A role for tyrosinase-related protein 1 in 4-tert-butylphenol-induced toxicity in melanocytes: Implications for vitiligo

Animal models unraveling the complexity of vitiligo pathogenesis

Vitiligo is a chronic skin condition marked by the gradual loss of pigmentation, leading to the emergence of white or depigmented patches on the skin. The exact cause of vitiligo remains not entirely understood, although it is thought to involve a blend of genetic, autoimmune, and environmental factors. While there is currently no definitive cure for vitiligo, diverse treatments exist that may assist in managing the condition and fostering repigmentation in specific instances. Animal models play a pivotal role in comprehending the intricate mechanisms that underlie vitiligo, providing valuable insights into the progression and onset of the disease, as well as potential therapeutic interventions. Although induced experimental models lack the nuanced characteristics observed in natural experimental models, relying solely on a single animal model might not fully capture the intricate pathogenesis of vitiligo. Different animal models simulate specific aspects of human vitiligo pathogenesis to varying degrees. This review extensively explores the array of animal models utilized in vitiligo research, shedding light on their respective advantages, disadvantages, and applications.

Leucoderma in Buffaloes (Bubalus bubalis) in the Amazon Biome

Leucoderma is a condition that affects the skin and hair of animals, causing depigmentation and acromotrichia. In buffaloes, this condition results in significant economic losses for the production chain due to its impact on the leather trade. This study aimed to investigate the epidemiological and clinicopathological aspects of leucoderma in buffaloes in the Amazon biome and describe the prophylactic treatment to control the disease. The study included 40 buffaloes, 16 males and 24 females, aged between 1 and 10 years, and were of the Murrah, Jafarabadi, Mediterranean, and Murrah × Mediterranean crossbreed breeds. The animals were raised without mineral supplementation. The clinical signs observed in the animals included acromotrichia and depigmentation, with varying degrees and distribution of skin lesions. Histological examination of the epidermis showed interrupted melanin production, mild dermal fibrosis, mild perivascular mononuclear inflammatory infiltrate, and pigmentary incontinence. None of the animals had the genotype for albinism. After 120 days of mineral supplementation based on the use of copper sulfate, the clinical signs of leucoderma regressed. There was no predisposition by breed, sex, or age for the occurrence of the disease. The regression of skin lesions after proper mineral supplementation suggests that copper deficiency may be considered an important factor for the occurrence of leucoderma in buffaloes in the Amazon biome.

Zebrafish as a new model for rhododendrol-induced leukoderma

Idiopathic leukoderma is a skin disorder characterized by patchy loss of skin pigmentation due to melanocyte dysfunction or deficiency. Rhododendrol (RD) was approved as a cosmetic ingredient in Japan in 2008. However, it was shown to induce leukoderma in approximately 20,000 customers. The prediction of cytotoxicity, especially to melanocytes in vivo, is required to avoid such adverse effects. Since the use of higher vertebrates is prohibited for medicinal and toxicological assays, we used zebrafish, whose melanocytes were regulated by mechanisms similar to mammals. Zebrafish larvae were treated with RD in breeding water for 3 days, which caused body lightening accompanied by a decrease in the number of melanophores. Interestingly, black particles were found at the bottom of culture dishes, suggesting that the melanophores peeled off from the body. In addition, RT-PCR analysis suggested that the mRNA levels of melanophore-specific genes were significantly low. An increase in the production of reactive oxygen species was found in larvae treated with RD. The treatments of the fish with other phenol compounds, which have been reported to cause leukoderma, also induced depigmentation and melanophore loss. These results suggest that zebrafish larvae could be used for the evaluation of leukoderma caused by chemicals, including RD.

Chemical Vitiligo: A Subset of Vitiligo

Chemical leucoderma, an under-diagnosed common condition often mimicking idiopathic vitiligo, represents an acquired depigmentation induced by repeated exposure to specific chemical compounds in subjects with genetic susceptibility to vitiligo. This has been increasing rapidly in incidence in recent decades in developing countries like India. The term 'chemical vitiligo' was first coined by us to indicate the possible relationship between chemical leucoderma and vitiligo, which has been supported recently by other authors to designate the term 'chemical-induced vitiligo'. The largest case series showed that household chemical exposure was the major etiological factor. Causative chemicals are mostly phenolic and catecholic derivatives. Vitiligo pathogenesis is induced by genetic and environmental factors like many other autoimmune diseases. Innate immunity acts as a bridge between cellular stress and adaptive immunity. Multiple patches are commonly seen; children below 12 years are also affected in good numbers. The most common presence of confetti macules indicates these as characteristic, although not pathognomonic, of chemical leucoderma. Chemical leucoderma has been broadened into 'chemical leucoderma syndrome' with proper staging. The clinical criteria for diagnosis of chemical leucoderma have been specifically outlined. Same pathomechanism of chemical leucoderma might elucidate trigger factors and reasons for progression and chronicity in idiopathic vitiligo. Depigmentation in chemical vitiligo spreads to distant sites, in the same way as generalized idiopathic vitiligo. The study showed that chemical triggering factors played a very significant role in the induction and progression of vitiligo. Thus it should be rational to consider chemical vitiligo not as a separate entity but as a major subset of vitiligo spectrum.

Mechanism of action of 4-substituted phenols to induce vitiligo and antimelanoma immunity

Monobenzone is a 4-substituted phenol that can induce vitiligo and antimelanoma immunity. We investigated the influence of the chemical structure on the biological activity of a series of structurally related 4-substituted phenols. All phenols inhibited cellular melanin synthesis, and eight of ten phenols inhibited tyrosinase activity, using the MBTH assay. These phenols also induced glutathione (GSH) depletion, indicative of quinone formation and protein thiol binding, which can increase the immunogenicity of melanosomal proteins. Specific T-cell activation was found upon stimulation with phenol-exposed pigmented cells, which also reacted with unexposed cells. In contrast, 4-tertbutylphenol induced immune activation was not restricted to pigment cells, analogous to contact sensitization. We conclude that 4-substituted phenols can induce specific T-cell responses against melanocytes and melanoma cells, also acting at distant, unexposed body sites, and may confer a risk of chemical vitiligo. Conversely, these phenols may be applicable to induce specific antimelanoma immunity.

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.

The nuclear factor (erythroid-derived 2)-like 2 (NRF2) antioxidant response promotes melanocyte viability and reduces toxicity of the vitiligo-inducing phenol monobenzone

Vitiligo, characterised by progressive melanocyte death, can be initiated by exposure to vitiligo-inducing phenols (VIPs). VIPs generate oxidative stress in melanocytes and activate the master antioxidant regulator NRF2. While NRF2-regulated antioxidants are reported to protect melanocytes from oxidative stress, the role of NRF2 in the melanocyte response to monobenzone, a clinically relevant VIP, has not been characterised. We hypothesised that activation of NRF2 may protect melanocytes from monobenzone-induced toxicity. We observed that knockdown of NRF2 or NRF2-regulated antioxidants NQO1 and PRDX6 reduced melanocyte viability, but not viability of keratinocytes and fibroblasts, suggesting that melanocytes were preferentially dependent upon NRF2 activity for growth compared to other cutaneous cells. Furthermore, melanocytes activated the NRF2 response following monobenzone exposure and constitutive NRF2 activation reduced monobenzone toxicity, supporting NRF2's role in the melanocyte stress response. In contrast, melanocytes from individuals with vitiligo (vitiligo melanocytes) did not activate the NRF2 response as efficiently. Dimethyl fumarate-mediated NRF2 activation protected normal and vitiligo melanocytes against monobenzone-induced toxicity. Given the contribution of oxidant-antioxidant imbalance in vitiligo, modulation of this pathway may be of therapeutic interest.

Reduced Nrf2 activation in PI3K phosphorylation-impaired vitiliginous keratinocytes increases susceptibility to ROS-generating chemical-induced apoptosis

Keratinocytes in affected epidermis of vitiligo patients are known to have impaired activation of the PI3K/AKT pathway. Based on critical roles of keratinocytes and oxidative stress in vitiligo development, this study examined whether keratinocytes with impaired PI3K activation were more vulnerable to apoptosis caused by oxidative stress from phenolic compounds, p-tert-butylphenol (4-TBP) and hydroquinone (HQ). Cell viability assay, FACS analysis, ELISA for TNF-α or IL-1a, ROS assay, Western blot analysis for Nrf2 expression, and confocal microscopy with anti-Nrf2 and phospho-PI3K antibodies were done on primary cultured normal human keratinocytes with or without PI3K knockdown in the presence or absence of chemical treatment or antioxidant. Immunofluorescence staining using anti-Nrf2, phospho-PI3K, TNF-ɑ, and IL-1ɑ antibodies, ROS assay using dihydroethidium, and TUNEL assay were performed on sets of depigmented and normally pigmented skin from vitiligo patients. Results showed that 4-TBP or HQ treatment increased apoptosis and the expression levels of TNF-ɑ, IL-1ɑ, and ROS in PI3K-knockdown keratinocytes which reduced Nrf2 nuclear translocation compared to control keratinocytes. These changes were significantly recovered by an antioxidant treatment. Depigmented epidermis of vitiligo patients also showed lower levels of Nrf2 and phospho-PI3K but higher levels of ROS, TNF-ɑ, IL-1ɑ, and ROS with more TUNEL-positive cells. Therefore, impaired PI3K activation in keratinocytes in depigmented epidermis of vitiligo patients are vulnerable to apoptosis caused by ROS-generating chemicals due to reduced Nrf2 activation.

Vitiligo blood transcriptomics provides new insights into disease mechanisms and identifies potential novel therapeutic targets

BACKGROUND

Significant gaps remain regarding the pathomechanisms underlying the autoimmune response in vitiligo (VL), where the loss of self-tolerance leads to the targeted killing of melanocytes. Specifically, there is incomplete information regarding alterations in the systemic environment that are relevant to the disease state.

METHODS

We undertook a genome-wide profiling approach to examine gene expression in the peripheral blood of VL patients and healthy controls in the context of our previously published VL-skin gene expression profile. We used several in silico bioinformatics-based analyses to provide new insights into disease mechanisms and suggest novel targets for future therapy.

RESULTS

Unsupervised clustering methods of the VL-blood dataset demonstrate a "disease-state"-specific set of co-expressed genes. Ontology enrichment analysis of 99 differentially expressed genes (DEGs) uncovers a down-regulated immune/inflammatory response, B-Cell antigen receptor (BCR) pathways, apoptosis and catabolic processes in VL-blood. There is evidence for both type I and II interferon (IFN) playing a role in VL pathogenesis. We used interactome analysis to identify several key blood associated transcriptional factors (TFs) from within (STAT1, STAT6 and NF-kB), as well as "hidden" (CREB1, MYC, IRF4, IRF1, and TP53) from the dataset that potentially affect disease pathogenesis. The TFs overlap with our reported lesional-skin transcriptional circuitry, underscoring their potential importance to the disease. We also identify a shared VL-blood and -skin transcriptional "hot spot" that maps to chromosome 6, and includes three VL-blood dysregulated genes (PSMB8, PSMB9 and TAP1) described as potential VL-associated genetic susceptibility loci. Finally, we provide bioinformatics-based support for prioritizing dysregulated genes in VL-blood or skin as potential therapeutic targets.

CONCLUSIONS

We examined the VL-blood transcriptome in context with our (previously published) VL-skin transcriptional profile to address a major gap in knowledge regarding the systemic changes underlying skin-specific manifestation of vitiligo. Several transcriptional "hot spots" observed in both environments offer prioritized targets for identifying disease risk genes. Finally, within the transcriptional framework of VL, we identify five novel molecules (STAT1, PRKCD, PTPN6, MYC and FGFR2) that lend themselves to being targeted by drugs for future potential VL-therapy.

Misbalanced CXCL12 and CCL5 Chemotactic Signals in Vitiligo Onset and Progression

Generalized nonsegmental vitiligo is often associated with the activation of melanocyte-specific autoimmunity. Because chemokines play an important role in the maintenance of immune responses, we examined chemotactic signatures in cultured vitiligo melanocytes and skin samples of early (≤2 months) and advanced (≥6 months) vitiligo. Analysis showed that melanocytes in early lesions have altered expression of several chemotaxis-associated molecules, including elevated secretion of CXCL12 and CCL5. Higher levels of these chemokines coincided with prominent infiltration of the skin with antigen presenting cells (APCs) and T cells. Most of the intralesional APCs expressed the CD86 maturation marker and co-localized with T cells, particularly in early vitiligo lesions. These observations were confirmed by in vivo animal studies showing preferential recruitment of APCs and T cells to CXCL12- and CCL5-expressing transplanted melanocytes, immunotargeting of the chemokine-positive cells, continuous loss of the pigment-producing cells from the epidermis, and development of vitiligo-like lesions. Taken together, our studies show that melanocyte-derived CXCL12 and CCL5 support APC and T-cell recruitment, antigen acquisition, and T-cell activation in early vitiligo and reinforce the role of melanocyte-derived CXCL12 and CCL5 in activation of melanocyte-specific immunity and suggest inhibition of these chemotactic axes as a strategy for vitiligo stabilization.

Spatial mapping of metals in tissue-sections using combination of mass-spectrometry and histology through image registration

We describe a new procedure for the parallel mapping of selected metals in histologically characterized tissue samples. Mapping is achieved via image registration of digital data obtained from two neighbouring cryosections by scanning the first as a histological sample and subjecting the second to laser ablation inductively coupled plasma mass spectrometry. This computer supported procedure enables determination of the distribution and content of metals of interest directly in the chosen histological zones and represents a substantial improvement over the standard approach, which determines these values in tissue homogenates or whole tissue sections. The potential of the described procedure was demonstrated in a pilot study that analysed Zn and Cu levels in successive development stages of pig melanoma tissue using MeLiM (Melanoma-bearing-Libechov-Minipig) model. We anticipate that the procedure could be useful for a complex understanding of the role that the spatial distribution of metals plays within tissues affected by pathological states including cancer.

Different effects of five depigmentary compounds, rhododendrol, raspberry ketone, monobenzone, rucinol and AP736 on melanogenesis and viability of human epidermal melanocytes

Numerous medications are used to treat hyperpigmentation. However, several reports have indicated that repeated application of some agents, such as rhododendrol (RD), raspberry ketone (RK) and monobenzone (MB), can be toxic to melanocytes. Although these agents had severe side effects in human trials, no current in vitro methods can predict the safety of such drugs. This study assessed the in vitro effects of five depigmentary compounds including leukoderma-inducing agents. In particular, we determined the effects of different concentrations and exposure times of different depigmentary agents on cell viability and melanogenesis in the presence and absence of ultraviolet B (UVB) radiation. Concentrations of RD, RK and MB that inhibit melanogenesis are similar to concentrations that are cytotoxic; however, concentrations of rucinol (RC) and AP736 that inhibit melanogenesis are much lower than concentrations that are cytotoxic. Furthermore, the concentrations that cause toxic effects depend on exposure duration, and prolonged exposure to RD, RK and MB had more cytotoxic effects than prolonged exposure to RC and AP736. The cytotoxic effects of RD and RK appear to be mediated by apoptosis due to increased expression of caspase-3 and caspase-8; UVB radiation increased the cytotoxicity of these agents and also increased caspase activity. Our results indicate that different leukoderma-inducing compounds have different effects on the viability of normal epidermal melanocytes and suggest that the in vitro assay used here can be used to predict whether an investigational compound that induces leukoderma may lead to adverse effects in human trials.

miR-196a-2 rs11614913 polymorphism is associated with vitiligo by affecting heterodimeric molecular complexes of Tyr and Tyrp1

Tyrosinase and tyrosinase-related protein 1 (Tyr-Tyrp1) complex plays a critical role in the synthesis of melanin intermediates, which involves the production of reactive oxygen species (ROS) and contributes to the development of vitiligo. Based on our previous observation that rs11614913 single nucleotide polymorphism (SNP) in miR-196a-2 could affect the risk of vitiligo by influencing Tyrp1, we hypothesized that the same SNP could also regulate the level of Tyr in vitiligo. The aim of this study was to evaluate the potential association between rs11614913 SNP in miR-196a-2 and serum Tyr level in vitiligo and the regulatory role of miR-196a-2 in the expression of Tyr in melanocytes. The serum Tyr level was detected in 116 patients with vitiligo and 116 controls by ELISA plate assay. The expression level of Tyrp1 and Tyr in PIG1(normal melanocyte cell lines) cells was analyzed by western blotting. The ROS level and apoptosis rate in PIG1 cells transfected with si-Tyr or control siRNA were tested by flow cytometry. The results show that the individuals with TT+TC genotypes in miR-196a-2 and higher Tyr level in serum had an increased risk of vitiligo compared with those who had the CC genotype and lower Tyr level (P < 0.001). Furthermore, the rs11614913 C allele in miR-196a-2 enhanced its inhibitory regulation on the expression of Tyr, the down-regulation of which in melanocytes successfully reduced the intracellular ROS levels and the apoptosis rate. In conclusion, our findings suggest that miR-196a-2 polymorphisms can regulate the Tyr levels, which influences the susceptibility of vitiligo.

The mechanism of melanocytes-specific cytotoxicity induced by phenol compounds having a prooxidant effect, relating to the appearance of leukoderma

Specific phenol compounds including rhododendrol (RD), a skin-brightening ingredient in cosmetics, are reported to induce leukoderma, inducing a social problem, and the elucidation of mechanism of leukoderma is strongly demanded. This study investigated the relationship among the cytotoxicities of six phenol compounds on B16F10 melanoma cells and HaCaT keratinocytes and generated reactive oxygen species (ROS). As a result, the cytotoxicity of RD on B16F10 cells was higher than that on HaCaT cells, and RD significantly increased intracellular ROS and hydrogen peroxide (H2O2) levels in B16F10 cells. Furthermore, although raspberry ketone (RK), RD derivative, also increased intracellular ROS in B16F10 cells, increase in ROS was suppressed by disodium dihydrogen ethylenediaminetetraacetate dehydrate (EDTA). The amounts of increased ROS with RK in HaCaT cells without melanocyte were further increased by tyrosinase. Therefore, tyrosinase, a metalloprotein having copper, was speculated to be one of causative agents allowing phenol compounds to work as a prooxidant. Hydroxyl radical was generated by adding a mixture of tyrosinase and H2O2 to RD, and the amount of the radical was further increased by UVB, indicating that RD cytotoxicity was caused by intracellularly increased ROS, which possibly related to phenol induced prooxidants.

Triterpene glycosides with stimulatory activity on melanogenesis from the aerial parts of Weigela subsessilis

Three new triterpene glycosides (Lonicerosides K, L and M) and 11 known compounds were isolated from the aerial parts of Weigela subsessilis. Among the known isolated compounds, loniceroside A, sweroside, kaempferol-3-O-glucopyranoside 6″-(3-hydroxy-3-methylglutarate), kaempferol-3-O-acetylglucoside and grandifloroside were reported for the first time in a Weigela genus plant. Their chemical structures were identified using extensive spectroscopic analysis including two-dimensional (2D)-NMR experiments, HR-ESI-QTOF-MS and comparison with reported data. Among these compounds, lonicerosides A and L had potent melanogenesis stimulatory activity in murine B16F0 melanoma cells. The structural relationship of active compounds was discussed.

The transcriptional response to oxidative stress during vertebrate development: effects of tert-butylhydroquinone and 2,3,7,8-tetrachlorodibenzo-p-dioxin

Oxidative stress is an important mechanism of chemical toxicity, contributing to teratogenesis and to cardiovascular and neurodegenerative diseases. Developing animals may be especially sensitive to chemicals causing oxidative stress. The developmental expression and inducibility of anti-oxidant defenses through activation of NF-E2-related factor 2 (NRF2) affect susceptibility to oxidants, but the embryonic response to oxidants is not well understood. To assess the response to chemically mediated oxidative stress and how it may vary during development, zebrafish embryos, eleutheroembryos, or larvae at 1, 2, 3, 4, 5, and 6 days post fertilization (dpf) were exposed to DMSO (0.1%), tert-butylhydroquinone (tBHQ; 10 µM) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 2 nM) for 6 hr. Transcript abundance was assessed by real-time qRT-PCR and microarray. qRT-PCR showed strong (4- to 5-fold) induction of gstp1 by tBHQ as early as 1 dpf. tBHQ also induced gclc (2 dpf), but not sod1, nqo1, or cyp1a. TCDD induced cyp1a but none of the other genes. Microarray analysis showed that 1477 probes were significantly different among the DMSO-, tBHQ-, and TCDD-treated eleutheroembryos at 4 dpf. There was substantial overlap between genes induced in developing zebrafish and a set of marker genes induced by oxidative stress in mammals. Genes induced by tBHQ in 4-dpf zebrafish included those involved in glutathione synthesis and utilization, signal transduction, and DNA damage/stress response. The strong induction of hsp70 determined by microarray was confirmed by qRT-PCR and by use of transgenic zebrafish expressing enhanced green fluorescent protein (EGFP) under control of the hsp70 promoter. Genes strongly down-regulated by tBHQ included mitfa, providing a molecular explanation for the loss of pigmentation in tBHQ-exposed embryos. These data show that zebrafish embryos are responsive to oxidative stress as early as 1 dpf, that responsiveness varies with development in a gene-specific manner, and that the oxidative stress response is substantially conserved in vertebrate animals.

Depigmentation caused by application of the active brightening material, rhododendrol, is related to tyrosinase activity at a certain threshold

BACKGROUND

Tyrosinase, the rate-limiting enzyme required for melanin production, has been targeted to develop active brightening/lightening materials for skin products. Unexpected depigmentation of the skin characterized with the diverse symptoms was reported in some subjects who used a tyrosinase-competitive inhibiting quasi-drug, rhododendrol.

OBJECTIVE

To investigate the mechanism underlying the depigmentation caused by rhododendrol-containing cosmetics, this study was performed.

METHODS

The mechanism above was examined using more than dozen of melanocytes derived from donors of different ethnic backgrounds. The RNAi technology was utilized to confirm the effect of tyrosinase to induce the cytotoxicity of rhododendrol and liquid chromatography-tandem mass spectrometry was introduced to detect rhododendrol and its metabolites in the presence of tyrosinase.

RESULTS

Melanocyte damage was related to tyrosinase activity at a certain threshold. Treatment with a tyrosinase-specific siRNA was shown to dramatically rescue the rhododendrol-induced melanocyte impairment. Hydroxyl-rhododendrol was detected only in melanocytes with higher tyrosinase activity. When an equivalent amount of hydroxyl-rhododendrol was administered, cell viability was almost equally suppressed even in melanocytes with lower tyrosinase activity.

CONCLUSION

The generation of a tyrosinase-catalyzed hydroxyl-metabolite is one of the causes for the diminishment of the melanocyte viability by rhododendrol.

Rhododendrol, a depigmentation-inducing phenolic compound, exerts melanocyte cytotoxicity via a tyrosinase-dependent mechanism

Rhododendrol, an inhibitor of melanin synthesis developed for lightening/whitening cosmetics, was recently reported to induce a depigmentary disorder principally at the sites of repeated chemical contact. Rhododendrol competitively inhibited mushroom tyrosinase and served as a good substrate, while it also showed cytotoxicity against cultured human melanocytes at high concentrations sufficient for inhibiting tyrosinase. The cytotoxicity was abolished by phenylthiourea, a chelator of the copper ions at the active site, and by specific knockdown of tyrosinase with siRNA. Hence, the cytotoxicity appeared to be triggered by the enzymatic conversion of rhododendrol to active product(s). No reactive oxygen species were detected in the treated melanocytes, but up-regulation of the CCAAT-enhancer-binding protein homologous protein gene responsible for apoptosis and/or autophagy and caspase-3 activation were found to be tyrosinase dependent. These results suggest that a tyrosinase-dependent accumulation of ER stress and/or activation of the apoptotic pathway may contribute to the melanocyte cytotoxicity.

Preferential secretion of inducible HSP70 by vitiligo melanocytes under stress

Inducible HSP70 (HSP70i) chaperones peptides from stressed cells, protecting them from apoptosis. Upon extracellular release, HSP70i serves an adjuvant function, enhancing immune responses to bound peptides. We questioned whether HSP70i differentially protects control and vitiligo melanocytes from stress and subsequent immune responses. We compared expression of HSP70i in skin samples, evaluated the viability of primary vitiligo and control melanocytes exposed to bleaching phenols, and measured secreted HSP70i. We determined whether HSP70i traffics to melanosomes to contact immunogenic proteins by cell fractionation, western blotting, electron microscopy, and confocal microscopy. Viability of vitiligo and control melanocytes was equally affected under stress. However, vitiligo melanocytes secreted increased amounts of HSP70i in response to MBEH, corroborating with aberrant HSP70i expression in patient skin. Intracellular HSP70i colocalized with melanosomes, and more so in response to MBEH in vitiligo melanocytes. Thus, whereas either agent is cytotoxic to melanocytes, MBEH preferentially induces immune responses to melanocytes.

Provoking factors, including chemicals, in Dutch patients with vitiligo

BACKGROUND

In vitiligo, many provoking factors have been described, but epidemiological data, especially on the role of contact with chemicals, are scarce.

OBJECTIVE

To obtain an insight into the patient-reported factors provoking vitiligo, including contact with chemicals.

METHODS

A retrospective cohort study was conducted on all 1264 patients with vitiligo who visited the Netherlands Institute for Pigment disorders from January 2003 to December 2007. Patients for whom an exogenous provoking factor was recorded were sent a questionnaire. Subsequently, patients who mentioned a chemical provoking factor were contacted to elucidate the alleged causal relationship between exposure to the chemical and the onset of vitiligo.

RESULTS

A total of 300 out of the 1264 patients indicated that provoking factors had played a role in their disease. Two hundred and forty-six patients were sent a questionnaire, which was returned by 177 (response rate of 72%). Emotional stress was indicated as a provoking factor in 98 patients (55.4%), 51 patients (28.8%) recorded sunburn, 34 patients (19.2%) recorded mechanical factors and 20 patients (11.3%) other factors. Of 29 patients (16.4%) who indicated a chemical factor, a presumed causal relationship could be corroborated in four. The chemicals involved were para-tertiary butylphenol (n = 2), captan (n = 1) and diphencyprone (n = 1).

CONCLUSION

The majority of the patients with vitiligo from this study did not mention provoking factors, but the ones who did point to emotional stress in more than half of the cases. Of the 29 patients who assigned chemical provoking factors, solvents were mainly indicated. However, a presumed relationship with the chemical could be corroborated in only four patients.

Basic evidence for epidermal H2O2/ONOO(-)-mediated oxidation/nitration in segmental vitiligo is supported by repigmentation of skin and eyelashes after reduction of epidermal H2O2 with topical NB-UVB-activated pseudocatalase PC-KUS

Nonsegmental vitiligo (NSV) is characterized by loss of inherited skin color. The cause of the disease is still unknown despite accumulating in vivo and in vitro evidence of massive epidermal oxidative stress via H2O2 and peroxynitrite (ONOO(-)) in affected individuals. The most favored hypothesis is based on autoimmune mechanisms. Strictly segmental vitiligo (SSV) with dermatomal distribution is a rare entity, often associated with stable outcome. Recently, it was documented that this form can be associated with NSV (mixed vitiligo). We here asked the question whether ROS and possibly ONOO(-) could be players in the pathogenesis of SSV. Our in situ results demonstrate for the first time epidermal biopterin accumulation together with significantly decreased epidermal catalase, thioredoxin/thioreoxin reductase, and MSRA/MSRB expression. Moreover, we show epidermal ONOO(-) accumulation. In vivo FT-Raman spectroscopy reveals the presence of H2O2, methionine sulfoxide, and tryptophan metabolites; i.e., N-formylkynurenine and kynurenine, implying Fenton chemistry in the cascade (n=10). Validation of the basic data stems from successful repigmentation of skin and eyelashes in affected individuals, regardless of SSV or segmental vitiligo in association with NSV after reduction of epidermal H2O2 (n=5). Taken together, our contribution strongly supports H2O2/ONOO-mediated stress in the pathogenesis of SSV. Our findings offer new treatment intervention for lost skin and hair color.

Vitiligo-inducing phenols activate the unfolded protein response in melanocytes resulting in upregulation of IL6 and IL8

Vitiligo is characterized by depigmented skin patches due to loss of epidermal melanocytes. Oxidative stress may play a role in vitiligo onset, while autoimmunity contributes to disease progression. In this study we sought to identify mechanisms that link disease triggers and spreading of lesions. A hallmark of melanocytes at the periphery of vitiligo lesions is dilation of the endoplasmic reticulum (ER). We hypothesized that oxidative stress results in redox disruptions that extend to the ER, causing accumulation of misfolded peptides, which activates the unfolded protein response (UPR). We used 4-tertiary butyl phenol (4-TBP) and monobenzyl ether of hydroquinone (MBEH), known triggers of vitiligo. We show that expression of key UPR components, including the transcription factor X-box binding protein 1 (XBP1), are increased following exposure of melanocytes to phenols. XBP1 activation increases production of immune mediators interleukin-6 (IL6) and IL8. Co-treatment with XBP1 inhibitors reduced IL6 and IL8 production induced by phenols, while over-expression of XBP1 alone increased their expression. Thus, melanocytes themselves produce cytokines associated with activation of an immune response following exposure to chemical triggers of vitiligo. These results expand our understanding of the mechanisms underlying melanocyte loss in vitiligo and pathways linking environmental stressors and autoimmunity.

Topical application of bleaching phenols; in-vivo studies and mechanism of action relevant to melanoma treatment

Skin depigmentation represents a well-established treatment for extensive vitiligo and may likewise be suited to prevent tumor recurrences and as a prophylactic treatment of familial melanoma, as common bleaching agents are cytotoxic to melanocytes. Effective melanoma prevention requires a bleaching agent-induced loss of exposed melanocytes supported by an immune response to distant pigment cells. Studies on human explant cultures treated with depigmenting agents such as 4-tertiary butyl phenol (4-TBP) or monobenzyl ether of hydroquinone (MBEH) showed a significant increase in the migration of Langerhans cells toward the dermis only upon treatment with MBEH, thus suggesting selective elicitation of an immune response. To assess the depigmenting potential of bleaching agents in vivo, 4-TBP and MBEH were topically applied to C57BL/6 wild type as well as k14-SCF transgenic, epidermally pigmented mice. MBEH-induced significant skin depigmentation in both strains was not observed upon treatment with 4-TBP. Cytokine expression patterns in skin treated with MBEH support activation of a Th1-mediated immune response corresponding to an influx of T cells and macrophages. Importantly, despite insensitivity of tumor cells to MBEH-induced cytotoxicity, significantly retarded tumor growth was observed in B16 challenged k14-SCF mice pretreated with MBEH, likely due to an abundance of cytotoxic T cells accompanied by an increased expression of Th1 and Th17 cytokines. These data support the use of MBEH as a prophylactic treatment for melanoma.

Increased level of serum Homocysteine in vitiligo

BACKGROUND

Vitiligo is an acquired depigmenting disorder caused by the destruction of melanocytes. The exact etiopathogenesis and mechanisms of vitiligo are not fully understood. Vitamin B12 and folic acid levels are decreased in vitiligo, which are the important cofactors required in the metabolism of Homocysteine (Hcy). Consequently, Hcy level increases in the circulation. Therefore, it is possible that increased Hcy plays a role in melanocytes destruction. The aim was to study for any association of vitiligo with serum Hcy level.

METHOD

A total of 30 vitiligo patients of both sexes and 30 control subjects were enrolled in this study. Sera from patients and controls were assayed for Hcy by Enzyme immunoassay. The collected data were analyzed by SPSS version-16.

RESULTS

The mean serum level of Hcy was significantly higher in patients with vitiligo as compared with healthy controls and its level was high in male patients as compared with female patients. The Hcy level in vegetarian patients was significantly higher as compared with nonvegetarian patients. The Hcy level was also significantly higher in active vitiligo patients as compared with stable vitiligo patients.

CONCLUSION

An increased serum Hcy may be a precipitating factor for vitiligo in the predisposed individuals. Serum Hcy is related to the gender of patients, activity of disease, and dietary habits of vitiligo patients.

Update on the genetics characterization of vitiligo

Vitiligo is an autoimmune skin disorder in which autoimmune-mediated destruction of melanocytes caused depigmentation of skin patches. The complex genetics of vitiligo involves multiple susceptibility loci, genetic heterogeneity and incomplete penetrance with gene-gene and gene-environment interactions. In order to clarify the genetic factors, two different principal approaches have applied for the identification of genomic regions or candidate genes that mediate susceptibility to vitiligo. First approach is the genome-wide linkage analyses, which is conducted by scanning of entire human genome for genomic regions that are linked to the development of vitiligo. The other approach is functional candidate gene association (FCGA) analyses that detect specific candidate genes, which are expected to involve in disease on the basis of their priori biological functions. Genomic-wide scans have provided a strong support for vitiligo susceptibility genes on chromosomes 4q13-q21, 1p31, 7q22, 8p12 and 17p13, while loci of interest at 6p, 6q, 14q, 9q, 13q, 19p and 22q required further follow-up. Whereas, FCGA studies have identified some candidate genes which are associated with vitiligo, such as HLA, AIRE, VIT1, CAT, FOXD3, ESR1, COMT, PTPN22, NALP1, PDGFRA, MYG1, MITF, CD117, XBP1, FAS, COX2, EDN1 and ACE, but few of them reports now appear to be false-positive. This review will provides an update on genetics of vitiligo based on the identification of novel candidate genes that represent, in my opinion as optimal utility for future therapeutic targets in the pathogenesis of vitiligo.

Tyrosinase related protein 1 (TYRP1/gp75) in human cutaneous melanoma

Melanoma prognosis is based on specific pathological features at the primary lesion. In metastatic patients, the extent of lymph node involvement is also an important prognosis indicator. Many progression markers both in tissues and serum, including circulating tumor cells, have been studied and new molecular markers are awaited from high-throughput screenings to discriminate between clinical stages and predict disease progression. The present review focuses on human tyrosinase related protein 1 also known as gp75 glycoprotein (Tyrp1/gp75), a melanosomal protein involved in the pigmentary machinery of the melanocyte and often used as differentiation marker, with a special emphasis on its emerging roles in the malignant melanocyte and melanoma progression.

Isolation and characterization of 4-tert-butylphenol-utilizing Sphingobium fuliginis strains from Phragmites australis rhizosphere sediment

We isolated three Sphingobium fuliginis strains from Phragmites australis rhizosphere sediment that were capable of utilizing 4-tert-butylphenol as a sole carbon and energy source. These strains are the first 4-tert-butylphenol-utilizing bacteria. The strain designated TIK-1 completely degraded 1.0 mM 4-tert-butylphenol in basal salts medium within 12 h, with concomitant cell growth. We identified 4-tert-butylcatechol and 3,3-dimethyl-2-butanone as internal metabolites by gas chromatography-mass spectrometry. When 3-fluorocatechol was used as an inactivator of meta-cleavage enzymes, strain TIK-1 could not degrade 4-tert-butylcatechol and 3,3-dimethyl-2-butanone was not detected. We concluded that metabolism of 4-tert-butylphenol by strain TIK-1 is initiated by hydroxylation to 4-tert-butylcatechol, followed by a meta-cleavage pathway. Growth experiments with 20 other alkylphenols showed that 4-isopropylphenol, 4-sec-butylphenol, and 4-tert-pentylphenol, which have alkyl side chains of three to five carbon atoms with α-quaternary or α-tertiary carbons, supported cell growth but that 4-n-alkylphenols, 4-tert-octylphenol, technical nonylphenol, 2-alkylphenols, and 3-alkylphenols did not. The rate of growth on 4-tert-butylphenol was much higher than that of growth on the other alkylphenols. Degradation experiments with various alkylphenols showed that strain TIK-1 cells grown on 4-tert-butylphenol could degrade 4-alkylphenols with variously sized and branched side chains (ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, tert-pentyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, and branched nonyl) via a meta-cleavage pathway but not 2- or 3-alkylphenols. Along with the degradation of these alkylphenols, we detected methyl alkyl ketones that retained the structure of the original alkyl side chains. Strain TIK-1 may be useful in the bioremediation of environments polluted by 4-tert-butylphenol and various other 4-alkylphenols.

Monobenzyl ether of hydroquinone and 4-tertiary butyl phenol activate markedly different physiological responses in melanocytes: relevance to skin depigmentation

Monobenzyl ether of hydroquinone (MBEH) is a Food and Drug Administration approved drug used for depigmentation therapy of advanced vitiligo. Here, the working mechanism of MBEH is explored in comparison to 4-tertiary butyl phenol (4-TBP), a known causative agent for occupational vitiligo mediating apoptotic melanocytic death. Cytotoxic experiments reveal that similar to 4-TBP, MBEH induces specific melanocyte death. To compare death pathways initiated by 4-TBP and MBEH, classical apoptotic hallmarks were evaluated in treated melanocytes. MBEH induced cell death without activating the caspase cascade or DNA fragmentation, showing that the death pathway is non-apoptotic. Release of High Mobility Group Box-1 protein by MBEH-treated melanocytes and ultrastructural features further confirmed a necrotic death pathway mediated by MBEH. A negative correlation between MBEH-induced cell death and cellular melanin content supports a cytoprotective role for melanin. Moreover, MBEH exposure upregulated the levels of melanogenic enzymes in cultured melanocytes and skin explants, whereas 4-TBP reduced the expression of the same. In summary, exposure to MBEH or 4-TBP has profoundly different consequences for melanocyte physiology and activates different death pathways. As the mode of cell death defines the nature of the immune response that follows, these findings help to explain the relative efficacy of these agents in mediating depigmentation.

Frontiers and controversies in the pathobiology of vitiligo: separating the wheat from the chaff

The pathogenesis of vitiligo is complex and not well understood. Genes play a role in all aspects of vitiligo pathogenesis, and studies are ongoing to identify these genes and understand their biology. There is a body of interlocking, compelling evidence supporting an autoimmune basis for most or all cases of generalized vitiligo. The development of an autoimmune disease generally involves three components; the immune system, environmental triggers and other exogenous precipitating factors, and the target tissue. In vitiligo, precipitating factors could induce melanocyte damage in genetically susceptible individuals and consequent cell death, loss of tolerance, and induction of melanocyte-directed autoimmunity. Future research will more precisely define the multiple biological events that regulate development of vitiligo.