Evidence for intestinal heterogenic expression of di-tripeptides transporter PepT1 during experimental cryptosporidiosis in neonatal rats.

Cryptosporidium parvum is a protozoan parasite that causes intestinal malabsorptive syndrome and malnutrition. Considering the importance of di-tripeptide absorption for nutritional status, we previously investigated the regulation of PepT1 transporter in the suckling rat model of acute cryptosporidiosis and showed that PepT1 protein expression and activity were not modified in the parasitized intestine. Here we used confocal microscopy performed on intestinal villi to determine the subcellular localization of PepT1 together with f-actin and parasites. For this purpose, confocal microscopy using vibratome thick sections was developed on the distal small intestine, the preferential site of parasite implantation. Results showed major heterogeneity of apical PepT1 expression among enterocytes, which did not correlate with actin staining or parasite implantation. These results underscore the importance of considering the effect of C. parvum at the cellular scale and not only in the entire epithelium.

Assessment of metabolic diversity within the intestinal microbiota from healthy humans using combined molecular and cultural approaches.

The human gut harbours a wide range of bacterial communities that play key roles in supplying nutrients and energy to the host through anaerobic fermentation of dietary components and host secretions. This fermentative process involves different functional groups of microorganisms linked in a trophic chain. Although the diversity of the intestinal microbiota has been studied extensively using molecular techniques, the functional aspects of this biodiversity remain mostly unexplored. The aim of the present work was to enumerate the principal metabolic groups of microorganisms involved in the fermentative process in the gut of healthy humans. These functional groups of microorganisms were quantified by a cultural approach, while the taxonomic composition of the microbiota was assessed by in situ hybridization on the same faecal samples. The functional groups of microorganisms that predominated in the gut were the polysaccharide-degrading populations involved in the breakdown of the most readily available exogenous and endogenous substrates and the predominant butyrate-producing species. Most of the functional groups of microorganisms studied appeared to be present at rather similar levels in all healthy volunteers, suggesting that optimal numbers of these various bacterial groups are crucial for efficient gut fermentation, as well as for host nutrition and health. Significant interindividual differences were, however, confirmed with respect to the numbers of methanogenic archaea, filter paper-degrading and acetogenic bacteria and the products formed by lactate-utilizing bacteria.

Cryptosporidiosis induces a transient upregulation of the oligopeptides transporter (PepT1) activity in neonatal rats.

Cryptosporidium parvum is a parasitic protozoa increasingly appreciated as a cause of intestinal malabsorptive syndrome leading to malnutrition and/or growth failure. Because a major mechanism for apical peptide absorption by small intestine is via the proton-coupled transporter PepT1, we investigated the expression and functionality of this transporter in our model of acute cryptosporidiosis. Four-day-old Sprague-Dawley rats were inoculated by gavage with 5 x 10(5) oocysts of C. parvum and killed at Day 12 (peak of the infection) or Day 21 (spontaneous clearance of the parasite). PepT1 expression and functionality were quantified in the distal small intestine, preferential site of C. parvum implantation, and in the proximal small intestine, free of parasite, using Western blot and Ussing chambers, respectively. No difference in total PepT1 protein expression or in glycyl-sarcosine fluxes was observed in C. parvum-infected rats compared with controls either on Day 12 or on Day 21, both in the proximal and in the distal small intestine. However, a significant decrease of apical membrane protein expression of PepT1 was observed in C. parvum-infected enterocytes compared with controls. This maintained dipeptide transport observed despite villous atrophy and decreased expression of the protein at the brush-border membrane strongly suggest a transient upregulation of PepT1 activity, probably related to gamma-interferon regulation.

Lactate has the potential to promote hydrogen sulphide formation in the human colon.

High concentrations of sulphide are toxic for the gut epithelium and may contribute to bowel disease. Lactate is a favoured cosubstrate for the sulphate-reducing colonic bacterium Desulfovibrio piger, as shown here by the stimulation of sulphide formation by D. piger DSM749 by lactate in the presence of sulphate. Sulphide formation by D. piger was also stimulated in cocultures with the lactate-producing bacterium Bifidobacterium adolescentis L2-32. Other lactate-utilizing bacteria such as the butyrate-producing species Eubacterium hallii and Anaerostipes caccae are, however, expected to be in competition with the sulphate-reducing bacteria (SRB) for the lactate formed in the human colon. Strains of E. hallii and A. caccae produced 65% and 96% less butyrate from lactate, respectively, in a coculture with D. piger DSM749 than in a pure culture. In triculture experiments involving B. adolescentis L2-32, up to 50% inhibition of butyrate formation by E. hallii and A. caccae was observed in the presence of D. piger DSM749. On the other hand, sulphide formation by D. piger was unaffected by E. hallii or A. caccae in these cocultures and tricultures. These experiments strongly suggest that lactate can stimulate sulphide formation by SRB present in the colon, with possible consequences for conditions such as colitis.