Selenium-Enriched Soybean Peptides as Novel Organic Selenium Compound Supplements: Inhibition of Occupational Air Pollution Exposure-Induced Apoptosis in Lung Epithelial Cells

Abstract

The occupational groups exposed to air pollutants, particularly PM2.5, are closely linked to the initiation and advancement of respiratory disorders. The aim of this study is to investigate the potential protective properties of selenium-enriched soybean peptides (Se-SPeps), a novel Se supplement, in mitigating apoptosis triggered by PM2.5 in A549 lung epithelial cells. The results indicate a concentration-dependent reduction in the viability of A549 cells caused by PM2.5, while Se-SPeps at concentrations of 62.5-500 µg/mL showed no significant effect. Additionally, the Se-SPeps reduced the production of ROS, proinflammatory cytokines, and apoptosis in response to PM2.5 exposure. The Se-SPeps suppressed the PM2.5-induced upregulation of Bax/Bcl-2 and caspase-3, while also restoring reductions in p-Akt in A549 cells. The antiapoptotic effects of Se-SPeps have been found to be more effective compared to SPeps, SeMet, and Na₂SeO₃ when evaluated at an equivalent protein or Se concentration. Our study results furnish evidence that supports the role of Se-SPeps in reducing the harmful effects of PM2.5, particularly in relation to its effect on apoptosis, oxidative stress, and inflammation.

Keywords: apoptosis; fine particulate matter; inflammatory; oxidative stress; protective effect; selenium-enriched soybean peptides.

Figure 1

Effect of different concentrations (0, 25, 50, 100, 150, and 200 μg/mL) of PM2.5 pretreatment on A549 cells for 24 h. (A) Viability of the A549 cells. (B) Cell morphological changes of the A549 cells. Scale bar = 100 μm. Data are shown as the mean ± SD, n = 8/group. Statistical analysis was performed using ANOVA followed by Tukey’s post hoc test. Different letters over bars indicate statistically significant differences (p < 0.05).

Figure 2

Effect of different concentrations (0, 62.5, 125, 250, 500, 1000, 2000, and 4000 μg/mL) of Se-SPep pretreatment on A549 cells for 24 h. (A) Viability of the A549 cells. (B) Cell morphological changes of the A549 cells. Scale bar = 100 μm. Data are shown as the mean ± SD, n = 8/group. Statistical analysis was performed using ANOVA followed by Tukey’s post hoc test. Different letters over bars indicate statistically significant differences (p < 0.05).

Figure 3

Effect of Se-SPep pretreatment on the cell viability in A549 cells exposed to PM2.5. The Se concentration in the SeMet and Na₂SeO₃ groups is 0.022 μg/mL, which is equivalent to the Se concentration in the 250 μg/mL Se-SPep group. Data are shown as the mean ± SD, n = 8/group. Statistical analysis was performed using ANOVA followed by Tukey’s post hoc test. Different letters over bars indicate statistically significant differences (p < 0.05).

Figure 4

Effect of Se-SPep pretreatment on cell apoptosis in A549 cells exposed to PM2.5. (A) Representative photomicrographs of A549 cells stained with Hoechst 33342 fluorescent dye. Scale bar = 300 μm. (B) Flow cytometry analysis of cell apoptosis induced by PM2.5. (C) The apoptosis ratio induced by PM2.5 after intervention with Se-SPeps. The Se concentration in the SeMet and Na₂SeO₃ groups is 0.022 μg/mL, which is equivalent to the Se concentration in the 250 μg/mL Se-SPep group. Data are shown as the mean ± SD, n = 3/group. Statistical analysis was performed using ANOVA followed by Tukey’s post hoc test. Different letters over bars indicate statistically significant differences (p < 0.05).

Figure 5

Effect of Se-SPep pretreatment on ROS generation in A549 cells exposed to PM2.5. (A) Representative photomicrographs of A549 cells stained with DCFH-DA fluorescent dye. Scale bar = 300 μm. (B) Relative fluorescence intensity of intracellular ROS of A549 cells. The Se concentration in the SeMet and Na₂SeO₃ groups is 0.022 μg/mL, which is equivalent to the Se concentration in the 250 μg/mL Se-SPep group. Data are shown as the mean ± SD, n = 3/group. Statistical analysis was performed using ANOVA followed by Tukey’s post hoc test. Different letters over bars indicate statistically significant differences (p < 0.05).

Figure 6

Effect of Se-SPep pretreatment on proinflammatory cytokines secretion in A549 cells exposed to PM2.5. (A) IL-1β secretion. (B) IL-6 secretion. (C) TNF-α secretion. The Se concentration in the SeMet and Na₂SeO₃ groups is 0.022 μg/mL, which is equivalent to the Se concentration in the 250 μg/mL Se-SPep group. Data are shown as the mean ± SD, n = 3/group. Statistical analysis was performed using ANOVA followed by Tukey’s post hoc test. Different letters over bars indicate statistically significant differences (p < 0.05).

Figure 7

Effect of Se-SPep pretreatment on the mitochondrial apoptotic pathway in A549 cells exposed to PM2.5. The expression of Bcl-2, Bax, caspase-3, Akt, and p-AKT in PM2.5-exposed A549 cells was analyzed using Western blotting. β-Actin was used as the internal control. (A) Protein expression of Bcl-2. (B) Protein expression of Bax. (C) Protein expression of Bax relative to Bcl-2. (D) Protein expression of caspase-3. (E) Protein expression of Akt. (F) Protein expression of p-Akt. (G) Protein expression of p-AKT relative to AKT. The Se concentration in the SeMet and Na₂SeO₃ groups is 0.022 μg/mL, which is equivalent to the Se concentration in the 250 μg/mL Se-SPep group. Data are shown as the mean ± SD, n = 3/group. Statistical analysis was performed using ANOVA followed by Tukey’s post hoc test. Different letters over bars indicate statistically significant differences (p < 0.05).