Selenium-independent antioxidant and anti-inflammatory effects of thioredoxin reductase inhibition in alveolar macrophages.

AIMS: Interleukin-1ß (IL-1ß) contributes to the development of bronchopulmonary dysplasia (BPD). Thioredoxin reductase-1 (Txnrd1) inhibition activates nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent responses. Txnrd1 activity is selenium (Se) dependent and Se deficiency is common in prematurity. Auranofin (AFN), a Txnrd1 inhibitor, decreases IL-1ß levels and increases Nrf2 activation in lipopolysaccharide (LPS) treated alveolar macrophages. In lung epithelia, AFN-induced Nrf2 activation is Se dependent. We tested the hypothesis that the effects of Txnrd1 inhibition in alveolar macrophages are Se dependent. MAIN METHODS: To establish Se sufficient (Se+) and deficient (Se-) conditions, alveolar (MH-S) macrophages were cultured in 2.5% fetal bovine serum (FBS) ± 25 nM Na2SeO3. Se- (2.5% FBS) and Se+ (2.5% FBS + 25 nM Na2SeO3) cells were cultured in the presence or absence of 0.05 µg/mL LPS and/or 0.5 µM AFN. Nrf2 activation was determined by measuring NADPH quinone oxidoreductase-1 (Nqo1) and glutathione levels. IL-1ß mRNA (Il1b) and protein levels were measured using qRT-PCR and ELISA. Data were analyzed by ANOVA followed by Tukey's post-hoc. KEY FINDINGS: We detected an independent effect of AFN, but not LPS, on Nqo1 expression and GSH levels in Se+ and Se- cells. LPS significantly increased Il1b and IL-1ß levels in both groups. AFN-mediated attenuation of this effect was not impacted by Se status. SIGNIFICANCE: The beneficial effects of Txnrd1 inhibition in alveolar macrophages are Se-independent and therefore unlikely to be diminished by clinical Se deficiency.

Selenium supplementation of lung epithelial cells enhances nuclear factor E2-related factor 2 (Nrf2) activation following thioredoxin reductase inhibition.

The trace element selenium (Se) contributes to redox signaling, antioxidant defense, and immune responses in critically ill neonatal and adult patients. Se is required for the synthesis and function of selenoenzymes including thioredoxin (Trx) reductase-1 (TXNRD1) and glutathione peroxidases (GPx). We have previously identified TXNRD1, primarily expressed by airway epithelia, as a promising therapeutic target to prevent lung injury, likely via nuclear factor E2-related factor 2 (Nrf2)-dependent mechanisms. The present studies utilized the TXNRD1 inhibitor auranofin (AFN) to test the hypothesis that Se positively influences Nrf2 activation and selenoenzyme responses in lung epithelial cells. Murine transformed Club cells (mtCCs) were supplemented with 0, 10, 25, or 100 nM Na2SeO3 to create a range of Se conditions and were cultured in the presence or absence of 0.5 µM AFN. TXNRD1 and GPX2 protein expression and enzymatic activity were significantly greater upon Se supplementation (p < 0.05). AFN treatment (0.5 µM AFN for 1 h) significantly inhibited TXNRD1 but not GPx activity (p < 0.001). Recovery of TXNRD1 activity following AFN treatment was significantly enhanced by Se supplementation (p < 0.041). Finally, AFN-induced Nrf2 transcriptional activation was significantly greater in mtCCs supplemented in 25 or 100 nM Na2SeO3 when compared to non-supplemented controls (p < 0.05). Our novel studies indicate that Se levels positively influence Nrf2 activation and selenoenzyme responses following TXNRD1 inhibition. These data suggest that Se status significantly influences physiologic responses to TXNRD1 inhibitors. In conclusion, correction of clinical Se deficiency, if present, will be necessary for optimal therapeutic effectiveness of TXNRD1 inhibitors in the prevention of lung disease.