Fibrinogen and Complement Factor H are promising CSF protein biomarker(s) for Parkinson's disease with cognitive impairment- A Proteomics and ELISA based study

Cognitive impairment is a debilitating non-motor symptom of Parkinsons disease (PD). The diagnosis of PD with cognitive impairment (PDCI) is essentially through clinical and neuropsychological examinations. There is an emerging need to identify biomarker(s) to foresee cognitive decline in PD patients, at an early stage. We performed label-free unbiased nontargeted proteomics (Q-TOF LC/MS-MS) in CSF of non-neurological control (NNC); PDCI; PD and normal pressure hydrocephalus (NPH), followed by targeted ELISA for validation. The diagnosis was confirmed by neuropsychological and MRI assessments prior to CSF collection. Of the 282 proteins identified by mass spectrometry, 42 were differentially altered in PD, PDCI and NPH. Further, 28 proteins were altered in PDCI and 25 in NPH. An interesting overlap of certain proteins was noted both in PDCI and NPH. Five significantly upregulated proteins in PDCI were fibrinogen, gelsolin, complement factor-H, apolipoprotein A-IV and apolipoprotein A-I. Whereas carnosine dipeptidase 1, carboxypeptidase E, dickkpof 3 and secretogranin 3 precursor proteins were down-regulated. NPH also had few uniquely altered proteins viz. insulin-like growth factor-binding protein, ceruloplasmin, -1 antitrypsin, VGF nerve growth factor, neural cell adhesion molecule L1 like protein. Interestingly, the ELISA-derived protein concentrations correlated well with the neuropsychological scores of certain cognitive domains. Executive function was affected both in PDCI and NPH. In PD, Wisconsin card sorting test (WCST) percentile correlated positively with ApoA-IV and negatively with the ratio of ApoAI: ApoA-IV. Thus assessment of a battery of proteins like fibrinogen--chain, CFAH and ApoAI: ApoA-IV ratio alongside neuropsychological could be reliable biomarkers to distinguish PDCI and NPH.