FAK-Src signalling through paxillin, ERK and MLCK regulates adhesion disassembly

Cell migration is a complex, highly regulated process that involves the continuous formation and disassembly of adhesions (adhesion turnover). Adhesion formation takes place at the leading edge of protrusions, whereas disassembly occurs both at the cell rear and at the base of protrusions. Despite the importance of these processes in migration, the mechanisms that regulate adhesion formation and disassembly remain largely unknown. Here we develop quantitative assays to measure the rate of incorporation of molecules into adhesions and the departure of these proteins from adhesions. Using these assays, we show that kinases and adaptor molecules, including focal adhesion kinase (FAK), Src, p130CAS, paxillin, extracellular signal-regulated kinase (ERK) and myosin light-chain kinase (MLCK) are critical for adhesion turnover at the cell front, a process central to migration.

Acute endothelin A receptor antagonism improves pulmonary and systemic haemodynamics in patients with pulmonary arterial hypertension that is primary or autoimmune and related to congenital heart disease

OBJECTIVE

To evaluate the acute haemodynamic effect of BQ-123, a selective endothelin A receptor antagonist, in severe chronic pulmonary arterial hypertension (PAH) of primary or autoimmune origin or related to congenital heart disease.

DESIGN

Prospective open clinical study.

SETTING

Cardiology tertiary referral centre.

PATIENTS

26 patients with chronic PAH were studied, with mean (SEM) age 29 (3) years (range 4-71 years), mean pulmonary artery pressure 68 (4) mm Hg, and pulmonary vascular resistance index 1694 (170) dyne x s x cm(-5). Patients were divided in three groups according to PAH aetiology: primary or autoimmune PAH (n = 12), and PAH associated with congenital heart defects with (n = 6) or without (n = 8) complete mixing.

INTERVENTION

BQ-123 200 nmol/min was infused for 60 minutes in the right atrium with sequential haemodynamic measurements at 30 minute intervals.

RESULTS

BQ-123 improved mean pulmonary artery pressure from 68 (4) to 64 (4) mm Hg (p < 0.05), pulmonary vascular resistance index from 1694 (170) to 1378 (145) dyne x s x cm(-5) (p < 0.001), pulmonary cardiac index from 3.0 (0.2) to 3.4 (0.3) l/min/m2 (p < 0.001), and effective cardiac index from 2.5 (0.2) to 2.7 (0.2) l/min/m2 (p < 0.01). Haemodynamic response was similar in all groups except for systemic cardiac index where a different (p = 0.0001, F = 5.53) response was observed; systemic cardiac index increased from 2.7 (0.2) to 2.9 (0.2) l/min/m2 (p < 0.001) when patients with complete mixing were excluded, in whom systemic cardiac index tended to decrease from 3.4 (1.0) to 3.0 (0.6) l/min/m2 (p = 0.06).

CONCLUSIONS

Acute endothelin A receptor antagonism induces substantial haemodynamic improvement in severe chronic PAH of primary or autoimmune origin or related to congenital heart disease.

Uric acid reduces exercise-induced oxidative stress in healthy adults

Uric acid (UA) possesses free-radical-scavenging properties, and systemic administration is known to increase serum antioxidant capacity. However, it is not known whether this protects against oxidative stress. The effects of raising UA concentration were studied during acute aerobic physical exercise in healthy subjects, as a model of oxidative stress characterized by increased circulating 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha) concentrations. Twenty healthy subjects were recruited to a randomized double-blind placebo-controlled crossover study, and underwent systemic administration of 0.5 g of UA in 250 ml of 0.1% lithium carbonate/4% dextrose vehicle or vehicle alone as control. Subjects performed high-intensity aerobic exercise for 20 min to induce oxidative stress. Plasma 8-iso-PGF2alpha concentrations were determined at baseline, after exercise and after recovery for 20 min. A single bout of high-intensity exercise caused a significant increase in plasma 8-iso-PGF2alpha concentrations from 35.0 +/- 4.7 pg/ml to 45.6 +/- 6.7 pg/ml (P<0.01). UA administration raised serum urate concentration from 293 +/- 16 to 487 +/- 16 micromol/l (P<0.001), accompanied by increased serum antioxidant capacity from 1786+/-39 to 1899 +/- 45 micromol/l (P<0.01). UA administration abolished the exercise-induced elevation of plasma 8-iso-PGF2alpha concentrations. High UA concentrations are associated with increased serum antioxidant capacity and reduced oxidative stress during acute physical exercise in healthy subjects. These findings indicate that the antioxidant properties of UA are of biological importance in vivo.

Synapse formation is regulated by the signaling adaptor GIT1

Dendritic spines in the central nervous system undergo rapid actin-based shape changes, making actin regulators potential modulators of spine morphology and synapse formation. Although several potential regulators and effectors for actin organization have been identified, the mechanisms by which these molecules assemble and localize are not understood. Here we show that the G protein-coupled receptor kinase-interacting protein (GIT)1 serves such a function by targeting actin regulators and locally modulating Rac activity at synapses. In cultured hippocampal neurons, GIT1 is enriched in both pre- and postsynaptic terminals and targeted to these sites by a novel domain. Disruption of the synaptic localization of GIT1 by a dominant-negative mutant results in numerous dendritic protrusions and a significant decrease in the number of synapses and normal mushroom-shaped spines. The phenotype results from mislocalized GIT1 and its binding partner PIX, an exchange factor for Rac. In addition, constitutively active Rac shows a phenotype similar to the GIT1 mutant, whereas dominant-negative Rac inhibits the dendritic protrusion formation induced by mislocalized GIT1. These results demonstrate a novel function for GIT1 as a key regulator of spine morphology and synapse formation and point to a potential mechanism by which mutations in Rho family signaling leads to decreased neuronal connectivity and cognitive defects in nonsyndromic mental retardation.

Enhanced vasodilatation to endothelin antagonism in patients with compensated cirrhosis and the role of nitric oxide

BACKGROUND AND AIMS

Patients with advanced cirrhosis have systemic vasodilatation and increased nitric oxide (NO) production despite activated vasopressor systems, including the endothelin system. The aims of this study were to assess the contribution of endogenous endothelin 1 (ET-1) and NO to the maintenance of basal forearm vascular tone in patients with preascitic cirrhosis (n=7) and in age and sex matched healthy controls (n=7).

METHODS

Using venous occlusion plethysmography, forearm blood flow (FBF) responses to subsystemic locally active intra-arterial infusion of BQ-123 (a selective endothelin type A receptor (ET(A)) receptor antagonist; 10 nmol/min) were measured before and during application of an "NO clamp": a balanced co-infusion of L-N(G)-monomethyl-arginine (a selective NO synthase inhibitor) and sodium nitroprusside (an exogenous NO donor) to block endogenous NO production and restore NO mediated basal FBF, respectively.

RESULTS

L-NMMA infusion produced a reduction in FBF (p<0.001) which was similar in both groups. Before applying the "NO clamp", BQ-123 caused an increase in FBF in both groups (p<0.001) that was greater in patients with cirrhosis (p<0.01). During the "NO clamp", BQ-123 induced vasodilatation was abolished in controls and attenuated in patients (p<0.001) but remained significantly greater in patients with cirrhosis (p<0.01).

CONCLUSIONS

These findings indicate a greater ET(A) mediated contribution of endogenous ET-1 to the maintenance of basal forearm vascular tone in patients with preascitic cirrhosis. In addition, enhanced vasodilatation to ET(A) receptor antagonism in cirrhosis cannot be entirely attributed to NO release but is likely to be related to reversal of direct ET-1 mediated tone.

Regulation of Rac1 activation by the low density lipoprotein receptor-related protein

The low density lipoprotein receptor-related protein (LRP-1) binds and mediates the endocytosis of multiple ligands, transports the urokinase-type plasminogen activator receptor (uPAR) and other membrane proteins into endosomes, and binds intracellular adaptor proteins involved in cell signaling. In this paper, we show that in murine embryonic fibroblasts (MEFs) and L929 cells, LRP-1 functions as a major regulator of Rac1 activation, and that this activity depends on uPAR. LRP-1-deficient MEFs demonstrated increased Rac1 activation compared with LRP-1-expressing MEFs, and this property was reversed by expressing the VLDL receptor, a member of the same gene family as LRP-1, with overlapping ligand-binding specificity. Neutralizing the activity of LRP-1 with receptor-associated protein (RAP) increased Rac1 activation and cell migration in MEFs and L929 cells. The same parameters were unaffected by RAP in uPAR-/- MEFs, prepared from uPAR gene knockout embryos, and in uPAR-deficient LM-TK- cells. Untreated uPAR+/+ MEFs demonstrated substantially increased Rac1 activation compared with uPAR-/- MEFs. In addition to Rac1, LRP-1 suppressed activation of extracellular signal-regulated kinase (ERK) in MEFs; however, it was Rac1 (and not ERK) that was responsible for the effects of LRP-1 on MEF migration. Thus, LRP-1 regulates two signaling proteins in the same cell (Rac1 and ERK), both of which may impact on cell migration. In uPAR-negative cells, LRP-1 neutralization does not affect Rac1 activation, and other mechanisms by which LRP-1 may regulate cell migration are not unmasked.

Autonomic neuropathy is associated with increased cardiovascular risk factors: the EURODIAB IDDM Complications Study

AIMS

To assess the prevalence of and risk factors for autonomic neuropathy in the EURODIAB IDDM Complications Study.

METHODS

The study involved the examination of randomly selected Type I (insulin-dependent) diabetic patients from 31 centres in 16 European countries. Neuropathic symptoms and two tests of autonomic function (changes in heart rate and blood pressure from lying to standing) were assessed and data from 3007 patients were available for the present analysis. Autonomic neuropathy was defined as an abnormality of at least one of the tests.

RESULTS

The prevalence of autonomic neuropathy was 36% with no sex differences. The frequency of one and two abnormal reflex tests was 30% and 6%, respectively. The R-R ratio was abnormal in 24% of patients while 18% had orthostatic hypotension defined as a fall in systolic blood pressure > 20 mmHg on standing. Significant correlations were observed between autonomic neuropathy and age (P < 0.01), duration of diabetes (P < 0.0001), HbA1c (P < 0.0001), diastolic blood pressure (P < 0.05), lower HDL-cholesterol (P < 0.01), the presence of retinopathy (P < 0.0001) and albuminuria (P < 0.0001). New associations have been identified from the study: the strong relationship of autonomic neuropathy to cigarette smoking (P < 0.01), total cholesterol/HDL-cholesterol ratio (P < 0.05) and fasting triglyceride (P < 0.0001). As a key finding, autonomic neuropathy was related to the presence of cardiovascular disease (P < 0.0001). All analyses were adjusted for age, duration of diabetes and HbA1c. However, data have been only partly confirmed by logistic regression analyses. Frequency of dizziness on standing up was 18%, while only 4% of patients had nocturnal diarrhoea and 5% had problems with bladder control.

CONCLUSION

Cardiovascular reflex tests, even in the form of the two tests applied, rather than a questionnaire, seem to be appropriate for the diagnosis of autonomic neuropathy. The study has identified previously known and new potential risk factors for the development of autonomic neuropathy, which may be important for the development of risk reduction strategies. Our results may support the role of vascular factors in the pathogenesis of autonomic neuropathy.

Distinct binding sites in the structure of alpha 2-macroglobulin mediate the interaction with beta-amyloid peptide and growth factors

Alpha(2)-macroglobulin (alpha(2)M) and its receptor, low density lipoprotein receptor-related protein (LRP), function together to facilitate the cellular uptake and degradation of beta-amyloid peptide (Abeta). In this study, we demonstrate that Abeta binds selectively to alpha(2)M that has been induced to undergo conformational change by reaction with methylamine. Denatured alpha(2)M subunits, which were immobilized on polyvinylidene difluoride membranes, bound Abeta, suggesting that alpha(2)M tertiary and quaternary structure are not necessary. To determine whether a specific sequence in alpha(2)M is responsible for Abeta binding, we prepared and analyzed defined alpha(2)M fragments and glutathione S-transferase-alpha(2)M peptide fusion proteins. A single sequence, centered at amino acids (aa) 1314-1365, was identified as the only major Abeta-binding site. Importantly, Abeta did not bind to the previously characterized growth factor-binding site (aa 718-734). Although the Abeta binding sequence is adjacent to the binding site for LRP, the results of experiments with mutated fusion proteins indicate that the two sites are distinct. Furthermore, a saturating concentration of Abeta did not inhibit LRP-mediated clearance of alpha(2)M-MA in mice. Using various methods, we determined that the K(D) for the interaction of Abeta with its binding site in the individual alpha(2)M subunit is 0.7-2.4 microm. The capacity of alpha(2)M to bind Abeta and deliver it to LRP may be greater than that predicted by the K(D), because each alpha(2)M subunit may bind Abeta and the bound Abeta may multimerize. These studies suggest a model in which alpha(2)M has three protein interaction sites with distinct specificities, mediating the interaction with Abeta, growth factors, and LRP.

GIT1 functions in a motile, multi-molecular signaling complex that regulates protrusive activity and cell migration

GIT1 is a multidomain protein that is thought to function as an integrator of signaling pathways controlling vesicle trafficking, adhesion and cytoskeletal organization. It regulates ARF GTPases and has binding domains for paxillin and PIX, which is a PAK-binding protein and an exchange factor for Rac. We show that GIT1 cycles between at least three distinct subcellular compartments, including adhesion-like structures, the leading edge and cytoplasmic complexes. The cytoplasmic structures, which also contain paxillin, PAK and PIX, do not detectably co-localize with endosomal Golgi or membrane markers, suggesting that they represent a novel supramolecular complex. The GIT1 cytoplasmic complexes are motile and tended to move toward the cell periphery where they joined existing adhesions. In retracting regions of the cells, the GIT1 complexes moved away from the disassembling adhesions toward the cell body. Using deletion mutants, we have identified domains that target GIT1 to each of the compartments. Localization to adhesions and the leading edge requires the paxillin-binding domain, which comprises the C-terminal 140 residues (cGIT1), whereas targeting to the cytoplasmic complexes requires the central region that contains ankyrin repeats and the PIX-binding domain. Expression of GIT1 or cGIT, but not nGIT1 in which the paxillin-binding domain is deleted, increases the rate of migration and the size and number of protrusions. The latter are inhibited when GIT1 is co-expressed with a kinase-dead PAK, suggesting that the GIT1 interaction with PAK is required for enhanced migration and protrusive activity. Furthermore,GIT1 targets constitutively activated PAK to adhesions and the leading edge via its interaction with paxillin. Since expression of cGIT targets endogenous GIT1 to the leading edge, it appears that the leading edge is the location of GIT1 responsible for these activities. Thus, GIT1 is a component of a motile,multimolecular complex that traffics a set of signaling components to specific locations in the cell where they regulate localized activities.

Adhesion assembly, disassembly and turnover in migrating cells -- over and over and over again

Cell migration is an integrated process that requires the continuous, coordinated formation and disassembly of adhesions. These processes are complex and require a regulated interaction of numerous molecules, and the activation of specific signalling pathways. Even though understanding these processes is challenging, important insights are beginning to emerge, and the technology to facilitate significant advances in this area is now in place.

Abnormal endothelin B receptor vasomotor responses in patients with Hirschsprung's disease

BACKGROUND

Hirschsprung's disease is associated with defects in the endothelin-3 and endothelin B receptor genes.

AIM

To assess the in vivo vasomotor responses to endothelin B receptor stimulation in patients with Hirschsprung's disease.

METHODS

Forearm blood flow was measured using venous occlusion plethysmography in 10 patients with Hirschsprung's disease and 10 matched healthy controls during intra-brachial infusion of the highly selective endothelin B receptor agonist, sarafotoxin S6c. To simulate endothelin B receptor dysfunction, sarafotoxin S6c was co-infused with the highly selective endothelin B receptor antagonist, BQ-788, in six of the healthy controls.

RESULTS

Sarafotoxin S6c caused a brief initial vasodilatation followed by a slow-onset, sustained vasoconstriction (p<0.001). Compared to control subjects, patients with Hirschsprung's disease had a substantial impairment of the initial vasodilatation whilst producing a more pronounced subsequent vasoconstriction (p<0.001). In healthy controls, co-infusion of BQ-788 and sarafotoxin S6c caused a similar pattern of responses to those obtained in patients with Hirschsprung's disease: abolition of the initial vasodilatation and augmentation of subsequent vasoconstriction (p<0.001).

DISCUSSION

In the majority of patients with Hirschsprung's disease, there is a functional defect of the vascular endothelin B receptor.

Hypercholesterolaemia and lipid lowering treatment do not affect the acute endogenous fibrinolytic capacity in vivo

OBJECTIVE

To assess acute tissue plasminogen activator (t-PA) release in vivo in patients with hypercholesterolaemia in the presence and absence of lipid lowering treatment and in matched normocholesterolaemic controls.

DESIGN

Parallel group comparison and double blind randomised crossover.

SETTING

University hospital.

PATIENTS

Eight patients with hypercholesterolaemia (> 7.8 mmol/l) and eight matched normocholesterolaemic controls (< 5.5 mmol/l).

METHODS

Blood flow and plasma fibrinolytic factors were measured in both forearms during unilateral brachial artery infusions of the endothelium dependent vasodilator substance P (2-8 pmol/min) and the endothelium independent vasodilator sodium nitroprusside (1-4 microg/min).

INTERVENTIONS

In patients, measurements were made on three occasions: at baseline and after six weeks of placebo or pravastatin 40 mg daily administered in a double blind randomised crossover design.

MAIN OUTCOME MEASURES

Acute release of t-PA.

RESULTS

Compared with patients, in normocholesterolaemic control subjects substance P caused greater dose dependent increases in forearm blood flow (p < 0.05) but similar increases in plasma t-PA antigen and activity concentrations. During pravastatin treatment in patients, total serum cholesterol fell by 22% from a mean (SEM) of 8.1 (0.3) to 6.4 (0.4) mmol/l (p = 0.002) and substance P induced vasodilatation was no longer significantly impaired in comparison with controls. However, despite reproducible responses, pravastatin treatment was not associated with significant changes in basal or substance P induced t-PA release.

CONCLUSIONS

Hypercholesterolaemia and lipid lowering treatment cause no demonstrable effects on acute substance P induced t-PA release in vivo. This suggests that the preventative benefits of lipid lowering treatment are unlikely to be mediated by improvements in endogenous fibrinolysis.

Microvascular correlates of blood pressure, plasma glucose, and insulin resistance in health

OBJECTIVES

The associations between hypertension, insulin resistance and glucose intolerance are poorly understood. Altered microvascular structure and function could contribute by increasing peripheral vascular resistance and decreasing tissue delivery of glucose. We addressed this hypothesis in a sample of healthy men.

METHODS

We studied 105 healthy young men aged 23-33 years. Insulin resistance was calculated using the Homeostasis Model Assessment (HOMA). Video capillaroscopy was used on the dorsum of the finger to measure skin capillary density, and in nailfold capillaries to measure capillary blood velocity. Skin vasodilatation was measured with laser Doppler fluximetry on the forearm following heating and iontophoresis of acetylcholine.

RESULTS

Higher systolic blood pressure was associated with insulin resistance (r=0.31, P<0.005), lower dermal capillary density (r= -0.25, P<0.05), and impaired maximum dermal blood flow after heating (r= -0.26, P<0.01), but not with capillary blood velocity (r=0.07) or dilator responses to acetylcholine (r=0.09). Insulin resistance did not correlate with indices of microvascular structure or function (all r<+/-0.15). However, higher fasting plasma glucose was associated with lower capillary density (r= -0.27, P<0.01), and increased capillary blood velocity (r=0.30, P<0.05).

CONCLUSIONS

The association between hypertension and insulin resistance is unlikely to be explained by altered microvascular structure and function. However, changes in the microvasculature are found in subjects with early and subtle elevations in blood pressure or fasting plasma glucose in advance of their crossing conventional thresholds for the diagnosis of hypertension or diabetes mellitus.

Effects of candesartan on cardiac and arterial structure and function in hypertensive subjects

OBJECTIVES

To study the effect of candesartan cilexetil on left ventricular mass index (LVMI), left ventricular systolic and diastolic function, arterial structure and function and blood pressure (BP) in hypertensive patients.

DESIGN AND METHODS

Patients (n=35), aged >20 years, with hypertension and average baseline LVMI of 89 g/m2 were treated for 24 weeks with candesartan, 16 mg o.d., following a four-week placebo run-in period. If diastolic BP remained above 95 mmHg, hydrochlorothiazide, 12.5 mg o.d.,was added. Left ventricular structure and function were assessed using transthoracic echocardiography. Arterial function and structure were assessed using pulse wave analysis to calculate augmentation index (AIx) and forearm plethysmography to calculate minimum vascular resistance. BP was measured in the office and by 24-hour ambulatory BP monitoring (ABPM).

RESULTS

The mean reduction in LVMI was 4.4 g/m2(p=0.022). Left ventricular systolic function was not significantly altered from baseline, but diastolic function significantly improved: the mean change in diastolic time was 54 ms (p=0.037), in peak velocity filling 6.3 cm/s (p=0.023); E:A ratio improved by 0.08 (p=0.049). The mean reduction in forearm vascular resistance was 15 units at rest (p=0.001) and 1.3 units after limb ischaemia (p=0.006). AIx decreased significantly, with a mean reduction of 9% (p<0.001). Central BP also significantly reduced(systolic blood pressure/diastolic blood pressure 31/20 mmHg; p<0.001). BP was significantly reduced, both in the office (22/16 mmHg; p<0.001) and by 24-hourABPM (18/12 mmHg; p<0.001).

CONCLUSIONS

Treatment with candesartan, 16 mg o.d., with or without hydrochlorothiazide, for 24 weeks, significantly reduced left ventricular mass and arterial hypertrophy in patients with hypertension. In parallel, there were significant improvements in left ventricular diastolic function and arterial function.

Short-term effects of transdermal nicotine on acute tissue plasminogen activator release in vivo in man

OBJECTIVE

Cigarette smoking impairs peripheral endothelium-dependent vasodilatation and acute tissue plasminogen activator (t-PA) release in man. The aim of the study was to determine if this endothelial dysfunction is, in part, mediated by the effects of nicotine.

METHODS

Blood flow and plasma fibrinolytic factors were measured in both forearms of eight healthy male non-smokers during unilateral brachial artery infusion of the endothelium-dependent vasodilator, substance P (2 to 8 pmol/min). Endothelium-independent vasodilatation was assessed using intra-arterial infusion of sodium nitroprusside (2 to 8 microg/min). Subjects attended after 7 days treatment with transdermal nicotine or placebo in a double blind randomised crossover design.

RESULTS

Plasma cotinine concentrations rose from 0.4+/-0.1 (placebo) to 125+/-25 ng/ml during nicotine administration (P<0.001). On both treatment days, substance P caused dose-dependent increases in blood flow and plasma t-PA antigen and activity concentrations (P<0.001 for all) but had no effect on plasma plasminogen activator inhibitor type 1 (PAI-1) concentrations. Compared with placebo, nicotine administration increased the substance-P-induced release of t-PA antigen and activity (P<0.05 for both) without an effect on endothelium-dependent or -independent vasodilatation.

CONCLUSIONS

Short-term transdermal nicotine treatment does not affect endothelium-dependent vasomotion but does increase substance-P-induced t-PA release in vivo in man. This suggests that nicotine administration alters specific aspects of endothelial function and enhances the acute endogenous fibrinolytic capacity in vivo. The long-term effects of nicotine exposure, including the potential to cause depletion of endothelial t-PA stores, now needs to be assessed.

Potentiation of bradykinin-induced tissue plasminogen activator release by angiotensin-converting enzyme inhibition

OBJECTIVES

The aim of the present study was to determine the effect of angiotensin-converting enzyme (ACE) inhibition on the local stimulated release of tissue plasminogen activator (t-PA) from the endothelium.

BACKGROUND

Angiotensin-converting enzyme inhibitor therapy may exert a beneficial effect on the endogenous fibrinolytic balance.

METHODS

Blood flow and plasma fibrinolytic factors were measured in both forearms of eight healthy males who received unilateral brachial artery infusions of the endothelium-dependent vasodilators substance P (2 to 8 pmol/min) and bradykinin (100 to 1,000 pmol/min), and the endothelium-independent vasodilator sodium nitroprusside (2 to 8 microg/min). These measurements were performed on each of three occasions following one week of matched placebo, quinapril 40 mg or losartan 50 mg daily administered in a double-blind randomized crossover design.

RESULTS

Sodium nitroprusside, substance P and bradykinin produced dose-dependent increases in the blood flow of infused forearm (analysis of variance [ANOVA], p < 0.001 for all). Although sodium nitroprusside did not affect plasma t-PA concentrations, they were increased dose-dependently in the infused forearm by substance P and bradykinin infusion (ANOVA, p < 0.001 for both). Bradykinin-induced release of active t-PA was more than doubled during treatment with quinapril in comparison to placebo or losartan (two-way ANOVA: p < 0.003 for treatment group, p < 0.001 for t-PA response and p = ns for interaction), whereas the substance P response was unaffected.

CONCLUSIONS

We have shown a selective and marked augmentation of bradykinin-induced t-PA release during ACE inhibition. These findings suggest that the beneficial clinical and vascular effects of ACE inhibition may, in part, be mediated through local augmentation of bradykinin-induced t-PA release.

Bradykinin contributes to the vasodilator effects of chronic angiotensin-converting enzyme inhibition in patients with heart failure

BACKGROUND

Bradykinin, an endogenous vasodilator peptide, is metabolized by ACE. The aims of the present study were to determine the doses of B9340, a bradykinin receptor antagonist, that inhibit vasodilatation to exogenous bradykinin and to assess the contribution of bradykinin to the maintenance of basal vascular tone in patients with heart failure receiving chronic ACE inhibitor therapy.

METHODS AND RESULTS

Forearm blood flow was measured using bilateral venous occlusion plethysmography. On three occasions in a double-blind randomized manner, 8 healthy volunteers received intrabrachial infusions of placebo or B9340 (at 4.5 and 13.5 nmol/min). On each occasion, placebo or B9340 was coinfused with bradykinin (30 to 3000 pmol/min) and substance P (4 to 16 pmol/min). B9340 caused no change in basal FBF but produced dose-dependent inhibition of the vasodilatation to bradykinin (P<0.001) but not substance P. The effects of bradykinin antagonism were studied in 17 patients with NYHA grade II through IV heart failure maintained on chronic ACE inhibitor therapy. Incremental doses of B9340, but not HOE-140, produced a dose-dependent vasoconstriction (P=0.01). After withdrawal of ACE inhibitor therapy, B9340 produced no significant change in forearm blood flow. After reinstitution of therapy, B9340 again resulted in vasoconstriction (P<0.03).

CONCLUSIONS

B9340 is a potent and selective inhibitor of bradykinin-induced vasodilatation. Bradykinin does not contribute to the maintenance of basal peripheral arteriolar tone in healthy humans or patients with heart failure but contributes to the vasodilatation associated with chronic ACE inhibitor therapy in patients with heart failure via the B(1) receptor.

Forearm blood flow and local responses to peptide vasodilators: a novel pharmacodynamic measure in the phase I trial of antagonist G, a neuropeptide growth factor antagonist

PURPOSE

Arg-D-Trp-NmePhe-D-Trp-Leu-Met-NH(2) (Antagonist G), a substance P (SP 6-11) analogue, inhibits mitogenesis stimulated by a broad spectrum of neuropeptides and has demonstrated antitumor activity in vitro and in vivo with IC(50) concentrations of 10-20 microM in small cell lung cancer and other cell lines. Because neuropeptides are part of complex neurohumoral pathways, we have sought to develop novel pharmacodynamic approaches as part of the early clinical development of this potential anticancer drug.

EXPERIMENTAL DESIGN

A Phase I trial was performed in two stages. In stage 1, Antagonist G was administered at 3- week intervals using an accelerated dose-escalation strategy until the target maximum plasma concentration (C(max)) of 10 microM was achieved. In stage 2, dose intensity was increased to weekly, and the inhibitory effect of i.v. Antagonist G was assessed by forearm blood flow (FBF) using SP as a vasodilator, as measured by venous plethysmography.

RESULTS

In stage 1, dose was escalated from 2 to 300 mg/m(2) in 12 dose levels using only 15 patients. In stage 2, nine patients were entered at three dose levels (300, 350, and 400 mg/m(2)) and a C(max) of 45 microM was achieved. Facial flushing was the only consistent toxicity but was not dose limiting. FBF studies demonstrated that Antagonist G consistently inhibited the vasodilatory effects of SP (mean, 62 +/- 2% inhibition).

CONCLUSIONS

Antagonist G can be safely administered up to 400 mg/m(2), achieving C(max)s >20 microM by weekly 6-h i.v. infusion. FBF studies in patients demonstrated that Antagonist G inhibits SP vasodilatory effects in vivo at these doses in the absence of dose-limiting toxicity.

Endogenously produced urokinase-type plasminogen activator is a major determinant of the basal level of activated ERK/MAP kinase and prevents apoptosis in MDA-MB-231 breast cancer cells

Urokinase-type plasminogen activator (uPA) binds to the uPA receptor (uPAR) and activates the Ras-extracellular signal-regulated kinase (ERK) signaling pathway in many different cell types. In this study, we demonstrated that endogenously produced uPA functions as a major determinant of the basal level of activated ERK in MDA-MB-231 breast cancer cells. When these cells were cultured in the presence of antibodies that block the binding of uPA to uPAR, the level of phosphorylated ERK decreased substantially. Furthermore, conditioned medium from MDA-MB-231 cells activated ERK in MCF-7 cells and this response was blocked by uPA-specific antibody. The mitogen-activated protein kinase kinase inhibitor, PD098059, decreased expression of uPA and uPAR in MDA-MB-231 cells. Thus, uPA and the uPAR-ERK signaling pathway form a positive feedback loop in these cells. When this feedback loop was disrupted with uPA- or uPAR-specific antibody, uPA mRNA-specific antisense oligodeoxynucleotides or PD098059, cell growth was inhibited and apoptosis was promoted, as determined by the increase in cytoplasmic nucleosomes and caspase-3 activity. Treating the cells simultaneously with PD098059 and uPA- or uPAR-specific antibody did not further promote apoptosis, compared with either reagent added separately, supporting the hypothesis that uPAR and ERK are components of the same cell growth/survival-regulatory pathway. The ability of uPA to signal through uPAR, maintain an elevated basal level of activated ERK and inhibit apoptosis represents a novel mechanism whereby the uPA-uPAR system may affect breast cancer progression in vivo.