Table 2.
List of biomarker studies in bio-fluidsand its outcome on KP metabolites of Parkinson's disease.
| Biofluid | Metabolites | Model | No. of subjects | Primary outcome | Analytical methods | Pathway | Results | Conclusion | Reference |
|---|---|---|---|---|---|---|---|---|---|
| CSF and serum | Human | 105 patients | Effect of age on KYN metabolites and analysis of the influence of medication use | LC-MS | Tryptophan metabolism | ↓KYNA in CSF | |||
| (n = 33 AD patients | ↑ KYN, KYNA and QUIN in serum | KP has a potential as a marker of disease progression or as a therapeutic target in neurodegeneration | [34] | ||||||
| n = 33 PD patients | |||||||||
| n = 39 control subjects) | |||||||||
| Serum | Knurenines | Human | 18 PD patients | Compare peripheral kynurenines with metabolic syndrome associated kynurenines | HPLC | Tryptophan metabolism | ↓ TRP concentration | ||
| 20 AD patients | ↑KYN: TRP ratio, KYN, AA and KYNA | Association between neurodegenerative disorders and metabolic syndromes | [54] | ||||||
| Plasma | 184 metabolites | Human | 82 PD patients | Quantified the plasma levels of metabolites | LC-TOFMS | Pathomechanistic pathways | ↓KYNA/KYN ratio | ||
| ↑ QUIN/KYNA ratio | Plasma biomarkers are available for predicting PD | [99] | |||||||
| Human | Catabolism of tryptophan and tyrosine in relation to the isoprenoid pathway in some neurological and psychiatric disorder | HPLC | ↑ QUIN | Hypercatabolism of tryptophan could be a consequence of the modifying effect of hypothalamic digoxin on amino acid transport. | [100] | ||||
| Urine | urinary metabolites | Human | |||||||
| Drosophila melanogaster | 106 PD | Identified the correlation between clinical phenotype and urinary metabolite profile | GC–MS | ||||||
| LC-MS | Tryptophan metabolism | ↑α-synuclein and modified tryptophan metabolism. | Urinary metabolites were assessed in PD | ||||||
| Urinary metabolomics profiling would benefit in relating metabolic pathway deviations and metabolites signatures to characterize PD | [96] | ||||||||
| Characterize the urinary metabolites in PD patients | – | ↑KYN | Alterations in metabolic profiling is associated with PD | [97] | |||||
| CSF | Human | 92 PD patients | Examine the function of KYN pathway and its interaction between oxidative stress and neuroinflammation | HPLC | |||||
| Human | 20 PD patients | ELISA | KYN pathway | ↑KYN and 3-HK | Dysfunctional KYN pathway may induce oxidative stress and neuroinflammation | [98] |
PD-Parkinson's disease; CSF-cerebrospinal fluid; KYNA - Kynurenic acid; KYN – kynreunine; QUIN – quinolinic acid; AA –Anthranilic acid; GC–MS-Gas chromatography mass spectrometry; LC-MS- Liquid chromatography–mass spectrometry; LC-TOFMS - liquid chromatography time-of-flight mass spectrometry; HPLC – High performance liquid chromatography; ELISA – Enzyme Linked Immunosorbent Assay.