Post-translational activation of non-selenium glutathione peroxidase of Chlamydomonas reinhardtii by specific incorporation of selenium

Short-term feed restriction induces inflammation and an antioxidant response via cystathionine-β-synthase and glutathione peroxidases in ruminal epithelium from Angus steers

Decreased intake is induced by stressors such as parturition, transportation, dietary transitions, and disease. An important function of one-carbon metabolism (OCM) is to produce the antioxidant glutathione to help reduce oxidative stress. Although various components of OCM are expressed in the bovine rumen and small intestine, the relationship between reduced feed intake, OCM, and antioxidant mechanisms in gut tissues is unknown. This study aimed to assess alterations in immune and antioxidant pathways in ruminal epithelium due to acute feed restriction (FR). Seven group-housed ruminally cannulated Angus steers (663 ± 73 kg body weight, 2 yr old) had ad libitum access to a finishing diet (dry-rolled corn, corn silage, modified wet distiller's grains) during 15 d of a pre-FR period (PRE). Subsequently, steers were moved to a metabolism barn with tie stalls and individually fed at 25% of estimated intake in PRE for 3 d (FR period, FRP). This was followed by 15 d of recovery (POST) during which steers had ad libitum access to the same diet as in PRE and FRP. Plasma and ruminal tissue biopsies were collected during each period. Plasma free fatty acid and IL1-β concentrations were higher (P ≤ 0.03) in FRP than PRE or POST. The mRNA abundance of the proinflammatory genes tumor necrosis factor, toll-like receptor 2 (TLR2), and TLR4 in the ruminal epithelium peaked (P < 0.05) at FRP and remained higher at POST. These responses agreed with the higher (P < 0.05) abundance of phosphorylated (p)-MAPK (an inflammation activator) and p-EEF2 (translational repressor) in FRP than PRE and POST. Although ruminal glutathione peroxidase (GPX) enzyme activity did not increase at FRP compared with PRE and POST, protein abundance of GPX1 and GPX3 along with the antioxidant response regulator NFE2L2 were highest (P < 0.01), and the activity of cystathionine-beta synthase tended (P = 0.06) to be highest during FR. Although FR had minimal negative effects on tissue integrity-related genes (only filamin A was downregulated), it led to a systemic inflammatory response and triggered inflammation and antioxidant mechanisms within the ruminal epithelium. Thus, deploying anti-inflammatory and antioxidant mechanisms via molecules that feed into OCM (e.g., dietary methyl donors such as methionine, choline, betaine, and folate) could potentially counteract the stressors associated with FR.

Selenium Interactions with Algae: Chemical Processes at Biological Uptake Sites, Bioaccumulation, and Intracellular Metabolism

Selenium (Se) uptake by primary producers is the most variable and important step in determining Se concentrations at higher trophic levels in aquatic food webs. We gathered data available about the Se bioaccumulation at the base of aquatic food webs and analyzed its relationship with Se concentrations in water. This important dataset was separated into lotic and lentic systems to provide a reliable model to estimate Se in primary producers from aqueous exposure. We observed that lentic systems had higher organic selenium and selenite concentrations than in lotic systems and selenate concentrations were higher in lotic environments. Selenium uptake by algae is mostly driven by Se concentrations, speciation and competition with other anions, and is as well influenced by pH. Based on Se species uptake by algae in the laboratory, we proposed an accurate mechanistic model of competition between sulfate and inorganic Se species at algal uptake sites. Intracellular Se transformations and incorporation into selenoproteins as well as the mechanisms through which Se can induce toxicity in algae has also been reviewed. We provided a new tool for risk assessment strategies to better predict accumulation in primary consumers and consequently to higher trophic levels, and we identified some research needs that could fill knowledge gaps.

Selenium and selenoproteins: it's role in regulation of inflammation

Abstract

Selenium is an essential immunonutrient which holds the human’s metabolic activity with its chemical bonds. The organic forms of selenium naturally present in human body are selenocysteine and selenoproteins. These forms have a unique way of synthesis and translational coding. Selenoproteins act as antioxidant warriors for thyroid regulation, male-fertility enhancement, and anti-inflammatory actions. They also participate indirectly in the mechanism of wound healing as oxidative stress reducers. Glutathione peroxidase (GPX) is the major selenoprotein present in the human body, which assists in the control of excessive production of free radical at the site of inflammation. Other than GPX, other selenoproteins include selenoprotein-S that regulates the inflammatory cytokines and selenoprotein-P that serves as an inducer of homeostasis. Previously, reports were mainly focused on the cellular and molecular mechanism of wound healing with reference to various animal models and cell lines. In this review, the role of selenium and its possible routes in translational decoding of selenocysteine, synthesis of selenoproteins, systemic action of selenoproteins and their indirect assimilation in the process of wound healing are explained in detail. Some of the selenium containing compounds which can acts as cancer preventive and therapeutics are also discussed. These compounds directly or indirectly exhibit antioxidant properties which can sustain the intracellular redox status and these activities protect the healthy cells from reactive oxygen species induced oxidative damage. Although the review covers the importance of selenium/selenoproteins in wound healing process, still some unresolved mystery persists which may be resolved in near future.

Graphic abstract

Effects of selenium on myocardial apoptosis by modifying the activity of mitochondrial STAT3 and regulating potassium channel expression

The present study investigated the effects of myocardial mitochondrial signal transduction and activator of transcription 3 (STAT3), succinate dehydrogenase activity and changes of potassium channel expression on cardiomyocyte apoptosis under low selenium conditions. Primary cultured cardiomyocytes from neonatal mice were divided into the non-toxic control group (0.1 µM sodium selenite) and low selenium treatment group (0.05 µM sodium selenite) according to different selenium concentrations. The expression of mitochondrial STAT3, p-STAT3, p-Kv1.2 potassium channel and apoptosis-related proteins, Bax and Bcl-2, were assessed by immunoblotting. Succinate dehydrogenase activity was measured by spectrophotometry. Flow cytometry was used to detect cardiomyocyte apoptosis. Low selenium treatment reduced the expression of p-STAT3, but did not affect the expression of STAT3. In addition, low selenium treatment reduced the activity of mitochondrial STAT3 and succinate dehydrogenase in cardiomyocytes, leading to injury of myocardial mitochondria. Compared with the control group, low selenium conditions reduced the activity of p-Kv1.2 and reduced the normal electrophysiological function of cardiomyocytes. In the low selenium-treated group, the expression of Bax protein increased, whereas the expression of Bcl-2 protein decreased. The apoptotic rate increased. In conclusion, selenium deficiency in cardiomyocytes leads to decreased potassium channel expression and decreased mitochondrial STAT3 activity and mitochondrial function, which in turn promotes the apoptosis of cardiomyocytes.