Using Proteomics Analysis to Identify Cerebrospinal Fluid Biomarkers in Normal Pressure Hydrocephalus

Background Normal Pressure Hydrocephalus (NPH) is a neurological condition where there is enlarged ventricular size with normal opening pressure at lumbar puncture. Etiology is uncertain but it is presumed to occur from an imbalance in the production and/or absorption of cerebrospinal fluid (CSF) leading to expansion of the ventricles. Clinical features include gait dysfunction, cognitive impairments, bladder incontinence. Diagnosis is challenging, given a large overlap in clinical and neuroradiological features and co‐morbidity with other more common diseases of aging, especially Alzheimer’s disease (AD) and Lewy body diseases. CSF amyloid and tau biomarkers can be helpful to identify AD pathology but do not exclude concurrent NPH. Currently, there are no biofluid biomarkers to assist in diagnosis of NPH. Here we describe a proteomic discovery pilot to identify candidate protein biomarkers associated with NPH. Method 176 banked CSF samples from the MassGeneral Institute for Neurodegenerative Disease biorepository were separated into three groups: NPH (n=30), AD (n=65), and cognitively unimpaired neurological controls (CU‐N; n=81). Diagnoses were established based on comprehensive chart review and CSF AD biomarkers. For proteomic analysis, samples were prepared in batches and analyzed by LC‐MS/MS on an Orbitrap Fusion using a data‐independent acquisition method with non‐overlapping windows from 400‐1000 m/z. Batches were run sequentially, and raw files were searched per batch using Scaffold‐DIA and a custom data‐dependent generated library. Result Five proteins present in hemoglobulin (HBD and HBB), immunoglobulins (LV39 and KV105), and fibrinogen (FIBA) were increased in NPH compared to AD (Benjamini‐Hochberg adjusted p‐value pAdj <0.05). CSF erythrocyte counts were undetectable in all but one NPH subjects suggesting that a traumatic LP was not the cause of the increased levels. Two neuron associated proteins (VGF and NPTXR) were detected at lower levels in NPH compared to CU‐N subjects (pAdj<0.0001). Alpha‐1‐antichymotrypsin (AACT), was detected at high concentrations both in NPH and AD compared to CU‐N subjects (pAdj<0.02). Conclusion Proteomic analysis in NPH may identify novel pathological processes involved in the disease process and aid in the development of biomarkers in NPH.