Vinyl Chloride—A Classical Industrial Toxicant of New Interest

Hepatocellular Carcinoma in Non-Fibrotic Liver: A Narrative Review

Hepatocellular carcinoma (HCC) in a non-fibrotic liver (F0) is considered to be rare, and there is a marked paucity of studies in the literature on this HCC type. A review of the literature shows some important clinical and tumor characteristics: (a) it occurs mainly in young female and elder male patients; (b) clinically, under normal hepatic function, alpha-fetoprotein level is often normal, and there are no risk factors; (c) associated with metabolic disease; (d) macroscopically, single large lesions are noted; and (e) microscopically, the lesions are well-differentiated and encapsulated. Radiological imaging results are straightforward, showing arterial hyperenhancement and later wash-out. The combined use of B-mode and contrast-enhanced (CE) ultrasound (US) is the most reliable and cost-effective diagnostic method. Few peri-and post-operative complications are noted and 5-year survival is not inferior to patients with HCC on fibrosis liver despite the lesion's large size. Most clinicians believe that HCC is unlikely to occur if patients have no symptoms and normal hepatic function. Although detailed clinical data are very limited, we expect that this review will help to improve the clinical management of HCC in non-fibrotic livers.

Detecting vinyl chloride by phytoscreening in the shallow critical zone at sites with potential human exposure

Chlorinated ethene (CE) contaminants are widespread in groundwater, and the occurrence of vinyl chloride (VC), among others, is a well-known issue due to its mobility, persistence, and carcinogenicity. Human exposure to VC may occur through inhalation after soil vapor intrusion into buildings at sites with shallow underground contamination. Soil vapor intrusion risk is traditionally assessed through indoor air and sub-slab sampling (direct evidence) or soil gas and groundwater surveys (indirect evidence). Phytoscreening (sampling and analysis of tree trunk matrices) was proven as a cost-effective alternative technique to indirectly detect shallow underground contamination by higher chlorinated ethenes and subsequent vapor intrusion risk. However, the technique has appeared barely capable to screen for the lower chlorinated VC, likely due to its fugacity and aerobic bio-degradability, with only one literature record to date showing successful detection in trees. We applied phytoscreening at two sites with severe CE contamination nearby residential buildings caused by illegal dumping of chlorinated pitches from petrochemical productions. The two sites show variable amounts of VC in the shallow groundwater (1e2 to 1e4 μg/L), posing potential sanitary risk issues. Former soil gas surveys did not detect VC in the vadose zone. At both sites, we sampled trunk micro-cores and trunk gas from poplar trees close to contaminated piezometers in different seasons. VC was detected in several instances, disproving the shared literature assumption of the inefficacy of phytoscreening towards this compound. Factors influencing the detectability of VC and other CEs in trees were analyzed through linear regressions. Two different conceptual models were proposed to explain the effective uptake of VC by trees at the two sites, i.e., direct uptake of contaminated groundwater at the first site and uptake of VC from an anoxic vadose zone at the second site. In planta reductive dechlorination of CEs is not expected based on current literature knowledge. Thus, the detection of VC in trunks would indicate its occurrence in the shallow underground, suggesting higher screening effectiveness of phytoscreening compared to soil gas; this has implications for indirect vapor intrusion risk assessment.

Long-term 14-year survival with primary hepatic angiosarcoma

Primary hepatic angiosarcomas (PHAs) are rare primary liver malignancies with poor outcomes due to their aggressive nature and the difficulty it presents in terms of diagnosis and management. However, early diagnosis and aggressive surgical resection combined with ongoing surveillance can confer prolonged survival in patients with PHA. Additionally, adjuvant radiotherapy may be of benefit in cases of involved surgical margins. Here we report the longest surviving patient with PHA in literature to date. The patient had an initial right hemihepatectomy 14 years ago and 10 years later had a segment III segmentectomy for recurrence on surveillance imaging. This was followed with adjuvant radiotherapy for involved margins. There has been no further recurrence noted on imaging to date, and the patient is continuing to thrive in the community.

Association between human herpesvirus-6 and primary brain tumors: a systematic review and meta-analysis

Aim: The present study aimed to find out the prevalence and any possible association between human herpesvirus (HHV-6) and primary brain tumors. Materials & methods: The systematic literature search was performed by finding related articles from major databases. Analysis was performed by comprehensive meta-analysis software. Results: A total of 13 (25 datasets) articles were included in the study, seven (15 datasets) of which were case/control and the rest (ten datasets) were cross-sectional studies. The pooled prevalence of HHV-6 among primary brain cancer patients was 29% (95% CI: 24–33%; I2 = 97.89%). An association was found between HHV-6 and primary brain cancer (summary odds ratio: 3.77% [95% CI: 2.59–5.49%; I2 = 19.0%]). Conclusion: Our analysis demonstrated that HHV-6 is associated with primary brain cancer. Reactivation of the virus could be triggered by the tumor, therefore, we cannot be certain that the virus appeared before the cancer development.

Environmental toxicant-induced maladaptive mitochondrial changes: A potential unifying mechanism in fatty liver disease?

Occupational and environmental exposures to industrial chemicals are well known to cause hepatotoxicity and liver injury. However, despite extensive evidence showing that exposure can lead to disease, current research approaches and regulatory policies fail to address the possibility that subtle changes caused by low level exposure to chemicals may also enhance preexisting conditions. In recent years, the conceptual understanding of the contribution of environmental chemicals to liver disease has progressed significantly. Mitochondria are often target of toxicity of environmental toxicants resulting in multisystem disorders involving different cells, tissues, and organs. Here, we review persistent maladaptive changes to mitochondria in response to environmental toxicant exposure as a mechanism of hepatotoxicity. With better understanding of the mechanism(s) and risk factors that mediate the initiation and progression of toxicant-induced liver disease, rational targeted therapy can be developed to better predict risk, as well as to treat or prevent this disease.

Mechanism of subchronic vinyl chloride exposure combined with a high-fat diet on hepatic steatosis

Vinyl chloride (VC) is a common industrial organic chlorine and environmental pollutant. In recent years, the dietary structure of residents especially Chinese has gradually shifted to western dietary patterns. VC aggravates dietary fatty acid-induced hepatic steatosis, but its mechanism is still unclear. And if the risk factors for steatosis persist, more severe diseases such as fibrosis and cirrhosis will occur. Therefore, we studied the effects and mechanisms of VC (160 and 800 mg/m³ ) and its metabolite (chloroacetaldehyde, 2.25, 4.5, and 9 μM) on hepatic steatosis of high-fat diet (HFD)-fed mice and palmitic acid (PA, 100 μM) treated HepG2 cells. Liver and serum biochemical indicators and pathological staining of the liver showed that the hepatic steatosis of VC combined with HFD groups was more severe than that of single-exposure groups (HFD group, low-dose VC group, and high-dose VC group). Moreover, VC enhanced HFD-induced oxidative stress (OS) and endoplasmic reticulum stress (ERS) and further upregulated the expression of sterol regulatory element-binding protein 1 (SREBP-1) and FAS. Besides, antioxidants and ERS inhibitors reduced the steatosis of HepG2 cells induced by VC metabolites and PA. These results suggest that VC exposure can enhance the degree of hepatic steatosis in HFD-fed mice. VC combined with HFD led to OS and ERS and upregulated the expression of de novo lipogenesis-related proteins, which may be related to the occurrence of hepatic steatosis. And the increased expression of CYP2E1 induced by VC combined with HFD may be the cause of OS.

Chemical Risk Factors of Primary Liver Cancer: An Update

Primary liver cancer has the sixth highest incidence and fourth highest cancer mortality worldwide. Hepatitis B is the leading cause of liver cancer, though its incidence is decreasing with vaccination. Alcohol is the leading cause of liver transplant, cirrhosis, and cancer in the developed world, and is projected to surpass hepatitis B as the leading hepatic cancer etiology worldwide. Tobacco smoking has shown a positive association with liver cancer in a majority of studies, though not all. Aflatoxin, a mycotoxin produced by Aspergillus, is estimated to account for 3–20% of global liver cancer cases, 40% of which occur in sub-Saharan Africa. These statistics are confounded by the prevalence of hepatitis B, which may have a synergistic effect on hepatic carcinogenesis. Aflatoxin is ingested and likely inhaled from agricultural products, placing farmers, food processors, and textile workers in developing nations at risk. Vinyl-chloride is used in the production of PVC plastics and causes rare liver angiosarcoma, hepatocellular carcinoma, and other neoplasms. Arsenic and cadmium are naturally-occurring, hepatocarcinogenic metals with high occupational exposure in industries involving coal, metals, plastics, and batteries. Millions of laborers in waste-disposal and manufacturing are exposed to organic solvents and N-nitrosamines, which vary from carcinogenic (group 1) to possibly carcinogenic (group 2B) in their IARC designation. Insecticide DDT is possibly hepatocarcinogenic (group 2B), though continues to be used for malaria control in the developing world. While suggested by case reports, anabolic steroids and oral contraceptives have not been shown to increase liver cancer risk in large studies.

Diffused hepatic angiosarcoma with Kasabach-Merritt syndrome-case report and literature review

Background

Hepatic angiosarcoma is a rare malignant tumor featured by highly aggressive behavior and poor prognosis. There are few reports about diffused hepatic angiosarcoma with Kasabach-Merritt syndrome till now.

Case presentation

A male patient with the chief complain of hepatic space-occupying lesion accompanied by disturbance of consciousness and jaundice. Hyperbilirubinemia, anemia, thrombocytopenia, prolonged prothrombin time, hypofibrinogenemia, decreased prothrombin activity, and increased fibrinogen degradation product and D-dimer were confirmed by blood analysis; multiple focal hypodense lesions in liver was detected by abdominal computed tomography. Liver failure and Kasabach-Merritt syndrome induced by hepatic hemangioma was diagnosed before operation and liver transplantation was performed. Hepatic angiosarcoma was finally proven by postoperative pathology. This patient died of tumor metastasis 2 months after operation.

Conclusions

Hepatic angiosarcoma which can generate Kasabach-Merritt syndrome and even liver failure has an extremely poor prognosis; liver transplantation option should not be considered in hepatic angiosarcoma regardless of the reason.

Role of endoplasmic reticulum stress and oxidative stress in vinyl chloride-induced hepatic steatosis in mice

Vinyl chloride (VC) is a common industrial organochlorine, shown to cause hepatic angiosarcoma and hepatic steatosis. However, the role of endoplasmic reticulum stress (ERS) and oxidative stress (OS) in hepatic steatosis after subchronic exposure to VC in mice, is unclear. Based on body weight, forty healthy SPF male C57BL/6 J mice were randomly divided into a control group and three VC exposure groups (57.3, 286.7, and 1433.6 ppm) (n = 10 each). VC was administered by static inhalation in a 50 L sealed plexiglass inhalation chamber for 2 h per day, five days per week for 16 weeks. Serum and liver tissues were analyzed for liver enzymes and lipids. Hepatic cytochrome P450 2E1 (CYP2E1) and OS related indicators malondialdehyde (MDA), glutathione (GSH), and superoxide dismutase (SOD) were measured. The mRNA expressions of ERS downstream genes, including glycoregulatory protein-78 (GRP-78), sterol regulatory element binding protein-1 (SREBP-1), Acetyl-CoA carboxylase (ACC), and fatty acid synthase (FAS) were detected by real-time PCR (RT-PCR) and their protein levels examined by western blotting. The CYP2E1 levels increased after VC administration in a dose-dependent manner. MDA levels increased (P < .05) and SOD and GSH levels decreased (P < .05) in the liver of each group with the increase in the dose of VC. ERS and expressions of downstream genes (GRP-78, SREBP-1, ACC, and FAS) were enhanced after VC administration. These results suggested that OS and ERS could be induced by VC, which may lead to an increase in fatty acid synthesis in the liver, further aggravating hepatic steatosis.

Dynamics of Excretion of Thiodiacetic Acid into Urine in Polyvinyl Chloride Production Workers

Background:

Thiodiacetic acid (TDAA) is the main metabolite of vinyl chloride (VC) and 1,2-dichloroethane (EDC) and its urinary level is correlated with the level of exposure to these chemicals.

Objective:

To study dynamics of the excretion of TDAA into urine of polyvinyl chloride (PVC) production workers.

Methods:

The study sample consisted of 65 workers of VC and PVC divisions with various time intervals following exposure to the chemicals, 10 shift workers from PVC division, and 34 workers not exposed to the chemicals (control group). Analysis of urinary TDAA was carried out with gas chromatography with mass-selective detector.

Results:

The concentrations of TDAA in the urine of workers of the VC division and in group of primary occupations who had a high level of exposure to the chemicals, were significantly (p<0.05) higher than that of workers of the PVC production division and group of auxiliary professions. The highest levels of TDAA in the urine of workers were found at the beginning of the next shift and during a long break, 24–48 hours after the cessation of the exposure.

Conclusion:

When conducting biomonitoring studies in PVC production workers, the optimal time for collecting urine samples is at the beginning of the next shift or during a long rest, 24–48 hours after the exposure.

Relative telomere length and gene expression of shelterin complex proteins among vinyl chloride monomer-exposed workers in China

Vinyl chloride monomer (VCM) is a confirmed carcinogen. The effects of VCM on telomeres and the gene expression of telomere complex proteins, shelterin, have not been well studied but could be of potential relevance to the carcinogenic mechanism of VCM and the health surveillance of VCM-exposed workers. A group of 241 VCM-exposed workers and 101 internal controls from the same plant in Shandong, China were recruited and quantitative polymerase chain reaction was preformed to measure relative telomere length (RTL) and gene expression of shelterin proteins. VCM cumulative exposure dose (CED) was estimated for the exposed workers. The differences in RTL and gene expression between groups were compared by Wald test fitted with robust regression. Shorter RTL was observed in VCM-exposed workers than in the controls (P < 0.001) and was related to CED of VCM. Shortened RTL was also significantly related to increasing age (P = 0.012) and high blood pressure (P = 0.056). Levels of gene expression of shelterin components in exposed workers were all lower than in controls except increased TIN2 expression, and the gene expression differences in TIN2 and POT1 among exposed and control groups were significant (P = 0.014 for TIN2 and P < 0.001 for POT1, respectively). VCM exposure is found associated with altered telomere length and gene expression of shelterin components. This provides new insights into the potential carcinogenic mechanisms of VCM and could be helpful for the health surveillance for VCM-exposed workers. Environ. Mol. Mutagen. 60:361-367, 2019. © 2018 Wiley Periodicals, Inc.

Vinyl chloride-induced interaction of nonalcoholic and toxicant-associated steatohepatitis: Protection by the ALDH2 activator Alda-1

Vinyl chloride (VC), an abundant environmental contaminant causes steatohepatitis at high levels, but is considered safe at lower (i.e., sub-OSHA) levels. However, we have previously shown that even lower VC levels exacerbate experimental nonalcoholic fatty liver disease (NAFLD) caused by high-fat diet (HFD). Mitochondrial oxidative injury and subsequent metabolic dysfunction appeared to play key roles in mediating this interaction. Mitochondrial aldehyde dehydrogenase 2 (ALDH2) serves as a key line of defense against endogenous and exogenous reactive aldehydes. The current study therefore tests the hypothesis that allosteric activation of ALDH2 with Alda-1 will protect against VC-enhanced NAFLD. Mice were exposed to low VC concentrations (<1 ppm), or room air for 6 h/day, 5 days/week for 12 weeks, while on HFD or low-fat control diet (LFD). Some mice received Alda-1 (20 mg/kg i.p., 3 × /week) for the last 3 weeks of diet/VC exposure. Indices of liver injury, oxidative stress, metabolic and mitochondrial (dys)function were measured. As observed previously, low-dose VC did not cause liver injury in control mice; while liver injury caused by HFD was enhanced by VC. VC decreased hepatic ALDH2 activity of mice fed HFD. Alda-1 attenuated oxidative stress, liver injury, and dysmetabolism in mice exposed to HFD+VC under these conditions. Importantly, alterations in mitochondrial function caused by VC and HFD were diminished by Alda-1. Previous studies have indicated that liver injury caused by HFD is mediated, at least in part, by enhanced mitochondrial autophagy (mitophagy). Here, Alda-1 suppressed PINK1/PARKIN-mediated mitophagy. Taken together, these results support the hypothesis that ALDH2 is a critical defense against mitochondrial injury caused by VC in experimental NAFLD. The ALDH2 activator Alda-1 conferred protection against liver damage under these conditions, most likely via increasing clearance of aldehydes and preserving mitochondrial respiratory function.

•

VC, combined with HFD impairs ALDH2 function, causing an accumulation of endogenous aldehydes and oxidative stress in vivo.

•

VC metabolite chloroacetaldehyde directly blocks ALDH2 activity in vitro.

•

Alda-1 treatment reverses pre-established liver injury, oxidative stress and metabolic dysregulation caused by VC and HFD.

•

Alda-1 increases overall autophagy caused by VC+HFD, but decreases mitophagy, likely to preserve mitochondrial function.

Association of Telomere Length With Chromosomal Damage Among Chinese Workers Exposed to Vinyl Chloride Monomer

OBJECTIVE

To explore the relationship between relative telomere length (RTL) and chromosomal damage represented by micronucleus (MN) frequencies among vinyl chloride monomer (VCM) -exposed workers.

METHODS

A group of 126 VCM-exposed workers, 60 internal controls, and 25 external controls were examined for RTL by Quantitative polymerase chain reaction and MN frequencies by cytokinesis-block micronucleus test. Cumulative exposure dose was used to estimate the exposure of VCM-exposed workers.

RESULTS

The RTL were significantly shorter in exposed workers and internal controls than in external controls. The exposed workers had significantly increased MN frequencies than both control groups. Additionally, MN frequencies were negatively associated with RTL in VCM-exposed group.

CONCLUSIONS

VCM exposure may alter telomere length, which could be a potential biomarker of susceptibility to chromosomal damage.

Surgically Diagnosed Primary Hepatic Angiosarcoma

Primary hepatic angiosarcoma is a rare tumor originating from endothelial cells in the liver and accounts for approximately 1% of all hepatic malignant tumors. It is difficult to diagnose due to the lack of specific symptoms or tumor markers. No effective treatment exists, but complete surgical resection may achieve a good outcome. Since most primary hepatic angiosarcomas are already at an advanced stage at diagnosis, few reports describe tumors smaller than 2 cm. We report a case of surgery for a 1.7-cm sized primary hepatic angiosarcoma. Further studies are required to improve the preoperative diagnosis of primary hepatic angiosarcoma.

Analysis of microRNA expression and micronuclei frequency in workers exposed to vinyl chloride monomer in China

AIM

To identify differently expressed miRNAs associated with vinyl chloride monomer (VCM) and micronuclei (MN) frequency.

METHOD

In discovery stage, we used microarray to detect miRNAs expression in peripheral blood lymphocytes between six low and six high VCM-exposed workers grouped by medium cumulative exposure dose. Then we validated four miRNAs using real-time quantitative reverse transcription PCR (qRT-PCR) and detected the micronuclei frequencies using cytokinesis-block micronucleus assay in 94 VCM-exposed workers and 53 healthy control subjects.

RESULTS & CONCLUSION

We found eight miRNAs significantly downregulated and seven miRNAs upregulated (|Fold Change| >2; p < 0.05) in the high-exposure group through microarray. We validate that miR-222-3p, miR-146a-5p and miR-151a-5p were downregulated, while miR-22-3p was upregulated in VCM-exposed group (all p < 0.01). Furthermore, we found that expression of miR-22-3p was upregulated in the high micronuclei (MN) frequency subjects. In conclusion, our study suggested that these four miRNAs could be biomarkers of VCM exposure, and moreover miR-22-3p was correlated with MN frequency.

Transient Kinetic Methods for Mechanistic Characterization of DNA Binding and Nucleotide Flipping

Enzymes that modify nucleobases in double-stranded genomic DNA, either as part of a DNA repair pathway or as an epigenetic modifying pathway, adopt a multistep pathway to locate target sites and reconfigure the DNA to gain access. Work on several different enzymes has shown that in almost all cases base flipping, also known as nucleotide flipping, is a key feature of specific site recognition. In this chapter, we discuss some of the strategies that can be used to perform a kinetic characterization for DNA binding and nucleotide flipping. The resulting kinetic and thermodynamic framework provides a platform for understanding substrate specificity, mechanisms of inhibition, and the roles of important amino acids. We use a human DNA repair glycosylase called alkyladenine DNA glycosylase as a case study, because this is one of the best-characterized nucleotide-flipping enzymes. However, the approaches that are described can be readily adapted to study other enzymes, and future studies are needed to understand the mechanism of substrate recognition in each individual case. As more enzymes are characterized, we can hope to uncover which features of DNA searching and nucleotide flipping are fundamental features shared by many different families of DNA modifying enzymes, and which features are specific to a particular enzyme. Such an understanding provides reasonable models for less characterized enzymes that are important for epigenetic DNA modification and DNA repair pathways.

Non‑infective occupational risk factors for hepatocellular carcinoma: A review (Review)

Liver cancer is the second leading worldwide cause of cancer‑associated mortalities. Hepatocellular carcinoma, which accounts for the majority of liver tumors, ranks fifth among types of human cancer. Well‑established risk factors for liver cancer include the hepatitis B and C viruses, aflatoxins, alcohol consumption, and oral contraceptives. Tobacco smoking, androgenic steroids, and diabetes mellitus are suspected risk factors. Current knowledge regarding non‑infective occupational risk factors for liver cancer is inconclusive. The relevance of liver disorders to occupational medicine lies in the fact that the majority of chemicals are metabolized in the liver, and toxic metabolites generated via metabolism are the predominant cause of liver damage. However, their non‑specific clinical manifestations that are similar in a number of liver diseases make diagnosis difficult. Furthermore, concomitant conditions, such as viral hepatitis and alcohol or drug abuse, may mask liver disorders that result from occupational hepatotoxic agents and block the demonstration of an occupational cause. The identification of environmental agents that result in human cancer is a long and often difficult process. The purpose of the present review is to summarize current knowledge regarding the association of non‑infective occupational risk exposure and HCC, to encourage further research and draw attention to this global occupational public health problem.

Role of dietary fatty acids in liver injury caused by vinyl chloride metabolites in mice

BACKGROUND

Vinyl chloride (VC) causes toxicant-associated steatohepatitis at high exposure levels. Recent work by this group suggests that underlying liver disease may predispose the liver to VC hepatotoxicity at lower exposure levels. The most common form of underlying liver disease in the developed world is non-alcoholic fatty liver disease (NAFLD). It is well-known that the type of dietary fat can play an important role in the pathogenesis of NAFLD. However, whether the combination of dietary fat and VC/metabolites promotes liver injury has not been studied.

METHODS

Mice were administered chloroethanol (CE - a VC metabolite) or vehicle once, 10weeks after being fed diets rich in saturated fatty acids (HSFA), rich in poly-unsaturated fatty acids (HPUFA), or the respective low-fat control diets (LSFA; LPUFA).

RESULTS

In control mice, chloroethanol caused no detectable liver injury, as determined by plasma transaminases and histologic indices of damage. In HSFA-fed mice, chloroethanol increased HSFA-induced liver damage, steatosis, infiltrating inflammatory cells, hepatic expression of proinflammatory cytokines, and markers of endoplasmic reticulum (ER) stress. Moreover, markers of inflammasome activation were increased, while markers of inflammasome inhibition were downregulated. In mice fed HPUFA all of these effects were significantly attenuated.

CONCLUSIONS

Chloroethanol promotes inflammatory liver injury caused by dietary fatty acids. This effect is far more exacerbated with saturated fat, versus poly-unsaturated fat; and strongly correlates with a robust activation of the NLRP3 inflammasome in the saturated fed animals only. Taken together these data support the hypothesis that environmental toxicant exposure can exacerbate the severity of NAFLD/NASH.

Assessment of urinary thiodiglycolic acid exposure in school-aged children in the vicinity of a petrochemical complex in central Taiwan

BACKGROUND

School-aged children living in the vicinity of vinyl chloride (VCM)/polyvinyl chloride (PVC) factories may have an increased risk of exposure to hazardous air pollutants.

OBJECTIVES

We aimed to evaluate the urinary thiodiglycolic acid (TDGA) level, as TDGA is a major metabolite of VCM, for students at elementary schools near a petrochemical complex in central Taiwan.

METHODS

We recruited 343 students from 5 elementary schools based on distance to the VCM/PVC factory. First-morning urine and blood samples were obtained from our subjects from October 2013 to September 2014. Urine samples were analyzed for urinary creatinine and TDGA using LC/MS-MS. Hepatitis virus infection were assessed using blood samples. We determined their vitamin consumption, resident location, parent's employment, and other demographic or lifestyle characteristics using a questionnaire.

RESULTS

Median urinary TDGA levels for 316 students at 5 elementary schools from the closest (<.9km) to the farthest (∼8.6km) with respect to the petrochemical complex were 147.6, 95.5, 115.5, 86.8, and 17.3μg/g creatinine, respectively. After adjusting for age, gender, hepatitis virus infection, vitamin B consumption, passive smoking, and home to source distance, we found that urinary TDGA levels for the closest students was significantly higher than those at other schools. Further, median urinary TDGA levels for students during school time were 4.1-fold higher than those during summer vacation.

CONCLUSIONS

After adjusting for confounders, urinary TDGA levels for the school-aged children decreased with increasing distances between the elementary schools and the petrochemical complex.

Hepatic Angiosarcoma Associated with Esophageal Variceal Hemorrhage

Primary hepatic angiosarcoma is a very rare malignancy with a poor prognosis. Because patients present with no specific symptoms, the cancer can grow undetected and most cases are diagnosed too late for resection. We present the case of a 78-year-old Japanese man admitted to our hospital with massive hematemesis and melena. A total gastrectomy had previously been performed on the patient to treat gastric cancer. Endoscopic injection sclerotherapy was performed to control the bleeding from varices over the anastomosis. Computed tomography revealed the presence of multiple atypical liver nodules in the enhanced image. Histological diagnosis of hepatic angiosarcoma was obtained by percutaneous ultrasound-guided liver biopsy. To our knowledge, this is the first report of a patient with hepatic angiosarcoma and acute variceal hemorrhage.

Reversal of DNA damage induced Topoisomerase 2 DNA-protein crosslinks by Tdp2

Mammalian Tyrosyl-DNA phosphodiesterase 2 (Tdp2) reverses Topoisomerase 2 (Top2) DNA-protein crosslinks triggered by Top2 engagement of DNA damage or poisoning by anticancer drugs. Tdp2 deficiencies are linked to neurological disease and cellular sensitivity to Top2 poisons. Herein, we report X-ray crystal structures of ligand-free Tdp2 and Tdp2-DNA complexes with alkylated and abasic DNA that unveil a dynamic Tdp2 active site lid and deep substrate binding trench well-suited for engaging the diverse DNA damage triggers of abortive Top2 reactions. Modeling of a proposed Tdp2 reaction coordinate, combined with mutagenesis and biochemical studies support a single Mg(2+)-ion mechanism assisted by a phosphotyrosyl-arginine cation-π interface. We further identify a Tdp2 active site SNP that ablates Tdp2 Mg(2+) binding and catalytic activity, impairs Tdp2 mediated NHEJ of tyrosine blocked termini, and renders cells sensitive to the anticancer agent etoposide. Collectively, our results provide a structural mechanism for Tdp2 engagement of heterogeneous DNA damage that causes Top2 poisoning, and indicate that evaluation of Tdp2 status may be an important personalized medicine biomarker informing on individual sensitivities to chemotherapeutic Top2 poisons.

Vinyl Chloride Metabolites Potentiate Inflammatory Liver Injury Caused by LPS in Mice

Vinyl chloride (VC) is a ubiquitous environmental contaminant for which human risk is incompletely understood. We have previously reported that high occupational exposure to VC directly caused liver damage in humans. However, whether VC may also potentiate liver injury from other causes is not known. C57Bl/6J mice were administered chloroethanol (CE), a major metabolite of VC, and lipopolysaccharide (LPS) 24 h after CE. Samples were harvested for determination of liver damage, inflammation, and changes in carbohydrate and lipid metabolism. In mice, CE exposure alone caused no detectable liver damage. LPS exposure caused inflammatory liver damage, oxidative stress, lipid accumulation, and glycogen depletion; the effect of all of these variables was potentiated by CE pre-exposure. In vitro experiments suggest that VC metabolite chloroacetaldehyde (CAA) directly damages mitochondria, which may explain the sensitization effect observed in vivo Moreover, co-exposure of cells to CAA and TNFα caused increased cell death, supporting the hypothesis of sensitization by VC metabolites. Taken together, these data demonstrate that exposure to VC/metabolites at levels that are not overtly hepatotoxic can potentiate liver injury caused by another hepatotoxicant. This serves as proof-of-concept that VC hepatotoxicity may be modified by an additional metabolic stress such as endotoxemia, which commonly occurs in acute (eg, sepsis) and chronic (eg, NAFLD) diseases.

Enzymatic MPG DNA repair assays for two different oxidative DNA lesions reveal associations with increased lung cancer risk

DNA repair is a major mechanism for minimizing mutations and reducing cancer risk. Here, we present the development of reproducible and specific enzymatic assays for methylpurine DNA glycosylase (MPG) repairing the oxidative lesions 1,N6-ethenoadenine (εA) and hypoxanthine (Hx) in peripheral blood mononuclear cells protein extracts. Association of these DNA repair activities with lung cancer was determined using conditional logistic regression with specimens from a population-based case-control study with 96 lung cancer cases and 96 matched control subjects. The mean MPG-εA in case patients was 15.8 units/μg protein (95% CI 15.3-16.3), significantly higher than in control subjects-15.1 (14.6-15.5), *P = 0.011. The adjusted odds ratio for lung cancer associated with a one SD increase in MPG-εA activity (2.48 units) was significantly bigger than 1 (OR = 1.6, 95% CI = 1.1-2.4; *P = 0.013). When activity of OGG1, a different DNA repair enzyme for oxidative damage, was included in the model, the estimated odds ratio/SD for a combined MPG-εA-OGG1 score was 2.6 (95% CI 1.6-4.2) *P = 0.0001, higher than the odds ratio for each single assay. The MPG enzyme activity assays described provide robust functional risk biomarkers, with increased MPG-εA activity being associated with increased lung cancer risk, similar to the behavior of MPG-Hx. This underscores the notion that imbalances in DNA repair, including high DNA repair, usually perceived as beneficial, can cause cancer risk. Such DNA repair risk biomarkers may be useful for risk assessment of lung cancer and perhaps other cancer types, and for early detection techniques such as low-dose CT.

Primary hepatic angiosarcoma and potential treatment options

Angiosarcomas account for a mere 2-3% of adult soft tissue sarcomas, with an overall poor outcome. Depending on the primary site, angiosarcomas have distinct prognosis. Primary hepatic angiosarcomas (PHAs) are much rare tumors, with worse prognosis compared with other angiosarcomas. PHA is reported to be associated with vinyl chloride, but the majority of patients were still with unknown etiology. As PHA lacks specific symptoms, signs, or images, pathological diagnosis is necessary. The review summarizes 25 articles published from January 2000 to December 2012, including 64 cases of PHA with detailed information. Survival curves are estimated using the Kaplan-Meier method by SPSS 21.0. We find that the median survival time is 5 months; local excision alone or combination with adjuvant therapy is the optimal choice, with median survival time of 17 months. In addition, liver transplant is abandoned for high recurrence rate; emergent transcatheter arterial embolization is thought to be an efficient method for controlling intra-abdominal bleeding; and transcatheter arterial chemoembolization and chemotherapy may be helpful in improving survival.

Polymorphisms in the p53 pathway genes and micronucleus occurrence in Chinese vinyl chloride-exposed workers

OBJECTIVES

To investigate the association between polymorphisms in the p53 pathway genes and chromosomal damage in vinyl chloride (VC)-exposed workers.

MATERIALS AND METHODS

Cytokinesis block micronucleus test was performed in 310 VC-exposed workers and 149 non-exposed workers to determine chromosomal damage. The polymerase chain reaction and restriction fragment length polymorphism technique were used to detect six SNPs in the p53 pathway genes involved in the cell cycle.

RESULTS

There was a highly significant dose-response relationship between VC exposure and chromosomal damage. Individuals carrying the variant genotypes were at higher risk for chromosomal damage compared with their wild type genotype: p53rs1042522, MDM2 Del1518rs3730485, MDM2rs2279744 and GADD45Ars532446. On the other hand, individuals possessing the variant genotype of CDKN2A rs3088440 had significantly decreased risk compared with the corresponding wild-type.

CONCLUSIONS

Genetic polymorphisms in P53 pathway genes may have an impact on VC-induced chromosomal damage.

Risk of hepatocellular carcinoma in workers exposed to chemicals

CONTEXT

Studies on experimental animals have shown liver is a common target of chemical carcinogens; this might suggest that occupational exposure to chemicals is another risk factor for HCC. However, the relationship between occupation and liver cancer has not been extensively studied, with the exception of the known association between vinyl chloride and angiosarcoma of the liver.

EVIDENCE ACQUISITION

A MEDLINE and conventional search of the past 50 years of the medical literature was performed to identify relevant articles on incidence and mechanisms of HCC due to occupational exposure to chemicals. Several important edited books and monographs were also identified and reviewed.

RESULTS

While laboratory data clearly indicate that the liver is an important target of chemical carcinogenesis, epidemiological studies provide very limited evidence on occupational risk factors for HCC. Nevertheless, we found some case reports and epidemiological data showing a moderately increased risk of HCC development in people exposed to vinyl chloride, organic solvents, pesticides, polychlorinated biphenyls, and arsenic.

CONCLUSIONS

Occupational exposure to chemicals may be another risk factor for HCC development, but the interpretation of currently available findings is limited by the small number of studies, questionable accuracy of the diagnosis of liver cancer, and potential confounding or modifying factors such as chronic hepatitis virus infection and alcohol consumption. Further relevant investigations are required for clarifying the actual contribution of occupational exposure to chemicals in HCC development.

Lipids promote survival, proliferation, and maintenance of differentiation of rat liver sinusoidal endothelial cells in vitro

Primary rat liver sinusoidal endothelial cells (LSEC) are difficult to maintain in a differentiated state in culture for scientific studies or technological applications. Relatively little is known about molecular regulatory processes that affect LSEC differentiation because of this inability to maintain cellular viability and proper phenotypic characteristics for extended times in vitro, given that LSEC typically undergo death and detachment around 48-72 h even when treated with VEGF. We demonstrate that particular lipid supplements added to serum-free, VEGF-containing medium increase primary rat liver LSEC viability and maintain differentiation. Addition of a defined lipid combination, or even oleic acid (OA) alone, promotes LSEC survival beyond 72 h and proliferation to confluency. Moreover, assessment of LSEC cultures for endocytic function, CD32b surface expression, and exhibition of fenestrae showed that these differentiation characteristics were maintained when lipids were included in the medium. With respect to the underlying regulatory pathways, we found lipid supplement-enhanced phosphatidylinositol 3-kinase and MAPK signaling to be critical for ensuring LSEC function in a temporally dependent manner. Inhibition of Akt activity before 72 h prevents growth of SEC, whereas MEK inhibition past 72 h prevents survival and proliferation. Our findings indicate that OA and lipids modulate Akt/PKB signaling early in culture to mediate survival, followed by a switch to a dependence on ERK signaling pathways to maintain viability and induce proliferation after 72 h. We conclude that free fatty acids can support maintenance of liver LSEC cultures in vitro; key regulatory pathways involved include early Akt signaling followed by ERK signaling.

Direct repair of 3,N(4)-ethenocytosine by the human ALKBH2 dioxygenase is blocked by the AAG/MPG glycosylase

Exocyclic ethenobases are highly mutagenic DNA lesions strongly implicated in inflammation and vinyl chloride-induced carcinogenesis. While the alkyladenine DNA glycosylase, AAG (or MPG), binds the etheno lesions 1,N(6)-ethenoadenine (ɛA) and 3,N(4)-ethenocytosine (ɛC) with high affinity, only ɛA can be excised to initiate base excision repair. Here, we discover that the human AlkB homolog 2 (ALKBH2) dioxygenase enzyme catalyzes direct reversal of ɛC lesions in both double- and single-stranded DNA with comparable efficiency to canonical ALKBH2 substrates. Notably, we find that in vitro, the non-enzymatic binding of AAG to ɛC specifically blocks ALKBH2-catalyzed repair of ɛC but not that of methylated ALKBH2 substrates. These results identify human ALKBH2 as a repair enzyme for mutagenic ɛC lesions and highlight potential consequences for substrate-binding overlap between the base excision and direct reversal DNA repair pathways.

Comparison of the in vitro replication of the 7-(2-oxoheptyl)-1,N2-etheno-2'-deoxyguanosine and 1,N2-etheno-2'-deoxyguanosine lesions by Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4)

Oligonucleotides were synthesized containing the 7-(2-oxoheptyl)-etheno-dGuo adduct, which is derived from the reaction of dGuo and the lipid peroxidation product 4-oxo-2-nonenal. The in vitro replication of 7-(2-oxoheptyl)-etheno-dGuo by the model Y-family polymerase Sulfolobus solfataricus P2 DNA Polymerase IV (Dpo4) was examined in two sequences. The extension products were sequenced using an improved LC-ESI-MS/MS protocol developed in our laboratories, and the results were compared to that of the 1,N(2)-etheno-dGuo adduct in the same sequence contexts. Both etheno adducts were highly miscoding when situated in 5'-TXG-3' local sequence contexts with <4% of the extension products being derived from error-free bypass. The major extension products resulted from the misinsertion of Ade opposite the adduct and a one-base deletion. The major extension products from replication of the etheno lesions in a 5'-CXG-3' local sequence context were the result of misinsertion of Ade, a one-base deletion, and error-free bypass. Other minor extension products were also identified. The 7-(2-oxoheptyl)-etheno-dGuo lesion resulted in a larger frequency of misinsertion of Ade, whereas the 1,N(2)-etheno-dGuo gave more of the one-base deletion product. Conformational studies of duplex DNA containing the 7-(2-oxoheptyl)-etheno-dGuo in a 5'-TXG-3' sequence context by NMR indicated the presence of a pH-dependent conformational transition, likely involving the glycosyl bond at the adducted guanosine; the pK(a) for this transition was lower than that observed for the 1,N(2)-epsilon-dGuo lesion. However, the 7-(2-oxoheptyl)-etheno-dGuo lesion, the complementary Cyt, and both flanking base pairs remained disordered at all pH values, which is attributed to the presence of the hydrophobic heptyl group of the 7-(2-oxoheptyl)-etheno-dGuo lesion. The altered pK(a) value and the structural disorder at the 7-(2-oxoheptyl)-etheno-dGuo lesion site, as compared to the same sequence containing the 1,N(2)-etheno-dGuo, may contribute to higher frequency of misinsertion of Ade.

Human base excision repair creates a bias toward -1 frameshift mutations

Frameshift mutations are particularly deleterious to protein function and play a prominent role in carcinogenesis. Most commonly these mutations involve the insertion or omission of a single nucleotide by a DNA polymerase that slips on a damaged or undamaged template. The mismatch DNA repair pathway can repair these nascent polymerase errors. However, overexpression of enzymes of the base excision repair (BER) pathway is known to increase the frequency of frameshift mutations suggesting competition between these pathways. We have examined the fate of DNA containing single nucleotide bulges in human cell extracts and discovered that several deaminated or alkylated nucleotides are efficiently removed by BER. Because single nucleotide bulges are more highly exposed we anticipate that they would be highly susceptible to spontaneous DNA damage. As a model for this, we have shown that chloroacetaldehyde reacts more than 18-fold faster with an A-bulge than with a stable A.T base pair to create alkylated DNA adducts that can be removed by alkyladenine DNA glycosylase. Reconstitution of the BER pathway using purified components establishes that bulged DNA is efficiently processed. Single nucleotide deletion is predicted to repair +1 frameshift events, but to make -1 frameshift events permanent. Therefore, these findings suggest an additional factor contributing to the bias toward deletion mutations.

Genetic polymorphisms of XRCC1, HOGG1 and MGMT and micronucleus occurrence in Chinese vinyl chloride-exposed workers

In this study, a group of 313 workers occupationally exposed to vinyl chloride monomer (VCM) and 141 normal unexposed referents were examined for chromosomal damage using the cytokinesis-blocked micronucleus (CBMN) assay in peripheral lymphocytes. We explored the relationship between genetic polymorphisms of XRCC1 (Arg194Trp, Arg280His and Arg399Gln), MGMT(Leu84Phe) and hOGG1 (Ser326Cys) and susceptibility of chromosomal damage induced by VCM. Polymerase chain reaction-restriction fragment length polymorphism techniques were used to detect polymorphisms in XRCC1, hOGG1 and MGMT. It was found that the micronuclei (MN) frequency of exposed workers (4.86 +/- 2.80) per thousand was higher than that of the control group (1.22 +/- 1.24) per thousand (P < 0.01). Increased susceptibility to chromosomal damage as evidenced by higher MN frequency was found in workers with hOGG1 326 Ser/Cys genotype [frequency ratio (FR) = 1.21, 95% confidence interval (CI): 1.02-1.46; P < 0.05], XRCC1 194 Arg/Trp (FR = 1.12, 95% CI: 1.00-1.25; P < 0.05) and XRCC1 280 Arg/His and His/His genotypes (FR = 1.12, 95% CI 1.00-1.26, P < 0.05). Moreover, among susceptibility diplotypes, CGA/CAG carriers had more risk of MN frequency compared with individuals with wild-type CGG/CGG (FR = 1.67, 95% CI: 1.19-2.23; P < 0.05). MN frequency also increased significantly with age in the exposed group (FR = 1.13, 95% CI: 1.00-1.28; P < 0.05). Thus, CB-MN was a sensitive index of early damage among VCM-exposed workers. Genotype XRCC1 Arg194Trp, Arg280His, hOGG1 Ser326Cys, diplotype CGA/CAG and higher age may have an impact on the chromosome damage induced by VCM.

Toxicant-associated steatohepatitis in vinyl chloride workers

Although nonalcoholic steatohepatitis (NASH) is typically associated with obesity, it has also been reported to occur in lean individuals exposed to industrial chemicals. Occupational exposure to vinyl chloride (VC) is a well-documented risk factor for hemangiosarcoma, but has not previously been associated with steatohepatitis. Here we evaluate liver biopsies from 25 nonobese, highly exposed VC workers for steatohepatitis. Next, we evaluate associated metabolic and cytokine abnormalities in affected workers controlled by 26 chemical workers with no to minimal VC exposures, and 11 unexposed, healthy volunteers. Among highly exposed VC workers the prevalence of steatohepatitis was 80%. Of these, 55% had fibrosis and four had hemangiosarcoma. We have coined the term toxicant-associated steatohepatitis (TASH) to describe this condition, which was not explained by obesity or alcohol. Although mean serum transaminases were normal in TASH, total cytokeratin 18, but not the caspase-cleaved fragment, was elevated. Despite the absence of obesity, workers with TASH had insulin resistance with reduced adiponectin levels. TASH was also associated with markedly elevated serum tumor necrosis factor alpha and interleukins 1beta, 6, and 8. Serum antioxidant activity was reduced in TASH.

CONCLUSION

TASH occurred frequently in these nonobese VC workers with high cumulative exposures and normal liver enzymes. Elevated total cytokeratin 18 suggested the presence of necrotic cell death in TASH and may be a useful serologic biomarker. TASH was further characterized by insulin resistance, elevated proinflammatory cytokines, and impaired antioxidant defenses. The threshold VC exposure and the role of other chemical agents in TASH are as yet unknown.

Vinyl chloride and the liver

Vinyl chloride monomer is a known cause of angiosarcoma of the liver. It also has other toxic effects on the liver, and it has recently been suggested that exposure to vinyl chloride also causes hepatocellular carcinoma. However, the data on which this conclusion is based is incomplete. There is inadequate ascertainment of unequivocal diagnoses. In the largest studies lack of data meant that confounding diseases such as viral hepatitis or alcoholic liver disease could not be assessed. At best, the increase in risk is minimal, based on more than 22,000 exposed workers and more than 640,000 person years of observation. However, based on the available data the hypothesis that vinyl chloride causes or contributes to the development of hepatocellular carcinoma remains unproven.

Plastics, the environment and human health: current consensus and future trends

Plastics have transformed everyday life; usage is increasing and annual production is likely to exceed 300 million tonnes by 2010. In this concluding paper to the Theme Issue on Plastics, the Environment and Human Health, we synthesize current understanding of the benefits and concerns surrounding the use of plastics and look to future priorities, challenges and opportunities. It is evident that plastics bring many societal benefits and offer future technological and medical advances. However, concerns about usage and disposal are diverse and include accumulation of waste in landfills and in natural habitats, physical problems for wildlife resulting from ingestion or entanglement in plastic, the leaching of chemicals from plastic products and the potential for plastics to transfer chemicals to wildlife and humans. However, perhaps the most important overriding concern, which is implicit throughout this volume, is that our current usage is not sustainable. Around 4 per cent of world oil production is used as a feedstock to make plastics and a similar amount is used as energy in the process. Yet over a third of current production is used to make items of packaging, which are then rapidly discarded. Given our declining reserves of fossil fuels, and finite capacity for disposal of waste to landfill, this linear use of hydrocarbons, via packaging and other short-lived applications of plastic, is simply not sustainable. There are solutions, including material reduction, design for end-of-life recyclability, increased recycling capacity, development of bio-based feedstocks, strategies to reduce littering, the application of green chemistry life-cycle analyses and revised risk assessment approaches. Such measures will be most effective through the combined actions of the public, industry, scientists and policymakers. There is some urgency, as the quantity of plastics produced in the first 10 years of the current century is likely to approach the quantity produced in the entire century that preceded.

Clinical features and treatment outcomes of advanced stage primary hepatic angiosarcoma

BACKGROUND

Primary hepatic angiosarcoma is a very rare malignancy with a poor prognosis. While surgical resection has been validated as curative choice, most cases are diagnosed too late for resection. Nonetheless, treatment protocols have not been established and also there are very few reports on the clinical features and treatment outcomes.

PATIENTS AND METHODS

Among 11,939 patients diagnosed with primary hepatic tumors from January 1985 to December 2007 at two centers, five patients were diagnosed with primary hepatic angiosarcoma. We analyzed patients' demographics, tumor characteristics, treatment modality, and outcomes using imaging, serology, and pathology.

RESULTS

All five patients were diagnosed at advanced stage with distant metastases. The most common symptom was abdominal pain. The levels of the tumor markers were within the normal range and serological tests were negative for hepatitis B and C viruses. Two of four patients who received chemotherapy died <3 months after diagnosis, but the other two patients survived >6 months.

CONCLUSIONS

A combination of chemotherapy resulted in an improved outcome for two of four patients, suggesting the potential usefulness of palliative chemotherapy to improve survival. This case study may aid in planning chemotherapy for patients with advanced hepatic angiosarcoma.

The formamidopyrimidine derivative of 7-(2-oxoethyl)-2'-deoxyguanosine

Vinyl chloride induces hepatic angiosarcomas, which are otherwise rare malignancies. The biochemical basis involves the formation of the epoxide, which reacts with DNA to give approximately 98% of the 7-(2-oxoethyl) adduct (4) of dGuo plus small amounts of the etheno derivatives of dGuo, dCyd, and dAdo. The carcinogenicity is generally ascribed to the etheno adducts, not 4, because 4 has been shown to disappear from cells rapidly and to have negligible mutagenicity, which argues against its biological importance, whereas etheno adducts are both persistent and mutagenic. It has also been shown that apurinic sites derived from 4 are unlikely to be crucial lesions. A confounding factor with regard to the etheno hypothesis is that etheno adducts arise in unexposed cells by reactions of various lipid peroxidation products. The present study explores the possibility that a major contributor to the carcinogenicity of vinyl chloride may be formamidopyrimidine (FAPy) 12, N-[2-amino-6-[(2-deoxy-beta-D-erythro-pentofuranosyl)amino]-3,4-dihydro-4-oxo-5-pyrimidinyl]-N-(2-oxoethyl)-formamide, which can arise by ring opening of 4, although its formation has not been observed until the present study. N7 adduct 4 undergoes deglycosylation to give 7-(2-oxoethyl)-Gua (13) in acid and imidazolium ring-opening to 12 in base. At pH 7.4, both processes occur with the formation of 12 representing approximately 10% of the product mixture. FAPy 12 spontaneously cyclizes to 22, which upon mild acid treatment yields the deglycosylation product 2-amino-3,4,7,8-tetrahydro-7-hydroxy-4-oxopteridine-5(6H)-carbaldehyde (14). The structure of 14 has been established by NMR and mass spectroscopy and by independent synthesis. Reaction of the epoxide of crotonaldehyde with dGuo failed to give either 13 or 14, indicating that both compounds are unique products of the reactions of dGuo with the epoxides of vinyl monomers. Although FAPy 12 was found to be unstable, carbinolamine 22 arising from cyclization of 12 may be an important contributor to the carcinogenicity of vinyl chloride.

Transcription processing at 1,N2-ethenoguanine by human RNA polymerase II and bacteriophage T7 RNA polymerase

The DNA lesion 1,N(2)-ethenoguanine (1,N(2)-epsilon G) is formed endogenously as a by-product of lipid peroxidation or by reaction with epoxides that result from the metabolism of the industrial pollutant vinyl chloride, a known human carcinogen. DNA replication past 1,N(2)-epsilon G and site-specific mutagenesis studies on mammalian cells have established the highly mutagenic and genotoxic properties of the damaged base. However, there is as yet no information on the processing of this lesion during transcription. Here, we report the results of transcription past a site-specifically modified 1,N(2)-epsilon G DNA template. This lesion contains an exocyclic ring obstructing the Watson-Crick hydrogen-bonding edge of guanine. Our results show that 1,N(2)-epsilon G acts as a partial block to the bacteriophage T7 RNA polymerase (RNAP), which allows nucleotide incorporation in the growing RNA with the selectivity A>G>(C=-1 deletion)>>U. In contrast, 1,N(2)-epsilon G poses an absolute block to human RNAP II elongation, and nucleotide incorporation opposite the lesion is not observed. Computer modeling studies show that the more open active site of T7 RNAP allows lesion bypass when the 1,N(2)-epsilon G adopts the syn-conformation. This orientation places the exocyclic ring in a collision-free empty pocket of the polymerase, and the observed base incorporation preferences are in agreement with hydrogen-bonding possibilities between the incoming nucleotides and the Hoogsteen edge of the lesion. On the other hand, in the more crowded active site of the human RNAP II, the modeling studies show that both syn- and anti-conformations of the 1,N(2)-epsilon G are sterically impermissible. Polymerase stalling is currently believed to trigger the transcription-coupled nucleotide excision repair machinery. Thus, our data suggest that this repair pathway is likely engaged in the clearance of the 1,N(2)-epsilon G from actively transcribed DNA.

Mechanism of 1,N2-etheno-2'-deoxyguanosine formation from epoxyaldehydes

Background levels of etheno adducts have been attributed to the reaction of DNA with 2,3-epoxyaldehydes, a proposed product of lipid peroxidation. We have examined the reaction of (2R,3S)-epoxyhexanal with dGuo to give 7-(1S-hydroxybutyl)-1,N(2)-etheno-dGuo. We observed that the stereochemistry of the side chain scrambled over time. This process provided insight into the mechanism for the formation of 1,N(2)-etheno-dGuo from 4,5-epoxy-2-decenal [Lee, S. H., et al.(2002) Chem. Res. Toxicol. 15, 300-304]. The mechanistic proposal predicts that 2-octenal is a by-product of the reaction. The reaction of 4,5-epoxy-2-decenal was reinvestigated, and the 2-octenal adduct of dGuo was identified as a product of this reaction in support of the mechanistic proposal. Also observed are products that appear to be derived from 2,3-epoxyoctanal, which can be formed through Schiff base formation of 4,5-epoxy-2-decenal with the dGuo followed by hydration of the double bond and retro-aldol reaction.

In vitro synthesis of 1,N6-etheno-2'-deoxyadenosine and 1,N2-etheno-2'-deoxyguanosine by 2,4-dinitrophenol and 1,3-dinitropyrene in presence of a bacterial nitroreductase

The formation of covalent nitro-PAH DNA adducts and nitro-PAH mediated oxidative lesions are two possible mechanisms for the initiation of nitro-PAH carcinogenesis. Sixty-minute incubation of 1,3-dinitropyrene (100 microM) or 1,4-dinitrophenol (100 microM) with a mixture of 150 microM NADH, 0.5 units of E. coli nitroreductase, 100 microM linoleic acid, 0.5 mM ferrous iron, and 100 microM 2'-deoxyadenosine (2'-dA) or 100 microM 2'-deoxyguanosine (2'-dG) were analyzed by liquid chromatography multistage mass spectrometry. Mixtures of 1,N(6)-etheno-2'-deoxyadenosine (epsilondA) plus 4-oxo-2-nonenal (4-ONE) and 1,N(2)-etheno-2'-deoxyguanosine (epsilondG) plus 4-ONE could be detected from 2'-dA and 2'-dG, respectively. Addition of 2% propanol inhibited the formation of etheno adducts. Analyses of disappearance kinetics of dA and dG showed that dG was more rapidly eliminated than does dA (t[1/2] = 23.3 min and 98.3 min for dG and dA, respectively). Curves of formation kinetics revealed that the peak of epsilondG was at 55.6 min while that of epsilondA was at 186.9 min. These peaks represented 1.43% and 1.25% of the original dG and dA, respectively. In both cases, the peaks were followed by rapid degradations of etheno adducts. The results, obtained in this system, do not allow any extrapolation to realistic cellular responses; nevertheless, these data questioned the validity of the use of unsubstituted etheno adducts as reliable oxidative stress and nitro-PAH exposure biomarkers.

Site specific synthesis and polymerase bypass of oligonucleotides containing a 6-hydroxy-3,5,6,7-tetrahydro-9H-imidazo[1,2-a]purin-9-one base, an intermediate in the formation of 1,N2-etheno-2'-deoxyguanosine

The reaction of DNA with certain bis-electrophiles such as chlorooxirane and chloroacetaldehyde produces etheno adducts. These lesions are highly miscoding, and some of the chemical agents that produce them have been shown to be carcinogenic in laboratory animals and in humans. An intermediate in the formation of 1,N2-ethenoguanine is 6-hydroxy-3,5,6,7-tetrahydro-9H-imidazo[1,2-a]purin-9-one (6-hydroxyethanoguanine), which undergoes conversion to the etheno adduct. The chemical properties and miscoding potential of the hydroxyethano adduct have not been previously studied. A synthesis of the hydroxyethano-adducted nucleoside was developed, and it was site specifically incorporated into oligonucleotides. This adduct had a half-life of between 24 and 48 h at neutral pH and 25 degrees C at the nucleoside and oligonucleotide levels. The miscoding potential of the hydroxyethano adduct was examined by primer extension reactions with the DNA polymerases Dpo4 and pol T7-, and the results were compared to the corresponding etheno-adducted oligonucleotide. Dpo4 preferentially incorporated dATP opposite the hydroxyethano adduct and dGTP opposite the etheno adduct; pol T7- preferentially incorporated dATP opposite the etheno adduct while dGTP and dATP were incorporated opposite the hydroxyethano adduct with nearly equal catalytic efficiencies. Collectively, these results indicate that the hydroxyethano adduct has a sufficient lifetime and miscoding properties to contribute to the mutagenic spectrum of chlorooxirane and related genotoxic species.