| Background Bisphenol A(BPA), which is a monomer material used for the manufacture of polycarbonate and epoxy resins, is widely used in the production of food packaging materials, beverage containers, braces and other plastics. As a typical environmental endocrine disruptor, BPA can enter human body through the digestive tract, respiratory tract, skin and other pathways. Many studies have shown that human is extensively exposed to environmental BPA. There is a growing body of research showing that there is a significant correlation between BPA and obesity. However, the mechanism of BPA induced obesity is still not clear. Obesity is a systematic chronic low-grade inflammation state, which is accompanied with the infiltration, accumulation and activation of macrophages. This can lead to the increase the secretion of inflammatory cytokines in adipose tissue. The accumulation of adipose tissue macrophages(ATMs) and their effects on obesity air closely related to their subtypes. Classically activated M1 macrophages can promote the process of inflammation by secreting inflammatory factors. Alternatively activated M2 macrophages can inhibit the inflammatory process by secreting anti-inflammatory factors. Macrophage subtypes is regulated by the polarization state of adipose tissue macrophages. Studies have shown that most macrophages in the adipose tissues of the normal or thin are M2 type. But, during the development of obesity, M2 type can convert into M1 type, which lead to M1 ATMs increased significantly. However, it is not clear that what change happened to the macrophage polarization state and its effects on the production and accumulation of inflammatory factors in adipose tissues in the process of BPA induced obesity. And it can provide experimental data for clarifying the mechanism of BPA induced obesity.Objective Verify the correlation between BPA and obesity through in vivo experiment. And analyze the adipose tissue inflammation and the accumulation and the polarization of ATMs. Explore the mechanism of the accumulation ATMs in adipose tissue in BPA induced obesity.Method Specific pathogen free(SPF) lever 4 week of 192 male C57BL/6J mice, were randomly divided into normal diet group(ND) and high fat diet(HFD). Meanwhile, the mice were treated with 10, 100 and 1000 n M BPA through drinking water and there were twenty-four mice in each group. Also the solvent control groups were established. At 8, 12, 16 and 20 weeks, body weight(BW) of mice was measured and sterile epididymal fat pad was collected and epididymal fat pad weight(EFPW) was measured. The accumulation of ATMs in adipose tissue was analyzed through histopathology(HP). The expression of inflammatory factors IL-1β and IL-6 was measured through immunological histological chemistry(IHC). The expression of F4/80 was analyzed through immunofluorescence. The number of M1 and M2 macrophages in stromal vascular fraction(SVF) of epididymal fat pad was detected through flow cytometry method(FCM). Data was analyzed by SPSS 17.0.Results 1. Effects of BPA exposure on obesity. 1.1 General condition During the experiment, mice were in good condition without adverse reaction and no mice died. There was no statistically significant difference between BPA treated groups and solvent control groups in terms of water intake and food intake(P>0.05). 1.2 Mice in HFD groups gained more weight comparing with mice in ND groups after BPA exposure. Compared with their own solvent control group, the body weight of BPA treated groups was increased in ND groups and HFD groups in a dose- and time-dependent manner. Compared with solvent control group, there was significant difference after 12 weeks in 1000 n M BPA group in terms of body weight in ND groups(P<0.05). And this took 19 weeks in 100 n M BPA group. Compared with solvent control group, there was significant difference after 11 weeks in 1000 n M BPA group in terms of body weight in HFD groups(P<0.05). And this took 15 weeks in 100 n M BPA group. 1.3 Effects of BPA exposure on mouse organ coefficients. 1.3.1 Mice epididymal fat pad coefficient in HFD groups increased more comparing with ND groups after BPA exposure. Compared with their own solvent control group, mice epididymal fat pad coefficient of BPA treated groups was increased in ND groups and HFD groups in a dose- and time-dependent manner. Compared with solvent control group, there was significant difference after 16 weeks in 1000 n M BPA group in terms of epididymal fat pad coefficient in ND groups(P<0.05). And this took 20 weeks in 100 n M BPA group. Compared with solvent control group, there was significant difference after 12 weeks in 1000 n M BPA group in terms of epididymal fat pad coefficient in HFD groups(P<0.05). And this took 16 weeks in 100 n M BPA group. 1.3.2 Mice liver coefficient in HFD groups increased more comparing with ND groups after BPA exposure. Compared with their own solvent control group, mice liver coefficient of BPA treated groups was increased in ND groups and HFD groups in a dose- and time-dependent manner. Compared with solvent control group, there was significant difference after 16 weeks in 1000 n M BPA group in terms of liver coefficient in ND groups(P<0.05). Compared with solvent control group, there was significant difference after 12 weeks in 1000 n M BPA group in terms of liver coefficient in HFD groups(P<0.05). And this took 16 weeks in 100 n M BPA group.1.3.3 There was no significant difference in spleen coefficient in both ND and HFD groups(P>0.05). 2. Effects of BPA exposure on adipose tissue inflammation. 2.1 Compared with their own solvent control group, adipose cell volume, cell gap and the infiltration of inflammatory cells in BPA treated groups were increased in ND groups and HFD groups in a dose- and time-dependent manner, analyzing by HP. Compared with ND groups, adipose cell volume, cell gap and the infiltration of inflammatory cells increased more in HFD groups. 2.2 Compared with their own solvent control group, the expression of IL-6 and IL-1β in adipose tissue in BPA treated groups was increased in ND groups and HFD groups in a dose- and time-dependent manner, analyzing by IHC. Compared with ND groups, the expression of IL-6 and IL-1βincreased more in HFD groups. 3. Effects of BPA exposure on the accumulation of ATMs. Compared with their own solvent control group, the expression of F4/80 in adipose tissue in BPA treated groups was increased in ND groups and HFD groups in a dose- and time-dependent manner, analyzing by IF. Compared with ND groups, the expression of F4/80 in adipose tissue increased more in HFD groups. 4. Effects of BPA exposure on the number of M1 and M2 ATMs Compared with their own solvent control group, the expression of CD11 c in BPA treated groups was increased in ND groups and HFD groups in a dose- and time-dependent manner, analyzing by FCM. Compared with ND groups, the expression of CD11 c increased more in HFD groups. Compared with solvent control group, there was significant difference at 8 weeks in 1000 n M BPA group in ND groups and in 100 n M and 1000 n M BPA groups in HFD groups in terms of the expression of CD11c(P<0.05). There was significant difference at 12, 16 and 20 weeks in 100 n M and 1000 n M BPA groups in both ND and HFD groups comparing with solvent control group(P<0.05). The expression of CD206 in ND solvent groups increased in a time-dependent manner. Compared with solvent control group, the expression of CD206 in 1000 n M BPA group at 16 weeks decreased(P<0.05). Compared with solvent control group, the expression of CD206 in 10, 100 and 1000 n M BPA groups at 20 weeks decreased(P<0.05). The expression of CD206 in HFD groups showed no significant difference between BPA treated groups and solvent control groups(P>0.05).Conclusion 1. Expose low dose of BPA by drinking water can increase the body weight and epididymal fat pad coefficient in mice. 2. BPA exposure can cause the infiltration of inflammatory cells and enhance the expression of inflammatory factors in adipose tissue. 3. BPA exposure can lead to the accumulation of ATMs in epididymal fat pad and increase the number of M1 macrophages dramatically. 4. Increased proinflammatory M1 ATM may promote the accumulation of the adipose tissue macrophages and compound adipose tissue inflammation in obesity inducted by BPA. It plays an important role in the development of the occurrence of obesity. |
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