Cerebrospinal Fluid Proteomic Changes in Older Non-Cardiac Surgical Patients with Postoperative Cognitive Dysfunction

Abstract Background: Postoperative cognitive dysfunction (POCD) is a syndrome of cognitive deficits that occurs in 10-40% of patients age > 60 within 1-12 months after surgery, hypothesized to be caused in part by neuroinflammation. However, the specific neuroinflammatory pathways involved remain unclear. Unbiased mass spectrometry-based proteomic analyses have been used to identify neuro-inflammatory pathways in multiple neurologic diseases and syndromes but have not yet been used in the POCD field. Thus, we used unbiased mass spectrometry-based proteomics to compare cerebrospinal fluid (CSF) samples from patients with and without POCD to identify potential neuroinflammatory pathways for further investigation in future studies. Methods: We performed unbiased LC-MS/MS proteomics on immunodepleted CSF samples obtained before, 24 hours, and 6 weeks after major non-cardiac surgery in older adults who developed (n=8) or did not develop POCD (n=6). General linear mixed models were used to identify peptides and proteins with intensity differences between groups or over time by groups. Kyoto Encyclopedia of Genes and Genomes analysis was used to identify pathways containing proteins/peptides with q values < 0.25 in the mixed model. Results: Mass spectrometry quantified 8258 peptides from 1222 proteins in >50% of patient samples at all three time points. Twelve peptides from 11 proteins showed differences in expression over time between groups (POCD vs non-POCD) at q < 0.05, including several from proteins previously implicated in neurodegenerative disease pathophysiology. Additionally, 283 peptides from 182 proteins were identified with trend-level differences (q < 0.25) in expression over time between these patient groups. Of these 283 peptides with trend-level significance, pathway analysis revealed that 50 of them were from 17 proteins that mapped to the complement and coagulation pathways (q=2.44*10-13).Conclusions: These data demonstrate the feasibility of performing unbiased mass spectrometry on perioperative CSF samples to identify peptides, proteins, and pathways associated with POCD. Additionally, they provide hypothesis-generating evidence for CSF complement and coagulation pathway changes in patients with POCD.