Aortic calcification in patients with rheumatoid arthritis and ankylosing spondylitis: a cross-sectional case-control study

Objectives: Vascular calcification contributes to cardiovascular consequences in rheumatoid arthritis (RA) and ankylosing spondilytis (AS). This study was to evaluate the aortic calcification in RA and AS, and investigate possible risk factors. Methods: The in-patients with RA or AS were consecutively recruited from a general hospital. Control subjects were healthy population recruited from the same hospital. The aortic calcification score (ACS) was obtained by 256-slice spiral CT scanners using the Heart Beat-CS program (Philips Medical Systems, Cleveland Ohio, USA). Results: 146 RA patients, 97 AS patients and 200 controls were included. Serum triglyceride, cholesterol, urate, high and low density liptein cholesterols in RA or AS were all lower than that in controls. The ACS was higher in RA group than in AS and control groups. Only young (≤50 yrs) female AS had ACS higher than controls. Compared with the controls, RA increased the risk for aortic calcification by 4.72 (95% CI 2.78-7.99) fold after adjusted for age and sex. While AS in general, did not. Advanced age, male sex and elevated blood glucose were the risk factors for ACS in controls; advanced age, high C-reactive protein (CRP) and more co-morbidities were the risk factors in AS; and advanced age, long disease course, high DAS28(CRP) were risk factors in RA. Conclusions: Patients with RA or AS were more likely to develop aortic calcification compared with age and sex-matched healthy controls. Long disease course and high inflammatory criteria were risk factors, which advocate an intense control of disease associated systemic inflammation.

Up to 30% of the patients will suffer co-morbidities like anterior uveitis, aortitis, cardio conduction abnormalities and pericarditis. A population-based study indicated that the 10-year cumulative incidence of cardiovascular disease in AS patients was three times higher than predicted (standardized incidence ratio 3.01, 95% CI 1.35-6.69) [3]. Other studies also revealed that the crude or age-and sex-adjusted mortalities were higher in AS patients than in general populations, and the major cause of death was CVD [4,5].
Meanwhile, RA patients present earlier, more overwhelming and more severe vascular calcification compared with non-RA patients, regardless of the conventional cardiovascular risk factors [6][7][8].
Vascular calcification of large arteries such as the aorta will result in increased arterial stiffness, left ventricular hypertrophy and congenital heart failure. These are the common feature of CVD among several so called systemic inflammatory conditions, such as diabetes mellitus and chronic kidney disease [9]. Patients with RA or AS have similar inflammatory status and CVD characteristics with these diseases. The risk of non-ischemic heart failure increased rapidly after RA onset, in contrast to the risk of ischemic heart failure; and high disease activity was associated mostly with non-ischemic heart failure [10].
So far, studies addressing CVD in RA or AS focused mainly on coronary artery calcification and seldom on aorta calcification. In this case control study, we investigated aortic calcification score (ACS) in RA and AS patients, and try to find clinical factors associated with it. It may provide us useful knowledge about CVD in RA and AS, and help with better management strategy and overall outcome in these diseases.

Study subjects
In this case-control study, patients with RA or AS were consecutively recruited from the Department

Clinical and biochemical parameters
Demographic and clinical data of each private patient were obtained from the electric health record, including the time of symptom experience and standardized therapy before enrollment, and the visual analogue score (VAS) of general health status. The tenderness and swollen of 28 joints were evaluated in patients with RA, Including the shoulders, elbow joints, wrists, knees and bilateral 1 st to 5 th metacarpophalangeal and proximal interphalangeal joints.
Erythrocyte sedimentation rate (ESR) was determined by sodium citrate anticoagulant and Wechsler method; C-reactive protein (CRP) was detected by a latex-enhanced turbidimetric assay using reagents and instrumentation provided by Goldsite (Shenzhen, China); total cholesterol (TC), triglyceride (TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol Scanning parameters were 120kV 55mA, frame rotation time 0.42 s, slice thickness 2.5mm, reconstruction interval 2.5mm. Scanning field would cover between the 2-3cm above the lung tip and the costal diaphragmatic angle.

Statistics
Demographic and clinical features were summarized using standard descriptive statistics including mean (standard deviation), or median (interquartile range), frequency or percent as appropriate.
Comparisons of variables between different groups were undertaken using independent t-test, Mann-Whitney U test, c 2 tests, one-way ANOVA and Kruskal-Wallis tests as appropriate. Spearman correlation analyses were applied for understanding the relationships between clinical factors and ACS in each group. Multivariate logistic regression models were established to explore independent risk factors for aortic calcification within each group, and the impact of disease on aortic calcification.
The aortic calcification was defined as ACS>0. Two-sided tests with a 5% significance level (p<0.05) were considered statistically significant. All statistical analyses were performed using SPSS version 23.0 (IBM, Armonk, NY, USA).

Clinical features
146 RA patients were included in the RA group, 97 in the AS group and 200 healthy anticipants in the control group (Table 1). There was no significant difference in age between RA, AS and the control group (53 (10) vs 52 (6) vs 51 (9) years, p = 0.21). There were more male patients in AS group than in RA group or in controls (50% vs 30.8% vs 38.5%, p = 0.01). Although the biochemical criteria were generally within normal ranges, the concentrations of TG, TC, LDL-C, HDL-C and SU were lower in RA and AS group than in control group (p < 0.005). Meanwhile the FBG level was lower in AS group compared with those in the other two groups (p = 0.002). RA patients had higher CRP (19.9 (5.5-46.5)    . These results are shown in Table 2. Table 2 Aortic calcification score (ACS) between RA, AS and control groups

Discussion
Vascular calcification is a pathological process of calcium and phosphate salts accumulation within the arterial wall. It involves mainly two forms, intimal calcification in atherosclerosis and cardiac valve calcification, and artery tunica media calcification (also known as Mönckeberg sclerosis) in aging, diabetes mellitus, and chronic kidney disease mediated calcification, with various degrees overlap of them [13,14]. Vascular medial calcification increases vascular wall hardness and reducing vascular compliance. Aortic medial calcification induces cardiac pressure overload, leading to cardiovascular events such as congestive heart failure. According to previous studies [2][3][4], CVD was the leading cause of mortality in both RA and AS patients. The cardiovascular lesions in RA patients are characterized by earlier and more severe arterial calcification, as well as increased incidence and mortality of non-ischemic heart failure but not the incidence of atheromatous plaque [8,10]. AS patients also manifest accelerated atherosclerosis, arterial stiffness and myocardial infarction after adjustment of traditional CVD risk factors [15,16]. These data applaud that vascular calcification, especially aortic calcification may be an underlying mechanism of CVD in RA and AS patients.  [2,10,15].
We further explored possible determinants for aortic calcification in all participants. Logistic regression analysis showed that only advanced age, male sex and FBG were independent risk factors for aortic calcification in healthy controls (Figure). Unlikely in studies concerning atherosclerosis [17], dislipidemia defined as high level of LDL-C, serum triglyceride and low level of HDL-C was not associated risk factor for aortic calcification in the present study. This implies a pathogenesis of calcification diversely from atherosclerosis. Although male sex had more severe coronary artery calcification score as reported by a Korean study [18], no convincing explanations available so far.
Aging attributes to vascular calcification through multifaceted mechanisms [19]. Several researchers reported similar results that advanced age and FBG were independently related to aortic calcification in non-rheumatic population [20][21][22][23]. The common explanation underlies aging and diabetes is systemic inflammation [9,24]..
Advanced age as a risk factor for aortic calcification was consistent in RA and AS patients, as it was in controls. AS patients had lower level of FBG, which may be a confounding factor for the ACS in this group. While other traditional factors like TG, LDL-C, FBG and SU were generally decreased and not involved in aortic calcification in either RA or AS patients. These data indicate that disease associated factors participate in developing arterial calcification in these patients. Disease duration and DAS28 (CRP) were impact factors for ACS in RA patients, and CRP and co-morbidities in AS patients. All these parameters are criteria for disease activity related systemic inflammation. Therefore, our study implies that chronic systemic inflammation may be the main contributors for aortic calcification in these patients. Recent studies have established that inflammatory joint diseases are associated with an increased risk of CVD development related in part to the chronic systemic inflammation, which is often marked in RA and usually moderate in AS [25]. Female AS patients had a higher CVD risk, with an OR of 5.75 in females and 2.85 in males [26,27]. Our data are completely consistent with these research and might provide the pathological explanation for them.
RA and AS are all chronic inflammatory diseases that may affect multiple systems of the body, including the vascular bed. A recent prospective study reported that women with RA had increased risks of total and CVD mortality compared with those without RA (HR = 1.40 and 1.45, respectively) [28]. While another study from Netherlands showed that patients of early-onset RA under tight controlled treatment did not [29]. A cohort study revealed a doubled incidence of heart failure and an increased risk of mortality attributable to heart failure in patients with RA, with the risk of heart failure associated with RF positivity, repeatedly high ESR, severe extra-articular manifestations and corticosteroid use, and a protective effect against heart failure with methotrexate use [30]. Although data are limited, studies have confirmed that low disease activity of AS did not promote vascular calcification, and inflammatory related indicators were associated with increased mortality in patients with AS [13,14]. Taking together, all these data suggested that the clinical markers of high systemic inflammation level confer an additional risk for CVD among these patients.  [34][35][36]. They found that there was a negative correlation between CRP and HDL-C levels in active RA and AS, which was consistent with the results of this study (r=-0.262, P = 0.001 in RA; r=-0.270, P = 0.007 in AS). Thus, our study also showed a systemic inflammatory profile prominently labeled by serum CRP levels in both RA and AS patients.
Meanwhile, evidences of the relationship between IL-6 and vascular calcification are spring up [37].
Co-morbidities reflect the degree of target organ involvement of the disease. 53.2% of RA patients with high disease activity were complicated with other conditions at the disease onset, of which 23% developed other co-morbidities during followed up [38,39]. This study found that the co-morbidity

Conclusion
This study highlights the role of ACS as the marker indicating long-term systemic inflammation in RA and AS patients. In addition, 256 slice spiral CT is commonly used in clinic, which can provide a reliable and reproducible method for the examination of aortic calcification. It also showed that there was no significant correlation between treatment time and ACS in RA patients, implying incomplete disease control and yielding for improving the treatment strategy in this group. More attentions should be paid to a complete disease evaluation including cardiovascular system in these patients.
Further studies are called on to investigate this phenomenon for the sake of a better prognosis in these patients.

Funding
This study was supported by the research projects grants from the National Natural Science Foundation of China (#81871288) and the Natural Science Foundation of Shandong Province (#ZR2018MH015).

Availability of data and materials
The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate
The study was approved by the ethics committee of Affiliated Hospital of Qingdao University, and informed consents were obtained from all patients.

Consent for publication
Not applicable.