Effects of 4-tertiary butyl catechol on tissue cultured melanocytes

Melanocytotoxic chemicals and their toxic mechanisms

Melanocyte cell death can lead to various melanocyte-related skin diseases including vitiligo and leukoderma. Melanocytotoxic chemicals are one of the most well-known causes of nongenetic melanocyte-related diseases, which induce melanocyte cell death through apoptosis. Various chemicals used in cosmetics, medicine, industry and food additives are known to induce melanocyte cell death, which poses a significant risk to the health of consumers and industrial workers. This review summarizes recently reported melanocytotoxic chemicals and their mechanisms of toxicity in an effort to provide insight into the development of safer chemicals.

Para-tertiary butyl catechol (PTBC), an industrial antioxidant induces human platelet apoptosis

The catecholic derivative para-tertiary butyl catechol (PTBC) is a conventional antioxidant and polymerization inhibitor, which exhibits melanocytotoxic effects and contact dermatitis often leading to occupational leucoderma or vitiligo. Although numerous industrial workers will be in constant exposure to PTBC and its chances of getting entry into blood are most expected, its effect on blood components is still undisclosed. As platelets play a prominent role in dermatitis, inflammation, and immunity, in this study we have evaluated the effect of PTBC on human platelets in vitro. Exposure of platelets to PTBC showed increased reactive oxygen species (ROS), intracellular calcium, cardiolipin oxidation, mitochondrial permeability transition pore (MPTP) formation, activation of caspases, phosphatidylserine (PS) externalization and decreased mitochondrial membrane potential. In addition, there was a significant decrease in cellular glutathione level, increased γ-glutamyltransferase (GGT) activity and cell death. These findings demonstrate that PTBC could induce toxic effects on blood components, which is often ignored field of research. Since dermal exposure of humans to toxic chemicals covers an important issue in various industries, there is a need of such work to understand and update the long-term toxicities induced by PTBC usage in industrial sectors and public domain.

Para-tertiary butyl catechol induces eryptosis in vitro via oxidative stress and hemoglobin leakage in human erythrocytes

Exposure of human population to industrial chemicals is believed as a significant contributing factor to the outgrowth of occupational diseases especially in developing countries due to improper safety measures and sanitary conditions. Para-tertiary butylcatechol (PTBC) widely employed in petrochemical, thermofax and phototypesetting industries, induces melanocytotoxicity and contact dermatitis leading to occupational leukoderma/vitiligo. Few vitiligo patients were reported for oxidative stress-induced hemolytic anemia and thrombocytopenia, however its impact on blood components is still not clear. Erythrocytes are the major cell population in circulation and play a prominent role in various diseases. In this work, the effect of PTBC on human erythrocytes is evaluated in vitro. PTBC induces oxidative stress-mediated eryptosis (erythrocyte death) causing detrimental changes such as depleted antioxidant levels, altered surface morphology, hemoglobin denaturation and heinz body formation. These findings validate that PTBC could induce toxic effects on human erythrocytes. Exposure of humans to toxic chemicals constitutes an important issue in various industries; one such issue is the exposure of PTBC at work place resulting in a spectrum of dermal complications. Therefore, it is imperative to appraise the long-term toxicities in order to further delineate the mechanisms of resultant disorders associated with PTBC and to establish the therapeutic interventions.

Interaction of several mono- and dihydroxybenzene derivatives of various depigmenting potencies with L-3,4-dihydroxyphenylalanine-melanin

Certain mono- and dihydroxybenzene derivatives cause depigmentation of skin and hair, and appear to be selectively cytotoxic for melanized pigment cells. As direct physical and/or chemical interaction between depigmenter (DP) and pigment melanin may play a role in depigmentation, we have carried out preliminary studies in model systems where such interactions may easily be separated from effects due to tyrosinase, melanosomal proteins, and other components. We have used synthetic L-3,4-hydroxyphenylalanine (L-DOPA)-melanin as a protein-free model pigment and potassium ferricyanide as a model electron acceptor. Compounds studied were catechol, 4-t-butylcatechol, 4-methylcatechol, 3,4-dihydroxyphenylalanine (DOPA), 3,4-dihydroxyphenylacetic acid, hydroquinone, 4-methoxyphenol, 4-t-butylphenol, and 2,6, di-t-butyl-4-methylphenol (BHT) in 0.1 M phosphate buffer, pH 7.4. These compounds vary widely in their ability to depigment hair and skin. Ferricyanide reduction by DP in the presence and absence of melanin was monitored spectrophotometrically. The sparingly soluble BHT and 4-t-butylphenol did not reduce ferricyanide in the absence or presence of melanin. For the other compounds, kinetic analysis demonstrated direct interaction between each DP and melanin. Except for dihydroxyphenylacetic acid, reduction kinetics were consistent with a mechanism involving noninteractive binding of both DP and ferricyanide to melanin prior to coupled electron transfer through the melanin backbone. Kinetic analysis afforded KB, a thermodynamic constant (M-1) for DP-melanin binding, and k', a rate parameter (M s-1) for electron transfer. A dimensionless enhancement factor (EF) was defined as k'KB/ks, with ks a pseudo-first-order constant (s-1) for ferricyanide reduction in the absence of melanin. Depending on the reductant, melanin either retards (EF less than 1) or accelerates (EF greater than 1) the rate of ferricyanide reduction. There appears to be a direct relationship between EF and depigmenting potency. There is no relationship between depigmenting power and the ability per se of the DP to bind to melanin or to reduce ferricyanide.

Stimulation of pheomelanogenesis in cultured B16 melanoma cells by 4-tertiary butylcatechol

Intermediates of pheomelanin in tissue cultured B16 melanoma cells were analyzed by high performance liquid chromatography, and reduced glutathione (GSH), L-dopa, 2-[(L)-S-cysteinyl]-L-dopa (2-SCD) and 5-[(L)-S-cysteinyl]-L-dopa (5-SCD) were quantified. The effects of 4-tertiary butylcatechol (TBC), an antioxidant which causes skin depigmentation, on the levels of the intermediate were then examined. A concentration of 10(-4) M TBC increased the intracellular levels of GSH, 2-SCD and 5-SCD, whereas the L-dopa level was unchanged. The time-course of the increased intermediates corresponded to the elevation of glutathione-metabolizing enzyme activities previously reported by Kawashima et al. [J. invest. Derm. 82, 53 (1984)] in the same cell line exposed to 10(-4) M TBC. The findings establish chemical evidence that TBC stimulates pheomelanogenesis in melanocytes.

Effects of 4-tertiary butyl catechol on glutathione-metabolizing enzymes in vivo and in vitro

4-Tertiary butyl catechol (TBC) causes depigmentation in humans and animals and stimulates formation of pheomelanosomes. In this study, we investigated the effects of noncytotoxic doses of TBC on glutathione S-transferase (GST) activity in the skin of Uscd strain mice and B16 murine melanoma cells in culture, in relation to changes in activities of glutathione reductase (GR) and gamma-glutamyl transpeptidase (GGT) reported to be involved in pheomelanogenesis. Occurrence of pheomelanosomes in skin melanocytes was demonstrated by electron microscopy and reduction (25%) of eumelanin content in melanoma cells was shown by spectrophotometry. Topical application of 1 M TBC-DMSO-acetone solution on the ear skin elevated GST activity about 27%, and activities of GGT and GR to 35% and 19%, respectively, within 1 week. Melanoma cells cultured in 10(-4) M TBC-containing medium for 2 h showed no changes in GST and GGT activities, but 12% increase of GR activity during the first 12 h. Activities of all 3 enzymes was elevated (11-17%) 24 h later. The elevation detected by 48 h was 25% for GST, 26% for GGT, and 14% for GR. The findings were interpreted to show that depigmentation produced by the antioxidant results from stimulated pheomelanogenesis through activation of glutathione-metabolizing enzymes and suppressed oxidation of eumelanin intermediates.

Reduction in eumelanin by the activation of glutathione reductase and gamma-glutamyl transpeptidase after exposure to a depigmenting chemical

Topical application of 4-tertiary butyl catechol (TBC) causes vitiligo in the skin of man and animals, and previous electron microscopic studies showed pheomelanin formation in the affected areas. In the present study, we investigated changes of enzyme activities, eumelanin content and amount of sulfur in tissue cultured human melanoma cells exposed to the depigmenting chemical. TBC enhanced glutathione reductase activity without changing the eumelanin content by 24 hr after exposure and subsequently (by 42 hr) increased gamma-glutamyl transpeptidase activity and sulfur content in the cells with a decrease in eumelanin content. It is suggested that this chemical alters the types of melanin formed by modulation of these enzyme activities.

Contact allergy and depigmentation from alstroemeria

Alstroemeria plants have increased in popularity in recent years, but surprisingly few cases of contact allergy have been reported. Observations of combined sensitivity between Alstroemeria and Tulipa have given support to the assumption that they contain identical sensitizing agents. A patient working as a gardner developed a dermatitis from Alstroemeria. Patch tests with Alstroemeria were positive, but patch tests with Tulipa were negative. 2 months after test application, the patient showed depigmented areas at the test sites and at the sites of a previous dermatitis. The depigmented test areas remained unchanged at least a year after test application. Whether the depigmentation was due to some unique character of the molecular structure of the unknown Alstroemeria allergen, or to a unique biological characteristic of the patient, remains to be determined.

Molecular basis of substrate and inhibitory specificity of tyrosinase: phenolic compounds

In order to investigate the molecular basis of substrates, and the inhibitory specificity of tyrosinase, a large series of phenolic compounds have been analysed by using a High Performance Liquid Chromatographic-Scanning Spectrophotometric system. Depending on their chemical structure, phenolic compounds may act as substrates or as competitive inhibitors of tyrosinase. The ability to act as substrates requires the presence in the molecule of electron donor groups, while competitive inhibition on the contrary requires the presence of powerful electron acceptor groups. Certain phenolic compounds used as therapeutic agents or as food preservatives are chemically capable of acting as alternative substrates or competitive inhibitors of tyrosinase in vitro; their effect on melanocytes in vivo therefore merits investigation.

Effects of 4-tertiary butyl catechol on melanocytes of hairless mice

Depigmentary effects of 4-tertiary butyl catechol (TBC) on UV-stimulated melanocytes on the flanks and naturally active melanocytes of ears were compared in Uscd strain hairless mice. UVB irradiation, twice a week for 1 or 2 mo, induced brown-black pigmentation on the flanks. A 1 M TBC application twice a week for 1 mo not only prevented the UV-stimulated pigmentation, but also promoted fading of the post-UV tanning. Dopa-stained split epidermal sheets showed a decrease in the number of melanocytes to less than one-half during the first month of TBC treatment. Melanocytes were often enlarged or lost their dendrites, and both premelanosomes and melanosomes showed ultrastructural changes. However, TBC application on the ears for 1 mo showed neither color change nor a decrease in the number of melanocytes. There were ultrastructural changes in melanocytes but the degree of abnormality was much less than those seen in UV-stimulated melanocytes. Continuation of TBC application for 2 mo with the UV irradiation on the flanks or the nonirradiated ears caused an increase in the number of melanocytes. These results suggest that the initial effect of TBC may be primarily cytotoxicity to melanocytes, and may correlate with their cellular functions. The stimulatory effects of TBC on melanocytes seen during the longer period of time requires further investigation.

Acute effects of two melanocytolytic agents, hydroquinone and beta-mercaptoethanolamine, upon tyrosinase activity and cyclic nucleotide levels in murine melanomas

The acute in vitro actions of two potent melanocytolytic agents, hydroquinone (HQ) and beta-mercaptoethanolamine (MEA), were determined in the B-16, Cloudman S-91 and Harding-Passey (HP) murine melanomas grown in vivo. Drug treated melanoma dice (5--480 min) were analyzed for tyrosinase activity and cyclic nucleotide levels (cAMP, cGMP). HQ and MEA effects on tyrosinase activity are complex and vary with tumor type, duration of treatment and agent tested. MEA or HQ inhibited B-16 tyrosinase activity. With combined drug therapy, low concentrations of MEA plus HQ stimulate B-16 tyrosinase activity while high concentrations of the drugs have little effect on enzymatic activity. MEA depresses tyrosinase activity while HQ elevates enzymatic activity in the S-19 melanoma. Both high and low concentrations of the combined drugs (MEA plus HQ) elicit the same response, stimulation at 10 min followed by continued depression of tyrosinase activity for the remainder of the 4 h study period. MEA initially stimulates HP tyrosinase activity followed by depression of enzymic activity. In contrast, HQ initially depresses HP tyrosinase activity followed by stimulation of enzyme activity. In combination the drugs inhibit HP tyrosinase activity. The effects of MEA and/or HQ on murine melanoma cyclic nucleotide levels are equally complex. MEA or HQ elevate cAMP and cGMP levels in all three tumors with the exception of S-91 cGMP levels which are not altered. In combination the drugs increase cyclic nucleotide levels in each of the three tumor types but at different times. No correlation is present between cyclic nucleotide levels and tyrosinase activity. Thus, the action of increased cyclic nucleotide levels in melanogenesis can not be separated from the direct actions of MEA and HQ upon melanogenesis. The divergent effects of MEA and/or HQ on tyrosinase activity and cyclic nucleotide levels in these melanomas are not correlated with the known in vivo melanocytolytic activity of these drugs. Thus, these parameters appear to be inadequate indicators of melanoma cell viability in chemotherapeutic screening of drugs effective in destroying malignant melanoma.

The interaction of L-DOPA melanin with p-tert-butylcatechol

The interaction between the skin depigmenter 4-tert-butylcatechol (tBC) and L-DOPA melanin was qualitatively studied by means of spectroscopically monitoring the binding of tBC melanin as well as the oxidation of tBC in the presence and absence of melanin. Additionally, we assessed the quantitative effect of tBC on melanin's chemical reactivity by using the reduction of potassium ferricyanide as a redox marker. The kinetics of ferricyanide reduction in the ternary (melanin/tBC/ferricyanide) system are essentially different from those in each of the binary components (i.e., melanin/ferricyanide and tBC/ferricyanide). The experiments indicate that tBC can bind to melanin (KB = 3.8 X 10(3) M-1) and that melanin can act as a "catalyst-like" electron transfer agent which couples ferricyanide reduction with tBC oxidation (k' = 1.3 X 10(-6) mole min-1). These kinetic and thermodynamic parameters may provide a means of quantitatively comparing melanins obtained from different biological and pathological situations, and they may make possible an understanding of cutaneous depigmentation processes on the molecular level.

Inhibition of tyrosinase activity by 4-tert-butylcatechol and other depigmenting agents

4-tert-Butylcatechol (TBC) is an antioxidant widely used in industry and a potent depigmenting agent to the skin of the workers. In this study, tyrosinase was extracted from tissue-cultured human melanoma cells and purified by polyacrylamide gel electrophoresis. T1 and T2 tyrosinase, which migrated differently on the gels, were treated with TBC as well as other depigmenting agents and natural substrates of tyrosinase. Changes in the enzyme activity on dopa oxidation were quantified by photometric and radiometric analysis. The enzyme activity was inhibited by TBC and hydroquinone, but only at a high concentration that is toxic to tissue-cultured melanocytes. The activity was also decreased by tyrosine, but was increased by dopa, particularly at a lower concentration. The results indicated that the reported methodology is useful for testing the effects of chemicals with depigmenting or pigmenting potential. TBC and hydroquinone are inhibitors of tyrosinase at concentrations higher than 1 x 10(-3) M. Dopa and tyrosine alter tyrosinase activity in the second step of melanogenesis in the same manner that has been reported to occur in the first step-conversion of tyrosine to dopa.

Detection of environmental depigmenting substances

We systematically screened the depigmenting capacity of several phenols, catechols and organic antioxidants. Clear-cut depigmentation was achieved with monomethyl ether of hydroquinone (MMH) and tertiary butyl catechol (TBC) using black guinea pigs and black mice as animal models. A goal was to establish a reliable in vivo method to demonstrate or to predict the depigmenting action of chemicals on mammalian melanocytes. There was no universal solvent or optimal body site, although all tested areas could be depigmented. Irritation induced by some vehicles and test materials produced false positive responses. False negative responses with known depigmenting chemicals were observed. Utilizing these observations, we propose a model for screening medicinal and industrial chemicals for depigmenting capacity.