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

Vitamin K for Vascular Calcification in Kidney Patients: Still Alive and Kicking, but Still a Lot to Learn

Patients with chronic kidney disease (CKD) suffer disproportionately from a high burden of cardiovascular disease, which, despite recent scientific advances, remains partly understood. Vascular calcification (VC) is the result of an ongoing process of misplaced calcium in the inner and medial layers of the arteries, which has emerged as a critical contributor to cardiovascular events in CKD. Beyond its established role in blood clotting and bone health, vitamin K appears crucial in regulating VC via vitamin K-dependent proteins (VKDPs). Among these, the matrix Gla protein (MGP) serves as both a potent inhibitor of VC and a valuable biomarker (in its inactive form) for reflecting circulating vitamin K levels. CKD patients, especially in advanced stages, often present with vitamin K deficiency due to dietary restrictions, medications, and impaired intestinal absorption in the uremic environment. Epidemiological studies confirm a strong association between vitamin K levels, inactive MGP, and increased CVD risk across CKD stages. Based on the promising results of pre-clinical data, an increasing number of clinical trials have investigated the potential benefits of vitamin K supplementation to prevent, delay, or even reverse VC, but the results have remained inconsistent.

Association of Alkaline Phosphatase with Cardiovascular Disease in Patients with Dyslipidemia: A 6-Year Retrospective Study

BACKGROUND AND AIM

Serum alkaline phosphatase (ALP) activity has been associated with atherosclerotic cardiovascular disease (ASCVD). We aimed to investigate the association of ALP with ASCVD in patients with dyslipidemia.

METHODS

We conducted a retrospective cohort study including consecutive adults with dyslipidemia followed-up for ≥3 years (from 1999 to 2022) in the outpatient Lipid Clinic of Ioannina University General Hospital, Greece. The primary endpoint was the association between baseline ALP and incident ASCVD after adjusting for traditional risk factors (i.e., sex, age, hypertension, diabetes, smoking, and dyslipidemia), baseline ASCVD, and lipid-lowering treatment. ALP levels were stratified by tertiles as follows: low: <67 U/L, middle: 67-79 U/L, high: ≥79 U/L.

RESULTS

Overall, 1178 subjects were included; 44% were males, and their median age was 57 years (range: 49-65). During a 6-year median follow-up (interquartile range: IQR: 4-9), 78 new ASCVD events (6.6%) occurred. A statistically significant association between baseline ALP levels and incident ASCVD was demonstrated (Odds Ratio, OR: 6.99; 95% Confidence Interval, CI: 2.29-21.03, p = 0.001). Subjects in the highest ALP tertile had the highest odds for ASCVD when compared with those in the lowest tertile (OR: 2.35; 95% CI: 1.24-4.41, p = 0.008).

CONCLUSIONS

The present study indicates an association between ALP and the development of ASCVD in patients with dyslipidemia, which underscores the potential of ALP as a predictive tool or a therapeutic target in the realm of ASCVD prevention within this population.

Current and Emerging Markers and Tools Used in the Diagnosis and Management of Chronic Kidney Disease-Mineral and Bone Disorder in Non-Dialysis Adult Patients

Chronic kidney disease (CKD) is a significant public health concern associated with significant morbidity and has become one of the foremost global causes of death in recent years. A frequent comorbidity of CKD is secondary hyperparathyroidism (SHPT), exemplified by high serum parathyroid hormone (PTH) levels. The mineral metabolism disturbances resulting from CKD and progression to SHPT are currently considered part of the definition of chronic kidney disease-mineral and bone disorder (CKD-MBD). However, CKD-MBD does not only include abnormalities in laboratory-measured parameters; it is a complex condition characterized by dysregulation of bone turnover, mineralization, growth and strength, accompanied by vascular or another soft-tissue calcification. Together, this increases the risk of bone fractures, cardiovascular disease, and overall mortality in CKD-MBD patients. Monitoring serum markers is essential in diagnosing SHPT and CKD-MBD, and there are several recognized indicators for prognosis, optimal clinical management and treatment response in late-stage kidney disease patients receiving dialysis. However, far fewer markers have been established for patients with non-dialysis CKD. This review provides an overview of current and emerging markers and tools used in the diagnosis and management of CKD-MBD in non-dialysis adult patients.

Alkaline Phosphatases: Biochemistry, Functions, and Measurement

Alkaline phosphatases (ALPs) are a group of isoenzymes, situated on the external layer of the cell membrane; they catalyze the hydrolysis of organic phosphate esters present in the extracellular space. Zinc and magnesium are significant co-factors for the biological activity of these enzymes. Although ALPs are available in various body tissues and have distinct physiochemical properties, they are true isoenzymes since they catalyze a similar reaction. In the liver, ALP is cytosolic and present in the canalicular membrane of the hepatocytes. ALPs are available in placenta, ileal mucosa, kidney, bone, and liver. However, most of the ALPs in serum (over 80%) are delivered from liver and bone and in more modest quantities from the intestines. Despite the fact that alkaline phosphatases are found in numerous tissues all through the body, their exact physiological function remains largely unknown.

Significant associations between bone mineral density and vascular calcification in patients with different stages of chronic kidney disease

Introduction

Chronic kidney disease—mineral and bone disorders (CKD-MBD) is characterised by generalised vascular calcification (VC) and impaired bone health. We aimed to investigate the relationship between VC and bone mineral density (BMD) in CKD patients.

Methods

We performed a cross-sectional study of patients with different stages of CKD. For assessment of VC of abdominal aorta lateral lumbar X-rays (Kauppila score), the ankle-brachial index (ABI) and echocardiography were used. Total body densitometry provided BMD.

Results

Ninety patients (41% male, median age 64 years (range 29–87)) were included, of whom 41.1% had a Kauppila score > 1. Evidence of peripheral VC as measured by ABI was detected in 23.3% of cases. Lesions of the heart valves were found in 46.7% of patients. There was a significant association between high ABI and lesions of the heart valves. In the multivariate regression model to analyse the independent determinants of abdominal aorta calcification (AAC) and ABI, the BMD of the femoral neck was identified as significant for both (p = 0.001, p = 0.001). The total spine BMD was found to be significant for AAC (p = 0.001), and the BMD of spine L1-L4 and the ribs were found to be significant for ABI (p = 0.01, p = 0.002 respectively). In factorial regression analysis, where BMD was independent determinant, valvular calcification was significant for BMD of femur, femoral neck and total BMD. Age and tALP were inversely correlated with the BMD of femur and femoral neck.

Conclusions

Our work highlighted clinically important relationships between VC and bone mineral density (BMD) in CKD patients. We detected inverse relationships between AAC, high ABI and BMD. Secondly, BMD at certain bone sites (femur, femoral neck) and total BMD were associated with important lesions of heart valves. Thirdly, a significant association between a high ABI and lesions of the heart valves. We believe that the results of our study will help in the planning of future research and in current clinical practice for the early diagnosis, further monitoring and management of CKD-MBD. Additionally, these results may have treatment implications on use of different CKD-MBD medications.

Gender-Related Differences in Chronic Kidney Disease-Associated Vascular Calcification Risk and Potential Risk Mediators: A Scoping Review

Vascular calcification (VC) involves the deposition of calcium apatite in vascular intima or media. Individuals of advanced age, having diabetes mellitus or chronic kidney disease (CKD) are particularly at risk. The pathogenesis of CKD-associated VC evolves considerably. The core driver is the phenotypic change involving vascular wall constituent cells toward manifestations similar to that undergone by osteoblasts. Gender-related differences are observed regarding the expressions of osteogenesis-regulating effectors, and presumably the prevalence/risk of CKD-associated VC exhibits gender-related differences as well. Despite the wealth of data focusing on gender-related differences in the risk of atherosclerosis, few report whether gender modifies the risk of VC, especially CKD-associated cases. We systematically identified studies of CKD-associated VC or its regulators/modifiers reporting data about gender distributions, and extracted results from 167 articles. A significantly higher risk of CKD-associated VC was observed in males among the majority of original investigations. However, substantial heterogeneity exists, since multiple large-scale studies yielded neutral findings. Differences in gender-related VC risk may result from variations in VC assessment methods, the anatomical segments of interest, study sample size, and even the ethnic origins of participants. From a biological perspective, plausible mediators of gender-related VC differences include body composition discrepancies, alterations involving lipid profiles, inflammatory severity, diversities in matrix Gla protein (MGP), soluble Klotho, vitamin D, sclerostin, parathyroid hormone (PTH), fibroblast growth factor-23 (FGF-23), and osteoprotegerin levels. Based on our findings, it may be inappropriate to monotonously assume that male patients with CKD are at risk of VC compared to females, and we should consider more background in context before result interpretation.

Differentiating the causes of adynamic bone in advanced chronic kidney disease informs osteoporosis treatment

Patients with chronic kidney disease (CKD) have an increased fracture risk because of impaired bone quality and quantity. Low bone mineral density predicts fracture risk in all CKD stages, including advanced CKD (CKD G4-5D). Pharmacological therapy improves bone mineral density and reduces fracture risk in moderate CKD. Its efficacy in advanced CKD remains to be determined, although pilot studies suggest a positive effect on bone mineral density. Currently, antiresorptive agents are the most commonly prescribed drugs for the prevention and therapy of osteoporosis. Their use in advanced CKD has been limited by the lack of large clinical trials and fear of causing kidney dysfunction and adynamic bone disease. In recent decades, adynamic bone disease has evolved as the most predominant form of renal osteodystrophy, commonly associated with poor outcomes, including premature mortality and progression of vascular calcification. Evolving evidence indicates that reduction of bone turnover by parathyroidectomy or pharmacological therapies, such as calcimimetics and antiresorptive agents, are not associated with premature mortality or accelerated vascular calcification in CKD. In contrast, chronic inflammation, oxidative stress, malnutrition, and diabetes can induce low bone turnover and associate with poor prognosis. Thus, the conditions causing suppression of bone turnover rather than the low bone turnover per se may account for the perceived association with outcomes. Anabolic treatment, in contrast, has been suggested to improve turnover and bone mass in patients with advanced CKD and low bone turnover; however, uncertainty about safety even exceeds that of antiresorptive agents. Here, we critically review the pathophysiological concept of adynamic bone disease and discuss the effect of low bone turnover on the safety and efficacy of anti-osteoporosis pharmacotherapy in advanced CKD.

Pharmacologic epigenetic modulators of alkaline phosphatase in chronic kidney disease

In chronic kidney disease (CKD), disturbance of several metabolic regulatory mechanisms cause premature ageing, accelerated cardiovascular disease (CVD), and mortality. Single-target interventions have repeatedly failed to improve the prognosis for CKD patients. Epigenetic interventions have the potential to modulate several pathogenetic processes simultaneously. Alkaline phosphatase (ALP) is a robust predictor of CVD and all-cause mortality and implicated in pathogenic processes associated with CVD in CKD.

Significance of acPWV for Survival of Hemodialysis Patients

BACKGROUND AND OBJECTIVES

Abnormal arterial stiffness (AS) is a major complication in end-stage kidney disease (ESKD) patients treated by dialysis. Our study aimed to determine the significance of AS for survival of prevalent dialysis patients, as well as its association with cardiovascular parameters or vascular calcification promoters/inhibitors or both and AS.

MATERIALS AND METHODS

The study involved 80 adult hemodialysis patients. Besides standard laboratory analyses, we also determined promoters and inhibitors of vascular calcification (bone biomarkers): serum levels of fibroblast growth factor 23 (FGF23), soluble Klotho, intact parathormone (iPTH), 1,25-dihydroxyvitamin D3, osteoprotegerin, sclerostin, AS measured as ankle carotid pulse wave velocity (acPWV), Ankle Brachial Index (ABI), and vascular calcification (VC) score. Patients were monitored for up to 28 months. According to the median acPWV value, we divided patients into a group with acPWV ≤ 8.8 m/s, and a group with acPWV > 8.8 m/s, and the two groups were compared.

RESULTS

Values for bone biomarkers were similar in both groups. Mean arterial blood pressure (MAP), central systolic and diastolic brachial blood pressure, heart rate, and pulse pressure were higher in the group with acPWV > 8.8 m/s than in the group with acPWV ≤ 8.8 m/s. The mortality was higher for patients with acPWV > 8.8 m/s at any given time over 28 months of follow-up. In multivariable analysis, predictors of higher acPWV were age >60.5, higher pulse rate, and higher central systolic or brachial diastolic blood pressure.

CONCLUSIONS

According to our results, we advise the measurement of acPWV preferentially in younger dialysis patients for prognosis, as well as intervention planning before the development of irreversible changes in blood vessels. In addition, measuring central systolic blood pressure seems to be useful for monitoring AS in prevalent hemodialysis patients.

Digital arterial pressure pulse wave analysis and cardiovascular events in the general population: the Prevention of Renal and Vascular End-stage Disease study

Background:

Arterial stiffness influences the contour of the digital pressure pulse wave.

Method:

Here, we investigated whether the digital pulse propagation index (DPPI), based on the digital pressure pulse wave, DPPI is associated with cardiovascular events, heart failure, and mortality in a large population-based cohort. Between 2001 and 2003, DPPI was measured with a PortaPres noninvasive hemodynamic monitoring device (FinaPres Medical Systems, Amsterdam, The Netherlands) in participants of the Prevention of Renal and Vascular End-stage Disease study, a community-based cohort. We assessed the main determinants of the DPPI and investigated associations of DPPI with cardiovascular events and mortality.

Results:

The study included 5474 individuals. Mean age was 52.3 ± 11.8 years and 50.5% was male. Median baseline DPPI was 5.81 m/s (interquartile range 5.47–6.20). Higher age, mean arterial blood pressure, body height, heart rate, current smoking, and lower HDL cholesterol levels and waist circumference were independent determinants of the DPPI (r² = 0.43). After adjustment for heart rate, high_logDPPI was associated with all-cause mortality [hazard ratio: 1.67, 95% confidence interval (1.55–1.81) per SD; P < 0.001], cardiovascular mortality [hazard ratio 1.95 (1.72–2.22); P < 0.001], and incident heart failure with reduced ejection fraction [hazard ratio 1.81 (1.60–2.06); P < 0.001]. These associations remained independent upon further adjustment for confounders. Optimal cutoff values for DPPI ranged between 6.1 and 6.3 m/s for all endpoints. After multivariable adjustment, DPPI was no longer associated with coronary artery disease events or cerebrovascular events.

Conclusion:

The DPPI is associated with an increased risk of development of new onset heart failure with reduced ejection fraction and all-cause and cardiovascular mortality, but not with coronary artery events or cerebrovascular events.

Bone alkaline phosphatase: An important biomarker in chronic kidney disease - mineral and bone disorder

Increased cardiovascular morbidity and mortality in chronic kidney disease (CKD) represents an emerging major health problem. Indeed, disturbances in mineral and bone metabolism occur frequently in CKD and are termed chronic kidney disease - mineral and bone disorder (CKD-MBD). These can lead to cardiovascular pathology, resulting in an increased cardiovascular risk. Bone alkaline phosphatase (BALP) is essential for biomineralization. Recent findings demonstrate a crucial role for BALP in the pathogenesis of vascular calcification and identified it as a promising predictor of mortality in CKD. In conjunction with parathyroid hormone (PTH), serum BALP has been suggested as a biomarker of bone turnover in CKD-MBD. In contrast to PTH, serum BALP demonstrates a lower variability and may thus be better suited for the diagnosis and longitudinal follow-up of bone turnover. The linear association with mortality, compared to the U-shaped curve for PTH, is an additional advantage, making BALP more suitable than PTH as a treatment target in CKD. Here we review the main characteristics of alkaline phosphatase isozymes/isoforms and the various assays currently used in clinical routine laboratories. We also discuss the role of BALP in both physiological and pathological mineralization, and the clinical benefit of BALP determination in CKD.

Changes in FGF-23, Neutrophil/Platelet Activation Markers, and Angiogenin in Advanced Chronic Kidney Disease and Their Effect on Arterial Stiffness

AIMS

The aims of this study were to measure changes in fibroblast growth factor 23 (FGF-23), neutrophil (elastase, lactoferrin)/platelet activation marker (mean platelet volume-to-platelet count ratio [MPR]), and angiogenin according to the stage of chronic kidney disease (CKD), and to evaluate the association of FGF-23, elastase, lactoferrin, MPR, and angiogenin with arterial stiffness using brachial-ankle pulse wave velocity (ba-PWV) in CKD patients.

METHODS

According to the estimated glomerular filtration rate (eGFR) calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, the patients were allocated to five groups: (1) normal controls (eGFR ≥90 mL/min/1.73 m2 without pathologic, urine [proteinuria], blood [electrolyte], and imaging abnormalities; n = 22); (2) CKD stage 2 (eGFR 60-89 mL/min/1.73 m2; n = 17); (3) CKD stage 3 (eGFR 30-59 mL/min/1.73 m2; n = 22); (4) CKD stage 4 (eGFR 15-30 mL/min/1.73 m2; n = 17); and (5) CKD stage 5-hemodialysis (HD) (n = 30). All the patients were free of clinically apparent cardiovascular disease. Serum FGF-23, elastase, lactoferrin, and angiogenin concentrations and the MPR were measured to study the association of the above parameters with the clinical (age, sex, presence of diabetes mellitus, and blood pressure), biochemical (calcium, phosphorus, uric acid, intact parathyroid hormone [PTH], low-density lipoprotein cholesterol, and high-sensitivity C-reactive protein), and ba-PWV values of the CKD patients.

RESULTS

(1) The mean ba-PWV values were 1,497.2 ± 206.4 cm/s in the controls, 1,649.0 ± 247.9 cm/s in the CKD stage 2 group (p < 0.05 vs. controls), 1,655.8 ± 260.3 cm/s in the CKD stage 3 group (p < 0.05 vs. controls), 1,823.0 ± 402.4 cm/s in the CKD stage 4 group (p < 0.05 vs. controls and CKD stages 2 and 3), and 1,905.2 ± 374.1 cm/s in the CKD stage 5-HD group (p < 0.05 vs. controls and CKD stage 2). (2) The mean log10(FGF-23) concentration values were 0.77 ± 0.27, 0.97 ± 0.48, 1.10 ± 0.35 (p < 0.05 vs. controls and CKD stage 2), 1.35 ± 0.48 (p < 0.05 vs. controls and CKD stages 2 and 3), and 2.12 ± 0.82 (p < 0.05 vs. controls and CKD stages 2-4); the mean angiogenin levels were 230.6 ± 70.5 pg/mL, 283.0 ± 53.5 pg/mL (p < 0.05 vs. controls), 347.3 ± 76.9 pg/mL (p < 0.05 vs. controls and CKD stage 2), 445.9 ± 90.6 pg/mL (p < 0.05 vs. controls and CKD stages 2 and 3), and 370.9 ± 142.4 pg/mL (p < 0.05 vs. controls and CKD stages 2 and 3). (3) In the stage 3-4 CKD/HD patients, the mean elastase-to-neutrophil and lactoferrin-to-neutrophil ratios were significantly lower than in the controls and the stage 2 CKD patients. (4) Our multivariate linear regression analyses showed that age, pulse pressure, mean arterial pressure, PTH, and FGF-23 were independently associated with ba-PWV values.

CONCLUSIONS

Circulating FGF-23 and angiogenin concentrations gradually increased as CKD advanced, whereas neutrophil activation markers were significantly lower in the stage 3-4 CKD/HD patients than in the controls and stage 2 CKD patients. FGF-23 was weakly associated with ba-PWV values in patients with CKD/HD and no previous cardiovascular disease.

Apabetalone lowers serum alkaline phosphatase and improves cardiovascular risk in patients with cardiovascular disease

BACKGROUND AND AIMS

In patients with cardiovascular disease, considerable residual risk remains despite evidence-based secondary prevention measures. Alkaline phosphatase (ALP) has been suggested as a modifiable cardiovascular risk factor. We sought to determine whether cardiovascular risk reduction by the bromodomain and extra-terminal (BET) protein inhibitor apabetalone is associated with the concomitant lowering of serum ALP.

METHODS

In a post-hoc analysis of 795 patients with established coronary heart disease and statin treatment, who participated in phase 2 placebo-controlled trials of apabetalone, we determined the effect of assigned treatment for up to 24 weeks on the incidence of major adverse cardiovascular events (MACE) and serum ALP.

RESULTS

Baseline ALP (median 72 U/L) predicted MACE (death, non-fatal myocardial infarction, coronary revascularization, or hospitalization for cardiovascular causes), independent of high-sensitivity C-reactive protein (hsCRP), sex, age, race, study, cardiovascular risk factors, chronic kidney disease (CKD), liver function markers and treatment allocation (hazard ratio [HR] per standard deviation [SD] 1.6, 95% CI 1.19-2.16, p = 0.002). Mean placebo-corrected decreases in ALP from baseline were 9.2% (p < 0.001) after 12-14 weeks and 7.7% (p < 0.001) after 24-26 weeks of apabetalone treatment. In the apabetalone group, a 1-SD reduction in ALP was associated with a HR for MACE of 0.64 (95% CI 0.46-0.90, p = 0.009).

CONCLUSIONS

Serum ALP predicts residual cardiovascular risk, independent of hsCRP, established cardiovascular risk factors and CKD, in patients with cardiovascular disease on statin treatment. Apabetalone lowers serum ALP, which was associated with a lower risk of cardiovascular events. Whether the beneficial cardiovascular effects of apabetalone are causally related to ALP reduction remains undetermined.

Fracture status in middle-aged individuals with early CKD: cross-sectional analysis of the CARTaGENE survey

Whether early chronic kidney disease (CKD) is associated with fracture in middle-aged adults is unclear. In a cross-sectional analysis of the CARTaGENE survey, we observed that early CKD was not associated with increased fracture, did not modify the association between calcaneal QUS and fracture, but modified the association between clinical, pharmacological parameters and fracture.

INTRODUCTION

The association between advanced CKD and increased fracture risk is well described. However, whether early CKD is associated with increased fractures, especially in middle-aged adults, is unclear. We aimed to assess if early CKD is associated with increased fracture status and whether early CKD status modifies the association between calcaneal quantitative ultrasound parameters, clinical, pharmacological parameters, and fractures.

METHODS

Cross-sectional analysis of CARTaGENE, a population-based survey of 40- to 69-year-old individuals. Individuals with CKD (stage 2, estimated glomerular filtration rate [eGFR] 60-89 ml/min/1.73 m²; stage 3, eGFR 30-59) were compared to non-CKD individuals (eGFR > 90). Fracture status (excluding face, toe, hand, and patella) was identified through a questionnaire at baseline. Calcaneal quantitative ultrasound (QUS) was measured in each participant.

RESULTS

A total of 17,608 individuals (656 CKD stage 3; 8227 stage 2; 8725 non-CKD) were included. CKD stage 2 and 3 individuals (mean eGFR 78 and 53 ml/min/1.73 m²) were older and had more diabetes, cardiovascular disease, and hypertension. Fracture status prevalence was 14.9% in CKD stage 3, 10.8% in CKD stage 2, and 9.0% in non-CKD individuals. Fracture status prevalence was similar between CKD and non-CKD individuals when stratified by age or after adjustment for demographic and clinical parameters. QUS stiffness index was associated with fracture status in both CKD stage 3 (standardized odds ratio [sOR] = 1.525 [1.200 to 1.939] per 1 SD decrease), stage 2 (sOR = 1.415 [1.310 to 1.530]), and non-CKD individuals (sOR = 1.477 [1.361 to 1.602]). The associations between blood pressure, antihypertensive, and fracture status followed a U-shape throughout the progression of CKD.

CONCLUSIONS

CKD stage 3 was not associated with an increase in fracture status. QUS parameters were similarly associated with fracture status in patients with and without CKD.

Nontraditional Cardiovascular Biomarkers and Risk Factors: Rationale and Future Perspectives

The primary prevention of cardiovascular (CV) disease depends on the capacity to identify subjects at higher risk long before the occurrence of CV clinical manifestations. Traditional risk factors do not cover fully prediction of individual risk. Moreover, there is an area of gray for patients at intermediate CV risk, which offers wide margins of improvement. These observations highlight the need for new additive tools for a more accurate risk stratification. An increasing number of candidate biomarkers have been identified to predict CV risk and events, although they generally give only a moderate increase when added to currently available predictive scores. The approach utilizing a relative small number of biomarkers in multiple combinations, but only weakly related to each other or unrelated, thus belonging to independent-pathways, and so able to catch the multidimensional characteristic of atherosclerosis, appears promising. We discuss vitamin D and bone turnover biomarkers, hepatitis C virus, and psycho-emotional factors that may reflect alternative pathways over those generally considered for atherosclerosis (e.g., aspects directly related to inflammation and thrombosis). These new biomarkers could facilitate a more accurate assessment of CV risk stratification if incorporated in the current risk assessment algorithms.

Relationship between Bone Health Biomarkers and Cardiovascular Risk in a General Adult Population

Purpose/Introduction: Osteoporosis (OP) and cardiovascular (CV) disease emerge as closely related conditions, showing common risk factors and/or pathophysiological mechanisms. The aim of this study was to evaluate the association between bone health markers (BHM) and individual CV risk factors and overall CV risk (FRAMINGHAM-FRS, and PROCAM scores) in a general adult population.

METHODS

In 103 subjects (21 males; age: 56 ± 12 years), vitamin D (25(OH)D), osteocalcin (OC), bone alkaline phospatase (BALP), procollagen I aminoterminal propeptide (P1NP), CTx-telopeptide, as well clinical history and life style were evaluated.

RESULTS

Aging (p < 0.001) and glycemia (p < 0.05) emerged as independent 25(OH)D predictors. Aging (p < 0.001), male sex (p < 0.05), and obesity (p < 0.05) represented independent OC determinants. Aging (p < 0.05) was the only independent BALP determinant. After multivariate adjustment, low 25(OH)D (<20 ng/mL) (Odds ratio OR (95% confidence intervals CI)) (5 (1.4-18) p < 0.05) and elevated OC (>75th percentile-16.6 ng/mL) (6.7 (1.9-23.8) p < 0.01) were found to be significant FRS predictors, while subjects with elevated OC and/or BALP (>75th percentile-9.8 μg/L) showed a higher CV risk as estimated by PROCAM (3.6 (1.2-10.7) p < 0.05). CTx and P1NP did not significantly correlate with CV risk factors or scores.

CONCLUSION

As we go further into bone and CV physiology, it is evident that a close relationship exists between these diseases. Further studies are needed to investigate mechanisms by which bone turnover markers are related to metabolic risk and could modulate CV risk. This knowledge may help to develop possible multiple-purpose strategies for both CV disease and OP prevention and treatment.

Calcifying circulating cells: an uncharted area in the setting of vascular calcification in CKD patients

Vascular calcification, occurring during late-stage vascular and valvular disease, is highly associated with chronic kidney disease-mineral and bone disorders (CKD-MBD), representing a major risk factor for cardiovascular morbidity and mortality. The hallmark of vascular calcification, which involves both media and intima, is represented by the activation of cells committed to an osteogenic programme. Several studies have analysed the role of circulating calcifying cells (CCCs) in vascular calcification. CCCs are bone marrow (BM)-derived cells with an osteogenic phenotype, participating in intima calcification processes and defined by osteocalcin and bone alkaline phosphatase expression. The identification of CCCs in diabetes and atherosclerosis is the most recent, intriguing and yet uncharted chapter in the scenario of the bone-vascular axis. Whether osteogenic shift occurs in the BM, the bloodstream or both, is not known, and also the factors promoting CCC formation have not been identified. However, it is possible to recognize a common pathogenic commitment of inflammation in atherosclerosis and diabetes, in which metabolic control may also have a role. Currently available studies in patients without CKD did not find an association of CCCs with markers of bone metabolism. Preliminary data on CKD patients indicate an implication of mineral bone disease in vascular calcification, as a consequence of functional and anatomic integrity interruption of BM niches. Given the pivotal role that parathyroid hormone and osteoblasts play in regulating expansion, mobilization and homing of haematopoietic stem/progenitors cells, CKD-MBD could promote CCC formation.

Longitudinal changes of the serum calcium levels and accelerated progression of arterial stiffness with age

BACKGROUND AND AIMS

The progression of arterial stiffness is accelerated by aging, although the underlying mechanisms have not yet been clarified. This prospective observational study was conducted to clarify whether longitudinal changes in the serum calcium/phosphate levels are associated with the accelerated progression of arterial stiffness with age.

METHODS

In a cohort of employees at a construction company (1507 middle-aged Japanese men), the serum calcium/phosphate levels and brachial-ankle pulse wave velocity (baPWV) were measured at the start and at the end of a 3-year study period.

RESULTS

A general linear model multivariate analysis revealed a significant interaction of the 2 factors {age and longitudinal changes of the serum calcium levels (delCa) during the follow-up period} on the longitudinal changes of the baPWV during the study period (delPWV). The delCa was significantly correlated with the delPWV even after adjustments for covariates in subjects aged ≥48 years. The delPWV in subjects aged ≥48 years with the delCa in the upper tertile (69 ± 137 cm/s) was significantly larger than that in the other groups even after adjustments for covariates (e.g., del PWV in subjects aged <48 years with the delCa in the lower tertile = 1 ± 94 cm/s) (p < 0.01).

CONCLUSIONS

The association between the arterial stiffness and serum calcium levels differed with age. Pathophysiological abnormalities related to increased serum calcium levels appeared to be associated with accelerated progression of arterial stiffness with age.

[The matrix-gla protein awakening may lead to the demise of vascular calcification]

Matrix-gla-protein (MGP) is mainly secreted by chondrocytes and smooth vascular muscle cells. This potent inhibitor of vascular calcification need to undergo 2 post-transcriptional steps to be fully active: one phosphorylation of 3 serine residues (on 5) and a carboxylation of 5 glutamate residues (on 9). Like other "Gla" proteins, this carboxylation is vitamin K dependant. Several forms of MGP thus circulate in the plasma, some of them being totally inactive (the unphosphorylated and uncarboxylated MGP), some others being partially or fully active, according to the number of phosphorylated or carboxylated sites. A theoretical link exists between MGP, vitamin K, vascular calcifications and cardiovascular diseases. This link is even more evident in patients suffering from chronic kidney diseases (CKD), and notably hemodialysis patients. If this link has been demonstrated in different experimental studies, clinical studies are mainly observational and their results must be interpreted accordingly. MGP concentrations are definitely not yet a surrogate to estimate the levels of vascular calcification, but could allow the monitoring of vitamin K treatment. Modulation of MGP concentrations may reduce vascular calcification in hemodialyzed patients, if the large ongoing trials show an efficiency of this treatment. In this review, we will summarize the role of MGP in the vascular calcifications process, describe the problems linked to the analytical determination of MGP in plasma and finally describe the different clinical studies on MGP and vascular calcifications in the general population and in CKD patients.

Vascular calcification: from pathophysiology to biomarkers

The link between vascular calcification (VC) and increased mortality is now well established. Over time, as clinical importance of this phenomenon has begun to be fully considered, scientists have highlighted more and more physiopathological mechanisms and signaling pathways that underlie VC. Several conditions such as diabetes, dyslipidemia and renal diseases are undoubtedly identified as predisposing factors. But even if the process is better understood, many questions still remain unanswered. This review briefly develops the various theories that attempt to explain mineralization genesis. Nonetheless, the main purpose of the article is to provide a profile of the various existing biomarkers of VC. Indeed, in the past years, a lot of inhibitors and promoters, which form a dense and interconnected network, were identified. Given importance to assess and control mineralization process, a focusing on accumulated knowledge of each marker seemed to be necessary. Therefore, we tried to define their respective role in the physiopathology and how they can contribute to calcification risk assessment. Among these, Klotho/fibroblast growth factor-23, fetuin-A, Matrix Gla protein, Bone morphogenetic protein-2, osteoprotegerin, osteopontin, osteonectin, osteocalcin, pyrophosphate and sclerostin are specifically discussed.

Poststroke hip fracture: prevalence, clinical characteristics, mineral-bone metabolism, outcomes, and gaps in prevention

Objective. To assess the prevalence, clinical and laboratory characteristics, and short-term outcomes of poststroke hip fracture (HF). Methods. A cross-sectional study of 761 consecutive patients aged ≥60 years (82.3 ± 8.8 years; 75% females) with osteoporotic HF. Results. The prevalence of poststroke HF was 13.1% occurring on average 2.4 years after the stroke. The poststroke group compared to the rest of the cohort had a higher proportion of women, subjects with dementia, history of TIA, hypertension, coronary artery disease, secondary hyperparathyroidism, higher serum vitamin B12 levels (>350 pmol/L), walking aid users, and living in residential care facilities. The majority of poststroke HF patients had vitamin D insufficiency (68%) and excess bone resorption (90%). This group had a 3-fold higher incidence of postoperative myocardial injury and need for institutionalisation. In multivariate analysis, independent indicators of poststroke HF were female sex (OR 3.6), history of TIA (OR 5.2), dementia (OR 4.1), hypertension (OR 3.2), use of walking aid (OR 2.5), and higher vitamin B12 level (OR 2.3). Only 15% of poststroke patients received antiosteoporotic therapy prior to HF. Conclusions. Approximately one in seven HFs occurs in older stroke survivors and are associated with poorer outcomes. Early implementation of fracture prevention strategies is needed.

The clinical utility of serum tartrate-resistant acid phosphatase 5b in the assessment of bone resorption in patients on peritoneal dialysis

OBJECTIVES

Serum tartrate-resistant acid phosphatase 5b (TRACP5b) is a bone resorption marker used in the assessment of bone metabolic status. The present study was designed to determine the clinical characteristics and utility of measuring serum TRACP5b levels in peritoneal dialysis (PD) patients.

DESIGN

Cross-sectional study.

PATIENTS

Forty-one patients receiving PD treatment in a single centre.

MEASUREMENT

Serum levels of the bone turnover markers TRACP5b, N-terminal cross-linking telopeptide of type 1 collagen (NTX), bone-specific alkaline phosphatase (BAP), and parathyroid hormone (PTH) were simultaneously measured. The correlation of serum TRACP5b with other established bone markers was analysed after logarithmic transformation. Multivariate linear regression analysis was performed to examine the effects of both renal and peritoneal Kt/V (an index for solute clearance) for urea on bone markers using age, sex, body mass index, and PTH as covariates. Bone markers were also measured in three patients before and after treatment with cinacalcet hydrochloride, alphacalcidol, and raloxifene hydrochloride.

RESULTS

Log TRACP5b was significantly correlated with log NTX, log BAP and log PTH. In the multivariate analysis, peritoneal Kt/V was not correlated with log NTX, log BAP or log TRACP5b. In contrast, renal Kt/V was significantly correlated with log NTX only. Responses to drug treatment were more accurately determined from serum TRACP5b and BAP than from serum NTX.

CONCLUSIONS

Serum TRACP5b and BAP are potentially useful biomarkers for the evaluation of bone turnover in PD patients because they correlate well with other established bone markers and they are not influenced by renal and peritoneal clearances.

Cardiovascular diseases in older patients with osteoporotic hip fracture: prevalence, disturbances in mineral and bone metabolism, and bidirectional links

BACKGROUND

Considerable controversy exists regarding the contribution of mineral/bone metabolism abnormalities to the association between cardiovascular diseases (CVDs) and osteoporotic fractures.

AIMS AND METHODS

To determine the relationships between mineral/bone metabolism biomarkers and CVD in 746 older patients with hip fracture, clinical data were recorded and serum concentrations of parathyroid hormone (PTH), 25-hydroxyvitamin D, calcium, phosphate, magnesium, troponin I, parameters of bone turnover, and renal, liver, and thyroid functions were measured.

RESULTS

CVDs were diagnosed in 472 (63.3%) patients. Vitamin D deficiency was similarly prevalent in patients with (78.0%) and without (82.1%) CVD. The CVD group had significantly higher mean PTH concentrations (7.6 vs 6.0 pmol/L, P < 0.001), a higher prevalence of secondary hyperparathyroidism (SPTH) (PTH > 6.8 pmol/L, 43.0% vs 23.3%, P < 0.001), and excess bone resorption (urinary deoxypyridinoline corrected by creatinine [DPD/Cr] > 7.5 nmol/μmol, 87.9% vs 74.8%, P < 0.001). In multivariate regression analysis, SHPT (odds ratio [OR] 2.6, P = 0.007) and high DPD/Cr (OR 2.8, P = 0.016) were independent indictors of CVD. Compared to those with both PTH and DPD/Cr in the normal range, multivariate-adjusted ORs for the presence of CVD were 17.3 (P = 0.004) in subjects with SHPT and 9.7 (P < 0.001) in patients with high DPD/Cr. CVD was an independent predicator of SHPT (OR 2.8, P = 0.007) and excess DPD/Cr (OR 2.5, P = 0.031). CVD was predictive of postoperative myocardial injury, while SHPT was also an independent predictor of prolonged hospital stay and in-hospital death.

CONCLUSION

SHPT and excess bone resorption are independent pathophysiological mediators underlying the bidirectional associations between CVD and hip fracture, and therefore are important diagnostic and therapeutic targets.

Vitamin K status in chronic kidney disease: a report of a study and a mini-review

Hepatic vitamin K-dependent proteins (e.g., Factors II, VII, IX and X) form part of the clotting cascade. Factor II (FII)/Prothrombin incorporates 10 Glu residues on the N-terminal region that are γ-carboxylated to Gla residues by the action of γ-glutamyl carboxylase to confer biological activity. Vitamin K is also required for the normal function of Matrix Gla Protein (MGP)--one of several non-clotting-related extra-hepatic vitamin K-dependent proteins. MGP is known to have protective action against vascular calcification--indeed it is a powerful tissue-bound inhibitory mechanism and can be found in blood vessel walls. The mature protein is also dependent on activation by γ-glutamyl carboxylase enzyme to convert Glu residues in its amino acid sequence to Gla. This reaction can only take place when the enzyme is activated in the presence of vitamin K. It is of great potential interest to investigate whether subtle deficiencies of vitamin K may, through its effect on the action of MGP, be a contributing factor to vascular calcification in CKD patients, in whom CV disease is greatly accelerated and in whom vascular calcification is not only common, but progresses aggressively, and is something for which as yet there is no clinically applicable remedy.

FGF23 is independently associated with vascular calcification but not bone mineral density in patients at various CKD stages

SUMMARY

The hormone fibroblast growth factor 23 (FGF23) is involved in mineral homeostasis but may also have a role in vascular calcification and bone mineralization. In a cohort of 142 patients with CKD stages 2-5D, plasma FGF23 was independently associated with aortic calcification but not with pulse wave velocity or bone mineral density.

INTRODUCTION

FGF23 is involved in mineral homeostasis but may also have a role in vascular calcification and bone mineralization. Previous studies related to FGF23 and vascular and bone outcomes have been restricted to dialysis patients. The aim of the present study was to establish whether or not plasma FGF23 is associated with aortic and coronary calcification, arterial stiffness, and bone mineral density in patients with early as well as late stages of CKD.

METHODS

In a cohort of 142 patients with CKD stages 2-5D, we made routine biochemistry and intact FGF23 determinations, and assessed aortic and coronary calcification, bone mineral density (BMD), and arterial stiffness by multislice spiral computed tomography and automated pulse wave velocity (PWV).

RESULTS

Plasma intact FGF23 levels were elevated in CKD patients; the elevation preceded that of serum phosphate in early-stage CKD. Patients with elevated FGF23 levels had higher aortic and coronary calcification scores than patients with lower FGF23 levels. Multivariate linear regression analysis indicated that only age (p < 0.001) and FGF23 (p = 0.008) were independently associated with aortic calcification score. Plasma FGF23 was neither associated with PWV nor with BMD.

CONCLUSION

Our data suggest that plasma FGF23 is an independent biomarker of vascular calcification in patients with various CKD stages including early stages. The association between vascular calcification and FGF23 levels appears to be independent of BMD. It remains to be seen whether this association is independent of bone turnover and bone mass.

Circulating sclerostin and Dickkopf-1 (DKK1) in predialysis chronic kidney disease (CKD): relationship with bone density and arterial stiffness

Abnormalities of bone metabolism and increased vascular calcification are common in chronic kidney disease (CKD) and important causes of morbidity and mortality. The Wnt signaling pathway may play a role in the bone and vascular disturbances seen in CKD, termed collectively "CKD-MBD." The aim of the study was to investigate the possible association of circulating concentrations of the secreted Wnt signaling inhibitors DKK1 and sclerostin with BMD and arterial stiffness in predialysis CKD. Seventy-seven patients (48 M, 29 F), mean age 57 (SD = 14) years with CKD stages 3B (n = 32) and 4 (n = 45) were studied. Sclerostin, DKK1, PTH, and 1,25(OH)(2)D were analyzed. BMD was measured at the lumbar spine (LS), femoral neck (FN), total hip (TH), and forearm (FARM). Arterial stiffness index was determined by contour analysis of digital volume pulse (SI(DVP)). There was a positive correlation between sclerostin and age (r = 0.47, p < 0.000). Sclerostin was higher in men than women (p = 0.013). Following correction for age and gender, there was a negative association between GFR and sclerostin (p = 0.002). We observed a positive association between sclerostin and BMD at the LS (p = 0.0001), FN (p = 0.004), and TH (p = 0.002). In contrast, DKK1 was negatively associated with BMD at the FN (p = 0.038). A negative association was seen between DKK1 and SI(DVP) (p = 0.027). Our data suggest that the Wnt pathway may play a role in CKD-MBD. Prospective studies are required to establish the clinical relevance of sclerostin and DKK1 as serological markers in CKD.

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.

Mineral and bone disorders in children with chronic kidney disease

As children with chronic kidney disease (CKD) have a long lifespan, optimal control of bone and mineral homeostasis is essential not only for the prevention of debilitating skeletal complications and for achieving adequate growth but also for preserving long-term cardiovascular health. As the growing skeleton is highly dynamic and at particular risk of deterioration, close control of bone and mineral homeostasis is required in children with CKD. However, assessment of bone disease is hampered by the limited validity of biochemical parameters-major controversy exists on key issues such as parathyroid hormone target ranges and the lack of useful imaging techniques. The role of newly discovered factors in bone and mineral homeostasis, such as fibroblast growth factor 23, is not yet established. Even though scientific evidence is limited in children with CKD, ergocalciferol or cholecalciferol supplementation and the use of calcium-free phosphate binders is recommended. The new drug cinacalcet is highly promising; however, pediatric experience is still limited to observational data and the effect of cinacalcet on longitudinal growth and pubertal development is unknown. Randomized, controlled trials are underway, including studies of cinacalcet pharmacokinetics and pharmacodynamics in infants.

Assessment of matrix Gla protein, Klotho gene polymorphisms, and oxidative stress in chronic kidney disease

Increased vascular calcification and oxidative stress are considered as extra renal risk factors at the pathogenesis cardiovascular events in chronic kidney disease (CKD). We investigated matrix Gla protein (MGP) (T-138C, Glu60X, Thr83Ala) and Klotho (Cys370Ser) gene polymorphisms, serum MGP levels, and oxidative stress status of 84 CKD patients and 37 healthy controls. The MGP gene Glu60X and Thr83Ala polymorphisms were significantly associated with CKD. The correlation between T-138C genotype of MGP gene, Cys370Ser genotype of Klotho gene, and CKD was not significant (p > 0.05). At the haplotype analysis, the combination of the X allele of Glu60X and the Thr allele of Thr83Ala showed a significantly increased risk of CKD (p < 0.05). X allele, Thr allele, and C allele of T-138C were associated with diabetes mellitus and CKD phenotypes occurring concurrently (p < 0.01). Serum zinc levels were significantly low in end-stage renal disease (ESRD) patients (p = 0.0001). The total comet score frequency of ESRD patients was higher than that of control group (p < 0.05). The urinary 8-hydroxy-2'-deoxyguanosine levels were significantly high in CKD patients (p < 0.05). According to this study, analyzing the distribution of MGP gene and oxidative stress status would be very informative in order to detect their role at CKD.

FGF-23 and osteoprotegerin are independently associated with myocardial damage in chronic kidney disease stages 3 and 4. Another link between chronic kidney disease-mineral bone disorder and the heart

BACKGROUND

Extra-skeletal calcification and disordered phosphate metabolism are hallmarks of chronic kidney disease-mineral bone disorder (CKD-MBD). Osteoprotegerin (OPG) and fibroblast growth factor 23 (FGF-23) are increased in chronic kidney disease (CKD) and have been associated with arterial and cardiac dysfunction and reduced survival. Troponin T (cTnT) is released from cardiac myocytes under conditions of stress and is predictive of mortality across a range of renal functions. However, the utility of this biomarker was formerly limited by the lower limit of assay detection. The introduction of a high-sensitivity assay has enabled more detailed study of myocyte stress below the previous limit of detection. We studied the association of mediators of CKD-MBD with arterial stiffness and also of these mediators and arterial stiffness with myocardial damage in patients with CKD stages 3-4.

METHODS

OPG and FGF-23 were measured in 200 CKD stages 3-4 patients. cTnT was measured using a high-sensitivity assay. Aortic stiffness was assessed using aortic pulse wave velocity (APWV).

RESULTS

Mean age was 69 ± 11 years, mean systolic and diastolic blood pressure was 151 ± 22/81 ± 11 mmHg and renal function was 33 ± 11 mL/min/1.73 m(2). OPG, FGF-23, high-sensitivity troponin T (hs-cTnT) and APWV all correlated with renal function. After multivariate analysis, OPG and age remained independently associated with aortic stiffness. OPG and FGF-23 were independently associated with hs-cTnT in addition to other non-traditional risk factors (Model R(2) = 0.596).

CONCLUSION

We have shown that changes in bone mediators and phosphate metabolism induced by CKD are independently associated with vascular and cardiomyocyte dysfunction. Our findings suggest that cardiac dysfunction may be specifically associated with such abnormalities in addition to recognized increases in vascular stiffness.

Serum fetuin-A and vitamin D in children with mild-to-severe chronic kidney disease: a cross-sectional study

BACKGROUND

Fetuin-A and vitamin D are significant correlates of cardiovascular morbidity in paediatric chronic kidney disease (CKD) patients. It is thus far unknown, whether or not serum fetuin-A is affected by the vitamin D status or treatment with vitamin D preparations in these patients.

METHODS

In a cross-sectional study, serum concentrations of fetuin-A, 25-hydroxyvitamin D(3) (25OHD) and 1,25-dihydroxyvitamin D(3) (calcitriol) levels were determined in 112 paediatric patients with mild-to-severe CKD (Stages 1-5) and after renal transplantation. A25OHD supplementation and/or calcitriol treatment were given in 64% of the patients.

RESULTS

Fetuin-A levels were clearly reduced in dialysis patients but were comparable to healthy controls in those with moderate CKD and after transplantation. Although 64 and 46% of all patients received 25OHD and/or calcitriol treatment, 48 and 20% of patients were 25OHD and/or calcitriol deficient, respectively. Within the whole patient cohort, fetuin-A correlated with serum calcium and yearly weight-related 25OHD dosage (each P < 0.01) but not with the vitamin D status per se. Multiple regression analysis revealed the need for dialysis treatment and cumulative 25OHD dosage as independent predictors of fetuin-A concentrations (model r(2) = 0.17). In dialysis patients, fetuin-A was inversely correlated with serum C-reactive protein but positively correlated with cumulative calcitriol dosage and serum parathormone (each P < 0.01).

CONCLUSIONS

Fetuin-A levels are clearly reduced in children on dialysis but not in those with moderate CKD and after transplantation. Besides the degree of microinflammation, the cumulative intake of 25OHD and calcitriol are significantly correlated to fetuin-A in these patients. The impact of vitamin D treatment appears to be at least partly mediated by serum calcium.