Different Effects of Low Selenite and Selenium-Nanoparticle Supplementation on Adipose Tissue Function and Insulin Secretion in Adolescent Male Rats

Uncovering the Role of Selenite and Selenium Nanoparticles (SeNPs) in Adolescent Rat Adipose Tissue beyond Oxidative Balance: Transcriptomic Analysis

Studies on adolescent rats, when body composition is changing deeply, reveal that the administration of sodium selenite and selenium nanoparticles (SeNPs), at the same dose, have opposite effects on adipogenesis in white adipose tissue (WAT). To investigate the mechanisms involved in these contrasting effects by means of transcriptomic analysis, three groups of male adolescent rats (n = 18) were used: control (C), selenite supplemented (S), and SeNPs supplemented (NS). Both treated groups received a twofold increase in Se dose compared to the control group through water intake for three weeks. Following treatment, WAT was removed and frozen at -80 °C until subsequent use for RNA extraction, endogenous antioxidant enzymatic activities determination, and quantification of H2O2 and malondialdehyde. NS rats displayed a larger number of differentially expressed genes and cellular processes impacted than S rats. Remarkably, these changes involved upregulation of gene expression associated with the immune system, catabolism, mitochondrial function, and oxidative balance. NS rats presented an increase in antioxidant enzymes activity, alongside an accumulation of H2O2 and malondialdehyde levels. The expression level of 81 genes related to oxidative stress was significantly affected in NS rats. Analyzing the KEGG pathway enrichment revealed that NS rats exhibited increased activity in key catabolic pathways and decreased activity in crucial growth signaling processes. These changes contribute to the mass decrease in WAT found in NS rats. These results suggest a possible application of SeNPs in WAT reduction and induction of the immune response during adolescence.

Blood Selenium Concentrations Are Inversely Associated with the Risk of Undernutrition in Older Adults

BACKGROUND

Selenium is an essential trace element with an antioxidant and anti-inflammatory capacity that has been associated in experimental studies with beneficial effects on appetite control, the regulation of the gut microbiota, and control of the anabolic-catabolic balance. The main aim of the present study was to evaluate the association between circulating selenium concentrations and the risk of developing undernutrition in older adults.

METHODS

This was a cohort study with 1398 well-nourished community-dwelling individuals aged ≥ 65 years residing in Spain in 2017, who were followed for a mean of 2.3 years. Whole blood selenium was measured at baseline using inductively coupled plasma-mass spectrometry. Undernutrition was assessed at baseline and at follow-up, and defined as having at least one of the three GLIM phenotypic criteria (involuntary weight loss, a low body mass index, and a reduced muscle mass) and at least one of the two etiologic criteria (reduced food consumption or nutrient assimilation and inflammation/disease burden).

RESULTS

During the follow-up, 142 participants (11%) developed moderate undernutrition and 113 (8.8%) severe undernutrition. The standardized relative risks of moderate and severe undernutrition at the 75th percentile of Se levels versus the 25th were 0.90 and 0.70, respectively. In dose-response analyses, the risk of severe undernutrition decreased linearly with increasing selenium concentrations. This association was independent of protein intake or diet quality and was stronger among participants with a diagnosis of a musculoskeletal disorder.

CONCLUSIONS

The results suggest that an adequate dietary selenium status is needed to prevent undernutrition in older adults. Also, this may open the door for clinical trials with selenium supplementation, at doses considered as safe, to prevent undernutrition.

Age-dependent assessment of selenium nanoparticles: biodistribution and toxicity study in young and adult rats

Aim: To study the biodistribution and toxicology of selenium nanoparticles (SeNPs) versus their bulk counterpart in young and adult male rats in a 28-day study. Methods: SeNPs were synthesized and conjugated with indocyanine green to assess comparative biodistribution by in vivo imaging and further characterized by transmission electron microscopy, Fourier transform infrared, scanning electron microscopy/energy dispersive x-ray spectroscopy, UV and ζ-analysis. The toxicity of bulk selenium was evaluated relative to its nano form by hematology indices, redox, inflammatory markers and histopathology. Results: Indocyanine green-conjugated nanoparticles showed preferential accumulation in the liver, followed by testis and kidney. The protective effect of SeNPs was more significantly observed in young livers than in adults compared with the bulk counterpart. Conclusion: Age-dependent monitoring and diagnosis of toxicity may need different biomarkers of selenium and may also provide better understanding of SeNPs as therapeutics.

Whole genome sequencing and analysis of selenite-reducing bacteria Bacillus paralicheniformis SR14 in response to different sugar supplements

The biosynthetic process of selenium nanoparticles (SeNPs) by specific bacterial strain, whose growth directly affects the synthesis efficiency, has attracted great attentions. We previously reported that Bacillus paralicheniformis SR14, a SeNPs-producing bacteria, could improve intestinal antioxidative function in vitro. To further analyze the biological characteristics of SR14, whole genome sequencing was used to reveal the genetic characteristics in selenite reduction and sugar utilization. The results reviewed that the genome size of SR14 was 4,448,062 bp, with a GC content of 45.95%. A total of 4300 genes into 49 biological pathways was annotated to the KEGG database. EC: 1.1.1.49 (glucose-6-phosphate 1-dehydrogenase) and EC: 5.3.1.9 (glucose-6-phosphate isomerase), were found to play a potential role in glucose degradation and EC:2.7.1.4 (fructokinase) might be involved in the fructose metabolism. Growth profile and selenite-reducing ability of SR14 under different sugar supplements were determined and the results reviewed that glucose had a better promoting effect on the reduction of selenite and growth of bacteria than fructose, sucrose, and maltose. Moreover, RT-qPCR experiment proved that glucose supplement remarkably promoted the expressions of thioredoxin, fumarate reductase, and the glutathione peroxidase in SR14. Analysis of mRNA expression showed levels of glucose-6-phosphate dehydrogenase and fructokinase significantly upregulated under the supplement of glucose. Overall, our data demonstrated the genomic characteristics of SR14 and preliminarily determined that glucose supplement was most beneficial for strain growth and SeNPs synthesis.

Ubiquitous Occurrence of Nano Selenium in Food Plants

Selenium is an essential trace element in human nutrition. Recent findings suggest that the biosynthesis of selenium nano particles (SeNPs) in plants might be a ubiquitous phenomenon. We investigated the potential of SeNP biosynthesis in food plants and our core objective was to explore the commonness and possible ubiquitousness of nano selenium in food plants and consequently in the human diet. By growing a variety of plants in controlled conditions and the presence of selenite we found strong evidence that SeNPs are widely present in vegetables. The shoots and roots of seven different plants, and additionally Brazil nuts, were analyzed with single-particle inductively coupled plasma mass spectrometry with a focus on edible plants including herbs and salads. SeNPs were found in every plant of our study, hence we conclude, that SeNPs are common ingredients in plant-based food and are therefore eaten daily by most humans. Considering the concerning worldwide prevalence of selenium deficiency and the great physiological properties of SeNPs, we see a high potential in utilizing this discovery.

Microbiota-Liver-Bile Salts Axis, a Novel Mechanism Involved in the Contrasting Effects of Sodium Selenite and Selenium-Nanoparticle Supplementation on Adipose Tissue Development in Adolescent Rats

Adolescence is a period during which body composition changes deeply. Selenium (Se) is an excellent antioxidant trace element related to cell growth and endocrine function. In adolescent rats, low Se supplementation affects adipocyte development differently depending on its form of administration (selenite or Se nanoparticles (SeNPs). Despite this effect being related to oxidative, insulin-signaling and autophagy processes, the whole mechanism is not elucidated. The microbiota-liver-bile salts secretion axis is related to lipid homeostasis and adipose tissue development. Therefore, the colonic microbiota and total bile salts homeostasis were explored in four experimental groups of male adolescent rats: control, low-sodium selenite supplementation, low SeNP supplementation and moderate SeNPs supplementation. SeNPs were obtained by reducing Se tetrachloride in the presence of ascorbic acid. Supplementation was received orally through water intake; low-Se rats received twice more Se than control animals and moderate-Se rats tenfold more. Supplementation with low doses of Se clearly affected anaerobic colonic microbiota profile and bile salts homeostasis. However, these effects were different depending on the Se administration form. Selenite supplementation primarily affected liver by decreasing farnesoid X receptor hepatic function, leading to the accumulation of hepatic bile salts together to increase in the ratio Firmicutes/Bacteroidetes and glucagon-like peptide-1 (GLP-1) secretion. In contrast, low SeNP levels mainly affected microbiota, moving them towards a more prominent Gram-negative profile in which the relative abundance of Akkermansia and Muribaculaceae was clearly enhanced and the Firmicutes/Bacteroidetes ratio decreased. This bacterial profile is directly related to lower adipose tissue mass. Moreover, low SeNP administration did not modify bile salts pool in serum circulation. In addition, specific gut microbiota was regulated upon administration of low levels of Se in the forms of selenite or SeNPs, which are properly discussed. On its side, moderate-SeNPs administration led to great dysbiosis and enhanced the abundance of pathogenic bacteria, being considered toxic. These results strongly correlate with the deep change in adipose mass previously found in these animals, indicating that the microbiota-liver-bile salts axis is also mechanistically involved in these changes.

Trends and recent progresses of selenium nanoparticles as novel autophagy regulators for therapeutic development

Autophagy, one of the major intracellular degradation systems, plays an important role in maintaining normal cellular physiological functions and protecting organisms from different diseases. Selenium (Se), an essential trace element, is involved in many metabolic regulatory signaling events and plays a key role in human health. In recent years, selenium nanoparticles (Se NPs) have attracted increasing attentions in biomedical field due to their low toxicity, high bioavailability and high bioactivity. Taking the advantage of their advanced biological activities, Se NPs can be used alone as potential therapeutic agents, or combine with other agents and served as carriers for the development of novel therapeutics. More interestingly, Se NPs have been widely reported to affect autophagy signaling, which therefor allow Se NPs to be used as potential therapeutic agents against different diseases. Here, this review suggested the relationships between Se and autophagy, followed by the trends and recent progresses of Se NPs for autophagy regulation in different diseased conditions. More importantly, this work discussed the roles and potential mechanisms of Se NPs in autophagy regulating, which might enhance our understanding about how Se NPs regulate autophagy for potential disease treatment. This work is expected to promote the potential application of Se NPs as novel autophagy regulators, which might benefit the development of novel autophagy associated therapeutics.