Vascular calcification contributes to the high risk of cardiovascular mortality in chronic kidney disease (CKD) patients. Dysregulation of calcium (Ca) and phosphate (P) metabolism is common in CKD patients, and drives vascular calcification. In this article, we review the physiological regulatory mechanisms for Ca and P homeostasis and the basis for their dysregulation in CKD. In addition, we highlight recent findings indicating that elevated Ca and P have direct effects on vascular smooth muscle cells (VSMCs) that promote vascular calcification, including stimulation of osteo/chondrogenic differentiation, vesicle release, apoptosis, loss of inhibitors, and ECM matrix degradation. These studies suggest a major role for elevated P in promoting osteo/chondrogenic differentiation of VSMC, whereas elevated Ca has a predominant role in promoting VSMC apoptosis and vesicle release. Furthermore, the effects of elevated Ca and P are synergistic providing a major stimulus for vascular calcification in CKD. Unravelling the complex regulatory pathways that mediate the effects of both Ca and P on VSMCs will ultimately provide novel targets and therapies to limit the destructive effects of vascular calcification in CKD patients.
calcium; phosphate; vascular calcification; chronic kidney disease
Vascular calcification is associated with significant cardiovascular morbidity and mortality in patients with chronic kidney disease (CKD). Factors unique to CKD patients, such as hyperphosphatemia, predispose these patients to early and progressive vascular calcification. Hyperphosphatemia appears to be involved in a number of mechanisms that trigger and advance progression of vascular calcification including (1) transition of vascular smooth muscle cells (VSMC) from a contractile to an osteochondrogenic phenotype and mineralization of VSMC matrix through sodium-dependent phosphate cotransporters; (2) induction of apoptosis of VSMC; (3) inhibition of monocyte/macrophage differentiation into osteoclast-like cells; (4) elevation of fibroblast growth factor 23 levels; and (5) decreases in klotho expression. Whether vascular calcification can be prevented or reversed with strategies aimed at maintaining phosphate homeostasis is currently unknown. The current review discusses these mechanisms in-depth, exploring the interplay among vascular calcification promoters, inhibitors and substrate that affect phosphorus handling leading to vascular calcification in individuals with CKD.
Vascular calcification is highly associated with cardiovascular morbidity and mortality, especially in patients with chronic kidney disease. The nuclear receptor farnesoid X receptor (FXR) has been implicated in the control of lipid, carbohydrate and bile acid metabolism in several cell types. Although recent studies have shown that FXR is also expressed in vascular smooth muscle cells, its physiological role in vasculature tissue remains obscure.
Here, we have examined the role of FXR in vascular calcification.
Methods and Results
The FXR gene, a bile acid nuclear receptor, was highly induced during osteogenic differentiation of bovine calcifying vascular cells (CVC) and in the aorta of apolipoprotein E (ApoE)−/− mice with chronic kidney disease which are common tissue culture and mouse model, respectively, for aortic calcification. FXR activation by a synthetic FXR agonist, 6α-ethyl chenodeoxycholic acid (INT-747) inhibited phosphate induced-mineralization and triglyceride accumulation in CVC. FXR dominant negative expression augmented mineralization of CVC and blocked the anti-calcific effect of INT-747 whereas VP16FXR that is a constitutively active form reduced mineralization of CVC. INT-747 treatment also increased phosphorylated c-Jun N-terminal kinase (JNK). SP600125 (specific JNK inhibitor) significantly induced mineralization of CVC and ALP expression, suggesting that the anti-calcific effect of INT-747 is due to JNK activation. We also found that INT-747 ameliorates chronic kidney disease (CKD) induced-vascular calcification in 5/6 nephrectomized ApoE−/− mice without affecting the development of atherosclerosis.
These observations provide direct evidence for that FXR is a key signaling component in regulation of vascular osteogenic differentiation and, thus representing a promising target for the treatment of vascular calcification.
farnesoid X receptor; vascular calcification; chronic kidney disease
Accelerated vascular calcification occurs in several human diseases including diabetes and chronic kidney disease (CKD). In CKD patients, vascular calcification is highly correlated with elevated serum phosphate levels. In vitro, elevated concentrations of phosphate induced vascular smooth muscle cell matrix mineralization, and the inorganic phosphate transporter-1 (PiT-1), was shown to be required. To determine the in vivo role of PiT-1, mouse conditional and null alleles were generated. Here we show that the conditional allele, PiT-1flox, which has loxP sites flanking exons 3 and 4, is homozygous viable. Cre-mediated recombination resulted in a null allele that is homozygous lethal. Examination of early embryonic development revealed that the PiT-1Δe3,4/Δe3,4 embryos displayed anemia, a defect in yolk sac vasculature, and arrested growth. Thus, conditional and null PiT-1 mouse alleles have been successfully generated and PiT-1 has a necessary, non-redundant role in embryonic development.
PiT-1; Slc20a1; yolk sac vasculature; anemia; knockout; conditional; mouse; embryonic lethal; type III sodium-dependent phosphate cotransporter
The proinflammatory cytokine S100A12 is associated with coronary atherosclerotic plaque rupture. We previously generated transgenic mice with vascular smooth muscle–targeted expression of human S100A12 and found that these mice developed aortic aneurysmal dilation of the thoracic aorta. In the current study, we tested the hypothesis that S100A12 expressed in vascular smooth muscle in atherosclerosis-prone apolipoprotein E (ApoE)–null mice would accelerate atherosclerosis.
Methods and Results
ApoE-null mice with or without the S100A12 transgene were analyzed. We found a 1.4-fold increase in atherosclerotic plaque size and more specifically a large increase in calcified plaque area (45% versus 7% of innominate artery plaques and 18% versus 10% of aortic root plaques) in S100A12/ApoE-null mice compared with wild-type/ApoE-null littermates. Expression of bone morphogenic protein and other osteoblastic genes was increased in aorta and cultured vascular smooth muscle, and importantly, these changes in gene expression preceded the development of vascular calcification in S100A12/ApoE-null mice. Accelerated atherosclerosis and vascular calcification were mediated, at least in part, by oxidative stress because inhibition of NADPH oxidase attenuated S100A12-mediated osteogenesis in cultured vascular smooth muscle cells. S100A12 transgenic mice in the wild-type background (ApoE+/+) showed minimal vascular calcification, suggesting that S100A12 requires a proinflammatory/proatherosclerotic environment to induce osteoblastic differentiation and vascular calcification.
Vascular smooth muscle S100A12 accelerates atherosclerosis and augments atherosclerosis-triggered osteogenesis, reminiscent of features associated with plaque instability.
calcification; coronary artery disease; genetically altered mice; vascular biology
S100A12 is a small calcium binding protein that is a ligand of the Receptor for Advanced Glycation End products (RAGE). RAGE has been extensively implicated in inflammatory states such as atherosclerosis, but the role of S100A12 as its ligand is less clear.
To test the role of S100A12 in vascular inflammation, we generated and analyzed mice expressing human S100A12 in vascular smooth muscle under control of the SM22α promoter since S100A12 is not present in mice.
Methods and Results
Transgenic mice displayed pathologic vascular remodeling with aberrant thickening of the aortic media, disarray of elastic fibers, and increased collagen deposition, together with increased latent MMP-2 protein and reduction in smooth muscle stress fibers leading to a progressive dilatation of the aorta. In primary aortic smooth muscle cell cultures, we found that S100A12-mediates increased IL-6 production, activation of TGF β pathways and increased metabolic activity with enhanced oxidative stress. To correlate our findings to human aortic aneurysmal disease, we examined S100A12 expression in aortic tissue from patients with thoracic aortic aneurysm and found increased S100A12 expression in vascular smooth muscle cells.
S100A12 expression is sufficient to activate pathogenic pathways through the modulation of oxidative stress, inflammation and vascular remodeling in vivo.
S100A12; calgranulins; smooth muscle cell differentiation; RAGE; aortic aneurysms
Cellular proliferation, migration, and expression of extracellular matrix proteins and MMPs contribute to neointimal formation upon vascular injury. Wild-type mice undergoing arterial endothelial denudation displayed striking upregulation of receptor for advanced glycation end products (RAGE) in the injured vessel, particularly in activated smooth muscle cells of the expanding neointima. In parallel, two of RAGE’s signal transducing ligands, advanced glycation end products (AGEs) and S100/calgranulins, demonstrated increased deposition/expression in the injured vessel wall. Blockade of RAGE, employing soluble truncated receptor or antibodies, or in homozygous RAGE null mice, resulted in significantly decreased neointimal expansion after arterial injury and decreased smooth muscle cell proliferation, migration, and expression of extracellular matrix proteins. A critical role for smooth muscle cell RAGE signaling was demonstrated in mice bearing a transgene encoding a RAGE cytosolic tail-deletion mutant, specifically in smooth muscle cells, driven by the SM22α promoter. Upon arterial injury, neointimal expansion was strikingly suppressed compared with that observed in wild-type littermates. Taken together, these data highlight key roles for RAGE in modulating smooth muscle cell properties after injury and suggest that RAGE is a logical target for suppression of untoward neointimal expansion consequent to arterial injury.
When compared to the available information for patients on dialysis (CKD stage 5D), data on the epidemiology and appropriate treatment of calcium and phosphate metabolism in the predialysis stages of chronic kidney disease (CKD) are quite limited. Perceptible derangements of calcium and phosphate levels start to become apparent when GFR falls below 30 mL/min in some, but not all, patients. However, hyperphosphatemia may be a significant morbidity and mortality risk predictor in predialysis CKD stages. The RIND study, evaluating progression of coronary artery calcification in incident hemodialysis patients, indirectly demonstrated that vascular calcification processes start to manifest in CKD patients prior to the dialysis stage, which may be closely linked to early and invisible derangements in calcium and phosphate homeostasis. Novel insights into the pathophysiology of calcium and phosphate handling such as the discovery of FGF23 and other phosphatonins suggest that a more complex assessment of phosphate balance is warranted, possibly including measurements of fractional phosphate excretion and phosphatonin levels in order to appropriately evaluate disordered metabolism in earlier stages of kidney disease. As a consequence, early and preventive treatment approaches may have to be developed for patients in CKD stages 3-5 to halt progression of CKD-MBD.
Chronic Kidney Disease-Mineral Bone Disorder (CKD-MBD) is a newly defined disorder that describes the interacting triad of (1) biochemical abnormalities of calcium, phosphorus, and PTH, (2) vascular calcification, and (3) abnormal bone in patients with CKD. We describe a novel animal model of slowly progressive CKD that spontaneously develops all three components of CKD-MBD while fed a normal phosphorus diet. The advantage of this model is the natural progression of the disease, allowing manipulation early in the course of CKD to better understand the pathophysiology of CKD-MBD. We further demonstrate that different sources of dietary protein, despite having similar total phosphorus contents, can have profound effects on the progression of CKD-MBD, likely due to differences in intestinal bioavailability of these phosphorus sources. Animals with early, but established, CKD fed a casein-based protein source, compared to grain-based protein source, had no differences in serum phosphorus. However, the casein protein-fed animals had increased urinary phosphorus excretion and elevated serum FGF23. Thus, this animal model will allow us to examine early changes in the course of CKD that may lead to CKD-MBD.
The relationship of circulating endogenous secretory receptor for advanced glycation end products (esRAGE) and chronic kidney disease (CKD) has not been well characterized. The aim of the study was to determine whether plasma esRAGE is associated with CKD and is predictive of developing CKD in older adults.
The relationship between plasma esRAGE and CKD (more than stage 3 of the National Kidney Foundation classification; estimated glomerular filtration rate <60 ml/min/1.73 m2) and CKD over 6 years of follow-up was examined in a cross-sectional and prospective study design in 1,016 men and women, ≥65 years, in the InCHIANTI study, a population-based cohort study of aging in Tuscany, Italy.
At enrollment, 158 (15.5%) had CKD. Mean (SD) plasma esRAGE was 0.45 (0.24) ng/ml. Plasma esRAGE (ng/ml) was associated with CKD (odds ratio per 1 SD = 1.30; 95% CI 1.1–1.6; p < 0.005) in a multivariable logistic regression model, adjusting for potential confounders. Plasma esRAGE was an independent predictor of incident CKD over 6 years of follow-up (hazard ratio per 1 SD = 1.37; 95% CI 1.1–1.7; p < 0.008) in a multivariable Cox proportional hazards model, adjusting for potential confounders.
Elevated plasma esRAGE is independently associated with CKD and is an independent predictor of incident CKD in older community-dwelling adults.
Advanced glycation end products; Aging; Chronic kidney disease; Endogenous secretory receptor for advanced glycation end products
Chronic kidney disease (CKD) is characterized by renal fibrosis that can lead to end-stage renal failure, and studies have supported a strong genetic influence on the risk of developing CKD. However, investigations of the underlying molecular mechanisms are hampered by the lack of suitable hereditary models in animals. We therefore sought to establish hereditary mouse models for CKD and renal fibrosis by investigating mice treated with the chemical mutagen N-ethyl-N-nitrosourea, and identified a mouse with autosomal recessive renal failure, designated RENF. Three-week old RENF mice were smaller than their littermates, whereas at birth they had been of similar size. RENF mice, at 4-weeks of age, had elevated concentrations of plasma urea and creatinine, indicating renal failure, which was associated with small and irregularly shaped kidneys. Genetic studies using DNA from 10 affected mice and 91 single nucleotide polymorphisms mapped the Renf locus to a 5.8Mbp region on chromosome 17E1.3. DNA sequencing of the xanthine dehydrogenase (Xdh) gene revealed a nonsense mutation at codon 26 that co-segregated with affected RENF mice. The Xdh mutation resulted in loss of hepatic XDH and renal Cyclooxygenase-2 (COX-2) expression. XDH mutations in man cause xanthinuria with undetectable plasma uric acid levels and three RENF mice had plasma uric acid levels below the limit of detection. Histological analysis of RENF kidney sections revealed abnormal arrangement of glomeruli, intratubular casts, cellular infiltration in the interstitial space, and interstitial fibrosis. TUNEL analysis of RENF kidney sections showed extensive apoptosis predominantly affecting the tubules. Thus, we have established a mouse model for autosomal recessive early-onset renal failure due to a nonsense mutation in Xdh that is a model for xanthinuria in man. This mouse model could help to increase our understanding of the molecular mechanisms associated with renal fibrosis and the specific roles of XDH and uric acid.
The receptor for advanced glycation end products (RAGE) is a single transmembrane receptor of the immunoglobulin superfamily that is mainly expressed on immune cells, neurons, activated endothelial and vascular smooth muscle cells, bone forming cells, and a variety of cancer cells. RAGE is a multifunctional receptor that binds a broad repertoire of ligands and mediates responses to cell damage and stress conditions. It activates programs responsible for acute and chronic inflammation, and is implicated in a number of pathological diseases, including diabetic complications, stroke, atheriosclerosis, arthritis, and neurodegenerative disorders. The availability of Rage knockout mice has not only advanced our knowledge on signalling pathways within these pathophysiological conditions, but also on the functional importance of the receptor in processes of cancer. Here, we will summarize molecular mechanisms through which RAGE signalling contributes to the establishment of a pro-tumourigenic microenvironment. Moreover, we will review recent findings that provide genetic evidence for an important role of RAGE in bridging inflammation and cancer.
We previously showed that kidney dysfunction/interstitial fibrosis by folate predisposes mice to sepsis mortality (normal/sepsis: 15%; folate/sepsis: 90%); agents that increased survival in normal septic mice were ineffective in the two-stage model. We used a recently characterized 5/6 nephrectomy (Nx) mouse model of progressive chronic kidney disease (CKD) to study how CKD impacts sepsis and acute kidney injury (AKI) induced by cecal ligation-puncture (CLP). CKD intensified sepsis severity (by kidney and liver injury, cytokines, and spleen apoptosis). Accumulation of HMGB1, VEGF, TNF-α, IL-6, or IL-10 was increased in CKD or sepsis alone and to a greater extent in CKD-sepsis, and only part of this effect could be explained by decreased renal clearance. Surprisingly, we found splenic apoptosis in CKD, even in the absence of sepsis. Although sFLT-1 effectively treated sepsis, it was ineffective against CKD-sepsis. Conversely, a single dose of HMGB1-neutralizing antiserum, administered 6h after sepsis alone was ineffective; however, CKD/sepsis was attenuated by anti-HMGB1. Splenectomy transiently decreased circulating HMGB1 levels, which reversed the effectiveness of anti-HMGB1 treatment on CKD/sepsis. We conclude that progressive CKD increases sepsis severity, in part, by reducing renal clearance of cytokines; CKD-induced splenic apoptosis and HMGB1 could be important common mediators for both CKD and sepsis.
Hypertriglyceridemia is a common metabolic complication of chronic kidney disease (CKD) and an important risk factor for coronary heart disease in this patient population. The mechanisms responsible for the development of hypertriglyceridemia in subjects with CKD are not clear.
We studied very low density lipoprotein triglyceride (VLDL-TG) and VLDL-apolipoprotein B-100 (VLDL-apoB-100) kinetics in vivo in 6 subjects with non-dialysis-dependent CKD (CKD-ND), 6 subjects with CKD treated with peritoneal dialysis (CKD-PD) and 24 sex-, age- and body mass index-matched control subjects with normal renal function (12 control subjects each matched with the CKD-ND and CKD-PD group, respectively).
The secretion rates of VLDL-TG and VLDL-apoB-100 into plasma were not different between CKD-ND or CKD-PD and their respective control groups. The mean residence times of VLDL-TG and VLDL-apoB-100 in plasma, which represents the time VLDL-TG and VLDL-apoB-100 spend in the circulation after secretion by the liver, tended to be greater in subjects with CKD-ND than in control subjects (222 ± 38 vs. 143 ± 21 min, p = 0.07, and 352 ± 102 vs. 200 ± 20 min, p = 0.06, respectively) and were about two-fold greater in subjects with CKD-PD compared with their control group (248 ± 51 vs. 143 ± 21 min and 526 ± 116 vs. 182 ± 16 min, respectively; both p ≤ 0.01).
Impaired plasma clearance of VLDL-TG and VLDL-apoB-100 is the major abnormality associated with hypertriglyceridemia in patients with either CKD-ND or CKD-PD.
Isotope tracer; Lipoprotein; Metabolism; Renal failure
Osteoporosis is a common complication of chronic kidney disease (CKD), and the latter is a major risk factor for cardiovascular mortality. Recent studies have elucidated some of the mechanisms by which CKD is a cardiovascular risk, and they relate to osteoporosis. Thus, the mechanisms of CKD induced cardiovascular risk provide valuable insight into the relationship between cardiovascular disease and osteoporosis, and they are reviewed here. Observational studies have determined hyperphosphatemia to be a cardiovascular risk factor in chronic kidney disease. Mechanistic studies have elucidated that hyperphosphatemia is a direct stimulus to vascular calcification, which is one cause of morbid cardiovascular events contributing to the excess mortality of chronic kidney disease. Hyperphosphatemia in chronic kidney is due to failure of excretion by the kidneys and excess bone resorption. It stimulates vascular cells to mineralize atherosclerotic plaques through osteoblastic processes. Hyperphosphatemia in chronic kidney disease is a distinct syndrome characterized by disordered skeletal remodeling, heterotopic mineralization and cardiovascular morbidity. The heterotopic mineralization stimulated by CKD is relevant to osteoporosis.
phosphorus; cardiovascular disease; osteoporosis; kidney disease; osteoblasts
Chronic kidney disease (CKD) is a worldwide health problem with increasing prevalence and poor outcomes including severe cardiovascular disease and renal osteodystrophy. With advances in medical treatment, CKD patients are living longer and require oral care. The aim of this study was to determine the effects of CKD and dietary phosphate on mandibular bone structure using a uremic mouse model.
Uremia (U) was induced in female DBA/2 mice by partial renal ablation. Uremic mice received either a normal phosphate (NP) or a high phosphate (HP) diet. Sham surgeries were performed in a control group of mice, and half received either a NP or a HP diet. At termination, animals were sacrificed and mandibles collected for microcomputed tomography (micro-CT) and histological analysis.
Sera levels of BUN, PTH and alkaline phosphatase were all significantly increased in U/NP and U/HP vs. Sham controls, while serum calcium was increased in the U/HP group and no differences were noted in serum phosphate levels between groups. Micro-CT analyses revealed a significant reduction in cortical bone thickness and an increase in trabecular thickness and trabecular bone volume/tissue volume in U/NP and U/HP groups compared to Sham/NP. A significant reduction in cortical bone thickness was also found in the Sham/HP vs. Sham/NP group. Histological evaluation confirmed increased trabeculation in the U groups.
CKD in mice, especially under conditions of high phosphate feeding, results in marked effects on alveolar bone homeostasis.
Bone biology; periodontal-systemic disease interactions; risk factor(s)
Impaired kidney function and subsequent skeletal responses play a critical role in disrupting phosphate balance in chronic kidney disease (CKD) patients with mineral and bone disorder (CKD-MBD). In patients with CKD-MBD, the inability of the kidney to maintain normal mineral ion balance affects bone remodeling to induce skeletal fracture and extraskeletal vascular calcification. In physiological conditions, bone-derived fibroblast growth factor 23 (FGF23) acts on the kidney to reduce serum phosphate and 1,25-dihydroxyvitamin D levels. In humans, increased bioactivity of FGF23 leads to increased urinary phosphate excretion, which induces hypophosphatemic diseases (e.g., rickets/osteomalacia). However, reduced FGF23 activity is associated with hyperphosphatemic diseases (e.g., tumoral calcinosis). In patients with CKD, high serum levels of FGF23 fail to reduce serum phosphate levels and lead to numerous complications, including vascular calcification, one of the important determinants of mortality of CKD-MBD patients. Of particular significance, molecular, biochemical and morphological changes in patients with CKD-MBD are mostly due to osteo-renal dysregulation of mineral ion metabolism. Furthermore, hyperphosphatemia can partly contribute to the development of secondary hyperparathyroidism in patients with CKD-MBD. Relatively new pharmacological agents including sevelamer hydrochloride, calcitriol analogs and cinacalcet hydrochloride are used either alone, or in combination, to minimize hyperphosphatemia and hyperparathyroidism associated complications to improve morbidity and mortality of CKD-MBD patients. This article will briefly summarize how osteo-renal miscommunication can induce phosphate toxicity, resulting in extensive tissue injuries.
Klotho; fibroblast growth factor 23; vitamin D; parathyroid hormone; chronic kidney disease
The term cardiorenal syndrome refers to the interaction between the heart and the kidney in disease and encompasses five distinct types according to the initial site affected and the acute or chronic nature of the injury. Type 4, or chronic renocardiac syndrome, involves the features of chronic renal disease (CKD) leading to cardiovascular injury. There is sufficient epidemiologic evidence linking CKD with increased cardiovascular morbidity and mortality. The underlying pathophysiology goes beyond the highly prevalent traditional cardiovascular risk burden affecting renal patients. It involves CKD-related factors, which lead to cardiac and vascular pathology, mainly left ventricular hypertrophy, myocardial fibrosis, and vascular calcification. Risk management should consider both traditional and CKD-related factors, while therapeutic interventions, apart from appearing underutilized, still await further confirmation from large trials.
Endothelial injury is a well-known complication in chronic kidney disease (CKD) and hemodialysis. One of the sites in which early vascular changes may be detected is the retina. Of course, these flow changes may not be detected in ophthalmologic exams, but it seems that color Doppler sonography of retinal arteries may be helpful in these cases.
In previous studies on CKD patients who underwent chronic hemodialysis,hemodynamic changes were noted in retinal arteries, but no study has been performed to determine which of the two processes (CKD or chronic hemodialysis) can produce these changes. In this study, we tried to answer this question.
Patients and Methods
Doppler ultrasonography of the orbital vasculature including the ophthalmic artery and the central retinal artery was carried out in 17 patients (34 eyes) with chronic renal failure (CRF) who underwent hemodialysis, 17 patients (34 eyes)with CRF without a history of hemodialysis and 17 normal patients (34 eyes). The peak systolic velocity (PSV), end diastolic velocity (EDV) and resistance index were measured excluding hypertensive, diabetic patients and patients with cardiovascular disease.
The mean PSV and EDV were lower only in the ophthalmic artery of CRF patients irrespective of the history of hemodialysis (PSV was 35.2 in hemodialysis, 38.8 in CRF and 51.6 in normal patients, P value = 0.001 and EDV was 7.4, 9.4, 11.8, respectively, P value =0.001) with no significant difference in the resistance index of the ophthalmic artery and other parameters [EDV, PSV, Resistance Index (RI)] in the central retinal artery.
The mean PSV and DSV in the ophthalmic artery were lower only in the ophthalmic artery of CRF patients regardless of the history of hemodialysis. No significant difference in the resistance index of the ophthalmic artery and other parameters (EDV, PSV) of the central retinal artery were noted between different groups.
These findings suggest that microvascular disease and endothelial cell dysfunction of the orbital vasculature are related to CRF and not to chronic hemodialysis.
Ultrasonography, Doppler, Color; Kidney Failure, Chronic; Renal Dialysis
The term ‘chronic kidney disease–mineral and bone disorder’ (CKD–MBD), coined in 2006, was introduced in a position statement by the Kidney Disease: Improving Global Outcomes (KDIGO) organization. According to the KDIGO guidelines, CKD–MBD is a systemic disorder and patients with vascular or valvular calcifications should be included in the group with the greatest cardiovascular risk. Therefore, the presence or absence of calcification is a key factor in strategy decisions for such patients. In particular, it is recommended that the use of calcium-based phosphate binders should be restricted in patients with hypercalcaemia, vascular calcification, low levels of parathyroid hormone (PTH) or adynamic bone disease. In this respect, it should be underscored that treatment with phosphate-binding agents can normalise the levels of phosphate and PTH, but the use of calcium carbonate can favour the progression of vascular calcifications. There is evidence of reduced progression of vascular calcification in patients treated with sevelamer compared with high doses of calcium-based binders, but there is as yet no strong evidence regarding hard outcomes, such as mortality or hospitalization, to support the use of one treatment over another. Nevertheless, a number of experimental and observational findings seem to suggest that sevelamer should be preferred over calcium-based binders, in as much as these can increase cardiovascular mortality when used in high doses. A threshold dose below which calcium-based binders can be used safely in CKD patients with hyperphosphatemia has yet to be established.
chronic kidney disease; hyperphosphataemia; phosphate binders; vascular calcification
Patients with chronic kidney disease (CKD) are at significantly higher risk of death from sepsis, although the mechanism by which CKD increases mortality has not been investigated. We established a mouse two-stage model of pre-existing renal disease with subsequent sepsis by combining folic acid (FA) injection and sub-lethal cecal ligation and puncture (CLP) surgery. Mice were injected with FA then made septic (FA-CLP) or were injected with vehicle then made septic (Veh-CLP). FA-CLP mice had significantly higher mortality than Veh-CLP mice. Sepsis increased serum creatinine in the FA-CLP but not in the Veh-CLP group. FA-CLP mice had more severe septic shock and significantly increased vascular permeability, plasma vascular endothelial growth factor (VEGF), bacteremia, serum IL-10 and splenocyte apoptosis compared to Veh-CLP. To evaluate the contribution of vascular and immunological dysfunction, we treated FA-CLP mice with soluble Flt-1 and chloroquine. Mice treated with combination therapy showed a significant improvement in kidney injury, hemodynamics, and survival. In conclusion, the sequential FA-CLP model mimics human sepsis that is frequently complicated with pre-existing conditions including CKD. This animal model would be useful to evaluate preventative and therapeutic strategies under conditions more typical of human sepsis.
Vascular calcifications produce a high impact on morbidity and mortality rates in patients affected by chronic kidney disease and mineral bone disorder (CKD-MBD). Effects are manifested from the more advanced stages of CKD (stages 3-4), particularly in patients undergoing dialysis (CKD5D). In recent years, a large number of therapeutic options have been successfully used in the treatment of secondary hyperparathyroidism (SHPT), despite eliciting less marked effects on nonbone calcifications associated with CKD-MBD. In addition to the use of Vitamin D and analogues, more recently treatment with calcimimetic drugs has also been undertaken. The present paper aims to analyze comparative and efficacy studies undertaken to assess particularly the impact on morbidity and mortality rates of non-calcium phosphate binders. Moreover, the mechanism of action underlying the depositing of calcium and phosphate along blood vessel walls, irrespective of the specific contribution provided in reducing the typical phosphate levels observed in CKD largely at more advanced stages of the disease, will be investigated. The aim of this paper therefore is to evaluate which phosphate binders are characterised by the above action and the mechanisms through which these are manifested.
Vascular calcification is a very common event in atients affected by diabetes and chronic kidney disease (CKD). Recently, it has been well documented that abnormalities in mineral and bone metabolism in CKD patients are associated with increased morbidity and mortality. Elevated serum phosphate and calcium-phosphate product levels play an important role in the pathogenesis of vascular mineralization in uremic patients and also appear to be associated with increased cardiovascular mortality. Together with classical passive precipitation of calcium-phosphate in soft tissues, during the last decade it has been demonstrated that inorganic phosphate may cause extraskeletal calcification directly through a real “ossification” of the tunica media in the vasculature of CKD patients. Therefore, control of phosphate retention is now an even more crucial target of treatment in patients affected by chronic kidney disease.
Vascular calcification; Phosphate; Chronic kidney disease
This review highlights the most recent publications addressing the relationship between bone and vascular calcification in patients with chronic and end-stage kidney disease.
The relatively new term “chronic kidney disease - mineral bone disorder” (CKD-MBD) reflects the growing reach of CKD research into the realm of systems physiology, involving a triad of renal, skeletal and vascular tissues. Recent studies address underlying mechanisms of the bone and vascular complications of CKD and point to a variety of biochemical factors, including phosphatonins [fibroblast growth factor-23, matrix-matrix extracellular phosphoglycoprotein], bone morphogenetic protein 7, osteoprotegerin, matrix GLA protein, ectonucleotide pyrophophatase/phosphodiesterase 1, alkaline phosphatase, and lipid oxidation products. Studies also demonstrate that agents used for treatment of one component of the triad often act on the other components of the triad - beneficially or adversely. These findings emphasize the importance of avoiding the subspecialty, single organ viewpoint when treating individual components of CKD-MBD.
The consistent synchrony among chronic kidney disease, aortic calcification and bone loss offers clues to underlying mechanisms for the systemic abnormalities.
Calcification; Vascular; Osteodystrophy; Kidney
Background. Vascular calcifications and the bone fractures caused by abnormal bone fragility, also called osteoporotic fractures, are frequent complications associated with chronic kidney diseases (CKD). The aim of this study was to investigate the association between vascular calcifications, osteoporotic bone fractures and survival in haemodialysis (HD) patients.
Methods. A total of 193 HD patients were followed up to 2 years. Vascular calcifications and osteoporotic vertebral fractures (quoted just as vertebral fractures in the text) were assessed by thoracic, lumbar spine, pelvic and hand X-rays and graded according to their severity. Clinical, biochemical and therapeutic data gathered during the total time spent on HD were collected.
Results. The prevalence of aortic calcifications was higher in HD patients than in a random-based general population (79% versus 37.5%, P < 0.001). Total time on any renal replacement therapy (RRT) and diabetes were positively associated with a higher prevalence of vascular calcifications. In addition to these factors, time on HD was also positively associated with the severity of vascular calcifications, and higher haemoglobin levels were associated with a lower prevalence of severe vascular calcifications in large and medium calibre arteries. The prevalence of vertebral fractures in HD patients was similar to that of the general population (26.5% versus 24.1%). Age and time on HD showed a positive and statistically significant association with the prevalence of vertebral fractures. Vascular calcifications in the medium calibre arteries were associated with a higher rate of prevalent vertebral fractures. In women, severe vascular calcifications and vertebral fractures were positively associated with mortality [RR = 3.2 (1.0–10.0) and RR = 4.8 (1.7–13.4), respectively].
Conclusions. Positive associations between vascular calcifications, vertebral fractures and mortality have been found in patients on HD.
haemodialysis; mortality; osteoporotic fractures; vascular calcifications; vertebral fractures