The effect of the high-fat diet supplemented with various forms of chromium on rats body composition, liver metabolism and organ histology Cr in liver metabolism and histology of selected organs
Introduction
Obesity is one of the most serious problems facing today's society. It is defined as regional and / or global excess fat accumulation in the body. The tendency to gain weight may have a genetic basis, but it is largely due to environmental factors, such as eating a high-calorie diet rich in fats with low physical activity [1]. Importantly, eating a high-fat diet dramatically increases the risk of developing many chronic diseases, such as diabetes, cardiovascular diseases and cancer [[2], [3], [4]]. In addition, obesity is associated with disturbances in the metabolism of nutrients, leading to excessive accumulation of fat in the liver. As a consequence, this leads to its damage and the occurrence of nonalcoholic fatty liver disease (NAFLD). Observations of patients and studies conducted in an animal model indicate that NAFLD is accompanied by lipotoxicity leading to apoptosis and even necrosis of hepatocytes, as well as intensification of oxidative stress and inflammation. As a consequence, it may lead to the development of insulin resistance, and in extreme cases even liver necrosis [5,6]. Therefore, in order to treat obesity and prevent its negative health effects, dietary supplements containing chromium (III) are increasingly used [7].
Chromium (III) is considered an essential trace element for humans and animals. It is involved in numerous processes in the body, of which its role in carbohydrate metabolism is the best known. The first reports on the role of chromium in carbohydrate metabolism appeared in the late 1950s, when Schwarz and Mertz isolated a protein component from porcine kidneys which restored impaired glucose tolerance in rats [8]. This component, called glucose tolerance factor (GTF), is a complex which, apart from chromium(III), also contains nicotinic acid and amino acids: glutamic acid, glycine and cysteine. Trivalent chromium is also part of chromodulin, a low-molecular-weight chromium-binding substance which enhances insulin receptor activity through phosphorylation [9]. Moreover, Chen et al. [10] demonstrated that chromium increases insulin-dependent translocation of glucose transporters (especially glucose transporter type 4-GLUT4) from the cytoplasm to the cell membrane, and consequently the initiation of active glucose transport into cells. In addition to regulating blood glucose levels, chromium also affects lipid metabolism. Studies in cattle and rats have demonstrated that a diet with a high level of chromium decreases levels of total cholesterol, LDL, and triglycerides, while increasing levels of HDL cholesterol [[11], [12], [13]]. Due to its ability to reduce body fat and increase the percentage of lean body mass, preparations containing chromium are used not only in the treatment of type II diabetes, but also as slimming aids [7]. Chromium is also involved in protein synthesis and nucleic acid metabolism [14]. Moreover, it contributes to the functioning of immune mechanisms by modulating synthesis of numerous cytokines: IL-1, IL-2, IL-6, INF and TNF-α [15]. In animal feeding, chromium has been used to improve growth performance, meat quality, insulin sensitivity, and immune reactions, as well as to reduce various stress responses [16]. Chen et al. [17] demonstrated that chromium attenuates inflammation and oxidative stress in mice fed a high-fat diet. In rats receiving a high-fat diet, in which hepatic steatosis is often observed, probably due to excessive accumulation of triglycerides, administration of chromium reduces insulin resistance and protects the liver against fatty changes, presumably by improving intracellular insulin signalling. Therefore, chromium is readily used not only in animal nutrition but also as an ingredient in supplements used in the treatment of obesity in humans [7]. Studies conducted both on patients suffering from type 2 diabetes and severe insulin resistance indicate that Cr supplementation improves insulin metabolism, and consequently also carbohydrate metabolism [18,19]. Moreover, the addition of Cr in the diet of obese people reduces appetite and reduces body weight [20]. Therefore, in order to maintain a proper body weight and health condition, a daily supplementation of Cr at the level of 25 μg and 35 μg is recommended for women and men, respectively [21].
Chromium appears in the animal diet and human obesity treatment in inorganic form, but this source is not well absorbed by organism [22]. It is estimated that the absorption efficiency of chromium from inorganic sources is only 0.4–2.5% [21]. During digestion, inorganic chromium compounds form insoluble complexes and can also adhere to carbohydrates in the diet, which may limit their absorption [23]. The availability of organic forms is thought to be ten times greater than that of inorganic forms [24]. Research is currently being conducted on the possibility of using chromium in nanoparticle form as a dietary supplement for animals [[24], [25], [26]], in line with the general trend of increasing interest in nanotechnology.
In the present study, we hypothesized that feeding rats a high-fat diet negatively affects liver metabolism and function and disturbs the histology of some internal organs. We also postulated that there is a form of chromium whose administration alleviates the negative effects of a high-fat diet in rats. To verify the hypotheses, we tested the effect of various forms of chrome (picolinate – Cr-Pic, Chromium(III)-methionine complex – Cr-Met, and chrome nanoparticles – Cr-NPs) applied at the recommended level on growth parameters, body fat, metabolism and functional disorders of the liver, and histological parameters of selected internal organs in rats fed a standard or high-fat diet.
Section snippets
Forms of chromium used in the experiment
Chromium picolinate (Cr-Pic; purity > 980 g/kg) was purchased from Sigma-Aldrich Sp. z o.o. (Poznan, Poland). Chromium-methionine complex (Cr-Met) was purchased from Innobio Co., Ltd. (Siheung, South Korea). Chromium nanopowder (Cr-NPs) with 99.9 % purity, size 60∼80 nm, spherical shape, specific surface area 6–8 m2/g, bulk density 0.15 g/cm3, and true density 8.9 g/cm3, was purchased from SkySpring Nanomaterials (Houston, TX, USA).
Animals and diets
The experiment was conducted on 56 male outbred Wistar rats (
Effect of a high-fat diet in rats
Administration of a high-fat diet to rats increased daily weight gain (P = 0.035) and final body weight (P = 0.008), while reducing daily food intake (P = 0.042) and kidney weight (P = 0.021; Table 2).
Administration of a high-fat diet for both 4 and 8 weeks increased body weight (P = 0.003 and P = 0.007, respectively) and the percentage of body fat (P = 0.021 and P = 0.003, respectively) in rats while reducing the proportion of lean tissue (P = 0.041 and P = 0.029, respectively). This
The effect of high-fat diet on growth parameters, body composition, blood parameters and organ histology
In this study, the energy density of the high-fat diet was 2.78 kcal/g greater than that of the control one. This difference was caused by the lard addition in place of a proportion of corn starch and cellulose, which were the dietary carbohydrate (4 kcal/g) and fibre (in that case 0 kcal/g) sources, respectively. Although the diet intake was significantly decreased by the high-fat treatment, the higher energy consumption during the feeding period was sufficient to induce obesity by the end of
Conclusions
The use of a high-fat diet disrupts the lipid-carbohydrate profile, worsens liver metabolism and function, reduces the expression of hepatic PPAR-α and leads to negative changes in the histological image of internal organs - liver, kidneys and pancreas.
The 8-week use of an chromium supplement in a high-fat diet, regardless of the form used, does not improve the ratio of fat tissue to lean tissue, worsens liver function and negatively affects on the histological image of the liver, kidneys and
CRediT authorship contribution statement
Katarzyna Ognik: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing - original draft. Wojciech Dworzański: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Validation, Visualization, Writing - original draft. Iwona Sembratowicz: Data curation, Formal analysis, Resources,
Declaration of Competing Interest
The authors report no declarations of interest.
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