Molecular and biochemical characterization of nitric oxide synthase isoforms and their intracellular distribution in human peripheral blood mononuclear cells

Characterizing the Linkage of Systemic Hypoxia and Angiogenesis in High-Grade Glioma to Define the Changes in Tumor Microenvironment for Predicting Prognosis

High-grade gliomas (HGG) comprising WHO grades 3 and 4 have a poor overall survival (OS) that has not improved in the past decade. Herein, markers representing four components of the tumor microenvironment (TME) were identified to define their linked expression in TME and predict the prognosis in HGG, namely, interleukin6 (IL6, inflammation), inducible nitric oxide synthase(iNOS), heat shock protein-70 (HSP70, hypoxia), vascular endothelial growth receptor (VEGF), and endothelin1 (ET1) (angiogenesis) and matrix metalloprotease-14 (MMP14) and intercellular adhesion molecule1 (ICAM1, extracellular matrix). To establish a non-invasive panel of biomarkers for precise prognostication in HGG. Eighty-six therapy-naive HGG patients with 45 controls were analyzed for the defined panel. Systemic expression of extracellular/secretory biomarkers was screened dot-immune assay (DIA), quantified by ELISA, and validated by immunocytochemistry (ICC). Expression of iNOS, HSP70, IL-6, VEGF, ET1, MMP14, and ICAM1 was found to be positively associated with grade. Quantification of circulating levels of the markers by ELISA and ICC presented a similar result. The biomarkers were observed to negatively correlate with OS (p < 0.0001). Cox-regression analysis yielded all biomarkers as good prognostic indicators and independent of confounders. On applying combination statistics, the biomarker panel achieved higher sensitivity than single markers to define survival. The intra-association of all seven biomarkers was significant, hinting of a cross-talk between the TME components and a hypoxia driven systemic inflammation upregulating the expression of other components. This is a first ever experimental study of a marker panel that can distinguish between histopathological grades and also delineate differential survival using liquid biopsy, suggesting that markers of hypoxia can be a cornerstone for personalized therapy. The panel of biomarkers of iNOS, HSP70, IL-6, VEGF, ET1, MMP14, and ICAM1 holds promise for prognostication in HGG.

Selective Inhibitors of the Inducible Nitric Oxide Synthase as Modulators of Cell Responses in LPS-Stimulated Human Monocytes

Inducible nitric oxide synthase (iNOS) is a crucial enzyme involved in monocyte cell response towards inflammation, and it is responsible for the production of sustained amounts of nitric oxide. This free radical molecule is involved in the defense against pathogens; nevertheless, its continuous and dysregulated production contributes to the development of several pathological conditions, including inflammatory and autoimmune diseases. In the present study, we investigated the effects of two new iNOS inhibitors, i.e., 4-(ethanimidoylamino)-N-(4-fluorophenyl)benzamide hydrobromide (FAB1020) and N-{3-[(ethanimidoylamino)methyl]benzyl}-l-prolinamidedihydrochloride (CM554), on human LPS-stimulated monocytes, using the 1400 W compound as a comparison. Our results show that CM544 and FAB1020 are selective and decrease cytotoxicity, IL-6 secretion and LPS-stimulated monocyte migration. Furthermore, the modulation of iNOS, nitrotyrosine and Nrf2 were analyzed at the protein level. Based on the collected preliminary results, the promising therapeutic value of the investigated compounds emerges, as they appear able to modulate the pro-inflammatory LPS-stimulated response in the low micromolar range in human monocytes.

Hyperbaric Oxygen Therapy and Vascular Complications in Diabetes Mellitus

Vascular complications in patients with diabetes mellitus (DM) are common. Since impaired oxygen balance in plasma plays an important role in the pathogenesis of chronic DM-associated complications, the administration of hyperbaric oxygen therapy (HBOT) has been recommended to influence development of vascular complications. Hyperbaric oxygen therapy involves inhalation of 100% oxygen under elevated pressure from 1.6 to 2.8 absolute atmospheres in hyperbaric chambers. Hyperbaric oxygen therapy increases plasma oxygen solubility, contributing to better oxygen diffusion to distant tissues and preservation of the viability of tissues reversibly damaged by atherosclerosis-induced ischemia, along with microcirculation restoration. Hyperbaric oxygen therapy exerts antiatherogenic, antioxidant, and cardioprotective effects by altering the level and composition of plasma fatty acids and also by promoting signal transduction through membranes, which are impaired by hyperglycemia and hypoxia. In addition, HBOT affects molecules involved in the regulation of nitric oxide synthesis and in that way exerts anti-inflammatory and angiogenic effects in patients with DM. In this review, we explore the recent literature related to the effects of HBOT on DM-related vascular complications.

Hematopoietic Cell-Expressed Endothelial Nitric Oxide Protects the Liver From Insulin Resistance

OBJECTIVE

Mice genetically deficient in endothelial nitric oxide synthase (Nos3^-/-) have fasting hyperinsulinemia and hepatic insulin resistance, indicating the importance of Nos3 (nitric oxide synthase) in maintaining metabolic homeostasis. Although the current paradigm holds that these metabolic effects are derived specifically from the expression of Nos3 in the endothelium, it has been established that bone marrow-derived cells also express Nos3. The aim of this study was to investigate whether bone marrow-derived cell Nos3 is important in maintaining metabolic homeostasis. Approach and Results: To test the hypothesis that bone marrow-derived cell Nos3 contributes to metabolic homeostasis, we generated chimeric male mice deficient or competent for Nos3 expression in circulating blood cells. These mice were placed on a low-fat diet for 5 weeks, a time period which is known to induce hepatic insulin resistance in global Nos3-deficient mice but not in wild-type C57Bl/6 mice. Surprisingly, we found that the absence of Nos3 in the bone marrow-derived component is associated with hepatic insulin resistance and that restoration of Nos3 in the bone marrow-derived component in global Nos3-deficient mice is sufficient to restore hepatic insulin sensitivity. Furthermore, we found that overexpression of Nos3 in bone marrow-derived component in wild-type mice attenuates the development of hepatic insulin resistance during high-fat feeding. Finally, compared with wild-type macrophages, the loss of macrophage Nos3 is associated with increased inflammatory responses to lipopolysaccharides and reduced anti-inflammatory responses to IL-4, a macrophage phenotype associated with the development of hepatic and systemic insulin resistance.

CONCLUSIONS

These results would suggest that the metabolic and hepatic consequences of high-fat feeding are mediated by loss of Nos3/nitric oxide actions in bone marrow-derived cells, not in endothelial cells.

Local anaesthetics upregulate nitric oxide generation in cord blood and adult human neutrophils

Nitric oxide (NO) generation by systemic neonatal neutrophils is not clarified. It is also not known whether local anaesthetics (LAs) transferred to the fetal systemic circulation following maternal epidural blockade may affect this process. In the present study, NO generation was evaluated in neutrophils from cord blood (CB, n = 11) and adult blood (n = 10) following exposure to bupivacaine (0.0005, 0.005, 1 mM), lidocaine (0.002, 0.02, 4 mM) and ropivacaine (0.0007, 0.007, 1.4 mM) using flow cytometry, as well as indirectly by determining nitrite concentrations in cell incubation media. To determine the role of NO synthase (NOS) isoforms in NO generation following exposure to LAs, experiments were repeated in the presence of the NOS inhibitors, N^G-nitro-L-arginine methyl ester and aminoguanidine; in addition, the expression of NOS isoforms was analysed. CB neutrophils produced less NO than adult neutrophils. LAs, especially ropivacaine and lidocaine, stimulated neutrophil NO generation, but in CB neutrophils this effect was negligible at clinically relevant drug concentrations. A mechanism involving NOS activity was responsible for the observed phenomena. In conclusion, LAs are able to upregulate neutrophil NO production, but in neonates this effect is likely to be clinically insignificant.

The dual effect of C-peptide on cellular activation and atherosclerosis: Protective or not?

C-peptide is a cleavage product of proinsulin that acts on different type of cells, such as blood and endothelial cells. C-peptide biological effects may be different in type 1 and type 2 diabetes. Besides, there are further evidence for a functional interaction between C-peptide and insulin. In this way, C-peptide has ambiguous effects, acting as an antithrombotic or thrombotic molecule, depending on the physiological environment and disease conditions. Moreover, C-peptide regulates interaction of leucocytes, erythrocytes, and platelets with the endothelium. The beneficial effects include stimulation of nitric oxide production with its subsequent release by platelets and endothelium, the interaction with erythrocytes leading to the generation of adenosine triphosphate, and inhibition of atherogenic cytokine release. The undesirable action of C-peptide includes the chemotaxis of monocytes, lymphocytes, and smooth muscle cells. Also, C-peptide was related with increased lipid deposits and elevated smooth muscle cells proliferation in the vessel wall, contributing to atherosclerosis. Purpose of this review is to explore these dual roles of C-peptide on the blood, contributing at one side to haemostasis and the other to atherosclerotic process.

Differential Expression of Human Peripheral Mononuclear Cells Phenotype Markers in Type 2 Diabetic Patients and Type 2 Diabetic Patients on Metformin

Background: Although peripheral blood mononuclear cells (PBMC) have been demonstrated to be in a pro-inflammatory state in obesity and type 2 Diabetes Mellitus (T2DM), characterization of circulating PBMC phenotypes in the obese and T2DM and the effect of Metformin on these phenotypes in humans is still ill-defined and remains to be determined. Methods: Thirty normal healthy adult volunteers of normal weight, 30 obese subjects, 20 obese newly diagnosed diabetics and 30 obese diabetics on Metformin were recruited for the study. Fasting blood samples were collected and PBMC were isolated from whole blood. Polarization markers (CD86, IL-6, TNFα, iNOS, CD36, CD11c, CD169, CD206, CD163, CD68, CD11b, CD16, and CD14) were measured by RT-qPCR. Gene expression fold changes were calculated using the 2^-ΔΔCT method for RT-qPCR. Results: Obesity and T2DM are associated an increased CD68 marker in PBMC. mRNA expression of CD11b, CD11c, CD169, and CD163 were significantly reduced in PBMC from T2DM subjects whereas CD11c was significantly inhibited in PBMC from obese subjects. On the other hand, macrophage M1-like phenotype was observed in T2DM circulation as demonstrated by increased mRNA expression of CD16, IL-6, iNOS, TNFα, and CD36. There were no significant changes in CD14 and CD86 in the obese and T2DM when compared to the lean subjects. Metformin treatment in T2DM reverted CD11c, CD169, IL-6, iNOS, TNFα, and CD36 to levels comparable to lean subjects. CD206 mRNA expression was significantly upregulated in PBMC of T2DM while Metformin treatment inhibited CD206 expression levels. Conclusions: These data support the notion that PBMC in circulation in T2DM express different pattern of phenotypic markers than the patterns typically present in M1 and M2 like cells. These phenotypic markers could be representative of metabolically activated macrophages (MMe)-like cells. Metformin, on the other hand, reduces MMe-like cells in circulation.

Inter- and intra-subject variability of nitric oxide levels in leukocyte subpopulations

Assessment of nitric oxide (NO) dynamics in immune cells, commonly measured using NO surrogates such as inducible nitric oxide synthase (iNOS) rather than NO itself, has been effective in understanding pathophysiology across a wide range of diseases. Although the intracellular measurement of NO is now feasible, many technical issues remain unresolved. The principle aim of our study was to determine the effect of storage time of whole blood on nitric oxide (NO) level expression in leukocytes. This is important because immune cells remain chemically dynamic even after they are removed from the circulation, and the impact of storage time must be known to optimally quantify the effect of a disease or condition on NO dynamics in circulating leukocytes. We measured NO levels using the fluorescent probe, diaminofluorescein (DAF-2DA), and flow cytometry in monocytes, neutrophils, and natural killer cells from healthy subjects immediately after blood draw (Time 0) and 30, 60, and 120 min following the blood draw. There was no significant difference among the 4 study time points in NO (DAF-2) levels, though there was wide intra-subject variability at all time points. Using LPS stimulation, we compared iNOS (the more traditional surrogate marker of NO dynamics) with NO (by DAF-2) in natural killer cells and monocytes and, we found no difference in the response patterns. In summary, we did find that within a 2-hour interval from blood draw to sample processing, there was a remarkably wide intra-subject variability in expression of intracellular NO (DAF-2) in leukocytes of healthy individuals at baseline and over time. The mechanism(s) for these differences are not known but could clearly confound efforts to detect changes in NO metabolism in white blood cells. We speculate that rapid pulsatility of NO could explain the wide variability seen.

Cross-talking between lymphocytes and platelets and its regulation by nitric oxide and peroxynitrite in physiological condition and endotoxemia

AIMS

Cross-talk between platelets and lymphocytes may play a role in different pathological conditions like sepsis. This study aimed to investigate the effect of lymphocytes on platelet aggregation in lipopolysaccharide (LPS)-stimulated and non-stimulated cells.

MAIN METHODS

Lymphocytes and platelet-rich plasma (PRP) were obtained from rat arterial blood. Platelets (1.2×10⁸platelets/ml) were incubated with lymphocytes (0.8×10⁶cells/ml) in the presence or not of LPS (100μg/ml), after which ADP (5μM)-induced platelet aggregation was carried out.

KEY FINDINGS

Lymphocytes inhibited by 51% the platelet aggregation, which was significantly prevented by the non-selective NO inhibitor l-NAME (300μM) or the selective iNOS inhibitor 1400W (100μM), as well as by the soluble guanylyl cyclase (sGC) inhibitor ODQ (10μM). The platelet inhibition by lymphocytes was accompanied by 2-fold increase of intraplatelet cGMP levels. Next, lymphocytes and platelets were co-incubated with LPS for 6h. In LPS-treated cells, lymphocytes produced a larger inhibition of platelet aggregation (62%), despite the same elevation of cGMP levels (2.2-fold increase). This inhibitory effect was prevented by l-NAME and 1400W, but rather unaffected by ODQ. The peroxynitrite (ONOO^-) scavenger -(-)epigallocatechin gallate (ECG, 100μM) abolished the inhibition by lymphocytes on platelet aggregation in LPS-treated cells, but not in non-treated cells.

SIGNIFICANCE

Our results show that lymphocytes act to inhibit platelet aggregation via iNOS-derived NO release and cGMP generation. In presence of LPS, ONOO^- production accounts for the platelet inhibition.

Oxidative stress signaling to chromatin in health and disease

Oxidative stress has a significant impact on the development and progression of common human pathologies, including cancer, diabetes, hypertension and neurodegenerative diseases. Increasing evidence suggests that oxidative stress globally influences chromatin structure, DNA methylation, enzymatic and non-enzymatic post-translational modifications of histones and DNA-binding proteins. The effects of oxidative stress on these chromatin alterations mediate a number of cellular changes, including modulation of gene expression, cell death, cell survival and mutagenesis, which are disease-driving mechanisms in human pathologies. Targeting oxidative stress-dependent pathways is thus a promising strategy for the prevention and treatment of these diseases. We summarize recent research developments connecting oxidative stress and chromatin regulation.

Impact of glycated LDL on endothelial nitric oxide synthase in vascular endothelial cells: involvement of transmembrane signaling and endoplasmic reticulum stress

Cardiovascular diseases are the major cause of mortality in diabetes patients. Increased levels of glycated low density lipoprotein (glyLDL) are detected in diabetic patients. Endothelial nitric oxide synthase (eNOS) generates nitric oxide, which is responsible to endothelium-dependent vasodilation. The impact of glyLDL on the expression and activity of eNOS in vascular endothelial cells (EC) remains unknown. The present study investigated the effect of glyLDL on the levels of protein, mRNA and activity of eNOS in cultured human umbilical vein EC. The results demonstrated that incubation of EC with physiological concentrations of glyLDL significantly reduced the abundances of eNOS protein in EC with the maximal inhibition at 100μg/ml for 24h. At the optimized condition, glyLDL decreased eNOS mRNA and reduced its activity in EC. Blocking antibody against the receptor for advanced glycation end products (RAGE) prevented glyLDL-induced downregulation of eNOS in EC. GlyLDL increased the translocation of H-Ras from cytoplasm to membrane in EC. Farnesyl-transferase inhibitor-276, an H-Ras antagonist, normalized glyLDL-induced downregulation of eNOS and prevented glyLDL-induced upregulation of H-Ras in EC membrane. Treatment with 4-phenylbutyric acid, an endoplasmic reticulum (ER) stress antagonist, prevented glyLDL-induced eNOS downregulation in EC. The results suggest that diabetes-associated metabolic stress inhibits the production and activity of eNOA in cultured human vascular EC through the activation of RAGE/H-Ras mediated upstream signaling pathway. ER stress induced by glyLDL is possibly involved in eNOS downregulation.

Construction of a Biocompatible Decellularized Porcine Hepatic Lobe for Liver Bioengineering

Objective

One of the major obstacles in applying decellularized organs for clinical use is the recellularization step, during which huge numbers of cells are required to develop whole livers. We established a simple protocol for constructing a bioartificial hepatic lobe and investigated its biocompatibility.

Methods

The right lateral lobe of porcine liver was decellularized using 0.1% sodium dodecyl sulfate through the right branch of the portal vein. Decellularized lobes were evaluated by histological and biochemical analyses. DNA content was quantified to validate the decellularization protocol. The presence of immunogenic and pathogenic antigens was checked to exclude potential rejection and thrombosis after xenotransplantation. Xeno-reactivity of decellularized tissue against human peripheral blood mononuclear cells was examined. Cytotoxicity was evaluated against hepatocarcinoma cells. Finally, scaffolds were incubated in collagenase for biodegradation testing.

Results

The decellularized lobe preserved the three-dimensional architecture, ultrastructure, extracellular matrix components, and vasculature. Scaffolds were almost depleted of DNA in addition to antigenic and pathogenic antigens, which are considered barriers to xenotransplantation. The human immune response against scaffolds was considered non-significant. Our matrices were biocompatible and biodegradable.

Conclusions

We successfully developed a non-cytotoxic, non-immunogenic, and biodegradable porcine hepatic lobe for future liver regeneration and bioengineering.

Nitric oxide production by monocytes in children with OSA and endothelial dysfunction

Endothelial dysfunction in the context of paediatric sleep apnoea is associated with distinctive alterations in circulating monocyte subsets and reduced NO production by monocytes.

Plant mitochondria: source and target for nitric oxide

Plant mitochondria generate nitric oxide (NO) under anoxia through the action of cytochrome c oxidase and other electron transport chain components on nitrite. This reductive mechanism operates under aerobic conditions at high electron transport rates. Indirect evidence also indicates that the oxidative pathway of NO production may be associated with mitochondria. We review the consequences of mitochondrial NO production, including the inhibition of oxygen uptake by cytochrome c oxidase, the inhibition of aconitase and succinate dehydrogenase, the induction of alternative oxidase, and the nitrosylation of several proteins, including glycine decarboxylase. The importance of these events in adaptation to abiotic and biotic stresses is discussed.

[Arginase and NO-synthase pathways of L-arginine metabolism in peripheral blood lymphocytes of patients with ovarian cancer]

The peculiarities ofarginase and NO-synthase pathways of L-arginine metabolism in peripheral blood lymphocytes of patients with ovarian cancer were studied. It was shown that the development of cancer pathology is associated with an imbalance in the NO synthesis in blood lymphocytes. The reason for such imbalance is the activation of arginase and inducible isoform of NO-synthase (iNOS) and significant inhibition of its constitutive isoform. The analysis of the kinetic properties of NOS of blood lymphocytes of patients with ovarian cancer was carried out. It was shown that the affinity constant of iNOS affinity for L-arginine is 5.4-fold lower than for eNOS of blood lymphocytes of persons in the control group. The inhibition of eNOS occurs via non-competitive type and is related to the reduction of maximum reaction rate.

Interaction of inducible nitric oxide synthase with rac2 regulates reactive oxygen and nitrogen species generation in the human neutrophil phagosomes: implication in microbial killing

AIMS

Present study explores importance of inducible nitric oxide synthase (iNOS) and its interaction with Rac2 in reactive oxygen species (ROS)/reactive nitrogen species (RNS) generation, protein-nitration and in microbial killing by neutrophils.

RESULTS

The iNOS transcript and protein were constitutively present in human as well as in mice neutrophils. iNOS protein was found in cytosol, granules containing elastase and gelatinase, and in other subcellular organelles in resting human neutrophils. After phagocytosis of bovine serum albumin (BSA) coated beads, both human and mice neutrophils showed significant elevation in superoxide radicals, nitric oxide (NO), ROS/RNS and consequent BSA nitration. These responses were significantly reduced in presence of iNOS, NADPH oxidase (NOX), myeloperoxidase or Rac inhibitors, as well as in iNOS, Nox2 and Rac2 silenced human or iNOS-knockout mice neutrophils. Complex formed on interaction of iNOS with Rac2 coprecipitated with anti-Rac2, predominantly in cytosol in resting human neutrophils, while iNOS-Rac2 complex translocated to phagosomes after phagocytosis. This was accompanied by generation of superoxide radicals, NO, ROS/RNS and consequent BSA-nitration. Importance of Rac2 in iNOS mediated NO formation and microbial killing was confirmed by pretreatment of mice with Rac inhibitor, NSC23766 that significantly abrogated NO release and microbial killing in vivo.

INNOVATION

Present study highlights previously undefined role of Rac2-iNOS interaction, in translocation of iNOS to phagosomal compartment and consequent NO, superoxide radicals, ROS/RNS generation, BSA nitration and microbial killing.

CONCLUSIONS

Altogether results obtained demonstrate the role of iNOS in NO and ROS/RNS generation, after phagocytosis of coated latex beads by human polymorphonuclear neutrophils. These studies imply functional importance of iNOS and its interaction with Rac2 in pathogen killing by the neutrophils.

Endothelial nitric oxide synthase in red blood cells: key to a new erythrocrine function?

Red blood cells (RBC) have been considered almost exclusively as a transporter of metabolic gases and nutrients for the tissues. It is an accepted dogma that RBCs take up and inactivate endothelium-derived NO via rapid reaction with oxyhemoglobin to form methemoglobin and nitrate, thereby limiting NO available for vasodilatation. Yet it has also been shown that RBCs not only act as "NO sinks", but exert an erythrocrine function - i.e an endocrine function of RBC - by synthesizing, transporting and releasing NO metabolic products and ATP, thereby potentially controlling systemic NO bioavailability and vascular tone. Recent work from our and others laboratory demonstrated that human RBCs carry an active type 3, endothelial NO synthase (eNOS), constitutively producing NO under normoxic conditions, the activity of which is compromised in patients with coronary artery disease. In this review we aim to discuss the potential role of red cell eNOS in RBC signaling and function, and to critically revise evidence to this date showing a role of non-endothelial circulating eNOS in cardiovascular pathophysiology.

Circulating blood endothelial nitric oxide synthase contributes to the regulation of systemic blood pressure and nitrite homeostasis

OBJECTIVE

Mice genetically deficient in endothelial nitric oxide synthase (eNOS(-/-)) are hypertensive with lower circulating nitrite levels, indicating the importance of constitutively produced nitric oxide (NO•) to blood pressure regulation and vascular homeostasis. Although the current paradigm holds that this bioactivity derives specifically from the expression of eNOS in endothelium, circulating blood cells also express eNOS protein. A functional red cell eNOS that modulates vascular NO• signaling has been proposed.

APPROACH AND RESULTS

To test the hypothesis that blood cells contribute to mammalian blood pressure regulation via eNOS-dependent NO• generation, we cross-transplanted wild-type and eNOS(-/-) mice, producing chimeras competent or deficient for eNOS expression in circulating blood cells. Surprisingly, we observed a significant contribution of both endothelial and circulating blood cell eNOS to blood pressure and systemic nitrite levels, the latter being a major component of the circulating NO• reservoir. These effects were abolished by the NOS inhibitor L-NG-nitroarginine methyl ester and repristinated by the NOS substrate L-arginine and were independent of platelet or leukocyte depletion. Mouse erythrocytes were also found to carry an eNOS protein and convert (14)C-arginine into (14)C-citrulline in NOS-dependent fashion.

CONCLUSIONS

These are the first studies to definitively establish a role for a blood-borne eNOS, using cross-transplant chimera models, that contributes to the regulation of blood pressure and nitrite homeostasis. This work provides evidence suggesting that erythrocyte eNOS may mediate this effect.

The constituents and mechanisms of generation of 'endothelial cell--colony forming units'

AIMS

The formation of endothelial cell-colony forming units (EC-CFUs) is increased by vascular injury, although their function in vivo is unclear. We, therefore, examined the constituents of EC-CFUs and the mechanisms of their generation.

METHODS AND RESULTS

We performed immunohistochemical characterization of EC-CFUs and their mononuclear precursors. Using fluorescent-activated cell sorting, we evaluated the capacity of mononuclear subpopulations to generate EC-CFUs, and monitored their migratory behaviour when co-incubated with EC-CFUs. Time-lapse microscopy was used to observe colony maturation. Cellular proliferation within EC-CFUs was assessed using bromodeoxyuridine (BrdU) and anti-proliferative agents. EC-CFUs exhibited typical endothelial characteristics; however, several endothelial markers were weakly expressed or absent. Macrophage and lymphocyte antigens were intensely expressed. EC-CFUs readily incorporated BrdU, and failed to develop in the presence of anti-proliferative agents (P < 0.01; n = 12). Time-lapse microscopy demonstrated that the characteristic EC-CFU 'spindle cells' are not EC-CFU progeny, but are mononuclear cells migrating towards, and incorporating into colonies. Only CD14(+) monocytes were necessary for EC-CFU formation. CD14 expression was progressively down-regulated during colony maturation (P < 0.001; n = 6). Although unable to generate EC-CFUs directly, CD34(+) cells could differentiate into CD14(+) cells and potentiate EC-CFU formation.

CONCLUSIONS

EC-CFUs exhibit endothelial characteristics, but are predominantly CD14(+) derived macrophages and are a potent stimulus for lymphocyte migration. Proliferation is necessary for EC-CFU generation; however, colony growth also occurs as a result of leucocyte migration. Although confirmatory in vivo studies are required, EC-CFU formation likely reflects leucocyte activation as a reparatory response to vascular denudation or tissue ischaemia.