Pharmacology and toxicology of diphenyl diselenide in several biological models

Trace elements and metal nanoparticles: mechanistic approaches to mitigating chemotherapy-induced toxicity-a review of literature evidence

Anticancer chemotherapy (ACT) remains a cornerstone in cancer treatment, despite significant advances in pharmacology over recent decades. However, its associated side effect toxicity continues to pose a major concern for both oncology clinicians and patients, significantly impacting treatment protocols and patient quality of life. Current clinical strategies to mitigate ACT-induced toxicity have proven largely unsatisfactory, leaving a critical unmet need to block toxicity mechanisms without diminishing ACT's therapeutic efficacy. This review aims to document the molecular mechanisms underlying ACT toxicity and highlight research efforts exploring the protective effects of trace elements (TEs) and their nanoparticles (NPs) against these mechanisms. Our literature review reveals that the primary driver of ACT toxicity is redox imbalance, which triggers oxidative inflammation, apoptosis, endoplasmic reticulum stress, mitochondrial dysfunction, autophagy, and dysregulation of signaling pathways such as PI3K/mTOR/Akt. Studies suggest that TEs, including zinc, selenium, boron, manganese, and molybdenum, and their NPs, can potentially counteract ACT-induced toxicity by inhibiting oxidative stress-mediated pathways, including NF-κB/TLR4/MAPK/NLRP3, STAT-3/NLRP3, Bcl-2/Bid/p53/caspases, and LC3/Beclin-1/CHOP/ATG6, while also upregulating protective signaling pathways like Sirt1/PPAR-γ/PGC-1α/FOXO-3 and Nrf2/HO-1/ARE. However, evidence regarding the roles of lncRNA and the Wnt/β-catenin pathway in ACT toxicity remains inconsistent, and the impact of TEs and NPs on ACT efficacy is not fully understood. Further research is needed to confirm the protective effects of TEs and their NPs against ACT toxicity in cancer patients. In summary, TEs and their NPs present a promising avenue as adjuvant agents for preventing non-target organ toxicity induced by ACT.

Diphenyl Diselenide Through Reduction of Inflammation, Oxidative Injury and Caspase-3 Activation Abates Doxorubicin-Induced Neurotoxicity in Rats

Neurotoxicity associated with chemotherapy is a debilitating side effect of cancer management in humans which reportedly involves inflammatory and oxidative stress responses. Diphenyl diselenide (DPDS) is an organoselenium compound which exhibits its anti-tumoral, anti-oxidant, anti-inflammatory and anti-mutagenic effects. Nevertheless, its possible effect on chemotherapy-induced neurotoxicity is not known. Using rat model, we probed the behavioral and biochemical effects accompanying administration of antineoplastic agent doxorubicin (7.5 mg/kg) and DPDS (5 and 10 mg/kg). Anxiogenic-like behavior, motor and locomotor insufficiencies associated with doxorubicin were considerably abated by both DPDS doses with concomitant enhancement in exploratory behavior as demonstrated by reduced heat maps intensity and enhanced track plot densities. Moreover, with exception of cerebral glutathione (GSH) level, superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities, biochemical data demonstrated reversal of doxorubicin-mediated decline in cerebral and cerebellar antioxidant status indices and the increase in acetylcholinesterase (AChE) activity by both doses of DPDS. Also, cerebellar and cerebral lipid peroxidation, hydrogen peroxide as well as reactive oxygen and nitrogen species levels were considerably diminished in rats administered doxorubicin and DPDS. In addition, DPDS administration abated myeloperoxidase activity, tumour necrosis factor alpha and nitric oxide levels along with caspase-3 activity in doxorubicin-administered rats. Chemoprotection of doxorubicin-associated neurotoxicity by DPDS was further validated by histomorphometry and histochemical staining. Taken together, DPDS through offsetting of oxido-inflammatory stress and caspase-3 activation elicited neuroprotection in doxorubicin-treated rats.

Reactions of hypobromous acid with dimethyl selenide, dimethyl diselenide and other organic selenium compounds: kinetics and product formation

Selenium (Se) is an essential micronutrient for many living organisms particularly due to its unique redox properties. We recently found that the sulfur (S) analog for dimethyl selenide (DMSe), i.e. dimethyl sulfide (DMS), reacts fast with the marine oxidant hypobromous acid (HOBr) which likely serves as a sink of marine DMS. Here we investigated the reactivity of HOBr with dimethyl selenide and dimethyl diselenide (DMDSe), which are the main volatile Se compounds biogenically produced in marine waters. In addition, the reactivity of HOBr with further organic Se compounds was tested, i.e., SeMet (as N-acetylated-SeMet), and selenocystine (SeCys2 as N-acetylated-SeCys2), as well as the phenyl-analogs of DMSe and DMDSe, respectively, diphenyl selenide (DPSe) and diphenyl diselenide (DPDSe). Apparent second-order rate constants at pH 8 for the reactions of HOBr with the studied Se compounds were (7.1 ± 0.7) × 107 M-1 s-1 for DMSe, (4.3 ± 0.4) × 107 M-1 s-1 for DMDSe, (2.8 ± 0.3) × 108 M-1 s-1 for SeMet, (3.8 ± 0.2) × 107 M-1 s-1 for SeCys2, (3.5 ± 0.1) × 107 M-1 s-1 for DPSe, and (8.0 ± 0.4) × 106 M-1 s-1 for DPDSe, indicating a very high reactivity of all selected Se compounds with HOBr. The reactivity between HOBr and DMSe is lower than for DMS and therefore this reaction is likely not relevant for marine DMSe abatement. However, the high reactivity of SeMet with HOBr suggests that SeMet may act as a relevant quencher of HOBr.

Attenuation of doxorubicin-induced hypothalamic-pituitary-testicular axis dysfunction by diphenyl diselenide involves suppression of hormonal deficits, oxido-inflammatory stress and caspase 3 activity in rats

BACKGROUND

Doxorubicin (DOX) is one of the popular anti-cancer drugs in the world and several literatures have implicated it in various toxicities especially cardiotoxicity and reproductive toxicity. Diphenyl diselenide (DPDS) is well acknowledged for its compelling pharmacological effects in numerous disease models and chemically-mediated toxicity. This study was carried out to investigate the effect of DPDS on DOX-induced changes in the reproductive indices of male Wistar rats.

METHODS

Rats were intraperitoneally injected with 7.5 mg/kg body weight of DOX alone once followed by treatment with DPDS at 5 and 10 mg/kg for seven successive days. Excised hypothalamus, testes and epididymis were processed for biochemical and histological analyses.

RESULTS

DPDS treatment significantly (p < 0.05) abated DOX-induced oxidative damage by decreasing the levels of oxidative stress indices such as hydrogen peroxide, reactive oxygen and nitrogen species, and lipid peroxidation with a respective improvement in the level of glutathione in the hypothalamic, testicular and epididymal tissues of DOX-treated rats. The activities of antioxidant enzymes such as catalase, superoxide dismutase, glutathione S-transferase and glutathione peroxidase were upregulated in the DPDS co-treated group. DPDS co-treatment alleviates the burden of DOX-induced inflammation by significant reductions in myeloperoxidase activity, levels of nitric oxide and tumor necrosis factor alpha with concomitant decline in the activity of caspase-3, an apoptotic biomarker. Consequently, significant improvement in the spermiogram, levels of reproductive hormones (follicle stimulating hormone, luteinizing hormone, prolactin, serum testosterone and intra-testicular testosterone) levels in the DPDS co-treatment group in comparison to DOX alone-treated group were observed. Histology results of the testes and epididymis showed that DPDS significantly alleviated pathological lesions induced by DOX in the animals.

CONCLUSION

DPDS may modulate reproductive toxicity associated with DOX therapy in male cancer patients.

Effectiveness of diphenyl diselenide against experimental sporotrichosis caused by Sporothrix brasiliensis

Diphenyl diselenide (PhSe)2 is a stable organoselenium compound with promising in vitro antifungal activity against several fungi, including Sporothrix brasiliensis. This species is associated with feline and zoonotic sporotrichosis, an emergent mycosis in Latin America. We evaluated the activity of (PhSe)2, alone and in association with itraconazole, in the treatment of sporotrichosis caused by S. brasiliensis, in a murine model. Sixty mice were subcutaneously infected with S. brasiliensis in the footpad and treated by gavage for 30 consecutive days. The six treatment groups received: no active treatment, itraconazole (50 mg/kg), (PhSe)2 at 1, 5, and 10 mg/kg dosages, or itraconazole (50 mg/kg) + (PhSe)2 1 mg/kg, once a day, starting seven days post-inoculation. A significant reduction in the fungal burden of internal organs was achieved in the groups treated with (PhSe)2 1 mg/kg or itraconazole alone in comparison with the untreated group. Higher dosages (5 and 10 mg/kg) of (PhSe)2 increased the clinical manifestation of sporotrichosis and mortality rate. Treatment with both itraconazole and (PhSe)2 1 mg/kg was better than their activities alone (P < .001). This is the first demonstration of the potential use of (PhSe)2, alone or with the present drug of choice, in the treatment of sporotrichosis.

Diphenyl Diselenide and SARS-CoV-2: in silico Exploration of the Mechanisms of Inhibition of Main Protease (Mpro) and Papain-like Protease (PLpro)

The SARS-CoV-2 pandemic has prompted global efforts to develop therapeutics. The main protease of SARS-CoV-2 (M^pro) and the papain-like protease (PL^pro) are essential for viral replication and are key targets for therapeutic development. In this work, we investigate the mechanisms of SARS-CoV-2 inhibition by diphenyl diselenide (PhSe)₂ which is an archetypal model of diselenides and a renowned potential therapeutic agent. The in vitro inhibitory concentration of (PhSe)₂ against SARS-CoV-2 in Vero E6 cells falls in the low micromolar range. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations [level of theory: SMD-B3LYP-D3(BJ)/6-311G(d,p), cc-pVTZ] are used to inspect non-covalent inhibition modes of both proteases via π-stacking and the mechanism of covalent (PhSe)₂ + M^pro product formation involving the catalytic residue C145, respectively. The in vitro CC₅₀ (24.61 μM) and EC₅₀ (2.39 μM) data indicate that (PhSe)₂ is a good inhibitor of the SARS-CoV-2 virus replication in a cell culture model. The in silico findings indicate potential mechanisms of proteases' inhibition by (PhSe)₂; in particular, the results of the covalent inhibition here discussed for M^pro, whose thermodynamics is approximatively isoergonic, prompt further investigation in the design of antiviral organodiselenides.

Lipid-core nanoparticles: Classification, preparation methods, routes of administration and recent advances in cancer treatment

Nanotechnological drug delivery platforms represent a new paradigm for cancer therapeutics as they improve the pharmacokinetic profile and distribution of chemotherapeutic agents over conventional formulations. Among nanoparticles, lipid-based nanoplatforms possessing a lipid core, that is, lipid-core nanoparticles (LCNPs), have gained increasing interest due to lipid properties such as high solubilizing potential, versatility, biocompatibility, and biodegradability. However, due to the wide spectrum of morphologies and types of LCNPs, there is a lack of consensus regarding their terminology and classification. According to the current state-of-the-art in this critical review, LCNPs are defined and classified based on the state of their lipidic components in liquid lipid nanoparticles (LLNs). These include lipid nanoemulsions (LNEs) and lipid nanocapsules (LNCs), solid lipid nanoparticles (SLNs) and nanostructured lipid nanocarriers (NLCs). In addition, we present a comprehensive and comparative description of the methods employed for their preparation, routes of administration and the fundamental role of physicochemical properties of LCNPs for efficient antitumoral drug-delivery application. Market available LCNPs, clinical trials and preclinical in vivo studies of promising LCNPs as potential treatments for different cancer pathologies are summarized.

Nano-based formulations as an approach for providing a novel identity for organoselenium compounds

The organoselenium compounds belong to a class of synthetic molecules that displays a remarkable spectrum of promising pharmacological properties. Despite the huge amount of preclinical data that supports a bright outlook for organoselenium compounds, some toxicity issues and physicochemical limitations delay the development of more advanced studies. Currently, several scientific reports demonstrated that the association of nanotechnology has emerged as an alternative to improve solubility and safety issues of these molecules as well as enhance pharmacological properties. Therefore, our main objective was to address studies that reported the development and biological evaluations of nano-based formulations to synthetic organoselenium compounds incorporation by constructing an integrative literature review. The data survey was performed using the Science Direct, PubMed, Web of Science, and SCOPUS online databases, covering studies that were published from January 2011 up to October 2021. In the last decade, there has been an exponential growth in research regarding the incorporation of synthetic organoselenium compounds into distinct nanocarrier systems such as nanocapsules, nanoemulsions, micelles, and others, reinforcing that the association of such molecules and nanotechnology is a promising alliance. The reports investigated many nanosystems containing selenium organic molecules intending oral, intravenous, and cutaneous applications. Besides that, these systems were evaluated in a variety of in vitro techniques and in vivo models, concerning their pharmacological potential, biodistribution profile, and safety. In summary, the findings indicate that the production of nano-based formulations containing organoselenium compounds either improved physicochemical and biological properties or minimize toxicological issues of compounds.

A comprehensive review on the neuropathophysiology of selenium

As an essential micronutrient, selenium (Se) exerts its biological function as a catalytic entity in a variety of enzymes. From a toxicological perspective, however, Se can become extremely toxic at concentrations slightly above its nutritional levels. Over the last few decades, there has been a growing level of concern worldwide regarding the adverse effects of both inorganic and organic Se compounds on a broad spectrum of neurological functions. A wealth of evidence has shown that exposure to excess Se may compromise the normal functioning of various key proteins, neurotransmitter systems (the glutamatergic, dopaminergic, serotonergic, and cholinergic systems), and signaling molecules involved in the control and regulation of cognitive, behavioral, and neuroendocrine functions. Elevated Se exposure has also been suspected to be a risk factor for the development of several neurodegenerative and neuropsychiatric diseases. Nonetheless, despite the various deleterious effects of excess Se on the central nervous system (CNS), Se neurotoxicity and negative behavioral outcomes are still disregarded at the expense of its beneficial health effects. This review focuses on the current state of knowledge regarding the neurobehavioral effects of Se and discusses its potential mode of action on different aspects of the central and peripheral nervous systems. This review also provides a brief history of Se discovery and uses, its physicochemical properties, biological roles in the CNS, environmental occurrence, and toxicity. We also review potential links between exposure to different forms of Se compounds and aberrant neurobehavioral functions in humans and animals, and identify key knowledge gaps and hypotheses for future research.

Organoselenium Compounds as Acetylcholinesterase Inhibitors: Evidence and Mechanism of Mixed Inhibition

Acetylcholinesterase (AChE) inhibitors are actively used for the effective treatment of Alzheimer's disease. In recent years, the neuroprotective effects of organoselenium compounds such as ebselen and diselenides on the AChE activity have been investigated as potential therapeutic agents. In this work, we have carried out systematic kinetic and intrinsic fluorescence assays in combination with docking and molecular dynamics (MD) simulations to elucidate the molecular mechanism of the mixed inhibition of AChE by ebselen and diphenyl diselenide (DPDSe) molecules. Our MD simulations demonstrate significant heterogeneity in the binding modes and allosteric hotspots for DPDSe on AChE due to non-specific interactions. We have further identified that both ebselen and DPDSe can strongly bind around the peripheral anionic site (PAS), leading to non-competitive inhibition similar to other PAS-binding inhibitors. We also illustrate the entry of the DPDSe molecule into the gorge through a "side door", which offers an alternate entry point for AChE inhibitors as compared to the usual substrate entry point of the gorge. Together with results from experiments, these simulations provide mechanistic insights into the mixed type of inhibition for AChE using DPDSe as a promising inhibitor for AChE.

(PhSe)2 and (pCl-PhSe)2 organochalcogen compounds inhibit Candida albicans adhesion to human endocervical (HeLa) cells and show anti-biofilm activities

Adhesion capacity on biological surfaces and biofilm formation is considered an important step in the infection process by Candida albicans. The ability of (PhSe)₂ and (pCl-PhSe)₂, two synthetic organic selenium (organochalcogen) compounds, to act on C. albicans virulence factors related to adhesion to human endocervical (HeLa) cell surfaces and their anti-biofilm activities was analyzed. Both organochalcogen compounds inhibited C. albicans adhesion to HeLa cells, dependent on compound concentrations. (PhSe)₂ (at 20 µM; p = 0.0012) was significantly more effective than (pCl-PhSe)₂ (at 20 µM; p = 0.0183) compared with the control. (PhSe)₂ inhibited biofilm formation and decreased biofilm viability in both early and mature biofilms more efficiently than (pCl-PhSe)₂. Overall, the organochalcogen compounds, especially (PhSe)₂, were demonstrated to be effective antifungal drugs against C. albicans virulence factors related to epithelial cell surface adhesion and the formation and viability of biofilms.

Selenium Compounds as Novel Potential Anticancer Agents

The high number of new cancer incidences and the associated mortality continue to be alarming, leading to the search for new therapies that would be more effective and less burdensome for patients. As there is evidence that Se compounds can have chemopreventive activity, studies have begun to establish whether these compounds can also affect already existing cancers. This review aims to discuss the different classes of Se-containing compounds, both organic and inorganic, natural and synthetic, and the mechanisms and molecular targets of their anticancer activity. The chemical classes discussed in this paper include inorganic (selenite, selenate) and organic compounds, such as diselenides, selenides, selenoesters, methylseleninic acid, 1,2-benzisoselenazole-3[2H]-one and selenophene-based derivatives, as well as selenoamino acids and Selol.

Design of Pegylated-Nanocapsules to Diphenyl Diselenide Administration: In Vitro Evidence of Hemocompatible and Selective Antiglioma Formulation

Diphenyl diselenide [(PhSe)₂] is a pleiotropic pharmacological agent, but it has low aqueous solubility. The nanoencapsulation of (PhSe)₂ allowed the preparation of an aqueous formulation as well as potentiated its in vitro antitumor effect and the effectiveness in a preclinical model of glioblastoma when administered by the intragastric route. Thus, aiming at maximizing the therapeutic potential of (PhSe)₂, the present study designed a pegylated-formulation intending to intravenous administration of the (PhSe)₂ as a new approach for glioma therapy. The poly(Ɛ-caprolactone) nanocapsules containing (PhSe)₂ were physically coated with polyethyleneglycol (PEG) using the preformed polymer interfacial deposition technique and evaluated through physicochemical, morphological, spectroscopic, and thermal characteristics. Hemocompatibility was determined by the in vitro hemolysis test and cytotoxicity assays were performed in astrocytes and glioma C6 cells (10-100 μM). The pegylated-nanocapsules had an average diameter of 218 ± 25 nm, polydispersity index of 0.164 ± 0.046, zeta potential of - 8.1 ± 1.6 mV, pH 6.0 ± 0.09, (PhSe)₂ content of 102.00 ± 3.57%, and encapsulation efficiency around 98%. Besides, the (PhSe)₂ pegylated-nanocapsules were spherical, presented absence of chemical interaction among the constituents, and showed higher thermal stability than the non-encapsulated materials. PEG-coated nanocapsules did not cause hemolytic effect while formulations without PEG induced a hemolysis rate above 10%. Moreover, pegylated-nanocapsules had superior in vitro antiglioma effect in comparison to free compound (IC₅₀: 24.10 μM and 74.83 μM, respectively). Therefore, the (PhSe)₂-loaded pegylated-nanocapsule suspensions can be considered a hemocompatible formulation for the glioma treatment by the intravenous route.

Interferon gamma/interleukin-4 modulation, anti-inflammatory and antioxidant effects of hesperidin in complete Freund's adjuvant (CFA)-induced arthritis model of rats

BACKGROUND

This study sought to assess the effect of hesperidin on serum inflammatory cytokines and oxidative damage in liver of complete Freund's adjuvant (CFA)-induced arthritic rats.

METHOD

Fifty-six adult female Wistar rats (220-250 g) were acclimatized for two weeks. Intraplantar injection of CFA was done for the induction of arthritis and confirmed on the 14th day prior to oral administration of 40 and 80 mg/kg of hesperidin or dexamethasone for 45 days.

RESULT

The result showed that treatment with both doses of hesperidin and dexamethasone in the joint of arthritic rats significantly (p < .05) diminished paw swelling/edema and arthritis score as well as enhanced latency in thermal hyperalgesia test. In addition, hesperidin treatment in arthritis rats showed significant (p < .01) improvement in red blood cells and platelets counts as well as hemoglobin and hematocrit compared to the arthritis control rat group. Furthermore, hesperidin treatment significantly (p < .05) reduced serum interferon gamma (IFN-γ) and interleukin-4 (IL-4) levels in arthritic rat. In addition, treatment with hesperidin significantly (p < .05) decreased the liver of thiobarbituric acid reactive species and reactive oxygen species levels but raised the levels of total and non-protein thiols of rat induced with CFA. The reduced activities of liver δ-aminolevulinate dehydratase, catalase, glutathione-S transferase in arthritic rats were significantly (p < .05) increased with hesperidin treatment in arthritic rats. This study suggests that hesperidin demonstrated an anti-arthritic effect via modulation of serum IFN-γ and IL-4 levels as well as protection against oxidative damage.

CONCLUSION

Hence, hesperidin could be a potential immune-modulatory, anti-inflammatory and anti-oxidant agent.

The Se…S/N interactions as a possible mechanism of δ-aminolevulinic acid dehydratase enzyme inhibition by organoselenium compounds: A computational study

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DPDS and PSA interacts with cysteine residues from AlaD active site.

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The Se…S interactions could be involved in the δ-AlaD inhibition.

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δ-AlaD from Cucumis sativus does not present cysteine residues in the active site.

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Se…N interactions could be involved in the organoselenium action.

Organoselenium compounds present many pharmacological properties and are promising drugs. However, toxicological effects associated with inhibition of thiol-containing enzymes, such as the δ-aminolevulinic acid dehydratase (δ-AlaD), have been described. The molecular mechanism(s) by which they inhibit thiol-containing enzymes at the atomic level, is still not well known. The use of computational methods to understand the physical–chemical properties and biological activity of chemicals is essential to the rational design of new drugs. In this work, we propose an in silico study to understand the δ-AlaD inhibition mechanism by diphenyl diselenide (DPDS) and its putative metabolite, phenylseleninic acid (PSA), using δ-AlaD enzymes from Homo sapiens (Hsδ-AlaD), Drosophila melanogaster (Dmδ-AlaD) and Cucumis sativus (Csδ-AlaD). Protein modeling homology, molecular docking, and DFT calculations are combined in this study. According to the molecular docking, DPDS and PSA might bind in the Hsδ-AlaD and Dmδ-AlaD active sites interacting with the cysteine residues by Se^…S interactions. On the other hand, the DPDS does not access the active site of the Csδ-AlaD (a non-thiol protein), while the PSA interacts with the amino acids residues from the active site, such as the Lys291. These interactions might lead to the formation of a covalent bond, and consequently, to the enzyme inhibition. In fact, DFT calculations (mPW1PW91/def2TZVP) demonstrated that the selenylamide bond formation is energetically favored. The in silico data showed here are in accordance with previous experimental studies, and help us to understand the reactivity and biological activity of organoselenium compounds.

Effect of m-trifluoromethyl-diphenyl diselenide on acute and subchronic animal models of inflammatory pain: Behavioral, biochemical and molecular insights

m-Trifluoromethyl-diphenyl diselenide [(m-CF₃-PhSe)₂] is an organoselenium molecule that displays multiple pharmacological actions, including the antinociceptive effect. The current study investigated the (m-CF₃-PhSe)₂ restorative properties in models of acute and chronic inflammatory pain induced by complete Freund's adjuvant (CFA). Male adult Swiss mice received an intraplantar injection of CFA in the hindpaw and 24 h (acute) or 14 days (subchronic) later they were treated with a single or repeated (m-CF₃-PhSe)₂ schedule via intragastric route, respectively. The mechanical and thermal hypernociceptive behaviors were assessed by von Frey hair and hot plate tests. Samples of injected paw were collected to evaluate the tissue edema and myeloperoxidase (MPO) activity while cerebral contralateral cortex samples were used to determine the inflammatory proteins content (subchronic protocol). The acute (m-CF₃-PhSe)₂ administration (1 and 10 mg/kg) reduced the hypernociceptive behavior and both paw thickness and MPO activity induced by CFA injection. In the subchronic protocol, the repeated administration with a low effective dosage of (m-CF₃-PhSe)₂ reduced the mechanical and thermal hypernociception as well as restored the edema and MPO activity in paw samples. In addition, the repeated treatment schedule mitigated the increase in TNF-α, IL-1β and COX-2 content in cerebral contralateral cortex induced by CFA injection. Collectively, these data showed that (m-CF₃-PhSe)₂ presents anti-inflammatory properties, which could be mediated by an interplay between peripheral and central mechanisms of action, reinforcing the potential biological properties of the compound.

Antitumor action of diphenyl diselenide nanocapsules: In vitro assessments and preclinical evidence in an animal model of glioblastoma multiforme

BACKGROUND

Gliomas are the most aggressive malignant tumors of the central nervous system. The diphenyl diselenide [(PhSe)₂] is an organoselenium compound that has multiple pharmacological properties. Previous reports showed that (PhSe)₂ nanoencapsulation potentiates its in vitro antitumoral action and reduces its toxicity.

OBJECTIVE

In this sense, the current study was designed to further evaluate the (PhSe)₂ antitumoral effect by a set of in vitro techniques using a glioma cell line as well as by an animal model of gliobastoma.

METHODS

For the in vitro tests, the cell viability, propidium iodide uptake and nitrite levels of rat glioma C6 cells were determined after incubation with free (PhSe)₂ or (PhSe)₂-loaded nanocapsules (NC). The glioblastoma model was induced by implantation of C6 glioma cells in the right striatum of rats. Following, animals were submitted to a repeated intragastric administration treatment with (PhSe)₂ or NC (PhSe)₂ (1 mg/kg/day for 15 days) to assess the possible antitumor effect.

MAIN FINDINGS

Both compound forms decreased the C6 glioma cells viability without causing any effect in astrocytes cells (healthy control). Importantly, the NC (PhSe)₂ had superior cytotoxic effect than its free form and increased the nitrite content. Independent of the (PhSe)₂ forms, the intragastric treatment reduced brain tumor size and caused neither alteration in the plasma renal and hepatic markers of function nor in the parameters of oxidative balance in brain, liver and kidneys.

PRINCIPAL CONCLUSIONS

The (PhSe)₂ nanoencapsulation improved its cytotoxic effect against C6 glioma cells and both compound forms attenuated the tumor development.

Zebrafish exposure to diphenyl diselenide-loaded polymeric nanocapsules caused no behavioral impairments and brain oxidative stress

Previous findings showed that the nanoencapsulation of diphenyl diselenide [(PhSe)₂], an organoselenium compound, provided superior biological effects and lower toxicological potential than its free form in vitro. However, few studies reported the behavioral and biochemical effects of this nanocapsules formulation in vivo. Zebrafish (Danio rerio) has emerged as a useful animal model to determine the pharmacological and toxicological effects of nanoparticles. Here, we evaluated the behavioral and brain oxidative effects after zebrafish exposure to (PhSe)₂-loaded nanocapsules. Formulations were prepared by interfacial deposition of preformed polymer method and later tested at concentrations ranging from 0.1 to 2.0 μM. Both locomotor and exploratory activities were assessed in the novel tank diving test. Moreover, brain oxidative status was determined by measuring thiobarbituric acid-reactive substance levels, glutathione peroxidase, glutathione redutase and glutathione S-transferase activities. (PhSe)₂-loaded nanocapsules showed no alteration on travelled distance, immobility, and erratic swimming, suggesting the absence of behavioral impairments. Interestingly, the higher concentration tested had anxiolytic-like effects, since animals spent more time in the top area and showed a decreased thigmotaxis behavior. Biochemical analysis demonstrated that the concentrations used in this study did not affect oxidative stress-related parameters in brain samples, reinforcing the low toxicological potential of the formulation. In conclusion, the exposure to (PhSe)₂-loaded nanocapsules caused no locomotor impairments as well as did not modify the oxidative status of zebrafish brain, indicating that this formulation is probably non-toxic and promising for future pharmacological studies.

Health benefits of subcutaneous zinc edetate and diphenyl diselenide in calves during the weaning period

The aims of this study were to investigate whether treatments with zinc edetate (Zn) and diphenyl diselenide ((PhSe)2) enhance performance, immune responses, protein metabolism, and oxidant/antioxidant status in calf serum and muscle. Animals were divided into four groups (n=6 each): control (without supplementation), and groups supplemented on days 50 and 70 of life with (PhSe)2, Zn, and a combination of (PhSe)2 and Zn. Animals treated with (PhSe)2 gained more weight by experimental day 220 than did the control group, but there was no difference by the end of the experiment (day 300). The absolute number of leukocytes and lymphocytes increased in groups Zn and (PhSe)2+Zn on day 20 of experiment, but decreased on day 40 in groups (PhSe)2, and (PhSe)2+Zn. The number of monocytes decreased in all groups compared with control. One of the principal findings was that (PhSe)2+Zn together had beneficial effects on protein metabolism, represented by increases total protein and globulin levels, compared with the control group. The combination of (PhSe)2 and Zn led to low levels of TBARS and ROS in serum and muscle, and stimulated antioxidant enzyme activities. Thus, supplementation with (PhSe)2+Zn may be a compelling approach to augmenting the calf antioxidant system during weaning.

Cytoprotective and antioxidant properties of organic selenides for the myelin-forming cells, oligodendrocytes

Here a new series of twenty-one organoselenides, of potential protective activity, were synthesized and tested for their intrinsic cytotoxicity, anti-apoptotic and antioxidant capacities in oligodendrocytes. Most of the organoselenides were able to decrease the ROS levels, revealing antioxidant properties. Compounds 5b and 7b showed a high glutathione peroxidase (GPx)-like activities, which were 1.5 folds more active than ebselen. Remarkably, compound 5a diminished the formation of the oligodendrocytes SubG1 peak in a concentration-dependent manner, indicating its anti-apoptotic properties. Furthermore, based on the SwissADME web interface, we performed an in-silico structure-activity relationship to explore the drug-likeness of these organoselenides, predicting the pharmacokinetic parameters for compounds of interest that could cross the blood-brain barrier. Collectively, we present new organoselenide compounds with cytoprotective and antioxidant properties that can be considered as promising drug candidates for myelin diseases.

Investigation into the intracellular fates, speciation and mode of action of selenium-containing neuroprotective agents using XAS and XFM

BACKGROUND

A variety of selenium compounds have been observed to provide protection against oxidative stress, presumably by mimicking the mechanism of action of the glutathione peroxidases. However, the selenium chemistry that underpins the action of these compounds has not been unequivocally established.

METHODS

The synchrotron based techniques, X-ray absorption spectroscopy and X-ray fluorescence microscopy were used to examine the cellular speciation and distribution of selenium in SH-SY5Y cells pretreated with one of two diphenyl diselenides, or ebselen, followed by peroxide insult.

RESULTS

Bis(2-aminophenyl)diselenide was shown to protect against oxidative stress conditions which mimic ischemic strokes, while its nitro analogue, bis(2-nitrophenyl)diselenide did not. This protective activity was tentatively assigned to the reductive cleavage of bis(2-aminophenyl)diselenide inside human neurocarcinoma cells, SH-SY5Y, while bis(2-nitrophenyl)diselenide remained largely unchanged. The distinct chemistries of the related compounds were traced by the changes in selenium speciation in bulk pellets of treated SH-SY5Y cells detected by X-ray absorption spectroscopy. Further, bis(2-aminophenyl)diselenide, like the known stroke mitigation agent ebselen, was observed by X-ray fluorescence imaging to penetrate into the nucleus of SH-SY5Y cells while bis(2-nitrophenyl)diselenide was observed to be excluded from the nuclear region.

CONCLUSIONS

The differences in activity were thus attributed to the varied speciation and cellular localisation of the compounds, or their metabolites, as detected by X-ray absorption spectroscopy and X-ray fluorescence microscopy.

SIGNIFICANCE

The work is significant as it links, for the first time, the protective action of selenium compounds against redox stress with particular chemical speciation using a direct measurement approach.

Induction of reactive oxygen species by diphenyl diselenide is preceded by changes in cell morphology and permeability in Saccharomyces cerevisiae

Organoselenium compounds, such as diphenyl diselenide (PhSe)₂ and phenylselenium zinc chloride (PhSeZnCl), show protective activities related to their thiol peroxidase activity. However, depending on experimental conditions, organoselenium compounds can cause toxicity by oxidising thiol groups of proteins and induce the production of reactive oxygen species (ROS). Here, we analysed the toxicity of (PhSe)₂ and PhSeZnCl in yeast Saccharomyces cerevisiae. Cell growth of S. cerevisiae after 1, 2, 3, 4, 6, and 16 h of treatment with 2, 4, 6, and 10 μM of (PhSe)₂ was evaluated. For comparative purpose, PhSeZnCl was analysed only at 16 h of incubation at equivalent concentrations of selenium (i.e. 4, 8, 12, and 20 μM). ROS production (DCFH-DA), size, granularity, and cell membrane permeability (propidium iodide) were determined by flow cytometry. (PhSe)₂ inhibited cell growth at 2 h (10 μM) of incubation, followed by increase in cell size. The increase of cell membrane permeability and granularity (10 μM) was observed after 3 h of incubation, however, ROS production occurs only at 16 h of incubation (10 μM) with (PhSe)₂, indicating that ROS overproduction is a more likely consequence of (PhSe)₂ toxicity and not its determinant. All tested parameters showed that only concentration of 20 μM induced toxicity in samples incubated with PhSeZnCl. In summary, the results suggest that (PhSe)₂ toxicity in S. cerevisiae is time and concentration dependent, presenting more toxicity when compared with PhSeZnCl.

Diphenyl diselenide derivatives inhibit microbial biofilm formation involved in wound infection

Background

Organoselenium compounds have antimicrobial activity against some bacteria and fungi; furthermore, the antioxidant activity of diselenides has been demonstrated. The aim of the present work was to examine the in vitro minimal inhibitory concentration of a panel of differently substituted diselenides and their effectiveness in inhibiting biofilm formation and dispersing preformed microbial biofilm of Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus pyogenes and Pseudomonas aeruginosa and the yeast Candida albicans, all involved in wound infections. Moreover, the cytotoxicity of the compounds was determined in human dermal fibroblast and keratinocytes. In closing, we tested their direct antioxidant activity.

Results

Diselenides showed different antimicrobial activity, depending on the microorganism. All diselenides demonstrated a good antibiofilm activity against S. aureus and S. epidermidis, the compounds camphor diselenide, bis[ethyl-N-(2’-selenobenzoyl) glycinate] and bis[2’-seleno-N-(1-methyl-2-phenylethyl) benzamide] were active against S. pyogenes and C. albicans biofilm while only diselenides 2,2’-diselenidyldibenzoic acid and bis[ethyl-N-(2’-selenobenzoyl) glycinate] were effective against P. aeruginosa. Moreover, the compounds bis[ethyl-N-(2’-selenobenzoyl) glycinate] and bis[2’-seleno-N-(1-methyl-2-phenylethyl) benzamide] showed an antioxidant activity at concentrations lower than the 50 % of cytotoxic concentration.

Conclusions

Because microbial biofilms are implicated in chronic infection of wounds and treatment failure, the combination of antimicrobial activity and potential radical scavenging effects may contribute to the improvement of wound healing. Therefore, this study suggests that bis[ethylN-(2’-selenobenzoyl) glycinate] and bis[2’-seleno-N-(1-methyl-2-phenylethyl) benzamide] are promising compounds to be used in preventing and treating microbial wound infections.

Diphenyl Diselenide Protects Against Mortality, Locomotor Deficits and Oxidative Stress in Drosophila melanogaster Model of Manganese-Induced Neurotoxicity

Several experimental and epidemiological reports have associated manganese exposure with induction of oxidative stress and locomotor dysfunctions. Diphenyl diselenide (DPDS) is widely reported to exhibit antioxidant, anti-inflammatory and neuroprotective effects in in vitro and in vivo studies via multiple biochemical mechanisms. The present study investigated the protective effect of DPDS on manganese-induced toxicity in Drosophila melanogaster. The flies were exposed, in a dietary regimen, to manganese alone (30 mmol per kg) or in combination with DPDS (10 and 20 µmol per kg) for 7 consecutive days. Exposure to manganese significantly (p < 0.05) increased flies mortality, whereas the survivors exhibited significant locomotor deficits with increased acetylcholinesterase (AChE) activity. However, dietary supplementation with DPDS caused a significant decrease in mortality, improvement in locomotor activity and restoration of AChE activity in manganese-exposed flies. Additionally, the significant decreases in the total thiol level, activities of catalase and glutathione-S-transferase were accompanied with significant increases in the generation of reactive oxygen and nitrogen species and thiobarbituric acid reactive substances in flies exposed to manganese alone. Dietary supplementation with DPDS significantly augmented the antioxidant status and prevented manganese-induced oxidative stress in the treated flies. Collectively, the present data highlight that DPDS may be a promising chemopreventive drug candidate against neurotoxicity resulting from acute manganese exposure.

Promising link between selenium and peroxisome proliferator activated receptor gamma in the treatment protocols of obesity as well as depression

Considerable interest has been given to the significance of peroxisome proliferator activated receptors (PPARs) in macronutrient metabolism, however, there is not sufficient data concerning the interactions between PPARs and micronutrients. Investigations performed on PPARγ and one of the essential micronutrients selenium (Se) have shown that both parameters may lead to alterations in obesity-related or mood disorders. Therefore, it is plausible to consider PPARγ and Se together as a powerful combination during the treatment of two associated diseases; obesity and depression. PPARγ has been shown to be involved in the antidepressant-like activity. It is also an important parameter to be considered in obesity as the master regulator of adipogenesis. The mechanism of action of PPARγ is initiated by ligand binding which induces a conformational change in the receptor. Se is capable of alleviating inflammatory signaling pathways. Obesity is associated with chronic low-grade inflammation. Depression is also defined as an inflammatory disorder. Inflammatory mediators such as tumor necrosis factor-alpha (TNFα) participate in the progression of depression. They are also obesity-associated parameters. Due to TNFα induced depressive-like behaviors and the positive association between this proinflammatory cytokine and obesity, TNFα-activated signaling pathways and those inhibiting them have recently gained importance as potential targets and therapeutic tools, respectively. More studies are necessary to develop compounds with therapeutic nature against depressive disorders and obesity. PPARγ is an important signaling pathway that occurs at the crossroads of depression and obesity. Se, aside from its anti-inflammatory, anticarcinogenic and antioxidative nature, affects also the way of PPARγ action. Se supplementation or fortification as well as the development of the partial agonists of PPARγ in which lipophilic Se compounds are used as ligand followed by experimental trials and human studies using the newly developed compounds will be promising approaches for future hope during the treatment of these diseases.

Free radical scavenging in vitro and biological activity of diphenyl diselenide-loaded nanocapsules: DPDS-NCS antioxidant and toxicological effects

Selenium compounds, such as diphenyl diselenide (DPDS), have been shown to exhibit biological activity, including antioxidant effects. However, the use of DPDS in pharmacology is limited due to in vivo pro-oxidative effects. In addition, studies have shown that DPDS-loaded nanocapsules (DPDS-NCS) have greater bioavailability than free DPDS in mice. Accordingly, the aim of this study was to investigate the antioxidant properties of DPDS-NCS in vitro and biological activity in mice. Our in vitro results suggested that DPDS-NCS significantly reduced the production of reactive oxygen species and Fe(II)-induced lipid peroxidation (LPO) in brain. The administration of DPDS-NCS did not result in death or change the levels of endogenous reduced or oxidized glutathione after 72 hours of exposure. Moreover, ex vivo assays demonstrated that DPDS-NCS significantly decreased the LPO and reactive oxygen species levels in the brain. In addition, the highest dose of DPDS-NCS significantly reduced Fe(II)- and sodium nitroprusside-induced LPO in the brain and Fe(II)-induced LPO in the liver. Also, δ-aminolevulinate acid dehydratase within the brain was inhibited only in the highest dose of DPDS-NCS. In conclusion, our data demonstrated that DPDS-NCS exhibited low toxicity in mice and have significant antioxidant characteristics, indicating that nanoencapsulation is a safer method of DPDS administration.

Diphenyl diselenide (PhSe)2 inhibits biofilm formation by Candida albicans, increasing both ROS production and membrane permeability

PROJECT

The opportunistic fungal Candida albicans can produce superficial and systemic infections in immunocompromised patients. An essential stage to both colonization and virulence by C. albicans is the transition from budding yeast form to filamentous form, producing biofilms.

PROCEDURE

In this work, we studied the effect of the organochalcogenide compound (PhSe)2 on both cell growth and biofilm formation by C. albicans.

RESULTS

(PhSe)2 inhibited both growth and biofilm formation by C. albicans. The inhibitory effects of (PhSe)2 depended on the cell density and (PhSe)2 concentration. We have also observed that (PhSe)2 stimulated ROS production (67%) and increased cell membrane permeability (2.94-fold) in C. albicans. In addition, (PhSe)2 caused a marked decrease in proteinase activity (6.8-fold) in relation to non-treated group.

CONCLUSIONS

(PhSe)2 decreased both cell growth and biofilm development, decreasing the release of extracellular proteinases, which is an important facet of C. albicans pathogenicity. The toxicity of (PhSe)2 towards C. albicans can be associated with an increase in ROS production, which can increase cell permeability. The permanent damage to the cell membranes can culminate in cell death.

Effects of organoselenium compounds on early and late brain biochemical alterations in sepsis-survivor rats

Studies have consistently reported the participation of oxidative stress, energetic metabolism impairment, and creatine kinase (CK) activity alterations in rat brain in early times in an animal model of sepsis and persist for up to 10 days. We have assessed the antioxidant effects of administration of Ebselen (Eb) e diphenyl diselenide (PhSe)2 two organoselenium compounds on brain oxidative stress, energetic metabolism, and CK activity 12, 24 h, and 10 days after sepsis by cecal ligation and perforation (CLP) in rats. Male Wistar rats underwent either sham operation or CLP and were treated with oral injection of Eb (50 mg/kg) or (PhSe)2 (50 mg/kg) or vehicle. 12, 24 h, and 10 days after CLP, the rats were sacrificed, and samples from brain (hippocampus, striatum, cerebellum, prefrontal cortex, and cortex) were obtained and assayed for thiobarbituric acid reactive species and protein carbonyls formation, mitochondrial respiratory chain, and CK activity. We observed in the results a reduction of oxidative damage to lipids and proteins in the different cerebral structures studied and times with the administration of (PhSe)2; however, Eb seems to exert the same effect. Such changes are reflected in the assessment of mitochondrial respiratory chain complexes by reversing the decreased activity of the complex caused by the model of CLP and CK activity. Our data provide the first experimental demonstration that (PhSe)2 was able to reduce the brain dysfunction associated with CLP-induced sepsis in rats, by decreasing oxidative stress parameters mitochondrial dysfunction and CK activity in early times and in late time.

Stable selones in glutathione-peroxidase-like catalytic cycle of selenonicotinamide derivative

Stable selone formation in 2,2′-diselenobis[3-amidopyridine], reduces unwanted sulfur exchange reaction in glutathione peroxidase like catalytic cycle and enhances its enzyme activity.

Diphenyl diselenide prevents cortico-cerebral mitochondrial dysfunction and oxidative stress induced by hypercholesterolemia in LDL receptor knockout mice

Recent studies have indicated a causal link between high dietary cholesterol intake and brain oxidative stress. In particular, we have previously shown a positive correlation between elevated plasma cholesterol levels, cortico-cerebral oxidative stress and mitochondrial dysfunction in low density lipoprotein receptor knockout (LDLr(-/-)) mice, a mouse model of familial hypercholesterolemia. Here we show that the organoselenium compound diphenyl diselenide (PhSe)2 (1 mg/kg; o.g., once a day for 30 days) significantly blunted the cortico-cerebral oxidative stress and mitochondrial dysfunction induced by a hypercholesterolemic diet in LDLr(-/-) mice. (PhSe)2 effectively prevented the inhibition of complex I and II activities, significantly increased the reduced glutathione (GSH) content and reduced lipoperoxidation in the cerebral cortex of hypercholesterolemic LDLr(-/-) mice. Overall, (PhSe)2 may be a promising molecule to protect against hypercholesterolemia-induced effects on the central nervous system, in addition to its already demonstrated antiatherogenic effects.

The influence of micronutrients in cell culture: a reflection on viability and genomic stability

Micronutrients, including minerals and vitamins, are indispensable to DNA metabolic pathways and thus are as important for life as macronutrients. Without the proper nutrients, genomic instability compromises homeostasis, leading to chronic diseases and certain types of cancer. Cell-culture media try to mimic the in vivo environment, providing in vitro models used to infer cells' responses to different stimuli. This review summarizes and discusses studies of cell-culture supplementation with micronutrients that can increase cell viability and genomic stability, with a particular focus on previous in vitro experiments. In these studies, the cell-culture media include certain vitamins and minerals at concentrations not equal to the physiological levels. In many common culture media, the sole source of micronutrients is fetal bovine serum (FBS), which contributes to only 5-10% of the media composition. Minimal attention has been dedicated to FBS composition, micronutrients in cell cultures as a whole, or the influence of micronutrients on the viability and genetics of cultured cells. Further studies better evaluating micronutrients' roles at a molecular level and influence on the genomic stability of cells are still needed.

Comparative excretion and tissue distribution of selenium in mice and rats following treatment with diphenyl diselenide

The purpose of this study was to provide data about in vivo tissue distribution and excretion of diphenyl diselenide ((PhSe)₂) in rats and mice through determination of selenium levels in different biological samples. (PhSe)₂ (500 mg/kg, dissolved in canola oil) was administered to animals once a day per oral. After this, mice and rats were housed in metabolic cages (one animal per cage) and urine and feces were collected at specific times after treatment. Three to five animals per group (for each time-point) were anesthetized and blood samples were collected at 0 and 30 min, 24 h, at day 5, 15, and 30 after (PhSe)₂ administration. The plasma and red blood cells were separated. Brain, liver, lungs, kidneys, and adipose tissue were also collected. The determination of selenium levels was performed by inductively coupled plasma atomic emission spectrometry. The main results indicate that: (1) urine is an important route of excretion of selenium originated from (PhSe)₂ in mice and rats; (2) a large amount of (PhSe)₂ or some of its metabolites are stored in fat; (3) the content of selenium found in plasma was low; and (4) liver and kidneys are the tissues with high amounts of selenium.

Diphenyl diselenide in vitro and in vivo activity against the oomycete Pythium insidiosum

This study evaluated the in vitro activity of diphenyl diselenide against 19 Pythium insidiosum isolates and the in vivo therapeutic response of rabbits with experimentally induced pythiosis. In vitro: susceptibility tests were performed using the broth macrodilution method in accordance with the CLSI document M38-A2. The criteria for interpretation were as follows: MIC-1 and MIC-2 (inhibition of 90% and 100% of mycelium growth, respectively) and the minimum fungicide concentration (MIC-3). In vivo: twenty rabbits were divided into four groups with five animals each and treated for 40 consecutive days: groups 1 and 2 (experimentally induced pythiosis) were treated with diphenyl diselenide (10mg/kg/day) and canola oil (1 mL/kg/day), respectively; groups 3 and 4 (controls) were treated with canola oil (1 mL/kg/day) and diphenyl diselenide (10mg/kg/day), respectively. Toxicity was evaluated using biochemical and haematological parameters. In vitro susceptibility tests showed that 89.4% of isolates had a MIC-1 ≤ 0.5 μg/mL, 84.2% of isolates had a MIC-2 ≤ 1.0 μg/mL and 94.7% of isolates had a MIC-3 ≤ 2.0 μg/mL. The in vivo assay suggested that this compound has a fungistatic activity, and the biochemical and haematological parameters indicated that there was no renal, hepatic or haematological toxicity. The comparison of the unsaturated iron binding capacity levels between animals with and without pythiosis suggested the involvement of iron metabolism in the pathogenesis of pythiosis. This study demonstrated the absence of detectable toxicity caused by diphenyl diselenide and the in vitro fungicidal and in vivo fungistatic activities of this drug, which makes it an option for future therapeutic approaches in the treatment of pythiosis.

Reduction of diphenyl diselenide and analogs by mammalian thioredoxin reductase is independent of their gluthathione peroxidase-like activity: a possible novel pathway for their antioxidant activity

Since the successful use of the organoselenium drug ebselen in clinical trials for the treatment of neuropathological conditions associated with oxidative stress, there have been concerted efforts geared towards understanding the precise mechanism of action of ebselen and other organoselenium compounds, especially the diorganyl diselenides such as diphenyl diselenide, and its analogs. Although the mechanism of action of ebselen and other organoselenium compounds has been shown to be related to their ability to generally mimic native glutathione peroxidase (GPx), only ebselen however has been shown to serve as a substrate for the mammalian thioredoxin reductase (TrxR), demonstrating another component of its pharmacological mechanisms. In fact, there is a dearth of information on the ability of other organoselenium compounds, especially diphenyl diselenide and its analogs, to serve as substrates for the mammalian enzyme thioredoxin reductase. Interestingly, diphenyl diselenide shares several antioxidant and neuroprotective properties with ebselen. Hence in the present study, we tested the hypothesis that diphenyl diselenide and some of its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxy-diphenyl diselenide, 4.4'-biscarboxydiphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could also be substrates for rat hepatic TrxR. Here we show for the first time that diselenides are good substrates for mammalian TrxR, but not necessarily good mimetics of GPx, and vice versa. For instance, bis-methoxydiphenyl diselenide had no GPx activity, whereas it was a good substrate for reduction by TrxR. Our experimental observations indicate a possible dissociation between the two pathways for peroxide degradation (either via substrate for TrxR or as a mimic of GPx). Consequently, the antioxidant activity of diphenyl diselenide and analogs can be attributed to their capacity to be substrates for mammalian TrxR and we therefore conclude that subtle changes in the aryl moiety of diselenides can be used as tool for dissociation of GPx or TrxR pathways as mechanism triggering their antioxidant activities.

Reduction of diphenyl diselenide and analogs by mammalian thioredoxin reductase is independent of their gluthathione peroxidase-like activity: a possible novel pathway for their antioxidant activity

Since the successful use of the organoselenium drug ebselen in clinical trials for the treatment of neuropathological conditions associated with oxidative stress, there have been concerted efforts geared towards understanding the precise mechanism of action of ebselen and other organoselenium compounds, especially the diorganyl diselenides such as diphenyl diselenide, and its analogs. Although the mechanism of action of ebselen and other organoselenium compounds has been shown to be related to their ability to generally mimic native glutathione peroxidase (GPx), only ebselen however has been shown to serve as a substrate for the mammalian thioredoxin reductase (TrxR), demonstrating another component of its pharmacological mechanisms. In fact, there is a dearth of information on the ability of other organoselenium compounds, especially diphenyl diselenide and its analogs, to serve as substrates for the mammalian enzyme thioredoxin reductase. Interestingly, diphenyl diselenide shares several antioxidant and neuroprotective properties with ebselen. Hence in the present study, we tested the hypothesis that diphenyl diselenide and some of its analogs (4,4'-bistrifluoromethyldiphenyl diselenide, 4,4'-bismethoxy-diphenyl diselenide, 4.4'-biscarboxydiphenyl diselenide, 4,4'-bischlorodiphenyl diselenide, 2,4,6,2',4',6'-hexamethyldiphenyl diselenide) could also be substrates for rat hepatic TrxR. Here we show for the first time that diselenides are good substrates for mammalian TrxR, but not necessarily good mimetics of GPx, and vice versa. For instance, bis-methoxydiphenyl diselenide had no GPx activity, whereas it was a good substrate for reduction by TrxR. Our experimental observations indicate a possible dissociation between the two pathways for peroxide degradation (either via substrate for TrxR or as a mimic of GPx). Consequently, the antioxidant activity of diphenyl diselenide and analogs can be attributed to their capacity to be substrates for mammalian TrxR and we therefore conclude that subtle changes in the aryl moiety of diselenides can be used as tool for dissociation of GPx or TrxR pathways as mechanism triggering their antioxidant activities.