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Effects of Honokiol on Activation of Transient Receptor Potential Channel V1 and Secretion of Thymic Stromal Lymphopoietin in HaCaT Keratinocytes

Objective: 
This study was performed to investigate the effects of honokiol on the activation of transient receptor potential channel V1 (TRPV1) and the secretion of thymic stromal lymphopoietin (TSLP) in a human benign epidermal keratinocyte line (HaCaT). 
 
 
Methods: 
HaCaT keratinocytes were cultivated and divided into six groups: capsaicin-induced model control group, capsazepine control group, solvent control group, and three honokiol treatment groups (7.81, 15.63, and 31.25 mg/L of honokiol). The effect of honokiol on calcium (Ca2+) influx was measured by a Ca2+ fluorescence imaging system. The fluorescence intensity (F) of cells was measured. The rate of change in F (ΔF/F0) was calculated, and the ΔF/F0-time curve was constructed. HaCaT keratinocytes were stimulated with polyinosinic:polycytidylic acid, recombinant human tumor necrosis factor α, and recombinant human interleukin 4. Different concentrations of honokiol (15.63, 7.81, and 3.91 mg/L) were added to the cells in the respective honokiol groups; 20 mg/L of dexamethasone or 0.5% dimethyl sulfoxide was added to the cells in the positive control group or solvent control group. The TSLP concentration in the HaCaT keratinocytes of each group was detected by enzyme-linked immunosorbent assay. Statistical analysis was performed by one-way analysis of variance and Dunnett t test. 
 
 
Results: 
The capsaicin-induced Ca2+ fluorescence intensity in HaCaT keratinocytes was significantly inhibited in the 31.25 mg/L honokiol group; ΔF/F0 at 45 second was 0.76 in the model control group and 0 in the 31.25 mg/L honokiol group. The TSLP level in the 15.63 and 7.81 mg/L honokiol groups was lower than that in the solvent control group (t= 7.382, P= 0.003, and t= 2.766, P= 0.023, respectively), while the TSLP level in the 3.91 mg/L honokiol group was not significantly different from that in the solvent control group (t= 1.872, P= 0.124). 
 
 
Conclusions: 
Honokiol inhibited the Ca2+ influx induced by capsaicin (TRPV1 agonist) in HaCaT keratinocytes. Honokiol has an inhibitory effect on TSLP secretion in HaCaT keratinocytes. 
 
 
Key words: 
honokiol; keratinocytes; transient receptor potential channel V1; thymic stromal lymphopoietin