Serum concentrations of small dense low‐density lipoprotein cholesterol and lipoprotein(a) are related to coronary arteriostenosis in Takayasu arteritis

Abstract Background Serum small dense low‐density lipoprotein cholesterol (sdLDL‐C) and lipoprotein(a) [Lp(a)] levels are related to coronary disease, but their specific associations with coronary arteriostenosis in Takayasu arteritis (TA) have not been ascertained. This study explored the correlations between serum sdLDL‐C and Lp(a) levels and coronary arteriostenosis in TA patients as well as the degree of artery stenosis. Methods This retrospective study included 190 TA patients and 154 healthy subjects. TA patients were divided into three categories based on the degree of coronary stenosis: Group I, stenosis >50%; Group II, stenosis 1%–50%; and Group III, stenosis 0%. Independent risk factors for coronary arteriostenosis in TA were identified by logistic regression, followed by receiver operating characteristic curve analysis to determine the specificity and sensitivity of risk factors and Youden's Index score calculation to determine the cutoff points. Results Takayasu arteritis patients had significantly higher serum levels of sdLDL‐C and Lp(a) than healthy controls (p < 0.0001). The total cholesterol, triglyceride, LDL‐C, sdLDL‐C, and Lp(a) levels and the sdLDL‐C/LDL‐C ratio in Group I were significantly higher than those in Groups II and III (p < 0.05). An elevated serum sdLDL‐C level elevated the risk of coronary arteriostenosis by 5‐fold (cutoff value, 0.605 mmol/l). An increased serum Lp(a) level increased the risk of coronary arteriostenosis by 3.9‐fold (cutoff value, 0.045 g/l). An elevated sdLDL‐C/LDL‐C ratio increased the risk of coronary arteriostenosis by 2.1‐fold (cutoff value, 0.258). Conclusions Serum sdLDL‐C and Lp(a) levels and sdLDL‐C/LDL‐C ratio may be used as diagnostic factors for coronary arteriostenosis in TA patients.


| INTRODUC TI ON
Takayasu arteritis (TA) is a rare vasculitis that mainly involves the aorta and its major branches. 1 TA is mainly seen in young women aged 20-40 years and is most often encountered in Japan, Southeast Asia, India, and Mexico. 2 Froving and Loken first reported coronary arteriostenosis in TA in 1951. 3 Since then, the incidence of coronary arteriostenosis in TA has varied in literature reports, depending on the study location and cohort. For example, some studies have reported that 10%-30% of TA patients had coronary arteriostenosis, 4 -11 and another study reported 7.7%. 12 However, research has consistently shown that coronary arteriostenosis is a risk factor for adverse outcomes and increased mortality in TA patients. [13][14][15] Due to nonspecific clinical features, TA patients with coronary arteriostenosis might be misdiagnosed or inappropriately treated. 12 As a result, detection of coronary stenosis in TA patients principally depends on computed tomography angiography (CTA); however, CTA can only detect 53.2% coronary stenosis in TA patients. 16 Therefore, it is imperative to develop methods for accurate and timely diagnosis of TA patients with coronary arteriostenosis to facilitate appropriate clinical management. The identification of blood biomarkers for TA with coronary arteriostenosis has been an active area of research in the field.
Dyslipidemia plays a role in the pathogenesis of TA, and the lipid profiles in TA patients are pro-atherogenic. 17,18 A previous study has shown that abnormal lipid metabolism, an elevated ratio of apolipoprotein B (apoB)/apolipoprotein A1 (apoA1), and reduced levels of apoA1 and high-density lipoprotein cholesterol (HDL-C) are associated with higher disease activity in TA, 17 and these results were confirmed in other studies. [19][20][21][22] These findings support the premise that abnormal lipid profiling is closely linked to the development of TA.
Small dense low-density lipoprotein cholesterol (sdLDL-C) is small and highly dense relative to other LDL-C particles and thought to be more atherogenic than the large buoyant LDL (lb-LDL) due to greater penetration into the arterial wall, a prolonged plasma half-life, lower hepatic LDL receptor affinity, and higher susceptibility to oxidation. 23,24 sdLDL-C is independently correlated with the progression of atherosclerosis in the Chinese population. [25][26][27][28] However, whether the serum sdLDL-C level is correlated with TA involving the coronary arteries is not clear. Lipoprotein(a) (Lp(a)), including the major components LDL-C, apoA, and apoB, 29 has long been considered an independent risk factor for coronary disease. 30 Although one case report showed a significantly elevated serum level of Lp(a) in a TA patient, 31 no systemic study has been performed to examine the link between serum levels of Lp(a) and TA involving the coronary arteries. This study aimed to explore the relationship between serum sdLDL-C and Lp(a) levels and the disease activity of TA patients, and whether elevated serum sdLDL-C and Lp(a) concentrations can be used as diagnostic factors in Chinese TA patients.

| Laboratory measurement
Early in the morning, venous blood samples were obtained from fasting TA patients and healthy controls. Our team previously compared methods for measuring sdLDL-C, 36 and a Beckman AU5400 (US) automatic biochemical analyzer was used in the present study to measure novel and traditional lipid parameters and biochemical indicators, including the sdLDL-C, Lp(a), total cholesterol (TC), LDL-C, HDL-C, and triglyceride (TG) concentrations within 5-6 h after sample collection. The Sysmex XE-2100 was used to determine complete blood counts. The experiments were accomplished following the manufacturer's instructions. In addition, all measurements were analyzed using the continuous monitoring method, and appropriate quality control was carried out before these analyses.

| Statistical analysis of data
The statistical analyses were performed using SPSS 23.0 (SPSS Inc.).
The measurement data were tested for normality. The normal distribution data are presented as mean ± standard error of the mean (SEM) and were compared with an independent sample t-test. Data with a skewed distribution are presented as median and interquartile range (25%, 75%Q) and were contrasted with the Mann-Whitney-Wilcoxon test. The chi-square test or Fisher's exact test was used to compare with counting data. One-way analysis of variance (ANOVA) or the Kruskal-Wallis test followed by Dunn's post hoc test was used to compare differences in variables among three or more groups. When a p-value was <0.05, the Mann-Whitney-Wilcoxon test or unpaired Student's t-test was used to perform multiple comparisons between two groups. Logistic regression was used to determine independent risk factors for TA patients with coronary arteriostenosis. Receiver operating characteristic (ROC) curves were used to determine the specificity and sensitivity of novel and traditional risk factors for coronary stenosis >50% and coronary arteriostenosis. The cutoff values of diagnostic indicators were determined by Youden's Index scores (sensitivity+specificity-1). A p-value <0.05 was regarded as statistically meaningful.

| Comparison of clinical manifestations and outcomes between active and inactive TA patients
As shown in Figure 1, TA patients had higher TC, TG, LDL-C, Lp(a), and sdLDL-C concentrations and a significantly higher sdLDL-C/ LDL-C ratio than the healthy controls. TA patients with active disease had a higher incidence of claudication than those with inactive disease (p = 0.018). Four TA patients with active disease had Numano subtype IIa, whereas no cases of Numano IIa were found in TA patients with inactive disease (p = 0.003). Also, patients with active TA had significantly lower serum HDL-C levels (p < 0.0001) but higher LDL-C levels (p = 0.037) than those with inactive TA. However, there were no significant differences in the serum sdLDL-C and Lp(a) levels between patients with active and inactive TA. The clinical details of active and inactive TA patients are presented in Table 2.

| Comparison of clinical manifestations and outcomes between TA patients with and without coronary arteriostenosis
TA patients were assigned to three groups based on the degree of coronary stenosis: Group I (n = 21), at least one site of coronary stenosis >50%; Group II (n = 19), at least one site of coronary stenosis 1-50%; and Group III (n = 150), no coronary stenosis (0%). The onset age of Groups II and III patients was lower than that of Group I patients (p < 0.05). Numano subtype V was mainly observed in the Group I patients (76.19%). There were significant differences in the frequencies of systemic symptoms among patients of Group I, Group II, and Group III (p < 0.05), including arthralgia/arthritis, headache, and chest tightness/pain. For results related to vascular reaction, there were significant differences in the frequencies of pulse deficit, asymmetric blood pressure, and hypertension in the Group I, Group II and Group III (p < 0.05) patients. Concerning the lipid parameters, Group I had higher TC, TG, LDL-C, sdLDL-C, and Lp(a) levels and a higher sdLDL-C/LDL-C ratio compared with Groups II and III (p < 0.05, Table 3 and Figure 1). The variables that showed significant differences between the three groups (Table 3) Table 4). The ROC curve analysis results for risk factors for coronary arteriostenosis in TA are given in Table 5.

| Determination of cutoff values for sdLDL-C and Lp(a) for predicting coronary arteriostenosis in TA
A serum cutoff point of 0.605 mmol/l for sdLDL-C maximized the diagnostic efficacy in assessing coronary arteriostenosis in TA, with a sensitivity of 60.00% and a specificity of 79.30% (Table 5).
A serum cutoff value of 0.045 g/L for Lp(a) maximized the diagnostic efficacy in assessing coronary arteriostenosis in TA, with a sensitivity of 95.00% and a specificity of 37.30% (Table 5).

| DISCUSS ION
To the best of our knowledge, this was the first study to investigate the correlations between serum sdLDL-C and Lp(a) levels and F I G U R E 1 Comparison of serum concentrations of sdLDL-C and Lp(a) among the different groups. A, Serum sdLDL-C concentrations were significantly different between TA patients and healthy subjects; B: serum Lp(a) concentrations were significantly different between TA patients and healthy subjects (p < 0.0001); C: Group II and III patients had lower sdLDL-C concentrations than Group I patients (p < 0.05); D: Group I patients had a higher Lp(a) concentration than Group II and III patients (p < 0.05). TA, Takayasu arteritis; Group I: coronary stenosis >50% in TA patients; Group II: coronary stenosis 1%-50% in TA patients; and Group III: coronary stenosis (0%) in TA patients coronary arteriostenosis in Chinese TA patients. We found TA patients had higher concentrations of serum sdLDL-C and Lp(a) than healthy controls. After grouping patients by the degree of coronary stenosis, Group I had significantly higher levels of sdLDL-C and Lp(a) than Groups II and III. We further identified that serum sdLDL-C and Lp(a) levels and sdLDL-C/LDL-C ratio may be used as diagnostic factors for coronary arteriostenosis in TA patients.
Takayasu arteritis is a rare autoimmune inflammatory vasculitis.
The prolongation of the process of inflammatory hyperplasia of the arterial intima and contraction of the fibrous matrix and the adventitia of the ascending aorta together cause coronary stenosis in TA patients. 37 Acceleration of atherosclerosis caused by vasculitis may be another mechanism behind coronary arteriostenosis in TA. 38 The rate of coronary arteriostenosis in TA is relatively low, and several studies have reported an incidence of coronary arteriostenosis in TA between 7% and 30%, [4][5][6][7][8][9] rates which are consistent with the incidence of ~21% in the present study. The prognosis of TA patients with coronary arteriostenosis is often poor, and many patients die of cardiac events. 39 Hence, it is necessary to make an early diagnosis in TA patients, especially in the prestenotic phase, and coronary revascularization and bypass grafting should be undertaken promptly during the stable stage for TA patients. 40,41 Previously, inflammatory factors such as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level have been used to evaluate the activity of TA. 42 Indeed, in the present study, we also detected significant differences in the ESR and CRP levels between active and inactive TA patients. However, no specific serum marker that can identify coronary arteriostenosis in patients with TA has been previously reported. According to its size and density, sdLDL-C, a subclass of LDL-C, has a greater tendency for endothelial infiltration and is associated with a higher susceptibility to atherogenesis. 43,44 sdLDL-C has a lower affinity for LDL receptors, resulting in a longer period of particle retention in circulation and increased sensitivity to glycosylation, oxidation, and scavenger receptor uptake. 44 In addition, sdLDL-C is more susceptible to oxidation and proteoglycan binding, consequently resulting in increased arterial thickness. 45 Therefore, sdLDL-C has a higher atherogenic profile.
Relevant studies have shown that the determination of sdLDL-C is helpful in risk assessment and the determination of cardiovascular residual risk. 46 Recent studies have shown that some diseases including obesity, 44,45 metabolic syndrome (MetS), 45,47,48 systemic hypertension, 49 and hepatic diseases 50,51 are associated with high sdLDL-C concentrations. Moreover, the sdLDL-C/ LDL-C ratio has been used as an alternative risk indicator in some comorbidities associated with the cardiovascular system. 45,49-5 4 In line with the previous findings, in the present study, we found that TA patients had higher sdLDL-C levels than the healthy subjects and that the Group I TA patients had a higher sdLDL-C level than the patients in Groups II and III, supporting the notion that serum sdLDL-C levels are correlated with the severity of coronary stenosis in TA patients.
Lp(a), a LDL-like lipid fraction, is a highly pro-atherogenic lipid fraction and believed to contribute to the pathogenesis of atherosclerosis by carrying oxidized phospholipid (OxPL). 55 Several studies have suggested a strong association between increased Lp(a) and cardiovascular disease, including stroke, and aortic stenosis. 56 Also, Lp(a) was shown to be positively correlated with interleukin (IL)-6 and CRP after acute myocardial infarcts, 57,58 indicating its involvement in immune and pro-inflammatory responses. Similar to sdLDL-C, in the present study, we also found that TA patients had a higher Lp(a) level than the healthy participants and that Group I had higher Lp(a) levels than Groups II and III, indicating that serum Lp(a) levels are associated with TA severity.
Abnormal blood lipid levels occur in many autoimmune diseases The limitations of this study should be noted. First, this was a single-center, retrospective study, which had some intrinsic shortcomings including sampling bias. Also, we did not take into consideration the potential effects of the treatments on serum levels of sdLDL-C and Lp(a). Thus, our conclusions should be further corroborated in the future by multi-center, prospective clinical studies.
In conclusion, we report here that TA patients had higher serum sdLDL-C and Lp(a) concentrations than healthy individuals. Also, TA patients with coronary arteriostenosis had significantly higher serum levels of sdLDL-C and Lp(a) than those without coronary arteriostenosis. Additionally, serum sdLDL-C and Lp(a) concentrations and the sdLDL-C/LDL-C ratio might be used as diagnostic factors for coronary arteriostenosis in TA patients.

CO N FLI C T O F I NTE R E S T
The authors declare that there is no conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
All data are available from the corresponding author upon reasonable request.