Accepted Manuscript

Title: Hyperaggregability and impaired nitric oxide productionin platelets from postmenopausal women

Author: Wanda V. Mury Tatiana M.C. Brunini Daniele C.Abrantes Iara K.S. Mendes Maria B.G.B. Campos Antonio C.Mendes-Ribeiro Cristiane Matsuura

PII: S0378-5122(14)00303-XDOI: http://dx.doi.org/doi:10.1016/j.maturitas.2014.10.002Reference: MAT 6261

To appear in: Maturitas

Received date: 1-7-2014Revised date: 29-9-2014Accepted date: 2-10-2014

Please cite this article as: Mury WV, Brunini TMC, Abrantes DC, Mendes IKS,Campos MBGB, Mendes-Ribeiro AC, Matsuura C, Hyperaggregability and impairednitric oxide production in platelets from postmenopausal women, Maturitas (2014),http://dx.doi.org/10.1016/j.maturitas.2014.10.002

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

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Highlights Postmenopausal women present increased platelet reactivity.

Plasma levels of L-arginine were 32% lower in postmenopausal women.

Postmenopausal women present reduced levels of platelet production of nitric oxide

Intraplatelet antioxidant defense is activated in postmenopausal women.

These findings may help to explain platelet dysfunction seen in this population.

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Hyperaggregability and impaired nitric oxide production in platelets from postmenopausal women

Wanda V. Murya, Tatiana M. C. Bruninia, Daniele C. Abrantesa, Iara K. S. Mendesa, Maria B.

G. B. Camposb, Antônio C. Mendes-Ribeiroa,c, Cristiane Matsuuraa

aDepartament of Pharmacolgy and Psychobiology, University of the State of Rio de Janeiro,

Rio de Janeiro, Brazil

bDepartament of Gynaecology, University of the State of Rio de Janeiro, Rio de Janeiro,

Brazil

cDepartament of Physiological Sciences, Federal University of the State of Rio de Janeiro,

Brazil

Mury WV, wandavianna@hotmail.com; Brunini TMC, tmcbrunini@yahoo.com.br; Abrantes

DC, danni.abrantes@gmail.com; Mendes IKS, iarakarise@hotmail.com; Campos MGB,

belaniza@yahoo.com.br; Mendes-Ribeiro AC, claudiomendesribeiro@yahoo.com.br;

Matsuura C, cristiane.matsuura@uerj.br.

Corresponding author: Cristiane Matsuura, Departamento de Farmacologia e Psicobiologia,

Universidade do Estado do Rio de Janeiro, Rio de Janeiro, 20551–030, Brazil. Tel/Fax: 00-

55-21-2868-8629. E-mail address: cristiane.matsuura@uerj.br

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AbstractObjective Cardiovascular mortality increases after menopause in women. Nitric oxide is

essential for proper platelet function inhibiting its aggregation and maintaining vascular

haemostasis. Here, we investigated whether platelet function and intraplatelet L-arginine-

nitric oxide pathway are impaired in postmenopausal women.

Study design Cross-sectional.

Main outcomes measures Blood was collected from 16 premenopausal and 12

postmenopausal women without any additional risk factor for cardiovascular disease. Platelet

reactivity was measured by light transmission aggregometry. L-arginine-nitric oxide pathway

was assessed measuring transmembrane L-[3H]-arginine transport, nitric oxide synthase

activity by the citrulline assay, and arginase activity by the conversion of L-[14C]arginine

to L-[14C]-urea. The activity of antioxidant enzymes was measured by spectrophotometric

assays. Protein expression was determined by Western Blotting.

Results Platelet aggregation was increased in postmenopausal compared to premenopausal

women. Postmenopausal women demonstrated reduced plasma levels of L-arginine, a lower

nitric oxide synthase activity, similar endothelial and inducible nitric oxide synthase

expression, and a compensatory increase in L-arginine transmembrane transport. Arginase

expression and activity did not differ between groups. In regard to oxidative stress, no

differences between groups were observed NAPDH oxidase subunits expression and protein

carbonylation. However, the activity of the antioxidant enzyme superoxide dismutase and

catalase protein levels in platelets were higher in postmenopausal women.

Conclusion Postmenopausal women present increased platelet reactivity, which may be due

to a reduction in intraplatelet nitric oxide synthesis. Platelet hyperaggregability is known to be

associated with arterial and venous thromboembolic event; therefore, it may contribute to the

heightened risk of cardiovascular adverse events in this population.

Keywords: nitric oxide, menopause, blood platelet, oxidative stress

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Abbreviations

BCA, bicinchoninic acid; BH4, tetrahydrobiopterin; CAT, catalase; cGMP, monophosphate

cyclic guanosine; eNOS, endothelial nitric oxide synthase; GPx, glutathione peroxidase;

iNOS, inducible nitric oxide synthase; NADPH, nicotinamide adenine dinucleotide

phosphate; NO, nitric oxide; NOS, nitric oxide synthase; ROS, reactive oxygen species; SOD,

superoxide dismutase

1

1 INTRODUCTION

It has long been recognized that cardiovascular morbidity and mortality is increased in

postmenopausal women [1]. Platelets play a pivotal role in haemostasis through the formation

of a haemostatic plug, and by the activation of coagulation mechanisms; but, when

hyperactivated, they may contribute to increased thrombogenicity. As such, it has been shown

that high basal platelet reactivity is associated with a 2- to 3-fold higher incidence of

myocardial infarction in premenopausal women [2], and large clinical trials have

demonstrated that antiplatelet therapy reduces the risk of ischaemic heart disease [3].

However, contrasting data are available on platelet function in postmenopausal women

without hormone replacement. Gu et al. [4] and Roshan et al. [5] showed that postmenopausal

women presented a significant increase in the platelet activation markers CD 62P and PAC-1

assessed by flow cytometry compared to premenopausal women. On the other hand, Singla et

al. [6] recently demonstrated that platelet reactivity did not differ between pre- and

postmenopausal women.

Impairment in nitric oxide (NO) signaling appears to be of fundamental importance in

the pathogenesis of cardiovascular diseases, possibly through accelerated thrombus formation

[7]. Nitric oxide is synthesized from L-arginine and O2 in a reaction catalyzed by the family

of enzymes NO synthases (NOS), with nicotinamide adenine dinucleotide phosphate

(NADPH) as electron donor. We have shown that both inducible (iNOS) and endothelial

(eNOS) isoforms of this enzyme are expressed in platelets, and their activities seem to be

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dependent on the influx of extracellular L-arginine, which occurs mainly through the amino

acid transporter system y+L and, secondarily, by diffusion [8, 9]. Nitric oxide mediates its

effects mainly via interaction with haem on guanylate cyclase, increasing the production of

intracellular cyclic guanosine monophosphate (cGMP) which inhibits platelet aggregation and

adhesion [10] (Figure 1).

Nitric oxide half-life can be reduced by the presence of reactive oxygen species

(ROS), as it can rapidly react with superoxide anion generating peroxynitrite. The enzyme

NADPH oxidase is a key enzyme in platelet ROS production, being recently suggested as a

target for antithrombotic therapy [11, 12]. On the other hand, the primary antioxidant

enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT),

which protect against the molecular and cellular damage caused by ROS, were identified in

platelets [13] (Figure 1). To our knowledge, there is only one study of oxidative status in

platelets from postmenopausal women. In this study, hormone replacement therapy affected

platelet membrane fatty acid content, reduced lipid peroxidation and the activity of

antioxidant enzymes [14]. Another important metabolic pathway of L-arginine is the urea

cycle. Platelets possess arginase II which, in intact cells, converts L-arginine into L-ornithine

and urea. Since both arginase and NOS use L-arginine as a substrate, simultaneous presence

of these enzymes would result in competition between the two pathways [15].

Considering the key role of nitric oxide in platelet activation, the aim of this study was

to investigate the L-arginine-NO-cGMP pathway in platelets from postmenopausal women, as

well as other factors such as oxidative stress and urea cycle which can affect NO

bioavailability.

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2 MATERIALS AND METHODS

2.1 Subjects

Twenty eight women volunteered to participate in the study, including sixteen

premenopausal women (control group, 27.0 ± 1.8, 95% CI [23.0 - 31.0] yr old) and twelve

postmenopausal (52.6 ± 1.0, 95% CI [50.3 - 54.9] yr old) women from Pedro Ernesto

University Hospital, Rio de Janeiro, Brazil. Menopause was defined as a clinical history of

amenorrhoea for at least 12 months in addition with follicle-stimulating hormone levels

higher than 40 mUI/mL, as shown in Table 1. Subjects were recruited from November 2012

to February 2014. Blood from the control group was collected within the first three days of

the menstrual cycle. Exclusion criteria: heart and renal failure, obesity, diabetes mellitus,

hypertension, ischemic heart disease, infection, dyslipidemia and recent blood transfusion;

and use of antiplatelet, nonsteroidal anti-inflamatory drugs for the past two weeks, hormonal

contraceptive or hormone replacement therapy.

This investigation conforms to the principles outlined in the Declaration of Helsinki as

revised in 2008. This study was approved by Pedro Ernesto University Hospital Ethical

Committee (n. 07049312.8.0000.5259) and written informed consent was obtained from the

patients. Haematological and biochemical analyses were performed at the laboratory of Pedro

Ernesto University Hospital (Table 1).

2.2 Sample preparation

Blood was collected by venipuncture from the antecubital fossa after a 12 h-fasting

using a butterfly needle 21 G, and transferred to appropriated anticoagulant containing tubes.

Platelet suspensions for the assessment of L-arginine-NO pathway were obtained by two

successive centrifugations (200 g, 15 minutes, followed by 900 g for 10 minutes) of venous

blood anticoagulated with citric acid-dextrose (73.7 mM citric acid, 85.9 mM trisodium

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citrate and 111 mM dextrose, pH 4.5) [16]. Pellet was resuspended in Krebs’ buffer (mmol/L)

(119 NaCl, 4.6 KCl, 1.5 CaCl2, 1.2 NaH2PO4, 1.2 MgCl2, 15 NaHCO3, and 11 glucose, pH

7.4). Platelets were counted using an automatic blood cell counter (ABX Pentra 60, Horiba,

Japan).

2.3 L-3H-arginine influx

Washed platelets were incubated at 37 °C with L-3H-arginine (1–50 µM), and its

influx was measured over 5 min [16]. Total transport was fractionated into diffusion and y+L

by cis-inhibition of y+L with 10 mM unlabelled L-leucine. Transport was interrupted by rapid

centrifugation followed by lysis with Triton for ß-scintillation counting. Results are expressed

in pmol/109 cells/min.

2.4 NOS activity

Nitric oxide synthases activity was determined by conversion of L-[3H]-arginine to L-

[3H]-citrulline [8]. Platelet suspensions were incubated at 37 oC in the presence of L-[3H]-

arginine (2 µCi/mL) plus unlabelled L-arginine (1 µM). All reactions were interrupted after

45 minutes by rapid centrifugation followed by two washes using Krebs’ buffer. The platelet

pellet was lysed with Triton and applied to a Dowex cation exchange resin column. The

radioactivity was measured by liquid scintillation counting, and the results are expressed in

pmol/108 cells.

2.5 Measurement of arginase activity

Basal arginase activity was measured in platelet lysates by the conversion of [14C]-L-

arginine into [14C]-urea [17]. In brief, platelets were isolated by centrifugation and the pellet

was resuspended in a lysis buffer composed of 50 mM Tris-HCl, 10 mM CHAPS, 2 mM

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EDTA, 1 mM dithiothreitol, 1 mM phenylmethylsulphonyl fluoride, 1 M pepstatin A and 2

M leupeptin (pH 7.4). The cells were sonicated and the homogenate was centrifuged at

14,000 g for 10 min at 4 oC. Aliquots of platelet lysates were incubated for 2 h at 37oC in a

buffer containing 9 mM Tris-HCl and 1 mM MnCl2 (pH 9.6) in the presence of [C14]-L-

arginine (0.08 Ci/mL) plus 100 M unlabeled L-arginine. The reaction was interrupted by

the addition of ice-cold stop buffer (250 mM sodium acetate and 100 mM urea). Samples

were applied to a Dowex cation exchange resin column and the radioactivity was measured by

a liquid scintillation counter (LS6500, Beckman Coulter Inc., CA, USA). Arginase activity is

expressed in pmol urea/mg protein/2 h.

2.6 Platelet aggregation

Platelet aggregation was assessed on platelet-rich plasma by light transmission

aggregometry. Briefly, blood samples were anticoagulated with 3.8% trisodium sodium and

centrifuged at 200 g for 15 minutes at room temperature. Platelet-poor plasma was obtained

by centrifuging the leftover blood at 900 g for 10 minutes. The platelet concentration in

platelet-rich plasma was adjusted with platelet-poor plasma to a constant count of 1.5 ×

108/mL. Aggregation was induced by collagen (4 g/mL) and the responses monitored for 5

minutes in a four-channel aggregometer (Chrono-Log, Havertown, PA, USA). Tests were

performed at 37◦C with a stirring speed of 900 rpm. Maximal aggregation is expressed in

percentage.

2.7 Biomarkers of oxidative stress

2.7.1 Activity of antioxidant enzymes

Superoxide dismutase activity was assayed by measuring the inhibition of adrenaline

auto-oxidation at 480 nm, GPx activity was measured by monitoring the oxidation of NADPH

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at 340 nm in the presence of hydrogen peroxide and catalase activity was measured by the

rate of decrease in hydrogen peroxide at 240 nm [17]. Antioxidant enzymes activity is

expressed in U/mg protein.

2.7.2 Sulfhydryl group

Total sulfhydryl group was measured in platelets using the spectrophotometric assay

based on the reaction of this group with 2,2-dithiobisnitrobenzoic acid [18]. Results are

expressed in µmol/mg protein.

2.7.3 Protein oxidation

Protein oxidation was assessed in platelets according to Wehr and Levine (2013) [19],

based on the reaction of carbonyl groups with 2.4-dinitrophenylhydrazine (Sigma, MO,

EUA). Values of absorbance were obtained by spectrophotometry at 380 nm and expressed in

nmol of carbonyl/mg of protein.

2.8 Western blotting

Samples containing 30 μg proteins were loaded onto a 10% sodium dodecyl sulfate -

polyacrylamide gel for electrophoresis (Invitrogen, CA, USA), and transferred to

polyvinylidene difluoride membranes. Afterwards, they were immunoblotted with mouse

monoclonal antibodies against human eNOS and iNOS, rabbit monoclonal antibody against

human arginase II, NADPH oxidase subunits gp91phox and p47phox, glutathione peroxidase,

catalase (1:1000 dilution) and β-tubulin at a 1:500 dilution. Gels were stained with Coomassie

blue to check protein transfer. All primary and secondary antibodies were purchased from

Santa Cruz Biotechnology, CA, USA, except anti-eNOS and anti-iNOS (BD Biosciences, NJ,

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USA). Western blotting was performed in samples from five subjects per group. The

expression of individual proteins was normalized to the respective β-tubulin expression.

2.8 Protein quantification

Protein content of each sample was determined using bicinchoninic acid assay kit

(Pierce, IL, USA), and expressed in mg/mL.

2.9 Plasma amino acid levels

Plasma levels of amino acids (arginine, aspartic acid, lysine, methionine, ornithine,

serine, tyrosine, threonine, tryptophan) were measured by high-performance liquid

chromatography at the DLE Laboratory (Rio de Janeiro, Brazil). Results are expressed in

µmol/L.

2.10 Determination of fibrinogen

Plasma samples were isolated and the concentration of fibrinogen was measured by

the Clauss Method [20]. Results are expressed in mg/dL.

2.11 Statistical analysis

Data are expressed as mean ± standard deviation, and 95% confidence interval (95%

CI). Unpaired t test was used for analysis of the differences between pre-menopausal and

postmenopausal women groups, after testing for its assumptions of normality and

homogeneity of variances. The results obtained from Western Blot were compared using the

Mann-Whitney test. Sample size was calculated assuming that a 10 % reduction in platelet

aggregation is expected with standard treatment with aspirin for the prevention of negative

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cardiovascular outcomes, with a two-sided significance of 0.05 and a power of 0.8. A total of

12 patients per group would be required to fulfill these assumptions [21].

3 RESULTS

Table 1 presents the clinical characteristics of the subjects included in the study. Due

to our exclusion criteria, women from both groups were free from any known cardiovascular

risk factors. Subjects presented normal body weight, blood pressure, blood lipids and glucose

levels, as well as normal blood cell count. As expected sexual hormone levels differed

between groups, with postmenopausal women demonstrating significantly higher levels of

FSH and LH, and lower levels of oestradiol.

3.1 Platelet aggregation

Women in the postmenopausal state presented a significant increase in platelet

aggregation measured in PRP in response to collagen compared to controls (Figure 2; 95%

CI, postmenopause [80.6 - 102.7], premenopause [65.5 - 84.8]; p = 0.02).

3.2 Plasma levels of amino acids

Plasma levels of L-arginine, the precursor of NO, were 32% lower in postmenopausal

compared to premenopausal women. A significant reduction in the plasma levels of

methionine and serine was also noted in postmenopausal group. No significant differences

were observed for the other amino acids between groups (Table 2).

3.3 L-arginine influx in platelets

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Figure 3 depicts the maximum velocity (Vmax) of L-arginine influx into platelets. In

the postmenopausal group, total L-arginine transport was significantly higher than in control

group (p = 0.01). The same was observed for L-arginine influx via saturable system y+L after

isolation with L-leucine (p = 0.001).

3.4 NOS activity in platelets and eNOS and iNOS protein expression

Nitric oxide synthase activity, assessed by the production of L-[3H]-citrulline from L-

[3H]-arginine, was decreased in platelets from postmenopausal patients when compared to

premenopausal women (Figure 4A, p = 0.03). No significant difference was observed for both

intraplatelet iNOS (Figure 4B, p = 0.73) nor eNOS (Figure 4C, p = 0.73) expression between

groups.

3.5 Activity and arginase protein levels in platelets

We measured both the activity and expression of the enzyme arginase, since it

competes with NOS for the same substrate, L-arginine. There was no difference in both

arginase activity (control: 106.6 ± 31.0, 95% CI [38.4 - 174.8]), postmenopause: 50.0 ± 12.9,

95% CI [20.3 - 79.7]) pmol urea/mg protein/2h, p = 0.30); nor arginase II expression (control:

1.48 ± 0.27, postmenopause: 1.47 ± 0.43 arbitrary unities, p = 0.99).

3.6 Fibrinogen levels in plasma

Plasma levels of fibrinogen were similar between control and postmenopausal groups

(Table 1).

3.7 Oxidative stress biomarkers

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The activity of the antioxidant enzyme SOD, but not catalase nor GPx, was enhanced

in postmenopause women compared to premenopausal women (Table 3). In regard to protein

expression, women in the postmenopausal state presented higher levels of catalase. No

significant differences between groups were observed for the antioxidant enzymes SOD and

GPx and for the pro-oxidant subunits gp91phox and p47phox of NADPH oxidase (Figure 5).

Increased levels of thiol groups was observed in the postmenopausal group (Table 3).

As described in Table 3, there was no difference in protein carbonylation between pre-

and postmenopausal women.

4 DISCUSSION

In this study, we aimed to investigate whether postmenopausal women presented

increased platelet reactivity, and also to study the L-arginine-NO-cGMP pathway in platelets

from this population. One important finding was that women in the early postmenopausal

state, and without any additional risk factor for cardiovascular disease, presented an increase

in platelet aggregation compared to premenopausal women. Controversial findings have been

reported in this respect. Roshan et al. [5] and Gu et al. [4] have shown elevated platelet

activation markers measured by flow cytometry, such as CD62P and PAC-1 in

postmenopausal women. On the other hand, Singla et al. [6] recently demonstrated that

platelet aggregation induced by collagen, adenosine diphosphate, and thrombin receptor

activating peptide measured by light transmission aggregometry did not differ between pre-

and postmenopausal women. We believe that the main difference from this to our study was

that our control group consisted of premenopausal women, with a mean age of 27 years old

(as opposed to 45 ± 4 years old).

It is possible that the elevated platelet activity observed in postmenopausal women

may be due to a reduced platelet production of NO. We observed impairment in NOS activity

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in these women, despite an unchanged expression of eNOS and iNOS, and an up-regulation of

transmembrane L-arginine transport. Nitric oxide is a cytochrome P450 reductase-like

haemoprotein that requires L-arginine as substrate, and flavin adenine dinucleotide, flavin

mononucleotide, calmodulin, and tetrahydrobiopterin (BH4) as cofactors for NO synthesis.

Despite an up-regulation of transmembrane L-arginine transport in platelets, it is possible that

the reduction of systemic L-arginine by 32% in postmenopausal women may contribute to

reduced NOS activity. Our group previously demonstrated low levels of L-arginine in chronic

renal and heart failure patients [22]. The increased L-arginine influx might also be a

compensatory response to the reduced NOS activity, as it would lead to an increased substrate

availability. Since both arginase and NOS use L-arginine as a substrate, an overxpression or

overactivity of the former would result in a limited substrate availability for NOS. However, it

was not observed a reduction in arginase expression nor its activity in postmenopausal

women, suggesting that L-arginine was not shifted to the urea cycle in platelets. Another

mechanism to explain the impairment of NOS activity in these women is the deficiency of

cofactors. Supporting this hypothesis, it was shown that ovariectomized rats possess reduced

BH4 content in aorta, and that its administration improved vascular endothelial function in this

experimental group [23].

Nitric oxide availability is also affected by oxidative stress status, since it rapidly

reacts with superoxide anion (6.7 x 109 M−1s−1) to form peroxynitrite. Superoxide anion

generated by NADPH oxidase serves as the starting material for the production of a vast

assortment of reactive oxidants, including oxidized halogens, free radicals, and singlet

oxygen. Platelets have been demonstrated to express only isoform 2 of NADPH oxidase [12].

Its structure is complex, consisting of two membrane-bound elements (gp91phox and p22 phox),

three cytosolic components (p67 phox, p47 phox and p40 phox), and a low-molecular-weight G

protein (either Rac 2 or Rac 1). Here we observed that platelet expression of gp91phox and p47

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phox, the last being responsible for transporting the cytosolic complex from the cytosol to the

membrane during enzyme activation, did not differ between the two groups. However, it is

not possible to conclude that platelet ROS formation is not increased in postmenopausal

women. Superoxide may be synthetized by other sources in platelets, such as cyclooxygenase,

xantine oxidase, cytochromes, and, in the absence of cofactors, even eNOS (‘eNOS

uncoupling’) [24]. Here, platelets from women in the postmenopausal state possessed

increased levels of thiol groups, and in the activity of SOD and expression of catalase, which

mediate ROS scavenging. The upregulation in antioxidant defense mechanisms usually occurs

in the presence of increased oxidative processes, so, although we did not observe any changes

in NADPH oxidase 2 subunits expression, we can not rule out the role of other superoxide

sources as stated before. In fact, the absence of superoxide anion or any other ROS

measurement was a limitation of this study.

The analysis of systemic amino acids revealed that other cationic amino acids that

compete for the same transporters of L-arginine – L-lysine and L-ornithine – were not altered

in postmenopausal women. On the other hand, the neutral amino acid methionine involved in

homocysteine metabolism, which is an important risk factor for cardiovascular disease was

reduced in postmenopausal compared to premenopausal women. Similarly, another neutral

amino acid, serine, which biosynthesis intersects glutaminolysis and together with this

pathway provides substrates for production of antioxidant gluthatione, was systemically

reduced after menopause.

The increased platelet reactivity may also be due to the reduced oestrogen levels that

follows menopause. Platelets have been shown to express both subtypes of oestrogen

receptors, α and β, with the predominance of β subtype [25]. Yet, the role of this hormone in

the modulation of platelet function is unclear. It has been demonstrated that female old mice

with deletion of type β oestrogen receptor present increased susceptibility to thrombogenesis

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compared to wild type animals [25]. However, inconsistent findings were observed in human

platelets. Nakano et al. [26] showed that platelets preincubation with β-oestradiol reduced its

activation, but Moro et al. [27] showed that β-oestradiol potentializated low dose thrombin-

induced platelet aggregation. It is also important to highlight that it is not known whether

menopause affects the expression of oestrogen receptors, and that both studies cited above

used platelets obtained not only from postmenopausal women. Unfortunately, our study

design does not allow us to ascribe our findings to reduced levels of oestrogen, since

modifications in the levels of this hormone are not the only biological changes after

menopause. In the same way, we can not affirm that hormone replacement therapy would

affect the variables measured.

Finally, circulating fibrinogen, which is independently associated with the incidence of

coronary events after adjusting for traditional cardiovascular risk factors, did not show any

alteration in postmenopausal women [28].

In conclusion, we have shown here the first evidence that NO generation is diminished

in platelets from postmenopausal women in the presence of low plasma levels of L-arginine,

with concomitant increase in platelet aggregation this group. In addition, intraplatelet

antioxidant defense is activated in these women. It is important to highlight that these women

did not present any known additional risk factor for cardiovascular disease. These findings

may contribute to a better understanding of platelet hyperaggregation in postmenopausal

women, which may help to further elucidate the heightened cardiovascular morbidity and

mortality in this population.

Contributions

WVM, TMC, ACMR and CM were involved in study conception and design, and data

analysis and interpretation. WVM, DCA, IRSM participated in data acquisition and drafted

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the manuscript. MBGBC participated in patient selection and data acquisition. TMC, ACMR,

MBGBC and CM revised the manuscript for important intellectual content. All authors

approved the final version of the manuscript.

Acknowledgements

This work was supported by the Brazilian funding agencies CNPq and FAPERJ.

5 REFERENCES

[1] Tuomikoski P, Mikkola TS. Postmenopausal hormone therapy and coronary heart disease

in early postmenopausal women. Ann Med 2014;46:1-7.

[2] Snoep JD, Roest M, Barendrecht AD, De Groot PG, Rosendaal FR, Van Der Bom JG.

High platelet reactivity is associated with myocardial infarction in premenopausal

women: a population-based case-control study. J Thromb Haemost 2010;8:906-13.

[3] Antithrombotic Trialists C, Baigent C, Blackwell L, Collins R, Emberson J, Godwin J, et

al. Aspirin in the primary and secondary prevention of vascular disease: collaborative

meta-analysis of individual participant data from randomised trials. Lancet

2009;373:1849-60.

[4] Gu J, Yang D, Wang L, Yin S, Kuang J. Effects of hormone replacement therapy on

platelet activation in postmenopausal women. Chin Med J (Engl) 2003;116:1134-6.

[5] Roshan TM, Normah J, Rehman A, Naing L. Effect of menopause on platelet activation

markers determined by flow cytometry. Am J Hematol 2005;80:257-61.

[6] Singla A, Bliden KP, Jeong YH, Abadilla K, Antonino MJ, Muse WC, et al. Platelet

reactivity and thrombogenicity in postmenopausal women. Menopause 2013;20:57-63.

[7] Erdmann J, Stark K, Esslinger UB, Rumpf PM, Koesling D, de Wit C, et al. Dysfunctional

nitric oxide signalling increases risk of myocardial infarction. Nature 2013;504:432-6.

Page 18 of 31

Accep

ted

Man

uscr

ipt

15

[8] Brunini TM, Yaqoob MM, Novaes Malagris LE, Ellory JC, Mann GE, Mendes Ribeiro

AC. Increased nitric oxide synthesis in uraemic platelets is dependent on L-arginine

transport via system y(+)L. Pflugers Arch 2003;445:547-50.

[9] Moss MB, Siqueira MA, Mann GE, Brunini TM, Mendes-Ribeiro AC. Platelet

aggregation in arterial hypertension: is there a nitric oxide-urea connection? Clin Exp

Pharmacol Physiol 2010;37:167-72.

[10] Ignarro LJ. Heme-dependent activation of guanylate cyclase by nitric oxide: a novel

signal transduction mechanism. Blood Vessels 1991;28:67-73.

[11] Babior BM. NADPH oxidase. Curr Opin Immunol 2004;16:42-7.

[12] Violi F, Pignatelli P. Platelet NOX, a novel target for anti-thrombotic treatment. Thromb

Haemost 2014;111:817-23.

[13] Siqueira MB, Firmino RT, Clementino MA, Martins CC, Granville-Garcia AF, Paiva

SM. Impact of traumatic dental injury on the quality of life of brazilian preschool

children. Int J Environ Res Public Health 2013;10:6422-41.

[14] Gokkusu C, Tata G, Ademoglu E, Tamer S. The benefits of hormone replacement

therapy on plasma and platelet antioxidant status and fatty acid composition in healthy

postmenopausal women. Platelets 2010;21:439-44.

[15] Chicoine LG, Paffett ML, Young TL, Nelin LD. Arginase inhibition increases nitric

oxide production in bovine pulmonary arterial endothelial cells. Am J Physiol

2004;287:L60-L8.

[16] Ribeiro AM, Brunini T, Yaqoob M, Aronson J, Mann G, Ellory J. Identification of

system y+ L as the high-affinity transporter for L-arginine in human platelets: up-

regulation of L-arginine influx in uraemia. Pflügers Archiv 1999;438:573-5.

Page 19 of 31

Accep

ted

Man

uscr

ipt

16

[17] Rodrigues Pereira N, Bandeira Moss M, Assumpcao CR, Cardoso CB, Mann GE,

Brunini TM, et al. Oxidative stress, l-arginine-nitric oxide and arginase pathways in

platelets from adolescents with anorexia nervosa. Blood Cells Mol Dis 2010;44:164-8.

[18] Ellman GL. Tissue sulfhydryl groups. Arch Biochem Biophys 1959;82:70-7.

[19] Wehr NB, Levine RL. Quantification of protein carbonylation. Cell Senescence:

Springer; 2013. p. 265-81.

[20] Ritchie J, Crawford V, McNulty M, Alexander H, Stout R. Effect of tourniquet pressure

and intra‐individual variability on plasma fibrinogen, platelet P‐selectin and monocyte

tissue factor. Clin Lab Haematol 2000;22:369-72.

[21] Florey CD. Sample size for beginners. BMJ 1993;306:1181-4.

[22] Ribeiro AM, Brunini T, Ellory J, Mann G. Abnormalities in L-arginine transport and

nitric oxide biosynthesis in chronic renal and heart failure. Cardiovasc Res 2001;49:697-

712.

[23] Lam K-K, Ho S-T, Yen M-H. Tetrahydrobiopterin improves vascular endothelial

function in ovariectomized rats. J Biomed Sci 2002;9:119-25.

[24] Pietraforte D, Vona R, Marchesi A, de Jacobis IT, Villani A, Del Principe D, et al. Redox

control of platelet functions in physiology and pathophysiology. Antioxid Redox Signal

2014;21:177-93.

[25] Jayachandran M, Preston CC, Hunter LW, Jahangir A, Owen WG, Korach KS, et al.

Loss of estrogen receptor beta decreases mitochondrial energetic potential and increases

thrombogenicity of platelets in aged female mice. Age (Dordr) 2010;32:109-21.

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Accep

ted

Man

uscr

ipt

17

[26] Nakano Y, Oshima T, Matsuura H, Kajiyama G, Kambe M. Effect of 17β-estradiol on

inhibition of platelet aggregation in vitro is mediated by an increase in NO synthesis.

Arteriosclerosis, thrombosis, and vascular biology 1998;18:961-7.

[27] Moro L, Reineri S, Piranda D, Pietrapiana D, Lova P, Bertoni A, et al. Nongenomic

effects of 17beta-estradiol in human platelets: potentiation of thrombin-induced

aggregation through estrogen receptor beta and Src kinase. Blood 2005;105:115-21.

[28] Corrado E, Rizzo M, Coppola G, Fattouch K, Novo G, Marturana I, et al. An update on

the role of markers of inflammation in atherosclerosis. J Atheroscler Thromb 2010;17:1-

11.

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Table 1 Clinical and laboratorial data of control and postmenopausal groups.

Postmenopausal Control p value

BMI (kg/m2)24.2 ± 0.8

(22.0 – 25.5)

21.7 ± 0.8

(20.1 – 23.4)

0.093

RBC (106/mm3)4.4 ± 0.1

(4.1 – 4.7)

4.6 ± 0.2

(4.2 – 4.9)

0.596

Leukocytes (103/mm3) 5.1 ± 1.2

(4.1 – 6.1)

5.6 ± 0.6

(4.3 – 6.9)

0.562

Haematocrit (%) 39.2 ± 0.9

(37.1 – 41.3)

38.5 ± 1.4

(35.4 – 41.6)

0.737

Haemoglobin (g/dL)12.9 ± 0.3

(12.2 – 13.7)

13.8 ± 0.4

(12.3 – 13.9)

0.794

Platelets (103/mm3)236.3 ± 15.7

(199 – 273)

223.4 ± 18.1

(185 – 262)

0.645

HDL Cholesterol (mg/dL) 65.0 ± 7.6

(46.9 – 83.1)

64.7 ± 4.2

(55.7 – 73.7)

0.972

LDL Cholesterol (mg/dL)127.8 ± 13.9

(92.0 – 164.0)

105.2 ± 9.7

(84.5 – 126.0)

0.216

Triglycerides (mg/dL)97.6 ± 18.6

(53.5 – 142.0)

69.9 ± 7.9

(53.0 – 86.9)

0.123

Glucose (mg/dL) 90.4 ± 2.9

(83.5 – 97.2)

86.3 ± 2.4

(81.0 – 91.6)

0.322

Creatinine (mmol/L)0.7 ± 0.1

(0.5 – 0.8)

0.8 ± 0.1

(0.7 – 0.9)

0.125

Oestradiol (mUI/mL)13.4 ± 1.3 *

(9.8 – 17.1)

74.0 ± 12.38

(39.6 – 108.3)

0.001

FSH (mUI/mL) 92.8 ± 6.9 *

(73.5 – 112.0)

5.2 ± 1.0

(2.3 – 8.1)

0.008

LH (mUI/mL)43.5 ± 5.7 *

(27.5 – 59.4)

3.6 ± 0.6

(1.9 – 5.3)

0.000

Progesterone (mUI/mL)0.11 ± 0.00*

(0.09 – 0.12)

0.19 ± 0.02

(0.12 – 0.25)

0.004

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Systolic pressure (mmHg) 113.6 ± 3.4

(106 – 121)

112.0 ± 2.5

(106 – 118)

0.706

Diastolic pressure (mmHg) 71.8 ± 2.3

(66.8 – 76.9)

72.0 ± 2.0

(67.5 – 76.5)

0.953

Fibrinogen (mg/dL)267.4 ± 21.8

(207.0 – 328.0)

280.2 ± 21.3

(231.0 – 329.0)

0.704

FSH, follicle stimulating hormone; HDL, high density lipoprotein; LDL, low density

lipoprotein; LH, Luteinizing hormone. Data are shown as mean ± SD (95% CI). *Different

from control (p ≤ 0.05).

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Table 2 – Plasma amino acid levels in control and postmenopausal groups.

Amino acid Postmenopausal Control p value

Aspartic Acid (µmol/L)

12.6 ± 0.8(10.3 – 14.9)

10.0 ± 2.5(2.1 - 17.9)

0.308

Arginine (µmol/L) 53.6 4.5 *(41.0 – 66.2)

79.2 3.3(68.6 – 89.9)

0.003

Lysine (µmol/L) 98.4 ± 3.4

(88.8 – 108.0)96.2 ± 3.9

(85.3 – 107.1)0.684

Methionine (µmol/L) 12.8 ± 0.7 *(10.8 – 14.8)

17.2 ± 1.2(13.3 – 21.2)

0,014

Ornithine (µmol/L) 38.8 ± 3.4

(29.3 – 48.3)42.5 ± 3.7

(30.5 – 54.5)0.491

Serine (µmol/L) 101.2 ± 4.8 *(87.9 – 114.5)

131.0 ± 8.4(104.4 – 157.6)

0.014

Tyrosine (µmol/L) 50.4 ± 2.8

(42.5 – 58.3)49.5 ± 2.4

(41.9 – 57.1)0.822

Threonine (µmol/L) 67.8 ± 7.0

(48.4 – 87.2)66.6 ± 8.2

(43.8 – 89.4)0.914

Tryptophan (µmol/L) 34.8 ± 4.5

(22.3 – 47.3)28.8 ± 2.4

(22.1 – 35.4)0.273

Data are show as mean ± SD (95% CI). *Different from control group (p ≤ 0.05).

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Table 3 - Biomarkers of oxidative stress in study groups.

Postmenopausal Control p value

Catalase (U/mg ptn)0.28 ± 0.05

(0.16 – 0.39)

0.27 ± 0.02

(0.22 – 0.32)0.610

SOD (U/mg ptn)167 ± 52 *

(48.52 – 287.30)

70 ± 9

(50.74 – 90.57)0.042

GPx (U/mg ptn)124 ± 17

(84.12 – 164.30)

156 ± 12

(130.90 – 182.60)0.129

Sulfhydryl group (µmol/mg ptn)12.77 ± 1.54 *

(9.38 – 16.15)

8.64 ± 0.57

(7.63 – 10.10)0.023

Protein oxidation (nmol/mg ptn)0.08 ± 0.01

(0.06 – 0.10)

0.08 ± 0.01

(0.06 – 0.10)0.917

Data are shown as mean ± SD (95% CI). *Different from control group (p ≤ 0.05). GPx,gluthatione peroxidase; SOD, superoxide dismutase.

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Figure 1. Schematic representation of intraplatelet L-arginine-nitric oxide pathway, including

the interplay between nitric oxide and superoxide anion. cGMP, cyclic guanosine

monophosphate; GPx, glutathione peroxidase; GTP, guanosine triphosphate; NO, nitric oxide;

NOS, nitric oxide synthase; NOX, NADPH oxidase; PDE 5, phosphodiesterase 5; PKG,

protein kinase G; sGC, soluble guanylyl cyclise; SOD, superoxide dismutase; XO, xanthine

oxidase.

Figure 2. Platelet aggregation induced by collagen (4 μg/mL). *Different from control group

(p = 0.02).

Figure 3. Total L-arginine transport and via system y+L in platelets. *Different from control

group (p ≤ 0.05).

Figure 4. Intraplatelet (A) activity and expression of iNOS (B) and eNOS (C) from

premenopausal and postmenopausal women. *Different from control group (p ≤ 0.05).

Figure 5. Protein expression of (A) catalase, (B) glutathione peroxidase (GPx), (C) NADPH

oxidase subunit p47phox, (E) NADPH oxidase subunit gp91phox. Representative Western Blots

are shown in (D). *Different from control group (p ≤ 0.05).

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Contributions

WVM, TMC, ACMR and CM were involved in study conception and design, and data

analysis and interpretation. WVM, DCA, IRSM participated in data acquisition and drafted

the manuscript. MBGBC participated in patient selection and data acquisition. TMC, ACMR,

MBGBC and CM revised the manuscript for important intellectual content. All authors

approved the final version of the manuscript.

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Figure 5