Introduction

Patients with inflammatory joint diseases (IJD), including rheumatoid arthritis (RA), ankylosing spondylitis (AS) and psoriatic arthritis (PsA) have reduced endothelial function compared to the general population [1]. According to hypotheses regarding development of atherosclerosis, the progressive impairment of endothelial function is an early step in the developing process of atherosclerotic plaques [2]. Furthermore, restoration of endothelial function has been proposed as an important mediator of atherosclerotic regression [3].

Flow-mediated vasodilation (FMD) of the brachial artery is a widely used noninvasive technique that quantifies endothelial function [4]. Reduced FMD has been shown to predict cardiovascular disease (CVD) events in other high-risk populations and in the general population [5]. Moreover, decreasing FMD correlates with the presence of carotid plaques (CP) [6], which are highly prevalent in RA patients [7]. The European recommendations on CVD prevention classify CP as a very high CVD risk factor [8]. Due to the ethical implications of not giving statin therapy to patients with CP, the ROsuvastatin in Rheumatoid Arthritis, Ankylosing Spondylitis and other inflammatory joint diseases (RORA-AS) study was a single-arm statin study from which we have previously reported that rosuvastatin therapy induced CP height regression in IJD patients [9].

The main objective of the present secondary endpoint analyses from the RORA-AS study was to evaluate the effect of long-term lipid lowering with rosuvastatin on FMD in IJD patients with established atherosclerotic disease. Furthermore, we aimed to examine if the change in FMD (∆FMD) induced by rosuvastatin would be correlated with CP height reduction. In addition, we evaluated if ∆FMD from baseline to study end could be predicted by, or was correlated with, the baseline levels of or the longitudinal changes in arterial stiffness, lipids, inflammatory parameters, rheumatic disease activity, carotid intima-media thickness (c-IMT) or rosuvastatin dose.

Methods

The study design of the open, prospective RORA-AS study has previously been described in detail [9]. In short, IJD patients with ultrasound-verified CP were treated with rosuvastatin for 18 months. The initial rosuvastatin dose (20 mg once daily (o.d.), except for patients > 70 years who received 5 mg) was doubled every fortnight, until low-density lipoprotein (LDL-c) target (<1.8 mmol/L) or maximal rosuvastatin dose (40 mg o.d.) was reached. The LDL-c target was defined in accordance with the most recent European guidelines [8]. The feasibility of reaching this target in IJD patients with low rates of adverse events has previously been reported [9, 10]. All patients signed an informed consent and the study was approved by the Norwegian South East Regional Health committee and registered with ClinicalTrials.gov Id: NCT01389388. The European Union Drug Regulating Authorities Clinical Trials (EudraCT) number is 2008-005551-20.

Endothelial function was assessed by the FMD method [4]. As the FMD measurement is dynamic in nature and can be impacted by several factors, all recordings were performed in fasting patients, including no smoking or medication. In addition, all RORA-AS study visits were independent from other visits to the rheumatology outpatient clinic throughout the study. Accordingly, there existed no systematic tendency toward the administration of disease-modifying antirheumatic drugs (DMARDs) in the days prior to the FMD measurements that would influence the results. All recordings were done with the patient in a supine position using a Vivid 7 scanner (GE Vingmed Ultrasound, Horten, Norway) with a 10 MHz transducer that was placed in a fixed position and stabilized with a custom-made tripod to optimize the stability. The results were analyzed offline from jpg images extracted from video files using Brachial Analyzer software (Medical Imaging Applications LLC, Coralville, IA, USA). FMD percentage was calculated as the percentage change between the baseline diameter and the largest diameter of the brachial artery within the first 2 minutes after 5 minutes occlusion of the right forearm. The examiner had no information pertaining to further patient characteristics. Recordings were performed and analyses were supervised by the same experienced ultrasonographer (JH) in accordance with international guidelines [4], and the intra- and inter-reader reliability for FMD showed a good correlation (intraclass correlations = 0.96 for both). Flow of the brachial artery was not obtained during the FMD examinations. The mean diameter of the brachial artery for all patients at both baseline and 18 months was plotted against time from 0 to 120 seconds and the area under the curve (AUC0–120) for both graphs were calculated as a millimeters multiplied with seconds (mm × sec) value.

To assess arterial stiffness, augmentation index (AIx) and aortic pulse wave velocity (aPWV) were measured by the Sphygmocor apparatus (Atcor Medical Pty Ltd., West Ryde, Australia) according to guidelines and as previously described [11].

Statistics

Descriptive statistics are expressed as number (%) for dichotomized variables, and mean ± standard deviation (SD) and median and interquartile range (IQR) for normally and non-normally distributed variables, respectively. Diagnosis groups were compared using analysis of variance (ANOVA), and chi-square tests as appropriate, in addition to the nonparametric Kruskal-Wallis test for number of CP. Non-normally distributed variables were logarithmically transformed.

The change in FMD from baseline to study end was analyzed using a paired-samples t test.

Both adjusted and unadjusted linear regression analyses with ∆FMD as the dependent variable were applied to:

  1. 1)

    Evaluate if ∆FMD could be predicted by baseline demographic data (age, gender), use of biologic DMARDs (bDMARDs), inflammation [C-reactive protein (CRP), erythrocyte sedimentation rate (ESR)], rheumatic disease activity [disease activity score in 28 joints (DAS28), ankylosing spondylitis disease activity score (ASDAS) or lipids [(low-density lipoprotein (LDL-c), high-density lipoprotein (HDL-c)]

  2. 2)

    Explore if ∆FMD was correlated with the changes in CP height, inflammation, rheumatic disease activity, lipids, arterial stiffness, c-IMT and rosuvastatin dose from baseline to study end

Model assumptions and validity were assessed using residuals. Two-sided p values <0.05 were considered significant. Statistical analyses were performed using the Statistical Package for the Social Sciences version 21 (IBM SPSS Statistics for Windows, Armonk, NY, USA).

Results

The RA (n = 53), AS (n = 24) and PsA (n = 8) patients were comparable concerning baseline characteristics (Table 1). However, we observed expected differences concerning gender (p = 0.01), baseline HDL-c levels (p = 0.02) and use of synthetic disease-modifying antirheumatic drugs (sDMARDS) (p = 0.002), attributable to the distinct characteristics of the three disease entities. Changes in lipid levels and CP height in the RORA-AS study has previously been reported [9]. An additional table has been provided that shows these changes in detail (see Additional file 1).

Table 1 Patient characteristics
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FMD was improved by 1.6 % from baseline to study end (Fig. 1), reflecting a mean ± SD FMD of 7.10 ± 3.14 % and 8.70 ± 2.98 %, respectively (p < 0.001). Figure 2 shows the relative change in vascular diameter as measured by FMD from 0 to 120 seconds. The AUC0–120 of the baseline measurements was increased by 27.7 % from baseline (19.3 mm × sec) to study end (24.6 mm × sec).

Fig. 1
figure 1

Change in flow-mediated vasodilation (FMD) from baseline to study end. Change in flow-mediated vasodilation (FMD) (%) from baseline to study end in patients with inflammatory joint diseases and established atherosclerosis (n = 85) after 18 months of rosuvastatin treatment. FMD flow-mediated vasodilation, SE standard error, SD standard deviation

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Fig. 2
figure 2

Mean brachial artery diameter plotted against time at baseline and study end. Flow-mediated vasodilation (FMD) mean brachial artery diameter (millimeters) plotted against time (seconds) in patients with inflammatory joint diseases and established atherosclerosis (n = 85), before and after 18 months of rosuvastatin treatment

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The adjusted and unadjusted analyses did not reveal any statistically significant predictors of ∆FMD in our study (Table 2). However, in the adjusted linear regression analyses, the changes in AIx and CP height were associated with ∆FMD, in the sense that patients who experienced reduced arterial stiffness measured by AIx and CP height reduction also had increased FMD (p < 0.05 and p = 0.001, respectively). The estimates from the corresponding unadjusted linear regression analyses were comparable. ∆FMD did not significantly correlate with baseline levels or change in inflammatory biomarkers, rheumatic disease activity, lipids, c-IMT or rosuvastatin dose in the linear regression analyses.

Table 2 Unadjusted and adjusted linear regression analyses with flow-mediated vasodilation (ΔFMD) as the dependent variable
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Discussion

In the present study, we have shown that endothelial function was significantly improved in IJD patients with established atherosclerosis who received rosuvastatin therapy for 18 months. Furthermore, we have demonstrated that the amelioration of FMD was correlated with CP regression and reduced arterial stiffness.

The improvement in FMD after statin treatment observed in our study is supported by the positive effect by statins on FMD reported from previous studies with smaller IJD patient cohorts and shorter follow-up time [12–14]. Interestingly, a meta-analysis by Inaba et al. reported that 1 % lower FMD was associated with a 13 % increase in risk of future CVD events. Accordingly, the 1.6 % improvement in FMD observed in our study may reflect a highly beneficial clinical effect by rosuvastatin [15].

The negative influence of endothelial dysfunction on the progression of atherosclerosis has previously been reported [16]. We show for the first time that carotid atherosclerosis regression was associated with improvement of FMD in statin-treated patients. Thus, our results support the existing evidence that restoration of endothelial function may be essential in the reversal of atherosclerosis [3]; however, studies to elucidate further details in this pathological process are warranted.

AIx and aPWV are predictors of CVD in the general population [17, 18] and are reported to be higher in patients with IJD [1]. The inverse relation between FMD and arterial stiffness in IJD patients has previously been described [19]. To our knowledge, this is the first report on longitudinal correlation between improved endothelial function and decreasing arterial stiffness. Although endothelial dysfunction and arterial stiffness represent different aspects of vascular disease, the pathogeneses of these vascular biomarkers are closely related [20]. Our results indicate that these biomarkers are also related in the process of atherosclerotic regression.

We found no significant correlation between ∆FMD and the levels of inflammatory biomarkers or rheumatic disease activity in our patients. This may be due to that the patients were largely well treated at baseline and throughout the study.

The lack of a placebo group in the RORA-AS study represents a possible limitation. However, as aging is related to progressive impairment of endothelial function [21], it is unlikely that the improved FMD in our study was a result of natural progression. Data concerning flow of the brachial artery in relation to the FMD measurements would have been preferable; however, such data were not obtained.

Conclusions

In conclusion, endothelial function was significantly improved in IJD patients with established atherosclerosis receiving long-term lipid-lowering therapy with rosuvastatin. The amelioration of FMD was correlated with reduced arterial stiffness and decreasing CP height and support the hypothesis that restoration of endothelial function is closely related to atherosclerotic regression.