Selenate enhances STAT3 transcriptional activity in endothelial cells: differential actions of selenate and selenite on LIF cytokine signaling and cell viability

Selenium and selenoproteins: from endothelial cytoprotection to clinical outcomes

The role of the vascular endothelium in inflammation was demonstrated experimentally through biomarkers of endothelial dysfunction and cytoprotection. Selenium is a trace element essential for cell protection against oxidative lesions triggered by reactive oxygen species or inflammatory responses. Preclinical studies have demonstrated a relationship between adhesion molecules as biomarkers of endothelial dysfunction and selenoproteins as biomarkers of selenium status under conditions that mimic different diseases. Most studies in humans indicate an association between selenium deficiency and increased risk of morbidity and mortality, yet the pathophysiology of selenium in endothelial activation remains unknown. Here, we summarize selenium-dependent endothelial function evaluation techniques and focus on the role of selenium in endothelial cytoprotection according to current scientific knowledge. Most studies on the role of selenium in endothelial processes show selenium-dependent endothelial functions and explain how cells and tissues adapt to inflammatory insults. Taken together, these studies show an increase in adhesion molecules and a decrease in the expression of selenoproteins following a decreased exposure to selenium. Few clinical trials have enough methodological quality to be included in meta-analysis on the benefits of selenium supplementation. Furthermore, the methodology adopted in many studies does not consider the relevant findings on the pathophysiology of endothelial dysfunction. Preclinical studies should be more frequently integrated into clinical studies to provide clearer views on the role of selenium status in endothelial cytoprotection.

Responses of an American eel brain endothelial-like cell line to selenium deprivation and to selenite, selenate, and selenomethionine additions in different exposure media

The effect of selenium deprivation and addition on the American eel brain endothelial cell line (eelB) was studied in three exposure media: complete growth medium (L15/FBS), serum-free medium (L15), and minimal medium (L15/ex). L15/ex contains only galactose and pyruvate and allowed the deprivation of selenium on cells to be studied. In L15/ex, without any obvious source of selenium, eelB cells survived for at least 7 d, formed capillary-like structures (CLS) on Matrigel, and migrated to heal wounds. Three selenium compounds were added to cultures: selenite, selenate, and selenomethionine (SeMet). Adding selenite or selenate to eelB cell cultures for 24 h caused dose-dependent declines in cell viability, regardless of the exposure media. Although varying with exposure media and viability end point, selenite was approximately 70-fold more cytotoxic than selenate. By contrast, 24 h exposures to either DL- or L-SeMet in the three media caused little or no cytotoxicity. However for 7 d exposures in L15/ex, DL- and L-SeMet were very cytotoxic, even at the lowest tested concentration of 31 μM. By contrast in L15 and L15/FBS, cytotoxicity was only observed with 500 and 1000 μM L-SeMet. In L15/FBS, eelB continued to migrate and form CLS in the presence of SeMet but at 500 μM, cell migration appeared stimulated. As judged from a colony-forming assay over 14 d in L15/FBS, 500 and 1000 μM DL- and L-SeMet inhibited cell proliferation. Overall, the responses of eel cells to selenium depended on the selenium form, concentration, and exposure media, with responses to SeMet being most dependent on exposure media.

Cerebrospinal fluid of newly diagnosed amyotrophic lateral sclerosis patients exhibits abnormal levels of selenium species including elevated selenite

Exposure to selenium, and particularly to its inorganic forms, has been hypothesized as a risk factor for amyotrophic lateral sclerosis (ALS), a fast progressing motor neuron disease with poorly understood etiology. However, no information is known about levels of inorganic and some organic selenium species in the central nervous system of ALS patients, and recent observations suggest that peripheral biomarkers of exposure are unable to predict these levels for several Se species including the inorganic forms. Using a hospital-referred case-control series and advanced selenium speciation methods, we compared the chemical species of selenium in cerebrospinal fluid from 38 ALS patients to those of 38 reference neurological patients matched on age and gender. We found that higher concentrations of inorganic selenium in the form of selenite and of human serum albumin-bound selenium were associated with increased ALS risk (relative risks 3.9 (95% confidence interval 1.2-11.0) and 1.7 (1.0-2.9) for 0.1μg/L increase). Conversely, lower concentrations of selenoprotein P-bound selenium were associated with increased risk (relative risk 0.2 for 1μg/L increase, 95% confidence interval 0.04-0.8). The associations were stronger among cases age 50 years or older, who are postulated to have lower rates of genetic disease origin. These results suggest that excess selenite and human serum albumin bound-selenium and low levels of selenoprotein P-bound selenium in the central nervous system, which may be related, may play a role in ALS etiology.

Acyloxy nitroso compounds inhibit LIF signaling in endothelial cells and cardiac myocytes: evidence that STAT3 signaling is redox-sensitive

We previously showed that oxidative stress inhibits leukemia inhibitory factor (LIF) signaling by targeting JAK1, and the catalytic domains of JAK 1 and 2 have a cysteine-based redox switch. Thus, we postulated that the NO sibling and thiophylic compound, nitroxyl (HNO), would inhibit LIF-induced JAK-STAT3 activation. Pretreatment of human microvascular endothelial cells (HMEC-1) or neonatal rat cardiomyocytes with the HNO donors Angeli’s salt or nitrosocyclohexyl acetate (NCA) inhibited LIF-induced STAT3 activation. NCA pretreatment also blocked the induction of downstream inflammatory genes (e.g. intercellular adhesion molecule 1, CCAAT/enhancer binding protein delta). The related 1-nitrosocyclohexyl pivalate (NCP; not a nitroxyl donor) was equally effective in inhibiting STAT3 activation, suggesting that these compounds act as thiolate targeting electrophiles. The JAK1 redox switch is likely not a target of acyloxy nitroso compounds, as NCA had no effect on JAK1 catalytic activity and only modestly affected JAK1-induced phosphorylation of the LIF receptor. However, pretreatment of recombinant human STAT3 with NCA or NCP reduced labeling of free sulfhydryl residues. We show that NCP in the presence of diamide enhanced STAT3 glutathionylation and dimerization in adult mouse cardiac myocytes and altered STAT3 under non-reducing conditions. Finally, we show that monomeric STAT3 levels are decreased in the Gαq model of heart failure in a redox-sensitive manner. Altogether, our evidence indicates that STAT3 has redox-sensitive cysteines that regulate its activation and are targeted by HNO donors and acyloxy nitroso compounds. These findings raise the possibility of new therapeutic strategies to target STAT3 signaling via a redox-dependent manner, particularly in the context of cardiac and non-cardiac diseases with prominent pro-inflammatory signaling.