Low-fat Mice Research Articles

Comparison of particle-exposure triggered pulmonary and systemic inflammation in mice fed with three different diets

BackgroundObesity can be linked to disease risks such as diabetes and cardiovascular disorders, but recently, the adipose tissue (AT) macrophage also emerges as actively participating in inflammation and immune function, producing pro- and anti-inflammatory factors. Connections between the AT and chronic lung diseases, like emphysema and asthma and a protective role of adipocyte-derived proteins against acute lung injury were suggested.In this study we addressed the question, whether a diet challenge increases the inflammatory response in the alveolar and the blood compartment in response to carbon nanoparticles (CNP), as a surrogate for ambient/urban particulate air pollutants.MethodsMice were fed a high caloric carbohydrate-rich (CA) or a fat-rich (HF) diet for six weeks and were compared to mice kept on a purified low fat (LF) diet, respectively. Bronchoalveolar lavage (BAL) and blood samples were taken 24 h after intratracheal CNP instillation and checked for cellular and molecular markers of inflammation.Results and discussionThe high caloric diets resulted in distinct effects when compared with LF mice, respectively: CA resulted in increased body and fat mass without affecting blood cellular immunity. Conversely, HF activated the blood system, increasing lymphocyte and neutrophil counts, and resulted in slightly increased body fat content. In contrast to higher pro-inflammatory BAL Leptin in CA and HF mice, on a cellular level, both diets did not lead to an increased pro-inflammatory basal status in the alveolar compartment per se, nor did result in differences in the particle-triggered response. However both diets resulted in a disturbance of the alveolar capillary barrier as indicated by enhanced BAL protein and lactate-dehydrogenase concentrations. Systemically, reduced serum Adiponectin in HF mice might be related to the observed white blood cell increase.ConclusionThe increase in BAL pro-inflammatory factors in high caloric groups and reductions in serum concentrations of anti-inflammatory factors in HF mice, clearly show diet-specific effects, pointing towards augmented systemic inflammatory conditions. Our data suggest that extended feeding periods, leading to manifest obesity, are necessary to generate an increased susceptibility to particle-induced lung inflammation; although the diet-challenge already was efficient in driving pro-inflammatory systemic events.

The Role of PDK4 in High Fat Diet - Induced Insulin Resistance

Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is a potential main regulator of the metabolic program that is shown to be activated by exercise and down-regulated by high fat feeding and sedentary lifestyle. It is shown that PGC-1α coactivates the pyruvate dehydrogenase kinase (PDK4) gene expression via the estrogen related receptor (ERRα). The expression of PDK4 is shown to be elevated with diabetes, fasting and other conditions associated with the switch from the utilization of glucose to fatty acids as an energy source. PURPOSE: Our aim in this study was to investigate the effects of high fat (HF) diet and physical activity in the expression levels of the above mentioned genes in the skeletal muscles of C57BL/6J mice. METHODS: In this experiment we induced insulin resistance by feeding high fat diet for 19 weeks to C57BL/6J mice. After 9 and 18 weeks on the diet, the fasting glucose and insulin levels were measured. The total cholesterol, free fatty acids and triglycerides were measured after the 19 - week experiment. The expression levels of the genes PGC-1α, ERRα and PDK4 were measured with quantitative RT-PCR and by Western blotting from the quadriceps femoris muscle. RESULTS:The HF animals had significantly higher diet - induced fasting glucose and insulin levels compared to low fat (LF) fed animals. The HOMA index indicated that after 18 weeks HF mice were more insulin resistant than LF mice, but no running effect could be seen. The HF animals showed an altered blood lipid profile suggesting changes in the overall lipid metabolism. Chronic HF feeding and voluntary running training did not have significant effects on PGC-1α mRNA or protein levels. Upregulation of ERRα and PDK4 was seen after HF diet and this combined with running had even more profound effects on the expression levels. CONCLUSIONS: We observed an up-regulated PDK4 expression along with more modest changes in PGC-1α and ERRα expression in response to both high fat diet and voluntary exercise. We speculate that this increased PDK4 expression is due to previous increase of the PGC-1α and ERRα expression, which subsequently blunts cellular glucose oxidation. In this scenario, PGC-1α is the master regulator of energy metabolism by regulating the increase of fatty acid oxidation and decreasing glucose oxidation via PGC-1α/ERRα pathway. Our data further suggests that the inhibition of pyruvate dehydrogenase complex by PDK4 must be contemplated as a possible mechanism or contributor to insulin resistance. The research was funded by the Finnish Ministry of Education and Culture.

Obesity and microglial activation: potential for synergism in neurodegenerative diseases

This study examines high fat diet feeding and obesity as a factor leading to the uncontrolled production of neuroinflammatory molecules by microglia, a hypothesized mechanism in the development of neurodegenerative diseases. We hypothesize that the inflammation resulting from a high fat diet and obesity activate microglia in the brain leading to increased neurodegeneration and will potentiate the neuroinflammation from a CNS insult. Weanling male mice were placed on a low fat (LF) or a high fat (HF) diet. After 4 weeks on the diet there is a modest, but significant, increase in leptin receptor expression on microglia from HF mice. In addition, there is a significant increase in the expression of toll‐like receptor (TLR) 2 on HF microglia. After 8 weeks, microglia from HF mice have significantly more TLR4/MD‐2 than LF microglia. MHC II is present on cells from both LF and HF mice at levels that are normally seen in young, healthy mice and there is no difference in MHCII expression between LF and HF microglia at these early time points. These data indicate that several cell surface proteins associated with microglial priming and activation are up‐regulated after only 4–8 weeks on a HF diet. As our population ages and becomes increasingly obese, the implications of diet on age related neurological conditions are a significant public health concern.This study was supported by the UNC NORC Grant DK56350.

Consumption of a high glycemic index diet increases abdominal adiposity but does not influence adipose tissue pro-oxidant and antioxidant gene expression in C57BL/6 mice

The hypothesis of this study is that consumption of a high glycemic index (GI) starch will increase adiposity, increase expression of the pro-oxidant enzyme (nicotinamide adenine dinucleotide phosphate [NADPH] oxidase), and decrease expression of the antioxidant enzymes (catalase, glutathione peroxidase [GPx], and superoxide dismutase [SOD]) in adipose tissue of mice. C57BL/6 mice (n = 5-8/group) were fed a diet containing either high-GI starch (100% amylopectin) or low-GI starch (60% amylose/40% amylopectin) under low-fat (LF) or high-fat (HF) conditions for 16 weeks. Meal tolerance tests (MTTs) indicated that the postprandial blood glucose response over 120 minutes for the high-GI mice under LF and HF conditions was significantly greater than for mice fed low-GI diets. This result was not due to increased food consumption by the high-GI mice during the MTT. Although there was no difference in body weight between mice fed high-GI or low-GI starch, LF high-GI mice had significantly greater adiposity compared to LF low-GI mice. High-fat mice had a significant increase in NADPH oxidase expression compared to LF mice, but there was no significant effect of starch on NADPH oxidase expression. High-fat diet significantly decreased the expression of GPx and catalase, but there was no significant effect of starch on GPx and catalase expression. There was no difference in SOD expression among any of the diet groups. In conclusion, high GI diets increase adiposity under LF conditions but do not influence pro-oxidant or antioxidant enzyme gene expression in adipose tissue of C57BL/6 mice.

Induction of muscle thermogenesis by high-fat diet in mice: association with obesity-resistance

The obesogenic effect of a high-fat (HF) diet is counterbalanced by stimulation of energy expenditure and lipid oxidation in response to a meal. The aim of this study was to reveal whether muscle nonshivering thermogenesis could be stimulated by a HF diet, especially in obesity-resistant A/J compared with obesity-prone C57BL/6J (B/6J) mice. Experiments were performed on male mice born and maintained at 30 degrees C. Four-week-old mice were randomly weaned onto a low-fat (LF) or HF diet for 2 wk. In the A/J LF mice, cold exposure (4 degrees C) resulted in hypothermia, whereas the A/J HF, B/6J LF, and B/6J HF mice were cold tolerant. Cold sensitivity of the A/J LF mice was associated with a relatively low whole body energy expenditure under resting conditions, which was normalized by the HF diet. In both strains, the HF diet induced uncoupling protein-1-mediated thermogenesis, with a stronger induction in A/J mice. Only in A/J mice: 1) the HF diet augmented activation of whole body lipid oxidation by cold; and 2) at 30 degrees C, oxygen consumption, total content, and phosphorylation of AMP-activated protein kinase (AMPK), and AICAR-stimulated palmitate oxidation in soleus muscle was increased by the HF diet in parallel with significantly increased leptinemia. Gene expression data in soleus muscle of the A/J HF mice indicated a shift from carbohydrate to fatty acid oxidation. Our results suggest a role for muscle nonshivering thermogenesis and lipid oxidation in the obesity-resistant phenotype of A/J mice and indicate that a HF diet could induce thermogenesis in oxidative muscle, possibly via the leptin-AMPK axis.

Effects of high-fat diet and/or body weight on mammary tumor leptin and apoptosis signaling pathways in MMTV-TGF-α mice

IntroductionObesity is a risk factor for postmenopausal breast cancer and is associated with shortened mammary tumor (MT) latency in MMTV-TGF-α mice with dietary-induced obesity. One link between obesity and breast cancer is the adipokine, leptin. Here, the focus is on diet-induced obesity and MT and mammary fat pad (MFP) leptin and apoptotic signaling proteins.MethodsMMTV-TGF-α mice were fed low-fat or high-fat diets from 10 to 85 weeks of age. High-Fat mice were divided into Obesity-Prone and Obesity-Resistant groups based on final body weights. Mice were followed to assess MT development and obtain serum, MFP, and MT.ResultsIncidence of palpable MTs was significantly different: Obesity-Prone > Obesity-Resistant > Low-Fat. Serum leptin was significantly higher in Obesity-Prone compared with Obesity-Resistant and Low-Fat mice. Low-Fat mice had higher MFP and MT ObRb (leptin receptor) protein and Jak2 (Janus kinase 2) protein and mRNA levels in comparison with High-Fat mice regardless of body weight. Leptin (mRNA) and pSTAT3 (phosphorylated signal transducer and activator of transcription 3) (mRNA and protein) also were higher in MTs from Low-Fat versus High-Fat mice. Expression of MT and MFP pro-apoptotic proteins was higher in Low-Fat versus High-Fat mice.ConclusionThese results confirm a connection between body weight and MT development and between body weight and serum leptin levels. However, diet impacts MT and MFP leptin and apoptosis signaling proteins independently of body weight.

Carbohydrate restriction, prostate cancer growth, and the insulin‐like growth factor axis

Recent evidence suggests carbohydrate intake may influence prostate cancer biology. We tested whether a no-carbohydrate ketogenic diet (NCKD) would delay prostate cancer growth relative to Western and low-fat diets in a xenograft model. Seventy-five male SCID mice were fed a NCKD (84% fat-0% carbohydrate-16% protein kcal), low-fat (12% fat-72% carbohydrate-16% protein kcal), or Western diet (40% fat-44% carbohydrate-16% protein kcal). Low-fat mice were fed ad libitum and the other arms fed via a modified-paired feeding protocol. After 24 days, all mice were injected with LAPC-4 cells and sacrificed when tumors approached 1,000 mm(3). Despite consuming equal calories, NCKD-fed mice lost weight (up to 15% body weight) relative to low-fat and Western diet-fed mice and required additional kcal to equalize body weight. Fifty-one days after injection, NCKD mice tumor volumes were 33% smaller than Western mice (rank-sum, P = 0.009). There were no differences in tumor volume between low-fat and NCKD mice. Dietary treatment was significantly associated with survival (log-rank, P = 0.006), with the longest survival among the NCKD mice, followed by the low-fat mice. Serum IGFBP-3 was highest and IGF-1:IGFBP-3 ratio was lowest among NCKD mice while serum insulin and IGF-1 levels were highest in Western mice. NCKD mice had significantly decreased hepatic fatty infiltration relative to the other arms. In this xenograft model, despite consuming more calories, NCKD-fed mice had significantly reduced tumor growth and prolonged survival relative to Western mice and was associated with favorable changes in serum insulin and IGF axis hormones relative to low-fat or Western diet.

PTP1B: A molecular mediator of leptin resistance.

Leptin acts in the brain to suppress food intake and body adiposity, but in most cases obesity is associated with a resistance to leptin action. Protein tyrosine phosphatase 1B (PTP1B) dephosphorylates key components of the leptin receptor signaling cascade, and represents a molecular mediator of leptin resistance. Our recent work demonstrates that hypothalamic PTP1B levels are elevated in a model of aging-induced leptin resistance, and that acute inhibition of PTP1B improves hypothalamic leptin sensitivity in this setting. We therefore tested whether hypothalamic PTP1B is increased in diet-induced obesity, another model of leptin resistance. Twenty-eight days of high-fat (HF) feeding increased body weight and fat pad weights ( P <0.05) compared to low-fat (LF), and also increased PTP1B protein levels in the mediobasal hypothalamus ( P =0.003). To define a mechanism underlying this HF-induced increase in PTP1B, the independent effects of hyperleptinemia and exposure to a high-fat diet were tested. Leptin-deficient ob/ob mice were fed LF or HF diets and treated with leptin or saline for 14 days. Leptin treatment increased hypothalamic PTP1B in the LF mice ( P =0.003), but had no effect in HF mice. However, HF mice exhibited a marked increase in hypothalamic PTP1B mRNA irrespective of leptin treatment ( P <0.001). These data are consistent with the hypothesis that increases in hypothalamic PTP1B contribute to leptin resistance in response to a high-fat diet. While chronic increases in circulating leptin are sufficient to increase PTP1B, HF diets also directly stimulate hypothalamic PTP1B via a leptin-independent mechanism.

No effect of dietary fat on short-term weight gain in mice treated with atypical antipsychotic drugs

Atypical antipsychotic drugs (AAD) induce significant weight gain in female C57BL/6J mice. The effect of dietary fat on weight gain and serum lipids in this model is unknown. Test the hypothesis that the obesigenic effects of these drugs are greater in the presence of a high-fat diet. Female C57BL/6J mice were treated with atypical antipsychotics for 3 weeks and fed either a low-fat or high-fat diet (4.6 vs 15.6% fat by wt). Food intake (FI), body weight (BW), body composition, and serum lipids were measured during treatment with optimized doses of olanzapine, quetiapine, and risperidone. Energy intake (EI) and feed efficiency (FE) were calculated. Group differences in change were analyzed via repeated measures analysis of variance (ANOVA). Serum lipid concentrations, EI and FE were compared using two-way ANOVA. AAD-treated mice gained significantly more weight than controls after 3 weeks (P<0.001). Treatment and diet had significant effects on FI and EI over time (P<0.001). AAD-treated mice had significantly higher FE than controls (P<0.05); however, there was no significant drug by diet interaction (P=0.65). Risperidone low-fat mice gained significantly more absolute fat mass than placebo low-fat mice (P<0.05). All treatment groups, except quetiapine low-fat and olanzapine high-fat, gained significantly more absolute lean mass than placebo controls (P<0.05). Cholesterol levels were significantly lower in quetiapine and risperidone than placebo (P<0.05). Risperidone low-fat mice had significantly higher triglyceride levels than placebo and risperidone high-fat mice (P<0.05). A high-fat diet does not increase AAD-induced BW gain in female mice during a 3-week treatment period.

Maternal diet composition alters serum steroid and free fatty acid concentrations and vaginal pH in mice

We examined the effects of three maternal diets (very high fat (VHF), low fat (LF), and control (Purina 5015)) on serum steroids, free fatty acids (FFA), and vaginal pH in National Institutes of Health Swiss mice. Females were fed (VHF, n = 33; LF, n = 33; 5015, n = 48) from 4 to 16 weeks of age. Following breeding, female serum was collected at 0.5 (pre-implantation, early diestrus) or 8.5 (post-implantation, mid-diestrus) days post-coitus (dpc). The serum concentrations of 17beta-estradiol, testosterone, progesterone, and FFA were analyzed at both collection points, and vaginal pH at 0.5 dpc. Striking differences in steroids and FFA were observed at 0.5 dpc among the groups. Estradiol was higher in the VHF (14.1 +/- 3.0 pg/ml), compared with LF mice (5.2 +/- 2.3 pg/ml; P< or = 0.05). In contrast, 0.5 dpc testosterone was lower in the VHF (10.5 +/- 3.0 pg/ml) versus the LF group (32.7 +/- 8.4 pg/ml; P< or = 0.05). At 8.5 dpc, progesterone was higher in the VHF (89.6 +/- 6.7 ng/ml) versus the 5015 group (60.1 +/- 4.9 ng/ml; P< or = 0.05). VHF mice had higher FFA concentrations at 0.5 dpc (1.0 +/- 0.2 mmol/l) than LF and control mice (0.5 +/- 0.1 and 0.6 +/- 0.1 mmol/l respectively; P< or = 0.05). At 8.5 dpc, VHF females had higher serum FFA (0.8 +/- 0.1 mmol/l) than LF and control females (0.4 +/- 0.1 and 0.6 +/- 0.1 mmol/l; P< or = 0.05). Mean vaginal pH of VHF females (6.41 +/- 0.09) was lower than 5015 females (6.76 +/- 0.10; P< or = 0.05). These diet-induced alterations in serum steroid and FFA concentrations might affect several reproductive processes, including preferential fertilization by one class of sperm over the other and sex bias in pre- and post-implantational embryonic development.

Diet-Induced Obesity and Mammary Tumor Development in MMTV-neu Female Mice

: Obesity is a risk factor for postmenopausal breast cancer and is associated with shortened latency and/or increased mammary tumor (MT) incidence in animals. Elevated body weight is usually associated with hormone-responsive tumors. In agreement with these data we previously showed that latency of hormone-responsive MTs in MMTV-TGF-α mice with diet-induced obesity was significantly shortened. Here, we used the same protocol to determine the impact of diet-induced obesity on estrogen receptor-negative MT development in MMTV-neu (strain 202) mice. Mice were fed a low-fat diet (n = 20) or a high-fat diet (n = 54) from 10 wk of age. Body weight at 19 wk of age was used to assign high-fat mice to obesity-prone, overweight, and obesity-resistant groups. Mice were euthanized due to MT size or at 85 wk of age. Final body weights of obesity-prone mice were heaviest, and those of obesity-resistant and low-fat groups were similar. Fat pad weights were heaviest in obesity-prone mice followed by overweight and obesity-resistant groups, and lightest in low-fat mice. Serum IGF-I levels were similar for low-fat and high-fat mice, whereas leptin was higher in high-fat mice (P < 0.0001). MT latency, incidence, metastasis, and burden were similar for all groups. These findings support that obesity is not a risk factor for development of estrogen-negative breast cancer.

Role of fat amount and type in ameliorating diet-induced obesity: insights at the level of hypothalamic arcuate nucleus leptin receptor, neuropeptide Y and pro-opiomelanocortin mRNA expression.

Dietary fatty acid profile, independent of caloric percent of fat, is a major regulator of body adiposity. This study examined the effects of dietary fat amount and types on fat storage and hypothalamic gene expression in the mouse model of chronic diet-induced obesity. The dietary interventions were in twofold: (1) the obesity was induced by a 13-week obesogenic fat diet compared with a low-fat (LF) diet, and (2) the reversibility was tested by using high n-3 polyunsaturated fat (PUFA) and LF diets. Fifty-four C57Bl/6 mice were fed a high-fat (59% in kcal) diet for 13 weeks and then classified as diet-induced obese (DIO) or diet-resistant (DR) mice according to upper and lower tertiles of body weight gain. The DIO mice were then subdivided into three groups for a 6-week secondary dietary intervention. Two of the groups were switched to either a high n-3 PUFA (DIO-n3) or a low-fat (10% in kcal, DIO-LF) diet, whereas the third (controls) and DR mice continued on the initial high-fat diet. Food efficiency was calculated as weekly body weight gain per gram of food intake. After switching the DIO mice to the n-3 PUFA or LF diet, their body weights were reduced to the level of the DR and LF mice. The food efficiencies were, from the highest to lowest, in the order: DIO>LF>DR>DIO-LF>DIO-n3. Using quantitative in situ hybridization, we found that the DIO mice had higher levels of leptin receptor (LR, +290%, p<0.005) and neuropeptide Y (NPY, +25%, p<0.05) mRNA expression in the hypothalamic arcuate nucleus (Arc) than the DR mice, whereas the level of pro-opiomelanocortin (POMC) mRNA expression was significantly reduced (-45%, p<0.01). All effects that were essentially returned to DR levels by the change to the n-3 PUFA diet and, with the exception of a failure to normalize Arc NPY mRNA levels, by the change to LF diet. Taken together, the present results show that both change in level and quality of dietary fat can potently alter hypothalamic neuropeptide expression and result in effective amelioration of diet-induced obesity. Interestingly, the n-3 PUFA diet when fed to already obese mice produced a pattern of hypothalamic gene expression similar to that in obesity resistant (DR) mice. It remains to be determined if the effects of n-3 fatty acids on brain neuropeptide gene expression are direct or indirect.

Size distribution of adipocytes and variation in adipocyte number in lines of mice selected for high or low body fat

1. 1. Adipocyte size and number were measured in epididymal fat pads from lines of mice selected for high or low body fat. 2. 2. Epididymal fat pad weight at 10 weeks of age was 4-fold greater in the high fat than the low fat mice, accompanied by a 7-fold greater adipocyte volume but there was no difference in adipocyte number. Smaller differences in fatness and cell volume were observed at younger ages. 3. 3. The high fat mice showed one or two populations of cells up to 5 weeks of age and at 7 weeks 3 days and 10 weeks showed two or more populations. In contrast, the low fat animals at all ages showed either one or two populations. 4. 4. These findings imply that greater lipogenesis and cell filling, not cell proliferation, is the primary mechanism of increased fatness in these selected lines of mice.

Effects of diet composition and fasting on glucose turnover in lean and polygenic obese mice

Effects of high beef tallow (BT), high corn oil (CO) or low-fat (LF) diets upon the outcome of genetic obesity were investigated. Diets were instituted ad libitum at the time of weaning. When mice were six months of age, blood samples were taken 1, 5, 15, 30, and 60 minutes after intravenous injection of glucose-U- 14C. Within dietary treatments, obese and lean mice showed similar plasma glucose-U- 14C disappearance patterns. Plasma glucose disappearance always tended to be faster in ad libitum-fed mice relative to 24-hour fasted mice. Body glucose pool sizes tended to be larger in fed obese BT and LF mice compared to their lean counterparts. This pattern was not seen in non-fasted CO mice. Fasting caused a decrease in body glucose pool sizes in all mice. In contrast to CO and LF mice, lean BT mice appeared to conserve glucose during fasting the same as the obese line. Since the glucose disappearance curves can be described by a two-exponential decay function, at least a two-component or two-pool system must be involved in plasma glucose turnover. Calculated rate constants were used to express interchanges of carbon molecules between the glucose and glycogen pool and the net movement of glucose carbon to a carbon pool representing “irreversible end products”. The data indicate that differences in glucose metabolism, in part, explain the possibility that dietary energy source can overcome the genetic tendency to leanness.