Coronary artery calcification, systemic inflammation markers and mineral metabolism in a peritoneal dialysis population

Vascular calcification inhibitors and cardiovascular events in peritoneal dialysis patients

The prevalence of cardiovascular diseases is high among patients with chronic kidney disease (CKD) and peritoneal dialysis (PD) patients, which increases morbidity and mortality in this population and represents a significant financial burden for both the patients and the healthcare systems. Vascular calcification (VC) is associated with increased morbidity and mortality and VC risk is higher in patients with CKD than in healthy individuals. Calcification inhibitors, compounds that inhibit VC, were discovered as a result of efforts to explain why some patients are spared. It was found that certain proteins (e.g., fetuin-A, osteopontin, osteoprotegerin, bone morphogenetic protein-7) inhibit calcification in dialysis patients. In this narrative review, we provide an overview of known calcification inhibitors, describe the relevant regulatory mechanisms, and discuss their relation to VC development in PD patients.

Does the OPG/RANKL system contribute to the bone-vascular axis in chronic kidney disease? A systematic review

Vascular calcification (VC) is highly prevalent in patients with chronic kidney disease (CKD) and is strongly associated with cardiovascular mortality and morbidity. Accumulating evidence over the past decade has challenged the hypothesis of close interaction between bone and VC what raises the possibility of a common underlying pathophysiological mechanism. Lately, bone regulatory proteins such as: osteoprotegerin (OPG) and Receptor Activator for Nuclear Factor κB Ligand (RANKL) has attracted attention of researchers as a possible key mediators of bone-vascular calcification imbalance. The literature search was carried out using the MEDLINE/PubMed database and a combination of keywords and MeSH terms, and only papers published since January 2005 to July 2016 were selected. The search resulted in 562 potential articles. After selection according to the eligibility criteria, 107 studies fulfilled were included (102 full texts and 5 was case reports). OPG and RANKL plays essential role in the regulation of bone metabolism and may be regarded as a possible link between VC, bone and mineral metabolism in CKD patients. Further studies are required to determine the diagnostic significance of these proteins in evaluation of progression and severity of VC process in CKD patients. Finally, the efficacy and safety, especially in regard to VC, of anti-RANKL therapy in CKD patients requires well-designed prospective, randomized trials.

Coronary Artery Calcification Score as A Predictor of All-Cause Mortality and Cardiovascular Outcome in Peritoneal Dialysis Patients

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BACKGROUND

This study aimed to examine whether the coronary artery calcification score (CaCS) was associated with the prognosis of peritoneal dialysis (PD) patients. ♦

METHODS

Adult PD patients who were clinically stable for at least 2 months were recruited for this prospective, observational cohort study. Coronary artery calcification was assessed using multislice spiral computed tomography and was recorded according to the Agatston score. The endpoints including all-cause mortality, cardiovascular events, and cardiovascular mortality were assessed. Multivariate Cox regression was used to identify independent predictors of all-cause mortality, cardiovascular events (CVEs), and cardiovascular mortality. ♦

RESULTS

A total of 179 PD patients (86 men) with a mean age of 63.5 ± 14.8 years were recruited for this study. Coronary artery calcification scores ranging from 0 to 5,257 were stratified as follows: no (CaCS = 0, n = 54), low (0 < CaCS < 400, n = 72), and high (CaCS ≥ 400, n = 53) calcification. The follow-up duration was 30.6 ± 16.2 (24-63) months. Compared with the no calcification group, patients with a higher CaCS were older and had lower diastolic blood pressure, residual renal function, and serum albumin, and higher HbA1C and serum insulin. Multivariate Cox regression revealed that the CaCS was an independent predictor for all the 3 endpoints after adjustment in PD patients. ♦

CONCLUSIONS

CaCS was an independent predictor of all-cause mortality, cardiovascular events, and cardiovascular mortality in patients receiving peritoneal dialysis.

Associations between Thyroid Hormones, Calcification Inhibitor Levels and Vascular Calcification in End-Stage Renal Disease

Introduction

Vascular calcification is a common, serious and elusive complication of end-stage renal disease (ESRD). As a pro-calcifying risk factor, non-thyroidal illness may promote vascular calcification through a systemic lowering of vascular calcification inhibitors such as matrix-gla protein (MGP) and Klotho.

Methods and Material

In 97 ESRD patients eligible for living donor kidney transplantation, blood levels of thyroid hormones (fT3, fT4 and TSH), total uncarboxylated MGP (t-ucMGP), desphospho-uncarboxylated MGP (dp-ucMGP), descarboxyprothrombin (PIVKA-II), and soluble Klotho (sKlotho) were measured. The degree of coronary calcification and arterial stiffness were assessed by means of cardiac CT-scans and applanation tonometry, respectively.

Results

fT3 levels were inversely associated with coronary artery calcification (CAC) scores and measures of arterial stiffness, and positively with dp-ucMGP and sKlotho concentrations. Subfractions of MGP, PIVKA-II and sKlotho did not associate with CAC scores and arterial stiffness. fT4 and TSH levels were both inversely associated with CAC scores, but not with arterial stiffness.

Discussion

The positive associations between fT3 and dp-ucMGP and sKlotho suggest that synthesis of MGP and Klotho is influenced by thyroid hormones, and supports a link between non-thyroidal illness and alterations in calcification inhibitor levels. However, the absence of an association between serum calcification inhibitor levels and coronary calcification/arterial stiffness and the fact that MGP and Klotho undergo post-translational modifications underscore the complexity of this association. Further studies, measuring total levels of MGP and membrane bound Klotho, should examine this proposed pathway in further detail.

Nonthyroidal illness: a risk factor for coronary calcification and arterial stiffness in patients undergoing peritoneal dialysis?

OBJECTIVES

Low triiodothyronine levels, as part of the nonthyroidal illness syndrome, are common in dialysis patients and have repeatedly been shown to be associated with increased (cardiovascular) mortality rates. We hypothesized that increased vascular calcification may mediate this relationship.

METHODS

A total of 84 patients from the Stockholm region receiving maintenance peritoneal dialysis were included in the study. Serum concentrations of free triiodothyronine (fT3), thyroxine and thyroid-stimulating hormone were measured. Coronary artery calcium (CAC) scores were assessed by cardiac computed tomography scans. Surrogates of arterial stiffness included aortic diastolic and systolic blood pressures, pulse pressure, augmentation pressure and Buckberg's subendocardial viability ratio measured by pulse waveform analyses. Patients were subsequently followed, and events of death and censoring were recorded. Thyroid hormone concentrations were associated with CAC scores, measures of arterial stiffness and all-cause mortality. The associations between CAC scores and arterial stiffness surrogates and mortality were also determined to evaluate a possible causal pathway.

RESULTS

Both CAC scores and arterial stiffness surrogates were substantially higher in individuals with low fT3 levels. These associations persisted in multivariate logistic and linear regression analyses. During a median (interquartile range) follow-up of 32 (22-42) months, 24 patients died. Both fT3 levels below the median value [HR crude 4.1, 95% confidence interval (CI) 1.4-12.6] and CAC scores above the median value (HR crude 5.8, 95% CI 1.7-20.1) were strongly associated with mortality.

CONCLUSIONS

In patients undergoing peritoneal dialysis, fT3 levels were strongly associated with arterial stiffness, coronary artery calcification and mortality. We speculate that the association between nonthyroidal illness and mortality may be partly mediated by acceleration of vascular calcification.

Relationship between glucose exposure via peritoneal dialysis solutions and coronary artery calcification in non-diabetic peritoneal dialysis patients

INTRODUCTION

Vascular calcification is frequent in dialysis patients and is associated with increased mortality. Impaired glucose metabolism is proposed as a contributing factor for vascular calcification. We investigated whether glucose exposure via dialysate may have a role in vascular calcification in non-diabetic peritoneal dialysis patients.

METHOD

We measured coronary artery calcification by multi-slice computerized tomography in 50 prevalent non-diabetic peritoneal dialysis patients and assessed its relations with fasting blood glucose, homeostasis model assessment of insulin resistance (HOMA-IR), and glucose exposure from peritoneal dialysis fluid.

RESULTS

Twenty-four patients (48%) had no coronary calcification. When patients were grouped according to the presence or absence of calcification, patients with calcification were mostly men and had higher burden of cardiovascular disease history, vitamin D dose intake, serum calcium, total glucose exposure from dialysis solution, and lower total weekly Kt/Vurea. In multivariate analysis, dialysate glucose exposure was an independent predictor of coronary artery calcification score, besides serum calcium and Kt/Vurea.

CONCLUSION

These data suggest that high glucose exposure from dialysis solution, which is potentially correctable, is a risk factor for vascular calcification in non-diabetic PD patients.

Matrix metalloproteinases and soluble Fas/FasL system as novel regulators of apoptosis in children and young adults on chronic dialysis

The system of membrane receptor Fas and its ligand FasL compose one of the main pathways triggering apoptosis. However, the role of their soluble forms has not been clarified yet. Although sFasL can be converted from the membrane-bound form by matrix metalloproteinases (MMPs), there are no data on relations between sFas/sFasL, MMPs and their tissue inhibitors (TIMPs) in patients on chronic dialysis—neither children nor adults. The aim of our study was to evaluate serum concentrations of sFas, sFasL, and their potential regulators (MMP-2, MMP-7, MMP-9, TIMP-1, TIMP-2), in children and young adults chronically dialyzed. Twenty-two children on automated peritoneal dialysis (APD), 19 patients on hemodialysis (HD) and 30 controls were examined. Serum concentrations of sFas, sFasL, MMPs and TIMPs were assessed by ELISA. Median values of sFas, sFasL, sFas/sFasL ratio, MMP-2, MMP-7, MMP-9, TIMP-1 and TIMP-2 were significantly elevated in all dialyzed patients vs. controls, the highest values being observed in subjects on HD. A single HD session caused the decrease in values of all parameters to the levels below those seen in children on APD. Regression analysis revealed that MMP-7 and TIMP-1 were the best predictors of sFas and sFasL concentrations. Children and young adults on chronic dialysis are prone to sFas/sFasL system dysfunction, more pronounced in patients on hemodialysis. The correlations between sFas/sFasL and examined enzymes suggest that MMPs and TIMPs take part in the regulation of cell death in the pediatric population on chronic dialysis, triggering both anti- (sFas) and pro-apoptotic (sFasL) mechanisms.

Endothelin but Not Angiotensin II May Mediate Hypertension-Induced Coronary Vascular Calcification in Chronic Kidney Disease

To understand the relationship between putative neurohormonal factors operative in hypertension and coronary artery calcification (CAC), the relevant cellular actions of angiotensin (Ang II) and endothelin-1 (ET-1) are reviewed. There is compelling evidence to implicate ET-1 in CAC. ET-1 increases phosphate transport with a 42 to 73% increase in V_max. Increased cellular phosphate may induce CAC through increased Ca x phosphate product, transformation of vascular smooth muscle cells into a bone-producing phenotype or cell apoptosis that releases procalcific substances. ET-1 is increased in several models of vascular calcification. ET-1 inhibits inhibitors of calcification, matrix Gla and osteoprotegerin, while enhancing pro-calcific factors such as BMP-2 and osteopontin. In contrast, Ang II inhibits phosphate transport decreasing V_max by 38% and increases matrix Gla. Ang II also stimulates bone resorption. Vascular calcification is reduced by ET-1 A receptor antagonists and to a greater extent than angiotensin receptor blockade although both agents reduce blood pressure.

Phosphate levels and cardiovascular disease in the general population

Phosphate levels are consistently linked with cardiac calcification, cardiovascular disease (CVD), and death in populations with chronic kidney disease. In addition, mechanistic insights suggest that phosphate levels that span the conventional normal range could lead to CVD. Examining these associations in the general population may be relevant because several interventions that may be suitable for primary or secondary prevention trials already exist. This review summarizes findings described from several community-based, prospective, observational studies. Graded associations with cardiac calcification, left ventricular hypertrophy, cardiovascular events, and death were evident, and cardiovascular risk seemed to accelerate with phosphate >3.5 to 4.0 mg/dl. Although the cause of these associations remains to be determined, several existing interventions may allow in-depth examination of the hypothesis that reducing phosphate levels could prevent CVD in the general population. Even as proof-of-concept trials and mechanistic studies are awaited, phosphate levels may be useful for cardiovascular risk stratification in adults without overt kidney disease.

Calcium-phosphate levels and cardiovascular disease in community-dwelling adults: the Atherosclerosis Risk in Communities (ARIC) Study

BACKGROUND

Calcium-phosphate levels, linked to vascular dysfunction in chronic kidney disease, may represent novel risk factors for coronary heart disease, stroke, and death in community-dwelling adults.

METHODS

We tested this hypothesis over 12.6 years of follow-up in the prospective, community-based Atherosclerosis Risk in Communities Study (n = 15,732).

RESULTS

At baseline, mean (SD) values were 9.8 (0.4) mg/dL for serum calcium, 3.4 (0.5) mg/dL for serum phosphate, 33.6 (5.3) mg(2)/dL(2) for calcium-phosphate product, 54.2 (5.7) years for age, and 93.1 (21.5) mL/min per 1.73 m(2) for glomerular filtration rate (GFR). Shared associations of calcium, phosphate, and calcium-phosphate product included older age, female sex, African American race, cigarette-years, current cigarette smoking, low body mass index, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, low serum albumin, low GFR, low caloric intake, and phosphorus intake. With adjustment for age, demographic characteristics, comorbid conditions, albumin, and GFR, calcium-associated hazards ratios for coronary heart disease, stroke, and death were, respectively, 1.01 (95% confidence interval 0.96-1.06), 1.16 (1.07-1.26, P = .0005), and 1.03 (0.98-1.08); phosphate-associated hazards ratios were 1.03 (0.98-1.08), 1.11 (1.02-1.21, P = .0219), and 1.14 (1.09-1.20, P < .0001); calcium-phosphate product-associated hazards ratios were 1.03 (0.98-1.08), 1.15 (1.05-1.26, P = .0017), and 1.15 (1.09-1.20, P < .0001).

CONCLUSIONS

Although calcium, phosphate, and calcium-phosphate product levels exhibit complex associations with traditional cardiovascular risk factors and outcomes, they may be potentially modifiable risk factors for stroke and death in community-dwelling adults.

Indexes of kidney function and coronary artery and abdominal aortic calcium (from the Framingham Offspring Study)

It is uncertain whether moderate chronic kidney disease (CKD) or measures of kidney function are associated with subclinical atherosclerosis as represented by coronary artery calcium (CAC) or abdominal aortic calcium (AAC). We used logistic and linear regression analyses to relate CKD (glomerular filtration rate <60 ml/min/1.73 m(2)), cystatin C (cysC), and microalbuminuria (MA) with CAC and AAC obtained using multidetector computed tomography in Framingham Heart Study Offspring participants (mean age 59 years, 55.3% women). Increased CAC and AAC were defined as > or =90th percentile age- and gender-specific cutpoints based on a healthy referent sample. Major cardiovascular disease risk factors were accounted for in multivariable models. Of 1,179 participants, 1,174 had AAC measurements and 1,147 had CAC measurements, 6.3% had CKD, and 8.3% had MA. CKD was not associated with CAC (multivariable-adjusted odds ratio [OR] for CKD 1.18, 95% confidence interval 0.59 to 2.36, p = 0.63) or AAC (multivariable-adjusted OR for CKD 1.11, 95% confidence interval 0.61 to 2.04, p = 0.73). CysC was associated with CAC in age- and gender-adjusted but not in multivariable models (age- and gender-adjusted OR for log cysC per SD increment and CAC 1.19, 95% confidence interval 1.01 to 1.41, p = 0.04; multivariable-adjusted OR 1.14, 95% confidence interval 0.95 to 1.38, p = 0.15). MA was not associated with CAC (OR 0.81, 95% confidence interval 0.41 to 1.61, p = 0.54). Neither cysC nor MA was significantly associated with AAC in age- and gender- or multivariable-adjusted models. In conclusion, CKD, cysC, and MA are not associated with CAC or AAC when accounting for cardiovascular disease risk factors.

Phosphate Balance on Peritoneal Dialysis

Hyperphosphatemia is an independent predictor of mortality in end-stage renal disease patients, and 40% – 50% of peritoneal dialysis (PD) patients have suboptimal control of serum phosphate. Systematically addressing this problem requires an understanding of phosphate balance on PD. The present review discusses the determinants of daily phosphate load and focuses on the factors influencing renal and peritoneal clearance of phosphate.

Vascular Calcification in Peritoneal Dialysis Patients

Vascular calcification (VC) is being recognized as a common complication at all stages of chronic kidney disease, particularly in patients on dialysis. Traditional and nontraditional cardiovascular risk factors both appear to be involved in the development of VC in this population. Although few studies focusing exclusively on peritoneal dialysis (PD) patients are available, some data support the view that VC constitutes an independent prognostic marker of morbidity and mortality in the PD population. In this review, we discuss the potential pathophysiologic pathways of VC in PD patients, and we examine the relevant clinical data.

The role of inflammation in coronary artery calcification

Vascular calcification is an age-dependent, common finding in human coronary arteries and begins as early as the second decade of life, just after fatty streak formation. Previous studies have showed that the severity of coronary calcification is closely related to atherosclerotic plaque burden and cardiac event rate. In the past few decades, coronary calcification has been considered passive and degenerative. With recent clinical and basic research, however, there is increasing recognition that coronary calcification is an active, regulated process. Current diagnostic methods for coronary artery calcification (CAC) are usually traditional coronary angiography, intravascular ultrasound (IVUS), electron beam computed tomography (EBCT) and multi-slice computed tomography (MSCT) while treatment for patients with calcified coronary arteries is troublesome. Several lines of evidence suggest that inflammation plays a major role in the development of atherosclerosis as well as its clinical manifestations. Recent study showed that inflammatory process might be also involved in coronary calcification. Accordingly, measurements of inflammatory markers such as C-reactive protein (CRP) may in part reflect indices of atherosclerosis, such as coronary calcification, and are likely to provide distinct information regarding cardiovascular risk. In this article, we review the current evidence of relationship between coronary calcification and inflammation for purpose of drawing the more attention on the inflammatory mechanism of coronary calcification, which may change our research as well as therapeutic strategies for coronary calcification in the future.

[Coronary artery disease and coronary angioplasty in chronic hemodialysis patients]

Chronic renal insufficiency leads to many cardiovascular complications and provide worst prognosis, especially when patients need hemodialysis. The atherosclerosis of chronic hemodialysis patients is qualified as "accelerated" by some authors, because of a very fast and large progression. To improve prognosis, it seems to be very important to detect and treat the frequent and serious underlying cardiovascular disease. Because of the high rate of diabetes mellitus, silent ischemia is a very frequent clinical situation. In the other hand, coronary artery disease in chronic hemodialysis patients is frequently complex, with a large coronary extension and high rate of coronary calcifications. Consequently, this disease needs a specific therapeutic approach. Even though, percutaneous coronary interventions (PCI) are more complex in this population, it provides good results, and improves patient's prognosis. However, the rate of complications of the vascular approach and the rate of restenosis is high. New devices, such as Drug Eluting Stents (DES) can critically decrease restenosis rate, and closure devices for trans-femoral approach, provides very encouraging results in this high risk population. Despite, good results of PCI with DES use, the mortality is still high in this population. To improve our efficiency, we have to progress in our therapeutic strategies and optimize medical approach to treat the important biological perturbations.