Polychlorinated biphenyl-77 induces adipocyte differentiation and proinflammatory adipokines and promotes obesity and atherosclerosis

Abstract

Background: Obesity, an inflammatory condition linked to cardiovascular disease, is associated with expansion of adipose tissue. Highly prevalent coplanar polychlorinated biphenyls (PCBs) such as 3,3',4,4'-tetrachlorobiphenyl (PCB-77) accumulate in adipose tissue because of their lipophilicity and increase with obesity. However, the effects of PCBs on adipocytes, obesity, and obesity-associated cardiovascular disease are unknown.

Objectives: In this study we examined in vitro and in vivo effects of PCB-77 on adipocyte differentiation, proinflammatory adipokines, adipocyte morphology, body weight, serum lipids, and atherosclerosis.

Methods: PCB-77 or 2,2',4,4,5,5'-hexachlorobiphenyl (PCB-153) was incubated with 3T3-L1 adipocytes either during differentiation or in mature adipocytes. Concentration-dependent effects of PCB-77 were contrasted with those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). For in vivo studies, we treated C57BL/6 wild-type (WT) or aryl hydrocarbon receptor (AhR)(-/-) mice with vehicle or PCB-77 (49 mg/kg, by intraperitoneal injection) and examined body weight gain. In separate studies, we injected ApoE(-/-) mice with vehicle or PCB-77 over a 6-week period and examined body weight, adipocyte size, serum lipids, and atherosclerosis.

Results: Low concentrations of PCB-77 or TCDD increased adipocyte differentiation, glycerol-3-phosphate dehydrogenase activity, and expression of peroxisome proliferator-activated receptor gamma, whereas higher concentrations inhibited adipocyte differentiation. Effects of PCB-77 were abolished by the AhR antagonist alpha-naphthoflavone. PCB-77 promoted the expression and release of various proinflammatory cytokines from 3T3-L1 adipocytes. Administration of PCB-77 increased body weight gain in WT but not AhR(-/-) mice. ApoE(-/-) mice injected with PCB-77 exhibited greater body weight, adipocyte hypertrophy, serum dyslipidemia, and augmented atherosclerosis.

Conclusions: Our findings suggest that PCB-77 may contribute to the development of obesity and obesity-associated atherosclerosis.

Keywords: adipocyte differentiation; aryl hydrocarbon receptor; ectopic lipid deposition; obesity; polychlorinated biphenyl.

Figure 1

Effect of PCB-77 and PCB-153 on adipocyte differentiation and mRNA expression of proinflammatory adipokines. (A) Macroscopic (left) and microscopic (right; 40× magnification) images of oil red O–stained adipocytes. (B) Quantification of oil red O staining. (C) mRNA expression of PPARγ, aP2, Ao, TNF-α, CD36, and adiponectin. Data are mean ± SE from five individual experiments. *Significantly different from vehicle (p < 0.05).

Figure 2

Effect of PCB-77 and PCB-153 on mRNA expression of proinflammatory adipokines in mature 3T3-L1 adipocytes. (A) GPDH activity (left) or oil red O staining (right). (B) mRNA expression of PPARγ, aP2, Ao, or CD36. Data are mean ± SE from five individual experiments. *Significantly different from vehicle (p < 0.05).

Figure 3

Effects of low and high concentrations of PCB-77 and TCDD on adipocyte differentiation (effects of PCB-77 are AhR mediated). (A) Oil red O staining (representative images from three individual experiments; 20× magnification). (B) Quantification of oil red O staining. Data are mean ± SE from three experiments. *Significantly different from vehicle (p < 0.05). **Significantly different from PCB-77/α-NF (p < 0.05).

Figure 4

Effect of PCB-77 on body weight gain in WT C57BL/6 and AhR^−/− mice. Arrows indicate times of vehicle or PCB-77 injections. Data are mean ± SE from 10 mice per group. *Significantly different from vehicle, within genotype.

Figure 5

Effect of PCB-77 on body weight, adipose mass, and liver weight in ApoE^−/− mice. (A) Body weight (arrows indicate times of vehicle or PCB-77 injections). (B) Weights of EF, RPF, and liver (percentage of body weight). (C) Tissue sections from mesenteric adipose tissue. (D) Quantification of adipocyte surface area (percentage of total section surface area; right) in representative tissue sections of mesenteric (Mes) adipose tissue. Data are mean ± SE from 10 mice per group. *Significantly different from vehicle (p < 0.05).

Figure 6

Effects of PCB-77 on total serum cholesterol and VLDL cholesterol concentrations, lipid deposition within the liver and abdominal cavity, and atherosclerosis in ApoE^−/− mice. (A) Total serum cholesterol concentrations (n = 10 mice per group). (B) Lipoprotein cholesterol distributions (n = 4 mice per group). (C) Representative tissue sections from livers of mice injected with vehicle or PCB-77. (D) Abdominal cavity from mice administered vehicle or PCB-77. (E) Aortic root sections stained with oil red O from vehicle or PCB-77− injected mice. *Significantly different from vehicle (p < 0.05).