In Vitro Methods for Predicting Chemical Leukoderma Caused by Quasi-Drug Cosmetics

Chemical- and Drug-Induced Allergic, Inflammatory, and Autoimmune Diseases Via Haptenation

Haptens are small molecules that only elicit an immune response when bound to proteins. Haptens initially bind to self-proteins and activate innate immune responses by complex mechanisms via inflammatory cytokines and damage-associated molecular patterns and the subsequent upregulation of costimulatory signals such as cluster of differentiation 86 (CD86) on dendritic cells. Subsequent interactions between CD86 and CD28 on T cells are critically important for properly activating naive T cells and inducing interleukin 2 production, leading to the establishment of adaptive immunity via effector and memory T cells. Accumulating evidence revealed the involvement of haptens in the development of various autoimmune-like diseases such as allergic, inflammatory, and autoimmune diseases including allergic contact dermatitis, atopy, asthma, food allergy, inflammatory bowel diseases, hemolytic anemia, liver injury, leukoderma, and even antitumor immunity. Therefore, the development of in vitro testing alternatives to evaluate in advance whether a substance might lead to the development of these diseases is highly desirable. This review summarizes and discusses recent advances in chemical- and drug-induced allergic, inflammatory, and autoimmune diseases via haptenation and the possible molecular underlying mechanisms, as well as in vitro testing alternatives to evaluate in advance whether a substance might cause the development of these diseases.

Upregulation of CD86 and IL-12 by rhododendrol in THP-1 cells cocultured with melanocytes through ROS and ATP

BACKGROUND

The tyrosinase inhibitor rhododendrol (RD), used as a skin whitening agent, reportedly has the potential to induce leukoderma.

OBJECTIVE

Although an immune response toward melanocytes was demonstrated to be involved in leukoderma, the molecular mechanism is not fully understood.

METHODS

We hypothesized that if RD is a pro-hapten and tyrosinase-oxidized RD metabolites are melanocyte-specific sensitizers, the sensitizing process could be reproduced by the human cell line activation test (h-CLAT) cocultured with melanocytes (h-CLATw/M) composed of human DC THP-1 cells and melanoma SK-MEL-37 cells. Cell surface expression, ROS generation and ATP release, mRNA expression, and the effects of several inhibitors were examined.

RESULTS

When RD was added to the h-CLATw/M, the expression of cell-surface CD86 and IL-12 mRNA was greatly enhanced in THP-1 cells compared with those in the h-CLAT. The rapid death of melanoma cells was induced, with ROS generation and ATP release subsequently being greatly enhanced, resulting in the cooperative upregulation of CD86 and IL-12. Consistent with those observations, an ROS inhibitor, ATP receptor P2X7 antagonist, or PERK inhibitor antagonized the upregulation. CD86 upregulation was similarly observed with another leukoderma-inducible tyrosinase inhibitor, raspberry ketone, but not with the leukoderma noninducible skin-whitening agents ascorbic acid and tranexamic acid.

CONCLUSION

RD is a pro-hapten sensitizer dependent on tyrosinase that induces ROS generation and ATP release from melanocytes for CD86 and IL-12 upregulation in DCs, possibly leading to the generation of tyrosinase-specific cytotoxic T lymphocytes. The coculture system h-CLATw/M may be useful for predicting the sensitizing potential to induce leukoderma.

Timeline of the Development of Skin-Lightening Active Ingredients in Japan

Japanese pharmaceutical cosmetics, often referred to as quasi-drugs, contain skin-lightening active ingredients formulated to prevent sun-induced pigment spots and freckles. Their mechanisms of action include suppressing melanin production in melanocytes and promoting epidermal growth to eliminate melanin more rapidly. For example, arbutin and rucinol are representative skin-lightening active ingredients that inhibit melanin production, and disodium adenosine monophosphate and dexpanthenol are skin-lightening active ingredients that inhibit melanin accumulation in the epidermis. In contrast, oral administration of vitamin C and tranexamic acid in pharmaceutical products can lighten freckles and melasma, and these products are more effective than quasi-drugs. On the basis of their clinical effectiveness, skin-lightening active ingredients can be divided into four categories according to their effectiveness and adverse effects. This review discusses academic research and development regarding skin-lightening ingredients in Japan.

Correction: Gu et al. In Vitro Methods for Predicting Chemical Leukoderma Caused by Quasi-Drug Cosmetics. Cosmetics 2017, 4, 31

The authors wish to make the following corrections to their paper [...]

Metabolism of Enantiomers of Rhododendrol in Human Skin Homogenate

We reported that raspberry ketone (RK) is produced from rhododendrol (RD) in excised mouse skin. We confirmed that RK is also produced from RD in human skin homogenates. We also observed more conversion of RD to RK when the oxidized form of nicotinamide adenine dinucleotide (NAD⁺), a coenzyme of alcohol dehydrogenase (ADH), was added to human skin homogenates. Chiral column analysis of the consumption of RD enantiomers in human skin homogenates also showed that more of the R enantiomers of RD remained than the S enantiomers of RD. This suggests that the S-enantiomer of RD is more easily oxidized in human skin. We confirmed that RD is partially metabolized to RK in human skin, thus suggesting that ADH in the skin may be the main cause of the appearance of this oxidation product.

Detection of Raspberry Ketone after Percutaneous Absorption of Rhododendrol-Containing Cosmetics and Its Mechanism of Formation

Here, we aimed to elucidate the mechanism of rhododendrol (RD)-induced leukoderma. We investigated the skin permeability of RD in an aqueous solution and in different cosmetic formulations (lotion and emulsion) in an in vitro skin permeation study. The samples were analyzed using high-performance liquid chromatography (HPLC), and an unknown substance appeared on the spectrum. For identification, we analyzed various possible substances, such as raspberry ketone (RK) and rhododendrol quinone, using HPLC and then compared the detected absorption spectra and further verified the matched components using liquid chromatography–mass spectrometry. The unknown substance was found to be RK. To clarify the mechanism of formation of RK, we conducted a 24-h skin permeation test on heat-treated skin. By quantifying the RK in the samples using HPLC, we observed that an enzyme in the skin seemed to be the cause of RK generation and that the components of the emulsion formulation could also be a cause. To investigate the enzyme, we reacted alcohol dehydrogenase with RD and observed that it was one of the converting enzymes. As RK has been reported to be a substance that causes leukoderma, the intraepidermal metabolism of RD to RK may be one of the mechanisms of susceptibility to leukoderma.

Inhibitory Effect and Mechanism of Scutellarein on Melanogenesis

Fairer skin is preferred in many Asian countries and there is a high demand for skin whitening and lightening products. However, in recent years, problems related to the safety of using whitening agents have emerged. This study demonstrates that plant-derived scutellarein effectively inhibits melanogenesis in B16 melanoma cells. However, baicalein, which is similar to scutellarein in its chemical structure, does not show any inhibitory effect on melanogenesis. Cellular tyrosinase activity is decreased by scutellarein in a dose-dependent manner. No cytotoxicity is observed at the effective concentration range. Additionally, both the protein and mRNA levels of tyrosinase are significantly decreased by scutellarein. Further, the risk of leukoderma development also is determined by evaluating the production of free hydroxyl radicals (˙OH); scutellarein treatment does not induce ˙OH production. Scutellarein shows no risk of causing leukoderma. Our results suggest that scutellarein or plant extracts containing high concentrations of scutellarein have the potential to inhibit melanin production and serve as cosmetic skin-lightening agents.