Obesogenic polystyrene microplastic exposures disrupt the gut-liver-adipose axis

Abstract

Microplastics (MP) derived from the weathering of polymers, or synthesized in this size range, have become widespread environmental contaminants and have found their way into water supplies and the food chain. Despite this awareness, little is known about the health consequences of MP ingestion. We have previously shown that the consumption of polystyrene (PS) beads was associated with intestinal dysbiosis and diabetes and obesity in mice. To further evaluate the systemic metabolic effects of PS on the gut-liver-adipose tissue axis, we supplied C57BL/6J mice with normal water or that containing 2 sizes of PS beads (0.5 and 5 µm) at a concentration of 1 µg/ml. After 13 weeks, we evaluated indices of metabolism and liver function. As observed previously, mice drinking the PS-containing water had a potentiated weight gain and adipose expansion. Here we found that this was associated with an increased abundance of adipose F4/80+ macrophages. These exposures did not cause nonalcoholic fatty liver disease but were associated with decreased liver:body weight ratios and an enrichment in hepatic farnesoid X receptor and liver X receptor signaling. PS also increased hepatic cholesterol and altered both hepatic and cecal bile acids. Mice consuming PS beads and treated with the berry anthocyanin, delphinidin, demonstrated an attenuated weight gain compared with those mice receiving a control intervention and also exhibited a downregulation of cyclic adenosine monophosphate (cAMP) and peroxisome proliferator-activated receptor (PPAR) signaling pathways. This study highlights the obesogenic role of PS in perturbing the gut-liver-adipose axis and altering nuclear receptor signaling and intermediary metabolism. Dietary interventions may limit the adverse metabolic effects of PS consumption.

Keywords: delphinidin; inflammation; metabolism disrupting chemical; microplastics; obesity; polystyrene.

Figure 1.

Adipose tissue immune cell infiltrate. White adipose tissue was collected from mice drinking unsupplemented water (water) or that containing either 0.5 or 5 µm polystyrene beads (PS) beads at euthanasia, digested, and analyzed for the presence of F4/80 macrophages (A), M2 macrophages (B), M1 macrophages (C), and CD3⁺ lymphocytes (D) by flow cytometry.*p < .05. n = 8–10.

Figure 2.

Plasma adipokines. Blood was collected from mice drinking unsupplemented water (water) or that containing 0.5 µm PS (PS) beads at euthanasia, the plasma was isolated and then analyzed for the presence of adiponectin (A), resistin (B), leptin (C), and PAI-1 (D). n = 10.

Figure 3.

β-catenin levels. Lysates were prepared from eWAT (A) and PVAT (B) samples collected from mice drinking unsupplemented water (H₂O) or that containing 0.5 µm polystyrene beads (PS) and then analyzed for the presence of β-catenin and GAPDH by Western blotting. Also illustrated is normalized group data (C). n = 4.

Figure 4.

Effects of delphinidin injection. Mice were supplied with unsupplemented water (U; n = 4) or that containing polystyrene beads (PS) and injected with either vehicle (Veh; n = 8) or delphinidin (Del; n = 8) as indicated. After 4 weeks of this treatment, we measured weight gain (A) and percent body fat (B).

Figure 5.

Liver phenotyping. Livers were collected from mice exposed to control water, 0.5 µm PS, or 5 µm PS and sections stained with H&E. Illustrated are representative images captured at 10× magnification. Scale bar: 300 µm (A). Also illustrated are: the liver:body weight ratios (B); levels of hepatic triglycerides (C); and levels of hepatic cholesterol levels (D) in the control and PS exposure groups. *p < .05.

Figure 6.

Hepatic differential gene expression. Illustrated is a bar graph depicting the number of differentially expressed genes (DEGs) in liver (mRNA-Seq) in the 0.5 µm PS versus water and the 5 µm PS versus water comparison groups (A). Listed are the log2-fold change values of the top 10 most upregulated and downregulated DEGs in the comparison groups by log2-fold change (B). A Venn diagram depicts the relationships between the DEGs in the comparison groups. Breakout boxes indicate the top 10 most upregulated (red) and downregulated (blue) regulated DEGs in the exposure groups (C). Cut-off values are q-value < 0.05. n = 10.

Figure 7.

Pathway analysis of liver differentially expressed genes (DEGs). DEGs (liver mRNA-Seq) were analyzed using ingenuity pathway analysis (IPA) software and the top enriched pathways for the comparison groups (0.5 µm PS vs water and 5 µm PS vs water) are provided. Two processes were predicted to be enriched in both exposure groups. n = 10.