Cerebrospinal fluid levels of high-mobility group box 1 and cytochrome C predict outcome after pediatric traumatic brain injury

Abstract

High-mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that is passively released from damaged and necrotic cells, and actively released from immune cells. In contrast, cytochrome c is released from mitochondria in apoptotic cells, and is considered a reliable biomarker of apoptosis. Thus, HMGB1 and cytochrome c may in part reflect the degree of necrosis and apoptosis present after traumatic brain injury (TBI), where both are felt to contribute to cell death and neurological morbidity. Ventricular cerebrospinal fluid (CSF) was obtained from children admitted to the intensive care unit (ICU) after TBI (n=37). CSF levels of HMGB1 and cytochrome c were determined at four time intervals (0-24 h, 25-48 h, 49-72 h, and>72 h after injury) using enzyme-linked immunosorbent assay (ELISA). Lumbar CSF from children without TBI served as controls (n=12). CSF HMGB1 levels were: control=1.78±0.29, 0-24 h=5.73±1.45, 25-48 h=5.16±1.73, 49-72 h=4.13±0.75,>72 h=3.80±0.90 ng/mL (mean±SEM). Peak HMGB1 levels were inversely and independently associated with favorable Glasgow Outcome Scale (GOS) scores at 6 mo (0.49 [0.24-0.97]; OR [5-95% CI]). CSF cytochrome c levels were: control=0.37±0.10, 0-24 h=0.69±0.15, 25-48 h=0.82±0.48, 49-72 h=1.52±1.08,>72 h=1.38±1.02 ng/mL (mean±SEM). Peak cytochrome c levels were independently associated with abusive head trauma (AHT; 24.29 [1.77-334.03]) and inversely and independently associated with favorable GOS scores (0.42 [0.18-0.99]). In conclusion, increased CSF levels of HMGB1 and cytochrome c were associated with poor outcome after TBI in infants and children. These data are also consistent with the designation of HMGB1 as a "danger signal." Distinctly increased CSF cytochrome c levels in infants and children with AHT and poor outcome suggests that apoptosis may play an important role in this unique patient population.

FIG. 1.

(A) Temporal profile of CSF HMGB1 levels in children with severe TBI versus controls. (B) Mean and peak CSF HMGB1 levels among TBI patients were increased versus controls (*p<0.05; CSF, cerebrospinal fluid; HMGB1, high-mobility group box 1; TBI, traumatic brain injury).

FIG. 2.

Peak CSF HMGB1 level plotted against 6-month Glasgow Outcome Scale (GOS) score. The peak HMGB1 level was found to be inversely proportional to GOS scores (r_s=−0.393, p=0.016; GOS: 1=dead, 2=vegetative state, 3=severe disability, 4=moderate disability, 5=normal; CSF, cerebrospinal fluid; HMGB1, high-mobility group box 1).

FIG. 3.

Temporal profile of CSF cytochrome c levels in children with severe TBI versus controls (CSF, cerebrospinal fluid; TBI, traumatic brain injury).

FIG. 4.

Peak CSF cytochrome c level plotted against 6-month Glasgow Outcome Scale (GOS) score. The peak cytochrome c level was found to be inversely proportional to GOS score (r_s=−0.347, p=0.036; GOS: 1=dead, 2=vegetative state, 3=severe disability, 4=moderate disability, 5=normal; CSF, cerebrospinal fluid).

FIG. 5.

Scatterplot of CSF HMGB1 versus cytochrome c in (A) patients with good outcomes (open circles; GOS score 4 or 5; r_s=0.473, p<0.001), or poor outcomes (solid circles; GOS score 1–3; r_s=0.320, p<0.025), and (B) patients with accidental TBI (open circles) and abusive head trauma (solid circles; r_s=0.122, p=0.54; CSF, cerebrospinal fluid; HMGB1, high-mobility group box 1; GOS, Glasgow Outcome Scale).

FIG. 6.

Receiver-operating characteristic (ROC) analysis using (A) peak CSF HMGB1 as a predictor of outcome at 6 months (AUC=0.70, 95% CI 0.51,0.90), and (B) peak CSF cytochrome c as a predictor of outcome at 6 months (AUC=0.78, 95% CI 0.61,0.95; CSF, cerebrospinal fluid; HMGB1, high-mobility group box 1; AUC, area under the curve).