Objective: To analyze the levels of different neuropeptides in patients with Parkinson’s disease (PD) compared to healthy individuals.

Background: Neuropeptides are bioactive molecules that play an essential role in maintaining the normal physiological conditions of the body. Growing evidence suggests that neuropeptide dysregulation in cerebrospinal fluid influences the pathophysiology of PD. In this study, we analyze somatostatin-like-immunoreactivity (SLI) and substance P-like-immunoreactivity (SPLI) levels in the CSF of PD patients compared to healthy controls.

Method: We systematically searched MEDLINE (PubMed), EMBASE, ScienceDirect, and Scopus using specific search strategies comprising terms related to PD, SLI, and SPLI from the date of database inception to March 2024. Following PRISMA guidelines, our screening and extraction included studies investigating neuropeptide concentrations in Parkinson’s patients’ cerebrospinal fluid (CSF). Utilizing the ‘meta’ R package, particularly the ‘metacont’ tool, we analyzed mean concentration levels and standard differences via the random effects model. Data pooling utilized inverse variance weighting, with I² and tau² assessing heterogeneity. The primary outcome was the mean difference(MD) in CSF neuropeptide levels between Parkinson’s patients and controls, considering reported units separately.

Results: Somatostatin like-immunoreactivity showed a mean difference of -5.86 fmol/mL (95% CI: -11.95 to 0.22, I² = 75%) in 5 studies (87 PD, 76 controls), a difference of 8.30 pg/mL  (95% CI: -44.23 to 60.84, I² = 92%) in 2 studies (26 PD, 37 controls), and a difference of -9.19 pmol/L (95% CI: -16.77 to -1.61, I² = 52%) in 2 studies (44 PD, 49 controls). Substance P-like-immunoreactivity showed a significant mean difference of -0.77 fmol/mL  (95% CI: -1.48 to -0.06, I² = 0%) in 4 studies (106 PD, 60 controls).

Conclusion: Substance P-like-immunoreactivity significantly decreases in the CSF of PD patients, while somatostatin-like-immunoreactivity shows no significant alterations. Further investigations are necessary to validate and expand upon these significant findings.

Mean difference: SLI in PD vs. healthy controls

Mean difference: SPLI in PD vs. healthy controls

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MDS Abstracts - https://www.mdsabstracts.org/abstract/neuropeptide-alterations-in-parkinsons-disease-a-meta-analysis/