ALH Inhibition as a Molecular Initiating Event in the Adverse Outcome Pathway of Benomyl Toxicity in Caenorhabditis elegans: Relevance for Parkinsonism

Abstract

Dithiocarbamate fungicides, including benomyl (methyl 1-butylcarbamoyl-2-benzimidazolecarbamate), share a common mechanism of toxicity by inhibiting aldehyde dehydrogenases (ALDHs), enzymes essential for detoxifying reactive aldehydes. One such aldehyde, 3,4-dihydroxyphenylacetaldehyde (DOPAL), a dopamine metabolite, is implicated in the catecholaldehyde hypothesis of Parkinson’s disease. This study examines ALDH inhibition as the molecular initiating event (MIE) within an adverse outcome pathway (AOP) leading to neurotoxicity. Caenorhabditis elegans at the L4 stage were exposed for 24 h to 10 or 100 μM benomyl. While 10 μM had no significant effect on lethality, growth, or reproduction, 100 μMinduced adverse effects, albeit with low lethality. Both doses inhibited ALH activity, an effect mitigated by Alda-1, a selective ALDH activator. Alda-1 alone increased ALH-1 protein levels but did not alter benomyl-induced protein localization and relative abundance. Benomyl exposure also elevated oxidative stress markers—superoxide dismutase, catalase, and lipid peroxidation—which Alda-1 reduced. Neurotoxicity was evidenced by dopaminergic dysfunction, including impaired basal slowing response, neuronal morphological abnormalities, and reduced locomotion upon optogenetic activation. Fluorescent reporter assays confirmed ALH-1 presence in dopaminergic neurons. These results identify ALH inhibition as the MIE in benomyl-induced neurotoxicity, linking dopaminergic degeneration and redox imbalance to the catecholaldehyde hypothesis, and providing mechanistic insights into an AOP relevant to neurodegenerative disorders.