Adjuvant Effect of an Alternative Plasticizer, Diisopropyl Adipate, on a Contact Hypersensitivity Mouse Model: Link with Sensory Ion Channel TRPA1 Activation

Abstract

Due to health concerns about phthalate esters, the use of alternative plasticizers is being considered. Phthalate esters enhance skin sensitization to fluorescein isothiocyanate (FITC) in mouse models. We have demonstrated that phthalate esters stimulate transient receptor potential ankyrin 1 (TRPA1) cation channels expressed on sensory neurons. We also found a correlation between TRPA1 activation and the enhancing effect on FITC-induced contact hypersensitivity (CHS) when testing various types of phthalate esters. Here we investigated the effects of an alternative plasticizer, diisopropyl adipate (DIA). Activation of TRPA1 by DIA was demonstrated by calcium mobilization using Chinese hamster ovary cells expressing TRPA1 in vitro. The effect of DIA was inhibited by a TRPA1-specific antagonist, HC-030031. The presence of DIA or dibutyl phthalate (DBP; positive control) during skin sensitization of BALB/c mice to FITC augmented the CHS response, as revealed by the level of ear-swelling. The enhancing effect of DIA was inhibited by in vivo pretreatment with HC-030031. FITC-presenting CD11c dendritic cell (DC)-trafficking to draining lymph nodes was facilitated both by DIA and by DBP. DBP and DIA were similarly active in the enhancement of interferon-γ production by draining lymph nodes, but the effect on interleukin-4 production was weaker with DIA. Overall, DIA activated TRPA1 and enhanced FITC-induced CHS, as DBP did. The adjuvant effects of adipate esters may need to be considered because they are used as ingredients in cosmetics and drug formulations topically applied to the skin. Key words adipate ester; adjuvant; contact hypersensitivity; transient receptor potential Plasticizers are widely used for plastics such as polyvinyl chloride. As plasticizers, phthalate esters are widely used for consumer products such as synthetic leather, vinyl flooring, wall coverings, paints, adhesive agents and cosmetics. Many studies have been conducted for assessment of the risk of exposure to phthalate esters in the air and food, and their accumulation in the body. 1,2) Epidemiological studies revealed an association between phthalate esters and allergies in children.3,4) A case of contact hypersensitivity in association with topical contact with dibutyl phthalate (DBP), a short-chain phthalate ester, has also been reported. 5) Due to health concerns about phthalate esters, the use of other types of acid esters is being considered. Adipate esters are candidate plasticizers.Diisopropyl adipate (DIA) is used as an emollient ingredient for cosmetics to protect the human skin from dryness. 6)DIA is also used in tacrolimus ointments as a skin penetration enhancer.7) As to drug formulations, adipate esters are used as plasticizers for biodegradable flexible films and for enhancement of skin penetration of hydrophilic drugs.8,9) Regarding safety assessment, DIA has been concluded to be safe as a cosmetic ingredient. 10,11)We have been studying fluorescein isothiocyanate (FITC)-induced contact hypersensitivity (CHS) mouse models. In ...

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

“…We have repeatedly demonstrated that 50% DBP enhanced the production of not only IL-4 but also IFN-γ. 9,10) In the present experiments, we showed that 2% DBP also enhanced the production of IL-4 as well as IFN-γ (Fig. 4).…”

“…We have demonstrated that DBP facilitated DC trafficking from skin to draining lymph nodes. 8,10) Twenty-four hours after epicutaneous treatment with FITC in the presence of 2% DBP, DBM or DBF, the number of FITC + CD11c + cells in brachial lymph nodes was increased as compared with the FITC treatment with acetone alone (Fig. 3).…”

“…9,10) In brief, on days 0 and 7, BALB/c mice were sensitized on shaved forelimbs with 160 µL of an FITC solution under anesthesia. The solvents were acetone alone, or acetone containing 2% DBM, 2% DBF or 2% DBP.…”

“…9,10) In brief, cytokines in the supernatants were captured with immobilized purified anti-IL-4 or anti-IFN-γ antibodies. To detect the captured IL-4 or IFN-γ, biotin-conjugated anti-IL-4 or anti-IFN-γ was applied followed by HRP-avidin.…”

“…12) However, our recent studies revealed that enhanced production of IFN-γ rather than IL-4 was involved in the adjuvant effect of an alternative plasticizer, diisopropyl adipate (DIA). 10) To evaluate the roles of cytokines on FITC-sensitization in the presence of DBM or DBF, draining lymph nodes were collected 24h after the second sensitization with FITC. At this point, FITC-primed T cells as well as FITC-presenting DC (Fig.…”