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(Ca^(2+))influx was measured by a Ca^(2+)fluorescence imaging system.The fluorescence intensity(F)of cells was measured.The rate of change in F(ΔF/F0)was calculated,and theΔF/F0-time curve was constructed.HaCaT keratinocytes were stimulated with polyinosinic:polycytidylic acid,recombinant human tumor necrosis factorα,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 Ca^(2+)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 Ca^(2+)influx induced by capsaicin(TRPV1 agonist)in HaCaT keratinocytes.Honokiol has an inhibitory effect on TSLP secretion in HaCaT keratinocytes.

Blockade of transient receptor potential cation channel subfamily V member 1 promotes regeneration after sciatic nerve injury

The transient receptor potential cation channel subfamily V member 1（TRPV1） provides the sensation of pain（nociception）. However, it remains unknown whether TRPV1 is activated after peripheral nerve injury, or whether activation of TRPV1 affects neural regeneration. In the present study, we established rat models of unilateral sciatic nerve crush injury, with or without pretreatment with AMG517（300 mg/kg）, a TRPV1 antagonist, injected subcutaneously into the ipsilateral paw 60 minutes before injury. At 1 and 2 weeks after injury, we performed immunofluorescence staining of the sciatic nerve at the center of injury, at 0.3 cm proximal and distal to the injury site, and in the dorsal root ganglia. Our results showed that Wallerian degeneration occurred distal to the injury site, and neurite outgrowth and Schwann cell regeneration occurred proximal to the injury. The number of regenerating myelinated and unmyelinated nerve clusters was greater in the AMG517-pretreated rats than in the vehicle-treated group, most notably 2 weeks after injury. TRPV1 expression in the injured sciatic nerve and ipsilateral dorsal root ganglia was markedly greater than on the contralateral side. Pretreatment with AMG517 blocked this effect. These data indicate that TRPV1 is activated or overexpressed after sciatic nerve crush injury, and that blockade of TRPV1 may accelerate regeneration of the injured sciatic nerve.