Protective efficacy of selenite against lead-induced neurotoxicity in Caenorhabditis elegans

Abstract

Background: Selenium is an essential micronutrient that has a narrow exposure window between its beneficial and toxic effects. This study investigated the protective potential of selenite (IV) against lead (Pb(II))-induced neurotoxicity in Caenorhabditis elegans.

Principal findings: The results showed that Se(IV) (0.01 µM) pretreatment ameliorated the decline of locomotion behaviors (frequencies of body bends, head thrashes, and reversal ) of C. elegans that are damaged by Pb(II) (100 µM) exposure. The intracellular ROS level of C. elegans induced by Pb(II) exposure was significantly lowered by Se(IV) supplementation prior to Pb(II) exposure. Finally, Se(IV) protects AFD sensory neurons from Pb(II)-induced toxicity.

Conclusions: Our study suggests that Se(IV) has protective activities against Pb(II)-induced neurotoxicity through its antioxidant property.

Figure 1. Se(IV) attenuated the declines of locomotion behaviors in aged C. elegans.

Synchronized wild-type L1 larvae were incubated with various concentrations of Se(IV) (0.01, 0.05, and 0.1 µM) or distilled water as the solvent control at 20°C. The worms at 0 and 5 days old were selected for analysis of the locomotory rate. (A) The number of body bends in 20 s and (B) the number of head thrashes in 1 min. Approximately thirty worms from each treatment at each time point were randomly selected for scoring. Error bars represent the standard error and differences were considered significant at P<0.05 (*), P<0.01 (**), and P<0.001 (***) by one-way ANOVA and LSD post hoc test. n.s., no significant.

Figure 2. Effects of Se(IV) on locomotion behaviors in C. elegans under Pb(II)-induced toxicity.

Synchronized L1 wild-type larvae were incubated with 0.01 µM of Se(IV) or distilled water as the solvent control for 40 h at 20°C. Subsequently, Se(IV)-pretreated and control young adult worms were divided into two aliquots and treated with or without 100 µM of Pb(II) for 24 h at 20°C. (A) The number of body bends in 20 s, (B) the number of head thrashes in 1 min, and (C) the reversal frequency in 3 min. Approximately thirty worms from each treatment at each time point were randomly selected for scoring. Error bars represent the standard error and differences were considered significant at P<0.05 (*), P<0.01 (**), and P<0.001 (***) by one-way ANOVA and LSD post hoc test. n.s., no significant. “Ctrl”, worms grown on a normal diet; “Se”, worms grown with Se(IV) supplementation; “Pb”, worms grown on a normal diet followed by Pb(II) exposure; “Se/Pb”, worms with Se(IV) pretreatment and followed by Pb(II) exposure.

Figure 3. Free radical-scavenging effect of Se(IV) on Pb(II)-induced oxidative stress in vivo.

Synchronized L1 wild-type larvae were incubated with 0.01 µM of Se(IV) or distilled water as the solvent control for 40 h at 20°C. Subsequently, Se(IV)-pretreated and control young adult worms were divided into two aliquots and treated with or without 100 µM of Pb(II) for 24 h at 20°C. Subsequently, intracellular ROS for adult animals was measured using 2′, 7′-dichlorodihydrofluoroscein diacetate. One hundred worms from each condition were used to analyze the intracellular ROS levels. The results are expressed as relative fluorescence units (RFU) of fluorescence relative to 100 worms. Error bars represent the standard error and differences were considered significant at P<0.05 (*), P<0.01 (**), and P<0.001 (***) by one-way ANOVA and LSD post hoc test. n.s., no significant. “Ctrl”, worms grown on a normal diet; “Se”, worms grown with Se(IV) supplementation; “Pb”, worms grown on a normal diet followed by Pb(II) exposure; “Se/Pb”, worms with Se(IV) pretreatment and followed by Pb(II) exposure.

Figure 4. Effects of Se(IV) on AFD sensory neurons by Pb(II) exposure in C. elegans.

Synchronized L1 Pgcy-8::GFP transgene larvae were incubated with 0.01 µM of Se(IV) or distilled water as the solvent control for 40 h at 20°C. Subsequently, Se(IV)-pretreated and control young adult worms were treated with 100 µM of Pb(II) for 24 h at 20°C to generate neuronal damage. (A) Representative images of morphological patterns of AFD sensory neurons labeled by Pgcy-8::GFP. (B) Relative sizes of fluorescent puncta for cell bodies of AFD sensory neurons. (C) Relative fluorescent intensities in cell bodies of AFD sensory neurons. Relative sizes of fluorescent puncta and relative fluorescent intensities were calculated by normalizing to that of control. Approximately thirty worms from each treatment at each time point were randomly selected for analysis. Error bars represent the standard error and differences were considered significant at P<0.05 (*), P<0.01 (**), and P<0.001 (***) by one-way ANOVA and LSD post hoc test. n.s., no significant. “Ctrl”, worms grown on a normal diet; “Se”, worms grown with Se(IV) supplementation; “Pb”, worms grown on a normal diet followed by Pb(II) exposure; “Se/Pb”, worms with Se(IV) pretreatment and followed by Pb(II) exposure.

Figure 5. Effects of Se(IV) on the expression of TTX-1, TAX-2, TAX-4, and CEH-14 upon Pb(II) exposure in C. elegans.

Synchronized L1 wild-type larvae were incubated with 0.01 µM of Se(IV) or distilled water as the solvent control for 40 h at 20°C. Subsequently, Se(IV)-pretreated and control young adult worms were divided into two aliquots and treated with or without 100 µM of Pb(II) for 24 h at 20°C. Subsequently, the total RNA from adult animals was extracted. mRNA levels of TTX-1, TAX-2, TAX-4, and CEH-14 were determined by quantitative real-time RT-PCR. The mRNA levels were normalized to the expression of ACT-1. The fold change was normalized to that observed in untreated control C. elegans samples. The test was performed three times. Error bars represent the standard error and differences were considered significant at P<0.05 (*), P<0.01 (**), and P<0.001 (***) by one-way ANOVA and LSD post hoc test. n.s., no significant. “Ctrl”, worms grown on a normal diet; “Se”, worms grown with Se(IV) supplementation; “Pb”, worms grown on a normal diet followed by Pb(II) exposure; “Se/Pb”, worms with Se(IV) pretreatment and followed by Pb(II) exposure.