Effects of streptozotocin-diabetes on rat intestinal mucin and goblet cells

Oral Coadministration of Zn-Insulin with d-Form Small Intestine-Permeable Cyclic Peptide Enhances Its Blood Glucose-Lowering Effect in Mice

Oral delivery of insulin remains a challenge owing to its poor permeability across the small intestine and enzymatic digestion in the gastrointestinal tract. In a previous study, we identified a small intestine-permeable cyclic peptide, C-DNPGNET-C (C-C disulfide bond, cyclic DNP peptide), which facilitated the permeation of macromolecules. Here, we showed that intraintestinal and oral coadministration of insulin with the cyclic DNP derivative significantly reduced blood glucose levels by increasing the portal plasma insulin concentration following permeation across the small intestine of mice. We also found that protecting the cyclic DNP derivative from enzymatic digestion in the small intestine of mice using d-amino acids and by the cyclization of DNP peptide was essential to enhance cyclic DNP derivative-induced insulin absorption across the small intestine. Furthermore, intraintestinal and oral coadministration of insulin hexamer stabilized by zinc ions (Zn-insulin) with cyclic D-DNP derivative was more effective in facilitating insulin absorption and inducing hypoglycemic effects in mice than the coadministration of insulin with the cyclic D-DNP derivative. Moreover, Zn-insulin was more resistant to degradation in the small intestine of mice compared to insulin. Intraintestinal and oral coadministration of Zn-insulin with cyclic DNP derivative also reduced blood glucose levels in a streptozotocin-induced diabetes mellitus mouse model. A single intraintestinal administration of the cyclic D-DNP derivative did not induce any cytotoxicity, either locally in the small intestine or systemically. In summary, we demonstrated that coadministration of Zn-insulin with cyclic D-DNP derivative could enhance oral insulin absorption across the small intestine in mice.

Diabetes Downregulates Allergen-Induced Airway Inflammation in Mice

Previous studies described that allergic diseases, including asthma, occur less often than expected in patients with type 1 diabetes. Here, we investigated the influence of diabetes on allergic airway inflammation in a model of experimental asthma in mice. Diabetes was induced by intravenous injection of alloxan into 12 h-fasted A/J mice, followed by subcutaneous sensitization with ovalbumin (OVA) and aluminum hydroxide (Al(OH)₃), on days 5 and 19 after diabetes induction. Animals were intranasally challenged with OVA (25 μg), from day 24 to day 26. Alloxan-induced diabetes significantly attenuated airway inflammation as attested by the lower number of total leukocytes in the bronchoalveolar lavage fluid, mainly neutrophils and eosinophils. Suppression of eosinophil infiltration in the peribronchiolar space and generation of eosinophilotactic mediators, such as CCL-11/eotaxin, CCL-3/MIP-1α, and IL-5, were noted in the lungs of diabetic sensitized mice. In parallel, reduction of airway hyperreactivity (AHR) to methacholine, mucus production, and serum IgE levels was also noted under diabetic conditions. Our findings show that alloxan diabetes caused attenuation of lung allergic inflammatory response in A/J mice, by a mechanism possibly associated with downregulation of IgE antibody production.

Oral exposure to the organophosphorus insecticide, Monocrotophos induces intestinal dysfunction in rats

There is limited experimental evidence to imply the role of organophosphorus insecticides on intestinal dysfunctions. Residues of Monocrotophos (MCP), above maximum residue limits (MRL), have been reported in fruits and vegetables from various parts of India. Hence, in this study, we investigated the potential of MCP to induce intestinal dysfunction in rats. MCP was administered orally to rats at sublethal doses (0.45, 0.9 and 1.8 mg/kgb.w/d) for 30 days. MCP at the highest dose significantly increased the unit weight of the small intestine. MCP increased the activities of intestinal brush border disaccharidases, intestinal alkaline phosphatase, glycyl-glycine dipeptidase, and Na(+)/K(+)-ATPase while it decreased cholesterol: phospholipid ratio. Histology and scanning electron microscopy of small intestine of MCP treated rats revealed disruption in terms of congestion, increased length of villi, goblet cell hyperplasia, infiltration of inflammatory cells and necrotic villi tip. Further, the intestinal transit rate was found to be increased in MCP treated rats. Collectively, our findings provide evidence that repeated oral intake of MCP has the propensity to alter small intestinal structure and functions, which might lead to intestinal dysfunctions and abnormal nutrient uptake and thereby affect the human health. Although we have employed doses, which are higher than those likely to be encountered as residues, we speculate that further studies should be performed to determine whether MCP residues in foods in the long-term will interfere with the digestive capacity of the small intestine and thus exert adverse effects on the health of human.

Effect of l-glutamine on myenteric neuron and of the mucous of the ileum of diabetic rats

The objective of this work was to investigate the effect of the L-glutamine supplementation to prevent - diabetes induced changes in myenteric neurons and also to verify the effect on the mucosa of the ileum of Wistar rats. The animals were divided in five groups (n = 5): untreated normoglycaemic (UN), normoglycaemic treated with L-glutamine (NG), untreated diabetics (UD), diabetics treated with L-glutamine, starting on the 4th (DG4) or 45th day following diabetes induction (DG45). The amino acid was added to the diet at 1%. The density and size of neurons, the metaphasic index in the crypt, the height of the villus, the depth of the crypt and the number of globet cells were determined. There was no difference in the neuronal density and in the cellular body area of the myosin-stained myenteric neurons of groups DG4 and DG45 when compared to group D. The metaphase index and the number of goblet cells showed no significant differences when all groups were compared (P > 0.05). The villi height of groups DG4 and DG45 were 45.5% (P < 0.05) and 32.4% (P > 0.05) higher than those in group UD, respectively. The analyzed crypts showed similar depth for all studied groups.

Vitamin E (alpha-tocopherol) supplementation in diabetic rats: effects on the proximal colon

Background

Neuropathy is one of the complications caused by diabetes mellitus which is directly related to the gastrointestinal manifestations of the disease. Antioxidant substances, such as vitamin E, may play an important role in the reduction of the neurological damage caused by diabetes mellitus. The aim of the present study was to determine whether vitamin E (α-tocopherol) at different concentrations induces any effects on the morphology of the intestinal wall and intrinsic innervation in the proximal colon of diabetic rats.

Methods

Thirty rats (90-day-old) were assigned to the following groups: N (normoglycemic), NE1 (normoglycemic supplemented with vitamin E 0.1%), NE2 (normoglycemic supplemented with vitamin E 2%), D (diabetic), DE1 (diabetic supplemented with vitamin E 0.1%), and DE2 (diabetic supplemented with vitamin E 2%). Animals received vitamin E supplementation for 120 days and were sacrificed when they were 210 days old. The proximal colon of each animal was subjected to histology to study the intestinal wall and goblet cells and processed for whole-mount preparations to morphoquantitatively determine the total myenteric population.

Results

Supplementation with vitamin E significantly reduced glycemia and glycated hemoglobin values and preserved the number of myenteric neurons in group DE2, without affecting intestinal area or thickness of the intestinal wall or muscular tunic.

Conclusion

Vitamin E (2%) influenced the glycemic parameters and had a neuroprotective effect on the total myenteric population, but the morphometric characteristics of the intestinal wall were unaffected.

Changes in intestinal morphology and permeability in the biobreeding rat before the onset of type 1 diabetes

OBJECTIVE

Type 1 diabetes is an autoimmune disorder that occurs in genetically susceptible individuals. It has been hypothesized that the disease could be triggered by environmental agents that gain entry into the body through small intestinal absorption. Increased intestinal permeability has been reported both in spontaneous animal models of type 1 diabetes and human type 1 diabetes. In these studies, we examined both the physical and functional permeability characteristics of the small intestine in diabetes-prone and control rats.

METHODS

In a series of studies, BioBreeding diabetes-prone(n = 31), BioBreeding diabetes-resistant (n = 20) and control Wistar (n = 25) rats were examined at intervals from 21 to 125 days of age.

RESULTS

The percentage of goblet cells and the mucosal crypt depth were significantly greater in BioBreeding diabetes-prone than BioBreeding diabetes-resistant rats (P < 0.001 and P = 0.01, respectively). BioBreeding diabetes-prone and BioBreeding diabetes-resistant rats expressed less of the tight junction protein claudin (P < 0.05) and exhibited greater intestinal permeability (P < 0.001) than did Wistar rats. Intestinal permeability measured both in vivo and ex vivo decreased in all rat strains as age increased (P < 0.001).

CONCLUSIONS

In a genetically susceptible rodent model of diabetes, early increased intestinal permeability might allow unregulated passage of environmental antigens that could potentially trigger the autoimmune response leading to type 1 diabetes.

A morphological study of the enteric mucosal epithelium in the streptozotocin-diabetic mouse

In the acutely diabetic rat, the polyphagia-induced increase in the weight of the small intestine is associated with reported increases in mucosal mass. Whereas, some of the individual mucosal components in the rat have been studied, comparable information for the acutely streptozotocin-diabetic mouse is lacking. A detailed morphological comparison of the epithelium of the small intestinal mucosa in control and untreated streptozotocin-diabetic mice was therefore undertaken. Samples from three small intestinal sites were examined by light and scanning electron microscopy and quantitative data obtained from histological sections. Although the morphological appearance of the small intestine in acutely diabetic mice was similar in many respects to literature accounts for the diabetic rat, infestation with filamentous microorganisms was present in the jejunum and ileum. The quantitative data showed that these sites also contained distorted villi, fewer crypt profiles, more goblet and Paneth cell profiles and a smaller epithelial volume in comparison to controls. These findings may represent differences between the rat and mouse models of streptozotocin-induced diabetes mellitus.

Role of bacterial adherence and the mucus barrier on bacterial translocation: effects of protein malnutrition and endotoxin in rats

OBJECTIVE

The purpose of the study was to investigate the potential relations between mucosal bacterial adherence, intestinal mucus and mucin content, and bacterial translocation.

SUMMARY BACKGROUND DATA

The attachment of bacteria to mucosal surfaces is the initial event in the pathogenesis of most bacterial infections that originate at mucosal surfaces, such as the gut. The intestinal mucus layer appears to function as a defensive barrier limiting micro-organisms present in the intestinal lumen from colonizing enterocytes. Consequently, studies focusing on the biology of bacterial adherence to the intestinal mucosa likely are to be important in clarifying the pathogenesis of gut origin sepsis.

METHODS

To explore the relations between intestinal bacterial adherence, mucus bacterial binding, and bacterial translocation, two models were used. One (protein malnutrition) in which profound alterations in intestinal morphology occurs in the absence of significant translocation and one (endotoxin challenge) in which bacterial translocation occurs and intestinal morphology is relatively normal.

RESULTS

Protein malnutrition was not associated with bacterial translocation and measurement of enteroadherent, mucosally associated bacterial population levels documented that the total number of gram-negative enteric bacilli adherent to the ileum and cecum was less in the protein-malnourished rats than in the normally nourished animals (p < 0.01). Furthermore, there was an inverse relation between the duration of protein malnutrition and bacterial adherence to the intestinal mucosa (r = 0.62, p < 0.002). In contrast, after endotoxin challenge, the level of enteroadherent bacteria was increased and bacterial translocation was observed. The binding of Escherichia coli to immobilized ileal mucus in vitro was decreased significantly in protein-malnourished rats, whereas E. coli binding to insoluble ileal mucus was increased in the rats receiving endotoxin.

CONCLUSIONS

This study indicates that the adherence of bacteria to the intestinal mucosal surface is an important factor in bacterial translocation, that intestinal mucus modulates bacterial adherence, and that increased levels of mucosally associated bacteria are associated with a loss intestinal barrier function to bacteria.

Characterization of quail intestinal mucin as a ligand for endogenous quail lectin

The S-type lectins have been shown to be components of mucosal scrapings, and in avian systems these lectins have been localized immunohistochemically to the mucosal surface and goblet cells of the intestine. The interaction of lectin specifically with purified mucin has not, however, been established. Quail intestinal mucin was purified by two subsequent isopycnic density-gradient centrifugations in CsCl and chromatography on Sepharose Cl-2B. Purified mucin, obtained from the void volume of the Sepharose column, was characterized by SDS/PAGE, amino acid and carbohydrate analyses, sensitivity to thiol reduction, and cross-reactivity with antibody preparations to rat and human intestinal mucins on Western blots. Antibody raised against purified quail mucin partially cross-reacts with purified rat, rabbit and human intestinal mucins, and specifically labels the mucosal surface and goblet cells of quail intestine by the immunoperoxidase technique. Protein eluted by lactose from an affinity matrix composed of quail intestinal mucin possessed the same molecular mass on SDS/PAGE as intestinal lectin and reacted on Western blots with a lectin-specific antibody. The data clearly demonstrate the co-localization of lectin and mucin in the quail intestine and also the ability of the lectin to specifically interact with the purified mucin, raising the question of the role of endogenous lectins in secretions.

Intestinal mucin secretion in streptozotocin-diabetic rats: lack of response to cholinergic stimulation and cholera toxin

In diabetic rats, intestinal mucin secretion is unusually high compared with that in normal rats. These studies demonstrate that mucin synthesis is also increased in the diabetic intestine. alpha- and beta-adrenergic agonists or antagonists did not affect mucin output in either normal or diabetic animals, suggesting that altered release in diabetes was not due to goblet cells responding abnormally to adrenergic agents. The cholinergic agonist bethanechol caused a dose-dependent and atropine-sensitive increase in mucin secretion from the normal intestine but had no effect on mucin release from diabetic tissue. Atropine alone did not reduce mucin secretion from the diabetic intestine to levels found in normal tissue. Cholera toxin caused an approximately fivefold increase in mucin output from normal rats but had no effect on mucin secretion from diabetic animals. Thus, goblet cell responses to cholinergic stimulation and cholera toxin in the diabetic intestine are markedly impaired. However, loss of cholinergic control does not appear to be responsible for altered baseline mucin secretion in diabetes.