History of Cardiovascular Disease Is Associated With Endothelial Progenitor Cells in Peritoneal Dialysis Patients

Micro- and Macrovascular Effects of Inflammation in Peripheral Artery Disease-Pathophysiology and Translational Therapeutic Approaches

Inflammation has a critical role in the development and progression of atherosclerosis. On the molecular level, inflammatory pathways negatively impact endothelial barrier properties and thus, tissue homeostasis. Conformational changes and destruction of the glycocalyx further promote pro-inflammatory pathways also contributing to pro-coagulability and a prothrombotic state. In addition, changes in the extracellular matrix composition lead to (peri-)vascular remodelling and alterations of the vessel wall, e.g., aneurysm formation. Moreover, progressive fibrosis leads to reduced tissue perfusion due to loss of functional capillaries. The present review aims at discussing the molecular and clinical effects of inflammatory processes on the micro- and macrovasculature with a focus on peripheral artery disease.

Risk factors and outcomes of cardiovascular disease readmission within the first year after dialysis in peritoneal dialysis patients

Background

In the first year of dialysis, patients are vulnerable to cardiovascular disease (CVD) hospitalization, but knowledge regarding the risk factors and long-term outcomes of cardiovascular readmission within the first year after dialysis in incident continuous ambulatory peritoneal dialysis (CAPD) patients is limited.

Methods

This retrospective cohort study was conducted in incident CAPD patients. The demographic characteristics, laboratory parameters, and CVD readmission were collected and analyzed. The primary outcome was all-cause mortality, and the secondary outcomes included CVD mortality, infection-related mortality and technique failure. A logistic regression was used to identify the risk factors associated with CVD readmission within the first year after dialysis. Cox proportional hazards models were used to evaluate the association between CVD readmission and the outcomes.

Results

In total, 1589 peritoneal dialysis (PD) patients were included in this study, of whom 120 (7.6%) patients had at least one episode of CVD readmission within the first year after dialysis initiation. Advanced age, CVD history, and a lower level of serum albumin were independently associated with CVD readmission. CVD readmission within the first year after dialysis was significantly associated with all-cause (HR 2.66, 95%CI 1.91–3.70, p < 0.001) and CVD (HR 3.42, 95%CI 2.20–5.31, p < 0.001) mortality, but not infection-related mortality or technique failure, after adjusting for confounders.

Conclusions

Our findings suggest that an advanced age, a history of CVD, and a lower level of serum albumin were independently associated with CVD readmission. Moreover, CVD readmission was associated with all-cause and cardiovascular mortality in incident CAPD patients.

Endothelial Progenitor Cells and Kidney Diseases

Endothelial progenitor cells (EPC) are bone marrow derived or tissue-resident cells that play major roles in the maintenance of vascular integrity and repair of endothelial damage. Although EPCs may be capable of directly engrafting and regenerating the endothelium, the most important effects of EPCs seem to be depended on paracrine effects. In recent studies, specific microvesicles and mRNAs have been found to mediate the pro-angiogenic and regenerative effects of EPCs on endothelium. EPC counts have important prognostic implications in cardiovascular diseases (CVD). Uremia and inflammation are associated with lower EPC counts which probably contribute to increased CVD risks in patients with chronic kidney disease. Beneficial effects of the EPC therapies have been shown in studies performed on different models of CVD and kidney diseases such as acute and chronic kidney diseases and glomerulonephritis. However, lack of a clear definition and specific marker of EPCs is the most important problem causing difficulties in interpretation of the results of the studies investigating EPCs.

Is chronic kidney disease-mineral and bone disorder associated with the presence of endothelial progenitor cells with a calcifying phenotype?

Background: Chronic kidney disease-mineral and bone disorder (CKD-MBD) has been implicated in vascular calcification pathogenesis. CKD-MBD results in alterations in the number and function of circulating endothelial progenitor cells (EPCs), physiological regulators of angiogenesis and vessel repair, commonly defined as proangiogenic progenitor cells (PACs) by the antigen pattern CD34+CD133+KDR+CD45– and putative EPCs by the pattern CD34+CD133−KDR+CD45–. These cells might acquire a calcifying phenotype in CKD-MBD, expressing mineralization biomarkers. We investigated the expression of vitamin D receptor (VDR) and osteocalcin (OC) on EPCs of healthy individuals and haemodialysis patients, and their possible associations with circulating biomarkers of inflammation and vascular calcification.

Methods: We compared EPC counts, expressing VDR or OC, in 23 healthy subjects versus 53 haemodialysis patients, 17 of them without vitamin D receptor agonist (VDRA) therapy and 35 treated with calcitriol (n  =  17) or paricalcitol (n  =  18). The correlations with serum levels of inflammatory and calcification indexes were also analysed.

Results: All subsets expressing VDR or OC were significantly higher in haemodialysis patients compared with healthy controls, but PACs were increased only in VDRA treatment subgroup, while putative EPCs showed a similar rise also in untreated patients. In VDRA-untreated patients, OC+  PACs correlated positively with calcium levels, while in VDRA-treated patients, VDR+ PACs correlated positively with interleukin 6 levels, and OC+  PACs correlated positively 25-hydroxyvitamin D levels.

Conclusions: Our data suggest that in CKD-MBD, EPCs undergo an endothelial-to-procalcific shift, representing a risk factor for vascular calcification. A link between mineral disorders and vitamin D replacement therapy emerged, with potential adverse effects for CKD patients.

Challenges and opportunities for stem cell therapy in patients with chronic kidney disease

Chronic kidney disease (CKD) is a global health care burden affecting billions of individuals worldwide. The kidney has limited regenerative capacity from chronic insults, and for the most common causes of CKD, no effective treatment exists to prevent progression to end-stage kidney failure. Therefore, novel interventions, such as regenerative cell-based therapies, need to be developed for CKD. Given the risk of allosensitization, autologous transplantation of cells to boost regenerative potential is preferred. Therefore, verification of cell function and vitality in CKD patients is imperative. Two cell types have been most commonly applied in regenerative medicine. Endothelial progenitor cells contribute to neovasculogenesis primarily through paracrine angiogenic activity and partly by differentiation into mature endothelial cells in situ. Mesenchymal stem cells also exert paracrine effects, including proangiogenic, anti-inflammatory, and antifibrotic activity. However, in CKD, multiple factors may contribute to reduced cell function, including older age, coexisting cardiovascular disease, diabetes, chronic inflammatory states, and uremia, which may limit the effectiveness of an autologous cell-based therapy approach. This Review highlights current knowledge on stem and progenitor cell function and vitality, aspects of the uremic milieu that may serve as a barrier to therapy, and novel methods to improve stem cell function for potential transplantation.

Effect of conversion from ciclosporin to tacrolimus on endothelial progenitor cells in stable long-term kidney transplant recipients

BACKGROUND

Endothelial progenitor cell (EPC) counts are proposed surrogate markers for vascular function and cardiovascular risk. The effect of tacrolimus (TAC) on EPC is unknown.

METHODS

In this randomized controlled trial, we assigned 148 stable long-term kidney transplant recipients (KTR) to maintaining ciclosporin (CSA) or to commencing TAC-based immunosuppression at a 2:1 ratio. EPC counts (CD34/KDR) after 24 months were defined as primary endpoint.

RESULTS

The intent-to-treat analysis included 141 KTR (estimated glomerular filtration rate, 46.7 [40.1-61.8] mL/min per 1.73 m). Median (interquartile range [IQR]) EPC counts at baseline and month 24 were 6 (2-9) and 3 (1-9) cells and 4 (2-8) and 2 (0-5) cells per 5×10 mononuclear cells in CSA and TAC, respectively. Median (IQR) circulating angiogenic cells at baseline and month 24 were 28 (10.7-57) and 44.33 (14.6-59.8) cells and 22 (10.8-41) and 21 (9.7-49.5) cells per high-power field in CSA and TAC, respectively. Median (IQR) endothelial cell colony-forming units count per well at baseline and month 24 were 10.5 (3.3-34.3) and 4.38 (1.7-26.5) in CSA and significantly declined from 9.31 (1.8-29.3) to 4.13 (1.1-9.5) in TAC (P=0.003). There were no cardiovascular events in either group.

CONCLUSION

Although late conversion from CSA to TAC appears safe in KTR, conversion to TAC has no favorable effect on EPC. Low EPC levels are associated with a higher risk of subsequent cardiovascular events and are therefore of prognostic value. Their trend to decline over time deserves further examination.

VDR expression on circulating endothelial progenitor cells in dialysis patients is modulated by 25(OH)D serum levels and calcitriol therapy

BACKGROUND/AIMS

Vitamin D deficiency is associated with endothelial dysfunction in uremic patients, possibly by the impairment in the number and function of endothelial progenitor cells (EPCs). In 89 hemodialysis patients, we investigated the factors associated with the number of circulating EPCs (CD34+/CD133+/KDR+ and CD34+/CD133-/KDR+ cells), the presence of VDR and the determinants of VDR expression on EPCs, in particular in calcitriol therapy.

METHODS

EPC counts, percentages of VDR-positive EPCs and VDR expression were assessed by flow cytometry. Cells isolated from a subgroup of patients were cultured to analyze colony-forming units, specific markers expression and a capillary-like structure formation.

RESULTS/CONCLUSIONS

Our study demonstrates the presence of VDR on EPCs. In our dialysis patients, the parameters studied on both CD34+/CD133+/KDR+ and CD34+/CD133-/KDR+ cells, in particular VDR expression, seem to be influenced by uremia-related factors, including anemia, inflammation, diabetes, 25(OH)D serum levels and calcitriol therapy.

Endothelial progenitor cells and cardiovascular events in patients with chronic kidney disease--a prospective follow-up study

Background

Endothelial progenitor cells (EPCs) mediate vascular repair and regeneration. Their number in peripheral blood is related to cardiovascular events in individuals with normal renal function.

Methods

We evaluated the association between functionally active EPCs (cell culture) and traditional cardiovascular risk factors in 265 patients with chronic kidney disease stage V receiving hemodialysis therapy. Thereafter, we prospectively assessed cardiovascular events, e.g. myocardial infarction, percutaneous transluminal coronary angioplasty (including stenting), aorto-coronary bypass, stroke and angiographically verified stenosis of peripheral arteries, and cardiovascular death in this cohort.

Results

In our patients EPCs were related only to age (r = 0.154; p = 0.01). During a median follow-up period of 36 months 109 (41%) patients experienced a cardiovascular event. In a multiple Cox regression analysis, we identified EPCs (p = 0.03) and patient age (p = 0.01) as the only independent variables associated with incident cardiovascular events. Moreover, a total of 70 patients died during follow-up, 45 of those due to cardiovascular causes. Log rank test confirmed statistical significance for EPCs concerning incident cardiovascular events (p = 0.02).

Conclusions

We found a significant association between the number of functionally active EPCs and cardiovascular events in patients with chronic kidney disease. Thus, defective vascular repair and regeneration may be responsible, at least in part, for the enormous cardiovascular morbidity in this population.

Levels of circulating endothelial progenitor cells are related to uremic toxins and vascular injury in hemodialysis patients

BACKGROUND

Patients suffering from chronic kidney diseases (CKD) exhibit cardiovascular diseases and profound endothelial dysfunction. CKD patients have reduced numbers of endothelial progenitor cells, but little is known about the factors influencing these numbers.

OBJECTIVES

Among these factors, we hypothesized that uremic toxins and vascular injury affect endothelial progenitor cells.

PATIENTS/METHODS

Thirty-eight hemodialysis patients were investigated and compared with 21 healthy controls. CD34+CD133+ immature progenitors, CD34+KDR+ endothelial progenitors cells (EPC) and myeloid EPC (mEPC) were counted in peripheral blood. Levels of uremic toxins beta(2)-microglobulin, indole-3 acetic acid, indoxylsulfate, p-cresylsulfate and homocysteine were measured. Vascular injury was assessed in hemodialysis (HD) patients by measuring aortic pulse wave velocity and plasma levels of endothelial microparticles. In vitro experiments were performed to study the effect of uremic toxins on apoptosis of progenitor cells.

RESULTS AND CONCLUSIONS

CD34+CD133+ immature progenitor cell number was negatively correlated with the levels of uremic toxins beta(2)-microglobulin and indole-3 acetic acid. In vitro, indole-3 acetic acid induced apoptosis of CD133+ cells. These data indicate uremic toxins have a deleterious role on progenitor cells, early in the differentiation process. Moreover, mEPC number was positively correlated with markers of vascular injury-pulse wave velocity and endothelial microparticle levels. This suggests that vascular lesions could stimulate progenitor cell mobilization, even in a context of reduced EPC induced by CKD. In conclusion, uremic toxins and vascular injury appear to affect endothelial progenitor cell biology in CKD.

Dialysis modality is independently associated with circulating endothelial progenitor cells in end-stage renal disease patients

BACKGROUND

Numbers of endothelial progenitor cells (EPC) have been shown to be decreased in subjects with end-stage renal disease (ESRD). It is not clear, however, whether dialysis modality affects circulating EPCs in ESRD subjects.

METHODS

We examined the number of circulating EPCs in 67 continuous ambulatory peritoneal dialysis (CAPD) patients and age- and gender-matched 142 haemodialysis (HD) patients, and 78 subjects without chronic kidney disease. Arterial stiffness was analysed as pulse-wave velocity (PWV) for these patients, and their mutual relationship with circulating EPCs was examined. EPCs were measured as CD34(+) CD133(+) CD45(low) VEGFR2(+) cells determined by flow cytometry.

RESULTS

The EPC numbers exhibited a strong correlation (R(2) = 0.866) with endothelial-colony forming units on culture assay. The levels of EPCs in HD or CAPD subjects were significantly lower than those in control subjects. Among ESRD subjects, the levels of EPC were significantly higher in CAPD subjects than those in HD subjects. In ESRD subjects, PWV levels tended to be associated with EPCs (Rs = -0.131, P = 0.058). However, the significant relationship between dialysis modality and circulating EPCs was independent of the levels of PWV. The association of circulating EPCs with dialysis modality was significant even after adjusting for other potential confounders, including age, gender, blood pressure, history of cardiovascular diseases, presence of diabetes, blood haemoglobin level and treatments with angiotensin-converting enzyme inhibitor/angiotensin II receptor blocker or statin.

CONCLUSIONS

CAPD treatment could be a positive regulator of number of circulating EPCs in subjects with ESRD, with the relationship independent of the status of arteriosclerosis.

Phosphate binders in chronic kidney disease and end-stage renal disease: a patient-centered approach

Disorders of calcium and phosphorus metabolism are associated with significant morbidity and mortality in patients with advanced chronic kidney disease. These patients typically require oral phosphate binders to maintain phosphorus homeostasis, but the choice of which among several agents to use has been actively investigated and debated. Recent debate has been polarized between those who favor calcium-based binders for their proven efficacy and relatively low cost and those who favor sevelamer for its putative beneficial effects on inflammatory biomarkers and vascular calcification. This review summarizes the current state of the art of prescribing phosphate binders, ranging from large-scale clinical trials to focused mechanistic studies, and proposes that the available evidence does not conclusively prove the relative superiority of any one binder.

Low circulating CD34+ cell count is associated with poor prognosis in chronic hemodialysis patients

Circulating CD34-positive (CD34(+)) cells, a population that includes endothelial progenitor cells, are believed to contribute to vascular homeostasis. Here we determine the prognostic value of CD34(+) cell measurements in 216 chronic hemodialysis patients. A total of 43 cardiovascular events and 13 deaths occurred over an average 23 months follow-up in this cohort. A cutoff number for circulating CD34(+) cells was determined by receiver operating characteristic curve analysis to maximize the power of the CD34(+) cell count in predicting future cardiovascular events. Based on this, 93 patients were categorized as having low and 123 patients as having high numbers of CD34(+) cells, determined by flow cytometry at the time of enrollment. Both cumulative cardiovascular event-free survival and all-cause survival were significantly less in the group of patients with low numbers of CD34(+) cells. By multivariate analyses, a low level of circulating CD34(+) cells was an independent and significant predictor for both cardiovascular events and all-cause mortality. Our study shows that a reduced number of circulating CD34(+) cells is significantly associated with vascular risks and all-cause mortality in patients on chronic hemodialysis. These cells may be a useful biomarker.

Associations between sympathetic activity, plasma concentrations of renin, aldosterone, and parathyroid hormone, and the degree of intractability of blood pressure control in modialysis patients

This study was designed to examine how such factors as hemodialysis parameters, body mass index, renin and aldosterone concentrations, sympathetic nervous activity, and parathyroid hormone concentrations are associated with the control of hypertension in hemodialysis patients. Hemodialysis patients (n=114) were grouped into four categories. Group 1 had normal BP without antihypertensive medication. Group 2 needed one antihypertensive drug, Group 3 needed combination of two or three categories of antihypertensive drugs without minoxidil. Group 4 needed more than three categories of antihypertensive drugs including minoxidil. Parathyroid hormone, beta2-microglobulin, renin and aldosterone, epinephrine, norepinephrine, and hemodialysis parameters were measured. The fractional clearance of urea as Kt/V urea was significantly lower in Group 3 and Group 4 than in Group 2 (p<0.01). Concentrations of parathyroid hormone were significantly higher in Group 4 than the other groups (p<0.01). Pre-hemodialysis norepinephrine concentrations were significantly higher in Group 4 than the other groups (p<0.05). Traditional factors associated with hypertension did not seem to be relevant to the degree of hypertension in hemodialysis patients in the present study. In conclusion, poor Kt/V urea, elevated parathyroid hormone concentrations, and elevated concentrations of plasma norepinephrine seemed to be the factors that might be associated with control of hypertension in hemodialysis patients.

Kidney transplantation substantially improves endothelial progenitor cell dysfunction in patients with end-stage renal disease

Endothelial progenitor cells (EPC) are involved in endothelial repair and maintenance. Dysfunction of EPC may contribute to accelerated arteriosclerosis in chronic kidney disease. Kidney transplantation (KTx) improves both survival and endothelial function of dialysis patients. In a prospective study, we tested to which extent KTx changes EPC biology. We studied number and function (migratory activity, adhesion to extracellular matrix proteins and to mature endothelial cells [EC]) of EPC in 20 patients during dialysis and 3, 6, 9 and 12 months after KTx. Twenty-two healthy volunteers served as matched controls. Circulating precursor populations were measured by flow cytometric analysis. Cytokines relevant for EPC mobilization were monitored. Compared to the dialysis state, KTx increased the migration of EPC to approximately 2-fold. Adhesion to fibronectin and to collagen type IV was significantly increased after KTx. An improved adhesion rate of EPC to mature EC was observed. The number of EPC decreased. The amount of precursor populations showed no difference compared to the pretransplant state. Our study shows an improved function of EPC after KTx. This finding indicates an improved potential for endothelial repair which in turn may contribute to enhanced endothelial function and reduced cardiovascular morbidity after KTx.

Endothelial Progenitor Cells in Chronic Renal Insufficiency

There is growing evidence for a role of endothelial progenitor cells (EPCs) in the repair of damaged endothelium. It remains unclear which cell populations are most useful for clinical trials. Administration of drugs increasing EPC numbers and/or improving functional properties seems attractive. Further basic research is necessary to understand the mechanisms of mobilization, differentiation and homing of EPC in general and in particular under uremic conditions. Nephrologists should search for strategies to ameliorate EPC dysfunction of uremia. In this way it might be possible to test whether improved EPC biology is associated with decreased cardiovascular mortality in uremic humans. In any such studies the difficulties are going to be related to the complex procedures for EPC isolation, the testing of their identity and differentiation and their propagation before use.

Endothelial Progenitor Cells in Kidney Transplant Recipients

BACKGROUND

Lower concentrations of endothelial progenitor cells (EPCs) may be associated with increased cardiovascular risk. EPC counts and their correlates have not yet been studied in kidney transplant recipients (KTR).

METHODS

We cross-sectionally studied EPC counts in 105 middle-aged KTR (mean estimated glomerular filtration rate 45.2 ml/min/1.73 m; range: 5.4 to 117.5). Using univariate and multivariate linear regression assuming a gamma distribution of the outcome, we examined the associations between counts of cultured EPCs and traditional cardiovascular disease risk factors (hypertension, diabetes, hyperlipidemia, smoking), kidney function, and immunosuppressive agents, amongst others.

RESULTS

The median count of cultured EPCs was 34 cells per high-power field (interquartile range: 19 to 64), comparable to healthy individuals. From multivariate analyses, we found independent inverse associations between counts of cultured EPCs and body mass index, mean arterial pressure, and history of cardiovascular disease. Statin use was associated with greater EPC counts, whereas patients receiving azathioprine or angiotensin II receptor treatment had lower EPC counts (all P<0.01).

CONCLUSIONS

This study suggests negative associations in KTR between EPC counts and body mass index, and blood pressure, whereas statin use was associated with greater EPC counts. These findings raise the hypothesis whether EPCs are responsible, at least in part, for the well established associations between these factors and cardiovascular outcomes in KTR.