The Effects of Short- and Long-Term Ingestion of Plastic Toxin Bisphenol A on Gastrointestinal Transit Time in Rats

Abstract

Introduction Exposure to bisphenol A (BPA), a toxic chemical released from plastic, affects various body functions, including reproduction, metabolism, and development. The most common route of exposure to BPA is oral, and the gastrointestinal (GI) tract is, therefore, the first body system to be exposed to BPA. BPA has been well-documented to impair gut contractility in rats, in vitro. It may therefore be hypothesized that BPA may adversely affect GI motility and hence slow down the movement of food, resulting in the increased transit of food bolus in the GI tract. There are no reports so far on the effects of BPA on GI transit time. Objectives The present study was undertaken to examine the impact of exposure to BPA by a single oral dose (termed as short-term ingestion of BPA) and chronic (28-day) oral dose (termed as long-term ingestion of BPA) on the transit time of food bolus in the gut of adult male albino rats. Methods and materials The study was conducted in the Department of Physiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India. In one set of experiments, each animal was fed a food pellet, once (short-term ingestion) containing BPA (2 µg/kg and 50 µg/kg in different groups), and in another set of experiments, each animal was fed a food pellet containing BPA (50 µg/kg/day) for 28 consecutive days (long-term ingestion). Control rats in both sets were fed food pellets without BPA. Subsequently, the gastric transit index (GTI), ileocecal transit index (ICTI), and colonic transit time (CTT) were determined by the standard charcoal marker method. Results One-time ingestion of a food pellet containing BPA caused a significant (p < 0.05) drop in the GTI and ICTI and an increase in the CTT with both doses of BPA (2 and 50 µg/kg). Similarly, after chronic (28-day), oral BPA exposure, a significant decrease in the GTI and ICTT and an increase in CTT were observed. Conclusion Both short-term (one-time) and long-term (28-day) oral exposure to BPA-containing food harmed GI transit. Slow GI transit may lead to metabolic disorders and GI motility disorders, such as constipation.

Keywords: bisphenol a; charcoal marker method; endocrine disrupting chemicals (edcs); gastrointestinal transit time; plastic chemical.

Figure 1. Flow chart showing the number of rats in each group and subgroup and the experimental protocol

BPA: bisphenol A; GTI: gastric transit index; ICTI: ileocecal transit index; CTT: colonic transit time; n: number of rats

Figure 2. Upper panel: A sample of the entire length of gut removed from the rat after 30 minutes of charcoal meal ingestion. Lower panel: The same with an enlarged view.

Please note the dark-colored food passing along the length of the small intestine. The black arrow indicates the point of the gut to which the dark marker (charcoal mixed food) traversed. This length of the rat gut up to this point was noted for the calculation of GTI. Also, note the two dilated segments indicating stomach (A) and cecum (B). GTI: gastric transit index

Figure 3. Upper panel: A sample of gut dissected out after 120 min of charcoal meal ingestion for recording the ICTI. Lower panel: The same with an enlarged view.

Please note the dark-colored food crossed the ileoceal junction. The black arrow indicates the point of the gut to which the dark marker (charcoal mixed food) traversed. This length of the rat gut up to this point was noted for the calculation of ICTI. Also, note the two dilated segments indicating stomach (A) and cecum (B). ICTI: ileocecal transit index

Figure 4. Image showing charcoal stained (dark) and normal fecal pellets indicated by black and red arrows, respectively. The CTT was determined based on the time taken for the elimination of the first dark pellet after a charcoal meal.

CTT: colonic transit time

Figure 5. Bar diagram showing the mean ± SD values of the percentage of the total gut length traveled by the marker in 30 minutes after the ingestion of charcoal meal (gastric transit index, GTI) in different groups.

Group 1 (n = 6) and Group 2 (n = 6) were exposed to a single food pellet containing 2 µg/kg BPA and 50 µg/kg BPA, respectively, while Group 3 (n = 6) was exposed to a single food pellet without BPA (sham-fed). The GTI in both BPA-fed groups was significantly different from that of the sham–fed group. The asterisks indicate a significant difference (p < 0.05) from the sham-fed group (one-way ANOVA test; post-hoc Tukey test). BPA: bisphenol A; GTI: gastric transit index; ANOVA: analysis of variance; SD: standard deviation, n: number of animals in each group

Figure 6. Bar diagram showing the mean ± SD values for the percentage of the total gut length traveled by the marker in 120 minutes after the ingestion of the charcoal meal (ileocecal transit index, ICTI) in different groups.

Group 1 (n = 6) and Group 2 (n = 6) were exposed to a single food pellet containing 2 µg/kg BPA and 50 µg/kg BPA, respectively, while Group 3 (n = 6) was exposed to a single food pellet without BPA (sham-fed). The ICTI in both BPA-fed groups was significantly different from the sham–fed group. The asterisks indicate a significant difference (p < 0.05) from the sham-fed group (one-way ANOVA test; post-hoc Tukey test). BPA: bisphenol A; ICTI: ileocaecal transit index; ANOVA: analysis of variance; SD: standard deviation; n: number of animals in each group

Figure 7. Bar diagram showing the mean ± SD values of the percentage of the total gut length traveled by the marker in 30 minutes after the ingestion of the charcoal meal (gastric transit index, GTI) in different groups.

Group 1 (n = 6) was exposed to a food pellet containing 50 µg/kg/day BPA while Group 2 (n = 6) was exposed to a food pellet without BPA (sham-fed) for 28 consecutive days. The GTI in the BPA-fed group was significantly different from that of the sham–fed group. The asterisk indicates a significant difference (p < 0.05) from the sham–fed group (independent t-test). GTI: gastric transit index; BPA: bisphenol A; SD: standard deviation; n: number of animals in each group

Figure 8. Bar diagram showing the mean ± SD values of the percentage of the total gut length traveled by the marker in 120 minutes after the ingestion of the charcoal meal (ileoceacal transit index, ICTI) in different groups.

Group 1 (n = 6) was exposed to a food pellet containing 50 µg/kg/day BPA while Group 2 (n = 6) was exposed to a food pellet without BPA (sham-fed) for 28 consecutive days. The ICTI in the BPA-fed group was significantly different from the sham–fed group. The asterisk indicates a significant difference (p < 0.05) as compared to the sham-fed group (independent t-test). ICTI: ileoceacal transit index; BPA: bisphenol A; SD: standard deviation; n: number of animals in each group