Soluble Klotho, a Potential Biomarker of Chronic Kidney Disease-Mineral Bone Disorders Involved in Healthy Ageing: Lights and Shadows.

Shortly after the discovery of Klotho, interest grew in its potential role in chronic kidney disease (CKD). There are three isoforms of the Klotho protein: αKlotho, ßKlotho and γKlotho. This review will focus on αKlotho due to its relevance as a biomarker in CKD. αKlotho is synthesized mainly in the kidneys, but it can be released into the bloodstream and urine as soluble Klotho (sKlotho), which undertakes systemic actions, independently or in combination with FGF23. It is usually accepted that sKlotho levels are reduced early in CKD and that lower levels of sKlotho might be associated with the main chronic kidney disease-mineral bone disorders (CKD-MBDs): cardiovascular and bone disease. However, as results are inconsistent, the applicability of sKlotho as a CKD-MBD biomarker is still a matter of controversy. Much of the inconsistency can be explained due to low sample numbers, the low quality of clinical studies, the lack of standardized assays to assess sKlotho and a lack of consensus on sample processing, especially in urine. In recent decades, because of our longer life expectancies, the prevalence of accelerated-ageing diseases, such as CKD, has increased. Exercise, social interaction and caloric restriction are considered key factors for healthy ageing. While exercise and social interaction seem to be related to higher serum sKlotho levels, it is not clear whether serum sKlotho might be influenced by caloric restriction. This review focuses on the possible role of sKlotho as a biomarker in CKD-MBD, highlighting the difference between solid knowledge and areas requiring further research, including the role of sKlotho in healthy ageing.

Phosphorus May Induce Phenotypic Transdifferentiation of Vascular Smooth Muscle Cells through the Reduction of microRNA-145.

Phosphorus is a vital element for life found in most foods as a natural component, but it is also one of the most used preservatives added during food processing. High serum phosphorus contributes to develop vascular calcification in chronic kidney disease; however, it is not clear its effect in a population without kidney damage. The objective of this in vivo and in vitro study was to investigate the effect of high phosphorus exposure on the aortic and serum levels of miR-145 and its effect on vascular smooth muscle cell (VSMCs) changes towards less contractile phenotypes. The study was performed in aortas and serum from rats fed standard and high-phosphorus diets, and in VSMCs exposed to different concentrations of phosphorus. In addition, miR-145 silencing and overexpression experiments were carried out. In vivo results showed that in rats with normal renal function fed a high P diet, a significant increase in serum phosphorus was observed which was associated to a significant decrease in the aortic α-actin expression which paralleled the decrease in aortic and serum miR-145 levels, with no changes in the osteogenic markers. In vitro results using VSMCs corroborated the in vivo findings. High phosphorus first reduced miR-145, and afterwards α-actin expression. The miR-145 overexpression significantly increased α-actin expression and partially prevented the increase in calcium content. These results suggest that miR-145 could be an early biomarker of vascular calcification, which could give information about the initiation of the transdifferentiation process in VSMCs.

Experimental Models to Study Diabetes Mellitus and Its Complications: Limitations and New Opportunities.

Preclinical biomedical models are a fundamental tool to improve the knowledge and management of diseases, particularly in diabetes mellitus (DM) since, currently, the pathophysiological and molecular mechanisms involved in its development are not fully clarified, and there is no treatment to cure DM. This review will focus on the features, advantages and limitations of some of the most used DM models in rats, such as the spontaneous models: Bio-Breeding Diabetes-Prone (BB-DP) and LEW.1AR1-iddm, as representative models of type 1 DM (DM-1); the Zucker diabetic fatty (ZDF) and Goto-kakizaki (GK) rats, as representative models of type 2 DM (DM-2); and other models induced by surgical, dietary and pharmacological-alloxan and streptozotocin-procedures. Given the variety of DM models in rats, as well as the non-uniformity in the protocols and the absence of all the manifestation of the long-term multifactorial complications of DM in humans, the researchers must choose the one that best suits the final objectives of the study. These circumstances, added to the fact that most of the experimental research in the literature is focused on the study of the early phase of DM, makes it necessary to develop long-term studies closer to DM in humans. In this review, a recently published rat DM model induced by streptozotocin injection with chronic exogenous administration of insulin to reduce hyperglycaemia has also been included in an attempt to mimic the chronic phase of DM in humans.

Mineral and bone metabolism markers and mortality in diabetic patients on haemodialysis.

BACKGROUND: Diabetic patients on haemodialysis have a higher risk of mortality than non-diabetic patients. The aim of this COSMOS (Current management of secondary hyperparathyroidism: a multicentre observational study) analysis was to assess whether bone and mineral laboratory values [calcium, phosphorus and parathyroid hormone (PTH)] contribute to this risk. METHODS: COSMOS is a multicentre, open-cohort, 3-year prospective study, which includes 6797 patients from 227 randomly selected dialysis centres in 20 European countries. The association between mortality and calcium, phosphate or PTH was assessed using Cox proportional hazard regression models using both penalized splines smoothing and categorization according to KDIGO guidelines. The effect modification of the association between the relative risk of mortality and serum calcium, phosphate or PTH by diabetes was assessed. RESULTS: There was a statistically significant effect modification of the association between the relative risk of mortality and serum PTH by diabetes (P = .011). The slope of the curve of the association between increasing values of PTH and relative risk of mortality was steeper for diabetic compared with non-diabetic patients, mainly for high levels of PTH. In addition, high serum PTH (>9 times the normal values) was significantly associated with a higher relative risk of mortality in diabetic patients but not in non-diabetic patients [1.53 (95% confidence interval 1.07-2.19) and 1.17 (95% confidence interval 0.91-1.52)]. No significant effect modification of the association between the relative risk of mortality and serum calcium or phosphate by diabetes was found (P = .2 and P = .059, respectively). CONCLUSION: The results show a different association of PTH with the relative risk of mortality in diabetic and non-diabetic patients. These findings could have relevant implications for the diagnosis and treatment of chronic kidney disease-mineral and bone disorders.

Effects of a Losartan-Antioxidant Hybrid (GGN1231) on Vascular and Cardiac Health in an Experimental Model of Chronic Renal Failure.

Drugs providing antihypertensive and protective cardiovascular actions are of clinical interest in controlling cardiovascular events and slowing the progression of kidney disease. We studied the effect of a hybrid compound, GGN1231 (derived from losartan in which a powerful antioxidant was attached), on the prevention of cardiovascular damage, cardiac hypertrophy, and fibrosis in a rat model of severe chronic renal failure (CRF). CRF by a 7/8 nephrectomy was carried out in male Wistar rats fed with a diet rich in phosphorous (0.9%) and normal calcium (0.6%) for a period of 12 weeks until sacrifice. In week 8, rats were randomized in five groups receiving different drugs including dihydrocaffeic acid as antioxidant (Aox), losartan (Los), dihydrocaffeic acid+losartan (Aox+Los) and GGN1231 as follows: Group 1 (CRF+vehicle group), Group 2 (CRF+Aox group), Group 3 (CRF+Los group), Group 4 (CRF+Aox+Los group), and Group 5 (CRF+GGN1231 group). Group 5, the CRF+GGN1231 group, displayed reduced proteinuria, aortic TNF-α, blood pressure, LV wall thickness, diameter of the cardiomyocytes, ATR1, cardiac TNF-α and fibrosis, cardiac collagen I, and TGF-ß1 expression. A non-significant 20% reduction in the mortality was also observed. This study showed the possible advantages of GGN1231, which could help in the management of cardiovascular and inflammatory processes. Further research is needed to confirm and even expand the positive aspects of this compound.

Role of Klotho and AGE/RAGE-Wnt/ß-Catenin Signalling Pathway on the Development of Cardiac and Renal Fibrosis in Diabetes.

Fibrosis plays an important role in the pathogenesis of long-term diabetic complications and contributes to the development of cardiac and renal dysfunction. The aim of this experimental study, performed in a long-term rat model, which resembles type 1 diabetes mellitus, was to investigate the role of soluble Klotho (sKlotho), advanced glycation end products (AGEs)/receptor for AGEs (RAGE), fibrotic Wnt/ß-catenin pathway, and pro-fibrotic pathways in kidney and heart. Diabetes was induced by streptozotocin. Glycaemia was maintained by insulin administration for 24 weeks. Serum and urine sKlotho, AGEs, soluble RAGE (sRAGE) and biochemical markers were studied. The levels of Klotho, RAGEs, ADAM10, markers of fibrosis (collagen deposition, fibronectin, TGF-ß1, and Wnt/ß-catenin pathway), hypertrophy of the kidney and/or heart were analysed. At the end of study, diabetic rats showed higher levels of urinary sKlotho, AGEs and sRAGE and lower serum sKlotho compared with controls without differences in the renal Klotho expression. A significant positive correlation was found between urinary sKlotho and AGEs and urinary albumin/creatinine ratio (uACR). Fibrosis and RAGE levels were significantly higher in the heart without differences in the kidney of diabetic rats compared to controls. The results also suggest the increase in sKlotho and sRAGE excretion may be due to polyuria in the diabetic rats.

Serum and Urinary Soluble α-Klotho as Markers of Kidney and Vascular Impairment.

This study was designed to investigate the controversy on the potential role of sKlotho as an early biomarker in Chronic Kidney Disease-Mineral Bone Disorder (CKD-MBD), to assess whether sKlotho is a reliable marker of kidney α-Klotho, to deepen the effects of sKlotho on vascular smooth muscle cells (VSMCs) osteogenic differentiation and to evaluate the role of autophagy in this process. Experimental studies were conducted in CKD mice fed a normal phosphorus (CKD+NP) or high phosphorus (CKD+HP) diet for 14 weeks. The patients' study was performed in CKD stages 2-5 and in vitro studies which used VSMCs exposed to non-calcifying medium or calcifying medium with or without sKlotho. The CKD experimental model showed that the CKD+HP group reached the highest serum PTH, P and FGF23 levels, but the lowest serum and urinary sKlotho levels. In addition, a positive correlation between serum sKlotho and kidney α-Klotho was found. CKD mice showed aortic osteogenic differentiation, together with increased autophagy. The human CKD study showed that the decline in serum sKlotho is previous to the rise in FGF23. In addition, both serum sKlotho and FGF23 levels correlated with kidney function. Finally, in VSMCs, the addition of sKlotho prevented osteogenic differentiation and induced autophagy. It can be concluded that serum sKlotho was the earliest CKD-MBD biomarker, a reliable indicator of kidney α-Klotho and that might protect against osteogenic differentiation by increasing autophagy. Nevertheless, further studies are needed to investigate the mechanisms of this possible protective effect.

MicroRNA-145 and microRNA-486 are potential serum biomarkers for vascular calcification.

INTRODUCTION: MicroRNAs (miRs) regulate vascular calcification (VC), and their quantification may contribute to suspicion of the presence of VC. METHODS: The study was performed in four phases. Phase 1: miRs sequencing of rat calcified and non-calcified aortas. Phase 2: miRs with the highest rate of change, plus miR-145 [the most abundant miR in vascular smooth muscle cells (VSMCs)], were validated in aortas and serum from rats with and without VC. Phase 3: the selected miRs were analyzed in epigastric arteries from kidney donors and recipients, and serum samples from general population. Phase 4: VSMCs were exposed to different phosphorus concentrations, and miR-145 and miR-486 were overexpressed to investigate their role in VC. RESULTS: miR-145, miR-122-5p, miR-486 and miR-598-3p decreased in the rat calcified aortas, but only miR-145 and miR-486 were detected in serum. In human epigastric arteries, miR-145 and miR-486 were lower in kidney transplant recipients compared with donors. Both miRs inversely correlated with arterial calcium content and with VC (Kauppila index). In the general population, the severe VC was associated with the lowest serum levels of both miRs. The receiver operating characteristic curve showed that serum miR-145 was a good biomarker of VC. In VSMCs exposed to high phosphorus, calcium content, osteogenic markers (Runx2 and Osterix) increased, and the contractile marker (α-actin), miR-145 and miR-486 decreased. Overexpression of miR-145, and to a lesser extent miR-486, prevented the increase in calcium content induced by high phosphorus, the osteogenic differentiation and the loss of the contractile phenotype. CONCLUSION: miR-145 and miR-486 regulate the osteogenic differentiation of VSMCs, and their quantification in serum could serve as a marker of VC.

Klotho, Oxidative Stress, and Mitochondrial Damage in Kidney Disease.

Reducing oxidative stress stands at the center of a prevention and control strategy for mitigating cellular senescence and aging. Kidney disease is characterized by a premature aging syndrome, and to find a modulator targeting against oxidative stress, mitochondrial dysfunction, and cellular senescence in kidney cells could be of great significance to prevent and control the progression of this disease. This review focuses on the pathogenic mechanisms related to the appearance of oxidative stress damage and mitochondrial dysfunction in kidney disease. In this scenario, the anti-aging Klotho protein plays a crucial role by modulating signaling pathways involving the manganese-containing superoxide dismutase (Mn-SOD) and the transcription factors FoxO and Nrf2, known antioxidant systems, and other known mitochondrial function regulators, such as mitochondrial uncoupling protein 1 (UCP1), B-cell lymphoma-2 (BCL-2), Wnt/ß-catenin, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1 alpha), transcription factor EB, (TFEB), and peroxisome proliferator-activated receptor gamma (PPAR-gamma). Therefore, Klotho is postulated as a very promising new target for future therapeutic strategies against oxidative stress, mitochondria abnormalities, and cellular senescence in kidney disease patients.

Vitamin D Treatment Prevents Uremia-Induced Reductions in Aortic microRNA-145 Attenuating Osteogenic Differentiation despite Hyperphosphatemia.

In chronic kidney disease, systemic inflammation and high serum phosphate (P) promote the de-differentiation of vascular smooth muscle cells (VSMC) to osteoblast-like cells, increasing the propensity for medial calcification and cardiovascular mortality. Vascular microRNA-145 (miR-145) content is essential to maintain VSMC contractile phenotype. Because vitamin D induces aortic miR-145, uremia and high serum P reduce it and miR-145 directly targets osteogenic osterix in osteoblasts, this study evaluated a potential causal link between vascular miR-145 reductions and osterix-driven osteogenic differentiation and its counter-regulation by vitamin D. Studies in aortic rings from normal rats and in the rat aortic VSMC line A7r5 exposed to calcifying conditions corroborated that miR-145 reductions were associated with decreases in contractile markers and increases in osteogenic differentiation and calcium (Ca) deposition. Furthermore, miR-145 silencing enhanced Ca deposition in A7r5 cells exposed to calcifying conditions, while miR-145 overexpression attenuated it, partly through increasing α-actin levels and reducing osterix-driven osteogenic differentiation. In mice, 14 weeks after the induction of renal mass reduction, both aortic miR-145 and α-actin mRNA decreased by 80% without significant elevations in osterix or Ca deposition. Vitamin D treatment from week 8 to 14 fully prevented the reductions in aortic miR-145 and attenuated by 50% the decreases in α-actin, despite uremia-induced hyperphosphatemia. In conclusion, vitamin D was able to prevent the reductions in aortic miR-145 and α-actin content induced by uremia, reducing the alterations in vascular contractility and osteogenic differentiation despite hyperphosphatemia.

Interdisciplinary management of FGF23-related phosphate wasting syndromes: a Consensus Statement on the evaluation, diagnosis and care of patients with X-linked hypophosphataemia.

X-linked hypophosphataemia (XLH) is the most frequent cause of hypophosphataemia-associated rickets of genetic origin and is associated with high levels of the phosphaturic hormone fibroblast growth factor 23 (FGF23). In addition to rickets and osteomalacia, patients with XLH have a heavy disease burden with enthesopathies, osteoarthritis, pseudofractures and dental complications, all of which contribute to reduced quality of life. This Consensus Statement presents the outcomes of a working group of the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases, and provides robust clinical evidence on management in XLH, with an emphasis on patients' experiences and needs. During growth, conventional treatment with phosphate supplements and active vitamin D metabolites (such as calcitriol) improves growth, ameliorates leg deformities and dental manifestations, and reduces pain. The continuation of conventional treatment in symptom-free adults is still debated. A novel therapeutic approach is the monoclonal anti-FGF23 antibody burosumab. Although promising, further studies are required to clarify its long-term efficacy, particularly in adults. Given the diversity of symptoms and complications, an interdisciplinary approach to management is of paramount importance. The focus of treatment should be not only on the physical manifestations and challenges associated with XLH and other FGF23-mediated hypophosphataemia syndromes, but also on the major psychological and social impact of the disease.

A single-oral bolus of 100,000 IU of cholecalciferol at hospital admission did not improve outcomes in the COVID-19 disease: the COVID-VIT-D-a randomised multicentre international clinical trial.

BACKGROUND: Vitamin D status has been implicated in COVID-19 disease. The objective of the COVID-VIT-D trial was to investigate if an oral bolus of cholecalciferol (100,000 IU) administered at hospital admission influences the outcomes of moderate-severe COVID-19 disease. In the same cohort, the association between baseline serum calcidiol levels with the same outcomes was also analysed. METHODS: The COVID-VIT-D is a multicentre, international, randomised, open label, clinical trial conducted throughout 1 year. Patients older than 18 years with moderate-severe COVID-19 disease requiring hospitalisation were included. At admission, patients were randomised 1:1 to receive a single oral bolus of cholecalciferol (n=274) or nothing (n=269). Patients were followed from admission to discharge or death. Length of hospitalisation, admission to intensive care unit (ICU) and mortality were assessed. RESULTS: In the randomised trial, comorbidities, biomarkers, symptoms and drugs used did not differ between groups. Median serum calcidiol in the cholecalciferol and control groups were 17.0 vs. 16.1 ng/mL at admission and 29.0 vs. 16.4 ng/mL at discharge, respectively. The median length of hospitalisation (10.0 [95%CI 9.0-10.5] vs. 9.5 [95%CI 9.0-10.5] days), admission to ICU (17.2% [95%CI 13.0-22.3] vs. 16.4% [95%CI 12.3-21.4]) and death rate (8.0% [95%CI 5.2-12.1] vs. 5.6% [95%CI 3.3-9.2]) did not differ between the cholecalciferol and control group. In the cohort analyses, the highest serum calcidiol category at admission (>25ng/mL) was associated with lower percentage of pulmonary involvement and better outcomes. CONCLUSIONS: The randomised clinical trial showed the administration of an oral bolus of 100,000 IU of cholecalciferol at hospital admission did not improve the outcomes of the COVID-19 disease. A cohort analysis showed that serum calcidiol at hospital admission was associated with outcomes. TRIAL REGISTRATION: COVID-VIT-D trial was authorised by the Spanish Agency for Medicines and Health products (AEMPS) and registered in European Union Drug Regulating Authorities Clinical Trials (EudraCT 2020-002274-28) and in ClinicalTrials.gov ( NCT04552951 ).

Pathophysiology of Vascular Calcification and Bone Loss: Linked Disorders of Ageing?

Vascular Calcification (VC), low bone mass and fragility fractures are frequently observed in ageing subjects. Although this clinical observation could be the mere coincidence of frequent age-dependent disorders, clinical and experimental data suggest that VC and bone loss could share pathophysiological mechanisms. Indeed, VC is an active process of calcium and phosphate precipitation that involves the transition of the vascular smooth muscle cells (VSMCs) into osteoblast-like cells. Among the molecules involved in this process, parathyroid hormone (PTH) plays a key role acting through several mechanisms which includes the regulation of the RANK/RANKL/OPG system and the Wnt/ß-catenin pathway, the main pathways for bone resorption and bone formation, respectively. Furthermore, some microRNAs have been implicated as common regulators of bone metabolism, VC, left ventricle hypertrophy and myocardial fibrosis. Elucidating the common mechanisms between ageing; VC and bone loss could help to better understand the potential effects of osteoporosis drugs on the CV system.

Survival with low- and high-flux dialysis.

BACKGROUND: Besides advances in haemodialysis (HD), mortality rates are still high. The effect of the different types of HD membranes on survival is still a controversial issue. The aim of this COSMOS (Current management Of Secondary hyperparathyroidism: a Multicentre Observational Study) analysis was to survey, in HD patients, the relationship between the use of conventional low- or high-flux membranes and all-cause and cardiovascular mortality. METHODS: COSMOS is a multicentre, open-cohort, 3-year prospective study, designed to evaluate mineral and bone disorders in the European HD population. The present analysis included 5138 HD patients from 20 European countries, 3502 randomly selected at baseline (68.2%), plus 1636 new patients with <1 year on HD (31.8%) recruited to replace patients who died, were transplanted, switched to peritoneal dialysis or lost to follow-up by other reasons. Cox-regression analysis with time-dependent variables, propensity score matching and the use of an instrumental variable (facility-level analysis) were used. RESULTS: After adjustments using three different multivariate models, patients treated with high-flux membranes showed a lower all-cause and cardiovascular mortality risks {hazard ratio (HR) = 0.76 [95% confidence interval (CI) 0.61-0.96] and HR = 0.61 (95% CI 0.42-0.87), respectively}, that remained significant after matching by propensity score for all-cause mortality (HR = 0.69, 95% CI 0.52-0.93). However, a facility-level analysis showed no association between the case-mix-adjusted facility percentage of patients dialysed with high-flux membranes and all-cause and cardiovascular mortality. CONCLUSIONS: High-flux dialysis was associated with a lower relative risk of all-cause and cardiovascular mortality. However, dialysis facilities using these dialysis membranes to a greater extent did not show better survival.

Real-world safety and effectiveness of sucroferric oxyhydroxide for treatment of hyperphosphataemia in dialysis patients: a prospective observational study.

BACKGROUND: The iron-based phosphate binder (PB), sucroferric oxyhydroxide (SFOH), is indicated to control serum phosphorus levels in patients with chronic kidney disease on dialysis. METHODS: This non-interventional, prospective, multicentre, cohort study conducted in seven European countries evaluated the safety and effectiveness of SFOH in dialysis patients with hyperphosphataemia in routine practice. Safety outcomes included adverse drug reactions (ADRs) and changes in iron-related parameters. SFOH effectiveness was evaluated by changes-from-baseline (BL) in serum phosphorus and percentage of patients achieving in-target phosphorus levels. RESULTS: The safety analysis set included 1365 patients (mean observation: 420.3 ± 239.3 days). Overall, 682 (50.0%) patients discontinued the study. Mean SFOH dose during the observation period was 1172.7 ± 539.9 mg (2.3 pills/day). Overall, 617 (45.2%) patients received concomitant PB(s) during SFOH treatment. ADRs and serious ADRs were observed for 531 (38.9%) and 26 (1.9%) patients. Most frequent ADRs were diarrhoea (194 patients, 14.2%) and discoloured faeces (128 patients, 9.4%). Diarrhoea generally occurred early during SFOH treatment and was mostly mild and transient. Small increases from BL in serum ferritin were observed (ranging from +12 to +75 µg/L). SFOH treatment was associated with serum phosphorus reductions (6.3 ± 1.6 mg/dL at BL versus 5.3 ± 1.8 mg/dL at Month 30; ΔBL: -1.0 mg/dL, P < 0.01). Percentage of patients achieving serum phosphorus ≤4.5 mg/dL increased from 12.0% at BL to 34.8% at Month 30, while the percentage achieving serum phosphorus ≤5.5 mg/dL increased from 29.9% to 63.0%. CONCLUSIONS: SFOH has a favourable safety and tolerability profile in a real-world setting, consistent with results of the Phase 3 study. Moreover, SFOH improved serum phosphorus control with a low daily pill burden.

Novel Immune Cell Subsets Exhibit Different Associations With Vascular Outcomes in Chronic Kidney Disease Patients-Identifying Potential Biomarkers.

Background and Aims: Alterations in novel immune cell subsets, such as angiogenic T cells (Tang), senescent T cells (CD4+CD28null), and monocyte subsets are associated with impaired vascular homeostasis in several inflammatory conditions. However, mediators underlying vascular deterioration in chronic kidney disease (CKD) are poorly characterized. This study assessed their role in the vascular deterioration of CKD using a broad spectrum of surrogate markers ranging from altered functionality to overt calcification. Methods: Tang (CD3+CD31+CXCR4+), CD4+CD28null cells, and monocytes [CD14/CD16 subsets and angiotensin-converting enzyme (ACE) expression] were measured in peripheral blood by flow cytometry in 33 CKD stage 5 patients undergoing peritoneal dialysis (CKD5-PD) and 15 healthy controls (HCs). Analyses were replicated in a hemodialysis cohort. Vascular surrogate markers (including adventitial vasa vasorum, pulse wave velocity, intima-media thickness, and vascular calcification) were assessed by appropriate imaging methods. Results: In CKD5-PD, decreased Tang levels (p < 0.001) were unrelated to clinical features or traditional cardiovascular (CV) risk factors but correlated negatively with troponin T levels (r = -0.550, p = 0.003). Instead, CD4+CD28null frequency was increased (p < 0.001), especially in those with vascular calcifications. Quantitative and qualitative differences were also observed within the monocyte pool, a shift toward CD16+ subsets and ACE expression being found in CKD. Equivalent results were observed in the replication cohort. Each subset associated distinctly with adverse vascular outcomes in univariate and multivariate analyses: while Tang depletion was linked to poor vascular function and subclinical atherosclerosis, increases in CD4+CD28null were associated with overt vascular thickening and calcification. Monocytes were not independently associated with vascular outcomes in CKD patients. Conclusions: Novel T cell and monocyte subsets are altered in CKD. Altered T-cell subpopulations, but not monocytes, exhibited distinct associations with different vascular outcomes in CKD. Tang are emerging biomarkers of subclinical vascular deterioration in CKD.

Contribution of phosphorus and PTH to the development of cardiac hypertrophy and fibrosis in an experimental model of chronic renal failure. / Contribución de fósforo y PTH al desarrollo de hipertrofia y fibrosis cardíaca en un modelo experimental de insuficiencia renal crónica.

BACKGROUND AND OBJECTIVE: Adequate serum phosphorus levels in patients with chronic kidney disease is essential for their clinical management. However, the control of hyperphosphatemia is difficult because is normally associated with increases in serum PTH. In the present study, the effects of hyperphosphatemia, in the presence of elevated and normal PTH, on cardiac inflammation, hypertrophy and fibrosis in an experimental renal failure model were analyzed. MATERIALS AND METHODS: Four groups of rats were formed. Two groups underwent total parathyroidectomy (PTx). Rats with Ca < 7.5 mg/dL and PTH < 50 pg/mL underwent 7/8 nephrectomy (CRF) and a subcutaneous pellet was placed that releases PTH 1-34 (5 µg/kg/day). One group received a diet with normal P (NP) (CRF + PTx + rPTH + NP group) and another with a high P diet (0.9% HP) (CRF + PTx + rPTH + HP group). Other two groups that only had CRF received NP (CRF + NP) and HP (CRF + HP) diet. A SHAM group for nephrectomy and parathyroidectomy was also added. After 14 weeks the rats were sacrificed. RESULTS: The groups with a diet high in phosphorus (CRF + H A and CRF + PTx + rPTH + HP) had a significant reduction in creatinine clearance and also in body weight with an increase in serum phosphorus regardless of parathyroidectomy, but not serum levels of calcium, FGF23 and calcitriol that were 2-3 times higher in the group with secondary hyperparathyroidism (CRF + HP). The diameter of the cardiomyocytes was greater in the CRF + HP group, while parathyroidectomy (CRF + PTx + rPTH + HP) significantly reduced them, despite the high and similar serum phosphorus values. TNF-α, Adam17 and cardiac fibrosis at the histological and molecular level showed a similar pattern with increases in the group with severe secondary hyperparathyroidism (CRF + HP). CONCLUSIONS: Hyperphosphatemia confirmed its importance in the genesis of secondary hyperparathyroidism, but also of kidney damage that was independent of PTH levels. However, inflammation, fibrosis, and cardiomyocyte growth were more closely related to PTH levels, since in the presence of similar severe hyperphosphatemia, parathyroidectomy reduced the values of inflammatory parameters, cardiac hypertrophy, and fibrosis.

Role of the RANK/RANKL/OPG and Wnt/ß-Catenin Systems in CKD Bone and Cardiovascular Disorders.

In the course of chronic kidney disease (CKD), alterations in the bone-vascular axis augment the risk of bone loss, fractures, vascular and soft tissue calcification, left ventricular hypertrophy, renal and myocardial fibrosis, which markedly increase morbidity and mortality rates. A major challenge to improve skeletal and cardiovascular outcomes in CKD patients requires a better understanding of the increasing complex interactions among the main modulators of the bone-vascular axis. Serum parathyroid hormone (PTH), phosphorus (P), calcium (Ca), fibroblast growth factor 23 (FGF23), calcidiol, calcitriol and Klotho are involved in this axis interact with RANK/RANKL/OPG system and the Wnt/ß-catenin pathway. The RANK/RANKL/OPG system controls bone remodeling by inducing osteoblast synthesis of RANKL and downregulating OPG production and it is also implicated in vascular calcification. The complexity of this system has recently increased due the discovery of LGR4, a novel RANKL receptor involved in bone formation, but possibly also in vascular calcification. The Wnt/ß-catenin pathway plays a key role in bone formation: when this pathway is activated, bone is formed, but when it is inhibited, bone formation is stopped. In the progression of CKD, a downregulation of the Wnt/ß-catenin pathway has been described which occurs mainly through the not coincident elevations of sclerostin, Dickkopf1 (Dkk1) and the secreted Frizzled Related Proteins (sFRPs). This review analyzes the interactions of PTH, P, Ca, FGF23, calcidiol, calcitriol and Klotho with the RANKL/RANKL/OPG system and the Wnt/ß-catenin, pathway and their implications in bone and cardiovascular disorders in CKD.

Effects of calcitriol and paricalcitol on renal fibrosis in CKD.

BACKGROUND: In chronic kidney disease, the activation of the renin-angiotensin-aldosterone system (RAAS) and renal inflammation stimulates renal fibrosis and the progression to end-stage renal disease. The low levels of vitamin D receptor (VDR) and its activators (VDRAs) contribute to worsen secondary hyperparathyroidism and renal fibrosis. METHODS: The 7/8 nephrectomy model of experimental chronic renal failure (CRF) was used to examine the anti-fibrotic effects of treatment with two VDRAs, paricalcitol and calcitriol, at equivalent doses (3/1 dose ratio) during 4 weeks. RESULTS: CRF increased the activation of the RAAS, renal inflammation and interstitial fibrosis. Paricalcitol treatment reduced renal collagen I and renal interstitial fibrosis by decreasing the activation of the RAAS through renal changes in renin, angiotensin receptor 1 (ATR1) and ATR2 mRNAs levels and renal inflammation by decreasing renal inflammatory leucocytes (CD45), a desintegrin and metaloproteinase mRNA, transforming growth factor beta mRNA and protein, and maintaining E-cadherin mRNA levels. Calcitriol showed similar trends without significant changes in most of these biomarkers. CONCLUSIONS: Paricalcitol effectively attenuated the renal interstitial fibrosis induced by CRF through a combination of inhibitory actions on the RAAS, inflammation and epithelial/mesenchymal transition.

Fibrosis in Chronic Kidney Disease: Pathogenesis and Consequences.

Fibrosis is a process characterized by an excessive accumulation of the extracellular matrix as a response to different types of tissue injuries, which leads to organ dysfunction. The process can be initiated by multiple and different stimuli and pathogenic factors which trigger the cascade of reparation converging in molecular signals responsible of initiating and driving fibrosis. Though fibrosis can play a defensive role, in several circumstances at a certain stage, it can progressively become an uncontrolled irreversible and self-maintained process, named pathological fibrosis. Several systems, molecules and responses involved in the pathogenesis of the pathological fibrosis of chronic kidney disease (CKD) will be discussed in this review, putting special attention on inflammation, renin-angiotensin system (RAS), parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), Klotho, microRNAs (miRs), and the vitamin D hormonal system. All of them are key factors of the core and regulatory pathways which drive fibrosis, having a great negative kidney and cardiac impact in CKD.