Dose-Dependent impacts of fluoride exposure on behavior, oxidative stress, liver metabolism, and molecular responses in Cyprinus carpio

This study investigates the effects of fluoride exposure on tissue accumulation, behavior, oxidative stress, neurotoxicity, metabolomic, and molecular alterations in Cyprinus carpio. The effects were evaluated at four different concentrations (Control: 0.8 mg/L, Group 1: 1.52 mg/L, Group 2: 3.0 mg/L, Group 3: 4.2 mg/L) over a 30-day period. Behavioral analysis revealed progressive neurobehavioral impairments including erratic swimming, lethargy, and respiratory distress. Fluoride accumulation followed the order: bone > gill > skin > muscle, indicating both systemic absorption and organ-specific retention. Enzymatic assays showed significant elevation of antioxidant enzymes (SOD, CAT, GPx) coupled with acetylcholinesterase inhibition, signifying oxidative stress and neurotoxicity. Metabolomic profiling demonstrated marked depletion of glutathione and ATP, with elevated lactate, AMP, and succinate levels, reflecting mitochondrial dysfunction and energy crisis. Concurrently, upregulation of IL-17, TNF-α, RORγ, and FoxO3a, alongside downregulation of IL-10 and Foxp3, indicated transcriptional signatures consistent with Th17-associated pro-inflammatory signaling and reduced Treg-related gene expression. Apoptotic gene activation (JNK, Bax, PUMA, Apaf-1, Caspase-9/3) and Bcl-2 suppression confirmed intrinsic mitochondrial apoptosis. Collectively, fluoride toxicity appears to progress through an integrated oxidative stress–mitochondrial dysfunction–immune imbalance–apoptotic cascade, which suggests that oxidative stress may function as an upstream trigger. These findings demonstrate that fluoride induces behavioral impairments, tissue accumulation, oxidative stress, metabolic disruption, immune imbalance, and apoptosis in C. carpio, with effects showing a strong dose-dependent (graded) response pattern, and identify key metabolites and molecular markers as early indicators of fluoride toxicity in aquatic environments.