Neo-epitope detection identifies extracellular matrix turnover in systemic inflammation and sepsis: an exploratory study

Abstract

Background: Sepsis is associated with high morbidity and mortality, primarily due to systemic inflammation-induced tissue damage, resulting organ failure, and impaired recovery. Regulated extracellular matrix (ECM) turnover is crucial for maintaining tissue homeostasis in health and in response to disease-related changes in the tissue microenvironment. Conversely, uncontrolled turnover can contribute to tissue damage. Systemic Inflammation is implicated to play a role in the regulation of ECM turnover, but the relationship between the two is largely unclear.

Methods: We performed an exploratory study in 10 healthy male volunteers who were intravenously challenged with 2 ng/kg lipopolysaccharide (LPS, derived from Escherichia coli) to induce systemic inflammation. Plasma samples were collected before (T0) and after (T 1 h, 3 h, 6 h and 24 h) the LPS challenge. Furthermore, plasma was collected from 43 patients with septic shock on day 1 of ICU admission. Circulating neo-epitopes of extracellular matrix turnover, including ECM degradation neo-epitopes of collagen type I (C1M), type III (C3M), type IV (C4Ma3), and type VI (C6M), elastin (ELP-3) and fibrin (X-FIB), as well as the ECM synthesis neo-epitopes of collagen type III (PRO-C3), collagen type IV (PRO-C4) and collagen type VI (PRO-C6) were measured by ELISA. Patient outcome data were obtained from electronic patient records.

Results: Twenty-four hours after LPS administration, all measured ECM turnover neo-epitopes, except ELP-3, were increased compared to baseline levels. In septic shock patients, concentrations of all measured ECM neo-epitopes were higher compared to healthy controls. In addition, concentrations of C6M, ELP-3 and X-FIB were higher in patients with septic shock who ultimately did not survive (N = 7) compared to those who recovered (N = 36).

Conclusion: ECM turnover is induced in a model of systemic inflammation in healthy volunteers and was observed in patients with septic shock. Understanding interactions between systemic inflammation and ECM turnover may provide further insight into mechanisms underlying acute and persistent organ failure in sepsis.

Keywords: Collagen; Extracellular matrix turnover; Human endotoxemia; Neo-epitope; Sepsis.

Fig. 1

Human endotoxemia induces alterations in circulating ECM neo-epitopes. Schematic depiction of the experimental human endotoxemia model (a) and the induced inflammatory response (b), derived from previously published data [15] Plasma concentrations of C1M (c), C3M (d), C4Ma3 (e), C6M (f), ELP-3 (g), X-FIB (h), and PRO-C3 (i), PRO-C4 (j) and PRO-C6 (k) were measured in 10 healthy male individuals at baseline (T0) and at 1 h, 3 h, 6 h and 24 h after LPS administration. The dotted line indicates the moment of LPS administration (immediately after T0). Data are presented as median and interquartile range. *p < 0.05; **p < 0.01; ***p < 0.001 compared with T0, calculated by Friedman test followed by post-hoc testing with Bonferroni correction. IL-6 Interleukin-6, IL-8 Interleukin-8, IL-10 Interleukin-10, TNF tumor necrosis factor, LPS lipopolysaccharide. Figure 1a and 1b were created with BioRender.com

Fig. 2

Patients with septic shock display elevated levels of circulating ECM neo-epitopes compared to healthy individuals. Plasma concentrations of C1M (a), C3M (b), C4Ma3 (c), C6M (d), ELP-3 (e), X-FIB (f), and PRO-C3 (g), PRO-C4 (h) and PRO-C6 (i) were measured in plasma samples collected at ICU admission from patients with septic shock (n = 43). Healthy control data of C3M, C4Ma3, C6M and X-FIB were obtained from the experimental human endotoxemia model at T0 (before LPS administration). Healthy control data for C1M and PRO-C4 levels were obtained from 33 healthy donors (in-house controls measured by Nordic Bioscience), and the levels of ELP-3 measured in control individuals were reported previously [19]. Each symbol represents a single individual or patient. The dotted lines represent the circulating levels in healthy individuals reported previously [–23]. Data are presented as median and interquartile range. ***p < 0.001 calculated using Mann–Whitney U tests

Fig. 3

Circulating levels of C6M, ELP-3, X-FIB, and PRO-C3 at ICU admission are associated with mortality of patients with septic shock. Plasma concentrations of C1M (a), C3M (b), C4Ma3 (c), C6M (d), ELP-3 (e), X-FIB (f), and PRO-C3 (g), PRO-C4 (h) and PRO-C6 (i) were measured in plasma samples collected at ICU admission from patients with septic shock (n = 43). The patients were divided into two groups, ICU survivors (n = 36) and ICU non-survivors (n = 7). Each symbol represents single patient. Data are presented as median and interquartile range. *p < 0.05; p < 0.01; ***p < 0.001 calculated using Mann–Whitney U tests