The objective of the current study was to determine if altered regulation of matrix metalloproteinases (MMPs) may predispose to extracellular matrix degradation, facilitating arterial calcification in chronic kidney disease (CKD) using a progressive model of CKD-MBD, the Cy/+ rat.
Sera were collected from normal or CKD rats at various times and MMP-2 and MMP-9 levels determined by ELISA or zymography. Aorta tissue was harvested at sacrifice for RT-PCR and immunostaining. Calcification of aorta rings was assessed with MMP inhibitors.
There was an increase in MMP-2, MMP-9, TIMP-1, and RUNX-2 expression in the aorta with progressive CKD, and increased MMP-2 activity in the serum. Immunostaining revealed increased expression of MMP-2 and MMP-9 in areas of aorta calcification. There was also an upregulation of MMP-2 and MMP-9 in vascular smooth muscle cells (VSMC) from CKD rats. MMP inhibitors decreased calcification of aorta rings from normal and CKD rats. High phosphorus increased MMP-2 and MMP-9 expressions in VSMC from normal rats but not from CKD rats.
MMP-2 and MMP-9 expression and activity are increased with progressive CKD, and blockade of MMP activity can inhibit arterial calcification. These data suggest degradation of the extracellular matrix is a critical step in the pathogenesis of arterial calcification in CKD.
Matrix metalloproteinase; Gelatinase; Vascular calcification; Chronic kidney disease
To investigate the osteogenic differentiation of vascular smooth muscle cells (VSMCs) in mice with chronic kidney disease (CKD) and to evaluate the effects of p53 on the osteogenic differentiation of the VSMCs.
Experimental models of CKD-associated vascular calcification generated by five-sixth (5/6) nephrectomy (Nx) and a high-phosphate (HP) diet were used in p53+/+ and p53–/– mice. Following 5/6 Nx, aortic calcification, markers of osteogenic differentiation, VSMCs and p53 protein in aortic tissues were studied.
Aortic calcification was observed after eight weeks following 5/6 Nx in mice of both genotypes, and expression of the markers of osteogenic differentiation in the VSMCs was increased. These changes were continuously observed up to 12 weeks after 5/6 Nx, and particularly after 5/6 Nx + HP. Compared with p53+/+ mice, aortic calcification in p53–/– mice was more severe (p < 0.001). Expression of the markers of osteogenic differentiation was noticeably increased (p < 0.001), while expression of the marker of VSMCs had decreased (p < 0.001). Statistical analysis demonstrated that the markers of osteogenic differentiation were negatively correlated with p53, and the marker of VSMCs was positively correlated with p53 (p < 0.001).
p53 has the potential to negatively regulate the osteogenic differentiation of VSMCs in CKD mice.
chronic kidney disease; mouse; osteogenic differentiation; P53; vascular smooth muscle cells
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
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
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
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 (CKD) is a public health problem, mediated by hemodynamic and non-hemodynamic events including oxidative stress. We investigated the effect of two glutathione (GSH) precursors, N-acetyl-cysteine (NAC) and cystine as the physiologic carrier of cysteine in GSH with added selenomethionine (F1) in preventing spermine (uremic toxin) induced apoptosis in cultured human aortic vascular smooth muscle cells (VSMC). VSMCs exposed to spermine (15 μM) with or without antioxidants (dose 50, 100, 200 and 500 μg/ml) were assessed for apoptosis, c-Jun-NH2-terminal kinase (JNK) activation and inducible nitric oxide synthase (iNOS) induction, and activation of intrinsic pathway signaling. Spermine exposure resulted in activation of JNK and iNOS induction, and apoptosis. NAC and F1 (dose range 50–500 μg/ml) attenuated spermine-induced acceleration of VSMC apoptosis, but only F1 (at 200 and 500 μg/ml) maintained spermine-induced apoptosis at control levels. Spermine-induced JNK activation was prevented by 200 μg/ml of both NAC and F1, while iNOS induction was blocked only by F1. Notably, the adverse effects of spermine on BAX/BCL-2 ratio, cytochrome c release, and caspase activation was fully attenuated by F1. In conclusion, F1 was more effective than NAC in preventing spermine-induced apoptosis and downstream changes in related signal transduction pathways in VSMCs. Further studies are needed to examine the effect of these compounds in preventing CKD-associated vascular disease.
Spermine; Apoptosis; vascular smooth muscle cells; antioxidants; chronic kidney disease
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
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.
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.
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.
Chronic kidney disease-mineral and bone disorder (CKD-MBD) defines a triad of interrelated abnormalities of serum biochemistry, bone and the vasculature associated with chronic kidney disease (CKD). The new kidney disease: improving global outcomes (KDIGO) guidelines define the quality and depth of evidence supporting therapeutic intervention in CKD-MBD. They also highlight where patient management decisions lack a strong evidence base. Expert interpretation of the guidelines, along with informed opinion, where evidence is weak, may help develop effective clinical practice. The body of evidence linking poor bone health and reservoir function (the ability of bone to buffer calcium and phosphorus) with vascular calcification and cardiovascular outcomes is growing. Treating renal bone disease should be one of the primary aims of therapy for CKD. Evaluation of the biochemical parameters of CKD-MBD (primarily phosphorus, calcium, parathyroid hormone and vitamin D levels) as early as CKD Stage 3, and an assessment of bone status (by the best means available), should be used to guide treatment decisions. The adverse effects of high phosphorus intake relative to renal clearance (including stimulation of hyperparathyroidism) precede hyperphosphatemia, which presents late in CKD. Early reduction of phosphorus load may ameliorate these adverse effects. Evidence that calcium load may influence progression of vascular calcification with effects on mortality should also be considered when choosing the type and dose of phosphate binder to be used. The risks, benefits, and strength of evidence for various treatment options for the abnormalities of CKD-MBD are considered.
kidney disease: improving global outcomes; chronic kidney disease; mineral and bone disorder; phosphorus; renal bone disease
Chronic kidney disease (CKD) patients present elevated advanced glycation end products (AGEs) blood levels. AGEs promote inflammation through binding to their receptor (RAGE), located on the membrane of mesangial cells, endothelial cells and macrophages. Several genetic polymorphisms influence RAGE transcription, expression and activity, including the substitution of a thymine with an adenine (T/A) in the position -374 of the gene promoter of RAGE. Our study investigates the role of -374 T/A RAGE polymorphism in CKD progression in subjects affected by nephrocardiovascular disease.
174 patients (119 males (68.4%) mean age 67.2±0.88 years; 55 females (31.6%): mean age 65.4±1.50 years) affected by mild to moderate nephrocardiovascular CKD were studied. Each subject was prospectively followed for 84 months, every 6–9 months. The primary endpoint of the study was a rise of serum creatinine concentrations above 50% of basal values or end stage renal disease.
Carriers of the A/A and T/A genotype presented higher plasma levels of interleukin 6 (A/A 29.5±15.83; T/A 30.0±7.89, vs T/T 12.3±5.04 p = 0.01 for both) and Macrophages chemoattractant protein 1 (A/A 347.1±39.87; T/A 411.8±48.41, vs T/T 293.5±36.20, p = 0.04 for both) than T/T subjects. Carriers of the A allele presented a faster CKD progression than wild type patients (Log-Rank test: Chi square = 6.84, p = 0,03). Cox regression showed that -374 T/A RAGE polymorphism (p = 0.037), albuminuria (p = 0.01) and LDL cholesterol (p = 0.038) were directly associated with CKD progression. HDL cholesterol (p = 0.022) and BMI (p = 0.04) were inversely related to it. No relationship was found between circulating RAGE and renal function decline.
-374 T/A RAGE polymorphism could be associated with CKD progression and inflammation. Further studies should confirm this finding and address whether inhibiting RAGE downstream signalling would be beneficial for CKD progression.
The elderly chronic kidney disease (CKD) population is growing. Both aging and CKD can disrupt calcium (Ca2+) homeostasis and cause alterations of multiple Ca2+-regulatory mechanisms, including parathyroid hormone, vitamin D, fibroblast growth factor-23/Klotho, calcium-sensing receptor and Ca2+-phosphate product. These alterations can be deleterious to bone mineral metabolism and soft tissue health, leading to metabolic bone disease and vascular calcification and aging, termed CKD-mineral and bone disorder (MBD). CKD-MBD is associated with morbid clinical outcomes, including fracture, cardiovascular events and all-cause mortality. In this paper, we comprehensively review Ca2+ regulation and bone mineral metabolism, with a special emphasis on elderly CKD patients. We also present the current treatment-guidelines and management options for CKD-MBD.
calcium homeostasis; aging; chronic kidney disease; mineral and bone disorder; vascular calcification; secondary hyperparathyroidism
Recent advances in our understanding of the excess mortality of chronic kidney disease (CKD) due to cardiovascular complications demonstrate through observational studies that vascular calcification and hyperphosphatemia are major cardiovascular risk factors. Mechanistic studies demonstrate that these two risk factors are related, and that hyperphosphatemia directly stimulates vascular calcification. The role of hyperphosphatemia in stimulating vascular calcification in CKD is associated with a block to the skeletal reservoir function in phosphate balance due to excess bone resorption. This has lead to the realization that renal osteodystrophy is linked to vascular calcification by disordered mineral homeostasis (phosphate), and that a multiorgan system fails in CKD leading to cardiovascular mortality. In children with renal disease the multiorgan system fails just as in adults, but the outcomes have been less well studied and perceptions of differences from adults are possibly incorrect. Vascular calcification and cardiovascular mortality are less prevalent but present. However, CKD induced vascular disease causes stiffness of the arterial tree causing systolic hypertension and left ventricular hypertrophy as early manifestations of the same pathology in the adult. Because of the role of the skeleton in these outcomes, renal osteodystrophy has been renamed as the CKD-mineral bone disorder (CKD-MBD). This review adapted to children describes our current state of knowledge with regards to the pathophysiology of the CKD-MBD, including the new discoveries related to early stages of CKD. As a new necessity, cardiovascular function issues are incorporated into the CKD-MBD, and new advances in our knowledge of this critical component of the disorder will lead to improved outcomes in CKD.
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
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
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
Vascular calcification is a common pathobiological process which occurs among
the elder population and in patients with diabetes and chronic kidney
disease. Osteoprotegerin, a secreted glycoprotein that regulates bone mass,
has recently emerged as an important regulator of the development of
vascular calcification. However, the mechanism is not fully understood. The
purpose of this study is to explore novel signaling mechanisms of
osteoprotegerin in the osteoblastic differentiation in rat aortic vascular
smooth muscle cells (VSMCs).
Methods and Results
VSMCs were isolated from thoracic aorta of Sprague Dawley rats. Osteoblastic
differentiation of VSMCs was induced by an osteogenic medium. We confirmed
by Von Kossa staining and direct cellular calcium measurement that
mineralization was significantly increased in VSMCs cultured in osteogenic
medium; consistent with an enhanced alkaline phosphatase activity. This
osteoblastic differentiation in VSMCs was significantly reduced by the
addition of osteoprotegerin in a dose responsive manner. Moreover, we
identified, by real-time qPCR and western blotting, that expression of
Notch1 and RBP-Jκ were significantly up-regulated in VSMCs cultured in
osteogenic medium at both the mRNA and protein levels, these effects were
dose-dependently abolished by the treatment of osteoprotegerin. Furthermore,
we identified that Msx2, a downstream target of the Notch1/RBP-Jκ signaling,
was markedly down-regulated by the treatment of osteoprotegerin.
Osteoprotegerin inhibits vascular calcification through the down regulation
of the Notch1-RBP-Jκ signaling pathway.