Occupational Vitiligo Research Articles

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.

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.

Effects of commonly used mitogens on the cytotoxicity of 4-tertiary butylphenol to human melanocytes.

In the search for environmental compounds responsible for contact or occupational vitiligo, it was found that the most potent was 4-tertiary butylphenol (4-TBP). Exposure to 4-TBP is widespread both in industry and in consumer items including synthetic leather, plastic, glues, and germicidal phenolic detergents. How 4-TBP causes depigmentation and the death of melanocytes is currently unclear. Growth mitogens for human melanocytes include alpha-melanocyte stimulating hormone (alpha-MSH), basic fibroblast growth factor (bFGF) and 12-o-tetradecanoylphorbol-13-acetate (TPA). The former two mitogens are physiological growth factors for melanocytes. We have studied the effects of these mitogens on the cytotoxicity of 4-TBP in human melanocytes. Our results demonstrated that deprivation of alpha-MSH or bFGF from melanocyte cultures resulted in reduced cytotoxicity to 4-TBP. Similar results were obtained upon treatment of melanocytes with an inhibitor of cAMP-dependent protein kinase A (PKA), that is known to be activated by alpha-MSH, or with an inhibitor of the tyrosine kinase bFGF receptor. In contrast, removal of fetal bovine serum or TPA from the culture medium did not influence the susceptibility of melanocytes to 4-TBP. These results suggest that activation of the cAMP and tyrosine kinase signaling pathways, both of which are involved in the mitogenic response of melanocytes, increase the susceptibility of these cells to the cytotoxic effects of 4-TBP.

Altered Gene Expression in Melanocytes Exposed to 4-Tertiary Butyl Phenol (4-TBP): Upregulation of the A2b Adenosine Receptor1

Exposure to phenolic agents contributes to the development of occupational vitiligo. Proposed as a causative factor for leukoderma in vivo, the para-substituted phenol 4-tertiary butyl phenol was chosen to investigate early cellular events responsible for selective disappearance of melanocytes from the epidermis of individuals sensitive to such agents. To this end, differential display of melanocyte mRNA isolated from three separate cultures was performed following a 12 h exposure of cells to 250 microM 4-tertiary butyl phenol or to vehicle alone. Fragments of cDNA representing differentially expressed messages were cloned and subsequently confirmed by reverse dot blotting. Alignment analysis revealed that the L30 ribosomal protein was upregulated by the treatment, potentially reflecting altered levels of protein synthesis in response to stress. In addition, a gene sequence upregulated following exposure to 4-tertiary butyl phenol was identified as the A2b receptor (a P1 receptor for adenosine). Differential expression of this gene was confirmed in an RNase protection assay. By reverse transcription-polymerase chain reaction, the gene was shown to be expressed in keratinocytes and fibroblasts as well. Flow cytometry confirmed differential expression in melanocytes and fibroblasts, but not in keratinocytes. Interestingly, it has been reported that P1 purinoceptor stimulation can induce apoptosis. This is in concordance with results reported elsewhere demonstrating induction of apoptosis by 4-tertiary butyl phenol in human melanocytes, as well as with morphologic changes observed in this study in cells exposed to 250 microM 4-tertiary butyl phenol for 72 h. In conclusion, differential display is useful to establish melanocyte components involved in the cellular response to phenolic agents.

In this Issue

In this Issue

ｐ‐ｔｅｒｔ‐Ｂｕｔｙｌｐｈｅｎｏｌ（ＰＴＢＰ）使用職場におけるＰＴＢＰ曝露評価

Two cases of occupational vitiligo were observed in a resin factory where p-tert-butylphenol (PTBP) has been used as a starting material or an intermediate of synthetic resin. In this resin factory (A shop) and another resin factory (B shop), occupational exposure to PTBP was assessed in workers charging this chemical into the reaction vessel by means of a gas-chromatographic measurement of the environmental PTBP concentration and their urinary PTBP excretion. Assessment in A shop was made after the working condition was partly improved. Geometrical mean values of 8 h-time-weighted-average (8 h-TWA) of PTBP in air near the charger's breathing zone (personal air) were 0.215 mg/m3 in A shop and 2.12 mg/m3 in B shop. Continuous measurements of PTBP concentration in some stationary air of the shops showed that the maximum environmental PTBP values occurred during charging. Urinary PTBP concentration was increased to the maximum values 2 to 4 h after charging of this chemical and then rapidly decreased. Biological half-lives of urinary PTBP were estimated as 4.4 h in A shop and 4.8 h in B shop. The urinary PTBP concentration was correlated to 8 h-TWA of PTBP in the personal air. In particular, PTBP in urine collected at the end of the shift showed an excellent correlation to PTBP in the personal air (r = 0.84, n = 9, A shop; r = 0.88, n = 11, B shop). These results indicate that biological monitoring using urinary PTBP concentration is a suitable means of assessing exposure to this alkylphenol and the urine collected at the end of shift is the best sample for monitoring. In addition, the present environmental and urinary PTBP values were compared with those described in the literature and the relation of the occupational vitiligo with PTBP exposure is discussed.

Occupational skin disease

It is opportune to discuss occupational skin disorders since recently a 'Save your Skin' Campaign has been undertaken in the United Kingdom by the Employment Advisory Service of the Health and Safety Executive to increase the awareness of employers and employees of the need to prevent skin problems in industry.' This was justified because skin disorders caused by substances at work are the most common occupational health problem. Contact dermatitis (eczematous dermatitis of predominantly exogenous aetiology) is the commonest form of occupational skin disease. However, other occupational skin disorders occur, often presenting to physicians of different disciplines, for example infectious conditions, occupational skin cancer, occupational vitiligo, vibration white finger. The purpose of this article is to outline the major occupational skin disorders and to give references to sources of information in greater depth. Since 1986 certain skin diseases linked to specified types of work must be reported in the United Kingdom.2 These include chrome ulceration of the nose or throat, or of the skin of the hands or forearms, in persons in work involving exposure to chromic acid or to any other chromium compound; folliculitis, acne, and skin cancer, in those whose work involves exposure to mineral oil, tar, pitch or arsenic; inflammation, ulceration or malignant disease of the skin is also reportable in those working with ionizing radiation. In addition to these listed skin diseases, anthrax is reportable whatever the person's occupation and vibration white finger is reportable in those exposed to a specified list of tools or processes in which vibration or percussive features occur. It is of interest that the most common dermatosis, contact dermatitis, is not a reportable disease under the present regulations. Diagnosis of occupational skin disease

Occupational Vitiligo Due to Unsuspected Presence of Phenolic Antioxidant Byproducts in Commercial Bulk Rubber

We investigated the occurrence of cutaneous depigmentation (vitiligo) among employees of a company that manufactured hydraulic pumps. The interiors of these pumps were injection-molded with rubber. We identified a small but significant cluster of vitiligo cases among a group of employees who frequently handled the rubber used in this injection molding process. Although none of the additives specified in the rubber formulations was a phenolic or catecholic derivative, known to be potential causes of chemically induced vitiligo, gas chromatographic analysis identified a para-substituted phenol (2,4-di-tert-butylphenol, DTBP) in solid samples of the most frequently used rubber. Surface wipe analysis confirmed that workers could be exposed to DTBP from simple handling of the rubber. We subsequently established that the solid bulk rubber used as the base in these stock rubber formulations contained both DTBP and smaller quantities of p-tert-butylphenol. Both had formed as unsuspected byproducts during chemical synthesis of two antioxidants added to the solid bulk rubber by a major rubber supplier. We conclude that the unsuspected presence of potential chemical depigmenting agents in solid bulk rubber, from which industrial rubber products are formulated, may contribute to the occurrence of occupational vitiligo, and that a simple review of ingredients in rubber formulations is inadequate to detect their presence.

Screening for occupational vitiligo in workers exposed to hydroquinone monomethyl ether and to paratertiary-amyl-phenol.

Two men reported previously with vitiligo after occupational exposure to hydroquinone monomethyl ether (HMME) have been reviewed after eight years. Repigmentation of significant degree was found in one man and of limited degree in the other. One hundred and sixty-nine men in the same works have been screened with Wood's light for evidence of vitiligo. No cases were found in the 148 men exposed to HMME (colleagues who screened 100 men exposed to HMME in two other factories also found no case) or in the 129 who had been exposed to paratertiary-amyl-phenol. Loss of light reflection on Wood's light examination was observed in 13 men due to scars or to other skin disorders.

Incidence of male genital vitiligo. Report of a screening programme.

One thousand consecutive new male patients attending a clinic for sexually transmitted diseases were screened with Wood's light for the presence of genital vitiligo. Two patients had idiopathic vitiligo and one probable occupational vitiligo.

Occupational Vitiligo Caused by Paratertiary Butylphenol

To the Editor.— Occupational vitiligo caused by paratertiary butylphenol (ptBP) has been reported in the United States, the USSR, Japan, and the Netherlands. In three cases reported recently in West Germany, 1-3 there were hepatic dysfunctions, with slight increases in the serum glutamic oxaloacetic transaminase and serum glutamic pyruvic transaminase levels and with distinct increases in the retention of sulfobromophthalein sodium. Polymorphism of the hepatocytes and disintegration of the cytoplasm were seen in liver biopsy specimens from all three patients; specimens from two patients showed disseminated fatty degeneration. With the use of scintigraphy, enlargement of the spleen was seen in two of the patients. In all three cases, the presence of diffuse strumas was confirmed scintigraphically. Extensive functional evaluation, with the use of long-acting thyroid stimulator, disclosed intrathyroidal disorders of thyroid hormone synthesis. Antibody evaluations were positive. I believe that these are the first three cases to be reported of