Identification of early molecular pathways affected by paraquat in rat lung

Possible involvement of transcriptional activation of nuclear factor erythroid 2-related factor 2 (Nrf2) in the protective effect of caffeic acid on paraquat-induced oxidative damage in Drosophila melanogaster

Paraquat (PQ) is a widely used herbicide with no antidote which is implicated in the pathogenesis of the Parkinson's disease. The present study then investigated the potential of caffeic acid (CA), a known antioxidant, cardioprotective and neuroprotective molecule to counteract oxidative stress mediated by PQ. In addition, molecular docking was performed to understand the mechanism underlying the inhibitory effect of CA against PQ poisoning. The fruit fly, Drosophila melanogaster, was exposed to PQ (0.44 mg/g of diet) in the absence or presence of CA (0.25, 0.5, 1 and 2 mg/g of died) for 7 days. Data showed that PQ-fed flies had higher incidence of mortality which was associated with mitochondrial dysfunction, increased free Fe(II) content and lipid peroxidation when compared to the control. Co-exposure with CA reduced mortality and markedly attenuated biochemical changes induced by PQ. The mechanism investigated using molecular docking revealed a strong interaction (-6.2 Kcal/mol) of CA with D. melanogaster transcriptional activation of nuclear factor erythroid 2-related factor 2 (Nrf2). This was characterized by the binding of CA to keap-1 domain of Nrf2. Taking together these results indicate the protective effect of CA against PQ-induced oxidative damage in D. melanogaster was likely through its coordination which hinders Nrf2-keap-1 binding leading to an increase of the antioxidant defense system.

Immunosuppression, oxidative stress, and glycometabolism disorder caused by cadmium in common carp (Cyprinus carpio L.): Application of transcriptome analysis in risk assessment of environmental contaminant cadmium

Cadmium (Cd), a hazardous environmental contaminant with irreversible toxicity to fish, has been detected in aquatic environment of many countries. The common carp is one of the most widely distributed fish in the world, so we used common carp to assess environmental contaminant risk. In present study, we investigated effects of Cd on immune function, oxidative defense, and glycometabolism in the spleens of common carp by transcriptome analysis. Obtained 3794 differentially expressed genes (including 1848 up-regulated and 1946 down-regulated genes) were enriched using databases of Kyoto Encyclopedia of Genes and Genomes, and Gene Ontology in David bioinformatics software (version 6.8). The pathways and gene functions of immune, oxidative defense, and glycometabolism were obtained and identified. Some relative genes were validated using qRT-PCR and gene expression of IL-1β, INF-γ, IL-6, Cxcl18b, HO-1a, CAT, GPx1, GCK, and FBA decreased; and gene expression of B4GALT1, GPAT3, and CYP26B1 increased. Our results indicated that Cd exposure led to immunosuppression, oxidative stress, and glycometabolism disorder in the common carp spleens. The present study gives a novel insight and method on environmental risk assessment.

Engineered cell and tissue models of pulmonary fibrosis

Pulmonary fibrosis includes several lung disorders characterized by scar formation and Idiopathic Pulmonary Fibrosis (IPF) is a particularly severe form of pulmonary fibrosis of unknown etiology with a mean life expectancy of 3years' post-diagnosis. Treatments for IPF are limited to two FDA approved drugs, pirfenidone and nintedanib. Most lead candidate drugs that are identified in pre-clinical animal studies fail in human clinical trials. Thus, there is a need for advanced humanized in vitro models of the lung to improve candidate treatments prior to moving to human clinical trials. The development of 3D tissue models has created systems capable of emulating human lung structure, function, and cell and matrix interactions. The specific models accomplish these features and preliminary studies conducted using some of these systems have shown potential for in vitro anti-fibrotic drug testing. Further characterization and improvements will enable these tissue models to extend their utility for in vitro drug testing, to help identify signaling pathways and mechanisms for new drug targets, and potentially reduce animal models as standard pre-clinical models of study. In the current review, we contrast different in vitro models based on increasing dimensionality (2D, 2.5D and 3D), with added focus on contemporary 3D pulmonary models of fibrosis.

Effect of resveratrol and tetracycline on the subacute paraquat toxicity in mice

Paraquat (PQ) is a nonselective bipyridyl herbicide widely used in agriculture to control weeds, but its accidental, occupational, or intentional exposure in humans is known to cause pneumo- and neurotoxicity which may proves fatal. Oxidative stress is reported as an underlined mechanism of PQ-induced toxicity in alveolar cells, neurons, and astroglia. PQ generates superoxides both through electron transport reaction (ETC) with nicotinamide adenine dinucleotide-dependent oxidoreductase and by the redox cycling via reaction with molecular oxygen. In lungs, it causes edema and inflammation resulting in neutrophils infiltration and subsequent activation of pro-inflammatory cytokines. In the present study, toxicity of subacute oral PQ exposure and effect of resveratrol (Res) and/or tetracycline (TC) on oxidative stress and inflammatory markers in lungs, brain, and liver was studied. Levels of glutathione and malondialdehyde and activities of myeloperoxidase, glutathione peroxidase, and catalase were measured in lungs, brain, and liver. PQ interferes in the function of mitochondrial ETC complexes causing decreased adenosine triphosphate levels, and hence the activities of complexes I and IV were studied in brain tissues. Res, a natural antioxidant, and TC, an antibiotic with its antimicrobial and anti-inflammatory properties, offered significant protection from severe oxidative stress and inflammation and ameliorated the general well-being of mice against the toxic outcome of PQ.

Impairment of striatal mitochondrial function by acute paraquat poisoning

Mitochondria are essential for survival. Their primary function is to support aerobic respiration and to provide energy for intracellular metabolic pathways. Paraquat is a redox cycling agent capable of generating reactive oxygen species. The aim of the present study was to evaluate changes in cortical and striatal mitochondrial function in an experimental model of acute paraquat toxicity and to compare if the brain areas and the molecular mechanisms involved were similar to those observed after chronic exposure. Sprague-Dawley rats received paraquat (25 mg/Kg i.p.) or saline and were sacrificed after 24 h. Paraquat treatment decreased complex I and IV activity by 37 and 21 % respectively in striatal mitochondria. Paraquat inhibited striatal state 4 and state 3 KCN-sensitive respiration by 80 % and 62 % respectively, indicating a direct effect on respiratory chain. An increase of 2.2 fold in state 4 and 2.3 fold in state 3 in KCN-insensitive respiration was observed in striatal mitochondria from paraquat animals, suggesting that paraquat redox cycling also consumed oxygen. Paraquat treatment increased hydrogen peroxide production (150 %), TBARS production (42 %) and cardiolipin oxidation/depletion (12 %) in striatal mitochondria. Also, changes in mitochondrial polarization was induced after paraquat treatment. However, no changes were observed in any of these parameters in cortical mitochondria from paraquat treated-animals. These results suggest that paraquat treatment induced a clear striatal mitochondrial dysfunction due to both paraquat redox cycling reactions and impairment of the mitochondrial electron transport, causing oxidative damage. As a consequence, mitochondrial dysfunction could probably lead to alterations in cellular bioenergetics.

Pulmonary Proteome and Protein Networks in Response to the Herbicide Paraquat in Rats

Paraquat (PQ) has been one of the most widely used herbicides in the world. PQ, when ingested, is toxic to humans and may cause acute respiratory distress syndrome. To investigate molecular perturbation in lung tissues caused by PQ, Sprague Dawley male rats were fed with PQ at a dose of 25 mg/kg body weight for 20 times in four weeks. The effects of PQ on cellular processes and biological pathways were investigated by analyzing proteome in the lung tissues in comparison with the control. Among the detected proteins, 321 and 254 proteins were over-represented and under-represented, respectively, in the PQ-exposed rat lung tissues in comparison with the no PQ control. All over- and under-represented proteins were subjected to Ingenuity Pathway Analysis to create 25 biological networks and 38 pathways of interacting protein clusters. Over-represented proteins were involved in the C-jun-amino-terminal kinase pathway, caveolae-mediated endocytosis signaling, cardiovascular-cancer-respiratory pathway, regulation of clathrin-mediated endocytosis, non-small cell lung cancer signaling, pulmonary hypertension, glutamate receptor, immune response and angiogenesis. Under-represented proteins occurred in the p53 signaling pathway, mitogen-activated protein kinase signaling pathway, cartilage development and angiogenesis inhibition in the PQ-treated lungs. The results suggest that PQ may generate reactive oxygen species, impair the MAPK/p53 signaling pathway, activate angiogenesis and depress apoptosis in the lungs.

Fluorofenidone-loaded PLGA microspheres for targeted treatment of paraquat-induced acute lung injury in rats

Lung-targeting fluorofenidone (AKF) loaded PLGA microspheres (AKF-MS) for the treatment of paraquat (PQ)-induced acute lung injury in rats, were constructed by a solvent evaporation method.

Pharmacological inhibition of CXCR2 chemokine receptors modulates paraquat-induced intoxication in rats

Paraquat (PQ) is an agrochemical agent commonly used worldwide, which is allied to potential risks of intoxication. This herbicide induces the formation of reactive oxygen species (ROS) that ends up compromising various organs, particularly the lungs and the brain. This study evaluated the deleterious effects of paraquat on the central nervous system (CNS) and peripherally, with special attempts to assess the putative protective effects of the selective CXCR2 receptor antagonist SB225002 on these parameters. PQ-toxicity was induced in male Wistar rats, in a total dose of 50 mg/kg, and control animals received saline solution at the same schedule of administration. Separate groups of animals were treated with the selective CXCR2 antagonist SB225002 (1 or 3 mg/kg), administered 30 min before each paraquat injection. The major changes found in paraquat-treated animals were: decreased body weight and hypothermia, nociception behavior, impairment of locomotor and gait capabilities, enhanced TNF-α and IL-1β expression in the striatum, and cell migration to the lungs and blood. Some of these parameters were reversed when the antagonist SB225002 was administered, including recovery of physiological parameters, decreased nociception, improvement of gait abnormalities, modulation of striatal TNF-α and IL-1β expression, and decrease of neutrophil migration to the lungs and blood. Taken together, our results demonstrate that damage to the central and peripheral systems elicited by paraquat can be prevented by the pharmacological inhibition of CXCR2 chemokine receptors. The experimental evidence presented herein extends the comprehension on the toxicodynamic aspects of paraquat, and opens new avenues to treat intoxication induced by this herbicide.

Paraquat increases connective tissue growth factor expression and impairs lung fibroblast proliferation and viscoelasticity

This in vitro study was designed to investigate the molecular mechanisms of paraquat-induced damage using cultured human fetal lung fibroblasts (MRC-5 cells), in order to promote the development of improved therapies for paraquat poisoning. Paraquat’s effects on proliferation were examined by flow cytometry, on viscoelasticity by the micropipette aspiration technique, and on connective tissue growth factor (CTGF) expression by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. Paraquat was found to significantly reduce the proliferation index of MRC-5 cells in a concentration-dependent manner ( p < 0.05) and to significantly impair the viscoelastic properties in a time-independent manner ( p < 0.05). Exposure to paraquat led to a significant and time-dependent increase in CTGF expression ( p < 0.05) and induced changes in the morphology and biomechanical characteristics of the MRC-5 cells. These findings not only provide novel insights into the mechanisms of paraquat-induced lung fibrosis but may represent useful targets of improved molecular-based therapies for paraquat poisoning.

Effect of transforming growth factor-β1 on acute lung injury caused by paraquat

In China, and other Asian countries, numerous patients have succumbed to pulmonary fibrosis induced by paquarat poisoning, but the early pathogenesis remains unclear. In this study the effect of cytokine transforming growth factor (TGF)-β1 was observed in early acute paraquat poisoning and examined the mechanism by which paraquat caused early acute lung injury. It was discovered that the rat serum TGF-β1 levels in the paraquat groups were significant higher than that in the control group (P<0.05) and the rat pulmonary TGF-β1 mRNA expression levels were also higher than that in the control group (P<0.05). Histological examination indicated that the rat lung tissue was broad and congested, and had been infiltrated by inflammatory cells. Masson's trichrome staining for collagen showed that the lung tissue appeared fibrotic following paraquat poisoning. Ultramicrostructure observation found that macrophages, red blood cells, lymphocytes and granulocytes infiltrated the alveolar space and there were cytolysosomes in the macrophages. The shape of the type II alveolar epithelial cell nuclei were irregular with karyopyknosis. The heterochromatin migrated to the cell edge and lamellar body vacuolization was also observed. Type I alveolar epithelial cells shrank. In conclusion, the effect of cytokine TGF-β1 on paraquat-induced acute lung tissue injury may be important.

Molecular mechanisms of paraquat-induced acute lung injury: a current review

Paraquat is an organic heterocyclic herbicide that is widely used in agriculture, especially in Asian countries. The prevalence of paraquat poisonings has increased dramatically in the past two decades in China. Nearly all paraquat poisonings resulted from intentional or accidental oral administration leading to acute lung injury and, ultimately, acute respiratory distress syndrome. The mortality rate has been reported to be greater than 90%. However, the exact toxic mechanism remains unclear. Herein, we reviewed and summarized the most recent publications related to the molecular mechanisms of paraquat-induced acute lung injury.

Paraquat poisoning induces TNF-α-dependent iNOS/NO mediated hyporesponsiveness of the aorta to vasoconstrictors in rats

Paraquat is a toxic herbicide that may induce acute lung injury, circulatory failure and death. The present work aimed at investigating whether there is systemic inflammation and vascular dysfunction after paraquat exposure and whether these parameters were related. There was neutrophilia and accumulation of neutrophils in lung and bronchoalveolar lavage of animals given paraquat. This was associated with an increase in serum levels of TNF-α. In rats given paraquat, the relaxant response of aortic rings to acetylcholine was not modified but the contractile response to phenylephrine was greatly reduced. Endothelium removal or treatment with non-selective (L-NAME) or selective (L-NIL) inhibitors of inducible nitric oxide synthase (iNOS) restored contraction of aortas. There was greater production of nitric oxide (NO), which was restored to basal level by L-NIL, and greater expression of iNOS in endothelial cells, as seen by Western blot analyses and confocal microscopy. Blockade of TNF-α reduced pulmonary and systemic inflammation and vascular dysfunction. Together, our results clearly show that paraquat causes pulmonary and systemic inflammation, and vascular dysfunction in rats. Vascular dysfunction is TNF-α dependent, associated with enhanced expression of iNOS in aortic endothelial cells and greater NO production, which accounts for the decreased responsiveness of aortas to vasoconstrictors. Blockers of TNF-α may be useful in patients with paraquat poisoning.

Protective effects of caffeic acid phenethyl ester on dose-dependent intoxication of rats with paraquat

PURPOSE

Paraquat (PQ; 1,1'dimethyl-bipyridilium 4,4'-dichloride), which is used extensively throughout the world, is highly toxic to humans. We aimed to investigate the protective effects of different doses of caffeic acid phenethyl ester (CAPE) on PQ-intoxicated rats.

MATERIALS AND METHODS

A total of 80 rats were divided into the following eight groups, comprising 10 rats in each group: group 1: control; group 2: administered with CAPE (10 µmol/kg); group 3: administered with 15 mg/kg PQ (PQ15 group); group 4: administered with 30 mg/kg PQ (PQ30 group); group 5: administered with 45 mg/kg PQ (PQ45 group); group 6: administered with 15 mg/kg PQ + CAPE; group 7: administered with 30 mg/kg PQ + CAPE and group 8: administered with 45 mg/kg PQ + CAPE. Both PQ and CAPE were injected intraperitoneally. Pancreatic tissue was examined with both haematoxylin and eosin and immunochemical staining.

RESULTS

The ratio of the immunohistochemical staining area to the total pancreatic area of the β cells revealed that statistically significant differences were observed only between the PQ and PQ + CAPE groups (p < 0.05).

DISCUSSION

The evaluation of the data suggests that CAPE can be used to prevent acute effects of PQ intoxication.

Effects of RNA interference-induced Smad3 gene silencing on pulmonary fibrosis caused by paraquat in mice

Paraquat (PQ) poisoning induces many physiological and histological changes in the human body, but PQ-induced pulmonary fibrosis is most often associated with death. The signaling pathway associated with pulmonary fibrosis is reliant on transforming growth factor-beta 1 (tgf-β(1)) activation of Smad3, as evidenced by Smad3-deficient mice being resistant to tgf-β(1)-induced pulmonary fibrosis. Thus, we sought to determine whether targeted silencing of Smad3 gene expression could inhibit PQ-induced pulmonary fibrosis in mice. We developed an RNA interference (RNAi) method using short hairpin RNAs (shRNAs) targeting Smad3. The shRNA expression cassettes capable of effectively silencing Smad3 in L929 mouse fibroblasts were transferred to an adenovirus vector and intratracheally administered into mouse lung. Treated mice presented with inhibited Smad3 mRNA and protein and were resistant to PQ-induced pulmonary fibrosis, as evidenced by suppressed expressions of procollagen type I mRNA and hydroxyproline amino acid. Thus, silencing of Smad3 appears to be a promising alternative strategy for the treatment of PQ-induced pulmonary fibrosis.

Increased expression of endothelial iNOS accounts for hyporesponsiveness of pulmonary artery to vasoconstrictors after paraquat poisoning

Paraquat is a toxic herbicide that induces severe acute lung injury (ALI) and pulmonary hypertension in humans. Although vascular disorders are present and contribute to increased mortality in ALI patients, there is little data available on vascular responsiveness after toxic exposure to paraquat. We aimed to evaluate the vascular response of isolated pulmonary arteries from rats treated with a dose of paraquat that induces ALI. Paraquat treatment did not modify the relaxant response of pulmonary artery to acetylcholine, but greatly reduced phenylephrine-induced contraction. Removal of the endothelium, inhibition of nitric oxide synthase (NOS) with L-NAME or selective inhibition of inducible NOS (iNOS) with L-NIL, restored contraction of vessels from paraquat poisoned rats to the same level as those not exposed to paraquat. The basal production of NO and expression of iNOS were increased in endothelium-intact but not in endothelium-denuded vessels from paraquat-poisoned rats. Expression of endothelial NOS was not modified. Our findings suggest that paraquat poisoning increases endothelial iNOS expression and basal NO production decreasing responsiveness of pulmonary artery to vasoconstrictors. Thus, our results do not support the hypothesis that pulmonary hypertension in paraquat-induced ALI is mediated by a reduction in endothelial NO production or increased contractility of pulmonary artery.

Glycogen content is affected differently in acute pulmonary and extra-pulmonary lung injury

Acute respiratory distress syndrome (ARDS) is the most severe form of acute lung injury (ALI). The aim of the present study was to investigate whether paraquat-induced acute pulmonary and extra-pulmonary lung injury (ALI-P and ALI-EX, respectively), in rats, affects glycogen content in different tissues. This measurement could indicate performance limitations of tissues, a new biochemical aspect of ARDS. ALI-P and ALI-EX were induced by injection into the trachea (0.5 mg/kg) and intraperitoneally (20 mg/kg) 24 hours prior to tissue collection. The control groups (CTRL) received the same volume of saline. Glycogen content (mg/g tissue) from different tissues was measured using the anthrone reagent. Glycogen content in the heart and kidney was higher in the ALI-EX group than the CTRL-EX group. Glycogen content in the gastrocnemius muscle was lower in the ALI-EX group than the CTRL-EX group. However, there were no significant differences in glycogen content in the diaphragm in the ALI-EX and ALI-P groups or in the gastrocnemius, heart and kidney in the ALI-P group when compared to the respective controls. ALI-EX caused a greater thickening of the alveolar walls, more areas of atelectasis and a greater abundance of inflammatory cells in comparison to ALI-P. These results demonstrate that glycogen content in ALI, induced by an herbicide that is highly toxic to humans and animals, is altered in different tissues depending on the location of the injury.