The role of Piper chaba Hunt. and its pure compound, piperine, on TRPV1 activation and adjuvant effect.

BACKGROUND: Piper chaba Hunt. is used as an ingredient in Thai traditional preparation for arthritis. Its isolated compound is piperine which shows anti-inflammatory activity. Piperine produces a burning sensation because it activates TRPV1 receptor. The TRPV1 activation involved with the analgesic and adjuvant effect. P. chaba Hunt. has not been reported about TRPV1 activation and adjuvant effect. The aim of this study was to investigate the effect of P. chaba extract and piperine on TRPV1 receptor, which is considered as a target for analgesic and their adjuvant effects to support the development of an analgesic drug from herbal medicine. METHODS: The effect of P. chaba extract and piperine on HEK cells expressing TRPV1 channel was examined by calcium imaging assay. Adjuvant effects of P. chaba extract and piperine were investigated by a fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS) model in mice. RESULTS: P. chaba extract induced calcium influx with EC50 value of 0.67 µg/ml. Piperine induced calcium influx with EC50 value of 0.31 µg/ml or 1.08 µM. For mouse CHS model, we found that 1% piperine, 5% piperine, 1% P. chaba extract and 5% P. chaba extract significantly enhanced sensitization to FITC as revealed by ear swelling responses. CONCLUSION: P. chaba extract and piperine activated TRPV1 channel and enhanced contact sensitization to FITC.

Adjuvant effect of short chain triacylglycerol tributyrin on a mouse contact hypersensitivity model.

Little attention has been paid to chemicals that can enhance hypersensitivity caused by other chemicals. We have demonstrated that phthalate esters with short chain alcohols enhance fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS) in a mouse model. Furthermore, phthalate esters with such an enhancing effect were found to activate transient receptor potential ankyrin 1 (TRPA1) cation channels, which are expressed on a part of sensory neurons, using a TRPA1-expressing cell line. In this study, we examined these activities of esters comprising glycerol and a short chain fatty acid, i.e. dibutyrin and tributyrin. We carried out chemical synthesis of dibutyrin isomers. Each dibutyrin isomer weakly activated TRPA1 and slightly enhanced skin sensitization to FITC. Unexpectedly, TRPA1 activation and enhancement of FITC-CHS were much more evident in the presence of tributyrin. Mechanistically, tributyrin induced increased dendritic cell trafficking from the skin to draining lymph nodes. Tributyrin enhanced interferon-γ (IFN-γ) production by draining lymph nodes, while its effect on interleukin-4 (IL-4) production was relatively less prominent. These results suggested that tributyrin concomitantly caused TRPA1 activation and an adjuvant effect on FITC-CHS.

Dibutyl Phthalate Rather than Monobutyl Phthalate Facilitates Contact Hypersensitivity to Fluorescein Isothiocyanate in a Mouse Model.

Dibutyl phthalate (DBP) is a plasticizer used for many consumer products including cosmetics. Potential health concerns regarding DBP include reproductive and developmental toxicity, endocrine disruption and neurotoxicity. DBP is a high priority chemical as to reduction of exposure of children to it. Through reproductive toxicity studies, monobutyl phthalate (MBP) has been proposed to be the active metabolite derived from DBP. We previously demonstrated that DBP activates transient receptor potential ankyrin 1 (TRPA1) cation channels expressed on sensory neurons. We have also shown that DBP enhanced skin sensitization in a fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS) mouse model. Through MBP formation by esterase in the skin, it is possible that MBP exerts a major effect on the biological activity we observed. To test this possibility, we directly compared DBP and MBP. A more than 40-fold higher concentration of MBP as compared with DBP was required for activation of TRPA1 in vitro. Unlike DBP, MBP did not enhance skin sensitization to FITC. These results demonstrated that DBP directly, i.e., not through its metabolite MBP, activates TRPA1 and enhances FITC-CHS. It is noteworthy that butyl benzoate, a related compound, activated TRPA1 and enhanced FITC-CHS.

Dibutyl Maleate and Dibutyl Fumarate Enhance Contact Sensitization to Fluorescein Isothiocyanate in Mice.

Di-n-butyl phthalate (DBP), a phthalate ester, has been shown to have an adjuvant effect on fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS) mouse models. Di-n-butyl maleate (DBM), widely used as a plasticizer for industrial application, has been reported to cause dermatitis in humans. DBM is a butyl alcohol ester of di-carboxylic acid that represents a part of the DBP structure, while di-n-butyl fumarate (DBF) is a trans isomer of DBM. We examined whether DBM or DBF exhibits an adjuvant effect like DBP does. When BALB/c mice were epicutaneously sensitized with FITC in the presence of DBM or DBF, the FITC-specific CHS response was enhanced, as we have observed for DBP. As to underlying mechanisms, DBM and DBF facilitated the trafficking of FITC-presenting CD11c(+) dendritic cells (DCs) from skin to draining lymph nodes and increased the cytokine production by draining lymph nodes. In conclusion, DBM and DBF may have an effect that aggravates contact dermatitis through a skin sensitization process.