Long term effects of high fat and sucrose diets on obesity and lymphocyte proliferation in mice

High fat intake aggravates hyperlipidemia and suppresses fatty liver symptoms induced by a high-sucrose diet in rats

Overconsumption of sucrose or fat is widely acknowledged as a prominent feature of unhealthy dietary patterns. Both factors commonly co-occur and are recognized as hallmarks of the Western diet, which is an important contributor to non-communicative diseases. In this study, we investigated the hazards of high sucrose or fat intake, either alone or in combination. Wistar rats were divided into four groups and fed a control starch diet, high-sucrose diet, high-fat diet, or high-sucrose/fat diet for 30 days. High fat intake increased body weight and visceral and subcutaneous adipose tissue weights. Both high-sucrose and -fat diets were associated with increased plasma triglyceride and glucose levels, and high sucrose also elevated plasma cholesterol levels. The combination of high sucrose and fat synergistically elevated plasma triglyceride levels. The high-sucrose diet increased liver weight and hepatic total lipid and triglyceride levels, whereas this increase was suppressed by the high-fat diet. The high sucrose increased the mRNA levels of hepatic genes involved in fatty acid synthesis and transport (ACLY, ACACA, FAS, ELOVL6, SCD1, SREBP1, and CD36), whereas the high fat suppressed the high sucrose-induced expression of these genes. We observed that high sucrose and fat contents differently exerted their effects on hyperlipidemia and fatty liver. Furthermore, high fat aggravated hyperlipidemia and suppressed fatty liver induced by high sucrose.

Increased Fruit and Vegetable Consumption Prevents Dysregulated Immune and Inflammatory Responses in High-Fat Diet-Induced Obese Mice

BACKGROUND

Obesity is often associated with impaired immune responses, including enlarged spleen, increased inflammation, and impaired T-cell-mediated function, which may lead to increased susceptibility to infections. Bioactive compounds found in various fruits and vegetables (F&V) have been shown to have strong anti-inflammatory effects. However, few prospective studies have examined the effects of F&V on preventing obesity-associated dysregulation of immune and inflammatory responses.

OBJECTIVE

The objective of this was to determine the impact of different levels of a mixture of F&V incorporated in a high-fat diet (HFD) on immune function changes in a diet-induced obesity animal model.

METHODS

Six-wk-old male C57BL/6J mice were randomly assigned to 1 of 5 groups (n = 12/group): matched low-fat control (LF, 10% kcal fat) or HFD (45% kcal fat) supplemented with 0%, 5%, 10%, or 15% (wt/wt) freeze-dried powder of the most consumed F&V (human equivalent of 0, 3, 5-7, 8-9 servings/d, respectively) for 20 wk. Spleen weight was recorded, and the immunophenotype of splenocytes was evaluated by flow cytometry. Ex vivo splenic lymphocyte proliferation was assessed by thymidine incorporation and serum cytokines concentrations were measured by Meso Scale Discovery.

RESULTS

Mice fed the HFD exhibited significantly higher spleen weight, decreased splenic CD8+ lymphocytes, suppressed T lymphocyte proliferation, and reduced serum IL-1ß and IFN-γ concentrations compared with those fed the LF diet. Feeding mice with the HFD supplemented with 10% or 15% F&V restored HFD-associated changes of these affected biomarkers compared with those fed HFD only. Furthermore, a significant correlation was found between immunologic markers and F&V level.

CONCLUSIONS

These results suggest that increased consumption of F&V has beneficial effects in preventing HFD-associated dysregulation of immune function.

Sex-Dependent T Cell Dysregulation in Mice with Diet-Induced Obesity

Obesity is an emerging public health problem. Chronic low-grade inflammation is considered a major promotor of obesity-induced secondary diseases such as cardiovascular and fatty liver disease, type 2 diabetes mellitus, and several cancer entities. Most preliminary studies on obesity-induced immune responses have been conducted in male rodents. Sex-specific differences between men and women in obesity-induced immune dysregulation have not yet been fully outlined but are highly relevant to optimizing prevention strategies for overweight-associated complications. In this study, we fed C57BL/6 female vs. male mice with either standard chow or an obesity-inducing diet (OD). Blood and spleen immune cells were isolated and analyzed by flow cytometry. Lean control mice showed no sex bias in systemic and splenic immune cell composition, whereas the immune responses to obesity were significantly distinct between female and male mice. While immune cell alterations in male OD mice were characterized by a significant reduction in T cells and an increase in myeloid-derived suppressor cells (MDSC), female OD mice displayed preserved T cell numbers. The sex-dependent differences in obesity-induced T cell dysregulation were associated with varying susceptibility to body weight gain and fatty liver disease: Male mice showed significantly more hepatic inflammation and histopathological stigmata of fatty liver in comparison to female OD mice. Our findings indicate that sex impacts susceptibility to obesity-induced T cell dysregulation, which might explain sex-dependent different incidences in the development of obesity-associated secondary diseases. These results provide novel insights into the understanding of obesity-induced chronic inflammation from a sex-specific perspective. Given that most nutrition, exercise, and therapeutic recommendations for the prevention of obesity-associated comorbidities do not differentiate between men and women, the data of this study are clinically relevant and should be taken into consideration in future trials and treatment strategies.

Impact of Plant-Based Dietary Fibers on Metabolic Homeostasis in High-Fat Diet Mice via Alterations in the Gut Microbiota and Metabolites

BACKGROUND

The gut microbiota contributes to metabolic disease, and diet shapes the gut microbiota, emphasizing the need to better understand how diet impacts metabolic disease via gut microbiota alterations. Fiber intake is linked with improvements in metabolic homeostasis in rodents and humans, which is associated with changes in the gut microbiota. However, dietary fiber is extremely heterogeneous, and it is imperative to comprehensively analyze the impact of various plant-based fibers on metabolic homeostasis in an identical setting and compare the impact of alterations in the gut microbiota and bacterially derived metabolites from different fiber sources.

OBJECTIVES

The objective of this study was to analyze the impact of different plant-based fibers (pectin, β-glucan, wheat dextrin, resistant starch, and cellulose as a control) on metabolic homeostasis through alterations in the gut microbiota and its metabolites in high-fat diet (HFD)-fed mice.

METHODS

HFD-fed mice were supplemented with 5 different fiber types (pectin, β-glucan, wheat dextrin, resistant starch, or cellulose as a control) at 10% (wt/wt) for 18 wk (n = 12/group), measuring body weight, adiposity, indirect calorimetry, glucose tolerance, and the gut microbiota and metabolites.

RESULTS

Only β-glucan supplementation during HFD-feeding decreased adiposity and body weight gain and improved glucose tolerance compared with HFD-cellulose, whereas all other fibers had no effect. This was associated with increased energy expenditure and locomotor activity in mice compared with HFD-cellulose. All fibers supplemented into an HFD uniquely shifted the intestinal microbiota and cecal short-chain fatty acids; however, only β-glucan supplementation increased cecal butyrate concentrations. Lastly, all fibers altered the small-intestinal microbiota and portal bile acid composition.

CONCLUSIONS

These findings demonstrate that β-glucan consumption is a promising dietary strategy for metabolic disease, possibly via increased energy expenditure through alterations in the gut microbiota and bacterial metabolites in mice.

T cells in obesity-associated inflammation: The devil is in the details

Obesity presents a significant health challenge, affecting 41% of adults and 19.7% of children in the United States. One of the associated health challenges of obesity is chronic low-grade inflammation. In both mice and humans, T cells in circulation and in the adipose tissue play a pivotal role in obesity-associated inflammation. Changes in the numbers and frequency of specific CD4+ Th subsets and their contribution to inflammation through cytokine production indicate declining metabolic health, that is, insulin resistance and T2D. While some Th subset alterations are consistent between mice and humans with obesity, some changes mainly characterize male mice, whereas female mice often resist obesity and inflammation. However, protection from obesity and inflammation is not observed in human females, who can develop obesity-related T-cell inflammation akin to males. The decline in female sex hormones after menopause is also implicated in promoting obesity and inflammation. Age is a second underappreciated factor for defining and regulating obesity-associated inflammation toward translating basic science findings to the clinic. Weight loss in mice and humans, in parallel with these other factors, does not resolve obesity-associated inflammation. Instead, inflammation persists amid modest changes in CD4+ T cell frequencies, highlighting the need for further research into resolving changes in T-cell function after weight loss. How lingering inflammation after weight loss affecting the common struggle to maintain lower weight is unknown. Semaglutide, a newly popular pharmaceutical used for treating T2D and reversing obesity, holds promise for alleviating obesity-associated health complications, yet its impact on T-cell-mediated inflammation remains unexplored. Further work in this area could significantly contribute to the scientific understanding of the impacts of weight loss and sex/hormones in obesity and obesity-associated metabolic decline.

Infections and immunity: associations with obesity and related metabolic disorders

About one-fourth of the global population is either overweight or obese, both of which increase the risk of insulin resistance, cardiovascular diseases, and infections. In obesity, both immune cells and adipocytes produce an excess of pro-inflammatory cytokines that may play a significant role in disease progression. In the recent coronavirus disease 2019 (COVID-19) pandemic, important pathological characteristics such as involvement of the renin-angiotensin-aldosterone system, endothelial injury, and pro-inflammatory cytokine release have been shown to be connected with obesity and associated sequelae such as insulin resistance/type 2 diabetes and hypertension. This pathological connection may explain the severity of COVID-19 in patients with metabolic disorders. Many studies have also reported an association between type 2 diabetes and persistent viral infections. Similarly, diabetes favors the growth of various microorganisms including protozoal pathogens as well as opportunistic bacteria and fungi. Furthermore, diabetes is a risk factor for a number of prion-like diseases. There is also an interesting relationship between helminths and type 2 diabetes; helminthiasis may reduce the pro-inflammatory state, but is also associated with type 2 diabetes or even neoplastic processes. Several studies have also documented altered circulating levels of neutrophils, lymphocytes, and monocytes in obesity, which likely modifies vaccine effectiveness. Timely monitoring of inflammatory markers (e.g., C-reactive protein) and energy homeostasis markers (e.g., leptin) could be helpful in preventing many obesity-related diseases.

Effects of in vitro vitamin D treatment on function of T cells and autophagy mechanisms in high-fat diet-induced obese mice

BACKGROUND/OBJECTIVES

Obesity is associated with the impaired regulation of T cells characterized by increased numbers of Th1 and Th17 cells and the dysregulation of vitamin D metabolism. Both obesity and vitamin D have been reported to affect autophagy; however, a limited number of studies have investigated the effects of vitamin D on T cell autophagy in obese mice. Therefore, we aimed to determine whether in vitro treatment with vitamin D affects the proliferation, function, and autophagy of T cells from obese and control mice.

MATERIALS/METHODS

Five-week-old male C57BL/6 mice were fed control or high-fat diets (10% or 45% kcal fat: CON or HFDs, respectively) for 12 weeks. Purified T cells were stimulated with anti-CD3 and anti-CD28 monoclonal antibodies and cultured with either 10 nM 1,25(OH)₂D₃ or 0.1% ethanol (vehicle control). The proliferative response; expression of CD25, Foxp3, RORγt, and autophagy-related proteins (LC3A/B, SQSTM1/P62, BECLIN-1, ATG12); and the production of interferon (IFN)-γ, interleukin (IL)-4, IL-17A, and IL-10 by T cells were measured.

RESULTS

Compared with the CON group, T cell proliferation tended to be lower, and the production of IFN-γ was higher in the HFD group. IL-17A production was reduced by 1,25(OH)2D₃ treatment in both groups. The LC3 II/I ratio was higher in the HFD group than the CON group, but P62 did not differ. We observed no effect of vitamin D treatment on T cell autophagy.

CONCLUSIONS

Our findings suggest that diet-induced obesity may impair the function and inhibit autophagy of T cells, possibly leading to the dysregulation of T cell homeostasis, which may be behind the aggravation of inflammation commonly observed in obesity.

Peculiarities of the effects of a high-calorie diet on the structural components of the lymph nodes and under melatonin correction

Obesity is a chronic recurrent disease that is manifested by excess accumulation of adipose tissue and is a consequence of an imbalance in energy utilization and consumption in persons with or without hereditary predisposition. The purpose of the study is to study the morphometric and histological changes of the parenchyma of the lymph nodes of rats in experimental obesity and under the conditions of melatonin correction. The study was performed on 66 white rats of reproductive age. Microanatomy of the structural components of lymph nodes of white rats under physiological norms was examined in 10 intact animals. Experimental animals were divided into 4 groups. Eight weeks after the experimental animals were on a high calorie diet (HCD), there was a significant decrease in the relative area of the cortical substance in the parenchyma of the lymph nodes of white rats of males and females by 10.3% and 8.3%, respectively, and an increase in the relative area of the medullary substance by 16.1% and 13.2%, respectively, compared to an intact group of animals.

The relative area of the cortical substance in the parenchyma of the lymph nodes of white rats, which were for two weeks on HCD, then six weeks on HCD and melatonin, exceeds the parameters of the intact group of animals by only 3.2% in males and 3.5% in females. The relative area of the medullary substance is less than that of the intact group of animals by 5.0% in males and 5.5% in females. Under the conditions of melatonin correction it is found that the germinal centers of the secondary lymph nodes in the cortical substance are slightly increased. Trabecules extending from the capsule are clearly expressed and thickened, while arteries and arterioles show thickened walls and are full-blooded. Moreover, the veins are enlarged and full-blooded.

High-Fat Diet-Induced Trefoil Factor Family Member 2 (TFF2) to Counteract the Immune-Mediated Damage in Mice

Simple Summary

High-fat (HF) diet induces both immune-mediated damage and trefoil factor family member 2 (Tff2) expression. As TFF2 has tissue repair and protection properties, this suggests that HF diet-induced Tff2 production and the resulting TFF2 mucosal protective effects would be a mechanism to counteract the HF diet-induced tissue damage. On the other hand, the induction of Tff2 by HF diet could indicate that TFF2 is a food intake regulator (appetite control) since Tff2 is also expressed in the brain. This highlights the importance of exploring TFF2-related pathways in the context of obesity management towards potential therapies.

Abstract

Physiological homeostasis requires a balance between the immunological functions and the resulting damage/side effects of the immunological reactions including those related to high-fat (HF) diet. Within this context, whereas HF diet, through diverse mechanisms (such as inflammation), leads to immune-mediated damage, trefoil factor family member 2 (Tff2) represents a HF diet-induced gene. On the other hand, TFF2 both promotes tissue repair and reduces inflammation. These properties are towards counteracting the immune-mediated damage resulting from the HF diet. These observations suggest that the HF diet-induction of Tff2 could be a regulatory pathway aiming to counteract the immune-mediated damage resulting from the HF diet. Interestingly, since Tff2 expression increases with HF diet and with Tff2 also expressed in the brain, we also hypothesize that TFF2 could be a HF diet-induced food intake-control signal that reduces appetite. This hypothesis fits with counteracting the immune damage since reducing the food intake will reduce the HF intake and therefore, reduces the HF diet-induced tissue damage. Such food intake signaling would be an indirect mechanism by which TFF2 promotes tissue repair as well as a pathway worth exploring for potential obesity management pharmacotherapies.

Maternal dietary imbalance between omega-6 and omega-3 fatty acids triggers the offspring's overeating in mice

The increasing prevalence of obesity and its effects on our society warrant intensifying basic animal research for understanding why habitual intake of highly palatable foods has increased due to recent global environmental changes. Here, we report that pregnant mice that consume a diet high in omega-6 (n-6) polyunsaturated fatty acids (PUFAs) and low in omega-3 (n-3) PUFAs (an n-6^high/n-3^low diet), whose n-6/n-3 ratio is approximately 120, induces hedonic consumption in the offspring by upregulating the midbrain dopaminergic system. We found that exposure to the n-6^high/n-3^low diet specifically increases the consumption of palatable foods via increased mesolimbic dopamine release. In addition, neurodevelopmental analyses revealed that this induced hedonic consumption is programmed during embryogenesis, as dopaminergic neurogenesis is increased during in utero access to the n-6^high/n-3^low diet. Our findings reveal that maternal consumption of PUFAs can have long-lasting effects on the offspring’s pattern for consuming highly palatable foods.

Sakayori et al. show that feeding pregnant mice with a diet high in omega-6 polyunsaturated fatty acids (PUFAs) and low in omega-3 PUFAs triggers hedonic consumption in the offspring by increasing its dopaminergic neurogenesis. This study suggests that maternal consumption of diets with unbalanced PUFAs contributes to the offspring’s overconsumption of foods.

Aloe Emodin Reduces Cardiac Inflammation Induced by a High-Fat Diet through the TLR4 Signaling Pathway

Background

Aloe emodin (AE) is a lipid-lowering agent, which could be used to treat hyperlipidemia, thereby reducing the risk of cardiovascular disease. Recent evidence suggests that hyperlipidemia is associated with many cardiac pathological alterations and might worsen myocardial damages.

Purpose

The purpose of this study is to evaluate the potential roles and mechanisms of AE in hyperlipidemia-induced oxidative stress and inflammation in the heart. Study Design. We established a hyperlipidemia-induced cardiac inflammation model in rats and cells then administered AE and observed its effect on hyperlipidemia-induced cardiac inflammation.

Methods

We used a mouse model of hyperlipidemia caused by a high-fat diet (HFD) for 10 weeks and cell culture experimental models of inflammation in the heart stimulated by PA for 14 h. Inflammatory markers were detected by qRT-PCR, WB, and immunofluorescence.

Results

We demonstrated that the expression levels of proinflammatory cytokines IL-1β, IL-6, and TNF-α were increased in the HFD group compared to the normal diet (ND) group, whereas AE treatment significantly reduced their levels in the myocardium. In addition, vascular cell adhesion molecule 1 (VCAM1) and intercellular adhesion molecule 1 (ICAM-1) protein expressions were also inhibited by AE. Our in vitro study showed AE treatment dose-dependently decreased the expression of IL-1β, IL-6, and TNF-α were increased in the HFD group compared to the normal diet (ND) group, whereas AE treatment significantly reduced their levels in the myocardium. In addition, vascular cell adhesion molecule 1 (VCAM1) and intercellular adhesion molecule 1 (ICAM-1) protein expressions were also inhibited by AE. Our κB, and p-P65l in vivo and in vitro study showed AE treatment dose-dependently decreased the expression of IL-1

Conclusion

Taken together, our findings disclose that AE could alleviate HFD/PA-induced cardiac inflammation via inhibition of the TLR4/NF-κB signaling pathway. Thus, AE may be a promising therapeutic strategy for preventing hyperlipidemia-induced myocardial injury.κB, and p-P65l

Obesity affects peripheral lymphoid organs immune response in murine asthma model

Asthma and obesity present rising incidence, and their concomitance is a reason for concern, as obese individuals are usually resistant to conventional asthma treatments and have more exacerbation episodes. Obesity affects several features in the lungs during asthma onset, shifting the T helper type 2 (Th2)/eosinophilic response towards a Th17/neutrophilic profile. Moreover, those individuals can present reduced atopy and delayed cytokine production. However, the impact of obesity on follicular helper T (Tfh) cells and B cells that could potentially result in antibody production disturbances are still unclear. Therefore, we aimed to assess the peripheral response to ovalbumin (OVA) in a concomitant model of obesity and asthma. Pulmonary allergy was induced, in both lean and obese female BALB/c mice, through OVA sensitizations and challenges. Mediastinal lymph nodes (MLNs) and spleen were processed for immunophenotyping. Lung was used for standard allergy analysis. Obese-allergic mice produced less anti-OVA IgE and more IgG2a than lean-allergic mice. Dendritic cells (CD11c⁺  MHCII^high ) expressed less CD86 and more PDL1 in obese-allergic mice compared with lean-allergic mice, in the MLNs. Meanwhile, B cells (CD19⁺  CD40⁺ ) were more frequent and the amount of PDL1/PD1⁺ cells was diminished by obesity, with the opposite effects in the spleen. Tfh cells (CD3⁺  CD4⁺  CXCR5⁺  PD1⁺ ) expressing FoxP3 were more frequent in obese mice, associated with the predominance of Th (CD3⁺  CD4⁺ ) cells expressing interleukin-4/GATA3 in the MLNs and interleukin-17A/RORγT in the spleen. Those modifications to the main components of the germinal centers could be resulting in the increased IgG2a production, which - associated with the Th17/neutrophilic profile - contributes to asthma worsening and represents an important target for future treatment strategies.

Rodent models of obesity

Obese or overweight people exceed one-third of the global population and obesity along with diabetes mellitus consist basic components of metabolic syndrome, both of which are known cardio-cerebrovascular risk factors with detrimental consequences. These data signify the pandemic character of obesity and the necessity for effective treatments. Substantial advances have been accomplished in preclinical research of obesity by using animal models, which mimic the human disease. In particular, rodent models have been widely used for many decades with success for the elucidation of the pathophysiology of obesity, since they share physiological and genetic components with humans and appear advantageous in their husbandry. The most representative rodents include the laboratory mouse and rat. Within this review, we attempted to consolidate the most widely used mice and rat models of obesity and highlight their strengths as well as weaknesses in a critical way. Our aim was to bridge the gap between laboratory facilities and patient's bed and help the researcher find the appropriate animal model for his/her obesity research. This tactful selection of the appropriate model of obesity may offer more translational derived results. In this regard, we included, the main diet induced models, the chemical/mechanical ones, as well as a selection of monogenic or polygenic models.

Dietary supplementation with blueberry partially restores T-cell-mediated function in high-fat-diet-induced obese mice

Blueberry, rich in antioxidant and anti-inflammatory phytochemicals, has been demonstrated to lower inflammatory status in adipose induced by high-fat diet (HFD) and obesity. The effect of blueberry on systemic immune functions has not been examined. C57BL/6 mice were randomised to one of three diets - low-fat diet (LFD), HFD and HFD plus 4 % (w/w) blueberry (HFD+B) - for 8 or 12 weeks. Ex vivo T-cell mitogens (concanavalin A (Con A); phytohaemagglutinin), T-cell antibody (anti-CD3; anti-CD3/CD28)-stimulated T-cell proliferation and cytokine production were assessed. After 8 weeks, both HFD groups weighed more (>4 g) than the LFD group; after 12 weeks, HFD+B-fed mice weighed more (>6 g) and had 41 % more adipose tissue than HFD-fed mice (P<0·05). After 12 weeks, T-cell proliferation was less in both HFD groups, compared with the LFD group. HFD-associated decrements in T-cell proliferation were partially (10-50 %) prevented by blueberry supplementation. At 12 weeks, splenocytes from HFD mice, but not from HFD+B mice, produced 51 % less IL-4 (CD3/CD28) and 57 % less interferon-γ (Con A) compared with splenocytes from LFD mice (P<0·05). In response to lipopolysaccharide challenge, splenocytes from both HFD groups produced 24-30 % less IL-6 and 27-33 % less TNF-α compared with splenocytes from LFD mice (P<0·05), indicating impaired acute innate immune response. By demonstrating deleterious impacts of HFD feeding on T-cell proliferation and splenocyte immune responses, our results provide insights into how HFD/obesity can disrupt systemic immune function. The protective effects of blueberry suggest that dietary blueberry can buttress T-cell and systemic immune function against HFD-obesity-associated insults.

Continuous feeding of a combined high-fat and high-sucrose diet, rather than an individual high-fat or high-sucrose diet, rapidly enhances the glucagon-like peptide-1 secretory response to meal ingestion in diet-induced obese rats

OBJECTIVES

Glucagon-like peptide-1 (GLP-1) is secreted by enteroendocrine L-cells in response to nutrient ingestion. To date, GLP-1 secretion in diet-induced obesity is not well characterized. We aimed to examine GLP-1 secretion in response to meal ingestion during the progression of diet-induced obesity and determinewhether a combined high-fat and high-sucrose (HFS) diet, an individual high-fat (HiFat), or a high-sucrose (HiSuc) diet affect adaptive changes in the postprandial GLP-1 response.

METHODS

Rats were fed a control, HiFat diet (30% weight), HiSuc diet (40% weight), or HFS (30% fat and 40% sucrose) diet for 5 wk. Meal tolerance tests were conducted to determine postprandial glucose, insulin, and GLP-1 responses to standard (control) diet ingestion every 2 wk.

RESULTS

After 5 wk, body weight gain of the HiFat (232.3 ± 7.8 g; P = 0.021) and HFS groups (228.0 ± 7.8; P = 0.039), but not the HiSuc group (220.3 ± 7.9; P = 0.244), were significantly higher than that of the control group (200.7 ± 5.4 g). In meal tolerance tests after 2 wk, GLP-1 concentration was significantly elevated in the HFS group only (17.2 ± 2.6 pM; P < 0.001) in response to meal ingestions, but the HiFat group (16.6 ± 3.7 pM; P = 0.156) had a similar response as the HFS group. After 4 wk, GLP-1 concentrations were similarly elevated at 15min in the HFS (14.1 ± 4.4; P = 0.010), HiFat (13.2 ± 2.0; P < 0.001), and HiSuc (13.0 ± 3.3; P = 0.016) groups, but the HFS (9.8 ± 1.0; P = 0.019) and HiFat (8.3 ± 1.5; P = 0.010) groups also had significant elevation at 30min.

CONCLUSIONS

These results demonstrate that the continuous ingestion of excessive fat and sucrose rapidly enhances the GLP-1 secretory response to luminal nutrients, and the HiFat diet may have a potent effect compared with the HiSuc diet on GLP-1 secretory responses. The increment of postprandial GLP-1 and insulinsecretion may have a role in normalizing postprandial glycaemia and slowing the establishment of glucose intolerance.

Modelos animais na síndrome metabólica

RESUMO O conhecimento sobre modelos animais para estudo metabólico representa a base da pesquisa nessa área. Este trabalho tem por objetivo revisar os principais modelos animais a serem utilizados no estudo da obesidade e da síndrome metabólica. Para isso, pesquisa no banco de dados Pubmed foi realizada usando as palavras-chave “animal models”, “obesity”, "metabolic syndrome”, e “bariatric surgery”. Várias espécies de animais podem ser usadas para o estudo de distúrbios metabólicos, no entanto, os roedores, tanto modelos monogênicos quanto modelos de obesidade induzida por dieta (DIO), são os animais mais utilizados nessa área. Animais monogênicos são a melhor escolha se apenas um aspecto estiver sendo avaliado. Animais DIO tendem a demonstrar melhor a interação entre doença, ambiente e gene. No entanto, eles ainda não são totalmente eficazes para a compreensão de todos os mecanismos dessa doença.

Effect of Low-Selenium/High-Fat Diet on Pig Peripheral Blood Lymphocytes: Perspectives from Selenoproteins, Heat Shock Proteins, and Cytokines

The aim of the present study was to clarify the effect of low selenium (Se)/high fat on the mRNA expression of selenoproteins, heat shock proteins (HSPs) and cytokines in pig peripheral blood lymphocytes. Forty crossbred boar piglets with healthy lean body weights of 10 kg were randomly divided into four treatment groups (group C, group L-Se, group H-fat, and group L-Se-H-fat) (n = 10/group) and fed with the corresponding diet for 16 weeks. The pig peripheral blood lymphocytes were extracted, and the mRNA expression of selenoproteins, HSPs, and cytokines was measured. Most mRNA levels for selenoproteins decreased in group L-Se, group H-fat, and group L-Se-H-fat, except Gpx1, Gpx2, Selt, and Selm, which were elevated in group H-fat. At the same time, low-Se/high-fat diet increased the expression of HSPs (HSP40, HSP60, HSP70, and HSP90) and inflammatory cytokines (IL-1α, IL-1β, IL-6, IL-8, IL-9, iNOS, COX-2, NF-κB, and TNF-α) in group L-Se, group H-fat, and group L-Se-H-fat, and genes in group L-Se-H-fat showed greater increases. Also, low-Se/high-fat diet inhibits the expression of TGF-β1 and IFN-γ. In summary, a low-Se/high-fat diet can cause relevant selenoprotein expression changes and promote the expression of pro-inflammatory factors and HSPs, and low Se enhances the expression of HSPs and inflammation factors induced by high fat. This information is helpful for understanding the effects of low-Se and high-fat diet on pig peripheral blood lymphocytes.

Obesity-induced diet leads to weight gain, systemic metabolic alterations, adipose tissue inflammation, hepatic steatosis, and oxidative stress in gerbils (Meriones unguiculatus)

BACKGROUND

Nowadays, the number of obese people in the world has reached alarming proportions. During the expansion of adipose tissue, a number of functions such as activation and release of cytokines and hormones may be affected. This leads the body to a pro-inflammatory pattern, which may affect the proper functioning of many tissues. Thus, studying the mechanisms by which obesity induces physiological disorders is necessary, and may be facilitated by the use of animal models, in particular rodents. We sought to characterize the metabolic and adipose tissue changes resulting from a diet rich in fats and simple sugars in gerbils.

METHODS

We divided 14 gerbils into two experimental groups that received a diet rich in simple carbohydrates and fats with 5,86 kcal/g (OB, n = 7) or a standard diet with 4.15 kcal/g (CT; n = 7) for 11 weeks. The animals had free access to water and food. The animal weight and food consumption were measured weekly. Blood, adipose tissue and liver of each animal were collected at the end of experiment. The following parameters were determined: cholesterol (COL), triglycerides (TGL) and glycemia (GLI) in the plasma; cytokines (IL-6, IL-10 and TNF-α) and hormones (adiponectin and leptin) in adipose tissue; activity of superoxide dismutase (SOD) and catalase (CAT), extraction and differentiation of fat and histology in liver.

RESULTS

The consumption of a diet rich in simple carbohydrates and fats led to increased total body weight and increased relative weights of liver and adipose tissue. In addition, we observed increased fasting glucose levels and circulating triglycerides, along with high TNF-α production in adipose tissue and increased total fat, cholesterol and triglyceride contents in the liver, contributing to higher intensity of hepatic steatosis. On the other hand, the animals of this group showed depletion in the enzyme activity of SOD and CAT in the liver, as well as reduction of IL-10 and adiponectin levels in adipose tissue.

DISCUSSION

High intake of saturated fat and simple carbohydrates establish the gerbil as an experimental model for the study of metabolic and hepatic abnormalities resulting from obesity.

Restoration of Declined Immune Responses and Hyperlipidemia by Rubus occidenalis in Diet-Induced Obese Mice

Hyperlipidemia, which is closely associated with a fatty diet and aging, is commonly observed in the western and aged society. Therefore, a novel therapeutic approach for this disease is critical, and an immunological view has been suggested as a novel strategy, because hyperlipidemia is closely associated with inflammation and immune dysfunction. In this study, the effects of an aqueous extract of Rubus occidentalis (RO) in obese mice were investigated using immunological indexes. The mice were fed a high-fat diet (HFD) to induce hyperlipidemia, which was confirmed by biochemical analysis and examination of the mouse physiology. Two different doses of RO and rosuvastatin, a cholesterol synthesis inhibitor used as a control, were orally administered. Disturbances in immune cellularity as well as lymphocyte proliferation and cytokine production were significantly normalized by oral administration of RO, which also decreased the elevated serum tumor necrosis factor (TNF)-α level and total cholesterol. The specific immune-related actions of RO comprised considerable improvement in cytotoxic T cell killing functions and regulation of antibody production to within the normal range. The immunological evidence confirms the significant cholesterol-lowering effect of RO, suggesting its potential as a novel therapeutic agent for hyperlipidemia and associated immune decline.

Novel Monoclonal Antibody Is an Allosteric Insulin Receptor Antagonist That Induces Insulin Resistance

A hallmark of type 2 diabetes is impaired insulin receptor (IR) signaling that results in dysregulation of glucose homeostasis. Understanding the molecular origins and progression of diabetes and developing therapeutics depend on experimental models of hyperglycemia, hyperinsulinemia, and insulin resistance. We present a novel monoclonal antibody, IRAB-B, that is a specific, potent IR antagonist that creates rapid and long-lasting insulin resistance. IRAB-B binds to the IR with nanomolar affinity and in the presence of insulin efficiently blocks receptor phosphorylation within minutes and is sustained for at least 3 days in vitro. We further confirm that IRAB-B antagonizes downstream signaling and metabolic function. In mice, a single dose of IRAB-B induces rapid onset of hyperglycemia within 6 h, and severe hyperglycemia persists for 2 weeks. IRAB-B hyperglycemia is normalized in mice treated with exendin-4, suggesting that this model can be effectively treated with a GLP-1 receptor agonist. Finally, a comparison of IRAB-B with the IR antagonist S961 shows distinct antagonism in vitro and in vivo. IRAB-B appears to be a powerful tool to generate both acute and chronic insulin resistance in mammalian models to elucidate diabetic pathogenesis and evaluate therapeutics.

Aloe QDM complex enhances specific cytotoxic T lymphocyte killing in vivo in metabolic disease mice

We developed spontaneous diet-induced metabolic disease in mice by feeding them a high-fat diet for 23 weeks and administered Aloe QDM complex for 16 weeks to examine its restorative effect on immune disorders and metabolic syndrome. A series of immune functional assays indicated Aloe QDM complex enhanced lymphocyte proliferation and antigen-specific immunity as determined by the restored functions of cytotoxic T lymphocytes (CTL) and IgG production. The elevated serum TNF-α level was also regulated by Aloe QDM complex treatment, which suggested its complex therapeutic potential. As for metabolic phenotypes, oral administration of Aloe QDM complex significantly improved diabetic symptoms, including high fasting glucose levels and glucose tolerance, and distinctly alleviated lipid accumulation in adipose and hepatic tissue. The simultaneous restoration of Aloe QDM complex on metabolic syndrome and host immune dysfunction, especially on the specific CTL killing was first elucidated in our study.

Prolonged Intake of Dietary Lipids Alters Membrane Structure and T Cell Responses in LDLr-/- Mice

Although it is recognized that lipids and membrane organization in T cells affect signaling and T cell activation, to what extent dietary lipids alter T cell responsiveness in the absence of obesity and inflammation is not known. In this study, we fed low-density lipoprotein receptor knockout mice a Western high-fat diet for 1 or 9 wk and examined T cell responses in vivo along with T cell lipid composition, membrane order, and activation ex vivo. Our data showed that high levels of circulating lipids for a prolonged period elevated CD4(+) and CD8(+) T cell proliferation and resulted in an increased proportion of CD4(+) central-memory T cells within the draining lymph nodes following induction of contact hypersensitivity. In addition, the 9-wk Western high-fat diet elevated the total phospholipid content and monounsaturated fatty acid level, but decreased saturated phosphatidylcholine and sphingomyelin within the T cells. The altered lipid composition in the circulation, and of T cells, was also reflected by enhanced membrane order at the activation site of ex vivo activated T cells that corresponded to increased IL-2 mRNA levels. In conclusion, dietary lipids can modulate T cell lipid composition and responses in lipoprotein receptor knockout mice even in the absence of excess weight gain and a proinflammatory environment.

Effects of obesity on immune responses to renal tumors

Kidney cancer incidence in the USA has been steadily increasing over the past several decades. The reasons for this are not completely clear, but an increased prevalence of known predisposing factors may be promoting this trend. Several major risk factors for kidney cancer have been identified. Among these, obesity is notable because its incidence has risen dramatically during this same period of time. Here, we will review the relationship between obesity and kidney cancer, and will explore the idea that obesity-mediated alterations in immune function may render immunotherapies for renal tumors ineffective. To support this idea, we will summarize characteristics of endogenous immune responses to renal tumors, as well as existing and developing immune-based therapies for kidney cancer patients. In doing so, we will highlight the ways in which altered immune function in obese individuals may render these therapies ineffective.

Regulatory effects of resveratrol on glucose metabolism and T-lymphocyte subsets in the development of high-fat diet-induced obesity in C57BL/6 mice

High-fat diet (HFD)-induced obesity is often associated with immune dysfunction. Resveratrol (trans-3,5,4'-trihydroxystilbene), which has well-founded immunity-related beneficial properties, was used to elucidate the regulatory effect on glucose metabolism and T-lymphocyte subsets in the development of HFD-induced obesity. Resveratrol, being associated with decreases of plasma leptin and plasma lipids and the release of oxidative stress, significantly decreased the body weight and fat masses in HF mice after 26 weeks of feeding. Furthermore, resveratrol decreased the fasting blood glucose and fasting plasma insulin and increased the CD3(+)CD4(+)/CD3(+)CD8(+) subsets percentages and the regulatory T cells (Tregs) production after 13 and 26 weeks of feeding. The results indicate that resveratrol, as an effective supplement for HFD, maintained glucose homeostasis by activating the PI3K and SIRT1 signaling pathways. Moreover, resveratrol activated the Nrf2 signaling pathway-mediated antioxidant enzyme expression to alleviate inflammation by protecting against oxidative damage and T-lymphocyte subset-related chronic inflammatory response in the development of HFD-induced obesity.

The many faces of asthma in obesity

Obesity is a major risk factor for the development of asthma, and causes severe, uncontrolled disease that responds poorly to therapy. The obese state alters early onset allergic asthma, and leads to the development of a novel form of late onset asthma secondary to obesity. The presentation of early onset allergic asthma is altered through effects on immune function. Factors such as mechanical loading, effects of adipokines on airways, altered diet, insulin resistance and altered metabolism of nitric oxide likely all contribute to increased airway reactivity in obesity, causing late onset asthma in obesity. Obesity also alters responses to environmental factors such as ozone and particulate matter. Focused studies to understand the importance of these factors in the pathogenesis of airway disease in obesity will be essential to develop therapies to intervene in this new epidemic of airway disease.

Impact of Korean pine nut oil on weight gain and immune responses in high-fat diet-induced obese mice

Korean pine nut oil (PNO) has been reported to have favorable effects on lipid metabolism and appetite control. We investigated whether PNO consumption could influence weight gain, and whether the PNO-induced effect would result in an improvement of immune function in high-fat diet (HFD)-induced obese mice. C57BL/6 mice were fed control diets with 10% energy fat from either PNO or soybean oil (SBO), or HFDs with 45% energy fat from 10% PNO or SBO and 35% lard, 20% PNO or SBO and 25% lard, or 30% PNO or SBO and 15% lard for 12 weeks. The proliferative responses of splenocytes upon stimulation with concanavalin A (Con A) or lipopolysaccharide (LPS), Con A-stimulated production of interleukin (IL)-2 and interferon (IFN)-γ, and LPS-stimulated production of IL-6, IL-1β, and prostaglandin E₂ (PGE₂) by splenocytes were determined. Consumption of HFDs containing PNO resulted in significantly less weight gain (17% less, P < 0.001), and lower weight gain was mainly due to less white adipose tissue (18% less, P = 0.001). The reduction in weight gain did not result in the overall enhancement in splenocyte proliferation. Overall, PNO consumption resulted in a higher production of IL-1β (P = 0.04). Replacement of SBO with PNO had no effect on the production of IL-2, IFN-γ, IL-6, or PGE₂ in mice fed with either the control diets or HFDs. In conclusion, consumption of PNO reduced weight gain in mice fed with HFD, but this effect did not result in the overall improvement in immune responses.

The potential benefits and inherent risks of vibration as a non-drug therapy for the prevention and treatment of osteoporosis

The delivery of mechanical signals to the skeleton using vibration is being considered as a non-drug treatment of osteoporosis. Delivered over a range of magnitudes and frequencies, vibration has been shown to be both anabolic and anti-catabolic to the musculoskeletal tissues, yet caution must be emphasized as these mechanical signals, particularly chronic exposure to higher intensities, is a known pathogen to many physiological systems. In contrast, accumulating preclinical and clinical evidence indicates that low intensity vibration (LIV) improves bone quality through regulating the activity of cells responsible for bone remodeling, as well as biasing the differentiation fate of their mesenchymal and hematopoietic stem cell progenitors. In vitro studies provide insights into the biologic mechanisms of LIV, and indicate that cells respond to these low magnitude signals through a distinct mechanism driven not by matrix strain but acceleration. These cell, animal, and human studies may represent the foundation of a safe, non-drug means to protect and improve the musculoskeletal system of the elderly, injured, and infirmed.

Spleen-derived interleukin-10 downregulates the severity of high-fat diet-induced non-alcoholic fatty pancreas disease

Obesity is associated with systemic low-grade inflammation and is a risk factor for non-alcoholic fatty pancreas disease (NAFPD), but the molecular mechanisms of these associations are not clear. Interleukin (IL)-10, a potent anti-inflammatory cytokine, is released during acute pancreatitis and is known to limit inflammatory responses by downregulating the release of proinflammatory mediators. The origin of IL-10 that suppresses pancreatitis has not been investigated. Since obesity is known to reduce expression of proinflammatory cytokines in the spleen, we examined whether spleen-derived IL-10 regulates NAFPD caused by high-fat (HF) diet-induced obesity. The following investigations were performed: 1) IL-10 induction from spleen was examined in male mice fed a HF diet; 2) triglyceride content, expression of pro- and anti-inflammatory cytokines and infiltration of M1 and M2 macrophages were determined to evaluate ectopic fat accumulation and inflammatory responses in the pancreas of splenectomy (SPX)-treated mice fed HF diet; 3) exogenous IL-10 was systemically administered to SPX-treated obese mice and the resulting pathogenesis caused by SPX was assessed; and 4) IL-10 knockout (IL-10KO) mice were treated with SPX and ectopic fat deposition and inflammatory conditions in the pancreas were investigated. Obesity impaired the ability of the spleen to synthesize cytokines, including IL-10. SPX aggravated fat accumulation and inflammatory responses in the pancreas of HF diet-induced obese mice and these effects were inhibited by systemic administration of IL-10. Moreover, SPX had little effect on fat deposition and inflammatory responses in the pancreas of IL-10KO mice. Our findings indicate that obesity reduces IL-10 production by the spleen and that spleen-derived IL-10 may protect against the development of NAFPD.

Bone structure and B-cell populations, crippled by obesity, are partially rescued by brief daily exposure to low-magnitude mechanical signals

Deterioration of the immune and skeletal systems, each of which parallel obesity, reflects a fragile interrelationship between adiposity and osteoimmunology. Using a murine model of diet-induced obesity, this study investigated the ability of mechanical signals to protect the skeletal-immune systems at the tissue, cellular, and molecular level. A long-term (7 mo) high-fat diet increased total adiposity (+62%), accelerated age-related loss of trabecular bone (-61%), and markedly reduced B-cell number in the marrow (-52%) and blood (-36%) compared to mice fed a regular diet. In the final 4 mo of the protocol, the application of low-magnitude mechanical signals (0.2 g at 90 Hz, 15 min/d, 5 d/wk) restored both bone structure and B cells to those levels measured in control mice fed a regular diet. These phenotypic outcomes were achieved, in part, by reductions in osteoclastic activity and a biasing of hematopoietic stem cell differentiation toward the lymphoid B-cell lineage and away from a myeloid fate. These results emphasize that obesity undermines both the skeletal and immune systems, yet brief exposure to mechanical signals, perhaps as a surrogate to the salutary influence of exercise, diminishes the consequences of diabetes and obesity, restoring bone structure and normalizing B-cell populations by biasing of the fate of stem cells through mechanosensitive pathways.

A novel anti-inflammatory role for spleen-derived interleukin-10 in obesity-induced inflammation in white adipose tissue and liver

Obesity is associated with systemic low-grade inflammation and obesity-related metabolic disorders. Considering that obesity decreases the expression of proinflammatory cytokines in the spleen, we assessed the role of interleukin (IL)-10, an anti-inflammatory cytokine produced by the spleen, in the pathogenesis of obesity. Changes in obesity-related pathogenesis, including inflammatory responses in multiple organs, were assessed after systemic administration of exogenous IL-10 to splenectomy (SPX)-treated obese wild-type and IL-10 knockout (IL-10KO) mice. Obesity resulted in the inability of the spleen to synthesize cytokines, including IL-10, and proinflammatory cytokines in obesity are then likely to emerge from tissues other than the spleen because serum levels of IL-10, but not proinflammatory cytokines, decreased despite the expression of these cytokines in the spleen being reduced in high fat-induced obese mice. SPX aggravated the inflammatory response in white adipose tissue (WAT) and the liver and suppressed adiposity in WAT. However, it accentuated adiposity in the liver. These SPX-induced changes were inhibited by systemic administration of IL-10. Moreover, SPX had little effect on the inflammatory responses in WAT and the liver of IL-10KO mice. These data show the role of spleen-derived IL-10 in diet-induced changes as a result of inflammatory responses in WAT and the liver.

Laboratory animals as surrogate models of human obesity

Obesity and obesity-related metabolic diseases represent a growing socioeconomic problem throughout the world. Great emphasis has been put on establishing treatments for this condition, including pharmacological intervention. However, there are many obstacles and pitfalls in the development process from pre-clinical research to the pharmacy counter, and there is no certainty that what has been observed pre-clinically will translate into an improvement in human health. Hence, it is important to test potential new drugs in a valid translational model early in their development. In the current mini-review, a number of monogenetic and polygenic models of obesity will be discussed in view of their translational character.

Short-term increase of body weight triggers immunological variables in dogs

Overweight in dogs is, as in other companion animals, a major risk factor for several metabolic disorders. However, it is not yet known whether immunity is challenged by increased body weight in dogs. The aim of this study was to investigate the effect of a short-term increase in body weight on immunological variables in adult healthy beagle dogs. Sixteen dogs, divided into a control group (CG) and weight gain group (WGG), were included. During a period of 13 weeks, the CG was fed at maintenance energy requirement (MER), whereas the WGG received a double amount of food. After 13 weeks, blood samples were taken for immunological and biochemical analyses. Weight gain and increased body condition score in the WGG were accompanied by a significant higher leptin concentration. Weight gain increased the number of lymphocytes and immunoglobulins A and M and was responsible for a higher proliferation of peripheral blood mononuclear cells (PBMC). Short-term increase of body weight thus seems to trigger immunological variables in dogs.

The burden of obesity on infectious disease

The world is now experiencing an epidemic of obesity. Although the effects of obesity on the development of metabolic and cardiovascular problems are well studied, much less is known about the impact of obesity on immune function and infectious disease. Studies in obese humans and with obese animal models have repeatedly demonstrated impaired immune function, including decreased cytokine production, decreased response to antigen/mitogen stimulation, reduced macrophage and dendritic cell function, and natural killer cell impairment. Recent studies have demonstrated that the impaired immune response in the obese host leads to increased susceptibility to infection with a number of different pathogens such as community-acquired tuberculosis, influenza, Mycobacterium tuberculosis, coxsackievirus, Helicobacter pylori and encephalomyocarditis virus. While no specific mechanism has been defined for the decreased immune response to infectious disease in the obese host, several obesity-associated changes such as excessive inflammation, altered adipokine signaling, metabolic changes and even epigenetic regulation could affect the immune response. This review will discuss what is currently known about the relationship between obesity and infectious disease.

Diet-induced obesity, exogenous leptin-, and MADB106 tumor cell challenge affect tissue leukocyte distribution and serum levels of cytokines in F344 rats

The adipocyte-derived catabolic protein leptin alters cell-mediated immunity and cytokine crosstalk. This may provide new insights into the altered immune response, seen in obese individuals. Therefore, we determined the tissue distribution of immune cells in diet-induced obese (dio) and normal weight F344 rats challenged with MADB106 tumor cells or leptin. Immune cell distribution in blood (by FACS analysis) and tissues (NK cells in spleen and liver, immunohistologically) as well as pro-inflammatory cytokines (IL-6, TNF-α; by flow cytometry) were investigated in 28 normal weight and 28 dio rats (n = 4-6/group). Pro-inflammatory cytokines were increased 3-fold for IL-6 and 7-fold for TNF-α in obese animals. Higher numbers of blood monocytes and NK cells were found in obese as compared to normal weight animals. In dio rats challenged with leptin and MADB106 tumor cells, monocyte numbers were decreased as compared to the obese control animals. Immunohistochemistry revealed an altered NK cell distribution in a compartment-, treatment-, and bodyweight-specific manner. In conclusion, our data reveal a distinct distribution pattern of monocytes and NK cells in dio rats as compared to normal weight littermates and an additional modulatory effect of a leptin- and MADB106 tumor cell challenge.