Effects of honokiol on activation of transient receptor potential channel in rat spinal dorsal root ganglion cells and pruritus in mouse models

Objective To evaluate the effect of honokiol on the activation of transient receptor potential (TRP) channel in rat spinal dorsal root ganglion cells and pruritus in mouse models. Methods Healthy male ICR mice aged 4-6 weeks were used to establish histamine-induced and acetone/ether/water (AEW) -induced itching models separately. Totally, mice were randomly divided into 7 groups (histamine-induced model experiment) or 6 groups (AEW-induced model experiment) : normal control group and model group both gavaged with sodium chloride physiological solution, solvent group gavaged with sodium carboxymethylcellulose solution, chlorphenamine group (only set up in the histamine-induced model experiment) gavaged with chlorphenamine, 50, 25 and 12.5 mg/kg honokiol groups gavaged with 50, 25 and 12.5 mg/kg honokiol respectively. In the histamine-induced model experiment, the mice were all injected with histamine except the normal control group injected with sodium chloride physiological solution 24 hours after the gavage treatment, while the mice in the AEW-induced model experiment were all topically treated with AEW except the normal control group topically treated with sodium chloride physiological solution for 4 days, followed by gavage with different drugs. The anti-itch effect of each treatment was evaluated by counting the scratching frequency within 30 minutes. Rat spinal dorsal root ganglion (DRG) cells were isolated and subjected to a primary culture. Then, the DRG cells were divided into 6 groups: capsaicin or allyl isothiocyanate (AITC) -induced model group pre-incubated with Hank′s balanced salt solution (HBSS) , 500 μmol/L capsazepine or 10 μmol/L HSC030031 group pre-incubated with capsazepine or HSC030031, solvent group pre-incubated with dimethyl sulfoxide (DMSO) , 3 honokiol groups pre-incubated with 7.81, 15.63 and 31.25 mg/L honokiol respectively, and Ca2+ fluorescence imaging system was used to observe changes of Ca2+ influx in these cells after capsaicin or AITC stimulation. Statistical analysis was carried out with SPSS 20.0 software by using one-way analysis of variance and Dunnett-t test. Results In the histamine-induced mouse models, the scratching frequency was significantly lower in the 50 and 25 mg/kg honokiol groups than in the model group (21.88 and 21.14 vs. 63.70, t=3.48, 3.49 respectively, both P=0.003) , while no significant difference in the scratching frequency was observed between the 12.5 mg/kg honokiol group and the model group (t=2.01, P=0.062) . After the treatment with 50 mg/kg honokiol in the AEW-induced mouse models, the scratching frequency significantly decreased compared with the model group (61.4 vs. 101.17, t=0.45, P=0.009) , while there were no significant differences among the 25, 12.5 mg/kg honokiol groups and the model group (all P > 0.05) . Compared with the capsaicin or AITC-induced model group, the increase of Ca2+ fluorescence signal in the DRG cells was significantly inhibited in the 31.25 mg/L honokiol group: at the 45th second, the rate of relative fluorescence intensity change (ΔF/F0) was 1.11 in the model group, but-0.11 in the 31.25 mg/L honokiol group in the capsaicin-induced model experiment, and 0.56 in the model group, but 0.00 in the 31.25 mg/L honokiol group in the AITC-induced model experiment. Conclusion Honokiol shows an inhibitory effect on mouse models of pruritus induced by histaminergic or non-histaminergic factors, likely by inhibiting Ca2+ influx through activated TRPV1 and TRPA1 channels in the DRG cells. Key words: Pruritus; Honokiol; Transient receptor potential channels; Disease models, animal