Objective: To analyze the levels of various monoamine metabolites in patients with Parkinson’s Disease as compared to healthy controls.

Background: Monoamine metabolites are the breakdown products of monoamines, including dopamine, serotonin, and norepinephrine, that play a crucial role in neurophysiological processes. Analyzing data from observational studies, we aim to explore the cerebrospinal fluid levels of monoamine metabolites in Parkinson’s disease patients. This understanding could unveil biomarkers for PD and enhance diagnostic and treatment strategies.

Method: Electronic databases (PubMed, EMBASE, Scopus, ScienceDirect) were systematically searched using predefined terms related to PD and monoamine metabolites from the date of database inception until March 2024. Studies reporting on monoamine metabolite levels in PD patients’ CSF compared to healthy controls were included. The combined effect size was computed using the inverse variance pooling method. Analyses were conducted in R (v4.3.1) using a random-effects model for pooled mean differences (MD) and 95% CI, with heterogeneity assessed by I² and tau².

Results: 5-Hydroxyindoleacetic acid (5-HIAA) showed a significant mean difference of -7.72 ng/mL (95% CI: -10.84 to -4.60, I² = 90%) in 14 studies (491 PD, 367 controls). Homovanillic acid (HVA) showed a significant mean difference of -18.47 ng/mL (95% CI: -25.49 to -11.45, I² = 98%) in 18 studies (647 PD, 446 controls), and a significant difference of -104.06 nmol/L (95% CI: -162.85 to -45.26, I² = 62%) in 4 studies (66 PD, 60 controls). 3,4-Dihydroxyphenylacetic acid (DOPAC) showed a significant mean difference of -0.34 ng/mL (95% CI: -0.58 to -0.10, I² = 66%) in 6 studies (132 PD, 199 controls), and a significant difference of -1.17 nmol/L (95% CI: -1.77 to -0.58, I² = 77%) in 3 studies (45 PD, 66 controls). Dihydroxyphenylglycol (DHPG) showed a significant mean difference of -2.20 nmol/L (95% CI: -2.44 to -1.95, I² = 0%) in 2 studies (58 PD, 70 controls).

Conclusion: Studies indicated significant decreases in serotonin metabolites (5-HIAA, HVA) in Parkinson’s patients, suggesting neurotransmitter level disruptions. Reductions in dopamine metabolite DOPAC and norepinephrine metabolite DHPG imply disturbances in respective pathways, highlighting a potential link to Parkinson’s pathophysiology.

Mean difference: 5-HIAA in PD CSF vs. controls

Mean difference: HVA in PD CSF vs. controls

Mean difference: HVA in PD CSF vs. controls

Mean difference: DOPAC in PD CSF vs. controls

Mean difference: DHPG in PD CSF vs. controls

Mean difference: DOPAC in PD CSF vs. controls

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