Parkinson's Disease Through the Lens of Metabolomics: A Targeted Systematic Review on Human Studies (2019-2024)

Background: Parkinson's disease (PD) is a chronic, progressive neurodegenerative disorder characterized by motor and non-motor symptoms. As conventional diagnostic methods are limited in their ability to detect early-stage PD or monitor its progression, there is growing interest in identifying molecular biomarkers with clinical utility. This systematic review synthesizes recent advancements in the application of metabolomics to PD, with a specific focus on human studies published between 2019 and 2024, a period of notable growth in the research area. Methods: Following PRISMA 2020 guidelines, a comprehensive literature search was conducted across major scientific databases. After screening, 16 eligible original studies were selected based on predefined criteria. Key features extracted included study design, biofluid type, analytical platform, statistical approach, and main findings. Results: Consistent metabolic alterations were observed across several biological pathways, including amino acid metabolism, lipid regulation, mitochondrial energy production, oxidative stress, polyamine metabolism, as well as in gut microbiota-derived metabolites. Biofluids analyzed included plasma, serum, cerebrospinal fluid, saliva, urine, and sebum. While plasma and serum remained the most studied matrices, emerging interest in non-invasive fluids such as saliva and sebum reflects their potential in clinical settings. Methodological heterogeneity was noted across studies, particularly in confounder adjustment and study design. Conclusions: Despite certain limitations, the included studies collectively point to the potential of metabolomics in identifying robust diagnostic and prognostic signatures for PD. This review emphasizes the need for longitudinal studies, methodological standardization, and integration with other omics approaches to advance biomarker discovery and support the development of precision medicine strategies for PD.