Incense Aerosol-Induced Neurotoxicity Disrupts α-Synuclein Homeostasis in a Cellular Parkinson’s Disease Model, Distinct from Cigarette Aerosols

Incense burning is a widespread indoor combustion practice, yet its neurotoxic potential and impact on α-synuclein (α-Syn) proteostasis remain poorly defined. Using SH-SY5Y cells overexpressing α-Syn as a cellular Parkinson's disease model, we exposed cells to size-fractionated incense aerosol extracts (IAE) prepared as organic-phase (OP) or water-soluble phase (WP). α-Syn overexpression augmented vulnerability to IAE, producing greater losses in viability and pronounced increases in intracellular hydrogen peroxide (H₂O₂), mitochondrial membrane potential depolarization, and engagement of programmed cell-death pathways. Live-cell fluorescence cross-correlation spectroscopy (FCCS) revealed that both OP-IAE and WP-IAE shifted α-Syn from oligomeric to monomeric states in the cytosol, indicating disruption of oligomerization equilibrium. Antioxidant intervention revealed mechanistic differences compared with other indoor air pollutants, cigarette smoke. OP-IAE-induced cytotoxicity cannot be mitigated by <i>N</i>-acetylcysteine (NAC) or rutin, whereas WP-IAE-induced toxicity was partially attenuated, with NAC surpassing rutin. By contrast, for cigarette aerosol extracts (CAE), both OP- and WP-CAEs were robustly rescued by NAC and, to a lesser extent, rutin. Together, these results indicate that incense aerosols, particularly OP-IAE, engage reactive oxygen species (ROS)-linked mitochondrial injury and programmed cell-death pathways while uniquely driving α-Syn monomerization, while exhibiting relative resistance to classical antioxidant intervention compared with cigarette aerosols. This work points out incense smoke as a distinct indoor neurotoxicant with implications for α-Syn homeostasis and Parkinsonian risk in exposed populations.