Concept: Glutathione peroxidase
Evidence that selenium affects the risk of type-2 diabetes is conflicting, with observational studies and a few randomized trials showing both lower and higher risk linked to the level of selenium intake and status. We investigated the effect of selenium supplementation on the risk of type-2 diabetes in a population of relatively low selenium status as part of the UK PRECISE (PREvention of Cancer by Intervention with SElenium) pilot study. Plasma adiponectin concentration, a recognised independent predictor of type-2 diabetes risk and known to be correlated with circulating selenoprotein P, was the biomarker chosen.
Sarcopenia is the progressive loss of skeletal muscle that contributes to the decline in physical function during aging. A higher level of oxidative stress has been implicated in aging sarcopenia. The current study aims to determine if the higher level of oxidative stress is a result of increased superoxide (O2 ) production by the NADPH oxidase (NOX) enzyme or decrease in endogenous antioxidant enzyme protection.
In contrast to the current belief that cholesterol reduction with statins decreases atherosclerosis, we present a perspective that statins may be causative in coronary artery calcification and can function as mitochondrial toxins that impair muscle function in the heart and blood vessels through the depletion of coenzyme Q10 and ‘heme A’, and thereby ATP generation. Statins inhibit the synthesis of vitamin K2, the cofactor for matrix Gla-protein activation, which in turn protects arteries from calcification. Statins inhibit the biosynthesis of selenium containing proteins, one of which is glutathione peroxidase serving to suppress peroxidative stress. An impairment of selenoprotein biosynthesis may be a factor in congestive heart failure, reminiscent of the dilated cardiomyopathies seen with selenium deficiency. Thus, the epidemic of heart failure and atherosclerosis that plagues the modern world may paradoxically be aggravated by the pervasive use of statin drugs. We propose that current statin treatment guidelines be critically reevaluated.
Isolated hepatocytes from young (4-6mo) and old (24-26mo) F344 rats were exposed to increasing concentrations of menadione, a vitamin K derivative and redox cycling agent, to determine whether the age-related decline in Nrf2-mediated detoxification defenses resulted in heightened susceptibility to xenobiotic insult. An LC50 for each age group was established, which showed that aging resulted in a nearly 2-fold increase in susceptibility to menadione (LC50 for young: 405μM; LC50 for old: 275μM). Examination of the known Nrf2-regulated pathways associated with menadione detoxification revealed, surprisingly, that NAD(P)H: quinone oxido-reductase 1 (NQO1) protein levels and activity were induced 9-fold and 4-fold with age, respectively (p=0.0019 and p=0.018; N=3), but glutathione peroxidase 4 (GPX4) declined by 70% (p=0.0043; N=3). These results indicate toxicity may stem from vulnerability to lipid peroxidation instead of inadequate reduction of menadione semi-quinone. Lipid peroxidation was 2-fold higher, and GSH declined by a 3-fold greater margin in old versus young rat cells given 300µM menadione (p<0.05 and p≤0.01 respectively; N=3). We therefore provided 400µMN-acetyl-cysteine (NAC) to hepatocytes from old rats before menadione exposure to alleviate limits in cysteine substrate availability for GSH synthesis during challenge. NAC pretreatment resulted in a >2-fold reduction in cell death, suggesting that the age-related increase in menadione susceptibility likely stems from attenuated GSH-dependent defenses. This data identifies cellular targets for intervention in order to limit age-related toxicological insults to menadione and potentially other redox cycling compounds.
Abstract Cadmium (Cd(2+)) produce toxic effects on various tissues as kidney and liver, so several studies have focused to explore the effect produced by different doses and exposure times of this metal. However, little has been reported about the effect that Cd(2+) shows in the brain in vivo. Hence, this study aimed at comparing the effect of chronic Cd(2+) exposure on antioxidant defense systems of kidney and brain in rats. Six groups of male rats were employed; five were administered for 45 days with different doses of cadmium chloride (0.187, 0.375, 0.562, 0.937 and 1.125 mg/kg; i.p.) and the other was used as control. Free radicals (FR) were directly quantified by electron paramagnetic resonance (EPR) spectroscopy; malondialdehyde (MDA), reduced glutathione (GSH), and the activity-expression of superoxide dismutase (SOD2) and catalase (CAT) were also measured. The EPR results showed that there was no increase in FR content in kidney or brain. MDA and GSH levels increased in kidney but not in the brain. The SOD2 activity was not altered, but its expression decreased in both tissues. On the other hand, CAT activity and expression tended to increase at low doses and decrease at high doses in both tissues. Therefore, these results suggest that both in kidney and brain exist compensatory mechanisms able to avoid the toxic effects exerted by Cd(2) at these doses and exposure time.
We undertook a study of Porphyra acanthophora var. brasiliensis to determine its responses under ambient conditions, photosynthetically active radiation (PAR), and PAR+UVBR (ultraviolet radiation-B) treatment, focusing on changes in ultrastructure, and cytochemistry. Accordingly, control ambient samples were collected in the field, and two different treatments were performed in the laboratory. Plants were exposed to PAR at 60 μmol photons m-2 s-1 and PAR + UVBR at 0.35 W m-2 for 3 h per day during 21 days of in vitro cultivation. Confocal laser scanning microscopy analysis of the vegetative cells showed single stellate chloroplast in ambient and PAR samples, but in PAR+UVBR-exposed plants, the chloroplast showed alterations in the number and form of arms. Under PAR+UVBR treatment, the thylakoids of the chloroplasts were disrupted, and an increase in the number of plastoglobuli was observed, in addition to mitochondria, which appeared with irregular, disrupted morphology compared to ambient and PAR samples. After UVBR exposure, the formation of carpospores was also observed. Plants under ambient conditions, as well as those treated with PAR and PAR+UVBR, all showed different concentrations of enzymatic response, including glutathione peroxidase and reductase activity. In summary, the present study demonstrates that P. acanthophora var. brasiliensis shows the activation of distinct mechanisms against natural radiation, PAR and PAR+UVBR.
Sexual dysfunction is one of the diabetic complications in males. The present study aimed to evaluate the antidiabetic effect of α-mangostin and its protective role in sexual dysfunction of streptozotocin (STZ) induced diabetic male rats. Male Wistar rats were divided as control, diabetic control, diabetic rats administered with 25, 50 mg/kg body weight (bw) of α-mangostin and 1 mg/kg bw of gliclazide. The α-mangostin was administered once daily for a period of 55 days. On day 55 animals were sacrificed, serum was analyzed for testosterone levels, and sperm was collected from the epididymis and sperm parameters analyzed. Testis and epididymis were examined for antioxidant enzymes like superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) levels, lipidperoxidation products, and histopathological alterations. In diabetic rats, sperm count, motile sperms, viable sperms, and hypo-osmotic swelling tail coiled sperms were significantly decreased while sperm malformations increased when compared with normal rats. Serum testosterone levels and testicular 3β and 17 β-hydroxysteroid dehydrogenase levels were significantly decreased in diabetic rats. Significant reduction in testicular and epididymal SOD, catalase, GPx levels, and elevation in lipid peroxidation products were observed. However, α-mangostin treatment showed noteworthy recovery in all parameters towards the control levels. It may therefore be suggested that α-mangostin showed a protective effect against sexual dysfunction in STZ induced diabetic rats.
This study investigated the changes in oxidative stress biomarkers and antioxidant status indices caused by a 3-week high-intensity interval training (HIT) regimen. Eight physically active males performed three HIT sessions/week over 3 weeks. Each session included four to six 30-s bouts of high-intensity cycling separated by 4 minutes of recovery. Before training, acute exercise elevated protein carbonyls (PC), thiobarbituric acid reactive substances (TBARS), glutathione peroxidase (GPX) activity, total antioxidant capacity (TAC) and creatine kinase (CK), which peaked 24 h post-exercise (252±30%, 135±17%, 10±2%, 85±14% and 36±13%, above baseline, respectively; p<0.01), while catalase activity (CAT) peaked 30 min post-exercise (56±18% above baseline; p<0.01). Training attenuated the exercise-induced increase in oxidative stress markers (PC by 13.3±3.7%; TBARS by 7.2±2.7%, p<0.01) and CK activity, despite the fact that total work done was 10.9±3.6% greater in the post- compared with the pre-training exercise test. Training also induced a marked elevation of antioxidant status indices (TAC by 38.4±7.2%; CAT by 26.2±10.1%; GPX by 3.0±0.6%, p<0.01). Short-term HIT attenuates oxidative stress and up-regulates antioxidant activity after only nine training sessions totaling 22 min of high intensity exercise, further supporting its positive effect not only on physical conditioning but also on health promotion.
We examined the impact of strong co-presence and function of glutathione peroxidase-1 (GPX-1) and glial cell line-derived neurotrophic factor (GDNF) on protecting rat dopaminergic pheochromocytoma cell line PC12 against 6-OHDA and H2O2 toxicities. Primarily, GPX-1 overexpression by PC12 cells infected with pLV-GPX1 lentivirus vectors significantly increased cell survival against 6-OHDA toxicity (P<0.01). Addition of conditioned medium collected from growing wild-type astrocytes (Control astro-CM) increased survival rate of pLV-GPX1 infectants by 10% compared to their un-treated counterparts (P<0.05) and 20% compared to their treated empty vector control (P<0.01). Treatment of pLV-GPX1 cells with astro-CM of GDNF-oversecreting astrocytes (Test astro-CM) significantly induced GPX-1 expression, peroxidase enzymatic activity and intracellular glutathione levels. These changes paralleled with protection of 90% of GDNF+/GPX1+ PC12 cells against toxicity, a rate that was 37% up from their un-infected un-treated (GDNF-/GPX1-) controls (P<0.001), and 12% up from pLV-GPX1 cells that received only Control astro-CM (GPX-1+/GDNF-) (P<0.01). GPX-1 overexpression per se suppressed intracellular H2O2 elevation upon 6-OHDA exposure and addition of GDNF medium significantly accelerated this suppression (P<0.01). Substitution of 6-OHDA with H2O2 induced similar intracellular changes and comparable protection levels. In all cell groups, increased cell survival against either compound was further confirmed by increased live cell counts measured by double staining. Following depletion of intracellular glutathione (GSH), only 46% of pLV-GPX1 cells survived 6-OHDA toxicity, whereas over 70% of them were saved upon GDNF treatment (P<0.001). Moreover, capase-3 activation was induced in pLV-GPX1 cells and maximized by addition of GDNF. Comparison analyses well established correlations between GPX-1-GDNF co-presence and both accelerated cell protection and diminished levels of activated caspase-3. Our data collectively indicate that GDNF is capable of inducing anti-oxidant activities of intracellular GPX-1 and that growth promoting potential of GDNF and anti-oxidant properties of GPX-1 can, in concert, maximize survival of dopaminergic neurons.
Hepatotoxicity of drug candidates is one of the major concerns in drug screening in early drug discovery. Detection of hepatic oxidative stress can be an early indicator of hepatotoxicity and benefits drug selection. The glutathione (GSH) and glutathione disulfide (GSSG) pair, as one of the major intracellular redox regulating couples, plays an important role in protecting cells from oxidative stress that is caused by imbalance between prooxidants and antioxidants. The quantitative determination of the GSSG/GSH ratios and the concentrations of GSH and GSSG have been used to indicate oxidative stress in cells and tissues. In this study, we tested the possibility of using the biliary GSSG/GSH ratios as a biomarker to reflect hepatic oxidative stress and drug toxicity. Four compounds that are known to alter GSH and GSSG levels were tested in this study. Diquat (diquat dibromide monohydrate) and acetaminophen were administered to rats. Paraquat and tert-butyl hydroperoxide were administered to mice to induce changes of biliary GSH and GSSG. The biliary GSH and GSSG were quantified using calibration curves prepared with artificial bile to account for any bile matrix effect in the LC-MS analysis and to avoid the interference of endogenous GSH and GSSG. With four examples (in rats and mice) of drug-induced changes in the kinetics of the biliary GSSG/GSH ratios, this study showed the potential for developing an exposure response index based on biliary GSSG/GSH ratios for predicting hepatic oxidative stress.