Impact of oral bisphenol A at reference doses on intestinal barrier function and sex differences after perinatal exposure in rats

Abstract

Bisphenol A (BPA), a chemical estrogen widely used in the food-packaging industry and baby bottles, is recovered in human fluids (0.1-10 nM). Recent studies have reported that BPA is hormonally active at low doses, emphasizing the debate of a risk for human health. Estrogen receptors are expressed in the colon, and although the major route of BPA exposure is food, the effects on gut have received no attention. We first examined the endocrine disrupting potency of BPA on colonic paracellular permeability (CPP), experimental colitis, and visceral sensitivity in ovariectomized rats orally exposed to 5 mg/kg/d BPA (i.e., the no observed adverse effect level), 50 microg/kg/d BPA (i.e., tolerable daily intake), or lower doses. BPA dose-dependently decreased basal CPP, with a half-maximal inhibitory dose of 5.2 microg/kg/d, 10-fold below the tolerable daily intake. This correlated with an increase in epithelial tight junction sealing, also observed in Caco-2 cells exposed to 10 nM BPA. When ovariectomized rats were fed with BPA at the no observed adverse effect level, the severity of colitis was reduced, whereas the same dose increased pain sensitivity to colorectal stimuli. We then examined the impact of perinatal exposure to BPA on intestinal permeability and inflammatory response in the offspring. In female rats, but not in male rats, perinatal BPA evoked a decrease of CPP in adulthood, whereas the proinflammatory response of colonic mucosa was strengthened. This study first demonstrates that the xenoestrogen BPA at reference doses influences intestinal barrier function and gut nociception. Moreover, perinatal exposure promotes the development of severe inflammation in adult female offspring only.

Fig. 1.

Comparative effects of BPA and estradiol on intestinal permeability in OVX rats. (A) Dose effect of BPA (0.5 μg to 5 mg/kg/d for 15 d by mouth) on colonic paracellular permeability (six to eight rats per group; P < 0.05, one-way ANOVA). (B) Effects of 15-d treatment with corn oil (control), BPA NOAEL or TDI, or EB with or without ICI 182.780 (ICI) on paracellular dextran flux (5–13 rats per group). **P < 0.01 vs. controls; ns, not significant on one-way ANOVA. Bars are means ± SEM of triplicate measurements.

Fig. 2.

Effects of BPA on TJ proteins and ER expression in OVX rats. (A) Representative Western blot lanes for occludin and JAM-A and corresponding densitometric analysis of protein levels in the colon of rats fed with BPA at NOAEL, TDI, or vehicle (control), with or without ICI 182.780. Note a dose-related increase of occludin and JAM-A in BPA-treated OVX rats. (B) Relative expression levels of ERα and ERβ mRNA in the colon of OVX rats treated with vehicle (control, set to 1) or BPA NOAEL. Using the same threshold for both ERs, ERβ exponential PCR amplification occurred at 4.2 ± 0.2 cycle thresholds earlier compared with ERα, consistent with predominant ERβ expression. Bars are means ± SEM of duplicate measurements (8–10 rats per group). *P < 0.05, **P < 0.01 vs. vehicle controls (t test).

Fig. 3.

Immunofluorescence detection of occludin (A) and JAM-A (B) in Caco-2 cells exposed for 24 h to ethanol vehicle (control) or BPA (10 nM) with or without ICI 182.780 (10 μM). Note that BPA increases occludin and JAM-A staining in epithelial cell membranes, and ICI 182.780 added 24 h before BPA blocked this effect. (Scale bars: 25 μm.)

Fig. 4.

Comparative effects of BPA and estradiol on colitis in OVX rats. (A) Colonic MPO 24 h after induction of TNBS colitis in OVX rats exposed for 15 d to corn oil (control), EB, or BPA at NOAEL or TDI with or without ICI 182.780 (ICI). Noninflamed (NI) controls received intracolonic saline solution. (B) Representative Western blot lanes and corresponding densitometric analysis of macrophage MIF in the same protein extracts. Bars are means ± SEM of duplicate measurements (5–13 rats per group). *P < 0.05, **P < 0.01 vs. inflamed controls (one-way ANOVA).

Fig. 5.

Comparative effects of BPA and estradiol on VMR to colorectal distension in OVX rats exposed for 15 d to (A) corn oil (control), EB, or BPA NOAEL or TDI, and (B) with ICI 182.780 (ICI) (5–14 rats per group). *P < 0.05, ***P < 0.001 vs. controls (two-way ANOVA).

Fig. 6.

(A) Intestinal permeability and (B) relative expression levels of ERα and ERβ mRNA in the colon of rats perinatally exposed to BPA NOAEL or vehicle (Ve). For each ER, data were calibrated to male controls (set to 1). Bars are means ± SEM of duplicate measurements (4–11 rats per group). **P < 0.01 vs. corresponding controls (t test).

Fig. 7.

(A) MPO and (B) Western blot analysis of MIF in the colon 24 h after induction of TNBS colitis in rats perinatally exposed to BPA NOAEL or vehicle (Ve). NI, noninflamed controls with intracolonic saline. Bars are means ± SEM of duplicate measurements (five to eight rats per group). ***P < 0.001 vs. corresponding noninflamed controls; ^aP < 0.05 (t test).