Recent data suggest that dietary fat promotes intestinal absorption of lipopolysaccharides (LPS) from the gut microflora, which might contribute to various inflammatory disorders. The mechanism of fat-induced LPS absorption is unclear, however. Intestinal-epithelial cells can internalize LPS from the apical surface and transport LPS to the Golgi. The Golgi complex also contains newly formed chylomicrons, the lipoproteins that transport dietary longchain fat through mesenteric lymph and blood. Because LPS has affinity for chylomicrons, we hypothesized that chylomicron formation promotes LPS absorption. In agreement with our hypothesis, we found that CaCo-2 cells released more cell-associated LPS after incubation with oleic-acid (OA), a long-chain fatty acid that induces chylomicron formation, than with butyric acid (BA), a short-chain fatty acid that does not induce chylomicron formation. Moreover, the effect of OA was blocked by the inhibitor of chylomicron formation, Pluronic L-81. We also observed that intragastric triolein (TO) gavage was followed by increased plasma LPS, whereas gavage with tributyrin (TB), or TO plus Pluronic L-81, was not. Most intestinally absorbed LPS was present on chylomicron remnants (CM-R) in the blood. Chylomicron formation also promoted transport of LPS through mesenteric lymph nodes (MLN) and the production of TNFa mRNA in the MLN. Together, our data suggest that intestinal epithelial cells may release LPS on chylomicrons from cell-associated pools. Chylomicron-associated LPS may contribute to postprandial inflammatory responses or chronic diet-induced inflammation in chylomicron target tissues.-Ghoshal, S., J. Witta, J. Zhong, W. de Villiers, and E. Eckhardt. Chylomicrons promote intestinal absorption of lipopolysaccharides. J. Lipid Res. 2009. 50: 90-97.

Although a strong clinical response to fontolizumab was not observed, significant decreases in C-reactive protein levels suggest a biological effect. Fontolizumab was well tolerated, and further studies to assess its efficacy are warranted.

BackgroundA small fraction of dietary protein survives enzymatic degradation and is absorbed in potentially antigenic form. This can trigger inflammatory responses in patients with celiac disease or food allergies, but typically induces systemic immunological tolerance (oral tolerance). At present it is not clear how dietary antigens are absorbed. Most food staples, including those with common antigens such as peanuts, eggs, and milk, contain long-chain triglycerides (LCT), which stimulate mesenteric lymph flux and postprandial transport of chylomicrons through mesenteric lymph nodes (MLN) and blood. Most dietary antigens, like ovalbumin (OVA), are emulsifiers, predicting affinity for chylomicrons. We hypothesized that chylomicron formation promotes intestinal absorption and systemic dissemination of dietary antigens.Methodology/Principal FindingsAbsorption of OVA into MLN and blood was significantly enhanced when OVA was gavaged into fasted mice together with LCT compared with medium-chain triglycerides (MCT), which do not stimulate chylomicron formation. The effect of LCT was blocked by the addition of an inhibitor of chylomicron secretion, Pluronic L-81. Adoptively transferred OVA-specific DO11.10 T-cells proliferated more extensively in peripheral lymph nodes when OVA was gavaged with LCT than with MCT or LCT plus Pluronic L-81, suggesting that dietary OVA is systemically disseminated. Most dietary OVA in plasma was associated with chylomicrons, suggesting that these particles mediate systemic antigen dissemination. Intestinal-epithelial CaCo-2 cells secreted more cell-associated, exogenous OVA when stimulated with oleic-acid than with butyric acid, and the secreted OVA appeared to be associated with chylomicrons.Conclusions/SignificancePostprandial chylomicron formation profoundly affects absorption and systemic dissemination of dietary antigens. The fat content of a meal may affect immune responses to dietary antigens by modulating antigen absorption and transport.

BackgroundObesity is associated with inflammation of visceral adipose tissues, which increases the risk for insulin resistance. Animal models suggest that T-lymphocyte infiltration is an important early step, although it is unclear why these cells are attracted. We have recently demonstrated that dietary triglycerides, major components of high fat diets, promote intestinal absorption of a protein antigen (ovalbumin, “OVA”). The antigen was partly transported on chylomicrons, which are prominently cleared in adipose tissues. We hypothesized that intestinally absorbed gut antigens may cause T-lymphocyte associated inflammation in adipose tissue.Methodology/Principal FindingsTriglyceride absorption promoted intestinal absorption of OVA into adipose tissue, in a chylomicron-dependent manner. Absorption tended to be higher in mesenteric than subcutaneous adipose tissue, and was lowest in gonadal tissue. OVA immunoreactivity was detected in stromal vascular cells, including endothelial cells. In OVA-sensitized mice, OVA feeding caused marked accumulation of CD3+ and osteopontin+ cells in mesenteric adipose tissue. The accumulating T-lymphocytes were mainly CD4+. As expected, high-fat (60% kCal) diets promoted mesenteric adipose tissue inflammation compared to low-fat diets (10% Kcal), as reflected by increased expression of osteopontin and interferon-gamma. Immune responses to dietary OVA further increased diet-induced osteopontin and interferon-gamma expression in mesenteric adipose. Inflammatory gene expression in subcutaneous tissue did not respond significantly to OVA or dietary fat content. Lastly, whereas OVA responses did not significantly affect bodyweight or adiposity, they significantly impaired glucose tolerance.Conclusions/SignificanceOur results suggest that loss or lack of immunological tolerance to intestinally absorbed T-lymphocyte antigens can contribute to mesenteric adipose tissue inflammation and defective glucose metabolism during high-fat dieting.

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