Cutaneous signs of systemic toxicity due to dioxins and related chemicals

Trajectory Shifts in Interdisciplinary Research of the Aryl Hydrocarbon Receptor-A Personal Perspective on Thymus and Skin

Identifying historical trajectories is a useful exercise in research, as it helps clarify important, perhaps even “paradigmatic”, shifts in thinking and moving forward in science. In this review, the development of research regarding the role of the transcription factor “aryl hydrocarbon receptor” (AHR) as a mediator of the toxicity of environmental pollution towards a link between the environment and a healthy adaptive response of the immune system and the skin is discussed. From this fascinating development, the opportunities for targeting the AHR in the therapy of many diseases become clear.

Role of the Aryl Hydrocarbon Receptor in Environmentally Induced Skin Aging and Skin Carcinogenesis

The skin is constantly exposed to a variety of environmental threats, including solar electromagnetic radiation, microbes, airborne particulate matter, and chemicals. Acute exposure to these environmental factors results in the activation of different signaling pathways that orchestrate adaptive stress responses to maintain cell and tissue homeostasis. Chronic exposure of skin to these factors, however, may lead to the accumulation of damaged macromolecules and loss of cell and tissue integrity, which, over time, may facilitate aging processes and the development of aging-related malignancies. One transcription factor that is expressed in all cutaneous cells and activated by various environmental stressors, including dioxins, polycyclic aromatic hydrocarbons, and ultraviolet radiation, is the aryl hydrocarbon receptor (AHR). By regulating keratinocyte proliferation and differentiation, epidermal barrier function, melanogenesis, and immunity, a certain degree of AHR activity is critical to maintain skin integrity and to adapt to acute stress situations. In contrast, a chronic activation of cutaneous AHR signaling critically contributes to premature aging and the development of neoplasms by affecting metabolism, extracellular matrix remodeling, inflammation, pigmentation, DNA repair, and apoptosis. This article provides an overview of the detrimental effects associated with sustained AHR activity in chronically stressed skin and pinpoints AHR as a promising target for chemoprevention.

The life-threatening rash of poisoning

Dermatology is frequently viewed by physician and surgical colleagues as a specialty with few emergencies. Although the majority of dermatology practice is in the office setting, cutaneous emergencies do occur through referrals from primary care and as ward consults. Even though cutaneous signs of poisoning would be an uncommon emergency consultation, it is important for dermatologists to be aware of the clinical presentations so as to be able instigate appropriate time critical treatments.

Aryl Hydrocarbon Receptor Activation Contributes to Benzanthrone-Induced Hyperpigmentation via Modulation of Melanogenic Signaling Pathways

Benzanthrone (BA), an oxidized polycyclic aromatic hydrocarbon (PAH), has been found to be a potential health threat to occupational workers involved in dye manufacturing factories. It has been observed that occupational workers become exposed to BA either during manufacturing, pulverization, or storage and developed various kinds of skin diseases like contact dermatitis, itching, erythema, roughness, and foremost, hyperpigmentation. It has been shown that some environmental organic pollutants (POPs) like dioxins, furans, and polychlorinated biphenyls (PCBs) may act as ligands for the aryl hydrocarbon receptor (AhR) and regulate hyperpigmentation. Here, we hypothesized that BA may also act as a ligand for AhR and possibly regulate the melanogenic pathway to induced hyperpigmentation. Our computation results indicate that BA has a high binding affinity toward AhR for the initiation of melanogenic signaling. Following the in silico predictions, we used primary mouse melanocytes (PMMs) and confirmed that exposure to BA (5, 10, and 25 μM) resulted in an increase in AhR expression, tyrosinase activity, and melanin synthesis. Moreover, to study the physiological relevance of these findings, C57BL/6 mice were topically exposed to BA, and enhanced pigmentation and melanin synthesis were observed. Furthermore, the study was extended to assess the mechanistic aspects involved in BA-induced hyperpigmentation in PMMs as well as in mouse skin. Our results suggest that BA exposure initiates AhR signaling and increases tyrosinase enzyme activity and melanin synthesis. Moreover, the genes that regulate the melanin synthesis, such as TRP-1, TRP-2 and the transcription factor MITF, were also found to be increased. Thus, altogether, we suggest that BA-AhR interactions are critical for BA-induced hyperpigmentation.

Skin diseases associated with Agent Orange and other organochlorine exposures

Organochlorine exposure is an important cause of cutaneous and systemic toxicity. Exposure has been associated with industrial accidents, intentional poisoning, and the use of defoliants, such as Agent Orange in the Vietnam War. Although long-term health effects are systematically reviewed by the Institute of Medicine, skin diseases are not comprehensively assessed. This represents an important practice gap as patients can present with cutaneous findings. This article provides a systematic review of the cutaneous manifestations of known mass organochlorine exposures in military and industrial settings with the goal of providing clinically useful recommendations for dermatologists seeing patients inquiring about organochlorine effects. Patients with a new diagnosis of chloracne, porphyria cutanea tarda, cutaneous lymphomas (non-Hodgkin lymphoma), and soft-tissue sarcomas including dermatofibrosarcoma protuberans and leiomyosarcomas should be screened for a history of Vietnam service or industrial exposure. Inconclusive evidence exists for an increased risk of other skin diseases in Vietnam veterans exposed to Agent Orange including benign fatty tumors, melanomas, nonmelanoma skin cancers, milia, eczema, dyschromias, disturbance of skin sensation, and rashes not otherwise specified. Affected veterans should be informed of the uncertain data in those cases. Referral to Department of Veterans Affairs for disability assessment is indicated for conditions with established associations.

The aryl hydrocarbon receptor: a review of its role in the physiology and pathology of the integument and its relationship to the tryptophan metabolism

The aryl hydrocarbon receptor (AHR) is a cytosolic receptor for low molecular weight molecules, of which the most widely recognized ligand is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and the most widely recognized effect, chloracne. Adverse effects of manipulation were most recently and graphically demonstrated by the poisoning of Viktor Yushchenko during the Ukrainian presidential elections of 2004. However, recent research has revealed a receptor with wide-ranging, and at times, paradoxical actions. It was arguably among the first biological receptors to be utilized by dermatologists, dating from the time of topical tar preparations as a therapeutic agent. I provide a review outlining the role AHR plays in the development, cellular oxidation/antioxidation, responses to ultraviolet light, melanogenesis, epidermal barrier function, and immune regulation and its relationship to tryptophan metabolism. Finally, I will review the role of AHR in diseases of the integument.

Functions of the aryl hydrocarbon receptor in the skin

Among other functions, the skin serves as the barrier against the environment and provides vital protection from physical or chemical harm and from infection. Skin cells express the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor and sensor of environmental chemicals; at the same time, AHR ligands are abundant in skin from exogenous or endogenous sources. For example, solar radiation, in particular ultraviolet (UV) B, generates AHR ligands from tryptophan in the skin. Recent evidence has shown that AHR is involved in the (patho)physiology of skin including the regulation of skin pigmentation, photocarcinogenesis, and skin inflammation. We here provide a state-of-the-art summary of work which relates to the role of the AHR in (1) adaptive responses against environmental challenges such as UVB or topical chemicals and (2) intrinsic developmental roles for homeostasis of skin cells and (3) skin immunity. We also discuss the existing evidence that AHR antagonists or AHR ligands may be used for the prevention and/or treatment of skin disease.

The aryl hydrocarbon receptor mediates UVB radiation-induced skin tanning

Melanogenesis is the vital response to protect skin cells against UVB-induced DNA damage. Melanin is produced by melanocytes, which transfer it to surrounding keratinocytes. Recently, we have shown that the aryl hydrocarbon receptor (AhR) is part of the UVB-stress response in epidermal keratinocytes. UVB triggers AhR signaling by generating the AhR ligand 6-formylindolo(3,2-b)carbazole from tryptophan. We show here that normal murine melanocytes express functional AhR. Using standard UVB tanning protocols, AhR-deficient mice were shown to tan significantly weaker than wild-type mice; in these mice, tyrosinase activity in the epidermis was lower as well. Tanning responses and tyrosinase activity, however, were normal in keratinocyte-specific conditional AhR knockout mice, indicating that release of melanogenic keratinocyte factors is unaffected by the UVB-AhR signaling pathway and that the diminished tanning response in AhR(-/-) mice is confined to the level of melanocytes. Accordingly, the number of dihydroxyphenylalanin-positive melanocytes increased significantly less on UVB irradiation in AhR(-/-) mice than in wild-type mice. This difference in melanocyte number was associated with a significantly reduced expression of stem cell factor-1 and c-kit in melanocytes of AhR(-/-) mice. Thus, the environmental signal sensor AhR links solar UVB radiation to skin pigmentation.

Dioxin-induced chloracne--reconstructing the cellular and molecular mechanisms of a classic environmental disease

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is among the most toxic pollutants known to date that serves as a prototype for a group of halogenated hydrocarbon compounds characterized by extraordinary environmental persistence and unique ability to concentrate in animal and human tissues. TCDD can elicit a complex array of pleiotropic adverse effects in humans, although chloracne, a specific type of acne-like skin disease, is the only consistent manifestation of dioxin intoxication, thus representing a 'hallmark' of TCDD exposure. Chloracne is considered to be one of the most specific and sensitive biomarkers of TCDD intoxication that allows clinical and epidemiological evaluation of exposure level at threshold doses. The specific cellular and molecular mechanisms involved in pathogenesis of chloracne are still unknown. In this review, we summarize the available clinical data on chloracne and recent progress in understanding the role of the dioxin-dependent pathway in the control of gene transcription and discuss molecular and cellular events potentially involved in chloracne pathogenesis. We propose that the dioxin-induced activation of skin stem cells and a shift in differentiation commitment of their progeny may represent a major mechanism of chloracne development.

Effluents from a pulp and paper mill: a skin and health survey of children living in upstream and downstream villages

OBJECTIVES

A health survey of three villages (upstream village Rantau Baru and two downstream villages, Sering and Pelalawan) in the vicinity of a pulp and paper mill along the Kampar river in the province of Riau, Indonesia was conducted to find whether exposure to the effluents from the mill was related to skin conditions and ill health.

METHODS

A cross sectional survey was carried out of children living in the three villages.

RESULTS

Common skin conditions such as dermatitis, fungal infections, insect bites, and miliaria were found. No significantly increased risk of dermatitis or any illness in general was found with increasing levels of exposure to river water for downstream villages when compared with the upstream village. However, there was an increased risk of diarrhoea in Sering especially with drinking water directly from the river (prevalence rate ratio (PRR) 4.9, 95% confidence interval (95% CI) 0.4 to 63.9). An increased risk was also found within the upstream village Rantau Baru (PRR 2.3, 95% CI 0.9 to 5.8) and downstream village Sering (PRR 1.4, 95% CI 0.4 to 5.2) when children who drank water directly from the river were compared with those who never did. Analysis of the river water also showed physical and chemical variables within the acceptable range except for faecal coliforms (6 MPN/100 ml) found in the sample taken from Sering.

CONCLUSIONS

The effluent from the mill is unlikely to be causing skin conditions and ill health. Diarrhoea may be due to faecal coliform contamination of the water because all raw sewerage is deposited in the river. Community health outreach programmes are being implemented based on these findings.

2,3,7,8-Tetrachlorodibenzo-p-dioxin alters the differentiation pattern of human keratinocytes in organotypic culture

Human exposure to the environmental toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces a severe skin pathology known as chloracne. In these studies we employed a three-dimensional, organotypic model system to study the effects of TCDD on human skin. This model uses the spontaneously immortalized human keratinocyte cell line NIKS and recapitulates both the three-dimensional microenvironment and epithelial-mesenchymal interactions found in intact human skin. Treatment of the organotypic cultures with TCDD causes alterations in the pattern of keratinocyte terminal differentiation. Analysis at both the light and electron microscope levels reveals a fully differentiated cornified layer in TCDD-treated organotypic cultures at earlier time points than observed in vehicle (dimethyl sulfoxide)-treated controls. Furthermore, TCDD-treated organotypic cultures exhibit aberrant distribution of several differentiation-specific protein markers. Basal cells in TCDD- and DMSO-treated organotypic cultures show no differences in proliferation as measured by quantification of 5-bromo-2'-deoxyuridine (BrdU)-positive nuclei. No aberrant BrdU uptake was detected outside of the basal layer. Neither TUNEL labeling nor immunohistochemical staining with an antibody to active caspase-3 revealed increased apoptosis in TCDD-treated organotypic cultures relative to controls. These data clearly indicate that TCDD modulates homeostasis in a model of human stratifying epithelium independent of changes in proliferation and apoptosis, exclusively by impacting keratinocyte terminal differentiation. This TCDD-induced effect on differentiation-specific proteins results in profound changes in the tissue architecture.

Serum dioxin, chloracne, and acne in veterans of Operation Ranch Hand

The possible relationship between exposure to Agent Orange and its contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin), during the Vietnam War and chloracne was investigated. The index subjects were veterans of Operation Ranch Hand, the unit responsible for aerial herbicide spraying in Vietnam from 1962 to 1971. Other Air Force veterans who served in Southeast Asia during the same period, but who were not involved with spraying herbicides, served as comparisons. None of the Ranch Hand veterans were diagnosed with chloracne; therefore, we restricted our analyses to acne. We found no meaningful or consistent association between dioxin exposure and prevalence of acne without or with regard to anatomical location. These results suggested that exposure of Ranch Hand veterans to dioxin was insufficient for the production of chloracne or perhaps the exposure may have caused chloracne that resolved and was currently undetectable.

Chloracne, palmoplantar keratoderma and localized scleroderma in a weed sprayer

The case of a 53-year-old man who developed chloracne, palmoplantar keratoderma and scleroderma after many years of exposure to a variety of chloracnegens is reported. Chloracne is a rare but important acneiform eruption associated with exposure to halogenated aromatic compounds used primarily in agriculture. However, to our knowledge, the association of palmoplantar keratoderma and scleroderma with exposure to chloracnegens has not been previously reported.

The penetration of 2,3,7,8-tetrachlorodibenzo-p-dioxin into viable and non-viable porcine skin in vitro

Freshly harvested, full thickness porcine skin was kept metabolically viable at 4 degrees C in a minimal essential medium for at least 48 h, as judged by the formation of lactate or 14CO2 from 14C-labeled glucose. In vitro topical exposure to the environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 65 ng/cm2) for up to 1000 min did not affect the viability of skin. The penetration and distribution of TCDD into porcine skin was studied in an in vitro system under a variety of conditions, such as viability status, different vehicles or concentrations, or artificial removal of the stratum corneum. Loss of viability of the skin increased the rate of penetration of TCDD by about 60%. Removal of the stratum corneum to mimic lesioned skin increased the rate of dermal penetration of TCDD about 3-fold. The use of acetone as the vehicle, simulating dermal exposure to TCDD as a dust or from a volatile solvent, resulted in higher rates of penetration than the use of mineral oil as the vehicle, which simulates the situation of industrial accidents. The percentage of dose absorbed was independent of the dose of TCDD (65 or 6.5 ng/cm2) administered to the surface of skin. Rates of dermal penetration of TCDD ranged form 14 to 985 pg/cm2 skin per h, or 0.2-1.5% of the dose/h, depending on the conditions of exposure. These rates of penetration are comparable with results obtained by others in several other species, with both in vitro and in vivo systems including human skin in vitro. Full thickness porcine skin, viable or previously frozen, is therefore a valid in vitro model to estimate dermal penetration of TCDD in humans.

Chloracne--study of an outbreak with new clinical observations

A recent outbreak of chloracne in 17 workers is reported at a plant manufacturing dichloroaniline derivatives. Comedones developed 6-12 weeks after accidental exposure to the chloracnegenic contaminants and were present in every case. Cutaneous xerosis and a folliculitis, previously only rarely described as manifestations of chloracne, were noted in half the patients. The pathogenesis of these lesions is uncertain but may involve a disorder of keratinization.

L-tryptophan-induced eosinophilia-myalgia syndrome associated with primary cutaneous malignant fibrous histiocytoma and extraabdominal desmoid tumor

A 57-year-old woman with L-tryptophan-induced eosinophilia-myalgia syndrome, 23 months after the onset of symptoms, experienced development of a parasternal malignant fibrous histiocytoma on previously scleroderma-like skin areas and, almost concurrently, an extraabdominal desmoid tumor of the left arm muscle fascia. The malignant fibrous histiocytoma was treated by surgical excision without sign of recurrence or metastasis 19 months later. Radiation therapy was performed on the extraabdominal desmoid tumor. We suspect that these two connective tissue tumors in this patient were related to the exposure to contaminated L-tryptophan, which interfered with connective tissue metabolism.

Decontamination of human skin exposed to 2,3,7,8-tetrachlorodibenzo-p-Dioxin (TCDD) in vitro

Human post-mortem skin was exposed in vitro to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at 32 degrees C, under controlled humidity. In one-half of the samples, damage to the surface of the skin was simulated by stripping of the stratum corneum. After incubation with TCDD for 100 min, four different decontamination protocols were performed: (1) the sample was wiped with dry, adsorbent material (cotton balls); (2) a 10-min topical treatment with mineral oil was followed by dry wiping with cotton balls; (3) a 10-min topical treatment with mineral oil was followed by wiping with acetone-soaked cotton balls; and (4) the sample was washed with water and soap. After decontamination, skin samples were incubated (up to 300 min) again at 32 degrees C. One set of both intact and stripped TCDD-exposed skin samples was incubated for 300 min--absent decontamination--and was used as a control. Mineral oil treatment and acetone wipes, or water and soap, were effective in reducing (i.e., about two-fold) the amount of TCDD in the stratum corneum of intact skin. Mineral oil plus dry wipes reduced the amount of TCDD in the stratum corneum by about one-third, whereas dry wiping alone was ineffective. All protocols, however, were similarly effective in reducing the amount of TCDD in the epidermis and upper dermis; TCDD concentrations were decreased locally by factors of up to ten. In the lower dermis, a minimal effect of the decontamination procedures was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Chloracne from pentachlorophenol-preserved wood

A patient is presented who developed chloracne after exposure to lumber which was pressure-treated with pentachlorophenol (PCP). It was presumed that his disease arose via percutaneous absorption of polychlorinated aromatic compounds (dioxins and furans) which are known to contaminate technical grade PCP. The patient's condition improved after treatment with oral isotretinoin.

Chloracne and chloracnegens

Chloracne, an acneform eruption resulting from poisoning by halogenated aromatic compounds, has been a considerable problem over the last 40 years. The condition is always a symptom of systemic poisoning and should be familiar to all practitioners, particularly dermatologists. It is difficult to treat and can last for long periods without known additional exposure to chloracnegens. Some chloracnegens are capable of causing a variety of systemic signs and symptoms and may be oncogenic. Although there are probably fewer than 4,000 persons with chloracne worldwide, those found with the disorder should be evaluated medically on a regular basis and followed, if possible, throughout their lives.