In the present study, the two groups at the beginning of the study were matched for serum levels of interleukins 13 and 22 to compare the two groups correctly. On the day of surgery and before induction, serum IL-22 levels were significantly decreased in the Melatonin group, whereas in the control group serum IL-22 levels were not significantly changed. Given that they had taken melatonin 2 weeks before surgery, the decrease in IL-22 was justified in this group. Also in the control group, no change in IL-22 was observed. There was also a significant difference between the two groups at this stage and the level of IL-22 in the Melatonin group was significantly lower.
In the third measurement step (T3), 6 hours after the pump was removed by the cardiac surgeon, both groups showed an increase in serum IL-22 levels, which was significant in relation to T2 in both groups and T1 only in the Melatonin group.
In the fourth measurement, serum levels of IL-22 did not change significantly in the two groups compared to the third stage, but compared to the T1 stage, both groups showed a significant increase in T4. It can be argued that the acute phase of IL-22 occurs at T3 and reaches its maximum level after which its level has decreased but its decrease has not been significant. Inter-group differences in the T4 level of IL-22 were also significantly higher in the control group than in the Melatonin group. Given that patients in the Melatonin group at the T3 stage also had lower IL-22, this is justified because no significant change in T4 over T3 was observed in either group.
In the present study, serum levels of IL-13 at T1 were similar between the two groups. But unlike IL-22, this cytokine did not show a significant difference between the two groups at all stages of T2 to T4. In the intra-group analysis in this study, IL-13 at T2 compared to T1 in the Melatonin group showed a decrease in IL-13 level, which was significant. But no significant changes were observed in the control group. A non-significant increase in IL-13 serum level was observed in T3 compared to T2 in both groups, which is justified since it is after CABG. There was a decrease in IL-13 in both groups at T4 compared to T3, which was not significant in either group.
It has been shown that the positive effects of melatonin in ischemia-reperfusion damages are related to the activation of the Nrf2 pathway. Nrf2 is a transcription factor. It plays its antioxidant role by binding to DNA antioxidant response element (ARE) and the Nrf2-ARE pathway has an important protective effect in ischemia-reperfusion injury (15). Nrf2 suppresses IL-13 and IL-22 secretion (16, 17). IL-13 and IL-22, upregulate the STAT3 pathway and cause inflammation (18, 19). By the decrease of IL-13 and IL-22, STAT3 is downregulated and prevent inflammation.
These changes in serum levels of cytokines after cardiac surgery have also been shown in other studies. Brull's study showed that 6 hours after CABG, serum IL-6 levels peaked. In that study, IL-6 levels reached 45 times their basal level, 6 hours after CABG (20). In the present study, as in the Brull study, peak levels of both IL-22 and IL-13 were observed 6 h after CABG. In the study of Czerny et al., patients with CABG had the highest serum IL-6 and IL-10 levels at the fourth hour and eighth hours after CABG, respectively (21). Nathan et al. evaluated the serum levels of IL-10, IL-4, and IL-13 in patients who had cardiopulmonary bypass (CPB). In that study, IL-10 peaked at the sixth hour after CPB. However, IL-13 peaked after 24 hours of CPB completion (22). In the Sablotzki study, serum levels of IL-10 were highest in CPB patients at the skin closure stage after CPB completion. However, there was a significant decrease of 6 h after CPB (23). The findings of these two studies are not in line with ours. The main reason for this difference may be the difference in the study population and the type of surgery. A study by Kawamura et al. investigated the changes in IL-10, IL-8, and IL-6 cytokines after aortic declamping. The results of this study showed that the peak of all three interleukins occurs 3 hours after aortic declamping (24). Hsing et al. showed that levels of IL-22 and IL-19 peaked after 8 hours of CPB (12). In the Wan study, it has been reported that the elevation of IL-10 begins 2 hours after CABG (25). The pattern of IL-10 changes in this study is similar to the pattern of IL-22 changes in our control group. IL-22 is functionally similar to IL-10 in that the two cytokines are in the same group (12), so the trend of changes in these two cytokines in the present study and the Wan study is justified. In Struber et al.'s study, serum IL-8 and IL-6 levels peaked at the eighth hour after CABG. C1-INH, TNF-R1, and TNF-R2 cytokines were also measured in this study, all of which increased after CABG surgery and peaked within 2 to 8 hours after surgery (26). Surgery causes a range of metabolic, endocrine, and immune alterations (27). The inflammatory response in cardiac surgery is made by complex interactions with several pathways such as production or activation of complement, neutrophils, thrombin, cytokines, mast cells, and some other multiple inflammatory mediators (28). Mechanisms such as exposure of blood to nonphysiologic surfaces, anesthesia, trauma, body temperature alterations, and ischemia or reperfusion injury may be responsible for these pathological effects (29), which results in immunologic reactions and release proinflammatory cytokines, arachidonic acid metabolites, platelet-activating factors, endothelins, endothelial, and leukocyte adhesion molecules which induce the overproduction of reactive oxygen species (30, 31).
During the inflammatory process, the stimulation of inflammation-related genes can happen as a result of activation of the nuclear transcription factor-kappa B (NF-κB) (32). Many studies have revealed that melatonin modulates the NF-κB signaling pathway throughout inflammation (33–35). Reports recommend that melatonin performs its anti-inflammatory effects by modulating both pro- and anti-inflammatory cytokines in various pathophysiological situations (36, 37). It was displayed that the presence of melatonin’s receptors in a mast cell line by inhibiting the release of TNF-α modulates an anti-inflammatory pathway (38). Other anti-inflammatory activities of melatonin are including prevention from the synthesis of prostaglandins, production of adhesion molecules (39, 40), and downregulation of cyclooxygenase 2 expressions in macrophages (41), and the decrease of the polymorphonuclear cell recruitment to the inflammation location (39, 42). Melatonin also counteracts inflammatory processes by scavenging free radicals, which contributes to inflammation (43–45).