A Novel Framework of an Adverse Outcome Pathway Targeting the Eye Lens: Mechanistic Insights from 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) Exposure in Cataract Etiology.

Although environmental pollutants are recognized as a hazard to visual health, the molecular targets and mechanistic pathways responsible for pollutant-induced visual impairment are still poorly understood. This study investigated the effects of the emerging marine contaminant 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one on eye structure and function using integrated ex vivo, in silico, in vitro, and in vivo approaches. A pull-down screening of eye tissues identified lens Crystallin proteins as direct molecular targets. Molecular docking, biolayer interferometry, and recombinant protein assays confirmed the binding between the contaminant and crystallins and showed that this interaction rapidly promoted Crystallin aggregation. Ex vivo exposure of isolated lenses caused progressive lens opacity, supporting a cataract-like pathological process. Life-cycle exposure of marine medaka to environmentally relevant concentrations resulted in accumulation of the contaminant in lens, increased lens opacity, and impaired optomotor responses. Gene expression profiling revealed concentration-dependent upregulation of multiple Crystallin and photoreceptor genes, consistent with adaptive responses to reduced lens clarity, while proteomic analyses demonstrated broad disturbance of lens protein homeostasis and altered abundances of Crystallin subtypes. These findings demonstrate a mechanistic cascade in which the contaminant accumulates in the lens, binds crystallins, disrupts protein stability, reduces lens transparency, and compromises visually mediated behavior. This study establishes a lens-targeted adverse outcome pathway for pollutant-induced visual toxicity and highlights the potential ecological and health risks associated with the increasing presence of this antifouling compound in marine environments.