ABC | Volume 114, Nº4, April 2020

Original Article Scherr et al. Interleukin-18 and thrombus precursor protein in CAD Arq Bras Cardiol. 2020; 114(4):692-698 The following exclusion criteria were adopted: Group I (acute): a) coronary artery bypass grafting surgery performed less than six months before. b) Chronic renal failure undergoing dialysis or clearance <30 mL / min. c) Terminal illnesses. d) Ejection fraction prior to ACS <40% (Simpson); e) Not signing the Free and Informed Consent (FIC) form. Group II (chronic): the same as group I plus, a) decompensated DM. b) AMI that occurred less than six months before. c) Unstable angina. d) Class IV stable angina according to the Canadian Cardiovascular Society. d) Functional class III and IV according to the New York Heart Association (NYHA). Group III (control) : a) presence of any obstructive coronary lesion, even if incipient. b) Chronic renal failure undergoing dialysis or clearance <30 mL / min. c) Terminal illnesses. d) Ejection fraction <40% (using the Simpson method). e) Stable angina. f) Unstable angina. g) AMI. h) Decompensated DM. i) NYHA functional class III and IV. j) Not signing the FIC form. Storage and laboratory methods For the measurement of TpP, 4 mL of venous blood were collected, placed in a tube with sodium citrate and centrifuged. After centrifugation, two 1-mL aliquots of plasma were removed to be frozen at -80 °C. The analysis was carried out later using the ELISA method. For the measurement of IL-18, 8 mL of venous blood were collected and placed in a serum gel tube. After collection, we waited 30 min for clot retraction and subsequent centrifugation. After centrifugation, two 1-mL aliquots of serum were removed to be frozen at -80 °C. The analysis was also performed later using the ELISA method. Statistical analysis The data obtained were analyzed using the statistical program SPSS (Statistical Package for the Social Sciences for Windows), version 17.0 of 2008. The level of significance was set at 0.05 or 5% (p <0.05) and the confidence interval at 95%. The following statistical methods were used: Analysis of variance (One-way ANOVA F): used to compare the means of variables that showed normal distribution and had homogeneity of variances by the Levene test. Tukey’s test: used as a complement to the analysis of variance, to compare the means of variables 2 by 2. Chi-square test ( χ ²): used to compare the frequency distributions of the categorical variables from independent samples. This study sample size was determined by a convenience sample; however, it followed the order of recruitment, that is, the first 39 patients in the acute phase of the two participating institutions, the first 40 chronic patients and the 40 controls. This study was approved by the Ethical Committees of HUPE and INC, where patients were recruited, under numbers 2667/2010 CAAE: 0115.0.228.000-10 and 141.432/2012 CAAE: 09086412.9.1001.5272, respectively. The participants signed the Free and Informed Consent (FIC) form before any procedure related to the study was performed. Results The mean age was 59.5 ± 9.7 years (range: 35-83 years), with no statistically significant difference between the groups. In groups I and II there was a predominance of males and in Group III, of females (p = 0.002). Regarding the risk factors of the overall sample, it is noteworthy the high incidence of sedentary lifestyle, overweight / obesity and arterial hypertension in all groups. Table 1 shows the risk factors for CAD between the studied groups. It was observed that only dyslipidemia, being an ex-smoker and physical inactivity showed a statistically significant difference. Group II had a higher prevalence of dyslipidemic individuals when compared to the other groups; Group III had a higher prevalence of non- smoking individuals than the other groups; and Group I had a higher prevalence of sedentary individuals compared to the others. There was no association between risk factors, ethnicity or gender with the results obtained of the markers in all analyzed groups. Mean of intergroup and intragroup IL-18 and TpP markers in table 2 Regarding the differences in the means of IL-18 levels between the groups, it was observed that Group I had higher values than the other groups (1325.44 ± 1860.13 pg / mL), with statistical significance. In the two-by-two comparison, Group I had a higher mean than Groups II (353.81 ± 273.65 pg / mL) and III (633.25 ± 993.93 pg / mL), but Groups II and III showed statistically equal means. Those with instability of atherosclerotic disease had higher levels of IL-18 when compared to patients who had stable coronary lesion or those who had risk factors for CAD in the absence of a coronary atherosclerotic process, allowing us to infer that the increase in IL-18 levels is associated with atherosclerotic plaque instability. Regarding the TpP biomarker between the groups, higher values were observed in Group I (35.86 ± 28.36 µg / mL), respectively, p <0.001) when compared with the other groups. In the two-by-two comparison, Group I also had a higher mean than Groups II (25.66 ± 12.17 µg / mL) and III (18.0 ± 8.45 µg / mL); however, when Groups II and III were compared, it was observed that the means were statistically equal (Table 2). Discussion The identification of asymptomatic individuals with atherosclerosis is essential to implement secondary treatment and prevention measures, as well as those with a possibly more unfavorable evolution. Mallat et al. 13 showed that plasma concentrations of IL-18 are increased in patients with ACS with or without myocardial necrosis, also pointing out that the concentrations correlate with the myocardial dysfunction severity. They studied a sample of 53 patients, admitted to a cardio-intensive unit with chest pain and alteration of the ST-segment in a sequential manner; after troponin analysis, they were selected for the UA or AMI group. The patients belonging to the UA group had a mean IL-18 level 694