Table 2.

Cluster analysis of keywords.

Clusters	Keywords
Cluster 1 (red) - 35 items	6-Hydroxydopamine, 6-ohda, antioxidants, apoptosis, reactive oxygen species, ros, ascorbic acid, autophagy, autoxidation, calcium, catecholamine, DNA damage, dopamine, erk, free radical, free radicals, gsh, heme oxygenase-1, jnk, l-dopa, lactacystin, manganese, neurotoxicity, nf-κb, nrf2, oxidation, p38, Parkinson disease, pc12 cell, pc12 cells, reactive oxygen species (ros), sh-sy5y cells, striatum, ubiquitin proteasome system, ups
Cluster 2 (green) - 32 items	Aggresome, aging, alpha-synuclein, alzheimer's disease, astrocytes, caspase, cysteine, cytochrome c, dementia with lewy bodies, dopaminergic neuron, dopaminergic neurons, electron transport chain, glutathione, inclusion, mpp+, n-acetyl-l-cysteine, neuroinflammation, Parkinson, Parkinson's disease, parkinsonism, pesticide, proteasome, proteasome inhibition, rotenone, sh-sy5y, sh-sy5y cell, stem cells, synuclein, thiol, ubiquitin, ubiquitin-proteasome system
Cluster 3 (blue) - 19 items	Anti-inflammatory, antioxidant, cell death, curcumin, cytotoxicity, deferoxamine, dj-1, glutamate, mitochondria, mitochondrial dysfunction, mitophagy, mptp, n-acetyl cysteine, n-acetylcysteine, neurodegenerative diseases, oxidative stress, paraquat, parkin, Parkinson's disease
Cluster 4 (yellow) - 19 items	Copper, er stress, ferroptosis, gene therapy, inflammation, iron, microglia, neurodegeneration, neuroprotection, nitric oxide, Parkinson's, proteasome inhibitor, redox, substantia nigra, unfolded protein response, glial cell line-derived neurotrophic factor

Note: bold words indicate keywords with the highest frequency of co-occurrence.