Abstract
Purpose: :
We previously showed that corneal epithelium uses Toll-like receptor 2 (TLR2) and TLR5 to activate innate immune responses against S. aureus and P. aeruginosa, respectively. In the present study, we examined the effects of a dietary compound curcumin in modulation of human corneal epithelial cells (HCECs) innate response to pathogen challenge.
Methods: :
HUCL, a telomerase-immortalized HCEC line, and primary culture of HCECs were pretreated with different dosages of curcumin (diferuloylmethane), a yellow pigment in turmeric (Curcuma longa L.), and then challenged either with TLR2 (Pam3Cys), TLR5 (flagellin) ligand or live bacteria. Cytotoxicity of curcumin was assessed by LDH release and its antibacterial effect was check by incubating the pathogens with various concentrations of curcumin and bacterial plate count. NF-ΚB activation was determined by the extent of IΚB-α phosphorylation and degradation and of nuclear p65 DNA binding. The activation of p38 JNK and ERK was assessed by Western blotting. The expression proinflammatory cytokine genes were assessed using semi-quantitative RT-PCR and the secretion of cytokines in the culture media was assessed using ELISA.
Results: :
Challenge of HCECs with TLR2/5 ligands and ocular pathogens S. aureus and P. aeruginosa, resultedin the activation of NF-ΚB and in the induction of pro-inflammatory cytokine/chemokine genes. Curcumin inhibited TLR ligand and bacterial-induced I-ΚB-α degradation, and NF-ΚB p65 DNA-binding but did not affect the activation of other MAPKs p38, JNK and ERK. Furthermore, the TLR ligand and bacterium-induced release of interleukin 8 (IL-8) and TNF-α was also inhibited by curcumin. Importantly, curcumin (up to 80µM) did not exert any toxic effects in cultured HCECs and the observed anti-inflammatory role of curcumin was independent of its antibacterial activity.
Keywords: cornea: epithelium • inflammation • bacterial disease