Circulating endothelial progenitor cells are reduced in hemodialysis patients

Stem cells and progenitor cells in renal disease

Stem cells and progenitor cells are necessary for repair and regeneration of injured renal tissue. Infiltrating or resident stem cells can contribute to the replacement of lost or damaged tissue. However, the regulation of circulating progenitor cells is not well understood. We have analyzed the effects of erythropoietin on circulating progenitor cells and found that low levels of erythropoietin induce mobilization and differentiation of endothelial progenitor cells. In an animal model of 5/6 nephrectomy we could demonstrate that erythropoietin ameliorates tissue injury. Full regeneration of renal tissue demands the existence of stem cells and an adequate local "milieu," a so-called stem cell niche. We have previously described a stem cell niche in the kidneys of the dogfish, Squalus acanthus. Further analysis revealed that in the regenerating zone of the shark kidney, stem cells exist that can be induced by loss of renal tissue to form new glomeruli. Such animal models improve our understanding of stem cell behavior in the kidney and may eventually contribute to novel therapies.

Challenging the Validity of the EPO Index

BACKGROUND

With use of recombinant erythropoietin (EPO) and intravenous iron, the majority of hemodialysis patients can achieve target hemoglobin concentrations. EPO resistance arises as a consequence of inflammation and other processes that can adversely affect survival. We hypothesized that the EPO dose-hematocrit (EPO/Hct) ratio, also known as the EPO index, may be a surrogate for inflammation and that greater EPO/Hct ratios would be associated with decreased survival.

METHODS

We used proportional hazards regression models and time-varying logistic models to analyze the association between EPO index and survival in US hemodialysis patients initiating hemodialysis therapy between January 1, 1999, and December 31, 2000, and followed up for up to 3 years until December 31, 2001.

RESULTS

We found an unexpected and consistent association between greater EPO index and survival in all models. The associations of EPO/Hct ratio were most prominent at intermediate Hct values and with longer dialysis vintage. Iron administration was associated with a lower risk for death independent of Hct. Conversely, greater average prior EPO dose was associated with a greater risk for death.

CONCLUSION

EPO resistance may be reflected better by total cumulative EPO dose than the EPO/Hct ratio. The mechanism(s) responsible for the association between a greater EPO/Hct ratio and survival remains to be established, but may be a result of nonerythrogenic effects of EPO.

Imbalance between detached circulating endothelial cells and endothelial progenitor cells in chronic kidney disease

BACKGROUND

Patients with chronic kidney disease (CKD) display endothelial dysfunction and are at a high risk for atherosclerotic cardiovascular disease (CVD). Recent studies suggest that circulating detached endothelial cells (CECs) and stimulated endothelial progenitor cells (EPCs) from the bone marrow may reflect endothelial damage.

METHODS

We correlated the levels of CECs expressing the endothelial cell inflammation marker (MICA+ cells) and EPCs (Tie-2+ or VEGFR-2+ cells) in a population of 19 (55 +/- 3 years; 42% males) patients with advanced CKD (median glomerular filtration rate 8 ml/min). In addition, the levels of CD-31+ cells were investigated. Twenty healthy age- (49 +/- 2 years) and gender- (50% men) matched subjects served as controls.

RESULTS

CECs expressing MICA were increased (7.6 +/- 2.7 vs. 1.6 +/- 0.3%; p < 0.05) in CKD patients, however EPCs expressing Tie-2 or VEGFR-2 were significantly decreased (0.16 +/- 0.07 vs. 0.53 +/- 0.15%; p < 0.05, and 0.42 +/- 0.10 vs. 2.80 +/- 0.72%; p < 0.01, respectively) as compared to controls. Furthermore, we also found that the levels of CD-31+ cells were significantly elevated (22.8 +/- 4.2 vs. 9.4 +/- 0.8%; p < 0.01) in CKD patients. Patients on angiotensin-converting enzyme (ACE) inhibitors tended (p = 0.06) to have higher levels of VEGFR-2+ cells (0.57 +/- 0.14 vs. 0.16 +/- 0.11%).

CONCLUSION

Our results suggest that there is a marked imbalance between the CEC and EPC numbers in patients with CKD. Further research is needed to evaluate the independent role of inflammatory endothelial markers as well as the effects of ACE inhibitors on mobilization of EPCs in patients with advanced CKD.

Nocturnal hemodialysis is associated with restoration of impaired endothelial progenitor cell biology in end-stage renal disease

Cardiovascular disease is the principal cause of death in end-stage renal disease (ESRD) patients. Endothelial progenitor cells (EPCs) play a critical role in vascular repair, and improving EPC biology represents a novel therapeutic target. Three groups of age- and gender-matched patients were studied: 1) 10 healthy control, 2) 12 conventional hemodialysis (CHD) patients, and 3) 10 nocturnal hemodialysis (NHD) patients. EPC number and migratory function were assessed. Left ventricular mass index (LVMI) was derived, and correlations between EPC biology, uremic clearance, and LVMI were made. Compared with controls, EPC number and function were markedly impaired in CHD patients [(3.48 ± 1.2 vs. 0.86 ± 0.20%/50,000 cells, P < 0.05) and (18.8 ± 2.64 vs. 3.75 ± 0.34 cells/high-power field, P < 0.05), respectively]. In contrast, EPC number and function were normal in NHD patients [(3.48 ± 1.17 vs. 3.83 ± 0.77%/50,000 cells) and (18.8 ± 2.6 vs. 22.2 ± 2.4 cells/high-power field), respectively]. Among ESRD patients, EPC number and function inversely correlated with predialysis urea concentration ( r = −0.40; r = −0.57), LVMI ( r = −0.41; −0.46) and systolic BP ( r = −0.58; r = −0.44). We demonstrate that NHD is associated with restoration of abnormal EPC biology in ESRD. Given the increasing importance of EPCs in the repair and restoration of cardiovascular function, these data have important clinical implications for vascular risk in ESRD patients.

Circulating endothelial progenitor cells after kidney transplantation

Circulating endothelial progenitor cells (EPCs) promote vascular repair and maintain integrity of the endothelial monolayer. Reduced EPCs number has been associated with endothelial dysfunction in various cardiovascular diseases. Cardiovascular disease risk is higher in renal transplant patients (RT) than the general population. We studied EPCs number and proliferation in RT, and examined the association with other cardiovascular risk factors such as reduced glomerular filtration rate (GFR) and LDL cholesterol. EPCs concentration was determined in 94 RT and 39 control subjects (C) by flow cytometry. EPCs proliferation was also studied after 7 days in culture. EPCs concentration was significantly reduced in RT versus C (median 33.5 [5-177] vs. 53 [9-257] EPCs/10(5) PMN cells, p=0.006). EPCs proliferation was also reduced in RT versus C (mean+/-SD; 372.7+/-229.3 vs. 539.8+/-291.3 EPCs x field, p=0.003). In multiple regression analysis, GFR, HDL, LDL and body weight were independent predictors of EPCs concentration in RT (r2=0.25, p<0.001). EPCs number is reduced in RT, particularly in patients with reduced GFR. Moreover, EPCs from RT studied in vitro, showed reduced proliferation, which is a sign of functional impairment. These alterations may be involved in increased cardiovascular risk of RT.

Endothelial progenitor cells

Endothelial progenitor cells are a circulating, bone marrow-derived cell population that appears to participate in both vasculogenesis and vascular homeostasis. Questions persist regarding their functional characteristics, as well as the precise panel of cell surface markers that uniquely define this newly described progenitor cell population. We review experimental results obtained from both animal studies and recent clinical trials that suggest this cell type may have tremendous therapeutic potential for a wide range of human diseases.

In Vivo Cell Seeding With Anti-CD34 Antibodies Successfully Accelerates Endothelialization but Stimulates Intimal Hyperplasia in Porcine Arteriovenous Expanded Polytetrafluoroethylene Grafts

Background— The patency of AV expanded polytetrafluoroethylene (ePTFE) grafts for hemodialysis is impaired by intimal hyperplasia (IH) at the venous outflow tract. The absence of a functional endothelial monolayer on the prosthetic grafts is an important stimulus for IH. In the present study, we evaluated the feasibility of capturing endothelial progenitor cells in vivo using anti-CD34 antibodies on ePTFE grafts to inhibit IH in porcine AV ePTFE grafts.

Methods and Results— In 11 pigs, anti-CD34–coated ePTFE grafts were implanted between the carotid artery and internal jugular vein. Bare ePTFE grafts were implanted at the contralateral side. After 3 (n=2) or 28 (n=9) days, the pigs were terminated, and the AV grafts were excised for histological analysis and SEM. At 3 and 28 days after implantation, 95% and 85% of the coated graft surface was covered by endothelial cells. In contrast, no cell coverage was observed in the bare graft at 3 days, whereas at 28 days, bare grafts were partly covered with endothelial cells (32%; P =0.04). Twenty-eight days after implantation, IH at the venous anastomosis was strongly increased in anti-CD34–coated grafts (5.96±1.9 mm 2 ) compared with bare grafts (1.70±0.4 mm 2 ; P =0.03). This increase in IH coincided with enhanced cellular proliferation at the venous anastomosis.

Conclusions— Autoseeding with anti-CD34 antibodies results in rapid endothelialization within 72 hours. Despite persistent endothelial graft coverage, IH at the outflow tract is increased profoundly at 4 weeks after implantation. Further modifications are required to stimulate the protective effects of trapped endothelial cells.

Circulating endothelial cells are associated with future vascular events in hemodialysis patients

BACKGROUND

Endothelial dysfunction and injury are thought to have a key role in the pathogenesis of cardiovascular disease. We hypothesized that the presence of circulating endothelial cells, as a reflection of ongoing endothelial injury, might provide a novel means for predicting cardiovascular events in hemodialysis subjects who are known to be at marked increased risk for cardiovascular disease.

METHODS

Circulating endothelial cell number was determined in 29 hemodialysis patients who were then followed for vascular events for 470 +/- 172 days. In a second cohort of 44 hemodialysis patients, circulating endothelial cell number was correlated with markers of inflammation, namely high sensitivity C-reactive protein (hs-CRP), interleukin (IL)-6, IL-10, and monocyte chemoattractant protein-1 (MCP-1), and endothelial dysfunction, soluble vascular cellular adhesion molecule-1 (VCAM-1).

RESULTS

Seven of the 19 subjects with elevated circulating endothelial cells (defined as >19 cells per mL) had cardiovascular (N= 5) or vascular (N= 5) events during follow-up, whereas no events occurred in subjects with a low number of circulating endothelial cells (</=19 CECs per mL) (P= 0.04 by Fisher Exact Test). In the second cohort, the number of circulating endothelial cells was independent of all markers of inflammation and endothelial dysfunction.

CONCLUSION

In this hemodialysis population, an increase in circulating endothelial cells was found to predict the development of cardiovascular and vascular events, and to be independent of other known markers of inflammation or endothelial dysfunction. These studies suggest that circulating endothelial cells may be a novel way to assess endothelial health and cardiovascular risk. Further studies to investigate the utility of circulating endothelial cells in predicting cardiovascular risk are needed.

Kidney Graft Function Determines Endothelial Progenitor Cell Number in Renal Transplant Recipients

BACKGROUND

Circulating bone marrow-derived endothelial progenitor cells (EPCs) promote vascular repair, and their number correlates with endothelial function and cardiovascular risk in humans. In uremic patients, the number of functionally active EPCs is reduced. Thus, we assessed EPCs in stable patients 6 months or more after renal transplantation.

METHODS

We analyzed circulating CD34+ hematopoietic progenitor cells (HPCs) using flow cytometry and EPCs (in vitro assay) in 74 renal transplant patients (51.6+/-11.5 years; 46 males), 74 age-matched healthy subjects, and 29 patients with preterminal renal failure.

RESULTS

EPC numbers were similar in renal transplant recipients and controls (232+/-92 vs. 250+/-103/high power field; n.s.), but were significantly higher than in uremic patients (160+/-97/high power field; P=0.004). In addition, transplant recipients had more HPCs than controls (2.71+/-1.65 vs. 1.99+/-1.12 /microl; P=0.004) and uremic patients (1.64+/-0.96/microl; P=0.001). EPCs in renal transplant recipients correlated significantly with graft function(that is, Cockcroft-Gault clearance [r=0.294; P=0.012]), but not with age or HPCs. Moreover, in the multiple regression analysis, graft function (r=0.332; P=0.01) and diastolic blood pressure (r=-0.278; P=0.03) were independent predictors of EPCs. In vitro, sera from renal transplant recipients with poor graft function significantly inhibited EPC differentiation compared with sera from patients with a clearance above 50 mL/min (151+/-54 vs. 274+/-94 EPCs/high power field; P=0.02).

CONCLUSIONS

EPC numbers in stable renal transplant recipients are comparable to those found in healthy subjects. In addition, graft function is a significant determinant of EPCs. Prospective studies should explore whether improvement of EPCs influences cardiovascular risk in renal transplant recipients.

Possible new role of monocyte chemoattractant protein-1 in hemodialysis patients with cardiovascular disease

AIMS

Reactive oxygen species have been implicated in increased vascular endothelial growth factor (VEGF) and monocyte chemoattractant protein (MCP-1) levels in vascular cells, which may promote atherosclerosis progression.

METHODS

We studied the association between pre-dialysis plasma levels of VEGF and MCP-1 in 45 hemodialysis (HD) patients with and without cardiovascular disease (CVD) in conditions of increased oxidative stress (SOX).

RESULTS

Compared to the controls, HD patients, especially those with CVD, showed a significant increase in plasma concentrations of Cu/Zn superoxide dismutase (Cu/Zn SOD), C-reactive protein (CRP), MCP-1 and VEGF. The levels of CRP, MCP-1 and VEGF were more increased in patients with CVD than in patients without CVD (all p < 0.01). VEGF strongly and positively correlated with MCP-1 only in HD patients with CVD. Additionally, both VEGF and MCP-1 were associated with Cu/Zn SOD in the whole HD group.

CONCLUSION

For the first time our data indicate a correlation between VEGF and MCP-1 levels in HD patients with CVD in conditions of increased SOX. This interaction may reflect the new role of MCP-1 as an arteriogenic factor in HD patients with CVD.