The Association of Serum AIM2 Level with the Prediction and Short-Term Prognosis of Coronary Artery Disease

Objective Coronary artery disease (CAD), one of the commonest cardiovascular diseases, has high morbidity and mortality. Absent in melanoma 2 (AIM2) is involved in atherosclerosis, and no clinical trials have explored the association between AIM2 and CAD. Therefore, this study was aimed at evaluating the predictive and short-term prognostic value of AIM2 for CAD. Methods 279 patients who underwent coronary angiography were enrolled in this study. The AIM2 level was detected from the serum of collected artery blood samples. The association of serum AIM2 level with the prediction and short-term prognosis of CAD was further assessed. Results The serum AIM2 level of the CAD group was significantly higher than the control group (5.5 ± 2.1 vs. 3.7 ± 1.7; p < 0.001). AIM2 was demonstrated to be the risk factor of CAD [odds ratio, 1.589; 95% confidence interval (CI), 1.346-1.876; p < 0.001]. The area under the receiver operating characteristic (ROC) curve of 0.738 showed the diagnostic value of AIM2 in CAD. Additionally, AIM2 was an independent predictor of major adverse cardiovascular events (hazard ratio, 1.453; 95% CI, 1.086-1.945; p = 0.012), and CAD patients with high AIM2 levels (>4.9 ng/mL) had a markedly lower survival rate (log-rank p = 0.040). Conclusions The serum AIM2 level > 4.9 ng/mL can predict CAD to a certain extent. AIM2 might be an independent predictor of its short-term poor prognosis.


Introduction
Coronary artery disease (CAD), one of the commonest cardiovascular diseases, has high morbidity and mortality, which threatens people's life and health [1]. Due to the complex pathogenesis of CAD, atherosclerosis is the basis [2]. Absent in melanoma 2 (AIM2), the receptor of cytosolic innate immune, can recognize and bind with doublestranded DNA (dsDNA), leading to AIM2, apoptosisassociated speck-like protein (ASC) and caspase-1 assembling to form AIM2 inflammasome [3]. After AIM2 inflammasome activation, N-terminal domain of gasdermin D (GSDMD-NT) released from GSDMD via caspase-1 cleavage eventually results in cell pyroptosis and proinflammatory factor interleukin-1β (IL-1β) and interleukin-18 (IL-18) release, which is involved in the initiation and progression of atherosclerosis [4,5].  Journal of the Renin-Angiotensin-Aldosterone System diagnosed with CAD and separated into the CAD group. Non-CAD was confirmed in the control group of 96 individuals. The following were exclusion criteria: myocarditis, cardiomyopathy, valvulopathy, severe cardiac, hepatic and renal dysfunction, autoimmune diseases, hematologic disorders, peripheral vascular diseases, infectious diseases, malignancies, allergy to iodine and iodinated contrasted medium, and loss to follow-up. The current study was approved by the institutional ethics committee for clinical research of our hospital (No. 2020ZDSYLL207-Y01). All selected participants signed a written informed consent.

Baseline Characteristics Collection and AIM2 Assay.
Baseline characteristics, including demographic data, past histories, echocardiography, laboratory parameters, and medications, were recorded by experienced clinicians. Venous blood samples for testing laboratory parameters were collected after overnight fasting and assayed by automatic biochemistry analyzers in the clinical laboratory. Serum was obtained from centrifugation of collected artery blood samples (5 mL) before CAG and maintained at -80°C refrigerator. The serum AIM2 level was detected by human AIM2 ELISA kits (Meimian Biotechnology, Yancheng, China).

Follow-Up and Endpoints.
All patients had a 180-day follow-up for major adverse cardiovascular events (MACEs), including cardiogenic death, target vessel revascularization (TVR), heart failure, nonfatal myocardial infarction, and stroke, and all these data were acquired through returning visits or telephone.
On ROC curve analysis (Figure 2), the AUC was 0.738 (95% CI: 0.679-0.797, p < 0:001), and the sensitivity and specificity of AIM2 were 60.1% and 76.0%, respectively, when the optimum cut-off was 4.9 ng/mL, demonstrating the diagnostic value of AIM2 in CAD. Control CAD AIM2 (ng/mL) Figure 1: The serum AIM2 levels in the CAD group and the control group. 3 Journal of the Renin-Angiotensin-Aldosterone System Then, the groups were divided into low (≤4.9 ng/mL, n = 73) and high (>4.9 ng/mL, n = 110) AIM2 level groups by the cut-off value of AIM2 level to study the effect of AIM2 on clinical outcomes of CAD. Table 4 shows that, during the 180-day follow-up, MACEs happened in 21 (19.1%) subjects in the high AIM2 level group and 6 (8.2%) subjects in the low AIM2 level group, and the difference was significant (p = 0:042). No significant differences were found between the two groups in cardiogenic death, TVR, heart failure, nonfatal myocardial infarction, and stroke. Kaplan-Meier survival analysis exhibited that CAD patients with high AIM2 levels (>4.9 ng/mL) had a markedly lower survival rate (log-rank p = 0:040) (Figure 3).

Discussion
Former strong evidence has shown that AIM2 was involved in atherosclerosis, and a high level of AIM2 was expressed in atherosclerotic plaque of the human carotid artery and mice [4,[6][7][8]. However, as of yet, the clinical significance of the serum AIM2 level in CAD patients has not been identified. Our study first revealed that the serum AIM2 level of CAD patients was higher than that of controls. Of note, AIM2 was positively correlated to LDL-C, Scr, and smoke, the CAD risk factors, and was the risk factor of CAD. These can be explained as follows: (i) atherogenic risk factors, like LDL-C and high glucose, and cytokines involved in atherosclerosis, like tumor necrosis factor-alpha (TNF-α) and interferon-γ (IFN-γ), can upregulate AIM2 expression [8][9][10][11][12]. (ii) AIM2 can enhance coronary artery endothelial cell injury, endothelial-monocyte adherence, monocyte recruitment, and macrophage accumulation in pathological parts [4,[12][13][14]. (iii) Migration from the vascular media to the intima of vascular smooth muscle cells (VSMCs) can be facilitated by AIM2 [6]. (iv) AIM2 inflammasome activation and atherogenic proinflammatory factor interleukin-1β (IL-1β) and interleukin-18 (IL-18) release promote inflammatory responses of atherosclerosis [7,12]. (v) Larger necrotic core and thinner fibrous cap caused by VSMC pyroptosis and inflammation via AIM2 decrease plaque stability [4,7,15,16]. The relationship between the AIM2 level and clinical outcomes of CAD remains unclear. In recent studies, Li et al. [17] found that upregulation of AIM2 aggravated myocardial damage in ischemia/reperfusion (I/R) mice. Devi et al. [18] revealed that the AIM2 inflammasome activation was associated with maladaptive left ventricle (LV) remodeling and dysfunction after myocardial infarction. Wang et al. [10] found that diabetic rats with higher AIM2 levels in heart induced by streptozotocin showed severe left heart insufficiency, including metabolic block, cardiomyocyte death, and myocardial fibrosis. Therefore, AIM2 was to be related to cardiac structure and function, which might affect the prognosis of CAD. The present study found that MACEs were more prone to be existed in patients with high AIM2 levels. More to the point, after the addition of various risk factors, AIM2 was still an independent predictor of MACEs. As above, the AIM2 level had close relationship with short-term cardiovascular events.
The research above may suggest that the new therapy of AIM2 for CAD is full of promise. Paulin et al. [7] found that the application of AIM2-antagonizing synthetic oligonucleotide A151 on hypercholesterolemic mice reduced VSMC death and necrotic core size, promoted lesional collagen deposition, and accelerated fibrous cap thickening, which decreased plaque vulnerability. Li et al. [17] found that using sevoflurane in myocardial I/R mice could reduce infarct size and cardiomyocyte apoptosis through the downregulated AIM2 expression in the myocardium. Although these discoveries have confirmed its feasibility in animal experiments, there have been no safe and practicable human tests until now, and it remains to be seen whether the same results can be obtained in human trials. What is more, pharmacological inhibition of AIM2 might produce side effects  Journal of the Renin-Angiotensin-Aldosterone System responsible for less inflammatory responses mediated by AIM2 inflammasome, which is also worthy of consideration. Several limitations existed in our study. First, its singlecenter performance, the small sample size, and the short follow-up time tended to impact the reliability of the results. Second, AIM2 may affect atherosclerosis through inflammation via inflammasome, but some involved inflammatory indicators were not detected. Finally, AIM2 made a difference to the pla-que stability, but the relation between AIM2 and plaque vulnerability in CAD patients was not investigated owing to the lack of plaque evaluation via instruments. Therefore, advanced researches with more subjects and longer follow-up times are required to validate these findings further, and additional evaluations of related inflammatory cytokines and plaque vulnerability would make the discoveries much more sense.

Conclusions
In conclusion, this study demonstrated that the serum AIM2 level > 4:9 ng/mL can predict CAD to a certain extent. Also, AIM2 might be an independent predictor of its short-term poor prognosis.

Data Availability
Data related to this paper can be made available from the corresponding author upon reasonable request.

Conflicts of Interest
The authors declare that they have no conflicts of interest.