Effects of Anthocyanin and Flavanol Compounds on Lipid Metabolism and Adipose Tissue Associated Systemic Inflammation in Diet-Induced Obesity

Abstract

Background. Naturally occurring substances from the flavanol and anthocyanin family of polyphenols have been proposed to exert beneficial effects in the course of obesity. We hypothesized that their effects on attenuating obesity-induced dyslipidemia as well as the associated inflammatory sequelae especially have health-promoting potential. Methods. Male C57BL/6J mice (n = 52) received a control low-fat diet (LFD; 10 kcal% fat) for 6 weeks followed by 24 weeks of either LFD (n = 13) or high-fat diet (HFD; 45 kcal% fat; n = 13) or HFD supplemented with 0.1% w/w of the flavanol compound epicatechin (HFD+E; n = 13) or an anthocyanin-rich bilberry extract (HFD+B; n = 13). Energy substrate utilization was determined by indirect calorimetry in a subset of mice following the dietary switch and at the end of the experiment. Blood samples were collected at baseline and at 3 days and 4, 12, and 20 weeks after dietary switch and analyzed for systemic lipids and proinflammatory cytokines. Adipose tissue (AT) histopathology and inflammatory gene expression as well as hepatic lipid content were analyzed after sacrifice. Results. The switch from a LFD to a HFD lowered the respiratory exchange ratio and increased plasma cholesterol and hepatic lipid content. These changes were not attenuated by HFD+E or HFD+B. Furthermore, the polyphenol compounds could not prevent HFD-induced systemic rise of TNF-α levels. Interestingly, a significant reduction in Tnf gene expression in HFD+B mice was observed in the AT. Furthermore, HFD+B, but not HFD+E, significantly prevented the early upregulation of circulating neutrophil chemoattractant mKC. However, no differences in AT histopathology were observed between the HFD types. Conclusion. Supplementation of HFD with an anthocyanin-rich bilberry extract but not with the flavanol epicatechin may exert beneficial effects on the systemic early inflammatory response associated with diet-induced obesity. These systemic effects were transient and not observed after prolongation of HFD-feeding (24 weeks). On the tissue level, long-term treatment with bilberry attenuated TNF-α expression in adipose tissue.

Figure 1

Body and organ weights. Polyphenol supplementation does not attenuate HFD-induced obesity (baseline 22.95 ± 0.18) (a-b), total weight of visceral adipose depot (c), or total liver weight. Dotted line depicts baseline value. Significant (p < 0.05) from HFD (^∗∗ p < 0.01, ^∗∗∗ p < 0.001).

Figure 2

Metabolite utilization. Respiratory exchange ratio (RER; O₂ consumed/CO₂ produced) measured before and after dietary switch (a) and after 23 weeks (b) shows distinctive drop for all HFD groups in both the short and long term which is not enhanced by polyphenol supplementation.

Figure 3

Systemic and hepatic lipids. Serial plasma (a) cholesterol (2.23 ± 0.04 at baseline), (b) triglycerides (0.34 ± 0.04 at baseline), and (c) free fatty acids (0.84 ± 0.06 at baseline), as well as hepatic (d) free cholesterol, (e) total cholesterol, and (f) triglyceride content, are not affected by polyphenol supplementation. Dotted lines depict baseline values. Significant from HFD (^∗ p < 0.05, ^∗∗ p < 0.01).

Figure 4

Systemic proinflammatory mediators. (a) Polyphenols do not prevent the HFD-induced increase in levels of TNF-α as measured in serial plasma samples (10.50 ± 0.29 at baseline). (b) Plasma levels of the neutrophil chemoattractant mKC are suppressed in the HFD+B group until 4 w but increase thereafter (49.00 ± 3.63 at baseline). Dotted lines depict baseline values. Significant from HFD (^∗ p < 0.05).

Figure 5

Adipose tissue inflammation at sacrifice. (a) Representative histological pictures of the visceral (gonadal) adipose tissue from different groups demonstrating an increase in the number of crown-like structures upon HFD-feeding which is not attenuated by polyphenols supplementation. (b) Quantification of crown-like structures (c) F4/80 and (d) MCP-1 gene expression confirm this phenotype. Expression of the IL-1β gene is not affected (e) in contrast to Tnf (f) which is significantly lower in the HFD+B group compared to HFD. Significant from HFD (^∗ p < 0.05, ^∗∗ p < 0.01, and ^∗∗∗ p < 0.001).