Serum fetuin-A concentration and fetuin-A-containing calciprotein particles in patients with chronic inflammatory disease and renal failure

Renal hyperparathyroidism- a risk factor in the development of encapsulating peritoneal sclerosis

Background

Encapsulating peritoneal sclerosis (EPS) is a rare complication of prolonged peritoneal dialysis (PD) exposure, characterised by peritoneal thickening, calcification, and fibrosis ultimately presenting with life-threatening bowel obstruction. The presence or role of peritoneal calcification in the pathogenesis of EPS is poorly characterised. We hypothesise that significantly aberrant bone mineral metabolism in patients on PD can cause peritoneal calcification which may trigger the development of EPS. We compared the temporal evolution of bone mineral markers during PD in EPS patients with non-EPS long-term PD controls.

Methods

Linear mixed model and logistic regression analysis were used to compare four-monthly serum levels of calcium, phosphate, parathyroid hormone, and alkaline phosphatase (ALP) over the duration of PD exposure in 46 EPS and 46 controls (PD, non-EPS) patients.

Results

EPS patients had higher mean calcium (2.51 vs. 2.41 mmol/L) and ALP (248.00 vs. 111.13 IU/L) levels compared with controls (p=0.01 and p<0.001 respectively, maximum likelihood estimation). Logistic regression analysis demonstrated that high serum calcium and phosphate levels during PD were associated with a 4.5 and 2.9 fold increase in the risk of developing EPS respectively.

Conclusion

High levels of calcium and phosphate in patients on PD were identified to be risk factors for EPS development. Possible reasons for this may be an imbalance of pro-calcifying factors and calcification inhibitors promoting peritoneal calcification which increases peritoneal stiffness. Mechanical alterations may trigger, unregulated fibrosis and subsequent development of EPS. Improved management of secondary hyperparathyroidism during PD may ultimately diminish the EPS risk.

The effects for inflammatory responses by CPP with different colloidal properties in hemodialysis patients

Calciprotein particles (CPPs) are colloids composed of solid-phase calcium-phosphate and serum protein fetuin-A. CPPs form a polydispersed system with different particle size and density. CPPs with specific physical properties can induce calcification and innate immune responses in cultured cells. In hemodialysis patients, blood CPP levels were reported to correlate with vascular calcification and inflammation. However, little is known about relation between these disorders and physical properties of CPPs. Here, we show that the association between physical properties of plasma CPPs and serum levels of inflammatory cytokines/chemokines in 78 hemodialysis out-patients by cross-sectional study. Patients with cardiovascular disease (CVD) had significantly higher high density CPP (H-CPP) levels than patients without CVD but not low density CPP (L-CPP). Seven cytokines/chemokines (EGF, eotaxin, IL-8, IP-10, MCP-1, MIP-1, MIP-1β and TNFα) were detectable in the serum samples from > 95% of the patients. In multivariate regression analysis, H-CPP was positively associated with eotaxin after adjusting for age, gender, smoking, serum phosphate and FGF23. L-CPP was negatively associated with IL-8 after adjusting for age, gender, serum albumin, phosphate and FGF23. High H-CPP levels were associated with pro-inflammatory response, whereas L-CPPs were associated with anti-inflammatory response. CPPs with different physical properties may impact differently on pathophysiology in HD patients.

Vascular Calcification: In Vitro Models under the Magnifying Glass

Vascular calcification is a systemic disease contributing to cardiovascular morbidity and mortality. The pathophysiology of vascular calcification involves calcium salt deposition by vascular smooth muscle cells that exhibit an osteoblast-like phenotype. Multiple conditions drive the phenotypic switch and calcium deposition in the vascular wall; however, the exact molecular mechanisms and the connection between vascular smooth muscle cells and other cell types are not fully elucidated. In this hazy landscape, effective treatment options are lacking. Due to the pathophysiological complexity, several research models are available to evaluate different aspects of the calcification process. This review gives an overview of the in vitro cell models used so far to study the molecular processes underlying vascular calcification. In addition, relevant natural and synthetic compounds that exerted anticalcifying properties in in vitro systems are discussed.

Reversal Of Arterial Disease by modulating Magnesium and Phosphate (ROADMAP-study): rationale and design of a randomized controlled trial assessing the effects of magnesium citrate supplementation and phosphate-binding therapy on arterial stiffness in moderate chronic kidney disease

Background

Arterial stiffness and calcification propensity are associated with high cardiovascular risk and increased mortality in chronic kidney disease (CKD). Both magnesium and phosphate are recognized as modulators of vascular calcification and chronic inflammation, both features of CKD that contribute to arterial stiffness. In this paper, we outline the rationale and design of a randomized controlled trial (RCT) investigating whether 24 weeks of oral magnesium supplementation with or without additional phosphate-binding therapy can improve arterial stiffness and calcification propensity in patients with stage 3–4 CKD.

Methods

In this multi-center, placebo-controlled RCT, a total of 180 participants with an estimated glomerular filtration rate of 15 to 50 ml/min/1.73 m2 without phosphate binder therapy will be recruited. During the 24 weeks intervention, participants will be randomized to one of four intervention groups to receive either magnesium citrate (350 mg elemental magnesium/day) or placebo, with or without the addition of the phosphate binder sucroferric oxyhydroxide (1000 mg/day). Primary outcome of the study is the change of arterial stiffness measured by the carotid-femoral pulse wave velocity over 24 weeks. Secondary outcomes include markers of calcification and inflammation, among others calcification propensity (T50) and high-sensitivity C-reactive protein. As explorative endpoints, repeated 18F-FDG and 18F-NaF PET-scans will be performed in a subset of participants (n = 40). Measurements of primary and secondary endpoints are performed at baseline, 12 and 24 weeks.

Discussion

The combined intervention of magnesium citrate supplementation and phosphate-lowering therapy with sucroferric oxyhydroxide, in stage 3–4 CKD patients without overt hyperphosphatemia, aims to modulate the complex and deregulated mineral metabolism leading to vascular calcification and arterial stiffness and to establish to what extent this is mediated by T50 changes. The results of this combined intervention may contribute to future early interventions for CKD patients to reduce the risk of CVD and mortality.

Trial registration

Netherlands Trial Register, NL8252 (registered December 2019), EU clinical Trial Register 2019-001306-23 (registered November 2019).

Reduced hip bone mineral density is associated with high levels of calciprotein particles in patients with Fabry disease

Calciprotein particles (CPP) are nanoscale mineralo-protein aggregates that help stabilize excess mineral in the circulation. We examined the relationship between CPP and bone mineral density in Fabry disease patients. We found an inverse correlation with total hip and femoral neck density, but none with lumbar spine.

PURPOSE

Calciprotein particles (CPP) are colloidal mineral-protein complexes made up primarily of the circulating glycoprotein fetuin-A, calcium, and phosphate. They form in extracellular fluid and facilitate the stabilization, transport, and clearance of excess minerals from the circulation. While most are monomers, they also exist in larger primary (CPP-I) and secondary (CPP-II) form, both of which are reported to be raised in pathological states. This study sought to investigate CPP levels in the serum of patients with Fabry disease, an X-linked systemic lysosomal storage disorder that is associated with generalized inflammation and low bone mineral density (BMD).

METHODS

We compared serum CPP-I and CPP-II levels in 59 patients with Fabry disease (37 female) with levels in an age-matched healthy adult cohort (n=28) and evaluated their association with BMD and biochemical data obtained from routine clinical review.

RESULTS

CPP-I and CPP-II levels were higher in male Fabry disease patients than female sufferers as well as their corresponding sex- and age-matched controls. CPP-II levels were inversely correlated with BMD at the total hip and femoral neck, but not the lumbar spine. Regression analyses revealed that these associations were independent of common determinants of BMD, but at the femoral neck, a significant association was only found in female patients.

CONCLUSION

Low hip BMD was associated with high CPP-II in patients with Fabry disease, but further work is needed to investigate the relevance of sex-related differences and to establish whether CPP measurement may aid assessment of bone disease in this setting.

Vascular Calcification Is Associated with Fetuin-A and Cortical Bone Porosity in Stone Formers

Background: Nephrolithiasis has been associated with bone loss and vascular calcification (VC), reflecting abnormal extraosseous calcium deposition. Fetuin-A (Fet-A) acts as a potent inhibitor of ectopic mineralization. The aim of the present study was to evaluate the prevalence of VC in stone formers (SF) and non-stone formers (NSF) and to investigate potential determinants of VC among SF, including circulating levels of Fet-A and bone microarchitecture parameters. Methods: Abdominal aortic calcification (AAC) was assessed using available computed tomography in SF and in age-, sex-, and BMI-matched NSF (potential living kidney donors). Serum Fet-A was measured in stored blood samples from SF. Bone microarchitecture parameters were obtained as a post hoc analysis of a cross-sectional cohort from young SF evaluated by high-resolution peripheral quantitative computed tomography (HR-pQCT). Results: A total of 62 SF (38.0 [28.0−45.3] years old) and 80 NSF (40.0 [37.0−45.8] years old) were included. There was no significant difference in AAC scores between SF and NSF. However, when dividing SF according to mean AAC score, below <5.8% (n = 33) or above ≥5.8% (n = 29), SF with higher AAC presented significantly higher BMI and tibial cortical porosity (Ct.Po) and significantly lower serum HDL, klotho, Fet-A, and eGFR. Urinary calcium did not differ between groups, but fractional excretion of phosphate was higher in the former. Upon multivariate regression, BMI, serum Fet-A, and tibial Ct.Po remained independently associated with AAC. Conclusions: This study suggests an association between reduced circulating Fet-A levels and increased bone Ct.Po with VC in SF.

Models and Techniques to Study Aortic Valve Calcification in Vitro, ex Vivo and in Vivo. An Overview

Aortic valve stenosis secondary to aortic valve calcification is the most common valve disease in the Western world. Calcification is a result of pathological proliferation and osteogenic differentiation of resident valve interstitial cells. To develop non-surgical treatments, the molecular and cellular mechanisms of pathological calcification must be revealed. In the current overview, we present methods for evaluation of calcification in different ex vivo, in vitro and in vivo situations including imaging in patients. The latter include echocardiography, scanning with computed tomography and magnetic resonance imaging. Particular emphasis is on translational studies of calcific aortic valve stenosis with a special focus on cell culture using human primary cell cultures. Such models are widely used and suitable for screening of drugs against calcification. Animal models are presented, but there is no animal model that faithfully mimics human calcific aortic valve disease. A model of experimentally induced calcification in whole porcine aortic valve leaflets ex vivo is also included. Finally, miscellaneous methods and aspects of aortic valve calcification, such as, for instance, biomarkers are presented.

Effect of nutritional calcium and phosphate loading on calciprotein particle kinetics in adults with normal and impaired kidney function

Plasma approaches metastability with respect to its calcium and phosphate content, with only minor perturbations in ionic activity needed to sustain crystal growth once nucleated. Physiologically, calcium and phosphate are intermittently absorbed from the diet each day, yet plasma concentrations of these ions deviate minimally post-prandially. This implies the existence of a blood-borne mineral buffer system to sequester calcium phosphates and minimise the risk of deposition in the soft tissues. Calciprotein particles (CPP), endogenous mineral-protein colloids containing the plasma protein fetuin-A, may fulfill this function but definitive evidence linking dietary mineral loading with their formation is lacking. Here we demonstrate that CPP are formed as a normal physiological response to feeding in healthy adults and that this occurs despite minimal change in conventional serum mineral markers. Further, in individuals with Chronic Kidney Disease (CKD), in whom mineral handling is impaired, we show that both fasting and post-prandial levels of CPP precursors are markedly augmented and strongly inversely correlated with kidney function. This study highlights the important, but often neglected, contribution of colloidal biochemistry to mineral homeostasis and provides novel insight into the dysregulation of mineral metabolism in CKD.

Association of circulating calciprotein particle levels with skeletal muscle mass and strength in middle-aged and older adults

Calciprotein particles (CPPs) are tiny mineral-protein aggregates consisting of calcium-phosphate and fetuin-A. Recent studies have suggested that CPPs may contribute to the pathogenesis of chronic inflammation and arteriosclerosis. Reduced skeletal muscle mass and strength reportedly contribute independently to increased serum phosphate levels. This finding suggests that reduced skeletal muscle mass and strength can endogenously induce an increase in circulating CPP levels. Therefore, we investigated the potential association between circulating CPP levels and skeletal muscle mass and strength in middle-aged and older adults. One hundred eighty-two middle-aged and older adults (age, 46-83 years) were included in this cross-sectional study (UMIN000034741). Circulating CPP levels were measured using the gel filtration method. Appendicular skeletal muscle mass was assessed using multifrequency bioelectrical impedance analysis with a tetrapolar eight-point tactile electrode system. The skeletal muscle mass index was calculated from appendicular skeletal muscle mass and height. Handgrip and knee extension strengths were used as measures of skeletal muscle strength. The skeletal muscle mass index was negatively correlated with circulating CPP levels (r = -0.31; P < 0.05). This association remained significant after adjustment for potential covariates (β = -0.34; P < 0.05). In contrast, skeletal muscle strength, represented by handgrip strength and knee extension strength, was not significantly associated with circulating CPP levels. In middle-aged and older adults, a lower skeletal muscle mass index was independently associated with higher circulating CPP levels. The present results suggest that maintaining skeletal muscle mass may prevent an increase in circulating CPP levels.

Non-Uremic Calciphylaxis: An Unexpected Complication With Recombinant Human Parathyroid Hormone

Calciphylaxis is a rare syndrome of calcific microvascular occlusion, whereas non-uremic calciphylaxis (NUC) is a subset of this disease in which renal impairment is not observed. Recombinant human parathyroid hormone (rhPTH) (1-84) is a medication approved for the management of hypocalcemia in patients with hypoparathyroidism. We present a case report of a 38-year-old woman with postoperative hypoparathyroidism treated with rhPTH who subsequently developed calciphylactic lesions on her abdomen. Multidisciplinary interventions included intravenous and intralesional sodium thiosulfate therapy, laboratory monitoring, dermatological wound care, and pain management. Calciphylaxis can rarely be precipitated by rhPTH due to its effect on calcium and phosphorus balance even in the setting of normal renal function. The use of calcium and calcitriol supplementation, complicated by factors such as female sex and obesity, may have contributed in this patient’s case. Hence, regular follow-up with tapering off of calcium and calcitriol supplementation is important in patients receiving rhPTH.

Reduction of Calciprotein Particles in Adults Receiving Infliximab for Chronic Inflammatory Disease

Patients with chronic inflammatory diseases (CID) experience accelerated loss of bone mineral density, which is often accompanied by increased vascular calcification. These disturbances can be attenuated by therapies for inflammation, such as the tumor necrosis factor inhibitor infliximab. Calciprotein particles (CPP) are circulating colloidal aggregates of calcium and phosphate together with the mineral-binding protein fetuin-A, which have emerged as potential mediators of vascular calcification. The precise origins of serum CPP are unclear, but bone turnover may be an important source. In this longitudinal observational study, we studied patients with CID undergoing treatment with infliximab to assess the temporal relationship between bone turnover and circulating CPP. Ten patients with active CID receiving infliximab induction therapy and an additional 3 patients with quiescent CID on maintenance infliximab therapy were studied for 8 weeks with repeated measures of bone turnover markers as well as CPP (calciprotein monomers [CPM], primary CPP [CPP-I], and secondary CPP [CPP-II]). Therapeutic response was appraised using validated disease activity scores. At baseline, those with active CID had elevated markers of bone resorption and suppressed bone formation markers as well as higher CPM and CPP-I compared with those with quiescent CID. In responders, there was an early but transient reduction in resorption markers by week 1, but a more sustained increase in bone formation markers compared with non-responders at week 8. This was accompanied by reductions in CPM (β = -6.5 × 10³ AU [95% CI -11.1, -1.8], p = 0.006) and CPP-I (β = -23.4 × 10⁴ particles/mL [95% CI -34.8, -11.9], p < 0.001). In contrast, no significant changes in any markers were observed in non-responders or those receiving maintenance therapy. Thus, CPP have a dynamic association with changes in bone turnover in response to infliximab therapy, adding to accumulating evidence of the role of bone as a determinant of systemic levels. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Calciprotein Particles: Balancing Mineral Homeostasis and Vascular Pathology

[Figure: see text].

Effects of fetuin-A-containing calciprotein particles on posttranslational modifications of fetuin-A in HepG2 cells

Fetuin-A is an inhibitor of ectopic calcification that is expressed mainly in hepatocytes and is secreted into the circulation after posttranslational processing, including glycosylation and phosphorylation. The molecular weight (MW) of fully modified fetuin-A (FM-fetuin-A) is approximately 60 kDa in an immunoblot, which is much higher than the estimated MW by amino acid sequence. Under conditions of calcification stress such as advanced stage chronic kidney disease, fetuin-A prevents calcification by forming colloidal complexes, which are referred to as calciprotein particles (CPP). Since the significance of CPP in this process is unclear, we investigated the effect of synthetic secondary CPP on the level of FM-fetuin-A in HepG2 cells. Secondary CPP increased the level of FM-fetuin-A in dose- and time-dependent manners, but did not affect expression of mRNA for fetuin-A. Treatment with O- and/or N-glycosidase caused a shift of the 60 kDa band of FM-fetuin-A to a lower MW. Preincubation with brefeldin A, an inhibitor of transport of newly synthesized proteins from the endoplasmic reticulum to the Golgi apparatus, completely blocked the secondary CPP-induced increase in FM-fetuin-A. Treatment with BAPTA-AM, an intracellular calcium chelating agent, also inhibited the CPP-induced increase in the FM-fetuin-A level. Secondary CPP accelerate posttranslational processing of fetuin-A in HepG2 cells.

Magnesium to prevent kidney disease-associated vascular calcification: crystal clear?

Vascular calcification is a prognostic marker for cardiovascular mortality in chronic kidney disease (CKD) patients. In these patients, magnesium balance is disturbed, mainly due to limited ultrafiltration of this mineral, changes in dietary intake and the use of diuretics. Observational studies in dialysis patients report that a higher blood magnesium concentration is associated with reduced risk to develop vascular calcification. Magnesium prevents osteogenic vascular smooth muscle cell transdifferentiation in in vitro and in vivo models. In addition, recent studies show that magnesium prevents calciprotein particle maturation, which may be the mechanism underlying the anti-calcification properties of magnesium. Magnesium is an essential protective factor in the calcification milieu, which helps to restore the mineral-buffering system that is overwhelmed by phosphate in CKD patients. The recognition that magnesium is a modifier of calciprotein particle maturation and mineralization of the extracellular matrix renders it a promising novel clinical tool to treat vascular calcification in CKD. Consequently, the optimal serum magnesium concentration for patients with CKD may be higher than in the general population.

Calciprotein particle inhibition explains magnesium-mediated protection against vascular calcification

Background

Phosphate (Pi) toxicity is a strong determinant of vascular calcification development in chronic kidney disease (CKD). Magnesium (Mg²⁺) may improve cardiovascular risk via vascular calcification. The mechanism by which Mg²⁺ counteracts vascular calcification remains incompletely described. Here we investigated the effects of Mg²⁺ on Pi and secondary crystalline calciprotein particles (CPP2)-induced calcification and crystal maturation.

Methods

Vascular smooth muscle cells (VSMCs) were treated with high Pi or CPP2 and supplemented with Mg²⁺ to study cellular calcification. The effect of Mg²⁺ on CPP maturation, morphology and composition was studied by medium absorbance, electron microscopy and energy dispersive spectroscopy. To translate our findings to CKD patients, the effects of Mg²⁺ on calcification propensity (T₅₀) were measured in sera from CKD patients and healthy controls.

Results

Mg²⁺ supplementation prevented Pi-induced calcification in VSMCs. Mg²⁺ dose-dependently delayed the maturation of primary CPP1 to CPP2 in vitro. Mg²⁺ did not prevent calcification and associated gene and protein expression when added to already formed CPP2. Confirmatory experiments in human serum demonstrated that the addition of 0.2 mmol/L Mg²⁺ increased T₅₀ from healthy controls by 51 ± 15 min (P < 0.05) and CKD patients by 44 ± 13 min (P < 0.05). Each further 0.2 mmol/L addition of Mg²⁺ led to further increases in both groups.

Conclusions

Our results demonstrate that crystalline CPP2 mediates Pi-induced calcification in VSMCs. In vitro, Mg²⁺ delays crystalline CPP2 formation and thereby prevents Pi-induced calcification.

Mud in the blood: the role of protein-mineral complexes and extracellular vesicles in biomineralisation and calcification

Protein-mineral interaction is known to regulate biomineral stability and morphology. We hypothesise that fluid phases produce highly dynamic protein-mineral complexes involved in physiology and pathology of biomineralisation. Here, we specifically focus on calciprotein particles, complexes of vertebrate mineral-binding proteins and calcium phosphate present in the systemic circulation and abundant in extracellular fluids - hence the designation of the ensuing protein-mineral complexes as "mud in the blood". These complexes exist amongst other extracellular particles that we collectively refer to as "the particle zoo".

Calciprotein Particles and Serum Calcification Propensity: Hallmarks of Vascular Calcifications in Patients with Chronic Kidney Disease

Cardiovascular complications are one of the leading causes of mortality worldwide and are strongly associated with atherosclerosis and vascular calcification (VC). Patients with chronic kidney disease (CKD) have a higher prevalence of VC as renal function declines, which will result in increased mortality. Serum calciprotein particles (CPPs) are colloidal nanoparticles that have a prominent role in the initiation and progression of VC. The T₅₀ test is a novel test that measures the conversion of primary to secondary calciprotein particles indicating the tendency of serum to calcify. Therefore, we accomplished a comprehensive review as the first integrated approach to clarify fundamental aspects that influence serum CPP levels and T₅₀, and to explore the effects of CPP and calcification propensity on various chronic disease outcomes. In addition, new topics were raised regarding possible clinical uses of T₅₀ in the assessment of VC, particularly in patients with CKD, including possible opportunities in VC management. The relationships between serum calcification propensity and cardiovascular and all-cause mortality were also addressed. The review is the outcome of a comprehensive search on available literature and could open new directions to control VC.

Vascular Calcification-New Insights Into Its Mechanism

Vascular calcification (VC), which is categorized by intimal and medial calcification, depending on the site(s) involved within the vessel, is closely related to cardiovascular disease. Specifically, medial calcification is prevalent in certain medical situations, including chronic kidney disease and diabetes. The past few decades have seen extensive research into VC, revealing that the mechanism of VC is not merely a consequence of a high-phosphorous and -calcium milieu, but also occurs via delicate and well-organized biologic processes, including an imbalance between osteochondrogenic signaling and anticalcific events. In addition to traditionally established osteogenic signaling, dysfunctional calcium homeostasis is prerequisite in the development of VC. Moreover, loss of defensive mechanisms, by microorganelle dysfunction, including hyper-fragmented mitochondria, mitochondrial oxidative stress, defective autophagy or mitophagy, and endoplasmic reticulum (ER) stress, may all contribute to VC. To facilitate the understanding of vascular calcification, across any number of bioscientific disciplines, we provide this review of a detailed updated molecular mechanism of VC. This encompasses a vascular smooth muscle phenotypic of osteogenic differentiation, and multiple signaling pathways of VC induction, including the roles of inflammation and cellular microorganelle genesis.

Lumenal calcification and microvasculopathy in fetuin-A-deficient mice lead to multiple organ morbidity

The plasma protein fetuin-A mediates the formation of protein-mineral colloids known as calciprotein particles (CPP)-rapid clearance of these CPP by the reticuloendothelial system prevents errant mineral precipitation and therefore pathological mineralization (calcification). The mutant mouse strain D2,Ahsg-/- combines fetuin-A deficiency with the calcification-prone DBA/2 genetic background, having a particularly severe compound phenotype of microvascular and soft tissue calcification. Here we studied mechanisms leading to soft tissue calcification, organ damage and death in these mice. We analyzed mice longitudinally by echocardiography, X-ray-computed tomography, analytical electron microscopy, histology, mass spectrometry proteomics, and genome-wide microarray-based expression analyses of D2 wildtype and Ahsg-/- mice. Fetuin-A-deficient mice had calcified lesions in myocardium, lung, brown adipose tissue, reproductive organs, spleen, pancreas, kidney and the skin, associated with reduced growth, cardiac output and premature death. Importantly, early-stage calcified lesions presented in the lumen of the microvasculature suggesting precipitation of mineral containing complexes from the fluid phase of blood. Genome-wide expression analysis of calcified lesions and surrounding (not calcified) tissue, together with morphological observations, indicated that the calcification was not associated with osteochondrogenic cell differentiation, but rather with thrombosis and fibrosis. Collectively, these results demonstrate that soft tissue calcification can start by intravascular mineral deposition causing microvasculopathy, which impacts on growth, organ function and survival. Our study underscores the importance of fetuin-A and related systemic regulators of calcified matrix metabolism to prevent cardiovascular disease, especially in dysregulated mineral homeostasis.

The effect of increasing dialysate magnesium on calciprotein particles, inflammation and bone markers: post hoc analysis from a randomized controlled clinical trial

Background

The formation of calciprotein particles (CPPs) may be an important component of the humoral defences against ectopic calcification. Although magnesium (Mg) has been shown to delay the transition of amorphous calcium-/phosphate-containing primary CPP (CPP-1) to crystalline apatite-containing secondary CPP (CPP-2) ex vivo, effects on the endogenous CPP pool are unknown.

Methods

We used post hoc analyses from a randomized double-blind parallel-group controlled clinical trial of 28 days treatment with high dialysate Mg of 2.0 mEq/L versus standard dialysate Mg of 1.0 mEq/L in 57 subjects undergoing maintenance hemodialysis for end-stage kidney disease. CPP load, markers of systemic inflammation and bone turnover were measured at baseline and follow-up.

Results

After 28 days of treatment with high dialysate Mg, serum total CPP (−52%), CPP-1 (−42%) and CPP-2 (−68%) were lower in the high Mg group (all P &lt; 0.001) but were unchanged in the standard dialysate Mg group. Tumour necrosis factor-α (−20%) and interleukin-6 (−22%) were also reduced with high dialysate Mg treatment (both P &lt; 0.01). High dialysate Mg resulted in higher levels of bone-specific alkaline phosphatase (a marker of bone formation) (+17%) but lower levels of tartrate-resistant acid phosphatase 5 b (a marker of bone resorption; −33%) (both P &lt; 0.01). Inflammatory cytokines and bone turnover markers were unchanged in the standard dialysate Mg group over the same period.

Conclusions

In this exploratory analysis, increasing dialysate Mg was associated with reduced CPP load and systemic inflammation and divergent changes in markers of bone formation and resorption.

Serum Calcification Propensity and Clinical Events in CKD

BACKGROUND AND OBJECTIVES

Patients with CKD are at high risk for cardiovascular disease, ESKD, and mortality. Vascular calcification is one pathway through which cardiovascular disease risks are increased. We hypothesized that a novel measure of serum calcification propensity is associated with cardiovascular disease events, ESKD, and all-cause mortality among patients with CKD stages 2-4.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Among 3404 participants from the prospective, longitudinal Chronic Renal Insufficiency Cohort Study, we quantified calcification propensity as the transformation time (T₅₀) from primary to secondary calciprotein particles, with lower T₅₀ corresponding to higher calcification propensity. We used multivariable-adjusted Cox proportional hazards regression models to assess the associations of T₅₀ with risks of adjudicated atherosclerotic cardiovascular disease events (myocardial infarction, stroke, and peripheral artery disease), adjudicated heart failure, ESKD, and mortality.

RESULTS

The mean T₅₀ was 313 (SD 79) minutes. Over an average 7.1 (SD 3.1) years of follow-up, we observed 571 atherosclerotic cardiovascular disease events, 633 heart failure events, 887 ESKD events, and 924 deaths. With adjustment for traditional cardiovascular disease risk factors, lower T₅₀ was significantly associated with higher risk of atherosclerotic cardiovascular disease (hazard ratio [HR] per SD lower T₅₀, 1.14; 95% confidence interval [95% CI], 1.05 to 1.25), ESKD within 3 years from baseline (HR per SD lower T₅₀, 1.68; 95% CI, 1.52 to 1.86), and all-cause mortality (HR per SD lower T₅₀, 1.16; 95% CI, 1.09 to 1.24), but not heart failure (HR per SD lower T₅₀, 1.06; 95% CI, 0.97 to 1.15). After adjustment for eGFR and 24-hour urinary protein, T₅₀ was not associated with risks of atherosclerotic cardiovascular disease, ESKD, and mortality.

CONCLUSIONS

Among patients with CKD stages 2-4, higher serum calcification propensity is associated with atherosclerotic cardiovascular disease events, ESKD, and all-cause mortality, but this association was not independent of kidney function.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_10_28_CJN04710419.mp3.

The interplay between mineral metabolism, vascular calcification and inflammation in Chronic Kidney Disease (CKD): challenging old concepts with new facts

Chronic kidney disease (CKD) is one of the most powerful predictors of premature cardiovascular disease (CVD), with heightened susceptibility to vascular intimal and medial calcification associated with a high cardiovascular mortality. Abnormal mineral metabolism of calcium (Ca) and phosphate (P) and underlying (dys)regulated hormonal control in CKD-mineral and bone disorder (MBD) is often accompanied by bone loss and increased vascular calcification (VC). While VC is known to be a multifactorial process and a major risk factor for CVD, the view of primary triggers and molecular mechanisms complexity has been shifting with novel scientific knowledge over the last years. In this review we highlight the importance of calcium-phosphate (CaP) mineral crystals in VC with an integrated view over the complexity of CKD, while discuss past and recent literature aiming to highlight novel horizons on this major health burden. Exacerbated VC in CKD patients might result from several interconnected mechanisms involving abnormal mineral metabolism, dysregulation of endogenous calcification inhibitors and inflammatory pathways, which function in a feedback loop driving disease progression and cardiovascular outcomes. We propose that novel approaches targeting simultaneously VC and inflammation might represent valuable new prognostic tools and targets for therapeutics and management of cardiovascular risk in the CKD population.

Serum Calcification Propensity and Coronary Artery Calcification Among Patients With CKD: The CRIC (Chronic Renal Insufficiency Cohort) Study

RATIONALE & OBJECTIVE

Coronary artery calcification (CAC) is prevalent among patients with chronic kidney disease (CKD) and increases risks for cardiovascular disease events and mortality. We hypothesized that a novel serum measure of calcification propensity is associated with CAC among patients with CKD stages 2 to 4.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

Participants from the Chronic Renal Insufficiency Cohort (CRIC) Study with baseline (n=1,274) and follow-up (n=780) CAC measurements.

PREDICTORS

Calcification propensity, quantified as transformation time (T₅₀) from primary to secondary calciprotein particles, with lower T₅₀ corresponding to higher calcification propensity. Covariates included age, sex, race/ethnicity, clinical site, estimated glomerular filtration rate, proteinuria, diabetes, systolic blood pressure, number of antihypertensive medications, current smoking, history of cardiovascular disease, total cholesterol level, and use of statin medications.

OUTCOMES

CAC prevalence, severity, incidence, and progression.

ANALYTICAL APPROACH

Multivariable-adjusted generalized linear models.

RESULTS

At baseline, 824 (65%) participants had prevalent CAC. After multivariable adjustment, T₅₀ was not associated with CAC prevalence but was significantly associated with greater CAC severity among participants with prevalent CAC: 1-SD lower T₅₀ was associated with 21% (95% CI, 6%-38%) greater CAC severity. Among 780 participants followed up an average of 3 years later, 65 (20%) without baseline CAC developed incident CAC, while 89 (19%) with baseline CAC had progression, defined as annual increase≥100 Agatston units. After multivariable adjustment, T₅₀ was not associated with incident CAC but was significantly associated with CAC progression: 1-SD lower T₅₀ was associated with 28% (95% CI, 7%-53%) higher risk for CAC progression.

LIMITATIONS

Potential selection bias in follow-up analyses; inability to distinguish intimal from medial calcification.

CONCLUSIONS

Among patients with CKD stages 2 to 4, higher serum calcification propensity is associated with more severe CAC and CAC progression.

Clinical implications of fetuin-A

Fetuin-A, also termed alpha2-Heremans-Schmid glycoprotein, is a 46kDa hepatocyte derived protein (hepatokine) and serves multifaceted functions.

Are Fetuin-A levels beneficial for estimating timing of sepsis occurrence?

Objectives:

To evaluated Fetuin-A levels of patients admitted in the intensive care unit with a diagnosis of sepsis.

Methods:

This study was conducted at the Faculty of Medicine, Çanakkale Onsekiz Mart University Hospital, Çanakkal, Turkey, between February 2015 and October 2015. Forty septic patients were included in the study. Subsequent to clinical suspicion of sepsis, serum levels of C-reactive protein (CRP) and procalcitonin; and white blood cell (WBC) counts were evaluated at 3 time-points: 0 (basal), 24, and 72 hours.

Results:

The mean Fetuin-A levels at the 3 time-points were 58.5 ± 29.2 ng/mL, 40.9 ± 23.6 ng/mL, and 47.8 ± 25.7 ng/mL, respectively. Fetuin-A levels at 24 hours were significantly lower than the basal level (p<0.05), where as no significant difference was observed between the basal levels and those at 72 hours (p>0.05). Correlation between the temporal changes in Fetuin-A levels and the changes in other inflammatory markers (CRP, procalcitonin and WBC) was examined. Fetuin A was found to have only a negative correlation with serum procalcitonin level (p<0.05).

Conclusion:

In this study, serum Fetuin-A levels in septic patients decreased significantly in the first 24 hours, followed by an insignificant increase at 72 hours. These findings suggest that monitoring of Fetuin-A levels may help predict the time of occurrence of sepsis and prognosis of sepsis.

Cellular Clearance and Biological Activity of Calciprotein Particles Depend on Their Maturation State and Crystallinity

Background: The liver-derived plasma protein fetuin-A is a systemic inhibitor of ectopic calcification. Fetuin-A stabilizes saturated mineral solutions by forming colloidal protein-mineral complexes called calciprotein particles (CPP). CPP are initially spherical, amorphous and soft, and are referred to as primary CPP. These particles spontaneously convert into secondary CPP, which are larger, oblongate, more crystalline, and less soluble. CPP mediate excess mineral transport and clearance from circulation. Methods: We studied by intravital two-photon microscopy the clearance of primary vs. secondary CPP by injecting i.v. synthetic fluorescent CPP in mice. We analyzed CPP organ distribution and identified CPP endocytosing cells by immunofluorescence. Cellular clearance was studied using bone marrow-derived mouse wildtype and scavenger receptor A (SRA)-deficient macrophages, as well as human umbilical cord endothelial cells (HUVEC), monocyte-derived macrophages (hMDM), and human aortic endothelial cells (haEC). We employed mouse wildtype and mutant immortalized macrophages to analyze CPP-induced inflammasome activation and cytokine secretion. Results: In live mice, only primary CPP were rapidly cleared by liver sinusoidal endothelial cells (LSEC), whereas primary and secondary CPP were cleared by Kupffer cells. Scavenger receptor A (SRA)-deficient bone marrow macrophages endocytosed secondary CPP less well than did wildtype macrophages. In contrast, primary CPP endocytosis did not depend on the presence of SRA, suggesting involvement of an alternative clearance pathway. CPP triggered TLR4 dependent TNFα and IL-1β secretion in cultured macrophages. Calcium content-matched primary CPP caused twice more IL-1β secretion than did secondary CPP, which was associated with increased calcium-dependent inflammasome activation, suggesting that intracellular CPP dissolution and calcium overload may cause this inflammation. Conclusions: Secondary CPP are endocytosed by macrophages in liver and spleen via SRA. In contrast, our results suggest that primary CPP are cleared by LSEC via an alternative pathway. CPP induced TLR4-dependent TNFα and inflammasome-dependent IL-1β secretion in macrophages suggesting that inflammation and calcification may be considered consequences of prolonged CPP presence and clearance.

Longitudinal changes in bone and mineral metabolism after cessation of cinacalcet in dialysis patients with secondary hyperparathyroidism

BACKGROUND

The calcimimetic agent cinacalcet is effective for the management of secondary hyperparathyroidism (SHPT) in dialysis patients. Changes to reimbursement of cinacalcet in Australia provided an opportunity to assess effects of medication cessation on biochemical and clinical outcomes in dialysis patients, including changes to novel biomarkers such as calciprotein particles (CPP). CPP are nanoparticles of mineral and protein in the circulation associated with increased vascular calcification in patients with chronic kidney disease.

METHODS

Dialysis patients from a single center who ceased cinacalcet between August 2015 and March 2016 were included in a prospective observational study. Bloods were taken at the time of cessation of cinacalcet and at 1, 6 and 12 months. Clinical and biochemical outcomes were compared with an age- and gender-matched cohort of cinacalcet-naïve dialysis patients.

RESULTS

Sixty-two patients participated in the study. Mean age was 69.6 ± 13.2 years. Biochemical changes over 12 months following cessation of cinacalcet included an increase in serum parathyroid hormone (PTH) (42.2 [IQR 27.8-94.6] pmol/L to 114.8 [83.9-159.1] pmol/L [p < 0.001]), serum calcium (2.31 ± 0.21 mmol/L to 2.46 ± 0.14 mmol/L [p < 0.001]) and primary CPP (CPP-I) (p = 0.002). Changes in CPP were associated with an increase in PTH (p = 0.007), calcium (p = 0.002) and ferritin (p = 0.02) but a reduction in serum albumin (p = 0.001). Over the 12-month period, there were two fractures, five cardiovascular events, one episode of calciphylaxis, and one parathyroidectomy, with a mortality rate of 19% (n = 13).

CONCLUSION

Uniquely we report the effects of cinacalcet withdrawal in a real world setting with demonstrated increases in PTH, serum calcium and CPP subsets, novel CKD-MBD related factors, over a 12-month period.

Biochemical transformation of calciprotein particles in uraemia

Calciprotein particles (CPP) have emerged as nanoscale mediators of phosphate-induced toxicity in Chronic Kidney Disease (CKD). Uraemia favors ripening of the particle mineral content from the amorphous (CPP-I) to the crystalline state (CPP-II) but the pathophysiological significance of this transformation is uncertain. Clinical studies suggest an association between CPP ripening and inflammation, vascular dysfunction and mortality. Although ripening has been modelled in vitro, it is unknown whether particles synthesised in serum resemble their in vivo counterparts. Here we show that in vitro formation and ripening of CPP in uraemic serum is characterised by extensive physiochemical rearrangements involving the accretion of mineral, loss of surface charge and transformation of the mineral phase from a spherical arrangement of diffuse domains of amorphous calcium phosphate to densely-packed lamellar aggregates of crystalline hydroxyapatite. These physiochemical changes were paralleled by enrichment with small soluble apolipoproteins, complement factors and the binding of fatty acids. In comparison, endogenous CPP represent a highly heterogeneous mixture of particles with characteristics mostly intermediate to synthetic CPP-I and CPP-II, but are also uniquely enriched for carbonate-substituted apatite, DNA fragments, small RNA and microbe-derived components. Pathway analysis of protein enrichment predicted the activation of cell death and pro-inflammatory processes by endogenous CPP and synthetic CPP-II alike. This comprehensive characterisation validates the use of CPP-II generated in uraemic serum as in vitro equivalents of their endogenous counterparts and provides insight into the nature and pathological significance of CPP in CKD, which may act as vehicles for various bioactive ligands.

Serum calcification propensity is independently associated with disease activity in systemic lupus erythematosus

Background

Systemic lupus erythematosus (SLE) is associated with severe cardiovascular complications. The T₅₀ score is a novel functional blood test quantifying calcification propensity in serum. High calcification propensity (or low T₅₀) is a strong and independent determinant of all-cause mortality in various patient populations.

Methods

A total of 168 patients with ≥ 4 American College of Rheumatology (ACR) diagnostic criteria from the Swiss Systemic lupus erythematosus Cohort Study (SSCS) were included in this analysis. Serum calcification propensity was assessed using time-resolved nephelometry.

Results

The cohort mainly consisted of female (85%), middle-aged (43±14 years) Caucasians (77%). The major determinants of T₅₀ levels included hemoglobin, serum creatinine and serum protein levels explaining 43% of the variation at baseline. Integrating disease activity (SELENA-SLEDAI) into this multivariate model revealed a significant association between disease activity and T₅₀ levels. In a subgroup analysis considering only patients with active disease (SELENA-SLEDAI score ≥4) we found a negative association between T₅₀ and SELENA-SLEDAI score at baseline (Spearman’s rho -0.233, P = 0.02).

Conclusions

Disease activity and T₅₀ are closely associated. Moreover, T₅₀ levels identify a subgroup of SLE patients with ongoing systemic inflammation as mirrored by increased disease activity. T₅₀ could be a promising biomarker reflecting SLE disease activity and might offer an earlier detection tool for high-risk patients.

Novel assessments of systemic calcification propensity

PURPOSE OF REVIEW

Blood is a biological fluid, which controls the precipitation of calcium and phosphate and transports mineral debris. This review presents and discusses the current concepts and novel assessment methods of systemic calcification propensity in blood.

RECENT FINDINGS

Calcium and phosphate combine with calcification-inhibiting proteins, mainly fetuin-A, to form amorphous calcium phosphate-containing primary calciprotein particles (CPPs). These nanosized mineral-protein clusters undergo spontaneous transformation to secondary CPP, which contain crystalline calcium phosphate. Two recently developed methods assess complementary aspects of the calcification propensity of serum. The CPP-fetuin-A method determines the amount of sedimentable fetuin-A, whereas the T50-Test determines the transformation time point T50 from amorphous to crystalline CPPs in artificially supersaturated serum.Clinical studies in renal patients have already demonstrated close associations of the CPP-fetuin-A method with all-cause mortality, severity of coronary calcification and aortic stiffness, and of the T50-Test with cardiovascular and all-cause mortality, renal graft failure and aortic stiffening.

SUMMARY

Systemic calcification propensity can be assessed by two novel methods providing complementary information about the status and performance of the humoral calcification-regulating system in serum. These tests may help guide better patient care in the future with the use of more individualized therapies.

The Role of Secondary Calciprotein Particles in the Mineralisation Paradox of Chronic Kidney Disease

Mineralisation paradox is prevalent in chronic kidney disease and ageing where increased vascular calcification is accompanied by reduced bone mineralisation and osteopenia. Secondary calciprotein particles (CPP2), colloidal nanoparticles containing hydroxyapatite crystal stabilised by a protein shell, have been implicated in vascular calcification in chronic kidney disease. Here, we describe the effect of CPP2 on osteoblasts and vascular smooth muscle cells (VSMC) mineralisation in an in vitro model system. The mineralisation paradox can be simulated in vitro by the addition of phosphate ions (Pi, 3 mM) and CPP2 (10 µg/ml of Ca equivalent). Pi alone induced osteoblast mineralisation but had no effect on VSMC mineralisation. CPP2 alone had no effect on mineralisation in either cell line, but when combined with elevated Pi, reduced osteoblast-like mineralisation (P < 0.001) whilst induced VSMC mineralisation (P < 0.001). These results suggest that in an in vitro system the synergistic interaction between Pi and CPP2 could mimic the mineralisation paradox, and may provide a potential mechanistic link to explain these clinical observations.

Diethyl citrate and sodium citrate reduce the cytotoxic effects of nanosized hydroxyapatite crystals on mouse vascular smooth muscle cells

OBJECTIVE

This study aimed to investigate the damage mechanism of nanosized hydroxyapatite (nano-HAp) on mouse aortic smooth muscle cells (MOVASs) and the injury-inhibiting effects of diethyl citrate (Et2Cit) and sodium citrate (Na3Cit) to develop new drugs that can simultaneously induce anticoagulation and inhibit vascular calcification.

METHODS

The change in cell viability was evaluated using a cell proliferation assay kit, and the amount of lactate dehydrogenase (LDH) released was measured using an LDH kit. Intracellular reactive oxygen species (ROS) and mitochondrial damage were detected by DCFH-DA staining and JC-1 staining. Cell apoptosis and necrosis were detected by Annexin V staining. Intracellular calcium concentration and lysosomal integrity were measured using Fluo-4/AM and acridine orange, respectively.

RESULTS

Nano-HAp decreased cell viability and damaged the cell membrane, resulting in the release of a large amount of LDH. Nano-HAp entered the cells and damaged the mitochondria, and then induced cell apoptosis by producing a large amount of ROS. In addition, nano-HAp increased the intracellular Ca2+ concentration, leading to lysosomal rupture and cell necrosis. On addition of the anticoagulant Et2Cit or Na3Cit, cell viability and mitochondrial membrane potential increased, whereas the amount of LDH released, ROS, and apoptosis rate decreased. Et2 Cit and Na3Cit could also chelate with Ca+ to inhibit the intracellular Ca2+ elevations induced by nano-HAp, prevent lysosomal rupture, and reduce cell necrosis. High concentrations of Et2Cit and Na3Cit exhibited strong inhibitory effects. The inhibitory capacity of Na3Cit was stronger than that of Et2Cit at similar concentrations.

CONCLUSION

Both Et2Cit and Na3Cit significantly reduced the cytotoxicity of nano-HAp on MOVASs and inhibited the apoptosis and necrosis induced by nano-HAp crystals. The chelating function of citrate resulted in both anticoagulation and binding to HAp. Et2Cit and Na3Cit may play a role as anticoagulants in reducing injury to the vascular wall caused by nano-HAp.

Hydrogen sulfide attenuates calcification of vascular smooth muscle cells via KEAP1/NRF2/NQO1 activation

BACKGROUND AND AIMS

Vascular calcification is a common health problem related to oxidative stress, inflammation, and circulating calciprotein particles (CPP). Hydrogen sulfide is an endogenous signaling molecule with antioxidant properties and potential for drug development targeting redox signaling. Yet, its molecular mechanisms of action in vascular smooth muscle cell (VSMC) calcification have not been delineated. We therefore sought to identify key pathways involved in the calcification-inhibitory properties of sulfide employing our recently developed CPP-induced VSMC calcification model.

METHODS

Using next-generation sequencing, we investigated the transcriptomic changes of sodium hydrosulfide-treated versus non-treated calcifying VSMCs. The potential role of candidate genes and/or regulatory pathways in prevention of calcification was investigated by small interfering RNA (siRNA).

RESULTS

CPP led to a pronounced accumulation of cell-associated calcium, which was decreased by sulfide in a concentration-dependent manner. Both, CPP-induced hydrogen peroxide production and enhanced pro-inflammatory/oxidative stress-related gene expression signatures were attenuated by sulfide-treatment. Gene ontology enrichment and in silico pathway analysis of our transcriptome data suggested NAD(P)H dehydrogenase [quinone] 1 (NQO1) as potential mediator. Corroborating these findings, silencing of Kelch-like ECH-associated protein 1 (KEAP1), an inhibitor of nuclear factor (erythroid-derived 2)-like 2 (NRF2) nuclear activity, enhanced NQO1 expression, whereas NRF2 silencing reduced the expression of NQO1 and abrogated the calcification-suppressing activity of sulfide. Moreover, immunofluorescence microscopy and Western blot analysis confirmed nuclear translocation of NRF2 by sulfide in VSMC.

CONCLUSIONS

Sulfide attenuates CPP-induced VSMC calcification in vitro via the KEAP1-NRF2 redox sensing/stress response system by enhancing NQO1 expression.

Coupling between phosphate and calcium homeostasis: a mathematical model

We developed a mathematical model of calcium (Ca) and phosphate (PO₄) homeostasis in the rat to elucidate the hormonal mechanisms that underlie the regulation of Ca and PO₄ balance. The model represents the exchanges of Ca and PO₄ between the intestine, plasma, kidneys, bone, and the intracellular compartment, and the formation of Ca-PO₄-fetuin-A complexes. It accounts for the regulation of these fluxes by parathyroid hormone (PTH), vitamin D₃, fibroblast growth factor 23, and Ca²⁺-sensing receptors. Our results suggest that the Ca and PO₄ homeostatic systems are robust enough to handle small perturbations in the production rate of either PTH or vitamin D₃ The model predicts that large perturbations in PTH or vitamin D₃ synthesis have a greater impact on the plasma concentration of Ca²⁺ ([Ca²⁺]_p) than on that of PO₄ ([PO₄]_p); due to negative feedback loops, [PO₄]_p does not consistently increase when the production rate of PTH or vitamin D₃ is decreased. Our results also suggest that, following a large PO₄ infusion, the rapidly exchangeable pool in bone acts as a fast, transient storage PO₄ compartment (on the order of minutes), whereas the intracellular pool is able to store greater amounts of PO₄ over several hours. Moreover, a large PO₄ infusion rapidly lowers [Ca²⁺]_p owing to the formation of CaPO₄ complexes. A large Ca infusion, however, has a small impact on [PO₄]_p, since a significant fraction of Ca binds to albumin. This mathematical model is the first to include all major regulatory factors of Ca and PO₄ homeostasis.

A novel fluorescent probe-based flow cytometric assay for mineral-containing nanoparticles in serum

Calciprotein particles, nanoscale aggregates of insoluble mineral and binding proteins, have emerged as potential mediators of phosphate toxicity in patients with Chronic Kidney Disease. Although existing immunochemical methods for their detection have provided compelling data, these approaches are indirect, lack specificity and are subject to a number of other technical and theoretical shortcomings. Here we have developed a rapid homogeneous fluorescent probe-based flow cytometric method for the detection and quantitation of individual mineral-containing nanoparticles in human and animal serum. This method allows the discrimination of membrane-bound from membrane-free particles and different mineral phases (amorphous vs. crystalline). Critically, the method has been optimised for use on a conventional instrument, without the need for manual hardware adjustments. Using this method, we demonstrate a consistency in findings across studies of Chronic Kidney Disease patients and commonly used uraemic animal models. These studies demonstrate that renal dysfunction is associated with the ripening of calciprotein particles to the crystalline state and reveal bone metabolism and dietary mineral as important modulators of circulating levels. Flow cytometric analysis of calciprotein particles may enhance our understanding of mineral handling in kidney disease and provide a novel indicator of therapeutic efficacy for interventions targeting Chronic Kidney Disease-Mineral Bone Disorder.

Inflammation and premature aging in advanced chronic kidney disease

Systemic inflammation in end-stage renal disease is an established risk factor for mortality and a catalyst for other complications, which are related to a premature aging phenotype, including muscle wasting, vascular calcification, and other forms of premature vascular disease, depression, osteoporosis, and frailty. Uremic inflammation is also mechanistically related to mechanisms involved in the aging process, such as telomere shortening, mitochondrial dysfunction, and altered nutrient sensing, which can have a direct effect on cellular and tissue function. In addition to uremia-specific causes, such as abnormalities in the phosphate-Klotho axis, there are remarkable similarities between the pathophysiology of uremic inflammation and so-called "inflammaging" in the general population. Potentially relevant, but still somewhat unexplored in this respect, are abnormal or misplaced protein structures, as well as abnormalities in tissue homeostasis, which evoke danger signals through damage-associated molecular patterns, as well as the senescence-associated secretory phenotype. Systemic inflammation, in combination with the loss of kidney function, can impair the resilience of the body to external and internal stressors by reduced functional and structural tissue reserves, and by impairing normal organ crosstalk, thus providing an explanation for the greatly increased risk of homeostatic breakdown in this population. In this review, the relationship between uremic inflammation and a premature aging phenotype, as well as potential causes and consequences, are discussed.

Magnesium Counteracts Vascular Calcification: Passive Interference or Active Modulation?

Over the last decade, an increasing number of studies report a close relationship between serum magnesium concentration and cardiovascular disease risk in the general population. In end-stage renal disease, an association was found between serum magnesium and survival. Hypomagnesemia was identified as a strong predictor for cardiovascular disease in these patients. A substantial body of in vitro and in vivo studies has identified a protective role for magnesium in vascular calcification. However, the precise mechanisms and its contribution to cardiovascular protection remain unclear. There are currently 2 leading hypotheses: first, magnesium may bind phosphate and delay calcium phosphate crystal growth in the circulation, thereby passively interfering with calcium phosphate deposition in the vessel wall. Second, magnesium may regulate vascular smooth muscle cell transdifferentiation toward an osteogenic phenotype by active cellular modulation of factors associated with calcification. Here, the data supporting these major hypotheses are reviewed. The literature supports both a passive inorganic phosphate-buffering role reducing hydroxyapatite formation and an active cell-mediated role, directly targeting vascular smooth muscle transdifferentiation. However, current evidence relies on basic experimental designs that are often insufficient to delineate the underlying mechanisms. The field requires more advanced experimental design, including determination of intracellular magnesium concentrations and the identification of the molecular players that regulate magnesium concentrations in vascular smooth muscle cells.

Regulatory inhibition of biological tissue mineralization by calcium phosphate through post-nucleation shielding by fetuin-A

In vertebrates, insufficient availability of calcium and inorganic phosphate ions in extracellular fluids leads to loss of bone density and neuronal hyper-excitability. To counteract this problem, calcium ions are usually present at high concentrations throughout bodily fluids-at concentrations exceeding the saturation point. This condition leads to the opposite situation where unwanted mineral sedimentation may occur. Remarkably, ectopic or out-of-place sedimentation into soft tissues is rare, in spite of the thermodynamic driving factors. This fortunate fact is due to the presence of auto-regulatory proteins that are found in abundance in bodily fluids. Yet, many important inflammatory disorders such as atherosclerosis and osteoarthritis are associated with this undesired calcification. Hence, it is important to gain an understanding of the regulatory process and the conditions under which it can go awry. In this manuscript, we extend mean-field continuum classical nucleationtheory of the growth of clusters to encompass surface shielding. We use this formulation to study the regulation of sedimentation of calcium phosphate salts in biological tissues through the mechanism of post-nuclear shielding of nascent mineral particles by binding proteins. We develop a mathematical description of this phenomenon using a countable system of hyperbolic partial differential equations. A critical concentration of regulatory protein is identified as a function of the physical parameters that describe the system.

Blood-borne phagocytes internalize urate microaggregates and prevent intravascular NETosis by urate crystals

Hyperuricemia is strongly linked to cardiovascular complications including atherosclerosis and thrombosis. In individuals with hyperuricemia, needle-shaped monosodium urate crystals (nsMSU) frequently form within joints or urine, giving rise to gouty arthritis or renal calculi, respectively. These nsMSU are potent instigators of neutrophil extracellular trap (NET) formation. Little is known on the mechanism(s) that prevent nsMSU formation within hyperuricemic blood, which would potentially cause detrimental consequences for the host. Here, we report that complement proteins and fetuins facilitate the continuous clearance by blood-borne phagocytes and resident macrophages of small urate microaggregates (UMA; <1 μm in size) that initially form in hyperuricemic blood. If this clearance fails, UMA exhibit bipolar growth to form typical full-sized nsMSU with a size up to 100 μm. In contrast to UMA, nsMSU stimulated neutrophils to release NETs. Under conditions of flow, nsMSU and NETs formed densely packed DNase I-resistant tophus-like structures with a high obstructive potential, highlighting the importance of an adequate and rapid removal of UMA from the circulation. Under pathological conditions, intravascularly formed nsMSU may hold the key to the incompletely understood association between NET-driven cardiovascular disease and hyperuricemia.

Case Report of a Patient Undergoing Peritoneal Dialysis with Encapsulating Peritoneal Sclerosis Superimposed With Calciphylaxis

Introduction

Encapsulating peritoneal sclerosis (EPS) is a rare but devastating complication of peritoneal dialysis (PD). Tamoxifen has been generally well-tolerated, even without randomized controlled trials.

Case Presentation

Herein, we report a case of a patient undergoing 12 years of PD who developed EPS and calciphylaxis simultaneously. We also provide a comprehensive discussion about the association between EPS and calciphylaxis. Moreover, although tamoxifen is used in EPS due to its inhibition of fibroblast-transforming growth factor beta (TGFβ) production, it may worsen the calciphylaxis due to a hypercoagulable state.

Conclusions

We suggest avoiding the use of tamoxifen for EPS in patients with superimposed calciphylaxis.

Calcification of vascular smooth muscle cells is induced by secondary calciprotein particles and enhanced by tumor necrosis factor-α

BACKGROUND AND AIMS

Vascular calcification is prevalent in clinical states characterized by low-grade chronic inflammation, such as chronic kidney disease (CKD). Calciprotein particles (CPP) are calcium phosphate-containing nano-aggregates, which have been found in the blood of CKD patients and appear pro-inflammatory in vitro. The interplay of CPPs and inflammatory cytokines with regard to the calcification of vascular smooth muscle cells (VSMC), in vitro, has not been investigated yet.

METHODS

Primary or secondary CPP were generated using phosphate-enriched culture medium (DMEM/10% FBS) incubated at 37 °C. Human VSMC were cultured with these media and mineralization was measured. Expression of TNF-α was detected by qPCR, ELISA and Western blot in calcified VSMC. To further characterize the significance of TNF-α and its receptors for the calcification of VSMC, RNA interference experiments using siTNF-α, siTNFR1 and siTNFR2 were performed.

RESULTS

The addition of phosphate to cell culture medium containing DMEM/10% FBS led to the rapid formation of primary CPP, which underwent spontaneous transformation to secondary CPP. Exposure of VSMC towards secondary CPP led to pronounced and concentration-dependent calcification, whereas exposure towards primary CPP did not. Importantly, secondary CPP induced oxidative stress, and led to the up-regulation and release of TNF-α. Addition of TNF-α to the cell culture medium enhanced, whereas the suppression of endogenous TNF-α or TNF receptor type 1 (TNFR1) expression by siRNA, ameliorated calcification.

CONCLUSIONS

Secondary, but not primary CPP, induce VSMC calcification. Secondary CPP induce the expression and release of TNF-α, which enhances calcification via its receptor TNFR1.

Fetuin-A-containing calciprotein particles in mineral trafficking and vascular disease

Calcium and phosphate combine to form insoluble precipitates in both inorganic and organic materials. This property is useful biologically and has been used by numerous organisms to create hard tissues, a process referred to as biomineralisation [1]. In humans, calcium and phosphate combine to form useful crystal structures largely composed of calcium hydroxyapatite [Ca10(PO4)6(OH)2] and these are essential in the growth, maintenance and strength of parts of the skeleton and other structures like teeth. However, it remains unclear how the body achieves the exquisite specificity involved in biomineralisation. In ageing and disease, these pathways are perturbed, resulting in ectopic calcium crystal deposition impairing tissue function and, interestingly, frequently accompanied by simultaneous loss of mineral from sites where it is useful (e.g. bone). One paradigm for this maladaptive situation is renal failure; a situation that we know is associated with vascular stiffening and calcification, along with mineral loss from the skeleton. Mineral trafficking is a loose term used to describe the movements of calcium salts around the body, and new insights into these pathways may explain some of the problems of previous models of bone mineral disease in renal failure and point to potential future therapeutic strategies.

Efficiency of Fetuin-A and Procalcitonin in the Diagnosis of Infection in Patients with Febrile Seizure

Fetuin-A is a negative acute phase reactant, while procalcitonin is an indicator of severe bacterial infection. Diagnosis of bacterial infection in febrile seizure (FS) is important for choosing the most suitable treatment. In this study, serum fetuin-A was estimated, for the first time, in the inpatients with FS and compared with procalcitonin and blood culture tests.

A total of 60 children (28 male and 32 female) with FS in addition to 30 sex- and age-matched children participated in the study. Patients were classified according to sex, age, PCT level (high PCT>0.5ng/mL), C-reactive protein (CRP, positive >6mg/L), and according to the results of the blood culture.

Fetuin-A level decreased and PCT level increased in FS patients in comparison to those in the control group. These changes are significantly increased (p<0.05) in the positive CRP group compared with that of the negative CRP group. Kernel density estimation showed that procalcitonin is a better indicator of the infection in FS children than fetuin-A . Procalcitonin is more sensitive and specific than fetuin-A and when used together they produce 100% sensitivity and specificity for the diagnosis of bacterial infection in FS patients.

Fetuin-A is low in FS patients and can be used with procalcitonin in the diagnosis of bacterial infection in FS.