Abnormal intestinal permeability to sugars in diabetes mellitus

Mechanisms of disease: the role of intestinal barrier function in the pathogenesis of gastrointestinal autoimmune diseases

The primary functions of the gastrointestinal tract have traditionally been perceived to be limited to the digestion and absorption of nutrients and electrolytes, and to water homeostasis. A more attentive analysis of the anatomic and functional arrangement of the gastrointestinal tract, however, suggests that another extremely important function of this organ is its ability to regulate the trafficking of macromolecules between the environment and the host through a barrier mechanism. Together with the gut-associated lymphoid tissue and the neuroendocrine network, the intestinal epithelial barrier, with its intercellular tight junctions, controls the equilibrium between tolerance and immunity to nonself-antigens. When the finely tuned trafficking of macromolecules is dysregulated in genetically susceptible individuals, both intestinal and extraintestinal autoimmune disorders can occur. This new paradigm subverts traditional theories underlying the development of autoimmunity, which are based on molecular mimicry and/or the bystander effect, and suggests that the autoimmune process can be arrested if the interplay between genes and environmental triggers is prevented by re-establishing intestinal barrier function. Understanding the role of the intestinal barrier in the pathogenesis of gastrointestinal disease is an area of translational research that encompasses many fields and is currently receiving a great deal of attention. This review is timely given the increased interest in the role of a 'leaky gut' in the pathogenesis of gastrointestinal diseases and the advent of novel treatment strategies, such as the use of probiotics.

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.

Ultrastructural mucosal alterations and increased intestinal permeability in non-celiac, type I diabetic patients

BACKGROUND

Increased intestinal permeability was described in several intestinal auto-immune conditions. There are very few and contradictory reports about type I diabetes mellitus, an auto-immune condition sometimes associated with celiac disease.

AIMS

To investigate intestinal permeability in type I diabetes mellitus patients with no concomitant celiac disease, with a comparison to ultra-structural aspects of duodenal mucosa.

PATIENTS

46 insulin dependent diabetes mellitus, non-celiac, patients (18 females and 28 males, mean age 15.8 +/- 5.3 [S.D.] years) were enrolled. The mean duration of the disease was 5.7 years.

METHODS

The morphological aspect of the small bowel mucosa, at standard light microscopy and electron transmission microscopy, along with intestinal permeability (by lactulose/mannitol test) were studied. Lactulose and mannitol urinary excretion were determined by means of high performance anion exchange chromatography-pulsed amperometric detection.

RESULTS

The lactulose/mannitol ratio was 0.038 [0.005-0.176] (median and range) in 46 patients compared to 0.014 [0.004-0.027] in 23 controls: insulin dependent diabetes mellitus group values being significantly higher than those of the controls (P < 0.0001, Mann-Whitney test). Eight insulin dependent diabetes mellitus patients underwent endoscopy and biopsies were analysed by means of light microscopy and transmission electron microscopy. At the light microscopy level, none of the biopsy samples showed any sign of atrophy nor inflammation, whereas transmission electron microscopy analysis showed remarkable ultra-structural changes in six out of the eight patients. Four parameters were evaluated: height and thickness of microvilli, space between microvilli and thickness of tight junctions.

CONCLUSIONS

This alteration of intestinal barrier function in non-celiac type I diabetes mellitus, frequently associated with mucosal ultra-structural alterations, could suggest that a loss of intestinal barrier function can be a pathogenetic factor in a subset of insulin dependent diabetes mellitus patients.

Increased intestinal permeability as a cause of fluctuating postprandial blood glucose levels in Type 1 diabetic patients

BACKGROUND

In diabetic patients, postprandial glucose levels, which have a major impact on metabolic control, are determined by the rate of nutrient delivery into the intestine, absorption of nutrients from the small intestine, and the metabolism of the absorbed nutrients by the liver. The present study addresses whether Type 1 diabetic patients have increased intestinal permeability and intestinal permeability predicts postprandial glucose variability.

MATERIAL AND METHODS

Thirty Type 1 diabetic patients together with 15 sex- and age-matched healthy controls were enrolled in the study. After an overnight fasting all patients and controls received 100 micro Ci 51Cr of EDTA as a radioactive tracer and the percentage of the isotope excreted in a 24-h urinary specimen was the permeability measure. Instant blood glucose was measured just before the test, and the patients performed and recorded self-monitoring of fasting and 2nd-hour postprandial blood glucose levels during the following week.

RESULTS

We found that intestinal permeability is increased in Type 1 diabetic patients compared with age- and sex-matched healthy controls. Increased intestinal permeability is related at least in part to the instant blood glucose level and the presence of diabetic autonomic neuropathy.

CONCLUSION

Increased intestinal permeability leads to higher variation in postprandial blood glucose levels, thereby worsening metabolic control.

Intestinal permeability in Crohn's disease patients and their first degree relatives

BACKGROUND

Family studies suggested that an altered intestinal permeability plays a role in the genesis of Crohn's disease.

AIM

Aim of the present study was to investigate a possible genetic alteration of the mucosal barrier in Crohn's disease.

SUBJECTS

16 Crohn's disease patients and 26 of their cohabiting first degree relatives were studied.

METHODS

To investigate intestinal permeability, Cellobiose/Mannitol test was administered to both groups.

RESULTS

In the two groups, we found that the median intestinal permeability values were higher and statistically different from those obtained in 32 healthy control subjects as well as in five healthy control families. Six (37.5%) Crohn's disease patients and three (11.5%) of their first degree relatives showed increased individual intestinal permeability values. Intestinal permeability alteration in Crohn's disease patients was unrelated to sex, age, disease activity, localisation, duration, treatment schedule, as well as to serum anti-Saccharomyces cervisiae antibody positivity in a pilot study conducted in 7 Crohn's disease patients; anti-Saccharomyces cervisiae antibody values were negative in all 10 first degree relatives investigated.

CONCLUSIONS

These findings demonstrate the increase in IP in 37% of the patients and in 11% of their relatives. More extensive investigation of the correlation between ASCA alterations and IP will be needed in both patients with Crohn's disease and their relatives.

Altered intestinal permeability to mannitol in diabetes mellitus type I

BACKGROUND

Intestinal permeability has seldom been investigated in diabetes mellitus, even though patients frequently report gastrointestinal symptoms, and it has recently been shown that the prevalence of celiac disease associated with diabetes mellitus is higher than expected.

METHODS

Intestinal permeability to cellobiose and mannitol was investigated in 31 patients affected by type I uncomplicated diabetes mellitus. Values were compared with those obtained in 32 normal subjects.

RESULTS

The percentage of mannitol recovery was far higher than normal in two thirds of the investigated patients and correlated with the length of disease, even though the probes' ratio (cellobiose/mannitol) was in the normal range.

CONCLUSIONS

A not previously reported increase of intestinal permeability to mannitol, clear-cut and not associated with that of the larger probe, is found in type I uncomplicated diabetes mellitus. These results may describe a primary feature of type I diabetes mellitus and the initial steps of evolution to celiac disease.

The sensitivity of the lactulose/rhamnose gut permeability test

BACKGROUND

The lactulose/rhamnose (L/R) intestinal permeability test is widely used. However, different quantities and proportions of lactulose and rhamnose are used. The aim of this study was to determine whether a low dosage of lactulose is able to discriminate between normal and increased permeability.

MATERIALS AND METHODS

Two groups of 10 healthy subjects were studied. In group 1, three different iso-osmolar test solutions were administered on 3 days. The solutions consisted of 10 g of L with 1 g of R, 5 g of L with 0.5 g of R and 1 g of L with 0.1 g of R in 65 mL of water. Group 2 ingested these solutions 1 h after ingestion of 750 mg of chenodeoxycholeic acid (CDCA), which is known to increase permeability. The urinary L/R ratio was determined using high-performance liquid chromatography. Data are presented as medians (range).

RESULTS

In group 1, no differences were observed between the three solutions. In Group 2, there was a significant difference (P = 0.045) between the three solutions. The L/R ratios were 0.0079 (0.0024-0.0152) (1L to 0.1R), 0.0138 (0.0066-0.0192) (5L to 0.5R) and 0.0144 (0.0074-0.0374) (10L to 1R). The L/R ratio differed significantly between Groups 1 and 2 (P < 0.001) using the 5L to 0.5R and 10L to 1R solutions respectively.

CONCLUSION

If the permeability is increased, the urinary L/R ratio depends on the quantity of lactulose and rhamnose administered in equal proportion. 5L to 0.5R is sufficient to discriminate between a normal and a moderately increased permeability.

Effect of lactulose on carbohydrate metabolism and diabetes mellitus

BACKGROUND

Unabsorbable disaccharides, by reducing transit time and possibly glucose absorption, are expected to affect carbohydrate metabolism.

AIM

To test the effects of a preparation containing fibre and lactulose in the form of biscuits on glucose and insulin levels in obesity.

METHODS

In 10 obese patients glucose and insulin were measured in the fasting state and in response to a meal during two consecutive days on a strictly controlled diet; on one day a total of 11 biscuits (10 g dietary fibre, 2 g raw fibre +8.2 g lactulose) were randomly substituted for an equicaloric part of a diet.

RESULTS

Glucose and insulin in response to breakfast and to lunch were blunted by dietary fibre and lactulose, without any trend towards post-meal hypoglycaemia. Average day-time glucose decreased by 0.53 +/- SD 0.28 mmol/L, and insulin by 74.6 +/- 45.2 pmol/L. Plasma amino acids were higher during supplementation, ruling out malabsorption as a cause of glucose flattening.

CONCLUSION

Because of the rationale of the preparation, good compliance of patients, and significant results in short-term experiments, the association of fibre and lactulose deserves more careful evaluation in long-term clinical studies.

Experimental streptozotocin-reduced diabetes and intestinal glucose metabolism in the rat, in vivo and in vitro

The intestine has a high glycolytic activity, but its metabolic role could be altered in diabetes mellitus. The aim of the present work was to investigate in vivo the glucose retained and the lactate produced by the intestine of normal and diabetic rats and in vitro the effect of different arterial glucose concentrations on glucose utilization and lactate, alanine, and pyruvate production in normal and diabetic rats when the glucose is supplied to the intestine exclusively via the vascular route. In vivo, the normal and diabetic rats retained similar percentages of the arterially supplied glucose (14.7 +/- 2.4, respectively). In vitro, when the preparations were perfused under hyperglycemic conditions, the glucose consumed, as a fraction of the quantity infused, was significantly lower (P < 0.05) in the diabetic (247.0 +/- 22.8 mumol/mmol infused glucose) than in normal (315 +/- 16.3 mumol/mmol infused glucose rats) rats. The lactate produced was significantly higher in diabetic than in normal rats whether the preparations were perfused under isoglycemic (P < 0.01; 1916.4 +/- 124.0 vs vs 1284 +/- 67.7 mumol/mmol consumed glucose) or hyperglycemic (P < 0.05; 1356.4 +/- 199.7 vs 898.0 +/- 87.3 mumol/mmol consumed glucose) conditions. There was significantly (P < 0.05) greater alanine release from the diabetic (123.7 +/- 21.8 mumol/mmol consumed glucose) than from the normal (40.7 +/- 10.3 mumol/mmol consumed glucose) rat preparations perfused under isoglycemic conditions.

Regional alterations in intestinal sucrase expression in streptozocin-treated chronically diabetic rats

In ad libitum-fed diabetic rats, sucrase specific activities in jejunum and ileum were significantly increased two- to threefold compared to controls, a response unaltered by pair-feeding. Gradients of sucrase activities along the ileal villus-to-crypt axis were readily measured in crypt regions in diabetic, but not in nondiabetic, rats. Changes in sucrase activities were commensurate with increases in sucrase immunoreactivity and not a result of altered functional activity. Insulin treatment reversed these effects, although insulin-deficiency, studied in food-deprived, nondiabetic rats, did not affect sucrase expression. We conclude that chronic diabetes significantly stimulates sucrase expression along the proximal-to-distal and villus-to-crypt axes of rat small intestine. In ileum, these changes suggest marked alterations in phenotypic development of enterocytes along the villus-to-crypt axis. Alterations in sucrase expression do not appear to correlate with insulin states and are not a consequence of altered functional activity.

Intestinal zinc transport: influence of streptozotocin-induced diabetes, insulin and arachidonic acid

The influence of arachidonic acid (AA) on the zinc flux rates of jejunal segments, isolated from streptozotocin-induced diabetic rats injected with saline or with insulin, was investigated using an Ussing chamber technique. Although the zinc flux rates from mucosa-to-serosa (Jms) of normal rats were inhibited by addition of 5 microM AA to the jejunal segment bathing medium (46.4 +/- 5.0 vs 32.6 +/- 4.3 nmol/hr/cm2), AA had no effect on the Jms of diabetic rats either with or without insulin treatment. Induction of diabetes also significantly reduced Jms (46.4 +/- 5.0 vs 22.1 +/- 4.9 nmol/hr/cm2), but 3 day insulin treatment (NPH 8 U/Kg/day subcutaneously) did not reverse this effect (29.2 +/- 5.1 nmol/hr/cm2). Addition of AA to the serosal side did not significantly alter the zinc flux rate from serosa-to-mucosa (Jsm) in either control, diabetic or diabetic rats treated with insulin. The net zinc absorption rate (Jnet) of jejunal segments was decreased in diabetic rats compared to controls (13.2 +/- 3.0 vs -0.7 +/- 2.1 nmol/hr/cm2), but normalization of blood glucose with 3 day insulin treatment did not increase Jnet. Addition of AA was associated with a tendency to increase zinc uptake capacity. This change reached statistical significance in insulin treated diabetic rats. Short-circuit current (Isc) for diabetic rats was increased compared to controls but addition of AA to the mucosal side bathing medium decreased Isc in all groups. The results indicate that the zinc flux rate in the small intestine of streptozotocin-induced diabetic rats is decreased, that zinc uptake capacity of the small intestine does not directly reflect the zinc flux rate across the small intestine, and that AA or one of its metabolites may play a significant role in the control of the zinc flux across the intestinal epithelium.