# Enhanced Toxicity Induced by Combined Exposure to Neonicotinoid Insecticides and Fluoroquinolone Antibiotics in Human Neuroblastoma SK-N-SH Cells

## TL;DR

Mixing insecticides and antibiotics increases toxicity in nerve cells, causing more harm than either alone.

## Contribution

Identifies synergistic toxicity of neonicotinoid insecticides and fluoroquinolone antibiotics in human neuroblastoma cells.

## Key findings

- Fluoroquinolones showed higher cytotoxicity than neonicotinoids in human neuroblastoma cells.
- Mixtures of ENR and OFX caused synergistic toxicity, with ENR-containing mixtures inducing the largest transcriptomic shifts.
- RNA-seq and RT-qPCR confirmed significant changes in gene expression related to neuronal signaling and cellular stress.

## Abstract

Neonicotinoid insecticides and fluoroquinolone antibiotics frequently co-occur in aquatic and terrestrial environments, posing a threat to human health, yet their combined neurotoxic potential remains poorly characterized. This study aimed to assess the cytotoxicity of typical neonicotinoids and fluoroquinolones as well as their mixtures in human neuroblastoma SK-N-SH cells and identify affected pathways. SK-N-SH cells were exposed to clothianidin (CLO), imidacloprid (IMI), enrofloxacin (ENR), and ofloxacin (OFX) individually and in fixed-ratio mixtures (50% of each compound’s IC50) for 24 h and 48 h, and cell viability was quantified using the alamarBlue® method. Single-compound dose–response testing showed time-dependent cytotoxicity, with higher potency for fluoroquinolones (24 h IC50: ENR 1.446 mM, OFX 2.742 mM; 48 h IC50: ENR 0.826 mM, OFX 2.005 mM) than neonicotinoids (24 h IC50: IMI 4.754 mM, CLO 5.356 mM; 48 h IC50: IMI 3.631 mM, CLO 4.029 mM). Concentration-addition analysis indicated that most mixtures produced synergistic interaction in reduction in cell viability, with ENR+OFX showing the strongest effect at 48 h (Observed viability 7.138% vs. Predicated viability 82.368%). RNA-seq (24 h) revealed that binary mixtures generally induced more differentially expressed genes than single exposures, and ENR-containing mixtures showed the largest transcriptomic shifts, enriching pathways related to cellular stress and injury as well as neuronal signaling and connectivity. RT-qPCR validated the changes in expressions of five key neurobiology-relevant genes (LMO3, NOS1, ADCY8, FGF7 and TNFRSF12A). These findings highlight the importance of assessing insecticide–antibiotic mixtures when evaluating their hazards in environment.