Benzalkonium chloride (BAK), a
quaternary ammonium compound widely used as disinfecting agent as well as preservative in
eye drops is known to induce toxic effects on the ocular surface with
inflammation and corneal nerve damage leading to
dry eye disease (DED) in the medium-to-long term. The aim of this study was to evaluate in vitro the toxicity of a
conditioned medium produced by corneal epithelial cells previously exposed to BAK (BAK-CM) on trigeminal neuronal cells. A human corneal epithelial (
HCE) cell line was exposed to 5.10-3% BAK (i.e. 0.005% BAK) for 15 min and let recover for 5 h to prepare a BAK-CM. This BAK concentration is the lowest one found in
eye drops. After this recovery period, BAK effect on
HCE cells displayed cytotoxicity, morphological alteration, apoptosis, oxidative stress,
ATP release, CCL2 and
IL6 gene induction, as well as an increase in CCL2,
IL-6 and MIF release. Next, a mouse trigeminal ganglion primary culture was exposed to the BAK-CM for 2 h, 4 h or 24 h. Whereas BAK-CM did not alter neuronal cell morphology, or induced neuronal cytotoxicity or oxidative stress, BAK-CM induced gene expression of Fos (neuronal activation marker), Atf3 (neuronal injury marker), Ccl2 and
Il6 (inflammatory markers). Two and 4 h BAK-CM exposure promoted a neuronal damage (ATF-3, phospho-p38 increases; phospho-Stat3 decreases) while 24 h-BAK-CM exposure initiated a prosurvival pathway activation (phospho-p44/42, phospho-Akt increases; ATF-3, GADD153, active
Caspase-3 decreases). In conclusion, this in vitro model, simulating paracrine mechanisms, represents an interesting tool to highlight the indirect toxic effects of BAK or any other
xenobiotic on corneal trigeminal neurons and may help to better understand the cellular mechanisms that occur during DED pathophysiology.