Cell death serum biomarkers are early predictors for survival in severe septic patients with hepatic dysfunction

Abstract

Introduction: Severe sepsis, septic shock, and resulting organ failure represent the most common cause of death in intensive care medicine, with mortality ranging from 40% to 70%. It is still unclear whether necrosis or apoptosis plays the predominant role in severe sepsis. Determining the prevalent mode of cell death would be valuable, as new therapeutic agents (eg, antiapoptotic drugs such as caspase inhibitors) may improve unsatisfactory outcomes in patients with severe sepsis. Furthermore, the prognostic value of newly developed cell death serum biomarkers is of great interest.

Methods: In total, 147 patients (101 patients with severe sepsis, 28 postoperative patients after major abdominal surgery, 18 healthy volunteers) were enrolled. Baseline and clinical data were evaluated. Blood samples from patients with severe sepsis were collected at the time of sepsis diagnosis, and 48 and 120 hours later; samples from healthy volunteers were collected once, and from postoperative patients, once immediately after surgery. We measured caspase-cleaved and uncleaved cytokeratin-18 (CK-18, intermediate filament protein) as a marker of cell death, isolated CK-18 fragments as a marker of apoptosis, as well as IL-6, soluble vascular cell adhesion molecule, and soluble intercellular adhesion molecule.

Results: Age and sex of patients with severe sepsis and postoperative patients were comparable, whereas healthy volunteers were significantly younger. In healthy volunteers, the mode of cellular turnover was primarily apoptotic cell death. Postoperative patients showed comparable levels of apoptotic activity, but necrotic cell death was markedly increased, probably due to surgical tissue injury. In contrast, patients with severe sepsis, and especially non-survivors of the septic group showed increased levels of markers for both apoptotic and necrotic cell death. In severe septic patients with liver dysfunction, necrosis is increased relative to severe septic patients with intact hepatic function. For severe septic patients with liver dysfunction, a cut-off value for caspase-cleaved and uncleaved cytokeratin-18 could be calculated, in order to identify patients at high risk for death due to severe sepsis.

Conclusions: The measurement of caspase-cleaved and uncleaved cytokeratin-18 appears to be an early predictor for survival in severe septic patients with hepatic dysfunction. Furthermore, the loss of parenchymal cells due to necrosis may be the primary mode of cell death in these patients. This may limit possible therapeutic options.

Figure 1

Comparison of cytokeratin measurements in the volunteer, postoperative, and septic groups at baseline and at 48 and 120 hours in the septic group. Concentrations were measured of total cytokeratin-18 (CK-18) and CK-18 fragments (CK-18-F), and the ratio of CK-18-F to total CK-18 was calculated from the sera of healthy volunteers ('Healthy', n = 18, white box), postoperative patients after major abdominal surgery ('Post-op', n = 28, light grey box), and patients with sepsis ('Sepsis', n = 101, dark grey box), at t0 (measured once for the volunteer group, immediately after surgery for the postoperative group, and at the time of diagnosis of sepsis for the sepsis group). In addition, for the septic group, the two other times of data collection are represented, t48 and t120 for 48 and 120 hours, respectively, after the diagnosis of sepsis. Data in box plots are given as median, 25^th percentile, 75^th percentile, and the 1.5 interquartile range. Outliers are shown in form of circles (1.5 to 3 interquartile ranges above 75^th percentile or below 25^th percentile) or rectangles (>3 interquartile ranges above 75^th percentile or below 25^th percentile). *** P < 0.001.

Figure 2

Comparison of cytokeratin measurements in survivors and non-survivors with impaired liver function in the septic group at baseline and at 48 and 120 hours. Concentrations were measured of total cytokeratin-18 (CK-18) and CK-18 fragments (CK-18-F), and the ratio of CK-18-F to total CK-18 was calculated from the sera of survivors (white box) and non-survivors (dark grey box) of the septic group with impaired liver function (bilirubin ≥1.2 mg/dL or 20.5 μmol/L according to Sequential Organ Failure Assessment (SOFA) score) at the time of diagnosis of sepsis (t0), and 48 hours (t48) and 120 hours (t120) later. Data in box plots are given as median, 25^th percentile, 75^th percentile and the 1.5 interquartile range. Outliers are shown in form of circles (1.5 to 3 interquartile ranges above 75^th percentile or below 25^th percentile) or rectangles (>3 interquartile ranges above 75^th percentile or below 25^th percentile).

Figure 3

Comparison of cytokeratin measurements in patients with impaired and preserved liver function in the septic group at baseline and at 48 and 120 hours. Concentrations were measured of total cytokeratin-18 (CK-18) and CK-18 fragments (CK-18-F), and the ratio of CK-18-F to total CK-18 was calculated from the sera of patients with sepsis and impaired liver function ('Liver-Sequential Organ Failure Assessment (SOFA) ≥1', bilirubin ≥1.2 mg/dL or 20.5 μmol/L according to SOFA score, dark grey box) compared with patients with sepsis and preserved liver function ('Liver-SOFA = 0', bilirubin <1.2 mg/dL or 20.5 μmol/L according to SOFA score, white box) at the time of diagnosis of sepsis (t0), and 48 hours (t48) and 120 hours (t120) later. Data in box plots are given as median, 25^th percentile, 75^th percentile, and the 1.5 interquartile range. Outliers are shown in form of circles (1.5 to 3 interquartile ranges above 75^th percentile or below 25^th percentile) or rectangles (>3 interquartile ranges above 75^th percentile or below 25^th percentile). * P < 0.05: ** P < 0.01.