Bioaccessibility of carotenoids and vitamin E from their main dietary sources

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Gene expression profiling of 3T3-L1 adipocytes exposed to phloretin

International audienceAdipocyte dysfunction plays a major role in the outcome of obesity, insulin resistance and related cardiovascular complications. Thus, considerable efforts are underway in the pharmaceutical industry to find molecules that target the now well-documented pleiotropic functions of adipocyte. We previously reported that the dietary flavonoid phloretin enhances 3T3-L1 adipocyte differentiation and adiponectin expression at least in part through PPARγ activation. The present study was designed to further characterize the molecular mechanisms underlying the phloretin-mediated effects on 3T3-L1 adipocytes using microarray technology. We show that phloretin positively regulates the expression of numerous genes involved in lipogenesis and triglyceride storage, including GLUT4, ACSL1, PEPCK1, lipin-1 and perilipin (more than twofold). The expression of several genes encoding adipokines, in addition to adiponectin and its receptor, is positively or negatively regulated in a way that suggests a possible reduction in systemic insulin resistance and obesity-associated inflammation. Improvement of insulin sensitivity is also suggested by the overexpression of genes associated with insulin signal transduction, such as CAP, PDK1 and Akt2. Many of these genes are PPARγ targets, confirming the involvement of PPARγ pathway in the phloretin effects on adipocytes. In light of these microarray data, it is reasonable to assume that phloretin may be beneficial for reducing insulin resistance, in a similar way to the thiazolidinedione class of antidiabetic drug

Comparison of different vehicles to study the effect of tocopherols on gene expression in intestinal cells

International audienceRecent studies have focused on the ability of tocopherols to regulate gene expression. For such experiments, the methodology used to deliver molecules to the cells is crucial and could lead to different results depending on the vehicle used. The objective of the present study was to compare commonly used tocopherol vehicles (ethanol, BSA and mixed micelles) in terms of toxicity, stabilization of tocopherols, uptake efficiency of tocopherols by cells and effect on gene expression. Lactate dehydrogenase measurements did not reveal cytotoxicity of any of the tested vehicles. Tocopherol recovery measurements showed that ∼80% of the tocopherol was lost in ethanolic solutions, while only ∼30% and 10% were lost in BSA and mixed micelles, respectively. After 24 h incubation, Caco-2 cell monolayers treated with mixed micelles exhibited the highest agr-tocopherol intracellular concentrations (5-times those measured with the two other vehicles). Similar results were obtained with γ-tocopherol. Vehicles, except mixed micelles that activate the FXR/bile acids signalling pathway, did not affect expression of nuclear receptors involved in lipid metabolism or their target genes. This study establishes mixed micelles as the best vehicle to deliver tocopherols to intestinal cell monolayers in cultur

Adiponectin expression is induced by vitamin E via a peroxisome proliferator-activated receptor gamma-dependent mechanism

International audienceAdiponectin is a well-known adipokine secreted by adipocytes that presents insulin-sensitizing properties. The regulation of expression of this adipokine by micronutrients is largely unknown. We demonstrate here that adiponectin expression is induced in adipocytes after exposure to tocopherols via the peroxisome proliferator-activated receptor {gamma} (PPAR{gamma}) pathway. Vitamin E force feeding resulted in an induction of adiponectin in mice at both mRNA and protein levels. Adiponectin mRNA and protein secretion were also increased by vitamin E ({alpha}- and {gamma}-tocopherol) in 3T3-L1 cells, together with PPAR{gamma} mRNA, independent of an antioxidant effect. In transient transfections, both {alpha}- and {gamma}-vitamers induced the luciferase gene reporter under the control of a human adiponectin promoter via a PPAR-responsive element. The induction of adiponectin by tocopherols seems to be PPAR{gamma} dependent, because it was blocked by the specific antagonist GW9662. Finally, we showed that intracellular concentrations of a PPAR{gamma} endogenous ligand, 15-deoxy-{Delta}12,14-prostaglandin J2, increased after treatment with tocopherols in 3T3-L1 cells. In summary, vitamin E up-regulates adiponectin expression via a mechanism that implicates PPAR{gamma} together with its endogenous ligand 15-deoxy-{Delta}12,14-prostaglandin J2. The induction of adiponectin via an original molecular mechanism could be considered as the basis for the beneficial effect of vitamin E on insulin sensitivit

Bioeffects of a combination of trace elements on adipocyte biology

International audienceThe white adipose tissue plays a major role in the development of obesity and associated metabolic complications by producing a variety of pro and anti-inflammatory adipokines. Recently, studies in humans or in animals have shown a beneficial effect of certain trace elements such as zinc on insulin resistance and adipokine secretion. The aim of our study was to test the effect of a zinc-nickel-cobalt solution (ZnNiCo) on adipocyte function and to identify potential health effects of this solution in the context of obesity and associated disorders. No impact of ZnNiCo on adipogenesis was observed in 3T3-L1 cells. Gene expression in murine and human adipocytes was examined in the presence of ZnNiCo using whole genome microarrays. This transcriptomic analysis indicated that ZnNiCo affected the expression levels of genes in adipocytes under basal conditions or incubated with TNF-alpha and showed a down regulation of several inflammatory genes belonging to the cytokine and chemokine families (P < 0.01). These data were confirmed in mice fed with a high fat diet supplemented with ZnNiCo (P < 0.05). A modulation of NF-kappa B activation (evaluated by ELISA; P < 0.05) by ZnNiCo could explain at least in part these observations. The trace elements present in ZnNiCo are able to modulate the expression level of several inflammation related transcripts in adipocytes. These studies suggest that ZnNiCo could play a role in the prevention of inflammation in adipose tissue in obesity

Lycopene attenuates LPS-induced TNF-alpha secretion in macrophages and inflammatory markers in adipocytes exposed to macrophage-conditioned media

International audienceScope Adipose tissue is infiltrated by an increasing number of macrophages during the development of obesity. These immune cells are suspected to be a major source of TNF-a that interferes with adipocyte function. Because lycopene possesses anti-inflammatory properties, we hypothesize that lycopene could reduce the production of TNF-a by macrophages and thus interfere in the cross-talk between macrophages and adipocytes. Methods and results We demonstrated that physiological concentrations of lycopene were able to attenuate the lipopolysaccharide (LPS)-mediated induction of TNF-a in RAW 264.7 macrophages, at both the mRNA and protein levels. The molecular mechanism was studied. It appeared that the LPS-activation of both JNK and NF-?B signaling pathways was modulated by lycopene. The anti-inflammatory effects of lycopene on macrophages were accompanied by a decrease in LPS-stimulated macrophage migration in the presence of lycopene. Furthermore, lycopene decreased macrophage conditioned medium-induced proinflammatory cytokine, acute phase protein, and chemokine mRNA expression in 3T3-L1 adipocytes. Conclusion These data indicate that lycopene displayed an anti-inflammatory effect on macrophages that beneficially impacted adipocyte function. Thus, these results suggest that lycopene could block the vicious cycle that occurs between adipocytes and macrophages in adipose tissue during obesity

Vitamin D reduces the inflammatory response and restores glucose uptake in adipocytes

International audienceScope Obesity is strongly associated with low-grade inflammation, notably due to an overproduction of proinflammatory markers by adipose tissue and adipocytes as well as a vitamin D deficiency. Whether these problems are interrelated has not been clearly established. Methods and results In the present report, decreases in the levels of inflammatory markers such as IL-6, MCP-1, and IL-1 beta (mRNA and protein level) in human adipocytes and in 3T3-L1 adipocytes were observed after 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) treatment. Such treatment also decreased the expression of the TNF-alpha-mediated proinflammatory marker in 3T3-L1 and human adipocytes. A similar effect was observed in adipocyte-macrophage co-culture systems in which 1,25-(OH)2D3 decreased proinflammatory marker expression under basal and TNF-alpha-stimulated conditions. The involvement of VDR and NF-kappa B was confirmed in these regulations. Incubation with 1,25-(OH)2D3 also resulted in the dephosphorylation of p38, which is linked to the transcriptional induction of several Dusp family members. Functional consequences of the 1,25-(OH)2D3 treatment on glucose uptake and AKT phosphorylation were observed. Conclusion The improvement of both proinflammatory status and glucose uptake in adipocytes under 1,25-(OH)2D3 effect suggests that low-grade inflammation could be linked to vitamin D deficiency. This observation offers new perspectives in the context of obesity and associated physiopathological disorders

Adiponectin expression is induced by vitamin E via a peroxisome proliferator-activated receptor gamma-dependent mechanism

International audienceAdiponectin is a well-known adipokine secreted by adipocytes that presents insulin-sensitizing properties. The regulation of expression of this adipokine by micronutrients is largely unknown. We demonstrate here that adiponectin expression is induced in adipocytes after exposure to tocopherols via the peroxisome proliferator-activated receptor {gamma} (PPAR{gamma}) pathway. Vitamin E force feeding resulted in an induction of adiponectin in mice at both mRNA and protein levels. Adiponectin mRNA and protein secretion were also increased by vitamin E ({alpha}- and {gamma}-tocopherol) in 3T3-L1 cells, together with PPAR{gamma} mRNA, independent of an antioxidant effect. In transient transfections, both {alpha}- and {gamma}-vitamers induced the luciferase gene reporter under the control of a human adiponectin promoter via a PPAR-responsive element. The induction of adiponectin by tocopherols seems to be PPAR{gamma} dependent, because it was blocked by the specific antagonist GW9662. Finally, we showed that intracellular concentrations of a PPAR{gamma} endogenous ligand, 15-deoxy-{Delta}12,14-prostaglandin J2, increased after treatment with tocopherols in 3T3-L1 cells. In summary, vitamin E up-regulates adiponectin expression via a mechanism that implicates PPAR{gamma} together with its endogenous ligand 15-deoxy-{Delta}12,14-prostaglandin J2. The induction of adiponectin via an original molecular mechanism could be considered as the basis for the beneficial effect of vitamin E on insulin sensitivit

: Vitamin E transport in enterocytes

Although cellular uptake of vitamin E was initially described as a passive process, recent studies in the liver and brain have shown that SR-BI (scavenger receptor class B type I) is involved in this phenomenon. As SR-BI is expressed at high levels in the intestine, the present study addressed the involvement of SR-BI in vitamin E trafficking across enterocytes. Apical uptake and efflux of the main dietary forms of vitamin E were examined using Caco-2 TC-7 cell monolayers as a model of human intestinal epithelium. (R,R,R)-gamma-tocopherol bioavailability was compared between wild-type mice and mice overexpressing SR-BI in the intestine. The effect of vitamin E on enterocyte SR-BI mRNA levels was measured by real-time quantitative reverse transcription-PCR. Concentration-dependent curves for vitamin E uptake were similar for (R,R,R)-alpha-, (R,R,R)-gamma-, and dl-alpha-tocopherol. (R,R,R)-alpha-tocopherol transport was dependent on incubation temperature, with a 60% reduction in absorption at 4 degrees C compared with 37 degrees C (p < 0.05). Vitamin E flux in enterocytes was directed from the apical to the basal side, with a relative 10-fold reduction in the transfer process when measured in the opposite direction (p < 0.05). Co-incubation with cholesterol, gamma-tocopherol, or lutein significantly impaired alpha-tocopherol absorption. Anti-human SR-BI antibodies and BLT1 (a chemical inhibitor of lipid transport via SR-BI) blocked up to 80% of vitamin E uptake and up to 30% of apical vitamin E efflux (p < 0.05), and similar results were obtained for (R,R,R)-gamma-tocopherol. SR-BI mRNA levels were not significantly modified after a 24-h incubation of Caco-2 cells with vitamin E. Finally, (R,R,R)-gamma-tocopherol bioavailability was 2.7-fold higher in mice overexpressing SR-BI than in wild-type mice (p < 0.05). The present data show for the first time that vitamin E intestinal absorption is, at least in part, mediated by SR-BI

Vitamin E decreases endogenous cholesterol synthesis and apo-AI-mediated cholesterol secretion in Caco-2 cellsstar, open

International audienceIntestine is the gateway for newly absorbed tocopherols. This organ also plays a crucial role in cholesterol metabolism. Because tocopherols are known to impact cholesterol metabolism in the liver, we hypothesized that tocopherols could also modulate cholesterol metabolism in the intestine. This study aimed to verify this hypothesis and to unveil the mechanisms involved, using Caco-2 cells as a model of the human intestinal cell. Both α- and γ-tocopherol significantly (P<.05) decreased endogenous cholesterol synthesis and apo-AI-mediated cholesterol secretion in Caco-2 cells. Tocopherols down-regulated (P<.05) up to half of the genes involved in the cholesterol synthesis pathway, together with CYP27A1, which is involved in oxysterol production. The activity of this enzyme, as well as the levels of intracellular oxysterols, was significantly diminished by tocopherols. Finally, tocopherols significantly reduced ABCA1 mRNA levels in Caco-2 cells. We conclude that tocopherols impair the endogenous synthesis and apo-AI-mediated secretion of cholesterol in Caco-2 cells. This effect involves a down-regulation of genes involved in the cholesterol synthesis pathway, resulting in down-regulation of CYP27A1 which, in turn, diminishes oxysterol concentrations. The outcome is a decrease of LXR activity, resulting in down-regulation of ABCA1. These data reinforce the effect of α- and γ-tocopherol on cholesterol metabolism via gene expression regulatio