Rationale and design of the Hunting for the off-target propertIes of Ticagrelor on Endothelial function and other Circulating biomarkers in Humans (HI-TECH) trial.

BACKGROUND: Among the 3 approved oral P2Y12 inhibitors for the treatment for patients with acute coronary syndrome (ACS), ticagrelor, but not prasugrel or clopidogrel, has been associated with off-target properties, such as improved endothelial-dependent vasomotion and increased adenosine plasma levels. METHODS: The HI-TECH study (NCT02587260) is a multinational, randomized, open-label, crossover study with a Latin squares design, conducted at 5 European sites, in which patients free from recurrent ischemic or bleeding events ≥30 days after a qualifying ACS were allocated to sequentially receive a 30 ± 5-day treatment with prasugrel, clopidogrel, and ticagrelor in random order. The primary objective was to evaluate whether ticagrelor, at treatment steady state (ie, after 30 ± 5 days of drug administration), as compared with both clopidogrel and prasugrel, is associated with an improved endothelial function, assessed with peripheral arterial tonometry. Thirty-six patients undergoing evaluable endothelial function assessment for each of the assigned P2Y12 inhibitor were needed to provide 90% power to detect a 10% relative change of the reactive hyperemia index in the ticagrelor group. CONCLUSION: The HI-TECH study is the first randomized, crossover study aiming to ascertain whether ticagrelor, when administered at approved regimen in post-ACS patients, improves endothelial function as compared with both clopidogrel and prasugrel.

Serum From Advanced Heart Failure Patients Promotes Angiogenic Sprouting and Affects the Notch Pathway in Human Endothelial Cells.

It is unknown whether components present in heart failure (HF) patients' serum provide an angiogenic stimulus. We sought to determine whether serum from HF patients affects angiogenesis and its major modulator, the Notch pathway, in human umbilical vein endothelial cells (HUVECs). In cells treated with serum from healthy subjects or from patients at different HF stage we determined: (1) Sprouting angiogenesis, by measuring cells network (closed tubes) in collagen gel. (2) Protein levels of Notch receptors 1, 2, 4, and ligands Jagged1, Delta-like4. We found a higher number of closed tubes in HUVECs treated with advanced HF patients serum in comparison with cells treated with serum from mild HF patients or controls. Furthermore, as indicated by the reduction of the active form of Notch4 (N4IC) and of Jagged1, advanced HF patients serum inhibited Notch signalling in HUVECs in comparison with mild HF patients' serum and controls. The circulating levels of NT-proBNP (N-terminal of the pro-hormone brain natriuretic peptide), a marker for the detection and evalutation of HF, were positively correlated with the number of closed tubes (r = 0.485) and negatively with Notch4IC and Jagged1 levels in sera-treated cells (r = -0.526 and r = -0.604, respectively). In conclusion, we found that sera from advanced HF patients promote sprouting angiogenesis and dysregulate Notch signaling in HUVECs. Our study provides in vitro evidence of an angiogenic stimulus arising during HF progression and suggests a role for the Notch pathway in it. J. Cell. Physiol. 231: 2700-2710, 2016. © 2016 Wiley Periodicals, Inc.

Circulating stem cell vary with NYHA stage in heart failure patients.

We have investigated the blood levels of sub-classes of stem cells (SCs) [mesenchymal stem cells (MSCs), haematopoietic stem cells (HSCs), endothelial progenitor cells/circulating endothelial cells (EPCs/CECs) and tissue-committed stem cells (TCSCs)] in heart failure (HF) patients at different stage of pathology and correlated it with plasmatic levels of proangiogenic cytokines. Peripheral blood level of SCs were analysed in 97 HF patients (24 in NYHA class I, 41 in class II, 17 in class III and 15 in class IV) and in 23 healthy controls. Plasmatic levels of PDGF-BB, bFGF, HGF, vascular endothelial growth factor (VEGF), SDF-1α, TNF-α and NTproBNP were also measured. Compared with healthy individuals, MSC, and in particular the sub-classes CD45(-) CD34(-) CD90(+) , CD45(-) CD34(-) CD105(+) and CD45(-) CD34(-) CXCR4(+) were significantly enhanced in NYHA class IV patients (16.8-, 6.4- and 2.7-fold, respectively). Level of CD45(-) CD34(-) CD90(+) CXCR4(+) cells progressively increased from class II to class IV (fold increases compared with controls: 8.5, 12 and 21.5, respectively). A significant involvement of CXCR4(+) subpopulation of HSC (CD45(+) CD34(+) CD90(+) CXCR4(+) , 1.4 versus 13.3 cells/µl in controls and NYHA class III patients, respectively) and TCSC (CD45(-) CD34(+) CXCR4(+) , 1.5 cells/ µl in controls versus 12.4 and 28.6 cells/µl in NYHA classes II and IV, respectively) were also observed. All tested cytokines were enhanced in HF patients. In particular, for PDGF-BB and SDF-1α we studied specific ligand/receptors pairs. Interestingly, the first one positively correlated with TCSCs expressing PDGFR (r = 0.52, P = 0.001), whereas the second one correlated with TCSCs (r = 0.34, P = 0.005) and with MSCs CD90(+) expressing CXCR4 (r = 0.39, P = 0.001). HF is characterized by the increase in the circulating levels of different MSC, HSC, EPC and TCSC subsets. Both the entity and kinetic of this process varied in distinct cell subsets. Specifically, differently from HSCs and EPCs/CECs, MSCs and TCSCs significantly increased with the progression of the disease, suggesting a possible distinct role of these cells in the pathophysiology of HF.

Different clinical models of CD34 + cells mobilization in patients with cardiovascular disease.

To test the role of necrosis, ischemia or both in bone marrow cells (BMC) mobilization in patients with cardiovascular disease. We studied three groups of patients: group 1, Iatrogenic Necrosis, with pure necrosis (28 patients undergoing transcatheter radiofrequency ablation); group 2, Ischemic Necrosis (30 patients with myocardial infarction); group 3, Pure Ischemia (24 patients with unstable angina). As control groups, we studied 27 patients with stable coronary artery disease (CAD), and 20 patients without CAD undergoing angiography for valvular diseases or cardiomiopathy. CD34 + cells and cytokines were evaluated at: T(0) (baseline), 48 h and 5, 7, 10, 14 days thereafter. We observed a significant increase of CD34 + cells at T(3) and T(4) only in Iatrogenic Necrosis and Ischemic Necrosis group. The peak of mobilization was observed ten days after the necrotic event (2.8 ± 1.4 vs. 5.9 ± 1.9 in the group 1, P = 0.03; and 3 ± 1.5 vs. 5.6 ± 2 in the group 2, P = 0.04; respectively). We found a good correlation between CD34 + and vascular endothelial growth factor (VEGF) and stromal derived factor (SDF-1α) peak values (r = 0.77 and r = 0.63, respectively). At multivariable analysis, myocardial necrosis (OR 3.5, 95%CI 2.2-4.2, P < 0.01), VEGF (OR 2, 95%CI 1.1-3, P = 0.01 as above versus below median value), and SDF-1α (OR 1.6, 95%CI 1.1-2.5, P = 0.02 as above versus below median value) emerged as independent predictors of C34 + cells increase. Myocardial necrosis with simultaneous elevation of VEGF and SDF-1α causes a significant CD34 + cells mobilization in patients with cardiovascular disease.

Angiotensin-converting enzyme (ACE) inhibitors have different selectivity for bradykinin binding sites of human somatic ACE.

The angiotensin-converting enzyme (ACE) has two natural substrates and two catalytic domains: one cleaving angiotensin I and one inactivating bradykinin. The aim of this study was to investigate the comparative binding affinity of ACE inhibitors for the two binding sites of human endothelial ACE. In vitro binding assays were performed to test the ability of bradykinin, angiotensin I, or various ACE inhibitors (enalaprilat, perindoprilat, quinaprilat, ramiprilat, and trandolaprilat) to displace a saturating concentration of [(125)I]351A, a radiolabeled lisinopril analogue, from ACE binding sites. The calculated IC(50) values for the ACE inhibitors were in the nanomolar range, while those for the natural substrates were in the micromolar range. The bradykinin/angiotensin I selectivity ratios calculated from double displacement experiments were: perindoprilat, 1.44; ramiprilat, 1.16; quinaprilat, 1.09; trandolaprilat, 1.08; enalaprilat, 1.00. The ACE inhibitors generally had higher affinity for the bradykinin than the angiotensin I binding sites, supporting the idea that these agents are primarily inhibitors of bradykinin degradation, and secondarily inhibitors of angiotensin II production. Perindoprilat had the highest selectivity for bradykinin versus angiotensin I binding sites, and enalaprilat has the lowest. These results indicate that there are differences in the affinity of ACE inhibitors toward sites for bradykinin degradation, which could lead to differences in efficacy in cardiovascular disease.

A Pulmonary Rehabilitation Decisional Score to Define Priority Access for COPD Patients.

This retrospective study aimed to evaluate, through an ad hoc 17-item tool, the Pulmonary Rehabilitation Decisional Score (PRDS), the priority access to PR prescription by respiratory specialists. The PRDS, scoring functional, clinical, disability, frailty, and participation parameters from 0 = low priority to 34 = very high priority for PR access, was retrospectively calculated on 124 specialist reports sent to the GP of subjects (aged 71 ± 11 years, FEV1% 51 ± 17) consecutively admitted to our respiratory outpatient clinic. From the specialist's report the final subject's allocation could be low priority (LP) (>60 days), high priority (HP) (30-60 days), or very high priority (VHP) (<30 days) to rehabilitation. The PRDS calculation showed scores significantly higher in VHP versus LP (p < 0.001) and significantly different between HP and VHP (p < 0.001). Comparing the specialist's allocation decision and priority choice based on PRDS cut-offs, PR prescription was significantly more appropriate in VHP than in HP (p = 0.016). Specialists underprescribed PR in 49% of LP cases and overprescribed it in 46% and 30% of the HP and VHP prescriptions, respectively. A multicomprehensive score is feasible being useful for staging the clinical priorities for PR prescription and facilitating sustainability of the health system.

Tumor necrosis factor-alpha receptor 1 is a major predictor of mortality and new-onset heart failure in patients with acute myocardial infarction: the Cytokine-Activation and Long-Term Prognosis in Myocardial Infarction (C-ALPHA) study.

BACKGROUND: Tumor necrosis factor alpha-alpha (TNF-alpha) activation is an independent prognostic indicator of mortality in patients with heart failure (HF). Despite the recognition that several TNF family cytokines are elevated during myocardial infarction, their role in predicting subsequent prognosis in these setting remains poorly understood. METHODS AND RESULTS: We performed a systematic evaluation of TNF-alpha and its type 1 and 2 soluble receptors, together with interleukin (IL)-6, IL-1 receptor antagonist, and IL-10, in 184 patients (132 men; mean age, 64+/-12) consecutively admitted for myocardial infarction. We correlated their values to short- and long-term incidence of death and HF (primary outcome). In 10 patients, we also studied the presence of transcardiac gradients for TNF-alpha and its soluble receptors. The control group comprised 45 healthy subjects who were sex and age matched (33 men; mean age, 65+/-6 years) to the patients. All tested cytokines were increased in patients, and no transcardiac or systemic AV difference was found. After a median follow-up of 406 days (range, 346 to 696 days), 24 patients died and 32 developed HF. Univariate analysis showed that all cytokines were related to outcome, whereas after adjustment for baseline and clinical characteristics, sTNFR-1 remained the only independent predictor of death and HF (hazard ratio, 2.9; 95% CI, 1.9 to 3.8, tertile 1 versus 3), together with left ventricular ejection fraction, Killip class, and creatine kinase-MB at peak. CONCLUSIONS: sTNFR-1 is a major short- and long-term predictor of mortality and HF in patients with acute myocardial infarction.

Neurohormones and inflammatory mediators in patients with heart failure undergoing cardiac resynchronization therapy: time courses and prediction of response.

Despite interest in neurohormonal activation as a determinant of prognosis in chronic heart failure (CHF) and as a target for pharmacological treatments, data are lacking on the time-related effects of electrical cardiac resynchronization therapy (CRT) on a broad spectrum of neurohormones and cytokines. The aim of this study was to assess time-courses and extents of changes within the neurohormonal profile of CHF patients treated with CRT. We performed a prospective follow-up study in 32 patients with NYHA class III-IV CHF to investigate the effects of CRT on a broad panel of neurohormones proposed for characterization of CHF patients. Levels of atrial and brain natriuretic peptides (ANP, BNP), epinephrine, norepinephrine, aldosterone, plasma renin activity, IL-6, TNF, soluble receptors sTNFR1 and 2, and chromogranin A were assessed before implantation and after 3 months of CRT; when feasible, measurements were also performed at 1 week, 1 month and 12 months (clinical evaluation, echocardiography and ECG were also performed at each time-point). The results showed that at 3 months improvement in NYHA class and echographically assessed left ventricular (LV) reverse structural remodeling were accompanied by significant reductions versus baseline in ANP and BNP, but not in other neurohormones. Moreover a baseline ANP concentration < or = 150 pg/ml was a good predictor of response to CRT in terms of NYHA class reduction and reverse LV remodeling. In conclusion 3 months of CRT significantly reduce natriuretic peptides concentrations, while values of other neurohormones and inflammatory cytokines are relatively unvaried. A baseline ANP concentration < or = 150 pg/ml might be a clinically useful predictor of medium-term response to CRT.

Serum from patients with acute coronary syndromes displays a proapoptotic effect on human endothelial cells: a possible link to pan-coronary syndromes.

BACKGROUND: Endothelial apoptosis of atherosclerotic lesions is a possible determinant for the stable-to-vulnerable plaque transition. Recent data support the notion that plaque activation may be a pan-coronary process, advocating the existence of circulating triggers. METHODS AND RESULTS: Serum from 40 healthy subjects (group 1) and 73 patients with stable angina (n=32; group 2) or acute coronary syndromes (n=41; group 3) was incubated with human umbilical vein endothelial cells. The percentage of apoptosis by flow cytometry and Fas, Bax, and Bcl-2 protein expression by immunoblotting were evaluated at entry in patients and control subjects and repeated after 12 months in group 3. At baseline, apoptotic nuclei were higher in group 3 (14+/-6%) than in group 2 (3.3+/-1.8%) and group 1 (1.35+/-0.8%) (P<0.001). Fas and Bcl-2 were increased in group 3 with respect to groups 1 and 2 (P<0.01). Coincubation of group 3 serum with anti-tumor necrosis factor-alpha and anti-interleukin-6 monoclonal antibodies did not affect the human umbilical vein endothelial cell apoptotic process, whereas addition of Trolox decreased apoptosis to <50%. The percentage of apoptosis in group 3 significantly correlated to the numbers of coronary complex lesions at angiography (r=0.58, P<0.0005). In group 3, apoptosis and the Bax/Bcl-2 ratio decreased at 1 year (P<0.0001, P<0.05 respectively). CONCLUSIONS: Serum from patients with acute coronary syndromes displays a proapoptotic effect on human endothelial cells, supporting the theory of the existence of circulating triggers potentially able to activate atherosclerotic lesions.

CD34+ and endothelial progenitor cells in patients with various degrees of congestive heart failure.

BACKGROUND: Peripheral blood CD34(+) cells and circulating endothelial progenitor cells (EPCs) increase in myocardial infarction and vascular injuries as a reflection of endothelial damage. Despite the occurrence of endothelial dysfunction in heart failure (HF), no data are available on EPC mobilization in this setting. We investigated the pattern of CD34(+) cells and EPC mobilization during HF and their correlation with the severity and origin of the disease. METHODS AND RESULTS: Peripheral blood CD34(+) cells (n=91) and EPCs (n=41), assessed both as CD34(+) cells coexpressing AC133 and vascular endothelial growth factor (VEGF) receptor-2 and as endothelial colony-forming units, were studied in HF patients (mean age 67+/-11 years) and 45 gender- and age-matched controls. Tumor necrosis factor-alpha (TNF-alpha) and its receptors (sTNFR-1 and sTNFR-2), VEGF, stromal derived factor-1 (SDF-1), granulocyte-colony stimulating factor (G-CSF), and B-type natriuretic peptide were also measured. CD34(+) cells, EPCs, TNF-alpha and receptors, VEGF, SDF-1, and B-type natriuretic peptide were increased in HF. CD34(+) cells and EPCs were inversely related to functional class and to TNF-alpha, being decreased in New York Heart Association class IV compared with class I and II and controls. No role was found for the origin of the disease. CONCLUSIONS: CD34(+) cells and EPC mobilization occurs in HF and shows a biphasic response, with elevation and depression in the early and advanced phases, respectively. This could be related to the myelosuppressive role of TNF-alpha.

Hydroxyl radical generation, levels of tumor necrosis factor-alpha, and progression to heart failure after acute myocardial infarction.

OBJECTIVES: We used acetylsalicylic acid (ASA) as a probing agent to quantify hydroxyl radical ((*)OH) in Controls and patients with coronary artery disease and to prospectively investigate (*)OH production in patients with myocardial infarction (MI) complicated by heart failure (HF). BACKGROUND: Oxidative stress status (OSS) is a mechanism for transition to HF in experimental heart injury models, but evidence for its causal role in humans is still limited. METHODS: Thirty healthy subjects (Controls), 12 patients with stable angina (Group 1), and 74 patients with ST-segment elevation MI (Group 2) were enrolled. A dose of 250 mg Flectadol was given intravenously before each blood collection to determine the 2,3-dihydroxybenzoic acid/salicylic acid (DHBA/SA) ratio. We also quantified vitamin E and coenzyme Q(10) to monitor antioxidant reserve, as well as tumor necrosis factor (TNF)-alpha, TNF-soluble receptors, interleukin (IL)-6, and IL-1ra to assess inflammatory status. All measurements were repeated at month 6 in Group 2. RESULTS: There were no differences between Controls and Group 1. Group 2 showed increased (*)OH production, peaking at 24 h, whereas vitamin E and coenzyme Q(10) progressively declined. Group 2 patients developing HF during hospitalization (Group 2Bi) presented with an increase of both (*)OH production at discharge and inflammatory status, as compared with patients without HF (Group 2Ai), persisting at month 6 in post-MI patients with HF (Group 2Bii). CONCLUSIONS: We found a distinct pattern of (*)OH generation in post-MI patients who show progression to HF. The interplay between OSS and inflammatory status should be targeted as a possible mechanism of progression to post-MI left ventricular dysfunction.

Comparison of the effect of valsartan and lisinopril on autonomic nervous system activity in chronic heart failure.

BACKGROUND: In chronic heart failure (CHF), the derangement of autonomic nervous system activity has a deep impact on the progression of the disease. It has been demonstrated that modulation of the renin-angiotensin aldosterone system (RAAS) increases autonomic control of heart rate and reduces adrenergic activity. We sought to evaluate, in CHF, the different effects of an ACE inhibitor (lisinopril) and of an AT1 receptor antagonist (valsartan) on heart rate variability, baroreflex sensitivity and norepinephrine plasma levels. METHODS: Ninety patients (61 +/- 10 years, 2.3 +/- 0.5, New York Heart Association class) with CHF and left ventricular ejection fraction <40% were randomly assigned in a double-blind fashion to receive lisinopril (uptitrated to 20 mg/d) or valsartan (uptitrated to 160 mg/d) therapy for 16 weeks. Heart rate variability (evaluated by measuring standard deviation of normal R-R intervals on 24-hour ECG recordings), spontaneous baroreflex sensitivity and aldosterone and norepinephrine plasma levels were assessed before and after drug therapy. RESULTS: There were no significant differences between valsartan and lisinopril in their effects on left ventricular function, arterial pressure, aldosterone plasma levels and autonomic control of heart rate. Both lisinopril and valsartan significantly reduced plasma norepinephrine levels, but the reduction induced by valsartan was significantly greater than that observed for lisinopril (27% vs 6%, P <.05). CONCLUSIONS: This study shows a comparable effect of ACE inhibition (lisinopril) and of AT1 receptor antagonism (valsartan) on cardiac vagal control of heart rate, whereas valsartan has shown a more effective modulation of sympathetic activity measured by plasma norepinephrine levels.

ACE inhibition modulates endothelial apoptosis and renewal via endothelial progenitor cells in patients with acute coronary syndromes.

BACKGROUND: The equilibrium between endothelial apoptosis and endothelial renewal is altered in acute coronary syndromes and may be related to differences in the beneficial effects of angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists (angiotensin receptor blockers). METHODS: We evaluated the effect of treatment on endothelial function in post-myocardial infarction (MI) patients treated with perindopril (group 2, n = 16) or valsartan (group 3, n = 17) at baseline and after 7, 15, and 30 days and in normal controls (group 1, n = 20). Endothelial apoptosis was determined by cultivating serum samples in vitro with human umbilical vein endothelial cells (HUVECs), while endothelial renewal was assessed by mobilization of CD34+ bone marrow cells. RESULTS: At baseline, post-MI patients had significantly elevated rates of apoptosis (16.6 ± 5.0% and 16.5 ± 8.4% in groups 2 and 3, respectively [both p = 0.01] vs 1.6 ± 0.7% in group 1), which declined in group 2 (10.5 ± 4.4% at 30 days, p = 0.04), but not in group 3. Similar results and trends were found for the Bax/Bcl-2 ratio. CD34+ mobilization was significantly increased in group 2 (3.0 ± 1.0 at baseline to 6.2 ± 1.6 at 15 days, p = 0.03), whereas in group 3 CD34+ mobilization did not change significantly. The findings in group 2 were accompanied by an increase in vascular endothelial growth factor at 15 days, and a reduction in tumor necrosis factor-α and its soluble receptors, versus no change in group 3. Similar findings were observed for angiotensin II and bradykinin. CONCLUSION: Our results indicate that perindopril, but not valsartan, reduces the proapoptotic effect of serum on the endothelium and increases endothelial renewal in patients with acute coronary syndromes.

Heart rate reduction with ivabradine improves energy metabolism and mechanical function of isolated ischaemic rabbit heart.

AIMS: The anti-anginal agent ivabradine slows heart rate (HR) by selectively inhibiting the I(f) current in the sinus node. We report an ex vivo study to evaluate the anti-ischaemic effect of ivabradine in terms of modulation of cardiac energy metabolism. METHODS AND RESULTS: A Langendorff-perfused rabbit heart model was subjected to low-flow ischaemia and reperfusion. Cardiac metabolism was studied by measuring cardiac high-energy phosphate contents via HPLC, mitochondrial respiration was analysed polarographically, and cardiac redox potentials by HPLC. Cardiac function was determined in terms of the recovery of developed pressure during reperfusion and release of creatine kinase (CK) (spectrophotometrically) and noradrenaline (HPLC) after reperfusion. Four concentrations of ivabradine (0.3, 1, 3, and 6 microM) were tested on aerobically perfused hearts to select the most effective without causing changes in mechanical parameters. This proved to be 3 microM, which was therefore the concentration selected for the ischaemia-reperfusion experiments. Ivabradine concentration-dependently reduced HR with a maximal effect of 41 +/- 4% at 3 microM (P < 0.001 vs. vehicle), without a negative inotropic effect. This concentration protected the heart against ischaemia-reperfusion damage by reducing the rise in diastolic pressure (from 66 +/- 3 with vehicle to 39 +/- 4 mmHg, P < 0.01) and improving developed pressure after 30 min reperfusion (39 +/- 3 vs. 18 +/- 3 mmHg with vehicle, P < 0.01). Ivabradine reduced both CK and noradrenaline release by 47% (both P < 0.05 vs. vehicle) and improved mitochondrial respiratory control index (from 6.9 +/- 0.3 to 11.9 +/- 1.3, P < 0.001). It preserved cardiac energy metabolism (ATP, from 3.7 +/- 0.3 to 11.0 +/- 0.6 microM/g dry weight, P < 0.001) and redox state (NADPH/NADP(+), from 2.5 +/- 0.5 to 4.2 +/- 0.5, P < 0.001). There was a significant correlation between HR reduction in the ivabradine-treated hearts and cardiac creatine phosphate (r = 0.574, P = 0.02) and ATP levels (ATP, r = 0.674, P = 0.0042) at the end of ischaemia. These benefits were no longer detectable during pacing. CONCLUSION: HR reduction by ivabradine confers a marked anti-ischaemic benefit. It significantly reduces cardiac energy consumption, preserves redox potentials during ischaemia, and enhances recovery at reperfusion.

Arginase pathway in human endothelial cells in pathophysiological conditions.

Objective. - Arginase is a nitric oxide synthase-alternative pathway for l-arginine breakdown leading to biosynthesis of urea and l-ornithine. Arginase pathway is inducible by inflammatory molecules-such as cytokines and bacterial endotoxin-in macrophages and smooth muscle cells. The presence of an arginase pathway in human endothelial cells and its possible modulation by inflammation are unknown. Methods. - We have: (i) characterised arginase pathway in terms of activity, isoform type and gene expression in a primary human umbilical vein endothelial cells (HUVEC) line; (ii) evaluated arginase functional role in cell proliferation with the aid of l-norvaline, an arginase inhibitor and (iii) determined the effects of tumour necrosis factor-alpha and endotoxin on arginase pathway. Results. - HUVEC showed a baseline arginase activity and expression of both arginase isoforms (arginase I and II (A-I and A-II, respectively)) which resulted in l-norvaline-inhibitable cellular polyamine synthesis. The baseline arginase activity is important for HUVEC proliferation as cell cycle analysis and nuclear factor Ki-67 immunostaining revealed. Following incubation with inflammatory molecules, arginase activity increased but HUVEC cell cycling decreased. Conclusions. - A-I and A-II are constitutively expressed in HUVEC where they take part to the regulation of cell cycling. Although arginase activity is positively modulated by inflammatory molecules, it is insufficient to counteract the overall cell cycling inhibiting effects of inflammation.