Lupus (2013) 22, 835838

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Aspirin resistance in systemic lupus erythematosus. A pilot study

A Akdogan1, L Kilic1, U Akman2, I Dogan1, O Karadag1, SA Bilgen1, Y Buyukasik2, S Kiraz1 and I Ertenli11Division of Rheumatology, Department of Internal Medicine, Hacettepe University Hospital, Turkey and 2Division of Hematology, Department

of Internal Medicine, Hacettepe University Hospital, Turkey

Systemic lupus erythematosus (SLE) patients are at increased risk of thrombosis and cardio-vascular diseases. Aspirin is an effective treatment option for these patients. The aim of thisstudy was to investigate the presence of aspirin resistance in SLE patients. We studied aspirinresistance in 33 SLE patients and nine healthy controls by using a Multiplate impedanceaggregometer (Dynabyte GmbH, Munich, Germany). Twenty-six SLE patients were on regu-lar aspirin treatment. Aspirin resistance was found in five (19.2%) out of 26 patients who wereon aspirin treatment. When the tests were repeated by adding acetylsalicylic acid in themedium, all of these patients became responsive to the aspirin. SLE disease activity, bodymass index, smoking status, and the presence of anticardiolipin antibodies or positive lupusanticoagulant test results were no different in patients with or without aspirin resistance.(p> 0.05 for all). Our results suggest that there may be a considerable number of SLE patientswith aspirin resistance. Lupus (2013) 22, 835838.

Key words: SLE; aspirin; aspirin resistance

Introduction

Systemic lupus erythematosus (SLE) patients are atincreased risk of thrombosis and cardiovasculardiseases. Women aged 3544 years with SLE havea 50 times greater risk of myocardial infarction.1

Cardiovascular diseases are the leading cause ofmortality in the late phase of the disease.1,2

Premature atherosclerosis in SLE cannot be fullyexplained by traditional cardiovascular risk factors.Annual screening of SLE patients for the presenceof cardiovascular diseases and cardiovascular riskfactors is recommended for early identication andtreatment of patients at high risk.2

Aspirin is an eective treatment option for bothprimary and secondary prevention of cardiovascu-lar diseases.3 Inhibition of thromboxane synthesisis considered to be the main mechanism of the anti-aggregant eect of aspirin.4 Response to aspirintreatment is variable and the presence of aspirinresistance is suggested to be associated with poorprognosis in cardiovascular disorders.5,6 Moreover,aspirin resistance can also be associated with

complications during pregnancy.7 The aim of thispilot study was to investigate the presence ofaspirin resistance in SLE patients.

Methods

The study was conducted in SLE patients who ful-lled the American College of Rheumatology clas-sication criteria for SLE8 and healthy controls.Pregnant patients, patients who were receiving non-steroidal anti-inammatory drugs or those who hadincreased serum creatinine levels (>1.2mg/dl) wereexcluded. All subjects had a complete history andphysical examination. Body mass index (BMI)(weight/height (kg/m2)) was determined in eachsubject. SLE disease activity was dened by usingSafety of Estrogens in Lupus ErythematosusNational Assessment-Systemic LupusErythematosus Disease Activity Index (SELENA-SLEDAI) scores.9

Hyperlipidemia was dened as low-density lipo-protein level> 160mg/dl or being on treatmentwith hypolipidemic drugs. Smoking status wasdened as smoker or nonsmoker. Family historyof atherosclerotic vascular disease was consideredpositive if a rst-degree relative had the diseasebefore 45 and 55 years of age in men and women,respectively.

Correspondence to: Levent Kilic, Hacettepe University Hospital,

Department of Internal Medicine, Division of Rheumatology,

Sihhiye Ankara 06100, Turkey.

Email: drleventkilic@yahoo.com

Received 12 November 2012; accepted 14 May 2013

! The Author(s), 2013. Reprints and permissions: http://www.sagepub.co.uk/journalsPermissions.nav 10.1177/0961203313493487

Aspirin resistance

The tests were performed by a Multiplate imped-ance aggregometer (Dynabyte GmbH, Munich,Germany). Three millimeters of blood sampleswere collected in the test tubes provided by themanufacturer of the instrument (Hirudin bloodtube, Dynabyte GmbH, Munich, Germany). Thesamples were kept at room temperature for 30min-utes before testing. Assays were performed withinone hour. Whole blood (300ml) was added to a testtube containing 300 ml of 0.9% saline at 37C. Afterincubation for 3minutes at 37C, 20mM agonist(1mM thrombin receptor activating peptide(TRAP), 0.2mM adenosine diphosphate or0.2mM arachidonic acid, Dynabyte GmbH,Munich, Germany) was added. The instrumentmeasures platelet aggregation for 6minutes byimpedance method in duplicate and gives themean value of area under the curve (AUC) meas-urements of the duplicate aggregation curves.Coecients of variations for the duplicate testresults were 4%7% for TRAP-induced and 5%7% for arachidonic acid (ASPI)-induced aggrega-tion tests (TRAPtest and ASPItest levels, DynabyteGmbH, Munich, Germany). Aspirin resistance wasdened if ASPI-induced and TRAP-induced aggre-gation test values were> 300 AUC and between800 and 1300 AUC, respectively.If the ASPI-induced tests were positive (indi-

cating insucient platelet inhibition with aspirin(> 300 AUC)), then the test was repeated in thepresence of 1mg/ml acetylsalicylic acid in themedium (ASA control, Dynabyte GmbH,Munich, Germany).

Statistics

Values are expressed as mean SD, unless indi-cated otherwise. We used Fishers exact and chisquare tests for comparison of categorical variablesor percentages. Kruskal-Wallis test and Mann-Whitney U test were used to compare parametersamong the groups whenever appropriate. A p valueof less than 0.05 was considered as statisticallysignicant.

Results

We studied 33 (female (F)/male (M): 29/4) SLEpatients and nine (F/M: 8/1) healthy controls.General characteristics of the SLE patients areshown in the Table 1. Twenty-six (78.8%) patientswere on regular aspirin treatment with 100mg dose,except one who received 100mg aspirin on alter-nate days. There were no dierences among

patients with and without aspirin treatment andhealthy controls in terms of age and gender(p 0.28 and p 0.36, respectively).Drugs used for controlling disease activity in SLE

patients were as follows: corticosteroids in 27(81.8%) patients, hydroxychloroquine in 33(100.0%), azathioprine in 11 (33.3%), methotrexatein one (3.0%), cyclophosphamide in two (6.1%),mycophenolate mofetil in four (12.1%), andrituximab in two (6.1%) patients. Twenty-twopatients were on low-dose corticosteroid treatment(

undetermined test results. The SELENA-SLEDAIscores (median 3 (range: 23) vs median 2 (range:08); p 0.47) and the mean BMI (22.99 3.27 vs26.81 5.94; p 0.19) were no dierent in SLEpatients with and without aspirin resistance. Thenumber of smokers (one of ve (20.0%) patientsvs seven of 19 (36.8%) patients; p 0.63), patientswith a history of thrombosis (0 of ve (0%) patientsvs four of 19 (21.1%) patients, p 0.54), patientswith positive anticardiolipin antibodies (aCL) orlupus anticoagulant (LA) test results (two of ve(40.0%) patients vs seven of 19 (36.8%) patients;p 1.00) were also no dierent between SLEpatients with and without aspirin resistance.There was no dierence in ASPI-induced aggre-

gation test results among SLE patients withaspirin resistance, SLE patients who were not onaspirin treatment, and healthy controls (p 0.10)(Figure 1).

Discussion

Aspirin resistance was present in 19.2% of the SLEpatients who were on regular aspirin treatment inthis study. In aspirin-resistant patients when thetests were repeated by adding ASA to themedium, all aspirin-resistant patients becameresponsive to aspirin. Neither SLE disease activitynor BMI were associated with aspirin resistance.The prevalence of aspirin resistance varies widely

in studies conducted in dierent populations and isreported to be present in up to 60% of subjects.4

Data on the presence of aspirin resistance are limitedin SLE. Avalos et al.10 studied urinary excretion ofthromboxane A2 metabolites in 74 SLE patients, ofwhom 16 were on regular aspirin treatment. In thatstudy 11-dehydro thromboxane B2 excretion was thesame among those taking aspirin and those whowere not, and four SLE patients (25%) who wereon aspirin had 11-dehydro thromboxane B2 excre-tion greater than the 75th percentile of the patientswho were not on aspirin.10 Our results are consistentwith the previous ndings. We detected aspirinresistance in 19.2% of SLE patients who were onregular aspirin treatment. Inammation, increasein thromboxane A2 synthesis, high platelet turnover,smoking, genetic variations, impaired renal func-tion, tachyphylaxis, and obesity can all be associatedwith reduced antithrombotic eects of aspirin.1113

Drug interactions should also be considered.11 Inthis study serum creatinine levels were withinnormal limits in all SLE patients. There was no dif-ference between SLE patients with and withoutaspirin resistance in terms of SLE disease activity,BMI, and smoking status.

Aspirin is recommended in SLE patients withknown cardiovascular disease, hypertension, dia-betes mellitus, hyperlipidemia, positive aCL, posi-tive LA test, and in smokers.1,14 In this study wedid not determine the indications for aspirin indi-vidually but it is clear that most SLE patients likelybenet from this treatment. On the other hand, arandomized, double-blind, placebo-controlled trialfocusing on primary thrombosis prevention inpatients with antiphospholipid syndrome, inwhich 65% of the patients had SLE, found no dif-ferences between patients treated with aspirin andplacebo.15

Aspirin dosage ranges from 50 to 650mg/day forthe treatment or prevention of cardiovascular dis-eases. Side eects of aspirin increase with thedosage. Therefore low-dose aspirin is recom-mended for the treatment of cardiovascular dis-eases.16 There was no dierence in ASPI-inducedaggregation test results among aspirin-resistantpatients, patients not on aspirin, and healthy con-trols in our study, indicating that low-dose aspirinhas no eect on some SLE patients. All of ouraspirin-resistant patients were considered to beresponsive to aspirin after repeating the tests byaddition of aspirin in vitro. Increased thromboxaneA2 synthesis is suggested as being one of the

Figure 1 Arachidonic acid (ASPI)-induced aggregation testresults. eGroup Ia Group IIb Group IIIc Group IVd aGroupI: aspirin-resistant SLE patients. bGroup II: aspirin-responsiveSLE patients. cGroup II: SLE patients who were not on aspirintreatment. dGroup IV: healthy controls. eAfter excluding SLEpatients with undetermined aggregation test results.SLE: systemic lupus erythematosus.

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mechanisms of reduced responsiveness to aspirintreatment in SLE.10 Aspirin resistance can bereversed by increasing the dose of aspirin.17 Inthis case increasing the dose of aspirin may be asimple solution. On the other hand SLE patients,as they are usually on multidrug treatment, areprone to aspirin side eects. Therefore using otheragents with antithrombotic eects such as clopido-grel or dipyridamole may be a potential alternativein this patient group.18

Aspirin usage was determined based on patientsdeclarations; we did not measure the serum salicyl-ate levels to conrm the patients compliance toaspirin. Patient compliance to treatment is one ofthe important points in the presence of aspirinresistance.11 Aspirin resistance can be changedover time but in this study we tested SLE patientsonly once.19 Our preliminary results should be sup-ported in larger series to document the associationbetween aspirin resistance and disease manifest-ations such as the presence of antiphospholipidsyndrome.In conclusion, our results suggest that there may

be a considerable number of SLE patients withaspirin resistance. Although the clinical signicanceof laboratory aspirin resistance is still controversial,accurate evaluation of the eectiveness of any drugis crucial in systemic diseases such as SLE.

Funding

This research received no specic grant from anyfunding agency in the public, commercial, or not-for-prot sectors.

Conflict of interest statement

The authors have no conicts of interest to declare.

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