Relative Abundance of SARS-CoV-2 Entry Genes in the Enterocytes of the Lower Gastrointestinal Tract

There is increasing evidence of gastrointestinal (GI) infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We surveyed the co-expression of SARS-CoV-2 entry genes ACE2 and TMPRSS2 throughout the GI tract to assess potential sites of infection. Publicly available and in-house single-cell RNA-sequencing datasets from the GI tract were queried. Enterocytes from the small intestine and colonocytes showed the highest proportions of cells co-expressing ACE2 and TMPRSS2. Therefore, the lower GI tract represents the most likely site of SARS-CoV-2 entry leading to GI infection.

Effect of purified β-glucans derived from Laminaria digitata, Laminaria hyperborea and Saccharomyces cerevisiae on piglet performance, selected bacterial populations, volatile fatty acids and pro-inflammatory cytokines in the gastrointestinal tract of pigs

β-Glucans have been identified as natural biomolecules with immunomodulatory activity. The first objective of the present study was to compare the effects of purified β-glucans derived from Laminaria digitata, L. hyperborea and Saccharomyces cerevisiae on piglet performance, selected bacterial populations and intestinal volatile fatty acid (VFA) production. The second aim was to compare the gene expression profiles of the markers of pro- and anti-inflammation in both unchallenged and lipopolysaccharide (LPS)-challenged ileal and colonic tissues. β-Glucans were included at 250 mg/kg in the diets. The β-glucans derived from L. hyperborea, L. digitata and S. cerevisiae all reduced the Enterobacteriaceae population (P<0·05) without influencing the lactobacilli and bifidobacteria populations (P>0·05) in the ileum and colon. There was a significant interaction between gastrointestinal region and β-glucan source in the expression of cytokine markers, IL-1α (<0·001), IL-10 (P<0·05), TNF-α (P<0·05) and IL-17A (P<0·001). β-Glucans did not stimulate any pro- or anti-inflammatory cytokine markers in the ileal epithelial cells. In contrast, the expression of a panel of pro- and anti-inflammatory cytokines (IL-1α, IL-10, TNF-α and IL-17A) was down-regulated in the colon following exposure to β-glucans from all the three sources. However, the data suggest that the soluble β-glucans derived from L. digitata may be acting via a different mechanism from the insoluble β-glucans derived from L. hyperborea and S. cerevisiae, as the VFA profile was different in the L. digitata-treated animals. There was an increase in IL-8 gene expression (P<0·05) in the gastrointestinal tract from the animals exposed to L. digitata following an LPS ex vivo challenge that was not evident in the other two treatment groups. In conclusion, β-glucans from both seaweed and yeast sources reduce Enterobacteriaceae counts and pro-inflammatory markers in the colon, though the mechanisms of action may be different between the soluble and insoluble fibre sources.

Transport of nicotinate and structurally related compounds by human SMCT1 (SLC5A8) and its relevance to drug transport in the mammalian intestinal tract

PURPOSE. To examine the involvement of human SMCT1, a Na+-coupled transporter for short-chain fatty acids, in the transport of nicotinate/structural analogs and monocarboxylate drugs, and to analyze its expression in mouse intestinal tract.

MATERIALS AND METHODS

We expressed human SMCT1 in X. laevis oocytes and monitored its function by [14C]nicotinate uptake and substrate-induced inward currents. SMCT1 expression in mouse intestinal tract was examined by immunofluorescence.

RESULTS

[14C]Nicotinate uptake was several-fold higher in SMCT1-expressing oocytes than in water-injected oocytes. The uptake was inhibited by short-chain/medium-chain fatty acids and various structural analogs of nicotinate. Exposure of SMCT1-expressing oocytes to nicotinate induced Na+-dependent inward currents. Measurements of nicotinate flux and associated charge transfer into oocytes suggest a Na+:nicotinate stoichiometry of 2:1. Monocarboxylate drugs benzoate, salicylate, and 5-aminosalicylate are also transported by human SMCTI. The transporter is expressed in the small intestine as well as colon, and the expression is restricted to the lumen-facing apical membrane of intestinal and colonic epithelial cells.

CONCLUSIONS

Human SMCTI transports not only nicotinate and its structural analogs but also various monocarboxylate drugs. The transporter is expressed on the luminal membrane of the epithelial cells lining the intestinal tract. SMCT1 may participate in the intestinal absorption of monocarboxylate drugs.

Expression and localization of an aquaporin-1 homologue in the avian kidney and lower intestinal tract

In birds, the kidneys and lower intestine function in osmoregulation. A 271-amino acid homologue to aquaporin-1 (AQP-1) was isolated from the kidneys, cecae, proximal and distal rectum, and coprodeum of the lower intestine in the house sparrow (Passer domesticus). This protein has six transmembrane domains connected by two cytoplasmic loops and three extracellular loops. It exhibits 94%, 88%, and 78% homology to AQP-1 sequences of chicken, human and toad, respectively. Many of the highly conserved amino acids that are characteristic of AQP-1 are found in the sparrow sequence. RT-PCR was performed and the presence of AQP-1 mRNA was detected in the kidney and all four regions of the lower intestine. Immunoblots of total protein identified a 28-kDa non-glycosylated AQP-1 band and a 56-kDa glycosylated AQP-1 band in the kidney and all four regions of the lower intestine. Immunohistochemistry demonstrated the presence of the AQP-1 protein within both the renal cortex and medulla. In the lower intestine, the protein was present in the proximal rectum, distal rectum, and in the coprodeum. As AQP-1 functions to allow water movement across mammalian cell membranes, its presence in water-permeable cells in a bird suggests it may have a similar function.

mRNA expression and binding sites for alpha2-adrenergic receptor subtypes in muscle layers of the ileum and spiral colon of dairy cows

OBJECTIVE

To measure maximum binding capacity (B(max)) and levels of mRNA expression for alpha(2)-adrenergic receptor (AR) subtypes in ileal and colonic muscle layers of healthy dairy cows.

SAMPLE POPULATION

Ileal and colonic muscle specimens from 6 freshly slaughtered cows.

PROCEDURES

Ileal and colonic muscle layers were obtained by scraping the mucosa and submucosa from full-thickness tissue specimens. Level of mRNA expression for alpha(2)-AR subtypes was measured by real-time reverse transcriptase-PCR analysis and expressed relative to the mean mRNA expression of glyceraldehyde phosphate dehydrogenase, ubiquitin, and 18S ribosomal RNA. Binding studies were performed with tritiated RX821002 ((3)H-RX821002) and subtype-selective ligands as competitors.

RESULTS

mRNA expression for alpha(2AD)-, alpha(2B)-, and alpha(2C)-AR subtypes was similar in ileal and colonic muscle layers. The mRNA expression for alpha(2AD)-AR was significantly greater than that for alpha(2B)- and alpha(2C)-AR subtypes, representing 92%, 6%, and 2%, respectively, of the total mRNA. Binding competition of (3)H-RX821002 with BRL44408, imiloxan, and MK-912 was best fitted by a 1-site model. The B(max) of alpha(2AD)- and alpha(2C)-AR sub-types was greater than that of alpha(2B)-AR. The B(max) and level of mRNA expression were only correlated (r = 0.8) for alpha(2AD)-AR. Ratio of B(max) to mRNA expression for alpha(2C)-AR was similar to that for alpha(2B)-AR, but significantly greater than for alpha(2AD)-AR.

CONCLUSIONS AND CLINICAL RELEVANCE

Subtypes of alpha(2)-AR in bovine intestinal muscle layers are represented by a mixture of alpha(2AD)- and alpha(2C)-ARs and of alpha(2B)-AR at a lower density. Information provided here may help in clarification of the role of AR subtypes in alpha(2)-adrenergic mechanisms regulating bovine intestinal motility.

Endocrine regulation of ion transport in the avian lower intestine

The lower intestine (colon and coprodeum) of the domestic fowl maintains a very active, transporting epithelium, with a microvillus brush border, columnar epithelial cells, and a variety of transport systems. The colon of normal or high salt-acclimated hens expresses sodium-linked glucose and amino acid cotransporters, while the coprodeum is relatively inactive. Following acclimation to low salt diets, however, both colon and coprodeum shift to a pattern of high expression of electrogenic sodium channels, and the colonic cotransporter activity is simultaneously downregulated. These changes in the transport patterns seem to be regulated, at least in part, by aldosterone. Our recent work with this tissue has focused on whether aldosterone alone can account for the low salt pattern of transport. Other work has looked at the changes in morphology and in proportions of cell types that occur during chronic acclimation to high or low salt diets, and on a cAMP-activated chloride secretion pathway. Recent findings suggesting effects of other hormones on lower intestinal transport are also presented.

An immunohistochemical study and review of potential markers of human intestinal M cells

M cells are found in intestinal follicle associated epithelium. Studies into the physiological and pathological roles of human M cells have been hampered by the lack of well-substantiated, specific markers for these cells. A critical literature review suggests the following molecules may potentially serve as such markers: CK7, FcaR (CD89), S100, CD1a, CD21, CD23, sialyl Lewis A, and cathepsin E. Normal ileum, appendix and colorectum were studied using paraffin-embedded, formalin-fixed tissue and immunohistochemistry for these 8 markers. Cathepsin E immunohistochemistry was also performed on cases of colorectal adenocarcinoma, colorectal adenoma, colorectal hyperplastic/metaplastic polyp, lymphocytic colitis, collagenous colitis, pseudomembranous colitis and active ulcerative colitis. Of the 8 markers tested, only cathepsin E appeared to be specific to follicle associated epithelium (expressed by cells with and without M cell morphology) and follicular crypt epithelium; this specificity was limited to the colorectum. Focal epithelial expression of cathepsin E was seen in adenocarcinoma, adenoma, hyperplastic/metaplastic polyp, ulcerative colitis and pseudomembranous colitis. In conclusion, cathepsin E is a specific marker of normal colorectal follicle associated epithelium and follicular crypt epithelium though is not specific to M cells within these compartments. None of the other 7 markers studied is exclusively expressed by human M cells.

Contribution of the gastrointestinal tract below the stomach to the 13C-urea breath test

BACKGROUND

Graham et al. [Lancet, I (1987) 1174] found a late increase of 13C enrichment in the 13C-urea breath test 120 min after administration of labeled urea to patients without Helicobacter pylori infection. This may give false positive results.

AIM

We designed this study to elucidate the contribution of the gastrointestinal tract below the stomach to the 13C-urea breath test.

PATIENTS

Twenty-eight patients with dyspeptic symptoms who gave their consent were enrolled.

METHODS

Patients underwent the 13C-urea breath tests both via the mouth (as usual) and the duodenum (labeled urea introduced to the second portion). Breath samples were collected at baseline, 5, 15, 30, 45, 60, 90, 120, 150 and 180 min for analysis. H. pylori status was defined by the CLOtest and by histological examination.

RESULTS

There was no late increase in 13C enrichment of 13C-urea breath test for eight H. pylori negative patients either via the mouth or the duodenum. For those H. pylori positive patients, seventeen had no late rise 13C enrichment of the 13C-urea breath test via the duodenum and three patients had a rise after 15 min.

CONCLUSIONS

No late rise in 13CO2 excretion to cause a positive 13C-urea breath test up to 180 min after the administration of labeled urea was found in the present study.