Impact of Dietary Lipids on Colonic Function and Microbiota: An Experimental Approach Involving Orlistat-Induced Fat Malabsorption in Human Volunteers

OBJECTIVES:

High-fat diets alter gut microbiota and barrier function, inducing metabolic endotoxemia and low-grade inflammation. Whether these effects are due to the high dietary lipid content or to the concomitant decrease of carbohydrate intake is unclear. The aim of this study was to determine whether higher amounts of dietary fat reaching the colon (through orlistat administration) affect the colonic ecosystem in healthy volunteers and the effect of the prebiotic oligofructose (OF) in this model.

METHODS:

Forty-one healthy young subjects were distributed among four groups: Control (C), Prebiotic (P), Orlistat (O), and Orlistat/Prebiotic (OP). They consumed a fat-standardized diet (60 g/day) during Week-1 (baseline) and after 1 week of washout, Week-3. During Week-3, they also received their respective treatment (Orlistat: 2 × 120 mg/day, OF: 16 g/day, and maltodextrin as placebo). A 72-h stool collection was carried out at the end of Week-1 (T0) and Week-3 (T1). Fecal fat, calprotectin, and short-chain fatty acids (SCFAs) as well as the antioxidant activity of fecal waters (ferric-reducing antioxidant power), fecal microbiota composition (by deep sequencing), and gut permeability (Sucralose/Lactulose/Mannitol test) were determined at these times.

RESULTS:

Fecal fat excretion was higher in the O (P=0.0050) and OP (P=0.0069) groups. This event was accompanied, in the O group, by an increased calprotectin content (P=0.047) and a decreased fecal antioxidant activity (P=0.047). However, these alterations did not alter gut barrier function and the changes observed in the composition of the fecal microbiota only affected bacterial populations with low relative abundance (<0.01%); in consequences, fecal SCFA remained mainly unchanged. Part of the colonic alterations induced by orlistat were prevented by OF administration.

CONCLUSIONS:

In the context of an equilibrated diet, the acute exposition of the colonic ecosystem to high amounts of dietary lipids is associated with an incremented excretion of fecal calprotectin and pro-oxidant activity of the colonic content, in the absence of significant changes in the microbiota.

Possible role of cAMP in the differentiation of Trypanosoma cruzi

To assess the possible action of cAMP on the cell differentiation of Trypanosoma cruzi, we determined both cAMP levels and cAMP-binding activities of epimastigotes and trypomastigotes of this parasite. Trypomastigotes showed a 4-fold higher cAMP content and a 2.5-fold increase in the specific activity of a cAMP-binding protein with identical properties to that of epimastigotes. The high levels of cAMP present in trypomastigotes strongly suggest a role of this cyclic nucleotide on the differentiation of T. cruzi.

Trypanosoma cruzi: polypeptide markers of epimastigotes and trypomastigotes

We compared the major polypeptides of epimastigotes and trypomastigotes of T. cruzi, by submitting total parasite lysates to electrophoresis in polyacrylamide gels (SDS-PAGE), protein staining with Coomassie brilliant blue, laser densitometry, or immunoblotting with sera derived from infected individuals (Chagas' disease). Epimastigotes and trypomastigotes displayed extensive homology, the differences being quantitative, except for a trypomastigote-specific band of Mr 75,000 which reacted with chagasic sera. Immunoblotting with chagasic sera confirmed the electrophoretic homology of epimastigotes and trypomastigotes. Upon antigenic dilution, a cluster of antigenic bands in the range of Mr 150,000 to 75,000 prevailed in the trypomastigotes, whereas the epimastigotes displayed more abundance of antigenic bands in the range of Mr 72,000 to 36,000.

The effect of proteolytic enzymes and protease inhibitors on the interaction Trypanosoma cruzi-fibroblasts

It has been shown previously that the capability to adhere to and infect fibroblastic cells by Trypanosoma cruzi is expressed only partially in trypomastigotes recently liberated from infected fibroblasts, but these parasites can increase several-fold their adhesion and infectivity by a time-dependent extracellular incubation. It is now shown that polyacrylamide gel electrophoresis patterns of 125I-labelled surface proteins of the parasites change during the activation process and that protease inhibitors of diverse specificity can block both these changes and the development of adhesion and infectivity. Treatment of fresh trypomastigotes with different proteases increases immediately adhesion and infection. The effect of trypsin has been studied in detail and it was found that this protease stimulates adhesion 4- to 6-fold, even in trypomastigotes obtained and assayed in the absence of serum. Trypomastigotes incubated for various periods and then exposed to trypsin increase their adhesion to values similar to those attained by prolonged incubation of trypomastigotes alone, but infection is stimulated in fresh trypomastigotes only. Trypomastigotes whose development of activation has been inhibited either by protease inhibitors, puromycin, and tunicamycin, and are thereafter trypsinized, show respectively, that: adhesion and infection are restored immediately to the same high values obtained when untreated controls are trypsinized, adhesion is restored, but not infection, and infection is not restored. These results suggest that the adhesion step of T. cruzi trypomastigotes to fibroblastic cells depends on a membrane protein(s) that is (are) already present in an inactive or hidden form in parasites recently liberated from infected fibroblasts. Upon extracellular maturation of these trypomastigotes this proteins(s) is activated or unmasked, probably through an endogenous proteolytic process, whose expression requires protein synthesis. The penetration step requires biosynthesis of a tunicamycin-sensitive glycoprotein(s) of the parasite and its full expression necessitates serum.

The effect of inhibitors of macromolecular biosynthesis on the in vitro infectivity and morphology of Trypanosoma cruzi trypomastigotes

The effect of inhibitors of RNA, protein, and glycoprotein biosynthesis has been studied on the development of in vitro infectivity and the transformation to spheromastigotes occurring when recently isolated trypomastigotes of Trypanosoma cruzi are incubated extracellularly. Puromycin (1 microgram/ml) blocks the development of parasite adhesion and penetration of Vero cells, as well as the transformation. Actinomycin D (8 ng/ml) and tunicamycin (30 ng/ml) inhibit completely the development of infectivity, without blocking adhesion and transformation. The last two parameters are inhibited by higher actinomycin D concentrations, but are unaffected by tunicamycin. The results obtained suggest that a parasite glycoprotein is involved in the penetration step of T. cruzi trypomastigotes into fibroblastic cells, and that adhesion, penetration, and transformation to spheromastigotes are three different processes, each one of them requiring de novo synthesis of distinct proteins.

Changes in morphology and infectivity of cell culture-derived trypomastigotes of Trypanosoma cruzi

Trypomastigotes of Trypanosoma cruzi, obtained from the first burst of infected Vero cells, have only a limited invasive capability for fibroblastic cells. Intracellular amastigotes and epimastigotes do not infect these cells at all. Preincubation of the isolated trypomastigotes with Eagle's minimal essential medium/10% fetal calf serum increases 5- to 15-fold their in vitro infectivity. This increased invasive capability is accompanied, in the case of the EP strain of T. cruzi, by a morphological transformation into an amastigote-like or spheromastigote form, which is similar, but not identical to replicating intracellular amastigotes. Trypomastigotes from another isolate (BEC) also increase their infectivity several fold upon preincubation, but before any morphological differentiation occurs, suggesting that these two events are independent. The phenomenon of increased infective capability of the parasite is expressed similarly in different host cells. Parasite adhesion is stimulated 4- to 12-fold upon preincubation of the trypomastigotes. The type of serum used (fetal calf, calf, human) affects the development of infectivity, as well as the process of cell infection in itself, but not the morphological differentiation. These processes are also temperature-dependent. The highly infective parasitic forms do not synthetize DNA, but are active in RNA and protein synthesis. The results obtained indicate the existence in T. cruzi trypomastigotes of an active system for infecting fibroblastic cells, which is only partially expressed in trypomastigotes recently released from host fibroblasts but which can undergo a further extracellular maturation, thus allowing studies on the mechanism of infection in cell-free media.

The effect of surface membrane modifications of fibroblastic cells on the entry process of Trypanosoma cruzi trypomastigotes

Treatment prior to infection with Trypanosoma cruzi trypomastigotes of Vero, MA-103, and chick muscle cells with concanavalin A, phytohemagglutinin, wheat germ agglutinin and ricin I results in a diminished parasite interiorization in these cells; succinylated concanavalin A is also inhibitory. The effect of these lectins is abolished by the corresponding sugar haptens. Trypsin and periodate treatment of the cells also inhibits infection, as well as calcium ionophore A23187 and drugs that disrupt microtubules and microfilaments directly, like colchicine, vinblastine and cytochalasin B. These results show that alteration(s) of a surface glycoprotein(s) and/or of the plasma membrane architecture of fibroblastic host cells inhibit infection, suggesting that the surface membrane of these cells does not play a passive role in the process of infection by T. cruzi.