Oxidative stress in rat cortical neurons and astrocytes induced by paraquatin vitro

Abstract

Oxidative stress has been discussed as crucial mechanism of neuronal cell death in the adult brain. However, it was not clear until now whether neurons are more sensitive to oxidative stress than the other cells in the brain, e.g. astrocytes. Therefore both cell types were exposed to oxidative stress provoked by the redox-cycling compound paraquat. Cortical neurons were found to be more sensitive towards paraquat toxicity than astrocytes as shown by MTT and Neutral Red assay, two different cytotoxicity assays. Mitochondrial functions were determined by the mitochondrial membrane potential and intracellular ATP concentrations. Again cortical neurons were more severely impaired (by paraquat than astrocytes). The production of reactive oxygen species after paraquat exposure was much higher in cortical neurons than in astrocytes and correlated with a higher depletion of GSH (intracellular glutathion). Lipid peroxidation could be shown in astrocytes via the breakdown product malondialdehyde (MDA) whereas in cortical neurons 4-hydroxynonenal (4-HNE) was detected as this endpoint. If and how oxidative stress influences the antioxidant defense was determined via changes in the expression of antioxidant enzymes. Paraquat exposure lead to a 2-3 fold increase of catalase, MnSOD and CuZnSOD mRNA expression in astrocytes. In contrast to astrocytes, in cortical neurons catalase and MnSOD mRNA levels were only marginally elevated above 1.5-fold by treatment with paraquat. Expression levels of glutathione peroxidase (GPx) mRNA were the only one that were not changed in both cell types after paraquat exposure. It is concluded that the more marked increase in expression levels of antioxidant enzymes may render astrocytes more resistant to oxidative stress than neuronal cells.

Neurotoxic Mode of Action of Artemisinin

“…The organophosphate mipafox and the herbicide paraquat served as control compounds. It was shown in cortical neurons that mipafox had no effect on mitochondrial functions, in contrast to paraquat (36,38), and this was also found in brain stem cultures (Table 1).…”

“…It was shown with paraquat that 4-HNE is the prominent degradation product in neuronal cells, whereas malondialdehyde is produced predominantly by nonneuronal cells (38).…”

“…Paraquat is one model compound that induces ROS by decoupling of the respiratory chain (36,38). Like paraquat, artemisinin produced ROS in brain stem (400% of the control at 0.01 g/ml) and cortical (175% of the control at 1 g/ml) cell cultures.…”

“…The expression of AOE can be regulated by oxidative stress itself (32,37,39,43), which could also be shown for, among others, astroglial cell cultures (34). It has been demonstrated that primary neuronal cell culture systems are suitable for detection of oxidative stress evoked by paraquat using specific endpoints such as ROS production, lipid peroxidation, and AOE expression (38).…”

Croton cajucara BENTH. Leaf Extract Scavenges the Stable Free Radical DPPH and Protects Against Oxidative Stress Induced by Paraquat

“…40) The results of our study show that the rise in oxidative stress indices was accompanied by a higher SOD activity in paraquat-treated rats. This effect, believed to be due to increased dismutation of superoxide anions generated through the paraquat toxicity mechanism, 41,42) was prevented by the Croton cajucara leaf extract, which suggests the possibility of a superoxide radical scavenger activity. A similar change in SOD renal activity has been reported in diabetic rats treated with extracts from Gongronema latifolium leaves.…”