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Curcumin, the active compound of the rhizome of Curcuma longa has anti-inflammatory, antioxidant and antiproliferative activities. This agent has been shown to regulate numerous transcription factors, cytokines, protein kinases, adhesion molecules, redox status and enzymes that have been linked to inflammation. While curcumin has been identified as an activator of apoptosis in several cell lines, the mechanism by which it initiates apoptosis, however, remains poorly understood. We considered curcumin from the point of view of its ability to protect against oxidative stress, the latter being one factor strongly implicated in the development of Parkinson's disease. Although the etiology of Parkinson's disease remains unknown, epidemiological studies have linked exposure to pesticides such paraquat to an increased risk of developing the condition. Analysis of the neurotoxic properties of these pesticide compounds has been focused on their ability to induce oxidative stress in neural cells. Given curcumin's capacity to protect against oxidative stress, it has been considered as a potential therapeutic agent for neurodegenerative diseases such as Parkinson's disease that involve an oxidative stress component. In the present report we describe the effect of curcumin in paraquat-mediated apoptosis of N27 mesencepahlic cells. We show that subtoxic concentrations of curcumin sensitize N27 mesencephalic cells to paraquat-mediated apoptosis.

The precise mechanism underlying the role of nitric oxide (NO) or nitric oxide synthases (NOSs) in paraquat-mediated toxicity is yet to be fully elucidated. The importance of the NADPH-diaphorase activity of NOSs in paraquat toxicity, in addition to the production of NO, has previously been reported as a mechanism of toxicity. However, other studies have highlighted the toxicity of NO alone and, conversely a protective role of NO in paraquat-mediated toxicity has also been described. The goal of this study was to clarify the involvement of NO and NOS in paraquat-mediated toxicity in an SH-SY5Y cell system, and to evaluate the putative role of 7-nitroindazole as a protective agent in human neural cells. Our results indicate that the three previously described isoforms of NOS are expressed in SH-SY5Y cells, with the data showing that these synthases act as paraquat diaphorases. While this process could occur at the expense of NO production, NO alone does play a toxic role, with its production leading to the formation of the toxicant peroxynitrite. Although the efficacies of the different inhibitors tested cannot be directly compared because the various NOS forms were probably inhibited to differing extents, the results support the idea that endogenous and inducible NO is a neurotoxic mediator of the effects of paraquat. The NADPH-diaphorase activity of NOS and NO production are therefore factors implicated in the toxicity mediated by the herbicide paraquat.

The role of autophagy as a survival strategy of cells constitutes an emerging topic in the study of the pathogenesis of several diseases with autophagic changes being described in a number of age-related neurodegenerative disorders, including Parkinson's disease (PD). Although the etiology of PD is still unknown, both environmental (for example, paraquat exposure) and genetic factors have been investigated as putative causes of the disease. In the latter case, mutations or changes in the protein DJ-1 have been reported to be associated with autosomal recessive, early-onset parkinsonism. In this paper we established a model system to study the involvement of the DJ-1 protein in paraquat-induced autophagy. When human neuroblastoma SH-SY5Y cells were transfected with DJ-1-specific small interfering RNAs and exposed to paraquat, we observed (i) sensitization additive with paraquat-induced apoptotic cell death, (ii) inhibition of the cytoplasmic accumulation of autophagic vacuoles as well as the recruitment of LC3 fusion protein to the vacuoles, (iii) exacerbation of apoptotic cell death in the presence of the autophagy inhibitor 3-methyladenine, and (iv) an increase in mammalian target of rapamycin phosphorylation. Taken together, these findings suggest an active role for DJ-1 in the autophagic response produced by paraquat, providing evidence for the role of PD-related proteins in the autophagic degradation pathway, a factor that should be considered in the design of potential therapies for the treatment of the disease.

Paraquat (PQ) (1,1-dimethyl-4,4'-bipyridinium dichloride), a widely used herbicide, has been suggested as a potential etiologic factor for the development of Parkinson's disease (PD). In this sense, understanding of the molecular mechanism underlying PQ-induced toxicity to neural cells is important for optimal use as well as for the development of new drugs. To gain insights into PQ-induced neurotoxicity, polymerase chain reaction (PCR) array analysis focused on a panel of apoptosis-related genes was performed using neuroblastoma SH-SY5Y cells. Up to 65 apoptosis-related genes were monitored. Our analysis of apoptotic process through microarray technology showed that in PQ-induced neuroblastoma SH-SY5Y cells, there is a different expression of BIK, CASP3, CASP7, CRADD, DAPK, FAS, and other related genes, in comparison to unstimulated cells. Evaluation of genes regulated differentially is essential for the development of therapeutic approaches in multifactorial diseases as PD. Our data provide a useful basis for screening candidate targets for early diagnosis and further intervention in PQ-mediated toxicity of neural cells.

Paraquat (PQ) (1, 1'-dimethyl-4, 4'-bipyridinium dichloride), a widely used herbicide, has been suggested as a potential etiologic factor for the development of Parkinson's disease (PD). In neurons from patients with PD display characteristics of autophagy, a degradative mechanism involved in the recycling and turnover of cytoplasmic constituents from eukaryotic cells. Low concentrations of paraquat have been recently found to induce autophagy in human neuroblastoma cells, and ultimately the neurons succumb to apoptotic death. Whereas caspase inhibition retarded cell death, autophagy inhibition accelerated the apoptotic cell death induced by paraquat. These findings suggest a relationship between autophagy and apoptotic cell death in human neuroblastoma cells treated with paraquat and open a new line of investigation to advance our knowledge regarding the origin of PD.

Autophagy is a degradative mechanism involved in the recycling and turnover of cytoplasmic constituents from eukaryotic cells. This phenomenon of autophagy has been observed in neurons from patients with Parkinson's disease (PD), suggesting a functional role for autophagy in neuronal cell death. On the other hand, it has been demonstrated that exposure to pesticides can be a risk factor in the incidence of PD. In this sense, paraquat (PQ) (1,1'-dimethyl-4,4'-bipyridinium dichloride), a widely used herbicide that is structurally similar to the known dopaminergic neurotoxicant MPP(+) (1-methyl-4-phenyl-pyridine), has been suggested as a potential etiologic factor for the development of PD. The current study shows, for the first time, that low concentrations of PQ induce several characteristics of autophagy in human neuroblastoma SH-SY5Y cells. In this way, PQ induced the accumulation of autophagic vacuoles (AVs) in the cytoplasm and the recruitment of a LC3-GFP fusion protein to AVs. Furthermore, the cells treated with PQ showed an increase of the long-lived protein degradation which is blocked in the presence of the autophagy inhibitor 3-methyladenine and regulated by the mammalian target of rapamycin (mTOR) signaling. Finally, the cells succumbed to cell death with hallmarks of apoptosis such as phosphatidylserine exposure, caspase activation, and chromatin condensation. While caspase inhibition retarded cell death, autophagy inhibition accelerated the apoptotic cell death induced by PQ. Altogether, these findings show the relationship between autophagy and apoptotic cell death in human neuroblastoma cells treated with PQ.

Paraquat is a herbicide with a potential risk to induce parkinsonism due to its demonstrated neurotoxicity and its strong structural similarity to 1-methyl-4-phenylpyridinium (MPP(+)), a well-known neurotoxin which causes a clinical syndrome similar to Parkinson's disease (PD). However, at present very little is known about the signaling pathways activated by paraquat in any cell system. In this study, we have investigated the effect of paraquat on extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and protein kinase B (PKB) activation in E18 cells. Low concentrations of paraquat stimulated very early increases in ERK1/2, JNK1/2, and PKB phosphorylation. The phosphatidylinositol 3-kinase (PI-3K) inhibitors wortmannin and LY 294002 (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one) inhibited early paraquat-induced increases in PKB phosphorylation. Furthermore, early paraquat-mediated increases in ERK1/2 activation were sensitive to the mitogen-activated protein kinase kinase 1 (MEK1) inhibitor PD 98059 (2'-amino-3'-methoxyflavone), whereas JNK1/2 responses were blocked by the JNK1/2 inhibitor SP 600125 (anthra[1-9-cd]pyrazol-6(2H)-one). Pretreatment with wortmannin, LY 294002, or PD 98059 had no effect on paraquat cell death in E18 cells. In contrast, SP 600125 significantly decreased paraquat-induced cell death in E18 cells. In conclusion, we have shown that low concentrations of paraquat stimulate robust very early increases in ERK1/2, JNK1/2, and PKB phosphorylation in E18 cells. Furthermore, the data presented clearly suggest that inhibition of the JNK1/2 pathway protects E18 cells from paraquat-induced cell death and support the fact that inhibition of early activation of JNK1/2 can constitute a potential strategy in PD treatment.

Exposure of cerebellar granule cells to 1-methyl-4-phenylpiridinium (MPP(+)) results in cell death. We have studied the implication of various membrane transporter systems on MPP(+) neurotoxicity, including the dopamine transporter system (DAT) and cationic amino acid transporters (CAT). We have showed a partial protection against MPP(+) toxicity when the dopamine transporter is inhibited by 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]4-(3-phenylpropyl)piperazinedihydrochloride (GBR-12909). However, almost full protection is only achieved by the simultaneous addition of GBR-12909 and cationic amino acids. These results suggest two ways system of MPP(+) entrance into cerebellar granule cells: the DAT with high activity and the CAT with low activity. We also demonstrated that 5,7-dichlorokynurenic acid (MK-801) failed to protect against MPP(+) exposure, evidencing that N-methyl-D-aspartate (NMDA) receptor is not involved in the MPP(+)-induced cell death.