Dihydrodiol dehydrogenase and its role in polycyclic aromatic hydrocarbon metabolism

Air Pollution and Atopic Dermatitis, from Molecular Mechanisms to Population-Level Evidence: A Review

Atopic dermatitis (AD) has increased in prevalence to become the most common inflammatory skin condition globally, and geographic variation and migration studies suggest an important role for environmental triggers. Air pollution, especially due to industrialization and wildfires, may contribute to the development and exacerbation of AD. We provide a comprehensive, multidisciplinary review of existing molecular and epidemiologic studies on the associations of air pollutants and AD symptoms, prevalence, incidence, severity, and clinic visits. Cell and animal studies demonstrated that air pollutants contribute to AD symptoms and disease by activating the aryl hydrocarbon receptor pathway, promoting oxidative stress, initiating a proinflammatory response, and disrupting the skin barrier function. Epidemiologic studies overall report that air pollution is associated with AD among both children and adults, though the results are not consistent among cross-sectional studies. Studies on healthcare use for AD found positive correlations between medical visits for AD and air pollutants. As the air quality worsens in many areas globally, it is important to recognize how this can increase the risk for AD, to be aware of the increased demand for AD-related medical care, and to understand how to counsel patients regarding their skin health. Further research is needed to develop treatments that prevent or mitigate air pollution-related AD symptoms.

Characterization, comparative, and functional analysis of arylacetamide deacetylase from Gnathostomata organisms

BACKGROUND

Arylacetamide deacetylase (AADAC) is a lipolytic enzyme involved in xenobiotic metabolism. The characterization in terms of activity and substrate preference has been limited to a few mammalian species. The potential role and catalytic activities of AADAC from other organisms are still poorly understood. Therefore, in this work, the physicochemical properties, proteomic analysis, and protein-protein interactions from Gnathostomata organisms were investigated.

RESULTS

The analysis were performed with 142 orthologue sequences with ~ 48-100% identity with human AADAC. The catalytic motif HGG[A/G] tetrapeptide block was conserved through all AADAC orthologues. Four variations were found in the consensus pentapeptide GXSXG sequence (GDSAG, GESAG, GDSSG, and GSSSG), and a novel motif YXLXP was found. The prediction of N-glycosylation sites projected 4, 1, 6, and 4 different patterns for amphibians, birds, mammals, and reptiles, respectively. The transmembrane regions of AADAC orthologues were not conserved among groups, and variations in the number and orientation of the active site and C-terminal carboxyl were observed among the sequences studied. The protein-protein interaction of AADAC orthologues were related to cancer, lipid, and xenobiotic metabolism genes.

CONCLUSION

The findings from this computational analysis offer new insight into one of the main enzymes involved in xenobiotic metabolism from mammals, reptiles, amphibians, and birds and its potential use in medical and veterinarian biotechnological approaches.

New Insight on Vitality Differences for the Penaeid Shrimp, Fenneropenaeus chinensis, in Low Salinity Environment Through Transcriptomics

Excessive rainfall changes salinity in shrimp farming ponds in short period and exerts low salinity stress on the outdoor breeding shrimp under global warming. Fenneropenaeus chinensis can have different performance on vitality in low salinity environments. To reveal mechanisms of vitality difference in shrimp living in low saline environments. This study based on the normal and moribund F. chinensis in 10 ppt salinity environment using high-throughput sequencing identifies 1,429 differentially expressed genes (DEGs), 586 of which are upregulated, while 843 of which are downregulated in the normal group (FCN10) as compared to the moribund group (FCM10). Meanwhile, another transcriptomic analysis is conducted on the normal and moribund shrimp from 25 ppt (FCN25 vs. FCM25) salinity environment as the control, in which 1,311 DEGs (upregulated: 327 genes, downregulated: 984 genes) are identified. In this study, intersective pathways, GO (Gene Ontology) categories and DEGs from the two groups of comparative transcriptome are investigated. The two intersective pathways (Metabolism of xenobiotics by cytochrome P450, Pentose, and glucuronate interconversions) significantly enriched by DEGs are related to detoxification. In these two pathways, there is one vitality regulation-related gene (VRRG), the Dhdh (dihydrodiol dehydrogenase), which is upregulated in both the groups of FCN10 and FCN25 as compared to the groups of FCM10 and FCM25, respectively. Similarly, in the 25 top intersective GO categories, four VRRGs are revealed. Three of them are upregulated (Itgbl, kielin/chordin-like protein, Slc2a8, solute carrier family 2, facilitated glucose transporter member 8-like protein and Cyp3a30, cytochrome P450 3A30-like protein); one of them is downregulated (Slc6a9, sodium-dependent nutrient amino acid transporter 1-like protein isoform X2). These GO categories are related to transmembrane transporter activity of substance, enzyme inhibitor activity, monooxygenase activity. RT-qPCR analysis further verifies the VRRGs. The study gives new insight into understanding the vitality differences for F. chinensis, in low salinity environment. The pathways and DEGs in response to low salinity stress in modulating the vitality of F. chinensis that could serve as tools in future genetic studies and molecular breeding.

Identification and quantification of phenanthrene ortho-quinones in human urine and their association with lipid peroxidation

Although human exposure to polycyclic aromatic hydrocarbons (PAH) has been associated with in vivo oxidative damage, and hydroxyPAH metabolites have been used as biomarkers to assess PAH-induced oxidative stress, few studies have looked at the likely causative compounds for oxidative stress in humans - PAH quinones. We developed a method using pre-column derivatization - liquid chromatography-heated electrospray ionization-tandem mass spectrometry (LC-HESI-MS/MS) to analyze ortho-phenanthrene quinones (PheQs) in human urine. 1,2-PheQ and 3,4-PheQ were identified and quantified in 3 mL of human urine; their total concentrations were higher in cigarette smokers (0.79 ± 0.98 nmol/6h urine) than in nonsmokers (0.20 ± 0.98 nmol/6h urine) (p < 0.01). The total of 1,2-PheQ and 3,4-PheQ were more strongly correlated with urinary (Z)-7-[1R,2R,3R,5S)-3,5-dihydroxy-2-[(E,3S)-3-hydroxyoct-1-enyl]cyclopentyl]hept-5-enoic acid (8-iso-PGF_2α), a biomarker of lipid peroxidation (R² = 0.53, p < 0.001), than the other phenanthrene metabolites including phenanthrene tetraol (PheT), phenanthrene-1,2-dihydrodiol (1,2-PheD), and total phenanthrene phenols (OHPhe), consistent with the concept that PheQs and likely other PAH quinones play a causal role in the generation of reactive oxygen species (ROS) in humans. Thus, PheQs may be suitable as biomarkers to assess human exposure to oxygenated PAH and the subsequent oxidative damage. This study provides unique support, by analysis of human urinary metabolites, for the PAH quinone mediated oxidative damage hypothesis of PAH carcinogenesis.

Polycyclic aromatic hydrocarbons: bioaccumulation in dragonfly nymphs (Anisoptera), and determination of alkylated forms in sediment for an improved environmental assessment

Road runoff carries a mixture of contaminants that threatens the quality of natural water bodies and the health of aquatic organisms. The use of sedimentation ponds is a nature-based solution for the treatment of road runoff. This study assessed the concentration of polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologues in sediment from seven highway sedimentation ponds and three natural urban ponds. In addition, the study explored the bioaccumulation of PAHs in dragonfly nymphs (Anisoptera). Finally, biota-sediment accumulation factors (BSAFs) were estimated. The results revealed a significant difference in the concentrations of 16 priority PAHs in sediment, with overall higher levels in sedimentation ponds (2,911 µg/kg on average) compared to natural urban ponds (606 µg/kg on average). PAH levels increased substantially once alkylated homologues were considered, with alkylated comprising between 42 and 87% of the total PAH in sediment samples. These results demonstrate the importance of alkylated forms in the environmental assessment of PAHs. The bioaccumulation assessment indicates that dragonfly nymphs bioaccumulate PAHs to a certain degree. It is not clear, however, whether they metabolize PAHs. BSAF results ranged from approx. 0.006 to 10 and indicate that BSAFs can be a powerful tool to determine the functionality of sedimentation ponds.

Transcriptomic analysis reveals insights into deep-sea adaptations of the dominant species, Shinkaia crosnieri (Crustacea: Decapoda: Anomura), inhabiting both hydrothermal vents and cold seeps

Background

Hydrothermal vents and cold seeps are typical deep-sea chemosynthetically-driven ecosystems that allow high abundance of specialized macro-benthos. To gather knowledge about the genetic basis of adaptation to these extreme environments, species shared between different habitats, especially for the dominant species, are of particular interest. The galatheid squat lobster, Shinkaia crosnieri Baba and Williams, 1998, is one of the few dominant species inhabiting both deep-sea hydrothermal vents and cold seeps. In this study, we performed transcriptome analyses of S. crosnieri collected from the Iheya North hydrothermal vent (HV) and a cold seep in the South China Sea (CS) to provide insights into how this species has evolved to thrive in different deep-sea chemosynthetic ecosystems.

Results

We analyzed 5347 orthologs between HV and CS to identify genes under positive selection through the maximum likelihood approach. A total of 82 genes were identified to be positively selected and covered diverse functional categories, potentially indicating their importance for S. crosnieri to cope with environmental heterogeneity between deep-sea vents and seeps. Among 39,806 annotated unigenes, a large number of differentially expressed genes (DEGs) were identified between HV and CS, including 339 and 206 genes significantly up-regulated in HV and CS, respectively. Most of the DEGs associated with stress response and immunity were up-regulated in HV, possibly allowing S. crosnieri to increase its capability to manage more environmental stresses in the hydrothermal vents.

Conclusions

We provide the first comprehensive transcriptomic resource for the deep-sea squat lobster, S. crosnieri, inhabiting both hydrothermal vents and cold seeps. A number of stress response and immune-related genes were positively selected and/or differentially expressed, potentially indicating their important roles for S. crosnieri to thrive in both deep-sea vents and cold seeps. Our results indicated that genetic adaptation of S. crosnieri to different deep-sea chemosynthetic environments might be mediated by adaptive evolution of functional genes related to stress response and immunity, and alterations in their gene expression that lead to different stress resistance. However, further work is required to test these proposed hypotheses. All results can constitute important baseline data for further studies towards elucidating the adaptive mechanisms in deep-sea crustaceans.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5753-7) contains supplementary material, which is available to authorized users.

Spliced leader-based analyses reveal the effects of polycyclic aromatic hydrocarbons on gene expression in the copepod Pseudodiaptomus poplesia

Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic and carcinogenic pollutants that can adversely affect the development, growth and reproduction of marine organisms including copepods. However, knowledge on the molecular mechanisms regulating the response to PAH exposure in marine planktonic copepods is limited. In this study, we investigated the survival and gene expression of the calanoid copepod Pseudodiaptomus poplesia upon exposure to two PAHs, 1, 2-dimethylnaphthalene (1, 2-NAPH) and pyrene. Acute toxicity responses resulted in 96-h LC₅₀ of 788.98μgL^-1 and 54.68μgL^-1 for 1, 2-NAPH and pyrene, respectively. Using the recently discovered copepod spliced leader as a primer, we constructed full-length cDNA libraries from copepods exposed to sublethal concentrations and revealed 289 unique genes of diverse functions, including stress response genes and novel genes previously undocumented for this species. Eighty-three gene families were specifically expressed in PAH exposure libraries. We further analyzed the expression of seven target genes by reverse transcription-quantitative PCR in a time-course test with three sublethal concentrations. These target genes have primary roles in detoxification, oxidative defense, and signal transduction, and include different forms of glutathione S-transferase (GST), glutathione peroxidases (GPX), peroxiredoxin (PRDX), methylmalonate-semialdehyde dehydrogenase (MSDH) and ras-related C3 botulinum toxin substrate (RAC1). Expression stability of seven candidate reference genes were evaluated and the two most stable ones (RPL15 and RPS20 for 1, 2-NAPH exposure, RPL15 and EF1D for pyrene exposure) were used to normalize the expression levels of the target genes. Significant upregulation was detected in GST-T, GST-DE, GPX4, PRDX6 and RAC1 upon 1, 2-NAPH exposure, and GST-DE and MSDH upon pyrene exposure. These results indicated that the oxidative stress was induced and that signal transduction might be affected by PAH exposure in P. poplesia. However, gene upregulation was followed by a reduction in expression level towards 96h, indicating a threshold value of exposure time that leads to depressed gene expression. Prolonged exposure may cause dysfunction of detoxification and antioxidant machinery in P. poplesia. The transcriptional responses of GST-T, GPX2 and GPX4 upon pyrene exposure were minimal. Our results reveal the different sensitivity of P. poplesia to two PAHs at both the individual and transcriptional levels. As the first attempt, this study proved that copepod spliced leader is useful for obtaining full-length cDNA in P. poplesia exposed to PAHs and provided a valuable gene resource for this non-model species. This approach can be applied to other calanoid copepods exposed to various stressors, particularly under field conditions.

Human aldo-keto reductases and the metabolic activation of polycyclic aromatic hydrocarbons

Aldo-keto reductases (AKRs) are promiscuous NAD(P)(H) dependent oxidoreductases implicated in the metabolic activation of polycyclic aromatic hydrocarbons (PAH). These enzymes catalyze the oxidation of non-K-region trans-dihydrodiols to the corresponding o-quinones with the concomitant production of reactive oxygen species (ROS). The PAH o-quinones are Michael acceptors and can form adducts but are also redox-active and enter into futile redox cycles to amplify ROS formation. Evidence exists to support this metabolic pathway in humans. The human recombinant AKR1A1 and AKR1C1–AKR1C4 enzymes all catalyze the oxidation of PAH trans-dihydrodiols to PAH o-quinones. Many human AKRs also catalyze the NADPH-dependent reduction of the o-quinone products to air-sensitive catechols, exacerbating ROS formation. Moreover, this pathway of PAH activation occurs in a panel of human lung cell lines, resulting in the production of ROS and oxidative DNA damage in the form of 8-oxo-2′-deoxyguanosine. Using stable-isotope dilution liquid chromatography tandem mass spectrometry, this pathway of benzo[a]pyrene (B[a]P) metabolism was found to contribute equally with the diol-epoxide pathway to the activation of this human carcinogen in human lung cells. Evaluation of the mutagenicity of anti-B[a]P-diol epoxide with B[a]P-7,8-dione on p53 showed that the o-quinone produced by AKRs was the more potent mutagen, provided that it was permitted to redox cycle, and that the mutations observed were G to T transversions, reminiscent of those observed in human lung cancer. It is concluded that there is sufficient evidence to support the role of human AKRs in the metabolic activation of PAH in human lung cell lines and that they may contribute to the causation of human lung cancer.

Extracts of Koelreuteria henryi Dummer induce apoptosis and autophagy by inhibiting dihydrodiol dehydrogenase, thus enhancing anticancer effects

Dihydrodiol dehydrogenase (DDH) is frequently detected in cancer cells, and its overexpression correlates with drug resistance, the downregulation of DNA repair mechanisms, increased frequency of tumor recurrence, cancer cell metastasis and poor prognosis. The silencing of DDH expression using siRNA, on the other hand, reduces drug resistance and cancer cell mobility. These data suggest that DDH may be an oncogene-related protein. However, no specific DDH inhibitor has been identified to date. Thus, in this study, we used DDH as a target enzyme in a live-cell enzyme-linked immunosorbent assay to screen Chinese medicinal herb extracts (CMHEs) with the aim of identifying a DDH inhibitor. Using this method, we found 49 among 796 CMHEs that inhibited DDH expression. We selected three potential extracts, which had the highest activity against DDH, for further fractionation using high-performance liquid chromatography. The active ingredient was identified by immunoblot analysis. The function of the active ingredient was characterized by cell function analysis. Our results revealed that the CMHE-purified compounds targeted DDH, inducing autophagy and reducing DNA repair, which in turn enhanced the cytotoxic effects of the anticancer drugs and irradiation.

Genetic association between obstructive bronchitis and enzymes of oxidative stress

OBJECTIVE

Obstructive respiratory diseases, mainly the chronic obstructive pulmonary disease (COPD) and asthma, are associated with functional polymorphisms of xenobiotic-metabolizing enzymes (XMEs). To date, association for obstructive bronchitis has not been described.

MATERIAL/METHODS

In this study, we investigated the genotypes from 26 functional polymorphisms of 20 XMEs in children (n, 1028) at the age of 6 years from the German prospective birth cohort study (LISAplus) and analyzed the associations between genotypes and obstructive bronchitis.

RESULTS

For the first time, we found noteworthy gene-disease associations for the functional PON1 M55L and EPHX1 H139R polymorphisms and gene-environment associations for the functional COMT V158M and NQO1 P187S polymorphisms after stratification for maternal active smoking behaviour during pregnancy. The noteworthy associations were substantiated by the biological findings that all the risk genotypes belong to genes involved in oxidative stress and code for proteins with a fast enzymatic activity or concomitantly appear in common estrogene-metabolizing pathway (COMT, NQO1).

CONCLUSION

The oxidative stress has to be taken into account in mechanism of the obstructive bronchitis in early childhood. The risk genotypes may serve as risk factors for respiratory obstruction rather than for signs of COPD or asthma.

Exposure to polycyclic aromatic hydrocarbons: bulky DNA adducts and cellular responses

Environmental and dietary carcinogens such as polycyclic aromatic hydrocarbons (PAHs) have been intensively studied for decades. Although the genotoxicity of these compounds is well characterized (i.e., formation of bulky PAH-DNA adducts), molecular details on the DNA damage response triggered by PAHs in cells and tissues remain to be clarified. The conversion of hazardous PAHs into carcinogenic intermediates depends on enzyme-catalyzed biotransformation. Certain cytochrome P450-dependent monooxygenases (CYPs) play a pivotal role in PAH metabolism. In particular, CYP1A1 and 1B1 catalyze oxidation of PAHs toward primary epoxide species that can further be converted into multiple follow-up products, both nonenzymatically and enzymatically. Distinct functions between these major CYP enzymes have only been appreciated since transgenic animal models had been derived. Electrophilic PAH metabolites are capable of forming stable DNA adducts or to promote depurination at damaged nucleotide sites. During the following DNA replication cycle, bulky PAH-DNA adducts may be converted into mutations, thereby affecting hot spot sites in regulatory important genes such as Ras, p53, and others. Depending on the degree of DNA distortion and cell cycle progression, PAH-DNA adducts trigger nucleotide excision repair (NER) and various DNA damage responses that might include TP53-dependent apoptosis in certain cell types. In fact, cellular responses to bulky PAH-DNA damage are complex because distinct signaling branches such as ATM/ATR, NER, TP53, but also MAP kinases, interact and cooperate to determine the overall outcome to cellular injuries initiated by PAH-DNA adducts. Further, PAHs and other xenobiotics can also confer DNA damage via an alternative route of metabolic activation, which leads to the generation of PAH semiquinone radicals and reactive oxygen species (ROS). One-electron oxidations mediated by peroxidases or other enzymes can result in PAH radical cations that mainly form unstable DNA adducts subjected to depurination. In addition, generation of ROS can also trigger multiple cellular signaling pathways not directly related to mutagenic or cytotoxic effects, including those mediated by NFκB, SAPK/JNK, and p38. In recent years, it became clear that PAHs may also be involved in inflammatory diseases, autoimmune disorders, or atherosclerosis. Further research is under way to better characterize the significance of such newly recognized systemic effects of PAHs and to reconsider risk assessment for human health.

Polycyclic aromatic hydrocarbons and digestive tract cancers: a perspective

Cancers of the colon are most common in the Western world. In majority of these cases, there is no familial history and sporadic gene damage seems to play an important role in the development of tumors in the colon. Studies have shown that environmental factors, especially diet, play an important role in susceptibility to gastrointestinal (GI) tract cancers. Consequently, environmental chemicals that contaminate food or diet during preparation become important in the development of GI cancers. Polycyclic aromatic hydrocarbons (PAHs) are one such family of ubiquitous environmental toxicants. These pollutants enter the human body through consumption of contaminated food, drinking water, inhalation of cigarette smoke, automobile exhausts, and contaminated air from occupational settings. Among these pathways, dietary intake of PAHs constitutes a major source of exposure in humans. Although many reviews and books on PAHs and their ability to cause toxicity and breast or lung cancer have been published, aspects on contribution of diet, smoking and other factors toward development of digestive tract cancers, and strategies to assess risk from exposure to PAHs have received much less attention. This review, therefore, focuses on dietary intake of PAHs in humans, animal models, and cell cultures used for GI cancer studies along with epidemiological findings. Bioavailability and biotransformation processes, which influence the disposition of PAHs in body and the underlying causative mechanisms of GI cancers, are also discussed. The existing data gaps and scope for future studies is also emphasized. This information is expected to stimulate research on mechanisms of sporadic GI cancers caused by exposure to environmental carcinogens.

Antioxidant and lipid peroxidation responses in Mytilus galloprovincialis exposed to mixtures of benzo(a)pyrene and copper

This study aimed to assess the antioxidant system potential and lipid peroxidative effects, in the gill and digestive gland of Mytilus galloprovincialis exposed to individual and binary mixtures of benzo(a)pyrene (BaP) and Cu for 7 days. Data demonstrated that in mussels exposed to BaP antioxidant enzymes (catalase--CAT, total glutathione peroxidase--tGPx, glutathione S-transferase--GST and glutathione reductase--GR) and lipid peroxidation (LPO) increased in the gill. On the contrary, in the digestive gland inhibitory antioxidant effects (superoxide dismutase-SOD, GR, metallothioneins-MT) and no changes in LPO levels were detected. Cu was also a potent oxidant agent since MT and LPO levels increased in mussel gill, despite no LPO effect in the digestive gland. For both single contaminants the organ specificity and distinct physiologic/metabolism roles were evident in terms of antioxidant capacity. Gill SOD inhibition, MT and GST unchanged was a result of "simple independent action" of exposure to BaP and Cu. "Interactions" in the binary mixtures, led to absence of changes in LPO effects. In the digestive gland, BaP and Cu interactions were also responsible for the GST and LPO enhancement (antagonistic effects). The current findings demonstrate the differences in antioxidant responses where the organ dependency highlights each contaminant particular mode of action. Generally, in the gill "non-interactive" effects occurred with the lowest Cu concentration while "interactions" exist for the mixture with the highest Cu concentrations. In the digestive gland, "interactions" and "no interaction" effects occurred in all the binary mixtures. Complex contaminant mixtures interact differently based on target tissue which may lead to an imbalance in the mussels health status.

Pharmacogenomic identification of c-Myc/Max-regulated genes associated with cytotoxicity of artesunate towards human colon, ovarian and lung cancer cell lines

Development of novel therapy strategies is one of the major pressing topics of clinical oncology to overcome drug resistance of tumors. Artesunate (ART) is an anti-malarial drug, which also exerts profound cytotoxic activity towards cancer cells. We applied a gene-hunting approach using microarray-based transcriptome-wide mRNA expression profiling and COMPARE analyses. We identified a set of genes, whose expression was associated either with high IC₅₀ values or low IC₅₀ values for ART. Therefore, these genes may function as resistance or sensitivity factors for response of tumor cells towards ART. This viewpoint is conceivable for genes involved in ribosomal activity, drug transport, cellular antioxidant defense, apoptosis, cell proliferation, cell cycle progression etc. An investigation of underlying signal transduction by pathway analysis suggested a role of the signaling pathways related to tumor necrosis factor (TNF) and the tumor suppressor p53. On the other hand, there were genes without obvious functional link to cellular response to ART, such as genes involved in the survival of cochlear outer and inner hair cells etc. We proved the hypothesis that ART influences the activity of transcription factors regulating downstream genes involved or not involved in response of cancer cells towards ART. This would explain the identification of genes with and without obvious relation to the cytotoxic activity of ART by microarray and COMPARE analyses. By analysis of the binding motifs for the transcription factors c-Myc and Max, we indeed found that 53 of 56 genes contained one or more binding sites for c-Myc/Max upstream of the gene-location. We conclude that c-Myc and Max-mediated transcriptional control of gene expression might contribute to the therapeutic effects of ART in cancer cells, but may also confer unwanted side effects by affecting therapy-unrelated genes.

Polycyclic aromatic hydrocarbons concentrations and biomarker responses in the clam Ruditapes decussatus transplanted in the Ria Formosa lagoon

Clams Ruditapes decussatus were transplanted in the Ria Formosa lagoon and the variation of PAH concentrations in the whole soft tissues measured, along with a suite of biomarkers, including the following: (a) phase I and phase II metabolism of xenobiotics enzymes: benzo[a]pyrene hydroxylase (BPH) and glutathione S-transferase (GST); (b) antioxidant enzymes: superoxide dismutase, catalase and glutathione peroxidases and (c) lipid peroxidation (LPO) levels. Individual PAHs were differently accumulated and eliminated by R. decussatus. During the metabolisation of PAHs by R. decussatus BPH was clearly induced in the digestive gland. Moreover, ROS lead to the induction of protective antioxidant enzymes still causing oxidative damage to membranes. Therefore, BPH seems to be a relevant indicator of PAHs in R. decussatus.

Overexpression of dihydrodiol dehydrogenase as a prognostic marker in resected gastric cancer patients

The cytoplasmic enzyme dihydrodiol dehydrogenase (DDH) plays an important role in detoxification. Patients with DDH overexpression have a significantly higher incidence of early tumor recurrence and distant metastasis. This study evaluated the correlation between clinicopathological data and DDH expression and the prognostic significance of DDH expression in patients with resected gastric cancer. Between January 1998 and September 2004, we retrospectively enrolled 81 patients who received surgical treatment for gastric cancer. Pathology samples were immunostained with monoclonal antibody to DDH. The relationship between DDH expression and clinicopathological data (age, gender, histological type, stage) was analyzed by chi-square analysis. Survival curves were plotted using the Kaplan-Meier method and compared using a log-rank test. The overexpression rate of DDH was 41.9%. Of patients with overexpressed DDH, 13% had stage I, 24% had stage II, 52% had stage III, and 78% had stage IV tumors. Among patients who died, DDH expression level differed significantly between high and low-expression groups (P = 0.042). Survival was significantly better in patients with low DDH expression (P = 0.048). Thus, DDH expression may be useful in identifying high-risk gastric cancer patients and distinguishing future candidates for curative and palliative treatment.

In vitro toxicity of naphthalene, 1-naphthol, 2-naphthol and 1,4-naphthoquinone on human CFU-GM from female and male cord blood donors

In animal models, naphthalene toxicity has been studied in different target organs and has been shown to be gender-dependent and metabolism related. In humans, it is readily absorbed and is metabolised by several cytochrome P450's. Naphthalene and its metabolites can cross the placental barrier and consequently may affect foetal tissues. The aim of this study was to compare the in vitro toxicity of naphthalene and its metabolites, 1-naphthol, 2-naphthol and 1,4-naphthoquinone, on human haematopoietic foetal progenitors (CFU-GM) derived from newborn male and female donors. The mRNA expression of Cyp1A2 and Cyp3A4 was also evaluated. Naphthalene did not affect CFU-GM proliferation, while 1-naphthol, 2-naphthol and particularly 1,4-naphthoquinone strongly inhibited the clonogenicity of progenitors, from both male and female donors. mRNA of Cyp1A2 and Cyp3A4 was not expressed neither at the basal level, nor after naphthalene treatment, while treatment with 1,4-naphthoquinone induced expression of both enzymes in both genders, with Cyp1A2 being expressed four times more than Cyp3A4. Female CFU-GM was significantly more sensitive to 1,4-naphthoquinone than male and after treatment both enzymes were expressed twice as much as in the male precursors. These results suggest that a gender-specific 1,4-naphthoquinone metabolic pathway may exist, which gives rise to unknown toxic metabolites.

Biotransformation of polycyclic aromatic hydrocarbons in marine polychaetes

Deposit-feeding polychaetes constitute the dominant macrofauna in marine environments that tend to be depositional centers for organic matter and contaminants. Polychaetes are known to accumulate polycyclic aromatic hydrocarbons (PAHs) from both particulate and dissolved phases but less is known about the mechanisms underlying elimination of accumulated PAHs. An important pathway of elimination is through biotransformation which results in increased aqueous solubility of the otherwise hydrophobic PAHs. Biotransformation in marine polychaetes proceeds in a two phased process similar to those well studied in vertebrates, phase I enzymes belonging to the Cytochrome P450 (CYP) enzyme family, along with a few phase II enzymes have been identified in marine polychaetes. In this review we aim at highlighting advances in the mechanistic understanding of PAH biotransformation in marine polychaetes by including data obtained using analytical chemistry and molecular techniques. In marine polychaetes induction of CYP enzyme activity after exposure to PAHs and the mechanism behind this is currently not well established. Conflicting results regarding the inducibility of CYP enzymes from polychaetes have led to the suggestion that induction in polychaetes is mediated through a different mechanistic pathway, which is corroborated by the apparent lack of an AhR homologous in marine polychaetes. Also, none of the currently identified CYP genes from marine polychaetes are isoforms of those regulated by the AhR in vertebrates. Relatively few studies of phase II enzymes in marine polychaetes are currently available and most of these studies have not measured the activity of specific phase II enzymes and identified phase II metabolites but used an extraction technique only allowing determination of the overall amount of phase II metabolites. Studies in insects and various marine invertebrates suggest that in invertebrates, enzymes in the important phase II enzyme family, UDP-glucuronosyl transferases primarily use glucoside as co-substrate as opposed to the vertebrate cosubstrate glucuronic acid. Recent studies in marine polychaetes have however identified glucuronidation of PAHs indicating no mechanistic difference in co-substrate preference among UDP-glucuronosyl transferases between vertebrates and marine polychaetes but it might suggest a mechanistic difference between marine polychaetes and insects.

Potential mechanisms of estrogen quinone carcinogenesis

There is a clear association between the excessive exposure to estrogens and the development of cancer in hormone-sensitive tissues (breast, endometrium). It has become clear that there are likely multiple overlapping mechanisms of estrogen carcinogenesis. One major pathway is the extensively studied hormonal pathway, by which estrogen stimulates cell proliferation through nuclear estrogen receptor (ER)-mediated signaling, thus resulting in an increased risk of genomic mutations during DNA replication. A similar "nongenomic pathway", potentially involving newly discovered membrane-associated ERs, also appears to regulate extranuclear estrogen signaling pathways. This perspective is focused on a third pathway involving the metabolism of estrogens to catechols mediated by cytochrome P450 and further oxidation of these catechols to estrogen o-quinones. Oxidative enzymes, metal ions, and in some cases molecular oxygen can catalyze o-quinone formation, so that these electrophilic/redox-active quinones can cause damage within cells by alkylation and/or oxidation of cellular proteins and DNA in many tissues. It appears that the endogenous estrogen quinones primarily form unstable N3-adenine or N7-guanine DNA adducts, ultimately resulting in mutagenic apurinic sites. In contrast, equine estrogen quinones, formed from estrogens present in popular hormone replacement therapy prescriptions, generate a variety of DNA lesions, including bulky stable adducts, apurinic sites, DNA strand cleavage, and oxidation of DNA bases. DNA damage induced by these equine quinones is significantly increased in cells containing ERs, leading us to hypothesize a mechanism involving ER binding/alkylation by the catchol/quinone, resulting in a "Trojan horse". The "Trojan horse" carries the highly redox-active catechol to estrogen -sensitive genes, where high amounts of reactive oxygen species are generated, causing selective DNA damage. Our data further suggest that other key protein targets for estrogen o-quinones could be redox-sensitive enzymes (i.e, GST P1-1, QR). These proteins are involved in stress response cascades that are known to contribute to the regulation of cell proliferation and apoptosis. Finally, it has been shown that catechol estrogens can transform breast epithelial cells into a tumorigenic phenotype and that these transformed cells had differential gene expression of several genes involved in oxidative stress. Given the direct link between excessive exposure to estrogens, metabolism of estrogens, and increased risk of breast cancer, it is crucial that factors that affect the formation, reactivity, and cellular targets of estrogen quinoids be thoroughly explored.

Investigating the relationship between embryotoxic and genotoxic effects of benzo[a]pyrene, 17alpha-ethinylestradiol and endosulfan on Crassostrea gigas embryos

Genotoxicity biomarkers are widely measured in ecotoxicology as molecular toxic endpoints of major environmental pollutants. However, the long-term consequences of such damage still have to be elucidated. Some authors have suggested that the accumulation of unrepaired DNA lesions could explain the embryotoxicity of certain chemical pollutants. As embryotoxicity exerts a direct impact on the recruitment rate, genotoxicity could be closely related to disturbances of ecological concern and produce a possible impact upon population dynamics. The aim of the present work was to study the genotoxicity and the embryotoxicity of three relevant pollutants for oyster embryos: the polycyclic aromatic hydrocarbon, benzo[a]pyrene (BaP), the synthetic estrogenic hormone, 17alpha-ethinylestradiol (EE2), and the organochlorine pesticide, endosulfan (ES). For each substance, gamete fertilization was performed and embryo development followed in contaminated reference seawater. Following exposure, embryotoxicity was evaluated by calculating the percentage of abnormal D-larvae obtained at 20 h development. Genotoxicity was measured in parallel by conducting a comet assay on enzymatically dissociated cells of pre-shelled larvae (16 h development). The oxidized DNA base, 8-oxodGuo, was also measured by HPLC coupled to electrochemical detection. For each contaminant, the relationship between genotoxicity and embryotoxicity was then studied to check for the possible significance of genotoxicity in the population dynamics of marine bivalves from polluted areas. For BaP, embryotoxicity and DNA strand breakage were both observed from the lowest tested concentration of 0.2 nM. Induction of 8-oxodGuo was significant from 20 nM. Endosulfan exposure resulted in similar effects for oyster embryos but from higher concentrations and followed a concentration-dependent manner. Embryotoxicity and genotoxicity in terms of DNA strand breaks were observed for endosulfan from 300 and 150 nM, respectively. No change in 8-oxodGuo level was observed following endosulfan exposure. EE2 displayed no toxic effect for oyster embryos within the range of tested concentrations (from 0.02 to 1.7 nM). Taking into account all the data collected during this study, a positive and significant correlation was demonstrated in oyster embryos between genotoxicity as measured by the comet assay and embryotoxicity.

The biochemistry of drug metabolism--an introduction: Part 2. Redox reactions and their enzymes

This review continues a general presentation of the metabolism of drugs and other xenobiotics started in a recent issue of Chemistry & Biodiversity. This Part 2 presents the numerous oxidoreductases involved, their nomenclature, relevant biochemical properties, catalytic mechanisms, and the very diverse reactions they catalyze. Many medicinally, environmentally, and toxicologically relevant examples are presented and discussed. Cytochromes P450 occupy a majority of the pages of Part 2, but a large number of relevant oxidoreductases are also considered, e.g., flavin-containing monooxygenases, amine oxidases, molybdenum hydroxylases, peroxidases, and the innumerable dehydrogenases/reductases.

Reversal of inflammation-associated dihydrodiol dehydrogenases (AKR1C1 and AKR1C2) overexpression and drug resistance in nonsmall cell lung cancer cells by wogonin and chrysin

Dihydrodiol dehydrogenase (DDH) is a member of the aldo-keto reductases superfamily (AKR1C1-AKR1C4), which plays central roles in the metabolism of steroid hormone, prostaglandin and xenobiotics. We have previously detected overexpression of DDH as an indicator of poor prognosis and chemoresistance in human non-small lung cancer (NSCLC). We also found DDH expression to be closely related to chronic inflammatory conditions. The aim of this study was to investigate the links between inflammation, DDH expression and drug resistance in NSCLC cells. We showed that pro-inflammatory mediators including interleukin-6 (IL-6) could induce AKR1C1/1C2 expression in NSCLC cells and increase cellular resistance to cisplatin and adriamycin. This effect was nullified by Safingol, a protein kinase C inhibitor. Moreover, the expression of AKR1C1/1C2 was inversely correlated to NBS1 and apoptosis-inducing factor (AIF). We also showed that IL-6-induced AKR1C1/1C2 expression and drug resistance were inhibited by wogonin and chrysin, which are major flavonoids in Scutellaria baicalensis, a widely used traditional Chinese and Japanese medicine. In conclusion, this study demonstrated novel links of pro-inflammatory signals, AKR1C1/1C2 expression and drug resistance in NSCLC. The protein kinase C pathway may play an important role in this process. Overexpression of AKR1C1/1C2 may serve as a marker of chemoresistance. Further studies are warranted to evaluate wogonin and chrysin as a potential adjuvant therapy for drug-resistant NSCLC, especially for those with AKR1C1/1C2 overexpression.

Dihydrodiol dehydrogenase in drug resistance and sensitivity of human carcinomas

We previously reported (UroOncology 1:165, 2001) cross-resistance and collateral-sensitivity to 2-chlorodeoxyadenosine (CldAdo) and fludarabine (FaraA), respectively, in a human renal cell carcinoma selected for resistance to 2'-deoxytubercidin (Caki-dTub). Insofar that these drugs generally demonstrate cross resistance rather than collateral sensitivity, we further examined the bases for this phenomenon. Both CldAdo and FaraA induce apoptosis, as the triphosphates, via binding to Apaf-1. In the presence of cytochrome c, this binding leads to activation of procaspase 9 to active caspase 9 that induces apoptosis through its activation of caspase 3. CldAdo and FaraA induced caspase 3 activities in wild type and Caki-dTub cell lines in a dose-dependent manner that paralleled the cross-resistance (CldAdo, 200-fold) or collateral sensitivity (FaraA, 20-fold) with regard to cell viability. The activation of caspase 3 was inhibited by the caspase 9 inhibitor, Z-LEHD-FMK, suggesting that both drugs act via the same pathway. By differential display and direct enzyme analysis, dihydrodiol dehydrogenase (DDH) was observed to be profoundly underexpressed in the Caki-dTub compared to wild-type Caki-1 cells. Stable transfection of the Caki-dTub cells with a vector encoding the enzyme led to partial reversal of the resistance to CldAdo. Resistance to cisplatin has recently been ascribed to overexpression of DDH in a human ovarian carcinoma cell line (Deng et al. in J Biol Chem 227:15035, 2002). It is tempting to speculate a mutation in the Apaf-1 nucleotide binding site that reduces (CldAdo) or increases (FaraA) toxicity in the Caki-dTub cells; however, the recent finding by others in a human ovarian carcinoma cell line suggests that DDH expression mediates the cross-resistance and perhaps, collateral-sensitivity.

Apo- and holo-structures of 3alpha-hydroxysteroid dehydrogenase from Pseudomonas sp. B-0831. Loop-helix transition induced by coenzyme binding

Bacterial 3alpha-hydroxysteroid dehydrogenase, which belongs to a short-chain dehydrogenase/reductase family and forms a dimer composed of two 26-kDa subunits, catalyzes the oxidoreduction of hydroxysteroids in a coenzyme-dependent manner. This enzyme also catalyzes the oxidoreduction of nonsteroid compounds that play an important role in xenobiotic metabolism of bacteria. We performed an x-ray analysis on the crystal of Ps3alphaHSD, the enzyme from Pseudomonas sp. B-0831 complexed with NADH. The resulting crystal structure at 1.8A resolution showed that Ps3alphaHSD exists as a structural heterodimer composed of apo- and holo-subunits. A distinct structural difference between them was found in the 185-207-amino acid region, where the structure in the apo-subunit is disordered whereas that in the holo-subunit consists of two alpha-helices. This fact proved that the NADH binding allows the helical structures to form the substrate binding pocket even in the absence of the substrate, although the region corresponds to the so-called "substrate-binding loop." The induction of alpha-helices in solution by the coenzyme binding was also confirmed by the CD experiment. In addition, the CD experiment revealed that the helix-inducing ability of NADH is stronger than that of NAD. We discuss the negative cooperativity for the coenzyme binding, which is caused by the effect of the structural change transferred between the subunits of the heterodimer.

Metabolism of cytostatically active 6-aminobenzo[c]phenanthridines by human and porcine hepatic microsomes and recombinant cytochrome P450 enzymes

A new and convenient two-step synthesis of 11-substituted 6-amino-11,12-dihydrobenzo[c]phenanthridines and 6-aminobenzo[c]phenanthridines (BPs and BP-Ds) was developed recently in the authors' laboratory. These compounds revealed a high antitumoral activity in in vitro and in vivo test systems. In particular, 11-phenyl-substituted derivatives with two or three methoxy groups showed good activity. It was not clear if the dihydro-derivatives (BPs) were transformed enzymatically into the phenanthridines (BP-Ds), thus acting as prodrugs. The in vitro metabolism of several of these cytostatically active 6-aminobenzo[c]phenanthridines was investigated using human and porcine liver microsomes and a range of expressed human cytochrome P450 enzymes. High-performance liquid chromatography and liquid chromatography-mass spectrometry analysis were used for the quantification and structural identification of the observed metabolites. Aromatic hydroxylation was observed to be the major metabolic pathway in addition to a number of other metabolites. The formation of N-hydroxy- and 6-oxo-derivatives was detected only in very small amounts. BP derivatives are not prodrugs of BP-Ds and no significant differences between human and porcine microsomes were observed, confirming the pig as a good model for metabolism studies of these compounds.

Expression of dihydrodiol dehydrogenase plays important roles in apoptosis- and drug-resistance of A431 squamous cell carcinoma

BACKGROUND

Dihydrodiol dehydrogenase (DDH) is a member of the aldo-keto reductases superfamily which may be involved in normal detoxification process of environmental mutagenic hazards like polycyclic aromatic hydrocarbons (PAH). Previous clinical studies have demonstrated the over-expression of DDH in various types of cancers, including cutaneous squamous cell carcinoma (SCC), and its correlation with tumor progression and grave prognosis.

OBJECTIVE

To investigate possible mechanisms for DDH's correlation with tumor progression and unfavorable prognosis.

METHODS

DDH expression in SCC A431 cell line was examined by quantitative real-time PCR and immunoblotting. RNA interference (RNAi) by transduction with retroviral vector containing DDH-targeting small interfering RNA was employed to inhibit DDH expression by A431 cells. With DDH expression inhibited or not, sensitivity of A431 cells to UVB-induced apoptosis and cytotoxicity of chemotherapeutic agent bleomycin were then examined and compared.

RESULTS

DDH was found highly expressed by SCC A431 cells, which was barely detectable in other normal or malignant cutaneous cells, including keratinocytes, fibroblast, and basal cell carcinoma cell line. RNAi Inhibition of DDH expression in A431 cells led to increased sensitivity to UVB-induced apoptosis and cytotoxicity of bleomycin treatment.

CONCLUSION

DDH may play important roles in tumor progression of SCC via induction of apoptosis- and drug-resistance.

Induction of AKR1C2 by phase II inducers: identification of a distal consensus antioxidant response element regulated by NRF2

AKR1C2, also referred to as the human bile acid binder and 3alpha-hydroxysteroid dehydrogenase type III, is a multifunctional oxidoreductase able to stereoselectively reduce steroids as well as oxidize or reduce polyaromatic hydrocarbons. Previously, this same protein was also identified by its robust induction by phase II inducers in HT29 cells. In HepG2 cells, both AKR1C2 and AKR1C1 (97% sequence homology) were induced by phase II inducers but not the highly related AKR1C3 and AKR1C4 family members (84% sequence homology). We now report the initial characterization of the proximal promoter of AKR1C2 in HepG2 cell line and the identification of a potent enhancer-like element responsive to phase II inducers located approximately 5.5 kilobases upstream from the transcription start site. DNA sequence analysis of this enhancer element revealed that it contained a consensus antioxidant response element (ARE), which was confirmed by mutation analysis. Treatment with phase II inducers leads to increased accumulation of nuclear factor-erythroid 2 p45-related factor (NRF) 2 in the nucleus, which was associated with increased binding to this ARE as determined by electrophoretic mobility shift assay. Transient transfection with Nrf2 increased the transcriptional activity of the ARE of AKR1C2 comparable with that observed with phase II inducers. Chromatin immunoprecipitation (ChIP) analysis also confirmed increased NRF2 binding to the ARE after induction by a phase II inducer. The AKR1C1 promoter also harbored this same ARE element in a highly homologous region, which was also bound by NRF2 in a ChiP analysis. No induction of the ARE of AKR1C2 was detected in Nrf2-/- fibroblasts. The regulation of AKR1C2 by this distal ARE suggests that AKR1C2 detoxifies products of reactive oxidant injury, which has important implications for both hormone and xenobiotic metabolism.

Evidence for the existence of PAH-quinone reductase and catechol-O-methyltransferase in Mycobacterium vanbaalenii PYR-1

Polycyclic aromatic hydrocarbon (PAH) quinone reductase (PQR) and catechol-O-methyltransferase (COMT), from the PAH-degrading Mycobacterium vanbaalenii PYR-1, were demonstrated to be constitutive enzymes located in the soluble fraction of cell extracts. PQR activities for the reduction of 9,10-phenanthrenequinone and 4,5-pyrene- quinone were 1.40+/-0.13 and 0.12+/-0.01 micromol min(-1) mg-protein(-1), respectively. The exogenous catechols alizarin, anthrarobin, 2,3-dihydroxynaphthalene and esculetin inhibited PQR activity. Anthrarobin (100 microM) and esculetin (100 microM) inhibited 4,5-pyrenequinone reduction by 64-92%. COMT was involved in the O-methylation of 1,2-dihydroxyphenanthrene to form 1-methoxy-2-hydroxyphenanthrene and 1,2-dimethoxyphenanthrene. Both pyrene and 1-hydroxypyrene were metabolized by M. vanbaalenii PYR-1 to form 1-methoxypyrene, 1-methoxy-2-hydroxypyrene, 1-hydroxy-2-methoxypyrene and 1,2-dimethoxypyrene. Among the catechols tested, anthrarobin showed the highest COMT activity (1.06+/-0.04 nmol/30 min(-1) mg-protein(-1)). These results suggest that the PQR and COMT activities of M. vanbaalenii PYR-1 may play an important role in the detoxification of PAH catechols.

Inverse expression of dihydrodiol dehydrogenase and glutathione-S-transferase in patients with esophageal squamous cell carcinoma

We investigated the significances of the expressions of dihydrodiol dehydrogenase (DDH) and glutathione-S-transferase (GST) in patients with esophageal squamous cell carcinoma (ESCC). By using immunohistochemistry, we measured expressions of DDH, GST, COX-2, nm23-H1, HER-2/neu and mdr-1 in 145 patients with ESCC. Expression of DDH was confirmed by immunoblotting and reverse transcription-polymerase chain reaction. Relation between DDH expression and clinicopathological parameters was analyzed by statistical analysis. Difference of survivals between different groups was compared by a log rank test. DDH overexpression was detected in 66.9% of pathological sections (97/145) and in 41.6% of metastatic lymph nodes (37/89). The nucleotide sequencing of DNA fragments from 16 tumorous specimens showed that the major isoform was DDH2 for ESCC. GST expression, however, was only detected weakly in 24 patients (16.6%). For patients with ESCC, DDH overexpression was positively correlated with smoking habit, tumor stage, number of metastatic lymph nodes, lymphovascular invasion and COX-2 expression, and inversely correlated with GST and nm23-H1 expressions, but not related to mdr-1 or HER-2/neu expressions. As compared to DDH overexpressed group, patients with low DDH expression had significantly lower incidence of tumor recurrences and better survival (p = 0.026). Using univariate analysis, prognostic factors included tumor stage, number of metastatic lymph nodes, cell differentiation, lymphovascular invasion and expressions of DDH and nm23-H1. Multivariate analysis showed significant correlation of tumor stage, number of metastatic lymph nodes and nm23-H1 expression with patient's survival. In conclusion, inverse expressions of DDH and GST may be associated with carcinogenesis and disease progression for ESCC patients, but their biological function and pathophysiological regulation in tumors require additional studies.

Oxidant mechanisms in response to ambient air particles

The toxic effects of air pollution are widely documented. In recent years, however, there has been an increasing interest in the study of the health effects of particulate matter (PM), a previously unexplored constituent of urban air pollution. Exposure to increased levels of PM of respirable size is strongly and consistently associated with increased cardiopulmonary morbidity and mortality. Conversely, improved air quality appears to correlate with decreased mortality. Particulate matter is a mixture of inorganic and organic components that vary in size, origin, and composition. The mechanisms of PM health effects are still poorly understood. However, studies in cellular and animal models suggest a variety of possible mechanisms including direct effects of particle components on the intracellular sources of reactive oxygen species (ROS), indirect effects due to pro-inflammatory mediators released from PM-stimulated macrophages, and neural stimulation after particle deposition in the lungs. The involvement of ROS in each one of these possible pathways is discussed.

Bone marrow cytotoxicity of benzo[a]pyrene is dependent on CYP1B1 but is diminished by Ah receptor-mediated induction of CYP1A1 in liver

We have previously used CYP1B1-null mice to demonstrate that dimethylbenz(a)anthracene (DMBA) requires CYP1B1 for bone marrow (BM) toxicity. Benzo(a)pyrene (BP), a much more potent Ah receptor ligand, shows very different responses that nevertheless depend on CYP1B1. Wild-type (AhR(b)) mice treated with DMBA for 48 h exhibit a large loss in BM cellularity and disruption of marrow structure that is not seen for BP treatment. In congenic mice with a low affinity AhR (AhR(d)), DMBA and BP are equally toxic to the BM whereas AhR(d) x CYP1B1-null mice are fully protected. In situ hybridization demonstrates that CYP1B1 mRNA is constitutively expressed in marrow cells and is induced by PAHs according to their AhR affinity (BP>DMBA), including lower levels in AhR(d) mice. Importantly, expression of CYP1A1 mRNA was undetectable in BM. In wild-type mice, BP treatment leads to a fivefold greater induction of hepatic CYP1A1 than that of DMBA treatment. Neither induction occurs in AhR(d) mice. Thus, hepatic metabolism may prevent BP from reaching the BM, where it can be bioactivated by CYP1B1. Flow cytometric analyses of BM cells showed that there were decreases in granulocytes and lymphocytes following DMBA treatment, but not after BP treatment. These data suggest that there is an inverse relationship between liver metabolism and BM toxicity resulting from limitations on the delivery of PAH to CYP1B1 present in BM, where only very low constitutive levels are needed.

Cancer prevention and therapy: strategies and problems

During the next years, molecular diagnostic science and the pharmaceutical industry will face increasing demand for personalized medicine. Therapeutic treatments should be tailored to the needs of individual patient. Patients will inquire for information about potential tumor detection at an early stage when disease can be more likely to be arrested or cured with specific regimens of drug therapy. To respond to this demand, science and industry need to modulate therapeutic approaches to the continuous development of cancer. Now more than ever, it is necessary to fill the knowledge hiatus between the "beginning" and the "end" of cancer development, i.e we need to critically analyze the extensive multi-step process of cancer development that still remains poorly understood.

Two polycyclic aromatic hydrocarbon o-quinone reductases from a pyrene-degrading Mycobacterium

Polycyclic aromatic hydrocarbon (PAH) o-quinone reductase (PQR) plays a crucial role in the detoxification of PAH o-quinones by reducing them to catechols. Two constitutive PQRs were found in cell extracts of a pyrene-degrading Mycobacterium sp. strain PYR100. The enzymes had an activity towards 9,10-phenanthrenequinone (PQ) and/or 4,5-pyrenequinone (PyQ), and the relative amounts varied with the pH of the culture media. PQR1, containing an FAD cofactor, was a monomer (20.1 kDa), and PQR2, with no flavin cofactor, was a homodimer (26.5 kDa subunits). There was no homology between the N-terminal sequences of PQR1 and PQR2. Dicumarol and quercetin inhibited PQR2 more strongly than PQR1. PQR1 had much lower specificity constants (k(cat)/K(m), 10(5)M(-1)s(-1)) for menadione (0.80) and PQ (5.19) than PQR2 (13.9 for menadione and 176 for PQ). Additionally, PQR2 exhibited a broad substrate specificity with high specificity constants for 1,4-naphthalenequinone, 1,2-naphthalenequinone, and PyQ.

Characterisation of a novel mouse liver aldo-keto reductase AKR7A5

We have characterised a novel aldo-keto reductase (AKR7A5) from mouse liver that is 78% identical to rat aflatoxin dialdehyde reductase AKR7A1 and 89% identical to human succinic semialdehyde (SSA) reductase AKR7A2. AKR7A5 can reduce 2-carboxybenzaldehyde (2-CBA) and SSA as well as a range of aldehyde and diketone substrates. Western blots show that it is expressed in liver, kidney, testis and brain, and at lower levels in skeletal muscle, spleen heart and lung. The protein is not inducible in the liver by dietary ethoxyquin. Immunodepletion of AKR7A5 from liver extracts shows that it is one of the major liver 2-CBA reductases but that it is not the main SSA reductase in this tissue.

Mutational analyses of cysteine residues of bovine dihydrodiol dehydrogenase 3

The cloning, bacterial expression and purification of bovine liver cytosolic dihydrodiol dehydrogenase 3 (DD3) cDNA (1330 bp in full length) using the pKK223-3 expression vector has been reported previously. Recombinant DD3 (rDD3) was characterized in terms of its substrate specificity and inhibitor sensitivity [Terada et al., Adv. Exp. Biol. Res. 414 (1997) 543-553]. The nucleotide sequence of DD3 cDNA completely matched with that of bovine liver-type prostaglandin F synthase [Suzuki et al., J. Biol. Chem. 274 (1999) 241-248]. In the present study, we succeeded in high level expression of rDD3 in Escherichia coli BL21 (DE3) using the pET28a expression vector. rDD3 was easily and quickly purified to apparent homogeneity by one-step column chromatography using Ni(2+)-affinity resin. Furthermore, rDD3 showed essentially the same substrate specificity and inhibitor sensitivity to that of purified liver DD3. To analyze the role of cysteines (145, 154, 188, 193 and 206) in the enzymatic activity of DD3, site-directed mutagenesis of DD3 using the polymerase chain reaction method was performed. Mutants (C145S, C154S, C188S, C193S and C206S) were analyzed for substrate specificity, cofactor binding and inactivation by disulfide (dithio-bis(2-nitrobenzoic acid), alkylating reagent (N-ethylmaleimide) and oxidants (naphthoquinone and H(2)O(2)) Results indicated that these five cysteines of rDD3 may not be directly involved in substrate or cofactor binding. Mutant C193S showed strong resistance to SH-reagents unlike wild-type DD3 (WT) or other mutants. Both the WT and the other mutants showed essentially the same sensitivity to SH-reagents. Cofactor (NADP(+)) protected mutants C145S, C188S and C206S from inactivation as well as WT, while NAD(+) was not protective. Our present results indicate that Cys193, which is located close to the NADP(+)-binding site, may be involved in the alteration of enzymatic activity.

Site-directed mutagenesis studies of bovine liver cytosolic dihydrodiol dehydrogenase: the role of Asp-50, Tyr-55, Lys-84, His-117, Cys-145 and Cys-193 in enzymatic activity

A previous report on the cloning, bacterial expression and purification of bovine liver cytosolic dihydrodiol dehydrogenase (DD3) cDNA (1,330 bp in full length) using pKK223-3 expression vector characterize the properties of the recombinant DD3 in the aspects of substrate specificity and inhibitor sensitivity (Terada et al., Adv. Exp. Biol. Res. 414 (1997) 543-53). The nucleotide sequence of this DD3 cDNA completely matches that of bovine liver-type prostaglandin F synthase (PGFS) (Suzuki et al., J. Biol. Chem. 274 (1999) 241-8). In the present study, a large amount of recombinant DD3 (rDD3) was expressed in Escherichia coli BL21 (DE3) with a pET28a expression vector. The recombinant DD3 (rDD3) was easily and quickly purified to an apparent homogeneity with one step column chromatography of Ni(2+)-affinity resin. The rDD3 showed essentially the same substrate specificity and inhibitor sensitivity as purified liver DD3 (DD3). To analyze the role of amino acid residues of DD3 in its enzymatic activity, site-directed mutagenesis of DD3 with PCR method was performed. The results of the analyses of these mutants in the aspects of substrate specificity and cofactor-binding suggested a variety of functions in the enzymatic activity: as an active site Tyr-55 may act as a general acid and Asp-50, Lys-84 and His-117 may play an important role in the control of protonation of Tyr-55 as a general acid in the dehydrogenase activity under higher pH conditions, though these residues may not be involved in reductase activity under lower pH conditions. Though the mutated DD3s (Cys to Ser) did not show significant differences in their substrate specificities, these mutants showed different sensitivities to SH-reagents. Present results indicate that Cys-193 may play an important role in the modulation of enzymatic activity under redox conditions generated with GSH+GSSG among five cysteines in DD3.

Enzymatic biomarker measurement and study of DNA adduct formation in benzo

The aim of this study was to improve the knowledge on the metabolic pathways involved in benzo[a]pyrene (B[a]P) activation and on the relationship between adduct levels and enzymatic biomarker activities. With this purpose, a model to assess pollutant exposure via food supply has been developed for the sentinel organism, Mytilus galloprovincialis. Mussels were fed for 4 weeks with B[a]P-contaminated feed (50 mg/kg dry weight mussel). Bioaccumulation was studied by determination of B[a]P concentration in whole mussel by GC/MS analysis. Different biomarkers of pollutant exposure were measured to assess the metabolic state of the exposed organisms. CYP1A-like immunopositive protein titration and B[a]P hydroxylase (BPH) activity were assessed as indicators of phase I biotransformation. Glutathione-S-transferase (GST) activity was measured as an indicator of the conjugation activities. Catalase (CAT) and DT-diaphorase (DTD) activities were assessed as potential biomarkers of oxidative stress, whereas acetylthiocholine esterase (AChE) activity was measured as an indication of possible neurotoxicity of B[a]P exposure. DNA adduct levels were determined in digestive gland DNA by applying the 32P-postlabeling technique with nuclease P1 enhancement. For the developed conditions of exposure, B[a]P concentration reached in whole mussel tissues was very high (>500 mg/kg d.w. mussel) and significant B[a]P-induced changes were recorded for each enzymatic biomarkers. BPH and CAT activities were significantly increased by B[a]P exposure, whereas GST in the gills, DTD and AChE were significantly depressed. On the other hand, no change in CYP1A-like immunopositive protein content was observed. Induction and increase with time of bulky B[a]P-related DNA adducts were demonstrated in the digestive gland, although at low levels (0.269+/-0.082 adduct/10e8 dNps at maximum) by the 32P-postlabeling assay. DNA adduct level was significantly correlated with whole mussel tissue B[a]P concentration, so were all the enzymatic biomarkers measured except to GST activity in both gill and digestive gland tissues. BPH, DTD, CAT and AChE displayed a strong correlation with adduct levels. These results demonstrate the neurotoxicity and the genotoxicity of B[a]P exposure in the mussel. The induction of bulky DNA adducts in mussels demonstrates the existence of activation pathways already identified in vertebrates. It validates also the suitability of this model for further studies on B[a]P metabolism in mussels. Our results support the proposal of BPH, AChE, DTD and CAT activities as suitable biomarkers of PAH exposure for these sentinel species.

Role of quinones in toxicology

Quinones represent a class of toxicological intermediates which can create a variety of hazardous effects in vivo, including acute cytotoxicity, immunotoxicity, and carcinogenesis. The mechanisms by which quinones cause these effects can be quite complex. Quinones are Michael acceptors, and cellular damage can occur through alkylation of crucial cellular proteins and/or DNA. Alternatively, quinones are highly redox active molecules which can redox cycle with their semiquinone radicals, leading to formation of reactive oxygen species (ROS), including superoxide, hydrogen peroxide, and ultimately the hydroxyl radical. Production of ROS can cause severe oxidative stress within cells through the formation of oxidized cellular macromolecules, including lipids, proteins, and DNA. Formation of oxidatively damaged bases such as 8-oxodeoxyguanosine has been associated with aging and carcinogenesis. Furthermore, ROS can activate a number of signaling pathways, including protein kinase C and RAS. This review explores the varied cytotoxic effects of quinones using specific examples, including quinones produced from benzene, polycyclic aromatic hydrocarbons, estrogens, and catecholamines. The evidence strongly suggests that the numerous mechanisms of quinone toxicity (i.e., alkylation vs oxidative stress) can be correlated with the known pathology of the parent compound(s).

Sequence and expression levels in human tissues of a new member of the aldo-keto reductase family

We have isolated a human cDNA clone from small intestine that represents a new member of the aldo-keto reductase family. This new member showed 70% identity at the protein level to human aldose reductase and around 80% identity to other Chinese hamster and mouse reductases. The expression pattern shows that this message is located primarily in the adrenal gland, thus suggesting an involvement in steroid metabolism. It is also strongly expressed in the intestinal tract and has been called human small intestine reductase.

Molecular cloning, expression and catalytic activity of a human AKR7 member of the aldo-keto reductase superfamily: evidence that the major 2-carboxybenzaldehyde reductase from human liver is a homologue of rat aflatoxin B1-aldehyde reductase

The masking of charged amino or carboxy groups by N-phthalidylation and O-phthalidylation has been used to improve the absorption of many drugs, including ampicillin and 5-fluorouracil. Following absorption of such prodrugs, the phthalidyl group is hydrolysed to release 2-carboxybenzaldehyde (2-CBA) and the pharmaceutically active compound; in humans, 2-CBA is further metabolized to 2-hydroxymethylbenzoic acid by reduction of the aldehyde group. In the present work, the enzyme responsible for the reduction of 2-CBA in humans is identified as a homologue of rat aflatoxin B1-aldehyde reductase (rAFAR). This novel human aldo-keto reductase (AKR) has been cloned from a liver cDNA library, and together with the rat protein, establishes the AKR7 family of the AKR superfamily. Unlike its rat homologue, human AFAR (hAFAR) appears to be constitutively expressed in human liver, and is widely expressed in extrahepatic tissues. The deduced human and rat protein sequences share 78% identity and 87% similarity. Although the two AKR7 proteins are predicted to possess distinct secondary structural features which distinguish them from the prototypic AKR1 family of AKRs, the catalytic- and NADPH-binding residues appear to be conserved in both families. Certain of the predicted structural features of the AKR7 family members are shared with the AKR6 beta-subunits of voltage-gated K+-channels. In addition to reducing the dialdehydic form of aflatoxin B1-8,9-dihydrodiol, hAFAR shows high affinity for the gamma-aminobutyric acid metabolite succinic semialdehyde (SSA) which is structurally related to 2-CBA, suggesting that hAFAR could function as both a SSA reductase and a 2-CBA reductase in vivo. This hypothesis is supported in part by the finding that the major peak of 2-CBA reductase activity in human liver co-purifies with hAFAR protein.

Tissue dose, DNA adducts, oxidative DNA damage and CYP1A-immunopositive proteins in mussels exposed to waterborne benzo[a]pyrene

A collaborative study was performed on Mediterranean mussels (Mytilus galloprovincialis) exposed to a wide dose-range (0.5-1000 ppb) of benzo[a]pyrene (B[a]P). We selected this model polycyclic aromatic hydrocarbon in order to confirm the formation of a specific DNA adduct, previously detected in gill DNA, and to clarify the in vivo effects of this mutagenic chemical requiring host-metabolism in mussels. B[a]P concentration reached consistently higher values in the digestive gland than in other analyzed tissues of mussels exposed to B[a]P for 2 or 3 days. With the exception of some values at 1000 ppb of B[a]P. DNA adduct levels increased significantly with the dose in gills and digestive gland and ranged from 0.054 to 0.789 adducts per 10(8) nucleotides (mean values per dose-point). Conversely, more complex dose-response relationships were found by detecting in parallel the levels of an oxidative DNA lesion (8-OHdG) and of CYP1A-immunopositive proteins (the latter measured in the digestive gland only). Overall, the formation of DNA adducts, the evidence of oxidative DNA damage, and changes in CYP1A-immunopositive protein levels support the hypothesis that B[a]P can induce DNA damage in mussels through a number of different molecular mechanisms.

Estrogen-nucleic acid adducts: reaction of 3,4-estrone-o-quinone radical anion with deoxyribonucleosides

Metabolic activation of estradiol leading to the formation of catechol estrogens is believed to be a prerequisite for its genotoxic effects. Previous studies have shown that 3,4-estronequinone (3,4-EQ) can redox-cycle and is capable of inducing exclusively single-strand DNA breaks in MCF-7 breast cancer cells [Nutter et al. (1991) J. Biol. Chem. 226, 16380-16386]. These studies, however, could not provide conclusive evidence about the mechanism of estrogen carcinogenesis. In order to explore this in more detail, we have shown previously that 3,4-EQ can react with adenine under electrochemical reductive conditions to yield an estrogen-nucleic acid adduct [Abul-Hajj et al. (1995) J. Am. Chem. Soc. 117, 6144-6145]. In this paper, we report the synthesis and identification of nine estrogen-nucleic acid adducts obtained from reaction of 3,4-EQ with deoxycytidine, deoxythymidine, deoxyadenosine, and deoxyguanosine. Purification of reaction mixtures using HPLC gave sufficient quantities of reaction products for identification using 1H-NMR and mass spectral determinations. Reaction of 3,4-EQ with dCyd, dThd, dAdo, and dGuo gave the following estrogen-nucleic acid adducts: N4-(4-hydroxyestron-1-yl)deoxycytidine, N4-(4-hydroxyestron-2-yl)deoxycytidine, N3-(4-hydroxyestron-1-yl)thymine, N3-(4-hydroxyestron-1-yl)deoxythymidine, N6-(4-hydroxyestron-1-yl)deoxyadenosine, 8-(4-hydroxyestron-1-yl)adenine, N2-(4-hydroxyestron-1-yl)deoxyguanosine, 8-(4-hydroxyestron-1-yl)guanine, and 8-(4-hydroxyestron-2-yl)guanine. Adduction through the NH2 group of dAdo, dGuo, and dCyd results in formation of chemically stable adducts. On the other hand, adduction at C-8 led to the formation of several depurination adducts identified as 4-OHE1-1-C8-Gua, 4-OHE1-2-C8-Gua, and 4-OHE1-1-C8-Ade.

Estrogen-nucleic acid adducts: reaction of 3,4-estrone o-quinone with nucleic acid bases

Metabolic activation of estradiol leading to the formation of catechol estrogens is believed to be a prerequisite for its genotoxic effects. Previous studies have shown that 3,4-estrone quinone (3,4-EQ) can redox-cycle and is capable of inducing exclusively single-strand DNA breaks in MCF-7 breast cancer cells [Nutter et al. (1991) J. Biol. Chem. 226, 16380-16386]. These studies, however, could not provide conclusive evidence about the mechanism of estrogen carcinogenesis. In order to explore this in more detail, we have shown previously that 3,4-EQ can react with adenine under electrochemical reductive conditions to yield an estrogen-nucleic acid adduct [Abul-Hajj et al. (1995) J. Am. Chem. Soc. 117, 6144-6145]. In this paper, we report the synthesis and identification of seven estrogen-nucleic acid adducts obtained from reaction of 3,4-EQ with adenine, thymine, and cytosine. Initial purification of reaction mixtures using TLC followed by HPLC gave sufficient quantities of reaction products for identification using 1H-NMR and mass spectral determinations. Reaction of 3,4-EQ with adenine, thymine, and cytosine gave the following estrogen-nucleic acid adducts: 8-(4-hydoxyestrone-1-yl)adenine, 3-adenylimino-1,5(10)-estradiene-4,17-dione,4-adenylimino-1, 5(10)-estradiene-3,17-dione, N1- [4-hydroxyestrone-1(alpha,beta)-yl]thymine, N4-(4-hydroxyestrone-1- yl)cytosine, and N4-(4-hydroxy- estrone-2-yl)cytosine. No reaction products were obtained with guanine presumably due to poor solubility in DMF.

Identification of a rat oltipraz-inducible UDP-glucuronosyltransferase (UGT1A7) with activity towards benzo(a)pyrene-7,8-dihydrodiol

Previous work has shown that polycyclic aromatic hydrocarbons and oltipraz both induce an unidentified rat liver UDP-glucuronosyltransferase with activity toward benzo(a)pyrene-7, 8-diol, the proximate carcinogenic form of benzo(a)pyrene. Here we report the isolation of a benzo(a)pyrene-7,8-diol transferase-encoding cDNA, LC14, from an adult rat hepatocyte-derived cell line (RALA255-10G LCS-3). The predicted amino acid sequence of LC14 is nearly identical (5 differences out of 531 residues) to that deduced from UGT1A7, recently cloned at the genomic DNA level (Emi, Y., Ikushiro, S., and Kyanagi, T. (1995) J. Biochem. (Tokyo) 117, 392-399). Northern analysis of RNA from female F344 rat liver and LCS-3 cells revealed over a 40-fold and 4.4-fold enhancement by oltipraz treatment, respectively. Benzo(a)pyrene-7, 8-diol glucuronidating activity was detected (0.4 nmol/10(6) cells/16 h) in AHH-1 cells transfected with the LC14 expression vector, pMF6-LC14-3. The LC14-encoded transferase exhibited even higher activity toward certain benzo(a)pyrene phenols, including the major 3- and 9-phenol metabolites (4.1 and 2.8 nmol/10(6) cells/16 h, respectively). The Km of the enzyme for (-)-trans benzo(a)pyrene-7, 8-diol and 3-OH-BP was 15.5 and 12.3 microM, respectively. Northern analyses of total RNA revealed expression of LC14 or LC14-like RNA in all extrahepatic tissues tested. Marked inducibility by oltipraz was observed only in liver and (to a lesser extent) intestine. The results suggest that induction of UGT1A7 may explain the increased glucuronidating activities toward benzo(a)pyrene-7,8-diol and other metabolites that occur following treatment with polycyclic aromatic hydrocarbon-type inducing agents and oltipraz. UGT1A7 appears to represent an important cellular chemoprotective enzyme which mediates conjugation and elimination of toxic benzo(a)pyrene metabolites.