Selenium and selenoproteins in thermogenic adipocytes

Selenium: 48-year journey of global clinical trials

Selenium, an essential trace mineral for health, has seen a rise in clinical trials over the past nearly 5 decades. Our aim here is to provide a comprehensive and concise overview of selenium clinical trials from 1976 to 2023. Overall, the evolution of selenium clinical trials over 48 years has advanced through phases of emergence, prosperity, and either stability or transition. The USA plays pivotal roles in establishing large research clusters and fostering strong collaborative ties of selenium clinical trials. Low-selenium levels are noted in a higher proportion of selenium observational trials, while selenium intervention trials are delineated by nine key functional classifications. The emphasis in intervention trials is that selenium product development should be on conducting clinical trials in diseases with higher efficacy, such as those involving antioxidant and endocrine and metabolic disease. Moreover, inorganic forms such as sodium selenite and semi-organic forms like selenized yeast were recognized as primary sources of selenium, while nano-selenium has emerged as a new selenium source in clinical treatments. Selenium is mainly consumed through tablets and oral administration, with a recommended upper limit of 200 µg per day for managing most diseases. In addition, genes encoding selenoproteins or factors of relevance for selenium metabolism, inflammation, and immunity, which have a higher number of records in all trials, are poised to steer future investigations into functional mechanisms of selenium. We believe this review will offer fresh perspectives on selenium clinical trials and identify potential avenues for future selenium research.

Biosafety and pharmacokinetic characteristics of polyethylene pyrrolidone modified nano selenium in rats

OBJECTIVE

This study aims to investigate the biocompatibility and pharmacokinetic characteristics of polyvinyl pyrrolidone-modified selenium nanoparticles (PVP-Se NPs). Understanding the biosafety of PVP-Se NPs is crucial due to their potential applications in mitigating oxidative stress-related diseases and improving drug delivery systems.

METHODS

Selenium nanoparticles were prepared using a sodium selenite solution, followed by PVP modification. Particle size analysis was conducted using dynamic light scattering (DLS), and particle morphology was observed using transmission electron microscopy (TEM). Different concentrations of PVP-Se NPs were intraperitoneally injected into SD rats, and the survival rate was observed. Liver and kidney tissues, urine, feces, and blood samples were collected at the highest safe dose, and the concentration of selenium ions was measured.

RESULTS

The average particle size of PVP-Se NPs was 278.4 ± 124.8 nm, exhibiting a semi-spherical shape. The maximum safe dose of PVP-Se NPs for intraperitoneal injection in rats was approximately 320 µg/kg. At this dose, the content of PVP-Se NPs significantly increased in the liver and kidney tissues from day 1 to day 3, in urine and feces during the first 8 h, and in blood during the first 2 h, followed by a gradual decrease.

CONCLUSION

When administered at a safe dose, PVP-Se NPs do not damage liver and kidney tissues and can be eliminated from the body through liver and kidney metabolism without accumulation.

Molecular Regulation of Thermogenic Mechanisms in Beige Adipocytes

Adipose tissue is conventionally recognized as a metabolic organ responsible for storing energy. However, a proportion of adipose tissue also functions as a thermogenic organ, contributing to the inhibition of weight gain and prevention of metabolic diseases. In recent years, there has been significant progress in the study of thermogenic fats, particularly brown adipose tissue (BAT). Despite this progress, the mechanism underlying thermogenesis in beige adipose tissue remains highly controversial. It is widely acknowledged that beige adipose tissue has three additional thermogenic mechanisms in addition to the conventional UCP1-dependent thermogenesis: Ca2+ cycling thermogenesis, creatine substrate cycling thermogenesis, and triacylglycerol/fatty acid cycling thermogenesis. This paper delves into these three mechanisms and reviews the latest advancements in the molecular regulation of thermogenesis from the molecular genetic perspective. The objective of this review is to provide readers with a foundation of knowledge regarding the beige fats and a foundation for future research into the mechanisms of this process, which may lead to the development of new strategies for maintaining human health.

The Circulating Selenium Concentration Is Positively Related to the Lipid Accumulation Product: A Population-Based Cross-Sectional Study

The lipid accumulation product (LAP) is a reliable marker of metabolic syndrome, which includes conditions like obesity. However, the correlation between the circulating selenium (CSe) concentration and the LAP is currently unclear. This study aimed to ascertain this correlation. Overall, 12,815 adults aged ≥20 years were enrolled in this study. After adjusting for all the confounding variables, CSe was positively correlated to the LAP (β = 0.41; 95% confidence interval [CI]: 0.28, 0.54; p < 0.001). Compared with the lowest quartile of CSe, the highest quartile of CSe was positively related to the LAP (β = 0.16; 95% CI: 0.12, 0.21; p < 0.001). Moreover, the correlation between CSe and the LAP revealed a positive non-linear trend. In the subgroup analysis, interaction effects were observed for age, sex, smoking, and stroke (p for interaction < 0.05). The effects were stronger for males (β = 0.64, 95% CI: 0.47, 0.80; p < 0.001) and individuals who smoke at the time of the trial (β = 0.64, 95% CI: 0.37, 0.91; p < 0.001). In conclusion, our results indicated that CSe was positively correlated with the LAP in a non-linear manner. Future research is warranted to explore their relationship and better understand the mechanisms underlying this association.

The Regulation of Selenoproteins in Diabetes: A New Way to Treat Diabetes

Selenium is an essential micronutrient required for the synthesis and function of selenoproteins, most of which are enzymes involved in maintaining oxidative balance in the body. Diabetes is a group of metabolic disorders characterized by high blood glucose levels over a prolonged period of time. There are three main types of diabetes: type 1, type 2, and gestational diabetes. This review summarizes recent advances in the field of diabetes research with an emphasis on the roles of selenoproteins on metabolic disturbance in diabetes. We also discuss the interaction between selenoproteins and glucose and lipid metabolism to provide new insights into the prevention and treatment of diabetes.

Mitochondrial Energy Metabolism in the Regulation of Thermogenic Brown Fats and Human Metabolic Diseases

Brown fats specialize in thermogenesis by increasing the utilization of circulating blood glucose and fatty acids. Emerging evidence suggests that brown adipose tissue (BAT) prevents the incidence of obesity-associated metabolic diseases and several types of cancers in humans. Mitochondrial energy metabolism in brown/beige adipocytes regulates both uncoupling protein 1 (UCP1)-dependent and -independent thermogenesis for cold adaptation and the utilization of excess nutrients and energy. Many studies on the quantification of human BAT indicate that mass and activity are inversely correlated with the body mass index (BMI) and visceral adiposity. Repression is caused by obesity-associated positive and negative factors that control adipocyte browning, de novo adipogenesis, mitochondrial energy metabolism, UCP1 expression and activity, and noradrenergic response. Systemic and local factors whose levels vary between lean and obese conditions include growth factors, inflammatory cytokines, neurotransmitters, and metal ions such as selenium and iron. Modulation of obesity-associated repression in human brown fats is a promising strategy to counteract obesity and related metabolic diseases through the activation of thermogenic capacity. In this review, we highlight recent advances in mitochondrial metabolism, thermogenic regulation of brown fats, and human metabolic diseases.