Environmental risk factors and Parkinson's disease: selective degeneration of nigral dopaminergic neurons caused by the herbicide paraquat

Environmental toxicants and, in particular, pesticides have been implicated as risk factors in Parkinson's disease (PD). The purpose of this study was to determine if selective nigrostriatal degeneration could be reproduced by systemic exposure of mice to the widely used herbicide paraquat. Repeated intraperitoneal paraquat injections killed dopaminergic neurons in the substantia nigra (SN) pars compacta, as assessed by stereological counting of tyrosine hydroxylase (TH)-immunoreactive and Nissl-stained neurons. This cell loss was dose- and age-dependent. Several lines of evidence indicated selective vulnerability of dopaminergic neurons to paraquat. The number of GABAergic cells was not decreased in the SN pars reticulata, and counting of Nissl-stained neurons in the hippocampus did not reveal any change in paraquat-treated mice. Degenerating cell bodies were observed by silver staining, but only in the SN pars compacta, and glial response was present in the ventral mesencephalon but not in the frontal cortex and cerebellum. No significant depletion of striatal dopamine followed paraquat administration. On the other hand, enhanced dopamine synthesis was suggested by an increase in TH activity. These findings unequivocally show that selective dopaminergic degeneration, one of the pathological hallmarks of PD, is also a characteristic of paraquat neurotoxicity. The apparent discrepancy between pathological (i.e., neurodegeneration) and neurochemical (i.e., lack of significant dopamine loss) effects represents another important feature of this paraquat model and is probably a reflection of compensatory mechanisms by which neurons that survive damage are capable of restoring neurotransmitter tissue levels.

Paraquat poisoning: significance of plasma-paraquat concentrations

Plasma-paraquat concentrations were measured in 79 patients who had ingested liquid or granular weedkillers containing paraquat. At any given time after ingestion, the plasma-paraquat concentrations in the patients who died usually exceeded those in the survivors. It is suggested that measurement of plasma-paraquat concentrations is useful in assessing the severity and predicting the outcome of poisoning. Patients whose plasma concentrations do not exceed 2.0, 0.6, 0.3, 0.16, and 0.1 mg/l at 4, 6, 10, 16, and 24 h respectively are likely to survive.

Vanin-1-/- mice exhibit a glutathione-mediated tissue resistance to oxidative stress

Vanin-1 is an epithelial ectoenzyme with pantetheinase activity and generating the amino-thiol cysteamine through the metabolism of pantothenic acid (vitamin B(5)). Here we show that Vanin-1(-/-) mice, which lack cysteamine in tissues, exhibit resistance to oxidative injury induced by whole-body gamma-irradiation or paraquat. This protection is correlated with reduced apoptosis and inflammation and is reversed by treating mutant animals with cystamine. The better tolerance of the Vanin-1(-/-) mice is associated with an enhanced gamma-glutamylcysteine synthetase activity in liver, probably due to the absence of cysteamine and leading to elevated stores of glutathione (GSH), the most potent cellular antioxidant. Consequently, Vanin-1(-/-) mice maintain a more reducing environment in tissue after exposure to irradiation. In normal mice, we found a stress-induced biphasic expression of Vanin-1 regulated via antioxidant response elements in its promoter region. This process should finely tune the redox environment and thus change an early inflammatory process into a late tissue repair process. We propose Vanin-1 as a key molecule to regulate the GSH-dependent response to oxidative injury in tissue at the epithelial level. Therefore, Vanin/pantetheinase inhibitors could be useful for treatment of damage due to irradiation and pro-oxidant inducers.

Lung tissue mechanics and extracellular matrix remodeling in acute lung injury

This study was undertaken to test whether there is structural remodeling of lung parenchyma that could lead to tissue mechanical changes at an early phase of varying degrees of acute lung injury (ALI). Tissue resistance (R), dynamic elastance (E), and hysteresivity (eta) were analyzed during sinusoidal oscillations of rat lung parenchymal strips 24 h after intraperitoneal injection of saline (C) or paraquat (P [10, 15, 25, and 30 mg/kg]). These strips were also stained in order to quantify the amount of collagen and of three types of elastic fibers (elaunin, oxytalan, and fully developed elastic fibers) in the alveolar septa. E augmented progressively from C to P25, but the data from the P25 and P30 groups were not different (p < 0.0001). R and eta increased from C to P10 and from P15 to P25 (p < 0.001). Collagen fiber content increased exponentially with the severity of the injury. Elaunin and fully developed elastic fibers remained unchanged in the five groups, while oxytalan fibers increased only in the P25 and P30 groups. In conclusion, the pronounced mechanical changes at the tissue level and fibroelastogenesis happened at an early phase of the disease and even in mildly abnormal lung parenchyma.

KEYWORDS

elastance; collagen fibers; elastin; paraquat

Prognosis and treatment of paraquat poisoning: a review of 28 cases

Paraquat poisoning is very severe. When it is ingested, this herbicide may be responsible for causative lesions of the digestive tract, cytolytic hepatitis, renal tubular necrosis, circulatory failure, and/or pulmonary fibrosis. Since a very low dose (as little as one mouthful) is potentially lethal, it is important to understand why 11 of our 28 patients who entered our department for paraquat poisoning survived. The main prognostic factors appear to be the following: Route of administration. Of four patients who had inhaled paraquat aerosols and/or contaminated their skin with the herbicide, all survived. Ingested amount. Above 50 mg/kg, patients died of circulatory failure within 72 h; between 35 and 50 mg/kg, a progressive pulmonary fibrosis occurred. Delay between ingestion and the last meal. Paraquat is adsorbed and neutralized by foodstuffs. Caustic gastric lesions revealed by early endoscopic examination. The occurrence of an organic renal failure. The plasma paraquat concentrations within the first 24 h. Patients whose plasma concentrations do not exceed 2.0, 0.6, 0.3, 0.16, and 0.1 mg/L at 4, 6, 10, 16, and 24 h, respectively, are likely to survive. The different treatments that have been tested (fuller's earth, forced diarrhea, furosemide, hemodialysis, hemoperfusion, artificial ventilation with hypoxic breathing mixtures) did not modify the initial prognosis. The 11 survivals are only linked to the circumstances of the poisonings (route of administration, ingested amount, delay between ingestion and the last meal, etc.). The treatments did not modify the outcome.

Oxidative stress does not influence carotenoid mobilization and plumage pigmentation

Oxidative stress has been suggested to create a link between 'good genes' and carotenoid coloration via an allocation conflict between external pigmentation and internal antioxidant functions. However, although carotenoid displays have been extensively investigated, there are no experimental tests of the antioxidant efficiency of carotenoids in vivo. We induced oxidative stress in a small passerine (the great tit, Parus major) under both carotenoid deprivation and supplementation, and investigated the effect on carotenoid mobilization (i.e. plasma) and allocation (i.e. deposition in feather incorporation and liver storage). We found no effects of the stressor on either mobilization or allocation of carotenoids. These results reject the previously suggested superior role of carotenoid's function as antioxidant in vivo with important implications for signal content and honesty.

Effects of paraquat on the substantia nigra of the wistar rats: neurochemical, histological, and behavioral studies

Effects of paraquat on the substantia nigra of the male Wistar rats we re studied pharmacologically by a intracerebral injection of paraquat. The neurochemical, morphological, and behavioral changes observed after a unilateral intranigral injection of paraquat (1-5 microgram) were as follows: (1) neurochemically, paraquat caused dose-dependent depletion of dopamine in the ipsilateral striatum starting 2 weeks after treatment; this effect was long-lasting and irreversible. The ipsilateral striatal dopamine level in animals treated with 3 microgram paraquat was even decreased by 91.5%. (2) Morphologically, 2 microgram of paraquat produced marked loss of Nissl substances and prominent glial reaction in the substantia nigra, while 3 microgram of paraquat caused a severe loss of neurons. (3) Behaviorally, paraquat caused a vigorous rotational behavior in rats contralateral to the lesioned side in response to apomorphine administration (0.5 mg/kg, sc). This effect was dose-dependent and lasted for the entire 16-week experimental period. Taken together, these data indicate that intranigrally injected paraquat may possess marked neurotoxicity and induce degeneration of the rat nigrostriatal dopaminergic system.

Protective effects of chlorogenic acid on paraquat-induced oxidative stress in rats

The protective effects of chlorogenic acid on paraquat-induced oxidative stress were examined in rats. The activities of erythrocytes and liver glutathione peroxidase, and of both liver catalase and glutathione reductase, which were increased by feeding paraquat, declined to the levels in the control rats by supplementing chlorogenic acid to the paraquat diet. The activity of superoxide dismutase was not changed by dietary paraquat or by supplementing chlorogenic acid to the paraquat diet. Paraquat in the diet markedly decreased the liver triacylglycerol and phospholipid concentrations, as well as the food intake and body weight gain, while chlorogenic acid protected against these decreases. These in vivo results and the in vitro superoxide anion scavenging activity of chlorogenic acid suggest that chlorogenic acid acted preventively against paraquat-induced oxidative stress.

Increase in gamma-glutamyltransferase by glutathione depletion in rat type II pneumocytes

The purpose of our study was to investigate the effect of oxidative stress or intracellular glutathione (GSH) depletion on gamma-glutamyltransferase (gamma-GT) activity in cultured type II pneumocytes. Twenty-four hours after isolation, primary cultures of rat type II pneumocytes were preincubated with one of four compounds: 15, 30, 60, 125, 250 microM L-buthionine-[SR]-sulfoximine (BSO) for 3 h; 100, 200, 400, 800 microM tertiary-butylhydroperoxide (t-BOOH) for 45 min; 10, 25, 50, 100 microM menadione for 15 min; 100, 1000 microM paraquat for 1 h. GSH levels, H2O2 and O2.- generation were measured immediately after the incubation, gamma-GT activity and GSH levels also up to 24 h or 48 h later. Exposure to BSO led to a persistent GSH depletion without increase in H2O2 or O2.- production, together with a dose and time-dependent increase (doubling) of gamma-GT activity with a nonsignificant increase in gamma-GT mRNA expression 24 h after exposure to BSO. Exposure to 100 microM menadione, which increased H2O2 production, decreased gamma-GT activity. t-BOOH or paraquat did not give rise to a measurable increase in H2O2 or O2.-. Paraquat did not affect initial GSH levels, but increased GSH and decreased gamma-GT activity 24 h later. t-BOOH (400 and 800 microM) initially decreased GSH, and tended to increase GSH 24 h later, 100 and 200 microM increased gamma-GT activity 24 h later, but 800 microM decreased it. Restoration of intracellular GSH levels by addition of GSH to the culture medium completely prevented the increase in gamma-GT activity by BSO, while the addition of catalase or DMTU had no effect. We conclude that at least two effects are operating upon gamma-GT activity: GSH depletion seems to increase gamma-GT activity, while exposure to compounds generating oxidative stress correlates with a decrease in gamma-GT activity.

Improvement in survival after paraquat ingestion following introduction of a new formulation in Sri Lanka

BACKGROUND

Pesticide ingestion is a common method of self-harm in the rural developing world. In an attempt to reduce the high case fatality seen with the herbicide paraquat, a novel formulation (INTEON) has been developed containing an increased emetic concentration, a purgative, and an alginate that forms a gel under the acid conditions of the stomach, potentially slowing the absorption of paraquat and giving the emetic more time to be effective. We compared the outcome of paraquat self-poisoning with the standard formulation against the new INTEON formulation following its introduction into Sri Lanka.

METHODS AND FINDINGS

Clinical data were prospectively collected on 586 patients with paraquat ingestion presenting to nine large hospitals across Sri Lanka with survival to 3 mo as the primary outcome. The identity of the formulation ingested after October 2004 was confirmed by assay of blood or urine samples for a marker compound present in INTEON. The proportion of known survivors increased from 76/297 with the standard formulation to 103/289 with INTEON ingestion, and estimated 3-mo survival improved from 27.1% to 36.7% (difference 9.5%; 95% confidence interval [CI] 2.0%-17.1%; p = 0.002, log rank test). Cox proportional hazards regression analyses showed an approximately 2-fold reduction in toxicity for INTEON compared to standard formulation. A higher proportion of patients ingesting INTEON vomited within 15 min (38% with the original formulation to 55% with INTEON, p < 0.001). Median survival time increased from 2.3 d (95% CI 1.2-3.4 d) with the standard formulation to 6.9 d (95% CI 3.3-10.7 d) with INTEON ingestion (p = 0.002, log rank test); however, in patients who did not survive there was a comparatively smaller increase in median time to death from 0.9 d (interquartile range [IQR] 0.5-3.4) to 1.5 d (IQR 0.5-5.5); p = 0.02.

CONCLUSIONS

The survey has shown that INTEON technology significantly reduces the mortality of patients following paraquat ingestion and increases survival time, most likely by reducing absorption.

Predictors of survival after acute paraquat poisoning

Acute paraquat poisoning is often fatal. Many studies have investigated successful treatment modalities, but no standard treatment yet exists. The purpose of this study was to determine the predictors of survival after acute paraquat poisoning in 602 patients. The paraquat exposure was assessed based on the amount of ingested paraquat and a semiquantitative measure of the urine level of paraquat. Initial clinical parameters including vital signs, hemoglobin, white-blood-cell count, pH, PaCO2, PaO2, blood urea nitrogen, creatinine, aspartate aminotransferase, alanine aminotransferase, total bilirubin, amylase, and glucose were obtained at the time of arrival at the emergency room. Outcomes after acute paraquat poisoning were categorized as survivors and nonsurvivors. Multiple logistic regression analysis was applied to assess the predictors of survival after acute paraquat poisoning. Some patients (55.5%) survived after oral ingestion of paraquat, whereas all those exposed to paraquat percutaneous or inhalational route survived. The amount of paraquat (24.5% concentrate of 1,1'-dimethyl-4,4'-bipyridium dichloride) ingested was 45.6 +/- 74.1 mL (mean +/- SD). In addition to degree of paraquat exposure, survival after acute paraquat poisoning was associated with age, respiratory rate, pH, PaCO2, hemoglobin, white-blood-cell count, blood urea nitrogen, amylase, and the number of failed organs in multiple logistic regression analysis. In conclusion, young age, percutaneous or inhalational route, exposure to less paraquat, and lesser degrees of leukocytosis, acidosis, and renal, hepatic, and pancreatic failures on admission are good prognostic factors of survival after acute paraquat poisoning.

Chronic inhalation of rotenone or paraquat does not induce Parkinson's disease symptoms in mice or rats

Epidemiological studies suggest that some pesticides might constitute a risk factor for Parkinson's disease (PD). However, risk assessment cannot be performed in the current experimental animal models because they use non-natural pathways of pesticide exposure, such as intraperitoneal or intravenous injection, that might bypass body defences. A new model based on daily inoculation of neurotoxins in the nasal cavity of C57BL/6 mice for 30 days was used to evaluate risk of three complex I inhibitors, 1-methyl-4-phenyl1,2,3,6-tetrahydropyridine (MPTP), rotenone and paraquat. These compounds displayed very different effects on motor activity, striatal dopamine and dihydroxyphenylacetic acid (DOPAC) levels and loss of dopaminergic neurons. MPTP-treated mice developed motor deficits that correlated with a severe depletion of striatal dopamine levels, and loss of tyrosine hydroxylase staining in substantia nigra and striatum. By contrast, rotenone-treated mice or rats were asymptomatic. Paraquat induced severe hypokinesia and vestibular damage but did not alter the nigrostriatal system. The new animal model described here, based on chronic intranasal inoculation of neurotoxicants, provides a new tool to assess the potential danger of environmental toxins as risk factors for development of PD.

Pulmonary ultrastructure after oral and intravenous dosage of paraquat to rats

Paraquat was administered to rats by gavage or intravenously at doses which were approximately equitoxic (680 mu. moles/kh and 65 mu. moles/kg respectively) and the lungs examined by light and electron microscopy at intervals up to 48 hours. No significant changes were observed in alveolar endothelial cells at any of the time intervals studied. After intravenous administration the first ultrastructural changes were observed at 4 hr in the type I cells which were less electron dense and contained few organelles. At 8 hr these lesions were more marked and in some places the basement memebrane was denuded. Type II cells were also showing damage to mitochondria and loss of microvilli. After oral dosing, the type and sequence of changes was similar but the first changes were not seen until 22 hr. Intravenous injection of 0-03 micron carbon particles 1 hr before killing showed no significant leakage from the alveolar endothelium. This study provides no morphological evidence that the oedema of the lung caused by paraquat in rats is due to damage to endothelial cells. It appears that, following dosing by the two routes, the difference in interval between dosing and the development of lesions is due to the accumulation of paraquat. Lesions in type I cells therefore occurred when a certain concentration of paraquat is known to be present in the lung. It is suggested that a prime compartment into which paraquat is accumulated is the alveolar epithelial cell.

Toxic influence of subchronic paraquat administration on dopaminergic neurons in rats

Paraquat is a toxin suggested to contribute to pathogenesis of Parkinson's disease. The aim of the present study was to examine toxic influence of subchronic treatment with this pesticide (5 days, one injection per day, 2-3 days of withdrawal) on dopaminergic, serotonergic, noradrenergic and GABAergic neurons. Paraquat decreased the number of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the substantia nigra by 22% (measured 3 days after withdrawal). Two days after withdrawal the levels of the dopamine metabolites and dopamine turnover in the caudate-putamen, substantia nigra and prefrontal cortex were reduced by ca. 20-60%, and the binding of [(3)H]GBR 12,935 to dopamine transporter dropped by 25-40% in the caudate-putamen. Three days after paraquat withdrawal, the level of dopamine in the caudate-putamen was significantly increased, and earlier decreases in DOPAC and HVA in the substantia nigra, as well as [(3)H]GBR 12,935 binding in the caudate-putamen were reversed. Moreover, an increase in serotonin turnover in the caudate-putamen and prefrontal cortex, and noradrenaline level in the former structure was observed 2-3 days after paraquat withdrawal. Three days after the last paraquat injection 24-35% decreases in the proenkephalin mRNA levels and 5-7% reduction in glutamic acid decarboxylase (GAD)67 mRNA were found in the caudate-putamen. The present study suggests that subchronic paraquat administration triggers processes characteristic of early stages of dopaminergic neuron degeneration, and activates compensatory mechanisms involving dopaminergic, noradrenergic, serotonergic and GABAergic transmissions.

Age-related impairment of the transcriptional responses to oxidative stress in the mouse heart

To investigate the transcriptional response to oxidative stress in the heart and how it changes with age, we examined the cardiac gene expression profiles of young (5-mo-old), middle-aged (15-mo-old), and old (25-mo-old) C57BL/6 mice treated with a single intraperitoneal injection of paraquat (50 mg/kg). Mice were killed at 0, 1, 3, 5, and 7 h after paraquat treatment, and the gene expression profile was obtained with high-density oligonucleotide microarrays. Of 9,977 genes represented on the microarray, 249 transcripts in the young mice, 298 transcripts in the middle-aged mice, and 256 transcripts in the old mice displayed a significant change in mRNA levels (ANOVA, P < 0.01). Among these, a total of 55 transcripts were determined to be paraquat responsive for all age groups. Genes commonly induced in all age groups include those associated with stress, inflammatory, immune, and growth factor responses. Interestingly, only young mice displayed a significant increase in expression of all three isoforms of GADD45, a DNA damage-responsive gene. Additionally, the number of immediate early response genes (IEGs) found to be induced by paraquat was considerably higher in the younger animals. These results demonstrate that, at the transcriptional level, there is an age-related impairment of specific inducible pathways in the response to oxidative stress in the mouse heart.

Degeneration of dopaminergic mesocortical neurons and activation of compensatory processes induced by a long-term paraquat administration in rats: implications for Parkinson's disease

A deficiency of the dopaminergic transmission in the mesocortical system has been suggested to contribute to cognitive disturbances in Parkinson's disease. Therefore, the aim of the present study was to examine whether the long-term administration of a commonly used herbicide, paraquat, which has already been found to induce a slowly progressing degeneration of the nigrostriatal neurons, influences mesocortical dopaminergic neurons in rats. Paraquat at a dose of 10 mg/kg i.p. was injected either acutely or once a week for 4, 8, 12 and 24 weeks. Acute treatment with this pesticide increased the level of homovanillic acid (HVA) and HVA/dopamine ratio in the prefrontal cortex. After 8 weeks of administration paraquat increased the number of stereologically counted tyrosine hydroxylase-immunoreactive (TH-ir) neurons and their staining intensity in the ventral tegmental area (VTA), which is a source of the mesocortical dopaminergic projection. At the same time, few TH-ir neurons appeared in different regions of the cerebral cortex: in the frontal, cingulate, retrosplenial and parietal cortices. Chronic paraquat administration did not influence the level of dopamine in the prefrontal cortex but increased the levels of its metabolites: 3,4-dihydroxyphenylacetic acid (after 8-12 weeks), HVA (after 4 and 12 weeks) and HVA/dopamine ratio (4 weeks). After 24 weeks this pesticide reduced the number of TH-ir neurons in the VTA by 42% and of the Nissl-stained neurons by 26%, and induced shrinkage of this structure by ca. 25%. Moreover, TH-ir neurons in the cortex were no more visible after such a long period of administration and levels of dopamine metabolites returned to control values. The present results suggest that the long-term paraquat administration destroys dopaminergic neurons of the VTA. However, compensatory activation of the VTA neurons and cortex overcomes progressing degeneration and maintains cortical dopaminergic transmission.

Long-term respiratory health effects of the herbicide, paraquat, among workers in the Western Cape

OBJECTIVE

To evaluate the possible effects of paraquat spraying among workers on deciduous fruit farms in the Western Cape, South Africa. Paraquat is a commonly used herbicide world wide and is a well documented cause of pulmonary fibrosis in studies of laboratory animals and in humans after exposure to a high dose (usually accidental or as parasuicide). The respiratory effects of long term, low dose exposure to paraquat have not been fully evaluated.

METHODS

A cross sectional study of 126 workers. Administered questionnaires generated information on exposure, respiratory symptoms, and potential confounding variables. Spirometry and gas transfer were measured and chest radiographs performed. Oxygen desaturation on exercise testing was by oximetry during a modified stage one exercise test.

RESULTS

No association was found between long term exposure to paraquat and reported symptoms, spirometry (forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), FEV1/FVC) and gas transfer (TLCO and KCO) or chest radiography. Multivariate analysis showed a significant relation between measures of long term exposure to paraquat and arterial oxygen desaturation during exercise independent of short term exposure.

CONCLUSION

Previous studies have not shown a significant relation between measures of exposure to paraquat and standard tests of lung function. Arterial oxygen desaturation during exercise represents a more sensitive test. The findings indicate that working with paraquat under usual field conditions is associated with abnormal exercise physiology in a dose dependent fashion independent of recent exposure and acute poisoning events.

Temporal effects of paraquat/maneb on microglial activation and dopamine neuronal loss in older rats

We investigated the effects of combined systemic exposure to the herbicide paraquat (PQ) and the fungicide maneb (MB) in 6-month-old rats, an animal model of Parkinson's disease resulting from environmental toxin exposure. Following two doses of PQ (10 mg/kg) and MB (30 mg/kg), 52% of animals developed fatal lung injury. Examination of the remaining animals showed degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta 6 weeks, but not 4 weeks, following PQ/MB. In contrast, microglial activation was observed at 4 weeks, but had abated by 6 weeks. Compared with our previous findings in younger rats, these results suggest increased susceptibility of older animals to lung and brain toxicity from PQ/MB exposure. Microglial activation preceded, and therefore likely contributed to, DA neurodegeneration. Further, electron microscopy revealed an abnormal appearance of the Golgi apparatus at 4 weeks that was confirmed using double immunostaining for tyrosine hydroxylase and Golgi. This suggests that PQ/MB causes protein processing dysfunction in nigral DA neurons that may be either a direct effect of PQ/MB or the result of microglial activation.

Pharmacokinetic, neurochemical, stereological and neuropathological studies on the potential effects of paraquat in the substantia nigra pars compacta and striatum of male C57BL/6J mice

The pharmacokinetics and neurotoxicity of paraquat dichloride (PQ) were assessed following once weekly administration to C57BL/6J male mice by intraperitoneal injection for 1, 2 or 3 weeks at doses of 10, 15 or 25 mg/kg/week. Approximately 0.3% of the administered dose was taken up by the brain and was slowly eliminated, with a half-life of approximately 3 weeks. PQ did not alter the concentration of dopamine (DA), homovanillic acid (HVA) or 3,4-dihydroxyphenylacetic acid (DOPAC), or increase dopamine turnover in the striatum. There was inconsistent stereological evidence of a loss of DA neurons, as identified by chromogenic or fluorescent-tagged antibodies to tyrosine hydroxylase in the substantia nigra pars compacta (SNpc). There was no evidence that PQ induced neuronal degeneration in the SNpc or degenerating neuronal processes in the striatum, as indicated by the absence of uptake of silver stain or reduced immunolabeling of tyrosine-hydroxylase-positive (TH(+)) neurons. There was no evidence of apoptotic cell death, which was evaluated using TUNEL or caspase 3 assays. Microglia (IBA-1 immunoreactivity) and astrocytes (GFAP immunoreactivity) were not activated in PQ-treated mice 4, 8, 16, 24, 48, 96 or 168 h after 1, 2 or 3 doses of PQ. In contrast, mice dosed with the positive control substance, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 10mg/kg/dose×4 doses, 2 h apart), displayed significantly reduced DA and DOPAC concentrations and increased DA turnover in the striatum 7 days after dosing. The number of TH(+) neurons in the SNpc was reduced, and there were increased numbers of degenerating neurons and neuronal processes in the SNpc and striatum. MPTP-mediated cell death was not attributed to apoptosis. MPTP activated microglia and astrocytes within 4 h of the last dose, reaching a peak within 48 h. The microglial response ended by 96 h in the SNpc, but the astrocytic response continued through 168 h in the striatum. These results bring into question previous published stereological studies that report loss of TH(+) neurons in the SNpc of PQ-treated mice. This study also suggests that even if the reduction in TH(+) neurons reported by others occurs in PQ-treated mice, this apparent phenotypic change is unaccompanied by neuronal cell death or by modification of dopamine levels in the striatum.

Protective role of thymoquinone against paraquat-induced hepatotoxicity in mice

Paraquat is a common and effective herbicide; although its poisoning could lead to severe oxidative organ damages and its main target organs are the lungs, kidneys, heart, and liver. Thymoquinone is the active ingredient of Nigella sativa which is traditionally used in herbal medicine; recent studies have shown that thymoquinone could inhibit oxidative stress. This study explores protective effects of thymoquinone on paraquat-induced hepatotoxicity in mice. Accordingly, adult male mice were randomly divided into nine groups for three continuous days intraperitoneal injection treatment: (1) control; (2) solvent; (3) 20 mg/kg vitamin E; (4) 20 mg/kg thymoquinone; (5) 20 mg/kg paraquat and Groups 6, 7, 8, and 9 received 20 mg/kg of vitamin E and 5, 10, and 20 mg/kg of thymoquinone, respectively. The last four groups, received 20 mg/kg paraquat just 24 h after pretreatments. We assessed serum liver enzymes activities, liver histopathology changes, oxidative (lipid peroxidation) and antioxidative (ferric reducing antioxidant power) potential, superoxide dismutase (SOD) and catalase activity, and total thiol groups content after administration of the poison and treatments. Pretreatment with 10 mg/kg thymoquinone inhibited, safely, the elevations in levels of liver function tests (LFTs) and lipid peroxidation, restored the activity of SOD, and ameliorated the histopathological alterations induced by paraquat. Eventually, our results indicate that thymoquinone performs its hepatoprotective role in mice by prevention of SOD suppression mediated by paraquat.