Seizures, ataxia and parvalbumin-expressing interneurons respond to selenium supply in Selenop-deficient mice

Selenium deficiency impedes maturation of parvalbumin interneurons, perineuronal nets, and neural network activity

Selenoproteins are fundamental players in redox signaling that are essential for proper brain development and function. They are indispensable for the vitality of GABAergic parvalbumin-expressing interneurons (PVIs), a cell type characterized by fast-spiking activity and heightened rates of metabolism. During development, PVIs are preferentially encapsulated by specialized extracellular matrix structures, termed perineuronal nets (PNNs), which serve to stabilize synaptic structure and act as protective barriers against redox insults. Consequently, alterations in PVIs and PNNs are well chronicled in neuropsychiatric disease, and evidence from animal models indicates that redox imbalance during adolescence impedes their maturation. Herein, we examined the influence of selenium on maturation of neural network structure and activity in primary cortical cultures. Cultures grown in selenium-deficient media exhibited reduced antioxidant activity, impaired PNN formation, and decreased synaptic input onto PVIs at 28 days in vitro, which coincided with increased oxidative stress. Parallel studies to monitor longitudinal maturation of in vitro electrophysiological activity were conducted using microelectrode arrays (MEA). Selenium content affected the electrophysiological profile of developing cultures, as selenium-deficient cultures exhibited impairments in long-term potentiation in conjunction with reduced spike counts for both network bursts and in response to stimulation. Finally, similar PNN deficits were observed in the cortex of mice raised on a selenium-deficient diet, providing corroborative evidence for the importance of selenium in PNN development. In sum, these findings show the vital role of selenium for the development of GABAergic inhibitory circuits.

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.

EEFSEC deficiency: A selenopathy with early-onset neurodegeneration

Inborn errors of selenoprotein expression arise from deleterious variants in genes encoding selenoproteins or selenoprotein biosynthetic factors, some of which are associated with neurodegenerative disorders. This study shows that bi-allelic selenocysteine tRNA-specific eukaryotic elongation factor (EEFSEC) variants cause selenoprotein deficiency, leading to progressive neurodegeneration. EEFSEC deficiency, an autosomal recessive disorder, manifests with global developmental delay, progressive spasticity, ataxia, and seizures. Cerebral MRI primarily demonstrated a cerebellar pathology, including hypoplasia and progressive atrophy. Exome or genome sequencing identified six different bi-allelic EEFSEC variants in nine individuals from eight unrelated families. These variants showed reduced EEFSEC function in vitro, leading to lower levels of selenoproteins in fibroblasts. In line with the clinical phenotype, an eEFSec-RNAi Drosophila model displays progressive impairment of motor function, which is reflected in the synaptic defects in this model organisms. This study identifies EEFSEC deficiency as an inborn error of selenocysteine metabolism. It reveals the pathophysiological mechanisms of neurodegeneration linked to selenoprotein metabolism, suggesting potential targeted therapies.

Low Levels of Selenoprotein P Are Associated With Cognitive Impairment in Patients Hospitalized for Heart Failure

BACKGROUND

Selenoprotein P (SELENOP) is a transporter for selenium and has been shown to protect selenium-status maintenance in the brain against deficiency and to support neuronal development, neurogenesis and neurocognitive function. Selenium deficiency has previously been associated with cognitive impairment in various populations, but no studies have been carried out in subjects with heart failure (HF).

PURPOSE

To explore whether SELENOP deficiency in subjects with acute HF is associated with cognitive impairment.

METHODS

Plasma SELENOP, as measured by an immunoassay analysis, is a well-validated marker of plasma selenium status and has the benefit of providing information on the bioavailable fraction of selenium to preferentially supplied cells equipped with receptors for SELENOP uptake. SELENOP was measured in 320 subjects hospitalized for HF. Of the subjects, 187 also underwent 4 cognitive tests assessing global cognitive function: Montreal Cognitive Assessment (MoCA); information processing (Symbol Digit Modalities Test [SDMT]); visual attention and task switching (Trailmaking Test A [TMT-A]); and executive speed (A Quick Test of Cognitive Speed [AQT] form and color). Appropriate cutoffs were used for each cognitive test to define cognitive impairment. Cross-sectional associations between SELENOP concentrations and cognitive impairment, as defined by each cognitive test, were explored using multivariable logistic models. Further, multivariable logistic models exploring associations between selenium deficiency, defined as the lowest quartile of SELENOP levels, and cognitive impairment, defined by each cognitive test, were carried out.

RESULTS

The 187 participants had a mean age of 73 (± 11.9) years; 31% were female and had a mean body mass index of 28.1 (± 5.6) kg/m2. Each 1 standard deviation increment in SELENOP concentrations was associated with lower odds of cognitive impairment, defined as a MoCA cut-off score < 23 (odds ratio [OR] 0.60; 95% CI 0.40-0.91; P = 0.017). Further, SELENOP concentrations in the lowest quartile (≤ 2.3 mg/L) were associated with cognitive impairment as measured by MoCA (OR 3.10; 95% CI 1.38-6.97; P = 0.006), SDMT (OR 2.26; 95% CI 1.10-4.67; P = 0.027) and TMT-A (OR 3.40; 95% CI 1.47-7.88; P = 0.004) but not by AQT form and color.

CONCLUSIONS

In subjects admitted for HF, higher SELENOP concentrations were associated with better performance on the MoCA test, reflecting global cognition, and SELENOP deficiency was associated with cognitive impairment as defined by 3 cognitive tests.

New-onset autoantibodies to selenoprotein P following severe burn injury

The liver-derived selenium (Se) transporter selenoprotein P (SELENOP) declines in critical illness as a negative acute phase reactant and has recently been identified as an autoantigen. Hepatic selenoprotein biosynthesis and cotranslational selenocysteine insertion are sensitive to inflammation, therapeutic drugs, Se deficiency, and other modifiers. As severe burn injury induces a heavy inflammatory burden with concomitant Se depletion, we hypothesized an impairment of selenoprotein biosynthesis in the acute post-burn phase, potentially triggering the development of autoantibodies to SELENOP (SELENOP-aAb). To test this hypothesis, longitudinal serum samples from severely burned patients were analyzed over a period of six months. Newly occurring SELENOP-aAb were detected in 8.4% (7/83) of the burn patients, with onset not earlier than two weeks after injury. Prevalence of SELENOP-aAb was associated with injury severity, as aAb-positive patients have suffered more severe burns than their aAb-negative counterparts (median [IQR] ABSI: 11 [7-12] vs. 7 [5.8-8], p = 0.023). Autoimmunity to SELENOP was not associated with differences in total serum Se or SELENOP concentrations. A positive correlation of kidney-derived glutathione peroxidase (GPx3) with serum SELENOP was not present in the patients with SELENOP-aAb, who showed delayed normalization of GPx3 activity post-burn. Overall, the data suggest that SELENOP-aAb emerge after severe injury in a subset of patients and have antagonistic effects on Se transport. The nature of burn injury as a sudden event allowed a time-resolved analysis of a direct trigger for new-onset SELENOP-aAb, which may be relevant for severely affected patients requiring intensified acute and long-term care.

Selenium as a Modulator of Redox Reactions in the Prevention and Treatment of Cardiovascular Diseases

Cardiovascular diseases stand as the predominant global cause of mortality, exerting a profound impact on both life expectancy and its quality. Given their immense public health burden, extensive efforts have been dedicated to comprehending the underlying mechanisms and developing strategies for prevention and treatment. Selenium, a crucial participant in redox reactions, emerges as a notable factor in maintaining myocardial cell homeostasis and influencing the progression of cardiovascular disorders. Some disorders, such as Keshan disease, are directly linked with its environmental deficiency. Nevertheless, the precise extent of its impact on the cardiovascular system remains unclear, marked by contradictory findings in the existing literature. High selenium levels have been associated with an increased risk of developing hypertension, while lower concentrations have been linked to heart failure and atrial fibrillation. Although some trials have shown its potential effectiveness in specific groups of patients, large cohort supplementation attempts have generally yielded unsatisfactory outcomes. Consequently, there persists a significant need for further research aimed at delineating specific patient cohorts and groups of diseases that would benefit from selenium supplementation.

By regulating the IP3R/GRP75/VDAC1 complex to restore mitochondrial dynamic balance, selenomethionine reduces lipopolysaccharide-induced neuronal apoptosis

Selenium (Se), as one of the essential trace elements, plays an anti-inflammatory, antioxidation, and immune-enhancing effect in the body. In addition, Se can also improve nervous system damage induced by various factors. Earlier studies have described the important role of mitochondrial dynamic imbalance in lipopolysaccharide (LPS)-induced nerve injury. The inositol 1,4,5-triphosphate receptor (IP3R)/glucose-regulated protein 75 (GRP75)/voltage-dependent anion channel 1 (VDAC1) complex is considered to be the key to regulating mitochondrial dynamics. However, it is not clear whether Selenomethionine (SeMet) has any influence on the IP3R/GRP75/VDAC1 complex. Therefore, the aim of this investigation was to determine whether SeMet can alleviate LPS-induced brain damage and to elucidate the function of the IP3R/GRP75/VDAC1 complex in it. We established SeMet and/or LPS exposure models in vivo and in vitro using laying hens and primary chicken nerve cells. We noticed that SeMet reversed endoplasmic reticulum stress (ERS) and the imbalance in mitochondrial dynamics and significantly prevented the occurrence of neuronal apoptosis. We made this finding by morphological observation of the brain tissue of laying hens and the detection of related genes such as ERS, the IP3R/GRP75/VDAC1 complex, calcium signal (Ca2+), mitochondrial dynamics, and apoptosis. Other than that, we also discovered that the IP3R/GRP75/VDAC1 complex was crucial in controlling Ca2+ transport between the endoplasmic reticulum and the mitochondrion when SeMet functions as a neuroprotective agent. In summary, our results revealed the specific mechanism by which SeMet alleviated LPS-induced neuronal apoptosis for the first time. As a consequence, SeMet has great potential in the treatment and prevention of neurological illnesses (like neurodegenerative diseases).

Autoantibodies to selenoprotein P in chronic fatigue syndrome suggest selenium transport impairment and acquired resistance to thyroid hormone

Chronic Fatigue Syndrome (CFS) presents with symptoms of hypothyroidism, including mental and physical fatigue, poor sleep, depression, and anxiety. However, thyroid hormone (TH) profiles of elevated thyrotropin and low thyroxine (T4) are not consistently observed. Recently, autoantibodies to the Se transporter SELENOP (SELENOP-aAb) have been identified in Hashimoto's thyroiditis and shown to impair selenoprotein expression. We hypothesized that SELENOP-aAb are prevalent in CFS, and associate with reduced selenoprotein expression and impaired TH deiodination. Se status and SELENOP-aAb prevalence was compared by combining European CFS patients (n = 167) and healthy controls (n = 545) from different sources. The biomarkers total Se, glutathione peroxidase (GPx3) and SELENOP showed linear correlations across the samples without reaching saturation, indicative of Se deficiency. SELENOP-aAb prevalence was 9.6-15.6% in CFS versus 0.9-2.0% in controls, depending on cut-off for positivity. The linear correlation between Se and GPx3 activity was absent in SELENOP-aAb positive patients, suggesting impaired Se supply of kidney. A subgroup of paired control (n = 119) and CSF (n = 111) patients had been characterized for TH and biochemical parameters before. Within this subgroup, SELENOP-aAb positive patients displayed particularly low deiodinase activity (SPINA-GD index), free T3 levels, total T3 to total T4 (TT3/TT4) and free T3 to free T4 (FT3/FT4) ratios. In 24 h urine, iodine concentrations were significantly lower in SELENOP-aAb positive than in SELENOP-aAb negative patients or controls (median (IQR); 43.2 (16.0) vs. 58.9 (45.2) vs. 89.0 (54.9) μg/L). The data indicate that SELENOP-aAb associate with low deiodination rate and reduced activation of TH to active T3. We conclude that a subset of CFS patients express SELENOP-aAb that disturb Se transport and reduce selenoprotein expression in target tissues. Hereby, TH activation decreases as an acquired condition not reflected by thyrotropin and T4 in blood. This hypothesis opens new diagnostic and therapeutic options for SELENOP-aAb positive CFS, but requires clinical evidence from intervention trials.

Selenium and Selenoproteins in Health

Selenium is a trace mineral that is essential for health. After being obtained from food and taken up by the liver, selenium performs various physiological functions in the body in the form of selenoproteins, which are best known for their redox activity and anti-inflammatory properties. Selenium stimulates the activation of immune cells and is important for the activation of the immune system. Selenium is also essential for the maintenance of brain function. Selenium supplements can regulate lipid metabolism, cell apoptosis, and autophagy, and have displayed significant alleviating effects in most cardiovascular diseases. However, the effect of increased selenium intake on the risk of cancer remains unclear. Elevated serum selenium levels are associated with an increased risk of type 2 diabetes, and this relationship is complex and nonlinear. Selenium supplementation seems beneficial to some extent; however, existing studies have not fully explained the influence of selenium on various diseases. Further, more intervention trials are needed to verify the beneficial or harmful effects of selenium supplementation in various diseases.

High throughput drug screening identifies resveratrol as suppressor of hepatic SELENOP expression

INTRODUCTION

Selenium (Se) is an essential trace element that exerts its effects mainly as the proteinogenic amino acid selenocysteine within a small set of selenoproteins. Among all family members, selenoprotein P (SELENOP) constitutes a particularly interesting protein as it serves as a biomarker and serum Se transporter from liver to privileged tissues. SELENOP expression is tightly regulated by dietary Se intake, inflammation, hypoxia and certain substances, but a systematic drug screening has hitherto not been performed.

METHODS

A compound library of 1861 FDA approved clinically relevant drugs was systematically screened for interfering effects on SELENOP expression in HepG2 cells using a validated ELISA method. Dilution experiments were conducted to characterize dose-responses. A most potent SELENOP inhibitor was further characterized by RNA-seq analysis to assess effect-associated biochemical pathways.

RESULTS

Applying a 2-fold change threshold, 236 modulators of SELENOP expression were identified. All initial hits were replicated as biological triplicates and analyzed for effects on cell viability. A set of 38 drugs suppressed SELENOP expression more than three-fold, among which were cancer drugs, immunosuppressants, anti-infectious drugs, nutritional supplements and others. Considering a 90% cell viability threshold, resveratrol, vidofludimus, and antimony potassium-tartrate were the most potent substances with suppressive effects on extracellular SELENOP concentrations. Resveratrol suppressed SELENOP levels dose-dependently in a concentration range from 0.8 μM to 50.0 μM, without affecting cell viability, along with strong effects on key genes controlling metabolic pathways and vesicle trafficking.

CONCLUSION

The results highlight an unexpected direct effect of the plant stilbenoid resveratrol, known for its antioxidative and health-promoting effects, on the central Se transport protein. The suppressive effects on SELENOP may increase liver Se levels and intracellular selenoprotein expression, thereby conferring additional protection to hepatocytes at the expense of systemic Se transport. Further physiological effects from this interaction require analyses in vivo and by clinical studies.