Structural characterisation of deer sinew peptides as calcium carriers, their promotion of MC3T3-E1 cell proliferation and their effect on bone deposition in mice

Deer sinew as a by-product has high collagen and nutritional value. This study focuses on its hydrolysate being used as a calcium carrier to develop functional foods. The chelation mechanism was analyzed by SEM, EDS, UV-vis, FTIR, and fluorescence spectroscopy and zeta potential analysis after using peptide-sequenced deer sinew peptides for chelation with calcium ions. The results showed that the chelation of deer sinew peptides with calcium ions occurs mainly at the O and N atoms of carboxyl, amino and amide bonds. In vitro and in vivo studies revealed that deer sinew peptide-calcium chelate (DSPs-Ca) promoted the proliferation of MC3T3-E1 cells without toxic side effects and increased the alkaline phosphatase activity. The DSPs-Ca group improved the bone microstructure induced by low calcium, as well as up-regulated the expression of genes responsible for calcium uptake in the kidneys, as evidenced by serum markers, bone sections, bone parameters, and gene expression analyses in low-calcium-fed mice. From the above, it can be concluded that DSPs-Ca is expected to be a calcium supplement food for promoting bone health.

Novel Biomarkers of Bone Metabolism

Bone represents a metabolically active tissue subject to continuous remodeling orchestrated by the dynamic interplay between osteoblasts and osteoclasts. These cellular processes are modulated by a complex interplay of biochemical and mechanical factors, which are instrumental in assessing bone remodeling. This comprehensive evaluation aids in detecting disorders arising from imbalances between bone formation and reabsorption. Osteoporosis, characterized by a reduction in bone mass and strength leading to heightened bone fragility and susceptibility to fractures, is one of the more prevalent chronic diseases. Some epidemiological studies, especially in patients with chronic kidney disease (CKD), have identified an association between osteoporosis and vascular calcification. Notably, low bone mineral density has been linked to an increased incidence of aortic calcification, with shared molecules, mechanisms, and pathways between the two processes. Certain molecules emerging from these shared pathways can serve as biomarkers for bone and mineral metabolism. Detecting and evaluating these alterations early is crucial, requiring the identification of biomarkers that are reliable for early intervention. While traditional biomarkers for bone remodeling and vascular calcification exist, they suffer from limitations such as low specificity, low sensitivity, and conflicting results across studies. In response, efforts are underway to explore new, more specific biomarkers that can detect alterations at earlier stages. The aim of this review is to comprehensively examine some of the emerging biomarkers in mineral metabolism and their correlation with bone mineral density, fracture risk, and vascular calcification as well as their potential use in clinical practice.

Higher sclerostin is associated with pulmonary hypertension in pre-dialysis end-stage kidney disease patients: a cross-sectional prospective observational cohort study

BACKGROUND

Pulmonary hypertension (PH) is a complication of chronic kidney disease (CKD) that contributes to mortality. Sclerostin, a SOST gene product that reduces osteoblastic bone formation by inhibiting Wnt/β-catenin signaling, is involved in arterial stiffness and CKD-bone mineral disease, but scanty evidence to PH. This study explored the relationship between sclerostin and PH in CKD 5, pre-dialysis end-stage kidney disease (ESKD) patients.

METHODS

This cross-sectional prospective observational cohort study included 44 pre-dialysis ESKD patients between May 2011 and May 2015. Circulating sclerostin levels were measured using an enzyme-linked immunosorbent assay. PH was defined as an estimated pulmonary artery systolic pressure > 35 mmHg on echocardiography.

RESULTS

Patients with higher sclerostin levels ≥ 218.18pmol/L had echocardiographic structural cardiac abnormalities, especially PH (P < 0.01). On multivariate logistic analysis, sclerostin over 218.19pmol/L was significantly associated with PH (odds ratio [OR], 41.14; 95% confidence interval [CI], 4.53-373.89, P < 0.01), but multivariate Cox regression analysis showed the systemic vascular calcification score over 1 point (Hazard ratio [HR] 11.49 95% CI 2.48-53.14, P = 0.002) and PH ([HR] 5.47, 95% CI 1.30-23.06, P = 0.02) were risk factors for all-cause mortality in pre-dialysis ESKD patients.

CONCLUSIONS

Serum sclerostin and PH have a positive correlation in predialysis ESKD patients. The higher systemic vascular calcification score and PH have an association to increase all-cause mortality in pre-dialysis ESKD patients.

Vascular calcification: from the perspective of crosstalk

Vascular calcification (VC) is highly correlated with cardiovascular disease morbidity and mortality, but anti-VC treatment remains an area to be tackled due to the ill-defined molecular mechanisms. Regardless of the type of VC, it does not depend on a single cell but involves multi-cells/organs to form a complex cellular communication network through the vascular microenvironment to participate in the occurrence and development of VC. Therefore, focusing only on the direct effect of pathological factors on vascular smooth muscle cells (VSMCs) tends to overlook the combined effect of other cells and VSMCs, including VSMCs-VSMCs, ECs-VMSCs, Macrophages-VSMCs, etc. Extracellular vesicles (EVs) are a collective term for tiny vesicles with a membrane structure that are actively secreted by cells, and almost all cells secrete EVs. EVs docked on the surface of receptor cells can directly mediate signal transduction or transfer their contents into the cell to elicit a functional response from the receptor cells. They have been proven to participate in the VC process and have also shown attractive therapeutic prospects. Based on the advantages of EVs and the ability to be detected in body fluids, they may become a novel therapeutic agent, drug delivery vehicle, diagnostic and prognostic biomarker, and potential therapeutic target in the future. This review focuses on the new insight into VC molecular mechanisms from the perspective of crosstalk, summarizes how multi-cells/organs interactions communicate via EVs to regulate VC and the emerging potential of EVs as therapeutic methods in VC. We also summarize preclinical experiments on crosstalk-based and the current state of clinical studies on VC-related measures.

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

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

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

Drugs providing antihypertensive and protective cardiovascular actions are of clinical interest in controlling cardiovascular events and slowing the progression of kidney disease. We studied the effect of a hybrid compound, GGN1231 (derived from losartan in which a powerful antioxidant was attached), on the prevention of cardiovascular damage, cardiac hypertrophy, and fibrosis in a rat model of severe chronic renal failure (CRF). CRF by a 7/8 nephrectomy was carried out in male Wistar rats fed with a diet rich in phosphorous (0.9%) and normal calcium (0.6%) for a period of 12 weeks until sacrifice. In week 8, rats were randomized in five groups receiving different drugs including dihydrocaffeic acid as antioxidant (Aox), losartan (Los), dihydrocaffeic acid+losartan (Aox+Los) and GGN1231 as follows: Group 1 (CRF+vehicle group), Group 2 (CRF+Aox group), Group 3 (CRF+Los group), Group 4 (CRF+Aox+Los group), and Group 5 (CRF+GGN1231 group). Group 5, the CRF+GGN1231 group, displayed reduced proteinuria, aortic TNF-α, blood pressure, LV wall thickness, diameter of the cardiomyocytes, ATR1, cardiac TNF-α and fibrosis, cardiac collagen I, and TGF-β1 expression. A non-significant 20% reduction in the mortality was also observed. This study showed the possible advantages of GGN1231, which could help in the management of cardiovascular and inflammatory processes. Further research is needed to confirm and even expand the positive aspects of this compound.

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

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

Microparticles from Hyperphosphatemia-Stimulated Endothelial Cells Promote Vascular Calcification Through Astrocyte-Elevated Gene-1

Endothelial microparticles (EMPs) can be released in chronic kidney disease (CKD). Plasma concentration of high inorganic phosphate (HP) is considered as a decisive determinant of vascular calcification in CKD. We therefore explored the role of HP-induced EMPs (HP-EMPs) in the vascular calcification and its potential mechanism. We observed the shape of HP-EMPs captured by vascular smooth muscle cells (VSMCs) dynamically changed from rare dots, rosettes, to semicircle or circle. Our results demonstrated that HP-EMPs could directly promote VSMC calcification, or accelerate HP-induced calcification through signal transducers and activators of transcription 3 (STAT3)/bone morphogenetic protein-2 (BMP2) signaling pathway. AEG-1 activity was increased through HP-EMPs-induced VSMC calcification, in arteries from uremic rats, or from uremic rats treated with HP-EMPs. AEG-1 deficiency blocked, whereas AEG-1 overexpression exacerbated, the calcium deposition of VSMCs. AEG-1, a target of miR-153-3p, could be suppressed by agomiR-153-3p. Notably, VSMC-specific enhance of miR-153-3p by tail vein injection of aptamer-agomiR-153-3p decreased calcium deposition in both uremia rats treated with HP-EMPs or not. HP-EMPs could directly induce VSMCs calcification and accelerate Pi-induced calcification, and AEG-1 may act as crucial regulator of HP-EMPs-induced vascular calcification. This study sheds light on the therapeutic agents that influence HP-EMPs production or AEG-1 activity, which may be of benefit to treat vascular calcification.

Compensatory elevated serum intermedin levels are associated with increased vascular calcification in hemodialysis patients

INTRODUCTION

Vascular calcification (VC), which is a pathological process of abnormal calcium and phosphorus deposition in blood vessels, valves, heart and other tissues, is highly prevalent and predicts mortality in dialysis patients. Its mechanisms are complex and unclear. We presume that intermedin (IMD), a kind of small molecule active peptide, may play roles in VC in hemodialysis (HD) patients. This study aims to evaluate serum IMD levels and establish their relation to VC and other parameters in HD patients.

METHODS

A total of 116 patients on maintenance HD treatment and 52 age- and sex-matched healthy controls were enrolled in this study. Serum IMD levels were measured by radioimmunoassay (RIA). VC was evaluated by abdominal aortic calcification scores.

RESULTS

Serum IMD levels were significantly lower in HD patients than in controls [24.89 (13.55, 50.24) pg/ml vs. 137.79 (93.21, 201.64) pg/ml, P < 0.0001]. In addition, IMD was negatively correlated with the serum phosphate level (P = 0.036) in HD patients. However, compared with the group whose IMD levels were above the median, patients with IMD levels less than the median had a lower incidence of VC (P = 0.031). Multivariate logistic regression analyses revealed that serum IMD levels more than 24.89 pg/ml (P = 0.014, OR = 0.285), higher serum iPTH levels (P < 0.0001, OR = 1.093) and older age (P = 0.009, OR = 1.003) were significant independent determinant factors for VC in HD patients.

CONCLUSION

The serum IMD levels were significantly lower in HD patients than that in healthy group. In addition to higher PTH levels and older age, compensatory elevated IMD levels may be an independently determinant factor for VC in HD patients. This was the first study about IMD and VC in dialysis patients.

Risk factors for mortality within 6 mo in patients with diabetes undergoing urgent-start peritoneal dialysis: A multicenter retrospective cohort study

BACKGROUND

The risk of early mortality of patients who start dialysis urgently is high; however, in patients with diabetes undergoing urgent-start peritoneal dialysis (USPD), the risk of, and risk factors for, early mortality are unknown.

AIM

To identify risk factors for mortality during high-risk periods in patients with diabetes undergoing USPD.

METHODS

This retrospective cohort study enrolled 568 patients with diabetes, aged ≥ 18 years, who underwent USPD at one of five Chinese centers between 2013 and 2019. We divided the follow-up period into two survival phases: The first 6 mo of USPD therapy and the months thereafter. We compared demographic and baseline clinical data of living and deceased patients during each period. Kaplan-Meier survival curves were generated for all-cause mortality according to the New York Heart Association (NYHA) classification. A multivariate Cox proportional hazard regression model was used to identify risk factors for mortality within the first 6 mo and after 6 mo of USPD.

RESULTS

Forty-one patients died within the first 6 mo, accounting for the highest proportion of mortalities (26.62%) during the entire follow-up period. Cardiovascular disease was the leading cause of mortality within 6 mo (26.83%) and after 6 mo (31.86%). The risk of mortality not only within the first 6 mo but also after the first 6 mo was higher for patients with obvious baseline heart failure symptoms than for those with mild or no heart failure symptoms. Independent risk factors for mortality within the first 6 mo were advanced age [hazard ratio (HR: 1.908; 95%CI: 1.400-2.600; P < 0.001), lower baseline serum creatinine level (HR: 0.727; 95%CI: 0.614-0.860; P < 0.001), higher baseline serum phosphorus level (HR: 3.162; 95%CI: 1.848-5.409; P < 0.001), and baseline NYHA class III-IV (HR: 2.148; 95%CI: 1.063-4.340; P = 0.033). Independent risk factors for mortality after 6 mo were advanced age (HR: 1.246; 95%CI: 1.033-1.504; P = 0.022) and baseline NYHA class III-IV (HR: 2.015; 95%CI: 1.298-3.130; P = 0.002).

CONCLUSION

To reduce the risk of mortality within the first 6 mo of USPD in patients with diabetes, controlling the serum phosphorus level and improving cardiac function are recommended.

Endoplasmic reticulum stress mediates parathyroid hormone-induced apoptosis in vascular smooth muscle cells

Vascular calcification is one of the most common complications of chronic kidney disease (CKD), which is closely associated with increased mortality and morbidity rates of CKD patients. It has been reported that increased parathyroid hormone (PTH) aggravates vascular calcification in CKD patients. However, the direct role of PTH in vascular smooth muscle cells (VSMCs) is less elucidated. Here, we present evidence that PTH promotes apoptosis of VSMCs and endoplasmic reticulum (ER) stress participates in this process. Human aorta vascular smooth muscle cells (HASMCs) were treated with different concentrations of PTH for various time. HASMC apoptosis was detected by flow cytometry. Expression of phosphorylated (p)-PERK, CHOP, IRE1, p-JNK, and cleaved caspase 3 was determined by Western blotting. We found that PTH induced HASMC apoptosis and increased the expression of cleaved caspase 3. Furthermore, PTH activated PERK-CHOP and IRE1-JNK ER stress pathways. Either inhibition of JNK by SP600125 or CHOP by siRNA ameliorated PTH-induced apoptosis in HASMCs. We therefore suggest that ER stress participates in PTH-induced apoptosis of VSMCs, which may be a possible mechanism of PTH-promoted vascular calcification in CKD patients.

Parathyroid Hormone 1 Receptor Signaling in Dental Mesenchymal Stem Cells: Basic and Clinical Implications

Parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) are two peptides that regulate mineral ion homeostasis, skeletal development, and bone turnover by activating parathyroid hormone 1 receptor (PTH1R). PTH1R signaling is of profound clinical interest for its potential to stimulate bone formation and regeneration. Recent pre-clinical animal studies and clinical trials have investigated the effects of PTH and PTHrP analogs in the orofacial region. Dental mesenchymal stem cells (MSCs) are targets of PTH1R signaling and have long been known as major factors in tissue repair and regeneration. Previous studies have begun to reveal important roles for PTH1R signaling in modulating the proliferation and differentiation of MSCs in the orofacial region. A better understanding of the molecular networks and underlying mechanisms for modulating MSCs in dental diseases will pave the way for the therapeutic applications of PTH and PTHrP in the future. Here we review recent studies involving dental MSCs, focusing on relationships with PTH1R. We also summarize recent basic and clinical observations of PTH and PTHrP treatment to help understand their use in MSCs-based dental and bone regeneration.

Contribution of phosphorus and PTH to the development of cardiac hypertrophy and fibrosis in an experimental model of chronic renal failure

BACKGROUND AND OBJECTIVE

Adequate serum phosphorus levels in patients with chronic kidney disease is essential for their clinical management. However, the control of hyperphosphatemia is difficult because is normally associated with increases in serum PTH. In the present study, the effects of hyperphosphatemia, in the presence of elevated and normal PTH, on cardiac inflammation, hypertrophy and fibrosis in an experimental renal failure model were analyzed.

MATERIALS AND METHODS

4 groups of rats were formed. Two groups underwent total parathyroidectomy (PTx). Rats with Ca <7.5 mg/dL and PTH < 50 pg/mL underwent 7/8 nephrectomy (CRF) and a subcutaneous pellet was placed that releases PTH 1-34 (5 µg/kg/day). One group received a diet with normal P (NP) (CRF + PTx + rPTH + NP group) and another with a high P diet (0.9% - HP) (CRF + PTx + rPTH + HP group). Other 2 groups that only had CRF received NP (CRF + NP) and HP (CRF + HP) diet. A SHAM group for nephrectomy and parathyroidectomy was also added. After 14 weeks the rats were sacrificed.

RESULTS

The groups with a diet high in phosphorus (CRF + H A and CRF + PTx + rPTH + HP) had a significant reduction in creatinine clearance and also in body weight with an increase in serum phosphorus regardless of parathyroidectomy, but not serum levels of calcium, FGF23 and calcitriol that were 2-3 times higher in the group with secondary hyperparathyroidism (CRF + HP). The diameter of the cardiomyocytes was greater in the CRF + HP group, while parathyroidectomy (CRF + PTx + rPTH + HP) significantly reduced them, despite the high and similar serum phosphorus values. TNF-α, Adam17 and cardiac fibrosis at the histological and molecular level showed a similar pattern with increases in the group with severe secondary hyperparathyroidism (CRF + HP).

CONCLUSIONS

Hyperphosphatemia confirmed its importance in the genesis of secondary hyperparathyroidism, but also of kidney damage that was independent of PTH levels. However, inflammation, fibrosis, and cardiomyocyte growth were more closely related to PTH levels, since in the presence of similar severe hyperphosphatemia, parathyroidectomy reduced the values ​​of inflammatory parameters, cardiac hypertrophy, and fibrosis.

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

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

Calciprotein Particles: Balancing Mineral Homeostasis and Vascular Pathology

[Figure: see text].

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

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

The receptor activator of nuclear factor κΒ ligand receptor leucine-rich repeat-containing G-protein-coupled receptor 4 contributes to parathyroid hormone-induced vascular calcification

BACKGROUND

In chronic kidney disease, serum phosphorus (P) elevations stimulate parathyroid hormone (PTH) production, causing severe alterations in the bone-vasculature axis. PTH is the main regulator of the receptor activator of nuclear factor κB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) system, which is essential for bone maintenance and also plays an important role in vascular smooth muscle cell (VSMC) calcification. The discovery of a new RANKL receptor, leucine-rich repeat-containing G-protein-coupled receptor 4 (LGR4), which is important for osteoblast differentiation but with an unknown role in vascular calcification (VC), led us to examine the contribution of LGR4 in high P/high PTH-driven VC.

METHODS

In vivo studies were conducted in subtotally nephrectomized rats fed a normal or high P diet, with and without parathyroidectomy (PTX). PTX rats were supplemented with PTH(1-34) to achieve physiological serum PTH levels. In vitro studies were performed in rat aortic VSMCs cultured in control medium, calcifying medium (CM) or CM plus 10-7 versus 10-9 M PTH.

RESULTS

Rats fed a high P diet had a significantly increased aortic calcium (Ca) content. Similarly, Ca deposition was higher in VSMCs exposed to CM. Both conditions were associated with increased RANKL and LGR4 and decreased OPG aorta expression and were exacerbated by high PTH. Silencing of LGR4 or parathyroid hormone receptor 1 (PTH1R) attenuated the high PTH-driven increases in Ca deposition. Furthermore, PTH1R silencing and pharmacological inhibition of protein kinase A (PKA), but not protein kinase C, prevented the increases in RANKL and LGR4 and decreased OPG. Treatment with PKA agonist corroborated that LGR4 regulation is a PTH/PKA-driven process.

CONCLUSIONS

High PTH increases LGR4 and RANKL and decreases OPG expression in the aorta, thereby favouring VC. The hormone's direct pro-calcifying actions involve PTH1R binding and PKA activation.

Serum sirtuin 1 is independently associated with intact PTH among patients with chronic kidney disease

Background

Sirtuin 1 is involved in the pathogenesis of age-related diseases.

Purpose

The aim of the study was to assess the clinical and diagnostic value of serum sirtuin 1 concentration in patients with CKD.

Patients and Methods

The serum sirtuin 1 level was evaluated using ELISA kit in 100 CKD patients stratified for five stages and in a control group of 24 healthy volunteers.

Results

Serum sirtuin 1 concentration was higher in the CKD group compared with the control group (p<0.05). Sirtuin 1 correlated with conventional CKD biomarkers and eGFR equations, intact parathyroid hormone (iPTH) and age (all p<0.05). Statins, AT₁ receptor antagonists and β-blockers use were associated with decreased sirtuin concentration (p<0.05). Sirtuin 1 was able to distinguish CKD from control group with high sensitivity and specificity (93% and 87%, respectively; AUC=0.954). Surprisingly, after adjustment only iPTH concentration was an independent predictor of sirtuin 1 level.

Conclusion

The association between sirtuin 1, eGFR equations and iPTH indicates its possible usefulness as a kidney function marker. In terms of iPTH being the only independent predictor of circulating sirtuin 1 it can be considered as an indirect cardiovascular risk biomarker regardless of renal function and provide additional information for patient management. Alternatively, sirtuin 1 is recognized as protective against vascular disease, and we demonstrated a positive correlation with iPTH, which may be related to accumulation of (7-84)-PTH having opposite biological effects to full-length PTH. Further studies are needed to explore the interplay between sirtuin 1, PTH and CKD-related vascular calcification as well as to assess its prognostic value in observational studies.

European Consensus Statement on the diagnosis and management of osteoporosis in chronic kidney disease stages G4-G5D

Controlling the excessive fracture burden in patients with chronic kidney disease (CKD) Stages G4-G5D remains an impressive challenge. The reasons are 2-fold. First, the pathophysiology of bone fragility in patients with CKD G4-G5D is complex and multifaceted, comprising a mixture of age-related (primary male/postmenopausal), drug-induced and CKD-related bone abnormalities. Second, our current armamentarium of osteoporosis medications has not been developed for, or adequately studied in patients with CKD G4-G5D, partly related to difficulties in diagnosing osteoporosis in this specific setting and fear of complications. Doubts about the optimal diagnostic and therapeutic approach fuel inertia in daily clinical practice. The scope of the present consensus paper is to review and update the assessment and diagnosis of osteoporosis in patients with CKD G4-G5D and to discuss the therapeutic interventions available and the manner in which these can be used to develop management strategies for the prevention of fragility fracture. As such, it aims to stimulate a cohesive approach to the management of osteoporosis in patients with CKD G4-G5D to replace current variations in care and treatment nihilism.

Contribution of phosphorus and PTH to the development of cardiac hypertrophy and fibrosis in an experimental model of chronic renal failure

BACKGROUND AND OBJECTIVE

Adequate serum phosphorus levels in patients with chronic kidney disease is essential for their clinical management. However, the control of hyperphosphatemia is difficult because is normally associated with increases in serum PTH. In the present study, the effects of hyperphosphatemia, in the presence of elevated and normal PTH, on cardiac inflammation, hypertrophy and fibrosis in an experimental renal failure model were analyzed.

MATERIALS AND METHODS

Four groups of rats were formed. Two groups underwent total parathyroidectomy (PTx). Rats with Ca < 7.5 mg/dL and PTH < 50 pg/mL underwent 7/8 nephrectomy (CRF) and a subcutaneous pellet was placed that releases PTH 1-34 (5 μg/kg/day). One group received a diet with normal P (NP) (CRF + PTx + rPTH + NP group) and another with a high P diet (0.9% HP) (CRF + PTx + rPTH + HP group). Other two groups that only had CRF received NP (CRF + NP) and HP (CRF + HP) diet. A SHAM group for nephrectomy and parathyroidectomy was also added. After 14 weeks the rats were sacrificed.

RESULTS

The groups with a diet high in phosphorus (CRF + H A and CRF + PTx + rPTH + HP) had a significant reduction in creatinine clearance and also in body weight with an increase in serum phosphorus regardless of parathyroidectomy, but not serum levels of calcium, FGF23 and calcitriol that were 2-3 times higher in the group with secondary hyperparathyroidism (CRF + HP). The diameter of the cardiomyocytes was greater in the CRF + HP group, while parathyroidectomy (CRF + PTx + rPTH + HP) significantly reduced them, despite the high and similar serum phosphorus values. TNF-α, Adam17 and cardiac fibrosis at the histological and molecular level showed a similar pattern with increases in the group with severe secondary hyperparathyroidism (CRF + HP).

CONCLUSIONS

Hyperphosphatemia confirmed its importance in the genesis of secondary hyperparathyroidism, but also of kidney damage that was independent of PTH levels. However, inflammation, fibrosis, and cardiomyocyte growth were more closely related to PTH levels, since in the presence of similar severe hyperphosphatemia, parathyroidectomy reduced the values of inflammatory parameters, cardiac hypertrophy, and fibrosis.

Vascular calcification relationship to vascular biomarkers and bone metabolism in advanced chronic kidney disease

BACKGROUND

Vascular calcification (VC) and renal osteodystrophy are important complications of advanced chronic kidney disease (CKD). High resolution peripheral quantitative computed tomography (HRpQCT) is able to assess bone microstructure in renal osteodystrophy and lower leg arterial calcification (LLAC) is usually seen as an incidental finding. LLAC can be a useful quantitative assessment of VC in CKD but the relationship between LLAC and vascular biomarkers and bone is unknown. We aimed to assess the relationship between LLAC and biomarkers, bone turnover and microstructure.

METHODS

In this cross-sectional study, fasting blood samples were taken from 69 CKD stages 4-5D patients and 68 healthy controls. HRpQCT of distal tibia and radius were performed. 43 CKD patients had trans-iliac bone biopsy after tetracycline labelling.

RESULTS

LLAC was more severe in CKD than controls (median [IQR] 1.043 [0.05-16.52] vs 0 [0-0.55] mgHA, p < 0.001). CKD patients with diabetes (28%) had significantly higher LLAC compared to non-diabetic CKD (median [IQR] 24.07 [3.42-61.30] vs 0.23 [0-3.78] mgHA, p < 0.001). LLAC mass in CKD correlated with serum phosphate (rho = 0.29, p < 0.05), calcium x phosphate product (rho = 0.31, p < 0.05), intact parathyroid hormone (rho = 0.38, p < 0.01), intact fibroblast growth factor-23 (iFGF23) (rho = 0.40, p = 0.001), total alkaline phosphatase (rho = 0.41, p < 0.001), bone alkaline phosphatase (rho = 0.29, p < 0.05), osteocalcin (rho = 0.32, p < 0.05), osteoprotegerin (rho = 0.40, p = 0.001) and dephosphorylated-uncarboxylated matrix Gla protein (rho = 0.31, p < 0.05). LLAC in CKD also correlated with worse distal tibia cortical bone mineral density, thickness and porosity. No association was found between LLAC and bone turnover, mineralization or volume on biopsy in CKD. In multivariate analysis, only age, diabetes, iPTH and iFGF23 were independently associated with LLAC in CKD.

CONCLUSIONS

High levels of PTH and FGF23, along with older age and the presence of diabetes may all play independent roles in the development of LLAC in advanced CKD.

A chronic high phosphate intake in mice is detrimental for bone health without major renal alterations

BACKGROUND

Phosphate intake has increased in the last decades due to a higher consumption of processed foods. This higher intake is detrimental for patients with chronic kidney disease, increasing mortality and cardiovascular disease risk and accelerating kidney dysfunction. Whether a chronic high phosphate diet is also detrimental for the healthy population is still under debate.

METHODS

We fed healthy mature adult mice over a period of one year with either a high (1.2% w/w) or a standard (0.6% w/w) phosphate diet, and investigated the impact of a high phosphate diet on mineral homeostasis, kidney function and bone health.

RESULTS

The high phosphate diet increased plasma phosphate, parathyroid hormone (PTH) and calcitriol levels, with no change in fibroblast growth factor 23 levels. Urinary phosphate, calcium and ammonium excretion were increased. Measured glomerular filtration rate was apparently unaffected, while blood urea was lower and urea clearance was higher in animals fed the high phosphate diet. No change was observed in plasma creatinine levels. Blood and urinary pH were more acidic paralleled by higher bone resorption observed in animals fed a high phosphate diet. Total and cortical bone mineral density was lower in animals fed a high phosphate diet and this effect is independent of the higher PTH levels observed.

CONCLUSIONS

A chronic high phosphate intake did not cause major renal alterations, but affected negatively bone health, increasing bone resorption and decreasing bone mineral density.

Klotho in Clinical Nephrology: Diagnostic and Therapeutic Implications

αKlotho (called Klotho here) is a membrane protein that serves as the coreceptor for the circulating hormone fibroblast growth factor 23 (FGF23). Klotho is also cleaved and released as a circulating substance originating primarily from the kidney and exerts a myriad of housekeeping functions in just about every organ. The vital role of Klotho is shown by the multiorgan failure with genetic deletion in rodents, with certain features reminiscent of human disease. The most common causes of systemic Klotho deficiency are AKI and CKD. Preclinical data on Klotho biology have advanced considerably and demonstrated its potential diagnostic and therapeutic value; however, multiple knowledge gaps exist in the regulation of Klotho expression, release, and metabolism; its target organs; and mechanisms of action. In the translational and clinical fronts, progress has been more modest. Nonetheless, Klotho has potential clinical applications in the diagnosis of AKI and CKD, in prognosis of progression and extrarenal complications, and finally, as replacement therapy for systemic Klotho deficiency. The overall effect of Klotho in clinical nephrology requires further technical advances and additional large prospective human studies.

Control of phosphorus and prevention of fractures in the kidney patient

Patients with chronic kidney disease have a higher risk of fractures than the general population due to the added factor of uraemia. Although the mechanisms behind uraemia-associated fractures are not fully understood, it is widely accepted that the decrease in bone mineral content and alteration in bone architecture both increase bone fragility. As chronic kidney disease progresses, the risk of fracture increases, especially once the patient requires dialysis. Among the many causes of the increased risk are advanced age, amenorrhoea, steroid exposure, decreased vitamin D, increased PTH, malnutrition and chronic inflammation. Serum phosphorus, whether high or very low, seems to correlate with the risk of fracture. Moreover, increased serum phosphate is known to directly and indirectly affect bone metabolism through the development of adaptive hormonal mechanisms aimed at preventing hyperphosphataemia, such as the increase in PTH and FGF23 and the reduction in calcitriol. These adaptive mechanisms are less intense if the intestinal absorption of phosphorus is reduced with the use of phosphorus captors, which seem to have a positive impact in reducing the risk of fractures. We describe here the possible mechanisms associating serum phosphorus levels, the adaptive mechanisms typical in kidney disease and the use of drugs to control hyperphosphataemia with the risk of fractures. We found no studies in the literature providing evidence on the influence of different treatments on the risk of fractures in patients with chronic kidney disease. We suggest that control of phosphorus should be an objective to consider.

Osteocalcin and Abdominal Aortic Calcification in Hemodialysis Patients: An Observational Cross-Sectional Study

OBJECTIVES

To investigate the serum level of osteocalcin (OC), also known as bone Gla protein, in maintenance hemodialysis (MHD) patients and its correlation with abdominal aortic calcification (AAC).

METHODS

From July 2017 to February 2020, we enrolled 108 adult MHD patients. Routine fasting blood laboratory tests were performed before the start of the second hemodialysis in a week. Abdominal aortic calcification score (AACs) was assessed within 1 month. Pearson correlation and Logistic regression were used to analyze the data.

RESULTS

The OC level was 231.56 (25.92,361.33) ng/ml, elevating significantly in this group of MHD patients. It had a positive correlation with serum phosphorus (r = 0.511, P = 0.001), intact parathyroid hormone(iPTH) (r = 0.594, P = 0.0001), fibroblast growth factor 23(FGF23) (r = 0.485, P = 0.003) and a negative correlation with age(r = -0.356, P = 0.039). Based on the AACs, patients were divided into two groups. Serum OC level were higher in patients with AACs≥5 (p=0.032). A multiple logistics regression analysis revealed that age (odds ratio [OR]1.14, P=0.005) and OC(OR=1.10, P=0.008)were risk factors for high AACs(≥5).

CONCLUSION

The study implicated that OC elevated significantly in this group of MHD patients.OC is positively correlated with phosphorus, iPTH, FGF23, and a negative correlation with age. OC was a risk factor for vascular calcification in this study, but this study did not classify osteocalcin as c-OC and unOC. Whether unOC is associated more directly with vascular calcification requires further study.

Duration of Serum Phosphorus Control Associated with Overall Mortality in Patients Undergoing Peritoneal Dialysis

BACKGROUND

Serum phosphorus (SP) level is closely associated with overall mortality and cardiovascular events, while the role of SP controlled duration is not fully recognized. Here, we conducted a retrospective cohort study in our department to identify the relationship of SP controlled duration with clinical outcomes in patients undergoing peritoneal dialysis (PD).

METHODS

PD patients in our center from January 1, 2009, to June 30, 2019, were followed up at 2-month (the first year) or 5-month (the next follow-up period) intervals, and until death, until PD withdrawal, or until June 30, 2019. Data at each follow-up point were collected from their medical records. SP levels, changed degree of SP over baseline, and SP controlled duration were analyzed with overall mortality, PD withdrawal (including death, transferred to hemodialysis, and received renal transplantation), and combined endpoint (including death, acute heart failure, cardiovascular event, and stroke).

RESULTS

A total of 530 patients entered the analysis. Of them, 456 (86.0%) had hyperphosphatemia before dialysis, and the SP levels decreased soon after dialysis. The degree of SP change over baseline was the maximum at the 3rd month after dialysis (-31.0%), and lower degree was associated with higher overall mortality (hazard ratio [HR], 1.012; 95% CI, 1.004-1.020; p = 0.003). The median SP controlled duration was 13 (5-28) months, and longer duration was significantly associated with lower overall mortality (HR, 0.968; 95% CI, 0.956-0.981; p < 0.001). After categorization, duration more than 12 months greatly improved overall mortality with a HR of 0.197 (0.082-0.458; p < 0.001 vs. SP never controlled group) and 0.329 (0.150-0.724; p = 0.006 vs. duration <12 months group). Longer SP controlled duration also improved PD withdrawal and combined endpoint.

CONCLUSIONS

In summary, both degree and duration of SP control were tightly associated with overall mortality. We should control SP levels as early, as possible, and as long as we could.

Uremic Toxins and Vascular Calcification-Missing the Forest for All the Trees

The cardiorenal syndrome relates to the detrimental interplay between the vascular system and the kidney. The uremic milieu induced by reduced kidney function alters the phenotype of vascular smooth muscle cells (VSMC) and promotes vascular calcification, a condition which is strongly linked to cardiovascular morbidity and mortality. Biological mechanisms involved include generation of reactive oxygen species, inflammation and accelerated senescence. A better understanding of the vasotoxic effects of uremic retention molecules may reveal novel avenues to reduce vascular calcification in CKD. The present review aims to present a state of the art on the role of uremic toxins in pathogenesis of vascular calcification. Evidence, so far, is fragmentary and limited with only a few uremic toxins being investigated, often by a single group of investigators. Experimental heterogeneity furthermore hampers comparison. There is a clear need for a concerted action harmonizing and standardizing experimental protocols and combining efforts of basic and clinical researchers to solve the complex puzzle of uremic vascular calcification.

Control of phosphorus and prevention of fractures in the kidney patient

Patients with chronic kidney disease have a higher risk of fractures than the general population due to the added factor of uraemia. Although the mechanisms behind uraemia-associated fractures are not fully understood, it is widely accepted that the decrease in bone mineral content and alteration in bone architecture both increase bone fragility. As chronic kidney disease progresses, the risk of fracture increases, especially once the patient requires dialysis. Among the many causes of the increased risk are advanced age, amenorrhoea, steroid exposure, decreased vitamin D, increased parathyroid hormone (PTH), malnutrition and chronic inflammation. Serum phosphorus, whether high or very low, seems to correlate with the risk of fracture. Moreover, increased serum phosphate is known to directly and indirectly affect bone metabolism through the development of adaptive hormonal mechanisms aimed at preventing hyperphosphataemia, such as the increase in PTH and fibroblast growth factor 23 (FGF23) and the reduction in calcitriol. These adaptive mechanisms are less intense if the intestinal absorption of phosphorus is reduced with the use of phosphorus captors, which seem to have a positive impact in reducing the risk of fractures. We describe here the possible mechanisms associating serum phosphorus levels, the adaptive mechanisms typical in kidney disease and the use of drugs to control hyperphosphataemia with the risk of fractures. We found no studies in the literature providing evidence on the influence of different treatments on the risk of fractures in patients with chronic kidney disease. We suggest that control of phosphorus should be an objective to consider.

Transcriptomics: a Solution for Renal Osteodystrophy?

PURPOSE OF REVIEW

The molecular mechanisms of the bone disease associated with chronic kidney disease (CKD), called renal osteodystrophy (ROD), are poorly understood. New transcriptomics technologies may provide clinically relevant insights into the pathogenesis of ROD. This review summarizes current progress and limitations in the study and treatment of ROD, and in transcriptomics analyses of skeletal tissues.

RECENT FINDINGS

ROD is characterized by poor bone quality and strength leading to increased risk of fracture. Recent studies indicate permanent alterations in bone cell populations during ROD. Single-cell transcriptomics analyses, successful at identifying specialized cell subpopulations in bone, have not yet been performed in ROD. ROD is a widespread poorly understood bone disease with limited treatment options. Transcriptomics analyses of bone are needed to identify the bone cell subtypes and their role in the pathogenesis of ROD, and to develop adequate diagnosis and treatment strategies.

The Role of Sclerostin in Bone and Ectopic Calcification

Sclerostin, a 22-kDa glycoprotein that is mainly secreted by the osteocytes, is a soluble inhibitor of canonical Wnt signaling. Therefore, when present at increased concentrations, it leads to an increased bone resorption and decreased bone formation. Serum sclerostin levels are known to be increased in the elderly and in patients with chronic kidney disease. In these patient populations, there is a high incidence of ectopic cardiovascular calcification. These calcifications are strongly associated with cardiovascular morbidity and mortality. Although data are still controversial, it is likely that there is a link between ectopic calcification and serum sclerostin levels. The main question, however, remains whether sclerostin exerts either a protective or deleterious role in the ectopic calcification process.

Phenotypic features of vascular calcification in chronic kidney disease

BACKGROUND

Patients with chronic kidney disease stage 5 (CKD5) are predisposed to vascular calcification (VC), but the combined effect of factors associated with VC was sparsely investigated. We applied the relaxed linear separability (RLS) feature selection model to identify features that concomitantly associate with VC in CKD5 patients.

METHODS

Epigastric arteries collected during surgery from living donor kidney transplant recipients were examined to score the histological extent of medial VC. Sixty-two phenotypic features in 152 patients were entered into RLS model to differentiate between no-minimal VC (n = 93; score 0-1) and moderate-extensive VC (n = 59; score 2-3). The subset of features associated with VC was selected on the basis of cross-validation procedure. The strength of association of the selected features with VC was expressed by the absolute value of 'RLS factor'.

RESULTS

Among 62 features, a subset of 17 features provided optimal prediction of VC with 89% of patients correctly classified into their groups. The 17 features included traditional risk factors (diabetes, age, cholesterol, BMI and male sex) and markers of bone metabolism, endothelial function, metabolites, serum antibodies and mitochondrial-derived peptide. Positive RLS factors range from 1.26 to 4.05 indicating features associated with increased risk of VC, and negative RLS factors range from -0.95 to -1.83 indicating features associated with reduced risk of VC.

CONCLUSION

The RLS model identified 17 features including novel biomarkers and traditional risk factors that together concomitantly associated with medial VC. These results may inform further investigations of factors promoting VC in CKD5 patients.

Mineral Bone Abnormalities and Vascular Calcifications

Vascular calcification (VC) is common in chronic kidney disease, increases in prevalence as patients progress to end-stage renal disease, and is significantly associated with mortality. VC is a complex and highly regulated process similar to bone formation whereby hydroxyapatite crystals deposit in the intimal or medial layer of arteries. Mineral bone abnormalities are common in chronic kidney disease; reduction in glomerular filtration rate and changes in vitamin D, parathyroid hormone, and fibroblast growth factor 23 result in the dysregulation of phosphorus and calcium metabolism. Cell culture studies, animal models, and observational and clinical studies all suggest this abnormal mineral metabolism plays a role in the initiation and progression of VC in kidney disease. This review will focus on these mineral bone abnormalities and how they may contribute to mechanisms that induce VC in kidney disease.

Parathyroidectomy in dialysis patients: Indications, methods, and consequences

Secondary hyperparathyroidism, characterized by increased PTH synthesis and secretion, is often seen in advanced stages of chronic kidney disease. Excessive proliferation of parathyroid cells leads to the development of diffuse hyperplasia that subsequently progresses to nodular histology. Refractory hyperparathyroidism occurs when parathyroid glands fail to respond to medical therapy. Parathyroidectomy (PTX), surgical resection of parathyroid glands, is usually performed in cases of persistent serum levels of PTH above 1000 pg/mL associated with hypercalcemia or when hyperparathyroidism is refractory to conservative therapy. Parathyroidectomy can be carried out using different procedures: subtotal PTX or total PTX with or without parathyroid autotransplantation. Parathyroid surgery may have undesirable consequences due to PTH oversuppression, such as the development of adynamic bone disease; hungry bone syndrome is quite common after this surgery. However, PTX improves survival and parameters of mineral metabolism. Parathyroidectomy needs to be considered in those patients with severe hyperparathyroidism with a poor response to pharmacological treatment and with distinct undesirable effects of PTH on bone and mineral metabolism parameters.