Atherosclerotic-dose TMAO accentuates redox imbalances and motor dysfunctions in a MPTP mouse model of Parkinson's disease.

Parkinson's Disease (PD) involves the loss of dopaminergic neurons and the formation of Lewy bodies consisting of alpha-synuclein (αSin) aggregates. Trimethylamine N-oxide (TMAO), a gut microbiota metabolite, has emerged as a molecule of interest due to pro-inflammatory, pro-oxidative, and neurodegenerative effects. We aim to assess whether lower doses of TMAO (40 mg/kg bw, gavage, once daily, day 0-42), as those used in atherosclerosis experimental models, can exacerbate oxidative stress, neuroinflammation, motor dysfunction, and neurodegeneration in a semi-acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) PD model (30 mg/kg bw MPTP, intraperitoneal, once daily, day 20-24). Motor behavioral testing functionally validated the model, with MPTP impairing performance across Rotarod latency time (p < 0.05), Wire Hang number of reaches and falls (p < 0.05), and Pole test time to descent (p < 0.01 MPTP vs. Control, p < 0.05 MPTP+TMAO vs. Control). A synergistic effect between TMAO and MPTP was observed in pole-turning time (p < 0.05). Increased TMAO serum was confirmed in treated animals (p < 0.05 TMAO vs. Control; p < 0.001 MPTP+TMAO vs. Control). Loss of tyrosine hydroxylase (TH) positive thalamic fibers, as well as substantia nigra neuronal fiber degeneration, and dopamine depletion was observed in the MPTP groups. A significant reduction in tyrosine hydroxylase (TH) expression in the midbrain was observed exclusively in the TMAO+MPTP group (p < 0.05 vs. Control). Neuroinflammatory profiling revealed selective elevation of IL-6 in the TMAO+MPTP group (p < 0.05), without microglial activation (p > 0.05), whereas NF-κB p65 was paradoxically increased only in the TMAO (p < 0.05) and MPTP (p < 0.05) groups. We hypothesize that this divergent pattern may indicate a shift toward necrotic rather than apoptotic cell death in the combined exposure group. MPTP and TMAO independently induced pro-oxidative states, evidenced by GSH depletion (p < 0.0001 MPTP vs. Control; p < 0.001 MPTP+TMAO vs. Control) and compensatory SOD upregulation (p < 0.01 TMAO vs. Control; p < 0.05 MPTP vs. Control and MPTP+TMAO vs. Control). The combination amplified the redox imbalance with significant elevation of MDA in the TMAO+MPTP group (p < 0.001 vs. Control and vs. TMAO; p < 0.01 vs. MPTP). These findings carry clinical relevance in the context of Parkinson's disease, suggesting that gut microbiome-derived metabolites may represent a pathological connection capable of increasing both cardiovascular risk and the progression of neurodegenerative disorders.