The Effect of Chronic Ozone Exposure on the Activation of Endoplasmic Reticulum Stress and Apoptosis in Rat Hippocampus.

The chronic exposure to low doses of ozone, like in environmental pollution, leads to a state of oxidative stress, which has been proposed to contribute to neurodegenerative disorders, including Alzheimer's disease (AD). It induces an increase of calcium in the endoplasmic reticulum (ER), which produces ER stress. On the other hand, different studies show that, in diseases such as Alzheimer's, there exist disturbances in protein folding where ER plays an important role. The objective of this study was to evaluate the state of chronic oxidative stress on ER stress and its relationship with apoptotic death in the hippocampus of rats exposed to low doses of ozone. We used 108 male Wistar rats randomly divided into five groups. The groups received one of the following treatments: (1) Control (air); (2) Ozone (O3) 7 days; (3) O3 15 days; (4) O3 30 days; (5) O3 60 days; and (6) O3 90 days. Two hours after each treatment, the animals were sacrificed and the hippocampus was extracted. Afterwards, the tissue was processed for western blot and immunohistochemistry using the following antibodies: ATF6, 78 kDa glucose-regulated protein (GRP78) and caspase 12. It was also subjected to terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and electronic microscopy. Our results show an increase in ATF6, GRP78 and caspase 12 as well as ER ultrastructural alterations and an increase of TUNEL positive cells after 60 and 90 days of exposure to ozone. With the obtained results, we can conclude that oxidative stress induced by chronic exposure to low doses of ozone leads to ER stress. ER stress activates ATF6 inducing the increase of GRP78 in the cytoplasm, which leads to the increase in the nuclear translocation of ATF6. Finally, the translocation creates a vicious cycle that, together with the activation of the cascade for apoptotic cell death, contributes to the maintenance of ER stress. These events potentially contribute in the neurodegeneration processes in diseases like AD.

Oxidative stress-dependent changes in immune responses and cell death in the substantia nigra after ozone exposure in rat.

Parkinson's disease has been associated with the selective loss of neurons in the substantia nigra pars compacta. Increasing evidence suggests that oxidative stress plays a major role. The resulting increase in reactive oxygen species triggers a sequence of events that leads to cell damage, activation of microglia cells and neuroinflammatory responses. Our objective was to study whether chronic exposure to low doses of ozone, which produces oxidative stress itself, induces progressive cell death in conjunction with glial alterations in the substantia nigra. Animals were exposed to an ozone-free air stream (control) or to low doses of ozone for 7, 15, 30, 60, or 90 days. Each group underwent (1) spectrophotometric analysis for protein oxidation; (2) western blot testing for microglia reactivity and nuclear factor kappa B expression levels; and (3) immunohistochemistry for cytochrome c, GFAP, Iba-1, NFkB, and COX-2. Our results indicate that ozone induces an increase in protein oxidation levels, changes in activated astrocytes and microglia, and cell death. NFkB and cytochrome c showed an increase until 30 days of exposure, while cyclooxygenase 2 in the substantia nigra increased from 7 days up to 90 days of repetitive ozone exposure. These results suggest that oxidative stress caused by ozone exposure induces changes in inflammatory responses and progressive cell death in the substantia nigra in rats, which could also be occurring in Parkinson's disease.

Effect of growth hormone on Cyclooxygenase-2 expression in the hippocampus of rats chronically exposed to ozone.

The aim of this study was to determine GH-effects on Cyclooxygenase-2 (COX-2) expression on hippocampus alterations caused by ozone exposure. Seventy male rats were divided into: (1) control; (2) exposed to ozone for 7, 15, and 30 days; (3) exposed to ozone and treated with GH, for 7, 15, and 30 days. Results showed that lipoperoxidation levels and number of COX-2-positive cells increased in all groups exposed to ozone compared to control. In the groups treated with GH, COX-2 immunoreactive cell number decreased with respect to the ozone group. Therefore, GH could provide protection against damage induced by oxidative stress.

Oxidative damage in substantia nigra and striatum of rats chronically exposed to ozone.

The purpose of this work was to study if chronic low-dose ozone exposure could per se induce oxidative damage to neurons of striatum and substantia nigra. Thirty male Wistar rats were divided into three groups--Group 1: exposed to an air stream free of ozone; Group 2: exposed for 15 days to ozone; Group 3: exposed for 30 days to ozone. Ozone exposure was carried out daily for 4 h at a 0.25 ppm dose. Each group was then tested for (1) motor activity, (2) quantification of lipid peroxidation levels, (3) Klüver-Barrera staining, and (4) immunohistochemistry for tyrosine hydroxylase (TH), dopamine and adenosine 3',5'-monophosphate-regulated phosphoprotein of 32 kD (DARPP-32), inducible nitric oxide synthase (iNOS), and superoxide dismutase (SOD), to study neuronal alterations in striatum and substantia nigra. Results indicate that ozone exposure causes a significant decrease in motor activity. Ozone produced lipid peroxidation, morphological alterations, loss of fibers and cell death of the dopaminergic neurons. The DARPP-32, iNOS and SOD expression increased with repetitive ozone exposure. These alterations suggest that ozone causes oxidative stress which induces oxidative damage to substantia nigra and striatum of the rat.

Antioxidant effects of taurine, vitamin C, and vitamin E on oxidative damage in hippocampus caused by the administration of 3-nitropropionic acid in rats.

The administration of 3-nitropropionic acid increases reactive oxygen species (ROS). Antioxidant defense mechanisms buffer these ROS converting them into non-damaging compounds. Taurine and vitamins C and E are antioxidants that play a role in the defense against cellular damage. This study examines the antioxidant effect of taurine, vitamin C, and vitamin E on acute hippocampal damage caused by 3-NP. Animals treated with 3-NP increased lipid peroxidation levels and astrocytic damage in the hippocampus. Administration of taurine, vitamin C, and vitamin E partially protected from oxidative damage, indicate that while all substances had antioxidant effects, only taurine showed morphological protection in surviving cells.