Vascular calcification and uremia: what do we know?

Analysis of risk factors for abdominal aortic calcification in dialysis patients and its influence on long-term recovery

This study investigated the risk factors of abdominal aortic calcification (AAC) in patients with stage 5 chronic kidney disease (CKD) and the effects of AAC and different dialysis methods on the 3-year survival rate of patients with stage 5 CKD. A retrospective cohort study was conducted on stage 5 CKD patients who received dialysis treatment. The general data were collected, and all fasting venous blood samples were harvested before the first dialysis to detect biochemical markers. The AAC was evaluated by lateral abdominal X-ray. The patients were followed up with a cut-off date of March 31, 2022, with all-cause mortality as the endpoint event. A total of 205 patients were included. multivariable Cox regression analysis confirmed that AAC (hazard ratio (HR) = 2.173, 95% CI 1.029-4.588, p = 0.042), advanced age (HR = 1.061, 95% CI 1.031-1.093, p < 0.001), duration of dialysis (HR = 1.015, 95% CI 1.007-1.032, p < 0.001), diabetes (HR = 3.966, 95% CI 2.164-7.269, p < 0.001), and hypertension (HR = 1.897, 95% CI 1.089-3.303, p = 0.024) were independent risk factors for 3-year mortality. However, peritoneal dialysis (HR = 0.366, 95% CI 0.165-0.812, p = 0.013), high albumin (HR = 0.882, 95% CI 0.819-0.950, p = 0.001), and high hemoglobin (HR = 0.969, 95% CI 0.942-0.997, p = 0.031) were protective factors for 3-year mortality in stage 5 CKD patients. Increased age, long-term dialysis, high level of intact parathyroid hormone, diabetes, and hypertension are closely related to the occurrence of AAC in patients with stage 5 CKD. In addition, AAC is an independent risk factor for all-cause mortality in patients with stage 5 CKD.

Pathogenesis of Pulmonary Calcification and Homologies with Biomineralization in Other Tissues

Lungs often present tissue calcifications and even ossifications, both in the context of high or normal serum calcium levels. Precise mechanisms governing lung calcifications have not been explored. Herein, we emphasize recent advances about calcification processes in other tissues (especially vascular and bone calcifications) and discuss potential sources of calcium precipitates in the lungs, involvement of mineralization promoters and crystallization inhibitors, as well as specific cytokine milieu and cellular phenotypes characteristic for lung diseases, which may be involved in pulmonary calcifications. Further studies are necessary to demonstrate the exact mechanisms underlying calcifications in the lungs, document homologies in biomineralization processes between various tissues in physiological and pathologic conditions, and unravel any locally specific characteristics of mineralization processes that may be targeted to reduce or prevent functionally relevant lung calcifications without negatively affecting the skeleton.

Impact of serum albumin level and variability on short-term cardiovascular-related and all-cause mortality in patients on maintenance hemodialysis

Studies have shown that low serum albumin (Salb) levels are associated with a high risk of mortality among patients on maintenance hemodialysis (MHD); however, the impact of Salb variability on short-term cardiovascular mortality remains unclear. Herein, we investigated the association between Salb levels and Salb variability on short-term all-cause and cardiovascular-related mortality in patients on MHD.Eligible patients on MHD at Chongqing General Hospital between June 2017 and June 2020 were recruited in this study. Patients were grouped by Salb levels (normal Salb, ≥3.8 g/dL; low Salb, 3.4-3.8 g/dL; and lower Salb, 2-3.4 g/dL) and Salb variability (decreased, >5% loss; increased, >5% gain; and steady, 5% loss to 5% gain). Associations between Salb levels, Salb variability, and all-cause and cardiovascular-related mortality were analyzed using Cox regression models. A survival analysis was performed using the Kaplan-Meier analysis.We enrolled a total of 181 patients on MHD with an average age of 65 years (interquartile range [IQR], 53-75 years). The mean Salb level was 3.8 ± 0.6 g/dL (IQR 2.9-4.4 g/dL), and the median Salb variability was 2.6% per year (IQR, -4.1 to 6.5). Fifty-two (29%) patients died, including 31 (17%) patients who died due to cardiovascular-related causes. Compared with the other groups, the lower Salb group had higher all-cause mortality (P < .01). Cox regression analyses revealed that lower Salb levels and decreased Salb variability were independently associated with all-cause mortality (hazard ratio [HR] = 1.95, 95% confidence interval [CI] 1.103-3.452; HR = 2.245, 95% CI 1.084-4.650), whereas increased Salb variability was independently associated with cardiovascular-related mortality (HR = 2.919, 95% CI 1.178-7.234; P < .05).Lower Salb levels were an independent predictor of all-cause mortality in patients on MHD. Increased Salb variability was strongly associated with cardiovascular-related mortality in the same population, especially in the short-term and in patients with normal Salb levels. Significantly elevated Salb variability should be evaluated to reduce cardiovascular-related mortality.

Additional prognostic value of toe-brachial index beyond ankle-brachial index in hemodialysis patients

Background

Ankle-brachial index (ABI), the first-line diagnostic test for peripheral artery disease, can be falsely elevated when ankle arteries are incompressible, showing a J-shaped association with mortality. In this situation, toe-brachial index (TBI) is the recommended test. However, whether TBI provides additional prognostic information beyond ABI in patients on hemodialysis is unknown.

Methods

In this retrospective cohort study of 247 Japanese prevalent hemodialysis patients (mean age 66.8 [SD 11.6] years), we evaluated mortality (116 deaths over a median follow-up of 5.2 years) related to quartiles of ABI and TBI, as well as three categories of low ABI (≤0.9), normal/high ABI (> 0.9) + low TBI (≤0.6), and normal/high ABI + normal TBI (> 0.6) using multivariable Cox models.

Results

ABI showed a J-shaped association with mortality (adjusted hazard ratio 2.72 [95% CI, 1.52–4.88] in the lowest quartile and 1.59 [95% CI, 0.87–2.90] in the highest quartile vs. the second highest). Lower TBI showed a potentially dose-response association with mortality (e.g., adjusted hazard ratios 2.63 [95% CI, 1.36–5.12] and 2.89 [95% CI, 1.49–5.61] in the lowest two quartiles vs. the highest). When three categories by both ABI and TBI were analyzed, those with low ABI (≤0.9) experienced the highest risk followed by normal/high ABI (> 0.9) + low TBI (≤0.6). Among patients with normal/high ABI (> 0.9), the increased mortality risk in individuals with low TBI (≤0.6) compared to those with normal TBI (> 0.6) were significant (adjusted hazard ratio 1.84 [95% CI, 1.12–3.02]).

Conclusions

Lower TBI was independently associated with mortality in patients on hemodialysis and has the potential to classify mortality risk in patients with normal/high ABI. Our results support the importance of evaluating TBI in addition to ABI in this clinical population.

Genetic variants of mineral metabolism in health and disease

PURPOSE OF REVIEW

Disturbances in mineral metabolism are common among individuals with chronic kidney disease and have consistently been associated with cardiovascular and bone disease. The current review aims to describe the current knowledge of the genetic aspects of mineral metabolism disturbances and to suggest directions for future studies to uncover the cause and pathogenesis of chronic kidney disease - mineral bone disorder.

RECENT FINDINGS

The most severe disorders of mineral metabolism are caused by highly penetrant, rare, single-gene disruptive mutations. More recently, genome-wide association studies (GWAS) have made an important contribution to our understanding of the genetic determinants of circulating levels of 25-hydroxyvitamin D, calcium, phosphorus, fibroblast growth factor-23, parathyroid hormone, fetuin-A and osteoprotegerin. Although the majority of these genes are known members of mineral homeostasis pathways, GWAS with larger sample sizes have enabled the discovery of many genes not known to be involved in the regulation of mineral metabolism.

SUMMARY

GWAS have enabled remarkable developments in our ability to discover the genetic basis of mineral metabolism disturbances. Although we are far from using these findings to inform clinical practice, we are gaining understanding of novel biological mechanisms and providing insight into ethnic variation in these traits.

The bone-vessel axis in chronic kidney disease: An update on biochemical players and its future role in laboratory medicine

Vascular wall calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD). In CKD, VC is more frequent and severe than in the general population and it is associated with increased cardiovascular mortality and morbidity. In the last years, laboratory and clinical evidence have drawn the attention to the relationship between bone disease and VC in CKD patients, leading to the concept of a bone-vessel or bone-vascular axis. It means that disorders of bone volume and bone turnover may influence the risk of VC and ultimately the high risk of cardiovascular mortality. In fact, a higher burden of VC has been associated to low bone volume and low bone turnover in hemodialysis (HD) patients with renal osteodystrophy characterized by histomorphometric evaluation of bone biopsies. The molecular mechanisms underlying the regulation of bone cells and vascular cells in CKD are poorly understood. In this review, we discuss relevant evidence linking bone disorders and VC in CKD and also rising molecular players involved in this bone-vascular axis. Indeed, accumulating data is available for two proposed systems: receptor activator for nuclear factor kB (RANK)/ RANK ligand (RANKL)/osteoprotegerin (OPG) system and inhibitors of Wnt signaling - mainly sclerostin. Although they are promising biochemical markers linking bone formation and bone reabsorption with VC, there is a long way to go as long evidence from laboratory studies is often divergent to the clinical data as will be discussed. Future prospective studies are needed in order to evaluate the role of these biochemical players as useful clinical markers for VC, bone volume and perhaps bone turnover.

Abdominal aortic calcification score as a predictor of clinical outcome in peritoneal dialysis patients: a prospective cohort study

Background

Abdominal aortic calcification assessed by X-ray is recommended to evaluate vascular calcification in dialysis patients. It has been shown that abdominal aortic calcification score (AACS) is a predictor of adverse outcomes in hemodialysis patients, but evidence regarding its prognostic value in peritoneal dialysis (PD) patients is still insufficient. We aimed to examine the predictive role of AACS for major adverse cardiac and cerebrovascular events (MACCE) and mortality in PD patients.

Methods

Eligible patients undergoing PD between July 2011 and July 2014 were recruited. AACS was quantified using lateral lumbar radiography at recruitment. Patients were prospectively followed up until death, PD cessation, or to the end of the study (August 31, 2018). Both subdistribution hazards and cause-specific hazards models were used to evaluate the association between AACS and MACCE as well as mortality.

Results

292 patients were enrolled, including 160 males (54.8%) with mean age 57.1 ± 15.2 years and median PD duration 28.4 (IQR 12.0, 57.8) months. Among them, 75 (25.7%) patients were comorbid with diabetes, and 94 (32.2%) patients had cardiovascular disease (CVD). The average AACS was 2.0 (0.0, 6.0). Patients were categorized on the tertiles of AACS (Low AACS group, AACS = 0, n = 125; Medium AACS group, AACS 1–4, n = 72; and High AACS group, AACS> 4, n = 95). AACS was associated with age (OR = 1.081, P < 0.001), PD duration (OR = 1.012, P = 0.003), CVD (OR = 1.919, P = 0.020) and diabetes (OR = 2.554, P = 0.002). During the follow-up period of 43.6 (24.6, 50.7) months, there were 65 MACCEs and 84 deaths. Significantly higher cumulative incidences of all-cause mortality (Log-rank = 35.992, P<0.001; Gray = 38.662, P < 0.001) and MACCE (Log-rank = 26.146, P<0.001; Gray = 27.810, P < 0.001) were observed in the upper AACS tertile. AACS was an independent predictor of all-cause mortality (HR = 2.438, 95% CI 1.246–4.772, P = 0.009; SHR = 2.323, 95%CI 1.229–4.389, P = 0.009) and MACCE (HR = 3.455, 95% CI 1.734–6.884, P < 0.001; SHR = 3.063, 95%CI 1.460–6.430, P = 0.003) in this study.

Conclusions

AACS was associated with age, PD duration, CVD and diabetes in PD patients. AACS could predict MACCE and all-cause mortality in this population. It thus might be a safe and feasible method to identify PD patients with adverse outcomes.

Comparison of the effects of lanthanum carbonate and calcium carbonate on the progression of cardiac valvular calcification after initiation of hemodialysis

Background

Although mineral metabolism disorder influences cardiac valvular calcification (CVC), few previous studies have examined the effects of non-calcium-containing and calcium-containing phosphate binders on CVC in maintenance hemodialysis patients. The aim of the present study was to compare the effects of lanthanum carbonate (LC) with calcium carbonate (CC) on the progression of CVC in patients who initiated maintenance hemodialysis and to investigate clinical factors related to CVC.

Methods

The current study included 50 subjects (mean age 65 years, 72% males) from our previous randomized controlled trial (LC group, N = 24; CC group, N = 26). CVC was evaluated as CVC score (CVCS) using echocardiography at baseline and 18 months after initiation of hemodialysis. We compared CVCS and the changes between the two groups. We also analyzed the associations between CVCS and any other clinical factors including arterial plaque score (PS) and serum phosphorus levels.

Results

Baseline characteristics of study participants including CVCS were almost comparable between the two groups. At 18 months, there were no significant differences in mineral metabolic markers or CVCS between the two groups, and CVCS were significantly correlated with PS (r = 0.39, p < 0.01). Furthermore, changes in CVCS were significantly correlated with average phosphorus levels (r = 0.36, p < 0.05), which were significantly higher in high serum phosphorus and high PS group compared to low serum phosphorus and low PS group (p < 0.05).

Conclusions

In the present study, there were no significant differences between LC and CC with regard to progression of CVC. However, serum phosphorus levels and arterial plaque seem to be important for the progression and formation of CVC in hemodialysis patients.

Pathological Mineralization: The Potential of Mineralomics

Pathological mineralization has been reported countless times in the literature and is a well-known phenomenon in the medical field for its connections to a wide range of diseases, including cancer, cardiovascular, and neurodegenerative diseases. The minerals involved in calcification, however, have not been directly studied as extensively as the organic components of each of the pathologies. These have been studied in isolation and, for most of them, physicochemical properties are hitherto not fully known. In a parallel development, materials science methods such as electron microscopy, spectroscopy, thermal analysis, and others have been used in biology mainly for the study of hard tissues and biomaterials and have only recently been incorporated in the study of other biological systems. This review connects a range of soft tissue diseases, including breast cancer, age-related macular degeneration, aortic valve stenosis, kidney stone diseases, and Fahr’s syndrome, all of which have been associated with mineralization processes. Furthermore, it describes how physicochemical material characterization methods have been used to provide new information on such pathologies. Here, we focus on diseases that are associated with calcium-composed minerals to discuss how understanding the properties of these minerals can provide new insights on their origins, considering that different conditions and biological features are required for each type of mineral to be formed. We show that mineralomics, or the study of the properties and roles of minerals, can provide information which will help to improve prevention methods against pathological mineral build-up, which in the cases of most of the diseases mentioned in this review, will ultimately lead to new prevention or treatment methods for the diseases. Importantly, this review aims to highlight that chemical composition alone cannot fully support conclusions drawn on the nature of these minerals.

Different type and dosage of heparin were not associated with the progression of coronary artery calcification in haemodialysis patients

AIM

Several studies have verified that unfractionated heparin (UFH) and low molecular heparin (LWMH) can induce bone loss, and bone mineral density has been inversely associated with vascular calcification in some clinical researches. But few have focused on the relationship between types and dosages of heparin and the progression of vascular calcification. We observed the progression of coronary artery calcification (CAC) in maintenance haemodialysis (MHD) patients who were treated with UFH and LMWH.

METHODS

This was a prospective prevalent cohort study of MHD patients. Computed tomography was performed at enrolment and 2 years after enrolment, and CAC score was obtained. Demographic and clinical data, baseline and time-average laboratory indices were collected. Multiple linear regression and logistic regression were used to estimate the influencing factors of progression of CAC.

RESULTS

In this study, (i) we initially enrolled 69 HD patients, and then 56 patients finished the follow-up. (ii) Among the total 56 patients, 27 patients (48.2%) were treated with UFH, 14 (25.0%) with LMWH and 15 (26.8%) with both. The median baseline CAC scores of three groups (UFH, LMWH and both users) were 91.0 (1.0, 1052.0), 134.0 (0, 1292.0) and 250.5 (27.0, 1139.0), respectively, with no significant difference (P = 0.663); the median CAC progression scores were 42.0 (0, 364.0), 172.0 (7.0, 653.0) and 118.5 (0, 434.0), respectively, with no significant difference (P = 0.660). (iii) Pearson and spearman correlation analysis shown that the progression of CAC was not associated with cumulative dosage of heparin used. (iv) After adjusted for diabetes mellitus, time-averaged intact parathyroid hormone, phosphate and alkaline phosphatase, logistic regression analysis showed using different types of heparin was not an independent risk factor for CAC progression; and multiple linear regression analysis showed that the type of heparin used was not associated with CAC progression.

CONCLUSION

There were no significant differences in the effects of the types and dosages of heparin on CAC progression in patients on haemodialysis.

Study on the Prevalence of Vascular Calcification in Different Types of Arteries and Influencing Factors in Maintenance Peritoneal Dialysis Patients

OBJECTIVE

To investigate the occurrence of vascular calcification (VC) in different types of arteries in patients with maintenance peritoneal dialysis (PD) patients and its influencing factors.

METHODS

This study enrolled PD patients with stable status who has received PD treatment for more than 6 months in Peking University People's Hospital. We used plain X-ray films of abdomen, pelvis, and hands to quantitatively evaluate VC of large artery (abdominal aorta, iliac artery), medium artery (femoral artery, radial artery), and small artery (finger arteries). Two radiologists read and scored radiographs blindly. Demographic data, clinical characteristics, Charlson comorbidity index (CCI), baseline and time-average laboratory indices including parameters of calcium phosphorus metabolism, serum albumin, PD adequacy were collected. A logistic regression model was used to estimate the influencing factors of different sites of VC.

RESULTS

(1) 154 PD patients were enrolled in this study: seventy-eight males, mean age was 60.4 ± 13.9 years, and median PD duration was 24 (16.39) months. The major primary disease was diabetic nephropathy (39%). (2) Among the 154 PD patients, the proportion of calcification of large artery was the highest (found in 100 patients, accounting for 64.9%); then the medium artery (66, 42.9%); and 15 of small artery, accounting for 9.7%. (3) Logistic regression showed that older age, longer dialysis duration, lower baseline serum intact parathyroid hormone (iPTH), and higher CCI scores were independent risk factors of large artery calcification (p < 0.05), and higher CCI scores, higher baseline serum triglycerides (TG), lower baseline serum iPTH, and time-average iPTH were independent risk factors of medium and small arteries.

CONCLUSIONS

In PD patients, the occurrence of large artery calcification was higher than others. Among different sites of VC, the abdominal aortic calcification was most likely to occur, and the proportion of small artery calcification was low. Calcification of medium and small arteries can exist alone without calcification of large artery. Large artery calcification was more likely to occur in patients with older age, longer dialysis duration, lower baseline serum iPTH levels and higher CCI scores. Patients with higher CCI scores, higher baseline TG and lower baseline iPTH, and time-average iPTH were more likely to develop small and medium artery calcification.

Osteonectin (SPARC) Expression in Vascular Calcification: In Vitro and Ex Vivo Studies

Osteonectin, also termed SPARC, is a noncollagenous protein of bone matrix. Since there are controversial results regarding its role during the process of vascular calcification, we investigated osteonectin expression in our in vitro calcification model. Rat vascular smooth muscle cells (VSMCs) were challenged with high phosphate (5 mmol/L Pi) and analyzed quantifying calcium levels, through immunohistochemical studies, and studying gene expression. We detected a peak of osteonectin expression at day 7 in cell treated with high phosphate. The time course of calcium deposition, reflected the expression of osteonectin, resulting extensively present at day 7. On the contrary, the expression of the mitotic marker Ki-67 had a peak at day 4, showing no correlation between osteonectin and cell proliferation. Moreover, 7 days was the time point in which Cbfα1/RUNX-2 had its maximal expression. Furthermore, ascorbic acid increased osteonectin expression, supporting a procalcifying role for this protein. Next we decided to study osteonectin expression ex vivo in fetal, adult not calcified, and adult calcific vessels. Immunohistochemical studies demonstrated a spread and strong reactivity in VSMCs of a 20-week fetus, confirming that osteonectin may have a potential role in regulation of mitosis and in cell differentiation. In adult not calcified arteries, osteonectin was constitutively expressed and its levels increased in atherosclerotic and in calcified plaques, where it could have a regulatory role in the calcification process. Our in vitro and ex vivo data show osteonectin expression during the calcification process and suggest its potential role as procalcifying factor.

Baroreflex dysfunction in chronic kidney disease

Chronic kidney disease (CKD) patients have high cardiovascular mortality and morbidity. The presence of traditional and CKD related risk factors results in exaggerated vascular calcification in these patients. Vascular calcification is associated with reduced large arterial compliance and thus impaired baroreflex sensitivity (BRS) resulting in augmented blood pressure (BP) variability and hampered BP regulation. Baroreflex plays a vital role in short term regulation of BP. This review discusses the normal baroreflex physiology, methods to assess baroreflex function, its determinants along with the prognostic significance of assessing BRS in CKD patients, available literature on BRS in CKD patients and the probable patho-physiology of baroreflex dysfunction in CKD.

Phosphate balance in ESRD: diet, dialysis and binders against the low evident masked pool

Phosphate metabolism is crucial in the pathophysiology of secondary hyperparathyroidism and vascular calcification. High phosphate levels have been consistently associated with unfavorable outcomes in dialysis patients, but several limitations are still hampering a resolutive definition of the optimal targets of phosphate serum levels to be achieved in this cohort. Nonetheless, hyperphosphatemia is a late marker of phosphate overload in humans. Clinical nephrologists routinely counteract the positive phosphate balance in dialysis patients through nutritional counseling, stronger phosphate removal by dialysis and prescription of phosphate binders. However, the superiority against placebo of phosphate control by diet, dialysis or binders in terms of survival has never been tested in dedicated randomized controlled trials. The present review discusses this conundrum with particular emphasis on the rationale supporting the value of a simultaneous intervention against phosphate overload in dialysis patients via the improvement of dietary intakes, dialysis efficiency and an individualized choice of phosphate binders.

A current understanding of vascular calcification in CKD

Patients with chronic kidney disease (CKD) and end-stage renal disease (ESRD) have significant cardiovascular morbidity and mortality that is in part due to the development of vascular calcification. Vascular calcification is an active, highly regulated process that shares many similarities with normal bone formation. New discoveries related to extracellular vesicles, microRNAs, and calciprotein particles continue to reveal the mechanisms that are involved in the initiation and progression of vascular calcification in CKD. Further innovations in these fields are critical for the development of biomarkers and therapeutic options for patients with CKD and ESRD.

Effect of different hemodialyzers on serum levels of interleukin-6, interleukin-10 and interleukin-18

BACKGROUND

The blood and membrane contact during dialysis may elicit an immune reaction. The current study looked at the impact of different dialyzers on blood levels of cytokines.

METHODS

During the first month, randomly selected patients were treated with one dialyzer (PF-170H) and then crossed over to another dialyzer (FLX-18GW) during the next month. Pre- and postdialysis blood samples were assayed for interleukin (IL)-6, IL-10 and IL-18.

RESULTS

A significant drop of postdialysis systolic blood pressure (pre vs. post 156.4 ± 31.8 vs. 143.1 ± 24.8 mm Hg, p = 0.014) and diastolic pressure (80.7 ± 12.7 vs. 73.4 ± 10.9 mm Hg, p = 0.002) were found when patients were dialyzed with PF-170H. A significant increase of postdialysis IL-18 levels was found in both groups (pre vs. post 605.5 ± 278.6 vs. 690.6 ± 315.3 pg/ml, p = 0.016, for PF-170H and 556.4 ± 231.0 vs. 647.3 ± 282.6 pg/ml, p = 0.067, for FLX-18GW). There was a positive correlation between IL-6 and IL-10 levels (p < 0.0001).

CONCLUSION

We demonstrated a significant increase of postdialysis serum IL-18 level when either dialyzer was used. There is a strong correlation between serum levels of IL-6 and IL-10.

[A case of isolated small intestinal wall calcification on patient with continuous ambulatory peritoneal dialysis]

The metastatic calcification is defined as the deposition of calcium salt in normal tissue with an abnormal serum biochemical environment, such as chronic kidney disease, hyperparathyroidism, and hypercalcemia related with malignancy. Although the metastatic calcification can develop in any organs and tissues, presenting its symptoms and complications are rare. Thus a few cases have been reported. This case shows the metastatic calcification of the small intestine without any peritoneal and mesenteric vascular calcification which was early diagnosed by computed tomography and mesenteric angiography in a patient with abdominal pain, receiving continuous ambulatory peritoneal dialysis due to end stage renal disease. The clinician should early consider the metastatic calcification as differential diagnosis when unidentified calcifications are noted in simple abdominal X-ray such as in the present case, and promptly confirm it by using appropriate diagnostic tests in order to prevent its complications and progression.

Physicochemical and biological properties of biomimetic mineralo-protein nanoparticles formed spontaneously in biological fluids

Recent studies indicate that mineral nanoparticles (NPs) form spontaneously in human body fluids. These biological NPs represent mineral precursors that are associated with ectopic calcifications seen in various human diseases. However, the parameters that control the formation of mineral NPs and their possible effects on human cells remain poorly understood. Here a nanomaterial approach to study the formation of biomimetic calcium phosphate NPs comparable to their physiological counterparts is described. Particle sizing using dynamic light scattering reveals that serum and ion concentrations within the physiological range yield NPs below 100 nm in diameter. While the particles are phagocytosed by macrophages in a size-independent manner, only large particles or NP aggregates in the micrometer range induce cellular responses that include production of mitochondrial reactive oxygen species, caspase-1 activation, and secretion of interleukin-1β (IL-1β). A comprehensive proteomic analysis reveals that the particle-bound proteins are similar in terms of their identity and number, regardless of particle size, suggesting that protein adsorption is independent of particle size and curvature. In conclusion, the conditions underlying the formation of mineralo-protein particles are similar to the ones that form in vivo. While mineral NPs do not activate immune cells, they may become pro-inflammatory and contribute to pathological processes once they aggregate and form larger mineral particles.

Mineral metabolism abnormalities and vitamin D receptor activation in cardiorenal syndromes

Over the last decade, it has become increasingly clear that the cardiovascular and renal systems are interdependent. Primary disorders of either system have been shown to disturb the other system. As a result, a class of cardiorenal syndromes (CRS) has been identified wherein a vicious cycle is established as an acute/chronic dysfunction of either the kidney or the heart exacerbates the loss of function in the other organ. Progressive loss of kidney function observed in patients with CRS (mostly types 2 and 4) leads to reduced production of calcitriol (active vitamin D) and an imbalance in calcium and phosphorus levels, which are correlated with increased rates of cardiovascular events and mortality. In addition, hypocalcemia can lead to prolonged and excessive secretion of parathyroid hormone (PTH), eventually leading to development of secondary hyperparathyroidism. Therefore, based on this important mechanism of organ damage, one of the major goals of therapy for patients with CRS is to restore regulatory control of PTH. Although administration of calcitriol increases serum calcium levels and reduces PTH levels, it is also associated with elevated serum levels of calcium-phosphorus product. Therefore, compounds that selectively activate vitamin D receptors, potentially reducing calcium × phosphate toxicity, are likely to enhance cardiorenal protection and provide significant clinical benefit.

Arterial stiffness, vascular calcification and bone metabolism in chronic kidney disease

Patients with chronic kidney disease (CKD) have an extremely poor cardiovascular outcome. Arterial stiffness, a strong independent predictor of survival in CKD, is connected to arterial media calcification. A huge number of different factors contribute to the increased arterial calcification and stiffening in CKD, a process which is in parallel with impaired bone metabolism. This coincidence was demonstrated to be part of the direct inhibition of calcification in the vessels, which is a counterbalancing effect but also leads to low bone turnover. Due to the growing evidence, the definition of “CKD mineral bone disorder” was created recently, underlining the strong connection of the two phenomena. In this review, we aim to demonstrate the mechanisms leading to increased arterial stiffness and the up-to date data of the bone-vascular axis in CKD. We overview a list of the different factors, including inhibitors of bone metabolism like osteoprotegerin, fetuin-A, pyrophosphates, matrix Gla protein, osteopontin, fibroblast growth factor 23 and bone morphogenic protein, which seem to play role in the progression of vascular calcification and we evaluate their connection to impaired arterial stiffness in the mirror of recent scientific results.

Metanephros transplantation inhibits the progression of vascular calcification in rats with adenine-induced renal failure

BACKGROUND/AIM

Recent research has shown that transplanted metanephroi form primitive vascularized kidneys with histologically recognizable renal features. The aim of the present study was to determine the metabolic function of transplanted metanephroi in rats with chronic renal failure (CRF), with particular reference to secondary hyperparathyroidism and vascular calcification.

METHODS

CRF was induced in 11-week-old male Wistar rats by maintaining them on a 0.75% adenine diet for 4 weeks, followed by normal diet for an additional 2 weeks. At the end of adenine loading, whole metanephroi from embryonic day 15 rats were transplanted into the omentum and epididymis of the transplantation group. Vascular calcification was evaluated 2 weeks after metanephroi transplantation.

RESULTS

Metanephros transplantation significantly reduced vascular calcium and phosphorus content and suppressed the progression of vascular calcification as indicated by von Kossa staining of the media of the thoracic aorta. However, no significant differences between the adenine-fed control and transplantation groups were found regarding the serum levels of 1,25(OH)2D3, calcium or phosphorus or the calcium × phosphorus product.

CONCLUSION

The present study has shown that transplantation of metanephroi suppresses the progression of vascular calcification via a mechanism that is independent of calcium-phosphorus dynamics.

Association of bone turnover markers and arterial stiffness in pre-dialysis chronic kidney disease (CKD)

Vascular calcification (VC) is highly prevalent in CKD and leads to increased vascular stiffness and cardiovascular disease (CVD). Non-traditional cardiovascular risk factors include abnormal bone turnover and/or dysregulation of the calcification inhibitors, although their relative contribution remains unclear. We investigated the association between bone turnover, the calcification inhibitors (matrix gla protein; MGP and Fetuin-A), and the phosphate regulating hormone; fibroblast growth factor-23 (FGF-23) and arterial stiffness in pre-dialysis CKD patients. One hundred and forty-five patients with CKD stages 1-4 (74 M, 71 F) aged (mean [SD]) 53 [14] years were studied. Bone turnover markers (bone-specific alkaline phosphatase (BALP) and tartrate-resistant acid phosphatase (TRACP)) and MGP, Fetuin-A and FGF-23 were determined. BMD was measured at the lumbar spine (LS), femoral neck (FN), forearm (FARM) and total hip (TH). Arterial stiffness was assessed by contour analysis of digital volume pulse (SI(DVP)). There was a significant positive correlation between TRACP:BALP ratio and SI(DVP) ( r=0.19, p=0.023). Following multi-linear regression analysis, significant associations were seen between serum BALP (p=0.037), TRACP (p=0.009) and TRACP:BALP ratio (p=0.001) and SI(DVP) independently of traditional CVD risk factors. No significant relationship between SI(DVP) and MGP, Fetuin-A and FGF-23 was observed. A significant negative correlation was seen between BMD at the FARM and SI(DVP) in CKD stage 4 (r=-0.35, p=0.024). The association remained significant following correction for age, gender and cardiovascular risk factors (p=0.029). Our data suggest a link between imbalances in bone turnover and arterial stiffness in pre-dialysis CKD. Longitudinal studies are needed to evaluate the clinical usefulness of these bone turnover markers as predictors of CVD in CKD.

Fetuin-A serum levels in patients with aortic aneurysms of Marfan syndrome and atherosclerosis

BACKGROUND

Fetuin-A is a glycoprotein that inhibits extraosseous and vascular calcification. Its serum level is lower in patients with atherosclerosis compared with healthy controls, but its role is unknown in aneurysmal diseases. The aim of our study was to investigate the association of serum fetuin-A levels with aortic aneurysms of different aetiology: Marfan syndrome and atherosclerosis.

MATERIAL AND METHODS

In a single centre cross-sectional observational study, 105 patients (30 with atherosclerotic aortic aneurysm, 15 with Marfan syndrome, 30 with peripheral arterial disease and 30 healthy controls) were examined; sera were analysed for fetuin-A, standard markers of possible inflammation, lipid profile, kidney and hepatic disease and diabetes. Systemic atherosclerosis was assessed by carotid intima-media thickness (IMT) measurement and arterial calcification score of cardiac valves, carotids, aorta and femoral arteries determined by ultrasound.

RESULTS

Serum fetuin-A levels (median and IQR) were significantly lower in the atherosclerotic aneurysm cohort than in patients with Marfan syndrome: 708 μg mL⁻¹ (612-780) and 756 μg mL⁻¹ (708-816), respectively, (P = 0·0428). Fetuin-A levels were 754 μg mL⁻¹ (713-777) in the control group and 654 μg mL⁻¹ (600-756) in patients with peripheral arterial disease. Mean and maximum IMT, ACS values and homocysteine levels were significantly higher in patients with atherosclerosis: P < 0·0001, P < 0·0001, P < 0·0001 and P = 0·0034, respectively. There was no significant difference between aneurysm groups analysing the results of lipid profile and acute-phase markers.

CONCLUSIONS

The significantly lower serum level of fetuin-A in the atherosclerotic aneurysm group supports the protective role of fetuin-A in the evolution of arterial calcification.

Relationship between Fibroblast Growth Factor-23 and Mineral Metabolism in Chronic Kidney Disease

Fibroblast growth factor- (FGF-)23 is a recently discovered regulator of calcium-phosphate metabolism. FGF-23 appears to decrease in synthesis and accelerated degradation of 1,25(OH)₂D. Together with its cofactor Klotho, FGF-23 maintains serum phosphate levels within the normal range by increasing renal phosphate excretion. In chronic kidney disease (CKD), FGF-23 levels rise in parallel with the decline in renal function long before a significant increase in serum phosphate concentration occurs. Both Klotho and FGF-23, linked by a receptor mechanism, affect vitamin D synthesis and parathyroid hormone (PTH) secretion. Previous studies have shown a close association between reduced FGF-23 or Klotho activities and vascular calcification. The possible association of FGF-23 and left ventricular hypertrophy or vascular dysfunction has been proposed. Finally, prospective studies have shown that high serum FGF-23 concentrations predict more rapid disease progression in CKD patients who were not on dialysis and increased mortality in patients on maintenance hemodialysis. FGF-23 may therefore prove to be an important therapeutic target for the management of CKD.

Chronic kidney disease bone and mineral disorder (CKD-MBD) in apolipoprotein E-deficient mice with chronic renal failure

BACKGROUND

Chronic kidney disease (CKD) is associated with disorders of mineral and bone metabolism (MBD) which include renal osteodystrophy and vascular calcifications. This is of clinical concern because the high risk of cardiovascular (CVD) complications observed in uremic patients may be linked with bone disease. In this context, our aim was to characterize the bone lesions in CKD-apolipoprotein E-deficient mice (apoE(-/-)) and analyze their relationships with the vascular calcifications which these animals develop rapidly in this model. With ApoE being also involved in bone metabolism, we compared the effects of CRF on the bone of apoE(-/-) mice to those observed in wild type mice (WT) of the same genetic background, C57/BL6.

METHODS

After CRF creation or sham surgery, 10 week-old female apoE(-/-) and WT mice were randomized to 4 groups (n=10-14/group) and fed with standard diet. Eight weeks later, animals were euthanized. Serum, aorta and femur were sampled. Femurs were imaged with 3-dimensional microtomography (microCT) and processed for bone histomorphometry (BHM). Additional quantitative histology was performed on atherosclerotic and calcified lesions in the aortas of apoE(-/-) mice.

RESULTS

First, apoE(-/-) mice exhibited higher cortical (10%) and trabecular (31%) bone mass than WT. CRF led to a further increase in trabecular BV/TV in WT and in apoE(-/-) mice (10.2% and 77.2%, respectively). We observed a similar increase in osteoid surface and osteoblastic parameters in CRF mice of both genotypes while resorption parameters were less augmented by CRF in apoE(-/-) mice. Finally, based on either BHM or microCT we found positive correlations between the extent of atherosclerotic lesions and bone volume parameters, and between the size of plaque calcification and osteoclast parameters in apoE(-/-) mice.

CONCLUSION

ApoE deficiency is associated with an increase in bone mass and volumetric mineral density in 20 week-old female mice. Bone mass is further increased, whereas bone mineral density is decreased, in response to CRF in association with histological features of osteitis fibrosa. Finally, our findings of correlations between changes in bone and aortic lesions in apoE(-/-) mice, are compatible with the hypothesis of a link between bone and vascular disease and require further study.

Vascular calcification in chronic kidney disease

VC (vascular calcification) is highly prevalent in patients with CKD (chronic kidney disease), but its mechanism is multifactorial and incompletely understood. In addition to increased traditional risk factors, CKD patients also have a number of non-traditional cardiovascular risk factors, which may play a prominent role in the pathogenesis of arterial calcification, such as duration of dialysis and disorders of mineral metabolism. The transformation of vascular smooth muscle cells into chondrocytes or osteoblast-like cells seems to be a key element in VC pathogenesis, in the context of passive calcium and phosphate deposition due to abnormal bone metabolism and impaired renal excretion. The process may be favoured by the low levels of circulating and locally produced VC inhibitors. VC determines increased arterial stiffness, left ventricular hypertrophy, a decrease in coronary artery perfusion, myocardial ischaemia and increased cardiovascular morbidity and mortality. Although current therapeutic strategies focus on the correction of phosphate, calcium, parathyroid hormone or vitamin D, a better understanding of the mechanisms of abnormal tissue calcification may lead to development of new therapeutic agents, which could reduce VC and improve cardiovascular outcome in CKD patients. The present review summarizes the following aspects: (i) the pathophysiological mechanism responsible for VC and its promoters and inhibitors, (ii) the methods for detection of VC in patients with CKD, including evaluation of arterial stiffness, and (iii) the management of VC in CKD patients.

Effects of bone and mineral metabolism on arterial elasticity in chronic renal failure

Arterial stiffness (Ast) individually predicts cardiovascular (CV) mortality. Ast increases via vascular calcification and can be characterized by pulse wave velocity (PWV). We assessed the influence of mineral and bone metabolism on Ast in dialyzed (D) and renal transplanted (Tx) children by measuring fetuin-A and bone markers [bone-specific alkaline phosphatase (BALP); beta-CrossLaps (beta)]. Normalized PWV/height (PWV/h) of 11 D and 17 Tx patients was measured by applanation tonometry. Levels of calcium (Ca), phosphate (P), fetuin-A, and bone markers were analyzed. Ca x P/fetuin-A ratio was calculated to characterize the balance of calcification and inhibition. Cumulative dose of calcitriol was also assessed. Fetuin-A was lower in D and Tx compared with healthy controls. Bone markers and Ca x P/ fetuin-A of D were significantly higher than those of Tx and controls. In D PWV/h correlated with Ca x P/fetuin-A and BALP (r=0.8; p=0.005, r=0.6, p=0.05, respectively); BALP correlated with Ca x P/fetuin-A (r=0.7, p=0.01). In Tx, there was a correlation between calcitriol administered before transplantation and PWV/h (r=0.5, p=0.04). Increased bone turnover was coupled with an increased potential of calcium-phosphate precipitation, as shown by the increased Ca x P/fetuin-A. It might explain the connection between disturbed mineral and bone metabolism and Ast. Tx might be beneficial on Ast, though follow-up studies are needed.

Noninvasive detection of acute and chronic injuries in human renal transplant by elevation of multiple cytokines/chemokines in urine

BACKGROUND

Injuries in kidney transplant is currently diagnosed by needle biopsy. A noninvasive test that sensitively detects these injuries would benefit the patients.

METHODS

Urine samples were collected from healthy controls and kidney transplant recipients. Urine samples were screened first with an antibody array consisting of 120 chemokines and cytokines and then with a multiplex beads assay. Representative parameters, including macrophage inflammatory protein-1Delta, osteoprotegerin, monokine induced by interferon-gamma (IFN), and IFN-gamma-induced protein of 10 kDa, were simultaneously determined by a quadruplex assay in urine samples from 84 patients with renal allograft injury, 29 patients with stable graft function, and 19 healthy individuals.

RESULTS

Twenty-three cytokines/chemokines were found to be elevated in urine samples of patients with acute rejection by the antibody array. The second round of screening confirmed that 11 of the 23 parameters were elevated in the patients but not in the healthy controls. Induced protein of 10 kDa and monokine induced by IFN-gamma were significantly elevated in urine samples of patients with acute renal injury, and macrophage inflammatory protein-1Delta and osteoprotegerin were significantly elevated in patients with both acute and chronic renal injuries. The combination of the four parameters had a high positive detection rate (97.6%) for renal transplant injury and could differentiate between acute and chronic injury.

CONCLUSION

These results might indicate that the present multiplex assay provides a basis to establish a noninvasive method for the diagnosis and monitoring of renal transplant injury.

Matrix metalloproteinase-1 and matrix metalloproteinase-3 gene promoter polymorphisms are associated with mortality in haemodialysis patients

BACKGROUND

Vascular calcification and accelerated atherosclerosis are major causes of death in haemodialysis (HD) patients. Matrix metalloproteinases (MMPs) are a family of enzymes, involved in the biology of extracellular matrix and in atherogenesis. MMP1 and MMP3 contribute to the enlargement and instability of atherosclerotic plaque, respectively. The common polymorphisms on MMP1 (2G/2G) and MMP3 (6A/6A) gene promoters have been related to increased coronary artery calcification and to carotid artery stenosis. The aim of this study was to evaluate the association of MMP1 and MMP3 polymorphisms with end-stage renal failure (ESRD) and all-cause mortality risk in HD.

METHODS

Ninety-nine HD patients, followed-up for 36 months, and 133 matched controls were genotyped for the two polymorphisms. HD patients' characteristics were age 64 +/- 13 years, males 64%, diabetic 24%, hypertensive 62%, smokers 38%, dyslipidaemic 28%, all undergoing standard HD thrice weekly.

RESULTS

ESRD was strongly associated with the combination of 2G/2G and 6A/6A homozygosity: OR 2.57 (0.95-7.4), P = 0.037, but not with isolated 2G/2G and 6A/6A homozygosity (P = 0.09 and P = 0.11, respectively). Isolated 2G/2G was associated with all-cause mortality risk independently from age, gender, diabetes, hypertension, smoking, dyslipidaemia, C-reactive protein, albumin, dialysis vintage and history of cardio-vascular disease: HR 2.96 (1.29-6.80), P = 0.01. A trend for the association of mortality and isolated 6A/6A homozygosity was also observed: HR 3.01 (0.88-10.26), P = 0.078. Combination of 2G/2G and 6A/6A homozygosity significantly increased the mortality risk in the same Cox regression model: HR 4.69 (1.72-12.81), P = 0.003.

CONCLUSIONS

In this study, we demonstrated for the first time that MMP-1 and MMP-3 gene polymorphisms are negative prognostic risk factors for all-cause mortality in HD patients, independently from traditional risk factors. These data may have important implications for better understanding the pathogenesis of the increased mortality in HD patients.

Does Fgf23-klotho activity influence vascular and soft tissue calcification through regulating mineral ion metabolism?

Recent studies describe a novel role of fibroblast growth factor-23 (Fgf23)-klotho activity in the systemic regulation of calcium and phosphate homeostasis. Both Fgf23 and klotho ablated mice develop extensive vascular and soft tissue calcification. Inability to clear the required amount of phosphate by the kidney, due to the absence of Fgf23-klotho activity, leads to increased accumulation of serum phosphate in these genetically modified mice, causing extensive calcification. Serum calcium and 1,25 hydroxyvitamin D levels are also elevated in both Fgf23 and klotho ablated mice. Moreover, increased sodium phosphate co-transporter activity in both Fgf23 and klotho ablated mice increases renal phosphate reabsorption which in turn can facilitate calcification. Collectively, these observations bring new insights into our understanding of the roles of the Fgf23-klotho axis in the development of vascular and soft tissue calcification.