Effects of arbitrarily high-fat diet feeding on food intake and body and tissue weights in swiss mice

134 HNUE JOURNAL OF SCIENCE DOI: 10.18173/2354-1059.2017-64 Chemical and Biological Science 2017, Vol. 62, Issue 10, pp. 134-142 This paper is available online at EFFECTS OF ARBITRARILY HIGH-FAT DIET FEEDING ON FOOD INTAKE AND BODY AND TISSUE WEIGHTS IN SWISS MICE Le Ngoc Hoan 1 , Nguyen Quang Huy 2 , Ho Thi Hong Van 3 and Nguyen Phuc Hung 1 1 Faculty of Biology, Hanoi National University of Education 2 The Olympia Schools, Hanoi 3 Vietnam Institute of Educational Science Abstract. In this study, we investigated effects of high-fat diet (HFD) on food intake and body and tissue masses in mice. Male Swiss mice at four-week of age were arbitrarily fed either a regular diet (RD) or a HFD (RD supplemented with 30% energy from lard) for 12 weeks. Results showed that feeding HFD significantly decreased the amount of food consumption. On the other hand, the HFD feeding did not affect body weight change in the early weeks but increased body weight at the later weeks of the feeding period. Consistent with this, white adipose tissue weights were higher in the HFD-fed mice. However, the liver and skeletal muscle weights were similar between the RD- and the HFD-fed mice. These findings suggest that the HFD-feeding has marked effects on food intake as well as body weight and white adipose tissue weight gain in mice. Keywords: High-fat diet, food intake, body weight, tissue weight. 1. Introduction The adverse effects of obesity on health expand across various organ systems and diseases. Obesity-induced metabolic dysfunction in fat tissue, liver, and skeletal muscle results in metabolic disorders, such as insulin resistance, type 2 diabetes, fatty liver diseases, and cardiovascular diseases [1]. Chronic inflammatory responses in adipose tissues, a remarkable feature of obesity and type 2 diabetes, is closely correlated with metabolic dysregulation in liver and muscle and leads, at least partly, to systemic inflammatory conditions [2]. Adipocytokines derived from adipose tissues such as tumor necrosis factor (TNF)-, interleukin (IL)-6, and monocyte chemoattractant protein (MCP)-1 play a key role in the induction of inflammation. These inflammatory molecules cause metabolic dysregulations [3, 4]. Additionally, it is also known that obesity is usually accompanied by nonalcoholic fatty liver disease (NAFLD) which contributes to Received September 25, 2017. Revised November 25, 2017. Accepted December 2, 2017. Contact Le Ngoc Hoan, e-mail address: lengochoan@gmail.com Effects of arbitrarily high-fat diet feeding on food intake and body and tissue weights in swiss mice 135 insulin resistance, hepatic steatosis, and lipid metabolic dysregulation, in the dependent visceral fats. NAFLD is characterized by the increased inflammatory cytokines and the number of immune cells [5]. These effects could be mediated by Kupffer cells living in liver, and/or by an immune cell populations migrated to the live in obese conditions [6]. Besides, there are also signs of enhanced inflammatory molecules release and increased inflammatory response in skeletal muscle of obesity. Muscle inflammation thus may be closely associated with infiltration of macrophages that are induced in obese muscle [7]. So far, it has been known that high-fat diet (HFD)-induced obesity is linked with increases in body weight and several tissue hypertrophy such as adipose tissues and liver both in human and mice [1, 8]. This is paralleled with increases in inflammatory responses and metabolic dysregulation in those as well as other tissues such as skeletal muscle [9]. Rodents have been considered as prominent experimental animals for studying models of human diseases, including obesity and metabolic disorders. Many such studies have been conducted in mice such as C57BL/6, AKR/J and DBA/2J in several laboratories in the world [10]. In Vietnam, several studies on obesity have been conducted in Swiss mice [11, 12], hence it is necessary to fully understand the relationship between high-fat diets and feeding regime and physiological conditions of this mouse model. Unfortunately, the effects of high-fat diet on food intake, body and tissue weights in the mice are not very clear yet. In the present study, we arbitrarily fed Swiss mice with a high-fat diet and determined changes in food intake, body weight and several metabolic tissue weights in the mice. 2. Content 2.1. Materials and Methods * Animals and diets Male Swiss mice at the four-week of age were purchased from the National Institute of Hygiene and Epidemiology (NIHE). Mice were housed in an animal facility, where 12-12 h light-dark cycle was maintained. For 12 weeks, the mice were fed a regular diet (RD) (5% energy from lipid) or a high-fat diet (30% energy from lard). The RD was also purchased from the NIHE. The mice were arbitrarily fed with food and water and were weighted weekly to monitor changes in their body weight. The added food and remained food in each group were also weighted weekly to determine differences in food intake. After 12 weeks, the animals were killed by decapitation. White adipose tissues, liver and skeletal muscles were dissected and measured. * Statistical analysis The results were shown as means ± standard error of the mean (SEM). Comparisons of variables were conducted by using Student’s t test or analysis of variation (ANOVA) with Duncan’s multiple-range examination. Differences were supposed to be significant when P<0.05. 2.2. Results and discussion 2.2.1. Effect of high-fat diet feeding on food intake and feed conversion ratio Obesity is resulted from higher food intake and/or lower energy expenditure. To test whether high-fat diet (HFD) feeding alters food intake, we compared amount of food Le Ngoc Hoan, Nguyen Quang Huy, Ho Thi Hong Van and Nguyen Phuc Hung 136 intake in RD- and HFD-fed mice. Surprisingly, the result showed that food intake of HFD-fed mice was significantly lower that of LFD-fed mice (Figure 1A). Indeed, previous studies have shown that high-fat diet seemingly suppressed food intake in mammals [13]. Fat intake is typically regulated via specific signals, which when overworking results in appetite suppression [14]. Several hormones have been described as regulators of the satiety for fat. Peptide YY (PYY), cholecystokinin (CCK), and neuropeptide Y (NPY) are found to inhibit fat intake [15-17]. Additionally, the previous study demonstrated that the satiety hormone CCK was secreted by fat infusion into the intestine [18]. And thus, this suggested that the effects of fat on satiety are related with the small intestine area where fat receptors are located. Fatty acids are crucial to stimulation of satiety hormone secretion, hence, a satiety property of fat is useable when fat digestion is completed [19]. When discussion on body weight with different diets, one of important parameters is feed conversion ratio (FCR) which is a ratio of amount of food intake (gram) per body weight gain (gram). This means that when a food has a low FCR, it spends less food amount to increase a gram of body weight than it would if the FCR was high [20]. In the present study, our data showed that FCR of the HFD-fed mice was significantly lower than that of the RD-fed mice (Figure 1B), suggesting that the HFD-fed mice had higher feed efficiency. Presumably, the HFD has a stronger effect on body weight gain than the normal diet does. Thus, feeding with the HFD will result in higher risk of obesity. 0 20 40 60 80 RD HFD ** F o o d i n ta k e ( g r a m /w e e k ) 0 10 20 30 RD HFD ** F e e d c o n v e r si o n r a ti o ( % ) A B Figure 1. Food intake and feed conversion ratio Four week-old male Swiss mice were fed a regular diet (RD) or a high-fat diet (HFD) for 12 weeks. (A) Change in food intake. (B) Difference in feed conversion ratio. Data are presented as means ± SEM; n = 6 in each group. **P<0.01 compared with RD-fed mice. 2.2.2. Effect of high-fat diet feeding on body weight The mice were arbitrarily fed with a RD or a HFD for 12 weeks. To test whether body weight is altered by HFD-feeding, we measured body weight of the HFD-fed mice and of the RD-fed control mice weekly. As shown in Figure 2A, the body weight of the HFD-fed mice was similar to that of the RD-fed mice from week 1 to week 6. However, from week 7 to week 12, the body weight of the HFD-fed was highly increased compared with that of the RD-fed mice. Consistent with this, the gross morphology of the HFD-fed mice was differed from that of the RD-fed mice at week 12 (Figure 2B). Effects of arbitrarily high-fat diet feeding on food intake and body and tissue weights in swiss mice 137 Since young age mammals have high metabolic rate, and aging is usually often associated with obesity [21], the HFD might give the effect on body weight at later weeks of the feeding period. There have been evidences supported a rise in such age-related obesity and metabolic disorders such as cardiovascular disease and diabetes [22]. Indeed, aging shares numerous biological similarities with the obesity such as chronic low grade- inflammation and increased reactive oxygen species [22, 23]. As a result, aging is also characterized by a progressive dysfunction of the white adipose tissue, leading to white adipose tissue hypertrophy [23]. 0 1 2 3 4 5 6 7 8 9 10 11 12 20 30 40 50 60 70 * * HFD RD B o d y w ei g h t (g ra m ) HFDRD B A Figure 2. Body weight changes and body shape of HFD-fed mice Four week-old male Swiss mice were fed a regular diet (RD) or a high-fat diet (HFD) for 12 weeks. (A) Weekly body weight changes. (B) Gross morphology of mice. Data are presented as means ± SEM; n = 6 in each group. *P<0.05 compared with RD-fed mice. 2.2.3. Effect of high-fat diet feeding on white adipose tissue weights Obesity is often accompanied by white adipose tissue dysfunction and hypertrophy [1]. To examine if HFD-feeding alters fat mass, we measured white adipose tissue weights of both mouse groups. As shown in Figure 3A, the weights of the epididymal and renal fat pads in the HFD-fed mice were significantly higher than those in the RD-fed mice. Parallel with this, the weight of the subcutaneous fat pads in the HFD-fed mice was also tended to be higher than that in the RD-fed mice. In addition, the gross morphology of the white adipose tissues showed the hypertrophy in epididymal, subcutaneous and renal adipose tissues of the HFD-fed mice (Figure 3B). There have been evidences to prove the relation between obesity and white adipose tissue dysfunction and hypertrophy. This is resulted from the interaction of genetic and environmental factors [24]. Dispersal fat accumulation such as epididymal and renal fats may be a result of adipose tissue dysfunction. Moreover, obesity-related adipose tissue dysfunction is also characterized by increased lipid storage, increased proinflammatory cytokine secretion, and decreased insulin sensitivity in adipocytes [25]. Le Ngoc Hoan, Nguyen Quang Huy, Ho Thi Hong Van and Nguyen Phuc Hung 138 Epididymal Subcutaneous Renal 0.0 0.5 1.0 1.5 2.0 2.5 RD * ** HFD A d ip o se t is su e w e ig h t (g r a m ) Epididymal Subcutaneous Renal RD HFD BA Figure 3.Adiposity in HFD-fed mice Four week-old male Swiss mice were fed a regular diet (RD) or a high-fat diet (HFD) for 12 weeks. (A) Adipose tissue weight. (B) Gross morphology of adipose tissues. Data are presented as means ± SEM; n = 6 in each group. *P<0.05, **P<0.01 compared with RD-fed mice. 2.2.4. Effect of high-fat diet feeding on liver weight To examine the effect of HFD-feeding on changes in liver weight, we compared the weights of liver tissues of the two mouse groups after a 12 week-feeding period. Unfortunately, in the current study, we did not observed the insight changes in the weight and gross morphology of liver tissues in the HFD-fed mice compared to those in the RD- fed mice (Figure4A and 4B, respectively)although the HFD-fed mice showed higher liver tissue weight compared with did the RD-fed mice (Figure 4A). 0 1 2 3 4 5 RD HFD L iv e r t is su e w e ig h t (g r a m ) HFDRD BA Figure 4.Liver weight and shape of HFD-fed mice Four week-old male Swiss mice were fed a regular diet (RD) or a high-fat diet (HFD) for 12 weeks. (A) Liver tissue weight. (B) Gross morphology of liver tissues. Data are presented as means ± SEM; n = 6 in each group. Effects of arbitrarily high-fat diet feeding on food intake and body and tissue weights in swiss mice 139 It has been known that obesity is also paralleled with ectopic fat (e.g., triglycerides) deposition in the liver, leading to increases in liver tissue weight and the risk of nonalcoholic fatty liver disease (NAFLD) as well as other metabolic disorders such as insulin resistant and type 2 diabetes [8, 26]. Obesity-related NAFLD is characterized by steatosis occurring when the rate of hepatic fatty acid influx from plasma and de novo liver fatty acid synthesis are higher than the rate of fatty acid oxidation and outflux [27]. Hence, a non-significant changes in liver weight observed in the present study might be attributed to differences in mouse mode and feeding time course. In sum, understanding the key factors involved in the pathophysiology of liver fatty may show important mechanisms responsible for the obesity and its related metabolic complications. 2.2.5. Effect of high-fat diet feeding on skeletal muscle weights The next was to compare the changes in skeletal muscle tissue weights between the HFD-fed mice and the RD-fed mice. As shown in Figure 5A, weights of quadriceps, gastrocnemious, and soleus muscles were not significantly altered by HFD-feeding. Consistent with this, the color and gross morphology of those muscles was the same between the two mouse groups (Figure 5B). Skeletal muscle is the biggest tissue in the human body, with a variety of physiology function, thus changes in muscle mass results in changes in metabolic function [28]. Indeed, it is reported that a mild increase in the skeletal muscle mass was paralleled with a reduction in the risk of type 2 diabetes [29]. Moreover, obesity is often accompanied by skeletal muscle atrophy which is characterized by decreased muscle mass [30-32]. Therefore, the mechanism involved in obesity-induced skeletal muscle atrophy may be due to the increase in inflammatory cytokines such as IL-6, MCP-1, TNF, that in turn enhance the expression of Atrogin-1 and MuRF1 (muscle ring-finger protein1) - key factors causing muscle atrophy [32-34]. In the present study, we did not observe the changes in skeletal muscle mass between the HFD-fed mice and the RD-fed mice. This also might be attributed to differences in mouse model, feeding time or other factors that need to be further uncovered. Quadriceps Gastrocnemius Soleus 0.0 0.2 0.4 0.6 0.8 RD HFD S k e lt a l m u sc le w e ig h t (g r a m ) HFDRD Quadriceps Gastrocnemius Soleus BA Figure 5. Skeletal muscle weight and shape of HFD-fed mice Four week-old male Swiss mice were fed a regular diet (RD) or a high-fat diet (HFD) for 12 weeks. (A) Skeletal muscle tissue weight. (B) Gross morphology of skeletal muscle tissues. Data are presented as means ± SEM; n = 6 in each group. 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