Consecutive administration of paraquat to rats induces enhanced cholesterol peroxidation and lung injury

Cholesterol is more readily oxidized than phospholipid linoleates in cell membranes to produce cholesterol hydroperoxides

Cholesterol is an essential component of cell membranes and serves as an important precursor of steroidal hormones and bile acids, but elevated levels of cholesterol and its oxidation products have been accepted as a risk factor for maintenance of health. The free and ester forms of cholesterol and fatty acids are the two major biological lipids. The aim of this hypothesis paper is to address the long-standing dogma that cholesterol is less susceptible to free radical peroxidation than polyunsaturated fatty acids (PUFAs). It has been observed that cholesterol is peroxidized much slower than PUFAs in plasma but that, contrary to expectations from chemical reactivity toward peroxyl radicals, cholesterol appears to be more readily autoxidized than linoleates in cell membranes. The levels of oxidation products of cholesterol and linoleates observed in humans support this notion. It is speculated that this discrepancy is ascribed to the fact that cholesterol and phospholipids bearing PUFAs are localized apart in raft and non-raft domains of cell membranes respectively and that the antioxidant vitamin E distributed predominantly in the non-raft domains cannot suppress the oxidation of cholesterol lying in raft domains which are relatively deficient in antioxidant.

Histopathological Findings in a Fatal Case of Paraquat Poisoning

ABSTRACT

Fatal paraquat ingestion presents many interesting pathological findings for the forensic pathologist. The majority of prior research regarding paraquat poisoning has focused on the lung and liver, this article is further directed to and presents some of the histopathological findings present in the brain. Typical macroscopic and histopathological findings of paraquat poisoning were identified in the liver and lungs. The brain was found to be edematous with widening of the centrum semiovale, whereas histologically, it was found that there was extravasation of erythrocytes into the surrounding Virchow-Robin spaces, a finding normally associated with blunt force head injury and, therefore, commonly interpreted by forensic pathologists as a cortical contusion hemorrhage.

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.

Oxidative stress affects sperm performance and ejaculate redox status in subordinate House Sparrows

Oxidative stress (OS) is the result of random cellular damage caused by reactive oxygen species that leads to cell death, ageing, or illness. Most physiological processes can result in OS, which in turn has been identified as a major cause of infertility. In promiscuous species, the fertilizing ability of the ejaculate partly determines the male reproductive success. When dominance determines access to fertile females, theory predicts that lower ranking males should increase resource investment into enhancing ejaculate quality. We hypothesized that subordinate males should thus prioritize antioxidant protection of their ejaculates to protect them from OS. We put this hypothesis to the test, by chronically dosing wild House Sparrows with diquat (∼1mg/kg), an herbicide that increases pro-oxidant generation. We found that, although they increased their antioxidant levels in the ejaculate, diquat-treated males produced sperm with reduced velocity. Importantly, and contrary to our hypothesis, males at the bottom of the hierarchy suffered the largest reduction in sperm velocity. We suggest that resource access hinders individuals' ability to cope with environmental hazards. Our results point at OS as a likely physiological mechanism mediating ejaculate quality, while individual ability to access resources may play a role in constraining the extent to which such resources can be allocated into the ejaculate.

Plant sterols from foods in inflammation and risk of cardiovascular disease: a real threat?

High dietary intakes of cholesterol together with sedentary habits have been identified as major contributors to atherosclerosis. The latter has long been considered a cholesterol storage disease; however, today atherosclerosis is considered a more complex disease in which both innate and adaptive immune-inflammatory mechanisms as well as bacteria play a major role, in addition to interactions between the arterial wall and blood components. This scenario has promoted nutritional recommendations to enrich different type of foods with plant sterols (PS) because of their cholesterol-lowering effects. In addition to cholesterol, PS can also be oxidized during food processing or storage, and the oxidized derivatives, known as phytosterol oxidation products (POPs), can make an important contribution to the negative effects of both cholesterol and cholesterol oxidation oxides (COPs) in relation to inflammatory disease onset and the development of atherosclerosis. Most current research efforts have focused on COPs, and evaluations of the particular role and physiopathological implications of specific POPs have been only inferential. Appreciation of the inflammatory role described for both COPs and POPs derived from foods also provides additional reasons for safety studies after long-term consumption of PS. The balance and relevance for health of all these effects deserves further studies in humans. This review summarizes current knowledge about the presence of sterol oxidation products (SOPs) in foods and their potential role in inflammatory process and cardiovascular disease.

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.

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.

Recombinant adenovirus Ad-RUNrf2 reduces paraquat-induced A549 injury

OBJECTIVE

An RU486-inducible recombinant adenovirus-Nrf2 construct (Ad-RUNrf2) was constructed and expressed in H460 cells to determine whether Nrf2 gene expression can be regulated and to observe the effect of the adenovirus Ad-RUNrf2 on inflammatory cytokines, oxidative stress and apoptotic factors that mediate paraquat (PQ)-induced A549 cell injury.

METHODS

The Nrf2 gene within the RU486 (mifepristone)-inducible system was introduced into an adenovirus vector. A549 cells were transfected with Ad-RUNrf2, and Nrf2 expression was detected using Western blotting and real time-polymerase chain reaction (RT-PCR). RT-PCR, Western blots and enzyme-linked immunosorbent assay were used for observing the effect of RU486-induced Nrf2 expression on the inflammatory cytokines (interleukin-6 (IL-6), IL-10 and tumor necrosis factor-α (TNF-α)), oxidative stress factors (catalase (CAT) and malondialdehyde (MDA)) and apoptosis factors (caspase-3, caspase-9 and cytochrome C) that mediated PQ-induced A549 cell injury.

RESULTS

After infection of H460 cells by Ad-RUNrf2, RT-PCR and Western blot analyses showed that Nrf2 expression increased with additional RU486 doses. IL-6 and TNF-α protein and gene expression levels were significantly reduced, and IL-10 protein levels were significantly increased. Although IL-10 expression increased, it remained significantly lower than that of noninduced adenovirus infection and the simple virus exposure group. RU486 induced a significant reduction in MDA expression and increased CAT protein levels. Caspase-9 and caspase-3 protein and gene expression levels decreased in the RU486 induction group (p < 0.05). Cytochrome C protein levels were not significantly reduced, but its gene expression was significantly decreased (p < 0.05).

CONCLUSION

Ad-RUNrf2 adenovirus was successfully constructed and can be stably expressed and regulated in cells. Ad-RUNrf2 can reduce PQ-induced inflammation, oxidative stress and apoptosis in A549 cells.

Free radical exposure creates paler carotenoid-based ornaments: a possible interaction in the expression of black and red traits

Oxidative stress could be a key selective force shaping the expression of colored traits produced by the primary animal pigments in integuments: carotenoids and melanins. However, the impact of oxidative stress on melanic ornaments has only recently been explored, whereas its role in the expression of carotenoid-based traits is not fully understood. An interesting study case is that of those animal species simultaneously expressing both kinds of ornaments, such as the red-legged partridge (Alectoris rufa). In this bird, individuals exposed to an exogenous source of free radicals (diquat) during their development produced larger eumelanin-based (black) plumage traits than controls. Here, we show that the same red-legged partridges exposed to diquat simultaneously developed paler carotenoid-based ornaments (red beak and eye rings), and carried lower circulating carotenoid levels as well as lower levels of some lipids involved in carotenoid transport in the bloodstream (i.e., cholesterol). Moreover, partridges treated with a hormone that stimulates eumelanin production (i.e., alpha-melanocyte-stimulating hormone) also increased blood carotenoid levels, but this effect was not mirrored in the expression of carotenoid-based traits. The redness of carotenoid-based ornaments and the size of a conspicuous eumelanic trait (the black bib) were negatively correlated in control birds, suggesting a physiological trade-off during development. These findings contradict recent studies questioning the sensitivity of carotenoids to oxidative stress. Nonetheless, the impact of free radicals on plasma carotenoids seems to be partially mediated by changes in cholesterol metabolism, and not by direct carotenoid destruction/consumption. The results highlight the capacity of oxidative stress to create multiple phenotypes during development through differential effects on carotenoids and melanins, raising questions about evolutionary constraints involved in the production of multiple ornaments by the same organism.

Pathological aspects of lipid peroxidation

Lipid peroxidation (LPO) product accumulation in human tissues is a major cause of tissular and cellular dysfunction that plays a major role in ageing and most age-related and oxidative stress-related diseases. The current evidence for the implication of LPO in pathological processes is discussed in this review. New data and literature review are provided evaluating the role of LPO in the pathophysiology of ageing and classically oxidative stress-linked diseases, such as neurodegenerative diseases, diabetes and atherosclerosis (the main cause of cardiovascular complications). Striking evidences implicating LPO in foetal vascular dysfunction occurring in pre-eclampsia, in renal and liver diseases, as well as their role as cause and consequence to cancer development are addressed.

Paraquat (PQ)-induced pulmonary fibrosis increases exercise metabolic cost, reducing aerobic performance in rats

Rats exposed to the quaternary herbicide paraquat (PQ) exhibit oxidative stress and lung injury. In the present study, we investigated the effect of multiple exposures to PQ on aerobic performance during progressive exercise on a treadmill in rats. PQ was dissolved in saline (SAL) (10 mg/ml) and administered intraperitoneally 7 mg/kg body wt to Wistar rats (n = 5) once a week for one month. Control rats received SAL (0.7 ml/kg body wt., intraperitoneally, n = 5) over the same time period. The animals were submitted to aerobic evaluation on a treadmill using a progressive protocol until fatigue prior to the administration of the first dose of PQ or SAL and repeated at 1 week and 40 days following the last dose of the herbicide. Twenty-four hours after the last performance tests, the animals were sacrificed, lungs removed and divided in two groups: PQ and SAL for histopathological analysis. The animals exposed to PQ exhibited decrease in aerobic performance and mechanical efficiency (ME) as well as increase in oxygen consumption during exercise in comparison to the controls forty days after the last dose of PQ. Lung histologic changes included atelectasis, interstitial edema, and inflammation cells in PQ group. The collagen system fibers, fraction area of alveolar collapse and influx of polymorphonuclear (PMN) cells in lung parenchyma were higher in PQ compared to SAL. In conclusion, multiple exposures to PQ induce pulmonary fibrosis, reduce the aerobic performance and mechanical efficiency and increase the metabolic cost of exercise in rats.

Pulmonary toxicity and environmental contamination: radicals, electron transfer, and protection by antioxidants

The atmosphere is replete with a mixture of toxic substances, both natural and man-made. Inhalation of toxic substances produces a variety of insults to the pulmonary system. Lung poisons include industrial materials, particulates from mining and combustion, agricultural chemicals, cigarette smoke, ozone, and nitrogen oxides, among a large number of other chemicals and environmental contaminants. Many proposals have been advanced to explain the mode of action of pulmonary toxicants. In this review we focus on mechanisms of pulmonary toxicity that involve ET, ROS, and OS. The vast majority of toxicants or their metabolites possess chemical ET functionalities that can undergo redox cycling. Such recycling may generate ROS that can injure various cellular constituents in the lung and in other tissues. ET agents include quinones, metal complexes, aromatic nitro compounds, and conjugated iminium ions. Often, these agents are formed metabolically from parent toxicants. Such metabolic reactions are often catalytic and require only small amounts of the offending material. Oxidative attack is commonly associated with lipid peroxidation and oxidation of DNA, and it may result in strand cleavage and 8-OH-DG production. Toxicity is often accompanied by depletion of natural AOs, which further exacerbates the toxic effect. It is not surprising that the use of AOs, both natural in fruits and vegetables, as well as synthetic, may provide protection from the adverse effects of toxicant exposure. The mechanistic framework described earlier is also applicable to some of the more prominent pulmonary illnesses, such as asthma, COPD, and cancer.

Antioxidants as potential therapeutics for lung fibrosis

Interstitial lung disease encompasses a large group of chronic lung disorders associated with excessive tissue remodeling, scarring, and fibrosis. The evidence of a redox imbalance in lung fibrosis is substantial, and the rationale for testing antioxidants as potential new therapeutics for lung fibrosis is appealing. Current animal models of lung fibrosis have clear involvement of ROS in their pathogenesis. New classes of antioxidant agents divided into catalytic antioxidant mimetics and antioxidant scavengers are being developed. The catalytic antioxidant class is based on endogenous antioxidant enzymes and includes the manganese-containing macrocyclics, porphyrins, salens, and the non-metal-containing nitroxides. The antioxidant scavenging class is based on endogenous antioxidant molecules and includes the vitamin E analogues, thiols, lazaroids, and polyphenolic agents. Numerous studies have shown oxidative stress to be associated with many interstitial lung diseases and that these agents are effective in attenuating fibroproliferative responses in the lung of animals and humans.