Parkinson's disease (PD) is a complex multi-factorial neurodegenerative disorder where various altered metabolic pathways contribute to the progression of the disease. Tryptophan (TRP) is a major precursor in kynurenine pathway (KP) and it has been discussed in various in vitro studies that the metabolites quinolinic acid (QUIN) causes neurotoxicity and kynurenic acid (KYNA) acts as neuroprotectant respectively. More studies are also focused on the effects of other KP metabolites and its enzymes as it has an association with ageing and PD pathogenesis. Until now, very few studies have targeted the role of genetic mutations in abnormal KP metabolism in adverse conditions of PD. Therefore, the present review gives an updated research studies on KP in connection with PD. Moreover, the review emphasizes on the urge for the development of biomarkers and also this would be an initiative in generating an alternative therapeutic approach for PD.

The selective degeneration of dopaminergic (DA) neurons in Parkinson’s disease (PD) has made an idol target for cell replacement therapies and other emerging surgical treatments. Certainly, by transplantation method, the therapeutic regimens such as human fetal ventral midbrain (hfVM) cells, human embryonic stem cells (hESCs), human neural stem/precursor/ progenitor cells (hNSCs/hNPCs), human mesenchymal stem cells (hMSCs), human induced neural stem cells (hiNSCs), and human induced pluripotent stem cells (hiPSCs) have been used into DA deficient striatum. In recent decades, surgical methods such as deep brain stimulation (DBS) and gene therapies have been used with the aim of treating PD. Though the technology has improved and many treating options arise, the permanent source for curing PD has not been identified yet. In this review, we examine how stem cell therapies have made advancement as a therapeutic source for PD when compared with surgical treatments.