Arthritis Care & Research Vol. 66, No. 10, October 2014, pp 1528 –1535 DOI 10.1002/acr.22340 © 2014, American College of Rheumatology

ORIGINAL ARTICLE

Relationship Between Homocysteine Levels and Hypertension in Systemic Lupus Erythematosus JOSE´ MARIO SABIO,1 JOSE´ ANTONIO VARGAS-HITOS,1 JOSEFINA MARTINEZ-BORDONADO,1 NURIA NAVARRETE-NAVARRETE,1 ANTONIO DI´AZ-CHAMORRO,1 CARMEN OLVERA-PORCEL,2 ´ NICA ZAMORA-PASADAS,1 AND JUAN JIME´NEZ-ALONSO1 MO

Objective. Homocysteine has been linked to atherosclerosis and hypertension (HT) in the general population. However, there is limited evidence regarding the effect of homocysteine on blood pressure and arterial stiffness in systemic lupus erythematosus (SLE). We examined whether homocysteine is associated with HT and arterial stiffness in women with SLE. Methods. In total, 99 women with SLE without a history of cardiovascular disease or diabetes mellitus and 101 matched controls were included in this cross-sectional study. Participants were analyzed for homocysteine levels, cardiovascular risk factors, and arterial stiffness assessed by means of carotid–femoral pulse wave velocity (PWV). Associations between homocysteine, systolic blood pressure (SBP), PWV, and HT were tested using univariate and multivariate analyses. Results. Homocysteine levels (mean ⴞ SD 12.3 ⴞ 4.8 versus 9.3 ⴞ 3.8 ␮moles/liter), PWV (mean ⴞ SD 7.54 ⴞ 1.1 versus 7.10 ⴞ 1.1 meters/second), SBP (mean ⴞ SD 119 ⴞ 13 versus 115 ⴞ 12 mm Hg), and the prevalence of hyperhomocysteinemia (23% versus 7%) and HT (43% versus 12%) were significantly higher in women with SLE (P < 0.050 for all). In the univariate analysis, homocysteine correlated positively with SBP (P ⴝ 0.001) and PWV (P ⴝ 0.023) in women with SLE but not in controls. In the multiple linear regression analysis, SBP was independently associated with homocysteine and body mass index (BMI) in women with SLE. Similarly, in the multivariate logistic regression analysis, homocysteine levels (or hyperhomocysteinemia), BMI, and daily prednisone dose were independently associated with HT in women with SLE. Conclusion. Homocysteine was independently associated with SBP and HT in women with SLE, but not in controls. Elevated homocysteine levels could increase the risk of HT in SLE.

INTRODUCTION Patients with systemic lupus erythematosus (SLE) have a 4 –10-fold increased risk of cardiovascular diseases (CVD) compared with the general population (1) because they experience early and accelerated atherosclerosis as a consequence of a complex interaction between systemic SLErelated inflammation, traditional cardiovascular risk factors, and side effects of therapies for SLE (2). Despite the comprehensive research carried out in recent decades, the 1 Jose´ Mario Sabio, MD, PhD, Jose´ Antonio Vargas-Hitos, MD, PhD, Josefina Martinez-Bordonado, MD, Nuria NavarreteNavarrete, MD, PhD, Antonio Dı´az-Chamorro, MD, Mo´nica Zamora-Pasadas, MD, PhD, Juan Jime´nez-Alonso, MD, PhD: Virgen de las Nieves University Hospital, Granada, Spain; 2 Carmen Olvera-Porcel, PhD: Investigacio´n Biosanitaria de Andalucı´a Oriental Foundation, Granada, Spain. Address correspondence to Jose´ Mario Sabio, MD, PhD, Department of Internal Medicine, 9th floor, Virgen de las Nieves University Hospital, Avenida Fuerzas Armadas Numero 2, 18012 Granada, Spain. E-mail: [email protected]. Submitted for publication November 12, 2013; accepted in revised form March 25, 2014.

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precise mechanisms involved in this phenomenon are not yet completely elucidated and new pathways must be explored. The prevalence of hypertension (HT) in SLE patients is higher than in the general population (3) and is one of the most important modifiable factors implicated in the development of atherosclerosis in SLE (4). The physiopathology of HT in SLE is complex (5) and a combination of SLErelated factors and conventional risk factors have been described (3). Elevated homocysteine has been shown to be a moderately strong and independent cardiovascular risk factor in healthy populations (6). This association appears to be particularly strong in older people, in which the level of homocysteine has even been shown to be a better predictor of cardiovascular mortality than models based on classic Framingham risk factors (7). Homocysteine also has been associated with arterial stiffness (8) and HT, especially in the elderly. In this regard, several studies have described a significant positive relationship between homocysteine and blood pressure (BP) (9) as well as higher homocysteine levels in hypertensive patients compared with normoten-

Hypertension and Homocysteine Levels in SLE

Significance & Innovations ●

Homocysteine levels were independently associated with systolic blood pressure and hypertension (HT) in women with systemic lupus erythematosus (SLE).

●

Homocysteine might play a role in the physiopathology of HT in SLE.

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SLE patients might be more vulnerable to the toxic effect of homocysteine on vasculature than the general population.

sive subjects (10). In SLE, elevated homocysteine has been associated with clinical CVD, atherothrombosis, higher coronary artery calcification, and increased arterial stiffness (11–14) and has also been found to be an independent risk factor for progression of atherosclerosis (15,16). However, to our knowledge, homocysteine has never been associated with BP in SLE patients, and studies linking hyperhomocysteinemia with HT in these patients are lacking. The purpose of the present study was to establish a possible association between homocysteine and systolic BP (SBP) and HT in a cohort of women with SLE and its impact on arterial stiffness as a surrogate marker of subclinical atherosclerosis.

PATIENTS AND METHODS Participants and study design. Consecutive nonpregnant women with SLE ⱖ18 years of age attending our Systemic Autoimmune Diseases Unit were included in the study. In addition, a control group matched for sex, age, and education level recruited mainly among nonmedical staff of our hospital that attended their annual medical health examination and who were invited to participate was included. A smaller proportion of controls were recruited from the investigators’ acquaintances. We excluded women with SLE who had ⬍1 year of followup or those who had not been reviewed at least once during the previous year since the beginning of the study. Likewise, participants with a history of overt CVD (acute myocardial infarction, angina pectoris, stroke, or peripheral arterial disease), diabetes mellitus, or morbid obesity, which may hinder pulse wave velocity (PWV) measurements, were also excluded. All participants were white. The study was approved by the Institutional Review Board of Virgen de las Nieves University Hospital and all subjects gave written informed consent. Participants were evaluated using a standardized clinical interview. Fasting blood specimens for biochemical and immunologic tests were collected and routinely processed using the techniques performed by the central laboratory of our hospital. Plasma homocysteine concentrations were determined using fluorescence polarization immunoassay (AxSYM Homocysteine; Abbott Laboratories). Hyperhomocysteinemia was defined as homocysteine levels in plasma ⱖ15 ␮moles/liter. The homeostatic

1529 model assessment-insulin resistance (HOMA-IR) was calculated using the formula (HOMA-IR ⫽ glucose [mmoles/ liter] ⫻ insulin [␮U/liter]/22.5). The estimated glomerular filtration rate (eGFR) was automatically calculated using the Modification of Diet in Renal Disease 7 equation (calculator online at http://www.semergencantabria.org/calc/ cacalc.htm). BP was measured in duplicate separated by 5 minutes on the dominant arm with the subject in a seated position after at least 5 minutes of rest using a validated automatic oscillometric device (HEM-7051T; Omron Health Care). BP was considered as the lowest measure taken. HT was deemed to be present if SBP was ⬎140 mm Hg and/or diastolic BP (DBP) was ⬎90 mm Hg or if the subject was taking medication for HT. Obesity was defined as body mass index (BMI) ⬎30 kg/m2. Participants were considered smokers if they had smoked at least 1 cigarette per day during the year before inclusion. Menopause status was considered as ⬎1 year since the last menstrual period. Low physical activity was defined as ⬍3 days/ week of at least 45 minutes of moderate to intense aerobic physical exercise. Metabolic syndrome was defined using the National Cholesterol Education Program Adult Treatment Panel III criteria (17). Disease activity and accrual of organ damage were measured using the Safety of Estrogens in Lupus Erythematosus National Assessment version of the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) (18) and the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI) (19), respectively. Arterial stiffness was evaluated by measuring carotid– femoral PWV using an automatic device (Complior Analyse; ALAM-MEDICAL) by a single blinded operator (JAV-H) unaware of patient information. PWV was assessed in subjects in the supine position by a tonometry system that detects the pulse waveforms of the right common carotid and right femoral arteries automatically. The distance traveled by the pulse wave is measured over the body surface as the distance between the 2 recording sites. Aortic PWV is automatically calculated as the ratio of the distance to the transit time (meters/second). The validation of this automatic method and its reproducibility has been well-established (20). Statistical analysis. Summary statistics are expressed as the percentage and odds ratio (OR; 95% confidence interval [95% CI]) for categorical data, mean ⫾ SD for approximately normally distributed continuous variables, and median (interquartile range [IQR]) for skewed continuous variables. Comparison between groups was made using the chi-square test for categorical data and Student’s t-test or the Mann-Whitney U test for continuous data, as appropriate. Unadjusted or linear regression analyses (Pearson’s correlation coefficient test) were used to determine the relationship between homocysteine concentrations or SBP and PWV and other clinical and analytical variables. A multiple linear regression analysis and multivariate logistic regression analysis was used to determine which variables were independently associated with SBP or HT in women with SLE, respectively. A 2-sided P value less than 0.05 was considered statistically significant. All

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Table 1. Demographic characteristics, cardiovascular disease risk factors, and SLE features of the women with SLE and controls* Women with SLE (n ⴝ 99)

Control group (n ⴝ 101)

37 ⫾ 11 36 (29–47)

37 ⫾ 11 37 (29–47)

66 34 26 ⫾ 11 11 ⫾ 7 24 ⫾ 4 119 ⫾ 13 75 ⫾ 10 43 6 24 51 25 44 86 ⫾ 25 12 101 ⫾ 25 60 ⫾ 15 91 ⫾ 42 15 26 ⫾ 24 0.1 (0.1–0.3) 12.3 ⫾ 4.8 23 9.1 ⫾ 6.2 1.6 (1.1–2.1) 11 2 (0–4) 0 (0–1) 7.54 ⫾ 1.1 43 89 ⫾ 21 15 ⫾ 7 15 25 20 40 2.5 (0–5) 58 88 40

70 30 – – 24 ⫾ 4 115 ⫾ 12 72 ⫾ 9 12 5 30 50 20 – 95 ⫾ 19 0 113 ⫾ 32 67 ⫾ 15 73 ⫾ 37 – 14 ⫾ 8 0.1 (0.1–0.2) 9.3 ⫾ 3.8 7 7.1 ⫾ 3.7 1.2 (0.9–1.7) 4 – – 7.10 ⫾ 1.1 – – – – – 3 6 – – – –

Age, years Median (interquartile range) Education level, % Secondary education University education Age at diagnosis, years SLE duration, years Body mass index, kg/m2 Systolic blood pressure, mm Hg Diastolic blood pressure, mm Hg Hypertension, % Obesity, % Current smoker, % Low physical activity, % Menopause status, % History of lupus nephritis, % eGFR, ml/minute/1.73 m2 eGFR ⬍60 ml/minute/1.73 m2, % Low density lipoprotein cholesterol, mg/dl High density lipoprotein cholesterol, mg/dl Triglycerides, mg/dl 24-hour proteinuria (⬎0.5 grams), % Erythrocyte sedimentation rate, mm/hour C-reactive protein level, mg/dl‡ Homocysteine, ␮moles/liter Hyperhomocysteinemia, % Insulin, ␮U/ml HOMA-IR‡ Metabolic syndrome, % SLEDAI score‡ SDI score‡ Pulse wave velocity, meters/second Positive anti-dsDNA (⬎30 U/liter), % C3 complement, mg/dl C4 complement, mg/dl Antiphospholipid syndrome, % Antiphospholipid antibodies, % Statin, % Antihypertensive drugs, % Current prednisone dosage, mg/day‡ Prednisone, % Hydroxychloroquine, % Immunosuppressive agents, %

P† 0.865

0.521 0.448 – – 0.417 0.028 0.031 ⬍ 0.001 0.763 0.428 0.779 0.399 – 0.009 ⬍ 0.001 0.004 0.002 0.001 – ⬍ 0.001 0.008 ⬍ 0.001 0.042 0.009 0.021 0.050 – – 0.006 – – – – – ⬍ 0.001 ⬍ 0.001 – – – –

* Values are the mean ⫾ SD unless indicated otherwise. SLE ⫽ systemic lupus erythematosus; eGFR ⫽ estimated glomerular filtration rate; HOMA-IR ⫽ homeostatic model assessment-insulin resistance; SLEDAI ⫽ Systemic Lupus Erythematosus Disease Activity Index; SDI ⫽ Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index; anti-dsDNA ⫽ anti– double-stranded DNA. † Student’s t-test. ‡ Values are the median (interquartile range).

analyses were completed using SPSS statistical software, version 15.0.

RESULTS We recruited 99 women with SLE and 101 controls. The median age of the women with SLE was 36 years (IQR 29 – 47 years), with a median disease duration of 10 years (IQR 6 –16 years). The majority of the patients had stable

disease, with a median SLEDAI score of 2 (IQR 0 – 4); 26% had a SLEDAI score of 0 and 92% had a SLEDAI score ⱕ4. Prednisone and hydroxychloroquine were taken by 58% and 88% of the patients, respectively. The median daily prednisone dose was 2.5 mg (IQR 0 –5), and the median accumulated prednisone dose in the last year was 0.9 grams (IQR 0 –1.9). Immunosuppressant drugs were used concurrently in 40% of the patients (5% azathioprine, 12% methotrexate, and 24% mycophenolate mofetil);

Hypertension and Homocysteine Levels in SLE

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Table 2. Comparison between women with SLE who did and did not have hyperhomocysteinemia and hypertension* Hyperhomocysteinemia Normohomocysteinemia (n ⴝ 23) (n ⴝ 76) Age, years Body mass index, kg/m2 Homocysteine, ␮moles/liter Hyperhomocysteinemia, % Systolic blood pressure, mm Hg Diastolic blood pressure, mm Hg Low density lipoprotein, mg/dl High density lipoprotein, mg/dl Triglycerides, mg/dl eGFR, ml/minute/1.73 m2 24-hour proteinuria, grams§ HOMA-IR§ Metabolic syndrome, % Hypertension, % Pulse wave velocity, meters/second Age at diagnosis, years SLE duration, years SLEDAI§ SDI§ C-reactive protein level, mg/dl ESR, mm/hour Anti-dsDNA antibodies, IU/ml C3 complement, mg/dl C4 complement, mg/dl Antihypertensive drugs, % ACE inhibitors Angiotensin II receptor blockers Calcium-channel blockers Beta-blockers Diuretics Statins, %

42 ⫾ 10 25 ⫾ 5 19.1 ⫾ 4.8 – 125 ⫾ 14

36 ⫾ 11 24 ⫾ 3 10.3 ⫾ 2.4 – 117 ⫾ 12

81 ⫾ 11

73 ⫾ 9

106 ⫾ 32

P†

Hypertensive Nonhypertensive (n ⴝ 43) (n ⴝ 56)

P‡

37 ⫾ 11 26 ⫾ 5 13.7 ⫾ 6.2 35 125 ⫾ 13

37 ⫾ 11 23 ⫾ 3 11.2 ⫾ 3.1 12 115 ⫾ 10

0.003

79 ⫾ 12

72 ⫾ 8

0.001

100 ⫾ 23

0.762

97 ⫾ 25

103 ⫾ 26

0.213

55 ⫾ 16

62 ⫾ 14

0.044

60 ⫾ 14

60 ⫾ 14

0.911

114 ⫾ 41 63 ⫾ 23 0.1 (0–0.5)

85 ⫾ 40 93 ⫾ 22 0 (0–0.2)

0.001 ⬍ 0.001 0.117

103 ⫾ 45 84 ⫾ 33 0.2 (0–0.7)

83 ⫾ 37 88 ⫾ 17 0 (0–1.0)

0.020 0.437 0.008

1.5 (1.1–1.9) 26 65 8.01 ⫾ 1.06

1.6 (1.0–2.2) 7 36 7.39 ⫾ 1.01

0.980 1.6 (1.2–2.3) 0.042 21 0.018 – 0.021 7.62 ⫾ 1.19

1.6 (1.0–2.1) 4 – 7.48 ⫾ 0.94

0.916 0.009 – 0.526

28 ⫾ 10 14 ⫾ 8 4.0 (0.8–4.0) 1.0 (0–2) 0.25 ⫾ 0.28

25 ⫾ 8 10 ⫾ 7 2.0 (0–4.4) 0 (0–0) 0.30 ⫾ 0.70

0.140 0.050 0.198 0.003 0.398

25 ⫾ 11 12 ⫾ 8 2.0 (0–4) 0 (0–2) 0.27 ⫾ 0.28

27 ⫾ 11 11 ⫾ 7 2.0 (1.3–4) 0 (0–0) 0.40 ⫾ 0.80

0.452 0.370 0.348 0.006 0.480

27 ⫾ 22 83 ⫾ 122

25 ⫾ 24 143 ⫾ 575

0.542 0.169

29 ⫾ 27 100 ⫾ 229

24 ⫾ 20 150 ⫾ 545

0.539 0.573

83 ⫾ 20 15 ⫾ 8 61 35 30

90 ⫾ 21 15 ⫾ 7 33 22 13

0.142 0.966 0.013 0.265 0.050

87 ⫾ 18 16 ⫾ 8

91 ⫾ 23 15 ⫾ 7

0.223 0.649

18

4

0.043

22 39 43

4 5 13

0.013 ⬍ 0.001 0.002

0.023 0.766 ⬍ 0.001 – 0.009

0.871 0.001 0.011 0.008 ⬍ 0.001

* Values are the mean ⫾ SD unless otherwise indicated. SLE ⫽ systemic lupus erythematosus; eGFR ⫽ estimated glomerular filtration rate; HOMA-IR ⫽ homeostatic model assessment-insulin resistance; SLEDAI ⫽ Systemic Lupus Erythematosus Disease Activity Index; SDI ⫽ Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index; ESR ⫽ erythrocyte sedimentation rate; anti-dsDNA ⫽ anti– doublestranded DNA; ACE ⫽ angiotensin-converting enzyme. † Mann-Whitney U test. ‡ Student’s t-test. § Values are the median (interquartile range).

these patients had a higher SLEDAI score than those patients who were not taking immunosuppressant drugs (median 3 [IQR 2– 4] versus median 2 [IQR 0 – 4]; P ⫽ 0.013). The main indications for the use of immunosuppressant drugs were lupus nephritis (52%), musculoskeletal manifestations (22%), cutaneous manifestations (15%), cytopenias (7%), and others (4%). The baseline demographic and clinical characteristics of the study participants are shown in Table 1. Homocysteine was significantly higher in women with SLE than in controls (mean ⫾ SD 12.3 ⫾ 4.8 versus 9.3 ⫾

3.8 ␮moles/liter; P ⫽ 0.009). Moreover, 23% of women with SLE and 7% of controls had hyperhomocysteinemia (OR 4.1 [95% CI 1.6 –10.8], P ⫽ 0.002). PWV in women with SLE was higher compared with controls (mean ⫾ SD 7.54 ⫾ 1.1 versus 7.10 ⫾ 1.1 meters/second; P ⫽ 0.006), denoting a greater atherosclerosis burden in this group. SBP and DBP were higher in women with SLE despite the fact that the intake of antihypertensive drugs was more than 6-fold greater in this group compared with controls (40% versus 6%; OR 11 [95% CI 4 –27], P ⬍ 0.001). The type of antihypertensives taken by women with SLE ver-

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sus controls was as follows: angiotensin-converting enzyme (ACE) inhibitor (25% versus 1%), angiotensin II receptor blockers (18% versus 4%), diuretics (13% versus 3%), and calcium-channel blockers and beta-blockers (8% versus 0%; P ⱕ0.009 in all comparisons). However, lowdensity lipoprotein cholesterol was lower in the SLE group (mean ⫾ SD 101 ⫾ 25 versus 113 ⫾ 32; P ⫽ 0.004), probably because the use of statins was considerably higher in this group (20% versus 3%; OR 8 [95% CI 2–27], P ⬍ 0.001). The differences between the women with SLE who did and did not have hyperhomocysteinemia are shown in the Table 2. The women with SLE who had hyperhomocysteinemia were older (P ⫽ 0.023), had higher SBP (P ⫽ 0.009) and DBP (P ⫽ 0.003), had higher eGFR (P ⬍ 0.001), had higher triglycerides (P ⫽ 0.001), had longer SLE duration (P ⫽ 0.050), had higher PWV (P ⫽ 0.021), and had lower high-density lipoprotein cholesterol (P ⫽ 0.044) than those who did not have hyperhomocysteinemia. Moreover, the prevalence of HT (65% versus 36%; OR 3.4 [95% CI 1.3– 8.8], P ⫽ 0.018) and metabolic syndrome (26% versus 7%; OR 4.2 [95% CI 1.1–16.0], P ⫽ 0.042) was higher in patients with hyperhomocysteinemia than in those without hyperhomocysteinemia. In the control group, no differences between the women with hyperhomocysteinemia and normohomocysteinemia were found, including SBP, DBP, and frequency of HT (data not shown). The differences between hypertensive and normotensive women with SLE are shown in Table 2. In contrast with controls (data not shown), hypertensive women with SLE had higher homocysteine levels than normotensive subjects (mean ⫾ SD 13.7 ⫾ 6.2 versus 11.2 ⫾ 3.1 ␮moles/ liter; P ⫽ 0.011) and the frequency of hyperhomocysteinemia was greater than in normotensive subjects (35% versus 12%; OR 3.9 [95% CI 1.4 –11], P ⫽ 0.008). In the univariate analysis, homocysteine was positively associated with PWV in SLE patients (r ⫽ 0.230, P ⫽ 0.023) but not in the control group. This association disappeared after adjustment for age, SBP, eGFR, or SDI. In the unadjusted univariate analysis, a significant correlation between SBP and homocysteine was found in women with SLE (r ⫽ 0.327, P ⫽ 0.001) but not in controls. In addition, SBP correlated with BMI (r ⫽ 0.327, P ⬍ 0.001) and SDI (r ⫽ 0.217, P ⫽ 0.029) but not with age (r ⫽ 0.172, P ⫽ 0.085), SLE duration, lipid profile, eGFR, HOMA-IR, SLEDAI, C3, C4, or daily prednisone dose. In the multiple linear regression analysis that included the abovementioned significant variables (i.e., homocysteine, BMI, and SDI), homocysteine and BMI emerged as indeTable 3. Variables independently associated with systolic blood pressure Variable

␤ coefficient

95% confidence interval

P*

Homocysteine Body mass index

0.75 1.10

0.27–1.24 0.47–1.72

0.003 0.001

* Multiple linear regression analysis.

Table 4. Variables independently associated with hypertension using homocysteine levels (model A) or hyperhomocysteinemia (model B) in the multivariate logistic regression analysis*

␤ coefficient Model A BMI Homocysteine Prednisone Model B BMI Hyperhomocysteinemia Prednisone

95% CI

P

1.28 1.15 1.16

1.09–1.50 1.01–1.32 1.01–1.32

0.003 0.038 0.032

1.30 3.88 1.15

1.10–1.53 1.11–13.5 1.01–1.33

0.002 0.033 0.032

* 95% CI ⫽ 95% confidence interval; BMI ⫽ body mass index; prednisone ⫽ daily prednisone dose.

pendent factors associated with SBP in women with SLE (Table 3). Finally, a multivariate regression analysis was carried out to identify factors independently associated with the presence of HT in women with SLE. The variables with significant differences between women with SLE who did and did not have HT (Table 2) were included in the analysis. Homocysteine was independently associated with HT, together with BMI and daily prednisone dose (Table 4). The same associations were found when the variable homocysteine level was substituted by hyperhomocysteinemia (Table 4).

DISCUSSION To our knowledge, this is the first time that an independent association between homocysteine levels and SBP or HT in women with SLE has been reported. This association was not found in controls. Although this study had a cross-sectional design, and no causality relations between homocysteine and HT can be established, there is a background of evidence that suggests that homocysteine might play a role in the pathogenesis of HT in SLE patients. Several population-based studies have identified elevated homocysteine levels as a risk factor for HT. Using data from the National Health and Nutrition Examination Survey, a positive, independent association between homocysteine levels and BP, particularly in women, was found. It was observed that a 1-SD increase in homocysteine was associated with an increase in SBP of 1.2 mm Hg and in DBP of 0.7 mm Hg (21). Controversial results have been observed in young subjects. Kahleova´ et al reported higher levels of homocysteine in adolescents and young adults with HT compared to normotensive matched controls, and a significant association with SBP was demonstrated (22). In contrast, Dinavahi et al found in a young African-American cohort an association between SBP and DBP and homocysteine only in premenopausal women, but this association was lost after adjustment for age and BMI (23). Interestingly, a recent study conducted in patients with rheumatoid arthritis (RA) found that HT was associated

Hypertension and Homocysteine Levels in SLE with increased concentrations of homocysteine but not with markers of inflammation (24). In this regard, we did not find an association between HT and either markers of SLE activity (SLEDAI index and C3, C4, and anti– doublestranded DNA antibody levels) or markers of inflammation (C-reactive protein level and erythrocyte sedimentation rate). Therefore, despite the fact that inflammation has been directly associated with endothelial dysfunction and arterial stiffness, and that both seem to predispose to the development of HT (25,26), these findings suggest that systemic inflammation itself might not be the main factor underlying the increased risk of HT in SLE and RA (24). As noted above, we did not find any association between homocysteine and SBP or HT in controls, contrary to the association observed in the SLE group. These conflicting results may be due to diverse causes. The prevalence of hyperhomocysteinemia in the control group was very low (7%) and the median values of homocysteine in controls were also relatively low (8.3 ␮moles/liter), with ⬃75% of controls having homocysteine levels ⱕ10 ␮moles/liter, which is below the level of homocysteine described by studies in the literature as toxic for the vasculature (⬃15 ␮moles/liter). Furthermore, the participants in our study were relatively young, and as mentioned previously, the evidence suggests that, in the general population, the association of homocysteine with CVD and HT appears to be particularly significant in older people, in which plasma homocysteine levels are higher (6 – 8). The fact that homocysteine was associated with HT in women with SLE despite their relative youth reinforces the idea of an early vascular aging that characterizes these patients. Interestingly, women with SLE also had relatively low homocysteine levels (median 11 ␮moles/liter [IQR 9 –15]) and only 23% had hyperhomocysteinemia. This finding is in accordance with similar results obtained by other authors. In a study examining the effect of homocysteine on the progression of carotid plaque in SLE (16), Roman et al found that only 10.7% of the SLE cohort had homocysteine concentrations ⱖ12 ␮moles/liter, and despite the low mean ⫾ SD level of homocysteine (7.7 ⫾ 3.4 ␮moles/liter), patients in the highest tertile (ⱖ7.9 ␮moles/liter) had the highest rate of plaque progression (56%), compared with 16.2% of those in the lowest tertile. Similarly, the Hopkins Lupus Cohort reported that baseline homocysteine was an independent risk factor for stroke (12), despite only 15% of patients having homocysteine levels above the upper limit of normal for this study (14.1 ␮moles/liter). On the basis of these findings, we hypothesized that the levels of homocysteine considered as nontoxic for the general population might have a harmful effect on the more vulnerable lupus vasculature predisposed to dysfunction as a consequence of diverse SLE-related factors (inflammatory cytokines, autoantibodies, etc.). Beyond a mere coincidence, the association between homocysteine and HT might have a causal relationship, as suggested by a few small, short-term clinical trials in which folate supplementation resulted in a decrease of homocysteine levels and BP (27). Homocysteine may promote HT by injuring the vascular endothelium that regulates vascular tone and BP and by endorsing arterial stiffness. Elevated levels of homocysteine may contribute to

1533 endothelial dysfunction by diverse mechanisms, such as oxidative stress or impairing nitric oxide– dependent vasodilatation, promoting endothelial cell apoptosis, or reducing the production of H2S, which is a strong antioxidant and vasorelaxation factor (28,29). In turn, homocysteine may increase vascular stiffness by damaging elastin fibers, increasing collagen production through the activation of metalloproteinases, and stimulating smooth muscle cell proliferation (30,31). It has been reported that some effects of homocysteine on endothelial cell function are mediated by asymmetric dimethylarginine (ADMA), an endogenous inhibitor of the nitric oxide synthase. In the general population, elevated levels of ADMA have been found to be associated with HT (32) among other cardiovascular conditions. In SLE patients, elevated ADMA levels have been associated with arterial stiffness (14), CVD (33), and more active SLE (34). Arterial stiffness is involved in the pathogenesis of CVD and acts as a major marker of cardiovascular risk (35). PWV assesses arterial stiffness and may help in the early detection of atherosclerosis (36). The association between PWV and homocysteine has been investigated in population-based studies with controversial results; an association has been found only in men (37), in both men and women (38,39), and in neither (40). In SLE, a positive correlation between homocysteine and PWV has also been reported (41). Despite our study showing a positive correlation between homocysteine and PWV in women with SLE in the univariate analysis, the loss of significance after adjustment for age, SBP, eGFR, or SDI suggests that other mechanisms involving homocysteine directly or indirectly might be implicated in the increased arterial stiffness of these patients. Therefore, BP and age are the most important factors contributing to arterial stiffness in the general population (42), and given the relatively strong association between homocysteine and SBP found in our study, it is plausible to consider that part of the increasing effect of homocysteine on arterial stiffness may be mediated by the elevation of SBP. In this regard, increased BP has been independently associated with PWV in SLE (43). Additionally, women with SLE who had hyperhomocysteinemia showed a greater prevalence of metabolic syndrome, and we recently reported that metabolic syndrome, a condition particularly prevalent in SLE patients (44), was also independently associated with increased PWV in SLE (44). Of note, apart from homocysteine, BMI and daily prednisone dose were independently associated with HT. The close link between obesity and BP is well known, with an estimated decrease of 1 mm Hg in SBP and DBP per 1 kg of weight lost (45). Regarding the effect of prednisone on BP, it was estimated in SLE patients that a 10-mg increase in mean daily prednisone dose was associated with an elevation of 1.6 mm Hg in SBP (46). In this regard, we previously reported that obesity and prednisone use were independently associated with HT in SLE patients ⬎40 years old (3). Many factors may affect homocysteine concentrations, including antihypertensive drugs. Most of the authors agree that thiazide-type diuretics can significantly increase homocysteine levels, but results regarding ACE inhibitors and other antihypertensive families remain controversial

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(47,48). The use of diuretics in the SLE group with hyperhomocysteinemia was significantly higher than the normohomocysteinemia group (39% versus 5%; OR 12.7 [95% CI 3.3– 46.0], P ⬍ 0.001), but the effect of this medication on homocysteine levels was uncertain. Several limitations must be considered. The size of the cohort was relatively small and some statistical significance between subgroups was probably not reached because of a lack of statistical power. Some factors that might influence homocysteine concentration, such as blood folate and vitamin B12 levels and polymorphisms of genes involved in the metabolism of homocysteine, were not taken into account. Given that this was a cross-sectional study, conclusions can only be used for hypothesis generation, and proof of causality or directionality, for which further appropriate investigations are required, cannot be obtained. In conclusion, homocysteine levels independently correlated with SBP and were independently associated with HT in women with SLE but not in controls. We suggest that increased homocysteine levels may contribute in part to the elevation of BP and consequently to the development of HT in SLE patients through both its toxic effect on endothelial cells and its capacity to increase arterial stiffness. This mechanism is not exclusive to SLE; however, this pathway could be potentiated in SLE patients because of a possible higher sensitivity to the toxic effect of homocysteine and its metabolites (i.e., ADMA) on the lupus vasculature, as suggested by the fact that this association was found at relatively low homocysteine levels. These findings may have implications for cardiovascular risk management in SLE patients in that closely monitoring HT in patients with elevated homocysteine may be particularly important. Finally, prospective controlled interventional studies should focus on the effect of folate supplementation on homocysteine levels, BP, and vascular stiffness in SLE.

AUTHOR CONTRIBUTIONS All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Sabio had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design. Sabio, Vargas-Hitos, MartinezBordonado, Navarrete-Navarrete, Dı´az-Chamorro, Olvera-Porcel, Zamora-Pasadas, Jime´nez-Alonso. Acquisition of data. Sabio, Vargas-Hitos, Martinez-Bordonado, Navarrete-Navarrete, Dı´az-Chamorro, Olvera-Porcel, ZamoraPasadas, Jime´nez-Alonso. Analysis and interpretation of data. Sabio, Vargas-Hitos, Martinez-Bordonado, Navarrete-Navarrete, Dı´az-Chamorro, Olvera-Porcel, Zamora-Pasadas, Jime´nez-Alonso.

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