Role of the Microbiome in Gut-Heart-Kidney Cross Talk.

Homeostasis is a prerequisite for health. When homeostasis becomes disrupted, dysfunction occurs. This is especially the case for the gut microbiota, which under normal conditions lives in symbiosis with the host. As there are as many microbial cells in and on our body as human cells, it is unlikely they would not contribute to health or disease. The gut bacterial metabolism generates numerous beneficial metabolites but also uremic toxins and their precursors, which are transported into the circulation. Barrier function in the intestine, the heart, and the kidneys regulates metabolite transport and concentration and plays a role in inter-organ and inter-organism communication via small molecules. This communication is analyzed from the perspective of the remote sensing and signaling theory, which emphasizes the role of a large network of multispecific, oligospecific, and monospecific transporters and enzymes in regulating small-molecule homeostasis. The theory provides a systems biology framework for understanding organ cross talk and microbe-host communication involving metabolites, signaling molecules, nutrients, antioxidants, and uremic toxins. This remote small-molecule communication is critical for maintenance of homeostasis along the gut-heart-kidney axis and for responding to homeostatic perturbations. Chronic kidney disease is characterized by gut dysbiosis and accumulation of toxic metabolites. This slowly impacts the body, affecting the cardiovascular system and contributing to the progression of kidney dysfunction, which in its turn influences the gut microbiota. Preserving gut homeostasis and barrier functions or restoring gut dysbiosis and dysfunction could be a minimally invasive way to improve patient outcomes and quality of life in many diseases, including cardiovascular and kidney disease.

Arterial stiffness in patients with type 1 diabetes and its comparison to cardiovascular risk evaluation tools.

BACKGROUND: Arterial stiffness is a potential biomarker for cardiovascular disease (CVD) risk in patients with type 1 diabetes (T1D). However, its relation with other CV risk evaluation tools in T1D has not been elucidated yet. This study aimed to evaluate arterial stiffness in T1D patients free from known CVD, and compare it to other CV risk evaluation tools used in T1D. METHODS: Cross-sectional study in adults with a T1D duration of at least 10 years and without established CVD. Patients were categorized in CVD risk groups based on 2019 European Society of Cardiology (ESC) guidelines, and the STENO T1D risk engine was used to estimate 10-year risk for CV events. Arterial stiffness was evaluated with carotid-femoral pulse wave velocity (cf-PWV). Coronary artery calcium (CAC) score was assessed and carotid ultrasound was performed. Ambulatory 24-h blood pressure and central hemodynamic parameters were evaluated. Data on renal function and diabetic kidney disease was retrieved. RESULTS: 54 patients (age: 46 ± 9.5 years; T1D duration: 27 ± 8.8 years) were included. One-fourth of patients showed prematurely increased aortic stiffness based on cf-PWV (24%). Cf-PWV was significantly associated with CAC score, carotid intima-media thickness, central hemodynamic parameters and diabetic kidney disease. Based on STENO, 20 patients (37%) were at low, 20 patients (37%) at moderate, and 14 patients (26%) at high 10-year risk for CV event. Cf-PWV was strongly associated with the STENO score (rs = + 0.81; R2 = 0.566, p < 0.001), increasing with each higher STENO group (p < 0.01). However, cf-PWV was not significantly different between the two CV risk groups (high versus very high) based on ESC criteria, and ESC criteria compared to STENO classified 10 patients more as having > 10% 10-year risk for CV events (n = 44/54; 81.5% versus n = 34/54; 63%). CONCLUSIONS: This study demonstrated that a substantial proportion of long-standing T1D patients free from known CVD show premature arterial stiffening. Cf-PWV strongly associates with the STENO risk score for future CV events and with cardiovascular imaging and function outcomes, thereby illustrating the clinical importance of arterial stiffness. The data, however, also show considerable heterogeneity in CV risk and differences in risk categorisation between the STENO tool and ESC criteria.There is a need for refinement of CV risk classification in T1D, and future studies should investigate if evaluation of arterial stiffness should be implemented in T1D clinical practice and which patients benefit the most from its assessment.

Patients with Severe Lactic Acidosis in the Intensive Care Unit: A Retrospective Study of Contributing Factors and Impact of Renal Replacement Therapy.

INTRODUCTION: Hyperlactatemia is a regular condition in the intensive care unit, which is often associated with adverse outcomes. Control of the triggering condition is the most effective treatment of hyperlactatemia, but since this is mostly not readily possible, extracorporeal renal replacement therapy (RRT) is often tried as a last resort. The present study aims to evaluate the factors that may contribute to the decision whether to start RRT or not and the potential impact of the start of RRT on the outcome in patients with severe lactic acidosis (SLA) (lactate ≥5 mmol/L). MATERIALS AND METHODS: We conducted a retrospective single-center cohort analysis over a 3-year period including all patients with a lactate level ≥5 mmol/L. Patients were considered as treated with RRT because of SLA if RRT was started within 24 h after reaching a lactate level ≥5 mmol/L. RESULTS: Overall, 90-day mortality in patients with SLA was 34.5%. Of the 1,203 patients who matched inclusion/exclusion criteria, 11% (n = 133) were dialyzed within 24 h. The propensity to receive RRT was related to the lactate level and to the SOFA renal and cardio score. The most frequently used modality was continuous RRT. Patients who were started on RRT versus those who did not have 2.3 higher odds of mortality, even after adjustment for the propensity to start RRT. CONCLUSIONS: Our analysis confirms the high mortality rate of patients with SLA. It adds that odds for mortality is even higher in patients who were started on RRT versus not. We suggest keeping an open mind to the factors that may influence the decision to start dialysis and bear in mind that without being a bridge to correction of the underlying condition, dialysis is unlikely to affect the outcome.

Free p-cresyl sulfate shows the highest association with cardiovascular outcome in chronic kidney disease.

BACKGROUND: Several protein-bound uraemic toxins (PBUTs) have been associated with cardiovascular (CV) and all-cause mortality in chronic kidney disease (CKD) but the degree to which this is the case per individual PBUT and the pathophysiological mechanism have only partially been unraveled. METHODS: We compared the prognostic value of both total and free concentrations of five PBUTs [p-cresyl sulfate (pCS), p-cresyl glucuronide, indoxyl sulfate, indole acetic acid and hippuric acid] in a cohort of 523 patients with non-dialysis CKD Stages G1-G5. Patients were followed prospectively for the occurrence of a fatal or non-fatal CV event as the primary endpoint and a number of other major complications as secondary endpoints. In addition, association with and the prognostic value of nine markers of endothelial activation/damage was compared. RESULTS: After a median follow-up of 5.5 years, 149 patients developed the primary endpoint. In multivariate Cox regression models adjusted for age, sex, systolic blood pressure, diabetes mellitus and estimated glomerular filtration rate, and corrected for multiple testing, only free pCS was associated with the primary endpoint {hazard ratio [HR]1.39 [95% confidence interval (CI) 1.14-1.71]; P = 0.0014}. Free pCS also correlated with a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (r = -0.114, P < 0.05), angiopoietin-2 (ANGPT2) (r = 0.194, P < 0.001), matrix metallopeptidase 7 (MMP-7; (r = 0.238, P < 0.001) and syndecan 1 (r = 0.235, P < 0.001). Of these markers of endothelial activation/damage, ANGPT2 [HR 1.46 (95% CI 1.25-1.70); P < 0.0001] and MMP-7 [HR 1.31 (95% CI 1.08-1.59); P = 0.0056] were also predictive of the primary outcome. CONCLUSIONS: Among PBUTs, free pCS shows the highest association with CV outcome in non-dialysed patients with CKD. Two markers of endothelial activation/damage that were significantly correlated with free pCS, ANGPT2 and MMP-7 were also associated with CV outcome. The hypothesis that free pCS exerts its CV toxic effects by an adverse effect on endothelial function deserves further exploration.

The urinary proteomics classifier chronic kidney disease 273 predicts cardiovascular outcome in patients with chronic kidney disease.

BACKGROUND: The urinary proteomic classifier chronic kidney disease 273 (CKD273) is predictive for the development and progression of chronic kidney disease (CKD) and/or albuminuria in type 2 diabetes. This study evaluates its role in the prediction of cardiovascular (CV) events in patients with CKD Stages G1-G5. METHODS: We applied the CKD273 classifier in a cohort of 451 patients with CKD Stages G1-G5 followed prospectively for a median of 5.5 years. Primary endpoints were all-cause mortality, CV mortality and the composite of non-fatal and fatal CV events (CVEs). RESULTS: In multivariate Cox regression models adjusting for age, sex, prevalent diabetes and CV history, the CKD273 classifier at baseline was significantly associated with total mortality and time to fatal or non-fatal CVE, but not CV mortality. Because of a significant interaction between CKD273 and CV history (P = 0.018) and CKD stages (P = 0.002), a stratified analysis was performed. In the fully adjusted models, CKD273 classifier was a strong and independent predictor of fatal or non-fatal CVE only in the subgroup of patients with CKD Stages G1-G3b and without a history of CV disease. In those patients, the highest tertile of CKD273 was associated with a >10-fold increased risk as compared with the lowest tertile. CONCLUSIONS: The urinary CKD273 classifier provides additional independent information regarding the CV risk in patients with early CKD stage and a blank CV history. Determination of CKD273 scores on a random urine sample may improve the efficacy of intensified surveillance and preventive strategies by selecting patients who potentially will benefit most from early risk management.

Multicenter Randomized Controlled Trial of Vitamin K Antagonist Replacement by Rivaroxaban with or without Vitamin K2 in Hemodialysis Patients with Atrial Fibrillation: the Valkyrie Study.

BACKGROUND: Vitamin K antagonists (VKAs), although commonly used to reduce thromboembolic risk in atrial fibrillation, have been incriminated as probable cause of accelerated vascular calcification (VC) in patients on hemodialysis. Functional vitamin K deficiency may further contribute to their susceptibility for VC. We investigated the effect of vitamin K status on VC progression in 132 patients on hemodialysis with atrial fibrillation treated with VKAs or qualifying for anticoagulation. METHODS: Patients were randomized to VKAs with target INR 2-3, rivaroxaban 10 mg daily, or rivaroxaban 10 mg daily plus vitamin K2 2000 µg thrice weekly during 18 months. Systemic dp-ucMGP levels were quantified to assess vascular vitamin K status. Cardiac and thoracic aorta calcium scores and pulse wave velocity were measured to evaluate VC progression. RESULTS: Baseline dp-ucMGP was severely elevated in all groups. Initiation or continuation of VKAs further increased dp-ucMGP, whereas levels decreased in the rivaroxaban group and to a larger extent in the rivaroxaban+vitamin K2 group, but remained nevertheless elevated. Changes in coronary artery, thoracic aorta, and cardiac valve calcium scores and pulse wave velocity were not significantly different among the treatment arms. All cause death, stroke, and cardiovascular event rates were similar between the groups. Bleeding outcomes were not significantly different, except for a lower number of life-threatening and major bleeding episodes in the rivaroxaban arms versus the VKA arm. CONCLUSIONS: Withdrawal of VKAs and high-dose vitamin K2 improve vitamin K status in patients on hemodialysis, but have no significant favorable effect on VC progression. Severe bleeding complications may be lower with rivaroxaban than with VKAs.

Syndecan-1 and Free Indoxyl Sulfate Levels Are Associated with miR-126 in Chronic Kidney Disease.

Chronic kidney disease (CKD) is a major cause of death worldwide and is associated with a high risk for cardiovascular and all-cause mortality. In CKD, endothelial dysfunction occurs and uremic toxins accumulate in the blood. miR-126 is a regulator of endothelial dysfunction and its blood level is decreased in CKD patients. In order to obtain a better understanding of the physiopathology of the disease, we correlated the levels of miR-126 with several markers of endothelial dysfunction, as well as the representative uremic toxins, in a large cohort of CKD patients at all stages of the disease. Using a univariate analysis, we found a correlation between eGFR and most markers of endothelial dysfunction markers evaluated in this study. An association of miR-126 with all the evaluated uremic toxins was also found, while uremic toxins were not associated with the internal control, specifically cel-miR-39. The correlation between the expression of endothelial dysfunction biomarker Syndecan-1, free indoxyl sulfate, and total p-cresyl glucuronide on one side, and miR-126 on the other side was confirmed using multivariate analysis. As CKD is associated with reduced endothelial glycocalyx (eGC), our results justify further evaluation of the role of correlated parameters in the pathophysiology of CKD.

Gut microbiota generation of protein-bound uremic toxins and related metabolites is not altered at different stages of chronic kidney disease.

Chronic kidney disease (CKD) is characterized by accumulation of protein-bound uremic toxins such as p-cresyl sulfate, p-cresyl glucuronide, indoxyl sulfate and indole-3-acetic acid, which originate in the gut. Intestinal bacteria metabolize aromatic amino acids into p-cresol and indole, (further conjugated in the colon mucosa and liver) and indole-3-acetic acid. Here we measured fecal, plasma and urine metabolite concentrations; the contribution of gut bacterial generation to plasma protein-bound uremic toxins accumulation; and influx into the gut of circulating protein-bound uremic toxins at different stages of CKD. Feces, blood and urine were collected from 14 control individuals and 141 patients with CKD. Solutes were quantified by ultra-high performance liquid chromatography. To assess the rate of bacterial generation of p-cresol, indole and indole-3-acetic acid, fecal samples were cultured ex vivo. With CKD progression, an increase in protein-bound uremic toxins levels was observed in plasma, whereas the levels of these toxins and their precursors remained the same in feces and urine. Anaerobic culture of fecal samples showed no difference in ex vivo p-cresol, indole and indole-3-acetic acid generation. Therefore, differences in plasma protein-bound uremic toxins levels between different CKD stages cannot be explained by differences in bacterial generation rates in the gut, suggesting retention due to impaired kidney function as the main contributor to their increased plasma levels. Thus, as fractional clearance decreased with the progression of CKD, tubular clearance appeared to be more affected than the glomerular filtration rate, and there was no net increase in protein-bound uremic toxins influx into the gut lumen with increased plasma levels.

Evaluation of vitamin K status and rationale for vitamin K supplementation in dialysis patients.

The cardinal biological role of vitamin K is to act as cofactor for the carboxylation of a number of vitamin K-dependent proteins, some of which are essential for coagulation, bone formation and prevention of vascular calcification. Functional vitamin K deficiency is common and severe among dialysis patients and has garnered attention as a modifiable risk factor in this population. However, no single biochemical parameter can adequately assess vitamin K status. For each biological function of vitamin K, the degree of carboxylation of the relevant vitamin K-dependent protein most accurately reflects vitamin K status. Dephosphorylated uncarboxylated matrix Gla protein (dp-ucMGP) is the best biomarker for vascular vitamin K status when cardiovascular endpoints are studied. Dp-ucMGP levels are severely elevated in haemodialysis patients and correlate with markers of vascular calcification and mortality in some but not all studies. The aetiology of vitamin K deficiency in haemodialysis is multifactorial, including deficient intake, uraemic inhibition of the vitamin K cycle and possibly interference of vitamin K absorption by phosphate binders. The optimal vitamin K species, dose and duration of supplementation to correct vitamin K status in dialysis patients are unknown. Dp-ucMGP levels dose-proportionally decrease with supraphysiological vitamin K2 supplementation, but do not normalize even with the highest doses. In the general population, long-term vitamin K1 or K2 supplementation has beneficial effects on cardiovascular disease, bone density and fracture risk, and insulin resistance, although some studies reported negative results. In haemodialysis patients, several trials on the effects of vitamin K on surrogate markers of vascular calcification are currently ongoing.

Different rates of progression and mortality in patients with chronic kidney disease at outpatient nephrology clinics across Europe.

The incidence of renal replacement therapy varies across countries. However, little is known about the epidemiology of chronic kidney disease (CKD) outcomes. Here we describe progression and mortality risk of patients with CKD but not on renal replacement therapy at outpatient nephrology clinics across Europe using individual data from nine CKD cohorts participating in the European CKD Burden Consortium. A joint model assessed the mean change in estimated glomerular filtration rate (eGFR) and mortality risk simultaneously, thereby accounting for mortality risk when estimating eGFR decline and vice versa, while also correcting for the measurement error in eGFR. Results were adjusted for important risk factors (baseline eGFR, age, sex, albuminuria, primary renal disease, diabetes, hypertension, obesity and smoking) in 27,771 patients from five countries. The adjusted mean annual eGFR decline varied from 0.77 (95% confidence interval 0.45, 1.08) ml/min/1.73m2 in the Belgium cohort to 2.43 (2.11, 2.75) ml/min/1.73m2 in the Spanish cohort. As compared to the Italian PIRP cohort, the adjusted mortality hazard ratio varied from 0.22 (0.11, 0.43) in the London LACKABO cohort to 1.30 (1.13, 1.49) in the English CRISIS cohort. These results suggest that the eGFR decline showed minor variation but mortality showed the most variation. Thus, different health care organization systems are potentially associated with differences in outcome of patients with CKD within Europe. These results can be used by policy makers to plan resources on a regional, national and European level.

Hereditary polycystic kidney disease is characterized by lymphopenia across all stages of kidney dysfunction: an observational study.

Background: Polycystic kidney disease (PKD) is characterized by urinary tract infections and extrarenal abnormalities such as an increased risk of cancer. As mutations in polycystin-1 and -2 are associated with decreased proliferation of immortalized lymphoblastoid cells in PKD, we investigated whether lymphopenia could be an unrecognized trait of PKD. Methods: We studied 700 kidney transplant recipients with (n = 126) or without PKD at the time of kidney transplantation between 1 January 2003 and 31 December 2014 at Ghent University Hospital. We also studied 204 patients with chronic kidney disease (CKD) with PKD and 204 matched CKD patients without PKD across comparable CKD strata with assessment between 1 January 1999 and 1 February 2016 at three renal outpatient clinics. We compared lymphocyte counts with multiple linear regression analysis to adjust for potential confounders. We analysed flow cytometric immunophenotyping data and other haematological parameters. Results: Lymphocyte counts were 264/µL [95% confidence interval (CI) 144-384] and 345/µL (95% CI 245-445) (both P < 0.001) lower in the end-stage kidney disease (ESKD) and CKD cohort, respectively, after adjustment for age, sex, ln(C-reactive protein) and estimated glomerular filtration rate (in the CKD cohort only). In particular, CD8+ T and B lymphocytes were significantly lower in transplant recipients with versus without PKD (P < 0.001 for both). Thrombocyte and monocyte counts were lower in patients with versus without PKD in both cohorts (P < 0.001 for all analyses except P = 0.01 for monocytes in the ESKD cohort). Conclusion: PKD is characterized by distinct cytopenias and especially lymphopenia, independent of kidney function. This finding has the potential to alter our therapeutic approach to patients with PKD.

Former smoking and early and long-term graft outcome in renal transplant recipients: a retrospective cohort study.

Smoking is associated with unfavourable outcome in solid-organ transplant recipients. Nicotine may predispose to kidney injury by increasing oxidative stress. We hypothesized that former smoking negatively affects graft outcome in kidney transplant recipients and especially those with delayed graft function (DGF). We included adult recipients of a kidney transplant between 1 January 2003 and 1 October 2015 at Ghent University Hospital and recorded outcomes until 31 October 2015. We used Kaplan-Meier and multivariable Cox proportional hazard analysis to examine the relationship between former smoking at the time of transplantation and the incidence of 10-year graft loss with and without censoring for death in 1013 participants. We evaluated mean differences in eGFR over time by a random intercept and slope model, considering a linear time effect. After adjusting for potential confounders, a history of smoking was associated with an increased hazard of graft loss (adjusted hazard ratio (aHR) 1.60; 95% CI: 1.17-2.17; P = 0.003) and death-censored graft loss (aHR 2.29; 95% CI: 1.41-3.72; P = 0.001). The linear time trend of eGFR was different between former and never smokers (P = 0.001). To conclude, former smoking exerts long-lasting negative effects on graft outcome and this independent of DGF.

Bisphosphonates for preventing bone disease in kidney transplant recipients: a meta-analysis of randomized controlled trials.

An estimated 60% of kidney transplant recipients have mineral bone disease and about 0.5% break their hip within the first year after transplantation. We conducted a systematic review of benefits and harms of bisphosphonates in kidney transplant recipients. We searched CENTRAL (Issue 5, 2015) for randomized controlled trials in all languages and screened the reference list of an earlier Cochrane review. One reviewer identified the trials, extracted all data, and assessed risk of bias. Meta-analysis used a random effects model, with results expressed as risk ratios (RR) or mean differences (MD) with 95% confidence intervals (CI). Bisphosphonates have uncertain effects on death (RR 0.45, CI 0.04-4.69) and vertebral fractures (RR 0.58, CI 0.24-1.43, I(2) 0%). Bisphosphonates moderately to importantly reduce the loss of vertebral bone mineral density (MD 5.98%, CI 3.77-8.18% change from baseline in g calcium/cm² at 12 months, I(2) 91%) and femoral bone mineral density (MD 5.57%, 3.12-8.01% change from baseline in g calcium/cm² at 12 months, I(2) 69%). At this stage, insufficient evidence exists to support routine use of bisphosphonates to reduce fracture risk after kidney transplantation. Data on important health outcomes are lacking, surrogate outcomes poorly reflect bone quality in kidney transplant recipients, and serious adverse events are not studied and reported systematically.

Pro-inflammatory cytokines and leukocyte oxidative burst in chronic kidney disease: culprits or innocent bystanders?

BACKGROUND: Pro-inflammatory cytokines are elevated in chronic kidney disease (CKD), a condition characterized by microinflammation with oxidative stress as key feature. However, their role in the inflammatory response at uraemic concentrations has not yet been defined. In this study, the contribution of cytokines on induction of leukocyte oxidative stress was investigated. METHODS: Whole blood from healthy donors was incubated with 20-1400 pg/mL TNFα, 5-102.8 pg/mL IL-6, 20-400 pg/mL IL-1ß and 75-1200 pg/mL IL-18 separately or in combination. Oxidative burst was measured, at baseline and after stimulation with fMLP (Phagoburst™). The effect of the TNFα blocker, adalimumab (Ada), was evaluated on TNFα-induced ROS production. Finally, the association between TNFα and the composite end point all-cause mortality or first cardiovascular event was analysed in a CKD population stage 4-5 (n = 121). RESULTS: While interleukin (IL)-6, IL-1ß and IL-18 alone induced no ROS activation of normal leukocytes, irrespective of concentrations, TNFα induced ROS activation at baseline (P < 0.01) and after fMLP stimulation (P < 0.05), but only at uraemic concentrations in the high range (400 and 1400 pg/mL). A similar pattern was observed with all cytokines in combination, but already at intermediate uraemic concentrations (all P < 0.05, except for monocytes after fMLP stimulation: n.s.), suggesting synergism between cytokines. ROS production induced by TNFα (400 pg/mL) and the cytokine combination was blocked with Ada. Uraemia-related oxidative stress in leukocytes of haemodialysis patients was however not blocked by Ada. In patients, TNFα was not associated to adverse events (HR: 1.52, 95% CI 0.81-2.85, P = 0.13). CONCLUSION: Among several pro-inflammatory cytokines, TNFα alone was pro-oxidative but only at high-range uraemic concentrations. Adding a TNFα blocker, Ada, blocked this ROS production, but not the oxidative stress in blood samples from haemodialysis patients, suggesting that other uraemic toxins than TNFα are more crucial in this process. However, the lack of association between TNFα and mortality suggests that the role of TNFα-linked oxidative stress is limited.

A European Renal Best Practice (ERBP) position statement on the Kidney Disease: Improving Global Outcomes (KDIGO) clinical practice guideline for the management of blood pressure in non-dialysis-dependent chronic kidney disease: an endorsement with some caveats for real-life application.

Developing guidelines on a subject as broad as hypertension is difficult, especially when the guidance relates to hypertension in the chronic kidney disease (CKD) population. The Kidney Disease: Improving Global Outcomes Guideline Development Group has applied a rigorous methodology in reviewing all available evidence, and their recommendations are consistent with the evidence-based approach. As a result, the European Renal Best Practice endorses most of its recommendations. However, the Work Group feels that some additional advice could help clinicians in daily practice: (i) individualization of treatment should be taken into account, especially (cardiovascular) co-morbidities, age, gender and race; (ii) side-effects, such as postural dizziness should be monitored closely, particularly in elderly, diabetics and patients with arterial stiffness; (iii) the importance of salt restriction should not be neglected; (iv) although angiotensin-converting enzyme inhibitors (ACE-Is) and angiotensin receptor blocker (ARBs) remain a cornerstone in the management of hypertension, and especially cardiovascular protection, in some particular situations such as in advanced CKD and in patients without proteinuria, their role is less well defined; (v) as most CKD patients need more than one antihypertensive drug to achieve blood pressure control, the specific (renal) (dis)advantages of other classes than ACE-I or ARB should be taken into account.

Predictive value of protein-bound uremic toxins for heart failure in patients with chronic kidney disease.

AIMS: This retrospective cohort study aimed to be the first to evaluate the association between plasma protein-bound uremic toxins (PBUTs) concentrations, echocardiographic parameters of heart failure (HF), and incident HF events in patients with chronic kidney disease (CKD) not on dialysis. METHODS AND RESULTS: Retrospective, single-centre, cohort study at the Ghent University Hospital, Belgium. Adults with CKD stages G1-G5, not on dialysis, could be included. Exclusion criteria were ongoing pregnancy, age <18 years, active acute infection, active malignancy, history of transplantation, or a cardiovascular event within 3 months prior to inclusion. Free and total concentrations of five PBUTs were quantified at baseline: indoxyl sulfate (IxS), p-cresyl sulfate (pCS), p-cresyl glucuronide (pCG), indole-3 acetic acid (IAA), and hippuric acid (HA). Patients were grouped into three echocardiographic categories: normal left ventricular ejection fraction (LVEF) and normal left ventricular end-diastolic pressure (LVEDP), normal LVEF and increased LVEDP, and reduced LVEF, based on available echocardiographic data in a time interval of ±6 months around the plasma sample collection. A total of 523 patients were included between January 2011 and January 2014. Echocardiographic data within the predefined timeframe were available for 210 patients (40% of patients). Levels of pCG and pCS were significantly higher in patients with reduced (<50%) versus normal LVEF (P < 0.05). After a median follow-up 5.5 years, 43 (8.4%) patients reached the composite endpoint of hospitalization or mortality due to HF. Free fractions of IxS, pCS, and pCG showed the strongest association with clinical outcome: free IxS: HR 1.71 (95% CI 1.11-2.63; P = 0.015), free pCS: HR 1.82 (95% CI 1.11-3.01; P = 0.019), and free pCG: HR 1.67 (95% CI 1.08-2.58; P = 0.020), and these results were independent of age, gender, body mass index, diabetes, and systolic blood pressure. In models that were also adjusted for serum creatinine, the free fractions of these PBUTs remained significant. CONCLUSIONS: Elevated free concentrations of IxS, pCG, and pCS were independently associated with an increased risk of HF events in non-dialysed CKD patients. Further research is necessary to confirm these findings and investigate the potential impact of PBUT-lowering interventions on HF events in this patient group.

Investigation of the human-gut-kidney axis by fecal proteomics, highlights molecular mechanisms affected in CKD.

Objective: The interplay of gut microbiota with the kidney system in chronic kidney disease (CKD), is characterized by increased concentrations of uric acid in the gut, which in turn, may increase bacterial uricase activity and may lead to the generation of uremic toxins. Nevertheless, knowledge on these underlying bidirectional molecular mechanisms is still limited. Methods: In this exploratory study, proteomic analysis was performed on fecal samples, targeting to investigate this largely unexplored biological material as a source of information reflecting the gut-kidney axis. Specifically, fecal suspension samples from patients with CKD1 (n = 12) and CKD4 (n = 17) were analysed by LC-MS/MS, using both the Human and Bacterial UniProt RefSeq reviewed databases. Results: This fecal proteomic analysis collectively identified 701 human and 1011 bacterial proteins of high confidence. Differential expression analysis (CKD4/CKD1) revealed significant changes in human proteins (n = 8, including proteins such as galectin-3-binding protein and prolactin-inducible protein), that were found to be associated with inflammation and CKD. The differential protein expression of pancreatic alpha-amylase further suggested plausible reduced saccharolytic fermentation in CKD4/CKD1. Significant changes in bacterial proteins (n = 9, such as glyceraldehyde-3-phosphate dehydrogenase and enolase), participating in various carbohydrate and metabolic pathways important for the synthesis of butyrate, in turn suggested differential butyrate synthesis in CKD4/CKD1. Further, targeted quantification of fecal pancreatic alpha-amylase and butyrate in the same fecal suspension samples, supported these hypotheses. Conclusion: Collectively, this exploratory fecal proteomic analysis highlighted changes in human and bacterial proteins reflecting inflammation and reduced saccharolytic fermentation in CKD4/CKD1, plausibly affecting the butyrate synthesis pathways in advanced stage kidney disease. Integrative multi-omics validation is planned.

Machine Learning-Based Urine Peptidome Analysis to Predict and Understand Mechanisms of Progression to Kidney Failure.

Introduction: The identification of patients with chronic kidney disease (CKD) at risk of progressing to kidney failure (KF) is important for clinical decision-making. In this study we assesed whether urinary peptidome (UP) analysis may help classify patients with CKD and improve KF risk prediction. Methods: The UP was analyzed using capillary electrophoresis coupled to mass spectrometry in a case-cohort sample of 1000 patients with CKD stage G3 to G5 from the French CKD-Renal Epidemiology and Information Network (REIN) cohort. We used unsupervised and supervised machine learning to classify patients into homogenous UP clusters and to predict 3-year KF risk with UP, respectively. The predictive performance of UP was compared with the KF risk equation (KFRE), and evaluated in an external cohort of 326 patients. Results: More than 1000 peptides classified patients into 3 clusters with different CKD severities and etiologies at baseline. Peptides with the highest discriminative power for clustering were fragments of proteins involved in inflammation and fibrosis, highlighting those derived from α-1-antitrypsin, a major acute phase protein with anti-inflammatory and antiapoptotic properties, as the most significant. We then identified a set of 90 urinary peptides that predicted KF with a c-index of 0.83 (95% confidence interval [CI]: 0.81-0.85) in the case-cohort and 0.89 (0.83-0.94) in the external cohort, which were close to that estimated with the KFRE (0.85 [0.83-0.87]). Combination of UP with KFRE variables did not further improve prediction. Conclusion: This study shows the potential of UP analysis to uncover new pathophysiological CKD progression pathways and to predict KF risk with a performance equal to that of the KFRE.

Contribution of Hypoalbuminemia and Anemia to the Prognostic Value of Plasma p-Cresyl Sulfate and p-Cresyl Glucuronide for Cardiovascular Outcome in Chronic Kidney Disease.

Free plasma concentrations of protein-bound uremic toxins (PBUTs) may be influenced by serum albumin and hemoglobin. The potential association of serum albumin and hemoglobin with free levels of p-cresyl sulfate (pCS) and p-cresyl glucuronide (pCG) and their predictive value for cardiovascular morbidity and mortality were explored. A total of 523 non-dialysis chronic kidney disease (CKD) stages G1-G5 patients were prospectively followed for the occurrence of fatal or non-fatal cardiovascular events over a 5.5-year period. A negative correlation was found between albumin and between hemoglobin, and both total and free pCS and pCG. In multiple linear regression, PBUTs were negatively associated with eGFR (estimated glomerular filtration rate) and hemoglobin but not albumin. In multivariate Cox regression analysis, albumin was a predictor of outcome, independent of pCS and pCG, without interactions between albumin and pCS or pCG. The relation of low hemoglobin with adverse outcome was lost when albumin was entered into the model. Lower concentrations of pCS and pCG are associated with higher serum albumin and hemoglobin. This may indicate that there are two pathways in the blood that potentially contribute to attenuating the vasculotoxic effects of these PBUTs. The association of PBUTs with cardiovascular risk is not explained by albumin levels, which remains a strong and independent predictor for adverse outcome.

The relation between hypomagnesaemia and vascular stiffness in renal transplant recipients.

BACKGROUND: Arterial stiffness is a strong predictor of outcome. Hypomagnesaemia, by its association with arterial hypertension, endothelial dysfunction, dyslipidaemia and inflammation, might affect vascular stiffness. As hypomagnesaemia is common in renal transplant recipients (RTR), we examined its potential association with arterial stiffness. METHODS: Cross-sectional analysis. Evaluation of vascular stiffness in 512 RTR from two university centres at a median of 72 months post-transplantation. Determination of carotid-femoral pulse wave velocity (PWV) (SphygmoCor). A multiple linear regression analysis was used to investigate the independent relationship between magnesium serum level and PWV with the following covariates: age, diabetes, smoking status, body mass index, blood pressure, heart rate (HR), C-reactive protein (CRP), high-density lipoprotein cholesterol, parathyroid hormone and use of angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, diuretics, calcium channel blockers, statins and calcineurin inhibitors next to their drug levels. RESULTS: Lower serum magnesium was independently associated with PWV (P = 0.018) in addition to age, CRP, HR, diabetes and mean arterial pressure (model R(2) = 0.45; P < 0.001). The relationship between magnesium and PWV was attenuated (P = 0.054) after adjustment for the use of sirolimus, which was associated with higher magnesium levels (P<0.001) and lower PWV (P = 0.013). In patients >55 years (median age), however (low), magnesium remained an independent predictor of PWV (P = 0.024) after accounting for the same covariates. CONCLUSIONS: Serum magnesium is an independent predictor of arterial stiffness in RTR, especially in patients >55 years.