The trichloroethylene metabolite S-(1,2-dichlorovinyl)-l-cysteine but not trichloroacetate inhibits pathogen-stimulated TNF-α in human extraplacental membranes in vitro

Abstract

Extraplacental membranes define the gestational compartment and provide a barrier to infectious microorganisms ascending the gravid female reproductive tract. We tested the hypothesis that bioactive metabolites of trichloroethylene (TCE) decrease pathogen-stimulated innate immune response of extraplacental membranes. Extraplacental membranes were cultured for 4, 8, and 24h with the TCE metabolites trichloroacetate (TCA) or S-(1,2-dichlorovinyl)-l-cysteine (DCVC) in the absence or presence of lipoteichoic acid (LTA) or lipopolysaccharide (LPS) to simulate infection. In addition, membranes were cocultured with DCVC and Group B Streptococcus (GBS). DCVC (5-50μM) significantly inhibited LTA-, LPS-, and GBS-stimulated cytokine release from tissue cultures as early as 4h (P≤0.05). In contrast, TCA (up to 500μM) did not inhibit LTA-stimulated cytokine release from tissue punches. Because cytokines are important mediators for host response to infectious microorganisms these findings suggest that TCE exposure could potentially modify susceptibility to infection during pregnancy.

Keywords: Dichlorovinyl cysteine; Group B Streptococcus; Pregnancy; Toxicant–pathogen interactions; Trichloroethylene.

Figure 1. DCVC effects on LTA-stimulated TNF-α over time

Punches of full thickness human extraplacental membranes were floated in culture with DCVC alone or co-exposed to DCVC and LTA (1 μg/mL) for 4, 8, and 24 h, and then the medium was assayed by ELISA for TNF-α. Columns represent mean ± SEM; N=5 women. Data were analyzed by ANOVA with Tukey's post-hoc test. #, Significant differences compared to control within each time point (medium only) (p≤ 0.05). *, Significantly different compared to LTA alone within each time point (p≤ 0.05).

Figure 2. DCVC effects on LTA-stimulated TNF-α mRNA expression

Punches of full thickness human extraplacental membranes were floated in culture with and without DCVC (10 μM) and LTA (1 μg/mL) for 4 h, and then the RNA was extracted and assayed by PCR for TNF-α expression. Data are presented as fold change in mRNA compared to control. Columns represent mean ± SEM; N=3 women. Data were analyzed by ANOVA with Tukey's post-hoc test. #, Significantly different compared to control (medium only) (p≤ 0.05). *, Significantly different (p≤ 0.05).

Figure 3. TCA effects on LTA-stimulated release of TNF-α

Punches of full thickness human extraplacental membranes were floated in culture with TCA alone or co-exposed to TCA and LTA (1 μg/mL) for 24 h, and then the medium was assayed by ELISA for TNF-α. Columns represent mean ± SEM; N=3 women. Data were analyzed by ANOVA with Tukey's post-hoc test. #, Significant differences compared to control (medium only) (p≤ 0.05).

Figure 4. DCVC effects on GBS-stimulated cytokines

DCVC effects on GBS-stimulated release of pro-inflammatory cytokines from extraplacental membranes in transwell cultures. Full thickness human extraplacental membranes were cocultured with live GBS for 24 h, and then the medium from the choriodecidua compartment was assayed by ELISA for IL-1β (A), IL-6 (B), IL-8 (C), and TNF-α (D). Columns represent mean ± SEM; N=5 women. Data were analyzed by ANOVA with Tukey's post-hoc test. #, Significant differences compared to control (medium only) (p≤ 0.05). *, Significant differences compared to GBS alone (p≤ 0.05).