Progression of alachlor-induced olfactory mucosal tumours

Biodegradation of Alachlor by a Newly Isolated Bacterium: Degradation Pathway and Product Analysis

Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl]acetamide] is a chloroacetanilide herbicide and has been widely used as a selective pre-emergent and post-emergent herbicide to control weeds and grass. Due to its wide usage, direct application on the ground, high solubility in water, and moderate persistence, alachlor and its metabolites have been detected in various environments. Therefore, there is an increasing concern about the environmental fate of alachlor and its metabolites. Microbial biodegradation is a main method of removal of alachlor in the natural environment. In this study, we isolated new alachlor degrading bacterium and proposed a novel alachlor-degrading pathway. The alachlor-degrading bacterial strain, GC-A6, was identified as Acinetobacter sp. using 16S rRNA gene sequence analysis. Acinetobacter sp. GC-A6 utilized alachlor as its sole carbon source and degraded 100 mg L−1 of alachlor within 48 h, which was the highest alachlor degradation efficiency. The degradation pathway of alachlor was studied using GC-MS analysis. Alachlor was initially degraded to 2-chloro-N-(2,6-diethylphenyl) acetamide, which was further degraded to 2,6-diethylaniline and 7-ethylindoline, respectively. 2,6-Diethylaniline was transformed into N-(2,6-diethylphenyl) formamide. N-(2,6-diethylphenyl) formamide was a first-reported intermediate during the degrading pathway of alachlor by single isolate.

A perspective review on impact and molecular mechanism of environmental carcinogens on human health

Cancer is one of the leading causes of death all around the world. It is a group of diseases characterized by abnormal and uncontrollable division of cells leading to severe health conditions and fatality if remains undiagnosed till later stages. Cancer can be caused due to mutation or sudden alterations by effect of certain external agents. Agents that can cause sudden alterations in the genetic content of an individual are known as mutagens. Mutations can lead to permanent changes in the genetic constituency of an individual and possibly lead to cancer. Mutagenic agents that possess the capacity to induce cancer in humans are called carcinogens. Carcinogens may be naturally present in the environment or generated by anthropogenic activities. However, with the progress in molecular techniques, genetic and/or epigenetic mechanisms of carcinogenesis of a wide range of carcinogens have been elucidated. Present review aims to discuss different types of environmental carcinogens and their respective mechanisms responsible for inducing cancer in humans.

Alachlor Use and Cancer Incidence in the Agricultural Health Study: An Updated Analysis

Background

The herbicide alachlor has been widely used in US agriculture since its introduction in 1969. Experimental animal studies show that alachlor causes tumors in vivo; however, few epidemiologic studies have examined associations with human cancer risk. We evaluated alachlor use and cancer incidence in the Agricultural Health Study, updating an earlier analysis that suggested associations with lymphohematopoietic cancers with an additional 540 142 person-years of follow-up and 5113 cancer cases.

Methods

Pesticide applicators in Iowa and North Carolina reported lifetime alachlor use at enrollment (1993-1997) and follow-up (1999-2005). Exposure was characterized by cumulative intensity-weighted days. We estimated relative risks (RRs) and 95% confidence intervals (CIs) using Poisson regression for incident cancers from enrollment through 2012(NC)/2013(IA). Models adjusted for age, tobacco, alcohol, and other pesticides. All statistical tests are two-sided.

Results

Among 49 685 applicators, 25 640 (51.6%) used alachlor, with 3534 alachlor-exposed cancers. The relative risks of laryngeal cancer (nexposed = 34) increased in the second (RR = 4.68, 95% CI = 1.95 to 11.23), third (RR = 6.04, 95% CI = 2.44 to 14.99), and fourth quartiles (RR = 7.10, 95% CI = 2.58 to 19.53) of intensity-weighted days of use compared with no use (Ptrend = .001). Risk of myeloid leukemia was elevated, though not statistically significantly so, in the fourth quartile of intensity-weighted days of use (RR = 1.82, 95% CI = 0.85 to 3.87, Ptrend = .17).

Conclusions

We observed a strong positive association with use of alachlor and laryngeal cancer and a weaker association with myeloid leukemia. The strength and robustness of the association with laryngeal cancer suggests that long-term occupational exposure to alachlor may be a risk factor for laryngeal cancer. This first report requires confirmation.

Cu/Zn-superoxide dismutase and glutathione are involved in response to oxidative stress induced by protein denaturing effect of alachlor in Saccharomyces cerevisiae

Alachlor is a widely used pre-emergent chloroacetanilide herbicide which has been shown to have many harmful ecological and environmental effects. However, the mechanism of alachlor-induced oxidative stress is poorly understood. We found that, in Saccharomyces cerevisiae, the intracellular levels of reactive oxygen species (ROS) including superoxide anions were increased only after long-term exposure to alachlor, suggesting that alachlor is not a pro-oxidant. It is likely that alachlor-induced oxidative stress may result from protein denaturation because alachlor rapidly induced an increased protein aggregation, leading to upregulation of SSA4 and HSP82 genes encoding heat shock proteins (Hsp) of Hsp70 and Hsp90 family, respectively. Although only SOD1 encoding Cu/Zn-superoxide dismutase (SOD), but not SOD2 encoding Mn-SOD, is essential for alachlor tolerance, both SODs play a crucial role in reducing alachlor-induced ROS. We found that, after alachlor exposure, glutathione production was inhibited while its utilization was increased, suggesting the role of glutathione in protecting cells against alachlor, which becomes more important when lacking Cu/Zn-SOD. Based on our results, it seems that alachlor primarily causes damages to cellular macromolecules such as proteins, leading to an induction of endogenous oxidative stress, of which intracellular antioxidant defense systems are required for elimination.

Profiling environmental chemicals for activity in the antioxidant response element signaling pathway using a high throughput screening approach

BACKGROUND

Oxidative stress has been implicated in the pathogenesis of a variety of diseases ranging from cancer to neurodegeneration, highlighting the need to identify chemicals that can induce this effect. The antioxidant response element (ARE) signaling pathway plays an important role in the amelioration of oxidative stress. Thus, assays that detect the up-regulation of this pathway could be useful for identifying chemicals that induce oxidative stress.

OBJECTIVES

We used cell-based reporter methods and informatics tools to efficiently screen a large collection of environmental chemicals and identify compounds that induce oxidative stress.

METHODS

We utilized two cell-based ARE assay reporters, β-lactamase and luciferase, to screen a U.S. National Toxicology Program 1,408-compound library (NTP 1408, which contains 1,340 unique compounds) for their ability to induce oxidative stress in HepG2 cells using quantitative high throughput screening (qHTS).

RESULTS

Roughly 3% (34 of 1,340) of the unique compounds demonstrated activity across both cell-based assays. Based on biological activity and structure-activity relationship profiles, we selected 50 compounds for retesting in the two ARE assays and in an additional follow-up assay that employed a mutated ARE linked to β-lactamase. Using this strategy, we identified 30 compounds that demonstrated activity in the ARE-bla and ARE-luc assays and were able to determine structural features conferring compound activity across assays.

CONCLUSIONS

Our results support the robustness of using two different cell-based approaches for identifying compounds that induce ARE signaling. Together, these methods are useful for prioritizing chemicals for further in-depth mechanism-based toxicity testing.

Utilizing toxicogenomic data to understand chemical mechanism of action in risk assessment

The predominant role of toxicogenomic data in risk assessment, thus far, has been one of augmentation of more traditional in vitro and in vivo toxicology data. This article focuses on the current available examples of instances where toxicogenomic data has been evaluated in human health risk assessment (e.g., acetochlor and arsenicals) which have been limited to the application of toxicogenomic data to inform mechanism of action. This article reviews the regulatory policy backdrop and highlights important efforts to ultimately achieve regulatory acceptance. A number of research efforts on specific chemicals that were designed for risk assessment purposes have employed mechanism or mode of action hypothesis testing and generating strategies. The strides made by large scale efforts to utilize toxicogenomic data in screening, testing, and risk assessment are also discussed. These efforts include both the refinement of methodologies for performing toxicogenomics studies and analysis of the resultant data sets. The current issues limiting the application of toxicogenomics to define mode or mechanism of action in risk assessment are discussed together with interrelated research needs. In summary, as chemical risk assessment moves away from a single mechanism of action approach toward a toxicity pathway-based paradigm, we envision that toxicogenomic data from multiple technologies (e.g., proteomics, metabolomics, transcriptomics, supportive RT-PCR studies) can be used in conjunction with one another to understand the complexities of multiple, and possibly interacting, pathways affected by chemicals which will impact human health risk assessment.

Comparison of rat olfactory mucosal responses to carcinogenic and non-carcinogenic chloracetanilides

Alachlor and butachlor are chloracetanilide herbicides that induce olfactory tumors in rats, whereas propachlor does not. The mechanism by which alachlor induces tumors is distinct from many other nasal carcinogens, in that alachlor induces a gradual de-differentiation of the olfactory mucosa (OM) to a more respiratory-like epithelium, in contrast to other agents that induce cytotoxicity, followed by an aberrant regenerative response. We studied biochemical and genomic effects of these compounds to identify processes that occur in common between alachlor- and butachlor-treated rats. Because we have previously shown that matrix metalloproteinase-2 (MMP2) is activated in OM by alachlor, in the present studies we evaluated both MMP2 activation and changes in OM gene expression in response to carcinogenic and non-carcinogenic chloracetanilide treatments. All three chloracetanilides activated MMP2, and >300 genes were significantly up- or downregulated between control and alachlor-treated rats. The most significantly regulated gene was vomeromodulin, which was dramatically upregulated by alachlor and butachlor treatment (>60-fold), but not by propachlor treatment. Except for similar gene responses in alachlor- and butachlor-treated rats, we did not identify clear-cut differences that would predict OM carcinogenicity in this study.

Effects of long-term alachlor exposure on hepatic antioxidant defense and detoxifying enzyme activities in crucian carp (Carassius auratus)

Alachlor has been widely used in agriculture all over the world. It is suggested that it may be a carcinogen and also an environmental estrogen. In this paper, the physiological and biochemical perturbations of crucian carp (Carassius auratus) exposed to alachlor at different concentrations over 60 days were investigated. The gonadosomatic index (GSI) and hepatosomatic index (HSI) were measured. The activity of hepatic antioxidant defense and detoxifying enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) and the content of glutathione (GSH) were determined and compared with the control group. The result showed that GSI and HSI decreased significantly (P<0.05) in almost all treatments. The activities of SOD, CAT and GST were induced continuously (P<0.05), while the content of reduced glutathione (GSH) was inhibited on the whole. These changes reflect that the antioxidant systems of the tested fishes were affected. The possible defense mechanistic implications about the changes were thus discussed. Furthermore, hepatic SOD and GST were sensitive to alachlor at low concentration, indicating that they might be potential biomarkers in early detection of alachlor contamination in aquatic ecosystems.

Nasal cytotoxic and carcinogenic activities of systemically distributed organic chemicals

Toxicity and carcinogenicity in the mucosa of the nasal passages in rodents has been produced by a variety of organic chemicals which are systemically distributed. In this review, 14 such chemicals or classes were identified that produced rodent nasal cytotoxicity, but not carcinogenicity, and 11 were identified that produced nasal carcinogenicity. Most chemicals that affect the nasal mucosa were either concentrated in that tissue or readily activated there, or both. All chemicals with effects in the nasal mucosa that were DNA-reactive, were also carcinogenic, if adequately tested. None of the rodent nasal cytotoxins has been identified as a human systemic nasal toxin. This may reflect the lesser biotransformation activity of human nasal mucosa compared to rodent and the much lower levels of human exposures. None of the rodent carcinogens lacking DNA reactivity has been identified as a nasal carcinogen or other cancer hazard to humans. Some DNA-reactive rodent carcinogens that affect the nasal mucosa, as well as other tissues, have been associated with cancer at various sites in humans, but not the nasal cavity. Thus, findings in only the rodent nasal mucosa do not necessarily predict either a toxic or carcinogenic hazard to that tissue in humans.

Comparative cytotoxicity of alachlor on RTG-2 trout and SH-SY5Y human cells

The cytotoxic effects of the herbicide alachlor were compared on rainbow trout gonadal RTG-2 and human neuroblastoma SH-SY5Y cell lines. The end points evaluated in both cells after 24, 48, and 72 h of exposure were total protein content (PC), lysosomal function, and mitochondrial's integrity by mitochondrial succinate dehydrogenase (SDH) activity. After 24 h, cytoplasmic membrane integrity by cytosolic lactate dehydrogenase (LDH) leakage and LDH intracellular activity were also studied. In addition, acetylcholinesterase activity (AChE) was quantified in SH-SY5Y cells. The possible biotransformation of alachlor by RTG-2 cells was investigated by analyzing the exposure culture medium by liquid chromatography-mass spectrometry. In RTG-2, EC50 values on PC, lysosomal function, and SDH activity after 24 h exposure ranged from 80 to 95 microM and decreased to approximately 40 microM for longer exposure time periods. SH-SY5Y cells were slightly more sensitive than RTG-2 cells, with EC50 values on PC and lysosomal function ranging from 87 to 75 microM at 24 h and decreasing to 47 microM and 34 microM at 72 h, respectively. AChE activity was increased, being the most sensitive marker for SH-SY5Y with an EC50 of 20 microM at 24 h. The metabolic enzyme SDH was stimulated in SH-SY5Y and reduced in RTG-2 cells. At the studied conditions, no metabolites of alachlor were detected in RTG-2 cultures. In conclusion, the proposed battery approach is an effective screening tool for the safety assessment of environmental contaminants as a complement to fish and animal toxicity procedures.

Molecular biology of the nasal airways: how do we assess cellular and molecular responses in the nose?

We summarize studies herein that relate to use of molecular techniques to assess mechanism of toxicant and carcinogen action on the nasal mucosa. Specifically, we present the results of an in vivo mutagenesis assay with the herbicide alachlor, which causes olfactory mucosal tumors in rats following dietary administration. A positive response was found in olfactory mucosa after 3 mo of treatment. There was no increase in mutant frequency in the adjacent nasal respiratory mucosa or in liver, which are both non-target tissues for alachlor carcinogenesis. We also summarize previous findings of gene expression studies. One on these was a GeneChip experiment aimed at elucidating the mechanism of alachlor olfactory carcinogenesis, wherein we found that oxidative stress and gelatinase genes were upregulated early in the carcinogenic process, while genes consistent with activation of Wnt signaling were activated later in the carcinogenic process. The final example presented summarizes the results of a microarray experiment designed to identify novel olfactory genes involved in the plasticity of the olfactory mucosa. Those studies identified novel olfactory mucosal genes including Sgpl1 and Pon1. In each instance, precise sampling is emphasized and proper controls are discussed, and examples of independent means of validation of genomics experiments are presented.

Reduction of alachlor-induced olfactory mucosal neoplasms by the matrix metalloproteinase inhibitor Ro 28-2653

Chronic exposure to the chloracetanilide herbicide alachlor has been shown to cause olfactory mucosal neoplasms. Genomic analysis of olfactory mucosa from rats given alachlor (126 mg/kg/d) for from 1 day to 18 mo suggested that matrix metalloproteinases MMP-2 and MMP-9 were upregulated in the month following initiation of treatment. The present studies were designed to confirm this latter finding and to explore the potential role of MMPs in alachlor-induced olfactory carcinogenesis. Zymographic analysis of olfactory mucosal extracts confirmed that MMP-2 activity is higher in the olfactory mucosa of alachlor-treated rats. Therefore, rats were fed alachlor (126 mg/kg/d in the diet for 1 year) either with or without the MMP-2/MMP-9 inhibitor Ro 28-2653 (100 mg/kg daily by gavage for the first 2 months of alachlor treatment). The number of olfactory mucosal neoplasms was reduced by 25% after 1 year of alachlor treatment in rats that received both alachlor and Ro 28-2653. The morphology of alachlor-induced olfactory tumors was similar whether or not Ro 28-2653 had been given; the MMP inhibitor itself had no impact on olfactory mucosal histology. These data confirm that olfactory mucosal MMP-2 activity is increased following short-term alachlor exposure and show that administration of an MMP-2/9 inhibitor reduced the incidence of olfactory neoplasms in alachlor-treated rats, thereby implicating MMP-2 activity as a mediator of alachlor-induced carcinogenicity.

Strain-specific of alachlor on murine olfactory mucosal responses

Chloracetanilide herbicides are multisite carcinogens in rodents. Progression of alachlor-induced olfactory tumors in rats is accompanied by cytoplasmic accumulation and nuclear localization of beta-catenin, suggesting activation of Wint signaling. Female CD-1 mice were resistant to alachlor-induced olfactory carcinogenesis. The current studies were performed to determine whether Apc(Min/+) mice, which have activated Wnt signaling due to mutation of the second allele of Apc, would be susceptible to alachlor olfactory carcinogenesis. Female and male Apc(Min/+) mice, as well as Apc(+/+) littermates received alachlor in the diet (260 mg/kg/d) for up to 3 months. Female A/J and C57BL/6J wild-type mice were also treated (for 10 and 14 months, respectively), as these strains vary in sensitivity to many respiratory tract insults. No olfactory mucosal tumors were observed in any of the mice, although alachlor-treated Apc(Min/+) mice developed histological changes similar to those in alachlor-treated rats. Alachlor-treated A/J mice developed pronounced intracellular accumulation of amorphous eosinophilic material in the olfactory mucosa, foci of respiratory-like metaplasia,and hyperplasia of nasal mucus glands. A similar but less intense response was seen in C57BL/6J mice. Mice and rats had equivalent levels of the putative bioactivating enzyme (CYP2A) in olfactory mucosa. and mice had induced hepatic CYP3A and CYP2B enzymes with alachlor treatment, which may increase alachlor elimination. These studies extend previous observations by describing alachlor-induced olfactory mucosal changes in mice and suggest that hepatic metabolic enzyme induction may be responsible for resistance of mice to alachlor-induced olfactory carcinogenesis.

Mortality and cancer incidence among alachlor manufacturing workers 1968-99

BACKGROUND

Alachlor is the active ingredient in pre-emergent herbicide formulations that have been used widely on corn, soybeans, and other crops. It has been found to cause nasal, stomach, and thyroid tumours in rodent feeding studies at levels that are much higher than likely human exposures.

AIMS

To evaluate mortality rates from 1968 to 1999 and cancer incidence rates from 1969 to 1999 for alachlor manufacturing workers at a plant in Muscatine, Iowa.

METHODS

Worker mortality and cancer incidence rates were compared to corresponding rates for the Iowa state general population. Analyses addressed potential intensity and duration of exposure.

RESULTS

For workers with any period of high alachlor exposure, mortality from all causes combined was lower than expected (42 observed deaths, SMR 64, 95% CI 46 to 86) and cancer mortality was slightly lower than expected (13 observed deaths, SMR 79, 95% CI 42 to 136). Cancer incidence for workers with potential high exposure was similar to that for Iowa residents, both overall (29 observed cases, SIR 123, 95% CI 82 to 177) and for workers exposed for five or more years and with at least 15 years since first exposure (eight observed cases, SIR 113, 95% CI 49 to 224). There were no cases of nasal, stomach, or thyroid cancer.

CONCLUSIONS

There were no cancers of the types found in toxicology studies and no discernible relation between cancer incidence for any site and years of alachlor exposure or time since first exposure. Despite the small size of this population, the findings are important because these workers had chronic exposure potential during extended manufacturing campaigns, while use in agriculture is typically limited to a few days or weeks each year.

Antioxidant perturbations in the olfactory mucosa of alachlor-treated rats

The chloracetanilide herbicide alachlor (2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide) induces olfactory mucosal tumors in rats following chronic dietary exposure. Previous reports demonstrated that alachlor exposure was associated with depletion of glutathione (GSH) in liver in vivo and in vitro, but did not address this issue in the target tissue for the carcinogenic response. In this study we investigated a potential oxidative stress pathway in olfactory tissue by examining perturbations in olfactory mucosal antioxidants. Male Long-Evans rats were fed alachlor for up to 10 days (10-126 mg/kg per day), and intracellular reduced GSH and ascorbate levels were measured in olfactory mucosa. Both GSH and ascorbate rapidly decreased in olfactory mucosa following alachlor exposure, with a subsequent increase in both antioxidants to approximately 160% of control levels in the high dose group, and recovery of GSH to control levels in all groups by 10 days. Using Western blot analysis, we found that the modifier subunit of the rate-limiting enzyme in GSH synthesis, glutamate-cysteine ligase, increased in olfactory mucosa and remained elevated (126 mg/kg per day group). Two ascorbate transporters were detected by RT-PCR in olfactory mucosa, but neither appeared to be upregulated by alachlor exposure, and ascorbate synthesis was not stimulated in olfactory mucosa by alachlor treatment. Dietary exposure to alachlor depletes olfactory mucosa antioxidants, which may contribute to DNA damage and tissue-specific tumor formation.