Distribution and Activation of cAMP- and cGMP-Dependent Protein Kinases in Highly Purified Human Platelet Plasma and Intracellular Membranes

Previously cAMP- and cGMP-dependent protein kinases (cAMP-PK, cGMP-PK) have been found predominantly associated with the particulate fraction in human platelets. We now report the distribution and activation of cAMP-PK and cGMP-PK in highly purified fractions of human platelet plasma (PM) and intracellular membranes (IM) prepared using high voltage free flow electrophoresis. Two non-hydrolys-able analogues of cAMP and cGMP namely Sp-5,6-DCl-cBiMPS and 8-p-CPT-cGMP have been used to activate cAMP-PK and cGMP-PK respectively. Addition of either agonist with [γ32P]ATP stimulated the endogenous activity of cAMP-PK or cGMP-PK in PM but not in IM. With PM Sp-5,6-DCl-cBiMPS stimulated the phosphorylation of protein substrates of Mr 16,22,24,46-50,66,90,160 and 250 kDa. A specific peptide inhibitor of cAMP-PK inhibited the phosphorylation of all of the substrates by Sp-5,6-DCl-cBiMPS. 8-pCPT-cGMP also induced the phosphorylation of a number of substrates particularly 16,22, 46-50, 90 and 250 kDa proteins. Inclusion of the cAMP-PK inhibitor peptide totally blocked the phosphorylation of the 16 and 22 kDa proteins, partially inhibited phosphorylation of 46-50 and 90 kDa proteins and had no effect on the 250 kDa protein indicating the 46-50, 90 and 250 kDa proteins were also cGMP-PK substrates. Western blotting with antibodies to cGMP-PK and the catalytic subunit of cAMP-PK revealed the presence of the kinases to be exclusively associated with PM with no detection in IM.

The presence of cAMP-PK substrates in IM was investigated by exogenous addition of catalytic subunit of cAMP-PK. Phosphoproteins of Mr 16, 22, 27, 30,45, 75,116 and 250 kDa were detected. A range of antibodies to cAMP-PK substrates were used to identify and localise the substrates. These antibodies revealed GPIb and VASP to be exclusively associated with PM fractions. Rap IB was also predominantly associated with PM with a small level detected in IM. Antibodies to the IP3 receptor (18A10 and 4C11) revealed the protein to be predominantly associated with IM. Additionally the antibody 4C11 recognised a 230 kDa protein band in PM that was not seen in IM. From the known specificity of these antibodies the results confirm the presence of a type IIP3 receptor in IM and a distinct (possible type III) IP3 receptor with the PM. the 16, 22, 27, 30, 75 and 116 kDa proteins in IM represent nwly detected substartes for camp-pk of presently unknown identity.

Impact of anti-infective periodontal therapy on parameters of vascular health

AIM

This study assessed the impact of anti-infective periodontal therapy on the status of vascular health.

MATERIALS AND METHODS

Periodontal and vascular health of 55 patients with severe untreated chronic periodontitis was evaluated before and 12 months after anti-infective periodontal therapy. Observed parameters were bleeding on probing (BoP), pocket probing depth (PPD), periodontal inflamed surface area index (PISA), pulse wave velocity (PWV), augmentation index (AIx), central pulse pressure (PPao) and peripheral systolic pressure (RRsys).

RESULTS

ΔPISA (baseline-12 months) correlated with ΔPWV (τ 0.21; p < .03), ΔAIx (τ 0.29; p < .002) and ΔPPao (τ 0.23; p < .02). ΔBoP% (baseline-12 months) correlated with ΔPWV (τ 0.18; p < .05) and ΔAIx (τ 0.25; p < .01), while mean ΔPPD (baseline-12 months) correlated with ΔPWV (τ 0.24; p < .01) and ΔAIx (τ 0.21; p < .03). Grouping patients evenly into three groups based on tertiles of BoP resolution after 12 months revealed a significant decrease in the observed PWV median value by -0.6 m/s (p < .04) in the best response tertile (ΔBoP ≥ 88%). In the worst response tertile (ΔBoP ≤ 66%), by contrast, significant increase in PPao (+10.5 mmHg; p < .02) and AIx (+5.5; p < .02) was observed.

CONCLUSION

Efficacious resolution of periodontal inflammation may beneficially impact on vascular health.

Flow Cytometry Analysis of Intracellular VASP Phosphorylation for the Assessment of Activating and Inhibitory Signal Transduction Pathways in Human Platelets

Increased platelet adhesion or aggregation are key events in the pathogenesis of cardiovascular diseases. Exact determination of the platelet activation state is essential to recognize, prevent, and treat cardiovascular complications due to platelet dysfunction. Initial phases of platelet activation and inhibition are characterized by phosphorylation of specific intracellular proteins. However, methodological problems often prevent analysis of platelet protein phosphorylation under clinical conditions. A novel flow cytometry-based method using a phosphorylation-specific antibody was developed for fast and easy quantification of the phosphorylation state of a specific intracellular platelet protein. This method was used to analyze various platelet receptors and their intracellular signaling which may be impaired in genetic or acquired disorders or altered due to therapeutic interventions. In a first clinical application, the inhibitory effects of ticlopidine and clopidogrel on the platelet P2YAC ADP receptor were monitored.

Abbreviations: ADP: adenosine 5’-diphosphate; cAMP: cyclic adenosine-3’,5’-monophosphate; cGMP: cyclic guanosine-3’,5’-monophosphate; HUVECs: human umbilical vein endothelial cells; MAPK: mitogen-activated protein kinase; PG-E1: prostaglandin E1; PRP: platelet-rich plasma; SNP: sodium nitroprusside; VASP: vasodilator-stimulated phosphoprotein

Inhibition of platelet activation in congestive heart failure by aldosterone receptor antagonism and ACE inhibition

An increased risk of thrombembolic events in congestive heart failure (CHF) has been attributed to a hypercoagulable state including vascular endothelial dysfunction and platelet activation.

After experimental myocardial infarction, male Wistar rats were treated with placebo, the ACE inhibitor trandolapril, the selective aldosterone receptor antagonist eplerenone or the combination of both, for 10 weeks. Platelet-bound fibrinogen and surface-expressed P-selectin were not modulated in rats without CHF compared with sham-operated animals, but were significantly increased in CHF rats (LVEDP>15mmHg). In CHF rats, ACE inhibition significantly reduced platelet P-selectin expression while bound fibrinogen was not modulated. Eplerenone reduced P-selectin expression to a comparable extent, while platelet-bound fibrinogen was normalised. Combination therapy with eplerenone and trandolapril completely abolished both the increased P-selectin expression as well as fibrinogen binding. Phosphorylation of platelet vasodila-tor-stimulated phosphoprotein (VASP) at both Ser157 and Ser239, which reflects the activity of platelet inhibitors including nitric oxide, was significantly reduced in platelets from placebo-treated CHF rats, and was completely normalised by combination treatment, but only marginally increased by either mono-therapy.

The results show that platelet activation was evident only in CHF rats. Monotherapy with ACE inhibition or eplerenone partially reduced this increased platelet activation, which was completely rescued to basal levels by combination therapy. Increased nitric oxide bioavailability can only partially explain the reduced platelet activation by eplerenone and ACE inhibition.

Increased platelet activation in young Zucker rats with impaired glucose tolerance is improved by acarbose

Patients with diabetes display increased platelet activation. Recent data show a markedly increased risk for cardiovascular events already in pre-diabetic individuals with impaired glucose tolerance (IGT). We investigated whether IGT is associated with platelet activation. Blood samples were collected from young lean (control) and obese Zucker rats, an established model of IGT, after single oral application of sucrose (4g·kg-1). Platelet-bound fibrinogen and platelet surface-expression of P-selectin were assessed as indices of platelet activation using flow cytometry. In lean Zucker rats, acute sucrose application induced fibrinogen-binding and P-selectin surface-expression, which was prevented by co-administration of acarbose (10mg·kg-1). In obese Zucker rats, platelet activation was already maximally increased under baseline conditions with no significant increase after sucrose application. Chronic treatment with acarbose (15mg·kg-1·day-1) significantly reduced platelet activation in these animals. Acute ingestion of sucrose induces platelet activation which is prevented by acarbose. IGT is associated with marked platelet activation that can be reduced by chronic administration of acarbose.The positive modulation of platelet activation by acarbose may contribute to the reduction of cardiovascular events in patients with IGT.

ADP-induced platelet aggregation frequently fails to detect impaired clopidogrel-responsiveness in patients with coronary artery disease compared to a P2Y12-specific assay

Incomplete P2Y12-inhibition during clopidogrel treatment is associated with increased cardiovascular events and mortality after coronary intervention. We investigated the incidence of impaired individual clopidogrel-responsiveness using a P2Y12-specific and pre-treatment-independent assay in a real world situation. One hundred consecutive patients with coronary artery disease (CAD) on combined acetylsalicylic acid and clopidogrel treatment (75 mg/d) and 33 patients on aspirin only were screened for platelet ADP-induced signalling by conventional aggregometry, platelet P-selectin expression and the platelet reactivity index (PRI). Impaired P2Y12-specific inhibition by clopidogrel was defined as a PRI>50%. Functional platelet reactivity was significantly lower in clopidogrel-treated patients compared to controls. Impaired individual response to treatment was diagnosed in 69% of clopidogrel-treated patients. Conventional assessment of maximum ADP-induced platelet aggregation failed to detect impaired P2Y12 inhibition in 36% of patients identified by PRI to have an impaired clopidogrel response. Impaired clopidogrel response was associated with lower HDL levels and a history of hyperlipidaemia. In conclusion, PRI as a P2Y12-specific assay to evaluate the treatment effect of clopidogrel in patients with CAD revealed insufficient P2Y12-inhibition in two thirds of patients in a real-world scenario indicating a markedly higher incidence than previously assumed. PRI detected significantly more patients with impaired response than conventional platelet aggregation.

Regular consumption of Lactobacillus reuteri-containing lozenges reduces pregnancy gingivitis: an RCT

Aim

This randomized controlled trial assessed the impact of Lactobacillus reuteri on pregnancy gingivitis in healthy women.

Materials and Methods

Forty‐five healthy women (24 test/21 placebo) with pregnancy gingivitis in the third trimester of pregnancy were enrolled. At baseline Gingival Index (GI) and Plaque Index (PlI) were assessed at the Ramfjord teeth and venous blood taken for TNF‐α analysis. Subsequently participants were randomly provided with lozenges to be consumed 2 × daily until birth (approx. 7 weeks) containing ≥10⁸CFU L. reuteri ATCC PTA 5289 and ≥10⁸CFU L. reuteri DSM 17938 (test) or being devoid of L. reuteri (placebo). Within 2 days after birth recording of GI, PlI and blood sampling were repeated.

Results

At baseline, mean GI and mean PlI did not differ significantly between both groups. In the test group mean TNF‐α serum level was significantly (p < 0.02) lower than in the placebo group. At reevaluation, mean GI and mean PlI of the test group were both significantly (p < 0.0001) lower than in the placebo group. Mean TNF‐α serum level did no longer differ significantly between the groups.

Conclusions

The consumption of L. reuteri lozenges may be a useful adjunct in the control of pregnancy gingivitis.

Stimulation of the nitrate-nitrite-NO-metabolism by repeated lettuce juice consumption decreases gingival inflammation in periodontal recall patients: a randomized, double-blinded, placebo-controlled clinical trial

AIM

This prospective, parallel group, two-armed, double-blind, placebo-controlled randomized trial evaluated the impact of dietary nitrate consumption on gingival inflammation in periodontal recall patients.

MATERIAL AND METHODS

Forty-four (23 test/21 placebo) periodontal recall patients with chronic gingivitis were enrolled. At baseline, gingival index (GI), plaque control record (PCR) and salivary nitrate level (SNL) were recorded, followed by sub- and supragingival debridement. Subsequently, participants were randomly provided with 100 ml bottles of a lettuce juice beverage to be consumed 3× daily over 14 days, containing either a standardized amount of nitrate resulting in an intake of approximately 200 mg nitrate per day (test) or being devoid of nitrate (placebo).

RESULTS

At baseline, mean GI, PCR and SNL did not differ significantly between the groups. At day 14, mean GI of the test group was significantly reduced compared to baseline and significantly lower (p = 0.002) than in the placebo group (GI 0.3 versus 0.5). Also, mean SNL in the test group was significantly higher than in the placebo group (54.0 μg/ml versus 27.8 μg/ml; p < 0.035). Mean PCR did not change significantly in both groups.

CONCLUSIONS

Dietary nitrate consumption may be a useful adjunct in the control of chronic gingivitis.

Differential diagnosis of primary failure of eruption (PFE) with and without evidence of pathogenic mutations in the PTHR1 gene

BACKGROUND

Primary failure of eruption (PFE) may be associated with pathogenic mutations in the PTHR1 gene. It has numerous manifestations and is characterized by severe posterior open bite. However, there are also phenotypically similar types of eruption anomalies not associated with a known pathogenic PTHR1 mutation. The purpose of this study was to evaluate whether a distinction can be made between PTHR1-mutation carriers and noncarriers based on clinical and radiological findings.

PATIENTS AND METHODS

A total of 36 patients with suspected PFE diagnoses were included and analyzed in accordance with specific clinical and radiographic criteria. In addition, all patients underwent Sanger DNA sequencing analysis of all coding sequences (and the immediate flanking intronic sequences) of the PTHR1 gene.

RESULTS

Of these patients, 23 exhibited a heterozygous pathogenic mutation in the PTHR1 gene (PTHR1-mutation carriers), while molecular genetic analysis revealed nosequence alteration in the other 13 patients (non-PTHR1-mutation carriers). Relevant family histories were obtained from 5 patients in the carrier group; hence, this group included a total of 13 familial and 10 simplex cases. The group of noncarriers revealed no relevant family histories. All patients in the carrier group met six of the clinical and radiographic criteria explored in this study: (1) posterior teeth more often affected; (2) eruption disturbance of an anterior tooth in association with additional posterior-teeth involvement; (3) affected teeth resorbing the alveolar bone located coronal to them; (4) involvement of both deciduous and permanent teeth; (5) impaired vertical alveolar-process growth; and (6) severe subsequent finding of posterior open bite. None of the analyzed criteria were, by contrast, met by all patients in the noncarrier group. All patients in the carrier group could be assigned to one of three classifications indicating the extent of eruption disturbance, whereas 4 of the 13 noncarriers presented none of these three patterns. The clinical and radiographic criteria employed in this study would have correctly identified 10 of the 13 PFE patients in the noncarrier group as possessing no detectable PTHR1 mutation.

CONCLUSION

The evaluation of clinical and radiographic characteristics can heighten the specificity of ruling out suspected PTHR1 involvement in PFE patients. A hereditary element of PTHR1-associated PFE is clearly identifiable. More studies with more patients are needed to optimize the sensitivity of this preliminary approach on the differential identification of PTHR1-mutation carriers versus noncarriers by multivariate analysis.

Neisseria meningitidis induces platelet inhibition and increases vascular endothelial permeability via nitric oxide regulated pathways

Despite antibiotic therapy, infections with Neisseria meningitidis still demonstrate a high rate of morbidity and mortality even in developed countries. The fulminant septicaemic course, named Waterhouse-Friderichsen syndrome, with massive haemorrhage into the adrenal glands and widespread petechial bleeding suggest pathophysiological inhibition of platelet function. Our data show that N. meningitidis produces the important physiological platelet inhibitor and cardiovascular signalling molecule nitric oxide (NO), also known as endothelium-derived relaxing factor (EDRF). N. meningitidis -derived NO inhibited ADP-induced platelet aggregation through the activation of soluble guanylyl cyclase (sGC) followed by an increase in platelet cyclic nucleotide levels and subsequent activation of platelet cGMP- and cAMP- dependent protein kinases (PKG and PKA). Furthermore, direct measurement of horseradish peroxidase (HRP) passage through a vascular endothelial cell monolayer revealed that N. meningitidis significantly increased endothelial monolayer permeability. Immunfluorescence analysis demonstrated NO dependent disturbances in the structure of endothelial adherens junctions after co-incubation with N. meningitidis . In contrast to platelet inhibition, the NO effects on HBMEC were not mediated by cyclic nucleotides. Our study provides evidence that NO plays an essential role in the pathophysiology of septicaemic meningococcal infection.

Inhibition of platelet activation in rats with severe congestive heart failure by a novel endothelial nitric oxide synthase transcription enhancer

AIMS

Increased risk of thrombo-embolic events in congestive heart failure (CHF) has been attributed to a hypercoagulable state including vascular endothelial dysfunction and reduced bioavailability of nitric oxide (NO) as well as platelet activation. We investigated whether treatment with a novel endothelial NO synthase (eNOS)-transcription enhancer positively modulates systemic NO bioavailability and reduces platelet activation in rats with CHF.

METHODS AND RESULTS

After experimental myocardial infarction, male Wistar rats were treated with either placebo or the eNOS-transcription enhancer, AVE9488 (25 ppm/day) for 10 weeks. In rats with severe CHF (left ventricular end-diastolic pressure >15 mmHg), platelet vasodilator-stimulated phosphoprotein (VASP)-phosphorylation reflecting the integrity of the NO/cGMP pathway was significantly reduced (mean immunofluorescence at Ser(157): Sham, 61.4 +/- 9.1; CHF-Placebo, 37.4 +/- 4.9; P < 0.05; Ser(239): Sham, 18.1 +/- 2.5; CHF-Placebo, 13.2 +/- 0.6; P < 0.05). Platelet surface expression of P-selectin and glycoprotein 53 were increased in CHF rats compared with sham-operated animals. Chronic treatment with AVE9488 significantly enhanced platelet VASP-phosphorylation in CHF rats (Ser(157): 70.4 +/- 16.2; Ser(239): 19.3 +/- 1.8). In parallel, platelet surface expression of P-selectin and glycoprotein 53 was reduced in the treatment group.

CONCLUSION

Platelet activation was evident in CHF rats. Therapy with the eNOS-transcription enhancer, AVE9488, reduced platelet activation in parallel to normalization of platelet NO bioavailability.

Phosphatidylserine surface expression and integrin alpha IIb beta 3 activity on thrombin/convulxin stimulated platelets/particles of different sizes

Platelets stimulated by a combination of thrombin/convulxin have been shown to develop two to three populations characterized by different phosphatidylserine (PS) surface expression and integrin alpha IIb beta 3 activity. To determine how these markers are distributed on the surface of platelets/particles, we studied Annexin V and PAC-1 binding to platelets/particles of different sizes by flow cytometry analysis and evaluated influences of calpain and caspase inhibitors on thrombin/convulxin-activated platelets. Analysed platelets/particles were divided by their sizes, according to the standard size beads, into seven populations from 0.37 to 4.8 microm. PAC-1 binding/microm(2) was almost equal in platelets/particles ranging from 1.2 to 4.8 microm and was significantly lower on smaller-sized particles sizes (0.37-0.7 microm). PS surface exposure/microm(2) was high in the particles of 0.37-1.2 microm and very low in platelets (2.6-4.8 microm). Upon thrombin/convulxin stimulation caspase inhibitors prevented microparticle (MP) formation, while a calpain inhibitor stimulated MP formation. It was also shown that stimulated platelets are heterogeneous not only in their ability to activate alpha IIb beta 3 integrin complex and expose PS on their surface, but also in the distribution of activation markers, which strongly depends on platelet/particle size and that platelets/particles of different sizes provide different responses to the same stimulus.

ADP-induced platelet aggregation frequently fails to detect impaired clopidogrel-responsiveness in patients with coronary artery disease compared to a P2Y12-specific assay

Incomplete P2Y(12)-inhibition during clopidogrel treatment is associated with increased cardiovascular events and mortality after coronary intervention. We investigated the incidence of impaired individual clopidogrel-responsiveness using a P2Y(12)-specific and pre-treatment-independent assay in a real world situation. One hundred consecutive patients with coronary artery disease (CAD) on combined acetylsalicylic acid and clopidogrel treatment (75 mg/d) and 33 patients on aspirin only were screened for platelet ADP-induced signalling by conventional aggregometry, platelet P-selectin expression and the platelet reactivity index (PRI). Impaired P2Y(12)-specific inhibition by clopidogrel was defined as a PRI>50%. Functional platelet reactivity was significantly lower in clopidogrel-treated patients compared to controls. Impaired individual response to treatment was diagnosed in 69% of clopidogrel-treated patients. Conventional assessment of maximum ADP-induced platelet aggregation failed to detect impaired P2Y(12) inhibition in 36% of patients identified by PRI to have an impaired clopidogrel response. Impaired clopidogrel response was associated with lower HDL levels and a history of hyperlipidaemia. In conclusion, PRI as a P2Y(12)-specific assay to evaluate the treatment effect of clopidogrel in patients with CAD revealed insufficient P2Y(12)-inhibition in two thirds of patients in a real-world scenario indicating a markedly higher incidence than previously assumed. PRI detected significantly more patients with impaired response than conventional platelet aggregation.

Cyclic nucleotide-regulated proliferation and differentiation vary in human hematopoietic progenitor cells derived from healthy persons, tumor patients, and chronic myelocytic leukemia patients

Although circulating hematopoietic progenitor cells (HPCs) are frequently used in therapeutic approaches, many aspects of their cellular biochemistry are still unclear. In the present study, the effects of cyclic nucleotide-elevating agents on HPC proliferation and differentiation were investigated. HPCs from different sources, including healthy persons, patients with tumors (medulloblastoma, seminoma, or multiple myeloma), and patients with chronic myelocytic leukemia (CML), were compared. HPCs were isolated by standard leukapheresis procedures and analyzed for proliferation and differentiation into the megakaryocytic and granulocytic lineages. HPCs contained high concentrations of cyclic guanosine monophosphate (cGMP)-dependent and cyclic adenosine monophosphate (cAMP)-dependent protein kinases G and A (PKG and PKA, respectively). Whereas PKG was partly down-regulated during culture, the PKA level remained constant. Stimulation of PKG in HPCs isolated from healthy donors or tumor patients resulted in a biphasic reaction: low cGMP concentrations inhibited proliferation and stimulated differentiation into megakaryocytes, whereas high concentrations revealed the opposite effect. In contrast, differentiation into granulocytes was inhibited in a concentration-dependent manner. Stimulation of PKA inhibited HPC differentiation; however, HPC proliferation was inhibited in controls and stimulated in HPCs from tumor patients. HPCs isolated from CML patients showed a nonhomogeneous reaction pattern to both cyclic nucleotides with high variability between the individual donors. We demonstrated the importance of the source of HPCs for the investigation of proliferation and differentiation. Cyclic nucleotide-regulated pathways are clearly involved in HPC proliferation and differentiation. Pharmacological strategies using cyclic nucleotide-elevating substances to influence HPC growth and differentiation in the bone marrow might support current strategies in HPC recovery from the peripheral blood.

Improvement of vascular function by acute and chronic treatment with the PDE-5 inhibitor sildenafil in experimental diabetes mellitus

BACKGROUND AND PURPOSE

Diabetes-associated vascular dysfunction contributes to increased cardiovascular risk. We investigated whether the phosphodiesterase-5 inhibitor sildenafil would improve vascular function in diabetic rats.

EXPERIMENTAL APPROACH

Male Wistar rats were injected with streptozotocin (50 mg kg(-1), i.v.) to induce insulin-deficient diabetes. Direct effects of sildenafil as well as modification of endothelium-dependent and -independent vasorelaxation were investigated in vitro. The effects of acute and chronic (2 week) treatment in vivo of sildenafil on vascular function were also characterized in isolated aortic segments in organ bath chambers 4 weeks after diabetes induction.

KEY RESULTS

Sildenafil induced a concentration-dependent vasorelaxation, which was attenuated by the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine. Acetylcholine-induced endothelium-dependent as well as endothelium-independent relaxation induced by the NO donor, DEA-NONOate, was significantly reduced in aortae from diabetic rats. Incubation with sildenafil in vitro normalized both endothelium-dependent and -independent relaxation in aortae from diabetic rats. Acute as well as chronic in vivo treatment with sildenafil resulted in enhanced endothelium-dependent and -independent vasorelaxation. Superoxide formation was increased in diabetes, associated with enhanced membrane expression of the NAD(P)H oxidase subunit gp91(phox) and Rac, which were both reduced by chronic treatment with sildenafil.

CONCLUSIONS AND IMPLICATIONS

We demonstrate that sildenafil treatment rapidly and chronically improves vascular relaxation in diabetic rats. Treatment with sildenafil might provide a similarly beneficial effect in diabetic patients.

Delayed Formation of Actin Filaments in the Outer Pillar Head Plate of VASP–/– Mice

Pillar cells with their rich network of tubulin and actin filaments have been reported to contribute to the rigidity of the organ of Corti. As the earliest expression of the actin filament enhancer vasodilator-stimulated phosphoprotein (VASP) in the outer pillar head plate has been found to be associated with the onset of hearing, we tested hearing development in VASP-/- compared to wild-type mice. Performing measurements of auditory brainstem responses on postnatal days (P) P14 and P21, we detected statistically significantly higher thresholds in VASP-/- compared to wild-type mice at P14, but no hearing differences at P21. Staining for prestin and synaptophysin at P12 in morphologically regularly developed cochleae of VASP-/- mice provided an immature prestin protein pattern but no evidence of developmental delay in hair cell innervations. Regularly intense staining of actin filaments in the outer pillar head plate was found only in wild-type but not in VASP-/- mice at P14. At P21, intensive actin filament staining was also observed in the outer pillar head plates of VASP-/- mice. The delayed hearing development in VASP-/- mice is supposed to be caused by a delayed formation of actin filaments in the outer pillar head plate indicating the importance of appropriate pillar cell stiffness in cochlear mechanics.

The CX3C Chemokine Fractalkine Induces Vascular Dysfunction by Generation of Superoxide Anions

OBJECTIVE

The chemokine fractalkine activates platelets and induces leukocyte adhesion to the endothelium. Expression of fractalkine and its receptor, CX3CR1, is elevated in coronary artery disease. We assessed the effects of fractalkine on vascular function in isolated rat aorta.

METHODS AND RESULTS

CX3CR1 expression was demonstrated in rat aortic endothelial and smooth muscle cells by immunohistochemistry, Western blot, and polymerase chain reaction (PCR). Fractalkine (up to 1 microg/mL) did not directly induce contractile or relaxant responses when applied to rat aortic rings in organ baths. Short-term incubation with fractalkine (1 microg/mL) for 5 minutes did not affect vascular reactivity. Pretreatment of isolated rat aortic rings with fractalkine for 2 hours impaired acetylcholine-induced nitric oxide (NO)-mediated relaxation after preconstriction with phenylephrine in a concentration-dependent manner. The concentration response to the NO donor DEA-NONOate was significantly shifted to the right. The radical scavenger tiron normalized the attenuated acetylcholine-induced relaxation after fractalkine incubation. Aortic superoxide formation was enhanced by fractalkine, which was inhibited by diphenyleneiodonium but not by inhibitors of xanthine oxidase or NO synthase.

CONCLUSIONS

In addition to its role as a chemokine and adhesion molecule, fractalkine induces vascular dysfunction by stimulating vascular reactive oxygen species resulting in reduced NO bioavailability.

Gene expression pattern in human brain endothelial cells in response to Neisseria meningitidis

To extend our knowledge of target proteins in endothelial cells infected with the meningitis-causing pathogen Neisseria meningitidis, we characterized the interaction between the bacterial and human brain microvascular endothelial cell (HBMEC) monolayers. By use of human cDNA microarrays, transcriptional analysis revealed distinct responses to 4 and 8 h of infection. We also addressed the question of whether the major virulence factor of meningococci, i.e., the capsule, influences the host cell response. Of the 1,493 (at 4 h postinfection) and 1,246 (at 8 h postinfection) genes with altered expression upon bacterial contact, about 49.4% and 45%, respectively, depended on capsule expression. In particular, we identified an increase of expression for genes encoding proteins involved in bacterial adhesion and invasion. High levels of apoptosis-related gene (bad, bak, asp, and immediate-early response gene 1) expression could also be detected in infected cells. Further analyses confirmed that HBMECs displayed several hallmarks of apoptosis in response to N. meningitidis infection, namely, phosphatidylserine translocation and activation of caspase 3 and AMP-activated protein kinase alpha. Moreover, several differentially regulated genes not previously known to respond to meningococcal infection were identified. Of these, genes encoding cell adhesion proteins (CD44, CD98, and CD99), genes involved in downstream signaling of integrins (integrin-linked kinase, mitogen-activated protein kinase kinase 1, and mitogen-activated protein kinase kinase kinase 10) as well as negative regulators of these pathways (dual-specificity phosphatases 1, 5, and 14 and G protein pathway suppressor 2), and genes involved in cytoskeleton reorganization (those encoding Arp2/3, p34-arc, actinin alpha 1, vasodilatator-stimulated protein, and Wiskott-Aldrich syndrome protein) were the most prominent. This global transcriptional analysis creates a new platform for further molecular and cellular analysis of the interaction between N. meningitidis and target cells.

Enhanced platelet activation by prolactin in patients with ischemic stroke

Prolactin and leptin are newly recognised platelet co-stimulators due to potentiation of ADP-induced platelet aggregation. Elevated leptin levels have recently been found to be a risk factor for ischemic stroke in both men and women, and especially in combination with increased blood pressure for hemorrhagic stroke in men. Until now an association between hyperprolactinemia and ischemic stroke has not been investigated systematically. We determined plasma prolactin and leptin levels as well as platelet P-selectin expression in 36 patients with ischemic stroke or transient ischemic attack and detected a significant correlation between increased prolactin values and enhanced ADP stimulated P-selectin expression on platelets. In contrast, no correlation of leptin values with platelet P-selectin expression was found. Next we determined plasma prolactin and leptin as well as acquired and congenital risk factors of thrombophilia in patients with first-ever non-hemorrhagic stroke with or without atrial fibrillation. Excluding patients with such preexisting risk factors, 21 patients with and 59 patients without atrial fibrillation were identified. Patients without atrial fibrillation revealed significantly higher plasma prolactin levels than patients with atrial fibrillation. Furthermore, the influence of aspirin or clopidogrel on prolactin stimulated P-selectin expression in vitro was tested, showing that aspirin was without effect, whereas clopidogrel significantly inhibited platelet P-selectin expression. In conclusion, hyperprolactinemia might be a novel risk factor for stroke mediating its thrombogenic effect through enhanced platelet reactivity, and this might correspond to a higher efficacy of antiplatelet combination therapy with clopidogrel compared to aspirin therapy alone.

Soluble guanylyl cyclase activation with HMR1766 attenuates platelet activation in diabetic rats

OBJECTIVE

Platelet activation significantly contributes to cardiovascular morbidity and mortality in diabetes. An association between impaired NO-mediated platelet inhibition and platelet activation has recently been demonstrated in experimental diabetes. Guanylyl cyclase activation enhances the reduced signaling via the NO/cGMP pathway. We investigated whether chronic guanylyl cyclase activation would beneficially modulate platelet activation in experimental diabetes mellitus.

METHODS AND RESULTS

Diabetes was induced by streptozotocin-injection in male Wistar rats. After 2 weeks, treatment with either placebo or the guanylyl cyclase activator HMR1766 (10 mg/kg twice daily by gavage) was initiated. Two weeks later, in vivo platelet activation and in vitro platelet reactivity were assessed. Chronic treatment with HMR1766 enhanced NO/cGMP-mediated signaling in platelets from diabetic rats determined by in vivo phosphorylation of platelet vasodilator-stimulated phosphoprotein (VASP) at Ser157 and Ser239. In parallel, platelet-binding of fibrinogen, surface-expression of P-selectin, appearance of platelet-derived microparticles, and platelet-aggregates with other blood cells were significantly reduced by chronic treatment with HMR1766.

CONCLUSIONS

Chronic activation of soluble guanylyl cyclase in diabetic rats improved markers of platelet activation and is a rationale approach for prevention of adverse cardiovascular events in diabetes.

Effects of growth hormone treatment on B-type natriuretic peptide as a marker of heart failure in adults with growth hormone deficiency

OBJECTIVE

Patients with growth hormone deficiency (GHD) have abnormalities of cardiac structure and function. Growth hormone replacement (GHR) therapy can induce an increase in cardiac mass and improvement in left ventricular ejection fraction. B-type natriuretic peptide (BNP) levels have been successfully used to identify patients with heart failure and they correlate with both disease severity and prognosis.

DESIGN

To investigate the effect of growth hormone replacement on BNP and inflammatory cardiovascular risk factors in adults with GHD we determined NT-proBNP and high sensitive C-reactive protein (CrP) before, 6 and 12 months after GHR.

PATIENTS

Thirty adults (14 males, 16 females) with GHD mean age: 41.7+/-14.5 years (range: 17.2 to 75.4 years) were recruited from the German KIMS cohort (Pfizer's International Metabolic Database).

RESULTS

During 12 months of GHR, a significant increase of IGF-1 (85.4+/-72.1 VS. 172.0+/-98 mug/dl; p=0.0001; IGF-1 SDS mean+/-SD: -3.85+/-3.09 VS. -0.92+/-1.82) was detectable. Mean baseline NT-proBNP was 112+/-130 pg/ml (range: 7 to 562). Twelve patients had normal BNP, whereas 18 revealed NT-proBNP values corresponding to those of patients with heart failure NYHA classification I (n=10), NYHA II (n=6) and NYHA III (n=2), respectively. Baseline BNP levels correlated significantly (p=0.044) with increased baseline CrP values. After 12 months of GHR, a significant decrease (p=0.001) in NT-proBNP levels mean: 68+/-81 pg/ml (range: 5 to 395) was detectable, associated with an improvement in NYHA performance status in 10 of the 18 with increased baseline NT-proBNP.

CONCLUSIONS

Based on our study, approximately two-thirds of patients with GHD have increased NT-proBNP levels which may be useful as screening/diagnostic laboratory parameter for heart failure in such patients. GHR therapy decreases BNP levels in most patients with GHD.

Group B streptococcus isolates from septic patients and healthy carriers differentially activate platelet signaling cascades

Infection with group B streptococcus (GBS) is the most common cause of early onset neonatal sepsis in many countries, leading to neonatal morbidity and mortality. There is much evidence for a direct involvement of platelets in the pathogenesis of inflammation and sepsis. Several bacteria are known to directly interact with platelets leading to activation and aggregation, a phenomenon also observed with GBS. Here, we demonstrate that GBS rapidly bound to platelets; however, only strains isolated from septic patients bound fibrinogen on their surface and induced platelet thromboxane synthesis, platelet aggregation, and P-selectin (CD62P) expression. In contrast, GBS strains isolated from healthy newborns or healthy pregnant women induced only shape change, but not platelet thromboxane synthesis, platelet aggregation, or CD62P expression. All GBS strains investigated were able to activate FcgammaRIIA receptor signaling pathways including phospholipase C gamma2 (PLCgamma2), as well as calcium/calmodulin-dependent myosin kinase II (CaMKII) and phosphorylation of myosin light chain (MLC). In contrast, protein kinase C (PKC) was exclusively activated by GBS strains isolated from septic patients, and p38 mitogen activated protein kinase (p38 MAP kinase) was preferentially activated by septic GBS strains. Furthermore, stress signaling kinase SEK1/MKK4 and focal adhesion kinase (FAK) were activated by all tested GBS strains in a FcgammaRIIA-independent way. This study demonstrates that septic, but not colonizing, GBS strains bind fibrinogen on their surface, and that septic GBS strains influence platelet function not only via the FcgammaRIIA receptor, but also via pathways distinct from IgG-mediated signalling. These mechanisms lead to platelet aggregation and secretion, thereby possibly modulating the pathophysiologic course of GBS infections.

Suppression of Endothelial Progenitor Cells in Human Coronary Artery Disease by the Endogenous Nitric Oxide Synthase Inhibitor Asymmetric Dimethylarginine

OBJECTIVES

We tested the hypothesis that asymmetric dimethylarginine (ADMA) may be an endogenous inhibitor of endothelial progenitor cells (EPCs).

BACKGROUND

Endothelial progenitor cells play a pivotal role in regeneration of injured endothelium, thereby limiting the formation of atherosclerotic lesions. Reduced numbers of EPCs may affect progression of coronary artery disease. Regulation of EPC mobilization and function is mediated in part by nitric oxide (NO). Endogenous inhibitors of NO synthases, such as ADMA, contribute to endothelial dysfunction and injury.

METHODS

We used flow cytometry and in vitro assays to investigate the relationship between EPC number and function with ADMA plasma levels in patients with stable angina.

RESULTS

The plasma concentration of ADMA was related to the severity of coronary artery disease and correlated inversely with the number of circulating CD34+/CD133+ progenitor cells (r = -0.69; p < 0.0001) and endothelial colony forming units (CFUs) (r = -0.75; p < 0.0001). Adjusting for all patient characteristics, we confirmed these findings in multivariate regression analyses. In vitro differentiation of EPCs was repressed by ADMA in a concentration-dependent manner. Compared with untreated cells, ADMA reduced EPC incorporation into endothelial tube-like structures to 27 +/- 11% (p < 0.001). Asymmetric dimethylarginine repressed the formation of CFUs from cultured peripheral blood mononuclear cells to 35 +/- 7% (p < 0.001). Asymmetric dimethylarginine decreased endothelial nitric oxide synthase activity in EPCs to 64 +/- 6% (p < 0.05) when compared with controls. Co-incubation with the hydroxymethyl glutaryl coenzyme A reductase inhibitor rosuvastatin abolished the detrimental effects of ADMA.

CONCLUSIONS

Asymmetric dimethylarginine is an endogenous inhibitor of mobilization, differentiation, and function of EPCs. This contributes to the cardiovascular risk in patients with high ADMA levels and may explain low numbers and function of EPCs in patients with coronary artery disease.

Variable extent of clopidogrel responsiveness in patients after coronary stenting

Clopidogrel is an effective and specific inhibitor of ADP-induced platelet aggregation. After metabolic activation, the active clopidogrel metabolite irreversibly impairs the human platelet P2Y12 ADP receptor. Gialpha-protein activation and inhibition of vasodilator-stimulated phosphoprotein (VASP) phosphorylation are two key elements of the P2Y12 receptor pathway suitable for quantitation of clopidogrel effects. So far, only limited data exist about a diminished responsiveness to clopidogrel and underlying possible mechanisms. We investigated clopidogrel effects in 57 patients after percutaneous coronary intervention and stent implantation by flow cytometry for the analysis of intracellular VASP phosphorylation. Patients were treated with a 300 mg clopidogrel loading dose, followed by 75 mg/day clopidogrel in combination with 100 mg/day aspirin. Samples were drawn after a median of 5 days of clopidogrel treatment. Considerable differences in the responsiveness to clopidogrel could be observed and it was shown that 17.5% (10/57) of the patients revealed an inadequate responsiveness to clopidogrel despite continuation of clopidogrel intake. Comparable amounts of Gialpha and VASP were found in two clopidogrel low-responding patients as well as in two responding patients. To exclude a molecular defect of P2Y12 ADP receptor, the P2Y12 receptor gene of eight clopidogrel treated patients (seven patients with inadequate responsiveness, one responder) was sequenced. We only found a single silent mutation in exon 2 at position 1828 (GA). We suggest that individual differences in clopidogrel metabolization could cause relevant variations in clopidogrel responsiveness despite the use of a 300 mg clopidogrel loading dose.

Rosuvastatin Reduces Platelet Activation in Heart Failure

OBJECTIVES

Endothelial dysfunction and platelet activation are part of the cardiovascular phenotype in congestive heart failure (CHF). We investigated whether 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibition would beneficially modulate vascular NO bioavailability and platelet activation in experimental CHF.

METHODS AND RESULTS

Chronic myocardial infarction was induced by coronary ligation in male Wistar rats. Animals were either treated with placebo or the HMG-CoA reductase inhibitor rosuvastatin. After 10 weeks, hemodynamic assessment was performed and endothelial function was determined in organ bath studies. NO bioavailability was assessed by in vivo platelet vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Markers of platelet degranulation (surface expression of P-selectin and glycoprotein 53) were determined as well as the amount of circulating platelet-leukocyte aggregates. Endothelium-dependent, acetylcholine-induced vasorelaxation was significantly impaired in aortic rings from CHF rats and improved by rosuvastatin. In parallel, in vivo VASP phosphorylation reflecting NO bioavailability was significantly attenuated in platelets from CHF rats and normalized by rosuvastatin. Platelet activation, which was increased in CHF, was reduced by treatment with rosuvastatin.

CONCLUSIONS

HMG-CoA reductase inhibition improved endothelial function, increased systemic NO bioavailability and inhibited exaggerated platelet activation in CHF rats. These mechanisms may contribute to the beneficial effects of statin treatment in CHF.

Interaction of Neisseria meningitidis with human brain microvascular endothelial cells: role of MAP- and tyrosine kinases in invasion and inflammatory cytokine release

Neisseria meningitidis traversal across the blood-cerebrospinal fluid barrier is an essential step in the pathogenesis of bacterial meningitis. We have previously shown that invasion of human brain microvascular endothelial cells (HBMEC) by meningococci is mediated by bacterial outer membrane protein Opc that binds fibronectin, thereby anchoring the bacterium to the integrin alpha 5 beta 1-receptor on the endothelial cell surface. However, subsequent signal transduction mechanisms essential for or regulated by N. meningitidis adhesion and invasion, or HBMEC responses to N. meningitidis are unknown. In this report we investigated the role of c-Jun N-terminal kinases 1 and 2 (JNK1 and JNK2), p38 mitogen-activated (MAP) kinase and protein tyrosine kinases in endothelial-N. meningitidis interaction. Binding of meningococci to HBMEC phosphorylated and activated JNK1 and JNK2 and p38 MAPK as well as their direct substrates c-Jun and MAP kinase activated kinase-2 (MAPKAPK-2), respectively. Non-invasive meningococcal strains lacking opc gene (opc mutants and sequence type 11 complex meningococci) still activated p38 MAPK, however, failed to activate JNK. Inhibition of JNK1 and JNK2 significantly reduced internalization of N. meningitidis by HBMEC without affecting its adherence. Blocking the endothelial integrin alpha 5 beta 1 also decreased N. meningitidis-induced JNK activation in HBMEC. These findings indicate the crucial role of JNK signalling pathway in N. meningitidis invasion in HBMEC. In contrast, p38 MAPK pathway was important for the control of interleukin-6 (IL-6) and IL-8 release by HBMEC. Genistein, a protein tyrosine kinase inhibitor, decreased both invasion of N. meningitidis into HBMEC and IL-6 and IL-8 release, indicating that protein tyrosine kinases, which link signals from integrins to intracellular signalling pathways are essential for both bacterial internalization and cytokine secretion by HBMEC.

Increased noise sensitivity and altered inner ear MENA distribution in VASP-/- mice

Vasodilator-stimulated phosphoprotein (VASP) and mammalian-enabled protein (MENA) share similar cellular localisation and functions (signal transduction pathways, regulation of actin cytoskeleton dynamics). Functional substitution and compensation among Ena/VASP proteins have been proposed as the reason for the absence of major morphological and functional deficits in VASP-/- mice. The aim of this study was to investigate VASP expression in the mouse cochlea, to analyse cochlear function in VASP-/- mice compared with wildtype mice, and to analyse cochlear MENA distribution taking into account that MENA protein might compensate VASP loss in the cochlea of VASP-/- mice. We confirmed specific VASP expression in the pillar cells of the mice organ of Corti as previously reported for rat cochlea. By analysing the hearing function in VASP-/- mice, we found no differences in auditory brainstem responses and distortion product otoacoustic emissions from those of wildtype mice but evidence for an increased noise sensitivity at lower frequencies. When MENA protein levels in cochlea tissue were tested in mutant and wildtype mice by Western blot analysis, no significant differences were found, as was also seen with regard to MENA mRNA levels in laser-microdissected single pillar cells. Most surprisingly, however, MENA protein was absent in pillar cells of VASP-/- mice, whereas it was detected in other cochlear cells. The finding of a cell-specific, and not organ-specific, redundancy of MENA protein expression noted for the first time in VASP-/- mice is proposed as the reason for the observed distinct cochlear phenotype.

Reduced vascular NO bioavailability in diabetes increases platelet activation in vivo

OBJECTIVE

Platelet activation is a feature of cardiovascular disease that is also characterized by endothelial dysfunction. The direct relationship between impaired endothelium-derived NO bioavailability and platelet activation remains unclear. We investigated whether acute inhibition of NO production modulates platelet activation in mice and whether specific rescue of endothelial function in diabetes modifies platelet activation.

METHODS AND RESULTS

Intravenous injection of the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester in wild-type (WT) mice significantly reduced platelet vasodilator-stimulated phosphoprotein (VASP) phosphorylation and increased platelet surface expression of P-selectin, CD40 ligand, and fibrinogen platelet binding, demonstrating that NO production exerts tonic inhibition of platelet activation in mice. Diabetes was induced by streptozotocin injection in WT or endothelial-targeted guanosine 5'-triphosphate cyclohydrolase I (GCH)-transgenic (GCH-Tg) mice protected from endothelial dysfunction in diabetes by sustained levels of tetrahydrobiopterin in vascular endothelium. Platelet VASP phosphorylation was significantly reduced in diabetic WT but not in diabetic GCH-Tg mice. P-selectin, CD40 ligand expression, and fibrinogen binding were increased in diabetic WT mice but remained unchanged compared with controls in endothelial-targeted GCH-Tg mice.

CONCLUSIONS

Platelet activation results from acute and chronic reduction in NO bioactivity. Rescue of platelet activation in diabetes by endothelial-specific restoration of NO production demonstrates that platelet function in vivo is principally regulated by endothelium-derived NO. Endothelial dysfunction caused by uncoupling of endothelial NO synthase is well described in diabetes mellitus and may lead to platelet activation. Acute loss of systemic NO bioavailability causes platelet activation. eNOS uncoupling prevention in diabetes preserved systemic NO bioavailability and maintained a physiological platelet state without activation in vivo.

Differences in platelet activation by prolactin and leptin

Hormones such as prolactin and leptin have recently been recognized as potent platelet aggregation co-activators, and have therefore been postulated as an additional risk factor for both arterial and venous thrombosis. Clinical situations exist that are known to be associated with higher leptin and/or prolactin levels (obesity, pregnancy, prolactinomas and anti-psychotic therapy respectively) and increased venous thrombosis or atherosclerosis risk. Therefore, we compared the impact of both hormones on platelet activation in vitro and in vivo. First, we investigated platelet aggregation and P-selectin expression after stimulation with 1,000 mU/l prolactin or 100 ng/ml leptin in five healthy volunteers in vitro. Prolactin revealed significant higher levels of P-selectin expression and platelet aggregation than leptin in all subjects. We also compared the correlation of prolactin and leptin values with the P-selection expression on platelets. Previously, we detected a significant correlation between prolactin values and ADP-stimulated P-selectin expression on platelets in pregnant women, patients with pituitary tumours, and patients on anti-psychotic therapy. In contrast, leptin did not correlate with P-selectin expression in all subject groups investigated. However, leptin correlated with body mass index in the subjects investigated. Our data indicate that prolactin has a stronger effect on platelet activation as leptin in vitro and in vivo. Moreover, our data suggest that the stronger effect of prolactin on ADP-stimulated platelet aggregation, compared to leptin, depends on higher stimulation of CD62p expression by prolactin.

Vasodilator-stimulated phosphoprotein regulates proliferation and growth inhibition by nitric oxide in vascular smooth muscle cells

OBJECTIVE

Vasodilator-stimulated phosphoprotein (VASP) was identified as a substrate for cGMP-dependent protein kinase (PKG) and cAMP-dependent protein kinase (PKA). It is preferentially phosphorylated at serine239 by PKG, whereas serine157 is a preferred phosphorylation site for PKA. In addition, serine157 is phosphorylated by PKC in response to serum. We have investigated the effects of VASP and VASP phosphorylation at serine157 and serine239 on smooth muscle cell (SMC) proliferation and nitric oxide (NO)-mediated growth inhibition.

METHODS AND RESULTS

Aortic SMCs derived from VASP-deficient mice were transduced with retroviral vectors encoding either wild-type VASP or VASP mutants (S157A-VASP and S239A-VASP), in which serine157 and serine239, respectively, were replaced by a nonphosphorylatable amino acid, alanine. Expression of wt-VASP and S239A-VASP significantly increased proliferation, whereas expression of S157A-VASP was inhibitory. Expression of S239A-VASP rendered SMCs less sensitive to growth inhibition by the NO donor, S-nitroso-n-acetylpenicillamine, when compared with cells expressing wt-VASP. Similar effects were observed in cultured rat SMCs in which wt-VASP, S157A-VASP, and S239A-VASP were expressed.

CONCLUSIONS

Our data suggest that VASP phosphorylation at serine157 is required for the growth-stimulatory effect of VASP in SMCs, whereas VASP phosphorylation at serine239 is involved in the growth inhibitory effects of NO on SMCs.

Reduced basal nitric oxide bioavailability and platelet activation in young spontaneously hypertensive rats

OBJECTIVE

To investigate the role of basal nitric oxide (NO) bioavailability for platelet activation in young spontaneously hypertensive rats before onset of hypertension. Phosphorylation of the vasodilator-stimulated phosphoprotein (VASP) in platelets was used as a sensitive monitor of in vivo NO bioavailability.

METHODS AND RESULTS

Whole blood samples were taken from 10-week-old Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). In vivo surface-expression of P-selectin and platelet-binding of fibrinogen were assessed by flow cytometry. Platelet VASP-phosphorylation at its serine 239 (Ser239) and serine 157 (Ser157) residues was assessed using specific antibodies to determine NO bioavailability in vivo, and compared with endothelial vasomotor function. The increment in vascular tone following inhibition of NO-synthase in slightly preconstricted aortic rings was reduced indicating less NO formation under physiological stimulation (WKY 71.1+/-4.1%; SHR 57.8+/-2.4%, P<0.05). In vivo platelet VASP-phosphorylation was significantly reduced at both phosphorylation sites in SHR (mean fluorescence for Ser239: WKY: 15.2+/-0.6; SHR: 11.7+/-0.5, P<0.01; Ser157: WKY: 53.0+/-3.0; SHR: 35.0+/-3.5, P<0.05). Surface-expression of P-selectin and membrane-bound fibrinogen were significantly enhanced in SHR compared with WKY (P-selectin: WKY: 23.2+/-3.4; SHR 58.3+/-7.9, P<0.001; platelet-bound fibrinogen: WKY: 8.6+/-0.5; SHR: 13.5+/-1.1, P<0.001). In vitro preincubation of platelets with the NO donor sodium nitroprusside normalized platelet surface-expression of P-selectin in SHR.

CONCLUSION

Using VASP-phosphorylation as a sensitive monitor of in vivo NO bioavailability, these data provide evidence that reduced vascular NO formation in vivo contributes to increased platelet activation in young SHR.

Rapid Regulation of Platelet Activation In Vivo by Nitric Oxide

Background— Platelet activation is a feature of many cardiovascular diseases characterized by endothelial dysfunction. The mechanistic relationship between impaired systemic nitric oxide (NO) bioavailability and platelet activation in vivo remains unclear. We investigated whether acute inhibition of NO production in humans modulates platelet activation in vivo and whether exogenous NO would counteract such an effect.

Methods and Results— Intravenous injection of the NO synthase inhibitor N G -monomethyl- l -arginine in healthy volunteers resulted in NO synthase inhibition as detected by increased blood pressure and by significantly reduced phosphorylation of platelet vasodilator-stimulated phosphoprotein, an indicator of NO signaling. NO synthase inhibition increased platelet activation as determined by enhanced platelet binding of fibrinogen and surface expression of P-selectin, glycoprotein 53, and CD40 ligand, demonstrating tonic inhibition of platelet activation by NO production in vivo. Sublingual administration of the NO donor glyceryl trinitrate normalized platelet VASP phosphorylation and restored markers of platelet activation to baseline levels.

Conclusions— Acute inhibition of endogenous NO production in humans causes rapid platelet activation in vivo, which is reversed by exogenous NO, demonstrating that platelet function in vivo is rapidly regulated by NO bioavailability.