Effects of hyperoxia and acrylonitrile on the phospholipase C isozyme protein levels in rat heart and brain

Protective effects of antioxidants on acrylonitrile-induced oxidative stress in female F344 rats

The induction of oxidative stress and damage appears to be involved in acrylonitrile induction of brain astrocytomas in rat. The present study examined the effects of dietary antioxidant supplementation on acrylonitrile-induced oxidative stress and oxidative damage in rats in vivo. To assess the effects of antioxidants on biomarkers of acrylonitrile-induced oxidative stress, female F344 rats were provided with diets containing vitamin E (0.05%), green tea polyphenols (GTP, 0.4%), N-acetyl cysteine (NAC, 0.3%), sodium selenite (0.1mg/kg), and taurine (10g/kg) for 7 days, and then co-administered with 0 and 100 ppm acrylonitrile in drinking water for 28 days. Significant increase in oxidative DNA damage in brain, evidenced by elevated 8OHdG levels, was seen in acrylonitrile-exposed rats. Supplementation with vitamin E, GTP, and NAC reduced acrylonitrile-induced oxidative DNA damage in brain while no protective effects were seen with the selenium or taurine supplementation. Acrylonitrile increased oxidative DNA damage, measured by the fpg-modified alkaline Comet assay in rat WBCs, which was reduced by supplementation of Vitamin E, GTP, NAC, selenium, and taurine. In addition to stimulation of oxidative DNA damage, acrylonitrile triggered induction of pro-inflammatory cytokines Tnfα, Il-1β, and Ccl2, and the growth stimulatory cyclin D1 and cyclin D2 genes, which were effectively down-regulated with antioxidant treatment. Antioxidant treatment also was able to stimulate the pro-apoptotic genes Bad, Bax, and FasL and DNA repair genes Xrcc6 and Gadd45α. The results of this study support the involvement of oxidative stress in the development of acrylonitrile-induced astrocytomas and suggest that antioxidants block acrylonitrile-mediated damage through mechanisms that may involve in the suppression of inflammatory responses, inhibition of cell proliferation and stimulation of apoptosis. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1808-1818, 2016.

pPKCα mediated-HIF-1α activation related to the morphological modifications occurring in neonatal myocardial tissue in response to severe and mild hyperoxia

In premature babies birth an high oxygen level exposure can occur and newborn hyperoxia exposure can be associated with free radical oxygen release with impairment of myocardial function, while in adult animal models short exposure to hyperoxia seems to protect heart against ischemic injury. Thus, the mechanisms and consequences which take place after hyperoxia exposure are different and related to animals age. The aim of our work has been to analyze the role played by HIF-1α in the occurrence of the morphological modifications upon hyperoxia exposure in neonatal rat heart. Hyperoxia exposure induces connective compartment increase which seems to allow enhanced blood vessels growth. An increased hypoxia inducible factor-1α (HIF-1α) translocation and vascular endothelial growth factor (VEGF) expression has been found upon 95% oxygen exposure to induce morphological modifications. Upstream pPKC-α expression increase in newborn rats exposed to 95% oxygen can suggest PKC involvement in HIF-1α activation. Since nitric oxide synthase (NOS) are involved in heart vascular regulation, endothelial NOS (e-NOS) and inducible NOS (i-NOS) expression has been investigated: a lower eNOS and an higher iNOS expression has been found in newborn rats exposed to 95% oxygen related to the evidence that hyperoxia provokes a systemic vasoconstriction and to the iNOS pro-apoptotic action, respectively. The occurrence of apoptotic events, evaluated by TUNEL and Bax expression analyses, seems more evident in sample exposed to severe hyperoxia. All in all such results suggest that in newborn rats hyperoxia can trigger oxygen free radical mediated membrane injury through a pPKCα mediated HIF-1α signalling system, even though specificity of such response could be obtained by in vivo administration to the rats of specific inhibitors of PKCα. This intracellular signalling can switch molecular events leading to blood vessels development in parallel to pro-apoptotic events due to an immature anti-oxidant defensive system in newborn rat hearts.

Calcium fluxes cause nuclear shrinkage and the translocation of phospholipase C-delta1 into the nucleus

Phospholipase C-delta1 (PLCdelta1) is the most fundamental form of the eukaryotic PLC and thought to play important roles in the regulation of cells. We previously reported that PLCdelta1 shuttles between the cytoplasm and nucleus, and an influx of Ca2+ triggers the nuclear import of PLCdelta1 via Ca2+-dependent interaction with importin beta1, although the physiological meaning of this is unclear. Here we have examined the distribution of PLCdelta1 using primary cultures of rat hippocampal neurons. Treatment of 7DIV neurons with ionomycin or thapsigargin caused the nuclear localization of PLCdelta1 as has been observed in other cell lines. Similar results were obtained with neurons treated with glutamate, suggesting that the nuclear localization of PLCdelta1 plays some roles in excitotoxicity associated with ischemic stress. Generally, cells undergoing ischemic or hypoxic cell death show nuclear shrinkage. We confirmed that a massive influx of Ca2+ caused similar results. Furthermore, overexpression of GFP-PLCdelta1 facilitated ionomycin-induced nuclear shrinkage in embryonic fibroblasts derived from PLCdelta1 gene-knockout mice (PLCdelta1KO-MEF). By contrast, an E341A mutant that cannot bind with importin beta1 and be imported into the nucleus by ionomycin and also lacks enzymatic activity did not cause nuclear shrinkage in PLCdelta1KO-MEF. Nuclear translocation and the PLC activity of PLCdelta1, therefore, may regulate the nuclear shape by controlling the nuclear scaffold during stress-induced cell death caused by high levels of Ca2+.

Neurovestibular toxicities of acrylonitrile and iminodipropionitrile in rats: a comparative evaluation of putative mechanisms and target sites

This investigation was aimed to study the effects of individual and concomitant exposures of the two nitrile compounds, the industrially important acrylonitrile (ACN; 5, 15, 45 mg/kg/day) and the positive control iminodipropionitrile (IDPN; 100 mg/kg/day) in rats. The six treatment groups were 1 (control), 2 (ACN 5), 3 (ACN 15), 4 (ACN 45), 5 (IDPN), and 6 (IDPN + ACN 15). Both the drugs were started on the same day and continued for 9 days (IDPN was given daily 30 min before ACN but stopped a day earlier). The animals were daily observed for neurobehavioral abnormalities including dyskinetic head movements, circling, tail hanging, air righting reflex, and contact inhibition of righting reflex. There was no dyskinetic behavioral abnormality in the animals treated with any of the three doses of ACN whereas all the rats in IDPN alone treated group developed clear symptoms of excitation, circling, and chorea syndrome (ECC syndrome) on day 9. Concomitant treatment of rats with ACN significantly attenuated the severity of IDPN-induced behavioral deficits. Administration of ACN significantly depleted glutathione (GSH) in striatum, hippocampus and cerebral cortex; IDPN significantly reduced the GSH only in striatum. The anterior striatum showed intense tyrosine hydroxylase (TH) expression in IDPN alone treated rat as compared to control and ACN alone treated rat. Cotreatment with ACN reduced the intensity of TH immunostaining in IDPN-treated rats. Administration of IDPN alone caused massive loss of vestibular sensory hair cells in the crista ampullaris whereas the sensory epithelium appeared intact in ACN alone treated groups. The animals receiving the combination of ACN and IDPN showed comparatively less degeneration of sensory hair cells than IDPN alone group. These findings suggest that ACN and IDPN produce different behavioral effects that are exerted through entirely different mechanisms; the nervous and vestibular systems appear to be the major target sites of these toxins, respectively.

Persistence of hyperbaric oxygen-induced oxidative effects after exposure in rat brain cortex tissue

Hyperbaric oxygen (HBO) causes oxidative stress in several organs and tissues. Due to its high rate of blood flow and oxygen consumption, the brain is one of the most sensitive organs to this effect. Many studies have reported oxidative effects of HBO, but there is no comprehensive data about how long this effect persists. The aim of this study was to elucidate the duration of HBO-induced oxidative/antioxidant action. Male Sprague-Dawley rats were divided into 5 groups. Except for the controls, the animals were subjected to 100% oxygen for 2 h at 3 atm and differed from each other by the time to dissection after exposure that began at 30, 60, 90, or 120 min. Thiobarbituric acid-reactive substances (TBARS), as well as superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity was determined in brain cortex tissue. Additionally, nitrite-nitrate (NO(x)) concentrations were measured. All measured parameters were found to be significantly increased 30 min after exposure. SOD and GSH-Px levels persisted at significantly high levels for 60 min. In conclusion, the oxidative effect of HBO was shown to persist only for 1 h. Further studies should be performed to elucidate the possible molecular interactions during this period.

Acrylonitrile-induced extracellular signal-regulated kinase (ERK) activation via protein kinase C (PKC) in SK-N-SH neuroblastoma cells

Acrylonitrile (ACN) is classified by IARC as a probable carcinogen. Chronic exposure to ACN increases the incidence of tumors in various organs of test animals, including the brain and lung. ERK1/2 activation plays crucial roles in cell proliferation and is involved in many steps of tumor progression. Therefore, this study examined whether ACN altered the activation state of ERK1/2 in human neuroblastoma SK-N-SH cells. Treatment of these cells with ACN greatly increased phosphorylation of ERK1/2 in dose- and time-dependent manners. This effect was inhibited by PD 98059 and U 0126, specific inhibitors of MEK, indicating that MEK, an upstream activator of ERK1/2, was directly involved in ACN-induced ERK1/2 activation. Furthermore, the activation of ERK1/2 by ACN was attenuated by inhibition of PKC with GF 109203X, rottlerin and prolonged incubation with PMA (phorbol 12-myristate 13-acetate). This demonstrated the participation of PKC in the ACN-stimulated activation of ERK1/2. Taken together, our results indicate that ACN-induced ERK1/2 activation involves PKC through a MEK-dependent pathway.

Differential expression profiles of PLC-β1 and -δ1 in primary cultured rat cortical neurons treated with N-methyl-d-aspartate and peroxynitrite

Phospholipase C (PLC)-delta1 protein appears to accumulate aberrantly in Alzheimer's disease brains and its expression is reported to be induced by overstimulation of N-methyl-D-aspartate (NMDA) receptor, but there is little knowledge on its physiological role. To clarify this, we examined the expression profile of PLC-delta1 in primary cultured rat cortical neurons treated with NMDA or peroxynitrite, in comparison with those of PLC-beta1 and -gamma1, the overexpression of both of which protects cells from oxidative stress. Overstimulation of NMDA receptor decreased and increased the expression of PLC-beta1 and -delta1, respectively, but did not affect that of PLC-gamma1, in the neurons. The viability of neurons decreased depending on the period of treatment with S-nitroso-N-acetyl D,L-penicillamine (SNAP), there being a significant decrease on 9 h treatment. On examination of the expression profiles of PLC isozymes after treatment of neurons with SNAP, PLC-beta1 was found to be increased after 1h treatment and decreased after 9 h treatment, while PLC-delta1 was significantly increased, especially after 5 h treatment. Peroxynitrite treatment caused a dose-dependent decrease in the viability of neurons, and expression of PLC-beta1 was increased by a nontoxic level of peroxynitrite and decreased by a toxic level of it, while that of PLC-delta1 was increased by a sublethal level of it. These findings suggested that induction of PLC-beta1 might protect neurons from oxidative stress, but that of PLC-delta1 might have the opposite role, although both isozymes responded to oxidative stress.