Abstract
BackgroundThe incidence of obesity has soared over the last several decades. There is mounting evidence suggesting that the increased presence of environmental endocrine disruptors (EEDs), including nonylphenol (NP), plays an important role in the incidence of lipid metabolism disorders. The aim of this work was to determine whether chronical exposure to NP could induce obesity and lipid metabolism disorders, both in vivo in Sprague–Dawley rats, and in vitro in 3T3-L1 preadipocytes. Forty rats (n = 10 per group) were gavaged with NP in corn oil at dose levels of 0.02 μg/kg/day (low dose, L), 0.2 μg/kg/day (middle dose, M), and 2.00 μg/kg/day (high dose, H) or corn oil alone (vehicle control, C) for 180 days. In vitro study, 3T3-L1 preadipocytes were exposed to NP at concentrations of 0, 40 pM, 40 nM, or 40 μM for 12 days.ResultsIn vivo, the fat weight (F = 103.605, P < 0.001) and fat coefficient (F = 169.807, P < 0.001) of NP-exposed rats were higher than those of control group rats. The serum levels of TC (F = 3.798, P < 0.05), LDL-C (F= 4.946,P < 0.05), and TG (F = 14.117,P < 0.05) in the H group were higher than those in the control group. Protein concentrations of CEBPα (F = 189.104, P < 0.001), FAS (F = 51.011, P < 0.001), PPARγ (F = 114.306,P < 0.001), and SREBP1 (F = 30.432,P < 0.001) in serum in the NP group were higher than those in the control group. The concentration of NP in adipose tissues of rats increased with an increase in NP exposure dose in a dose–response manner (F = 561.353,P < 0.001). The numbers of adipocytes in the M and H groups decreased, and the volume of a single cell increased with cells’ membranes ruptured. With the increase in NP exposure dose, the number of adipocytes per microscope decreased gradually (F = 85.873, P < 0.001). The expression levels of PPARγ (F = 169.936, P < 0.001) and FAS (F = 295.249, P < 0.001) proteins in the H group were higher than those in the control group. CEBPα (F = 101.086, P < 0.001) mRNA expression was up-regulated in the M and H groups; and FAS (F = 439.600, P < 0.001), PPARγ (F = 10.540, P < 0.001), and SREBP1 (F = 123.499, P < 0.001) mRNA expression in NP-exposed groups were significantly higher than those in the control group. In vitro, compared with the control group, the Oil Red Staining of adipocytes in the NP groups was darker, the fat cells were more densely distributed, and some of them fused into large lipid droplets. Expressions of CEBPα (F = 539.103, P < 0.001), FAS (F = 715.740, P < 0.001), PPARγ(F = 114.783, P < 0.001), and SREBP1 (F = 139.600, P < 0.001) proteins in 3T3-L1 preadipocytes were higher in group exposed to 40 μM NP than those in the control group.ConclusionsThe results of this in vivo and in vitro experiment were consistent, and both have demonstrated that NP exposure interfered with the expression of proteins and/or mRNAs of lipid metabolism-related regulators (CEBPα, FAS, SREBP1, PPARγ), promoted the proliferation and differentiation of adipocytes and intracellular accumulation of lipids, and eventually lead to blood lipid disorders and obesity in rats.
Highlights
The incidence of obesity has soared over the last several decades
NP level in adipose tissue increased with NP exposure dose in a dose–response manner
During 26 weeks (180 days) of NP exposure, there was a continuous increase of body weight showing as follows: H group > M group > L group > control group (F26w = 3.569,P26w = 0.023, Fig. 1)
Summary
There is mounting evidence suggesting that the increased presence of environmental endocrine disruptors (EEDs), including nonylphenol (NP), plays an important role in the incidence of lipid metabolism disorders. EEDs is lipophilic, which increases the duration in adipose tissue This will increase the incidence of obesity, and reinforce the retention of other lipophilic pollution chemicals, which in turn will produce more adverse reactions [12]. This may explain why obesity is a potential risk factor for many diseases, including cancers. Current epidemiological or animal experiments found [1, 12, 13] that some EEDs (such as bisphenol A, tributyltin, and phthalates) interfered with lipid accumulation and fat metabolism and resulted in obesity
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