Epithelial cell renewal of the small intestinal mucosa

Meta-analysis of the turnover of intestinal epithelia in preclinical animal species and humans

Due to the rapid turnover of the small intestinal epithelia, the rate at which enterocyte renewal occurs plays an important role in determining the level of drug-metabolizing enzymes in the gut wall. Current physiologically based pharmacokinetic (PBPK) models consider enzyme and enterocyte recovery as a lumped first-order rate. An assessment of enterocyte turnover would enable enzyme and enterocyte renewal to be modeled more mechanistically. A literature review together with statistical analysis was employed to establish enterocyte turnover in human and preclinical species. A total of 85 studies was identified reporting enterocyte turnover in 1602 subjects in six species. In mice, the geometric weighted combined mean (WX) enterocyte turnover was 2.81 ± 1.14 days (n = 169). In rats, the weighted arithmetic mean enterocyte turnover was determined to be 2.37 days (n = 501). Humans exhibited a geometric WX enterocyte turnover of 3.48 ± 1.55 days for the gastrointestinal epithelia (n = 265), displaying comparable turnover to that of cytochrome P450 enzymes in vitro (0.96-4.33 days). Statistical analysis indicated humans to display longer enterocyte turnover as compared with preclinical species. Extracted data were too sparse to support regional differences in small intestinal enterocyte turnover in humans despite being indicated in mice. The utilization of enterocyte turnover data, together with in vitro enzyme turnover in PBPK modeling, may improve the predictions of metabolic drug-drug interactions dependent on enzyme turnover (e.g., mechanism-based inhibition and enzyme induction) as well as absorption of nanoparticle delivery systems and intestinal metabolism in special populations exhibiting altered enterocyte turnover.

Micronutrients and diarrheal disease

Diarrhea is a leading cause of death among children <5 years of age and can be exacerbated by micronutrient malnutrition. Vitamin A supplementation given every 6 months reduces the mortality rate by 23% among children 6-59 months of age and reduces the severity of diarrhea, but it does not affect overall diarrhea-associated morbidity. When given for the treatment of diarrhea, vitamin A appears to have no effect on the duration of the diarrheal episode and is not recommended for routine treatment of diarrhea. Regular zinc supplementation has been shown to reduce diarrhea prevalence and mortality, yet global programmatic recommendations regarding prophylactic zinc supplementation have not been made. Short-course daily zinc supplementation shortens the duration (a 15%-24% reduction) and severity of the episode and is now recommended for the treatment of all episodes of diarrhea occurring among children <5 years of age. Folic acid supplementation does not appear to be effective in the prevention or treatment of diarrheal disease.

Functional Expression of the Interleukin-11 Receptor α-Chain and Evidence of Antiapoptotic Effects in Human Colonic Epithelial Cells

A tissue-protective effect of interleukin-11 (IL-11) for the intestinal mucosa has been postulated from animal models of inflammatory bowel disease (IBD). Despite the fact that the clinical usefulness of the anti-inflammatory effects of this cytokine is presently investigated in patients with IBD, there are no data available regarding the target cells of IL-11 action and the mechanisms of tissue protection within the human colonic mucosa. IL-11 responsiveness is restricted to cells that express the interleukin-11 receptor alpha-chain (IL-11Ralpha) and an additional signal-transducing subunit (gp130). In this study, we identified the target cells for IL-11 within the human colon with a new IL-11Ralpha monoclonal antibody and investigated the functional expression of the receptor and downstream effects of IL-11-induced signaling. Immunohistochemistry revealed expression of the IL-11Ralpha selectively on colonic epithelial cells. HT-29 and colonic epithelial cells (CEC) constitutively expressed IL-11Ralpha mRNA and protein. Co-expression of the signal-transducing subunit gp130 was also demonstrated. IL-11 induced signaling through triggering activation of the Jak-STAT pathway without inducing anti-inflammatory or proliferative effects in colonic epithelial cells. However, IL-11 stimulation resulted in a dose-dependent tyrosine phosphorylation of Akt, a decreased activation of caspase-9, and a reduced induction of apoptosis in cultured CEC. In HLA-B27 transgenic rats treated with IL-11, a reduction of apoptotic cell numbers was found. This study demonstrates functional expression of the IL-11Ralpha restricted on CEC within the human colonic mucosa. IL-11 induced signaling through triggering activation of the Jak-STAT pathway, without inducing anti-inflammatory or proliferative effects. The beneficial effects of IL-11 therapy are likely to be mediated by CEC via activation of the Akt-survival pathway, mediating antiapoptotic effects to support mucosal integrity.

Micronutrients as adjunct therapy of acute illness in children: impact on the episode outcome and policy implications of current findings

Role of micronutrients namely vitamin A, zinc and folate, as adjunct therapy of illness episodes in children in developing countries have been discussed in the light of health policy. Apart from a selective review, attempts have been made to statistically combine results of several studies to address policy issues. In children, vitamin A supplementation during illness has (a) a profound effect in reducing mortality in measles, (b) possibly a significant effect in reducing persistent diarrhea episodes in children with acute diarrhea, and (c) no benefit in pneumonia. Use of large dose vitamin A is recommended during measles episodes but not in non-measles pneumonia. Its use in acute diarrhea is debatable but recommended in persistent diarrhea and in severe malnutrition as a component of a micronutrient mixture. Large dose vitamin A supplementation should be used with caution in young infants as there are unresolved concerns about its safety particularly, bulging fontanelle observed in infants when co-administered at immunization. In children, zinc supplementation during illness, (a) had a marked effect in reducing prolonged episodes and a modest effect on episode duration in acute diarrhea, (b) resulted in reduced rate of treatment failure and death in persistent diarrhea, (c) had no effect in measles and non-measles pneumonia, and (d) probably had a detrimental effect of increasing death rate when a large dose was used in severely malnourished children. The desirability of routine zinc supplementation therapy of undernourished children with acute diarrhea should be assessed further. Concerning policy, zinc supplementation as a component of a micronutrient mixture is recommended in the rehabilitation of severely malnourished children and in persistent diarrhea. However, recommendation for its routine use in all cases of acute diarrhea in children needs additional studies on effectiveness, cost, operations and safety. In two randomized controlled trials folate has been evaluated in acute and persistent diarrhea and found to have no beneficial effect. Folate is not recommended as adjunct therapy of diarrhea. Role of folate in preventing severe disease and/or death deserves further evaluation.

Interactions mediating bacterial translocation in the immature intestine

Systemic disease caused by transmucosal passage of enterovirulent bacteria and toxins from the gut lumen into the mesenteric lymph nodes (MLN) is reviewed, with particular concern for bacterial interactions in the developing gut of premature newborns. Anaerobic bacteria are rarely observed to translocate to the MLN. Bifidobacterial strains have been tested for their abilities to adhere to enterocyte-like Caco-2 cells in culture. We have investigated the inhibitory effect of adherent human bifidobacterial strains against colonization by a number of diarrheagenic bacteria (Escherichia coli O157; Salmonella typhimurium) and viruses (murine and rhesus rotavirus), in various in vitro and in vivo models. The phagocytic cell (macrophage) may be a key factor in bacterial translocation (BT). Human breast milk contains abundant bioactive substances (immunologic, nutritional) that provide protective effects through inhibition of bacterial overgrowth and BT. New biotherapeutic therapies that stimulate beneficial anaerobic microflora (Lactobacillus, Bifidobacterium) are promising avenues of research to combat BT in disease treatment.

Cytochemical analysis of alkaline phosphatase and esterase activities and of lectin-binding and anionic sites in rat and mouse Peyer's patch M cells

M cells in Peyer's patch follicle epithelium endocytose and transport luminal materials to intraepithelial lymphocytes. We examined (1) enzymatic characteristics of the epithelium covering mouse and rat Peyer's patches by using cytochemical techniques, (2) distribution of lectin-binding sites by peroxidase-labeled lectins, and (3) anionic site distribution by using cationized ferritin to develop a profile of M cell surface properties. Alkaline phosphatase activity resulted in deposits of dense reaction product over follicle surfaces but was markedly reduced over M cells, unlike esterase which formed equivalent or greater product over M cells. Concanavalin A, ricinus communis agglutinin, wheat germ agglutinin and peanut agglutinin reacted equally with M cells and with surrounding enterocytes over follicle surfaces. Cationized ferritin distributed in a random fashion along microvillus membranes of both M cells and enterocytes, indicating equivalent anionic site distribution. Staining for alkaline phosphatase activity provides a new approach for distinguishing M cells from enterocytes at the light microscopic level. Identical binding of lectins indicates that M cells and enterocytes share common glycoconjugates even though molecular groupings may differ. Lectin binding and anionic charge similarities of M cells and enterocytes may facilitate antigen sampling by M cells of particles and compounds that adhere to intestinal surfaces in non-Peyer's patch areas.

Enumeration of Paneth cells in coeliac disease: comparison of conventional light microscopy and immunofluorescence staining for lysozyme

By conventional light microscopy, a reduced number of Paneth cells per intestinal crypt was found in the jejunal mucosa of patients with untreated or gluten-challenged coeliac disease as compared with histologically normal control specimens. A much better detection sensitivity was obtained when Paneth cells were counted by fluorescence microscopy after immunostaining for lysozyme with a rhodamine-labelled rabbit IgG conjugate. This method showed that there was no numerical reduction of Paneth cells in coeliac disease, but that the proportion of cells with a low lysozyme content was increased. Most of these cells were probably missed by conventional microscopy in which identification of Paneth cells is principally based on a substantial cellular complement of acidophilic granules. A reduced number of lysozyme-containing granules in coeliac disease may reflect increased discharge enhanced secretory activity, or a raised turnover of the Paneth cells.

Morphological and histochemical changes in the mucosa of the continent ileostomy reservoir 6--10 years after its construction

Morphological and histochemical changes in the mucosa of the continent ileostomy reservoir were studied in 13 patients who had been provided with a continent ileostomy reservoir 6--10 years before the investigation. Biopsy specimens were taken for evaluation of basal morphology, morphometry, and enzyme histochemical analyses. The villi were predominantly finger-like, but the villus height was reduced compared with normal. The crypt layer and the number of cells in each crypt were increased. The number of mitoses was normal or slightly subnormal. In comparison with biopsies taken 1 year after construction of the reservoir, there was an increase in villus height and mucosal volume and a decrease in the number of mitoses, whereas the number of cells per crypt was unchanged. The surface to volume ratio decreased progressively during the 6- to 10-year period. This decrease was partly caused by an increase of the mucosal volume. The epithelial cell layer was intact, and no changes were seen in the microvillus layer. No alarming changes in terms of dysplasia, fibrosis, or progressive atrophy were found. Histochemical investigation showed a high enzymatic activity in the epithelial cells as concerns both the oxidative metabolism and the secretory function.

[Cytostatica and small intestine (author's transl)]

Cytostatica not only suppress proliferation in tumor cells but it also checks proliferation in small intestinal epithelium. The consequence is cell reduction and damage resulting in a diminished function. Because of the high reserve capacity of the small intestinal epithelium, clinical signs of diminished function are mostly seen after repeated high doses or one extremely high doses of Cytostatica. Although there is abundant information on the effect of Cytostatica on the small intestinal epithelium (cell turnover, morphology, digestive enzymes and absorption) there are other areas that are as urgent for the interested clinician to work on: 1. Would it be possible to coincide the dose and dosage rate with the cell cycles to reduce the chance of damage to small intestinal epithelium? 2. Which role has the luminal content when there is damage from Cytostatica? Is it possible to concentrate on changing the luminal contents (antibiotics, "elemental diet", cultivate desirable microflora, etc.) Therefore diminishing the damage from Cytostatica? 3. How would Cytostatica influence the barrier function on the intestinal wall? Should the patient on Cytostatica therapy receive special protection against intestinal infection? 4. Does Cytostatica affect the biotransformation in the small intestinal epithelium, especially when taken orally? How important is this biotransformation in small intestinal epithelium damaged by Cytostatica therapy? 5. What factors determine the regeneration of the small intestinal epithelium after Cytostatica damage?