The intake of high-fat diet rich in saturated fat is associated with the pathogenesis of obesity and metabolic diseases. Several methods are used to minimize the effects of excessive body fat deposition, including foods rich in bioactive compounds. Results from previous studies have demonstrated the anti-obesity properties of compounds, such as whey peptides [2, 12, 25].
Our results suggest that treatment of Swiss mice with a high-fat diet for 9 weeks did not increase weight gain, findings which support the results of previous work [26, 27], or induce significant changes in OGTT. Although the high-fat treatment did not induce changes in glucose homeostasis and weight, it was effective in triggering inflammatory processes as was seen in the decrease adiponectin/SAT ratio and the increased phosphorylation of the p50 subunit from the NF-κB complex in MES adipose tissue.
The lipopolysaccharides (LPS) and saturated fatty acids act on receptors of family Toll Like Receptor (TLR), in particular TLR4, activating the track of NF-κB, which favors the gene expression of pro-inflammatory adipokines [28, 29]. Signal transmission mediated by connection between LPS and TLR4 constitutes a highly complex and varied phenomenon, mediated through reactions involving phosphorylation and ubiquitination of target proteins. Specifically involved is MyD88 protein activation of the complex IRAK (IL-1 receptor associated Kinase) -TRAF 6 (TNF receptor-associated factor), the latter belongs to the ubiquitin ligases class (E3 ligases) and appearsto be essential for the NF-κB uncoupling, its inhibitory protein (Iκ-B). NF-κB, once released, migrates to the nucleus by binding to DNA, starting the genic amplification of proteins related to inflammation .
TLR-4 activation by FFA or lipopolysaccharides (LPS) in adipocytes may be involved in the development of IR in obesity and DM2 [31, 32].
Adipose tissue serves as an energy reserves in addition to functioning as an endocrine organ which secretes proteins and cytokines [33, 34]. For example adiponectin, an adipokine secreted almost exclusively by adipose tissue increases insulin sensitivity and has anti-atherogenic effect by reducing the inflammatory process, and is usually found in lower amount in obese individuals [35, 36].
In this experimental study we attempted to induce metabolic changes with the administration of a high-fat diet to mice for five weeks and subsequently treated the animals with chitosan coacervate WP for four more weeks concurrently with the diet. It was expected that the coacervate reduced body weight, similarly to other studies of WP, but our findings for coacervate WB were not consistent with the literature. The HC group animals showed an increase in body weight gain compared to the other experimental groups and SAT increased compared with group C. We hypothesize that the body mass gain of the HC animals was not due solely to fat depots, as was evident once differences in fatty tissue between the H and HC groups were not observed. Probably the body mass gain could be related to the increase of body fat free mass.
Analyzing the serum lipid profile, we found that H and HC groups showed lower concentrations of triacylglycerol than group C. This result can be explained by differences in the carbohydrate rate offers in the control and high-fat diet, where the high fat diet groups received a minor CHO rate. The high-fat diet possibly increased lipoprotein lipase activity and consequently stimulated the uptake of fatty acids by adipose tissue and reducing the hepatic lipogenesis, resulting in a decrease in serum TG [37, 38].
The IL-10 is a pleiotropic cytokine that controls inflammatory processes by eliminating the pro-inflammatory cytokines production such as IL-1, IL-6, IL-8 and TNF-α is produced mainly by monocytes, macrophages, lymphocytes, mast cells and mature adipocytes . The IL-10/TNF-α ratio has been considered an important indicator of inflammatory status as low values are often associated with increased morbidity and mortality risk [40, 41].
Interestingly, we observed an increase of the IL-10/TNF-α ratio in MES of group HC despite the expectation of finding a reduced ratio in this group. We believe that because of the short period of the treatment the animals may still be attempting to reverse their pro inflammatory state, which increased IL-10/TNF-α ratio leading to an anti-inflammatory state. With increased length of treatment we may have found a reduced ratio of IL-10/TNF-α. According the results of this study coacervate may have protected the mice from a pro inflammatory state triggered by the treatment diet, since this ratio was equal to the control, however, a study involving a longer treatment period may be required to discern this possible effect.
Differences between mesenteric adipose tissue and other fatty tissues responses can be explained by the difference in inflammatory marker secretory capacity and in the number of resident macrophages in both depots. Cytokine production of macrophages is higher in MES, and these cells are important to adipose tissue maintenance being highly responsive to inflammatory effects .
Multiple intracellular pathways are involved in the secretion of newly synthesized IL-10 from macrophages following TLR4 activation with LPS, as well, trafficking pathways for IL-6 and TNF-α in macrophages can simultaneously produce pro-inflammatory cytokines . Our results support this pathway due to the finding of a positive association between TNF-α, LPS with IL-10 in the liver tissue in the HC group. This result reinforces the view that the increase in the IL-10 concomitantly to LPS and TNF-α concentration is an important mechanism in reversing the inflammatory process.
The treatment time and the total body composition analysis can be considered as limitations of our study. A longer treatment time may lead to an increase an increase in body weight and alter the OGTT. Additionally, the fat free body mass measurement can explain the high body weight gain in the HC group. We showed the potential positive effects of coacervate whey protein supplementation on the metabolic profile and inflammatory pathways in mice fed with high-fat diet. We also provide evidence of the association between IL-10 and LPS in hepatic tissue when treated with coacervate. In future investigations os the effects of coacervate whey protein we suggest the evaluation of antioxidant enzymes activity, which may additionally illustrate the inflammatory cascade of TLR-4 activated by LPS, reflecting the endotoxemia caused by high-fat diet administration.
The inflammatory process is a complex reaction, in which the adipokines, cytokines, hormones and thousands of molecules appear to interact and play multiple roles on several metabolic pathways. In order to further validate the data previously presented. In addition, an analysis of correlation between IL-10 and TNF-α in MES adipose tissue, RET and liver of animals in the HC group, suggest an increase in the production of IL-10, could be useful in further elucidating the role of coacervate in reversing the inflammatory effets triggered by a high-fat diet.