With an aim to explore the associated biomarkers of LHI and MCE, we enrolled patients admitted within 24 h after the onset of AIS, and collected their blood samples on admission. We found that a higher level of serum concentration of MIF at baseline was significantly associated with LHI, and had possible association with a higher risk of MCE. We also found that a higher level of serum concentration of MMP-9 at baseline was associated with both LHI and MCE. However, we didn’t find any association between TLR2/4 and LHI or MCE.
Macrophage migration inhibitory factor (MIF) is involved in various physiological processes such as immune response, hypoxia adaptation, and inflammation. Previous clinical and experimental studies of ischemic stroke have found that the expression of MIF is significantly increased after cerebral infarction[13, 20, 21]. LHI is the type of cerebral infarction with the worst prognosis due to its dangerous condition and many complications[22]. At present, the diagnosis of LHI mainly relies on CT or MRI. However, in the early stage of AIS, CT is not sensitive for infarct lesions[23]. To compensate for the defect of CT in early stage of stroke, DWI (diffusion-weighted imaging) is required for early detection of LHI. For some remote areas, DWI could not be performed, so biomarkers related to LHI, such as MIF and MMP-9, could help to identify the occurrence of LHI. Li’s study showed that serum MIF levels at admission were positively correlated with infract volume in patients with AIS[24]. This conclusion supported our study’s result, and we found the direct correlation between MIF and LHI, which extended Li’s study. The potential mechanism could be that increased MIF levels promote monocyte and neutrophil recruitment and infiltration in brain lesions following stroke[24]]. Therefore, other inflammatory biomarkers related to MIF might also have the association with LHI.
Thus, we also found a positive linear correlation between MIF and MMP-9. Wang's study found that in oral squamous cell carcinoma, MIF could affect its progression and metastasis by regulating MMP-2/9 upstream[25]. In addition, both the findings in murine macrophages and osteoblasts suggested that MIF can lead to upregulation of MMP-9 expression by activating inflammatory pathways. After AIS, MIF promotes blood-brain barrier disruption and expands infarct area by downregulating tight junction associated proteins[26, 27]. Therefore, we reasoned that MIF could affect the occurrence of complications such as MCE through the regulation of MMP-9 in patients with LHI.
There was no clinical study that demonstrated an association between Toll-like receptors and LHI or M CE. Our study found that TLR2/4 was lower in patients with LHI. In vivo knockdown of the TLR2 gene in mice reduced inflammatory cell infiltration and neuronal apoptotic damage after brain infarction, and knockdown of theTLR4 gene reduced infarct area[15, 17]. This result was opposite to our findings, and the reasons were as following. Firstly, this study was study in animal model, but we studied TLRs level in patients’ serum. Animal experiments might behave differently from humans. Secondly, TLRs were associated with inflammatory responses to subacute stress[15, 28]. The median time of our blood sample was 3 hours, so the time was the early stage of stroke. According to the temporal analysis of our study, levels of TLRs might not change at 3 hours. Thirdly, the sample size was not large enough to draw the conclusion.
All these four biomarkers can be easily measured and had available assays, and it is useful to create a panel included these 4 biomarkers and use it as a routine blood test in patients with AIS to find the patients who had ability to develop LHI or MCE early. Our findings suggested detecting the multiple biomarkers at baseline was a good way to identify high-risk patients with LHI or MCE. patients who had several elevated biomarkers, needed to choose the suitable therapeutic interventions and reduce the occurrence of complication[29].
The limitations of our study were as following: firstly, we enrolled 263 AIS patients into analysis, and the proportion of patients with LHI was higher than 15.65-20% in patients as pervious reported. The reason is that some of the AIS patients without LHI were unwilling to provide blood sample. Secondly, up to now, evidence is lacking to prove the combined impact of MIF, TLR2/4 and MMP-9. Therefore, some of our hypotheses need animal experiments to verify the mechanism. Thirdly, it is worth discussing whether the level of biochemical markers in serum could reflect the level of markers in brain. Although our conclusion was significant in plasma, whether the same change in the brain barrier needs more direct detection methods, such as the detection of biochemical markers in cerebrospinal fluid. Nevertheless, considering the clinical implementation and patient acceptance, it was easier to predict the malignant outcome through the detection of serum biomarkers. Because the number of patients at different time points was not large enough to perform the analysis, the study on the dynamic changes of the four biomarkers only described the median level of the biomarkers at different time points.