Elevations in Circulating sST2 Levels Are Associated With In-Hospital Mortality and Adverse Clinical Outcomes After Blunt Trauma

Abstract

Background: Soluble suppression of tumorigenicity 2 (sST2), a decoy receptor for interleukin (IL)-33, has emerged as a novel biomarker in various disease processes. Recent studies have elucidated the role of the sST2/IL-33 complex in modulating the balance of Th1/Th2 immune responses after tissue stress. However, the role of sST2 as a biomarker after traumatic injury remains unclear. To address this, we evaluated serum sST2 correlations with mortality and in-hospital adverse outcomes as endpoints in blunt trauma patients.

Methods: We retrospectively analyzed clinical and biobank data of 493 blunt trauma victims 472 survivors (mean age: 48.4 ± 0.87; injury severity score [ISS]: 19.6 ± 0.48) and 19 nonsurvivors (mean age: 58.8 ± 4.5; ISS: 23.3 ± 2.1) admitted to the intensive care unit. Given the confounding impact of age on the inflammatory response, we derived a propensity-matched survivor subgroup (n = 19; mean age: 59 ± 3; ISS: 23.4 ± 2) using an IBM SPSS case-control matching algorithm. Serial blood samples were obtained from all patients (3 samples within the first 24 h and then once daily from day [D] 1 to D5 after injury). sST2 and twenty-nine inflammatory biomarkers were assayed using enzyme-linked immunosorbent assay and Luminex, respectively. Two-way analysis of variance on ranks was used to compare groups (P < 0.05). Spearman rank correlation was performed to determine the association of circulating sST2 levels with biomarker levels and in-hospital clinical outcomes.

Results: Circulating sST2 levels of the nonsurvivor cohort were statistically significantly elevated at 12 h after injury and remained elevated up to D5 when compared either to the overall 472 survivor cohort or a matched 19 survivor subcohort. Admission sST2 levels obtained from the first blood draw after injury in the survivor cohort correlated positively with admission base deficit (correlation coefficient [CC] = 0.1; P = 0.02), international normalized ratio (CC = 0.1, P = 0.03), ISS (CC = 0.1, P = 0.008), and the average Marshall multiple organ dysfunction score between D2 and D5 (CC = 0.1, P = 0.04). Correlations with ISS revealed a positive correlation of ISS with plasma sST2 levels across the mild ISS (CC = 0.47, P < 0.001), moderate ISS (CC = 0.58, P < 0.001), and severe ISS groups (CC = 0.63, P < 0.001). Analysis of biomarker correlations in the matched survivor group over the initial 24 h after injury showed that sST2 correlates strongly and positively with IL-4 (CC = 0.65, P = 0.002), IL-5 (CC = 0.57, P = 0.01), IL-21 (CC = 0.52, P = 0.02), IL-2 (CC = 0.51, P = 0.02), soluble IL-2 receptor-α (CC = 0.5, P = 0.02), IL-13 (CC = 0.49, P = 0.02), and IL-17A (CC = 0.48, P = 0.03). This was not seen in the matched nonsurvivor group. sST2/IL-33 ratios were significantly elevated in nonsurvivors and patients with severe injury based on ISS ≥ 25.

Conclusions: Elevations in serum sST2 levels are associated with poor clinical trajectories and mortality after blunt trauma. High sST2 coupled with low IL-33 associates with severe injury, mortality, and worse clinical outcomes. These findings suggest that sST2 could serve as an early prognostic biomarker in trauma patients and that sustained elevations of sST2 could contribute to a detrimental suppression of IL-33 bioavailability in patients with high injury severity.

Keywords: Acute inflammation; Base deficit; Blunt trauma; Clinical outcomes; Coagulopathy; Inflammatory biomarkers; Injury severity; Intensive care unit; Multiple organ dysfunction syndrome; Soluble suppression of tumorigenicity.

Figure 1. Time course analysis of sST2 (A) and IL-33 (B) in the overall cohort (472 survivors and 19 non-survivors) from time of injury up to day 5 post-injury compared to healthy volunteers (n = 12).

Data presented as mean ± SEM. *P < 0.05 by Two-Way ANOVA.

Figure 2. Time course analysis of sST2 (A) and IL-33 (B) in the matched sub-cohorts (19 survivors vs. 19 non-survivors) from time of injury up to day 5 post-injury compared to healthy volunteers (n = 12).

Data presented as mean ± SEM. *P < 0.05 by Two-Way ANOVA.

Figure 3. Time course analysis of sST2 (A) and IL-33 (B) in the injury severity score (ISS)-based groups compared to healthy volunteers (n = 12).

Mild ISS group (n = 180; average ISS = 10 ± 0.3), moderate ISS group (n = 170; average ISS = 19.4 ± 0.2), and severe ISS group (n = 122; average ISS = 34.1 ± 0.7) from time of injury up to day 5 post-injury. Data presented as mean ± SEM. *P < 0.05 by Two-Way ANOVA.

Figure 4. Spearman correlation of plasma sST2 with injury severity score (ISS) within the first 24 h post-injury.

(A) Plasma sST2 correlation with ISS in the overall survivor cohort (n=472; correlation coefficient [CC] = 0.46; 95% confidence interval [CI] = 0.39 – 0.53; P < 0.001). (B) Plasma sST2 correlation with the mild ISS group (n=180; CC = 0.47; 95% CI = 0.35 – 0.58; P < 0.001). (C) Plasma sST2 correlation with the moderate ISS group (n=170; CC = 0.58; 95% CI = 0.46 – 0.67; P < 0.001). (D) Plasma sST2 correlation with the severe ISS group (n=122; CC = 0.63; 95% CI = 0.51 – 0.73; P < 0.001).

Figure 5. Time course analysis of soluble ST2 in: (A) the base deficit ≥ 4 mEq/L (n=84) vs. BD < 4 mEq/L (n=70) groups; and (B) the trauma-induced coagulopathy (TIC, n=98) vs. no TIC (n=98) groups.

Data presented as mean ± SEM. *P < 0.05 by Two-Way ANOVA.

Figure 6. Soluble ST2 to IL-33 ratio from the first blood draw upon admission to the emergency department. (A) sST2/IL-33 ratio in the mild, moderate, and severe ISS groups.

Data presented as mean ± SEM. *P < 0.05 by One-Way ANOVA between the mild and severe groups. # P < 0.05 by One-Way ANOVA between the moderate and severe ISS groups. (B) sST2/IL-33 ratio in the matched survivors and non-survivors (n=19 each). *P = 0.038 by Mann-Whitney U-Test.