Selective inhibition of leukotriene B4 biosynthesis in rat pulmonary alveolar macrophages by dietary selenium deficiency

Levels of trace blood elements associated with severe sleep disturbance in maintenance hemodialysis patients

PURPOSE

Sleep disturbance is frequently observed in patients on maintenance hemodialysis (MHD), and this population usually presents imbalances in trace elements. We investigated the association between blood trace element levels and sleep quality in patients on MHD.

METHODS

This cross-sectional and single-center study was performed in September 2019. Patients regularly undergoing hemodialysis for > 3 months at our center were recruited, and demographic, clinical, and laboratory parameters were recorded. The Pittsburgh Sleep Quality Index (PSQI) was applied to define sleep disturbance. Blood trace element (zinc, manganese, copper, selenium, and lead) levels were measured using an inductively coupled plasma mass spectrometer.

RESULTS

In total, 121 patients on MHD (male/female = 68:53) were enrolled in the study (mean age 63.7 ± 13.9 years, median dialysis vintage 38.0 [20.0, 60.0] months). According to PSQI, 56 (46%) patients experienced severe sleep disturbance. These patients were characterized by older age, higher serum parathyroid hormone levels, and lower blood selenium levels (all P < 0.05). No significant differences in blood zinc, manganese, copper, and lead levels were observed between groups. Univariate binary logistic regression showed that lower blood selenium levels were associated with severe sleep disturbance (odds ratio = 0.976, 95% confidence interval: 0.954-0.999, P = 0.038). Multivariate analyses also confirmed the results after adjusting for confounding factors.

CONCLUSION

Our study indicated an association between lower blood selenium levels and the occurrence of severe sleep disturbances in patients on MHD. However, a prospective study with a larger sample size and assessing the importance of selenium supplementation are needed to confirm the results.

Down-regulation of microRNA-155 promotes selenium deficiency-induced apoptosis by tumor necrosis factor receptor superfamily member 1B in the broiler spleen

The aim of this work was to explore the microRNA profile and the effect of microRNA-155 on apoptosis in the spleen of selenium-deficient broilers. We replicated the splenic-apoptotic model in selenium-deficient broilers. In vitro, microRNA-155 oligonucleotides were transfected into lymphocytes and subsequently treated with H₂O₂. We observed that selenium deficiency altered the microRNA profile and decreased the expression of microRNA-155 in the broiler spleens. Tumor necrosis factor receptor superfamily member 1B was verified as a target of microRNA-155 in the splenocytes. Morphological changes, increased levels of tumor necrosis factor receptor superfamily member 1B, c-Jun N-terminal kinase, Bak, Bax, Cyt-c, caspase9 and caspase3 and decreased levels of Bcl-2 demonstrated that selenium deficiency induced apoptosis in the spleen tissues. In vitro, microRNA-155 m inhibited the levels of ROS and reduced apoptosis compared with microRNA-155i in the lymphocytes. These results suggested that the reduced levels of microRNA-155 due to selenium deficiency could promote oxidative stress-induced apoptosis by increased tumor necrosis factor receptor superfamily member 1B in splenic cells.

Reduced macrophage selenoprotein expression alters oxidized lipid metabolite biosynthesis from arachidonic and linoleic acid

Uncontrolled inflammation is an underlying etiology for multiple diseases and macrophages orchestrate inflammation largely through the production of oxidized fatty acids known as oxylipids. Previous studies showed that selenium (Se) status altered the expression of oxylipids and magnitude of inflammatory responses. Although selenoproteins are thought to mediate many of the biological effects of Se, the direct effect of selenoproteins on the production of oxylipids is unknown. Therefore, the role of decreased selenoprotein activity in modulating the production of biologically active oxylipids from macrophages was investigated. Thioglycollate-elicited peritoneal macrophages were collected from wild-type and myeloid-cell-specific selenoprotein knockout mice to analyze oxylipid production by liquid chromatography/mass spectrometry as well as oxylipid biosynthetic enzyme and inflammatory marker gene expression by quantitative real-time polymerase chain reaction. Decreased selenoprotein activity resulted in the accumulation of reactive oxygen species, enhanced cyclooxygenase and lipoxygenase expression and decreased oxylipids with known anti-inflammatory properties such as arachidonic acid-derived lipoxin A₄ (LXA₄) and linoleic acid-derived 9-​oxo-octadecadienoic acid (9-oxoODE). Treating RAW 264.7 macrophages with LXA₄ or 9-oxoODE diminished oxidant-induced macrophage inflammatory response as indicated by decreased production of TNFα. The results show for the first time that selenoproteins are important for the balanced biosynthesis of pro- and anti-inflammatory oxylipids during inflammation. A better understanding of the Se-dependent control mechanisms governing oxylipid biosynthesis may uncover nutritional intervention strategies to counteract the harmful effects of uncontrolled inflammation due to oxylipids.

Effects of in vitro supplementation of bovine mammary gland macrophages and peripheral blood lymphocytes with alpha-tocopherol and sodium selenite: implications for udder defences

vitamin E and selenium have been observed to enhance the functions of bovine mammary gland macrophages and peripheral blood lymphocytes. In vitro supplementation with these compounds enhanced the production of neutrophil chemotaxins by macrophages stimulated with opsonised Staphylococcus aureus. Supplementation also enhanced the proliferation of peripheral blood lymphocytes in response to stimulation with concanavalin A but not to phytohaemagglutinin or pokeweed mitogen. There was no evidence of additive or synergistic effects of vitamin E and selenium. Results suggest that supplementation of cattle may optimise resistance to mastitis by enhancing the functions of resident macrophage and lymphocyte populations.

Effects of selenium supplement on the de novo biosynthesis of glycerolipids in the isolated rat heart

The effect of selenium supplement on glycerolipid biosynthesis in the isolated rat heart was investigated. Selenium was administered to the rat by intraperitoneal injection of 4.33 mumol/kg per day for 3 consecutive days. Animals administered with an equal volume of saline were used as controls. Hearts from both animal groups were perfused in Krebs-Henseleit buffer containing labelled glycerol. Subsequent to perfusion, the radioactivity associated with each glycerolipid group was determined. Selenium supplement caused elevations in the labelling of phosphatidic acid and phosphatidylcholine but not in other phospholipids, diacylglycerol or triacylglycerol. The mechanisms for the enhancement of labelling into phosphatidic acid and phosphatidylcholine were examined. The activity of the enzymes responsible for the synthesis of phosphatidic acid in the rat heart was not changed by selenium supplement. However, a 51% increase in the acyl-CoA level was detected which might account for the elevated labelling of phosphatidic acid in the selenium supplemented animal. The 2-fold increase in the activity of CDPcholine:diacylglycerol cholinephosphotransferase might also account for the increase in the labelling of phosphatidylcholine in the heart of the selenium-supplemented rat. It is clear from this study that selenium plays a regulatory role in the control of cellular lipid metabolism.

Dietary selenium effects on milk eicosanoid concentration in dairy cows during coliform mastitis

The effect of selenium deficiency on the product profile of arachidonic acid oxidation by enzymatic pathways in Holstein cows with experimentally-induced coliform mastitis was investigated. The animals were fed dairy rations containing 0.05 mg Se/kg dry matter, with the supplemented group receiving additional Se to increase the dietary concentration to approximately 0.35 mg Se/kg dry matter. Cows were inoculated intracisternally with 30 colony-forming-units of Escherichia coli at 14-16 weeks of lactation. Eicosanoids and bacteria numbers were recorded at various intervals of time for 60 h postinoculation. Milk from cows fed the Se-depleted diet had significantly higher (p less than 0.05) concentrations of TXB2 between 24 and 48 h and 6-keto-PGF1 alpha between 24 and 60 h postinoculation. Milk PGE2 concentration was significantly higher in the Se-deficient group at 24 h, whereas LTB4 was higher between 36 and 60 h postinoculation in the Se-deficient cows (p less than 0.05). Milk bacteria numbers were significantly higher between 16 and 24 h postinoculation in the Se-deficient group and three of the four cows in this group required euthanasia, whereas all four cows in the Se-supplemented group recovered without therapeutic intervention. These data indicate marked effects of dietary Se on milk eicosanoid concentrations in response to an E. coli infection. The changes in eicosanoid concentrations may be associated with the altered pathogenesis and outcome of mastitis in a Se-deficient state.

Selenium in rheumatic diseases

Selenium is involved in several important biochemical pathways relevant to rheumatic diseases. Experimental and clinical studies suggest that selenium modulates the inflammatory and immune responses. Patients suffering from inflammatory rheumatic diseases often have low selenium levels, but this finding does not correlate with disease severity. Selenium supplementation needs stricter selection criteria and better ascertainment of dose to obtain a stimulatory or inhibitory effect relevant to the disease state. Prevention of marginal selenium deficiency by moderate supplementation might enhance host defense mechanisms.

Effects of inadequate vitamin E and/or selenium nutrition on the release of arachidonic acid metabolites in rat alveolar macrophages

Effects of vitamin E and/or selenium (Se) deficiency on the secretion of arachidonic acid metabolites by zymosan-stimulated pulmonary alveolar macrophages (AM) were examined using cells from male Long-Evans hooded rats fed torula-yeast based diets with or without the supplementation of vitamin E (150 IU/kg) or Se (0.5 mg/kg). Alveolar macrophages obtained by lavage were purified by adherence and cultured for 4 h in Hank's balanced salt solution containing bovine serum albumin (0.1%) and zymosan (300 micrograms/ml). The arachidonic acid metabolites present in the culture supernatant were measured by radioimmunoassay. Altered vitamin E and Se nutrition had no effect on the number of cells or cell types recovered from the pulmonary airways. Alveolar macrophages derived from animals fed on diets deficient in vitamin E or Se or both nutrients secreted higher levels of prostaglandin E2 and thromboxane B2. Levels of both 5-hydroxyeicosatetraenoic acid and leukotriene B4 were significantly increased only in the group fed the diet adequate in Se but deficient in vitamin E. Our data suggest that vitamin E and Se might play an important role to control the levels of several physiologically and pathologically important arachidonic acid metabolites.

Antilung cancer activities of selenium

Selenium is considered an essential trace element in most animal and plant species, although still reported in many texts as a highly toxic material. Epidemiological investigations have reported an inverse relationship between selenium and lung cancer. Explanations of reported observations have resulted in numerous mechanistic theories. Only recently have selenium metabolites involved in excretion been considered potential agents for antilung cancer activity. Anticancer properties have been shown in occupationally exposed copper smelter workers, dietary investigations and experimental studies. Supplementation with selenium of public water supplies, as is currently done with fluoride, is a potential method for increasing the blood concentration. This may permit development of a population prevention strategy against lung cancer and other diseases.

Selective inhibition of 5-lipoxygenase pathway in rat pulmonary alveolar macrophages by cigarette smoking

Pulmonary alveolar macrophages from sham or cigarette-smoke-exposed rats were examined for their ability to transform exogenously added arachidonate to metabolites of lipoxygenase and cyclooxygenase pathways. Synthesis of 5-HETE and leukotriene B4 was selectively inhibited by cigarette smoke exposure, whereas the formation of prostaglandin E2 and thromboxane B2 remained unchanged. Selective inhibition of the lipoxygenase pathway was further reflected by the reduced content of leukotriene B4 in bronchoalveolar fluid of smoke-exposed rats. These results suggest that lipoxygenase-derived products may play a unique role in smoking-induced pulmonary diseases.

Cigarette smoke-induced alterations in the release of arachidonate metabolites by pulmonary alveolar macrophage from selenium-fed and selenium-deficient rats

Male weanling F-344 rats were maintained on selenium-supplemented or -deficient diets and were exposed to fresh cigarette smoke daily for 28 weeks. The deficient status of animals was demonstrated by a significant reduction in the pulmonary and hepatic glutathione peroxidase (GSH-Px) activity of rats on selenium-deficient diet. Sham and smoke treatment did not influence the GSH-Px activity in either diet group. Elevated levels of blood carboxyhemoglobin and pulmonary aryl hydrocarbon hydroxylase activity in the smoke-exposed rats of both diet groups indicated effective inhalation of cigarette smoke by animals. Studies of the extracellular release of arachidonate metabolites by pulmonary alveolar macrophages (PAMs) indicated that resting cells released small amounts of prostaglandin E2 (PGE2), thromboxane B2 (TXB2) and leukotriene B4 (LTB4). Upon phagocytic challenge by opsonized zymosan particles, the release of the three metabolites was substantially increased in all diet and treatment groups. While the release of cyclooxygenase products, PGE2 and TXB2, remained unaffected by cigarette smoke, an inhibition of approximately 50% in the release of lipoxygenase product, LTB4, was observed in cells from selenium-fed animals. In selenium-deficient animals, cigarette smoke almost completely inhibited (greater than 80%) the zymosan-stimulated release of LTB4 by PAMs and additionally caused about 50% reduction in TXB2 release. These results suggest a specific inhibition of lipoxygenase pathway by cigarette smoke in PAMs of selenium-fed rats and suggest that cigarette smoke may additionally impair enzymes of the cyclooxygenase pathway in PAMs of selenium-deficient animals.