LncRNA Meg3-mediated regulation of the Smad pathway in atRA-induced cleft palate.

Palatal mesenchymal cell proliferation is essential to the process of palatogenesis, and the proliferation of mouse embryonic palate mesenchymal (MEPM) cells is impacted by both all-trans retinoic acid (atRA) and the TGF-ß/Smad signaling pathway. The long non-coding RNA (lncRNA) MEG3 has been shown to activate TGF-ß/Smad signaling and to thereby regulate cell proliferation, differentiation, and related processes. Herein, we found that atRA treatment (100 mg/kg) promoted Meg3 upregulation in MEPM cells, and that such upregulation was linked to the suppression of MEPM cell proliferation in the context of secondary palate fusion on gestational day (GD) 13 and 14. Moreover, the demethylation of specific CpG sites within the lncRNA Meg3 promoter was detected in atRA-treated MEPM cells, likely explaining the observed upregulation of this lncRNA. Smad signaling was also suppressed by atRA treatment in these cells, and RNA immunoprecipitation analyses revealed that Smad2 can directly interact with Meg3 in MEPM cells following atRA treatment. Therefore, we propose a model wherein Meg3 is involved in the suppression of MEPM cell proliferation, functioning at least in part via interacting with the Smad2 protein and thereby suppressing Smad signaling in the context of atRA-induced cleft palate.

Behavioral and biochemical effects of the antifouler and antidandruff zinc pyrithione on the freshwater fish Gambusia holbrooki.

The presence of pharmaceutical residues in the aquatic environment is receiving great attention since the levels of these substances have significantly increased in this compartment, potentially leading to adverse ecological effects. Zinc pyrithione (ZnPt) is a widely used organometallic biocide, which is incorporated into antifouling formulas, such as paints, to prevent the establishment of biofilms on surfaces exposed to the aquatic environment. It is also used in cosmetics, such as antidandruff shampoos and soaps. Considering this wide use, and the absence of a significant amount of data on the toxicity of ZnPt especially towards non-target organisms, the objective of this study was to characterize the toxicity of ZnPt, on several ecological relevant endpoints assessed in the fish Gambusia holbrooki. For this purpose, we measured traits related to feeding and aggressive behavior, as well as indicators of oxidative stress (CAT and GSTs), neurotoxicity (AChE), and anaerobic metabolism (LDH), after acute and chronic exposures to ZnPt. In terms of behavioral features, the feeding test showed the occurrence of significant differences between the control animals and those exposed to a concentration of ZnPt of 45 µg/L. In addition, ZnPt caused changes in terms of oxidative stress biomarkers (CAT and GSTs), for both exposure periods. ZnPt was also capable of causing changes in the cholinergic neurotransmission functioning and anaerobic metabolism, but only following the chronic exposure.

Mitochondrial dysfunction is implicated in retinoic acid-induced spina bifida aperta in rat fetuses.

Neural tube defects (NTDs) are the most common and severe congenital malformations, which result from failure of the neural tube to close during embryonic development. The etiology of NTDs is complex, caused by interactions between genetic defects and environmental factors, but the exact mechanisms of this disease are still not fully understood. We herein employ a Seahorse Bioscience microplate-based extracellular flux (XF) analyzer to determine mitochondrial function and quantify respiratory coupling to various bioenergetic functions using specific pharmacological inhibitors of bioenergetic pathways. We demonstrate that changes in coupling between ATP turnover and proton leak are correlated with NTDs. Further, we determined that the ATP content and oxidative stress levels in posterior spinal cords of rat embryos with NTDs between E11 and E14 was lower than that of normal controls. The present study reveals that mitochondrial dysfunction is associated with all-trans retinoic acid (atRA)-induced NTDs in rat embryos. Oxidative stress results from decreased antioxidant enzyme activity. This study provides a novel viewpoint for exploring the embryonic pathogenesis of atRA-induced NTDs.

Acute toxic responses of embryo-larval zebrafish to zinc pyrithione (ZPT) reveal embryological and developmental toxicity.

Zinc pyrithione (ZPT) is widely used in industrial and human daily life, due to its broad antimicrobial spectrum activity. Persistent accumulation of ZTP in the aquatic environment and bioaccumulation in the living organisms attracts more and more attention. However, only very limited information is available so far for the evaluation of systematic toxicity effects of ZPT on multiple organs development. This study intends to deepen our knowledge about the potential toxicity elicited by ZPT by assessing its acute effects on zebrafish (Danio rerio) through morphological, histological and molecular investigations. It has been verified that ZPT exhibits a broad spectrum of toxicity which causes growth retardation and tissue pathological and physiology alternations in heart, liver, eye, notochord, kidney and other organisms of zebrafish. The acute toxicity values of LC50 (95% CI) 96-h is calculated as 0.073 µM. Furthermore, the organ toxicity was verified due to up-regulation of expression of biomarker genes related to organ function and development. In sum, this study demonstrats systematic acute embryological and developmental toxicity of the ZPT on zebrafish embryos/larvae.

Recent advances in toxicological testing of the stratum corneum.

α-Hydroxy acid (AHA) formulations are commonly used for skin chemical peelings. The primary target is the stratum corneum (SC). The aim of this study was to assess the effects of various glycolic acid concentrations and commercial phenolic acid formulations on the SC. Quantitative colorimetry of a corneoxenometry bioassay was used. The test procedure involved glycolic acid concentrations ranging from 3% to 70% in alcoholic solution. Exposure times were set for 1 min and 3 min. The bioassay showed consistent reactivity with a dose-effect relationship when using the selected low exposure times. In a similar procedure the aggressiveness of commercially available phenolic acid formulations was identified not using hazardous in vivo testing. Corneoxenometry appears useful for in vitro testing of AHA peeling agents during short exposure times.

Cytotoxic and genotoxic effects of acitretin, alone or in combination with psoralen-ultraviolet A or narrow-band ultraviolet B-therapy in psoriatic patients.

Acitretin is currently used alone or combined with PUVA (psoralen + UVA) or with narrow-band ultraviolet B (NBUVB), to treat moderate and severe psoriasis. However, little is known about the potential genotoxic/carcinogenic risk and the cytostatic/cytotoxic effects of these treatments. Our aim was to study the cytotoxic and genotoxic effects of acitretin - alone or in combination with PUVA or NBUVB - by performing studies with blood from patients with psoriasis vulgaris who were treated with acitretin, acitretin+PUVA or acitretin+NBUVB for 12 weeks, and in vitro studies with blood from healthy volunteers, which was incubated with acitretin at different concentrations. The cytotoxic and genotoxic effects were evaluated by the cytokinesis-blocked micronucleus test and the comet assay. Our results show that psoriatic patients treated with acitretin alone or with acitretin+NBUVB, did not show genotoxic effects. In addition, these therapies reduced the rate of proliferation and induced apoptosis and necrosis of lymphocytes; the same occurred with lymphocyte cultures incubated with acitretin (1.2-20µM). The acitretin+PUVA reduced also the proliferation rate, and increased the necrotic lymphocytes. Our studies suggest that therapy with acitretin alone or combined with NBUVB, as used in psoriatic patients, does not show genotoxic effects, reduces the rate of proliferation and induces apoptosis and necrosis of lymphocytes. The combination of acitretin with PUVA also reduces the proliferation rate and increases the number of necrotic lymphocytes. However, as it induced slight genotoxic effects, further studies are needed to clarify its genotoxic potential.

The effects of alcohol on the metabolism and toxicology of anti-psoriasis drugs.

INTRODUCTION: Alcohol has long been suspected to be a triggering and precipitating factor of psoriasis. Alcohol misuse is common in patients with moderate-to-severe psoriasis and appears to impair treatment outcome. AREAS COVERED: In this article, the authors review the available data regarding the metabolic and toxicological interactions between anti-psoriasis systemic drugs and ethanol and/or alcoholic beverages. Special attention is given to the influence of alcohol consumption on the hepatotoxic risk of some anti-psoriasis drugs. The article was prepared using a MEDLINE literature search. EXPERT OPINION: The available knowledge highlights the existence of a few significant pharmacological interactions, such as the reduced exposure to cyclosporine by red wine, the possible increase of cyclosporine levels following a heavy acute alcohol intake, and, especially, the conversion of acitretin to etretinate, in the presence of ethanol, with important implications in females of child-bearing potential. There are limited data on the contributing role of alcohol in the hepatotoxicity induced by some anti-psoriasis drugs and the existing information on this topic is still controversial. However, further investigation is needed to assess the relevance of interactions between alcohol consumption and drug therapy for psoriasis, under both pharmacological and toxicological perspectives. Long-term prospective studies on large cohorts of patients are warranted to disclose the actual significance of such potential interactions in clinical practice.

Synergistic phototoxic effects of glycolic acid in a human keratinocyte cell line (HaCaT).

BACKGROUND: Glycolic acid (GA) has been widely used in cosmetic agents and superficial chemical peeling in recent years. It has long been concerned that UV irradiation would enhance the photosensitivity of GA on human skin. Therefore, it is mandatory to explore the biologic effects of concomitant exposure of GA and UV irradiation in human keratinocytes. OBJECTIVE: The aim of the study is to explore the effects of concomitant exposure of GA and UVB in a human keratinocyte cell line (HaCaT). METHODS: We used HaCaT to investigate the effects of GA (5mM), UVB (50mJ/cm(2)), and co-treatment with GA and UVB (GA+UVB) in human keratinocytes. We used a phase contrast microscope to observe morphological changes of the cells, and employed flow cytometry to detect cell viability, cell cycle, and mitochondrial membrane potential (MMP), and intracellular reactive oxygen species (ROS) levels. Cell damage was detected by DAPI stain, and Western blot was used to detect the activities of apoptosis- related and cycle checkpoint-related proteins such as Bax, Bcl-2, caspases-3, -4, -9, Endo G, AIF, and p21, p27, p53, cdk2, cyclin E, cyclin A. RESULTS: We found that either GA or UVB alone had inhibitory effect on cell proliferation, and co-treatment with GA and UVB had synergistic anti-proliferative effect. GA alone did not affect the cell cycle, and UVB induced HaCaT cells accumulated at S phase, and co-treatment with GA and UVB arrested cells at S phase more prominently. Moreover, all the treatment with GA, UVB, and GA+UVB in HaCaT cells induced apoptosis. We further demonstrated that GA had synergistic apoptotic effect in human keratinocytes. GA and UVB both had effects on the decline of MMP and increase of ROS release, and GA had synergistic increase in the level of ROS in UVB-treated HaCaT cells. Besides, co-treatment with GA and UVB had synergistic effect on apoptosis through the over-expressions of Bax, p21, p53, caspases-3, -4, -9, Endo G and AIF, and confocal microscopy disclosed translocation of AIF and Endo G from cytoplasm to the nucleus. Therefore, apoptosis induced by co-treatment by GA+UVB was initiated and executed by multiple pathways including mitochondria- and ER-dependent, and caspase-dependent and caspase-independent pathways. CONCLUSION: We demonstrated that GA, UVB, GA+UVB inhibited proliferation and induced apoptosis in HaCaT cells. The mechanisms of apoptosis induced by co-treatment of GA and UVB involve multiple pathways. The synergistic photo-toxicity may be related to cell cycle arrest and apoptosis in UVB-treated HaCaT cells. These results highlight the potential adverse effects of GA-containing cosmetic agents on human skin.

Effect of genetic polymorphism of GSTM1 and GSTT1 genotypes on cytogenetic biomarkers among coaltar workers.

Chromosomal aberrations (CAs) in peripheral blood lymphocytes and micronuclei (MN) in exfoliated buccal cells have been used for decades as cytogenetic biomarkers to investigate genotoxicity among occupationally or environmentally exposed population. In our study, we investigated the association of increased cytogenetic damage with genetic polymorphism in glutathione-S transferase genotypes among occupationally exposed 115 coaltar workers and 105 unexposed controls. We found higher mean value of chromosome aberrations (chromatid type-2.01±1.76; chromosomal type-2.22±1.73) and buccal micronuclei (BMN-7.10±1.56) in exposed subjects when compared to referents (chromatid type-0.82±.51; chromosomal type-0.87±.54; BMN-5.09±2.88). We observed that individuals having null genotype of GSTM1 and GSTT1 have significantly higher frequency of CAs and MN. Despite of small sample size, our findings suggest a significant association between polymorphism of glutathione-S transferase genotypes and cytogenetic biomarkers which are considered as early effects of genotoxic carcinogens.

Stress responses of human dermal fibroblasts exposed to zinc pyrithione.

Zinc pyrithione is used as a topical agent in a range of medicinal and cosmetic applications. Despite its extensive use and reported beneficial effects in treatment of various dermal problems, its potential toxicity towards skin cells remains relatively underexplored. In this work we investigated effects of nM zinc pyrithione on cell stress response pathways of primary human skin fibroblasts during 24h of exposure. We demonstrate that zinc pyrithione-induced cytotoxity in dermal fibroblasts is dose-dependent and it associates with increased intracellular zinc concentrations and activated stress response pathways including p53 and stress kinase p38. Higher zinc pyrithione concentrations (500nM and above) stimulate oxidative stress and moderate DNA damage which occur in the presence of activated p38 kinase. Cells further upregulate the expression of p53 which increases its transcriptional activity while mitogenic signaling exemplified by mTOR (mammalian target of rapamycin) expression is suppressed and these steps lead to mitochondrial, caspase-dependent apoptosis. Conversely, lower zinc concentrations (125nM) fail to induce oxidative stress and significant DNA damage; however, treated cells still activate p38 and upregulate the expression and transcriptional activity of p53 and its target gene p21 as well as the expression of p16 in the presence of active mTOR pathway and a changed DNA methylation pattern. The end result is premature senescence phenotype. Specific pharmacological inhibitors as well as gene knockdown technology prove that an interaction between p38, p53 and mTOR might be responsible for these observed endpoints. Taken together, exposure of dermal fibroblasts to varying concentrations of zinc pyrithione may result in either cell death-apoptosis or cellular premature senescence which attests to the ability of this compound to affect this type of cells in an in vitro model system.

Influence of trichloroacetic acid peeling on the skin stress response system.

Although trichloroacetic acid (TCA) peeling is widely applied for cosmetic treatment of photodamaged skin, the entire biological mechanisms have yet to be determined. The skin stress response system (SSRS) involves corticotropin-releasing hormone (CRH) and proopiomelanocortin (POMC) products that are locally-generated in response to locally-provided stressors or pro-inflammatory cytokines. This system would restrict tissue damage and restore local homeostasis. To determine the influence of TCA peeling on the SSRS in vitro and in vivo, expressions of POMC, melanocortin receptor 1 (MC1R), CRH and CRH receptor 1 (CRHR1) mRNA were examined by reverse transcription polymerase chain reaction in Pam212 murine keratinocytes, murine plantar and healthy human abdominal skin specimens after TCA treatment. In addition, their protein expressions as well as those of POMC-derived peptides were examined immunohistochemically. After TCA treatment, transient upregulation of POMC and MC1R mRNA expressions was observed in both murine and human skin, as well as in Pam212. Enhanced POMC protein, recovery of once-impaired MC1R protein, and no enhancement of POMC-derived peptide productions were revealed immunohistochemically in both murine and human epidermis. In contrast, neither expression levels of CRH and CRHR1 mRNA nor epidermal protein were enhanced after TCA application in murine and human skin, except for induction of human CRH mRNA expression. These results suggest that TCA activates the SSRS by inducing POMC and MC1R productions of keratinocytes in the CRH-independent manner, and that the biological effects of POMC itself are responsible for the TCA-induced epidermal SSRS activation.

Irreversible effects of retinoic acid pulse on Xenopus jaw morphogenesis: new insight into cranial neural crest specification.

Jaws are formed by cephalic neural crest (CNCCs) and mesodermal cells migrating to the first pharyngeal arch (PA1). A complex signaling network involving different PA1 components then establishes the jaw morphogenetic program. To gather insight on this developmental process, in this study, we analyze the teratogenic effects of brief (1-15 min) pulses of low doses of retinoic acid (RA: 0.25-2 µM) or RA agonists administered to early Xenopus laevis (X.l.) embryos. We show that these brief pulses of RA cause permanent craniofacial defects specifically when treatments are performed during a 6-hr window (developmental stages NF15-NF23) that covers the period of CNCCs maintenance, migration, and specification. Earlier or later treatments have no effect. Similar treatments performed at slightly different developmental stages within this temporal window give rise to different spectra of malformations. The RA-dependent teratogenic effects observed in Xenopus can be partially rescued by folinic acid. We provide evidence suggesting that in Xenopus, as in the mouse, RA causes craniofacial malformations by perturbing signaling to CNCCs. Differently from the mouse, where RA affects CNCCs only at the end of their migration, in Xenopus, RA has an effect on CNCCs during all the period ranging from their exit from the neural tube until their arrival in the PA1. Our findings provide a conceptual framework to understand the origin of individual facial features and the evolution of different craniofacial morphotypes.

The topical antimicrobial zinc pyrithione is a heat shock response inducer that causes DNA damage and PARP-dependent energy crisis in human skin cells.

The differentiated epidermis of human skin serves as an essential barrier against environmental insults from physical, chemical, and biological sources. Zinc pyrithione (ZnPT) is an FDA-approved microbicidal agent used worldwide in clinical antiseptic products, over-the-counter topical antimicrobials, and cosmetic consumer products including antidandruff shampoos. Here we demonstrate for the first time that cultured primary human skin keratinocytes and melanocytes display an exquisite vulnerability to nanomolar concentrations of ZnPT resulting in pronounced induction of heat shock response gene expression and impaired genomic integrity. In keratinocytes treated with nanomolar concentrations of ZnPT, expression array analysis revealed massive upregulation of genes encoding heat shock proteins (HSPA6, HSPA1A, HSPB5, HMOX1, HSPA1L, and DNAJA1) further confirmed by immunodetection. Moreover, ZnPT treatment induced rapid depletion of cellular ATP levels and formation of poly(ADP-ribose) polymers. Consistent with an involvement of poly(ADP-ribose) polymerase (PARP) in ZnPT-induced energy crisis, ATP depletion could be antagonized by pharmacological inhibition of PARP. This result was independently confirmed using PARP-1 knockout mouse embryonic fibroblasts that were resistant to ATP depletion and cytotoxicity resulting from ZnPT exposure. In keratinocytes and melanocytes, single-cell gel electrophoresis and flow cytometric detection of gamma-H2A.X revealed rapid induction of DNA damage in response to ZnPT detectable before general loss of cell viability occurred through caspase-independent pathways. Combined with earlier experimental evidence that documents penetration of ZnPT through mammalian skin, our findings raise the possibility that this topical antimicrobial may target and compromise keratinocytes and melanocytes in intact human skin.

Genotoxic hazard and cellular stress in pediatric patients treated for psoriasis with the Goeckerman regimen.

The Goeckerman regimen (GR) represents a local treatment of psoriasis and includes topical dermal application of crude coal tar (containing polycyclic aromatic hydrocarbons) and exposure to UV-irradiation. The aim of the study was to evaluate contribution of GR to genotoxic risk and cellular stress in pediatric patients who represent a sensitive population subgroup. Genotoxic risk (42 patients) was evaluated by using chromosomal aberrations (CA) in peripheral lymphocytes. Cellular stress (26 patients) was assessed by using heat shock proteins (Hsp70). All indicators were determined in blood samples collected before GR and immediately after GR. Decreasing of psoriasis area and severity index (PASI) score indicated higher likelihood of GR (p < 0.001). Significantly increased CA (p < 0.001) and Hsp70 (p < 0.05) indicated higher genotoxic risk and cellular stress in sensitive pediatric patients, immediately after GR.

Retinoic acid-induced lumbosacral neural tube defects: myeloschisis and hamartoma.

OBJECTS: To observe the morphological features of the lumbosacral neural tube defects (NTDs) induced by all-trans retinoic acid (atRA) and to explore the pathogenesis of these defects. METHODS: Rat embryos with lumbosacral NTDs were obtained by treating pregnant rats with administration of atRA. Rat embryos were obtained by cesarean. Fetuses were sectioned and stained with hematoxylin-eosin (H&E). Relevant structures including caudal neural tube were examined. In the atRA-treated rats, about 48% embryos showed lumbosacral NTDs. There appeared a dorsally and rostrally situated, neural-plate-like structure (myeloschisis) and a ventrally and caudally located cell mass containing multiple canals (hamartoma) in the lumbosacral NTDs induced by atRA. CONCLUSIONS: Retinoic acid could disturb the notochord and tail bud development in the process of primary and secondary neurulation in rat embryos, which cause lumbosacral NTDs including myeloschisis and hamartoma. The morphology is very similar to that happens in humans.

Coping with the isotretinoin registry.

The isotretinoin registry has arrived. It has a lofty goal of preventing all isotretinoin pregnancies. How we got to this point and what the registry means to prescribers and patients have many dermatologists confused and concerned. Will it be burdensome, will it preclude the use in most offices of this most important drug? Will it breed a new group of "isotretinologists" who are willing to take on the challenge? This article endeavors to answer these questions and to put most concerns at rest. The new system seems ultimately to have few changes compared to the risk management program we are already (technically) following. The difference is that compliance with all the rules will be monitored and mandatory. The system seems user friendly, is accessible to the computer-savvy as well as those of us still addicted to telephone, and may well turn out to be much fuss made over minimal hassle. What is clear is that this is likely our last chance to save this wonderful drug from oblivion. It is time for dermatologists to step to the plate and do what is in the best interest of their patients.

Influence of light in acute toxicity bioassays of imidacloprid and zinc pyrithione to zooplankton crustaceans.

The acute toxicity of imidacloprid, a neonicotinoid insecticide, and zinc pyrithione (Zpt), a biocide used in anti-dandruff shampoos and protective antifouling paints, to three species of ostracods and two waterfleas, including Daphnia magna, was determined and compared under light and dark conditions. Under normal laboratory conditions, UV light had no significant influence on the outcome of toxicity bioassays, although in the case of imidacloprid both EC(50) and LC(50) calculated values were twice as high under the light as in the dark. No influence of UV light was observed on bioassays conducted with Zpt, in spite of the fast aqueous photolysis exhibited by this compound. Imidacloprid 48-h LC(50) for cladocerans (65-133mg/L) were two orders of magnitude higher than for ostracods (301-715microg/L); values of EC(50) for cladocerans and ostracods were 2-6mg/L and 3-16microg/L, respectively. Toxicity of Zpt to both ostracod and cladoceran species appears to be similar, with 48-h LC(50) in the range 137-524 and 75-197microg/L for ostracods and cladocerans, respectively, and similar values for EC(50)s. The mortality endpoint (LC(50)), however, is not a reliable predictor of the effects of imidacloprid under field situations (e.g. rice paddies), because the paralysis effect induced by this insecticide takes place at much lower concentrations than those required to cause the death of the animals: regardless of the taxa, differences as large as 100- or 600-fold were observed between the EC(50) and LC(50) for the same exposures. As a consequence, immobilization tests and EC(50) values are recommended for this class of compounds, while caution should be exercised in environmental risk assessments of this and possibly other related neonicotinoid insecticides with similar activity.

Chronic oral treatment with 13-cis-retinoic acid (isotretinoin) or all-trans-retinoic acid does not alter depression-like behaviors in rats.

Oral treatment with the anti-acne drug Accutane (isotretinoin, 13-cis-retinoic acid) has been associated with suicide ideation and depression. Here, depression-like behaviors (i.e., behavioral despair and anhedonia) were quantified in adult Sprague-Dawley rats gavaged daily beginning at postnatal day (PND) 82 with 13-cis-RA (7.5 or 22.5 mg/kg) or all-trans-retinoic acid (10 or 15 mg/kg ). Tested at PND 130-131 in the Forced Swim Test, 7.5 mg/kg 13-cis-RA marginally decreased immobility and slightly increased climb/struggle durations whereas neither all-trans-retinoic acid group differed from controls. Voluntary saccharin solution (0.03%) intake at PND 102-104 and PND 151-153 was not different from controls in any treated group, although all RA-treated groups had lower intakes. Swim speed in a water maze at PND 180 was similar across groups, indicating no RA-induced differences in physical ability. Open field activity was mildly decreased at PND 91 in 7.5 mg/kg-treated males only, but it was within the control range at PND 119, 147, and 175. Thus, at serum levels similar to those in humans receiving the drug, chronic 13-cis-RA treatment did not severely affect depression-like behaviors in rats. These data do not substantiate the hypothesis of 13-cis-RA-induced depression.

Toxicity assessment of the antifouling compound zinc pyrithione using early developmental stages of the ascidian Ciona intestinalis.

This study investigated the toxicity of zinc pyrithione (Zpt) on the early stages of development of the ascidian Ciona intestinalis. Larval morphological abnormalities were studied after the exposure of C. intestinalis embryos at different stages of development. The median effective concentrations (EC50) ranged from 226-590 nM. The larval settlement stage was the most sensitive to Zpt. Toxic effects of Zpt on larval settlement were detected at 9 nM (EC10). The inhibition of C. intestinalis embryonic development was also used to study the loss of toxicity in Zpt solutions exposed to direct sunlight and laboratory UV light. The results showed that the toxicity of Zpt solutions decreased but did not disappear after 4 h exposure to direct sunlight (EC50 = 484 nM) or UV light (EC50 = 453 nM), compared to control Zpt solutions prepared in dark conditions. On the basis of the present data, predicted no effect concentrations of Zpt to C. intestinalis larvae are lower than predicted environmental concentrations of Zpt in certain polluted areas and therefore, may pose a risk to C. intestinalis populations.

Application of benzo(a)pyrene and coal tar tumor dose-response data to a modified benchmark dose method of guideline development.

Assessment of cancer risk from exposure to polycyclic aromatic hydrocarbons (PAHs) has been traditionally conducted by applying the conservative linearized multistage (LMS) model to animal tumor data for benzo(a)pyrene (BaP), considered the most potent carcinogen in PAH mixtures. Because it has been argued that LMS use of 95% lower confidence limits on dose is unnecessarily conservative, that assumptions of low-dose linearity to zero in the dose response imply clear mechanistic understanding, and that "acceptable" cancer risk rests on a policy decision, an alternative cancer risk assessment approach has been developed. Based in part on the emerging benchmark dose (BMD) method, the modified BMD method we used involves applying a suite of conventional mathematical models to tumor dose-response data. This permits derivation of the average dose corresponding to 5% extra tumor incidence (BMD0.05) to which a number of modifying factors are applied to achieve a guideline dose, that is, a daily dose considered safe for human lifetime exposure. Application of the modified BMD method to recent forestomach tumor data from BaP ingestion studies in mice suggests a guideline dose of 0.08 microg/kg/day. Based on this and an understanding of dietary BaP, and considering that BaP is a common contaminant in soil and therefore poses human health risk via soil ingestion, we propose a BaP soil guideline value of 5 ppm (milligrams per kilogram). Mouse tumor data from ingestion of coal tar mixtures containing PAHs and BaP show that lung and not forestomach tumors are most prevalent and that BaP content cannot explain the lung tumors. This calls into question the common use of toxicity equivalence factors based on BaP for assessing risk from complex PAH mixtures. Emerging data point to another PAH compound--H-benzo(c)fluorene--as the possible lung tumorigen.