Transgenic glutathione peroxidase mouse models for neuroprotection studies

Licochalcone B confers protective effects against LPS-Induced acute lung injury in cells and mice through the Keap1/Nrf2 pathway

BACKGROUND

Acute lung injury (ALI) is a severe and often fatal pulmonary disease. Current treatments for ALI and acute respiratory distress syndrome (ARDS) are limited. Natural product metabolites have shown promise as therapeutic alternatives. However, the effects of Licochalcone B (LCB) on ALI are largely unknown.

METHODS

We investigated the effects of LCB on lipopolysaccharide-challenged mice and human pulmonary microvascular endothelial cells. Cell viability, apoptosis, and ROS production were assessed. Lung tissue histopathology and oxidative stress and inflammation markers were evaluated. Protein expression levels were measured.

RESULTS

LCB had no cytotoxic effects on cells and increased cell viability. It reduced apoptosis and ROS levels in cells. In mice with ALI, LCB decreased lung tissue weight and improved oxidative stress and inflammation markers. It also enhanced expression levels of Nrf2, HO-1, and NQO1 while reducing Keap1.

CONCLUSION

LCB protects against LPS-induced acute lung injury in cells and mice. The Keap1/Nrf2 pathway may be involved in its protective effects. LCB shows potential as a strategy to alleviate ALI caused by LPS.

Impacts on antioxidative enzymes and transcripts in darter (Etheostoma spp.) brains in the Grand River exposed to wastewater effluent

The Grand River watershed is the largest in southern Ontario and assimilates thirty wastewater treatment plants (WWTP) with varied degrees of treatment. Many WWTPs are unable to effectively eliminate several contaminants of emerging concern (CECs) from final effluent, leading to measurable concentrations in surface waters. Exposures to CECs have reported impacts on oxidative stress measured through antioxidative enzymes (SOD, CAT, GPX). This study focuses on the effects of WWTP effluent on four Etheostoma (Darter) species endemic to the Grand River, by investigating if increased antioxidative response markers are present in darter brains downstream from the effluent outfall compared to an upstream reference site relative to the Waterloo, ON WWTP across two separate years (Oct 2020 and Oct 2021). This was assessed using transcriptional and enzyme analysis of antioxidant enzymes and an enzyme involved in serotonin synthesis, tryptophan hydroxylase (tph). In fall 2020, significant differences in transcript markers were found between sites and sexes in GSD with SOD and CAT showing increased expression downstream, in JD with both sexes showing increased SOD downstream, and an interactive effect for tph in RBD. Changes in transcripts aligned with enzyme activity where interactive effects with sex-related differences were observed in fish collected fall 2020. In contrast, transcripts measured in fall 2021 were increased upstream compared to downstream species in RBD and GSD. This study additionally displayed yearly, species and sex differences in antioxidant responses. Continued investigation on the impacts of CECs in effluent in non-target species is required to better understand WWTP effluent impacts.

Assessment of the effect of perineural dexmedetomidine on oxidative stress during peritoneal dialysis catheter insertion: a randomized, controlled trial

Purpose

This study aimed to evaluate the effect of the addition of dexmedetomidine to ropivacaine on oxidative stress during transversus abdominis plane (TAP) and rectus sheath (RS) blockades for patients with end-stage renal disease (ESRD) undergoing peritoneal dialysis (PD) catheter insertion.

Methods

Sixty patients with ESRD undergoing PD catheter insertion to receive left ultrasound-guided TAP and RS blockades were randomly divided into two groups: the dexmedetomidine plus ropivacaine group (25 mL of 0.3% ropivacaine + 1 μg/kg dexmedetomidine) and the ropivacaine group (25 mL of 0.3% ropivacaine). Primary outcomes were oxidative stress marker levels during the procedure.

Results

A total of 60 patients (30 patients in each group) were evaluated. Compared with the ropivacaine group, the dexmedetomidine plus ropivacaine group had significantly lower serum malondialdehyde levels (P < 0.05) and increased glutathione peroxidase (P < 0.01) and superoxide dismutase levels at 24 h after the procedure (P < 0.01).

Conclusion

The addition of 1 μg/kg of dexmedetomidine to ropivacaine for ultrasound-guided TAP and RS blockades could inhibit oxidative stress in patients with ESRD undergoing PD catheter insertion.

Trial registration This study was registered at www.chictr.org.cn on June 7, 2021 (ChiCTR2100047050).

Effect of dexmedetomidine administration on analgesic, respiration and inflammatory responses in patients undergoing percutaneous endoscopic lumbar discectomy: a prospective observational study

Background

Local anesthesia has been recommended for percutaneous endoscopic lumbar discectomy (PELD) in recent years; however, the efficacy, including oxidative stress, inflammatory reactions and ventilation effects, when intravenous dexmedetomidine (DEX) is administered during PELD has not been described.

Methods

Sixty adult patients undergoing PELD were randomly allocated to either an intravenous DEX sedation group (Group A) or a normal saline group (Group B). Respiratory data, including minute ventilation (MV), tidal volume (TV), and respiratory rate (RR), were recorded using a respiratory volume monitor (RVM), and peripheral oxygen saturation (SpO₂) was monitored by pulse oximetry. The visual analog score (VAS) was used to assess the level of pain. The serum levels of inflammatory biomarkers including interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were to assess inflammatory reactions. The serum levels of oxidative stress biomarkers including malondialdehyde (MDA) and glutathione peroxidase (GSH-PX) were also recorded to evaluate oxidative stress.

Results

There were no significant differences in RR, MV, TV and SpO₂ between the two groups at any time point (P > 0.05). Group B exhibited lower serum levels of GSH-PX (P < 0.0001) and higher serum levels of MDA (p < 0.0001) than Group A at the end of surgery. Twenty-four hours after surgery, Group B exhibited higher serum levels of IL-6 (P = 0.0033), TNF-α (P = 0.0002), and MDA (P < 0.0001) and lower serum levels of GSH-PX (P < 0.0001) than Group A. In addition, Group A exhibited lower VAS (P < 0.0001) than Group B during surgery.

Conclusions

DEX administration using RVM not only provides analgesia without ventilatory depression but also alleviates oxidative stress and inflammatory reactions in patients undergoing PELD.

Alteration in Downstream Hypoxia Gene Signaling in Neonatal Glutathione Peroxidase Overexpressing Mouse Brain after Hypoxia-Ischemia

We have previously shown that glutathione peroxidase (GPx) overexpressing mice (hGPx-tg) have reduced brain injury after neonatal hypoxia-ischemia (HI) as a consequence of reduced hydrogen peroxide accumulation. However, this protection is reversed with hypoxia preconditioning, raising the question of the roles of the genes regulated by hypoxia-inducible factor-1α (HIF-1α) and their transcription products, such as erythropoietin (EPO), in both the initial protection and subsequent reversal of protection. hGPx-tg and their wild-type (WT) littermates underwent the Vannucci procedure of HI brain injury at postnatal day 9 - left carotid artery ligation followed by exposure to 10% oxygen for 50 min. Brain cortices and hippocampi were subsequently collected 0.5, 4 and 24 h later for the determination of protein expression by Western blot for GPx, HIF-1α, HIF-2α, EPO, EPO receptor, ERK1/2, phospho-ERK1/2, spectrin 145/150 (as a marker of calpain-specific necrotic cell death), and spectrin 120 (as a marker of apoptotic cell death mediated via caspase-3). As expected, the GPx overexpressing mouse cortex had approximately 3 times the GPx expression as WT naïve. Also, GPx expression remained higher in the GPx overexpressing brain than WT at all time points after HI (0.5, 4, 24 h). HIF-1α was not significantly changed in hGPx-tg as a consequence of HI but decreased in the WT cortex 4 h after HI. HIF-2α decreased in the WT hippocampus after HI. EPO was higher in the GPx overexpressing cortex and hippocampus 30 min after HI compared to WT, but the EPO receptor was unchanged by HI. ERK1/2 phosphorylation increased in the hippocampus at 4 h after HI and in the cortex at 24 h after HI in both WT and hGPx-tg. Spectrin 145/150 was increased in the WT cortex at 4 and 24 h after HI, and spectrin 120 increased 24 h after HI, perhaps reflecting greater injury in the WT brain, especially at 24 h when brain injury is more evident. The effect of GPx overexpression does not appear to upregulate the HIF pathway, yet EPO was upregulated, perhaps via ERK. This might explain, in part, why cell death takes a necrotic or apoptotic path. This may also be an explanation for why the GPx overexpressing brain cannot be preconditioned. This information may prove valuable in the development of therapies for neonatal HI brain injury.

Glutathione peroxidase overexpression causes aberrant ERK activation in neonatal mouse cortex after hypoxic preconditioning

BACKGROUND

Preconditioning of neonatal mice with nonlethal hypoxia (HPC) protects the brain from hypoxic-ischemic (HI) injury. Overexpression of human glutathione peroxidase 1 (GPx1), which normally protects the developing murine brain from HI injury, reverses HPC protection, suggesting that a certain threshold of hydrogen peroxide concentration is required for activation of HPC signaling.

METHODS

Activation (phosphorylation) of extracellular-regulated kinase (ERK) 1/2 and Akt, and induction of hypoxia-inducible factor (HIF)-1α were assessed in the cortex, one of the main structures affected by HI and protected by HPC, at different time points after reoxygenation in wild-type (WT) and GPx1-overexpressing animals.

RESULTS

GPx1 overexpression prevented both the global and nuclear increase in activated ERK at 0.5 h after HPC and caused a significant decrease in phospho-ERK (pERK)/ERK levels at 24 h after HPC. In contrast, HIF-1α induction at the end of hypoxia was unaffected by GPx1 overexpression. In the cortex of preconditioned WT animals, enhanced pERK staining was primarily observed in neurons and to a lower extent in astrocytes and endothelial cells, with a nuclear prominence.

CONCLUSION

Aberrant activation of ERK probably explains the paradoxical reversal of HPC protection by GPx1 overexpression. The results identify hydrogen peroxide as an important mediator of neuroprotective ERK signaling.

Effects of a Rubus coreanus Miquel supplement on plasma antioxidant capacity in healthy Korean men

Korean raspberry, Rubus coreanus Miquel (RCM), contains high concentrations of phenolic compounds, which prevent oxidative stress. To determine the effect of RCM on antioxidant capacity in humans, we assessed in vivo lipid oxidation and antioxidant enzyme activities from plasma in 15 healthy men. The subjects ingested 30 g of freeze-dried RCM daily for 4 weeks. Blood was taken at baseline and at the end of the study to determine blood lipid profiles, fasting plasma glucose, liver function, lipid peroxidation, and antioxidant enzyme activities. RCM supplementation had no effect on blood lipid or fasting plasma glucose concentrations but decreased alkaline phosphatase activity. RCM supplementation increased glutathione peroxidase activities (P < 0.05) but had no effect on lipid peroxidation. These results suggest that short-term RCM supplementation may offer health benefits by enhancing antioxidant capacity in a healthy population.

Catalase and glutathione peroxidase mimics

Overproduction of the reactive oxygen species (ROS) superoxide (O(2)(-)) and hydrogen peroxide (H(2)O(2)) are increasingly implicated in human disease and aging. ROS are also being explored as important modulating agents in a number of cell signaling pathways. Earlier work has focused on development of small catalytic scavengers of O(2)(-), commonly referred to as superoxide dismutase (SOD) mimetics. Many of these compounds also have substantial abilities to catalytically scavenge H(2)O(2) and peroxynitrite (ONOO(-)). Peroxides have been increasingly shown to disrupt cell signaling cascades associated with excessive inflammation associated with a wide variety of human diseases. Early studies with enzymatic scavengers like SOD frequently reported little or no beneficial effect in biologic models unless SOD was combined with catalase or a peroxidase. Increasing attention has been devoted to developing catalase or peroxidase mimetics as a way to treat overt inflammation associated with the pathophysiology of many human disorders. This review will focus on recent development of catalytic scavengers of peroxides and their potential use as therapeutic agents for pulmonary, cardiovascular, neurodegenerative and inflammatory disorders.

Hypoxic preconditioning reverses protection after neonatal hypoxia-ischemia in glutathione peroxidase transgenic murine brain

The effect of hypoxic preconditioning (PC) on hypoxic-ischemic (HI) injury was explored in glutathione peroxidase (GPx)-overexpressing mice (human GPx-transgenic [hGPx-tg]) mice. Six-day-old hGPx-tg mice and wild-type (Wt) littermates were pre-conditioned with hypoxia for 30 min and subjected to the Vannucci procedure of HI 24 h after the PC stimulus. Histopathological injury was determined 5 d later (P12). Additional animals were killed 2 h or 24 h after HI and ipsilateral cerebral cortices assayed for GPx activity, glutathione (GSH), and hydrogen peroxide (H2O2). In line with previous studies, hypoxic PC reduced injury in the Wt brain. Preconditioned Wt brain had increased GPx activity, but reduced GSH, relative to naive 24 h after HI. Hypoxic PC did not reduce injury to hGPx-tg brain and even reversed the protection previously reported in the hGPx-tg. GPx activity and GSH in hGPx-tg cortices did not change. Without PC, hGPx-tg cortex had less H2O2 accumulation than Wt at both 2 h and 24 h. With PC, H2O2 remained low in hGPx-tg compared with Wt at 2 h, but at 24 h, there was no longer a difference between hGPx-tg and Wt cortices. Accumulation of H2O2 may be a mediator of injury, but may also induce protective mechanisms.

Selective gene expression in magnocellular neurons in rat supraoptic nucleus

Oxytocin- and vasopressin-producing magnocellular neurons (MCNs) of the hypothalamo-neurohypophysial system are the only neuronal phenotypes present in the rat supraoptic nucleus (SON). Laser microdissection of the SON, extraction and T7-based amplification of its RNAs, and analysis of the resulting cDNAs by hybridization on a 35, 319 element DNA microarray have provided a detailed composite view of the gene expression profile of the MCNs. The genes expressed in the SON were compared with those expressed in a reference tissue consisting of total hypothalamus, and this "expression ratio" indicated which genes were preferentially expressed in the SON. Of the 26,000 unique genes on the array, 1385 were found to be expressed in the SON at levels more than two times greater than in the hypothalamus as a whole. Of these, 123 were expressed > or =3.4-fold higher in the SON versus hypothalamus. Most of these preferentially expressed genes were not previously known to be expressed in the MCNs. Quantitative and double-label in situ hybridization histochemistry was used selectively to confirm a number of these microarray observations and to evaluate the osmotic regulation and cell-specific expression of these genes, respectively.

A randomized, double-blind, placebo controlled trial of melatonin add-on therapy in epileptic children on valproate monotherapy: effect on glutathione peroxidase and glutathione reductase enzymes

AIMS

To compare the effect of add-on melatonin with placebo on the antioxidant enzymes (glutathione peroxidase and glutathione reductase) in epileptic children on valproate monotherapy.

METHODS

In a double-blind, randomized, placebo controlled trial, the effect of add-on melatonin administration on the antioxidant enzymes in epileptic children on valproate (VPA) monotherapy was assessed. A total of 31 patients met the entry criteria. 16 patients were randomly allocated to receive add-on melatonin, and 15 to receive add-on placebo. Blood samples (5 ml) were collected just before the morning dose of valproate for baseline values of glutathione peroxidase and glutathione reductase enzymes, and then after 14 days of add-on melatonin/placebo. Blood was then centrifuged at 3500 r.p.m., serum separated and stored in deep freezer at -20 degrees C until assay of glutathione reductase. Heparinized blood was collected and stored at -20 degrees C in eppendorfs in the deep freezer for assay of glutathione peroxidase. All activity assays were performed on the Ames (Technicon) RA 50 chemistry analyser.

RESULTS

Fifteen patients in the add-on melatonin group and 14 patients in the add-on placebo group were finally assessed. There was an increase in the activity of antioxidant enzymes, glutathione peroxidase (GSH-Px) and glutathione reductase (GSSG-Rd), in the add-on melatonin (MEL) group as compared with a reduction in the same in the add-on placebo group (P). After the addition of melatonin/placebo in the respective groups, there was a 7.5% decrease in GSH-Px in the valproate + placebo group, whereas a 11.9% increase in the valproate + melatonin group was observed, the difference between the groups being not statistically significant (P = 0.29). On administration of melatonin/placebo, the post-treatment concentrations of GSSG-Rd in the valproate + placebo group decreased from 92.0 U l(-1) to 67.0 U l(-1) and increased from 82.0 U l(-1) to 113.0 U l(-1), in the valproate + melatonin group, respectively, the difference between them being statistically significant (P = 0.05). The percentage change in the values of GSSG-Rd in the two groups was statistically significant (P = 0.005).

CONCLUSIONS

Melatonin exerts neuroprotection due to its antioxidant, antiexcitotoxic and free radical scavenging properties within the central nervous system. Melatonin, thus, as an adjunct, can be a putative neuroprotector in conditions involving oxidative stress like epilepsies.

Manipulation of antioxidant pathways in neonatal murine brain

To assess the role of brain antioxidant capacity in the pathogenesis of neonatal hypoxic-ischemic brain injury, we measured the activity of glutathione peroxidase (GPX) in both human-superoxide dismutase-1 (hSOD1) and human-GPX1 overexpressing transgenic (Tg) mice after neonatal hypoxia-ischemia (HI). We have previously shown that mice that overexpress the hSOD1 gene are more injured than their wild-type (WT) littermates after HI, and that H(2)O(2) accumulates in HI hSOD1-Tg hippocampus. We hypothesized that lower GPX activity is responsible for the accumulation of H(2)O(2). Therefore, increasing the activity of this enzyme through gene manipulation should be protective. We show that brains of hGPX1-Tg mice, in contrast to those of hSOD-Tg, have less injury after HI than WT littermates: hGPX1-Tg, median injury score = 8 (range, 0-24) versus WT, median injury score = 17 (range, 2-24), p < 0.01. GPX activity in hSOD1-Tg mice, 2 h and 24 h after HI, showed a delayed and bilateral decline in the cortex 24 h after HI (36.0 +/- 1.2 U/mg in naive hSOD1-Tg versus 29.1 +/- 1.7 U/mg in HI cortex and 29.2 +/- 2.0 for hypoxic cortex, p < 0.006). On the other hand, GPX activity in hGPX1-Tg after HI showed a significant increase by 24 h in the cortex ipsilateral to the injury (48.5 +/- 5.2 U/mg, compared with 37.2 +/- 1.5 U/mg in naive hGPX1-Tg cortex, p < 0.008). These findings support the hypothesis that the immature brain has limited GPX activity and is more susceptible to oxidative damage and may explain the paradoxical effect seen in ischemic neonatal brain when SOD1 is overexpressed.

An imbalance in antioxidant defense affects cellular function: the pathophysiological consequences of a reduction in antioxidant defense in the glutathione peroxidase-1 (Gpx1) knockout mouse

Aerobic cells are subjected to damaging reactive oxygen species (ROS) as a consequence of oxidative metabolism and/or exposure to environmental toxins. Antioxidants limit this damage, yet peroxidative events occur when oxidant stress increases. This arises due to increased radical formation or decreased antioxidative defenses. The two-step enzymatic antioxidant pathway limits damage to important biomolecules by neutralising superoxides to water. However, an imbalance in this pathway (increased first-step antioxidants relative to second-step antioxidants) has been proposed as etiological in numerous pathologies. This review presents evidence that a shift in favor of hydrogen peroxide and/or lipid peroxides has pathophysiological consequences. The involvement of antioxidant genes in the regulation of redox status, and ultimately cellular homeostasis, is explored in murine transgenic and knockout models. The investigations of Sod1 transgenic cell-lines and mice, as well as Gpx1 knockout mice (both models favor H(2)O(2) accumulation), are presented. Although in most instances accumulation of H(2)O(2) affects cellular function and leads to exacerbated pathology, this is not always the case. This review highlights those instances where, for example, increased Sod1 levels are beneficial, and indicates a role for superoxide radicals in pathogenesis. Studies of Gpx1 knockout mice (an important second-step antioxidant) lead us to conclude that Gpx1 functions as the primary protection against acute oxidative stress, particularly in neuropathological situations such as stroke and cold-induced head trauma, where high levels of ROS occur during reperfusion or in response to injury. In summary, these studies clearly highlight the importance of limiting ROS-induced cellular damage by maintaining a balanced enzymatic antioxidant pathway.

Immunocytochemical evidence that amyloid beta (1-42) impairs endogenous antioxidant systems in vivo

Amyloid beta, the major constituent of the senile plaques in the brains of patients with Alzheimer's disease, is cytotoxic to neurons and has a central role in the pathogenesis of the disease. We have previously demonstrated that potent antioxidants idebenone and alpha-tocopherol prevent learning and memory impairment in rats which received a continuous intracerebroventricular infusion of amyloid beta, suggesting a role for oxidative stress in amyloid beta-induced learning and memory impairment. To test the hypothesis, in the present study, we investigated alterations in the immunoreactivity of endogenous antioxidant systems such as mitochondrial Mn-superoxide dismutase, glutathione, glutathione peroxidase and glutathione-S-transferase following the continuous intracerebroventricular infusion of amyloid beta for 2 weeks. The infusion of amyloid beta (1-42) resulted in a significant reduction of the immunoreactivity of these antioxidant substances in such brain areas as the hippocampus, parietal cortex, piriform cortex, substantia nigra and thalamus although the same treatment with amyloid beta (40-1) had little effect. The alterations induced by amyloid beta (1-42) were not uniform, but rather specific for each immunoreactive substance in a brain region-dependent manner. These results demonstrate a cytological effect of oxidative stress induced by amyloid beta (1-42) infusion. Furthermore, our findings may indicate a heterogeneous susceptibility to the oxidative stress produced by amyloid beta.

Glutathione peroxidase-1 protects from CD95-induced apoptosis

Through the induction of apoptosis, CD95 plays a crucial role in the immune response and the elimination of cancer cells. Ligation of CD95 receptor activates a complex signaling network that appears to implicate the generation of reactive oxygen species (ROS). This study investigated the place of ROS production in CD95-mediated apoptosis and the role of the antioxidant enzyme glutathione peroxidase-1 (GPx1). Anti-CD95 antibodies triggered an early generation of ROS in human breast cancer T47D cells that was blocked by overexpression of GPx1 and inhibition of initiator caspase activation. Enforced expression of GPx1 also resulted in inhibition of CD95-induced effector caspase activation, DNA fragmentation, and apoptotic cell death. Resistance to CD95-mediated apoptosis was not due to an increased expression of anti-apoptotic molecules and could be reversed by glutathione-depleting agents. In addition, whereas the anti-apoptotic protein Bcl-xL prevented CD95-induced apoptosis in MCF-7 cells, it did not inhibit the early ROS production. Moreover, Bcl-xL but not GPx1 overexpression could suppress the staurosporine-induced late generation of ROS and subsequent cell death. Altogether, these findings suggest that GPx1 functions upstream of the mitochondrial events to inhibit the early ROS production and apoptosis induced by CD95 ligation. Finally, transgenic mice overexpressing GPx1 were partially protected from the lethal effect of anti-CD95, underlying the importance of peroxide formation (and GPx1) in CD95-triggered apoptosis.

Animal models of oxidative stress, aging, and therapeutic antioxidant interventions

Oxidative stress is a ubiquitous phenomena in all cell types, and it is primarily produced in mitochondria which are essential for multicellular life. Oxidative stress targets can be wide ranging and include nucleic acids and a variety of macromolecules. This review discusses the role of oxidative stress in the context of animal models, focusing in particular on animal models of aging, as well as the development of a new class of therapeutic small molecular weight antioxidants that have proven effective in extending the lifespan of a simple invertebrate nematode.

Impairment of synaptic transmission by transient hypoxia in hippocampal slices: improved recovery in glutathione peroxidase transgenic mice

There is increasing evidence that oxygen free radicals contribute to ischemic brain injury. It is unclear, however, to what extent specific antioxidant enzymes can prevent or reverse the impairment of synaptic function caused by transient hypoxia. In this study, we investigated in transgenic (Tg) mice whether a moderate increase in glutathione peroxidase-1 (GPx1) may improve the capacity of CA1 pyramidal cells to recover synaptic transmission after a short period of hypoxia in vitro. In control hippocampal slices, transient hypoxia (7-9 min) produced irreversible loss of excitatory postsynaptic potentials. Complete recovery of synaptic transmission was observed with homozygous Tg-MT-GPx-6 mice after reoxygenation, and, after repeated episodes of hypoxia, synaptic transmission was still viable in most Tg slices, in contrast to non-Tg slices. Moreover, hypoxic episodes abolished the capacity of hippocampal slices to generate long-term potentiation in area CA1 of control mice, whereas a significant extent of long-term potentiation expression was still preserved in Tg tissues. We also demonstrated that susceptibility to N-methyl-d-aspartate-mediated oxidative injury was reduced in Tg hippocampal slices. In conclusion, our results suggest that a moderate GPx increase can be sufficient to prevent irreversible functional damage produced by transient hypoxia in the hippocampus and to help maintain basic electrophysiological mechanisms involved in memory formation.

Neuroprotective effects of a new glutathione peroxidase mimetic on neurons of the chick embryo's retina

During their period of naturally occurring neuronal death, retinal ganglion cells are particularly vulnerable to axotomy. The resulting cell death requires protein synthesis and is redox-regulated, since antioxidants protect axotomized-ganglion cells when given in doses that maintain the redox status near an optimal set-point. Here we report the effects of BXT-51072, a new glutathione peroxidase mimetic, on ganglion cell death induced in various ways in the retinas of chick embryos. The intraocular injection of BXT-51072 protected axotomized neurons at doses in a narrow (tenfold) range. It also reduced the deleterious effects of intraocular tert-butyl hydroperoxide, an inducer of lipid peroxidation, and diminished the excitotoxic degeneration induced by N-methyl-D-aspartate. However, BXT-51072 did not noticeably reduce naturally occurring cell death. Globally, our results show that BXT-51072 has numerous protective effects in the retina. In accordance with published data, the present report indicates that glutathione peroxidase mimetics may have potential applications for neurologic or degenerative diseases.

Increased resistance of GPx-1 transgenic mice to tumor promoter-induced loss of glutathione peroxidase activity in skin

Reactive oxygen species formation is strongly suspected to play a role in multistep carcinogenesis, notably in tumor promotion. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces peroxide production, oxidative damage to DNA and inflammation in mouse skin. TPA is also known to cause a decrease in the activity of several antioxidant enzymes including glutathione peroxidases (GPx). The observation that several anti-oxidants can inhibit TPA-mediated tumor promotion suggests that a decline in GPx activity could contribute to tumor promotion. We report here the effects of TPA on GPx activity in the skin of transgenic GPx mice that contain human GPx-1 transgenes under the regulation of a metallothionein IIA promoter. As expected, no significant difference in basal level of skin GPx activity was detected in the 3 lines of tg-MT-GPx mice investigated compared with non-transgenic controls. A single topical application of TPA induced gradually, over 20 hr, a small but detectable increase in GPx mRNA and protein levels in skin of non-transgenic mice and a contrasting decrease in both selenium-dependent and selenium-independent GPx activity. The extent of GPx induction was more pronounced in transgenic mice, and in contrast with non-transgenic mice, no significant loss of GPx activity was observed in the TPA-treated skin of these mice. Transgenic mice may, therefore, offer a novel model suitable to assess the role of GPx-1 in skin carcinogenesis, without the potential disadvantage of abnormally high levels of GPx activity produced constitutively in other transgenic models.

Congenital disorders sharing oxidative stress and cancer proneness as phenotypic hallmarks: prospects for joint research in pharmacology

In spite of very distinct genotypic assets, a number of congenital conditions include oxidative stress as a phenotypic hallmark. These disorders include Fanconi's anaemia, ataxia telangiectasia, xeroderma pigmentosum and Bloom's syndrome, as well as two frequent congenital conditions: Down's syndrome and cystic fibrosis. Cancer proneness is a clinical feature shared by these disorders, while other manifestations include early ageing, neurological symptoms or congenital malformations. The onset of oxidative stress has been related to excess formation, or defective detoxification, of reactive oxygen species (ROS). This can arise from either the abnormal expression or inducibility of ROS-detoxifying enzymes, or by defective absorption of nutrient antioxidants. Resulting oxidative injury has been characterized through: (i) DNA, protein or lipid oxidative damage; (ii) excess ROS formation (in vitro and ex vivo); (iii) sensitivity to oxygen-related toxicity; (iv) improvement of cellular defects by either hypoxia or antioxidants; and (v) circumstantial evidence for in vivo oxidative stress (as e.g. clastogenic factors). Investigations conducted so far have been confined to individual disorders. Comparative studies of selected indicators for oxidative stress could provide further insights into the pathogenesis of each individual condition. Such a unified approach may have wide-ranging consequences for studies of ageing and cancer.

Chronic glutathione depletion alters expression of enteric inhibitory neurochemicals in the mouse

Antioxidants may delay or prevent neural diseases. Depletion of the non-enzymatic antioxidant, glutathione, in a mouse model was produced by inhibiting its rate-limiting enzyme, gamma-glutamylcysteine synthetase, for 7 weeks. Ileum and colon were obtained from treated and control (saline) mice. Glutathione levels and nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity were determined by spectrophotometric assays; vasoactive intestinal peptide (VIP) levels were measured by radioimmunoassay. Glutathione levels were higher in ileum than colon. Colonic glutathione was decreased in treated mice compared to controls; there were no differences in ileal glutathione levels. VIP was decreased in ileum compared to controls, while NADPH diaphorase activity was decreased in colon compared to controls. In this chronic mouse model, glutathione appeared to regulate expression of enteric inhibitory nerve cell products.

New directions for studying the role of free radicals in aging

Oxidative damage caused by free radicals in vivo is believed to play an important role in the etiology of aging and age-associated degenerative diseases. The most direct evidence supporting this theory is the recent finding that the transgenic Drosophila that overexpress the antioxidant enzymes catalase and superoxide dismutase exhibit an increase in life span. Although the increase in life span in Drosophila by these enzymes is certainly important, the next logical direction is to demonstrate whether increased antioxidant protection occurs similarly in mammals. Several transgenic mouse models that overexpress antioxidant enzymes are currently available. However, one major shortcoming in using these transgenic mice is the difficulty of producing antioxidant overexpression in more than a few tissues. Despite the potential shortcomings of using transgenic mice, these animals provide a unique system in which individual components of a complex system, such as the antioxidant defense system, can be modulated and examined independently. Transgenic mice are therefore potentially powerful tools to study the role of various components of the antioxidant system in the aging process. A parallel direction in the study of free radical roles in aging is to investigate the modulation of transcription factors by oxidative stress. Among these, the transcription factors, NF-κB and AP-1 are implicated in oxidative stress. The activities of these oxidative stress-response transcription factors are regulated by upstream signaling molecules, which involve a cascade of phosphorylation and dephosphorylation events leading to their activation. In this article, we review recent studies that use molecular approaches to investigate the biological role of oxidant stress. Each of these studies potentially provide new insights into the roles of free radicals and free radical damage in the aging process.

Murine models of brain aging and age-related neurodegenerative diseases

In the past, structural changes in the brain with aging have been studied using a variety of animal models, with rats and nonhuman primates being the most popular. With the rapid evolution of mouse genetics, murine models have gained increased attention in the neurobiology of aging. The genetic contribution of age-related traits as well as specific mechanistic hypotheses underlying brain aging and age-related neurodegenerative diseases can now be assessed by using genetically-selected and genetically-manipulated mice. Against this background of increased demand for aging research in mouse models, relatively few studies have examined structural alterations with aging in the normal mouse brain, and the data available are almost exclusively restricted to the C57BL/6 strain. Moreover, many older studies have used quantitative techniques which today can be questioned regarding their accuracy. Here we review the state of knowledge about structural changes with aging in outbred, inbred, genetically-selected, and genetically-engineered murine models. Moreover, we suggest several new opportunities that are emerging to study brain aging and age-related neurodegenerative diseases using genetically-defined mouse models. By reviewing the literature, it has become clear to us that in light of the rapid progress in genetically-engineered and selected mouse models for brain aging and age-related neurodegenerative diseases, there is a great and urgent need to study and define morphological changes in the aging brain of normal inbred mice and to analyze the structural changes in genetically-engineered mice more carefully and completely than accomplished to date. Such investigations will broaden knowledge in the neurobiology of aging, particularly regarding the genetics of aging, and possibly identify the most useful murine models.

Immunocytochemical localization of seleno-glutathione peroxidase in the adult mouse brain

Cytoplasmic seleno-glutathione peroxidase, by reducing hydrogen peroxide and fatty acid hydroperoxides, may be a major protective enzyme against oxidative damage in the brain. Oxidative damage is strongly suspected to contribute to normal aging and neurodegenerative process of Alzheimer's and Parkinson's diseases. We report here an immunocytochemical analysis of the localization of glutathione peroxidase in the adult mouse brain, carried out with an affinity-purified polyclonal antibody. Most of the brain areas analysed showed weak to strong glutathione peroxidase immunoreactivity, expressed in both neurons and glial cells. The strongest immunoreactivity was found in the reticular thalamic and red nuclei. Highly immunoreactive neurons were observed in the cerebral cortex (layer II), the CA1, dentate gyrus and pontine nucleus. Other regions, such as the caudate-putamen, septum nuclei, diagonal band of Broca, hippocampus, thalamus and hypothalamus, showed moderate staining. This study provides original information about the wide distribution of glutathione peroxidase in the mouse brain. Double-staining experiments indicated that specific subsets of cholinergic neurons in septal and diagonal band nuclei were negative for this antigen. Similarly, many dopaminergic neurons of the substantia nigra pars compacta expressed low levels of glutathione peroxidase antigen, in contrast to the ventral tegmental area, wherein most catecholaminergic cells were strongly positive. A lack of glutathione peroxidase in subsets of dopaminergic or cholinergic neurons may thus confer a relative sensitivity of these cells to oxidative injury of various origins, including catecholamine oxidation, neurotoxins and excitotoxicity.

Transgenic mice and knockout mutants in the study of oxidative stress in brain injury

A rapid increase in the need to explore the molecular basis of cellular function and injury in the central nervous system has led neuroscientists to employ transgenic mouse technology. The successful making of transgenic mice (Tg) overexpressing human CuZn-superoxide dismutase (SOD-1) activity has made it possible to investigate the role of oxygen free radicals in ischemic and traumatic brain injury in a molecular fashion. It has been demonstrated that the 3-fold increase in SOD-1 transgene activity in SOD-1 Tg mice offers protection against cerebral ischemia and reperfusion in two different models of focal cerebral ischemia, as compared to nontransgenic wild-type littermates. Studies involving traumatic brain injury have also demonstrated that acute injuries, including brain edema and blood-brain barrier permeability, are significantly reduced in SOD-1 Tg mice. Furthermore, chronic neurological deficits, such as beam walking, beam balance, and body weight, are significantly improved in these transgenic animals following traumatic brain injury. In addition to the SOD-1 Tg mice being a useful tool for the study of CNS injury, targeted disruption of the mouse gene for mitochondrial manganese SOD (SOD-2) has been successful. These SOD-2 knockout mutant mice, in addition to the recently developed knockout mutants of neuronal nitric oxide synthase (NOS), are believed to offer a unique opportunity to elucidate the oxidative mechanisms in brain injury following stroke and trauma.

Melatonin reduces H2O2-induced lipid peroxidation in homogenates of different rat brain regions

The ability of melatonin to modify H2O2-induced lipid peroxidation in brain homogenates was determined. The concentrations of brain malonaldehyde (MDA) and 4-hydroxyalkenals (4-HDA) were assayed as an index of induced membrane oxidative damage. Homogenates from five different regions of the brain (cerebral cortex, cerebellum, hippocampus, hypothalamus, and corpus striatum) derived from two different strains of rats, Sprague-Dawley and Wistar, were incubated with either H2O2 (5 mM) alone or H2O2 together with melatonin at increasing concentrations ranging from 0.1 to 4 mM. The basal level of lipid peroxidation was strain-dependent and about 100% higher in homogenates from the brain of Wistar rats than those measured in Sprague-Dawley rats. MDA + 4-HDA levels increased after H2O2 treatment in homogenates obtained from each region of the brain in both rat strains but the sensitivity of the homogenates from Sprague-Dawley rats was greater than that for the homogenates from Wistar rats (increases after H2O2 from 45 to 165% compared 20 to 40% for Sprague-Dawley and Wistar rats, respectively). Melatonin co-treatment reduced H2O2-induced lipid peroxidation in brain homogenates in a concentration-dependent manner; the degree of protection against lipid peroxidation was similar in all brain regions.

Melatonin administration prevents lipopolysaccharide-induced oxidative damage in phenobarbital-treated animals

The protective effect of melatonin on lipopolysaccharide (LPS)-induced oxidative damage in phenobarbital-treated rats was measured using the following parameters: changes in total glutathione (tGSH) concentration, levels of oxidized glutathione (GSSG), the activity of the antioxidant enzyme glutathione peroxidase (GSH-PX) in both brain and liver, and the content of cytochrome P450 reductase in liver. Melatonin was injected intraperitoneally (ip, 4mg/kg BW) every hour for 4 h after LPS administration; control animals received 4 injections of diluent. LPS was given (ip, 4 mg/kg) 6 h before the animals were killed. Prior to the LPS injection, animals were pretreated with phenobarbital (PB), a stimulator of cytochrome P450 reductase, at a dose 80 mg/kg BW ip for 3 consecutive days. One group of animals received LPS together with Nw-nitro-L-arginine methyl ester (L-NAME), a blocker of nitric oxide synthase (NOS) (for 4 days given in drinking water at a concentration of 50 mM). In liver, PB, in all groups, increased significantly both the concentration of tGSH and the activity of GSH-PX. When the animals were injected with LPS the levels of tGSH and GSSG were significantly higher compared with other groups while melatonin and L-NAME significantly enhanced tGSH when compared with that in the LPS-treated rats. Melatonin alone reduced GSSG levels and enhanced the activity of GSH-PX in LPS-treated animals. Additionally, LPS diminished the content of cytochrome P450 reductase with this effect being largely prevented by L-NAME administration. Melatonin did not change the content of P450 either in PB- or LPS-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Melatonin stimulates brain glutathione peroxidase activity

Exogenously administered melatonin causes a 2-fold rise in glutathione peroxidase activity within 30 min in the brain of the rat. Furthermore, brain glutathione peroxidase activity is higher at night than during the day and is correlated with high night-time tissue melatonin levels. Glutathione peroxidase is thought to be the principal enzyme eliminating peroxides in the brain. This antioxidative enzyme reduces the formation of hydroxyl radicals formed via iron-catalyzed Fenton-type reactions from hydrogen peroxide by reducing this oxidant to water. Since the hydroxyl radical is the most noxious oxygen radical known, induction of brain glutathione peroxidase might be an important mechanism by which melatonin exerts its potent neuroprotective effects.