Condition of vascular wall and endothelial function in children with systemic lupus erythematosus
Background. Since systemic inflammatory connective tissue diseases, including systemic lupus erythematosus (SLE), are considered to be risk factors for early atherosclerosis. Children with SLE are the target group for the detection of early signs of subclinical vascular lesions.
Materials and methods. Seventeen children with SLE and twenty one healthy children were included in the study. Brachial artery flow-mediated dilation, measuring of common carotid artery intima-media thickness and carotid artery stiffness index were performed in all children using duplex sonography.
Results. Children with SLE had significantly increased common carotid artery stiffness index and thickened carotid intima-media complex compared to healthy controls. These changes were progressing during disease course and were significantly more pronounced after 2 years of disease duration comparing to SLE patients with disease duration less than 2 years. Duration of glucocorticoid treatment and the total glucocorticoid cumulative dose were factors that directly affected carotid artery stiffness index and carotid intima-media thickness in SLE patients. In patients with SLE brachial artery flow-mediated dilation values were impaired comparing to controls. Endothelial dysfunction in SLE patients revealed even in children with inactive disease.
Conclusions. In children with SLE subclinical vascular lesions and impaired endothelial function are revealed. Endothelial dysfunction is persisting even in children with inactive disease.
Background. Systemic lupus erythematosus (SLE) – is an inflammatory connective tissue disease characterized by breakdown of immune tolerance and synthesis of a wide spectrum of autoantibodies to nuclear antigens predominantly of own cells with subsequent development of immunocomplex vasculitis, leading to tissue damage . Data on the epidemiology of SLE among children around the world is not enough. Separate studies have shown pediatric morbidity in U.S. to be in average 0,53-0,6 per 100 thousand children per year , and prevalence — 4.4 per 100 thousand among girls and 1-1,6 per 100 thousand children population among boys . According to Pelkonen et al (1994) SLE takes first place by incidence and prevalence among systemic inflammatory connective tissue diseases in children. The same situation in Ukraine was shown in the analysis of the incidence and prevalence of SLE among children aged 0-17 years that were respectively 0.05 and 0.34 per 1000 of child population .
Since 80th of the twentieth century, when Rosner S. et al (1982) have shown in a multicenter study that in SLE female patients under 40 years of age the risk of atherosclerosis and its complications (coronary artery disease, myocardial infarction, stroke) 4-8 times higher than in general population , SLE relationship with atherogenesis is being studied actively. Moreover, it was found that regardless of the cause of death in 50% of adult patients with SLE at autopsy significant atherosclerosis lesions were revealed . A new understanding of the relationship between these issues gave their intersection in the plane of pathogenesis of atherosclerosis as phasic process in which a significant role is played by subclinical inflammation of the vascular wall and endothelial dysfunction.
Endothelium performs many important functions as a barrier between the vasculature cavity and intercellular environment. Due to the synthesis of many biologically active substances it regulates vascular tone (nitric oxide, prostaglandins, endothelin-1), adhesion and migration of immune cells in the vessel wall (adhesion molecules), platelet adhesion (prostaglandins), coagulation (von Willebrand factor), regulates the permeability of vascular wall for many substances . Endothelial function dependents on its status (activated or inactive). In the inactive state endothelium maintains normal vascular tone, prevents adhesion of immune cells and platelets to the vessel wall, supports normal blood viscosity. When endothelium is activated all of these functions become violated. Nowadays term "endothelial dysfunction" is used to refer to a disruption of endothelium functioning due to its transition to a state of activation.
To date, the cause of accelerated atherogenesis in patients with systemic inflammatory connective tissue diseases is considered to be persistent endothelial activation that accompanies chronic inflammation in these patients. Increased blood levels of proinflammatory cytokines (IL-6, TNF-α) and acute phase proteins (C-reactive protein and fibrinogen) are the main causes of chronic endothelial activation in SLE patients [11, 14]. One research has shown induction of endothelial activation with exposure to IL-6, TNF-α and acute phase proteins . Endothelial activation leads to increased deposition of oxidized low-density lipoproteins in the vascular wall, macrophage migration and phagocytosis of these substances leading to transformation into "foamy" cells. These processes gradually lead to atherosclerotic lesions of the vascular wall.
Many studies have shown that atherosclerosis is a long-term process that often begins in childhood. In children with risk factors (obesity, diabetes, hypertension and others.) after the age of 8 years during autopsies initial atherosclerotic lesions of the aorta at the stage of yellow stripes often can be revealed, and in some cases — small atherosclerotic plaques in the coronary arteries were found . Thus detection of atherosclerosis at an early stage, such as endothelial dysfunction, increased stiffness of the vascular wall or thickening of intima-media complex (IMT) of vessels in children with risk factors for early atherogenesis is important for pediatrics and preventive cardiology. Since systemic inflammatory connective tissue diseases, including SLE, are considered to be risk factors for early atherosclerosis , children with SLE are the target group for the detection of subclinical vascular lesions early signs.
Generally used instrumental method for diagnosing of endothelial dysfunction is flow-mediated dilation of brachial artery assessed with duplex sonography (FMD). The method implies brachial artery (BA) compression by tonometer cuff for a short period time. During ischemia in the BA and nitric oxide is accumulated in its branches (the ammount of which depends on the endothelium functional state), and the restoration of blood flow in the BA vascular bed leads to vasodilation under the accumulated nitric oxide action. This results in increase of linear blood flow velocity and vessel diameter that can be measured during duplex sonography. These changes are directly proportional to the number of nitric oxide that accumulated during ischemia period and, therefore, depend on the functional state of the endothelium . Kerekes et al (2008) and El-Magadmi et al (2004) among adult patients with SLE showed a significant decrease in FMD indexes compared with the control group, S.V.Shevchuk (2008) also showed a decrease of FMD indexes in 65.7% of adult patients with SLE, indicating endothelial dysfunction in these patients .
With persistent endothelial dysfunction atherosclerotic process initially leads to increase rigidity of the vascular wall, and then — to its thickening. Shang et al (2008) in the study of arterial stiffness by measuring pulse wave amplitude found its significant increase in women with SLE compared to the control group. Chow et al (2007) showed increased stiffness index of the carotid wall by duplex sonography in adolescents with SLE. Pascal et al (2010) conducted a meta-analysis of 60 common carotid artery IMT studies by duplex sonography involving 3761 adult patients with rheumatic diseases, of which 35% suffered from SLE. In these patients significant thickening of the carotid IMT was observed compared with healthy patients. S.V. Shevchuk (2008) also showed thickening of the carotid IMT in 52.7% of patients with SLE .
Thus, in adult patients with SLE, before the stenotic stage of atherosclerosis and its complications develop, early signs of vascular lesions, which are termed "subclinical atherosclerosis", can be revealed. They considered to be a risk factors for cardiovascular disease . However, literature data on the status and vascular wall and endothelial function in children with SLE in not enough. Based on the above, the purpose of our study was to examine vascular wall and endothelial function condition in children with SLE by duplex sonography.
Materials and methods. Seventeen children with SLE were included in our study. The diagnosis was established on the basis of the American College of Rheumatology criteria, developed in 1982 and revised in 1997, in the presence of four or more criteria [9, 17].
Among patients with SLE there were 4 (23,5 ± 10,3%) boys, and 13 (76,5 ± 10,3%) girls. The average age of patients was 14,5 ± 2,8 years (minimal age — 10 maximum years — 17 years). Fifteen (88,2 ± 7,8%) patients had subacute disease, acute same as chronic course were in one patient for each. Control group consisted of 21 healthy children between 9 and 17 years o age. Among them there were 10(47.6%) girls and 11 (52.4%) boys.
Based on the clinical and laboratory examination disease activity level in SLE patients was established according to the standard classification . At the time of the study 3 (17.6%) patients had moderate disease activity, 6 (35.3%) — mild disease activity, 8 (47.1%) children had inactive disease according to clinical and laboratory assessments.
In 8 (47,1 ± 12,1%) children with SLE clinical and laboratory signs of lupus nephritis manifested: in 5 (29,4 ± 11,1%) — tubulointerstitial nephritis, in 1 — isolated urinary syndrome, in 2 — nephrotic syndrome with hematuria.
Among SLE patients 12 (70.6%) received treatment with glucocorticoids, the average duration of which was 43,6 ± 10,0 months, the average cumulative dose of glucocorticoids was 14,5 ± 3,5 g. Nine (52.9%) patients received Chloroquine or Hydroxychloroquine at a dose of 5-8 mg / kg / day, 4 (23.5%) — azathioprine at a dose of 1-2 mg / kg per day. In three cases methotrexate was used at a dose of 10 mg / m2 / week orally with 5 mg of folic acid orally weekly one day after receiving methotrexate. In one patient mofetil mycophenolate was used at dose of 1000 mg / day. Due to the presence of lupus nephritis enalapril was used in a dose of 2.5-5 mg / day in a single dose in 5 (29.4%) children, one patient received irbesartan 150 mg / day, two children were on combined therapy with enalapril and irbesartan in the indicated dosages.
Children were divided by the duration of the disease into two groups: with a term of disease less than 2 years and more than 2 years. The first group included 8 (47.1%) children, the second — 9 (52.9%) patients. In all SLE patients and children of control group carotid IMT, carotid stiffness index and BA FMD were reformed by duplex sonography using ultrasound scanner Philips EnVisor C according to American Heart Association guidelines . To assess BA FMA in children we evaluated two parameters: ΔV (difference in peak systolic blood flow velocity of brachial artery before and after the test) and ΔD (difference in diastolic brachial artery diameter before and after the test). Statistical analysis was performed using Microsoft Excel 2007.
Results and discussion. Mean values of carotid IMT and carotid stiffness index are shown in Table 1.
The average value of carotid IMT in SLE patients with disease duration less than 2 years was 0,49 ± 0,007 mm and was significantly higher than the average value in the control group (p0.001). Average value of carotid IMT in SLE patients with disease duration more than 2 years was 0,53 ± 0,008 mm and was significantly thicker than the average value in control group (p0.001), and the group of SLE patients with disease duration less than 2 years (p0.01). We found a moderate direct correlation between carotid IMT and disease duration (r = 0,69, p0.01), duration of glucocorticoid therapy and total cumulative dose of glucocorticoids (r = 0,65, p0.05 and r = 0 53, p0.05, respectively). We found no correlation between carotid IMT in SLE patients and the degree of disease activity. Significant difference between average values of carotid IMT in SLE patients with and without lupus nephritis was not found (0,5 ± 0,03 and 0,51 ± 0,01 mm, respectively, p0.05).
Average values of carotid artery stiffness index in children with SLE with disease duration less and more than 2 years (4,26 ± 0,09 and 4,52 ± 0,05 respectively) showed a significant increase comparing to the control group (p0.001 for both groups). In addition mean value of carotid artery stiffness index in children with disease duration more than 2 years was significantly higher than in children with disease duration less than 2 years (p0.05). We found a moderate direct correlation between carotid stiffness index value and disease duration (r = 0,69, p0.01), duration of glucocorticoid therapy (r = 0,59, p0.01) and total cumulative dose of glucocorticoids ( r = 0,62, p0.05). We have not found significant correlation between carotid stiffness index in SLE patients and the degree of disease activity. Significant difference in the average value of carotid stiffness index of SLE patients with and without lupus nephritis were not found (4,29 ± 0,08 and 4,45 ± 0,08 respectively, p0.05).
Results of BA FMD in SLE patients and control group are shown in Table 2.
The average values of ΔV and ΔD in SLE patients were respectively 7,86 ± 0,2% and 8,7 ± 0,16%, and were significantly lower than the corresponding values in control group (p0.001). We found a moderate inverse correlation between BA FMD values and degree of SLE activity in our study (r = -0,68, p0.01 for ΔV and r = -0,69, p0.01 for ΔD), and mild inverse correlation between ΔV, ΔD and disease duration (r = -0,31, p 0.05 and r = -0,36, p 0.05, respectively). SLE patients with inactive disease had significantly higher average values of BA FMD comparing to control group (8,45 ± 0,29%, p0.001 for ΔV and 9,13 ± 0,24%, p0.001 for ΔD). Significant difference between average values of BA FMD in SLE patients with and without lupus nephritis were not found (8,01 ± 0,36 and 7,74 ± 0,2%, respectively, p0.05 for ΔV and 8,8 ± 0,3 and 8,6 ± 0,16% respectively, p0.05).
Thus, children with SLE had significantly increased common carotid artery stiffness index and thickened carotid intima-media complex compared to healthy controls. These changes were progressing during disease course and were significantly more pronounced after 2 years of disease duration comparing to SLE patients with disease duration less than 2 years. Duration of glucocorticoid treatment and the total glucocorticoid cumulative dose were factors that directly affected carotid artery stiffness index and carotid intima-media thickness in SLE patients. The presence of lupus nephritis and the degree of disease activity did not affect the properties of the vascular wall of children with SLE.
On the other hand, in patients with SLE brachial artery flow-mediated dilation values were impaired comparing to controls and were independent of disease duration, but depended on the degree of disease activity. This can be explained by the fact that in systemic inflammatory connective tissue diseases increased levels of circulating proinflammatory cytokines cause endothelial activation and dysfunction and these cytokines levels depend on the degree of disease activity.
Endothelial dysfunction in SLE patients revealed even in children with inactive disease indicates persistent activation of the endothelium in these patients. This data suggests that SLE patients with inactive disease have impaired function of vascular endothelium that is the risk factor for early atherosclerotic changes.
The recommendations of the American Society of Echocardiography identified four reasons for carotid intima-media thickening and increased carotid artery stiffness index: age, professional sports, subclinical atherosclerosis and vasculitis . The first two factors are not important in children with SLE, because until the age of 20 carotid intima-media thickness and carotid stiffness index remain relatively constant , and professional sports in children with SLE is mostly contraindicated. The absence of correlation between degree of carotid intima-media thickening, carotid stiffness index and the degree of disease activity points against vasculitic nature of revealed changes . Thus the most likely cause of vascular changes remains atherosclerotic lesions in children with SLE.
The data must be considered when developing treatment and rehabilitation of children with SLE.
Conclusions. 1. In children with systemic lupus erythematosus changes in the vascular wall such as a thickening of intima-media complex and increased stiffness index of common carotid arteries compared with healthy children were revealed. They directly correlate with disease duration, duration of glucocorticoid therapy and cumulative glucocorticoid dose.
2. In children with systemic lupus erythematosus endothelial dysfunction were revealed and manifested as significant decline in flow-mediated dilation values of the brachial artery and directly correlated with the degree of disease activity. These changes were observed both in children with active and inactive disease.