Polychlorinated biphenyl 153 is a diet-dependent obesogen that worsens nonalcoholic fatty liver disease in male C57BL6/J mice

Abstract

Background: Polychlorinated biphenyls (PCBs) are persistent environmental pollutants that are detectable in the serum of all American adults. Amongst PCB congeners, PCB 153 has the highest serum level. PCBs have been dose-dependently associated with obesity, metabolic syndrome and nonalcoholic fatty liver disease (NAFLD) in epidemiological studies.

Objective: The purpose of this study is to determine mechanisms by which PCB 153 worsens diet-induced obesity and NAFLD in male mice fed a high-fat diet (HFD).

Methods: Male C57BL6/J mice were fed either control or 42% milk fat diet for 12 weeks with or without PCB 153 coexposure (50 mg/kg ip ×4). Glucose tolerance test was performed, and plasma and tissues were obtained at necropsy for measurements of adipocytokine levels, histology and gene expression.

Results: In control diet-fed mice, addition of PCB 153 had minimal effects on any of the measured parameters. However, PCB 153 treatment in high-fat-fed mice was associated with increased visceral adiposity, hepatic steatosis and plasma adipokines including adiponectin, leptin, resistin and plasminogen activator inhibitor-1 levels. Likewise, coexposure reduced expression of hepatic genes implicated in β-oxidation while increasing the expression of genes associated with lipid biosynthesis. Regardless of diet, PCB 153 had no effect on insulin resistance or tumor necrosis factor alpha levels.

Conclusion: PCB 153 is an obesogen that exacerbates hepatic steatosis, alters adipocytokines and disrupts normal hepatic lipid metabolism when administered with HFD but not control diet. Because all US adults have been exposed to PCB 153, this particular nutrient-toxicant interaction potentially impacts human obesity/NAFLD.

Keywords: ALT; AST; AUC; AhR; CAR; CD; CPT1A; CPT2; FAS; GAPDH; GTT; H&E; HDL; HFD; HOMA-IR; IL-10; IL-6; LDL; NAFLD; NHANES; NTP; PCB; PCBs; PCR; POPs; PPARα; PXR; S.E.M.; TASH; TCDD; TNFα; alanine transaminase; area under the curve; aryl hydrocarbon receptor; aspartate transaminase; carnitine palmitoyl transferase; carnitine palmitoyl transferase 1A; constitutive androstane receptor; control diet; fatty acid synthase; glucose tolerance test; glyceraldehyde-3-phosphate dehydrogenase; hematoxylin–eosin; high-density lipoproteins; high-fat diet; homeostasis model assessment of insulin resistance; interleukin-10; interleukin-6; low-density lipoproteins; national health and nutrition examination survey; national toxicology program; nonalcoholic fatty liver disease; peroxisome proliferator-activated receptor alpha; persistent organic pollutants; polychlorinated biphenyls; polymerase chain reaction; pregnane X receptor; standard error mean; tPAI-1; tetrachlorodibenzo-p-dioxin; tissue plasminogen activator inhibitor 1.; toxicant associated steatohepatitis; tumor necrosis factor alpha.

Fig. 1

PCB 153 increased body weight and visceral adiposity in mice fed a high fat diet. (A) The % increase in body weight for C57BL/6J mice (n=10) treated with a 42% milk fat diet (vs. control diet) ± PCB 153 (200 mg/kg cumulative). Body weight measurements were taken from week 1 to week 12 (12 weeks) and the body weight at week 1 was taken as 100%. (B) Chronic PCB 153 (cumulative dose 200 mg/kg i.p.) increased visceral adiposity in C57BL/6J mice fed with a high fat diet. * P <0.05. CD-control diet, HFD-high fat diet, PCB-polychlorinated biphenyl.

Fig. 2

High fat diet increased adipocyte cell size and this was unaffected by PCB 153. (A) epipdidymal adipose tissue was stained with H&E. (B) Adipocyte area was measured and average cell size of >100 cells for each of the groups (n=10) was calculated. * P <0.05. CD-control diet, HFD-high fat diet, PCB-polychlorinated biphenyl.

Fig. 3

PCB 153 worsened NAFLD in mice fed a high fat diet. (A) Oil Red O staining of hepatic sections established the occurrence of micro-vesicular steatosis in the HFD+PCB 153 mice. (B) The same group of mice also showed macro-vesicular steatosis by H&E staining. (C) Plasma AST and (D) Plasma ALT levels (U/L) were measured (n=10) using Cobas Mira Plus automated chemical analyzer. * P <0.05. CD-control diet, HFD-high fat diet, PCB-polychlorinated biphenyl, AST-aspartate transaminase, ALT-alanine transaminase.

Fig. 4

PCB 153 increased hepatic triglycerides and cholesterol in mice fed a high fat diet but did not change hepatic TNFα expression levels. Hepatic levels of (A) triglycerides and (B) cholesterol were quantified (μg/mg tissue) in mice (n=5) fed with control diet or high fat diet with or without PCB 153. (C) Hepatic TNFα mRNA expression. * P <0.05. CD-control diet, HFD-high fat diet, PCB-polychlorinated biphenyl, TNFα-tumor necrosis factor alpha.

Fig. 5

High fat diet increased insulin resistance and this was unaffected by PCB 153 co-exposure. (A) HOMA-IR was caluclated from fasting blood glucose and insulin levels for all four groups of animals (n=10) with HFD and HFD+PCB 153 animals showing higher levels. (B) Fasting blood glucose levels (mg/dL) were measured (C) Glucose tolerance test was performed and blood glucose levels were measured for mice (n=10) fed with a control diet or high fat diet, with or without PCB 153 (D) Area under the curve was calculated and HFD and HFD+PCB 153 groups showed higher AUC levels than CD or CD+PCB 153 groups. * P <0.05. CD-control diet, HFD-high fat diet, PCB-polychlorinated biphenyl.

Fig. 6

PCB exposure altered expression of some but not all genes involved in hepatic lipid metabolism. Real-time PCR experiments showed the changes in hepatic mRNA expressions caused by either PCB 153 or high fat diet or both as compared to animals fed with a control diet for (A) FAS, (B) PPARα, (C) CPT1A, (D) CPT2. All values were normalized to control diet group, (n=10),* P <0.05. CD-control diet, HFD-high fat diet, PCB-polychlorinated biphenyl, FAS-fatty acid synthase, PPARα-peroxisome proliferator-activated receptor alpha, CPT1A-carnitine palmitoyl transferase 1A, CPT2-carnitine palmitoyl transferase 2.

Fig. 7

High fat diet and PCB 153 co-exposure led to serum adipokine dysregulation. Plasma levels of (A) leptin (pg/mL) and (B) adiponectin (μg/mL) were measured using the Luminex IS 100 system (n=10). * P <0.05. CD-control diet, HFD-high fat diet, PCB-polychlorinated biphenyl.