Recent advances in small bowel diseases: Part I

Differential roles of the fish chitinous membrane in gut barrier immunity and digestive compartments

The chitin-based peritrophic matrix (PM) is a structure critical for both gut immunity and digestion in invertebrates. PM was traditionally considered lost in all vertebrates, but a PM-like chitinous membrane (CM) has recently been discovered in fishes, which may increase the knowledge on vertebrate gut physiology and structural evolution. Here, we show that in zebrafish, the CM affects ingestion behavior, microbial homeostasis, epithelial renewal, digestion, growth, and longevity. Young mutant fish without CM appear healthy and are able to complete their life cycle normally, but with increasing age they develop gut inflammation, resulting in gut atrophy. Unlike mammals, zebrafish have no visible gel-forming mucin layers to protect their gut epithelia, but at least in young fish, the CM is not a prerequisite for the antibacterial gut immunity. These findings provide new insights into the role of the CM in fish prosperity and its eventual loss in tetrapods. These findings may also help to improve fish health and conservation, as well as to advance the understanding of vertebrate gut physiology and human intestinal diseases.

Small Intestinal Infections

Small intestinal infections are extremely common worldwide. They may be bacterial, viral, or parasitic in etiology. Most are foodborne or waterborne, with specific etiologies differing by region and with diverse pathophysiologies. Very young, very old, and immune-deficient individuals are the most vulnerable to morbidity or mortality from small intestinal infections. There have been significant advances in diagnostic sophistication with the development and early application of molecular diagnostic assays, though these tests have not become mainstream. The lack of rapid diagnoses combined with the self-limited nature of small intestinal infections has hampered the development of specific and effective treatments other than oral rehydration. Antibiotics are not indicated in the absence of an etiologic diagnosis, and not at all in the case of some infections.

Clinical relevance of intestinal peptide uptake

AIM: To determine available information on an independent peptide transporter 1 (PepT1) and its potential relevance to treatment, this evaluation was completed.

METHODS: Fully published English language literature articles sourced through PubMed related to protein digestion and absorption, specifically human peptide and amino acid transport, were accessed and reviewed. Papers from 1970 to the present, with particular emphasis on the past decade, were examined. In addition, abstracted information translated to English in PubMed was also included. Finally, studies and reviews relevant to nutrient or drug uptake, particularly in human intestine were included for evaluation. This work represents a summary of all of these studies with particular reference to peptide transporter mediated assimilation of nutrients and pharmacologically active medications.

RESULTS: Assimilation of dietary protein in humans involves gastric and pancreatic enzyme hydrolysis to luminal oligopeptides and free amino acids. During the ensuing intestinal phase, these hydrolytic products are transported into the epithelial cell and, eventually, the portal vein. A critical component of this process is the uptake of intact di-peptides and tri-peptides by an independent PepT1. A number of “peptide-mimetic” pharmaceutical agents may also be transported through this carrier, important for uptake of different antibiotics, antiviral agents and angiotensin-converting enzyme inhibitors. In addition, specific peptide products of intestinal bacteria may also be transported by PepT1, with initiation and persistence of an immune response including increased cytokine production and associated intestinal inflammatory changes. Interestingly, these inflammatory changes may also be attenuated with orally-administered anti-inflammatory tripeptides administered as site-specific nanoparticles and taken up by this PepT1 transport protein.

CONCLUSION: Further evaluation of the role of this transporter in treatment of intestinal disorders, including inflammatory bowel disease is needed.

Paneth cell metaplasia in newly diagnosed inflammatory bowel disease in children

Background

Paneth cell metaplasia (PCM) is well described in adults but little is known about the distribution of colonic Paneth cells and the occurrence of PCM in a paediatric population. The aim of this study is to determine whether Paneth cell hyperplasia or metaplasia characteristically occurs in the colons of children with newly diagnosed idiopathic inflammatory bowel disease (IBD).

Methods

We retrospectively reviewed colonic series from 28 new diagnoses of paediatric IBD at a tertiary referral centre, and from a further 14 children with IBD-like symptoms whose colonic biopsies and ancillary investigations were normal. Paneth cells were counted at 6 anatomical sites in the colon, and at each site acute and chronic inflammation were assessed semi-quantitatively and the presence or absence of crypt architectural distortion and eosinophilia was documented.

Results

In control, ulcerative colitis (UC) and Crohn’s disease (CD) groups there was a gradient of decreasing Paneth cell numbers from caecum to rectum. Paneth cells were not seen in the distal colon in the control group, but they were present there in 11 of 13 patients with ulcerative colitis and 14 of 15 with Crohn’s disease. Only patients with IBD showed Paneth cell hyperplasia, assessed as more than 10 Paneth cells per 10 well-oriented crypts at any site. There was a statistically significant increase in Paneth cells in the caecum, ascending, transverse and descending colon in UC and in the ascending, transverse, descending and sigmoid colon in CD compared with controls. There was no significant difference between UC and CD. There was no correlation between the site of PCM and acute or chronic inflammation, crypt distortion or eosinophilia.

Conclusion

Paneth cells are found in the proximal but not the distal colon in otherwise normal paediatric colonic series. A high proportion of UC and CD patients show PCM in the distal colon. This is present early in the disease and does not correlate with histological features of chronicity.

Expression of nucleobindin-2/nesfatin-1 in gastrointestinal tissues of high-fat diet-induced obese rats

AIM: To investigate the expression of the NUCB2 gene and NUCB2/nesfatin-1 protein in gastrointestinal tissues of obese and normal rats.

METHODS: Thirty male Wistar rats were randomly divided into two groups to be fed a high-fat diet or a normal diet. At the end of eight weeks, gastric, duodenal, small intestinal and colonic tissues were collected to detect the expression of NUCB2 mRNA and NUCB2/nesfatin-1 protein by real-time RT-PCR and immunohistochemistry, respectively.

RESULTS: The expression levels of NUCB2 mRNA in gastric, duodenal, and small intestinal tissues of obese rats were 2.02, 1.49 and 1.23 times higher than those in corresponding tissues of normal controls (t = 4.256, 3.455, 2.402; P = 0.000, 0.002, 0.026), showing a significant positive correlation with Lee's index (r = 0.677, 0.561, 0.538; P = 0.006, 0.030, 0.039); however, the expression level of NUCB2 mRNA in colonic tissue showed no significant difference between the two groups (t = 1.835, P = 0.077). NUCB2/nesfatin-1 protein was localized in the lower 2/3 of gastric mucosal glands, Brunner's glands and Paneth cells of the duodenum, and Paneth cells of the small intestine. The expression level of NUCB2/nesfatin-1 protein in gastric tissues was significantly increased in obese rats compared with normal controls (Z = -2.955, P = 0.003), and was positively correlated with Lee's index (r = 0.677, P = 0.008). The expression level of NUCB2/nesfatin-1 protein in Paneth cells of the duodenum and small intestine in obese rats significantly decreased compared with normal controls (Z = -2.026, -2.648; P = 0.043, 0.008), showing a significant negative correlation with Lee's index (r = -0.557, -0.617; P = 0.031, 0.014).

CONCLUSION: NUCB2/nesfatin-1 is widely expressed in gastrointestinal tissues of rats, and the expression of NUCB2 mRNA and NUCB2/nesfatin-1 protein is up-regulated in gastric tissues of obese rats, while NUCB2/nesfatin-1 protein is down-regulated in Paneth cells in obese rats.