Numerous studies have demonstrated that the inflammatory level is increased in the ACS patients [11, 12, 28, 29]. Shantsila and Lip  highlighted that monocytes were actively involved in the pathological processes related to ACS, which promoted the synthesis of pro-inflammatory molecules, such as IL-6, tumor necrosis factor-α (TNF-α) and hs-CRP. Among them, hs-CRP has been proved to be the strongest and most significant predictor of the inflammatory level and the risk of plaque instability and rupture [31–33]. Our studies showed that the serum concentration of hs-CRP and the total white blood cells were elevated in the ACS group, which was in accordance with previously published studies [34, 35], indicated that inflammation was correlated with the development of cardiovascular events.
Among the inflammatory factors, IL-6 induces the production and secretion of CRP . In the present study, we found that the expressions of IL-6 mRNA and protein in PBMCs were significantly increased in ACS group and then levels of IL-6 mRNA were positively correlated with the serum concentration of hs-CRP, which indicated that PBMCs were actived in the ACS group and more inflammatory factors were synthesized in cells.
The disruption of unstable coronary artery plaques is responsible for the majority of incidents of ACS [1–3, 37]. FAS is a significant contributor to the rupture of atherosclerotic plaques. Firstly, increased SFA concentrations, which is inversely associated with cap thickness, might reflect a predisposition to rupture . Results also showed that increased FAS in PBMCs promote synthesis of SFA . Secondly, as already noted, the disrupted plaques are intimately related to the accumulation of lipid-filled macrophages at their edges. Macrophage cells produce cytokines that activate neighboring smooth muscle cells, resulting in extracellular matrix formation, fibrosis, and plaque instability, which play key roles in ACS [5, 38, 39]. FAS is also the key enzyme of the maturation of macrophages, as the uptake of modified lipoproteins is inhibited when fatty synthesis is suppressed during the differentiation process of the monocyte . Therefore, FAS increase the occurence of ACS by regulating the synthesis of SFA and augmenting numbers of mature macrophages in the lipid core. Our results showed that, compared with the control group, the expression levels of FAS mRNA were significantly increased in the ACS group, which provided important evidence for the association between FAS and ACS.
A study showed that inflammation upregulated mRNA and protein expression of FAS, and stimulated lipogenesis in non-adipose tissues, causing ectopic lipid deposition . We hypothesized that the composition of SFA in plaques was further increased as a result of upregulated FAS expression in the inflammatory state. Our studies proved that compared with the control group, the expression levels of FAS mRNA were positively correlated with the serum concentration of hs-CRP, which showed that the variation of fatty acid metabolism reflected high levels of inflammatory status in vivo. Therefore, it could be speculated that the expression of FAS in PBMCs was closely correlated with the vulnerable state of plaques and the inflammatory levels in the ACS patients.
Furthermore, our study also showed that the increased expression of FAS mRNA and protein in PBMCs from the ACS group were dose-dependently inhibited by sEHi. This result seems to be in agreement with a previous study in Mesenchymal stem cells (MSCs) which demonstrated that the decrease of FAS was dose dependent in MSCs treated with EETs . In their study, they provided direct evidence that EETs induced increased expression of heme oxygenase-1 (HO-1) led to the increases in adiponectin, phosphorylation/inactivation of Acetyl-CoA carboxylase 1 (ACC1) and consequently decreased levels of FAS . Most important, they concluded that increased expression of HO-1 might be a trigger for changes in lipid metabolism. HO-1, widely expressed in cells and tissues, is a rate-limiting enzyme that catabolizes heme and is important for the suppression of inflammatory responses . Based on these data, we speculated the possible mechanism of our study was that sEHi lead to augmented circulation levels of EETs, which increased expression of HO-1, triggered a series reaction, consequently attenuated the levels of FAS expression. But the detail of the mechanism is unknown, and further studies are required.
Rae and Graham  showed that the C75, which was found to be an inhibitor of FAS , effectively blocked pro-atherogenic metabolic responses to a inflammatory factor, preventing this factor from inducing increases in macrophage triacylglycerol and cholesteryl ester content. It has been suggested that lipid accumulation induced by inflammation in cells could be reduced by inhibiting the synthesis of fatty acid by FAS. Moreover, the last study showed that induction of fatty acid synthesis by FAS was absolutely necessary for monocyte differentiation and the phagocytic activity of macrophages . The inhibition of FAS could prevent lipoprotein uptake during monocyte differentiation , which was the crucial step of the maturation of macrophages. Additionally, it has been demonstrated previously that treatment with sEHi reduced the area of atherosclerotic lesions, and these effects were associated with a reduction of serum lipid and IL-6 .
IL-6 plays a significant role in the development of acute inflammatory responses, including endothelial and lymphocyte activation . In our study, the increased expression of IL-6 mRNA and protein in PBMCs from the ACS group were inhibited by sEHi in a dose-dependent manner, which was consistent with the anti-inflammatory properties of sEHi in previous studies [22, 43]. Resident macrophages would not produce pro-inflammatory proteins, such as TNF-α, IL-6, without nuclear factor kappa B (NF-κB) translocation to the nucleus . Therefore, activated NF-κB was the underlying mechanism for elevated expression levels of IL-6 in PBMCs from patients with ACS. Furthermore, it was not difficult to deduce that anti-inflammatory properties of sEHi, especially lower expression levels of IL-6, might involve inhibition of NF-κB activation, though NF-κB activation was not measured directly in these studies. However, future studies need to elucidate the underlying mechanisms.
Some limitations of our study should be considered. Firstly, although SFA played an important role in the development of ACS, we did not monitor the SFA in plaques or plasma. In fact, we have realized the important role of measurement of SFA in plaques, however there are some difficulties: (1) as noted in our manuscript, we expected the concentration of SFA in plaques was reduced by regulating FAS, consequently decreased the occurrence of ACS. But it was impossible to get the plaques of ACS patients. (2) Afterwards, we figured out whether it was feasible to detect the concentration of SFA in plasma instead of plaques? But the answer is negative. Because the concentration of SFA in plasma was liable to be influenced by food metabolism. Moreover, a study showed that the concentration of SFA in plaques was not associated with it in plasma . So it is not feasible to detect SFA in plasma instead of plaques. Taken together, we could not detect the concentration of SFA but speculated the reduction of SFA in plaques theoretically. Secondly, ACS encompass unstable angina, ST-elevation myocardial infarction (STEMI), and non-STEMI; however, we did not study the expression of FAS among these different categories of ACS. Thirdly, in our study, we studied the function of FAS in vitro, but the results in vivo remained unknown. Finally, the potential mechanisms underlying the observed effects were undefined.