Evaluation of vascular cell adhesion molecule-1, intracellular cell adhesion molecule-1 and E-selectin levels in preeclampsia: A Systematic Review and Meta-Analysis.

Background Soluble adhesive molecules are potential mediators of endothelial dysfunction in preeclampsia. The purpose of this study was to examine the relationship between pre-eclampsia and maternal circulation vascular cell adhesion molecule-1 (VCAM-1), Intracellular cell adhesion molecule-1(ICAM-1) and E-selectin. Methods VCAM-1, ICAM-1 and E-selectin studies of maternal circulation in preeclampsia and normal pregnant women were reported by systematic literature search in PubMed (Medline), with 21 eligible reports. The standardized mean difference (MD) and their 95% condence intervals (CIs) were calculated as random effect analysis of association among studies. Results Preeclampsia is associated with elevated VCAM-1 [mean difference (MD) = 1.17 ng/ml, 95% condence interval (CI) 0.85-1.50 ng/ml], and E-Selectin (MD = 2.18ng/ml, 95% CI 1.16-3.20ng/ml), but not associated with ICAM-1 (MD= 0.43ng/ml, 95% CI -0.03-0.90ng/ml). In the subgroup analysis of mild and severe preeclampsia, VCAM-1, ICAM-1 and E-selectin all showed increased levels compared with normal pregnancy women. Conclusion The meta-analyses have shown elevated VCAM-1 and E-selectin levels in the circulation of pregnant women with preeclampsia. performed a subgroup analysis of preeclampsia patients. Subgroup 1, mild preeclampsia (M-PE); Subgroup 2, severe preeclampsia(S-PE).


Background
Preeclampsia is a high blood pressure disorder that occurs during pregnancy and affects about 2 to 8% of pregnant women (1). Preeclampsia is signi cantly associated with maternal and fetal morbidity, including maternal eclampsia and HELLP syndrome, as well as premature birth and intrauterine growth restriction. Moreover, the effects of Preeclampsia on the health and quality of life of women and their offspring after delivery are lifelong (2).
Previous studies have shown that in ammatory mediators such as soluble adhesive molecule may be potential mediators of endothelial dysfunction in preeclampsia (3). Adhesion between leukocytes and endothelial cells is mainly affected by adhesion molecules, including vascular cell adhesion molecule-1 (VCAM-1), Intracellular cell adhesion molecule-1(ICAM-1) and E-selectin. In ammation-mediated endothelial injury results in a pro-in ammatory signaling cascade and the expression of VCAM-1, which recruit blood monocytes to the vascular wall so that more cytokines and chemokines are permanently released at the site of injury (4). VCAM-1 can cause endothelial dysfunction by providing an adhesion phenotype to vascular endothelium (5). ICAM-1 is a member of the immunoglobulin superfamily by binding to leukocyte 2-integrin and mediating its functional activity (6). ICAM-1 plays an important role in regulating leukocyte adhesion to endothelial cells and leukocyte migration (7). E-selectin is a member of the selectin family involved in mediating the interaction between white blood cells and endothelial cells, and is expressed only in endothelial cells, while the increased circulating level of e-selectin may indicate the activation and injury of endothelial cells (8) .
The soluble form of these molecules can be measured and considered as a biomarker for monitoring endothelial function in preeclampsia (9)(10)(11). However, whether there is a systematic increase in cytokine concentrations in preeclampsia remains controversial because of con icting reports from clinical studies.
Based on this, the purpose of this meta-analysis was to systematically investigate the circulating levels of VCAM-1, ICAM-1 and E-selectin in pregnant women with and without preeclampsia. It is helpful to understand whether these molecules are involved in the pathological process of preeclampsia, elucidating the state of endothelial function in this disease, and ultimately may help us better understand the process of this disease.

Methods
This meta-analysis was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (see additional le 3).

Inclusion and exclusion criteria
Only studies assessing the relationship between soluble VCAM-1, ICAM-1 or E-selectin and PE were included. Meeting the following four criteria can be included in the meta-analysis: (1) Original prospective, retrospective, cross-sectional or prospective case controlled design are accepted for soluble adhesive molecule concentration detection studies. (2) PE was diagnosed as hypertension (140/90 mmHg or blood pressure elevation 15 mmHg) with proteinuria (300 mg/24 h or 1+ dipstick 6h apart) without pre-existing hypertension. Women with systolic blood pressure >160 mmHg and/or diastolic blood pressure >110 mmHg, accompanied by proteinuria >5 g in a 24-hr collection or with ≥3+ on a dipstick, were de ned as severe preeclampsia. Mild pre-eclampsia is de ned as ful lling the criteria for pre-eclampsia but not ful lling the criteria for severe pre-eclampsia. Controls were healthy pregnant women. (3) Maternal peripheral blood was used for concentration detection. (4)Original data should be included in the study and be represented by mean (SD or SE).
Besides, due to the lack of comparability, duplicate publications, review articles, non-English articles, studies in non-pregnant period, studies on the detection of cytokine concentrations in placenta, peripheral blood cytokines and amniotic uid, or detecting cytokine concentrations after exogenous test stimulation, or studies provided with case-only were excluded.

Data extraction
The following information was extracted from each study: author, publication year, study design, and other essential characteristics. For continuity variables, information was collected including the number of case groups and control groups, the mean concentration and standard difference (SD) of maternal plasma or serum VCAM-1, ICAM-1 and E-selectin. If the data provided by the study is standard error (SE), the SE shall be converted into SD according to the formula (SD=SE* ). In addition, ng/ml is the concentration unit of VCAM-1, ICAM-1 and E-selectin for analysis.

Study quality assessment
Two reviewers independently reviewed the titles/abstracts of all possible studies. Since most articles do not show relevant data in their respective abstracts, the most are reviewed in full. In the event of disagreement, the decision is made by the third reviewer.

Statistical processing
For the continuous outcomes, we used an inverse-variance weighted mode(18) to calculate the standardized mean difference (MD) and 95% con dence intervals (CIs). Funnel plot (19) and egger's test (20) was used to evaluate publication bias. If there was no heterogeneity (P ≥ 0.1, I 2 ≤ 50%), we used the xedeffects model. If there was a signi cant heterogeneity (P < 0.1, I 2 > 50%), the random-effects model was adopted to allow for the inherent heterogeneity found between studies. Forest plots of the parametric data were generated using the Stata 15.0 software (Stata Corporation, College Station, TX, USA).

Description of the included studies
Using the initial search for VCAM-1, ICAM-1 or E-selectin related literature, there were 144 potentially eligible citations. VCAM-1, ICAM-1 and E-selectin had a total of 85 articles excluded due to title duplication, animal or in vitro studies, additional interventions, non-english publication, and other exclusion criteria, respectively. In the remaining literatures, 38 articles did not meet the inclusion criteria, respectively. Finally, 21 articles meet these requirements of VCAM-1, ICAM-1 or E-selectin (Fig. 1).

Basic information
Based on the principle of Cochrane systematic review, 21 published cohort studies (6, 7, 11, 14, 16, 21-36) were included in this meta-analysis according to the inclusion and exclusion criteria of the meta-analysis. In the study of VCAM-1, ICAM-1 and E-selectin, there were 934 cases , 585 cases and 400 cases in the group with preeclampsia and 878 cases, 565 cases and 422 cases in the normal blood pressure group, respectively. Table 1-3 describes the experimental characteristics of these studies in more detail (see Additional le 1).

Vascular cell adhesion molecule-1
A total of 17 studies included 934 women with preeclampsia and 878 women with normal pregnancies. The level of VCAM-1 in peripheral blood of preeclampsia pregnant women was higher than that of normal pregnant women (mean difference (MD) = 1.17 ng/ml, 95% con dence interval (CI) 0.85-1.50 ng/ml, Fig 2).The subgroup analysis of mild and severe preeclampsia included 314 women with preeclampsia (174 with mild and 140 with severe) and 184 women with normal pregnancy. Circulating VCAM-1 levels in women with severe and mild preeclampsia were higher than those in normal pregnancy women, respectively (MD = 1.68ng/ml, 95% CI 1.10-2.26ng/ml and MD = 1.12ng/ml, 95% CI 0.67-1.57ng/ml) (Fig. 2).

Intracellular cell adhesion molecule-1
A total of 585 preeclampsia women and 565 normal pregnant women participated in 11 studies. There was no statistical difference in the level of ICAM-1 in peripheral blood of preeclampsia pregnant women compared with normal pregnant women (MD = 0.43ng/ml, 95% CI -0.03-0.90ng/ml, Fig 3). In the subgroup analysis of mild and severe preeclampsia, the studies including 289 patients with preeclampsia (136 with mild and 153 with severe). ICAM-1 circulating levels were slightly higher in women with severe and mild preeclampsia than in women with normal pregnancy (MD = 0.36ng/ml, 95% CI 0.11-0.62ng/ml and MD = 0.31ng/ml, 95% CI 0.07-0.56ng/ml) (Fig. 3). In addition, in the original study without subgroup information, there was no statistical difference in the two groups (MD = 0.49ng/ml, 95% CI -0.35-1.32ng/ml, Fig. 3).

E-Selectin
A total of 400 women with preeclampsia and 422 women with normal pregnancy were included in the analysis. The level of peripheral blood E-Selectin in preeclampsia pregnant women was higher than that in normal pregnant women (MD = 2.18ng/ml, 95% CI 1.16-3.20ng/ml , Fig 4). At the same time, mild preeclampsia also had higher peripheral blood E-Selectin levels than normal pregnant women (MD = 0.92ng/ml, 95% CI 0.51-1.33ng/ml), but the E-selectin levels in severe preeclampsia women were comparable with normal control (MD = 1.80ng/ml, 95% CI -0.11-3.72ng/ml, Fig 4).

Discussion
In this study, we conducted a meta-analysis of the included studies to evaluate the effect of soluble adhesive molecule on preeclampsia. The results showed that compared with the normal pregnancy group, the circulating level of VCAM-1 and E-Selectin was signi cantly increased in the preeclampsia group. However, there was a slight difference of ICAM-1 level between preeclampsia group and normal pregnancy group.
Under normal non-pregnant physiological conditions, VCAM-1 has a low expression on endothelial cells. In normal pregnant women, white blood cells are activated in peripheral blood of, which is mainly regulated by adhesion molecules expressed on the surface of white blood cells and endothelial cells. However, in pathological conditions such as preeclampsia, VCAM-1 is shed to the cell surface and enters the blood circulation after vascular endothelial cell injury, further causing endothelial cells dysfunction (5). In this analysis, we found that the level of VCAM-1 in the preeclampsia group was higher than that in the normal pregnancy group, and was correlated with the severity of preeclampsia, indicating the importance of endothelial cell injury in the pathogenesis of preeclampsia.
ICAM-1 can induce circulating white blood cells to adhere to activated endothelial cells and migrate to the intima of blood vessels, which is an important process of in ammation (37). In this analysis, no difference was found in the level of ICAM-1 between the preeclampsia pregnancy group and the normal pregnancy group in the original studies without subgroup information. However, there were differences in subgroup analysis. Probably because broblasts, white blood cells, endothelial cells, epithelial cells and other cells are activated by various cytokines and then produce many membrane ICAM-1 in the process of in ammation(38). Membrane ICAM-1 rarely falls off into the blood circulation. It could also be due to race or small sample size. Further detection of changes in cell surface adhesion molecules in preeclampsia is needed. E-selectin is expressed by activated endothelial cells under in ammatory stimulation, such as bacterial endotoxin, IL-1, or TNF-α (8). Our results suggest that the expression of adhesive molecule E-selectin is enhanced in patients with preeclampsia and is associated with the severity of the disease. So E-selectin may exacerbate the early in ammatory state of preeclampsia. Moreover, previous studies have found that E-selectin, which is stimulated by TNF-α, plays a pathological mechanism through the NF-κB and JNK/p38 mitogen-activated protein kinase (p38MAPK) pathways, (39). Therefore, understanding the pathogenesis of TNF-α may contribute to understanding the role of E-selectin in preeclampsia.
At present, the changes of VCAM-1, ICAM-1 and E-selectin in maternal circulation are in the same direction, which emphasizes the importance of meta-analysis of the reported parametric data. Preeclampsia is a heterogeneous disease with multiple clinical symptoms. Soluble adhesive molecule of individuals related to preeclampsia can be affected by various factors. It is not surprising that high heterogeneity was found in the meta-analysis, so we need to carefully interpret the results of the analysis. The sources of heterogeneity may be due to differences in gestational weeks (although most of them are in the third trimester), differences in age and weight, inconsistencies in the treatment and collection methods of specimens, different sensitivity of reagents and other unknown confounding factors, which lead to the inability to nd the sources of heterogeneity in this study. It is also possible that we do not know other clinical data, including other speci c conditions such as physical tness or even race at that time, which make it impossible to explain all heterogeneity in this study.
Funnel plot analysis of the parameter data of preeclampsia pregnancy showed that the funnel plot of all three cytokines was asymmetric (data not shown).
However, further detection of publication bias found no publication bias among the three cytokines. This indicates that the asymmetry of funnel plot is not caused by publication bias. However, considering the small number of studies included, the results of this meta-analysis may be greatly in uenced by the studies excluded from this analysis.
It is noteworthy that the soluble VCAM-1, ICAM-1 and E-selectin levels in serum can re ect the role of endothelial cell injury in preeclampsia. These three adhesive molecules interacting with their receptors at the appropriate time and place can play important roles in the in ammatory response. However, this complex and coordinated interaction may be affected by many regulatory factors. Therefore, there are limitations to the interpretation of elevated serum or plasma VCAM-1, ICAM-1 and E-selectin levels.

Conclusion
This meta-analysis showed that maternal circulating levels of VCAM-1, ICAM-1 and E-selectin in preeclampsia women were elevated compared with normal pregnant women, and were correlated with the severity of preeclampsia, suggesting that soluble VCAM-1, ICAM-1 and E-selectin levels were associated with endothelial dysfunction in preeclampsia. However, the value of VCAM-1, ICAM-1 and E-selectin in the evaluation of endothelial dysfunction in pre-eclampsia needs to be veri ed by further well-designed large sample studies.

Consent for publication
Not applicable.

Availability of data and materials
All data generated or analyzed during this study are included in this published article and its supplementary information les.

Competing interests
The authors declare that they have no competing interests.     Forrest blot analysis of serum or plasma concentrations of VCAM-1. The subgroup difference test represents the difference between mild and severe preeclampsia.

Figure 3
Forrest blot analysis of serum or plasma concentrations of ICAM-1. The subgroup difference test represents the difference between mild and severe preeclampsia.

Figure 4
Forrest blot analysis of serum or plasma concentrations of E-selectin. The subgroup difference test represents the difference between mild and severe preeclampsia.