Glutathione Is Required for the Early Alert Response and Subsequent Acclimation in Cadmium-Exposed Arabidopsis thaliana Plants

Pollution by cadmium (Cd) is a worldwide problem, posing risks to human health and impacting crop yield and quality. Cadmium-induced phytotoxicity arises from an imbalance between antioxidants and pro-oxidants in favour of the latter. The Cd-induced depletion of the major antioxidant glutathione (GSH) strongly contributes to this imbalance. Rather than being merely an adverse effect of Cd exposure, the rapid depletion of root GSH levels was proposed to serve as an alert response. This alarm phase is crucial for an optimal stress response, which defines acclimation later on. To obtain a better understanding on the importance of GSH in the course of these responses and how these are defined by the rapid GSH depletion, analyses were performed in the GSH-deficient cadmium-sensitive 2-1 (cad2-1) mutant. Cadmium-induced root and leaf responses related to oxidative challenge, hydrogen peroxide (H2O2), GSH, ethylene, and aminocyclopropane-1-carboxylic acid (ACC) were compared between wild-type (WT) and mutant Arabidopsis thaliana plants. Although the cad2-1 mutant has significantly lower GSH levels, root GSH depletion still occurred, suggesting that the chelating capacity of GSH is prioritised over its antioxidative function. We demonstrated that responses related to GSH metabolism and ACC production were accelerated in mutant roots and that stress persisted due to suboptimal acclimation. In general, the redox imbalance in cad2-1 mutant plants and the lack of proper transient ethylene signalling contributed to this suboptimal acclimation, resulting in a more pronounced Cd effect.

Physiological Roles of Red Carrot Methanolic Extract and Vitamin E to Abrogate Cadmium-Induced Oxidative Challenge and Apoptosis in Rat Testes: Involvement of the Bax/Bcl-2 Ratio

The precise analysis of the contents of the red carrot is still ambiguous and its role in the maintenance of male fertility needs to be further reconnoitered. Hence, this study targets the physiological impacts of either red carrot methanolic extract (RCME) or vitamin E (Vit. E), co-administrated with cadmium chloride (CdCl2) on rat testes, specifically those concerned with apoptosis and oxidative challenge. Four groups of adult male rats (n = 12) are used; control, CdCl2, CdCl2+Vit. E and CdCl2 + RCME. LC-MS analysis of RCME reveals the presence of 20 different phytochemical compounds. Our data clarify the deleterious effects of CdCl2 on testicular weights, semen quality, serum hormonal profile, oxidative markers and Bax/ Bcl-2 ratio. Histopathological changes in testicular, prostatic and semen vesicle glandular tissues are also observed. Interestingly, our data clearly demonstrate that co-administration of either RCME or Vit. E with CdCl2 significantly succeeded in the modulation (p < 0.05) of all of these negative effects. The most striking is that they were potent enough to modulate the Bax/Bcl-2 ratio as well as having the ability to correct the impaired semen picture, oxidant status and hormonal profile. Thus, RCME and Vit. E could be used as effective prophylactic treatments to protect the male reproductive physiology against CdCl2 insult.

475 The Effect of Increasing Total Sulfur Amino Acids to Lysine Level and Methionine Source on Growth Performance and Oxidative Parameters of Nursery Pigs Fed Oxidized Soybean Oil

Total sulfur amino acids (TSAA): Lys level and Met source effects on growth performance and oxidative status were evaluated in nursery pigs fed oxidized soybean-oil. A total of 240 weaned pigs (BW=5.84± 0.96kg) were blocked by BW and randomly allotted to 60 pens. Treatments included a positive control containing fresh soybean-oil (PC) and 4 peroxidized soybean-oil treatments in a 2×2 factorial of 2 Met sources (DL-Met vs. 2-hydroxy-4-(methylthio)butanoate [HMTBa]) and 2 standardized ileal digestible TSAA: Lys levels (L1=0.58 vs. L2=0.65). Diets were fed for 42d. One pig per pen was euthanized at d42 for tissue analyses. Data were analyzed using PROC MIXED procedure of SAS. TSAA: Lys ratio did not affect ADG and ADFI. Met source did not affect ADG. HMTBa tended to increase ADFI compared to DL-Met (P = 0.08). There was a tendency for interaction between TSAA: Lys level and Met source for G: F (P = 0.07); pigs fed HMTBa-L1 tended to have decreased G: F compared to HMTBa-L2 and DL-Met-L1-L2. HMTBa had increased liver total antioxidant status (TAS) compared to DL-Met (P = 0.02). There was no TSAA:Lys level effect on TAS. Comparing PC to peroxidized treatments: pigs fed HMTBa-L1 and DL-Met-L1 tended to have decreased ADG (P ≤ 0.10) and DL-Met-L2 had decreased ADG (P &lt; 0.05) than PC. HMTBa-L2 was similar to PC. Pigs fed DL-Met-L1 had decreased (P &lt; 0.05) and DL-Met-L2 tended to have decreased ADFI (P ≤ 0.10) than PC. HMTBa-L1-L2 were similar to PC. All peroxidized treatments had similar G:F compared to PC. Pigs fed DL-Met-L2 tended to have decreased TAS compared to PC (P ≤ 0.10), but PC was similar to pigs fed DL-Met-L1 and HMTBa-L1-L2. In conclusion, under an oxidative challenge, HMTBa, at a TSAA: Lys ratio of 0.65, maintained nursery pigs’ growth performance and oxidative status.

Thioredoxin Reductase Inhibition for Cancer Therapy

The cytosolic selenoprotein thioredoxin reductase 1 (TrxR1, TXNRD1), and to some extent mitochondrial TrxR2 (TXNRD2), can be inhibited by a wide range of electrophilic compounds. Many such compounds also yield cytotoxicity toward cancer cells in culture or in mouse models, and most compounds are likely to irreversibly modify the easily accessible selenocysteine residue in TrxR1, thereby inhibiting its normal activity to reduce cytosolic thioredoxin (Trx1, TXN) and other substrates of the enzyme. This leads to an oxidative challenge. In some cases, the inhibited forms of TrxR1 are not catalytically inert and are instead converted to prooxidant NADPH oxidases, named SecTRAPs, thus further aggravating the oxidative stress, particularly in cells expressing higher levels of the enzyme. In this review, the possible molecular and cellular consequences of these effects are discussed in relation to cancer therapy, with a focus on outstanding questions that should be addressed if targeted TrxR1 inhibition is to be further developed for therapeutic use. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Antenatal Selenium Deficiency Decreases Neonatal Pulmonary Selenium-Containing Antioxidant Enzymes

Objectives Bronchopulmonary dysplasia (BPD) is the most common complication of prematurity. Selenium (Se) deficiency increases the risk for oxygen requirement at 28 days and BPD and thus may be a modifiable nutritional intervention. Se is an essential trace mineral that is incorporated into Se-containing antioxidant enzymes (AOE). An infant's Se status at birth is regulated by the mother's Se supply during pregnancy, however, it is unknown if any neonatal Se-containing AOE in the lung are decreased by antenatal Se deficiency. We hypothesize that antenatal Se deficiency will decrease neonatal pulmonary expression of Se-containing AOE. Methods C57Bl/6 mice were allocated to sufficient (SeS, 0.4 ppm Se) or deficient (SeD, &lt; 0.01 ppm Se) diets before breeding. Breeding pairs were allowed to serially breed, and pups from the 1st-4th pregnancies were evaluated. Pups were sacrificed at PN0. Glutathione peroxidase (GPx) activity was measured in the lung by enzyme activity assay. Pulmonary GPx1, GPx3, thioredoxin reductase 1 (Trxrd1) and selenoprotein N (SelenoN) protein content were measured by Western blot. F and M pups were analyzed as separate groups. Results Weights were similar at postnatal day 0 (PN0) and PN4 for SeS and SeD pups, but by PN7 through adulthood, both male and female SeD mice weighed less then SeS mice. At PN0, pulmonary GPx activity was decreased in all SeD pups, with similar decreases in the protein content of both GPx1 and GPx3 (n = 6–10). We observed a progressive impact of SeD on the pups based on the dam's pregnancy. GPx activity and protein contents were more significantly decreased in pups born after a dam's 3rd or 4th pregnancy than the 1st or 2nd (n = 4–6). Trxrd1 and SelenoN protein content were not decreased in pups born after a dam's 1st or 2nd pregnancy (n = 4–6). However, both were decreased in the lungs of pups born to a dam's 3rd or 4th gestation (n = 6). Conclusions Neonatal pups exposed to antenatal SeD demonstrate decreased pulmonary GPx protein content and activity level without sex differences. Pups born to a SeD dam's third or fourth gestation exhibited a further decline in pulmonary Trxrd1 and SelenoN content. We speculate that SeD neonates may be vulnerable to pulmonary oxidative stresses secondary to low antioxidant enzymatic defense. Impaired ability to respond to oxidative challenge in the lung may predispose SeD infants to BPD. Funding Sources NIH/NHLBI.

The Pharmacology and Therapeutic Utility of Sodium Hydroselenide

Metabolically active gasotransmitters (nitric oxide, carbon monoxide and hydrogen sulfide) are important signalling molecules that show therapeutic utility in oxidative pathologies. The reduced form of selenium, hydrogen selenide (HSe−/H2Se), shares some characteristics with these molecules. The simple selenide salt, sodium hydroselenide (NaHSe) showed significant metabolic activity, dose-dependently decreasing ex vivo O2 consumption (rat soleus muscle, liver) and transiently inhibiting mitochondrial cytochrome C oxidase (liver, heart). Pharmacological manipulation of selenoprotein expression in HepG2 human hepatocytes revealed that the oxidation status of selenium impacts on protein expression; reduced selenide (NaHSe) increased, whereas (oxidized) sodium selenite decreased the abundance of two ubiquitous selenoproteins. An inhibitor of endogenous sulfide production (DL-propargylglycine; PAG) also reduced selenoprotein expression; this was reversed by exogenous NaHSe, but not sodium hydrosulfide (NaHS). NaHSe also conferred cytoprotection against an oxidative challenge (H2O2), and this was associated with an increase in mitochondrial membrane potential. Anesthetized Wistar rats receiving intravenous NaHSe exhibited significant bradycardia, metabolic acidosis and hyperlactataemia. In summary, NaHSe modulates metabolism by inhibition of cytochrome C oxidase. Modification of selenoprotein expression revealed the importance of oxidation status of selenium therapies, with implications for current clinical practice. The utility of NaHSe as a research tool and putative therapeutic is discussed.

Induction of the reactive chlorine-responsive transcription factor RclR in Escherichia coli following ingestion by neutrophils

Neutrophils generate hypochlorous acid (HOCl) and related reactive chlorine species as part of their defence against invading microorganisms. In isolation, bacteria respond to reactive chlorine species by upregulating responses that provide defence against oxidative challenge. Key questions are whether these responses are induced when bacteria are phagocytosed by neutrophils, and whether this provides them with a survival advantage. We investigated RclR, a transcriptional activator of the rclABC operon in Escherichia coli that has been shown to be specifically activated by reactive chlorine species. We first measured induction by individual reactive chlorine species, and showed that HOCl itself activates the response, as do chloramines (products of HOCl reacting with amines) provided they are cell permeable. Strong RclR activation was seen in E. coli following phagocytosis by neutrophils, beginning within 5 min and persisting for 40 min. RclR activation was suppressed by inhibitors of NOX2 and myeloperoxidase, providing strong evidence that it was due to HOCl production in the phagosome. RclR activation demonstrates that HOCl, or a derived chloramine, enters phagocytosed bacteria in sufficient amount to induce this response. Although RclR was induced in wild-type bacteria following phagocytosis, we detected no greater sensitivity to neutrophil killing of mutants lacking genes in the rclABC operon.

Chemical Compositional Changes in Over-Oxidized Fish Oils

A recent study has reported that the administration during gestation of a highly rancid hoki liver oil, obtained by oxidation through sustained exposure to oxygen gas and incident light for 30 days, causes newborn mortality in rats. This effect was attributed to lipid hydroperoxides formed in the omega-3 long-chain polyunsaturated fatty acid-rich oil, while other chemical changes in the damaged oil were overlooked. In the present study, the oxidation condition employed to damage the hoki liver oil was replicated, and the extreme rancidity was confirmed. A detailed analysis of temporal chemical changes resulting from the sustained oxidative challenge involved measures of eicosapentaenoic acid/docosahexaenoic acid (EPA/DHA) omega-3 oil oxidative quality (peroxide value, para-anisidine value, total oxidation number, acid value, oligomers, antioxidant content, and induction time) as well as changes in fatty acid content, volatiles, isoprostanoids, and oxysterols. The chemical description was extended to refined anchovy oil, which is a more representative ingredient oil used in omega-3 finished products. The present study also analyzed the effects of a different oxidation method involving thermal exposure in the dark in contact with air, which is an oxidation condition that is more relevant to retail products. The two oils had different susceptibility to the oxidation conditions, resulting in distinct chemical oxidation signatures that were determined primarily by antioxidant protection as well as specific methodological aspects of the applied oxidative conditions. Unique isoprostanoids and oxysterols were formed in the over-oxidized fish oils, which are discussed in light of their potential biological activities.