Cardiovascular diseases have recently been shown to be the leading causes of morbidity and mortality in patients with systemic autoimmune diseases. Some evidence shows that in autoimmune disorders, such as SLE, rheumatoid arthritis and antiphospholipid syndrome, the systemic inflammatory state itself predisposes to atherosclerotic diseases [32
MCTD is a systemic autoimmune disease, involving many organs, while the most frequent, serious outcome is the development of proliferative vascular lesions in the lungs and other organs. Anti-U1
RNP autoantibodies may have an effect on endothelial cells; in some studies on MCTD, however, the presence of antiphospholipid or anti-endothelial antibodies, in addition to anti-RNP antibodies, showed functional properties such as endothelial cell activation - changing the phenotype of endothelial cells, which become proinflammatory/procoagulant [36
]. No previous studies, however, have been carried out to assess the atherosclerotic risk factors in MCTD patients.
In our study population, we investigated the traditional risk factors, in association with clinical symptoms and autoantibodies, in MCTD patients with and without cardiovascular events. This is the first study where endothelial stiffness markers are measured, including FMD, NMD and carotid IMT.
In our patients with MCTD, serum triglycerides, HDL-C and LDL-C did not differ from healthy subjects, while total cholesterol and the ApoA1 levels and serum PON1 activity within the liporpotein fraction were lower compared with controls.
Decreased PON1 activity and mild elevation in hs-CRP have drawn considerable interest, in relation to the development of atherosclerosis that exemplifies a low-grade chronic inflammatory process [37
Decreased percentage FMD and increased IMT was found in patients with MCTD. Our results indicated that reduced FMD can clearly distinguish MCTD patients from controls and, moreover, MCTD patients with and without cardiovascular events. Decreased percentage FMD showed a close correlation with the disease duration, systolic blood pressure, and inflamatory parameters (hs-CRP and ESR).
High serum levels of hs-CRP have been shown to have a close association with CVDs, representing a link between chronic inflammation and hs-CRP with athrerosclerosis [39
]. A strong correlation was described between hs-CRP and CVD events, when hs-CRP exceeded 3 mg/l [40
]. In our series, both hs-CRP and the ESR were elevated in MCTD patients, escpecially in the MCTD/CVD+
group, and percentage FMD showed a close negative correlation with elevated ESR. These results may suggest that MCTD patients have ongoing low-grade inflammation, and these patients have an increased risk of severe CV events. A close association between SLAM score and percentage FMD shows that the disease activity involves endothelial cell inflammation, causing endothelial cell dysfunction.
Serum concentration of anti-U1RNP autoantibodies and levels of AECA were elevated in the patients'sera, and both antibodies were higher in the MCTD/CVD+ patients compared with the MCTD/CVD- group. Furthermore, we showed that the markers of endothelial cell dysfunction, vWFAg and soluble TM were higher in patients with MCTD than in the healthy individuals.
In MCTD, high serum levels of vWFAg imply an activated state of endothelial cells and can play a pathogenic role in the development of atherothrombotic events [41
]. Accordingly, in MCTD/CVD+
patients the soluble TM levels were significant higher than in the MCTD/CVD-
group. TM is an endothelial cell activation marker, and its shedding from the endothelial cell increases the risk of cardiovascular and thrombotic events [12
In patients with atherosclerotic diseases, soluble TM was elevated and its level showed correlation with the severity of coronary artery disease, and also an association with worse outcome in survivals after acute myocardial infarction [42
]. Moreover, soluble TM is a good marker of disease activity in SLE with lupus nephritis [43
vWFAg is a circulating glycoprotein, synthesized by endothelial cells - and an increased serum concentration of vWFAg has been shown to be a marker of endothelial dysfunction in scleroderma, SLE and MCTD patients with PAH [10
In our patients with MCTD, percentage FMD strongly correlated with disease duration, autoantibodies to anti-U1RNP, AECA and anti-CL, and endothelial cell markers, such as TM and vWFAg. These data indicate that the reduced FMD is a good marker for monitoring cardiovascular complications in MCTD.
One of the earliest stages of atherosclerosis is the endothelial cell dysfunction [45
]. Endothelium-dependent FMD was described previously to be significantly impaired in SLE [34
], in rheumatoid arthritis [35
], and in antiphospholipid syndrome [29
]. In our earlier study we also found decreased FMD in patients with undifferentiated connective tissue disease (UCTD), which is an early stage of well-established connective tissue diseases [46
]. Mosca and colleagues also investigated the vascular reactivity in UCTD, and found that FMD and the response to glyceryl trinitrate-mediated vasodilation were similar in UCTD patients and healthy subjects. UCTD patients were characterized, however, by having reduced response to both acethylcholine and sodium nitroprusside in the forearm microcirculation, indirectly indicating that reduced endothelium-dependent vasodilation, a peripheral microvascular risk factor, signifies UCTD [47
In the present study we found that FMD decreased and the IMT was elevated in the MCTD/CVD+ patient group, but there was no significant difference in NMD between the MCTD/CVD+ and MCTD/CVD- patient groups. We further described the presence of anti-CL antibodies and AECA besides anti-U1RNP antibodies in MCTD; moreover, serum levels of anti-U1RNP antibodies, anti-CL IgG and AECA were higher in the MCTD/CVD+ group compared with MCTD/CVD- patients.
We assume that AECA in MCTD patients could contribute to endothelial cell dysfunction. AECAs are often associated with phospholipid reactivity, present in SLE and in primary antiphospholipid syndrome.
In contrast to the data by Lima and colleagues, we found that FMD showed a correlation with the activity score [48
]. Among the clinical symptoms, Raynaud's phenomenon was more frequent in the MCTD/CVD+
group - our data being similar to the findings of Aizer and colleagues [49
]. Interestingly, anti-CL antibodies and AECAs were more frequent in patients with Raynaud's phenomenon, and these antibodies could provoke endothelial cell damage. We assume that decreased FMD may occur as a result of continuous endothelial cell activation and impairment.
The daily doses of CS and other immunosuppressive treatment were similar in the CVD+ and CVD- groups. Based on our data we believe that the vascular protection is essential in patients with MCTD, especially in Raynaud's penomenon and PAH, and also aspirin and statin therapy is important from the early stage of MCTD.
Carotid IMT was significant higher in MCTD patients and showed an association with age, with disease duration and with traditional risk factors such as total cholesterol levels, systolic blood pressure and diastolic blood pressure. Ultrasound measurements of the carotid artery IMT identify early structural vascular abnormalities. An inverse correlation has been described previously between the IMT and brachial arterial FMD. Endothelial dysfunction showed a correlation with the IMT, suggesting that the carotid IMT alone was a valid surrogate marker for early atherosclerosis and had an important predicting feature in cardiovascular events in the general population [50