Inflammasome proteins in cerebrospinal fluid of brain-injured patients as biomarkers of functional outcome: clinical article

Abstract

Object: Traumatic brain injury (TBI), the third most common CNS pathology, plagues 5.3 million Americans with permanent TBI-related disabilities. To evaluate injury severity and prognosis, physicians rely on clinical variables. Here, the authors seek objective, biochemical markers reflecting molecular injury mechanisms specific to the CNS as more accurate measurements of injury severity and outcome. One such secondary injury mechanism, the innate immune response, is regulated by the inflammasome, a molecular platform that activates caspase-1 and interleukin-1β.

Methods: The authors investigated whether inflammasome components were present in the CSF of 23 patients with TBI and whether levels of inflammasome components correlate with outcome. The authors performed an immunoblot analysis of CSF samples from patients who suffered TBI and nontrauma controls and assessed the outcomes 5 months postinjury by using the Glasgow Outcome Scale. Data were analyzed using Mann-Whitney U-tests and linear regression analysis.

Results: Patients with severe or moderate cranial trauma exhibited significantly higher CSF levels of the inflammasome proteins ASC, caspase-1, and NALP-1 than nontrauma controls (p < 0.0001, p = 0.0029, and p = 0.0202, respectively). Expression of each protein correlated significantly with the Glasgow Outcome Scale score at 5 months postinjury (p < 0.05). ASC, caspase-1, and NALP-1 were significantly higher in the CSF of patients with unfavorable outcomes, including death and severe disability (p < 0.0001).

Conclusions: NALP-1 inflammasome proteins are potential biomarkers to assess TBI severity, outcome, and the secondary injury mechanisms impeding recovery, serving as adjuncts to clinical predictors.

Fig. 1

Scatter plots of expression of inflammasome proteins in control and TBI patients. N = the number of TBI samples analyzed. Samples were immuoblotted for (A) ASC, (B) Caspase-1, and (C) NALP-1. P values in the upper left corner represent results of a Mann-Whitney U test. Densitometric analysis revealed a significant increase in expression of ASC, Caspase-1 (p20), and NALP-1 in the CSF of TBI patients compared to non-trauma controls. Solid lines denote mean values for each group. Different shapes correspond to patient outcomes at 5 months post injury. ★ GOS-5.■ GOS-4.○ GOS-3. ▽ GOS-1. Representative immunoblots are shown. Samples were run on the same gel but were noncontiguous.

Fig. 2

Boxplots of expression of inflammasome proteins sorted by outcome category. The ends of the whiskers represent the lowest datum within 1.5 interquartile range (IQR) of the lower quartile and the highest datum within 1.5 IQR of the upper quartile. Outliers are represented as *. Mann-Whitney U tests indicate higher expression of (A) ASC, (B) Caspase-1 (p20), (C) and NALP-1 are significantly associated with an unfavorable outcome 5 months after injury (P < 0.0001). Representative immunoblots of each protein are shown. Samples were run on the same gel but were noncontiguous.

Fig. 3

Scatter plots and estimated linear regression of (A) ASC, (B) Caspase-1 (p20), and (C) NALP-1 expression in the CSF with GOS. P values of the linear regression are shown in the top left of each graph. Expression of each protein correlated significantly with GOS at 5 months post-injury. The P values on the X-axis represent post-hoc comparisons of a Kruskal-Wallis test. Representative immunoblots are shown. Samples were run on the same gel but were noncontiguous.