Celebrating Two Centuries of Research in Selenium Chemistry: State of the Art and New Prospective

Multiple Binding Modes of Inhibitors to Human Carbonic Anhydrases: An Update on the Design of Isoform-Specific Modulators of Activity

Human carbonic anhydrases (hCAs) are widespread zinc enzymes that catalyze the hydration of CO2 to bicarbonate and a proton. Currently, 15 isoforms have been identified, of which only 12 are catalytically active. Given their involvement in numerous physiological and pathological processes, hCAs are recognized therapeutic targets for the development of inhibitors with biomedical applications. However, despite massive development efforts, very few of the presently available hCA inhibitors show selectivity for a specific isoform. X-ray crystallography is a very useful tool for the rational drug design of enzyme inhibitors. In 2012 we published in Chemical Reviews a highly cited review on hCA family (Alterio, V. et al. Chem Rev. 2012, 112, 4421-4468), analyzing about 300 crystallographic structures of hCA/inhibitor complexes and describing the different CA inhibition mechanisms existing up to that date. However, in the period 2012-2023, almost 700 new hCA/inhibitor complex structures have been deposited in the PDB and a large number of new inhibitor classes have been discovered. Based on these considerations, the aim of this Review is to give a comprehensive update of the structural aspects of hCA/inhibitor interactions covering the period 2012-2023 and to recapitulate how this information can be used for the rational design of more selective versions of such inhibitors.

SEPHS1 Gene: A new master key for neurodevelopmental disorders

The SEPHS1 (Selenophosphate Synthetase 1) gene encodes a critical enzyme for synthesizing selenophosphate, the active donor of selenium (Se) necessary for selenoprotein biosynthesis. Selenoproteins are vital for antioxidant defense, thyroid hormone metabolism, and cellular homeostasis. Mutations in SEPHS1 gene, are associated with neurodevelopmental disorders with developmental delay, poor growth, hypotonia, and dysmorphic features. Due to Se's critical role in brain development and function, SEPHS1 gene has taken center stage in neurodevelopmental research. This review explores the structure and function of the SEPHS1 gene, its role in neurodevelopment, and the implications of its dysregulation for neurodevelopmental disorders. Therapeutic strategies, including Se supplementation, gene therapy, and targeted therapies, are discussed as potential interventions to address SEPHS1 associated neurodevelopmental dysfunction. The study's findings reveal how SEPHS1 mutations disrupt neurodevelopment, emphasizing the gene's intolerance to loss of function. Future research should focus on functional characterization of SEPHS1 variants, broader genetic screenings, and therapeutic developments.

The Role of Nutrition on Thyroid Function

Thyroid function is closely linked to nutrition through the diet-gut-thyroid axis. This narrative review highlights the influence of nutritional components and micronutrients on thyroid development and function, as well as on the gut microbiota. Micronutrients such as iodine, selenium, iron, zinc, copper, magnesium, vitamin A, and vitamin B12 influence thyroid hormone synthesis and regulation throughout life. Dietary changes can alter the gut microbiota, leading not just to dysbiosis and micronutrient deficiency but also to changes in thyroid function through immunological regulation, nutrient absorption, and epigenetic changes. Nutritional imbalance can lead to thyroid dysfunction and/or disorders, such as hypothyroidism and hyperthyroidism, and possibly contribute to autoimmune thyroid diseases and thyroid cancer, yet controversial issues. Understanding these relationships is important to rationalize a balanced diet rich in essential micronutrients for maintaining thyroid health and preventing thyroid-related diseases. The synthetic comprehensive overview of current knowledge shows the importance of micronutrients and gut microbiota for thyroid function and uncovers potential gaps that require further investigation.

Current Understanding of Human Polymorphism in Selenoprotein Genes: A Review of Its Significance as a Risk Biomarker

Selenium has been proven to influence several biological functions, showing to be an essential micronutrient. The functional studies demonstrated the benefits of a balanced selenium diet and how its deficiency is associated with diverse diseases, especially cancer and viral diseases. Selenium is an antioxidant, protecting the cells from damage, enhancing the immune system response, preventing cardiovascular diseases, and decreasing inflammation. Selenium can be found in its inorganic and organic forms, and its main form in the cells is the selenocysteine incorporated into selenoproteins. Twenty-five selenoproteins are currently known in the human genome: glutathione peroxidases, iodothyronine deiodinases, thioredoxin reductases, selenophosphate synthetase, and other selenoproteins. These proteins lead to the transport of selenium in the tissues, protect against oxidative damage, contribute to the stress of the endoplasmic reticulum, and control inflammation. Due to these functions, there has been growing interest in the influence of polymorphisms in selenoproteins in the last two decades. Selenoproteins' gene polymorphisms may influence protein structure and selenium concentration in plasma and its absorption and even impact the development and progression of certain diseases. This review aims to elucidate the role of selenoproteins and understand how their gene polymorphisms can influence the balance of physiological conditions. In this polymorphism review, we focused on the PubMed database, with only articles published in English between 2003 and 2023. The keywords used were "selenoprotein" and "polymorphism". Articles that did not approach the theme subject were excluded. Selenium and selenoproteins still have a long way to go in molecular studies, and several works demonstrated the importance of their polymorphisms as a risk biomarker for some diseases, especially cardiovascular and thyroid diseases, diabetes, and cancer.

Urea Hydrogen Peroxide and Ethyl Lactate, an Eco-Friendly Combo System in the Direct C(sp2)-H Bond Selenylation of Imidazo[2,1-b]thiazole and Related Structures

Herein, we describe a urea hydrogen peroxide-mediated sustainable protocol for the synthesis of selenylated imidazo[2,1-b]thiazole by using half molar equivalent diorganyl diselenides in ethyl lactate as a greener solvent. The reaction features high yields, easy performance on gram scale, metal-free conditions, as well as applicability to imidazopyridine and imidazopyrimidine.

Population status of selenium in Colombia and associated factors: a cross-sectional study

OBJECTIVES

This study aims to investigate the population status of selenium in Colombia and other associated factors.

METHODS

Cross-sectional study, in population of urban or rural origin (n=412). Main outcome measures were: median serum selenium, thyrotropin, the prevalence of and positivity of anti-thyroid peroxidase, anti-thyroglobulin, and anti-TSH receptor.

RESULTS

This study found that 96.6% of the subjects had normal selenium levels, and no significant associations were found between the population median of selenium and overweight/obesity, sociodemographic variables, age, goiter, and thyroid antibody positivity.

CONCLUSIONS

In Colombia, the population status of selenium is normal, and the geological characteristics may contribute to the state of selenium in this population. However, additional studies are required to evaluate the content of selenium in plants and other foods.

Selenium, Iodine and Iron-Essential Trace Elements for Thyroid Hormone Synthesis and Metabolism

The adequate availability and metabolism of three essential trace elements, iodine, selenium and iron, provide the basic requirements for the function and action of the thyroid hormone system in humans, vertebrate animals and their evolutionary precursors. Selenocysteine-containing proteins convey both cellular protection along with H₂O₂-dependent biosynthesis and the deiodinase-mediated (in-)activation of thyroid hormones, which is critical for their receptor-mediated mechanism of cellular action. Disbalances between the thyroidal content of these elements challenge the negative feedback regulation of the hypothalamus-pituitary-thyroid periphery axis, causing or facilitating common diseases related to disturbed thyroid hormone status such as autoimmune thyroid disease and metabolic disorders. Iodide is accumulated by the sodium-iodide-symporter NIS, and oxidized and incorporated into thyroglobulin by the hemoprotein thyroperoxidase, which requires local H₂O₂ as cofactor. The latter is generated by the dual oxidase system organized as 'thyroxisome' at the surface of the apical membrane facing the colloidal lumen of the thyroid follicles. Various selenoproteins expressed in thyrocytes defend the follicular structure and function against life-long exposure to H₂O₂ and reactive oxygen species derived therefrom. The pituitary hormone thyrotropin (TSH) stimulates all processes required for thyroid hormone synthesis and secretion and regulates thyrocyte growth, differentiation and function. Worldwide deficiencies of nutritional iodine, selenium and iron supply and the resulting endemic diseases are preventable with educational, societal and political measures.

Selenium species transforming along soil-plant continuum and their beneficial roles for horticultural crops

Selenium (Se) acquirement from daily diet can help reduce the risk of many diseases. The edible parts of crop plants are the main source of dietary Se, while the Se content in crops is determined by Se bioavailability in soil. We summarize recent research on the biogeochemical cycle of Se driven by specific microorganisms and emphasize the oxidizing process in the Se cycle. Moreover, we discuss how plant root exudates and rhizosphere microorganisms affect soil Se availability. Finally, we cover beneficial microorganisms, including endophytes, that promote crop quality and improve crop tolerance to environmental stresses. Se availability to plants depends on the balance between adsorption and desorption, reduction, methylation and oxidation, which are determined by interactions among soil properties, microbial communities and plants. Reduction and methylation processes governed by bacteria or fungi lead to declined Se availability, while Se oxidation regulated by Se-oxidizing microorganisms increases Se availability to plants. Despite a much lower rate of Se oxidization compared to reduction and methylation, the potential roles of microbial communities in increasing Se bioavailability are probably largely underestimated. Enhancing Se oxidation and Se desorption are crucial for the promotion of Se bioavailability and uptake, particularly in Se-deficient soils. Beneficial roles of Se are reported in terms of improved crop growth and quality, and enhanced protection against fungal diseases and abiotic stress through improved photosynthetic traits, increased sugar and amino acid contents, and promoted defense systems. Understanding Se transformation along the plant-soil continuum is crucial for agricultural production and even for human health.

Selenium-Containing Agents Acting on Cancer-A New Hope?

Selenium-containing agents are more and more considered as an innovative potential treatment option for cancer. Light is shed not only on the considerable advancements made in understanding the complex biology and chemistry related to selenium-containing small molecules but also on Se-nanoparticles. Numerous Se-containing agents have been widely investigated in recent years in cancer therapy in relation to tumour development and dissemination, drug delivery, multidrug resistance (MDR) and immune system-related (anti)cancer effects. Despite numerous efforts, Se-agents apart from selenocysteine and selenomethionine have not yet reached clinical trials for cancer therapy. The purpose of this review is to provide a concise critical overview of the current state of the art in the development of highly potent target-specific Se-containing agents.

Seleno-Metabolites and Their Precursors: A New Dawn for Several Illnesses?

Selenium (Se) is an essential element for human health as it is involved in different physiological functions. Moreover, a great number of Se compounds can be considered potential agents in the prevention and treatment of some diseases. It is widely recognized that Se activity is related to multiple factors, such as its chemical form, dose, and its metabolism. The understanding of its complex biochemistry is necessary as it has been demonstrated that the metabolites of the Se molecules used to be the ones that exert the biological activity. Therefore, the aim of this review is to summarize the recent information about its most remarkable metabolites of acknowledged biological effects: hydrogen selenide (HSe-/H2Se) and methylselenol (CH3SeH). In addition, special attention is paid to the main seleno-containing precursors of these derivatives and their role in different pathologies.

Discovery of Novel Bicyclic Phenylselenyl-Containing Hybrids: An Orally Bioavailable, Potential, and Multiacting Class of Estrogen Receptor Modulators against Endocrine-Resistant Breast Cancer

Breast cancer (BC) is a multifactorial disease and is prone to drug resistance during treatment. In this study, we described a new class of multifunctional estrogen receptor (ER) modulators ground on a prerogative indirect antagonism skeleton (OBHS, oxabicycloheptene sulfonate) of ER containing a phenylselenyl group. Compound 34b showed significant antiproliferative activities against tamoxifen-sensitive (MCF-7) and -resistant (LCC2) cells. Moreover, hexokinase 1 (HK1) was identified as a direct target of 34b. Further mechanism investigations proved that 34b induced apoptosis, which was associated with mitochondrial dysfunction caused by the synergistic effects of downregulating mitochondrial-bound HK1 protein and promoting reactive oxygen species generation. In vivo, 34b had a favorable pharmacokinetic profile with a bioavailability of 23.20% and exhibited more potent tumor suppression than tamoxifen both in MCF-7 and LCC2 tumor xenograft models. Collectively, our studies showed that 34b is a promising new multifunctional candidate compound for ERα⁺ BC treatment, particularly for tamoxifen-resistant BC.

Immunomodulatory and Anti-Inflammatory Properties of Selenium-Containing Agents: Their Role in the Regulation of Defense Mechanisms against COVID-19

The review presents the latest data on the role of selenium-containing agents in the regulation of diseases of the immune system. We mainly considered the contributions of selenium-containing compounds such as sodium selenite, methylseleninic acid, selenomethionine, and methylselenocysteine, as well as selenoproteins and selenium nanoparticles in the regulation of defense mechanisms against various viral infections, including coronavirus infection (COVID-19). A complete description of the available data for each of the above selenium compounds and the mechanisms underlying the regulation of immune processes with the active participation of these selenium agents, as well as their therapeutic and pharmacological potential, is presented. The main purpose of this review is to systematize the available information, supplemented by data obtained in our laboratory, on the important role of selenium compounds in all of these processes. In addition, the presented information makes it possible to understand the key differences in the mechanisms of action of these compounds, depending on their chemical and physical properties, which is important for obtaining a holistic picture and prospects for creating drugs based on them.

Microbial reduction and resistance to selenium: Mechanisms, applications and prospects

Selenium is an essential trace element for humans, animals and microorganisms. Microbial transformations, in particular, selenium dissimilatory reduction and bioremediation applications have received increasing attention in recent years. This review focuses on multiple Se-reducing pathways under anaerobic and aerobic conditions, and the phylogenetic clustering of selenium reducing enzymes that are involved in these processes. It is emphasized that a selenium reductase may have more than one metabolic function, meanwhile, there are several Se(VI) and/or Se(IV) reduction pathways in a bacterial strain. It is noted that Se(IV)-reducing efficiency is inconsistent with Se(IV) resistance in bacteria. Moreover, we discussed the links of selenium transformations to biogeochemical cycling of other elements, roles of Se-reducing bacteria in soil, plant and digestion system, and the possibility of using functional genes involved in Se transformation as biomarker in different environments. In addition, we point out the gaps and perspectives both on Se transformation mechanisms and applications in terms of bioremediation, Se fortification or dietary supplementation.

Catalytic Antioxidant Activity of Bis-Aniline-Derived Diselenides as GPx Mimics

Herein, we describe a simple and efficient route to access aniline-derived diselenides and evaluate their antioxidant/GPx-mimetic properties. The diselenides were obtained in good yields via ipso-substitution/reduction from the readily available 2-nitroaromatic halides (Cl, Br, I). These diselenides present GPx-mimetic properties, showing better antioxidant activity than the standard GPx-mimetic compounds, ebselen and diphenyl diselenide. DFT analysis demonstrated that the electronic properties of the substituents determine the charge delocalization and the partial charge on selenium, which correlate with the catalytic performances. The amino group concurs in the stabilization of the selenolate intermediate through a hydrogen bond with the selenium.

Small molecule selenium-containing compounds: Recent development and therapeutic applications

Selenium (Se) is an essential micronutrient of organism and has important function. It participates in the functions of selenoprotein in several manners. In recent years, Se has attracted much attention because of its therapeutic potential against several diseases. Many natural and synthetic organic Se-containing compounds were studied and explored for the treatment of cancer and other diseases. Studies have showed that incorporation of Se atom into small molecules significantly enhanced their bioactivities. In this paper, according to different applications and structural characteristics, the research progress and therapeutic application of Se-containing compounds are reviewed, and more than 110 Se-containing compounds were selected as representatives which showed potent activities such as anticancer, antioxidant, antifibrolytic, antiparasitic, antibacterial, antiviral, antifungal and central nervous system related effects. This review is expected to provide a basis for further study of new promising Se-containing compounds.

Semisynthesis of Selenoauraptene

Selenium-containing compounds are gaining more and more interest due to their valuable and promising pharmacological properties, mainly as anticancer and antioxidant agents. Ebselen, the up to now only approved drugs, is well known to possess very good glutathione peroxidase mimicking effects. To date, the most of efforts have been directed to build pure synthetic Se containing molecules, while less attention have been devoted to Se-based semisynthetic products resembling natural compounds like terpenes, polyphenols, and alkaloids. The aim of this short communication is to report the synthesis of the first example of a Se-phenylpropanoids, namely selenoauraptene, containing a selenogeranyl side chain in position 7 of the umbelliferone core. The key step was the Newman-Kwart rearrangement to obtain a selenocarbamate in which the Se atom was directly attached to umbelliferone (replacing its 7-OH function) followed by hydrolysis to get diumbelliferyl diselenide, which was finally easily converted to the desired Se-geranyl derivative in quite a good overall yield (28.5%). The synthesized adduct displayed a greater antioxidant and a radical scavenger in vitro activity than parent auraptene. The procedure we describe herein, to the best of our knowledge for the first time in the literature, represents an easy-to-handle method for the synthesis of a wide array of seleno analogues of naturally occurring biologically active oxyprenylated secondary metabolites.

Selenoxide Elimination Triggers Enamine Hydrolysis to Primary and Secondary Amines: A Combined Experimental and Theoretical Investigation

We discuss a novel selenium-based reaction mechanism consisting in a selenoxide elimination-triggered enamine hydrolysis. This one-pot model reaction was studied for a set of substrates. Under oxidative conditions, we observed and characterized the formation of primary and secondary amines as elimination products of such compounds, paving the way for a novel strategy to selectively release bioactive molecules. The underlying mechanism was investigated using NMR, mass spectrometry and density functional theory (DFT).

Melatonin Participates in Selenium-Enhanced Cold Tolerance of Cucumber Seedlings

Melatonin is an important and widespread plant hormone. However, the underlying physiological and molecular mechanisms of melatonin as a secondary messenger in improving cold tolerance by selenium are limited. This study investigated the effects of selenite on the cold stress of cucumber seedlings. The results showed that exogenous application of selenite improved the cold tolerance of cucumber seedlings, which was dependent on the concentration effect. In the present experiment, 1 μM of selenite showed the best effect on alleviating cold stress. Interestingly, we found that in the process of alleviating cold stress, selenite increased the content of endogenous melatonin by regulating the expression of melatonin biosynthesis genes (TDC, T5H, SNAT, and COMT). To determine the interrelation between selenite and melatonin in alleviating cold stress, melatonin synthesis inhibitor p-chlorophenylalanine and melatonin were used for in-depth study. This study provides a theoretical basis for cucumber cultivation and breeding.

Fluoxetine scaffold to design tandem molecular antioxidants and green catalysts

Fluoxetine finds application in the treatment of depression and mood disorders. This selective serotonin-reuptake inhibitor (SSRI) also contrasts oxidative stress by direct ROS scavenging, modulation of the endogenous antioxidant defense system, and/or enhancement of the serotonin antioxidant capacity. We synthesised some fluoxetine analogues incorporating a selenium nucleus, thus expanding its antioxidant potential by enabling a hydroperoxides-inactivating, glutathione peroxidase (GPx)-like activity. Radical scavenging and peroxidatic activity were combined in a water-soluble, drug-like, tandem antioxidant molecule. Selenofluoxetine derivatives were reacted with H₂O₂ in water, and the mechanistic details of the reaction were unravelled combining nuclear magnetic resonance (NMR), electrospray ionisation-mass spectrometry (ESI-MS) and quantum chemistry calculations. The observed oxidation–elimination process led to the formation of seleninic acid and cinnamylamine in a trans-selective manner. This mechanism is likely to be extended to other substrates for the preparation of unsaturated cinnamylamines.

We modified fluoxetine by incorporating a selenium nucleus enabling a hydroperoxide-inactivating, glutathione peroxidase (GPx)-like activity and paving the way for its use as green catalyst.

Development and Therapeutic Potential of Selenazo Compounds

Incorporation of selenium (Se) atom into small molecules can substantially enhance their antioxidant, anti-inflammatory, antimutagenic, antitumoral or chemopreventive, antiviral, antibacterial, antifungal, antiparasitic, and neuroprotective effects. Specifically, selenazo compounds have received great attention owing to their chemical properties, pharmaceutical applications, and low toxicity. In this Perspective, we compile extensive literature evidence with the description and discussion of the most recent advances in different selenazo and selenadiazo motifs as potential pharmacological candidates. We also provide some perspectives on the challenges and future directions in the advancement of these selenazo compounds, each of which could generate drug candidates for various diseases.

Syntesis of thio- and seleno-acetamides bearing benzenesulfonamide as potent inhibitors of human carbonic anhydrase II and XII

A novel series of thio- and seleno-acetamides bearing benzenesulfonamide were synthetized and tested as human carbonic anhydrase inhibitors. These compounds were tested for the inhibition of four human (h) isoforms, hCA I, II, IX, and XII, involved in pathologies such as glaucoma (CA II and XII) or cancer (CA IX/XII). Several derivatives showed potent inhibition activity in low nanomolar range such as 3a, 4a, 7a and 8a. Furthermore, based on the tail approach we explain the interesting and selective inhibition profile of compound such as 5a and 9a, which were more selective for hCA I, 9b which was selective for hCA II, 3f selective for hCA IX and finally, 3e and 4b selective for hCA XII, over the other three isoforms. They are interesting leads for the development of more effective and isoform-selective inhibitors.

Serum Selenium Level in Early Healthy Pregnancy as a Risk Marker of Pregnancy Induced Hypertension

Selenium (Se) is an antioxidant nutrient whose deficiency can influence adverse outcomes of pregnancy. The aim of this study is to determine whether serum Se level in early healthy pregnancy may be a risk marker for pregnancy induced hypertension. We obtained data from our prospective study in which we recruited healthy women in weeks 10–14 of a single pregnancy. In this analysis, we examined 121 women who subsequently developed pregnancy-induced hypertension and matched 363 women who remained normotensive. We measured Se levels (using the ICP-MS technique) in the serum in weeks 10–14 of the pregnancy. The odds ratios of pregnancy-induced hypertension (95% confidence intervals) were calculated using multivariate logistic regression. We found that the mean Se level was lower in the case group compared to the control (57.51 vs. 62.89 μg/L; p = 2.6 × 10⁻¹⁰). Excessive body mass index (BMI) and smoking influenced the estimated odds ratios. In the subgroup of women who had never smoked with normal pre-pregnancy BMI, the adjusted odds ratio (AOR) of pregnancy-induced hypertension was 15.34 (95% CI: 2.73–86.31, p = 0.002) for Se levels in the lowest quartile (≤57.68 µg/L), as compared to the highest quartile (>66.60 µg/L), after adjusting for all the accepted confounders. In the whole cohort, the prognostic value of Se by logistic regression showed that the area under curve (AUC) = 0.814. In our study, one can consider the role of Se as a risk marker of pregnancy-induced hypertension.

Selenylated plant polysaccharides: A survey of their chemical and pharmacological properties

Polysaccharides from plants and fungi are considered nowadays as powerful pharmacological tools with a great therapeutic potential. In the meantime, efforts have been addressed to set up effective chemical modifications of naturally occurring polysaccharides to improve their biological effects as well as to positively modify some key parameters like solubility, bioavailability, pharmacokinetic, and similar. To this concern much attention has been focused during the last decade to the selenylation of natural polysaccharides from plants, algae, and fungi, the use of which is already encoded in ethnomedical traditions. The aim of this review article is to provide a detailed survey of the in so far reported literature data and a deeper knowledge about the state of the art on the chemical and pharmacological properties of selenylated polysaccharides of plant, algal, and fungal origin in terms of anti-oxidant, anti-cancer, anti-diabetic, and immunomodulatory activities. In all cases, literature data revealed that selenylation greatly improved such properties respect to the parent polysaccharides, indicating that selenylation is a valid, alternative, and effective chemical modification of naturally occurring carbohydrates.