Characteristics of selenazolidine prodrugs of selenocysteine: toxicity, selenium levels, and glutathione peroxidase induction in A/J mice

Differential Inhibition of Anaplerotic Pyruvate Carboxylation and Glutaminolysis-Fueled Anabolism Underlies Distinct Toxicity of Selenium Agents in Human Lung Cancer

Past chemopreventive human trials on dietary selenium supplements produced controversial outcomes. They largely employed selenomethionine (SeM)-based diets. SeM was less toxic than selenite or methylseleninic acid (MSeA) to lung cancer cells. We thus investigated the toxic action of these Se agents in two non-small cell lung cancer (NSCLC) cell lines and ex vivo organotypic cultures (OTC) of NSCLC patient lung tissues. Stable isotope-resolved metabolomics (SIRM) using 13C6-glucose and 13C5,15N2-glutamine tracers with gene knockdowns were employed to examine metabolic dysregulations associated with cell type- and treatment-dependent phenotypic changes. Inhibition of key anaplerotic processes, pyruvate carboxylation (PyC) and glutaminolysis were elicited by exposure to MSeA and selenite but not by SeM. They were accompanied by distinct anabolic dysregulation and reflected cell type-dependent changes in proliferation/death/cell cycle arrest. NSCLC OTC showed similar responses of PyC and/or glutaminolysis to the three agents, which correlated with tissue damages. Altogether, we found differential perturbations in anaplerosis-fueled anabolic pathways to underlie the distinct anti-cancer actions of the three Se agents, which could also explain the failure of SeM-based chemoprevention trials.

HOCl-Activated Reactive Organic Selenium Delivery Platform for Alleviation of Inflammation

Selenium plays an important role in the biological system and can be used to treat various types of diseases. However, the current selenium delivery systems face the problems of low activity of released Se-containing compounds or nonspecific toxicity of reactive organic selenium donors in living systems. In response to these problems, we constructed a reactive organic selenium delivery platform by the activation of HOCl. Compared with prodrugs without activation capability, the hypochloroselenoite derivatives released from the present platform after activation displayed higher reactivity and could react with various nucleophiles to participate in specific life processes. Taking the selected compound (DHU-Se1) as an example, we found that it could alleviate the process of inflammation by blocking the polarization of macrophages from M0 to M1. Therefore, the development of this system is of great significance for expanding the application of selenium-containing compounds and treating related diseases.

Antioxidant role of selenium against maneb-induced cardiotoxicity in mice

The current study was conducted to assess the beneficial effect of selenium (Se) on maneb-induced cardiotoxicity and fatty acid alterations in adult mice. Swiss albino male mice were assigned into four experimental groups. The first group consisted of negative controls. The second group represented the positive controls where mice received daily, via the diet, sodium selenite at a dose of 0.2 mg/kg. For the third group, mice were subjected to intraperitoneal injections of maneb (30 mg/kg BW). The fourth group (MB+Se) received daily the same dose of maneb as group 3 along with sodium selenite at the same dose as group 2. Mice exposure to maneb caused cardiotoxicity as indicated by an increase in malondialdehyde, hydrogen peroxide, and protein carbonyl levels, and an alteration of the antioxidant defense system (catalase, glutathione peroxidase, superoxide dismutase, glutathione, and vitamin C). Plasma lactate dehydrogenase activity and total cholesterol, triglyceride, and low-density lipoprotein cholesterol levels increased, while high-density lipoprotein cholesterol level decreased. Results showed also a decrease in the amount of n-3 PUFA, docosahexaenoic, docosapentaenoic, and eicosapentaenoic acids. However, an increase in the levels of MUFA, cis-vaccenic, and palmitoleic acids was observed. Co-administration of Se restored the parameters indicated above to near control values. The histopathological findings confirmed the biochemical results. Selenium could be a useful and efficient agent against maneb-induced cardiotoxicity.

Role of Proline in Pathogen and Host Interactions

SIGNIFICANCE

Proline metabolism has complex roles in a variety of biological processes, including cell signaling, stress protection, and energy production. Proline also contributes to the pathogenesis of various disease-causing organisms. Understanding the mechanisms of how pathogens utilize proline is important for developing new strategies against infectious diseases. Recent Advances: The ability of pathogens to acquire amino acids is critical during infection. Besides protein biosynthesis, some amino acids, such as proline, serve as a carbon, nitrogen, or energy source in bacterial and protozoa pathogens. The role of proline during infection depends on the physiology of the host/pathogen interactions. Some pathogens rely on proline as a critical respiratory substrate, whereas others exploit proline for stress protection.

CRITICAL ISSUES

Disruption of proline metabolism and uptake has been shown to significantly attenuate virulence of certain pathogens, whereas in other pathogens the importance of proline during infection is not known. Inhibiting proline metabolism and transport may be a useful therapeutic strategy against some pathogens. Developing specific inhibitors to avoid off-target effects in the host, however, will be challenging. Also, potential treatments that target proline metabolism should consider the impact on intracellular levels of Δ1-pyrroline-5-carboxylate, a metabolite intermediate that can have opposing effects on pathogenesis.

FUTURE DIRECTIONS

Further characterization of how proline metabolism is regulated during infection would provide new insights into the role of proline in pathogenesis. Biochemical and structural characterization of proline metabolic enzymes from different pathogens could lead to new tools for exploring proline metabolism during infection and possibly new therapeutic compounds.

Toxicological study of sodium selenite on fetal development and DNA fragmentation in liver cells of pregnant rats

The present study was carried out to evaluate the effects of sodium selenite on fetal development and DNA in liver of rats. Pregnant rats were divided into three groups: control group, group treated orally with 5 µg Se/kg body wt. and group treated orally with 10 µg Se/kg body wt. Dams were treated orally with sodium selenite from day 7 to 19 of gestation. Sodium selenite treatment revealed decrease in maternal body weight, reduction in fetal weight, length and number of viable fetuses, increased number of resorbed fetuses and post-implantation loss at the two doses tested. Fetal skeleton showed signs of developmental delay in skull and limbs of the treated groups. Sodium selenite treatment revealed significant reduction of placental and liver weights in treated dams. Sodium selenite-induced oxidative stress in liver tissue of rats as evidenced by increase in lipid peroxidation and glutathione peroxidase activity, while catalase was significantly decreased. Also, increase in DNA fragmentation, marked reduction of hepatic DNA content, and many histopathological changes in the liver were recorded. The results demonstrated that treatment of pregnant rats with sodium selenite at the toxic dosages chosen showed maternal and fetal toxicity that may be concerned with hepatic oxidative stress accompanied with DNA fragmentation and depletion of total DNA content.

Thioredoxin reductase 1 knockdown enhances selenazolidine cytotoxicity in human lung cancer cells via mitochondrial dysfunction

Thioredoxin reductase (TR1) is a selenoprotein that is involved in cellular redox status control and deoxyribonucleotide biosynthesis. Many cancers, including lung, overexpress TR1, making it a potential cancer therapy target. Previous work has shown that TR1 knockdown enhances the sensitivity of cancer cells to anticancer treatments, as well as certain selenocompounds. However, it is unknown if TR1 knockdown produces similar effect on the sensitivity of human lung cancer cells. To further elucidate the role of TR1 in the mechanism of selenocompounds in lung cancer, a lentiviral microRNA delivery system to knockdown TR1 expression in A549 human lung adenocarcinoma cells was utilized. Cell viability was assessed after 48 hr treatment with the selenocysteine prodrug selenazolidines 2-butylselenazolidine-4(R)-carboxylic acid (BSCA) and 2-cyclohexylselenazolidine-4-(R)-carboxylic acid (ChSCA), selenocystine (SECY), methylseleninic acid (MSA), 1,4-phenylenebis(methylene)selenocyanate (p-XSC), and selenomethionine (SEM). TR1 knockdown increased the cytotoxicity of BSCA, ChSCA, and SECY but did not sensitize cells to MSA, SEM, or p-XSC. GSH and TR1 depletion together decreased cell viability, while no change was observed with GSH depletion alone. Reactive oxygen species generation was induced only in TR1 knockdown cells treated with the selenazolidines or SECY. These three compounds also decreased total intracellular glutathione levels and oxidized thioredoxin, but in a TR1 independent manner. TR1 knockdown increased selenazolidine and SECY-induced mitochondrial membrane depolarization, as well as DNA strand breaks and AIF translocation from the mitochondria. These results indicate the ability of TR1 to modulate the cytotoxic effects of BSCA, ChSCA and SECY in human lung cancer cells through mitochondrial dysfunction.

Differential effects of sodium selenite and nano-Se on growth performance, tissue se distribution, and glutathione peroxidase activity of avian broiler

The present research evaluated differential effects of sodium selenite and nano-Se on growth performance, tissue Se distribution, and glutathione peroxidase (GSH-Px) activity of avian broiler. Broilers were randomly segregated into 12 groups so that three replicates were available for each of the three treatments (T-1, T-2, and T-3) and control groups. The control groups were fed basal diets without Se addition. T-1, T-2, and T-3 were fed with diets containing 0.2 mg kg(-1) sodium selenite, 0.2 mg kg(-1) nano-Se, and 0.5 mg kg(-1) nano-Se, respectively. Compared with the control, Se supplementation remarkably improved daily weight gain and survival rate and decreased feed conversion ratio (P < 0.05). However, no significant difference was observed between T-1, T-2, and T-3. The tissue Se content was significantly higher (P < 0.05) in Se-supplemented groups than the control, and T-3 showed the highest. Furthermore, higher Se content was observed in liver, and there was a significant difference (P < 0.05) compared with that in muscle. As for serum and hepatic GSH-Px activities, Se supplementation remarkably improved GSH-Px activity (P < 0.05), and there was no significant difference (P > 0.05) between treatments (T-1, T-2, and T-3).

Modulation of redox status in human lung cell lines by organoselenocompounds: selenazolidines, selenomethionine, and methylseleninic acid

Cancer prevention strategies utilizing selenium-containing compounds have demonstrated reduced cancer mortality and efficacy for some cancer types but considerable differences in cellular effects exist among the selenocompounds employed. The variability of the effects on cell viability, redox modulation, and disruption of subcellular compartments by the conventional selenium-containing amino acid, selenomethionine, the oxidized selenosugar metabolite, methylseleninic acid, and selenazolidines was investigated in A549 and BEAS-2B human lung cell lines. Selenomethionine had little effect whereas methylseleninic acid increased cellular thiols and stress in the endoplasmic reticulum. The cyclohexylselenazolidine increased mild oxidative stress in the adenocarcinoma cell line, A549, but the effects were attenuated in the normal, but virally transformed cell line, BEAS-2B. These data demonstrate that all selenocompounds are not equal and that the form of the organic selenocompound is a major determinant in the expected cellular response.

A role for dietary selenium and selenoproteins in allergic airway inflammation

Asthma is driven by allergic airway inflammation and involves increased levels of oxidative stress. This has led to speculation that antioxidants like selenium (Se) may play important roles in preventing or treating asthma. We fed diets containing low (0.08 parts per million), medium (0.25 parts per million), or high (2.7 parts per million) Se to female C57BL/6 mice and used an established OVA challenge protocol to determine the relationship between Se intake and the development of allergic airway inflammation. Results demonstrated that mice fed medium levels of Se had robust responses to OVA challenge in the lung as measured by lung cytokine levels, airway cellular infiltrate, eosinophilia, serum anti-OVA IgE, airway hyperreactivity, goblet cell hyperplasia, and phosphorylated STAT-6 levels in the lung. In contrast, responses to OVA challenge were less robust in mice fed low or high levels of Se. In particular, mice fed low Se chow showed significantly lower responses compared with mice fed medium Se chow for nearly all readouts. We also found that within the medium Se group the expression of lung glutathione peroxidase-1 and liver selenoprotein P were increased in OVA-challenged mice compared with PBS controls. These data suggest that Se intake and allergic airway inflammation are not related in a simple dose-response manner, which may explain the inconsistent results obtained from previous descriptive studies in humans. Also, our results suggest that certain selenoproteins may be induced in response to Ag challenges within the lung.

Susceptibility of Escherichia coli to L-selenaproline and other L-proline analogues in laboratory culture media and normal human urine

AIMS

The aims of this study were to identify analogues of L-proline which inhibit the growth of Escherichia coli in both laboratory culture media and normal human urine and to study their mechanisms of uptake.

METHODS AND RESULTS

The susceptibility of E. coli to L-proline analogues was studied by radial streak assays on agar plates and by minimal inhibitory concentration determinations in liquid media. Only L-selenaproline (SCA) inhibited growth in Mueller-Hinton medium and human urine as well as in glucose minimal medium. L-Proline did not prevent the inhibition of growth by SCA and strains defective in L-proline transport were as susceptible to SCA as wild-type strains. However, E. coli was resistant to SCA in the presence of L-cysteine and L-cystine. Spontaneous mutants selected for resistance to SCA or L-selenocystine were resistant to the other compound and had reduced growth in minimal medium containing L-cysteine or L-cystine as the sole sulfur source.

CONCLUSIONS

L-selenaproline inhibited the growth of E. coli under conditions that may occur in the urinary tract and appeared to be taken up by the L-cystine transport system.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although urinary tract infections caused by E. coli can be treated with sulfamethoxazole/trimethoprim and quinolones, resistance to these antibiotics has been increasing. These results suggest that L-selenaproline may represent a new class of compounds that could be used to treat these infections.

Chemopreventive activity of selenocysteine prodrugs against tobacco-derived nitrosamine (NNK) induced lung tumors in the A/J mouse

Prodrugs of L-selenocysteine have potential utility in cancer chemoprevention. This study reports the efficacy of three selenazolidine-4(R)-carboxylic acids, (2-unsubstituted, 2-oxo, and 2-methyl derivatives; SCA, OSCA, and MSCA, respectively) against tobacco-related lung tumorigenesis in a mouse model. Seven days after initiation of an AIN-76A diet supplemented with sodium selenite (5 ppm Se), L-selenomethionine (3.75 ppm Se), Se-methyl-L-selenocysteine (3 ppm Se), L-selenocystine (15 ppm Se), SCA (15 ppm Se), OSCA (15 ppm Se), or MSCA (15 ppm Se), mice received 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK; 10 micromol, i.p.). After an additional 16 weeks on the diets, two compounds, OSCA and selenocystine, significantly reduced lung adenoma multiplicity from 7.2 tumors per mouse in the NNK group to 4.5 and 4.6 tumors per mouse, respectively. Neither selenium concentration nor glutathione peroxidase activity in either RBCs or liver served as surrogate indicators of tumor reduction. Hepatic selenium levels were significantly elevated by all selenium-containing compounds except Se-methyl-L-selenocysteine and SCA; RBC selenium levels by all except sodium selenite and MSCA. With the exception of L-selenomethionine, RBC glutathione peroxidase activity was increased along with the elevated selenium levels. Hepatic glutathione peroxidase activity was elevated by all Se-compounds except SCA. The two compounds showing significant tumor reduction (OSCA and selenocystine) were the only two compounds that showed ubiquity of changes, elevating both selenium levels and GPx activity in both liver and RBC.