Contact sensitization to methylisothiazolinone in Finland--a multicentre study

Background. Antimicrobials constitute the second most common cause of contact allergy to cosmetics. Methylisothiazolinone (MI), previously always used together with methylchloroisothiazolinone (MCI), has recently been approved in the EU for use on its own in cosmetics and also various industrial products. MCI has been classified as an extreme–strong and MI as a strong–moderate sensitizer. Objectives. To study the frequency of positive patch test reactions to MI, and its relevance and relation to MCI/MI sensitivity, in Finland. Methods. Over a period of 3 years (2006–2008), MI 0.1% (1000 ppm) and 0.03% (300 ppm) were patch tested in 10 821 patients at eight Finnish dermatological clinics. During 2008, patients with positive reactions to MI were asked to take part in a repeated open application test (ROAT). Results. Of the patients tested, 1.4% and 0.6% showed positive patch test reactions to 0.1% and 0.03% MI, respectively. Sixty‐six per cent of those who were MI‐positive were also positive to 100 ppm MCI/MI. Thirty‐three agreed to undergo the use test, and 10 of these gave positive results (30%). Conclusions. Our data show that MI used alone also potentially induces contact allergy. Careful monitoring is needed to determine whether or not this antimicrobial is safe to use in cosmetics.     

In vitro and in vivo evidence of tyrosinase inhibitory activity of a synthesized (Z)‐5‐(3‐hydroxy‐4‐methoxybenzylidene)‐2‐thioxothiazolidin‐4‐one (5‐HMT)

Tyrosinase is a key enzyme that catalyses the initial rate‐limiting steps of melanin synthesis. Due to its critical role in melanogenesis, various attempts were made to find potent tyrosinase inhibitors although many were not safe and effective in vivo. We evaluated tyrosinase inhibitory activity of six compounds. Among them, (Z)‐5‐(3‐hydroxy‐4‐methoxybenzylidene)‐2‐thioxothiazolidin‐4‐one (5‐HMT) had the greatest inhibitory effect and potency as the IC₅₀ value of 5‐HMT was lower than that of kojic acid, widely‐known tyrosinase inhibitor. Based on in silico docking simulation, 5‐HMT had a greater binding affinity than kojic acid with a different binding conformation in the tyrosinase catalytic site. Furthermore, its skin depigmentation effect was confirmed in vivo as 5‐HMT topical treatment significantly reduced UVB‐induced melanogenesis in HRM2 hairless mice. In conclusion, our study demonstrated that 5‐HMT has a greater binding affinity and inhibitory effect on tyrosinase and may be a potential candidate for a therapeutic agent for preventing melanogenesis.     

4‐(4‐Hydroxyphenyl)‐2‐butanol (rhododendrol)‐induced melanocyte cytotoxicity is enhanced by UVB exposure through generation of oxidative stress

4‐(4‐Hydroxyphenyl)‐2‐butanol (rhododendrol, RD), a skin‐whitening agent, was reported to cause skin depigmentation in some users, which is attributed to its cytotoxicity to melanocyte. It was reported that cytotoxicity to melanocyte is possibly mediated by oxidative stress in a tyrosinase activity‐dependent manner. We examined the effect of UV radiation (UVR) on RD‐induced melanocyte cytotoxicity as an additional aggravating factor. UVR enhanced RD‐induced cytotoxicity in normal human epidermal melanocytes (NHEMs) via the induction of endoplasmic reticulum (ER) stress. Increased generation of intracellular reactive oxygen species (ROS) was detected. Pretreatment with N‐acetyl cysteine (NAC), antioxidant and precursor of glutathione significantly attenuated ER stress‐induced cytotoxicity in NHEMs treated with RD and UVR. Increase in cysteinyl‐RD‐catechol and RD‐pheomelanin in NHEMs treated with RD and UVR suggested that, after UVR excitation, RD or RD metabolites are potent ROS‐generating substances and that the tendency to produce RD‐pheomelanin during melanogenesis amplifies ROS generation in melanocytes. Our results help to elucidate the development mechanisms of RD‐induced leukoderma and provide information for innovation of safe skin‐whitening compounds.     

5‐Bromo‐2′‐deoxyuridine induced effluvium via p53‐mediated CD326‐positive keratinocyte apoptosis in C57BL/6 mice

Anagen effluvium develops because of disturbances in the hair follicle cycle, leading to acute and severe hair loss in humans. The objective of this study was to establish a mouse model of anagen effluvium by 5‐bromo‐2′‐deoxyuridine (BrdU) treatment, and evaluate the pathological changes and underlying mechanisms. We treated 9–10‐day‐old pups and 3–7‐week‐old C57BL/6 mice with BrdU. After successfully inducing hair loss in the neonatal pups, microscopic, immunohistochemical and flow cytometry analyses were conducted. BrdU induced early onset alopecia in neonates and caused epidermal thickening and hair shaft breakage. BrdU appeared to incorporate the CD326‐positive keratinocyte layer and induced p53‐related apoptosis. Keratinocyte apoptosis caused immune cell infiltration in the dermal region; M2 macrophages and neutrophils were dominant. The BrdU‐induced hair loss was dose‐dependent, and alopecia was visible at a dose range of 25–200 μg/g bodyweight. The BrdU‐induced anagen effluvium mouse model is novel and easily established by administrating four simple BrdU injections to pups; these mice showed synchronized onset of alopecia symptoms with little individual variation. Moreover, this model showed an alopecia phenotype similar to that of human anagen effluvium with acute, severe and widespread hair loss.     

Active sensitization and contact allergy to methyl 2‐octynoate

Background: Methyl 2‐octynoate is a synthetic fragrance which was first described to have sensitizing properties in 1935. It is one of the 26 fragrances to be labelled on the ingredient list according to current European cosmetics regulation. Objectives: To report the experience with patch testing with methyl 2‐octynoate 1% and 2% in pet. Methods: 230 eczema patients were consecutively patch tested with 1% methyl 2‐octynoate at department of Dermato‐allergology Gentofte Hospital, Denmark and 120 eczema patients were consecutively patch tested with 2% M2O in Finn Chambers® at the Départment de Dermatologie, CHU Saint Jacques, France. Results: Three cases of active sensitization were observed. 2 (0.87%) of the 230 Danish subjects tested with 1% in pet. and of the 120 French subjects patch tested with 2% in pet. 1 (0.83%). There was no statistical difference in active sensitization between the two groups (P = 0.72). Allergic contact dermatitis was observed in two patients (1.67%) in the French group and none in the Danish group. Conclusion: Contact allergy to methyl 2‐octynoate was frequently seen when patch testing with 2% in pet. However, active sensitization was also observed, when patch testing with concentrations of 1% and 2% methyl 2‐octynoate. The patch test concentration should be below 1% in pet., but a safe concentration remains to be defined.