Circulating calcification inhibitors are associated with arterial damage in pediatric patients with primary hypertension

Background Circulating calcification inhibitors: fetuin A (FA) and osteoprotegerin (OPG) together with soluble ligand of receptor activator of nuclear factor kappa-B (sRANKL) have been linked to vascular calcifications and arterial damage. This study aimed to evaluate relationships between FA, OPG, sRANKL, and arterial damage in children with primary hypertension (PH). Methods In this cross-sectional single-center study, calcification inhibitors (FA, OPG, sRANKL) levels were measured in blood samples of 60 children with PH (median age 15.8, IQR: [14.5–16.8] years) and 20 age-matched healthy volunteers. In each participant, peripheral and central blood pressure evaluation (BP) and ambulatory BP monitoring (ABPM) were performed. Arterial damage was measured using common carotid artery intima media thickness (cIMT), pulse wave velocity (PWV), augmentation index (AIx75HR), and local arterial stiffness (ECHO-tracking—ET) analysis. Results Children with PH had significantly higher peripheral and central BP, BP in ABPM, thicker cIMT, higher PWV, and AIx75HR. FA was significantly lower in patients with PH compared to healthy peers without differences in OPG, sRANKL, and OPG/sRANKL and OPG/FA ratios. In children with PH, FA level correlated negatively with cIMT Z-score and ET AIx; sRANKL level correlated negatively with ABPM systolic blood pressure (SBP), SBP load, diastolic BP load, and AIx75HR; OPG/sRANKL ratio correlated positively with SBP load, while OPG/FA ratio correlated positively with ET AIx. In multivariate analysis, FA was a significant determinant of cIMT (mm) and cIMT Z-score. Conclusions This study reveals that in children with primary hypertension, arterial damage is related to lower fetuin A concentrations. Graphical abstract

Plasma Exosomes Derived From Patients With End-Stage Renal Disease and Renal Transplant Recipients Have Different Effects on Vascular Calcification

End-stage renal disease (ESRD) patients usually develop extensive and progressive vascular calcification, and lots of calcification inhibitors as well as procalcifying factors are involved in the process. However, the mechanisms of vascular calcification in ESRD patients are still ill-defined. In the present study, we found that the plasma exosomes derived from ESRD patients (ESRD-Ex) promoted calcification of vascular smooth muscle cells (VSMCs) significantly, while plasma exosomes from renal transplant recipients (RTR-Ex) could partially attenuate VSMCs calcification. Moreover, the protein concentration of ESRD-Ex was significantly higher than plasma exosomes from the normal health control group (Nor-Ex) and RTR-Ex, and the content of both matrix gla protein (MGP) and Fetuin-A, the calcification inhibitors, were prominently lower in ESRD-Ex than those in Nor-Ex. The content of Annexin-A2, one of the calcification promoters, was significantly higher in ESRD-Ex and RTR-Ex than that in Nor-Ex. However, bone morphogenetic protein (BMP-2) and receptor activator for nuclear factor-κB ligand (Rankl) had no significant difference among the three groups. In addition, the content of Fetuin-A in RTR-Ex was higher than that in ESRD-Ex, although it was still lower than that in Nor-Ex. Furthermore, the levels of both Fetuin-A and MGP in plasma exosomes were negatively while the levels of Annexin-A2 in plasma exosomes was positively correlated to coronary artery calcification scores (CACS). These results indicated that ESRD-Ex significantly promoted VSMCs calcification, while renal transplantation could partially attenuate the procalcification effect of exosomes. Fetuin-A and MGP were decreased, but Annexin-A2 was increased in ESRD-Ex, and renal transplantation could increase the level of Fetuin-A rather than MGP.

Effects of Chronic Kidney Disease and Uremic Toxins on Extracellular Vesicle Biology

Vascular calcification (VC) is a cardiovascular complication associated with a high mortality rate, especially in patients with diabetes, atherosclerosis or chronic kidney disease (CKD). In CKD patients, VC is associated with the accumulation of uremic toxins, such as indoxyl sulphate or inorganic phosphate, which can have a major impact in vascular remodeling. During VC, vascular smooth muscle cells (VSMCs) undergo an osteogenic switch and secrete extracellular vesicles (EVs) that are heterogeneous in terms of their origin and composition. Under physiological conditions, EVs are involved in cell-cell communication and the maintenance of cellular homeostasis. They contain high levels of calcification inhibitors, such as fetuin-A and matrix Gla protein. Under pathological conditions (and particularly in the presence of uremic toxins), the secreted EVs acquire a pro-calcifying profile and thereby act as nucleating foci for the crystallization of hydroxyapatite and the propagation of calcification. Here, we review the most recent findings on the EVs’ pathophysiological role in VC, the impact of uremic toxins on EV biogenesis and functions, the use of EVs as diagnostic biomarkers and the EVs’ therapeutic potential in CKD.

A novel assay to measure calcification propensity: from laboratory to humans

Cardiovascular calcification (CVC) contributes to morbidity and mortality in patients undergoing dialysis. We examined the pharmacodynamic effects of SNF472, a calcification inhibitor, on plasma calcium phosphate crystallization using spectrometric measurements, and its correlations with effects on CVC in rats or humans. Rats (N = 38) injected with vitamin D (days 1–3) to induce CVC were infused with saline or SNF472 (days 1–12). Inhibition of CVC was 50–65% with SNF472 3 mg/kg and ~ 80% with SNF472 10 or 30 mg/kg. SNF472 dose-dependently inhibited calcium phosphate crystallization, which correlated with inhibition of CVC (r = 0.628, P = 0.005). In patients with calciphylaxis (N = 14), infusion of SNF472 (~ 7 mg/kg) during hemodialysis for 12 weeks inhibited calcium phosphate crystallization by nearly 70%. In patients with CVC (N = 274), infusion of SNF472 during hemodialysis for 52 weeks inhibited calcium phosphate crystallization (placebo: 15%; 300 mg: 61%; 600 mg: 75%), which correlated with inhibition of CVC (r = 0.401, P = 0.003). These findings show a direct correlation between inhibition of calcium phosphate crystallization in plasma and inhibition of CVC both in a rat model and in humans, supporting the use of the pharmacodynamic assay in clinical trials as a potentially predictive tool to evaluate the activity of calcification inhibitors.

Plasma exosomes derived from patients with end-stage renal disease and renal transplant recipients have different effects on vascular calcification

Background End-stage renal disease (ESRD) patients usually develop extensive and progressive vascular calcification, and lots of calcification inhibitors as well as pro-calcifying factors are involved in the process. However, the mechanisms of vascular calcification in ESRD patients are still ill-defined. Methods The participants in the study were selected at the Second Xiangya Hospital, Central South University, and the plasma exosomes derived from ESRD patients (ESRD-Ex), renal transplant recipients (RTR-Ex), and the normal health control group (Nor-Ex) were isolated by ExoQuick-TC kit. Transmission electron microscopy and molecular size analysis were used to assess the morphology and size of exosomes. Alizarin Red S staining was carried out to detect calcification of vascular smooth muscle cells (VSMCs). Protein levels of Fetuin-A, matrix gla protein (MGP), Annexin-A2, bone morphogenetic protein (BMP-2), and receptor activator for nuclear factor-κ B ligand (Rankl) were measured by Western Blot analysis and the contents of that were detected using ELISA. Coronary artery calcification scores (CACS) were quantified via Agaston and analysed by Siemens CaScoring software. Results Compared with Nor-Ex, the ESRD-Ex promoted calcification of VSMCs significantly, and RTR-Ex could attenuate VSMCs calcification. Moreover, the protein concentration of ESRD-Ex was significantly higher than Nor-Ex and RTR-Ex, and the content of both MGP and Fetuin-A, the calcification inhibitors, were prominently lower in ESRD-Ex than those in Nor-Ex. The content of Annexin-A2, one of the calcification promoters, was significantly higher in ESRD-Ex and RTR-Ex than that in Nor-Ex. But, BMP-2 and Rankl had no significant difference among the three groups. In addition, the content of Fetuin-A in RTR-Ex was higher than that in ESRD-Ex, though it was still lower than in Nor-Ex. Furthermore, the content of both plasma Fetuin-A and MGP were negatively while that of Annexin-A2 was negatively correlated to CACS. Conclusions These results indicated that ESRD-Ex significantly promoted VSMCs calcification while renal transplantation could partially attenuate the effect of exosomes. Fetuin-A and MGP were decreased but Annexin-A2 was increased in ESRD-Ex, and renal transplantation could increase the level of Fetuin-A rather than MGP.

Pseudoxanthoma Elasticum and Cardiorenal Disease: A Case Report

Pseudoxanthoma elasticum (PXE) is a rare genetic disorder characterized by calcification of elastic fibres, skin lesions, fundus lesions and systemic vascular complications. PXE affects approximately 1 in 160,000 people, typically appearing as a formation of yellow papules containing abnormally calcified elastic fibres. The renal involvement of PXE has been reported. Several factors are known to promote soft tissue and accelerated arterial calcification in chronic kidney disease, including systemic inflammation, altered calcium and phosphate homeostasis, hypertension and a deficiency of endogenous calcification inhibitors. Given the impact of this disease, nephrologists may seek additional supportive features to improve and avoid the risk of complications. Moreover, PXE per se represents an interesting model to evaluate vascular disease in the early stages of renal disease.

Vitamin K Dependent Proteins in Kidney Disease

Patients with chronic kidney disease (CKD) have an increased risk of developing vascular calcifications, as well as bone dynamics impairment, leading to a poor quality of life and increased mortality. Certain vitamin K dependent proteins (VKDPs) act mainly as calcification inhibitors, but their involvement in the onset and progression of CKD are not completely elucidated. This review is an update of the current state of knowledge about the relationship between CKD and four extrahepatic VKDPs: matrix Gla protein, osteocalcin, growth-arrest specific protein 6 and Gla-rich protein. Based on published literature in the last ten years, the purpose of this review is to address fundamental aspects about the link between CKD and circulating VKDPs levels as well as to raise new topics about how the interplay between molecular weight and charge could influence the modifications of circulating VKDPs at the glomerular level, or whether distinct renal etiologies have effect on VKDPs. This review is the output of a systematic literature search and may open future research avenues in this niche domain.