Traumatic brain injury (TBI) is the leading cause of mortality and morbidity of young people worldwide 1, 2, 3, 4. Oxidative stress has been implicated with the excitotoxic brain injury 5 including TBI 6, 7, but the association between plasma markers of oxidative stress and the severe TBI patients' prognosis remains controversial 8. We have demonstrated recently that the plasma enhancement of thiobarbituric acid‐reactive species (TBARS, an index of lipid peroxidation) and carbonyl groups (an index of oxidative o proteins) observed up to 3 days after severe TBI are not independently associated with hospital mortality of patients 8. To the best of our knowledge, there is no previous study investigating the association between serum biomarker levels during the acute TBI phase and the cognitive prognosis of patients. Here, we correlate the TBARS and carbonyl plasma levels after severe TBI and the cognitive performance of patients evaluated on average 17.3 (SD ± 5) months later.
Included patients hospitalized between May 2006 and September 2009 showed: (1) Glasgow Coma Scale (GCS) score ≤8; (2) 18 years of age or older. There were no victims of gunshot injuries. Among the 51 consecutive survivor patients, 22 (43.1%) completed the cognitive assessment. The study was approved by our Ethics Committee, and written informed consent was obtained from relatives (during hospitalization) and patients (chronic period). The TBARS and carbonyl levels determined in the plasma of patients as previously described 6, 7, 8, 9 in median 11 h (IQ 6–19.0), 30 h (IQ 24–37), and 70 h (IQ 55–78) after the severe TBI were compared with 10 healthy controls matched for age and sex. The biochemical analysis was blinded for all clinical and cognitive variables of patients.
The variables collected during hospitalization 2, 3, 8 were gender, age, GCS score, pupillary status, computed tomography (CT) scan classification according to Marshall's classification 3, presence of subarachnoid hemorrhage in the CT, and presence of associated trauma (spine, thorax, or abdomen). The analyzed parameters at the time of the first blood sampling collection were blood pressure, heart and respiratory rate, and positive end‐expiratory pressure. The laboratorial variables analyzed in the same sample used for TBARS and carbonyl measurements were arterial blood gases, sodium, potassium, urea, creatinine, hematocrit, hemoglobin, leukocytes, and platelets.
The neuropsychological evaluation was blinded for all the hospitalization variables and includes 10: Letters and Category Fluency, Rey Auditory Verbal Learning Test (RAVLT), Wechsler Memory Scale III (WMS‐III) subtests Logical Memory First Recall (LM 1st), Logical Memory I (LM I), Logical Memory II (LM II), and Visual Reproduction I (VR I), Visual Reproduction II (VR II), Visual Reproduction Recognition (VR Rec), Wechsler Adult Intelligence Scale III (WAIS‐III) subtests Digit Span, Similarities, Vocabulary and Block Design. For comparison, healthy control subjects (n = 23) without previous history of neurological or psychiatric disorders, matched for gender, age, and education level, were recruited during the same period.
As previously demonstrated 8, plasma levels of TBARS of patients were significantly higher than controls (P < 0.001), showing a time‐dependent enhancement at 11, 30, and 70 h after the TBI. The plasma carbonyls also were significantly higher than controls (P < 0.01) at 30 and 70 h after the TBI (data not shown).
There were no significant differences between the cognitively evaluated (n = 22) and nonevaluated (n = 29) patients according to the hospitalization variables (P ≥ 0.26), plasma TBARS levels (P ≥ 0.12), and plasma carbonyl levels (P ≥ 0.33; see Table 1).
Table 1.
Clinical, demographic, laboratory, radiological, neurosurgical, and oxidative stress of patients with severe TBI
| Variables | Cognitive examination | |
|---|---|---|
| Nonevaluated n = 29 (56.9%) | Evaluated n = 22 (43.1%) | |
| Sex | ||
| Male | 25 (85.2) | 20 (90.9) |
| Marshall CT classification | ||
| Type I injury | 01 (3.4) | 02 (9.1) |
| Type II injury | 10 (34.5) | 07 (31.8 |
| Type III injury | 03 (10.3 | 02 (9.1) |
| Type IV injury | 03 (10.3) | 03 (13.6) |
| Evacuated mass lesion | 06 (20.7) | 04 (18.2) |
| Nonevacuated lesion | 06 (20.7) | 04 (18.2) |
| SAH on admission cranial CT | 13 (44.8) | 14 (63.6) |
| Brain surgery | ||
| Yes | 14 (48.3) | 12 (54.5) |
| Associated trauma | 17 (56.6) | 16 (72.7) |
| Admission Glasgow Coma Scale | ||
| 7 or 8 | 13 (44.8) | 11 (50.0) |
| 5 or 6 | 08 (27.6) | 04 (18.2) |
| 3 or 4 | 8 (27.6) | 07 (31.8) |
| Admission Pupils | ||
| Isocorics | 17 (58.6) | 14 (63.6) |
| Anisocorics | 10 (34.5) | 08 (36/4) |
| Mydriatics | 2 (6.9) | 0 |
| Age in years | 34.8 ± 16.2 | 31.7 ± 11.1 |
| Days in the ICU | 12 ± 8 | 11 ± 5 |
| Days of Hospitalization | 30 (19) | 28 (23) |
| Systolic blood pressure, mmHg | 127 (27) | 128 (35) |
| Diastolic blood pressure, mmHg | 76 (16) | 75 (23) |
| Heart rate/min | 90 (15) | 90 (25) |
| Respiratory rate/min | 22 (18) | 18 (14) |
| Glucose levels, mg/dL | 158 (74) | 149 (39) |
| Hematocrit, % | 34.2 (5.3) | 33.1 (87.9) |
| Hemoglobin, g/100 mL | 11.7 (1.8) | 13.2 (7.9) |
| Leukocytes/mm3 | 15,578 (6978) | 15,346 (8024) |
| Carbonyl levels, nmol/mg protein 10−14 | ||
| First blood sample (n = 51) | 25.3 (IQ 9.0–86.6) | 26.2 (IQ 9.5–95.0) |
| Second blood sample (n = 42) | 32.6 (IQ 10.3–110.8) | 52.7 (IQ 16.9–145.3) |
| Third blood sample (n = 42) | 33.2 (IQ 14.6–142.0) | 46.3 (IQ 18.8–145.0) |
| TABARS levels, nmol/mg protein 10−5 | ||
| First blood sample (n = 51) | 38.9 (IQ 13.4–196.9) | 48.7 (IQ 8.1–199.5) |
| Second blood sample (n = 42) | 23.1 (IQ 14.7–242.9) | 44.6 (IQ 33.0–236.0) |
| Third blood sample (n = 42) | 74.5 (IQ 53.2–417.3) | 72.9 (IQ 59.2–321.3) |
TBI, traumatic brain injury; CT, computed tomography; SAH, Subarachnoid hemorrhage.
The laboratorial variables were determined in the first blood sample, and the clinical data were collected at the time of the first blood sample collection.
The first, second, and third blood samples were collected respectively 11 (IQ 6–19.0), 30 (IQ 24–37), and 70 h (IQ 55–78) after TBI.
There were no statistically significant differences between the evaluated and nonevaluated patients among the studied variables (P > 0.20). Analysis was carried out by Fisher's exact test, Student's “t” test or Mann–Whitney U‐test.
Patients showed significant lower scores in Letters and Category Fluency, RAVLT, LM 1st, LM I, LM II, VR I, VR II, Vocabulary and Block Design (P < 0.001). Patients also showed a trend for lower scores than controls in the Digit Span (P = 0.08) and similarities (P = 0.06), and a normal VR Rec test performance. The findings were not because of gender, age, education level, and hand dominance imbalances between patients and controls (data not shown).
Table 2 shows the correlation between plasma levels of TBARS, carbonyl, and cognitive tests. There was no significant correlation between the serum level of TBARS and carbonyl and the cognitive performance of patients (P > 0.25). Among the 15 evaluated cognitive tests, only the vocabulary scores correlate significantly (Spearman coefficient 0.50 and P = 0.04) with TBARS levels (third collected blood sample), but this result was not confirmed after the correction for age and education (P = 0.23, data not shown).
Table 2.
Correlation between TBARS and carbonyl plasma levels of survivor patients with severe TBI and their long‐term cognitive performance
| TBARS | Carbonyl | |||||
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 1 | 2 | 3 | |
| Letter fluency | 0.26 | 0.14 | 0.14 | −0.34 | −0.20 | 0.03 |
| Category fluency | 0.12 | 0.11 | 0.15 | −0.25 | −0.21 | 0.08 |
| Similarities | 0.34 | 0.26 | 0.30 | −0.09 | 0.24 | 0.10 |
| Vocabulary | 0.27 | 0.32 | 0.50 | −0.05 | 0.22 | 0.24 |
| Block design | 0.42 | 0.26 | 0.40 | 0.10 | 0.06 | 0.26 |
| RAVLT‐total | 0.15 | 0.23 | 0.26 | −0.03 | −0.10 | 0.32 |
| RAVLT‐delayed | −0.08 | 0.23 | 0.26 | −0.03 | −0.10 | 0.32 |
| VP II | 0.12 | 0.23 | 0.39 | −0.06 | −0.03 | 0.27 |
| VP Rec | −0.01 | 0.14 | 0.16 | 0.09 | −0.01 | 0.21 |
| LM 1st | 0.24 | 0.32 | 0.14 | −0.04 | 0.10 | 0.08 |
| LM I | 0.27 | 0.34 | 0.20 | −0.05 | 0.04 | 0.14 |
| LM II | 0.17 | 0.03 | 0.08 | −0.09 | −0.24 | −0.02 |
TBARS, thiobarbituric acid‐reactive species; TBI, traumatic brain injury; RAVLT, Rey Auditory Verbal Learning Test; VP, Visual Production; VP Rec, Visual Production Recognition ; LM, Logical Memory.
1, First blood sample; 2, Second blood sample; 3, Third blood sample.
TBARS and carbonyl levels were determined the first blood sample of all patients and in second and third blood sample of 21 and 19 patients, respectively.
There was no significant correlation between the serum level of TBARS and carbonyl and the cognitive performance of patients (P > 0.25). Among the 15 evaluated cognitive tests, only the vocabulary scores correlate significantly (Spearman coefficient 0.50 and P = 0.04) with TBARS levels (third collected blood sample), but this result was not confirmed after the correction for age and education (P = 0.23, data not shown).
The reader should also be aware of the study limitations. The used biochemical reaction for TBARS determination is not specific 8 for the free radical‐induced lipid peroxidation. The wide range of both TBARS and carbonyl levels and the relative small sample size of patients may reduce the study. Missing cases in the follow‐up could raise doubt whether the evaluated patients represent the survivor group as a whole. However, we minimized the missing problem by controlling the distribution of the several hospitalization and demographic variables between the evaluated and nonevaluated patients.
In conclusion, the present findings indicate that measurement of plasma TABARS and carbonyl levels up to 70 h after the severe TBI are not useful biomarkers to predict the cognitive morbidity of patients with severe TBI.
Conflict of Interest
The authors declare no conflict of interest.
Acknowledgments
This work was supported by CPNq (Brazilian Council for Scientific and Technologic Development, Brazil), FAPESC (Foundation for Scientific Research and Technology of the State of Santa Catarina). PRONEX program CNPq/FAPESC (NENASC project).
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