk was higher: 2.53% to 6.23% for women and 4.35% to 10.58% for men.

CONCLUSIONS

Young AAs were at highest risk for CKD, and APOL1 renal-risk variants drove some of this risk. Understanding the genetic profile of young AA potential living kidney donors in the context of baseline health characteristics may help to inform candidate selection and counseling.

Modulation of stroke risk in chronic kidney disease

Stroke is the second most common cause of death and the leading cause of neurological disability worldwide, with huge economic costs and tragic human consequences. Both chronic kidney disease (CKD) and end-stage kidney disease are associated with a significantly increased risk of stroke. However, to date this has generated far less interest compared with the better-recognized links between cardiac and renal disease. Common risk factors for stroke, such as hypertension, hypercholesterolaemia, smoking and atrial fibrillation, are shared with the general population but are more prevalent in renal patients. In addition, factors unique to these patients, such as disorders of mineral and bone metabolism, anaemia and its treatments as well as the process of dialysis itself, are all also postulated to further increase the risk of stroke. In the general population, advances in medical therapies mean that effective primary and secondary prevention therapies are available for many patients. The development of specialist stroke clinics and acute stroke units has also improved outcomes after a stroke. Emerging therapies such as thrombolysis and thrombectomy are showing increasingly beneficial results. However, patients with CKD and on dialysis have different risk profiles that must be taken into account when considering the potential benefits and risks of these treatments. Unfortunately, these patients are either not recruited or formally excluded from major clinical trials. There is still much work to be done to harness effective stroke treatments with an acceptable safety profile for patients with CKD and those on dialysis.

Aggravated Cardiac Remodeling post Aortocaval Fistula in Unilateral Nephrectomized Rats

Background

Aortocaval fistula (AV) in rat is a unique model of volume-overload congestive heart failure and cardiac hypertrophy. Living donor kidney transplantation is regarded as beneficial to allograft recipients and not particularly detrimental to the donors. Impact of AV on animals with mild renal dysfunction is not fully understood. In this study, we explored the effects of AV in unilateral nephrectomized (UNX) rats.

Methods

Adult male Sprague-Dawley (SD) rats were divided into Sham (n = 10), UNX (right kidney remove, n = 10), AV (AV established between the levels of renal arteries and iliac bifurcation, n = 18) and UNX+AV (AV at one week after UNX, n = 22), respectively. Renal outcome was measured by glomerular filtration rate, effective renal plasma flow, fractional excretion of sodium, albuminuria, plasma creatinine, and cystatin C. Focal glomerulosclerosis (FGS) incidence was evaluated by renal histology. Cardiac function was measured by echocardiography and hemodynamic measurements.

Results

UNX alone induced compensatory left kidney enlargement, increased plasma creatinine and cystatin C levels, and slightly reduced glomerular filtration rate and increased FGS. AV induced significant cardiac enlargement and hypertrophy and reduced cardiac function and increased FGS, these changes were aggravated in UNX+AV rats.

Conclusions

Although UNX only induces minor renal dysfunction, additional chronic volume overload placement during the adaptation phase of the remaining kidney is associated with aggravated cardiac dysfunction and remodeling in UNX rats, suggesting special medical care is required for UNX or congenital monokidney subjects in case of chronic volume overload as in the case of pregnancy and hyperthyroidism to prevent further adverse cardiorenal events in these individuals.

Sex differences in risk factors for retinopathy in non-diabetic men and women: the Tromsø Eye Study

PURPOSE

  To determine the prevalence and risk factors for retinopathy in a nondiabetic population.

METHODS

  The study population included 5869 participants without diabetes aged 38-87 years from the Tromsø Eye Study, a substudy of the population-based Tromsø Study in Norway. Retinal images from both eyes were graded for retinopathy. We collected data on risk factors from self-report questionnaires, clinical examinations, laboratory measurements and case note reviews. The cross-sectional relationship between potential risk factors and retinopathy was assessed using logistic regression analysis.

RESULTS

  The overall prevalence of retinopathy was 14.8%. Men had a higher prevalence of retinopathy compared with women (15.9% versus 14.0%, p=0.04). In men, retinopathy was associated with hypertension (odds ratio [OR], 1.59; 95% confidence interval [CI], 1.24-2.04) and HbA1c (OR per %, 1.41; 95% CI, 1.01-1.96). In women, retinopathy was associated with age (OR per 10 years, 1.32; 95% CI, 1.14-1.52), log-transformed urinary albumin excretion (OR per log unit, 1.46; 95% CI, 1.14-1.87) and hypertension (OR, 1.36; 95% CI, 1.08-1.71). In women, retinopathy was associated with very low levels of urinary albumin excretion (urinary albumin/creatinine ratio >0.43 mg/mmol).

CONCLUSION

  This study confirms results from previous studies on the strong association between blood pressure and retinopathy. A novel finding is the sex differences in risk factors for retinopathy, suggesting a sex difference in the pathogenesis leading to retinopathy.

Effect of A Reduction in glomerular filtration rate after NEphrectomy on arterial STiffness and central hemodynamics: rationale and design of the EARNEST study

Background

There is strong evidence of an association between chronic kidney disease (CKD) and cardiovascular disease. To date, however, proof that a reduction in glomerular filtration rate (GFR) is a causative factor in cardiovascular disease is lacking. Kidney donors comprise a highly screened population without risk factors such as diabetes and inflammation, which invariably confound the association between CKD and cardiovascular disease. There is strong evidence that increased arterial stiffness and left ventricular hypertrophy and fibrosis, rather than atherosclerotic disease, mediate the adverse cardiovascular effects of CKD. The expanding practice of live kidney donation provides a unique opportunity to study the cardiovascular effects of an isolated reduction in GFR in a prospective fashion. At the same time, the proposed study will address ongoing safety concerns that persist because most longitudinal outcome studies have been undertaken at single centers and compared donor cohorts with an inappropriately selected control group.

Hypotheses

The reduction in GFR accompanying uninephrectomy causes (1) a pressure-independent increase in aortic stiffness (aortic pulse wave velocity) and (2) an increase in peripheral and central blood pressure.

Methods

This is a prospective, multicenter, longitudinal, parallel group study of 440 living kidney donors and 440 healthy controls. All controls will be eligible for living kidney donation using current UK transplant criteria. Investigations will be performed at baseline and repeated at 12 months in the first instance. These include measurement of arterial stiffness using applanation tonometry to determine pulse wave velocity and pulse wave analysis, office blood pressure, 24-hour ambulatory blood pressure monitoring, and a series of biomarkers for cardiovascular and bone mineral disease.

Conclusions

These data will prove valuable by characterizing the direction of causality between cardiovascular and renal disease. This should help inform whether targeting reduced GFR alongside more traditional cardiovascular risk factors is warranted. In addition, this study will contribute important safety data on living kidney donors by providing a longitudinal assessment of well-validated surrogate markers of cardiovascular disease, namely, blood pressure and arterial stiffness. If any adverse effects are detected, these may be potentially reversed with the early introduction of targeted therapy. This should ensure that kidney donors do not come to long-term harm and thereby preserve the ongoing expansion of the living donor transplant program (NCT01769924).