Prebiotics Supplementation Impact on the Reinforcing and Motivational Aspect of Feeding.

Energy homeostasis is tightly regulated by the central nervous system which responds to nervous and circulating inputs to adapt food intake and energy expenditure. However, the rewarding and motivational aspect of food is tightly dependent of dopamine (DA) release in mesocorticolimbic (MCL) system and could be operant in uncontrolled caloric intake and obesity. Accumulating evidence indicate that manipulating the microbiota-gut-brain axis through prebiotic supplementation can have beneficial impact of the host appetite and body weight. However, the consequences of manipulating the implication of the microbiota-gut-brain axis in the control motivational and hedonic/reinforcing aspects of food are still underexplored. In this study, we investigate whether and how dietary prebiotic fructo-oligosaccharides (FOS) could oppose, or revert, the change in hedonic and homeostatic control of feeding occurring after a 2-months exposure to high-fat high-sugar (HFHS) diet. The reinforcing and motivational components of food reward were assessed using a two-food choice paradigm and a food operant behavioral test in mice exposed to FOS either during or after HFHS exposure. We also performed mRNA expression analysis for key genes involved in limbic and hypothalamic control of feeding. We show in a preventive-like approach, FOS addition of HFHS diet had beneficial impact of hypothalamic neuropeptides, and decreased the operant performance for food but only after an overnight fast while it did not prevent the imbalance in mesolimbic markers for DA signaling induced by palatable diet exposure nor the spontaneous tropism for palatable food when given the choice. However, when FOS was added to control diet after chronic HFHS exposure, although it did not significantly alter body weight loss, it greatly decreased palatable food tropism and consumption and was associated with normalization of MCL markers for DA signaling. We conclude that the nature of the diet (regular chow or HFHS) as well as the timing at which prebiotic supplementation is introduced (preventive or curative) greatly influence the efficacy of the gut-microbiota-brain axis. This crosstalk selectively alters the hedonic or motivational drive to eat and triggers molecular changes in neural substrates involved in the homeostatic and non-homeostatic control of body weight.

Differential effects of macronutrient content in 2 energy-restricted diets on cardiovascular risk factors and adipose tissue cell size in moderately obese individuals: a randomized controlled trial.

BACKGROUND: The most effective and safe dietary approach for weight loss and its impact on the metabolic functions and morphology of adipose tissue remain unclear. OBJECTIVES: We evaluated whether an energy-restricted high-protein diet with a low glycemic index and soluble fiber (LC-P-LGI) would be more effective than a low-calorie conventional diet (LC-CONV) on weight loss and related metabolic risk factors. We further determined factors that may influence adipocyte size during energy restriction. DESIGN: Thirteen obese participants were randomly assigned in a crossover design to 2 periods of a 4-wk hypocaloric diet as either LC-P-LGI or LC-CONV, separated by 8-wk washout intervals. RESULTS: In comparison with the LC-CONV diet, the main effect of the LC-P-LGI diet was a greater decrease in adipocyte diameter (P = 0.048), plasma plasminogen activator inhibitor protein-1 (P = 0.019), vascular endothelial growth factor (P = 0.032), and interferon-γ inducible protein 10 (P = 0.010). Whereas fasting plasma glucose and high-sensitivity C-reactive protein decreased only after the LC-P-LGI diet, with no differences between diets, fasting plasma insulin and insulin resistance were lower after the LC-CONV diet. The diet results did not differ for body composition and lipid variables. Kinetic modifications in adipocyte diameter were associated with metabolic variables and genes implicated in adipocyte proliferation, apoptosis, and angiogenesis. CONCLUSIONS: In comparison with the LC-CONV diet, the LC-P-LGI diet was associated with improvement in some cardiometabolic risk factors and greater reduction in adipocyte size. Profiles of genes involved in inhibiting adipogenesis and angiogenesis, but increasing apoptosis, were correlated with decreased adipocyte size. This study provides insight into the adipose tissue-remodeling changes that induce regulation of adipocyte size during dietary weight loss. This trial was registered at clinicaltrials.gov as NCT01312740.

Overproduction of angiotensinogen from adipose tissue induces adipose inflammation, glucose intolerance, and insulin resistance.

Although obesity is associated with overactivation of the white adipose tissue (WAT) renin-angiotensin system (RAS), a causal link between the latter and systemic insulin resistance is not established. We tested the hypothesis that overexpression of angiotensinogen (Agt) from WAT causes systemic insulin resistance via modulation of adipose inflammation. Glucose tolerance, systemic insulin sensitivity, and WAT inflammatory markers were analyzed in mice overexpressing Agt in the WAT (aP2-Agt mice). Proteomic studies and in vitro studies using 3T3-L1 adipocytes were performed to build a mechanistic framework. Male aP2-Agt mice exhibited glucose intolerance, insulin resistance, and lower insulin-stimulated glucose uptake by the skeletal muscle. The difference in glucose tolerance between genotypes was normalized by high-fat (HF) feeding, and was significantly improved by treatment with angiotensin-converting enzyme (ACE) inhibitor captopril. aP2-Agt mice also had higher monocyte chemotactic protein-1 (MCP-1) and lower interleukin-10 (IL-10) in the WAT, indicating adipose inflammation. Proteomic studies in WAT showed that they also had higher monoglyceride lipase (MGL) and glycerol-3-phosphate dehydrogenase levels. Treatment with angiotensin II (Ang II) increased MCP-1 and resistin secretion from adipocytes, which was prevented by cotreating with inhibitors of the nuclear factor-κB (NF-κB) pathway or nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In conclusion, we show for the first time that adipose RAS overactivation causes glucose intolerance and systemic insulin resistance. The mechanisms appear to be via reduced skeletal muscle glucose uptake, at least in part due to Ang II-induced, NADPH oxidase and NFκB-dependent increases in WAT inflammation.

A Western-like fat diet is sufficient to induce a gradual enhancement in fat mass over generations.

The prevalence of obesity has steadily increased over the last few decades. During this time, populations of industrialized countries have been exposed to diets rich in fat with a high content of linoleic acid and a low content of alpha-linolenic acid compared with recommended intake. To assess the contribution of dietary fatty acids, male and female mice fed a high-fat diet (35% energy as fat, linoleic acid:alpha-linolenic acid ratio of 28) were mated randomly and maintained after breeding on the same diet for successive generations. Offspring showed, over four generations, a gradual enhancement in fat mass due to combined hyperplasia and hypertrophy with no change in food intake. Transgenerational alterations in adipokine levels were accompanied by hyperinsulinemia. Gene expression analyses of the stromal vascular fraction of adipose tissue, over generations, revealed discrete and steady changes in certain important players, such as CSF3 and Nocturnin. Thus, under conditions of genome stability and with no change in the regimen over four generations, we show that a Western-like fat diet induces a gradual fat mass enhancement, in accordance with the increasing prevalence of obesity observed in humans.

Deficiency of angiotensin type 2 receptor rescues obesity but not hypertension induced by overexpression of angiotensinogen in adipose tissue.

Increased angiotensinogen (AGT) production by white adipose tissue has been related to not only obesity but also hypertension. Several studies have highlighted the importance of the angiotensin II type 2 receptor (AT2) in the regulation of blood pressure and fat mass, but the relevance of this transporter in a physiopathological model of increased AGT production, as it occurs in obesity, has not yet been investigated. We used transgenic mice that display either a deletion of AT2 (AT2 KO), an overexpression of AGT (OVEX), or both compound mutants (KOVEX). Results demonstrated that adipocyte hypertrophy and increased lipogenic gene expression induced by adipose AGT overproduction was rescued by deletion of AT2. In line with AGT overexpression, KOVEX and OVEX mice have similar increased plasma AGT levels. However, KOVEX mice display a higher blood pressure than OVEX mice. In kidney, renin expression was clearly reduced in OVEX mice, and its expression was normalized in KOVEX mice. Taken together, we demonstrated that the loss of AT2 expression was sufficient to rescue obesity induced by adipose tissue AGT overexpression and confirmed the necessary role of AT2 for the onset of obesity in this model. Furthermore, despite a reduction of adipose mass in KOVEX, AT2 deficiency caused increased renin production, further worsening the hypertension caused by AGT overexpression.

Oxytocin controls differentiation of human mesenchymal stem cells and reverses osteoporosis.

Osteoporosis constitutes a major worldwide public health burden characterized by enhanced skeletal fragility. Bone metabolism is the combination of bone resorption by osteoclasts and bone formation by osteoblasts. Whereas increase in bone resorption is considered as the main contributor of bone loss that may lead to osteoporosis, this loss is accompanied by increased bone marrow adiposity. Osteoblasts and adipocytes share the same precursor cell and an inverse relationship exists between the two lineages. Therefore, identifying signaling pathways that stimulate mesenchymal stem cells osteogenesis at the expense of adipogenesis is of major importance for developing new therapeutic treatments. For this purpose, we identified by transcriptomic analysis the oxytocin receptor pathway as a potential regulator of the osteoblast/adipocyte balance of human multipotent adipose-derived stem (hMADS) cells. Both oxytocin (OT) and carbetocin (a stable OT analogue) negatively modulate adipogenesis while promoting osteogenesis in both hMADS cells and human bone marrow mesenchymal stromal cells. Consistent with these observations, ovariectomized (OVX) mice and rats, which become osteoporotic and exhibit disequilibrium of this balance, have significant decreased OT levels compared to sham-operated controls. Subcutaneous OT injection reverses bone loss in OVX mice and reduces marrow adiposity. Clinically, plasma OT levels are significantly lower in postmenopausal women developing osteoporosis than in their healthy counterparts. Taken together, these results suggest that plasma OT levels represent a novel diagnostic marker for osteoporosis and that OT administration holds promise as a potential therapy for this disease.

In vivo evidence for a role of adipose tissue SR-BI in the nutritional and hormonal regulation of adiposity and cholesterol homeostasis.

OBJECTIVES: This study examines the role of insulin and angiotensin II in high-density lipoprotein (HDL) metabolism by focusing on the regulation and function of scavenger receptor type-BI (SR-BI) in adipose tissue. METHODS AND RESULTS: Insulin or angiotensin II injection in wild-type mice induced a decrease in circulating HDL and it was associated with the translocation of SR-BI from intracellular sites to the plasma membrane of adipose tissue. Refeeding upregulated adipose HDL selective cholesteryl esters uptake and SR-BI proteins through transcriptional and posttranscriptional mechanisms. This occurred along with a decrease in serum HDL and an increase in adipose cholesterol content. Similar results were obtained with transgenic mice overexpressing locally angiotensinogen in adipose tissue. In adipose 3T3-L1 cell line, HDL induced lipogenesis by increasing liver X receptor binding activity. This mechanism was dependent of insulin and angiotensin II. CONCLUSIONS: Our results raise the possibility that adipose tissue SR-BI translocation might be a link between adipose tissue lipid storage and HDL clearance.

Temporal changes in dietary fats: role of n-6 polyunsaturated fatty acids in excessive adipose tissue development and relationship to obesity.

The importance of a high fat intake in the increasing prevalence of childhood and adult obesity remains controversial. Moreover, qualitative changes (i.e. the fatty acid composition of fats) have been largely disregarded. Herein is reviewed the role of polyunsaturated fatty acids (PUFAs) of the n-6 series in promoting adipogenesis in vitro and favouring adipose tissue development in rodents during the gestation/suckling period. Epidemiological data from infant studies as well as the assessment of the fatty acid composition of mature breast milk and infant formulas over the last decades in the Western industrialized world are revisited and appear consistent with animal data. Changes over decades in the intake of n-6 and n-3 PUFAs, with a striking increase in the linoleic acid/alpha-linolenic ratio, are observed. In adults, using a consumption model based upon production data, similar changes in the PUFA content of ingested lipids have been found for France, and are associated with an increase of fat consumption over the last 40 years. These profound quantitative and qualitative alterations can be traced in the food chain and shown to be due to changes in human dietary habits as well as in the feeding pattern of breeding stock. If prevention of obesity is a key issue for future generations, agricultural and food industry policies should be thoroughly reevaluated.

The adipose renin-angiotensin system modulates systemic markers of insulin sensitivity and activates the intrarenal renin-angiotensin system.

BACKGROUND: The adipose tissue renin-angiotensin system (RAS) contributes to regulation of fat mass and may also impact systemic functions such as blood pressure and metabolism. METHODS AND RESULTS: A panel of mouse models including mice lacking angiotensinogen, Agt (Agt-KO), mice expressing Agt solely in adipose tissue (aP2-Agt/Agt-KO), and mice overexpressing Agt in adipose tissue (aP2-Agt) was studied. Total body weight, epididymal fat pad weight, and circulating levels of leptin, insulin, and resistin were significantly decreased in Agt-KO mice, while plasma adiponectin levels were increased. aP2-Agt mice exhibited increased adiposity and plasma leptin and insulin levels compared to wild type (WT) controls. Angiotensinogen and type I Ang II receptor protein levels were also elevated in kidney of aP2-Agt mice. CONCLUSION: These findings demonstrate that alterations in adipose RAS activity significantly impact both local and systemic physiology in a way that may contribute to the detrimental health effects of obesity.

The adipose-tissue renin-angiotensin-aldosterone system: role in the metabolic syndrome?

Overfeeding of rodents leads to increased local formation of angiotensin II due to increased secretion of angiotensinogen from adipocytes. Whereas angiotensin II promotes adipocyte growth and preadipocyte recruitment, increased secretion of angiotensinogen from adipocytes also directly contributes to the close relationship between adipose-tissue mass and blood pressure in mice. In contrast, angiotensin II acts as an antiadipogenic substance in human adipose tissue, and the total increase in adipose-tissue mass may be more important in determining human plasma angiotensinogen levels than changes within the single adipocyte. However, as increased local formation of angiotensin II in adipose tissue may be increased especially in obese hypertensive subjects, a contribution of the adipose-tissue renin-angiotensin system to the development of insulin resistance and hypertension is conceivable in humans, but not yet proven. Insulin resistance may be aggravated by the inhibition of preadipocyte recruitment, which results in the redistribution of triglycerides to the liver and skeletal muscle, and blood pressure may be influenced by local formation of angiotensin II in perivascular adipose tissue. Thus, although the mechanisms are still speculative, the beneficial effects of ACE-inhibition and angiotensin-receptor blockade on the development of type 2 diabetes in large clinical trials suggest a pathophysiological role of the adipose-tissue renin-angiotensin system in the metabolic syndrome.

Arachidonic acid and prostacyclin signaling promote adipose tissue development: a human health concern?

High fat intake is associated with fat mass gain through fatty acid activation of peroxisome proliferator-activated receptors delta and gamma, which promote adipogenesis. We show herein that, compared to a combination of specific agonists to both receptors or to saturated, monounsaturated, and omega-3 polyunsaturated fatty acids, arachidonic acid (C20:4, omega-6) promoted substantially the differentiation of clonal preadipocytes. This effect was blocked by cyclooxygenase inhibitors and mimicked by carbacyclin, suggesting a role for the prostacyclin receptor and activation of the cyclic AMP-dependent pathways that regulate the expression of the CCAAT enhancer binding proteins beta and delta implicated in adipogenesis. During the pregnancy-lactation period, mother mice were fed either a high-fat diet rich in linoleic acid, a precursor of arachidonic acid (LO diet), or the same isocaloric diet enriched in linoleic acid and alpha-linolenic acid (LO/LL diet). Body weight from weaning onwards, fat mass, epididymal fat pad weight, and adipocyte size at 8 weeks of age were higher with LO diet than with LO/LL diet. In contrast, prostacyclin receptor-deficient mice fed either diet were similar in this respect, indicating that the prostacyclin signaling contributes to adipose tissue development. These results raise the issue of the high content of linoleic acid of i) ingested lipids during pregnancy and lactation, and ii) formula milk and infant foods in relation to the epidemic of childhood obesity.

Angiotensinogen, adipocyte differentiation and fat mass enlargement.

PURPOSE OF REVIEW: Angiotensinogen and components of the renin-angiotensin system are expressed in adipose tissue of rodents and humans, but the role of generated angiotensin II has remained intriguing. Moreover, the functional importance of angiotensin II receptor subtypes in preadipocytes and adipocytes still remains a controversial subject. RECENT FINDINGS: Recent findings in transgenic mice have emphasized the upregulation of angiotensinogen expression by glucocorticoids. Furthermore, angiotensinogen products, that is angiotensin II and possibly angiotensin II-related products, have been found to act locally in modulating adipose tissue growth in an autocrine/paracrine manner. Cellularity measurements show that fat mass enlargement is associated with adipocyte hypertrophy, consistent with the upregulation of the fatty acid synthetase gene by angiotensin II depicted at the molecular level. Together, these findings suggest a mechanism by which transient or chronic overexpression of angiotensinogen in adipose tissue favors lipogenesis in adipocytes and leads to a 'vicious' circle whereby adipose tissue development is further increased. SUMMARY: Additional studies are warranted to characterize angiotensin II-related receptors, if any, and to clarify the role played by angiotensin II receptor subtypes and metabolites in various metabolic aspects of white adipose tissue.