2.1 Solutions and Drugs. We used the water-soluble form of Quercetin “Corvitin” (PJSC SIC “Borshchahivskiy CPP”, Kyiv, Ukraine). RPMI medium, fetal bovine serum (FBS), antibiotics, Hoechst 33342, phorbol myristate acetate (PMA), Percoll, Hanks balanced salt solution (HBSS), glucose, and salts were purchased from Sigma Chemical (USA). Free DNA concentration was measured using the Quant-iTPicoGreen dsDNA assay kit (Invitrogen).
2.2 Animals and bioethics. All of the manipulations with laboratory animals were performed in accordance with the guidelines of the Declaration of Helsinki, Directive 2010/63/EU of the European Parliament and of the Council on the protection of animals used for scientific purposes (22.09.2010) and Document №3447-IV (2006) of the Parliament of Ukraine “On the Protection of Animals from Brutal Treatment”. The protocol of the study was approved by the Institutional Committee on Bioethics.
Thirty-two male Wistar rats, 330–350 g of weight, were housed in standard conditions and kept on a 12 h light/dark cycle with ad libitum access to food and water. Animals were randomized into three groups: sham-operated (n = 10), MI group (n = 11), and MI + Quercetin (MI + Q) group (n = 11).
2.3. In vivo model of MI and cardiodynamics assay. MI was induced by ligation of the left anterior descending coronary artery (LAD). Briefly, rats were anesthetized with 1,5 g/kg of urethane and fixed at the surgery table. When the adequacy of anesthesia was monitored by loss of muscular tone, the trachea was catheterized and connected to a small animal lung ventilation apparatus (Harvard apparatus, USA). The right carotid artery was separated and catheterized with the ultrathin catheter (2F) with the Pressure-Volume sensor (Millar Instruments, USA). The catheter was moved further to the left ventricle of the heart to obtain a clear P-V loop at a monitor. After 15–20 min of steady state, the cut between the fifth and the sixth ribs was performed, and an extender was placed to get access to the heart. Then, the LAD artery was ligated with a 5 − 0 propylene suture (3/8, 6/0, 10 mm, Medicor-Budapest) for 40 min. Reperfusion was initiated by removing the ligature from the LAD. Next, recording of cardiodynamic parmeters was continued for the following 90 min.
In the sham-operated group, the procedure was stopped after the ligature was undergone below the LAD artery without making a nod. In the MI + Q group, Quercetin was injected 10 min before the start of reperfusion at the dose of 50 mg/kg into the tail vein.
Digital signal from 2F as P-V loop was recorded with data acquisition system throughout the experiment in online mode and later analyzed with PVan-400 software. The following cardiodynamic parameters were assessed: end-diastolic pressure (EDP), end-systolic pressure (ESP), +dP/dtmax and -dP/dtmax, end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF), the heart rate, cardiac output (CO), and stroke work (SW). Data were analyzed starting from baseline values, at the 5th and the 40th min after LAD artery ligation, and at the 5th, 30th, 60th and 90th min of reperfusion.
2.4. PMNs isolation and NETs detection. In order to obtain PMNs, the blood of animals was collected and stabilized by EDTA in monovettes (Sarstedt), mixed with 0.9% NaCl in a ratio of 1:1, and carefully laminated on the Percoll gradient with layer densities of 45%, 54%, and 63%. After gradient centrifugation of the blood (3,000 rpm for 15 min), PMNs were detected between the second and third layers. The granulocytes were then washed with HBSS buffer and diluted in RPMI media with 10% (v/v) of heat inactivated FBS. The PMNs were plated in the 24-well dish or in the cell culture Petri dish with a density of 100 000 cells/cm2. To stimulate NETs formation as a positive control, 20 nM of PMA were added to cell cultures for 3 h. Detection of NETs was performed using a fluorescence microscope with the staining of cells with fluorogenic dyes Hoechst 33342 (biz-benzamide) and propidium iodide that directly stain chromatin (3.75 mM).
Additionally, the concentration of DNA released into the blood stream was measured in blood plasma using Hitachi 4000 spectrophotometer with a Quant-iTPicoGreen dsDNA assay kit (Invitrogen) following the manufacturer’s instruction.
2.5. Statistics
Shapiro-Wilk test was used to evaluate the normality of the distribution of data in each group. Levine’s test was used to detect the homogeneity of variance among groups. In the case of homogeneity, a one-way analysis of variance (ANOVA) was applied to compare means between homogeneous groups followed by the Bonferroni post hoc test. While comparing heterogeneous or not normally distributed data, the Kruskal-Wallis test with Mann-Whitney post hoc analysis was adopted. P < 0.05 was assumed as statistically significant.