Neurotoxicity and mechanisms of deltamethrin and its metabolite 3-PBA in HT22 cells

Deltamethrin (DLM) along with its main metabolite 3-phenoxybenzoic acid (3-PBA) are increasingly detected in environmental media. They both have the ability to accumulate on human by food chains with potential neurotoxicity. However, at present, there are relatively few studies on the neurotoxic effects of DLM and 3-PBA. This study investigated the neurotoxicity and mechanism in HT22 hippocampal neurons by DLM (5, 25, 50, 100, and 150 μM) and 3-PBA (100, 500, 1000, 1500, and 2000 μM). Cytotoxicity assays revealed that both DLM and 3-PBA dose-dependently inhibited HT22 cell viability. Notably, DLM exhibited higher potency than 3-PBA, as evidenced by its lower IC₅₀ value. Enzyme-linked immunoassay showed that exposure to DLM and 3-PBA interfered with the secretion of neurotransmitters (Ach, DA, GABA) and disrupted the transmission of signaling molecules (NO). Biochemical analysis revealed that both compounds reduced intracellular antioxidants (SOD and GSH-Px), and surged ROS production. This oxidative imbalance led to mitochondrial dysfunction and subsequent apoptosis. Oxidative damage mechanism study showed that DLM and 3-PBA exposure reduced the expression levels of Nrf2, HO-1, and AKT proteins, as well as the transcription of Nrf2, HO-1, and Akt genes in the Nrf2/HO-1 antioxidant pathway, reducing the antioxidant capacity of HT22 cells. Apoptotic mechanism showed that DLM and 3-PBA reduced the expression levels of Bcl-2, Bcl-xL proteins and genes. They also increased the expression levels of JNK, BAX, Cyto c, Caspase-9 proteins, alongside the upregulation of JNK, BAX, Cyto c, and Caspase-9 genes in the endogenous apoptotic signaling pathway. Meanwhile, DLM and 3-PBA exposure also increased the expression levels of FasL, FADD, Caspase-8, Caspase-3 proteins, as well as FasL, FADD, Caspase-8, and Caspase-3 genes in the exogenous apoptotic signaling pathway, thereby inducing apoptosis. These findings highlight the potential neurotoxicity and molecular mechanisms of DLM and 3-PBA, emphasizing the need for further research to assess and mitigate the health risks associated with pesticide exposure.