Expression of discoidin domain receptor 1 and E-cadherin in epidermis affects melanocyte behavior in rhododendrol-induced leukoderma mouse model

Vitiligo is a depigmentation disease characterized by gradual loss of melanin and melanocytes from the epidermis. The mechanism of melanocyte loss is not yet known. In this report, we showed that the expression of discoidin domain receptor 1 and E-cadherin, known adhesion molecules, was variable or absent in the epidermis of rhododendrol-induced leukoderma (RDIL) mice during the depigmentation process. Our findings suggest that melanocyte damage by rhododendrol promotes reduction of adhesion molecules not only in melanocytes but also in keratinocytes, and this is associated with the detachment of melanocytes from the basal layer.     

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.     

Chronic actinic dermatitis with vitiligo-like depigmentation

This report describes two patients suffering from severe chronic actinic dermatitis. Unusual widespread vitiligo-like depigmentation occurred during the course of the disease. The progression of these lesions was triggered by the chronic actinic dermatitis. Loss of pigment and complete absence of tyrosinase positive melanocytes were found in depigmented skin of both cases. Immunohistological investigation of the inflammatory infiltrate in case 2 revealed a predominance of CD-8 positive cytotoxic/-suppressor lymphocytes. Analysing the adjacent pigmented epidermis of progressive depigmenting lesions a dense exocytosis of CD-8 T-cells was notable. This distribution suggests cytotoxic destruction of melanocytes as the cause for the vitiligo-like depigmentation.     

The in vivo melanocytotoxicity and depigmenting potency of N-2,4-acetoxyphenyl thioethyl acetamide in the skin and hair

Summary It has been shown previously that N-acetyl-4-S-cysteaminylphenol (N-Ac-4-S-CAP) is a tyrosinase Substrate and a potent depigmenting agent of dark skin and black hair. The present study evaluated the depigmenting potency of an acetyl derivative of N-Ac-4-S-CAP. N-2,4-acetoxyphenyl thioethyl acetamide (NAP-TKA) in the skin and hair. We tested for (i) in vitro metabolites in the skin after topical application. and (ii) in vivo depigmenting potency in the skin and hair. We found that NAPTEA was stable in water. but was converted to N-Ac-4-S-CAP after topical application to human skin. Therefore. although NAP-TEA was not a tyrosinase substrate. it could react with tyrosinase after being converted to N-Ac-4-S-CAP by 0-deacetylation in vivo. NAP-TEA produced marked depigmentation of dark skin (Yucatan pig) after daily topical application. When given by intraper-itoneal injection. it resulted in complete loss of hair colour (white) grown at the epilated site in adnlt C57 black mice after daily administration for l0 days, and incomplete loss of coat colour (silver grey) in newborn C57 black mice after a single administration, The depigmentation of the skin and hair was reversible, Splil-dopa preparalion and eieclron microsnipy indicated thal lliis depigmentation is primarily related to (i) a marked decrease in the number of functioning melanocytes and melanized melanosomes, (ii) a decrease in the number of melanosomes transferred to keratinocytes, and (iii) selective degeneration/inactivation of melanocytes. and deposition of melanin-like malerial in the Golgi cisternae. coated vesicles and melanosomes. where tyrosinase is reported to be located. We propose the NAP-TEA is converted in vivo to N-Ac-4-.S-CAP which. via interaction with tyrosinase. causes reversible depigmentation of the skin and hair.     

Chemical leukoderma: Fact or fancy

Leukoderma is reported to be caused by chemicals. This type of depigmentation and the chemicals that might cause it have not been clearly documented. We attempted to address this issue by reviewing the Western literature related to this topic. We propose that chemical leukoderma be defined as depigmentation that is caused by the cutaneous application of specific chemicals that destroy the epidermal melanocytes. We found data that suggest a group of agents are capable of killing epidermal melanocytes. Most chemicals in this group are the phenols with an aliphatic or aromatic side chain. There are no data to confirm that chemically pure hydroquinone itself can cause depigmentation. Therefore, we exclude pure hydroquinone as a cause of clinical leukoderma. We propose the hypothesis that some forms of vitiligo vulgaris are in fact chemical leukoderma caused by unidentified melanocytotoxic chemicals in the environment.     

Leukoderma syphiliticum: ultrastructural observations on melanocyte function

A case of genital leukoderma syphiliticum was analysed submicroscopically. No treponema pallidum organisms could be detected intra- or extracellularly in the epidermis or in the dermis. The melanocytes were only slightly reduced in number and had mostly normal outlines. The melanogenesis was impaired and small melanosomes with decreased deposition of melanin were mostly produced at the expense of normal melanin granules. A partial block in the melanin transfer mechanism seems to be in evidence. As no direct destructive action of spirochetes on the melanocytes is observed, an indirect effect is assumed, e.g. by a tyrosinase inhibitor.     

Melanoma-associated leukoderma

A case is presented of a man with a history of melanoma treated with sentinel lymphadenectomy and interferon therapy, who subsequently developed diffuse hypopigmented patches thought to be consistent with a diagnosis of melanoma-associated leukoderma. Clinically, melanoma-associated leukoderma is a diffuse macular hypomelanosis or depigmentation, which often develops at sites distant to the location of the primary melanoma. The leukoderma may be hypomelanotic and mottled or depigmented and milk-white. Spontaneous repigmentation may occur. A recent study has demonstrated that T cells involved in the destruction of neoplastic melanocytes are identical clones of those that accumulate in melanoma-associated leukoderma.     

Mannosylerythritol lipids inhibit melanogenesis via suppressing ERK‐CREB‐MiTF‐tyrosinase signalling in normal human melanocytes and a three‐dimensional human skin equivalent

Hyperpigmentation is caused by excessive production of melanin in melanocytes. Mannosylerythritol lipids (MELs) are glycolipid biosurfactants that are abundantly produced by yeasts and used commercially in cosmetics. However, the potential depigmenting efficacy of MELs has not been evaluated. In this study, the depigmentary effect of MELs was tested in primary normal human melanocytes (NHMs), α‐melanocyte‐stimulating hormone (MSH)‐stimulated B16 cells (murine melanoma cells) and a human skin equivalent (MelanoDerm) using photography, Fontana‐Masson (F&M) staining and two‐photon microscopy. Mannosylerythritol lipids significantly decreased the melanin contents in NHMs and α‐MSH‐stimulated B16 cells. Consistent with these findings, MELs treatment had a clear whitening effect in a human skin equivalent, brightening the tissue colour and reducing the melanin content. The molecular mechanism underlying the anti‐melanogenic effect of MELs treatment was examined by real‐time PCR and Western blotting. Mechanistically, MELs clearly suppressed the gene expression levels of representative melanogenic enzymes, including tyrosinase, Tyrp‐1 and Tyrp‐2, by inhibiting the ERK/CREB/MiTF signalling pathway in NHMs. This work demonstrates for the first time that MELs exert whitening effects on human melanocytes and skin equivalent. Thus, we suggest that MELs could be developed as a potent anti‐melanogenic agent for effective whitening, beyond their use as a biosurfactant in cosmetics.     

Langerhans' cells in hair follicles of the depigmenting C57Bl/Ler-vit.vit mouse. A model for human vitiligo

The C57Bl/Ler-vit.vit mouse grows a black pelage after birth. During successive hair molts, the fur loses its pigmentation. By 6 months of age, most of the fur of the animal is white. The epidermis of the ears and tail also loses its pigmentation. Histologic studies confirm that in the epidermis and hair follicles there is an absence of pigment cells identifiable by various histochemical or electron microscopic techniques. This mouse may be an excellent model in which to study the role of Langerhans' cells and the immune response in the pathogenesis of vitiligo, a study not easily done in humans. From results of prior studies, we postulated that if Langerhans' cells were involved in the destruction of melanocytes, they would be abnormal (either more or less numerous) in number during the active phase of depigmentation and normal in number after depigmentation was complete. To determine whether the Langerhans cell (Ia+/adenosine triphosphatase dendritic epidermal cell) might be involved in destruction of pigment cells, we quantified the number of Ia+ and adenosine triphosphatase dendritic cells in the hair follicles in skin from the ear, abdomen, back, and tail from male C57Bl/Ler-vit.vit mice while the fur and skin were depigmenting and after depigmentation was almost completed. We found that Langerhans' cells were normal in number during depigmentation and were most numerous after depigmentation. Previous studies indicate that Langerhans' cells in these mice are functionally defective and respond poorly to some contact allergens. From these morphologic and functional data, we conclude that Langerhans' cells probably are uninvolved in causing depigmentation in these mice. We also observed that the epithelium of hair follicles has a significantly higher (up to 1600/mm2) population density of Langerhans' cells than interfollicular skin.     

Role of IL‐17A receptor blocking in melanocyte survival: A strategic intervention against vitiligo

Cytokines regulate immune response and inflammation and play an important role in depigmentation process of an autoimmune disease, vitiligo. We sought to determine how inflammatory cytokines influence the progression of vitiligo, and based on that, we develop a logical therapeutic intervention using primary melanocyte culture. Melanocytes were cultured and exposed to IL‐17A, IL‐1β, IFN‐γ and TGF‐β for 4 days. Melanocytes proliferation, tyrosinase assay and melanin content were measured. Real‐Time PCR was used to analyse mRNA expression of genes specific for melanocytes growth and pigmentation. Anti‐IL‐17A receptor antibody was used to block IL‐17A receptors expressed on melanocytes. Protein expression of MITF and TYR was assessed by immunofluorescence and Western blotting. A gradual decline in the melanocyte population, melanin content and tyrosinase activity was observed after different cytokine treatment. The expression of MITF and its downstream genes after blocking with anti‐IL‐17RA, an increased melanin content, increased expression of TYR, MITF along with its downstream genes, and cell proliferation was observed.     

Effect of dicarboxylic acids on lentigo maligna.

Dicarboxylic acids from C8 to C14 are competitive inhibitors of tyrosinase in vitro, and here, the effect of a cream containing 15% azelaic acid (C9) on 3 cases of lentigo maligna is described. The lesions were treated for 90 days, with remarkable clinical and histological effect, maintained for up to 2 yr after cessation of treatment. Progress during treatment of one case was additionally monitored by electron microscopy, which revealed progressive elimination of abnormal melanocytes both basally and suprabasally, and their replacement by essentially normal cells engaged in normal melanogenesis. There was also progressive diminution in the general disorganization of the epidermis, and disappearance of lymphocyte response. It is concluded that dicarboxylic acids have a direct inhibitory and cytotoxic effect on abnormally active or structurally disordered melanocytes in lentigo maligna, but further investigations are required to establish their precise mode of action. Similar application of dicarboxylic acids to normal skin affects only a small proportion of melanocytes, suggesting that some phasic factor, or individual states of activity, may be concerned in their susceptibility.     

Induction of occupational leucoderma and vitiligo. Can butylated hydroxytoluene induce vitiligo similarly to p-tert-butylphenol?

Background

While vitiligo is usually idiopathic, some cases are caused by chemicals. If occupational exposure to p-tert-butylphenol (ptBP) leads to vitiligo, the legal requirements for occupational disease Nr.?1314 can be fulfilled in Germany. Chemicals of similar structure can induce local and more widespread symmetrical depigmentation with genital involvement, making the differential diagnosis more complicated. Occupationally caused depigmentation from other chemicals can also be treated according to §?9 sec.?2 of the occupational disease regulations.

Materials and Methods

Some substances can cause leukoderma only in animals; others in animals and humans; in some cases systemic vitiligo-like changes develop. The effects on human skin cannot always be predicted from the structural analogies of the involved chemicals.

Results

Based on a case of occupational exposure to butyl hydroxytoluene with possible induction of vitiligo, a careful updated literature analysis of substances inducing depigmentation is presented.

Conclusion

The literature contains discrepancies in the evidence for the ability of some substances??especially BHT??to cause vitiligo. A more exact analysis indicates that BHT does not cause vitiligo or leukoderma.     

Contact leukoderma due to 'Bindi' and footwear

3 cases of contact leukoderma due to 'Bindi' and footwear occurring together in the same patients are reported. In 2 patients depigmentation occurred at the patch test sites with 'Bindi', most probably due to the adhesive in it.     

Thiotepa-induced leukoderma.

Periorbital depigmentation developed in a black man approximately six months after the application of an ophthalmic solution containing thiotepa. The drug was used postoperatively to prevent revascularization after removal of a pterygium. By light and electron microscopy, melanocytes were apparently absent in the depigmented area. The list of medications and chemicals that can cause cutaneous depigmentation is growing. An appropriate history may be of considerable value in the evaluation of vitiligo-like conditions.     

The color of skin: white diseases of the skin,nails, and mucosa

White diseases are a heterogenous group characterized by hypopigmentation or depigmentation. Skin and eye color are determined by the number and size of melanosomes present. Melanin is produced by melanosomes in the melanocytes present within the epidermis of the skin, uvea, and retinal pigmented epithelium (RPE). Conditions altering the number of melanocytes or concentration of melanin result in a lack of pigmentation, appearing as “white diseases” ranging from the well-known albinism and vitiligo to more esoteric white hand syndrome and Degos disease.     

The cytotoxicity and apoptosis induced by 4-tertiary butylphenol in human melanocytes are independent of tyrosinase activity

It has been known for several decades that cutaneous depigmentation, i.e., contact/occupational vitiligo, can be caused by some phenolic derivatives that have a similar structure to tyrosine. Among these phenolic depigmenting agents, 4-tertiary butylphenol is the most potent. The cutaneous depigmentation induced by phenolic derivatives results from the loss of functional melanocytes. Tyrosinase is a melanocyte specific copper-containing enzyme that catalyzes the conversion of the amino acid tyrosine, through a complex series of intermediates, to melanin. In this study we tested the hypothesis that the cytotoxicity induced by 4-tertiary butylphenol is mediated by tyrosinase and occurs via an apoptotic process. Melanocyte cultures derived from African-American and Caucasian donors exhibiting a 3-fold difference in tyrosinase activity and 14-fold difference in melanin content demonstrate comparable concentration-dependent sensitivity to 4-tertiary butylphenol. In addition, cultures of dermal fibroblasts and epidermal keratinocytes exhibited similar and reduced sensitivity, respectively, to 4-tertiary butylphenol compared with autologous melanocytes. Two melanoma cell lines, one melanotic and one amelanotic lacking the expression of both tyrosinase protein and activity, when transfected with the tyrosinase cDNA, exhibited no alteration in its sensitivity to 4-tertiary butylphenol. These data suggest that 4-tertiary butylphenol cytotoxicity is not mediated via tyrosinase. Melanocytes treated with 4-tertiary butylphenol, however, did exhibit plasma membrane blebbing, DNA fragmentation, and phosphatidylserine relocalization indicating that 4-tertiary butylphenol induced melanocyte destruction occurs by an apoptotic process.     

Enhanced bleaching treatment: opportunities for immune‐assisted melanocyte suicide in vitiligo

Depigmentation in vitiligo occurs by progressive loss of melanocytes from the basal layer of the skin, and can be psychologically devastating to patients. T cell‐mediated autoimmunity explains the progressive nature of this disease. Rather than being confronted with periods of rapid depigmentation and bouts of repigmentation, patients with long‐standing, treatment‐resistant vitiligo can undergo depigmentation treatment. The objective is to remove residual pigmentation to achieve a cosmetically acceptable result – that of skin with a uniform appearance. In the United States, only the use of mono‐benzyl ether of hydroquinone (MBEH) is approved for this purpose. However, satisfactory results can take time to appear, and there is a risk of repigmentation. MBEH induces necrotic melanocyte death followed by a cytotoxic T‐cell response to remaining, distant melanocytes. As cytotoxic T‐cell responses are instrumental to depigmentation, we propose that combining MBEH with immune adjuvant therapies will accelerate immune‐mediated melanocyte destruction to achieve faster, more definitive depigmentation than with MBEH alone. As Toll‐like Receptor (TLR) agonists – imiquimod, CpG, and Heat Shock Protein 70 (HSP 70) – all support powerful Th1 responses, we propose that using MBEH in combination with these agents can achieve superior depigmentation results for vitiligo patients.     

中药治疗白癜风作用机制的研究进展

白癜风(vitiligo)是一种常见的后天性皮肤色素脱失性疾病。该病的病因和发病机制尚不清楚。目前大多数学者认为该病发生是具有遗传因素的个体在多种内外因素的作用下,出现免疫功能、神经精神及内分泌、代谢等多方面的功能紊乱,导致酪氨酸酶系统的抑制或黑素细胞的破坏,最终使皮肤色素脱失。目前发病原因主要有4个学说,即自身免疫学说、黑素细胞自毁学说、神经化学因子学说、遗传学说等。中药治疗白癜风在辨证论治的基础上取得了较好的疗效,但作用机制尚不明确。该文主要从自身免疫学说、黑素细胞自毁学说、神经化学因子学说综述中药治疗白癜风的客观依据。     

The haptenation theory of vitiligo and melanoma rejection: a close-up

The 'Haptenation theory' concerns the multicausal pathogenesis of vitiligo ending ultimately in the (partial) disappearance of melanocytes from the skin and/or hairs. The melanocyte specificity is attributed to the tyrosinase-catalysed production of haptogenic ortho-quinones that covalently bind to tyrosinase or other melanosomal proteins to generate neo-antigens. These latter, in turn, trigger an immunological cascade resulting in a melanocyte-specific delayed-type hypersensitivity reaction that eliminates melanocytes and produces the characteristic depigmentation. This causal chain of events is critically discussed with special reference to factors modifying the process and the possible influence of various biochemical changes, such as raised levels of catecholamines and epidermal hydrogen peroxide, which have been reported to be associated with the onset of vitiligo. This all adds up to the typical vitiligo reaction pattern or syndrome, which demands a treatment strategy involving most of the already known therapies. Similar pathogenetic mechanisms might be engaged in the enhancement of cellular immunity (vaccination) against melanoma.