Developmental toxicity of diphenyl ether herbicides in nestling American kestrels

Bifenox compromises porcine trophectoderm and luminal epithelial cells in early pregnancy by arresting cell cycle progression and impairing mitochondrial and calcium homeostasis

Bifenox is a widely used herbicide that contains a diphenyl ether group. However its global usage, the cell physiological effects that induce toxicity have not been elucidated. In this study, the effect of bifenox was examined in porcine trophectoderm and uterine epithelial cells to investigate the potential toxicity of the implantation process. To uncover the toxic effects of bifenox, cell viability and apoptosis following treatment with bifenox were evaluated. To investigate the underlying cellular mechanisms, mitochondrial and calcium homeostasis were investigated in both cell lines. In addition, the dysregulation of cell signal transduction and transcriptional alterations were also demonstrated. Bifenox reduced cell viability and significantly increased the number of cells arrested at the sub-G1 stage. Moreover, bifenox depolarized the mitochondrial membrane and upregulated the calcium flux into the mitochondria in both cell lines. Cytosolic calcium flux increased in porcine trophectoderm (pTr) cells and decreased in porcine luminal epithelium (pLE) cells. In addition, bifenox activated the mitogen-activated protein kinase and phosphoinositide 3-kinase signaling pathways. Furthermore, bifenox inhibited the expression of retinoid receptor genes, such as RXRA, RXRB, and RXRG. Chemokine CCL8 was also downregulated at the mRNA level, whereas CCL5 expression remained unchanged. Overall, the results of this study suggest that bifenox deteriorates cell viability by arresting cell cycle progression, damaging mitochondria, and controlling calcium levels in pTr and pLE cells. The present study indicates the toxic potential of bifenox in the trophectoderm and luminal epithelial cells, which can lead to implantation disorders in early pregnancy.

Establishment of baseline cytology metrics in nestling American kestrels (Falco sparverius): Immunomodulatory effects of the flame retardant isopropylated triarylphosphate isomers

Avian populations must mount effective immune responses upon exposure to environmental stressors such as avian influenza and xenobiotics. Although multiple immune assays have been tested and applied to various avian species, antibody-mediated immune responses in non-model avian species are not commonly reported due to the lack of commercially available species-specific antibodies. The objectives of the present study were to advance methods for studying wild bird immune responses and to apply these to the evaluation of cytological responses after exposure of American kestrels, Falco sparverius, to a commercial flame retardant mixture containing isopropylated triarylphosphate isomers (ITP). Hatchlings were gavaged daily with safflower oil or 1.5 ug/g bw/day of ITP suspended in safflower oil, then bled on days 9, 17, and 21. The ITP treatment group (n = 18) and a subset of controls (Poly I:C treatment group; n = 10) were injected on days 9 and 15 with a synthetic analog of viral double-stranded RNA, polyinosinic:polycytidylic acid (Poly I:C), a toll-like receptor ligand and synthetic viral mimic, and responses compared to a sham injected control group (n = 8). The hypotheses tested whether kestrels showed immunological differences among treatment groups, genetic sex, and/or white blood cell (WBC) subpopulation type over time. A flow cytometry (FCM) gating strategy categorized heterophils (H), lymphocytes (L), and monocytes (M) and their proportions, and measured relative fluorescence in response to anti-chicken CD4 binding. Fluorescent cell surfaces and some granular/vacuolar inclusions were visualized by epifluorescence microscopy. A fourth subpopulation with higher levels of granularity than M but less than H became increasingly apparent with time and was gated along with the H subpopulation; its frequency of occurrence was lowest in the ITP group (P = 0.0023). The percentages of cells differed among treatment groups, days, and sexes (P = 0.0001). For both sexes, percentages of H and L were higher than M in control and Poly I:C. In the ITP group, L percentages were higher than H and M (P = 0.0457), and H and L were higher than M on days 9 and 21 (P = 0.0001). The ratios of H:L and H:WBC, indicators of robust immunity, were also higher on days 9 and 21 than on 17 (P = 0.0079). For each sex, the highest levels of activity measured by FCM geometric means (GEO) of fluorescence (indicative of antibody binding) were observed on day 9 (P = 0.0001 female, and P = 0.0011 male) in H over both L and M (P < 0.0001 for each). In males, GEO of the Poly I:C group was higher than that of the ITP group (P = 0.0374), with no difference observed among females over all days. By using a FCM algorithm for population comparisons of fluorescence to investigate binding within H, the T(x) scores indicated higher fluorescence in control and Poly I:C groups over ITP (P = 0.0001). Unlike chickens, Gallus gallus, which express CD4 primarily on L, kestrels bound the commercial antibody primarily within the gated H subpopulation, suggesting an immunophenotypic difference between taxa, despite a ~60% identity of Falco CD4 amino acid sequences with chicken CD4. The emergent cell subset within the gated H presented dendritic-like cell (DLC) morphological and functional properties, apparently serving as an effector cell. This study adds interpretive context to ecological investigations of infection and of potential immunomodulation by emerging compounds, whereby the early innate responses are mediated by the various cell subsets serving as useful quantitative markers of immunological condition. Data showed that dietary exposure to ITP was immunosuppressive for male and female kestrels over the course of the experiment, reducing DLC frequency compared to the Poly I:C controls. Heterophils and DLC were important in facilitating innate immunological responses.

Aclonifen causes developmental abnormalities in zebrafish embryos through mitochondrial dysfunction and oxidative stress

The herbicide aclonifen is commonly used in agriculture. Aclonifen is toxic to experimental animals, causing developmental abnormalities, decreased energy production for survival, and impaired organogenesis. However, no studies have reported the functional defects and toxicity caused by aclonifen in embryonic development. We hypothesized that the mechanism underlying the toxicity of several herbicides in various organisms involves mitochondrial dysfunction, which subsequently promotes genotoxicity, cytotoxicity, and acute organotoxicity. In the present study, we demonstrated that mitochondrial dysfunction during development results in decreased body length, delayed yolk sac absorption, malformed spinal cord, disrupted brain and eye formation, and the activation of apoptosis in zebrafish embryos. Aclonifen induced oxidative stress by elevating the level of reactive oxygen species, causing mitochondrial damage. Likewise, impaired embryonic vascularization can promote cardiovascular disorders. In this study, we characterized the toxicity of aclonifen in a non-target organism. These findings increase our understanding of the toxicological effects of herbicides in unexpected environments.

Plant Photodynamic Stress: What's New?

In the 1970's, an unconventional stressful photodynamic treatment applied to plants was investigated in two directions. Exogenous photosensitizer treatment underlies direct photodynamic stress while treatment mediating endogenous photosensitizer over-accumulation pinpoints indirect photodynamic stress. For indirect photodynamic treatment, tetrapyrrole biosynthesis pathway was deregulated by 5-aminolevulenic acid or diphenyl ether. Overall, photodynamic stress involves the generation of high amount of reactive oxygen species leading to plant cell death. All these investigations were mainly performed to gain insight into new herbicide development but they were rapidly given up or limited due to the harmfulness of diphenyl ether and the high cost of 5-aminolevulinic acid treatment. Twenty years ago, plant photodynamic stress came back by way of crop transgenesis where for example protoporphyrin oxidases from human or bacteria were overexpressed. Such plants grew without dramatic effects of photodamage suggesting that plants tolerated induced photodynamic stress. In this review, we shed light on the occurrence of plant photodynamic stress and discuss challenging issues in the context of agriculture focusing on direct photodynamic modality. Indeed, we highlighted applications of exogenous PS especially porphyrins on plants, to further develop an emerged antimicrobial photodynamic treatment that could be a new strategy to kill plant pathogens without disturbing plant growth.

PbaR, an IclR family transcriptional activator for the regulation of the 3-phenoxybenzoate 1',2'-dioxygenase gene cluster in Sphingobium wenxiniae JZ-1T

The 3-phenoxybenzoate (3-PBA) 1',2'-dioxygenase gene cluster (pbaA1A2B cluster), which is responsible for catalyzing 3-phenoxybenzoate to 3-hydroxybenzoate and catechol, is inducibly expressed in Sphingobium wenxiniae strain JZ-1(T) by its substrate 3-PBA. In this study, we identified a transcriptional activator of the pbaA1A2B cluster, PbaR, using a DNA affinity approach. PbaR is a 253-amino-acid protein with a molecular mass of 28,000 Da. PbaR belongs to the IclR family of transcriptional regulators and shows 99% identity to a putative transcriptional regulator that is located on the carbazole-degrading plasmid pCAR3 in Sphingomonas sp. strain KA1. Gene disruption and complementation showed that PbaR was essential for transcription of the pbaA1A2B cluster in response to 3-PBA in strain JZ-1(T). However, PbaR does not regulate the reductase component gene pbaC. An electrophoretic mobility shift assay and DNase I footprinting showed that PbaR binds specifically to the 29-bp motif AATAGAAAGTCTGCCGTACGGCTATTTTT in the pbaA1A2B promoter area and that the palindromic sequence (GCCGTACGGC) within the motif is essential for PbaR binding. The binding site was located between the -10 box and the ribosome-binding site (downstream of the transcriptional start site), which is distinct from the location of the binding site in previously reported IclR family transcriptional regulators. This study reveals the regulatory mechanism for 3-PBA degradation in strain JZ-1(T), and the identification of PbaR increases the variety of regulatory models in the IclR family of transcriptional regulators.

A novel angular dioxygenase gene cluster encoding 3-phenoxybenzoate 1',2'-dioxygenase in Sphingobium wenxiniae JZ-1

Sphingobium wenxiniae JZ-1 utilizes a wide range of pyrethroids and their metabolic product, 3-phenoxybenzoate, as sources of carbon and energy. A mutant JZ-1 strain, MJZ-1, defective in the degradation of 3-phenoxybenzoate was obtained by successive streaking on LB agar. Comparison of the draft genomes of strains JZ-1 and MJZ-1 revealed that a 29,366-bp DNA fragment containing a putative angular dioxygenase gene cluster (pbaA1A2B) is missing in strain MJZ-1. PbaA1, PbaA2, and PbaB share 65%, 52%, and 10% identity with the corresponding α and β subunits and the ferredoxin component of dioxin dioxygenase from Sphingomonas wittichii RW1, respectively. Complementation of pbaA1A2B in strain MJZ-1 resulted in the active 3-phenoxybenzoate 1',2'-dioxygenase, but the enzyme activity in Escherichia coli was achieved only through the coexpression of pbaA1A2B and a glutathione reductase (GR)-type reductase gene, pbaC, indicating that the 3-phenoxybenzoate 1',2'-dioxygenase belongs to a type IV Rieske non-heme iron aromatic ring-hydroxylating oxygenase system consisting of a hetero-oligomeric oxygenase, a [2Fe-2S]-type ferredoxin, and a GR-type reductase. The pbaC gene is not located in the immediate vicinity of pbaA1A2B. 3-Phenoxybenzoate 1',2'-dioxygenase catalyzes the hydroxylation in the 1' and 2' positions of the benzene moiety of 3-phenoxybenzoate, yielding 3-hydroxybenzoate and catechol. Transcription of pbaA1A2B and pbaC was induced by 3-phenoxybenzoate, but the transcriptional level of pbaC was far less than that of pbaA1A2B, implying the possibility that PbaC may not be the only reductase that can physiologically transfer electrons to PbaA1A2B in strain JZ-1. Some GR-type reductases from other sphingomonad strains could also transfer electrons to PbaA1A2B, suggesting that PbaA1A2B has a low specificity for reductase.

Bacterial degradation of aromatic compounds via angular dioxygenation

Dioxygenation is one of the important initial reactions of the bacterial degradation of various aromatic compounds. Aromatic compounds, such as biphenyl, toluene, and naphthalene, are dioxygenated at lateral positions of the aromatic ring resulting in the formation of cis-dihydrodiol. This "normal" type of dioxygenation is termed lateral dioxygenation. On the other hand, the analysis of the bacterial degradation of fluorene (FN) analogues, such as 9-fluorenone, dibenzofuran (DF), carbazole (CAR), and dibenzothiophene (DBT)-sulfone, and DF-related diaryl ether compounds, dibenzo-p-dioxin (DD) and diphenyl ether (DE), revealed the presence of the novel mode of dioxygenation reaction for aromatic nucleus, generally termed angular dioxygenation. In this atypical dioxygenation, the carbon bonded to the carbonyl group in 9-fluorenone or to heteroatoms in the other compounds, and the adjacent carbon in the aromatic ring are both oxidized. Angular dioxygenation of DF, CAR, DBT-sulfone, DD, and DE produces the chemically unstable hemiacetal-like intermediates, which are spontaneously converted to 2,2',3-trihydroxybiphenyl, 2'-aminobiphenyl-2,3-diol, 2',3'-dihydroxybiphenyl-2-sulfinate, 2,2',3-trihydroxydiphenyl ether, and phenol and catechol, respectively. Thus, angular dioxygenation for these compounds results in the cleavage of the three-ring structure or DE structure. The angular dioxygenation product of 9-fluorenone, 1-hydro-1,1a-dihydroxy-9-fluorenone is a chemically stable cis-diol, and is enzymatically transformed to 2'-carboxy-2,3-dihydroxybiphenyl. 2'-Substituted 2,3-dihydroxybiphenyls formed by angular dioxygenation of FN analogues are degraded to monocyclic aromatic compounds by meta cleavage and hydrolysis. Thus, after the novel angular dioxygenation, subsequent degradation pathways are homologous to the corresponding part of that of biphenyl. Compared to the bacterial strains capable of catalyzing lateral dioxygenation, few bacteria having angular dioxygenase have been reported. Only a few degradation pathways, CAR-degradation pathway of Pseudomonas resinovorans strain CA10, DF/DD-degradation pathway of Sphingomonas wittichii strain RW1, DF/DD/FN-degradation pathway of Terrabacter sp. strain DBF63, and carboxylated DE-degradation pathway of P. pseudoalcaligenes strain POB310, have been investigated at the gene level. As a result of the phylogenetic analysis and the comparison of substrate specificity of angular dioxygenase, it is suggested that this atypical mode of dioxygenation is one of the oxygenation reactions originating from the relaxed substrate specificity of the Rieske nonheme iron oxygenase superfamily. Genetic characterization of the degradation pathways of these compounds suggests the possibility that the respective genetic elements constituting the entire catabolic pathway have been recruited from various other bacteria and/or other genetic loci, and that these pathways have not evolutionary matured.

Cloning, nucleotide sequence, and expression of the gene encoding a novel dioxygenase involved in metabolism of carboxydiphenyl ethers in Pseudomonas pseudoalcaligenes POB310

Pseudomonas pseudoalcaligenes strain POB310 degrades 3- and 4-carboxydiphenyl ether. The initial reaction involves an angular dioxygenation yielding an unstable hemiacetal that spontaneously decays to phenol and protocatechuate. We cloned a DNA fragment containing the gene encoding the initial dioxygenase from an unstable, self-transmissible plasmid. Sequence analysis revealed two open reading frames encoding proteins with putative molecular masses of 46.3 and 33.6 kDa. The deduced amino acid sequences showed homologies to oxygenase and reductase subunits of aromatic ring-activating dioxygenases, and contained regions identical to consensus sequences that bind chloroplast-like and Rieske-type [2Fe2S] clusters, suggesting that the initial dioxygenase is a class IA aromatic ring-activating dioxygenase system. Initial dioxygenase activity was induced in bacteria grown in M9 minimal medium containing 3- or 4-carboxydiphenyl ether or phenol as carbon source, indicating that the regulation is dependent on the phenol pathway. The maximal specific activity was measured at the beginning of the exponential growth phase.