Comparative chemical and biological analysis of coal tar-based therapeutic agents to other coal-derived materials

The Role of KEAP1-NRF2 System in Atopic Dermatitis and Psoriasis

The Kelch-like erythroid cell-derived protein with cap‘n’collar homology-associated protein 1 (KEAP1)-nuclear factor erythroid-2-related factor 2 (NRF2) system, a thiol-based sensor-effector apparatus, exerts antioxidative and anti-inflammatory effects and maintains skin homeostasis. Thus, NRF2 activation appears to be a promising treatment option for various skin diseases. However, NRF2-mediated defense responses may deteriorate skin inflammation in a context-dependent manner. Atopic dermatitis (AD) and psoriasis are two common chronic inflammatory skin diseases caused by a defective skin barrier, dysregulated immune responses, genetic predispositions, and environmental factors. This review focuses on the role of the KEAP1-NRF2 system in the pathophysiology of AD and psoriasis and the therapeutic approaches that utilize this system.

Aryl Hydrocarbon Receptors: Evidence of Therapeutic Targets in Chronic Inflammatory Skin Diseases

The aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor, is important for xenobiotic metabolism and binds to various endogenous and exogenous ligands present in the skin. AhR is known to be associated with diseases in various organs; however, its functions in chronic inflammatory skin diseases, such as atopic dermatitis (AD) and psoriasis (PS), have recently been elucidated. Here, we discuss the molecular mechanisms of AhR related to chronic inflammatory skin diseases, such as AD and PS, and the mechanisms of action of AhR on the skin immune system. The importance of AhR molecular biological pathways, clinical features in animal models, and AhR ligands in skin diseases need to be investigated. In conclusion, the therapeutic effects of AhR ligands are demonstrated based on the relationship between AhR and skin diseases. Nevertheless, further studies are required to elucidate the detailed roles of AhR in chronic inflammatory skin diseases.

Coal tar induces AHR-dependent skin barrier repair in atopic dermatitis

Topical application of coal tar is one of the oldest therapies for atopic dermatitis (AD), a T helper 2 (Th2) lymphocyte-mediated skin disease associated with loss-of-function mutations in the skin barrier gene, filaggrin (FLG). Despite its longstanding clinical use and efficacy, the molecular mechanism of coal tar therapy is unknown. Using organotypic skin models with primary keratinocytes from AD patients and controls, we found that coal tar activated the aryl hydrocarbon receptor (AHR), resulting in induction of epidermal differentiation. AHR knockdown by siRNA completely abrogated this effect. Coal tar restored filaggrin expression in FLG-haploinsufficient keratinocytes to wild-type levels, and counteracted Th2 cytokine-mediated downregulation of skin barrier proteins. In AD patients, coal tar completely restored expression of major skin barrier proteins, including filaggrin. Using organotypic skin models stimulated with Th2 cytokines IL-4 and IL-13, we found coal tar to diminish spongiosis, apoptosis, and CCL26 expression, all AD hallmarks. Coal tar interfered with Th2 cytokine signaling via dephosphorylation of STAT6, most likely due to AHR-regulated activation of the NRF2 antioxidative stress pathway. The therapeutic effect of AHR activation herein described opens a new avenue to reconsider AHR as a pharmacological target and could lead to the development of mechanism-based drugs for AD.

Screening-level population risk assessment of nasal tumors in the US due to naphthalene exposure

Several naphthalene Unit Risk Factors (URFs) were proposed by the US Environmental Protection Agency in 2004 using data on the development of olfactory epithelial neuroblastomas and nasal respiratory epithelial adenomas in rats, but these URFs may be inappropriate and unnecessarily conservative for estimating human cancer risks. The purpose of the present exercise was to perform a screening-level population risk assessment of the US population to compare the observed number of naphthalene-induced nasal tumors in the US to the number that would be predicted if the URFs for naphthalene were as proposed. Nine scenarios were evaluated to represent the range of exposures individuals have typically experienced. Results indicate that the total predicted burden of naphthalene-induced nasal tumors per year in the US (65,905 rare nasal tumors, of which 29,121 are olfactory epithelial neuroblastomas) is much greater than the number of these tumors actually observed per year (910 total nasal tumors, of which 66 are olfactory neuroblastomas) over the period 1973-2006. This suggests that using rat nasal tumor data to derive a naphthalene URF for humans should be re-evaluated.

Final safety assessment of Coal Tar as used in cosmetics

Coal Tar is a semisolid by-product obtained in the destructive distillation of bituminous coal, which functions in cosmetic products as a cosmetic biocide and denaturant--antidandruff agent is also listed as a function, but this is considered an over-the-counter (OTC) drug use. Coal Tar is a nearly black, viscous liquid, heavier than water, with a naphthalene-like odor and a sharp burning taste, produced in cooking ovens as a by-product in the manufacture of coke. Crude Coal Tar is composed of 48% hydrocarbons, 42% carbon, and 10% water. In 2002, Coal Tar was reported to the Food and Drug Administration (FDA) to be used in four formulations, all of which appear to be OTC drug products. Coal Tar is monographed by the FDA as Category I (safe and effective) OTC drug ingredient for use in the treatment of dandruff, seborrhoea, and psoriasis. Coal Tar is absorbed through the skin of animals and humans and is systemically distributed. In short-term studies, mice fed a diet containing Coal Tar found it unpalatable, but no adverse effects were reported other than weight loss; rats injected with Coal Tar experienced malaise in one study and decreased water intake and increased liver weights in another; rabbits injected with Coal Tar residue experienced eating avoidance, respiratory difficulty, sneezing, and weight loss. In a subchronic neurotoxicity study using mice, a mixture of phenols, cresols, and xylenols at concentrations approximately equal to those expected in Coal Tar extracts produced regionally selective effects, with a rank order of corpus striatum > cerebellum > cerebral cortex. Coal Tar applied to the backs of guinea pigs increases epidermal thickness. Painting female rabbits with tar decreases the absolute and relative weights of the ovaries and decreased the number of interstitial cells in the ovary. Four therapeutic Coal Tar preparations used in the treatment of psoriasis were mutagenic in the Ames assay. Urine and blood from patients treated with Coal Tar were genotoxic in bacterial assays. Coal Tar was genotoxic in a mammalian genotoxicity assay and induced DNA adducts in various tissue types. Chronic exposure of mice to Coal Tar significantly decreased survival and liver neoplasms were seen in a significant dose-related trend; in other studies using mice lung tumors and perianal skin cancers were found. Coal Tar was comedogenic in three small clinical studies. Folliculitis is associated with the prolonged use of some tars. Several published reports describe cases of contact sensitivity to Coal Tar. Polycyclic aromatic hydrocarbons, which make up Coal Tar, are photosensitizers and cause phototoxicity by an oxygen-dependent mechanism. A retrospective study of the reproductive toxicity of Coal Tar in humans compared exposed women to controls and found little difference in spontaneous abortion and congenital disorders. Cancer epidemiology studies of patients who have received Coal Tar therapy of one form or other have failed to link treatment with an increase in the risk of cancer. Although the Cosmetic Ingredient Review (CIR) Expert Panel believes that Coal Tar use as an antidandruff ingredient in OTC drug preparations is adequately addressed by the FDA regulations, the Panel also believes that the appropriate concentration of use of Coal Tar in cosmetic formulations should be that level that does not have a biological effect in the user. Additional data needed to make a safety assessment include product types in which Coal Tar is used (other than as an OTC drug ingredient), use concentrations, and the maximum concentration that does not induce a biological effect in users.

In vitro toxicity of 7H-dibenzo[c,g]carbazole in human liver cell lines

7H-Dibenzo[c,g]carbazole (DBC) is a model N-heterocyclic aromatic compound (NHA) which is both a hepatotoxin and hepatocarcinogen in rodents. The focus of this investigation was to determine whether human liver cell lines display differential sensitivities to DBC-induced toxicity. Treatment of cell lines with increasing DBC concentrations produced apoptosis only in HepG2 cells. Although DBC inhibited the clonogenic growth of all cell lines at high concentrations, only the survival of HepG2 cells was reduced at lower concentrations. DBC inhibited DNA synthesis in two (HepG2, HLF) of the three cell lines at lower concentrations and was effective only at a high concentration in Mahlavu cells. Differences in DBC uptake were not observed in any of the cell lines, suggesting that bioavailability was not a limiting factor. DBC-DNA adducts were not detected in HLF or Mahlavu cells at either low or high concentrations of DBC. Consistent with the DNA adduct data, RP-HPLC analysis indicated that DBC was metabolized to a lesser degree in the HLF and Mahlavu cells. These results suggest that human liver cell lines differ markedly in the ability to metabolize DBC to toxic species and that DBC-induced apoptosis is only observed in cells that produce detectable metabolites and DBC-DNA adducts.

A comparison of apoptosis and necrosis induced by hepatotoxins in HepG2 cells

7H-Dibenzo[c,g]carbazole (DBC), an N-heterocyclic aromatic hydrocarbon, is cytotoxic and carcinogenic in rodent liver. While DBC leads to necrotic lesions in the liver, the induction of apoptosis by DBC has not been investigated. The focus of this study was to determine the degree to which apoptosis and necrosis contributed to DBC cytotoxicity in a human hepatoma cell line (HepG2). To determine if these effects were unique to DBC, the results were compared to another hepatotoxin, aflatoxin B(1) (AFB(1)). DBC produced a distinct biphasic LDH release curve within 24 h of exposure. During the same time period lower concentrations of DBC (<10 microM) induced the formation of DBC-DNA adducts and increased p53 protein levels followed by apoptotic cell death. However, increasing the concentration of DBC to 80 microM led to lower DNA adduct and p53 protein levels. At this concentration, intracellular ATP levels were rapidly depleted followed by cell swelling and loss of membrane integrity consistent with necrotic cell death. In contrast to DBC, a biphasic LDH release curve was not observed for AFB(1). Instead, AFB(1) induced a concentration-dependent increase in apoptosis that reached two- to threefold higher levels than DBC. These results suggest that differences exist in the extent and type of cell death induced by DBC and AFB(1) at equimolar concentrations. Apoptosis and necrosis result from low and high concentrations of DBC, respectively, and may be dependent upon intracellular ATP levels.

Biodegradation of carbazole by Ralstonia sp. RJGII.123 isolated from a hydrocarbon contaminated soil

The use of microorganisms for bioremediation of contaminated soils may be enhanced with an understanding of the pathways involved in their degradation of hazardous compounds. Ralstonia sp. strain RJGII.123 was isolated from soil located at a former coal gasification plant, based on its ability to mineralize carbazole, a three-ring N-heterocyclic pollutant. Experiments were carried out with strain RJGHII.123 and 14C-carbazole (2 mg/L and 500 mg/L) as the sole organic carbon source. At 15 days, 80% of the 2 mg/L carbazole was recovered as CO2, and <1% remained as undegraded carbazole, while 24% of the 500 mg/L carbazole was recovered as CO2 and approximately 70% remained as undegraded carbazole. Several stable intermediates were formed during this time. These intermediates were separated by high performance liquid chromatography (HPLC) and were characterized using high resolution mass spectroscopy (HR-MS) and gas chromatography - mass spectroscopy (GC-MS). At least 10 ring cleavage products of carbazole degradation were identified; four of these were confirmed as anthranilic acid, indole-2-carboxylic acid, indole-3-carboxylic acid, and (1H)-4-quinolinone by comparison with standards. These data indicate that strain RJGII.123 shares aspects of carbazole degradation with previously described Pseudomonas spp., and may be useful in facilitating the bioremediation of NHA from contaminated soils.

Comparative carcinogenicity, metabolism, mutagenicity, and DNA binding of 7H-dibenzo[c,g]carbazole and dibenz[a,j]acridine

Complex mixtures that are produced from the combustion of organic materials have been associated with increased cancer mortality. These mixtures contain homocyclic and heterocyclic polycyclic aromatic hydrocarbons (PAHs), many of which are known carcinogens. In particular, N-heterocyclic aromatic compounds (NHA) are present in these mixtures. Studies to determine the metabolic activation of these compounds have been undertaken. The purpose of this review is to compare and contrast the metabolic activation and biological effects of two NHA, 7H-dibenzo[c,g]carbazole (DBC) and dibenz[a,j]acridine (DBA), in order to better assess the contribution of NHA to the carcinogenic potency of complex mixtures and to develop biomarkers of the carcinogenic process. DBC has both local and systemic effects in the mouse; it is a potent skin and liver carcinogen following topical application and a lung carcinogen following i.p. application. On the other hand, DBA is a moderate mouse skin carcinogen following topical application and a lung carcinogen following subcutaneous injection. The biological differences for DBC and DBA are reflected in target organ-specific proximate and mutagenic metabolites and DNA adduct patterns.

Toxicology of coal liquefaction products: an overview

Repeated exposure to coal liquefaction products produces a broad range of systemic effects. Among these, growth suppression, anaemia, leucocytosis and other haematological disorders are most prominent. Bone marrow, liver and kidney are the target organs affected by treatment. The effects are more severe with heavy distillates and male rats are more sensitive than females. Other changes included increased serum transaminases, alkaline phosphatase and cholesterol. Depending on the route of administration, the skin or lung may also be affected. Inhalation exposure produces the most severe changes, and oral exposure the least. Distillates containing N-PAHs and sulphur-containing PAHs are also more biologically active. Teratological effects were only observed if animals were exposed to the heavy distillate. Similarly, heavy distillates have mutagenic or carcinogenic properties. Teratological effects, as well as mutagenicity and carcinogenicity, of the coal liquefaction distillates seem to be linked to their PAH content, especially the N-PAHs. From the data presented in this review, it should become evident that the potential effects of coal liquefaction products on human health could be severe, especially with long-term exposure. Limited information exists on the occupational effects to coal liquefaction materials because most of the work to date has been with pilot plants. Careful and good judgement is required in order to extrapolate data from pilot plants to commercial-scale production. Experience in health effects of workers in the petroleum industry and coke-oven operations can serve as a guide for the implementation of industrial hygiene programmes for coal liquefaction operations. These programmes include engineering controls, health education, personal monitoring and hygienic practices, medical surveillance and long-term epidemiology studies, and they should be implemented to make coal liquefaction a healthy and environmentally sustainable industry.

Comparative tumor-initiating ability of 7H-dibenzo(c,g)carbazole and dibenz(a,j)acridine in mouse skin

N-heterocyclic aromatics are environmentally important carcinogenic pollutants produced by incomplete combustion of organic material. 7H-Dibenzo-(c,g)carbazole (DBC), is a potent skin and systemic carcinogen, whereas dibenz(a,j)acridine (DBA), is a carcinogen with local effects. Therefore, the overall objective of these studies was to determine the initiating ability of DBC and DBA in mouse skin using an initiation-promotion protocol. Acetone-, TPA- or BaP-treated animals were used as negative and positive controls, respectively. DBC, DBA or BaP (200 nmol) dissolved in acetone was applied once to the backs of thirty shaved Hsd:(ICR)Br female mice, followed 2 weeks later with 2 micrograms of TPA in 50 microliters of acetone applied twice a week for up to 24 weeks. Skin tumors developed in 26, 17 and 27 animals, respectively. DBC plus TPA produced a significant influx of dermal macrophages similar to that seen for BaP. Initiation with BaP, DBC or DBA moderated the effect of TPA on most other dermal parameters, particularly neutrophils. These data indicate that, DBC, with apparently different activation pathways than BaP shows similar tumor initiating ability and morphological changes as BaP.

Comparative carcinogenic potencies of 7H-dibenzo[c,g]carbazole, dibenz[a,j]acridine and benzo[a]pyrene in mouse skin

The relative carcinogenic potencies of three combustion products of fossil fuels, 7H-dibenzo[c,g]carbazole (7H-DB[c,g]C), dibenz[a,j]acridine (DB[a,j]A) and benzo[a] pyrene (B[a]P) were compared using complete carcinogenicity C3H mouse skin bioassays. Both 7H-DB[c,g]C and B[a]P produced tumors in 48 of 50 mice with latency periods of 36.6 and 32.4 weeks, respectively. DB[a,j]A produced tumors in 25 of 50 mice with a latency period of 80 weeks. 7H-DB[c,g]C was found to be as potent a carcinogen as B[a]P when applied to mouse skin. These results have important implications in the determination of relative carcinogenic potencies of complex mixtures.

Benzo(a)pyrene diol epoxide-I-DNA adduct formation in the epidermis and lung of SENCAR mice following topical application of crude coal tar

The levels of benzo[a]pyrene diol epoxide-I-deoxyguanosine (BPDE-I-dG) adduct formation in epidermis and lung of SENCAR mice following the topical application of benzo[a]pyrene (BP) alone, crude coal tar (CCT) alone, and the two combined were determined in an enzyme linked immunosorbent (ELISA) assay using monoclonal antibodies. Topical application of two doses of BP (20 micrograms) at 72-h intervals, with sacrifice 24 h later resulted in the formation of 197 fmol and 205 fmol BPDE-I-dG adducts per mg DNA in epidermis and lung, respectively. Topical application of 0.5 ml CCT alone resulted in the formation of 278 fmol and 410 fmol BPDE-I-dG adducts per mg DNA in epidermis and lung, respectively. Simultaneous topical application of 20 micrograms BP and CCT (0.1-0.5 ml) resulted in substantially lower BPDE-I-dG adducts in the epidermis as well as in the lung. Our results suggest that CCT may contain inhibitors of carcinogen-DNA adduct formation and that topical application of CCT produces greater effects on DNA-adduct formation in lung than in epidermis. Thus the cancer-causing potency of the polycyclic aromatic hydrocarbons (PAHs) in CCT may be reduced by other anticarcinogenic constituents present in CCT and systemic absorption of carcinogenic PAHs in CCT applied to skin might have tumorigenic effects in other tissues.