Monitoring of Protein Biomarkers of Inflammation in Human Traumatic Brain Injury Using Microdialysis and Proximity Extension Assay Technology in Neurointensive Care

Traumatic brain injury (TBI) is followed by secondary injury mechanisms strongly involving neuroinflammation. To monitor the complex inflammatory cascade in human TBI, we used cerebral microdialysis (MD) and multiplex proximity extension assay (PEA) technology and simultaneously measured levels of 92 protein biomarkers of inflammation in MD samples every three hours for five days in ten patients with severe TBI under neurointensive care. One µL MD samples were incubated with paired oligonucleotide‐conjugated antibodies binding to each protein, allowing quantification by real‐time qPCR. Sixty‐nine proteins were suitable for statistical analysis. We found five different patterns with either early (<48 h; e.g. CCL20, IL6, LIF, CCL3), mid (48–96 h; e.g. CCL19, CXCL5, CXCL10, MMP1), late (>96 h; e.g. CD40, MCP2, MCP3), biphasic peaks (e.g. CXCL1, CXCL5, IL8) or stable (e.g. CCL4, DNER, VEGFA)/low trends. High protein levels were observed for e.g. CXCL1, CXCL10, MCP1, MCP2, IL8, while e.g. CCL28 and MCP4 were detected at low levels. Several proteins (CCL8, ‐19, ‐20, ‐23, CXCL1, ‐5, ‐6, ‐9, ‐11, CST5, DNER, Flt3L and SIRT2) have not previously been studied in human TBI. Cross‐correlation analysis revealed that LIF and CXCL5 may play a central role in the inflammatory cascade.

This study provides a unique data set with individual temporal trends for potential inflammatory biomarkers in patients with TBI. We conclude that the combination of MD and PEA is a powerful tool to map the complex inflammatory cascade in the injured human brain. The technique offers new possibilities of protein profiling of complex secondary injury pathways.