Analysis of the effect of leptin on immune function in vivo using diet-induced obese mice

The Effect of Moderate-Intensity Physical Exercise on Some Serum Inflammation Markers and the Immune System in Rats Fed Intermittent Fasting with a High-Fat Diet

Background and Objectives: This study aimed to investigate the impact of moderate-intensity physical exercise on serum inflammation markers and the immune system in rats that were fed a high-fat diet (HFD) with intermittent fasting. Materials and Methods: A total of 48 Wistar albino male rats were included in the study and divided into eight groups, each consisting of six rats. Group 1 served as the control group (CG), receiving a standard diet. Group 2 followed the standard nutrition program with intermittent fasting (CG + IF). Group 3 underwent exercise with a standard diet (CG + E). Group 4 underwent both a standard diet with intermittent fasting and exercise (CG + IF + E). Group 5 was fed a high-fat diet (HFD). Group 6 received a high-fat diet with intermittent fasting (HFD + IF). Group 7 followed a high-fat diet with exercise (HFD + E). Group 8 underwent both a high-fat diet with intermittent fasting and exercise (HFD + IF + E). The study lasted for 8 weeks. Results: The results of the analysis show that lymphocyte cell levels in groups HFD + IF, HFD + IF, and HFD + IF + E were higher compared to groups CG-HFD (p < 0.05). Additionally, B lymphocyte and monocyte cell levels were higher in group HFD + IF + E compared to groups CG, CG + IF, and CG + IF + E, as well as CG, CG + IF, and CG + E, respectively. TNF-α levels were significantly higher in group HFD compared to the other groups. Furthermore, IL 10 levels were higher in group HFD + IF + E compared to the other groups. Conclusions: These findings indicate that moderate exercise and intermittent fasting, particularly in groups fed a high-fat diet, increased anti-inflammatory cytokine levels, and certain immune system cell counts, while decreasing pro-inflammatory cytokine levels.

Time restricted feeding modifies leukocyte responsiveness and improves inflammation outcome

Time restricted eating, the dietary approach limiting food intake to a maximal 10-hour period of daytime is considered beneficial in metabolic dysfunctions, such as obesity and diabetes. Rhythm of food intake and parallel changes in serum nutrient levels are also important entrainment signals for the circadian clock, particularly in tissues involved in metabolic regulation. As both the metabolic state and the circadian clock have large impact on immune functions, we investigated in mice whether time restricted feeding (TRF) affects systemic inflammatory potential. TRF slackened the symptoms in K/BxN serum-transfer arthritis, an experimental model of human autoimmune joint inflammation. Compared to ad libitum conditions TRF reduced the expression of inflammatory mediators in visceral adipose tissue, an integrator and coordinator of metabolic and inflammatory processes. Furthermore, TRF strengthened the oscillation of peripheral leukocyte counts and alongside decreased the pool of both marginated and tissue leukocytes. Our data suggest that the altered leukocyte distribution in TRF mice is related to the attenuated expression of adhesion molecules on the surface of neutrophils and monocytes. We propose that TRF modifies both rhythm and inflammatory potential of leukocytes which contribute to the milder reactivity of the immune system and therefore time-restricted eating could serve as an effective complementary tool in the therapy of autoinflammatory processes.

The Inhibitory Role of α2,6-Sialylation in Adipogenesis

Adipose tissue plays critical roles in obesity and related diseases such as diabetes and cardiovascular diseases. Previous reports suggest that glycans, the most common posttranslational modifications, are involved in obesity-related diseases, but what type of glycan regulates adipogenesis during obesity remains unclear. In this study, we first quantified the mRNA levels of 167 genes (encoding 144 glycosyltransferases and 23 related enzymes) in visceral adipose tissues (VATs) from control mice and high-fat diet (HFD)-induced obese mice. We found that a gene encoding β-galactoside α2,6-sialyltransferase-1 (St6gal1), a key enzyme responsible for the biosynthesis of α2,6-linked sialic acid in N-linked glycans, was most down-regulated in VATs from obese mice. We confirmed the reduction in α2,6-sialic acid in VATs from obese mice and differentiated adipocyte model 3T3-L1 cells. Using proteomic analysis, integrin-β1 was identified as one of the target α2,6-sialylated proteins in adipose tissues, and phosphorylation of its downstream molecule focal adhesion kinase was found to be decreased after HFD feeding. St6gal1 overexpression in differentiating 3T3-L1 cells inhibited adipogenesis with increased phosphorylation of focal adhesion kinase. Furthermore, St6gal1 knockout mice exhibited increased bodyweight and VAT weight after HFD feeding. The down-regulation of St6gal1 during adipogenesis was canceled by treatment with a DNA methyltransferase inhibitor, suggesting an involvement of epigenetic DNA methylation in St6gal1 silencing. Our findings suggest that ST6GAL1 has an inhibitory role in adipogenesis through integrin-β1 activation, providing new insights into the roles and regulation mechanisms of glycans in adipocytes during obesity.

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.

Obesity, diabetes and pneumonia: the menacing interface of non-communicable and infectious diseases

OBJECTIVES

To review current knowledge on the epidemiological, clinical and biological impact of the pandemic of obesity and diabetes on pneumonias.

METHODS

We conducted a literature review using PubMed and EMBASE, supplemented by various sources. Given the disparate and fragmented nature of the literature, a formal systematic review was not possible.

RESULTS

In 2008, globally 10% of men and 14% of women were obese and an estimated 371 million had diabetes; half undiagnosed and many obese. Numbers are rising rapidly in low- and middle-income countries where the majority reside, but reliable data are lacking. The most frequent pneumonias in obesity and diabetes are tuberculosis, influenza and pneumococcal, staphylococcal and opportunistic pathogens. Diabetes impacts tuberculosis control and increases drug resistance and mortality. Mortality and morbidity from pneumococcal pneumonia and influenza are increased in obesity and diabetes. In addition to mechanical and physiological effects, there are considerable immunological abnormalities characterised by chronic, low-grade inflammation. Simultaneous up-regulation and dysregulation of both innate and adaptive immune responses impair control and killing of invading organisms. Prevention in those at risk is poorly practised, although screening for tuberculosis in diabetes is beginning in high-burden settings.

CONCLUSIONS

Pneumonia is a threat globally in obesity and diabetes with increased incidence and severity of disease. There is uncertainty about whether vaccines are equally effective in those with obesity and diabetes. Increased epidemiological, clinical and biological knowledge will be crucial to face this 21st century challenge.

Maternal protein deficiency during a gastrointestinal nematode infection alters developmental profile of lymphocyte populations and selected cytokines in neonatal mice

Neonatal immune development begins in pregnancy and continues into lactation and may be affected by maternal diet. We investigated the possibility that maternal protein deficiency (PD) during a chronic gastrointestinal (GI) nematode infection could impair neonatal immune development. Beginning on d 14 of pregnancy, mice were fed protein-sufficient (PS; 24%) or protein-deficient (PD; 6%) isoenergetic diets and were infected weekly with either 0 (sham) or 100 Heligmosomoides bakeri larvae. Pups were killed on d 2, 7, 14, and d 21 and dams on d 20 of lactation. Lymphoid organs were weighed. Cytokine concentration in maternal and pup serum and in milk from pup stomachs and lymphoid cell populations in pup spleen and thymus were determined using luminex and flow cytometry, respectively. GI nematode infection increased Th2 cytokines (IL-4, IL-5, IL-13), IL-2, IL-10, and eotaxin in serum of dams whereas PD reduced IL-4 and IL-13. The lower IL-13 in PD dams was associated with increased fecal egg output and worm burdens. Maternal PD increased vascular endothelial growth factor in pup milk and eotaxin in pup serum. Maternal infection increased eotaxin in pup serum. Evidence of impaired neonatal immune development included reduced lymphoid organ mass in pups associated with both maternal infection and PD and increased percentage of T cells and T:B cell ratio in the spleen associated with maternal PD. Findings suggest that increases in specific proinflammatory cytokines as a result of the combination of infection and dietary PD in dams can impair splenic immune development in offspring.

In vivo effects of leptin on lymphocyte subpopulations in mice

Leptin, a hormone-cytokine mainly produced by the adipose tissue, has pleitropic effects on many biological system including metabolic, endocrine, and immune system. Although it is well known that leptin controls food intake on hypothalamic regions of brain, the role of leptin in hematopoietic and immune processes has been mainly investigated with in vitro and transgenic mouse studies. The aim of this study was to investigate the effects of peripheral leptin on lymphocyte subpopulation. Initially forty male Swiss albino mice were divided into five groups. Mice in group I (Control) were given serum physiologic (SP) and group L100, group L250, group L500, and group L1000 were given 100, 250, 500 and 1000 μg/kg/day recombinant mouse leptin, respectively. Leptin or SP was injected subcutaneously for the next 6 days. Daily food/water intake was recorded for each group. At the end of the study, whole blood samples (500 μl) were obtained via intracardiac punction in anesthetized mice. Leptin levels and lymphocyte subpopulations in blood samples were analyzed. We show that no in vivo dose-dependent effect of leptin is existed on lymphocyte subpopulations count in mice. Treatment of mice with high-dose leptin led to increase only CD4+ cells (P<0.05). In addition, high-dose leptin slightly increased CD3+ cells but this was not statistically confirmed (P=0.08). Notably, it was found that leptin caused insignificant changes on body weight and food intake in normal body weight mice. The data support that high-dose leptin has proliferative effect on CD4+ cells in vivo. However, more in vivo study needs to be examined to clarify how leptin affect lymphocyte subpopulations.

Bariatric surgery reverses natural killer (NK) cell activity and NK-related cytokine synthesis impairment induced by morbid obesity

BACKGROUND

Obesity is related to a higher rate of infections and some types of cancer. Here we analyzed the impact of obesity and weight loss induced by Roux-en-Y gastric bypass (RYGB) on immunological parameters, i.e., cytokine productions and natural killer cell function.

METHODS

We analyzed 28 morbidly obese patients before and 6 months after RYGB. Biochemical parameters were analyzed in plasma. The percent of natural killer (NK) cells, their cytotoxicity, and the production of cytokines by peripheral blood mononuclear cells were analyzed. The percent of NK cells was determined by flow cytometry and cytokine production determined by enzyme-linked immunosorbent assay. NK cytotoxicity was determined by the lactate dehydrogenase release assay.

RESULTS

The weight loss 6 months following surgery was 35.3 ± 4.5 kg. RYGB also improves biochemical parameters. No significant difference was found in the percent of NK cells after surgery. We found an increase in the production of interferon-γ, interleukin (IL)-12 and IL-18, but not in IL-2, 6 months after RYGB. Cytotoxic activity of NK cells was significantly enhanced 6 months after RYGB [17.1 ± 14.7% before RYGB vs 51.8 ± 11.3% at 6 months after, at 40:1 effector to target cell ratio; p < 0.001]. We observed significant post-surgical improvement in the cytotoxic activity curve in 22 out of 28 patients (78.6%), irrespective of the target to effector cell ratio.

CONCLUSIONS

The weight loss induced by RYGB modifies the production of cytokines related with NK cell function and improves its activity.

A time course study on prothrombotic parameters and their modulation by anti-platelet drugs in hyperlipidemic hamsters

The present study was undertaken to assess the chronology of major pathological events associated with high cholesterol (HC) diet and their modulation by anti-platelet drugs. Male Golden Syrian hamsters were fed HC diet up to 90 days. Plasma lipid, glucose and coagulation parameters (commercial kits), platelet activation (whole blood aggregation and static adhesion), endothelial dysfunction (aortic ring vasoreactivity), splenocyte TNF-α, IFN-γ and iNOS mRNA transcripts (RT-PCR), and ferric chloride (time to occlusion) induced thrombosis were monitored at 15, 30, 60, and 90 days after HC feeding and compared with normolipidemic hamsters. A significant increase in plasma lipid levels was observed at 15 days of HC feeding, but other parameters remain unaltered. Enhanced ADP, collagen, and thrombin-induced platelet aggregation, splenocyte TNF-α expression along with endothelial dysfunction were observed from 30 to 90 days of HC feeding. Platelet adhesion on collagen-/fibrinogen-coated surface and IFN-γ expression were augmented only after 60 days, while enhanced iNOS expression, reduction in thrombin time, and potentiation of ferric chloride-induced thrombosis was observed only at 90 days of HC feeding. Thus, pathological changes induced by HC diet depend on the duration and extent of hyperlipidemia. Moreover, hamsters treated with anti-platelet drugs aspirin (5 mg/kg) or clopidogrel (10 mg/kg) along with HC feeding exhibited reduction in platelet activation as well as subsequent changes observed in the abovementioned parameters following HC feeding. Since reduction in TNF-α was associated with reversion in endothelial dysfunction and prothrombotic state, the role of platelets is implicated in the pathological changes associated with HC feeding.

Nutritional imbalances and infections affect the thymus: consequences on T-cell-mediated immune responses

The thymus gland, where T lymphocyte development occurs, is targeted in malnutrition secondary to protein energy deficiency. There is a severe thymic atrophy, resulting from massive thymocyte apoptosis (particularly affecting the immature CD4+CD8+ cell subset) and decrease in cell proliferation. The thymic microenvironment (the non-lymphoid compartment that drives intrathymic T-cell development) is also affected in malnutrition: morphological changes in thymic epithelial cells were found, together with a decrease of thymic hormone production, as well as an increase of intrathymic contents of extracellular proteins. Profound changes in the thymus can also be seen in deficiencies of vitamins and trace elements. Taking Zn deficiency as an example, there is a substantial thymic atrophy. Importantly, marginal Zn deficiency in AIDS subjects, children with diarrhoea and elderly persons, significantly impairs the host's immunity, resulting in an increased risk of opportunistic infections and mortality; effects that are reversed by Zn supplementation. Thymic changes also occur in acute infectious diseases, including a severe thymic atrophy, mainly due to the depletion of CD4+CD8+ thymocytes, decrease in thymocyte proliferation, in parallel to densification of the epithelial network and increase in the extracellular matrix contents, with consequent disturbances in thymocyte migration and export. In conclusion, the thymus is targeted in several conditions of malnutrition as well as in acute infections. These changes are related to the impaired peripheral immune response seen in malnourished and infected individuals. Thus, strategies inducing thymus replenishment should be considered as adjuvant therapeutics to improve immunity in malnutrition and/or acute infectious diseases.

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.

Impact of adiposity on immunological parameters

Studies evaluating immune function in obese humans and experimental animals indicate that the excess adiposity is associated with impaired in immune responses. Obesity is related to a higher rate of infections and to some types of cancer. Nutritional, metabolic and endocrine factors are implicated in the immunological changes. The adipose tissue directly produces substances with various functions related to immune system. Furthermore, some investigations suggest that certain types of weight reduction strategies can alter the immune function. Nevertheless, long-term studies should be carried out to address whether these changes positively affects the ability of these obese individuals to control infections and tumor development.

Thymic microenvironmental alterations in experimentally induced diabetes

Little is known about the immunologic consequences from endocrine changes observed in diabetes. Since a preserved thymic microenvironment is of critical importance for the T cell development and maturation, we have examined the thymus from alloxan-diabetic mice. An intense thymic atrophy accompanied by changes in histological pattern and in thymocyte subpopulations were observed in diabetic mice. Laminin and fibronectin, which are closely associated with thymocytes maturation, were evaluated, but, only laminin presented an altered distribution and density in thymuses from diabetes group. the expression of fibronectin and laminin receptors was found to be decreased in diabetic mice. There was also intense decrease in the expression of two important chemokines for thymus, CCL25 and CXCL12, and in the CCR9 (CCL25 receptor), but the expression of CXCR4 (CXCL12 receptor) did not drop on cells. However, no significant difference was observed in the in vitro thymocytes migratory capacity from diabetic mice. The results show significant alterations in thymus microenvironment in diabetes and offer insights for studies involving endocrine influences on lymphatic organs and T cell maturation.

Diet-induced obesity increases NF-kappaB signaling in reporter mice

The nuclear factor (NF)-kappaB is a primary regulator of inflammatory responses and may be linked to pathology associated with obesity. We investigated the progression of NF-kappaB activity during a 12-week feeding period on a high-fat diet (HFD) or a low-fat diet (LFD) using NF-kappaB luciferase reporter mice. In vivo imaging of luciferase activity showed that NF-kappaB activity was higher in the HFD mice compared with LFD-fed mice. Thorax region of HFD females displayed fourfold higher activity compared with LFD females, while no such increase was evident in males. In male HFD mice, abdominal NF-kappaB activity was increased twofold compared with the LFD males, while females had unchanged NF-kappaB activity in the abdomen by HFD. HFD males, but not females, exhibited evident glucose intolerance during the study. In conclusion, HFD increased NF-kappaB activity in both female and male mice. However, HFD differentially increased activity in males and females. The moderate increase in abdomen of male mice may be linked to glucose intolerance.

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

OBJECTIVE

To clarify the effect of prolonged feeding of a high-fat and sucrose, and to clarify the effect of sucrose instead of other carbohydrate on obesity and immunity in C57BL/6J mice.

METHODS

We investigated the development of obesity and immune cell function in four groups of mice fed high-fat, high-fat plus high-sucrose, high-sucrose, and control diet for 7 months.

RESULTS

Mice fed high-fat and high-fat plus high-sucrose groups developed severe obesity. Body weight, adipose tissue weight, serum leptin, blood glucose, and insulin were significantly higher, while the level of serum soluble leptin receptor was significantly lower in mice fed high-fat and high-fat plus high-sucrose diets than in mice fed the control or high-sucrose diets. Splenocyte proliferation stimulated by T-cell mitogen (PHA, ConA, and anti-CD 3 antibody) and B-cell mitogen (LPS) was significantly lower in both obese, high-fat and high-fat plus high-sucrose groups than in control and high-sucrose groups. However, these parameters did not differ between high-fat and high-fat plus high-sucrose groups.

CONCLUSIONS

Long-term feeding of high-fat diet and high-fat plus high-sucrose diet similarly induced severe obesity in C57BL/6J mice. Not only T-cell, but also B-cell function may be impaired in mice made severely obese by the high-fat or high-fat plus high-sucrose diets.

The thymus is a common target in malnutrition and infection

Malnutrition, secondary to deficiency in intake of proteins, minerals or vitamins, consistently results in changes in the thymus. This organ undergoes a severe atrophy due to apoptosis-induced thymocyte depletion, particularly affecting the immature CD4+CD8+ cells, as well as a decrease in cell proliferation. This feature is apparently linked to a hormonal imbalance, involving a decrease in leptin and consequent increase in glucocorticoid hormone levels in the serum. The thymic microenvironment is also affected in malnutrition: morphological changes in thymic epithelial cells have been found, together with a decrease of thymic hormone production by these cells. Additionally, intrathymic contents of extracellular proteins, such as fibronectin, laminin and collagens, are increased in thymuses from malnourished children. Taken together, these data clearly point to the notion that the thymus is significantly affected in malnutrition. Similar patterns of thymic changes occur in acute infectious diseases, including a severe atrophy of the organ, mainly due to the apoptosis-related depletion of immature CD4+CD8+ thymocytes. Additionally, thymocyte proliferation is compromised in acutely-infected subjects. The microenvironmental compartment of the thymus is also affected in acute infections, with an increased density of the epithelial network and an increase in the deposition of extracellular matrix. In conclusion, it seems clear that the thymus is targeted in malnutrition as well as in acute infections. These changes are related to the impaired peripheral immune response seen in malnourished and infected individuals. Thus, strategies inducing thymus replenishment should be considered in therapeutic approaches, in both malnutrition and acute infectious diseases.

Oral-tolerance induction in diet-induced obese mice

OBJECTIVE

It is known that immune functions are altered in various ways by obesity. However, changes in the intestinal immune system resulting from obesity remain poorly understood. Oral tolerance is a system that suppresses antigen specific immune responses to orally administrated antigens. The intestinal immune system is intimately associated with the oral tolerance system, that acts to prevent allergic and inflammatory diseases. In this study we investigated the effect of obesity on induction of oral tolerance to ovalbumin (OVA) in an animal model of obesity.

RESEARCH METHODS AND PROCEDURES

Obese mice induced by a high fat diet and control mice were allowed free access for 3 days to a 1%-ovalbumin (OVA) solution in drinking water. After continuous feeding of the antigen, all the mice were immunized by two intraperitoneal injections of OVA administered 7 days apart.

RESULTS

In the control mice, induction of oral tolerance caused an increase in antigen specific IgG1 levels and a decrease in IgG2a levels. In contrast, the IgG1/IgG2a ratio was reversed in obese mice. OVA-specific IL-2 production was suppressed by antigen feeding in both the control and obese mice; however, suppression of OVA-specific IL-10 was observed only in the control mice. Although OVA-specific IgA and IgM were not affected by antigen feeding, the obese groups of mice had significantly lower titers of antibodies.

DISCUSSION

These findings suggest that obesity may affect induction of oral tolerance following antigen feeding and that these changes may be related to the inflammatory reaction.

Leptin in immunology

Leptin is an adipokine which conveys information on energy availability. In humans, leptin influences energy homeostasis and regulates neuroendocrine function primarily in states of energy deficiency. As a cytokine, leptin also affects thymic homeostasis and, similar to other proinflammatory cytokines, leptin promotes Th1 cell differentiation and cytokine production. We review herein recent advances on the role of leptin in the pathophysiology of immune responses.