Functional and proteomic analysis of serum and cerebrospinal fluid derived from patients with traumatic brain injury: a pilot study

Background: An enhanced fracture healing response has been reported in patients with traumatic brain injury (TBI). This has been attributed to circulating humoral factors that are thought to be proteins produced and released by the injured brain. However, these factors remain unknown. The aim of this study was to identify osteogenic factors in serum and cerebrospinal fluid (CSF) from TBI patients. This was carried out using in vitro proliferation assays with the human foetal osteoblastic 1.19 cell line (hFOB) combined with a novel proteomic approach. Methods: Serum was collected from brain-injured (n = 12) and non-brain-injured (n = 9) patients with a comorbid femur shaft fracture. Similarly, CSF was obtained from TBI (n = 7) and non-TBI (n = 9) patients. The osteoinductive potential of these samples was determined by measuring the in vitro proliferation rate of hFOB cells. Highly osteogenic serum and CSF samples of TBI patients were chosen for protein analysis and were compared to those of non-brain-injured patients. A new hFOB cell-based method was used to enrich the proteins in these samples, which had a functional affinity for these osteoprogenitor cells. These enriched protein fractions were mapped using two-dimensional gel electrophoresis and protein imaging methods displaying serum and CSF proteins of brain-injured and control subjects that had an affinity for human osteoprogenitor cells. Results: Serum and CSF derived from brain-injured patients demonstrated a greater osteoinductive potential (P < 0.05) than their non-brain-injured counterparts. Clear-cut differences in the pattern of proteins in two-dimensional gels were detected between TBI and control patients. Fourteen proteins were exclusively present in the serum of TBI patients, while other proteins were either up- or downregulated in samples collected from TBI patients (P < 0.05). Conclusion: Osteoinductive factors are present in the serum and CSF of brain-injured patients. These may include one or more of those proteins identified as having an affinity for osteoprogenitor cells that are either exclusively present or up- or downregulated in the serum and CSF of brain-injured patients.