Intergenerational toxicity of flonicamid in zebrafish: Immune-inflammatory stress as a driver of parental and offspring effects.

Flonicamid (FLO) is a pyridine carboxamide insecticide with a unique mode of action. After parental exposure to FLO for 21 days in zebrafish, this study evaluated the effects of FLO on both the exposed parental generation (F0) and their non-exposed F1 offspring at various developmental stages. FLO accumulates in parental zebrafish in a concentration-dependent and tissue-specific pattern, and it can be detected in the brain tissues of two-month-old F1 offspring (F1-2). In the F0 generation, exposure to FLO induced significant behavioral abnormalities, accompanied by marked oxidative stress and the activation of apoptosis. The intergenerational effects were more pronounced in the F1-2, which demonstrated significantly more severe behavioral abnormalities alongside a marked suppression of caspase-3 and -9 activities, as compared to the 4-month-old F1 offspring (F1-4). Oxidative stress, characterized by disrupted antioxidant activities and elevated MDA content, was observed in both F1-2 and F1-4 groups. Transcriptome sequencing revealed consistent enrichment of immune-inflammatory biological processes and classical inflammatory pathways in both F0 generation and F1 offspring. Total 120 differentially expressed genes (DEGs) related to immune-inflammatory responses in F0 parents and F1 offspring were selected, which consisted mainly by cytokines. PPI network analysis showed that these DEGs are tightly interconnected, forming a regulatory network anchored by ten hub genes (e.g., cxc18, tnfa, pdgfra). These results collectively reveal the neurotoxic effects of FLO and its potential mechanisms of action. This finding suggests that the core toxic effects of immune-inflammatory stress induced by parental FLO exposure may be transmitted from parents to their unexposed offspring.