Different effects of paraquat on microsomal lipid peroxidation in mouse brain, lung and liver

An Investigation of the Neurotoxic Effects of Malathion, Chlorpyrifos, and Paraquat to Different Brain Regions

Acute or chronic exposures to pesticides have been linked to neurotoxicity and the potential development of neurodegenerative diseases (NDDs). This study aimed to consider the neurotoxicity of three widely utilized pesticides: malathion, chlorpyrifos, and paraquat within the hippocampus (HC), corpus striatum (CS), cerebellum (CER), and cerebral cortex (CC). Neurotoxicity was evaluated at relatively low, medium, and high pesticide dosages. All pesticides inhibited acetylcholinesterase (AChE) and neuropathy target esterase (NTE) in each of the brain regions, but esterase inhibition was greatest in the HC and CS. Each of the pesticides also induced greater disruption to cellular bioenergetics within the HC and CS, and this was monitored via inhibition of mitochondrial complex enzymes I and II, reduced ATP levels, and increased lactate production. Similarly, the HC and CS were more vulnerable to redox stress, with greater inhibition of the antioxidant enzymes catalase and superoxide dismutase and increased lipid peroxidation. All pesticides induced the production of nuclear Nrf2 in a dose-dependent manner. Collectively, these results show that pesticides disrupt cellular bioenergetics and that the HC and CS are more susceptible to pesticide effects than the CER and CC.

Resveratrol: Isolation, and Its Nanostructured Lipid Carriers, Inhibits Cell Proliferation, Induces Cell Apoptosis in Certain Human Cell Lines Carcinoma and Exerts Protective Effect Against Paraquat-Induced Hepatotoxicity

Resveratrol (RES) (trans-3, 5,-4'-trihydroxystilebene) is a multi-biofunctional compound found in a variety of plants such as grapes and mulberries. Studies of nanoencapsulated resveratrol have indicated that this compound can inhibit the growth of cancer cells and free radicals. The aim of this study was to isolate resveratrol from Vitis vinifera, develop and evaluate resveratrol nanostructured lipid carriers (NLCs) and/or resveratrol encapsulated chitosan-coated nanostructured lipid carriers (CSNLCs) using low-viscous chitosan for anticancer therapy. In addition, our study was carried out to examine the prophylactic potential of RES, NLC, and CSNLC on paraquat-induced injury in rat hepatocytes. In this study we isolated resveratrol and encapsulated NLCs in phosphate-buffered saline solution using a phase inversion method. In addition, CSNLCs were prepared by ionic gelation method of NLCs using chitosan. NLCs and CSNLCs were then characterized for their particle size, zeta potential, morphology, and entrapment efficiency. Furthermore, NLCs and CSNLCs were evaluated for their cytotoxic effect on Hep-G2, human HCT-116 (colorectal cancer cell line), lymphoblastic leukemia (1301), and human MCF-7 (Michigan Cancer Foundation-7) cells as well as their effect on caspase-3 and death receptor (DR-4). In addition, incubation of hepatocytes with paraquat resulted in increased formation of TBARS (thiobarbituric acid reactive substances) with a parallel increase in lactate dehydrogenase (LDH) leakage at 1 h after incubation. Time-dependent depletion of cellular glutathione (GSH) was observed starting 2 h after incubation with paraquat. The mean particle size of NLC and CSNLC were 67.0 and 98.41 nm, zeta potential were (-) 24.8 and (+) 31.6 mV, entrapment efficiency were 74.15% and 85.46%, respectively, with the observed shapes of nanoparticle being spherical. The treatment of Hep-G2, human HCT-116, lymphoblastic leukemia (1301), and human MCF-7 cells with NLC led to high inhibition in the cell proliferation as concluded by the low IC₅₀ values 27.7, 17.43, 35.39, and 47.66 μg/mL, respectively, whereas CSNLC had high cytotoxic effect on Hep-G2, human HCT-116, lymphoblastic leukemia (1301), and human MCF-7 cells with low IC₅₀ values 13.29, 10.56, 16.79 and 22.60 μg/mL, respectively. Both NLC and CSNLC possess apoptotic properties through activation of the caspase-3 and death receptor (DR-4). In addition, incubation of hepatocytes with RES, NLC, and CSNLC markedly protected against paraquat-induced formation of TBARS, increase in LDH leakage, and prevented GSH depletion. The most effective doses for ethyl acetate, ethanolic, and aqueous extracts were 7.5, 10, and 12.5 μg, respectively. The results presented here may suggest that nanoencapsulated resveratrol isolated from the stems of V. vinifera to obtain NLC and CSNLC possess anticancer and apoptotic effects on cell proliferation, and therefore, can be used as new approach of pharmaceutical drugs. In addition, the results clearly suggest that the RES, NLC, and CSNLC exerted protective effect against cytotoxicity induced by paraquat. On the contrary, the effect decreased in order of CSNLC, NLC, and RES.

Continuous hypoxia attenuates paraquat-induced cytotoxicity in the human A549 lung carcinoma cell line

Paraquat (1,1'-dimethyl-4,4'-bipyridinium dichloride; PQ), an effective and widely used herbicide, was commercially introduced in 1962. It is reduced by the electron donor NADPH, and then reduced PQ transfers the electrons to molecular oxygen, resulting in the production of reactive oxygen species (ROS), which are related to cellular toxicity. However, the influence of continuous hypoxia on PQ-induced ROS production has not fully been investigated. We evaluated in vitro the protective effect of continuous hypoxia on PQ-induced cytotoxicity in the human carcinogenic alveolar basal epithelial cell line (A549 cells) by using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay and live and dead assay, and by measuring lactate dehydrogenase (LDH) release. To elucidate the mechanism underlying this effect, we monitored the immunofluorescence of intracellular ROS and measured malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities. Continuous hypoxia protected the A549 cells from PQ-induced cytotoxicity. Continuous hypoxia for a period of 24 h significantly reduced intracellular ROS, decreased MDA concentration in the supernatant, and normalized SOD and GPx activities. Continuous hypoxia attenuated PQ-induced cell toxicity in A549 cells. This protective effect might be attributable to the suppression of PQ-induced ROS generation.

Prooxidant properties of ascorbic acid in the nigrostriatal dopaminergic system of C57BL/6 mice

Ascorbic acid (AA) is a well-known reducing agent; however, under appropriate condition, it can facilitate oxidation. In this study, we investigated the effect of AA on dopamine (DA) and glutathione levels in the nigrostriatal dopaminergic system of male seven-week-old C57BL/6 mice (weight, 23-25 g). Mice were treated with AA (400 mg/kg, i.p.) once per day for four weeks, and changes in tyrosine hydroxylase (TH) immunoreactivity, DA and its metabolites, and glutathione (reduced and oxidized) in the substantia nigra pars compacta (SNpc) and striatum were measured. After repeated AA administration, TH-positive immunoreactivity (TH-IR) decreased compared to the control both in the SNpc and striatum. AA treatment also significantly reduced DA levels, and the reduction of which corresponded to changes in TH expression within the same region. In addition, AA increased DA oxidative metabolism according to increases in the DOPAC/DA ratio both in the SNpc and the striatum, whereas the O-methylation pathway in the striatum remained unchanged. Levels of reduced glutathione (GSH) in both the SNpc and striatum were decreased more in the AA treated group than in the control group. Likewise, levels of total glutathione were also decreased in the corresponding regions. Taken together, our data suggest that repeated AA injection induces dopaminergic neurotoxicity through generation of oxidative stress, and that this toxicity is related to the decline of GSH in both the SNpc and striatum. This neurotoxic mechanism may specifically involve enhancement of the oxidative pathway of DA metabolism through coupling with the antioxidant GSH system of the nigrostriatal dopaminergic system.

Prolonged toxicokinetics and toxicodynamics of paraquat in mouse brain

BACKGROUND

Paraquat (PQ) has been implicated as a risk factor for the Parkinson disease phenotype (PDP) in humans and mice using epidemiologic or experimental approaches. The toxicokinetics (TK) and toxicodynamics (TD) of PQ in the brain are not well understood.

OBJECTIVES

The TK and TD of PQ in brain were measured after single or repeated doses.

METHODS

Brain regions were analyzed for PQ levels, amount of lipid peroxidation, and functional activity of the 20S proteasome.

RESULTS

Paraquat (10 mg/kg, ip) was found to be persistent in mouse ventral midbrain (VM) with an apparent half-life of approximately 28 days and was cumulative with a linear pattern between one and five doses. PQ was also absorbed orally with a concentration in brain rising linearly after single doses between 10 and 50 mg/kg. The level of tissue lipid peroxides (LPO) was differentially elevated in three regions, being highest in VM, lower in striatum (STR), and least in frontal cortex (FCtx), with the earliest significant elevation detected at 1 day. An elevated level of LPO was still present in VM after 28 days. Despite the cumulative tissue levels of PQ after one, three, and five doses, the level of LPO was not further increased. The activity of the 20S proteasome in the striatum was altered after a single dose and reduced after five doses.

CONCLUSIONS

These data have implications for PQ as a risk factor in humans and in rodent models of the PDP.

Neurotoxicant-induced animal models of Parkinson?s disease: understanding the role of rotenone, maneb and paraquat in neurodegeneration

The etiologic basis of Parkinson's disease (PD), the second most common age-related neurodegenerative disorder, is unknown. Recent epidemiological and experimental studies indicate that exposure to environmental agents, including a number of agricultural chemicals, may contribute to the pathogenesis of this disorder. Animal models are important tools in experimental medical science for studying the pathogenesis and therapeutic intervention strategies of human diseases. Since many human disorders do not arise spontaneously in animals, characteristic functional changes have to be mimicked by neurotoxic agents. Recently, agricultural chemicals, when administrated systemically, have been shown to reproduce specific features of PD in rodents, thus opening new routes for the development of animal models for this disorder. In addition to a brief historical overview of the toxin-induced PD models, this study provides a detailed description of exiting models in which Parkinsonism is initiated via the exposure of animals to such agricultural chemicals as rotenone, paraquat, and maneb. Suggested neurotoxicity mechanisms of these chemicals are considered, and the major lessons learned from the analysis of pesticide-induced PD models are discussed.

Paraquat: a useful tool for the in vivo study of mechanisms of neuronal cell death

The present article reviews the results of experimental studies on paraquat neurotoxicity, started by our group several years ago--when clinical and experimental reports had increased the interest for the possibility that environmental chemicals, including paraquat, may be related to the development of Parkinson's disease-, and which are still continuing since paraquat appears to be a promising tool to study the mechanisms of neuronal cell death in vivo. Our observations have demonstrated that paraquat causes evident neurotoxic effects after intracerebroventricular or intracerebral injection in experimental animals; however, it seems that the herbicide does not exibit a selective neurotoxicity towards the dopaminergic nigro-striatal system since potent behavioural and electrocortical changes are induced by paraquat after injection in brain areas other than the substantia nigra and caudate nucleus. By studying the mechanisms through which paraquat induces neurotoxic effects in vivo, it was shown that either free radical production and activation of cholinergic and glutamatergic transmission may be regarded as related events which play a crucial role in paraquat-induced neurotoxicity. In addition, it was observed that in rats paraquat penetrates the blood-brain barrier following systemic administration to give rise to a differential brain regional distribution; the latter observation rises some concern over the hazard of paraquat as a potential environmental neurotoxin. Indeed, paraquat, administered systemically in rats produces behavioural excitation and brain damage. The brain damage appears to be selective for the pyriform cortex and this does not seem to be strictly related to the high concentrations reached by the herbicide in this area but to the higher vulnerability of this cortical area to the enhanced cholinergic transmission. The recent observation that paraquat, injected into the rat hippocampus, induces the expression of apoptotic neuronal cell death, appears of valuable interest also with a view to paraquat as an useful experimental model in the development of neuroprotective drugs able to block the molecular events which, once activated, are responsible for the induction of neuronal cell death.

Mitochondrial NADH-quinone oxidoreductase of the outer membrane is responsible for paraquat cytotoxicity in rat livers

We investigated the existence of an NADH-dependent paraquat (PQ) reduction system in rat liver mitochondria (Mt) in respect to the cytotoxic mechanisms of PQ. The outer membrane fractions, free from the contamination of inner membranes but with a few microsomes, catalyzed rotenone-insensitive NADH, but not NADPH, oxidation by menadione or PQ. Anti-NADH-cytochrome b5 reductase antibody and its inhibitor p-hydroxymercuribenzonate did not inhibit the NADH-PQ reduction activity. Therefore, the respiratory systems of the inner membranes and microsomal cytochrome P450 systems could not have been responsible for the reaction. Dicoumarol, an inhibitor of NAD(P)H-quinone oxidoreductase (NQO), dose dependently suppressed the NADH oxidation in the outer membrane via PQ as well as menadione, with I50 values of 190 (for menadione) and 150 microM (for PQ). Because of a lower sensitivity to NADPH and the higher doses of dicoumarol required for its inhibition, the activity in the outer membrane may be an "NADH-quinone oxidoreductase" which partly differs from the NQO previously reported. This outer membrane enzyme produced superoxide anions in the presence of both NADH and PQ and was too tightly membrane-bound to be extracted by Triton X-100 and deoxycholate. From these results, we concluded that the free radical-producing mitochondrial NADH-quinone oxidoreductase is a novel oxidation-reduction system participating in PQ toxicity. This is in good agreement with our previous results showing that PQ selectively damaged Mt in vivo and in vitro, resulting in cell death (K.-I. Hirai et al., 1992, Toxicology 72, 1-16).

Xanthine oxidase mediates paraquat-induced toxicity on cultured endothelial cell

The role of xanthine oxidase in paraquat toxicity was investigated using cultured bovine pulmonary artery endothelial cells. Exposure to paraquat 0.1 mM was done for 24 hr with or without tungsten pretreatment and in the presence or absence of xanthine oxidase inhibitors. Exposure to paraquat significantly increased O2- production and relative xanthine oxidase activity (xanthine oxidase activity divided by total xanthine dehydrogenase plus xanthine oxidase) while depressing cell growth. In contrast, tungsten and allopurinol inhibited the increase of xanthine oxidase activity and decreased O2- release. Cell injury was assessed by leakage of lactate dehydrogenase and by fluorescein diacetate staining; it was found that oxidase inhibitors (both allopurinol and tungsten) reduced paraquat cytotoxicity. Thus the toxicity of paraquat was at least partly due to intracellular O2- production mediated by xanthine oxidase and the subsequent formation of other free radicals.

Oxygen free radicals in rat limbic structures after kainate-induced seizures

Several indices of free radical generation were determined in limbic structures after kainate (KA)-induced seizure activity in adult and postnatal day (PND) 12 and 17 rats. Superoxide dismutase, catalase, and glutathione peroxidase activities were measured in piriform cortex and hippocampal subfields at 8, 16, 48 h, and 5 days after KA injection in adults and pups, and also at 3 weeks postinjection in adults. KA-induced seizure activity had no significant effect on enzyme activities in PND 12 and 17 rats. In adults, superoxide dismutase and catalase activities were significantly increased at 5 days after KA administration, and returned to preinjection levels by 3 weeks. Glutathione peroxidase activity was also increased significantly at 5 days postinjection, but remained elevated at 3 weeks. Lipid peroxidation, as indicated by malondialdehyde (MDA) concentration, exhibited an early significant increase at 8 and 16 h, followed at 48 h and 5 days by a significant decrease. At 3 weeks postinjection, MDA levels were still significantly decreased in CA3 and dentate gyrus. KA administration in PND 12 and 17 rats had no significant effect on MDA content. KA-induced seizure activity in adults also resulted in a large and sustained increase in protein oxidation in piriform cortex and hippocampus. The early increase in MDA and protein oxidation in adult rats strongly suggests the involvement of oxygen free radicals in the initial phases of KA-induced pathology, whereas the changes in scavenging enzyme activities and MDA content at 5 days and 3 weeks post KA injection possibly reflect glial proliferation subsequent to neuronal death.

Microsomal membrane peroxidation by an Fe3+/paraquat system. Consequences of phenobarbital induction

Descriptions of the effects of paraquat (P2+) on the peroxidation of liver microsomes are very divergent. Therefore, the presence of ferric iron in the medium and the activity of microsomal mixed-function oxidase system are two factors that we have taken into consideration to explain the discrepancies. The results showed that 100 microM P2+ potentializes the slight production of MDA induced by low concentrations of Fe3+ (< or = 15 microM). In these conditions, P+., arising from the one-step reduction of P2+ by NADPH-cytochrome C reductase, could reduce Fe3+ and cause the formation of species that initiate peroxidation. However, unlike the results obtained with CBrCl3, for animals induced by phenobarbital (Ph), the production of MDA in the presence of FeCl3 and of P2+ was weaker than for the controls. The establishment of a new Fe3+/Fe2+ equilibrium owing to increased production of P+. could be responsible.

Neurodegeneration produced by intrahippocampal injection of paraquat is reduced by systemic administration of the 21-aminosteroid U74389F in rats

The behavioural, electrocortical (ECoG) and neurodegenerative effects of intrahippocampal injection of paraquat, a well-known free radical producing agent, were studied in rats. Injection of paraquat (100 nmol) into one dorsal hippocampus produced limbic motor and ECoG seizures. These effects were accompanied at 24 h by severe damage to CA1, CA3 and CA4 hippocampal pyramidal neurones and dentate gyrus granule cells. In comparison to the cell number counted in control, untreated, side of the hippocampus, significant (P < 0.05) neuronal loss was observed in the CA1 and CA3 pyramidal cell layers of the treated hippocampus. A lower dose of the herbicide (10 nmol) did not produce consistent motor and ECoG effects and in no instance was significant neuronal loss observed. A pretreatment with U74389F [21-4-(2,6-di-l-pyrrodinyl-4-pyridinyl)-1-piperazinyl-pregna-1,4,9 (11)triene-3,20-dione monomethansulfonate] (30 mg/kg i.p., 15 min before paraquat) completely protected rats from motor and ECoG epileptogenic effects induced by intrahippocampal paraquat (100 nmol). This dose of U74389F also reduced the hippocampal damage typically produced by paraquat and no significant neuronal loss was reported in the CA1 and CA3 pyramidal cell layers. A lower dose of U74389F (10 mg/kg i.p.) did not afford any protection against the epileptogenic effects produced by paraquat (100 nmol); in these animals hippocampal damage was still evident though neuronal loss did not reach statistical significance. In conclusion, the present data show that systemic administration of U74389F possesses neuroprotective effects against seizures and neurodegeneration typically elicited by intrahippocampal injection of paraquat.

Involvement of opioid receptors in shaking behaviour induced by paraquat in rats

Paraquat (30-70 mg/kg intraperitoneally) caused typical shaking behaviour in rats in a dose-dependent manner. Myoclonus also appeared after the shaking behaviour in several rats treated with the highest dose of paraquat. Morphine (5 mg/kg intraperitoneally, 30 min. before paraquat) significantly reduced the frequency of shaking behaviour. The alleviation by morphine disappeared when naloxone (1.5 mg/kg intraperitoneally 15 min. after morphine) was coadministered. Although there was no histological change in brain slices of paraquat-treated rats (70 mg/kg intraperitoneally), the fluorescein uptake into brain was increased by the treatment. Morphine prevented the increase of fluorescein uptake, but naloxone failed to antagonize this effect. On the other hand, intracerebroventricularly administered paraquat (25.7 micrograms/rat) caused tremor in all rats, but not shaking behaviour nor myoclonus. These findings suggest that paraquat administered systemically as well as centrally may be toxic to the brain. Although the actions of paraquat on the brain seem to be complicated, opioid receptors may play a role in the actions.

Ascorbate radical levels in human sera and rat plasma intoxicated with paraquat and diquat

To clarify the toxicological mechanism of action of paraquat and diquat, the level of ascorbate radical, an oxidized product of ascorbic acid, was examined using the electron spin resonance (ESR) method. The ascorbate radical level increased to twice the normal level in sera from humans acutely intoxicated with a 1:1 mixture of paraquat and diquat, and to more than 1.5 times the normal level in rat plasma containing moderate levels of paraquat. The dosage level for rats was 0.025% paraquat dichloride in the diet. The ascorbate radical in both intoxicated human sera and rat plasma decayed much faster than that in normal samples.

Mechanism of paraquat-stimulated lipid peroxidation in mouse brain and pulmonary microsomes

Paraquat-stimulated NADPH-dependent lipid peroxidation in mouse brain and pulmonary microsomes was inhibited by superoxide dismutase and singlet oxygen quenchers, but not by catalase or hydroxyl radical scavengers. MnCl2, which might form a salt with unsaturated lipid, inhibited the lipid peroxidation in brain microsomes, but not that in pulmonary microsomes. These findings suggest that activated oxygen species, especially superoxide and singlet oxygen, may play a major role in the stimulation of microsomal lipid peroxidation by paraquat in both brain and lung, and that the nature of the lipids exposed to peroxidative attack may be different in microsomes of the two organs.