Emulsified lipids increase endotoxemia: possible role in early postprandial low-grade inflammation

Abstract

Low-grade inflammation is a risk factor for the onset of atherosclerosis. Little is known about the involvement of endotoxin absorption from the gut during the digestion of lipids. In the present study, we first investigated in humans the impact of a mixed meal containing dispersed lipids on postprandial endotoxemia and inflammation. We then investigated the effect of (i) oil emulsification in vivo in rats and (ii) fatty acid amounts in vitro using Caco-2 cells on postprandial endotoxemia. In humans, postprandial endotoxemia increased early after the meal. Moreover, we evidenced that the endotoxin receptor sCD14 increased during digestion and that chylomicrons could contribute to absorbed endotoxin transport. This could explain the significant peak of inflammatory cytokine IL-6 that we observed 2 h after the mixed meal. Interestingly, in rats, the emulsion led to both higher endotoxemia and hypertriglyceridemia than oil and compared to a control saline load. In vitro, incubation of Caco-2 cells with increasing fatty acid concentrations enhanced epithelial absorption of endotoxin. To our knowledge, this is the first study evidencing in healthy humans that, following a mixed meal containing lipids, increased endotoxemia is associated with raised sCD14 and a peak of IL-6. On a repeated basis, this may thus be a triggering cascade for the onset of atherosclerosis. In this respect, optimizing both dietary fat amount and structure could be a possible strategy to limit such low-grade endotoxemia and inflammation by the control of postprandial lipemia.

Molecular and Cellular Mechanisms Responsible for Cellular Stress and Low-grade Inflammation Induced by a Super-low Dose of Endotoxin

“…This may contribute to chronic low-grade inflammation as manifested in chronic diseases such as diabetes, Parkinson disease, and atherosclerosis (2)(3)(4)(5)(6). Mechanistically, a super-low dose of endotoxin results in a mildly sustained activation of proinflammatory mediators without the activation of anti-inflammatory mediators, allowing low-grade, non-resolving inflammation to persist (7).…”

Endotoxemia Analysis by the Limulus Amoebocyte Lysate Assay in Different Mammal Species Used in Metabolic Studies

“…In this study we have shown the importance of the dilution factor in human, mice, rat and pigs; and compared 4 different dilution factors in pigs to explain our rationale. The methodology used in our case to measure endotoxemia combined dilution, heat and sonication to increase the dispersion of LPS in the sample [4]. Moreover great care was taken to avoid contaminations during the experiment.…”

“…Endotoxins of the Gram-negative bacteria, when released into the intestinal lumen after cell lysis, have a high pyrogenic activity and can induce and maintain a low-grade inflammation [3,4]. For a long time the measurement of pyrogenic molecules has been a regulatory requirement for some pharmaceutical supplies including injectables, medical and surgical equipment and dialysis samples.…”

“…The presence of an inhibition can be detected when endotoxins added to serum or plasma (positive product control, so-called "spike") fails to react with the LAL reagent. Several methods have been used to remove inhibition of the LAL test such as dilution, heating [4,14], solvent extraction [11] and acid treatment [14,15]. The combination of dilution and heating processes has been shown to be efficacious, yet we have also added a sonication step as the extraction of LPS is also influenced significantly by physical characteristics that determine its aggregation [4,16].…”

“…Several methods have been used to remove inhibition of the LAL test such as dilution, heating [4,14], solvent extraction [11] and acid treatment [14,15]. The combination of dilution and heating processes has been shown to be efficacious, yet we have also added a sonication step as the extraction of LPS is also influenced significantly by physical characteristics that determine its aggregation [4,16]. In fact, Komuro et al [16], showed sonication may disperse the aggregates of LPS into smaller and more uniform particle which facilitates the measure of biological activities in aqueous media.…”